S-Adenosylmethionine increases circulating very-low density lipoprotein clearance in non-alcoholic fatty liver disease

Molecular mechanism and therapeutic significance of essential amino acids in metabolically associated fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), also known as metabolically associated fatty liver disease (MAFLD), is a systemic metabolic disease characterized by lipid accumulation in the liver, lipid toxicity, insulin resistance, intestinal dysbiosis, and inflammation that can progress from simple steatosis to nonalcoholic steatohepatitis (NASH) and even cirrhosis or cancer. It is the most prevalent illness threatening world health. Currently, there are almost no approved drug interventions for MAFLD, mainly dietary changes and exercise to control weight and regulate metabolic disorders. Meanwhile, the metabolic pathway involved in amino acid metabolism also influences the onset and development of MAFLD in the body, and most amino acid metabolism takes place in the liver. Essential amino acids are those amino acids that must be supplemented from outside the diet and that cannot be synthesized in the body or cannot be synthesized at a rate sufficient to meet the body's needs, including leucine, isoleucine, valine (collectively known as branched-chain amino acids), tryptophan, phenylalanine (which are aromatic amino acids), histidine, methionine, threonine and lysine. The metabolic balance of the body is closely linked to these essential amino acids, and essential amino acids are closely linked to the pathophysiological process of MAFLD. In this paper, we will focus on the metabolism of essential amino acids in the body and further explore the therapeutic strategies for MAFLD based on the studies conducted in recent years.

In Vivo Tissue Lipid Uptake in Antisense Oligonucleotide (ASO)-Treated Mice

The prevalence of obesity has increased to pandemic levels over the past years. Associated comorbidities linked with the accumulation of lipids in different tissues and blood are responsible for the high mortality in these patients. The increased dietary lipid uptake contributes to these metabolic diseases. Identifying which pathways might be dysregulated in these patients will contribute to find new therapeutic targets. Thus, here, a protocol to follow up the distribution of dietary lipids in blood and tissues is provided. For this, radiolabeled triglyceride in olive oil is administered by oral gavage. To ascertain more precisely the capacity of each tissue for fatty acid uptake, not considering the intestinal barrier, the intravenous (IV) administration of radiolabeled lipids is also described.

Liver PP2A-Cα Protects From Parenteral Nutrition-associated Hepatic Steatosis

BACKGROUND & AIMS

Parenteral nutrition (PN) is a lifesaving therapy for patients with intestinal failure. Hepatic steatosis is a potentially fatal complication of long-term PN, but the involved pathological mechanisms are incompletely unclarified. Herein, we identify the role of protein phosphatase 2A (PP2A) in the pathogenesis of parenteral nutrition-associated hepatic steatosis (PNAHS).

METHODS

Proteomic/phosphoproteomic analyses of liver samples from patients with PNAHS were applied to identify the mechanism of PNAHS. Total parenteral nutrition (TPN) mice model, in vivo, and in vitro experiments were used to assess the effect of PP2A-Cα on liver fatty acid metabolism.

RESULTS

Reduced expression of PP2A-Cα (catalytic subunit) enhanced activation of serine/threonine kinase Akt2 and decreased activation of adenosine monophosphate-activated protein kinase (AMPK) were associated with hepatic steatosis in patients with PNAHS. Mice given PN for 14 days developed hepatic steatosis, down-regulation of PP2A-Cα, activation of Akt2, and inhibition of AMPK. Hepatocyte-specific deletion of PP2A-Cα in mice given PN exacerbated Akt2 activation, AMPK inhibition, and hepatic steatosis through an effect on fatty acid degradation, whereas hepatocyte-specific PP2A-Cα overexpression significantly ameliorated hepatic steatosis accompanied with Akt2 suppression and AMPK activation. Additionally, pharmacological activation of Akt2 in mice overexpressing PP2A-Cα led to the aggravation of hepatic steatosis.

CONCLUSIONS

Our findings demonstrate that hepatic PP2A-Cα serves as a protective factor of PNAHS due to ameliorating hepatic steatosis and improving liver function. Our study provides a strong rationale that PP2A-Cα may be involved in the pathogenesis of PNAHS.

Characterization and Roles of Membrane Lipids in Fatty Liver Disease

Obesity has reached global epidemic proportions and it affects the development of insulin resistance, type 2 diabetes, fatty liver disease and other metabolic diseases. Membrane lipids are important structural and signaling components of the cell membrane. Recent studies highlight their importance in lipid homeostasis and are implicated in the pathogenesis of fatty liver disease. Here, we discuss the numerous membrane lipid species and their metabolites including, phospholipids, sphingolipids and cholesterol, and how dysregulation of their composition and physiology contribute to the development of fatty liver disease. The development of new genetic and pharmacological mouse models has shed light on the role of lipid species on various mechanisms/pathways; these lipids impact many aspects of the pathophysiology of fatty liver disease and could potentially be targeted for the treatment of fatty liver disease.

Methionine cycle in nonalcoholic fatty liver disease and its potential applications

As a chronic metabolic disease affecting epidemic proportions worldwide, the pathogenesis of Nonalcoholic Fatty Liver Disease (NAFLD) is not clear yet. There is also a lack of precise biomarkers and specific medicine for the diagnosis and treatment of NAFLD. Methionine metabolic cycle, which is critical for the maintaining of cellular methylation and redox state, is involved in the pathophysiology of NAFLD. However, the molecular basis and mechanism of methionine metabolism in NAFLD are not completely understood. Here, we mainly focus on specific enzymes that participates in methionine cycle, to reveal their interconnections with NAFLD, in order to recognize the pathogenesis of NAFLD from a new angle and at the same time, explore the clinical characteristics and therapeutic strategies.

Perilipins at a glance

Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling molecules. While compositional differences in the phospholipid monolayer or neutral lipid core of LDs impact their metabolism and function, the proteome of LDs has emerged as a major influencer in all aspects of LD biology. The perilipins (PLINs) are the most studied and abundant proteins residing on the LD surface. This Cell Science at a Glance and the accompanying poster summarize our current knowledge of the common and unique features of the mammalian PLIN family of proteins, the mechanisms through which they affect cell metabolism and signaling, and their links to disease.

Phosphatidylethanolamine N-methyltransferase: from Functions to Diseases

Locating on endoplasmic reticulum and mitochondria associated membrane, Phosphatidylethanolamine N-methyltransferase (PEMT), catalyzes phosphatidylethanolamine methylation to phosphatidylcholine. As the only endogenous pathway for choline biosynthesis in mammals, the dysregulation of PEMT can lead to imbalance of phospholipid metabolism. Dysregulation of phospholipid metabolism in the liver or heart can lead to deposition of toxic lipid species that adversely result in dysfunction of hepatocyte/cardiomyocyte. Studies have shown that PEMT^-/- mice increased susceptibility of diet-induced fatty liver and steatohepatitis. However, knockout of PEMT protects against diet-induced atherosclerosis, diet-induced obesity, and insulin resistance. Thus, novel insights to the function of PEMT in various organs should be summarized. Here, we reviewed the structural and functional properties of PEMT, highlighting its role in the pathogenesis of obesity, liver diseases, cardiovascular diseases, and other conditions.

Combined Metabolic Activators Decrease Liver Steatosis by Activating Mitochondrial Metabolism in Hamsters Fed with a High-Fat Diet

Although the prevalence of non-alcoholic fatty liver disease (NAFLD) continues to increase, there is no effective treatment approved for this condition. We previously showed, in high-fat diet (HFD)-fed mice, that the supplementation of combined metabolic activators (CMA), including nicotinamide riboside (NAD+ precursor) and the potent glutathione precursors serine and N-acetyl-l-cysteine (NAC), significantly decreased fatty liver by promoting fat oxidation in mitochondria. Afterwards, in a one-day proof-of-concept human supplementation study, we observed that this CMA, including also L-carnitine tartrate (LCT), resulted in increased fatty acid oxidation and de novo glutathione synthesis. However, the underlying molecular mechanisms associated with supplementation of CMA have not been fully elucidated. Here, we demonstrated in hamsters that the chronic supplementation of this CMA (changing serine for betaine) at two doses significantly decreased hepatic steatosis. We further generated liver transcriptomics data and integrated these data using a liver-specific genome-scale metabolic model of liver tissue. We systemically determined the molecular changes after the supplementation of CMA and found that it activates mitochondria in the liver tissue by modulating global lipid, amino acid, antioxidant and folate metabolism. Our findings provide extra evidence about the beneficial effects of a treatment based on this CMA against NAFLD.

Obeticholic Acid Inhibits Anxiety via Alleviating Gut Microbiota-Mediated Microglia Accumulation in the Brain of High-Fat High-Sugar Diet Mice

Anxiety is one of the complications of metabolic disorders (MDs). Obeticholic acid (OCA), the bile acids (BAs) derivative, is a promising agent for improving MDs in association with gut dysbiosis. Yet, its protective effect on MDs-driven anxiety remains unknown. Here, we assessed the serum biochemical parameters and behavioral performance by open field and Morris water maze tests in HFHS diet-induced MDs mice after OCA intervention for nine and 18 weeks. Moreover, antibiotics intervention for microbial depletion was conducted simultaneously. We found that OCA treatment inhibited the initiation and progression of anxiety in HFHS diet-MDs mice via a microbiota–BAs–brain axis: OCA decreased the neuroinflammatory microglia and IL-1β expression in the hippocampus, reversed intestinal barrier dysfunction and serum proinflammatory LPS to a normal level, modified the microbial community, including the known anxiety-related Rikenellaceae and Alistipes, and improved the microbial metabolites especially the increased BAs in feces and circulation. Moreover, the OCA-reversed bile acid taurocholate linked disordered serum lipid metabolites and indole derivatives to anxiety as assessed by network analysis. Additionally, microbial depletion with antibiotics also improved the anxiety, microgliosis and BAs enrichment in the experimental MDs mice. Together, these findings provide microbiota–BAs–brain axis as a novel therapeutic target for MDs-associated neuropsychiatric disorders.

Study of the Relationship Between Serum Amino Acid Metabolism and Lymph Node Metastasis in Patients with Colorectal Cancer

Purpose

Lymph node metastasis is one of the important prognostic factors of colorectal cancer, and an important index of individualized treatment. The purpose of this study is to use metabonomics to identify potential molecular markers of lymph node metastasis in colorectal cancer (CRC).

Patients and Methods

Peripheral blood samples of 223 CRC patients were collected. The metabolic levels of amino acids and carnitine in peripheral blood of CRC patients, with and without lymph node metastasis, were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Results

The results show that there were significant differences in the levels of serum amino acids and carnitine between lymph node metastatic patients and lymph node non-metastatic patients. The diagnostic model that was constructed by 9 types of serum metabolites has a high diagnostic ability.

Conclusion

LC-MS/MS is a detection method that has a broad application in predicting CRC prognosis, individualized treatment, and in studying the mechanism of lymph node metastasis.

Relationship between circulating miR-132 and non-alcoholic fatty liver disease in a Chinese population

Background

Non-invasive diagnostic markers are of great importance for early screening nonalcoholic fatty liver disease (NAFLD). MicroRNAs (miRNAs) play significant roles in many metabolic disease, including NAFLD. Therefore, this study focusd on a Chinese population to explore the possible correlation between circulating miR-132 and NAFLD.

Results

Serum miR-132 was positively associated with NAFLD in non-type 2 diabetes mellitus (T2DM) groups by logistic regression (OR = 3.082 [1.057, 8.988], P = 0.039) after adjusting age, sex, and body mass index (BMI). Additionally, in non-T2DM subgroup, after adjusting age, sex, bmi, serum miR-132 was significantly associated with ALT (β ± SE = 0.005 ± 0.002, P = 0.018), TG (β ± SE = 0.072 ± 0.029, P = 0.015), FPG (β ± SE = 0.123 ± 0.058, P = 0.036), γ-GT (β ± SE = 0.002 ± 0.001, P = 0.047), apoE (β ± SE = 0.038 ± 0.002, P = 0.017) .

Conclusions

Serum miR-132 was found to be associated with NAFLD risk in a Chinese cross-section study. This finding provides a prospective research direction for early screening and diagnosing NAFLD.

Design, synthesis and evaluation of 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione-Based fibrates as potential hypolipidemic and hepatoprotective agents

Six novel target compounds 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADT) based fibrates were synthesized and evaluated. All the synthesized compounds were preliminarily screened by using the Triton WR-1339-induecd hyperlipidemia model, in which T1 exhibited more potent hypolipidemic property than positive drug fenofibrate (FF). T1 also significantly decreased serum triglycerides (TG), total cholesterol (TC) and low density lipoprotein cholesterin (LDL) in methionine solution (Mets) induced hyperlipidemic mice. Moreover, hepatic transaminases (AST and ALT) were obviously ameliorated after treatment with T1 and the histological observation indicated that T1 ameliorated the injury in liver tissue and inhibited the hepatic lipid accumulation. In the livers of T1-administrated rat, the levels of PPARα related to lipids metabolism were up-regulated. Additional effects such as antioxidant, anti-inflammatory and H₂S releasing action confirmed and reinforced the activity of T1 as a potential multifunctional hypolipidemic and hepatoprotective agent.

Total liver phosphatidylcholine content associates with non-alcoholic steatohepatitis and glycine N-methyltransferase expression

BACKGROUND & AIMS

Alterations in liver phosphatidylcholine (PC) metabolism have been implicated in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Although genetic variation in the phosphatidylethanolamine N-methyltransferase (PEMT) enzyme synthesizing PC has been associated with disease, the functional mechanism linking PC metabolism to the pathogenesis of non-alcoholic steatohepatitis (NASH) remains unclear.

METHODS

Serum PC levels and liver PC contents were measured using proton nuclear magnetic resonance (NMR) spectroscopy in 169 obese individuals [age 46.6 ± 10 (mean ± SD) years, BMI 43.3 ± 6 kg/m² , 53 men and 116 women] with histological assessment of NAFLD; 106 of these had a distinct liver phenotype. All subjects were genotyped for PEMT rs7946 and liver mRNA expression of PEMT and glycine N-methyltransferase (GNMT) was analysed.

RESULTS

Liver PC content was lower in those with NASH (P = 1.8 x 10^-6 ) while serum PC levels did not differ between individuals with NASH and normal liver (P = 0.591). Interestingly, serum and liver PC did not correlate (r_s  = -0.047, P = 0.557). Serum PC and serum cholesterol levels correlated strongly (r_s  = 0.866, P = 7.1 x 10^-49 ), while liver PC content did not correlate with serum cholesterol (r_s  = 0.065, P = 0.413). Neither PEMT V175M genotype nor PEMT expression explained the association between liver PC content and NASH. Instead, liver GNMT mRNA expression was decreased in those with NASH (P = 3.8 x 10^-4 ) and correlated with liver PC content (r_s  = 0.265, P = 0.001).

CONCLUSIONS

Decreased liver PC content in individuals with the NASH is independent of PEMT V175M genotype and could be partly linked to decreased GNMT expression.

miR-873-5p targets mitochondrial GNMT-Complex II interface contributing to non-alcoholic fatty liver disease

Objective

Non-alcoholic fatty liver disease (NAFLD) is a complex pathology in which several dysfunctions, including alterations in metabolic pathways, mitochondrial functionality and unbalanced lipid import/export, lead to lipid accumulation and progression to inflammation and fibrosis. The enzyme glycine N-methyltransferase (GNMT), the most important enzyme implicated in S-adenosylmethionine catabolism in the liver, is downregulated during NAFLD progression. We have studied the mechanism involved in GNMT downregulation by its repressor microRNA miR-873-5p and the metabolic pathways affected in NAFLD as well as the benefit of recovery GNMT expression.

Methods

miR-873-5p and GNMT expression were evaluated in liver biopsies of NAFLD/NASH patients. Different in vitro and in vivo NAFLD murine models were used to assess miR-873-5p/GNMT involvement in fatty liver progression through targeting of the miR-873-5p as NAFLD therapy.

Results

We describe a new function of GNMT as an essential regulator of Complex II activity in the electron transport chain in the mitochondria. In NAFLD, GNMT expression is controlled by miR-873-5p in the hepatocytes, leading to disruptions in mitochondrial functionality in a preclinical murine non-alcoholic steatohepatitis (NASH) model. Upregulation of miR-873-5p is shown in the liver of NAFLD/NASH patients, correlating with hepatic GNMT depletion. Importantly, NASH therapies based on anti-miR-873-5p resolve lipid accumulation, inflammation and fibrosis by enhancing fatty acid β-oxidation in the mitochondria. Therefore, miR-873-5p inhibitor emerges as a potential tool for NASH treatment.

Conclusion

GNMT participates in the regulation of metabolic pathways and mitochondrial functionality through the regulation of Complex II activity in the electron transport chain. In NAFLD, GNMT is repressed by miR-873-5p and its targeting arises as a valuable therapeutic option for treatment.

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The microRNA miR-873-5p is upregulated in human and murine NAFLD/NASH livers.

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miR-873-5p upregulation downregulates GNMT in the liver.

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miR-873-5p inhibition reduces liver steatosis, inflammation and fibrosis in in vivo NAFLD mouse models.

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GNMT is a hepatic metabolic hub with mitochondria activity through the regulation of Complex II of the ETC.

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Mitochondrial GNMT deficiency compromises ETC functionality and metabolism.

SEIPIN overexpression in the liver may alleviate hepatic steatosis by influencing the intracellular calcium level

SEIPIN deficiency leads to a severe lipodystrophic phenotype with loss of fat tissue. Interestingly, SEIPIN knockout in non-adipocytes is reported to promote intracellular triacylglycerol (TG) accumulation. However, the underlying mechanisms remain unclear at present. Here, we have shown that SEIPIN knockdown and overexpression exert opposite effects on hepatic lipometabolism. Our experimental data suggest that depletion of SEIPIN induces an increase in intracellular TG via activation of ER stress while its overexpression triggers a decrease in the intracellular TG content via increasing PGC-1α, which drives increased mitochondrial activity. Adeno-associated virus-mediated SEIPIN overexpression alleviated high fat diet-induced hepatosteatosis in mice. The collective results indicate that the effects of SEIPIN on TG and PGC-1α are dependent on calcium concentrations, signifying regulatory activity on hepatic lipometabolism through alterations in the intracellular calcium level, and support the potential utility of modulating intracellular SEIPIN and calcium levels as novel therapeutic strategies for fatty liver.

p107 Deficiency Increases Energy Expenditure by Inducing Brown-Fat Thermogenesis and Browning of White Adipose Tissue

SCOPE

The tumor suppressor p107, a pocket protein member of the retinoblastoma susceptibility protein family, plays an important role in the cell cycle and cellular adipocyte differentiation. Nonetheless, the mechanism by which it influences whole body Energy homeostasis is unknown.

METHODS AND RESULTS

The phenotype of p107 knockout (KO) mixed-background C57BL6/129 mice phenotype is studied by focusing on the involvement of white and brown adipose tissue (WAT and BAT) in energy metabolism. It is shown that p107 KO mice are leaner and have high-fat diet resistence. This phenomenon is explained by an increase of energy expenditure. The higher energy expenditure is caused by the activation of thermogenesis and may be mediated by both BAT and the browning of WAT. Consequently, it leads to the resistance of p107 KO mice to high-fat diet effects, prevention of liver steatosis, and improvement of the lipid profile and glucose homeostasis.

CONCLUSION

These data allowed the unmasking of a mechanism by which a KO of p107 prevents diet-induced obesity by increasing energy expenditure via increased thermogenesis in BAT and browning of WAT, indicating the relevance of p107 as a modulator of metabolic activity of both brown and white adipocytes. Therefore, it can be targeted for the development of new therapies to ameliorate the metabolic syndrome.

Deregulation of methionine metabolism as determinant of progression and prognosis of hepatocellular carcinoma

The under-regulation of liver-specific MAT1A gene codifying for S-adenosylmethionine (SAM) synthesizing isozymes MATI/III, and the up-regulation of widely expressed MAT2A, MATII isozyme occurs in hepatocellular carcinoma (HCC). MATα1:MATα2 switch strongly contributes to the fall in SAM liver content both in rodent and human liver carcinogenesis. SAM administration to carcinogen-treated animals inhibits hepatocarcinogenesis. The opposite occurs in Mat1a-KO mice, in which chronic SAM deficiency is followed by HCC development. This review focuses upon the changes, induced by the MATα1:MATα2 switch, involved in HCC development. In association with MATα1:MATα2 switch there occurs, in HCC, global DNA hypomethylation, decline of DNA repair, genomic instability, and deregulation of different signaling pathways such as overexpression of c-MYC (avian myelocytomatosis viral oncogene homolog), increase of polyamine (PA) synthesis and RAS/ERK (Harvey murine sarcoma virus oncogene homolog/extracellular signal-regulated kinase), IKK/NF-kB (I-k kinase beta/nuclear factor kB), PI3K/AKT, and LKB1/AMPK axes. Furthermore, a decrease in MATα1 expression and SAM level induces HCC cell proliferation and survival. SAM treatment in vivo and enforced MATα1 overexpression or MATα2 inhibition, in cultured HCC cells, prevent these changes. A negative correlation of MATα1:MATα2 and MATI/III:MATII ratios with cell proliferation and genomic instability and a positive correlation with apoptosis and global DNA methylation are present in human HCC. Altogether, these data suggest that the decrease of SAM level and the deregulation of MATs are potential therapeutic targets for HCC.

Glycine N-methyltransferase deletion in mice diverts carbon flux from gluconeogenesis to pathways that utilize excess methionine cycle intermediates

Glycine N-methyltransferase (GNMT) is the most abundant liver methyltransferase regulating the availability of the biological methyl donor, S-adenosylmethionine (SAM). Moreover, GNMT has been identified to be down-regulated in hepatocellular carcinoma (HCC). Despite its role in regulating SAM levels and association of its down-regulation with liver tumorigenesis, the impact of reduced GNMT on metabolic reprogramming before the manifestation of HCC has not been investigated in detail. Herein, we used ²H/¹³C metabolic flux analysis in conscious, unrestrained mice to test the hypothesis that the absence of GNMT causes metabolic reprogramming. GNMT-null (KO) mice displayed a reduction in blood glucose that was associated with a decline in both hepatic glycogenolysis and gluconeogenesis. The reduced gluconeogenesis was due to a decrease in liver gluconeogenic precursors, citric acid cycle fluxes, and anaplerosis and cataplerosis. A concurrent elevation in both hepatic SAM and metabolites of SAM utilization pathways was observed in the KO mice. Specifically, the increase in metabolites of SAM utilization pathways indicated that hepatic polyamine synthesis and catabolism, transsulfuration, and de novo lipogenesis pathways were increased in the KO mice. Of note, these pathways utilize substrates that could otherwise be used for gluconeogenesis. Also, this metabolic reprogramming occurs before the well-documented appearance of HCC in GNMT-null mice. Together, these results indicate that GNMT deletion promotes a metabolic shift whereby nutrients are channeled away from glucose formation toward pathways that utilize the elevated SAM.

S-Adenosylmethionine attenuates bile duct early warm ischemia reperfusion injury after rat liver transplantation

Warm ischemia reperfusion injury (IRI) plays a key role in biliary complication, which is a substantial vulnerability of liver transplantation. The early pathophysiological changes of IRI are characterized by an excessive inflammatory response. S-Adenosylmethionine (SAM) is an important metabolic intermediate that modulates inflammatory reactions; however, its role in bile duct warm IRI is not known. In this study, male rats were treated with or without SAM (170 μmol/kg body weight) after orthotopic autologous liver transplantation. The histopathological observations showed that bile duct injury in the IRI group was more serious than in the SAM group. The alanine aminotransferase (ALT), alkaline phosphatase (ALP) and direct bilirubin (DBIL) levels in the serum of the IRI group were significantly increased compared to the SAM group (P < .05). Simultaneously, SAM effectively improved the survival of the transplant recipients. Furthermore, the H₂O₂ and malondialdehyde (MDA) of the IRI group were much higher compared to the SAM group (P < .05). The GSH/GSSG ratio in the SAM group was significantly increased by SAM treatment compared to the IRI group (P < .05). SAM administration significantly inhibited macrophage infiltration in liver and bile duct tissues, down-regulated TNF-α levels and up-regulated IL-10 expression in bile duct tissues compared to the IRI group (P < .05). The number of apoptotic biliary epithelial cells and caspase-3-positive cells in IRI rat livers were much higher compared to those in SAM-treated rats at 24 h after liver transplantation (P < .05). These data suggested that SAM protected bile ducts against warm IRI by suppressing oxidative stress, inflammatory reactions and apoptosis of biliary epithelial cells after liver transplantation.α.

IMM-H007, a new therapeutic candidate for nonalcoholic fatty liver disease, improves hepatic steatosis in hamsters fed a high-fat diet

Nonalcoholic fatty liver disease (NAFLD), the most common chronic liver disease in humans, is characterized by the accumulation of triacylglycerols (TGs) in hepatocytes. We tested whether 2′,3′,5′‐tri‐acetyl‐N6‐(3‐hydroxylaniline) adenosine (IMM‐H007) can eliminate hepatic steatosis in hamsters fed a high‐fat diet (HFD), as a model of NAFLD. Compared with HFD‐only controls, IMM‐H007 treatment significantly lowered serum levels of TG, total cholesterol, and free fatty acids (FFAs) in hamsters fed the HFD, with a prominent decrease in levels of serum transaminases and fasting insulin, without affecting fasting glucose levels. Moreover, ¹H‐MRI and histopathological analyses revealed that hepatic lipid accumulation and fibrosis were improved by IMM‐H007 treatment. These changes were accompanied by improvement of insulin resistance and oxidative stress, and attenuation of inflammation. IMM‐H007 reduced expression of proteins involved in uptake of hepatic fatty acids and lipogenesis, and increased very low density lipoprotein secretion and expression of proteins responsible for fatty acid oxidation and autophagy. In studies in vivo, IMM‐H007 inhibited fatty acid import into hepatocytes and liver lipogenesis, and concomitantly stimulated fatty acid oxidation, autophagy, and export of hepatic lipids. These data suggest that IMM‐H007 resolves hepatic steatosis in HFD‐fed hamsters by the regulation of lipid metabolism. Thus, IMM‐H007 has therapeutic potential for NAFLD.

Hypothalamic AMPK-ER Stress-JNK1 Axis Mediates the Central Actions of Thyroid Hormones on Energy Balance

Thyroid hormones (THs) act in the brain to modulate energy balance. We show that central triiodothyronine (T3) regulates de novo lipogenesis in liver and lipid oxidation in brown adipose tissue (BAT) through the parasympathetic (PSNS) and sympathetic nervous system (SNS), respectively. Central T3 promotes hepatic lipogenesis with parallel stimulation of the thermogenic program in BAT. The action of T3 depends on AMP-activated protein kinase (AMPK)-induced regulation of two signaling pathways in the ventromedial nucleus of the hypothalamus (VMH): decreased ceramide-induced endoplasmic reticulum (ER) stress, which promotes BAT thermogenesis, and increased c-Jun N-terminal kinase (JNK) activation, which controls hepatic lipid metabolism. Of note, ablation of AMPKα1 in steroidogenic factor 1 (SF1) neurons of the VMH fully recapitulated the effect of central T3, pointing to this population in mediating the effect of central THs on metabolism. Overall, these findings uncover the underlying pathways through which central T3 modulates peripheral metabolism.

Hepatic p63 regulates steatosis via IKKβ/ER stress

p53 family members control several metabolic and cellular functions. The p53 ortholog p63 modulates cellular adaptations to stress and has a major role in cell maintenance and proliferation. Here we show that p63 regulates hepatic lipid metabolism. Mice with liver-specific p53 deletion develop steatosis and show increased levels of p63. Down-regulation of p63 attenuates liver steatosis in p53 knockout mice and in diet-induced obese mice, whereas the activation of p63 induces lipid accumulation. Hepatic overexpression of N-terminal transactivation domain TAp63 induces liver steatosis through IKKβ activation and the induction of ER stress, the inhibition of which rescues the liver functions. Expression of TAp63, IKKβ and XBP1s is also increased in livers of obese patients with NAFLD. In cultured human hepatocytes, TAp63 inhibition protects against oleic acid-induced lipid accumulation, whereas TAp63 overexpression promotes lipid storage, an effect reversible by IKKβ silencing. Our findings indicate an unexpected role of the p63/IKKβ/ER stress pathway in lipid metabolism and liver disease.

The critical role of phosphatidylcholine and phosphatidylethanolamine metabolism in health and disease

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most abundant phospholipids in all mammalian cell membranes. In the 1950s, Eugene Kennedy and co-workers performed groundbreaking research that established the general outline of many of the pathways of phospholipid biosynthesis. In recent years, the importance of phospholipid metabolism in regulating lipid, lipoprotein and whole-body energy metabolism has been demonstrated in numerous dietary studies and knockout animal models. The purpose of this review is to highlight the unappreciated impact of phospholipid metabolism on health and disease. Abnormally high, and abnormally low, cellular PC/PE molar ratios in various tissues can influence energy metabolism and have been linked to disease progression. For example, inhibition of hepatic PC synthesis impairs very low density lipoprotein secretion and changes in hepatic phospholipid composition have been linked to fatty liver disease and impaired liver regeneration after surgery. The relative abundance of PC and PE regulates the size and dynamics of lipid droplets. In mitochondria, changes in the PC/PE molar ratio affect energy production. We highlight data showing that changes in the PC and/or PE content of various tissues are implicated in metabolic disorders such as atherosclerosis, insulin resistance and obesity. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Multi-omics analyses reveal metabolic alterations regulated by hepatitis B virus core protein in hepatocellular carcinoma cells

Chronic hepatitis B virus (HBV) infection is partly responsible for hepatitis, fatty liver disease and hepatocellular carcinoma (HCC). HBV core protein (HBc), encoded by the HBV genome, may play a significant role in HBV life cycle. However, the function of HBc in the occurrence and development of liver disease is still unclear. To investigate the underlying mechanisms, HBc-transfected HCC cells were characterized by multi-omics analyses. Combining proteomics and metabolomics analyses, our results showed that HBc promoted the expression of metabolic enzymes and the secretion of metabolites in HCC cells. In addition, glycolysis and amino acid metabolism were significantly up-regulated by HBc. Moreover, Max-like protein X (MLX) might be recruited and enriched by HBc in the nucleus to regulate glycolysis pathways. This study provides further insights into the function of HBc in the molecular pathogenesis of HBV-induced diseases and indicates that metabolic reprogramming appears to be a hallmark of HBc transfection.

Glycine N-methyltransferase deficiency in female mice impairs insulin signaling and promotes gluconeogenesis by modulating the PI3K/Akt pathway in the liver

Background

Glycine N-methyltransferase (GNMT) is abundantly expressed in the normal liver but is down-regulated in liver cancer tissues. GNMT knockout (Gnmt−/−) mice can spontaneously develop chronic hepatitis, fatty liver, and liver cancer. We previously demonstrated that hepatic GNMT is decreased in high-fat-diet-induced type 2 diabetes mellitus, but its contribution to metabolic syndrome is unclear. Here we show that GNMT modulates key aspects of metabolic syndrome in mice.

Methods

Eleven-week-old Gnmt−/− and wild-type (WT) mice with a C57BL/6 genetic background were used in this study. The metabolic defects of GNMT deficiency were measured by glucose and insulin tolerance tests, lipid homeostasis, gluconeogenesis, and insulin signaling.

Results

Gnmt−/− mice, especially females, exhibited glucose intolerance and insulin resistance. However, their body fat and lean mass, food and water intakes, and energy expenditure did not differ from those of WT mice. In addition, glucose-stimulated insulin secretion and insulin-stimulated glucagon secretion were normal in the serum and pancreatic islets of Gnmt−/− mice. Importantly, we found that GNMT deficiency increased lipogenesis and triglycerides in the liver. The elevated triglycerides disrupted the ability of insulin to induce Akt and S6 ribosomal protein phosphorylation, and then triggered insulin resistance and gluconeogenesis in female Gnmt−/− mice.

Conclusions

Our data indicate that hepatic GNMT regulates lipid and glucose homeostasis, and provide insight into the development of insulin resistance through modulating the PI3K/Akt pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0278-8) contains supplementary material, which is available to authorized users.

The Oncogene PDRG1 Is an Interaction Target of Methionine Adenosyltransferases

Methionine adenosyltransferases MAT I and MAT III (encoded by Mat1a) catalyze S-adenosylmethionine synthesis in normal liver. Major hepatic diseases concur with reduced levels of this essential methyl donor, which are primarily due to an expression switch from Mat1a towards Mat2a. Additional changes in the association state and even in subcellular localization of these isoenzymes are also detected. All these alterations result in a reduced content of the moderate (MAT I) and high Vmax (MAT III) isoenzymes, whereas the low Vmax (MAT II) isoenzyme increases and nuclear accumulation of MAT I is observed. These changes derive in a reduced availability of cytoplasmic S-adenosylmethionine, together with an effort to meet its needs in the nucleus of damaged cells, rendering enhanced levels of certain epigenetic modifications. In this context, the putative role of protein-protein interactions in the control of S-adenosylmethionine synthesis has been scarcely studied. Using yeast two hybrid and a rat liver library we identified PDRG1 as an interaction target for MATα1 (catalytic subunit of MAT I and MAT III), further confirmation being obtained by immunoprecipitation and pull-down assays. Nuclear MATα interacts physically and functionally with the PDRG1 oncogene, resulting in reduced DNA methylation levels. Increased Pdrg1 expression is detected in acute liver injury and hepatoma cells, together with decreased Mat1a expression and nuclear accumulation of MATα1. Silencing of Pdrg1 expression in hepatoma cells alters their steady-state expression profile on microarrays, downregulating genes associated with tumor progression according to GO pathway analysis. Altogether, the results unveil the role of PDRG1 in the control of the nuclear methylation status through methionine adenosyltransferase binding and its putative collaboration in the progression of hepatic diseases.

Herbal medicines and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), which is characterized by excessive fat accumulation in the liver of patients who consume little or no alcohol, becomes increasingly common with rapid economic development. Long-term excess fat accumulation leads to NAFLD and represents a global health problem with no effective therapeutic approach. NAFLD is considered to be a series of complex, multifaceted pathological processes involving oxidative stress, inflammation, apoptosis, and metabolism. Over the past decades, herbal medicines have garnered growing attention as potential therapeutic agents to prevent and treat NAFLD, due to their high efficacy and low risk of side effects. In this review, we evaluate the use of herbal medicines (including traditional Chinese herbal formulas, crude extracts from medicinal plants, and pure natural products) to treat NAFLD. These herbal medicines are natural resources that can inform innovative drug research and the development of treatments for NAFLD in the future.

B vitamin treatments modify the risk of myocardial infarction associated with a MTHFD1 polymorphism in patients with stable angina pectoris

BACKGROUND

Methylenetetrahydrofolate dehydrogenase (MTHFD1) catalyzes three sequential reactions that metabolize derivatives of tetrahydrofolate (THF) in folate-dependent one-carbon metabolism. Impaired MTHFD1 flux has been linked to disturbed lipid metabolism and oxidative stress. However, limited information is available on its relation to the development of atherothrombotic cardiovascular disease.

METHODS AND RESULTS

We explored the association between a MTHFD1 polymorphism (rs1076991 C > T) and acute myocardial infarction (AMI), and potential effect modifications by folic acid/B12 and/or vitamin B6 treatment in suspected stable angina pectoris patients (n = 2381) participating in the randomized Western Norway B Vitamin Intervention Trial (WENBIT). During the median follow-up of 4.9 years 204 participants (8.6%) suffered an AMI. After adjusting for established CVD risk factors, the MTHFD1 polymorphism was significantly associated with AMI (HR: 1.49; 95% CI, 1.23-1.81). A similar association was observed among patients allocated to treatment with vitamin B6 alone (HR: 1.53; 95% CI, 1.01-2.31), and an even stronger relationship was seen in patients treated with both vitamin B6 and folic acid/B12 (HR: 2.35; 95% CI, 1.55-3.57). However, no risk association between the MTHFD1 polymorphism and AMI was seen in patients treated with placebo (HR: 1.29; 95% CI, 0.86-1.93) or folic acid/B12 (1.17; 95% CI, 0.83-1.65).

CONCLUSION

A common and functional MTHFD1 polymorphism is associated with increased risk of AMI, although the risk seems to be dependent on specific B vitamin treatment. Further studies are warranted to elucidate the possible mechanisms, also in order to explore potential effect modifications by nutritional factors.

Liver-specific loss of Perilipin 2 alleviates diet-induced hepatic steatosis, inflammation, and fibrosis

Hepatic inflammation and fibrosis are key elements in the pathogenesis of nonalcoholic steatohepatitis (NASH), a progressive liver disease initiated by excess hepatic lipid accumulation. Lipid droplet protein Perilipin 2 (Plin2) alleviates dietary-induced hepatic steatosis when globally ablated; however, its role in the progression of NASH remains unknown. To investigate this further, we challenged Plin2 liver-specific knockout mice (designated L-KO) and their respective wild-type (WT) controls with a methionine-choline-deficient (MCD) diet for 15 days to induce a NASH phenotype of increased hepatic triglyceride levels through impaired phosphatidylcholine (PC) synthesis and very-low-density lipoprotein (VLDL) secretion. Results on liver weights, body weights, fat tissue mass, and histology in WT and L-KO mice fed the MCD diet revealed signs of hepatic steatosis, fibrosis, and inflammation; however, these effects were blunted in L-KO mice. In addition, levels of PC and VLDL were unchanged, and hepatic steatosis was reduced in L-KO mice fed the MCD diet, due in part to an increase in remodeling of PE to PC via the enzyme phosphatidylethanolamine N-methyltransferase (PEMT). These mice also exhibited decreased hepatic expression of proinflammatory markers cyclooxygenase 2, IL-6, TNF-α, IL-1β, and reduced expression of endoplasmic reticulum (ER) stress proteins C/EBP homologous protein and cleaved caspase-1. Taken together, these results suggest that Plin2 liver-specific ablation alleviates diet-induced hepatic steatosis and inflammation via a PEMT-mediated mechanism that involves compensatory changes in proteins involved in phospholipid remodeling, inflammation, and ER stress that work to alleviate diet-induced NASH. Overall, these findings support a role for Plin2 as a target for NASH therapy.

S-adenosylmethionine Administration Attenuates Low Brain-Derived Neurotrophic Factor Expression Induced by Chronic Cerebrovascular Hypoperfusion or Beta Amyloid Treatment

Chronic cerebrovascular hypoperfusion is a high-risk factor for Alzheimer's disease (AD) as it is conducive to beta amyloid (Aβ) over-production. Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family widely expressed in the central nervous system. The structure of the rat BDNF gene is complex, consisting of eight non-coding exons (I-VIII) and one coding exon (IX). The BDNF gene is transcribed from multiple promoters located upstream of different 5' non-coding exons to produce a heterogeneous population of BDNF mRNAs. S-adenosylmethionine (SAM) produced in the methionine cycle is the primary methyl donor and the precursor of glutathione. In this study, a cerebrovascular hypoperfusion rat model and an Aβ intrahippocampal injection rat model were used to explore the expression profiles of all BDNF transcripts in the hippocampus with chronic cerebrovascular hypoperfusion or Aβ injection as well as with SAM treatment. We found that the BDNF mRNAs and protein were down-regulated in the hippocampus undergoing chronic cerebrovascular hypoperfusion as well as Aβ treatment, and BDNF exons IV and VI played key roles. SAM improved the low BDNF expression following these insults mainly through exons IV and VI. These results suggest that SAM plays a neuroprotective role by increasing the expression of endogenous BDNF and could be a potential target for AD therapy.

Methionine and S-adenosylmethionine levels are critical regulators of PP2A activity modulating lipophagy during steatosis

BACKGROUND & AIMS

Glycine N-methyltransferase (GNMT) expression is decreased in some patients with severe non-alcoholic fatty liver disease. Gnmt deficiency in mice (Gnmt-KO) results in abnormally elevated serum levels of methionine and its metabolite S-adenosylmethionine (SAMe), and this leads to rapid liver steatosis development. Autophagy plays a critical role in lipid catabolism (lipophagy), and defects in autophagy have been related to liver steatosis development. Since methionine and its metabolite SAMe are well known inactivators of autophagy, we aimed to examine whether high levels of both metabolites could block autophagy-mediated lipid catabolism.

METHODS

We examined methionine levels in a cohort of 358 serum samples from steatotic patients. We used hepatocytes cultured with methionine and SAMe, and hepatocytes and livers from Gnmt-KO mice.

RESULTS

We detected a significant increase in serum methionine levels in steatotic patients. We observed that autophagy and lipophagy were impaired in hepatocytes cultured with high methionine and SAMe, and that Gnmt-KO livers were characterized by an impairment in autophagy functionality, likely caused by defects at the lysosomal level. Elevated levels of methionine and SAMe activated PP2A by methylation, while blocking PP2A activity restored autophagy flux in Gnmt-KO hepatocytes, and in hepatocytes treated with SAMe and methionine. Finally, normalization of methionine and SAMe levels in Gnmt-KO mice using a methionine deficient diet normalized the methylation capacity, PP2A methylation, autophagy, and ameliorated liver steatosis.

CONCLUSIONS

These data suggest that elevated levels of methionine and SAMe can inhibit autophagic catabolism of lipids contributing to liver steatosis.

Choline, Its Potential Role in Nonalcoholic Fatty Liver Disease, and the Case for Human and Bacterial Genes

Our understanding of the impact of poor hepatic choline/phosphatidylcholine availability in promoting the steatosis characteristic of human nonalcoholic fatty liver disease (NAFLD) has recently advanced and possibly relates to phosphatidylcholine/phosphatidylethanolamine concentrations in various, membranes as well as cholesterol dysregulation. A role for choline/phosphatidylcholine availability in the progression of NAFLD to liver injury and serious hepatic consequences in some individuals requires further elucidation. There are many reasons for poor choline/phosphatidylcholine availability in the liver, including low intake, estrogen status, and genetic polymorphisms affecting, in particular, the pathway for hepatic de novo phosphatidylcholine synthesis. In addition to free choline, phosphatidylcholine has been identified as a substrate for trimethylamine production by certain intestinal bacteria, thereby reducing host choline bioavailability and providing an additional link to the increased risk of cardiovascular disease faced by those with NAFLD. Thus human choline requirements are highly individualized and biomarkers of choline status derived from metabolomics studies are required to predict those at risk of NAFLD induced by choline deficiency and to provide a basis for human intervention trials.

Plasma Glycine and Risk of Acute Myocardial Infarction in Patients With Suspected Stable Angina Pectoris

Background

Glycine is an amino acid involved in antioxidative reactions, purine synthesis, and collagen formation. Several studies demonstrate inverse associations of glycine with obesity, hypertension, and diabetes mellitus. Recently, glycine‐dependent reactions have also been linked to lipid metabolism and cholesterol transport. However, little evidence is available on the association between glycine and coronary heart disease. Therefore, we assessed the association between plasma glycine and acute myocardial infarction (AMI).

Methods and Results

A total of 4109 participants undergoing coronary angiography for suspected stable angina pectoris were studied. Cox regression was used to estimate the association between plasma glycine and AMI, obtained via linkage to the CVDNOR project. During a median follow‐up of 7.4 years, 616 patients (15.0%) experienced an AMI. Plasma glycine was higher in women than in men and was associated with a more favorable baseline lipid profile and lower prevalence of obesity, hypertension, and diabetes mellitus (all P<0.001). After multivariate adjustment for traditional coronary heart disease risk factors, plasma glycine was inversely associated with risk of AMI (hazard ratio per SD: 0.89; 95% CI, 0.82–0.98; P=0.017). The inverse association was generally stronger in those with apolipoprotein B, low‐density lipoprotein cholesterol, or apolipoprotein A‐1 above the median (all P_interaction≤0.037).

Conclusions

Plasma glycine was inversely associated with risk of AMI in patients with suspected stable angina pectoris. The associations were stronger in patients with apolipoprotein B, low‐density lipoprotein cholesterol, or apolipoprotein A‐1 levels above the median. These results motivate further studies to elucidate the relationship between glycine and lipid metabolism, in particular in relation to cholesterol transport and atherosclerosis.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00354081.

Hepatocyte-Specific Depletion of UBXD8 Induces Periportal Steatosis in Mice Fed a High-Fat Diet

We showed previously that UBXD8 plays a key role in proteasomal degradation of lipidated ApoB in hepatocarcinoma cell lines. In the present study, we aimed to investigate the functions of UBXD8 in liver in vivo. For this purpose, hepatocyte-specific UBXD8 knockout (UBXD8-LKO) mice were generated. They were fed with a normal or high-fat diet, and the phenotypes were compared with those of littermate control mice. Hepatocytes obtained from UBXD8-LKO and control mice were analyzed in culture. After 26 wk of a high-fat diet, UBXD8-LKO mice exhibited macrovesicular steatosis in the periportal area and microvesicular steatosis in the perivenular area, whereas control mice exhibited steatosis only in the perivenular area. Furthermore, UBXD8-LKO mice on a high-fat diet had significantly lower concentrations of serum triglyceride and VLDL than control mice. A Triton WR-1339 injection study revealed that VLDL secretion from hepatocytes was reduced in UBXD8-LKO mice. The decrease of ApoB secretion upon UBXD8 depletion was recapitulated in cultured primary hepatocytes. Accumulation of lipidated ApoB in lipid droplets was observed only in UBXD8-null hepatocytes. The results showed that depletion of UBXD8 in hepatocytes suppresses VLDL secretion, and could lead to periportal steatosis when mice are fed a high-fat diet. This is the first demonstration that an abnormality in the intracellular ApoB degradation mechanism can cause steatosis, and provides a useful model for periportal steatosis, which occurs in several human diseases.