Voltammetric measurement of entacapone in the presence of other medicines against Parkinson's disease by a screen-printed electrode modified with sulfur-tin oxide nanoparticles

A screen-printed electrode (SPE) is described modified with sulfur-tin oxide nanoparticles (S@SnO₂NP) for the determination of entacapone (ENT) in the presence of other medicines against Parkinson's disease (PD). The S@SnO₂NP was synthesized through the hydrothermal method and used in the modification of the SPE. The smart utilization of the S@SnO₂NP and the SPE provided excellent properties such as high surface area and current density amplification by embedding an efficient sensing interface for highly selective electrochemical measurement. Under optimized experimental conditions, the anodic peak current related to the ENT oxidation onto the sensor surface at 0.46 V presented a linear response towards different ENT concentration sin the range 100 nM to 75 μM. The limit of detection (LOD) and electrochemical sensitivity were estimated to be 0.010 μM and 2.27 μA·μM^-1·cm^-2, respectively. The applicability of the sensor was evaluated during ENT determination in the presence of other conventional medicines againts, including levodopa (LD), carbidopa (CD), and pramipexole (PPX). The results of the analysis of human urine and pharmaceutical formulation as real samples using the developed sensor were in good agreement withre sults of high-performance liquid chromatography (HPLC) as a standard method. These findings demonstrated that the strategy based on the SPE is a cost-effective platform creating a promising candidate for practical determination of ENT in routine clinical testing.Graphical abstract.

A novel method for the quantitation of gingerol glucuronides in human plasma or urine based on stable isotope dilution assays

The bio-active compounds of ginger (Zingiber officinale Roscoe), the gingerols, are gaining considerable attention due to their numerous beneficial health effects. In order to elucidate the physiological relevance of the ascribed effects their bioavailability has to be determined taking their metabolization into account. To quantitate in vivo generated [6]-, [8]- and [10]-gingerol glucuronides in human plasma and urine after ginger tea consumption, a simultaneous and direct liquid chromatography-tandem mass spectrometry method based on stable isotope dilution assays was established and validated. The respective references as well as the isotopically labeled substances were synthesized and characterized by mass spectrometry and NMR. Selective isolation of gingerol glucuronides from human plasma and urine by a mixed-phase anion-exchange SPE method led to recovery rates between 80.8 and 98.2%. LC-MS/MS analyses in selected reaction monitoring modus enabled a highly sensitive quantitation of gingerol glucuronides with LoQs between 3.9-9.8nmol/L in plasma and 39.3-161.1nmol/L in urine. The method precision in plasma and urine varied in the range±15%, whereas the intra-day accuracy in plasma and urine showed values between 78 and 122%. The developed method was then applied to a pilot study in which two volunteers consumed one liter ginger tea. Pharmacokinetic parameters like the maximum concentration (cmax), the time to reach cmax (tmax), area under the curve (AUC), elimination rate constant (kel) and elimination half-life (t1/2) were calculated from the concentration-time curve of each gingerol glucuronide. The obtained results will enable more detailed investigation of gingerol glucuronides as bioactives in their physiologically relevant concentrations.

[10]-Gingerdiols as the major metabolites of [10]-gingerol in zebrafish embryos and in humans and their hematopoietic effects in zebrafish embryos

Gingerols are a series of major constituents in fresh ginger with the most abundant being [6]-, [8]-, and [10]-gingerols (6G, 8G, and 10G). We previously found that ginger extract and its purified components, especially 10G, potentially stimulate both the primitive and definitive waves of hematopoiesis (blood cell formation) in zebrafish embryos. However, it is still unclear if the metabolites of 10G retain the efficacy of the parent compound toward pathological anemia treatment. In the present study, we first investigated the metabolism of 10G in zebrafish embryos and then explored the biotransformation of 10G in humans. Our results show that 10G was extensively metabolized in both zebrafish embryos and humans, in which two major metabolites, (3S,5S)-[10]-gingerdiol and (3R,5S)-[10]-gingerdiol, were identified by analysis of the MS(n) spectra and comparison to authentic standards that we synthesized. After 24 h of treatment of zebrafish embryos, 10G was mostly converted to its metabolites. Our results clearly indicate that the reductive pathway is a major metabolic route for 10G in both zebrafish embryos and humans. Furthermore, we investigated the hematopoietic effect of 10G and its two metabolites, which show similar hematopoietic effects as 10G in zebrafish embryos.

Characterization of thiol-conjugated metabolites of ginger components shogaols in mouse and human urine and modulation of the glutathione levels in cancer cells by [6]-shogaol

SCOPE

Shogaols, a series of major constituents in dried ginger with the most abundant being [6]-, [8]-, and [10]-shogaols, show much higher anticancer potencies than gingerols. Previously, we reported the mercapturic acid pathway as a major metabolic route for [6]-shogaol in mice. However, it is still unclear how the side chain length affects the metabolism of shogaols and how shogaols are metabolized in humans.

METHODS AND RESULTS

We first investigate the metabolism of [10]-shogaol in mouse urine, and then investigate the biotransformation of shogaols in human urine. Our results show that eight major thiol-conjugated metabolites of [10]-shogaol were detected in mouse urine, while six major thiol-conjugated metabolites of [6]-shogaol, two thiol-conjugated metabolites of [8]-shogaol, and two thiol-conjugated metabolites of [10]-shogaol were detected in urine collected from human after drinking ginger tea, using LC/ESI-MS/MS. Our results clearly indicate the mercapturic acid pathway is a major metabolic route for [10]-shogaol in mice and for shogaols in human. Furthermore, we also investigated the regulation of glutathione (GSH) by [6]-shogaol in human colon cancer cells HCT-116. Our results show [6]-shogaol, after initially depleting glutathione levels, can subsequently restore and increase GSH levels over time.

CONCLUSION

Shogaols are metabolized extensively in mouse and human to form thiol-conjugated metabolites and GSH might play an important role in the cancer-preventive activity of ginger.

H-point curve isolation method for determination of catechol in complex unknown mixtures

In this work, the combination of H-point curve isolation method (HPCIM) and H-point standard additions method (HPSAM) was used for determination of catechol in the presence of phenolic interferents. Spectrophotometric multivariate calibration data constructed by successive standard additions of an analyte in an unknown matrix was used by the method. A cumulative spectrum for interferents in sample was extracted by HPCIM and then HPSAM is used for determination of the catechol concentration by obtained cumulative interferents spectrum. The method was tested with simulated data set. The spectrum obtained from applying HPCIM to the simulated data well agrees with the cumulative spectra of the interferents. The method was applied to the determination of catechol in the presence of highly overlapping interferents in synthetic ternary mixtures using spectrophotometric data. Moreover, the proposed method was successfully used for determination of catechol in real complicated matrices of tea and urine samples. Percent recoveries were between 95.4 and 113.6.

Identification of phase II metabolites of thiol-conjugated [6]-shogaol in mouse urine using high-performance liquid chromatography tandem mass spectrometry

Ginger is frequently consumed as a spice and has numerous medicinal properties. Extensive research has characterized the anti-inflammatory, antioxidant, and antitumor activities of ginger. Previously, we reported the mercapturic acid pathway as a major metabolic route of [6]-shogaol in mice and the thiol conjugates of [6]-shogaol existed in the glucuronidated and sulfated forms in mouse urine. However, their structures are still unknown. In the present study, we further investigated the phase II metabolism of thiol-conjugated [6]-shogaol in mouse urine, in which we identified sixteen phase II metabolites of thiol-conjugated [6]-shogaol: 5-cysteinyl-[6]-shogaol glucuronide (9), 5-N-acetylcysteinyl-[6]-shogaol glucuronide (10), 5-cysteinylglycinyl-[6]-shogaol glucuronide (11), 5-methylthio-[6]-shogaol glucuronide (12), 5-cysteinyl-M6 glucuronide (13 and 14), 5-cysteinyl-M6 sulfate (15 and 16), 5-N-acetylcysteinyl-M6 glucuronide (17 and 18), 5-cysteinylglycinyl-M6 glucuronide (19 and 20), 5-cysteinylglycinyl-M6 sulfate (21 and 22), and 5-methylthio-M6 glucuronide (23 and 24) using liquid chromatography/electrospray ionization tandem mass spectrometry. The structures of these metabolites were confirmed by analyzing their MS(n) (n=1-4) spectra as well as comparing with the tandem mass spectra of authentic standards. To the best of our knowledge, this is the first report involving identification of phase II urinary metabolites of [6]-shogaol in mice.

Toxicological determination and in vitro metabolism of the designer drug methylenedioxypyrovalerone (MDPV) by gas chromatography/mass spectrometry and liquid chromatography/quadrupole time-of-flight mass spectrometry

A method for the toxicological screening of the new designer drug methylenedioxypyrovalerone (MDPV) is described; with an emphasis on its application for anti-doping analysis. The metabolism of MDPV was evaluated in vitro using human liver microsomes and S9 cellular fractions for CYP450 phase I and uridine 5'-diphosphoglucuronosyltransferase (UGT) and sulfotransferase (SULT) phase II metabolism studies. The resulting metabolites were subsequently liquid/liquid extracted and analyzed using gas chromatography/mass spectrometry (GC/MS) as trimethylsilyl (TMS) derivatives. The structures of the metabolites were further confirmed by accurate mass measurement using a liquid chromatography/quadrupole time-of-flight (LC/QTOF) mass spectrometer. The studies demonstrated that the main metabolites of MDPV are catechol and methyl catechol pyrovalerone, which are in turn sulfated and glucuronated. The method for the determination of MDPV in urine has been fully validated by assessing the limits of detection and quantification, linearity, repeatability, and accuracy. This validation demonstrates the suitability for screening of this stimulant substance for anti-doping and forensic toxicology purposes.

Pharmacokinetics of [6]-shogaol, a pungent ingredient of Zingiber officinale Roscoe (Part I)

To investigate the pharmacokinetics of [6]-shogaol, a pungent ingredient of Zingiber officinale Roscoe, the pharmacokinetic parameters were determined by using (14)C-[6]-shogaol (labeled compound) and [6]-shogaol (non-labeled compound). When the labeled compound was orally administered to rats, the maximum plasma concentration (C (max)) and the area under the curve (AUC) of plasma radioactivity concentration increased in a dose-dependent manner. When the labeled compound was orally administered at a dose of 10 mg/kg, 20.0 + or - 1.8% of the radioactivity administered was excreted into urine, 64.0 + or - 12.9% into feces, and 0.2 + or - 0.1% into breath. Thus, more of the radioactivity was excreted into feces than into urine, and almost no radioactivity was excreted into breath. Furthermore, when the labeled compound was orally administered at a dose of 10 mg/kg, cumulative biliary radioactivity excretion over 48 h was 78.5 + or - 4.5% of the radioactivity administered, and cumulative urinary radioactivity excretion over 48 h was 11.8 + or - 2.7%, showing that about 90% of the dose administered orally was absorbed from the digestive tract and most of the fecal excretion was via biliary excretion. On the other hand, when the non-labeled compound [6]-shogaol was orally administered, the plasma concentration and biliary excretion of the unchanged form were extremely low. When these results are combined with those obtained with the labeled compound, it would suggest that [6]-shogaol is mostly metabolized in the body and excreted as metabolites.

Human benzene metabolism following occupational and environmental exposures

We previously reported evidence that humans metabolize benzene via two enzymes, including a hitherto unrecognized high-affinity enzyme that was responsible for an estimated 73% of total urinary metabolites [sum of phenol (PH), hydroquinone (HQ), catechol (CA), E,E-muconic acid (MA), and S-phenylmercapturic acid (SPMA)] in nonsmoking females exposed to benzene at sub-saturating (ppb) air concentrations. Here, we used the same Michaelis-Menten-like kinetic models to individually analyze urinary levels of PH, HQ, CA and MA from 263 nonsmoking Chinese women (179 benzene-exposed workers and 84 control workers) with estimated benzene air concentrations ranging from less than 0.001-299 ppm. One model depicted benzene metabolism as a single enzymatic process (1-enzyme model) and the other as two enzymatic processes which competed for access to benzene (2-enzyme model). We evaluated model fits based upon the difference in values of Akaike's Information Criterion (DeltaAIC), and we gauged the weights of evidence favoring the two models based upon the associated Akaike weights and Evidence Ratios. For each metabolite, the 2-enzyme model provided a better fit than the 1-enzyme model with DeltaAIC values decreasing in the order 9.511 for MA, 7.379 for PH, 1.417 for CA, and 0.193 for HQ. The corresponding weights of evidence favoring the 2-enzyme model (Evidence Ratios) were: 116.2:1 for MA, 40.0:1 for PH, 2.0:1 for CA and 1.1:1 for HQ. These results indicate that our earlier findings from models of total metabolites were driven largely by MA, representing the ring-opening pathway, and by PH, representing the ring-hydroxylation pathway. The predicted percentage of benzene metabolized by the putative high-affinity enzyme at an air concentration of 0.001 ppm was 88% based upon urinary MA and was 80% based upon urinary PH. As benzene concentrations increased, the respective percentages of benzene metabolized to MA and PH by the high-affinity enzyme decreased successively to 66 and 77% at 0.1 ppm, 20 and 58% at 1 ppm, and 2.7 and 17% at 10 ppm. This indicates that the putative high-affinity enzyme was active primarily below 1 ppm and favored the ring-opening pathway.

Development of a stable isotope dilution analysis with liquid chromatography-tandem mass spectrometry detection for the quantitative analysis of di- and trihydroxybenzenes in foods and model systems

A straightforward stable isotope dilution analysis (SIDA) for the quantitative determination of the di- and trihydroxybenzenes catechol (1), pyrogallol (2), 3-methylcatechol (3), 4-methylcatechol (4), and 4-ethylcatechol (5) in foods by means of liquid chromatography-tandem mass spectrometry was developed. With or without sample preparation involving phenylboronyl solid phase extraction, the method allowed the quantification of the target compounds in complex matrices such as coffee beverages with quantification limits of 9 nmol/L for 4-ethylcatechol, 24 nmol/L for catechol, 3-methyl-, and 4-methylcatechol, and 31 nmol/L for pyrogallol. Recovery rates for the analytes ranged from 97 to 103%. Application of the developed SIDA to various commercial food samples showed that quantitative analysis of the target compounds is possible within 30 min and gave first quantitative data on the amounts of di- and trihydroxybenzenes in coffee beverage, coffee powder, coffee surrogate, beer, malt, roasted cocoa powder, bread crust, potato crisps, fruits, and cigarette smoke and human urine. Model precursor studies revealed the carbohydrate/amino acid systems as well as the plant polyphenols catechin and epicatechin as precursors of catechol and 5-O-caffeoylquinic acid, caffeic acid as a precursor of catechol and 4-ethylcatechol, and gallocatechin, epigallocatechin, and gallic acid as precursors of pyrogallol.

Angiotensin-II type 1 receptor-mediated hypertension in D4 dopamine receptor-deficient mice

Dopamine receptors are important in systemic blood pressure regulation. D4 receptors are expressed in the kidney and brain, but their role in cardiovascular regulation is unknown. In pentobarbital-anesthetized mice, systolic and diastolic blood pressures were elevated in sixth-generation D4 receptor-deficient (D4(-/-)) mice and in tenth-generation D4(-/-) mice compared with D4 wild-type (D4(+/+)) littermates. The conscious blood pressures measured via a chronic arterial (femoral) catheter or telemetry (carotid) were also higher in D4(-/-) mice than in D4 littermates. Basal renal and plasma renin concentrations were similar in the 2 mouse strains. The protein expression of angiotensin II type 1 receptor was increased in homogenates of kidney (330+/-53%, n=5) and brain (272+/-69%, n=5) of D4(-/-) mice relative to D4(+/+) mice (kidney: 100+/-12%, n=5; brain: 100+/-32%, n=5). The expression of the receptor in renal membrane was also increased in D4(-/-) mice (289+/-28%, n=8) relative to D4(+/+) mice (100+/-14%, n=10). In contrast, the expression in the heart was similar in the 2 strains. Bolus intravenous injection of angiotensin II type 1 receptor antagonist losartan initially decreased mean arterial pressures to a similar degree in D4(-/-) and D4(+/+) littermates. However, the hypotensive effect of losartan dissipated after 10 minutes in D4(+/+) mice, whereas the effect persisted for >45 minutes in D4(-/-) mice. We conclude that the absence of the D(4) receptor increases blood pressure, possibly via increased angiotensin II type 1 receptor expression.

Using urinary biomarkers to elucidate dose-related patterns of human benzene metabolism

Although the toxicity of benzene has been linked to its metabolism, the dose-related production of metabolites is not well understood in humans, particularly at low levels of exposure. We investigated unmetabolized benzene in urine (UBz) and all major urinary metabolites [phenol (PH), E,E-muconic acid (MA), hydroquinone (HQ) and catechol (CA)] as well as the minor metabolite, S-phenylmercapturic acid (SPMA), in 250 benzene-exposed workers and 139 control workers in Tianjin, China. Median levels of benzene exposure were approximately 1.2 p.p.m. for exposed workers (interquartile range: 0.53-3.34 p.p.m.) and 0.004 p.p.m. for control workers (interquartile range: 0.002-0.007 p.p.m.). (Exposures of control workers to benzene were predicted from levels of benzene in their urine.) Metabolite production was investigated among groups of 30 workers aggregated by their benzene exposures. We found that the urine concentration of each metabolite was consistently elevated when the group's median benzene exposure was at or above the following air concentrations: 0.2 p.p.m. for MA and SPMA, 0.5 p.p.m. for PH and HQ, and 2 p.p.m. for CA. Dose-related production of the four major metabolites and total metabolites (micromol/l/p.p.m. benzene) declined between 2.5 and 26-fold as group median benzene exposures increased between 0.027 and 15.4 p.p.m. Reductions in metabolite production were most pronounced for CA and PH<1 p.p.m., indicating that metabolism favored production of the toxic metabolites, HQ and MA, at low exposures.

Insulin enhances l-dopa renal proximal tubule uptake: a regulatory mechanism impaired in insulin resistance

A stimulatory role for insulin in the uptake of neutral amino acids has been reported for a variety of tissues. Here we examine the effect of insulin on L-dopa uptake by proximal tubule cells (PT cells) isolated from control and fructose-fed rats (FR-rats, 10% w/v fructose solution in tap water), a model of insulin resistance. Insulin (200 microU/ml) increased L-dopa uptake into PT cells by about 50% (705+/-186 vs.1117+/-140 pmol L-dopa/mg protein per minute) (p<0.05). The higher uptake correlated with a 40% increase in the number of high-affinity L-dopa transport sites (L-dopa 0.2 microM) (0.59+/-0.05 vs. 0.82+/-0.09 pmol L-dopa/mg protein per minute), without changing their affinity. The effect of insulin was not modified by ouabain (1 mM), nocodazole (1-10 microM) or colchicine (50-100 microM), whereas it was abolished by cytochalasin D or latrunculin B (both 1 microM). This suggests that the process is independent of Na(+),K(+)-ATPase activity or the microtubule network but that it requires the integrity of the actin cytoskeleton. L-dopa transport by the low-affinity transport sites (L-dopa 5 microM) was not affected by insulin, neither was the effect of insulin observed in PT cells isolated from FR-rats. In line with this, FR-rats showed lower renal L-dopa reabsorption as compared to control animals (81+/-4 vs. 51+/-9%). Taken together, our results support the involvement of insulin in the multifactorial regulation of renal L-dopa reabsorption.

Use of stable isotopically labeled benzene to evaluate environmental exposures

The use of stable, isotopically labeled compounds in controlled exposure experiments at environmentally relevant levels allows for the distinguishing of urinary metabolites associated with known exposure from background levels generally present in the urine. Exposures of volunteers to (13)C-benzene for 2 h at 40+/-10 p.p.b. were conducted after obtaining informed consent, and urinary phenol, catechol, hydroquinone and trans,trans- muconic acid were measured. Each isotopically labeled urinary metabolite was determined in the presence of significantly higher concentrations of the unlabeled metabolite. Following exposure, free and acid hydrolyzed phenol, acid hydrolyzed catechol and hydroquinone, and free trans,trans-muconic acid were determined by GC/MS. The percentage of trans,trans-muconic acid excreted was higher than reported following exposure at occupational levels. The use of isotopically labeled compounds has the potential to investigate the metabolism of common environmental contaminants for validation of toxicokinetic models and improve risk extrapolation from high concentration occupational exposures and animal studies to environmentally relevant pollutant levels.

In vitro formation of quinoid metabolites of the dietary supplement Cimicifuga racemosa (black cohosh)

Botanical dietary supplements containing Cimicifuga racemosa (Actaea racemosa; black cohosh) are used commonly by women to assuage menopausal symptoms including hot flashes and sleep disorders. Despite the popularity of such supplements, little is known about the metabolism or possible toxicity of many compounds that could be concentrated therein. The aim of this study was to selectively identify phase I metabolites resulting from metabolic bioactivation of constituents of black cohosh in vitro and to determine whether evidence of such metabolites could be found in the urine of perimenopausal women taking black cohosh oral supplements. A variation of an ultrafiltration mass spectrometric assay devised previously was used to screen an extract of black cohosh for the formation of electrophilic phase I metabolites that had been trapped as GSH conjugates. Mercapturates (N-acetylcysteine conjugates) corresponding to the GSH conjugates identified during screening were synthesized and characterized using LC-MS/MS with product-ion scanning. During a phase I clinical trial of black cohosh in perimenopausal women, urine was collected from seven subjects, each of whom took a single oral dose of either 32, 64, or 128 mg of the black cohosh extract. These urine samples were analyzed for the presence of mercapturate conjugates using positive-ion electrospray LC-MS and LC-MS/MS. On the basis of their propensity to form GSH adducts following metabolic activation by hepatic microsomes and NADPH in vitro, a total of eight electrophilic metabolites of black cohosh were detected, including quinoid metabolites of fukinolic acid, fukiic acid, caffeic acid, and cimiracemate B. Additional quinoid metabolites were formed from hydroxytyrosol and dihydroxyphenyl lactic acid, neither of which had been isolated previously from black cohosh. However, mercapturate conjugates of these black cohosh constituents were not detected in urine samples from women who consumed single oral doses of up to 256 mg of a standardized black cohosh extract. Therefore, for moderate doses of a dietary supplement containing black cohosh, this study found no cause for safety concerns over the formation of quinoid metabolites in women.

Comparison of electrospray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization in the identification of apomorphine, dobutamine, and entacapone phase II metabolites in biological samples

The applicability of different ionization techniques, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and a novel atmospheric pressure photoionization (APPI), were tested for the identification of the phase II metabolites of apomorphine, dobutamine, and entacapone in rat urine and in vitro incubation mixtures (rat hepatocytes and human liver microsomes). ESI proved to be the most suitable ionization method; it enabled detection of 22 conjugates, whereas APCI and APPI showed only 12 and 14 conjugates, respectively. Methyl conjugates were detected with all ionization methods. Glucuronide conjugates were ionized most efficiently with ESI. Only some of the glucuronides detected with ESI were detected with APCI and APPI. Sulfate conjugates were detected only with ESI. MS/MS experiments showed that the site of glucuronidation or sulfation could not be determined, since the primary cleavage was a loss of the conjugate group (glucuronic acid or SO3), and no site-characteristic product ions were formed. However, it may be possible to determine the site of methylation, since methylated products are more stable than glucuronides or sulfates. Furthermore, the loss of CH3 is not necessarily the primary cleavage, and site characteristic products may be formed. Identification and comparison of conjugates formed from the current model drugs were successfully analyzed in different biological specimens of common interest to biomedical research. A fairly good relation was obtained between the data from in vivo and in vitro models of drug metabolism.

[Studies on the spectroscopic property of p-hydroxyphenol derivatives]

In the paper, properties of p-hydroxyphenol derivatives are described. The results prove that p-hydroxyphenol derivatives with different function groups show different spectroscopic properties. Some methods will be proposed to analyze a series of p-hydroxyphenol derivatives in blood or urine so as to identify the cancer mark.

Adrenergic and endothelin B receptor-dependent hypertension in dopamine receptor type-2 knockout mice

Polymorphism of the dopamine receptor type-2 (D(2)) gene is associated with essential hypertension. To assess whether D(2) receptors participate in regulation of blood pressure (BP), we studied mice in which the D(2) receptor was disrupted. In anesthetized mice, systolic and diastolic BPs (in millimeters of mercury) were higher in D(2) homozygous and heterozygous mutant mice than in D(2)+/+ littermates. BP after alpha-adrenergic blockade decreased to a greater extent in D(2)-/- mice than in D(2)+/+ mice. Epinephrine excretion was greater in D(2)-/- mice than in D(2)+/+ mice, and acute adrenalectomy decreased BP to a similar level in D(2)-/- and D(2)+/+ mice. An endothelin B (ET[B]) receptor blocker for both ET(B1) and ET(B2) receptors decreased, whereas a selective ET(B1) blocker increased, BP in D(2)-/- mice but not D(2)+/+ mice. ET(B) receptor expression was greater in D(2)-/- mice than in D(2)+/+ mice. In contrast, blockade of ET(A) and V(1) vasopressin receptors had no effect on BP in either D(2)-/- or D(2)+/+ mice. The hypotensive effect of an AT(1) antagonist was also similar in D(2)-/- and D(2)+/+ mice. Basal Na(+),K(+)-ATPase activities in renal cortex and medulla were higher in D(2)+/+ mice than in D(2)-/- mice. Urine flow and sodium excretion were higher in D(2)-/- mice than in D(2)+/+ mice before and after acute saline loading. Thus, complete loss of the D(2) receptor results in hypertension that is not due to impairment of sodium excretion. Instead, enhanced vascular reactivity in the D(2) mutant mice may be caused by increased sympathetic and ET(B) receptor activities.

Pharmacokinetics of entacapone, a peripherally acting catechol-O-methyltransferase inhibitor, in man. A study using a stable isotope techique

OBJECTIVE

This study investigated the pharmacokinetics of the catechol-O-methyltransferase (COMT) inhibitor entacapone by giving simultaneously stable non-radioactive isotope 13C-entacapone intravenously (i.v.) and unlabelled entacapone orally. In comparison with a crossover design, the simultaneous i.v. and oral administration made it possible to minimise intra-individual variation, sample size and the duration of the study and still obtain accurate pharmacokinetic data.

METHODS

Eight healthy male volunteers were enrolled in this study. They were given a 20-mg i.v. dose of 13C-entacapone as a 1-mg/ml infusion at a constant rate of 5 mg/min over 4 min and a 100-mg dose of unlabelled entacapone orally immediately after the infusion. Blood samples were drawn at -5 (before onset of infusion), 0 (upon termination of infusion), 2, 5, 10, 20, 30 and 45 min and 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 and 12 h after the tablet ingestion. Urine during the 48 h after dosing was collected in fractions. Concentrations of 13C-entacapone and entacapone in plasma samples and urine fractions were determined using gas chromatography-mass spectrometry.

RESULTS

The decay of i.v. 13C-entacapone in plasma was tri-exponential and its pharmacokinetics were described using an open three-compartment model. The volume of the central compartment (Vc) and the volume of distribution at steady state (Vss) were 0.08+/-0.03 l/kg and 0.27+/-0.10 l/kg, respectively. Total plasma clearance (Cltot) averaged 11.7+/-1.9 ml/min kg(-1). The half-lives for the distribution phase and for the rapid and terminal elimination phases (t1/2alpha, t1/2beta and t1/2gamma) were 0.05+/-0.01 h, 0.38+/-0.16 h and 2.40+/-1.70 h, respectively. The terminal elimination phase accounted for only 9% of the total area under the plasma concentration-time curve (AUC), which was 409 +/- 98 ng h/ml after the i.v. dose. Oral entacapone was absorbed rapidly with a time to reach the peak concentration (tmax) of 0.9+/-0.4 h, a maximum concentration (Cmax) of 457+/-334 ng/ml and an AUC of 497+/-118 ng h/ml. During the 48 h after dosing, the recovery of free and conjugated unchanged 13C-entacapone in urine was 38.1+/-7.2% of the i.v. dose and the recovery of free and conjugated unchanged entacapone 13.3+/-3.9% of the oral dose. The bioavailability of oral entacapone was 25% based on the AUC values and 35% based on urinary excretion.

CONCLUSION

The results of the present study using stable isotope technique indicate that entacapone is rapidly absorbed, distributed to a small volume and rapidly eliminated by mainly non-renal routes. The pharmacokinetic profile of entacapone provides the rationale for a concomitant and frequently repeated simultaneous dosing of entacapone with levodopa and dopa decarboxylase inhibitors in the treatment of Parkinson's disease. This study confirmed the previously published data and fully support the validity of the technique used.

Direct analysis of nitrocatechol-type glucuronides in urine by capillary electrophoresis-electrospray ionisation mass spectrometry and tandem mass spectrometry

Direct, quantitative capillary electrophoresis-electrospray ionisation mass spectrometric (CE-ESI-MS) and tandem mass spectrometric (CE-ESI-MS-MS) methods are described for the quantitation of 3-O-glucuronides of E- and Z-entacapone isomers (EEG and EZG) and tolcapone (TG) in urine. 3-O-Glucuronide of nitecapone was used as internal standard. Good separation of glucuronides was achieved with 20 mM ammonium acetate as separation solution at pH 6.84. Stacking was used to increase the sensitivity of the method by introducing samples in 5 mM ammonium acetate. CE-ESI-MS and CE-ESI-MS-MS methods are linear with correlation coefficients better than 0.9983 and 0.9982, and repeatable with relative standard deviations below 9 and 14%, respectively. The limit of detection (LOD) in CE-ESI-MS at signal-to-noise ratio 3 is 100 ng/ml for EEG and EZG and 250 ng/ml for TG. The CE-ESI-MS-MS method was the more sensitive; LOD was 7 ng/ml for all compounds, without any concentration of the sample.

Human toxicokinetics of inhaled monochlorobenzene: latest experimental findings regarding re-evaluation of the biological tolerance value

OBJECTIVE

The aim of this study was to obtain toxicokinetic data on the absorption and elimination of monochlorobenzene (MCB) in blood and its main metabolite 4-chlorocatechol (4-ClCat) as well as on the isomeric chlorophenols (o-ClPh, m-ClPh, and especially p-CIPh as the main ClPh metabolite) in urine for reevaluation of the biological tolerance (BAT) value of MCB.

METHODS

Eight subjects performed 8-h inhalation tests daily over five successive days in an exposure chamber, at a maximum allowable concentration at the workplace (MAK) value of 10 ppm MCB. Five and two probands carried out the test series during physical activity levels of 75 and 50 W, respectively, for 10 min/h on a bicycle ergometer, and one subject was exposed continuously while at rest. MCB and its metabolites were analyzed by gas chromatography in combination with mass spectrometry.

RESULTS

The mean MCB blood concentration of the five subjects exposed during physical activity of 75 W was 217 +/- 42 microg/l. The relationship of the mean blood concentration measured under the conditions of rest or 50 and 75 W activity levels was in a ratio of about 1:1.7:2.8. The half-life values in the first hour after ending the exposures were 53 min and 150 min for the ensuing period, with steady-state being reached after 45 min. The mean 4-ClCat concentration in urine at the end of the five days was 150 +/- 13 mg/g creatinine in the case of the subjects exposed at 75 W, which decreased to 25 mg/g creatinine at the beginning of the next exposure. The analogous p-ClPh concentrations were 25 +/- 2 and 9 +/- 2 mg/g creatinine. The elimination half-life values of the ClPh isomers ranged from 12.4 to 16.5 h, and the half-life of 4-ClCat was 6.4 h. There was no apparent tendency for MCB and its metabolites to accumulate in blood or urine.

CONCLUSIONS

The results are in accordance with relevant field and laboratory studies. Taken into consideration with the 95th percentile, the evaluated BAT values should be set at levels of 300 microg MCB/l blood, 175 mg 4-ClCat/g creatinine or alternatively at 30 mg p-ClPh/g creatinine in urine after the end of a shift. At the beginning of the next shift, the BAT values of the metabolites should be 35 and 15 mg/g creatinine, respectively.

Validation of biomarkers in humans exposed to benzene: urine metabolites

BACKGROUND

The present study was conducted among Chinese workers employed in glue- and shoe-making factories who had an average daily personal benzene exposure of 31+/-26 ppm (mean+/-SD). The metabolites monitored were S-phenylmercapturic acid (S-PMA), trans, trans-muconic acid (t,t-MA), hydroquinone (HQ), catechol (CAT), 1,2, 4-trihydroxybenzene (benzene triol, BT), and phenol.

METHODS

S-PMA, t,t-MA, HQ, CAT, and BT were quantified by HPLC-tandem mass spectrometry. Phenol was measured by GC-MS.

RESULTS

Levels of benzene metabolites (except BT) measured in urine samples collected from exposed workers at the end of workshift were significantly higher than those measured in unexposed subjects (P < 0.0001). The large increases in urinary metabolites from before to after work strongly correlated with benzene exposure. Concentrations of these metabolites in urine samples collected from exposed workers before work were also significantly higher than those from unexposed subjects. The half-lives of S-PMA, t,t-MA, HQ, CAT, and phenol were estimated from a time course study to be 12.8, 13.7, 12.7, 15.0, and 16.3 h, respectively.

CONCLUSIONS

All metabolites, except BT, are good markers for benzene exposure at the observed levels; however, due to their high background, HQ, CAT, and phenol may not distinguish unexposed subjects from workers exposed to benzene at low ambient levels. S-PMA and t,t-MA are the most sensitive markers for low level benzene exposure.

Metabolism and disposition of 4-t-butylcatechol in rats and mice

4-t-Butylcatechol (TBC) is an antioxidant used primarily as a polymerization inhibitor for reactive monomers. Annual production and use of TBC in the United States is approximately 1.5 million pounds. The absorption, tissue distribution, metabolism, and excretion of [(14)C]TBC, labeled in the methine carbon, was investigated in male Fischer 344 rats and B6C3F(1) mice after i.v., oral, and dermal administration. Oral (2 and 200 mg/kg in rats; 3 and 300 mg/kg in mice) and dermal (0.6, 6, and 63 mg/kg in rats; 1.3 and 157 mg/kg in mice) doses of TBC were well absorbed, then rapidly metabolized and excreted primarily in urine. Dermal absorption of the highest dose in the rat (87% of the 63 mg/kg dose) was significantly higher than that of the two lower doses (0.6 and 6 mg/kg, 44 and 57%, respectively). Dermally administered TBC was also well absorbed in the mouse (72-86%). Polar metabolites of TBC comprise all of the radioactivity in the urine of both species after all routes of administration. These were shown to consist mostly of the sulfate conjugates (and lesser amounts of the glucuronides) of TBC and of a less polar metabolite. The deconjugated metabolite was isolated and determined by mass spectrometry and (1)H-NMR to be mono-O-methylated TBC.

Modifications in the metabolic pathways of benzene in streptozotocin-induced diabetic rat

Benzene is a ubiquitous environmental pollutant primarily metabolized by a cytochrome P-450 (CYP-450) isoenzyme, CYP-450 IIE1. A consistent induction of CYP450 IIE1 has been observed in both rat and human affected by diabetes mellitus. The aim of this study was to evaluate whether streptozotocin (STZ)-induced diabetes determines modifications in the metabolic pathways of benzene in rat. Benzene (100 mg/kg per day, dissolved in corn oil) was administered i.p. once a day for 5 days. Urine samples were collected every day in STZ-treated and normoglycaemic animals, treated and untreated with benzene (n = 10). Urinary levels of trans,trans-muconic acid and of phenol, catechol and hydroquinone (free and conjugated with sulphuryl and glucuronic group) were measured by high-performance liquid chromatography (HPLC). In normoglycaemic rats during the 5 days of treatment with benzene we observed a progressive and significant decrement in the urinary excretion of phenol, phenyl sulphate and glucuronide, catechol, catechol glucuronide, hydroquinone, hydroquinone glucuronide and t,t-muconic acid (P < 0. 05). In the diabetic animals, conversely, the same metabolites showed progressively increasing urinary levels (P < 0.05). Catechol sulphate and hydroquinone sulphate levels were below the instrument's detection limit. In the comparison between diabetic and normoglycaemic benzene treated rats, the inter-group difference was significant (P < 0.05) from day 3 of treatment for t,t-muconic acid, and from day 1 for free and conjugated phenol, free and glucuronide catechol and free hydroquinone. In the normoglycaemic rat exposed to benzene the decreasing trend observed in urinary excretion of free and conjugated metabolites may be due to their capability to reduce cytochromial activity. Conversely, in the diabetic rat, urinary levels of benzene metabolites tended to increase progressively, probably due to the consistent induction of CYP-450 IIE1 observed in diabetes, which would overwhelm the inhibition of this isoenzyme caused by phenolic metabolites. Furthermore, the metabolic switch towards detoxification metabolites observed after administration of high doses of benzene is not allowed in the diabetic because of reduced glutathione-S-transferase activity. As a consequence, higher levels of hydroquinone, phenol and catechol, considered the actual metabolites responsible for benzene toxicity, will accumulate in the diabetic rat. Extrapolating these data to human, we may thus suggest that occupational exposure to benzene of a diabetic subject poses a higher risk level, as his metabolism tends to produce and accumulate higher levels of reactive benzene catabolites.

Development of liquid chromatography-electrospray ionization-tandem mass spectrometry methods for determination of urinary metabolites of benzene in humans

To investigate the ways in which different levels of exposure affect the metabolic activation pathways of benzene in humans, and to examine the relationship between urinary metabolites and other biological markers, we have developed two sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for quantitation of the benzene metabolites trans,transmuconic acid (t,t-MA), S-phenylmercapturic acid (S-PMA), hydroquinone (HQ), catechol (CAT), and for estimation of 1,2,4-trihydroxybenzene (BT). In our first assay, urinary S-PMA and t,t-MA were measured simultaneously by liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring (LC-ESI-MS/MS-SRM) in the negative ionization mode. In this assay, the metabolites [13C6]-S-PMA and [13C6]-t,t-MA were used as internal standards. The efficacy of this specific assay was evaluated in human urine specimens from 28 smokers and 18 nonsmokers serving as the benzene-exposed and nonexposed groups, respectively. The coefficient of variation (CV) of analyses on different days (n = 8) for S-PMA was 7% for samples containing 9.4 micrograms/L urine, and for t,t-MA was 10% for samples containing 0.07 mg/L. The mean levels of S-PMA and t,t-MA in smokers were 1.9-fold (p = 0.02) and 2.1-fold (p = 0.03) higher, respectively, than those in nonsmokers.

Micellar electrokinetic capillary chromatography method for direct determination of glucuronides of entacapone and its (Z)-isomer in human urine

This paper describes the validation of a micellar electrokinetic capillary chromatography method for the direct determination of the 3-O-glucuronides of entacapone and its (Z)-isomer, the main urinary metabolites of entacapone in humans. Entacapone is a novel drug which, as a potent inhibitor of catechol-O-methyltransferase (COMT), is used as an adjunct in the standard therapy of Parkinson's disease. The 3-O-glucuronide of another COMT inhibitor, nitecapone, was used as internal standard (I.S.). The validation experiments were performed by using spiked urine samples that were extracted with Sep-Pak C18 cartridges before analysis. Determinations were carried out in a buffer of pH 7.0 containing 25 mM of phosphate, 50 mM of borate and 20 mM of sodium dodecyl sulfate, and by applying 15 kV over a 67 cm (60 cm to the detector) x 75 microns fused-silica capillary. UV detection was at 335 nm. The validity of the method was assessed by investigating the identity of the analytes, selectivity, limit of quantitation, linearity, within-day precision, extraction recovery, between-day precision and accuracy, electroosmotic flow stability and analyte stability. The method proved to be reproducible, sufficiently selective and accurate. Extraction recoveries of the analytes were > 94%. The limit of quantitation (LOQ) was 2 micrograms/ml and the assay was linear in the range 2-150 micrograms/ml with correlation coefficients better than 0.999 for both glucuronides. The repeatability of the method, expressed as the ratio of corrected peak area of the analytes to that of I.S., gave RSD values of < 5% even at the LOQ. Between-day precision (RSD) was < 7.5% for both glucuronides at 7.5 micrograms/ml. Determination of the glucuronide concentrations in urine samples of 34 patients treated with entacapone either orally (200 mg) or intravenously (25 mg) showed the method to be suitable for monitoring the concentrations of the glucuronide of entacapone after both oral and intravenous administration and those of the glucuronide of its (Z)-isomer after oral administration. The limited long term stability of the system requires, however, frequent recalibration in applications involving long sample series.

Urinary excretion of phenol, catechol, hydroquinone, and muconic acid by workers occupationally exposed to benzene

OBJECTIVES

Animal inhalation studies and theoretical models suggest that the pattern of formation of benzene metabolites changes as exposure to benzene increases. To determine if this occurs in humans, benzene metabolites in urine samples collected as part of a cross sectional study of occupationally exposed workers in Shanghai, China were measured.

METHODS

With organic vapour monitoring badges, 38 subjects were monitored during their full workshift for inhalation exposure to benzene. The benzene urinary metabolites phenol, catechol, hydroquinone, and muconic acid were measured with an isotope dilution gas chromatography mass spectroscopy assay and strongly correlated with concentrations of benzene air. For the subgroup of workers (n = 27) with urinary phenol > 50 ng/g creatinine (above which phenol is considered to be a specific indicator of exposure to benzene), concentrations of each of the four metabolites were calculated as a ratio of the sum of the concentrations of all four metabolites (total metabolites) and were compared in workers exposed to > 25 ppm v < or = 25 ppm.

RESULTS

The median, 8 hour time weighted average exposure to benzene was 25 ppm. Relative to the lower exposed workers, the ratio of phenol and catechol to total metabolites increased by 6.0% (p = 0.04) and 22.2% (p = 0.007), respectively, in the more highly exposed workers. By contrast, the ratio of hydroquinone and muconic acid to total metabolites decreased by 18.8% (p = 0.04) and 26.7% (p = 0.006), respectively. Similar patterns were found when metabolite ratios were analysed as a function of internal benzene dose (defined as total urinary benzene metabolites), although catechol showed a more complex, quadratic relation with increasing dose.

CONCLUSIONS

These results, which are consistent with previous animal studies, show that the relative production of benzene metabolites is a function of exposure level. If the toxic benzene metabolites are assumed to be derived from hydroquinone, ring opened products, or both, these results suggests that the risk for adverse health outcomes due to exposure to benzene may have a supralinear relation with external dose, and that linear extrapolation of the toxic effects of benzene in highly exposed workers to lower levels of exposure may underestimate risk.

Biological monitoring of vehicle mechanics and other workers exposed to low concentrations of benzene

It has been suggested that the threshold limit value (TLV) for the time-weighted average (TWA), of benzene be lowered because of its possible leukemogenic effect at low exposure concentrations. This requires the development of new methods of biological monitoring. In this cross-sectional study the diagnostic power of blood and breath benzene and of urinary phenol, catechol, hydroquinone, S-phenylmercapturic acid, and muconic acid were compared in a population of 410 male workers exposed to benzene in garages, in two coke plants, and in a by-product plant. Benzene exposure was assessed by personal air sampling (charcoal tube and passive dosimeter). In all, 95% of the workers were exposed to less than 0.5 ppm benzene. According to the multiple regression equation, the muconic acid and S-phenylmercapturic acid concentrations detected in nonsmokers exposed to 0.5 ppm benzene were 0.3 mg/g and 6 micrograms/g, respectively (range 0.2-0.6 mg/g and 1.2-8.5 micrograms/g, respectively). With muconic acid very few false-positive test results were found, and this determination remained reliable even around a cutoff level of 0.1 ppm benzene. Moreover, the diagnostic power of this test proved to be good even when diluted or concentrated urine samples were not excluded. S-Phenylmercapturic acid (S-PMA) also performed fairly well. Blood and breath benzene as well as urinary phenol (PH) and hydroquinone (HQ) were clearly less suitable biomarkers than muconic acid (MA). Catechol (CA) was not associated with occupational benzene exposure. According to the results of biological monitoring, the skin resorption of benzene from gasoline or other fuels seems negligible. Correlation, multiple regression, and likelihood ratios consistently showed that MA and S-PMA concentrations were fairly good indicators of benzene exposure in the 0.1- to 1-ppm range, even in a population comprising both smokers and nonsmokers. PH, HQ, CA, and blood and breath benzene were less suitable, if at all, in the same exposure range.

Demethylation of 3-O-methyldopa in the kidney: a possible source for dopamine in urine

The possibility that demethylation of 3-O-methyldopa (OM-dopa) in the kidney could provide a source for dopamine in the urine was explored in male Wistar rats aged 60-90 days, using in vivo and in vitro approaches. The results showed that endogenous OM-dopa is filtered, reabsorbed and extensively metabolized in the kidney. Infusion of OM-dopa into anesthetized rats increased significantly urinary excretion of Na+, dopa, dopamine, and 3,4 dihydroxyphenylacetic acid. Whole kidney homogenates, slices from renal cortex, and microdissected proximal tubules produced significant amounts of both dopa and dopamine when incubated with OM-dopa. Renal cortex slices produced dose-dependent amounts of dopa and dopa-mine when incubated with 1-100 microM OM-dopa. Incubation of microdissected proximal tubule segments with 1 microM OM-dopa produced a fourfold (P < 0.025) increment in dopa and a twofold (P < 0.05) increment in dopamine (an effect similar to that observed with 1 microM L-dopa). One micromolar OM-dopa or 1 microM L-dopa decreased (P < 0.05) Na(+)-K(+)-adenosinetriphosphatase activity measured at maximal velocity condition in proximal tubules. In conclusion, these experiments show that in vitro the kidney is able to produce dopamine by demethylation of OM-dopa, while the results of the OM-dopa infusion suggest that this conversion may also occur in vivo.

Biomarkers of exposure to low concentrations of benzene: a field assessment

OBJECTIVE

To carry out a comprehensive field investigation to evaluate various conventional and recently developed biomarkers for exposure to low concentrations of benzene.

METHODS

Analyses were carried out on environmental air, unmetabolised benzene in blood and urine, urinary trans, transmuconic acid, and three major phenolic metabolites of benzene: phenol, catechol, and hydroquinone. Validations of these biomarkers were performed on 131 never smokers occupationally exposed to the time weighed average benzene concentration of 0.25 ppm (range, 0.01 to 3.5 ppm).

RESULTS

Among the six biomarkers studied, unmetabolised benzene in urine correlated best with environmental benzene concentration (correlation coefficient, r = 0.76), followed by benzene in blood (r = 0.64). When urinary metabolites were compared with environmental benzene, trans, trans-muconic acid showed a close correlation (r = 0.53) followed by hydroquinone (r = 0.44), and to a lesser extent with urinary phenol (r = 0.38). No correlation was found between catechol and environmental benzene concentrations. Although unmetabolised benzene in urine correlates best with benzene exposure, owing to serious technical drawbacks, its use is limited. Among the metabolites, trans, trans-muconic acid seems to be more reliable than other phenolic compounds. Nevertheless, detailed analyses failed to show that it is specific for monitoring benzene exposures below 0.25 ppm.

CONCLUSION

The overall results suggest that most of the currently available biomarkers are unable to provide sufficient specificity for monitoring of low concentrations of benzene exposure. If a lower occupational exposure limit for benzene is to be considered, the reliability of the biomarker and the technical limitations of measurements have to be carefully validated.

Evaluation of biomarkers for occupational exposure to benzene

OBJECTIVE

To evaluate the relations between environmental benzene concentrations and various biomarkers of exposure to benzene.

METHODS

Analyses were carried out on environmental air, unmetabolised benzene in urine, trans, trans-muconic acid (ttMA), and three major phenolic metabolites of benzene; catechol, hydroquinone, and phenol, in two field studies on 64 workers exposed to benzene concentrations from 0.12 to 68 ppm, the time weighted average (TWA). Forty nonexposed subjects were also investigated.

RESULTS

Among the five urinary biomarkers studied, ttMA correlated best with environmental benzene concentration (correlation coefficient, r = 0.87). When urinary phenolic metabolites were compared with environmental benzene, hydroquinone correlated best with benzene in air. No correlation was found between unmetabolised benzene in urine and environmental benzene concentrations. The correlation coefficients for environmental benzene and end of shift catechol, hydroquinone, and phenol were 0.30, 0.70, and 0.66, respectively. Detailed analysis, however, suggests that urinary phenol was not a specific biomarker for exposure below 5 ppm. In contrast, ttMA and hydroquinone seemed to be specific and sensitive even at concentrations of below 1 ppm. Although unmetabolised benzene in urine showed good correlation with atmospheric benzene (r = 0.50, P < 0.05), data were insufficient to suggest that it is a useful biomarker for exposure to low concentrations of benzene. The results from the present study also showed that both ttMA and hydroquinone were able to differentiate the background level found in subjects not occupationally exposed and those exposed to less than 1 ppm of benzene. This suggests that these two biomarkers are useful indices for monitoring low concentrations of benzene. Furthermore, these two metabolites are known to be involved in bone marrow leukaemogenesis, their applications in biological monitoring could thus be important in risk assessment.

CONCLUSION

The good correlations between ttMA, hydroquinone, and atmospheric benzene, even at concentrations of less than 1 ppm, suggest that they are sensitive and specific biomarkers for benzene exposure.

Catecholaminergic effects of prolonged head-down bed rest

Prolonged head-down bed rest (HDBR) provides a model for examining responses to chronic weightlessness in humans. Eight healthy volunteers underwent HDBR for 2 wk. Antecubital venous blood was sampled for plasma levels of catechols [norepinephrine (NE), epinephrine, dopamine, dihydroxyphenylalanine, dihydroxyphenylglycol, and dihydroxyphenylacetic acid] after supine rest on a control (C) day and after 4 h and 7 and 14 days of HDBR. Urine was collected after 2 h of supine rest during day C, 2 h before HDBR, and during the intervals 1-4, 4-24, 144-168 (day 7), and 312-336 h (day 14) of HDBR. All subjects had decreased plasma and blood volumes (mean 16%), atriopeptin levels (31%), and peripheral venous pressure (26%) after HDBR. NE excretion on day 14 of HDBR was decreased by 35% from that on day C, without further trends as HDBR continued, whereas plasma levels were only variably and nonsignificantly decreased. Excretion rates of dihydroxyphenylglycol and dihydroxyphenylalanine decreased slightly during HDBR; excretion rates of epinephrine, dopamine, and dihydroxyphenylacetic acid and plasma levels of catechols were unchanged. The results suggest that HDBR produces sustained inhibition of sympathoneural release, turnover, and synthesis of NE without affecting adrenomedullary secretion or renal dopamine production. Concurrent hypovolemia probably interferes with detection of sympathoinhibition by plasma levels of NE and other catechols in this setting. Sympathoinhibition, despite decreased blood volume, may help to explain orthostatic intolerance in astronauts returning from spaceflights.

Effect of variation of exposure to airborne chlorobenzene on internal exposure and concentrations of urinary metabolite

OBJECTIVES

This study aimed to develop a physiologically based pharmacokinetic model for chlorobenzene and to investigate the effect of variation in exposure to chlorobenzene on the chlorobenzene concentration in blood and the urinary concentration of 4-chlorocatechol.

METHODS

A physiologically based pharmacokinetic model was developed and the simulated results of urinary 4-chlorocatechol concentrations were compared with the values found in experiments and field surveys. The area under the chlorobenzene concentration-time curve in blood (CBBauc) was selected as the measure of internal exposure related to the chronic effect of chlorobenzene. The maximum one-hour time weighted average value of chlorobenzene concentration in blood (CBBmax) was chosen as the measure of internal exposure related to the acute effect of chlorobenzene. The total amount of urinary 4-chlorocatechol (TOTCC) and that excreted during the last four hours (CC(4-8)) or two hours (CC(6-8)) of exposure as well as that excreted during two hours on the next morning (CC(22-24)) were used to represent concentrations of urinary metabolites. The effects of variation of the one-hour time weighted averages of airborne chlorobenzene exposure (CBAs) on the internal exposures and the concentrations of urinary metabolites were investigated with the pharmacokinetic model.

RESULTS

The comparison of the simulated results with the observed data showed that the pharmacokinetic model can be used to estimate the urinary concentrations of 4-chlorocatechol. The CBBauc and TOTCC were not affected by changes in both the geometric SD (GSD) of CBAs or the variations in CBAs. The CBBmax varied with changes in both the GSD and CBAs. The CC(4-8) and CC(6-8) did not vary with the GSD, but these concentrations were affected by the change in the CBAs. Although there was little effect of the GSD and CBAs on the CC(22-24), this value highly reflected the exposure over the preceding days.

CONCLUSION

To protect workers from the chronic effect of chlorobenzene, it may be sufficient to control the daily average exposure. To protect from the acute effect, however, the short term exposure must be controlled as well. The values of CC(4-8) and CC(6-8) were acceptable for estimating daily average exposure, but the CC(22-24) was not.

Studies on hypoxoside and rooperol analogues from Hypoxis rooperi and Hypoxis latifolia and their biotransformation in man by using high-performance liquid chromatography with in-line sorption enrichment and diode-array detection

Methanol extracts of the corms of Hypoxis rooperi and H. latifolia were studied for their hypoxoside content by an in-line sorption enrichment HPLC technique [Kruger et al., J. Chromatogr., 612 (1993) 191]. Hypoxoside is the trivial name for (E)-1,5-bis(3'-hydroxy-4'-O-beta-D-glucopyranosyl-phenyl) pent-1-en-4-yne and rooperol the aglucone obtained from beta-glucosidase treatment. Hypoxoside and rooperol analogues containing 4, 3 and 2 hydroxyl groups resolved as separate peaks with the proportion of the latter two markedly higher in H. latifolia than in H. rooperi. After oral ingestion of hypoxoside by humans, no hypoxoside or rooperol appeared in the serum. Only rooperol was present in the faeces. The serum and urine contained at least three phase II metabolite peaks. Selective enzyme hydrolysis showed that they represent the diglucuronide, disulfate and glucuronide-sulfate conjugates of all three rooperol analogues.

Etoposide pharmacokinetics and pharmacodynamics after acute and chronic exposure to cisplatin

PURPOSE

The objectives of this study were to determine etoposide pharmacokinetics after both acute and chronic exposure to cisplatin and to evaluate the relationship between etoposide systemic exposure and toxicity in children with neuroblastoma.

PATIENTS AND METHODS

Seventeen children with newly diagnosed stage C or D neuroblastoma were given continuous infusions of 780 mg/m2 etoposide over 72 hours as part of multiagent chemotherapy. Etoposide pharmacokinetic parameters were estimated on three occasions in each patient: (1) 21 days after the first cisplatin dose (etoposide was given immediately after cyclophosphamide; cumulative cisplatin dose, 90 mg/m2), (2) 2 days after the third cisplatin dose (cumulative cisplatin dose, 270 mg/m2), and (3) 21 days after the final cisplatin dose (etoposide again immediately after cyclophosphamide; cumulative cisplatin dose, 360 mg/m2). Toxicity was scored on the basis of transfusion requirements and need for hospitalization.

RESULTS

Etoposide systemic clearance decreased acutely when administered 2 days after cisplatin (median of 15.5 ml/min/m2) compared with both the first study (20.0 ml/min/m2) and the third study (19.7 ml/min/m2; p < 0.001). The decrease in clearance resulted in a median 31% increase in etoposide area under the concentration-time curve (AUC) compared with the first study and a 36% increase compared with the third study. Toxicity scores were higher after the second study than after the first or third study (p = 0.01), and etoposide AUC was significantly correlated with toxicity score (p = 0.006). Neither etoposide renal clearance nor catechol excretion differed significantly among the courses.

CONCLUSION

There was an acute decrease in etoposide systemic clearance when etoposide immediately followed cisplatin. No persistent decrease in etoposide clearance was noted after a cumulative dose of 360 mg/m2 cisplatin. Etoposide AUC was positively correlated with toxicity in a multidrug regimen.

Mitogenic effects of propoxur on male rat bladder urothelium

Propoxur produces bladder tumors in rats, but not other species. The hyperplastic and tumorigenic effects do not occur if urinary pH is lowered by administering propoxur in a semi-synthetic diet or co-administering it with ammonium chloride (NH4Cl). We fed propoxur at 8000 p.p.m. in Altromin 1321 diet to male Wistar rats for 4 weeks, with or without NH4Cl as 10,000 p.p.m. of the diet. The urine of rats fed control diet with or without propoxur had a relatively high urinary pH (approximately 8); the addition of NH4Cl lowered the urinary pH by approximately 0.5-1.0 units. There was no evidence of urinary calculi or amorphous precipitate nor was there an increase in microcrystals or formation of different crystals than occur in normal rat urine. Propoxur produced hyperplasia of the urothelium, as observed by light and scanning electron microscopy, and increased the labeling index for proliferating cell nuclear antigen. These effects were significantly inhibited by co-administration with NH4Cl. There was no evidence of urothelial necrosis. Thus, the hyperplasia appears to result from a direct mitogenic effect of propoxur or a metabolite on the urothelium, rather than from toxicity and consequent regeneration. Based on the present study and previous investigations, the urothelial effects of propoxur in the rat are dependent on high urinary pH and high administered doses, factors which need to be incorporated into any mechanistic model for the chemical and into any extrapolation to potential effects in humans.

Metabolite profiles of two [14C]-labelled catechol O-methyltransferase inhibitors, nitecapone and entacapone, in rat and mouse urine and rat bile

The metabolites of two inhibitors of catechol O-methyltransferase, nitecapone [3-(3,4-dihydroxy-5-nitrobenzylidene)2,4-pentanedione] and entacapone [(E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)propenamide++ +], excreted in urine and bile by rats and in urine by mice, were compared and quantified by using HPLC with radiochemical detection after administration of [14C]-labelled compounds. With the exception of 3-O-methylated nitecapone, no major metabolites were found in rat bile that were not found in rat urine. For both compounds the major biotransformations were the same in the mouse and the rat. However, a bisulfite adduct of nitecapone was found in rat urine only, and reduction of the C = C and C = O groups of the nitecapone side chain was more extensive in the mouse. After entacapone administration, the products of amide N-dealkylation were more abundant in rat urine than in mouse urine. Most of the dose was excreted in urine and bile as O-conjugates. Most abundant were the O-glucuronides, while smaller amounts of O-sulfates and O-methylated metabolites were found in both species. One non-glucuronide glycoside of entacapone was found in urine of both rats and mice.

Concentrations of urinary metabolites in workers exposed to monochlorobenzene and variation in the concentration during a workshift

Urinary concentrations of metabolites of monochlorobenzene were examined in 10 male workers exposed to the compound while synthesising intermediate products for dyes. Their individual exposure concentrations were monitored for the whole workshift and samples of urine were collected at the start and end of the workshift, during it, and during the noon recess. The concentrations of four metabolites, 4-chlorocatechol and o-, m-, and p-chlorophenol, in the urine samples were measured. The investigation was performed on Monday and Tuesday in one week and on Tuesday and Wednesday in another week. The concentrations of 4-chlorocatechol in urine collected during the last four hours and at the end of the workshift were proportional to the eight hour time weighted average exposure to monochlorobenzene. The concentration in urine collected during the noon recess showed a linear correlation with the four hour time weighted average in the morning. Similarly, linear relations were obtained for urinary p-chlorophenol. The ratio (as monochlorobenzene) of p-chlorophenol to 4-chlorocatechol concentrations at the start of the workshift was 0.39 and at the end of the workshift was 0.22. The ratios of the urinary concentrations 15 hours after exposure to those at the end of exposure were 0.24 for 4-chlorocatechol and 0.44 for p-chlorophenol. The present study also showed that variations in exposure at the workplace were reflected by changes in concentrations of urinary metabolites during the workshift.

O- and S-methylated bromothiocatechols

Bromobenzene is metabolized by the Hartley guinea pig to two different bromothiocatechols, 4-bromo-2-hydroxythiophenol and 5-bromo-2-hydroxythiophenol. Both the thiol and phenol functional groups of thiocatechol undergo biological methylation. Methylation at the thiol group leads to the formation of (methylthio)bromophenol (S-methylated bromothiocatechol), while methylation of the phenol group leads to methoxybromothiophenol (O-methylated bromothiocatechol). This resulted in the urinary excretion of four O- and S-methylated bromothiocatechols. Bromothiocatechols could be formed by dehydrogenation of their corresponding bromodihydrobenzene thiolols. Both the 3-S- and 4-S-bromodihydrobenzene thiolols, as S-methylated products, were found as urinary metabolites of bromobenzene in the Hartley guinea pig. All four O- and S-methylated bromothiocatechols and two S-methylated bromodihydrobenzene thiolols were also found as urinary metabolites of bromobenzene in the golden Syrian hamster.

Identification of major urinary metabolites of the catechol-O-methyltransferase inhibitor entacapone in the dog

Metabolites of entacapone, (E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl) propenamide, a potent inhibitor of catechol-O-methyltransferase, were isolated from dog urine. After hydrolysis of glucuronides and sulfates, 5 metabolites were identified in addition to unchanged entacapone by HPLC with diode-array UV detection, electron ionization mass spectrometry and IR spectroscopy. The (Z)-isomer of entacapone was the most abundant phase I metabolite while less abundant metabolites were formed through cleavage or reduction of the side chain carbon-carbon double bond, hydrolysis of the amide bond or through hydration of the nitrile group. The most abundant urinary metabolites were glucuronides. The glucuronidation site of these ortho-nitrocatechols was shown to be the hydroxyl meta to the nitro group.

Simultaneous determination of hydroquinone, catechol and phenol in urine using high-performance liquid chromatography with fluorimetric detection

A method was developed for simultaneous determination of urinary hydroquinone, catechol and phenol using high-performance liquid chromatography (HPLC) with variable-wavelength fluorimetric detection. Urine samples, after acid hydrolysis, were saturated with sodium sulphate and extracted by diethyl ether. The two buffers used for gradient elution were (A) 10 mM sodium acetate containing 0.5% (v/v) acetic acid and (B) the same as buffer A but containing an additional 20% (v/v) acetonitrile. Hydroquinone, catechol and phenol were separated in a C18 column and detected at 2.9, 6.8 and 13.6 min, respectively. The recovery and reproducibility were generally over 90%. Over 300 extracted samples were analysed and no change in column efficiency was noted. Comparisons were also made with HPLC using ultraviolet (UV) detection and with gas chromatography (GC). The proposed method appears to be more sensitive and reliable than other existing methods. This new method was also validated with urine samples collected from cigarette smokers and from refinery workers exposed to low concentrations of benzene.

Identification of major metabolites of the catechol-O-methyltransferase inhibitor nitecapone in the rat and dog

Metabolites of nitecapone [3-(3,4-dihydroxy-5-nitrobenzylidene)-2,4-pentanedione], a potent catechol-O-methyltransferase inhibitor with gastroprotective and antiulcerogenic effects, were isolated by extraction and HPLC from dog and rat urine after enzymatic hydrolysis and as glucuronic acid and sulfate conjugates. Eight and 10 nonconjugated metabolites and unchanged nitecapone were found in hydrolyzed dog and rat urine, respectively, and identified by HPLC with diode-array UV detection, electron ionization mass spectrometry, and IR spectroscopy. In both species the main phase I metabolic pathways were: 1) reduction of the side chain carbon-carbon double bond and carbonyl groups and 2) cleavage of the side-chain double bond, giving an aromatic aldehyde that was partly oxidized to the corresponding carboxylic acid. These phase I metabolites and unchanged nitecapone were excreted in urine mainly as their glucuronides and sulfates in both species. Additionally, the 3-O-methylated metabolite, not found in urine, was identified in rat plasma.

Identification of major metabolites of the catechol-O-methyltransferase inhibitor entacapone in rats and humans

Metabolites of entacapone [(E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)propenamide++ +], a potent inhibitor of catechol-O-methyltransferase, were isolated from human and rat urine. After hydrolysis of glycosides and sulfates, four human and eight rat metabolites were identified, in addition to unchanged entacapone by HPLC with diode-array UV detection, electron ionization mass spectrometry, and IR spectroscopy. In man 10% of an oral dose was excreted in urine during 8 hr. The glucuronides of entacapone and its (Z)-isomer represented about 70 and 25% of the urinary metabolites, respectively. The (Z)-isomer of entacapone and two less abundant urinary metabolites, formed through cleavage or reduction of the side chain carbon-carbon double bond, were also formed in an erythrocyte incubation. The (Z)-isomer was the only phase I metabolite found in addition to entacapone in human plasma. The nitro group of entacapone seems to hinder methylation of the catechol hydroxyls in man, because no methylation products were detected. Twenty-four hr after iv administration of 14C-labeled entacapone to rats, over 50% was excreted in the feces and approximately 35% extensively metabolized in the urine. Entacapone and its phase I metabolites were excreted mainly as glucuronides and sulfates in rat urine. The most abundant urinary metabolite was the glucuronide of entacapone. Unchanged, N-dealkylated, and O-methylated entacapone, the (Z)-isomer of entacapone, and 3,4-dihydroxy-5-nitrobenzaldehyde were found in both plasma and urine from rats. Two minor urinary metabolites were formed through reduction of the side chain carbon-carbon double bond and through acetylation of the amino group resulting from nitro reduction.

Liquid chromatographic determination of a new catechol-O-methyltransferase inhibitor, entacapone, and its Z-isomer in human plasma and urine

Assay procedures for analysis of entacapone, (E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)-propenamide++ +, and its Z-isomer in human plasma and urine are described. The methods were based on reversed-phase liquid chromatography with amperometric detection. Entacapone and its Z-isomer were extracted with n-hexane-ethyl acetate mixtures after acidification with hydrochloric acid. From urine extracts the analytes were back-extracted into phosphate buffer (pH 7.2). During sample treatment 1-2% of entacapone was changed to the Z-isomer. With recoveries exceeding 75% the relative standard deviations for within-day precision were less than 11% for plasma and less than 6% for urine at the quantitation limit (10 ng ml-1) and less than 6% for both methods at higher concentrations (20-2000 ng ml-1). The assays were specific with respect to all known metabolites and selective, sensitive and precise enough for determination of entacapone and its Z-isomer in plasma and urine down to 10 ng ml-1. The methods are thus suitable for the kind of pharmacokinetic studies exemplified in this paper.

Determination of benzene metabolites in urine of mice by solid-phase extraction and high-performance liquid chromatography

A method was developed for quantitative measurement of trans,trans-muconic acid, catechol, hydroquinone and phenol in urine. Hydrolysis of esterified and glucuronized phenolic compounds was effected by specific enzymes. The hydrolysed mixture was purified and separated by solid-phase extraction with an anion exchanger, followed by extraction with diethyl ether. By using a clean-up procedure the natural background from mouse urine could be reduced, so that the detection limit of the metabolites was in the range 3-60 mg/l. Optimization of the chromatographic conditions resulted in a short high-performance liquid chromatography analysis time. Phenol had the longest retention time of about 10 min. The clean-up procedure could also be used for phenylmercapturic acid, an additional benzene metabolite, but for sensitive high-performance liquid chromatographic detection of phenylmercapturic acid other conditions are necessary.

Glucagon and clonidine testing in the diagnosis of pheochromocytoma

We assessed the sensitivity and specificity of glucagon stimulation and clonidine suppression tests in the diagnosis of pheochromocytoma in 113 hypertensive patients, 39 with and 74 without the tumor. In the glucagon stimulation test, blood was sampled 2 minutes after intravenous injection of 0.28 mumol (1 mg) glucagon, and in the clonidine suppression test, blood was sampled 3 hours after administration of oral clonidine, 1.30 mumol (0.3 mg)/70 kg body wt. Baseline levels of catechols in antecubital venous blood were abnormal, with norepinephrine greater than 7.10 nmol/l (1,200 pg/m), epinephrine greater than 1.51 nmol/l (276 pg/ml), norepinephrine/dihydroxyphenylglycol (DHPG) ratio greater than 1.09, or dopa greater than 35.53 nmol/l (7,000 pg/ml), in 30 of 39 patients with pheochromocytoma (sensitivity 77%) and 1 of 74 patients without pheochromocytoma (specificity 99%). Results of the glucagon test were abnormal (norepinephrine greater than 11.83 nmol/l [2,000 pg/ml] or more than threefold increase from baseline) in 25 of 31 patients with pheochromocytoma (sensitivity 81%) and 0 of 72 patients without pheochromocytoma (specificity 100%). Results of the clonidine test were abnormal (after clonidine norepinephrine greater than 2.96 nmol/l [500 pg/ml] or less than 50% decrease from baseline) in 29 of 30 patients with pheochromocytoma (sensitivity 97%) and in 7 of 30 patients without pheochromocytoma (specificity 67%). Very high baseline levels of catechols therefore indicated the presence of pheochromocytoma, but there were several false-negative results when normal levels were obtained. The glucagon test alone was highly specific but not sensitive, and the clonidine test was highly sensitive but less specific.(ABSTRACT TRUNCATED AT 250 WORDS)