Numerous investigations, including those in our laboratory, have demonstrated that hydrophilic d-alpha-tocopheryl hemisuccinate (vitamin E succinate, TS) is superior to lipophilic unesterified d-alpha- tocopherol (T) as an antioxidant and a cytoprotective agent. Because TS- mediated cytoprotection has been observed for numerous cell types, species and toxic insults, we suggest that this protective compound intervenes in a critical cellular event(s) that is responsible for chemical-induced cell death. It is our belief that by defining the cellular and molecular mechanism of TS cytoprotection, we will increase our understanding of the molecular events that are responsible for toxic cell injury as well as suggest therapeutic strategies to prevent or limit this toxic event. Thus the primary objective of this proposed research is to determine the mechanism of vitamin E succinate cytoprotection against chemical toxicity. Our recent studies suggest that TS cytoprotection is dependent on vitamin E succinate's unique ability to accumulate and release T in cells, prevent lipid peroxidation and the loss of protein thiols and maintain mitochondrial function and structure. Furthermore our data also suggest that increasing the water-solubility of T (in the form of TS) Increases tocopherol's ability to accumulate in cells and offer protection. Thus we propose as our central hypothesis that the superior hepatoprotective properties of TS result from the unique abilIty of hydrophilic T esters (e.g. TS) to accumulate and release """"""""active"""""""" T at a critIcal subcellular site (mitochondria) that preserves membrane lipid and protein thiol integrity, mitochondrial function and cell viability during a toxic chemical insult. This hypothesis will be tested both in vitro (using rat hepatocytes, and subcellular fractions including mitochondria) and in vivo, using the toxic insults, ethyl methanesulfonate, carbon tetrachloride, and ADP- iron.
The specific aims of the proposed research are to 1) determine the role of tissue and subcellular accumulation of T and T precursors (e.g. TS) in TS cytoprotection, 2) determine the role of mitochondrial tocopherol, derived from TS, in the preservation of mitochondrial function and structure during a toxic chemical insult, 3) determine the role of chemical accumulation and chemical alkylation of cells and mitochondria in TS-mediated protection and toxic chemical injury, and 4) determine the role of cellular and mitochondrial lipid peroxidation, protein oxidation and protein thiol depletion and reactivity in TS-mediated cytoprotection and toxic chemical injury. Demonstrating that hydrophilic forms of T can be rapidly and extensively incorporated into intracellular membranes in an active form, will not only help explain the present study's interest in why TS protects liver, hepatocytes and mitochondria from toxic chemical Injury but would also have tremendous implications for the treatment and prevention of numerous disease states.
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