Glutathione, glutathione-dependent enzymes and antioxidant status in erythrocytes from children treated with high-dose paracetamol

Prenatal exposure to acetaminophen and asthma in children

OBJECTIVE

To estimate whether prenatal exposure to acetaminophen is associated with risk of diagnosed asthma and asthma symptoms in children.

METHODS

The authors prospectively followed 1,505 pregnant women and their children until 6 years (+/-3 months) of life. Acetaminophen use in the first and third trimesters of pregnancy was assessed before 24 weeks of gestation and within 1 month of delivery, and asthma in children was assessed when the child was 6 years old. Adjusted odds ratios (aORs) were derived from logistic regression models controlling for potential confounders.

RESULTS

Acetaminophen was used by 69% of women during pregnancy. Use of acetaminophen did not significantly increase the risk of asthma (aOR 0.76, 95% confidence interval [CI] 0.53-1.10). Acetaminophen use during both the first and the third trimester was associated with a significantly reduced risk of asthma (aOR 0.59, 95% CI 0.36-0.98). There was no evidence of a dose response, and consumption greater than 10,400 mg (32 tablets) a month did not increase risk (aOR 0.99, 95% CI 0.19-5.30).

CONCLUSION

Our results suggest that acetaminophen use during pregnancy does not increase risk of asthma in children.

LEVEL OF EVIDENCE

II.

Prenatal exposure to acetaminophen and respiratory symptoms in the first year of life

BACKGROUND

Prevalence of asthma in developed countries increased between the 1970s and the 1990s. One factor that might contribute to the trends in asthma is the increased use of acetaminophen vs aspirin in children and pregnant women.

OBJECTIVE

To examine relationships between in utero exposure to acetaminophen and incidence of respiratory symptoms in the first year of life.

METHODS

A total of 345 women were recruited in the first trimester of pregnancy and followed up with their children through the first year of life. Use of acetaminophen in pregnancy was determined by questionnaire and related to incidence of respiratory symptoms.

RESULTS

Use of acetaminophen in middle to late but not early pregnancy was significantly related to wheezing (odd ratio, 1.8; 95% confidence interval, 1.1-3.0) and to wheezing that disturbed sleep (odds ratio, 2.1; 95% confidence interval, 1.1-3.8) in the first year of life after control for potential confounders.

CONCLUSION

This study suggests that use of acetaminophen in middle to late but not early pregnancy may be related to respiratory symptoms in the first year of life. Additional follow-up will examine relationships of maternal and early childhood use of acetaminophen with incidence of asthma at ages 3 to 5 years, when asthma diagnosis is more firmly established.

Kinetics of uptake and deacetylation of N-acetylcysteine by human erythrocytes

Overproduction of reactive oxygen species associated with several diseases including sickle cell anaemia reduces the concentration of glutathione, a principal cellular antioxidant. Glutathione depletion in sickle erythrocytes increases their conversion to irreversible sickle cells that promote vaso-occlusion. Therapeutically, N-acetylcysteine partially restores glutathione concentrations but its mode of action is controversial. Following glutathione depletion, glutathione synthesis is limited by the supply of cysteine and it has been assumed that deacetylation of N-acetylcysteine within erythrocytes provides cysteine to accelerate glutathione production. To determine whether this is the case we studied the kinetics of transport and deacetylation of N-acetylcysteine. Uptake of N-acetylcysteine had a first order rate constant of 2.40+/-0.070min(-1) and only saturated above 10mM. Inhibition experiments showed that 56% of N-acetylcysteine transport was via the anion exchange protein. Deacetylation, measured using (1)H NMR, had a K(m) of 1.49+/-0.16mM and V(max) of 2.61+/-0.08micromolL(-1)min(-1). Oral doses of N-acetylcysteine increase glutathione concentrations in sickle erythrocytes at plasma N-acetylcysteine concentrations of approximately 10microM. At this concentration, calculated rates of N-acetylcysteine uptake and deacetylation were approximately 5% of the rate required to maintain normal glutathione production. We concluded that on oral administration, intracellular deacetylation of N-acetylcysteine supplies little of the cysteine required for accelerated glutathione production. Instead, N-acetylcysteine acts by freeing bound cysteine in the plasma that then enters the erythrocytes. To be effective, intracellular cysteine precursors must be designed to enter erythrocytes rapidly and employ enzymes with high activity within erythrocytes to liberate the cysteine.

Mice deficient in Cu,Zn-superoxide dismutase are resistant to acetaminophen toxicity

Although antioxidants are used to treat an overdose of the analgaesic/antipyretic drug APAP (acetaminophen), roles of antioxidant enzymes in APAP-induced hepatotoxicity remain controversial. Our objective was to determine impacts of knockout of SOD1 (superoxide dismutase; Cu,Zn-SOD) alone or in combination with selenium-dependent GPX1 (glutathione peroxidase-1) on APAP-induced hepatotoxicity. All SOD1-null (SOD1-/-) and SOD1- and GPX1-double-knockout mice survived an intraperitoneal injection of 600 mg of APAP per kg of body mass, whereas 75% of WT (wild-type) and GPX1-null mice died within 20 h. Survival time of SOD1-/- mice injected with 1200 mg of APAP per kg of body mass was longer than that of the WT mice (934 compared with 315 min, P<0.05). The APAP-treated SOD1-/- mice had less (P<0.05) plasma ALT (alanine aminotransferase) activity increase and attenuated (P<0.05) hepatic glutathione depletion than the WT mice. The protection conferred by SOD1 deletion was associated with a block of the APAP-mediated hepatic protein nitration and a 50% reduction (P<0.05) in activity of a key APAP metabolism enzyme CYP2E1 (cytochrome P450 2E1) in liver. The SOD1 deletion also caused moderate shifts in the APAP metabolism profiles. In conclusion, deletion of SOD1 alone or in combination with GPX1 greatly enhanced mouse resistance to APAP overdose. Our results suggest a possible pro-oxidant role for the physiological level of SOD1 activity in APAP-mediated hepatotoxicity.

Repeated supratherapeutic doses of paracetamol in children--a literature review and suggested clinical approach

The safety of paracetamol when given in the recommended dosage is well documented. However, in recent years there have been many reports of liver failure associated with repeated exposure to supratherapeutic doses of paracetamol. This paper reviews the literature on chronic supratherapeutic paracetamol exposure in children and the different dosing guidelines. Based on which, we suggest the following approach: liver injury secondary to repeated dosing of paracetamol should be considered when a child has received more than 75 mg/kg/d for at least 2 d, or if risk factors for paracetamol toxicity have been identified. Liver transaminases, coagulation factors, and paracetamol serum concentrations should be measured in these children and in symptomatic children with vomiting, right upper quadrant abdominal pain, and jaundice who have taken paracetamol. Treatment with N-acetyl cysteine should be started regardless of paracetamol concentrations if transaminases or INR are elevated.

CONCLUSION

Liver injury secondary to repeated dosing of paracetamol is rare but may result in severe morbidity and mortality. The cumulative dose of paracetamol should not exceed 75 mg/kg/d. Children treated with higher doses for more than 2 d should be evaluated for possible liver injury and treated with N-acetyl cysteine if evidence of liver injury is found.

Anti-oxidant enzyme activities and expression and oxidative damage in patients with non-immediate reactions to drugs

Adverse drug reactions with an immunological basis (ADRIB) may involve activation of other concomitant, non-specific mechanisms, amplifying the specific response and contributing to the severity and duration. One concomitant mechanism could be the generation of reactive oxygen species (ROS) and/or their detoxification by anti-oxidants, including anti-oxidant enzymes. We analysed the activity of the anti-oxidant enzymes Cu/Zn-superoxide dismutase (SOD), catalase (CAT) and cellular glutathione peroxidase (GPX), as well as certain markers of oxidative damage (thiobarbituric acid reactive substances (TBARS) and carbonyl content) in peripheral blood mononuclear cells from patients with non-immediate ADRIB using spectrophotometric methods and the anti-oxidant enzymes expression by quantitative real-time reverse transcription-polymerase chain reaction. SOD activity and expression were increased in all types of non-immediate reactions (urticaria, maculopapular exanthema and toxic epidermal necrolysis). Regarding oxidative damage, TBARS were increased in urticaria and maculopapular exanthema, and carbonyl groups in all types of reactions. Our observations indicate that oxidative damage occurs in non-immediate reactions. Carbonyl stress and the inadequacy of the anti-oxidant defences are probable causes.

[Synthesis of two new acetanilide derivatives and their effect on the serum antioxidant vitamins (A, E, and C) and the MDA level in rats]

Acetanilide derivatives, 2,2'-thiobis[N-(4-nitrophenyl)acetamide] and 2,2'-thiobis[N-(4-chlorophenyl)acetamide], were synthesized and characterized. They were shown to cause a considerable oxidative stress in rats.

How much acetaminophen do paediatricians prescribe? A survey among Israeli paediatricians

OBJECTIVE

To describe the current practice of Israeli paediatricians regarding acetaminophen dosing.

METHODS

A cross-sectional survey among 200 paediatricians. The paediatricians were questioned of the recommended dose of acetaminophen, and whether they give prescriptions for acetaminophen and instruct their patients how to use it.

RESULTS

The response rate was 36%. When asked on the recommended dose of acetaminophen, 30 (42%) physicians gave doses different from the dose recommended by the Israeli formulary. Thirty (42%) of the paediatricians answered that they usually or always give prescriptions for antipyretics.

CONCLUSIONS

A large percentage of Israeli paediatricians do not provide parents proper instructions regarding the correct dosing of acetaminophen.

Glutathione depletion and anaesthesia in mice alter heme and drug metabolising enzymes

The effects of enflurane and isoflurane on heme metabolism, its regulation, and on some parameters involved in the hepatic drug metabolising system in animals under GSH depletion were investigated. A single dose of the anaesthethics (1 ml kg(-1), i.p.) was administered to control and GSH depleted mice, animals were sacrificed 20 min after. As a consequence of GSH depletion, a significant inhibition in delta-Aminolevulinic acid synthetase activity, the first enzyme of heme biosynthesis, and a striking induction in Heme oxygenase activity, the main enzyme of heme metabolism, were observed. Cytochrome P-450 levels and the activities of P-4502E1 and glutathione S-transferase were increased. These changes in heme metabolism and drug metabolising enzyme system were not altered further by the administration of enflurane or isoflurane. These findings would indicate that the status of oxidative stress produced by GSH depletion could not be affected by these anaesthetics and/or that disturbances in heme metabolism were already too important to undergo further variations.

Drug-induced liver disease in 2003

Drug-induced liver disease remains an important topic of concern for all prescribers as well as drug manufacturers. The withdrawal of troglitazone (Rezulin) and bromfenac (Duract) a few years ago remains fresh in the minds of regulatory authorities as well as clinicians and researchers who are focusing renewed attention on ways to better understand mechanisms of injury to predict and avert serious drug-induced liver disease in the future from drugs under development as well as existing agents known to cause liver injury. As in past years, this review describes new and first-time reports of various aspects of drug-induced liver disease for several classes of compounds, including herbal products (such as kava kava), reviews the risk factors seen with antiretroviral and antituberculosis agents among others. It provides a sampling of experimental hepatoprotection studies that may hold the key to treatment and prevention of drug-induced liver disease in the future and discusses the ongoing approaches to be taken to restrict the availability of acetaminophen that have proved successful in reducing the number of overdoses, deaths, and liver transplantations from this drug in the United Kingdom. Given the fact that acetaminophen is the single most important cause of acute liver failure here and abroad, such efforts to limit its use seem appropriate for other nations as well.