RESUMO
BACKGROUND: Serum leptin variation is commonly associated with fat percentage (%), body mass index (BMI), and activity. In this investigation, we report population differences in mean leptin levels in healthy men as well as associations with fat % and BMI that are independent of these factors and reflect likely variation resulting from chronic environmental conditions. METHODS: Serum leptin levels, fat %, and BMI were compared between lean American distance runners and healthy Ache Native Americans of Paraguay. Mean levels were compared as were the regressions between fat %, BMI, and leptin. Comparisons were performed between male American distance runners (n = 13, mean age 32.2 +/- 9.2 SD) and highly active male New World indigenous population (Ache of Paraguay, n = 20, mean age 32.8 +/- 9.2) in order to determine whether significant population variation in leptin is evident in physically active populations living under different ecological circumstances independent of adiposity and BMI. RESULTS: While the Ache were hypothesized to exhibit higher leptin due to significantly greater adiposity (fat %, Ache 17.9 +/- 1.8 SD; runners 9.7 +/- 3.2, p < 0.0001), leptin levels were nonetheless significantly higher in American runners (Ache 1.13 ng/ml +/- 0.38 SD; runners 2.19 +/- 1.15; p < 0.007). Significant differences in the association between leptin and fat % was also evident between Ache and runner men. Although fat % was significantly related with leptin in runners (r = 0.90, p < 0.0001) fat % was negatively related in Ache men (r = -0.50, p < 0.03). CONCLUSION: These results illustrate that chronic ecological conditions in addition to activity are likely factors that contribute to population variation in leptin levels and physiology. Population variation independent of adiposity should be considered to be an important source of variation, especially in light of ethnic and population differences in the incidence and etiology of obesity, diabetes, and other metabolic conditions.
RESUMO
Mexican Americans (MA) exhibit high risk for the insulin resistance syndrome characterized by subclinical inflammation and greater risk for type 2 diabetes compared with non-Hispanic white (NHW) adults. The reasons for this phenomenon remain obscure. Because the inflammatory cytokine, tumor necrosis factor-alpha (TNF alpha), is associated with insulin resistance in various models of obesity and diabetes, we sought to determine whether circulating concentrations of this cytokine and its soluble receptors are higher in MA than NHW, and also to determine if the TNF alpha system is related to the lower insulin sensitivity in MA. Fasting blood samples were used to determine concentrations of TNF alpha, soluble TNF receptors 1 (sTNFR1) and 2 (sTNFR2) in the same 13 MA (7 women, 6 men, age=27.0+/-2.0 years, BMI=23.0+/-0.7) and 13 NHW (7 women, 6 men, age=24.8+/-1.5 years, BMI=22.8+/-0.6) previously shown to exhibit differences in insulin sensitivity. Circulating TNF alpha was significantly higher (3.11+/-0.38 vs. 2.10+/-0.24 pg/ml, p<0.05) and sTNFR2 was significantly lower (1324+/-85 vs. 1925+/-127 pg/ml, p<0.05) among MA compared with NHW subjects. Soluble TNFR1 was not different between groups (MA: 970+/-111 pg/ml vs. NHW: 1218+/-73 pg/ml, p=0.07). TNF alpha, sTNFR1 and sTNFR2 were not correlated with HOMA-IR when the two groups were analyzed in aggregate. This study documents higher circulating TNF alpha concentrations in non-obese, non-diabetic MA, a population group at increased risk for the metabolic syndrome and the untoward effects of sub-clinical inflammation. The clinical implications of this difference, if any, are not yet known.
Assuntos
Resistência à Insulina/etnologia , Fator de Necrose Tumoral alfa/biossíntese , Adolescente , Adulto , Estatura , Índice de Massa Corporal , Peso Corporal , Feminino , Glucose/metabolismo , Humanos , Inflamação , Insulina/metabolismo , Masculino , Americanos Mexicanos , México , Obesidade/sangue , Receptores Tipo I de Fatores de Necrose Tumoral/sangue , Receptores Tipo II do Fator de Necrose Tumoral/sangue , Risco , Estados UnidosRESUMO
We determined whether lower insulin sensitivity persists in young, nonobese, nondiabetic Mexican-American [MA; n = 13, 27.0 +/- 2.0 yr, body mass index (BMI) 23.0 +/- 0.7] compared with non-Hispanic white (NHW; n = 13, 24.8 +/- 1.5 yr, BMI 22.8 +/- 0.6) males and females after accounting for cardiorespiratory fitness (maximal O(2) uptake), abdominal fat distribution (computed tomography scans), dietary intake (4-day records), and skeletal muscle insulin-signaling protein abundance from muscle biopsies (Western blot analysis). MA were significantly less insulin sensitive compared with their NHW counterparts when estimated by homeostatic model assessment of insulin resistance (MA: 1.53 +/- 0.22 vs. NHW: 0.87 +/- 0.16, P < 0.05) and the revised quantitative insulin sensitivity check index (MA: 0.45 +/- 0.08 vs. NHW: 0.58 +/- 0.19, P = 0.05). However, skeletal muscle protein abundance of insulin receptor-beta (IRbeta), phosphatidylinositol 3-kinase p85 subunit, Akt1, Akt2, and GLUT4 were not significantly different. Differences in indexes of insulin sensitivity lost significance after percent dietary intake of palmitic acid, palmitoleic acid, and skeletal muscle protein abundance of IRbeta were accounted for. We conclude that differences in insulin sensitivity between nonobese, nondiabetic MA and NHW persist after effects of chronic and acute exercise and total and abdominal fat distribution are accounted for. These differences may be mediated, in part, by dietary fat intake.