A histopathologic study of the nervous system after inhalation exposure of 1-bromopropane in rat

High-fat diet exacerbates 1-Bromopropane-induced loss of dopaminergic neurons in the substantia nigra of mice through mitochondrial damage associated necroptotic pathway

In recent years, accumulating evidence supports that occupational exposure to solvents is associated with an increased incidence of Parkinson's disease (PD) among workers. The neurotoxic effects of 1-bromopropane (1-BP), a widely used new-type solvent, are well-established, yet data on its relationship with the etiology of PD remain limited. Simultaneously, high-fat consumption in modern society is recognized as a significant risk factor for PD. However, whether there is a synergistic effect between a high-fat diet and 1-BP exposure remains unclear. In this study, adult C57BL/6 mice were fed either a chow or a high-fat diet for 18 weeks prior to 12-week 1-BP treatment. Subsequent neurobehavioral and neuropathological examinations were conducted to assess the effects of 1-BP exposure on parkinsonian pathology. The results demonstrated that 1-BP exposure produced obvious neurobehavioral abnormalities and dopaminergic degeneration in the nigral region of mice. Importantly, a high-fat diet further exacerbated the impact of 1-BP on motor and cognitive abnormalities in mice. Mechanistic investigation revealed that mitochondrial damage and mtDNA release induced by 1-BP and high-fat diet activate NLRP3 and cGAS-STING pathway- mediated neuroinflammatory response, and ultimately lead to necroptosis of dopaminergic neurons. In summary, our study unveils a potential link between chronic 1-BP exposure and PD-like pathology with motor and no-motor defects in experimental animals, and long-term high-fat diet can further promote 1-BP neurotoxicity, which underscores the pivotal role of environmental factors in the etiology of PD.

Allyl Sulfide Counteracts 1-Bromopropane-Induced Neurotoxicity by Inhibiting Neuroinflammation and Oxidative Stress

Chronic exposure to 1-bromopropane (1-BP), an alternative to ozone-depleting solvents, produces potential neurotoxicity in occupational populations. However, no therapeutic strategy is available currently. Accumulating evidence suggests that cytochrome P4502E1 (CYP2E1) is critical for the active metabolism of 1-BP. The purpose of this study is aimed to test whether inhibition of CYP2E1 by allyl sulfide, a specific inhibitor of CYP2E1, could be able to protect against 1-BP-induced neurotoxicity. Male Wistar rats were intoxicated with 1-BP for 9 continuous weeks with or without allyl sulfide pretreatment. Results clearly demonstrated that 1-BP exposure induced decrease in NeuN+ cells and increase in cleaved caspase-3 expression and TUNEL+ cells in motor cortex of rats, which was significantly ameliorated by allyl sulfide. Allyl sulfide treatment also recovered the motor performance of rats treated with 1-BP. Mechanistically, allyl sulfide-inhibited 1-BP-induced expression of CYP2E1 in microglia, which was associated with suppression of microglial activation and M1 polarization in motor cortex of rats. Reduced oxidative stress was also observed in rats treated with combined allyl sulfide and 1-BP compared with 1-BP alone group. Furthermore, we found that allyl sulfide abrogated 1-BP-induced activation of Nuclear factor(NF)-κB and GSH/Thioredoxin/ASK1 pathways, the key factor for the maintenance of M1 microglial inflammatory response and oxidative stress-related neuronal apoptosis, respectively. Thus, our results showed that allyl sulfide exerted neuroprotective effects in combating 1-BP-induced neurotoxicity through inhibition of neuroinflammation and oxidative stress. Blocking CYP2E1 activity by allyl sulfide might be a promising avenue for the treatment of neurotoxicity elicited by 1-BP and other related neurotoxicants.

NMDA Receptor Antagonist MK801 Protects Against 1-Bromopropane-Induced Cognitive Dysfunction

Occupational exposure to 1-bromopropane (1-BP) induces learning and memory deficits. However, no therapeutic strategies are currently available. Accumulating evidence has suggested that N-methyl-D-aspartate receptors (NMDARs) and neuroinflammation are involved in the cognitive impairments in neurodegenerative diseases. In this study we aimed to investigate whether the noncompetitive NMDAR antagonist MK801 protects against 1-BP-induced cognitive dysfunction. Male Wistar rats were administered with MK801 (0.1 mg/kg) prior to 1-BP intoxication (800 mg/kg). Their cognitive performance was evaluated by the Morris water maze test. The brains of rats were dissected for biochemical, neuropathological, and immunological analyses. We found that the spatial learning and memory were significantly impaired in the 1-BP group, and this was associated with neurodegeneration in both the hippocampus (especially CA1 and CA3) and cortex. Besides, the protein levels of phosphorylated NMDARs were increased after 1-BP exposure. MK801 ameliorated the 1-BP-induced cognitive impairments and degeneration of neurons in the hippocampus and cortex. Mechanistically, MK801 abrogated the 1-BP-induced disruption of excitatory and inhibitory amino-acid balance and NMDAR abnormalities. Subsequently, MK801 inhibited the microglial activation and release of pro-inflammatory cytokines in 1-BP-treated rats. Our findings, for the first time, revealed that MK801 protected against 1-BP-induced cognitive dysfunction by ameliorating NMDAR function and blocking microglial activation, which might provide a potential target for the treatment of 1-BP poisoning.

Elevation of 4-hydroxynonenal and malondialdehyde modified protein levels in cerebral cortex with cognitive dysfunction in rats exposed to 1-bromopropane

1-Bromopropane (1-BP), an alternative to ozone-depleting solvents (ODS), exhibits central nervous system (CNS) toxicity in animals and humans. This study was designed to relate CNS damage by Morris water maze (MWM) test and oxidative stress to 1-BP exposure in the rat. Male Wistar rats were randomly divided into 4 groups (n=10), and treated with 0, 200, 400 and 800 mg/kgbw 1-BP for consecutive 12 days, respectively. From day 8 to day 12 of the experiment, MWM test was employed to assess the cognitive function of rats. The cerebral cortex of rats was obtained immediately following the 24h after MWM test conclusion. Glutathione (GSH), oxidized glutathione (GSSG) and total thiol (total-SH) content, GSH reductase (GR) and GSH peroxidase (GSH-Px) activities, malondialdehyde (MDA) level, as well as 4-hydroxynonenal (4-HNE) and MDA modified proteins in homogenates of cerebral cortex were measured. The obtained results showed that 1-BP led to cognitive dysfunction of rats, which was evidenced by delayed escape latency time and swimming distances in MWM performance. GSH and total-SH content, GSH/GSSG ratio, GR activity significantly decreased in cerebral cortex of rats, coupling with the increase of MDA level. 4-HNE and MDA modified protein levels obviously elevated after 1-BP exposure. GSH-Px activities in cerebral cortex of rats also increased. These data suggested that 1-BP resulted in enhanced lipid peroxidation of brain, which might play an important role in CNS damage induced by 1-BP.

Apoptosis contributes to testicular toxicity induced by two isomers of bromopropanes

The aim of this study was to investigate the different testicular toxicity and the role of apoptosis in the possible mechanism induced by the two isomers of bromopropanes (BPs) in the same dosage. Following the 14-day treatment with a single dose of 1-BP and 2-BP (1 g/kg), male rats were killed and a series of experiments were performed. 1-BP and 2-BP both significantly decreased the epididymal sperm count, while only 2-BP induced an increase in sperms with abnormal heads. Morphological evaluation showed that 1-BP did not cause morphological changes in seminiferous epithelium, but 2-BP treatment resulted in the disappearance of spermatogonia, atrophy of the seminiferous tubules and degeneration of germ cells. 2-BP significantly increased the TUNEL-positive cells and the activation of caspase-3 and decreased the genes and proteins expression of Bax, Bcl-2 and p53. In contrast, there were no significant changes in the expression of apoptosis-related genes and proteins in 1-BP group, though the TUNEL-positive cells were significantly increased. Taken together, this study indicated that those two isomers both have toxicity in male rats, however, the testicular toxicity and the role of apoptosis in the toxic mechanism induced by 1-BP and 2-BP may be different.

Severe neurotoxicity associated with exposure to the solvent 1-bromopropane (n-propyl bromide)

BACKGROUND

1-bromopropane was recently substituted for traditional ozone-depleting solvents in the industrial setting.

CASE SERIES

We report a cohort of six cases of 1-bromopropane neurotoxicity occurring in foam cushion gluers exposed to 1-bromopropane vapors from spray adhesives. Patients 1-5 were exposed 30-40 hours per week over three years; patient 6 had been employed for the previous three months. Exposure had peaked over the previous month when ventilatory fans were turned off. All patients complained of subacute onset of lower extremity pain or paresthesias. Five of six complained of difficulty walking and on examination had spastic paraparesis, distal sensory loss, and hyperreflexia. Three patients initially had nausea and headache. Serum bromide concentrations ranged from 44 to 170 mg/dL (reference 0-40 mg/dL). Apparent hyperchloremia was present with serum chloride concentrations of 105 to 139 mmol/L (reference 98-107 mmol/L). Air samples taken at the workplace during gluing operations revealed the mean air concentration of 1-bromopropane to be 130 ppm (range 91-176 ppm) with a seven hour time-weighted average of 108 ppm (range 92-127 ppm), well above the EPA-proposed limit of 25 ppm. Two years after exposure, the two most severely affected patients had minimal improvement of function and they, with a third patient, continued to experience chronic neuropathic pain.

CONCLUSION

This report supports the growing recognition of 1-bromopropane neurotoxicity in humans consisting most commonly of headache, nausea, and subacute spastic paraparesis with distal sensory loss. The pathogenesis of 1-BP neurotoxicity in humans has yet to be fully elucidated but may reflect a central distal axonopathy syndrome.

Alteration of brain levels of neurotransmitters and amino acids in male F344 rats induced by three-week repeated inhalation exposure to 1-bromopropane

The present study investigated the effects of 1-bromopropane (1BP) on brain neuroactive substances of rats to determine the extent of its toxicity to the central nervous system (CNS). We measured the changes in neurotransmitters (acetylcholine, catecholamine, serotonin and amino acids) and their metabolites or precursors in eight brain regions after inhalation exposure to 1BP at 50 to 1,000 ppm for 8 h per day for 7 d per week for 3 wk. Rats were sacrificed at 2 h (Case 1), or at 19 h (Case 2) after the end of exposure. In Case 1, the level of 5-hydroxyindoleacetic acid (5HIAA) was lowered in some brain regions by 1BP exposure. The decrease of 5HIAA in the frontal cortex was statistically significant at 50 ppm 1BP exposure. In Case 2, gamma-amino butyric acid (GABA) and taurine were decreased in many brain regions of exposed rats, and a significant decrease of taurine in the midbrain occurred at 50 ppm 1BP exposure. In both cases of 2-h and 19-h intervals from the end of exposure to sacrifice, aspartate and glutamine levels were elevated in many brain regions, but the acetylcholine level did not change in any brain region. Three-week repeated exposure to 1BP produced significantly changes in amino acid contents of rat brains, particularly at 1,000 ppm.

Severe Illness in Furniture Makers Using a New Glue: 1-Bromopropane Toxicity Confounded by Arsenic

OBJECTIVE

To describe the illnesses of four workers with high concentrations of serum bromide after exposure to glue containing 1-bromopropane (1-BP).

METHODS

We reviewed all available clinical records, examined the workers, and obtained additional urinary arsenic values. We used standard autoanalyzer and other routine methods for blood and urinalysis.

RESULTS

All four workers had symptoms and abnormal physical findings when hospitalized, remaining symptomatic with abnormal examinations 3 months later. Milder symptoms persisted in two workers, 8 years after their initial illnesses. Both have returned to work. Follow-up was unavailable for the other two workers.

CONCLUSIONS

Severe illness occurred in four gluers after 1-BP exposures associated with elevated levels of serum bromide. All had elevated urinary arsenic concentrations, the source of which remains unknown, but which confound interpretation of the abnormal bromide levels and clinical findings present during the acute illnesses.

Neuro-reproductive toxicities of 1-bromopropane and 2-bromopropane

2-Bromopropane was used as an alternative to chlorofluorocarbons in a Korean electronics factory and caused reproductive and hematopoietic disorders in male and female workers. This causality was revealed by animal studies, and target cells were identified in subsequent studies. After identification of 2-bromopropane toxicity, 1-bromopropane was introduced to the workplace as a new alternative to ozone-depleting solvents. 1-Bromopropane was considered less mutagenic than 2-bromopropane, but, in contrast, animal experiments revealed that 1-bromopropane is a potent neurotoxic compound compared with 2-bromopropane. It was also revealed that 1-bromopropane has reproductive toxicity, but the target cells are different from those of 2-bromopropane. Exposure to 1-bromopropane inhibits spermiation in male rats and disrupts the development of follicles in female rats, in contrast to 2-bromopropane, which targets spermatogonia and oocytes in primordial follicles. After the first animal study describing the neurotoxicity of 1-bromopropane, human cases were reported. Those cases showed decreased sensation of vibration and perception, paresthesia in the lower extremities, decreased sensation in the ventral aspects of the thighs and gluteal regions, stumbling and headache, as well as mucosal irritation, as the initial symptoms. The dose-response of bromopropanes in humans and mechanism(s) underlying the differences in the toxic effects of the two bromopropanes remain to be determined.

Inhalation of 1-bromopropane causes excitation in the central nervous system of male F344 rats

The present study investigates the effects of 1-bromopropane (1BP) on animal behavior to determine the extent of toxicity to the central nervous system (CNS). We measured the spontaneous locomotor activity (SLA) of rats before and after 3 weeks of exposure to 1BP for 8 h per day. In control and 10 ppm groups, the SLA values were similar to pre-exposure levels on post-exposure Day 1 and thereafter. However, the SLA values in the 50 and 200 ppm groups were higher than pre-exposure levels. Open-field behavior was evaluated after exposure and freezing time decreased with exposure to increasing concentrations of 1BP. Ambulation and rearing scores in the exposed groups were higher than control values, particularly in the 50 and 200 ppm groups. The frequency of defecation and urination decreased almost dose-dependently. Exposure to 50-1000 ppm of 1BP did not affect passive avoidance behavior examined using a step-through type apparatus. The amount of time swimming in the water maze test was not affected in the controls, or groups exposed to 50 and 200 ppm 1BP, but that in the 1000 ppm group was increased compared with control. Exposure at 50-1000 ppm dose-dependently decreased the traction performance of rats, indicating decreased muscle strength. We found that 10-200 ppm of 1BP exposure did not affect motor coordination determined by rota-rod performance. The increased SLA values and open-field activity support the notion that 1BP has excitatory effects on the CNS of F344 male rats. In addition, 1BP reduced the grip or muscle strength of the rats. Memory function was not disordered and the motor coordination of all four limbs remained normal.

Dose-dependent biochemical changes in rat central nervous system after 12-week exposure to 1-bromopropane

1-Bromopropane is used as a cleaning agent or adhesive solvent in the workplace. The present study investigated the long-term effects of exposure to 1-bromopropane on biochemical components in the central nervous system (CNS) of rats. Four groups, each of nine male Wistar rats, were exposed to 200, 400, or 800 ppm 1-bromopropane or fresh air only, 8h per day, 7 days a week for 12 weeks. We measured the levels of neuron-specific gamma-enolase, glia-specific beta-S100 protein, creatine kinase (CK) subunits B and M, heat shock protein Hsp27 (by enzyme immunoassay), enzymatic activity of CK and levels of glutathione (GSH), oxidized glutathione (GSSG) and sulfhydrul (SH) base in the cerebrum, cerebellum, brainstem and spinal cord. gamma-Enolase decreased dose-dependently in the cerebrum, which showed a decrease in wet weight, at 400 ppm or over, but no change was noted in beta-S100 protein in any brain region or spinal cord. Hsp27 decreased in the cerebellum, brainstem and spinal cord. Protein-bound SH base, non-protein SH base and total glutathione decreased in every brain region. CK activity decreased dose-dependently at 200 ppm or over, and the ratio of CK activity to CK-B concentration tended to decrease in all regions. The decrease in gamma-enolase in the cerebrum suggests the involvement of biochemical changes in neurons with decrease in the wet weight of the cerebrum. Glutathione depletion and changes in proteins containing SH base as a critical site might be the underlying neurotoxic mechanism of 1-bromopropane. The biochemical changes in the cerebrum indicate that long-term exposure to 1-bromopropane has effects on the CNS.