Risk assessment of skin lightening cosmetics containing hydroquinone.

Following reports on potential risks of hydroquinone (HQ), HQ for skin lightening has been banned or restricted in Europe and the US. In contrast, HQ is not listed as a prohibited or limited ingredient for cosmetic use in Japan, and many HQ cosmetics are sold without restriction. To assess the risk of systemic effects of HQ, we examined the rat skin permeation rates of four HQ (0.3%, 1.0%, 2.6%, and 3.3%) cosmetics. The permeation coefficients ranged from 1.2 × 10-9 to 3.1 × 10-7 cm/s, with the highest value superior than the HQ aqueous solution (1.6 × 10-7 cm/s). After dermal application of the HQ cosmetics to rats, HQ in plasma was detected only in the treatment by highest coefficient cosmetic. Absorbed HQ levels treated with this highest coefficient cosmetic in humans were estimated by numerical methods, and we calculated the margin of exposure (MOE) for the estimated dose (0.017 mg/kg-bw/day in proper use) to a benchmark dose for rat renal tubule adenomas. The MOE of 559 is judged to be in a range safe for the consumer. However, further consideration may be required for regulation of cosmetic ingredients.

Rapid endoglin determination in serum samples using an amperometric magneto-actuated disposable immunosensing platform.

A sensitive and rapid method for the determination of the clinically relevant biomarker human endoglin (CD105) in serum samples is presented, involving a magneto-actuated immunoassay and amperometric detection at disposable screen-printed carbon electrodes (SPCEs). Micro-sized magnetic particles were modified with a specific antibody to selectively capture the target protein which was further sandwiched with a secondary HRP-labeled antibody. The immunocomplexes attached to the magnetic carriers were amperometrically detected at SPCEs using the hydroquinone (HQ)/H2O2/HRP system. The magneto-actuated immunosensing platform was able to detect 5 pmoles of endoglin (in 25µL of sample, 0.2µM) in 30min providing statistically similar results to those obtained using a commercial ELISA kit for the determination of endogenous content of endoglin in human serum samples.

Analysis of hydroquinone and catechol in peripheral blood of benzene-exposed workers.

We have developed a gas chromatography-mass spectrometry method for analysis of benzene (BZ) metabolites in human urine and blood. Here we describe peripheral blood concentrations of hydroquinone (HQ(1)) and catechol (CAT(2)) in total, protein-bound, and unbound (free) forms obtained from BZ-exposed factory workers and controls. Total and unbound metabolites were directly measured in independent experiments, while bound forms were calculated as [total]-[unbound]. In this subset of a larger study, breathing zone benzene, toluene, and xylene were measured for the duration of a workshift, and end-shift blood samples taken from 143 subjects and controls. Potential lifestyle and environmental influences were assessed by questionnaire and bioassay, and single nucleotide polymorphisms in xenobiotic metabolizing enzymes NQO1, MPO, CYP2E1, and GSTT1 were also analyzed for potential contribution to differences in blood metabolite concentration. Total CAT, bound CAT, total HQ, and bound HQ correlated well with benzene exposure, while unbound CAT and HQ displayed no correlation. Nearly all of the metabolites found in blood were bound to protein (CAT 96-99+%, HQ 78-92+%), and when the ratio of bound to unbound metabolites were compared in subsets of exposed workers, the increase in blood metabolite concentration was nearly all due to an increase in the protein-bound molecule. These findings suggest that a threshold for conjugation does not exist within the exposure spectrum studied (0.01-78.8 mg/m(3)). This method demonstrates the feasibility of analyzing benzene metabolites in human blood, and should allow for further investigation of the health effects of benzene and its metabolites.

Recovery and long-term renal excretion of propofol, its glucuronide, and two di-isopropylquinol glucuronides after propofol infusion during surgery.

BACKGROUND: The metabolism of the short-acting anaesthetic agent propofol has been described over the first 24 h. However, the long-term disposition of propofol and its metabolites is unclear. We describe the pharmacokinetics (renal excretion rates and renal clearance) of propofol and its metabolites over 60 h. METHODS: Ten patients undergoing lung surgery were included in the study. They received anaesthesia with continuous i.v. propofol at an average rate of 10 mg min(-1). During surgery and 60 h thereafter, we sampled blood and urine. Propofol and its metabolites were measured using gradient high performance liquid chromatography (HPLC). RESULTS: In nine patients, propofol and its glucuronides were found in the plasma over the first 15 h. In the urine, however, even after 60 h, propofol and its quinol glucuronides were still detectable. One patient had a markedly different pharmacokinetic profile, showing a limited renal excretion or absorption of 12% of the dose. CONCLUSIONS: After an infusion of propofol, patients excrete propofol and its metabolites in the urine over a period in excess of 60 h. We hypothesize that (re)absorption of propofol and its metabolites by the kidney is a major process in elimination and that the reabsorbed compounds are gradually conjugated in the kidney and excreted in the urine. One patient showed a different pharmacokinetic profile for which we currently have no explanation.

Determination of tertiary-butylhydroquinone and its metabolites in rat serum by liquid chromatography-ion trap mass spectrometry.

A new method applying sensitive and selective liquid chromatography coupled with mass spectrometry (LC/MS/MS) for analyzing tertiary-butylhydroquinone (TBHQ) and its metabolites in rat serum was validated. Using an extracted ion chromatogram (EIC) of m/z 149, free TBHQ was observed in rat serum after dosing TBHQ at 350 mg/kg to male and female Sprague-Dawley (SD) rats. Four major metabolites of TBHQ were identified-a TBHQ-sulfate, two TBHQ-sulfate-derived substances and a TBHQ-glucuronide through MS(n) spectra. Besides its simplicity, the sample treatment allows one to obtain a very good recovery of analysts, namely around 95%. This result suggests that the method described here is useful for the analysis of TBHQ and its metabolites in rat serum. Moreover, the metabolism of TBHQ was investigated using the method. After oral administration, TBHQ appear to be more completely absorbed and bio-transformed by males than females, which may result in higher acute oral toxicity of TBHQ for males than females.

Cigarette smoke-related oxidants and the development of sub-RPE deposits in an experimental animal model of dry AMD.

PURPOSE: Oxidative injury to the retinal pigment epithelium (RPE) has been proposed to be an important injury stimulus relevant to the accumulation of subretinal deposits in age-related macular degeneration (AMD). Cigarette smoking is a major risk factor for AMD, and cigarette smoke-related tar contains high concentrations of a potent oxidant, hydroquinone (HQ). This study was an investigation of the effects of cigarette smoke (CS) and HQ in the development of sub-RPE deposits in an experimental mouse model. METHODS: Sixteen-month-old C57BL/6 female mice were fed a high-fat diet (HFD) for 4.5 months. Mice were divided into two major experimental groups, one to examine the effects of cigarette smoke and one to study the effects of a defined cigarette smoke component such as HQ. In the first group, mice eyes were exposed to blue-green light (positive controls) or to whole cigarette smoke. A third group with no intervention served as the negative control. In the second experimental group, animals received a purified diet with HQ (0.8%) with low or high fat content for 4.5 months. Mice in both groups were euthanatized at 4.5 months and eyes processed for transmission electron microscopy. RESULTS: As previously demonstrated by our laboratory and others, most mice fed an HFD without other oxidant exposure demonstrated normal morphology or, in a few cases, small nodular basal laminar deposits. Eyes of mice exposed to whole cigarette smoke or to HQ in the food demonstrated a variable degree of basal laminar deposits and diffusely thickened Bruch's membrane. The choriocapillaris endothelium was variably hypertrophic. CONCLUSIONS: Exposure to cigarette smoke or the smoke-related redox molecule, HQ, results in the formation of sub-RPE deposits, thickening of Bruch's membrane, and accumulation of deposits within Bruch's membrane. Smoke-related oxidants may be another oxidative injury stimulus to the choriocapillaris and RPE, and may explain the association between cigarette smoking and early AMD.

Specific immune responses in workers exposed to benzene.

UNLABELLED: The aim of this study was to elaborate a method for detection of specific IgG antibodies (Abs) to the haptenes p-benzoquinone (p-BQ) and hydroquinone (HQ) for assessment of specific humoral immune responses. Plasma and urine, collected from petrochemical plant workers have been analyzed. The workers were divided into three professional groups in ascending order of benzene exposure. The concentration of benzene in the air was determined by gas chromatography with mass-spectrometry and trans,trans-muconic acid (biomarker of benzene exposure) in urine-by liquid chromatography with UV-detection. Specific IgG Abs to haptenes p-BQ and HQ in plasma were determined with newly developed ELISA. The relationships "exposure-effect," revealed increased levels of specific IgG to haptens correlating with the benzene exposure. The "exposure-response" relationships demonstrated that workers with value of OD over X+2SD were 62% low exposure group, 68% in group with level of exposure on Threshold Limit Value (TLV) and 91% in the highest exposure group. The data obtained show that there is a good correlation between antibody production and the biomarker of exposure t,t-muconic acid. CONCLUSION: The newly developed method is applicable for assessment of specific humoral immune responses in workers exposed to benzene. There was a good correlation between benzene exposure and formation of antibodies against benzene metabolites.

Pharmacokinetic studies in Tg.AC and FVB mice administered [14C] benzene either by oral gavage or intradermal injection.

Chronic benzene toxicity has been demonstrated to result in either aplastic anemia or acute myelogenous leukemia, a form of granulocytic leukemia, in exposed people (Snyder and Kalf, Crit. Rev. Toxicol. 24, 177-209, 1994). Aplastic anemia has been demonstrated in animal models following benzene exposure but, heretofore, it has not been possible to replicate benzene-induced granulocytic leukemia in animals. The Tg.AC mouse appears to be the first animal model in which a granulocytic leukemia was produced by treatment with benzene (Tennant et al., The Use of Short- and Medium-Term Tests for Carcinogenic Hazard Evaluation, 1999; French and Saulnier, J. Toxicol. Environ. Health 61, 377-379, 2000). Leukemia was observed in Tg.AC mice to which benzene was administered dermally. Neither orally dosed Tg.AC mice or mice of the parental FVB strain treated by either route of exposure developed leukemia. It is well established that benzene metabolism is required to produce benzene toxicity. To determine whether metabolic differences arising from differences in route of exposure or strain of mouse directed the development of leukemia, the pharmacokinetics of benzene were compared between the two strains and between the two routes of administration. Regardless of the route of exposure or the strain of mouse, seven major metabolites plus unmetabolized benzene were detected in most samples at most time points. Few differences were observed between the two strains following either route of administration. These results suggest that the genetic modification in the Tg.AC mouse, i.e., insertion of the v-Ha-ras construct into the genome, did not disrupt any major pathways involved in determining the pharmacokinetics of benzene. Two significant differences were observed between the two routes of exposure: first, benzene was absorbed more slowly after intradermal injection than after oral gavage, and second, the intradermally dosed mice produced more conjugates of hydroquinone than did the orally dosed mice. These differences in metabolism may be involved in the previously observed differences in hematotoxicity between the two routes of exposure.

The role of human lungs in the biotransformation of propofol.

BACKGROUND: The metabolism of propofol is very rapid, and its transformation takes place mainly in the liver. There are reports indicating extrahepatic metabolism of the drug, and the alimentary canal, kidneys, and lungs are mentioned as the most probable places where the process occurs. The aim of this study was to determine whether the human lungs really take part in the process of propofol biotransformation. METHODS: Blood samples were taken from 55 patients of American Society of Anesthesiologists grade 1-3 scheduled for elective intracranial procedures (n = 47) or for pulmonectomy (n = 8). All patients were premedicated with diazepam (10 mg) administered orally 2 h before anesthesia. Propofol total intravenous anesthesia was performed at the following infusion rates: 12 mg. kg-1. h-1, 9 mg. kg-1. h-1, and 6 mg. kg-1. h-1. Fentanyl and pancuronium bromide were also administered intermittently. After tracheal intubation, the lungs were ventilated to normocapnia with an oxygen-air mixture (fraction of inspired oxygen = 0.33). Blood samples for propofol and 2,6-diisopropyl-1, 4-quinol analysis were taken simultaneously from the right atrium and the radial artery, or the pulmonary artery and the radial artery. The concentration of both substances were measured with high-performance liquid chromatography and gas chromatography-mass spectroscopy. RESULTS: The concentration of propofol in the central venous system (right atrium or pulmonary artery) is greater than in the radial artery, whereas the opposite is observed for propofol's metabolite, 2,6-diisopropyl-1,4-quinol. Higher propofol concentrations are found in blood taken from the pulmonary artery than in the blood collected from the radial artery. CONCLUSIONS: Human lungs take part in the elimination of propofol by transforming the drug into 2,6-diisopropyl-1,4-quinol.

Hydroquinone: genotoxicity and prevention of genotoxicity following ingestion.

Plant-derived polyphenolics and other chemicals with antioxidant properties have been reported to inhibit the expression of genotoxic activity by pro-oxidant chemicals (Sai et al., 1992, 1994; Teel and Castonguay, 1992). In vitro and in vivo studies with ionizing radiation suggest that hydroquinone (HQ) may have similar protective effects (Babaev et al., 1994). The present study was conducted to determine whether HQ is capable of inhibiting the induction of micronuclei in the bone marrow of mice following exposure to an oxidant, potassium bromate or KBrO3 (Nakajima et al., 1989; Sai et al., 1992, 1994). To be able to interpret the results of this work, it was also necessary to determine whether HQ is itself genotoxic when fed in the diet. HQ diets (0.8%) fed to mice for 6 days reduced the background incidence of micronuclei compared with the basal diet. KBrO3 dosed ip (12.5-100 mg/kg) produced a dose-dependent increase in micronuclei as reported by others. Mice fed 0.8% HQ diets 6 days, and then dosed intraperitoneally with KBrO3, showed a 36% reduction in micronuclei across the range of KBrO3 dose levels. This effect was associated with a reduction in the background micronucleus response as well as a reduction in response to KBrO3. Statistical significance (P < or = 0.05), observed at a dose of 25 mg/kg KBrO3 in the mice fed the control diet, was abolished in the group fed 0.8% HQ. When mice were given 50 mg HQ/kg by oral gavage and then given 50 mg KBrO3/kg ip 20 min later, the micronucleus response induced by KBrO3, was lower in animals given HQ. The results of this study demonstrate that large doses of HQ may be given orally without induction of micronuclei or bone marrow depression, that HQ reduces the background micronucleus response in animals fed a basal diet, and that the HQ reduces the micronucleus response to KBrO3 as well as background incidence of micronuclei in KBrO3-dosed animals. The protective effect of HQ may be due to enzyme induction or a direct antioxidant effect of HQ against oxidants commonly present in the diet.

Bioavailability and metabolism of hydroquinone after intratracheal instillation in male rats.

The purpose of this study was to investigate the rate and extent of hydroquinone (HQ) absorption and first pass metabolism in the lungs of male rats in vivo. [14C]HQ in physiological saline was administered intratracheally via an indwelling endotracheal tube to simulate inhalation exposure to HQ dust. The bioavailability of HQ was determined by blood sampling simultaneously at arterial and venous sites beginning immediately after administration to conscious rats. Pulmonary absorption and metabolism, and systemic metabolism and elimination were determined by chromatographic analysis of parent compound and metabolites in blood samples after intratracheal administration of [14C]HQ at 0.1, 1.0, and 10 mg/kg. Pulmonary absorption of HQ was found to be very rapid with [14C]HQ detectable in arterial blood, and to a lesser extent in venous blood, within 5 to 10 s after dose administration. Only [14C]HQ was detected in the initial (5-10 s) arterial blood samples at all dose levels, indicating that pulmonary metabolism of HQ was not extensive. However, later blood samples (45-720 s) indicated rapid metabolism and elimination of the parent compound and metabolites after intratracheal absorption. The elimination half-life from the 0.1 mg/kg dose was allometrically scaled to human proportions and used to estimate the steady-state (maximum) human blood concentrations of HQ resulting from presupposed workplace exposures. The estimates indicated minimal levels of HQ in human blood after respiratory exposures of greater than 1 h at 0.1 or 2.0 mg/m3; these levels were less than background concentrations of HQ detected in human blood in previous studies.

Direct high-performance liquid chromatography determination of propofol and its metabolite quinol with their glucuronide conjugates and preliminary pharmacokinetics in plasma and urine of man.

Propofol (P) is metabolized in humans by oxidation to 1,4-di-isopropylquinol (Q). P and Q are in turn conjugated with glucuronic acid to the respective glucuronides, propofol glucuronide (Pgluc), quinol-1-glucuronide (Q1G) and quinol-4-glucuronide (Q4G). Propofol and quinol with their glucuronide conjugates can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic hydrolysis. The glucuronide conjugates were isolated by preparative HPLC from human urine samples. The glucuronides of P and Q were present in plasma and urine, P and Q were present in plasma, but not in urine. Quinol in plasma was present in the oxidised form, the quinone. Calibration curves of the respective glucuronides were constructed by enzymic deconjugation of isolated samples containing different concentrations of the glucuronides. The limit of quantitation of P and quinone in plasma are respectively 0.119 and 0.138 microg/ml. The limit of quantitation of the glucuronides in plasma are respectively: Pgluc 0.370 microg/ml, Q1G 1.02 microg/ml and Q4G 0.278 microg/ml. The corresponding values in urine are: Pgluc 0.264 microg/ml, Q1G 0.731 microg/ml and Q4G 0.199 microg/ml. A pharmacokinetic profile of P with its metabolites is shown, and some preliminary pharmacokinetic parameters of P and Q glucuronides are given.

Prodrug for bioreductive activation-independent delivery of menahydroquinone-4: human liver enzymatic activation and its action in warfarin-poisoned human liver.

The N,N-dimethylglycine esters of menahydroquinone-4 (1-mono, 1; 4-mono, 2; 1,4-bis, 3) were established in previous reports as prodrugs that could achieve the systemic bioreductive activation-independent delivery of menahydroquinone-4 (MKH), the active form of menaquinone-4 (MK-4), in rat. The present study was undertaken to investigate if the prodrugs could undergo cleavage to parent drug (MKH) by a human tissues enzyme catalyzed hydrolytic pathway, the mechanism of the prodrugs for vitamin K-dependent carboxylation in human liver and their action in the warfarin poisoned human liver. The hydrolysis of the esters was shown to be catalyzed by esterases located in human liver but not in human plasma. The susceptibility of the esters to undergo human liver esterase hydrolysis was affected by the esterified position: 1>2>3. By using a human liver microsomal test system, the stimulation of vitamin K-dependent carboxylation with the prodrugs was determined. The prodrug could stimulate the carboxylation activity in the absence of dithiothreitol, an artificial activator of the reductive activation pathway of MK-4. The carboxylation activity of the prodrug was strongly inhibited in the presence of eserine, an esterase inhibitor. The prodrug could also stimulate the carboxylase under warfarin-poisoned conditions, where the vitamin K cycle was strongly inhibited. The results confirmed that the prodrug could generate MKH in human liver (active site), and that the resultant MKH could act as a cofactor for the carboxylase without reductive activation processes of MK-4 to MKH. Such bioreductive activation-independent vitamin K-dependent carboxylation characteristic of the prodrug leads to enhanced pharmacological efficacy in the treatment of hypoprothrombinaemia induced in patients with coumarin and cephalosporin therapies.

Influence of gender and acetone pretreatment on benzene metabolism in mice exposed by nose-only inhalation.

Benzene (BZ) requires oxidative metabolism catalyzed by cytochrome P-450 2E1 (CYP 2E1) to exert its hematotoxic and genotoxic effects. We previously reported that male mice have a two-fold higher maximum rate of BZ oxidation compared with female mice; this correlates with the greater sensitivity of males to the genotoxic effects of BZ as measured by micronuclei induction and sister chromatid exchanges. The aim of this study was to quantitate levels of BZ metabolites in urine and tissues, and to determine whether the higher maximum rate of BZ oxidation in male mice would be reflected in higher levels of hydroxylated BZ metabolites in tissues and water-soluble metabolites in urine. Male and female B6C3F, mice were exposed to 100 or 600 ppm 14C-BZ by nose-only inhalation for 6 h. An additional group of male mice was pretreated with 1% acetone in drinking water for 8 d prior to exposure to 600 ppm BZ; this group was used to evaluate the effect of induction of CYP 2E1 on urine and tissue levels of BZ and its hydroxylated metabolites. BZ, phenol (PHE), and hydroquinone (HQ) were quantified in blood, liver, and bone marrow during exposure and postexposure, and water-soluble metabolites were analyzed in urine in the 48 h after exposure. Male mice exhibited a higher flux of BZ metabolism through the HQ pathway compared with females after exposure to either 100 ppm BZ (32.0 2.03 vs. 19.8 2.7%) or 600 ppm BZ (14.7 1.42 vs. 7.94 + 0.76%). Acetone pretreatment to induce CYP 2E1 resulted in a significant increase in both the percent and mass of urinary HQ glucuronide and muconic acid in male mice exposed to 600 ppm BZ. This increase was paralleled by three- to fourfold higher steady-state concentrations of PHE and HQ in blood and bone marrow of acetone-pretreated mice compared with untreated mice. These results indicate that the higher maximum rate of BZ metabolism in male mice is paralleled by a greater proportion of the total flux of BZ through the pathway for HQ formation, suggesting that the metabolites formed along this pathway may be responsible for the genotoxicity observed following BZ exposure.

High sensitivity determination of the remoxipride hydroquinone metabolite NCQ-344 in plasma by coupled column reversed-phase liquid chromatography and electrochemical detection.

An HPLC method for the determination of NCQ-344, a remoxipride metabolite with a hydroquinone structure, in human plasma is described. Special precautions for the sampling were necessary as the compound rapidly decomposes. An efficient clean-up of the plasma samples was necessary to make use of the inherent sensitivity of the electrochemical detector. This was accomplished by a fast and simple liquid-liquid extraction at pH 7.05 combined with further cleaning on-line by using a short cyanopropyl column as the first column in a column switching system. A heart-cut from the cyanopropyl column containing the NCQ-344 fraction was then injected onto the analytical octadecyl silica column and NCQ-344 was detected at an oxidation potential of 0.70 V. The absolute recovery was > 95% and concentrations down to 0.10 nM could be determined with acceptable precision. The NCQ-344 levels in a limited number of samples from patients given remoxipride were found to be between 0.10 and 1 nM. The remoxipride concentrations in the same samples were 5,000-20,000 nM.

Differences in rates of benzene metabolism correlate with observed genotoxicity.

Benzene (BZ) requires oxidative metabolism via cytochrome P450 2E1 (CYP 2E1) to exert its hematotoxic and genotoxic effects. Male mice are two- to threefold more sensitive to the genotoxic effects of BZ as measured by micronuclei induction and sister chromatid exchanges. The purpose of our study was to investigate sex-related differences in the metabolism of BZ, phenol (PHE) and hydroquinone (HQ) in order to understand the metabolic basis for sex-dependent differences in BZ genotoxic susceptibility in mice. Rates of BZ oxidation were quantitated using closed chamber gas uptake studies with male and female B6C3F1 mice exposed to initial low (400-500 ppm), intermediate (1200-1300 ppm), and high (2600-2800 ppm) BZ concentrations. Acetone-pretreated and diethyldithiocarbamate-pretreated male mice were also studied to determine the extent to which induction and inhibition of CYP 2E1, respectively, would alter in vivo BZ oxidation rates. Elimination of PHE and HQ from blood was also compared in male and female mice to complement previously reported data on sex-related differences in urinary excretion of conjugated metabolites following iv administration of PHE. Based on PBPK model analysis, the optimized rate of metabolism (Vmax) of BZ was almost twofold higher in male mice (14.0 mumol/hr-kg) than in female mice (7.9 mumol/hr-kg); both male and female mice gas-uptake data were well fit with a KM of 3.0 microM. Pretreatment of male mice with 1% acetone in drinking water for 8 days to specifically induce CYP 2E1 enhanced the rate of BZ oxidation by approximately fivefold (Vmax = 75 mumol/hr-kg), while diethyldithiocarbamate pretreatment (320 mg/kg ip 30 min prior to uptake study) completely inhibited BZ oxidation (Vmax = 0 mumol/hr-kg). Thus, both pretreatment regimens are potentially useful investigative tools to study the metabolic basis for benzene toxicity. Elimination of PHE from blood was significantly faster in male mice, while elimination of HQ did not differ between male and female mice. Previous data indicated male mice produce more of the oxidized and conjugated metabolite, HQ glucuronide, after PHE administration, suggesting that HQ production from PHE is greater in male mice. Taken together, these data support the hypothesis that the greater sensitivity of male mice to the genotoxic effects of BZ compared to females is a function of greater oxidative metabolism toward both BZ and PHE in male mice. These data also suggest that differences in hepatic human CYP 2E1 activity may be an important factor to consider when evaluating human risk for benzene-induced hematotoxic and genotoxic effects.

Human exposure to naturally occurring hydroquinone.

Hydroquinone (HQ) is a nonvolatile chemical used in the photographic, rubber, chemical, and cosmetic industries. HQ is also known to occur in nature as the beta-D-glucopyranoside conjugate (arbutin), and free HQ is a known component of cigarette smoke. Low concentrations of HQ have been detected in the urine and plasma of humans with no occupational or other known exposure to HQ. The studies reported here investigate dietary and other potential sources of HQ and their contribution to HQ concentrations in the plasma and urine of human volunteers. Analysis of possible food sources of HQ by GC indicated significant amounts of arbutin in wheat products (1-10 ppm), pears (4-15 ppm), and coffee and tea (0.1 ppm). Free HQ was found in coffee (0.2 ppm), red wine (0.5 ppm), wheat cereals (0.2-0.4 ppm), and broccoli (0.1 ppm). After consuming a meal including arbutin- and HQ-containing foods, volunteers showed significant increases in plasma and urinary levels of HQ and its conjugated metabolites (total HQ). Mean plasma concentrations of total HQ peaked at 5 times background levels at 2 h after the completion of the meal, and mean urinary excretion rates of total HQ peaked at 12 times background at 2-3 h after the meal. Immediately after smoking four cigarettes in approximately 30 min, mean plasma concentrations of total HQ were maximally 1.5 times background levels; mean urinary excretion rates of total HQ peaked at 2.5 times background at 1-3 h after smoking. These data indicate that considerable human exposure to HQ can result from plant-derived dietary sources and, to a lesser extent, from cigarette smoke.

Pharmacokinetic interaction between benzene metabolites, phenol and hydroquinone, in B6C3F1 mice.

There is strong evidence that metabolites are responsible for adverse effects of benzene. Benzene myelotoxicity, reproduced by coadministering phenol (PH) and hydroquinone (HQ) but not when these benzene metabolites were administered alone, has been postulated to be induced by PH stimulating the myeloperoxidase-mediated oxidation of HQ to the toxic 1,4-benzoquinone in bone marrow. A pharmacokinetic interaction between PH and HQ is also hypothesized to contribute to the observation. Both metabolites are sulfoconjugated and glucuronoconjugated. Sulfoconjugation of phenolic substrates has been shown to approach saturation at high concentrations in rats. Thus, more PH may be converted to HQ and HQ conjugation may be diminished. These effects would increase the amounts of PH and HQ present and result (by further oxidation) in the formation of more 1,4-benzoquinone. To test this hypothesis, we investigated the pharmacokinetics in blood and the recovery of hydroquinone and phenol in urine when the metabolites were administered intraperitoneally alone or in combination at 75 mg/kg each to B6C3F1 mice. The combination resulted in a 2.6-fold increase in the area under the blood concentration-time curve (AUC) of HQ compared to the sum of AUC values observed after administration of each compound alone. The half-life of HQ was also increased from 9 +/- 2 to 15 +/- 3 min. The AUC of PH was increased by a factor of 1.4. The clearance of phenol decreased from 89 +/- 13 ml/min per kilogram when injected alone to 62 +/- 7 ml/min per kilogram after coadministration. A decreased clearance of formation of each conjugate demonstrated that both conjugation pathways were diminished. This interaction may contribute to the observed production of myelotoxicity when these metabolites are coadministered.

Simultaneous assay of pentachlorophenol and its metabolite, tetrachlorohydroquinone, by gas chromatography without derivatization.

A sensitive capillary gas chromatographic method was developed for the simultaneous determination of pentachlorophenol and its major metabolite, tetrachlorohydroquinone, in plasma, urine and feces. The method involved a simple one-step liquid-liquid extraction with diethyl ether and electron-capture detection gas chromatography on a fused-silica capillary column coated with 50% methylsilicone-50% trifluoropropylsilicone. The detection limit of both compounds was 50 ng/ml in plasma (from an initial volume of 0.1 ml), 100 ng/ml in urine and 100 ng/g in feces. Optimal conditions for both chemical and enzymatic hydrolysis were defined to measure conjugates of both pentachlorophenol and tetrachlorohydroquinone in urine. Tetrachlorohydroquinone was found to be unstable in plasma and urine; means to prevent its degradation during sample collection and storage by addition of ascorbic acid and ethylenediaminetetracetic acid are presented. This chromatographic method was shown to be precise, accurate and specific. It was successfully applied to toxicokinetic studies in rat.

Comparison of serum hydroquinidine determination by fluorescence polarization immunoassay and liquid chromatography.

Hydroquinidine is a structural analogue of quinidine. It is used in the treatment and prevention of cardiac arrhythmias and necessitates serum monitoring. Fluorescence polarization immunoassay (FPIA) of quinidine has been proposed and we have tested the performance of this assay for hydroquinidine using its cross-reaction with quinidine. Tracer (quinidine labelled with fluorescein) and anti-serum were purchased from Abbott S.A. Standard curves were obtained using specifically prepared hydroquinidine calibrators and within-run and run-to-run precision values (expressed as relative standard deviation) (RSD) lower than 5.3% (n = 10). In order to evaluate specificity of this assay in the clinical situation, FPIA and liquid chromatography results were compared.