Anti-mycobacterial effects of ascorbic acid in human macrophage-lymphocyte co-culture model

Abstract

Background: Tuberculosis (TB) causes oxidative stress in patients contracting it while antioxidant vitamins such as ascorbic acid (AA) demonstrated anti-mycobacterial (anti-MTB) effects. Ascorbate’s anti-MTB effect in 7H9 media depended on high iron concentration. However, high iron concentration in vivo rather favored mycobacterial growth. Iron dynamics in TB infected macrophages is also complex making it difficult to extrapolate ascorbate’s in vivo effect based on observations in 7H9 media. To address this issue, we assessed ascorbate’s anti-MTB effect in human macrophage cell culture model.
Methods: We collected 20 ml blood from HIV negative subjects, isolated Peripheral Blood Mononuclear Cells (PBMCs) and separated monocytes from the PBMCs. Monocytes were allowed to mature, were infected with Mycobacterium TB (MTB) and were incubated in RPMI plus autologous serum after adding different concentrations of ascorbate. Colony Forming Units (CFU) were counted and compared among cultures incubated with different ascorbate concentrations. Ascorbate’s anti-MTB effect was also assessed in 7H9 media for comparison.
Results: At concentrations of 10-1 mM, 1 mM and 10 mM, ascorbate reduced MTB CFU in cell culture model by 13%, 53% and 71% respectively while in 7H9 medium CFU reductions were 2.8%, 58.7% and 99.3% respectively.
Conclusions: Despite low iron concentration in human cell culture, ascorbate showed dose dependent anti-MTB effect in the cell culture and hence ascorbate can be further investigated in clinical trials to assess its use as an adjunct to anti-TB drugs