Response of microbodies in Morris hepatoma 9618A to clofibrate

Peroxisome proliferation in neoplastic nodules and hepatocellular carcinomas induced by ciprofibrate in the rat

Neoplastic nodules (NN) and hepatocellular carcinomas (HCC) induced in the rat by ciprofibrate were analyzed for peroxisome proliferation. The volume density of peroxisomes in NN and HCC was 5.7 +/- 2.7 and 6.6 +/- 2.9, respectively; whereas in adjacent uninvolved liver the volume density was 16.3 +/- 5.0. No ultrastructural differences between NN were found to discriminate nodule from carcinoma. The results of this study indicate that the peroxisome proliferative response of NN and HCC to ciprofibrate is similar and can not be used as a marker to differentiate these lesions.

Morphometric and cytochemical evaluation of clofibrate-induced peroxisomal proliferation in adult rat hepatocytes cultured on floating collagen gels

The present ultrastructural morphometric and cytochemical studies demonstrate clofibrate induced changes in peroxisomes in adult rat hepatocytes maintained for 14 days in primary culture on floating collagen gels. Catalase activity and the number and diameter of peroxisomes were reduced in hepatocytes cultured for between 2/3 and 7 days. However, hepatocytes cultured for 7-14 days had well-developed peroxisomes containing crystalloid nucleoids. The number of anucleoid peroxisomes in hepatocytes treated with 2 mM Na clofibrate increased with culture age, and by day 14 the number was 2.9 times greater than in freshly isolated hepatocytes. Catalase activity, as well as the number of nucleoid-containing peroxisomes were much greater in treated hepatocytes than in untreated controls, but decreased slightly with culture age. The diameter of peroxisomes was not reduced in the treated cells. These results suggest that the treatment with Na clofibrate is effective both for proliferation and maintenance of peroxisomes and for enhancing catalase activity. In treated hepatocytes, matrical plates were formed in peroxisomes from days 5 to 14 and the number of plate-containing peroxisomes increased with culture age.

Peroxisomes in human foetal kidney: variations in size and number during development

The kidneys of 15 human foetuses (10-18 weeks of age) were used for morphometric studies on peroxisomes during gestational development and in organ culture. The catalase positive organelles revealed by DAB were round to ovoid with a granular matrix delimited by a membrane occasionally deformed by marginal plates. Generally, the distribution was uniform in cells of proximal tubules. In the same cell, size and density varied. The number fluctuated from cell to cell. No significant difference in the mean diameter was observed from the 10th to 18th weeks of gestation, although the mean value (0.36 +/- 0.1 micron) was significantly less than the adult figure. These results indicate that size modifications might occur later on in gestation or after birth to reach the adult value. During the studied period, the mean number of peroxisomes per 100 micron2 of surface area did not differ significantly from that of the 10-12 week group (10.5 +/- 1.97). No important changes of peroxisome morphology in kidney explants cultured for 7 days were noticed on day 3-4. Thereafter, the shape of many peroxisomes became elongated or irregular; marginal plates were frequent. A decrease in the diameter of peroxisomes began at day 4, became significant on day 5 and more accentuated on day 7. In addition, as the culture matured, there was a progressive reduction in catalase activity, revealed by a diminished density of the peroxisomal matrix. The number of DAB positive organelles per surface area decreased steadily with culture age, and significantly on day 2 (p less than 0.01) to become drastically low on day 5 and negligible on day 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of peroxisomes and their induction by clofibrate in normal adult rat hepatocytes in primary culture

Alterations in peroxisomes and catalase activity and their responsiveness to clofibrate in adult rat hepatocytes in primary culture were investigated. The numbers of peroxisomes with and without crystalloid nucleotids per unit cytoplasmic area were preserved in cultured hepatocytes for 2 d after seeding at a level comparable to that of freshly isolated hepatocytes. At Day 3 in culture, the number of anucleoid peroxisomes was reduced in untreated hepatocytes, accompanied by more significant reduction in the number of nucleoid-containing peroxisomes, which decreased until Day 5. Peroxisome diameters were reduced in untreated hepatocytes at Day 2 and this decrease in the diameter was continued until Day 7. Catalase activity in untreated hepatocytes decreased markedly with culture age. The number of anucleoid peroxisomes was significantly greater in hepatocytes treated with 2 mM clofibrate in culture than in freshly isolated hepatocytes for 2 d or in untreated hepatocytes of the same culture age through 7 d. The number of nucleoid-containing peroxisomes in the treated cells began to decrease in 3 d, but was greater than that of untreated cells at Days 3 and 5. Peroxisomes with well-developed nucleoids were observed frequently in the treated cells even at Day 7. Peroxisome diameters were greater in the treated cells than in untreated cells at Days 3, 5, and 7. Catalase activity was always higher in the treated cells than in untreated cells. These results suggest that clofibrate is effective in inducing peroxisome proliferation as well as in maintaining the organelles in cultured hepatocytes.

The short- and long-term effects of bezafibrate in the rat

Bezafibrate is a potent hypolipidemic agent, which causes marked proliferation of peroxisomes in rat liver. At the same dosage, bezafibrate is more effective in male than in female rats. This is probably related to divergent pharmacokinetics, which cause differences in drug level in serum and liver. The volume density of peroxisomes and several of their enzymes such as carnitine acetyl transferase and acyl-COA oxidase increase in a dose-related fashion. The hypolipidemic effect of bezafibrate, however, does not correlate with the used dosage. This implies that peroxisomal proliferation may play only a minor role in the hypolipidemic action of bezafibrate. In animals treated for 26 months with 300, 750, or 1500 ppm bezafibrate, the relative liver weight and serum triglycerides did not differ significantly from controls. Peroxisomal proliferation varied in different cells, being most prominent in single hepatocytes. The liver catalase activity was significantly reduced, but carnitine acetyl transferase was increased. Abnormal peroxisomes and mitochondria with longitudinal cristae were quite frequent. In one focus, catalase activity was severely diminished ahd peroxisomes were markedly reduced. The incidence of liver tumors was the same (1-3%) in treated animals as in controls.

The proliferative response of hepatic peroxidomes of neonatal rats to treatment with SU-13 437 (nafenopin)

The repeated administration of the hypolipidemic agent Su-13 437 (nafenopin) to neonatal rats roughly doubled the number of peroxisomes in the liver tissue and caused a sixfold volumetric expansion of the peroxisomal compartment. During the proliferative response, the size-distribution of the peroxisomes was reversibly altered, enlarged particles appearing in numbers varying according to the dose given. By means of a new method for quantitative autoradiography, it was shown that (a) the concentration of silver grains over peroxisomes was comparable to that found over the endoplasmic reticulum; (b) the peak incorporation of [3H]arginine into the peroxisomes was dealyed in comparison with that into the endoplasmic reticulum; (c) the label, once incorporated into the expanding peroxisomal compartment, displayed the same shift to large particles as did the whole population. These results are compatible with the biosynthetic pathway for peroxisomal catalase proposed earlier (cf. reference 12), and with the notion that the drug-induced size-shift might have resulted from progressive growth of a particular class of peroxisomes formed in the presence of the agent. Evidence is presented to show that during the recovery period the larger peroxisomes are removed preferentially.