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*Periportal fibrosis progresses to bridging fibrosis  
*Periportal fibrosis progresses to bridging fibrosis  
*Increased proliferation of smaller bile ductules leading to regenerative nodule formation.
*Increased proliferation of smaller bile ductules leading to regenerative nodule formation.
 
<references />
==Pathophysiology of Alcoholic liver disease==
*[[Ethanol]] [[metabolism]] in the [[liver]] is carried out mainly by two [[enzymes]]:<ref name="pmid25548474">{{cite journal |vauthors=Ceni E, Mello T, Galli A |title=Pathogenesis of alcoholic liver disease: role of oxidative metabolism |journal=World J. Gastroenterol. |volume=20 |issue=47 |pages=17756–72 |year=2014 |pmid=25548474 |pmc=4273126 |doi=10.3748/wjg.v20.i47.17756 |url=}}</ref>
**[[Alcohol dehydrogenase]]
**[[Aldehyde dehydrogenase]]
*Both of these [[enzymes]] use [[Nicotinamide adenine dinucleotide|NAD]]+ as a cofactor. [[Alcohol]] is converted to [[acetaldehyde]] and [[acetaldehyde]] is then further [[oxidized]] to [[acetate]]. [[Acetaldehyde]] is the [[toxic]] [[metabolite]] in this process.
*The [[metabolism]] of [[alcohol]] in the [[liver]] ends up producing an excess of reduced [[nicotinamide adenine dinucleotide]] (NADH). This changes the reduction-oxidation potential in the [[liver]] and inhibits key [[metabolic]] processes in the [[liver]] such as, the [[tricarboxylic acid cycle]] and the [[oxidation]] of [[Fatty acid|fatty acids]] and thereby ends up promoting lipogenesis.<ref name="pmid15194557">{{cite journal |vauthors=You M, Crabb DW |title=Recent advances in alcoholic liver disease II. Minireview: molecular mechanisms of alcoholic fatty liver |journal=Am. J. Physiol. Gastrointest. Liver Physiol. |volume=287 |issue=1 |pages=G1–6 |year=2004 |pmid=15194557 |doi=10.1152/ajpgi.00056.2004 |url=}}</ref>
*Since [[acetaldehyde]] has an [[electrophilic]] nature it can form [[covalent]] chemical bonds with [[Protein|proteins]], [[Lipid|lipids]] and [[DNA]]. These [[Covalent bond|covalent]] bonds that are formed are extremely [[pathogenic]], as they have the ability to alter [[cell]] environments, [[protein]] structures and they can enable [[DNA]] damage and [[mutation]].<ref name="pmid16088993">{{cite journal |vauthors=Freeman TL, Tuma DJ, Thiele GM, Klassen LW, Worrall S, Niemelä O, Parkkila S, Emery PW, Preedy VR |title=Recent advances in alcohol-induced adduct formation |journal=Alcohol. Clin. Exp. Res. |volume=29 |issue=7 |pages=1310–6 |year=2005 |pmid=16088993 |doi= |url=}}</ref><ref name="pmid17590995">{{cite journal |vauthors=Niemelä O |title=Acetaldehyde adducts in circulation |journal=Novartis Found. Symp. |volume=285 |issue= |pages=183–92; discussion 193–7 |year=2007 |pmid=17590995 |doi= |url=}}</ref><ref name="pmid11841919">{{cite journal |vauthors=Tuma DJ |title=Role of malondialdehyde-acetaldehyde adducts in liver injury |journal=Free Radic. Biol. Med. |volume=32 |issue=4 |pages=303–8 |year=2002 |pmid=11841919 |doi= |url=}}</ref><ref name="pmid15540799">{{cite journal |vauthors=Tuma DJ, Casey CA |title=Dangerous byproducts of alcohol breakdown--focus on adducts |journal=Alcohol Res Health |volume=27 |issue=4 |pages=285–90 |year=2003 |pmid=15540799 |doi= |url=}}</ref><ref name="pmid16054980">{{cite journal |vauthors=Brooks PJ, Theruvathu JA |title=DNA adducts from acetaldehyde: implications for alcohol-related carcinogenesis |journal=Alcohol |volume=35 |issue=3 |pages=187–93 |year=2005 |pmid=16054980 |doi=10.1016/j.alcohol.2005.03.009 |url=}}</ref><ref name="pmid17718399">{{cite journal |vauthors=Seitz HK, Becker P |title=Alcohol metabolism and cancer risk |journal=Alcohol Res Health |volume=30 |issue=1 |pages=38–41, 44–7 |year=2007 |pmid=17718399 |pmc=3860434 |doi= |url=}}</ref><ref name="pmid9857222">{{cite journal |vauthors=Biewald J, Nilius R, Langner J |title=Occurrence of acetaldehyde protein adducts formed in various organs of chronically ethanol fed rats: an immunohistochemical study |journal=Int. J. Mol. Med. |volume=2 |issue=4 |pages=389–96 |year=1998 |pmid=9857222 |doi= |url=}}</ref><ref name="pmid17543846">{{cite journal |vauthors=Seitz HK, Meier P |title=The role of acetaldehyde in upper digestive tract cancer in alcoholics |journal=Transl Res |volume=149 |issue=6 |pages=293–7 |year=2007 |pmid=17543846 |doi=10.1016/j.trsl.2006.12.002 |url=}}</ref>
 
*The [[cytochrome]] [[Cytochrome P450|P450]] enzymes (CYP) are a part of the [[Microsomal Ethanol Oxidizing System|microsomal ethanol oxidizing system]]. These are a large group of enzymes involved in numerous oxidizing reactions on different substrates. They catalyze many different reactions in order to make them in to more polar metabolites that are easier to excrete.<ref name="pmid3678578">{{cite journal |vauthors=Guengerich FP, Beaune PH, Umbenhauer DR, Churchill PF, Bork RW, Dannan GA, Knodell RG, Lloyd RS, Martin MV |title=Cytochrome P-450 enzymes involved in genetic polymorphism of drug oxidation in humans |journal=Biochem. Soc. Trans. |volume=15 |issue=4 |pages=576–8 |year=1987 |pmid=3678578 |doi= |url=}}</ref>
 
*There is an ethanol inducible form of CYP enzymes that is working in a small amount under normal physiological conditions. This enzyme [[CYP2E1]] is converting [[ethanol]] to [[acetaldehyde]] and then to [[acetate]]. When there is chronic [[alcohol]] abuse, there is induction of the microsomal system and there is an increase in the expression of [[CYP2E1]]. This increase in [[CYP2E1]] expression under chronic [[ethanol]] consumption can be hazardous, as this [[oxidation]] reaction can produces many different ROS; O<sub>2</sub><sup>-</sup>, H<sub>2</sub>O<sub>2</sub>, OH<sup>-</sup> and hydroxyethyl radical (HER).<ref name="pmid36785782">{{cite journal |vauthors=Guengerich FP, Beaune PH, Umbenhauer DR, Churchill PF, Bork RW, Dannan GA, Knodell RG, Lloyd RS, Martin MV |title=Cytochrome P-450 enzymes involved in genetic polymorphism of drug oxidation in humans |journal=Biochem. Soc. Trans. |volume=15 |issue=4 |pages=576–8 |year=1987 |pmid=3678578 |doi= |url=}}</ref><ref name="pmid5009602">{{cite journal |vauthors=Lieber CS |title=Metabolism of ethanol and alcoholism: racial and acquired factors |journal=Ann. Intern. Med. |volume=76 |issue=2 |pages=326–7 |year=1972 |pmid=5009602 |doi= |url=}}</ref><ref name="pmid4402282">{{cite journal |vauthors=Lieber CS, DeCarli LM |title=The role of the hepatic microsomal ethanol oxidizing system (MEOS) for ethanol metabolism in vivo |journal=J. Pharmacol. Exp. Ther. |volume=181 |issue=2 |pages=279–87 |year=1972 |pmid=4402282 |doi= |url=}}</ref><ref name="pmid9114822">{{cite journal |vauthors=Lieber CS |title=Cytochrome P-4502E1: its physiological and pathological role |journal=Physiol. Rev. |volume=77 |issue=2 |pages=517–44 |year=1997 |pmid=9114822 |doi= |url=}}</ref><ref name="pmid2333153">{{cite journal |vauthors=Hansson T, Tindberg N, Ingelman-Sundberg M, Köhler C |title=Regional distribution of ethanol-inducible cytochrome P450 IIE1 in the rat central nervous system |journal=Neuroscience |volume=34 |issue=2 |pages=451–63 |year=1990 |pmid=2333153 |doi= |url=}}</ref><ref name="pmid17760783">{{cite journal |vauthors=Donohue TM, Cederbaum AI, French SW, Barve S, Gao B, Osna NA |title=Role of the proteasome in ethanol-induced liver pathology |journal=Alcohol. Clin. Exp. Res. |volume=31 |issue=9 |pages=1446–59 |year=2007 |pmid=17760783 |doi=10.1111/j.1530-0277.2007.00454.x |url=}}</ref><ref name="pmid17854134">{{cite journal |vauthors=Osna NA, Donohue TM |title=Implication of altered proteasome function in alcoholic liver injury |journal=World J. Gastroenterol. |volume=13 |issue=37 |pages=4931–7 |year=2007 |pmid=17854134 |pmc=4434615 |doi= |url=}}</ref><ref name="pmid18078827">{{cite journal |vauthors=Lu Y, Cederbaum AI |title=CYP2E1 and oxidative liver injury by alcohol |journal=Free Radic. Biol. Med. |volume=44 |issue=5 |pages=723–38 |year=2008 |pmid=18078827 |pmc=2268632 |doi=10.1016/j.freeradbiomed.2007.11.004 |url=}}</ref><ref name="pmid1545775">{{cite journal |vauthors=Yun YP, Casazza JP, Sohn DH, Veech RL, Song BJ |title=Pretranslational activation of cytochrome P450IIE during ketosis induced by a high fat diet |journal=Mol. Pharmacol. |volume=41 |issue=3 |pages=474–9 |year=1992 |pmid=1545775 |doi= |url=}}</ref><ref name="pmid2005876">{{cite journal |vauthors=Raucy JL, Lasker JM, Kraner JC, Salazar DE, Lieber CS, Corcoran GB |title=Induction of cytochrome P450IIE1 in the obese overfed rat |journal=Mol. Pharmacol. |volume=39 |issue=3 |pages=275–80 |year=1991 |pmid=2005876 |doi= |url=}}</ref><ref name="pmid11826398">{{cite journal |vauthors=Woodcroft KJ, Hafner MS, Novak RF |title=Insulin signaling in the transcriptional and posttranscriptional regulation of CYP2E1 expression |journal=Hepatology |volume=35 |issue=2 |pages=263–73 |year=2002 |pmid=11826398 |doi=10.1053/jhep.2002.30691 |url=}}</ref><ref name="pmid7700245">{{cite journal |vauthors=De Waziers I, Garlatti M, Bouguet J, Beaune PH, Barouki R |title=Insulin down-regulates cytochrome P450 2B and 2E expression at the post-transcriptional level in the rat hepatoma cell line |journal=Mol. Pharmacol. |volume=47 |issue=3 |pages=474–9 |year=1995 |pmid=7700245 |doi= |url=}}</ref><ref name="pmid9765518">{{cite journal |vauthors=Peng HM, Coon MJ |title=Regulation of rabbit cytochrome P450 2E1 expression in HepG2 cells by insulin and thyroid hormone |journal=Mol. Pharmacol. |volume=54 |issue=4 |pages=740–7 |year=1998 |pmid=9765518 |doi= |url=}}</ref><ref name="pmid1822117">{{cite journal |vauthors=Terelius Y, Norsten-Höög C, Cronholm T, Ingelman-Sundberg M |title=Acetaldehyde as a substrate for ethanol-inducible cytochrome P450 (CYP2E1) |journal=Biochem. Biophys. Res. Commun. |volume=179 |issue=1 |pages=689–94 |year=1991 |pmid=1822117 |doi= |url=}}</ref><ref name="pmid9726291">{{cite journal |vauthors=Wu YS, Salmela KS, Lieber CS |title=Microsomal acetaldehyde oxidation is negligible in the presence of ethanol |journal=Alcohol. Clin. Exp. Res. |volume=22 |issue=5 |pages=1165–9 |year=1998 |pmid=9726291 |doi= |url=}}</ref><ref name="pmid9309320">{{cite journal |vauthors=Brooks PJ |title=DNA damage, DNA repair, and alcohol toxicity--a review |journal=Alcohol. Clin. Exp. Res. |volume=21 |issue=6 |pages=1073–82 |year=1997 |pmid=9309320 |doi= |url=}}</ref>
 
*[[Ethanol]] [[metabolism]] additionally promotes [[lipogenesis]] through the inhibition of peroxisome proliferator activated receptor α (PPAR-α) and AMP kinase, as well as the stimulation of sterol regulatory element binding protein 1, which is a membrane bound [[Transcription (genetics)|transcription]] factor. The sequence of all these events results in a fat storing metabolic remodeling of the liver.<ref name="pmid12791698">{{cite journal |vauthors=Fischer M, You M, Matsumoto M, Crabb DW |title=Peroxisome proliferator-activated receptor alpha (PPARalpha) agonist treatment reverses PPARalpha dysfunction and abnormalities in hepatic lipid metabolism in ethanol-fed mice |journal=J. Biol. Chem. |volume=278 |issue=30 |pages=27997–8004 |year=2003 |pmid=12791698 |doi=10.1074/jbc.M302140200 |url=}}</ref><ref name="pmid15578517">{{cite journal |vauthors=You M, Matsumoto M, Pacold CM, Cho WK, Crabb DW |title=The role of AMP-activated protein kinase in the action of ethanol in the liver |journal=Gastroenterology |volume=127 |issue=6 |pages=1798–808 |year=2004 |pmid=15578517 |doi= |url=}}</ref><ref name="pmid16879892">{{cite journal |vauthors=Ji C, Chan C, Kaplowitz N |title=Predominant role of sterol response element binding proteins (SREBP) lipogenic pathways in hepatic steatosis in the murine intragastric ethanol feeding model |journal=J. Hepatol. |volume=45 |issue=5 |pages=717–24 |year=2006 |pmid=16879892 |doi=10.1016/j.jhep.2006.05.009 |url=}}</ref>
 
*Two key factors that play an important role in the [[inflammatory]] process that leads to the alcohol mediated liver injury are:<ref name="pmid6433728">{{cite journal |vauthors=Tsukamoto H, Reidelberger RD, French SW, Largman C |title=Long-term cannulation model for blood sampling and intragastric infusion in the rat |journal=Am. J. Physiol. |volume=247 |issue=3 Pt 2 |pages=R595–9 |year=1984 |pmid=6433728 |doi= |url=}}</ref><ref name="pmid11431739">{{cite journal |vauthors=Uesugi T, Froh M, Arteel GE, Bradford BU, Thurman RG |title=Toll-like receptor 4 is involved in the mechanism of early alcohol-induced liver injury in mice |journal=Hepatology |volume=34 |issue=1 |pages=101–8 |year=2001 |pmid=11431739 |doi=10.1053/jhep.2001.25350 |url=}}</ref>
**[[Endotoxin]]
**Gut permeability
*[[Endotoxin]] is associated to the [[lipopolysaccharide]] (LPS) component of the outer wall of [[gram-negative bacteria]] and is thought to be the key trigger in this [[Inflammation|inflammatory]] process.<ref name="pmid15723320">{{cite journal |vauthors=Wiest R, Garcia-Tsao G |title=Bacterial translocation (BT) in cirrhosis |journal=Hepatology |volume=41 |issue=3 |pages=422–33 |year=2005 |pmid=15723320 |doi=10.1002/hep.20632 |url=}}</ref><ref name="pmid8171045">{{cite journal |vauthors=Nanji AA, Khettry U, Sadrzadeh SM |title=Lactobacillus feeding reduces endotoxemia and severity of experimental alcoholic liver (disease) |journal=Proc. Soc. Exp. Biol. Med. |volume=205 |issue=3 |pages=243–7 |year=1994 |pmid=8171045 |doi= |url=}}</ref>
*Gut permeability is the factor that is either enabling or preventing the transfer of the LPS-endotoxin from the intestinal lumen into the portal circulation.<ref name="pmid7806045">{{cite journal |vauthors=Adachi Y, Moore LE, Bradford BU, Gao W, Thurman RG |title=Antibiotics prevent liver injury in rats following long-term exposure to ethanol |journal=Gastroenterology |volume=108 |issue=1 |pages=218–24 |year=1995 |pmid=7806045 |doi= |url=}}</ref><ref name="pmid6141332">{{cite journal |vauthors=Bjarnason I, Peters TJ, Wise RJ |title=The leaky gut of alcoholism: possible route of entry for toxic compounds |journal=Lancet |volume=1 |issue=8370 |pages=179–82 |year=1984 |pmid=6141332 |doi= |url=}}</ref>
*The fact that long term exposure to [[alcohol]] increases gut permeability has been observed in humans as LPS-endotoxin levels have been found to be elevated in patients with [[alcoholic]] [[liver]] injury.<ref name="pmid11236841">{{cite journal |vauthors=Urbaschek R, McCuskey RS, Rudi V, Becker KP, Stickel F, Urbaschek B, Seitz HK |title=Endotoxin, endotoxin-neutralizing-capacity, sCD14, sICAM-1, and cytokines in patients with various degrees of alcoholic liver disease |journal=Alcohol. Clin. Exp. Res. |volume=25 |issue=2 |pages=261–8 |year=2001 |pmid=11236841 |doi= |url=}}</ref>
 
*After the entry of LPS-[[endotoxin]] in to the [[portal]] [[circulation]] it binds to the LPS-binding protein, this is a key step in the inflammatory and histopathological response to [[alcohol]] ingestion.<ref name="pmid11884468">{{cite journal |vauthors=Uesugi T, Froh M, Arteel GE, Bradford BU, Wheeler MD, Gäbele E, Isayama F, Thurman RG |title=Role of lipopolysaccharide-binding protein in early alcohol-induced liver injury in mice |journal=J. Immunol. |volume=168 |issue=6 |pages=2963–9 |year=2002 |pmid=11884468 |doi= |url=}}</ref>
*The LPS-LPS binding protein complex binds to the [[CD14]] receptor on the cell surface membrane of the [[Kupffer cells]] in the [[liver]]. 
*Activation of these [[Kupffer cell|Kupffer cells]] requires 3 main cellular proteins:<ref name="pmid8045507">{{cite journal |vauthors=Adachi Y, Bradford BU, Gao W, Bojes HK, Thurman RG |title=Inactivation of Kupffer cells prevents early alcohol-induced liver injury |journal=Hepatology |volume=20 |issue=2 |pages=453–60 |year=1994 |pmid=8045507 |doi= |url=}}</ref>
**[[CD14]] (monocyte differentiation antigen)<ref name="pmid11254735">{{cite journal |vauthors=Yin M, Bradford BU, Wheeler MD, Uesugi T, Froh M, Goyert SM, Thurman RG |title=Reduced early alcohol-induced liver injury in CD14-deficient mice |journal=J. Immunol. |volume=166 |issue=7 |pages=4737–42 |year=2001 |pmid=11254735 |doi= |url=}}</ref>
**Toll-like receptor 4 (TLR4)<ref name="pmid18792393">{{cite journal |vauthors=Hritz I, Mandrekar P, Velayudham A, Catalano D, Dolganiuc A, Kodys K, Kurt-Jones E, Szabo G |title=The critical role of toll-like receptor (TLR) 4 in alcoholic liver disease is independent of the common TLR adapter MyD88 |journal=Hepatology |volume=48 |issue=4 |pages=1224–31 |year=2008 |pmid=18792393 |doi=10.1002/hep.22470 |url=}}</ref>
**MD2, a protein, binds [[TLR 4|TLR4]] with LPS-LPS binding protein
*The [[TLR 4|TLR4]] then signals activation of early growth response 1 (EGR1), which is an early gene-zinc-finger transcription factor.<ref name="pmid11477402">{{cite journal |vauthors=Akira S, Takeda K, Kaisho T |title=Toll-like receptors: critical proteins linking innate and acquired immunity |journal=Nat. Immunol. |volume=2 |issue=8 |pages=675–80 |year=2001 |pmid=11477402 |doi=10.1038/90609 |url=}}</ref> 
*The nuclear factor-kB ([[NF-kB]]) and the [[TLR 4|TLR4]] adapter also play an important role in the activation of the [[Kupffer cell|kupffer cells]].<ref name="pmid18713975">{{cite journal |vauthors=Zhao XJ, Dong Q, Bindas J, Piganelli JD, Magill A, Reiser J, Kolls JK |title=TRIF and IRF-3 binding to the TNF promoter results in macrophage TNF dysregulation and steatosis induced by chronic ethanol |journal=J. Immunol. |volume=181 |issue=5 |pages=3049–56 |year=2008 |pmid=18713975 |pmc=3690475 |doi= |url=}}</ref> 
*EGR1 plays the pivotal role in [[lipopolysaccharide]]-stimulated [[Tumor necrosis factor-alpha|TNF-α]] production. 
*In mice the absence of EGR1 prevents [[alcohol]] induced [[liver]] injury.<ref name="pmid15940638">{{cite journal |vauthors=McMullen MR, Pritchard MT, Wang Q, Millward CA, Croniger CM, Nagy LE |title=Early growth response-1 transcription factor is essential for ethanol-induced fatty liver injury in mice |journal=Gastroenterology |volume=128 |issue=7 |pages=2066–76 |year=2005 |pmid=15940638 |pmc=1959407 |doi= |url=}}</ref>
 
*[[Ethanol]] administration stimulates the release of [[mitochondrial]] [[cytochrome]] c and the expression of the [[Fas ligand]], this leads to hepatic cell apoptosis mediated by the cascade-3 activation pathway.<ref name="pmid11438480">{{cite journal |vauthors=Zhou Z, Sun X, Kang YJ |title=Ethanol-induced apoptosis in mouse liver: Fas- and cytochrome c-mediated caspase-3 activation pathway |journal=Am. J. Pathol. |volume=159 |issue=1 |pages=329–38 |year=2001 |pmid=11438480 |pmc=1850406 |doi=10.1016/S0002-9440(10)61699-9 |url=}}</ref> 
*The cumulative effect of [[Tumor necrosis factor-alpha|TNF-α]] and Fas-mediated apoptotic signals make the hepatocytes more susceptible to injury by stimulating an increase in natural killer T cells in the [[liver]].<ref name="pmid15131799">{{cite journal |vauthors=Minagawa M, Deng Q, Liu ZX, Tsukamoto H, Dennert G |title=Activated natural killer T cells induce liver injury by Fas and tumor necrosis factor-alpha during alcohol consumption |journal=Gastroenterology |volume=126 |issue=5 |pages=1387–99 |year=2004 |pmid=15131799 |doi= |url=}}</ref>

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief:

Overview

Cirrhosis occurs due to long term liver injury which causes an imbalance between matrix production and degradation. Early disruption of the normal hepatic matrix results in its replacement by scar tissue, which in turn has deleterious effects on cell function.

Pathophysiology

Pathophysiology [1][2][3][4][5][6]

  • When an injured issue is replaced by a collagenous scar, it is termed as fibrosis. The development of fibrosis requires several months, or even years, of ongoing injury.
  • When fibrosis of the liver reaches an advanced stage where distortion of the hepatic vasculature also occurs, it is termed as cirrhosis of the liver. If the damage progresses, panlobular cirrhosis may result.
  • The cellular mechanisms responsible for cirrhosis are similar regardless of the type of initial insult and site of injury within the liver lobule.
  • Viral hepatitis involves the periportal region, whereas involvement in alcoholic liver disease is largely pericentral.
  • Cirrhosis involves the following steps: [7]
    • Inflammation
    • Hepatic stellate cell activation
    • Angiogenesis
    • Fibrogenesis
  • Kupffer cells are hepatic macrophages responsible for Hepatic Stellate cell activation during injury.
  • The stellate cell, a cell type that normally stores vitamin A, plays a pivotal role in the development of cirrhosis.
  • Damage to the hepatic parenchyma leads to activation of the stellate cell, which becomes contractile (called myofibroblast) and obstructs blood flow in the circulation.
  • The hepatic stellate cell (also known as the perisinusoidal cell or Ito cell) plays a key role in the pathogenesis of liver fibrosis/cirrhosis.
  • Hepatic stellate cells(HSC) are usually located in the subendothelial space of Disse and become activated to a myofibroblast-like phenotype in areas of liver injury.
  • The stellate cell secretes TGF-β1, which leads to a fibrotic response and proliferation of connective tissue.
  • Connective tissue proliferation leads to the formation of extracellular matrix around hepatocytes and is composed of collagens (especially type I, III, IV), glycoprotein and proteoglycans.
  • Collagen and non collagenous matrix proteins responsible for fibrosis are produced by the activated Hepatic Stellate Cells(HSC).
  • Hepatocyte damage causes the release of lipid peroxidases from injured cell membranes leading to necrosis of parenchymal cells.
  • Activated HSC produce numerous cytokines and their receptors, such as PDGF and TGF-f31 which are responsible for fibrogenesis.
  • The matrix formed due to HSC activation is deposited in the space of Disse and leads to loss of fenestrations of endothelial cells, which is a process called capillarization.
  • Stellate cell activation leads to disturbance of the balance between matrix metalloproteinases and the naturally occurring inhibitors (TIMP 1 and 2). This is followed by matrix breakdown and replacement by connective tissue-secreted matrix.[8]
  • Matrix metalloproteinase (MMP) are calcium dependent enzymes that specifically degrade collagen and non collagenous substrate.
  • MMP-2 and stromyelysin-1 are produced by stellate cells.
  • MMP-2 degrades collagen and stromelysin-1 degrades proteoglycan and glycoprotein.
  • Cirrhosis leads to hepatic microvascular changes characterised by [9]
    •  formation of intra hepatic shunts (due to angiogenesis and loss of parenchymal cells) 
    • hepatic endothelial dysfunction
  • Sinusoidal endothelial cells are also important contributors of early fibrosis. Endothelial cells from a normal liver produces collagen, laminin and fibronectin.[10][11]
  • The endothelial dysfunction is characterised by [12]
    • insufficient release of vasodilators, such as nitric oxide due to oxidative stress
    • increased production of vasoconstrictors (mainly adrenergic stimulation and activation of endothelins and RAAS)
  • The liver responds to injury with new blood vessel formation. Mediators involved in angiogenesis include:
  • Angiogenesis in cirrhosis results in the production of immature and permeable VEGF induced neo-vessels that further exacerbate liver injury. [13][14]
  • Fibrosis eventually leads to formation of septae that grossly distort the liver architecture which includes both the liver parenchyma and the vasculature. A cirrhotic liver compromises hepatic sinusoidal exchange by shunting arterial and portal blood directly into the central veins (hepatic outflow). Vascularized fibrous septa connect central veins with portal tracts leading to islands of hepatocytes surrounded by fibrous bands without central veins.[15][16][17]
  • These mechanisms simultaneously occurring in the liver lead to fibrous tissue band (septa) and regenerative hepatocyte nodule formation, which eventually replace the entire liver architecture, leading to decreased blood flow throughout.
  • The formation of fibrotic bands is accompanied by regenerative nodule formation in the hepatic parenchyma.
  • Advancement of cirrhosis may lead to parenchymal dysfunction and development of portal hypertension.
  • The pathological hallmark of cirrhosis is the development of scar tissue that replaces normal parenchyma, leading to blockade of portal blood flow and disturbance of normal liver function.
  • Due to portal hypertension, the spleen becomes congested, which leads to hypersplenism and increased platelet sequestration.
  • Pathogenesis of cirrhosis based upon its individual cause is as follows:
  • The pathological hallmark of cirrhosis is the development of scar tissue that replaces normal parenchyma, leading to blockade of portal blood flow and disturbance of normal liver function.
  • The development of fibrosis requires several months, or even years, of ongoing injury.
  • Stellate cell activation leads to disturbance of the balance between matrix metalloproteinases and the naturally occurring inhibitors (TIMP 1 and 2). This is followed by matrix breakdown and replacement by connective tissue-secreted matrix.[22]
  • Matrix metalloproteinase (MMP) are calcium dependent enzymes that specifically degrade collagen and non collagenous substrate.
  • MMP-2 and stromyelysin-1 are produced by stellate cells.
  • MMP-2 degrades collagen and stromelysin-1 degrades proteoglycan and glycoprotein.
  • These mechanisms simultaneously occurring in the liver lead to fibrous tissue band (septa) and regenerative hepatocyte nodule formation, which eventually replace the entire liver architecture, leading to decreased blood flow throughout.
  • Portal hypertension may develop as a consequence of cirrhosis.
  • Due to portal hypertension, the spleen becomes congested, which leads to hypersplenism and increased platelet sequestration.
  • Portal hypertension is responsible for the most severe complications of cirrhosis.

Cirrhosis

Pathophysiology [1][2][3][4][5][6]

  • When an injured issue is replaced by a collagenous scar, it is termed as fibrosis.
  • When fibrosis of the liver reaches an advanced stage where distortion of the hepatic vasculature also occurs, it is termed as cirrhosis of the liver.
  • The cellular mechanisms responsible for cirrhosis are similar regardless of the type of initial insult and site of injury within the liver lobule.
  • Viral hepatitis involves the periportal region, whereas involvement in alcoholic liver disease is largely pericentral.
  • If the damage progresses, panlobular cirrhosis may result.
  • Cirrhosis involves the following steps: [7]
    • Inflammation
    • Hepatic stellate cell activation
    • Angiogenesis
    • Fibrogenesis
  • Kupffer cells are hepatic macrophages responsible for Hepatic Stellate cell activation during injury.
  • The hepatic stellate cell (also known as the perisinusoidal cell or Ito cell) plays a key role in the pathogenesis of liver fibrosis/cirrhosis.
  • Hepatic stellate cells(HSC) are usually located in the subendothelial space of Disse and become activated to a myofibroblast-like phenotype in areas of liver injury.
  • Collagen and non collagenous matrix proteins responsible for fibrosis are produced by the activated Hepatic Stellate Cells(HSC).
  • Hepatocyte damage causes the release of lipid peroxidases from injured cell membranes leading to necrosis of parenchymal cells.
  • Activated HSC produce numerous cytokines and their receptors, such as PDGF and TGF-f31 which are responsible for fibrogenesis.
  • The matrix formed due to HSC activation is deposited in the space of Disse and leads to loss of fenestrations of endothelial cells, which is a process called capillarization.
  • Cirrhosis leads to hepatic microvascular changes characterised by [9]
    •  formation of intra hepatic shunts (due to angiogenesis and loss of parenchymal cells) 
    • hepatic endothelial dysfunction
  • The endothelial dysfunction is characterised by [12]
    • insufficient release of vasodilators, such as nitric oxide due to oxidative stress
    • increased production of vasoconstrictors (mainly adrenergic stimulation and activation of endothelins and RAAS)
  • Fibrosis eventually leads to formation of septae that grossly distort the liver architecture which includes both the liver parenchyma and the vasculature. A cirrhotic liver compromises hepatic sinusoidal exchange by shunting arterial and portal blood directly into the central veins (hepatic outflow). Vascularized fibrous septa connect central veins with portal tracts leading to islands of hepatocytes surrounded by fibrous bands without central veins.[15][16][17]
  • The formation of fibrotic bands is accompanied by regenerative nodule formation in the hepatic parenchyma.
  • Advancement of cirrhosis may lead to parenchymal dysfunction and development of portal hypertension.
  • Portal HTN results from the combination of the following:
    • Structural disturbances associated with advanced liver disease account for 70% of total hepatic vascular resistance.
    •  Functional abnormalities such as endothelial dysfunction and increased hepatic vascular tone account for 30% of total hepatic vascular resistance.

Pathogenesis of Cirrhosis due to Alcohol:

  • More than 66 percent of all American adults consume alcohol.
  • Cirrhosis due to alcohol accounts for approximately forty percent of mortality rates due to cirrhosis.
  • Mechanisms of alcohol-induced damage include:
    • Impaired protein synthesis, secretion, glycosylation
  • Ethanol intake leads to elevated accumulation of intracellular triglycerides by:
    • Lipoprotein secretion
    • Decreased fatty acid oxidation
    • Increased fatty acid uptake
  • Alcohol is converted by Alcohol dehydrogenase to acetaldehyde.
  • Due to the high reactivity of acetaldehyde, it forms acetaldehyde-protein adducts which cause damage to cells by:
    • Trafficking of hepatic proteins
    • Interrupting microtubule formation
    • Interfering with enzyme activities
  • Damage of hepatocytes leads to the formation of reactive oxygen species that activate Kupffer cells.[6]
  • Kupffer cell activation leads to the production of profibrogenic cytokines that stimulates stellate cells.
  • Stellate cell activation leads to the production of extracellular matrix and collagen.
  • Portal triads develop connections with central veins due to connective tissue formation in pericentral and periportal zones, leading to the formation of regenerative nodules.
  • Shrinkage of the liver occurs over years due to repeated insults that lead to:
    • Loss of hepatocytes
    • Increased production and deposition of collagen


Pathology

  • There are four stages of Cirrhosis as it progresses:
    • Chronic nonsuppurative destructive cholangitis - inflammation and necrosis of portal tracts with lymphocyte infiltration leading to the destruction of the bile ducts.
    • Development of biliary stasis and fibrosis
  • Periportal fibrosis progresses to bridging fibrosis
  • Increased proliferation of smaller bile ductules leading to regenerative nodule formation.
  1. ↑ 1.0 1.1 Arthur MJ, Iredale JP (1994). "Hepatic lipocytes, TIMP-1 and liver fibrosis". J R Coll Physicians Lond. 28 (3): 200–8. PMID 7932316.
  2. ↑ 2.0 2.1 Friedman SL (1993). "Seminars in medicine of the Beth Israel Hospital, Boston. The cellular basis of hepatic fibrosis. Mechanisms and treatment strategies". N. Engl. J. Med. 328 (25): 1828–35. doi:10.1056/NEJM199306243282508. PMID 8502273.
  3. ↑ 3.0 3.1 Iredale JP (1996). "Matrix turnover in fibrogenesis". Hepatogastroenterology. 43 (7): 56–71. PMID 8682489.
  4. ↑ 4.0 4.1 Gressner AM (1994). "Perisinusoidal lipocytes and fibrogenesis". Gut. 35 (10): 1331–3. PMC 1374996. PMID 7959178.
  5. ↑ 5.0 5.1 Iredale JP (2007). "Models of liver fibrosis: exploring the dynamic nature of inflammation and repair in a solid organ". J. Clin. Invest. 117 (3): 539–48. doi:10.1172/JCI30542. PMC 1804370. PMID 17332881.
  6. ↑ 6.0 6.1 6.2 Arthur MJ (2002). "Reversibility of liver fibrosis and cirrhosis following treatment for hepatitis C". Gastroenterology. 122 (5): 1525–8. PMID 11984538.
  7. ↑ 7.0 7.1 Wanless IR, Wong F, Blendis LM, Greig P, Heathcote EJ, Levy G (1995). "Hepatic and portal vein thrombosis in cirrhosis: possible role in development of parenchymal extinction and portal hypertension". Hepatology. 21 (5): 1238–47. PMID 7737629.
  8. ↑ Iredale JP. Cirrhosis: new research provides a basis for rational and targeted treatments. BMJ 2003;327:143-7.Fulltext. PMID 12869458.
  9. ↑ 9.0 9.1 Fernández M, Semela D, Bruix J, Colle I, Pinzani M, Bosch J (2009). "Angiogenesis in liver disease". J. Hepatol. 50 (3): 604–20. doi:10.1016/j.jhep.2008.12.011. PMID 19157625.
  10. ↑ Maher JJ, McGuire RF (1990). "Extracellular matrix gene expression increases preferentially in rat lipocytes and sinusoidal endothelial cells during hepatic fibrosis in vivo". J. Clin. Invest. 86 (5): 1641–8. doi:10.1172/JCI114886. PMC 296914. PMID 2243137. Unknown parameter |month= ignored (help)
  11. ↑ Herbst H, Frey A, Heinrichs O; et al. (1997). "Heterogeneity of liver cells expressing procollagen types I and IV in vivo". Histochem. Cell Biol. 107 (5): 399–409. PMID 9208331. Unknown parameter |month= ignored (help)
  12. ↑ 12.0 12.1 García-Pagán JC, Gracia-Sancho J, Bosch J (2012). "Functional aspects on the pathophysiology of portal hypertension in cirrhosis". J. Hepatol. 57 (2): 458–61. doi:10.1016/j.jhep.2012.03.007. PMID 22504334.
  13. ↑ Lee JS, Semela D, Iredale J, Shah VH (2007). "Sinusoidal remodeling and angiogenesis: a new function for the liver-specific pericyte?". Hepatology. 45 (3): 817–25. doi:10.1002/hep.21564. PMID 17326208. Unknown parameter |month= ignored (help)
  14. ↑ Rosmorduc O, Housset C (2010). "Hypoxia: a link between fibrogenesis, angiogenesis, and carcinogenesis in liver disease". Semin. Liver Dis. 30 (3): 258–70. doi:10.1055/s-0030-1255355. PMID 20665378. Unknown parameter |month= ignored (help)
  15. ↑ 15.0 15.1 Schuppan D, Afdhal NH (2008). "Liver cirrhosis". Lancet. 371 (9615): 838–51. doi:10.1016/S0140-6736(08)60383-9. PMC 2271178. PMID 18328931.
  16. ↑ 16.0 16.1 Desmet VJ, Roskams T (2004). "Cirrhosis reversal: a duel between dogma and myth". J. Hepatol. 40 (5): 860–7. doi:10.1016/j.jhep.2004.03.007. PMID 15094237.
  17. ↑ 17.0 17.1 Wanless IR, Nakashima E, Sherman M (2000). "Regression of human cirrhosis. Morphologic features and the genesis of incomplete septal cirrhosis". Arch. Pathol. Lab. Med. 124 (11): 1599–607. doi:10.1043/0003-9985(2000)124<1599:ROHC>2.0.CO;2. PMID 11079009.
  18. ↑ Maher JJ, McGuire RF (1990). "Extracellular matrix gene expression increases preferentially in rat lipocytes and sinusoidal endothelial cells during hepatic fibrosis in vivo". J. Clin. Invest. 86 (5): 1641–8. doi:10.1172/JCI114886. PMC 296914. PMID 2243137. Unknown parameter |month= ignored (help)
  19. ↑ Herbst H, Frey A, Heinrichs O; et al. (1997). "Heterogeneity of liver cells expressing procollagen types I and IV in vivo". Histochem. Cell Biol. 107 (5): 399–409. PMID 9208331. Unknown parameter |month= ignored (help)
  20. ↑ Lee JS, Semela D, Iredale J, Shah VH (2007). "Sinusoidal remodeling and angiogenesis: a new function for the liver-specific pericyte?". Hepatology. 45 (3): 817–25. doi:10.1002/hep.21564. PMID 17326208. Unknown parameter |month= ignored (help)
  21. ↑ Rosmorduc O, Housset C (2010). "Hypoxia: a link between fibrogenesis, angiogenesis, and carcinogenesis in liver disease". Semin. Liver Dis. 30 (3): 258–70. doi:10.1055/s-0030-1255355. PMID 20665378. Unknown parameter |month= ignored (help)
  22. ↑ Iredale JP. Cirrhosis: new research provides a basis for rational and targeted treatments. BMJ 2003;327:143-7.Fulltext. PMID 12869458.
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