Physiological significance of resistin and resistin-like molecules in the inflammatory process and insulin resistance.

Resistin was initially identified as a protein, secreted by adipocytes, which inhibits insulin action and adipose differentiation. The three proteins homologous to resistin were termed resistin-like molecules (RELM) alpha, beta and gamma. Resistin and RELMalpha are abundantly expressed in adipose, but RELMbeta and RELMgamma are secreted mainly from the gut. Recently, resistin and RELMs were reported to be associated with inflammation. For example, RELMalpha, viewed as an inflammation-related protein, was originally identified in broncho-alveolar lavage fluid obtained from animals with experimentally induced pulmonary inflammation. RELMbeta is also related to bacterial colonization, but RELMbeta injection or hepatic overexpression of RELMbeta induced insulin resistance. RELMgamma isolated from rat nasal respiratory epithelium was found to be altered by cigarette smoke. Thus, resistin and RELMs could be useful for assessing the inflammatory condition in vivo. On the other hand, whether the serum resistin or RELM concentration is strongly related to insulin resistance remains unclear. However, taking recent studies showing a close relationship between inflammation and insulin resistance in diabetes into consideration, these proteins may have interactive roles linking inflammation and insulin resistance, both of which major involvement in the progression of atherosclerosis. If so, the serum resistin or RELM concentration may be a good marker of atherosclerotic risk. In addition, these proteins or unidentified receptors are potential therapeutic targets for the treatment of diabetes and prevention of atherosclerosis. These possibilities merit further study.