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ORIGINAL RESEARCH COMMUNICATION |
1 From the Obesity and Diabetes Clinical Research Section, NIDDK/NIH/DHHS, Phoenix, AZ (JK, NS, CW, CB, JK, and JCB); Carl T Hayden Veterans Affairs Medical Center, Phoenix, AZ (PAP); the Department of Internal Medicine and Molecular Science, Graduate School of Medicine, Osaka University, Osaka, Japan (MS and TF); Pennington Biomedical Research Center, Baton Rouge, LA (SRS); and the Department of Kinesiology, Laval University, Quebec, Canada (DRJ)
Background: Enlargement of adipocytes from subcutaneous abdominal adipose tissue (SAT), increased intrahepatic lipid content (IHL), intramyocellular lipid content (IMCL), and low circulating adiponectin concentrations are associated with insulin resistance.
Objective: Because adiponectin increases fat oxidation in skeletal muscle and liver, and the expression of the adiponectin gene in SAT is inversely associated with adipocyte size, we hypothesized that hypoadiponectinemia links hypertrophic obesity with insulin resistance via increased IMCL and IHL.
Design: Fifty-three obese Pima Indians with a mean (±SD) age of 27 ± 8 y, body fat of 35 ± 5%, and normal glucose regulation (normal fasting and 2-h glucose concentration per WHO 1999 criteria) underwent euglycemic-hyperinsulinemic clamp, biopsies of SAT and vastus lateralis muscle, and magnetic resonance imaging of the abdomen.
Results: Adipocyte diameter (AD) correlated positively with body fat (P < 0.0001) and IHL (estimated from magnetic resonance imaging intensity of liver; P = 0.047). No association was found between AD and plasma adiponectin or IMCL. Plasma adiponectin negatively correlated with type II IMCL (IIA, P = 0.004; IIX, P = 0.009) or IHL (P = 0.02). In a multivariate analysis, plasma adiponectin, AD, and visceral adipose tissue (VAT) independently predicted IHL. Low insulin-mediated glucose disposal was associated with low plasma adiponectin (P = 0.02) and high IHL (P = 0.0003), SAT (P = 0.02), and VAT (P = 0.04). High IHL was the only predictor of reduced insulin-mediated suppression of hepatic glucose production (P = 0.02) and the only independent predictor of insulin-mediated glucose disposal in a multivariate analysis.
Conclusions: Increased lipid content in the liver may independently link hypoadiponectinemia, hypertrophic obesity, and increased visceral adiposity with peripheral and hepatic insulin resistance.
Key Words: Obesity • adipocyte size • adiponectin • intrahepatic fat • intramyocellular fat • insulin action
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