The peroxisome proliferator-activated receptor ␣ (PPAR␣) is a member of the nuclear receptor superfamily and mediates the biological effects of peroxisome proliferators. To determine the physiological role of PPAR␣ in cardiac fatty acid metabolism, we examined the regulation of expression of cardiac fatty acid-metabolizing proteins using PPAR␣-null mice. The capacity for constitutive myocardial ␤-oxidation of the medium and long chain fatty acids, octanoic acid and palmitic acid, was markedly reduced in the PPAR␣-null mice as compared with the wild-type mice, indicating that mitochondrial fatty acid catabolism is impaired in the absence of PPAR␣. In contrast, constitutive ␤-oxidation of the very long chain fatty acid, lignoceric acid, did not differ between the mice, suggesting that the constitutive expression of enzymes involved in peroxisomal ␤-oxidation is independent of PPAR␣ . Indeed, PPAR␣-null mice had normal levels of the peroxisomal ␤-oxidation enzymes except the D-type bifunctional protein. At least seven mitochondrial fatty acid-metabolizing enzymes were expressed at much lower levels in the PPAR␣-null mice, whereas other fatty acid-metabolizing enzymes were present at similar or slightly lower levels in the PPAR␣-null, as compared with wild-type mice. Additionally, lower constitutive mRNA expression levels of fatty acid transporters were found in the PPAR␣-null mice, suggesting a role for PPAR␣ in fatty acid transport and catabolism. Indeed, in fatty acid metabolism experiments in vivo, myocardial uptake of iodophenyl 9-methylpentadecanoic acid and its conversion to 3-methylnonanoic acid were reduced in the PPAR␣-null mice. Interestingly, a decreased ATP concentration after exposure to stress, abnormal cristae of the mitochondria, abnormal caveolae, and fibrosis were observed only in the myocardium of the PPAR␣-null mice. These cardiac abnormalities appeared to proceed in an age-dependent manner. Taken together, the results presented here indicate that PPAR␣ controls constitutive fatty acid oxidation, thus establishing a role for the receptor in cardiac fatty acid homeostasis. Furthermore, altered expression of fatty acid-metabolizing proteins seems to lead to myocardial damage and fibrosis, as inflammation and abnormal cell growth control can cause these conditions.

The mechanisms underlying alcoholic liver disease are not completely understood, but lipid accumulation seems to be central to the cause of this disease. The peroxisome proliferator-activated receptor alpha (PPARalpha) plays an important role in the control of lipid homeostasis, metabolism of bioactive molecules, and modulation of inflammatory responses. To investigate the roles of PPARalpha in alcoholic liver injury, wild-type and PPARalpha-null mice were continuously fed a diet containing 4% ethanol, and liver injury was analyzed. PPARalpha-null mice fed ethanol exhibited marked hepatomegaly, hepatic inflammation, cell toxicity, fibrosis, apoptosis, and mitochondrial swelling. Some of these hepatic abnormalities were consistent with those of patients with alcoholic liver injury and were not found in wild-type mice. Next, the molecular mechanisms of ethanol-induced liver injury in PPARalpha-null mice were investigated, and changes related to ethanol and acetaldehyde metabolism, oxidative stress, inflammation, hepatocyte proliferation, fibrosis, and mitochondrial permeability transition activation occurred specifically in PPARalpha-null mice as compared with wild-type mice. In conclusion, these studies suggest a protective role for PPARalpha in alcoholic liver disease. Humans may be more susceptible to liver toxicity induced by ethanol as PPARalpha expression in human liver is considerably lower compared to that of rodents.

Fatty acids bound to albumin are filtered through glomeruli, reabsorbed by proximal tubular epithelial cells, and metabolized. Because albumin serves as a carrier, an increase in delivery of fatty acids to the proximal tubule may occur in proteinuric states, possibly leading to toxic effects. At present, the contribution of fatty acids to tubulointerstitial damage and the mechanisms underlying this toxicity remain unclear. We recently found that the transcription factor peroxisome proliferator-activated receptor ␣ (PPAR␣) regulates fatty acid metabolism in proximal tubules, so we tested its role in tubular damage under proteinuric conditions. We induced protein-overload nephropathy in Ppara-null or wildtype (WT) mice by injecting fatty acids bound to BSA. Ppara-null mice exhibited greater renal dysfunction from severe proximal tubular injury than WT mice. Kidneys from Ppara-null mice injected with albumin alone showed little injury. Acute tubular injury was associated with deranged fatty acid homeostasis, increased oxidative stress, increased apoptosis, and activation of NFB signaling. These results suggest a role for fatty acids in proteinuria-associated tubular toxicity, as well as a protective role for PPAR␣. Modulation of PPAR␣ may be a future therapeutic option for tubular toxicity from fatty acids.

The mechanisms underlying alcoholic liver disease are not completely understood, but lipid accumulation seems to be central to the cause of this disease. The peroxisome proliferator-activated receptor alpha (PPARalpha) plays an important role in the control of lipid homeostasis, metabolism of bioactive molecules, and modulation of inflammatory responses. To investigate the roles of PPARalpha in alcoholic liver injury, wild-type and PPARalpha-null mice were continuously fed a diet containing 4% ethanol, and liver injury was analyzed. PPARalpha-null mice fed ethanol exhibited marked hepatomegaly, hepatic inflammation, cell toxicity, fibrosis, apoptosis, and mitochondrial swelling. Some of these hepatic abnormalities were consistent with those of patients with alcoholic liver injury and were not found in wild-type mice. Next, the molecular mechanisms of ethanol-induced liver injury in PPARalpha-null mice were investigated, and changes related to ethanol and acetaldehyde metabolism, oxidative stress, inflammation, hepatocyte proliferation, fibrosis, and mitochondrial permeability transition activation occurred specifically in PPARalpha-null mice as compared with wild-type mice. In conclusion, these studies suggest a protective role for PPARalpha in alcoholic liver disease. Humans may be more susceptible to liver toxicity induced by ethanol as PPARalpha expression in human liver is considerably lower compared to that of rodents.

The triglyceride-lowering effect of bezafibrate in humans has been attributed to peroxisome proliferator-activated receptor (PPAR) ␣ activation based on results from rodent studies. However, the bezafibrate dosages used in conventional rodent experiments are typically higher than those in clinical use (Ն50 versus Յ10 mg/kg/day), and thus it remains unclear whether such data can be translated to humans. Furthermore, because bezafibrate is a pan-PPAR activator, the actual contribution of PPAR␣ to its triglyceride-lowering properties remains undetermined. To address these issues, bezafibrate at clinically relevant doses (10 mg/kg/day; low) was administered to wild-type and Ppara-null mice, and its effects were compared with those from conventionally used doses (100 mg/kg/day; high). Pharmacokinetic analyses showed that maximum plasma concentration and area under the concentration-time curve in bezafibrate-treated mice were similar to those in humans at low doses, but not at high doses. Low-dose bezafibrate decreased serum/liver triglycerides in a PPAR␣-independent manner by attenuation of hepatic lipogenesis and triglyceride secretion. It is noteworthy that instead of PPAR activation, down-regulation of sterol regulatory element-binding protein (SREBP)-1c was observed in mice undergoing low-dose treatment. High-dose bezafibrate decreased serum/liver triglycerides by enhancement of hepatic fatty acid uptake and ␤-oxidation via PPAR␣ activation, as expected. In conclusion, clinically relevant doses of bezafibrate exert a triglyceride-lowering effect by suppression of the SREBP-1c-regulated pathway in mice and not by PPAR␣ activation. Our results may provide novel information about the pharmacological mechanism of bezafibrate action and new insights into the treatment of disorders involving SREBP-1c.Bezafibrate and other fibrate drugs are clinically used as hypolipidemic agents to preferentially lower serum triglyceride (TG) levels. Several large-scale clinical trials have demonstrated a relationship between the TG-lowering effect of fibrates and a reduction in the risk of cardiovascular events in patients with dyslipidemia, type 2 diabetes mellitus, and metabolic syndrome (BIP Study Group, 2000;Keech et al., 2005;Tenenbaum et al., 2005). The mechanisms accounting for the hypolipidemic effect of fibrates in humans are explained mainly as an increase in the lipolysis of TG-rich lipoproteins, such as very-low-density lipoprotein (VLDL),

Sulfatides, normal components of serum lipoproteins, may play an important role in cardiovascular disease due to their various modulatory functions in haemostasis. The incidence of cardiovascular disease in patients with end-stage renal failure undergoing maintenance hemodialysis has been reported to be approximately 10 to 30 times higher than that in the general population. To elucidate the possible roles of serum sulfatides in this high incidence, we measured the level of sulfatides in 59 such patients, by converting them to lysosulfatides according to a recently developed quantitative, qualitative, high-throughput technique using matrix-assisted laser desorption ionization-time of flight mass spectrometry. The mean level of sulfatides in patients 3.58 +/- 1.18 nmol/ml was significantly lower than that in age-matched normal subjects (8.21 +/- 1.50 nmol/ml; P < 0.001). Patients receiving maintenance hemodialysis over a longer period had lower levels of sulfatides. When the mean levels of sulfatides were compared between patients with cardiovascular disease (N = 22) and those without the disease (N = 37), the level in the former group 2.85 +/- 0.67 nmol/ml was found to be significantly lower than that in the latter group 4.01 +/- 1.22 nmol/ml (P < 0.001). These findings reveal a close correlation between low levels of serum sulfatides and a high risk of cardiovascular disease in these patients. Determination of the level of serum sulfatides can contribute to predictions of the incidence of cardiovascular disease in patients with end-stage renal failure undergoing maintenance hemodialysis.

Abstract. Peroxisome proliferator-activated receptor ␣ (PPAR␣) is a member of the steroid/nuclear receptor superfamily that is intensively expressed in the kidney, but its physiologic function is unknown. In this study, PPAR␣-null mice were used to help clarify the function. Starved PPAR␣-null mice were found to secrete significantly more quantities of urine albumin than starved wild-type mice. Furthermore, the appearance of giant lysosomes, marked accumulation of albumin, and an impaired ability concerning albumin digestion were found only in proximal tubules of the starved PPAR␣-null mice. These abnormalities were probably derived from ATP insufficiency as a result of the starvation-induced decline of carbohydrate metabolism and a lack of PPAR␣-dependent fatty acid metabolism. It is interesting that these abnormalities disappeared when glucose was administered. Taken together, these findings demonstrate important functions of PPAR␣ in the proximal tubules, the dynamic regulation of the proteindegradation system through maintenance of ATP homeostasis, and emphasize the importance of the fatty acid metabolism in renal physiology.Recently, considerable attention has been paid to the peroxisome proliferator-activated receptor ␣ (PPAR␣), which is known as a member of the steroid/nuclear receptor superfamily (1). According to some studies (2,3), a high level of PPAR␣ is found in the kidney and mainly localizes in the proximal tubules, although its physiologic function has not yet been clarified. Proximal tubular epithelial cells are highly differentiated cells that reabsorb many substances that are essential to the body from glomerular filtrate and secrete several physiologically active compounds. It was suggested that ATP produced in the proximal tubular epithelial cells, which contain a greater density of mitochondria, is necessary for supporting its specific functions and maintaining basic cell functions (4).To elucidate the physiologic role of PPAR␣ in the kidney, we examined the reabsorption process in the proximal tubules, using PPAR␣-null mice. We focused on albumin reabsorption, a typical component of the filtered protein handling, done through efficient receptor-mediated endocytosis in which megalin acts as the main receptor (5-8). The relationship between albumin reabsorption and energy production was also determined, because PPAR␣ is known to play an important role as a potent regulator of mitochondrial energy production in the liver and heart (9,10). In addition, we used starved mice to increase the dependence on fatty acids as an energy fuel source and to reduce the effect of carbohydrate metabolites. Materials and Methods MaterialsAnti-mouse albumin IgG was purchased from Bethyl Laboratories (Montgomery, TX). Anti-rat cathepsin D IgG, ATP, acetyl-CoA, and tripalmitin were from Wako (Osaka, Japan). Anti-Rab5a IgG, antiRab7 IgG, and anti-mouse cathepsin L IgG were from Santa Cruz Biotechnology (Santa Cruz, CA). Anti-LAMP-1 IgG was from American Research Products (Belmont, MA). Anti-megalin polyclonal ant...

The mechanism of trichloroethylene-induced liver peroxisome proliferation and the sex difference in response was investigated using wild-type Sv/129 and peroxisome proliferator-activated receptor alpha (PPARalpha)-null mice. Trichloroethylene treatment (0.75 g/kg for 2 weeks by gavage) resulted in liver peroxisome proliferation in wild-type mice, but not in PPARalpha-null mice, suggesting that trichloroethylene-induced peroxisome proliferation is primarily mediated by PPARalpha. No remarkable sex difference was observed in induction of peroxisome proliferation, as measured morphologically, but a markedly higher induction of several enzymes and PPARalpha protein and mRNA was found in males. On the other hand, trichloroethylene induced liver cytochrome P450 2E1, the principal enzyme responsible for metabolizing trichloroethylene to chloral hydrate, only in males, which resulted in similar expression levels in both sexes after the treatment. Trichloroethylene influenced neither the level of catalase, an enzyme involved in the reduction of oxidative stress, nor aldehyde dehydrogenase, the main enzyme catalyzing the conversion to trichloroacetic acid. These results suggest that trichloroethylene treatment causes a male-specific PPARalpha-dependent increase in cellular oxidative stress.