In this study, we investigated the
antiviral activity of lyophilized crude leaf extracts of the Philippine marshmint (Mentha arvensis L., commonly called yerba buena) against DENV-2 in vitro. The plant specimen was authenticated by
DNA barcoding analysis using standard primers for amplification of rbcL, matK, ITS1, ITS2 and trnH-psbA. Aqueous,
methanol and
ethanol leaf extracts were prepared, and lyophilized prior to testing for its cytotoxicity and
antiviral activities. All extracts presented cytotoxic activities against Vero cells in a dose-dependent manner. Half maximal cytotoxicity concentration (CC50) was calculated at 2,889.60 µg/mL for the aqueous extract, 1,928.62 µg/mL for the
methanol extract, and 3,380.30 µg/mL for the
ethanol extract.
Antiviral activities assessed by plaque reduction assay revealed reduced DENV-2 viral infectivity, with the
ethanol extract observed to have the strongest activity decreasing plaque numbers by 62% relative to the control. The
methanol extract was observed to be most effective when added before
infection causing 72% reduction in plaque numbers, whereas none of the extracts inhibited plaque formation by more than 40% when added after
infection. DENV-2 NS1
antigen production was significantly reduced by the
methanol extract, while
viral RNA levels were also decreased as determined by real time RT-PCR.
Phytochemical analysis revealed the presence of
flavonoids, phenolics,
tannins,
proteins, reducing
sugars and
saponins. Our preliminary results are promising, however, it should be interpreted with caution as further studies are needed to establish its potential therapeutic application against
dengue infection.