[Progress on the mechanism of n-hexane induced toxic effects in vitro and in vivo].

Hexane is a widely used organic solvent in industry, and chronic hexane poisoning is the main occupational toxic lesion in China. In particular, axonal and myelin lesions in the distal thick fibers of the peripheral nervous system may be caused by 2, 5-hexanedione (2, 5-HD), an intermediate metabolite of n-hexane in humans. Hexane has toxic effects not only on the nervous system but also on the liver, kidneys, and reproductive organs. In this paper, we review the progress of research on the mechanism of n-hexane toxic neuropathy.

Progress on the mechanism of n-hexane induced toxic effects in vitro and in vivo / 中华劳动卫生职业病杂志

Hexane is a widely used organic solvent in industry, and chronic hexane poisoning is the main occupational toxic lesion in China. In particular, axonal and myelin lesions in the distal thick fibers of the peripheral nervous system may be caused by 2, 5-hexanedione (2, 5-HD), an intermediate metabolite of n-hexane in humans. Hexane has toxic effects not only on the nervous system but also on the liver, kidneys, and reproductive organs. In this paper, we review the progress of research on the mechanism of n-hexane toxic neuropathy.

Exploring the utility of the Threshold of Toxicological Concern (TTC) as a screening approach for complex substances.

The Threshold of Toxicological Concern (TTC) has been applied to assess chemical safety for use, particularly in the food safety area. Although the TTC was developed for application to an individual chemical structure, more recently this concept has been suggested for the assessment of combined exposures to multiple chemicals. This study evaluated the potential for applying the TTC to a specific type of co-exposure, that of a complex substance of variable composition which contains multiple constituents, following the World Health Organization/International Programme on Chemical Safety framework for risk assessment of combined exposure to multiple chemicals. The results indicated that the TTC threshold was lower (i.e., more conservative) than regulatory thresholds derived for the same substance or even its most toxic constituent, providing assurance that the TTC could meet the requirements for a conservative screening process. This case study indicates that the TTC concept can be a useful tool to screen for potential risks from complex substances, with the consideration of additional aspects such as variability in chemical constituents and their relative proportions within the substance.

Another brick in the wall: is hexane neuropathy a 'nodo-paranodopathy'?

n-Hexane gives cause to one of the most common toxic polyneuropathies seen in poorly ventilated factories. It is a sensory-motor polyneuropathy ending up with axonal degeneration. Nerve biopsy reveals paranodal axonal swelling and secondary myelin retraction in early stages. Myelin retraction imitates demyelination causing focal conduction block and failure before axonal degeneration emerges. This brings to mind the new category of nodo-paranodopathy described first for anti-ganglioside antibody-mediated neuropathies, which can be proved by electrophysiological re-evaluations. We, herein, discuss the clinical and electrophysiological follow-up of three patients with n-hexane neuropathy and remark overlaps with new concept nodo-paranodopathy.

Assessment of the potential risk of 1,2-hexanediol using phytotoxicity and cytotoxicity testing.

1,2-Hexanediol is commonly used in the cosmetic industry as a preservative, an emollient, and a moisturizing agent. However, studies on the scientific toxicity of 1,2-hexanediol are limited. In this study, we evaluated the potential toxic effects of 1,2-hexanediol using phytotoxicity and cytotoxicity testing methods. Phytotoxicity tests using Brassica campestris subsp. napus and Latuca sativa L. showed that 1,2-hexanediol significantly inhibited seed germination and root elongation at the lowest concentration (0.1%). Additionally, plants treated with 1,2-hexanediol failed to survive. In cytotoxicity tests, RAW 264.7 and HK-2 cells treated with 1.0% 1,2-Hexanediol showed a significant decline in viability, followed by death. Since most personal care products contain >2% 1,2-hexanediol, it is highly likely that 1,2-hexanediol is toxic to humans. Moreover, if 1,2-hexanediol enters the human body either via oral intake or through an open wound, it could have critical effects. Furthermore, upon release into the environment, 1,2-hexanediol could cause considerable damage to plants and other organisms. Therefore, further investigation of 1,2-hexanediol is required to prevent toxicity to humans and other living organisms.

Neuroprotein Targets of γ-Diketone Metabolites of Aliphatic and Aromatic Solvents That Induce Central-Peripheral Axonopathy.

Peripheral neuropathy associated with chronic occupational and deliberate overexposure to neurotoxic organic solvents results from axonal degeneration in the central and peripheral nervous system. Human and experimental studies show that axonopathy is triggered by the action of neuroprotein-reactive γ-diketone metabolites formed from exposure to certain aliphatic solvents (n-hexane, 2-hexanone) and aromatic compounds (1,2-diethylbenzene, 1,2-4-triethylbenzene, 6-acetyl-1,1,4,4-tetramethyl-7-ethyl-1,2,3,4-tetralin). Neuroprotein susceptibility is related primarily to their differential content of lysine, the ∊-amino group of which is targeted by γ-diketones. Specific neuroprotein targets have been identified, and the sequence of molecular mechanisms leading to axonal pathology has been illuminated. While occupational n-hexane neuropathy continues to be reported, lessons learned from its experimental study may have relevance to other causes of peripheral neuropathy, including those associated with aging and diabetes mellitus.

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.

No-observed-adverse-effect level of hair pyrrole adducts in chronic n-hexane intoxication in rats.

n-Hexane has been reported to induce serious peripheral neuropathy in workers. Pyrrole adducts are the unique reaction products of n-hexane in organisms and have been demonstrated to be critical to n-hexane neuropathy. Our previous studies have demonstrated that pyrrole adducts could accumulate in hair and showed high correlation with neuropathy at the end of experiments in rat models. In the present study, we examined the time course of hair pyrrole adducts and behavioral changes in rats exposed to different dosages of n-hexane in both treatment (24 weeks) and recovery phases. Our results showed: 1. After treatment, 1.0, 2.0, and 4.0 g/kg dosage groups all lost weight, but the 0.5 g/kg dosage group showed no impairment; after recovery, all impaired rats regained weight. 2. After treatment, 1.0, 2.0, and 4.0 g/kg dosage groups all showed a rise in gait scores, decreased rotarod latency, and decreased motor nerve conduction velocity, whereas the 0.5 g/kg dosage group showed no impairment; after recovery, all impaired rats were completely rehabilitated. 3. After treatment, levels of pyrrole adducts in serum, urine, and hair of experimental groups increased; after recovery, serum and urine pyrrole adducts showed no difference from the control (P > 0.05), whereas hair pyrrole adducts were significantly different from the control (P < 0.01). 4. The half-lives of serum and urine pyrrole adducts were 47.8-78.0 h and 42.7-52.9 h, while the half-life of hair pyrrole adducts was 14-24 weeks. 5. During treatment and recovery, levels of serum, urine, and hair pyrrole adducts showed high correlation with gait scores (P < 0.01), and hair pyrrole adducts had the largest partial correlation coefficient. In conclusion, hair pyrrole adducts could serve as a stable and reliable biomarker for the prevention of n-hexane intoxication. Furthermore, the no-observed-adverse-effect level of hair pyrrole adducts in rats is 275.2 ±â€¯61.5 nmol/g protein. Further studies are required for the definition of the biological exposure limit in humans.

[Study on the effect of diallyl sulfide on peripheral nerve injury in n-hexane intoxicated rats].

Objective: To investigate the antagonistic effect of diallyl sulfide (DAS) against peripheral nerve injury induced by n-hexane in rats. Methods: A total of 68 adult male Wistar rats were selected, among which 50 were randomly selected and divided into blank control group, DAS control group (100 mg/kg·bw) , n-hexane model group, low-dose DAS intervention group (50 mg/kg·bw) , and high-dose DAS intervention group (100 mg/kg·bw) . A rat model of peripheral nerve injury was established by n-hexane exposure, and the rats were treated with DAS at different doses. The changes in pyrrole adducts and behavior were observed, a metabolic analysis was performed for serum pyrrole adducts, and the intervention effect was evaluated. The remaining 18 rats were randomly assigned to the n-hexane model group, the low-dose DAS intervention group, and the high-dose DAS intervention group, with 6 rats in each group, as satellite groups used for the toxicokinetic analysis of serum pyrrole adducts. Results: Compared with the blank control group, the n-hexane model group and low-and high-dose DAS intervention groups had a significant reduction in body weight since week 2 (P<0.01) . Compared with the n-hexane model group at the end of the experiment at week 7, the high-dose DAS intervention group had a significantly higher body weight (P<0.05) , while there was no significant difference in body weight between the n-hexane model group and the low-dose DAS intervention group (P>0.05) . The n-hexane model group developed gait abnormality at week 2 of poisoning, while the low-and high-dose DAS intervention groups developed gait abnormality at weeks 3 and 5 of poisoning, respectively. At the end of the experiment, the n-hexane model group and the low-and high-dose DAS intervention groups had a significantly higher gait score than the blank control group (P<0.01) . At the end of the experiment, the n-hexane model group and the low-dose DAS intervention group had significantly shorter latency in rotarod test than the blank control group (P<0.01) , while there was no significant difference in latency between the DAS control group and the high-dose DAS intervention group (P>0.05) . Compared with the n-hexane model group, the low-and high-dose DAS intervention groups had a significant increase in latency in rotarod test (P<0.01) . Compared with blank control group, the n-hexane model group and the low-dose DAS intervention group had a significant increase in mean nerve conduction velocity (P<0.01) , while there was no significant difference between the blank control group and the DAS control group or high-dose DAS intervention group (P>0.05) , and compared with the n-hexane model group, the low-and high-dose DAS intervention groups had a significant increase in nerve conduction velocity (P<0.01) . Compared with the blank control group at the end of the experiment at week 7, the n-hexane model group and the low-and high-dose DAS intervention groups had significant increases in the concentration of pyrrole adducts in serum, urine, and hair (P<0.01) , while there was no significant difference between the blank control group and the DAS control group (P>0.05) , and the high-dose DAS intervention group had a significantly lower concentration of pyrrole adducts in serum, urine, and hair than the low-dose DAS intervention group (P<0.05) . Serum pyrrole adducts reached the peak level at 9-12 hours and then started to decrease. Compared with the n-hexane model group, the high-and low-dose DAS intervention groups had a significantly shorter half-life period of serum pyrrole adducts (P<0.01) . Compared with the n-hexane model group, the high-and low-dose DAS intervention groups had a significant reduction in the area under the curve of serum pyrrole adducts (P<0.05) . Conclusion: DAS can antagonize peripheral nerve injury induced by n-hexane.

Hexane exposure and persistent peripheral neuropathy in automotive technicians.

Automotive technicians are commonly exposed to organic and chlorinated solvents, particularly through use of cleaning products. Mainly during the period 1989-2002, n-hexane was a component of some of these products. In other occupational contexts, n-hexane has been shown to be a cause of peripheral neuropathy. The purpose of the present study was to investigate whether previous exposures to low concentrations of n-hexane were a cause of persistent peripheral neuropathy in automotive technicians. Enrolled in the study were 830 San Francisco Bay Area automotive technicians. Each participant underwent a battery of tests to investigate peripheral nervous system impairment. Test results regressed against estimated hexane and total solvent exposures showed only limited evidence of association with solvent exposures. Exposures to both hexane and general solvents were well below their occupational exposure limits. Generally, our results provide reassurance about persistent peripheral neuropathic effects in automotive technicians who previously used hexane-containing automotive cleaning products. This may reflect repair processes, since the exposures occurred some years previous to the study. However, we cannot exclude the possibility that the absence of observed effect in this study may be attributable to low exposures, exposure misclassification and/or the healthy worker survivor effect.

[Effects of n-hexane on learning and memory and the expressions of nerve growth factor mRNA and nerve growth factor receptor mRNA of brain tissue in mice exposed to N-hexane].

Objective: To Effects of n-hexane on learning and memory and the expressions of nerve growth factor (NGF) mRNA and nerve growth factor receptor (NGFR) mRNA of brain tissue in mice exposed to N-hexane. Methods: 40 Kunming mice were randomly divided into low-dose group, meddle-dose group, high-dose dose group and control group, with 10 mice in each group. All the groups were orally exposed to n-hexane in different doses: low-dose group with 43.5 mg/kg, middle-dose group with 86.5 mg/kg and high-dose group with 173.0 mg/kg, 1 time per day for 20 d. After the poisoning, the Y-arm test and the expressions of NGF mRNA and NGFR mRNA and the concentrations of NGF and NGFR in the brain tissues of each group were measured. Results: In the first Y-arm test, there existed a significant difference in correct reaction rate generally in all groups (P<0.05), and correct reaction rate in the middle-dose group and the high-dose group were low significantly compared with that in the control group(P<0.05). In the second Y-arm test, there existed a significant differences in total electric shock time and correct reaction rate generally in all groups (P<0.01), and the total electric shock time prolonged significantly and the correct response rate decreased significantly in 3 dose groups compared with those of the control group(P<0.05). The expression levels of NGF mRNA in brain tissues of low, meddle and high dose-groups were 0.81±0.66, 0.67±0.37 and 0.69±0.26, and the expression levels of NGFR mRNA were 1.22±0.42, 1.98±0.84 and 2.01±2.01, respectively. Compared with the control group, the expressions of NGF mRNA in the 3 dose groups decreased significantly (P<0.05), and the expression of NGFR mRNA in middle-and high-dose groups increased significantly (P<0.05). The concentrations of NGF in brain tissues of low,meddle and high dose-groups were 39.97±7.24 ng/L, 39.26±7.88 ng/L,31.70±8.21 ng/L,and the concentrations of NGFR were 17.37±6.82 ng/L,21.37±7.16 ng/L, 22.46±7.70 ng/L, respectively. Compared with the control group, the concentrations of NGF in high-dose groups decreased significantly(P<0.05), and the concentrations of NGFR in middle-and high-dose groups increased significantly (P<0.05). Conclusion: N-hexane exposure can result in decrease of learning and memory in mice, which may be related to abnormal expression of NGF mRNA and NGFR mRNA in brain tissue.

N-hexane exposure: a cause of small fiber neuropathy.

A 59-year-old woman presented with progressive paresthesias of all of her limbs for 4 years, associated with neuropathic pain, tingling in the tongue and allodynia, consistent with small fiber neuropathy (SFN). Several systemic symptoms and signs were found on clinical examination and laboratory work-up. Neurological investigations including neurophysiologic test and skin biopsy supported the diagnosis of SFN. Chronic exposure to N-hexane was then disclosed and suspected to be the cause of the disease. Following the discontinuation of chronic N-hexane exposure, the patient had a progressive improvement of all signs and symptoms, reinforcing the correlation between exposure to N-hexane, and development of SFN. Exposure to N-hexane may be considered as a novel reversible cause of SFN, which underlines the need to look for toxic etiologies in the diagnosis of SFN.

Hair pyrrole adducts serve as biomarkers for peripheral nerve impairment induced by 2,5-hexanedione and n-hexane in rats.

Pyrrole adducts are specific reaction products of 2,5-hexadione (2,5-HD) in vivo and are considered highly relevant to the pathogenesis of peripheral nerve impairments after exposure to n-hexane, though the exact mechanism remains unclear. In this study, 40 male Wistar rats were randomly divided into three experimental groups and one control group, in which all rat's hair were shaved completely at the beginning. The rats in three experimental groups were treated with 2,5-HD by gavage at dosages of 100, 200 and 300 mg/kg per day respectively, six times per week for 8 weeks. Abnormality of gait and changes in the rota-rod latency were surveilled. Pyrrole adducts in hair, urine and serum of all rats were measured at the endpoint. Results showed that the increased pyrrole adducts in hair, urine and serum accumulated in dose-response relationship. Spearman's correlation analysis between pyrrole adducts and gait scores showed that hair pyrrole adducts were highly relevant to the gait scores. Moreover, we treated rats with n-hexane and succeed to verify the results aforesaid. Further, multiply linear regression analysis showed that hair pyrrole adducts have higher partial correlation coefficients than these in serum and urine in both 2,5-HD and n-hexane treated models. Our findings draw the conclusion that the hair pyrrole adducts might serve as a promising biomarker of n-hexane induced peripheral neuropathy.

Diallyl trisulfide attenuated n-hexane induced neurotoxicity in rats by modulating P450 enzymes.

Chronic exposure to n-hexane can induce serious nerve system impairments without effective preventive medicines. Diallyl trisulfide (DATS) is a garlic-derived organosulfur compound, which has been demonstrated to have many beneficial effects. The current study was designed to evaluate whether DATS could restrain n-hexane induced neurotoxicity in rats and to explore the underlying mechanisms. Rats were treated with n-hexane (3 g/kg, p.o.) and different doses of DATS (10, 20 and 30 mg/kg, p.o.) for 8 weeks. Behavioral assessment showed that DATS could inhibit n-hexane induced neurotoxicity, demonstrated by the improvement of the grip strength and decline of gait scores. Toxicokinetic analysis revealed that the Cmax and AUC0-t of 2,5-hexanedione (product of n-hexane metabolic activation) and 2,5-hexanedione protein adducts in serum were significantly declined in DATS-treated rats, and the levels of pyrrole adducts in tissues were significantly reduced. Furthermore, DATS activated CYP1A1 and inhibited n-hexane induced increased expression and activity of CYP2E1 and CYP2B1. Collectively, these findings indicated that DATS protected the rats from n-hexane-induced neurotoxicity, which might be attributed to the modulation of P450 enzymes by DATS.

Disruption of YLR162W in Saccharomyces cerevisiae results in increased tolerance to organic solvents.

OBJECTIVE: To identify a novel gene responsible for organic solvent-tolerance by screening a transposon-mediated deletion mutant library based on Saccharomyces cerevisiae L3262. RESULTS: One strain tolerant of up to 0.5 % (v/v) n-hexane and cyclohexane was isolated. The determination of transposon insertion site identified one gene, YLR162W, and revealed disruption of the ORF of this gene, indicating that organic solvent tolerance can be conferred. Such a tolerant phenotype reverted to the sensitive phenotype on the autologous or overexpression of this gene. This transposon mutant grew faster than the control strain when cultured at 30 °C in YPD medium containing 0.5 % (v/v) n-hexane and cyclohexane respectively. CONCLUSION: Disruption of YLR162W in S. cerevisiae results in increased tolerance to organic solvents.

Effects of anionic surfactant on n-hexane removal in biofilters.

The biodegradability of three anion surfactants by biofilm microorganisms and the toxicity of the most readily biodegradable surfactant to biofilm microorganisms were examined using batch experiments, and the optimal concentration of SDS for enhanced removal of hexane was investigated using two biotrickling filters (BTFs) for comparison. Results showed that SDS could be biodegraded by microorganisms, and its toxicity to microorganisms within the experimental range was negligible. The best concentration of SDS in biofiltration of n-hexane was 0.1 CMC and the elimination capacity (EC) of 50.4 g m(-3) h(-1) was achieved at a fixed loading rate (LR) of 72 g m(-3) h(-1). When an inlet concentration of n-hexane increased from 600 to 850 mg m(-3), the removal efficiency (RE) decreased from 67% to 41% by BTF2 (with SDS) and from 52% to 42% by BTF1 (without SDS). SDS could enhance hexane removal from 43% (BTF1) to 60% (BTF2) at gas empty-bed residence time (EBRT) of 7.5 s and an inlet concentration of 200 mg m(-3).

Comparison of outcomes obtained in murine local lymph node assays using CBA/J or CBA/Ca mice.

CBA/J and CBA/Ca mice are the recommended strains for local lymph node assays (LLNAs). Here, we report quantitative and qualitative comparisons between both mouse strains to provide useful information for the strain selection of sensitization testing. LLNA was conducted, in accordance with Organisation for Economic Co-operation and Development Test Guideline No. 429, with CBA/J and CBA/Ca mice using five chemicals including typical contact sensitizers and non-sensitizers: 2,4-dinitrochlorobenzene (DNCB), isoeugenol, α-hexylcinnamic aldehyde (HCA), propylene glycol (PG), and hexane; then outcomes were compared based on the raw data (disintegrations per minute, DPM), stimulation index (SI) values, EC3 values and positive/negative decisions. Although a significant difference was noted between DPM values derived from each strain of mice, SI values exhibited no considerable difference. The EC3 values for DNCB in CBA/J and CBA/Ca mice were 0.04 and 0.03, those for isoeugenol were 1.4 and 0.9, and those for HCA were 7.7 and 6.0, respectively. All EC values derived from each test system were almost equivalent and were within the range of acceptance criteria of the ICCVAM performance standard for LLNA. Positive/negative outcomes for all test chemicals were consistent. In conclusion, no considerable differences were observed in the final outcomes derived from CBA/J and CBA/Ca mice in LLNA. Copyright © 2015 John Wiley & Sons, Ltd.

Gestational N-hexane inhalation alters the expression of genes related to ovarian hormone production and DNA methylation states in adult female F1 rat offspring.

Research has revealed that n-hexane can disrupt adult female endocrine functions; however, few reports have focused on endocrine changes in adult F1 females after maternal exposure during gestation. In this study, female Wistar rats inhaled 100, 500, 2500, or 12,500 ppm n-hexane for 4 h daily during their initial 20 gestational days. The F1 female offspring exhibited abnormal oestrus cycles. Compared with the controls, the in vitro-cultured ovarian granulosa cells of the 12,500 ppm group showed significantly reduced in vitro progesterone and oestradiol secretion. Elevated progesterone secretion was observed in the 500 ppm group, and decreased and significantly upregulated mRNA expression of the Star, Cyp11a1, Cyp17a1, and Hsd3b genes was observed in the 12,500 ppm and 500 ppm groups, respectively. The protein expression levels were consistent with the mRNA expression levels. Methylation screening of the promoter regions of these genes was performed using MeDIP-chip and confirmed by methylation-sensitive high-resolution melting (MS-HRM), and the observed methylation state changes of the promoter regions were correlated with the gene expression levels. The results suggest that the hormone levels in the female offspring after gestational n-hexane inhalation correspond to the expression levels and DNA methylation states of the hormone production genes.