HIV-1 adopts several factors of host machinery to generate a permissive environment for viral replication and transmission. HIV-1 enhances the activity of mTORC1 which appears to be necessary for the optimal expression of the structural viral protein Gag. In addition, HIV-1 hijacks the Rag GTPase/mTORC1 complex to modulate host cell function for optimal virus trafficking, assembly and/or budding. Exosomal release of HIV proteins primes cells for new infection. Metformin (1,1-dimethyl biguanide hydrochloride) is a USA Food and Drug Administration (FDA)-approved biguanide derivative and the most widely prescribed antihyperglycemic drug which is used as first-line therapy for diabetes mellitus type 2. Metformin inhibits mTORC1 by activation of AMPK. It has recently been shown that metformin can exert antiviral effects against Hepatitis B, Dengue, and Zika viruses. In this project, we aim to determine the effect of metformin on HIV replication/release using HIV transfected/infected cells.
MTT (Methylthiazolyldiphenyl-tetrazolium bromide) was used to determine cell viability. Reverse transcriptase assay (RT) activity assay was used to determine the levels of virus replication and production in cells. Western blotting was used to determine intracellular protein expression. Western blotting followed by semiquantitative protein band detection was performed using a Bio-Rad ChemiDoc imaging system (Bio-Rad). Band intensities were calculated by measuring the ratio between the protein of interest to beta-actin. HIV LTR promoter-driven luciferase reporter cell line TZM-bl was used to determine the LTR promoter activity.
Results: No effects on cell proliferation were noted in both 293T and TZM-bl treated up to 4 mM Metformin. Metformin did not alter HIV promoter activity. Metformin increased HIV virus production. Consistent with this finding, Metformin increased intracellular HIV gene expression, specifically Gag expression and Tat expression. In addition, Metformin did not appear to have any effects on the activity of HIV reverse transcriptase.
Conclusion: These findings demonstrated that Metformin enhances HIV gene expression and production and suggest that Metformin may regulate steps of the HIV life cycle other than reverse transcription and HIV LTR promoter transcription. These findings also provide evidence to support metformin as a potential, low cost supplementary therapeutic agent for the elimination of latent viral reservoirs.||