Association between metabolic gene polymorphisms and susceptibility to peripheral nerve damage in workers exposed ton-hexane: A preliminary study

Short-term ozone exposure and serum neural damage biomarkers in healthy elderly adults: Evidence from a panel study

BACKGROUND

Although converging lines of research have pointed to the adverse neural effects of air pollution, evidence linking ozone (O3) and neural damage remains limited.

OBJECTIVES

To investigate the subclinical neural effects of short-term ozone (O3) exposure in elderly adults.

METHODS

A panel of healthy elderly individuals was recruited, and five repeated measurements were conducted from December 2018 to April 2019 in Xinxiang, China. Serum neural damage biomarkers, including brain-derived neurotrophic factor (BDNF), neurofilament light chain (NfL), neuron-specific enolase (NSE), protein gene product 9.5 (PGP9.5), and S100 calcium-binding protein B (S100B) were measured at each follow-up session. Personal O3 exposure levels were calculated based on outdoor monitoring and sampling times. A linear mixed-effects model was adopted to quantify the acute effect of O3 on serum neural damage biomarkers. Stratification analysis based on sex, education level, physical activity, and glutathione S-transferases (GST) gene polymorphism analysis was performed to explore their potential modifying effects.

RESULTS

A total of 34 healthy volunteers aged 63.7 ± 5.7 y were enlisted and completed the study. The concentration of the daily maximum 8-h average O3 (O3-8h) ranged from 19.5 to 160.5 μg/m3 during the study period. Regression analysis showed that short-term O3 exposure was associated positively with serum concentrations of neural damage biomarkers. A 10 μg/m3 increase in O3-8h exposure was associated with an increment of 74 % (95 % CI:1 %-146 %) and 197 % (95 % CI:39 %-356 %) in BDNF (lag 2 d) and NfL (lag 1 d), respectively. The stratification results suggest that males, people with lower education levels, lower physical activity, and GST theta 1 (GSTT1)-sufficient genotype might be marginally more vulnerable.

CONCLUSIONS

This study provides new evidence for the neural damage risk posed by O3 exposure, even at relatively low concentrations, which, therefore, requires that stringent air quality standards be developed and implemented.

Diallyl sulfide-induced attenuation of n-hexane-induced peripheral nerve impairment is associated with metabolic inhibition of n-hexane

Chronic exposure to n-hexane could induced serious peripheral nerve impairments. It has been well documented that the metabolic activation from n-hexane to 2,5-hexanedione (2,5-HD) is vital in the pathogenesis. Diallyl sulfide (DAS) is an extract of garlic and able to block the bioactivation of xenobiotic. The current study was designed to investigate whether DAS can attenuate n-hexane induced neuropathy. Male Wistar rats were pretreated with DAS (50 or 100 mg/kg.bw) and then n-hexane (3 g/kg.bw) for 7 weeks. Behavioral performance, biomarker measurement and toxicokinetic studies were performed. Enzymatic methods and western blotting analyses were also conducted to investigate the hepatic phase I enzymes (including cytochrome P450(CYP)2E1, CYP1A1 and CYP2B1) and phase II enzymes (including glutathione S transferase theta 1 (GSTT1) and NA(D)PH dehydrogenase quinone 1 (NQO1)). The results showed that DAS improved the behavioral performance while reducing the toxic metabolite: 2,5-HD and pyrrole adducts. Besides, DAS reduced the expression of CYP2E1 with a proportional decrease in activity, which largely decreased the bioactivation of n-hexane in vivo. The results suggested that DAS decreased the toxic metabolites of n-hexane to attenuate n-hexane-induced peripheral neuropathy.

Pulmonary Toxicity Induced by N-Hexane in Wistar Male Rats After Oral Subchronic Exposure

Studies of pulmonary toxicity induced by oral exposure to n-hexane are very few, in contrast to those studying the exposure by inhalation. This research tackles the oral toxic effect of n-hexane solvent on the lungs after subchronic exposure of Wistar male rats at 300, 600, and 1200 mg/kg, respectively, each day for 8 weeks. The pneumotoxicity observed in this study was marked by an immune toxicity in the form of a significant increase in the levels of white blood cells, lymphocytes, granulocytes, and eosinophils, as well as a significant increase in relative and absolute lung weight in both groups treated at the doses of 600 and 1200 mg/kg. n-Hexane also resulted in a significant increase in serum total proteins and acid phosphatase in the 3 doses tested daily for 8 weeks. In addition, we found a significant increase in total protein and a decrease in glutathione at 600 and 1200 mg/kg, in the pulmonary homogenate. Furthermore, the rate of lipid peroxidation increased in the 3 doses tested. Histological findings revealed a pneumonia characterized by bronchopneumonia, fibronecrotic lesions, congestion, hemorrhage, type II pneumocyte hyperplasia, alveolar lesions, bronchial epithelium degradation, and inflammation.

Impairment of hepatic and renal functions by 2,5-hexanedione is accompanied by oxidative stress in rats

2,5-Hexanedione (2,5-HD) is the toxic metabolite of n-hexane which is widely used as solvent in numerous industries. The present study elucidated the precise mechanism of 2,5-HD in hepatorenal toxicity by determining the involvement of oxidative stress in rats. Adult male Wistar rats were exposed to 0, 0.25, 0.5, and 1% 2,5-HD in drinking water for 21 days. Exposure to 2,5-HD caused liver and kidney atrophy evidenced by significant elevation in serum aminotransferases, alkaline phosphatase, albumin, bilirubin, urea, creatinine, and electrolytes levels compared with control. The marked dose-dependent increase in total cholesterol (TC), triglyceride (TG), and low-density lipoprotein (LDL) was accompanied with significant decrease in high-density lipoprotein (HDL) levels in 2,5-HD-exposed animals when compared with the control. Administration of 2,5-HD significantly diminished glutathione (GSH) level but increased the activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glutathione-S-transferase (GST) concomitantly with marked elevation in hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels in liver and kidney of the treated groups compared with control. These findings suggest that undue exposure to 2,5-HD at environmentally relevant levels may impair liver and kidney functions through induction of oxidative stress.

Urinary 2,5-hexanedione excretion in cryptogenic polyneuropathy compared to the general Swedish population

Background

2,5-hexanedione (2,5-HD) is the main neurotoxic metabolite of methyl-n-butyl ketone (MBK) and n-hexane, and known to cause polyneuropathy. The aim of our study was to compare the urinary levels of 2,5-HD between cases with cryptogenic polyneuropathy and the general Swedish population, and to elucidate the role of certain external factors.

Methods

Morning urine samples were collected from 114 cases with cryptogenic polyneuropathy (77 men and 37 women) and 227 referents (110 men and 117 women) randomly selected from the population registry. None had any current occupational exposure to n-hexane or MBK. The urine samples were analysed by a gas chromatographic method based on acidic hydrolysis.

Results

Cases had statistically higher urinary levels of 2,5-HD (0.48 mg/L) than the general population (0.41 mg/L) and men higher excretion than women (0.48 mg/L and 0.38 mg/L, respectively). There was no difference in 2,5-HD levels between current smokers and non-smokers. Occupational exposure to xylene, alcohol consumption and ever exposed to general anaesthesia were associated with lower excretion in men while for occupational exposure to nitrous oxide in women higher excretion was seen. Higher excretion of 2,5 HD was inversely related to increasing age.

Conclusions

Significantly higher levels of urinary 2,5-HD were seen in men and cryptogenic polyneuropathy cases seemingly unexposed to n-hexane. Hypothetically, this might be due to either differences in metabolic patterns or some concealed exposure. The difference in means between cases and the general population is small and can therefore not allow any firm conclusions of the causality, however.

Polymorphisms of GSTT1, GSTM1, and EPHX genotypes in patients with cryptogenic polyneuropathy: a case-control study

The aim of this study was to analyze whether polymorphisms for the null alleles of Glutathione S-Transferase Mu-1 (GSTM1), Glutathione S-Transferase Theta-1 (GSTT1), and a low-activity genetic variation of epoxide hydrolase exon three (EPHX*3) affect the risk of developing polyneuropathy. The enzymes of these genes are important in the metabolism of toxic compounds. Seventy-nine patients with cryptogenic polyneuropathy (equivalent to chronic idiopathic axonal neuropathy) and 398 controls were tested for the genetic polymorphism. Medical records were reviewed to collect data regarding clinical findings at diagnosis, and exposure data was collected via questionnaires. The odds ratios (ORs) for the null forms of GSTM1 and GSTT1 and the normal activity YY form of EPHX*3 were close to one except GSTT1, which reached 1.86. The highest risk of polyneuropathy was found in smokers with GSTT1 null, who had a 3.7 times increased risk. Interactions between genes were analyzed and confirmed the increased OR for GSTT1, which was strongest if the patients had the low-activity HH form of EPHX*3 (OR 2.37). Our hypothesis is that the GSTT1 null polymorphism may be related to an impaired metabolism of toxic substances that could lead to nerve damage in the peripheral nervous system.

Independent and combined effects of ethanol self-administration and nicotine treatment on hepatic CYP2E1 in African green monkeys

Cytochrome P450 2E1 metabolizes ethanol and also bioactivates many toxins and procarcinogens. Elevated levels of hepatic CYP2E1 are associated with an increased susceptibility to chemical toxicity and carcinogenesis. This study investigated the induction of hepatic CYP2E1 by ethanol and nicotine, alone and in combination, in a nonhuman primate model. Monkeys that self-administered ethanol and that received subcutaneous injections of nicotine (0.5 mg/kg b.i.d.), alone and in combination, were compared with control animals (four groups, n = 10/group). Chlorzoxazone (CZN) was used as a probe drug to phenotype in vivo CYP2E1 activity before and after chronic ethanol and/or nicotine exposure. CYP2E1 protein levels and in vitro chlorzoxazone metabolism were assessed in liver microsomes. Average daily ethanol consumption was ≈3.0 g/kg (blood ethanol levels ≈24 mM) and was unaffected by nicotine treatment. Ethanol self-administration and nicotine treatment, alone and in combination, significantly increased in vivo CZN disposition compared with that in control animals. The effect of ethanol was only observed at higher levels of intake. Ethanol and nicotine increased CYP2E1 protein levels and in vitro CZN metabolism, with combined exposure to both drugs resulting in the greatest increase. The effect of ethanol was also dependent on level of intake. Chronic exposure to ethanol and nicotine induced hepatic CYP2E1 activity and protein levels, particularly when both drugs were used in combination and when ethanol intake was high. These results have important implications for public health, given the association between elevated CYP2E1 and disease, and the large proportion of individuals who are exposed to ethanol and nicotine, often in combination.

Workplace exposures and the risk of amyotrophic lateral sclerosis

BACKGROUND

Occupation has been suggested to play a role in amyotrophic lateral sclerosis (ALS) etiology, but detailed information on the importance of specific workplace exposures is lacking.

OBJECTIVES

Our aim was to assess the relationship between workplace exposures and the risk of ALS and to evaluate potential interactions between these exposures and smoking.

METHODS

We conducted a case-control study in New England between 1993 and 1996, comprising 109 cases and 253 controls who completed a structured interview covering occupations and workplace exposures. Unconditional logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for ALS. Analyses were conducted among the entire study population and after stratification by smoking.

RESULTS

We observed a higher risk of ALS for construction workers excluding supervisors (OR = 2.9; 95% CI, 1.2-7.2) and precision metal workers (OR = 3.5; 95% CI, 1.2-10.5). Self-reported exposures to paint strippers; cutting, cooling, or lubricating oils; antifreeze or coolants; mineral or white spirits; and dry cleaning agents each appeared to be associated with a 60-90% higher risk. Specific chemicals related to a > 50% increase in risk of ALS included aliphatic chlorinated hydrocarbons, glycols, glycol ethers, and hexane. Relative risks associated with these workplace exposures and chemicals were greater among nonsmokers and persisted in mutually adjusted models.

CONCLUSIONS

Our data suggest that certain occupations and workplace exposures may be associated with increased risk of ALS. These results need to be confirmed in independent populations.

Toxic neuropathy due to N-hexane: report of three cases

Chronic exposure to n-hexane is one of the well known causes of peripheral neuropathy. This type of neuropathy is commonly seen among individuals employed in shoe and bag factories with inadequate ventilation. We describe three patients with acute and sub-acute neuropathy following n-hexane exposure via inhalation of glue. All of the patients had history of working in the same place. The results of laboratory examinations were in normal ranges except the electroneuromyographic (ENMG) findings which were showing the neuropathy. All patients were hospitalized and rehabilitation programs were carried out. Symptomatic relief was achieved following this treatment, however the pathologic ENMG findings still persisted.

Environmental metabolite, 1,2-diacetylbenzene, produces cytotoxicity through ROS generation in HUVEC cells

Organic solvents are ubiquitous in industrial and household surroundings, and thus individuals are easily exposed. 1,2-Diethylbenzene (DEB) is one of organic solvents contained in gasoline or jet fuels. DEB is absorbed by dermal or inhalation routes, metabolized by cytochrome P-450 in the liver, and ultimately affects mammalian functions. 1,2-Diacetylbenzene (1,2-DAB), which is a putative metabolite of 1,2-DEB, resulted in neuropathological effects on rodent central and peripheral nervous systems. To elucidate the possibility of 1,2-DAB effects on the vascular system, studies were undertaken to examine whether 1,2-DAB induces endothelial cytotoxicity through reactive oxygen species (ROS) generation. Incubation of human umbilical vein endothelial cells (HUVEC) with lower concentrations (4 or 8 microM) of 1,2-DAB induced inhibition of cellular growth and at higher amounts (16 or 32 microM) produced apoptosis. Endothelial cells cultured with 1,2-DAB also showed increased intracellular ROS production and morphological alterations indicative of senescence. Pretreatment with the well-known antioxidant glutathione or N-acetylcysteine (NAC) reduced cytotoxicity induced by 1,2-DAB. Taken together, the results provide evidence that cytotoxicity induced by 1,2-DAB in endothelial cells may be mediated by ROS generation.