Platycodin D: A promising anti tilapia lake virus natural compound from Platycodon grandiflorus

Abstract

Tilapia lake virus (TiLV) poses a significant threat to the worldwide tilapia aquaculture sector, and there currently exists no efficient method of containment for this lethal pathogen. Given the widespread utilization of herbal medicines in the treatment of various aquatic animal diseases, it becomes imperative to evaluate and identify herbs that can be used for developing effective drugs against TiLV. We evaluated the efficacy of 20 herbs to inhibit TiLV proliferation in a TiLV infection model (Oreochromis niloticus) through two rounds of screening, with Platycodon grandiflorus extract showing the strongest inhibitory effect on TiLV replication (IC50 = 72.619 mg/L), survival of TiLV-infected tilapia was also improved in individual experiments. Platycodin D (PD), the principal bioactive compound found in Platycodon grandiflorus, demonstrated a dose-dependent reduction in viral load when used for treatment and enhanced the survival rate of tilapia infected with TiLV (42.3 %). The results of serum enzyme activity showed that PD treatment at a concentration of 5 mg/kg significantly enhance the non-specific parameters in tilapia (GSH, ACP, and AKP) (**p < 0.01). Additionally, immune-related gene analysis indicated that PD up-regulated IFN-I, CC2 and other genes expression while down-regulated the expression of pro-inflammatory factors (TNF-α, IL-1β) and TLR2 in the spleen and kidney of tilapia, implying that PD could induce IFN-I expression resulting in potential antiviral effects and inhibit some pro-inflammatory factors to alleviate oxidative stress and inflammatory responses in tilapia. The aforementioned findings suggest that Platycodon grandiflorus could potentially serve as a promising candidate for the development of drugs targeting TiLV. In particular, the bioactive component PD showed a strong anti-TiLV effect, which needs to be further explored.