Stiffness indexes beta of the common carotid and femoral arteries are associated with insulin resistance in NIDDM

Macrovascular disease risk factors and insulin resistance in Aboriginal and Torres Strait Islander people

It has been proposed that insulin resistance (IR) underlies a cluster of cardiovascular disease (CVD) risk factors constituting a "metabolic syndrome." CVD is a leading cause of premature mortality among indigenous Australians. In a group of younger (15-44 years, fasting glucose <7.8 mmol/l) Aboriginal (n=643) and Torres Strait Islander (n=220) people participating in community-based risk factor surveys, we identified high prevalences of metabolic syndrome components: glucose intolerance, dyslipidaemia, hypertension, and IR. There were inconsistent associations of IR with other risk factors, and the data do not support a direct causal relationship between insulin and other metabolic variables. Rather, metabolic syndrome components may arise from social and environmental factors interacting with behavioural and biochemical factors in individuals.

Increased arterial wall stiffness limits flow volume in the lower extremities in type 2 diabetic patients

OBJECTIVE

To document an association between arterial wall stiffness and reduced flow volume in the lower-extremity arteries of diabetic patients.

RESEARCH DESIGN AND METHODS

We recruited 60 consecutive type 2 diabetic patients who had no history or symptoms of peripheral arterial disease (PAD) in the lower extremities and normal ankle/brachial systolic blood pressure index at the time of the study (non-PAD group) and 20 age-matched nondiabetic subjects (control group). We used an automatic device to measure pulse wave velocity (PWV) in the lower extremities as an index of arterial wall stiffness. At the popliteal artery, we evaluated flow volume and the resistive index as an index of arterial resistance to blood flow using gated two-dimensional cine-mode phase-contrast magnetic resonance imaging.

RESULTS

Consistent with previous reports, we confirmed that the non-PAD group had an abnormally higher PWV compared with that of the control group (P < 0.001). To further demonstrate decreased flow volume and abnormal flow pattern at the popliteal artery in patients with a higher degree of arterial wall stiffness, we assigned the 60 non-PAD patients to tertiles based on their levels of PWV. In the highest group, magnetic resonance angiograms of the calf and foot arteries showed decreased intravascular signal intensity, indicating the decreased arterial inflow in those arteries. The highest group was also characterized by the lowest late diastolic and total flow volumes as well as the highest resistive index among the groups. From stepwise multiple regression analysis, PWV and autonomic function were identified as independent determinants for late diastolic flow volume (r(2) = 0.300; P < 0.001).

CONCLUSIONS

Arterial wall stiffness was associated with reduced arterial flow volume in the lower extremities of diabetic patients.

Diabetes mellitus, aortic stiffness, and cardiovascular mortality in end-stage renal disease

Cardiovascular mortality is elevated in patients with end-stage renal disease (ESRD), especially in those with diabetes mellitus. Although the higher cardiovascular death rate in diabetic ESRD patients may be the result of more advanced atherosclerotic changes of the arterial wall, this has not been documented previously. Aortic stiffness was compared between ESRD patients with and without diabetes, and the impact of aortic stiffness on cardiovascular mortality was examined in a prospective, observational cohort study. The cohort consisted of 265 ESRD patients on hemodialysis, including 50 diabetic patients studied between June 1992 and December 1998. At baseline, the diabetic ESRD patients had significantly higher aortic pulse wave velocity (PWV), a noninvasive measure of aortic stiffness, than the nondiabetic patients. During a mean follow-up period of 63 mo, 81 deaths, including 36 cardiovascular deaths, were recorded. Kaplan-Meier analysis revealed higher all-cause or cardiovascular mortality rates in the diabetic as compared with the nondiabetic patients and also in those with higher aortic PWV than those with lower aortic PWV. The effect of diabetes on cardiovascular death was significant in the Cox model, including age, years on hemodialysis, gender, smoking, C-reactive protein, hematocrit, and body mass index as covariates. However, when aortic PWV was included as a covariate, the impact of diabetes was no longer significant, whereas aortic PWV was a significant predictor. In a model including 13 covariates, aortic PWV remained a significant predictor for cardiovascular and overall mortality but not for non-cardiovascular death. These results demonstrate that the increased aortic stiffness of the ESRD patients with diabetes mellitus contributed to the higher all-cause and cardiovascular mortality rates.

The insertion/deletion polymorphism of the ACE gene is related to insulin sensitivity in overweight women

OBJECTIVE

The ACE insertion/deletion (I/D) polymorphism has been identified as a genetic risk factor for coronary heart disease (CHD). The deletion (D) allele of the ACE gene may be associated with higher insulin sensitivity. Individuals who are homozygous for the DD allele have higher ACE levels and possibly more angiotensin II, which, when infused exogenously, causes an increase in insulin sensitivity. The purpose of this study was to investigate the association of the I/D polymorphism of the ACE gene with insulin sensitivity and CHD risk factors.

RESEARCH DESIGN AND METHODS

The study included 66 women (ages 57 +/- 1 years) who were overweight or obese (means +/- SEM, BMI = 33 +/- 1 kg/m(2)) and sedentary (VO(2max) = 19.6 +/- 0.4 ml. kg(-1). min(1)). Total body fat mass and percent fat were determined by dual-energy X-ray absorptiometry, and abdominal fat was by computed tomography. Insulin sensitivity was measured during the last 30 min of 3-h hyperinsulinemic-euglycemic clamps (40 mU. m(-2). min(-1)). Comparisons were made among women with the II (n = 9), ID (n = 36), and DD (n = 21) genotypes.

RESULTS

Age, percent body fat, waist-to-hip ratio, visceral and subcutaneous abdominal fat areas, plasma lipid levels, and systolic and diastolic blood pressures did not differ by ACE genotype. Fasting glucose and 2-h glucose levels were similar among genotypes, but fasting plasma insulin levels were lower in DD women than in ID women (P < 0.05). Glucose utilization was higher in women with the DD genotype than in women with the II genotype (53.1 +/- 3.9 vs. 36.0 +/- 3.8 micromol. kg(-1) FFM. min(-1), P = 0.01) and was higher in ID women than in II women (48.5 +/- 2.5 micromol. kg(-1) FFM. min(-1), P = 0.04).

CONCLUSIONS

These data suggest that the I/D polymorphism is not associated with risk factors for CHD in overweight sedentary women; however, women who are homozygous for the D allele of the ACE gene are more insulin sensitive, whereas women who are homozygous for the I allele of the ACE gene have greater insulin resistance and potential risk for type 2 diabetes.

Femoral artery wall thickness and stiffness in evaluation of peripheral vascular disease in type 2 diabetes mellitus

Stiffening and thickening of arterial wall are two important components of atherosclerosis. The purpose of this study was to evaluate the effects of femoral artery wall stiffness on clinical manifestation of peripheral vascular disease (PVD) in type 2 diabetes mellitus. The subjects were 315 patients with type 2 diabetes. Presence of intermittent claudication and/or leg pain at rest and reduced ankle-brachial blood pressure index (ABI<0.9) were used as a subjective and an objective index of PVD, respectively. Femoral artery intima-media thickness (FA-IMT) and stiffness parameter beta (FA-stiffness beta) were measured by ultrasound methods. Symptomatic patients (N=58) showed greater values for both FA-IMT and FA-stiffness beta than those without symptom (N=257). Similarly, patients with reduced ABI (N=56) had greater FA-IMT and FA-stiffness beta than those without (N=259). However, correlation between FA-IMT and FA-stiffness beta was not impressive, especially in the symptomatic patients. To evaluate the effect of FA-stiffness beta on PVD symptoms, the subjects were divided into three subgroups according to FA-IMT, and then FA-stiffness beta was compared between those with and without PVD symptoms in each subgroup. The symptomatic patients had greater FA-stiffness beta values than the asymptomatic subjects in all the three subgroups. Multiple logistic regression analysis indicated that the presence of PVD symptoms was associated more closely with increased FA-stiffness beta than with increased FA-IMT, whereas reduced ABI was associated more closely with FA-IMT than with FA-stiffness beta. These data suggest that stiffening of arterial wall has a significant impact on PVD manifestations, particularly on the leg symptoms, in patients with type 2 diabetes.

Late systolic wave on brachial artery blood flow velocity pattern in patients with coronary artery disease and its relation to vascular stiffness

Duplex-Doppler study typically exhibits triphasic brachial artery blood flow velocity pattern in subjects classified as normal without clinically evident atherosclerotic complications, heart disease, hypertension, or diabetes mellitus. In this study, the authors described the late systolic wave on the brachial artery blood flow velocity pattern in patients with coronary artery disease and investigated the relation between late systolic wave and vascular stiffness. Blood flow profile and velocity of the brachial artery were determined noninvasively by ultrasound pulsed-Doppler technique under the guidance of a B-mode ultrasound image in 96 patients with coronary artery disease (CAD). The control group consisted of 23 healthy subjects with no or maximally 2 risk factors (only among age, cigarette smoking, obesity, and gender) for vascular disease. None of the patients and controls had clinical evidence of arterial disorders at upper extremities. In 32 patients (33%) with CAD, a late systolic wave was observed in the brachial artery Doppler study. On the other hand, no late systolic wave was observed in the healthy subjects. In addition, multivessel disease, hypertension, advanced age, diabetes, and smoking were significantly more frequent in patients with the late systolic wave. In conclusion, peripheral arterial abnormalities induced by vascular stiffness may produce alterations in regional wave reflections, and the normal triphasic pattern of the brachial artery blood flow may change by the appearance of the late systolic wave.

Impact of insulin resistance and nephropathy on homocysteine in type 2 diabetes

OBJECTIVE

To assess the impacts of insulin resistance and renal function on plasma total homocysteine (tHcy) levels in patients with type 2 diabetes with a wide range of nephropathy.

RESEARCH DESIGN AND METHODS

Plasma tHcy levels were measured using the enzyme immunoassay method in 75 patients with type 2 diabetes and compared with those in 54 healthy control subjects. Insulin sensitivity indexes were assessed in patients with type 2 diabetes by hyperinsulinemic-euglycemic clamp using artificial pancreas.

RESULTS

Plasma tHcy levels and their log-translormed values (log tHcy) were significantly higher in all patients with diabetes than in control subjects (tHcy, 12.0 +/- 0.7 [SE] vs. 8.7 +/- 0.3 micromol/l, P < 0.0001; log tHcy, 1.040 +/- 0.021 vs. 0.920 +/- 0.016 micromol/l, P < 0.0001). Plasma tHcy levels in patients with diabetes were significantly increased according to degree of nephropathy (P < 0.0001). On simple regression analyses, log tHcy correlated with insulin sensitivity indexes (r = -0.319, P = 0.005) as well as creatinine clearance (r = 0.634, P < 0.0001) in all patients with diabetes. Multiple regression analyses showed that insulin sensitivity indexes (beta = -0.245) as well as creatinine clearance were independent contributors to log tHcy in all patients with diabetes (R2 = 0.750, P < 0.0001). For the 59 patients with diabetes with creatinine clearance >60 ml/min, insulin sensitivity indexes were also shown to be a significant contributor to log tHcy (beta = -0.438, R2 = 0.561, P < 0.001).

CONCLUSION

Insulin resistance and renal function are independent determinants of tHcy levels in patients with type 2 diabetes.

Peripheral vascular disease and type 2 diabetes mellitus

Patients with Type 2 diabetes mellitus frequently have peripheral vascular disease, with a predilection for the lower legs. In this review potential mechanisms for this high prevalence and altered distribution are explored. It is hypothesised that the metabolic abnormalities in the prediabetic phase predispose to a more distal and aggressive atherosclerosis. Once diabetes has developed this process is accelerated due to chronic hyperglycaemia. Furthermore, endothelial damage, non-enzymatic glycosylation and polyneuropathy could lead to impaired vascular remodelling and collateral formation.

Insulin and the vasculature

Under physiologic conditions, insulin plays a vasculoprotective role by acting as a vasodilator through the stimulation of nitric oxide synthesis and release from the endothelium. In addition, insulin may decrease the contractile response of vascular smooth muscle cells (VSMC) to vasoactive agents by decreasing the intracellular calcium concentration i. However, in the insulin resistance syndrome, the vasodilator effect of insulin may be blunted, an abnormality that may be related to endothelial dysfunction. Insulin resistance correlates with carotid wall thickness and stiffness, but the relationship is modified by sex and ethnic factors. Insulin can act as growth factor stimulating VSMC growth in culture. Insulin-sensitizing agents are efficacious in improving the vascular pathology associated with insulin resistance.

Change in common carotid artery diameter, distensibility and compliance in subjects with a recent history of impaired glucose tolerance: a 3-year follow-up study

OBJECTIVE

To assess the development of common carotid artery properties (diameter, distensibility and compliance) in a cohort of 140 subjects (mean age 65.8 years, SD 7.5 years) originally diagnosed as impaired glucose tolerant in a population-based study, and to explore determinants of changes observed.

DESIGN

An observational, longitudinal study over a 3-year-period.

METHODS

Vessel wall movement detector system based on ultrasonography, linear generalized estimating equations.

RESULTS

Carotid artery diameter rose from 6.87-7.02 mm (+ 2.2%, P<0.001). Distensibility decreased from 11.8 to 10.9 x 10-3 kPa-1 (-8.3%, P=0.009). Compliance decreased from 0.44-043 mm2 kPa-1 (P=0.17). Changes in blood pressure level were negatively associated with changes in distensibility and compliance. Baseline fasting glucose levels were positively associated with changes in diameter, while fasting insulin levels were negatively associated with changes in distensibility and compliance in men, but not in women.

CONCLUSIONS

In subjects with a recent history of impaired glucose tolerance, we observed an increase in carotid artery diameter and a decrease in distensibility. Change in blood pressure level and baseline fasting glucose and HbA1c levels were positively related to the increase in diameter. In men, but not in women, baseline fasting insulin levels were associated with an acceleration of these changes.