Cytokine-mediated Induction of Ceramide Production Is Redox-sensitive

Abstract

The present study underlines the importance of reactive oxygen species in cytokine-mediated degradation of sphingomyelin (SM) to ceramide. Treatment of rat primary astrocytes with tumor necrosis factor-␣ (TNF-␣) or interleukin-1␤ led to marked alteration in cellular redox (decrease in intracellular GSH) and rapid degradation of SM to ceramide. Interestingly, pretreatment of astrocytes with N-acetylcysteine (NAC), an antioxidant and efficient thiol source for glutathione, prevented cytokine-induced decrease in GSH and degradation of sphingomyelin to ceramide, whereas treatment of astrocytes with diamide, a thiol-depleting agent, alone caused degradation of SM to ceramide. Moreover, potent activation of SM hydrolysis and ceramide generation were observed by direct addition of an oxidant like hydrogen peroxide or a prooxidant like aminotriazole. Similar to NAC, pyrrolidinedithiocarbamate, another antioxidant, was also found to be a potent inhibitor of cytokineinduced degradation of SM to ceramide indicating that cytokine-induced hydrolysis of sphingomyelin is redoxsensitive. Besides astrocytes, NAC also blocked cytokine-mediated ceramide production in rat primary oligodendrocytes, microglia, and C 6 glial cells. Inhibition of TNF-␣-and diamide-mediated depletion of GSH, elevation of ceramide level, and DNA fragmentation (apoptosis) in primary oligodendrocytes by NAC, and observed depletion of GSH, elevation of ceramide level, and apoptosis in banked human brains from patients with neuroinflammatory diseases (e.g. X-adrenoleukodystrophy and multiple sclerosis) suggest that the intracellular level of GSH may play a critical role in the regulation of cytokine-induced generation of ceramide leading to apoptosis of brain cells in these diseases.

Divergence in Regulation of Nitric-oxide Synthase and Its Cofactor Tetrahydrobiopterin by Tumor Necrosis Factor-α

“…To examine the role of ceramide generation in iNOS expression, we utilized the antioxidant PDTC, which has been shown to inhibit ceramide generation in C6 cells induced by TNF-␣ (22). In agreement with previous results (32), PDTC completely blocked iNOS expression induced by TNF-␣.…”

“…To study the potential role of ceramide in cytokine-stimulated BH 4 production, we used C6 rat astroglioma cells, a convenient model astrocyte cell line. Furthermore, in this cell line, as in primary astrocytes, TNF-␣ has been shown to stimulate degradation of sphingomyelin to ceramide (22). Although ceramide generation, similar to TNF-␣ treatment potentiated NO and iNOS expression induced by IFN-␥ plus IL-1␤, surprisingly, we found that it did not mimic the effects of TNF-␣ on BH 4 or GTPCH expression.…”

“…Recently, it was shown that ceramide potentiated LPS and cytokine-induced NO and iNOS expression in rat primary astrocytes (20). Because TNF-␣ has been shown to stimulate hydrolysis of sphingomyelin to ceramide in many types of cells, including C6 cells (22), it was of interest to analyze the involvement of ceramide in TNF-␣-induced NO and BH 4 biosynthesis in these cells, as they express many of the properties of astrocytes.…”

Ceramide: A common pathway for atherosclerosis?

“…TNF-α-stimulated cells are redox-sensitive [28]. Some studies showed that ROS participate in TNF-α-mediated ceramide formation, suggesting that the ROS-sensitive pathway may be located upstream of ceramide formation [29]. While other studies demonstrated that ceramide plays a role as an intermediate in TNF-α-mediated ROS production [30].…”

Cytokine-Stimulated, But Not HIV-Infected, Human Monocyte-Derived Macrophages Produce Neurotoxic Levels of l-Cysteine

“…Thus, HIV-infected macrophages may be rendered incapable of producing excessive cysteine because of oxidative stress and subsequent glutathione depletion. In fact, this cytokine-mediated induction of ceramide and glutathione depletion is redox sensitive, and therefore can be reversed with cysteine derivatives (55).…”