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Association of serum lipids and lipoproteins with plasma C-peptide concentration in non-insulin-dependent diabetic and non-diabetic subjects
Association of Serum Lipids and Lipoproteins With Plasma C-Peptide Concentration in Non-Insulin-Dependent Diabetic and Non-Diabetic Subjects H. Sarlund,
M. Laakso,
K. Pyijr%i,
and I. Penttili
Serum lipids and lipoproteins were studied in 149 non-insulin-dependent diabetic subjects treated with diet or oral drugs (75 men, 74 women) and in 101 nondiabetic control subjects (49 men, 52 women) in relation to endogenous insulin secretion capacity measured by plasma C-peptide response to intravenous glucagon. Serum HDL- and HDL,-cholesterol concentrations were lower and VLDL-cholesterol and total and VLDL-triglyceride concentrations higher in subjects with high C-peptide response (above the median) than in subjects with low C-peptide response (lower or equal to median) both in diabetic and control subjects of both sexes. Adjustment for the effect of obesity abolished these differences in serum lipids and lipoproteins in diabetic subjects but not in control subjects. This may indicate that obesity has stronger influence on serum lipids in diabetic subjects than in nondiabetic subjects. B 1987 by Grune & Stratton,
Inc.
EVERAL REPORTS indicating an inverse relationship between serum high density lipoprotein (HDL) cholesterol and plasma insulin level in nondiabetic subjects have recently been published.‘-’ In insulin-dependent diabetic subjects HDL-cholesterol level has generally been found to be similar or higher than in nondiabetic subjects6-8 and this has been suggested to be related to peripheral hyperinsulinemia? In non-insulin-dependent diabetic subjects, however, serum HDL- cholesterol level has been found to be lower than in non-diabetic subjects irrespective of their generally elevated plasma insulin level.‘@” Our recent study in middle-aged insulin-treated diabetic subjects indicated an inverse relationship between serum HDL- and HDL,-cholesterol concentration and endogenous insulin secretion capacity as measured by C-peptide response to glucagon.‘4 Serum total triglyceride level has been found to be positively associated with plasma insulin level in nondiabetic subjects.2q4*5 In non-insulin-dependent diabetic subjects hypertriglyceridemia is the most common lipid abnormality, “J~.‘~ which has been suggested to be associated with hyperinsulinemia in them.” In the following we report results concerning the relationship between serum lipids and lipoproteins and endogenous insulin secretion capacity measured by C-peptide response to glucagon in middle-aged diabetic subjects treated with diet or oral drugs and in nondiabetic subjects.
S
MATERIALS AND METHODS
Subjects The study population comprised of 149 non-insulin-dependent diabetic subjects (75 men, 74 women) and 101 nondiabetic control subjects (49 men, 52 women). The subjects were randomly selected from a larger study concerning the prevalence of coronary heart disease and its risk factors in 510 non-insulin-dependent diabetic and 649 nondiabetic control subjects aged from 45 to 64 years in the district of the Kuopio University Central Hospital.16 Non-insulin-
From the Departments of Medicine and Clinical Chemistry, Kuopio University Central Hospital. Kuopio, Finland. Supported by a grant of Medical Research of the Academy of Finland. Address reprint requests to Helena Sarlund. MD, University of Kuopio, PO3 6. SF-7021 I Kuopio. Finland. o I987 by Grune & Stratton. Inc. 0026-0495/87/3609-0005%03.00/0 840
dependent diabetic subjects included into the present study were treated with diet only (46 subjects), with sulphonylureas (67 subjects), with metformin (4 subjects) or with sulphonylurea and metformin (32 subjects). Nondiabetic control subjects had their fasting plasma glucose value below 8.0 mmol/L. None of the subjects studied was taking hypolipidemic drugs or had renal, liver, or thyroid disease according to laboratory investigations (serum aminotransferases, alkaline phosphatase, gamma-glutamyltransferase, creatinine, urinary protein, and serum free thyroxine index).
Methods Serum lipids and lipoproteins were determined from unfrozen, fresh serum samples drawn after a 12-hour overnight fast. Lipoprotein fractionation was performed using ultracentrifugation” and selective precipitation. ‘* Spinnings were done at loo C with a Kontron TGA-65 ultracentrifuge. Serum samples were centrifuged at density (d) 1.006 (105,000 x g for 18 hours) to separate the VLDL-fraction. Total HDL was determined directly with dextrane sulphate and magnesium chloride precipitation, which correlates closely with the results obtained by ultracentrifugation.is LDL (including IDL, d = 1.006-1.063) was calculated as a difference between the total lipid concentration and the sum of the lipid concentrations of VLDL- and HDL-fractions. HDLz and HDL, subfractions were separated running the total HDL-fraction at d 1.125 ( 105,000 x g for 40 hours) and the fractions were isolated by the tube-slicing technique. Cholesterol and triglycerides were determined by automated enzymatic methods (Boehringer-Mannheim, West Germany). The mean interassay variation in HDL-cholesterol measurements was 3.3% and the intra-assay variation 0.95%. Serum apolipoproteins were determined by commercial immunoturbidimetric method based on measurement of immunoprecipitation at a wavelength of 340 nm (Orion Diagnostica, Finland). The intra-assay variation was less than 5% and the measurement range for apolipoprotein Al 0.3 to 3.5 g/L and for apolipoprotein B 0.4 to 3.6 g/L. Endogenous insulin secretion capacity was assessed by plasma C-peptide response to intravenous administration of glucagoni9 Plasma C-peptide was determined by radioimmunoassay (antiserum M 1230, Novo, Denmark) with a detection limit of 0.017 nmol/L and intra-assay variation less than 5%. Plasma glucose was determined by glucose dehydrogenase method (Merck Diagnostica, West Germany). Obesity was expressed as body mass index (BMI, weight(kg)/height(m)‘). Alcohol intake was determined according to a subject’s estimate of the average number of beer or drinks ingested per week (transformed to absolute alcohol g/wk). Subjects were classified as physically active if they exercised during leisure time for at least 30 minutes at least two times a week (walking, bicycling, swimming, etc) or if their physical activity at work was high (eg, heavy industrial work, lumberjacking). Metabolism, Vol 36, No 9 (September),
1987:
pp 840-845
841
LIPIDS AND C-PEPTIDE IN DIABETICS Table 1. Characteristics of Diabetic and Control Subjects as a Whole Group Women
MFJll Controls
N = 49
Diabetics
Controls
N = 75
N = 52
Diabetics N = 74
Age (yr)
55.7 + 0.8
59.3 + 0.6$
57.2 + 0.7
60.1 2 0.6t
BMI (kg/m’)
27.0 ? 0.5
27.6 + 0.4
26.3 i- 0.5
28.7 k 0.7t
5.5 + 0.1
11.o + 0.5$
5.4 t 0.1
12.8 + 0.5$
0.70 + 0.04
0.78 + 0.04
0.61 + 0.03
0.86 % 0.05$
2.79 +- 0.20
2.23 k 0.13$
2.28 + 0.12
2.28 t 0.15
5.4 * 1.5
1.0 2 0.4
FP-glucose (mmol/L) FP-C-peptide (nmol/L) Postglucagon C-peptide (nmol/L)
43 + 8
Alcohol intake (g/wk)
48 + 10
Current smokers (%1
31
33
7.7
9.5t
Phvsicallv active
88
67’
83
53
Values are given as mean 2 SEM, except the prevalence estimates as percentages. lP < .05, tP < .Ol,
Statistical
$P < ,001:
comparison between diabetic and control subjects (Student’s two-tailed t-test or x test).
Characteristics
Methods
The results are expressed as mean 2 SEM. The difference between the groups was assessed by the x2 test and Student’s two-tailed t-test for independent samples. The adjustment for confounding factors was done with the analysis of covariance (ANCOVA). Spearman’s correlation coefficients and multiple regression analysis were used to assess the effects of BMI, glucose and postglucagon C-peptide concentration on serum lipid and lipoprotein concentrations. In these analyses logaritmic transformation of C-peptide concentration was used because of its skewed distribution.
50
I.4
12345
E
II1
x 2
C
ul 12345
Y
I b 1
! 3 4 5
of the Study Population
The characteristics of diabetic and control subjects are shown in Table 1. Both male and female diabetic subjects were significantly older than corresponding control subjects. Female diabetic subjects were significantly more obese and their fasting C-peptide concentration was higher than female control subjects. Male diabetic subjects showed significantly lower plasma postglucagon C-peptide concentration than male control subjects. The number of physically active subjects was significantly lower in male diabetic than in male control subjects. No difference in alcohol intake or smoking was observed between diabetic and control subjects, but diabetic subjects were more inactive than control subjects. The distribution of plasma postglucagon C-peptide in study groups is presented in Fig 1. The proportion of subjects having the lowest C-peptide response (postglucagon C-peptide below 1 SO nmol/L) was somewhat higher in diabetic subjects than in nondiabetic subjects. Correspondingly, the proportion of subjects having the C-peptide value exceeding the limit of 3.0 nmol/L was higher in nondiabetic than diabetic subjects. Because the distributions were not normally distributed the major part of the analyses have been made using median values of postglucagon C-peptide as a cut-off point. Subjects were classified as low C-peptide responders, if their plasma postglucagon C-peptide value was below the median value for their group or equal to it and to high responders, if it was above the median value. The median postglucagon plasma C-peptide concentrations were as follows: 2.44 nmol/L for male control subjects, 2.03 nmol/L for female control subjects, I.88 nmol/L for male diabetic subjects, and 1.98 nmol/L for female diabetic subjects. The characteristics of the study population by sex and by C-peptide response to glucagon are shown in Table 2. The male diabetics with low C-peptide response were signifciantly older than the male diabetics with high C-peptide response, but the age between other groups did not differ according to C-peptide response. In all study groups subjects with high C-peptide response were more obese than subjects with low C-peptide response. Duration of diabetes did not differ in diabetics according to C-pcptide response. Diabetics with low C-peptide response had significantly higher fasting plasma glucose level than diabetics with high response, but no such difference was found in control subjects. Alcohol intake, current smoking, and physical activity did not differ in diabetic or in control subjects according to C-peptide response.
d 12345
L
Fig 1. Distribution of plasma C-peptide concentrations after glucagon stimulation in control and diabetic subjects, men and women separately (1 = C-peptide 0.23-1.95: 2 = C-peptide 1.96-3.96; 3 = C-peptide 3.70-5.43; 4 = C-peptide 5.44-7.17: 5 = C-peptide 7.18-6.86) (A), Male controls; (6) female controls; (C) male diabetic: ID) female diabetics.
RESULTS
The association of obesity, glucose, C-peptide with serum HDL-cholesterol
and postglucagon and VLDL-tri-
842
SARLUND ET AL
Table 2. Characteristics
of Diabetic end Control Subjects Grouped According to the C-Peptide Men
Response
Women
Controls
Diabetics
Controls
Diabetics
Low response
N = 24
N = 37
N = 25
N = 37
High response
N = 25
N = 38
N = 27
N = 37
Age (yrj Low response
55.7
f 1.0
60.0
f 0.8
56.6
* 1.0
60.0
+ 1.0
High response
55.8
f 1.2
58.0
f 0.9*
57.8
+ 1.0
60.2
f 0.8
Low response
25.5
+ 0.5
26.2
f 0.6
25.9
k 0.8
27.3
5 1.0
High response
28.4
+ 0.7T
28.9
k 0.6t
26.7
f 0.80
30.1
+ 0.8’
BMI (kg/m’)
Duration of DM (yr) Low response
12.2 f 0.8 11.1 + 0.5
-
10.2 f 0.5
High response
12.7 f 0.6
5.6 t 1.5
14.2 ? 0.7
5.4 + 0.1
11.3 f 0.6t
10.5 f 0.6
FP-glucose (mmol/Lj Low response
5.4 f 0.1
High response
5.6 & 0.1
9.4 + 0.6$
Alcohol intake (g/wkj Low response
33.5
* 11.0
47.8
k 15.1
5.6 + 1.5
1.3 f 0.6
High response
63.0
& 15.1
37.8
+ 7.9
5.2 f 2.6
0.6 + 0.4
Current smokers (%j Low response
25.0
27.0
12.0
8.1
High response
36.0
39.5
3.7
10.8
Low response
91.7
59.4
88.0
56.8
Hiah resoonse
84.0
73.4
77.8
48.6
Physically active (%I
Values are given as mean + SEM, except the prevalence estimates as percentages. Low response, C-peptide response below; high response, C-peptide response over the median. lP < .05, tP -c .Ol,
$P -c .OO 1, 5.1
r P > .05; comparison between the groups of low and high response (Student’s two-tailed t-test or x test).
glycerides was assessed by Spearman’s correlation coefficients. BMI showed a statistically significant inverse correlation with HDL-cholesterol concentration (from -0.230 to -0.337) and a significant positive correlation with VLDLtriglycerides (from 0.210 to 0.248) in all study groups. Glucose concentration was not consistently associated with HDL-cholesterol or VLDL-triglycerides in any of the study groups. Postglucagon C-peptide showed an inverse correlation with HDL cholesterol (from -0.131 to -0.559) and a positive correlation with VLDL triglycerides (from 0.177 to 0.409), but the correlation coefficients were statistically significant only in control subjects. Table 3.
Serum Total and Lipoprotein
Cholesterol
The effects of obesity, glucose, and postglucagon C-peptide on HDL-cholesterol and VLDL-triglyceride concentrations were assessed by multiple regression analyses. All these three variables were included as independent variables in the same regression model and HDL cholesterol and VLDL triglycerides as dependent variables, each one separately. BMI was inversely associated with HDL-cholesterol in male and female diabetic subjects (P = .040 and P = .009, respectively) but not in control subjects. Glucose was not associated significantly with HDL cholesterol in any of the study groups. In male control subjects postglucagon C-peptide was inversely associated with HDL cholesterol
and Triglyceride
(mmol/L)
and Apolipoprotein
Al end B Levels (g/L)
in Diabetic and Control Subjects Women
Men
Controls
Diabetics
Controls
Diabetics
Total cholesterol
6.45
HDL-cholesterol
1.09 + 0.04
1.06 f 0.03
1.39 f 0.04
1.13 + 0.04t
HDL,-cholesterol
0.72
r 0.04
0.70
* 0.03
0.94
r 0.05
0.73
HDL,-cholesterol
0.36
+ 0.02
0.36
f 0.02
0.45
+_0.03
0.39
+ 0.02
LDL-cholesterol
4.26
f 0.14
4.04
+ 0.12
4.27
f 0.18
4.19
+ 0.13
r 0.05
+ 0.17
6.60
& 0.22
6.64
f 0.20
6.97
f O.lB$ * 0.03t
VLDL-cholesterol
1.11 f 0.07
1.50 f 0.19
0.98
Total triglycerides
1.70 f 0.12
2.95
+ 0.53’
1.36 & 0.07
3.07
HDL-triglycerides
0.12
f 0.01
0.14
f 0.01
0.13
+ 0.01
0.17
& O.OlT
LDL-triglycerides
0.44
f 0.02
0.50
+ 0.03
0.39
+ 0.02
0.57
f 0.03t
VLDL-triglycerides
1.14 r 0.10 1.24 + 0.03
2.32
? 0.51’
0.84
+ 0.06
2.33
+ 0.33t
Apoprotein A 1
1.19 * 0.03
1.44 * 0.04
1.32 t 0.04’
Apoprotein 8
1.28 + 0.05
1.26 f 0.05
1.19 r 0.05
1.37 + 0.05’
Values are given as mean * SEM. lP < .05, tP < .Ol, $.l > P > .05; comparison between diabetic and control subjects (Student’s two-tailed t-test).
1.65 + 0.15f f 0.35T
a43
LIPIDS AND C-PEPTIDE IN DIABETICS
Table 4.
Serum Total and Lipoprotein
Cholesterol
Levels (mmol/L)
According to the C-Peptide
in Diabetic and Control Subjects
Response
M.9ll Controls
W0mell Controls
Diabetics
Diabetics
Total cholesterol Low response
6.58
+ 0.22
6.30
f 0.19
6.56
+ 0.32
7.04
+ 0.30
High response
6.33
f 0.25
6.90
k 0.39
6.72
k 0.26
6.90
+ 0.20
HDL-cholesterol Low response
1.23 f 0.04
1.13 f 0.05
1.47 + 0.07
1.17 + 0.06
High response
0.95
f 0.04t
0.98
i 0.04’
1.32 + 0.05$
1.08 + 0.04
Low response
0.85
? 0.06
0.75
t 0.05
1.06 f 0.06
0.80
+ 0.05
High response
0.60
r 0.03t
0.64
+ 0.04f
0.83
+ 0.06*
0.66
+ 0.04.
Low response
0.38
+ 0.03
0.38
f 0.02
0.40
+ 0.02
0.37
f 0.02
High response
0.35
+ 0.02
0.34
* 0.02
0.29
+ 0.06
0.42
_t 0.03
HDL,-cholesterol
HDL,-cholesterol
LDL-cholesterol Low response
4.33
t 0. ia
4.05
+ 0.17
4.24
+ 0.26
4.26
t 0.21
High response
4.19
+ 0.21
4.03
k 0.17
4.29
k 0.24
4.13
k 0.16
k 0.07
1.62 + 0.26
VLDL-cholesterol Low response
1.03 i 0.10
1.12 + 0.08
0.85
High response
1.19 + 0.11
1.87 f 0.371
1.11 k 0.07*
1.68 + 0.15
Values are given as mean -t SEM. Low response, C-peptide response below: high response, C-peptide response over the median. lP < .05, tf’ < .OO 1, $. 1 > P > .05; comparison between the groups of low and high response (Student’s two-tailed t-test)
(P = .015), but not in other groups. Neither BMI, nor glucose, nor postglucagon C-peptide was significantly associated with VLDL triglycerides in any of the study groups. Serum lipid, lipoprotein, and apolipoprotein Al and B concentrations in diabetic and control subjects are presented in Table 3. Male diabetic subjects had significantly higher serum total and VLDL-triglyceride concentrations than male control subjects. There was a trend to a higher serum total cholesterol level in female diabetic subjects as com-
Table 5. Serum Total and Lipoprotein
Triclyceride
lmmol/Lf
pared to female control subjects (.l < P < .05). Female diabetic subjects had significantly lower serum HDL- and HDL,-cholesterol and apolipoprotein Al and higher VLDLcholesterol, total, HDL-, LDL-, and VLDL-triglyceride and apolipoprotein B concentration than female control subjects. Tables 4 and 5 show serum lipids, lipoproteins and apolipoproteins according to C-peptide response in diabetic and control subjects. Serum HDL-cholesterol concentration was higher in subjects with low C-peptide response than in those
and Apolipoprotein
Al and B Levels (g/U
in Diabetic and Control Subjects
According to the C-Peptide Response Mell
Controls
Women Diabetics
Controls
Diabetics
Total triglycerides 1.46 + 0.14
2.04
+ 0.18
1.25 + 0.09
3.02
+ 0.63
1.93 + 0.18*
3.84
f 1.02’
1.46 + 0.11
3.13
f 0.30
Low response
0.11
+ 0.02
0.14
* 0.01
0.13
+ 0.01
0.18
+ 0.01
High response LDL-triglycerides
0.13
* 0.01
0.14
* 0.02
0.13
5 0.01
0.16
k 0.01
Low response
0.39
k 0.03
0.46
k 0.03
0.35
r 0.03
0.54
* 0.03
0.48
k 0.04t
0.53
i 0.05
0.43
-t 0.03t
0.61
2 0.04
0.95
+ 0.12
1.44 + 0.16
0.77
+ 0.07
2.31
t 0.61
3.16
0.91
* 0.10
2.36
+ 0.27
Low response High response HDL-triglycerides
High response VLDL-triglycerides Low response High response Apoprotein Al Low response High response Apoprotein 8
1.32 t 0.16t
f 0.98’
1.32 + 0.04
1.18 k 0.05
1.44 + 0.07
1.32 + 0.06
1.18 t 0.04*
1.20 + 0.04
1.43 + 0.04
1.33 r 0.04
Low response
1.23 f 0.09
1.29 + 0.07
1.19 + 0.07
i .3a
High response
1.32 k 0.06
1.23 + 0.06
1.19 + 0.08
1.37 -t 0.06
Values are given as mean + SEM. Low response. C-peptide response below: high response, C-peptide response over the median. ‘P < .05. t. 1 z P > .05: comparison between the groups of low and high response (Student’s two-tailed t-test),
+ 0.07
844
SAALUND ET AL
with high C-peptide response both in diabetic and in control subjects. The difference in HDL-cholesterol concentration reached the conventional level of statistical significance (P < .05) only in men and persisted in male control subjects after adjustment for BMI (P < .05, ANCOVA) and even after adjustment for age, BMI, exercise, alcohol intake, and smoking (P < .05, ANCOVA). Serum HDL,-cholesterol concentration was higher in subjects with low C-peptide response than in subjects with high C-peptide response. These differences in HDL,-cholesterol concentrations were statistically significant (P < .05) for male and female control subjects and female diabetic subjects and persisted in control subjects after adjustment for BMI or even after adjustment for age, BMI, exercise, alcohol intake, and smoking (P < .05, ANCOVA). Serum VLDL-cholesterol concentration was significantly lower in male diabetic and female control subjects with low C-peptide response than with high C-peptide response and the difference persisted in female control subjects after adjustment for BMI (P < .05, ANCOVA). Serum total triglyceride concentration in male diabetic and control subjects and VLDL-triglyceride concentration in male diabetic subjects were significantly lower in subjects with low C-peptide response than with high C-peptide response, but the difference persisted only in male control subjects after adjustment for BMI (P < .05, ANCOVA). This difference persisted even after adjustment for age, BMI, exercise, alcohol intake, and smoking (P < .05, ANCOVA). Serum apolipoprotein Al concentration was significantly higher in male control subjects with low C-peptide response than with high C-peptide response even after adjustment for age, BMI exercise, alcohol intake, and smoking (P < .05, ANCOVA).
DISCUSSION
Serum HDL- and HDL,-cholesterol concentrations have been shown to be lower in non-insulin-dependent diabetic than in control subjects.‘0-‘3 In the present study this difference in serum HDL- and HDL,-cholesterol concentrations between diabetic and nondiabetic subjects was observed only in women. A stronger impact of non-insulin-dependent diabetes on serum HDL-cholesterol concentration in women than in men has previously been observed in some,2o but not in all studiesI In the present study serum HDL- and HDL,-cholesterol concentrations were higher in subjects with low C-peptide response than in those with high C-peptide response both in male and female diabetic and control subjects. Although our findings concerning the association between serum HDLand HDL,-cholesterol concentrations and endogenous insulin secretion capacity were to some extent different in men and women, there was, however, a similar trend towards a lower HDL- and HDL,-cholesterol concentration in high C-peptide responders in both sexes. Generally, all differences
in serum lipoprotein concentrations between low and high C-peptide responses were smaller in female diabetic subjects than in male diabetic subjects. Therefore, C-peptide may be a much poorer indicator of lipid and lipoprotein levels in female diabetic subjects than in male diabetic subjects. In the present study the low and high responder groups were formed on the basis of the median value of the postglucagon C-peptide in each group. This probably weakens the difference between the high and low responders with respect to HDL and HDL, cholesterol as compared to our previous study in which the low responders had undetectable postglucagon C-peptide and high responders had postglucagon C-peptide exceeding the limit of 0.60 nmol/L.14 Serum HDL- and HDL,-cholesterol concentrations are known to be inversely associated with obesity.7*‘4 In the present study, BMI was inversely associated in regression analyses with HDL cholesterol in diabetic subjects, but not in control subjects. BMI was also higher in subjects with higher C-peptide response than in subjects with lower C-peptide response. The differences in serum HDL- and HDL,-cholesterol concentrations in relation to C-peptide response persisted only in control subjects after adjustment for obesity. Therefore, obesity seems to have more effect on serum HDL-cholesterol concentration in diabetic than in control subjects. Serum HDL-cholesterol level has been shown to be inversely associated with plasma glucose level and glycemic control in diabetic subjects. ‘J According to regression analysis, glucose level was not significantly associated with HDL cholesterol in any of the study groups and, therefore, plasma glucose levels were not included in analyses concerning the association between lipoproteins and C-peptide response. However, in diabetic subjects plasma glucose level was higher in subjects with low C-peptide response than in subjects with high C-peptide response, probably due to decreased insulin secretion in the former group. Therefore, hyperglycemia per se did not have any association with HDL-cholesterol concentration in these subjects. In addition to the differences in HDL-cholesterol concentration according to C-peptide response VLDL-triglyceride concentration tended to be higher in high C-peptide responders than in low C-peptide responders. VLDL-triglyceride concentration, however, seemed to be more closely related with obesity than with C-peptide response both in diabetic and in control subjects. In conclusion, the results of the present study indicate that in spite of somewhat different HDL- and HDL,-cholesterol concentrations in diabetic and in control subjects serum HDL- and HDL,-cholesterol concentrations were inversely related to endogenous insulin secretion capacity both in non-insulin dependent diabetic subjects and in control subjects. Serum total and VLDL-triglyceride concentrations seemed also to be associated with insulin secretion capacity, but even more strongly with obesity.
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LIPIDS AND C-PEPTIDE IN DIABETICS
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M. Laakso,
K. Pyijr%i,
and I. Penttili
Serum lipids and lipoproteins were studied in 149 non-insulin-dependent diabetic subjects treated with diet or oral drugs (75 men, 74 women) and in 101 nondiabetic control subjects (49 men, 52 women) in relation to endogenous insulin secretion capacity measured by plasma C-peptide response to intravenous glucagon. Serum HDL- and HDL,-cholesterol concentrations were lower and VLDL-cholesterol and total and VLDL-triglyceride concentrations higher in subjects with high C-peptide response (above the median) than in subjects with low C-peptide response (lower or equal to median) both in diabetic and control subjects of both sexes. Adjustment for the effect of obesity abolished these differences in serum lipids and lipoproteins in diabetic subjects but not in control subjects. This may indicate that obesity has stronger influence on serum lipids in diabetic subjects than in nondiabetic subjects. B 1987 by Grune & Stratton,
Inc.
EVERAL REPORTS indicating an inverse relationship between serum high density lipoprotein (HDL) cholesterol and plasma insulin level in nondiabetic subjects have recently been published.‘-’ In insulin-dependent diabetic subjects HDL-cholesterol level has generally been found to be similar or higher than in nondiabetic subjects6-8 and this has been suggested to be related to peripheral hyperinsulinemia? In non-insulin-dependent diabetic subjects, however, serum HDL- cholesterol level has been found to be lower than in non-diabetic subjects irrespective of their generally elevated plasma insulin level.‘@” Our recent study in middle-aged insulin-treated diabetic subjects indicated an inverse relationship between serum HDL- and HDL,-cholesterol concentration and endogenous insulin secretion capacity as measured by C-peptide response to glucagon.‘4 Serum total triglyceride level has been found to be positively associated with plasma insulin level in nondiabetic subjects.2q4*5 In non-insulin-dependent diabetic subjects hypertriglyceridemia is the most common lipid abnormality, “J~.‘~ which has been suggested to be associated with hyperinsulinemia in them.” In the following we report results concerning the relationship between serum lipids and lipoproteins and endogenous insulin secretion capacity measured by C-peptide response to glucagon in middle-aged diabetic subjects treated with diet or oral drugs and in nondiabetic subjects.
S
MATERIALS AND METHODS
Subjects The study population comprised of 149 non-insulin-dependent diabetic subjects (75 men, 74 women) and 101 nondiabetic control subjects (49 men, 52 women). The subjects were randomly selected from a larger study concerning the prevalence of coronary heart disease and its risk factors in 510 non-insulin-dependent diabetic and 649 nondiabetic control subjects aged from 45 to 64 years in the district of the Kuopio University Central Hospital.16 Non-insulin-
From the Departments of Medicine and Clinical Chemistry, Kuopio University Central Hospital. Kuopio, Finland. Supported by a grant of Medical Research of the Academy of Finland. Address reprint requests to Helena Sarlund. MD, University of Kuopio, PO3 6. SF-7021 I Kuopio. Finland. o I987 by Grune & Stratton. Inc. 0026-0495/87/3609-0005%03.00/0 840
dependent diabetic subjects included into the present study were treated with diet only (46 subjects), with sulphonylureas (67 subjects), with metformin (4 subjects) or with sulphonylurea and metformin (32 subjects). Nondiabetic control subjects had their fasting plasma glucose value below 8.0 mmol/L. None of the subjects studied was taking hypolipidemic drugs or had renal, liver, or thyroid disease according to laboratory investigations (serum aminotransferases, alkaline phosphatase, gamma-glutamyltransferase, creatinine, urinary protein, and serum free thyroxine index).
Methods Serum lipids and lipoproteins were determined from unfrozen, fresh serum samples drawn after a 12-hour overnight fast. Lipoprotein fractionation was performed using ultracentrifugation” and selective precipitation. ‘* Spinnings were done at loo C with a Kontron TGA-65 ultracentrifuge. Serum samples were centrifuged at density (d) 1.006 (105,000 x g for 18 hours) to separate the VLDL-fraction. Total HDL was determined directly with dextrane sulphate and magnesium chloride precipitation, which correlates closely with the results obtained by ultracentrifugation.is LDL (including IDL, d = 1.006-1.063) was calculated as a difference between the total lipid concentration and the sum of the lipid concentrations of VLDL- and HDL-fractions. HDLz and HDL, subfractions were separated running the total HDL-fraction at d 1.125 ( 105,000 x g for 40 hours) and the fractions were isolated by the tube-slicing technique. Cholesterol and triglycerides were determined by automated enzymatic methods (Boehringer-Mannheim, West Germany). The mean interassay variation in HDL-cholesterol measurements was 3.3% and the intra-assay variation 0.95%. Serum apolipoproteins were determined by commercial immunoturbidimetric method based on measurement of immunoprecipitation at a wavelength of 340 nm (Orion Diagnostica, Finland). The intra-assay variation was less than 5% and the measurement range for apolipoprotein Al 0.3 to 3.5 g/L and for apolipoprotein B 0.4 to 3.6 g/L. Endogenous insulin secretion capacity was assessed by plasma C-peptide response to intravenous administration of glucagoni9 Plasma C-peptide was determined by radioimmunoassay (antiserum M 1230, Novo, Denmark) with a detection limit of 0.017 nmol/L and intra-assay variation less than 5%. Plasma glucose was determined by glucose dehydrogenase method (Merck Diagnostica, West Germany). Obesity was expressed as body mass index (BMI, weight(kg)/height(m)‘). Alcohol intake was determined according to a subject’s estimate of the average number of beer or drinks ingested per week (transformed to absolute alcohol g/wk). Subjects were classified as physically active if they exercised during leisure time for at least 30 minutes at least two times a week (walking, bicycling, swimming, etc) or if their physical activity at work was high (eg, heavy industrial work, lumberjacking). Metabolism, Vol 36, No 9 (September),
1987:
pp 840-845
841
LIPIDS AND C-PEPTIDE IN DIABETICS Table 1. Characteristics of Diabetic and Control Subjects as a Whole Group Women
MFJll Controls
N = 49
Diabetics
Controls
N = 75
N = 52
Diabetics N = 74
Age (yr)
55.7 + 0.8
59.3 + 0.6$
57.2 + 0.7
60.1 2 0.6t
BMI (kg/m’)
27.0 ? 0.5
27.6 + 0.4
26.3 i- 0.5
28.7 k 0.7t
5.5 + 0.1
11.o + 0.5$
5.4 t 0.1
12.8 + 0.5$
0.70 + 0.04
0.78 + 0.04
0.61 + 0.03
0.86 % 0.05$
2.79 +- 0.20
2.23 k 0.13$
2.28 + 0.12
2.28 t 0.15
5.4 * 1.5
1.0 2 0.4
FP-glucose (mmol/L) FP-C-peptide (nmol/L) Postglucagon C-peptide (nmol/L)
43 + 8
Alcohol intake (g/wk)
48 + 10
Current smokers (%1
31
33
7.7
9.5t
Phvsicallv active
88
67’
83
53
Values are given as mean 2 SEM, except the prevalence estimates as percentages. lP < .05, tP < .Ol,
Statistical
$P < ,001:
comparison between diabetic and control subjects (Student’s two-tailed t-test or x test).
Characteristics
Methods
The results are expressed as mean 2 SEM. The difference between the groups was assessed by the x2 test and Student’s two-tailed t-test for independent samples. The adjustment for confounding factors was done with the analysis of covariance (ANCOVA). Spearman’s correlation coefficients and multiple regression analysis were used to assess the effects of BMI, glucose and postglucagon C-peptide concentration on serum lipid and lipoprotein concentrations. In these analyses logaritmic transformation of C-peptide concentration was used because of its skewed distribution.
50
I.4
12345
E
II1
x 2
C
ul 12345
Y
I b 1
! 3 4 5
of the Study Population
The characteristics of diabetic and control subjects are shown in Table 1. Both male and female diabetic subjects were significantly older than corresponding control subjects. Female diabetic subjects were significantly more obese and their fasting C-peptide concentration was higher than female control subjects. Male diabetic subjects showed significantly lower plasma postglucagon C-peptide concentration than male control subjects. The number of physically active subjects was significantly lower in male diabetic than in male control subjects. No difference in alcohol intake or smoking was observed between diabetic and control subjects, but diabetic subjects were more inactive than control subjects. The distribution of plasma postglucagon C-peptide in study groups is presented in Fig 1. The proportion of subjects having the lowest C-peptide response (postglucagon C-peptide below 1 SO nmol/L) was somewhat higher in diabetic subjects than in nondiabetic subjects. Correspondingly, the proportion of subjects having the C-peptide value exceeding the limit of 3.0 nmol/L was higher in nondiabetic than diabetic subjects. Because the distributions were not normally distributed the major part of the analyses have been made using median values of postglucagon C-peptide as a cut-off point. Subjects were classified as low C-peptide responders, if their plasma postglucagon C-peptide value was below the median value for their group or equal to it and to high responders, if it was above the median value. The median postglucagon plasma C-peptide concentrations were as follows: 2.44 nmol/L for male control subjects, 2.03 nmol/L for female control subjects, I.88 nmol/L for male diabetic subjects, and 1.98 nmol/L for female diabetic subjects. The characteristics of the study population by sex and by C-peptide response to glucagon are shown in Table 2. The male diabetics with low C-peptide response were signifciantly older than the male diabetics with high C-peptide response, but the age between other groups did not differ according to C-peptide response. In all study groups subjects with high C-peptide response were more obese than subjects with low C-peptide response. Duration of diabetes did not differ in diabetics according to C-pcptide response. Diabetics with low C-peptide response had significantly higher fasting plasma glucose level than diabetics with high response, but no such difference was found in control subjects. Alcohol intake, current smoking, and physical activity did not differ in diabetic or in control subjects according to C-peptide response.
d 12345
L
Fig 1. Distribution of plasma C-peptide concentrations after glucagon stimulation in control and diabetic subjects, men and women separately (1 = C-peptide 0.23-1.95: 2 = C-peptide 1.96-3.96; 3 = C-peptide 3.70-5.43; 4 = C-peptide 5.44-7.17: 5 = C-peptide 7.18-6.86) (A), Male controls; (6) female controls; (C) male diabetic: ID) female diabetics.
RESULTS
The association of obesity, glucose, C-peptide with serum HDL-cholesterol
and postglucagon and VLDL-tri-
842
SARLUND ET AL
Table 2. Characteristics
of Diabetic end Control Subjects Grouped According to the C-Peptide Men
Response
Women
Controls
Diabetics
Controls
Diabetics
Low response
N = 24
N = 37
N = 25
N = 37
High response
N = 25
N = 38
N = 27
N = 37
Age (yrj Low response
55.7
f 1.0
60.0
f 0.8
56.6
* 1.0
60.0
+ 1.0
High response
55.8
f 1.2
58.0
f 0.9*
57.8
+ 1.0
60.2
f 0.8
Low response
25.5
+ 0.5
26.2
f 0.6
25.9
k 0.8
27.3
5 1.0
High response
28.4
+ 0.7T
28.9
k 0.6t
26.7
f 0.80
30.1
+ 0.8’
BMI (kg/m’)
Duration of DM (yr) Low response
12.2 f 0.8 11.1 + 0.5
-
10.2 f 0.5
High response
12.7 f 0.6
5.6 t 1.5
14.2 ? 0.7
5.4 + 0.1
11.3 f 0.6t
10.5 f 0.6
FP-glucose (mmol/Lj Low response
5.4 f 0.1
High response
5.6 & 0.1
9.4 + 0.6$
Alcohol intake (g/wkj Low response
33.5
* 11.0
47.8
k 15.1
5.6 + 1.5
1.3 f 0.6
High response
63.0
& 15.1
37.8
+ 7.9
5.2 f 2.6
0.6 + 0.4
Current smokers (%j Low response
25.0
27.0
12.0
8.1
High response
36.0
39.5
3.7
10.8
Low response
91.7
59.4
88.0
56.8
Hiah resoonse
84.0
73.4
77.8
48.6
Physically active (%I
Values are given as mean + SEM, except the prevalence estimates as percentages. Low response, C-peptide response below; high response, C-peptide response over the median. lP < .05, tP -c .Ol,
$P -c .OO 1, 5.1
r P > .05; comparison between the groups of low and high response (Student’s two-tailed t-test or x test).
glycerides was assessed by Spearman’s correlation coefficients. BMI showed a statistically significant inverse correlation with HDL-cholesterol concentration (from -0.230 to -0.337) and a significant positive correlation with VLDLtriglycerides (from 0.210 to 0.248) in all study groups. Glucose concentration was not consistently associated with HDL-cholesterol or VLDL-triglycerides in any of the study groups. Postglucagon C-peptide showed an inverse correlation with HDL cholesterol (from -0.131 to -0.559) and a positive correlation with VLDL triglycerides (from 0.177 to 0.409), but the correlation coefficients were statistically significant only in control subjects. Table 3.
Serum Total and Lipoprotein
Cholesterol
The effects of obesity, glucose, and postglucagon C-peptide on HDL-cholesterol and VLDL-triglyceride concentrations were assessed by multiple regression analyses. All these three variables were included as independent variables in the same regression model and HDL cholesterol and VLDL triglycerides as dependent variables, each one separately. BMI was inversely associated with HDL-cholesterol in male and female diabetic subjects (P = .040 and P = .009, respectively) but not in control subjects. Glucose was not associated significantly with HDL cholesterol in any of the study groups. In male control subjects postglucagon C-peptide was inversely associated with HDL cholesterol
and Triglyceride
(mmol/L)
and Apolipoprotein
Al end B Levels (g/L)
in Diabetic and Control Subjects Women
Men
Controls
Diabetics
Controls
Diabetics
Total cholesterol
6.45
HDL-cholesterol
1.09 + 0.04
1.06 f 0.03
1.39 f 0.04
1.13 + 0.04t
HDL,-cholesterol
0.72
r 0.04
0.70
* 0.03
0.94
r 0.05
0.73
HDL,-cholesterol
0.36
+ 0.02
0.36
f 0.02
0.45
+_0.03
0.39
+ 0.02
LDL-cholesterol
4.26
f 0.14
4.04
+ 0.12
4.27
f 0.18
4.19
+ 0.13
r 0.05
+ 0.17
6.60
& 0.22
6.64
f 0.20
6.97
f O.lB$ * 0.03t
VLDL-cholesterol
1.11 f 0.07
1.50 f 0.19
0.98
Total triglycerides
1.70 f 0.12
2.95
+ 0.53’
1.36 & 0.07
3.07
HDL-triglycerides
0.12
f 0.01
0.14
f 0.01
0.13
+ 0.01
0.17
& O.OlT
LDL-triglycerides
0.44
f 0.02
0.50
+ 0.03
0.39
+ 0.02
0.57
f 0.03t
VLDL-triglycerides
1.14 r 0.10 1.24 + 0.03
2.32
? 0.51’
0.84
+ 0.06
2.33
+ 0.33t
Apoprotein A 1
1.19 * 0.03
1.44 * 0.04
1.32 t 0.04’
Apoprotein 8
1.28 + 0.05
1.26 f 0.05
1.19 r 0.05
1.37 + 0.05’
Values are given as mean * SEM. lP < .05, tP < .Ol, $.l > P > .05; comparison between diabetic and control subjects (Student’s two-tailed t-test).
1.65 + 0.15f f 0.35T
a43
LIPIDS AND C-PEPTIDE IN DIABETICS
Table 4.
Serum Total and Lipoprotein
Cholesterol
Levels (mmol/L)
According to the C-Peptide
in Diabetic and Control Subjects
Response
M.9ll Controls
W0mell Controls
Diabetics
Diabetics
Total cholesterol Low response
6.58
+ 0.22
6.30
f 0.19
6.56
+ 0.32
7.04
+ 0.30
High response
6.33
f 0.25
6.90
k 0.39
6.72
k 0.26
6.90
+ 0.20
HDL-cholesterol Low response
1.23 f 0.04
1.13 f 0.05
1.47 + 0.07
1.17 + 0.06
High response
0.95
f 0.04t
0.98
i 0.04’
1.32 + 0.05$
1.08 + 0.04
Low response
0.85
? 0.06
0.75
t 0.05
1.06 f 0.06
0.80
+ 0.05
High response
0.60
r 0.03t
0.64
+ 0.04f
0.83
+ 0.06*
0.66
+ 0.04.
Low response
0.38
+ 0.03
0.38
f 0.02
0.40
+ 0.02
0.37
f 0.02
High response
0.35
+ 0.02
0.34
* 0.02
0.29
+ 0.06
0.42
_t 0.03
HDL,-cholesterol
HDL,-cholesterol
LDL-cholesterol Low response
4.33
t 0. ia
4.05
+ 0.17
4.24
+ 0.26
4.26
t 0.21
High response
4.19
+ 0.21
4.03
k 0.17
4.29
k 0.24
4.13
k 0.16
k 0.07
1.62 + 0.26
VLDL-cholesterol Low response
1.03 i 0.10
1.12 + 0.08
0.85
High response
1.19 + 0.11
1.87 f 0.371
1.11 k 0.07*
1.68 + 0.15
Values are given as mean -t SEM. Low response, C-peptide response below: high response, C-peptide response over the median. lP < .05, tf’ < .OO 1, $. 1 > P > .05; comparison between the groups of low and high response (Student’s two-tailed t-test)
(P = .015), but not in other groups. Neither BMI, nor glucose, nor postglucagon C-peptide was significantly associated with VLDL triglycerides in any of the study groups. Serum lipid, lipoprotein, and apolipoprotein Al and B concentrations in diabetic and control subjects are presented in Table 3. Male diabetic subjects had significantly higher serum total and VLDL-triglyceride concentrations than male control subjects. There was a trend to a higher serum total cholesterol level in female diabetic subjects as com-
Table 5. Serum Total and Lipoprotein
Triclyceride
lmmol/Lf
pared to female control subjects (.l < P < .05). Female diabetic subjects had significantly lower serum HDL- and HDL,-cholesterol and apolipoprotein Al and higher VLDLcholesterol, total, HDL-, LDL-, and VLDL-triglyceride and apolipoprotein B concentration than female control subjects. Tables 4 and 5 show serum lipids, lipoproteins and apolipoproteins according to C-peptide response in diabetic and control subjects. Serum HDL-cholesterol concentration was higher in subjects with low C-peptide response than in those
and Apolipoprotein
Al and B Levels (g/U
in Diabetic and Control Subjects
According to the C-Peptide Response Mell
Controls
Women Diabetics
Controls
Diabetics
Total triglycerides 1.46 + 0.14
2.04
+ 0.18
1.25 + 0.09
3.02
+ 0.63
1.93 + 0.18*
3.84
f 1.02’
1.46 + 0.11
3.13
f 0.30
Low response
0.11
+ 0.02
0.14
* 0.01
0.13
+ 0.01
0.18
+ 0.01
High response LDL-triglycerides
0.13
* 0.01
0.14
* 0.02
0.13
5 0.01
0.16
k 0.01
Low response
0.39
k 0.03
0.46
k 0.03
0.35
r 0.03
0.54
* 0.03
0.48
k 0.04t
0.53
i 0.05
0.43
-t 0.03t
0.61
2 0.04
0.95
+ 0.12
1.44 + 0.16
0.77
+ 0.07
2.31
t 0.61
3.16
0.91
* 0.10
2.36
+ 0.27
Low response High response HDL-triglycerides
High response VLDL-triglycerides Low response High response Apoprotein Al Low response High response Apoprotein 8
1.32 t 0.16t
f 0.98’
1.32 + 0.04
1.18 k 0.05
1.44 + 0.07
1.32 + 0.06
1.18 t 0.04*
1.20 + 0.04
1.43 + 0.04
1.33 r 0.04
Low response
1.23 f 0.09
1.29 + 0.07
1.19 + 0.07
i .3a
High response
1.32 k 0.06
1.23 + 0.06
1.19 + 0.08
1.37 -t 0.06
Values are given as mean + SEM. Low response. C-peptide response below: high response, C-peptide response over the median. ‘P < .05. t. 1 z P > .05: comparison between the groups of low and high response (Student’s two-tailed t-test),
+ 0.07
844
SAALUND ET AL
with high C-peptide response both in diabetic and in control subjects. The difference in HDL-cholesterol concentration reached the conventional level of statistical significance (P < .05) only in men and persisted in male control subjects after adjustment for BMI (P < .05, ANCOVA) and even after adjustment for age, BMI, exercise, alcohol intake, and smoking (P < .05, ANCOVA). Serum HDL,-cholesterol concentration was higher in subjects with low C-peptide response than in subjects with high C-peptide response. These differences in HDL,-cholesterol concentrations were statistically significant (P < .05) for male and female control subjects and female diabetic subjects and persisted in control subjects after adjustment for BMI or even after adjustment for age, BMI, exercise, alcohol intake, and smoking (P < .05, ANCOVA). Serum VLDL-cholesterol concentration was significantly lower in male diabetic and female control subjects with low C-peptide response than with high C-peptide response and the difference persisted in female control subjects after adjustment for BMI (P < .05, ANCOVA). Serum total triglyceride concentration in male diabetic and control subjects and VLDL-triglyceride concentration in male diabetic subjects were significantly lower in subjects with low C-peptide response than with high C-peptide response, but the difference persisted only in male control subjects after adjustment for BMI (P < .05, ANCOVA). This difference persisted even after adjustment for age, BMI, exercise, alcohol intake, and smoking (P < .05, ANCOVA). Serum apolipoprotein Al concentration was significantly higher in male control subjects with low C-peptide response than with high C-peptide response even after adjustment for age, BMI exercise, alcohol intake, and smoking (P < .05, ANCOVA).
DISCUSSION
Serum HDL- and HDL,-cholesterol concentrations have been shown to be lower in non-insulin-dependent diabetic than in control subjects.‘0-‘3 In the present study this difference in serum HDL- and HDL,-cholesterol concentrations between diabetic and nondiabetic subjects was observed only in women. A stronger impact of non-insulin-dependent diabetes on serum HDL-cholesterol concentration in women than in men has previously been observed in some,2o but not in all studiesI In the present study serum HDL- and HDL,-cholesterol concentrations were higher in subjects with low C-peptide response than in those with high C-peptide response both in male and female diabetic and control subjects. Although our findings concerning the association between serum HDLand HDL,-cholesterol concentrations and endogenous insulin secretion capacity were to some extent different in men and women, there was, however, a similar trend towards a lower HDL- and HDL,-cholesterol concentration in high C-peptide responders in both sexes. Generally, all differences
in serum lipoprotein concentrations between low and high C-peptide responses were smaller in female diabetic subjects than in male diabetic subjects. Therefore, C-peptide may be a much poorer indicator of lipid and lipoprotein levels in female diabetic subjects than in male diabetic subjects. In the present study the low and high responder groups were formed on the basis of the median value of the postglucagon C-peptide in each group. This probably weakens the difference between the high and low responders with respect to HDL and HDL, cholesterol as compared to our previous study in which the low responders had undetectable postglucagon C-peptide and high responders had postglucagon C-peptide exceeding the limit of 0.60 nmol/L.14 Serum HDL- and HDL,-cholesterol concentrations are known to be inversely associated with obesity.7*‘4 In the present study, BMI was inversely associated in regression analyses with HDL cholesterol in diabetic subjects, but not in control subjects. BMI was also higher in subjects with higher C-peptide response than in subjects with lower C-peptide response. The differences in serum HDL- and HDL,-cholesterol concentrations in relation to C-peptide response persisted only in control subjects after adjustment for obesity. Therefore, obesity seems to have more effect on serum HDL-cholesterol concentration in diabetic than in control subjects. Serum HDL-cholesterol level has been shown to be inversely associated with plasma glucose level and glycemic control in diabetic subjects. ‘J According to regression analysis, glucose level was not significantly associated with HDL cholesterol in any of the study groups and, therefore, plasma glucose levels were not included in analyses concerning the association between lipoproteins and C-peptide response. However, in diabetic subjects plasma glucose level was higher in subjects with low C-peptide response than in subjects with high C-peptide response, probably due to decreased insulin secretion in the former group. Therefore, hyperglycemia per se did not have any association with HDL-cholesterol concentration in these subjects. In addition to the differences in HDL-cholesterol concentration according to C-peptide response VLDL-triglyceride concentration tended to be higher in high C-peptide responders than in low C-peptide responders. VLDL-triglyceride concentration, however, seemed to be more closely related with obesity than with C-peptide response both in diabetic and in control subjects. In conclusion, the results of the present study indicate that in spite of somewhat different HDL- and HDL,-cholesterol concentrations in diabetic and in control subjects serum HDL- and HDL,-cholesterol concentrations were inversely related to endogenous insulin secretion capacity both in non-insulin dependent diabetic subjects and in control subjects. Serum total and VLDL-triglyceride concentrations seemed also to be associated with insulin secretion capacity, but even more strongly with obesity.
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LIPIDS AND C-PEPTIDE IN DIABETICS
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