Black-white Differences in High Density Lipoproteins, Apolipoproteins, and Triglycerides: Relationships to Coronary Heart Disease in Non-uremic Populations and in Uremic Subjects Receiving Hemodialysis

Although black Americans have more hypertension and more severe clinical manifestations of hypertension (1,6), the mortality from coronary heart disease (CHD) in black men is less than that in white men (1, 3). CHD mortality is equal in black and white women, and greater in black women than black men (3). In the Evans County study, at any level of CHD risk factors, the observed CHD risk for black men was lower than for white men (3). The curves of observed CHD as plotted against CHD risk were parallel for black and white men, but the black curve was at a lower level (3). This suggested that factors other than those measured, such as high density lipoprotein cholesterol (HDLC) might act upon these lower CHD event rates in blacks. In addition to the relative excess of hypertension among blacks (3, 6), blacks tend to have a relative excess of other CHD risk factors, including pandemic obesity in black women (7), equivalent or higher prevalence of familial aggregations of hyperlipoproteinemia (8, 10), and lower socio-economic status (5, 11, 12). Given the relative excess of CHD risk factors among blacks, it has been speculated that among other proposed "protective" factors, consistently higher HDLC levels in blacks may playa leading role in the relative protection of blacks from CHD (12, 17), given the strong inverse association of HDLC and CHD (18, 19). Within the above frame of reference, the recent report by Goldberg et al (20) of higher cardiovascular mortality in white male chronic uremics undergoing long-term hemodialysis, as compared to black uremic men, is not unexpected. White men had higher levels of plasma triglyceride and lower levels of HDLC, apoprotein Aland A2, than did black men; the concentrations of HDLC, apoprotein Al, and A2 were also lower in white than in black women (20). HDL2 concentrations were also found to be higher in black than in white men, and the distribution of HDL subfractions was normal in black and abnormal in white men receiving hemodialysis (20). Goldberg concluded " . there may be important differences between the races and sexes in coronary risk factors and in the incidence of mortality from atherosclerotic causes in patients receiving hemodialysis who are at high risk for cardiovascular disease. There is a need to identify patients receiving hemodialysis who have "atherogenic" lipoprotein profiles, to determine the pathogenesis of their abnormalities, and to plan appropriate therapeutic interventions. " Given the persistence of atherogenic lipoprotein patterns in both races of uremic subjects as compared to non-uremic subjects (20), attention should be focused on CHD risk factors in all uremic subjects irrespective of race, with an eye to reducing the otherwise high risk of cardiovascular morbidity and mortality (21). When present, diabetes mellitus should be tightly controlled to reduce hyperglycemia-related hypertriglyceridemia and hypoalphalipoproteinemia. Major efforts should be made to discontinue cigarette smoking, because cigarette smoking is directly associated with lower levels of HDLC and apo A1. Where possible, amelioration of obesity may help to reduce triglyceride levels and increase HDLC. Supervised exercise programs may have utility in elevating HDLC and/or reducing triglyceride levels; exercise training in hemodialysis patients has been shown to result in lowered triglyceride levels and increased plasma HDLC levels, as well as improvement in glucose intolerance and hyperinsulinism (22). Pharmacologic therapy designed to reduce triglyceride or elevate HDLC needs to be approached cautiously, due to the amplification of side effects of lipid lowering drugs in uremic patients, particularly those with lower albumin levels. Nevertheless, a recent report has provided encouraging evidence of significant increments in HDLC and reductions in triglycerides in uremic patients receiving gemfibrozil (Lopid) with a minimal level of side effects (23). In a sense, the report by Goldberg (20) explicates an "experiments of nature" suggesting that higher HDLC, A 1, and A2, and lower triglycerides in uremic patients may be associated with lower CHD mortality. This suggests, speculatively, that modifications in diet, exercise, smoking, relative ponderosity, and therapeutic intervention, all designed to elevate HDLC and reduce triglycerides, in uremic patients, might, over the long-term, have beneficial effects in reducing CHD mortality in this high risk cohort.