Objective The objectives of this study were to investigate the mRNA and protein expression of biomarkers related to absorption in the small intestinal mucosa of humans and determine the relationships between small intestinal diseases and nutrition. Methods The study subjects consisted of patients scheduled to undergo double-balloon endoscopy (DBE) or total colonoscopy for suspected gastrointestinal disorder in a clinical practice. Biopsies were taken from apparently normal mucosa in the visible areas of 6 parts of the intestines from the duodenum to the colon. The mRNA expression of specific biomarkers (SGLT1, SGLT5, GIP, GLP, LAT1, LAT2, and NPC1L1) in the mucosa was compared among three patient groups: Inflammation, Tumor, and Control. Results Sixty-six patients participated in this study. Both routes of DBE were performed in 20 patients, in whom biopsy samples were obtained from the mucosa for all sections. There were no remarkable differences in the mRNA expression levels among the 3 groups. However, SGLT1, GIP, GLP, and NPC1L1 exhibited specific distribution patterns. The expression levels of GIP and NPC1L1 were highest in the upper jejunum, but were extremely low in the terminal ileum and colon. A comparison of the mRNA expression profile in each intestinal section revealed that the SGLT1 mRNA expression in the Tumor group and the GIP mRNA expression in the Inflammation group were significantly higher than the corresponding levels in the Control group in the upper jejunum. Conclusion The gastrointestinal mucosa of patients with small bowel diseases can maintain proper nutrient absorption, except in the upper jejunum.
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