Depletion by styrene of glutathione in plasma and bronchioalveolar lavage fluid of non-Swiss albino (NSA) mice

Molecular mechanisms of action of styrene toxicity in blood plasma and liver

Styrene is an aromatic colorless hydrocarbon available in liquid form and highly volatile. In its pure form, it gives a sweet smell. The primary source of exposure in the environment is from plastic materials, rubber industries, packaging materials, insulations, and fiber glass and carpet industry. Natural sources of styrene include: few metabolites in plants which are transferred through food chain. The current study was designed to evaluate styrene toxicity, including: superoxide dismutase (SOD) and protein carbonyl, oxidative stress, glucose-6-phosphatase (G6Pase), glycogen phosphorylase (GP), and phosphoenolpyruvate carboxykinase (PEPCK) activities, adenosine triphosphate (ATP) to adenosine diphosphate (ADP) ratio, and changes in gene expressions such as glutamate dehydrogenase 1 (GLUD1), glucose transporter 2 (GLUT2), and glucokinase (GCK) in the rat liver tissue. For this purpose, styrene was dissolved in corn oil and was administered via gavage, at doses 250, 500, 1000, 1500, 2000, mg/kg/day per mL and control (corn oil) to each rat with one day off in a week, for 42 days. Plasma SOD and protein carbonyl of plasma were significantly up-regulated in 1000, 1500, and 2000 mg/kg/day styrene administrated groups (P < .001). In addition, styrene caused an increase in lipid peroxidation (LPO) and reactive oxygen species (ROS) in the dose-dependent manners in liver tissue (P < .001). Furthermore, the ferrous reducing antioxidant power (FRAP) and total thiol molecules (TTM) in styrene-treated groups were significantly decreased in liver tissue (P < .001) with increasing doses. In treated rats, styrene significantly increased G6Pase activity (P < .001) and down-regulated GP activity (P < .001) as compared to the control group. The PEPCK activity was significantly raised in a dose-dependent manner (P < .001). The ATP/ADP ratio of live cells was significantly raised by increasing the dose (P < .001). There was significantly an up-regulation of GLUD1 and GCK at 2000 mg/kg group (P < .01) and a down-regulation for GLUT2 at the same dose. While in the rest of group, GLUT2 showed up-regulation of relative fold change. By targeting genes such as GLUD1, GLUT2, and GCK, disruption of hepatic gluconeogenesis, glycogenolysis, and insulin secretory functions are obvious. The present study illustrates that induction of oxidative stress followed by changes in G6Pase, GP, and PEPCK activities and the genes responsible for glucose metabolism are the mechanisms of styrene's action in the liver.

Effect of styrene exposure on plasma parameters, molecular mechanisms and gene expression in rat model islet cells

Styrene is an aromatic hydrocarbon compound present in the environment and have primary exposure through plastic industry. The current study was designed to evaluate styrene-induced toxicity parameters in rat plasma fasting blood glucose (FBG) level, oral glucose tolerance, insulin secretion, oxidative stress, and inflammatory cytokines in cellular and molecular levels. Styrene was dissolved in corn oil and administered at different doses (250, 500, 1000, 1500, 2000mg/kg/day and control) to each rat, for 42days. In treated groups, styrene significantly increased fasting blood glucose, plasma insulin (p<0.001) and glucose tolerance. Glucose tolerance, insulin resistance and hyperglycemia were found to be the main consequences correlating gene expression of islet cells. Styrene caused a significant enhancement of oxidative stress markers (p<0.001) and inflammatory cytokines in a dose and concentration-dependent manner in plasma (p<0.001). Moreover, the activities of caspase-3 and -9 of the islet cells were significantly up-regulated by this compound at 1500 and 2000mg/kg/day styrene administrated groups (p<0.001). The relative fold change of GLUD1 was downregulated (p<0.05) and upregulated at 1500 and 2000mg/kg, respectively (p<0.01). The relative fold changes of GLUT2 were down regulated at 250 and 1000mg/kg and up regulated in 500, 1500 and 2000mg/kg doses of styrene (p<0.01). The expression level of GCK indicated a significant upregulation at 250mg/kg and downregulation of relative fold changes in the remaining doses of styrene, except for no change at 2000mg/kg of styrene for GCK. Targeting genes (GLUD1, GLUT2 and GCK) of the pancreatic islet cells in styrene exposed groups, disrupted gluconeogenesis, glycogenolysis pathways and insulin secretory functions. The present study illustrated that fasting blood glucose, insulin pathway, oxidative balance, inflammatory cytokines, cell viability and responsible genes of glucose metabolism are susceptible to styrene, which consequently lead to other abnormalities in various organs.

The Protective Effects of Gadolinum Chloride on Pneumotoxic Effects of Styrene in Rat

Objective

The aim of the present study was to evaluate the protective effects of gadoli- num on pneumotoxic effects of styrene in rats as an experimental model.

Materials and Methods

In this experimental study a total number of 40 adult male Sprague Dawley rats that weighed 200 ± 13 g were randomly divided into five groups: i. styrene (St, N=10), ii. styrene+gadolinium chloride (GdCl₃, N=10), iii. control (N=10), iv. GdCl₃ (N=5) and v. normal saline (Nor.Sal, as a solvent of GdCl₃, N=5). Normal saline, as a sham control group, was otherwise treated identically. Rats from the experimental groups were exposed to St in an exposure chamber for 6 days/week, 4 hours/day for up to 3 weeks. At the end of the experi- ment, rats from all groups were killed by deep anesthesia. Their lungs were removed, then fixed in formalin and weighed. Tissue samples were processed routinely and sections stained by the hematoxylin and eosin (H&E) and periodic acid Schiff (PAS) methods. We measured the thicknesses of the respiratory epithelia and interalveolar septa. Obtained data were ana- lyzed by ANOVA, the Tukey test and the paired t test.

Results

Shedding of apical cytoplasm in the bronchiole was a prominent feature of the St group. PAS staining revealed histochemical changes in goblet cells in the epithelium of the St group. While there were no significant changes in lung weights and respiratory epithelial thicknesses between all studied groups, statistical analysis showed a significant alteration in the thickness of interalveolar septa in the St and St+GdCl₃ group compared to the control groups (P<0.001).

Conclusion

Styrene induced structural and histochemical changes in bronchiole, interalveolar septa and alveolar organization in the rats’ lungs. Gadolinium appeared to partially reduce the toxic effects of styrene on the lungs.

Pulmonary function and oxidative stress in workers exposed to styrene in plastic factory: occupational hazards in styrene-exposed plastic factory workers

Styrene is a volatile organic compound used in factories for synthesis of plastic products. The pneumotoxicity of styrene in experimental animals is known. The aim of the present study was to study the effect of styrene on lung function and oxidative stress in occupationally exposed workers in plastic factory. Thirty-four male workers, between 18 and 40 years of age, exposed to styrene for atleast 8 hours a day for more than a year were studied, while 30 age- and sex-matched healthy subjects not exposed to styrene served as controls. Assessment of lung functions showed a statistically significant reduction (p < 0.05) in most of the lung volumes, capacities (FVC, FEV(1), VC, ERV, IRV, and IC) and flow rates (PEFR, MEF(75%), and MVV) in the study group (workers) as compared to controls. Malondialdehyde (MDA) was observed to be significantly high (p < 0.05) while ferric-reducing ability of plasma (FRAP) was significantly low (p < 0.05) in styrene-exposed subjects. Reduced glutathione (GSH) level was significantly depleted in exposed subjects as compared to control group. The mean value of serum cytochrome c in styrene-exposed subjects was found to be 1.1 ng/ml (0.89-1.89) while in control its levels were under detection limit (0.05 ng/ml). It shows that styrene inhalation by workers leads to increased level of oxidative stress, which is supposed to be the cause of lung damage.

Comparison of styrene oxide enantiomers for hepatotoxic and pneumotoxic effects in microsomal epoxide hydrolase-deficient mice

Styrene is hepatotoxic and pneumotoxic in mice. Styrene oxide, the active metabolite, is detoxified via hydrolysis by microsomal epoxide hydrolase (mEH). Racemic styrene oxide was previously found to be more lethal and produced increased toxicity in mEH-/- mice compared to wild-type mice. The hepatotoxicity and pneumotoxicity of the R- and S-styrene oxide (SO) enantiomers were compared in wild-type and mEH-deficient mice (mEH-/-). Twenty-four hours following administration of 150 mg/kg ip, neither enantiomer produced hepatotoxicity, but S-SO was more pneumotoxic. However, in mEH-/- mice R-SO produced greater decreases in hepatic glutathione levels 3 h after administration. The basis for the unusual greater toxicity of S-SO, rather than the generally more toxic R-SO, in mEH-/- mice may be related to differences in detoxification by EH.

Metabolism and toxicity of styrene in microsomal epoxide hydrolase-deficient mice

Styrene, which is widely used in manufacturing, is both acutely and chronically toxic to mice. Styrene is metabolized by cytochromes P-450 to the toxic metabolite styrene oxide, which is detoxified via hydrolysis with microsomal epoxide hydrolase (mEH) playing a major role. The purpose of these studies was to characterize the importance of this pathway by determining the hepatotoxicity and pneumotoxicity of styrene in wild-type and mEH-deficient (mEH(-/-)) mice. While the mEH(-/-) mice metabolized styrene to styrene oxide at the same rate as the wild-type mice, as expected there was minimal metabolism of styrene oxide to glycol. mEH(-/-) mice were more susceptible to the lethal effects of styrene. Twenty-four hours following the administration of 200 mg/kg ip styrene, mice demonstrated a greater hepatotoxic response due to styrene, as measured by increased serum sorbitol dehydrogenase activity and greater pneumotoxicity as shown by increased protein levels, cell numbers, and lactate dehydrogenase activity in bronchioalveolar lavage fluid. mEH(-/-) mice were also more susceptible to styrene-induced oxidative stress, as indicated by greater decreases in hepatic glutathione levels 3 h after styrene. Styrene oxide at a dose of 150 mg/kg did not produce hepatotoxicity in either wild-type or mEH(-/-) mice. However, styrene oxide produced pneumotoxicity that was similar in the two strains. Thus, mEH plays an important role in the detoxification of styrene but not for exogenously administered styrene oxide.