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Synergistic induction of DNA strand breakage caused by nitric oxide together with catecholamine: implications for
1Unit of Endogenous Cancer Risk Factors, International Agency for Research on Cancer, Lyon, France.
Abstract:
Oxidative damage in neuronal cells and DNA has been implicated in the pathogenesis of various neurodegenerative diseases. We have demonstrated that DNA strand breakage is induced synergistically when plasmid DNA is incubated in the presence of both an NO-releasing compound (diethylamine NONOate, spermine NONOate, sodium nitroprusside) and a catecholamine (e.g., L-DOPA, dopamine, etc.). Either an NO-releasing compound or a catecholamine alone induced much fewer strand breaks. Tyrosine and tyramine as well as O-methylated derivatives of DOPA and dopamines did not exert this synergistic effect in the presence of NO. The DNA strand breakage induced by NO plus dopamine was inhibited by carboxy-PTIO (a trapping agent of NO and possibly other radicals), superoxide dismutase, and antioxidants such as N-acetylcysteine and ascorbate but not by HO. scavengers such as dimethyl sulfoxide, ethanol, and D-mannitol. These results suggest that the free HO. is not involved; rather a new oxidant(s) formed by the reaction between NO and catecholamine could be responsible for causing the DNA strand breakage. We propose that one of the responsible compounds is peroxynitrite (ONOO-), which is a strong oxidant and nitrating agent formed by the reaction between NO and O2.-. NO has been shown to oxidize catecholamines to form quinone derivatives, which lead to the generation of O2.- by the quinone/hydroquinone redox system. O2.- then reacts rapidly with NO to form peroxynitrite. However, it is also possible that other compounds such as NOx generated from catecholamines and NO may cause DNA damage. Our results implicate a synergistic interaction of catecholamines formed in dopaminergic neurons and NO formed by microglia or astrocytes or the two compounds produced within the same neuronal cells to produce a potent oxidant(s) which could cause damage in cells and DNA, thus playing an important role in the pathogenesis of various neurodegenerative diseases.
Insights
Nitric oxide (NO) and catecholamines synergistically damage DNA, contributing to neurodegenerative diseases. This interaction forms potent oxidants like peroxynitrite, highlighting a key mechanism in neuronal cell damage.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Oxidative damage to DNA and neuronal cells is a significant factor in neurodegenerative disease pathogenesis.
- Nitric oxide (NO) and catecholamines are biologically active molecules implicated in neuronal function and dysfunction.
Purpose of the Study:
- To investigate the synergistic effect of NO-releasing compounds and catecholamines on DNA strand breakage.
- To elucidate the mechanisms and reactive species involved in NO- and catecholamine-induced DNA damage.
Main Methods:
- Incubation of plasmid DNA with NO-releasing agents (e.g., diethylamine NONOate) and catecholamines (e.g., dopamine).
- Assessment of DNA strand breakage using established biochemical assays.
- Inhibition studies using radical scavengers (e.g., carboxy-PTIO, superoxide dismutase, N-acetylcysteine) and antioxidant agents.
Main Results:
- Combined NO-releasing compounds and catecholamines induced significant synergistic DNA strand breakage, far exceeding the effects of individual agents.
- Specific catecholamines (L-DOPA, dopamine) but not their derivatives (tyrosine, tyramine) showed this synergistic effect with NO.
- DNA damage was inhibited by NO/radical scavengers and antioxidants, but not by hydroxyl radical scavengers, suggesting a role for peroxynitrite or related species.
Conclusions:
- A synergistic interaction between NO and catecholamines generates potent oxidants, likely including peroxynitrite, responsible for DNA strand breakage.
- This mechanism is implicated in the pathogenesis of neurodegenerative diseases, involving interactions between microglia/astrocytes and neurons or within neuronal cells.
- Understanding this oxidative stress pathway offers insights into therapeutic strategies for neurodegenerative conditions.