Alpha-lipoic acid (ALA) is a naturally occurring organosulfur compound with antioxidant and anti-inflammatory activities. The time-dependent effects of ALA and mechanism of interaction with cystathionine-γ-lyase (CSE—an enzyme responsible for hydrogen sulfide—H2S synthesis) in RAW 264.7 macrophages remain unknown. In this study, we report results supporting the hypothesis that anti-inflammatory effects of ALA are associated with the reduction in CSE expression. To investigate the temporal effect of ALA in lipopolysaccharide (LPS—a potent stimulator of inflammation) treated RAW 264.7 macrophages, ALA was administered 1 h before LPS stimulation and 1, 3, and 6 h post LPS stimulation. Effects of ALA on different inflammatory and oxidative stress biomarkers including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), catalase activity (CAT), and malondialdehyde (MDA) levels were investigated. LPS stimulation significantly increased TNF- α, IL-6, MCP-1, MDA levels, and CSE expression and decreased CAT activity compared with the control group (p < 0.05 to 0.0001). ALA treatment at 1000 µM significantly attenuated LPS-stimulated inflammatory response in the macrophages across different time points (p < 0.05 to 0.0001). Furthermore, we found that ALA treatment reduced the expression of CSE in both pre- and post-treated LPS-stimulated macrophages in a time-dependent manner. In conclusion, this study demonstrated for the first time that the protective effects of ALA are dependent on the reduction in CSE expression in LPS-stimulated RAW 264.7 macrophages.
Shahid et al. (Sun,) studied this question.