Influence of 2-dimethylaminoethanol on the hepatotoxicity of paracetamol in rats and mice (author's transl)

2-Dimethylaminoethanol (DMAE; 0.1--0.5 g/kg) significantly reduced the paracetamol-induced increments of serum-enzyme activities (GOT, GPT, SDH) in rats and mice. This hepatoprotective effect of DMAE depended on the applied dose in rats, but there was no complete protection following the highest dose. Paracetamol-induced depletion of hepatic glutathione (GSH) was not influenced by the simultaneous administration of DMAE in rats and mice. Metabolic disposition of paracetamol in the urine of rats showed an enhanced elimination of free paracetamol and the glucuronide in the DMAE-treated group, whereas the mercapturate excretion remained unchanged. Diminished p-hydroxylation of aniline in a 9000Xg supernatant of rat and mouse liver homogenates in the presence of DMAE indicated an inhibition of microsomal mixed-function oxidase activity, which is also involved in the metabolic activation of paracetamol.     

Influence of dithiocarb, (+)-catechin and silybine on halothane hepatotoxicity in the hypoxic rat model

In phenobarbital (phenemalum NFN)-pretreated male rats exposed to 1% halothane for 2 hrs under hypoxic conditions (10% O2), significant increases in serum enzyme activities of alanine aminotransferase and sorbitol dehydrogenase were observed 24 and 48 hrs later indicating liver damage. In this known model of halothane hepatotoxicity, pretreatment with (+)-catechin (200 mg/kg orally) or silybine (150 mg/kg orally) protected against halothane-induced liver injury, whereas diethyldithiocarbamate (200 mg/kg orally) failed to be effective. Halothane decreased the concentration of reduced glutathione in liver only under hypoxic conditions indicating that glutathione might be involved in the non-oxidative metabolic pathways of halothane. Free fluoride in plasma was used as a measure of non-oxidative defluorination of halothane. Higher plasma fluoride levels were observed under conditions which led to hepatotoxicity but did not correlate with the protective effects of the antidotes. This further supports the assumption that 2-chloro-1,1,1-trifluoroethane might be the radical intermediate responsible for halothane hepatotoxicity.     

Relations between hepatotoxicity and pharmacokinetics of paracetamol in rats and mice

A dose-dependent increase of paracetamol serum half-life (t1/2) was found after oral and intravenous application in rats and oral application in mice. The hepatotoxic effects of paracetamol were not correlated with this prolongation of t1/2. Dithiocarb protected rats against paracetamol liver damage but did not change paracetamol t1/2. Paracetamol t1/2 was not influenced either by a hepatotoxic dose of carbon tetrachloride. In conclusion, the dose-dependent prolongation of paracetamol serum half-life is not due to paracetamol-induced liver damage but merely the consequence of saturated elimination processes.     

Inhibition of halothane-induced lipid peroxidation by misoprostol without hepatoprotection

In mice, the synthetic prostaglandin derivative misoprostol failed to protect against liver damage induced by acetaminophen, carbon terachloride,1,1-dichloroethylene or thioacetamide. In rats, misoprostol (20-100 micrograms/kg p.o.) markedly reduced early increments of plasma enzyme activities (glutamate-pyruvate-transaminase, GPT; sorbitol dehydrogenase, SDH) in a model of halothane-induced liver injury; the most effective dose in this respect (20 micrograms/kg) significantly depressed halothane-induced ethane exhalation indicating in vivo lipid peroxidation. Repeated treatment with misoprostol (20 micrograms/kg p.o.) still diminished halothane-induced elevations of enzyme activities over 48 h, but failed to prove hepatoprotection by histomorphological examinations. It is concluded that the antiperoxidative properties of misoprostol are not paralleled by an hepatoprotection, which was indicated by significant reductions of liver-specific plasma enzyme activities, but not confirmed by the morphological picture.     

Comparative study of the absorption,elimination and acute hepatotoxic action of ethanol in guinea pigs and rats

In fed guinea pigs, an oral dose of 6.4 g/kg of ethanol given as a 40% solution (v/v) produced a maximal blood alcohol level of 6.8±0.3 mg/ml, whereas in fed rats, blood alcohol levels after the same dose did not exceed 2.1±0.2 mg/ml. Maximal blood alcohol levels in fasted animals after an oral load of 4.8 g/kg of ethanol were 6.3±0.2 mg/ml in guinea pigs and 3.7±0.3 mg/ml for rats. However, i.v. injected ethanol (1 g/kg) was eliminated at the same rate in both species (275 mg per kg · h), and ADH activity of the liver related to body weight was by 20% greater in guinea pigs than in rats.Therefore, absorption of ethanol occurs at a much slower rate in rats than in guinea pigs. This is possibly due to the fact that high ethanol concentrations strongly delay emptying of the rat stomach. Lowering the ethanol concentration accelerates absorption rate in the rat. However, even after gavage of a 10% solution peak levels of blood alcohol were still lower by 36% in rats than in guinea pigs.In guinea pigs, increased serum activities of GOT, GPT, and GLDH occurred after an oral dose of 4.8 g/kg or 6.4 g/kg of ethanol, respectively. SGOT already increased after 1.6 g/kg of ethanol p.o. After 6.4 g/kg of ethanol given to rats serum transaminase levels increased only slightly, and GLDH activity not at all. Vacuolar degeneration was the morphological substrate of ethanol-induced liver damage in guinea pigs and rats. In guinea-pigs, it occurred already after 1.6 g/kg of ethanol, whereas in rats only after 6.4 g/kg.In conclusion, the guinea pig seems to be better suited for research on alcohol toxicity than the rat.     

The role of iron in the NADPH-dependent lipid peroxidation due to glutathione depletion by phorone

Enhanced NADPH-dependent LPO in rat liver postmitochondrial supernatants in vitro due to depletion of GSH by treatment with phorone (diisopropylidene acetone) in vivo was inhibited by Fe2+-chelating agents (desferrioxamine, DETAPAC), but not by scavengers of .O2-, H2O2, singlet oxygen or .OH-radicals, indicating that a perferryl ion (Fe2+ . O2) is needed as an initiating factor. In vivo, rats treated with phorone (250 mg/kg i.p.) exhaled 1.4 times as much ethane within 4 h as compared to controls. Pretreatment with FeSO4 resulted in a 6.9-fold enhancement of LPO as compared to Fe2+-pretreated controls. Our results indicate that GSH-depletion results in a strong enhancement of NADPH-dependent LPO also in vivo, provided that an initiating factor is present.     

Inhibitory Action of some Flavonoids on Enhanced Spontaneous Lipid Peroxidation Following Glutathione Depletion.

Depletion of hepatic glutathione in phenobarbital-induced rats by phorone (diisopropylidene acetone) led to an enhancement of spontaneous lipid peroxidation IN VITRO. Addition of exogenous glutathione, dithiocarb or one of the flavonoids (+)-catechin, (-)-epicatechin, 3-O-methylcatechin, quercetin, taxifolin, rutin, naringin or naringenin led in every case to a dose-dependent inhibition of this peroxidative activity. The concentration values yielding 50% inhibition (I (50)) varied from 1.0 x 10 (-6) M for glutathione to 1.9 x 10 (-5) M for naringenin. Naringin and naringenin, which lack the 3'-OH-group, were the least active inhibitors. The only structural feature of the flavonoids which affects their antioxidative action appears thus to be the 3',4'-dihydroxy-grouping.     

The influence of fasting on the susceptibility of mice to hepatotoxic injury

The hepatotoxic effects of eight compounds as determined by serum activities of glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), and sorbitol dehydrogenase (SDH) were investigated in normally fed mice on the one hand and 24-hr-fasted mice on the other. Fasting strongly enhanced serum-enzyme elevations induced by carbon tetrachloride, paracetamol, thioacetamide, and bromobenzene. The hepatotoxic effects of phalloidin and allyl alcohol were only moderately increased by fasting and those of α-amanitin and praseodymium not at all. The fasting-induced aggravation of CCl₄ hepatotoxicity (evidenced also by histological findings) appeared already after 12 hr and was maximal after 24 hr of food deprivation. Fasting for 24 hr decreased the liver weight by 29%, hepatic glycogen by 93%, and hepatic glutathione (GSH) by 50% but increased liver triglycerides by 162%. Aniline hydroxylase and aminopyrine N-demethylase activities were higher in the liver homogenate supernatants from fasted than from fed mice but microsomal protein content as well as microsomal NADPH-cytochrome c-reductase activity remained unchanged and microsomal cytochrome P-450 content even decreased upon fasting. Fasting did not influence the in vitro irreversible binding of ¹⁴CCl₄ and [³H]paracetamol to hepatic microsomal proteins nor the in vivo binding to hepatic proteins of [³H]paracetamol. It enhanced, however, the total concentration of ¹⁴CCl₄ in the liver by 30% and produced a trend toward higher values in the extent of ¹⁴CCl₄ bound in vivo to hepatic protein. Spontaneous and CCl₄-induced lipid peroxidation were the same in hepatic microsomes from fed and fasted mice. No unique explanation can be made for the increased susceptibility of mouse liver to toxic injury induced by fasting. Several factors must be considered: depletion of both hepatic glycogen and glutathione as well as hepatic lipid accumulation. Overnight fasting of mice (and of other small animals presumably too) may change the results of toxicological experiments to an unpredictable degree and should thus be avoided.