Impaired Fatty Acid Β-oxidation Research Articles

Sirtuin-5 Is Recruited to Hepatic Peroxisomes in Mice Fed Dodecanedioic Acid but Has Little Impact on the Peroxisomal Succinylome.

Lysine succinylation, and its reversal by sirtuin-5 (SIRT5), is known to modulate mitochondrial fatty acid β-oxidation (FAO). We recently showed that feeding mice dodecanedioic acid, a 12-carbon dicarboxylic acid (DC12) that can be chain-shortened four rounds to succinyl-CoA, drives high-level protein hypersuccinylation in the peroxisome, particularly on peroxisomal FAO enzymes. However, the ability of SIRT5 to reverse DC12-induced peroxisomal succinylation, or to regulate peroxisomal FAO in this context, remained unexplored. Here, we showed that feeding DC12 strongly recruits SIRT5 into hepatic peroxisomes. Knocking out SIRT5 impaired peroxisomal FAO as evidenced by reduced 14C-DC12 flux in liver homogenates and elevated levels of partially shortened DC12 catabolites in urine. Further, mass spectrometry revealed a trend toward less peroxisomal protein succinylation in SIRT5 knockout liver. This is consistent with a reduced flux of DC12 through the peroxisomal FAO pathway, thereby reducing the production of the succinyl-CoA that chemically reacts with lysine residues to produce protein succinylation. Mass spectrometry comparisons of site-level succinylation in wildtype and SIRT5 knockout liver did not reveal any clear pattern of SIRT5 target sites in the peroxisome after DC12 feeding. However, SIRT5 co-immunoprecipitated with 15 peroxisomal proteins, including the key peroxisomal FAO enzymes acyl-CoA oxidase-1 and enoyl-CoA/3-hydroxyacyl-CoA dehydrogenase (EHHADH). In vitro, recombinant SIRT5 partially desuccinylated chemically modified recombinants ACOX1a, ACOX1b, and EHHADH. Desuccinylation by SIRT5 had no effect on enzyme activity for ACOX1a and EHHADH. For ACOX1b, SIRT5-mediated desuccinylation decreased activity by ~15%. Possible interpretations of these data are discussed.

Hepatocyte-Specific PEX16 Abrogation in Mice Leads to Hepatocyte Proliferation, Alteration of Hepatic Lipid Metabolism, and Resistance to High-Fat Diet (HFD)-Induced Hepatic Steatosis and Obesity.

Obesity results in hepatic fat accumulation, i.e., steatosis. In addition to fat overload, impaired fatty acid β-oxidation also promotes steatosis. Fatty acid β-oxidation takes place in the mitochondria and peroxisomes. Usually, very long-chain and branched-chain fatty acids are the first to be oxidized in peroxisomes, and the resultant short chain fatty acids are further oxidized in the mitochondria. Peroxisome biogenesis is regulated by peroxin 16 (PEX16). In liver-specific PEX16 knockout (Pex16Alb-Cre) mice, hepatocyte peroxisomes were absent, but hepatocytes proliferated, and liver mass was enlarged. These results suggest that normal liver peroxisomes restrain hepatocyte proliferation and liver sizes. After high-fat diet (HFD) feeding, body weights were increased in PEX16 floxed (Pex16fl/fl) mice and adipose-specific PEX16 knockout (Pex16AdipoQ-Cre) mice, but not in the Pex16Alb-Cre mice, suggesting that the development of obesity is regulated by liver PEX16 but not by adipose PEX16. HFD increased liver mass in the Pex16fl/fl mice but somehow reduced the already enlarged liver mass in the Pex16Alb-Cre mice. The basal levels of serum triglyceride, free fatty acids, and cholesterol were decreased, whereas serum bile acids were increased in the Pex16Alb-Cre mice, and HFD-induced steatosis was not observed in the Pex16Alb-Cre mice. These results suggest that normal liver peroxisomes contribute to the development of liver steatosis and obesity.

Inhibition of Fatty Acid β-Oxidation by Fatty Acid Binding Protein 4 Induces Ferroptosis in HK2 Cells Under High Glucose Conditions.

Ferroptosis, which is caused by an iron-dependent accumulation of lipid hydroperoxides, is a type of cell death linked to diabetic kidney disease (DKD). Previous research has shown that fatty acid binding protein 4 (FABP4) is involved in the regulation of ferroptosis in diabetic retinopathy. The present study was constructed to explore the role of FABP4 in the regulation of ferroptosis in DKD. We first detected the expression of FABP4 and proteins related to ferroptosis in renal biopsies of patients with DKD. Then, we used a FABP4 inhibitor and small interfering RNA to investigate the role of FABP4 in ferroptosis induced by high glucose in human renal proximal tubular epithelial (HG-HK2) cells. In kidney biopsies of DKD patients, the expression of FABP4 was elevated, whereas carnitine palmitoyltransferase-1A (CP-T1A), glutathione peroxidase 4, ferritin heavy chain, and ferritin light chain showed reduced expression. In HG-HK2 cells, the induction of ferroptosis was accompanied by an increase in FABP4. Inhibition of FABP4 in HG-HK2 cells changed the redox state, sup-pressing the production of reactive oxygen species, ferrous iron (Fe2+), and malondialdehyde, increasing superoxide dismutase, and reversing ferroptosis-associated mitochondrial damage. The inhibition of FABP4 also increased the expression of CPT1A, reversed lipid deposition, and restored impaired fatty acid β-oxidation. In addition, the inhibition of CPT1A could induce ferroptosis in HK2 cells. Our results suggest that FABP4 mediates ferroptosis in HG-HK2 cells by inhibiting fatty acid β-oxidation.

MO067: Role of ANT2 in the Development of Obesity-Induced Chronic Kidney Disease

Abstract BACKGROUND AND AIMS Obesity, a widespread condition with an ever-increasing prevalence, imposes a great medical concern since it serves as a risk factor for a wide range of conditions, including the development of chronic kidney disease (CKD). Lipid accumulation and impaired fatty acid β-oxidation in the renal proximal tubular cells (RPTCs) as well as an overall mitochondrial dysfunction have been shown to induce kidney injury, inflammation and fibrosis, leading to the development of CKD. However, the molecular mechanisms linking mitochondrial dysfunction in RPTCs to obesity-induced CKD are not fully understood and require further examination. Adenine nucleotide translocases (ANTs), which transport ADP and ATP through the mitochondrial inner membrane, play an essential role in energy metabolism of eukaryotic cells. ANT2 (Slc25a5) mediates fatty acid-induced uncoupled respiration, and its complete deletion is embryonic lethal. Here we explore its specific role in RPTCs in the development of obesity-induced CKD. METHOD ANT2 protein levels were measured using western blot and immunohistochemistry analyses. RPTC-ANT2-/- animals were generated using the Cre/loxP system. The null mice and their wild-type littermate controls were fed with either a high-fat diet (HFD) or a standard diet (STD) for 24 weeks. Kidney function and lipid content were assessed by biochemical analysis. Histological techniques were used to visualize the morphological changes in the kidney as well as fibrogenesis. Kidney injury and inflammatory markers were measured via qPCR and ELISAs. Mitochondrial function was tested in primary mouse RPTCs extracted from the null and WT animals by measuring oxygen consumption rate via Seahorse as well as reactive oxygen species (ROS) production by DCFDA staining. RESULTS As evident from the double-stained immunofluorescence staining of mouse kidney, high levels of ANT2 were found in RPTCs. Interestingly, its protein expression was downregulated in HFD-fed WT mice. Nullification of ANT2 specifically in RPTCs prevented the obesity-induced kidney dysfunction as reflected by lowered albumin-to-creatinine ratio. This was associated with the improved renal morphology in HFD-fed RPTC-ANT2-/- mice, evident by the reduction in obesity-related increased glomerular and Bowman's space areas and mesangial expansion. Compared with their littermate controls, obese RPTC-ANT2-/- mice showed reduced renal KIM-1 and NGAL protein levels and downregulation in the expression levels of Mcp1 and Lcn2, markers of renal injury and inflammation, respectively. The null mice were also protected from obesity-induced fibrosis, measured by trichrome staining, as well as accumulation of triglycerides and cholesterol in the kidney. In addition, preserved mitochondrial function was found in primary mouse RPTCs lacking ANT2, measured by increased spare respiratory capacity and decreased ROS production. Lastly, downregulated Hif1α gene and protein expression levels were found in RPTCs and kidney tissue lacking ANT2. CONCLUSION Our findings introduce ANT2 in the RPTCs as a key player in the development of obesity-induced CKD. Deletion of RPTC-ANT2 protects the kidney from the deleterious effects of lipotoxicity. Therefore, targeted manipulation of renal mitochondrial metabolism, particularly via inhibiting ANT2, may represent a novel approach for the treatment of obesity-induced CKD.

Ketogenesis acts as an endogenous protective programme to restrain inflammatory macrophage activation during acute pancreatitis.

SummaryBackgroundInnate immunity and metabolites link to the pathogenesis and severity of acute pancreatitis (AP). However, liver metabolism and its role in immune response and AP progression remain elusive. We investigated the function of liver metabolism in the pathogenesis of AP.MethodsCirculating ketone body β-hydroxybutyrate (βOHB) levels were determined in AP clinical cohorts and caerulein-induced AP (CER-AP) mouse models receiving seven (Cer*7) or twelve (Cer*12) injection regimens at hourly intervals. Liver transcriptomics and metabolomics were compared between CER-AP (Cer*7) and CER-AP (Cer*12). Inhibition of fatty acid β-oxidation (FAO)-ketogenesis, or supplementation of βOHB was performed in mouse models of AP. The effect and mechanism of βOHB were examined in vitro.FindingsElevated circulating βOHB was observed in patients with non-severe AP (SAP) but not SAP. These findings were replicated in CER-AP (Cer*7) and CER-AP (Cer*12), which manifested as limited and hyperactive immune responses, respectively. FAO-ketogenesis was activated in CER-AP (Cer*7), while impaired long-chain FAO and mitochondrial function were observed in the liver of CER-AP (Cer*12). Blockage of FAO-ketogenesis (Cpt1a antagonism or Hmgcs2 knockdown) worsened, while supplementation of βOHB or its precursor 1,3-butanediol alleviated the severity of CER-AP. Mechanistically, βOHB had a discernible effect on pancreatic acinar cell damage, instead, it greatly attenuated the activation of pancreatic and systemic proinflammatory macrophages via class I histone deacetylases.InterpretationOur findings reveal that hepatic ketogenesis is activated as an endogenous protective programme to restrain AP progression, indicating its potential therapeutic value.FundingThis work was supported by the National Natural Science Foundation of China, Shanghai Youth Talent Support Programme, and Shanghai Municipal Education Commission-Gaofeng Clinical Medicine Grant.

Mildronate triggers growth suppression and lipid accumulation in largemouth bass (Micropterus salmoides) through disturbing lipid metabolism.

Many metabolic diseases in fish are often associated with lowered mitochondrial fatty acid β-oxidation (FAO). However, the physiological role of mitochondrial FAO in lipid metabolism has not been verified in many carnivorous fish species, for example in largemouth bass (Micropterus salmonids). In the present study, a specific mitochondrial FAO inhibitor, mildronate (MD), was used to investigate the effects of impaired mitochondrial FAO on growth performance, health status, and lipid metabolism of largemouth bass. The results showed that the dietary MD treatment significantly suppressed growth performance and caused heavy lipid accumulation, especially neutral lipid, in the liver. The MD-treated fish exhibited lower monounsaturated fatty acid and higher long-chain polyunsaturated fatty acids in the muscle. The MD treatment downregulated the gene expressions in lipolysis and lipogenesis, as well as the expressions of the genes and some key proteins in FAO without enhancing peroxisomal FAO. Additionally, the MD-treated fish had lower serum aspartate aminotransferase activity and lower pro-inflammation- and apoptosis-related genes in the liver. Taken together, MD treatment markedly induced lipid accumulation via depressing lipid catabolism. Our findings reveal the pivotal roles of mitochondrial FAO in maintaining health and lipid homeostasis in largemouth bass and could be hopeful in understanding metabolic diseases in farmed carnivorous fish.

Using comprehensive lipid profiling to study effects of PFHxS during different stages of early zebrafish development

PFHxS (Perfluorohexane sulfonic acid) is one of the short-chain perfluoroalkyl substances (PFASs) which are widely used in many industrial and consumer applications. However, limited information is available on the molecular mechanism of PFHxS toxicity (e.g. lipid metabolism). This study provides in-depth information on the lipid regulation of zebrafish embryos with and without PFHxS exposure. Lipid changes throughout zebrafish development (4 to 120 h post fertilization (hpf)) were closely associated with lipid species and lipid composition (fatty acyl chains). A comprehensive lipid analysis of four different PFHxS exposures (0, 0.3, 1, 3, and 10 μM) at different zebrafish developmental stages (24, 48, 72, and 120 hpf) was performed. Data on exposure concentration, lipids, and developmental stage showed that all PFHxS concentrations dysregulated the lipid metabolism and these were developmental-dependent. The pattern of significantly changed lipids revealed that PFHxS caused effects related to oxidative stress, inflammation, and impaired fatty acid β-oxidation. Oxidative stress and inflammation caused the remodeling of glycerophospholipid (phosphatidylcholine (PC) and phosphatidylethanolamine (PE)), with increased incorporation of omega-3 PUFA and a decreased incorporation of omega-6 PUFA.

Diminished retinal complex lipid synthesis and impaired fatty acid β-oxidation associated with human diabetic retinopathy.

BACKGROUNDThis study systematically investigated circulating and retinal tissue lipid determinants of human diabetic retinopathy (DR) to identify underlying lipid alterations associated with severity of DR.METHODSRetinal tissues were retrieved from postmortem human eyes, including 19 individuals without diabetes, 20 with diabetes but without DR, and 20 with diabetes and DR, for lipidomic study. In a parallel study, serum samples from 28 American Indians with type 2 diabetes from the Gila River Indian Community, including 12 without DR, 7 with mild nonproliferative DR (NPDR), and 9 with moderate NPDR, were selected. A mass-spectrometry–based lipidomic platform was used to measure serum and tissue lipids.RESULTSIn the postmortem retinas, we found a graded decrease of long-chain acylcarnitines and longer-chain fatty acid ester of hydroxyl fatty acids, diacylglycerols, triacylglycerols, phosphatidylcholines, and ceramide(NS) in central retina from individuals with no diabetes to those with diabetes with DR. The American Indians’ sera also exhibited a graded decrease in circulating long-chain acylcarnitines and a graded increase in the intermediate-length saturated and monounsaturated triacylglycerols from no DR to moderate NPDR.CONCLUSIONThese findings suggest diminished synthesis of complex lipids and impaired mitochondrial β-oxidation of fatty acids in retinal DR, with parallel changes in circulating lipids.TRIAL REGISTRATIONClinicalTrials.gov NCT00340678.FUNDINGThis work was supported by NIH grants R24 DK082841, K08DK106523, R03DK121941, P30DK089503, P30DK081943, P30DK020572, P30 EY007003; The Thomas Beatson Foundation; and JDRF Center for Excellence (5-COE-2019-861-S-B).

Abstract 5274: Multi-omics integration analysis robustly predicts high grade patient survival and identified altered fatty acid metabolism in high grade bladder cancer

Abstract Cancer metabolism varies depending on tumor grade. Currently, there is an absence of integration of multi-omics data to predict Bladder cancer (BLCA) survival. We aimed to identify a metabolic signature in high-grade BLCA by integration of unbiased metabolomics, lipidomics and transcriptomics to predict patient survival and to discover novel therapeutic targets. In the current study, using a robust mass spectrometry platform, we conducted global unbiased metabolic and lipid profiling analysis. We identified 518 differential metabolites and 19 lipids of various classes using the NIST MS metabolomics compendium and lipidblast MS/MS libraries, respectively, between low-grade and high-grade BLCA then mapped them to associated genes. Pathway analysis revealed a unique set of biochemical pathways highly deregulated in high-grade BLCA. Integromics analysis identified a molecular gene signature associated with patient poor survival. Importantly, low expression of fatty acid associated enzymes in high-grade tumors was associated with low fatty acid β- oxidation and acyl carnitines in high-grade BLCA and confirmed using tissue microarray. Our key finding is that impaired fatty acid β-oxidation (FAO) by downregulation of fatty acid associate enzymes suggests a crucial role in the progression of low grade to high grade BLCA. Using a metabolic-centered multi-omics based integrative analysis provided a system-level perspective of BLCA that would facilitate the development of novel therapeutics for high-grade BLCA. Note: This abstract was not presented at the meeting. Citation Format: Venkata Rao Vantaku, Jianrong Dong, Chandrashekar R Ambati, Dimuthu Perera, Sri Ramya Donepudi, Chandra Sekhar Amara, Vasanta Putluri, Ravi Shiva Shankar, Matthew J Robertson, Danthasinghe Waduge Badrajee Piyarathna, Mariana Villanueva, Friedrich-Carl von Rundstedt, Balasubramanyam Karanam, Leomar Y Ballester, Martha K. Terris, Seth P. Lerner, Apolo B Andrea, Hugo Villanueva, Andrew Sikora, Yair Lotan, Arun Sreekumar, Cristian Coarfa, Nagireddy Putluri. Multi-omics integration analysis robustly predicts high grade patient survival and identified altered fatty acid metabolism in high grade bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5274.

Protein acetylation in skeletal muscle mitochondria is involved in impaired fatty acid oxidation and exercise intolerance in heart failure.

BackgroundExercise intolerance is a common clinical feature and is linked to poor prognosis in patients with heart failure (HF). Skeletal muscle dysfunction, including impaired energy metabolism in the skeletal muscle, is suspected to play a central role in this intolerance, but the underlying mechanisms remain elusive. Lysine acetylation, a recently identified post‐translational modification, has emerged as a major contributor to the derangement of mitochondrial metabolism. We thus investigated whether mitochondrial protein acetylation is associated with impaired skeletal muscle metabolism and lowered exercise capacity in both basic and clinical settings of HF.MethodsWe first conducted a global metabolomic analysis to determine whether plasma acetyl‐lysine is a determinant factor for peak oxygen uptake (peak VO2) in HF patients. We then created a murine model of HF (n = 11) or sham‐operated (n = 11) mice with or without limited exercise capacity by ligating a coronary artery, and we tested the gastrocnemius tissues by using mass spectrometry‐based acetylomics. A causative relationship between acetylation and the activity of a metabolic enzyme was confirmed in in vitro studies.ResultsThe metabolomic analysis verified that acetyl‐lysine was the most relevant metabolite that was negatively correlated with peak VO2 (r = −0.81, P < 0.01). At 4 weeks post‐myocardial infarction HF, a treadmill test showed lowered work (distance × body weight) and peak VO2 in the HF mice compared with the sham‐operated mice (11 ± 1 vs. 23 ± 1 J, P < 0.01; 143 ± 5 vs. 159 ± 3 mL/kg/min, P = 0.01; respectively). As noted, the protein acetylation of gastrocnemius mitochondria was 48% greater in the HF mice than the sham‐operated mice (P = 0.047). Acetylproteomics identified the mitochondrial enzymes involved in fatty acid β‐oxidation (FAO), the tricarboxylic acid cycle, and the electron transport chain as targets of acetylation. In parallel, the FAO enzyme (β‐hydroxyacyl CoA dehydrogenase) activity and fatty acid‐driven mitochondrial respiration were reduced in the HF mice. This alteration was associated with a decreased expression of mitochondrial deacetylase, Sirtuin 3, because silencing of Sirtuin 3 in cultured skeletal muscle cells resulted in increased mitochondrial acetylation and reduced β‐hydroxyacyl CoA dehydrogenase activity.ConclusionsEnhanced mitochondrial protein acetylation is associated with impaired FAO in skeletal muscle and reduced exercise capacity in HF. Our results indicate that lysine acetylation is a crucial mechanism underlying deranged skeletal muscle metabolism, suggesting that its modulation is a potential approach for exercise intolerance in HF.

Deletion of Cyclophilin D Impairs β-Oxidation and Promotes Glucose Metabolism.

Cyclophilin D (CypD) is a mitochondrial matrix protein implicated in cell death, but a potential role in bioenergetics is not understood. Here, we show that loss or depletion of CypD in cell lines and mice induces defects in mitochondrial bioenergetics due to impaired fatty acid β-oxidation. In turn, CypD loss triggers a global compensatory shift towards glycolysis, with transcriptional upregulation of effectors of glucose metabolism, increased glucose consumption and higher ATP production. In vivo, the glycolytic shift secondary to CypD deletion is associated with expansion of insulin-producing β-cells, mild hyperinsulinemia, improved glucose tolerance, and resistance to high fat diet-induced liver damage and weight gain. Therefore, CypD is a novel regulator of mitochondrial bioenergetics, and unexpectedly controls glucose homeostasis, in vivo.

Nutritional models of foetal programming and nutrigenomic and epigenomic dysregulations of fatty acid metabolism in the liver and heart

Barker's concept of 'foetal programming' proposes that intrauterine growth restriction (IUGR) predicts complex metabolic diseases through relationships that may be further modified by the postnatal environment. Dietary restriction and deficit in methyl donors, folate, vitamin B12, and choline are used as experimental conditions of foetal programming as they lead to IUGR and decreased birth weight. Overfeeding and deficit in methyl donors increase central fat mass and lead to a dramatic increase of plasma free fatty acids (FFA) in offspring. Conversely, supplementing the mothers under protein restriction with folic acid reverses metabolic and epigenomic phenotypes of offspring. High-fat diet or methyl donor deficiency (MDD) during pregnancy and lactation produce liver steatosis and myocardium hypertrophy that result from increased import of FFA and impaired fatty acid β-oxidation, respectively. The underlying molecular mechanisms show dysregulations related with similar decreased expression and activity of sirtuin 1 (SIRT1) and hyperacetylation of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). High-fat diet and overfeeding impair AMPK-dependent phosphorylation of PGC-1α, while MDD decreases PGC-1α methylation through decreased expression of PRMT1 and cellular level of S-adenosyl methionine. The visceral manifestations of metabolic syndrome are under the influence of endoplasmic reticulum (ER) stress in overnourished animal models. These mechanisms should also deserve attention in the foetal programming effects of MDD since vitamin B12 influences ER stress through impaired SIRT1 deacetylation of HSF1. Taken together, similarities and synergies of high-fat diet and MDD suggest, therefore, considering their consecutive or contemporary influence in the mechanisms of complex metabolic diseases.

Acylcarnitine profiles in acetaminophen toxicity in the mouse: comparison to toxicity, metabolism and hepatocyte regeneration.

High doses of acetaminophen (APAP) result in hepatotoxicity that involves metabolic activation of the parent compound, covalent binding of the reactive intermediate N-acetyl-p-benzoquinone imine (NAPQI) to liver proteins, and depletion of hepatic glutathione. Impaired fatty acid β-oxidation has been implicated in previous studies of APAP-induced hepatotoxicity. To better understand relationships between toxicity and fatty acid β-oxidation in the liver in APAP toxicity, metabolomic assays for long chain acylcarnitines were examined in relationship to established markers of liver toxicity, oxidative metabolism, and liver regeneration in a time course study in mice. Male B6C3F1 mice were treated with APAP (200 mg/kg IP) or saline and sacrificed at 1, 2, 4, 8, 24 or 48 h after APAP. At 1 h, hepatic glutathione was depleted and APAP protein adducts were markedly increased. Alanine aminotransferase (ALT) levels were elevated at 4 and 8 h, while proliferating cell nuclear antigen (PCNA) expression, indicative of hepatocyte regeneration, was apparent at 24 h and 48 h. Elevations of palmitoyl, oleoyl and myristoyl carnitine were apparent by 2–4 h, concurrent with the onset of Oil Red O staining in liver sections. By 8 h, acylcarnitine levels were below baseline levels and remained low at 24 and 48 h. A partial least squares (PLS) model suggested a direct association of acylcarnitine accumulation in serum to APAP protein adduct and hepatic glutathione levels in mice. Overall, the kinetics of serum acylcarnitines in APAP toxicity in mice followed a biphasic pattern involving early elevation after the metabolism phases of toxicity and later depletion of acylcarnitines.

Argininosuccinate synthase conditions the response to acute and chronic ethanol-induced liver injury in mice

Argininosuccinate synthase (ASS) is the rate-limiting enzyme in both the urea and the L-citrulline/nitric oxide (NO·) cycles regulating protein catabolism, ammonia levels, and NO· generation. Because a proteomics analysis identified ASS and nitric oxide synthase-2 (NOS2) as coinduced in rat hepatocytes by chronic ethanol consumption, which also occurred in alcoholic liver disease (ALD) and in cirrhosis patients, we hypothesized that ASS could play a role in ethanol binge and chronic ethanol-induced liver damage. To investigate the contribution of ASS to the pathophysiology of ALD, wildtype (WT) and Ass(+/-) mice (Ass(-/-) are lethal due to hyperammonemia) were exposed to an ethanol binge or to chronic ethanol drinking. Compared with WT, Ass(+/-) mice given an ethanol binge exhibited decreased steatosis, lower NOS2 induction, and less 3-nitrotyrosine (3-NT) protein residues, indicating that reducing nitrosative stress by way of the L-citrulline/NO· pathway plays a significant role in preventing liver damage. However, chronic ethanol-treated Ass(+/-) mice displayed enhanced liver injury compared with WT mice. This was due to hyperammonemia, lower phosphorylated AMP-activated protein kinase alpha (pAMPKα) to total AMPKα ratio, decreased sirtuin-1 (Sirt-1) and peroxisomal proliferator-activated receptor coactivator-1α (Pgc1α) messenger RNAs (mRNAs), lower fatty acid β-oxidation due to down-regulation of carnitine palmitoyl transferase-II (CPT-II), decreased antioxidant defense, and elevated lipid peroxidation end-products in spite of comparable nitrosative stress but likely reduced NOS3. Partial Ass ablation protects only in acute ethanol-induced liver injury by decreasing nitrosative stress but not in a more chronic scenario where oxidative stress and impaired fatty acid β-oxidation are key events.

Effect of heat stress and bezafibrate on mitochondrial β-oxidation: Comparison between cultured cells from normal and mitochondrial fatty acid oxidation disorder children using in vitro probe acylcarnitine profiling assay

Hyperpyrexia occasionally triggers acute life-threatening encephalopathy-like illnesses, including influenza-associated encephalopathy (IAE) in childhood, and can be responsible for impaired fatty acid β-oxidation (FAO). In this regard, patients with impaired FAO may be more susceptible to febrile episodes. The effects of heat stress and a hypolipidemic drug, bezafibrate, on mitochondrial FAO were investigated using cultured cells from children with FAO disorders and from normal controls, using an in vitro probe acylcarnitine (AC) profiling assay. Fibroblasts were incubated in medium loaded with unlabelled palmitic acid for 96 h at 37 and 41 °C, with or without bezafibrate. AC profiles in culture medium were analyzed by electrospray ionization tandem mass spectrometry. Heat stress, introduced by 41 °C, significantly increased acetylcarnitine (C2) but slightly decreased the other acylcarnitines (ACs) in controls and medium-chain acyl-CoA dehydrogenase (MCAD)-deficient cells. On the other hand, in very long-chain acyl-CoA dehydrogenase (VLCAD)-deficient cells, accumulation of long-chain ACs were enhanced at 41 °C, compared with that at 37 °C. In contrast, bezafibrate decreased long-chain ACs with significant increase of C2 in both control and VLCAD-deficient cells at 37 °C. These data suggest that heat stress specifically inhibits long-chain FAO, whereas bezafibrate recovers the impaired FAO. Our approach is a simple and promising strategy to evaluate the effects of heat stress or therapeutic drugs on mitochondrial FAO.

Mutation in Caenorhabditis elegans Krüppel-like factor, KLF-3 results in fat accumulation and alters fatty acid composition

In vertebrates, adipose tissue stores energy in the form of fat. Fat storage is tightly controlled by and dynamically balanced with energy expenditure under physiological settings; the perturbation of fat in either excess (obese) or deficit (lipodystrophy) has devastating pathologic consequences in the fueling of homeostasis and organismal fitness. The process by which fat storage is coordinated through positive and negative feedback signals is still poorly understood. To address potential mechanisms underlying fat storage we study a Caenorhabditis elegans Krüppel-like transcription factor, Ce-klf-3 and demonstrate that klf-3 is a hitherto unrecognized key regulator of fat metabolism in C. elegans. The Ce-klf-3 is highly expressed during larval development and predominantly present in intestine: the site of fat digestion, absorption, storage, and utilization. We found a strong positive correlation between klf-3 expression and fat deposition in a worm's intestine. Significantly, a klf-3 ( ok1975) loss-of-function mutation, characterized by the deletion of a 1658-bp sequence spanning the 3′ end of exon 2 through to the 5′ end of exon 3 of klf-3, enhanced fat deposition in the intestine and caused severe defects in worm reproduction. Although klf-3 mutants seemed very similar to wild type worms in appearance and life span, 70% of mutants became semi-sterile, each producing 40–50 viable progenies, and the remaining 30% were rendered completely sterile toward adulthood. Notably, both mutant types displayed extensive deposition of fat in the intestine. Our study also demonstrates that klf-3 is critical for maintaining normal fatty acid composition by regulating genes involved in a fatty acid desaturation pathway. Strikingly, klf-3 mutant animals with impaired fatty acid β-oxidation pathway genes resulted in fat accumulation in the mutant worm. We present the first clear in vivo evidence supporting essential regulatory roles of KLF-3 in fat storage in C. elegans and shed light on the human equivalent in disease–gene association.

Causes and prevention of tamoxifen-induced accumulation of triacylglycerol in rat liver

Tamoxifen can induce hepatic steatosis in women. In this study, we wanted to elucidate the mechanism behind the tamoxifen-induced accumulation of triacylglycerol in liver in female rats, and we hoped to prevent this development by combination treatment with the modified fatty acid tetradecylthioacetic acid (TTA). The increased hepatic triacylglycerol level after tamoxifen treatment was accompanied by decreased acetyl-coenzyme A carboxylase (ACC) and FAS activities, increased glycerol-3-phosphate acyltransferase (GPAT) activity, and a tendency to increased diacylglycerol acyltransferase (DGAT) activity. The activities and mRNA levels of enzymes involved in beta-oxidation, ketogenesis, and uptake of lipids from liver were unaffected by tamoxifen, whereas the uptake of lipoproteins was unchanged and the uptake of fatty acids was decreased. Combination treatment with tamoxifen and TTA (Tam+TTA) normalized the hepatic triacylglycerol level and increased the activities of ACC, FAS, GPAT, and DGAT compared with tamoxifen-treated rats. The activities and mRNA levels of enzymes involved in beta-oxidation, ketogenesis, and uptake of lipids were increased after Tam+TTA treatment. In conclusion, tamoxifen increased the hepatic triacylglycerol level, probably as a result of increased triacylglycerol biosynthesis combined with unchanged beta-oxidation. The tamoxifen-induced accumulation of triacylglycerol was prevented by cotreatment with TTA, through mechanisms of increased mitochondrial and peroxisomal beta-oxidation.

Aromatase-deficient (ArKO) mice are retrieved from severe hepatic steatosis by peroxisome proliferator administration

Tamoxifen is a potent antagonist of estrogen, and hepatic steatosis is a frequent complication in adjuvant tamoxifen for breast cancer. Recently, aromatase-deficient (ArKO, Ar−/−) mice lacking intrinsic estrogen was developed and the molecular mechanism involved in progression of massive hepatic steatosis in estrogen-deficiency was elucidated; impairment in hepatic fatty acid β-oxidation of peroxisomes, microsomes and mitochondria. This impairment is latent, but is potentially serious, because hepatic energy supply depends greatly on fatty acid β-oxidation. Therefore in the present study, we tried to conquer impaired hepatic fatty acid β-oxidation by administrating bezafibrate, a potent peroxisome proliferator, to Ar−/− mice through activating fatty acid β-oxidation via the peroxisome proliferator activated receptor-α mediated signaling pathway. Northern blot analysis of Ar−/− mice liver revealed a significant restoration of mRNA expression of very long fatty acyl-CoA synthetase in peroxisome, peroxisomal fatty acyl-CoA oxidase, and medium-chain acyl-CoA dehydrogenase in mitochondria, essential enzymes in fatty acid β-oxidation by administration of bezafibrate. Severe hepatic steatosis observed in Ar−/− mice regressed dramatically. Consistent findings were obtained in the in vitro assays of fatty acid β-oxidation activity. These findings demonstrate that bezafibrate is capable of restoring impaired fatty acid β-oxidation in vivo via the peroxisome proliferator-activated receptor-α mediated signaling pathway and is potent enough to regress severe hepatic steatosis in mice deficient in intrinsic estrogen.