The Aluminum(III) Chemistry of Antiperspirants and its Possible
Links to Alzheimer's Disease
An Honors Thesis (HONRS 499)
by
Diana L. Maniak
Thesis Director
Pr
Ball State University
Muncie, Indiana
April 29, 1991
Expected Graduation May 4, 1991
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Alzheimer's Disease, a specific type of senile dementia currently affecting
two million Americans (66), is a disorder of memory and cognition occurring in
middle to late life. Generally, "dementia" is a clinical term referring to
progressive loss of cognitive functions commonly involving memory, orientation,
abstraction and the ability to learn new tasks (71). Diseases classified as
dementias, which affect 10-15% of those 65 and older (73), include senile
demetias (often caused by normal aging processes or vascular disease),
Parkinson's Disease and amyotrophic lateral sclerosis (ALS). Of the 10-15%
of the older population stricken,
50-6~/a
of these suffer from Alzheimer's
Disease (AD). CUrrently, the rate of new AD cases is approximately 100,000
per year, greater than those of heart attacks and strokes. Considering the
recent trends in demographics, the 65+ population is expected to reach
36.6 million by the year 2000
(1~/a)
and 58.8 million by 2025 (20%), meaning
that upwards of 5 million persons may eventually fall victim to AD (8).
Because the symptoms of AD closely resemble those of many of the senile
dementias, diagnosis is only possible by neuropathological exam of post-
-
mortem or biopsied brain tissue. However, the physical and mental effects
are severely pronounced. The progression of the disease, which may last
anywhere from 18 months to 27 years (average=10 years), follows a gradual
steady decline in mental abilities, first memory then psychomotor and
language skills (8). Personality characteristics may also be altered
dramatically, with victims often experiencing social avoidance, fearfulness,
paranoia or delusion, irritability and agitation (46). In many cases, verbal
and physical aggression toward family members and caregivers is not uncommon.
Though AD victims appear well at first, the ability to execute simple daily
tasks such as remembering names, finding the right word, recalling having
done something and eventually even eating becomes impaired. Ultimately
unable to speak, think or take care of themselves, most victims end up
dying from complications
af~cting
bedridden patients.
CHARACTERISTICS OF ALZHEIMER'S DISEASE
Biologically, little is known about the pathogenesis of AD because of
problems in accurate diagnosis and lack of accepted animal models. Though
dementias have been recognized since ancient times, this particular type
was first identified by the German physician Alois Alzheimer in 1906 (3).
The disease he described was a presenile dementia associated with histologic
2
-
findings of neocortical intraneuronal fibrils and parenchymal "senile"
plaques (34), which, unfortunately, are still the only identification
markers we have today. Extensive studies of the neuropathological changes
in AD have shown consistent characteristic chemical and structural changes
in the brain, including disturbance of specific neurotransmitter systems,
neuronal loss and the presence of neurofibrillary tangles and protein-based
plaques.
The first of these neuropathological changes originally obsereved by
Alzheimer, the
~-amyloid
"senile" plaque, has since been found to consist of a
central core surrounded by a spherical cluster of dystrophic
neurites and glial cells located mostly in the cerebral cortex and hippocampus (59). These extracellular deposits
of~
•
-pleated sheet polypeptide
fibrils are approximately 20-150uM in diameter and completely insoluble
in all physiological fluids, indicating that
such~
-amyloid accumulation
may cause neuronal loss (71). Though these plaques occur to a small extent
in the brains and vascular systems of normal aged humans, the quantity is
-
much greater in AD, with the genesis thought to develop slowly (for decades)
before the advent of symptoms.
A second structural abnormality specific to AD is the neurofibrillary
tangle (NFT). Present in large numbers in the neocortex and hippocampus
(6-40 times greater than normal aging), these structures are the most pathologically significant evidence of AD. Composed of accumulations of dense
fibrous strands within neuronal cytoplasm, the NFT's exist exclusively as
pairs of lOnm filamentous protein wound in helical fashion. These.paired
helical filaments (PHF), because they are aberrations of normal cytoskeletal
growth, may directly cause neuronal loss or interfere with neural signal
and transmitter transport (72).
Most recently, the focus on neurochemical changes has made great strides
toward unlocking the secrets vital to developing combative drug therapy.
While the plaques and tangles may yield information about the pathology of
AD, it will eventually be chemical intervention that leads to a cure. Some
of the important changes in neurotransmitter systems discovered include
1) reductions in presynaptic markers for cholinergic neurotransmission,
-
2) changes in noradrenergic systems, 3) severe decreases in somatostatin
levels and 4) neuronal degeneration in the amygdala, hippocampal formation
and neocortex (73).
-
3
While the causes and effects of the neuropathological changes observed in
AD are sketchily understood at best, specific distinguishing differences
between AD, "regular" senile dementia (SD) and normal aging have been confirmed.
First, SD displays a less uniform and less severe progression than AD, producing varying symptoms in victims. Second, the neuronal loss caused by SD
is not greater than that caused by normal aging, and is much less than that
caused by AD. In fact, the number and location of plaques, tangles and dead
neurons are often used as "threshold" parameters in preliminary AD diagnosis.
Third, most of the SD changes affect the white matter, while AD almost
exclusively affects gray matter. Fourth, the concentration changes of transmitters and the imbalances observed among different neurotransmitter systems
in AD are significantly different from those observed in SD (62,76,87).
THE IMPLICATION OF ALUMINUM
Considering the lack of concrete definition of the disease itself, it
is not surprising to note how many disparate theories on the etiology of
~
AD have been advanced. Though some point to an infectious agent or bloodflow deficiency as possible causes, these theories have been given little
credence (86). During the late 1980's, familial patterns of AD incidence
led to widespread investigation of a possible genetic link. Though some
AD symptoms (PHF's, senile plaques containing amyloid fibrils and amyloidladen cerebral vessels) were the same as those found in Down's Syndrome,
no gene was ever discovered on chromosome 21, causing this theory also to
be dismissed (33). Studies of the~ -amyloid protein involved in plaque
formation have uncovered a specific protein sequence of 43 amino acids
which may be directly responsible for the genesis of plaques (33,59), but
still others argue that the plaques are a posttraumatic event. Another
promising theory advanced recently stems from the discovery that cholineacetyl transferase (CAT) is reduced by
9~fo
in AD. The subsequent reduction
in acetylcholine mediated transmission of nerve impulses may affect memory
formation (86).
Based on geographic differences and correlations in the incidence of
-
AD, environmental factors have also been implicated, and various "toxin"
models proposed (66). Out of all such theories, one toxin has consistently
-
4
surfaced and resurfaced during the course of AD research: aluminum.
Aluminum, one of the major components of the earth's crust and one of the
most pervasive elements in the daily environment, is present in the air,
in drinking water and in common foods and drugs (especially processed
cheeses, antacids and buffered aspirins). Though we are now aware of the
potential correlation between Al and AD, the implication of Al has had a
rather interesting history.
The earliest indications that Ai could cause neural damage was the
discovery in the 1950's that dialysis patients often suffered from
encephalopethy, a form of irreversibly fatal dementia eventually attributed
to high Al concentrations in the water used during the treatment process.
These patients exhibited both an increased body load of Al and elevated
brain Al levels, though no plaques or tangles were observed (49,79,87).
About one decade later, a more concrete connection between ingested
Al and AD-like symptoms
llaS
confirmed. For years, certain communities in
Guam had been subject to devastating numbers of amyotrophic lateral
sclerosis cases, with correspondingly high brain Al levels and neurofibral
tangles. In the mid-1960's, it was discovered that the drinking water supply
was especially high in Al and low in calcium. Since Ca deficiency in water
could enhance Al absorption, a direct link was proposed (86).
As a result of these "ingestion" connections, several major investiga-
tions of Al in drinking water, food and cooking utensils were performed in
the 1970's. Because of the difficulty in quantitating and isolating the
amount of Al ingested from specific sources, most of these studies were
found to be inconclusive. However, one study comparing the Al concentrations
of the drinking water in England and Wales for a 10-year period to the
incidence of AD showed a seemingly significant correlation. The risk of AD
was found to be 1.5 times higher where the average Al concentration was
greater than 0.11 rng/l, compared to concentrations of less than O.Olug/l,
but these differences in concentration were so dramatic that the increased
risk was virtually dismissed as unrelated (36,51).
ALUMINUM AND ALZHEIMER I S SYMPTOMS
Following belatedly from the discovery of dialysis encephalopathy, new
studies attempting to link brain Al accumulation to AD symptoms were undertaken in the 1980's. Ai salts were injected directly into the subcortical
5
space or spinal cords of animals, and it was found that encephalopathy
resulted, though the disease symptoms were different than dialysis
encephalopathy and AD (13,32,83). Though neurofibral tangles, neural
degeneration and mental deterioration are observed in all three diseases,
the most significant differences are 1) the courses of neurotoxicity
symptoms differ, 2) the rates of progression differ, with AD being the
slowest and most universally predictable, 3) the NFT's occur in different
locations and do not have the same structure and 4) very few plaques are
observed in the induced encephalopathies (51,87).
Beginning with the first identification of Al localized within AD
plaques in 1976 (20), widespread investigation of the location and activity
of Al in the central nervous system has led to a wealth of potentially
useful but apparently unrelated pieces of lG1owledge. Though there is no
known biological role for Al, its exclusive existence as Al+ 3 allows it
to interrupt biochemical processes by acting as an oxidizing agent, ligand
or foreign electrochemical transmitter. Specific Al accumulation has been
observed to occur mainly on cellular nuclei in the brain, with the toxicity
altered by the formation of hydrated states and ligand complexes (19). Al
has also been found to interact with DNA, causing pH and concentration
dependent alterations in transcription by the formation of three Al-OH-DNA
complexes (44). Having found Al located on chromatin, it is thought that
genetic and metabolic processes may be affected (19).
Perhaps more importantly, Al has been found within the structures of
both senile plaques and paired helical filaments. A study involving X-ray
dispersion techniques showed Al and silicon colocalized in the central
region of senile plaque cores, present as both tetrahedral and octahedral
amorphous aluminosilicates (14,15). Because other essential elements (S,K,
Mg,Ca,Fe) did not show focal concentration in plaques, a specific mechanism
involving Al in the initiation of early stages of plaque formation has been
suggested (14).
Raised Al and silicon concentrations have also been reported in neurofibrillary tangle bearing neurons in AD (14). Focal Al concentration in the
nuclear region of tangle-bearing cells (38.4%) was found, especially in the
hippocampus, while adjacent neurons showed no presence of Al (72). Several
possible NFT formation methods involving Al have been proposed, one being
-
6
that they may be caused by abnormal phosphorylation of 200-kd neurofilament proteins, a process interrupted by the formation of insoluble
Al-phosphate complexes (37). Another theory proposes the modification of
normal cytoskeletal components (neurotubules, neurofilaments and actin)
by Al located in the cytoplasm (37). A third possible method is Al induced
protein polymerization, which could cause the assembly of highly insoluble
aberrant protein within the perikaryon, giving rise to tangles and
eventually destroying neurons (76).
In addition to the possible roles of Al in producing structural changes,
the chemical activity of Al in the brain has also been investigated. One
important Jiscovery was that Al may induce large populations of electrically
silent neurons, neurons that remain electrically active but whose spike
generating mechanism is functionally disconnected from the dendrites (19).
Such electrophysiological changes have been directly related to alterations
in learning, memory and motor performance, and apparent correlations have
been made between the number of silent neurons and degenerative neurons in
the neocortex, an area largely affected by AD.
Al +3 has been found to interfere w"ith neurotransmitter binding to
receptor sites, especially inhibiting the activity of acetylcholine in
neuroblastoma cells (51). It also inhibits specific metabolic processes,
such as hexokinase activity (which is responsible for catalyzing glycolysis
reactions in the brain), ferroxidase activity ( Fe metabolism) and other
glycolytic enzymes associated with fast axoplasmic transport (2).
3
Al+ is known to inhibit many regulatory mechanisms, especially those
involving calcium and magnesium. For example, Al+ 3 inhibits Na-K and Mg
activated ATPase activity, disrupts ca+ 2 dependent electrophysiologic
2.
( especlally
.
.
.
f unctlons
and lntracellular
Ca+
regulatlon
t h e Ca+2/Mg +2
ATPase calcium pump regulated by calmodulin) and may influence the Mg+2
•
requiring phosphate transferring systems involving ATP (2,51).
Certain crucial membrane properties in the brain are also affected by
+3
. . d peroxldatlon
'"
.
.
.
ln the braln,
causlng
modlfications
Al . Al +3 enhances llPl
of lipid membrane layers and membrane properties. Al+ 3 binds directly to
-
the phosphoryl head group in phospholipid membranes, affecting protein
mobility and receptor activity (51). Most notably, Al+ 3 is thought to
affect the properties of the blood-brain barrier, which may result either
7
in the direct entry of Al+ 3 or interruption of the normal exchange
functions for other essential elements (5,9,31,38,74).
Though aluminum does not affect cerebral blood flow or blood-brain
barrier (BBB) integrity, it does have certain specific effects on the
..
.
.
properties of the membrane. Blndlng dlrectly to endothellal cells, Al
+3
increases rigidification and fusion of membranes at concentrations of
25uM (31). Formation of amphoteric Al complexes on the surface of the
BBB also serves to neutralize the membrane, making it more approachable to
3
other charged molecules. Electrochemically, Al+ inhibits the closure of
the voltage gated channels governing the passage of some molecules, while
it selectively inhibits the saturable transport systems of others (5).
Besides causing these alterations in BBB regulation of ion exchange,
Al
+3
may also cross itself by displacing any of several ions from their
respective carriers, including Zn, Cd, Se, Na, Mg and Fe (5).
In the blood plasma, where Al+ 3 is almost exclusively found, the ion
is bound primarily to transferrin (58). In normal adults, the plasma Al+
,~
3
concentration is approximately 3ug/l, with a total transferrin-bound load
of 10 ug (81). Despite the fact that raised serum Al levels have not been
confirmed in AD, passage of Al through the BBB by a specific carrier such
as transferrin could cause much more damage than unbound Al because it
3
is taken directly to the site of a specific biochemical reaction. Al+ is
also knO'Vll to bind to lactate, citrate, phosphate and acetate in the bloodstream, ligands which commonly carry other ions (23,47,48,57,84). Thus,
aluminum could conceivably enter the bloodstream as Al
+3
and subsequently
form a complex, or especially in the case of phosphates and citrates, the
Al may enter from
the gastrointestinal tract already bound.
ALUMINUM ENTRY
lVhile many possible routes for the transport of Al
+3
to the brain have
been considered, the most direct and most probable pathway is through the
bloodstream to the blood-brain barrier. If this is indeed the case, the
crucial question then becomes how the Al passes from the external environ-
-
ment to the bloodstream. As previously discussed, absorption of Al from the
gastrointestinal tract has been extensively studied, ,. . ith some,. . hat contradictory results. Generally, the daily intake of Al from food and water
8
-
is 1-20 mg (51). Of this amount,
10-2~/o
is taken up by the intestinal mucosa
and 80-90% is excreted through the membrane of the small intestine to the
urinary tract (36,43). Thus, the net intestinal absorption estimated from
the sum of daily urinary excretion ( 20ug) and the probable rate of tissue
3
accumulation ( 2ug) is 0.1-0.5% of the Al+ ingested orally, or at least
1-5ug per day (36,51).
Another important entryway of Al is through the respiratory tract. The
3
average adult carries about lOmg of Al+ in his lungs, received mainly as
particles of aluminosilicates and poorly soluble compounds (2,51). Though
"
3"
the lungs have the h1ghest
Al +
concentrat1on
of all organs, most of t h"1S
is taken up by macrophages in the lung tissue and remains there indefinitely,
eliminating the respiratory tract as a direct portal to the bloodstream.
Considering the pervasity of Al in the environment, one potentially
important pathway that has received little attention is the skin. Though
the skin is considered to be virtually impermeable to metals and other
inorganic compounds, many organic substances are known to penetrate to the
bloodstream quite effectively, a fact utilized extensively by the pharmaceutical industry.
~~ile
few people regularly use dermatological preparations,
many of the same organic vehicles are used in cosmetic products, one of
which is used daily by most of the adult population: antiperspirants.
Antiperspirants, the active ingredients of which are aluminum salts, also
contain a wide variety of organic sUbstances that could possibly act to
3"
""
enhance Al +
penetrat10n
through the ax1llary
t1ssue.
The barrier function of the skin, which consists of epidermal and dermal
layers, is thought to reside primarily in the outermost sublayer of the
epidermis, the stratum corneum (Sc). This layer, also knOvffi as the horny
layer, consists of dead keratin deposits and cornified cells and is thereby
highly inelastic and impermeable. Underneath the stratum corneum, the
epidermis extends through four more sublayers to a depth of 30-15 um, the
deepest of which (the basal cell layer) is highly metabolically active.
The overall function of the epidermis is to protect the dermis and to
perform a major portion of the biochemical transformations on entering
substances (34,61).
Underneath the epidermis, beginning at a depth of 50-200 um, lies the
dermis. The dermis consists of two major layers, the papillary dermis,
FOLL\LLes /~'r:rf1CEOUS GLAtJDS
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gland
FIG. I.-Development of the se!.aceou, J!lanci from the follicular epithelium of the hair. From Pinkus (59),
(Reproduced hy permissioll "f "prin):,"- \ .. rlag
FIG. 2.-Plastic reconstruction 01 a s.. !.act'ou, !!Iand, From l'inkus (:;IJ I, (){epruduced
SpriDpr- V...... )
r..:- -
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A nH lomas IS
.round hllr
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supply
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and .dlpou
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Diagrammatic representation of blood supply to
the epidermiS. and the plexus of vessels around
the hair Ihatt-inserts demonstrate alkaline phosphatae
actIVity of: (A) half papilla; (B) shaft; (e) eplderrnts.
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21
EPIDERMIS
30-ao lAID
DERMAL PAPILLARy
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50-200 lAID
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.,
DERMIS
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SUBCUTANEOUS FAT
FiOUre 13.1
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"r~'
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-e:-"'-
EndoII"e~um
SmOOlll muse
Fig. 1-25 Schematic depiction 01 the microcirculation
units 01 skin. The artenal vessels are shown In while and
the veins are black. A represents papillary dermIS, B the
reticular dermiS, C the pilosebaceous apparatus, and D
an eccrine sweat gland and duct. "1" identifies some ar·
tenovenous communications at dilterent levels In the skin
and subcutaneous tissue. (From J. M. Short. 1974. With
pemllSSlOn. Harper and Row)
Ie
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appendagcal diffUliion shunu.
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cvT.ANEOVS
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From l.obitz and Mason (\09 (Reproduced by
permission of Dr. Lobitz and the :\merican Medical
AtIoc:iation, )
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Fig. oJ. Dia'frammatic rl'prf'Semation of the mechanisms of transcapillary exchange. 1 = diffusion.:.1 = transport by pinocvtosis. J. Y = ultrafiltration and lihration, oJ = 'open junctions',
a = capillary Ilimen. h = .. ndOlhdial cl'li. c ~ haseml'm rnemhran(', cI = pericapillary
(Reproduced with permission of. \bramson.1
u.ue.
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9
which contains all of the microcirculatory vessels, and the reticular
dermis (1000-3000um), which consists of fibrous collagen and is relatively
acellular and avascular. Derived fron mesodermal origin, the dermis is a
thick, chemically inert layer which serves mainly as connective tissue to
support the epidermis. It does, however, contain all of the blood supply,
nerve networks and glands of the skin. Therefore, materials exchange
occurs exclusively in the papillary dermis, with the passage of exiting
waste products and metabolites occurring at the basal cell interface. By
the reverse process, entering substances may drift through the epidermis,
be metabolized in the papillary dermis and pass directly into the bloodstream (34,61).
Aside from direct passage through the epidermal tissue, substances may
also enter through several skin appendages, including the hair follicles,
sebaceous glands and sweat glands. The hair follicles extend through the
epidermis at a slight angle to the papillary dermis, where the shaft opens
into a bulblike structure bathed in highly vaSCUlarized and metabolically
active connective tissue (61). Despite the outward flux of keratinized
cells during periods of hair growth, penetration during inactive periods
has not been disproved.
The sebaceous glands, whose function is to secrete sebum, an oily
material consisting of fats that lubricates the skin and prevents moisture
loss, are situated next to the hair follicles. The gland itself surrounds
the upper third of the follicle and grows out into the surrounding dermis.
The glandular duct directly empties the sebum produced into the shaft of
the
hair follicle, through which it travels to the skin. Because of the
density and secretory rate of the sebum, however, the sebaceous glands are
not a probable penetration route (77).
Another class of appendages, the sweat glands, consists of two types of
glands: the eccrine glands and the apocrine glands. In general, both types
of sweat glands share the same structural features. They are tubular glands
consisting of a secretory part, located immediately below the dermis in the
subcutaneous tissue, and an excretory duct, which follows a spiral pathway
through the dermis and epidermis and opens in surfaces of ridges of the
skin. The secretory portion is coiled and twisted on itself, engulfed on
all sides by blood vessels, making it a potential exchange site. Of the
two types of sweat glands, the apocrine glands are much more inactive.
10
Larger than eccrine glands and localized in certain body areas (primarily
the axillae), the apocrines secrete a turbid, viscous material directly
into the pilary canal, just like the sebaceous glands. On the whole, they
are poorly innervated and produce a relatively small amount of sweat (29).
The primary function of the eccrine glands, which are distributed over the
entire body surface, is to secrete water to dissipate body heat and cool the
skin. They are tubular coiled glands, seated at the border of the subdermis
and dermis, and whose ducts spiral through the epidermis to independent
openings on the skin surface. Whereas apocrine secretion consists mainly
of protein and carbohydrate waste material, eccrine sweat is 95-99% water
and NaCl (77).
Though several studies on the activity and structure of the eccrine
glands have suggested penetration of surfactants to the dermal layer may
be possible, little conclusive evidence on the modes of transport has
been produced (42,52,55,68,78). Considering the process of percutaneous
absorption, however, many factors favorable to establishing the penetration
of Al from antiperspirants may be advanced.
Traditionally, the skin has been knO'VTI to allow virtually free passage
of water and some gases, but also to be extremely vulnerable to chemical
attack (55). Because of its keratinized and cornified cells, the stratum
corneum is the principal barrier to absorption. Diffusion of substances
through the SC is not at all metabolic, but directly dependent on the physical
properties of the membrane and governed by passive diffusion mathematics
(61,77). According to Fick's Law of Diffusion, the penetration of a substance
depends mainly on its permeability and diffusion constants and the SC
thickness. Based on permeability and diffusion constants, materials that
penetrate poorly are polar compounds, inorganic/organic salts, complex
polymers and electrolytes. Some good penetrators are nonpolar (lipidsoluble) compounds, substances forming hydrogen-bonds and ambiphilic
solvents such as DMSO (77).
The effectiveness of the SC, however, may be altered by any number of
factors. Hydration is known to, promote transepidermal transport and increase
the diffusion rate of most substances (55,77). Diffusion also increases
exponentially with temperature (61). Physical or chemical injury to the
skin, such as by solvents or detergents, may cause a secondary reduction
in barrier function by damaging the SC and viable epidermis (55). Occlusion
--
11
of the skin surface, considered to be a form of physical injury, may cause
upwards of a twenty-fold increase in penetration because of increased
temperature and hydration (61). Most importantly, the vehicle in which a
penetrant is carried may cause any number of destructive effects. For
example, alcohols are notoriously harsh vehicles that enhance penetration
by attacking the lipid building processes of the cell membranes. Certain
vehicles may also affect transfollicular absorption by bringing the penetrant into closer contact with the follicular pore or canal (77). OVerall,
since absorption flux is proportional to the SC/vehicle partition coefficient,
a lipophilic solute may penetrate either faster or slower than a comparable
water soluble substance. For low molecular weight compounds, however, the
diffusion constant is generally higher in water than in other liquids (34).
Once a substance diffuses through the stratum corneum, it is desorbed
into the viable epidermis, where it is subject to the metabolizing properties
of this layer. From there, it diffuses through the epidermis to the papillary
-
dermis, where it reaches the capillary plexus and is transferred to the
circulating blood. While some compounds cannot diffuse through the epidermis
without biochemical transformation, the lack of dermal metabolism may
sometimes allow passage of unchanged chemicals into systematic circulation (55).
Depending on the chemical characteristics of a given penetrant, it may
diffuse by several modes. Polar, water-soluble substances will diffuse
transcellularly through individual cells and cell walls. Nonpolar, lipidsolubles may diffuse either intracellularly or intercellularly, through
the lipid material filling the interstitial spaces. The principal pathv2Y
for 'later-soluble nonelectrolytes is transcellular, with the principal
diffusion resistance being hydrated intracellular keratin. Lipid soluble
compounds diffuse by different, specific mechanisms. Usually, lipophilic
solutes will segregate into and diffuse through lipid regions, though the
exact location of lipid pockets in the epidermis are not knowm (55).
For aluminum, which is not lipid soluble in either the metallic or ionic
form, the number of possible penetration sites is limited. Having ruled out
the sebaceous and apocrine sweat glands as absorption sites, penetration
-
must occur through the hair follicles, eccrine sweat glands or unbroken
stratum corneum. The hair follicles, though a viable pathway for some
small organic molecules,are usually filled with keratin and sebum, Ivhich
-
12
would readily prevent diffusion of a metal ion. In the case of the eccrine
+3
s,,,eat glands, it is possible that Al
may penetrate to the secretory cells
by a sort of electrochemical gradient caused by
the ionic flow of Na+ (52,
64). Also, the intraepidermal duct ,vall has its own lining epithelium vlhich
may have a higher permeability than the SC (55). Though penetration through
the unbroken SC is not likely for an electrolyte, conversion to a lipidsoluble compound or action of a strong vehicle could greatly increase the
permeability of Al, allowing it to follow a passive diffusion route and enter
the circulation at the capillary endothelium (55).
Because the key to Al penetration seems to be its lipid-sOlubility, the
presence of organic substances with which to form Al complexes becomes very
icr~ortant.
From the secretion of sebum and eccrine/apocrine sweat, the skin
is constantly covered with a film of surface lipids, primarily a fine emulsion
of fats and ,,,aste products in cholesterol and ,,,ax alcohols. The composition
of each type of glandular secretion is the foIIOl"ing:
Eccrine s,,,eat
95-9~/o water, NaCI, urea
Glucose, lactic acid
Vi~ami~s B+C,A'~1D
+2
Na ,CI , K , Ca , Mg , SO 2- PO 3-, Fe+ 2
4 '
4
(29,64,77)
Apocrine sw"eat
Protein/carbohydrate fragments
water, NaCI
P9)
Sebum
Free fatty acids
Paraffins
Squalene
Wax
2.2-2. ~/o
Sterol ester
31.3-46.4% Triglycerides
.6-1.8%
Free sterol
0-8.1%
Polar material
16-30%
.8-1.3%
10.2-12.8%
20.0-21.5%
(61)
Though no specific Al complexes have been observed to directly penetrate
the SC, metals are knOlm to form lipid-soluble complexes with fatty acids
to form metal oleates, both inside and outside of the body (77). In
addition, other heavy metals have been sho,m to penetrate percutaneously
-
and enter systematic circulation, including Hg, Pb, Sn, CU, As, Bi and
Ag (61, 77).
13
Recalling that skin permeability is greatly enhanced by hydrolysis,
alcohols, occlusion and injury, the potential for Al absorption is even
stronger in the case of antiperspirants. The active ingredients used in most
antiperspirants are simple Al salts (AlC1 3 6H20 and Al2(S04)3 18H20), basic
Al-halide salts (Al (OH) m(X) n , where m+n=6), basic Al/Zr salts (Al 2 (OIf) m(Cl) n
2
ZrO(OH)Cl glycine) and basic complexed Al salts (Al chlorohydrex propyleneglycol, Al chlorohydrex polypropylene glycol). Of these active Al complexes,
the most commonly used are AlC1 3 6H20, Al 2 (OH)m(Cl)n ' Al/Zr chlorohydrex
and Al chlorohydrex PG (52).
Several theories on the possible modes of effectiveness of these compounds
have been proposed, including 1) blocking of the sweat gland, 2) making the
walls of the sweat duct permeable to sweat and 3) reduction of sweat production in the gland (41). Presently, the prevailing hypothesis is that
antiperspirants have an astringent effect which acts
to shrink shut the
pore of the sweat gland, or to precipitate protein and form a keratin
plug \.,rhich obstructs the flm.,r of sweat to the skin surface (52). Relatively
speaking, the effectiveness of the various Al compounds in preventing
sweating may depend on their ability to penetrate the eccrine sweat duct.
Studies involving transmission electron micrography and tape-stripping of
duct openings have sho,vn that AlC1
penetrates at least to the level of
3
the intraepidermal duct, while aluminum chlorohydrate inhibits sweat gland
activity as deep as the viable epidermis. Aluminum-zirconium complexes have
the most superficial but most prolonged antiperspirant effect, inhibiting
50-60% of surface eccrine activity and lasting as long as 78 days per
application (52).
Considering the known ability of the aluminum salts to penetrate at
least the eccrine glands, the constant contact of high Al concentrations
with the skin would favor •the establishment of diffusion equilibrium. In
fact, absorption through the appendages (also known as shunts) may even be
likely, since electrolytes do not penetrate the stratum corneum well.
Returning to the concept of passive diffusion matehematics, the rate of
-
penetration of a surfactant will at first increase, eventually reach a
steady state if the external concentration is maintained, then will slowly
decrease as the surface concentration decreases. For shunt diffusion,
14
overall ionic transport rate is low and nonselective, meaning that it is
almost always favored for slowly diffusing substances (such as hydrated
Al+ 3 ). Because of the lag time in achieving the diffusion steady state,
however, the penetration of ions and nonelectrolytes with low lipid solubility may actually be favored early and late in the penetration process.
Though the diffusion rates of poor penetrators are slow, they remain
relatively constant, meaning they will be more likely to penetrate while
the rates of other stronger penetrators are equilibrating. If a high
surfactant concentration is maintained, shunt diffusion
of ions may even
be high during the steady state (34,42). Theoretical predictions of the ionic
3
diffusion rate in the eccrine duct indicate that Al(H 20)6+ penetrates
relatively quickly, with half the applied concentration reaching a depth
of 0.2rnrn in 20 minutes under occluded conditions. If the applied solution
is allowed to concentrate by solvent evaporation, 1% of the applied
concentration will penetrate to 2rnm within 50 minutes (41). with an average
application dose of 0.4-0.8 g antiperspirant and average product Ai content of 10-15% (unpublished data), upwards of 0.5 mg Al per application
may penetrate to the papillary dermis at these rates, easily comparable
to the 1-5 ug absorbed daily by the gastrointestinal tract (36,43,51).
Besides the high aluminum content, antiperspirants also contain many
compounds that cause occlusion and injury. In addition to the astringent
and blocking properties of the Ai salts themselves, it is also thought
that the hydroxide gel used as a base for most preparations effectively
plugs almost all of the axillary pores (52). Almost all the antiperspirants
contain large percentages of alcohols, vehicles whose abrasive properties
unquestionably enhance penetration. Most preparations contain 25-75% water
as well (unpublished data), which serves to hydrate the stratum corneum,
causing it to swell and subsequently reducing the outward flux of sweat (52).
Aside from the shunt diffusion of Al+ 3 , many of the matrix components in
antiperspirants could conceivably promote tissue absorption. Though the
ionic mobility through the tissue is limited by the polyhydration of Al+ 3
and its ion charge interaction with other fixed and mobile charges, the
-
species does have a diffusion constant comparable to Na, K and Br (k =
6
10- cm/h) (34). Coupled with a small molecular weight organic compo~nd,
the lipid solubility would greatly increase, allowing the Al+ 3 to penetrate
15
by any of the primary SC permeation routes, or even a specific lipid
mechanism. Some of the most common matrix components and their functions
are:
ethyl alcohol, stearyl alcohol
propylene glycol (PG), polypropylene glycol (PPG),
polyethylene glycol (PEG)
polyethylene
water
Vehicles
Gell ing
-
sodium stearate
quaternium hectorite
agents
Preservatives,
Antibacterials
methylparaben, propylparaben
Triclosan
Emulsifiers
glycerol
mineral oil
hydrogenated castor oil
isocetyl alcohol
Drying agents
talc
Fragrances
natural oil extracts
(6,52)
Al(lll) CHEMISTRY
While the solution chemistry of Al+ 3 has been extensively documented,
few fully collaborating results have been produced (1,12,23,47,52,25,84,85).
Because Al
+3
may act amphoterically, its behavior in aqueous solution is
affected by innumerable factors and is thereby highly unpredictable. For
the most part, Al+ 3 chemistry is dominated by hydrolysis ana oxidation
reactions. Though Al
+3
has a relatively low ligand exchange rate, it readily
undergoes successive hydrolyses to form a variety of mononuclear species:
pk =5.0
+
+ H
+
+ H
-
1
pk =4.8
2
pk 3= 5.7
pk4 =7.6
16
-
Though these processes attain rapid, reversible equilibria, they
3
5.0, the stable ionic species Al(H20)6+
perdominates. As the pH increases from about 5-6.5, the successive depro-
directly depend on pH. At pH
tonations to Al(OH)+2 and Al(OH)+ occur. At neutral pH, the aluminum
hydroxides congregate to form a gelatinous Al(OH)3 precipitate that will
redissolve in basic solution to tetrahedral Al(OH)4-. Once basic pH is
reached, however, the time-dependent formation of some polynuclear species
occurs (12,52). Aqueous aluminum systems are often characterized by the
neutralization ratio, n, which is simply the OH/Al ratio. For systems
in which n
2.5, small mononuclear and dimeric ion species form first,
.
+4
+5
followed by the small polynuclear specles A1 2 (OH)2
and Al 3 (OH)4 .
After a few hours, large stable polynuclear species, predominantly
+7
Al 0 (OH)24 ,may form depending on the exact n, temperature and rate of
13 4
OH addition. Over a period of weeks, an undisturbed solution may form
high molecular weight polymers or amorphous solids, such as gibbsite or
bayerite (52).
.
.
Overall, the Solutlon
chemlstry
0f
'
Ai +3.lS governed
y n,b
solutlon
concentration, ionic strength, temperature, pH, concentration of other
ions (especially Cl - , S04 -2 and N0 ), time, form and rate of OH addition
3
and equilibrium status (1,52,56,75).
Whether the chemistry of Al+ 3 changes in the presence of other organic
and inorganic compounds remains to be seen, however, as few such studies
have been reported. While the solution chemistry of the aluminum salts
used to manufacture antiperspirants has been sufficiently documented (12,52),
no literature references on the behavior of Al in the actual product matrix
have been found. Considering the potential of an environment containing
high Al concentrations, abrasive vehicles and lipid-soluble components to
promote absorption, investigation of the chemistry involved could produce
some of the information needed to establish a "new·" route to the bloodstream. In this light, the task of this project was to first quantitate
the amount of Ai in various types of preparations, then to attempt to
separate some of the smaller organic compounds in the matrices and
-
determine if any could be aluminum complexes.
l7
-
EXPERIMENTAL METHODS AND RESULTS
I. Selection of Samples
Six brands of commercial antiperspirant products were chosen on the basis
of the main active ingredient, the matrix components and mode of application
(roll-on, stick and cream). The samples selected were:
Al Salt
--
Arrid extra-dry
solid
Al chlorohydrate
Ban Ocean-breeze
roll-on
Al chlorohydrate
Major Matrix Components
Diisopropyl adipate,cyclomethicone,
PPG-butyl ether,stearyl alcohol
,vater,stearyl ether,steareth
cyclomethicone,stearyl alcohol,
isocetyl alcohol,Triclosan
Dial regular
solid
Al/zr tetrachlorohydrex gly
Secret regular
cream
Zr-Al-glycine
water,glyceral stearate, PEG stearate,
glycerin
Sure unscented
rOll-on
Al/zr trichlorohydrex gly
cyclomethicone,dimethicone,polyethylene,
quaterniumr18 hectorite
Tussy regular
roll-on
Al chlorohydrate
water,PEG-stearate,cetyl alcohol,
isodecyl oleate,Mg-Al silicate
II. Digestion of Wet Samples
In order to perform quantitative analysis on the samples, it was necessary
to bring them into aqueous solution by digestion. Heating for 15 minutes to
2 hours in 10-20 ml concentrated RN0
and H S0 did not completely dissolve
2 4
3
any of the samples, instead forming "gummy" solid lumps. The addition of
5-50 ml
3~1o
H20 2 to the digestion mixture improved dissolution somewhat,
but only after extensive strong heating (1-3 hours).
Noting that RN0
and H S0 woulc possibly interfere with later AA
3
2 4
experiments, HC104 was used at all the conditions previously tested, with
little improvement in results. ~~ile some of the samples almost completely
dissolved, some still contained gummy solids or flaky solid precipitates.
Some solutions, though apparently dissolved, also formed gelatinous or solid
white precipitates upon the addition of water, especially at temperatures
-
higher than room temperature.
18
Next, to decrease the required heating time, the sample size was decreased
from 0.5-2.0 g to 0.1-0.2 g. The samples were first treated with 1-3 ml HCI04 ,
stirred at room temperature or very low heat for 5-15 minutes, until all of
the solid dissolved. 2-5 ml 30% H 0 was added, and the solutions stirred
2 2
vigorously at medium heat until all of the organic film and gummy solids
diSSOlved, approximately 5-10 minutes. Additional peroxide was added to
some samples that were not colorless to insure complete oxidation. The
solutions were allowed to cool to room temperature and brought to volume
with deionized water. Optimal digestion procedures for each product are as
follows (for 0.1 g samples):
HCI04
(ml)
B~
3
4
Dial
3
Secret
2
S~e
4
Tussy
2
Arrid
H20 2 Medium
Slight
Stir
cool (min)heat (min) (ml) heat (min)
10
1
8
7
6
4
2
-
-
Final Solution
clear ,colorless
clear ,colorless
5
2
10
clear ,colorless
10
2
15
clear,colorless
5
1
5
clear, colorless
5
1
5
clear ,colorless
III. water Content of Samples
To determine the water content of the products, 1-4 g samples were dried
0
in an electric oven at temperatures of 100-125 C for periods of 10-210 hours.
Samples were weighed out and placed in predried weighing bottles, partially
covered with lids to prevent splattering. Three trials were performed,
increasing the drying period each time. Changes of less than 5% occurred for
some of the samples (Arrid, Ban and Tussy), while the weight loss for the
others continued to increase with increased drying time.
At
temperat~es
•
0
of 100-125 C, no components other than water should have
evaporated, based on published boiling points of the product ingredients.
Though all of the brands contained alcohols, which might be expected to
e
boil at less than 125 C, these alcohols (primarily stearyl, cetyl and
isocetyl) consist of relatively large organic parents, raising their
boiling points to 160-190 oC.
19
o
The maximum water content determined for each brand at 110-115 C was:
Water Content (%)
Drying Time (hrs}
210
Arrid
49.1
Ban
139
79.2
Dial
210
56.3
Secret
139
78.3
Sure
210
58.4
Tussy
139
76.3
IV. Digestion of Dried Samples
In order to compare the relative aluminum contents of the dried samples
to those of the wet samples, digestions of the oven-dried samples were also
performed. Three sets of digestions, run at the various conditions and
parameters previously described for the wet samples, showed that the
optimum procedure was again slight heating in minimal HCI0
then medium
4
heating with H20 2 . However, additional difficulties were experienced with
some of the samples, due primarily to the hardening and/or gelling caused
-
by drying.
Each dried sample was mixed and around either into a rough powder or a
viscous paste, depending on its characteristics. The Ban, Dial and Sure samples
dried to extremely hard solid chunks, while the Arrid, Secret and Sure samples
dried to oily, gummy pastes, making them difficult to mix to consistent
composition. Approximately 0.075-0.150 g samples were digested by the
following procedures:
HCL0
(rnl )
Heat
(min)
HCL0
(rnl )
4
Heat
(min)
H0
2 2
(rnl )
Heat
(min)
medium
4
3
medium
slight
10
10
7
slight
2
slight
3
Ban
5
15
medium
slight
5
Dial
3
10
15
slight
slight
3
Secret
3
1Q
5
s1.10
slight
3
Sure
5
med.15
15
10
slight
slight
Tussy
5
5
10
*Solutlons flltered on Whatrnan 54-grade ash fllter paper
after addition of water.
Arrid
-
4
3
Final Solution
clear, colorless
small white flakes
clear, colorless
clear,colorless
flat white flakes*
clear,very Sllghtly
yellow
clear ,colorless
flat tan flakes*
clear,slightly
yellow/brown
,-
20
v.
Aluminum Content of Wet and Dried Samples by FAA
Standard aluminum solutions were prepared from Spex Plasma Emission
Spectroscopy aluminum standard (1000 ppm) and deionized water. 50ul
3~fo
H 0 and 100ul 7~fo HCL0 were added to each standard to approximate the
4
2 2
matrices of the digested samples. All absorbance measurements were done
on a Perkin-Elmer Model 306 Atomic Absorption Spectrophotometer with a
nitrous oxide-acetylene flame. The absorbance wavelength used was 309.3nm,
at a slit width of 3(0.4 rum). Standards ranging in concentration from 0.550.0 ppm were run, and the linear working range determined to be 5.0-50ppm.
Concentrations below 2.0ppm were not detectable.
Two sets of absorbance readings were taken for each digested wet and dry
sample, with the average aluminum contents found to be:
,-
Wet Samples
£2!!!
Arrid
Ban
Dial
Secret
Sure
Tussy
164
% Al in Original Sample
14.9
13.7
11.1
138
134
82
108
94
4.8
572
611
177
269
N/A
522
35.7
55.4
16.0
24.5
N/A
43.5
9.0
9.4
Dried Samples
Arrid
Ban
Dial
Secret
Sure
Tussy
Standard additions were also run on each set of samples to determine
whether matrix interferences were affecting the results. 10ml standard
solutions were prepared from 5m1 digested sample, 100ul H 0 , 100ul HC10 ,
4
2 2
deionized water and stock ~luminum spikes of concentrations Ox,lx and 2x,
where x=50 ppm. The aluminum contents of each solution by this method were:
-
Wet Samples
Arrid
Ban
Dial
Secret
Sure
Tussy
ppm Al
170
146
132
57
113
115
21
ppm Al
567
597
171
230
820
Dried Samples
Arrid
Ban
Dial
Secret
Tussy
Comparison of the results obtained from the calibration curve and
standard additions methods show that interferences affected the absorbance
of each sample differently. As would be expected with organic matrix
interferences, the aluminum content of both the wet and dry Tussy samples
and the wet Ban sample were higher by standard addtions. For all of the
other samples, the aluminum content was found to be significanyly higher
by the calibration curve, indicating some component was present in the
standards that was not present in the samples.
Since any viscosity, ion mobility or hydrolysis problems should have
-
been prevented by the HC10 in the standards, these factors were ruled out
4
as possible interferences. Though the nitrous oxide flame should have been
hot enough to vaporize all of the organic compounds in the samples, as well
as refractory aluminum oxides, chemical interferences would also seem to be
discountable.
Because the pH of the standard and sample solutions may have affected
3
the chemistry of the Al+ ions in solution, the pH of each was measured on
an Orion Combination 501 Digital Ionalyzer. While the readings showed
differences of up to 0.7 pH units between the standards and samples, the
pH's of all the solutions were easily acidic enough to insure the exclusive
existence of the aluminum as Al(H 0) +3
2
Standards
10 ppm
20 ppm
30 ppm
40 ppm
2.10
2.05
2.00
1.92
Samples
Arrid,wet
Arrid, dry
Ban ,wet
Ban,dry
Dial, wet
Dial, dry
1.55
1.31
1.48
1. 75
1.42
1.38
E!
E!
6
22
Samples
Secret ,wet
Secret ,dry
Sure ,wet
Tussy ,wet
ill
1.44
1.53
1.50
1.43
Considering all of these factors, the most probable cause of the observed
interferences may have been simply the predominance of organic compounds in
the products, which could have affected the nebulization rate or suppressed
the absorption of energy by the aluminum atoms in the flame.
No reported
ionic interferences for aluminum determinations were present in any of the
products.
VI. Aluminum Content of Wet and Dried Samples by ICP-EM
To overcome the observed interference effects in the FAA analyses, the
aluminum content of each wet and dried sample was also determined by ICP-EM.
All emission measurements were made on a Perkin-Elmer 5500 Inductively
Coupled Plasma system. The wavelength used was 396.2 nm, at a slit width
of 0.2 nm, gain of 325-350 and reading time of 0.2 seconds (averages of
every ten readings were recorded). Originally, the primary aluminum emission
wavelength of 309.8 nm was used, but secondary line interference was
experienced.
Several runs of standards and sample solutions were
tried at various
parameters, with the optimal conditions being those described above, along
with a viewing height of 1-2 mm. Standard solutions were prepared from the
Spex stock at concentrations of 5-50 ppm, with 250 ul HCI0 and 250 ul
4
H20 2 per 100 ml. Though aluminum concentrations of 0.5 ppm were observable,
the linear working range was 5-30 ppm. The average aluminum contents of the
samples were found to be:
-
Wet Samples
Arrid
Ban
Dial
Secret
Sure
Tussy
.P.P!!!
57
105
24
18
26
.40
% Al in Original Sample
6.5
5.7
3.2
1.6
4.1
5.6
23
Dried Samples
Arrid
Ban
Dial
Secret
Sure
Tussy
~
163
441
149
99
69
714
% Al in Original Sample
15.7
28.3
10.0
10.1
8.8
25.8
Unexpectedly, the aluminum contants found by
rcp were 1/2 to 2/3 lower
than those determined by FAA for every sample. Assuming that matrix interferences had reduced the previously observed concentrations, the aluminum
contents should have been 5-25% higher. The fact that they were lower
indicates one of several possible differences occurred: 1) the age of the
solutions affected the aluminum chemistry (the FAA solutions were 3 months
old, while the rcp solutions were less than one week old), 2) some of the
matrix components actually enhanced the observed absorption in the flame,
which might also explain the lower concentrations by standard additions or
-
3) secondary emission lines by other ions decreased the aluminum signal in
the rcp experiments. OVerall, considering the high temperature of the plasma,
rcp results were probably more reliable. However, one other factor that
the
was noticed during the rcp experiments was that the deionized water used to
make the solutions contained about 3 ppm Al, necessitating blank corrections.
Standard additions were also run on all of the wet samples, with these
results:
Em!!
%Al in Original Sa!!!]2le
Arrid
84
9.6
Ban
121
6.6
Dial
Secret
40
5.5
43
3.6
Sure
40
6.2
Tussy
48
6.7
By this method, the aluminum contents were found to be 3-4% higher
than by the standard curve, which was somewhat unexpected since no matrix
interferences were anticipated. These findings show either that some secondary
ionic emission interference may have occurred, or that the relative blank
24
-
readings were not precise. When the standard additions solutions were
prepared, they were brought to volume by different amounts of vlater, meaning
that the blank aluminum concentration was not exactly the same for every
solution. At such small concentrations and volumes (10ml) , differences of
hundreds of microliters may have been significant.
VII. Daily Application Doses
The average daily antiperspirant application doses (both axillae) for
Sure roll-on and Mennen solid were recorded for adult subjects for a period
of one week. For the roll-on, the range was 0.5117-0.8178 g/day, with an
average of 0.644 g/day. For the solid, the range was 0.260-0.700 g/day,
with an average of 0.445 g/day. At an average aluminum content of 6%,
the amount of aluminum applied daily is approximately 25-50 rng/day.
VIII. Solubility of Wet Samples in Organic Solvents
Anticipating infrared, GC and HPLC analysis of the products, the
solubility of each in methanol, carbon tetrachloride, dichloromethane,
-
ethanol and acetonitrile was tested. Approximately 1-3 g samples were
dissolved in 2-5 m1 solvent and shaken vigorously. Relative solubilities
and characteristics were the following:
Methanol
SOlubility
sl.sol.
very sol
mod. sol.
Characteristics
cloudy white suspension
cloudy white sol'n,surface film
Sure
sl.sol.
sl.sol.
Tussy
mod. sol.
Arrid
Ban
Dial
Secret
clear sOlution
cloudy yfhi te solution
dense white suspension
cloudy "fhi te solution
..
CCl-4
Solubility
sl.sol.
Characteristics
white gelatinous emulsion
large oily vlhi te droplets
Sure
insol
sl.sol.
insol.
sl.sol.
even emulsion
large oily white droplets
thick whlte emUlSlon
Tussy
insol.
large white oily droplets
Arrid
Ban
Dial
Secret
25
Dichlorornethane
Arrid
Solubility
mod. sol.
Ban
sl. sol.
Characteristics
slightly cloudy vlhlte Solutlon
clear sol'n,whlte surface S011d
Dial
Secret
sol.
insol.
clear sol'n,white surface solid
cloudy white sol'n,small olly drople-cs
Sure
insol
Tussy
mod. sol.
thick cloudy white solution
clear solin, white surface SOlld
Ethanol
--
Arrid
Solubility
51. sol.
Characteristics
thick whlte suspenslon
Ban
very sol.
clear Solutlon
Dial
mod. sol.
Secret
51.501.
Sure
51.501.
opaque white solution
opaqlle white solution
Tussy
sol.
clear sclution
slightly cloudy white Solutlon
ACN
Solubility
lnsol.
Characteristics
very sllgnt Q1SSOJ.utlon
Secret
51.501.
51.501.
mod. sol.
thin white suspension
thin white suspension
opaque white solution
Sure
51.501.
thin white suspension
Tussy
insol.
large solid clumps
Arrid
Ban
Dial
-
OI
SOllO
26
IX. Infrared Analysis of Antiperspirants
Infrared spectra of the products were taken on a Nicolet 580ZDX FT-IR
-1
spectrophotometer at a resolution of 4 em
. Standard NaCl salt plates were
used for all of the neat spectra, onto which a thin film of antiperspirant
was allowed to dry. The sample compartment was sealed and purged with
nitrogen gas for at least one minute prior to each scan, and ten interferograms were collected before the fourier-transform. The infrared spectra
and a listing of the major bands for each are given on the following pages.
Comparison of the observed bands for the products to the published data
for aluminum hydroxide chloride solutions (75) and to standard (Sadtler)
infrared spectra for some of the matrix components showed few similarities.
For aluminum hydroxide chloride solutions, the bands reported were:
-
1
Frequency (em
_ - )_
3520(s)
3300(s)
3130(s)
2500(w)
1950(w)
1080(s)
980(s)
790(s)
630(s)
Assignment
bridging Al-OH-Al stretch
bridging stretch
OH stretch of Al-OH
2
-symmetric
AI-O-H bend
Al-O-H bend
2
Though most of the spectra suffered from poor resolution, a prominent
Al-O-H band was observed for all of the samples except Dial and Secret,
and at lower intensity for those products containing Al/Zr complexes.
Due to broad OH bands on every spectrum, none of the Al-OH-Al bridging
bands were observed between 3100-3500 em- 1 . The unassigned band at 790 em- 1
was observed on all spectra.
Some prominent spectral features of organic matrix components were also
present for most of the products. The series of small sharp peaks between
1200-1500 em- 1 characteristic of stearyl-based compounds were observed for
Arrid, while strong Al-stearate "doublets" at 2925-2950 cm-1 were observed
-
for Dial and Secret. The Ban and Dial spectra exhibi.ted sharp "triple"
1
peaks at 2850 em- similar to those for glycerin and propylene glycol.
The bands for Secret between 1000-1400 em-1 almost perfectly matched the
ethylene glycol spectrum.
27
In order to use infrared spectra as qualitative or quantitative tools
in the analysis of antiperspirants, the spectral resolution should be
improved. The most prominent and universal band to utilize for identification
and quantitative analysis of Al contents is probably the Al-O-H band at
1080 em-I, since this chemicalinteraction would be expected to occur in
most solvents, especially alcohols. However, the spectra obtained by the
present methods were not reproducible or resolved enough in this region.
In an attempt to achieve better resolution, samples dissolved in
and dichloromethane were analyzed in a liquid cell equipped
4
with NaCl plates and having a cell pathlength of 0.1 mm. Solvent background
methanol, CC1
spectra were taken prior to each set of experiments and subtracted from the
sample spectra. This method did not work well for the CH 2C1 2 and CC1 4
because the diameter of the cell was too thick and good resolution of the
background spectra could not be achieved. A reasonable background was
obtained for methanol, but the subtraction process was plagued by several
problems, one being impurities in the solvent and another being inconsistencies in spectral intensity. Though the methanol should not have
evaporated from the liquid cell, consecutive runs of equal intensity were
rarely observed. As a result, most of the spectral features were lost upon
subtraction. In addition, dissolved sample concentrations high enough to be
observed through the methanol spectrum could not be produced without causing
precipitates or emulsions in the solutions.
Intending to determine whether any organic components had been driven
off during the drying process, or at least to eliminate water bands from the
spectra, the dried samples were analyzed by both liquid and mull techniques.
A few spectral features were observable for methanol solutions, but the
solubilities of the dried samples were even less than the wet samples, producing
mainly methanol spectra. Nujol mulls of each sample "I.iere prepared and spread
thinly on NaCl plates. A mineral oil background was subtracted from each
sample spectrum. Sample concentrations in the mulls were apparently higher
than in the methanol solutions, as the resultant spectra exhibited features
-
distinct from those of the background. However, spectral resolution was too
poor to reliably identify any of the bands.
Major Infrared Bands for Antiperspirant Samples (frequency in em-I)
Arrid
Ban
1015
1010
1100
1190
llOO
1260
1260
1350
1380
Dial
1010
Secret
Sure
Tussy
1000
1050
1015
1010
lll0
lll0
1190
1210
1455
1475
1630
1260
1355
1390
1425
1270
1350
1390
1425
1390
1450
1480
1480
1625
1455
1720
1750
1750
2370
2855
2930
2850
2920
2850
2925
2975
3400-50
-
2925
2960
2980
3410
2325
2370
2325
2380
2850
2960
3400-10
3400-20
a
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\J)TI.EH
ETHYLENE
Mol. Vlt.
W. . . . . . . . . . .
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CIIII-·
1131
B. P._l 0), 9°C
(
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IN ~I 1100
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1000
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loo~_
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al. ... loP
1200
1100
~ ~ ----~----~------~------+--~------4----+-----~------4-----~
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-- - - ______
--~-----.----- - - - - - -______
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12
I]
WA\II L!N6'IH IN IoOClt00S
Je_"'U~
~ADTLfR
1962
ItESEAICH LABORATORIES, INC.
PHILADELPtIIA, PA., 191().l, U.S .....
'fro~ylf.~c. ~'1CO I
I .2· PlDPAIIED10~
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14
INFRAREO SPECTROGRAM
5000
~~NI
:~~Cl1
~ n.
-"1J,oo ...
r.
mOC
(~;60L1~400
6475
0.1-'
1100
1200
100
1000
1100
100
10
U
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3""'-lr'Ce:
F3r yater
MICRONS
:!atheson, Gole:-:an :t. 3ell
169
!'1oL. We. 92.09
GLYC£l.lN!
eM.1
100 SOOO
1m 1400
2000
3000
4QQQ
l30Q
1200
INFRARED SPECTROGRAM
1000
1100
,----._-----------.------_.
(
g
'lOO
1
ZQQ
~_t__,--.--,,/~------'\""'._T.......
=_::----,--_..,.-------,--,----.---__;.---..-----,-----(
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10
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MIDGET
EDITION
170
Mol. We. 270.48
-
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Betwean
1200
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1100
'''''
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{
INFRARED SPECTROGRAM
1!OO.1OO
V
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44217
STEARIC ACID, OCTADECYL ESTER
(
Mol. Wc. 536.97
Source:
Lachat Chemicals, Inc.,
Chicago Heights, Illinois
Capillary Cell:
Melt (Crystallized)
100
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Sadf/er ,.....rclt Labor.torln, IftC., SutJ.idiary of Blocl< Engineering, Inc.
"lol.
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1=
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1400
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1200 CM.' 'Ioe
INAIA-aEO SPKTROGRAM
1000
000
lIOO
1 5 65 5
71lO
(
10
,-
!1
KBr "'afer
12
13
14
15
28
X. GC Analysis of Antiperpirants
To dtermine if the antiperspirant matrix could be separated into small or
medium molecular weight organic compounds, 1-2 g samples of Ban rOll-on were
dissolved in a minimum of methanol and run on a GowMac Series 150 Thermal
Conductivity Detector gas chromatograph. OUt of all the products, Ban was
chosen because it was the only one that dissolved completely in any of the
organic solvents tested. Though some of the others dissolved sparingly in
methanol, filtering removed most of the product from solution.
The samples were run on a 15% Carbowax 20M (polyethyleneglycol) column at
a helium flow rate of 120rnl/min. Chromatographs were recorded at temperatures
from 60-175c C. The methanol peak occurred at anywhere from 55-135 seconds, with
retention time decreasing consistently with increasing temperature. At temp~
e
eratures from 60-90 C and 105-150 C, one large methanol peak and one smaller
broader peak were observed. This second peak emerged approximately 120 seconds
after the methanol peak, and could not further resolved at any temperature.
The chrometographs taken at
90-10~C
contained these two primary peaks and
sometimes two or three very broad and shallow peaks at times of 3-5 minutes.
At temperatures above 150°C, only a broad methanol peak was observed, which
completely obscured the second peak.
From these preliminary results, the best temperature for separation at this
flow rate seems to be about 90°C. The broad trailing shape of the second peak
and the fact that it was obscured by the methanol at 150°C indicate that it
probably represents several compounds with boiling points below 130-135e C.
Since Ban contains no alcohols, this second peak was probably water, along with
some fragrance elements or EDTA (used as an ion complexing agent). The other
antiperspirant matrix ingredients were stearyl(octadecanoic acid) ethers and
polypropylene glycol, of which only ethers and glycol(ethanediol) have boiling
points below 175°C. Considering that the ethanediol should dissolve fairly
readily in methanol, the broad shallow peaks observed in some of the chromatographs (90-105~C) may have been due to glycol fragments. Even if the stearyl
ethers dissolved slightly in the methanol, the compound pieces would still be
too bulky to emerge in 3-5 minutes.
29
XI. HPLC Analysis of Antiperspirants
A saturated solution of Ban roll-on in methanol was run on Isco Model 23S0
4
high pressure liquid pumps equipped with a v deuterium lamp absorbance
detector and an Alltech Asorb C cartridge (lSOmm x 4.6mm, cat.no. 28841).
18
All experiments were performed at the following parameters:
3%
8 sec.
1 sec.
Offset
Min. peak width
Min.baseline duration
Peak detection sensitivity
Min. peak height
Smoothing factor
Baseline sensitivity
.2
3",t,
11
O.OS
Chromatographs of the antiperspirant solution were produced using various
solvents, eluent ratios and flow rates, with the best resolution obtained at
8S% methanol/1S% water and 1.2 ml/min. Acetonitrile/water and isopropanol/water
solvents were also tested, but neither yielded good separation. Because the
sample was only moderately soluble in ACN, filtering reduced the concentration
too low to be able to distinguish the peaks from the background noise. In the
case of isopropanol, the sample was completely soluble, but an extremely noisy
baseline consistently occurred at every eluent ratio (30/70 to 70/30), flow
rate (1.0-1.S ml/min) and sensitivity (0.OS-1.0) tested. Periodic spikes in
the baseline were observed at each pump stroke, after which the pressure would
drop 30-40 psi.
Suspecting that a combination of isopropanol viscosity and a plugged column
may have been causing the baseline difficulties, the column was replaced with
an Alltech Econosphere C su cartridge (2SOrnm x 4.6mm, cat.no.71011). The
18
sample was run at several isopropanol/water solvent ratios, with no improvement
in results. In addtion to the pump fluctuation peaks, occasional bursts of air
or solute from the column also caused large spikes. Conditioning the column
•
w"ith isopropanol for 30-4S minutes did not eliminate any of the spiking, so the
original column was reinstalled.
For the experiments using methanol/water solvent, the sample was analyzed
at every ratio between 30/70 and 90/10 (at S% increments). The water used
initially was Millipore-filtered, degassed and buffered in O.lM HOAc to pH 3.S.
Though some baseline noise and occasional spiking occurred, the pump pressure
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30
fluctuations were less than 10 psi, and the sample peaks were distinguishable
from the baseline down to a sensitivity of 0.05. With the buffered water, the
best separation was obtained using 80 meth/ 20 water at 1.2 ml/min, with at
least twenth peaks occurring between 80-450 seconds. This same ratio was run at
1.0 ml/min, with some loss of resolution between the smaller peaks but increased
intensity for others.
Under these conditions, only 15 peaks were observed from
80-600 seconds.
Having determined that methanol/water ratios of at least 80/20 were needed
for separation, ratios of 80/20, 85/15 and 90/10 were run using unbuffered
HPLC water (pH 6.2). Since the dissolved antiperspirant solution had a pH of
3.9, it was expected that the buffered water used previously should have given
optimal separation. However, much better resolution was achieved using the
unbuffered water, though only 14-15 peaks occurred during the first 600 seconds.
Flow rates of 1.0, 1.2 and 1.5 ml/min were tried at each of the three solvent
ratios as well, with 1.2 ml/min again producing the best separation and most
symmetrical peaks. The average number of plates for the peaks were rather poor,
at 500-2000, indicating
the column may be deteriorating.
XII. Proposed Experimentation
Having developed successful methods for drying the samples, digesting them
and determining the aluminum content by ICP, the separation of the antiperspirants
into their smaller organic components is currently the most important goal. To
this end, further HPLC analysis of the samples is suggested, eventually leading
to the collection of eluent fractions, identification of the compounds contained
in each by infrared or NMR analysis, and quantitation of the aluminum contents
of each. However, several possible improvements in the separation technique
must first be explored:
1)
2)
3)
4)
Elimination of baseline noise and spikes
Reproducibility of chromatographs
Improving the number of plates to at least 10,000
Use of a new CIS column, or Cs or ion-exchange columns
Past the successful separation and collection of fractions, the infrared
sampling process would need to be improved or the samples analyzed on another
instrument to achieve the resolution needed to use the spectra
for structural
identification and quantitative analysis. NMR might also be used to identify
small matrix components
if the fractions were not too complicated.
-
31
Further , if any Al-organic compounds are identified in the antiperspirants, the effects of pH variation and sweat on the chemistry might also be
investigated. Ultimately, physiological studies of the actual permeation
capabilities of aluminum compounds through the axillary tissue and glands
would be necessary to determine if aluminum in antiperspirants may actually
be linked to Alzheimer's Disease.
,-
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-