Diallyl trisulfide attenuated n-hexane induced neurotoxicity in rats by modulating P450 enzymes.

Chronic exposure to n-hexane can induce serious nerve system impairments without effective preventive medicines. Diallyl trisulfide (DATS) is a garlic-derived organosulfur compound, which has been demonstrated to have many beneficial effects. The current study was designed to evaluate whether DATS could restrain n-hexane induced neurotoxicity in rats and to explore the underlying mechanisms. Rats were treated with n-hexane (3 g/kg, p.o.) and different doses of DATS (10, 20 and 30 mg/kg, p.o.) for 8 weeks. Behavioral assessment showed that DATS could inhibit n-hexane induced neurotoxicity, demonstrated by the improvement of the grip strength and decline of gait scores. Toxicokinetic analysis revealed that the Cmax and AUC0-t of 2,5-hexanedione (product of n-hexane metabolic activation) and 2,5-hexanedione protein adducts in serum were significantly declined in DATS-treated rats, and the levels of pyrrole adducts in tissues were significantly reduced. Furthermore, DATS activated CYP1A1 and inhibited n-hexane induced increased expression and activity of CYP2E1 and CYP2B1. Collectively, these findings indicated that DATS protected the rats from n-hexane-induced neurotoxicity, which might be attributed to the modulation of P450 enzymes by DATS.

Novel bicyclo[3.1.0]hexane analogs as antagonists of metabotropic glutamate 2/3 receptors for the treatment of depression.

Negative modulators of metabotropic glutamate 2 & 3 receptors demonstrate antidepressant-like activity in animal models and hold promise as novel therapeutic agents for the treatment of major depressive disorder. Herein we describe our efforts to prepare and optimize a series of conformationally constrained 3,4-disubstituted bicyclo[3.1.0]hexane glutamic acid analogs as orthosteric (glutamate site) mGlu2/3 receptor antagonists. This work led to the discovery of a highly potent and efficacious tool compound 18 (hmGlu2 IC50 46±14.2nM, hmGlu3 IC50=46.1±36.2nM). Compound 18 showed activity in the mouse forced swim test with a minimal effective dose (MED) of 1mg/kg ip. While in rat EEG studies it exhibited wake promoting effects at 3 and 10mg/kg ip without any significant effects on locomotor activity. Compound 18 thus represents a novel tool molecule for studying the impact of blocking mGlu2/3 receptors both in vitro and in vivo.

Cellular Internalization Mechanisms of Polyanhydride Particles: Implications for Rational Design of Drug Delivery Vehicles.

Polyanhydride nanoparticles have emerged as a versatile delivery platform, due to their ability to encapsulate diverse drugs, immunogens, antibodies, and proteins. However, mechanistic studies on the effects of particle chemistry interactions with immune cells have yet to be described. Understanding the mechanism by which these particles are internalized by immune cells will enable rational selection of delivery vehicles for specific applications. In the present study, the internalization, mechanism(s) of uptake by monocytes, and intracellular fate of polyanhydride nanoparticles were evaluated using copolymers based on 1,6-bis(p-carboxyphenoxy)hexane (CPH), sebacic acid (SA), and 1,8-bis(p-carboxyphenoxy)3,6-dioxaoctane (CPTEG). The results showed that 20:80 CPH:SA and 20:80 CPTEG:CPH nanoparticles were internalized to a greater extent by monocytes as compared to the 50:50 CPH:SA and 50:50 CPTEH:CPH nanoparticles. Further, cytochalasin-D treatment of cells inhibited uptake of all the particles, regardless of chemistry, indicating that actinmediated uptake is the primary mechanism of cellular entry for these particles. The insights gained from these studies were used to identify lead nanoparticle formulations to enhance treatment of intracellular bacterial infections. The use of doxycycline-loaded nanoparticles exhibited enhanced therapeutic efficacy compared to soluble drug in treating monocyte monolayers infected with the virulent intracellular pathogen Brucella abortus. Altogether, these studies demonstrate how rational design and selection of nanoscale delivery platforms can be used for a wide spectrum of biomedical applications.

Evaluation of occupational exposure: comparison of biological and environmental variabilities using physiologically based toxicokinetic modeling.

PURPOSE: Few studies compare the variabilities that characterize environmental (EM) and biological monitoring (BM) data. Indeed, comparing their respective variabilities can help to identify the best strategy for evaluating occupational exposure. The objective of this study is to quantify the biological variability associated with 18 bio-indicators currently used in work environments. METHOD: Intra-individual (BV(intra)), inter-individual (BV(inter)), and total biological variability (BV(total)) were quantified using validated physiologically based toxicokinetic (PBTK) models coupled with Monte Carlo simulations. Two environmental exposure profiles with different levels of variability were considered (GSD of 1.5 and 2.0). RESULTS: PBTK models coupled with Monte Carlo simulations were successfully used to predict the biological variability of biological exposure indicators. The predicted values follow a lognormal distribution, characterized by GSD ranging from 1.1 to 2.3. Our results show that there is a link between biological variability and the half-life of bio-indicators, since BV(intra) and BV(total) both decrease as the biological indicator half-lives increase. BV(intra) is always lower than the variability in the air concentrations. On an individual basis, this means that the variability associated with the measurement of biological indicators is always lower than the variability characterizing airborne levels of contaminants. For a group of workers, BM is less variable than EM for bio-indicators with half-lives longer than 10-15 h. CONCLUSION: The variability data obtained in the present study can be useful in the development of BM strategies for exposure assessment and can be used to calculate the number of samples required for guiding industrial hygienists or medical doctors in decision-making.

Discovery and synthesis of a new class of opioid ligand having a 3-azabicyclo[3.1.0]hexane core. An example of a 'magic methyl' giving a 35-fold improvement in binding.

In looking for a novel achiral µ opioid receptor antagonist for the treatment of pruritus, we designed and synthesised azabicyclo[3.1.0]hexane compounds as a new class of opioid ligand. During optimisation, an addition of a single methyl resulted in a 35-fold improvement in binding. An early example from the series had excellent µ opioid receptor antagonist antagonist activity and was very effective in an in vivo pruritus study.

Triazolyl azabicyclo[3.1.0]hexanes: A class of potent and selective dopamine D(3) receptor antagonists.

Herein we report a detailed description of the structure-activity relationships for a novel series of "C-linked" 1,2,4-triazolylazabicyclo[3.1.0]hexanes. These derivatives are endowed with very high in vitro affinity and selectivity for the dopamine D(3) receptor. An optimization with respect to undesired affinity toward the hERG potassium channel is also reported. Members of this compound series also show excellent in vitro and in vivo pharmacokinetic properties.

[Effects of garlic oil on n-hexane metabolized to 2, 5-hexanedione in mice serum].

OBJECTIVE: To investigate the effects of garlic oil (GO) on n-hexane metabolized to 2, 5-hexanedione (2, 5-HD) in mice. METHODS: Adult healthy Kunming-mice were treated with n-hexane and GO. The serum was obtained and extracted with ethyl acetate, and the levels of the serum 2, 5-HD were determined by gas chromatography. RESULTS: (1) The concentration of 2, 5-HD in serum increased firstly after a single exposure to n-hexane (4 000 mg/kg). The peak value occurred at 10 hours after n-hexane treatment, but could hardly be detected at 20 h. (2) There was no 2, 5-HD in serum of control mice. The content of 2, 5-HD in serum increased along with the exposure dose of n-hexane. The serum 2, 5-HD contents of the 2000, 4000 and 6000 mg/kg groups mice were 8.04, 16.68 and 22.38 microg/ml at 8 h in pretreated mice, respectively, and showed significant dose-effect relationship. (3) When the different age mice were exposed to the same dose of n-hexane, the contents of 2, 5-HD in serum were significantly different after 8 hours (P<0.05). The serum 2, 5-HD level of the 5 weeks old mice (22.83 microg/ml) was much higher than the 4 (19.59 microg/ml) and 6 (16.42 microg/ml) weeks old mice. (4) When the different gender mice were exposed to the same dose of n-hexane, the concentration of 2, 5-HD in serum of female mice (13.22 microg/ml) was higher than that of the female mice (10.34 microg/ml, P<0.05). (5) GO significantly inhibited the increase of the serum 2, 5-HD levels of both the pretreatment and post-treatment groups treated with 80 mg/kg n-hexane respectively, but the pretreatment with GO exhibited the more suppressive effects than the post-treatment (P>0.05). Compared with the n-hexane group, the concentrations of serum 2, 5-HD in GO-pretreated groups mice decreased by 16.2%, 20.8%, 22.8% (P<0.05) and 32.1% (P<0.01), respectively, and showed significant dose-effect relationship. CONCLUSION: The serum content of 2, 5-HD, the metabolite of n-hexane, is different in different genders and age mice after exposed to the same dose of n-hexane. GO can effectively inhibit the production of n-hexane metabolized to 2, 5-HD in mice serum.

Probing mechanisms of axonopathy. Part II: Protein targets of 2,5-hexanedione, the neurotoxic metabolite of the aliphatic solvent n-hexane.

Neuroprotein changes in the spinal cord of rodents with aliphatic gamma-diketone axonopathy induced by 2,5-hexanedione (2,5-HD) are compared with those reported previously in aromatic gamma-diketone-like axonopathy induced by 1,2-diacetylbenzene (1,2-DAB). Sprague-Dawley rats were treated intraperitoneally with 500 mg/kg/day 2,5-HD, equimolar doses of 2,3-hexanedione (negative control), or an equivalent amount of saline containing 50% dimethyl sulfoxide (vehicle), 5 days a week, for 3 weeks. Analysis of the lumbosacral proteome by 2-dimensional differential in-gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight/tandem mass spectrometry revealed 34 proteins markedly modified by 2,5-HD of which neurofilament triplet L, gelsolin, protein disulfide isomerase, glutathione S-transferase, nicotinamide adenine dinucleotide (reduced) dehydrogenase 1 alpha, pyruvate kinase, and fatty acid synthase were also modified by 1,2-DAB. The expression of proteins involved in maintaining the physical integrity of the cytoskeleton or controlling the redox and protein-folding mechanisms was reduced, whereas that of proteins supporting energy metabolism was mainly increased. The similarity of the neuroproteomic patterns of 2,5-HD and 1,2-DAB axonopathy suggests common biomarkers and/or mechanisms of neurotoxicity associated with exposure to their parent chemicals, namely the industrial solvents n-hexane and 1,2-diethylbenzene, respectively.

The pharmacokinetics of subcutaneously injected Bimosiamose disodium in healthy male volunteers.

Bimosiamose is a novel synthetic pan-selectin antagonist developed for the treatment of acute and chronic inflammatory disorders. Therefore the pharmacokinetics of Bimosiamose disodium were studied in healthy male volunteers after single and multiple subcutaneous injections. A randomized, double-blind, placebo-controlled dose escalation trial was carried out. The subjects received subcutaneous injections of placebo or 100, 200 or 300 mg Bimosiamose disodium into the abdomen. Plasma and urine concentrations of Bimosiamose were determined. The maximum plasma concentration was 2.17+/-0.70 microg/ml and the AUC(0-infinity) 11.1+/-2.9 h microg/ml after the highest dose on day 1 (mean+/-SD). For the apparent clearance CL/f 28.7+/-7.3 l/h and the terminal half life t(1/2) 3.7+/-0.6 h were calculated. The mean residence time MRT(infinity) of 5.5 to 6.3 h for s.c. injection exceeded that after i.v. infusion due to an extended absorption time. For multiple dosing, constant pre-dose concentrations of about 20 ng/ml may be reached after two subsequent doses of 200 or 300 mg Bimosiamose disodium once daily. Almost 15% of the administered drug was excreted unchanged in urine. Moreover, Bimosiamose was well tolerated.

Effect of physical exertion on the biological monitoring of exposure to various solvents following exposure by inhalation in human volunteers: II. n-Hexane.

This study evaluated the impact of physical exertion on two n-hexane (HEX) exposure indicators in human volunteers exposed under controlled conditions in an inhalation chamber. A group of four volunteers (two women, two men) were exposed to HEX (50 ppm; 176 mg/m(3)) according to several scenarios involving several periods when volunteers performed either aerobic (AERO), muscular (MUSC), or both AERO/MUSC types of exercise. The target intensities for 30-min exercise periods separated by 15-min rest periods were the following: REST, 50W AERO [time-weighted average intensity including resting period (TWAI): 38W], 50W AERO/MUSC (TWAI: 34W), 100W AERO/MUSC (TWAI: 63W), and 100W AERO (TWAI: 71W) for 7 hr (two 3-hr exposure periods separated by 1 hr without exposure) and 50W MUSC for 3 hr (TWAI: 31W). Alveolar air and urine samples were collected at different time intervals before, during, and after exposure to measure unchanged HEX in expired air (HEX-A) and urinary 2,5-hexanedione (2,5-HD). HEX-A levels during exposures involving AERO activities (TWAI: 38W and 71W) were significantly enhanced (approximately +14%) compared with exposure at rest. MUSC or AERO/MUSC exercises were also associated with higher HEX-A levels but only at some sampling times. In contrast, end-of-exposure (7 hr) urinary 2,5-HD (mean +/- SD) was not modified by physical exertion: 4.14 +/- 1.51 micromol/L (REST), 4.02 +/- 1.52 micromol/L (TWAI 34W), 4.25 +/- 1.53 micromol/L (TWAI 38W), 3.73 +/- 2.09 micromol/L (TWAI 63W), 3.6 +/- 1.34 micromol/L (TWAI 71W) even though a downward trend was observed. Overall, this study showed that HEX kinetics is practically insensitive to moderate variations in workload intensity; only HEX-A levels increased slightly, and urinary 2,5-HD levels remained unchanged despite the fact that all types of physical exercise increased the pulmonary ventilation rate.

Tolerability and pharmacokinetics of inhaled bimosiamose disodium in healthy males.

AIMS: The aim of these first-in-human studies was to investigate the tolerability and the pharmacokinetics of bimosiamose disodium (TBC1269Z) administered by inhalation. METHODS: Two randomized, double-blind, placebo-controlled Phase I trials were performed in healthy males. In a single-dose escalating study 48 subjects received doses of 2-140 mg bimosiamose disodium by inhalation and in a multiple-dose study 32 subjects received 8-70 mg bimosiamose disodium twice daily. In both studies 4 ml of the drug solution was administered via nebulizer over 15 min. Adverse events, vital signs, ECG, clinical laboratory parameters and forced expiratory volume in 1 s (FEV(1)) data were recorded and nasopharyngeal examinations were performed to address the safety and tolerability. Blood was collected for the determination of plasma concentrations of bimosiamose. RESULTS: All subjects completed the study. No deaths or severe adverse events occurred. Eleven mild adverse events occurred in the dose-escalation study and 34 in the multiple-dose study after inhalation of bimosiamose disodium. Adverse events were more frequent at the highest dose (140 mg) of the dose-escalation study. For placebo treatment one moderate adverse event was observed in the dose-escalation study after placebo treatment, eight mild and three moderate adverse events occurred in the multiple-dose study. Bimosiamose was detected in plasma (maximum concentration 64 ng ml(-1)) only at doses > or =50 mg given twice daily and 105 mg once daily. For the highest dose a median value of 5746 h ng ml(-1) was determined for the AUC over the entire period of treatment of the multiple-dose study. CONCLUSION: The results suggest that single and multiple inhalation of bimosiamose disodium up to 70 mg is well tolerated in healthy males. Systemic bioavailability after inhalation is low.

Phase partition of gaseous hexane and surface hydrophobicity of Fusarium solani when grown in liquid and solid media with hexanol and hexane.

The filamentous fungus, Fusarium solani, was grown in liquid and solid culture with glucose, glycerol, 1-hexanol and n-hexane. The partition coefficient with gaseous hexane (HPC) in the biomass was lower when grown in liquid medium with 1-hexanol (0.4) than with glycerol (0.8) or glucose (1) The HPC for surface growth were 0.2 for 1-hexanol, 0.5 for glycerol, 0.6 for glucose, and 0.2 for F. solani biomass obtained from a biofilter fed with gaseous n-hexane. These values show a 200-fold increase in n-hexane solubility when compared to water (HPC = 42). Lower HPC values can be partially explained by increased lipid accumulation with 1-hexanol, 10.5% (w/w) than with glycerol (8.5% w/w) or glucose (7.1% w/w). The diameter of the hyphae diminished from 3 microm to 2 microm when F. solani was grown on solid media with gaseous n-hexane thereby doubling the surface area for gaseous substrate exchange. The surface hydrophobicity of the mycelia increased consistently with more hydrophobic substrates and the contact angle of a drop of water on the mycelial mat was 113 degrees when grown on n-hexane as compared to 75 degrees with glucose. The fungus thus adapts to hydrophobic conditions and these changes may explain the higher uptake of gaseous hydrophobic substances by fungi in biofilters.

Physiochemical properties, safety and pharmacokinetics of bimosiamose disodium after intravenous administration.

OBJECTIVE: Bimosiamose is a novel synthetic panselectin antagonist being developed for the treatment of acute and chronic inflammatory disorders. Therefore, we have studied the pharmacokinetics and tolerability and determined the pharmacokinetically relevant physicochemical characteristics of bimosiamose. METHOD: A randomized, double-blind, placebo-controlled dose-escalation trial in healthy male subjects has been carried out. The subjects received intravenous infusions of 0.5-30 mg/kg bimosiamose disodium. RESULTS AND CONCLUSIONS: The maximum plasma concentration (Cmax) was 675 +/- 11 microg/ml with a tmax of 0.36 +/- 0.13 h (mean +/- SD). The elimination half-life t1/2 was 4.1 +/- 1.0 h, and the AUC(o-inf) was 1,360 +/- 393 h microg/ml after the 30 mg/kg dose. The clearance and the apparent volume of distribution decreased with increasing dose to 22 +/- 6 ml/kg/h and 40 +/- 13 ml/kg/h at the highest dose, respectively, and the mean residence time increased to 1.8 +/- 0.35 h. Bimosiamose was safe and well-tolerated.

Performance of an internal-loop airlift bioreactor for treatment of hexane-contaminated air.

Hexane is a toxic volatile organic compound that is quite abundant in gas emissions from chemical industries and printing press and painting centers, and it is necessary to treat these airstreams before they discharge into the atmosphere. This article presents a treatment for hexane-contaminated air in steady-state conditions using an internal-loop airlift bioreactor inoculated with a Pseudomonas aeruginosa strain. Bioprocesses were conducted at 20-mL/min, a load of 1.26 gm3 of C6H14, and a temperature of 28 degrees C. The results of hexane removal efficiencies were presented as a function of the inoculum size (approx 0.07 and 0.2 g/L) and cell reuse. Bioprocess monitoring comprises quantification of the biomass, the surface tension of the medium, and the hexane concentration in the fermentation medium as well as in the inlet and outlet airstreams. The steady-state results suggest that the variation in inoculum size from 0.07 to 0.2 g/L promotes hexane abatement from the influent from 65 to 85%, respectively. Total hydrocarbon removal from the waste gas was achieved during experiments conducted using reused cells at an initial microbial concentration of 0.2 g/L.

Simulation of the toxicokinetics of trichloroethylene, methylene chloride, styrene and n-hexane by a toxicokinetics/toxicodynamics model using experimental data.

The toxicokinetics/toxicodynamics (TKTD) model simulates the toxicokinetics of a chemical based on physiological data such as blood flow, tissue partition coefficients and metabolism. In this study, Andersen and Clewell's TKTD model was used with seven compartments and ten differential equations for calculating chemical balances in the compartments (Andersen and Clewell 1996, Workshop on physiologically-based pharmacokinetic/pharmacodynamic modeling and risk assessment, Aug. 5-16 at Colorado State University, U.S.A) . Using this model, the authors attempted to simulate the behavior of four chemicals: trichloroethylene, methylene chloride, styrene and n-hexane, and the results were evaluated. Simulations of the behavior of trichloroethylene taken in via inhalation and oral exposure routes were also done. The differences between simulations and measurements are due to the differences between the absorption rates of the exposure routes. By changing the absorption rates, the simulation showed agreement with the measured values. The simulations of the other three chemicals showed good results. Thus, this model is useful for simulating the behavior of chemicals for preliminary toxicity assessment.

Improving hexane removal by enhancing fungal development in a microbial consortium biofilter.

The removal of hydrophobic pollutants in biofilters is often limited by gas liquid mass transfer to the biotic aqueous phase where biodegradation occurs. It has been proposed that the use of fungi may improve their removal efficiency. To confirm this, the uptake of hexane vapors was investigated in 2.6-L perlite-packed biofilters, inoculated with a mixed culture containing bacteria and fungi, which were operated under neutral or acid conditions. For a hexane inlet load of around 140 g.m-3.h-1, elimination capacities (EC) of 60 and 100 g.m-3.h-1 were respectively reached with the neutral and acid systems. Increasing the inlet hexane load showed that the maximum EC obtained in the acid biofilter (150 g.m-3.h-1) was twice greater than in the neutral filter. The addition of bacterial inhibitors had no significant effect on EC in the acid system. The biomass in the acid biofilter was 187 mg.g-1 (dry perlite) without an important pressure drop (26.5 mm of water.m-1reactor). The greater efficiency obtained with the acid biofilter can be related to the hydrophobic aerial hyphae which are in direct contact with the gas and can absorb the hydrophobic compounds faster than the flat bacterial biofilms. Two fungi were isolated from the acid biofilter and were identified as Cladosporium and Fusarium spp. Hexane EC of 40 g.m-3.h-1 for Cladosporium sp. and 50 g.m-3.h-1 for Fusarium sp. were obtained in short time experiments in small biofilters (0.230 L). A biomass content around 30 mg.g-1 (dry perlite) showed the potential for hexane biofiltration of the strains.

Physiologically based modeling of n-hexane kinetics in humans following inhalation exposure at rest and under physical exertion: impact on free 2,5-hexanedione in urine and on n-hexane in alveolar air.

We used a modified physiologically based pharmacokinetic (PBPK) to describe/predict n-hexane (HEX) alveolar air concentrations and free 2,5-HD urinary concentrations in humans exposed to n-HEX by inhalation during a typical workweek. The effect of an increase in workload intensity on these two exposure indicators was assessed and, using Monte Carlo simulation, the impact of biological variability was investigated. The model predicted HEX alveolar air concentrations at rest of 19.0 ppm (25 ppm exposure) and 38.7 ppm (50 ppm exposure) at the end of the last working day (day 5), while free 2,5-HD urinary concentrations of 3.4 micromol/L (25 ppm) and 6.3 micromol/L (50 ppm) were predicted for the same period (last 4.5 hours of Day 5). Monte Carlo simulations showed that the range of values expected to occur in a group of 1000 individuals exposed to 50 ppm of HEX (95% confidence interval) for free 2,5-HD (1.7-14.7 micromol/L) is much higher compared with alveolar air HEX (33.4-46 ppm). Simulations of exposure at 50 ppm with different workloads predicted that an increase in workload intensity would not greatly affect both indicators studied. However, the alveolar air HEX concentration is more sensitive to modifications of workload intensity and time of sampling, after the end of exposure, compared with 2,5-HD. The PBPK model successfully described the HEX alveolar air concentrations and free 2,5-HD urinary concentrations measured in human volunteers and is the first, to our knowledge, to describe the excretion kinetics of free 2,5-HD in humans over a 5-day period.

Development of a physiologically based pharmacokinetic model for volatile fractions of gasoline using chemical lumping analysis.

Physiologically based pharmacokinetic (PBPK) models have often been used to describe the absorption, distribution, metabolism, and excretion of chemicals in animals but have been limited to single chemicals and simple mixtures due to the numerous parameters required in the models. To overcome the barrier to modeling more complex mixtures, we used a chemical lumping approach, used in the past in chemical engineering but not in pharmacokinetic modeling, in a rat PBPK model for gasoline hydrocarbons. Our previous gasoline model consisted of five individual components (benzene, toluene, ethylbenzene, xylene, and hexane) and a lumped chemical that included all remaining components of whole gasoline. Despite being comprised of hundreds of components, the lumped component could be described using a single set of chemical parameters that depended on the blend of gasoline. In the present study, we extend this approach to evaporative fractions of gasoline. The PBPK model described the pharmacokinetics of all of the volatility-weighted fractions of gasoline when differences in partitioning and metabolism between fractions were taken into account. Adjusting the ventilation rate parameter to account for respiratory depression at high exposures also allowed a much improved description of the data. At high exposure levels, gasoline components competitively inhibit each other's metabolism, and the model successfully accounted for binary interactions of this type, including between the lumped component and the five other chemicals. The model serves as a first example of how the engineering concept of chemical lumping can be used in pharmacokinetics.

Urinary 2,5 hexanedione as a biomarker of n-hexane exposure.

n-Hexane is a saturated aliphatic hydrocarbon widely used in industry. In most cases it is used as a mixture with hexane isomers and various others solvents in the form of commercial hexane. n-Hexane is metabolized oxidatively to a number of compounds, including 2,5-hexanedione (2,5-HD), which is eliminated through the urine and is implicated in the neurotoxic effect of this solvent. The main objective of this study was to evaluate urinary 2,5-HD as a biomarker of n-hexane exposure. The study was carried out in seven industrial units. Post-shift urine samples from 111 workers who handled commercial hexane were collected and analysed for 2,5-HD by capillary gas chromatography. Air sampling was performed in the breathing zones of the workers, and the air samples were analysed using validated methods. Monitoring individual exposures showed that n-hexane exposure varied from 5 to 70 p.p.m. (mean +/- SD = 15.24 +/- 2.98 p.p.m.). Significant correlation was observed between exposure to n-hexane and urinary 2,5-HD levels, with high correlation coefficients (rho = 0.81, p = 0.000), suggesting that urinary 2,5-HD is a good biomarker of occupational exposure to n-hexane. Urinary 2,5-HD is recommended as a better tool than air monitoring in the assessment of health risk, namely the early detection of n-hexane neurotoxicity.

Changes in n-hexane toxicokinetics in short-term single exposure due to co-exposure to methyl ethyl ketone in volunteers.

OBJECTIVES: Animal studies demonstrate that the formation of the neurotoxic metabolite, 2,5-hexanedione (HD) decreases during co-exposure to methyl ethyl ketone (MEK). The aim of the present study was to describe the influence of co-exposure to MEK on n-hexane toxicokinetics in humans. METHODS: Four healthy male volunteers were exposed, on different occasions, to three different combinations of vapor of these solvents, namely: 50 ppm n-hexane alone, and in combination with 100 and 200 ppm MEK, for 2 h during light physical exercise (50 W). Arterialized capillary blood, venous blood, and urine were sampled at scheduled intervals before, during, and up to 24 h after the onset of the exposure. HD in venous blood and urine was analyzed by gas chromatography with electron capture detector after derivatization with O-(pentafluorobenzyl) hydroxylamine. RESULTS: Serum HD decreased with increasing exposure to MEK at 2 h after the onset of the exposure, from an average concentration of 2.2 micromol/l in the n-hexane-alone condition to 1.2 and 0.44 micromol/l in the 100 and 200-ppm MEK conditions, respectively. The area under the concentration-time curve of HD in venous blood and the concentration of HD at 2 and 4 h after the end of exposure decreased with increasing MEK. These results suggest that combined exposure to MEK and n-hexane at occupationally realistic levels depresses the metabolism of n-hexane in a dose-dependent fashion. CONCLUSION: The internal exposure to the toxic metabolite of n-hexane decreased with co-exposure to MEK in a dose-dependent fashion. Estimation of external exposure by HD in serum or urine could be confounded by the co-exposure to MEK.