Specific Inhibition of Acyl-CoA Oxidase-1 by an Acetylenic Acid Improves Hepatic Lipid and Reactive Oxygen Species (ROS) Metabolism in Rats Fed a High Fat Diet

Nicotinate-curcumin improves NASH by inhibiting the AKR1B10/ACCα-mediated triglyceride synthesis

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a prevalent chronic liver condition. However, the potential therapeutic benefits and underlying mechanism of nicotinate-curcumin (NC) in the treatment of NASH remain uncertain.

METHODS

A rat model of NASH induced by a high-fat and high-fructose diet was treated with nicotinate-curcumin (NC, 20, 40 mg·kg- 1), curcumin (Cur, 40 mg·kg- 1) and metformin (Met, 50 mg·kg- 1) for a duration of 4 weeks. The interaction between NASH, Cur and Aldo-Keto reductase family 1 member B10 (AKR1B10) was filter and analyzed using network pharmacology. The interaction of Cur, NC and AKR1B10 was analyzed using molecular docking techniques, and the binding energy of Cur and NC with AKR1B10 was compared. HepG2 cells were induced by Ox-LDL (25 µg·ml- 1, 24 h) in high glucose medium. NC (20µM, 40µM), Cur (40µM) Met (150µM) and epalrestat (Epa, 75µM) were administered individually. The activities of ALT, AST, ALP and the levels of LDL, HDL, TG, TC and FFA in serum were quantified using a chemiluminescence assay. Based on the changes in the above indicators, score according to NAS standards. The activities of Acetyl-CoA and Malonyl-CoA were measured using an ELISA assay. And the expression and cellular localization of AKR1B10 and Acetyl-CoA carboxylase (ACCα) in HepG2 cells were detected by Western blotting and immunofluorescence.

RESULTS

The results of the animal experiments demonstrated that NASH rat model induced by a high-fat and high-fructose diet exhibited pronounced dysfunction in liver function and lipid metabolism. Additionally, there was a significant increase in serum levels of FFA and TG, as well as elevated expression of AKR1B10 and ACCα, and heightened activity of Acetyl-CoA and Malonyl-CoA in liver tissue. The administration of NC showed to enhance liver function in rats with NASH, leading to reductions in ALT, AST and ALP levels, and decrease in blood lipid and significant inhibition of FFA and TG synthesis in the liver. Network pharmacological analysis identified AKR1B10 and ACCα as potential targets for NASH treatment. Molecular docking studies revealed that both Cur and NC are capable of binding to AKR1B10, with NC exhibiting a stronger binding energy to AKR1B10. Western blot analysis demonstrated an upregulation in the expression of AKR1B10 and ACCα in the liver tissue of NASH rats, accompanied by elevated Acetyl-CoA and Malonyl-CoA activity, and increased levels of FFA and TG. The results of the HepG2 cell experiments induced by Ox-LDL suggest that NC significantly inhibited the expression and co-localization of AKR1B10 and ACCα, while also reduced levels of TC and LDL-C and increased level of HDL-C. These effects are accompanied by a decrease in the activities of ACCα and Malonyl-CoA, and levels of FFA and TG. Furthermore, the impact of NC appears to be more pronounced compared to Cur.

CONCLUSION

NC could effectively treat NASH and improve liver function and lipid metabolism disorder. The mechanism of NC is related to the inhibition of AKR1B10/ACCα pathway and FFA/TG synthesis of liver.

Hairless (Hr) Deficiency Mitigates High-Fat Diet-Induced Obesity and Insulin Resistance in Mice

Obesity is a significant global health concern linked to excessive dietary energy intake. This research focuses on the mammalian hairless protein (HR), known for its role in skin and hair function, and its impact on metabolism. Examining male wild-type (Hr+/+) and Hr null (Hr-/-) mice over a 14-week normal chow diet (NCD) or high-fat diet (HFD) intervention. This study reveals that HR deficiency exhibited a protective effect against HFD-induced obesity and insulin resistance. This protective effect is attributed to increased energy expenditure in Hr-/- mice. Moreover, the brown adipose tissue (BAT) of Hr-/- mice displays elevated levels of the thermogenic protein, uncoupling protein 1 (Ucp1), and its key transcriptional regulators (PPARγ and PGC1α), compared to Hr+/+ mice. In summary, the findings underscore the protective role of HR deficiency in countering HFD-induced adiposity by enhancing insulin sensitivity, raising energy expenditure, and augmenting thermogenic factors in BAT. Further exploration of HR metabolic regulation holds promise for potential therapeutic targets in addressing obesity-related metabolic disorders.

Essential phospholipids impact cytokine secretion and alter lipid-metabolizing enzymes in human hepatocyte cell lines

BACKGROUND

Essential phospholipids (EPL) are hepatoprotective.

METHODS

The effects on interleukin (IL)-6 and -8 secretion and on certain lipid-metabolizing enzymes of non-cytotoxic concentrations of EPL (0.1 and 0.25 mg/ml), polyenylphosphatidylcholine (PPC), and phosphatidylinositol (PtdIns) (both at 0.1 and 1 mg/ml), compared with untreated controls, were assessed in human hepatocyte cell lines (HepG2, HepaRG, and steatotic HepaRG).

RESULTS

Lipopolysaccharide (LPS)-induced IL-6 secretion was significantly decreased in HepaRG cells by most phospholipids, and significantly increased in steatotic HepaRG cells with at least one concentration of EPL and PtdIns. LPS-induced IL-8 secretion was significantly increased in HepaRG and steatotic HepaRG cells with all phospholipids. All phospholipids significantly decreased amounts of fatty acid synthase in steatotic HepaRG cells and the amounts of acyl-CoA oxidase in HepaRG cells. Amounts of lecithin cholesterol acyltransferase were significantly decreased in HepG2 and HepaRG cells by most phospholipids, and significantly increased with 0.1 mg/ml PPC (HepaRG cells) and 1 mg/ml PtdIns (steatotic HepaRG cells). Glucose-6-phosphate dehydrogenase activity was unaffected by any phospholipid in any cell line.

CONCLUSIONS

EPL, PPC, and PtdIns impacted the secretion of pro-inflammatory cytokines and affected amounts of several key lipid-metabolizing enzymes in human hepatocyte cell lines. Such changes may help liver function improvement, and provide further insights into the EPL's mechanism of action.

Liver ACOX1 regulates levels of circulating lipids that promote metabolic health through adipose remodeling

The liver gene expression of the peroxisomal β-oxidation enzyme acyl-coenzyme A oxidase 1 (ACOX1), which catabolizes very long chain fatty acids (VLCFA), increases in the context of obesity, but how this pathway impacts systemic energy metabolism remains unknown. Here, we show that hepatic ACOX1-mediated β-oxidation regulates inter-organ communication involved in metabolic homeostasis. Liver-specific knockout of Acox1 (Acox1-LKO) protects mice from diet-induced obesity, adipose tissue inflammation, and systemic insulin resistance. Serum from Acox1-LKO mice promotes browning in cultured white adipocytes. Global serum lipidomics show increased circulating levels of several species of ω-3 VLCFAs (C24-C28) with previously uncharacterized physiological role that promote browning, mitochondrial biogenesis and Glut4 translocation through activation of the lipid sensor GPR120 in adipocytes. This work identifies hepatic peroxisomal β-oxidation as an important regulator of metabolic homeostasis and suggests that manipulation of ACOX1 or its substrates may treat obesity-associated metabolic disorders.

ANGPTL3 Downregulation Increases Intracellular Lipids by Reducing Energy Utilization

BACKGROUND

ANGPTL3 (angiopoietin-like protein 3) is a circulating protein with a key role in maintaining lipoprotein homeostasis. A monoclonal antibody against ANGPTL3 is an approved and well-tolerated treatment to reduce lipoproteins in familial hypercholesterolemia homozygotes. However, the reduction of hepatic ANGPTL3 synthesis using an antisense oligonucleotide unexpectedly resulted in a dose-dependent increase in liver lipid content and circulating transaminases, resulting in the termination of the clinical trial. Meanwhile, the use of silencing RNAs remains an area of active investigation. Our study sought to investigate whether intracellular downregulation of ANGPTL3 may lead to a primary increase in neutral lipids within the hepatocyte.

METHODS

We downregulated ANGPTL3 by silencing RNA in primary human hepatocytes 3-dimensional spheroids, HepG2/LX-2 3-dimensional spheroids, and in HepG2, Hep3B2, and Huh7 cultured in 2 dimensions.

RESULTS

ANGPTL3 downregulation increased neutral lipids in all models investigated. Interestingly, ANGPTL3 induced lower intracellular deiodinase type 1 protein levels resulting in a reduction in beta-oxidation and causing an increase in triglycerides stored in lipid droplets.

CONCLUSIONS

In conclusion, intracellular ANGPTL3 downregulation by silencing RNA led to an increase in triglycerides content due to a reduction in energy substrate utilization resembling a primary intracellular hepatocyte hypothyroidism.

Dietary dicarboxylic acids provide a non-storable alternative fat source that protects mice against obesity

Dicarboxylic fatty acids are generated in the liver and kidney in a minor pathway called fatty acid ω-oxidation. The effects of consuming dicarboxylic fatty acids as an alternative source of dietary fat have not been explored. Here, we fed dodecanedioic acid, a 12-carbon dicarboxylic (DC12), to mice at 20% of daily caloric intake for nine weeks. DC12 increased metabolic rate, reduced body fat, reduced liver fat, and improved glucose tolerance. We observed DC12-specific breakdown products in liver, kidney, muscle, heart, and brain, indicating that oral DC12 escaped first-pass liver metabolism and was utilized by many tissues. In tissues expressing the "a" isoform of acyl-CoA oxidase-1 (ACOX1), a key peroxisomal fatty acid oxidation enzyme, DC12 was chain shortened to the TCA cycle intermediate succinyl-CoA. In tissues with low peroxisomal fatty acid oxidation capacity, DC12 was oxidized by mitochondria. In vitro, DC12 was catabolized even by adipose tissue and was not stored intracellularly. We conclude that DC12 and other dicarboxylic acids may be useful for combatting obesity and for treating metabolic disorders.

Proanthocyanidins and Phenolic Compounds from the Twigs of Salix chaenomeloides and Their Anti-Lipogenic Effects on 3T3-L1 Preadipocytes

The present study investigated potential bioactive natural products from the EtOH extract of Salix chaenomeloides twigs using column chromatography, leading to the isolation of six compounds (1-6), which were characterized as two proanthocyanidins, procyanidin B2 (1) and procyanidin B1 (2), and four phenolic compounds, 4-hydroxybenzoic acid β-D-glucosyl ester (3), di-O-methylcrenatin (4), p-coumaric acid glucoside (5), and syringin (6) by the comparison of their NMR spectra with the reported data and high-resolution (HR)-electrospray ionization mass spectroscopy (ESI-MS) analysis. We investigated the potential of six compounds (1-6) to inhibit adipogenesis in 3T3-L1 preadipocytes, which showed that the compounds (1-6) significantly reduced lipid accumulation in 3T3-L1 adipocytes without affecting cell proliferation. Notably, compound 1 demonstrated a remarkable 60% and 90% reduction in lipid levels with 50 and 100 µM treatments, respectively. Oil Red O staining results indicated that compound 1 significantly inhibits the formation of lipid droplets, comparable to the effect of T863, an inhibitor of triglyceride used as a positive control, in adipocytes. Compound 1 had no effect on the regulators PPARγ, C/EBPα, and SREBF1 of adipocyte differentiation in 3T3-L1 preadipocytes, but compound 1 activated the fatty acid oxidation regulator, PPARα, compared to the lipogenic-induced control. It also suppressed fatty acid synthesis by downregulating the expression of fatty acid synthase (FAS). Finally, compound 1 induced the mRNA and protein levels of CPT1A, an initial marker of mitochondrial fatty acid oxidation in 3T3-L1. This finding substantiates the anti-lipogenic and lipolytic effects of procyanidin B2 (1) in 3T3-L1 preadipocytes, emphasizing its pivotal role in modulating obesity-related markers.

ATM deficiency differentially affects expression of proteins related to fatty acid oxidation and oxidative stress in a sex-specific manner in response to Western-type diet prior to and following myocardial infarction

AIMS

Published work has shown that ataxia-telangiectasia mutated kinase (ATM) deficiency is associated with cardioprotective effects in Western-type diet (WD)-fed female mice. This study assessed the expression of proteins related to fatty acid oxidation (FAO) and oxidative stress in WD-fed male and female mouse hearts, and investigated if sex-specific cardioprotective effects in WD-fed female ATM-deficient mice are maintained following myocardial infarction (MI).

MAIN METHODS

Wild-type (WT) and ATM-deficient (hKO) mice (both sexes) were placed on WD for 14 weeks. Myocardial tissue from a subset of mice was used for western blot analyses, while another subset of WD-fed mice underwent MI. Heart function was analyzed by echocardiography prior to and 1 day post-MI.

KEY FINDINGS

CPT1B (mitochondrial FAO enzyme) expression was lower in male hKO-WD, while it was higher in female hKO-WD vs WT-WD. WD-mediated decrease in ACOX1 (peroxisomal FAO enzyme) expression was only observed in male WT-WD. PMP70 (transports fatty acyl-CoA across peroxisomal membrane) expression was lower in male hKO-WD vs WT-WD. Catalase (antioxidant enzyme) expression was higher, while Nox4 (pro-oxidant enzyme) expression was lower in female hKO-WD vs WT-WD. Heart function was better in female hKO-WD vs WT-WD. However, post-MI heart function was not significantly different among all MI groups. Post-MI, CPT1B and catalase expression was higher in male hKO-WD-MI vs WT-WD-MI, while Nox4 expression was higher in female hKO-WD-MI vs WT-WD-MI.

SIGNIFICANCE

Increased mitochondrial FAO and decreased oxidative stress contribute towards ATM deficiency-mediated cardioprotective effects in WD-fed female mice which are abolished post-MI with increased Nox4 expression.

Inhibition of ACOX1 enhances the therapeutic efficacy of obeticholic acid in treating non-alcoholic fatty liver disease and mitigates its lipotoxicity

Background and aims

High-dose Obeticholic acid exhibits promise for non-alcoholic fatty liver disease (NAFLD) treatment but can induce lipotoxicity. Our study sought to understand this mechanism and propose a solution.

Approach and Results

In a non-alcoholic fatty liver disease (NAFLD) model induced by a high-fat diet in FXR-/- mice, we pinpointed that FXR regulated the expression of ACOX1 through RNA-Seq analysis. In the livers of FXR-/- mice, both ACOX1 mRNA and protein expression notably decreased. In both HL-7702 and HEP-G2 cells, the silencing of FXR through shRNA plasmids decreased ACOX1 expression, while FXR activation with GW4064 increased it. These effects were reversible with the ACOX1-specific inhibitor, 10,12-Tricosadiynoic acid. In the NAFLD model of FXR-/- mice, The activation of ACOX1 is correlated with elevated serum LDL, triglycerides, and aggravated hepatic steatosis. However, the combination of 10,12-Tricosadiynoic acid with low-dose obeticholic acid effectively treated hepatic steatosis, reducing LDL levels in the NAFLD model of wild-type mice. This combination therapy demonstrated efficacy comparable to high-dose obeticholic acid alone. Notably, the combined drug regimen treats hepatic steatosis by inhibiting the IL-1β and α-SMA pathways in NAFLD.

Conclusion

Combining ACOX1-specific inhibitors with low-dose obeticholic acid effectively treats high-fat diet-induced hepatic steatosis and reduces serum LDL. This approach enhances the therapeutic effects of obeticholic acid and mitigates its lipotoxicity by inhibiting the IL-1β and α-SMA pathways.

ACOX1 deficiency-induced lipid metabolic disorder facilitates chronic interstitial fibrosis development in renal allografts

Chronic interstitial fibrosis presents a significant challenge to the long-term survival of transplanted kidneys. Our research has shown that reduced expression of acyl-coenzyme A oxidase 1 (ACOX1), which is the rate-limiting enzyme in the peroxisomal fatty acid β-oxidation pathway, contributes to the development of fibrosis in renal allografts. ACOX1 deficiency leads to lipid accumulation and excessive oxidation of polyunsaturated fatty acids (PUFAs), which mediate epithelial-mesenchymal transition (EMT) and extracellular matrix (ECM) reorganization respectively, thus causing fibrosis in renal allografts. Furthermore, activation of Toll-like receptor 4 (TLR4)-nuclear factor kappa-B (NF-κB) signaling induced ACOX1 downregulation in a DNA methyltransferase 1 (DNMT1)-dependent manner. Overconsumption of PUFA resulted in endoplasmic reticulum (ER) stress, which played a vital role in facilitating ECM reorganization. Supplementation with PUFAs contributed to delayed fibrosis in a rat model of renal transplantation. The study provides a novel therapeutic approach that can delay chronic interstitial fibrosis in renal allografts by targeting the disorder of lipid metabolism.

ACOX1-mediated peroxisomal fatty acid oxidation contributes to metabolic reprogramming and survival in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is still an incurable disease, with many patients developing resistance to conventional and targeted therapies. To better understand the physiology of CLL and facilitate the development of innovative treatment options, we examined specific metabolic features in the tumor CLL B-lymphocytes. We observed metabolic reprogramming, characterized by a high level of mitochondrial oxidative phosphorylation activity, a low glycolytic rate, and the presence of C2- to C6-carnitine end-products revealing an unexpected, essential role for peroxisomal fatty acid beta-oxidation (pFAO). Accordingly, downmodulation of ACOX1 (a rate-limiting pFAO enzyme overexpressed in CLL cells) was enough to shift the CLL cells' metabolism from lipids to a carbon- and amino-acid-based phenotype. Complete blockade of ACOX1 resulted in lipid droplet accumulation and caspase-dependent death in CLL cells, including those from individuals with poor cytogenetic and clinical prognostic factors. In a therapeutic translational approach, ACOX1 inhibition spared non-tumor blood cells from CLL patients but led to the death of circulating, BCR-stimulated CLL B-lymphocytes and CLL B-cells receiving pro-survival stromal signals. Furthermore, a combination of ACOX1 and BTK inhibitors had a synergistic killing effect. Overall, our results highlight a less-studied but essential metabolic pathway in CLL and pave the way towards the development of new, metabolism-based treatment options.

ACAT2 may be a novel predictive biomarker and therapeutic target in lung adenocarcinoma

BACKGROUND

Acyl-coenzyme A cholesterol acyltransferase (ACAT) is a membrane-binding enzyme localized in the endoplasmic reticulum. ACAT2 can promote the development of colon cancer, but its efficacy in lung adenocarcinoma (LUAD) remains uncertain.

METHOD

ACAT2 expression was performed by using the TIMER2.0 database. The GEPIA database was utilized to analyze the correlation between ACAT2 expression and pathological stage of the tumor. Clinical prognosis was assessed through the Kaplan-Meier analysis. The CancerSEA database was employed to scrutinize the correlations between the ACAT2 expression and the functional status of various tumors, which were subsequently visualized as a heatmap. Furthermore, molecular interaction network analysis was performed by the STRING tool.

RESULTS

High ACAT2 expression was associated with a poor DFS and OS in LUAD patients. Cox regression analysis indicated that the poor outcomes may be related to tumor stage, nodal stage, distant metastatic stage. ACAT2 was found to play a crucial role in various biological processes, including the cell cycle, DNA repair, DNA damage response, and proliferation. Enrichment pathway analysis revealed four ACAT2 related genes, ACOX1, EHHADH, OXCT1, and DLAT.

CONCLUSION

Our study showed that ACAT2 was upregulated in LUAD, and had a worse survival. ACAT2 could be a novel predictive biomarker and therapeutic target in LUAD.

Shenge Formula attenuates high-fat diet-induced obesity and fatty liver via inhibiting ACOX1

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease worldwide. Shenge Formula (SGF) is a traditional Chinese medicine that has been used in the clinical treatment of NAFLD, and its therapeutic potential in patients and NAFLD animal models has been demonstrated in numerous studies. However, its underlying mechanism for treating NAFLD remains unclear.

PURPOSE

The aim of this study was to investigate the mechanism of SGF in the treatment of NAFLD using the proteomics strategy.

METHODS

Ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) was used to determine the main components of SGF. A mouse model of nonalcoholic fatty liver disease was constructed by feeding mice with a high-fat diet for 16 weeks. SGF was administered for an additional 8 weeks, and metformin was used as a positive control. Liver sections were subjected to histopathological assessments. LC-MS/MS was used for the label-free quantitative proteomic analysis of liver tissues. Candidate proteins and pathways were validated both in vivo and in vitro through qRT-PCR, western blot, and immunohistochemistry. The functions of the validated pathways were further investigated using the inhibition strategy.

RESULTS

Thirty-nine ingredients were identified in SGF extracts, which were considered to be key compounds in the treatment of NAFLD. SGF administration attenuated obesity and fatty liver by reducing the body weight and liver weight in HFD-fed mice. It also relieved HFD-induced insulin resistance. More importantly, hepatic steatosis was significantly attenuated by SGF administration both in vivo and in vitro. Proteomic profiling of mouse liver tissues identified 184 differential expressed proteins (DEPs) associated with SGF treatment. Bioinformatic analysis of DEPs revealed that regulating the lipid metabolism and energy consumption process of hepatocytes was the main role of SGF in NAFLD treatment. This also indicated that ACOX1 might be the potential target of SGF, which was subsequently verified both in vitro and in vivo. The results demonstrated that SGF inhibited ACOX1 activity, thereby activating PPARα and upregulating CPT1A expression. Increased CPT1A expression promoted mitochondrial β-oxidation, leading to reduced lipid accumulation in hepatocytes.

CONCLUSIONS

Overall, our findings confirmed the protective effect of SGF against NAFLD and revealed the underlying molecular mechanism of regulating lipid metabolism.

Virgin Camellia Seed Oil Improves Glycolipid Metabolism in the Kidney of High Fat-Fed Rats through AMPK-SREBP Pathway

Camellia seed oil (CO) is used as edible oil in southern China because of its excellent fatty acid composition and abundant bioactive compounds. Chronic kidney disease (CKD) is one of the most common chronic degenerative diseases in China, and active compounds in vegetable oil, like virgin olive oil, have been demonstrated to be efficacious in the management of CKD. In this study, virgin CO was refined using a standard process. The refining had minimal impact on the fatty acid composition, but significantly reduced the presence of bioactive compounds like polyphenols in CO. Sprague-Dawley (SD) rats fed with high fat diet (Group G) were treated with either virgin (Group Z) or refined CO (Group R). The oral administration of CO alleviated lipid accumulation and decreased body and kidney weight gain. Furthermore, treatment with virgin CO increased the renal ATP content. The renal expression levels of AMPK and key enzymes involved in fatty acid oxidation (CPT-1 and ACOX1) and glycolysis (HK, PFK, PK and GAPDH) were up-regulated in Group Z, thereby enhancing the ATP production. Virgin CO treatment downregulated the expression level of SREBP2 and its downstream target genes, such as ACC, FAS, and HMGCR, which reduced lipid synthesis. These findings indicate that virgin CO improves glycolipid metabolism and restores energy homeostasis in the kidneys of rats fed with a high-fat diet by modulating the AMPK-SREBP-signaling pathway, suggesting the potential of active compounds in virgin CO for managing the renal failure associated with glycolipid dysmetabolism.

Modulatory effects of extract of Heinsia crinita against fructose/streptozotocin-induced oxidative stress in diabetic rat models

Oxidative stress plays a crucial role in the development of type 2 diabetes and the associated microvascular and cardiovascular complications. In the study, we have investigated the effects of Heinsia crinita (H. crinita) extracts on lipid peroxidation and oxidative stress responses using diabetic rats. Type 2 diabetes was induced with 10 % fructose/40 mg/kg body weight streptozotocin (STZ). H. crinita extract was administered at 200 and 400 mg/kg body weight twice daily for 21 days, in addition to metformin (MET: 500 mg/kg body weight) control. Molecular docking analysis was performed to determine the binding affinity of H. crinita extracts to the DNA binding domains of peroxisome proliferator-activated receptor (Ppar) and retinoid x receptor (Rxr) protein crystal structures, showing different binding affinities for putative active compounds from the plant. Fasting blood glucose (FBG), body and organ weight changes were determined showing that H. crinita extract induced an anti-hyperglycemic effect in the treated animals, with changes (either decrease or increase) in liver and kidney weights. A decrease in mRNA expression of peroxisome proliferator-activated receptors (ppar), sterol regulatory element-binding protein 1 (srebp-1c), liver x-receptor (lxr), retinoid x receptors (rxr), cytochrome p45041 (cyp4a1) and acyl-CoA oxidase (acox1) in diabetic animals were observed, compared to the control. A dose-specific decrease or increase in antioxidant enzymes (superoxide dismutase: SOD, catalase: CAT, reduced glutathione: GSH, glutathione peroxidase: GPx) transcripts and activity levels were also observed. We also observed exposure-specific decrease or increase of malondialdehyde (MDA) levels. Our data suggested that H. crinita extract possesses protective effects against diabetes-induced oxidative stress. These effects might be attributed to their binding and activation of nuclear receptors, indicating their cellular mode of action that is comparable to MET.

Under peroxisome proliferation acyl-CoA oxidase coordinates with catalase to enhance ethanol metabolism

In peroxisomes, acyl-CoA oxidase (ACOX) oxidizes fatty acids and produces H2O2, and the latter is decomposed by catalase. If ethanol is present, ethanol will be oxidized by catalase coupling with decomposition of H2O2. Peroxisome proliferator-activated receptor α (PPARα) agonist WY-14,643 escalated ethanol clearance, which was not observed in catalase knockout (Cat-/-) mice or partially blocked by an ACOX1 inhibitor. WY-14,643 induced peroxisome proliferation via peroxin 16 (PEX16). PEX16 liver-specific knockout (Pex16Alb-Cre) mice lack intact peroxisomes in liver, but catalase and ACOX1 were upregulated. Due to lacking intact peroxisomes, the upregulated catalase and ACOX1 in the Pex16Alb-Cre mice were mislocated in cytosol and microsomes, and the escalated ethanol clearance was not observed in the Pex16Alb-Cre mice, implicating that the intact functional peroxisomes are essential for ACOX1/catalase to metabolize ethanol. Alcohol-associated liver disease (ALD) is a spectrum of liver disorders ranging from alcoholic steatosis to steatohepatitis. WY-14,643 ameliorated alcoholic steatosis but tended to enhance alcoholic steatohepatitis. In mice lacking nuclear factor erythroid 2-related factor 2 (Nrf2-/-), WY-14,643 still induced PEX16, ACOX1 and catalase to escalate ethanol clearance and blunt alcoholic steatosis, which was not observed in the PPARα-absent Nrf2-/- mice (Pparα-/-/Nrf2-/-) mice, suggesting that WY-14,643 escalates ethanol clearance through PPARα but not through Nrf2.

Long-chain dicarboxylic acids play a critical role in inducing peroxisomal β-oxidation and hepatic triacylglycerol accumulation

Recent studies provide evidence that peroxisomal β-oxidation negatively regulates mitochondrial fatty acid oxidation, and induction of peroxisomal β-oxidation causes hepatic lipid accumulation. However, whether there exists a triggering mechanism inducing peroxisomal β-oxidation is not clear. Long-chain dicarboxylic acids (LCDAs) are the product of mono fatty acids subjected to ω-oxidation, and both fatty acid ω-oxidation and peroxisomal β-oxidation are induced under ketogenic conditions, indicating there might be a crosstalk between. Here, we revealed that administration of LCDAs strongly induces peroxisomal fatty acid β-oxidation and causes hepatic steatosis in mice through the metabolites acetyl-CoA and hydrogen peroxide. Under ketogenic conditions, upregulation of fatty acid ω-oxidation resulted in increased generation of LCDAs and induction of peroxisomal β-oxidation, which causes hepatic accumulation of lipid droplets in animals. Inhibition of fatty acid ω-oxidation reduced LCDA formation and significantly lowered peroxisomal β-oxidation and improved hepatic steatosis. Our results suggest that endogenous LCDAs act as triggering molecules inducing peroxisomal β-oxidation and hepatic triacylglycerol deposition. Targeting fatty acid ω-oxidation might be an effective pathway in treating fatty liver and related metabolic diseases through regulating peroxisomal β-oxidation.

Hepatic Acyl CoA Oxidase1 Inhibition Modifies Brain Lipids and Electrical Properties of Dentate Gyrus

Introduction

Peroxisomes are essential organelles in lipid metabolism. They contain enzymes for β-oxidation of very long-chain fatty acids (VLCFA) that cannot be broken down in mitochondria. Reduced expression in hepatic acyl-CoA oxidase 1 (ACOX1), a peroxisome β-oxidation enzyme, followed by modification of the brain fatty acid profile has been observed in aged rodents. These studies have suggested a potential role for peroxisome β-oxidation in brain aging. This study was designed to examine the effect of hepatic ACOX1 inhibition on brain fatty acid composition and neuronal cell activities of young rats (200-250 g).

Methods

A specific ACOX1 inhibitor, 10, 12- tricosadiynoic acid (TDYA), 100 μg/kg (in olive oil) was administered by daily gavage for 25 days in male Wistar rats. The brain fatty acid composition and electrophysiological properties of dentate gyrus granule cells were determined using gas chromatography and whole-cell patch-clamp, respectively.

Results

A significant increase in C20, C22, C18:1, C20:1, and a decrease of C18, C24, C20:3n6, and C22:6n3 were found in 10, 12- tricosadiynoic acid (TDYA) treated rats compared to the control group. The results showed that ACOX1 inhibition changes fatty acid composition similar to old rats. ACOX1 inhibition caused hyperpolarization of resting membrane potential, and also reduction of input resistance, action potential duration, and spike firing. Moreover, ACOX1 inhibition increased rheobase current and afterhyperpolarization amplitude in granule cells.

Conclusion

The results indicated that systemic inhibition of ACOX1 causes hypo-excitability of neuronal cells. These results provide new evidence on the involvement of peroxisome function and hepatic ACOX1 activity in brain fatty acid profile and the electrophysiological properties of dentate gyrus cells.

PPARα/ACOX1 as a novel target for hepatic lipid metabolism disorders induced by per- and polyfluoroalkyl substances: An integrated approach

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are persistent and ubiquitous environmental contaminants with well-documented hepatotoxicity. However, the mechanistic linkage between PFAS exposure and non-alcoholic fatty liver disease (NAFLD) remains largely elusive.

OBJECTIVES

This study aimed to explore PFAS-to-NAFLD link and the relevant molecular mechanisms.

METHODS

The cross-sectional analyses using National Health and Nutrition Examination Survey (NHANES) data were conducted to investigate the association between PFAS exposure and NAFLD. A combination of in silico toxicological analyses, bioinformatics approaches, animal experiments, and in vitro assays was used to explore the molecular initiating events (MIEs) and key events (KEs) in PFAS-induced hepatic lipid metabolism disorders.

RESULTS

The cross-sectional analyses with NHANES data revealed the significant association between PFAS exposure and hepatic steatosis/NAFLD. The in silico toxicological analyses showed that PPARα activation induced by perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), prototypical representatives of PFAS, is the critical MIE associated with NAFLD-predominant liver diseases. Transcriptome-based bioinformatic annotation and analyses identified that transcriptional upregulation of hepatic acyl-CoA oxidase 1 (ACOX1) in PPARα-regulated peroxisomal β-oxidation pathway was the KE involved with PFOA/PFOS-perturbed hepatic lipid metabolic pathways in humans, mice and rats. The in vivo and in vitro assays further verified that ACOX1-mediated oxidative stress contributed to mitochondrial compromise and lipid accumulation in PFOA/PFOS-exposed mouse hepatocytes, which could be mitigated by co-treatment with ACOX1 inhibitor and mitochondria ROS scavenger. Additionally, we observed that besides PFOA and PFOS, hepatic ACOX1 exhibited good-fit response to short-term exposures of long-chain (C7-C10) perfluoroalkyl carboxylic acids (PFHpA, PFNA, PFDA) and perfluoroalkyl sulfonic acids (PFHpS, PFDS) in human hepatocyte spheroids through benchmark dose (BMD) modeling.

CONCLUSION

Our study unveils a novel molecular target for PFAS-induced hepatic lipid metabolic disorders, shedding new light on prediction, assessment, and mitigation of PFAS hepatotoxicity.

A nutrigenomics approach to study the effects of ω-3 fatty acids in laying hens under physiological stress

Supplement of ω-3 fatty acids can decrease the harmful effects of stress. However, the potential molecular mechanisms that are modulated by dietary ω-3 fatty acids in laying hens under stress remain unknown. Hence, RNA-sequencing (RNA-Seq) technology was used to gain new insights into different gene expression profiles and potential pathways involved in response to stress in the liver of 35-week-old Lohmann LSL-Lite laying hens supplemented with ω-3. Three groups including control (non-stress), stress, and stress_ω-3 fatty acids (three layers per each group) were applied. A total of 1,321 genes were detected as differentially expressed genes of which 701, 1,049, and 86 DEGs belonged to stress vs. control, stress_ω-3 vs. control, and stress vs. stress_ω-3 pairwise comparisons, respectively. Gene ontology and KEGG pathway analysis indicated that the DEGs were enriched in particular regulation of steroid and cholesterol biosynthetic process, fatty acid degradation, AMPK signaling pathway, fatty acid biosynthesis, and immune response. Our data represented a promising approach regarding the importance of ω-3 as anxiolytic and anti-stress. In this context, UNC13B and ADRA1B genes were downregulated in the stress_ω-3 group compared to the stress group, which are associated with decreased activity of glutamatergic stimulatory neurons and probably play important role in facilitating the response to stress. This study extends the current understanding of the liver transcriptome response to physiological stress, and provides new insights into the molecular responses to stress in laying hens fed a diet supplemented with ω-3 fatty acids.

PGRMC1 Ablation Protects from Energy-Starved Heart Failure by Promoting Fatty Acid/Pyruvate Oxidation

Heart failure (HF) is an emerging epidemic with a high mortality rate. Apart from conventional treatment methods, such as surgery or use of vasodilation drugs, metabolic therapy has been suggested as a new therapeutic strategy. The heart relies on fatty acid oxidation and glucose (pyruvate) oxidation for ATP-mediated contractility; the former meets most of the energy requirement, but the latter is more efficient. Inhibition of fatty acid oxidation leads to the induction of pyruvate oxidation and provides cardioprotection to failing energy-starved hearts. One of the non-canonical types of sex hormone receptors, progesterone receptor membrane component 1 (Pgrmc1), is a non-genomic progesterone receptor associated with reproduction and fertility. Recent studies revealed that Pgrmc1 regulates glucose and fatty acid synthesis. Notably, Pgrmc1 has also been associated with diabetic cardiomyopathy, as it reduces lipid-mediated toxicity and delays cardiac injury. However, the mechanism by which Pgrmc1 influences the energy-starved failing heart remains unknown. In this study, we found that loss of Pgrmc1 inhibited glycolysis and increased fatty acid/pyruvate oxidation, which is directly associated with ATP production, in starved hearts. Loss of Pgrmc1 during starvation activated the phosphorylation of AMP-activated protein kinase, which induced cardiac ATP production. Pgrmc1 loss increased the cellular respiration of cardiomyocytes under low-glucose conditions. In isoproterenol-induced cardiac injury, Pgrmc1 knockout resulted in less fibrosis and low heart failure marker expression. In summary, our results revealed that Pgrmc1 ablation in energy-deficit conditions increases fatty acid/pyruvate oxidation to protect against cardiac damage via energy starvation. Moreover, Pgrmc1 may be a regulator of cardiac metabolism that switches the dominance of glucose-fatty acid usage according to nutritional status and nutrient availability in the heart.

Peroxisomes attenuate cytotoxicity of very long-chain fatty acids

One of the major functions of peroxisomes in mammals is oxidation of very long-chain fatty acids (VLCFAs). Genetic defects in peroxisomal β-oxidation result in the accumulation of VLCFAs and lead to a variety of health problems, such as demyelination of nervous tissues. However, the mechanisms by which VLCFAs cause tissue degeneration have not been fully elucidated. Recently, we found that the addition of small amounts of isopropanol can enhance the solubility of saturated VLCFAs in an aqueous medium. In this study, we characterized the biological effect of extracellular VLCFAs in peroxisome-deficient Chinese hamster ovary (CHO) cells, neural crest-derived pheochromocytoma cells (PC12), and immortalized adult Fischer rat Schwann cells (IFRS1) using this solubilizing technique. C20:0 FA was the most toxic of the C16-C26 FAs tested in all cells. The basis of the toxicity of C20:0 FA was apoptosis and was observed at 5 μM and 30 μM in peroxisome-deficient and wild-type CHO cells, respectively. The sensitivity of wild-type CHO cells to cytotoxic C20:0 FA was enhanced in the presence of a peroxisomal β-oxidation inhibitor. Further, a positive correlation was evident between cell toxicity and the extent of intracellular accumulation of toxic FA. These results suggest that peroxisomes are pivotal in the detoxification of apoptotic VLCFAs by preventing their accumulation.

Comparative Metabolomic Profiling of Horse Gram (Macrotyloma uniflorum (Lam.) Verdc.) Genotypes for Horse Gram Yellow Mosaic Virus Resistance

Horse gram (Macrotyloma uniflorum (Lam.) Verdc.) is an under-utilized legume grown in India. It is a good source of protein, carbohydrates, dietary fiber, minerals, and vitamins. We screened 252 horse gram germplasm accessions for horse gram yellow mosaic virus resistance using the percent disease index and scaling techniques. The percentage values of highly resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible were 0.34, 13.89, 38.89, 46.43, and 0.34, respectively. Repetitive trials confirmed the host-plant resistance levels, and yield loss was assessed. The present disease index ranged from 1.2 to 72.0 and 1.2 to 73.0 during the kharif and rabi seasons of 2018, respectively. The maximum percent yield loss was noticed in the HS (75.0 -89.4), while HR possessed the minimum (1.2-2.0). The methanolic leaf extracts of highly resistant and highly susceptible genotypes with essential controls were subjected to gas chromatography-mass spectrometry analysis. Differential accumulation of metabolites was noticed, and a total of 81 metabolites representing 26 functional groups were identified. Both highly resistant and susceptible genotypes harbored eight unique classes, while ten biomolecules were common. The hierarchical cluster analysis indicated a distinct metabolite profile. Fold change in the common metabolites revealed an enhanced accumulation of sugars, alkanes, and carboxylic acids in the highly resistant genotype. The principal component analysis plots explained 93.7% of the variation. The metabolite profile showed a significant accumulation of three anti-viral (octadecanoic acid, diphenyl sulfone, and 2-Aminooxazole), one insecticidal (9,10-Secocholesta-5,7,10(19)-triene-3,24,25-triol), one antifeedant (cucurbitacin B), and six metabolites with unknown biological function in the highly resistant genotype.

The physiological functions of human peroxisomes

Peroxisomes are subcellular organelles that play a central role in human physiology by catalyzing a range of unique metabolic functions. The importance of peroxisomes for human health is exemplified by the existence of a group of usually severe diseases caused by an impairment in one or more peroxisomal functions. Among others these include the Zellweger spectrum disorders, X-linked adrenoleukodystrophy, and Refsum disease. To fulfill their role in metabolism, peroxisomes require continued interaction with other subcellular organelles including lipid droplets, lysosomes, the endoplasmic reticulum, and mitochondria. In recent years it has become clear that the metabolic alliance between peroxisomes and other organelles requires the active participation of tethering proteins to bring the organelles physically closer together, thereby achieving efficient transfer of metabolites. This review intends to describe the current state of knowledge about the metabolic role of peroxisomes in humans, with particular emphasis on the metabolic partnership between peroxisomes and other organelles and the consequences of genetic defects in these processes. We also describe the biogenesis of peroxisomes and the consequences of the multiple genetic defects therein. In addition, we discuss the functional role of peroxisomes in different organs and tissues and include relevant information derived from model systems, notably peroxisomal mouse models. Finally, we pay particular attention to a hitherto underrated role of peroxisomes in viral infections.

Targeting peroxisomal fatty acid oxidation improves hepatic steatosis and insulin resistance in obese mice

Obesity and diabetes normally cause mitochondrial dysfunction and hepatic lipid accumulation, while fatty acid synthesis is suppressed and malonyl-CoA is depleted in the liver of severe obese or diabetic animals. Therefore, a negative regulatory mechanism might work for the control of mitochondrial fatty acid metabolism that is independent of malonyl-CoA in the diabetic animals. As mitochondrial β-oxidation is controlled by the acetyl-CoA/CoA ratio, and the acetyl-CoA generated in peroxisomal β-oxidation could be transported into mitochondria via carnitine shuttles, we hypothesize that peroxisomal β-oxidation might play a role in regulating mitochondrial fatty acid oxidation and inducing hepatic steatosis under the condition of obesity or diabetes. This study reveals a novel mechanism by which peroxisomal β-oxidation controls mitochondrial fatty acid oxidation in diabetic animals. We determined that excessive oxidation of fatty acids by peroxisomes generates considerable acetyl-carnitine in the liver of diabetic mice, which significantly elevates the mitochondrial acetyl-CoA/CoA ratio and causes feedback suppression of mitochondrial β-oxidation. Additionally, we found that specific suppression of peroxisomal β-oxidation enhances mitochondrial fatty acid oxidation by reducing acetyl-carnitine formation in the liver of obese mice. In conclusion, we suggest that induction of peroxisomal fatty acid oxidation serves as a mechanism for diabetes-induced hepatic lipid accumulation. Targeting peroxisomal β-oxidation might be a promising pathway in improving hepatic steatosis and insulin resistance as induced by obesity or diabetes.

The Adaptive Characteristics of Cholesterol and Bile Acid Metabolism in Nile Tilapia Fed a High-Fat Diet

Since high-fat diet (HFD) intake elevates liver cholesterol and enhanced cholesterol-bile acid flux alleviates its lipid deposition, we assumed that the promoted cholesterol-bile acid flux is an adaptive metabolism in fish when fed an HFD. The present study investigated the characteristic of cholesterol and fatty acid metabolism in Nile tilapia (Oreochromis niloticus) after feeding an HFD (13% lipid level) for four and eight weeks. Visually healthy Nile tilapia fingerlings (average weight 3.50 ± 0.05 g) were randomly distributed into four treatments (4-week control diet or HFD and 8-week control diet or HFD). The liver lipid deposition and health statue, cholesterol/bile acid, and fatty acid metabolism were analyzed in fish after short-term and long-term HFD intake. The results showed that 4-week HFD feeding did not change serum alanine transaminase (ALT) and aspartate transferase (AST) enzyme activities, along with comparable liver malondialdehyde (MDA) content. But higher serum ALT and AST enzyme activities and liver MDA content were observed in fish fed 8-week HFD. Intriguingly, remarkably accumulated total cholesterol (mainly cholesterol ester, CE) was observed in the liver of fish fed 4-week HFD, along with slightly elevated free fatty acids (FFAs) and comparable TG contents. Further molecular analysis in the liver showed that obvious accumulation of CE and total bile acids (TBAs) in fish fed 4-week HFD was mainly attributed to the enhancement of cholesterol synthesis, esterification, and bile acid synthesis. Furthermore, the increased protein expressions of acyl-CoA oxidase 1/2 (Acox1 and Acox2), which serve as peroxisomal fatty acid β-oxidation (FAO) rate-limiting enzymes and play key roles in the transformation of cholesterol into bile acids, were found in fish after 4-week HFD intake. Notably, 8-week HFD intake remarkably elevated FFA content (about 1.7-fold increase), and unaltered TBAs were found in fish liver, accompanied by suppressed Acox2 protein level and cholesterol/bile acid synthesis. Therefore, the robust cholesterol-bile acid flux serves as an adaptive metabolism in Nile tilapia when fed a short-term HFD and is possibly via stimulating peroxisomal FAO. This finding enlightens our understanding on the adaptive characteristics of cholesterol metabolism in fish fed an HFD and provides a new possible treatment strategy against metabolic disease induced by HFD in aquatic animals.

Obesity downregulates lipid metabolism genes in first trimester placenta

Placentas of obese women have low mitochondrial β-oxidation of fatty acids (FA) and accumulate lipids in late pregnancy. This creates a lipotoxic environment, impairing placental efficiency. We hypothesized that placental FA metabolism is impaired in women with obesity from early pregnancy. We assessed expression of key regulators of FA metabolism in first trimester placentas of lean and obese women. Maternal fasting triglyceride and insulin levels were measured in plasma collected at the time of procedure. Expression of genes associated with FA oxidation (FAO; ACOX1, CPT2, AMPKα), FA uptake (LPL, LIPG, MFSD2A), FA synthesis (ACACA) and storage (PLIN2) were significantly reduced in placentas of obese compared to lean women. This effect was exacerbated in placentas of male fetuses. Placental ACOX1 protein was higher in women with obesity and correlated with maternal circulating triglycerides. The PPARα pathway was enriched for placental genes impacted by obesity, and PPARα antagonism significantly reduced ³H-palmitate oxidation in 1^st trimester placental explants. These results demonstrate that obesity and hyperlipidemia impact placental FA metabolism as early as 7 weeks of pregnancy.

Role of acyl-coenzyme A oxidase 1 (ACOX1) on palmitate-induced inflammation and ROS production of macrophages in large yellow croaker (Larimichthys crocea)

Acyl-coenzyme A oxidase 1 (ACOX1) is the rate-limiting enzyme in peroxisomal β-oxidation, and it plays an essential role in mediating the inflammatory response and reactive oxygen species (ROS) metabolism in mammals. However, the role of ACOX1 in fish has not been completely elucidated. Herein, this study was conducted to investigate the role of large yellow croaker (Larimichthys crocea) ACOX1 (Lc-ACOX1) on palmitate (PA)-induced inflammation and ROS production. In this study, Lc-ACOX1 was cloned and characterized. The full-length CDS of Lc-acox1 was 1986 bp, encoding 661 amino acids. Tissue distribution results showed that the gene expression of Lc-acox1 was the highest in the intestine and the lowest in the spleen. Moreover, results showed that the mRNA expression of Lc-acox1 was upregulated by PA, with elevated pro-inflammatory gene expression, including il-1β, il-6, il-8, tnf-α, cox2 and ifn-γ, as well as ROS content in macrophages of large yellow croaker. Furthermore, the role of Lc-ACOX1 in inflammation induced by PA was investigated by using the ACOX1 inhibitor TDYA. Treatment of macrophages with TDYA reduced the mRNA expression of pro-inflammatory genes induced by PA. Moreover, inhibition of ACOX1 reduced the elevated level of ROS caused by PA and increased the mRNA expression of antioxidant genes. In conclusion, this study first identified that fish ACOX1 was involved in the PA-induced inflammatory response and ROS production.

Carotenoids in orange carrots mitigate non-alcoholic fatty liver disease progression

Background

Carotenoids are abundant in colored fruits and vegetables. Non-alcoholic fatty liver disease (NAFLD) is a global burden and risk factor for end-stage hepatic diseases. This study aims to compare the anti-NAFLD efficacy between carotenoid-rich and carotenoid-deficient vegetables.

Materials and methods

Male C57BL/6J mice were randomized to one of four experimental diets for 15 weeks (n = 12 animals/group): Low-fat diet (LFD, 10% calories from fat), high-fat diet (HFD, 60% calories from fat), HFD with 20% white carrot powders (HFD + WC), or with 20% orange carrot powders (HFD + OC).

Results

We observed that carotenoids in the orange carrots reduced HFD-induced weight gain, better than white carrots. Histological and triglyceride (TG) analyses revealed significantly decreased HFD-induced hepatic lipid deposition and TG content in the HFD + WC group, which was further reduced in the HFD + OC group. Western blot analysis demonstrated inconsistent changes of fatty acid synthesis-related proteins but significantly improved ACOX-1 and CPT-II, indicating that orange carrot carotenoids had the potential to inhibit NAFLD by improving β-oxidation. Further investigation showed significantly higher mRNA and protein levels of PPARα and its transcription factor activity.

Conclusion

Carotenoid-rich foods may display more potent efficacy in mitigating NAFLD than those with low carotenoid levels.

Peroxisomal regulation of energy homeostasis: Effect on obesity and related metabolic disorders

BACKGROUND

Peroxisomes are single membrane-bound organelles named for their role in hydrogen peroxide production and catabolism. However, their cellular functions extend well beyond reactive oxygen species (ROS) metabolism and include fatty acid oxidation of unique substrates that cannot be catabolized in mitochondria, and synthesis of ether lipids and bile acids. Metabolic functions of peroxisomes involve crosstalk with other organelles, including mitochondria, endoplasmic reticulum, lipid droplets and lysosomes. Emerging studies suggest that peroxisomes are important regulators of energy homeostasis and that disruption of peroxisomal functions influences the risk for obesity and the associated metabolic disorders, including type 2 diabetes and hepatic steatosis.

SCOPE OF REVIEW

Here, we focus on the role of peroxisomes in ether lipid synthesis, β-oxidation and ROS metabolism, given that these functions have been most widely studied and have physiologically relevant implications in systemic metabolism and obesity. Efforts are made to mechanistically link these cellular and systemic processes.

MAJOR CONCLUSIONS

Circulating plasmalogens, a form of ether lipids, have been identified as inversely correlated biomarkers of obesity. Ether lipids influence metabolic homeostasis through multiple mechanisms, including regulation of mitochondrial morphology and respiration affecting brown fat-mediated thermogenesis, and through regulation of adipose tissue development. Peroxisomal β-oxidation also affects metabolic homeostasis through generation of signaling molecules, such as acetyl-CoA and ROS that inhibit hydrolysis of stored lipids, contributing to development of hepatic steatosis. Oxidative stress resulting from increased peroxisomal β-oxidation-generated ROS in the context of obesity mediates β-cell lipotoxicity. A better understanding of the roles peroxisomes play in regulating and responding to obesity and its complications will provide new opportunities for their treatment.

Characterization of Acyl-CoA Oxidases from the Lipolytic Yeast Candida aaseri SH14

The lipolytic yeast Candida aaseri SH14 contains three Acyl-CoA oxidases (ACOXs) which are encoded by the CaAOX2, CaAOX4, and CaAOX5 genes and catalyze the first reaction in the β-oxidation of fatty acids. Here, the respective functions of the three CaAOX isozymes were studied by growth analysis of mutant strains constructed by a combination of three CaAOX mutations in minimal medium containing fatty acid as the sole carbon source. Substrate specificity of the CaAOX isozymes was analyzed using recombinant C. aaseri SH14 strains overexpressing the respective genes. CaAOX2 isozyme showed substrate specificity toward short- and medium-chain fatty acids (C6-C12), while CaAOX5 isozyme preferred long-chain fatty acid longer than C12. CaAOX4 isozyme revealed a preference for a broad substrate spectrum from C6-C16. Although the substrate specificity of CaAOX2 and CaAOX5 covers medium- and long-chain fatty acids, these two isozymes were insufficient for complete β-oxidation of long-chain fatty acids, and therefore CaAOX4 was indispensable.

Physicochemical, Nutritional Properties and Metabolomics Analysis Fat Deposition Mechanism of Chahua Chicken No. 2 and Yao Chicken

Poultry is an important dietary source of animal protein, accounting for approximately 30% of global meat consumption. Because of its low price, low fat and cholesterol content, and no religious restrictions, chicken is considered a widely available healthy meat. Chahua chicken No. 2 is a synthetic breed of Chahua chicken derived from five generations of specialized strain breeding. In this study, Chahua chicken No. 2 (CH) and Yao chicken (Y) were used as the research objects to compare the differences in physicochemical and nutritional indicators of meat quality between the two chicken breeds, and metabolomics was used to analyze the differences in metabolites and lipid metabolism pathways and to explore the expression of genes involved in adipogenesis. The physical index and nutritional value of CH are better than that of Y, and the chemical index of Y is better than that of CH. However, the chemical index results of CH are also within the normal theoretical value range. Comprehensive comparison shows that the meat quality of CH is relatively good. Metabolomics analysis showed that CH and Y had 85 different metabolites, and the differential metabolites were mainly classified into eight categories. KEGG pathway enrichment analysis revealed 13 different metabolic pathways. The screened PPARG, FABP3, ACSL5, FASN, UCP3 and SC5D were negatively correlated with muscle fat deposition, while PPARα, ACACA and ACOX1 were positively correlated with muscle fat deposition. The meat quality of CH was better than Y. The metabolites and metabolic pathways obtained by metabonomics analysis mainly involved the metabolism of amino acids and fatty acids, which were consistent with the differences in meat quality between the two breeds and the contents of precursors affecting flavor. The screened genes were associated with fatty deposition in poultry.

Lotus seed resistant starch ameliorates high-fat diet induced hyperlipidemia by fatty acid degradation and glycerolipid metabolism pathways in mouse liver

We investigated the potential efficacy and underlying mechanisms of Lotus seed Resistant Starch (LRS) for regulating hyperlipidemia in mice fed a High-fat Diet (HFD). Mouse were fed a normal diet (Normal Control group, NC group), HFD alone (MC group), HFD plus lovastatin (PC group), or HFD with low/medium/high LRS (LLRS, MLRS, and HLRS groups, respectively) for 4 weeks. LRS supplementation significantly decreased body weight and significantly reduced serum levels of total cholesterol, triglycerides, low-density lipoprotein cholesterol, and high-density lipopro-tein cholesterol compared with the MC group. LRS also significantly alleviated hepatic steatosis, especially in the MLRS group, which also showed a significantly reduced visceral fat index. LLRS supplementation significantly regulated genes associated with glycerolipid metabolism and steroid hormone biosynthesis (Lpin1 and Ugt2b38), MLRS significantly regulated genes related to fatty acid degradation, fatty acid elongation, and glycerolipid metabolism (Lpin1, Hadha, Aldh3a2, and Acox1), whereas HLRS significantly regulated genes related to fatty acid elongation and glycerolipid metabolism (Lpin1, Elovl3, Elovol5, and Agpat3). The fatty acid-degradation pathway regulated by MLRS thus exerts better control of serum lipid levels, body weight, visceral fat index, and liver steatosis in mice compared with LLRS- and HLRS-regulated pathways.

Suppression of Anti-Inflammatory Mediators in Metabolic Disease May Be Driven by Overwhelming Pro-Inflammatory Drivers

Obesity is a multifactorial disease and is associated with an increased risk of developing metabolic syndrome and co-morbidities. Dysregulated expansion of the adipose tissue during obesity induces local tissue hypoxia, altered secretory profile of adipokines, cytokines and chemokines, altered profile of local tissue inflammatory cells leading to the development of low-grade chronic inflammation. Low grade chronic inflammation is considered to be the underlying mechanism that increases the risk of developing obesity associated comorbidities. The glucocorticoid induced protein annexin A1 and its N-terminal peptides are anti-inflammatory mediators involved in resolving inflammation. The aim of the current study was to investigate the role of annexin A1 in obesity and associated inflammation. To achieve this aim, the current study analysed data from two feasibility studies in clinical populations: (1) bariatric surgery patients (Pre- and 3 months post-surgery) and (2) Lipodystrophy patients. Plasma annexin A1 levels were increased at 3-months post-surgery compared to pre-surgery (1.2 ± 0.1 ng/mL, n = 19 vs. 1.6 ± 0.1 ng/mL, n = 9, p = 0.009) and positively correlated with adiponectin (p = 0.009, r = 0.468, n = 25). Plasma annexin A1 levels were decreased in patients with lipodystrophy compared to BMI matched controls (0.2 ± 0.1 ng/mL, n = 9 vs. 0.97 ± 0.1 ng/mL, n = 30, p = 0.008), whereas CRP levels were significantly elevated (3.3 ± 1.0 µg/mL, n = 9 vs. 1.4 ± 0.3 µg/mL, n = 31, p = 0.0074). The roles of annexin A1 were explored using an in vitro cell based model (SGBS cells) mimicking the inflammatory status that is observed in obesity. Acute treatment with the annexin A1 N-terminal peptide, AC2-26 differentially regulated gene expression (including PPARA (2.8 ± 0.7-fold, p = 0.0303, n = 3), ADIPOQ (2.0 ± 0.3-fold, p = 0.0073, n = 3), LEP (0.6 ± 0.2-fold, p = 0.0400, n = 3), NAMPT (0.4 ± 0.1-fold, p = 0.0039, n = 3) and RETN (0.1 ± 0.03-fold, p < 0.0001, n = 3) in mature obesogenic adipocytes indicating that annexin A1 may play a protective role in obesity and inflammation. However, this effect may be overshadowed by the continued increase in systemic inflammation associated with rapid tissue expansion in obesity.

Molecular and cellular regulatory roles of sirtuin protein

Sirtuins (SIRT) are unique posttranslational modification enzymes that utilize NAD + as co-substrate to remove acyl groups from lysine residues. SIRT act on variety of substrates and impact major metabolic process. All seven members of SIRT family are unique and targets wide range of cellular proteins in nucleus, cytoplasm, and mitochondria for post-translational modification by acetylation (SIRT1, 2, 3, and 5) or ADP-ribosylation (SIRT4 and 6). Each member of SIRT family is distinct. SIRT2 was first to be discovered that incited research on mammalian SIRT. Enzymatic activities of SIRT 4 are yet to be elucidated while only SIRT7 is localized in nucleoli that govern the transcription of RNA polymerase I. SIRT 5 and 6 exhibit weakest deacetylase activity. Out of all SIRT analogs, SIRT1 is identified as nutrient sensor. Increased expression of only SIRT3 is linked with longevity in humans. Since SIRT is regulated by the bioenergetic state of the cell, nutrition impacts it but very few studies about diet-mediated effect on SIRT are reported. The present review elaborates distribution, specific biological role and prominent effect of all SIRT on vital human tissue along with highlighting need to trace molecular mechanisms and identifying foods that may augment it beneficially.

Impacts of diethylhexyl phthalate and overfeeding on physical fitness and lipid mobilization in Danio rerio (zebrafish)

As the prevalence of obesity has steadily increased on a global scale, research has shifted to explore potential contributors to this pandemic beyond overeating and lack of exercise. Environmental chemical contaminants, known as obesogens, alter metabolic processes and exacerbate the obese phenotype. Diethylhexyl phthalate (DEHP) is a common chemical plasticizer found in medical supplies, food packaging, and polyvinyl materials, and has been identified as a probable obesogen. This study investigated the hypothesis that co-exposure to DEHP and overfeeding would result in decreased lipid mobilization and physical fitness in Danio rerio (zebrafish). Four treatment groups were randomly assigned: Regular Fed (control, 10 mg/fish/day with 0 mg/kg DEHP), Overfed (20 mg/fish/day with 0 mg/kg DEHP), Regular Fed + DEHP (10 mg/fish/day with 3 mg/kg DEHP), Overfed + DEHP (20 mg/fish/day with 3 mg/kg DEHP). After 24 weeks, swim tunnel assays were conducted on half of the zebrafish from each treatment to measure critical swimming speeds (U_crit); the other fish were euthanized without swimming. Body mass index (BMI) was measured, and tissues were collected for blood lipid characterization and gene expression analyses. Co-exposure to DEHP and overfeeding decreased swim performance as measured by U_crit. While no differences in blood lipids were observed with DEHP exposure, differential expression of genes related to lipid metabolism and utilization in the gastrointestinal and liver tissue suggests alterations in metabolism and lipid packaging, which may impact utilization and ability to mobilize lipid reserves during physical activity following chronic exposures.

Effects of naringin and valproate interaction on liver steatosis and dyslipidaemia parameters in male C57BL6 mice

Valproate is a common antiepileptic drug whose adverse effects include liver steatosis and dyslipidaemia. The aim of our study was to see how natural flavonoid antioxidant naringin would interact with valproate and attenuate these adverse effects. For this reason we treated male C57BL6 mice with a combination of 150 mg/kg of valproate and 25 mg/kg naringin every day for 10 days and compared their serum triglycerides, cholesterol, LDL, HDL, VLDL, and liver PPAR-alpha, PGC-1 alpha, ACOX1, Nrf2, SOD, CAT, GSH, and histological signs of steatosis. Valproate increased lipid peroxidation parameters and caused pronounced microvesicular steatosis throughout the hepatic lobule in all acinar zones, but naringin co-administration limited steatosis to the lobule periphery. In addition, it nearly restored total serum cholesterol, LDL, and triglycerides and liver ACOX1 and MDA to control levels. and upregulated PPAR-alpha and PGC-1 alpha, otherwise severely downregulated by valproate. It also increased SOD activity. All these findings suggest that naringin modulates key lipid metabolism regulators and should further be investigated in this model, either alone or combined with other lipid regulating drugs or molecules.

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.

Peroxisome-generated succinate induces lipid accumulation and oxidative stress in the kidneys of diabetic mice

Diabetes normally causes lipid accumulation and oxidative stress in the kidneys, which plays a critical role in the onset of diabetic nephropathy; however, the mechanism by which dysregulated fatty acid metabolism increases lipid and reactive oxygen species (ROS) formation in the diabetic kidney is not clear. As succinate is remarkably increased in the diabetic kidney, and accumulation of succinate suppresses mitochondrial fatty acid oxidation and increases ROS formation, we hypothesized that succinate might play a role in inducing lipid and ROS accumulation in the diabetic kidney. Here we demonstrate a novel mechanism by which diabetes induces lipid and ROS accumulation in the kidney of diabetic animals. We show that enhanced oxidation of dicarboxylic acids by peroxisomes leads to lipid and ROS accumulation in the kidney of diabetic mice via the metabolite succinate. Furthermore, specific suppression of peroxisomal β-oxidation improved diabetes-induced nephropathy by reducing succinate generation and attenuating lipid and ROS accumulation in the kidneys of the diabetic mice. We suggest that peroxisome-generated succinate acts as a pathological molecule inducing lipid and ROS accumulation in kidney, and that specifically targeting peroxisomal β-oxidation might be an effective strategy in treating diabetic nephropathy and related metabolic disorders.

Peroxisomal β-oxidation stimulates cholesterol biosynthesis in the liver in diabetic mice

Although diabetes normally causes an elevation of cholesterol biosynthesis and induces hypercholesterolemia in animals and human, the mechanism linking diabetes to the dysregulation of cholesterol biosynthesis in the liver is not fully understood. As liver peroxisomal β-oxidation is induced in the diabetic state and peroxisomal oxidation of fatty acids generates free acetate, we hypothesized that peroxisomal β-oxidation might play a role in liver cholesterol biosynthesis in diabetes. Here, we used erucic acid, a specific substrate for peroxisomal β-oxidation, and 10,12-tricosadiynoic acid, a specific inhibitor for peroxisomal β-oxidation, to specifically induce and suppress peroxisomal β-oxidation. Our results suggested that induction of peroxisomal β-oxidation increased liver cholesterol biosynthesis in streptozotocin-induced diabetic mice. We found that excessive oxidation of fatty acids by peroxisomes generated considerable free acetate in the liver, which was used as a precursor for cholesterol biosynthesis. In addition, we show that specific inhibition of peroxisomal β-oxidation decreased cholesterol biosynthesis by reducing acetate formation in the liver in diabetic mice, demonstrating a crosstalk between peroxisomal β-oxidation and cholesterol biosynthesis. Based on these results, we propose that induction of peroxisomal β-oxidation serves as a mechanism for a fatty acid-induced upregulation in cholesterol biosynthesis and also plays a role in diabetes-induced hypercholesterolemia.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

Analysis of bioactive compounds and chemical composition of Malaysian stingless bee propolis water extracts

Propolis is a resinous substance collected by stingless bees containing bioactive compounds which exert various biological properties. The present study focused on the evaluation of chemical profiles produced by three Indo-Malayan stingless bee propolis extracted using water. Fresh propolis was collected from the same area and ecosystem conditions in Selangor, Malaysia, namely Tetrigona apicalis, Tetrigona binghami, and Heterotrigona fimbriata. The bioactive compounds and chemical composition of propolis extracts were then analyzed using gas chromatography–mass spectrometry (GC–MS). Results showed that propolis from the three different stingless bee species consisted of major groups such as sugar (31.4%), carboxylic acid (17.1%), terpenoid (14.3%), sugar alcohol (11.4%), hydrocarbon (5.7%), aldehyde (5.7%) amino acid (2.9%) and other constituents (11.4%). Heterotrigona fimbriata displayed the highest amount for both total phenolics (13.21 mg/mL) and flavonoids (34.53 mg/mL) compared to other propolis extracts. There is also no significant difference detected between all samples since p ≤ 0.05. In conclusion, this study shows that Malaysian stingless bee propolis contain bioactive components that have great potential to be used for their therapeutic and medicinal benefits. However, more investigations and analysis of stingless bee propolis need to be carried out in order to enhance the understanding and applications of propolis in the future.

TG68, a Novel Thyroid Hormone Receptor-β Agonist for the Treatment of NAFLD

Activation of thyroid hormone receptor β (THRβ) has shown beneficial effects on metabolic alterations, including non-alcoholic fatty liver disease (NAFLD). Here, we investigated the effect of TG68, a novel THRβ agonist, on fatty liver accumulation and liver injury in mice fed a high-fat diet (HFD). C57BL/6 mice fed HFD for 17 or 18 weeks, a time when all mice developed massive steatohepatitis, were then given TG68 at a dose of 9.35 or 2.8 mg/kg for 2 or 3 weeks, respectively. As a reference compound, the same treatment was adopted using equimolar doses of MGL-3196, a selective THRβ agonist currently in clinical phase III. The results showed that treatment with TG68 led to a reduction in liver weight, hepatic steatosis, serum transaminases, and circulating triglycerides. qRT-PCR analyses demonstrated activation of THRβ, as confirmed by increased mRNA levels of Deiodinase-1 and Malic enzyme-1, and changes in lipid metabolism, as revealed by increased expression of Acyl-CoA Oxidase-1 and Carnitine palmitoyltransferase-1. The present results showed that this novel THRβ agonist exerts an anti-steatogenic effect coupled with amelioration of liver injury in the absence of extra-hepatic side effects, suggesting that TG68 may represent a useful tool for the treatment of NAFLD.

Lactobacillus rhamnosus Strain LRH05 Intervention Ameliorated Body Weight Gain and Adipose Inflammation via Modulating the Gut Microbiota in High-Fat Diet-Induced Obese Mice

SCOPE

This study aims to investigate the underlying mechanism of a specific probiotic strain on suppression of adipogenesis and inflammatory response in white adipose tissue (WAT) of high-fat diet (HFD)-fed mice.

METHODS AND RESULTS

Eight strains are screened in vitro for candidates of potential probiotics. Lactobacillus rhamnosus LRH05 (LRH05) and Lactobacillus reuteri LR47 (LR47) are screened out with lower triglyceride expression in vitro. The mice are fed a control diet (CD), HFD, or HFD supplemented with a dose of LRH05 or LR47 at 10⁹ CFU per mouse per day for 10 weeks (n = 8), respectively. The results demonstrate that LRH05, but not LR47, significantly reduce body weight gain and the weight of WAT, as well as improve hepatic steatosis and glucose intolerance. LRH05 regulates the Mogat1, Igf-1, Mcp-1, and F4/80 mRNA expression and decreases macrophage infiltration in WAT. LRH05 shows an increase in butyric and propionic acid-producing bacteria, including Lachnoclostridium, Romboutsia, and Fusobacterium that is coincident with the increased fecal propionic acid and butyric acid levels.

CONCLUSION

LRH05 shows a strain-specific effect on ameliorating the pro-inflammatory process by reducing inflammatory macrophage infiltration and the expression of inflammation-related genes in mice. Thus, LRH05 can be considered a potential probiotic strain to prevent obesity.

Determination of Total Phenolics, Flavonoids, and Antioxidant Activity and GC-MS Analysis of Malaysian Stingless Bee Propolis Water Extracts

Propolis contains polyphenolic compounds such as flavonoids and phenols that are able to demonstrate a broad spectrum of biological activities including antioxidant, antibacterial, and many more. This study was carried out to determine the total phenolics, flavonoids, and antioxidant activity of water-extracted propolis samples from three different Indo-Malayan stingless bee species, namely, Tetrigona apicalis, Tetrigona binghami, and Homotrigona fimbriata. Total phenolic and flavonoid contents were evaluated using Folin-Ciocalteu colorimetric and aluminium chloride methods, respectively, while the antioxidant activity was analysed using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay. Results indicated that H. fimbriata extracts exhibit the highest TPC, TFC, and antiradical activity among all samples tested. Interestingly, the data also showed that the higher the concentration of the extract used, the higher the antioxidant activity exhibited by the samples. Statistically, there were no significant differences recorded between the different bee species' propolis studied. In conclusion, the propolis extracts showed stronger antioxidant potential with higher TPC and TFC values. This study also noted the presence of bioactive compounds from local stingless bee propolis that could potentially be utilised for their medicinal and health benefits.

1H NMR Metabolomics and Full-Length RNA-Seq Reveal Effects of Acylated and Nonacylated Anthocyanins on Hepatic Metabolites and Gene Expression in Zucker Diabetic Fatty Rats

Anthocyanins have been reported to possess antidiabetic effects. Recent studies indicate acylated anthocyanins have better stability and antioxidative activity compared to their nonacylated counterparts. This study compared the effects of nonacylated and acylated anthocyanins on hepatic gene expression and metabolic profile in diabetic rats, using full-length transcriptomics and ¹H NMR metabolomics. Zucker diabetic fatty (ZDF) rats were fed with nonacylated anthocyanin extract from bilberries (NAAB) or acylated anthocyanin extract from purple potatoes (AAPP) at daily doses of 25 and 50 mg/kg body weight for 8 weeks. Both anthocyanin extracts restored the levels of multiple metabolites (glucose, lactate, alanine, and pyruvate) and expression of genes (G6pac, Pck1, Pklr, and Gck) involved in glycolysis and gluconeogenesis. AAPP decreased the hepatic glutamine level. NAAB regulated the expression of Mgat4a, Gstm6, and Lpl, whereas AAPP modified the expression of Mgat4a, Jun, Fos, and Egr1. This study indicated different effects of AAPP and NAAB on the hepatic transcriptomic and metabolic profiles of diabetic rats.

Fasting induces hepatic lipid accumulation by stimulating peroxisomal dicarboxylic acid oxidation

Fasting induces lipid accumulation in the liver, while the mechanisms by which fasting dysregulates liver fatty acid oxidation are not clear. Fatty acid ω-oxidation is induced in the fasting state, and administration of dicarboxylic acids to fasting animals decreases plasma ketone bodies. We hypothesized that endogenous dicarboxylic acids might play a role in controlling mitochondrial β-oxidation in fasting animals. A peroxisome proliferator-activated receptor-alpha agonist and an inhibitor for peroxisomal β-oxidation were administered to the fasting rats to investigate the role of dicarboxylic acids in liver fatty acid oxidation and lipid homeostasis. We observed that excessive β-oxidation of endogenous dicarboxylic acids by peroxisomes generated considerable levels of succinate in the liver. Excessive succinate oxidation subsequently increased the mitochondrial NADH/NAD⁺ ratio and led to an accumulation of 3-OH-CoA and 2-enoyl-CoA intermediates in the liver. This further induced feedback suppression of mitochondrial β-oxidation and promoted hepatic lipid deposition and steatosis. Specific inhibition of peroxisomal β-oxidation attenuated fasting-induced lipid deposition in the liver by reducing succinate production and enhancing mitochondrial fatty acid oxidation. We conclude that suppression of mitochondrial β-oxidation by oxidation of dicarboxylic acids serves as a mechanism for fasting-induced hepatic lipid accumulation and identifies cross talk between peroxisomal and mitochondrial fatty acid oxidation.