Browsing by Author "Tulloch-Reid, Marshall K"

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    ApoC-III and visceral adipose tissue contribute to paradoxically normal triglyceride levels in insulin-resistant African-American women
    (2013-12-23) Sumner, Anne E; Furtado, Jeremy D; Courville, Amber B; Ricks, Madia; Younger-Coleman, Novie; Tulloch-Reid, Marshall K; Sacks, Frank M
    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 (37and#8201;and#177;and#8201;9 vs. 38and#8201;and#177;and#8201;11y (meanand#8201;and#177;and#8201;SD), P =and#8201;0.72) and BMI (32.4and#8201;and#177;and#8201;7.2 vs. 29.3and#8201;and#177;and#8201;6.0and#160;kg/m2, P =and#8201;0.21). A standard diet (33% fat, 52% carbohydrate, 15% protein) was given for 7and#160;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: 3.6and#8201;and#177;and#8201;1.3 vs. 5.6and#8201;and#177;and#8201;2.6and#160;mU/L-1.min-1, P andlt;and#8201;0.01) with less VAT (75and#8201;and#177;and#8201;59 vs. 102and#8201;and#177;and#8201;71and#160;cm2, P andlt;and#8201;0.01). TG, apoB and apoC-III content of light and dense VLDL were lower in African-Americans (all P andlt;and#8201;0.05 except for apoC-III in light VLDL, P =and#8201;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
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    Limitations of fasting indices in the measurement of insulin sensitivity in Afro-Caribbean adults
    (2014-02-20) Thompson, Debbie S; Boyne, Michael S; Osmond, Clive; Ferguson, Trevor S; Tulloch-Reid, Marshall K; Wilks, Rainford J; Barnett, Alan T; Forrester, Terrence E
    Abstract Background Insulin sensitivity can be estimated using glucose disposal rate (M) measured during a hyperinsulinemic euglycemic clamp (HEC) or insulin sensitivity index (SI) derived from a frequently sampled intravenous glucose tolerance test (FSIVGTT). The commonly used homeostatic model assessment of insulin resistance (HOMA-IR) which utilizes fasting glucose and insulin has been validated against M across several populations (rand#8201;=and#8201;0.5-0.8). This study sought to validate HOMA-IR against SI and M in an Afro-Caribbean population. Findings Sixty participants completed a 180-minute FSIVGTT and another 50 completed a 150-minute hyperinsulinemic euglycemic clamp. In both groups, HOMA-IR was calculated and anthropometry and body composition using dual energy x-ray absorptiometry (DEXA) were measured.FSIVGTT: The participants were 55% male, age 23.1and#8201;and#177;and#8201;0.05and#160;years, BMI 24.8and#8201;and#177;and#8201;6.3and#160;kg/m2 and % body fat 25.0and#8201;and#177;and#8201;15.2 (meanand#8201;and#177;and#8201;SD). HEC: The participants were 44% male, age 27.3and#8201;and#177;and#8201;8.1and#160;years, BMI 23.6and#8201;and#177;and#8201;5.0and#160;kg/m2 and % body fat 24.7and#8201;and#177;and#8201;14.2 (meanand#8201;and#177;and#8201;SD). While HOMA-IR, SI and M correlated with waist, BMI and % body fat (P-valuesand#8201;andlt;and#8201;0.01) there were no significant correlations between HOMA-IR with either SI or M-value (P-valuesand#8201;andgt;and#8201;0.2). Conclusions In young Afro-Caribbean adults, HOMA-IR compared poorly with other measures of insulin sensitivity. It remains important to determine whether similar findings occur in a more insulin resistant population. However, HOMA-IR correlated with clinical measures of insulin sensitivity (i.e. adiposity), so it may still be useful in epidemiological studies.