胆汁酸可使肠外营养动物恢复肠道微生物多样性

　　营养支持的同时使用相关药物或药理营养素可改善肠黏膜的萎缩。圣路易斯大学、威斯康星儿童医院、韦恩州立大学通过对乳猪研究，发现单纯给予肠外营养（PN）会导致肠黏膜萎缩，肠道微生物多样性降低。而肠内给予胆汁酸受体激动剂齐墩果酸，可使肠重量、绒毛高度/隐窝深度比值（v/c）增加，减轻肠黏膜萎缩，并恢复肠道微生物多样性。这些作用可能是通过增加肠上皮G蛋白偶联受体TGR5的表达，上调肝细胞胆汁酸转运体来实现的。

JPEN J Parenter Enteral Nutr. 2016;40(4):115.

Preserved Gut Microbial Diversity Accompanies Upregulation of TGR5 and Hepatobiliary Transporters in Bile Acid-Treated Animals on Parenteral Nutrition.

Jain AK, Sharma A, Arora S, Blomenkamp KS, Jun I, Luong R, Westrich D, Mittal A, Long JP, Teckman J.

Saint Louis University, St Louis, MO, USA; Children's Hospital of Wisconsin, Milwaukee, WI, USA; Wayne State University, Detroit, MI, USA.

PURPOSE: Parenteral nutrition (PN) is a lifesaving therapy where essential nutrients are delivered via intravenous access. This therapy bypasses the enteric system in critically ill patients unable to tolerate enteral nutrition (EN). While the role of PN in clinical settings cannot be understated, the benefits of this lifesaving therapy tend to come at the cost of severe gut mucosal atrophy and gut inflammation. TGR5, a G-protein-coupled receptor, has been shown to modulate intestinal growth and immune responses. Recent evidence also indicates that the gut mucosal barrier is influenced by the gut microflora. Additionally, inflammation is known to downregulate hepatobiliary transporters bile salt export pump (BSEP) and sodium taurocholate cotransporting polypeptide (NTCP) involved in the normal enterohepatic circulation. We hypothesize that bile acid (BA) treatment regulates TGR5 and induces gut microbial changes contributing to improved pathology.

METHODS: Based on our previously published ambulatory PN animal model, piglets (n = 12) were randomized to receive approximately 2 weeks of isocaloric enteral swine milk (EN), PN only, or PN with an enteral BA receptor agonist, oleanolic acid (OA). Tissue, serum, and feces were collected. Culture-independent identification of fecal bacterial populations was determined by 16S rRNA sequencing. Sequences were subjected to the unweighted UniFrac metric. Statistical analysis was performed with Jackknife sample clusters found in the UniFrac workflow. Additionally, sequences were classified up to the genus level via the RDP Classifier algorithm. Alpha diversity was calculated at the phylum level with Shannon's diversity index.

RESULTS: PN resulted in marked gut atrophy when compared with EN animals. OA led to preservation of gut mass, demonstrated grossly and histologically. The mean gut density (g/cm, ± SD) was 0.31 ± 0.03 for EN, 0.18 ± 0.03 for PN (P < .05 EN vs PN), and 0.27 ± 0.01 for PN + OA (P < .05, PN + OA vs PN). OA preserved the markedly decreased villous:crypt ratio noted with PN. The mean ratio was 3.51 ± 0.59 for EN, 1.69 ± 0.10 for PN (P < .05, EN vs PN), and 2.90 ± 0.23 for PN + OA (P < .05, PN + OA vs PN). Gut TGR5 mRNA expression was significantly elevated with OA. When normalized for EN, mean TGR5 transcript value was 0.91 ± 0.14 for PN vs 2.27 ± 0.58 for OA. Additionally, there was a trend for NTCP and BSEP upregulation with OA. In subgroup analysis, clustering was noted with unweighted UniFrac metric based on the treatment. Branch points were supported by Jackknife analysis for PN vs other groups but not well supported for the other branches (>95% for PN). Additionally, a shift toward the proinflammatory phylum Bacteroidetes was noted with PN based on the RDP classifier algorithm. No statistical difference with the Bacteroidetes phylum was noted in EN or PN + OA animals (P = .4). Furthermore, the mean alpha diversity was significantly different among the groups (df = 2, F = 61.57, P < .0001) at 0.1351, 0.6403, 1.077 for PN, EN, and PN + OA, respectively.

CONCLUSIONS: We show that microbial communities diverge with PN. Such therapy leads to an overall reduced microbial diversity and gut atrophy. Additionally, a statistically significant expansion of the proinflammatory phylum Bacterioides occurs in PN animals. This study thus explores a potential novel relationship between gut microbiota and key mediators in the enterohepatic circulation. It provides direct evidence that treatment with BA receptor agonists, while upregulating TGR5, BSEP, and NTCP, also preserve gut growth and microbial diversity.

FINANCIAL SUPPORT: American Society for Parenteral and Enteral Nutrition, North American Society for Pediatric Gastroenterology Hepatology and Nutrition.