Efficacy and Possible Mechanism(s) of Action of Gallium Tetraphenylporphyrin Nanoparticles against HIV-TB Coinfection in an <i>In Vitro</i> Granuloma Structure Model

Coinfection of <i>Mycobacterium tuberculosis</i> (Mtb) and human immunodeficiency virus-1 (HIV) is a significant public health concern. Treatment is challenging due to prolonged duration of therapy and drug interactions between antiretroviral therapy (ART) and anti-TB drugs. Noniron gallium <i>meso</i>-tetraphenyl porphyrin (GaTP), a heme mimetic, has shown broad antimicrobial activity. Here, we investigated the efficacy of nanoparticle encapsulating GaTP (GaNP) for the treatment of HIV and Mtb coinfection or single infection in <i>in vitro</i> granuloma structures. GaNP significantly reduced viable Mtb within primary human <i>in vitro</i> granuloma structures infected with Mtb H37Rv-lux and significantly reduced levels of HIV in CD4+ T cells infected with the virus axenically. Similarly, GaNP exhibited significant antimicrobial activity against HIV/Mtb-coinfected granuloma structures created <i>in vitro</i>, which contain the primary immune cells seen in human TB granulomas, including CD4+ T cells and macrophages, as assessed by a luciferase assay for Mtb and p24 ELISA for HIV detection. Furthermore, mechanistic studies revealed that GaTP increases the level of reactive oxygen species and inhibits catalase in Mtb. A significant increase in Mtb nitrate reductase activity was also observed when Mtb was incubated with GaTP and sodium nitrate. Overall, increased oxidative stress and nitrite levels induced by GaTP are consistent with the possibility that GaTP inhibits Mtb aerobic respiration, which leads to incomplete O₂ reduction and a shift to respiration using exogenous NO₃. These cumulative data continue to support the potential for developing the noniron heme analog GaTP and its nanoparticle GaNP as new therapeutic approaches for the treatment of HIV/Mtb coinfection.