Inhibition of HIV-1 lentiviral particles infectivity by Gynostemma pentaphyllum extracts in a viral vectorbased assay
Three different extracts of Gynostemma pentaphyllum (Cucurbitaceae), a medicinal plant used for a variety of ailments in complementary and alternative medicine (CAM) including those caused by viral infections with claims of efficacy against HIV-1 infections were screened. These claims motivated the study in which the inhibition of viral vector infectivity of HeLa cells was assessed flow cytometrically by measuring the expression of green fluorescent protein (GFP) transgene incorporated in the lentiviral vector construct. An infectious VSV-G-pseudotyped, human immunodeficiency virus type 1-based, selfinactivating lentivirus vector particles were generated by transient co-transfection of the vector plasmid (pHIV-1 CSCG), with packaging plasmids encoding tat, rev, gag-pol (pCMVΔR8.2), a VSV-G expression plasmid (pHIT-G) and a secretory alkaline phosphate expression plasmid (pSEAP) all necessary for viral infectivity. The extracts studied were obtained by solvent extraction of the leaf powder of G. pentaphyllum with ethyl ether (EG), methanol (MG), and water (AG). The AG, MG and EG were all active against the HIV-1 lentiviral vector and inhibited the early events of the viral replication cycle on HeLa cells in a concentration-dependent manner with a IC50 of 6.21 μg AG/ml, 8.32 μg MG/ml and 5.8 μg EG/ml, respectively. The cytotoxicity of the extracts to HeLa cells evaluated in parallel by the 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay method showed TC50 values of 36.77 μg AG/ml, 38.68 μg MG/ml and 41.02 μg EG/ml with selectivity indices (SI) of 5.92, 4.65 and 7.02, respectively. The results of the study show that the extracts of G. pentaphyllum possess potent and selective anti-retroviral potentials and could serve as possible source of lead antiviral drugs against HIV.
Key words: Antiviral activity, antiviral screening, Gynostemma pentaphyllum, HIV-1, viral vector-based screening.