ApoC-III and visceral adipose tissue contribute to paradoxically normal triglyceride levels in insulin-resistant African-American women

Abstract

Background: African-Americans are more insulin-resistant than whites but have lower triglyceride (TG) concentrations. The metabolic basis for this is unknown. Our goal was to determine in a cross-sectional study the effect of insulin resistance, visceral adipose tissue (VAT) and the apolipoproteins, B, C-III and E, on race differences in TG content of very low density lipoproteins (VLDL).

Methods: The participants were 31 women (16 African-American, 15 white) of similar age (37 ± 9 vs. 38 ± 11y (mean ± SD), P = 0.72) and BMI (32.4 ± 7.2 vs. 29.3 ± 6.0 kg/m2, P = 0.21). A standard diet (33% fat, 52% carbohydrate, 15% protein) was given 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. VAT was measured at L2-3. The influence of race, SI, VAT and apolipoproteins on the TG content of VLDL was determined by random effects models (REM).

Results: African-Americans were more insulin-resistant (SI: 3.6 ± 1.3 vs. 5.6 ± 2.6 mU/L-1.min-1, P < 0.01) with less VAT (75 ± 59 vs. 102 ± 71 cm2, P < 0.01). TG, apoB and apoC-III content of light and dense VLDL were lower in African-Americans (all P < 0.05 except for apoC-III in light VLDL, P = 0.11). ApoE content did not vary by race. In REM, VAT but not SI influenced the TG concentration of VLDL. In models with race, SI, VAT and all apolipoproteins entered, race was not significant but apoC-III and VAT remained significant determinants of TG concentration in light and dense VLDL.

Conclusions: Low concentrations of apoC-III and VAT in African-Americans contribute to race differences in TG concentrations.

Trial registration: ClinicalTrials.gov Identifier: NCT00484861.

Figures

Figure 1

Fasting TG concentrations at baseline and after 7 days of the standard diet. Bar graph data presented as mean ± SE. Notation: a = difference between African-Americans and whites, b = difference in African-Americans from baseline, *P = <0.05. Difference in whites before and after 7 day diet was not significant, P = 0.18).

Figure 2

TG and apolipoprotein concentration of each of the lipoproteins at baseline and 2, 4 and 6 hours postprandially. Columns present: light VLDL, dense VLDL, IDL and LDL. The rows present the TG, ApoB, ApoC-III and ApoE concentration in each lipoprotein. Data is from random effect multiple models constructed to determine the effect of race on the TG, ApoB, ApoC-III and ApoE content of each lipoprotein. The P-value for the effect of race is presented in each diagram. African-American women: solid lines; white women: dotted lines.