Discussions of their role in the pathogenesis of atherosclerosis usually emphasize high triglycerides and cholesterol and low HDL-cholesterol levels. These abnormalities are frequently observed in diabetes, and their impact on risk of coronary artery disease is at least as high as in the nondiabetic population [274–278]. The significance of postprandial hypertriglyceridemia in diabetes may have been underestimated in the past [279–281]. Insulin substitution favors an antiatherogenic lipoprotein pattern [282]. In well-controlled type 1 diabetes, lipids tend to be fairly normal. By contrast, dyslipidemia is usually observed as a part of the metabolic syndrome in obese subjects with impaired glucose tolerance and type 2 diabetes [276]. It also develops in poorly controlled type 1 diabetes and in subjects with nephropathy [283,284] (Table 1.14). Lipid abnormalities seem to be more pronounced in women than in men [285,286].
In the presence of insulin and under the influence of high serum glucose, free fatty acids, and amino acids, VLDL synthesis is increased in the liver. Peripheral triglyceride uptake is delayed because of low lipoprotein lipase activity, resulting in hypertriglyceridemia. Hypertriglyceridemia correlates with PAI-1 activity and is associated with low HDL-cholesterol and alterations in the metabolism of other lipoproteins.
In addition to these quantitative alterations, the generation of abnormal lipoproteins seems to be very important [287,288]. The dyslipoproteinemia of diabetes is characterized by the formation of triglyceriderich particles (VLDLI) and abnormal LDL [274,289,290], Small, dense LDL (LDL III) are susceptible to lipid oxidation and strongly related to cardiovascular risk [291–295]. Another effect is the lowering of cardioprotective HDL2, usually measured as low HDL-cholesterol [290,296–298].
Lipoproteins are also subject to glycation of their apoproteins and phospholipids [227]. Glycation promotes lipid oxidation and markedly changes the functional properties of lipoproteins. They become immunogenic and bind to specific scavenger receptors. This excludes them from the regulated lipid metabolism [299] and drains them into foam cell formation. They also act as stimulators of kinin release from endothelial cells and monocytes/macrophages. Thus, diabetic dyslipoproteinemia is related to a variety of factors that may enhance the risk of macroangiopathy [290,295,298].
The correlation of insulin and its precursors with macroangiopathy has received much attention [300]. It has been shown that insulin stimulates the migration, proliferation, LDL binding, and cholesterol synthesis of vascular smooth muscle cells. It may also raise blood pressure by enhancing sodium reabsorption and the sympathetic tone of vessel walls. Insulin is a prerequisite of increased VLDL synthesis, which is an important early step in the development of dyslipoproteinemia. Insulin, proinsulin, and hypertriglyceridemia stimulate PAI-1 synthesis in endothelial cells and liver and inhibit fibrinolysis [301]. However, the possible role of insulin in the pathogenesis of macroangiopathy remains a matter of debate. It may make a difference whether insulin is being used to restore insulin deficiency or whether it occurs as hyperinsulinemia in insulin-resistant states.
Clinical Picture and Management of Coronary Heart Disease
Considering the high mortality associated with myocardial infarction and the high risk of reinfarction, primary and secondary prevention of coronary heart disease (CHD) is of utmost importance.
In both types of diabetes mellitus, myocardial infarction and macroangiopathy are related to metabolic control, but a significant lowering of risk by lowering HbA1c alone could not be shown [127,130]. Treatment of obese type 2 diabetic subjects with metformin significantly lowered the incidence of myocardial infarction [133], indicating that this drug has not only anti-diabetic effects, but also others. In type 2 diabetes myocardial infarction is also associated with hypertension [159]. However, as shown in the UKPDS [158], which used calcium channel and β-receptor blockers, lowering of blood pressure by itself was not able to reduce significantly the risk of myocardial infarction. In contrast, studies with ACE inhibitor ramipril significantly lowered the risk of myocardial infarction, stroke, and cardiovascular death [222,302], indicating that other than blood pressure lowering effects must be important.
Primary and secondary prevention with aspirin has been recommended [138,303,304], and dyslipidemia should also be treated. In secondary prevention, clinical data showed that β-blockers [305] and ACE inhibitors [306,307] were beneficial.
From the list of known risk factors (Table 1.13) it is evident that primary prevention of macroangiopathy should pay attention to more than just the risk factors considered in the Diabetes Control and Complications Study (DCCT) and UKPDS. The need for a holistic view [308] is underlined by intervention studies in diabetic populations [309,310].
In myocardial infarction in diabetic subjects, most frequently the left coronary artery is occluded, and often two or three arteries are
