article · Biochemistry
Production of all-male Nile tilapia fry relies heavily on the synthetic androgen 17alpha-methyltestosterone, but this hormone disrupts the immune system of the fish. Supplementing with vitamin C helps counteract this immunotoxicity. Combining vitamin C with the hormone resulted in the highest levels of phagocytic activity, phagocytic index, and lysozyme activity, reversing the suppression of phagocytic measures seen with the hormone alone. Vitamin C also reduced the elevated expression of several innate immune-related genes triggered by the hormone, including interleukin 1beta, interleukin 8, tumor necrosis factor alpha, CC-chemokine, Toll-like receptor 7, immunoglobulin M heavy chain, and cellular apoptosis susceptibility. Furthermore, the combination significantly improved micronucleus frequency compared to hormone treatment alone. While internal organs showed mostly normal structure across groups, melanomacrophage centres appeared frequently in the spleen and kidney of fish receiving vitamin C. Upregulation of immune-related genes was notably found not to equate directly to enhanced immunity.
Commercial fish farming depends on hormones to produce male tilapia, yet these treatments compromise fish immunity and health. Demonstrating that vitamin C can offset the immune damage caused by synthetic androgens offers a practical method to protect stock health. This insight also clarifies that higher expression of immune genes does not always mean an animal has a stronger, healthier immune system.
Hatcheries and tilapia producers could potentially use vitamin C as a feed additive during hormonal sex-reversal protocols to protect fry from immune damage and genetic toxicity. The findings represent applied, tested laboratory research that directly targets standard aquaculture practices. Further validation would be required before establishing commercial feed formulation guidelines or protocols for industrial fish farming operations.
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The synthetic androgen 17α-methyltestosterone (MT) is profusely used and practically needed in the production of all-male Nile tilapia fry; however, such androgenic hormones badly disrupt the immune system. This study aimed to alleviate or counteract the immunotoxic effect of MT using vitamin C (ascorbic acid or vit C). Our results show that the highest phagocytic activity (PA), phagocytic index (PI), and lysozyme activity were detected in the vit C group and the MT plus vit C group. Furthermore, PA and PI were significantly suppressed, but lysozyme activity was stronger in the MT group than in the control. No differences were detected in the differential leukocyte count among the studied groups. Moreover, vit C obviously reduced the upregulated expression level of the innate immune-related genes, interleukin 1β (il1β), interleukin 8 (il8), tumor necrosis factor α (tnfα), CC-chemokine, Toll-like receptor 7 (tlr7), immunoglobulin M (IgM) heavy chain, and cellular apoptosis susceptibility (cas) induced by MT, excluding tnfα in the liver and CC-chemokine and tlr7 in the kidney. The micronucleus frequency was found to significantly improve in the vit C plus MT group in comparison to that in the MT group. Normal histoarchitecture of the liver, kidney, and spleen was observed in all the groups, except for the frequently observed melanomacrophage centers in the spleen and kidney of the fish that were treated with vit C and vit C plus MT. More importantly, our findings demonstrate that the upregulation of immune-related genes is not necessarily a sign of a stimulated or enhanced immune system.
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DOI: 10.1021/acs.biochem.6b01284
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