Reciprocal metabolic inhibition of toluene and trichloroethylene in vivo and in vitro

Summary Administration of trichloroethylene to rats in addition to toluene suppressed the urinary excretion of hippuric acid, a main metabolite of the aromatic compound. Reversely, when co-administered with trichloroethylene, toluene reduced the amount of urinary total trichloro-compounds, the metabolites of the chlorinated ethylene. Kinetic approach in vitro to this reciprocal metabolic suppression revealed that trichloroethylene is a non-competitive inhibitor of side-chain hydroxylation of p-nitrotoluene, a substrate analogue of toluene, and toluene, in turn, inhibits oxidation of trichloroethylene non-competitively. Toxicological significance of this observation as well as circumspection in biological monitoring of organic solvent exposure in relation to metabolic suppression are briefly discussed.This work was supported in part by a research grant from the Fujiwara Memorial Foundation.     

Changes of neurobehavioral and sensory functions due to toluene exposure below 50ppm?

Data of a follow up study with four examinations were summarized by odds ratio statistics in order to scrutinize the results of the earlier studies with cross sectional approaches.

For a “high”- (n = 106) and a “low”-exposed group (references, n = 86) current toluene exposures of 26 ppm versus 3 ppm and lifetime weighted average exposures of 45 ppm versus 9 ppm were ascertained. As measures of sensory functions vibration thresholds, colour discrimination, and auditory thresholds were used. Measures of psychological performances were attention (symbol–digit substitution, switching attention, simple reaction), memory (digit span forward, delayed reproduction of pictures), and psychomotor functions (steadiness, line tracing, aiming, tapping, peg board). Additionally, the frequency of diseases and symptoms were ascertained.

By odds ratio statistics including relevant cofactors no significant increase of “cases with impaired functions” among the high-exposed workers was found. Evidence for neurobehavioral effects due to long-term toluene exposure below 50 ppm was not established.     

Applications of dosimetry modeling to assessment of neurotoxic risk

Risk assessment procedures can be improved through better understanding and use of tissue dose information and linking tissue dose level to adverse outcomes. For volatile organic compounds, such as toluene and trichloroethylene (TCE), blood and brain concentrations can be estimated with physiologically based pharmacokinetic (PBPK) models. Acute changes in the function of the nervous system can be linked to the concentration of test compounds in the blood or brain at the time of neurological assessment. This set of information enables application to a number of risk assessment situations. For example, we have used this approach to recommend duration adjustments for acute exposure guideline levels (AEGLs) for TCE such that the exposure limits for each exposure duration yield identical tissue concentrations at the end of the exposure period. We have also used information on tissue concentration at the time of assessment to compare sensitivity across species, adjusting for species-specific pharmacokinetic differences. Finally this approach has enabled us to compare the relative sensitivity of different compounds on a tissue dose basis, leading to expression of acute solvent effects as ethanol-dose equivalents for purposes of estimating cost–benefit relationships of various environmental control options.     

Organic solvent-induced proximal tubular cell apoptosis via caspase-9 activation

Long-term exposure to solvents is associated with apoptosis, which is implicated in the development and progression of tubulo-interstitial fibrosis and chronic renal failure. In our previous study, we demonstrated that toluene and p-xylene as the most commonly used organic solvents induced proximal tubular cells apoptosis. This study was conducted to assess the apoptotic pathway of toluene and p-xylene induced proximal tubular apoptosis. This was assessed by measuring the caspase-9 activity LLC-PK1 cells exposed to both compounds. A model of proximal tubular cell (LLC-PK1) cytotoxicity exposed to 1 mM of either p-xylene or toluene was compared to untreated control for caspase-9 activity and Bax/Bcl-2 protein level. Furthermore, DNA fragmentation in the presence of caspase-9 inhibitor (Z-LEHD-FMK) in a dose-dependent manner was assessed. Both compounds induced caspase-9 activity, which was accompanied by up-regulation of Bax, whereas Bcl-2 level did not change. DNA fragmentation induced by both solvents was inhibited by caspase-9 inhibitor in dose-dependent manner. This data suggest that p-xylene or toluene induces nephrotoxicity via mitochondrial caspase-9 pathway. This mechanism involves up-regulation of the apoptotic protein, Bax.     

Glutathione-conjugated toluene diisocyanate causes airway inflammation in sensitised mice

Toluene diisocyanate (TDI) is a highly volatile compound that reacts readily with nucleophilic compounds, sulfhydryl groups in particular. Since the epithelial lining fluid of the airways contains high levels of the sulfhydryl, glutathione (GSH), inhalation of TDI is likely to result in the formation of GS-TDI conjugates. We therefore investigated whether GS-TDI is capable of provoking irritant and/or allergic reactions. Irritant effects of GS-TDI were studied after intratracheal administration of a range of doses of GS-TDI in saline to naive BALB/c mice. GS-TDI caused a dose-dependent increase in neutrophils in the lungs 24 h after instillation. A dose equivalent to 150 g of TDI or lower had no effect. For provocation of allergic reactions, mice were sensitised by application of 1% TDI onto the skin on days 0 and 1, and challenged intratracheally with a sub-irritant dose of GS-TDI on day 8. GS-TDI did not induce non-specific tracheal hyperreactivity to carbachol 24 and 48 h after challenge in TDI-sensitised mice. However, it increased the numbers of neutrophils in the lungs as compared with the control mice. These findings suggest that GSH conjugation does not diminish the capacity of TDI to elicit irritant-induced inflammation in the lungs of mice at doses above 150 g of TDI in the conjugate. Moreover, the capacity to induce allergic-specific inflammation was retained at concentrations of GS-TDI being devoid of irritant activity. However, the GS-TDI conjugate failed to induce non-specific tracheal hyperreactivity. This may be the consequence of the deposition of excess of GSH upon local dissociation of the conjugate.     

Occupational asthma (OA) with sensitization to diphenylmethane diisocyanate (MDI) presenting at the onset like a reactive airways dysfunction syndrome (RADS)

BACKGROUND: Two types of OA are distinguished: immunological (OA with sensitization) and non-immunological, i.e., irritant induced asthma or reactive airways dysfunction syndrome (RADS). METHODS: We describe the case of a worker who developed respiratory symptoms after a spill of diphenylmethane diisocyanate (MDI) at the workplace. RADS was initially diagnosed and the worker resumed working. The progressive worsening of symptoms and the appearance of symptoms-work relationship one year later, when concentrations of isocyanates were no longer "irritant," suggested immunological OA. RESULTS: The diagnosis was confirmed by specific inhalation challenge test, followed by removal from exposure and complete recovery. CONCLUSIONS: In the case of RADS due to an agent with both irritant and sensitizing properties, history should be repeatedly assessed for a possible symptom-work relationship. If this is found, further investigations should be carried out, including specific inhalation challenges, to confirm the possibility of immunological OA.     

Toluene exposure increases aminophylline-induced seizure susceptibility in mice

The effects of toluene on the sensitivity to seizures induced by aminophylline were investigated. Mice were pretreated with an ip injection of corn oil or toluene (100-500 mg/kg) followed by a timed intravenous infusion of aminophylline at various time intervals to assess the seizure thresholds and lethal doses. Toluene increased seizure susceptibility to aminophylline in a dose- and time-dependent manner. Toluene-induced enhancement of seizure susceptibility to aminophylline occurred as early as 30 min and persisted for at least 3 days after a single administration of toluene (500 mg/kg). Treatment of benzaldehyde, one of toluene's metabolites, also showed an increase in the susceptibility to aminophylline. The enhancing effect was also observed in caffeine-induced seizures 1 h, but not 1 day after toluene treatment. These results suggest that individuals with toluene exposure may increase the risk for convulsive and even lethal complications associated with the therapeutic use of aminophylline.     

Respiratory diseases caused by occupational exposure to 1,5-naphthalene-diisocyanate (NDI): Results of workplace-related challenge tests and antibody analyses

BACKGROUND: 1,5-naphthalene-diisocyanate (NDI) is an aromatic diisocyanate with a very low vapor pressure which is mainly used in the automotive industry. METHODS: In the present study we described five cases with workplace-related asthma and one case with extrinsic allergic alveolitis associated with pulmonary hemorrhage after NDI exposure. RESULTS: Corresponding to case histories, extrinsic alveolitis on asthmatic reactions in three subjects and a rhinitis reaction in one patient could be reproduced by inhalative challenge tests to NDI at a concentration of 10 ppb. Preliminary IgE and IgG antibody analyses in patients' sera did not produce significantly positive results. CONCLUSIONS: According to the outcome of our tests and in comparison with several other studies, we conclude that NDI should be classified as potent airway-sensitizing substance. Improved workplace conditions and decrease in threshold limit values should therefore be recommended.     

Quantitative analysis of urinary glycine conjugates by high performance liquid chromatography: excretion of hippuric acid and methylhippuric acids in the urine of subjects exposed to vapours of toluene and xylenes

Summary A new method for the direct determination of hippuric acid (HA) and o-, m- and p-methylhippuric acids (MHAs) in the urine, metabolites of toluene and o-, m- and p-xylenes by high performance liquid chromatography (HPLC) is described. A stainless-steel column packed with silica gel having dinitrophenyl residue and a mixed solution of methanol/water/acetic acid (80/20/0.2) containing tetra-n-butylammonium bromide (0.2% w/v) as mobile phase was used. Concentrations of HA and MHAs were estimated from their peak height at a wave length of 225 nm. Urine can be analyzed directly without solvent extraction or pretreatment to obtain complete separation of HA and o-, m- and p-MHAs. Urine samples from male workers exposed to toluene or xylenes were analyzed for HA or MHAs. The urinary levels of HA and MHAs increased by exposure to toluene and xylenes in proportion to the environmental concentrations of the solvents, although there is a considerable variation in metabolite concentrations. The slope of regression line between toluene and HA and that between m-xylene and m-MHA were similar. The urinary concentrations of HA and MHAs corresponding to 100 ppm (TLV) of toluene was 2.35 g/g creatinine and that of m-MHA corresponding to 100 ppm (TLV) of m-xylene was 2.05 g/g creatinine. The warning levels of the urinary metabolite concentrations of a group of workers and that of an individual worker corresponding to TLV of organic solvent concentration is discussed.     

二苯甲烷二异氰酸酯作业工人血清中抗原特异性IgG抗体测定

观察２５例二苯甲烷二异氰酸酯（ＭＤＩ）作业工人、８例ＭＤＩ哮喘患者和３０例正常非接触者的血中抗原特异性ＩｇＧ水平，用ＭＤＩ－ＨＳＡ（人血清白蛋白）作抗原，ＥＬＩＳＡ法测定特异性ＩｇＧ抗体，三组的ＯＤ均值分别为０．５１±０．３１、０．７３±０．２９和０．２７±０．１０，阳性率分别为４４％（１１例）、８７．５％（７例）和６．７％（２例）。表明ＭＤＩ接触者血清特异性ＩｇＧ水平明显增高，且与呼吸道症状高度相关（ｒ＝０．８８，Ｐ＜０．００１），此指标可作为ＭＤＩ的接触标志和ＭＤＩ哮喘的病因诊断依据。