Monocyte chemoattractant protein-1 in subcutaneous abdominal adipose tissue: characterization of interstitial concentration and regulation of gene expression by insulin.

CONTEXT: The chemokine monocyte chemoattractant protein-1 (MCP-1) is implicated in obesity-associated chronic inflammation, insulin resistance, and atherosclerosis.
OBJECTIVES: The objectives of this study were to: 1) characterize the interstitial levels and the gene expression of MCP-1 in the sc abdominal adipose tissue (SCAAT), 2) elucidate the response of MCP-1 to acute hyperinsulinemia, and 3) determine the relationship between MCP-1 and arterial stiffness.
DESIGN: Nine lean (L) and nine uncomplicated obese (OB) males were studied in the fasting state and during a euglycemic-hyperinsulinemic clamp combined with the microdialysis technique. Interstitial and serum MCP-1 (iMCP-1 and sMCP-1, respectively) levels, pulse wave analysis, and SCAAT biopsies were characterized at baseline and after hyperinsulinemia.
RESULTS: OB showed elevated sMCP-1 (P < 0.01) but similar iMCP-1 levels as compared with L. Basal iMCP-1 concentrations were considerably higher than sMCP-1 (P < 0.0001), and a gradient between iMCP-1 and sMCP-1 levels was maintained throughout the hyperinsulinemia. At baseline, SCAAT gene expression profile revealed a "co-upregulation" of MCP-1, MCP-2, macrophage inflammatory protein-1alpha, and CD68 in OB, and whole-body glucose disposal inversely correlated with the MCP-1 gene expression. After hyperinsulinemia, MCP-1 and MCP-2 mRNA levels significantly increased in L, but not in OB. Finally, sMCP-1 excess in the OB positively correlated with the stiffer vasculature.
CONCLUSIONS: These observations demonstrate similar interstitial concentrations and a differential gene response to hyperinsulinemia of MCP-1 in the SCAAT from L and OB individuals. In human obesity, we suggest the SCAAT MCP-1 gene overexpression as a biomarker of an "inflamed" adipose organ and impaired glucose metabolism.