Circulating TNF-alpha and leptin levels in offspring of NIDDM patients do not correlate to individual insulin sensitivity

Obesity plays a central role in the development of skeletal muscle insulin resistance. The molecular mechanism causing skeletal muscle insulin resistance in obese people is still poorly understood. It has been speculated that circulating factors derived from adipose tissue impair insulin signalling in the skeletal muscle cell. TNF-alpha and leptin, which are overproduced in fat tissue of obese insulin resistant animal models and in obese humans, might mediate such an inhibitory effect on insulin signalling in skeletal muscle. The aim of the present study was to evaluate whether circulating TNF-alpha and leptin correlates to the individual skeletal muscle insulin sensitivity in individuals with different degrees of obesity and insulin resistance. We measured circulating TNF-alpha and leptin values in non diabetic offsprings of NIDDM patients. 36 German and 47 Finnish subjects participated in the study. The GDR of each participant was determined by the euglycemic hyperinsulinemic clamp technique, a range between 1.37 to 14.01 mg/kg LBM x min was observed. Percent of desirable body weight (PDW) covered also a wide range (87.58% to 197.06%). Although linear regression analysis suggested a dependence between TNF-alpha and GDR (Germany group: r = -0.37, p < 0.05, Finnish group: r = -0.32, p < 0.05) and a dependence between TNF and PDW (German group: r = 0.46, p < 0.05, Finnish group: r = 0.38, p < 0.05), in multiple linear regression analysis only the correlation with PDW was significant. Leptin levels were measured from 29 German and 36 Finnish subjects and a strong association was found between leptin and PDW (German group: r = 0.55, p < 0.05, Finnish group: r = 0.73, p < 0.05). In contrast, leptin levels did not correlate with GDR and TNF-alpha. In summary, even though, in a few insulin resistant subjects, higher circulating TNF-alpha or leptin levels with the individual insulin sensitivity can be demonstrated, the data suggest that the circulating pool of TNF-alpha and leptin in blood is unlikely to be a major contributing factor for obesity induced insulin resistance in the vast majority of individuals at high risk to develop NIDDM.     

Proinsulin and insulin concentrations in relation to carotid wall thickness: Insulin Resistance Atherosclerosis Study

BACKGROUND AND PURPOSE: Insulin resistance and hyperinsulinemia have been associated with atherosclerosis. Recent attention has focused on the possible role of proinsulin because most radioimmunoassays for insulin cross-react with proinsulin. Therefore, it is not known which of the two, insulin per se or proinsulin, is more strongly related to atherosclerosis. METHODS: We examined the relation between fasting proinsulin, fasting split proinsulin, fasting and 2-hour insulin (after oral glucose load), and intima-media wall thickness (IMT) in the common carotid artery (CCA) and internal carotid artery (ICA) in 985 nondiabetic subjects from the Insulin Resistance Atherosclerosis Study, a multiethnic study of insulin resistance and atherosclerosis. RESULTS: In the overall population, a weak but significant relation between proinsulin and CCA IMT was observed (r=0.07, P=0.029). However, the relation between proinsulin and IMT was stronger in Hispanics and non-Hispanic whites than in African Americans. In non-Hispanic whites and Hispanics, significant correlations between CCA and proinsulin (r=0.087) and between ICA and proinsulin (r=0.101), split proinsulin (r = 0.092), and fasting insulin (r = 0.087) were observed. The significant correlations became more attenuated (and nonsignificant) after adjustment for cardiovascular risk factors, especially plasminogen activator inhibitor-1 (PAI-1). CONCLUSIONS: The association between proinsulin and IMT, while weak, appears to be stronger than the association between insulin and IMT. Adjustment for PAI-1 markedly attenuated the association between proinsulin and IMT, suggesting a possible mediating role for PAI-1 in this association. It is possible that proinsulin may represent a marker of atherosclerosis rather than a causal factor for atherosclerosis. Studies of the insulin resistance syndrome and atherosclerosis that use insulin as a surrogate for insulin resistance should consider the use of specific insulin assays as well as determination of proinsulin concentrations.     

Fluctuations in the affinity and concentration of insulin receptors on circulating monocytes of obese patients: effects of starvation, refeeding, and dieting

The binding of 125I-insulin to insulin receptors on circulating monocytes of obese patients and normal volunteers has been determined under various dietary states. In the basal, fed state the monocytes of obese patients with clinical insulin resistance (n= 6) bound less insulin than normals (n =10) because of a decrease in insulin receptor concentration (obese = 6,000-13,000 sites per monocyte versus normals 15,000-28,000 sites per monocyte). The single obese patient without evidence of clinical insulin resistance demonstrated normal binding of insulin with 16,000 sites per monocyte. In all patients, the total receptor concentration was inversely related to the circulating levels of insulin measured at rest after an overnight fast. For the obese patients with basally depressed insulin binding, a 48-72-h fast lowered circulating insulin and increased binding to normal levels but only at low hormone concentrations; this limited normalization of 125I-insulin binding was associated with increased receptor affinity for insulin without change in receptor concentration. Refeeding after the acute fasting periods resulted in return to the elevated plasma insulin levels, the basal receptor affinity, and the depressed insulin binding observed in the basal, fed state. Chronic diet restored plasma insulin levels, insulin binding, and receptor concentration to normal without change in affinity. When the data from this study are coupled with previous in vivo and in vitro findings they suggest that the insulin receptor of human monocytes is more sensitive to regulation by ambient insulin than the receptors of obese mice and cultured human lymphocytes. The results further indicate than an insulin receptor undergoes in vivo modulation of its interaction with insulin by changing receptor concentration and by altering the affinity of existing receptors.     

Preliminary characterization of glial-secreted factors responsible for the induction of high electrical resistances across endothelial monolayers in a blood-brain barrier model

Low levels of sex hormone-binding globulin (SHBG) are considered to be an indirect index of hyperinsulinemia, predicting the later onset of diabetes mellitus type 2. In the insulin resistance state and in the presence of an increased pancreatic beta-cell demand (e.g. obesity) both absolute and relative increases in proinsulin secretion occur. In the present study we investigated the correlation between SHBG and pancreatic beta-cell secretion in men with different body compositions. Eighteen young men (30.0 +/- 2.4 years) with normal glucose tolerance and body mass indexes (BMI) ranging from 22.6 to 43.2 kg/m2 were submitted to an oral glucose tolerance test (75 g) and baseline and 120-min blood samples were used to determine insulin, proinsulin and C-peptide by specific immunoassays. Baseline SHBG values were significantly correlated with baseline insulin (r = -0.58, P < 0.05), proinsulin (r = -0.47, P < 0.05), C-peptide (r = -0.55, P < 0.05) and also with proinsulin at 120 min after glucose load (r = -0.58, P < 0.05). Stepwise regression analysis revealed that proinsulin values at 120 min were the strongest predictor of SHBG (r = -0.58, P < 0.05). When subjects were divided into obese (BMI > 28 kg/m2, N = 8) and nonobese (BMI < or = 25 kg/m2, N = 10) groups, significantly lower levels of SHBG were found in the obese subjects. The obese group had significantly higher baseline proinsulin, C-peptide and 120-min proinsulin and insulin levels. For the first time using a specific assay for insulin determination, a strong inverse correlation between insulinemia and SHBG levels was confirmed. The finding of a strong negative correlation between SHBG levels and pancreatic beta-cell secretion, mainly for the 120-min post-glucose load proinsulin levels, reinforces the concept that low SHBG levels are a suitable marker of increased pancreatic beta-cell demand.     

The insertion allele of the ACE gene I/D polymorphism. A candidate gene for insulin resistance?

BACKGROUND: The insertion/deletion (ID) polymorphism of the angiotensin-converting enzyme (ACE) gene has been associated with increased coronary heart disease (CHD), although the mechanism of this association is not apparent. We tested the hypothesis that the deletion allele of the ACE gene is associated with insulin resistance. METHODS AND RESULTS: We related ACE genotype to components of the insulin-resistance syndrome in 103 non-insulin-dependent diabetic (NIDDM) and 533 nondiabetic white subjects. NIDDM subjects with the DD genotype had significantly lower levels of specific insulin (DD 38.6, ID 57.1, and II 87.4 pmol.L-1 by ANOVA, P = .011). Non-insulin-treated subjects with the DD genotype had increased insulin sensitivity by HOMA % (DD 56.4%, II 29.4%, P = .027) and lower levels of des 31,32 proinsulin (DD 3.3, II 7.6 pmol.L-1, P = .012) compared with II subjects. There were no differences in prevalence of CHD or levels of blood pressure, serum lipids, or plasminogen activator inhibitor-1 (PAI-1) activity between the three ACE genotypes. In nondiabetic subjects there were no differences in insulin sensitivity, levels of insulin-like molecules, blood pressure, PAI-1, serum lipids, or CHD prevalence between the three ACE genotypes. CONCLUSIONS: We conclude that increased cardiovascular risk of the DD genotype is not mediated through insulin resistance or abnormalities in fibrinolysis. Conversely, we report an increased sensitivity in NIDDM subjects with the ACE DD genotype.     

No changes of peripheral insulin resistance in polycystic ovary syndrome after long-term reduction of endogenous androgens with leuprolide

The aim of this study was to investigate the relationship between plasma insulin levels, peripheral insulin sensitivity and androgen secretion in ten patients with polycystic ovary syndrome and in six obese women as compared with six normal-weight control subjects. During a euglycemic-hyper-insulinemic clamp no significant change of testosterone, androstenedione or dehydroepiandrosterone sulfate plasma levels was observed in the two groups of patients or in the control subjects; insulin sensitivity was clearly reduced and was similar in polycystic ovary patients and in obese women, in spite of the different plasma androgen levels. A long-term (5 months) androgen suppression with the gonadotropin-releasing hormone agonist leuprolide was not able to improve significantly the insulin sensitivity. These results demonstrate that the short-term hyperinsulinemia achieved with the clamp technique does not affect androgen secretion and that insulin resistance, measured with the same technique, is not influenced by long-term suppression of plasma androgen levels in polycystic ovary syndrome.     

Specific insulin assays, insulin sensitivity and blood pressure

Serum insulin concentrations have been used as markers of insulin resistance in population studies examining the relationship between insulin resistance and blood pressure, but the relationship is variable among studies. We hypothesized that differences in cross-reactivity of insulin assays with proinsulin and its split/des-amino products might account for the variation. We therefore examined fasting and post-glucose load serum insulin concentrations (determined by both specific and conventional assays), insulin sensitivity (measured by the euglycaemic clamp technique), and blood pressure, in a group of 56 diabetic (NIDDM) and non-diabetic subjects. Insulin concentrations as measured by the two methods were highly correlated (r = 0.97, p < 0.0001), and the relationships among serum insulin concentrations, insulin sensitivity and blood pressure were independent of assay method; for example, in non-diabetic subjects the univariate correlation between log10AUC insulin and insulin sensitivity index was similar with both methods [r = -0.81 vs. r = -0.82, p < 0.0001 (specific vs. conventional assay)]. Discrepancies between studies in the relationship between serum insulin concentrations and blood pressure are unlikely to be due to cross-reactivity of conventional insulin assays with proinsulin-like molecules.     

Multiple metachronous metastasis of adenocarcinoma of the kidneys in crossed ectopy with fusion

OBJECTIVE: Hyperandrogenism in patients with polycystic ovary syndrome has been shown to correlate with hyperinsulinaemia of insulin resistance. We have investigated if basal levels of insulin and the response to the intravenous administration of glucagon can reveal insulin resistance in patients with polycystic ovary syndrome. PATIENTS: Nine obese (BMI > 25 kg/m2) and nine non-obese (BMI 19-25 kg/m2) women with PCOS, chosen from a population of 91 women attending the infertility clinic, and 19 normally cycling women (seven obese, 12 non-obese) were studied. Oligo or amenorrhoea, hirsutism, and 12 or more follicles in a given ovary were selection criteria. MEASUREMENTS: Glucagon, 1 mg, was given intravenously to 18 of the 91 women and to the control subjects. Blood was taken at -5, 0, 5, 10 and 15 minutes for measurements of integrated areas under the response curve for insulin, C-peptide and glucose, respectively. Basal blood samples were drawn for fasting insulin, C-peptide, glucose, testosterone, sex hormone-binding globulin (SHBG), free fatty acids and IGF-I measurements. The free androgen index was calculated according to the formula FAI = testosterone x 100/SHBG. RESULTS: There were no significant differences in maximal increment and area under the response curve for glucose, C-peptide and insulin. FAI was significantly higher in all patients with features of polycystic ovary syndrome. However, fasting insulin levels were significantly higher only in obese patients when compared with obese control subjects and lean patients. CONCLUSIONS: The administration of 1 mg glucagon i.v. did not distinguish patients with polycystic ovary syndrome from control subjects. The mild insulin resistance of polycystic ovary syndrome is related only to obesity and is therefore unlikely to play an important role in the hyperandrogenism associated with the syndrome.     

Association of proinsulin-like molecules with lipids and fibrinogen in non-diabetic subjects--evidence against a modulating role for insulin

Elevated concentrations of proinsulin-like molecules, other than insulin, may be associated with abnormalities of cardiovascular risk factors, promoting atherogenesis and thrombosis. Using specific assays we examined the relationship of levels of insulin, intact proinsulin and des-31,32 proinsulin to blood pressure, lipids, fibrinogen, factor VII and albumin excretion rate in 270 europids with normal glucose tolerance. After correcting for age and body mass index, fasting and 2-h insulin concentrations were significantly associated with those of total and LDL-cholesterol (r = 0.18-0.22), HDL-cholesterol (both r = -0.20) and triglycerides (r = 0.21 and 0.18), but not with blood pressure. Concentrations of intact and des-31,32 proinsulin showed significant associations with those of total and LDL-cholesterol (r = 0.20-0.23), HDL-cholesterol (r = -0.31 and -0.32) and triglycerides (r = 0.22 and 0.26). Fasting insulin and intact proinsulin concentrations were significantly associated with fibrinogen (r = -0.15 and 0.18). Concentrations of proinsulin-like molecules comprised less than 10% of all insulin-like molecules, and so were calculated not to influence previously described relationships between insulin concentrations and cardiovascular risk factors measured using non-specific assays. In multiple regression analyses des-31,32 proinsulin concentration was more strongly associated with those of HDL-cholesterol (negatively), LDL-cholesterol and triglycerides than fasting insulin concentrations, while intact proinsulin replaced insulin concentrations in their relationships with fibrinogen. Our results show correlations between dyslipidaemia and proinsulin-like molecules at concentrations at which biological, insulin-like, activity appears unlikely. We also show relationships between LDL-cholesterol and fibrinogen and the proinsulin-like molecules.(ABSTRACT TRUNCATED AT 250 WORDS)     

'True' fasting serum insulin level, insulin resistance syndrome and coronary artery disease

BACKGROUND: Increased fasting serum insulin level not associated with hypoglycemia is considered to be a practical indicator of the insulin resistance syndrome, a frequent risk factor for atherosclerosis in industrialized countries. However, in most studies, insulin was measured by using antibodies which cross-react with proinsulin and 31/32, 32/33 split products of insulin. We re-examined the correlations between the insulin resistance syndrome and 'true' fasting serum insulin level. METHODS: We studied 242 post-menopausal women (age 63 +/- 8 years), a population in whom insulin resistance syndrome is particularly frequent. Serum insulin was measured by a recent specific microparticle immunoassay. RESULTS: There was a significant correlation between elevated 'true' fasting serum insulin level and various constituents of the insulin resistance syndrome, such as obesity, dyslipidemia (hypertriglyceridemia, increased apolipoprotein B and decreased high-density lipoprotein cholesterol and apolipoprotein A1 concentrations), increased serum glucose, uric acid levels, and plasminogen activator inhibitor type I concentration, as well as increased frequency of diabetes. There was also a correlation between insulin level and various manifestations of coronary artery disease: patients in the highest quartile of 'true' insulin level had significantly more entirely occluded coronary arteries than in the lowest one. Similarly, in the highest insulin quartile more patients had occluded arteries with lumen diameter stenoses greater than 50% (P < 0.05) and more of them had history of previous myocardial infarction approaching the level of significance (P = 0.0587) than in the lowest one. Most of these correlations were also noted in nondiabetic people. CONCLUSIONS: An increase of 'true' fasting serum insulin level is a useful practical index to identify patients with the insulin resistance syndrome exposed to increased risk of coronary artery disease.     

Risk factors for the development of NIDDM in Yonchon County, Korea

OBJECTIVE: To determine the risk factors for the development of NIDDM in Yonchon County of Korea. RESEARCH DESIGN AND METHODS: We studied 1,193 Korean nondiabetic subjects at baseline who participated in a 2-year follow-up study on diabetes in Yonchon County. A 75-g oral glucose tolerance test was performed 2 years after the baseline examination. Age, sex, and anthropometric and metabolic characteristics at baseline were analyzed simultaneously as potential predictors of conversion to NIDDM. We also designed a nested case-control study to determine the role of hyperinsulinemia and/or hyperproinsulinemia in the conversion to NIDDM in patients with newly developed diabetes and control subjects matched for age, sex, BMI, and waist-to-hip-ratio. RESULTS: At 2 years, 67 subjects developed diabetes, as defined by World Health Organization criteria. The age-adjusted incidence was significantly higher in men (6.4%) than in women (3.0%), and the incidence increased as age increased in both sexes. Multiple logistic regression analysis revealed age, male sex, and fasting and 2-h glucose levels to be significant risk factors for the development of NIDDM, whereas waist-to-hip ratio and BMI were not. In a nested case-control study, baseline proinsulin but not insulin levels were significantly higher in subjects who progressed to NIDDM than in those who did not. CONCLUSIONS: In the Korean population, beta-cell dysfunction, as measured by high proinsulin levels, seems to be associated with subsequent development of NIDDM, whereas regional and general obesity and fasting insulin levels, which may be a surrogate for insulin resistance, were not.     

Plasma leptin is not associated with insulin resistance and proinsulin in non-diabetic South Asian Indians

In an earlier study, we observed only a weak association between plasma insulin (non-specific assay) and leptin in South Asian Indians. This was in contrast to the observations in many other ethnic groups. With the availability of measurements of specific insulin (SI) and proinsulin (PI) in the same study group, we have reanalysed the data to look for possible correlation of leptin with proinsulin and with insulin resistance calculated from the fasting values of specific insulin and glucose using the HOMA model. Subjects with normoglycaemia (n = 117) and impaired glucose tolerance (n = 27, WHO criteria) were included in the analysis. Leptin values were higher in women. Multiple linear regression analysis showed that the variations in leptin concentrations in men were associated with BMI, WHR, and 2 h SI values (R2 = 56.2%) while fasting SI and proinsulin concentrations had no significant association. In women BMI and age showed a significant association with serum leptin values (R2 = 40.1%). Univariate and multivariate analyses using insulin resistance as the dependent variable showed that it had no association with leptin in both genders. Leptin had no correlation with proinsulin also. This study confirmed that in Asian Indians the association between plasma leptin and insulin concentrations is weak and that leptin has no influence on insulin resistance. Proinsulin and leptin are also not correlated in this population. Insulin resistance shows correlation with the beta-cell function both in men and women.     

Glucose tolerance in the elderly: the role of insulin and its receptor

Oral glucose tolerance tests were performed in young and elderly subjects with minimal risk factors for diabetes mellitus. Compared to the normal glucose tolerance in the young there was a 45% rate of impaired tolerance in the elderly. Fasting insulin levels were significantly lower in the elderly but post-glucose insulin responses in the first hour were similar in young and elderly subjects. Peripheral insulin action was assessed in terms of the 125 monoiodoinsulin binding to specific insulin receptor sites on circulating lymphocytes in the young, the elderly and a group of age and sex matched obese maturity-onset diabetics. Specific insulin binding was not significantly different in the elderly than in the young but was significantly lower in the diabetics than the young and the elderly. The results suggest that neither defective insulin binding are major causative factors in the reduced glucose tolerance of the elderly.     

Regulation of skeletal muscle hexokinase II by insulin in nondiabetic and NIDDM subjects

Impaired muscle glucose phosphorylation to glucose-6-phosphate by hexokinases (HKs)-I and -II may contribute to insulin resistance in NIDDM and obesity. HK-II expression is regulated by insulin. We tested the hypothesis that basal and insulin-stimulated expression of HK-II is decreased in NIDDM and obese subjects. Skeletal muscle HK-I and HK-II activities were measured in seven lean and six obese normal subjects and eight patients with NIDDM before and at 3 and 5 h of a hyperinsulinemic (80 mU x m(-2) x min(-1)) euglycemic clamp. To assess whether changes in HK-II expression seen during a glucose clamp are likely to be physiologically relevant, we also measured HK-I and HK-II activity in 10 lean normal subjects before and after a high-carbohydrate meal. After an overnight fast, total HK, HK-I, and HK-II activities were similar in lean and obese control subjects; but HK-II was lower in NIDDM patients than in lean subjects (1.42 +/- 0.16 [SE] vs. 2.33 +/- 0.24 nmol x min(-1) x mg(-1) molecular weight, P < 0.05) and accounted for a lower proportion of total HK (33 +/- 3 vs. 47 +/- 3%, P < 0.025). HK-II (but not HK-I) activity increased during the clamp in lean and obese subjects by 34 and 36% after 3 h and by 14 and 22% after 5 h of hyperinsulinemia; no increase was found in the NIDDM patients. In the lean subjects, muscle HK-II activity also increased by 15% 4 h after the meal, from 2.47 +/- 0.19 basally to 2.86 +/- 0.28 nmol x min(-1) x mg(-1) protein (P < 0.05). During the clamps, muscle HK-II activity correlated with muscle citrate synthase activity in the normal subjects (r = 0.58, P < 0.05) but not in the NIDDM patients. A weak relationship was noted between muscle HK-II activity and glucose disposal rate at the end of the clamp when all three groups were combined (r = 0.49, P < 0.05). In summary, NIDDM patients have lower muscle HK-II activity basally and do not increase the activity of this enzyme in response to a 5-h insulin stimulus. This defect may contribute to their insulin resistance. In nondiabetic obese subjects, muscle HK-II expression and its regulation by insulin are normal.     

Relationship between insulin secretory function and endogenous hypertriglyceridemia in obese humans with insulin resistance

Eighteen obese inpatients with insulin resistance revealed by i.v. insulin test and expressed in various grades of hyperinsulinemia and hyperglycemia were examined for plasma lipid levels. A significant positive correlation was found to be present between the plasma triglyceride (TG) level and the insulin response to glucose load. A stepwise multiple regression analysis revealed that the insulin secretory response, the plasma cholesterol level and the relative body weight contributed to the level of plasma TG. No difference was found in the grades of insulin resistance between patients with and without elevated TG. The ratio of sum of plasma insulin values to that of blood glucose values during glucose tolerance test was markedly increased in patients with elevated TG. The patients with relatively blunted insulin response and impaired glucose tolerance curves showed only slight slight hypertriglyceridemia. Endogenous hypertriglyceridemia in obesity seems to be more closely correlated with plasma insulin level, and therefore, with insulin action rather than insulin resistance.     

UKPDS 19: heterogeneity in NIDDM: separate contributions of IRS-1 and beta 3-adrenergic-receptor mutations to insulin resistance and obesity respectively with no evidence for glycogen synthase gene mutations. UK Prospective Diabetes Study

Insulin receptor substrate-1 (IRS-1), beta 3-adrenergic-receptor (beta 3-AR) and glycogen synthase (GS) genes are candidate genes for non-insulin-dependent diabetes mellitus (NIDDM), insulin resistance, dyslipidaemia and obesity. We studied white Caucasian subjects with NIDDM, 227 being randomly selected, 49 NIDDM within the top two percentiles of insulin resistance; 54 with dyslipidaemia in the top quintile of triglyceride/insulin and the bottom quintile of HDL, and 166 non-diabetic control subjects. We examined the association of the simple tandem repeat DNA polymorphisms (STRPs) near the IRS-1 and GS genes, and the prevalence of mutations at codons of IRS-1 513 and 972, beta 3-AR 64 and GS 464 using restriction fragment length polymorphism (RFLP). The STRP alleles in IRS-1 were significantly different between NIDDM and control subjects (p = 0.015). The IRS-1 972 mutation was significantly different between the four groups with increased prevalence in the insulin resistant and dyslipidaemia subjects (18 and 26% compared with 11% in control subjects; p < 0.0005). Those with or without IRS-1 mutations had similar clinical characteristics and impaired insulin sensitivity. beta 3-AR 64 mutation was not significantly different between the four groups but those with the mutation were more obese, with a test for linear association between number of alleles and degree of obesity in an analysis of variance showing a significant association (p = 0.029). The GS 464 mutation was not detected in any of the diabetic or control subjects and the population association study using GS STRP showed no difference in allelic frequencies between NIDDM patients and control subjects. A mutation in lipoprotein lipase at codon 291, associated in the general population with low HDL cholesterol, was not at increased prevalence in the NIDDM patients with dyslipidaemia. In conclusion, IRS-1 972 had an increased prevalence in subjects with insulin resistance, with or without dyslipidaemia. beta 3-AR 64 was associated with increased obesity but not with insulin resistance or dyslipidaemia. These separate contributions to different features of NIDDM are an example of the polygenic inheritance of this heterogeneous disorder.     

Chronic exposure to free fatty acid reduces pancreatic beta cell insulin content by increasing basal insulin secretion that is not compensated for by a corresponding increase in proinsulin biosynthesis translation

The pancreatic beta cell normally maintains a stable balance among insulin secretion, insulin production, and insulin degradation to keep optimal intracellular stores of the hormone. Elevated levels of FFA markedly enhance insulin secretion; however, the effects of FFA on insulin production and intracellular stores remain unclear. In this study, twofold elevation in total circulating FFA effected by infusion of lard oil and heparin into rats for 6 h under normoglycemic conditions resulted in a marked elevation of circulating insulin levels evident after 4 h, and a 30% decrease in pancreatic insulin content after a 6-h infusion in vivo. Adding 125 muM oleate to isolated rat pancreatic islets cultured with 5.6 mM glucose caused a 50% fall in their insulin content over 24 h, coupled with a marked enhancement of basal insulin secretion. Both effects of fatty acid were blocked by somatostatin. In contrast to the stimulatory effects of oleate on insulin secretion, glucose-induced proinsulin biosynthesis was inhibited by oleate up to 24 h, but was unaffected thereafter. This result was in spite of a two- to threefold oleate-induced increase in preproinsulin mRNA levels, underscoring the importance of translational regulation of proinsulin biosynthesis in maintaining beta cell insulin stores. Collectively, these results suggest that chronically elevated FFA contribute to beta cell dysfunction in the pathogenesis of NIDDM by significantly increasing the basal rate of insulin secretion. This increase in turn results in a decrease in the beta cell's intracellular stores that cannot be offset by commensurate FFA induction of proinsulin biosynthesis.     

The insulin resistance in women with hyperandrogenism is partially reversed by antiandrogen treatment: evidence that androgens impair insulin action in women

To assess whether androgen excess per se might impair insulin action, insulin sensitivity was measured by a two-step (20 and 80 mU/m2.min) hyperinsulinemic euglycemic clamp combined with indirect calorimetry and tracer glucose infusion in 43 women (13 obese and 30 nonobese) with normal glucose tolerance and clinical evidence of increased androgen action (hirsutism and/or polycystic ovary syndrome) as well as 12 age- and body mass index-matched healthy controls. Hyperandrogenic women were studied basally and after 3-4 months of antiandrogen treatment with 3 different drugs: spironolactone (n = 23), flutamide (n = 10), or the GnRH agonist buserelin (n = 10). Six women given spironolactone were also reexamined after 1 yr of therapy. At baseline, insulin-mediated glucose uptake was lower in hyperandrogenic women than in controls (by ANOVA, F = 14.3; P < 0.001). Insulin resistance was observed in both ovarian and nonovarian hyperandrogenism, as distinguished by acute GnRH agonist testing. After antiandrogen therapy, insulin action on glucose metabolism significantly increased for both the patients as a whole (F = 7.4; P < 0.01) and each treatment group separately. However, insulin action remained lower than in controls and showed no further improvement in patients reevaluated after I yr of treatment. Increases in both oxidative and nonoxidative glucose metabolism accounted for the improvement in substrate disposal induced by antiandrogen drugs. The increase in the effectiveness of insulin was greater in the lean subjects, whereas the change was small and not statistically significant in the obese women. Response to treatment was more pronounced in women with nonovarian hyperandrogenism, particularly at the low insulin infusion rate. Endogenous glucose production in hyperandrogenic patients was similar to that in healthy women and was unaffected by therapy. In conclusion, antiandrogen treatment partially reversed the peripheral insulin resistance associated with hyperandrogenism regardless of which antiandrogen was used. These data strongly suggest that in women, androgen excess per se contributes to impairment of insulin action.     

Tumor necrosis factor-alpha in sera of obese patients: fall with weight loss

In view of the recent demonstration that obesity in animals and humans is associated with an increase in tumor necrosis factor-alpha (TNFalpha) expression, that this expression falls with weight loss, and that TNFalpha may specifically inhibit insulin action, the possibility that TNFalpha may be a mediator of insulin resistance has been raised. We have undertaken this study to investigate whether serum TNFalpha concentrations are elevated in obese subjects, whether they fall after weight loss, and whether this fall parallels the fall in insulin release after glucose challenge. Obese patients (age range: 25-54, weight mean +/- SD: 96.4 +/- 13.8 kg, body mass index: 35.7 +/- 5.6 kg/m2) were started on a diet program. The mean weight fell to 84.5 +/- 11.3 (P < 0.0001) and body mass index to 31.3 +/- 4.9 (P < 0.0001). Plasma TNFalpha concentrations were markedly elevated in the obese (3.45 +/- 0.16 pg/mL), when compared with controls (0.72 +/- 0.28 pg/mL), and fell significantly (2.63 +/- 1.40 pg/mL) after weight loss (P < 0.02). The magnitude of insulin release after glucose (75 g) challenge (area under the curve) also fell significantly (P < 0.01) after weight loss. The magnitude of weight loss and fall in TNFalpha were related to basal body weight (r = 0.57, P < 0.001) and basal TNFalpha (r = 0.55, P < 0.001) concentrations, respectively, but not to each other or to the glucose-induced insulin release (area under the curve). We conclude that obesity is associated with increased plasma TNFalpha concentrations, which fall with weight loss. Because circulating TNFalpha may mediate insulin resistance in the obese, a fall in TNFalpha concentrations may contribute to the restoration of insulin resistance after weight loss, Thus, TNFalpha may be an important circulating cytokine, which may provide a potentially reversible mechanism for mediating insulin resistance.