Arylacetamide deacetylase attenuates fatty-acid-induced triacylglycerol accumulation in rat hepatoma cells

Progress of arylacetamide deacetylase research in metabolic diseases

Arylacetamide deacetylase (AADAC), a microsomal serine esterase belonging to the polygenic hydrolase family, is predominantly localized in the liver and intestine. It plays a significant role in drug metabolism, lipid metabolism, and the pathogenesis of various diseases. In the context of drug metabolism, AADAC is vital for ensuring the safety of ester-based drugs. Its substrate specificity for short-chain acyl groups, along with genetic polymorphisms among individuals and species, influences drug-related processes. Regarding lipid metabolism, The lipase activity of AADAC is involved in the hydrolysis of cholesterol and triglycerides, lipid mobilization, and the assembly of lipoproteins. The expression of AADAC is regulated by multiple factors. It is associated with metabolic disorders; for instance, its decreased expression in the liver during obesity may impact triglyceride metabolism, and it may also have an indirect role in diabetes. In cardiovascular diseases, AADAC holds potential as a diagnostic marker. Its role in cancer is heterogeneous, being downregulated in certain cancers while upregulated in others, such as pancreatic and ovarian cancers, where it acts to inhibit cancer progression. Within the nervous system, AADAC may influence neurotransmitter regulation and drug metabolism. Currently, research on AADAC agonists is limited, and the development of inhibitors presents challenges, underscoring the necessity for further investigation in this area.

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

Landscape genomics analysis provides insights into future climate change-driven risk in rhesus macaque

Climate change significantly affects the suitability of wildlife habitats. Thus, understanding how animals adapt ecologically and genetically to climate change is important for targeted species protection. Rhesus macaques (Macaca mulatta) are widely distributed and multi-climatically adapted primates. This study explored how rhesus macaques adapt to climate change by integrating ecological and genetic methods and applying species distribution models (SDMs) and a gradient forest (GF) model. The findings suggested that temperature seasonality primarily affects habitat suitability and indicated that climate change will have a dramatic impact on macaque populations in the future. We also applied genotype-environment association (GEA) analyses and selection signature analyses to identify genes associated with climate change and provide possible explanations for the adaptation of rhesus macaques to climatic environments. The population genomics analyses suggested that the Taihang population has the highest genomic vulnerability with inbreeding and low heterozygosity. Combined with the higher ecological vulnerability, additional conservation strategies are required for this population under higher risk of climate change. Our work measured the impact of climate change and enabled the identification of populations that exhibit high vulnerability to severe climate change. Such information is useful for selecting populations of rhesus macaques as subject of long-term monitoring or evolutionary rescue under future climate change.

Development and validation of an ultra-performance liquid chromatography-tandem mass spectrometry method for the determination of baloxavir in rat plasma and its application to pharmacokinetic studies

In this study, an ultra-performance liquid chromatography-tandem mass spectrometry method was established for the development and validation of baloxavir acid (BXA) concentrations and the active ingredients of the antiviral drug baloxavir marboxil (BXM). Further, the method was applied to study the pharmacokinetics of BXA. BXA was determined by the electrospray ionization multiple reaction monitoring positive ion mode, and the mass-to-charge ratios (m/z) of BXA and internal standard baloxavir-d4 were 484.2 → 247.2 and 488.1 → 247.2. An Oasis max online column (2.1 × 20 mm, 30 μm) was used with 1% formic acid in water (A) and 2% formic acid in acetonitrile (B) as mobile phases at a flow rate of 0.5 mL·min-1 for chromatographic separation. The linearity was good in the range of 3-200 ng·mL-1 (r = 0.9994), with 3.00 ng·mL-1 lower limit of quantification. The relative standard deviation of the inter-assay precision was less than or equal to 6.51%, and the accuracy was in the range of 91.28%-104.29%. This method is suitable for the determination of BXA and for performing pharmacokinetic studies in clinical research.

Characterization, comparative, and functional analysis of arylacetamide deacetylase from Gnathostomata organisms

BACKGROUND

Arylacetamide deacetylase (AADAC) is a lipolytic enzyme involved in xenobiotic metabolism. The characterization in terms of activity and substrate preference has been limited to a few mammalian species. The potential role and catalytic activities of AADAC from other organisms are still poorly understood. Therefore, in this work, the physicochemical properties, proteomic analysis, and protein-protein interactions from Gnathostomata organisms were investigated.

RESULTS

The analysis were performed with 142 orthologue sequences with ~ 48-100% identity with human AADAC. The catalytic motif HGG[A/G] tetrapeptide block was conserved through all AADAC orthologues. Four variations were found in the consensus pentapeptide GXSXG sequence (GDSAG, GESAG, GDSSG, and GSSSG), and a novel motif YXLXP was found. The prediction of N-glycosylation sites projected 4, 1, 6, and 4 different patterns for amphibians, birds, mammals, and reptiles, respectively. The transmembrane regions of AADAC orthologues were not conserved among groups, and variations in the number and orientation of the active site and C-terminal carboxyl were observed among the sequences studied. The protein-protein interaction of AADAC orthologues were related to cancer, lipid, and xenobiotic metabolism genes.

CONCLUSION

The findings from this computational analysis offer new insight into one of the main enzymes involved in xenobiotic metabolism from mammals, reptiles, amphibians, and birds and its potential use in medical and veterinarian biotechnological approaches.

AADAC protects colorectal cancer liver colonization from ferroptosis through SLC7A11-dependent inhibition of lipid peroxidation

Background

Oxidative stress is a highly active metabolic process in the liver, that poses great threats to disseminated tumor cells during their colonization. Here, we aimed to investigate how colorectal cancer (CRC) cells overcome lipid peroxidation to sustain their metastatic colonization in the liver.

Methods

Orthotopic colorectal liver metastasis (CRLM) and CRC liver colonization mouse models were constructed to determine the roles of lipid peroxidation and AADAC in CRC liver colonization. The levels of lipid peroxidation were detected in cells or tissues. AADAC overexpression in LMs and its clinical relevance were analyzed. The oncogenic role of AADAC in CRC liver colonization was evaluated in cell experiments.

Results

Compared with primary tumors (PTs), liver metastases (LMs) showed significantly lower glutathione to oxidized glutathione (GSH/GSSG) ratio and higher malondialdehyde (MDA) levels in CRLM patients and orthotopic mouse models. Inhibition of lipid peroxidation by liproxstatin-1 promoted CRC liver colonization in mouse models. RNA-seq results revealed AADAC as the most significantly upregulated lipid metabolism related gene in LMs compared with PTs. Analyses of datasets and patient and mouse model samples confirmed that AADAC was upregulated in LMs compared with PTs, and was correlated with poor prognosis. AADAC promoted cell proliferation, and facilitated liver colonization in a mouse model by reducing ROS accumulation, which led to lipid peroxidation and ferroptosis. Mechanistically, AADAC upregulated SLC7A11 by activating NRF2 to inhibit lipid peroxidation, thereby protecting metastatic cells from ferroptosis.

Conclusions

AADAC protects metastatic CRC cells from ferroptosis by inhibiting lipid peroxidation in an SLC7A11-dependent manner, thus effectively promoting their metastatic colonization and growth in the liver. Together, our findings suggest that AADAC can act as a prognostic indicator and potential therapeutic target for CRLM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02493-0.

Genomic Analyses for Selective Signatures and Genes Involved in Hot Adaptation Among Indigenous Chickens From Different Tropical Climate Regions

Climate change, especially weather extremes like extreme cold or extreme hot, is a major challenge for global livestock. One of the animal breeding goals for sustainable livestock production should be to breed animals with excellent climate adaptability. Indigenous livestock and poultry are well adapted to the local climate, and they are good resources to study the genetic footprints and mechanism of the resilience to weather extremes. In order to identify selection signatures and genes that might be involved in hot adaptation in indigenous chickens from different tropical climates, we conducted a genomic analysis of 65 indigenous chickens that inhabit different climates. Several important unique positively selected genes (PSGs) were identified for each local chicken group by the cross-population extended haplotype homozygosity (XP-EHH). These PSGs, verified by composite likelihood ratio, genetic differentiation index, nucleotide diversity, Tajima’s D, and decorrelated composite of multiple signals, are related to nerve regulation, vascular function, immune function, lipid metabolism, kidney development, and function, which are involved in thermoregulation and hot adaptation. However, one common PSG was detected for all three tropical groups of chickens via XP-EHH but was not confirmed by other five types of selective sweep analyses. These results suggest that the hot adaptability of indigenous chickens from different tropical climate regions has evolved in parallel by taking different pathways with different sets of genes. The results from our study have provided reasonable explanations and insights for the rapid adaptation of chickens to diverse tropical climates and provide practical values for poultry breeding.

Recent advances in cytoplasmic lipid droplet metabolism in intestinal enterocyte

Processing of dietary fats in the intestine is a highly regulated process that influences whole-body energy homeostasis and multiple physiological functions. Dysregulated lipid handling in the intestine leads to dyslipidemia and atherosclerotic cardiovascular disease. In intestinal enterocytes, lipids are incorporated into lipoproteins and cytoplasmic lipid droplets (CLDs). Lipoprotein synthesis and CLD metabolism are inter-connected pathways with multiple points of regulation. This review aims to highlight recent advances in the regulatory mechanisms of lipid processing in the enterocyte, with particular focus on CLDs. In-depth understanding of the regulation of lipid metabolism in the enterocyte may help identify therapeutic targets for the treatment and prevention of metabolic disorders.

KIAA1363-A Multifunctional Enzyme in Xenobiotic Detoxification and Lipid Ester Hydrolysis

KIAA1363, annotated as neutral cholesterol ester hydrolase 1 (NCEH1), is a member of the arylacetamide deacetylase (AADAC) protein family. The name-giving enzyme, AADAC, is known to hydrolyze amide and ester bonds of a number of xenobiotic substances, as well as clinical drugs and of endogenous lipid substrates such as diglycerides, respectively. Similarly, KIAA1363, annotated as the first AADAC-like protein, exhibits enzymatic activities for a diverse substrate range including the xenobiotic insecticide chlorpyrifos oxon and endogenous substrates, acetyl monoalkylglycerol ether, cholesterol ester, and retinyl ester. Two independent knockout mouse models have been generated and characterized. However, apart from reduced acetyl monoalkylglycerol ether and cholesterol ester hydrolase activity in specific tissues and cell types, no gross-phenotype has been reported. This raises the question of its physiological role and whether it functions as drug detoxifying enzyme and/or as hydrolase/lipase of endogenous substrates. This review delineates the current knowledge about the structure, function and of the physiological role of KIAA1363, as evident from the phenotypical changes inflicted by pharmacological inhibition or by silencing as well as knockout of KIAA1363 gene expression in cells, as well as mouse models, respectively.

Recombinant humanized IgG1 maintain liver triglyceride homeostasis through Arylacetamide deacetylase in ApoE-/- mice

BACKGROUND & AIMS

Hyperlipidemia is a lipid metabolism disorder associated with elevated serum triglyceride (TG) and/or cholesterol. Over the years, studies have shown that hyperlipidemia is associated with combordities, incluing diabetes and obesity, gradually becoming a public health concern. Current treatment approaches remain limited due to the lack of effective drugs. Here we investigated the function of recombinant humanized IgG1 in maintaining liver TG homeostasis and the underlying mechanisms.

METHODS

ApoE^-/- mice were fed a high-fat diet (HFD) for 20 weeks to induce hyperlipidemia. RNA sequencing (RNA-Seq) was performed to identify differences in gene expression in different groups of ApoE^-/- mice liver. In vitro lipid accumulation in primary mouse hepatocytes was induced using a free fatty acid (FFA) mixture. Gene and protein expression were assessed in primary mouse hepatocytes by qPCR and Western blot. Gene reporter assays and ChIP-PCR were used to determine arylacetamide deacetylase (Aadac) promoter activity.

RESULTS

Recombinant humanized IgG1 could significantly decrease the serum level of TG and low-density lipoproteins (LDL-C). Moreover, hepatic TG and lipid droplets were also reduced compared to the HFD group. Mouse liver RNA-Seq revealed that administration of recombinant humanized IgG1 significantly elevated the expression of Aadac. In vitro, knock-down of Aadac could nullify the effect of recombinant humanized IgG1 on decreasing the lipid droplets induced by FFA in primary mouse hepatocytes. Gene Reporter assays and ChIP-PCR demonstrated that the foxa1 response element in the Aadac promoter played a key role in Aadac expression induced by recombinant humanized IgG1. Moreover, recombinant humanized IgG1 repressed phosphorylation of PKCδ and resulted in foxa1 elevation. Finally, neonatal Fc receptor (FcRn) knock-down reversed the effect of recombinant humanized IgG1 on the expression of PKCδ phosphorylation, foxa1 and Aadac.

CONCLUSIONS

Our findings suggest that recombinant humanized IgG1 plays an important role in maintaining liver TG homeostasis via the FcRn/PKCδ/foxa1/Aadac pathway.

Dynamic Expression and Regulatory Network of Circular RNA for Abdominal Preadipocytes Differentiation in Chicken (Gallus gallus)

Circular RNA (circRNA), as a novel endogenous biomolecule, has been emergingly demonstrated to play crucial roles in mammalian lipid metabolism and obesity. However, little is known about their genome-wide identification, expression profile, and function in chicken adipogenesis. In present study, the adipogenic differentiation of chicken abdominal preadipocyte was successfully induced, and the regulatory functional circRNAs in chicken adipogenesis were identified from abdominal adipocytes at different differentiation stages using Ribo-Zero RNA-seq. A total of 1,068 circRNA candidates were identified and mostly derived from exons. Of these, 111 differentially expressed circRNAs (DE-circRNAs) were detected, characterized by stage-specific expression, and enriched in several lipid-related pathways, such as Hippo signaling pathway, mTOR signaling pathway. Through weighted gene co-expression network analyses (WGCNA) and K-means clustering analyses, two DE-circRNAs, Z:35565770|35568133 and Z:54674624|54755962, were identified as candidate regulatory circRNAs in chicken adipogenic differentiation. Z:35565770|35568133 might compete splicing with its parental gene, ABHD17B, owing to its strictly negative co-expression. We also constructed competing endogenous RNA (ceRNA) network based on DE-circRNA, DE-miRNA, DE-mRNAs, revealing that Z:54674624|54755962 might function as a ceRNA to regulate chicken adipogenic differentiation through the gga-miR-1635-AHR2/IRF1/MGAT3/ABCA1/AADAC and/or the novel_miR_232-STAT5A axis. Translation activity analysis showed that Z:35565770|35568133 and Z:54674624|54755962 have no protein-coding potential. These findings provide valuable evidence for a better understanding of the specific functions and molecular mechanisms of circRNAs underlying avian adipogenesis.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.

Carboxylesterase 1d (Ces1d) does not contribute to cholesteryl ester hydrolysis in the liver

The liver is the central organ regulating cholesterol synthesis, storage, transport, and elimination. Mouse carboxylesterase 1d (Ces1d) and its human ortholog CES1 have been described to possess lipase activity and play roles in hepatic triacylglycerol metabolism and VLDL assembly. It has been proposed that Ces1d/CES1 might also catalyze cholesteryl ester (CE) hydrolysis in the liver and thus be responsible for the hydrolysis of HDL-derived CE; this could contribute to the final step in the reverse cholesterol transport (RCT) pathway, wherein cholesterol is secreted from the liver into bile and feces, either directly or after conversion to water-soluble bile salts. However, the proposed function of Ces1d/CES1 as a CE hydrolase is controversial. In this study, we interrogated the role hepatic Ces1d plays in cholesterol homeostasis using liver-specific Ces1d-deficient mice. We rationalized that if Ces1d is a major hepatic CE hydrolase, its absence would (1) reduce in vivo RCT flux and (2) provoke liver CE accumulation after a high-cholesterol diet challenge. We found that liver-specific Ces1d-deficient mice did not show any difference in the flux of in vivo HDL-to-feces RCT nor did it cause additional liver CE accumulation after high-fat, high-cholesterol Western-type diet feeding. These findings challenge the importance of Ces1d as a major hepatic CE hydrolase.

Profiling of MicroRNA Targets Using Activity-Based Protein Profiling: Linking Enzyme Activity to MicroRNA-185 Function

MicroRNAs (miRNAs) act as cellular signal transducers through repression of protein translation. Elucidating targets using bioinformatics and traditional quantitation methods is often insufficient to uncover global miRNA function. Herein, alteration of protein function caused by miRNA-185 (miR-185), an immunometabolic miRNA, was determined using activity-based protein profiling, transcriptomics, and lipidomics. Fluorophosphonate-based activity-based protein profiling of miR-185-induced changes to human liver cells revealed that exclusively metabolic serine hydrolase enzymes were regulated in activity, some with roles in lipid and endocannabinoid metabolism. Lipidomic analysis linked enzymatic changes to levels of cellular lipid species, such as components of very-low-density lipoprotein particles. Additionally, inhibition of one miR-185 target, monoglyceride lipase, led to decreased hepatitis C virus levels in an infectious model. Overall, the approaches used here were able to identify key functional changes in serine hydrolases caused by miR-185 that are targetable pharmacologically, such that a small molecule inhibitor can recapitulate the miRNA phenotype.

Spatially Resolved Activity-based Proteomic Profiles of the Murine Small Intestinal Lipases

Despite the crucial function of the small intestine in nutrient uptake our understanding of the molecular events underlying the digestive function is still rudimentary. Recent studies demonstrated that enterocytes do not direct the entire dietary triacylglycerol toward immediate chylomicron synthesis. Especially after high-fat challenges, parts of the resynthesized triacylglycerol are packaged into cytosolic lipid droplets for transient storage in the endothelial layer of the small intestine. The reason for this temporary storage of triacylglycerol is not completely understood. To utilize lipids from cytosolic lipid droplets for chylomicron synthesis in the endoplasmic reticulum, stored triacylglycerol has to be hydrolyzed either by cytosolic lipolysis or lipophagy. Interestingly, triacylglycerol storage and chylomicron secretion rates are unevenly distributed along the small intestine, with the proximal jejunum exhibiting the highest intermittent storage capacity. We hypothesize that correlating hydrolytic enzyme activities with the reported distribution of triacylglycerol storage and chylomicron secretion in different sections of the small intestine is a promising strategy to determine key enzymes in triacylglycerol remobilization. We employed a serine hydrolase specific activity-based labeling approach in combination with quantitative proteomics to identify and rank hydrolases based on their relative activity in 11 sections of the small intestine. Moreover, we identified several clusters of enzymes showing similar activity distribution along the small intestine. Merging our activity-based results with substrate specificity and subcellular localization known from previous studies, carboxylesterase 2e and arylacetamide deacetylase emerge as promising candidates for triacylglycerol mobilization from cytosolic lipid droplets in enterocytes.

The Impacts of Herbal Medicines and Natural Products on Regulating the Hepatic Lipid Metabolism

The dysregulation of hepatic lipid metabolism is one of the hallmarks in many liver diseases including alcoholic liver diseases (ALD) and non-alcoholic fatty liver diseases (NAFLD). Hepatic inflammation, lipoperoxidative stress as well as the imbalance between lipid availability and lipid disposal, are direct causes of liver steatosis. The application of herbal medicines with anti-oxidative stress and lipid-balancing properties has been extensively attempted as pharmaceutical intervention for liver disorders in experimental and clinical studies. Although the molecular mechanisms underlying their hepatoprotective effects warrant further exploration, increasing evidence demonstrated that many herbal medicines are involved in regulating lipid accumulation processes including hepatic lipolytic and lipogenic pathways, such as mitochondrial and peroxisomal β-oxidation, the secretion of very low density lipoprotein (VLDL), the non-esterified fatty acid (NEFA) uptake, and some vital hepatic lipogenic enzymes. Therefore, in this review, the pathways or crucial mediators participated in the dysregulation of hepatic lipid metabolism are systematically summarized, followed by the current evidences and advances in the positive impacts of herbal medicines and natural products on the lipid metabolism pathways are detailed. Furthermore, several herbal formulas, herbs or herbal derivatives, such as Erchen Dection, Danshen, resveratrol, and berberine, which have been extensively studied for their promising potential in mediating lipid metabolism, are particularly highlighted in this review.

The metabolic characteristics of susceptibility to wooden breast disease in chickens with high feed efficiency

This study was conducted to characterize metabolic differences between high feed efficiency (HFE) and low feed efficiency (LFE) chickens to investigate why feed efficient chickens are more susceptible to muscle abnormalities such as wooden breast disease. Gene expression profiles were generated by RNA sequencing of pectoralis major muscle samples from 10 HFE and 13 LFE broiler chickens selected from a modern broiler population. Metabolism-associated differentially expressed genes were identified and interpreted by Ingenuity Pathway Analysis and literature mining. Our RNA-seq data indicate decreased glycolytic capacity, increased fatty acid uptake, mitochondrial oxidation of fatty acids, and several other metabolic alterations in the pectoralis major muscle of HFE chickens. We also quantified glycogen content of the pectoralis major muscle and found that the HFE chickens had a significantly (P ≤ 0.05) lower glycogen content. Collectively, this study indicates extensive metabolic differences in the pectoralis major muscle between HFE and LFE chickens and helps identify metabolic features of susceptibility to muscle disorders in modern broiler chickens.

MicroRNA-124 Regulates Fatty Acid and Triglyceride Homeostasis

MicroRNAs (miRNAs) are part of a complex regulatory network that modulates cellular lipid metabolism. Here, we identify miR-124 as a regulator of triglyceride (TG) metabolism. This study advances our knowledge of the role of miR-124 in human hepatoma cells. Transcriptional profiling of Huh7.5 cells overexpressing miR-124 reveals enrichment for host factors involved in fatty acid oxidation among repressed miRNA targets. In addition, miR-124 down-regulates arylacetamide deacetylase (AADAC) and adipose triglyceride lipase, lipases proposed to mediate breakdown of hepatic TG stores for lipoprotein assembly and mitochondrial β-oxidation. Consistent with the inhibition of TG and fatty acid catabolism, miR-124 expression promotes cellular TG accumulation. Interestingly, miR-124 inhibits the production of hepatitis C virus, a virus that hijacks lipid pathways during its life cycle. Antiviral activity of miR-124 is consistent with repression of AADAC, a pro-viral host factor. Overall, our data highlight miR-124 as a novel regulator of TG metabolism in human hepatoma cells.

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miR-124 regulates triglyceride and fatty acid metabolism

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miR-124 represses genes associated with fatty acid and triglyceride breakdown

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miR-124 promotes triglyceride accumulation in hepatoma cells

Pharmacological intervention of liver triacylglycerol lipolysis: The good, the bad and the ugly

Excessive triacylglycerol (TG) accumulation is the distinctive feature of obesity. In the liver, sustained TG accretion leads to nonalcoholic fatty liver disease (NAFLD), eventually progressing to non-alcoholic steatohepatitis (NASH) and cirrhosis, which is associated with complications including hepatic failure, hepatocellular carcinoma and death. Pharmacological interventions are actively pursued to prevent lipid accumulation in hepatocytes and, therefore, to ameliorate the associated pathophysiological conditions. Here, we sought to provide an overview of the pharmacological approaches to up- or downregulate the expression and activities of the enzymes involved in hepatic TG hydrolysis. Fatty acids (FA) released by hydrolysis of hepatic TG can be used for β-oxidation, signaling, and for very low-density lipoprotein (VLDL)-TG synthesis. Originally, lipolysis was believed to be centered in the adipose and to be catalyzed by only two lipases, hormone-sensitive lipase (HSL) and monoacylglycerol lipase (MAGL). However, genetic ablation of HSL expression in mice failed to erase TG hydrolysis in adipocytes leading to the identification of a third lipase termed adipose triglyceride lipase (ATGL). Although these three enzymes are considered to be the main players governing lipolysis in the adipocyte, other lipolytic enzymes have been described to contribute to hepatic TG metabolism. These include adiponutrin/patatin-like phospholipase domain containing 3 (PNPLA3), some members of the carboxylesterase family (CES/Ces), arylacetamide deacetylase (AADAC), lysosomal acid lipase (LAL) and hepatic lipase (HL). This review highlights the consequences of pharmacological interventions of liver lipases that degrade TG in cytosolic lipid droplets, in the endoplasmic reticulum, in the late endosomes/lysosomes and along the secretory route.

Human Carboxylesterase 2 Reverses Obesity-Induced Diacylglycerol Accumulation and Glucose Intolerance

Serine hydrolases are a large family of multifunctional enzymes known to influence obesity. Here, we performed activity-based protein profiling to assess the functional level of serine hydrolases in liver biopsies from lean and obese humans in order to gain mechanistic insight into the pathophysiology of metabolic disease. We identified reduced hepatic activity of carboxylesterase 2 (CES2) and arylacetamide deacetylase (AADAC) in human obesity. In primary human hepatocytes, CES2 knockdown impaired glucose storage and lipid oxidation. In mice, obesity reduced CES2, whereas adenoviral delivery of human CES2 reversed hepatic steatosis, improved glucose tolerance, and decreased inflammation. Lipidomic analysis identified a network of CES2-regulated lipids altered in human and mouse obesity. CES2 possesses triglyceride and diacylglycerol lipase activities and displayed an inverse correlation with HOMA-IR and hepatic diacylglycerol concentrations in humans. Thus, decreased CES2 is a conserved feature of obesity and plays a causative role in the pathogenesis of obesity-related metabolic disturbances.

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Obesity decreases hepatic activity of AADAC and CES2 in humans

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CES2 depletion impairs lipid and glucose metabolism in primary human hepatocytes

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Human CES2 expression reverses hepatic steatosis and glucose intolerance in mice

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CES2 controls a hepatic lipid network dysregulated in human and mouse obesity

Effects of dietary supplementation with EPA and/or α-lipoic acid on adipose tissue transcriptomic profile of healthy overweight/obese women following a hypocaloric diet

In obesity, the increment of adiposity levels disrupts the whole body homeostasis, promoting an over production of oxidants and inflammatory mediators. The current study aimed to characterize the transcriptomic changes promoted by supplementation with eicosapentaenoic acid (EPA, 1.3 g/day), α-lipoic acid (0.3 g/day), or both (EPA + α-lipoic acid, 1.3 g/day + 0.3 g/day) in subcutaneous abdominal adipose tissue from overweight/obese healthy women, who followed a hypocaloric diet (30% of total energy expenditure) during ten weeks, by using a microarray approach. At the end of the intervention, a total of 33,297 genes were analyzed using Affymetrix GeneChip arrays. EPA promoted changes in extracellular matrix remodeling gene expression, besides a rise of genes associated with either chemotaxis or wound repair. α-Lipoic acid decreased expression of genes related with cell adhesion and inflammation. Furthermore, α-lipoic acid, especially in combination with EPA, upregulated the expression of genes associated with lipid catabolism while downregulated genes involved in lipids storage. Together, all these data suggest that some of the metabolic effects of EPA and α-lipoic acid could be related to their regulatory actions on adipose tissue metabolism. © 2016 BioFactors, 43(1):117-131, 2017.

Multidimensional profiling platforms reveal metabolic dysregulation caused by organophosphorus pesticides

We are environmentally exposed to countless synthetic chemicals on a daily basis, with an increasing number of these chemical exposures linked to adverse health effects. However, our understanding of the (patho)physiological effects of these chemicals remains poorly understood, due in part to a general lack of effort to systematically and comprehensively identify the direct interactions of environmental chemicals with biological macromolecules in mammalian systems in vivo. Here, we have used functional chemoproteomic and metabolomic platforms to broadly identify direct enzyme targets that are inhibited by widely used organophosphorus (OP) pesticides in vivo in mice and to determine metabolic alterations that are caused by these chemicals. We find that these pesticides directly inhibit over 20 serine hydrolases in vivo leading to widespread disruptions in lipid metabolism. Through identifying direct biological targets of OP pesticides, we show heretofore unrecognized modes of toxicity that may be associated with these agents and underscore the utility of using multidimensional profiling approaches to obtain a more complete understanding of toxicities associated with environmental chemicals.

Arylacetamide deacetylase: a novel host factor with important roles in the lipolysis of cellular triacylglycerol stores, VLDL assembly and HCV production

BACKGROUND & AIMS

Very low density lipoproteins (VLDLs) are triacylglycerol (TG)-rich lipoproteins produced by the human liver. VLDLs derive the majority of their TG cargo from the lipolysis of TG stored in hepatocellular lipid droplets (LDs). Important roles for LDs and the VLDL secretory pathway in the cell culture production of infectious hepatitis C virus (HCV) have been established. We hypothesized that TG lipolysis and VLDL production are impaired during HCV infection so that these cellular processes can be diverted towards HCV production.

METHODS

We used an HCV permissive cell culture system (JFH-1/HuH7.5 cells) to examine the relationship between TG lipolysis, VLDL assembly, and the HCV lifecycle using standard biochemical approaches.

RESULTS

Lipolysis of cellular TG and VLDL production were impaired in HCV infected cells during the early peak of viral infection. This was partially explained by an apparent deficiency of a putative TG lipase, arylacetamide deacetylase (AADAC). The re-introduction of AADAC to infected cells restored cellular TG lipolysis, indicating a role for HCV-mediated downregulation of AADAC in this process. Defective lipolysis of cellular TG stores and VLDL production were also observed in HuH7.5 cells stably expressing a short hairpin RNA targeting AADAC expression, proving AADAC deficiency contributes to these defective pathways. Finally, impaired production of HCV was observed with AADAC knockdown cells, demonstrating a role for AADAC in the HCV lifecycle.

CONCLUSIONS

This insight into the biology of HCV infection and possibly pathogenesis identifies AADAC as a novel and translationally relevant therapeutic target.

Activation of intestinal peroxisome proliferator-activated receptor-α increases high-density lipoprotein production

AIMS

Peroxisome proliferator-activated receptor (PPAR)-α is a transcription factor controlling lipid metabolism in liver, heart, muscle, and macrophages. Peroxisome proliferator-activated receptor-α activation increases plasma HDL cholesterol and exerts hypotriglyceridaemic actions via the liver. However, the intestine expresses PPAR-α, produces HDL and chylomicrons, and is exposed to diet-derived PPAR-α ligands. Therefore, we examined the effects of PPAR-α activation on intestinal lipid and lipoprotein metabolism.

METHODS AND RESULTS

The impact of PPAR-α activation was evaluated in term of HDL-related gene expression in mice, ex vivo in human jejunal biopsies and in Caco-2/TC7 cells. Apolipoprotein-AI/HDL secretion, cholesterol esterification, and trafficking were also studied in vitro. In parallel to improving plasma lipid profiles and increasing liver and intestinal expression of fatty acid oxidation genes, treatment with the dual PPAR-α/δ ligand GFT505 resulted in a more pronounced increase in plasma HDL compared with fenofibrate in mice. GFT505, but not fenofibrate, increased the expression of HDL production genes such as apolipoprotein-AI and ATP-binding cassette A1 transporter in murine intestines. A similar increase was observed upon PPAR-α activation of human biopsies and Caco-2/TC7 cells. Additionally, HDL secretion by Caco-2/TC7 cells increased. Moreover, PPAR-α activation decreased the cholesterol esterification capacity of Caco-2/TC7 cells, modified cholesterol trafficking, and reduced apolipoprotein-B secretion.

CONCLUSION

Peroxisome proliferator-activated receptor-α activation reduces cholesterol esterification, suppresses chylomicron, and increases HDL secretion by enterocytes. These results identify the intestine as a target organ of PPAR-α ligands with entero-hepatic tropism to reduce atherogenic dyslipidaemia.

A novel polymorphic allele of human arylacetamide deacetylase leads to decreased enzyme activity

Human arylacetamide deacetylase (AADAC) is responsible for the hydrolysis of clinically used drugs such as flutamide, phenacetin, and rifamycins. Our recent studies suggested that human AADAC is a relevant enzyme pharmacologically and toxicologically. To date, the genetic polymorphisms that affect enzyme activity in AADAC have been unknown. In this study, we found single-nucleotide polymorphisms in the human AADAC gene in a liver sample that showed remarkably low flutamide hydrolase activity. Among them, g.13651G > A (V281I) and g.14008T > C (X400Q) were nonsynonymous. The latter would be predicted to cause a C-terminal one-amino acid (glutamine) extension. The AADAC*2 allele (g.13651G > A) was found in all populations investigated in this study (European American, African American, Korean, and Japanese), at allelic frequencies of 52.6 to 63.5%, whereas the AADAC*3 allele (g.13651G > A/g.14008T > C) was found in European American (1.3%) and African American (2.0%) samples. COS7 cells expressing AADAC.1 (wild-type) exhibited flutamide, phenacetin, and rifampicin hydrolase activities with intrinsic clearance (CLint) values of 1.31 ± 0.06, 1.00 ± 0.02, and 0.39 ± 0.02 μl x min(-1) x unit(-1), respectively. AADAC.2, which is a protein produced from the AADAC*2 allele, showed moderately lower or similar CLint values, compared with AADAC.1, but AADAC.3 showed substantially lower CLint values (flutamide hydrolase, 0.21 ± 0.02 μl x min(-1) x unit(-1); phenacetin hydrolase, 0.12 ± 0.00 μl x min(-1) x unit(-1); rifampicin hydrolase, 0.03 ± 0.01 μl x min(-1) x unit(-1), respectively). Microsomes from a liver sample genotyped as AADAC*3/AADAC*3 showed decreased enzyme activities, compared with those genotyped as AADAC*1/AADAC*1, AADAC*1/AADAC*2, and AADAC*2/AADAC*2. In conclusion, we found an AADAC allele that yielded decreased enzyme activity. This study should provide useful information on interindividual variations in AADAC enzyme activity.

Liver triacylglycerol lipases

The hallmark of obesity and one of the key contributing factors to insulin resistance, type 2 diabetes and cardiovascular disease is excess triacylglycerol (TG) storage. In hepatocytes, excessive accumulation of TG is the common denominator of a wide range of clinicopathological entities known as nonalcoholic fatty liver disease, which can eventually progress to cirrhosis and associated complications including hepatic failure, hepatocellular carcinoma and death. A tight regulation between TG synthesis, hydrolysis, secretion and fatty acid oxidation is required to prevent lipid accumulation as well as lipid depletion from hepatocytes. Therefore, understanding the pathways that regulate hepatic TG metabolism is crucial for development of therapies to ameliorate pathophysiological conditions associated with excessive hepatic TG accumulation, including dyslipidemias, viral infection and atherosclerosis. This review highlights the physiological roles of liver lipases that degrade TG in cytosolic lipid droplets, endoplasmic reticulum, late endosomes/lysosomes and along the secretory route. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Role of endoplasmic reticulum neutral lipid hydrolases

Lipid droplets are universal intracellular organelles composed of a triglyceride, cholesteryl ester and retinyl ester core, surrounded by a monolayer of phospholipids and free (unesterified) cholesterol and lipid droplet-associated proteins. Core lipids are hydrolyzed by lipases to provide fatty acids, cholesterol and retinol for various cellular functions. In addition to cytosolic adipose triglyceride lipase and hormone-sensitive lipase, recent studies show the existence of other neutral lipid hydrolases that reside in the endoplasmic reticulum. In this review we highlight the role of these novel lipases including several members of the carboxylesterase family and enzymes termed arylacetamide deacetylase and KIAA1363/neutral cholesteryl ester hydrolase1/arylacetamide deacetylase-like 1. Some of these enzymes might be attractive targets for the treatment of dyslipidemias, viral infection and atherosclerosis.

Enzymes involved in hepatic acylglycerol metabolism in the chicken

In laying hens, massive hepatic mobilization of fatty acids is required for the synthesis of oocyte-targeted very-low density lipoproteins (VLDL). The current study aims at identification of enzymes that hydrolyze hepatic acylglycerol stores regulated in a fashion compatible with supporting enhanced VLDL synthesis. We show that unlike mammals, chickens express adipose triglyceride lipase (ATGL) also in liver, where it is upregulated by fasting, while the enzyme patatin-like phospholipase domain-containing lipase 3 (PNPLA3) is suppressed. For the first time in any system, we show that hepatic arylacetamide deacetylase (AADA) is upregulated by fasting, and that its affinity for an insoluble carboxylester substrate is compatible with an in-vivo function similar to that of ATGL. Unknown heretofore, hepatic expression of chicken AADA is estrogen-responsive, and is induced to the same degree as the stimulation of VLDL-production by estrogen. These observations support roles of chicken ATGL, PNPLA3, and AADA in acylglycerol metabolism related to the high rates of VLDL synthesis that are essential for reproduction.

Adipose triglyceride lipase is a major hepatic lipase that regulates triacylglycerol turnover and fatty acid signaling and partitioning

Despite advances in our understanding of the ways in which nutrient oversupply and triacylglycerol (TAG) anabolism contribute to hepatic steatosis, little is known about the lipases responsible for regulating hepatic TAG turnover. Recent studies have identified adipose triglyceride lipase (ATGL) as a major lipase in adipose tissue, although its role in the liver is largely unknown. Thus, we tested the contribution of ATGL to hepatic lipid metabolism and signaling. Adenovirus-mediated knockdown of hepatic ATGL resulted in steatosis in mice and decreased hydrolysis of TAG in primary hepatocyte cultures and in vitro assays. In addition to altering TAG hydrolysis, ATGL was shown to play a significant role in partitioning hydrolyzed fatty acids between metabolic pathways. Although ATGL gain and loss of function did not alter hepatic TAG secretion, fatty acid oxidation was increased by ATGL overexpression and decreased by ATGL knockdown. The effects on fatty acid oxidation coincided with decreased expression of peroxisome proliferator-activated receptor α (PPAR-α) and its target genes in mice with suppressed hepatic ATGL expression. However, PPAR-α agonism was unable to normalize the effects of ATGL knockdown on PPAR-α target gene expression, and this suggests that ATGL influences PPAR-α activity independently of ligand-induced activation.

CONCLUSION

Taken together, these data show that ATGL is a major hepatic TAG lipase that plays an integral role in fatty acid partitioning and signaling to control energy metabolism.

Secretion of triacylglycerol-poor VLDL particles from McA-RH7777 cells expressing human hepatic lipase

Hepatic lipase (HL) plays a role in the catabolism of apolipoprotein (apo)B-containing lipoproteins through its lipolytic and ligand-binding properties. We describe a potential intracellular role of HL in the assembly and secretion of VLDL. Transient or stable expression of HL in McA-RH7777 cells resulted in decreased (by 40%) incorporation of [(3)H]glycerol into cell-associated and secreted triacylglycerol (TAG) relative to control cells. However, incorporation of [(35)S]methionine/cysteine into cell and medium apoB-100 was not decreased by HL expression. The decreased (3)H-TAG synthesis/secretion in HL expressing cells was not attributable to decreased expression of genes involved in lipogenesis. Fractionation of medium revealed that the decreased [(3)H]TAG from HL expressing cells was mainly attributable to decreased VLDL. Expression of catalytically-inactive HL (HL(SG)) (Ser-145 at the catalytic site was substituted with Gly) in the cells also resulted in decreased secretion of VLDL-[(3)H]TAG. Examination of lumenal contents of microsomes showed a 40% decrease in [(3)H]TAG associated with lumenal lipid droplets in HL or HL(SG) expressing cells as compared with control. The microsomal membrane-associated [(3)H]TAG was decreased by 50% in HL expressing cells but not in HL(SG) expressing cells. Thus, expression of HL, irrespective of its lipolytic function, impairs formation of VLDL precursor [(3)H]TAG in the form of lumenal lipid droplets. These results suggest that HL expression in McA-RH7777 cells result in secretion of [(3)H]TAG-poor VLDL.