Leptin is involved in the regulation of food intake and is mainly secreted by adipocytes. Major secretagogues are cytokines such as TNF-alpha or IL-1. Leptin in turn upregulates inflammatory immune responses. Elevated leptin serum levels have been detected in patients with liver cirrhosis, a disease frequently associated with elevated levels of circulating cytokines as well as hypermetabolism and altered body weight. Recently, leptin has been detected in activated hepatic stellate cells in vitro and an involvement of leptin in liver fibrogenisis has been suggested. The current study was designed to further clarify the role of leptin in liver disease by characterizing leptin and leptin receptor expression in the development and onset of experimental liver fibrosis. Liver fibrosis and cirrhosis was induced in rats by use of phenobarbitone and increasing doses of CCl (4). Leptin and leptin receptor mRNA expression was determined by semiquantitative RT-PCR, protein expression by Western blot analysis and localization of leptin and its receptor by immunohistochemistry. Normal liver tissue does not express leptin, but leptin receptor mRNA. Increasing levels of leptin mRNA were detected in fibrotic and cirrhotic livers correlated to the degree of fibrosis. Leptin receptor mRNA expression was not significantly altered in damaged livers. Increasing levels of leptin were detected in fibrotic and cirrhotic livers, whereas protein expression of the receptor remained unchanged. Throughout different stages of liver fibrosis, leptin immunoreactivity was localized in activated hepatic stellate cells only, whereas immunoreactivity for the receptor was mainly seen on hepatocytes. In conclusion, leptin is expressed at increasing levels in activated hepatic stellate cells in vivo, which may therefore be a source of increased leptin tissue and serum levels contributing to the pathophysiology and morphological changes of chronic liver disease.
Expression of prolactin, overexpression of prolactin receptors in colorectal cancers, and mitogenic effects of prolactin suggest a role for this hormone in a subgroup of colorectal cancers, which is presumably mediated by paracrine/autocrine pathways.
Our results suggest that patients with advanced breast cancer and an elevated serum-neu-protein level may have a poor clinical outcome. This test might be a useful tool for monitoring patients with advanced breast carcinoma, but not those with early disease. Further prospective studies are warranted to elucidate the question of whether this test can contribute to determining prognosis and treatment strategies.
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