The circulating peptide leptin, which is the product of the ob gene, provides feedback information on the size of fat stores to central Ob receptors that control food intake and body-weight homeostasis. Leptin has so far been reported to be secreted only by adipocytes and the placenta. Here we show that leptin messenger RNA and leptin protein are present in rat gastric epithelium, and that cells in the glands of the gastric fundic mucosa are immunoreactive for leptin. The physiological function of this previously unsuspected source of leptin is unknown. However, both feeding and administration of CCK-8 (the biologically active carboxy-terminal end of cholecystokinin) result in a rapid and large decrease in both leptin cell immunoreactivity and the leptin content of the fundic epithelium, with a concomitant increase in the concentration of leptin in the plasma. These results indicate that gastric leptin may be involved in early CCK-mediated effects activated by food intake, possibly including satiety.

Leptin plays a key role regulating food intake, body weight and fat mass. These critical parameters are associated with an increased risk for digestive and mammary gland cancer in the Western population. Here we determined whether leptin contributes to the invasive phenotype of colonic and kidney epithelial cells at various stages of the neoplastic progression. First, leptin potently (EC50 = 10-30 ng/ml) induces invasion of collagen gels by premalignant familial adenomatous colonic cells PC/AA/C1 and nontumorigenic MDCK kidney epithelial cells, their src-transformed counterparts, and the human adenocarcinoma colonic cells LoVo and HCT-8/S11. Leptin and its Ob-Rb receptors were consistently identified by RT-PCR and immunoblotting in these cell lines, as well as in human colonic epithelial crypts, polyps, colonic tumor resections, and adjacent mucosa. Leptin-induced invasion was effectively blocked by pharmacological inhibitors of several downstream signaling pathways involved in cell transformation, namely, JAK2 tyrosine kinase (AG490), phosphoinositide PI3'-kinase (wortmannin and LY294002), mTOR kinase (rapamycin), and protein kinases C (GF109203X, Gö6976). Accordingly, leptin induces transient elevation of the PI3'-kinase lipid products in JAK2 immunoprecipitates prepared from parental MDCK cells. The leptin effect on invasion was potentiated by the activated form of the small GTPase RhoA and was abrogated by dominant negative mutants of RhoA, Rac1, and the p110alpha of PI3'-K. Our data indicate that leptin may exert a local and beneficial effect on migration of normal colonic epithelial cells and reparation of the inflamed or wounded digestive mucosa. We also emphasize a new role for leptin, linking the nutritional and body fat status to digestive cancer susceptibility by stimulating the invasive capacity of colonic epithelial cells at early stages of neoplasia. This finding has potential clinical implications for colon cancer progression and management of obesity.

Background and aim-The circulating peptide leptin produced by fat cells acts on central receptors to control food intake and body weight homeostasis. Contrary to initial reports, leptin expression has also been detected in the human placenta, muscles, and recently, in rat gastric chief cells. Here we investigate the possible presence of leptin and leptin receptor in the human stomach. Methods-Leptin and leptin receptor expression were assessed by immunohistochemistry, reverse transcriptasepolymerase chain reaction (RT-PCR), and western blot analysis on biopsy samples from 24 normal individuals. Fourteen (10 healthy volunteers and four patients with non-ulcer dyspepsia and normal gastric mucosa histology) were analysed for gastric secretions. Plasma and fundic mucosa leptin content was determined by radioimmunoassay. Results-In fundic biopsies from normal individuals, immunoreactive leptin cells were found in the lower half of the fundic glands. mRNA encoding ob protein was detected in the corpus of the human stomach. The amount of fundic leptin was 10.4 (3.7) ng leptin/g mucosa, as determined by radioimmunoassay. Intravenous infusions of pentagastrin or secretin caused an increase in circulating leptin levels and leptin release into the gastric juice. The leptin receptor was present in the basolateral membranes of fundic and antral gastric cells. mRNA encoding Ob-RL was detected in both the corpus and antrum, consistent with a protein of ∼120 kDa detected by immunoblotting. Conclusion-These data provide the first evidence of the presence of leptin and leptin receptor proteins in the human stomach and suggest that gastric epithelial cells may be direct targets for leptin. Therefore, we conclude that leptin may have a physiological role in the human stomach, although much work is required to establish this.