Nile crab Potamonautes niloticus shell extract: Chromatographic and molecular elucidation of potent antioxidant and anti-inflammatory capabilities

Diseases emerging from oxidative stress and inflammatory imbalance are deeply threatening the modern world. Fisheries by-products are rich in bioactive metabolites. However, they are usually discarded, posing a real environmental burden. Herein we aimed to explore the bioactive compounds, anti-oxidant, and anti-inflammatory capabilities of the shell of the freshwater Nile crab Potamonautes niloticus. Methanolic extract of crab shell was subjected to GC/MS and HPLC analyses of total lipids, flavonoids, and phenolic acids. Also, zebrafish Danio rerio was subjected to inflammatory status using CuSO4, then treated with different doses of shell extract. Total antioxidant capacity and QPCR analyses for gene expression of different antioxidant enzymes, i.e. superoxide dismutase(sod), catalase (cat), and glutathione peroxidase (gpx) and pro-inflammatory cytokines, i.e. tumor necrosis factor alpha (tnf-alpha), nuclear factor kappa B (nf-kappa b), interleukin 1-Beta (il-1b) were assessed. The results showed the richness of crab shell extract with omega -9 (32.78 %), omega -7 (6.37 %), and omega -6 (4 %) unsaturated fatty acids. Diverse phenolic acids and flavonoids were found, dominaed by Benzoic acid (11.24 mu g mL(-1)), Syringic acid (11.4 mu g mL(-1)), Ferulic acid (10.55 mu g mL(-1)), Kampferol (9.47 mu g mL(-1)), Quercetin (6.33 mu g mL(-1)), and Naringin (4.16 mu g mL(-1)). Crab extract also increased the total antioxidant capacity and oxidative stress enzymes mRNA levels by 1.3-2.15 folds. It down-regulated pro-inflammatory cytokines mRNA levels by 1.3-2 folds in comparison to positive control (CuSO4-induced) zebrafishes. The net results indicated that Nile crab shell extract is a rich source of anti-oxidant and anti-inflammatory compounds. Therefore, we recommend to continuously explore the bioactive capabilities of exoskeletons of different shellfish species. This can provide additive values for these products and reduce the environmental burden of their irresponsible discarding.