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

Modulation of trichloroethylene in vitro metabolism by different drugs in human

Toxicological interactions with drugs have the potential to modulate the toxicity of trichloroethylene (TCE). Our objective is to identify metabolic interactions between TCE and 14 widely used drugs in human suspended hepatocytes and characterize the strongest using microsomal assays. Changes in concentrations of TCE and its metabolites were measured by headspace GC-MS. Results with hepatocytes show that amoxicillin, cimetidine, ibuprofen, mefenamic acid and ranitidine caused no significant interactions. Naproxen and salicylic acid showed to increase both TCE metabolites levels, whereas acetaminophen, carbamazepine and erythromycin rather decreased them. Finally, diclofenac, gliclazide, sulphasalazine and valproic acid had an impact on the levels of only one metabolite. Among the 14 tested drugs, 5 presented the most potent interactions and were selected for confirmation with microsomes, namely naproxen, salicylic acid, acetaminophen, carbamazepine and valproic acid. Characterization in human microsomes confirmed interaction with naproxen by competitively inhibiting trichloroethanol (TCOH) glucuronidation (Ki=2.329 mM). Inhibition of TCOH formation was also confirmed for carbamazepine (partial non-competitive with Ki=70 μM). Interactions with human microsomes were not observed with salicylic acid and acetaminophen, similar to prior results in rat material. For valproic acid, interactions with microsomes were observed in rat but not in human. Inhibition patterns were shown to be similar in human and rat hepatocytes, but some differences in mechanisms were noted in microsomal material between species. Next research efforts will focus on determining the adequacy between in vitro observations and the in vivo situation.

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

Assessment of occupational health risk from multiple exposure: review of industrial solvent interaction and implication for biological monitoring of exposure

This review is a critical survey and evaluation of recent literature on solvent interactions for the assessment of health risk. It addresses the implications of multiple solvent exposures 1) by examining the influence of solvent-solvent and ethanol-solvent interactions on the biological indices of chemical exposure, and 2) by indicating how the eventual modifying effects can be considered in the biological monitoring of mixed exposure. Reviewed studies reveal the effects of toxicokinetic interactions on the biological parameters, and the gaps in our knowledge. The measurement of potentially toxic molecular species is suggested for the biological monitoring of multiple chemical exposure. This approach appears to be important for drawing better quantitative conclusions on the internal exposure to biologically active chemical species. Finally, research needs arising from the critical analysis of the literature are briefly described.

Health effects of the alkylbenzenes. I. Toluene

The alkylbenzenes, toluene being the most common example, represent a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points and are used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are also integral components of gasoline, distillate fuels and other petroleum products. These substituted aromatics are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, xylene, ethylbenzene, styrene and cumene are toxicologically important since they are produced, used or disposed of in the largest quantities and therefore might pose significant and potential health risks to man and the environment. In general, the toxicity of alkylbenzenes has been found to be relatively low. Also, for the most part, human and environmental risks are low; however, there may be a few operations where the potential for high exposure could exist. These exposures are minimized by workplace controls or personal protective equipment. Furthermore, health risks for humans are minimized by guidelines for maximum allowable exposure concentrations which have been established for the workplace. This present paper reviews the toxicology and disposition of toluene in animals and humans.

Mechanisms for modification of bromobenzene hepatotoxicity by coadministered toluene and chlorobenzene

Hepatotoxicity of bromobenzene (2 mmole/kg) in combination with toluene or chlorobenzene (4 mmole/kg each) were studied in vivo on the basis of GPT elevation and histological examinations. Both toluene and chlorobenzene suppressed bromobenzene hepatotoxicity 24 hr after the treatment, and chlorobenzene dramatically potentiated the toxicity at 48 hr. The glutathione level became lower at 12 hr and recovered at 24 hr when bromobenzene was given alone. The recovery delayed until 48 hr when chlorobenzene was coadministered. In experiments in vitro with microsomes from phenobarbital-pretreated rats, both toluene and chlorobenzene at 0.6 mM inhibited p-bromophenol formation noncompetitively but had no effect on o-isomer formation. Multiple factors may determine overall hepatotoxicity in combined exposure; bromobenzene hepatotoxicity will be suppressed in the early phase owing to metabolic inhibition of 3,4-epoxidation, but potentiated later because of delayed recovery in the glutathione level. A time-saving yet reliable assay system with an ECD-gas chromatograph was developed for bromobenzene metabolism study.

An experimental study on the combined effects of n-hexane and toluene on the peripheral nerve of the rat

An electrophysiological study was undertaken to determine whether toluene affected the neurotoxicity of n-hexane. Separate groups of eight rats were exposed to 1000 ppm n-hexane, 1000 ppm toulene, 1000 ppm n-hexane plus 1000 ppm toluene, of fresh air in an exposure chamber for 12 hours a day for 16 weeks. The body weight, MCV, DL, MNCVs were measured before exposure, after four, eight 12, and 16 weeks exposure; and four weeks after exposure was discontinued. Exposure to 1000 ppm n-hexane considerably impaired the function of the peripheral nerve, but exposure to a mixture of 1000 ppm n-hexane plus 1000 ppm toluene resulted in only slight impairment; 1000 ppm toluene had little effect. These results strongly suggest that toluene decreases the toxic effects of n-hexane on the peripheral nerve.

Different role of biotransformation in the elimination of some important pharmaceuticals and industrial xenobiotics

Unlike lipophilic pharmaceuticals, many lipophilic industrial xenobiotics may be excreted unchanged due to their volatility. Consequently, enzyme induction of inhibition may thus affect only the rate of metabolism of the lipophilic drugs, whereas in case of volatile xenobiotics it is both the rate and the extent (metabolized portion) of their biotransformation which are influenced by these processes. The influence of these metabolic changes on the rate of elimination is more pronounced in lipophilic pharmaceuticals than in volatile xenobiotics whose alternative elimination via lungs compensates for the metabolic rate differences.