Peroxynitrite‐Mediated Inhibition of DOPA Synthesis in PC12 Cells

Abstract

Experimental evidence has implicated oxidative stress in the development of Parkinson's disease, amyotrophic lateral sclerosis, and other degenerative neuronal disorders. Recently, peroxynitrite, which is formed by the nearly diffusion‐limited reaction of nitric oxide with superoxide, has been suggested to be a mediator of oxidant‐induced cellular injury. The potential role of peroxynitrite in the pathology associated with Parkinson's disease was evaluated by examining its effect on DOPA synthesis in PC12 pheochromocytoma cells. Peroxynitrite was generated from the compound 3‐morpholinosydnonimine (SIN‐1), which releases superoxide and nitric oxide simultaneously. Exposure of PC12 cells to peroxynitrite for 60 min greatly diminished their ability to synthesize DOPA without apparent cell death. The inhibition was due neither to the formation of free nitrotyrosine nor the oxidation of DOPA by peroxynitrite. The inhibition in DOPA synthesis by SIN‐1 was abolished when superoxide was scavenged by the addition of superoxide dismutase. These data indicated that neither nitric oxide nor hydrogen peroxide generated by the dismutation of superoxide is responsible for the SIN‐1‐mediated inhibition of DOPA production. The inhibition of DOPA synthesis at high concentration of SIN‐1 persisted even after removal of SIN‐1. The inactivation of the tyrosine hydroxylase may be responsible for the significant decline in DOPA formation by peroxynitrite. Inactivation of tyrosine hydroxylase may be part of the initial insult in oxidative damage that eventually leads to cell death.

Chronic estradiol exposure induces oxidative stress in the hypothalamus to decrease hypothalamic dopamine and cause hyperprolactinemia

“…There is evidence to indicate that an increase in NO-related free radicals can increase nitration of tyrosine residues on TH, the rate-limiting enzyme in DA biosynthesis (19,21). Peroxynitrite, one of the products of NO metabolism, facilitates the formation of nitrotyrosine, which results in nitration of tyrosine residues in proteins (19,21).…”

“…Peroxynitrite, one of the products of NO metabolism, facilitates the formation of nitrotyrosine, which results in nitration of tyrosine residues in proteins (19,21). Nitration of tyrosine residues is one of the important hallmarks of NO-induced pathology and can lead to inactivation of protein function, particularly of proteins like TH that contain several tyrosine residues in their structure (2).…”

Differential Mechanisms of Nitric Oxide- and Peroxynitrite-Induced Cell Death

“…Ϫ at 3 mM that is maintained for at least 1 h (Ischiropoulos et al, 1995). NO formation by SIN-1 is undetectable unless superoxide dismutase is present.…”

“…Therefore, we compared the effects of three NO donors: DETA/NO and Sper/NO of the NONOate class and SIN-1. Although SIN-1 is referred to as an "NO donor", it generates NO and superoxide in equimolar amounts, thereby producing ONOO Ϫ (Ischiropoulos et al, 1995;Feelisch, 1998). Sper/NO and DETA/NO both release NO according to first-order kinetics, with halflives of 39 min and 20 h, respectively (Keefer et al, 1996).…”

Peroxynitrite-induced Nitration of Tyrosine Hydroxylase

“…The mechanisms by which 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine damages dopamine neurons are complex and are thought to involve, at least in part, the production of peroxynitrite (ONOO Ϫ ) (2). TH is inhibited by ONOO Ϫ in vitro (1,3) and in PC12 cells (4). The ONOO Ϫ -induced inhibition of TH is associated with nitration of tyrosine residues (1) and oxidation of cysteine residues (3), yet neither the identity of the modified residues in TH nor the relative contribution of these posttranslational modifications to loss of catalytic function is known.…”