Racial differences between African-American and white women in insulin resistance and visceral adiposity are associated with differences in apoCIII containing apoAI and apoB lipoproteins

Abstract

Background: African-Americans have higher HDL, less visceral adipose tissue (VAT) and lower triglyceride (TG) and apoCIII concentrations than whites, despite being more insulin-resistant. We studied in African-American and white women the influences of insulin resistance and VAT on the apoAI concentrations of two HDL subspecies, one that contains apoCIII that is associated with increased risk of coronary heart disease (CHD) and one that does not have apoCIII that is associated with decreased CHD; and on the apoCIII concentrations of HDL and of the apoB lipoproteins.

Methods: The participants were 32 women (14 African-Americans, 18 white) of similar age (39 ± 12 vs. 42 ± 11y). Mean BMI was 34 kg/m(2) in the African-Americans compared to 30 in the whites. A standard diet (33% fat, 52% carbohydrate, 15% protein) was provided for 7 days followed by a test meal (40% fat, 40% carbohydrate, 20% protein) on Day 8. Insulin sensitivity index (SI) was calculated from the minimal model.

Results: After controlling for SI, African-Americans have a higher mean apoAI level in HDL with apoCIII compared with whites (12.9 ± 2.8 and 10.9 ± 2.9 mg/dL, respectively, P = 0.05). SI was associated with higher apoAI in HDL with apoCIII, whereas VAT was not associated with this HDL subspecies. This pattern of results was reversed for apoCIII concentrations in apoB lipoproteins. After adjusting for SI, African-Americans had lower apoCIII in apoB lipoproteins. SI was associated with lower apoCIII in total apoB lipoproteins, whereas VAT was associated with higher apoCIII in all the apoB lipoproteins. Additional adjustment for VAT tended to reduce the difference in apoCIII between the groups.

Conclusions: African-American women have a higher HDL with apoCIII level than whites when controlled for insulin sensitivity. African-Americans have lower insulin sensitivity. Insulin sensitivity is associated with higher levels of HDL with apoCIII. ApoCIII levels in VLDL are lower in African-American women than whites, also affected by insulin sensitivity which is associated with low apoCIII in VLDL. VAT has a strong association with apoCIII in apoB lipoproteins but not with apoAI in HDL with apoCIII.

Trial registration: ClinicalTrials.gov Identifier: NCT00484861.

Keywords: African-Americans; ApoAI; ApoB lipoproteins; ApoCIII; Coronary heart disease; HDL; Insulin resistance; Visceral adipose tissue.

Figures

Figure 1

ApoAI concentrations of HDL with or without apoCIII at baseline, 2, 4 and 6 hours postprandially. The rows present the apoAI concentration in HDL with apoCIII (A) and HDL without apoCIII (B). Panels present unadjusted (left panel) and adjusted for SI (right panel). Data is from random effect multiple models constructed to determine the effect of race on the apoAI concentration in each HDL subfraction. The P-value for the effect of race is presented in each diagram. African-American women: solid lines; white women: dashed lines.

Figure 2

ApoCIII concentrations in HDL and apoB lipoproteins at baseline, 2, 4 and 6 hours postprandially. The rows present the apoCIII concentration in HDL (A), total apoB lipoproteins (B), light VLDL (C), dense VLDL (D), IDL (E) and LDL (F). Columns present unadjusted (left panel) and adjusted for SI (right panel). Data are from random effect multiple models constructed to determine the effect of race on the apoCIII concentration in each lipoprotein. The P-value for the effect of race is presented in each diagram. African-American women: solid lines; white women: dashed lines.

Figure 3

Metabolic pathways suggested by the results of this study. Increased visceral adipose tissue increases flux of FFA to the liver. The liver responds by increasing the secretion of apoC-III in apoB lipoproteins. Lower total body insulin sensitivity including in skeletal muscle and peripheral adipose tissue increases plasma FFA, which increases secretion of apoC-III in apoB lipoproteins. Lower insulin sensitivity reduces apoAI level in HDL with apoCIII, and in HDL without apoCIII. African-American race is associated with increased apoAI of HDL with apoCIII, and decreased apoCIII in apoB lipoproteins, independent of differences in insulin sensitivity and VAT.