The influence of thyroid hormones and propylthioracil on salicylate hepatotoxicity in monolayer cell cultures

Effect of n-propylthiouracil or thyroxine on arsenic trioxide toxicity in the liver of rat

Involvement of thyroid gland in the hepatotoxic manifestations of arsenic trioxide (As(III)) has been studied in rat. The effects of n-propylthiouracil (PTU) (a thyrotoxic compound) and L-thyroxine (a thyroid hormone) have been studied with reference to T(3) and T(4) values in the serum, arsenic concentration in the liver, Ca(2+) accumulation in the liver, aspartate transaminase, alanine transaminase and bilirubin values as the indicators of liver function, histopathological observations and finally the ultrastructural studies. It is concluded that hypothyroid condition protects against As(III) toxicity. Scavenging of reactive oxygen species (ROS) that significantly contribute in As(III) toxicity, by high intracellular concentration of reduced glutathione, as a consequence of PTU treatment is proposed as the plausible protective mechanism.

Acute effects of propylthiouracil on hemodynamics and oxygen content in patients with alcoholic cirrhosis

BACKGROUND/AIMS

The antithyroid drug propylthiouracil has been suggested for the treatment of alcoholic liver disease. Its beneficial effects could be due to either a decrease in hepatic oxygen consumption or an increase in hepatic blood flow. The aim of this study was to test these two hypotheses in patients with proven alcoholic cirrhosis.

METHODS

The pharmacokinetic parameters after intravenous administration of 300 mg of propylthiouracyl were first determined in four patients. Then, the effects on systemic and splanchnic hemodynamics, and oxygen content were measured 45 and 90 min after the intravenous administration of 300 mg (n=6) or 600 mg (n=6) of propylthiouracil.

RESULTS

Systemic hemodynamics (heart rate, arterial pressure, cardiac output and systemic vascular resistance) and splanchnic hemodynamics (hepatic venous pressure gradient, hepatic and azygos blood flows) were not modified 45 and 90 min after the administration of 300 mg or 600 mg of propylthiouracil. Moreover, neither oxygen content in the radial artery, pulmonary artery or hepatic vein, nor systemic oxygen uptake was modified after propylthiouracyl administration. The absence of effect of propylthiouracyl administration was also confirmed in patients with cirrhosis with proven acute alcoholic hepatitis (n=7).

CONCLUSIONS

In patients with alcoholic cirrhosis, acute administration of propylthiouracyl has no effect on systemic and splanchnic hemodynamics or on oxygen contents. The presence of acute alcoholic hepatitis does not modify these results.

Long-term treatment of alcoholic liver disease with propylthiouracil

Propylthiouracil has been shown experimentally to protect against alcohol-induced hepatocellular necrosis in hypoxic conditions. An earlier, short-term study of patients with alcoholism and liver disease indicated clinical improvement with propylthiouracil, but the effect on mortality could not be assessed. In the present study, we investigated the effect of propylthiouracil on mortality in patients with alcoholic liver disease in a long-term, double-blind, randomized clinical trial involving 310 compliant patients who received propylthiouracil (n = 157) or placebo (n = 153) for a maximum of two years. There were no differences between the two groups in demographic and clinical characteristics and biopsy-confirmed diagnoses at randomization, or in daily urinary alcohol levels during the study. The cumulative dropout rate over two years was not significantly different (propylthiouracil group, 0.68; placebo group, 0.60). The group receiving propylthiouracil (300 mg per day) had a cumulative mortality rate half that in the group receiving placebo (0.13 vs. 0.25 [P less than 0.05] in the total sample, and 0.25 vs. 0.55 [P less than 0.03] in a subgroup of severely ill patients [propylthiouracil group, n = 56; placebo group, n = 41]). Proportional-hazards stepwise regression analyses indicated that only propylthiouracil treatment, prothrombin time, hemoglobin levels, and mean daily urinary alcohol levels significantly affected mortality. The hazards ratio for the complete group indicated that mortality in the propylthiouracil group was 0.38 (95 percent confidence interval, 0.20 to 0.83) that of the placebo group. Protection by propylthiouracil was not observed in patients with high morning urinary alcohol levels. No clinically important side effects of propylthiouracil were observed at the dose used. We conclude that the administration of propylthiouracil can reduce mortality due to alcoholic liver disease.

Effects of propylthiouracil on D-galactosamine hepatotoxicity in the rat. Evidence for a non-thyroidal effect

The cytoprotective effects of propylthiouracil (PTU) were studied in rats treated with the hepatotoxin D-galactosamine (D-GNH2). Five days of PTU pretreatment prior to D-GNH2 caused hypothyroidism and a significant reduction in liver injury as assessed by serum transaminase levels. When PTU was administered as a single dose with D-GNH2, significant decreases in transaminase also occurred at times when thyroid function was unchanged. Furthermore, aminopyrine oxidation showed significant impairment after D-GNH2 and was normalized by one dose of PTU. Further studies were carried out in thyroidectomized rats. PTU caused significant reductions in transaminase levels when given for 5 days pretreatment or as a single dose. Animals receiving pretreatment with PTU plus thyroxine (T4) also had significant decreases in serum transaminase. The antithyroid drug methimazole also had a hepatoprotective effect, while two other potent antithyroid compounds (2-thiouracil and 2-thiobarbituric acid) did not. These data suggest that PTU can protect against liver injury induced by D-GNH2, that the effect is independent of thyroid function, and that this effect is not common to all thiol-containing antithyroid drugs.