Resolvin E1 and chemerin C15 peptide do not improve rodent non-alcoholic steatohepatitis

The role of novel adipokines and adipose-derived extracellular vesicles (ADEVs): Connections and interactions in liver diseases

Adipose tissues (AT) are an important endocrine organ that secretes various functional adipokines, peptides, non-coding RNAs, and acts on AT themselves or other distant tissues or organs through autocrine, paracrine, or endocrine manners. An accumulating body of evidence has suggested that many adipokines play an important role in liver metabolism. Besides the traditional adipokines such as adiponectin and leptin, many novel adipokines have recently been identified to have regulatory effects on the liver. Additionally, AT can produce extracellular vesicles (EVs) that act on peripheral tissues. However, under pathological conditions, such as obesity and diabetes, dysregulation of adipokines is associated with functional changes in AT, which may cause liver diseases. In this review, we focus on the newly discovered adipokines and EVs secreted by AT and highlight their actions on the liver under the context of obesity, nonalcoholic fatty liver diseases (NAFLD), and some other liver diseases. Clarifying the action of adipokines and adipose tissue-derived EVs on the liver would help to identify novel therapeutic targets or biomarkers for metabolic diseases.

Bioactive signalling lipids as drivers of chronic liver diseases

Lipids are important in multiple cellular functions, with most having structural or energy storage roles. However, a small fraction of lipids exert bioactive roles through binding to G protein-coupled receptors and induce a plethora of processes including cell proliferation, differentiation, growth, migration, apoptosis, senescence and survival. Bioactive signalling lipids are potent modulators of metabolism and energy homeostasis, inflammation, tissue repair and malignant transformation. All these events are involved in the initiation and progression of chronic liver diseases. In this review, we focus specifically on the roles of bioactive lipids derived from phospholipids (lyso-phospholipids) and poly-unsaturated fatty acids (eicosanoids, pro-resolving lipid mediators and endocannabinoids) in prevalent chronic liver diseases (alcohol-associated liver disease, non-alcoholic fatty liver disease, viral hepatitis and hepatocellular carcinoma). We discuss the balance between pathogenic and beneficial bioactive lipids as well as potential therapeutic targets related to the agonism or antagonism of their receptors.

Omega-3 Lipid Mediators: Modulation of the M1/M2 Macrophage Phenotype and Its Protective Role in Chronic Liver Diseases

The complex interplay between dietary factors, inflammation, and macrophage polarization is pivotal in the pathogenesis and progression of chronic liver diseases (CLDs). Omega-3 fatty acids (FAs) have brought in attention due to their potential to modulate inflammation and exert protective effects in various pathological conditions. Omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have shown promise in mitigating inflammation and enhancing the resolution of inflammatory responses. They influence the M1/M2 macrophage phenotype balance, promoting a shift towards the M2 anti-inflammatory phenotype. Specialized pro-resolving mediators (SPMs), such as resolvins (Rvs), protectins (PDs), and maresins (MaRs), have emerged as potent regulators of inflammation and macrophage polarization. They show anti-inflammatory and pro-resolving properties, by modulating the expression of cytokines, facilitate the phagocytosis of apoptotic cells, and promote tissue repair. MaR1, in particular, has demonstrated significant hepatoprotective effects by promoting M2 macrophage polarization, reducing oxidative stress, and inhibiting key inflammatory pathways such as NF-κB. In the context of CLDs, such as nonalcoholic fatty liver disease (NAFLD) and cirrhosis, omega-3s and their SPMs have shown promise in attenuating liver injury, promoting tissue regeneration, and modulating macrophage phenotypes. The aim of this article was to analyze the emerging role of omega-3 FAs and their SPMs in the context of macrophage polarization, with special interest in the mechanisms underlying their effects and their interactions with other cell types within the liver microenvironment, focused on CLDs and the development of novel therapeutic strategies.

Adipokines in Non-Alcoholic Fatty Liver Disease: Are We on the Road toward New Biomarkers and Therapeutic Targets?

Simple Summary

Non-alcoholic fatty liver disease (NAFLD) is an unmet medical need due to its increasingly high incidence, severe clinical consequences, and the absence of feasible diagnostic tools and effective drugs. This review summarizes the preclinical and clinical data on adipokines, cytokine-like hormones secreted by adipose tissue, and NAFLD. The aim is to establish the potential of adipokines as diagnostic and prognostic biomarkers, as well as their potential as therapeutic targets for NAFLD. The limitations of current research are also discussed, and future perspectives are outlined.

Abstract

Non-alcoholic fatty liver disease (NAFLD) has become the major cause of chronic hepatic illness and the leading indication for liver transplantation in the future decades. NAFLD is also commonly associated with other high-incident non-communicable diseases, such as cardiovascular complications, type 2 diabetes, and chronic kidney disease. Aggravating the socio-economic impact of this complex pathology, routinely feasible diagnostic methodologies and effective drugs for NAFLD management are unavailable. The pathophysiology of NAFLD, recently defined as metabolic associated fatty liver disease (MAFLD), is correlated with abnormal adipose tissue–liver axis communication because obesity-associated white adipose tissue (WAT) inflammation and metabolic dysfunction prompt hepatic insulin resistance (IR), lipid accumulation (steatosis), non-alcoholic steatohepatitis (NASH), and fibrosis. Accumulating evidence links adipokines, cytokine-like hormones secreted by adipose tissue that have immunometabolic activity, with NAFLD pathogenesis and progression; however, much uncertainty still exists. Here, the current knowledge on the roles of leptin, adiponectin, ghrelin, resistin, retinol-binding protein 4 (RBP4), visfatin, chemerin, and adipocyte fatty-acid-binding protein (AFABP) in NAFLD, taken from preclinical to clinical studies, is overviewed. The effect of therapeutic interventions on adipokines’ circulating levels are also covered. Finally, future directions to address the potential of adipokines as therapeutic targets and disease biomarkers for NAFLD are discussed.

Hepatocyte expressed chemerin-156 does not protect from experimental non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a rapidly growing liver disease. The chemoattractant chemerin is abundant in hepatocytes, and hepatocyte expressed prochemerin protected from NASH. Prochemerin is inactive and different active isoforms have been described. Here, the effect of hepatocyte expressed muChem-156, a highly active murine chemerin isoform, was studied in the methionine–choline deficient dietary model of NASH. Mice overexpressing muChem-156 had higher hepatic chemerin protein. Serum chemerin levels and the capability of serum to activate the chemerin receptors was unchanged showing that the liver did not release active chemerin. Notably, activation of the chemerin receptors by hepatic vein blood did not increase in parallel to total chemerin protein in patients with liver cirrhosis. In experimental NASH, muChem-156 had no effect on liver lipids. Accordingly, overexpression of active chemerin in hepatocytes or treatment of hepatocytes with recombinant chemerin did not affect cellular triglyceride and cholesterol levels. Importantly, overexpression of muChem-156 in the murine liver did not change the hepatic expression of inflammatory and profibrotic genes. The downstream targets of chemerin such as p38 kinase were neither activated in the liver of muChem-156 producing mice nor in HepG2, Huh7 and Hepa1-6 cells overexpressing this isoform. Recombinant chemerin had no effect on global gene expression of primary human hepatocytes and hepatic stellate cells within 24 h of incubation. Phosphorylation of p38 kinase was, however, increased upon short-time incubation of HepG2 cells with chemerin. These findings show that muChem-156 overexpression in hepatocytes does not protect from liver steatosis and inflammation.

Specialized Pro-Resolving Mediators Derived from N-3 Polyunsaturated Fatty Acids: Role in Metabolic Syndrome and Related Complications

Significance: Metabolic syndrome (MetS) prevalence continues to grow and represents a serious public health issue worldwide. This multifactorial condition carries the risk of hastening the development of type 2 diabetes (T2D), non-alcoholic fatty liver disease (NAFLD), and cardiovascular diseases (CVD). Another troubling aspect of MetS is the requirement of poly-pharmacological therapy not devoid of side effects. Therefore, there is an urgent need for prospecting alternative nutraceuticals as effective therapeutic agents for MetS. Recent Advances: Currently, there is an increased interest in understanding the regulation of metabolic derangements by specialized pro-resolving lipid mediators (SPMs), especially those derived from the long chain n-3 polyunsaturated fatty acids. Critical Issues: The SPMs are recognized as efficient modulators that are capable of inhibiting the production of pro-inflammatory cytokines, blocking neutrophil activation/recruitment, and inducing non-phlogistic (anti-inflammatory) activation of macrophage engulfment and removal of apoptotic inflammatory cells and debris. The aim of the present review is precisely to first underline key concepts relative to SPM functions before focusing on their status and actions on MetS components (e.g., obesity, glucose dysmetabolism, hyperlipidemia, hypertension) and complications such as T2D, NAFLD, and CVD. Future Directions: Valuable data from preclinical and clinical investigations have emphasized the SPM functions and influence on oxidative stress- and inflammation-related MetS. Despite these promising findings obtained without compromising host defense, additional efforts are needed to evaluate their potential therapeutic applications and further develop practical tools to monitor their bioavailability to cope with cardiometabolic disorders. Antioxid. Redox Signal. 37, 54-83.

Pro-Resolving Lipid Mediator Resolvin E1 Mitigates the Progress of Diethylnitrosamine-Induced Liver Fibrosis in Sprague-Dawley Rats by Attenuating Fibrogenesis and Restricting Proliferation

Liver fibrosis is a complex process associated to most types of chronic liver disease, which is characterized by a disturbance of hepatic tissue architecture and the excessive accumulation of extracellular matrix. Resolvin E1 (RvE1) is a representative member of the eicosapentaenoic omega-3 lipid derivatives, and is a drug candidate of the growing family of endogenous resolvins. Considering the aforementioned, the main objective of this study was to analyze the hepatoprotective effect of RvE1 in a rat model of liver fibrosis. Male Sprague-Dawley rats received diethylnitrosamine (DEN, 70 mg/mg body weight intraperitoneally (i.p)) as an inductor of liver fibrosis once weekly and RvE1(100 ng/body weight i.p) twice weekly for four weeks. RvE1 suppressed the alterations induced by DEN, normalizing the levels of alanine aminotransferase (ALT), albumin, and lactate dehydrogenase (LDH), and ameliorated DEN injury by decreasing the architecture distortion, inflammatory infiltration, necrotic areas, and microsteatosis. RvE1 also limited DEN-induced proliferation through a decrease in Ki67-positive cells and cyclin D1 protein expression, which is related to an increase of the levels of cleaved caspase-3. Interestingly, we found that RvE1 promotes higher nuclear translocation of nuclear factor κB (NF-κB)p65 than DEN. RvE1 also increased the levels of nuclear the nuclear factor erythroid 2-related factor 2 (Nrf2), but with no antioxidant effect, measured as an increase in glutathione disulfide (GSSG) and a decrease in the ratio of glutathione (GSH)/GSSG. Taken together, these results suggest that RvE1 modulates the fibrogenesis, steatosis, and cell proliferation in a model of DEN induced fibrosis.

Limited potential of resolvin D1 in treatment of cholestatic liver fibrosis

Background

Several studies suggest a role for EPA- and DHA-derived pro-resolving mediators like resolvins in reversing metabolic and inflammatory disturbances seen in various chronic diseases. Here, we investigated the effects of resolvin D1 (RvD1) on bile duct ligation (BDL)-induced cholestatic liver injury.

Methods

Mice were treated daily with RvD1 or 0.1% ethanol (control) from the day of BDL until the final observation time points. Blood and liver tissue were collected 2, 5 and 14 days after BDL for different analyses.

Results

RvD1 treatment of mice had no impact on the extent of cholestatic liver injury upon BDL, neither in the acute phase nor in the progressive state of liver fibrosis. Although RvD1 treatment resulted in a significantly reduced activity of hepatic stellate cells as well as reduced deposition of extracellular matrix 2 days after BDL, mice were not protected from inflammation and further fibrosis progression.

Conclusions

These data indicate that RvD1 has a limited therapeutic potential to treat cholestatic liver diseases, as it has no significant impact on regression of hepatic necroinflammation and fibrotic changes in bile duct-ligated mice.

Chemerin as a Driver of Hypertension: A Consideration

The protein chemerin (tazarotene-induced gene, TIG2; RARRES2) is a relatively new adipokine. Many studies support that circulating chemerin levels associate strongly and positively with body mass index, visceral fat, and blood pressure. Here, we focus on the specific relationship of chemerin and blood pressure with the goal of understanding whether and how chemerin drives (pathological) changes in blood pressure such that it could be interfered with therapeutically. We dissect the biosynthesis of chemerin and how current antihypertensive medications change chemerin metabolism. This is followed with a review of what is known about where chemerin is synthesized in the body and what chemerin and its receptors can do to the physiological function of organs important to blood pressure determination (e.g., brain, heart, kidneys, blood vessels, adrenal, and sympathetic nervous system). We synthesize from the literature our best understanding of the mechanisms by which chemerin modifies blood pressure, with knowledge that plasma/serum levels of chemerin may be limited in their pathological relevance. This review reveals several gaps in our knowledge of chemerin biology that could be filled by the collective work of protein chemists, biologists, pharmacologists, and clinicians.

Omega-3 derivatives, specialized pro-resolving mediators: Promising therapeutic tools for the treatment of pain in chronic liver disease

The main causes of liver injury are associated with inflammation and permanent damage. They can cause chronic liver disease (CLD), which is mainly related to viral hepatitis, alcohol consumption and non-alcoholic steatohepatitis, leading to fibrosis, cirrhosis and hepatocellular carcinoma. These conditions prevent the liver from working normally and make it begin to fail, which in turn may prompt a liver transplant. CLD and cirrhosis are the eleventh cause of death worldwide. At present, there are no approved pharmacological treatments to prevent, treat or resolve liver fibrosis. The prevalence of pain in the hepatic disease is elevated with ranges between 30% and 40%. Most of the pain drugs require hepatic function; therefore, the suitable control of pain is still a clinical challenge. Specialized pro-resolving mediators (SPM): lipoxins, resolvins, protectins and maresins, are potent endogenous molecules (nM concentrations) that modulate inflammatory body responses by reducing neutrophil infiltration, macrophage activity and pain sensitization. SPM have anti-inflammatory properties, stimulate tissue resolution, repair and regeneration, and exhibit anti-nociceptive actions. Furthermore, SPM were tried on different cellular, animal models and human observational data of liver injury, improving the pathogenesis of inflammation and fibrosis. In the present work, we will describe recent evidence that suggests that SPM can be used as a therapeutic option for CLD. Additionally, we will examine the role of SPM in the control of pain in pathologies associated with liver injury.

Variations in hepatic lipid species of age-matched male mice fed a methionine-choline-deficient diet and housed in different animal facilities

Background

Non-alcoholic steatohepatitis (NASH) is a common disease and feeding mice a methionine-choline-deficient (MCD) diet is a frequently used model to study its pathophysiology. Genetic and environmental factors influence NASH development and liver lipid content, which was studied herein using C57BL/6 J mice bred in two different animal facilities.

Methods

Age-matched male C57BL/6 J mice bred in two different animal facilities (later on referred to as WT1 and WT2) at the University Hospital of Regensburg were fed identical MCD or control chows for 2 weeks. Hepatic gene and protein expression and lipid composition were determined.

Results

NASH was associated with increased hepatic triglycerides, which were actually higher in WT1 than WT2 liver in both dietary groups. Cholesterol contributes to hepatic injury but was only elevated in WT2 NASH liver. Ceramides account for insulin resistance and cell death, and ceramide species d18:1/16:0 and d18:1/18:0 were higher in the NASH liver of both groups. Saturated sphingomyelins only declined in WT1 NASH liver. Lysophosphatidylcholine concentrations were quite normal in NASH and only one of the 12 altered phosphatidylcholine species declined in NASH liver of both groups. Very few phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol species were comparably regulated in NASH liver of both animal groups. Seven of these lipid species declined and two increased in NASH. Notably, hepatic mRNA expression of proinflammatory (F4/80, CD68, IL-6, TNF and chemerin) and profibrotic genes (TGF beta and alpha SMA) was comparable in WT1 and WT2 mice.

Conclusions

Mice housed and bred in different animal facilities had comparable disease severity of NASH whereas liver lipids varied among the groups. Thus, there was no specific lipid signature for NASH in the MCD model.

Electronic supplementary material

The online version of this article (10.1186/s12944-019-1114-4) contains supplementary material, which is available to authorized users.

Low circulating chemerin levels correlate with hepatic dysfunction and increased mortality in decompensated liver cirrhosis

Nutritional status, infections, inflammation and extrahepatic organ dysfunction are critical factors for the progression of chronic liver disease. Chemerin is an immune-metabolically and chemotactically active adipokine and we hypothesized that it is associated with disease severity and prognosis in patients with advanced decompensated cirrhosis. Therefore, we measured serum concentrations of chemerin in a prospectively characterized cohort of 80 patients with decompensated cirrhosis and ascites and assessed the associations with markers of disease severity and short-term outcome at 28 days. In a subset of patients (n = 40), ascitic fluid chemerin was determined. Advanced liver disease was associated with decreased serum but not ascitic chemerin levels. Serum chemerin correlated with markers of hepatic function (total bilirubin, albumin, INR) and inversely correlated with indicators of portal hypertension (platelet count, gastrointestinal bleeding) but not with extrahepatic organ failure and systemic inflammation. Patients presenting with acute-on-chronic liver failure or infection did not exhibit altered serum or ascitic fluid chemerin concentrations. However, serum chemerin levels below 87 ng/ml predicted an increased risk for mortality or liver transplantation within 28 days independently of MELD and infections. We conclude that low serum chemerin is an independent adverse prognostic factor in patients with advanced decompensated cirrhosis.

The chemerin knockout rat reveals chemerin dependence in female, but not male, experimental hypertension

Measures of the adipokine chemerin are elevated in multiple cardiovascular diseases, including hypertension, but little mechanistic work has been done to implicate chemerin as being causative in such diseases. The chemerin knockout (KO) rat was created to test the hypothesis that removal of chemerin would reduce pressure in the normal and hypertensive state. Western analyses confirmed loss of chemerin in the plasma and tissues of the KO vs. wild-type (WT) rats. Chemerin concentration in plasma and tissues was lower in WT females than in WT males, as determined by Western analysis. Conscious male and female KO rats had modest differences in baseline measures vs. the WT that included systolic, diastolic, mean arterial and pulse pressures, and heart rate, all measured telemetrically. The mineralocorticoid deoxycorticosterone acetate (DOCA) and salt water, combined with uninephrectomy as a hypertensive stimulus, elevated mean and systolic blood pressures of the male KO higher than the male WT. By contrast, all pressures in the female KO were lower than their WT throughout DOCA-salt treatment. These results revealed an unexpected sex difference in chemerin expression and the ability of chemerin to modify blood pressure in response to a hypertensive challenge.-Watts, S. W., Darios, E. S., Mullick, A. E., Garver, H., Saunders, T. L., Hughes, E. D., Filipiak, W. E., Zeidler, M. G., McMullen, N., Sinal, C. J., Kumar, R. K., Ferland, D. J., Fink, G. D. The chemerin knockout rat reveals chemerin dependence in female, but not male, experimental hypertension.

Alpha-syntrophin null mice are protected from non-alcoholic steatohepatitis in the methionine-choline-deficient diet model but not the atherogenic diet model

Adipose tissue dysfunction contributes to the pathogenesis of non-alcoholic steatohepatitis (NASH). The adapter protein alpha-syntrophin (SNTA) is expressed in adipocytes. Knock-down of SNTA increases preadipocyte proliferation and formation of small lipid droplets, which are both characteristics of healthy adipose tissue. To elucidate a potential protective role of SNTA in NASH, SNTA null mice were fed a methionine-choline-deficient (MCD) diet or an atherogenic diet which are widely used as preclinical NASH models. MCD diet mediated loss of fat mass was largely improved in SNTA-/- mice compared to the respective wild type animals. Hepatic lipids were mostly unchanged while the oxidative stress marker malondialdehyde was only induced in the wild type mice. The expression of inflammatory markers and macrophage immigration into the liver were reduced in SNTA-/- animals. This protective function of SNTA loss was absent in atherogenic diet induced NASH. Here, hepatic expression of inflammatory and fibrotic genes was similar in both genotypes though mutant mice gained less body fat during feeding. Hepatic cholesterol and ceramide were strongly induced in both strains upon feeding the atherogenic diet, while hepatic sphingomyelin, phosphatidylserine and phosphatidylethanolamine levels were suppressed. SNTA deficient mice are protected from fat loss and NASH in the experimental MCD model. NASH induced by an atherogenic diet is not influenced by loss of SNTA. The present study suggests the use of different experimental NASH models to study the pathophysiological role of proteins like SNTA in NASH.

Chemokine-Like Receptor 1 mRNA Weakly Correlates with Non-Alcoholic Steatohepatitis Score in Male but Not Female Individuals

The chemokine-like receptor 1 (CMKLR1) ligands resolvin E1 and chemerin are known to modulate inflammatory response. The progression of non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH) is associated with inflammation. Here it was analyzed whether hepatic CMKLR1 expression is related to histological features of NASH. Therefore, CMKLR1 mRNA was quantified in liver tissue of 33 patients without NAFLD, 47 patients with borderline NASH and 38 patients with NASH. Hepatic CMKLR1 mRNA was not associated with gender and body mass index (BMI) in the controls and the whole study group. CMKLR1 expression was similar in controls and in patients with borderline NASH and NASH. In male patients weak positive correlations with inflammation, fibrosis and NASH score were identified. In females CMKLR1 was not associated with features of NAFLD. Liver CMKLR1 mRNA tended to be higher in type 2 diabetes patients of both genders and in hypercholesterolemic women. In summary, this study shows that hepatic CMKLR1 mRNA is weakly associated with features of NASH in male patients only.