LC-MS/MS determination of N-acetyl-l-cysteine in chicken plasma

N-acetyl-l-cysteine (NAC) shows beneficial effects in cases of aflatoxicosis and heat stress in poultry but little is known about its pharmacokinetics in chickens. Therefore, the study aimed to develop and validate a sensitive LC-MS/MS analytical method for quantitative analysis of NAC in chicken plasma. A split calibration curve approach was used for determination of NAC in chicken plasma. Standard curves for low (0.05-2.5 μg/ml) and high (2.5-100 μg/ml) ranges of concentrations were prepared. The standard curves for low (r2 = 0.9987) and high (r2 = 0.9899) concentrations were linear within the tested range. The limits of detection (LOD) and of quantification (LOQ) for the standard at low concentrations were 0.093 and 0.28 μg/ml, respectively. The accuracy was from 97.35 to 101.33%. The values of LOD and LOQ for the standard at high concentrations were 0.76 and 2.30 μg/ml, respectively. The accuracy was between 99.77 and 112.14%. The intra- and inter-day precisions for all concentrations from both standards did not exceed 8.57% and 10.69%, respectively. The recovery for all concentrations was between 92.45 and 105.52%. The validated method for determination of NAC in chicken plasma can be applied in future pharmacokinetic studies in chickens without dilution of samples and their repeated analysis.

Acrolein but not its metabolite, 3-Hydroxypropylmercapturic acid (3HPMA), activates vascular transient receptor potential Ankyrin-1 (TRPA1): Physiological to toxicological implications

Acrolein, an electrophilic α,β-unsaturated aldehyde, is present in foods and beverages, and is a product of incomplete combustion, and thus, reaches high ppm levels in tobacco smoke and structural fires. Exposure to acrolein is linked with cardiopulmonary toxicity and cardiovascular disease risk. The hypothesis of this study is the direct effects of acrolein in isolated murine blood vessels (aorta and superior mesenteric artery, SMA) are transient receptor potential ankyrin-1 (TRPA1) dependent. Using isometric myography, isolated aorta and SMA were exposed to increasing levels of acrolein. Acrolein inhibited phenylephrine (PE)-induced contractions (approximately 90%) in aorta and SMA of male and female mice in a concentration-dependent (0.01-100 μM) manner. The major metabolite of acrolein, 3-hydroxypropylmercapturic acid (3HPMA), also relaxed PE-precontracted SMA. As the SMA was 20× more sensitive to acrolein than aorta (SMA EC50 0.8 ± 0.2 μM; aorta EC50 > 29.4 ± 4.4 μM), the mechanisms of acrolein-induced relaxation were studied in SMA. The potency of acrolein-induced relaxation was inhibited significantly by: 1) mechanically-impaired endothelium; 2) Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME); 3) guanylyl cyclase (GC) inhibitor (ODQ); and, 4) a TRPA1 antagonist (A967079). TRPA1 positive immunofluorescence was present in the endothelium. Compared with other known TRPA1 agonists, including allyl isothiocyanate (AITC), cinnamaldehyde, crotonaldehyde, and formaldehyde, acrolein stimulated a more potent TRPA1-dependent relaxation. Acrolein, at high concentration [100 μM], induced tension oscillations (spasms) independent of TRPA1 in precontracted SMA but not in aorta. In conclusion, acrolein is vasorelaxant at low levels (physiological) yet vasotoxic at high levels (toxicological).

Antioxidants other than vitamin C may be detected by glucose meters: Immediate relevance for patients with disorders targeted by antioxidant therapies

Owing to their ease of use, glucose meters are frequently used in research and medicine. However, little is known of whether other non-glucose molecules, besides vitamin C, interfere with glucometry. Therefore, we sought to determine whether other antioxidants might behave like vitamin C in causing falsely elevated blood glucose levels, potentially exposing patients to glycemic mismanagement by being administered harmful doses of glucose-lowering drugs. To determine whether various antioxidants can be detected by seven commercial glucose meters, human blood samples were spiked with various antioxidants ex vivo and their effect on the glucose results were assessed by Parkes error grid analysis. Several of the glucose meters demonstrated a positive bias in the glucose measurement of blood samples spiked with vitamin C, N-acetylcysteine, and glutathione. With the most interference-sensitive glucose meter, non-blood solutions of 1 mmol/L N-acetylcysteine, glutathione, cysteine, vitamin C, dihydrolipoate, and dithiothreitol mimicked the results seen on that glucose meter for 0.7, 1.0, 1.2, 2.6, 3.7 and 5.5 mmol/L glucose solutions, respectively. Glucose meter users should be alerted that some of these devices might produce spurious glucose results not only in patients on vitamin C therapy but also in those being administered other antioxidants. As discussed herein, the clinical relevance of the data is immediate in view of the current use of antioxidant therapies for disorders such as the metabolic syndrome, diabetes, cardiovascular diseases, and coronavirus disease 2019.

The acute effect of metabolic cofactor supplementation: a potential therapeutic strategy against non-alcoholic fatty liver disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) continues to increase dramatically, and there is no approved medication for its treatment. Recently, we predicted the underlying molecular mechanisms involved in the progression of NAFLD using network analysis and identified metabolic cofactors that might be beneficial as supplements to decrease human liver fat. Here, we first assessed the tolerability of the combined metabolic cofactors including l-serine, N-acetyl-l-cysteine (NAC), nicotinamide riboside (NR), and l-carnitine by performing a 7-day rat toxicology study. Second, we performed a human calibration study by supplementing combined metabolic cofactors and a control study to study the kinetics of these metabolites in the plasma of healthy subjects with and without supplementation. We measured clinical parameters and observed no immediate side effects. Next, we generated plasma metabolomics and inflammatory protein markers data to reveal the acute changes associated with the supplementation of the metabolic cofactors. We also integrated metabolomics data using personalized genome-scale metabolic modeling and observed that such supplementation significantly affects the global human lipid, amino acid, and antioxidant metabolism. Finally, we predicted blood concentrations of these compounds during daily long-term supplementation by generating an ordinary differential equation model and liver concentrations of serine by generating a pharmacokinetic model and finally adjusted the doses of individual metabolic cofactors for future human clinical trials.

Pharmacokinetic profile of N-acetylcysteine amide and its main metabolite in mice using new analytical method

N-acetylcysteine amide (NACA) is the amide derivative of N-acetylcysteine (NAC) that is rapidly converted to NAC after systemic administration. It has emerged as a promising thiol antioxidant for multiple indications; however, the pharmacokinetic property is yet unclear due to lack of an accurate quantification method. The present investigation aimed to develop an analytical method for simultaneous quantification of NACA and NAC in plasma. A new reagent (2-(methylsulfonyl)-5-phenyl-1,3,4-oxadiazole, MPOZ) was introduced for thiol stabilization during sample processing and storage. Further, we utilized tris (2-carboxyethyl) phosphine (TCEP) to reduce the oxidized forms of NACA and NAC. After derivatization, NACA-MPOZ and NAC-MPOZ were quantified using liquid chromatography-mass spectrometry (LC-MS). The new method was validated and found to have high specificity, linearity, accuracy, precision, and recovery for the quantification of NACA and NAC in plasma. Furthermore, the formed derivatives of NACA and NAC were stable for 48 h under different conditions. The method was utilized in pharmacokinetic study which showed that the bioavailability of NACA is significantly higher than NAC (67% and 15%, respectively). The pharmacokinetic of NACA obeyed a two-compartment open model. The glutathione (GSH)-replenishing capacity was found to be three to four-fold higher after the administration of NACA compared to that observed after the administration of NAC. In conclusion, the present method is simple, robust and reproducible, and can be utilized in both experimental and clinical studies. NACA might be considered as a prodrug for NAC. Furthermore, this is the first report describing the pharmacokinetics and bioavailability of NACA in mouse.

N-acetylcysteine use among patients undergoing cardiac surgery: A systematic review and meta-analysis of randomized trials

Background

Cardiac surgeries are complex procedures aiming to re-establish coronary flow and correct valvular defects. Oxidative stress, caused by inflammation and ischemia-reperfusion injury, is associated with these procedures, increasing the risk of adverse outcomes. N-acetylcysteine (NAC) acts as an antioxidant by replenishing the glutathione stores, and emerging evidence suggests that NAC may reduce the risk of adverse perioperative outcomes. We conducted a systematic review and meta-analysis to investigate the addition of NAC to a standard of care among adult patients undergoing cardiac surgery.

Methods

We searched four databases (PubMed, EMBASE, CENTRAL, LILACS) from inception to October 2018 and the grey literaure for randomized controlled trials (RCTs) investigating the effect of NAC on pre-defined outcomes including mortality, acute renal insufficiency (ARI), acute cardiac insufficiency (ACI), hospital length of stay (HLoS), intensive care unit length of stay (ICULoS), arrhythmia and acute myocardial infarction (AMI). Reviewers independently screened potentially eligible articles, extracted data and assessed the risk of bias among eligible articles. We used the GRADE approach to rate the overall certainty of evidence for each outcome.

Results

Twenty-nine RCTs including 2,486 participants proved eligible. Low to moderate certainty evidence demonstrated that the addition of NAC resulted in a non-statistically significant reduction in mortality (Risk Ratio (RR) 0.71; 95% Confidence Interval (CI) 0.40 to 1.25), ARI (RR 0.92; 95% CI 0.79 to 1.09), ACI (RR 0.77; 95% CI 0.44 to 1.38), HLoS (Mean Difference (MD) 0.21; 95% CI -0.64 to 0.23), ICULoS (MD -0.04; 95% CI -0.29 to 0.20), arrhythmia (RR 0.79; 95% CI 0.52 to 1.20), and AMI (RR 0.84; 95% CI 0.48 to 1.48).

Limitations

Among eligible trials, we observed heterogeneity in the population and interventions including patients with and without kidney dysfunction and interventions that differed in route of administration, dosage, and duration of treatment. This observed heterogeneity was not explained by our subgroup analyses.

Conclusions

The addition of NAC during cardiac surgery did not result in a statistically significant reduction in clinical outcomes. A large randomized placebo-controlled multi-centre trial is needed to determine whether NAC reduces mortality.

Registration

PROSPERO CRD42018091191.

Simultaneous detection of the tetrachloroethylene metabolites S-(1,2,2-trichlorovinyl) glutathione, S-(1,2,2-trichlorovinyl)-L-cysteine, and N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine in multiple mouse tissues via ultra-high performance liquid chromatography electrospray ionization tandem mass spectrometry

Tetrachloroethylene (perchloroethylene; PERC) is a high-production volume chemical and ubiquitous environmental contaminant that is hazardous to human health. Toxicity attributed to PERC is mediated through oxidative and glutathione (GSH) conjugation metabolites. The conjugation of PERC by glutathione-s-transferase to generate S-(1,2,2-trichlorovinyl) glutathione (TCVG), which is subsequently metabolized to form S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) is of special importance to human health. Specifically, TCVC may be metabolized to N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine (NAcTCVC) which is excreted through urine, or to electrophilic metabolites that are nephrotoxic and mutagenic. Little is known regarding toxicokinetics of TCVG, TCVC, and NAcTCVC as analytical methods for simultaneous determination of these metabolites in tissues have not yet been reported. Hence, an ultra-high-performance liquid chromatography electrospray ionization tandem mass spectrometry-based method was developed for analysis of TCVG, TCVC, and NAcTCVC in liver, kidneys, serum, and urine. The method is rapid, sensitive, robust, and selective for detection all three analytes in every tissue examined, with limits of detection (LOD) ranging from 1.8 to 68.2 femtomoles on column, depending on the analyte and tissue matrix. This method was applied to quantify levels of TCVG, TCVC, and NAcTCVC in tissues from mice treated with PERC (10 to 1000 mg/kg, orally) with limits of quantitation (LOQ) of 1-2.5 pmol/g in liver, 1-10 pmol/g in kidney, 1-2.5 pmol/ml in serum, and 2.5-5 pmol/ml in urine. This method is useful for further characterization of the GSH conjugative pathway of PERC in vivo and improved understanding of PERC toxicity.

Phase I randomized clinical trial of N-acetylcysteine in combination with an adjuvant probenecid for treatment of severe traumatic brain injury in children

Background

There are no therapies shown to improve outcome after severe traumatic brain injury (TBI) in humans, a leading cause of morbidity and mortality. We sought to verify brain exposure of the systemically administered antioxidant N-acetylcysteine (NAC) and the synergistic adjuvant probenecid, and identify adverse effects of this drug combination after severe TBI in children.

Methods

IRB-approved, randomized, double-blind, placebo controlled Phase I study in children 2 to 18 years-of-age admitted to a Pediatric Intensive Care Unit after severe TBI (Glasgow Coma Scale [GCS] score ≤8) requiring an externalized ventricular drain for measurement of intracranial pressure (ICP). Patients were recruited from November 2011-August 2013. Fourteen patients (n = 7/group) were randomly assigned after obtaining informed consent to receive probenecid (25 mg/kg load, then 10 mg/kg/dose q6h×11 doses) and NAC (140 mg/kg load, then 70 mg/kg/dose q4h×17 doses), or placebos via naso/orogastric tube. Serum and CSF samples were drawn pre-bolus and 1–96 h after randomization and drug concentrations were measured via UPLC-MS/MS. Glasgow Outcome Scale (GOS) score was assessed at 3 months.

Results

There were no adverse events attributable to drug treatment. One patient in the placebo group was withdrawn due to adverse effects. In the treatment group, NAC concentrations ranged from 16,977.3±2,212.3 to 16,786.1±3,285.3 in serum and from 269.3±113.0 to 467.9±262.7 ng/mL in CSF, at 24 to 72 h post-bolus, respectively; and probenecid concentrations ranged from 75.4.3±10.0 to 52.9±25.8 in serum and 5.4±1.0 to 4.6±2.1 μg/mL in CSF, at 24 to 72 h post-bolus, respectively (mean±SEM). Temperature, mean arterial pressure, ICP, use of ICP-directed therapies, surveillance serum brain injury biomarkers, and GOS at 3 months were not different between groups.

Conclusions

Treatment resulted in detectable concentrations of NAC and probenecid in CSF and was not associated with undesirable effects after TBI in children.

Trial registration

ClinicalTrials.gov NCT01322009

DNA damage and repair capacity in workers exposed to low concentrations of benzene

DNA damage and cellular repair capacity were studied in 18 male fuel tanker drivers and 13 male filling-station attendants exposed to low and very low concentrations of benzene, respectively, and compared to 20 males with no occupational exposure (controls). Exposure to airborne benzene was measured using passive personal samplers, and internal doses were assayed through the biomarkers t,t-muconic acid, S-phenylmercapturic acid and urinary benzene. DNA damage was evaluated using tail intensity (TI) determined by the comet assay in peripheral lymphocytes. Urinary 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) was measured as a biomarker of oxidative damage. DNA repair kinetics were assessed using the comet assay in lymphocytes sampled 20 and 60 min post H2O2 exposure. Benzene exposure differed significantly between the drivers (median 246.3 µg/m(3)), attendants (median 13.8 µg/m(3)), and controls (median 4.1 µg/m(3)). There were no differences in TI and 8-oxodG among the three groups, or between smokers and non-smokers. DNA repair kinetics were similar among the drivers, attendants and controls, although the comet assay on H2 O2 -damaged lymphocytes after 60 min revealed significantly lower levels of TI only in drivers. The DNA repair process in smokers was similar to that observed in drivers. In conclusion, this study found no relationship between low levels of benzene exposure and DNA damage, although there was evidence that exposure interferes with DNA repair kinetics. The biological impact of this finding on the onset of genotoxic effects in exposed workers has still to be ascertained.

N-Acetylcysteine inhibits platelet-monocyte conjugation in patients with type 2 diabetes with depleted intraplatelet glutathione: a randomised controlled trial

AIMS/HYPOTHESIS

The aim of this study was to determine whether oral dosing with N-acetylcysteine (NAC) increases intraplatelet levels of the antioxidant, glutathione (GSH), and reduces platelet-monocyte conjugation in blood from patients with type 2 diabetes.

METHODS

In this placebo-controlled randomised crossover study, the effect of oral NAC dosing on platelet-monocyte conjugation and intraplatelet GSH was investigated in patients with type 2 diabetes (eligibility criteria: men or post-menopausal women with well-controlled diabetes (HbA(1c) < 10%), not on aspirin or statins). Patients (n = 14; age range 43-79 years, HbA(1c) = 6.9 ± 0.9% [52.3 ± 10.3 mmol/mol]) visited the Highland Clinical Research Facility, Inverness, UK on day 0 and day 7 for each arm of the study. Blood was sampled before and 2 h after oral administration of placebo or NAC (1,200 mg) on day 0 and day 7. Patients received placebo or NAC capsules for once-daily dosing on the intervening days. The order of administration of NAC and placebo was allocated by a central office and all patients and research staff involved in the study were blinded to the allocation until after the study was complete and the data fully analysed. The primary outcome for the study was platelet-monocyte conjugation.

RESULTS

Oral NAC reduced platelet-monocyte conjugation (from 53.1 ± 4.5% to 42.5 ± 3.9%) at 2 h after administration and the effect was maintained after 7 days of dosing. Intraplatelet GSH was raised in individuals with depleted GSH and there was a negative correlation between baseline intraplatelet GSH and platelet-monocyte conjugation. There were no adverse events.

CONCLUSIONS/INTERPRETATION

The NAC-induced normalisation of intraplatelet GSH, coupled with a reduction in platelet-monocyte conjugation, suggests that NAC might help to reduce atherothrombotic risk in type 2 diabetes.

FUNDING

Chief Scientist Office (CZB/4/622), Scottish Funding Council, Highlands & Islands Enterprise and European Regional Development Fund.

TRIAL REGISTRATION

isrctn.org ISRCTN89304265.

Limited validity of o-cresol and benzylmercapturic acid in urine as biomarkers of occupational exposure to toluene at low levels

This study was initiated to evaluate o-cresol and benzylmercapturic acid in urine in comparison with other biomarkers, as tools to estimate the intensity of occupational exposure to toluene at low levels. In total, 108 solvent exposed workers (engaged in tape production) and 17 non-exposed controls (all men) participated in the study. The surveys were conducted in the second half of working weeks. Diffusive sampling was conducted to measure 8-h time-weighted average intensity of occupational exposure to toluene. Blood and urine samples were collected at the end of a working shift. Blood samples were subjected to analysis for toluene (Tol-B), and urine samples were analyzed for benzyl alcohol (BeOH-U), benzylmercapturic acid (BMA-U), o-cresol (o-CR-U), hippuric acid (HA-U) and toluene (Tol-U) by the methods previously described. The toluene concentrations in workplaces were low in general, with a geometric mean (GM) and the maximum concentration of 1.9 ppm and 8.8 ppm, respectively. The statistical analyses of the six biomarkers for correlation with air-borne toluene showed that both Tol-B and Tol-U gave a high correlation coefficient of 0.58 to 0.61 (p<0.01), whereas the coefficients for BeOH-U and BMA-U together with HA-U were all low (up to 0.22, depending on the correction for urine density) and statistically insignificant (p>0.10) in most cases. o-CR-U had an intermediary coefficient of 0.20 (p<0.05). Comparison with previous publications disclosed that BeOH-U, BMA-U and HA-U correlate with toluene in air when the exposure is intense (e.g., 50 ppm or above), but no longer proportional to air-borne toluene when the exposure is low, e.g., 2 ppm. Such appeared to be also the case for o-CR-U. In over-all evaluation, the validity of o-CR-U in monitoring occupational exposure to toluene at low levels (e.g., 2 ppm) appear to be limited, and BMA-U is not an appropriate biomarker. BeOH-U and HA-U are also inappropriate for this purpose. Only Tol-B and Tol-U may be employed to estimate toluene exposure at low levels.

Causal role of oxidative stress in liver preconditioning by thyroid hormone in rats

Hepatic ischemia-reperfusion (IR) injury, a major clinical drawback during surgery, is abolished by L-3,3',5-triiodothyronine (T(3)) administration. Considering that the triggering mechanisms are unknown, the aim of this study is to assess the role of oxidative stress in T(3) preconditioning using N-acetylcysteine (NAC) before T(3) administration. Male Sprague-Dawley rats given a single dose of 0.1 mg of T(3)/kg were subjected to 1 h ischemia followed by 20 h reperfusion, in groups of animals pretreated with 0.5 g of NAC/kg 0.5 h before T(3) or with the respective control vehicles. At the end of the reperfusion period, blood and liver samples were taken for analysis of serum aspartate aminotransferase (AST) and hepatic histology, glutathione (GSH) and protein carbonyl contents, and nuclear factor-kappaB (NF-kappaB) and activating protein 1 (AP-1) DNA binding. The IR protocol used led to a 4.5-fold increase in serum AST levels and drastic changes in liver histology, with significant GSH depletion and enhancement of protein carbonyl levels and of the protein carbonyl/GSH content ratio, whereas NF-kappaB and AP-1 DNA binding was decreased and enhanced, respectively. In a time window of 48 h, T(3) exerted protection against hepatic IR injury, with 88% reduction in the protein carbonyl/GSH ratio and normalization of NF-kappaB and AP-1 DNA binding, changes that were suppressed by NAC administration before T(3). Data presented suggest that a transient increase in the oxidative stress status of the liver is an important trigger for T(3) preconditioning, evidenced in a warm IR injury model through antioxidant intervention.

Randomised, double blind, placebo controlled trial of intravenous antioxidant (n-acetylcysteine, selenium, vitamin C) therapy in severe acute pancreatitis

BACKGROUND

Based on equivocal clinical data, intravenous antioxidant therapy has been used for the treatment of severe acute pancreatitis. To date there is no randomised comparison of this therapy in severe acute pancreatitis.

METHODS

We conducted a randomised, double blind, placebo controlled trial of intravenous antioxidant (n-acetylcysteine, selenium, vitamin C) therapy in patients with predicted severe acute pancreatitis. Forty-three patients were enrolled from three hospitals in the Manchester (UK) area over the period June 2001 to November 2004. Randomisation stratified for APACHE-II score and hospital site, and delivered groups that were similar at baseline.

RESULTS

Relative serum levels of antioxidants rose while markers of oxidative stress fell in the active treatment group during the course of the trial. However, at 7 days, there was no statistically significant difference in the primary end point, organ dysfunction (antioxidant vs placebo: 32% vs 17%, p = 0.33) or any secondary end point of organ dysfunction or patient outcome.

CONCLUSIONS

This study provides no evidence to justify continued use of n-acetylcysteine, selenium, vitamin C based antioxidant therapy in severe acute pancreatitis. In the context of any future trial design, careful consideration must be given to the risks raised by the greater trend towards adverse outcome in patients in the treatment arm of this study.

Cinnabaramides A-G: analogues of lactacystin and salinosporamide from a terrestrial streptomycete

The cinnabaramides A-G (1-7) were isolated from a terrestrial strain of Streptomyces as potent and selective inhibitors of the human 20S proteasome. Their chemical and biological properties resemble those of salinosporamide A, a recently identified lead compound from an obligate marine actinomycete, which is currently under development as an anticancer agent. Cinnabaramides F and G (6, 7) combine essential structural features of salinosporamide A and lactacystin and show about equal potency in vitro, with IC50 values in the 1 nM range. The properties and phylogenetic position of the producer organism, the production and isolation of compounds 1-7, their structure elucidation by MS and NMR, and their biological activities are reported. Additionally, an X-ray crystal structure was obtained from cinnabaramide A (1).

Are 4-hydroxy-2(E)-nonenal derived mercapturic acids and 1H NMR metabonomics potential biomarkers of chemically induced oxidative stress in the kidney?

Various markers derived from radical-mediated oxidative damage to cellular macromolecules have been proposed as tools for the detection of alterations in redox status, but there is strong debate as to which may be the most sensitive and reliable indicator of oxidative stress conditions. This study was aimed to investigate the use of mercapturic acids derived from conjugation of the lipid peroxidation product 4-hydroxy-2(E)-nonenal (HNE) with glutathione and (1)H NMR metabonomics in two rodent models of oxidative kidney damage. Treatment of rats with FeNTA resulted in a marked increase in the concentrations of 4-hydroxy-2(E)-nonenal derived mercapturic acids in plasma and kidney within 5h. 1,4-dihydroxynonenal mercapturic acid (DHN-MA) remained elevated 24h after compound administration, while other markers returned to control levels, suggesting that DHN-MA may present a more stable indicator of lipid peroxidation. However, significant changes were only evident in the presence of severe nephrotoxicity, indicating that HNE-derived mercapturic acids were less sensitive than nonspecific markers of renal injury. In contrast to FeNTA, continuous administration of potassium bromate for 2 weeks had no effect on the concentrations of DHN-MA or 4-hydroxyononenal-3-yl-mercapturic acid in kidney, plasma or urine of treated animals, although a dose-dependent increase in 8-oxo-7,8-dihydro-2'deoxyguanosine was observed in kidney DNA in the absence of nephrotoxicity. These data suggest that markers of lipid peroxidation may not be suitable to detect alterations in redox status induced by potassium bromate at doses known to cause tumors after chronic treatment. Alterations in urine (1)H NMR spectra were detected in both models but reflect nonspecific alterations as a result of impaired renal function rather than specific changes indicative of oxidative stress. In summary, it appears that - depending on the pathological circumstances and the chemical nature of the insult - different types of oxidative stress exist, and it is therefore not possible to define a universal marker of oxidative stress.

Quantitative measurement of sulforaphane, iberin and their mercapturic acid pathway metabolites in human plasma and urine using liquid chromatography-tandem electrospray ionisation mass spectrometry

A quantitative liquid chromatography positive ion electrospray tandem mass spectrometric method for the simultaneous determination of sulforaphane, iberin and their metabolites in human urine and plasma is described. The stability of the metabolites was determined in aqueous solution and in human plasma. Gradient liquid chromatographic separation was performed on a Zorbax SB-Aq 3.5 microm (100 x 2.1mm) column, using a mobile phase (flow rate 0.25 mL/min) consisting of ammonium acetate buffer at pH 4 and acetonitrile. Butyl thiocarbamoyl l-cysteine was used as internal standard. The assay was linear (r(2)>0.99) over the range of 0.03-300 microM in urine and 0.03-15 microM in plasma with intra- and inter-day assay precision (<10% CV) and accuracy (<20%). The lower limits of quantitation were in the range of 10-150 nmol/L. The method has been used to report, for the first time, individual quantitative measurement of each of the mercapturic acid pathway metabolites of sulforaphane and iberin in both human plasma and urine following a dietary study of broccoli consumption.

Oxygen radicals and matrix metalloproteinases mediate reperfusion liver injury

Many pathological processes involve the breakdown and remodeling of the extracellular matrix, which is mediated by the family of important enzymes known as matrix metalloproteinases (MMPs). One such process is warm ischemia/reperfusion (I/R) injury, the most important cause of dysfunction of liver allografts. We monitored protein expression of MMP-9 by Western blotting in rat liver after I/R. We also monitored changes in total MMP activity in the serum before and after I/R. Ischemia was induced by clamping the common hepatic artery and portal vein for 40 minutes and reperfusing for 90 minutes. Blood samples collected before ischemia and after reperfusion were analyzed for AST, hydroxyl radical, and tumor necrosis factor (TNFalpha). This protocol resulted in a high level of MMP-9 expression in liver tissue. Total MMP activity in serum was also significantly increased. Levels of AST, hydroxyl radicals, and TNF alpha were concomitantly increased. Ilomastat, an MMP inhibitor, attenuated the I/R-induced liver injury. After administration of the oxygen radical scavenger N-acetylcysteine (NAC), total MMP activity was suppressed, and liver injury was again attenuated. These results indicated that reperfusion liver injury induced an increase in MMP-9 protein expression and in serum MMP activity. The protective effects of an MMP inhibitor and NAC indicate that oxygen radical production is involved in MMP expression and liver injury associated with I/R.

Pharmacokinetics of intravenous N-acetylcysteine in men at rest and during exercise

OBJECTIVE

We aimed to determine the pharmacokinetics (PK) of N-acetylcysteine (NAC) at rest and during exercise when given by continuous intravenous infusion intended to maintain relatively constant plasma concentrations.

METHODS

Plasma concentrations of NAC were measured in 24 healthy male subjects during and after a two-stage intravenous infusion designed to provide constant NAC concentrations during cycling exercise, including intense exercise to fatigue.

RESULTS

A three-compartment, open PK model was the best fit using population PK analysis with NONMEM. Whole-body clearance (CL) was 0.58 l kg(-1) h(-1) (95% CI 0.44-0.72) for reduced NAC (NACR) and 0.16 (0.13-0.20) l kg(-1) h(-1) for total NAC (NACT). The central volume of distribution (V1) was 0.064 (0.008-0.12) l kg(-1) for NACR and 0.037 (0.02-0.06) l kg(-1) for NACT. Exercise was a significant covariate in the model, resulting in a 25 and 23% reduction in CL of NACR and NACT, respectively. V1 in our subjects was smaller than expected, resulting in higher-than-anticipated initial concentrations of NAC. Despite these findings, the incidence of adverse effects attributable to NAC was minimal without using prophylactic or concomitant drug therapy.

CONCLUSIONS

NAC can be given to healthy exercising men by intravenous infusion and to the plasma concentrations seen in this study with minimal adverse effects due to the drug. The PK parameters of NAC at rest in volunteers are consistent with previously reported values and are significantly altered by vigorous cycling exercise.

Doctors and Nurses Estimation of the Weight of Patients: A Preventable Source of Systematic Error

BACKGROUND

Although accurate determination of body weight is important in the management of the poisoned patient, many patients have their weight estimated rather than formally measured.

OBJECTIVE

To determine how good medical staff are at estimating patients*** body weights.

METHODS

Medical staff were asked to estimate the weight of six patients on a poisons ward. Estimated and actual patient weights were statistically compared.

RESULTS

Medical staff produced a large range of estimated weights for all patients. Patient weight was incorrectly estimated by greater than 10% in 61% of individual estimations. There was poor statistical correlation between actual and estimated weight.

CONCLUSIONS

All patients administered medication based on body weight and those treated following an overdose of any substance should have formal body weight determined as part of their standard management.

Does Oxidative Stress Alter Quadriceps Endurance in Chronic Obstructive Pulmonary Disease?

The role of exercise-induced oxidative stress in the reduced quadriceps endurance of chronic obstructive pulmonary disease (COPD) patients has never been shown. We conducted a randomized, double-blind, and crossover study in which nine severe patients performed localized dynamic quadriceps endurance tests at 40% of maximal strength after oral treatment with the antioxidant, N-acetylcysteine (NAC), and placebo. Venous blood was sampled before, immediately after exercise, and 6 hours later. Endurance time improved by 25% after NAC treatment compared with placebo (p < 0.05). Superoxide anion (oxidant) release by stimulated phagocytes decreased after treatment (p < 0.05). No change in the antioxidant system was observed. Lipid peroxidation, an index of oxidative stress, was significantly increased 6 hours after exercise in the placebo condition (p < 0.05) but not after treatment. Advanced oxidized protein products, another index of oxidative stress, were also increased 6 hours after exercise by 139 +/- 27% in the placebo condition but only by 54 +/- 19% after treatment (p < 0.05). This study shows that NAC treatment in COPD reduced basal disturbance in the prooxidant system, improved endurance time, and prevented exercise-induced oxidative stress. Oxidative stress thus seems to be implicated in the reduced quadriceps endurance of patients with COPD.

Biological monitoring in occupational exposure to low levels of 1,3-butadiene

Exposure to 1,3-butadiene (BD), a probable carcinogen to humans, was investigated in two groups of subjects working in a petrochemical plant where BD is produced and used to prepare polymers: 42 occupationally exposed workers and 43 internal non-occupationally exposed controls. BD personal exposure was very low but significantly different in the two groups (median airborne BD 1.5 and 0.4 microg/m(3) in exposed and controls, respectively). Similarly, BD in blood and urine, but not in exhaled air, was higher in the exposed workers than in controls (blood BD 3.7 ng/l versus <1.8 ng/l, urinary BD 2.4 ng/l versus <1.0 ng/l). These three biomarkers correlated significantly with personal exposure ( 0.283 < or = Pearson's r < or = 0.383) and between them (0.780 < or = r < or = 0.896). Excretion of urinary mercapturic acids N-acetyl-S-(3,4-hydroxybutyl)-l-cysteine (MI), N-acetyl-S-(1-hydroxymethyl-2-propenyl)-l-cysteine and N-acetyl-S-(2-hydroxy-3-butenyl)-l-cysteine (MII), chromosomal aberrations (CA), and sister chromatid exchanges (SCE) in peripheral blood lymphocytes were not influenced by occupational exposure. Our results show that unmetabolised BD in biological fluids, and particularly urinary BD, represents the biomarker of choice for assessing occupational exposure to low airborne concentrations of BD.

Creatine kinase activity in amyotrophic lateral sclerosis patients

The aim of this study was to investigate creatine kinase (CK) in the serum of amyotrophic lateral sclerosis (ALS) patients. Previous investigations have shown an increased CK activity in ALS patients and this has been suggested to be an indicator of patients survival. The study was conducted at the Department of Neurology, University School of Medicine in Lublin. Thirty ALS patients took part in the study. The average duration of the disease was 17 months. Serum CK levels were measured by the enzymatic method with N-acethylcysteine. CK was elevated in 43.3% of the ALS patients. There were no significant differences in the serum CK level between the groups of the ALS patients depending on age, sex, duration of the disease, or clinical condition of patients. The CK level was significantly higher in the serum of the patients with a limb onset than in patients with a bulbar onset of ALS. Our study confirmed the increase in the serum CK activity in ALS patients. CK activity depends on a limb onset or a bulbar onset of ALS, but not on the duration of the disease and the severity of the clinical condition.

Effects of N-acetylcysteine on dense cell formation in sickle cell disease

The extent to which dense and irreversible sickle cells (ISCs) contribute to vaso-occlusive episodes in sickle cell disease remains unclear. N-Acetylcysteine (NAC) inhibits dense cell and ISC formation in sickle erythrocytes in vitro and restores glutathione levels toward normal. A phase II double-blind randomized clinical trial was completed to determine the efficacy of NAC in decreasing dense cell and ISC formation, and vaso-occlusive episodes in sickle cell disease. Twenty-one subjects with a history of at least two vaso-occlusive episodes per year and 6% dense cells were enrolled. Four treatment groups were analyzed; NAC at a dose of 2,400 mg per day decreased the percent dense cells from 20.1 +/- 2.9 to 12.6 +/- 2.1 (P < 0.05) and increased red cell glutathione levels from 292.8 +/- 74.5 to 576.7 +/- 155.1 (P < 0.05). In addition, we observed a decrease in vaso-occlusive episodes from 0.03 to 0.006 episodes per person-days and a decreased in relative risk to R = 0.39. Although NAC did not significantly decrease the number of ISCs, there was a downward trend at all doses tested. In summary, NAC inhibited dense cell formation, restored glutathione levels toward normal, and decreased vaso-occlusive episodes at a well-tolerated dose of 2,400 mg per day. To determine the long-term efficacy and safety of NAC, a multicenter phase III clinical trial is required.

N-acetylcysteine infusion alters blood redox status but not time to fatigue during intense exercise in humans

Infusion of the antioxidant N-acetylcysteine (NAC) reduces fatigability in electrically evoked human muscle contraction, but due to reported adverse reactions, no studies have investigated NAC infusion effects during voluntary exercise in humans. We investigated whether a modified NAC-infusion protocol (125 mg. kg(-1). h(-1) for 15 min, then 25 mg. kg(-1). h(-1)) altered blood redox status and enhanced performance during intense, intermittent exercise. Eight untrained men participated in a counterbalanced, double-blind, crossover study in which they received NAC or saline (control) before and during cycling exercise, which comprised three 45-s bouts and a fourth bout that continued to fatigue, at 130% peak oxygen consumption. Arterialized venous blood was analyzed for glutathione status, hematology, and plasma electrolytes. NAC infusion induced no severe adverse reactions. Exercise decreased the reduced glutathione (P < 0.005) and increased oxidized glutathione concentrations (P < 0.005); NAC attenuated both effects (P < 0.05). NAC increased the rise in plasma K(+) concentration-to-work ratio (P < 0.05), indicating impaired K(+) regulation, although time to fatigue was unchanged (NAC 102 +/- 45 s; saline 107 +/- 53 s). Thus NAC infusion altered blood redox status during intense, intermittent exercise but did not attenuate fatigue.

Kinetic analysis of covalent binding between N-acetyl-L-cysteine and albumin through the formation of mixed disulfides in human and rat serum in vitro

PURPOSE

Covalent binding between N-acetyl-L-cysteine (NAC) and albumin was evaluated kinetically by conducting in vitro experiments.

METHOD

After 14C-NAC was incubated with human or rat serum, the solution was analyzed by anion-exchange HPLC. The albumin-bound 14C-NAC was quantified by measuring the radioactivity in the albumin fraction.

RESULTS

Ultraviolet chromatograms and/or radiochromatograms indicated the presence of a stable covalent bond between 14C-NAC and either human or rat albumin. By analyzing the time dependence of this protein binding in serum, the first-order binding and dissociation rate constants (k(on) and k(off) were obtained. The serum was treated in a CO2 incubator to avoid oxidative interference, and the initial rates were determined separately. The k(on) values obtained were 0.33 (h(-1)) and 0.48 (h(-1)) for human and rat serum, respectively. L-Cysteine was required to initiate the dissociation of 14C-NAC bound to albumin. Following the addition of appropriate amounts of L-cysteine, the k(off) values were determined to be 0.30-1.0 h(-1) and 0.54-1.4 h(-1) for human and rat serum, respectively.

CONCLUSIONS

The k(on) and k(off) values obtained for rat serum were in good agreement with the in vivo plasma protein binding kinetics of NAC in rats, indicating the reliability of this in vitro method for evaluating protein binding. No species differences in protein binding kinetics were found between human and rat serum.

In vivo kinetic analysis of covalent binding between N-acetyl-L-cysteine and plasma protein through the formation of mixed disulfide in rats

PURPOSE

This investigation was undertaken to study the relationship between plasma drug clearance and covalent protein-binding kinetics of N-acetyl-L-cysteine (NAC).

METHODS

NAC was intravenously administered to rats via a bolus injection or continuous infusion. Plasma concentrations of protein-unbound and total NAC were analyzed using a compartment model, taking into consideration of the protein binding process, and the apparent first-order binding and dissociation rate constants (kon and koff) were obtained.

RESULTS

Plasma total NAC after a bolus injection showed biphasic elimination with an inflection point at 1 hr. After 1 hr, NAC was largely present in the covalent protein-bound form. During the steady state of the infusion, approximately 30%-40% of plasma NAC bound with protein covalently. The kon, koff, and the elimination rate constant of protein-unbound drug (ke) were 0.23, 0.57, and 4.3 hr(-1). The dissociation half-life of NAC from protein estimated from koff was in agreement with the elimination half-life of plasma total NAC. This suggests that the dissociation of NAC from protein rate-limited the drug elimination in plasma (koff < ke).

CONCLUSION

We demonstrated that plasma total drug clearance is kinetically limited by covalent protein binding. The compartmental model described here is useful for analyzing its kinetics in vivo.

N-acetyl-L-cysteine exerts direct anti-aggregating effect on human platelets

BACKGROUND

N-acetyl-L-cysteine, a thiol compound, has been shown to potentiate the inhibition of platelet aggregation exerted by organic nitrates and to increase the anti-aggregating effect of L-arginine, which promotes endogenous synthesis of nitric oxide (NO) acting as substrate of platelet constitutive nitric oxide synthase (NOS). It is not known whether this thiol can exert direct effects on platelet aggregability.

MATERIALS AND METHODS

14 healthy male volunteers provided platelet samples to investigate whether N-acetyl-L-cysteine directly influences platelet function and intraplatelet levels of 3',5' cyclic guanosine monophosphate (cGMP), which represents the second messenger involved in NO-induced antiaggregation. Some experiments were repeated in the presence of NOS inhibitor NG-monomethyl-L-arginine (L-NMMA), of nitric oxide-sensitive guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), of the selective cGMP phosphodiesterase inhibitor zaprinast and of calcium ionophores (A23187, ionomycin).

RESULTS

N-acetyl-L-cysteine at 3000-6000 micromol L-1 decreases the responses of human platelets both in platelet-rich plasma (aggregation induced by adenosine 5-diphosphate) and in whole blood (aggregation induced by collagen). The anti-aggregating effect was prevented by preincubation with L-NMMA and guanylyl cyclase inhibitor ODQ. In resting platelets, N-acetyl-L-cysteine increased the levels of cGMP starting from a concentration of 3000 micromol L-1. Permeabilized platelets exhibited an increased sensitivity to the anti-aggregating effect of N-acetyl-L-cysteine. Also, cGMP phosphodiesterase inhibition or the increase in calcium availability, enhanced N-acetyl-L-cysteine effects on platelets.

CONCLUSION

N-acetyl-L-cysteine exerts direct anti-aggregating effects through an increased bioavailability of platelet nitric oxide.

Determination of reduced, protein-unbound, and total concentrations of N-acetyl-L-cysteine and L-cysteine in rat plasma by postcolumn ligand substitution high-performance liquid chromatography

A high-performance liquid chromatographic assay was developed for the quantitative determination of the sulfur-containing amino acids N-acetyl-L-cysteine (NAC) and L-cysteine (Cys) in rat plasma. The thiols were separated by reverse-phase ion-pair chromatography, and the column eluent was continuously mixed with an iodoplatinate-containing solution. The substitution of sulfur of the thiol compound with iodide was quantitatively determined by measuring changes in the absorption at 500 nm. The low-molecular-weight disulfides and mixed disulfide conjugates of thiols with proteins were entirely reduced to the original reduced compounds by dithiothreitol. By reducing these two types of disulfides separately during sample pretreatment, the reduced, protein-unbound, and total thiol concentrations could also be determined. Validation testing was performed, and no problems were encountered. The limit of detection was approximately 20 pmol of thiol on the column. The present method was used to measure the plasma concentrations of NAC and Cys in the rat after a bolus intravenous administration of NAC, focusing on disulfide formation. The binding of NAC to protein through mixed disulfide formation proceeds in a time-dependent and reversible manner. Moreover, this "stable" covalent binding might limit total drug elimination, while the unbound NAC is rapidly eliminated. Consequently, the analytical method described in this study is very useful for the determination of plasma NAC and Cys, including disulfide conjugates derived from them.

Stability of thioTEPA and its metabolites, TEPA, monochloroTEPA and thioTEPA-mercapturate, in plasma and urine

The degradation of N,N',N"-triethylenethiophosphoramide (thioTEPA) and its metabolites N,N',N"-triethylenephosphoramide (TEPA), N, N'-diethylene,N"-2-chloroethylphosphoramide (monochloroTEPA) and thioTEPA-mercapturate in plasma and urine has been investigated. ThioTEPA, TEPA and monochloroTEPA were analyzed using a gas chromatographic (GC) system with selective nitrogen/phosphorous detection; thioTEPA-mercapturate was analyzed on a liquid chromatography-mass spectrometric (LC-MS) system. The influences of pH and temperature on the stability of thioTEPA and its metabolites were studied. An increase in degradation rate was observed with decreasing pH as measured for all studied metabolites. In urine the rate of degradation at 37 degrees C was approximately 2.5+/-1 times higher than at 22 degrees C. At 37 degrees C thioTEPA and TEPA were more stable in plasma than in urine, with half lives ranging from 9-20 h for urine and 13-34 h for plasma at pH 6. Mono- and dichloro derivatives of thioTEPA were formed in urine and the monochloro derivative was found in plasma. Degradation of TEPA in plasma and urine resulted in the formation of monochloroTEPA. During the degradation of TEPA in plasma also the methoxy derivative of TEPA was formed as a consequence of the applied procedure. The monochloro derivative of thioTEPA-mercapturate was formed in urine, whereas for monochloroTEPA no degradation products could be detected.

Determination of N-acetylcysteine in human plasma by liquid chromatography coupled to tandem mass spectrometry

An analytical method for the determination of total N-acetylcysteine in human plasma has been developed, validated and applied to the analysis of samples from a phase I clinical trial. The analytical method consists of plasma digestion with dithiothreitol in order to reduce all the oxidized forms of N-acetylcysteine, and extraction with ethyl acetate followed by determination of levels by an LC-MS-MS method. The intra- and inter-assay precision and accuracy of this technique were good and the limit of quantitation was 50 ng/ml of plasma. The concentration working range was established between 50 ng/ml and 1000 ng/ml. This method has been used in the analysis of approximately 800 human plasma samples from a clinical study with 24 volunteers; the precision of the quality controls was in the range 8.7 to 13.4% and the accuracy was in the range -5.9 to 8.5%, expressed as the RSD and the relative error, respectively.

Serum and lung levels of thiamphenicol after administration of its glycinate N-acetylcysteinate ester in experimentally infected guinea pigs

Thiamphenicol is an analogue of chloramphenicol and is characterised by a broad spectrum of action. In this study, serum and lung levels of thiamphenicol (TAP) were studied in infected guinea pigs after the administration of thiamphenicol glycinate N-acetylcysteinate (TGA). Animals received a single dose of TGA (15 mg/kg, subcutaneously) immediately after intra-tracheal infection with Haemophilus influenzae (about 10(7) CFU/animal). Serum and lung concentrations of TAP were determined at 0, 1, 3, 6, 12 and 24 h after drug administration by means of HPLC. TAP serum levels were elevated at 1 h and remained detectable for 24 h after drug administration. Tissue lung levels were comparable to peak serum concentrations but remained higher and decreased more slowly than serum concentrations.

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.

Pharmacokinetics of intravenous N-acetylcysteine in pre-term new-born infants

BACKGROUND

Reactive oxygen species have been considered to play a role in several clinical complications in pre-term infants. The aim of this study was to determine the pharmacokinetics of intravenous N-acetylcysteine in pre-term neonates. This information is needed to evaluate the use of N-acetylcysteine as an antioxidant in this patient group.

METHODS

N-acetylcysteine was infused intravenously in ten patients (gestational age 24.9-31.0 weeks, weight 500-1384 g) for 24 h (3.4-4.6 mg/kg/h), starting 2.0-11.2 h from birth (study I) and in six patients (gestational age 25.9-29.7 weeks, weight 520-1335 g) for 6 days (0.3-1.3 mg/kg/h), starting at the age of 24 h (study II). Arterial plasma N-acetylcysteine and cyst(e)ine concentrations were determined from timed samples taken during (study I and II) and after (study I) the N-acetylcysteine infusion.

RESULTS

In study I, the mean elimination half-life of N-acetylcysteine was 11 h (range 7.8-15.2 h). The mean plasma clearance of N-acetylcysteine was 37 ml/kg/h (range 13-62 ml/kg/h) and the mean volume of distribution was 573 ml/kg (range 167-1010 ml/kg). The plasma clearance and volume of distribution correlated with weight (r = 0.81, P < 0.01, and r = 0.78, P < 0.01, respectively) and with gestational age (r = 0.71, P < 0.05, and r = 0.64, P < 0.05, respectively). In study II, the steady-state concentration of N-acetylcysteine was reached in 2-3 days in five of six patients during a constant infusion.

CONCLUSIONS

The pharmacokinetics of N-acetylcysteine in pre-term infants depend markedly on weight and gestational age. The elimination of N-acetylcysteine is much slower in pre-term new-borns than in adults.

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.

[Blood levels of homocysteine by high pressure liquid chromatography and comparison with two other techniques]

Cardio-vascular diseases are the most common cause of death in industrialized countries. A new marker has emerged among offending risk factors in the past few years: homocysteine. This sulphured amino-acid is an important intermediate in transsulphuration and remethylation reactions of methionine's metabolism. We proposed to evaluate a home made method of determination for this parameter by high performance liquid chromatography (HPLC) and to compare it to fluorescence polarization immunoassay technique (FPIA) and to gaz phase chromatography (CG-SM). This method associated with good sensibility and precision remain much less expensive than FPIA technique.

Fates and vascular action of S-nitrosoglutathione and related compounds in the circulation

To know the metabolism of low-molecular-weight S-nitrosothiols (RS-NO) in the circulation, we analyzed the stability and depressor effects of S-nitrosoglutathione (GS-NO) and the l- and d-forms of S-nitrosocysteine (Cys-NO). Although half-lives of these RS-NO in fresh plasma were longer than 50 min, their depressor effects disappeared within 5 min after intravenous administration of these compounds. Acivicin (AT-125), an inhibitor of gamma-glutamyltransferase (gamma-GTP), prolonged the depressor effect of GS-NO but not of Cys-NO. The depressor effect of GS-NO disappeared in AT-125-treated rats within 10 min after administration, which is still shorter than its half-life in vitro. Although S-conjugates of l-cysteine, but not of d-cysteine, rapidly enter into cells via an active transport system and disappear from the circulation, both forms of Cys-NO exhibited similar activity to decrease blood pressure to that of NO. Thus, NO might be rapidly released from Cys-NO in the circulation and shortly exhibited its depressor action. These observations suggested that the circulating GS-NO is rapidly decomposed by gamma-GTP to form Cys-NO and that the release of NO from both GS-NO and Cys-NO is enhanced significantly in the circulation.

High-performance liquid chromatographic analysis of nitrite and nitrate in human plasma as S-nitroso-N-acetylcysteine with ultraviolet absorbance detection

A rapid HPLC method with UV absorbance detection at 333 nm for the measurement of nitrite and nitrate in ultrafiltrate samples of human plasma is described. The method is based on hydrochloric acid-catalyzed conversion of nitrite by N-acetyl-L-cysteine to S-nitroso-N-acetyl-L-cysteine and isocratic elution using 10 mM NaH2PO4 in acetonitrile-water, pH 2.0 (15:85, v/v). The limit of detection of the method is 50 nM nitrite. The method was validated by gas chromatography-mass spectrometry.

Efficient hepatic uptake and concentrative biliary excretion of a mercapturic acid

The role of the liver in the disposition of circulating mercapturic acids was examined in anesthetized rats and in the isolated perfused rat liver using S-2,4-dinitrophenyl-N-acetylcysteine (DNP-NAC) as the model compound. When DNP-NAC was infused into the jugular vein (150 or 600 nmol over 60 min) it was rapidly and nearly quantitatively excreted as DNP-NAC into bile (42-36% of the dose) and urine (48-62% of dose). Some minor metabolites were detected in bile (<4%), with the major metabolite coeluting on HPLC with the DNP conjugate of glutathione (DNP-SG). Isolated rat livers perfused single pass with 3 microM DNP-NAC removed 72 +/- 9% of this mercapturic acid from perfusate. This rapid DNP-NAC uptake was unaffected by sodium omission, or by L-cysteine, L-glutamate, L-cystine, or N-acetylated amino acids, but was decreased by inhibitors of hepatic sinusoidal organic anion transporters (oatp), indicating that DNP-NAC is a substrate for these transporters. The DNP-NAC removed from perfusate was promptly excreted into bile, eliciting a dose-dependent choleresis. DNP-NAC itself constituted approximately 75% of the total dose recovered in bile, reaching a concentration of 9 mM when livers were perfused in a recirculating mode with an initial DNP-NAC concentration of 250 microM. Other biliary metabolites included DNP-SG, DNP-cysteinylglycine, and DNP-cysteine. DNP-SG was likely formed by a spontaneous retro-Michael reaction between glutathione and DNP-NAC. Subsequent degradation of DNP-SG by biliary gamma-glutamyltranspeptidase and dipeptidase activities accounts for the cysteinylglycine and cysteine conjugates, respectively. These findings indicate the presence of efficient hepatic mechanisms for sinusoidal uptake and biliary excretion of circulating mercapturic acids in rat liver and demonstrate that the liver plays a role in their whole body elimination.

The effect of N-acetylcysteine on oxygen transport and uptake in patients with fulminant hepatic failure

We have investigated the effect of N-acetylcysteine on hemodynamic variables, oxygen delivery (DO2), oxygen consumption (VO2), and oxygen extraction in patients with fulminant hepatic failure using independent methods of determining DO2 and VO2, thereby eliminating the effect of mathematical coupling, which may have biased previous studies. In 11 patients with severe fulminant hepatic failure, we documented the hemodynamic effects of N-acetylcysteine during the first 5 hours of a standard infusion regime and simultaneously measured VO2 using a method based on respiratory gas analysis. We related physiological changes to plasma N-acetylcysteine concentrations, and compared this group with 7 patients who received placebo infusions. A variable hemodynamic response to N-acetylcysteine was observed that did not differ significantly in comparison with the placebo group, and did not correlate with plasma drug concentrations. The most significant relationship observed between DO2 and VO2 in any patient predicted a 13-mL x min(-1) x m(-2) increase in VO2 when DO2 increased by 100 mL x min(-1) x m(-2); in 8 patients, VO2 was independent of DO2 over the range observed. In the group that received N-acetylcysteine, a small (mean 6 [SD 6] mL x min(-1) x m[-2]) increase in VO2 occurred in comparison with baseline after 1 hour of infusion (P < .01), but changes were not significantly different from the placebo group and were not sustained. N-Acetylcysteine infusion did not increase oxygen extraction or result in an improvement in whole-blood lactate levels or base excess during the study period. We conclude that N-acetylcysteine infusion does not result in clinically relevant improvements in global VO2, or in clinical markers of tissue hypoxia in patients with severe fulminant hepatic failure.

Analysis of cysteine and N-acetylcysteine in human plasma by high-performance liquid chromatography at the basal state and after oral administration of N-acetylcysteine

A high-performance liquid chromatographic method for the determination of free reduced cysteine and N-acetylcysteine in human plasma at the basal state and after oral administration of N-acetylcysteine is described. The method is based on acid-catalysed conversion of plasma thiols to the corresponding S-nitroso derivatives by excess of nitrite and their subsequent cation-pairing RP-HPLC with detection at 333 nm. Recovery rates of cysteine and N-acetylcysteine added to human plasma were 94.6 and 99.6%, respectively. Inter- and intra-day precision were below 6%. In healthy humans (n = 5), free reduced cysteine was determined to be (mean+/-S.E.) 10.0+/-0.96 microM. No N-acetylcysteine was detected in plasma of these subjects above the limit of detection (e.g. 170 nM). The method was successfully applied to a pharmacokinetic study on orally administered N-acetylcysteine to healthy volunteers.

[Determination of total plasma homocysteine and other aminothiols by liquid chromatography coupled to the detection by fluorescence]

Plasma concentrations of homocysteine, cysteine, cysteinylglycine and glutathione were measured using a HPLC technique with fluorescence detection of the derivatives obtained with 7-fluoro-2,1,3-benzoxadiazole-4-sulfonamide (ABD-F). Blood was drawn into chilled EDTA-evacuated tubes. After centrifugation at 4 degrees C without delay, plasma samples were kept frozen at -20 degrees C until analysis. Reduction of protein bound aminothiols and disulfides standards was achieved with tri-n-butylphosphine. N-acetylcysteine was used as internal standard. After protein precipitation, derivatization was carried out at pH 8.0 and 50 degrees C for 20 min. Stability of ABD-thiols was ensured for at least 5 days by lowering pH to 2. Derivatives were separated by isocratic elution on a Waters mu Bondapak C18 column (10 microns, 3.9 x 300 mm) with 0.1 M phosphate buffer pH 3.2 containing 10% acetonitrile. Excitation and emission wavelengths were 385 and 515 nm. Retention times were 4.9, 5.8, 7.3, 9.9 and 20.1 min respectively for cysteine, cysteinylglycine, homocysteine, glutathione and N-acetylcysteine. Peaks were quantified by comparison to a standard curve prepared by plotting peak height versus the different levels of known standard solutions after normalization with internal standard. Between-run CVs varied from 5 to 8.5%. The detection limit was < 0.5 mumol/l for homocysteine and glutathione. In plasma samples from healthy subjects, concentration of homocysteine was higher in men than in women (11.0 +/- 2.9 versus 9.2 +/- 2.7 mumol/l, p < 0.01). These values are similar to those obtained with other widely used methods.

Oral N-acetylcysteine protects against perfluoroisobutene toxicity in rats

1. Perfluoroisobutene, a pyrolysis product of polyetrafluoroethene may cause pulmonary oedema and death when inhaled. Oral N-acetylcysteine has shown protection against inhalation of perfluoroisobutene and in this study we have tried to elucidate the mechanism by which protection is mediated. 2. Protection against the lethal effects of inhaled perfluoroisobutene has been shown when N-acetylcysteine has been orally administered 4, 6 or 8 h before gas exposure. 3. Plasma levels of cysteine, glutathione and N-acetylcysteine were increased for up to 7 h following oral administration of Nac. 4. N-acetylcysteine was not detected in the bronchioalveolar lavage fluid following oral administration. 5. Duration of protection in vivo has been related to the duration of increased thiol levels in the plasma.

Placental transfer of N-acetylcysteine following human maternal acetaminophen toxicity

OBJECTIVE

To determine whether the antidote for acetaminophen poisoning, N-acetylcysteine, administered to pregnant women with acetaminophen toxicity, crosses the placenta and can be measured in the newborn circulation following delivery.

DESIGN

Over a 15-month period, four pregnant women with acetaminophen toxicity, who delivered their infants while receiving the antidote N-acetylcysteine, were studied. Maternal and cord blood from three viable infants, and cardiac blood sampled during an autopsy on the fourth, were analyzed for the presence of N-acetylcysteine using high-performance liquid chromatography. Maternal and cord blood aminotransferase activities, and autopsy findings on the nonviable infant were used to assess hepatic injury.

RESULTS

N-Acetylcysteine was detected in the cord blood of three viable infants and in cardiac blood of a fourth, sampled at the time of autopsy. The mean N-acetylcysteine concentration in cord blood was 9.4 micrograms/mL (+/-1.3). This is well within the range associated with therapeutic doses of N-acetylcysteine typically administered to adults with acetaminophen poisoning. No adverse sequelae developed in the three viable infants. The fourth infant, delivered at 22 weeks gestational age died 3 h after birth. All mothers recovered and none of the four infants had evidence of acetaminophen-related toxicity.

CONCLUSIONS

This is the first study documenting placental transfer of N-acetylcysteine in humans and provides impetus for research establishing a direct antidotal effect of N-acetylcysteine in the fetus.

4-hydroxynonenal is degraded to mercapturic acid conjugate in rat kidney

The cytotoxic lipid peroxidation product 4-hydroxynonenal (HNE) was infused into rat kidney. During the first 2 min a rapid degradation of a 100 microM HNE solution was demonstrated. After 5 min the consumption rate of 4-HNE reached a steady state of about 75 nmoles/ml. The total HNE consumption rate was about 200 nmoles/g w.w./min. The excretion rate into urine was about 0.1% of total HNE consumption. It could be demonstrated that the HNE-mercapturic acid formation takes place in the kidney. The formation of the HNE-mercapturic acid contributes up to 6% to total HNE consumption. Within 10 min of perfusion 2% of the HNE-mercapturic acid were excreted into urine. The residual 98% flow back into the blood circulation.

[Biological monitoring of exposure to alkylating xenobiotics by determining them in complexes with plasma proteins, hemoglobin, mercapturic acids from urine of rats and industrial workers. I. Acrylonitrile]

A parent molecule of acrylonitrile (cyanoethylene, CE) may be isolated from its the model compound S-(2-cyanoethylene)-1-cysteine, as well as from its N-acetyl derivative and hemoglobin (Hb) and plasma proteins from the intoxicated animals and workers engaged in manufacturing synthetic rubber made from acrylonitrile. The developed procedure consists in the 1.5% H2O2 oxidation of a CE adduct for 30 min, followed by addition of a sample into the gas chromatographic injector at 250 degrees C, resulting in the release of CE from the adducts and in the current ingress of carrier gas into the capillary column in order to separate and determine with a FTD detector. There was a dose-response relationship between the formation of CE adducts with rat blood proteins, urinary mercapturic acids when the poison was given in a dose of 1-50 mg/kg. CE covalently bound to Hb was detected in the workers exposed to its monomer in working places.