Dietary Periplaneta americana chitin maintains inflammatory homeostasis and enhances innate immunity in juvenile common carp (Cyprinus carpio) via the Nrf2/NF-κB network.

This study systematically investigates the immunomodulatory and antioxidant properties of dietary chitin derived from the American cockroach (Periplaneta americana) in juvenile common carp (Cyprinus carpio), with emphasis on its tissue-dependent regulation of antioxidant and inflammatory responses. Juvenile carp (initial weight ∼5 g) were fed five isonitrogenous and isoenergetic diets supplemented with 0%, 2.5%, 5%, 10%, and 20% P. americana chitin for nine weeks. Results demonstrated that 2.5% chitin supplementation improved selected innate immune and antioxidant parameters, as evidenced by elevated serum immunoglobulin M (IgM), total antioxidant capacity (T-AOC), and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). At the tissue level, 2.5% inclusion reduced intestinal malondialdehyde (MDA) content, indicating mitigated lipid peroxidation, while enhancing specific antioxidant enzyme activities across the spleen, intestine, and head kidney. Mechanistically, the 2.5% dietary chitin modulated the expression of genes associated with the Nrf2-Keap1 axis in a tissue-dependent manner, rather than uniformly suppressing keap1 transcription. Furthermore, the 2.5% inclusion level was associated with the regulation of inflammatory homeostasis, as indicated by changes in the anti-inflammatory cytokine gene il-10, nf-κb, and downstream pro-inflammatory cytokine genes, including tnf-α and il-1β, in a tissue-dependent manner. Transcriptomic profiling (RNA-Seq) further corroborated these findings, identifying broad transcriptional changes across tissues, ranging from 1240 differentially expressed genes (DEGs) in the spleen to 5689 DEGs in the head kidney. These critical DEGs exhibited significant enrichment in core immune and redox pathways, including Toll-like receptor signaling, NOD-like receptor signaling, phagosome, and cytokine-cytokine receptor interactions. Notably, the modulatory effects exhibited tissue specificity and dose dependence; conversely, the high-dose inclusion level (20%) was associated with intestinal oxidative stress and reduced immune-related responses. In conclusion, 2.5% dietary P. americana chitin showed beneficial effects on selected antioxidant and innate immune responses in juvenile common carp, possibly associated with tissue-dependent modulation of Nrf2-Keap1 and NF-κB-related signaling.