Anti-inflammatory and immunostimulant effect of different timing-related administration of dietary polyphenols on intestinal inflammation in zebrafish, Danio rerio

A short-term study was performed to assess the effects of diets supplemented with polyphenols (CSVP), extracted from the chestnut (Castanea sativa) shell, agri-food waste rich in tannins, and mullein (Verbascum macrurum), a perennial spontaneous plant rich in flavonoids, on a zebrafish (Danio rerio) model of k-carrageenan-induced intestinal inflammation. Morphological asset of intestine, immunodensity of the pro-inflammatory mediator Tumor necrosis factor α (TNFα) and Cyclooxygenase-2 (COX-2), immunoexpression of the two antioxidant enzymes Catalase (Cat) and Superoxide dismutase 2 (Sod2), quantitative gene expression of pro- and anti-inflammatory cytokines including TNFα, COX2A, Interleukin-1β (IL-1β) and IL-10, and the activated cell pathways were analyzed. Seven experimental diets were formulated including: peeled A. salina (Control group), peeled A. salina + 0.1% of k-carrageenan (Inflamed group), peeled A. salina + CSVP followed by k-carrageenan inflammatory diet (CSVP pre-treated group), peeled A. salina + 0.1% of k-carrageenan + CSVP (CSVP co-treated group), peeled A. salina + 0.1% of k-carrageenan followed by CSVP (CSVP post-treated group), peeled A. salina + CSVP (CSVP group) and peeled A. salina + 0.1% of k-carrageenan followed by 10 days of control diet (polyphenols control group or CP) to determine the efficacy of schedule administering polyphenols in preventing or ameliorating the intestinal inflammation induced in adult zebrafish by k-carrageenan with mean weight of 400 ± 100 mg (mean ± SD; total n = 250). The obtained results indicated that k-carrageenan caused morphological alterations such as the decrease of intestinal folds with consequent expansion of gut lumen, and increased number of goblet cells, as well as the over-regulation of pro-inflammatory markers and reduction of the antioxidant enzymes immunoexpression. Polyphenols supplementation ameliorated the inflammatory status, downregulated the pro-inflammatory markers, and upregulated IL-10, the main anti-inflammatory cytokine, and antioxidant activity when administered before the inflammation caused by k-carrageenan. The post- and co-treatment reverted only in part the morphological and physiological alterations. Moreover, the results showed that polyphenols modulated the anti-inflammatory effects acting on the Mitogen-activated protein kinase (MAPK) pathway, by inhibiting p38 phosphorylation and increasing extracellular-signal-regulated kinase (ERK) activation, which subsequently led to suppression of nuclear factor kappa B cells (NF-kB) pathway. Based on the findings achieved, the scheduled administration of bioactive phytochemicals like polyphenols could represent a suitable strategy for ameliorating intestinal inflammation in zebrafish and could be considered as a beneficial and sustainable feed additive in the aquaculture sector.