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The mechanisms regulating the induction of hepatic DNA synthesis by PPARα agonists are currently incompletely understood, and we set out to determine whether there are different mechanisms of induction for PPARα agonists and other hepatic growth agents. High levels of hepatic DNA synthesis (3–7%) were induced by a PPARα agonist, ciprofibrate, and by a PXRα agonist, cyproterone acetate, and liver samples were taken for transcriptomic analysis in a contemporaneous experiment. Microarray analysis of tissue RNAs detected gene induction at 24 hours after dosing, but failed to detect any biologically plausible response at 1–5 hours after dosing. RNA sequencing of control and ciprofibrate samples at 3 hours after dosing revealed 527 perturbed genes, including known PPARα target genes. Seven candidate genes of interest in regulating cell growth and apoptosis were examined by RT-PCR, and were confirmed to be induced by ciprofibrate treatment. Cyproterone acetate, TCPOBOP and partial hepatectomy induced a distinct spectrum of gene induction for ciprofibrate, demonstrating that ciprofibrate induces DNA synthesis through a unique mechanism. These data show that RNA sequencing is a powerful tool for analysis of differentially induced genes in rat liver, and for identification of candidate genes that mediate the induction of DNA synthesis by PPARα agonists.

Fibrates, such as ciprofibrate, fenofibrate, and clofibrate, are peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists that have been in clinical use for many decades for treatment of dyslipidemia. When mice and rats are given PPARalpha agonists, these drugs cause hepatic peroxisome proliferation, hypertrophy, hyperplasia, and eventually hepatocarcinogenesis. Importantly, primates are relatively refractory to these effects; however, the mechanisms for the species differences are not clearly understood. Cynomolgus monkeys were exposed to ciprofibrate at various dose levels for either 4 or 15 days, and the liver transcriptional profiles were examined using Affymetrix human GeneChips. Strong upregulation of many genes relating to fatty acid metabolism and mitochondrial oxidative phosphorylation was observed; this reflects the known pharmacology and activity of the fibrates. In addition, (1) many genes related to ribosome and proteasome biosynthesis were upregulated, (2) a large number of genes downregulated were in the complement and coagulation cascades, (3) a number of key regulatory genes, including members of the JUN, MYC, and NFkappaB families were downregulated, which appears to be in contrast to the rodent, where JUN and MYC are reported to upregulated after PPARalpha agonist treatment, (4) no transcriptional signal for DNA damage or oxidative stress was observed, and (5) transcriptional signals consistent with an anti-proliferative and a pro-apoptotic effect were seen. We also compared the primate data to literature reports of hepatic transcriptional profiling in PPARalpha-treated rodents, which showed that the magnitude of induction in beta-oxidation pathways was substantially greater in the rodent than the primate.

The 6 antihyperlipidemic agents—bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil—were separated on octadecyl (C18) and cyano (CN) chemically bonded columns using mobile phases containing phosphate buffer and different amounts of acetonitrile, dioxane, propan-2-ol, methanol, and tetrahydrofuran. Relationships between log k values and mobile phase composition have been examined for these systems. Analysis was performed on a Waters LC system with Merck LichroCART C18 and CN 125 mm columns using a flow rate of 1 mL/min and 227 nm detection. More than one-half of the results fitted Snyder-Soczewinski equations with r > 0.995. Separation of all drugs was achieved on the C18 column with a mobile phase containing 45% propan-2-ol in phosphate buffer (pH = 2.145) and on a CN column with 20% acetonitrile in the same buffer. The best mobile phase, containing 45% propan-2-ol, was used to quantitate bezafibrate, ciprofibrate, fenofibrate, and gemfibrozil in pharmaceutical formulations. The active substances were extracted with methanol. The calibration curve was constructed in the 0.1–0.8 mg/mL range for all drugs and provided satisfactory linearity (Lack-of-Fit test and Mandel's test). The recovery function was sufficiently linear in all cases, with an insignificant intercept and slope very close to 1. Accuracy was tested by quantitating 3 fortified samples (50, 100, and 150%), which gave results without significant differences. None of the excipients interfered in the analysis. The recovery was 99.85% for bezafibrate, 99.02% for ciprofibrate, 99.53% for fenofibrate, and 99.92% for gemfibrozil, with relative standard deviation values of 0.63, 1.61, 1.84, and 0.88%, respectively.

Nuclear factor-kappaB (NF-kappaB) is an oxidative stress-activated transcription factor involved in the regulation of cell proliferation and apoptosis. We found previously that the peroxisome proliferator ciprofibrate activates NF-kappaB in the livers of rats and mice. These species are sensitive to the hepatocarcinogenic effects of peroxisome proliferators, whereas other species such as Syrian hamsters are not. In the present study we examined the effects of 3 different peroxisome proliferators on NF-kappaB activation in rats and Syrian hamsters. The peroxisome proliferators Wy-14,643, gemfibrozil, and dibutyl phthalate were administered to animals for 6, 34, or 90 days. NF-kappaB activity was determined using electrophoretic mobility-shift assays and confirmed using supershift assays. Wy-14,643 increased the DNA binding activity of NF-kappaB at all 3 time points in rats and produced the highest activation of the 3 chemicals tested. Gemfibrozil and dibutyl phthalate increased NF-kappaB activation to a lesser extent in rats and not at all times. There were no differences in hepatic NF-kappaB levels between control hamsters and hamsters treated with any of the peroxisome proliferators. This study demonstrates species-specific differences in hepatic NF-kappaB activation by peroxisome proliferators.

Background. Some reports indicate that fibrates can induce renal dysfunction. However, the clinical characteristics of these episodes, and the respective nephrotoxicity of the four main fibrates used—namely, Introduction fenofibrate, bezafibrate, ciprofibrate, and gemfibrozil— remain ill defined. Hypercholesterolaemia and hypertriglyceridaemia are Methods. To better characterize this side-effect, we important risk factors for the development of atherofirst reviewed the charts of 27 patients from our sclerosis [1–3]. Lipid-lowering drugs are therefore freinstitution who developed an impairment of renal quently prescribed among the general population. function during fibrate therapy. We next analysed the Hypolipaemic agents are also often administered to articles (n=24) that contained data on renal function patients suffering from chronic nephropathies [4], as in patients taking fibrates (n=2676). well as in transplanted patients treated by cyclosporin Results. Among our 27 patients, 25 were on fenofibrate or corticosteroids. Indeed, these conditions are associtherapy, one was taking bezafibrate, and one ciproated with an increased incidence of hyperlipidaemia fibrate. Nineteen were recipients of solid-organ trans

There are good news for the alcohol field. In the past few years, peroxisome proliferator-activator drugs were reported to reduce voluntary alcohol intake in animal models. Barson et al. (2009) showed that gemfibrozil reduced alcohol drinking in rats. Recently, similar results were obtained with fenofibrate in high-alcohol-drinker UChB rats (Karahanian et al. , 2014) and mice (Blednov et al. , 2015). Moreover, a phase 2 clinical trial led by Barbara Mason (The Scripps Research Institute) was started to test the hypothesis that alcohol-dependent subjects treated with fenofibrate will report decreased craving for alcohol following cue-exposure and will report less drinking post treatment (clinicaltrials.gov/ct2/show/NCT02158273). The peroxisome proliferator-activated receptors (PPARs) are transcription factors (nuclear receptors) that play essential roles in the regulation of cellular differentiation, development and metabolism. Three types of PPARs have been identified: alpha, gamma and beta/delta. PPARα is the most abundant isoform in the liver; PPARβ/δ is expressed ubiquitously in all tissues; and PPARγ is expressed mainly in adipose tissue. PPARα is activated by natural ligands (some types of fatty acids) and by synthetic agonists such as fibrate drugs (clofibrate, gemfibrozil, ciprofibrate, bezafibrate and fenofibrate). Fibrates are widely used in the clinic for the treatment of high blood-triglyceride levels. The mechanisms by which PPARα agonists are effective in reducing alcohol consumption are not fully understood. Currently, there are two views: (a) fibrates would act in the brain, changing the expression of genes …

Peroxisome proliferators cause liver cell proliferation in addition to other pleiotropic effects such as peroxisome proliferation and induction of certain peroxisomal and cytosolic enzymes in liver. Since dexamethasone has been shown to inhibit mitogen-induced liver cell hyperplasia, we examined whether dexamethasone inhibits only cell proliferation without affecting peroxisome proliferation induced by peroxisome proliferators such as ciprofibrate. Livers of rats fed a diet containing ciprofibrate (0.025%) with or without added dexamethasone (0.5 mg or 1 mg/kg diet) for 1 week were evaluated for hepatocyte proliferation and peroxisome proliferation. Dexamethasone administration resulted in abrogation of ciprofibrate-induced cell proliferation as shown by bromodeoxyuridine (BrdU) labeling and mitoses counts. The hepatocyte proliferative index measured after administration of a single dose of BrdU was 18.3 +/- 1.1 and 2.3 +/- 0.7% (p < 0.01) in ciprofibrate and ciprofibrate + dexamethasone treated rats, respectively. With multiple injections of BrdU (daily injections for 7 days) the proliferative index was 225 +/- 10 and 183 +/- 2% (p < 0.02), respectively, in these two groups. Interestingly, whereas the levels of peroxisome proliferator-induced Mr 80,000 polypeptide and catalase and peroxisomal bifunctional enzyme, and the corresponding mRNAs and peroxisome volume density were unaffected. These results show that dexamethasone selectively inhibits only cell proliferation without inhibiting the peroxisome proliferation caused by ciprofibrate. This model should be useful for examining the role of cell proliferation versus oxidative stress in peroxisome proliferator-induced hepatocarcinogenesis.

To understand the mechanism of peroxisome proliferator-induced oxidative stress in non-mutagenic carcinogenesis, the effect of ciprofibrate, a peroxisome proliferator, on the activities and protein amounts of various antioxidant enzymes in different subcellular compartments was examined. Ciprofibrate treatment for short-term (3 weeks) as well as long-term (12 weeks) duration increased the total cellular catalase activity, whereas superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities were decreased significantly. Withdrawal of ciprofibrate from the diet did not normalize these activities. The observed decreases in total cellular SOD and GPX activities following ciprofibrate treatment were due to significant decreases in cytosolic CuZn SOD and GPX, whereas mitochondrial levels of Mn SOD and GPX were relatively unchanged. The peroxisomal CuZn SOD and GPX activities were increased significantly after both short- and long-term treatment, whereas catalase activity was reduced. Western blot analysis of cytoplasm for GPX and CuZn SOD showed a significant decrease in GPX and CuZn SOD proteins. Mitochondrial GPX protein was found to be slightly decreased, whereas Mn SOD protein levels did not show any significant change. The excessive production of H2O2 by oxidases and O2- by the cytochrome P450 enzyme system, along with the observed loss of antioxidant protection by loss of activities of catalase in peroxisomes and GPX and CuZn SOD in cytoplasm, may be the critical factors in peroxisomal proliferator-induced oxidative stress and initiation and promotion of carcinogenesis by this class of non-mutagenic agents. Both enzyme activities, as well as protein amounts of GPX and CuZn SOD, were higher in peroxisomes but lower in cytoplasm in ciprofibrate-treated liver as compared to control liver. The Mn SOD protein was decreased in peroxisomes, whereas mitochondrial Mn SOD was relatively unaffected in ciprofibrate-treated liver as compared to control. These observations suggest that the regulation of expression of peroxisomal CuZn SOD and Mn SOD is different from their counterparts in other cellular compartments.

The majority of genotoxic carcinogen-induced liver tumours of the sensitive B6C3F1 mouse contain activated H-ras oncogenes. Such mutations also occur in hepatocarcinogenesis-resistant strains. In order to determine whether this is true of non-genotoxic carcinogen-induced tumours, liver tumours induced in B6C3F1 and C57BL/10J mice by methylclofenapate (MCP) were compared. Polymerase chain reaction (PCR) analysis revealed H-ras codon 61 mutations in 11/46 B6C3F1 and 4/31 C57BL/10J liver tumours. The nude mouse tumorigenicity (NMT) assay was used to analyse tumours without codon 61 mutations. Of the 12 B6C3F1 liver tumour DNAs subjected to this assay, one contained a H-ras codon 117 mutation. Further PCR analysis on frozen tumour samples (46 B6C3F1 and 15 C57BL/10J) revealed no codon 12 mutations; one additional codon 117 mutation was identified in a B6C3F1 tumour. Overall, then, H-ras codon 61 mutations were detected in MCP-induced B6C3F1 tumours less frequently than in genotoxin-induced tumours. Two B6C3F1 tumours contained codon 117 mutations similar to those previously found in tumours induced by ciprofibrate, furan and furfural, and in at least one spontaneous tumour. Ras mutations were also detected in some C57BL/10J tumours, providing further evidence that ras oncogenes can participate in hepatocarcinogenesis in resistant mice.

Lack of Peroxisome Proliferation in Marmoset Liver Following Treatment with Ciprofibrate for 3 Years. Graham, M. J., Wilson, S. A., Winham, M. A., Spencer, A. J., Rees, J. A., Old, S. L., and Bonner, F. W. (1994). Fundam. Appl. Toxicol. 22, 58-64. The effect of treatment of marmosets with ciprofibrate for 3 years on activities of hepatic enzymes, hepatic histomorphology, and ultrastructure were investigated. Male and female marmosets were dosed with ciprofibrate (2, 10, and 20 mg/kg) by oral gavage once daily for 3 years. No effect on liver weight (adjusted for body weight) or liver morphology was observed. The activities of catalase, glutathione peroxidase, α-glycerophosphate dehydrogenase, benzphetamine N-demethylase, and ethoxyresorufin O-deethylase were unaffected by treatment with ciprofibrate. Activity of glutathione transferase was increased in the low dosage group but unaffected in the mid and high dosage groups. Modest increases in activities of peroxisomal β-oxidation (2.5-fold, maximal), carnitine acetyl transferase (1.7-fold, maximal), an carnitine palmitoyl transferase (2-fold, maximal) were observed. Cytochemical staining and quantitative image analysis failed to indicate any effect on peroxisomal number, size, or volume density. Similarly, there was no increase in lipofuscin deposition. This study provides data on the effects of a potent peroxisome proliferator on primate liver following a dosing period much greater than that used in previously published studies and is further evidence that the marmoset is relatively insensitive to the well-documented effects that ciprofibrate and other peroxisome proliferators have on rat liver.

The response of promoter-exposed hepatocytes to the complete hepatic mitogens hepatocyte growth factor (HGF), epidermal growth factor (EGF) and acidic fibroblast growth factor (aFGF) was studied. Male Fisher 344 rats were administered phenobarbital or ciprofibrate. Hepatocytes were isolated at various time points and cultured in type I collagen gels, a 3-dimensional culture system that allows stable long-term hepatocyte differentiation. DNA synthetic activity in response to addition of HGF, aFGF or EGF to the cultures was assayed by incorporation of [3H]thymidine. Administration of ciprofibrate to rats caused an immediate decreased growth response in hepatocytes to all three growth factors. Phenobarbital administration caused a gradual decrease in responsiveness to the growth factors: after 10 days, hepatocytes became insensitive to the mitogenic effects of HGF, EGF and aFGF. However, an early increase in responsiveness to HGF and aFGF occurred in phenobarbital-exposed hepatocytes. The results indicate that phenobarbital and ciprofibrate have similar inhibitory effects on hepatocyte DNA synthesis in culture after long-term in vivo exposure. However, their early effects on hepatocyte growth response differ considerably, suggesting that their effects on cellular proliferation occur via different mechanisms.

For the analysis of the molecular mechanism of the action of peroxisome proliferators, we attempted to establish the optimal conditions for obtaining the effects of the chemicals in vitro, employing an established cell line, Reuber rat hepatoma H4IIEC3. Histochemical analyses revealed a marked increase in the number, size, and catalase content of peroxisomes in the cells cultured on a medium containing 0.5 mM ciprofibrate, a peroxisome proliferator. The activity of acyl-CoA oxidase, the initial enzyme of the peroxisomal beta-oxidation system, was increased by more than 10-fold by the same treatment. Catalase was also induced significantly, whereas the activities of glutamate dehydrogenase and lactate dehydrogenase, mitochondrial and cytosolic marker enzymes, did not change upon the treatment. Immunoblotting and RNA-blotting analyses confirmed the increases in the amount of protein and mRNA for all the three enzymes of the peroxisomal beta-oxidation system. Cell fractionation experiments gave a partial separation of peroxisomes from other organelles for the induced culture. Thus, H4IIEC3 cells offer a good in vitro model system of the induction of peroxisomes and peroxisomal beta-oxidation enzymes by peroxisome proliferators.

The peroxisome proliferator ciprofibrate was tested for its ability to induce DNA damage in the form of 5-hydroxymethyl-2'-deoxyuridine (HMdU), an adduct that results from the reaction of thymine in DNA with hydroxyl radicals. In order to quantify HMdU, DNA containing [3H]thymidine of high specific activity had to be obtained. Since hepatocytes normally have a very low rate of DNA synthesis, rats were subjected to partial hepatectomy to stimulate DNA synthesis and then were administered [methyl-3H]thymidine by three p.o., i.p. or i.v. injections 20, 22 and 24 h after partial hepatectomy; or by slow infusion through the portal vein, starting 20 h after partial hepatectomy for 4 h. The specific activity of DNA in rats receiving [3H]thymidine through the portal vein was considerably higher than in rats receiving p.o., i.p. or i.v. injections. Rats were then exposed to various doses of gamma-irradiation after partial hepatectomy and infusion of [6-3H]thymidine through the portal vein. DNA from the liver was extracted, enzymatically hydrolyzed and analyzed by HPLC. The percentage of HMdU in DNA increased in a dose-dependent manner. Rats were then treated with the carcinogens 2-acetylaminofluorene (AAF) or diethylnitrosamine (DEN) in conjunction with partial hepatectomy and infusion of [methyl-3H]thymidine. There was an increase in HMdU formation after a single administration of DEN or AAF. Another group of rats was fed a diet containing the peroxisome proliferator ciprofibrate for 3 weeks. After partial hepatectomy and infusion of [6-3H]thymidine, these rats were fed the same ciprofibrate-containing diet for 2-4 more weeks. HMdU was detected in DNA at 2-4 weeks after [6-3H]thymidine infusion, but the level at 4 weeks was nearly 50% less than at 2 weeks. This study shows that oxidative DNA damage in the form of HMdU is induced in the liver by gamma-irradiation, DEN, AAF and peroxisome proliferation.

Peroxisome proliferators are a class of non-mutagenic hepatocarcinogens, which induce a similar pleiotropic response such as hepatomegaly, proliferation of the peroxisomes in hepatocytes and hepatocarcinogenesis. Peroxisome proliferators are not detectable by the Ames assay and various other short-term tests. Recently a system for intrachromosomal recombination in yeast (DEL) has been shown to be inducible by a variety of non-mutagenic carcinogens. These include many carcinogens that are not detectable by the Ames assay or by various other short-term tests. In the present study the peroxisome proliferators [4-chloro-6-(2,3-xylidino)-2-pyrimidinyl-thio]acetic acid (Wy-14,643); methyl-2-[4-(p-chlorophenyl)phenoxy]2-methyl propionate (methyl clofenopate); 2-methyl-2[p-(1,2,3,4-tetrahydro-1- naphthyl)phenoxy]-propionic acid (nafenopin); 2-[4-(2,2-dichlorocyclopropyl)phenoxy]2-methyl-propionic acid (ciprofibrate); [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio(N-beta-hydroxyethyl)-acetam ide] (BR-931); and ethyl alpha-p-chlorophenoxyisobutyrate (clofibrate) have been tested for their potential to induce DEL as well as interchromosomal recombination in yeast. No evidence for induction of either system has been found in the presence or the absence of the supernatant (S9) from rat liver homogenate. The data support the notion that peroxisome proliferators are truly non-mutagenic carcinogens.

The ECL-cell hyperplasia and ECL-cell carcinoids occurring during long-term treatment with ciprofibrate, have been attributed to hypergastrinemia secondary to an inhibitory effect on acid secretion. However, nobody has given any explanation of the mechanism by which ciprofibrate and related phenoxyisobutyrate derivates inhibit acid secretion. Moreover, the reported inhibition of acid secretion has only been moderate, in contrast to the profound inhibition of acid secretion needed to induce similar ECL-cell changes. To re-examine the effect of ciprofibrate on gastric acidity and serum gastrin, we randomly assigned 33 male Fisher rats into three treatment groups (100 or 20 mg/kg/day of ciprofibrate and control) during a period of 4 weeks. Daily assessments of gastric acidity was done by gastric intubation, using a tube with a diameter of 2.0 mm allowing the introduction of an infant pH-catheter. Measurements were done in all animals 5 days a week. Ciprofibrate did not raise gastric pH. On the contrary, the highest dose increased the acidity. Serum gastrin levels measured in blood taken by vein puncture before the initiation of the drug treatment and on the last day of the 4 week treatment period, revealed a dose-related significant hypergastrinemic effect of ciprofibrate. The slight increase in gastric acidity in the ciprofibrate high-dose group is most likely due to the hypergastrinemia provoked by the drug. This hypergastrinemia is therefore not secondary to an inhibition of acid secretion, but may be due to a direct effect of ciprofibrate on the G-cell. The ECL-cell hyperplasia and the ECL-cell carcinoids, which develop during treatment with peroxysome-proliferators are thus due to hypergastrinemia, which is not secondary to inhibition of acid secretion.

In their recent report, Whitfield et al. (1) suggest that serum γ-glutamyltransferase (GGT) may originate from atheromotous plaques. This interesting proposal can be further supported. There is evidence showing that human platelets may be a source of GGT (2)(3), but this contribution may be small (3). Therefore, increased platelet consumption at the site of these plaques may contribute to an increase in serum GGT activity. In Table 1 of their report, the authors (1) do not consider serum bilirubin among the variables correlating with serum GGT activity. It may be interesting to assess that link because bilirubin concentrations may be lower in patients with vascular disease (4). Stronger evidence indicates that women and …

Studies with regenerating liver and hepatocyte cultures have shown that the alpha-1 adrenergic receptor (A1AR) is involved in the early events which transmit a mitogenic signal to hepatocytes after 2/3 partial hepatectomy. In this study, we investigated the role of A1AR in DNA synthesis associated with the augmentative hyperplasia stimulated by the xenobiotic hepatic tumor promoters phenobarbital (PB) and alpha-hexachlorocyclohexane (alpha-HCH), and the peroxisome proliferator ciprofibrate. Male F344 rats were treated with each of the three xenobiotics to stimulate hepatic DNA synthesis. When either phenobarbital or alpha-HCH administration was preceded and accompanied by the A1AR antagonist prazosin, DNA synthesis was significantly inhibited, as measured by [3H]thymidine incorporation or 5-bromo-2'-deoxyuridine (BrdU) nuclear labeling index. There was no inhibition of DNA synthesis by prazosin in the ciprofibrate treated group. The inhibition of hepatic DNA synthesis by prazosin was accompanied by non-significant changes in the number of alpha-1 binding sites in the PB and alpha-HCH treated groups, but a significantly reduced number of alpha-1 binding sites in the ciprofibrate treated group. These studies suggest that A1AR is involved in generating the mitogenic signal leading to hepatic DNA synthesis induced by xenobiotic hepatic tumor promoters phenobarbital and alpha-HCH. A1AR is not involved in the mitogenic pathway generated by the peroxisome proliferator ciprofibrate.

Hepatocarcinogenic peroxisome proliferators, clofibrate, ciprofibrate, Wy-14643 or di(2-ethylhexyl)phthalate, were administered once daily by gavage to groups of three male F344 rats for 3 days and the rats were killed 2 h after the last dose. The DNA isolated from the livers was analyzed for possible carcinogen-DNA adducts, by a most sensitive 32P-postlabeling technique which can detect one adduct in 10(10) nucleotides. No adducts were detected by this assay in the DNA isolated from the livers of rats treated with any of the peroxisome proliferators. Adducts were also not found in the DNA of hepatocytes exposed in vitro to these peroxisome proliferators for 4 h in primary suspension cultures. Failure to detect peroxisome proliferator DNA adducts in hepatocytes under in vivo and in vitro conditions supports the contention that formation of a peroxisome proliferator-DNA adduct is not an essential step in the carcinogenesis by this novel class of carcinogens.

The distribution of radiolabel in male mice was studied by whole-body autoradiography at intervals after oral administration of [14C]ciprofibrate, a carcinogenic hepatic peroxisome proliferator. Radioactivity was rapidly taken up by the liver and to a lesser extent by the brown fat within 9 h after oral dosing of ciprofibrate. The radioactivity levels in blood, interstitial fluid and fat decreased during the first 3 days after dosing, but the liver remained densely labeled. Between 3 and 27 days after dosing, liver exhibited a stippled pattern as a result of heavier labeling apparently around the central veins. The relatively low levels of radiolabel in extra-hepatic tissues observed after oral dosing, together with the prolonged retention in this region of the liver, is consistent with the hepatotropic effects (i.e. hepatic peroxisome proliferation and development of liver tumors) exerted by this compound.

Previous studies revealed that putative preneoplastic and neoplastic lesions induced in the liver by Wy-14,643, a peroxisome proliferator, were gamma-glutamyl transpeptidase (GGT) negative. For ascertainment as to whether phenotypes of foci and carcinomas induced by all peroxisome proliferators are similarly GGT negative, altered areas (AAs), neoplastic nodules (NNs), and hepatocellular carcinomas (HCCs) induced in the livers of male F344 rats by chronic dietary administration of ciprofibrate (0.025% wt/wt in chow; CAS: 52214-84-3) were analyzed histochemically for GGT activity. Eighty-nine percent of AAs, 91% of NNs, and 91% of HCCs were GGT negative. The GGT-negative property of these various hepatic preneoplastic and neoplastic lesions persisted at 8 weeks after the withdrawal of ciprofibrate treatment. The results of this study indicate that the absence of GGT activity is a common feature in hepatic lesions induced by structurally unrelated peroxisome proliferators and is not related to the drug toxicity. The proposal was made that peroxisome proliferators do not derepress the activity of the GGT gene during hepatocarcinogenesis in the rat.