Evaluating the in Vitro Efficacy of Quassinoids from Eurycoma longifolia and Eurycoma harmandiana against Common Cold Human Coronavirus OC43 and SARS-CoV-2 Using In-Cell Enzyme-Linked Immunosorbent Assay.

Coronavirus disease-2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, has become a pandemic and public health crisis. SARS-CoV-2 and the seasonal common cold coronavirus (HCoV-OC43) belong to the beta genus of human coronaviruses (HCoVs). In-cell ELISA assays were performed using HCoV-OC43 and SARS-CoV-2 and evaluated the antiviral activity of herbal plants. Eurycoma longifolia (EL) and Eurycoma harmandiana (EH) roots (antipyretic properties) and their constituent quassinoids, especially chaparrinone and eurycomalactone, showed potent anti-HCoV-OC43 and SARS-CoV-2 activities, and the low IC50 values of the mentioned constituents were observed in the range of 0.32-0.51 µM. Eurycomanone and 13ß,21-dihydroeurycomanone may contribute to the antiviral activity of EL, whereas chaparrinone is the major and active antiviral constituent of EH root. The content of quassinoids, ß-carboline, and canthin-6-one alkaloids and the cytotoxicity profile of EL and EH extracts were varied regarding extraction solvents. The boiled water and 50% EtOH extractions of both plants were less toxic than those with 95% EtOH as the extraction solvent. Our research suggests that quassinoids, which come from EL and EH roots and are anti-coronavirus compounds, are potential treatment candidates for COVID-19 and merit further in vivo investigations.

Effectiveness of neutral electrolyzed water in inactivating HCoV-OC43 and SARS-CoV-2 on the surfaces of plastic and the medicinal plant Centella asiatica (L.) urban.

Concerns have been raised about viral contamination, including in crops due to the recent coronavirus disease 2019 pandemic. Limited evidence is available to support the use of sanitizing agents for human coronavirus-contaminated medicinal plants. Thus, we aimed to investigate the persistence of infectious human coronavirus OC43 (HCoV-OC43) as a SARS-CoV-2 surrogate in storage conditions and the capability of neutral electrolyzed water (NEW) to inactivate coronavirus, including in fresh plants such as C. asiatica. The levels of infectious HCoV-OC43 and the triterpenoid content of C. asiatica were quantified using a plaque assay and high-performance liquid chromatography, respectively. The results showed that the persistence of HCoV-OC43 on C. asiatica leaves is identical to that on inert polystyrene. When covered and kept at room temperature with high humidity (>90% RH), HCoV-OC43 can be stable on C. asiatica leaves for at least 24 h. NEW with 197 ppm of available chlorine concentration (ACC) was effective in inactivating both infectious HCoV-OC43 and SARS-CoV-2 in suspension (≥3.68 and ≥4.34 log reduction, respectively), and inactivated dried HCoV-OC43 on the surfaces of C. asiatica leaves (≥2.31 log reduction). Soaking C. asiatica leaves for 5 min in NEW with 205 ppm of ACC or water resulted in significantly higher asiaticoside levels (37.82 ± 0.29 and 35.32 ± 0.74 mg/g dry weight, respectively), compared to the unsoaked group (29.96 ± 0.78 mg/g dry weight). These findings suggest that although coronavirus-contaminated C. asiatica leaves can pose a risk of transmission, NEW could be an option for inactivation.