Journal of Diabetology, February 2011; 1:3
http://www.journalofdiabetology.org/
Original Article:
Study of Pro-insulin Level and Its Role in a Cohort of Women with
Gestational Diabetes in Alexandria, Egypt
*F.E. Amara1 , M.E. Meleis 2 , M .A. Seif 3 , E.Y. Moursy 1 , S.A. El-Sheikh1 ,
M .H Megallaa 1 , H. Hassan 1
Abstract:
To study the levels of serum pro-insulin or pro-insulin/insulin ratio (PIR) in women suffering from
gestational diabetes mellitus (GDM), as an additional factor to their insulin resistance state during
pregnancy; and to evaluate any change or reversibility of serum pro-insulin or PIR during the
postpartum period. The study was conducted on 30 pregnant women in their second or third trimester
and 10 age-matched non pregnant, normoglycemic women, as a reference group. The pregnant
women were divided into 3 equal groups; normoglycemic women with normal oral glucose tolerance
test (OGTT), obese women with GDM and lean women with GDM. Diagnostic OGTT was performed
and pro-insulin levels, insulin levels, C-peptide levels, pro-insulin/insulin ratio (PIR) and insulin sensitivity
were determined. These tests were repeated after 4-8 weeks of the postpartum period. Serum levels of
pro-insulin and the PIR were significantly higher in obese and lean women with GDM than the control
and reference groups during pregnancy and after delivery (p=0.0001). Insulin sensitivity index was
significantly lower and relative resistance for insulin was significantly higher in GDM women (p<0.0001).
After delivery the sensitivity index was significantly higher than during pregnancy in pregnant women,
recruited in the study. C-peptide levels were significantly higher in GDM patients versus control and
reference groups during pregnancy. After delivery, C-peptide levels were significantly lower in the 3
pregnant groups (p<0.0001). Women with GDM have elevated serum pro-insulin and increased PIR
which might serve as a marker for the disease. Moreover, this characteristic profile might be useful for
the prediction of gestational diabetes mellitus (GDM).
Key words: Pro-insulin, Gestational diabetes mellitus, Pro-insulin/insulin ratio.
Introduction
Gestational diabetes mellitus (GDM) is defined as
any degree of glucose intolerance with onset or
first recognition during pregnancy. The definition
applies regardless of whether insulin or only diet
modifications is used for treatment or whether the
condition persists after pregnancy.(1)
1Department
of Internal Medicine. Alexandria
University, Alexandria, Egypt.
2Department
Gynecology
&
Obstetrics,
Alexandria University, Alexandria, Egypt.
3Department
Clinical Pathology
University, Alexandria, Egypt.
Alexandria
*Corresponding Author:
Fahmy Amara
Emeritus Professor of Internal Medicine, Unit of
Diabetes & Metabolism, Department of Internal
Medicine, Alexandria University, Alexandria,
Egypt.
E-mail: fahmyamara@hotmail.com
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GDM is detected through the screening of
pregnant women for clinical risk factors and
testing for abnormal glucose tolerance. As many
women with GDM are asymptomatic, screening
for the disease would be very important. GDM
appears to result from the same broad spectrum
of physiological and genetic abnormalities that
characterize diabetes without pregnancy (2).
Indeed, women with GDM are at high risk for
developing diabetes later in the life (2). Thus,
GDM provides a unique opportunity to study the
early pathogenesis of diabetes and to develop
interventions to prevent the disease (2).
Normal
pregnancy
is
accompanied
by
progressive insulin resistance that begins near
mid-pregnancy and progresses through the third
trimester to levels that approximate the insulin
resistance seen in individuals with type 2
diabetes. This appears to result from a
combination of increased maternal adiposity
and
the
insulin-desensitization
effects
of
hormonal products of the placenta. The
pancreatic ß cells normally increase their insulin
secretion to compensate for the insulin resistance
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Journal of Diabetology, February 2011; 1:3
of pregnancy. As a result, changes in circulating
glucose levels over the course of pregnancy are
quite small compared with the large changes in
insulin sensitivity (3,4).
GDM is a form of hyperglycemia that results from
an insulin supply that is inadequate to meet the
tissue demands for normal blood glucose
regulation (5). It is likely that there is not a single
underlying biochemical etiology for the chronic
insulin resistance that frequently accompanies
GDM and most likely contributes to the high risk
of type 2 diabetes. Women with GDM tend to be
obese; small studies have revealed increased
circulating levels of leptin and the inflammatory
markers, tumor necrosis factor-a (TNF-a) and Creactive protein (C-RP), and decreased levels of
adiponectin, in women with GDM (6-8).
Increased content of fat in the liver and muscle
has also been reported in women with previous
GDM (9,10). Defects in the binding of insulin to it's
receptors in skeletal muscle do not appear to be
involved in the exaggerated insulin resistance of
GDM. Alterations in the insulin signaling pathway,
abnormal subcellular localization of glucose
transporter 4 (GLUT4), reduced expression of
PPAR?
(peroxisome
proliferator-activated
receptors
gamma),
increased
expression
membrane glycoprotein PC-1 and reduced
insulin-mediated glucose transport have been
found in skeletal muscle or fat cells of women
with GDM (11,12).
Progressive ß-cells dysfunction has been reported
in women with GDM that, over years, leads to
progressive hyperglycemia and diabetes after
pregnancy (13). Longitudinal studies of lean and
obese women before pregnancy, at the second
trimester and in the third trimester also reveal an
increase in the insulin secretion in association with
the acquired insulin resistance of pregnancy.
However, GDM appears when the increase of
insulin secretion is not enough to compensate for
the increased insulin resistance in pregnant
women (2,13).
Proinsulin is a 9-K dalton peptide, containing the
A and B chains of insulin joined by a connecting
peptide (C-peptide) of 30-35 amino acids. The
structural conformations of proinsulin and insulin
are very similar, and the major function of Cpeptide is to facilitate the correct folding of A
and B chains. The enzymes remove the Cpeptide and cleavage peptides, yielding insulin
which has a lower solubility and hence coprecipitates with zinc to form micro-crystals within
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the secretory granules. Insulin and C-peptide are
stored in equimolar amounts; under normal
conditions, 95% of the biosynthetic products are
secreted as insulin and less than 5% as
unconverted proinsulin (14).
The aim of the present study was to study the
levels of serum proinsulin or proinsulin/insulin ratio
(PIR) in women suffering from gestational
diabetes mellitus (GDM) as an additional factor
to their insulin resistance during pregnancy, and
to evaluate any change or reversibility of serum
proinsulin or PIR during the postpartum period.
Methodology
The study included 40 age matched women
divided into 4 groups as follow:
Group I: included 10 non diabetic pregnant
women as a control group.
Group II: included 10 obese GDM women.
Group III: included 10 lean GDM women.
Group
IV:
included
10
non
pregnant
normoglycemic women as a reference group.
The women included in this study were selected
from the outpatient clinic of the Gynecology and
Obstetric Department and admitted to the
Diabetes and Metabolism Unit, Alexandria Main
University Hospital. Medical history of each
woman enrolled in the study was recorded and
clinical evaluation performed. Body weight (Kg)
and height (m) were determined for all women
and body mass index (BMI) was calculated
according to the Quetelet equation. The study
was approved by the hospital ethics committee,
and written informed consent was obtained from
all subjects.
During pregnancy, OGTT (1) was performed in
the morning after an overnight fast of at least 8
hours; the recommendations are for 8-10 hours
fasting and after at least 3 days of unrestricted
diet and physical activity. The test was done by
using 100 gm glucose orally. Blood samples were
withdrawn at 0, 30, 60, 120, 180 minutes for blood
glucose measurements. After delivery, the
subjects were scheduled for a 2-hour 75 gm OGTT
a t 4-8 weeks, post partum. Blood samples were
withdrawn at 0, 30, 60, 120 minutes. peripheral
blood samples were taken by venipuncture of
antecubital vein and the serum was used to
measure blood glucose levels using the standard
techniques for oxidase method. The remaining
serum was stored at -20°c for insulin assay.
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Journal of Diabetology, February 2011; 1:3
Proinsulin measurement was done by ELISA
technique (15). Proinsulin EIA is a solid phase
enzyme-linked immunosorbent assay (ELISA),
based on the sandwiched principle (15);
microtiter wells are coated with a monoclonal
antibody directed towards a unique antigenic
site on a proinsulin molecule. An aliquot of
patient
sample
containing
endogenous
proinsulin is incubated in the wells after washing
off the samples in the second step an enzyme
conjugate, which is an anti-proinsulin antibody
conjugated with horseradish peroxidase is
incubated in the wells. After incubation the
unbound conjugate is washed off with solution.
Having added the substrate solution, the intensity
of the color developed is proportional to the
concentration of proinsulin in the patient sample.
Similarly, the insulin estimation was performed
using ELISA kit; the ACTIVE INSULIN ELISA is an
enzymatically amplified one step sandwich-type
immunoassay (16). Both proinsulin and insulin
ELISA Kits were manufactured by Mercodia AB
Company, Uppsala, Sweden.
Peripheral insulin sensitivity (SI) and insulin release
in response to glucose (IRG) were assessed in all
patients by the use of 100 gm OGTT. Plasma
glucose and insulin were measured at 0, 30, 60,
120, 180 minutes during the OGTT. The total areas
under glucose and insulin curves were
calculated. These areas were divided by 2h to
yield the mean plasma glucose and the insulin
concentrations during the OGTT. IRG was
expressed as the ratio of the area under the
insulin curve to that of the glucose curve above
fasting levels. The peripheral glucose uptake rate
(M) during the OGTT was measured as the
difference between the glucose load and the
increase in the amount of glucose in the glucose
space during OGTT. SI was expressed as the ratio
of the metabolic clearance rate (M/mean
plasma glucose) to log mean serum insulin.
Relative peripheral insulin resistance is equal to
1/M (17).
Estimation of C-peptide was done for all study
subjects using immulite assay immunoassay
system
(16).
The
immulite
automated
immunoassay analyzer is a continuous random
access instrument which performs automated
chemiluminescent immunoassay. This system
utilizes assay-specific antibody or antigen coated
plastic beads as the solid phase, alkaline
phosphatase-labeled
reagent,
a
chemiluminescent enzyme substrate (16). All
these tests were repeated 4-8 weeks postpartum
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to evaluate the difference between
homeostasis during and after pregnancy.
insulin
Statistical Analysis
Data were represented as mean ± SD. For
intergroup comparisons, measured variables
were analyzed by one way ANOVA test. The
level of significance was determined at P less
than 0.05. Correlation coefficient was used to
study
correlation
between
measured
parameters.
Results
All women were age matched. The mean values
of their age were 28.9±1.37 years, 28.7±2.67 years,
29.3±1.83 years and 28.2±3.01 years in controls,
obese women with GDM, lean women with GDM
and non pregnant women respectively (p>0.05).
The BMI ranged from 23-30 Kg/m² in control
group with a mean value of (26.6±2.52 Kg/m²). In
obese GDM women BMI mean value (31.8±2.72
Kg/m²) was significantly higher than that of other
3 groups (p<0.05). In lean GDM women BMI
mean value (22.8±1.38 Kg/m²) was significantly
lower than that of control group, obese GDM
women and non pregnant women (p<0.05). In
non pregnant women (reference group) BMI
mean value (27.4±2.5Kg/m²) was significantly
lower than that of obese GDM and significantly
higher than lean GDM women (p<0.05) (Table I)
During pregnancy, the mean plasma glucose
levels during 100gm OGTT were significantly
higher in women with gestational diabetes (both
obese and lean) compared with normal glucose
tolerant pregnant women at the fasting state
and at 30, 60, 120 and 180 minutes (p<0.05).
Futhermore; at 30 minutes the mean plasma
glucose level was significantly higher in lean than
obese GDM women (P<0.05), while at 60 minutes,
the mean plasma glucose level was significantly
higher in obese than lean GDM women (P<0.05).
After delivery, the mean plasma glucose levels
during 75 gm OGTT were significantly higher at 30
and 60 minutes in GDM women (both obese and
lean) than in the non diabetic pregnant women
(group I) and the non pregnant non diabetic
women (group IV) (P<0.05).
At 120 minutes, the mean plasma glucose levels
were significantly higher in GDM women (both
obese and lean) than in group I and in obese
GDM women than in group IV (P<0.05).
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Journal of Diabetology, February 2011; 1:3
Table I: Comparison between the four studied groups as regards age and BMI
Age (years)
Range
Mean ± SD
BMI (Kg/m²)
Range
Mean ± SD
Group I
non diabetic
pregnant
women
Group II
obese GDM
women
Group III
lean GDM
women
Group IV
non pregnant
non diabetic
women
27-31
28.9±1.37
25-33
28.7±2.67
27-32
29.3±1.83
22-33
28.2±3.01
P=0.736
23-30
26.6±2.52
28.5-37
31.8±2.72*
20.9-24.6
22.8±1.38*#
23-31.7
27.4±2.5# •
P=0.0001
ANOVA
test
P is significant if <0.05*: significant versus group I
# : significant versus obese GDM women (group II)
• : significant versus lean GDM women (group III)
Table II: Comparison between the four studied groups as regards proinsulin, proinsulin/insulin ratio and
C-peptide during pregnancy
Proinsulin (Pmol/l)
Range
Mean ± SD
Proinsulin/insulin
ratio
Range
Mean ± SD
C-peptide (ng/ml)
Range
Mean ± SD
Group I
non diabetic
pregnant
women
Group II
obese GDM
women
Group III
lean GDM
women
Group IV
non pregnant
non diabetic
women
5.30-6.60
5.60±0.77
13.5-15.8
14.62±0.75*
14-17.8
16.04±1.30*#
2.4-4.2
3.01±0.62*# •
P=0.000001
0.29-0.59
0.396±0.09
0.34-0.51
0.435±0.05*
0.49-0.51
0.580±0.08*#
0.27-0.56
0.367±0.09# •
P=0.00001
0.5-0.8
0.599±0.08
0.58-1.0
0.794±0.12*
0.66-0.92
0.738±0.08*
0.50-0.55
0.525±0.02# •
P=0.002
ANOVA
test
P is significant if <0.05 * : significant versus group I
# : significant versus obese GDM women (group II)
• : significant versus lean GDM women (group III)
During pregnancy, the mean values of insulin
levels during OGTT (100gm) were significantly
higher in GDM women (both obese and lean) as
compared to non diabetic pregnant control
group at the fasting, 30, 60, 120 and 180 minutes
(P<0.05). Also, the mean values of insulin levels
were significantly higher in obese than lean GDM
women at all points of the OGTT (p<0.05). After
delivery, the mean values of serum insulin during
OGTT (75 gm) were significantly lower in obese
GDM women as compared to other groups at 30
and 120 minutes (P<0.05). No significant
differences were found in the mean serum insulin
at 60 minutes between the four studied groups
(P>0.05).
During pregnancy the mean values of proinsulin,
proinsulin/insulin ratio and C-peptide levels
weresignificantly higher in obese and lean GDM
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women than the control group (non diabetic
pregnant women) and reference group (non
diabetic non pregnant women) (P<0.05) (Table
II). After delivery, the mean values of proinsulin
and proinsulin/insulin ratio were significantly
higher in both obese and lean GDM women than
the control group (p<0.05) and the mean Cpeptide level was significantly higher in obese
GDM women as compared to the reference
group (Table III). Comparing these parameters
during pregnancy and after labor, it was found
that the mean values of proinsulin were
significantly higher during pregnancy than after
delivery in the three studied pregnant groups
(P<0.05). The mean proinsulin/insulin ratios were
significantly higher in non diabetic pregnant
women (group I) and significantly lower in GDM
women (both obese and lean), during
pregnancy than after delivery (P<0.05).
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Journal of Diabetology, February 2011; 1:3
Table III: Comparison between the four studied groups as regards proinsulin, proinsulin/insulin ratio and
C-peptide after delivery
Group I
normoglycemic
pregnant
women
Group II
obese GDM
women
Group III
lean GDM
women
Group IV
non pregnant
non diabetic
women
1.90-4.00
2.87±0.64
9.8-12
10.83±0.67*
9.8-12.7
11.37±0.89*#
2.4-4.2
3.01±0.62# •
P=0.00001
0.19-0.44
0.310±0.08
0.58-1.44
0.930±0.24*
0.64-1.15
0.989±0.14*
0.27-0.56
0.367±0.09# •
P=0.0001
0.53-0.71
0.584±0.05
0.51-0.67
0.583±0.04
0.50-0.63
0.561±0.04
0.50-0.55
0.525±0.02*#
P=0.010
Proinsulin (Pmol/l)
Range
Mean ± SD
Proinsulin/insulin
ratio
Range
Mean ± SD
C-peptide (ng/ml)
Range
Mean ± SD
ANOVA
test
P is significant if <0.05
* : significant versus group I
# : significant versus obese GDM women (group II)
• : significant versus lean GDM women (group III)
Table IV: Comparison between the levels of proinsulin, proinsulin/insulin ratio and C-peptide during
pregnancy and after delivery in the three pregnant studied groups
Proinsulin
During pregnancy
After delivery
Paired t-test
Proinsulin/insulin
ratio
During pregnancy
After delivery
Paired t-test
C-peptide
During pregnancy
After delivery
Paired t-test
Group I
normoglycemic
pregnant women
Group II
obese GDM women
Group III
lean GDM women
7.60±0.97
2.87±0.64
t=12.99*, P=0.0001
14.62±0.75
10.83±0.67
t= 11.660*, P=0.0001
16.04±1.30
11.73±0.89
t= 7.467*, P=0.0001
0.396±0.09
0.310±0.08
t= 3.151*, P=0.001
0.435±0.05
0.930±0.24
t=7.294*, P=0.0001
0.580±0.08
0.989±0.14
t=8.331*, P=0.0001
0.599±0.08
0.584±0.05
t=0.853, P=0.416
0.794±0.12
0.538±0.04
t= 6.640*, P=0.001
0.738±0.08
0.561±0.04
t=9.132*, P=0.0001
P is significant if <0.05* : significant
The mean C-peptide levels were significantly
higher during pregnancy than after delivery in
GDM women (both obese and lean) (P<0.05). No
significant
difference
was
found
during
pregnancy and after delivery in the mean Cpeptide level in the control group (group I)
(P>0.05) (Table IV).
During pregnancy (Table V), the insulin sensitivity
index (SI) was significantly lower and the relative
resistance for insulin was significantly higher in
women with gestational diabetes (both obese
and lean), compared with the normal glucose
tolerant pregnant women (P<0.05) as well as
after delivery (Table VI). Comparing these two
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parameters of insulin action during pregnancy
and after delivery, it was found that the SI was
significantly higher and the relative resistance for
insulin was significantly lower after delivery than
during pregnancy in GDM women (both obese
and lean) as well as in pregnant women with
normal glucose tolerance (P<0.05) (Table VII). A
significant inverse relation was found between
the proinsulin/insulin ratio and the sensitivity index
in the GDM women (both obese and lean) as
well as in the normal glucose tolerant pregnant
women (r= -0.725, -0.772, -0.767) respectively
P<0.05. (Table VIII).
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Journal of Diabetology, February 2011; 1:3
Table V: Comparison between the three pregnant studied groups as regards insulin sensitivity index
and relative resistance for insulin during pregnancy
Insulin sensitivity index
Range
Mean ± SD
Relative resistance for
insulin
Range
Mean ± SD
P is significant if <0.05
Group I
normoglycemic
pregnant
women
Group II
obese GDM
women
Group III
lean GDM
women
4.51-7.54
6.03±0.92
1.36-3.70
2.44±0.67*
1.53-3.78
2.82±0.61*
P=0.00001
2.1-2.89
2.52±0.25
3.09-6.00
4.12±1.00*
3.06-6.07
3.88±0.84*
P=0.0001
ANOVA test
* : significant versus group I
Table VI: Comparison between the four studied groups as regards insulin sensitivity index and relative
resistance for insulin after delivery
Insulin sensitivity index
Range
Mean ± SD
Relative resistance
insulin
Range
Mean ± SD
Group I
normoglycemic
pregnant
women
Group II
obese GDM
women
Group III
lean
GDM
women
Group IV
non pregnant
non diabetic
women
7.66-19.64
12.1±3.29
4.43-11.75
7.36±2.32*
6.8913.57
9.41±1.96
6.51-13.57
13.22±3.90 #
•
P=0.00001
1.91-2.99
2.39±0.34
2.21-4.29
3.15±0.68*
1.81-2.33
2.95±0.15
2.03-3.67
2.46±0.56 # •
P=0.00001
for
ANOVA
test
P is significant if <0.05
* : significant versus group I
# : significant versus obese GDM women (group II)
• : significant versus lean GDM women (group III)
Table VII: Comparison between the levels of insulin sensitivity index and relative resistance for insulin
during pregnancy and after delivery in the three pregnant studied groups
Group I
normoglycemic pregnant
women
Group II
obese GDM
women
Group III
lean GDM women
6.03±0.92
12.06±3.29
t=6.352*, P=0.001
2.44±0.67
7.36±2.32
t=6.714*, P=0.001
2.82±0.61
9.41±1.96
t=11.368*, P=0.0001
2.52±0.25
2.39±0.34
t=1.047, P=0.322
4.12±1.00
3.15±0.68
t=2.757*, P=0.022
3.88±0.84
2.15±0.15
t=6.368*, P=0.001
Insulin sensitivity index
During pregnancy
After delivery
Paired t-test
Relative resistance for
insulin
During pregnancy
After delivery
Paired t-test
P is significant if <0.05
* : significant
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Table VIII: Correlation between proinsulin, proinsulin/insulin ratio and the sensitivity index in the
three pregnant studied groups.
Pro-insulin
Pro-insulin/insulin
ratio
r = correlation coefficient
SI= sensitivity index
Group I
normoglycemic
pregnant women
SI
r = 0.034
P= 0.975
r = -0.767*
P= 0.036
Group III
lean GDM women
SI
r = 0.048
P= 0.942
r = -0.725*
P= 0.039
SI
r = 0.253
P=0.715
r = -0.772*
P= 0.028
P is significant if <0.05
Discussion
It is widely accepted now that insulin resistance
and hyperinsulinemia are characteristic features
of late pregnancy and that gestational diabetes
is associated with a failure in insulin secretory
capacity to compensate for insulin resistance.
Gestational diabetes mellitus is one of the most
common complications of pregnancy (2) and
frequently predictive of later maternal impaired
glucose tolerance or type 2 diabetes mellitus
(18). Pathophysiological abnormalities detected
in women who develop gestational diabetes
may provide clues to the etiology of type 2
diabetes mellitus (2,18).
The important feature in the results of this study is
that the mean levels of proinsulin were
significantly higher during pregnancy than after
delivery in groups I (normoglycemic women), II
(obese GDM women) and III (lean GDM women).
During pregnancy the mean values of proinsulin
were significantly higher in both group II (obese
GDM women) and group III (lean GDM women)
compared with group I (normoglycemic
pregnant women) and group IV (non-pregnant
non-diabetic women). Moreover, the mean
values of proinsulin after delivery were
significantly higher in group II and group III,
compared with group I and group II (Tables III &
IV).
Another important observation is the mean
values of proinsulin/insulin ratio during pregnancy
and after delivery. This ratio was significantly
higher in gestational diabetic women (both
obese and lean) than the control and reference
groups (P= 0.00001). After delivery, the
proinsulin/insulin ratio showed similar profile i.e.
was also significantly higher in groups II and III,
compared with groups I and IV (P=0.0001).
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Group II
obese GDM women
Kautzky-Willer et al (19) studied the kinetics and
secretion of Islet Amyloid Pancreatic Polypeptide
(IAPP), the serum concentrations of proinsulin
and the fasting proinsulin/insulin ratio both before
and after delivery in lean pregnant women with
gestational
diabetes
mellitus
(GDM)
in
comparison to those with normal glucose
tolerance (NGT) and to non-pregnant healthy
lean (control) and obese insulin-resistant women,
during oral glucose tolerance tests. They found
that both serum proinsulin and proinsulin/insulin
ratio were significantly higher in GDM patients
compared with control subjects. They also
reported that after delivery the proinsulin/insulin
ratios remained elevated. So they concluded
that increased proinsulin concentrations and a
raised proinsulin/insulin ratio are specific for GDM
and might thus serve as its marker and potentially
even identify subjects at high risk for the
development of type 2 diabetes.
Pathophysiological abnormalities detected in
women who develop GDM may provide clues to
the etiology of type 2 diabetes. It has been
established that in type 2 diabetes the ß-cell
secretes a higher proportion of partially
processed insulin precursors than is the case in
normoglycemic individuals (20). Even at the
stage of IGT, elevated proinsulin levels are found.
These relatively biologically inactive precursor
molecules cross- react in most conventional
radioimmunoassays for insulin, thus suggesting
that many previous studies of insulin secretion in
type 2 diabetes may have underestimated the
degree to which impairment of insulin secretion
contributes to the disease (20). While, a number
of studies have attempted to define the insulin
secretory status of women with GDM, few studies
have used assays that specially measure insulin
and its various precursor forms. Dornhorst et al
(21) have demonstrated an increased fasting
intact proinsulin level in women with GDM as
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Journal of Diabetology, February 2011; 1:3
compared to pregnant control subjects. Swinn et
al (22) studied more specifically specific
correlating abnormalities of glucose metabolism
which is the 32, 33 split proinsulin. They reported
elevated levels of such proinsulin in GDM patients
both fasting and 120-min versus pregnant
normoglycemic control subjects.
The prospective follow-up study of Hanson et al
(23) did not support the hypothesis that an
increased fasting proinsulin -to- insulin ratio (PI/I) is
a marker for later development of type 2
diabetes or impaired glucose tolerance in former
GDM subjects. This is because their results
demonstrate that an increased PI/I in former
GDM subjects seems to be a consistent finding
because there was a significant correlation
between the PI/I in the first follow up ( 3-4 years
after an index pregnancy) and the second follow
up ( 3 years after the first follow up) studies.
Because there was no association between the
PI/I in subsequent follow ups, they could not
support that an elevated PI/I is a marker for
future development of glucose intolerance..
Furthermore, Festa et al (24) investigated the
levels of proinsulin (PI), specific insulin (SpI) and
the proinsulin-to-specific insulin (PI/SpI) ratio in
consecutive pregnant women with normal
glucose tolerance (NGT), and with gestational
diabetes (GDM), in comparison to 32 healthy,
non-pregnant women. They found no significant
differences in the levels of PI and the PI/SpI ratio
between pregnant and non pregnant women,
and between pregnant women with GDM and
NGT. So, they suggested that in normoglycemic
pregnancy as well as GDM metabolic alterations
including enhanced insulin resistance and
hyperglycemia did not result in an increase in
circulating levels of specific insulin, as indicated
by proinsulin -to- specific insulin ratio.
In the present study, the insulin sensitivity index
was significantly lower and the relative resistance
for insulin was significantly higher in the women
with gestational diabetes (both obese and lean)
compared with the normal glucose tolerant
pregnant women (P=0.00001). Comparing the
markers of insulin action during pregnancy and
after delivery, it was found that the insulin
sensitivity index was significantly higher and the
relative resistance for insulin was significantly
lower after delivery both in normoglycemic
women and patients with GDM (both obese and
lean).
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It is known, and was further confirmed in this
study, that women with GDM are known to be
insulin resistant, hyperinsulinemic and have a high
risk of developing type 2 diabetes later in the life.
Such insulin resistance that develops during
gestation and extends into the postpartum
period was not explained on the basis of age or
body mass index. It is likely to have both genetic
and environmental components that are
analogous to the resistance reported in other
groups at risk of having type 2 diabetes (25-31).
Several studies suggest that women with a history
of GDM often have ß-cell defect compared with
women without such history. Thus, the women
had a marked defect in first phase ß-cell function
at a time when they had normal glucose
tolerance.(32) Also, increased proinsulin-to- insulin
ratio was found in GDM women when compared
with control subjects, suggesting a ß-cell defect
which was not simply the result of chronic
hyperglycemia (32,33). This was confirmed in our
study, when significant negative correlations of
the proinsulin-to-insulin ratio with the sensitivity
index in the GDM women (both obese and lean)
were found.
These data are consistent with the data of Ryan
et al (34), but differ from the data of Fisher et al
(35) and Buchanan et al (36) who showed no
significant difference in insulin sensitivity between
women with gestational diabetes mellitus and a
control group. The difference in results of insulin
sensitivity may be explained in part by the
methods used to estimate insulin sensitivity and
by the evaluation of subjects only in late
gestation, when differences in insulin sensitivity
between groups are less pronounced.
In this study, the mean values of C-peptide were
significantly higher in both group II and group III
as compared to the control and reference
groups during pregnancy (P = 0.002). After
delivery these C-peptide levels were significantly
higher in group II (obese GDM women) versus the
group IV (non pregnant reference group)
(P=0.010). Comparing the mean values of Cpeptide, it was found that these mean values
were significantly lower after delivery than during
pregnancy, in the three pregnant study groups.
Kautzky et al (19) showed that fasting C-peptide
was found to be higher in GDM than in nondiabetic
non-pregnant
women
and
normoglycemic pregnant women, meanwhile
markedly lower than in obese insulin-resistant
non-pregnant women. Prager et al (37) studied
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Journal of Diabetology, February 2011; 1:3
the
pronounced
insulin
resistance
and
inadequate ß-cell secretion in lean gestational
diabetes during and after pregnancy. They
demonstrated that the fasting concentrations of
C-peptide were higher in GDM than pregnant
non-diabetics. After delivery, women with GDM
showed significant reduction of C-peptide levels
and basal insulin secretion. They reported that
this might indicate that impaired insulin secretion
is the predominant defect in GDM, which thus
may be regarded as a prediabetic entity, distinct
from IGT.
In our study, the glucose homeostasis during
pregnancy was studied by 100 gm oral glucose
tolerance test.It was found that the mean
plasma glucose levels at fasting state and at 1, 2,
3 hour intervals were significantly higher in
women with gestational diabetes (both obese
and lean) compared with the normal glucose
tolerant women. After delivery (4-8 weeks), the
mean plasma glucose levels during 75 gm OGTT
were significantly higher at 30 and 60 minutes in
GDM women (both obese and lean) than in the
non diabetic pregnant women (group I) and the
non pregnant non diabetic women (group IV)
(P<0.05). At 120 minutes, the mean plasma
glucose levels were significantly higher in GDM
women
(both
obese
and
lean)
than
normoglycemic pregnant women and nonpregnant non-diabetic women.
Several studies have demonstrated that a
significant proportion of women with gestational
diabetes have abnormal glucose tolerance in
the early postpartum period. One of the
important risk factors linked to this fact has been
an early diagnosis of gestational diabetes, mainly
before 24 weeks gestation. In other words, the
earlier the diagnosis of GDM, the greater would
be the chance to have an abnormal glucose
metabolism in the post-partum period (38-40).
Bartha et al (41) studied the postpartum glucose
metabolism in women with gestational diabetes
diagnosed in early pregnancy; they found that
the percentages of overt diabetes and abnormal
glucose tolerance were significantly higher in the
early-pregnancy group than those with lateonset gestational diabetes. It could be
suggested that the women with gestational
diabetes in early pregnancy could have had
abnormal
carbohydrate
tolerance
before
gestation. If so, most of them should have
impaired
carbohydrate
tolerance
in
the
postpartum period.
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In the present study, the pregnant women
presented with a metabolic pattern suggestive of
enhanced insulin resistance, namely increased
fasting and post load insulin levels. This was
demonstrated as the mean values of plasma
insulin during pregnancy which was significantly
higher in GDM women (both obese and lean)
compared with the control group, measured by
oral glucose tolerance test. Also these mean
values were significantly higher in obese GDM
compared with lean GDM women at the
different points of the test. After delivery, no
significant differences were found, regarding the
plasma insulin, between the obese and lean
GDM women. However, the mean values of
plasma insulin were still significantly higher in
GDM women (both obese and lean) compared
with the controls (normal glucose tolerant
pregnant women) and the reference group (non
pregnant healthy women).
Homko et al (5) studied the insulin secretion
during late gestation (third trimester) and
postpartum. They found that during late
gestation, women with GDM were more insulin
resistant than non diabetic controls and had
significantly lower insulin secretion rates (ISRS) in
response to hyperglycemia. Postpartum, insulin
resistance, ISRS and plasma insulin levels
improved in both groups, and ISRS were no
longer significantly different in patients with GDM
and controls. Insulin resistance, however,
remained higher in women with GDM. They
concluded that the women with GDM had a
major beta-cell defect that made it impossible
for them to compensate for their increased level
of insulin resistance, which occurred during late
pregnancy.
Catalano et al (42) studied the longitudinal
changes
in
glucose
metabolism,
during
pregnancy, in obese women with normal
glucose tolerance and gestational diabetes. The
results showed increase in first-phase and
second-phase
insulin
response
that
was
significantly greater in the gestational diabetes
mellitus group than in the control group. They
concluded that obese women in whom
gestational diabetes develops have a significant
increase in insulin response but decrease in insulin
sensitivity with advancing gestation with respect
to a matched control group.
From the current study, we can conclude that
gestational diabetes mellitus is characterized by
elevated serum proinsulin concentrations and an
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Journal of Diabetology, February 2011; 1:3
increased proinsulin-to-insulin ratio which reflects
ß-cell decompensation in such women. These
precursor molecules are specific to GDM and
might thus serve as a marker for the disease and
potentially even identify the subjects at high risk
for the development of type 2 diabetes.
Furthermore, it may be possible to detect such ßcell stress earlier in the pregnancy and to use
these phenomena in the assistance of better
prediction of GDM. Furthermore, our data, show,
that women with gestational diabetes mellitus
feature more pronounced insulin resistance
during pregnancy than pregnant subjects with
normal glucose tolerance. This insulin resistance
state seems to improve after delivery. In addition,
women with GDM exhibit lower ß-cell sensitivity to
glucose and an inadequate insulin secretory
capacity. This might indicate that impaired insulin
secretion is a major defect in GDM, which thus
may be regarded as prediabetic entity distinct
from impaired glucose tolerance.
Ethical Clearance
All the steps and procedures performed
throughout this work were in accordance with
the ethical standards of the Alexandria University
Ethical Committee as well as the Helsinki
Declaration of 1975, as revised in 1983.
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