Response to thyroxine of lamellar bodies, peroxisomes and peroxisomal enzymes in the adult rat lung.
ABSTRACT Adult male rats were fed a standard diet containing 25 mg/kg L-thyroxine for 2 weeks. The hyperthyreotic condition of the animals was checked by monitoring the metabolic rates and liver glycerol-3-phosphate dehydrogenase. In the postnuclear fraction of the lung the activity of fatty acyl-CoA oxidase, the enzyme responsible for the rate limiting first step of peroxisomal fatty acid beta-oxidation, showed a twofold increase. Catalase, the marker enzyme of peroxisomes, showed a similar increase. Electron microscopic examination of alveolar type II cells did not reveal changes in the number and distribution frequency of peroxisomes and lamellar bodies. Similarly the content of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (dipalmitoyl phosphatidylcholine), the main constituent of alveolar surfactant, was not altered significantly by thyroxine feeding. On the other hand the volume density of the peroxisomal compartment was found to be doubled according to the measured increase of catalase and acyl-CoA oxidase. Our data suggest that the induction of peroxisomal matrix enzymes, such as catalase and fatty acyl-CoA oxidase, does not influence the surfactant content.
Article: Differential induction of peroxisomal enzymes by hypolipidaemics in human (HepG2) and rat (MH1C1) hepatoma cell lines.[show abstract] [hide abstract]
ABSTRACT: Human (HepG2) and rat (MH1C1) hepatoblastoma cells were incubated with different concentrations of the hypolipidaemics cetaben, clofibrate and thyroxine. The enzymatic activities of catalase, peroxisomal bifunctional enzyme, succinate dehydrogenase, and 3-oxoacyl-CoA thiolase were measured. In order to determine the point of regulation of the enzymatic activities Northern and Slot blot experiments with probes for peroxisomal bifunctional enzyme, catalase and fatty acyl CoA oxidase were performed on total RNA. Catalase activity was enhanced in HepG2 cells treated with 3 mmol/l clofibric acid to 135% of control and the mRNA value to 2.6 fold, whereas in cetaben treated cells the enhancement (up to 119% of control) was less pronounced. In MH1C1 cells catalase activity was not changed by any of the drugs. The activity of the peroxisomal bifunctional enzyme was not affected in HepG2 cells by clofibric acid and cetaben, whereas the mRNA level was elevated to 2.3 fold by 10 micromol/l cetaben. At high concentrations of cetaben all enzyme activities were decreased in both cell lines due to its high cytotoxicity. Our data show that, due to the differences in the genomic organisation, the regulation of the enzyme activities is different in human and rat, but the results from the human and rat hepatoblastoma cells correlate with the findings in whole man and rat, so that a human in vitro system is more suitable for pharmacological tests. These results suggest that the human hepatoma cell line HepG2 may be a useful model system for studies of the influence of hypolipidaemics on the peroxisomal enzyme system.European journal of clinical chemistry and clinical biochemistry: journal of the Forum of European Clinical Chemistry Societies 12/1995; 33(11):775-83.