Prevention of thioacetamide-induced liver necrosis by prior administration of substrates of microsomal flavin-containing monooxygenase

Two photostable pyrethroids, deltamethrin and cypermethrin, were tested against fourth instar larvae of a susceptible (S) strain and a resistant (R) strain of Plutella xylostella L. by topical application. Both compounds were very effective against the S strain larvae (LD50 for deltamethrin = 0.0014 micrograms/larva, LD50 for cypermethrin = 0.0046 micrograms/larva, at 48 h). However, the R strain collected from the field was greater than 1600-fold resistant to deltamethrin and greater than 30 000-fold resistant to cypermethrin. Deltamethrin was poorly synergised with piperonyl butoxide in the S strain, but much stronger synergism was obtained in the R strain. The possible reasons for such high levels of resistance and the potential use of synergised pyrethroids in Plutella control programmes are discussed.     

Effect of thioacetamide-induced hepatic necrosis on the regioselective metabolism of S-warfarin by rat liver mixed-function oxidase enzymes

The biotransformation of S-warfarin was examined using liver microsomes prepared from rats 6-96 hr after treatment with a necrotizing dose (5.6 mmoles/kg) of thioacetamide. Four catalytically distinct classes of enzyme activity were observed which declined in activity with different half-lives after thioacetamide intoxication. S-Warfarin 7-hydroxylase activity was destroyed with a half-life of 16.6 +/- 3.1 hr. 6-Hydroxylase activity was destroyed with a half-life of 25.3 +/- 3.0 hr. 4'-Hydroxylase activity was destroyed with a half-life of 34.6 +/- 4.8 hr, which paralleled the loss of total hepatic cytochrome P-450 with a half-life of 33.4 +/- 3.6 hr. Production of an unidentified metabolite was not affected by thioacetamide intoxication during the first 48 hr. The ratio of rates of product formation were used as an alternative method to test the homogeneity of distinct enzyme catalytic activities. The ratio of measured responses (e.g. chromatographic peak heights) was used directly to determine the product ratios, provided that the rate of formation of each product was directly proportional to the experimentally measured response for each product. The use of product response ratios to discriminate between catalytic activities was inherently more precise because calibration errors were eliminated. Differences in the rates of destruction of warfarin hydroxylases provided further evidence of the multiplicity of hepatic mixed-function oxidases and suggested topographical differences in their location within the liver lobule.     

Early changes in thioacetamide-induced liver damage

Plasma amino acids, serum enzymes, liver glutathione and the hepatic lipid peroxidation capacity of the rat were investigated in acute thioacetamide toxicity. These were examined in parallel with the earliest pathological changes shown by electron microscopy. Plasma arginine levels were significantly lowered 3 h after dosing thioacetamide and by 9 h were indistinguishable. This finding correlates with other workers demonstrating urea cycle damage in alcohol and carbon tetrachloride damaged rat liver. Depressed arginine plasma levels were detectable before any of the biochemical or pathological processes co-examined and as such may prove useful as a sensitive in vivo method for detection of acute liver damage.     

Effect of S-adenosyl-L-methionine on thioacetamide-induced liver damage in rats

S-Adenosyl-L-methionine (Ado-met) administration to rats significantly improved liver necrosis induced by thioacetamide (TAA) as evidenced by reduction of TAA-elevated catalytic activity of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALAT). Ado-met, however, was not effective in reduction of catalytic activity of serum alkaline phosphatase (ALP) which increased as a consequence of TAA administration. Histologic analysis of the livers supported the biochemical data. Hepatocellular damage was evident from the first day of TAA treatment at daily (i.p.) doses of 50 mg/kg body wt. Maximal necrosis was apparent after 3 days of TAA administration. When rats were treated once a day, for 3 days with Ado-met (2 mg/kg body wt) as well as with TAA, significant reduction of hepatic necrotic area was observed. A similar effect was obtained when doses of 200 mg/kg body wt. of Ado-met were utilized.     

Effect of Tinospora crispa on thioacetamide-induced liver cirrhosis in rats

Objectives:

This study was conducted to determine the effect of ethanolic extract of the dried stems of Tinospora crispa in a male rat model of hepatic fibrosis caused by the hepatotoxin, thioacetamide.

Materials and Methods:

The extract was gavaged daily to the rats, at doses of 100 and 200 mg/kg along with thioacetamide at a dose of 200 mg/kg twice weekly. To assess the effectivity of extract, against thioacetamide, the activity of aminotransferases (alanine aminotransferase, aspartate aminotransferase), alkaline phosphatase (AP); and bilirubin were measured, together with morphological and histopathological indices in the liver of healthy and thioacetamide-treated rats.

Results:

A significant increase in the activity of liver enzymes, bilirubin and G-glutamyl transferase and gross and histopathological changes were determined. Although previous in vitro study established that this extract had strong antioxidant activity, this in vivo study establishes that this extract contains hepatotoxins whose identity may be quite different from those compounds with antioxidant properties.

Conclusion:

The study confirms that complete reliance on data obtained using in vitro methodologies may lead to erroneous conclusions pertaining to the safety of phytopharmaceuticals.     

Detrimental effects of nicotine on thioacetamide-induced liver injury in mice

Aim: Nicotine exerts a number of physiological effects. The purpose of this study was to determine the effects of nicotine on thioacetamide (TAA)-induced liver fibrosis in mice.

Materials and methods: For in vivo experiments, hepatic fibrosis was induced by TAA (0.25?g/kg, i.p.) three times a week for 6?weeks. Mice of TAA treated groups were administered daily with distilled water and nicotine (50 or 100?μg/mL) via gastrogavage throughout the experimental period. For in vitro experiments, HepG2 (human liver cancer cell line) and LX-2 (human hepatic stellate cell line) were used to determine oxidative stress and fibrosis, respectively.

Results: Compared to control groups, TAA treated groups had significantly differences in serum alanine transferase and aspartate aminotransferase levels and nicotine accentuated liver injury. Moreover, nicotine increased the mRNA levels of TAA-induced transforming growth factor-β (TGF-β) and collagen type I alpha 1 in the liver. Nicotine also increased TAA-induced oxidative stress. Histological examination confirmed that nicotine aggravated the degree of fibrosis caused by TAA treatment. Additionally, nicotine enhanced hepatic stellate cell activation via promoting the expression of α-smooth muscle actin.

Conclusions: Oral administration of nicotine significantly aggravated TAA-induced hepatic fibrosis in mice through enhancing TGF-β secretion and TAA-induced oxidative stress. The increase in TGF-β levels might be associated with the strengthening of oxidative processes, subsequently leading to increased hepatic stellate cell activation and extracellular matrix deposition. These results suggest that patients with liver disease should be advised to abandon smoking since nicotine may exacerbate hepatic fibrosis.     

Lipid peroxidation in thioacetamide-induced macronodular rat liver cirrhosis

Microsomes and isolated hepatocytes from thioacetamide (TAA)-induced macronodularly cirrhotic rat livers were analysed for their susceptibility to unstimulated and stimulated lipid peroxidation measured as malondialdehyde (MDA) formation. In microsomes from TAA-induced macronodularly cirrhotic livers the MDA production stimulated either by ascorbate-iron or by ADP-iron in a NADPH-regenerating system was decreased. Hepatic microsomes from TAA-treated rats exhibited a reduced cytochrome P450 content and lowered activities of ethylmorphine N-demethylase, ethoxycoumarin O-deethylase and epoxide hydrolase. Besides this, the microsomal fatty acid pattern of phosphatidylcholine and phosphatidylethanolamine was significantly changed after 6 months of TAA administration. The 182/204 ratio of phospholipid fatty acids was markedly increased. In contrast to the microsomes, in isolated hepatocytes from macronodularly cirrhotic livers the iron- and ascorbate-iron-stimulated MDA formation was increased. The hepatocellular GSH content was unaffected by TAA pretreatment, whereas the GSSG content exhibited a significant increase, thus leading to a pronounced reduction of the GSH/GSSG ratio. The calcium channel blocker verapamil (200 M), known to be able to scavenge OH radicals produced by the Fenton reaction, revealed an inhibitory effect on ascorbate-iron- and ADP-iron-stimulated lipid peroxidation in hepatocytes from normal as well as TAA-treated livers which is attributed to its antioxidative properties. In summary, lipid peroxidation is altered in TAA-induced macronodularly cirrhotic rat livers. Furthermore, the data clearly show that isolated microsomes and parenchymal cells prepared from cirrhotic livers react differently to prooxidant stimuli.     

穿心莲内酯调控硫代乙酰胺诱发小鼠肝纤维化的作用机制

目的 利用硫代乙酰胺(TAA)诱发小鼠肝纤维化的动物模型,探讨穿心莲内酯(AG)减缓肝纤维化的作用及其分子机制.方法 每周给予小鼠2次100 mg· kg-TAA,分别于第1、4周取样,并同时喂食高(100 mg· kg-1)、低(20 mg·kg-1)剂量AG,于第4周后取肝脏组织做组织切片、免疫组织化学染色、双重免疫荧光染色,收集血清做丙氨酸氨基转移酶分析.结果 AG可降低TAA所诱发肝内炎性物质与过氧化反应的表达,降低肝组织中Neutrophil、CD11b、F4/80的表达以及NF-κB、COX-2、p-cPLA2、Nrf2蛋白质等的表达量,并能调控肝内脂质过氧化作用,上调SMP30蛋白质水平;组织切片染色显示:给予TAA4周后的小鼠肝脏有明显纤维化,而随着给予AG剂量的增加有显著改善作用;随着AG剂量的增加减少了肝脏内d-SMA、TGF-βR1蛋白质的表达量;使用双重免疫荧光染色法发现AG减缓肝纤维化的作用与调控星状细胞活化相关.结论 AG能调控肝内炎性病变进而减缓TAA所引起的肝脏纤维化.     

Characteristics of nitrogen metabolism in rats with thioacetamide-induced liver cirrhosis.

Female Sprague-Dawley rats were given 0.03% thioacetamide (TAA) in their drinking water daily for 4 or 12 weeks, and were then given normal water for 4 weeks after the end of a 12-week TAA treatment to investigate amino acid metabolism. In the malnourished precirrhotic stage (stage 1) and the malnourished cirrhotic stage (stage 2), the aromatic amino acids (AAA), Glu, Asp, Orn, Arg and Cit increased, and the branched-chain amino acids (BCAA) decreased slightly. Because these changes normalized in the well-nourished cirrhotic stage (stage 3), they might have resulted from impairment of hepatocytes and malnutrition. The net uptake of BCAA into the liver increased in stage 2, but the AAA uptake did not exceed that in normal controls. Portal venous plasma AAA increased to the same level as arterial plasma AAA. These results suggest that the decrease in BCAA was partially due to liver uptake and that the increase in AAA was induced by reduction of liver uptake and overproduction in extrahepatic tissues. The liver contents of BCAA and AAA were unchanged in all stages, so were fully utilized in the impaired liver. The increases in Glu, Asp, Orn and Cit might have resulted from overproduction in the liver, because these contents of the liver increased in stage 2. In conclusion, the changes in amino acid metabolism in rats with cirrhosis induced by TAA closely resemble those seen in human liver cirrhosis.     

Enhancement by estradiol 3-benzoate in thioacetamide-induced liver cirrhosis of rats.

As part of an investigation on the role of estrogen in liver disease, we tested the effects of estradiol-3-benzoate (EB) in the thioacetamide (TAA)-induced rat liver cirrhosis model. Male F344 rats (n = 100) were divided into six groups. Animals of groups 1-4 received TAA (0.03% in drinking water) for 12 weeks, and groups 5 and 6 served as controls without TAA. For the exposure period, EB pellets were implanted subcutaneously to give doses of 0 (groups 1 and 5), 1 (group 2), 10 (group 3), and 100 mug (groups 4 and 6) simultaneously. All animals were sacrificed at week 12. Significant increase of liver cirrhosis, liver weight, collagen content, and lipid peroxidation in the livers was evident in groups 3 and 4 (p < 0.05) compared with group 1. Formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) was significantly elevated in group 4 (p < 0.01), along with expression of alpha-smooth muscle actin (alpha-SMA) and stellate cell activation-associated protein (STAP), as determined by RT-PCR analysis (p < 0.01). However, there were no differences in liver weight, collagen content, lipid peroxidation, 8-OHdG formation, and alpha-SMA and STAP mRNA expression between groups 5 and 6. We conclude that EB treatment enhances TAA-induced cirrhosis, associated with increase of oxidative stress and activation of hepatic stellate cells.     

Hepatoprotective effects of reynosin against thioacetamide-induced apoptosis in primary hepatocytes and mouse liver

The aim of this study was to identify the hepatoprotective effects of reynosin, sesquiterpenes from the leaves of Laurus nobilis, against thioacetamide (TAA)-induced apoptosis in primary hepatocyte cultures and an in vivo mouse model. Rat hepatocytes were isolated and pretreated with 0.13, 0.64, or 3.22 μM reynosin and then exposed to 100 mM TAA. Reynosin treatment significantly inhibited TAA-induced apoptosis and hepatocellular DNA damage in primary rat hepatocytes. We observed an increase in levels of antiapoptotic Bcl-2, Bcl-XL mRNA and a decrease in levels of proapoptotic Bax mRNA following reynosin treatment of hepatocytes. Apoptosis in BALB/c mice was induced with intra-peritoneal injection of 200 mg/kg TAA for 2 weeks every other day. Then reynosin (5 mg/kg) and TAA were intragastrically given for 3 weeks every other day. Aspartate aminotransferase and alanine aminotransferase levels in the blood of mice were decreased in the reynosin administration group. Bcl-2 and Bcl-XL mRNA levels were increased, and the Bax mRNA level was decreased in reynosin-treated mice. Thus, reynosin inhibited TAA-induced apoptosis in primary hepatocytes and an in vivo mouse model.     

Taurine has a protective effect against thioacetamide-induced liver cirrhosis by decreasing oxidative stress

Thioacetamide (TAA) administration (0.3 g/l of tap water for a period of 3 months) to rats resulted in hepatic cirrhosis as assessed by biochemical and histopathological findings. This treatment caused an increase in the levels of malondialdehyde (MDA) and diene conjugates (DCs) and a decrease in the levels of glutathione (GSH), vitamin E, vitamin C and the activities of glutathione peroxidase (GSH-Px) in the liver of rats. Superoxide dismutase (SOD) activities were unchanged. Taurine (2% w/w, added to the chow diet) was administered together with TAA (0.3 g/l of drinking water) for 3 months. Taurine was found to decrease TAA-induced hepatic lipid peroxidation and to increase TAA-depleted vitamin E levels and GSH-Px activities. Histopathological findings also suggested that taurine has an inhibitive effect on TAA-induced hepatic cirrhosis. These results indicate that taurine treatment has a protective effect against TAA-induced liver cirrhosis by decreasing oxidative stress.     

Studies on liver toxicants

In acute oral studies, the effect of bromobenzene on hepatic microsomal enzymes was investigated. Neither glucuronyltransferases nor cytochrome c reductase showed significant changes. Most of the mixed-function oxidases studied were inhibited with the exception of ketamine-N-demethylase. The data indicate that bromobenzene or its epoxide acts on cytochrome P-450 but not on all cytochrome P-450 species, and does not affect the reductase and the glucuronyltransferases. Microsomal lipoperoxidation and microsomal H₂O₂ formation were increased.Dedicated to Prof. R. Sammet on occasion of his 60th birthday     

Studies on liver toxicants

In liver microsomes of rats 5 h after intraperitoneal administration of bromobenzene, the activities of a series of drug-metabolizing mixed-function oxidases, i. e., ketamine and aminopyrine N-demethylases, methylayapanine and methoxybiphenyl O-demethylases, and ethoxycoumarin O-deethylase, as well as glutathione and cytochrome b₅ contents were found to be decreased, whereas the activities of microsomal, NADPH-dependent cytochrome c and neotetrazolium reductases as well as cytochrome P-450 were unchanged.Dedicated to Professor Dr. med. Herbert Remmer on the occasion of his 65th Birthday     

Translocation of phosphatidate phosphohydrolase from the cytosol to microsomal membranes in thioacetamide-induced liver tumours in rats

The translocation of phosphatidate phosphohydrolase induced by oleate was higher (two-fold) in liver homogenates obtained from long-term thioacetamide-treated rats than from control rats. These differences between thioacetamide-treated and control livers were noticeably higher (four-fold) in the presence of physiological concentrations of salt (0.15 M KCl). In homogenates from control rats, there was a lack of response when physiological concentrations of the salt were present. The enhanced response to translocate phosphatidate phosphohydrolase activity in liver homogenates from thioacetamide-treated rats was due to an increased binding ability of microsomal membranes.     

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.     

An overview of thioacetamide-induced hepatotoxicity

Abstract

Thioacetamide (C₂H₅NS; TAA), an organosulfur compound is formally used in leather processing, laboratories, textile and paper industries. TAA is a model hepatotoxicant, consumed to induce acute and chronic liver injury due to its effects on protein synthesis, RNA, DNA and Gamma-glutamyl transpeptidase activity. TAA undergoes a two-step bioactivation to sulfine, and afterward to sulfene, a reactive metabolite. Sulfine is accountable for the enlargement of nucleoli, increase in nuclear volume and intracellular concentration of Ca⁺⁺, change in cell permeability, and inhibit mitochondrial activity. At the same time Sulfene is responsible for the release of nitric oxide synthase and NF-jB directing to centrilobular necrosis, protein denaturation and lipid peroxidation. Furthermore, it impairs the urea cycle and the activity of ornithine aminotransferase. Prolonged oral intake of this compound directs to macro liver nodules, liver cell adenomas, cholangiomas and hepatocarcinomas, histologically similar to that caused due to viral hepatitis infection.     

1,3-二苯-1,3-丙二酮对硫代乙酰胺致小鼠急性肝损伤的保护作用

目的:探讨1,3-二苯-1,3-丙二酮(DPPD)对硫代乙酰胺(TAA)致小鼠急性肝损伤的保护作用。方法:雄性ICR小鼠共40只,随机分为正常组、模型组和DPPD低、中、高剂量组,DPPD组分别灌胃给予DPPD 250,500和1 000 mg·kg-1·d-1,qd,给药4 d,正常组和模型组给予生理氯化钠溶液。d 4给予DPPD 0．5 h后,模型组和DPPD组腹腔注射TAA 80 mg·kg-1,正常组不染毒。所有动物均在染毒TAA 24 h后处死。分离血清,测定血清中丙氨酸转氨酶(ALT)、天冬氨酸转氨酶(AST)、乳酸脱氢酶(LDH)和碱性磷酸酶(ALP)的活性。留取部分肝组织用作常规病理切片检查;并取部分肝组织测定组织中还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)的含量。结果:与正常组比较,模型组小鼠血清ALT,AST,LDH和ALP活性均显著上升,GSH显著下降。与模型组比较,低、中、高剂量的DPPD组小鼠血清ALT,AST,LDH和ALP活性均显著降低,并呈剂量-依赖性,GSH显著上升。病理切片显示DPPD能够明显减轻TAA对肝组织的炎症性破坏。结论:DPPD对TAA引起的急性肝损害有一定的保护作用。     

Cytochrome P450 dysregulations in thioacetamide-induced liver cirrhosis in rats and the counteracting effects of hepatoprotective agents

Dysregulations of cytochromes P450 (P450s) under liver injury have been extensively studied. However, little is known about the possible reversing effects of hepatoprotective agents, the understanding of which is of great importance in guiding clinical dosage adjustment for patients with liver injury. This study aims to investigate the dysregulation patterns of major P450s in thioacetamide (TAA)-induced liver cirrhosis in rats and the potential counteracting effects of hepatoprotective agents schisandra lignans extract (SLE) and dimethyl diphenyl bicarboxylate (DDB). TAA intoxications for 6 weeks induced apparent liver injury and dramatically reduced the hepatic protein expressions of CYP1A2, CYP2C6, CYP2E1, and CYP3A2 to 18, 71, 30, and 21% of that in the normal control, respectively. Both SLE and DDB treatments could significantly reverse the TAA-induced loss of P450 protein levels, which may be ascribed to their hepatoprotective effects and direct P450-inducing effects that have been confirmed in healthy rats. However, the recovery of enzyme activities of most P450s by SLE and DDB treatment was less evident than that for the protein expression levels. TAA exhibited NADPH-, time-, and concentration-dependent inactivating effects on all of the four major P450 isozymes; both DDB and GSH showed little effects on counteracting such an inactivation efficacy. These findings provided a good explanation on the disproportional effects of hepatoprotective agents in recovering the protein levels and enzyme activities of TAA-induced dysregulated P450s.     

Testicular toxicity of DEHP, but not DEHA, is elevated under conditions of thioacetamide-induced liver damage

As part of an investigation of possible enhancement by liver disease of testicular toxicity caused by phthalates, we tested the effects of di(2-ethylhexyl)phthalate (DEHP) and di(2-ethylhexyl)adipate (DEHA) in a thioacetamide (TAA)-induced rat liver damage model. Male, 6-week-old, F344 rats (n=60) were divided into ten groups. Animals of groups 1-5 received TAA (200 mg/kg, intraperitoneal, three times per week) for 4 weeks, and groups 6-10 served as controls without TAA. After a 1 week interval, at week 5, powder diet containing DEHP or DEHA was provided to the animals of groups 1 and 6 (DEHP 25000 ppm), groups 2 and 7 (DEHP 6000 ppm), groups 3 and 8 (DEHA 25000 ppm) and groups 4 and 9 (DEHA 6000 ppm), while groups 5 and 10 received basal diet. All animals were sacrificed at week 9. Significant decrease in sperm numbers and motility and increase in morphology abnormalities were evident in group 1 as compared to groups 5 and 6 (p<0.01). However, DEHA treatment was not associated with any apparent testicular toxicity in either TAA- or vehicle-treated animals. Histopathological examination of the testes revealed severe atrophy and degeneration of testicular tubules in all animals given TAA and DEHP at high dose, only mild to moderate lesions being found with DEHP alone. We conclude that liver toxicity induced by TAA is associated with the enhancement of testicular toxicity of DEHP, but not DEHA, in rats.