Anti-Inflammatory Effects of Alpha-Lipoic Acid Modulate Cystathionine-γ-Lyase Expression in RAW 264.7 Macrophages

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.