Effect of platelet-activating factor (PAF) receptor antagonist (BN52021) on acetaminophen-induced acute liver injury and regeneration in rats.

BACKGROUND: Platelet-activating factor (PAF) is an endogenous lipid mediator that plays a key role in catalyzing various pro-inflammatory processes associated with acute liver injury. In the present study, the possible influence of PAF-R antagonist (BN52021) on the protection of liver injury after 4-hydroxyacetanilide, N-acetyl-p-aminophenol, paracetamol (APAP) intoxication was investigated. METHODS: Thereby, one group of rats was treated with a toxic dose of APAP (3.5 g/kg body weight (b.w.). The animals were killed at 56, 66, 72, 84 and 96 h after treatment. RESULTS: APAP was found to cause an acute hepatic injury, evident by alterations of biochemical (serum enzymes: aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase) and liver histopathological (degree of necrosis and apoptosis) indices, which was followed by liver regeneration, evident by three independent indices ([3H] thymidine incorporation into hepatic DNA, liver thymidine kinase activity and hepatocyte mitotic index). The protective effects of BN52021 were qualified during post-treatment time by: (1) significant reduction of hepatic injury as showed by all biochemical and histological parameters, (2) high decrease of regenerating activity showed by three regenerative markers and (3) remarkable increase of PAF-acetylhydrolase (PAF-AH) activity. CONCLUSION: These results suggest that PAF may play an important role in APAP-induced liver injury and regeneration, and PAF-R antagonist (BN52021) attenuates liver damage.

Platelet-activating factor (PAF) involvement in acetaminophen-induced liver toxicity and regeneration.

Acetaminophen-induced toxicity has been attributed to cytochrome P-450-generated metabolites, which covalently modify target proteins. However, the mechanism of liver injury pathogenesis needs to be further elucidated. Platelet-activating factor (PAF) is one of the mediators involved in inflammatory tissue alterations associated with acute liver failure. In this study, alterations in blood PAF levels and the serum activity of PAF-acetylhydrolase (PAF-AH) were investigated over the time course of liver injury and regeneration induced by acetaminophen treatment in rats. The administration of a toxic dose of acetaminophen (3.5 g/kg) in rats caused acute hepatic injury, as evident by alterations of biochemical (serum enzymes: ALT, AST and ALP) and liver histopathological (degree of inflammation and apoptosis) indices between 20 and 40 h post-treatment. The hepatic damage was followed by liver regeneration, made evident by three independent indices ([3H]thymidine incorporation into hepatic DNA, liver thymidine kinase activity and hepatocyte mitotic index), presenting a peak at 72 h. The PAF levels were elevated at 24 and 28 h, presenting a remarkable peak at 32 h post-treatment. PAF-AH activity presented different kinetics to that of PAF. The enzyme activity was relatively low at all time points examined before the rise in PAF activity, peaking later, at 72, 84 and 96 h. Our data demonstrate that PAF is involved in the pathogenesis of acute liver failure and in augmented compensatory liver tissue repair post-acetaminophen treatment. However, the putative role of PAF during liver toxicity and regeneration remains to be established.

Levels of hepatic stimulator substance in liver regenerating process of partially hepatectomized rats pretreated with a single dose of carbon tetrachloride.

Liver regeneration after injury with carbon tetrachloride (CCl4) followed by partial hepatectomy is a complex model involving toxicological, inflammatory, and necrotic processes. In the present study, the time-course of hepatic regenerative process was investigated in relation to hepatic stimulator substance (HSS) activity, administration of a single dose of CCl4 and partial (70%) hepatectomy in male rats. To evaluate liver injury events, the levels of serum aspartic aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) were measured. Hepatic DNA synthesis reached a maximum at 36 hr after hepatectomy in contrast to the reported 24-hr and 32-hr peaks observed in nontreated hepatectomized rats. On the other hand, HSS activity appeared to peak at 28, 40, and 44 hr after hepatectomy in CCl4-treated rats, and it was quite a lot lower at 24, 32, 36, 48, and 60 hr. The hypothesis that HSS promotes liver regeneration but it does not initiate it, as other factors have been found to do, is discussed.

Hepatic stimulator substance activity in the liver of thioacetamide-intoxicated rats.

AIMS/BACKGROUND: Hepatic stimulator substance (HSS) is a known hepatic growth factor which appears to be organ-specific but species non-specific. We have recently shown that the administration of HSS enhanced hepatocyte proliferation occurring due to thioacetamide (TAA)-induced liver injury in rats (Theocharis SE, et al., Scand J Gastroenterol 1998; 33: 656-63). In the present study, we examined the activity of the endogenously produced HSS in the liver of TAA administered rats during injury and regeneration. METHODS: TAA at a dose of 300 mg/kg of body weight was injected intraperitoneally in male Wistar rats. The animals were sacrificed at 0, 12, 24, 36, 48, 60 and 72 h after TAA administration. The rate of tritiated thymidine incorporation into hepatic DNA, the enzymatic activity of liver thymidine kinase and the assessment of mitotic index in hepatocytes were used to estimate liver regeneration. HSS extract was obtained from the livers of TAA-treated rats, sacrificed at the above mentioned time points. This HSS extract was injected in 34% partially hepatectomized rats, to assess its activity. The ability of the injected HSS extract to increase hepatocellular proliferation over that normally occurring 24 h following 34% partial hepatectomy was used to express the activity of HSS by determining the above mentioned indices of liver regeneration. RESULTS: The administration of TAA caused severe hepatic injury recognized histopathologically as well as by the increased activities of serum hepatic enzymes aspartate and alanine aminotrasferases. The hepatic injury, which peaked at 24 and 36 h post-TAA treatment (p<0.001), was followed by hepatocyte proliferation, presenting peaks at 48 and 60 h (p<0.001). The activity of the endogenously produced HSS from livers of TAA-treated rats increased at 36 h after TAA administration as well as being highly expressed at 48 and 60 h thus coinciding with the peak of hepatocyte proliferation. At other time points, HSS activity was decreased. CONCLUSIONS: The observed variations of HSS activity in rat liver suggest active participation of this growth factor in hepatocyte replication which follows toxin-induced liver injury as a repair mechanism process.

Effect of hepatic stimulator substance administration on tissue regeneration due to thioacetamide-induced liver injury in rats.

BACKGROUND: Hepatic stimulator substance (HSS) is a known hepatic growth factor that appears to be organ-specific but species-nonspecific. In the present study we investigated the effect of HSS administration in a rat model of liver injury and regeneration induced by thioacetamide (TAA) injection. METHODS: TAA (300 mg/kg body weight) was injected intraperitoneally in male Wistar rats (group I). HSS (50 mg protein/kg body weight) was administered intraperitoneally either at 24 h (group II) or at 36 h (group III) after TAA treatment. The animals were killed at different time points after TAA injection, and the rate of tritiated thymidine incorporation into hepatic DNA, the activity of the enzyme thymidine kinase in liver, and the assessment of the mitotic index in hepatocytes were used to estimate liver regeneration. RESULTS: The administration of TAA caused severe hepatic injury recognized histopathologically and by increased activities of the serum hepatic enzymes aspartate and alanine aminotransferases. The hepatic injury, which peaked at 24 h and 36 h after TAA injection, was followed by a regenerative process of hepatocytes which presented peaks after 48 h and 60 h (group I). The regenerative process of hepatocytes remained unaffected when HSS was administered 24 h after the injection of TAA (group II). In the case of HSS administration 36 h after the injection of TAA (group III) the examined indices of hepatocyte proliferation were statistically significantly increased at 48 h (P < 0.001), compared with those observed in group I. CONCLUSIONS: The administration of HSS enhanced the hepatocyte proliferative capacity, induced by TAA treatment, depending on the time of its administration.

Effect of interferon-alpha2b administration on rat liver regeneration after partial hepatectomy.

The purpose of the present study was to delineate the effect of interferon-alpha2b (IFN-alpha2b) administration on the liver regenerative capacity after partial hepatectomy in rats. The administration of IFN-alpha2b simultaneously with partial hepatectomy did not affect hepatic proliferation in a statistically significant manner. When IFN-alpha2b was administered either 2 or 12 hr postoperatively, an inhibition of hepatocyte proliferation was observed 24 hr postoperatively, while at further time intervals up to 48 hr, DNA synthesis remained similar to that observed in the simply partially hepatectomized rats. The enzyme thymidine kinase (TK), has been implicated in the suppression of proliferation in interferon-treated cell cultures. In all IFN-alpha2b-treated groups of rats, alterations of TK activity were observed without being correlated to the liver regenerative status. Additionally, the administration of the polyamine putrescine in partially hepatectomized rats treated at the time of surgery with IFN strongly enhanced TK activity, but did not affect DNA biosynthesis. In the above-mentioned in vivo model of controlled cellular proliferation, the administration of IFN-alpha2b affected the rate of hepatocyte proliferation depending on the time of its administration; this effect was not correlated to the enzymatic activity of TK, as inhibited TK activity is responsible for the suppressed DNA synthesis in in vitro systems.

Effect of subtotal pancreatectomy on the rate of liver regeneration: the role of hepatic stimulator substance.

The endogenous signals controlling liver regeneration are becoming rapidly defined. One of the key findings during liver regeneration following partial hepatectomy is the appearance of peripheral blood factors that stimulate DNA synthesis in the parenchymal cells. Hepatopoietin A, or hepatocyte growth factor, has been described as a complete mitogen for hepatocytes, one of its major tissue sources being the pancreas. The changes in the rate of DNA synthesis (incorporation of [3H] thymidine into DNA) in both subtotally pancreatectomized-partially hepatectomized (Group A) and partially hepatectomized (Group B) male rats were determined at different postoperation times. DNA synthesis in Group A was increased progressively, reaching a maximum at 40 hr after operation in contrast to the 24- and 32-hr peaks obtained in nonpancreatectomized rats (Group B). However, liver regeneration in Group A was significantly lower than in Group B. To evaluate the effects of hepatic stimulator substance (HSS) on liver regeneration, the time course of HSS biological activity during the liver regeneration process was determined in the livers of Group A rats. A concurrent change of HSS activity and rate of liver regeneration was observed. These results support the hypothesis that HSS biological activity may be delayed but not suppressed by subtotal pancreatectomy.

Cadmium-induced hepatotoxicity in three different rat strains.

Cadmium (Cd) is a highly toxic element able to induce acute liver injury in rats after intraperitoneal administration. The dose-dependent Cd-induced hepatotoxicity was examined in three different rat strains. A difference in hepatotoxicity was observed in the three rat strains, determined by the examination of serum enzymes' activities and other biochemical parameters, all markedly altered after Cd intoxication. The histological findings came to confirm the variations of the above-mentioned parameters. It is concluded that the administration of this toxic agent caused different toxicity in the three rat strains examined, indicating a more intense damage in Wistar than in Quinster and Lewis rats.

Immobilization of native and denatured DNA on Sephadex G200.

An efficient method for the immobilization of DNA on Sephadex G200 in the presence of water soluble carbodiimide is described and investigated in this paper. An increase in the extent of binding was observed when the incubation temperature of the DNA-Sephadex mixture was changed. It was found that native DNA immobilized to Sephadex with higher efficiency than denatured DNA. However, the stability of native DNA-Sephadex complex was about the same as that of denatured DNA-Sephadex. The size of DNA released by DNA-Sephadex after incubation of a suspension of the complex was the same as that of the DNA used for immobilization. The binding mechanism of DNA to Sephadex is discussed.

Influence of two preparations of bovine albumin on the total bilirubin as determined by Thomson's method in its reference solution.

The influence of bovine albumin on the determined total bilirubin was examined by estimation of bilirubin in standard solutions prepared with albumin solutions of five different concentrations. The determinations were made by six different methods. The results show that when bilirubin was determined by Thompson's method the estimated bilirubin decreases by increasing the concentration of albumin. This discrepancy appears in preparations from two different industrial sources of albumin.

The effect of phenobarbital on the serum bilirubin level in normal and CCI-4 liver-damaged rats. Biochemical and histologic study.

The present study was designed to determine the effect of phenobarbital on bilirubin metabolism in rats, following intraperitoneal injection of blood incubated at 37 degrees C for 24 hr to produce hyperbilirubinaemia. Blood was taken from the rats to determine the total serum bilirubin before and 6, 12, 24, 36 and 48 hours after the intraperitoneal transfusion. Comparison of the bilirubin curves shows that the serum bilirubin levels were always significantly lower in the phenobarbital pretreated animals. It is proposed that several mechanisms may be responsible for the favorable effect of the phenobarbital on the bilirubin metabolism.