Signaling Nodes Associated with Endoplasmic Reticulum Stress during NAFLD Progression

Adipokines regulate the development and progression of MASLD through organellar oxidative stress

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD), which is increasingly being recognized as a leading cause of chronic liver pathology globally, is increasing. The pathophysiological underpinnings of its progression, which is currently under active investigation, involve oxidative stress. Human adipose tissue, an integral endocrine organ, secretes an array of adipokines that are modulated by dietary patterns and lifestyle choices. These adipokines intricately orchestrate regulatory pathways that impact glucose and lipid metabolism, oxidative stress, and mitochondrial function, thereby influencing the evolution of hepatic steatosis and progression to metabolic dysfunction-associated steatohepatitis (MASH). This review examines recent data, underscoring the critical interplay of oxidative stress, reactive oxygen species, and redox signaling in adipokine-mediated mechanisms. The role of various adipokines in regulating the onset and progression of MASLD/MASH through mitochondrial dysfunction and endoplasmic reticulum stress and the underlying mechanisms are discussed. Due to the emerging correlation between adipokines and the development of MASLD positions, these adipokines are potential targets for the development of innovative therapeutic interventions for MASLD management. A comprehensive understanding of the pathogenesis of MASLD/MASH is instrumental for identifying therapies for MASH.

FXR activation remodels hepatic and intestinal transcriptional landscapes in metabolic dysfunction-associated steatohepatitis

The escalating obesity epidemic and aging population have propelled metabolic dysfunction-associated steatohepatitis (MASH) to the forefront of public health concerns. The activation of FXR shows promise to combat MASH and its detrimental consequences. However, the specific alterations within the MASH-related transcriptional network remain elusive, hindering the development of more precise and effective therapeutic strategies. Through a comprehensive analysis of liver RNA-seq data from human and mouse MASH samples, we identified central perturbations within the MASH-associated transcriptional network, including disrupted cellular metabolism and mitochondrial function, decreased tissue repair capability, and increased inflammation and fibrosis. By employing integrated transcriptome profiling of diverse FXR agonists-treated mice, FXR liver-specific knockout mice, and open-source human datasets, we determined that hepatic FXR activation effectively ameliorated MASH by reversing the dysregulated metabolic and inflammatory networks implicated in MASH pathogenesis. This mitigation encompassed resolving fibrosis and reducing immune infiltration. By understanding the core regulatory network of FXR, which is directly correlated with disease severity and treatment response, we identified approximately one-third of the patients who could potentially benefit from FXR agonist therapy. A similar analysis involving intestinal RNA-seq data from FXR agonists-treated mice and FXR intestine-specific knockout mice revealed that intestinal FXR activation attenuates intestinal inflammation, and has promise in attenuating hepatic inflammation and fibrosis. Collectively, our study uncovers the intricate pathophysiological features of MASH at a transcriptional level and highlights the complex interplay between FXR activation and both MASH progression and regression. These findings contribute to precise drug development, utilization, and efficacy evaluation, ultimately aiming to improve patient outcomes.

Esrra regulates Rplp1-mediated translation of lysosome proteins suppressed in metabolic dysfunction-associated steatohepatitis and reversed by alternate day fasting

OBJECTIVE

Currently, little is known about the mechanism(s) regulating global and specific protein translation during metabolic dysfunction-associated steatohepatitis (MASH; previously known as non-alcoholic steatohepatitis, NASH).

METHODS

Unbiased label-free quantitative proteome, puromycin-labelling and polysome profiling were used to understand protein translation activity in vitro and in vivo.

RESULTS

We observed a global decrease in protein translation during lipotoxicity in human primary hepatocytes, mouse hepatic AML12 cells, and livers from a dietary mouse model of MASH. Interestingly, proteomic analysis showed that Rplp1, which regulates ribosome and translation pathways, was one of the most downregulated proteins. Moreover, decreased Esrra expression and binding to the Rplp1 promoter, diminished Rplp1 gene expression during lipotoxicity. This, in turn, reduced global protein translation and Esrra/Rplp1-dependent translation of lysosome (Lamp2, Ctsd) and autophagy (sqstm1, Map1lc3b) proteins. Of note, Esrra did not increase its binding to these gene promoters or their gene transcription, confirming its regulation of their translation during lipotoxicity. Notably, hepatic Esrra-Rplp1-dependent translation of lysosomal and autophagy proteins also was impaired in MASH patients and liver-specific Esrra knockout mice. Remarkably, alternate day fasting induced Esrra-Rplp1-dependent expression of lysosomal proteins, restored autophagy, and reduced lipotoxicity, inflammation, and fibrosis in hepatic cell culture and in vivo models of MASH.

CONCLUSIONS

Esrra regulation of Rplp1-mediated translation of lysosome/autolysosome proteins was downregulated during MASH. Alternate day fasting activated this novel pathway and improved MASH, suggesting that Esrra and Rplp1 may serve as therapeutic targets for MASH. Our findings also provided the first example of a nuclear hormone receptor, Esrra, to not only regulate transcription but also protein translation, via induction of Rplp1.

The Role of Endoplasmic Reticulum Stress in Metabolic Diseases

The endoplasmic reticulum (ER), the center of protein folding, also controls the cell's life-and-death signaling mechanisms. ER stress caused by unfolded or misfolded proteins leads to the activation of the unfolded protein response (UPR) in the cell. The UPR utilizes three main signaling pathways to restore disrupted ER homeostasis. These signaling pathways are protein kinase R-like endoplasmic reticulum kinase, inositol-requiring enzyme 1, and activating transcription factor 6. Studies have reported that ER stress (ERS) plays a role in the pathogenesis of metabolic disorders such as diabetes, obesity, atherosclerosis, and nonalcoholic liver disease. This review will briefly discuss the ERS response in these metabolic diseases.

Application of PPAR Ligands and Nanoparticle Technology in Metabolic Steatohepatitis Treatment

Metabolic dysfunction-associated steatotic liver disease/steatohepatitis (MASLD/MASH) is a major disease worldwide whose effective treatment is challenging. Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor superfamily and function as ligand-activated transcription factors. To date, three distinct subtypes of PPARs have been characterized: PPARα, PPARβ/δ, and PPARγ. PPARα and PPARγ are crucial regulators of lipid metabolism that modulate the transcription of genes involved in fatty acid (FA), bile acid, and cholesterol metabolism. Many PPAR agonists, including natural (FAs, eicosanoids, and phospholipids) and synthetic (fibrate, thiazolidinedione, glitazar, and elafibranor) agonists, have been developed. Furthermore, recent advancements in nanoparticles (NPs) have led to the development of new strategies for MASLD/MASH therapy. This review discusses the applications of specific cell-targeted NPs and highlights the potential of PPARα- and PPARγ-targeted NP drug delivery systems for MASLD/MASH treatment.

Endoplasmic Reticulum Stress Activates Hepatic Macrophages through PERK-hnRNPA1 Signaling

Endoplasmic reticulum (ER) stress plays a crucial role in liver diseases, affecting various types of hepatic cells. While studies have focused on the link between ER stress and hepatocytes as well as hepatic stellate cells (HSCs), the precise involvement of hepatic macrophages in ER stress-induced liver injury remains poorly understood. Here, we examined the effects of ER stress on hepatic macrophages and their role in liver injury. Acute ER stress led to the accumulation and activation of hepatic macrophages, which preceded hepatocyte apoptosis. Notably, macrophage depletion mitigated liver injury induced by ER stress, underscoring their detrimental role. Mechanistic studies revealed that ER stress stimulates macrophages predominantly via the PERK signaling pathway, regardless of its canonical substrate ATF4. hnRNPA1 has been identified as a crucial mediator of PERK-driven macrophage activation, as the overexpression of hnRNPA1 effectively reduced ER stress and suppressed pro-inflammatory activation. We observed that hnRNPA1 interacts with mRNAs that encode UPR-related proteins, indicating its role in the regulation of ER stress response in macrophages. These findings illuminate the cell type-specific responses to ER stress and the significance of hepatic macrophages in ER stress-induced liver injury. Collectively, the PERK-hnRNPA1 axis has been discovered as a molecular mechanism for macrophage activation, presenting prospective therapeutic targets for inflammatory hepatic diseases such as acute liver injury.

Endoplasmic reticulum stress PERK-ATF4-CHOP pathway is involved in non-alcoholic fatty liver disease in type 1 diabetic rats: The rescue effect of treatment exercise and insulin-like growth factor I

Endoplasmic Reticulum Stress (ERS) is a key factor in the development of Non-Alcoholic Fatty Liver Disease (NAFLD) in diabetes. The current study aimed to examine the effects of exercise and IGF-I on ERS markers in liver tissue. Rats were divided into five groups (n = 8 per group), including control (CON), diabetes (DIA), diabetes + exercise (DIA + EX), diabetes + IGF-I (DIA + IGF-I), and diabetes + exercise + IGF-I (DIA + EX + IGF-I). Type 1 diabetes was induced by an I.P. injection of streptozotocin (60 mg/kg). After 30 days of treatment with exercise or IGF-I alone or in combination, liver tissue was assessed for caspase 12, 8, and CHOP protein levels, and expression of ERS markers (ATF-6, PERK, IRE-1A) and lipid metabolism-involved genes (FAS, FXR, SREBP-1c) by western immunoblotting. In addition, for the evaluation of histopathological changes in the liver, Hematoxylin - Eosin and Masson's Trichrome staining were done. Compared to the control group, diabetes significantly caused liver fibrosis, induced ERS, increased caspase 12 and 8 levels in the liver, and changed expression levels of genes associated with lipid metabolism, including FAS, FXR, and SREBP-1c. Treatment with either exercise or IGF-I reduced fibrosis levels suppressed ER stress markers and apoptosis, and improved expression of genes associated with lipid metabolism. In addition, simultaneous treatment with exercise and IGF-I showed a synergistic effect compared to DIA + E and DIA + IGF-I. The results suggest that IGF-1 and exercise reduced liver fibrosis possibly by reducing ERS, creating adaptive ER stress status, and improving protein folding.

(+)-Lipoic acid reduces mitochondrial unfolded protein response and attenuates oxidative stress and aging in an in vitro model of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a liver disorder characterized by the ac-cumulation of fat in hepatocytes without alcohol consumption. Mitochondrial dysfunction and endoplasmic reticulum (ER) stress play significant roles in NAFLD pathogenesis. The unfolded protein response in mitochondria (UPRmt) is an adaptive mechanism that aims to restore mitochondrial protein homeostasis and mitigate cellular stress. This study aimed to investigate the effects of ( +)-Lipoic acid (ALA) on UPRmt, inflammation, and oxidative stress in an in vitro model of NAFLD using HepG2 cells treated with palmitic acid and oleic acid to induce steatosis.

RESULTS

Treatment with palmitic and oleic acids increased UPRmt-related proteins HSP90 and HSP60 (heat shock protein), and decreased CLPP (caseinolytic protease P), indicating ER stress activation. ALA treatment at 1 μM and 5 μM restored UPRmt-related protein levels. PA:OA (palmitic acid:oleic acid)-induced ER stress markers IRE1α (Inositol requiring enzyme-1), CHOP (C/EBP Homologous Protein), BIP (Binding Immunoglobulin Protein), and BAX (Bcl-2-associated X protein) were significantly reduced by ALA treatment. ALA also enhanced ER-mediated protein glycosylation and reduced oxidative stress, as evidenced by decreased GPX1 (Glutathione peroxidase 1), GSTP1 (glutathione S-transferase pi 1), and GSR (glutathione-disulfide reductase) expression and increased GSH (Glutathione) levels, and improved cellular senescence as shown by the markers β-galactosidase, γH2Ax and Klotho-beta.

CONCLUSIONS

In conclusion, ALA ameliorated ER stress, oxidative stress, and inflammation in HepG2 cells treated with palmitic and oleic acids, potentially offering therapeutic benefits for NAFLD providing a possible biochemical mechanism underlying ALA beneficial effects.

GLP-1/GLP-1RAs: New Options for the Drug Treatment of NAFLD

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a global public health concern. Currently, the cornerstone of NAFLD treatment is lifestyle modification and, if necessary, weight loss. However, compliance is a challenge, and this approach alone may not be sufficient to halt and treat the more serious disease development, so medication is urgently needed. Nevertheless, no medicines are approved to treat NAFLD. Glucagon-like peptide-1 (GLP-1) is an enteropeptide hormone that inhibits glucagon synthesis, promotes insulin secretion, and delays gastric emptying. GLP-1 has been found in recent studies to be beneficial for the management of NAFLD, and the marketed GLP-1 agonist drugs have different degrees of effectiveness for NAFLD while lowering blood glucose. In this article, we review GLP-1 and its physiological roles, the pathogenesis of NAFLD, the correlation between NAFLD and GLP-1 signaling, and potential strategies for GLP-1 treatment of NAFLD.

Transient receptor potential channel 3 in human liver and gallbladder - An investigation in body donors

Since the discovery of TRP proteins in 1969, during studies of the fruit fly Drosophila melanogaster, interest around them and the subfamily of TRPC channels has remained high. TRPC3 was able to be detected in a number of organs in rodents, such as rats and mice, and also in various human tissues. For the most part, these investigations were carried out using gene expression of TRPC3. Further work has already confirmed the relevance of TRPC3 in the context of neurodegenerative diseases, such as spinocerebellar ataxia, and carcinogenic entities, such as ovarian carcinoma. An association with TRPC3 has also been demonstrated for diseases that affect the liver. In order to confirm the expression of TRPC3 in the human liver, this study uses samples taken from eight (n = 8) fixated human body donors and analyzed with immunohistochemistry. In accordance with the macroscopic anatomy of the organs, six samples (n = 6) of liver tissue and three (n = 3) of gallbladder tissue were obtained. TRPC3 was clearly detected in all liver and gallbladder samples examined. Thus, it is not unlikely that TRPC3 plays a role in the extensive metabolic processes of the liver and could also serve as a target for pharmacological interventions in an imbalance of calcium homeostasis.

Hepatic Insulin Resistance Model in the Male Wistar Rat Using Exogenous Insulin Glargine Administration

Metabolic diseases are a worldwide health problem. Insulin resistance (IR) is their distinctive hallmark. For their study, animal models that provide reliable information are necessary, permitting the analysis of the cluster of abnormalities that conform to it, its progression, and time-dependent molecular modifications. We aimed to develop an IR model by exogenous insulin administration. The effective dose of insulin glargine to generate hyperinsulinemia but without hypoglycemia was established. Then, two groups (control and insulin) of male Wistar rats of 100 g weight were formed. The selected dose (4 U/kg) was administered for 15, 30, 45, and 60 days. Zoometry, a glucose tolerance test, insulin response, IR, and the serum lipid profile were assessed. We evaluated insulin signaling, glycogenesis and lipogenesis, redox balance, and inflammation in the liver. Results showed an impairment of glucose tolerance, dyslipidemia, hyperinsulinemia, and peripheral and time-dependent selective IR. At the hepatic level, insulin signaling was impaired, resulting in reduced hepatic glycogen levels and triglyceride accumulation, an increase in the ROS level with MAPK-ERK1/2 response, and mild pro-oxidative microenvironmental sustained by MT, GSH, and GR activity. Hepatic IR coincides with additions in MAPK-p38, NF-κB, and zoometric changes. In conclusion, daily insulin glargine administration generated a progressive IR model. At the hepatic level, the IR was combined with oxidative conditions but without inflammation.

The Effect of Bioactive Aliment Compounds and Micronutrients on Non-Alcoholic Fatty Liver Disease

In the current review, we focused on identifying aliment compounds and micronutrients, as well as addressed promising bioactive nutrients that may interfere with NAFLD advance and ultimately affect this disease progress. In this regard, we targeted: 1. Potential bioactive nutrients that may interfere with NAFLD, specifically dark chocolate, cocoa butter, and peanut butter which may be involved in decreasing cholesterol concentrations. 2. The role of sweeteners used in coffee and other frequent beverages; in this sense, stevia has proven to be adequate for improving carbohydrate metabolism, liver steatosis, and liver fibrosis. 3. Additional compounds were shown to exert a beneficial action on NAFLD, namely glutathione, soy lecithin, silymarin, Aquamin, and cannabinoids which were shown to lower the serum concentration of triglycerides. 4. The effects of micronutrients, especially vitamins, on NAFLD. Even if most studies demonstrate the beneficial role of vitamins in this pathology, there are exceptions. 5. We provide information regarding the modulation of the activity of some enzymes related to NAFLD and their effect on this disease. We conclude that NAFLD can be prevented or improved by different factors through their involvement in the signaling, genetic, and biochemical pathways that underlie NAFLD. Therefore, exposing this vast knowledge to the public is particularly important.

Mechanisms of NLRP3 inflammasome-mediated hepatic stellate cell activation: Therapeutic potential for liver fibrosis

The liver injury leads to an inflammatory response, which causes the activation of hepatic stellate cells (HSCs) that further secrete ECM proteins and play an important role in liver fibrosis. Moreover, the inflammatory response is a driving force for fibrogenesis, which is triggered by many types of injuries. Exaggerated inflammatory immune responses are mediated by cytoplasmic protein complexes known as inflammasomes, which are involved in many chronic liver diseases. Inflammasomes are pattern recognition receptors (PRRs) that can sense any microbial motifs known as pathogen-associated molecular patterns (PAMPs), and host- or environmental-derived stress signals known as damage-associated molecular patterns (DAMPs). The inflammasomes cause caspase-mediated proteolytic cleavage of pro-IL-1β and pro-IL-18 into active IL-1β and IL-18. In this review, we provide a comprehensive summary of the important roles of NLRP3 inflammasome in the pathogenesis of liver fibrosis with an emphasis on several direct and indirect pathways responsible for the NLRP3 inflammasome-mediated HSCs activation and fibrogenesis. In addition, we discuss the general pharmacological and genetics strategies for the inhibition of NLRP3 inflammasome activation and its downstream signaling with examples of emerging pharmacotherapeutics, targeting the NLRP3 inflammasome signaling as well as a possible way to develop effective and safer NLRP3 inflammasome inhibitors.

Effect of Isoquercitrin on Free Fatty Acid-Induced Lipid Accumulation in HepG2 Cells

Liver metabolic disorders and oxidative stress are crucial factors in the development of nonalcoholic fatty liver disease (NAFLD); however, treatment strategies to combat NAFLD remain poorly established, presenting an important challenge that needs to be addressed. Herein, we aimed to examine the effect of isoquercitrin on lipid accumulation induced by exogenous free fatty acids (FFA) using HepG2 cells and elucidate the underlying molecular mechanism. The cells were exposed to 0.5 mM FFA to induce intracellular lipid accumulation, followed by co-treatment with isoquercitrin to confirm the potential inhibitory effect on FFA-induced lipid production. HepG2 cells exposed to FFA alone exhibited intracellular lipid accumulation, compromised endoplasmic reticulum (ER) stress, and enhanced expression of proteins and genes involved in lipid synthesis; however, co-treatment with isoquercitrin decreased the expression of these molecules in a dose-dependent manner. Furthermore, isoquercitrin could activate AMP-activated protein kinase (AMPK), a key regulatory protein of hepatic fatty acid oxidation, suppressing new lipid production by phosphorylating acetyl-CoA carboxylase (ACC) and inhibiting sterol regulatory element-binding transcription factor 1 (SREBP-1)/fatty acid synthase (FAS) signals. Overall, these findings suggest that isoquercitrin can be employed as a therapeutic agent to improve NAFLD via the regulation of lipid metabolism by targeting the AMPK/ACC and SREBP1/FAS pathways.

Exercise and Metformin Intervention Prevents Lipotoxicity-Induced Hepatocyte Apoptosis by Alleviating Oxidative and ER Stress and Activating the AMPK/Nrf2/HO-1 Signaling Pathway in db/db Mice

Objective

Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2DM) commonly coexist and act synergistically to drive adverse clinical outcomes. This study is aimed at investigating the effects of exercise intervention and oral hypoglycaemic drug of metformin (MET) alone or combined on hepatic lipid accumulation. To investigate if oxidative stress and endoplasmic reticulum stress (ERS) are involved in lipotoxicity-induced hepatocyte apoptosis in diabetic mice and whether exercise and/or MET alleviated oxidative stress or ERS-apoptosis by AMPK-Nrf2-HO-1 signaling pathway.

Methods

Forty db/db mice with diabetes (random blood glucose ≥ 250 mg/dL) were randomly allocated into four groups: control (CON), exercise training alone (EX), metformin treatment alone (MET), and exercise combined with metformin (EM) groups. Hematoxylin-eosin and oil red O staining were carried out to observe hepatic lipid accumulation. Immunohistochemical and TUNEL methods were used to detect the protein expression of the binding immunoglobulin protein (BiP) and superoxide dismutase-1 (SOD1) and the apoptosis level of hepatocytes. ERS-related gene expression and the AMPK-Nrf2-HO-1 signaling pathway were tested by western blotting.

Results

Our data showed that db/db mice exhibited increased liver lipid accumulation, which induced oxidative and ER stress of the PERK-eIF2α-ATF4 pathway, and hepatocyte apoptosis. MET combined with exercise training significantly alleviated hepatic lipid accumulation by suppressing BiP expression, the central regulator of ER homeostasis, and its downstream PERK-eIF2α-ATF4 pathway, as well as upregulated the AMPK-Nrf2-HO-1 signaling pathway. Moreover, the combination of exercise and MET displayed protective effects on hepatocyte apoptosis by downregulating Bax expression and TUNEL-positive staining, restoring the balance of cleaved-caspase-3 and caspase-3, and improving the antioxidant defense system to prevent oxidative damage in db/db mice.

Conclusion

Compared to MET or exercise intervention alone, the combined exercise and metformin exhibited significant effect on ameliorating hepatic steatosis, inhibiting oxidative and ER stress-induced hepatocyte apoptosis via improving the capacity of the antioxidant defense system and suppression of the PERK-eIF2α-ATF4 pathway. Furthermore, upregulation of AMPK-Nrf2-HO-1 signaling pathway might be a key crosstalk between MET and exercise, which may have additive effects on alleviating hepatic lipid accumulation.

Identification of Key Endoplasmic Reticulum Stress-Related Genes in Non-Alcoholic Fatty Liver Disease

Background: Endoplasmic reticulum stress (ERS) is involved in the etiology of non-alcoholic fatty liver disease (NAFLD). Thus, the current study was designed to identify key ERS-associated genes in NAFLD. Methods: RNA-Seq data of NAFLD and controls were sourced from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) in NAFLD and controls were identified by limma. By overlapping DEGs and ERS-related genes, ERS-related DEGs were identified. The function of ERS-related DEGs was characterized by clusterProfiler. Next, the protein–protein interaction (PPI) network was created using the Cytoscape software and the STRING database to identify key ERS-related genes in NAFLD. Furthermore, the correlations among key ERS-related genes were calculated. Results: A total of 8965 DEGs were identified between NAFLD and controls in the GSE126848 dataset. After overlapping these DEGs and ERS-related genes, 20 genes were identified as ERS-related DEGs in NAFLD. Functional analysis revealed that the genes mainly participated in ER-related functions, such as the ER–nucleus signaling pathway, regulation of ERS response, and protein processing in ER. The PPI network revealed the interactions among 17 ERS-related DEGs, including ERN1, ATF6, and EIF2S1 as the key genes. The expressions of ERN1, ATF6, and EIF2S1 were significantly down-regulated in NAFLD and were strongly positively correlated with each other. Further, the expression of ERN1 and ATFA6 was also similar in the GSE89632 datasets. Conclusion: The present study identified ERN1, ATF6, and EIF2S1 as key ERS-related genes in NAFLD. These findings may provide a molecular basis for the role of ERS in NAFLD.

Oyster broth concentrate and its major component taurine alleviate acute alcohol-induced liver damage

Our previous study showed that oyster hydrolysate (OH) protected against the liver damage caused by a single instance of ethanol (EtOH) binge drinking. Oyster broth concentrate (OBC) was discovered in the process of searching for a different substance derived from oysters (Crassostrea gigas) with economic value. OBC is a by-product of boiling oysters at 95°C for 3 min. In this study, we investigated the effects of OBC and its major component taurine on blood and liver tissues obtained from a single-EtOH-binge-drinking mouse model. The preadministration of OBC enhanced EtOH metabolism by increasing the activities of alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and catalase. In addition, the preadministration of OBC reduced cytochrome P450 2E1 (CYP2E1) activity, reactive oxygen species (ROS) generation, Ca2+ concentrations, apoptotic signals, and inflammatory mediators in liver tissues. The reduction of apoptotic and inflammatory signals by OBC resulted from the downregulation of endoplasmic reticulum (ER) stress molecules and NF-κB activity. Taurine administration showed similar effects to OBC. These results show that OBC protected against acute EtOH-induced liver damage through the action of taurine. Our findings suggest that OBC could be an economically valuable substance and a functional food with hepatoprotective effects.

A Molecular Insight into the Role of Antioxidants in Nonalcoholic Fatty Liver Diseases

Nonalcoholic fatty liver disease (NAFLD) defines fat accumulation in the liver, and it is commonly associated with metabolic syndromes like diabetes and obesity. Progressive NAFLD leads to nonalcoholic steatohepatitis (NASH) and ultimately causes cirrhosis and hepatocellular carcinoma, and NASH is currently a frequent cause of liver transplantation. Oxidative stress is often contributed to the progression of NAFLD, and hence, antioxidants such as silymarin, silybin, or silibinin, pentoxifylline, resveratrol, and vitamins A, C, and E are used in clinical trials against NAFLD. Silymarin induces the peroxisome proliferator-activated receptor α (PPARα), a fatty acid sensor, which promotes the transcription of genes that are required for the enzymes involved in lipid oxidation in hepatocytes. Silybin inhibits sterol regulatory element-binding protein 1 and carbohydrate response element-binding protein to downregulate the expression of genes responsible for de novo lipogenesis by activating AMP-activated protein kinase phosphorylation. Pentoxifylline inhibits TNF-α expression and endoplasmic reticulum stress-mediated inflammatory nuclear factor kappa B (NF-κB) activation. Thus, it prevents NAFLD to NASH progression. Resveratrol inhibits methylation at Nrf-2 promoters and NF-κB activity via SIRT1 activation in NAFLD conditions. However, clinically, resveratrol has not shown promising beneficial effects. Vitamin C is beneficial in NAFLD patients. Vitamin E is not effectively regressing hepatic fibrosis. Hence, its combination with antifibrotic agents is used as an adjuvant to produce a synergistic antifibrotic effect. However, to date, none of these antioxidants have been used as a definite therapeutic agent in NAFLD patients. Further, these antioxidants should be studied in NAFLD patients with larger populations and multiple endpoints in the future.

Selective PPARα Modulator Pemafibrate and Sodium-Glucose Cotransporter 2 Inhibitor Tofogliflozin Combination Treatment Improved Histopathology in Experimental Mice Model of Non-Alcoholic Steatohepatitis

Ballooning degeneration of hepatocytes is a major distinguishing histological feature of non-alcoholic steatosis (NASH) progression that can lead to cirrhosis and hepatocellular carcinoma (HCC). In this study, we evaluated the effect of the selective PPARα modulator (SPPARMα) pemafibrate (Pema) and sodium-glucose cotransporter 2 (SGLT2) inhibitor tofogliflozin (Tofo) combination treatment on pathological progression in the liver of a mouse model of NASH (STAM) at two time points (onset of NASH progression and HCC survival). At both time points, the Pema and Tofo combination treatment significantly alleviated hyperglycemia and hypertriglyceridemia. The combination treatment significantly reduced ballooning degeneration of hepatocytes. RNA-seq analysis suggested that Pema and Tofo combination treatment resulted in an increase in glyceroneogenesis, triglyceride (TG) uptake, lipolysis and liberated fatty acids re-esterification into TG, lipid droplet (LD) formation, and Cidea/Cidec ratio along with an increased number and reduced size and area of LDs. In addition, combination treatment reduced expression levels of endoplasmic reticulum stress-related genes (Ire1a, Grp78, Xbp1, and Phlda3). Pema and Tofo treatment significantly improved survival rates and reduced the number of tumors in the liver compared to the NASH control group. These results suggest that SPPARMα and SGLT2 inhibitor combination therapy has therapeutic potential to prevent NASH-HCC progression.

HA15 alleviates bone loss in ovariectomy-induced osteoporosis by targeting HSPA5

The imbalance between osteogenesis and adipogenesis in the bone marrow is the main characteristic of osteoporosis (OP). Thus, exploring regulation of the differentiation of bone marrow stromal cells (BMSCs) into osteoblasts and adipocytes is important to identify novel targets for the treatment of OP. In the present study, the master regulator of endoplasmic reticulum (ER) stress, heat shock protein family A (Hsp70) member 5 (HSPA5) was shown to significantly accumulate in osteoblasts and adipocytes, but not in osteoclasts in bone sections from aged and postmenopausal OP mice. In vitro study revealed that HSPA5 negatively modulated osteogenic differentiation and positively promoted adipogenic differentiation, and that targeting HSPA5 with its inhibitor HA15 enhanced osteogenic differentiation and inhibited adipogenic differentiation. Also, HA15 treatment induces ER stress and autophagy, and decreases apoptosis in cells. We constructed a postmenopausal OP model in mice with ovariectomy surgery, and treated the mice with HA15. The results showed that HA15 treatment induced appropriate ER stress, activated autophagy and decreased apoptosis in osteoblasts, thereby alleviating bone loss in vivo. Our results indicated that HSPA5 participated in OP pathogenesis by regulating the differentiation of BMSCs. HSPA5 may serve as a new target for the treatment of OP, and targeting HSPA5 with HA15 prevents the progression of OP and provides a candidate therapeutic molecule for postmenopausal OP.

Metabolic-associated fatty liver disease and lipoprotein metabolism

BACKGROUND

Non-alcoholic fatty liver disease, or as recently proposed 'metabolic-associated fatty liver disease' (MAFLD), is characterized by pathological accumulation of triglycerides and other lipids in hepatocytes. This common disease can progress from simple steatosis to steatohepatitis, and eventually end-stage liver diseases. MAFLD is closely related to disturbances in systemic energy metabolism, including insulin resistance and atherogenic dyslipidemia.

SCOPE OF REVIEW

The liver is the central organ in lipid metabolism by secreting very low density lipoproteins (VLDL) and, on the other hand, by internalizing fatty acids and lipoproteins. This review article discusses recent research addressing hepatic lipid synthesis, VLDL production, and lipoprotein internalization as well as the lipid exchange between adipose tissue and the liver in the context of MAFLD.

MAJOR CONCLUSIONS

Liver steatosis in MAFLD is triggered by excessive hepatic triglyceride synthesis utilizing fatty acids derived from white adipose tissue (WAT), de novo lipogenesis (DNL) and endocytosed remnants of triglyceride-rich lipoproteins. In consequence of high hepatic lipid content, VLDL secretion is enhanced, which is the primary cause of complex dyslipidemia typical for subjects with MAFLD. Interventions reducing VLDL secretory capacity attenuate dyslipidemia while they exacerbate MAFLD, indicating that the balance of lipid storage versus secretion in hepatocytes is a critical parameter determining disease outcome. Proof of concept studies have shown that promoting lipid storage and energy combustion in adipose tissues reduces hepatic lipid load and thus ameliorates MAFLD. Moreover, hepatocellular triglyceride synthesis from DNL and WAT-derived fatty acids can be targeted to treat MAFLD. However, more research is needed to understand how individual transporters, enzymes, and their isoforms affect steatosis and dyslipidemia in vivo, and whether these two aspects of MAFLD can be selectively treated. Processing of cholesterol-enriched lipoproteins appears less important for steatosis. It may, however, modulate inflammation and consequently MAFLD progression.