Ruffle formation in the evaluation of stimulatory state of hepatic macrophages in rats

ABSTRACT— Morphological changes in hepatic macrophages after stimulation were observed with a transmission electron microscope in rats. In the normal liver ruffle formation occupied less than 30% of the cell surface facing the sinusoidal space in 21 of 25 macrophages. When the rats received a dose of carbon tetrachloride, hepatic macrophages I day later showed ruffle formation to the same extent as in normal rats. In contrast, in rats 6 days after a dose of Corynebacterium parvum, ruffle formation was intensified, and in 19 of 25 macrophages it was seen to occupy more than 30% of the cell surface (p<0.01); 9 of 10 macrophages with more than 70% of the cell surface affected belonged to these rats. Considering that hepatic macrophages at I or 6 days after treatment with carbon tetrachloride or Corynebacterium parvum are at the responsive or primed stages, respectively, measurement of the extent of ruffle formation in hepatic macrophages with a transmission electron microscope may provide a useful tool in estimating their stimulatory stage.     

Intravascular coagulation in the development of massive hepatic necrosis induced by Corynebacterium parvum and endotoxin in rats

When Escherichia coli endotoxin was intravenously injected into rats given killed Corynebacterium parvum 6 days previously, fibrin deposition and endothelial cell injury occurred in hepatic sinusoids at 1.5 h and were intensified thereafter. Serum alanine aminotransferase values were increased along with prothrombin time and decreased plasma levels of antithrombin III and coagulation factor VIII:C at 5 h. Antithrombin III concentrate (plus heparin) or superoxide dismutase infused concurrently with injection of endotoxin significantly attenuated the derangements of these variables and the histologic extent of liver injury at 5 h. Intravascular coagulation, probably developing through the action of superoxide anion, may contribute to the development of massive hepatic necrosis induced by C. parvum and endotoxin in rats.     

Provocation of massive hepatic necrosis by endotoxin after partial hepatectomy in rats

When rats received endotoxin 48 hours after two-thirds liver resection, 50% of them died within 12 hours with massive hepatic necrosis at a dose that did not affect sham-operated rats. In the hepatic sinusoids, fibrin deposition and endothelial cell destruction occurred 5 hours after endotoxin administration. When antithrombin III concentrate was infused concomitantly with endotoxin administration, all rats survived 12 hours, and the extent of hepatic necrosis and the deranged serum glutamic pyruvic transaminase values were significantly attenuated at 5 hours compared with those in the control rats. Similar improvements in the incidence of mortality and liver injury were observed after treatment with gum arabic before hepatectomy. The stimulatory state of Kupffer cells based on the ability to produce superoxide anions estimated by formazan deposition after liver perfusion with nitro blue tetrazolium and phorbol myristate acetate was increased between 24 and 72 hours after operation. This increase disappeared after gum arabic treatment. It is concluded that massive hepatic necrosis can occur as a result of sinusoidal fibrin deposition provoked by endotoxin in partially hepatectomized rats. Activated Kupffer cells may contribute to this provocation.     

Pathogenesis of focal and random hepatocellular necrosis in endotoxemia: microscopic observation in vivo

Abstract: The present study was undertaken in rats to clarify the role of sinusoidal circulatory disturbances due to fibrin thrombi in the development of focal and random hepatocellular necrosis in endotoxemia. Sinusoidal circulation was examined microscopically in vivo in rats injected with endotoxin or heparin, or both. The sinusoids in places were occluded by adherent fibrin and neutrophils soon after endotoxin injection, and subsequently the sinusoidal blood flow stagnated, reversed, or detoured. Most of these sinusoidal circulatory disturbances recovered in a few hours. However, when the sinusoidal occlusion developed simultaneously in clusters of adjacent sinusoids, the sinusoidal circulatory disturbance persisted and induced ischemic foci and then hepatocellular coagulative necrosis. Pretreatment with heparin definitely prevented the adherence of fibrin and neutrophils to the sinusoidal walls, and focal hepatocellular necrosis did not appear. These results suggest that focal and random hepatocellular necrosis in endotoxemia is caused by circulatory disturbances due to fibrin thrombi in clusters of adjacent sinusoids.     

The influence of endotoxin in vitro on hepatic macrophage lysosomal enzyme release in different rat models of hepatic injury

ABSTRACT— Since bacterial endotoxin is known to be involved in the pathogenesis of hepatic injury, the influence of endotoxin on lysosomal enzyme production by hepatic macrophages has been investigated. Macrophages have been isolated from the livers of normal rats, from the livers of rats given stilboestrol subcutaneously 4 days previously and from the livers of rats given Corynebacterium parvum intravenously 6 days previously. Following isolation and overnight culture, the macrophages have been maintained in in vitro culture for a further 24 h and the production of N-acetyl-β-glucosaminidase (NAG) has been measured. Histological assessment has shown that in the stilboestrol model an approximate doubling of sinusoidal cell numbers occurs and in the C. parvum model a heavy mononuclear cell infiltrate is present, together with granuloma formation. These changes are reflected in the numbers of macrophages isolated from the respective models. Levels of NAG production by resident macrophages from normal livers are low (0.25±0.05 nmol substrate hydrolysed/μg cell protein/h) and unchanged following endotoxin exposure (0.25±0.05 units). Macrophages isolated from the stilboestrol model show levels of NAG production similar to normal (0.34±0.06 units), but this increases significantly following exposure to endotoxin (0.42±0.07 units). Macrophages from the C. parvum model demonstrate markedly enhanced production (0.61±0.09 units), but this does not increase significantly following endotoxin exposure (0.65±0.09 units). In contrast to macrophages from normal rat livers, macrophages recently recruited in the stilboestrol model demonstrate enhanced lysosomal enzyme production following endotoxin exposure. It is suggested that endotoxin, as well as other mediators of macrophage activation, may promote hepatic damage through this influence on newly recruited macrophages.     

Intravascular coagulation in acute liver failure in rats and its treatment with antithrombin III.

Liver damage was induced in rats by injection of dimethylnitrosamine (DMN) or carbon tetrachloride (CCl4). Fibrin clots were observed in the hepatic sinusoids at 12 hours and soluble fibrin monomer complexes were markedly detected at 24 hours only in the rats given DMN. When antithrombin III concentrate was infused at 12 hours there was a dose dependent improvement of the values of serum total bilirubin, SGPT, prothrombin time, peripheral platelet count, and plasma fibrinogen and coagulation factor VIIIC and of the histological degree of liver injury at 24 hours in the DMN group. The CCl4-group showed no such improvement. Intravascular coagulation may complicate the course of certain types of acute liver injury and contribute to its aggravation in rats. Under such circumstances, treatment with antithrombin III concentrate would be beneficial.     

Effect of FK506 on the activation state of hepatic macrophages in Propionibacterium acnes-treated rats

Activated hepatic macrophages can provoke massive liver necrosis following endotoxin stimulation through microcirculatory disturbances due to sinusoidal fibrin deposition in rats pretreated with heat-killed Propionibacterium acnes. In these rats, FK506 (tachlorinus) administered 24 h before and at the time of endotoxin injection, significantly attenuated liver injury compared with the rats given no FK506. The effect of FK506 on hepatic macrophage activation and its action sites were studied in Propionibacterium acnes-treated rats. When rats received Propionibacterium acnes intravenously, hepatic-mRNA expression of interferon-γ-inducing factor and interleukin-2 and splenic-mRNA expression of interferon-γ were significantly increased compared with normal rats. Hepatic-mRNA expression of CD14, a receptor for lipopolysaccharide and its binding protein complex, was also increased preceding the expressions of the three cytokines in the liver and spleen. FK506 administration attenuated hepatic-mRNA expression of interleukin-2 and both superoxide anions as well as tumour necrosis factor-α production by hepatic macrophages, but did not change CD14-mRNA expression in Propionibacterium acnes-treated rats. It is suggested that a cytokine network through interferon-γ-inducing factor, interferon-γ and interleukin-2 may operate during activation of hepatic macrophages in rats treated with heat-killed Propionibacterium acnes, while CD14 expression on the cells may increase independently of this network. FK506 seems to attenuate such activation by suppressing hepatic interleukin-2 expression, without affecting CD14 expression on the cells.     

Deranged blood coagulation equilibrium as a factor of massive liver necrosis following endotoxin administration in partially hepatectomized rats

Activated Kupffer cells provoke massive liver necrosis after endotoxin stimulation through microcirculatory disturbance caused by sinusoidal fibrin deposition in rats undergoing 70% hepatectomy. In these rats, serum activities of purine nucleoside phosphorylase (PNP) and alanine transaminase (ALT) were increased at 1 and 5 hours, respectively, following endotoxin administration. When 70% resected liver was perfused with Dulbecco's modified Eagle medium (DMEM) containing heat-inactivated fetal calf serum, the increase in both enzyme activities was not affected by addition of endotoxin during perfusion, suggesting that activated Kupffer cells injured neither sinusoidal endothelial cells nor hepatocytes. The activity of tissue factor, an initiator of blood coagulation cascade, was much higher in Kupffer cells isolated from partially hepatectomized rats than in those from normal rats. In contrast, mRNA expressions of tissue factor pathway inhibitor (TFPI) as well as thrombomodulin were almost undetectable in normal and partially resected livers. When recombinant human TFPI was injected intravenously in 70% hepatectomized rats, TFPI was markedly stained on the surfaces of sinusoidal endothelial cells and microvilli of hepatocytes on immunohistochemistry. In these rats, endotoxin-induced liver injury was significantly attenuated compared with rats given no TFPI. Similar attenuation was also found in rats receiving recombinant human thrombomodulin. These results suggest that fibrin deposition developing in 70% hepatectomized rats after endotoxin administration may be caused by deranged blood coagulation in the hepatic sinusoids through increasing tissue factor activity in Kupffer cells and minimal TFPI and thrombomodulin in endothelial cells. The destruction of sinusoidal endothelial cells as well as hepatocytes may occur as a result of microcirculatory disturbance caused by such sinusoidal fibrin deposition.     

Chronic Systemic Endotoxin Exposure: An Animal Model in Experimental Hepatic Encephalopathy

Plasma levels of gut-derived endotoxins (lipopolysaccharides, LPS) are often elevated in cirrhotics and are thought to contribute to hepatic encephalopathy. Circulating LPS activates macrophages to produce tumor necrosis factor ά (TNF-ά) and other potentially cytotoxic proinflammatory mediators. A pathogenic role forendotoxins is supported by studies showing that treatment with Lactobacillusor antibiotics, both of which reduce LPS-producingintestinal Gram-negative bacteria, alleviates experimental liver damage. To mimic the “leaky gut” syndrome with endotoxin translocation into the circulation in cirrhotics, a new animal model was developed. Rats were chronically exposed to ethanol and for the four last weeks also infused with endotoxin into the jugular vein from subcutaneously implanted osmotic minipumps. Animals receiving endotoxin had elevated hepatic expression of both pro- and anti-inflammatory cytokines, but compared to ethanol treatment alone hepatic steatosis and inflammatory changes were only marginally increased. This demonstrates marked endotoxin tolerance, probably as a consequence of a counteracting anti-inflammatory cytokine response. The role of gut-derived endotoxin in hepatic encephalopathy has recently received considerable attention. To further delineate the role and actions of endotoxin and its extrahepatic effects, studies applying both acute challenge and chronic infusion seem warranted. The chronic endotoxin model, mimicking the “leaky gut,” may best be combined with more robust ways to impair liver function, such as carbon tetrachloride treatment, bile duct ligation, or galactosamine administration.     

Role of adhesion molecules in the development of massive hepatic necrosis in rats

Massive hepatic necrosis develops after endotoxin administration in rats pretreated with heat-killed Propionibacterium acnes as a result of microcirculatory disturbance caused by endothelial cell destruction by activated macrophages in the hepatic sinusoids. Immunohistochemical hepatic expression of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen 1 alpha (LFA-1 alpha) and the effect of monoclonal antibodies against both adhesion molecules on liver necrosis provoked after endotoxin administration was studied in these rats. There were increased stains of ICAM-1 in endothelial cells and LFA-1 alpha in macrophages in the hepatic sinusoids in Propionibacterium acnes-pretreated rats compared with normal rats. Such stains were further increased soon after endotoxin administration, followed by development of hepatic necrosis. Monoclonal antibodies against both adhesion molecules significantly attenuated the extent of liver injury compared with controls, without affecting the infiltration and activation of hepatic macrophages. Polyclonal antibodies against polymorphonuclear leukocytes eradicated circulating neutrophils, but did not change such liver injury, although gum arabic, which suppressed macrophage activation, attenuated the extent of liver injury. Thus, adhesion between endothelial cells and activated macrophages in the hepatic sinusoids via ICAM-1 and LFA-1 alpha is essential for the initiation of massive hepatic necrosis of this type. Contribution of neutrophils seems less likely. (Hepatology 1996 Feb;23(2):320-8)     

Significance of intravascular coagulation and fibrinolysis in acute hepatic failure

Twenty-two patients with acute hepatic failure were studied to determine the incidence and magnitude of intravascular coagulation and fibrinolysis and their relation to the severity of bleeding and prognosis. The mean platelet count, Thrombotest, plasminogen activator, and plasminogen were reduced; the reduction in fibrinogen was not statistically significant. Fibrin/fibrinogen degradation products were only moderately increased. Hepatic fibrin deposition was not extensive, being present in 11 of 22 hepatic sections, more in areas of confluent necrosis than in the sinusoids. The combination of increased fibrin/fibrinogen degradation products with decreased plasminogen activator, plasminogen, and thrombocytopenia is consistent with a diagnosis of intravascular coagulation and secondary local fibrinolysis. However, neither of these processes was severe. Severity of bleeding was related only to plasminogen levels and prognosis only to Thrombotest levels. There was no relation between hepatic histological and haematological findings. Heparin therapy is not indicated in the routine management of acute hepatic failure, as intravascular coagulation is not severe and heparin may itself cause massive bleeding.     

Biphasic effect of colchicine on acute liver injury induced by carbon tetrachloride or by dimethylnitrosamine in mice

BACKGROUND/AIMS: The effects of colchicine on acute liver injury induced by carbon tetrachloride or by dimethylnitrosamine in mice were examined. METHODS: Nonlethal acute liver injury was induced in male BALB/c mice by a single intraperitoneal injection of 0.8 ml/kg carbon tetrachloride or 15 mg/kg dimethylnitrosamine. 0.6 mg/kg colchicine was administered 18 h or 2 h intraperitoneally before hepatotoxin treatment. RESULTS: Reversible centrilobular to mid-zone necrosis and apoptosis occupying half the liver lobular area was evoked by carbon tetrachloride, and dimethylnitrosamine, respectively. Administration of colchicine 18 h before hepatotoxins markedly suppressed liver injury, whereas colchicine administration 2 h before the hepatotoxins accelerated it. The hepatoprotective effect evoked by colchicine was due to reduction in liver cytochrome P450 content and P450 2E1 activity. In contrast, the hepatodestructive effect seen in the carbon tetrachloride model was related to the extent of lipid peroxidation promoting plasma membrane destruction, while the hepatodestructive effect in the dimethylnitrosamine model was due to suppression of Bcl-X(L) expression, leading to acceleration of apoptosis. CONCLUSIONS: A biphasic effect of colchicine on carbon tetrachloride- and dimethylnitrosamine-induced acute liver injury was seen. The time interval between colchicine administration and the hepatotoxin treatment is crucial to the subsequent development of liver lesions.     

Autopsy case of acute liver failure due to scrub typhus

Scrub typhus (Tsutsugamushi disease) is an acute febrile disease caused by infection with Orientia tsutsugamushi transmitted by mites. Although patients with scrub typhus commonly display mild liver injury, few die of acute liver failure. We describe herein an autopsy case of acute liver failure due to scrub typhus, which was complicated by disseminated intravascular coagulation and showed rapid progression of liver injury just before death. Histopathological findings revealed submassive hepatocellular necrosis, inflammatory cell infiltration in Glisson’s capsules, and sporadic fibrin thrombi in the hepatic sinusoids. Cause of death was primarily associated with acute liver failure related to disseminated intravascular coagulation.     

Antithrombin III injection via the portal vein suppresses liver damage

AIM: To investigate the effects of antithrombin III (AT III) injection via the portal vein in acute liver failure.METHODS: Thirty rats were intraperitoneally challenged with lipopolysaccharide (LPS) and D-galactosamine (GalN) and divided into three groups: a control group; a group injected with AT III via the tail vein; and a group injected with AT III via the portal vein. AT III (50 U/kg body weight) was administrated 1 h after challenge with LPS and GalN. Serum levels of inflammatory cytokines and fibrin degradation products, hepatic fibrin deposition, and hepatic mRNA expression of hypoxia-related genes were analyzed.RESULTS: Serum levels of alanine aminotransferase, tumor necrosis factor-α and interleukin-6 decreased significantly following portal vein AT III injection compared with tail vein injection, and control rats. Portal vein AT III injection reduced liver cell destruction and decreased hepatic fibrin deposition. This treatment also significantly reduced hepatic mRNA expression of lactate dehydrogenase and heme oxygenase-1.CONCLUSION: A clinically acceptable dose of AT III injection into the portal vein suppressed liver damage, probably through its enhanced anticoagulant and anti-inflammatory activities.     

Glutathione Depletion Enhances the Formation of Superoxide Anion Released Into Hepatic Sinusoids After Lipopolysaccharide Challenge

Background: We examined the effects of glutathione depletion on the level of superoxide anion released into hepatic sinusoids after lipopolysaccharide challenge. Methods: Rats were given 1 mg/kg of maleic acid diethyl ester to deplete glutathione in vivo and then 0.5 mg/kg body weight of lipopolysaccharide. Results: This treatment significantly depleted serum reduced glutathione (32.7 ±1.7 vs. 23.0 ± 3.2 mM, p = 0.002). However, it did not affect the serum oxidized glutathione concentration (2.88 ± 0.56 vs. 3.10 ± 0.78 mM, not significant). The lipopolysaccharide challenge caused significant superoxide anion formation as compared with controls (0.12 ± 0.04 vs. 0.22 ± 0.05 o.d., p < 0.001), and it was enhanced significantly by glutathione depletion (0.28 ± 0.04 o.d., p < 0.05). There were no significant differences in levels of lipopolysaccharide (2142 ± 452 vs. 2503 ± 612 pg/ml) and tumor necrosis factor α (277 ± 186 vs. 252 ± 88 pg/ml) after the lipopolysaccharide challenge between the glutathione-depleted and nondepleted rats. Moreover, the purine nucleoside phosphorylase/glutamic-pyruvic transaminase ratio in liver perfusates, a marker of damage to endothelial cells in hepatic sinusoids, was significantly higher in the glutathione-depleted rats than in the nondepleted rats. Conclusions: The reduced form of glutathione can decrease levels of the superoxide anion released into hepatic sinusoids and can decrease subsequent damage to endothelial cells in these sinusoids caused by lipopolysaccharide; that is, it can reduce lipopolysaccharide-induced liver injury.     

整合素α6在肝窦毛细血管化中的表达

目的探讨整合素α6在肝窦毛细血管化时的表达情况. 方法皮下注射四氯化碳制备大鼠肝纤维化模型,进行层粘连蛋白(LN)及其整合素受体α6免疫组织化学检测及整合素α6斑点免疫印迹研究. 结果动态观察了LN在肝纤维化时沿肝窦在Disse间隙沉积形成肝窦毛细血管化;正常时整合素α6局限于汇管区血管内皮和胆管内皮细胞膜上,窦内皮细胞(SEC)上无表达,肝窦毛细血管化时,SEC出现整合素α6阳性表达沿肝窦连续分布,整合素α6在纤维化时组织中含量明显高于正常(P＜0.05). 结论肝窦毛细血管化时SEC出现整合素α6亚基的诱导表达.     

Experimental hepatic necrosis: Studies on coagulation abnormalities, plasma clearance, and organ distribution of 125I-labelled fibrinogen

Studies in the rat with hepatic necrosis induced by carbon tetrachloride showed that the abnormalities in one-stage coagulation tests and the increased catabolism of fibrinogen were similar to those found in man with acute viral or drug-induced hepatic necrosis. Determination of the distribution of the radioactive label shows that excessive deposition was maximal in the liver but also occurred in the spleen. The appearance is delayed by heparin but accelerated by tranexamic acid.     

Beraprost sodium, a prostacyclin (PGI) analogue, ameliorates concanavalin A-induced liver injury in mice.

BACKGROUND/AIMS: Prostacyclin (PGI(2)) is a potent mediator in the inflammatory and coagulation processes. The aim of this study was to test whether beraprost sodium, a PGI(2) analogue, could prevent experimental hepatic injury induced by concanavalin A (Con A), which is a model of fulminant hepatic failure. METHODS: Beraprost (100 microg/kg) was administered intraperitoneally simultaneously with Con A (40 mg/kg) in C57B6J mice. Blood circulation in the liver was determined by laser-Doppler flowmetry. Plasma levels of alanine aminotransferase (ALT), tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and interleukin (IL)-6 were determined. Levels of TNF-alpha and IFN-gamma in culture supernatant of splenocytes were also determined. RESULTS: Beraprost administration reduced the incidence of death following hepatic failure (76.5% vs. 29.4%, P<0.05). Plasma levels of ALT were significantly lower in the beraprost-treated group than in the control group, and in the former, there was concomitant suppression of the histological features of injury. Beraprost significantly increased hepatic blood flow volume in Con A-treated mice. Plasma levels of TNF-alpha and IFN-gamma were significantly reduced at 6 and 12 h after Con A injection, respectively, but the levels of IL-6 were increased at 6 h. In vitro, beraprost also suppressed Con A-induced TNF-alpha production in splenocytes, while it stimulated IFN-gamma production. CONCLUSION: These findings imply that beraprost suppresses Con A-induced liver injury. These data also suggest that beraprost, which is clinically effective in treating pulmonary hypertension, may have therapeutic potential for preventing hepatic injury.     

Influence of somatostatin and octreotide on liver microcirculation in an experimental mouse model of cirrhosis studied by intravital fluorescence microscopy

Background and Aims: Chronic liver damage causes hepatic stellate cell (HSC) activation and contraction, leading to intrahepatic microvascular and structural changes. In vitro endothelin‐1 (ET‐1)‐induced contraction of HSCs can be reduced by somatostatin (SST); however, intrahepatic in vivo effects have never been studied. Methods: Sinusoidal diameter was measured by intravital fluorescence microscopy in carbon tetrachloride (CCl₄) and control mice before and after an intravenous (IV) bolus and after 0, 5, 10 and 15 min of an IV infusion of saline, 8 μg/kg/h SST or 8 μg/kg/h octreotide. Results: The baseline sinusoidal diameter in CCl₄ mice (3.01±0.05 μm) was significantly smaller than that in controls (4.37±0.06 μm). The sinusoidal diameter increased significantly in both groups after a bolus (27, 16% respectively) and following 5 min of SST IV infusion (28, 14% respectively). The percentage increase was significantly higher in CCl₄ mice as compared with controls. This dilatory effect continued for at least 15 min. SST did not influence the mean arterial blood pressure (MAP) and portal venous inflow. In none of the groups did octreotide or saline have any influence on sinusoidal diameters, MAP and portal venous inflow. Conclusions: Sinusoidal diameter in cirrhotic mice is significantly smaller than that in controls. SST causes significant sinusoidal dilation following a bolus and for at least 15 min of IV infusion. Octreotide does not have any influence on liver sinusoids. These results demonstrate for the first time the in vivo dilatory effect of SST on liver sinusoids.     

Retinyl palmitate reduces hepatic fibrosis in rats induced by dimethylnitrosamine or pig serum

Background/Aims: Lipid peroxidation has been found to be associated with Ito cell activation. Ito cells are the principal collagen-producing cells and the main storage sites of retinoids. However, the relationship between retinoids and hepatic fibrosis is complex. The aim of this study was to elucidate the role of retinoids as a fibrosuppressant: the effects of retinoids on hepatic fibrosis induced in rats by dimethylnitrosamine or pig serum, as well as on rat Ito cells in primary culture, were examined in order to assess the antioxidant activity of retinoids.Methods: Male Wistar rats were given a single injection of 40 mg/kg dimethylnitrosamine or 0.5 ml PS twice weekly for 10 weeks. In each model, rats were treated with retinyl palmitate for 2 weeks before hepatotoxin treatments or for the last 2 weeks of the treatments. The cumulative amount of retinyl palmitate administered in each experiment was 2, 10, or 20×10⁴ IU/rat.Results: Retinyl palmitate treatment before or after administration of dimethylnitrosamine or pig serum suppressed the induction of hepatic fibrosis, restored hepatic retinyl palmitate levels, prevented increases in hepatic levels of collagen and malondialdehyde, a product of lipid peroxidation, and prevented increases in deposition of type III collagen and the number of α-smooth muscle actin (α-SMA) positive-Ito cells in the liver. Retinyl palmitate supplementation resulted in a dose-dependent reduction of α-SMA expression and an oxidative burst in cultured Ito cells. In addition, retinyl palmitate inhibited Fe²⁺/adenosine 5′-diphosphate-induced lipid peroxidation in rat liver mitochondria and showed radical scavenging activity.Conclusions: These findings suggest that retinyl palmitate may suppress the induction of hepatic fibrosis, at least in part, by the inhibition of Ito cell activation through its antioxidant activity.