Neonatal exposure to toluene: effects on the development of liver microsomal cytochrome P-450 and serum hormone levels in the rat

Developmental and reproductive effects of chemicals associated with unconventional oil and natural gas operations

Unconventional oil and gas (UOG) operations have the potential to increase air and water pollution in communities located near UOG operations. Every stage of UOG operation from well construction to extraction, operations, transportation, and distribution can lead to air and water contamination. Hundreds of chemicals are associated with the process of unconventional oil and natural gas production. In this work, we review the scientific literature providing evidence that adult and early life exposure to chemicals associated with UOG operations can result in adverse reproductive health and developmental effects in humans. Volatile organic compounds (VOCs) [including benzene, toluene, ethyl benzene, and xylene (BTEX) and formaldehyde] and heavy metals (including arsenic, cadmium and lead) are just a few of the known contributors to reduced air and water quality that pose a threat to human developmental and reproductive health. The developing fetus is particularly sensitive to environmental factors, which include air and water pollution. Research shows that there are critical windows of vulnerability during prenatal and early postnatal development, during which chemical exposures can cause potentially permanent damage to the growing embryo and fetus. Many of the air and water pollutants found near UOG operation sites are recognized as being developmental and reproductive toxicants; therefore there is a compelling need to increase our knowledge of the potential health consequences for adults, infants, and children from these chemicals through rapid and thorough health research investigation.

Thymoquinone reestablishes spermatogenesis after testicular injury caused by chronic toluene exposure in rats

The aim of this study was designed to evaluate the possible protective effects of thymoquinone (TQ) on the spermatogenesis after testicular injury caused by chronic toluene exposure in rats. The rats were randomly allotted into one of three experimental groups: control, toluene-treated and toluene treated with TQ; each group contained 10 animals. Control group received 1 mL serum physiologic and toluene treatment was performed by inhalation of 3000 ppm toluene, in an 8-hour/day and 6-day/week order for 12 weeks. The rats in TQ-treated group was given TQ (50 mg/kg body weight) once a day orally for 12 weeks starting just after toluene exposure. Tissue samples were obtained for histopathological investigation. To date, no histopathological changes of testis in rats after chronic toluene exposure by TQ treatment have been reported. Spermatogenesis and mean seminiferous tubule diameter (MSTD) were significantly decreased in toluene treated groups when compared to the control group. Furthermore, the TQ-treated animals showed an improved histological appearance in toluene-treated group. Our data indicate a significant reduction in the activity of in situ identification of apoptosis using terminal dUTP nick end-labeling (TUNEL), endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and there was a rise in the expression of proliferating cell nuclear antigen (PCNA) in testis tissues of the toluene-treated group with TQ therapy. Electron microscopy of the testes of the rats demonstrated that pretreatment with TQ was particularly effective in preventing the mitochondrial degeneration, dilatation of smooth endoplasmic reticulum (SER) and enlarged intercellular spaces in both Sertoli and spermatid cells in the toluene-treated animals. We believe that further preclinical research into the utility of TQ may indicate its usefulness as a potential treatment on the spermatogenesis after testicular injury caused by chronic toluene exposure in rats.

Effects of maternal toluene exposure on testosterone levels in fetal rats

The goal of our study was to determine if toluene affected the synthesis and secretion of testosterone in fetal rats. Dams were exposed to atmospheres that contained 0.09 ppm, 0.9 ppm or 9 ppm of toluene for 90 min/day from gestational days (GDs) 14.5 to 18.5 via nasal inhalation. Fetal plasma testosterone concentrations determined by enzyme immunoassay were significantly reduced on GD 18.5 after exposure to 0.9 and 9 ppm, but not to 0.09 ppm, of toluene in male, but not in female, fetuses. We measured, using real-time PCR methods, mRNA levels in fetal testes for several steroidogenic enzymes involved in testosterone synthesis and insulin-like 3 (Insl3), a maker of Leydig cell differentiation. The mRNA levels of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) were significantly reduced after exposure to 0.9-ppm toluene. However, the mRNA levels of cytochrome P450 cholesterol side-chain cleavage, cytochrome P450 17alpha-hydroxylase/c17-20 lyase, 17beta-hydroxysteroid dehydrogenase, and Insl3 were not significantly altered by exposure to 0.9-ppm toluene. In addition, immunohistochemical analysis showed reduced 3beta-HSD-immunoreactive areas in the interstitial region of fetal testes after exposure to 0.9 and 9 ppm, but not 0.09 ppm, toluene. These findings indicate that toluene reduced the synthesis and secretion of testosterone in fetal testes from rats possibly as a consequence of reduced 3beta-HSD expression.

Organ growth functions in maturing male Sprague-Dawley rats based on a collective database

Ten different organ weights (liver, spleen, kidneys, heart, lungs, brain, adrenals, testes, epididymes, and seminal vesicles) of male Sprague-Dawley (S-D) rats of different ages (1-280 d) were extracted based on a thorough literature survey database. A generalized Michaelis-Menten (GMM) model, used to fit organ weights versus age in a previous study (Schoeffner et al., 1999) based on a limited data, was used to find the best fit model for the present expanded data compilation. The GMM model has the functional form: Wt = (Wt(o).K(gamma) + Wt(max).Age(gamma))/(K(gamma) + Age(gamma)) where Wt is organ/tissue weight at a specified age, Wt(o) and Wt(max) are weight at birth and maximal growth, respectively, and K and gamma are constants. Organ weights were significantly correlated with their respective ages for all organs and tissues. GMM-derived organ growth and percent body weight (%BW) fractions of different tissues were plotted against animal age and compared with experimental values as well as previously published models. The GMM-based organ growth and %BW fraction profiles were in general agreement with our empirical data as well as with previous studies. The present model was compared with the GMM model developed previously for six organs--liver, spleen, kidneys, heart, lungs, and brain--based on a limited data, and no significant difference was noticed between the two sets of predictions. It was concluded that the GMM models presented herein for different male S-D rats organs (liver, spleen, kidneys, heart, lungs, brain, adrenals, testes, epididymes, and seminal vesicles) are capable of predicting organ weights and %BW ratios accurately at different ages.

Developmental neurotoxicity after toluene inhalation exposure in rats

Rats were exposed to 1200 ppm or 0 ppm toluene (CAS 108-88-3) for 6 h per day from day 7 of pregnancy until day 18 postnatally. Developmental and neurobehavioral effects in the offspring were investigated using a test battery including assessment of functions similar to those in the proposed OECD TG for Developmental Neurotoxicity Study, i.e., physical development, reflex ontogeny, motor function, motor activity, sensory function, and learning and memory. The exposure did not cause maternal toxicity or decreased viability of the offspring. Lower birth weight, delayed ontogeny of reflexes, and increased motor activity in the open field was registered in the exposed offspring. Impaired cognitive function was revealed in the exposed female offspring at the age of 3.5 months, i.e., they used more time to locate the hidden platform in the Morris water maze after platform relocation. The difference was not related to poorer swimming capabilities, because swim speeds were similar to control values. The results show that exposure to 1200 ppm toluene during brain development caused long-lasting developmental neurotoxicity in rats.

Effects of prenatal exposure to toluene on postnatal development and behavior in rats

Development and neurobehavioral effects of prenatal exposure to toluene (CAS 108-88-3) were studied after exposing pregnant rats (Mol:WIST) to 1800 ppm of the solvent for 6 h daily on days 7-20 of gestation. Body weights of exposed offspring were lower until day 10 after parturition. Neurobehavioral evaluation of the pups revealed no effects on motor function (rotarod), activity level (open field), acoustic startle, and prepulse inhibition. Measurements of hearing function using auditory brain stem response revealed small effects in male-exposed offspring. Performance in a Morris water maze during initial learning gave some indications of impaired cognitive functions, which was confirmed during further testing, especially in reversal and new learning. Effects on cognitive functions seemed most marked in female offspring.

Induction of cytochrome P450 by toluene

At least six cytochrome P450 (P450) isoenzymes, including CYP1A1/2, CYP2A1, CYP2B1/2, CYP2C6, CYP2C11 and CYP2E1, are involved in the metabolism of toluene in rat liver. Toluene exposure induces CYP1A1/2, CYP2B1/2, CYP2E1 and CYP3A1, but decreases CYP2C11/6 and CYP2A1 in adult males. Both sex and age influence the induction of P450s by toluene: in general, the inductive effect is more prominent in younger than in older animals; in males than in females. Neonatal exposure to toluene causes significant changes in liver microsomal P450 dependent monooxygenase activities during the early stage of life, whereas the effects on the rats of more than 3 weeks of age are small. Although structurally related chemicals of toluene also influence similar hepatic P450 isoenzymes, the degree of CYP2B1/2 induction increases, whilst that of CYP2E1 decreases with increasing molecular weight and aliphatic moieties. Unlike liver, exposure to toluene does not influence the distribution of pulmonary or renal microsomal P450-related enzyme activity in rats. In humans, occupational exposure to toluene is so low that it could not lead to the induction of P450. However, the induction may be seen in toluene sniffers who are exposed to high concentrations.

Monoclonal antibody-directed assessment of toluene induction of rat hepatic cytochrome P450 isozymes

Cytochrome P450 isozymes induced in rat liver by a range of concentrations of toluene were studied with monoclonal antibodies (MAbs) to specific P450 isozymes and by enzyme assays. Nitrosodimethylamine demethylase activity was significantly increased in microsomes from rats exposed to more than 1000 ppm of toluene, an increase that was dose-dependent. Anti-CYP2E1 significantly inhibited the metabolism of toluene to benzyl alcohol (BA) by about 50%, in microsomes from 1000 to 4000 ppm toluene-exposed rats, at low substrate concentration (0.2 mM). With anti-CYP2B1/2, the rate of BA formation was decreased by 15-17% in microsomes from rats of 2000 and 4000 ppm toluene exposures at high substrate concentration (5.0 mM). On the other hand, anti-CYP2C11/6 inhibited the rate of formation of BA in all of the microsomes, but the extent of inhibition was progressively decreased from 55% in control to 33% in 4000 ppm exposure. Immunoblot analysis with anti-CYP2E1 and anti-CYP2B1/2 revealed stronger immunoreactive bands in microsomes from rats exposed to more than 1000 and 2000 ppm of toluene, respectively. Stronger bands were also observed in microsomes from rats of 2000-4000 ppm toluene exposures with anti-CYP3A1/2, but no immunoreactivity appeared with anti-CYP1A1/2. These results suggest that toluene induces CYP2E1, CYP2B1/2 and CYP3A1/2, but reduces CYP2C11/6, and has no effect on CYP1A1/2.

Developmental toxicity of in utero exposure to toluene on malnourished and well nourished rats

The aim of the present study was to investigate the effects of toluene on fetal development in well nourished and malnourished rats. Long-term behavioural consequences after in utero exposure were also studied. Toluene (1.2 g/kg s.c.) was administered daily to well nourished and to malnourished (food restricted to 50% of ad libitum intake) pregnant rats, during the second (8-15 days) or the third week of pregnancy (14-20 days). Offspring were evaluated for malformations, development of the skeleton, prenatal growth of the brain and liver, postnatal growth and long lasting behavioural effects. In utero exposure to toluene during the third week of pregnancy resulted in low body weight at birth, which persisted in the male offspring into adulthood. Malnutrition increased fetal susceptibility to the effects of toluene as indicated by evaluation of the development of the skeleton. Behavioral tests performed when the pups were 30 and 90 days old showed effects of in utero malnutrition (increased ambulation and worse performance in a shuttle box), but no behavioural effects related to toluene exposure were detected. These data indicate that in utero exposure to toluene can have long lasting effects on body growth and that maternal malnutrition increases the risk for toluene fetotoxicity.

The effect of low-level toluene exposure on the developing hippocampal region of the rat: histological evidence and volumetric findings

With the intention of investigating possible morphological alterations effected by toluene in the developing CNS, rat pups were exposed to 100 ppm and 500 ppm of atmospheric toluene from postnatal day 1 until sacrifice at postnatal day 28, when the hippocampal region (area dentata, Ammon's horn, subiculum) was examined light microscopically and alterations in the volumes of the layers of the subdivisions were determined. The layers of Ammon's horn and the subiculum were not affected qualitatively or quantitatively by the 500 ppm exposure. Within the area dentata, the volume of the granule cell layer was 6% smaller in animals exposed to 100 ppm and 13% smaller in animals exposed to 500 ppm than they were in controls. The volumes of the hilus, which is a terminal field of granule cell axons, and the commissural-associational zone of the dentate molecular layer, which is the terminal field of the hilar projection to the granule cells, were smaller (12% and 19%) in animals exposed to 500 ppm than they were in controls. Argyrophilic cells were found in the granule cell layer of all animals exposed to 500 ppm. Pronounced granule cell degeneration was found in one animal exposed to 500 ppm. The granule cell layer of animals exposed to 100 ppm appeared qualitatively normal. The alterations reported here support the few earlier reports of morphological alterations in the CNS of adult laboratory animals. Effects of toluene similar to those described, that is alterations in specific neuron populations and their afferent and efferent terminal fields may complement changes in neurophysiology and behavior that have been observed in prenatally and perinatally exposed rodent pups. Causal relationships, however, remain to be elucidated.