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Vitamin A-adequate and vitamin A-deficient C57B1/6 mice were treated for ten days with 0.02% (w/w) perfluorooctanoic acid (PFOA) in their diet. Treated vitamin A-adequate and -deficient mice demonstrated approximately the same increases in liver somatic index (g liver/g body weight) (somewhat more than 2-fold) and mitochondrial protein content (5-fold). PFOA treatment resulted in a 26-fold increase in hepatic peroxisomal lauroyl-CoA oxidase activity in vitamin A-adequate mice, whereas the same activity was unchanged in vitamin A-deficient mice. Vitamin A deficiency itself caused a 3- to 4-fold increase in cytosolic catalase activity and a smaller increase in the activity of microsomal cytochrome P-450 IVA (lauric acid ω- and ω-1 hydroxylase) in this same organ. The induction of the activities of these enzymes was less prominent in vitamin A-deficient mice compared with the effect caused by PFOA in vitamin A-adequate mice, resulting in approximately the same maximal values for these parameters in both groups (i.e. approx. 21 mmol/g liver · min and 350 nmol/g liver · min, respectively). A 70 kDa protein, presumably the multifunctional protein, was shown by Commassie blue staining of SDS-polyacrylamide gels and by immunoblotting (with antibodies towards the multifunctional protein) to be induced to approximately the same degree in vitamin A-adequate and -deficient mice. A morphometric study revealed that PFOA causes the same extent of hepatic peroxisome proliferation in vitamin A-deficient as in vitamin A-adequate mice. The possibility that PFOA exerts its effect in vivo through at least two different mechanisms is discussed.

Morris hepatoma 7800C1 cells (a Wistar rat cell line) were exposed to 100 microM arachidonic acid in the medium for seven days. This treatment resulted in 150% and 60% increases (above control activities) in acyl-CoA oxidase (which catalyzes the first step in peroxisomal beta-oxidation) and catalase activities, respectively. Arachidonic acid (C20:4) can be metabolized to 20- and 19-hydroxy-arachidonic acid by cytochrome P-450IVA and it was shown that our cells are capable of forming 20-hydroxyarachidonic acid. However, 20-hydroxyarachidonic acid (0.1-0.8 microM, 4 days) had no effects on lauroyl-CoA oxidase and catalase activities in Morris hepatoma cells. Treatment of 7800C1 cells with 100 microM all-trans-retinoic acid resulted in inductions of catalase (160% above the control activity) and carnitine acetyltransferase (140% above the control activity) activities. The activity of lauroyl-CoA oxidase was often, but not always, slightly induced by treatment with all-trans-retinoic acid. When all-trans-retinoic acid was administered together with arachidonic acid, these two compounds had a synergistic effect on the induction of acyl-CoA oxidase activity (almost 700% above the control activity). However, treatment of Morris hepatoma cells with the man-made peroxisome proliferator, perfluorooctanoic acid, together with all-trans-retinoic acid did not result in any synergistic effect on this same enzyme activity. In summary, this study (1) corroborates findings from transfection experiments indicating that the heterodimer PPAR-RXR alpha activates transcription of the acyl-CoA oxidase gene using the Morris hepatoma cell line; (2) shows that arachidonic acid induces the activity of lauroyl-CoA oxidase; (3) suggests that transcription of the catalase gene is not regulated by a PPAR-RXR alpha heterodimer in this system; and (4) demonstrates that peroxisome proliferation in Morris hepatoma cells by perfluorooctanoic acid is not as dependent on the level of retinoic acid as is the same process caused by arachidonic acid.