Modulation of intestinal microbiota and metabolites mediates the improvement of cyclophosphamide-induced immunodeficiency in mice by Monopterus albus slime protein.

Immunodeficiency significantly compromises host defense mechanisms and contributes to various pathologies. Monopterus albus whole slime (MS) is an underutilized aquatic by-product rich in proteins. This study examined the therapeutic effects and underlying mechanisms of MS and its purified protein (MSP) against cyclophosphamide (CTX)-induced immunodeficiency in mice. The results revealed that MSP significantly increased body weight, immune organ indices (spleen and thymus), cellular immune parameters (including counts of WBC, PLT, lymphocyte, and granulocyte), and humoral immune markers (including serum levels of IFN-γ, IL-2, and IgA) in immunocompromised mice. Furthermore, MSP demonstrated superior efficacy compared to MS in promoting thymic recovery and enhancing IgA production (p < 0.05). Concurrently, MSP ameliorated intestinal integrity through improved villus structure, upregulation of tight junction proteins (ZO-1 and occludin), attenuation of oxidative stress (evidenced by decreased MDA level and increased SOD and GSH-Px activities), and elevated secretory IgA (SIgA) levels. Gut microbiota analysis indicated that MSP promoted the enrichment of beneficial bacterial genera (norank_f__Muribaculaceae, Muribaculum) while suppressing pathogenic bacteria (Desulfovibrio, Lachnospiraceae_UCG-006, Eubacterium_xylanophilum_group). Fecal metabolomic analysis revealed that both MS and MSP altered the profiles of various metabolites, with enriched pathways involved in nucleotide metabolism, ABC transporters, and taurine and hypotaurine metabolism. Collectively, these findings suggest that MSP may mitigate CTX-induced immunodeficiency through a potential "gut microbiota-metabolite-intestinal barrier" axis, thereby establishes the theoretical groundwork for the development of slime-derived proteins as potential immunomodulatory agents.