Umbelliferone immersion therapy controls viral hemorrhagic septicemia virus in olive flounder (Paralichthys olivaceus) via direct virucidal and immunomodulatory effects.

Abstract

Viral hemorrhagic septicemia virus (VHSV) is a major threat to global aquaculture, but no effective therapeutics currently exist. In this study, we identified umbelliferone (7-hydroxycoumarin) as a potent immersion-based antiviral agent against VHSV. Umbelliferone showed complete direct virucidal effects in vitro concentration- and time-dependently. Molecular docking predicted umbelliferone may bind to the pleckstrin homology domain of VHSV glycoprotein, a possible mechanism for viral inhibition. Immersion treatment of olive flounder (Paralichthys olivaceus) decreased the VHSV replication in na&#xef;ve recipients and infected donors after cohabitation for 72&#xa0;h. Efficacy of umbelliferone on the challenged fish was tested, with the efficacy of immersion treatment increasing with shorter immersion periods. Immersion for 2&#xa0;h&#xa0;&#xd7;&#xa0;3 days at 10&#xa0;mg/L had the highest efficacy, improving survival up to 90&#xa0;% (P < 0.0001) by suppressing viral gene expression and the viral titer. Umbelliferone was found to modulate key innate immune responses, including the downregulation of ifn-&#x3b1; and the upregulation of ifn-&#x3b3;, isg15 in the kidneys, and proinflammatory cytokines in the skin. Subsequent pharmacokinetic analysis based on immersion treatment at 10&#xa0;mg/L revealed rapid distribution, and elimination in olive flounder. Cbeing lower than in vitro ICof 13.86&#xa0;&#x3bc;g/mL suggested pivotal role of immunomodulation than direct virucidal activity in conferring efficacy. Umbelliferone exhibited a half-life of 8.1 days at 15&#xa0;&#xb0;C in seawater, highlighting its fast degradation in environment and warranting environmental safety assessment. Overall, umbelliferone immersion treatment is safe and practical, positioning it as a promising candidate for the control of VHS in aquaculture.