Less extrahepatic induction of fatty acid beta-oxidation enzymes by PPAR alpha

State of art on the mechanisms of laparoscopic sleeve gastrectomy in treating type 2 diabetes mellitus

Obesity and type-2 diabetes mellitus (T2DM) are metabolic disorders. Obesity increases the risk of T2DM, and as obesity is becoming increasingly common, more individuals suffer from T2DM, which poses a considerable burden on health systems. Traditionally, pharmaceutical therapy together with lifestyle changes is used to treat obesity and T2DM to decrease the incidence of comorbidities and all-cause mortality and to increase life expectancy. Bariatric surgery is increasingly replacing other forms of treatment of morbid obesity, especially in patients with refractory obesity, owing to its many benefits including good long-term outcomes and almost no weight regain. The bariatric surgery options have markedly changed recently, and laparoscopic sleeve gastrectomy (LSG) is gradually gaining popularity. LSG has become an effective and safe treatment for type-2 diabetes and morbid obesity, with a high cost-benefit ratio. Here, we review the me-chanism associated with LSG treatment of T2DM, and we discuss clinical studies and animal experiments with regard to gastrointestinal hormones, gut microbiota, bile acids, and adipokines to clarify current treatment modalities for patients with obesity and T2DM.

Metabolic landscape in cardiac aging: insights into molecular biology and therapeutic implications

Cardiac aging is evident by a reduction in function which subsequently contributes to heart failure. The metabolic microenvironment has been identified as a hallmark of malignancy, but recent studies have shed light on its role in cardiovascular diseases (CVDs). Various metabolic pathways in cardiomyocytes and noncardiomyocytes determine cellular senescence in the aging heart. Metabolic alteration is a common process throughout cardiac degeneration. Importantly, the involvement of cellular senescence in cardiac injuries, including heart failure and myocardial ischemia and infarction, has been reported. However, metabolic complexity among human aging hearts hinders the development of strategies that targets metabolic susceptibility. Advances over the past decade have linked cellular senescence and function with their metabolic reprogramming pathway in cardiac aging, including autophagy, oxidative stress, epigenetic modifications, chronic inflammation, and myocyte systolic phenotype regulation. In addition, metabolic status is involved in crucial aspects of myocardial biology, from fibrosis to hypertrophy and chronic inflammation. However, further elucidation of the metabolism involvement in cardiac degeneration is still needed. Thus, deciphering the mechanisms underlying how metabolic reprogramming impacts cardiac aging is thought to contribute to the novel interventions to protect or even restore cardiac function in aging hearts. Here, we summarize emerging concepts about metabolic landscapes of cardiac aging, with specific focuses on why metabolic profile alters during cardiac degeneration and how we could utilize the current knowledge to improve the management of cardiac aging.

Adiponectin Is a Component of the Inflammatory Cascade in Rheumatoid Arthritis

Adiponectin is a secretory protein of adipocytes that plays an important role in pathological processes by participation in modulating the immune and inflammatory responses. The pro-inflammatory effect of adiponectin is observed in rheumatoid arthritis (RA). In this study, we examined adiponectin plasma levels and the expression of adiponectin in bone marrow tissue samples, synovium samples, and infrapatellar fat pad samples from patients with osteoarthritis (OA) and RA. Additionally we examined the expression of adiponectin receptors AdipoR1 and AdipoR2 in synovium samples and infrapatellar fat pad samples from patients with OA and RA. We also assessed the correlations between adiponectin plasma concentrations, adiponectin expression in bone marrow, synovium, infrapatellar fat pad, and plasma levels of selected cytokines. We found increased expression of adiponectin in synovium samples and infrapatellar fat pad samples from patients with RA as compared to patients with OA. There were no statistically significant differences of adiponectin plasma levels and adiponectin expression in bone marrow tissue samples between OA and RA patients. There were no differences in the expression of AdipoR1 and AdipoR2 at the mRNA level in synovial tissue and the infrapatellar fat pad between RA and OA patients. However, in immunohistochemical analysis in samples of the synovial membrane from RA patients, we observed very strong expression of adiponectin in intima cells, macrophages, and subintimal fibroblasts, such as synoviocytes, vs. strong expression in OA samples. Very strong expression of adiponectin was also noted in adipocytes of Hoffa’s fat pad of RA patients. Expression of AdipoR1 was stronger in RA tissue samples, while AdipoR2 expression was very similar in both RA and OA samples. Our results showed increased adiponectin expression in the synovial membrane and Hoffa’s pad in RA patients compared to that of OA patients. However, there were no differences in plasma adiponectin concentrations and its expression in bone marrow. The results suggest that adiponectin is a component of the inflammatory cascade that is present in RA. Pro-inflammatory factors enhance the expression of adiponectin, especially in joint tissues—the synovial membrane and Hoffa’s fat pad. In turn, adiponectin also increases the expression of further pro-inflammatory mediators.

The Contribution of Cardiac Fatty Acid Oxidation to Diabetic Cardiomyopathy Severity

Diabetes is a major risk factor for the development of cardiovascular disease via contributing and/or triggering significant cellular signaling and metabolic and structural alterations at the level of the heart and the whole body. The main cause of mortality and morbidity in diabetic patients is cardiovascular disease including diabetic cardiomyopathy. Therefore, understanding how diabetes increases the incidence of diabetic cardiomyopathy and how it mediates the major perturbations in cell signaling and energy metabolism should help in the development of therapeutics to prevent these perturbations. One of the significant metabolic alterations in diabetes is a marked increase in cardiac fatty acid oxidation rates and the domination of fatty acids as the major energy source in the heart. This increased reliance of the heart on fatty acids in the diabetic has a negative impact on cardiac function and structure through a number of mechanisms. It also has a detrimental effect on cardiac efficiency and worsens the energy status in diabetes, mainly through inhibiting cardiac glucose oxidation. Furthermore, accelerated cardiac fatty acid oxidation rates in diabetes also make the heart more vulnerable to ischemic injury. In this review, we discuss how cardiac energy metabolism is altered in diabetic cardiomyopathy and the impact of cardiac insulin resistance on the contribution of glucose and fatty acid to overall cardiac ATP production and cardiac efficiency. Furthermore, how diabetes influences the susceptibility of the myocardium to ischemia/reperfusion injury and the role of the changes in glucose and fatty acid oxidation in mediating these effects are also discussed.

Galangin Resolves Cardiometabolic Disorders through Modulation of AdipoR1, COX-2, and NF-κB Expression in Rats Fed a High-Fat Diet

Galangin is a natural flavonoid. In this study, we evaluated whether galangin could alleviate signs of metabolic syndrome (MS) and cardiac abnormalities in rats receiving a high-fat (HF) diet. Male Sprague–Dawley rats were given an HF diet plus 15% fructose for four months, and they were fed with galangin (25 or 50 mg/kg), metformin (100 mg/kg), or a vehicle for the last four weeks. The MS rats exhibited signs of MS, hypertrophy of adipocytes, impaired liver function, and cardiac dysfunction and remodeling. These abnormalities were alleviated by galangin (p < 0.05). Interleukin-6 and tumor necrosis factor-α concentrations and expression were high in the plasma and cardiac tissue in the MS rats, and these markers were suppressed by galangin (p < 0.05). These treatments also alleviated the low levels of adiponectin and oxidative stress induced by an HF diet in rats. The downregulation of adiponectin receptor 1 (AdipoR1) and cyclooxygenase-2 (COX-2) and the upregulation of nuclear factor kappa B (NF-κB) expression were recovered in the galangin-treated groups. Metformin produced similar effects to galangin. In conclusion, galangin reduced cardiometabolic disorders in MS rats. These effects might be linked to the suppression of inflammation and oxidative stress and the restoration of AdipoR1, COX-2, and NF-κB expression.

Role of Adiponectin in the Pathogenesis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic chronic inflammatory autoimmune joint disease, characterized by progressive articular damage and joint dysfunction. One of the symptoms of this disease is persistent inflammatory infiltration of the synovial membrane, the principle site of inflammation in RA. In the affected conditions, the cells of the synovial membrane, fibroblast-like synoviocytes and macrophage-like synovial cells, produce enzymes degrading cartilage and underlining bone tissue, as well as cytokines increasing the infiltration of immune cells. In patients with RA, higher levels of adiponectin are measured in the serum and synovial fluid. Adiponectin, a secretory product that is mainly white adipose tissue, is a multifunctional protein with dual anti-inflammatory and pro-inflammatory properties. Several studies underline the fact that adiponectin can play an important pro-inflammatory role in the pathophysiology of RA via stimulating the secretion of inflammatory mediators. This narrative review is devoted to the presentation of recent knowledge on the role played by one of the adipokines produced by adipose tissue—adiponectin—in the pathogenesis of rheumatoid arthritis.

Multifaceted Physiological Roles of Adiponectin in Inflammation and Diseases

Adiponectin is the richest adipokine in human plasma, and it is mainly secreted from white adipose tissue. Adiponectin circulates in blood as high-molecular, middle-molecular, and low-molecular weight isoforms. Numerous studies have demonstrated its insulin-sensitizing, anti-atherogenic, and anti-inflammatory effects. Additionally, decreased serum levels of adiponectin is associated with chronic inflammation of metabolic disorders including Type 2 diabetes, obesity, and atherosclerosis. However, recent studies showed that adiponectin could have pro-inflammatory roles in patients with autoimmune diseases. In particular, its high serum level was positively associated with inflammation severity and pathological progression in rheumatoid arthritis, chronic kidney disease, and inflammatory bowel disease. Thus, adiponectin seems to have both pro-inflammatory and anti-inflammatory effects. This indirectly indicates that adiponectin has different physiological roles according to an isoform and effector tissue. Knowledge on the specific functions of isoforms would help develop potential anti-inflammatory therapeutics to target specific adiponectin isoforms against metabolic disorders and autoimmune diseases. This review summarizes the current roles of adiponectin in metabolic disorders and autoimmune diseases.

Metabolic remodelling in heart failure

The heart consumes large amounts of energy in the form of ATP that is continuously replenished by oxidative phosphorylation in mitochondria and, to a lesser extent, by glycolysis. To adapt the ATP supply efficiently to the constantly varying demand of cardiac myocytes, a complex network of enzymatic and signalling pathways controls the metabolic flux of substrates towards their oxidation in mitochondria. In patients with heart failure, derangements of substrate utilization and intermediate metabolism, an energetic deficit, and oxidative stress are thought to underlie contractile dysfunction and the progression of the disease. In this Review, we give an overview of the physiological processes of cardiac energy metabolism and their pathological alterations in heart failure and diabetes mellitus. Although the energetic deficit in failing hearts - discovered >2 decades ago - might account for contractile dysfunction during maximal exertion, we suggest that the alterations of intermediate substrate metabolism and oxidative stress rather than an ATP deficit per se account for maladaptive cardiac remodelling and dysfunction under resting conditions. Treatments targeting substrate utilization and/or oxidative stress in mitochondria are currently being tested in patients with heart failure and might be promising tools to improve cardiac function beyond that achieved with neuroendocrine inhibition.

Activation of PPARα by Oral Clofibrate Increases Renal Fatty Acid Oxidation in Developing Pigs

The objective of this study was to evaluate the effects of peroxisome proliferator-activated receptor α (PPARα) activation by clofibrate on both mitochondrial and peroxisomal fatty acid oxidation in the developing kidney. Ten newborn pigs from 5 litters were randomly assigned to two groups and fed either 5 mL of a control vehicle (2% Tween 80) or a vehicle containing clofibrate (75 mg/kg body weight, treatment). The pigs received oral gavage daily for three days. In vitro fatty acid oxidation was then measured in kidneys with and without mitochondria inhibitors (antimycin A and rotenone) using [1-¹⁴C]-labeled oleic acid (C18:1) and erucic acid (C22:1) as substrates. Clofibrate significantly stimulated C18:1 and C22:1 oxidation in mitochondria (p < 0.001) but not in peroxisomes. In addition, the oxidation rate of C18:1 was greater in mitochondria than peroxisomes, while the oxidation of C22:1 was higher in peroxisomes than mitochondria (p < 0.001). Consistent with the increase in fatty acid oxidation, the mRNA abundance and enzyme activity of carnitine palmitoyltransferase I (CPT I) in mitochondria were increased. Although mRNA of mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme A synthase (mHMGCS) was increased, the β-hydroxybutyrate concentration measured in kidneys did not increase in pigs treated with clofibrate. These findings indicate that PPARα activation stimulates renal fatty acid oxidation but not ketogenesis.

Nrf2 activation is required for curcumin to induce lipocyte phenotype in hepatic stellate cells

Hepatic fibrosis is a reversible scarring response that commonly occurs with chronic liver injury. During hepatic fibrogenesis, the major effector hepatic stellate cells (HSCs) become activated, featured by disappeared intracellular lipid droplets, decreased retinoid storage, and dysregulated expression of genes associated with lipid and retinoid metabolism. Compelling evidence suggested that recovery of retinoid droplets could inhibit HSC activation, while the precise molecular basis underlying the phenotypical switch still remained unclear. In this study, curcumin increased the abundance of lipid droplets and content of triglyceride in activated HSCs. In addition, curcumin could concentration-dependently regulate genes associated with lipid and retinoid metabolism. Further, consistent results were obtained from in vivo experiments. Curcumin increased Nrf2 expression and nuclear translocation, and its binding activity to DNA, which might be associated with suppression of Kelch-like ECH-associated protein 1 in HSCs. Of interest was that Nrf2 overexpression plasmids, in contract to Nrf2 siRNA, strengthened the effect of curcumin on induction of lipocyte phenotype. In in vivo system, Nrf2 knockdown mediated by Nrf2 shRNA lentivirus not only accelerated the lipid degradation in HSCs but also promoted the progression of CCl₄-induced hepatic fibrosis in mice. Noteworthily, Nrf2 knockdown abolished the protective effect of curcumin. In conclusion, curcumin could induce lipocyte phenotype of activated HSCs via activating Nrf2. Nrf2 could be a target molecule for antifibrotic strategy.

The Peroxisome-Mitochondria Connection: How and Why?

Over the past decades, peroxisomes have emerged as key regulators in overall cellular lipid and reactive oxygen species metabolism. In mammals, these organelles have also been recognized as important hubs in redox-, lipid-, inflammatory-, and innate immune-signaling networks. To exert these activities, peroxisomes must interact both functionally and physically with other cell organelles. This review provides a comprehensive look of what is currently known about the interconnectivity between peroxisomes and mitochondria within mammalian cells. We first outline how peroxisomal and mitochondrial abundance are controlled by common sets of cis- and trans-acting factors. Next, we discuss how peroxisomes and mitochondria may communicate with each other at the molecular level. In addition, we reflect on how these organelles cooperate in various metabolic and signaling pathways. Finally, we address why peroxisomes and mitochondria have to maintain a healthy relationship and why defects in one organelle may cause dysfunction in the other. Gaining a better insight into these issues is pivotal to understanding how these organelles function in their environment, both in health and disease.

Perfluoroalkyl acids-induced liver steatosis: Effects on genes controlling lipid homeostasis

Persistent presence of perfluoroalkyl acids (PFAAs) in the environment is due to their extensive use in industrial and consumer products, and their slow decay. Biochemical tests in rodent demonstrated that these chemicals are potent modifiers of lipid metabolism and cause hepatocellular steatosis. However, the molecular mechanism of PFAAs interference with lipid metabolism remains to be elucidated. Currently, two major hypotheses are that PFAAs interfere with mitochondrial beta-oxidation of fatty acids and/or they affect the transcriptional activity of peroxisome proliferator-activated receptor α (PPARα) in liver. To determine the ability of structurally-diverse PFAAs to cause steatosis, as well as to understand the underlying molecular mechanisms, wild-type (WT) and PPARα-null mice were treated with perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), or perfluorohexane sulfonate (PFHxS), by oral gavage for 7days, and their effects were compared to that of PPARα agonist WY-14643 (WY), which does not cause steatosis. Increases in liver weight and cell size, and decreases in DNA content per mg of liver, were observed for all compounds in WT mice, and were also seen in PPARα-null mice for PFOA, PFNA, and PFHxS, but not for WY. In Oil Red O stained sections, WT liver showed increased lipid accumulation in all treatment groups, whereas in PPARα-null livers, accumulation was observed after PFNA and PFHxS treatment, adding to the burden of steatosis observed in control (untreated) PPARα-null mice. Liver triglyceride (TG) levels were elevated in WT mice by all PFAAs and in PPARα-null mice only by PFNA. In vitro β-oxidation of palmitoyl carnitine by isolated rat liver mitochondria was not inhibited by any of the 7 PFAAs tested. Likewise, neither PFOA nor PFOS inhibited palmitate oxidation by HepG2/C3A human liver cell cultures. Microarray analysis of livers from PFAAs-treated mice indicated that the PFAAs induce the expression of the lipid catabolism genes, as well as those involved in fatty acid and triglyceride synthesis, in WT mice and, to a lesser extent, in PPARα-null mice. These results indicate that most of the PFAAs increase liver TG load and promote steatosis in mice We hypothesize that PFAAs increase steatosis because the balance of fatty acid accumulation/synthesis and oxidation is disrupted to favor accumulation.

Nutrigenomic regulation of adipose tissue development - role of retinoic acid: A review

To improve the efficiency of animal production, livestock have been extensively selected or managed to reduce fat accumulation and increase lean growth, which reduces intramuscular or marbling fat content. To enhance marbling, a better understanding of the mechanisms regulating adipogenesis is needed. Vitamin A has recently been shown to have a profound impact on all stages of adipogenesis. Retinoic acid, an active metabolite of vitamin A, activates both retinoic acid receptors (RAR) and retinoid X receptors (RXR), inducing epigenetic changes in key regulatory genes governing adipogenesis. Additionally, Vitamin D and folates interact with the retinoic acid receptors to regulate adipogenesis. In this review, we discuss nutritional regulation of adipogenesis, focusing on retinoic acid and its impact on epigenetic modifications of key adipogenic genes.

Peroxisomes in Different Skeletal Cell Types during Intramembranous and Endochondral Ossification and Their Regulation during Osteoblast Differentiation by Distinct Peroxisome Proliferator-Activated Receptors

Ossification defects leading to craniofacial dysmorphism or rhizomelia are typical phenotypes in patients and corresponding knockout mouse models with distinct peroxisomal disorders. Despite these obvious skeletal pathologies, to date no careful analysis exists on the distribution and function of peroxisomes in skeletal tissues and their alterations during ossification. Therefore, we analyzed the peroxisomal compartment in different cell types of mouse cartilage and bone as well as in primary cultures of calvarial osteoblasts. The peroxisome number and metabolism strongly increased in chondrocytes during endochondral ossification from the reserve to the hypertrophic zone, whereas in bone, metabolically active osteoblasts contained a higher numerical abundance of this organelle than osteocytes. The high abundance of peroxisomes in these skeletal cell types is reflected by high levels of Pex11β gene expression. During culture, calvarial pre-osteoblasts differentiated into secretory osteoblasts accompanied by peroxisome proliferation and increased levels of peroxisomal genes and proteins. Since many peroxisomal genes contain a PPAR-responsive element, we analyzed the gene expression of PPARɑ/ß/ɣ in calvarial osteoblasts and MC3T3-E1 cells, revealing higher levels for PPARß than for PPARɑ and PPARɣ. Treatment with different PPAR agonists and antagonists not only changed the peroxisomal compartment and associated gene expression, but also induced complex alterations of the gene expression patterns of the other PPAR family members. Studies in M3CT3-E1 cells showed that the PPARß agonist GW0742 activated the PPRE-mediated luciferase expression and up-regulated peroxisomal gene transcription (Pex11, Pex13, Pex14, Acox1 and Cat), whereas the PPARß antagonist GSK0660 led to repression of the PPRE and a decrease of the corresponding mRNA levels. In the same way, treatment of calvarial osteoblasts with GW0742 increased in peroxisome number and related gene expression and accelerated osteoblast differentiation. Taken together, our results suggest that PPARß regulates the numerical abundance and metabolic function of peroxisomes via Pex11ß in parallel to osteoblast differentiation.

Peroxisome-mitochondria interplay and disease

Peroxisomes and mitochondria are ubiquitous, highly dynamic organelles with an oxidative type of metabolism in eukaryotic cells. Over the years, substantial evidence has been provided that peroxisomes and mitochondria exhibit a close functional interplay which impacts on human health and development. The so-called "peroxisome-mitochondria connection" includes metabolic cooperation in the degradation of fatty acids, a redox-sensitive relationship, an overlap in key components of the membrane fission machineries and cooperation in anti-viral signalling and defence. Furthermore, combined peroxisome-mitochondria disorders with defects in organelle division have been revealed. In this review, we present the latest progress in the emerging field of peroxisomal and mitochondrial interplay in mammals with a particular emphasis on cooperative fatty acid β-oxidation, redox interplay, organelle dynamics, cooperation in anti-viral signalling and the resulting implications for disease.

Activating PPARα prevents post-ischemic contractile dysfunction in hypertrophied neonatal hearts

RATIONALE

Post-ischemic contractile dysfunction is a contributor to morbidity and mortality after the surgical correction of congenital heart defects in neonatal patients. Pre-existing hypertrophy in the newborn heart can exacerbate these ischemic injuries, which may partly be due to a decreased energy supply to the heart resulting from low fatty acid β-oxidation rates.

OBJECTIVE

We determined whether stimulating fatty acid β-oxidation with GW7647, a peroxisome proliferator-activated receptor-α (PPARα) activator, would improve cardiac energy production and post-ischemic functional recovery in neonatal rabbit hearts subjected to volume overload-induced cardiac hypertrophy.

METHODS AND RESULTS

Volume-overload cardiac hypertrophy was produced in 7-day-old rabbits via an aorto-caval shunt, after which, the rabbits were treated with or without GW7647 (3 mg/kg per day) for 14 days. Biventricular working hearts were subjected to 35 minutes of aerobic perfusion, 25 minutes of global no-flow ischemia, and 30 minutes of aerobic reperfusion. GW7647 treatment did not prevent the development of cardiac hypertrophy, but did prevent the decline in left ventricular ejection fraction in vivo. GW7647 treatment increased cardiac fatty acid β-oxidation rates before and after ischemia, which resulted in a significant increase in overall ATP production and an improved in vitro post-ischemic functional recovery. A decrease in post-ischemic proton production and endoplasmic reticulum stress, as well as an activation of sarcoplasmic reticulum calcium ATPase isoform 2 and citrate synthase, was evident in GW7647-treated hearts.

CONCLUSIONS

Stimulating fatty acid β-oxidation in neonatal hearts may present a novel cardioprotective intervention to limit post-ischemic contractile dysfunction.

Mitochondrial fatty acid oxidation alterations in heart failure, ischaemic heart disease and diabetic cardiomyopathy

Heart disease is a leading cause of death worldwide. In many forms of heart disease, including heart failure, ischaemic heart disease and diabetic cardiomyopathies, changes in cardiac mitochondrial energy metabolism contribute to contractile dysfunction and to a decrease in cardiac efficiency. Specific metabolic changes include a relative increase in cardiac fatty acid oxidation rates and an uncoupling of glycolysis from glucose oxidation. In heart failure, overall mitochondrial oxidative metabolism can be impaired while, in ischaemic heart disease, energy production is impaired due to a limitation of oxygen supply. In both of these conditions, residual mitochondrial fatty acid oxidation dominates over mitochondrial glucose oxidation. In diabetes, the ratio of cardiac fatty acid oxidation to glucose oxidation also increases, although primarily due to an increase in fatty acid oxidation and an inhibition of glucose oxidation. Recent evidence suggests that therapeutically regulating cardiac energy metabolism by reducing fatty acid oxidation and/or increasing glucose oxidation can improve cardiac function of the ischaemic heart, the failing heart and in diabetic cardiomyopathies. In this article, we review the cardiac mitochondrial energy metabolic changes that occur in these forms of heart disease, what role alterations in mitochondrial fatty acid oxidation have in contributing to cardiac dysfunction and the potential for targeting fatty acid oxidation to treat these forms of heart disease.

Heart failure and loss of metabolic control

Heart failure is a leading cause of morbidity and mortality worldwide, currently affecting 5 million Americans. A syndrome defined on clinical terms, heart failure is the end result of events occurring in multiple heart diseases, including hypertension, myocardial infarction, genetic mutations and diabetes, and metabolic dysregulation, is a hallmark feature. Mounting evidence from clinical and preclinical studies suggests strongly that fatty acid uptake and oxidation are adversely affected, especially in end-stage heart failure. Moreover, metabolic flexibility, the heart's ability to move freely among diverse energy substrates, is impaired in heart failure. Indeed, impairment of the heart's ability to adapt to its metabolic milieu and associated metabolic derangement are important contributing factors in the heart failure pathogenesis. Elucidation of molecular mechanisms governing metabolic control in heart failure will provide critical insights into disease initiation and progression, raising the prospect of advances with clinical relevance.

Highly expressed MT-ND3 positively associated with histological severity of hepatic steatosis

Hepatic steatosis is the accumulation of an excess amount of triglycerides and other fats inside liver cells resulting from abnormal hepatic lipid metabolism. Mitochondrial structural and molecular defects are involved in the progression of hepatic steatosis pathogenesis. Hepatic methylation and transcriptional activity of the mitochondrial-encoded NADH dehydrogenase (MT-ND) play a critical role in the progression of non-alcoholic fatty liver disease (NAFLD). However, the expression of MT-ND3 in hepatic steatosis has not been extensively studied. In this study, liver specimens were collected from different patients, and were subjected to immunohistochemistry. Primary hepatocytes were treated with oxidative stress, hypoxia, and lipotoxicity to investigate the respective roles of these factors on MT-ND3 expression and cell apoptosis by western blotting and flow cytometry, respectively. We found that increased MT-ND3 expression in human hepatic steatosis was positively associated with histological severity of hepatic steatosis. Hypoxia, H2O2 , and saturated fatty acid treatment induced cell apoptosis mediated by mitochondria. These three factors all had effects on MT-ND3 expression in cultured hepatocytes. Taken together, MT-ND3 may play important roles in hepatic steatosis progress. Hypoxia, oxidative stress, and lipotoxicity could all influence expression of MT-ND3 and thus may play a role in the progression of hepatic steatosis.

Immunohistochemical localization of mitochondrial fatty acid β-oxidation enzymes in rat testis

The testis consists of two types of tissues, the interstitial tissue and the seminiferous tubule, which have different functions and are assumed to have different nutritional metabolism. The localization of enzymes of the mitochondrial fatty acid β-oxidation system in the testis was investigated to obtain a better understanding of nutrient metabolism in the testis. Adult rat testis tissues were subjected to immunoblot analysis for quantitation of the amounts of enzyme proteins, to DNA microarray analysis for gene expression, and to immunofluorescence and immunoelectron microscopy for localization. Quantitative analysis by immunoblot and DNA microarray revealed that enzymes occur abundantly in Leydig cells in the interstitial tissue but much less so in the seminiferous tubules. Immunohistochemistry revealed that Leydig cells in the interstitial tissue and Sertoli cells in the seminiferous tubules contain a full set of mitochondrial fatty acid β-oxidation enzymes in relatively plentiful amounts among the cells in the testis, but that this is not so in spermatogenic cells. This characteristic localization of the mitochondrial fatty acid β-oxidation system in the testis needs further elucidation in terms of a possible role for it in the nutritional metabolism of spermatogenesis.

β-Catenin regulates hepatic mitochondrial function and energy balance in mice

BACKGROUND & AIMS

Wnt signaling regulates hepatic function and nutrient homeostasis. However, little is known about the roles of β-catenin in cellular respiration or mitochondria of hepatocytes.

METHODS

We investigated β-catenin's role in the metabolic function of hepatocytes under homeostatic conditions and in response to metabolic stress using mice with hepatocyte-specific deletion of β-catenin and their wild-type littermates, given either saline (sham) or ethanol (as a model of binge drinking and acute ethanol intoxication).

RESULTS

Under homeostatic conditions, β-catenin-deficient hepatocytes demonstrated mitochondrial dysfunctions that included impairments to the tricarboxylic acid cycle and oxidative phosphorylation (OXPHOS) and decreased production of adenosine triphosphate (ATP). There was no evidence for redox imbalance or oxidative cellular injury in the absence of metabolic stress. In mice with β-catenin-deficient hepatocytes, ethanol intoxication led to significant redox imbalance in the hepatocytes and further deterioration in mitochondrial function that included reduced OXPHOS, fatty acid oxidation (FAO), and ATP production. Ethanol feeding significantly increased liver steatosis and oxidative damage, compared with wild-type mice, and disrupted the ratio of nicotinamide adenine dinucleotide. β-catenin-deficient hepatocytes also had showed disrupted signaling of Sirt1/peroxisome proliferator-activated receptor-α signaling.

CONCLUSIONS

β-catenin has an important role in the maintenance of mitochondrial homeostasis, regulating ATP production via the tricarboxylic acid cycle, OXPHOS, and fatty acid oxidation; β-catenin function in these systems is compromised under conditions of nutrient oxidative stress. Reagents that alter Wnt-β-catenin signaling might be developed as a useful new therapeutic strategy for treatment of liver disease.

Metabolic stress in the myocardium: adaptations of gene expression

The heart is one of the highest ATP consuming organs in mammalian organisms. Its metabolic function has evolved a remarkable degree of efficiency to meet high demand and plasticity in response to varying changes in energy substrate supply. Given the high flux of energy substrates and the centrality of their appropriate use for optimal cardiac function, it is not surprising that the heart has intricate signaling mechanisms through which it responds to metabolic stress. This review focuses on the changes in gene expression in myocardial and vascular tissues during metabolic stress that affect mRNAs and subsequent protein synthesis with an eye toward understanding the manner in which these changes effect adaptive and maladaptive responses of the heart. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

The PPARalpha-PGC-1alpha Axis Controls Cardiac Energy Metabolism in Healthy and Diseased Myocardium

The mammalian myocardium is an omnivorous organ that relies on multiple substrates in order to fulfill its tremendous energy demands. Cardiac energy metabolism preference is regulated at several critical points, including at the level of gene transcription. Emerging evidence indicates that the nuclear receptor PPARα and its cardiac-enriched coactivator protein, PGC-1α, play important roles in the transcriptional control of myocardial energy metabolism. The PPARα-PGC-1α complex controls the expression of genes encoding enzymes involved in cardiac fatty acid and glucose metabolism as well as mitochondrial biogenesis. Also, evidence has emerged that the activity of the PPARα-PGC-1α complex is perturbed in several pathophysiologic conditions and that altered activity of this pathway may play a role in cardiomyopathic remodeling. In this review, we detail the current understanding of the effects of the PPARα-PGC-1α axis in regulating mitochondrial energy metabolism and cardiac function in response to physiologic and pathophysiologic stimuli.

L-Carnitine induces recovery of liver lipid metabolism in cancer cachexia

Cancer cachexia causes metabolic alterations with a marked effect on hepatic lipid metabolism. L-Carnitine modulates lipid metabolism and its supplementation has been proposed as a therapeutic strategy in many diseases. In the present study, the effects of L-carnitine supplementation on gene expression and on liver lipid metabolism-related proteins was investigated in cachectic tumour-bearing rats. Wistar rats were assigned to receive 1 g/kg of L-carnitine or saline. After 14 days, supplemented and control animals were assigned to a control (N), control supplemented with L-carnitine (CN), tumour-bearing Walker 256 carcinosarcoma (TB) and tumour-bearing supplemented with L-carnitine (CTB) group. The mRNA expression of carnitine palmitoyltransferase I and II (CPT I and II), microsomal triglyceride transfer protein (MTP), liver fatty acid-binding protein (L-FABP), fatty acid translocase (FAT/CD36), peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and organic cation transporter 2 (OCTN2) was assessed, and the maximal activity of CPT I and II in the liver measured, along with plasma and liver triacylglycerol content. The gene expression of MTP, and CPT I catalytic activity were reduced in TB, who also showed increased liver (150%) and plasma (3.3-fold) triacylglycerol content. L-Carnitine supplementation was able to restore these parameters back to control values (p<0.05). These data show that L-carnitine preserves hepatic lipid metabolism in tumour-bearing animals, suggesting its supplementation to be of potential interest in cachexia.

Peroxisome proliferator activated receptor-alpha (PPARα) and PPAR gamma coactivator-1alpha (PGC-1α) regulation of cardiac metabolism in diabetes

Cardiovascular disease is a leading cause of mortality among patients with diabetes, and heart failure exists even in the absence of coronary disease. Myocardial metabolism is altered in the diabetic heart as a result of changes in substrate availability secondary to insulin resistance. The nuclear receptor peroxisome proliferator activated receptor-alpha (PPARα) and PPAR-gamma coactivator-1alpha (PGC-1α) play important roles in transcriptional regulation of myocardial metabolism and contribute significantly to the changes that occur in the diabetic heart. This review summarizes the role of PPARα and PGC-1α in myocardial metabolism in the normal heart and in the diabetic heart.

Targeting fatty acid and carbohydrate oxidation--a novel therapeutic intervention in the ischemic and failing heart

Cardiac ischemia and its consequences including heart failure, which itself has emerged as the leading cause of morbidity and mortality in developed countries are accompanied by complex alterations in myocardial energy substrate metabolism. In contrast to the normal heart, where fatty acid and glucose metabolism are tightly regulated, the dynamic relationship between fatty acid β-oxidation and glucose oxidation is perturbed in ischemic and ischemic-reperfused hearts, as well as in the failing heart. These metabolic alterations negatively impact both cardiac efficiency and function. Specifically there is an increased reliance on glycolysis during ischemia and fatty acid β-oxidation during reperfusion following ischemia as sources of adenosine triphosphate (ATP) production. Depending on the severity of heart failure, the contribution of overall myocardial oxidative metabolism (fatty acid β-oxidation and glucose oxidation) to adenosine triphosphate production can be depressed, while that of glycolysis can be increased. Nonetheless, the balance between fatty acid β-oxidation and glucose oxidation is amenable to pharmacological intervention at multiple levels of each metabolic pathway. This review will focus on the pathways of cardiac fatty acid and glucose metabolism, and the metabolic phenotypes of ischemic and ischemic/reperfused hearts, as well as the metabolic phenotype of the failing heart. Furthermore, as energy substrate metabolism has emerged as a novel therapeutic intervention in these cardiac pathologies, this review will describe the mechanistic bases and rationale for the use of pharmacological agents that modify energy substrate metabolism to improve cardiac function in the ischemic and failing heart. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Supplementation with the reduced form of Coenzyme Q10 decelerates phenotypic characteristics of senescence and induces a peroxisome proliferator-activated receptor-alpha gene expression signature in SAMP1 mice

Our present study reveals significant decelerating effects on senescence processes in middle-aged SAMP1 mice supplemented for 6 or 14 months with the reduced form (Q(10)H(2), 500 mg/kg BW/day) of coenzyme Q(10) (CoQ(10)). To unravel molecular mechanisms of these CoQ(10) effects, a genome-wide transcript profiling in liver, heart, brain and kidney of SAMP1 mice supplemented with the reduced (Q(10)H(2)) or oxidized form of CoQ(10) (Q(10)) was performed. Liver seems to be the main target tissue of CoQ(10) intervention, followed by kidney, heart and brain. Stringent evaluation of the resulting data revealed that Q(10)H(2) has a stronger impact on gene expression than Q(10), primarily due to differences in the bioavailability. Indeed, Q(10)H(2) supplementation was more effective than Q(10) to increase levels of CoQ(10) in the liver of SAMP1 mice. To identify functional and regulatory connections of the "top 50" (p<0.05) Q(10)H(2)-sensitive transcripts in liver, text mining analysis was used. Hereby, we identified Q(10)H(2)-sensitive genes which are regulated by peroxisome proliferator-activated receptor-alpha and are primarily involved in cholesterol synthesis (e.g. HMGCS1, HMGCL and HMGCR), fat assimilation (FABP5), lipoprotein metabolism (PLTP) and inflammation (STAT-1). These data may explain, at least in part, the decelerating effects on degenerative processes observed in Q(10)H(2)-supplemented SAMP1 mice.

PPARalpha and PPARgamma are co-expressed, functional and show positive interactions in the rat urinary bladder urothelium

Some dual-acting PPARalpha + gamma agonists cause cancer in the rat urinary bladder, in some cases overrepresented in males, by a mechanism suggested to involve chronic stimulation of PPARalpha and PPARgamma, i.e. exaggerated pharmacology. By western blotting, we found that the rat urinary bladder urothelium expressed PPARalpha at higher levels than the liver and heart, and comparable to kidney. Urothelial expression of PPARgamma was above that of fat, heart, skeletal muscle and kidney. Male rats exhibited a higher PPARalpha/PPARgamma expression balance in the bladder urothelium than did female rats. Rats were treated by gastric gavage with rosiglitazone (PPARgamma agonist), fenofibrate (PPARalpha agonist) or a combination of rosiglitazone and fenofibrate for 7 days. In the urothelium, the transcription factor Egr-1 was induced to significantly higher levels in rats co-administered rosiglitazone and fenofibrate than in rats administered either rosiglitazone or fenofibrate alone. Egr-1 was also induced in the heart and liver of rats treated with fenofibrate, but a positive interaction between rosiglitazone and fenofibrate with regards to Egr-1 induction was only seen in the urothelium. Thus, in the rat urinary bladder urothelium, PPARalpha and PPARgamma were expressed at high levels, were functional and exhibited positive interactions. Interestingly, fenofibrate induced the peroxisome membrane protein PMP70 not only in liver, but also in the bladder urothelium, opening the possibility that oxidative stress may contribute to rat urothelial carcinogenesis by dual-acting PPARalpha + gamma agonists.

Shedding light on the enigma of myocardial lipotoxicity: the involvement of known and putative regulators of fatty acid storage and mobilization

Excessive fatty acid (FA) uptake by cardiac myocytes is often associated with adverse changes in cardiac function. This is especially evident in diabetic individuals, where increased intramyocardial triacylglycerol (TG) resulting from the exposure to high levels of circulating FA has been proposed to be a major contributor to diabetic cardiomyopathy. At present, our knowledge of how the heart regulates FA storage in TG and the hydrolysis of this TG is limited. This review concentrates on what is known about TG turnover within the heart and how this is likely to be regulated by extrapolating results from other tissues. We also assess the evidence as to whether increased TG accumulation protects against FA-induced lipotoxicity through limiting the accumulations of ceramides and diacylglycerols versus whether it is a maladaptive response that contributes to cardiac dysfunction.

PPARalpha: energy combustion, hypolipidemia, inflammation and cancer

The peroxisome proliferator-activated receptor alpha (PPARalpha, or NR1C1) is a nuclear hormone receptor activated by a structurally diverse array of synthetic chemicals known as peroxisome proliferators. Endogenous activation of PPARalpha in liver has also been observed in certain gene knockout mouse models of lipid metabolism, implying the existence of enzymes that either generate (synthesize) or degrade endogenous PPARalpha agonists. For example, substrates involved in fatty acid oxidation can function as PPARalpha ligands. PPARalpha serves as a xenobiotic and lipid sensor to regulate energy combustion, hepatic steatosis, lipoprotein synthesis, inflammation and liver cancer. Mainly, PPARalpha modulates the activities of all three fatty acid oxidation systems, namely mitochondrial and peroxisomal beta-oxidation and microsomal omega-oxidation, and thus plays a key role in energy expenditure. Sustained activation of PPARalpha by either exogenous or endogenous agonists leads to the development of hepatocellular carcinoma resulting from sustained oxidative and possibly endoplasmic reticulum stress and liver cell proliferation. PPARalpha requires transcription coactivator PPAR-binding protein (PBP)/mediator subunit 1(MED1) for its transcriptional activity.

Be different--the diversity of peroxisomes in the animal kingdom

Peroxisomes represent so-called "multipurpose organelles" as they contribute to various anabolic as well as catabolic pathways. Thus, with respect to the physiological specialization of an individual organ or animal species, peroxisomes exhibit a functional diversity, which is documented by significant variations in their proteome. These differences are usually regarded as an adaptational response to the nutritional and environmental life conditions of a specific organism. Thus, human peroxisomes can be regarded as an in part physiologically unique organellar entity fulfilling metabolic functions that differ from our animal model systems. In line with this, a profound understanding on how peroxisomes acquired functional heterogeneity in terms of an evolutionary and mechanistic background is required. This review summarizes our current knowledge on the heterogeneity of peroxisomal physiology, providing insights into the genetic and cell biological mechanisms, which lead to the differential localization or expression of peroxisomal proteins and further gives an overview on peroxisomal biochemical pathways, which are specialized in different animal species and organs. Moreover, it addresses the impact of proteome studies on our understanding of differential peroxisome function describing the utility of mass spectrometry and computer-assisted algorithms to identify peroxisomal target sequences for the detection of new organ- or species-specific peroxisomal proteins.

Myocardial fatty acid metabolism in health and disease

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

PPARs: diverse regulators in energy metabolism and metabolic diseases

The nuclear receptor PPARs are fundamentally important for energy homeostasis. Through their distinct yet overlapping functions and tissue distribution, the PPARs regulate many aspects of energy metabolism at the transcriptional level. Functional impairment or dysregulation of these receptors leads to a variety of metabolic diseases, while their ligands offer many metabolic benefits. Studies of these receptors have advanced our knowledge of the transcriptional basis of energy metabolism and helped us understand the pathogenic mechanisms of metabolic syndrome.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Cardiac peroxisome proliferator-activated receptor-alpha activation causes increased fatty acid oxidation, reducing efficiency and post-ischaemic functional loss

AIMS

Myocardial fatty acid (FA) oxidation is regulated acutely by the FA supply and chronically at the transcriptional level owing to FA activation of peroxisome proliferator-activated receptor-alpha (PPARalpha). However, in vivo administration of PPARalpha ligands has not been shown to increase cardiac FA oxidation. In this study we have examined the cardiac response to in vivo administration of tetradecylthioacetic acid (TTA, 0.5% w/w added to the diet for 8 days), a PPAR agonist with primarily PPARalpha activity.

METHODS AND RESULTS

Despite the fact that TTA treatment decreased plasma concentrations of lipids [FA and triacylglycerols (TG)], hearts from TTA-treated mice showed increased mRNA expression of PPARalpha target genes. Cardiac substrate utilization, ventricular function, cardiac efficiency, and susceptibility to ischaemia-reperfusion were examined in isolated perfused hearts. In accordance with the mRNA changes, myocardial FA oxidation was increased 2.5-fold with a concomitant reduction in glucose oxidation. This increase in FA oxidation was abolished in PPARalpha-null mice. Thus, it appears that the metabolic effects of TTA on the heart must be owing to a direct stimulatory effect on cardiac PPARalpha. Hearts from TTA-treated mice also showed a marked reduction in cardiac efficiency (because of a two-fold increase in unloaded myocardial oxygen consumption) and decreased recovery of ventricular contractile function following low-flow ischaemia.

CONCLUSION

This study for the first time observed that in vivo administration of a synthetic PPARalpha ligand elevated FA oxidation, an effect that was also associated with decreased cardiac efficiency and reduced post-ischaemic functional recovery.

Administration of ciprofibrate to lactating mothers induces PPARalpha-signaling pathway in the liver and kidney of suckling rats

It is well known that the hypolipidemic drug ciprofibrate induces peroxisome proliferation in rodent liver, which in turn leads to the oxidative stress, and modifies some parameters related to cell proliferation and apoptosis. The administration of ciprofibrate to rats during the lactating period determined in their pups significant modifications in hepatic peroxisome enzyme activities, induction of the PPARalpha-target gene, Cyp4a10, and perturbation in cell proliferation and apoptosis, which affected the size of the liver. Moreover, this modification was associated to about two-fold induction of mRNA-PPARalpha. On the contrary, in the kidney, although a similar two-fold up-regulation of PPARalpha was detected, the induction of both peroxisomal enzyme activities and Cyp4a10 were weak, and no alterations were detected, neither in cell cycle nor in the size of the tissue. Our results indicate that the response to ciprofibrate is stronger in the liver than in the kidney of newborn rats.

Peroxisome proliferator-activated receptors and inflammation: take it to heart

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors acting as key regulators of lipid metabolism as well as modulators of inflammation. The role of PPARalpha and PPARgamma in cardiac ischaemia-reperfusion injury, infarct healing and hypertrophy is the subject of intense research. Due to the later development of PPARdelta-specific ligands, the role of this PPAR isoform in cardiac disease remains to be established. Although many studies point to salutatory effects of PPAR ligands in cardiac disease, the exact molecular mechanism is still largely unsolved. Both the metabolic (via transactivation) and the more recently discovered anti-inflammatory (via transrepression) effects of PPARs are likely to play a role. In this review the reported, and sometimes contradictory, effects of PPAR ligands on ischaemia-reperfusion, infarct healing and cardiac hypertrophy are critically evaluated. In particular the role of inflammation in these disease processes, the ability of PPARs to interfere with pro-inflammatory processes, and the mechanisms of transrepression are discussed. Currently, the significance of PPARs as therapeutic targets in cardiovascular disease is receiving widespread attention. Accordingly, detailed understanding of the mechanisms controlling the activity of these nuclear hormone receptors is essential.

Fenofibrate modulates cardiac and hepatic metabolism and increases ischemic tolerance in diet-induced obese mice

Peroxisome proliferator-activated receptors (PPARs) play an important role in the transcriptional regulation of lipid utilization and storage in several organs, including liver and heart. Our working hypothesis is that treatment of obesity/hyperlipedemia with the PPARalpha ligand fenofibrate leads to drainage of plasma lipids by the liver, resulting in reduced myocardial lipid supply, reduced myocardial fatty acid oxidation and improved myocardial tolerance to ischemic stress. Thus, we investigated changes in substrate utilization in heart and liver, as well as post-ischemic functional recovery in hearts from diet-induced obese (DIO) mice following long-term (11-12 weeks) treatment with fenofibrate. The present study shows that DIO mice express increased plasma lipids and glucose, as well as increased myocardial fatty acid oxidation and a concomitant decrease in glucose oxidation. The lipid-lowering effect of fenofibrate was associated with increased hepatic mitochondrial and peroxisomal fatty acid oxidation, as indicated by a more than 30% increase in hepatic palmiotyl-CoA oxidation and more than a 10-fold increase in acyl-CoA oxidase (ACO) activity. In line with an adaptation to the reduced myocardial lipid supply, isolated hearts from fenofibrate-treated DIO mice showed increased glucose oxidation and decreased fatty acid oxidation, as well as reduced ACO activity. Fenofibrate treatment also prevented the diet-induced decrease in cardiac function and improved post-ischemic functional recovery. We also found that, while fenofibrate treatment markedly increased the expression of PPARalpha target genes in the liver, there were no such changes in the heart. These data demonstrate that fenofibrate results in a direct activation of PPARalpha in the liver with increased hepatic drainage of plasma lipids, while the cardiac effect of the compound most likely is secondary to its lipid-lowering effect.

Clofibrate-induced changes in the liver, heart, brain and white adipose lipid metabolome of Swiss-Webster mice

Peroxisome proliferator activated receptor alpha (PPARα) agonists are anti-hyperlipidemic drugs that influence fatty acid combustion, phospholipid biosynthesis and lipoprotein metabolism. To evaluate impacts on other aspects of lipid metabolism, we applied targeted metabolomics to liver, heart, brain and white adipose tissue samples from male Swiss-Webster mice exposed to a 5 day, 500 mg/kg/day regimen of i.p. clofibrate. Tissue concentrations of free fatty acids and the fatty acid content of sphingomyelin, cardiolipin, cholesterol esters, triglycerides and phospholipids were quantified. Responses were tissue-specific, with changes observed in the liver > heart ≫ brain > adipose. These results indicate that liver saturated fatty acid-rich triglycerides feeds clofibrate-induced monounsaturated fatty acid (MUFA) synthesis, which were incorporated into hepatic phospholipids and sphingomyelin. In addition, selective enrichment of docosahexeneoic acid in the phosphatidylserine of liver (1.7-fold), heart (1.6-fold) and brain (1.5-fold) suggests a clofibrate-dependent systemic activation of phosphatidylserine synthetase 2. Furthermore, the observed ~20% decline in cardiac sphingomyelin is consistent with activation of a sphingomeylinase with a substrate preference for polyunsaturate-containing sphingomyelin. Finally, perturbations in the liver, brain, and adipose cholesterol esters were observed, with clofibrate exposure elevating brain cholesterol arachidonyl-esters ~20-fold. Thus, while supporting previous findings, this study has identified novel impacts of PPARα agonist exposure on lipid metabolism that should be further explored.

Effects of PPARalpha on cardiac glucose metabolism: a transcriptional equivalent of the glucose-fatty acid cycle?

Cardiovascular disease is exceptionally prevalent in patients with diabetes mellitus and is the most common cause of death. With the emerging pandemic of obesity and resulting metabolic abnormalities, the occurrence of cardiovascular disease is almost nearly certain to increase at a remarkable rate in the near future. Currently, several ligands for the peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors are prescribed as lipid-lowering and insulin-sensitizing drugs. The PPARs are ligand-activated transcription factors that influence the expression of the entire program of fatty acid utilization enzymes. It is believed that these compounds remedy glucose homeostasis and cardiovascular disease by lowering circulating lipid levels, improving the profile of secreted adipokines, as well as via their anti-inflammatory properties. Conversely, overexpression of the PPARalpha isoform in the muscle or heart of mice drives diminished glucose transporter gene expression and glucose uptake into those insulin target tissues. Although the effects of overexpressing PPARalpha in a specific tissue obviously differ from activating PPARalpha in a systemic manner, studies such as this may influence the development of the next generation of PPAR ligands.

Tesaglitazar, a dual PPARα/γ agonist, ameliorates glucose and lipid intolerance in obese Zucker rats

Insulin resistance, impaired glucose tolerance, high circulating levels of free fatty acids (FFA), and postprandial hyperlipidemia are associated with the metabolic syndrome, which has been linked to increased risk of cardiovascular disease. We studied the metabolic responses to an oral glucose/triglyceride (TG) (1.7/2.0 g/kg lean body mass) load in three groups of conscious 7-h fasted Zucker rats: lean healthy controls, obese insulin-resistant/dyslipidemic controls, and obese rats treated with the dual peroxisome proliferator-activated receptor α/γ agonist, tesaglitazar, 3 μmol·kg−1·day−1for 4 wk. Untreated obese Zucker rats displayed marked insulin resistance, as well as glucose and lipid intolerance in response to the glucose/TG load. The 2-h postload area under the curve values were greater for glucose (+19%), insulin (+849%), FFA (+53%), and TG (+413%) compared with untreated lean controls. Treatment with tesaglitazar lowered fasting plasma glucose, improved glucose tolerance, substantially reduced fasting and postload insulin levels, and markedly lowered fasting TG and improved lipid tolerance. Fasting FFA were not affected, but postprandial FFA suppression was restored to levels seen in lean controls. Mechanisms of tesaglitazar-induced lowering of plasma TG were studied separately using the Triton WR1339 method. In anesthetized, 5-h fasted, obese Zucker rats, tesaglitazar reduced hepatic TG secretion by 47%, increased plasma TG clearance by 490%, and reduced very low-density lipoprotein (VLDL) apolipoprotein CIII content by 86%, compared with obese controls. In conclusion, the glucose/lipid tolerance test in obese Zucker rats appears to be a useful model of the metabolic syndrome that can be used to evaluate therapeutic effects on impaired postprandial glucose and lipid metabolism. The present work demonstrates that tesaglitazar ameliorates these abnormalities and enhances insulin sensitivity in this animal model.