Influence of triglyceride concentration on the relationship between lipoprotein cholesterol and apolipoprotein B and A-I levels

A sample of 2,103 men aged 47 to 76 years from the Quebec Cardiovascular St udy cohort was examined to quantify the influence of plasma triglyceride (T G) levels on the relationship between plasma lipoprotein cholesterol and ei ther apolipoprotein A-I (apo A-I) or apo B concentrations. Regression analy ses between high-density lipoprotein cholesterol (HDL-C) and apo A-I throug h TG tertiles showed highly significant correlations (.62 less than or equa l to r less than or equal to .75, P < .0001) in all TG tertiles between the se 2 variables. The associations for plasma apo B versus low-density lipopr otein cholesterol (LDL-C) and non-HDL-C levels were also studied on the bas is of TG concentrations, and correlation coefficients between either LDL-C or non-HDL-C and apo B were essentially similar among TG tertiles (.78 less than or equal to r less than or equal to .85 and .83 less than or equal to r less than or equal to .86 for LDL-C and non-HDL-C, respectively, P < .00 01). Regression analyses also showed that lower HDL-C levels were found for any given apo A-I concentration among men in the 2 upper TG tertiles, wher eas lower LDL-C concentrations were observed at any given apo B level among subjects in the upper TG tertile, We further investigated whether there we re synergistic alterations in the HDL-C/apo A-I and LDL-C/apo B ratios as a function of increasing plasma TG. A significant association was noted betw een these 2 ratios (r = .37; P < .0001), Mean HDL-C/apo A-I and LDL-C/apo B ratios were then calculated across quintiles of plasma TG concentrations. Increased TG concentrations were first associated with a reduced HDL-C/apo A-I ratio, followed by a decreased LDL-C/apo B ratio. These results suggest that a relatively modest increase in TG may rapidly alter the relative cho lesterol content of HDL particles. Finally, the cholesterol content of the non-HDL fraction appears to be influenced less by TG levels than HDL-C and LDL-C fractions, Thus, the plasma apo B-containing lipoprotein cholesterol level may provide a better index of number of atherogenic particles than th e LDL-C concentration, particularly in the presence of hypertriglyceridemia (HTG). Copyright (C) 2000 by W.B. Saunders Company.