Effect of different chemicals on thioacetamine-induced liver necrosis

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.

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.

Role of the microsomal FAD-containing monooxygenase in the liver toxicity of thioacetamide S-oxide

To evaluate the different contributions of either microsomal FAD-containing ( FADM ) or cytochrome P-450 dependent monooxygenases in the bioactivation and liver toxicity of thioacetamide-S-oxide ( TASO ) (a proximate metabolite of the liver toxin and carcinogen thioacetamide), this compound: (i) was given to rats pretreated with methimazole (a substrate and inhibitor of FADM ), SKF 525-A (an inhibitor of cytochrome P-450) and cobalt protoporphyrin IX (a synthetic porphyrin which induces a long-lasting depletion of the hepatic cytochrome P-450); and (ii) was added to liver microsomes performing oxidation of model FADM or cytochrome P-450 substrates. Whereas the prior administration of methimazole alleviated the TASO induced liver necrosis, SKF 525-A was almost ineffective. Also pretreatment with cobalt protoporphyrin IX prevented liver necrosis. However, this porphyrin derivative was found to depress both cytochrome P-450 dependent and the FADM dependent biotransformations. On the other hand, addition of TASO to liver microsomes in vitro induced changes in the kinetics of S-oxidation of thiobenzamide and of N-oxidation of dimethylaniline, whereas the O-deethylation of ethoxycoumarin was unchanged. The overall results show the necessity of TASO bioactivation by mixed-function monooxygenases for the toxic action to be apparent; at the same time, the findings suggest FADM as the system mainly involved in TASO metabolism.

Modulation of galactosamine-induced liver injury by some amino acids or Triton WR1339

Galactosamine administration to rats (600 mg/kg, i.p.) produces a severe liver necrosis at 24 h. Pretreatment with cystine, tryptophan or methionine (600 mg/kg, p.o., 30 min before the hepatotoxin) significantly prevents galactosamine-induced liver necrosis. Glutamic or aspartic acids, however, were not protective under a similar dosage regimen. The prior administration of Triton WR1339 (1 g/kg, i.v., 30 min before galactosamine) significantly enhanced the liver response to galactosamine-induced liver injury, whereas the administration of tyrosine resulted in death of the animals.

Prevention of thioacetamide-induced liver necrosis by prior aminoacetonitrile or imidazole administration

Prior administration of aminoacetonitrile (AAN) or imidazole but not isoxazole to rats, was able partially to prevent thioacetamide (TAC)-induced liver necrosis at 24 h. AAN and isoxazole did not prolong the pentobarbital sleeping time of the rats, while imidazole did. These and previous observations suggest a possible participation of non-cytochrome P-450 (P-450)-dependent aminoxidases in TAC activation to a necrogenic metabolite.