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Abstract
Ocimum plants are traditionally used to manage HIV/AIDS in various African countries. The effects of Ocimum labiatum extract on HIV-1 protease (PR) and reverse transcriptase (RT) is presented here along with characterization of an identified bioactive compound, achieved through 1H- and 13C-NMR. The extract’s effect on HIV-1 replication was assessed by HIV-1 p24 antigen capture. Cytotoxicity of samples was evaluated using tetrazolium dyes and real-time cell electronic sensing (RT-CES). Ocimum labiatum inhibited HIV-1 PR with an IC50 value of 49.8 ± 0.4 μg/mL and presented weak inhibition (21%) against HIV-1 RT. The extract also reduced HIV-1 replication in U1 cells at a non-cytotoxic concentration (25 μg/mL). The CC50 value of the extract in U1 cells was 42.0 ± 0.13 μg/mL. The HIV-1 PR inhibiting fraction was purified using prep-HPLC and yielded a chlorophyll derivative, pheophytin-a (phy-a). Phy-a inhibited HIV-1 PR with an IC50 value of 44.4 ± 1.5 μg/mL (51 ± 1.7 μM). The low cytotoxicity of phy-a in TZM-bl cells was detected by RT-CES and the CC50 value in U1 cells was 51.3 ± 1.0 μg/mL (58.9 ± 1.2 μM). This study provides the first in vitro evidence of anti-HIV activity of O. labiatum and isolated phy-a, supporting further investigation of O. labiatum for lead compounds against HIV-1.
Highlights
Natural products are still being explored as potential antiviral agents and more importantly as inhibitors of the various steps of the HIV life cycle [1,2]
The proton NMR spectrum of the isolated compound was similar to the spectrum of pheophytin-a (Figure 1)
The chemical shifts (Table 1) were in agreement with those reported in the literature [8,23] and the propionic side chains in the spectrum (2.0–2.7 ppm) were identical to those illustrated by Smith et al [23]
Summary
Natural products are still being explored as potential antiviral agents and more importantly as inhibitors of the various steps of the HIV life cycle [1,2]. Various classes of phytochemicals with potential antiviral activity have been isolated from several hundred plant and herb species [7]. Types of plant constituents isolated include flavonoids, terpenoids, lignans, sulphides, polyphenolics, coumarins, saponins, proteins and chlorophyll derivatives [7,8]. The mechanisms of action of some of these phytochemicals include inhibiting the formation of viral DNA or RNA or inhibiting other viral reproduction steps [7]. Chlorophyll derivatives such as pheophytin-a have been implicated in the inhibition of viral protease from hepatitis C virus [8]
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