Synergistic effects of the ß-1,3 glucan paramylon and vitamin C on immunological responses of hybrid striped bass (Morone chrysops × M. saxatilis) were pronounced in vitro but more moderate in vivo

Authors: YAMAMOTO, FERNANDO - Texas A&M University; CASTILLO, SERGIO - Texas A&M University; DE CRUZ, CLEMENT - Texas A&M University; CHEN, KEQUAN - Texas A&M University; Hume, Michael; GATLIN, DELBERT - Texas A&M University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2020
Publication Date: 9/15/2020
Citation: Yamamoto, F.Y., Castillo, S., De Cruz, C.R., Chen, K., Hume, M.E., Gatlin, D.M. 2020. Synergistic effects of the ß-1,3 glucan paramylon and vitamin C on immunological responses of hybrid striped bass (Morone chrysops × M. saxatilis) were pronounced in vitro but more moderate in vivo. Aquaculture. 526(2020). Article 735394. https://doi.org/10.1016/j.aquaculture.2020.735394.
DOI: https://doi.org/10.1016/j.aquaculture.2020.735394

Interpretive Summary: The objective of this study was to evaluate if dietary beta-glucan (BG), a long-chain complex sugar, stimulation of the hybrid striped bass (HSB) immune system could be enhanced by vitamin C (vit. C). Two separate trials were conducted in test tubes and in live HSB. Treatment of HSB blood with BG significantly increased antibacterial protein activity. Treatment of blood with vit. C increased the concentration of protective immunity proteins. Treatment of blood and isolated white blood cells with vit. C and BG together decreased concentrations of harmful oxygen molecules. Next, feeding BG to live HSB significantly decreased fish growth and water content in body tissues. Feeding BG to HSB significantly increased protective immunity proteins in the blood, increased compounds protective against harmful oxygen molecules, and increased proteins in the intestine protective against bacteria. An additive effect was seen when feeding both BG and vit. C to the HSB to increase protective proteins in the intestine and protection in the blood against harmful oxygen molecules. In conclusion, enhanced effects were observed for inclusion of vit. C with BG in the diet of HSB with protective results in the blood and the intestine. Based on the results from both trials in the test tube and in live HSB, additive effects were observed between BG and vit. C on the immune system. Results were greater in the test tube experiments than in live HSB experiments. These results are of interest to researchers and producers seeking alternatives to traditional antimicrobials in aquaculture production. Results demonstrate the use of readily available natural compounds to enhance the immune system and fight harmful intestinal bacteria in HSB.

Technical Abstract: The objective of this study was to evaluate if beta-glucan (BG) immunostimulation could be further enhanced synergistically with vitamin C (vit. C) for hybrid striped bass (HSB). Two separate trials were conducted ex vivo and in vivo, using a 2 × 2 factorial design, where the main effects were BG and vit. C. Paramylon, a BG derived from Euglena gracilis, vit. C (as dehydroascorbic acid), or their combination (BG + vit. C), were incubated with HSB whole blood and isolated phagocytes ex vivo to measure possible synergistic effects on various immunological responses. Supplementation of BG in the whole-blood significantly (P<0.001) increased the plasma lysozyme activity, and vit. C supplementation increased the concentration of total protein (P<0.01) and immunoglobulins (P<0.001) in the plasma. Synergistic effects (P<0.0001) were observed for the production of reactive oxygen species in whole-blood and isolated phagocytes. After corroborating the interaction of BG and vit. C ex vivo, a feeding trial was conducted using HSB juveniles (~9.30 g initial weight). Fish were fed diets with 100 mg of BG kg**-1, 500 mg of vit. C kg**-1 or their combination (100 mg of BG + 500 mg of vit. C kg**-1). A basal diet with no supplementation served as the control. Fish were fed for 8 weeks after which production parameters were recorded, and proximate composition of whole-body tissues, blood components, phagocytes isolated from the head kidney, intestinal microbial composition, and enzyme activities in intestinal sections were analyzed. Supplementation of BG slightly but significantly (P<0.05) impaired HSB growth performance and feed efficiency and decreased the moisture content of whole-body tissues when compared to the non-supplemented group. However, fish fed diets supplemented with BG presented higher (P<0.05) concentrations of plasma immunoglobulins, intracellular superoxide anion production, acid phosphatase activity in the posterior part of the intestine, and lysozyme activity in the anterior part of the intestine. A synergistic effect between BG and vit. C was highly significant (P<0.0001) for acid phosphatase activity in the anterior part of the intestine, and significant (P<0.05) for whole-blood respiratory burst. Dietary treatment did not affect the microbial composition of the transient digesta. Based on the results from both trials, synergistic effects between BG and vit. C on immunological responses of HSB were observed but more pronounced in the ex vivo experiment.