The protective effect of glycyrrhizic acid on acetic acid–induced intestinal injury in Epinephelus coioides

Intestinal health is critical for nutrient absorption and immune defense in aquatic animals. Glycyrrhizic acid (GA), an active compound derived from licorice, possesses notable anti-inflammatory and antioxidant properties; however, its protective effects on the intestines of marine fish remain to be elucidated. This study aimed to evaluate the mitigating effects and potential mechanisms of dietary GA supplementation on acetic acid (AA)-induced intestinal injury in orange-spotted grouper (Epinephelus coioides). Fish were fed diets supplemented with varying concentrations of GA (0, 50, 100, 200, and 400 mg/kg) for 8 weeks, followed by intraperitoneal injection of AA to induce intestinal damage. Intestinal health was systematically assessed through histological examination, serum biochemical analyses, gene expression profiling, apoptosis assays, and 16S rDNA sequencing. Results indicated that AA exposure significantly disrupted intestinal architecture, elevated serum enzyme activities (ALP, AST, LDH), and upregulated the expression of inflammatory mediators (NF-κB, COX-2, CRP), pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), and apoptosis-related genes (caspase-3, caspase-8, caspase-9). Conversely, dietary GA supplementation, particularly at 200 mg/kg, effectively ameliorated these pathological alterations, as evidenced by restored intestinal morphology, reduced expression of inflammatory and apoptotic markers, and improved gut microbiota composition—characterized by increased abundance of probiotics such as Lactobacillus and decreased levels of Pseudomonas and Escherichia-Shigella. In conclusion, GA alleviated AA-induced intestinal injury in E. coioides through anti-inflammatory, anti-apoptotic, and microbiota-modulating mechanisms, providing theoretical support for its application as a functional feed additive in marine aquaculture.