Exposure of Zebrafish to Cadmium and Melatonin Induces Changes in Gut Organization,Oxidative Damage,and Microbial Diversity
Cadmium(Cd)is a heavy metal and a globally common and highly toxic environmental pollutant that can threaten aquatic health through oxidative stress.Melatonin(MT),a known antioxidant and free radical scavenger,has been shown to be effective in mitigating heavy metal-induced intestinal damage.However,only a few studies have been conducted on the use of MT to ameliorate Cd-induced oxidative damage and improve microbial diversity in the intestinal tissues of aquatic organisms.In this study,adult zebrafish(Danio rerio)were used as experimental subjects for a 30-day exposure experiment using a semi-static exposure method,which was divided into four groups:control group,Cd group,MT group,and Cd+MT group(mixture of the two substances).Intestinal pathology slides were used to determine intestinal hydrogen peroxide(H2O2),malondialdehyde(MDA)content,superoxide dismutase(SOD),and glutathione peroxidase(GSH-PX)activities.Intestinal flora Alpha and Beta diversity,intestinal flora composition,relative abundance of dominant flora,and biomarkers of each group were analyzed by high-throughput sequencing of intestinal flora 16SrDNA.The results showed that the intestinal wall of zebrafish in the Cd group was thinned,the intestinal villi appeared to be partially abraded and detached,the tips of the villi were exposed,the epithelial gap of the intestinal villi was enlarged,the number of vacuolated cells was increased,the cells were extensively lysed,the cytoplasmic damage was dispersed,and the phenomenon of relaxation of connective tissues occurred simultaneously,whereas the intestinal tissues of the zebrafish that were co-exposed to Cd and MT were partly restored to the integrity of the intestinal tissues,and the phenomenon of intestinal damage was significantly reduced.Cd led to a significant increase in zebrafish intestinal MDA and H2O2 content and a significant decrease in GSH-PX and SOD activities.However,co-treatment decreased H2O2 and MDA content and elevated GSH-PX and SOD activities.16SrDNA sequencing revealed that Cd caused changes in the diversity of zebrafish intestinal flora,the Shannon index and Simpsoneven index increased,and the number of dominant flora decreased,while the addition of MT alleviated the effect of Cd on intestinal flora diversity and partially restored dysbiosis to a certain extent.The current study showed that melatonin could reduce Cd-induced oxidative damage and protect the diversity of intestinal flora in adult zebrafish caused by Cd,which provides a theoretical basis for the development of products against Cd poisoning.
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