Leptin induces the expression of tumorigenic genes in the gastric mucosa of male Sprague-Dawley rats

Leptin promotes the growth of gastric cancer cells in vitro. It is, however, unknown if leptin induces gastric cancer in vivo. This study therefore investigated the effect of leptin on the histology and expression of tumorigenic genes in the stomach of rats following 40 weeks of leptin treatment. Male Sprague-Dawley rats, aged 6 weeks, were randomized into control and experimental groups (n = 8 per group). The experimental group was given intraperitoneal injections of leptin (60 µg/kg/day) once daily for 40 weeks, whereas the control group received intraperitoneal injection of an equal volume of normal saline daily. Rats were housed in polypropylene cages for the duration of the study. Body weight was measured weekly. Upon completion of treatment, rats were euthanized and their stomachs were collected for histopathological examination, microarray, and RT-qPCR. Data were analyzed using one-way ANOVA and Fisher’s exact test. On histology, one rat (12.5%) in the leptin-treated group had a large red-colored tumor nodule at the pyloric antrum of the stomach. Microscopically, stomachs of two leptin-treated rats (25%) showed hyperplasia or dysplasia. Microarray analysis revealed significant upregulation of a number of genes in the stomachs of leptin-treated rats that have been shown to be associated with tumorigenesis in other tissues, including Furin (protein maturation), Eef1a1 and Eif4g2 (translation factors), Tmed2 (vesicular trafficking), Rab7a (plasma membrane trafficking), Rfwd2 (protein degradation), Fth1 and Ftl1 (oxygen transport), Tspan8, Tspan1, Fxyd3, and Rack1 (cell migration), Pde4d (signal transduction), Nupr1 and Ybx1 (transcription factors), Ptma and Tmem134 (oncogenes), Srsf2 (mRNA maturation), and Reep5 (cell proliferation). None of the known oncogenes were, however, significantly up-regulated. In conclusion, although the overall effect of leptin on gastric carcinogenesis seems inconclusive, the findings of dysplasia and the up-regulation of some of the cancer-related genes nevertheless warrant further scrutiny on the role of leptin in gastric cancer. Impact statement: Gastric cancer is the third most common cause of death due to cancer in the world. Obese individuals are at risk of developing gastric cancer, and the reason for this is unknown. Serum leptin levels are high in obese individuals and leptin is known to induce proliferation of gastric cancer cells in vitro. However, to date, no reports exist on the tumorigenic effects of leptin on the stomach in vivo. This study therefore determines if chronic leptin administration induces gastric carcinogenesis in non-obese rats, which might serve as a useful animal model for future studies. Although the findings are somewhat inconclusive, to our knowledge, however, this is the first study to show the up-regulation of numerous potential driver genes that highlight the potential role of leptin in the higher prevalence of gastric cancer among obese individuals. The findings certainly necessitate further scrutiny of leptin gastric cancer.