Is common genetic variation at IRS1, ENPP1 and TRIB3 loci associated with cardiometabolic phenotypes in type 2 diabetes? An exploratory analysis of the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 5

BACKGROUND AND AIMS

Insulin resistance is a hallmark of type 2 diabetes (T2DM), it is often accompanied by defective beta-cell function (BF) and is involved in the pathophysiology of cardiovascular disease (CVD). Commonalities among these traits may recognize a genetic background, possibly involving the genetic variation of insulin signaling pathway genes. We conducted an exploratory analysis by testing whether common genetic variability at IRS1, ENPP1 and TRIB3 loci is associated with cardiovascular risk traits and metabolic phenotypes in T2DM.

METHODS AND RESULTS

In 597 drug-naïve, GADA-negative, newly-diagnosed T2DM patients we performed: 1) genotyping of 10 independent single-nucleotide polymorphisms covering ∼ 90% of common variability at IRS1, ENPP1 and TRIB3 loci; 2) carotid artery ultrasound; 3) standard ECG (n = 450); 4) euglycaemic insulin clamp to assess insulin sensitivity; 5) 75 g-OGTT to estimate BF (derivative and proportional control) by mathematical modeling. False discovery rate of multiple comparisons was set at 0.20. After adjustment for age, sex and smoking status, rs4675095-T (IRS1) and rs4897549-A (ENPP1) were significantly associated with carotid atherosclerosis severity, whilst rs7265169-A (TRIB3) was associated with ECG abnormalities. Rs858340-G (ENPP1) was significantly associated with decreased insulin sensitivity, independently of age, sex and body-mass-index. No consistent relationships were found with BF.

CONCLUSION

Some associations were found between intermediate phenotypes of CVD and common genetic variation of gatekeepers along the insulin signaling pathway. These results need be replicated to support the concept that in T2DM the CVD genetic risk clock may start ticking long before hyperglycemia appears. ClinicalTrials.gov Identifier: NCT01526720.

Relationship between fasting insulin and cardiovascular risk factors is already present in young men: the Verona Young Men Atherosclerosis Risk Factors Study

The associations between fasting plasma insulin concentration and risk factors for cardiovascular disease were examined in 979 18-year-old men participating in the Verona Young Men Atherosclerosis Risk Factors Study, a cross-sectional population-based study. Body mass index (BMI), waist-to-hip ratio (WHR), plasma triglycerides and uric acid concentrations, and blood pressure values significantly increased, and the high-density lipoprotein (HDL)-total cholesterol ratio decreased, across quartiles of fasting insulin. Total and low-density lipoprotein cholesterol, concentrations did not change significantly with the increase in fasting insulin levels. After adjustment for BMI, WHR, smoking, alcohol intake and physical activity, only plasma triglycerides significantly increased across insulin quartiles (F = 7.1; P < 0.001). However, systolic blood pressure and uric acid were close to statistical significance (P = 0.06-0.07). Multiple linear regression analysis confirmed that plasma insulin was independently correlated with plasma triglycerides and, to a lesser extent, with blood pressure and uric acid concentration. This analysis pointed out that BMI was a stronger independent predictor of all cardiovascular disease risk factors than fasting insulin. When subjects were categorized according to the number of metabolic and haemodynamic disorders occurring within the same individual, subjects with multiple disorders (i.e, three or four) had higher plasma insulin levels than those with none or few disorders, even after adjusting for BMI, WHR and behavioural variables (F = 4.0; P < 0.01). These results indicate that hyperinsulinaemia is already associated with a cluster of cardiovascular disease risk factors in young adulthood, the strongest independent association being with plasma triglycerides.

Relationship of uric acid concentration to cardiovascular risk factors in young men. Role of obesity and central fat distribution. The Verona Young Men Atherosclerosis Risk Factors Study

OBJECTIVE

To examine the relationships of serum uric acid concentration with several risk factors of cardiovascular diseases (CVD).

SUBJECTS

957 men 18 y old participating in the Verona Young Men Atherosclerosis Risk Factors Study, a cross-sectional population-based study.

MEASUREMENTS

Body mass index (BMI), waist/hip ratio (WHR), serum uric acid, serum lipids, blood pressure, fasting insulin and behavioural variables.

RESULTS

Serum uric acid concentration showed positive associations with BMI (r = 0.24; P < 0.0001), WHR (r = 0.19; P < 0.0001) and serum triglyceride levels (r = 0.19; P < 0.0001); it was also significantly correlated to systolic (r = 0.08; P < 0.01) and diastolic (r = 0.11; P < 0.001) blood pressure, fasting insulin (r = 0.11; P < 0.001), total (r = 0.12; P < 0.001) and LDL cholesterol (r = 0.10; P < 0.01) plasma concentrations. Life-style characteristics, such as smoking and physical activity did not show any significant association, while daily alcohol intake was positively associated with uric acid concentration (r = 0.09; P < 0.01). While the adjustment for fasting insulin did not substantially change these results, the magnitude of the correlations between uric acid and CVD risk factors markedly decreased when allowance was made for BMI and WHR. Only triglycerides maintained an independent correlation with uric acid levels (r = 0.17; P < 0.0001). In multivariate regression analysis, serum triglycerides, BMI and WHR (at borderline significance) were independent positive predictors of uric acid (R2 of the model 0.122, P < 0.001), while fasting insulin concentration did not give any independent contribution to explain the variability uric acid levels.

CONCLUSIONS

These data indicate that, already in young, essentially health subjects, hyperuricaemia associates with several components of the so-called insulin resistance syndrome, thus suggesting that increased levels of uric acid might be another member of this syndrome. In addition, these data suggest that obesity and central body fat distribution, rather than hyperinsulinaemia/insulin resistance, play a major role in linking hyperuricaemia with CVD risk factors clustering in the insulin resistance syndrome. Nevertheless, hypertrigliceridemia is related to hyperuricemia independently of obesity and central body fat distribution.

Cardiovascular risk profile in 38-year and 18-year-old men. Contribution of body fat content and regional fat distribution

OBJECTIVE

To evaluate whether young and middle-age men differ in blood pressure and serum lipid profiles and, if so, to what extent these differences are dependent on total body fat, regional fat distribution, plasma insulin and behavioural variables.

SUBJECTS

Random samples of 94 young (18 year-old) and 94 middle-age (38 year-old) healthy men matched for body mass index (BMI).

MEASUREMENTS

BMI, total body fat (by bioelectrical impedance), regional fat distribution (by anthropometry), serum lipids, blood pressure, fasting insulin and some behavioural variables.

RESULTS

Total body fat was similar in the two groups (mean +/- s.e.: 16.6 +/- 0.5 vs 16.0 +/- 0.6 kg and 20.8 +/- 0.5 vs 20 +/- 0.5%), while waist/hip circumference ratio (WHR) was significantly higher in middle-age as compared to young men (0.96 +/- 0.001 vs 0.92 +/- 0.003, P < 0.0001). The former also had significantly higher serum concentrations of total cholesterol (6.21 +/- 0.13 vs 4.10 +/- 0.10 mmol/l; P < 0.0001). LDL-cholesterol (4.24 +/- 0.11 vs 2.34 +/- 0.10 mmol/l; P < 0.0001), triglycerides 1.40 +/- 0.09 vs 1.02 +/- 0.06 mmol/l; P < 0.01) as well as higher systolic (134.0 +/- 1.6 vs 126.3 +/- 1.4 mmHg; P < 0.0001) and diastolic (86.8 +/- 0.9 vs 82.0 +/- 1.1 mmHg; P < 0.001) blood pressure values. HDL-cholesterol and fasting insulin concentrations were similar in the two groups (1.33 +/- 0.03 vs 1.28 +/- 0.03 mmol/l and 13.7 +/- 0.6 vs 14.7 +/- 0.7 mU/l, respectively). Significant differences in the two groups also were found in daily alcohol consumption (49.6 +/- 5.7 vs 20.0 +/- 3.4 g/day; P < 0.0001), whereas no significant differences were found in smoking and physical activity level. The comparison of subgroups (n = 41) of young and middle-age men matched for both BMI and WHR showed virtually unchanged differences in serum lipids and blood pressure. When age, BMI, WHR, fasting insulin and behavioural variables were included as independent variables in a multiple linear regression analysis in which subjects of the two groups were pooled, age was a significant predictor of total and LDL cholesterol, triglycerides and systolic blood pressure, insulin predicted HDL cholesterol and systolic blood pressure, BMI predicted triglycerides and diastolic blood pressure and WHR was not an independent predictor of any risk factor.

CONCLUSIONS

These results indicate that middle-age men have a cardiovascular risk profile less favourable than young men, which is largely independent of differences in total body fat content, regional fat distribution and behavioural variables.

Non-invasive detection of early endothelial dysfunction in hypercholesterolaemic subjects

Hypercholesterolaemia is associated with accelerated atherogenesis. Before the evidence of morphological lesions or plaques, endothelial dysfunctions, such as impairment in endothelium-dependent vascular tone regulation, may occur. We studied 32 subjects, 16 with primary hypercholesterolaemia and 16 normocholesterolaemic controls. Flow-dependent vasodilation, an endothelium-dependent phenomenon, was evaluated by measuring femoral artery diameter and flow velocity in basal conditions and during distal post-ischemic hyperaemia, using a high resolution echo-Doppler. Arterial distensibility and compliance were evaluated for the common carotid and femoral arteries, using a pulsed echo-tracking system and measuring the absolute and relative stroke change in arterial diameter. In the hypercholesterolaemic group there was no flow-dependent arterial relaxation, indicated by the area under the curve of percentage diameter variation as a function of time. This parameter was inversely correlated with both total and LDL-cholesterol values in all population subjects. No difference was observed between the two groups in endothelium-independent vasodilation induced by glyceryl trinitrate administration or arterial wall distensibility and compliance, confirming the hypothesis of a functional defect.

Serum retinol levels throughout 2 years of cholesterol-lowering therapy

Some studies have reported an inverse correlation between serum cholesterol level and risk of cancer. This correlation might be due to a decrease in serum retinol, a lipid-soluble vitamin that controls cell proliferation and differentiation. We evaluated the influence of cholesterol-lowering therapy on serum retinol in 102 subjects (mean +/- SE: aged 47.1 +/- 4.1 years; body mass index, 23.8 +/- 0.6 kg/m2) with primary hypercholesterolemia treated for 2 years with different therapeutic protocols. Twenty-two subjects had been treated with diet alone, 35 with diet and fibrates, 37 with diet and hepatic hydroxymethyl glutaryl coenzyme A (HMG CoA) reductase inhibitors (statins), and eight with diet and cholestyramine. Postabsorptive serum retinol, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglyceride levels were determined at baseline and every 3 months. Baseline TC and LDL-C were significantly lower in the diet-treated group than in other groups. No intergroup differences were found in pretreatment levels of triglycerides and serum retinol. After 2 years of treatment, TC and LDL-C serum levels were not significantly decreased in the diet-alone group, whereas they were decreased by 20% and 24%, respectively, in the gemfibrozil group, 28% and 34% in the statins group; and 21% and 27% in the cholestyramine group. In the entire population (N = 102), serum retinol was 3.46 +/- 0.08 mumol/L before therapy and 3.76 +/- 0.07 after 2 years of therapy (P < .001). Serum retinol increased in diet- and statin-treated groups, but not in fibrate- and resin-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Sustained therapy with 3-hydroxy-3-methylglutaryl-coenzyme-A reductase inhibitors does not impair steroidogenesis by adrenals and gonads

Plasma lipoproteins are a major source of cholesterol for steroid hormone synthesis. 3-Hydroxy-3-methylglutaryl-coenzyme-A (HMG-CoA) reductase inhibitors, which reduce both intracellular cholesterol synthesis and serum cholesterol levels, thus have a potential negative impact on steroidogenesis. In this study, we evaluated basal and maximally stimulated adrenocortical and testicular steroidogenesis in 24 hypercholesterolemic male subjects during 6-36 months of statin treatment. One group was evaluated before treatment and after 6 months of treatment. A second group, which received long term treatment, was evaluated after 24-36 months and then 2 months after treatment had been discontinued. Fourteen subjects were given simvastatin, and 12 were given pravastatin, both at the maximum therapeutic dosage of 40 mg/day. During statin therapy, serum cholesterol was lowered by about 30%. Basal serum and urinary cortisol levels as well as serum cortisol response to ACTH were not influenced by statin therapy. Basal serum testosterone and its response to hCG were also unchanged by statin treatment. In addition, steroid hormone urinary metabolites were strikingly similar when patients were given HMG-CoA reductase inhibitors and when they were not. These results indicate that maximum therapeutic doses of statins have no negative impact on adrenocortical and testicular steroidogenesis even when these glands are maximally stimulated.

Mononuclear leukocytes from obese patients with type II diabetes have reduced activity of hexokinase, 6-phosphofructokinase and glucose-6-phosphate dehydrogenase

In the present study we measured the activity of some cytosolic enzymes involved in intracellular glucose metabolism in mononuclear leukocytes from 77 obese subjects of which 39 were nondiabetic and 38 had newly-diagnosed untreated type II diabetes mellitus. 28 subjects (19 nondiabetic and 18 diabetic) had also a study of insulin binding to monocytes. 35 subjects (14 nondiabetic, 21 diabetic) underwent an insulin tolerance test for the evaluation of in vivo insulin action. Mononuclear leukocytes from diabetic obese patients showed significantly lower activities of hexokinase (HK), 6-phosphofructokinase (PFK) and glucose-6-phosphate dehydrogenase (G6PDH), while pyruvate kinase (PK) and 6-phosphogluconate dehydrogenase (6PGDH) activities were similar in the two groups. In the whole population HK and G6PDH activities inversely correlated with fasting and 2-h OGTT plasma glucose levels. Neither plasma insulin levels nor maximal specific insulin binding to monocytes were significantly correlated with any of the enzyme activities measured. Conversely, the parameter of insulin action generated by insulin tolerance test significantly correlated with HK, G6PDH and 6PGDH. These results indicate that in obese subjects the presence of diabetes is associated with a reduced activity of some enzymes of glucose metabolism in mononuclear leukocytes. This multiple enzymatic defect is correlated with the impairment of in vivo insulin action.

Influence of body fat and its regional localization on risk factors for atherosclerosis in young men

A study was carried out in 1988 in Verona, Italy, to examine the relation of body fat and its localization to several risk factors for atherosclerosis in young men. Total body fat (bioelectrical impedance), waist and hip circumferences, and waist/hip circumference ratio were measured in 1,293 18-year-old men. Fasting serum levels of total cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, triglycerides, and insulin, as well as systolic and diastolic blood pressure, were also measured. Significant differences were found in all metabolic and hemodynamic variables among quartiles of total body fat. Most of these differences remained significant after the authors controlled for the independent effect of fat localization and behavioral factors such as smoking, alcohol intake, and physical activity. Triglycerides, insulin, and blood pressure were significantly different among quartiles of waist/hip ratio, but these differences disappeared after the authors controlled for the independent effect of total body fat. These results indicate that in young men, irrespective of its regional localization, an excess of body fat is associated with a poor profile of risk for atherosclerosis. On the other hand, the prevalent localization of fat in the central part of the body is not independently associated with any risk factor.

Studies on the mechanism of action of sulphonylureas in type II diabetic subjects: gliquidone

The mechanism of action of sulphonylureas is not completely understood. In the present study we evaluated the effects of gliquidone, a second-generation compound, on several metabolic parameters in 22 patients with untreated newly-diagnosed type II (noninsulin-dependent) diabetes mellitus. After either 1 or 6 months of treatment with gliquidone plus isocaloric diet we observed: 1) a significant decrease in fasting plasma glucose and glycemic profile after oral glucose load; 2) unchanged fasting and postglucose plasma insulin levels; 3) no change in fasting C-peptide levels but a significant increase in C-peptide concentrations after glucose challenge; 4) a significant increase in glucose disappearance rate from plasma following iv insulin injection; 5) an increase in the insulin-induced reduction of plasma levels of free-fatty acids; 6) no change in plasma C-peptide levels following iv insulin injection; 7) a significant increase in specific insulin binding to monocytes. After 6 but not 1 month of gliquidone therapy we also found an increase in the activity of hexokinase in circulating mononuclear leukocytes. These results suggest that the hypoglycemic effect of gliquidone occurs through either an increased beta cell response to glucose stimulus or an enhanced insulin sensitivity. The latter effect seems to depend on both receptor and postreceptor mechanisms.

B cell secretion and insulin sensitivity in hypertensive and normotensive obese subjects

To test the hypothesis that in obesity hypertension is associated with more pronounced hyperinsulinaemia and insulin resistance we compared plasma insulin levels and insulin sensitivity in a group of 6 obese subjects with untreated hypertension and in a group of 6 obese subjects with normal blood pressure. The two groups were similar for sex, age, body mass index and glucose tolerance. Six nonobese subjects served as controls. The study consisted of a 2-h hyperglycaemic clamp (steady-state plasma glucose = 11 mmol/l) and a 15-min insulin tolerance test (0.1 U/kg body wt). During hyperglycaemic clamp, insulin and C-peptide plasma levels were similar in normotensive and hypertensive obese subjects: the area under the plasma insulin curve was 36,000 +/- 3000 pmol/l X 120 min in the former and 34,000 +/- 1000 pmol/l X 120 min in the latter; the area under the plasma C-peptide curve was 298,000 +/- 26,000 pmol/l X 120 min in the former and 246,000 +/- 26,000 pmol/l X 120 min in the latter (P = n.s.). The ratio M/I between the amount of glucose metabolized (M) and the mean plasma insulin levels (I) during hyperglycaemic clamp was similar in the two groups: 0.59 +/- 0.09 in normotensive and 0.58 +/- 0.08 mg/min X m2 per pmol/l in hypertensive obese subjects (P = n.s.). Also the rate coefficient of glucose disappearance from plasma (K(itt)) after i.v. insulin injection was similar in the two groups (4.08 +/- 0.51 vs. 3.87 +/- 0.53 per cent/min).(ABSTRACT TRUNCATED AT 250 WORDS)