DOI: 10.4103/jfcm.jfcm_300_26 ISSN: 2230-8229

Inhibition of human immunodeficiency virus-1 reverse transcriptase by thymoquinone and Nigella sativa extracts in vitro

Ayad M. Salem
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Abstract:

BACKGROUND:

Reverse transcriptase (RT) enzyme inhibitors are used to treat human immunodeficiency virus (HIV). The aim of this study was to investigate the anti-HIV-RTenzyme activity of Nigella sativa (NS) and its active ingredient, thymoquinone (TQ).

MATERIALS AND METHODS:

Purified TQ and NS extract powder with 0.5% and 5% TQ were tested for their inhibition of HIV-1 RT in a biochemical assay using a nonradioactive HIV-RT enzyme-linked immunosorbent assay kit. Five dilutions of TQ (0.125, 0.25, 0.5, 1, and 2 mg/ml) were made and tested. The assay was conducted in triplicate, and doxorubicin was used as a positive control. The inhibition percentage and half-maximal inhibitory concentration (IC 50 ) values were calculated using Excel and GraphPad Prism software. Data were analyzed using SPSS. The TQ concentration–response relationship was analyzed by nonlinear regression using a four-parameter logistic model to estimate the IC50 and corresponding 95% confidence interval (CI).

RESULTS:

NS powders containing 0.5% TQ and 5% TQ showed a weak inhibitory effect on HIV-RT activity, with only 20% and 31% inhibition, respectively, which was significantly lower than the 89.6% inhibition in RT activity caused by the positive control (doxorubicin, P = 0.003 and P = 0.007, respectively). Purified TQ produced 82.5% inhibition of HIV-1 RT, whereas doxorubicin produced 89.6% inhibition; the difference between the two treatments did not reach statistical significance under the conditions of this assay ( P = 0.182). TQ exhibited anti-HIV-1 RT activity in a dose–response manner, with concentrations of 0.125 mg/ml, 0.25 mg/ml 0.5 mg/ml, 1 mg/ml, and 2 mg/ml produced 29%, 57.1%, 71.7%, 77.7%, and 82.5% inhibition in the HIV RT activity, respectively, with a calculated IC 50 value of 0.167 mg/mL (95% confidence interval: 0.147–0.190 mg/mL), corresponding to approximately 1.02 mM.

CONCLUSION:

Purified TQ demonstrated concentration-dependent inhibition of HIV-1 RT in the present in vitro enzyme assay. These findings provide preliminary biochemical evidence that supports further investigation of TQ as a potential inhibitor of HIV-1 RT.

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