Hyperinsulinemia in offspring of non-insulin-dependent diabetes mellitus patients: the role played by abnormal clearance of insulin

Normal insulin sensitivity in lean offspring of obese parents

OBJECTIVE

Offspring of diabetic or hypertensive patients are insulin resistant at a prediabetic/prehypertensive stage. We tested the hypothesis that insulin action may be impaired in the offspring of obese nondiabetic parents.

RESEARCH METHODS AND PROCEDURES

Twenty-one lean offspring of nonobese subjects [(OL) 22 +/- 3 years of age] were matched to 23 lean offspring of obese subjects (OOb) by gender distribution, age, BMI, and waist circumference. Anthropometry, oral glucose tolerance, in vivo insulin sensitivity [by a euglycemic insulin clamp (6 pmol/min per kilogram(FFM); where FFM represents fat-free mass)], and thermogenesis (by indirect calorimetry) were measured in each subject. The study subjects were from a population of 267 nuclear families (one offspring and both his/her parents) in which there was statistically significant (chi2 = 30.2, p = 0.001) concordance of BMI between parents and offspring.

RESULTS

In comparing OOb with OL, no statistically significant difference or trend toward a difference was detected in fasting plasma glucose and insulin concentrations, glucose and insulin responses to oral glucose, insulin sensitivity [metabolism value = 45 +/- 12 (OOb) vs. 47 +/- 17 micro mol/min per kilogram(FFM) (OL)], insulin-induced inhibition of protein and lipid oxidation, stimulation of glucose oxidation and nonoxidative glucose disposal, respiratory quotient, resting energy expenditure, and glucose-induced thermogenesis.

DISCUSSION

The metabolic similarity between lean offspring of obese parents and those of nonobese parents suggests that insulin resistance and its correlates are not co-inherited with the predisposition to develop obesity.

Insulin secretion, insulin sensitivity, and hepatic insulin extraction in first-degree relatives of type 2 diabetic patients

To identify early metabolic abnormalities in type 2 diabetes mellitus, we measured insulin secretion, sensitivity to insulin, and hepatic insulin extraction in 48 healthy normal glucose-tolerant Brazilians, first-degree relatives of type 2 diabetic patients (FH+). Each individual was matched for sex, age, weight, and body fat distribution with a person without history of type 2 diabetes (FH-). Both groups were submitted to a hyperglycemic clamp procedure (180 mg/dl). Insulin release was evaluated in its two phases. The first was calculated as the sum of plasma insulin at 2.5, 5.0, 7.5, and 10.0 min after the beginning of glucose infusion, and the second as the mean plasma insulin level in the third hour of the clamp procedure. Insulin sensitivity index (ISI) was the mean glucose infusion rate in the third hour of the clamp experiment divided by the mean plasma insulin concentration during the same period of time. Hepatic insulin extraction was determined under fasting conditions and in the third hour of the clamp procedure as the ratio between C-peptide and plasma insulin levels. FH+ individuals did not differ from FH- individuals in terms of the following parameters [median (range)]: a) first-phase insulin secretion, 174 (116-221) vs 207 (108-277) microU/ml, b) second-phase insulin secretion, 64 (41-86) vs 53 (37-83) microU/ml, and c) ISI, 14.8 (9.0-20.8) vs 16.8 (9.0-27.0) mg kg-1 min-1/ microU ml-1. Hepatic insulin extraction in FH+ subjects was similar to that of FH- ones at basal conditions (median, 0.27 vs 0.27 ng/microU) and during glucose infusion (0.15 vs 0.15 ng/ micro U). Normal glucose-tolerant Brazilian FH+ individuals well-matched with FH- ones did not show defects of insulin secretion, insulin sensitivity, or hepatic insulin extraction as tested by hyperglycemic clamp procedures.

Family and genetic studies of indices of insulin sensitivity and insulin secretion in Pima Indians

BACKGROUND

The present analyses were conducted to examine the extent to which insulin sensitivity and insulin secretion, assessed using simple indices derived from an oral glucose tolerance test, are influenced by genetic factors, and to assess whether these genetic factors overlap with those influencing susceptibility to type 2 diabetes in Pima Indians.

METHODS

Indices calculated from fasting and 2-h post-load insulin (I(0), I(120)) and glucose (G(0), G(120)) concentrations included insulin sensitivity index [ISI(0)=10(4)/(I(0).G(0))] and corrected insulin response [CIR(120)=I(120)/[G(120).(G(120)-70 mg/dl)]]. Heritability (h(2)) was determined using variance components methods in 1421 non-diabetic individuals from 446 sibships. Among 595 individuals in 186 sibships, genome-wide quantitative trait linkage analyses of ISI(0) and CIR(120) were conducted and affected-sibling analyses of diabetic siblings stratified by prediabetic measurements of ISI(0) and CIR(120) were also performed.

RESULTS

Both ISI(0) (h(2)=0.37+/-0.06) and CIR(120) (h(2)=0.25+/-0.07) were moderately heritable. Modest evidence for linkage with CIR(120) (logarithm of odds (LOD)=1.6) was observed on chromosome 1q in a region previously shown to have linkage with young-onset diabetes in Pimas. When diabetic siblings were stratified by CIR(120), evidence for linkage in this region was strongest (LOD=1.5) among those with a low CIR(120). Additional regions with modest evidence for linkage with ISI(0) were observed on chromosomes 9p (LOD=2.0) and 14p (LOD=1.7).

CONCLUSIONS

The present analyses suggest that insulin sensitivity and insulin secretion are influenced by genetic factors in Pima Indians. The linkage analyses suggest that the putative diabetes-susceptibility gene on chromosome 1q affects insulin secretion. Published in 2001 by John Wiley & Sons, Ltd.

Alterations in the glucose-stimulated insulin secretory dose-response curve and in insulin clearance in nondiabetic insulin-resistant individuals

Plasma glucose and insulin responses to a graded i.v. infusion of glucose were compared in two groups of glucose-tolerant women divided on the basis of their insulin sensitivity. Resistance to insulin-mediated glucose disposal was measured using the insulin suppression test, and the women studied were chosen to represent the highest and lowest quartiles of insulin resistance seen in the normal population. The sensitivity of the pancreatic beta-cell to glucose was assessed by measuring the glucose, insulin, and C peptide concentrations in response to continuous graded i.v. infusions of glucose at rates of 1, 2, 3, 4, 6, and 8 mg/kg x min for 40 min each. In addition, insulin secretion rates in response to the graded glucose infusion, calculated over each sampling period, were derived from deconvolution of peripheral plasma C peptide concentrations, using a two-compartment model of C peptide kinetics and standard parameters for C peptide clearance. Although plasma glucose concentrations were only slightly higher throughout the glucose infusion, the insulin concentrations were approximately doubled in the insulin-resistant subjects. When expressed as a function of the molar increments in plasma glucose achieved during the glucose infusion studies, the insulin-resistant women had a 90% higher (684 +/- 55 vs. 360 +/- 36 pmol/L x mmol/L; P < 0.001) total integrated plasma insulin response as the glucose concentration was increased from 5 to 9 mmol/L. However, the total integrated insulin secretory rate was only increased by 37% (1494 +/- 133 vs. 1093 +/- 125 pmol/mmol/L x min; P < 0.05) in the insulin-resistant group. This discrepancy suggested that insulin clearance was lower in the insulin-resistant subjects, and the calculation of this value, as the ratio of the total secretion of insulin to the area under the plasma insulin curve, was significantly lower in the insulin-resistant group (1.25 +/- 0.05 vs. 1.87 +/- 0.16 L/min x m2; P < 0.005). These results show that the hyperinsulinemia of insulin resistance results from an increase in insulin secretion secondary to a shift to the left of the glucose-stimulated insulin response curve as well as a decrease in insulin clearance.

Characterization of alterations in glucose and insulin metabolism in Prader-Willi subjects

Obesity is a common component of non-insulin-dependent diabetes mellitus (NIDDM) and plays an important role in the development of insulin resistance and hyperinsulinemia. Prader-Willi syndrome (PWS) has been associated with morbid obesity and an increased propensity for early development of NIDDM. It has been assumed that the etiology for this increased rate of NIDDM is related to the morbid obesity and concomitant insulin resistance, but this remains controversial. To shed light on the glucoregulatory mechanisms in PWS, we studied both pediatric and adult PWS patients with normoglycemia. The objectives of our study were (1) to examine glucose, insulin, and C-peptide responses to oral (OGTT) and intravenous (IVGTT) glucose tolerance tests; (2) to characterize acute first- and second-phase insulin secretion during an IVGTT; (3) to assess hepatic insulin extraction (HIE) and insulin clearance (IC) in PWS subjects; and (4) to determine whether beta-cell function in PWS is age-dependent. These results in PWS were compared with values obtained in age-, sex-, and body mass index (BMI)-matched non-PWS obese controls. Three groups were studied. Group I consisted of nine PWS subjects under the age of 13 years and 22 age-, sex-, weight-, and puberty stage-matched obese subjects who underwent OGTT. Group II consisted of 14 adult PWS subjects and 10 age-, weight-, and BMI-matched obese adults who underwent OGTT. Group III consisted of nine adult PWS subjects and eight age-, sex-, and weight-matched obese adults who underwent frequently sampled IVGTT (FSIVGTT). During the OGTT in the pediatric group, fasting (86 +/- 3 v 89 +/- 2 mg/dL), peak (144 +/- 11 v 147 +/- 4 mg/dL), and total area under the curve (AUC) (6,984 +/- 1,320 v 6,963 +/- 615 mg/dL x min) glucose levels were not significantly different in PWS versus obese children, respectively. In contrast, fasting (20 +/- 6 v 37 +/- 4 microU/mL), peak (114 +/- 24 v 214 +/- 23 microU [correction of mU]/mL), and total AUC (12,673 +/- 2,176 v 26,734 +/- 2,608 microU/mL microU/mL min) insulin levels were significantly lower in pediatric PWS. During the OGTT in the adult groups, neither fasting insulin (16.7 +/- 2.8 v 13.5 +/- 2.5 microU/mL) nor total AUC for insulin (10,664 +/- 1,955 v 11,623 +/- 1,584 microU/mL x min) were significantly different in adult PWS and obese groups. During the IVGTT in adults, both first-phase (138 +/- 42 v 454 +/- 102 microU/mL x min) and second-phase (295 +/- 66 v 1,015 +/- 231 microU/mL x min) insulin release were significantly reduced in PWS subjects despite similar glucose levels. Similarly, first-phase (8.6 +/- 2.3 v 21 +/- 4.6 ng/dL x min) and second-phase (47 +/- 4.6 v 75 +/- 14 ng/dL x min) C-peptide responses were also significantly reduced in PWS subjects. In contrast, mean HIE and IC was 33% higher in PWS subjects versus obese controls (15.4 +/- 1.5 v 10.3 +/- 1.6). Similarly, poststimulation HIE and IC was significantly greater (5.2 +/- 0.8 v 2.4 +/- 0.4) in the PWS group compared with the obese group (P < .01). In summary, this study demonstrates that nondiabetic PWS subjects manifest (1) a reduced beta-cell response to glucose stimulation, (2) a significantly increased HIE compared with obese controls, and (3) a dissociation of obesity and insulin resistance, in contrast to normal obese subjects. We conclude that glucoregulatory mechanisms are different in obese PWS versus non-PWS subjects.