A study was conducted to investigate the antiviral activity of aqueous extracts from Orthosiphon stamineus (OS). Extraction was done using different parts of OS. The whole plant except root (WPOS), leaves (LOS) and flowers (FOS) of OS were extracted using aqueous extraction method. Cytotoxicity was assessed using 3-(4,5-dimethylthiazol-2,5-diphenyl tetrazolium bromide (MTT) assay. Plaque reduction assays were carried out to evaluate the antiviral activity of OS extract against herpes simplex virus type 1 (HSV-1). These include post-treatment, pre-treatment and virucidal assays. High antiviral activity was observed in post-treatment and virucidal assay with 100% reduction of HSV-1 plaque at 0.39 mg/ mL in LOS, FOS and WPOS. In pre-treatment assay, 79%, 84% and 97% plaque reduction using the same concentration was observed in FOS, LOS and WPOS, respectively. In conclusion, this study showed that OS aqueous extract has promising potential to be explored as anti-HSV-1 agent regardless of the mode of treatment.
Aims: Phytochemical analysis showed Orthosiphon stamineus (OS) possessed bioactive compounds with antiviral properties against Herpes Simplex Virus Type 1 (HSV-1). However, there isn't any study reported so far on OS virucidal properties towards HSV-1. Thus, this study aims to investigate virucidal mechanism of OS aqueous extract that possibly acts as a potent entry inhibitor against HSV-1 infection. Methodology and results: Virucidal attachment and penetration assays were done via plaque assay to investigate the virucidal anti-HSV-1 mechanism of OS. The aqueous extract of OS leaves (OSA) was found to reduce HSV-1 plaques in virucidal assays. Inhibitory effect by OSA was observed as early as 30 min after exposing OSA to HSV-1 in a concentration-dependent manner suggesting a direct anti-HSV-1 property of OSA. Further investigation of the stages in which OSA inhibits HSV-1 shows virions treated with OSA failed to attach onto the host cell which implicated a role of OSA in blocking HSV-1 attachment to its host. OSA was also found to reduce HSV-1 plaques in penetration assay. Further evaluation using transmission electron microscopy (TEM) on OSA treated virion showed defective HSV-1 virion without envelope and the remaining capsid was altered. Conclusion, significance and impact of study: These findings concluded that Orthosiphon stamineus leaves extract have virucidal activity by disintegrating HSV-1 virion structure and interfering with the attachment and penetration of the virus into the host cell. Thus, through the new mechanism against HSV-1, OS has the potential to be further developed as an anti-HSV-1 agent.
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