Atherosclerotic disease is much less common in Chinese subjects compared with Caucasian subjects. We have previously demonstrated that traditional atherosclerosis risk factors, such as aging and smoking, have less adverse effects on arterial endothelial function and structure in Chinese subjects(1,2). Because diabetes is an important risk factor for the development of coronary heart disease, and because it is associated with endothelial dysfunction in Caucasian subjects, we studied the arterial function of Chinese adults with type 1 diabetes.
We studied arterial endothelial function in 36 asymptomatic Chinese adults(age 29 ± 6 years). Of these subjects, 18 had type 1 diabetes and 18 were age- and sex-matched normoglycemic control subjects. No subjects in either group had clinical evidence of atherosclerosis, and none were taking any lipid-lowering drugs or cardiovascular medications. Arterial endothelial function was measured by the same operator, using a high-resolution B-mode ultrasound scan with regard to flow-mediated (endothelium-dependent) dilation(FMD) and glyceryl trinitrate (GTN)-induced (endothelium-independent) dilation of the brachial artery (% change of vessel diameter)(1,2).
The diabetic subjects (11 men and 7 women) were aged 29 ± 7 years;mean duration of diabetes was 7.4 ± 5.0 years (range 1.0-19.0) with a mean HbAlc of 7.9 ± 1.8% (normal <6.5%). There were no significant differences between the two groups in anthropometric parameters,blood pressure, or lipid profile. The baseline flow and vessel size were similar between both groups. The diabetic group had lower FMD (6.8 ±2.2 vs. 9.1 ± 2.0%, P = 0.003) and a lower GTN-induced dilation (13.9 ± 3.4 vs. 18.3 ± 4.0%, P = 0.001) when compared with the control subjects. In a multiple regression analysis of the two groups, diabetes was the only significant predictor for impaired FMD(model F = 3.4, R2 = 0.69, P = 0.005), whereas vessel size (β = -0.52, P = 0.005), age (β = -0.27, P = 0.04), and diabetes (β = -0.66, P < 0.001) were significant predictors of GTN responses (F = 11.6, R2 = 0.49, P = 0.001).
The prevalence of cardiovascular mortality in Chinese men and women is∼16-fold and ∼6-fold less, respectively, compared with that in age-matched Caucasian adults. The underlying mechanism for this apparent protection in the Chinese remains unclear. This may be related to genetic and/or environmental differences. The major findings in this study were that of impaired endothelium and smooth muscle-dependent arterial dilation in asymptomatic young Chinese subjects with type 1 diabetes, similar to the findings reported in the Caucasian subjects(3). In comparison with our previous observations regarding the less deleterious effects of aging and smoking on Chinese versus Caucasian arteries(1,2),diabetes may be a more potent risk factor for vascular dysfunction in Chinese subjects.
The mechanism of diabetes-related endothelial and smooth muscle dysfunction remains unclear. It may be related to decreased baseline nitric oxide production and/or increased vascular superoxide generation. Accumulation of advanced glycosylation products in the subendothelial space and/or impaired smooth muscle responsiveness may also be contributory.
All of the subjects were free of atherosclerosis risk factors apart from diabetes, thus allowing a relatively independent assessment of diabetes-related pathophysiology in the present study. Because arterial endothelial dysfunction is an early key event in atherogenesis, the increasing prevalence of diabetes in developing countries, including China, may be associated with increased morbidity and mortality from atherosclerotic vascular events. Therefore, diabetes may be a particularly important risk factor for Chinese people.