1-Bromopropane, an alternative to ozone layer depleting solvents, is dose-dependently neurotoxic to rats in long-term inhalation exposure.

1-Bromopropane has been newly introduced as an alternative to ozone layer-depleting solvents. We aimed to clarify the dose-dependent effects of 1-bromopropane on the nervous system. Forty-four Wistar male rats were randomly divided into 4 groups of 11 each. The groups were exposed to 200, 400, or 800 ppm of 1-bromopropane or only fresh air 8 h per day for 12 weeks. Grip strength of forelimbs and hind limbs, maximum motor nerve conduction velocity (MCV), and distal latency (DL) of the tail nerve were measured in 9 rats of each group every 4 weeks. The other 2 rats of each group were perfused at the end of the experiment for morphological examinations. The rats of the 800-ppm group showed poor kicking and were not able to stand still on the slope. After a 12-week exposure, forelimb grip strength decreased significantly at 800 ppm and hind limb grip strength decreased significantly at both 400 and 800 ppm or after a 12-week exposure. MCV and DL of the tail nerve deteriorated significantly at 800 ppm. Ovoid or bubble-like debris of myelin sheaths was prominent in the unraveled muscular branch of the posterior tibial nerve in the 800-ppm group. Swelling of preterminal axons in the gracile nucleus increased in a dose-dependent manner. Plasma creatine phosphokinase (CPK) decreased dose-dependently with significant changes at 400 and 800 ppm. 1-Bromopropane induced weakness in the muscle strength of rat limbs and deterioration of MCV and DL in a dose-dependent manner, with morphological changes in peripheral nerve and preterminal axon in the gracile nucleus. 1-Bromopropane may be seriously neurotoxic to humans and should thus be used carefully in the workplace.

Reproductive toxicity of 1-bromopropane, a newly introduced alternative to ozone layer depleting solvents, in male rats.

1-Bromopropane has been newly introduced as an alternative to ozone-depleting solvents. We aimed to clarify its dose-dependent reproductive toxicity in male rats. Thirty-six Wistar male rats were randomly divided into 4 groups of 9. The groups were exposed to 200, 400, or 800 ppm 1-bromopropane or only fresh air, 8 h per day for 12 weeks. Epididymal sperm indices were evaluated after a 12-week exposure. The testes, epididymides, seminal vesicle, prostate, and other organs were weighed and examined histopathologically. Spermatogenic cells, in stage VII seminiferous tubules, and retained spermatids, at the basal region of stages IX-XI seminiferous epithelium, were counted. Plasma testosterone levels were measured by radioimmunoassay. The testicular weight did not significantly change, but the weight of epididymides, seminal vesicle, and prostate dose-dependently decreased. The weight of seminal vesicle decreased significantly at the lowest concentration of 200-ppm and over. 1-Bromopropane induced a dose-dependent decrease in the epididymal sperm count and in motility, as well as an increase in tailless sperm and sperm with an immature head shape. The spermatogonia, preleptotene spermatocytes, pachytene spermatocytes, and round spermatids did not decrease significantly at stage VII. Retained, elongated spermatids near the basement membrane at the postspermiation stages IX-XI increased dose-dependently. Plasma testosterone levels significantly decreased at the 800-ppm dosage. 1-Bromopropane caused failure of spermiation. Its reproductive toxicity is different from that of 2-bromopropane, which specifically impairs spermatogonia. Thus, this solvent may have serious reproductive toxic effects in men, and should be used very cautiously in the workplace.

Effect of inhalation exposure to 2-bromopropane on the nervous system in rats.

Exposure to 2-bromopropane (2-BP) is suspected to have adverse effects on the nervous system. The aim of this study was to investigate whether the exposure of rats to 2-BP had neurotoxic effects using histological and electrophysiological studies. Wistar strain male rats were exposed daily to either 100 or 1000 ppm 2-BP or to fresh air for 8 h a day for 12 weeks. Body weight was measured before exposure and every 2 weeks. Motor nerve conduction velocity (MCV) and distal latency (DL) were measured before exposure and every 4 weeks during exposure. Histological examination of the nervous system was also performed. Exposure of rats (n = 9) to 1000 ppm resulted in suppression of body weight gain and a significant decrease in brain weight compared to the control (n = 9). Electrophysiological measurements showed a significant decrease in MCV in 1000 ppm exposed rats at 8 weeks and significant prolongation of DL at 8 and 12 weeks. Abnormalities of the myelin sheath were detected in the common peroneal nerves. In 100-ppm exposed rats (n = 9), no significant changes were noted in body weight and the peripheral nerve. In conclusions, long-term exposure to 1000 ppm of 2-BP may result in peripheral neuropathy in rats.

Nerve-specific marker proteins as indicators of organic solvent neurotoxicity.

Effects of chronic exposure to n-hexane and toluene on some nerve-specific marker proteins in rat central nervous system (CNS) and peripheral nervous system (PNS) were assessed and compared. The rats were exposed to 2000 ppm n-hexane, 12 hr/day, 6 days/week, for 24 weeks, and to 1000 ppm toluene, 8 hr/day, 6 days/week, for 16 weeks. The level of neuron-specific enolase (NSE), creatine kinase-B (CK-B), and beta-S100 protein in cortex, cerebellum, spinal cord, and proximal and distal sciatic nerve was determined by enzyme immunoassay method. In n-hexane-exposed rats, the level of NSE, CK-B, and beta-S100 decreased significantly in the distal segment of the sciatic nerve, while the marker proteins in CNS and proximal sciatic nerve remained unchanged. In contrast, chronic exposure to toluene mostly affected these marker proteins in CNS tissues, displaying the increase of NSE, CK-B, beta-S100 in cerebellum, as well as the increase of beta-S100 in spinal cord. No quantitative changes of the three proteins in distal sciatic nerve were observed after exposure to toluene. n-Hexane-induced peripheral distal neuropathy and toluene-induced brain gliosis appeared to be responsible for this different pattern of biochemical changes. The present study suggests the usefulness of using these nerve-specific marker proteins to assess the solvent-related CNS and PNS neurotoxicity.

Chronic exposure to n-hexane induces changes in nerve-specific marker proteins in the distal peripheral nerve of the rat.

1. After long-term n-hexane exposure (2000 ppm, 12 h d-1, 6 d week-1, for 24 weeks), the content of neuron-specific enolase (gamma-enolase), creatine kinase-B and beta-S100 protein in the cortex, cerebellum, spinal cord and proximal and distal sciatic nerves of rats was determined by enzyme immunoassay. 2. The amounts of the three proteins decreased significantly in the distal segment of sciatic nerve, whereas they remained unchanged in the brain and proximal sciatic nerve. The quantitative decline in these marker proteins in the distal sciatic nerve could be related to neurophysiological deficits in the peripheral nerves. 3. This study indicates that the biochemical changes observed are consistent with the clinical and pathological findings of n-hexane neuropathy. These nerve-specific marker proteins can be used to assess solvent-related peripheral neurotoxicity.

Dose dependent effects of chronic exposure to toluene on neuronal and glial cell marker proteins in the central nervous system of rats.

The dose dependent effects of chronic exposure to toluene on the neuronal marker proteins (gamma-enolase, calbindin-D28k) and glial cell marker proteins (alpha-enolase, creatine kinase-B, and beta-S100 protein) were investigated in the central nervous system (CNS) of rats. Three groups of animals were exposed to 100 ppm, 300 ppm, or 1000 ppm toluene vapour eight hours a day, six days a week for 16 weeks. The contents of the marker substances were determined with enzyme immunoassays. A significant increase in the three glial cell marker proteins was noted in the cerebellum after exposure to 100 ppm toluene; a more pronounced increase occurred at the higher toluene concentrations. beta-S100 protein also exhibited a dose dependent increase in the brainstem and spinal cord. On the other hand, the two neuronal cell markers did not show a quantitative decrease in the CNS. This means that the development of gliosis, rather than neurone death, is induced by chronic exposure to toluene. The significant biochemical changes induced around the threshold limit value and the concentration dependent alterations suggest that these nerve specific marker proteins may be used to evaluate solvent related damage to the CNS.

[Effect of diuretic, azosemide (SK-110), in combination with antibiotic, cephaloridine, on kidney].

This study was performed to compare the acute-renal toxicity of azosemide (SK-110) or furosemide (FM) treatment in combination with cephaloridine (CER). 1) Initially, the acute-renal toxicity of CER was studied after a subcutaneous administration at dose levels of 500, 1000, 1500 and 2000 mg/kg. The values of BUN, creatinine and relative kidney weights were increased in rats given CER at dose levels above 1500 mg/kg. consequently, it was considered that the threshold of CER with regard to acute-renal toxicity was 1000 mg/kg. 2) Secondarily, the acute-renal toxicity of SK-110 or FM were studied after oral administration of 40, 80, 160 or 320 mg/kg doses alone or in combination with CER. Acute-renal toxicity was evident in the 320 mg/kg-treated rats after both SK-110 and FM alone, as revealed by analysis of a number of parameters, i.e., BUN, serum creatinine, urine sediment and composition and pathological data composing both kidney weights and studies at the microscope level. However, the increase of BUN and relative kidney weights values, elevated numbers of epithelial cells in the urine and necrosis observed in the uriniferous-tubular epithelium on histopathological examination of kidneys were noted in rats given at dose levels of only 80 mg/kg with SK-110 + CER, whereas they were seen in animals treated with FM even at the lowest applied dose of 40 mg/kg in combination with CER. In conclusion, this study showed that the minimum dose of SK-110 or FM in combination with CER which causes acute-renal toxicity were, respectively, 80 mg/kg or less than 40 mg/kg.

[Effect of azosemide (SK-110) and its metabolites on mouse liver].

The effect of azosemide (SK-110), and its metabolites, 5-(2'-amino-4'-chloro-5'-sulfamoylphenyl)-tetrazole (M-1), 2-thiophenecarboxylic acid (TC), on mouse liver was investigated using biochemical and pathological parameters as indices of hepatotoxicity. The effects were compared with that of furosemide (FM) administration. A single dose of each compound was administered orally, or intraperitoneally, while multiple oral dosing was carried out once daily for a week. The results are summarized as follows: 1) SK-110 did not produce hepatotoxicity even after a single p.o. dose as high as 5000 mg/kg, a single i.p. dose of 400 mg/kg, or multiple p.o. doses of 700 mg/kg/day. 2) M-1 also did not produce hepatotoxicity even after a single p.o. dose of 4000 mg/kg or multiple p.o. doses of 550 mg/kg/day. TC did not exert hepatotoxicity after a single i.p. dose of 150 mg/kg or multiple p.o. doses of 250 mg/kg/day, but did produce hepatotoxicity after a single p.o. dose of more than 1000 mg/kg. However, it was presumed that, in vivo, TC formed as a metabolite of administered SK-110 would hardly produce hepatotoxicity. 3) FM produced hepatotoxicity after a single p.o. dose of more than 800 mg/kg, or a single i.p. dose of more than 200 mg/kg, but not after multiple p.o. doses of 700 mg/kg/day. Based on these findings, it was concluded that, in contrast to FM, SK-110 had no hepatotoxic effect on the mouse liver.