Significant associations between lipoprotein(a) and corrected apolipoprotein B-100 levels in African-Americans

Abstract

Objectives: Lipoprotein(a), Lp(a), represents an apolipoprotein (apo) B-carrying lipoprotein, yet the relationship between Lp(a) and apoB levels has not been fully explored.

Methods: We addressed the relationship between Lp(a) and apoB-containing lipoprotein levels in 336 Caucasians and 224 African-Americans. Our approach takes unique molecular properties of Lp(a) as well as contribution of Lp(a) to the levels of these lipoproteins into account.

Results: Levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apoB and apoB/apoA-1 did not differ across ethnicity. African-Americans had higher levels of Lp(a) and high-density lipoprotein cholesterol and lower triglyceride levels compared to Caucasians. Lp(a) levels were correlated with levels of TC (p < 0.005), LDL-C (p < 0.001), apoB (p < 0.05) or apoB/apoA-1 (p < 0.05) in both ethnic groups. These associations remained significant only in African-Americans after adjustments for the contribution of Lp(a)-cholesterol or Lp(a)-apoB. Furthermore, taking Lp(a)-apoB into account, allele-specific apo(a) levels were significantly associated with apoB levels and the apoB/apoA-1 ratio in African-Americans. The latter associations in African-Americans remained significant for allele-specific apo(a) levels for smaller apo(a) sizes (<26 K4 repeats), after controlling for the effects of age, sex, and BMI.

Conclusions: Although TC, LDL-C, and apoB levels were comparable between African-Americans and Caucasians, the associations of these parameters with Lp(a) and allele specific apo(a) levels differed between these two ethnic groups. In African-Americans, apoB and apoB/apoA-1 remained consistently and positively associated with both Lp(a) and allele-specific apo(a) levels after adjustments for the contribution of Lp(a)-apoB. The findings suggest an interethnic difference with a closer relationship between Lp(a) and apoB among African-Americans.

Keywords: Apo(a) sizes; Corrections for the contribution of Lp(a); Ethnicity; K4 repeats; Plasma lipids.

Figure 1. The effects of correction for the contribution of Lp(a)-cholesterol or -apoB content on apoB-containing atherogenic lipoprotein levels in Caucasians versus African-Americans

Differences in TC, LDL-C and ApoB levels before and after correction for the contribution of Lp(a)-cholesterol or -apoB content were calculated per each individual, and expressed as a percentage (%) change from the before correction level. Based on the individual percentage change, the mean percentage changes in TC, LDL-C, and apoB levels per each ethnic group were computed, and are shown in the graph. For details on calculations of corrected levels, see the footnote of Table 2 or the Methods section. *: p<0.001 versus Caucasians Abbreviations: TC, total cholesterol, LDL-C, low-density lipoprotein cholesterol, apoB, apolipoprotein B;

Figure 2. Association of Lp(a) (nmol/L) level with apoB (nmol/L) level before and after correction for the contribution of Lp(a)-apoB content in Caucasians versus African-Americans

The relationship between apoB and square root transformed Lp(a) levels before (A and B) and after (C and D) correction for the contribution of Lp(a)-apoB content is described by partial correlation coefficients controlling for the effects of age, sex, and BMI. At molecular level, Lp(a) remained significantly and positively associated with apoB levels after corrections in African-Americans (D), but not in Caucasians (C). For conversion of apoB levels in mg/dL into nmol/L and calculations of non-Lp(a) apoB levels, see the Methods section. Abbreviations: SqRt, square root; apoB, apolipoprotein B;