IRS1 gene variants, dysglycaemic metabolic changes and type-2 diabetes risk

BACKGROUND AND AIMS

A recent genome-wide association study identified rs2943641C > T, 500 kb from the insulin receptor substrate-1 gene (IRS1), as a type-2 diabetes (T2D) susceptibility locus. We aimed to replicate this association by meta-analysis and examine whether common variants within IRS1, present on the HumanCVD BeadChip, were associated with T2D risk.

METHODS AND RESULTS

We genotyped rs2943641 in 2389 prevalent or incident T2D patients and 6494 controls from two prospective and three case studies based in UK and in the European Atherosclerosis Research Study-II (EARSII; n = 714). Thirty-three IRS1 variants had been genotyped in the prospective Whitehall-II study (n = 4752) using the HumanCVD BeadChip. In a fixed-effects meta-analysis of the UK study cohorts rs2943641T allele was associated with 6% lower risk of T2D (p = 0.18), with T-allele carriers having an odds ratio (OR) of 0.89 (95% confidence interval [CI]: 0.80-1.00, p = 0.056) compared to CC subjects. The T-allele was also associated with lower fasting insulin and homeostasis model assessment index of insulin resistance in Whitehall-II and with lower post-load insulin after an oral glucose tolerance test in EARSII (all p < 0.05). None of the IRS1 variants on the chip showed linkage disequilibrium with rs2943641. In silico analysis with follow-up genotyping (total n = 9313) identified that the rare allele of the IRS1 promoter variant rs6725556A > G showed association with reduced T2D risk (OR per G-allele: 0.82, 95%CI: 0.69-0.96, p = 0.015).

CONCLUSIONS

We confirm the association of rs2943641T with T2D protection. There is a possible independent effect on risk of a putative IRS1 promoter variant.

Relation between insulin kinetics and insulin sensitivity in pregnancy

BACKGROUND

Different time-concentration profiles of plasma insulin following insulin modification of a frequently sampled intravenous glucose-tolerance-test (FSIVGTT) were observed in a study investigating maternal metabolism and fetal macrosomia. We aimed to investigate whether these differences were related to the volume of distribution of insulin, insulin clearance, or both.

DESIGN

Forty-four women were studied between 33 and 35 weeks' gestation using an insulin-modified FSIVGTT. Specific insulin was assayed with an enzyme-linked immunosorbent assay. Insulin sensitivity was calculated using the minimal model and the homeostasis model assessment (HOMA). The volume of distribution and clearance of insulin were calculated from measurements between 2 and 155 min after insulin modification using a one-compartment model.

RESULTS

In accordance with the method for deriving the volume of distribution, there was a significant negative correlation between the increment in insulin concentration and the volume of distribution (rho=-0.92, P<0.0001). The insulin increment was also related negatively to the clearance of insulin (rho=-0.88, P<0.0001). There was a significant correlation between the volume of distribution and both the insulin sensitivity index (rho=0.56, P<0.0001) and HOMA-%S (rho=0.30, P=0.048), and between the clearance of insulin and both the insulin sensitivity index (rho=0.83, P<0.0001)) and HOMA-%S (rho=0.34, P=0.025).

CONCLUSION

The different time-concentration profiles of plasma insulin resulted from differences in the volume of distribution and clearance of insulin. There was a correlation between insulin kinetics and the insulin sensitivity index. Further research is required to investigate possible mechanisms by which insulin kinetics may be related to insulin sensitivity.

Safety evaluation of modern oral contraceptives. Effects on lipoprotein and carbohydrate metabolism

An ideal oral contraceptive should either be neutral as regards metabolic risk markers for arterial disease or should only change them in directions that would be expected to reduce risk. Depending on their formulation, modern low dose oral contraceptives affect systems such as hemostasis, lipoprotein metabolism, and glucose and insulin metabolism. Some of these actions would be expected to decrease the risk of arterial disease and some might be expected to increase risk. Despite these associations there is at present no justification for widespread metabolic screening as a strategy to further improve oral contraceptive safety. Recent developments in atherosclerosis research support the introduction of progestogens such as desogestrel that allow the estrogenic increase in high density lipoprotein levels to persist and that may cause less of an elevation in plasma insulin responses to glucose. The predicted benefit of these formulations in terms of arterial disease is difficult to demonstrate in an epidemiological setting because of the rarity of the disease in young women.

Evidence for a role of tumor necrosis factor alpha in disturbances of triglyceride and glucose metabolism predisposing to coronary heart disease

Elevated plasma levels of triglyceride-rich lipoproteins, a decreased high-density lipoprotein (HDL) cholesterol concentration, hyperinsulinemia, and impaired fibrinolytic function frequently aggregate in patients with premature coronary heart disease (CHD). Experimental studies suggest that the cytokine tumor necrosis factor alpha (TNFalpha) produced by adipocytes plays a part in the regulation of triglyceride and glucose metabolism. The present study examined whether TNFalpha is implicated in these metabolic and fibrinolytic disturbances in young postinfarction patients. TNFalpha levels were determined in two groups of young (age <45 years) male postinfarction patients (n = 92 and 60) and in matched, population-based control subjects (n = 63). Plasma TNFalpha was higher in patients than in controls (4.1 +/- 1.6 v2.5 +/- 0.4 pg/mL, P < .0001). In hyperlipidemic patients, TNFalpha levels correlated significantly with the concentrations of very-low-density lipoprotein (VLDL) triglyceride and cholesterol and negatively with HDL cholesterol. Treatment with bezafibrate decreased VLDL triglycerides and increased HDL cholesterol, but did not affect TNFalpha levels. The TNFalpha concentration also correlated significantly with fasting glucose and proinsulin concentrations, as well as glucose and proinsulin levels after glucose ingestion. In contrast, no relations were found with the insulin level or degree of insulin resistance. The present results provide clinical evidence for a basic role of TNFalpha in hypertriglyceridemia, glucose intolerance, and the etiology of premature CHD.

Insulin, intact and split proinsulin, and coronary artery disease in young men

BACKGROUND

Glucose intolerance and hyperinsulinemia are common disturbances in nondiabetic men with premature coronary artery disease (CAD). To investigate the relation between insulin-like molecules and severity of coronary atherosclerosis, 62 consecutive nondiabetic men presenting with a first myocardial infarction before the age of 45 were studied along with 41 healthy, age-matched, male, population-based control subjects.

METHODS AND RESULTS

Specific two-site immunoradiometric assays were used to distinguish intact proinsulin, (des 31,32) proinsulin, and "true" insulin in fasting plasma and during an oral glucose tolerance test (OGTT). Global coronary atherosclerosis and number and severity of distinct stenoses were determined in the patients in 15 proximal coronary arterial segments by use of separate semiquantitative classification systems. The patients had a two- to threefold increase in insulin and insulin propeptide concentrations in the fasting state as well as during the OGTT. Severity of coronary atherosclerosis correlated significantly (P < .05 to P < .01) with basal proinsulin (r = .40) and the proinsulin area under the curve (AUC) (r = .34), basal insulin (r = .31), basal C peptide (r = .30), and the glucose AUC (r = .30). In multiple stepwise regression analysis including insulin-like molecules, major plasma lipoproteins, and lipoprotein subfractions, basal proinsulin (increase in R2 = .09) and dense LDL triglycerides (increase in R2 = .10) predicted 19% of the variation of the global coronary atherosclerosis score after adjustment for age, body mass index, fasting insulin concentration, and VLDL triglycerides.

CONCLUSIONS

This study shows that young, nondiabetic, male survivors of myocardial infarction are truly hyperinsulinemic during an OGTT and suggests a close association between proinsulin and coronary atherosclerosis.

Associations between insulin sensitivity, and free fatty acid and triglyceride metabolism independent of uncomplicated obesity

Insulin resistance is associated with hypertriglyceridemia and elevated free fatty acid (FFA) concentrations in obese and diabetic individuals, but it is unclear to what extent this relationship is independent of obesity and is present in healthy individuals. We studied 92 healthy middle-aged males selected from the top, middle, and lowest quintiles of the insulin sensitivity index (Si) determined in a group of 182 men using the minimal model of glucose disappearance. Plasma FFA, triglyceride, glucose, insulin, and C-peptide concentrations were measured during a 3-hour intravenous glucose tolerance test (IVGTT). The low-Si (most insulin-resistant) group had more central body fat distribution (subscapular/triceps skinfold thickness) and a higher median body mass index (BMI) of 26.8 (range, 21.1 to 41.1) kg.m-2 compared with the middle- and high-Si groups with BMIs of 24.9 (19.1 to 31.5) and 23.7 (18.8 to 33.2) kg.m-2 (P < .05). Relatively minor glucose intolerance in the low-Si group was no longer significant when central adiposity was accounted for. Glucose tolerance was maintained by increased insulin secretion, leading to IVGTT insulin responses twofold and fourfold higher in the middle- and low-Si groups, respectively, compared with the high-Si group (P < .01). Fasting FFA and triglyceride concentrations were increased in the low-Si group relative to the other groups independent of BMI or central adiposity (P < .01). During the IVGTT, FFA decreased to similar minimum concentrations in all three groups. Triglyceride concentrations during the IVGTT increased above their minimum levels, particularly in the low-Si group (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Danazol induces resistance to both insulin and glucagon in young women

1. Danazol elevates plasma insulin, plasma glucagon and serum low-density lipoprotein concentrations and reduces the serum high-density lipoprotein concentration. 2. Associations between these disturbances were studied in 17 women receiving danazol therapy for endometriosis. Eleven women underwent intravenous glucose tolerance tests with measurement of plasma glucose, insulin, C-peptide and glucagon concentrations and modelling analysis of intravenous glucose tolerance test concentration profiles. Six women underwent glucagon sensitivity tests. Serum concentrations of lipids and lipoproteins were measured in all cases. 3. Danazol reduced the fasting plasma glucose and insulin concentrations, but markedly raised the fasting plasma glucagon concentration. The insulin and C-peptide responses to the intravenous glucose tolerance test were increased twofold and the net decrement in glucagon concentration was increased tenfold. The glucose response to the intravenous glucose tolerance test was unaffected. Insulin sensitivity was reduced by 55%. Both first-phase plasma insulin responsiveness and net first-phase pancreatic insulin secretion were increased; insulin half-life was prolonged. The glucose response to the glucagon sensitivity test was reduced on treatment. The calculated low-density lipoprotein cholesterol level rose by 20%, whereas high-density lipoprotein cholesterol level fell by 47%. None of these changes in serum lipoprotein levels correlated with changes in insulin metabolism. In general, metabolic changes normalized after 3 months. 4. Danazol increases the sensitivity of pancreatic insulin and glucagon secretion to glucose. Danazol-induced insulin and glucagon resistance could be due to receptor down-regulation resulting from hypersecretion of insulin and glucagon.

The effects of reverse sequential anti-androgen therapy (cyproterone acetate and ethinyl estradiol) on hematological parameters

Hematological parameters were studied in female patients receiving reverse-sequential anti-androgen therapy for hirsutism and acne. A significant fall in hemoglobin, total red cell count and packed cell volume occurred after 3-month treatment in 30 patients during the 10-day cyproterone acetate and ethinyl estradiol phase; this change was sustained in 14 patients studied to 12 months. A fall in hemoglobin and packed cell volume alone occurred after 3 months in 31 patients in the ethinyl estradiol phase. Reverse-sequential therapy may influence hemopoiesis by its anti-androgenic action on erythropoiesis, although we found no relationship between changes in hematological parameters and total testosterone levels.

Effects of oral contraceptives on carbohydrate metabolism

Both estrogens and progestogens modify carbohydrate metabolism, and their ultimate effect depends upon the ratio of one to the other. The effect of progestogens themselves, which are responsible for increased insulin secretion and for insulin resistance, varies according to their androgenicity but increases according to the series pregnane, estrane and gonane. In contrast, estrogens impair the initial secretion of insulin by the pancreas. The prolonged use of combined oral contraceptives containing the powerful progestogen levonorgestrel is associated with mild but continuing glucose intolerance and with marked insulin resistance.

Normal values for peripheral blood white cell counts in women of four different ethnic origins

Total and differential white cell counts were studied in 399 women living in the same community in Britain but drawn from four different ethnic groups. The groups were white (northern European), Indian, black (African and West Indian), and Oriental. The total white cell count and absolute neutrophil count were significantly lower in the black group than in each of the other groups. The absolute monocyte count was higher in whites than in each of the other groups. Contrary to earlier reports, the absolute eosinophil count in blacks was no higher than in whites, suggesting that the high eosinophil counts previously found had an environmental rather than a genetic cause. The eosinophil count of Indians was only marginally higher than that of whites and the difference was not significant, again suggesting that high eosinophil counts previously reported had an environmental cause. No ethnic variation was found in the absolute lymphocyte count. The lower white cell count and neutrophil count found in blacks is of considerable practical importance, and blacks should not be assessed in relation to reference ranges derived for whites. Nevertheless, the eosinophil count in healthy blacks is no higher than that of whites and counts above reference ranges for whites should be considered clinically important. The differences between white cell counts of Indians and Orientals and those of whites are minor and for practical purposes they can be assessed in relation to reference ranges derived for whites.

Comparison of effects of different combined oral-contraceptive formulations on carbohydrate and lipid metabolism

Oral glucose-tolerance tests were performed and fasting serum cholesterol and triglyceride levels measured in 1628 Caucasian women taking combined oestrogen/progestagen oral contraceptives (o.c.) and 577 women not taking O.C. The former were divided into six groups according to the composition of the O.C Glucose tolerance deteriorated in all O.C. groups containing oestrane progestagens (nortestosterone-derived) or the gonane, norgestrel, but was unaltered by O.C. containing a pregnane progestagen (derived from progesterone). The greatest deterioration was with O.C. containing 75 microgram or more oestrogen, and this was associated with impairment of the early insulin response to glucose. In O.C. containing a pregnane progestagen insulin secretion was unaffected. In the remaining O.C. groups insulin secretion was increased; this was most pronounced with the O.C. containing a gonane progestagen. Serum-cholesterol was elevated only with O.C. containing 75 microgram or more oestrogen and an oestrane progestagen and tended to be lower in O.C. containing a gonane progestagen. O.C.-induced hypertriglyceridaemia was oestrogen-dose-related, and this effect was potentiated by the pregnane progestagen. The gonane progestagen antagonised oestrogen-induced hypertriglyceridaemia.