Treatment of paracetamol (acetaminophen) poisoning with N-acetylcysteine

Antioxidants suppress lymphoma and increase longevity in Atm-deficient mice

Ataxia telangiectasia (AT), a human hereditary disorder resulting from mutations in the ATM gene, is characterized by a high incidence of lymphoid malignancies, neurodegeneration, immunodeficiency, premature aging, elevated radiosensitivity, and genomic instability. Evidence has been accumulating that ATM-deficient cells are in a continuous state of oxidative stress. A variety of markers of oxidative stress were detected in AT patients as well as Atm-deficient mice, used as an animal model of AT. Since then, it has been proposed that oxidative stress contributes to the clinical phenotype of AT, especially carcinogenesis and neurodegeneration, and several animal studies were conducted to determine whether exogenous antioxidants mitigate the symptoms of AT. Tempol, EUK-189, and N-acetyl cysteine have been tested as chemopreventive antioxidants in Atm-deficient mice. We review these findings, mainly focusing on the effect of N-acetyl cysteine, which is known as a safe and efficient drug and nutritional supplement.

Simulation of the detoxification of paracetamol using on-line electrochemistry/liquid chromatography/mass spectrometry

On-line electrochemistry/liquid chromatography/mass spectrometry was used to simulate the detoxification mechanism of paracetamol in the body. In an electrochemical flow-through cell, paracetamol was oxidized at a porous glassy carbon working electrode at a potential of 600 mV vs. Pd/H2 with formation of a quinoneimine intermediate. The quinoneimine further reacted with glutathione and/or N-acetylcysteine to form isomeric adducts via the thiol function. The adducts were characterized on-line by liquid chromatography/mass spectrometry. These reactions are similar to those occurring between paracetamol and glutathione under catalysis by cytochrome P450 enzymes in the body.

Antioxidant N-acetyl cysteine reduces incidence and multiplicity of lymphoma in Atm deficient mice

Hereditary human disorder ataxia telangiectasia (AT) is characterized by an extremely high incidence of lymphoid malignancies, neuromotor dysfunction, immunodeficiency and radiosensitivity. Cells from AT patients show genetic instability and a continuous state of oxidative stress. We examined the effect of long-term dietary supplementation with the thiol-containing antioxidant, N-acetyl-L-cysteine (NAC), on survival and cancer formation in Atm (AT-mutated) deficient mice, used as an animal model of AT. NAC was chosen because it is well-tolerated in animals and humans. It can be used by the oral route and for long-term at high concentrations. In addition, NAC suppresses carcinogenesis-associated biological markers in Atm deficient mice, such as DNA deletions and oxidative DNA damage (R. Reliene, E. Fischer, R.H. Schiestl, Effect of N-acetyl cysteine on oxidative DNA damage and the frequency of DNA deletions in atm-deficient mice, Cancer Res. 64 (2004) 5148-5153). In this study, NAC significantly increased the lifespan and reduced both the incidence and multiplicity of lymphoma in Atm deficient mice. The life span increased from 50 to 68 weeks and the incidence of lymphoma decreased by two-fold (76.5% versus 37.5%). Moreover, in mice with lymphoma, multiplicity of tumors decreased from 4.6 to 2.8 tumors per mouse. Thus, dietary supplementation with NAC may turn out to be protective against lymphomagenesis in AT patients.

Acetaminophen poisoning: an evidence-based consensus guideline for out-of-hospital management

The objective of this guideline is to assist poison center personnel in the appropriate out-of-hospital triage and initial management of patients with suspected ingestions of acetaminophen. An evidence-based expert consensus process was used to create this guideline. This guideline applies to ingestion of acetaminophen alone and is based on an assessment of current scientific and clinical information. The expert consensus panel recognizes that specific patient care decisions may be at variance with this guideline and are the prerogative of the patient and the health professionals providing care. The panel's recommendations follow. These recommendations are provided in chronological order of likely clinical use. The grade of recommendation is provided in parentheses. 1) The initial history obtained by the specialist in poison information should include the patient's age and intent (Grade B), the specific formulation and dose of acetaminophen, the ingestion pattern (single or multiple), duration of ingestion (Grade B), and concomitant medications that might have been ingested (Grade D). 2) Any patient with stated or suspected self-harm or who is the recipient of a potentially malicious administration of acetaminophen should be referred to an emergency department immediately regardless of the amount ingested. This referral should be guided by local poison center procedures (Grade D). 3) Activated charcoal can be considered if local poison center policies support its prehospital use, a toxic dose of acetaminophen has been taken, and fewer than 2 hours have elapsed since the ingestion (Grade A). Gastrointestinal decontamination could be particularly important if acetylcysteine cannot be administered within 8 hours of ingestion. Acute, single, unintentional ingestion of acetaminophen: 1) Any patient with signs consistent with acetaminophen poisoning (e.g., repeated vomiting, abdominal tenderness in the right upper quadrant or mental status changes) should be referred to an emergency department for evaluation (Grade D). 2) Patients less than 6 years of age should be referred to an emergency department if the estimated acute ingestion amount is unknown or is 200 mg/kg or more. Patients can be observed at home if the dose ingested is less than 200 mg/kg (Grade B). 3) Patients 6 years of age or older should be referred to an emergency department if they have ingested at least 10 g or 200 mg/kg (whichever is lower) or when the amount ingested is unknown (Grade D). 4) Patients referred to an emergency department should arrive in time to have a stat serum acetaminophen concentration determined at 4 hours after ingestion or as soon as possible thereafter. If the time of ingestion is unknown, the patient should be referred to an emergency department immediately (Grade D). 5) If the initial contact with the poison center occurs more than 36 hours after the ingestion and the patient is well, the patient does not require further evaluation for acetaminophen toxicity (Grade D). Repeated supratherapeutic ingestion of acetaminophen (RSTI): 1) Patients under 6 years of age should be referred to an emergency department immediately if they have ingested: a) 200 mg/kg or more over a single 24-hour period, or b) 150 mg/kg or more per 24-hour period for the preceding 48 hours, or c) 100 mg/kg or more per 24-hour period for the preceding 72 hours or longer (Grade C). 2) Patients 6 years of age or older should be referred to an emergency department if they have ingested: a) at least 10 g or 200 mg/kg (whichever is less) over a single 24-hour period, or b) at least 6 g or 150 mg/kg (whichever is less) per 24-hour period for the preceding 48 hours or longer. In patients with conditions purported to increase susceptibility to acetaminophen toxicity (alcoholism, isoniazid use, prolonged fasting), the dose of acetaminophen considered as RSTI should be greater than 4 g or 100 mg/kg (whichever is less) per day (Grade D). 3) Gastrointestinal decontamination is not needed (Grade D). Other recommendations: 1) The out-of-hospital management of extended-release acetaminophen or multi-drug combination products containing acetaminophen is the same as an ingestion of acetaminophen alone (Grade D). However, the effects of other drugs might require referral to an emergency department in accordance with the poison center's normal triage criteria. 2) The use of cimetidine as an antidote is not recommended (Grade A).

Successful treatment of doxorubicin and cisplatin resistant hepatoblastoma in a child with Beckwith-Wiedemann syndrome with high dose acetaminophen and N-acetylcysteine rescue

High dose acetaminophen (HDAC) with N-acetylcysteine (NAC) has been effective in adults with advanced malignancies. We report HDAC with NAC in a child with progressive hepatoblastoma, confirmed at biopsy of an unresectable hepatic mass. Alpha-fetoprotein (AFP) increased despite four courses of doxorubicin and one course of cisplatin, 5-flurouracil, and vincristine. Following HDAC with NAC, AFP markedly decreased. A continued response without toxicity was observed during four subsequent courses of HDAC with NAC and cisplatin. The residual necrotic tumor was resected. The child is now over 8 years disease free. HDAC and NAC are effective and well tolerated for progressive hepatoblastoma.

Acute poisoning: understanding 90% of cases in a nutshell

The acutely poisoned patient remains a common problem facing doctors working in acute medicine in the United Kingdom and worldwide. This review examines the initial management of the acutely poisoned patient. Aspects of general management are reviewed including immediate interventions, investigations, gastrointestinal decontamination techniques, use of antidotes, methods to increase poison elimination, and psychological assessment. More common and serious poisonings caused by paracetamol, salicylates, opioids, tricyclic antidepressants, selective serotonin reuptake inhibitors, benzodiazepines, non-steroidal anti-inflammatory drugs, and cocaine are discussed in detail. Specific aspects of common paediatric poisonings are reviewed.

An update of N-acetylcysteine treatment for acute acetaminophen toxicity in children

PURPOSE OF REVIEW

Acetaminophen poisoning accounts for a disproportionate percentage of all toxic ingestions, and can be life-threatening. This article reviews the mechanism and presentation of acetaminophen toxicity, as well as its treatment, including current thinking and treatment recommendations.

RECENT FINDINGS

N-acetylcysteine acts to detoxify acetaminophen in several ways, but primarily by increasing the synthesis and availability of glutathione, which binds and inactivates the highly reactive and hepatotoxic acetaminophen metabolite N-acetyl-p-benzoquinoneimine. The US Food and Drug Administration has approved an intravenous formulation of N-acetylcysteine, thus allowing the treatment time to be decreased from the 72 hr most commonly used for the oral regimen, to only 20 hr. This comes after many years of accepted intravenous N-acetylcysteine use in Europe and Canada, and much controversy as to the superiority of both treatments. This review summarizes this controversy, and offers a framework to develop a safe treatment plan that has the optimal outcome for the patient, as well as reflecting knowledge of the potential caveats at work. It describes side effects of N-acetylcysteine treatment, as well as relative indications to choose one route of treatment over the other.

SUMMARY

Acetaminophen can lead to irreversible liver damage and even death in acute overdose. Outcome is related to the swiftness in which the antidote (N-acetylcysteine) is provided. In the United States, there are now available both the oral and intravenous forms of N-acetylcysteine, and pros and cons exist for each. With brisk and adequate treatment using either route, recovery can be complete, and liver function can be restored.

A Clinical and Pharmacoeconomic Justification for Intravenous Acetylcysteine

Paracetamol (acetaminophen) poisoning remains the most common exposure reported to US poison information centres and the leading cause of poisoning-related fatalities, despite the availability of an effective antidote, acetylcysteine. Oral acetylcysteine solution has been approved for the management of acetaminophen poisoning in the US for four decades. Until the recent approval of intravenous acetylcysteine in the US, it was necessary to compound the oral solution for intravenous administration. The effectiveness and tolerability of oral and intravenous acetylcysteine for the prevention of hepatotoxicity induced by paracetamol poisoning are well established in the literature. Intravenous acetylcysteine may be preferred over oral administration based on improved tolerability, ease of administration and the shortened course of therapy (20 hours intravenous vs 72 hours oral). The two intravenous acetylcysteine regimens documented in the literature, 48 hours and 20 hours, have similar efficacy when started within 8-10 hours of ingestion. Although there are no legal concerns with continuing the routine compounding of the oral solution to an intravenous product, new standards for pharmacy compounding of sterile preparations set forth by the US Pharmacopoeia highlight that the risk of compounding products for intravenous use must be assessed carefully. Changing the route of administration of a sterile oral solution to an intravenous preparation, when a commercial sterile and pyrogen-free product is available, may not be advisable. The best cost-containment strategies must be used for introduction of the more costly sterile, pyrogen-free intravenous acetylcysteine formulation by hospitals and healthcare systems. The intravenous acetylcysteine product is more cost effective when given for 20 hours than other treatment protocols based on the costs of acetylcysteine and hospitalisation. If used per protocol, the 20-hour intravenous acetylcysteine regimen may decrease hospital length of stay, thereby, offsetting the increased drug cost. Data conflict on the efficacy and administration of intravenous acetylcysteine for off-label uses, such as radiographic contrast media-induced nephropathy prevention and reperfusion in orthotopic liver transplantation. The costs for the intravenous formulation for these indications is significantly higher than use of the oral formulation for oral administration in radiographic contrast media-induced nephropathy prevention and compounded for intravenous use in orthotopic liver transplantation. The oral solution should be retained by healthcare systems for oral and inhalation applications, such as respiratory conditions, oral administration for radiographic contrast media nephropathy prevention, or the use of the 72-hour oral protocol to treat paracetamol poisoning, when the intravenous preparation cannot be used.

Anaphylactoid reactions to intravenous N-acetylcysteine: a prospective case controlled study

INTRODUCTION

Since its introduction in 1977, intravenous N-acetylcysteine has become the treatment of choice for paracetamol overdose. The aim of our study was to investigate the existence of predictive factors in the likelihood of developing anaphylactoid reactions to N-acetylcysteine.

METHODS

Prospective case-controlled study of all patients who presented to our emergency department (ED) between January 1997 and June 1999, and who were treated with intravenous N-acetylcysteine on the short stay observation ward.

RESULTS

Sixty-four patients received N-acetylcysteine infusions; thirty-one (48.4%) developed an anaphylactoid reaction. Nineteen patients who reacted were commenced on N-acetylcysteine prior to receipt of paracetamol concentrations and fifteen (48.4%) were categorised as high-risk. Seventy-one percent of reactions occurred within the first 15 min. Thirteen patients who developed a reaction, had levels which fell below the treatment lines. The levels of a further nine reactors lay above the high-risk but below the normal-risk lines. Only five patients who reacted had levels above the normal-risk line. Two of the patients who reacted to intravenous N-acetylcysteine presented at a later date with a further paracetamol overdose. Both required treatment with intravenous N-acetylcysteine, the first bag being infused over one hour. Neither developed a reaction.

CONCLUSION

We report a substantially higher incidence of anaphylactoid reactions to intravenous N-acetylcysteine than has previously been documented. It appears that these reactions are more likely to occur in high-risk patients, when plasma paracetamol concentrations were found to be below the treatment lines and in late presenters. Perhaps, giving the loading dose of N-acetylcysteine over 60 min could reduce the incidence of adverse reactions.

Fish tolerance to organophosphate-induced oxidative stress is dependent on the glutathione metabolism and enhanced by N-acetylcysteine

Dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) is an organophosphorus (OP) insecticide and acaricide extensively used to treat external parasitic infections of farmed fish. In previous studies we have demonstrated the importance of the glutathione (GSH) metabolism in the resistance of the European eel (Anguilla anguilla L.) to thiocarbamate herbicides. The present work studied the effects of the antioxidant and glutathione pro-drug N-acetyl-L-cysteine (NAC) on the survival of a natural population of A. anguilla exposed to a lethal concentration of dichlorvos, focusing on the glutathione metabolism and the enzyme activities of acetylcholinesterase (AChE) and caspase-3 as biomarkers of neurotoxicity and induction of apoptosis, respectively. Fish pre-treated with NAC (1 mmol kg(-1), i.p.) and exposed to 1.5 mg l(-1) (the 96-h LC85) of dichlorvos for 96 h in a static-renewal system achieved an increase of the GSH content, GSH/GSSG ratio, hepatic glutathione reductase (GR), glutathione S-transferase (GST), glutamate:cysteine ligase (GCL), and gamma-glutamyl transferase (gammaGT) activities, which ameliorated the glutathione loss and oxidation, and enzyme inactivation, caused by the OP pesticide. Although NAC-treated fish presented a higher survival and were two-fold less likely to die within the study period of 96 h, Cox proportional hazard models showed that hepatic GSH/GSSG ratio was the best explanatory variable related to survival. Hence, tolerance to a lethal concentration of dichlorvos can be explained by the individual capacity to maintain and improve the hepatic glutathione redox status. Impairment of the GSH/GSSG ratio can lead to excessive oxidative stress and inhibition of caspase-3-like activity, inducing cell death by necrosis, and, ultimately, resulting in the death of the organism. We therefore propose a reconsideration of the individual effective dose or individual tolerance concept postulated by Gaddum 50 years ago for the log-normal dose-response relationship. In addition, as NAC increased the tolerance to dichlorvos, it could be a potential antidote for OP poisoning, complementary to current treatments.

Paracetamol poisoning: Which nomogram should we use?

OBJECTIVES

To determine the type of paracetamol nomograms used in Australasian EDs. To review the literature to determine the evidence base for existing nomograms.

METHODS

A cross sectional descriptive study via postal survey of all Australasian EDs accredited for specialist emergency medicine training by the Australasian College for Emergency Medicine (ACEM). A literature review using Knowledge Finder search engine was employed.

RESULTS

The response rate was 87%. The most commonly used nomogram had a four-hour treatment level of 1300 mumol/L (69%). A total of 22% of respondents used a four-hour treatment level of 1000 mumol/L. Two departments (3%) treated all patients above the 660 mumol/L line. Eleven departments (15%) did not have a treatment line below 1300 mumol/L.

CONCLUSION

Practice varies in Australasian EDs. Patients with paracetamol levels below the 1300 mumol/L have been reported in the literature to develop hepatotoxicity, and deaths have been documented. N-acetylcysteine is extremely safe when used in the recommended dosages.

Acetaminophen intoxication and length of treatment: how long is long enough?

The currently recommended dosing scheme for treating acetaminophen overdose in the United States consists of a loading dose of oral N-acetylcysteine 140 mg/kg, followed by 70 mg/kg every 4 hours for 17 doses, for a total of 72 hours of oral N-acetylcysteine therapy. This protocol has been both effective and safe. We critically evaluated the evidence that supports reducing the course of N-acetylcysteine therapy from 72 hours to 24 or 36 hours. This shorter regimen offers important benefits for both the patient and the patient's family, such as increased drug tolerability and reduced hospital stay. Patients who intentionally ingested acetaminophen with harmful intent could receive appropriate psychosocial treatment more quickly. In addition, shorter courses of N-acetylcysteine therapy have positive financial ramifications by reducing the hospital stay by 1 or 2 days. Clearly, a shorter treatment regimen would not be appropriate for all patients, particularly those who seek treatment late (> 24 hrs after ingestion) and those with evidence of organ toxicity. In order to provide the necessary evidence to support a change in accepted clinical practice, further investigation on the safety and efficacy of a shorter N-acetylcysteine regimen should be conducted by clinical researchers in a controlled manner.

Stability and microbiology of inhalant N-acetylcysteine used as an intravenous solution for the treatment of acetaminophen poisoning

STUDY OBJECTIVE

Intravenous N-acetylcysteine has been used as an antidote for acetaminophen poisoning for more than 25 years in Europe and Canada. In the United States, only the oral administration of N-acetylcysteine is approved by the US Food and Drug Administration. Many physicians routinely use the inhalant preparation as an intravenous formulation; however, no stability, microbiology, or pyrogen studies have been performed. In this study, we evaluate the stability and microbiology of inhalational N-acetylcysteine compounded as an intravenous formulation.

METHODS

A total of 8 N-acetylcysteine solutions (solution A through H) were prepared by injecting 150 mL of 20% solution through a 22-microm filter to 1 L of 5% dextrose (D(5)W; 2.6% solution). Solutions A through C were prepared at ambient conditions (25 degrees C [77 degrees F], 65% relative humidity), and solution D was prepared at accelerated conditions (40 degrees C [104 degrees F], 75% relative humidity) for stability testing. The assays were performed by means of high-performance liquid chromatography at 0, 4, 8, 12, 24, 36, 48, 60, and 72 hours according to US Pharmacopeia XXIV methodology. Solutions E through G were assessed for bacterial growth, and solution H underwent pyrogen testing by using a Limulus amebocyte lysate method.

RESULTS

Solutions A through C remained stable for at least 60 hours (<10% decomposition), but at 72 hours, there was a 10.3%, 14.9%, and 13.4% degradation, respectively. Under accelerated conditions (solution D), stability lasted for more than 72 hours. Solutions E through G remained free from bacterial growth at 72 hours, and solution H tested negative for endotoxins-pyrogens.

CONCLUSION

Inhalational N-acetylcysteine prepared as an intravenous solution meets US Pharmacopeia standards for stability up to 60 hours and is free from bacteria and their byproducts, offering a viable alternative to the traditional use of oral N-acetylcysteine.

Acetaminophen hepatotoxicity

Unlike the bulk of medications, described in this fascicle, that cause liver injury in humans, acetaminophen is a non-prescription drug that can be purchased in drug stores and supermarkets without a physician's involvement. Death or severe injury is far more likely to occur with its use than with all the other medications considered in this study. Whereas attempts to control the quantity of drug ingested have been made in the United Kingdom and elsewhere in Europe, no comparable moves have taken place in the United States. The Food and Drug Administration claims to have concerns about the situation, however, but has yet to make an effort to more closely regulate the marketing and distribution of the drug. It is to be hoped that this will not be the case by the time the next issue of Drug Hepatotoxicity is scheduled for this series.

Acetylcysteine protects against acute renal damage in patients with abnormal renal function undergoing a coronary procedure

OBJECTIVES

We sought to evaluate the efficacy of the antioxidant acetylcysteine in limiting the nephrotoxicity after coronary procedures.

BACKGROUND

The increasingly frequent use of contrast-enhanced imaging for diagnosis or intervention in patients with coronary artery disease has generated concern about the avoidance of contrast-induced nephrotoxicity (CIN). Reactive oxygen species have been shown to cause CIN.

METHODS

We prospectively studied 121 patients with chronic renal insufficiency (mean [+/-SD] serum creatinine concentration 2.8 +/- 0.8 mg/dl) who underwent a coronary procedure. Patients were randomly assigned to receive either acetylcysteine (400 mg orally twice daily) and 0.45% saline intravenously, before and after injection of the contrast agent, or placebo and 0.45% saline. Serum creatinine and blood urea nitrogen were measured before, 48 h and 7 days after the coronary procedure.

RESULTS

Seventeen (14%) of the 121 patients had an increase in their serum creatinine concentration of at least 0.5 mg/dl at 48 h after administration of the contrast agent: 2 (3.3%) of the 60 patients in the acetylcysteine group and 15 (24.6%) of the 61 patients in the control group (p < 0.001). In the acetylcysteine group, the mean serum creatinine concentration decreased significantly from 2.8 +/- 0.8 to 2.5 +/- 1.0 mg/dl (p < 0.01) at 48 h after injection of the contrast medium, whereas in the control group, the mean serum creatinine concentration increased significantly from 2.8 +/- 0.8 to 3.1 +/- 1.0 mg/dl (p < 0.01).

CONCLUSIONS

Prophylactic oral administration of the antioxidant acetylcysteine, along with hydration, reduces the acute renal damage induced by a contrast agent in patients with chronic renal insufficiency undergoing a coronary procedure.

Tissue distribution of and species differences in deacetylation of N-acetyl-L-cysteine and immunohistochemical localization of acylase I in the primate kidney

Species differences in the biotransformation of N-acetyl-L-cysteine (NAC) have been investigated to evaluate the usefulness of NAC as a constituent in parenteral nutrition solutions in place of cysteine. The activity of NAC-deacetylating enzyme (acylase) was measured in various tissues of different species (rat, rabbit, dog, monkey, and man). Acylase activity was highest in the kidney in all species studied. Enzyme activity in the liver was 10 %-22 % of that in the kidney in the rat, rabbit, monkey, and man, but almost no hepatic activity was seen in the dog. NAC-deacetylating activity was very low in other organs. The tissue distribution of acylase I was determined by Western blotting and an immunohistochemical method employing specific antibody against porcine acylase I (EC 3.5.1.14). The immunoblotting study showed a 46-kDa protein band corresponding to porcine acylase I in the kidney of all species. In liver cytosol, 46 kDa and/or 29 kDa bands were observed in the rat, rabbit, monkey, and man, but not in the dog. In the immunohistochemical study, positive staining with anti-acylase I antibody was observed clearly in the renal proximal tubules in the monkey and man. These results suggested that the kidney and liver were the main organs responsible for the biotransformation of NAC to cysteine in mammals other than the dog.

Inhibition of the antibody production by acetaminophen independent of liver injury in mice

The causal relationship between the inhibition of antibody production and liver injury induced by single doses of acetaminophen (APAP) was investigated in mice. The liver injury and antibody production were evaluated using the serum transaminase activity and the number of antibody forming cells against sheep red blood cells (SRBC), respectively. The relevance of APAP hepatotoxicity with inhibiting antibody production was elucidated in fasted and fed mice treated with a single oral administration of APAP. In fasted mice, the oral administration of APAP produced serious liver injury, while it was not the case in the fed mice. As the antibody production was measured under these conditions, APAP significantly depressed the antibody production in fed mice as well as in fasted mice. The rate of B220 positive cells in the splenocytes was significantly decreased by APAP administration in both the fasted and fed mice. Splenocytes proliferative responses following mitogenic stimulation with concanavalin A or lipopolysaccharide were inhibited by APAP. Moreover, APAP added directly to the splenocyte culture also inhibited the in vitro antibody-producing response to SRBC. These findings indicate that the APAP-induced depression of antibody production may not be a secondary response to APAP-hepatitis, but may be a primary response to APAP.

Antioxidants suppress mortality in the female NZB x NZW F1 mouse model of systemic lupus erythematosus (SLE)

Inflammation produces reactive oxygen intermediates (ROI) that cause vascular damage and activate T lymphocytes. Conversely, antioxidants not only protect tissue from oxidative damage but also suppress immune reactivity. The objective of this study was to examine immunomodulatory effects of the non-enzymatic antioxidants, N-acetylcysteine (NAC) and cysteamine (CYST), on autoimmune disease, glomerulonephritis, and mortality in the female B/W mouse model of human systemic lupus erythematosus (SLE). The development of murine lupus was assessed during the lifespan of female B/W mice given NAC or CYST. Morbidity and mortality were assessed daily. At 6 week intervals mice were examined for weight change, albuminuria, serum BUN, antibodies to DNA, and IgG immunoglobulin levels. Serum prolactin, estrogen and progesterone were measured at 18 weeks of age. In a parallel study, NAC- and CYST-treated and control B/W mice were examined at 24 weeks of age for interval renal histopathology, lymphocyte adhesion molecule expression, and antibody titers and in vitro cytokine production in response to immunization with DNP-KLH. CYST significantly suppressed development of albuminuria and azotemia at 36 and 42 weeks of age compared to control and NAC-treated mice. NAC significantly suppressed anti-DNA antibody levels at 24 weeks. In contrast CYST significantly increased anti-DNA antibody levels at 18 weeks of age (P < 0.001 CYST vs control and NAC-treated mice). Kidneys of CYST-treated mice also had accelerated inflammatory histologic changes despite their lower incidence of albuminuria and azotemia. Mean (+/- s.e.m.) survival of control mice was 33 +/- 2 weeks compared to 38 +/- 2 weeks in NAC-treated mice (P < 0.05 vs control), and 48 +/- 2 weeks in the CYST-treated group (P < 0.01 vs control mice). The antioxidants, NAC and CYST, significantly improved mortality in the female B/W mouse model of SLE. NAC suppressed autoantibody formation and modestly prolonged survival. CYST, despite its augmentation of anti-DNA levels and renal inflammatory changes, inhibited the development of renal insufficiency and markedly improved survival. These findings suggest that ROIs play a role in the pathogenesis of lupus nephritis and that antioxidants reduce the damage causing renal insufficiency. Antioxidants may be a beneficial adjunctive therapy in the treatment of human SLE.

Effects of 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid on extrahepatic sulfhydryl levels in mice treated with acetaminophen

The cysteine (Cys) precursor 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid (PTCA) has been shown to protect against acetaminophen (APAP)-induced hepatic GSH, GSSG, and Cys depletion and hepatic necrosis. The aim of this study was to determine the effects of PTCA on the concentrations of sulfhydryl compounds in extrahepatic tissues, including renal cortex, whole blood, and brain, in C57BL/6 mice treated with hepatotoxic doses of APAP. PTCA (1-5 mmol/kg, i.p.) was administered 30 min after the administration of APAP at a dose (800 mg/kg; 5.29 mmol/kg, i.p.) that depleted hepatic GSH and Cys at 4 hr by 95 and 86%, respectively. Tissue concentrations of GSH and Cys were determined by HPLC. At 4 hr following APAP administration, renal cortical GSH and Cys concentrations were decreased to 64 and 39%, respectively, of vehicle-treated control values, and blood concentrations were decreased to 87 and 30%, respectively, of vehicle controls. Brain GSH and Cys were not depleted by APAP. PTCA at 5 mmol/kg (i) attenuated the APAP-induced depletion of GSH and Cys at 4 hr in renal cortex (78 and 65%, respectively, of vehicle controls), (ii) prevented APAP-induced Cys depletion in blood (670% of vehicle controls) with no effect on GSH concentration (94% of vehicle controls), and (iii) increased GSH and Cys concentrations in brain (119 and 411%, respectively, of vehicle controls). The results demonstrate a high degree of tissue selectivity in the APAP-induced depletion of GSH and Cys, and in the effectiveness of PTCA in maintaining and even elevating sulfhydryl levels in extrahepatic tissues of APAP-treated mice.

Acetaminophen selectively reduces glioma cell growth and increases radiosensitivity in culture

Glioblastoma multiforme (GBM) is a highly lethal brain cancer. Using cultures of rodent and human malignant glioma cell lines, we demonstrated that millimolar concentrations of acetylsalicylate, acetaminophen, and ibuprofen all significantly reduce cell numbers after several days of culture. However, their mechanisms of action may vary, as demonstrated by (1) differences in the morphological changes produced by these compounds; (2) varied responses to these drugs with respect to toxicity kinetics; and (3) respective rates of cell proliferation, DNA synthesis, and mitotic index. We studied the effects of acetaminophen on relative cell number further. Evidence is presented that acetaminophen induced cell death by an apoptotic mechanism after a brief burst of mitosis in which cell numbers increased transiently, followed by a reduction in cell number and an increase in DNA fragmentation, as evidenced by terminal deoxytransferase-mediated dUTP-biotin nick end labeling (TUNEL) analysis. Using cultures of adult human brain and embryonic rat brain, we demonstrated that glioma cells were several-fold more sensitive to acetaminophen than normal brain cells in culture. Finally, subtoxic doses of acetaminophen increased the sensitivity of the human glioma cells in culture to ionizing radiation. Taken together, these results suggest that acetaminophen may prove to be a useful therapeutic agent in the treatment of human brain tumors.

Prevention of acetaminophen-induced liver toxicity by 2(R,S)-n-propylthiazolidine-4(R)-carboxylic acid in mice

The cysteine (Cys) precursor 2(R,S)-n-propylthiazolidine-4(R)-carboxylic acid (PTCA) was shown previously to maintain near normal levels of hepatic GSH and GSSG at 24 hr and to protect against hepatic necrosis and mortality at 48 hr after toxic doses of acetaminophen (APAP) in mice. Studies were performed in C57BL/6 mice to determine: (a) the time course of APAP-induced hepatic sulfhydryl depletion, and (b) the effectiveness of PTCA in preventing APAP-induced decreases in sulfhydryl concentrations at the time of maximal depletion. APAP (400-800 mg/kg in 50% propylene glycol; 2.65-5.29 mmol/kg) and PTCA (1-5 mmol/kg 30 min after APAP) were administered i.p. Hepatic GSH, GSSG, and Cys concentrations were determined by HPLC. Hepatocellular damage was assessed by elevations in serum glutamate-pyruvate transaminase (SGPT) activity and histopathologic examination. APAP and PTCA produced dose-dependent effects. At 4 hr after the highest dose of APAP, hepatic GSH and Cys concentrations were reduced to 5 and 14%, respectively, of values in vehicle-treated controls, and the GSSG concentration was below the sensitivity of the analytical method. At 24 hr, recovery of hepatic sulfhydryls was incomplete, and there was hepatic necrosis with an approximately 100-fold increase in SGPT activity. At the highest dose of PTCA, the concentrations of GSH, Cys, and GSSG at 4 hr after APAP (800 mg/kg) were 66, 116, and 111%, respectively, of vehicle controls. PTCA in doses of 1.75 to 5 mmol/kg attenuated the APAP-induced increases in SGPT activity. It was concluded that the protective effect of PTCA is most likely related to prevention of hepatic sulfhydryl depletion.

Can antioxidants be beneficial in the treatment of lead poisoning?

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydryl-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and/or increasing susceptibility of cells to oxidative attack by altering the membrane integrity and fatty acid composition. Consequently, it is plausible that impaired oxidant/antioxidant balance can be partially responsible for the toxic effects of lead. Where enhanced oxidative stress contributes to lead-induced toxicity, restoration of a cell's antioxidant capacity appears to provide a partial remedy. Several studies are underway to determine the effect of antioxidant supplementation following lead exposure. Data suggest that antioxidants may play an important role in abating some hazards of lead. To explain the importance of using antioxidants in treating lead poisoning the following topics are addressed: (i) Oxidative damage caused by lead poisoning; (ii) conventional treatment of lead poisoning and its side effects; and (iii) possible protective effects of antioxidants in lead toxicity.

Transcriptional activation of heme oxygenase-1 and its functional significance in acetaminophen-induced hepatitis and hepatocellular injury in the rat

BACKGROUND/AIM

Glutathione depletion contributes to acetaminophen hepatotoxicity and is known to induce the oxidative stress reactant heme oxygenase-1. The metabolites of the heme oxygenase pathway, biliverdin, carbon monoxide, and iron may modulate acetaminophen toxicity. The aim of this study was to assess cell-type specific expression of heme oxygenase-1 and its impact on liver injury and microcirculatory disturbances in a model of acetaminophen-induced hepatitis.

METHODS

Gene expression of heme oxygenase-1 was studied by Northern- and Western analysis as well as immunohistochemistry. The time course of heme oxygenase-1 and -2, cytokine-induced neutrophil chemoattractant-1, and intercellular adhesion molecule-1 was studied by Northern analysis. DNA-binding activity of nuclear factor-kappaB was determined by electrophoretic mobility shift assay. Sinusoidal perfusion and leukocyte-endothelial interactions were assessed by intravital microscopy.

RESULTS

Acetaminophen caused a moderate sinusoidal perfusion failure (-15%) and infiltration of neutrophils along with activation of nuclear factor-kappaB and intercellular adhesion molecule-1 and cytokine-induced neutrophil chemoattractant-1 mRNAs. Induction of heme oxygenase-1 mRNA and protein (approximately 30-fold) in hepatocytes and non-parenchymal cells paralleled the inflammatory response. Blockade of heme oxygenase activity with tin-protoporphyrin-IX abrogated acetaminophen-induced hepatic neutrophil accumulation and nuclear factor-kappaB activation, but failed to affect sinusoidal perfusion and liver injury.

CONCLUSIONS

The inflammatory response associated with acetaminophen hepatotoxicity is modulated by the parallel induction of the heme oxygenase-1 gene. However, heme oxygenase-1 has no permissive effect on sinusoidal perfusion and does not affect liver injury in this model. These data argue against a central role of nuclear factor-kappaB activation and neutrophil infiltration as perpetuating factors of liver injury in acetaminophen toxicity.

TANAX(T-61): an overview

In this overview the authors describe the use of Tanax (T-61) for euthanasia. Tanax is a solution with three components (embutramide, mebenzonium iodide and tetracaine hydrochloride) used for painless death in pets and laboratory animals. It is also used for malicious intoxication in animals and for suicide attempts in humans. After a description of the modality and outcome of intoxication, the authors report the secondary toxic effects evoked by N, N -dimethyl-formamide, the solvent employed to dissolve the three components of Tanax. Finally, the analytical methods used to identify Tanax components in biological fluids and tissues are described.

In-vivo glutathione elevation protects against hydroxyl free radical-induced protein oxidation in rat brain

Glutathione deficiency has been associated with a number of neurodegenerative diseases including Lou Gehrig's disease, Parkinson's disease, and HIV. A crucial role for glutathione is as a free radical scavenger. Alzheimer's disease (AD) brain is characterized by oxidative stress, manifested by protein oxidation, lipid oxidation, oxidized glutathione, and decreased activity of glutathione S-transferase, among others. Reasoning that elevated levels of endogenous glutathione would offer protection against free radical-induced oxidative stress, rodents were given in vivo injections of N-acetylcysteine (NAC), a known precursor of glutathione, to study the vulnerability of isolated synaptosomal membranes treated with Fe2+/H2O2, a known hydroxyl free radical producer. Protein carbonyls, a marker of protein oxidation, were measured. NAC significantly increased endogenous glutathione levels in cortical synaptosome cytosol (P < 0.01). As reported previously, protein carbonyl levels of the Fe2+/H2O2-treated synaptosomes were significantly higher compared to that of non-treated controls (P < 0.01), consistent with increased oxidative stress. In contrast, protein carbonyl levels in Fe2+/H2O2-treated synaptosomes isolated from NAC-injected animals were not significantly different from saline-injected non-treated controls, demonstrating protection against hydroxyl radical induced oxidative stress. These results are consistent with the notion that methods to increase endogenous glutathione levels in neurodegenerative diseases associated with oxidative stress, including AD, may be promising.

Oral or intravenous N-acetylcysteine: which is the treatment of choice for acetaminophen (paracetamol) poisoning?

BACKGROUND

The optimal route and duration of administration for N-acetyl-cysteine in the management of acetaminophen (paracetamol) poisoning are controversial. It has been stated on the basis of a selected post-hoc analysis that oral N-acetylcysteine is superior to intravenous N-acetylcysteine in presentations later than 15 hours.

AIM OF STUDY

To investigate the efficacy of intravenous or oral N-acetylcysteine.

PATIENTS AND METHODS

We analyzed a series of acetaminophen poisonings treated with a protocol including activated charcoal and intravenous N-acetylcysteine. The outcomes assessed included use of N-acetylcysteine, adverse effects of intravenous N-acetylcysteine, and the occurrence of hepatotoxicity (transaminase > 1000 U/L). We incorporated these results in a meta-analysis of previously reported series of acetaminophen poisonings to compare the outcomes from intravenous and oral N-acetylcysteine use.

RESULTS

Of 981 patients admitted over 10 years, 4% (40) presented later than 24 hours and 10% (100) had concentrations of acetaminophen that indicated a probable or high risk of hepatotoxicity. The 30 patients who developed hepatotoxicity presented later, took larger amounts, had higher concentrations, and received N-acetylcysteine later than those who did not. No patients received a liver transplant but 2 patients died (one after referral to a transplant unit and one just before). Adverse reactions to intravenous N-acetylcysteine occurred in 6% (12/205) of patients but none prevented completion of the treatment. In the meta-analysis, those with probable or high risk concentrations had similar outcomes with intravenous (pooled n = 341) and oral N-acetylcysteine (pooled n = 1462) administration. Rates of hepatotoxicity for those treated within 10 hours (3 and 6%), late (10-24 hours: 30 and 26%), and overall (0-24 hours: 16 and 19%) were all similar. The proportion of patients classified as presenting later than 10 hours is much greater in the oral N-acetylcysteine studies (64%) than in many of the intravenous N-acetylcysteine studies (38%, 44%, and 63%).

CONCLUSIONS

The differences claimed between oral and intravenous N-acetylcysteine regimes are probably artifactual and relate to inappropriate subgroup analysis. A shorter hospital stay, patient and doctor convenience, and the concerns over the reduction in bioavailability of oral N-acetylcysteine by charcoal and vomiting make intravenous N-acetylcysteine preferable for most patients with acetaminophen poisoning.

Determination of reduced and oxidized homocysteine and related thiols in plasma by thiol-specific pre-column derivatization and capillary electrophoresis with laser-induced fluorescence detection

A new sensitive and rapid capillary electrophoresis (CE) assay for measuring reduced and oxidized thiols in human plasma has been developed. To prevent oxidation of the thiols, whole blood was immediately centrifuged after collection and the plasma proteins were precipitated with perchloric acid. The reduced thiols in the supernatant were derivatized quantitatively at 25 degrees C, pH 7.5 with a fluorescent reagent, fluorescein-5-maleimide (FM). The total plasma concentration of thiols, including the fraction coupled to proteins, was assayed after an initial reduction of the disulfide linkage in plasma with dithiothreitol. The separation of FM-thiols was performed in an acetonitrile/10 mM sodium phosphate-50 mM SDS buffer [25:75 (v/v); pH 7.0] using a fused-silica capillary (57 cm x 75 microm I.D.) at 45 degrees C. A 3-mW argon-ion laser (lambda(ex) 488 nm/lambda(em) 520 nm) was employed for FM-thiol detection. With the electric field of 530 V/cm, the time needed for the separation of FM-homocysteine, FM-glutathione and FM-N-acetylcysteine was less than 8 min. The lower limit of detection was 3 microM for the total thiols and 10 nM for the reduced thiols. The method was applied to, the determination of homocysteine levels in plasma from patients with end-stage renal disease.

N -Acetyl-cysteine reduces homocysteine plasma levels after single intravenous administration by increasing thiols urinary excretion

A decrease of plasma homocysteine (Hcy) may represent a therapeutic promise for reducing the impact of atherosclerosis. N -Acetyl-cysteine (NAC) is a thiol-containing compound interfering with endogenous thiols, cysteine (Cys) and Hcy, by forming with them mixed disulphides with a possibly more efficient renal clearance. The aim of this work was to assess the effect of NAC intravenous infusion on plasma levels of different forms of Hcy and particularly to verify the effect on Hcy renal excretion. We collected basal blood samples at 0.5, 1, 2, 5, 8 and 24 h after the beginning of NAC infusion (50 mg kg(-1)body wt.) and also 24-h urine samples of the day of NAC infusion and of the day before and of the day after the infusion in ten healthy subjects (mean age 73+/-15). Urinary and plasma thiols (Hcy, Cys and NAC) were assayed by HPLC. Both total plasma Hcy (approx. 69%vs basal values) and Cys (approx. 40%vs basal values) fell progressively, reaching a minimum 5 h after infusion start; total free (i.e. not bound to proteins) Hcy (2.2+/-1.8 down from 4.4+/-4.2 nmol ml(-1)) and Cys (70.4+/-39.8 down from 113. 3+/-61.2 nmol ml(-1)) decreased as well. Reduced (thiolic-free form) Hcy and Cys decreased during infusion, though not as pronounced as for the other forms. Percentagewise, out of the total plasma levels, Hcy and Cys total free form and reduced form tended to increase over infusion as well as their difference (i.e. the plasma mixed disulphide moiety), thus supporting the idea that excess NAC displaces thiols from their plasma binding sites forming mixed disulphides. Urinary total Cys and Hcy excretion significantly increased at the end of the day of NAC infusion (tenfold for Cys and fivefold for Hcy) and reduced appreciably on the following day. Also urinary excretion of the free form of Cys and Hcy increased at the end of the day of NAC infusion, although in a lower amount with respect of total amounts, meaning a reduction of percentage Cys and Hcy excreted as the free form; for none of the patients had proteinuria, the 'free' form of urine thiols has to be identified in the 'reduced' form, the difference between the total and free form reflecting the 'mixed disulphide' moiety. NAC intravenous administration induces an efficient and rapid reduction of plasma thiols, particularly of Hcy; our data support the hypothesis that NAC displaces thiols from their binding protein sites and forms, in excess of plasma NAC, mixed disulphides (NAC-Hcy) with an high renal clearance. This effect may represent the start of an alternative approach in the treatment of hyperhomocysteinaemic conditions.

N-acetylcysteine in pig liver transplantation from non-heart-beating donors

Lipid peroxidation due to oxygen free radicals (OFR) seems to play a major role in loss of liver graft viability after warm ischemia, preservation, and transplantation. N-acetylcysteine (NAC) is an antioxidant that has a direct effect on OFR, and is also a glutathione precursor, another antioxidant. This study was designed to evaluate the efficacy of NAC in preventing ischemia-reperfusion damage of liver grafts harvested from non-heart-beating donors. Liver transplantation was performed on pigs divided into five groups: group 1 (control group; n=5) received livers from heart-beating donors; livers were subjected to 30 min of warm ischemia in groups 2 (n=3, no NAC) and group 3 (n=3; NAC treatment); warm ischemia time lasted 60 min in groups 4 (n=4; no NAC) and 5 (n=5; NAC treatment). Studied parameters included graft survival for more than 3 days, aspartate aminotransferase plasma levels, liver histology, and hepatic total glutathione concentrations. Graft survival was 100% in groups 1, 2, and 3, 0% in group 4, and 20% in group 5. NAC treatment did not influence initial mean aspartate aminotransferase release which was greater in warm ischemic livers than in controls. NAC treatment had no effect on liver hepatic total glutathione after reperfusion of animals receiving warm ischemic grants. Finally, no effect on liver histology was observed with NAC treatment. Our study suggests that in liver transplantation from non-heart-beating donors, NAC has no effect in both graft viability and lipid peroxidation. The role of OFR in primary dysfunction of transplanted warm ischemic livers remains controversial.

An update on the role of free radicals and antioxidant defense in human disease

Mounting clinical and experimental evidence indicates that free radicals play important roles in many physiological and pathological conditions. The wider application of free radical measurement has increased awareness of functional implications of radical-induced impairment of the oxidative/antioxidative balance. In the following review, the role of oxygen free radicals in some human and experimental pathological conditions is described, with particular emphasis on the mechanisms by which they produce oxidative damage to lipids, proteins, and nucleic bases. The role of free radicals and the activation of the antioxidant systems in arteriosclerosis and ageing, diabetes, ischemia/reperfusion injury, ethanol intoxication, and liver steatosis is discussed. Therapeutic approaches to the use of antioxidants have been described and prospects for clinical use have been considered.

Antioxidant effects of N-acetylcysteine and succimer in red blood cells from lead-exposed rats

This study examined whether lead-induced alterations in selected parameters that are indicative of oxidative stress accompany the toxic effects of lead in red blood cells (RBCs) in vivo. It also explored the possibility that treatment with N-acetylcysteine (NAC) or succimer (meso-2,3-dimercaptosuccinic acid) was capable of reversing parameters indicative of lead-induced oxidative stress. Fisher 344 rats were given 2000 ppm lead acetate in their drinking water for 5 weeks. The lead was then removed and the animals were given NAC (800 mg/kg/day) or succimer (90 mg/kg/day) in their drinking water for 1 week, after which the RBCs were harvested. Animals not given lead and those given lead, but not NAC or succimer, served as negative and positive controls, respectively. At the end of the experiment, blood-lead levels were 35 +/- 4 microg/dl in lead-treated animals, which were reduced to 2.5 +/- 1 microg/dl by treatment with succimer and to 25 +/- 3 microg/dl by treatment with NAC. Lead-exposed animals demonstrated signs of anemia as evidenced by anisocytosis, poikilocytosis, and alterations in hemoglobin, hematocrit, and mean corpuscular volume. Lipid peroxidation, as evidenced by increased malondialdehyde (MDA) content, as well as decreases in reduced glutathione (GSH) and increases in catalase and glucose 6-phosphate dehydrogenase (G6PD) activity were noted in RBCs from lead-treated rats, suggesting that the lead induced oxidative stress. In addition, a significant reduction in blood delta-aminolevulinic acid dehydratase (ALAD) activity suggested that accumulation and autooxidation of delta-aminolevulinic acid might contribute to lead-induced oxidative stress. Treatment with either NAC or succimer reversed lead-induced alterations in MDA and GSH content, but only succimer appeared to partially restore ALAD activity. These results provide in vivo evidence supporting the hypothesis that lead induces oxidative stress in RBCs, which is reversible by treatment with a thiol antioxidant (NAC), as well as a chelating agent (succimer).

Temporal and kinetic determinants of the inhibition of LDL oxidation by N-acetylcysteine (NAC)

We investigated the ability of NAC to inhibit in vitro LDL oxidation, and the effects of the timing of NAC addition, repeated additions of NAC, and the presence of preoxidized LDL, on the oxidation reaction. NAC inhibited in vitro LDL oxidation induced by copper sulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, and UV light, and protected LDL against depletion of antioxidant vitamins. Glutathione was similarly effective against copper-mediated LDL oxidation. NAC's effectiveness was inversely related to the timing of its addition. Sequential NAC additions prolonged the lag phase more effectively than initial addition of the same total dose. NAC reduced CD formation during the oxidation of native LDL by oxidized LDL. NAC's effectiveness as an inhibitor of in vitro LDL oxidation is dependent on the temporal sequence of the oxidation reaction, sequential additions, and the presence of previously oxidized LDL.

2-Methyl-thiazolidine-2,4-dicarboxylic acid as prodrug of L-cysteine. Protection against paracetamol hepatotoxicity in mice

Toxic doses of paracetamol (acetaminophen) destroy the cellular defense system in hepatic tissue. The degree of the destruction can be assessed be measuring the metabolism of sulfhydryl compounds, oxygen radicals and the release of certain enzymes. Administration of 2-methyl-thiazolidine-2,4-dicarboxylic acid (CP; 1.2 mmol/kg) to mice 12 h prior to a toxic dose of paracetamol (600 mg/kg) suppressed the increase of aminotransferase activities in blood serum and the levels of reactive oxygen species in liver tissue. A protective effect of CP was also observed with respect to depletion of non-protein sulfhydryl compounds, cysteine and glycogen. The findings demonstrate that the cysteine prodrug CP is effective in preventing liver damage of a hepatotoxic dose of paracetamol in vivo. A further advantage of the new compound is the long duration of the effect of more than 12 h.

Cimetidine enhances the hepatoprotective action of N-acetylcysteine in mice treated with toxic doses of paracetamol

Paracetamol, in toxic doses, is associated with extensive liver damage. This represents one of the common causes of morbidity and mortality in drug poisoning cases. This study was undertaken to investigate the possible potentiation of the hepatoprotective action of N-acetylcysteine (NAC) by cimetidine (CMD), an inhibitor of hepatic microsomal oxidative enzymes. The effects of NAC, cimetidine and the two in combination, administered 2 h post-paracetamol dose, on mortality, plasma glutamic oxaloacetic (GOT) and glutamic pyruvic (GPT) transaminase activities and hepatic reduced glutathione (GSH) levels were investigated in mice 24 h after treatment with a single oral dose of paracetamol (400 mg/kg). Both NAC and cimetidine caused a partial improvement of survival rate, plasma GOT and GPT activities. In addition, they prevented the depletion of hepatic GSH contents. However, concomitant administration of NAC and cimetidine produced a 100% survival rate and a marked reduction in plasma GOT and GPT activities to within the normal range, while significantly raising hepatic GSH concentrations to values close to those measured in saline-treated control animals. It is therefore concluded that cimetidine and N-acetylcysteine may have an additive hepatoprotective action in the treatment of paracetamol overdose.

Pharmacokinetics of N-acetylcysteine are altered in patients with chronic liver disease

BACKGROUND

The threshold plasma paracetamol concentration at which N-acetylcysteine (NAC) treatment is recommended to treat paracetamol poisoning in a patient with induced liver enzymes (for example, with chronic liver disease or taking anticonvulsant drugs) is 50% lower than in a patient without induced liver enzymes. More patients with chronic liver disease might therefore be expected to be exposed to NAC treatment than previously. In addition, there is increasing use of NAC in patients with chronic liver disease for multiorgan failure or hepatorenal syndrome. Little is known of NAC's pharmacokinetic properties in patients with cirrhosis.

AIM

The aim was to determine if the pharmacokinetics of NAC are altered by chronic liver disease.

SUBJECTS AND METHODS

NAC was given intravenously in a dose of 600 mg over 3 min to nine patients with biopsy-proven cirrhosis (Child's grade; 1 A, 4 B, 4 C: aetiology: 7 alcohol-related, 1 primary biliary cirrhosis, 1 secondary biliary stenosis) and six healthy matched controls. Venous blood was taken at 20, 40, 60 and 90 min then at 2, 3, 4, 6, 8 and 10 h after NAC administration. Serum NAC was estimated by HPLC. The data were normalized to a standard body weight of 70 kg.

RESULTS

The area under the serum concentration-time curve was increased (152.34 mg/L.h +/- 50.38 s.d.) in cirrhotics compared with normal controls (93.86 mg/L.h +/- 9.60 s.d.) (P < 0.05). The clearance of NAC was reduced in patients with chronic liver disease (4.52 L/h +/- 1.87 s.d.) compared with controls (6.47 L/h +/- 0.78: P < 0.01).

CONCLUSIONS

Increased vigilance for untoward anaphylactoid reactions is necessary in cirrhotics as they may have higher plasma NAC concentrations. Further studies to determine the optimum dosage regimen in such patients are required.

Hyperhomocysteinemia induced by folic acid deficiency and methionine load--applications of a modified HPLC method

The increasing possibility that homocysteine might be involved in atherosclerosis in non-homocysteinuric subjects has required the measurement of low concentrations of this aminothiol in biological samples. The procedure described here represents an improvement of different HPLC methods. We utilized an isocratic HPLC system with fluorescence detection of plasma total homocysteine derivatized after reaction with ammonium 7-fluoro-benzo-2-oxa-1,3-diazole-4-sulphonate. With the help of the rapidly eluting internal standard N-acetyl-cysteine, the method ensures very good recovery (approximately 100%), reproducibility and precision (within-assay: 2.31%; day-to-day: 2.8%) in the physiological concentration range. This procedure allowed us to validate various animal models of hyperhomocysteinemia such as dietary folic acid deficiency in rat and acute methionine loads in rat and hamster. Using this method, we also confirmed that men have higher plasma total homocysteine levels than women. Due to its simplicity and reliability, our procedure is suitable for routine analysis of total homocysteine and other aminothiols (cysteine, cysteinyl-glycine and glutathione) in biological samples, as required in clinical and research laboratories.

Hepatotoxicity of N, N-dimethylformamide (DMF) in acute poisoning with the veterinary euthanasia drug T-61

1. We report on a patient who was resuscitated after a suicide attempt with the veterinary euthanasia product T-61 and treated with N-acetylcysteine (NAC) to prevent hepatotoxicity from N,N-dimethylformamide (DMF), the solvent of T-61. 2. Serum concentrations of DMF were high as compared with values published on occupational exposure. 3. The patient showed only a transient increase in liver enzymes with eventually a full recovery. 4. The hepatoprotective effect of NAC was studied in a rat model using the rise in serum sorbitol dehydrogenase (SDH) as a marker for DMF-induced hepatotoxicity. 5. Four series of randomized, controlled and double-blind experiments were carried out and consistently showed a lower increase in SDH in NAC-treated animals in each series. The difference was statistically significant only when the data of the 4 series were pooled. This is probably due to the large interindividual variations in the effect of DMF. 6. We hypothesize that in the rat NAC may have a protective effect. Whether NAC is also protective in patients, in which it is administered after exposure to DMF, cannot be concluded from the present experiments.

Treatment of advanced malignancies with high-dose acetaminophen and N-acetylcysteine rescue

High-dose acetaminophen (HDAC) produces hepatocellular necrosis and cytotoxic changes in other tissues that express mixed-function-oxidase (MFO) activity. N-acetylcysteine (NAC), administered within 8 hr of HDAC exposure, replenishes reduced glutathione and prevents these effects. Numerous cell culture and animal studies have demonstrated that NAC may differentially protect normal cells compared with malignant cells from the toxic effects of chemotherapeutic agents and radiation. It was therefore proposed that HDAC with NAC rescue may be effective in malignancies that express MFO activity. To test this hypothesis, a phase I trial of HDAC with NAC rescue was conducted on 19 patients with advanced cancer. HDAC was escalated from 6 to 20 g/m2 PO using a standard IV NAC rescue regimen. A total of 78 treatments were administered. Moderate fatigue, anorexia, and weight loss were the main toxicities observed. Transient grade 3 liver toxicity was noted following 1 treatment. Alopecia and renal and hematological toxicities were not observed. Responses after 4 courses administered weekly were as follows: response in at least 1 site-8 (partial 3, improved 3, mixed 2); stable disease-3; progressive disease-3; inevaluable-5. In conclusion, HDAC was tolerated with moderate fatigue, anorexia, and weight loss but few other effects using a standard IV NAC rescue regimen. A maximum tolerated dose was not reached at 20 g/m2. A 3/19 (15.8%) partial response rate was observed.

Plasma homocysteine and thiol compound fractions after oral administration of N-acetylcysteine

The total concentration of the atherogenic aminothiol acid homocysteine in plasma of healthy volunteers was decreased after oral administration of N-acetylcysteine (NAC), whereas the reduced and free (non-protein bound) fractions of homocysteine were increased. The decrease of the total fraction varied between 20 and 50% and was dose-related. Cysteinylglycine was also decreased after the administration of NAC, whereas cysteine did not change. Administration of high amounts of NAC probably displaces homocysteine and cysteinylglycine from their protein binding sites by disulfide interchange reactions. This leads to the formation of mixed low molecular-weight cysteine and NAC disulfides with high renal clearance and possibly also increased metabolic bio-availability, thereby eliminating homocysteine and cysteinylglycine from plasma. Since only a small amount of additional urinary homocysteine was recovered it is likely that this aminothiol acid is taken up by the tubular cells and further metabolized.

Paracetamol (acetaminophen) poisoning

Paracetamol poisoning caused by intentional overdose remains a common cause of morbidity. In this article the mechanism of toxicity and the clinical effects and treatment of poisoning, including specific antidotal therapy, are reviewed. Areas for further research directed at reducing morbidity and mortality from paracetamol poisoning are considered.

Acute ethanol administration reduces the antidote effect of N-acetylcysteine after acetaminophen overdose in mice

1. The combined antidote effect of N-acetylcysteine and ethanol on the toxicity of acetaminophen was investigated. 2. Fed male mice were given acetaminophen i.p. (600 mg kg-1) and after 5 min in addition ethanol i.p. (0.2 ml, 19% v/v), N-acetylcysteine i.p. (1.2 g kg-1, 0.2 ml), N-acetylcysteine + ethanol i.p. (same doses as given individually) or saline i.p. (0.4 ml). Survival rates were determined after 24, 48, 72 and 96 h. 3. In the N-acetylcysteine group the survival rate was 85%. This rate was significantly reduced to 43% in the N-acetylcysteine + ethanol group (P = 0.0001). In the groups given ethanol or saline alone only 7% and 3%, respectively, survived 96 h. 4. The data suggest that the protective effect of N-acetylcysteine on acetaminophen-induced toxicity in fed mice is reduced by concomitant administration of ethanol. This may explain the clinical observation that ingestion of ethanol worsens the prognosis after acetaminophen intoxication.

Nephrotoxicity of paracetamol in the rat--mechanistic and therapeutic aspects

Besides hepatotoxicity, paracetamol may exert nephrotoxic effects in experimental animals and patients. The present study in rats shows that antidotes known to protect against hepatotoxicity, such as methionine or N-acetylcysteine, are not effective in preventing paracetamol-induced kidney damage. Only diethyldithiocarbamate, an inhibitor of microsomal monooxygenases, provided complete protection against both hepato- and nephrotoxicity. While a marked depletion of glutathione was observed in the liver, no such effect was seen in the kidney. These data suggest that the mechanism of paracetamol nephrotoxicity seems to be quite different from that responsible for the hepatotoxicity. The hypothesis that a C-S-lyase-mediated final metabolism of paracetamol-S conjugates in the kidney might be responsible for nephrotoxicity needs support by further experimental investigations.