Publications by authors named "Ariel E Feldstein"

174 Publications

Dynamic Shifts in the Composition of Resident and Recruited Macrophages Influence Tissue Remodeling in NASH.

Cell Rep 2021 Jan;34(2):108626

Diabetes Research Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA; Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO, USA; Center for Human Nutrition, Washington University School of Medicine, St. Louis, MO, USA. Electronic address:

Macrophage-mediated inflammation is critical in the pathogenesis of non-alcoholic steatohepatitis (NASH). Here, we describe that, with high-fat, high-sucrose-diet feeding, mature TIM4 Kupffer cells (KCs) decrease in number, while monocyte-derived Tim4 macrophages accumulate. In concert, monocyte-derived infiltrating macrophages enter the liver and consist of a transitional subset that expresses Cx3cr1/Ccr2 and a second subset characterized by expression of Trem2, Cd63, Cd9, and Gpmnb; markers ascribed to lipid-associated macrophages (LAMs). The Cx3cr1/Ccr2-expressing macrophages, referred to as C-LAMs, localize to macrophage aggregates and hepatic crown-like structures (hCLSs) in the steatotic liver. In C-motif chemokine receptor 2 (Ccr2)-deficient mice, C-LAMs fail to appear in the liver, and this prevents hCLS formation, reduces LAM numbers, and increases liver fibrosis. Taken together, our data reveal dynamic changes in liver macrophage subsets during the pathogenesis of NASH and link these shifts to pathologic tissue remodeling.
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http://dx.doi.org/10.1016/j.celrep.2020.108626DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7877246PMC
January 2021

Sphingomyelin synthase 1 mediates hepatocyte pyroptosis to trigger non-alcoholic steatohepatitis.

Gut 2020 Nov 18. Epub 2020 Nov 18.

Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, South Korea

Objective: Lipotoxic hepatocyte injury is a primary event in non-alcoholic steatohepatitis (NASH), but the mechanisms of lipotoxicity are not fully defined. Sphingolipids and free cholesterol (FC) mediate hepatocyte injury, but their link in NASH has not been explored. We examined the role of free cholesterol and sphingomyelin synthases (SMSs) that generate sphingomyelin (SM) and diacylglycerol (DAG) in hepatocyte pyroptosis, a specific form of programmed cell death associated with inflammasome activation, and NASH.

Design: Wild-type C57BL/6J mice were fed a high fat and high cholesterol diet (HFHCD) to induce NASH. Hepatic SMS1 and SMS2 expressions were examined in various mouse models including HFHCD-fed mice and patients with NASH. Pyroptosis was estimated by the generation of the gasdermin-D N-terminal fragment. NASH susceptibility and pyroptosis were examined following knockdown of SMS1, protein kinase Cδ (PKCδ), or the NLR family CARD domain-containing protein 4 (NLRC4).

Results: HFHCD increased the hepatic levels of SM and DAG while decreasing the level of phosphatidylcholine. Hepatic expression of but not was higher in mouse models and patients with NASH. FC in hepatocytes induced expression, and knockdown prevented HFHCD-induced NASH. DAG produced by SMS1 activated PKCδ and NLRC4 inflammasome to induce hepatocyte pyroptosis. Depletion of prevented hepatocyte pyroptosis and the development of NASH. Conditioned media from pyroptotic hepatocytes activated the NOD-like receptor family pyrin domain containing 3 inflammasome (NLRP3) in Kupffer cells, but knockout mice were not protected against HFHCD-induced hepatocyte pyroptosis.

Conclusion: SMS1 mediates hepatocyte pyroptosis through a novel DAG-PKCδ-NLRC4 axis and holds promise as a therapeutic target for NASH.
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http://dx.doi.org/10.1136/gutjnl-2020-322509DOI Listing
November 2020

Characterization and Proteome of Circulating Extracellular Vesicles as Potential Biomarkers for NASH.

Hepatol Commun 2020 Sep 3;4(9):1263-1278. Epub 2020 Jul 3.

Department of Pediatrics University of California San Diego La Jolla CA.

Nonalcoholic fatty liver disease (NAFLD) is currently one of most common forms of chronic liver disease globally. NAFLD represents a wide spectrum of liver involvement from nonprogressive isolated steatosis to nonalcoholic steatohepatitis (NASH), characterized by liver necroinflammation and fibrosis and currently one of the top causes of end-stage liver disease and hepatocellular carcinoma. At present, there is a lack of effective treatments, and a central barrier to the development of therapies is the requirement for an invasive liver biopsy for diagnosis of NASH. Discovery of reliable, noninvasive biomarkers are urgently needed. In this study, we tested whether circulating extracellular vesicles (EVs), cell-derived small membrane-surrounded structures with a rich cargo of bioactive molecules, may serve as reliable noninvasive "liquid biopsies" for NASH diagnosis and assessment of disease severity. Total circulating EVs and hepatocyte-derived EVs were isolated by differential centrifugation and size-exclusion chromatography from serum samples of healthy individuals, patients with precirrhotic NASH, and patients with cirrhotic NASH. EVs were further characterized by flow cytometry, electron microscopy, western blotting, and dynamic light scattering assays before performing a proteomics analysis. Our findings suggest that levels of total and hepatocyte-derived EVs correlate with NASH clinical characteristics and disease severity. Additionally, using proteomics data, we developed understandable, powerful, and unique EV-based proteomic signatures for potential diagnosis of advanced NASH. Our study shows that the quantity and protein constituents of circulating EVs provide strong evidence for EV protein-based liquid biopsies for NAFLD/NASH diagnosis.
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http://dx.doi.org/10.1002/hep4.1556DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7471415PMC
September 2020

Mechanisms of nonalcoholic fatty liver disease and implications for surgery.

Langenbecks Arch Surg 2021 Feb 24;406(1):1-17. Epub 2020 Aug 24.

Department of Surgery, TUM School of Medicine, Klinikum rechts der Isar, Technical University of Munich, 81675, Munich, Germany.

Background: Nonalcoholic fatty liver disease (NAFLD) has become the most common form of chronic liver disease in both adults and children worldwide. Understanding the pathogenic mechanisms behind NAFLD provides the basis for identifying risk factors, such as metabolic syndrome, pancreatoduodenectomy, and host genetics, that lead to the onset and progression of the disease. The progression from steatosis to more severe forms, such as steatohepatitis, fibrosis, and cirrhosis, leads to an increased number of liver and non-liver complications.

Purpose: NAFLD-associated end-stage liver disease (ESLD) and hepatocellular carcinoma (HCC) often require surgery as the only curative treatment. In particular, the presence of NAFLD together with the coexisting metabolic comorbidities that usually occur in these patients requires careful preoperative diagnosis and peri-/postoperative management. Bariatric surgery, liver resection, and liver transplantation (LT) have shown favorable results for weight loss, HCC, and ESLD in patients with NAFLD. The LT demand and the increasing spread of NAFLD in the donor pool reinforce the already existing lack of donor organs.

Conclusion: In this review, we will discuss the diverse mechanisms underlying NAFLD, its implications for surgery, and the challenges for patient management.
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http://dx.doi.org/10.1007/s00423-020-01965-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7870612PMC
February 2021

Hepatocyte pyroptosis and release of inflammasome particles induce stellate cell activation and liver fibrosis.

J Hepatol 2021 Jan 4;74(1):156-167. Epub 2020 Aug 4.

Department of Pediatrics, University of California San Diego, La Jolla, CA, USA. Electronic address:

Background & Aims: Increased hepatocyte death contributes to the pathology of acute and chronic liver diseases. However, the role of hepatocyte pyroptosis and extracellular inflammasome release in liver disease is unknown.

Methods: We used primary mouse and human hepatocytes, hepatocyte-specific leucine 351 to proline Nlrp3CreA mice, and Gsdmd mice to investigate pyroptotic cell death in hepatocytes and its impact on liver inflammation and damage. Extracellular NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes were isolated from mutant NLRP3-YFP HEK cells and internalisation was studied in LX2 and primary human hepatic stellate cells. We also examined a cohort of 154 adult patients with biopsy-proven non-alcoholic fatty liver disease (Sir Charles Gairdner Hospital, Nedlands, Western Australia).

Results: We demonstrated that primary mouse and human hepatocytes can undergo pyroptosis upon NLRP3 inflammasome activation with subsequent release of NLRP3 inflammasome proteins that amplify and perpetuate inflammasome-driven fibrogenesis. Pyroptosis was inhibited by blocking caspase-1 and gasdermin D activation. The activated form of caspase-1 was detected in the livers and in serum from patients with non-alcoholic steatohepatitis and correlated with disease severity. Nlrp3CreA mice showed spontaneous liver fibrosis under normal chow diet, and increased sensitivity to liver damage and inflammation after treatment with low dose lipopolysaccharide. Mechanistically, hepatic stellate cells engulfed extracellular NLRP3 inflammasome particles leading to increased IL-1β secretion and α-smooth muscle actin expression. This effect was abrogated when cells were pre-treated with the endocytosis inhibitor cytochalasin B.

Conclusions: These results identify hepatocyte pyroptosis and release of inflammasome components as a novel mechanism to propagate liver injury and liver fibrosis development.

Lay Summary: Our findings identify a novel mechanism of inflammation in the liver. Experiments in cell cultures, mice, and human samples show that a specific form of cell death, called pyroptosis, leads to the release of complex inflammatory particles, the NLRP3 inflammasome, from inside hepatocytes into the extracellular space. From there they are taken up by other cells and thereby mediate inflammatory and pro-fibrogenic stress signals. The discovery of this mechanism may lead to novel treatments for chronic liver diseases in the future.
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http://dx.doi.org/10.1016/j.jhep.2020.07.041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7749849PMC
January 2021

The Power of Single-Cell Analysis for the Study of Liver Pathobiology.

Hepatology 2021 Jan;73(1):437-448

Department of Pediatrics, University of California San Diego, California and Rady Children's Hospital, San Diego, CA.

Single cell transcriptomics has emerged as a powerful lens through which to study the molecular diversity of complex tissues such as the liver, during health and disease, both in animal models and in humans. The earliest gene expression methods measured bulk tissue RNA, but the results were often confusing because they derived from the combined transcriptomes of many different cell types in unknown proportions. To better delineate cell-type-specific expression, investigators developed cell isolation, purification, and sorting protocols, yet still, the RNA derived from ensembles of cells obscured recognition of cellular heterogeneity. Profiling transcriptomes at the single-cell level has opened the door to analyses that were not possible in the past. In this review, we discuss the evolution of single cell transcriptomics and how it has been applied for the study of liver physiology and pathobiology to date.
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http://dx.doi.org/10.1002/hep.31485DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7854989PMC
January 2021

A Low ω-6 to ω-3 PUFA Ratio (n-6:n-3 PUFA) Diet to Treat Fatty Liver Disease in Obese Youth.

J Nutr 2020 09;150(9):2314-2321

Department of Pediatrics, Yale School of Medicine, New Haven, CT, USA.

Background: Recent literature suggests that the Western diet's imbalance between high ω-6 (n-6) and low ω-3 (n-3) PUFA intake contributes to fatty liver disease in obese youth.

Objectives: We tested whether 12 wk of a low n-6:n-3 PUFA ratio (4:1) normocaloric diet mitigates fatty liver and whether the patatin-like containing domain phospholipase 3 (PNPLA3) rs738409 variant affects the response.

Methods: In a single-arm unblinded study, obese youth 9-19 y of age with nonalcoholic fatty liver disease were treated with a normocaloric low n-6:n-3 PUFA ratio diet for 12 wk. The primary outcome was change in hepatic fat fraction (HFF%), measured by abdominal MRI. Metabolic parameters included alanine aminotransferase (ALT), lipids, measures of insulin sensitivity, and plasma oxidized linoleic acid metabolites (OXLAMs). Outcomes were also analyzed by PNPLA3 rs738409 genotype. Wilcoxon's signed rank test, the Mann-Whitney U test, and covariance pattern modeling were used.

Results: Twenty obese adolescents (median age: 13.3 y; IQR: 10.5-16.4 y) were enrolled and 17 completed the study. After 12 wk of dietary intervention, HFF% decreased by 25.8% (P = 0.009) despite stable weight. We observed a 34.4% reduction in ALT (P = 0.001), 21.9% reduction in triglycerides (P = 0.046), 3.28% reduction in LDL cholesterol (P = 0.071), and a 26.3% improvement in whole body insulin sensitivity (P = 0.032). The OXLAMs 9-hydroxy-octadecandienoic acid (9-HODE) (P = 0.011), 13-HODE (P = 0.007), and 9-oxo-octadecadienoic acid (9-oxoODE) (P = 0.024) decreased after 12 wk. HFF% declined in both the not-at-risk (CC/CG) and at-risk (GG) PNPLA3 rs738409 genotype groups, with significant (P = 0.016) HFF% reduction in the GG group. Changes in 9-HODE (P = 0.023), 9-oxoODE (P = 0.009), and 13-oxoODE (P = 0.003) differed between the 2 genotype groups over time.

Conclusions: These data suggest that, independently of weight loss, a low n-6:n-3 PUFA diet ameliorates the metabolic phenotype of adolescents with fatty liver disease and that response to this diet is modulated by the PNPLA3 rs738409 genotype.This trial was registered at clinicaltrials.gov as NCT01556113.
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http://dx.doi.org/10.1093/jn/nxaa183DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7467848PMC
September 2020

Comprehensive characterization of hepatocyte-derived extracellular vesicles identifies direct miRNA-based regulation of hepatic stellate cells and DAMP-based hepatic macrophage IL-1β and IL-17 upregulation in alcoholic hepatitis mice.

J Mol Med (Berl) 2020 07 18;98(7):1021-1034. Epub 2020 Jun 18.

Southern California Research Center for ALPD and Cirrhosis, Los Angeles, CA, USA.

Extracellular vesicles (EVs) have been growingly recognized as biomarkers and mediators of alcoholic liver disease (ALD) in human and mice. Here we characterized hepatocyte-derived EVs (HC-EVs) and their cargo for their biological functions in a novel murine model that closely resembles liver pathology observed in patients with alcoholic hepatitis (AH), the most severe spectrum of ALD. The numbers of circulating EVs and HC-EVs were significantly increased by 10-fold in AH mice compared with control mice. The miRNA (miR)-seq analysis detected 20 upregulated and 4 downregulated miRNAs (P < 0.001-0.05) in AH-HC-EVs. Treatment of murine primary hepatic stellate cells (HSCs) with AH-HC-EVs induced α-SMA (P < 0.05) and Col1a1 (P < 0.001). Smad7 and Nr1d2 genes, which were downregulated in HSCs from the AH mice, were predicted targets of 20 miRs upregulated in AH-HC-EVs. Among them were miR-27a and miR-181 which upon transfection in HSCs, indeed repressed Nr1d2, the quiescent HSC marker. AH-HC-EVs were also enriched with organelle proteins and mitochondrial DNA (10-fold, P < 0.05) and upregulated IL-1β and IL-17 production by hepatic macrophages (HMs) from AH mice in a TLR9-dependent manner. These results demonstrate HC-EV release is intensified in AH and suggest that AH-HC-EVs orchestrate liver fibrogenesis by directly targeting the quiescent HSC transcripts via a unique set of miRNAs and by amplifying HSC activation via DAMP-based induction of profibrogenic IL-1β and IL-17 by HMs. KEY MESSAGES: • Circulating EVs and HC-EVs were increased in AH mice compared with control mice • AH-HC-EVs were enriched in miRNAs, organelle proteins, and mitochondrial DNA • AH-HC-EVs increased cytokine production by AH-HMs in a TLR9-dependent manner.
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http://dx.doi.org/10.1007/s00109-020-01926-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7810220PMC
July 2020

The NLRP3 Inflammasome in Alcoholic and Nonalcoholic Steatohepatitis.

Semin Liver Dis 2020 Aug 11;40(3):298-306. Epub 2020 Jun 11.

Department of Pediatric Gastroenterology, University of California, San Diego (UCSD), San Diego, California and Rady Children's Hospital, San Diego, California.

Nonalcoholic steatohepatitis (NASH) and alcoholic hepatitis (ASH) are advanced forms of fatty liver diseases that are associated with a high morbidity and mortality worldwide. Patients with ASH or NASH are more susceptible to the progression of fibrosis and cirrhosis up to the development of hepatocellular carcinoma. Currently, there are limited medical therapies available. Accompanied by the asymptomatic disease progression, the demand for liver transplants is high. This review provides an overview about the growing evidence for a central role of NLR family pyrin domain containing 3 (NLRP3) inflammasome, a multiprotein complex that acts as a central driver of inflammation via activation of caspase 1, maturation and release of pro-inflammatory cytokines including interleukin-1β, and trigger of inflammatory pyroptotic cell death in both NASH and ASH. We also discuss potential therapeutic approaches targeting NLRP3 inflammasome and related upstream and downstream pathways to develop prognostic biomarkers and medical treatments for both liver diseases.
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http://dx.doi.org/10.1055/s-0040-1708540DOI Listing
August 2020

ASK1 inhibition reduces cell death and hepatic fibrosis in an Nlrp3 mutant liver injury model.

JCI Insight 2020 01 30;5(2). Epub 2020 Jan 30.

Department of Pediatrics, School of Medicine, UCSD, La Jolla, California, USA.

Hepatic inflammasome activation is considered a major contributor to liver fibrosis in NASH. Apoptosis signal-regulating kinase 1 (ASK1) is an apical mitogen-activated protein kinase that activates hepatic JNK and p38 to promote apoptosis, inflammation, and fibrosis. The aim of the current study was to investigate whether pharmacologic inhibition of ASK1 could attenuate hepatic fibrosis driven by inflammasome activation using gain-of-function NOD-like receptor protein 3 (Nlrp3) mutant mice. Tamoxifen-inducible Nlrp3 knock-in (Nlrp3A350V/+CreT-KI) mice and WT mice were administered either control chow diet or diet containing the selective ASK1 inhibitor GS-444217 for 6 weeks. Livers of Nlrp3-KI mice had increased inflammation, cell death, and fibrosis and increased phosphorylation of ASK1, p38, and c-Jun. GS-444217 reduced ASK1 pathway activation, liver cell death, and liver fibrosis. ASK1 inhibition resulted in a significant downregulation of genes involved in collagen production and extracellular matrix deposition, as well as in a reduced hepatic TNF-α expression. ASK1 inhibition also directly reduced LPS-induced gene expression of Collagen 1A1 (Col1a1) in hepatic stellate cells isolated from Nlrp3-KI mice. In conclusion, ASK1 inhibition reduced liver cell death and fibrosis downstream of inflammatory signaling induced by NLRP3. These data provide mechanistic insight into the antifibrotic mechanisms of ASK1 inhibition.
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http://dx.doi.org/10.1172/jci.insight.123294DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7098717PMC
January 2020

Designing Clinical Trials in Pediatric Nonalcoholic Steatohepatitis: Tips for Patient Selection and Appropriate Endpoints.

Hepatol Commun 2019 Dec 8;3(12):1563-1570. Epub 2019 Nov 8.

Department of Pediatric Gastroenterology University of California San Diego La Jolla CA.

Nonalcoholic fatty liver disease (NAFLD) is common in children and may progress to nonalcoholic steatohepatitis (NASH), advanced fibrosis, and even cirrhosis in childhood or early adulthood, indicating the need for pharmacologic treatment in this age group. Multiple trials are evaluating different therapeutic targets for NASH with fibrosis in adults, and the U.S. Food and Drug Administration has recently provided clear guidance to the pharmaceutical industry on developing drugs for the treatment of noncirrhotic NASH with liver fibrosis. Pediatric NAFLD has several unique aspects that distinguish it from the adult disease in terms of histology, our understanding of the natural history, and the utility of noninvasive tests. These differences have the potential to impact the design of clinical trials to test different drugs in the pediatric population. The aim of this article is to provide a review of common misconceptions regarding pediatric NAFLD and key differences from adult NAFLD. We have provided our recommendations on the design of early proof-of-concept and late phase 2 trials based on lessons learned from previous clinical trials. We believe that clinical drug development for children with NAFLD should happen in parallel with ongoing adult trials.
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http://dx.doi.org/10.1002/hep4.1449DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6887671PMC
December 2019

Identification of actin network proteins, talin-1 and filamin-A, in circulating extracellular vesicles as blood biomarkers for human myalgic encephalomyelitis/chronic fatigue syndrome.

Brain Behav Immun 2020 02 20;84:106-114. Epub 2019 Nov 20.

Department of Pediatrics, University of California San Diego (UCSD), La Jolla, CA 92093, USA.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a serious, debilitating disorder with a wide spectrum of symptoms, including pain, depression, and neurocognitive deterioration. Over 17 million people around the world have ME/CFS, predominantly women with peak onset at 30-50 years. Given the wide spectrum of symptoms and unclear etiology, specific biomarkers for diagnosis and stratification of ME/CFS are lacking. Here we show that actin network proteins in circulating extracellular vesicles (EVs) offer specific non-invasive biomarkers for ME/CFS. We found that circulating EVs were significantly increased in ME/CFS patients correlating to C-reactive protein, as well as biological antioxidant potential. Area under the receiver operating characteristic curve for circulating EVs was 0.80, allowing correct diagnosis in 90-94% of ME/CFS cases. From two independent proteomic analyses using circulating EVs from ME/CFS, healthy controls, idiopathic chronic fatigue, and depression, proteins identified from ME/CFS patients are involved in focal adhesion, actin skeletal regulation, PI3K-Akt signaling pathway, and Epstein-Barr virus infection. In particular, talin-1, filamin-A, and 14-3-3 family proteins were the most abundant proteins, representing highly specific ME/CFS biomarkers. Our results identified circulating EV number and EV-specific proteins as novel biomarkers for diagnosing ME/CFS, providing important information on the pathogenic mechanisms of ME/CFS.
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http://dx.doi.org/10.1016/j.bbi.2019.11.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7010541PMC
February 2020

MicroRNA 223 3p Negatively Regulates the NLRP3 Inflammasome in Acute and Chronic Liver Injury.

Mol Ther 2020 02 13;28(2):653-663. Epub 2019 Sep 13.

Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, USA; Rady Children's Hospital San Diego, 3020 Children's Way, MC 5030, San Diego, CA 92103-8450, USA. Electronic address:

The granulocyte-specific microRNA-223 (miR-223) has recently emerged as a negative regulator of NOD-like receptor 3 (NLRP3) expression, a central key player in chronic hepatic injuries such as fibrotic nonalcoholic steatohepatitis (NASH), as well as in other liver conditions including acute hepatitis. In this study, we evaluated the therapeutic effect of the synthetic miR-223 analog miR-223 3p in a murine model of lipopolysaccharide (LPS)/D-GalN-induced endotoxin acute hepatitis (EAH) or fibrotic NASH resultant of long-term feeding with a high-fat, fructose, and cholesterol (FFC) diet. miR-223 3p ameliorated the infiltration of monocytes, neutrophils, and early activated macrophages and downregulated the transcriptional expression of the pro-inflammatory cytokines Il6 and Il12 and the chemokines Ccl2, Ccl3, Cxcl1, and Cxcl2 in EAH. In fibrotic NASH, treatment with miR-223 3p led to a remarkable mitigation of fibrosis development and activation of hepatic stellate cells (HSCs). miR-223 3p disrupted the activation of the NLRP3 inflammasome by impairing the synthesis of cleaved interleukin-1β (IL-1β), mature IL-1β, and NLRP3, and the activation of caspase-1 p10 in both EAH and fibrotic NASH. Our data enlightens miR-223 3p as a post-transcriptional approach to treat acute and chronic hepatitis by silencing the activation of the NLRP3 inflammasome.
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http://dx.doi.org/10.1016/j.ymthe.2019.09.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7000998PMC
February 2020

Neutrophils contribute to spontaneous resolution of liver inflammation and fibrosis via microRNA-223.

J Clin Invest 2019 07 11;129(10):4091-4109. Epub 2019 Jul 11.

Department of Pediatrics, School of Medicine, UCSD, San Diego, California, USA.

Persistent, unresolved inflammation in the liver represents a key trigger for hepatic injury and fibrosis in various liver diseases and is controlled by classically activated pro-inflammatory macrophages, while restorative macrophages of the liver are capable of reversing inflammation once the injury trigger ceases. Here we have identified a novel role for neutrophils as key contributors to resolving the inflammatory response in the liver. Using two models of liver inflammatory resolution, we found that mice undergoing neutrophil depletion during the resolution phase exhibited unresolved hepatic inflammation, activation of the fibrogenic machinery and early fibrosis. These findings were associated with an impairment of the phenotypic switch of pro-inflammatory macrophages into a restorative stage after removal of the cause of injury and an increased NLRP3 / miR-223 ratio. Mice with a deletion of the granulocyte specific miR-223 gene showed a similarly impaired resolution profile that could be reversed by restoring miR-223 levels using a miR-223 3p mimic or infusing neutrophils from wildtype animals. Collectively, our findings reveal a novel role for neutrophils in the liver as resolving effector cells that induce pro-inflammatory macrophages into a restorative phenotype, potentially via miR-223.
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http://dx.doi.org/10.1172/JCI122258DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6763256PMC
July 2019

NAFLD in children: new genes, new diagnostic modalities and new drugs.

Nat Rev Gastroenterol Hepatol 2019 09 5;16(9):517-530. Epub 2019 Jul 5.

Texas Liver Institute, UT Health San Antonio, San Antonio, TX, USA.

Nonalcoholic fatty liver disease (NAFLD) has rapidly become the most common form of chronic liver disease in children and adolescents. Over the past 5 years, developments have revolutionized our understanding of the genetic factors, natural history, diagnostic modalities and therapeutic targets for this disease. New polymorphisms, such as those in PNPLA3, TM6SF2, MBOAT7 and GCKR, have been identified and used to predict the development and severity of NAFLD in both adults and children, and their interaction with environmental factors has been elucidated. Studies have demonstrated the true burden of paediatric NAFLD and its progression to end-stage liver disease in adulthood. In particular, nonalcoholic steatohepatitis can progress to advanced fibrosis and cirrhosis, emphasizing the importance of early diagnosis. Non-invasive imaging tests, such as transient elastography, will probably replace liver biopsy for the diagnosis of nonalcoholic steatohepatitis and the assessment of fibrosis severity in the near future. The therapeutic landscape is also expanding rapidly with the development of drugs that can modify liver steatosis, inflammation and fibrosis, indicating that pharmacotherapy for NAFLD will become available in the future. In this Review, we summarize current knowledge and new advances related to the pathogenesis and management of paediatric NAFLD.
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http://dx.doi.org/10.1038/s41575-019-0169-zDOI Listing
September 2019

Human induced pluripotent stem cell-derived extracellular vesicles reduce hepatic stellate cell activation and liver fibrosis.

JCI Insight 2019 06 11;5. Epub 2019 Jun 11.

Department of Pediatrics, UCSD, La Jolla, California, USA.

Progression of fibrosis and the development of cirrhosis are responsible for the liver related morbidity and mortality associated with chronic liver diseases. There is currently a great unmet need for effective anti-fibrotic strategies. Stem cells play a central role in wound healing responses to restore liver homeostasis following injury. Here we tested the hypothesis that extracellular vesicles (EVs) isolated from induced pluripotent stem cells (iPSC) modulate hepatic stellate cell (HSCs) activation and may have anti-fibrotic effects. Human iPSCs were generated by reprogramming primary skin fibroblasts. EVs were isolated by differential centrifugation, quantified by flow cytometry (FACS) and characterized by dynamic light scattering (DLS) and electron microscopy (TEM). Primary human HSCs were activated with TGFβ (10 ng/mL) and exposed to iPSC-EVs. Efficacy of iPSC-EVs was tested on HSC in vitro and in two murine models of liver injury (CCl4 and bile duct ligation). Characterization of iPSC-derived EVs by flow cytometry identified a large population of EVs released by iPSC, primarily with a diameter of 300 nm and that could be visualized by TEM as round, cup-shaped objects. Fluorescent tracing assays detected iPSC-EVs in HSC cytosol after a short incubation and EV uptake by HSCs resulted in both decrease of pro-fibrogenic markers αSMA, CollagenIα1, Fibronectin and TIMP-1 and HSC pro-fibrogenic responses such as chemotaxis and proliferation. Genomics analyses of iPSC-EV miRNA cargo revealed 22 highly expressed miRNAs, among which miR-92a-3p resulted the most abundant. Transcriptome analysis identified 60 genes down-modulated and 235 up-regulated in TGF-β-primed HSC in presence or absence of iPSC-EVs. Intravenous injection of iPSC-EVs in CCl4 and bile duct ligation-induced liver fibrosis resulted in anti-fibrotic effects at protein and gene levels. Results of this study identify iPSC-EVs as a novel anti-fibrotic approach that may reduce or reverse liver fibrosis in patients with chronic liver disease.
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http://dx.doi.org/10.1172/jci.insight.125652DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6675559PMC
June 2019

Novel Drivers of the Inflammatory Response in Liver Injury and Fibrosis.

Semin Liver Dis 2019 07 17;39(3):275-282. Epub 2019 May 17.

Department of Pediatric Gastroenterology, University of California, San Diego (UCSD), San Diego, California and Rady Children's Hospital, San Diego, California.

Hepatocyte demise as well as signals released by stressed hepatocytes have been now recognized as important triggers of liver inflammation. While traditional concepts classically viewed hepatocyte cell death to occur by either a nonlytic, noninflammatory form (apoptosis), or lytic, proinflammatory nonregulated cell death (necrosis), recent studies have provided evidence for additional mechanisms that can contribute to both acute and chronic liver damage. Two novel forms of cell death, pyroptosis and necroptosis, are of particular importance as they are highly regulated and intrinsically proinflammatory. Additionally, stressed hepatocytes may also release signals to attract and activate monocytes into proinflammatory macrophages. In this review, the authors discuss recent developments supporting the role of novel triggers of liver inflammation in various forms of liver injury and their potential translational implications.
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http://dx.doi.org/10.1055/s-0039-1685515DOI Listing
July 2019

Extracellular vesicles, the liquid biopsy of the future.

J Hepatol 2019 06 12;70(6):1292-1294. Epub 2019 Apr 12.

Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN, USA.

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http://dx.doi.org/10.1016/j.jhep.2019.01.030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7094760PMC
June 2019

Extracellular Vesicles in Liver Diseases: Meeting Report from the International Liver Congress 2018.

Hepatol Commun 2019 Feb 2;3(2):305-315. Epub 2019 Jan 2.

Department of Oncology, Hematology and Rheumatology University Hospital Bonn Bonn Germany.

Extracellular vesicles (EVs) are small and heterogeneous membrane-bound structures released by cells and found in all biological fluids. They are effective intercellular communicators, acting on a number of close and/or distant target cells. EV cargo may reflect the cell of origin as well as the specific stress that induces their formation and release. They transport a variety of bioactive molecules, including messenger RNA, noncoding RNAs, proteins, lipids, and metabolites, that can be transferred among cells, regulating various cell responses. Alteration in the concentration and composition of EVs in biological fluids is a typical hallmark of pathologies in different liver diseases. Circulating EVs can serve as biomarkers or as messengers following uptake by other cells. This review is a meeting report from the International Liver Congress 2018 (European Association for the Study of the Liver) celebrated in Paris (Symposium: Extracellular vesicles and signal transmission) that discusses the role of EVs in several liver diseases, highlighting their potential value as disease biomarkers and therapeutic opportunities.
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http://dx.doi.org/10.1002/hep4.1300DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6357829PMC
February 2019

Non-alcoholic fatty liver disease in pediatric type 2 diabetes: Metabolic and histologic characteristics in 38 subjects.

Pediatr Diabetes 2019 02 9;20(1):41-47. Epub 2018 Dec 9.

Pediatric Gastroenterology, University of California San Diego and Rady Children's Hospital San Diego, San Diego, California.

Background: Obesity and type 2 diabetes (T2D) is risk factors for non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). In children with T2D and liver biopsies, we investigated correlations between NAFLD/NASH and transaminase activity, A1c, lipids, and histologic changes in repeat biopsies.

Methods: Liver histology of children with T2D was evaluated using the NASH CRN scoring system and NAFLD Activity Score (NAS). We included results ≤6 months from biopsy and A1c nearest biopsy.

Results: Thirty-eight subjects (21 females, 17 males, 63.2% Hispanic, 15.8% Caucasian) had T2D diagnosed at 13.4 ± 2.7 years, 78.9% using metformin and 50% on insulin. Histological diagnosis of NAFLD occurred at mean age 14.3 ± 2.3 years, notable for NASH in 61%. Steatosis grade was higher in children with NASH than those without (mean 2.6 ± 0.7 vs 2.1 ± 0.5 (P < 0.001). Stage 3 fibrosis was noted only in subjects with NASH (26%). ALT was higher in NASH vs those without (112 ± 56 vs 85 ± 112, P = 0.016). NAS correlated with A1c (r = 0.51, P < 0.01) and triglycerides (r = 0.5, P < 0.01), and inversely with high-density lipoprotein (HDL) (r = -0.42, P = 0.04). Males had lower HDL and higher triglycerides (P < 0.04). In eight subjects with repeat biopsies, NAS was equal (37.5%) or improved (62.5%), and steatosis decreased (68.1% to 32.8%, P = 0.027).

Conclusions: In children with T2D and NAFLD, NASH is common. Having advanced fibrosis in 26% of NASH cases at this age is concerning. Better control of lipids, weight, and diabetes may help avoid worsening in NAS.
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http://dx.doi.org/10.1111/pedi.12798DOI Listing
February 2019

Extracellular vesicles in non-alcoholic and alcoholic fatty liver diseases.

Liver Res 2018 Mar 28;2(1):30-34. Epub 2018 Feb 28.

Division of Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Rady's Children Hospital, University of California San Diego, San Diego, CA, USA.

Fatty liver diseases, non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are the most common causes of chronic liver disease around the world. NAFLD and ALD can progress towards a more severe form of the disease, including as non-alcoholic steatohepatitis (NASH) and alcoholic steatohepatitis (ASH). In both instances central pathogenic events include hepatocyte death, liver inflammation, pathological angiogenesis, and fibrosis, followed by cirrhosis and cancer. Over the last few years, extracellular vesicles (EVs) have been identified as effective cell-to-cell communicators that contain a cell- and stress-specific cargo from the cell of origin and are capable of transferring this cargo to a target or acceptor cell. In this review, we focus on the growing evidence supporting a role for EVs in the pathophysiology of NASH and ASH as well as their potential roles as targets for novel biomarkers for these conditions.
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http://dx.doi.org/10.1016/j.livres.2018.01.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6190912PMC
March 2018

Differential Activation of Hepatic Invariant NKT Cell Subsets Plays a Key Role in Progression of Nonalcoholic Steatohepatitis.

J Immunol 2018 11 15;201(10):3017-3035. Epub 2018 Oct 15.

Division of Gastroenterology, Department of Medicine, University of California San Diego, La Jolla, CA 92093;

Innate immune mechanisms play an important role in inflammatory chronic liver diseases. In this study, we investigated the role of type I or invariant NKT (iNKT) cell subsets in the progression of nonalcoholic steatohepatitis (NASH). We used α-galactosylceramide/CD1d tetramers and clonotypic mAb together with intracytoplasmic cytokine staining to analyze iNKT cells in choline-deficient l-amino acid-defined (CDAA)-induced murine NASH model and in human PBMCs, respectively. Cytokine secretion of hepatic iNKT cells in CDAA-fed C57BL/6 mice altered from predominantly IL-17 to IFN-γ and IL-4 during NASH progression along with the downmodulation of TCR and NK1.1 expression. Importantly, steatosis, steatohepatitis, and fibrosis were dependent upon the presence of iNKT cells. Hepatic stellate cell activation and infiltration of neutrophils, Kupffer cells, and CD8 T cells as well as expression of key proinflammatory and fibrogenic genes were significantly blunted in Jα18 mice and in C57BL/6 mice treated with an iNKT-inhibitory RAR-γ agonist. Gut microbial diversity was significantly impacted in Jα18 and in CDAA diet-fed mice. An increased frequency of CXCR3IFN-γT-bet and IL-17A iNKT cells was found in PBMC from NASH patients in comparison with nonalcoholic fatty liver patients or healthy controls. Consistent with their in vivo activation, iNKT cells from NASH patients remained hyporesponsive to ex-vivo stimulation with α-galactosylceramide. Accumulation of plasmacytoid dendritic cells in both mice and NASH patients suggest their role in activation of iNKT cells. In summary, our findings indicate that the differential activation of iNKT cells play a key role in mediating diet-induced hepatic steatosis and fibrosis in mice and its potential involvement in NASH progression in humans.
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http://dx.doi.org/10.4049/jimmunol.1800614DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219905PMC
November 2018

Ethanol and unsaturated dietary fat induce unique patterns of hepatic ω-6 and ω-3 PUFA oxylipins in a mouse model of alcoholic liver disease.

PLoS One 2018 26;13(9):e0204119. Epub 2018 Sep 26.

Division of Gastroenterology, Hepatology, and Nutrition, Department of Medicine, University of Louisville, Louisville, Kentucky, United States of America.

Alcoholic liver disease (ALD), a significant health problem, progresses through the course of several pathologies including steatosis, steatohepatitis, fibrosis, and cirrhosis. There are no effective FDA-approved medications to prevent or treat any stages of ALD, and the mechanisms involved in ALD pathogenesis are not well understood. Bioactive lipid metabolites play a crucial role in numerous pathological conditions, as well as in the induction and resolution of inflammation. Herein, a hepatic lipidomic analysis was performed on a mouse model of ALD with the objective of identifying novel metabolic pathways and lipid mediators associated with alcoholic steatohepatitis, which might be potential novel biomarkers and therapeutic targets for the disease. We found that ethanol and dietary unsaturated, but not saturated, fat caused elevated plasma ALT levels, hepatic steatosis and inflammation. These pathologies were associated with increased levels of bioactive lipid metabolites generally involved in pro-inflammatory responses, including 13-hydroxy-octadecadienoic acid, 9,10- and 12,13-dihydroxy-octadecenoic acids, 5-, 8-, 9-, 11-, 15-hydroxy-eicosatetraenoic acids, and 8,9- and 11,12-dihydroxy-eicosatrienoic acids, in parallel with an increase in pro-resolving mediators, such as lipoxin A4, 18-hydroxy-eicosapentaenoic acid, and 10S,17S-dihydroxy-docosahexaenoic acid. Elucidation of alterations in these lipid metabolites may shed new light into the molecular mechanisms underlying ALD development/progression, and be potential novel therapeutic targets.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0204119PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6157879PMC
March 2019

Complex Network of NKT Cell Subsets Controls Immune Homeostasis in Liver and Gut.

Front Immunol 2018 11;9:2082. Epub 2018 Sep 11.

Laboratory of Immune Regulation, University of California, San Diego, La Jolla, CA, United States.

The liver-gut immune axis is enriched in several innate immune cells, including innate-like unconventional and adaptive T cells that are thought to be involved in the maintenance of tolerance to gut-derived antigens and, at the same time, enable effective immunity against microbes. Two subsets of lipid-reactive CD1d-restricted natural killer T (NKT) cells, invariant NKT (iNKT) and type II NKT cells present in both mice and humans. NKT cells play an important role in regulation of inflammation in the liver and gut due to their innate-like properties of rapid secretion of a myriad of pro-inflammatory and anti-inflammatory cytokines and their ability to influence other innate cells as well as adaptive T and B cells. Notably, a bi-directional interactive network between NKT cells and gut commensal microbiota plays a crucial role in this process. Here, we briefly review recent studies related to the cross-regulation of both NKT cell subsets and how their interactions with other immune cells and parenchymal cells, including hepatocytes and enterocytes, control inflammatory diseases in the liver, such as alcoholic and non-alcoholic steatohepatitis, as well as inflammation in the gut. Overwhelming experimental data suggest that while iNKT cells are pathogenic, type II NKT cells are protective in the liver. Since CD1d-dependent pathways are highly conserved from mice to humans, a detailed cellular and molecular understanding of these immune regulatory pathways will have major implications for the development of novel therapeutics against inflammatory diseases of liver and gut.
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http://dx.doi.org/10.3389/fimmu.2018.02082DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6141878PMC
September 2019

NLR Family Pyrin Domain-Containing 3 Inflammasome Activation in Hepatic Stellate Cells Induces Liver Fibrosis in Mice.

Hepatology 2019 02 3;69(2):845-859. Epub 2019 Jan 3.

Department of Pediatrics, University of California San Diego, La Jolla, CA.

The NLR family pyrin domain-containing 3 (NLRP3) inflammasome plays an important role in liver fibrosis (LF) development. However, the mechanisms involved in NLRP3-induced fibrosis are unclear. Our aim was to test the hypothesis that the NLRP3 inflammasome in hepatic stellate cells (HSCs) can directly regulate their activation and contribute to LF. Primary HSCs isolated from wild-type (WT), Nlrp3 , or Nlrp3 knock-in crossed to inducible (estrogen receptor Cre-CreT) mice were incubated with lipopolysaccharide (LPS) and adenosine triphosphate (ATP), or 4OH-tamoxifen, respectively. HSC-specific Nlrp3 knock-in mice were generated by crossing transgenic mice expressing lecithin retinol acyltransferase (Lrat)-driven Cre and maintained on standard rodent chow for 6 months. Mice were then sacrificed; liver tissue and serum were harvested. Nlrp3 inflammasome activation along with HSC phenotype and fibrosis were assessed by RT-PCR, western blotting, fluorescence-activated cell sorting (FACS), enzyme-linked immunosorbent assay, immunofluorescence (IF), and immunohistochemistry (IHC). Stimulated WT HSCs displayed increased levels of NLRP3 inflammasome-induced reactive oxygen species (ROS) production and cathepsin B activity, accompanied by an up-regulation of mRNA and protein levels of fibrotic makers, an effect abrogated in Nlrp3 HSCs. Nlrp3 CreT HSCs also showed elevated mRNA and protein expression of fibrotic markers 24 hours after inflammasome activation induced with 4-hydroxytamoxifen (4OHT). Protein and mRNA expression levels of fibrotic markers were also found to be increased in isolated HSCs and whole liver tissue from Nlrp3 Lrat Cre mice compared to WT. Liver sections from 24-week-old Nlrp Lrat Cre mice showed fibrotic changes with increased alpha smooth muscle actin (αSMA) and desmin-positive cells and collagen deposition, independent of inflammatory infiltrates; these changes were also observed after LPS challenge in 8-week-old Nlrp Lrat Cre mice. Conclusion: Our results highlight a direct role for the NLRP3 inflammasome in the activation of HSCs directly triggering LF.
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http://dx.doi.org/10.1002/hep.30252DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6351190PMC
February 2019

Liquid biopsy for liver diseases.

Gut 2018 12 3;67(12):2204-2212. Epub 2018 Sep 3.

Department of Pediatrics, University of California, San Diego, California, USA.

With the growing number of novel therapeutic approaches for liver diseases, significant research efforts have been devoted to the development of liquid biopsy tools for precision medicine. This can be defined as non-invasive reliable biomarkers that can supplement and eventually replace the invasive liver biopsy for diagnosis, disease stratification and monitoring of response to therapeutic interventions. Similarly, detection of liver cancer at an earlier stage of the disease, potentially susceptible to curative resection, can be critical to improve patient survival. Circulating extracellular vesicles, nucleic acids (DNA and RNA) and tumour cells have emerged as attractive liquid biopsy candidates because they fulfil many of the key characteristics of an ideal biomarker. In this review, we summarise the currently available information regarding these promising and potential transformative tools, as well as the issues still needed to be addressed for adopting various liquid biopsy approaches into clinical practice. These studies may pave the way to the development of a new generation of reliable, mechanism-based disease biomarkers.
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http://dx.doi.org/10.1136/gutjnl-2017-315846DOI Listing
December 2018

Serum Wisteria floribunda agglutinin-positive Mac-2-binding protein levels predict the presence of fibrotic nonalcoholic steatohepatitis (NASH) and NASH cirrhosis.

PLoS One 2018 30;13(8):e0202226. Epub 2018 Aug 30.

Department of Pediatrics, University of California - San Diego, La Jolla, California, United States of America.

Objective: The race for finding effective treatments for nonalcoholic fatty liver disease (NAFLD) has been slowed down by the high screen-failure rate for including patients in trials due to the lack of a noninvasive biomarker that can identify patients with significant disease. Recently, Wisteria floribunda agglutinin-positive Mac-2-binding protein (WFA+ -M2BP) has shown promise in predicting liver fibrosis. The aims of this study were to evaluate the utility of WFA+ -M2BP as a biomarker to sub-classify patients with NAFLD according to their disease severity and to assess its correlation with histologic features of NAFLD.

Methods: Patients undergoing biopsy for clinical suspicion of NAFLD and healthy controls were included. Patients with NAFLD were classified into: NAFL, early NASH (F0-F1), fibrotic NASH (F2-F3), and NASH cirrhosis (F4). Levels of WFA+ -M2BP in sera was measured by a HISCL™ M2BPGi™ assay kit using an automated immunoanalyzer (HISCL™-800; Sysmex, Kobe, Japan). Analysis of covariance was used to assess difference in WFA+ -M2BP between the groups and Spearman's correlation coefficients were used to assess correlation with histological features.

Results: Our cohort consisted of 20 healthy controls and 198 patients with biopsy-proven NAFLD divided as follows: 52 with NAFL, 62 with early NASH, 52 with fibrotic NASH, and 32 with NASH cirrhosis. WFA+ -M2BP level was found to be significantly increased in the fibrotic NASH and NASH cirrhosis groups compared to healthy controls and those with early NAFLD after adjusting for age, gender and BMI. Furthermore, patients with NASH cirrhosis had significantly higher WFA+ -M2BP levels (2.4[1.5, 4.2] C.O.I (Cut-off Index)) than those with fibrotic NASH (1.2[0.79, 1.9]), p < 0.001. WFA+ -M2BP level had moderate correlation with inflammation, ballooning and NAFLD activity score and strong correlation with fibrosis stage. Additionally, ROC curve analysis demonstrated that WFA+ -M2BP accurately differentiated F2-4 from F0-F1.

Conclusion: In a large cohort of patients with the full spectrum of NAFLD, WFA+ -M2BP levels predicted the presence of advanced disease and correlated strongly with fibrosis stage.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0202226PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6116978PMC
February 2019

Oxidized linoleic acid metabolites induce liver mitochondrial dysfunction, apoptosis, and NLRP3 activation in mice.

J Lipid Res 2018 09 3;59(9):1597-1609. Epub 2018 Jul 3.

Department of Pediatrics, University of California San Diego, La Jolla, CA. Electronic address:

Circulating oxidized linoleic acid (LA) metabolites (OXLAMs) are increased in patients with nonalcoholic steatohepatitis (NASH) and their levels correlate with disease severity. However, the mechanisms by which OXLAMs contribute to NASH development are incompletely understood. We tested the hypothesis that LA or OXLAMs provided directly through the diet are involved in the development of hepatic injury. C57BL/6 mice were fed an isocaloric high-fat diet containing low LA, high LA, or OXLAMs for 8 weeks. The livers of OXLAM-fed mice showed lower triglyceride concentrations, but higher FA oxidation and lipid peroxidation in association with increased oxidative stress. OXLAM-induced mitochondrial dysfunction was associated with reduced Complex I protein and hepatic ATP levels, as well as increased mitochondrial biogenesis and cytoplasmic mitochondrial DNA. Oxidative stress increased thioredoxin-interacting protein (TXNIP) in the liver and stimulated the activation of mitochondrial apoptosis signal-regulating kinase 1 (ASK1) leading to apoptosis. We also found increased levels of NOD-like receptor protein 3 (NLRP3) inflammasome components and Caspase-1 activation in the livers of OXLAM-fed mice. In vitro, OXLAMs induced hepatocyte cell death, which was partly dependent on Caspase-1 activation. This study identified key mechanisms by which dietary OXLAMs contribute to NASH development, including mitochondrial dysfunction, hepatocyte cell death, and NLRP3 inflammasome activation.
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http://dx.doi.org/10.1194/jlr.M083741DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121934PMC
September 2018

Effects of diets enriched in linoleic acid and its peroxidation products on brain fatty acids, oxylipins, and aldehydes in mice.

Biochim Biophys Acta Mol Cell Biol Lipids 2018 10 25;1863(10):1206-1213. Epub 2018 Jul 25.

Department of Food Science and Technology, College of Agriculture and Environmental Sciences, University of California, Davis, CA, USA.

Background: Linoleic acid (LA) is abundant in modern industrialized diets. Oxidized LA metabolites (OXLAMs) and reactive aldehydes, such as 4-hydroxy-2-nonenal (4-HNE), are present in heated vegetable oils and can be endogenously synthesized following consumption of dietary LA. OXLAMs have been implicated in cerebellar degeneration in chicks; 4-HNE is linked to neurodegenerative conditions in mammals. It unknown whether increasing dietary LA or OXLAMs alters the levels of oxidized fatty acids (oxylipins), precursor fatty acids, or 4-HNE in mammalian brain.

Objectives: To determine the effects of increases in dietary OXLAMs and dietary LA, on levels of fatty acids, oxylipins, and 4-HNE in mouse brain tissues.

Methods: Mice (n = 8 per group) were fed one of three controlled diets for 8 weeks: (1) a low LA diet, (2) a high LA diet, or (3) the low LA diet with added OXLAMs. Brain fatty acids, oxylipins, and 4-HNE were quantified in mouse cerebellum and cerebral cortex by gas chromatography-flame ionization detection, liquid chromatography-tandem mass spectrometry, and immunoblot, respectively.

Results: Increasing dietary LA significantly increased omega-6 fatty acids, decreased omega-3 fatty acids, and increased OXLAMs in brain. Dietary OXLAMs had minimal effect on oxidized lipids but did decrease both omega-6 and omega-3 fatty acids. Neither dietary LA nor OXLAMs altered 4-HNE levels.

Conclusion: Brain fatty acids are modulated by both dietary LA and OXLAMs, while brain OXLAMs are regulated by endogenous synthesis from LA, rather than incorporation of preformed OXLAMs.
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http://dx.doi.org/10.1016/j.bbalip.2018.07.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6180905PMC
October 2018