A bioactive product lipoxin A4 attenuates liver fibrosis in an experimental model by regulating immune response and modulating the expression of regeneration genes

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.

N-acetylcysteine acts as a potent anti-inflammatory agent altering the eicosanoid profile in the development of simple steatosis and its progression to hepatitis

Aim of the study

We aimed to examine the influence of N-acetylcysteine (NAC) on the development of metabolic dysfunction-associated steatotic liver disease (MASLD) in rats with a specific focus on the eicosanoid pathway.

Material and methods

The experiment was conducted on male Wistar rats fed a standard diet or a high-fat diet (HFD) for eight weeks. In the entire experiment, half of rats from both groups received intragastrically NAC solution prepared in normal saline. H + E staining was used for the histological assessment of liver tissue. The gas-liquid chromatography (GLC) technique was used for the assessment of the activity of n-3 and n-6 polyunsaturated fatty acid (PUFA) pathways and arachidonic acid concentration. ELISA and multiplex immunoassay kits were applied for the measurement of eicosanoid, cytokine, and chemokine levels. The Western blot technique was applied to determine the expression of proteins involved in the inflammation pathway.

Results

NAC decreased hepatic n-6 PUFA activity in all examined lipid pools and decreased the hepatic content of arachidonic acid as a pro-inflammatory precursor in each lipid pool, especially in the phospholipid fraction in rats with fatty lipid disease. NAC administration abolished 5-LOX expression, leading to a decrease in the content of pro-inflammatory leukotriene B4 and leukotriene C4. In rats with steatosis, NAC weakened NF-κB expression and raised Nrf-2 expression, inhibiting the synthesis of pro-inflammatory cytokines and chemokines.

Conclusions

NAC treatment significantly rate-limited the progression of simple hepatic steatosis to hepatitis in a rat model of MASLD.

α-Lipoic acid - a promising agent for attenuating inflammation and preventing steatohepatitis in rats fed a high-fat diet

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent liver disorder affecting a significant part of the global population. This study aimed to investigate the potential therapeutic effects of α-lipoic acid (α-LA) on the inflammatory response during simple steatosis development and progression into steatohepatitis. The study used the MASLD model in male Wistar rats that were fed a standard diet or a high-fat diet (HFD) for 8 weeks. Throughout the entire experiment, half of the animals received α-LA supplementation. The hepatic activity of pro-inflammatory n-6 and anti-inflammatory n-3 polyunsaturated fatty acid (PUFA) pathways and the concentration of arachidonic acid (AA) in selected lipid fractions were determined by the gas-liquid chromatography (GLC). The hepatic expression of proteins from inflammatory pathway was measured by the Western blot technique. The level of eicosanoids, cytokines and chemokines was assessed by the ELISA or multiplex assay kits. The results showed that α-LA supplementation attenuated the activity of n-6 PUFA pathway in FFA and DAG and increased the activity of n-3 PUFA pathway in PL, TAG and DAG. In addition, the administration of α-LA decreased the concentration of AA in DAG and FFA, indicating its potential protective effect on the deterioration of simple hepatic steatosis. The supplementation of α-LA also increased the expression of COX-1 and COX-2 with the lack of significant changes in prostaglandins profile. We observed an increase in the expression of 12/15-LOX, which was reflected in an increase in lipoxin A4 (LXA4) level. A decrease in pro-inflammatory cytokines and an increase in anti-inflammatory cytokines was also noticed in the liver of rats treated with HFD and α-LA. Our observations confirm that α-LA treatment has potential protective effects on inflammation development in the MASLD model. We believe that α-LA has a preventive impact when it comes to the progression of simple steatosis lesions to steatohepatitis.

Is hepatitis-B immunization effective during chronic liver fibrosis? Investigation of secretory and cellular immune responses on an experimental model

OBJECTIVE

Adults with end-stage of chronic liver diseases have lower antibody titers after hepatitis-B vaccination. We have less amount of knowledge about the effect of non-viral cause chronic liver fibrosis on vaccination. In this study, we investigated the effect of non-viral chronic liver fibrosis on hepatitis B vaccine and the effect of tetanous toxoid co-administration at the level of humoral and cellular immune responses in an experimental model.

METHODS

Hepatitis B vaccine was administered either alone or in combination with tetanus toxoid in thioacetamide-induced fibrotic BALB/c mice. Fibrosis level was determined by Knodell scoring. Anti-HBsAg, biochemical parameters, inflammatory (IL-1β, TNF-α), and anti-inflammatory (IL-10) cytokine levels were investigated in serum samples by automated systems and ELISA; respectively. Frequencies of activated lymphocytes were determined in flow cytometer.

RESULTS

Antibody titers significantly decreased after immunization of fibrotic mice. However, co-administration of toxoid significantly elevated antibody titer. The percentage of CD19⁺CD69⁺ B lymphocytes was found to be lower in vaccinated fibrotic group compared to vaccinated naive group. Simultaneous administration of toxoid significantly increased the frequencies of CD4⁺ and CD8⁺ T cells expressing CD69 and CD127. Interestingly, CD19⁺CD5⁺CD1^high Breg cells were significantly reduced in the group vaccinated with hepatitis B vaccine and toxoid, simultaneously. The reduction in Breg percentage did not expose a significant decrease in the level of IL-10.

CONCLUSION

Non-viral chronic liver fibrosis causes a reduction on specific antibody level after vaccination. Reduction on Breg cell frequency may have an effect on elevation of antibody level after co-administration of tetanus toxoid.

Pro- and anti-inflammatory bioactive lipids imbalance contributes to the pathobiology of autoimmune diseases

Autoimmune diseases are driven by T_H17 cells that secrete pro-inflammatory cytokines, especially IL-17. Under normal physiological conditions, autoreactive T cells are suppressed by TGF-β and IL-10 secreted by microglia and dendritic cells. When this balance is upset due to injury, infection and other causes, leukocyte recruitment and macrophage activation occurs resulting in secretion of pro-inflammatory IL-6, TNF-α, IL-17 and PGE2, LTs (leukotrienes) accompanied by a deficiency of anti-inflammatory LXA4, resolvins, protecting, and maresins. PGE2 facilitates T_H1 cell differentiation and promotes immune-mediated inflammation through T_H17 expansion. There is evidence to suggest that autoimmune diseases can be suppressed by anti-inflammatory bioactive lipids LXA4, resolvins, protecting, and maresins. These results imply that systemic and/or local application of LXA4, resolvins, protecting, and maresins and administration of their precursors AA/EPA/DHA could form a potential therapeutic approach in the prevention and treatment of autoimmune diseases.

Gamma-Linolenic Acid (GLA) Protects against Ionizing Radiation-Induced Damage: An In Vitro and In Vivo Study

Radiation is pro-inflammatory in nature in view of its ability to induce the generation of reactive oxygen species (ROS), cytokines, chemokines, and growth factors with associated inflammatory cells. Cells are efficient in repairing radiation-induced DNA damage; however, exactly how this happens is not clear. In the present study, GLA reduced DNA damage (as evidenced by micronuclei formation) and enhanced metabolic viability, which led to an increase in the number of surviving RAW 264.7 cells in vitro by reducing ROS generation, and restoring the activities of desaturases, COX-1, COX-2, and 5-LOX enzymes, TNF-α/TGF-β, NF-kB/IkB, and Bcl-2/Bax ratios, and iNOS, AIM-2, and caspases 1 and 3, to near normal. These in vitro beneficial actions were confirmed by in vivo studies, which revealed that the survival of female C57BL/6J mice exposed to lethal radiation (survival~20%) is significantly enhanced (to ~80%) by GLA treatment by restoring altered levels of duodenal HMGB1, IL-6, TNF-α, and IL-10 concentrations, as well as the expression of NF-kB, IkB, Bcl-2, Bax, delta-6-desaturase, COX-2, and 5-LOX genes, and pro- and anti-oxidant enzymes (SOD, catalase, glutathione), to near normal. These in vitro and in vivo studies suggest that GLA protects cells/tissues from lethal doses of radiation by producing appropriate changes in inflammation and its resolution in a timely fashion.

Discovery of a Potent and Orally Active Dual GPBAR1/CysLT1R Modulator for the Treatment of Metabolic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are two highly prevalent human diseases caused by excessive fat deposition in the liver. Although multiple approaches have been suggested, NAFLD/NASH remains an unmet clinical need. Here, we report the discovery of a novel class of hybrid molecules designed to function as cysteinyl leukotriene receptor 1 (CysLT₁R) antagonists and G protein bile acid receptor 1 (GPBAR1/TGR5) agonists for the treatment of NAFLD/NASH. The most potent of these compounds generated by harnessing the scaffold of the previously described CystLT₁R antagonists showed efficacy in reversing liver histopathology features in a preclinical model of NASH, reshaping the liver transcriptome and the lipid and energy metabolism in the liver and adipose tissues. In summary, the present study described a novel orally active dual CysLT₁R antagonist/GPBAR1 agonist that effectively protects against the development of NAFLD/NASH, showing promise for further development.

Formyl peptide receptor 2 determines sex-specific differences in the progression of nonalcoholic fatty liver disease and steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is an important health concern worldwide and progresses into nonalcoholic steatohepatitis (NASH). Although prevalence and severity of NAFLD/NASH are higher in men than premenopausal women, it remains unclear how sex affects NAFLD/NASH pathophysiology. Formyl peptide receptor 2 (FPR2) modulates inflammatory responses in several organs; however, its role in the liver is unknown. Here we show that FPR2 mediates sex-specific responses to diet-induced NAFLD/NASH. NASH-like liver injury was induced in both sexes during choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) feeding, but compared with females, male mice had more severe hepatic damage. Fpr2 was more highly expressed in hepatocytes and healthy livers from females than males, and FPR2 deletion exacerbated liver damage in CDAHFD-fed female mice. Estradiol induced Fpr2 expression, which protected hepatocytes and the liver from damage. In conclusion, our results demonstrate that FPR2 mediates sex-specific responses to diet-induced NAFLD/NASH, suggesting a novel therapeutic target for NAFLD/NASH.

Essential Fatty Acids and Their Metabolites in the Pathobiology of Inflammation and Its Resolution

Arachidonic acid (AA) metabolism is critical in the initiation and resolution of inflammation. Prostaglandin E2 (PGE2) and leukotriene B4/D4/E4 (LTB4/LD4/LTE4), derived from AA, are involved in the initiation of inflammation and regulation of immune response, hematopoiesis, and M1 (pro-inflammatory) macrophage facilitation. Paradoxically, PGE2 suppresses interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) production and triggers the production of lipoxin A4 (LXA4) from AA to initiate inflammation resolution process and augment regeneration of tissues. LXA4 suppresses PGE2 and LTs' synthesis and action and facilitates M2 macrophage generation to resolve inflammation. AA inactivates enveloped viruses including SARS-CoV-2. Macrophages, NK cells, T cells, and other immunocytes release AA and other bioactive lipids to produce their anti-microbial actions. AA, PGE2, and LXA4 have cytoprotective actions, regulate nitric oxide generation, and are critical to maintain cell shape and control cell motility and phagocytosis, and inflammation, immunity, and anti-microbial actions. Hence, it is proposed that AA plays a crucial role in the pathobiology of ischemia/reperfusion injury, sepsis, COVID-19, and other critical illnesses, implying that its (AA) administration may be of significant benefit in the prevention and amelioration of these diseases.

Role of eicosanoids in liver repair, regeneration and cancer

Eicosanoids are lipid signaling molecules derived from the oxidation of ω-6 fatty acids, usually arachidonic acid. There are three major pathways, including the cyclooxygenase (COX), lipoxygenase (LOX), and P450 cytochrome epoxygenase (CYP) pathway. Prostanoids, which include prostaglandins (PG) and thromboxanes (Tx), are formed via the COX pathway, leukotrienes (LT) and lipoxins (LX) by the action of 5-LOX, and hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs) by CYP. Although eicosanoids are usually associated with pro-inflammatory responses, non-classic eicosanoids, as LX, have anti-inflammatory and pro-resolving properties. Eicosanoids like PGE₂, LTB₄ and EETs have been involved in promoting liver regeneration after partial hepatectomy. PGE₂ and LTB₄ have also been reported to participate in the regenerative phase after ischemia and reperfusion (I/R), while cysteinyl leukotrienes (Cys-LT) contribute to the inflammatory process associated with I/R and are also involved in liver fibrosis and cirrhosis. However, LX, another product of 5-LOX, have the opposite effect, acting as pro-resolving mediators in these pathologies. In liver cancer, most studies show that eicosanoids, with the exception of LX, promote the proliferation of hepatocellular carcinoma cells and favor metastasis. This review summarizes the synthesis of different eicosanoids in the liver and discusses key findings from basic research linking eicosanoids to liver repair, regeneration and cancer and the impact of targeting eicosanoid cascade. In addition, studies in patients are presented that explore the potential use of eicosanoids as biomarkers and show correlations between eicosanoid production and the course and prognosis of liver disease.

Expression pattern of mitogen-activated protein kinase kinase 4 and regulation to antibacterial factor ABF-1/2 in response to bacterial challenge from Artemia parthenogenetica

Mitogen-activated protein kinase 4, MKK4, is a key upstream kinase in the JNK/p38 MAPK pathway that has been reported to participate in multiple immune responses. In this study, the gene that encodes ApMKK4 was isolated and identified from Artemia parthenogenetica. It was found to contain a 1134 bp open reading frame encoding 378 amino acids. The predicted protein contains D domain, DVD domain and kinase domain. Homology analysis revealed that ApMKK4 shares 38-69% identity with MKK4 homologs from other species. Results revealed that ApMKK4 was mainly expressed during early development of which highest at the gastrula stage. After challenged by Vibrio harveyi and Micrococcus lysodeikticus, ApMKK4 was remarkably upregulated at 10 and 10³ cfu/mL bacterial concentrations, respectively. Through siRNAi, the transcript level of ApMKK4 was significantly decreased by 46-67%. Intriguingly, when the ApMKK4-knockdown nauplii faced with bacterial stimulation, the expression of ApMKK4 was completely restored in a short time. Moreover, this phenomenon also occurred in related antimicrobial peptide genes, ABF-1 and ABF-2. Our research reveals that ApMKK4 plays a pivotal role during early development and immune responses against bacterial infections.

LXA4-FPR2 signaling regulates radiation-induced pulmonary fibrosis via crosstalk with TGF-β/Smad signaling

Radiation therapy is an important modality in the treatment of lung cancer, but it can lead to radiation pneumonitis, and eventually radiation fibrosis. To date, only few available drugs can effectively manage radiation-induced pulmonary fibrosis. Lipoxins are endogenous molecules exhibit anti-inflammatory and pro-resolving effects. These molecules play a vital role in reducing excessive tissue injury and chronic inflammation; however, their effects on radiation-induced lung injury (RILI) are unknown. In this study, we investigated the effects of lipoxin A₄ (LXA₄) on RILI using our specialized small-animal model of RILI following focal-ablative lung irradiation (IR). LXA₄ significantly inhibited immune-cell recruitment and reduced IR-induced expression of pro-inflammatory cytokines and fibrotic proteins in the lung lesion sites. In addition, micro-CT revealed that LXA₄ reduced IR-induced increases in lung consolidation volume. The flexiVent^TM assays showed that LXA4 significantly reversed IR-induced lung function damage. Moreover, LXA4 downregulated the activities of NF-κB and the Smad-binding element promoters. The expression of FPR2, an LXA₄ receptor, increased during the development of IR-induced pulmonary fibrosis, whereas silencing of endogenous LXA₄ using an antagonist (WRW4) or FPR2 siRNA resulted in impaired development of pulmonary fibrosis in response to IR. Collectively, these data suggest that LXA₄ could serve as a potent therapeutic agent for alleviating RILI.

Bioinformatics-Based Study to Investigate Potential Differentially Expressed Genes and miRNAs in Pediatric Sepsis

BACKGROUND Sepsis is an extremely common health issue with a considerable mortality rate in children. Our understanding about the pathogenic mechanisms of sepsis is limited. The aim of this study was to identify the differential expression genes (DEGs) in pediatric sepsis through comprehensive analysis, and to provide specific insights for the clinical sepsis therapies in children. MATERIAL AND METHODS Three pediatric gene expression profiles (GSE25504, GSE26378, GSE26440) were downloaded from the Gene Expression Omnibus (GEO) database. The difference expression genes (DEGs) between pediatric sepsis and normal control group were screened with the GEO2R online tool. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the DEGs were performed. Cytoscape with CytoHubba were used to identify the hub genes. Finally, NetworkAnalyst was used to construct the targeted microRNAs (miRNAs) of the hub genes. RESULTS Totally, 160 overlapping upward genes and 61 downward genes were identified. In addition, 5 KEGG pathways, including hematopoietic cell lineage, Staphylococcus aureus infection, starch and sucrose metabolism, osteoclast differentiation, and tumor necrosis factor (TNF) signaling pathway, were significantly enriched using a database for labeling, visualization, and synthetic discovery. In combination with the results of the protein-protein interaction (PPI) network and CytoHubba, 9 hub genes including ITGAM, TLR8, IL1ß, MMP9, MPO, FPR2, ELANE, SPI1, and C3AR1 were selected. Combined with DEG-miRNAs visualization, 5 miRNAs, including has-miR-204-5p, has-miR-211-5p, has-miR-590-5p, and has-miR-21-5p, were predicted as possibly the key miRNAs. CONCLUSIONS Our findings will contribute to identification of potential biomarkers and novel strategies for pediatric sepsis treatment.