Ablation of histone methyltransferase Suv39h2 in hepatocytes attenuates NASH in mice.

AIMS: Non-alcoholic steatohepatitis (NASH) is characterized by aberrant lipid metabolism in hepatocytes. We investigated the involvement of a histone H3K9 methyltransferase Suv39h2 in the pathogenesis of NASH. METHODS AND MATERIALS: NASH is induced by feeding the mice with a high-fat high-carbohydrate (HFHC) diet or a high-fat choline-deficient amino acid defined (HFD-CDAA) diet. The Suv39h2f/f mice were crossbred with the Alb-Cre mice to specifically delete Suv39h2 in hepatocytes. KEY FINDINGS: Ablation of Suv39h2 in hepatocytes improved insulin sensitivity of the mice fed either the HFHC diet or the CDAA-HFD diet. Importantly, Suv39h2 deletion significantly ameliorated NAFLD as evidenced by reduced lipid accumulation, inflammation, and fibrosis in the liver. RNA-seq uncovered Vanin-1 (Vnn1) as a novel transcriptional target for Suv39h2. Mechanistically, Suv39h2 repressed Vnn1 transcription in hepatocytes exposed to free fatty acids. Consistently, Vanin-1 knockdown normalized lipid accumulation in Suv39h2-null hepatocytes. Importantly, a significant correlation between Suv39h2, Vanin-1, and hepatic triglyceride levels was identified in NASH patients. SIGNIFICANCE: Our study uncovers a novel mechanism whereby Suv39h2 may contribute to NASH pathogenesis and suggests that targeting the Suv39h2-Vanin-1 axis may yield novel therapeutic solutions against NASH.

Gp78 deficiency in hepatocytes alleviates hepatic ischemia-reperfusion injury via suppressing ACSL4-mediated ferroptosis.

Ferroptosis, which is driven by iron-dependent lipid peroxidation, plays an essential role in liver ischemia-reperfusion injury (IRI) during liver transplantation (LT). Gp78, an E3 ligase, has been implicated in lipid metabolism and inflammation. However, its role in liver IRI and ferroptosis remains unknown. Here, hepatocyte-specific gp78 knockout (HKO) or overexpressed (OE) mice were generated to examine the effect of gp78 on liver IRI, and a multi-omics approach (transcriptomics, proteomics, and metabolomics) was performed to explore the potential mechanism. Gp78 expression decreased after reperfusion in LT patients and mice with IRI, and gp78 expression was positively correlated with liver damage. Gp78 absence from hepatocytes alleviated liver damage in mice with IRI, ameliorating inflammation. However, mice with hepatic gp78 overexpression showed the opposite phenotype. Mechanistically, gp78 overexpression disturbed lipid homeostasis, remodeling polyunsaturated fatty acid (PUFA) metabolism, causing oxidized lipids accumulation and ferroptosis, partly by promoting ACSL4 expression. Chemical inhibition of ferroptosis or ACSL4 abrogated the effects of gp78 on ferroptosis and liver IRI. Our findings reveal a role of gp78 in liver IRI pathogenesis and uncover a mechanism by which gp78 promotes hepatocyte ferroptosis by ACSL4, suggesting the gp78-ACSL4 axis as a feasible target for the treatment of IRI-associated liver damage.

Mitochondrial hydrogen peroxide production by pyruvate dehydrogenase and α-ketoglutarate dehydrogenase in oxidative eustress and oxidative distress.

Pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KGDH) are vital entry points for monosaccharides and amino acids into the Krebs cycle and thus integral for mitochondrial bioenergetics. Both complexes produce mitochondrial hydrogen peroxide (mH2O2) and are deactivated by electrophiles. Here, we provide an update on the role of PDH and KGDH in mitochondrial redox balance and their function in facilitating metabolic reprogramming for the propagation of oxidative eustress signals in hepatocytes and how defects in these pathways can cause liver diseases. PDH and KGDH are known to account for ∼45% of the total mH2O2 formed by mitochondria and display rates of production several-fold higher than the canonical source complex I. This mH2O2 can also be formed by reverse electron transfer (RET) in vivo, which has been linked to metabolic dysfunctions that occur in pathogenesis. However, the controlled emission of mH2O2 from PDH and KGDH has been proposed to be fundamental for oxidative eustress signal propagation in several cellular contexts. Modification of PDH and KGDH with protein S-glutathionylation (PSSG) and S-nitrosylation (PSNO) adducts serves as a feedback inhibitor for mH2O2 production in response to glutathione (GSH) pool oxidation. PSSG and PSNO adduct formation also reprogram the Krebs cycle to generate metabolites vital for interorganelle and intercellular signaling. Defects in the redox modification of PDH and KGDH cause the over generation of mH2O2, resulting in oxidative distress and metabolic dysfunction-associated fatty liver disease (MAFLD). In aggregate, PDH and KGDH are essential platforms for emitting and receiving oxidative eustress signals.

Discovery and SAR analysis of phenylbenzo[d][1,3]dioxole-based proprotein convertase subtilisin/kexin type 9 inhibitors.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a novel therapeutic target for the development of cholesterol-lowering drugs. In the discovery of PCSK9/LDLR (low-density lipoprotein receptor) protein-protein interaction (PPI) impairing small molecules, a total of 47 phenylbenzo[d][1,3] dioxole-based compounds were designed and synthesised. The result revealed that the 4-chlorobenzyl substitution in the amino group is important for the PPI disrupting activity. In the hepatocyte-based functional tests, active compounds such as A12, B1, B3, B4 and B14, restored the LDLR levels on the surface of hepatic HepG2 cells and increased extracellular LDL uptake in the presence of PCSK9. It is notable that molecule B14 exhibited good performance in all the evaluations. Collectively, novel structures targeting PCSK9/LDLR PPI have been developed with hypolipidemic potential. Further structural modification of derived active compounds is promising in the discovery of lead compounds with improved activity for the treatment of hyperlipidaemia-related disorders.

Cell proliferation effects of S-allyl-L-cysteine are associated with phosphorylation of janus kinase 2, insulin-like growth factor type-I receptor tyrosine kinase, and extracellular signal-regulated kinase 2 in primary cultures of adult rat hepatocytes.

The cell proliferation effect of S-allyl-L-cysteine (SAC) and its mechanisms were examined in primary cultures of adult rat hepatocytes. In serum-free cultivation, SAC (10-6 M)-stimulated hepatocytes showed significant proliferation compared to control at 5-h culture; the effect was dependent on the culture time and the dose of SAC (EC50 value 8.58 × 10-8 M). In addition, SAC-stimulated hepatocytes significantly increased mRNA expression levels of c-Myc and c-Fos at 1 h and cyclin B1 at 3.5 and 4 h, respectively. In contrast, alliin and allicin, structural analogs of SAC, did not show these effects observed with SAC. The SAC-induced hepatocyte proliferation effects were completely suppressed by monoclonal antibodies against growth hormone receptor and insulin-like growth factor type-I (IGF-I) receptor, respectively. Furthermore, the Janus kinase 2 (JAK2) inhibitor TG101209, phospholipase C (PLC) inhibitor U-73122, IGF-I receptor tyrosine kinase (RTK) inhibitor AG538, PI3 kinase inhibitor LY294002, MEK inhibitor PD98059, and mTOR inhibitor rapamycin completely suppressed the SAC-induced hepatocyte proliferation. JAK2 (p125 kDa) phosphorylation in cultured hepatocytes peaked 5 min after SAC stimulation. SAC-induced IGF-I RTK (p95 kDa) and ERK2 (p42 kDa) phosphorylation had slower rises than JAK2, peaking at 20 and 30 min, respectively. These results indicate that SAC promoted cell proliferation by growth hormone receptor/JAK2/PLC pathway activation followed by activation of the IGF-I RTK/PI3K/ERK2/mTOR pathway in primary cultures of adult rat hepatocytes.

Loss of mitochondrial ATPase ATAD3A contributes to nonalcoholic fatty liver disease through accumulation of lipids and damaged mitochondria.

Mitochondrial ATPase ATAD3A is essential for cholesterol transport, mitochondrial structure, and cell survival. However, the relationship between ATAD3A and nonalcoholic fatty liver disease (NAFLD) is largely unknown. In this study, we found that ATAD3A was upregulated in the progression of NAFLD in livers from rats with diet-induced nonalcoholic steatohepatitis and in human livers from patients diagnosed with NAFLD. We used CRISPR-Cas9 to delete ATAD3A in Huh7 human hepatocellular carcinoma cells and used RNAi to silence ATAD3A expression in human hepatocytes isolated from humanized liver-chimeric mice to assess the influence of ATAD3A deletion on liver cells with free cholesterol (FC) overload induced by treatment with cholesterol plus 58035, an inhibitor of acetyl-CoA acetyltransferase. Our results showed that ATAD3A KO exacerbated FC accumulation under FC overload in Huh7 cells and also that triglyceride levels were significantly increased in ATAD3A KO Huh7 cells following inhibition of lipolysis mediated by upregulation of lipid droplet-binding protein perilipin-2. Moreover, loss of ATAD3A upregulated autophagosome-associated light chain 3-II protein and p62 in Huh7 cells and fresh human hepatocytes through blockage of autophagosome degradation. Finally, we show the mitophagy mediator, PTEN-induced kinase 1, was downregulated in ATAD3A KO Huh7 cells, suggesting that ATAD3A KO inhibits mitophagy. These results also showed that loss of ATAD3A impaired mitochondrial basal respiration and ATP production in Huh7 cells under FC overload, accompanied by downregulation of mitochondrial ATP synthase. Taken together, we conclude that loss of ATAD3A promotes the progression of NAFLD through the accumulation of FC, triglyceride, and damaged mitochondria in hepatocytes.

Natural (dihydro)phenanthrene plant compounds are direct activators of AMPK through its allosteric drug and metabolite-binding site.

AMP-activated protein kinase (AMPK) is a central energy sensor that coordinates the response to energy challenges to maintain cellular ATP levels. AMPK is a potential therapeutic target for treating metabolic disorders, and several direct synthetic activators of AMPK have been developed that show promise in preclinical models of type 2 diabetes. These compounds have been shown to regulate AMPK through binding to a novel allosteric drug and metabolite (ADaM)-binding site on AMPK, and it is possible that other molecules might similarly bind this site. Here, we performed a high-throughput screen with natural plant compounds to identify such direct allosteric activators of AMPK. We identified a natural plant dihydrophenathrene, Lusianthridin, which allosterically activates and protects AMPK from dephosphorylation by binding to the ADaM site. Similar to other ADaM site activators, Lusianthridin showed preferential activation of AMPKß1-containing complexes in intact cells and was unable to activate an AMPKß1 S108A mutant. Lusianthridin dose-dependently increased phosphorylation of acetyl-CoA carboxylase in mouse primary hepatocytes, which led to a corresponding decrease in de novo lipogenesis. This ability of Lusianthridin to inhibit lipogenesis was impaired in hepatocytes from ß1 S108A knock-in mice and mice bearing a mutation at the AMPK phosphorylation site of acetyl-CoA carboxylase 1/2. Finally, we show that activation of AMPK by natural compounds extends to several analogs of Lusianthridin and the related chemical series, phenanthrenes. The emergence of natural plant compounds that regulate AMPK through the ADaM site raises the distinct possibility that other natural compounds share a common mechanism of regulation.

A Major Intestinal Catabolite of Quercetin Glycosides, 3-Hydroxyphenylacetic Acid, Protects the Hepatocytes from the Acetaldehyde-Induced Cytotoxicity through the Enhancement of the Total Aldehyde Dehydrogenase Activity.

Aldehyde dehydrogenases (ALDHs) are the major enzyme superfamily for the aldehyde metabolism. Since the ALDH polymorphism leads to the accumulation of acetaldehyde, we considered that the enhancement of the liver ALDH activity by certain food ingredients could help prevent alcohol-induced chronic diseases. Here, we evaluated the modulating effects of 3-hydroxyphenylacetic acid (OPAC), the major metabolite of quercetin glycosides, on the ALDH activity and acetaldehyde-induced cytotoxicity in the cultured cell models. OPAC significantly enhanced the total ALDH activity not only in mouse hepatoma Hepa1c1c7 cells, but also in human hepatoma HepG2 cells. OPAC significantly increased not only the nuclear level of aryl hydrocarbon receptor (AhR), but also the AhR-dependent reporter gene expression, though not the nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent one. The pretreatment of OPAC at the concentration required for the ALDH upregulation completely inhibited the acetaldehyde-induced cytotoxicity. Silencing AhR impaired the resistant effect of OPAC against acetaldehyde. These results strongly suggested that OPAC protects the cells from the acetaldehyde-induced cytotoxicity, mainly through the AhR-dependent and Nrf2-independent enhancement of the total ALDH activity. Our findings suggest that OPAC has a protective potential in hepatocyte models and could offer a new preventive possibility of quercetin glycosides for targeting alcohol-induced chronic diseases.

Obesity induced Ext1 reduction mediates the occurrence of NAFLD.

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder with intricate etiology. It is closely associated with metabolic syndrome, insulin resistance and endoplasmic reticulum (ER) stress. Exostosin1 (Ext1) is an ER-resident transmembrane glycosyltransferase, which plays an important role in ER homeostasis. Loss-of-function mutations in Ext1 link to hereditary multiple exostosis (HME). The present research was undertaken to identify the effect of Ext1 in the progress of NAFLD. High-fat-diet induced mice obesity, hepatic steatosis and decreased hepatic Ext1 expression. In consistent with evaluation of NAFLD mice possessing down-regulated Ext1 expression, free fatty acid (FFA) treatment blunted Ext1 expression in hepatocytes. In human subjects, HME patients presented elevated fasting blood glucose-one of the criteria that define insulin resistance. In vitro experiments, Ext1 deficiency promoted FFA-induced insulin resistance in hepatocytes by analysis of glycogen storage and hallmarks of gluconeogenesis, ascertaining its association with insulin resistance. Mechanically, Ext1 silencing exacerbated ER stress triggered by FFA, which severely disrupted autophagy in hepatocytes, and thereby accelerated the progression of NAFLD. In conclusion, our study demonstrates a beneficial role for Ext1 during the development of NAFLD, which establishes a novel correlation between Ext1 and ER stress-induced perturbations of autophagy during NAFLD progression.

Identification and characterization of potent, selective, and efficacious inhibitors of human arylamine N-acetyltransferase 1.

Arylamine N-acetyltransferase 1 (NAT1) plays a pivotal role in the metabolism of carcinogens and is a drug target for cancer prevention and/or treatment. A protein-ligand virtual screening of 2 million chemicals was ranked for predicted binding affinity towards the inhibition of human NAT1. Sixty of the five hundred top-ranked compounds were tested experimentally for inhibition of recombinant human NAT1 and N-acetyltransferase 2 (NAT2). The most promising compound 9,10-dihydro-9,10-dioxo-1,2-anthracenediyl diethyl ester (compound 10) was found to be a potent and selective NAT1 inhibitor with an in vitro IC50 of 0.75 µM. Two structural analogs of this compound were selective but less potent for inhibition of NAT1 whereas a third structural analog 1,2-dihydroxyanthraquinone (a compound 10 hydrolysis product also known as Alizarin) showed comparable potency and efficacy for human NAT1 inhibition. Compound 10 inhibited N-acetylation of the arylamine carcinogen 4-aminobiphenyl (ABP) both in vitro and in DNA repair-deficient Chinese hamster ovary (CHO) cells in situ stably expressing human NAT1 and CYP1A1. Compound 10 and Alizarin effectively inhibited NAT1 in cryopreserved human hepatocytes whereas inhibition of NAT2 was not observed. Compound 10 caused concentration-dependent reductions in DNA adduct formation and DNA double-strand breaks following metabolism of aromatic amine carcinogens beta-naphthylamine and/or ABP in CHO cells. Compound 10 inhibited proliferation and invasion in human breast cancer cells and showed selectivity towards tumorigenic versus non-tumorigenic cells. In conclusion, our study identifies potent, selective, and efficacious inhibitors of human NAT1. Alizarin's ability to inhibit NAT1 could reduce breast cancer metastasis particularly to bone.

Curcumin Ameliorates Doxorubicin-Induced Cardiotoxicity and Hepatotoxicity Via Suppressing Oxidative Stress and Modulating iNOS, NF-κB, and TNF-α in Rats.

Doxorubicin (DOX) is one of the widely used anti-tumor drugs. However, DOX-induced cardiotoxicity (DIC) and hepatotoxicity (DIH) are among the side effects that limited its therapeutic efficiency and clinical applicability. This study aimed to investigate the cardioprotective and hepatoprotective potentials of curcumin (CMN)-a bioactive polyphenolic compound-in alleviating DOX-induced cardiotoxicity (DIC) and hepatotoxicity (DIH) in male rats. A single intraperitoneal (i.p.) dose of DOX (20 mg/kg) was used to induce DIC and DIH. DOX-intoxicated rats were co-treated with CMN (100 mg/kg, oral) for 10 days before and 5 days after a single dose of DOX. We studied the anti-inflammatory and anti-oxidative activities of CMN on biochemical and immunohistochemical aspects. DOX disrupted cardiac and hepatic functions and stimulated oxidative stress and inflammation in both tissues that was confirmed biochemically and immunohistochemically. DOX enhanced inflammatory interferon-gamma (IFN-γ) and upregulated immunoexpression of nuclear factor-κB (NF-κB), inducible nitric oxide synthase (iNOS), and tumor necrosis factor-alpha (TNF-α). DOX induced structural alterations in both cardiac and hepatic tissues. CMN demonstrated cardioprotective potential through reducing cardiac troponin I (cTn1) and aspartate amino transaminase (AST). In addition, CMN significantly ameliorated liver function through decreasing alanine amino transaminase (ALT) and, gamma-glutamyl transferase (GGT), total cholesterol (TC), and triglycerides (TG). CMN demonstrated anti-inflammatory potential through decreasing IFN-γ levels and immunoexpression of iNOS, NF-κB, and TNF-α. Histopathologically, CMN restored DOX-associated cardiac and liver structural alterations. CMN showed anti-oxidative and anti-inflammatory potentials in both the cardiac and hepatic tissues. In addition, cTn1, IFN-γ, and AST could be used as blood-based biomarkers.

Activation of UQCRC2-dependent mitophagy by tetramethylpyrazine inhibits MLKL-mediated hepatocyte necroptosis in alcoholic liver disease.

Hepatocyte necroptosis is a core pathogenetic event during alcoholic liver disease. This study was aimed to explore the potential of tetramethylpyrazine (TMP), an active hepatoprotective ingredient extracted from Ligusticum Wallichii Franch, in limiting alcohol-triggered hepatocyte necroptosis and further specify the molecular mechanism. Results revealed that TMP reduced activation of receptor-interacting protein kinase 1 (RIPK1)/RIPK3 necrosome in ethanol-exposed hepatocytes and phosphorylation of mixed-lineage kinase domain-like protein (MLKL), which thereby diminished necroptosis and leakage of damage-associated molecular patterns. Suppression on mitochondrial translocation of p-MLKL by TMP contributed to recovery of mitochondrial function in ethanol-damaged hepatocytes. TMP also disrupted necroptotic signal loop by interrupting mitochondrial reactive oxygen species (ROS)-dependent positive feedback between p-MLKL and RIPK1/RIPK3 necrosome. Further, TMP promoted clearance of impaired mitochondria in ethanol-incubated hepatocytes via restoring PINK1/parkin-mediated mitophagy. Ubiquinol-cytochrome c reductase core protein 2 (UQCRC2) was downregulated in ethanol-exposed hepatocytes, which was restored after TMP treatment. In vitro UQCRC2 knockdown lowered the capacities of TMP in reducing mitochondrial ROS accumulation, relieving mitochondria damage, and enhancing PINK1/parkin-mediated mitophagy in ethanol-exposed hepatocytes. Analogously, systematic UQCRC2 knockdown interrupted the actions of TMP to trigger autophagic signal, repress necroptotic signal, and protect against alcoholic liver injury, inflammation, and ROS overproduction. In conclusion, this work concluded that TMP rescued UQCRC2 expression in ethanol-challenged hepatocytes, which contributed to necroptosis inhibition by facilitating PINK1/parkin-mediated mitophagy. These findings uncovered a potential molecular pharmacological mechanism underlying the hepatoprotective action of TMP and suggested TMP as a promising therapeutic candidate for alcoholic liver disease.

Antioxidant, Anti-Inflammatory, and Antidiabetic Activities of Bioactive Compounds from the Fruits of Livistona chinensis Based on Network Pharmacology Prediction.

In this study, a chemical investigation on the fruits of Livistona chinensis (FLC) led to the isolation and identification of 45 polyphenols and 5 alkaloids, including two new compounds (Livischinol (1) and Livischinine A (46)), an undescribed compound (47) and 47 known compounds. FLC was predicted with novel potential antidiabetic function by collecting and analyzing the potential targets of the ingredients. Compound 32 exhibited significant α-glucosidase inhibitory activity (IC50 = 5.71 µM) and 1, 6, and 44 showed the PTP1B inhibitory activity with IC50 values of 9.41-22.19 µM, while that of oleanolic acid was 28.58 µM. The competitive inhibitors of PTP1B (compounds 1 and 44) formed strong binding affinity, with catalytic active sites, proved by kinetic analysis, fluorescence spectra measurements, and computational simulations, and stimulated glucose uptake in the insulin-resistant HepG2 cells at the dose of 50 µM. In addition, FLC was rich in antioxidant and anti-inflammatory bioactive compounds so that they could be developed as nutraceuticals against diabetes.

Carnosol alleviates nonalcoholic fatty liver disease by inhibiting mitochondrial dysfunction and apoptosis through targeting of PRDX3.

Mitochondrial dysfunction is a major factor in nonalcoholic fatty liver disease (NAFLD), preceding insulin resistance and hepatic steatosis. Carnosol (CAR) is a kind of diterpenoid with antioxidant, anti-inflammatory and antitumor activities. Peroxiredoxin 3 (PRDX3), a mitochondrial H2O2-eliminating enzyme, undergoes overoxidation and subsequent inactivation under oxidative stress. The purpose of this study was to investigate the protective effect of the natural phenolic compound CAR on NAFLD via PRDX3. Mice fed a high-fat diet (HFD) and AML-12 cells treated with palmitic acid (PA) were used to detect the molecular mechanism of CAR in NAFLD. We found that pharmacological treatment with CAR notably moderated HFD- and PA- induced steatosis and liver injury, as shown by biochemical assays, Oil Red O and Nile Red staining. Further mechanistic investigations revealed that CAR exerted anti-NAFLD effects by inhibiting mitochondrial oxidative stress, perturbation of mitochondrial dynamics, and apoptosis in vivo and in vitro. The decreased protein and mRNA levels of PRDX3 were accompanied by intense oxidative stress after PA intervention. Interestingly, CAR specifically bound PRDX3, as shown by molecular docking assays, and increased the expression of PRDX3. However, the hepatoprotection of CAR in NAFLD was largely abolished by specific PRDX3 siRNA, which increased mitochondrial dysfunction and exacerbated apoptosis in vitro. In conclusion, CAR suppressed lipid accumulation, mitochondrial dysfunction and hepatocyte apoptosis by activating PRDX3, mitigating the progression of NAFLD, and thus, CAR may represent a promising candidate for clinical treatment of steatosis.

PinX1 Depletion Improves Liver Injury in a Mouse Model of Nonalcoholic Fatty Liver Disease via Increasing Telomerase Activity and Inhibiting Apoptosis.

PIN2/TRF1-interacting telomerase inhibitor 1 (PinX1) can inhibit tumor growth by inhibiting telomerase activity. However, only few studies investigated the expression and function of PinX1 in nonalcoholic fatty liver disease (NAFLD). Thus, here we aimed to explore the roles of PinX1 in high-fat diet (HFD)-induced NAFLD in mice and in isolated hepatocytes. The mRNA expression of PinX1 and mTERT as well as telomere length were analyzed by RT-PCR. Pathological changes were detected by HE staining and oil red O staining. Triglyceride, cholesterol, alanine aminotransferase, aspartic aminotransferase, and telomerase activity were detected by ELISA. Hepatocyte apoptosis was determined by TUNEL and flow cytometry, and protein expression was analyzed by western blotting. We found that the expression of PinX1 was upregulated in the HFD group compared with the WT group. PinX1 knockout improved HFD-induced liver injury in mice and exhibited less lipid accumulation in hepatocytes. Moreover, telomere length, telomerase activity, and mTERT expression were significantly reduced in liver tissues of HFD-induced mice and palmitic acid-induced hepatocytes, while PinX1 knockout attenuated the effect. Furthermore, HFD-induced PinX1-/- mice exhibited less hepatocyte apoptosis than HFD-induced WT mice. Besides, PinX1 knockout inhibited the increase of cleaved caspase-3 and cleaved PARP expression in vivo and in vitro. Moreover, inhibition of mTERT reversed the effect of PinX1 knockout in hepatocytes. Taken together, our findings indicate that PinX1 promotes hepatocyte apoptosis and lipid accumulation by decreasing telomere length and telomerase activity in the development of NAFLD. PinX1 might be a target for the treatment of NAFLD.

CELSR2 deficiency suppresses lipid accumulation in hepatocyte by impairing the UPR and elevating ROS level.

Cadherin EGF LAG seven-pass G-type receptor 2 (CELSR2), a mammalian orthologue of drosophila flamingo, belongs to the cadherin subfamily. CELSR2 mainly function in neural development and cilium polarity. Recent studies showed that the CELSR2 gene is related to many human diseases, including coronary artery disease, idiopathic scoliosis, and cancer. Genome-Wide Association Studies data showed that SNP in the CELSR2-PSRC1-SORT1 gene loci has a strong association with circulating lipid levels and coronary artery disease. However, the function and underlying mechanism of CELSR2 in hepatic lipid metabolism remain unknown. Here, we found that CELSR2 expression is decreased in the liver of NAFLD/NASH patients and db/db mice. Depletion of CELSR2 significantly decreased the lipid accumulation in hepatocytes by suppressing the expression of lipid synthesis enzymes. Moreover, CELSR2 deficiency impaired the physiological unfolded protein response (UPR), which damages the ER homeostasis, and elevates the reactive oxygen species (ROS) level by decreasing the antioxidant expression. Scavenging of ROS by N-acetylcysteine treatment could restore the decreased lipid accumulation of CELSR2 knockdown cells. Furthermore, CELSR2 loss impaired cell survival by suppressing cell proliferation and promoting apoptosis. Our results uncovered a new role of CELSR2 in regulating lipid homeostasis and UPR, suggesting CELSR2 may be a new therapeutic target for non-alcoholic fatty liver disease.

Genotoxicity evaluation using primary hepatocytes isolated from rhesus macaque (Macaca mulatta).

Non-human primates (NHPs) have played a vital role in fundamental, pre-clinical, and translational studies because of their high physiological and genetic similarity to humans. Here, we report a method to isolate primary hepatocytes from the livers of rhesus macaques (Macaca mulatta) after in situ whole liver perfusion. Isolated primary macaque hepatocytes (PMHs) were treated with various compounds known to have different pathways of genotoxicity/carcinogenicity and the resulting DNA damage was evaluated using the high-throughput CometChip assay. The comet data were quantified using benchmark dose (BMD) modeling and the BMD50 values for treatments of PMHs were compared with those generated from primary human hepatocytes (PHHs) in our previous study (Seo et al. Arch Toxicol 2020, 2207-2224). The results showed that despite varying CYP450 enzyme activities, PMHs had the same sensitivity and specificity as PHHs in detecting four indirect-acting (i.e., requiring metabolic activation) and seven direct-acting genotoxicants/carcinogens, as well as five non-carcinogens that are negative or equivocal for genotoxicity in vivo. The BMD50 estimates and their confidence intervals revealed species differences for DNA damage potency, especially for direct-acting compounds. The present study provides a practical method for maximizing the use of animal tissues by isolating primary hepatocytes from NHPs. Our data support the use of PMHs as a reliable surrogate of PHHs for evaluating the genotoxic hazards of chemical substances for humans.

Metabolic activation and deactivation of dietary-derived coumarin mediated by cytochrome P450 enzymes in rat and human liver preparations.

Dietary-derived coumarin is of clinical interest for its potential hepatotoxicity in humans because such toxicity is especially evident in rats. In this study, the oxidative metabolism of coumarin to active coumarin 3,4-epoxide (as judged by the formation rates of o-hydroxyphenylacetic acid) and excretable 7-hydroxycoumarin was investigated in liver fractions from rats and humans. In rat liver microsomes, the formation rate of o-hydroxyphenylacetic acid (~6 pmol/min/mg microsomal protein) from coumarin at 10 µM was dependent on the presence of liver cytosolic fractions. Rat hepatocytes mediated similar formation rates of o-hydroxyphenylacetic acid and 7-hydroxycoumarin (~0.1 nmol/hr/106 cells) at 0.20-20 µM coumarin. Human hepatocytes mediated the biotransformation of coumarin to o-hydroxyphenylacetic acid at roughly similar rates to those of rat hepatocytes. In contrast, the formation rates of 7-hydroxycoumarin by human hepatocytes were around 10-fold higher at ~1 nmol/hr/106 cells. In the presence of human liver cytosolic fractions, the oxidative formation rate of o-hydroxyphenylacetic acid was relatively high in cytochrome P450 (P450) 1A2-rich human liver microsomes. The inhibitory effects of furafylline/α-naphthoflavone and 8-methoxypsoralen, P450 1A2 and 2A6 inhibitors, respectively, were seen on the rates of o-hydroxyphenylacetic and 7-hydroxylation formations, respectively, in pooled human liver microsomes. Human liver microsomes selectively inactivated for P450 1A2 and 2A6 showed low rates of o-hydroxyphenylacetic acid and 7-hydroxylation formation (~20-30% of control), respectively. Among the P450 isoforms tested, recombinant human P450 1A2 predominantly mediated o-hydroxyphenylacetic formation. These results suggested that the metabolic activation and deactivation of coumarin were mediated mainly by P450 1A2 and 2A6 enzymes, respectively. The metabolic oxidation of coumarin via 3,4-epoxidation forming o-hydroxyphenylacetic acid could inform individual human risk assessments of dietary-derived coumarin, for which hepatotoxicity is especially evident in rats.

Reaction Phenotyping of Low-Turnover Compounds in Long-Term Hepatocyte Cultures Through Persistent Selective Inhibition of Cytochromes P450.

Recognizing the challenges of determining the relative contribution of different drug metabolizing enzymes to the metabolism of slowly metabolized compounds, a cytochrome P450 reaction phenotyping (CRP) method using cocultured human hepatocytes (HEPATOPAC) has been established. In this study, the emphasis on the relative contribution of different cytochrome P450 (P450) isoforms was assessed by persistently inhibiting P450 isoforms over 7 days with human HEPATOPAC. P450 isoform-selective inhibition was achieved with the chemical inhibitors furafylline (CYP1A2), tienilic acid (CYP2C9), (+)-N-3-benzylnirvanol (CYP2C19), paroxetine (CYP2D6), azamulin (CYP3A), and a combination of 1-aminobenzotriazole and tienilic acid (broad spectrum inhibition of P450s). We executed this CRP method using HEPATOPAC by optimizing for the choice of P450 inhibitors, their selectivity, and the temporal effect of inhibitor concentrations on maintaining selectivity of inhibition. In general, the established CRP method using potent and selective chemical inhibitors allows to measure the relative contribution of P450s and to calculate the fraction of metabolism (f m) of low-turnover compounds. Several low-turnover compounds were used to validate this CRP method by determining their hepatic intrinsic clearance and f m, with comparison with literature values. We established the foundation of a robust CRP for low-turnover compound test system which can be expanded to include inhibition of other drug metabolizing enzymes. This generic CRP assay, using human long-term hepatocyte cultures, will be an essential tool in drug development for new chemical entities in the quantitative assessment of the risk as a victim of drug-drug interactions. SIGNIFICANCE STATEMENT: An ongoing trend is to develop drug candidates which have limited metabolic clearance. The current studies report a generic approach to conducting reaction phenotyping studies with human HEPATOPAC, focusing on P450 metabolism of low-turnover compounds. Potent and selective chemical inhibitors were used to assess the relative contribution of the major human P450s. Validation was achieved by confirming hepatic intrinsic clearance and fraction of metabolism for previously reported low-turnover compounds. This approach is adaptable for assessment of all drug metabolizing enzymes.

A luminescence-based protocol for assessing fructose metabolism via quantification of ketohexokinase enzymatic activity in mouse or human hepatocytes.

Ketohexokinase (KHK) catalyzes the first step of fructose metabolism. Inhibitors of KHK enzymatic activity are being evaluated in clinical trials for the treatment of non-alcoholic fatty liver disease (NAFLD) and diabetes. Here, we present a luminescence-based protocol to quantify KHK activity. The accuracy of this technique has been validated using knockdown and overexpression of KHK in vivo and in vitro. The specificity of the assay has been verified using 3-O-methyl-D-fructose, a non-metabolizable analog of fructose, heat inactivation of hexokinases, and depletion of potassium. For complete details on the use of this protocol, please refer to Damen et al. (2021).