Date of Award
Doctor of Philosophy
Patricia A. Murphy
Data on interspecies peroxisomal metabolism are limited almost entirely to rodents. Species differences are likely and the application of rodent data to man is questionable. An alternative to rodent models is desirable. Porcine tissue offers such an alternative and was explored. Porcine hepatocyte organelles were separated by isopycnic sucrose gradient centrifugation from livers of 6-month-old Yorkshire pigs. The presence of a peroxisomal palmityl-CoA oxidizing pathway, peroxisomal superoxide dismutase (SOD), and a peroxisomal NAD:aldehyde dehydrogenase (ALDH) with high K[subscript] m for acetaldehyde was demonstrated. Peroxisomal palmitate oxidizing capacity was found to be equal to that of the surviving mitochondria. The high K[subscript] misozyme of ALDH was mainly located in the mitochondria (54%), with a significant portion in the peroxisomes (32%). Remaining activity is distributed among the microsome (8.3%) and cytosol (4.6%). The low K[subscript] m isozyme was confined almost exclusively to the mitochondria. ALDH may exist in the peroxisome as a detoxification mechanism and contribute to shorter half-lives of reactive aldehydes in the cell. SOD was distributed among the peroxisomes (10%), mitochondria (20%), and cytosol (70%). SOD may scavenge reactive species of oxygen produced through peroxisomal [beta]-oxidation. A protocol for the isolation and growth of viable porcine hepatocytes is reported. The effects of clofibric acid on isolated porcine hepatocytes was investigated. Activity of selected enzymes from intact tissue were compared to isolated cells not exposed to the drug. Catalase activity was lower in isolated cells, but NAD:glutamate dehydrogenase, peroxisomal [beta]-oxidation, mitochondrial [beta]-oxidation, aldehyde dehydrogenase, and NADPH:cytochrome c reductase were similar. Isolated hepatocytes were exposed to clofibric acid concentrations ranging from 0 to 3.0 mM. Catalase, mitochondrial [beta]-oxidation, and peroxisomal [beta]-oxidation were not affected by treatments. Treatments did result in a 40% increase in protein content, a 900% increase in NADPH:cytochrome c reductase, a 400% increase in both isozymes of aldehyde dehydrogenase, and a 40% induction of superoxide dismutase activity. Responses were significantly quadratic. Porcine hepatocyte peroxisomes appear to differ significantly from those of rodents. Our data support the hypothesis that phylogenetically higher animals are different from rodents in peroxisome metabolism. Interspecies differences in metabolism is discussed.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Kenneth Wayne Turteltaub
Turteltaub, Kenneth Wayne, "Effects of clofibric acid on porcine hepatocytes: a new model for the study of peroxisomal metabolism " (1987). Retrospective Theses and Dissertations. 9309.