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3NPA INDUCES MITOCHONDRIAL DYSFUNCTION
IN CARDIAC TOXICITY IN MICE
3-Nitropropionic acid (3NPA), a plant and fungal environmental toxin, produces striatal neurodegeneration in humans and has been used to produce an animal model for Huntington’s disease. The mechanism of 3NPA neurotoxicity may be largely due to the irreversible inhibition of succinate dehydrogenase (SDH), reduction of cellular ATP and oxidative stress. We tested acute and chronic toxicity of 3NPA and found both striatal and cardiac damage in 4 different strains of inbred mice. In an acute toxicity study, survival rate was 80% in C57BL/6 mice and 20% in 129 mice. The cause of death in both strains was due to heart toxicity. Since the cardiac toxicity has not been previously reported we characterized the mechanism of toxicity using isolated mitochondria from both mouse strains. Compared to the more resistant C57BL/6 mice, the 129 mice were metabolically impaired earlier (24 hrs post 1st IP injection) with significantly decreased state III respiration rates using both complex I and II substrates. After the 2nd injection, C57BL/6 and 129 treated mice had similar succinate State III rates (90% of control). SDH enzyme activity in the control 129 mice was significantly higher compared to control C57BL/6. We also found that heart mitochondria from 3NPA treated mice (both strains- post 2nd injection) built less DY (mitochondrial membrane potential), which collapsed much faster when compared to mitochondria from control mice. In addition, mitochondria from treated mice showed a higher sensitivity to calcium-induced membrane depolarization. These effects were completely inhibited by cyclosporin A, suggesting the involvement of the permeability transition pore in the mitochondrial damage mechanism. We used a spin trapping technique and electron paramagnetic resonance (EPR) spectroscopy to analyze the formation of oxygen-derived free radicals in succinate driven state IV respiration of heart mitochondria from saline or 3NPA treated mice. Heart mitochondria from 129 mice produced significantly higher amounts of DMPO-OH radicals in state IV respiration compared to C57BL/6 mice. In both strains, mitochondria from treated mice show a trend for increased production of DMPO-OH radicals over controls. SOD eliminated the EPR signal suggesting that the original radical produced is superoxide. The addition of 3NPA to control mitochondria also generated superoxide (2-4 fold increase). In conclusion, these results reveal that the increased vulnerabilty of 129 mice may be due to the severity of their metabolic impairment and their greater production of superoxide compared to the less vulnerable C57BL/6 mice. Our results suggest that the cardiac toxicity of 3NPA may be due to accumulation of radical-derived damage to enzyme complexes and other mitochondrial proteins leading to increased membrane permeability. This in conjunction with a decreased ATP production would, in turn, lead to cellular dysfunction.
For further information contact...Carmen Mannella: carmen@wadsworth.org |
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