Oxidative Stress–Induced Liver Damage and Remodeling of the Liver Vasculature

As an organ critically important for targeting and clearing viruses, bacteria, and other foreign material, the liver operates via immune-tolerant, anti-inflammatory mechanisms indispensable to the immune response. Stress and stress-induced factors disrupt the homeostatic balance in the liver, inflicting tissue damage, injury, and remodeling. These factors include oxidative stress (OS) induced by viral infections, environmental toxins, drugs, alcohol, and diet. A recurrent theme seen among stressors common to multiple liver diseases is the induction of mitochondrial dysfunction, increased reactive oxygen species expression, and depletion of ATP. Inflammatory signaling additionally exacerbates the condition, generating a proinflammatory, immunosuppressive microenvironment and activation of apoptotic and necrotic mechanisms that disrupt the integrity of liver morphology. These pathways initiate signaling pathways that significantly contribute to the development of liver steatosis, inflammation, fibrosis, cirrhosis, and liver cancers. In addition, hypoxia and OS directly enhance angiogenesis and lymphangiogenesis in chronic liver diseases. Late-stage consequences of these conditions often narrow the outcomes for liver transplantation or result in death. This review provides a detailed perspective on various stress-induced factors and the specific focus on role of OS in different liver diseases with special emphasis on different molecular mechanisms. It also highlights how resultant changes in the liver vasculature correlate with pathogenesis. As an organ critically important for targeting and clearing viruses, bacteria, and other foreign material, the liver operates via immune-tolerant, anti-inflammatory mechanisms indispensable to the immune response. Stress and stress-induced factors disrupt the homeostatic balance in the liver, inflicting tissue damage, injury, and remodeling. These factors include oxidative stress (OS) induced by viral infections, environmental toxins, drugs, alcohol, and diet. A recurrent theme seen among stressors common to multiple liver diseases is the induction of mitochondrial dysfunction, increased reactive oxygen species expression, and depletion of ATP. Inflammatory signaling additionally exacerbates the condition, generating a proinflammatory, immunosuppressive microenvironment and activation of apoptotic and necrotic mechanisms that disrupt the integrity of liver morphology. These pathways initiate signaling pathways that significantly contribute to the development of liver steatosis, inflammation, fibrosis, cirrhosis, and liver cancers. In addition, hypoxia and OS directly enhance angiogenesis and lymphangiogenesis in chronic liver diseases. Late-stage consequences of these conditions often narrow the outcomes for liver transplantation or result in death. This review provides a detailed perspective on various stress-induced factors and the specific focus on role of OS in different liver diseases with special emphasis on different molecular mechanisms. It also highlights how resultant changes in the liver vasculature correlate with pathogenesis. Stress-induced health issues are one of the major challenges in modern society. Stress, which is defined by "conditions where an environmental demand exceeds the natural regulatory capacity of an organism, in particular situations that include unpredictability and uncontrollability,"1Koolhaas J.M. Bartolomucci A. Buwalda B. de Boer S.F. Flugge G. Korte S.M. Meerlo P. Murison R. Olivier B. Palanza P. Richter-Levin G. Sgoifo A. Steimer T. Stiedl O. van Dijk G. Wohr M. Fuchs E. Stress revisited: a critical evaluation of the stress concept.Neurosci Biobehav Rev. 2011; 35: 1291-1301Crossref PubMed Scopus (982) Google Scholar can alter the normal homeostasis of human physiological and psychological status.2Vere C.C. Streba C.T. Streba L.M. Ionescu A.G. Sima F. Psychosocial stress and liver disease status.World J Gastroenterol. 2009; 15: 2980-2986Crossref PubMed Scopus (65) Google Scholar,3Joung J.Y. Cho J.H. Kim Y.H. Choi S.H. Son C.G. A literature review for the mechanisms of stress-induced liver injury.Brain Behav. 2019; 9e01235Crossref PubMed Scopus (43) Google Scholar Both experimental and clinical studies show that stress significantly impacts hepatic physiology and contributes to liver diseases. Furthermore, it can also worsen the conditions of the patients with cardiovascular diseases, cancer, and HIV/AIDS.2Vere C.C. Streba C.T. Streba L.M. Ionescu A.G. Sima F. Psychosocial stress and liver disease status.World J Gastroenterol. 2009; 15: 2980-2986Crossref PubMed Scopus (65) Google Scholar, 3Joung J.Y. Cho J.H. Kim Y.H. Choi S.H. Son C.G. A literature review for the mechanisms of stress-induced liver injury.Brain Behav. 2019; 9e01235Crossref PubMed Scopus (43) Google Scholar, 4Cohen S. Janicki-Deverts D. Miller G.E. Psychological stress and disease.JAMA. 2007; 298: 1685-1687Crossref PubMed Scopus (1952) Google Scholar Liver, the largest solid organ of the body, is the center of metabolism and detoxification, and it is also a site for complex immunologic activity controlled by diverse immune cells populations, as well as nonhematopoietic cells.5Robinson M.W. Harmon C. O'Farrelly C. Liver immunology and its role in inflammation and homeostasis.Cell Mol Immunol. 2016; 13: 267-276Crossref PubMed Scopus (598) Google Scholar Liver receives the digested products, microbial agents, and antigens from the body through the portal vein, which can elicit immune cell activation and cause persistent and regulated inflammation.6Racanelli V. Rehermann B. The liver as an immunological organ.Hepatology. 2006; 43: S54-S62Crossref PubMed Scopus (967) Google Scholar Prolonged exposure to high-fat diet, alcohol, drugs, and stress hormones causes chronic liver inflammation, leading to chronic liver diseases.7Ozkan A. Stolley D. Cressman E.N.K. McMillin M. DeMorrow S. Yankeelov T.E. Rylander M.N. The influence of chronic liver diseases on hepatic vasculature: a liver-on-a-chip review.Micromachines (Basel). 2020; 11: 487Crossref PubMed Google Scholar Episodes of stress conditions such as physiological, psychological, or environmental stressors can have a negative impact with long-term consequences on the patients with pre-existing conditions, such as hepatitis B virus (HBV),8Kunkel E.J. Kim J.S. Hann H.W. Oyesanmi O. Menefee L.A. Field H.L. Lartey P.L. Myers R.E. Depression in Korean immigrants with hepatitis B and related liver diseases.Psychosomatics. 2000; 41: 472-480Crossref PubMed Scopus (57) Google Scholar hepatitis C virus (HCV),9Nagano J. Nagase S. Sudo N. Kubo C. Psychosocial stress, personality, and the severity of chronic hepatitis C.Psychosomatics. 2004; 45: 100-106Crossref PubMed Scopus (38) Google Scholar alcoholic hepatitis,10Fukudo S. Suzuki J. Tanaka Y. Iwahashi S. Nomura T. Impact of stress on alcoholic liver injury; a histopathological study.J Psychosom Res. 1989; 33: 515-521Crossref PubMed Google Scholar nonalcoholic steatohepatitis,11Elwing J.E. Lustman P.J. Wang H.L. Clouse R.E. Depression, anxiety, and nonalcoholic steatohepatitis.Psychosom Med. 2006; 68: 563-569Crossref PubMed Scopus (100) Google Scholar oxidative stress (OS), or endoplasmic reticulum (ER) stress in patients with hepatocellular carcinoma (HCC).12Luna-Marco C. Ubink A. Kopsida M. Heindryckx F. Endoplasmic reticulum stress and metabolism in hepatocellular carcinoma.Am J Pathol. 2023; 193: 1377-1388Abstract Full Text Full Text PDF PubMed Google Scholar,13Brahma M.K. Gilglioni E.H. Zhou L. Trepo E. Chen P. Gurzov E.N. Oxidative stress in obesity-associated hepatocellular carcinoma: sources, signaling and therapeutic challenges.Oncogene. 2021; 40: 5155-5167Crossref PubMed Scopus (16) Google Scholar In these stress-mediated liver damages, both the hepatocytes as well as the nonparenchymal cells, present in the liver vasculature, are impacted.7Ozkan A. Stolley D. Cressman E.N.K. McMillin M. DeMorrow S. Yankeelov T.E. Rylander M.N. The influence of chronic liver diseases on hepatic vasculature: a liver-on-a-chip review.Micromachines (Basel). 2020; 11: 487Crossref PubMed Google Scholar The current review highlights the principal contributing factors for stress-induced damage in liver and the liver vasculature, leading to the progression of liver disease. The liver is a highly vascularized organ with a dense network of blood vessels, bile ducts, and lymphatic vessels. It plays a critical role in transforming toxic substances of the body into a form that can be eliminated. Compared with other organs of the body, the liver has a high capacity to receive the cardiac output, and can receive up to 25% of cardiac output at rest.14Abdel-Misih S.R. Bloomston M. Liver anatomy.Surg Clin North Am. 2010; 90: 643-653Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar It is also the first organ to receive nutrient-rich blood from the intestines and participates in immune response.15Gibert-Ramos A. Sanfeliu-Redondo D. Aristu-Zabalza P. Martinez-Alcocer A. Gracia-Sancho J. Guixe-Muntet S. Fernandez-Iglesias A. The hepatic sinusoid in chronic liver disease: the optimal milieu for cancer.Cancers (Basel). 2021; 13: 5719Crossref PubMed Scopus (4) Google Scholar It is unique because of the superimposition of two inlet networks (ie, the hepatic artery and the portal vein), running in parallel; and one outlet network composed of central veins, or hepatic veins.16Lorente S. Hautefeuille M. Sanchez-Cedillo A. The liver, a functionalized vascular structure.Sci Rep. 2020; 1016194Crossref Scopus (28) Google Scholar The hepatic artery and portal vein play a major role in maintaining the blood supply in the liver. Liver is divided into hexagonal hepatic lobules, which consist of the central vein, portal triads, and liver resident cells. The portal triad is composed of portal vein, hepatic artery, and bile ducts7Ozkan A. Stolley D. Cressman E.N.K. McMillin M. DeMorrow S. Yankeelov T.E. Rylander M.N. The influence of chronic liver diseases on hepatic vasculature: a liver-on-a-chip review.Micromachines (Basel). 2020; 11: 487Crossref PubMed Google Scholar,17Fleischer J.R. Jodszuweit C.A. Ghadimi M. De Oliveira T. Conradi L.C. Vascular heterogeneity with a special focus on the hepatic microenvironment.Front Physiol. 2020; 11591901Crossref PubMed Scopus (4) Google Scholar (Figure 1). The portal vein collects blood from digestive tract, pancreas, and spleen, and contributes to approximately 75% of the liver's blood supply, whereas the remaining 25% is supplied by hepatic artery. The venous blood mixes with oxygenated blood from hepatic artery and flows through the liver sinusoid, the microvascular bed of liver. The sinusoids send the blood to the central vein.7Ozkan A. Stolley D. Cressman E.N.K. McMillin M. DeMorrow S. Yankeelov T.E. Rylander M.N. The influence of chronic liver diseases on hepatic vasculature: a liver-on-a-chip review.Micromachines (Basel). 2020; 11: 487Crossref PubMed Google Scholar,17Fleischer J.R. Jodszuweit C.A. Ghadimi M. De Oliveira T. Conradi L.C. Vascular heterogeneity with a special focus on the hepatic microenvironment.Front Physiol. 2020; 11591901Crossref PubMed Scopus (4) Google Scholar The liver sinusoidal endothelial cells (LSECs) are both morphologically and functionally different from the blood endothelial cells, as they form clustered fenestrations on sieve plates,16Lorente S. Hautefeuille M. Sanchez-Cedillo A. The liver, a functionalized vascular structure.Sci Rep. 2020; 1016194Crossref Scopus (28) Google Scholar form a discontinuous arrangement, lack the typical basement membrane, and have the attenuated extracellular matrix with fibronectin as the major component.18Xu B. Broome U. Uzunel M. Nava S. Ge X. Kumagai-Braesch M. Hultenby K. Christensson B. Ericzon B.G. Holgersson J. Sumitran-Holgersson S. Capillarization of hepatic sinusoid by liver endothelial cell-reactive autoantibodies in patients with cirrhosis and chronic hepatitis.Am J Pathol. 2003; 163: 1275-1289Abstract Full Text Full Text PDF PubMed Google Scholar In adult human liver, the length of sinusoids is approximately 250 μm, and their diameter varies between 7 and 15 μm.19Vollmar B. Menger M.D. The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair.Physiol Rev. 2009; 89: 1269-1339Crossref PubMed Scopus (368) Google Scholar Under normal physiological conditions, the unique arrangement of the LSECs facilitates exchange of large molecules and pathogens between hepatocytes and blood.18Xu B. Broome U. Uzunel M. Nava S. Ge X. Kumagai-Braesch M. Hultenby K. Christensson B. Ericzon B.G. Holgersson J. Sumitran-Holgersson S. Capillarization of hepatic sinusoid by liver endothelial cell-reactive autoantibodies in patients with cirrhosis and chronic hepatitis.Am J Pathol. 2003; 163: 1275-1289Abstract Full Text Full Text PDF PubMed Google Scholar Bile ducts carry bile from the liver to the gallbladder in a direction opposite to the liver sinusoids.20Du Y. Khandekar G. Llewellyn J. Polacheck W. Chen C.S. Wells R.G. A bile duct-on-a-chip with organ-level functions.Hepatology. 2020; 71: 1350-1363Crossref PubMed Scopus (41) Google Scholar Along with the blood vasculature, the liver has dense lymphatic vasculature, and a lymphatic system critical for the maintenance of body fluid homeostasis, inflammation, and immune response.21Burchill M.A. Goldberg A.R. Tamburini B.A.J. Emerging roles for lymphatics in chronic liver disease.Front Physiol. 2019; 10: 1579Crossref PubMed Scopus (11) Google Scholar,22Roy S. Banerjee P. Ekser B. Bayless K. Zawieja D. Alpini G. Glaser S.S. Chakraborty S. Targeting lymphangiogenesis and lymph node metastasis in liver cancer.Am J Pathol. 2021; 191: 2052-2063Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar Recent studies in murine models show that the liver lymphatics are organized segmentally, and intrahepatic lymphatic vessels are populated around the portal triad.23Frenkel N.C. Poghosyan S. Verheem A. Padera T.P. Rinkes I. Kranenburg O. Hagendoorn J. Liver lymphatic drainage patterns follow segmental anatomy in a murine model.Sci Rep. 2020; 1021808Crossref Scopus (11) Google Scholar Lymphatic capillaries, the thin-walled vessels composed of single layered lymphatic endothelial cells (LECs), collect the lymph, which is rich in cellular proteins, lipoproteins, and lymphocytes, and drain it into the collecting lymphatic vessels. Collecting lymphatic vessels, unlike the lymphatic capillaries, are covered by lymphatic muscle cells, which can pump the lymph from the liver to the lymph nodes.21Burchill M.A. Goldberg A.R. Tamburini B.A.J. Emerging roles for lymphatics in chronic liver disease.Front Physiol. 2019; 10: 1579Crossref PubMed Scopus (11) Google Scholar,24Tanaka M. Iwakiri Y. The hepatic lymphatic vascular system: structure, function, markers, and lymphangiogenesis.Cell Mol Gastroenterol Hepatol. 2016; 2: 733-749Abstract Full Text Full Text PDF PubMed Google Scholar About 70% to 80% of adult human liver is composed of parenchymal hepatocytes. Hepatocytes play crucial roles in metabolism, detoxification, innate immune regulation, protein synthesis, and protein secretion in the circulation.25Schulze R.J. Schott M.B. Casey C.A. Tuma P.L. McNiven M.A. The cell biology of the hepatocyte: a membrane trafficking machine.J Cell Biol. 2019; 218: 2096-2112Crossref PubMed Scopus (80) Google Scholar,26Zhou Z. Xu M.J. Gao B. Hepatocytes: a key cell type for innate immunity.Cell Mol Immunol. 2016; 13: 301-315Crossref PubMed Scopus (247) Google Scholar The main proteins secreted by the hepatocytes include α-fetoprotein, serum albumin, transferrin, plasminogen, fibrinogen, α-1-antitrypsin, C-reactive protein, and blood clotting factors (except for factor VIII).25Schulze R.J. Schott M.B. Casey C.A. Tuma P.L. McNiven M.A. The cell biology of the hepatocyte: a membrane trafficking machine.J Cell Biol. 2019; 218: 2096-2112Crossref PubMed Scopus (80) Google Scholar Hepatocytes are the first site for initiation of bile acid (BA) synthesis, which is then transported to the bile canaliculi. BAs take part in the emulsification, digestion of dietary fats, and removal of metabolic wastes.25Schulze R.J. Schott M.B. Casey C.A. Tuma P.L. McNiven M.A. The cell biology of the hepatocyte: a membrane trafficking machine.J Cell Biol. 2019; 218: 2096-2112Crossref PubMed Scopus (80) Google Scholar Bile is transported through a series of bile ductules to bile ducts and eventually transferred to the gallbladder and stored there until being hormonally stimulated and released into intestines. However, BAs retained in the liver because of impaired secretion cause hepatocellular toxicity.27Fang Y. Han S.I. Mitchell C. Gupta S. Studer E. Grant S. Hylemon P.B. Dent P. Bile acids induce mitochondrial ROS, which promote activation of receptor tyrosine kinases and signaling pathways in rat hepatocytes.Hepatology. 2004; 40: 961-971Crossref PubMed Scopus (106) Google Scholar Under pathologic conditions, enhanced level of BAs, deoxycholic acids, and taurodeoxycholic acids in the liver induce reactive oxygen species (ROS) production, which, in turn, activates the downstream signaling of extracellular signal-regulated kinase 1/2 and AKT pathways.27Fang Y. Han S.I. Mitchell C. Gupta S. Studer E. Grant S. Hylemon P.B. Dent P. Bile acids induce mitochondrial ROS, which promote activation of receptor tyrosine kinases and signaling pathways in rat hepatocytes.Hepatology. 2004; 40: 961-971Crossref PubMed Scopus (106) Google Scholar Hepatocytes are the major targets of ROS-mediated damage. High level of ROS stimulates mitochondrial hypertonicity, leading to the release of cytochrome c and hepatocyte apoptosis.28Wei S. Ma X. Zhao Y. Mechanism of hydrophobic bile acid-induced hepatocyte injury and drug discovery.Front Pharmacol. 2020; 11: 1084Crossref PubMed Scopus (26) Google Scholar The three-dimensional network of bile duct, or biliary tree, is lined with the heterogeneous, highly dynamic population of epithelial cells or cholangiocytes, which represent only 3% to 5% of total liver cell population.29Banales J.M. Huebert R.C. Karlsen T. Strazzabosco M. LaRusso N.F. Gores G.J. Cholangiocyte pathobiology.Nat Rev Gastroenterol Hepatol. 2019; 16: 269-281Crossref PubMed Scopus (237) Google Scholar However, cholangiocytes are responsible for up to 30% of total bile flow in humans, and the remaining 70% is produced from hepatocytes.29Banales J.M. Huebert R.C. Karlsen T. Strazzabosco M. LaRusso N.F. Gores G.J. Cholangiocyte pathobiology.Nat Rev Gastroenterol Hepatol. 2019; 16: 269-281Crossref PubMed Scopus (237) Google Scholar Cholangiocytes are activated by several stimuli, which include xenobiotic stimuli, cholestasis, ischemia, infections, and OS. Activated cholangiocytes have altered proliferation capacity and secrete a variety of profibrotic and proinflammatory factors.29Banales J.M. Huebert R.C. Karlsen T. Strazzabosco M. LaRusso N.F. Gores G.J. Cholangiocyte pathobiology.Nat Rev Gastroenterol Hepatol. 2019; 16: 269-281Crossref PubMed Scopus (237) Google Scholar,30Ostrycharz E. Wasik U. Kempinska-Podhorodecka A. Banales J.M. Milkiewicz P. Milkiewicz M. Melatonin protects cholangiocytes from oxidative stress-induced proapoptotic and proinflammatory stimuli via miR-132 and miR-34.Int J Mol Sci. 2020; 21: 9667Crossref PubMed Scopus (13) Google Scholar Hepatic stellate cells (HSCs), which represent approximately 10% of the liver cells, are the liver-specific fibroblasts that reside in the space of Disse, the space between the LSECs and hepatocytes (Figure 1). In healthy liver, HSCs are the primary storage site and metabolism sites of vitamin A.15Gibert-Ramos A. Sanfeliu-Redondo D. Aristu-Zabalza P. Martinez-Alcocer A. Gracia-Sancho J. Guixe-Muntet S. Fernandez-Iglesias A. The hepatic sinusoid in chronic liver disease: the optimal milieu for cancer.Cancers (Basel). 2021; 13: 5719Crossref PubMed Scopus (4) Google Scholar In case of liver injury, the HSCs get activated, differentiate into myofibroblasts, produce extracellular matrix components, and cause fibrosis in the liver. Interestingly, activated HSCs also produce a plethora of cytokines and chemokines, which include monocyte chemoattractant protein 1, IL-6, and transforming growth factor-β, which enable leukocyte recruitment into the liver. Recruited leukocytes secrete the proinflammatory factors and elicit the immune response as well as contribute to further activation of HSCs.31Winau F. Quack C. Darmoise A. Kaufmann S.H. Starring stellate cells in liver immunology.Curr Opin Immunol. 2008; 20: 68-74Crossref PubMed Scopus (70) Google Scholar Under OS, ROS activate the quiescent HSCs and cause extracellular matrix production, which, in the long run, contribute to fibrosis, cirrhosis, and HCC.32Ramos-Tovar E. Muriel P. Molecular mechanisms that link oxidative stress, inflammation, and fibrosis in the liver.Antioxidants (Basel). 2020; 9: 1279Crossref PubMed Scopus (99) Google Scholar Kupffer cells (KCs) are the main liver resident macrophages and are present in the liver sinusoid and adherent to the LSECs of the sinusoidal wall (Figure 1). The KCs serves as the first line of defense against bacterial infection and play important roles in host immune response.33Fox E.S. Thomas P. Broitman S.A. Comparative studies of endotoxin uptake by isolated rat Kupffer and peritoneal cells.Infect Immun. 1987; 55: 2962-2966Crossref PubMed Google Scholar, 34Bilzer M. Roggel F. Gerbes A.L. Role of Kupffer cells in host defense and liver disease.Liver Int. 2006; 26: 1175-1186Crossref PubMed Scopus (651) Google Scholar, 35Bleriot C. Dupuis T. Jouvion G. Eberl G. Disson O. Lecuit M. Liver-resident macrophage necroptosis orchestrates type 1 microbicidal inflammation and type-2-mediated tissue repair during bacterial infection.Immunity. 2015; 42: 145-158Abstract Full Text Full Text PDF PubMed Scopus (309) Google Scholar Under pathologic conditions, KCs are differentiated into M1-like (classic) or M2-like (alternative) macrophages. KCs are major sources of proinflammatory cytokines, which can cause liver damage.36Liu C. Tao Q. Sun M. Wu J.Z. Yang W. Jian P. Peng J. Hu Y. Liu C. Liu P. Kupffer cells are associated with apoptosis, inflammation and fibrotic effects in hepatic fibrosis in rats.Lab Invest. 2010; 90: 1805-1816Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar,37Zhang W. Zhu X.D. Sun H.C. Xiong Y.Q. Zhuang P.Y. Xu H.X. Kong L.Q. Wang L. Wu W.Z. Tang Z.Y. Depletion of tumor-associated macrophages enhances the effect of sorafenib in metastatic liver cancer models by antimetastatic and antiangiogenic effects.Clin Cancer Res. 2010; 16: 3420-3430Crossref PubMed Scopus (313) Google Scholar In response to stimuli, oxidized low-density lipoprotein, and lipopolysaccharide, the KCs and infiltrating macrophages in the liver produce ROS through the activation of NADPH oxidase 2 (Nox2), which eventually stimulate the KCs to secrete proinflammatory cytokines [eg, tumor necrosis factor (TNF)-α, IL-6, and IL-1β].38Kim S.Y. Jeong J.M. Kim S.J. Seo W. Kim M.H. Choi W.M. Yoo W. Lee J.H. Shim Y.R. Yi H.S. Lee Y.S. Eun H.S. Lee B.S. Chun K. Kang S.J. Kim S.C. Gao B. Kunos G. Kim H.M. Jeong W.I. Pro-inflammatory hepatic macrophages generate ROS through NADPH oxidase 2 via endocytosis of monomeric TLR4-MD2 complex.Nat Commun. 2017; 8: 2247Crossref PubMed Scopus (147) Google Scholar The highly specialized LSECs are specialized endothelial cells in the liver that form the interface between the lumen of sinusoid and the liver hepatocytes and hepatic stellate cells. In contrast to the other endothelial cells, LSECs display clusters of fenestrations that form the sieve plates.39Wisse E. De Zanger R.B. Charels K. Van Der Smissen P. McCuskey R.S. The liver sieve: considerations concerning the structure and function of endothelial fenestrae, the sinusoidal wall and the space of Disse.Hepatology. 1985; 5: 683-692Crossref PubMed Scopus (581) Google Scholar Because of the lack of organized basement membrane, the LSECs form highly permeable membrane.40Braet F. Wisse E. Structural and functional aspects of liver sinusoidal endothelial cell fenestrae: a review.Comp Hepatol. 2002; 1: 1Crossref PubMed Scopus (572) Google Scholar In normal liver, LSECs selectively control the diffusion of substrate between the blood and the space of Disse.41Poisson J. Lemoinne S. Boulanger C. Durand F. Moreau R. Valla D. Rautou P.E. Liver sinusoidal endothelial cells: physiology and role in liver diseases.J Hepatol. 2017; 66: 212-227Abstract Full Text Full Text PDF PubMed Scopus (549) Google Scholar,42Geraud C. Evdokimov K. Straub B.K. Peitsch W.K. Demory A. Dorflinger Y. Schledzewski K. Schmieder A. Schemmer P. Augustin H.G. Schirmacher P. Goerdt S. Unique cell type-specific junctional complexes in vascular endothelium of human and rat liver sinusoids.PLoS One. 2012; 7e34206Crossref PubMed Scopus (48) Google Scholar The phenotypes of the LSECs are maintained by the vascular endothelial growth factor-A (VEGF-A) stimulation of nitric oxide–dependent or nitric oxide–independent signaling.43Xie G. Wang X. Wang L. Wang L. Atkinson R.D. Kanel G.C. Gaarde W.A. Deleve L.D. Role of differentiation of liver sinusoidal endothelial cells in progression and regression of hepatic fibrosis in rats.Gastroenterology. 2012; 142: 918-927.e6Abstract Full Text Full Text PDF PubMed Scopus (259) Google Scholar In healthy liver, LSECs keep the HSCs quiescent. HSCs are the major source of fibrillar collagens and other components of the liver scar.44Wells R.G. Cellular sources of extracellular matrix in hepatic fibrosis.Clin Liver Dis. 2008; 12 (viii): 759-768Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar,45Kisseleva T. Brenner D. Molecular and cellular mechanisms of liver fibrosis and its regression.Nat Rev Gastroenterol Hepatol. 2021; 18: 151-166Crossref PubMed Scopus (594) Google Scholar In diseased condition, the damaged LSECs secrete proinflammatory cytokines and transforming growth factor-β and stimulate the HSCs and liver hepatocytes, which, in turn, causes further liver damage.7Ozkan A. Stolley D. Cressman E.N.K. McMillin M. DeMorrow S. Yankeelov T.E. Rylander M.N. The influence of chronic liver diseases on hepatic vasculature: a liver-on-a-chip review.Micromachines (Basel). 2020; 11: 487Crossref PubMed Google Scholar,34Bilzer M. Roggel F. Gerbes A.L. Role of Kupffer cells in host defense and liver disease.Liver Int. 2006; 26: 1175-1186Crossref PubMed Scopus (651) Google Scholar Liver is the largest lymph-producing organ of the body, and it has a highly dense lymphatic system.46Tanaka M. Iwakiri Y. Lymphatics in the liver.Curr Opin Immunol. 2018; 53: 137-142Crossref PubMed Scopus (38) Google Scholar The plasma component of the blood is filtered through the fenestrae of the LSECs and transferred to the space of Disse. This fluid flows through the space of mall, enters the interstitial space of the portal triad, and finally enters the lymphatic capillaries.24Tanaka M. Iwakiri Y. The hepatic lymphatic vascular system: structure, function, markers, and lymphangiogenesis.Cell Mol Gastroenterol Hepatol. 2016; 2: 733-749Abstract Full Text Full Text PDF PubMed Google Scholar The lymphatic vessels are primarily located around the portal triad and drain the lymph to nearby draining lymph nodes outside the liver.47Ohtani O. Ohtani Y. Lymph circulation in the liver.Anat Rec (Hoboken). 2008; 291: 643-652Crossref PubMed Scopus (138) Google Scholar Inside the liver, the lymphatic vessels are composed of LECs, which are identified by specific markers lymphatic vessel endothelial hyaluronan receptor 1 (Lyve-1), prospero homeobox protein 1 (Prox1), and podoplanin, and absence of α-smooth muscle actin–positive cells (smooth muscle cells/pericytes). LSECs also express Lyve-1, and hepatocytes express Prox1.48Truman L.A. Bentley K.L. Smith E.C. Massaro S.A. Gonzalez D.G. Haberman A.M. Hill M. Jones D. Min W. Krause D.S. Ruddle N.H. ProxTom lymphatic vessel reporter mice reveal Prox1 expression in the adrenal medulla, megakaryocytes, and platelets.Am J Pathol. 2012; 180: 1715-1725Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar Thus, the co-existence of the above three markers identifies LECs. In normal healthy livers, LECs are required to maintain the homeostasis of fat metabolism as they can uptake the cholesterol through the scavenger receptor class B type I.49Lim H.Y. Thiam C.H. Yeo K.P. Bisoendial R. Hii C.S. McGrath K.C. Tan K.W. Heather A. Alexander J.S. Angeli V. Lymphatic vessels are essential for the removal of cholesterol from peripheral tissues by SR-BI-mediated transport of HDL.Cell Metab. 2013; 17: 671-684Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar,50Martel C. Randolph G.J. Atherosclerosis and transit of HDL through the lymphatic vasculature.Curr Atheroscler Rep. 2013; 15: 354Crossref PubMed Scopus (22) Google Scholar Several studies report that, under pathologic conditions, enhanced level of OS, which is associated with production of ROS, increases the proliferation of LECs and causes expansion of the lymphatic network or lymphangiogenesis.24Tanaka M. Iwakiri Y. The hepatic lymphatic vascular system: structure, function, markers, and lymphangiogenesis.Cell Mol Gastroenterol Hepatol. 2016; 2: 733-749Abstract Full Text Full Text PDF PubMed Google Scholar,51Banerjee P. Kumaravel S. Roy S. Gaddam N. Odeh J. Bayless K.J. Glaser S. Chakraborty S. Conjugated bile acids promote lymphangiogenesis by modulation of the reactive oxygen species-p90RSK-vascular endothelial growth factor receptor 3 pathway.Cells. 2023; 12: 526Crossref PubMed Scopus (0) Google Scholar, 52Singla B. Aithabathula R.V. Kiran S. Kapil S. Kumar S. Singh U.P. Reactive oxygen species in regulating lymphangiogenesis and lymphatic function.Cells. 2022; 11: 1750Crossref PubMed Scopus (4) Google Schola