[CANCER RESEARCH 55, 5459-5464,
November 15, 19951
Apoptosis in Tumors and Normal Tissues Induced by Whole Body Hyperthermia
in Rats1
Yoshihisa
Sakaguchi,2
L. Clifton
Stephens,
Masato
Makino,3
Tetsuya
Kaneko,3
Frederick
R. Strebel,
Lynn L Danhauser, Gaye N. Jenkins, and Joan M. C@Bull4
Division of Oncolog v. Department of Internal Medicine, University of Texas Medical School [V. S., M. M., T. K.. F. R. S.. L L D., G. N. J.. I. M. C. B.]. Houston, Texas 77225,
and Section of Veterinary Pathology, M. D. Anderson Cancer Center IL C. S.], Houston, Texas 77030
ABSTRACT
Apoptosis in tumor and normal tissues was examined in rats treated
with whole-body hyperthermia (WBH; 41.5°Cfor 2 h). WBH alone pro
duced 0.5 day of tumor
growth delay (TGD) in a fibrosarcoma
and 5.8
days of TGD in the Ward colon carcinoma. This difference in WBH
induced TGD indicates that the fibrosarcoma is relatively resistant to
WBH, whereas the Ward colon carcinoma is relatively heat sensitive. A
quantitative histological assay for apoptosis demonstrated
16) and in the intestinal mucosal epithelium (17—20).
Apoptotic
that the extent
of apoptosis in the fibrosarcoma reached a maximum level of 19% 4 h
after WBH and returned to the control level by 24 h. In contrast, WBH
induced apoptosis with a peak value of 43% at 8 h in the Ward colon
carcinoma, and the apoptotic level remained elevated above the control
level until 48 h after WBH. Within normal tissues, the spleen and the
lymph nodes showed WBH-induced
apoptosis;
however, the highest level
of WBH-induced apoptosis as well as the most prolonged increase in
apoptotic
levels occurred
in the thymus. The WBH-induced
apoptosis
tosis has been recognized in tumors in vivo (13), the kinetics of
hyperthermia-induced
apoptosis in tumor tissues and, even more
importantly, the relationship of apoptosis to tumor response have not
received close attention.
It is well known that apoptosis in normal tissues occurs under
physiological conditions (14). Chemotherapeutic drugs and irradiation
have also been shown to induce apoptosis in normal thymocytes (15,
in
the thymus remained elevated above the control level until 48 h after
WBH. Within the entire gastrointestinal tract, the small intestine was the
most sensitive to WBH. Apoptotic cells were observed in the small bowel
mucosa following WBH exposure. We also noted a minor WBH-lnduced
increase in the apoptotic level in the bone marrow. Except for the case of
the thymus, increased apoptotic levels In the normal tissues declined after
peak levels at 4 h, and apoptosis above control levels was not seen beyond
12 h following WBH. Thus, within the normal tissues, WBH-induced
apoptosis declined to basal levels within 12—48
h. These data indicate that
both the extent and the kinetics of WBH-induced apoptosis differ between
the two tumors and, meaningfully, between tumor and normal tissues. The
extent and duration of apoptosis seem to correlate with tumor response to
WBH.
changes in normal tissues may be related closely to treatment-induced
toxicity. Therefore, hyperthermia-induced apoptosis in the normal
tissues will be important to understand; yet, there are very few studies
that examine the effect of heat on normal tissues. Allan et a!. de
scribed hyperthermia-induced apoptosis in both the small intestine
(21) andthetestis(22). To optimizethetherapeutic
efficacyof WBH
as an anticancer treatment, it may be important to identify the critical
normal tissue targets of WBH-induced apoptotic cell death and to
increase our understanding of the kinetics of WBH-mediated apopto
sis in other normal tissues in vivo.
In these studies, comparing two transplantable tumors with differ
ent sensitivities to hyperthermia, we examined the in vivo kinetics of
apoptosis induced by WBH (41.5°Cfor 2 h) histologically and then
correlated the extent of apoptosis with tumor response. In addition, we
examined the extent and kinetics of WBH-mediated apoptosis in
normal tissues of rats.
MATERIALSAND METHODS
Animals. Experiments were performed using female Fischer 344 rats (Har
lan Sprague-Dawley, Inc., Indianapolis, IN) with body weights ranging from
b40 to 170 g. Rats were fed standard laboratory chow, allowed free access to
INTRODUCTION
Apoptotic cell death is a process distinguishable from necrotic cell
death. Apoptosis occurs in both physiological and pathological con
ditions and plays an important role in the regulation of tissue devel
opment (1—3).Apoptosis occurs in tumor cells in response to thera
peutic stimuli such as cytotoxic drugs and radiation (4—9).
Hyperthermia also activates the process of apoptosis in tumors (4, 5,
10, 11). Harmon et a!. (11) demonstrated that the type of cell death
changed from apoptosis to necrosis when the thermal dose was
increased. It is generally believed that mild forms of injury induce
water, and housed under controlled conditions with a 12-h light/dark cycle. All
rats were allowed a 1-week environmental adaptation period before their
apoptosis,
occurred in 100% of the transplanted rats. Treatment was initiated when
tumors reached 6—8mm in thickness.
WBH. Using a modification ofthe technique described by Lord et a!. (26),
whereas
more severe
forms of insult result
in necrosis
(1,
12). Thus, the mode of cell death following hyperthermia is dependent
on the severity of the heat stress. WBH5 at moderate temperature
elevations induces apoptosis in tumors. Although heat-induced apop
experimental use.
Tumors. We used two transplantable tumors: a fibrosarcoma (23) and the
Ward colon carcinoma (24), which were grown and maintained in donor rats
by monthly and bimonthly implantation,
respectively.
For experiments
using
the fibrosarcoma, viable tumor cells (106), assessed using trypan blue, were
injected s.c. into the left flank of rats. Tumors were produced in 100% of the
injected rats (25). For experiments using the Ward colon carcinoma, tumor
fragments (1 mm3) were implanted s.c. into the left flank of rats. Tumors
rats were anesthetized with halothane and placed tumor side down on gauze
hammocks on the surface of a warm water bath maintained at 41.5°C. The
necessary anesthetic depth during WBH treatment was maintained by elevating
Received 8/24/95; accepted 9/14/95.
The costs of publication of this article were defrayed in part by the payment of page
charges. This article must therefore be hereby marked advertisement in accordance with
the head of the rat out of the water and fitting the nose of the rat into a
halothane anesthetic inhalation mask (27). The ties of the hammocks that
18 U.S.C. Section 1734 solely to indicate this fact.
suspend the rats in the water were pinned to the outside of the water bath so
that the degree of immersion of the rat's body in the water could be controlled
by loosening or tightening the ties of the hammock to lower or raise, respec
I Supported
2 On
leave
by
National
from
Cancer
Department
Institute
of
Surgery
Grants
R01-CA-43O90
II, Faculty
of
and
Medicine,
R01-CA-41581.
Kyushu
University,
Fukuoka 812, Japan.
3 On leave from First Department
of Surgery,
Faculty of Medicine,
Tottori
University,
Yonago 683, Japan.
4 To
whom
requests
the core
body temperature of the rat could be regulated easily and maintained at the
for
reprints
should
be
addressed,
at
Division
of
Oncology,
The
University of Texas Medical School, P.O. Box 20708, Houston, TX 77225.
5 The abbreviations
tively, the level of the body of the rat in the water (23). In this manner,
used are: WBH,
whole-body
hyperthermia;
YSI, Yellow
Instrument Co.; TGD, tumor growth delay; H & E, hematoxylin and eosin.
Springs
water bath temperature of 41 .5°Cfor the duration of the 2-h WBH treatment
time. The thermostatically controlled circulating water bath was maintained at
41.5°C,using a Haake model E 12 circulator and heater as described previ
5459
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Research.
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APOPTOSIS INDUCED BY HYPERThERMIA
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ously (23). Both the water bath temperature and the rat core body temperature
were monitored continuously to an accuracy of 0.01°Cby YSI Nol 402
thermistor
small animal rectal probes connected
to a YSI model 4002 12-
channel switch box and a YSI model 49TA digital display telethermometer
@
(YSI, Yellow Springs, OH; Ref. 25). The probes were calibrated against a
@
mercury thermometer (Ertco; American Society of Testing and Materials
standard MC) certified by the National Institute of Standards and Technology.
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Body
temperature
was
recorded
every
S mm.
An average
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treatment, both the water bath and the rat core body temperature were main
@-
tamed for 2 h at a temperature of 41.5 ±0.1°C.General anesthesia using 1%
halothane in pure oxygen was administered for all WBH treatments. This
anesthesia affects neither tumor growth nor normal tissue toxicity (27, 28).
Antitumor Effects of WBH. The antitumor effects of WBH were deter
mined by an in vivo TGD assay, as described previously (28). Briefly, tumor
size was measured by using a vernier caliper to determine three perpendicular
diameters (d), and the tumor volume (v) was calculated by using the formula:
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(dl X t12 X d3)/2.
Tumor size was measured every 2 days in the fibrosarcoma or every 3 days
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of 30 mm was
required for the rectal temperature to first reach 41.5°C.Throughout the WBH
v
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in the Ward colon carcinoma. These time intervals used to monitor tumor size
I,
are based on previously established growth curves of the two tumors. The
Ward colon carcinoma is a much slower-growing tumor compared with the
fibrosarcoma.
TOD was calculated as the difference between control and treated rats in the
tumor growth time to reach bO times the initial treatment volume for the
fibrosarcoma or 3 times the initial treatment volume for the Ward colon
carcinoma, respectively. Each group consisted of five to six rats.
1I:.x.:;
.@?4r,
at indicated
times after WBH.
Tissues
were fixed in 10% buffered
formalin (jH 6.9—7.1).From each paraffin-embedded sample, 4-gxm-thick
sections were prepared and stained with H & E for light microscopic evalua
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tion. Each group making up time points after WBH consisted of three rats.
The quantitative assay for apoptosis in tumor tissue was performed using a
nuclear aberration assay as described previously (8, 9). Briefly, five fields of
nonnecrotic areas were selected in each specimen, and 100 nuclei in each field
were categorized as normal, mitotic, or aberrant. The aberrations were char
acterized by overall shrinkage and homogeneous dark basophilia. Infrequently,
several small apoptotic fragments were encountered in close proximity. On the
.
;*
Histopathological
Studies ofApoptosis.
Separate tumor-bearing rats were
used for the histopathological examination of apoptosis induced by WBH. To
determine the extent of apoptosis in tumors and normal tissues, rats were
euthanized
S
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Fig. 1. Photomicrographs of H & E-stained sections of the fibrosarcoma (X400). A, the
untreated tumor is composed of sheets of highly pleomorphic cells. B, the treated tumor
4 h after WBH. There are widely scattered apoptotic cells in the tumor. Arrows point to
apoptotic cells.
basis of size and clustering, such fragments were considered to represent the
remains of a single cell and were counted as one apoptotic nucleus. The levels
of apoptosis in normal tissues were scored on a graded scale of 0—4:0, none;
1, modest; 2, mild; 3, moderate; and 4, severe. All histopathological exami
@
Apoptosis in the Tumor Tissues. Apoptosis in the two tumors
induced by WBH was examined histopathologically between 4 and 48
nations were performed in a blinded fashion by the same veterinary pathologist
h after WBH. The transplanted fibrosarcoma grows as a noncircum
(L C. S.).
scribed s.c. mass with invasion of surrounding tissues. The tumor is
composed of sheets of highly pleomorphic cells (Fig. lÀ). The tumor
cells have large irregular shaped nuclei that have vesiculated chroma
RESULTS
tin and large prominent nucleoli. Fig. lB shows the tumor 4 h after the
Antitumor Effects. Table 1 shows the TGDs for WBH against
WBH treatment. The tumor has widely scattered apoptotic cells. The
fibrosarcoma and Ward colon carcinoma. The fibrosarcoma used in transplanted Ward colon carcinoma grows as a multilobulated non
this study is resistant to WBH and showed only a minor and nonsig
encapsulated mass, which compresses and invades the surrounding
nificant TGD of 0.5 day. In contrast, the Ward colon carcinoma is tissues. The tumor is composed of variable-size disorganized clumps
relatively sensitive to WBH and showed a significant TGD of 5.8 days
of cells (Fig. 14). The tumor cells have moderate to abundant cyto
(P < 0.05 compared with control).
plasm and ovoid nuclei that contain single or multiple large nucleoli.
The tumor contains a few cells that show the features of apoptosis.
Fig. 2B shows the tumor 4 h after the WBH treatment. The tumor
carcinomaTumorTreatmentTG@
Table 1 Antitumor
effects ofWBH in the fibrosarcoma and the Ward colon
contains
widespread extensive apoptosis accompanied by coagulative
(days)Fibrosarcoma
(days)TGDb
necrosis. Destruction of the tumor is extensive.
We examined the kinetics of apoptosis induced by WBH. Fig. 3
±0.7'
WBH
7.5 ±0.7
shows the difference in the kinetics of apoptosis comparing the two
ward coloncarcinomaControl
tumors.
8.9 ±1.8
Control
We observed: (a) the timing of the induction of a peak level of
147@35d0.5
5@8d
WBH7.0
aTumorgrowth
time(TGT)wasthetimeforthetumortoreach10timesand3times apoptosis following WBH treatment was similar for both tumors.
treatment volume in the fibrosarcoma and the Ward colon carcinoma, respectively.
WBH induced a fairly rapid increase in apoptosis such that the
b TGD was calculated as the difference in TGT between control and treated rats.
percentage
of apoptosis was greatest at 4 h after WBH for the
CMean ±SD.
fibrosarcoma and at 4 to 8 h after WBH for the Ward colon tumor;
d
< o.os compared
with control.
5460
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lymph nodes, mesenteric lymph nodes, and gut-associated lymphoid
tissues. In the gastrointestinal tract, apoptosis was prominent in the
small intestine. Apoptotic cells were observed in the epithelium and
the lamina propria of the mucosal villus zone (Fig. 4F) in specimens
collected at 4 and 8 h after the beginning the 2-h WBH treatment at
41.5°C.These apoptotic bodies seemed to be of lymphoid origin. At
these same time points following WBH treatment, but to a lesser
degree, apoptosis was also observed in the crypt epithelium. Apopto
sis was insignificant in the large intestine, and the stomach did not
demonstrate any apoptosis following WBH exposure.
In the bone marrow, there were increased numbers of apoptotic
cells among the developing myeloid elements associated with a gen
eralized marrow hypocellularity after WBH (Fig. 4H). Throughout the
time period of examination, we observed only negligible to nonexist
ent WBH-mediated apoptosis in the heart, lung, kidney, liver, pan
creas, salivary glands, adrenal gland, ovary, and uterus.
Fig. 5 shows the kinetics of apoptosis in the thymus, spleen, small
intestine, and bone marrow. In the thymus, the level of apoptosis was
greatest at 8 h after WBH. Thereafter, the cortex became thin with
hypocellularity associated with a decrease in apoptotic cells. Although
apoptotic cells were seen in some areas even 24 h after WBH, the
thymus was atrophic without any apoptotic cells at 48 h, suggesting
that cell loss was complete. Apoptosis in the spleen, in contrast,
peaked 4 h after WBH, and then levels declined rapidly to pretreat
ment levels by 12 h after WBH. At 12 h, the spleen showed hypo
cellularity resulting from cell loss by apoptosis, but apoptotic cells
were not seen. Thereafter, overall increased numbers of lymphoid
cells in the lymphoid tissue with plentiful mitotic figures were ob
served. The peak of apoptosis in the small intestine also occurred 4 h
after WBH. Only a few apoptotic cells remained 4 h later and the
mucosa reverted completely to normal 12 h after WBH. The bone
marrow showed minimal apoptotic changes. Although there was an
observable increase in the number of apoptotic cells at 4 h, the
apoptotic cells disappeared almost completely by 8 h after WBH. At
that time, hyperplasia occurred with increased numbers of erythroid
and myeloid cells accompanied by numerous megakaryocytes.
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Fig. 2. Photomicrographs of H & E-stained sections of the Ward colon carcinoma
(X400). A, the untreated tumor is composed of disorganized clumps of cells of variable
size. There are a few spontaneous apoptotic cells. B, the treated tumor 4 h after WBH. The
tumor contains widespread, extensive numbers of apoptotic cells, accompanied by coag
ulative necrosis. Arrows point to apoptotic cells.
DISCUSSION
(b) the magnitude of the peak level of apoptosis was significantly
greater for the Ward colon tumor (39 and 43% at 4 and 8 h, respec
tively, after WBH) in comparison to the fibrosarcoma (19% at 4 h
Tumors consist of cell populations in which cell gain and cell loss
occur simultaneously. The balance between cell gain and cell loss
after WBH; P < 0.05); and (c) although apoptosis was rapidly induced
in both the Ward colon carcinoma and the fibrosarcoma,
the duration
of increased apoptosis due to WBH treatment was considerably longer
for the Ward colon tumor in comparison to the fibrosarcoma. In the
Ward colon tumor, the peak level of apoptosis of about 40% was
maintained for at least 4 h (at 4 and 8 h after WBH), followed by a
relatively gradual decline in the percentage of apoptosis to pretreat
ment levels by 48 h after WBH. In contrast, the peak level of 19%
(I)
(I)
0
apoptosis at 4 h after WBH in the fibrosarcoma
was of a much shorter
duration, declining rapidly to 8% by 6 h after WBH and then further
decreasing
gradually to pretreatment
levels by 24 h after WBH.
Apoptosis in the Normal Tissues. Apoptosis in the normal tissues
induced by WBH was examined histologically from 4 to 48 h after
WBH. Fig. 4 shows the microscopic features of normal tissues exam
med 4 h after WBH. We observed the greatest increase in apoptosis
following WBH exposure in the thymus. All lobules have clumps of
apoptotic
cells throughout
the cortex
cellular loss by apoptosis was
spleen. Most of the splenic
the marginal zones contain
Changes in the incidence of
apoptosis
observed
WBH
were
0
12
24
36
48
with a lesser level of apoptosis
in the medulla (Fig. 4B). WBH-induced
also observed in the white pulp of
periarteriolar lymphoid sheaths and
clumps of apoptotic cells (Fig. 4D).
following
I
also
in the mediastinal
Time
after
the
beginning
of
WBl-I
(h)
Fig. 3. Kinetics of apoptosis in tumor tissues induced by WBH. Rats bearing fibro
sarcoma (0) or Ward colon carcinoma (•)were euthanized at the indicated times after the
beginning of'WBH treatment, and apoptosis was quantified as described in “Materials
and
Methods.―The control values for tumor apoptosis are indicated at the zero time point on
the X axis. The error bars indicate the SD for the mean value at each data point.
5461
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Research.
APOPTOSISINDUCEDBY HYPERTHERMIA
.‘ is
)J@.#,
,
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.E:
Fig. 4. Photomicrographs
of H & E-stained sections of the normal tissues (X400). Treated rats were euthanized 4 h after the beginning of WBH. The photomicrographs
are of
representative animals from the control and treated groups. A, thymus of a control rat. B, thymus of a treated rat. There are numerous apoptotic cells seen throughout the cortex. C,
spleen of a control rat. D, Spleen of a treated rat. The white pulp contains widespread apoptotic celis, especially in the periarteriolar lymphoid sheaths. E, small intestine of a control
rat. F, small intestine of a treated rat. The lamina propria of the villi contains apoptotic cells. G, bone marrow of a control rat. H, bone marrow of a treated rat. There are scattered
apoptotic cells. Arrows point to apoptotic cells.
5462
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Research.
APOPTOSIS INDUCED BY HYPERThERMIA
I
0
12
24
Twv* aft8f
tPe be@irnsng
30
of
WBH
48
Oi)
Fig. 5. Kinetics of apoptosis in normal tissues induced by WBH. Rats were euthanized
at the indicated times after the beginning of WBH, and apoptosis in the thymus (A), spleen
(L@@),
small intestine
(•),and bone marrow
(0) was scored on a graded scale of 0—4: 0,
none; 1, modest; 2, mild; 3, moderate; and 4, severe. The error bars indicate the SD for
the mean value at each data point.
determines whether a tumor mass grows or regresses (29). Loss of
cells in a tissue results largely from cell death through apoptosis
and/or necrosis. Both apoptosis and necrosis occur spontaneously
within tumors (30). Cell death, however, is also the end result of
cytotoxicity induced by therapeutic modalities that produce antitumor
effects.
Hyperthermia induces apoptosis in tumor cells in vitro (4, 5, 10,
11). Harmon et a!. (13) quantified the incidence of apoptosis in four
in vivo murine tumors and showed that the ability of hyperthermia to
induce apoptosis varied from tumor to tumor. In that study, however,
the level of apoptosis was examined only at one time point (4 h after
treatment), and the correlation between the extent of apoptosis and the
tumor response was not discussed. Takano et a!. (10) examined
heat-induced apoptosis using three cell lines in vitro and demonstrated
that the kinetics of apoptosis differed between those cell lines. These
findings indicate the need to evaluate both the extent and the kinetics
of apoptosis in tumors in vivo. In this study, we measured WBH
induced apoptosis in two tumors, one of which is relatively resistant
and the other relatively sensitive to WBH (41.5°Cfor 2 h). We found
differences between the two tumors in both the extent and the kinetics
of apoptosis following treatment. The differing levels of apoptosis
correlated with the differing WBH-induced response seen in the two
tumors.
Spontaneous apoptosis occurred in both tumors, but the level was
higher in the heat-sensitive Ward colon carcinoma than in the heat
resistant fibrosarcoma. Moreover, the kinetics of WBH-induced ap
optosis was different when comparing these two tumors. WBH in
duced apoptosis rapidly, and a marked increase of apoptotic cells was
observed
in both tumors
4 h after the beginning
of WBH.
The extent
of apoptosis, however, was greater in the Ward colon carcinoma
(39%) compared with the fibrosarcoma (19%). In the fibrosarcoma,
the number of apoptotic cells decreased rapidly (by 8 h following
WBH), and meaningful increases in apoptotic cell numbers could no
longer be observed by 24 h. The elimination of apoptotic cells occurs
by phagocytosis of neighboring cells and macrophages (1). On the
other hand, in the Ward colon carcinoma, the percent of apoptotic
cells remained at a peak level (43%) at 8 h and then decreased more
gradually to the pretreatment level 48 h after WBH. Thus, there was
considerable difference in the extent of WBH-mediated apoptosis
between these two tumors in terms of both the peak values and overall
kinetics
of apoptosis.
In addition,
the extent
of apoptosis
seemed
to
correlate with the sensitivity of each tumor to WBH-induced cell
killing, as measured by TGD.
In the Ward colon carcinoma treated with WBH, necrosis was
observed, as well as apoptosis. Increasing the dose of stimuli may
cause a switch from cell death by apoptosis to cell death by necrosis
(1 1, 12). Both necrosis and apoptosis, however, can occur simulta
neously in the tissues through independent processes. Why cells enter
the different paths of cell death in response to hyperthermia is not
clear. Possibly the induction of necrosis is partially due to an indirect
effect of hyperthermia altering tumor microcirculation in solid tumors,
in addition to direct heat-induced cytotoxicity. The antitumor effect of
WBH, of course, is an outcome of cell loss through at least these two
processes of apoptosis and necrosis.
Apoptosis is an essential process for living tissues to maintain
their architecture and functions. Large numbers of cells can be
deleted physiologically from living normal tissues by apoptosis
under a variety of physiological situations as a normal biological
response, which is activated when a multicellular organ requires
the deletion of specific cells (14). Apoptosis also occurs in normal
tissues in response to cytotoxic modalities such as radiation, che
motherapeutic drugs, and hyperthermia (17—22).In this study, we
demonstrated and characterized the occurrence of WBH-induced
apoptosis in normal tissues.
Physiological
apoptosis
in normal
tissues
occurs
particularly
in
tissues with a high cellular turnover (14), because cell death must keep
pace with cell production in systems with extensive tissue renewal to
prevent tissue expansion. Wyllie (30) suggested that cells in the
high-turnover
state are primed
or programmed
for apoptosis
and, thus,
are killed by means of apoptosis in response to a variety of lethal
stimuli. We showed that WBH also induced apoptosis in organs with
rapidly renewing cell populations such as lymphoid tissues, intestine
(in particular, cells of lymphoid origin in the lamina propria of the
mucosa), and bone marrow. Lymphoid tissues, especially the thymus,
were most sensitive to WBH-induced cell death by apoptosis. We
observed hypocellularity in the thymus during the time period after
WBH when the levels of apoptosis were decreasing, and this was
followed by cellular hyperplasia. The apoptotic change in bone mar
row following WBH treatment was relatively mild, but bone marrow
hyperplasia
was recognized
soon after the deletion
of apoptotic
bod
ies. Apoptosis is a physiological response to remove damaged cells
from tissues and may play an important role for maintenance of organ
structure and/or functions altered by drug or heat treatment.
In contrast, the mucosa of the intestine returned to its normal
cellular status after WBH exposure without secondary mucosal hy
perplasia. Also, the extent of apoptosis occurring in the small intestine
after WBH treatment was less than that observed in the thymus or the
spleen. Apoptotic cells in the mucosa are phagocytosed rapidly by
neighboring healthy enterocytes or extruded into the lumen soon after
their formation (17, 18). Potten (31) analyzed apoptosis induced by
irradiation and chemotherapeutic drugs in the intestine and suggested
that apoptosis in the intestine may protect the surrounding uninjured
intestinal cells against drug-induced toxicity. Because cell death via
apoptosis is a process in which cells die singly and are rapidly
eliminated without causing any inflammatory damage to the surround
ing tissue, the intestinal tissue is able to maintain its overall cellular
architecture and continue to function. Therefore, apoptosis in the
normal tissues could be considered an event initiated by both extrinsic
and intrinsic forces and may exist as a mechanism of cell deletion that
protects neighboring cells from damage (14). In organ systems sen
sitive to WBH-induced damage, a large number of cells that are
actually damaged by WBH seem to be removed by apoptosis within
12—48h, which may allow the organ system to continue its normal
function.
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Research.
APOPTOSIS INDUCED BY HYPERTHERMIA
Topoisomerase Il-reactive chemotherapeutic drugs induce apoptosis in thymocytes.
Cancer Res., 51: 1078—1085,1991.
We describe the extent and kinetic features of WBH-induced ap
optosis in tumor and normal tissues in vivo. Our fmdings suggest that
apoptosis may play a pivotal role in the outcome of therapy. Indeed,
the induction of apoptosis by heat, radiation, or chemotherapy may
foreordain both tumor and normal tissue response to the treatment.
16. Storey, M. D., Stephens, L. C., Tomasovic, S. P., and Meyn, R. E. A role for calcium
in regulation of apoptosis in rat thymocytes irradiated in vitro. Int. J. Radait. Biol., 61:
243—251,1992.
17. Searle, J., Lawson, T. A., Abbott, P. J., Harmon, B., and Kerr, J. F. R. An electron
microscope study of the mode of cell death induced by cancer-chemotherapeutic
agents in populations of proliferating normal and neoplastic cells. J. Pathol., 116:
129—138,1975.
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5464
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Research.
Apoptosis in Tumors and Normal Tissues Induced by Whole
Body Hyperthermia in Rats
Yoshihisa Sakaguchi, L. Clifton Stephens, Masato Makino, et al.
Cancer Res 1995;55:5459-5464.
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