Reversibility of the Adverse Effects of 1-Bromopropane Exposure in Rats

Role of cytochrome P450s in the male reproductive toxicity of 1-bromopropane

1-Bromopropane (1BP) is widely used as an alternative to ozone-depleting solvents. The present study investigated the role of P450s in 1BP-induced male reproductive toxicity. Mice co-treated with 1-aminobenzotriazole (ABT), a non-selective P450 inhibitor, were exposed to 1BP at 0, 50, 250, or 1200 ppm, while saline-treated control mice were exposed to 1BP at 0, 50, or 250 ppm, for 4 weeks. In the saline-treated mice, exposure to 1BP at 250 ppm decreased the sperm count and sperm motility. Histopathological examination showed that exposure to 1BP at 50 and 250 ppm increased the number of elongated spermatids retained at the basal region of stage IX, X and XI seminiferous tubules, while exposure to 1BP at 250 ppm increased the number of periodic acid-Schiff (PAS)-positive round structures in stage IX, X, and XI seminiferous tubules. Co-treatment with ABT prevented the above changes induced by exposure to 1BP at 50 or 250 ppm. However, ABT-treated mice exposed to 1BP in the 1200 ppm group showed decreases in the weights of reproductive organs, epididymal sperm count and motility, increases in epididymal sperm with abnormal heads, retained spermatids and PAS-positive round structures in stages IX-XI, depletion of spermatogenic cells in part of the seminiferous tubules, and a small number of round spermatids in stage VII seminiferous tubules. The results at 50 and 250 ppm of 1-BP exposure indicate that P450s play important roles in 1BP-induced testicular toxicity. The control of P450 activity reduced 1BP-induced male reproductive toxicities including spermiation failure, reduction of epididymal sperm count and motility, and formation of PAS-positive round structures at postspermiation stages.

Effect of 4-week inhalation exposure to 1-bromopropane on blood pressure in rats

The pathophysiology of hypertension is complex and multifactorial, and includes exposure to various chemical substances. Several recent studies have documented the reproductive and neurological toxicities of 1-bromopropane (1-BP). Given that 1-BP increased reactive oxygen species in the brain of rats, we hypothesized that 1-BP also has cardiovascular toxicity through increased oxidative stress. To test this hypothesis, male F344 and Wistar Nagoya rats (n = 7-8 per group per test) were exposed to 0 or 1000 ppm of 1-BP via inhalation for 4 weeks (8 h per day, 7 days per week). The exposure to 1-BP increased systolic blood pressure. This effect was associated with a significant decrease in the reduced/oxidized glutathione ratio. A significant increase in nitrotyrosine levels, activation of the NADPH oxidase pathway, which was evidenced by upregulation of gp91phox, a NADPH oxidase subunit, and significant decreases in the expressions of antioxidant molecules such as Cu/Zn- and Mn-superoxide dismutase catalase, and nuclear factor erythroid 2-related factor 2, were observed in the aortas of Wistar Nagoya rats exposed to 1-BP. Our results indicate that subacute (4-week) inhalation exposure to 1-BP increases blood pressure and suggest that this cardiovascular toxic effect is due, at least in part, to increased oxidative stress mediated through activation of the NADPH oxidase pathway. Further study is needed to assess whether NADPH oxidase activation causes the increase in blood pressure in the rats exposed to 1-BP. Copyright © 2016 John Wiley & Sons, Ltd.

Rats with metabolic syndrome resist the protective effects of N-acetyl l-cystein against impaired spermatogenesis induced by high-phosphorus/zinc-free diet

Consumption of relatively high amounts of processed food can result in abnormal nutritional status, such as zinc deficiency or phosphorus excess. Moreover, hyperphosphatemia and hypozincemia are found in some patients with diabetic nephropathy and metabolic syndrome. The present study investigated the effects of high-phosphorus/zinc-free diet on the reproductive function of spontaneously hypertensive rats/NDmcr-cp (SHR/cp), a model of the metabolic syndrome. We also investigated the effects of antioxidant, N-acetyl-l-cysteine (NAC), on testicular dysfunction under such conditions. Male SHR/cp and control rats (Wistar Kyoto rats, WKY) were divided into three groups; rats fed control diet (P 0.3%, w/w; Zn 0.2%, w/w), high-phosphorus and zinc-deficient diet (P 1.2%, w/w; Zn 0.0%, w/w) with vehicle, or high-phosphorus and zinc-deficient diet with NAC (1.5mg/g/day) for 12 weeks (n=6 or 8 rats/group). The weights of testis and epididymis were significantly reduced by high-phosphate/zinc-free diet in both SHR/cp and WKY. The same diet significantly reduced caudal epididymal sperm count and motility and induced histopathological changes in the testis in both strains. Treatment with NAC provided significant protection against the toxic effects of the diet on testicular function in WKY, but not in SHR/cp. The lack of the protective effects of NAC on impaired spermatogenesis in SHR/cp could be due to the more pronounced state of oxidative stress observed in these rats compared with WKY.

Effects of exposure to 1-bromopropane on astrocytes and oligodendrocytes in rat brain

OBJECTIVES

Human cases of 1-bromopropane (1-BP) toxicity showed ataxic gait and cognitive dysfunction, whereas rat studies showed pyknotic shrinkage in cerebellar Purkinje cells and electrophysiological changes in the hippocampus. The present study investigated the effects of 1-BP on astrocytes and oligodendrocytes in the rat cerebellum and hippocampus to find sensitive markers of central nervous system toxicity.

METHODS

Forty-eight F344 rats were divided into four equal groups and exposed to 1-BP at 0, 400, 800 and 1,000 ppm for 8 h/day; 7 days/week, for 4 weeks. Nine and three rats per group were used for biochemical and histopathological studies, respectively.

RESULTS

Kluver-Barrera staining showed pyknotic shrinkage in the cytoplasm of Purkinje cells and nuclei of granular cells in the cerebellum at 1,000 ppm. Immunohistochemical analysis showed increased length of glial fibrillary acidic protein (GFAP)-positive processes of astrocytes in the cerebellum, hippocampus and dentate gyrus at 800 and 1,000 ppm. The myelin basic protein (MBP) level was lower at 1,000 ppm. The numbers of astrocytes and granular cells per tissue volume increased at 400 ppm or higher.

CONCLUSION

The present study showed that elongation of processes of astrocytes accompanies degeneration of granular cells and Purkinje cells in the cerebellum of the rats exposed to 1-BP. The decrease in MBP and number of oligodendrocytes suggest adverse effects on myelination. The increase in astrocyte population per tissue volume in the cerebellum might be a sensitive marker of 1-BP neurotoxicity, but the underlying mechanism for this change remains elusive.

In vitro human epidermal penetration of 1-bromopropane

1-Bromopropane (1-BP; CAS number 106-94-5), also known as n-propyl bromide, is a halogenated short-chain alkane used as an organic solvent with numerous commercial and industrial applications, including garment dry cleaning and vapor degreasing of metals. The purpose of this study was to determine the dermal absorption characteristics and corrosivity of 1-BP. Heat-separated human epidermal membranes were mounted on static diffusion cells. Different exposure scenarios were studied (infinite dose, finite dose, and transient exposure) using neat 1-BP and saturated aqueous solution as donor. Steady-state fluxes for infinite-dose neat 1-BP exposure averaged 625 to 960 μg cm(-2) h(-1). The finite-dose (10 μl/cm(2) = 13.5 mg/cm(2)) unoccluded donor resulted in penetration of <0.2% of the applied dose (22 μg/cm(2)). A 10-min transient exposure to infinite dose resulted in total penetration of 179 μg/cm(2). Steady-state 1-BP fluxes from neat application of a commercial dry cleaning solvent were similar (441 to 722 μg cm(-2) h(-1)). The permeability coefficient of 1-BP in water vehicle was 0.257 ± 0.141 cm/h. The absorption potential of 1-BP following dermal exposure is dependent upon the type and duration of exposure. Donor losses due to evaporation were approximately 500-fold greater than dermal absorption flux; evaporation flux was 420 mg cm(-2) h(-1). 1-BP is cytotoxic but not corrosive, based on results from a cultured reconstructed human epidermal model (EpiDerm Skin Corrosivity Test).

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.

Increased susceptibility of Nrf2-null mice to 1-bromopropane-induced hepatotoxicity

1-Bromopropane (1-BP) was introduced as an alternative to ozone-depleting solvents. However, it was found to exhibit neurotoxicity, reproductive toxicity, and hepatotoxicity in rodents and neurotoxicity in human. However, the mechanisms underlying the toxicities of 1-BP remain elusive. The present study investigated the role of oxidative stress in 1-BP-induced hepatotoxicity using nuclear factor erythroid 2-related factor 2 (Nrf2)-null mice. Groups of 24 male Nrf2-null mice and 24 male wild-type (WT) C57BL/6J mice were each divided into three groups of eight and exposed to 1-BP at 0, 100, or 300 ppm for 8 h/day for 28 days by inhalation. Liver histopathology showed significantly larger area of necrosis in Nrf2-null mice relative to WT mice at the same exposure level. Nrf2-null mice also had greater malondialdehyde (MDA) levels, higher ratio of oxidized glutathione/reduced form of glutathione, and lower total glutathione content. The constitutive level and the increase in ratio per exposure level of glutathione S-transferase (GST) activity were lower in the liver of Nrf2-null mice than WT mice. Exposure to 1-BP at 300 ppm increased the messenger RNA levels of heme oxygenase-1 (HO-1), glutamate-cysteine ligase modifier subunit (GcLm), glutamate-cysteine synthetase (GcLc), glutathione reductase, and NAD(P)H: quinone oxidoreductase 1 (NQO1) in WT mice but not in Nrf2-null mice except for GST Yc2. Nrf2-null mice were more susceptible to 1-BP-induced hepatotoxicity. That oxidative stress plays a role in 1-BP hepatotoxicity is deduced from the low expression levels and activities of antioxidant enzymes and high MDA levels in Nrf2-null mice.

Comparative study on susceptibility to 1-bromopropane in three mice strains

Previous studies indicate that 1-bromopropane (1BP) has neurotoxicity and reproductive toxicity both in humans and animals. The present study investigated strain differences in susceptibility to 1BP and identified possible biological factors that determine such susceptibility. Twenty-four male mice of each of the three strains (C57BL/6J, DBA/2J, and BALB/cA) were divided into four groups of six each and exposed to 1BP at 0, 50, 110, and 250 ppm for 8 h/day for 28 days by inhalation. At the end of exposure period, the relative susceptibilities of each strain to 1BP-mediated hepatotoxicity and male reproductive toxicity were evaluated. The contributing factors to strain-dependent susceptibility were assessed by determination of hepatic CYP2E1 levels, glutathione-S-transferase (GST) activity, glutathione (GSH) status, and NAD(P)H:quinone oxidoreductase and heme oxygenase-1 mRNA levels. Liver histopathology showed significantly larger area of liver necrosis and more degenerative lobules in BALB/cA in the order of BALB/cA > C57BL/6J > DBA/2J. BALB/cA showed higher CYP2E1 protein level and lower total GSH content and GST activity in the liver than DBA/2J. These results indicate that BALB/cA mice are the most susceptible to hepatotoxicity of 1BP among the three strains tested, and that CYP2E1, GSH level/GST activity may contribute to the susceptibility to 1BP hepatotoxicity. Exposure to > or = 50 ppm of 1BP also decreased sperm count and sperm motility and increased sperms with abnormal heads in all three strains mice in a dose-dependent manner. Comparison with previous studies in rats indicates that mice are far more susceptible than rats to 1BP regarding hepatotoxicity and reproductive toxicity.