Glycyrrhetinic acid reverses antibiotic-induced intestinal epithelial injury through RNA-binding protein human antigen R (HuR)

Background: The application/abuse of antibiotics can cause antibiotic-induced intestinal injury (AIJ), a typical clinical issue that disturbs intestinal homeostasis. However, the underlying post-transcriptional mechanism of AIJ remains unknown. Glycyrrhetinic acid (GA) is one of the main components of Glycyrrhiza uralensis Fisch. and Glycyrrhiza inflata Batalin (Fabaceae), and findings of our previous study showed that GA can maintain intestinal homeostasis post-transcriptionally through the RNA-binding protein human antigen R (HuR). Purpose: This study aimed to elucidate the role of HuR in AIJ and the protective effects of GA on AIJ. Study design and methods: Clindamycin hydrochloride was used to clarify the effect of the antibiotic on the intestinal epithelium. Intestinal epithelium cell-6 (IEC-6) and Caco2 cells were used to demonstrate the in vitro effects of the antibiotic and GA on intestinal cells. HuR plasmid and siRNA were used to overexpress or silence HuR in vitro. SD rats were induced by using clindamycin hydrochloride capsules (250 mg/kg i.g.) for 7 consecutive days to construct the in vivo AIJ model. Rats of the AIJ model group were administrated GA (10 and 20 mg/kg i.g.) for 7 days, and subsequently, the protective effect of GA on the intestinal epithelium was evaluated. Results: In vitro results showed that the antibiotic (150-500 mu M) suppressed proliferation, induced a delay in restitution after wounding, and caused cell cycle arrest at the G0/G1 phase in IEC-6 and Caco-2 cells. Moreover, the expression levels of HuR and its downstream gene, occludin and cyclin D1, decreased after treatment with the antibiotic (500 mu M). Overexpression of HuR and GA (10 and 20 mu M) reversed the antibiotic-induced inhibition of proliferation and G0/G1 phase arrest, and the antibiotic-induced decrease in HuR, occludin, and cyclin D1 expression was reversed after GA treatment (10 and 20 mu M) in IEC-6 cells. In vivo results revealed the antibiotic-induced epithelial injury of both the small intestines (shortened and spared mucosa) and the large intestines (injured/deformed glands, reduced number of cup cells, and evident inflammatory cell infiltration), all of which were ameliorated after GA treatment (10 and 20 mu M). Conclusion: Antibiotics induce intestinal epithelial injury through HuR, and GA can exert a protective effect on AIJ by restoring HuR levels.