The broad objective of this application is to extend past and ongoing research aimed at defining the basic mechanisms which underlie the porphyrinogenic and tissue damaging properties of trace metals in biological tissues. The research will focus on the mechanisms by which trace metals cause porphyrin accumulation (porphyria) and cell injury (nephrotoxicity) in mammalian kidney, a principal target organ of numerous metals of toxicologic importance. The principal hypothesis to be tested is that renal porphyria and nephrotoxicity have a common mechanistic etiology in the formation of reactive oxidants (peroxides, free radicals) and depletion of cellular glutathione (GSH) which occur during prolonged metal exposures. These events promote oxidation of reduced porphyrins and peroxidation of cellular constituents, leading progressively to porphyria and cell injury, respectively. Studies are proposed to define the precise mechanisms by which metals (1) deplete cellular GSH and (2) elicit the formation of reactive oxidants, and to identify how these events interact to (3) promote porphyria nd (4) cause cell injury. A prolonged-exposure model of methyl mercury-induced porphyria and cell injury in Sprague-Dawley rat kidney developed in this laboratory for study of these mechanisms will be used as the principal experimental model. Highly sensitive HPLC-spectrofluorometric assay procedures will be used to measure porphyrinogenic events in kidney fractions and to quantitate metal effects on GSH metabolism. Reactive oxidant formation by renal cells will be measured by established spectrophotometric procedures. Ultrastructural/morphometric and enzymatic microdetermination techniques will be employed to determine if lipid peroxidation of cell constituents resulting from GSH depletion and reactive oxidant formation is a cause of renal cell injury during metal exposure. The proposed research will add substantially to current understanding of the mechanisms by which toxic trace metals alter the regulation of GSH metabolism and promote reactive oxidant formation i biological tissues, and the role of these events in metal-induced porphyria and nephrotoxicity. Identification of a common mechanistic etiology of the porphyrinogenic and tissue damaging properties of metals will establish the biological and potential diagnostic significance of renal porphyria as a pre-toxic manifestation of biochemical events associated with the initiation of metal toxicity in kidney cells.
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