Role of sterile inflammation in fatty liver diseases

Sterile inflammation is a ubiquitous response of tissues to stress and injury,and occurs to a high degree in the liver.This results in high levels of tissue damage after development of the metabolic syndrome,and with alcohol excess.Inflammatory cytokines such as interleukin(IL)-1βare key in the initiation and propagation of inflammation and tissue damage.IL-1βis activated by a cytosolic machinery collectively termed the inflammasome,and by proteases released by neutrophils.Most of the inflammatory response is driven by macrophages,but hepatocytes,stellate and sinusoidal endothelial cells also have key roles.Hepatocytes for example release acute phase reactants which have pro-and anti-inflammatory effects,and are also a major source of pro-inflammatory damage associated molecules.Stellate cells can regulate differentiation of regulatory T cells by the production of transforming growth factor(TGF)βand all-trans retinoic acid,but the overall effect seems to be context dependent.The strong hepatic inflammatory response is regulated in many ways,with epigenetic regulation playing a major role.This is seen most notably with the rapid development of non-alcoholic steatohepatitis(NASH)in pups of female mice kept on a high fat diet prior to conception,but is likely occurring in adults that have been under metabolic stress for extended periods of time.Epigenetic regulation is of key importance due to its clinical implications,and potential to reveal new pathways for liver inflammation.

New uses for an old remedy:Digoxin as a potential treatment for steatohepatitis and other disorders

Repurposing of the widely available and relatively cheap generic cardiac glycoside digoxin for non-cardiac indications could have a wide-ranging impact on the global burden of several diseases.Over the past several years,there have been significant advances in the study of digoxin pharmacology and its potential noncardiac clinical applications,including anti-inflammatory,antineoplastic,metabolic,and antimicrobial use.Digoxin holds promise in the treatment of gastrointestinal disease,including nonalcoholic steatohepatitis and alcoholassociated steatohepatitis as well as in obesity,cancer,and treatment of viral infections,among other conditions.In this review,we provide a summary of the clinical uses of digoxin to date and discuss recent research on its emerging applications.

Sterile signals generate weaker and delayed macrophage NLRP3 inflammasome responses relative to microbial signals

Inflammation is the host response to microbial infection or sterile injury that aims to eliminate the insult, repair the tissue and restore homeostasis. Macrophages and the NLRP3 inflammasome are key sentinels for both types of insult. Although it is well established that the NLRP3 inflammasome is activated by microbial products and molecules released during sterile injury, it is unclear whether the responses elicited by these different types of signals are distinct. In this study, we used lipopolysaccharide and tumor necrosis factor as prototypical microbial and sterile signal 1 stimuli, respectively, to prime the NLRP3 inflammasome. We then used the bacterial toxin nigericin and a common product released from necrotic cells, ATP, as prototypical microbial and sterile signal 2 stimuli, respectively, to trigger the assembly of the NLRP3 inflammasome complex in mouse and human macrophages. We found that NLRP3 inflammasome responses were weakest when both signal 1 and signal 2 were sterile, but responses were faster and stronger when at least one of the two signals was microbial. Ultimately, the most rapid and potent responses were elicited when both signals were microbial. Together, these data suggest that microbial versus sterile signals are distinct, both kinetically and in magnitude, in their ability to generate inflammasome-dependent responses. This hierarchy of NLRP3 responses to sterile versus microbial stimuli likely reflects the urgent need for the immune system to respond rapidly to the presence of infection to halt pathogen dissemination.

Molecular pathogenesis of acetaminophen-induced liver injury and its treatment options

Acetaminophen,also known as N-acetyl-p-aminophenol(APAP),is commonly used as an antipyretic and analgesic agent.APAP overdose can induce hepatic toxicity,known as acetaminophen-induced liver injury(AILI).However,therapeutic doses of APAP can also induce AILI in patients with excessive alcohol intake or who are fasting.Hence,there is a need to understand the potential pathological mechanisms underlying AILI.In this review,we summarize three main mechanisms involved in the pathogenesis of AILI:hepatocyte necrosis,sterile inflammation,and hepatocyte regeneration.The relevant factors are elucidated and discussed.For instance,N-acetyl-p-benzoquinone imine(NAPQI)protein adducts trigger mitochondrial oxidative/nitrosative stress during hepatocyte necrosis,danger-associated molecular patterns(DAMPs)are released to elicit sterile inflammation,and certain growth factors contribute to liver regeneration.Finally,we describe the current potential treatment options for AILI patients and promising novel strategies available to researchers and pharmacists.This review provides a clearer understanding of AILI-related mechanisms to guide drug screening and selection for the clinical treatment of AILI patients in the future.

Acetaminophen-induced Liver Injury: from Animal Models to Humans

Drug-induced liver injury is an important clinical problem and a challenge for drug development.Whereas progress in understanding rare and unpredictable (idiosyncratic) drug hepatotoxicity is severely hampered by the lack of relevant animal models,enormous insight has been gained in the area of predictable hepatotoxins,in particular acetaminopheninduced liver injury,from a broad range of experimental models.Importantly,mechanisms of toxicity obtained with certain experimental systems,such as in vivo mouse models,primary mouse hepatocytes,and metabolically competent cell lines,are being confirmed in translational studies in patients and in primary human hepatocytes.Despite this progress,suboptimal models are still being used and experimental data can be confusing,leading to controversial conclusions.Therefore,this review attempts to discuss mechanisms of drug hepatotoxicity using the most studied drug acetaminophen as an example.We compare the various experimental models that are used to investigate mechanisms of acetaminophen hepatotoxicity,discuss controversial topics in the mechanisms,and assess how these experimental findings can be translated to the clinic.The success with acetaminophen in demonstrating the clinical relevance of experimental findings could serve as an example for the study of other drug toxicities.

Pre-treatment twice with liposomal clodronate protects against acetaminophen hepatotoxicity through a pre-conditioning effect

Background and aim:Acetaminophen(APAP)overdose is a major cause of acute liver injury,but the role of macrophages in the propagation of the hepatotoxicity is controversial.Early research revealed that macrophage inhibitors protect against APAP injury.However,later work demonstrated that macrophage ablation by acute pre-treatment with liposomal clodronate(LC)exacerbates the toxicity.To our surprise,during other studies,we observed that pre-treatment twice with LC seemed to protect against APAP hepatotoxicity,in contrast to acute pre-treatment.The aim of this study was to confirm that observation and to explore the mechanisms.Methods:We treated mice with empty liposomes(LE)or LC twice per week for 1 week before APAP overdose and collected blood and liver tissue at 0,2,and 6 h post-APAP.We then measured liver injury(serum alanine aminotransferase activity,histology),APAP bioactivation(total glutathione,APAP-protein adducts),oxidative stress(oxidized glutathione(GSSG)),glutamate-cysteine ligase subunit c(Gclc)mRNA,and nuclear factor erythroid 2-related factor(Nrf2)immunofluorescence.We also confirmed the ablation of macrophages by F4/80 immunohistochemistry.Results:Pre-treatment twice with LC dramatically reduced F4/80 staining,protected against liver injury,and reduced oxidative stress at 6 h post-APAP,without affecting APAP bioactivation.Importantly,Gclc mRNA was higher in the LC group at 0 h and total glutathione was higher at 2 h,indicating accelerated glutathione re-synthesis after APAP overdose due to greater basal glutamate-cysteine ligase.Oxidative stress was lower in the LC groups at both time points.Finally,total Nrf2 immunofluorescence was higher in the LC group.Conclusions:We conclude that multiple pre-treatments with LC protect against APAP by accelerating glutathione re-synthesis through glutamate-cysteine ligase.Investigators using twice or possibly more LC pre-treatments to deplete macrophages,including peritoneal macrophages,should be aware of this possible confounder.

Anti-Inflammatory Effect of Dendrobium Huoshanense Polysaccharides on Carrageenan-Induced Air Pouch Synovitis in Mice

Objective:The purpose was to observe the anti-inflammatory effects of Dendrobium huoshanense polysaccharides(DHPs)on carrageenan-induced sterile air pouch synovitis.Materials and Methods:A total of 30 Institute of Cancer Research(ICR)mice were randomly and equally assigned to the control,carrageenan-induced air pouch synovitis model(model),and carrageenan-induced air pouch synovitis model+DHP(200 mg/kg of body weight)(model+DHP)groups.Mice in the model+DHP group were intragastrically administered 200 mg/kg BW of DHP solution daily for 10 days.Mice in the control and model groups were intragastrically administered the same amount of distilled water.Two hours after intragastric administration on day 10,1 mL of a 1%carrageenan solution in a sterile 0.9%saline solution was injected into the air pouch of mice in the model and model+DHP groups.Six hours later,the mice were sacrificed and 4 mL of ice-cold sterile 0.9%saline solution was injected into the air pouch to fully wash its inner wall.The lavage fluid was collected to observe the color and turbidity of the lavage fluid,as well as the appearance of the backside of the air pouch.The exudate volume,total number of leukocytes,protein content,levels of malondialdehyde(MDA),interleukin-1β(IL-1β),and tumor necrosis factor-alpha(TNF-α),and total superoxide dismutase(T-SOD)activity of the lavage fluid were analyzed.Results:The results showed that pretreatment with DHPs reduced the carrageenan-induced exudate volume(P<0.01),total leukocytes(P<0.05),and protein content(P<0.01)in the air pouch lavage fluid.Furthermore,mice in the model+DHP group had significantly higher(P<0.01)T-SOD activity and lower MDA content(P<0.05),IL-1β(P<0.05),and TNF-α(P<0.01)levels in the air pouch lavage fluid compared with the model group.Conclusion:It is concluded that DHPs partially alleviated carrageenan-induced sterile inflammation,and its mechanism may be related to reducing exudation and scavenging oxygen-free radicals,inhibiting lipid peroxidation,and reducing the level of the proinflammatory factors,such as IL-1βand TNF-α.

Mitophagy deficiency activates stimulator of interferon genes activation and aggravates pathogenetic cardiac remodeling

Stimulator of interferon genes(STING)has recentlybeen found to play a crucial role in cardiac sterile inflammation and dysfunction.The role of stimulator of interferon genes(STING)in cardiac sterile inflammation and dysfunction has been recently discovered.This study aims to examine the involvement of STING in pathological cardiac remodeling and the mechanisms that govern the activation of the STING pathway.To investigate this,transverse aortic constriction(TAC)was performed on STING knockout mice to induce pressure over-load-induced cardiac remodeling.Subsequently,cardiac function,remodeling,and inflammation levels were evaluated.The STING pathway was found to be activated in the pressure overload-stressed heart and angiotensin II(Ang Il)-stimulated cardiac fibroblasts.Loss of STING expression led to a significant reduction in inflammatory responses,mitochondrial fragmenta-tion,and oxidative stress in the heart,resulting in attenuated cardiac remodeling and dysfunc-tion.Furthermore,the exacerbation of pressure overload-induced sTING-mediated inflammation and pathological cardiac remodeling was observed when mitophagy was sup-pressed through the silencing of Parkin,an E3 ubiquitin ligase.Taken together,these findings indicate that STING represents a newly identified and significant molecule implicated in the process of pathological cardiac remodeling and that mitophagy is an upstream mechanism that regulates STING activation.Targeting STING may therefore provide a novel therapeutic strategy for pathological cardiac remodeling and heart failure.