Human intestine luminal ACE2 and amino acid transporter expression increased by ACE-inhibitors.

Sodium-dependent neutral amino acid transporter B(0)AT1 (SLC6A19) and imino acid (proline) transporter SIT1 (SLC6A20) are expressed at the luminal membrane of small intestine enterocytes and proximal tubule kidney cells where they exert key functions for amino acid (re)absorption as documented by their role in Hartnup disorder and iminoglycinuria, respectively. Expression of B(0)AT1 was shown in rodent intestine to depend on the presence of the carboxypeptidase angiotensin-converting enzyme 2 (ACE2). This enzyme belongs to the renin-angiotensin system and its expression is induced by treatment with ACE-inhibitors (ACEIs) or angiotensin II AT1 receptor blockers (ARBs) in many rodent tissues. We show here in the Xenopus laevis oocyte expression system that human ACE2 also functionally interacts with SIT1. To investigate in human intestine the potential effect of ACEIs or ARBs on ACE2, we analysed intestinal biopsies taken during routine gastroduodenoscopy and ileocolonoscopy from 46 patients of which 9 were under ACEI and 13 ARB treatment. Analysis of transcript expression by real-time PCR and of proteins by immunofluorescence showed a co-localization of SIT1 and B(0)AT1 with ACE2 in the brush-border membrane of human small intestine enterocytes and a distinct axial expression pattern of the tested gene products along the intestine. Patients treated with ACEIs displayed in comparison with untreated controls increased intestinal mRNA levels of ACE2, peptide transporter PEPT1 (SLC15A1) and AA transporters B(0)AT1 and PAT1 (SLC36A1). This study unravels in human intestine the localization and distribution of intestinal transporters involved in amino acid absorption and suggests that ACEIs impact on their expression.

Noncoagulating Enteral Formula Can Empty Faster From the Stomach: A Double-Blind, Randomized Crossover Trial Using Magnetic Resonance Imaging.

BACKGROUND: The gastric accumulation of enteral formulas in tube-fed patients leads to an increased risk of vomiting and regurgitation. Gastric secretion-induced coagulation of proteins in enteral formulas might lead to gastric accumulation of solid protein particles that further increase the risk of upper digestive intolerance. This study used magnetic resonance imaging to noninvasively assess the half-emptying time (t50) of enteral formulas differing in protein composition. METHODS: Three isocaloric (450 kcal) and isovolumetric (300 mL) enteral formulas, 1 with a noncoagulating P4 protein blend and 2 with coagulating casein-dominant protein blends, were compared in a double-blind, randomized, 3-way crossover study in 21 healthy volunteers. Gastric content emptying curves were fitted with the LinExp model to compute t50 and the parameter κ with κ > 1 reflecting the accumulation of gastric secretion. t50 and κ were compared between all 3 enteral formulas. The formula that emptied fastest was identified by an ordinal mixed model using the ranks of t50. RESULTS: As indicated by values for κ > 1, all enteral formulas induced gastric secretion. No differences were detected for t50. However, the noncoagulating formula emptied fastest in 74% of all participants (P = .004). CONCLUSION: This study demonstrates that a noncoagulating enteral formula can empty faster from the stomach compared with coagulating formulas in a large cohort of healthy volunteers. Investigations on the efficiency of the noncoagulating P4 protein blend in patients requiring tube feeding will further elucidate its potential for reducing upper digestive intolerance during enteral nutrition. Trial NTR2979.