원위부소장 자극에 따른 위장관 호르몬 분비 및 유전자 발현 연구

Abstract

Introduction: The hindgut hypothesis suggests that enhanced secretion of hindgut hormones such as glucagon-like peptide-1 (GLP-1) induces improvement of hyperglycemia after bariatric surgery. Ileal transposition (IT) is a good model for investigating the hindgut effect because distal ileum is expeditely stimulated by undigested chime without altering other gastrointestinal anatomy. IT induces L-cell secretion and it promotes metabolic benefits. We investigated the effect of IT on gut hormone secretion and plasma lipopolysaccharide (LPS) levels which could contribute to metabolic disorders. In addition, gene expression following stimulation of the distal small intestine was evaluated to find candidate genes of novel incretin hormones. Methods: Sprague-Dawley rats underwent either IT or sham operation. After 4 weeks, oral glucose tolerance tests (OGTT) were performed and fasting plasma LPS and gut histology were analyzed. For cDNA microarray analysis, transposed ileum of IT and ileum in situ of sham were used. To verify immediate genetic alterations, an 1 week model was also adopted. Expression of candidate genes for novel incretin hormones was validated by RT-PCR. Results: The IT group showed decreased food intake, body weight, and insulin resistance. During OGTTs, plasma levels of glucagon, GLP-1, GLP-2, and peptide YY (PYY) were significantly higher in the IT group than in the sham group. Villi length and muscle thickness increased in the transposed ileum (IT) compared with the ileum in situ (sham). The density of GLP-1 and glucose-dependent insulinotropic polypeptide co-expressing cells (K/L-cells) was significantly higher in the IT group. Fasting plasma LPS levels were lower in the IT group than in the sham group (5.6 ± 0.2 vs. 6.8 ± 0.1 EU/ml, P = 0.002), and significantly correlated with insulin resistance (r = 0.755, P < 0.001). Plasma LPS levels negatively correlated with PYY (r = -0.710, P = 0.001) or GLP-2 (r = -0.625, P = 0.007) secretion. We found 47 differentially expressed genes (DEGs) which were up regulated both in 1 week and 4 week models. From the 4 week model, 611 up regulated DEGs were found and there were 96 DEGs for secretory peptide. After review of biological processes, 16 candidate genes were found in terms of preservation of beta-cell function and intestinal proliferation. RT-PCR showed that Reg1a and Dmbt1 genes were significantly increased after IT surgery. Conclusion: IT surgery showed improved insulin sensitivity and increased L-cell secretion. There seemed to be a link between reduced plasma LPS levels and the improvement of insulin sensitivity after IT possibly via increased PYY and GLP-2 secretion. Diverse changes of gene expression were shown in microarray analysis and further studies will be needed to analyze functional properties of candidate genes such as Reg1a and Dmbt1. It will provide possibility of new drug development for obesity and diabetes.