Salvianolic acid A exerts antiviral effects by targeting the S protein, a virulence factor of porcine epidemic diarrhea virus.

Porcine epidemic diarrhea virus (PEDV), a member of the Coronaviridae family, infects the small intestinal epithelial cells of pigs, causing porcine epidemic diarrhea (PED), which is particularly severe in young piglets. Owing to its strong immunogenicity, the S1 subunit of the PEDV spike (S) protein mediates viral invasion by recognizing host cell receptors and inducing neutralizing antibodies. However, effective antiviral drugs against PEDV are lacking, and current control measures are limited. In this study, the truncated S1 protein was expressed and used in surface plasmon resonance screening of 416 natural compounds. Salvianolic acid A (SalA) exhibited the strongest antiviral activity against PEDV, with a dissociation constant KD of 4.54 × 10⁻⁷ M. Molecular docking revealed multiple hydrogen bonds between SalA and key amino acid residues of the S1 protein. In vitro assays demonstrated that SalA significantly reduced viral RNA copy number, titer, and N protein expression in a dose-dependent manner. SalA inhibited viral adsorption, replication, and release and showed direct virucidal activity. In a piglet challenge model, SalA treatment improved survival, alleviated clinical symptoms and intestinal lesions, and reduced viral loads in blood, feces, and tissues. Overall, SalA was identified as a potent natural compound that targets the PEDV S1 protein and exhibits strong antiviral effects both in vitro and in vivo, highlighting its promise as a therapeutic candidate for PEDV infection. IMPORTANCE: Porcine epidemic diarrhea virus (PEDV) causes severe diarrhea and high mortality in piglets, resulting in substantial economic losses to the global swine industry. However, effective antiviral therapeutics are still lacking. In this study, salvianolic acid A (SalA), a natural polyphenolic compound derived from Salvia miltiorrhiza, was identified as a potent inhibitor of PEDV through direct targeting of its spike (S1) protein. SalA efficiently suppressed viral replication, release, and infectivity in vitro and markedly alleviated intestinal damage, viral load, and clinical symptoms in infected piglets. Molecular docking and dynamic simulations further confirmed the stable binding between SalA and the S1 protein. Overall, this study provides the first comprehensive experimental evidence that SalA exhibits both prophylactic and therapeutic antiviral activities against PEDV, clearly highlighting its potential as a promising lead compound for the development of effective antiviral drugs to control PEDV and related coronavirus infections in livestock.