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      Obacunone Attenuates Liver Fibrosis with Enhancing Anti-Oxidant Effects of GPx-4 and Inhibition of EMT


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          Obacunone, a limonin triterpenoid extracted from Phellodendronchinense Schneid or Dictamnus dasycarpusb Turcz plant, elicits a variety of pharmacological effects such as anti-inflammatory, anti-neoplastic, anti-oxidation, and anti-lung-fibrosis ones. However, the anti-fibrotic effect of obacunone and the detailed underlying mechanism in liver fibrosis remain unclear. Liver fibrosis is a debilitating disease threatening human health. Transforming growth factor (TGF)-β/P-Smad is a major pathway of fibrosis featured with epithelia mesenchymal transformations (EMT) and collagen depositions, accompanying with excessive oxygen-free radicals. Nrf-2 acts as a key anti-oxidative regulator driving the expressions of various antioxidant-related genes. Glutathionperoxidase-4 (GPx-4) is a member of the glutathione peroxidase family that directly inhibits phospholipid oxidation to alleviate oxidative stress. In the present study, we aimed to explore the role of obacunone in mouse liver fibrosis model induced by carbon tetrachloride (CCl4) and in hepatic stellate cells (LX2 cell line) challenging with TGF-β. Obacunone demonstrated potent ameliorative effects on liver fibrosis both in activated LX2 and in mice liver tissues with reduced levels of α-SMA, collagen1, and vimentin. Obacunone also remarkably suppressed the TGF-β/P-Smad signals and EMT process. Meanwhile, obacunone exerted a potent anti-oxidation effect by reducing the levels of reactive oxygen species (ROS) in both models. The antioxidant effect of obacunone was attributed to the activation of GPx-4 and Nrf-2. In addition, the therapeutic effect of obacunone on LX2 cells was significantly removed in vitro plus with GPx-4 antagonist RSL3, in parallel with the re-elevated levels of ROS. Thus, we demonstrate that obacunone is able to attenuate liver fibrosis via enhancing GPx-4 signal and inhibition of the TGF-β/P-Smad pathway and EMT process.

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          The basics of epithelial-mesenchymal transition.

          The origins of the mesenchymal cells participating in tissue repair and pathological processes, notably tissue fibrosis, tumor invasiveness, and metastasis, are poorly understood. However, emerging evidence suggests that epithelial-mesenchymal transitions (EMTs) represent one important source of these cells. As we discuss here, processes similar to the EMTs associated with embryo implantation, embryogenesis, and organ development are appropriated and subverted by chronically inflamed tissues and neoplasias. The identification of the signaling pathways that lead to activation of EMT programs during these disease processes is providing new insights into the plasticity of cellular phenotypes and possible therapeutic interventions.
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            Hepatotoxicity and mechanism of action of haloalkanes: carbon tetrachloride as a toxicological model.

            The use of many halogenated alkanes such as carbon tetrachloride (CCl4), chloroform (CHCl3) or iodoform (CHI3), has been banned or severely restricted because of their distinct toxicity. Yet CCl4 continues to provide an important service today as a model substance to elucidate the mechanisms of action of hepatotoxic effects such as fatty degeneration, fibrosis, hepatocellular death, and carcinogenicity. In a matter of dose,exposure time, presence of potentiating agents, or age of the affected organism, regeneration can take place and lead to full recovery from liver damage. CCl4 is activated by cytochrome (CYP)2E1, CYP2B1 or CYP2B2, and possibly CYP3A, to form the trichloromethyl radical, CCl3*. This radical can bind to cellular molecules (nucleic acid, protein, lipid), impairing crucial cellular processes such as lipid metabolism, with the potential outcome of fatty degeneration (steatosis). Adduct formation between CCl3* and DNA is thought to function as initiator of hepatic cancer. This radical can also react with oxygen to form the trichloromethylperoxy radical CCl3OO*, a highly reactive species. CCl3OO* initiates the chain reaction of lipid peroxidation, which attacks and destroys polyunsaturated fatty acids, in particular those associated with phospholipids. This affects the permeabilities of mitochondrial, endoplasmic reticulum, and plasma membranes, resulting in the loss of cellular calcium sequestration and homeostasis, which can contribute heavily to subsequent cell damage. Among the degradation products of fatty acids are reactive aldehydes, especially 4-hydroxynonenal, which bind easily to functional groups of proteins and inhibit important enzyme activities. CCl4 intoxication also leads to hypomethylation of cellular components; in the case of RNA the outcome is thought to be inhibition of protein synthesis, in the case of phospholipids it plays a role in the inhibition of lipoprotein secretion. None of these processes per se is considered the ultimate cause of CCl4-induced cell death; it is by cooperation that they achieve a fatal outcome, provided the toxicant acts in a high single dose, or over longer periods of time at low doses. At the molecular level CCl4 activates tumor necrosis factor (TNF)alpha, nitric oxide (NO), and transforming growth factors (TGF)-alpha and -beta in the cell, processes that appear to direct the cell primarily toward (self-)destruction or fibrosis. TNFalpha pushes toward apoptosis, whereas the TGFs appear to direct toward fibrosis. Interleukin (IL)-6, although induced by TNFalpha, has a clearly antiapoptotic effect, and IL-10 also counteracts TNFalpha action. Thus, both interleukins have the potential to initiate recovery of the CCl4-damaged hepatocyte. Several of the above-mentioned toxication processes can be specifically interrupted with the use of antioxidants and mitogens, respectively, by restoring cellular methylation, or by preserving calcium sequestration. Chemicals that induce cytochromes that metabolize CCl4, or delay tissue regeneration when co-administered with CCl4 will potentiate its toxicity thoroughly, while appropriate CYP450 inhibitors will alleviate much of the toxicity. Oxygen partial pressure can also direct the course of CCl4 hepatotoxicity. Pressures between 5 and 35 mmHg favor lipid peroxidation, whereas absence of oxygen, as well as a partial pressure above 100 mmHg, both prevent lipid peroxidation entirely. Consequently, the location of CCl4-induced damage mirrors the oxygen gradient across the liver lobule. Mixed halogenated methanes and ethanes, found as so-called disinfection byproducts at low concentration in drinking water, elicit symptoms of toxicity very similar to carbon tetrachloride, including carcinogenicity.
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              Pathobiology of liver fibrosis: a translational success story.

              Reversibility of hepatic fibrosis and cirrhosis following antiviral therapy for hepatitis B or C has advanced the prospect of developing antifibrotic therapies for patients with chronic liver diseases, especially non-alcoholic steatohepatitis. Mechanisms of fibrosis have focused on hepatic stellate cells, which become fibrogenic myofibroblasts during injury through 'activation', and are at the nexus of efforts to define novel drug targets. Recent studies have clarified pathways of stellate cell gene regulation and epigenetics, emerging pathways of fibrosis regression through the recruitment and amplification of fibrolytic macrophages, nuanced responses of discrete inflammatory cell subsets and the identification of the 'ductular reaction' as a marker of severe injury and repair. Based on our expanded knowledge of fibrosis pathogenesis, attention is now directed towards strategies for antifibrotic therapies and regulatory challenges for conducting clinical trials with these agents. New therapies are attempting to: 1) Control or cure the primary disease or reduce tissue injury; 2) Target receptor-ligand interactions and intracellular signaling; 3) Inhibit fibrogenesis; and 4) Promote resolution of fibrosis. Progress is urgently needed in validating non-invasive markers of fibrosis progression and regression that can supplant biopsy and shorten the duration of clinical trials. Both scientific and clinical challenges remain, however the past three decades of steady progress in understanding liver fibrosis have contributed to an emerging translational success story, with realistic hopes for antifibrotic therapies to treat patients with chronic liver disease in the near future.

                Author and article information

                Role: Academic Editor
                09 January 2021
                January 2021
                : 26
                : 2
                [1 ]The College of Life Sciences, Northwest University, Xi’an 710127, China; Byqyongquan@ 123456163.com (Y.B.); m920659372@ 123456163.com (L.M.); wangfr1216@ 123456163.com (F.W.); myruio0405@ 123456163.com (R.S.); m13892081758@ 123456163.com (C.L.); 3025054@ 123456163.com (Q.X.)
                [2 ]State Key Laboratory of Cancer Biology, Department of Biopharmaceutics, Air Force Military Medical University, Xi’an 710083, China; kjjydwangww@ 123456163.com (W.W.); wanglilaura@ 123456163.com (L.W.)
                [3 ]Department of Pharmacology, School of Pharmacy, Air Force Medical University, Xi’an 710083, China; zhaidongsheng.ok@ 123456163.com
                Author notes
                [* ]Correspondence: fmmu.cg@ 123456163.com (G.C.); luzfliuq@ 123456fmmu.edu.cn (Z.L.); Tel.: +86-186-2904-7181 (G.C.); +86-152-0296-3679 (Z.L.)

                These authors contributed equally to this work.

                © 2021 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).


                obacunone,liver fibrosis,emt,hepatic stellate cells,gpx-4,tgf-β,oxidative stress


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