Peroxisome proliferators do not activate the transcription factors AP-1, early growth response-1, or heat shock factors 1 and 2 in rats or hamsters

Di (2-ethyl hexyl) phthalate (DEHP)-induced kidney injury in quail (Coturnix japonica) via inhibiting HSF1/HSF3-dependent heat shock response

Di (2-ethyl hexyl) phthalate (DEHP) as a plasticizer can leach away from the plastic and hence entrances into the animal food chain which caused serious hazard in organs of animals, but there are few studies on DEHP kidney toxicity. The heat-shock response (HSR) consisting of the HSPs and HSFs plays an important role in various toxicity stress conditions. To investigate the influence on kidney toxicity and the modulation of HSR during DEHP exposure, female quail were fed the diet with 0, 250, 500 and 750 mg/kg DEHP by gavage administration for 45 days. The shrinkages of glomeruli and dilation of kidney tubule epithelia cells were observed in the kidney of DEHP-exposed quail. DEHP treatment could significantly decrease the expressions of HSP25, HSP27, HSP47, HSP60, while the expressions of HSP10, HSP40, HSP70, HSP90, HSP110 were upregulated in the kidney. In addition, the expression levels of HSF1 and HSF3 were significantly increased under DEHP. This is the first study to demonstrate quail exposure to DEHP is in fact detrimental to bird kidney. Besides, DEHP could attack HSR by affecting the synthesis of HSFs to mediate the transcription of the HSPs resulting in kidney damage.

Hepatoprotective effects of fermented field water-dropwort (Oenanthe javanica) extract and its major constituents

Dropwort (Oenanthe javanica) has been used for many years for the treatment of inflammatory conditions, including hepatitis. We investigated the protective effects of fermented field water-dropwort extract (FDE) on tert-butyl hydroperoxide (t-BHP)-induced hepatotoxicity in HepG2 cells and carbon tetrachloride (CCl4)-induced liver damage in rats. Pretreatment with FDE prior to the t-BHP treatment of HepG2 cells inhibited cell death and lactate dehydrogenase (LDH) leakage in a dose-dependent manner. In addition FDE significantly prevented the increase of hepatic enzyme markers (ALT, AST) in vivo. Moreover, FDE administration for 7 days significantly affected CYP2E1, CYP4A2, and PPARγ gene expressions. CYP2E1 and CYP4A2 gene expression in the liver, increased 2 and 22-fold by CCl4 administration, respectively, was attenuated to normal levels by pretreatment with FDE. PPARγ gene expression, completely blocked by CCl4 treatment, was increased by FDE pretreatment compared to normal control group. Histopathological examination of the livers also revealed that FDE reduced the incidence of liver lesions. Caffeic acid and chlorogenic acid were identified as major constituents of FDE. These results demonstrate the protective effects of FDE against hepatocytotoxicity induced by CCl4 and t-BHP in rats and HepG2 cells, thus indicating the potential of FDE as a therapeutic for acute liver diseases.

Regulation of Proteome Maintenance Gene Expression by Activators of Peroxisome Proliferator-Activated Receptor α

The nuclear receptor peroxisome proliferator-activated receptor α (PPARα) is activated by a large number of xenobiotic and hypolipidemic compounds called peroxisome proliferator chemicals (PPCs). One agonist of PPARα (WY-14,643) regulates responses in the mouse liver to chemical stress in part by altering expression of genes involved in proteome maintenance (PM) including protein chaperones in the heat shock protein (Hsp) family and proteasomal genes (Psm) involved in proteolysis. We hypothesized that other PPARα activators including diverse hypolipidemic and xenobiotic compounds also regulate PM genes in the rat and mouse liver. We examined the expression of PM genes in rat and mouse liver after exposure to 7 different PPCs (WY-14,643, clofibrate, fenofibrate, valproic acid, di-(2-ethylhexyl) phthalate, perfluorooctanoic acid, and perfluorooctane sulfonate) using Affymetrix microarrays. In rats and mice, 174 or 380 PM genes, respectively, were regulated by at least one PPC. The transcriptional changes were, for the most part, dependent on PPARα, as most changes were not observed in similarly treated PPARα-null mice and the changes were not consistently observed in rats treated with activators of the nuclear receptors CAR or PXR. In rats and mice, PM gene expression exhibited differences compared to typical direct targets of PPARα (e.g., Cyp4a family members). PM gene expression was usually delayed and in some cases, it was transient. Dose-response characterization of protein expression showed that Hsp86 and Hsp110 proteins were induced only at higher doses. These studies demonstrate that PPARα, activated by diverse PPC, regulates the expression of a large number of genes involved in protein folding and degradation and support an expanded role for PPARα in the regulation of genes that protect the proteome.

Effects of the PPARα Agonist and Widely Used Antihyperlipidemic Drug Gemfibrozil on Hepatic Toxicity and Lipid Metabolism

Gemfibrozil is a widely prescribed hypolipidemic agent in humans and a peroxisome proliferator and liver carcinogen in rats. Three-month feed studies of gemfibrozil were conducted by the National Toxicology Program (NTP) in male Harlan Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters, primarily to examine mechanisms of hepatocarcinogenicity. There was morphologic evidence of peroxisome proliferation in rats and mice. Increased hepatocyte proliferation was observed in rats, primarily at the earliest time point. Increases in peroxisomal enzyme activities were greatest in rats, intermediate in mice, and least in hamsters. These studies demonstrate that rats are most responsive while hamsters are least responsive. These events are causally related to hepatotoxicity and hepatocarcinogenicity of gemfibrozil in rodents via peroxisome proliferator activated receptor-α (PPARα) activation; however, there is widespread evidence that activation of PPARα in humans results in expression of genes involved in lipid metabolism, but not in hepatocellular proliferation.

Analysis of the heat shock response in mouse liver reveals transcriptional dependence on the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha)

Background

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARα) regulates responses to chemical or physical stress in part by altering expression of genes involved in proteome maintenance. Many of these genes are also transcriptionally regulated by heat shock (HS) through activation by HS factor-1 (HSF1). We hypothesized that there are interactions on a genetic level between PPARα and the HS response mediated by HSF1.

Results

Wild-type and PPARα-null mice were exposed to HS, the PPARα agonist WY-14,643 (WY), or both; gene and protein expression was examined in the livers of the mice 4 or 24 hrs after HS. Gene expression profiling identified a number of Hsp family members that were altered similarly in both mouse strains. However, most of the targets of HS did not overlap between strains. A subset of genes was shown by microarray and RT-PCR to be regulated by HS in a PPARα-dependent manner. HS also down-regulated a large set of mitochondrial genes specifically in PPARα-null mice that are known targets of PPARγ co-activator-1 (PGC-1) family members. Pretreatment of PPARα-null mice with WY increased expression of PGC-1β and target genes and prevented the down-regulation of the mitochondrial genes by HS. A comparison of HS genes regulated in our dataset with those identified in wild-type and HSF1-null mouse embryonic fibroblasts indicated that although many HS genes are regulated independently of both PPARα and HSF1, a number require both factors for HS responsiveness.

Conclusions

These findings demonstrate that the PPARα genotype has a dramatic effect on the transcriptional targets of HS and support an expanded role for PPARα in the regulation of proteome maintenance genes after exposure to diverse forms of environmental stress including HS.

Role of Oxidative Stress in Peroxisome Proliferator-Mediated Carcinogenesis

In this review, the evidence about the role of oxidative stress in the induction of hepatocellular carcinomas by peroxisome proliferators is examined. The activation of PPAR-alpha by peroxisome proliferators in rats and mice may produce oxidative stress, due to the induction of enzymes like fatty acyl coenzyme A (CoA) oxidase (AOX) and cytochrome P-450 4A1. The effect of peroxisome proliferators on the antioxidant defense system is reviewed, as is the effect on endpoints resulting from oxidative stress that may be important in carcinogenesis, such as lipid peroxidation, oxidative DNA damage, and transcription factor activation. Peroxisome proliferators clearly inhibit several enzymes in the antioxidant defense system, but studies examining effects on lipid peroxidation and oxidative DNA damage are conflicting. There is a profound species difference in the induction of hepatocellular carcinomas by peroxisome proliferators, with rats and mice being sensitive, whereas species such as nonhuman primates and guinea pigs are not susceptible to the effects of peroxisome proliferators. The possible role of oxidative stress in these species differences is also reviewed. Overall, peroxisome proliferators produce changes in oxidative stress, but whether these changes are important in the carcinogenic process is not clear at this time.

Proteasome activity or expression is not altered by activation of the heat shock transcription factor Hsf1 in cultured fibroblasts or myoblasts

Heat shock proteins (Hsps) with chaperoning function work together with the ubiquitin-proteasome pathway to prevent the accumulation of misfolded, potentially toxic proteins, as well as to control catabolism of the bulk of cytoplasmic, cellular protein. There is evidence for the involvement of both systems in neurodegenerative disease, and a therapeutic target is the heat shock transcription factor, Hsf1, which mediates upregulation of Hsps in response to cellular stress. The mechanisms regulating expression of proteasomal proteins in mammalian cells are less well defined. To assess any direct effect of Hsf1 on expression of proteasomal subunits and activity in mammalian cells, a plasmid encoding a constitutively active form of Hsf1 (Hsf1act) was expressed in mouse embryonic fibroblasts lacking Hsf1 and in cultured human myoblasts. Plasmid encoding an inactivatible form of Hsf1 (Hsf1inact) served as control. In cultures transfected with plasmid hsf1act, robust expression of the major stress-inducible Hsp, Hsp70, occurred but not in cultures transfected with hsf1inact. No significant changes in the level of expression of representative proteasomal proteins (structural [20Salpha], a nonpeptidase beta subunit [20Sbeta3], or 2 regulatory subunits [19S subunit 6b, 11 Salpha]) or in chymotrypsin-, trypsin-, and caspaselike activities of the proteasome were measured. Thus, stress-induced or pharmacological activation of Hsf1 in mammalian cells would upregulate Hsps but not directly affect expression or activity of proteasomes.

The transcriptional response to a peroxisome proliferator-activated receptor alpha agonist includes increased expression of proteome maintenance genes

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha), in addition to regulating lipid homeostasis, controls the level of tissue damage after chemical or physical stress. To determine the role of PPARalpha in oxidative stress responses, we examined damage after exposure to chemicals that increase oxidative stress in wild-type or PPARalpha-null mice. Primary hepatocytes from wild-type but not PPARalpha-null mice pretreated with the PPAR pan-agonist WY-14,643 (WY) were protected from damage to cadmium and paraquat. The livers from intact wild-type but not PPARalpha-null mice were more resistant to damage after carbon tetrachloride treatment. To determine the molecular basis of the protection by PPARalpha, we identified by transcript profiling genes whose expression was altered by a 7-day exposure to WY in wild-type and PPARalpha-null mice. Of the 815 genes regulated by WY in wild-type mice (p < or = 0.001; > or =1.5-fold or < or =-1.5-fold), only two genes were regulated similarly by WY in PPARalpha-null mice. WY increased expression of stress modifier genes that maintain the health of the proteome, including those that prevent protein aggregation (heat stress-inducible chaperones) and eliminate damaged proteins (proteasome components). Although the induction of proteasomal genes significantly overlapped with those regulated by 1,2-dithiole-3-thione, an activator of oxidant-inducible Nrf2, WY increased expression of proteasomal genes independently of Nrf2. Thus, PPARalpha controls the vast majority of gene expression changes after exposure to WY in the mouse liver and protects the liver from oxidant-induced damage, possibly through regulation of a distinct set of proteome maintenance genes.

Activation of PPAR-alpha in streptozotocin-induced diabetes is essential for resistance against acetaminophen toxicity

Diabetic (DB) mice exhibit significant resistance to hepatotoxicants. The role of peroxisome proliferator receptor (PPAR)-alpha activation in diabetes, in protection against lethal acetaminophen (APAP) challenge, was investigated. Upon treatment with APAP (600 mg/kg, i.p., a LD100 dose in wild-type [WT] non-DB mice), WT-DB mice showed only 30% mortality and 40% less liver injury as measured by alanine aminotransferase and histopathology. In contrast, diabetes in PPAR knockout (PPAR-alpha-/-) mice failed to protect against APAP toxicity, suggesting the importance of PPAR-alpha in diabetes-induced protection. S-phase DNA synthesis and PCNA immunohistochemical staining after injury showed early and robust tissue repair in WT-DB mice, but not in the PPAR-alpha-/--DB mice. Microarray analyses were performed on livers from non-DB and DB (WT and PPAR-alpha-/-) mice at 0 and 12 h after APAP. Microarray data were confirmed via real-time polymerase chain reaction analysis of several genes, including stress response, immediate early genes, DNA damage, heat shock proteins, and cell cycle regulators, followed by Western analyses of selected proteins. Gel shift assays revealed higher activation of nuclear factor-kappaB in WT-DB mice after APAP treatment. These findings suggest PPAR-alpha activation as a hepatoprotective adaptive response mediating protection against APAP in diabetes.

Screening of stress enhancer based on analysis of gene expression profiles: enhancement of hyperthermia-induced tumor necrosis by an MMP-3 inhibitor

To improve the therapeutic benefit of hyperthermia, we examined changes of global gene expression after heat shock using DNA microarrays consisting of 12 814 clones. HeLa cells were treated for 1 h at 44 degrees C and RNA was extracted from the cells 0, 3, 6, and 12 h after heat shock. The 664 genes that were up or down-regulated after heat shock were classified into 7 clusters using fuzzy adaptive resonance theory (fuzzy ART). There were 41 genes in two clusters that were induced in the early phase after heat shock. In addition to shock response genes, such as hsp70 and hsp40, the stress response genes c-jun, c-fos and egr-1 were expressed in the early phase after heat shock. We also found that expression of matrix metalloproteinase 3 (MMP-3) was enhanced during the early response. We therefore investigated the role of MMP-3 in the heat shock response by examining HeLa cell survival after heat treatment in the presence and absence of an MMP-3 inhibitor, N-isobutyl-N-(4-methoxyphenylsulfonyl)glycylhydroxamic acid (NNGH) or N-hydroxy-2(R)-[[4- methoxysulfonyl](3-picolyl)amino]-3-methylbutaneamide hydrochloride (MMI270). The number of surviving cells 3 days after heat treatment significantly decreased, reaching 3.5% for NNGH and 0.2% for MMI270. These results indicate that the MMP-3 inhibitors enhanced heat shock-induced cell death and behaved as stress enhancers in cancer cells. This valuable conclusion was reached as a direct result of the gene expression profiling that was performed in these studies.