Anti-dengue virus serotype 2 activity of tannins from porcupine dates

Background: Dengue fever is currently endemic in tropical and subtropical countries worldwide and effective drug against DENV infection is still unavailable. Porcupine dates, which are traditionally used to treat dengue fever, might contain potential anti-dengue compounds. Two porcupine dates, black date (BD) and powdery date (PD) from Himalayan porcupine (Hystrix brachyura), were investigated for their antiviral activities against DENV-2 in vitro. Methods: The methanol crude extracts (MBD and MPD) were prepared from the raw material of porcupine dates. The tannin-rich fractions (BDTF and PDTF) were isolated from their methanol crude extracts using column chromatography. The presence of tannins in BDTF and PDTF extracts was determined by fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses. The cytotoxicity and anti-DENV-2 activities including virus yield inhibition, virucidal, virus attachment and pre-treatment assays of the extracts were examined in Vero cells. Results: Our findings revealed that all the extracts of porcupine dates exhibited antiviral activity against DENV-2 in Vero cells. The IC₅₀ of BDTF and PDTF were 25 μg/mL and 11 μg/mL respectively, while their methanol crude extracts demonstrated lower antiviral efficacy (IC₅₀ ≈ 101-107 μg/mL). BDTF and PDTF also exerted a similar higher virucidal effect (IC₅₀ of 11 μg/mL) than methanol crude extracts (IC₅₀ ≈ 52-66 μg/mL). Furthermore, all the extracts inhibited the attachment of DENV-2 by at least 80%. Pre-treatments of cells with BDTF and PDTF markedly prevented DENV-2 infection when compared to methanol crude extracts. Conclusion: This study suggests that porcupine dates possess antiviral properties against DENV-2, which is attributed to its tannin compounds.