Macrophage potentiates the recovery of liver zonation and metabolic function after acute liver injury.

The liver is an exclusive organ with tremendous regenerative capacity. Liver metabolic functions exhibit spatial heterogeneity, reflecting liver zonation. The mechanisms controlling the proliferation of hepatocytes and the accompanying matrix reconstruction during regeneration have been well explored, but the recovery potential of differentiated metabolic functions and zonation after liver injury remains unclear. We employed a mouse model of carbon tetrachloride (CCl4) induced-acute liver injury with clodronate-induced macrophage depletion to clarify the impact of liver injury on liver metabolism and recovery dynamics of metabolic function and liver zonation during regeneration. Depleting macrophages suppressed tissue remodelling and partially delayed cell proliferation during regeneration after liver injury. In addition, recovery of metabolic functions was delayed by suppressing the tissue remodelling caused by the depleted macrophages. The model revealed that drug metabolic function was resilient against the dysfunction caused by liver injury, but glutamine synthesis was not. Metabolomic analysis revealed that liver branched-chain amino acid (BCAA) and carbohydrate metabolism were suppressed by injury. The plasma BCAA concentration reflected recovery of hepatic function during regeneration. Our study reveals one aspect of the regenerative machinery for hepatic metabolism following acute liver injury.

Nootkatone confers hepatoprotective and anti-fibrotic actions in a murine model of liver fibrosis by suppressing oxidative stress, inflammation, and apoptosis.

In this study, the hepatoprotective and anti-fibrotic actions of nootkatone (NTK) were investigated using carbon tetrachloride (CCl4 )-induced liver fibrosis in mice. CCl4 administration elevated serum aspartate and alanine transaminases levels, respectively. In addition, CCl4 produced hepatic oxidative and nitrative stress, characterized by diminished hemeoxygenase-1 expression, antioxidant defenses, and accumulation of 4-hydroxynonenal and 3-nitrotyrosine. Furthermore, CCl4 administration evoked profound expression of pro-inflammatory cytokine expressions such as tumor necrosis factor-α, monocyte chemoattractant protein-1, and interleukin-1ß in hepatic tissues, which corroborated with nuclear factor κB activation. Additionally, CCl4 -treated animals exhibited higher apoptosis, characterized by increased caspase 3 activity, DNA fragmentation, and poly (ADP-ribose) polymerase activation. Moreover, histological and biochemical investigations revealed marked fibrosis in the livers of CCl4 -administered animals. However, NTK treatment mitigated CCl4 -induced phenotypic changes. In conclusion, our findings suggest that NTK exerts hepatoprotective and anti-fibrotic actions by suppressing oxidative stress, inflammation, and apoptosis.

Hepatoprotective activities of Antrodia camphorata and its triterpenoid compounds against CCl4-induced liver injury in mice.

ETHNOPHARMACOLOGY RELEVANCE: Antrodia camphorata (AC) is a rare and precious fungus indigenous to Taiwan used as a traditional medicine for the treatment of liver injury. Triterpenoids are the major bioactive constituents of A. camphorata and have been reported to possess hepatoprotective activities. To meet the increasing demand, artificial cultivation techniques have been developed. AIM OF THE STUDY: This study aims to evaluate the hepatoprotective activities of AC samples derived from different cultivation techniques and to dissect the main active triterpenoid compounds. MATERIALS AND METHODS: The ethanol extracts of five batches of AC samples, including wild growing fruiting bodies, cutting wood culture fruiting bodies, dish cultures, cutting wood culture mycelia, and submerged fermentation mycelia were orally administered (50mg/kg or 200mg/kg) to ICR mice for 7 days. On the last day, CCl4 (0.2%, 7mL/kg, i.p.) was used to induce liver injury, and the activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were determined 24h after the injection. Moreover, a HepG2 cell model treated with CCl4 (0.35%) was used to screen the protective activities of 29 AC triterpenoids. After incubation for 6h, viabilities of the cells were tested using MTS assay. The in vivo hepatoprotective activities of antcin B and antcin K were further studied on the mice model by ALT and AST tests and histopathologic examinations. To elucidate the mechanisms, the mRNA levels of iNOS, COX2, TNF-α and IL-1ß, and the protein levels of NF-κB (p65/p-p65), iNOS and COX2 in liver tissues were determined. RESULTS: The wild growing or cutting wood culture fruiting bodies, and the dish cultures of AC showed more potent activities than the mycelia (P<0.001). At 20µM, 16 of 29 triterpenoids showed significant protective activities, increasing HepG2 cell viability from 46% of the CCl4 group to >90%. Antcin B and antcin K could dose-dependently (10 or 50mg/kg, 7 days, i.g.) decrease the serum levels of ALT and AST, and decrease the incidence of liver necrosis. The effects of 50mg/kg of antcin K or antcin B were almost identical to those of 100mg/kg silymarin. Furthermore, qRT-PCR and Western blotting analyses revealed they could down-regulate IL-1ß, TNF-α, iNOS, COX-2 and NF-κB in liver tissues at both transcriptional and translational levels. CONCLUSION: The results indicate that cultivation techniques remarkably affect the hepatoprotective activities of AC. Antcin K and antcin B are the major hepatoprotective compounds of A. camphorata, and the mechanism is related with anti-inflammation. Given its high natural abundance and good oral absorption, antcin K could be a promising drug candidate for liver injury.

Hepatoprotective Effect of Low Doses of Caffeine on CCl4-Induced Liver Damage in Rats.

Several studies have shown the hepatoprotective effect of the consumption of coffee and tea, which is mainly attributed to caffeine. Many experimental studies have demonstrated this effect; however, these studies used high caffeine doses that are not related to human consumption. The aim of this study was to evaluate the hepatoprotective effect of low doses of caffeine on carbon tetrachloride (CCl4)-treated rats. Low doses of caffeine (CAFF) 5 and 10 mg/kg (CAFF5 and CAFF10) were evaluated in chronic liver damage induced by CCl4 (0.75 mL/kg) in rats. CAFF treatment was administered once a day and CCl4 administration was twice weekly for 10 weeks. Liver function tests (biochemical markers) and functional (sleeping time) and histological (hematoxylin-eosin and Masson trichrome stains) parameters were carried out at the end of damage treatment. Daily treatments of CAFF5 and CAFF10 exhibited a hepatoprotective effect supported by a decrease of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (AP) serum activities and bilirubin serum levels compared with control and also restored serum albumin levels and liver glutathione (GSH). Moreover, CAFF prevented CCl4-induced prolongation in pentobarbital sleeping time and a decrease of liver fibrosis and cell death. Our results demonstrated that low doses of CAFF exert a hepatoprotective effect against CCl4 -induced liver damage in rats.

Liver Regeneration Induced By Extracorporeal Portal Vein Arterialization in a Swine Model of Carbon Tetrachloride Intoxication.

INTRODUCTION: This study aimed to determine whether a controlled portal blood arterialization by a liver extracorporeal device (L.E.O2 NARDO) is effective in treating acute hepatic failure (AHF) induced in swine by carbon tetrachloride (CCl4) administration. MATERIALS AND METHODS: Sixteen swine with AHF induced by intraperitoneal injection of CCl4 in oil solution were randomly divided into 2 groups: animals that received L.E.O2 NARDO treatment 48 hours after the intoxication (study group; n = 8); and animals that were sham operated 48 hours after the intoxication (control group; n = 8). Blood was withdrawn from the iliac artery and reversed in the portal venous system by an interposed extracorporeal device. Each treatment lasted 6 hours. The survival was assessed at 5 days after L.E.O2 NARDO treatment or sham operation. In both groups blood samples were collected for biochemical analysis at different study time and liver biopsies were performed 48 hours after intoxication and at humane killing. RESULTS: In the study group decreased transaminases levels and a more rapid international normalized ratio (INR) recover were detected as compared with the control group. Six animals of the study group (75%) versus 1 animal (12.5%) of the control group survived at 5 days after surgery with a statistically significant difference (P < .05). Liver biopsies performed at humane killing showed damaged areas of the livers reduced in the study group compared with biopsies of the control group. CONCLUSIONS: Arterial blood supply in the portal system through the L.E.O2 NARDO device is easily applicable, efficacious, and safe in a swine model of AHF induced by CCl4 intoxication.

Role of the sympathetic nervous system in carbon tetrachloride-induced hepatotoxicity and systemic inflammation.

Carbon tetrachloride (CCl4) is widely used as an animal model of hepatotoxicity and the mechanisms have been arduously studied, however, the contribution of the sympathetic nervous system (SNS) in CCl4-induced acute hepatotoxicity remains controversial. It is also known that either CCl4 or SNS can affect systemic inflammatory responses. The aim of this study was to establish the effect of chemical sympathectomy with 6-hydroxydopamine (6-OHDA) in a mouse model of CCl4-induced acute hepatotoxicity and systemic inflammatory response. Mice exposed to CCl4 or vehicle were pretreated with 6-OHDA or saline. The serum levels of aminotransferases and alkaline phosphatase in the CCl4-poisoning mice with sympathetic denervation were significantly lower than those without sympathetic denervation. With sympathetic denervation, hepatocellular necrosis and fat infiltration induced by CCl4 were greatly decreased. Sympathetic denervation significantly attenuated CCl4-induced lipid peroxidation in liver and serum. Acute CCl4 intoxication showed increased expression of inflammatory cytokines/chemokines [eotaxin-2/CCL24, Fas ligand, interleukin (IL)-1α, IL-6, IL-12p40p70, monocyte chemoattractant protein-1 (MCP-1/CCL2), and tumor necrosis factor-α (TNF-α)], as well as decreased expression of granulocyte colony-stimulating factor and keratinocyte-derived chemokine. The overexpressed levels of IL-1α, IL-6, IL-12p40p70, MCP-1/CCL2, and TNF-α were attenuated by sympathetic denervation. Pretreatment with dexamethasone significantly reduced CCl4-induced hepatic injury. Collectively, this study demonstrates that the SNS plays an important role in CCl4-induced acute hepatotoxicity and systemic inflammation and the effect may be connected with chemical- or drug-induced hepatotoxicity and circulating immune response.

Hepatoprotective effect of methylsulfonylmethane against carbon tetrachloride-induced acute liver injury in rats.

This study evaluated the effect of methylsulfonylmethane (MSM) on carbon tetrachloride (CCl4)-induced acute liver injury in rats. A single injection of CCl4 (2 ml/kg, i.p.) increased serum aminotransferases (ALT and AST) activities. In addition, CCl4 treatment led to elevation of hepatic malondialdehyde (MDA) content as well as decrease in superoxide dismutase (SOD) and catalase (CAT) activities. Furthermore, cytochrome P450 2E1 (CYP2E1) content was suppressed while proinflammatory cytokines tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels increased in liver tissue after CCl4 administration. We showed that acute CCl4-induced damage was accompanied by a rise in Bax/Bcl2 ratio indicating apoptosis. Pre-treatment with MSM (400 mg/kg) inhibited the increases of serum ALT and AST activities, decreased hepatic MDA, TNF-α, IL-6 and Bax/Bcl2 ratio compared to CCl4 treated group. On the other hand, MSM raised SOD and CAT activities as well as CYP2E1 level in liver tissues. The present study shows that MSM possesses a hepatoprotective effect against CCl4-induced liver injury in rats. This protective effect might be through its antioxidant, anti-inflammatory and antiapoptotic properties.

Reduced hepatic stellate cell expression of Kruppel-like factor 6 tumor suppressor isoforms amplifies fibrosis during acute and chronic rodent liver injury.

UNLABELLED: Kruppel-like factor 6 (KLF6), a zinc finger transcription factor and tumor suppressor, is induced as an immediate-early gene during hepatic stellate cell (HSC) activation. The paradoxical induction of a tumor suppressor in HSCs during proliferation led us to explore the biology of wildtype KLF6 (KLF6(WT) ) and its antagonistic, alternatively spliced isoform KLF6(SV1) in cultured HSCs and animal models. The animal models generated include a global heterozygous KLF6 mouse (Klf6+/-), and transgenic mice expressing either hKLF6(WT) or hKLF6(SV1) under the control of the Collagen α2 (I) promoter to drive HSC-specific gene expression following injury. The rat Klf6 transcript has multiple splice forms that are homologous to those of the human KLF6 gene. Following a transient increase, all rat Klf6 isoforms decreased in response to acute carbon tetrachloride (CCl(4)) liver injury and culture-induced activation. After acute CCl(4), Klf6+/- mice developed significantly increased fibrosis and enhanced fibrogenic messenger RNA (mRNA) and protein expression. In contrast, HSC-specific transgenic mice overexpressing KLF6(WT) or KLF6(SV1) developed significantly diminished fibrosis with reduced expression of fibrogenic genes. Chromatin IP and quantitative reverse-transcription polymerase chain reaction in mouse HSCs overexpressing KLF6(WT) demonstrated KLF6(WT) binding to GC boxes in promoters of Colα1 (I), Colα2 (I), and beta-platelet-derived growth factor receptor (ß-Pdgfr) with reduced gene expression, consistent with transcriptional repression by KLF6. Stellate cells overexpressing either KLF6(WT) or KLF6(SV1) were more susceptible to apoptotic stress based on poly (ADP-ribose) polymerase (PARP) cleavage. CONCLUSION: KLF6 reduces fibrogenic activity of HSCs by way of two distinct mechanisms, direct transcriptional repression of target fibrogenic genes and increased apoptosis of activated HSCs. These results suggest that following its initial induction, sustained down-regulation of KLF6 in liver injury may allow de-repression of fibrogenic genes and decreased stellate cell clearance by inhibiting apoptosis.

Resveratrol nanoparticle system improves dissolution properties and enhances the hepatoprotective effect of resveratrol through antioxidant and anti-inflammatory pathways.

Resveratrol (RES), a well-known antioxidant and anti-inflammatory compound, is abundant in red wine and exerts numerous pharmacological effects, including hepatoprotection and cadioprotection. Unfortunately, RES is restricted in clinical application due to poor dissolution property and adsorption. In addition, red wine as a supplement for preventing disease is not recommended for patients with alcohol-related disorders. To address these limitations, we successfully developed a novel RES nanoparticle system (RESN) and demonstrated that RESN could circumvent the physicochemical drawbacks of raw RES with respect to dissolution, such as the reduction of particle size, amorphous transformation, and hydrogen-bond formation. In addition, we employed an animal model of CCl4-induced hepatotoxicity to estimate the potential of the nanoparticle formulation to improve the hepatoprotective effect of orally administered RES. Our results demonstrated that RESN can diminish liver function markers (aspartate aminotransferase and alanine aminotransferase) by decreasing hepatocyte death due to CCl4-induced hepatotoxicity in rats, when compared with RES administration. The effect was achieved by reducing oxidative stress (decreased reactive oxygen species and lipid peroxidation) and lowering inflammatory cytokines (decreased tumor necrosis factor-α and interleukin 1ß) and protein expression (cyclooxygenase-2, inducible nitric oxide synthase, cytosolic phospholipase A2, and caspase-3). In conclusion, enhancement of the dissolution of RES through a nanoparticle engineering process can result in increased hepatoprotective effects mediated by antioxidant and anti-inflammatory activities. Consequently, we suggest that RESN deserves further study, perhaps in prophylaxis of chronic liver diseases.

Protective effects of salecan against carbon tetrachloride-induced acute liver injury in mice.

Carbon tetrachloride (CCl4) is a well-established model for screening hepato-protective drugs. The aim of the present study was to evaluate the potential protective effects of a novel soluble ß-glucan salecan on acute liver injury induced by CCl4 in mice and to further explore the underlying mechanisms. Mice were given salecan (40 mg kg⁻¹) or phosphate-buffered saline for 3 days prior to treatment with a single intraperitoneal dose of CCl4 (1 ml kg⁻¹ body weight). Animals were sacrificed at 0, 12, 24, 48, 72 and 96 h post-injection of CCl4. Serum liver enzyme levels, histology, lipid peroxidation, glutathione (GSH) content, expression of antioxidant enzymes and hepatocyte proliferation were subsequently evaluated. The serum levels of hepatic enzyme markers were markedly reduced in the salecan pretreatment group compared with the control group. Histopathological examination of the livers revealed that hepatocellular degeneration and necrosis were significantly attenuated at an early stage during CCl4 intoxication and liver recovery was markedly accelerated at a later stage in salecan pre-administered mice. Furthermore, salecan administration remarkably alleviated lipid peroxidation and restored GSH depletion. Meanwhile, the expression of antioxidant genes was significantly elevated in the salecan-treated group. Interestingly, the administration of salecan remarkably enhanced hepatocyte proliferation in the recovery phase after CCl4 injection. Taken together, these results demonstrated that salecan exhibits a protective action on acute hepatic injury induced by CCl4 through attenuating oxidative stress and accelerating hepatocyte regeneration.

Transcription factors ETF, E2F, and SP-1 are involved in cytokine-independent proliferation of murine hepatocytes.

UNLABELLED: The cellular basis of liver regeneration has been intensely investigated for many years. However, the mechanisms initiating hepatocyte "plasticity" and priming for proliferation are not yet fully clear. We investigated alterations in gene expression patterns during the first 72 hours of C57BL/6N mouse hepatocyte culture on collagen monolayers (CM), which display a high basal frequency of proliferation in the absence of cytokines. Although many metabolic genes were down-regulated, genes related to mitogen-activated protein kinase (MAPK) signaling and cell cycle were up-regulated. The latter genes showed an overrepresentation of transcription factor binding sites (TFBS) for ETF (TEA domain family member 2), E2F1 (E2F transcription factor 1), and SP-1 (Sp1 transcription factor) (P < 0.001), all depending on MAPK signaling. Time-dependent increase of ERK1/2 phosphorylation occurred during the first 48 hours (and beyond) in the absence of cytokines, accompanied by an enhanced bromodeoxyuridine labeling index of 20%. The MEK inhibitor PD98059 blunted these effects indicating MAPK signaling as major trigger for this cytokine-independent proliferative response. In line with these in vitro findings, liver tissue of mice challenged with CCl(4) displayed hepatocytes with intense p-ERK1/2 staining and nuclear SP-1 and E2F1 expression. Furthermore, differentially expressed genes in mice after partial hepatectomy contained overrepresented TFBS for ETF, E2F1, and SP-1 and displayed increased expression of E2F1. CONCLUSION: Cultivation of murine hepatocytes on CM primes cells for proliferation through cytokine-independent activation of MAPK signaling. The transcription factors ETF, E2F1, and SP-1 seem to play a pronounced role in mediating proliferation-dependent differential gene expression. Similar events, but on a shorter time-scale, occur very early after liver damage in vivo.

Acute renal failure induced by carbon tetrachloride in rats with hepatic cirrhosis.

Relationship between cirrhosis and renal dysfunction is not yet fully understood. A model of cirrhosis with acute hepatic and renal damage (RF), produced by CCl4 in rats, with hemodynamic and renal functional alterations, similar to those observed in decompensated cirrhosis (DC) in man, was used to study chemical nephrotoxicity in animals. We performed in male Wistar rats hepatic and renal functional and hemodynamic studies in control, cirrhotic and decompensated cirrhotic (DC) groups. Cirrhosis was induced with carbon tetrachloride by chronic administration. Association between liver and renal functional alterations was detected in rats with decompensated cirrhosis, showing fall in mean arterial pressure and reduction of glomerular filtration rate and filtration fraction. Renal hemodynamics did not change in cirrhotic rats, similarly to what occurs in compensated cirrhotic patients. However, DC rats exhibited increased sodium, glucose and phosphate urinary excretions and decreased ATP in renal cortex. DC animals had severe hypoglycemia. There was an extensive liver fibrosis. Glomeruli had hypercellularity and tubules showed extensive vacuolization in cirrhotic and DC rats. The present study suggests that in this model, damage typical of acute tubular necrosis ensues in cirrhotic rats. We describe functional and morphological damage in liver and kidney in a model of cirrhosis that might predispose to the development of acute renal failure when an individual with hepatic damage is exposed in acute way to chemical toxicants.

Duration-dependent hepatoprotective effects of propolis extract against carbon tetrachloride-induced acute liver damage in rats.

Propolis is a natural product produced by bees that was discovered through the study of traditional cures and knowledge of indigenous people throughout the world. It is rich in vitamins A, B, C, and E, and in amino acids, copper, iron, manganese, and zinc. The investigators studied the duration-dependent hepatoprotective effects of propolis extract (200 mg/kg, orally) against carbon tetrachloride (CCl 4; 1.5 mL/kg, intraperitoneally)-induced liver damage in rats. Administration of CCl 4 caused a sharp elevation in the activity of serum transaminases and serum alkaline phosphatase. A significant depletion in hepatically reduced glutathione was observed with significantly enhanced hepatic lipid peroxidation. After CCl 4 administration, glycogen contents and activities of alkaline phosphatase, adenosine triphosphatase, and succinic dehydrogenase were significantly decreased, whereas total protein contents and activity of acid phosphatase were increased in the liver and kidney. Propolis extract reversed alterations in all parameters when administered within 6, 12, and 24 h of toxicant exposure. Propolis therapy produced duration-dependent protection, with maximal protection achieved at 24 h after CCl 4 exposure. It is believed that propolis in its natural form has general pharmacologic value and marked hepatoprotective potential because of its composition of minerals, flavonoids, and phenolic compounds.

Differentiation of a hepatic phenotype after heterotropic transplantation of heart, kidney, brain, and skin tissues into liver in F344 rats.

While organ-specific stem cells with roles in tissue injury repair have been documented, their pathogenic significance in diseases and the factors potentially responsible for their activation remain largely unclear. In the present study, heart, kidney, brain, and skin samples from F344 transgenic rats carrying the GFP gene were transplanted into normal F344 rat liver one day after an intraperitoneal injection (i.p.) of carbon tetrachloride (CCl(4)) to test their differentiation capacity. The transplantation was carried out by female donors to male recipients, and vice versa. One week after transplantation, GFP antigen-positive cells with phenotypic characteristics of hepatocytes were noted. After two weeks, their extent increased, and at 4 weeks, large areas of strongly GFP-stained cells developed. All recipient livers had GFP antigen-positive hepatocyte cells. PCR analysis coupled with laser capture micro-dissection (LCM) revealed those cells to contain GFP DNA. Thus, our results indicate that tissue stem cells have multipotential ability, differentiating into hepatocytes when transplanted into an injured liver.

Novel cyclooxygenase-catalyzed bioactive prostaglandin F2alpha from physiology to new principles in inflammation.

Prostaglandin F2alpha (PGF2alpha), a foremost stable vasoactive cyclooxygenase (COX)-catalyzed prostaglandin, regulates a number of key physiological functions such as luteolysis, ovarian function, luteal maintenance of pregnancy, and parturition as a constitutive part of ongoing reproductive processes of the body. It has recently been implicated in the regulation of intricate pathophysiological processes, such as acute and chronic inflammation, cardiovascular and rheumatic diseases. Since the discovery of a second isoform of COXs, it has been shown that PGF2alpha can be formed in vivo from arachidonic acid through both isoforms of COXs, namely cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Being synthesized in various parts of the body, it metabolizes instantly to a number of rather inactive metabolites mainly in the lungs, liver, kidney, and efficiently excretes into the urine. 15-Keto-dihydro-PGF2alpha, a major stable metabolite of PGF2alpha that reflects in vivo PGF2alpha biosynthesis, is found in larger quantities than its parent compound in the circulation and urine in basal physiological conditions, with short-lived pulses during luteolysis, induced termination of pregnancy and parturition, and is increased in tissues and various body fluids during acute, sub-chronic, and severe chronic inflammation. Further, the close relationship of PGF2alpha with a number of risk factors for atherosclerosis indicates its major role in inflammation pathology. This review addresses multiple aspects of PGF2alpha in addition to its emerging role in physiology to inflammation.

Tightly regulated induction of the adhesion molecule necl-5/CD155 during rat liver regeneration and acute liver injury.

TuAg1/TagE4, the rat ortholog of the human poliovirus receptor CD155, is expressed on a high percentage of rat hepatocellular carcinomas. Recent studies have shown that TuAg1/TagE4/CD155 is a member of the nectin family of immunoglobulin (Ig)-like cell adhesion molecules, designated necl-5. Necl-5 is present at exceedingly low levels in adult epithelial tissues but is upregulated in primary cultures of rat hepatocytes, suggesting that disruption of liver architecture triggers its expression. To explore this possibility, we examined expression of necl-5 after two-thirds partial hepatectomy or carbon tetrachloride (CCl4)-induced acute injury. Using quantitative real-time polymerase chain reaction (QPCR), we found that necl-5 mRNA levels increased 15-fold by 9 hours, and decreased to 4-fold above baseline by 24 hours after partial hepatectomy. Necl-5 mRNA levels increased over 100-fold 6 hours after treatment with CCl4, reaching a peak of 140-fold above baseline by 10 hours, and thereafter rapidly declining. Necl-5 was localized at the membrane of midlobular and centrilobular hepatocytes 10 to 48 hours after CCl4 exposure. Northern blot analysis demonstrated a close correlation between the kinetics of necl-5 expression and the immediate-early response gene c-myc. Subconfluent cultures of the non-transformed liver epithelial cell line WB-F344 expressed high levels of necl-5, which was down-regulated as cells approached confluence. The transformed WB-F344 line GP7TB did not demonstrate density-dependent regulation of necl-5 expression. In conclusion, we report the in vivo induction of necl-5 in rat hepatocytes and provide evidence that both necl-5 mRNA and protein are tightly regulated in adult epithelial cells and tissue.

The third gas: H2S regulates perfusion pressure in both the isolated and perfused normal rat liver and in cirrhosis.

The regulation of sinusoidal resistance is dependent on the contraction of hepatic stellate cells (HSC) around sinusoidal endothelial cell (SEC) through paracrine cross-talk of vasoconstrictor and vasodilator agents. Hydrogen sulfide (H2S), a recently discovered gas neurotransmitter, is a putative vasodilator whose role in hepatic vascular regulation and portal hypertension is unexplored. Four-week bile duct-ligated (BDL) rats with cirrhosis and control rats were treated daily with NaHS (56 micromol/kg) for 5 days. Isolated livers were perfused first with NaHS for 20 minutes and then with norepinephrine (NE) and the intrahepatic resistance studied. In normal rats and animals with cirrhosis, administration of NE resulted in a dose-dependent increase of portal pressure. This effect was attenuated by H2S treatment (P < .05). The H2S-induced relaxation of hepatic microcirculation was attenuated by glibenclamide, an adenosine triphosphate (ATP)-sensitive K+ channel inhibitor. L-Cysteine, a substrate of cystathionine-gamma-lyase (CSE), decreased vasoconstriction in normal rat livers (P < .05) but failed to do so in livers with cirrhosis. BDL resulted in a downregulation of CSE mRNA/protein levels and activity (P < .05). Our in vitro data demonstrate that CSE is expressed in hepatocytes, HSCs, but not in sinusoidal endothelial cells (SEC). HSC activation downregulates CSE mRNA expression, resulting in a defective production of H2S and abrogation of relaxation induced by L-cysteine. In conclusion, CSE-derived H2S is involved in the maintenance of portal venous pressure. The reduction of CSE expression in the liver with cirrhosis contributes to the development of increased intrahepatic resistance and portal hypertension.

Hepatotoxicity and mechanism of action of haloalkanes: carbon tetrachloride as a toxicological model.

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

Mediators of inflammation and acute phase response in the liver.

The acute phase response is a generalized response of the organism to multiple disturbances of its physiological homeostasis. It consists of local and systemic reactions. Inflammatory processes are the main causes for the initiation of these defence mechanisms. Responsible mediators for the acute phase response are predominantly cytokines, whereby the liver is the predominant target organ. Changes in hepatocyte gene expression profiles result in dramatic changes in serum concentrations of specific plasma proteins, called acute phase proteins. IL-6 was identified as the principal mediator of this reaction. Via its cellular signal transducer gp130 IL-6 induces DNA-binding of STAT transcription factors on regulatory elements of target genes. While IL-6 dependent processes are mainly conferred to be protective other inflammatory cytokines are attributed to be cytotoxic for the liver. TNF-alpha was shown to be involved in several models of liver failure as a mediator for both cytotoxicity and cell proliferation. TNF-alpha leads via caspases to the onset of apoptosis, the so-called programmed cell death. On the other hand it activates NF-kappaB thereby triggering inflammatory processes. In this review we display the relevance for intracellular actions of both cytokines in several models of liver injury. Especially we refer to the T-cell mediated Concanavalin A induced liver failure and to liver regeneration induced by CCL4 and partial hepatectomy. Both cytokines contribute in concert to a cellular balance during these pathophysiological conditions.

Expression of the peripheral-type benzodiazepine receptor and apoptosis induction in hepatic stellate cells.

BACKGROUND AND AIMS: Hepatic stellate cell (HSC) transformation and proliferation play an important role in liver fibrogenesis, and HSC apoptosis may be involved in the termination of this response. METHODS: Expression of the peripheral benzodiazepine receptor (PBR) and PBR-ligand-induced apoptosis were studied in cultured rat liver HSC. RESULTS: Transformation of HSC led to a transient expression of PBR at the messenger RNA and protein level, which was maximal after about 3 and 7 days of culture, respectively, and declined thereafter. Immunoreactive PBR showed a punctate staining and colocalized with mitochondrial manganese-dependent superoxide dismutase and adenine nucleotide translocator 1. The selective PBR ligands 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK11195) and 4' chlorodiazepam (Ro5-4864), but not the centrally acting benzodiazepine ligand clonazepam, induced dose-dependent apoptosis in HSC. The apoptotic potency of PK11195 paralleled the level of PBR expression. PK11195 induced dephosphorylation of protein kinase B/Akt and Bad and a downregulation of Bcl-2. Collapse of the mitochondrial membrane potential preceeded PBR-ligand-induced apoptosis. No apoptosis was induced by PK11195 in parenchymal cells, despite the presence of PBR, and PK11195 had no effect in these cells on Bad phosphorylation and Bcl-2 expression. CONCLUSIONS: Transformation of HSC leads to a transient expression of PBR and renders the cells sensitive to PBR-ligand-induced apoptosis, involving protein kinase B/Akt and Bad-dependent mechanisms.