Studies on thioacetamide-induced liver necrosis

Even at concentration as high as 20 mm, thioacetamide neither results in any type of spectral change by interaction with liver microsomal suspensions nor modifies the in vitro NADPH cytochrome P-450 reductase activity. Thioacetamide administration to rats does not induce a microsomal lipid peroxidation process. The ability of thioacetamide to induce liver necrosis in rats is age dependent, appearing at about the age of 20 days; the 30-day-old rats are already fully responsive to thioacetamide action. Thioacetamide-induced necrosis is as intense in control males as is in females or in castrated males. The previous administration of inhibitors of cytochrome P-450-mediated transformations does not prevent thioacetamide-induced necrosis (2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride, SKF 525A, or ethyl N-2-diethylaminoethyl-2-phenyl-2-ethylmalonate, Sch 5706). The effect of thioacetamide on livers from phenobarbital-preinduced rats is as intense as it is in control rats. Previous treatment with either cystamine or disulfiram partially prevented thioacetamide-induced liver necrosis. The results suggest that cytochrome P-450 or NADPH cytochrome P-450 reductase does not control the process of activation of thioacetamide to the ultimate necrogen.     

Role of flavin-containing-monooxygenase-dependent neutrophil activation in thioacetamide-induced hepatic inflammation in rats

Thioacetamide is widely used in industry and is known to be one of the most potent hepatotoxicants in experimental animals. We investigated the involvement of flavin-containing monooxygenase (FMO)-dependent hepatic-neutrophil activation and the release of proinflammatory mediators in thioacetamide-induced hepatic injury in rats. Thioacetamide (100 mg/kg, intraperitoneally) increased, within 12 h, hepatic serum aspartate transferase and alanine transferase levels, tumor necrosis factor-α production, interleukin-1β and nitrite levels, and myeloperoxidase activity. Rabbit anti-neutrophil serum markedly inhibited all thioacetamide-altered parameters. In addition, FMO-competitive inhibitor methimazole reduced thioacetamide-induced myeloperoxidase activity, hepatic tumor necrosis factor-α, interleukin-1β, nitrite, inducible nitric oxide synthase, and hepatic damage in thioacetamide-treated rats. Thus, we conclude that FMO-dependent hepatic neutrophil activation initiates the release of proinflammatory mediators in thioacetamide-treated rats.     

Protective effect of andrographolide against concanavalin A-induced liver injury

This study was designed to investigate the hepatic protective effect and the molecular mechanisms of andrographolide in concanavalin A-induced liver injury model. Results showed that andrographolide (Ag) attenuated concanavalin A (Con-A)-induced liver injury and inhibited hepatocyte apoptosis. Further results showed that oxidative stress response genes were significantly elevated during the pathogenesis induced by Con-A. Meanwhile, gadolinium chloride and N-acetyl-l-cysteine (NAC) treatment, which inactivates Kupffer cells or reduces reactive oxygen species, respectively, prevented the liver injury. So the messenger RNA levels of the oxidative response genes mentioned above were detected, and the following results showed that Ag treatment reduced their expression. Besides, serum lactate dehydrogenase and myeloperoxidase activity was significantly reduced by Ag. Finally, Ag treatment did not further reduce serum tumor necrosis factor-α production compared with NAC treatment alone. Thus, our results indicate that Ag prevents Con-A-induced liver injury and reduced the hepatic oxidative stress response. The hepatic protective effect of Ag indicates that Ag supplementation may be beneficial in the treatment of immune-mediated liver injury.     

热休克蛋白70在小鼠酒精性肝纤维化过程中的表达

目的探讨热休克蛋白70(HPS70)在酒精性肝纤维化过程中的表达。方法按照体重将雄性C57BL/6J小鼠随机分为2组:正常组10只和模型组40只。模型组用Lieber-DeCarli酒精液体饲料喂养,取0,2,4,6和8周5个时间点造模。4周后腹腔注射5%CCl_4橄榄油2 mL·kg^-1,2次/周,造成酒精性肝纤维化模型。每个时间点各杀4只小鼠并分离血清,检测谷草转氨酶(GOT)活性,苏木精-伊红(HE)染色观察肝组织病理形态改变和坏死积分,用蛋白质印迹法检测小鼠肝组织中HSP70蛋白的相对表达量(相对灰度值)。结果随着时间增加,小鼠血清GOT酶活性和HE染色坏死积分逐渐升高,第8周达到最高;在第8周,正常组和模型组的GOT分别是(110±14)和(509±111)U·L^-1;这2组的肝组织坏死积分分别是0和2分。肝中HSP70的蛋白表达量在第4周达到最高值;正常组和第4周模型组的HSP70的蛋白表达量分别是1.02±0.22和4.62±1.2。随着损伤修复,HSP70表达量逐渐降低。上述指标:模型组与正常组比较,差异均有统计学意义(均P<0.01)。结论HSP70的表达与酒精性肝纤维化发生发展密切相关。     

Pretreatment of male BALB/c mice with beta-ionone potentiates thioacetamide-induced hepatotoxicity

A possible role of metabolic activation by cytochrome P450 (P450) in thioacetamide-induced hepatotoxicity was investigated in male BALB/c mice. The mice were pretreated with the P450 inducer, beta-ionone, subcutaneously at 600 mg/kg, 72 and 48 h prior to an intraperitoneal administration of either 100 or 200 mg/kg of thioacetamide. The elevated activities of serum alanine aminotransferase and serum aspartate aminotransferase by thioacetamide were greatly potentiated by the pretreatment with beta-ionone. Moreover, the potentiation of thioacetamide-induced hepatotoxicity was also observed in the histopathological examination of livers. The hepatic necrosis by thioacetamide was potentiated when mice were pretreated with beta-ionone. In liver microsomes, the activities of P450 2B-specific pentoxyresorufin O-depentylase and benzyloxyresorufin O-debenzylase were significantly induced by the treatment with beta-ionone. Beta-ionone also induced other P450-associated monooxygenases. Because the pretreatment with beta-ionone was not hepatotoxic at the dose inducing P450s. our present results suggest that beta-ionone may be a useful model inducer of P450 enzyme(s) in studying toxic mechanism of certain chemicals which require metabolic activation by P450s in mice.     

Pretreatment with 1,8-cineole potentiates thioacetamide-lnduced hepatotoxicity and immunosuppression

The effect of 1,8-cineole on cytochrome P450 (CYP) expression was investigated in male Sprague Dawley rats and female BALB/c mice. When rats were treated orally with 200, 400 and 800 mg/kg of 1,8-cineole for 3 consecutive days, the liver microsomal activities of benzyloxyresorufin- and pentoxyresorufin-omicron-dealkylases and erythromycin N-demethylase were dose-dependently induced. The Western immunoblotting analyses clearly indicated the induction of CYP 2B1/2 and CYP 3A1/2 proteins by 1,8-cineole. At the doses employed, 1,8-cineole did not cause toxicity, including hepatotoxicity. Subsequently, 1,8-cineole was applied to study the role of metabolic activation in thioacetamide-induced hepatotoxicity and/or immunotoxicity in animal models. To investigate a possible role of metabolic activation by CYP enzymes in thioacetamide-induced hepatotoxicity, rats were pre-treated with 800 mg/kg of 1 ,8-cineole for 3 days, followed by a single intraperitoneal treatment with 50 and 100 mg/kg of thioacetamide in saline. 24 h later, thioacetamide-induced hepatotoxicity was significantly potentiated by the pretreatment with 1,8-cineole. When female BALB/c mice were pretreated with 800 mg/kg of 1,8-cineole for 3 days, followed by a single intraperitoneal treatment with 100 mg/kg of thioacetamide, the antibody response to sheep red blood cells was significantly potentiated. In addition, the liver microsomal activities of CYP 2B enzymes were significantly induced by 1,8-cineole as in rats. Taken together, our results indicated that 1,8-cineole might be a useful CYP modulator in investigating the possible role of metabolic activation in chemical-induced hepatotoxicity and immunotoxicity.     

巯基氧化剂对急性肝损伤时库普弗细胞功能的影响

目的　观察巯基氧化剂在急性肝损伤时对库普弗细胞功能的影响。方法　采用半乳糖胺 /脂多糖 (Galn/LPS)所致急性肝损伤模型 ,雄性昆明种小鼠于注射Galn/LPS(每只 4kg/g)前 1h ,腹腔注射巯基氧化剂马来酸二乙酯 (DEM)每周 5mmol/kg ,并分别于Galn/LPS注射后 6h ,测定血浆丙氨酸转氨酸 (ALT)活性、肿瘤坏死因子 (TNF) α水平、肝脏谷胱甘肽 (GSH)含量和库普弗细胞的吞噬功能。结果　DEM预处理可抑制Galn/LPS导致的血浆ALT活性、TNF α水平、库普弗细胞的吞噬功能升高。结论　巯基氧化剂DEM可通过改变肝脏GSH含量的变化 ,影响细胞氧化还原状态 ,抑制LPS导致的库普弗细胞活化 ,从而减轻肝损伤的发生     

Inflammation, an inducer of metallothionein, inhibits carbon-tetrachloride-induced hepatotoxicity in rats.

Inflammation, induced by turpentine (0.1 ml i.m.), protected against carbon tetrachloride (CCl4)-induced hepatotoxicity based on serum activities of sorbitol dehydrogenase. Inflammation was confirmed by elevated serum ceruloplasmin activities, and was associated with high hepatic levels of metallothionein, a zinc protein proposed to protect against CCl4-induced injury. Inflammation suppressed cytochrome P-450 activities, but this was not associated with protection against CCl4-promoted liver microsomal injury as assessed by glucose-6-phosphatase activity loss. Thus, protection against plasma membrane injury did not result primarily from depressed microsomal activation of CCl4. Each effect of inflammation reported here resembled effects of zinc injections. This similarity strengthens the hypothesis that metallothionein protects against CCl4-induced hepatic plasma membrane injury.     

Investigation of antioxidant,anti-inflammatory and DNA-protective properties of eugenol in thioacetamide-induced liver injury in rats

The present study investigated the preventive effect of eugenol, a naturally occurring food flavouring agent on thioacetamide (TA)-induced hepatic injury in rats. Adult male Wistar rats of body weight 150–180 g were used for the study. Eugenol (10.7 mg/kg b.w./day) was administered to rats by oral intubation for 15 days. TA was administered (300 mg/kg b.w., i.p.) for the last 2 days at 24 h interval and the rats were sacrificed on the 16th day. Markers of liver injury (aspartate transaminase, alanine transaminase, alkaline phosphatase, γ-glutamyl transferase and bilirubin), inflammation (myeloperoxidase, tumor necrosis factor-α and interleukin-6), oxidative stress (lipid peroxidation indices, protein carbonyl and antioxidant status) and cytochrome P4502E1 activity were assessed. Expression of cyclooxygenase-2 (COX-2) and the extent of DNA damage were analyzed using immunoblotting and comet assay, respectively. Liver injury and collagen accumulation were assessed using histological studies by hematoxylin and eosin and Masson trichrome staining. Rats exposed to TA alone showed increased activities of hepatocellular enzymes in plasma, lipid peroxidation indices, inflammatory markers and pro-inflammatory cytokines and decreased antioxidant status in circulation and liver. Hepatic injury and necrosis were also evidenced by histology. Eugenol pretreatment prevented liver injury by decreasing CYP2E1 activity, lipid peroxidation indices, protein oxidation and inflammatory markers and by improving the antioxidant status. Single-cell gel electrophoresis revealed that eugenol pretreatment prevented DNA strand break induced by TA. Increased expression of COX-2 gene induced by TA was also abolished by eugenol. These findings suggest that eugenol curtails the toxic effects of TA in liver.     

Geranylgeranylacetone protects against acetaminophen-induced hepatotoxicity by inducing heat shock protein 70

Geranylgeranylacetone (GGA), an anti-ulcer drug, has been reported to induce heat shock protein (HSP) 70 in several animal organs. The present study was performed to determine whether GGA protects mouse liver against acetaminophen (APAP)-induced injury and whether it has potential as a therapeutic agent for APAP overdose. Hepatic damage was induced by single oral administration of APAP (500 mg/kg). GGA at 400 mg/kg was given orally 4 or 8h before, or 0.5h after APAP administration. Treatment of mice with GGA 4h before or 0.5h after APAP administration suppressed increases in transaminase activities and ammonia content in blood as well as hepatic necrosis. Such GGA treatment significantly increased hepatic HSP70 accumulation after APAP administration. Furthermore, GGA inhibited increases in hepatic lipid peroxide content and hepatic myeloperoxidase activity after APAP administration. In contrast, GGA neither inhibited hepatic cytochrome P450 2E1 activity nor suppressed hepatic glutathione depletion after APAP administration. The protective effect of GGA treatment 4h before APAP on hepatotoxicity induced by APAP was completely inhibited with quercetin, known as an HSP inhibitor. In conclusion, GGA has been identified as a new antidote to APAP injury, acting by induction of HSP70. The potential of GGA as a therapeutic tool is strongly supported by its ability to inhibit hepatic injury even when administered after ingestion of APAP.     

阿魏酸钠对异烟肼和利福平肝损害小鼠的保护作用

目的：观察阿魏酸钠对异烟肼(INH)和利福平(RFP)肝毒性的保护作用。方法：分别测定血清谷丙转氨酶(ALT)的活性，肝匀浆中谷胱甘肽(GSH)及脂质过氧化物丙二醛(MDA)的含量，肝微粒体中细胞色素P450及其亚型2E1的活性。结果：阿魏酸钠可对抗INH和RFP合用引起的肝指数、血清ALT水平、肝匀浆中的MDA含量，以及细胞色素P450与亚型P450 2E1活性的升高，增加肝匀浆中GSH含量。病理学检查，阿魏酸钠明显减轻肝细胞的变性和坏死。结论：阿魏酸钠时INH和RFP肝毒性的保护作用与保护肝细胞膜、抑制脂质过氧化反应、清除自由基、降低RFP诱导的细胞色素P450酶系统有关。     

Differential effects of isoflurane and halothane on the induction of heat shock proteins.

Isoflurane is considered to be a less hepatotoxic volatile anesthetic than halothane since it not only undergoes quantitatively much less metabolism to form toxic reactive intermediates, but also preserves better hepatic blood flow. However, the biochemical basis for the reduced hepatotoxicity has not been elucidated. In this study, we examined the induction of two heat shock proteins, heat shock protein 70 (HSP70) and heme oxygenase-1 (HO-1), in the livers of rats pretreated with or without phenobarbital, followed by exposure to isoflurane or halothane under hypoxic conditions. In the phenobarbital-pretreated rats, the maximal induction of HSP70 was observed by halothane-hypoxia treatment, followed by a half-maximal induction by isoflurane-hypoxia treatment, and less than 30% induction by hypoxia treatment alone. Serum alanine aminotransferase (ALT) activity, an indicator of hepatic dysfunction, which correlated well with the extent of centrilobular necrosis, showed similar changes with increases in HSP70 mRNA. In contrast, HO-1 mRNA was induced only by treatment with halothane-hypoxia. In addition, changes in the expression of HSP70 and HO-1 mRNAs were correlated with their protein expression in the liver. In non-pretreated rats, neither isoflurane-hypoxia exposure nor halothane-hypoxia exposure caused apparent hepatic injury. There was also no induction of HSP70 or HO-1 mRNA by these treatments in non-pretreated animals. These findings demonstrate that there is a significant difference in hepatic injury, and in the induction of HO-1 and HSP70 between halothane-hypoxia and isoflurane-hypoxia treatments. Isoflurane is known to be safer than halothane, which may, in part, be accounted for by the generation of less oxidative stress in the presence of isoflurane, as assessed by reduced induction of heat shock proteins compared with halothane treatment.     

The effect of thioacetamide on rat liver plasma membrane enzymes and its potentiation by fasting

Thioacetamide, given intraperitoneally (1.4 mmol/kg body mass) to male Wistar rats 24 h before sacrifice promoted a marked elevation of serum aminotransferases, loss of microsomal cytochrome P-450 content and a significant reduction (about 50%) of the liver plasma membrane enzymatic activities (5'-nucleotidase; K+, Na+- and Mg2+-adenosine triphosphatases; and gamma-glutamyl transferase). Previous starvation for 48 h, immediately prior to thioacetamide administration, strongly potentiated the effects of thioacetamide on the serum, microsomal and liver plasma membrane parameters, while fasting itself did not affect them. The liver plasma membrane damage may be one of the reasons for the cell death in thioacetamide-intoxicated rat livers.     

Metabolism-dependent hepatotoxicity of methimazole in mice depleted of glutathione.

Methimazole (MMI) (>0.1 mmol kg(-1), p.o.) given in combination with DL-buthionine sulphoximine (BSO) (3 mmol kg(-1), i.p., 1 h before MMI administration), an inhibitor of glutathione (GSH) synthesis, caused liver injury in mice. The injury was characterized by centrilobular necrosis of hepatocytes and an increase in serum alanine transaminase (ALT) activity. Methionazole (2 mmol kg(-1)) alone resulted in only a marginal increase in serum ALT activity, but produced no histopathological changes in the liver. Pretreatment with hepatic cytochrome P-450 monooxygenase inhibitors--cobalt chloride, isosafrole, methoxsalen, metyrapone and piperonyl butoxide-prevented or tended to suppress the hepatotoxicity induced by MMI in combination with BSO. Treatment with N,N-dimethylaniline and ethyl methyl sulphide, competitive substrates of flavin-containing monooxygenases (FMO), also resulted in remarkable suppression of the hepatotoxicity caused by MMI in combination with BSO. These results suggest that MMI is activated by reactions mediated by both cytochrome P-450 monooxygenases and FMO, and that the inadequate rates of detoxification of the resulting metabolite are responsible for the hepatotoxicity in GSH-depleted mice.     

Distribution of zinc-binding metallothionein in cirrhotic liver of rats administered zinc

This study was undertaken in order to investigate the effect of zinc (Zn) administration on induction of Zn-binding metallothionein in rat liver with thioacetamide-induced cirrhosis, and the localization of metallothionein in the liver. Normal and cirrhotic rats received intraperitoneal injections with or without Zn. Subsequently, metal analyses, purification of metallothionein by gel filtration and immunohistochemical assessments of metallothionein were carried out. Although in Zn-injected cirrhotic rats, the Zn contents in the liver and plasma increased significantly depending upon the dose of Zn, the Zn contents in the liver and plasma of the cirrhotic rats were lower than those of normal rats after the same dose of Zn. The results of gel filtration also showed that the levels of Zn-metallothionein in the cirrhotic liver were reduced in comparison with those of the normal liver. By the immunohistochemical method, the presence of metallothionein in the parenchymal areas but not in the fibrotic areas of the cirrhotic liver was confirmed. These results suggested that the induced metallothionein was only located in the parenchymal areas. The metallothionein induced in the parenchymal areas was considered to play a role in protecting the parenchymal cells against the progression of fibrosis, because metallothionein has been thought to be involved in the cellular defense against oxidative stress.     

Effects of defibrotide,a novel oligodeoxyribonucleotide,on ischaemia and reperfusion injury of the rat liver

1. The purpose of this study was to investigate the protective effects of defibrotide, a single-stranded polydeoxyribonucleotide, on ischaemia-reperfusion injury to the liver using a rat model. 2. Ischaemia of the left and median lobes was created by total inflow occlusion for 30 min followed by 60 min of reperfusion. Hepatic injury was assessed by the release of liver enzymes (alanine transferase, ALT and lactic dehydrogenase, LDH). Hepatic oxidant stress was measured by superoxide production, lipid peroxidation and nitrite/nitrate formation. Leukocyte-endothelium interaction and Kupffer cell mobilization were quantified by measuring hepatic myeloperoxidase (MPO), polymorphonuclear leukocyte adherence to superior mesenteric artery (SMA) and immunostaining of Kupffer cell. 3. Defibrotide treatment resulted in a significant inhibition of postreperfusion superoxide generation, lipid peroxidation, serum ALT activity, serum LDH activity, MPO activity, serum nitrite/nitrate level, leukocyte adherence to SMA, and Kupffer cell mobilization, indicating a significant attenuation of hepatic dysfunction. 4. A significant correlation existed between liver ischaemia/reperfusion and hepatic injury, suggesting that liver ischaemia/reperfusion injury is mediated predominantly by generation of oxygen free radicals and mobilization of Kupffer cells. 5. We conclude that defibrotide significantly protects the liver against liver ischaemia/reperfusion injury by interfering with Kupffer cell mobilization and formation of oxygen free radicals. This study provides strong evidence that defibrotide has important beneficial effects on acute inflammatory tissue injury such as that occurring in the reperfusion of the ischaemic liver.     

Prevention of hemorrhagic shock-induced lung injury by heme arginate treatment in rats

Hemorrhagic shock followed by resuscitation (HSR) induces oxidative stress, which leads to acute lung injury. Heme oxygenase (HO)-1 (EC 1.14.99.3), the rate-limiting enzyme in heme catabolism, is inducible by oxidative stress and is thought to play an important role in the protection from oxidative tissue injuries. In this study, we examined expression of HO-1 as well as tissue injuries in the lung, liver, and kidney after HSR in rats. We also pretreated animals with heme arginate (HA), a strong inducer of HO-1, and examined its effect on the HSR-induced lung injury. HO-1 expression significantly increased in the liver and kidney following HSR, while its expression in the lung was very low and unchanged after HSR. In contrast to HO-1 expression, tissue injury and tumor necrosis factor-alpha (TNF-alpha) gene expression was more prominent in the lung compared with those in the liver and kidney. HA pretreatment markedly induced HO-1 in pulmonary epithelial cells, and ameliorated the lung injury induced by HSR as judged by the improvement of histological changes, while it decreased TNF-alpha and inducible nitric oxide synthase gene expression, lung wet weight to dry weight ratio, and myeloperoxidase activity. In contrast, inhibition of HO-1 by tin-mesoporphyrin administration abolished the beneficial effect of HA pretreatment. These findings suggest that tissues with higher HO-1 may be better protected than those with lower HO-1 from oxidative tissue injury induced by HSR. Our findings also indicate that HA pretreatment can significantly suppress the HSR-induced lung injury by virtue of its ability to induce HO-1.     

Distribution of Zinc‐Binding Metallothionein in Cirrhotic Liver of Rats Administered Zinc

This study was undertaken in order to investigate the effect of zinc (Zn) administration on induction of Zn‐binding metallothionein in rat liver with thioacetamide‐induced cirrhosis, and the localization of metallothionein in the liver. Normal and cirrhotic rats received intraperitoneal injections with or without Zn. Subsequently, metal analyses, purification of metallothionein by gel filtration and immunohistochemical assessments of metallothionein were carried out. Although in Zn‐injected cirrhotic rats, the Zn contents in the liver and plasma increased significantly depending upon the dose of Zn, the Zn contents in the liver and plasma of the cirrhotic rats were lower than those of normal rats after the same dose of Zn. The results of gel filtration also showed that the levels of Zn‐metallothionein in the cirrhotic liver were reduced in comparison with those of the normal liver. By the immunohistochemical method, the presence of metallothionein in the parenchymal areas but not in the fibrotic areas of the cirrhotic liver was confirmed. These results suggested that the induced metallothionein was only located in the parenchymal areas. The metallothionein induced in the parenchymal areas was considered to play a role in protecting the parenchymal cells against the progression of fibrosis, because metallothionein has been thought to be involved in the cellular defense against oxidative stress.