Supplementary Material for: Mitochondrial Inhibitor Models of Huntington’s Disease and Parkinson’s Disease Induce Zinc Accumulation and Are Attenuated by Inhibition of Zinc Neurotoxicity in vitro or in vivo

Background: Inhibition of mitochondrial function occurs in many neurodegenerative diseases, and inhibitors of mitochondrial complexes I and II are used to model them. The complex II inhibitor, 3-nitroproprionic acid (3-NPA), kills the striatal neurons susceptible in Huntington’s disease. The complex I inhibitor N-methyl-4-phenylpyridium (MPP+) and 6-hydroxydopamine (6-OHDA) are used to model Parkinson’s disease. Zinc (Zn2+) accumulates after 3-NPA, 6-OHDA and MPP+ in situ or in vivo. Objective: We will investigate the role of Zn2+ neurotoxicity in 3-NPA, 6-OHDA and MPP+. Methods: Murine striatal/midbrain tyrosine hydroxylase positive, or near-pure cortical neuronal cultures, or animals were exposed to 3-NPA or MPP+ and 6-OHDA with or without neuroprotective compounds. Intracellular zinc ([Zn2+]i), nicotinamide adenine dinucleotide (NAD+), NADH, glycolytic intermediates and neurotoxicity were measured. Results: We showed that compounds or genetics which restore NAD+ and attenuate Zn2+ neurotoxicity (pyruvate, nicotinamide, NAD+, increased NAD+ synthesis, sirtuin inhibition or Zn2+ chelation) attenuated the neuronal death induced by these toxins. The increase in [Zn2+]i preceded a reduction in the NAD+/NADH ratio that caused a reversible glycolytic inhibition. Pyruvate, nicotinamide and NAD+ reversed the reductions in the NAD+/NADH ratio, glycolysis and neuronal death after challenge with 3-NPA, 6-OHDA or MPP+, as was previously shown for exogenous Zn2+. To test efficacy in vivo, we injected 3-NPA into the striatum of rats and systemically into mice, with or without pyruvate. We observed early striatal Zn2+ fluorescence, and pyruvate significantly attenuated the 3-NPA-induced lesion and restored behavioral scores. Conclusions: Together, these studies suggest that Zn2+ accumulation caused by MPP+ and 3-NPA is a novel preventable mechanism of the resultant neurotoxicity.