Elevated interlukin-6 levels as a consequence, not the cause of obesity and insulin resistance

• Several population-based studies have reported that serum interleukin-6 (IL-6) levels are positively correlated with obesity and insulin resistance. This has lead to the hypothesis of a causal relationship between elevated IL-6 levels and insulin resistance. This notion is further strengthened by the observation that obesity is associated with a chronic low-grade inflammation in adipose tissue, which is postulated to be causal in the development of insulin resistance and type-2 diabetes. A recent study of weight gain demonstrates however that insulin resistance develops even in the absence of a significant signs of adipose inflammation. This suggests that inflammation in adipose tissue occurs subsequent to peripheral insulin resistance in humans. More and more data also supports the hypothesis that increased adiposity in itself, independent of the increased IL-6 levels, is a predictor of diabetes risk. IL-6 levels tend to also increase with age and since the incidence of insulin resistance and type-2 diabetes also increases with age, this could explain some of the observed correlations. Taken together, the above studies provide an association of metabolic disorder with IL-6, but not causation. An emerging concept is that IL-6 appears to have different effects on different tissues, and the effects depend on whether the IL-6 levels are acutely or chronically elevated. Given the opposing views of the impact of IL-6 on glucose homeostasis, many investigations have aimed at clarifying the effects of IL-6 on insulin action. A recent study shows that IL-6, either released from skeletal muscle or adipose tissue, induces GLP-1 release, leading to insulin secretion, improved beta-cell function and glycemic control. Still, the causal relationships between IL-6, obesity and type-2 diabetes remain a matter of debate. This review summarizes the current data on IL-6, supporting an association, but not a causative relationship, between IL-6 and metabolic disturbances. © 2013 Nova Science Publishers, Inc. All rights reserved.

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MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Fysiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Physiology (hsv//eng)

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