N-Acetylcysteine and Celecoxib Lessen Cadmium Cytotoxicity Which Is Associated with Cyclooxygenase-2 Up-regulation in Mouse Neuronal Cells

Abstract

In many neurodegenerative disorders, aggregates of ubiquitinated proteins are detected in neuronal inclusions, but their role in neurodegeneration remains to be defined. To identify intracellular mechanisms associated with the appearance of ubiquitin-protein aggregates, mouse neuronal HT4 cells were treated with cadmium. This heavy metal is a potent cell poison that mediates oxidative stress and disrupts the ubiquitin/ proteasome pathway. In the current studies, the following intracellular events were found to be also induced by cadmium: (i) a specific rise in cyclooxygenase-2 (COX-2) gene expression but not COX-1; (ii) an increase in the extracellular levels of the proinflammatory prostaglandin E2, a product of COX-2; and (iii) production of 4-hydroxy-2-nonenal-protein adducts, which result from lipid peroxidation. In addition, cadmium treatment led to the accumulation of high molecular weight ubiquitin-COX-2 conjugates and perturbed COX-2 glycosylation. The thiol-reducing antioxidant N-acetylcysteine, and, to a lesser extent, the COX-2 inhibitor celecoxib, attenuated the loss of cell viability induced by cadmium demonstrating that oxidative stress and COX-2 activation contribute to cadmium cytotoxicity. These findings establish that disruption of the ubiquitin/proteasome pathway is not the only event triggered by cadmium. This oxidative stressor also activates COX-2 function. Both events could be triggered by formation of 4-hydroxy-2-nonenal as a result of cadmium-induced lipid peroxidation. Proinflammatory responses stimulated by oxidative stressors that mimic the cadmium effects may, therefore, be important initiators of the neurodegenerative process and exacerbate its progress.

Cadmium Renal Toxicity <i>via</i> Apoptotic Pathways

“…19) Moreover, cadmium causes an increase in intracellular p53 protein levels and/or phosphorylated p53 protein levels in several cells. [57][58][59][60][61][62][63][64][65] These observations also support our findings that the p53-mediated pathway is one of the critical pathways for inducing apoptosis in chronic cadmium-exposed proximal tubular cells in the kidney.…”

Cadmium toxicity is caused by accumulation of p53 through the down-regulation of Ube2d family genes in vitro and in vivo

“…Ubiquitinated proteins that are not degraded by the proteasome can accumulate and cause toxic cell damage. Previous studies have shown that Cd increases the accumulation of ubiquitinated proteins in several cell lines, such as mouse neuronal HT4 cells (Figueiredo-Pereira et al, 2002), rat sertoli cell-gonocyte cocultures (Yu et al, 2008) and rat proximal tubule cells (Thévenod and Friedmann, 1999). These findings suggest that Cd may cause toxic cell damage through the accumulation of unnecessary proteins.…”

Glucosamine Hydrochloride Specifically Inhibits COX-2 by Preventing COX-2 N-Glycosylation and by Increasing COX-2 Protein Turnover in a Proteasome-dependent Manner

“…The proteasomal pathway is involved in COX-2 protein turnover (31)(32)(33)(34). This promptly led us to investigate whether the proteasomal pathway is associated with increased turnover of high molecular species of COX-2 by GS-HCl during translation.…”