Ethyl palmitate, an anti-chikungunya virus principle from Sauropus androgynus, a medicinal plant used to alleviate fever in ethnomedicine

Abstract

Ethnopharmacological relevance: Sauropus androgynus is a medicinal shrub used for the treatment of fever in ethnomedical traditions in various Southeast Asian countries.

Aim of the study: This study was aimed to identify antiviral principles from S. androgynus against Chikungunya virus (CHIKV), a major mosquito-borne pathogen that re-emerged in the last decade, and to unravel their mechanism of action.

Materials and methods: Hydroalcoholic extract of S. androgynus leaves was screened for anti-CHIKV activity using cytopathic effect (CPE) reduction assay. The extract was subjected to activity guided isolation and the resultant pure molecule was characterized by GC-MS, Co-GC and Co-HPTLC. The isolated molecule was further evaluated for its effect by plaque reduction assay, Western blot and immunofluorescence assays. In silico docking with CHIKV envelope proteins and molecular dynamics simulation (MD) analyses were used to elucidate its possible mechanism of action.

Results: S. androgynus hydroalcoholic extract showed promising anti-CHIKV activity and its active component, obtained by activity guided isolation, was identified as ethyl palmitate (EP), a fatty acid ester. At 1 μg/mL, EP led to 100% inhibition of CPE and a significant 3 log₁₀ reduction in CHIKV replication in Vero cells at 48 h post-infection. EP was highly potent with an EC₅₀ of 0.0019 μg/mL (0.0068 μM) and a very high selectivity index. EP treatment significantly reduced viral protein expression, and time of addition studies revealed that it acts at the stage of viral entry. A strong binding to the viral envelope protein E1 homotrimer during entry, thus preventing viral fusion, was identified as a possible mechanism by which EP imparts its antiviral effect.

Conclusions: S. androgynus contains EP as a potent antiviral principle against CHIKV. This justifies the use of the plant against febrile infections, possibly caused by viruses, in various ethnomedical systems. Our results also prompt more studies on fatty acids and their derivatives against viral diseases.

Keywords: Activity guided isolation; Ethnomedicine; Ethyl palmitate; MD simulation; Plaque assay; Sauropus androgynus; anti-Chikungunya virus activity.