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 g/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 g/mL). The CC50 value of the extract in U1 cells was
42.0 0.13 g/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 g/mL (51 1.7 M). 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 g/mL (58.9 1.2 M). 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.