Identification of 3H-benzo[b] [1,4] diazepine derivatives as PPARα agonists by in silico studies and biochemical evaluation

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world, whose pathologic features include dysregulated glucose homeostasis and lipid accumulation. Peroxisome proliferators-activated receptor α (PPARα) is a key regulator of fatty acid metabolism and ketogenesis due to its regulatory pathways involve activating fatty acid uptake, accelerating fatty acid oxidation, inhibiting gluconeogenesis, and suppressing inflammation and fibrosis. Therefore, PPARα is considered as a potential target for the treatment of NAFLD and some agonists have entered clinical trials, which drove us to discover more novel PPARα agonists. In current work, new 3H-benzo[b] [1,4] diazepine PPARα agonists were identified from the ChemDiv database by pharmacophore modeling, molecular docking, derivative structure search, and bioassays, where compound LY-2 and its derivatives (LY-10∼LY-19) were discovered to promote the expression of PPARα downstream gene, carnitine palmitoyl transterase-1 α (cpt1α). Among these active compounds, the EC50 value of LY-2 against increasing cpt1α was 2.169 μΜ. Furthermore, the effect of LY-2 on cpt1α was weakened when PPARα knock down, which confirmed that it is a PPARα agonist again. Finally, the results from molecular dynamics simulations and binding free energy calculations showed that π-π stacking and hydrogen bonding interactions played key roles in the binding of LY-2 and PPARα protein and their complex maintained a stable structure to facilitate LY-2 to have a better binding affinity with PPARα protein. Taken together, compound LY-2 might be a novel lead compound for the development of potent PPARα agonists.Communicated by Ramaswamy H. Sarma.

Fenofibrate protects the neurovascular unit and ameliorates plasma corticosterone levels in pentylenetetrazole-induced kindling seizure in mice

Epileptic seizures are the most common neurological diseases that change the function of neurovascular unit at molecular levels accompanied by activation of a wide variety of neurodegenerative cascades. Based on the pleiotropic functions of peroxisome proliferator-activated receptor-alpha (PPARα), the current study evaluated the neuroprotective effects of fenofibrate (an effective PPARα agonist) on the brain injuries induced by pentylenetetrazole (PTZ)-induced kindling seizure. Adult male NMRI mice were randomly assigned into four groups (n = 14) as follows; control, untreated kindled mice (PTZ) and two fenofibrate-treated kindled groups. Repeated intraperitoneal injections of PTZ (45 mg/kg) were used to develop kindling seizure every 48 h for 21 days. Treated mice were administered orally fenofibrate at doses of 30 and 50 mg/kg/day during the study. Plasma corticosterone and brain levels of brain-derived neurotrophic factor (BDNF), malondialdehyde (MDA) and mRNA transcription of p53, as well as blood-brain barrier (BBB) permeability, were determined at termination of the study. Fenofibrate considerably improved seizure latency and anxiety-like behaviors in treated kindled mice. Fenofibrate at doses of 30 and 50 mg/kg significantly (P < 0.001) decreased plasma corticosterone (56.88 ± 0.80 and 54.81 ± 0.29 ng/mL, respectively) compared to PTZ group (74.96 ± 1.60 ng/mL). It also significantly (P < 0.05) decreased BDNF levels in both treatment groups (8.13 ± 0.14 and 8.74 ± 0.09 ng/mL, respectively) compared to PTZ group (9.68 ± 0.20 ng/mL). Fenofibrate particularly at higher dose significantly (P < 0.01) decreased MDA content and mRNA expression levels of p53 in treated kindled mice by 67% and 28%, respectively, compared to PTZ group. Similarly, 50 mg/kg fenofibrate significantly (P < 0.05) decreased Evans blue extravasation into brain in treated kindled mice (8.72 ± 0.96 µg/g) compared to PTZ group (15.31 ± 2.18 µg/g). Our results revealed the anticonvulsive and neuroprotective effects of fenofibrate in PTZ-induced kindling seizure in mice. Fenofibrate also improved the neurovascular functions at molecular levels in kindling seizure that might be associated with ameliorating the seizure behaviors.

2,4-Dihydroxyphenyl-benzo[d]thiazole (MHY553), a synthetic PPARα agonist, decreases age-associated inflammatory responses through PPARα activation and RS scavenging in the skin

We previously reported that 2,4-dihydroxyphenyl-benzo[d]thiazole (MHY553) is a PPARα agonist, which has been shown to inhibit tyrosinase activity in murine melanocyte and alleviate hepatic steatosis in aged rats. This study investigated the effects of MHY553 on the age-related occurrence of inflammatory responses via the molecular modulation of the nuclear factor-κB (NF-κB) signaling pathway in the skin of aged rats and skin fibroblast cells. Moreover, we investigated the antioxidant effect of MHY553 via in vitro assays of reactive oxygen species (ROS) and peroxynitrite (ONOO^-) scavenging activities. We also scrutinized the ability of MHY553 as a PPARα activator in aged rat skin and H₂O₂-induced Hs27 fibroblast cells. In vivo experiments were performed in young, aged, and MHY553-fed aged rats (3 mg or 5 mg∙kg ^-1∙day ^-1 for 4 weeks). MHY553 dose-dependently scavenged ROS and ONOO^-. Furthermore, we found that MHY553 suppressed the NF-κB transcription factor and downregulated mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1) signaling. MHY553 also inhibited the expression of pro-inflammatory cytokines including COX-2, iNOS, IL-1β, and IL-6. Our findings indicate the MHY553 scavenges ROS/reactive nitrogen species and inhibits inflammatory cytokines through PPARα activation in the skin. Thus, these results suggest that MHY553 may be of therapeutic interest for protecting skin from oxidative stress-induced damage and intrinsic aging.

The marine-derived furanone reduces intracellular lipid accumulation in vitro by targeting LXRα and PPARα

Recent studies have demonstrated that commercially available lipid‐lowering drugs cause various side effects; therefore, searching for anti‐hyperlipidaemic compounds with lower toxicity is a research hotspot. This study was designed to investigate whether the marine‐derived compound, 5‐hydroxy‐3‐methoxy‐5‐methyl‐4‐butylfuran‐2(5H)‐one, has an anti‐hyperlipidaemic activity, and the potential underlying mechanism in vitro. Results showed that the furanone had weaker cytotoxicity compared to positive control drugs. In RAW 264.7 cells, the furanone significantly lowered ox‐LDL‐induced lipid accumulation (~50%), and its triglyceride (TG)‐lowering effect was greater than that of liver X receptor (LXR) agonist T0901317. In addition, it significantly elevated the protein levels of peroxisome proliferator‐activated receptors (PPARα) and ATP‐binding cassette (ABC) transporters, which could be partially inhibited by LXR antagonists, GSK2033 and SR9243. In HepG2 cells, it significantly decreased oleic acid‐induced lipid accumulation, enhanced the protein levels of low‐density lipoprotein receptor (LDLR), ABCG5, ABCG8 and PPARα, and reduced the expression of sterol regulatory element‐binding protein 2 (~32%). PPARα antagonists, GW6471 and MK886, could significantly inhibit the furanone‐induced lipid‐lowering effect. Furthermore, the furanone showed a significantly lower activity on the activation of the expression of lipogenic genes compared to T0901317. Taken together, the furanone exhibited a weak cytotoxicity but had powerful TC‐ and TG‐lowering effects most likely through targeting LXRα and PPARα, respectively. These findings indicate that the furanone has a potential application for the treatment of dyslipidaemia.

Computational investigation reveals Picrasidine C as selective PPARα lead: binding pattern, selectivity mechanism and ADME/tox profile

Natural products and their derivatives have been recognized as an important source of therapeutic agents for many years. Previously we isolated a dimeric β-carboline-type alkaloid Picrasidine C from the root of Picrasma quassioides as subtype-selective peroxisome proliferator-activated receptor α (PPARα) agonist. In order to modify this natural product for better affinity and druggability, we investigated a series of properties exhibited by Picrasidine C, such as its binding mode with PPARα, the selectivity mechanism over PPARγ, as well as ADME/Tox profile through computational methods including sequence alignment, molecular docking, pharmacophore modeling and molecular dynamics simulations. The detailed information of binding pattern and affinity for Picrasidine C elucidated here will be valuable for chemical modification. Besides, the steric hindrance of residue Phe363 in PPARγ pocket was speculated as the main isoform selectivity mechanism for Picrasidine C, which would be helpful for the design of selective derivatives. ADME/Tox prediction was conducted to avoid potential undesirable pharmacokinetic properties for reducing the risk of failure. Finally, novel skeletons were derived from lead compound by core hopping method, validated through molecular dynamic simulations and MM-GBSA calculation. In short, the information obtained from computational strategy would be valuable for us to find more potent, safe and selective PPARα agonists during structural optimization.

PPARα ligand, AVE8134, and cyclooxygenase inhibitor therapy synergistically suppress lung cancer growth and metastasis

Background

Lung cancer (LC) is one of the leading causes of death worldwide, which highlights the urgent need for better therapies. Peroxisome proliferator-activated nuclear receptor alpha (PPARα), known as a key nuclear transcription factor involved in glucose and lipid metabolism, has been also implicated in endothelial proliferation and angiogenesis. However, the effects and potential mechanisms of the novel PPARα ligand, AVE8134, on LC growth and progression remain unclear.

Methods

A subcutaneous tumour was established in mice by injecting TC-1 lung tumour cells (~ 1 × 10⁶ cells) into their shaved left flank. These mice were treated with three different PPARα ligands: AVE8134 (0.025% in drinking water), Wyeth-14,643 (0.025%), or Bezafibrate (0.3%). Tumour sizes and metastasis between treated and untreated mice were then compared by morphology and histology, and the metabolites of arachidonic acid (AA) were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Inhibition of either Cyp2c44 expression by genetic disruption or cyclooxygenase (COX) activity by indomethacin was used to test the mechanisms by which AVE8134 affects tumour growth.

Results

The pharmacodynamics effects of AVE8134, Wyeth-14,643, and Bezafibrate on lipids control were similar. However, their effects on tumour suppression were different. Eicosanoid profile analysis showed that all PPARα ligands reduced the production of AA-derived epoxyeicosatrienoic acids (EETs) and increased the hydroxyl product, 11-hydroxyeicosatetraenoic acids (11-HETE). Moreover, increased 11-HETE promoted endothelial proliferation, angiogenesis, and subsequent tumour deterioration in a dose-dependent manner possibly via activating the AKT/extracellular signal-regulated kinase (ERK) pathway. The increased 11-HETE partly neutralized the benefits provided by the Cyp2c44-EETs system inhibited by PPARα ligands in tumour-bearing mice. AVE8134 treatment worsened the tumour phenotype in Cyp2c44 knockout mice, indicating that AVE8134 has contradictory effects on tumour growth. The COX inhibitor indomethacin strengthened the inhibitory actions of AVE8134 on tumour growth and metastasis by inhibiting the 11-HETE production in vivo and in vitro.

Conclusion

In this study, we found that the degrees of inhibition on LC growth and metastasis by PPARα ligands depended on their bidirectional regulation on EETs and 11-HETE. Considering their safety and efficacy, the novel PPARα ligand, AVE8134, is a potentially ideal anti-angiogenesis drug for cancer treatment when jointly applied with the COX inhibitor indomethacin.

PPARα agonist alleviates tumor growth and chemo-resistance associated with the inhibition of glucose metabolic pathway

As a nuclear receptor, peroxisome-proliferator-activated receptor α (PPARα) plays a critical role in regulation of metabolism and cancer, while the effect of PPARα agonist on cancer cell glucose metabolism-linked tumor growth is still unclear. Here we found that PPARα agonist (Wy14,643) decreased Glut1 (Glucose transporter 1) gene and protein expressions of colorectal cancer cell lines in response to normoxia or hypoxia. Dual-luciferase analysis showed that Wy14,643 inhibited Glut1 transcription activity. Importantly, ChIP-qPCR analysis showed that Wy14,643 increased the binding of PPARα to Glut1 promoter region. Wy14,643 suppressed Glut1 transcription activity resulting in reduced influx of glucose in cancer cells in response to normoxia or hypoxia. Further analysis showed that Wy14,643-mediated inhibition of tumor growth and chemo-resistance was associated with inhibition of mTOR pathway. Taken together, PPARα agonist Wy14,643 suppressed Glut1 transcription activity, glucose uptake and mTOR pathway in colorectal cancer cells, which was involved in reduced tumor growth and chemo-resistance. These findings provided a novel therapy strategy for cancer progression.

Structural development of 1H-pyrazolo-[3,4-b]pyridine-4-carboxylic acid derivatives as human peroxisome proliferator-activated receptor alpha (PPARα)-selective agonists

We previously reported that 1H-pyrazolo-[3,4-b]pyridine-4-carboxylic acid derivative 6 is an agonist of human peroxisome proliferator-activated receptor alpha (hPPARα). Here, we prepared a series of 1H-pyrazolo-[3,4-b]pyridine-4-carboxylic acid derivatives in order to examine the structure-activity relationships (SAR). SAR studies clearly indicated that the steric bulkiness of the substituent on 1H-pyrazolo-[3,4-b]pyridine ring, the position of the distal hydrophobic tail part, and the distance between the distal hydrophobic tail part and the acidic head part are critical for hPPARα agonistic activity. These SAR results are somewhat different from those reported for fibrate-class hPPARα agonists. A representative compound (10f) was as effective as fenofibrate in reducing the elevated plasma triglyceride levels in a high-fructose-fed rat model.

Rosa rugosa flavonoids exhibited PPARα agonist-like effects on genetic severe hypertriglyceridemia of mice

ETHNOPHARMACOLOGICAL RELEVANCE

Rosa rugosa Thunb. is a traditional Chinese medicine that was used in the treatment of cardiovascular diseases and relative risk factors such as diabetes, hyperlipidemia, hypertension, and inflammation. Rosa rugosa flavonoids (RRFs) are the main components in Rosa rugosa Thunb. Several studies have demonstrated that RRFs can regulate plasma lipid contents, but the related mechanism of which has not yet been elucidated clearly.

AIM OF THE STUDY

The goal of this study was to clarify the effects of RRFs on triglyceride metabolism and its related mechanisms.

MATERIALS AND METHODS

RRFs were obtained by ethanol extraction from Rosa rugosa Thunb.. Transgenic mice expressing human Apolipoprotein C3 (ApoC3) were used as a mouse model of hypertriglyceridemia. Fenofibrate (FNB), a PPARα agonist, was used as a positive control drug of decreasing high triglyceride. FNB (100 mg/kg) or RRFs (300 mg/kg) were given to the mice by gavage daily. Two weeks later, the changes of plasma lipid levels in the mice were measured by commercial kits, the clearance of triglyceride was evaluated by oral fat load test, and expression of the genes related to lipid β-oxidation and synthesis was detected in the mice livers by real time PCR.

RESULTS

RRFs, as well as FNB, were found to significantly reduce plasma triglyceride (TG) levels in ApoC3 transgenic mice after administration of the drug for two weeks. Plasma lipid clearance rate was increased and lipid content in the mice livers was reduced after administration of RRF. Treatment with RRFs up-regulated mRNA expression of PPARα and its downstream gene of ACOX, while down-regulated mRNA expression of the genes related to fatty acid synthesis (FASN, SREBP-1c, and ACC1). The expression of LPL was raised, while the expression of ApoC3 was decreased, and Foxo1 was inhibited by RRFs in the mice livers.

CONCLUSION

RRFs can reduce plasma TG levels by repressing the expression of ApoC3 and inducing the expression of LPL in liver. RRFs could also reduce triglyceride in hepatocytes through increasing β-oxidation and decreasing synthesis of the lipids. These findings show the potency of further clinical application of RRFs as a hypolipidemic drug for treatment of cardiovascular diseases.

A ligand-induced structural change in fatty acid-binding protein 1 is associated with potentiation of peroxisome proliferator-activated receptor α agonists

Peroxisome proliferator-activated receptor α (PPARα) is a transcriptional regulator of lipid metabolism. GW7647 is a potent PPARα agonist that must reach the nucleus to activate this receptor. In cells expressing human fatty acid-binding protein 1 (FABP1), GW7647 treatment increases FABP1's nuclear localization and potentiates GW7647-mediated PPARα activation; GW7647 is less effective in cells that do not express FABP1. To elucidate the underlying mechanism, here we substituted residues in FABP1 known to dictate lipid signaling by other intracellular lipid-binding proteins. Substitutions of Lys-20 and Lys-31 to Ala in the FABP1 helical cap affected neither its nuclear localization nor PPARα activation. In contrast, Ala substitution of Lys-57, Glu-77, and Lys-96, located in the loops adjacent to the ligand-binding portal region, abolished both FABP1 nuclear localization and GW7647-induced PPARα activation but had little effect on GW7647-FABP1 binding affinity. Using solution NMR spectroscopy, we determined the WT FABP1 structure and analyzed the dynamics in the apo and GW7647-bound structures of both the WT and the K57A/E77A/K96A triple mutant. We found that GW7647 binding causes little change in the FABP1 backbone, but solvent exposes several residues in the loops around the portal region, including Lys-57, Glu-77, and Lys-96. These residues also become more solvent-exposed upon binding of FABP1 with the endogenous PPARα agonist oleic acid. Together with previous observations, our findings suggest that GW7647 binding stabilizes a FABP1 conformation that promotes its interaction with PPARα. We conclude that full PPARα agonist activity of GW7647 requires FABP1-dependent transport and nuclear localization processes.

Hepatoprotective Effects of MHY3200 on High-Fat, Diet-Induced, Non-Alcoholic Fatty Liver Disease in Rats

This study investigated the effects of 2-(4-(5-chlorobenzo[d]thiazol-2-yl)phenoxy)-2,2-difluoroacetic acid (MHY3200) on high-fat diet (HFD)-induced hepatic lipid accumulation and inflammation. The measurement of peroxisome proliferator-activated receptor (PPAR)α activity by using a luciferase assay indicated that MHY3200 was more potent than a known PPARα agonist, WY14643, in AC2F cells. Six-month-old male SD rats were fed chow or HFD for 1 month, and after, with or without added MHY3200 (1 or 2 mg/kg/day) for 4 weeks. The oral administration of MHY3200 caused a significant decrease in serum triglyceride (TG), glucose, alanine aminotransferase, and insulin, as well as a slight decrease in the level of free fatty acid and aspartate transaminase. No weight gain was detected when compared with HFD rats, and hepatic TG content was also attenuated by the administration of MHY3200. Furthermore, phosphorylation of the ER stress marker, inositol-requiring kinase 1 and its downstream gene, c-Jun N-terminal kinase, in addition to serine phosphorylation of insulin receptor substrate 1 were suppressed by MHY3200. Consistent with these results, MHY3200 administration reduced the levels of activation of protein-1, cyclooxygenase-2, and inducible nitric oxide synthase. Our results suggested that MHY3200 ameliorated HFD-induced hepatic lipid accumulation and inflammation, and improved insulin resistance through PPARα activation.

Novel PPARα agonist MHY553 alleviates hepatic steatosis by increasing fatty acid oxidation and decreasing inflammation during aging

Hepatic steatosis is frequently observed in obese and aged individuals. Because hepatic steatosis is closely associated with metabolic syndromes, including insulin resistance, dyslipidemia, and inflammation, numerous efforts have been made to develop compounds that ameliorate it. Here, a novel peroxisome proliferator-activated receptor (PPAR) α agonist, 4-(benzo[d]thiazol-2-yl)benzene-1,3-diol (MHY553) was developed, and investigated its beneficial effects on hepatic steatosis using young and old Sprague-Dawley rats and HepG2 cells.

Docking simulation and Western blotting confirmed that the activity of PPARα, but not that of the other PPAR subtypes, was increased by MHY553 treatment. When administered orally, MHY553 markedly ameliorated aging-induced hepatic steatosis without changes in body weight and serum levels of liver injury markers. Consistent with in vivo results, MHY553 inhibited triglyceride accumulation induced by a liver X receptor agonist in HepG2 cells. Regarding underlying mechanisms, MHY553 stimulated PPARα translocation into the nucleus and increased mRNA levels of its downstream genes related to fatty acid oxidation, including CPT-1A and ACOX1, without apparent change in lipogenesis signaling. Furthermore, MHY553 significantly suppresses inflammatory mRNA expression in old rats. In conclusion, MHY553 is a novel PPARα agonist that improved aged-induced hepatic steatosis, in part by increasing β-oxidation signaling and decreasing inflammation in the liver. MHY553 is a potential pharmaceutical agent for treating hepatic steatosis in aging.

4',6-Dimethoxyisoflavone-7-O-β-D-glucopyranoside (wistin) is a peroxisome proliferator-activated receptor α (PPARα) agonist in mouse hepatocytes

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors that regulate lipid and glucose metabolism. PPARα mainly affects fatty acid metabolism, and its activation lowers lipid levels. PPARγ is involved in the regulation of adipogenesis, insulin sensitivity, energy balance, and lipid biosynthesis. We have previously reported that 4',6-dimethoxyisoflavone-7-O-β-D-glucopyranoside (wistin) can activate PPARγ. The purpose of the present study is to investigate the PPARα agonist activity of wistin. Using a luciferase reporter assay system of PPARα in monkey COS7 kidney cells, we showed that wistin could activate PPARα (P < 0.01 at 10 μg/mL) in a dose-dependent manner. Moreover, the addition of wistin upregulated the expression of PPARα (P < 0.01 at 10 μg/mL) and PPARα target genes including carnitine palmitoyltransferase 1a (P < 0.05 at 10 μg/mL), acyl-CoA oxidase (P < 0.01 at 10 μg/mL), acyl-CoA synthase (P < 0.05 at 10 μg/mL), PPARγ coactivator 1α (P < 0.05 at 10 μg/mL), uncoupling protein 2 (P < 0.05 at 1 μg/mL), and uncoupling protein 3 (P < 0.05 at 10 μg/mL), which are genes involved in lipid efflux and energy expenditure, in mouse primary hepatocytes. Furthermore, wistin inhibited cellular triglyceride accumulation in hepatocytes (P < 0.05 at 10 μg/mL) in a dose-dependent manner. These results indicate that wistin could suppress lipid accumulation through PPARα activation. The action of wistin on PPARα could be of interest for the amelioration of lipid metabolic disorders. To the best of our knowledge, wistin is the first reported isoflavonoid O-glycoside with PPARα agonist activity.

Up-regulation of Nrf2 is involved in FGF21-mediated fenofibrate protection against type 1 diabetic nephropathy

The lipid lowering medication, fenofibrate (FF), is a peroxisome proliferator-activated receptor-alpha (PPARα) agonist, possessing beneficial effects for type 2 diabetic nephropathy (DN). We investigated whether FF can prevent the development of type 1 DN, and the underlying mechanisms. Diabetes was induced by a single intraperitoneal injection of streptozotocin in C57BL/6J mice. Mice were treated with oral gavage of FF at 100mg/kg every other day for 3 and 6 months. Diabetes-induced renal oxidative stress, inflammation, apoptosis, lipid and collagen accumulation, and renal dysfunction were accompanied by significant decrease in PI3K, Akt, and GSK-3β phosphorylation as well as an increase in the nuclear accumulation of Fyn [a negative regulator of nuclear factor (erythroid-derived 2)-like 2 (Nrf2)]. All these adverse effects were significantly attenuated by FF treatment. FF also significantly increased fibroblast growth factor 21 (FGF21) expression and enhanced Nrf2 function in diabetic and non-diabetic kidneys. Moreover, FF-induced amelioration of diabetic renal damage, including the stimulation of PI3K/Akt/GSK-3β/Fyn pathway and the enhancement of Nrf2 function were abolished in FGF21-null mice, confirming the critical role of FGF21 in FF-induced renal protection. These results suggest for the first time that FF prevents the development of DN via up-regulating FGF21 and stimulating PI3K/Akt/GSK-3β/Fyn-mediated activation of the Nrf2 pathway.

Evaluation of chronic toxicity and carcinogenicity of ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate in Sprague-Dawley rats

Ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate, developed for use as a polymerization processing aid in the manufacture of fluoropolymers, was tested for its potential chronic toxicity and carcinogenicity in a 2-year oral dosing study in Sprague-Dawley rats. Male rats were given daily doses of either 0, 0.1, 1 or 50 mg/kg; females were given either 0, 1, 50 or 500 mg/kg. Body weights, food consumption and clinical signs were monitored daily; clinical pathology was conducted at designated intervals and animals were given a complete pathological evaluation after 12 months and 24 months of dosing. Normal survival was seen in all groups, no abnormal clinical signs were seen, and body weight gain was reduced only in female rats at 500 mg/kg. Both sexes at the high dose had mild decreases in red cell mass which were somewhat more pronounced in females. Clinical pathology indicative of liver injury was present in males that received 50 mg/kg and correlated with histomorphological liver changes that included both hypertrophic and degenerative/necrotic lesions. Similar histomorphological lesions were seen in the livers of females at 500 mg/kg. Previous shorter term toxicity studies have identified this chemical as a PPARα agonist and the finding of benign tumors of the liver, pancreas and/or testes in males at 50 mg/kg and females at 500 mg/kg is consistent with the rat response to peroxisome proliferators and is of questionable human relevance. Changes in the kidney, tongue, and stomach were observed only at the highest dose of 500 mg/kg in females. The no-observed-adverse-effect-level in this study lies between 1 and 50 mg/kg for males and between 50 and 500 mg/kg for females.