Zinc Regulation & Toxicity in Cellular Energy Metabolism

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DESCRIPTION (provided by applicant): Recently a growing number of reports have attempted to link changes intracellular free Zn++ to pathological processes, particularly in the nervous system. Increased intracellular Zn++ is correlated with mitochondria dysfunction, loss of mitochondria defenses, increased production of ROS and cellular death. We have demonstrating that 1) Elevated Zn++ interferes with mitochondria energy utilization (respiration), due in part to inhibition of enzymes that play a role in carbohydrate metabolism, in particular alpha-ketoglutarate dehydrogenase. 2) Zn++ lowers mitochondria membrane potential and induces the opening of the mitochondria permeability pore, which releases Ca2+ and inhibits ATP generation. 3) Zn++ also inhibits the activity of pyridine nucleotide-dependent thiol reductases, which are critical to maintenance of mitochondria redox defenses. 4) Zn++ activates the NADH-oxidase activity of the mitochondria enzyme lipoamide dehydrogenase. This accelerates generation of superoxide (O2) and hydrogen peroxide (H2O2). 5) Zn++ induces release of mitochondria cytochrome c, which is a cytosolic propagator of apoptosis. Our hypotheses are that: Mitochondria and metallothioneins form a physiological feedback loop that utilizes Zn2+ as signal to regulate the balance of production between ATP, (ROS) and reduced thiols. Elevated intracellular Zn++ (is transported into mitochondria and) reduces cellular energy utilization directly by inhibiting enzymes involved in carbohydrate metabolism and electron transport and indirectly by interfering with mitochondrial redox balance. Excess (pathological) levels of cytosolic Zn2+ reduce mitochondria protection and destabilize mitochondria integrity (membrane permeability). Zn++ also induces mitochondria release of ROS and cytochrome c. Specifically, we will: 1) Characterize the spectrum of reactive products of the NADH-dehydrogenase activity of LADH that are stimulated by Zn++. 2) Characterize the inhibitory effect of Zn++ on thiol-redox activity at both the enzyme and mitochondrial level. 3) Establish the order of mitochondria events following exogenous addition of Zn++ in rat liver mitochondria. 4) Redox balance and other Zn++ -induced changes discovered and characterized in liver mitochondria in Aims 2 and 3 will be confirmed in rat brain mitochondria.