Effects of Dietary Bitter Melon Extract on Growth Performance, Antioxidant Capacity, Inflammatory Cytokines Expression, and Intestinal Microbiota in Common Carp (Cyprinus carpio L.)

Abstract

Bitter melon extract (BME), which contains a variety of natural bioactive substances, has diversified biological functions. The present study is aimed at evaluating the effects of dietary supplementation of BME on growth performance, antioxidant capacity, inflammatory cytokine expression, and intestinal microbiota in common carp (Cyprinus carpio L.). An 8-week feeding trial was conducted using four isonitrogenous and isoenergetic diets containing different levels of BME (0%, 0.25%, 0.5%, and 1% for control, LBME, MBME, and HBME groups, respectively). The results showed that there were no significant differences in the growth performance of common carp among all groups, including final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), and viscera index (VSI) ( $p>0.05$ ), but the condition factor (CF) was decreased by all BME treatments ( $p<0.05$ ). Serum superoxide dismutase (SOD) activity was significantly improved in all BME groups ( $p<0.05$ ), and serum catalase (CAT) activity was significantly higher in the MBME group ( $p<0.05$ ). Serum malondialdehyde (MDA) level was lowest while serum total antioxidant capacity (T-AOC) was highest in the HBME group ( $p<0.05$ ). Dietary BME supplementation inhibited proinflammatory cytokine (il-1β and il-8) mRNA expression, while anti-inflammatory cytokine (il-6 and il-10) mRNA expressions were promoted ( $p<0.05$ ). Furthermore, principal coordinate analysis (PCoA) showed that there were no differences in bacterial communities among different groups, and Shannon index and Simpson index of intestinal microbiota were unaffected ( $p>0.05$ ). Whereas dietary BME reduced Firmicutes abundance and the ratio of Firmicutes to Bacteroidetes at phylum level, the relative abundance of streptococcaceae at family level, Streptococcus and Exiguobacterium at genus level were also decreased ( $p<0.05$ ). Overall, these results suggested that dietary supplementation of BME improved serum antioxidant capacity, anti-inflammatory activity, and modified intestinal microbiota in common carp.