Toxicology and Industrial Health

n-Hexane is an organic solvent widely used in industry. 2,5-Hexanedione (2,5-HD), the major neurotoxic metabolite of n-hexane, decreases the levels of neurofilaments (NFs) in neurons. Neurogenesis occurs throughout life, and the hippocampal dentate gyrus is one of two major brain areas showing neurogenesis in adulthood. In the current study, rats were intraperitoneally injected with normal saline solution or 2,5-HD five times per week for five continuous weeks. 2,5-HD was administered to the low-dose and high-dose groups at 200 and 400 mg/kg/day, respectively. Then, immunoreactive cells were counted in the hippocampal granule cell layer (GCL) and subgranular zone (SGZ). Ki67⁺ cells significantly decreased in the high-dose group, while the percentage of proliferative Sox2⁺ cells significantly increased, consistent with high hippocampal Sox2 expression. Additionally, western blotting showed that exposure to high doses of 2,5-HD led to decreased NF-L in both the cortex and hippocampus, whereas low doses led to a significant reduction in the cortex only. In conclusion, 2,5-HD increases the percentage of proliferating neural stem and progenitor (Sox2⁺) cells in the SGZ/GCL.

We investigated the effects of melatonin on sperm parameters and some biochemical markers in lead-exposed male Wistar rats. Lead (50 mg/kg bw/day) and/or melatonin (4 mg/kg or 10 mg/kg bw/day) was administered for 4 weeks, while 2-week lead exposure was preceded by or followed by 2-week treatment with both doses of melatonin in other groups. Lead reduced glutathione, catalase, adjusted testes weight, semen parameters but did not change malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase, and total antioxidant capacity. Though independent of prolactin, lead-induced gonadotoxicity was both centrally and peripherally mediated, as it reduced gonadotropin-releasing hormone and testosterone levels, while gonadotropin levels did not change significantly probably due to negative feedback by elevated estradiol. However, pre-, simultaneous, or posttreatment of lead-exposed rats with melatonin reduced MDA, SOD, and estradiol but dose-dependently increased other parameters. Conclusively, lead causes male gonadotoxicity through oxidative stress and endocrine mechanisms, and these could be dose-dependently prevented and ameliorated by melatonin.

Needlestick and sharp instrument injuries are common in dental practice and present the risk of direct exposure to blood-borne pathogens, including hepatitis B virus. This cross-sectional study was carried out to determine the risk factors of injury and infection in three types of dental clinic in Riyadh, Saudi Arabia. A total of 274 male and 241 female dentists completed a structured questionnaire on demographic factors, compliance with infection control practices, and past exposure to injury and infection hazards. Dentists with more years of professional experience were significantly less likely to report having had an injury in the past (unadjusted odds ratios (ORs) and 95% confidence intervals (CIs) were 0.48, 0.27–0.87 and 0.38, 0.16–0.89 for dentists with 10–20 years and for those with over 20 years of experience, respectively). Greater compliance with infection control procedures was associated with significantly fewer reports of previous infection (OR 0.31, 95% CI 0.12–0.84). Experience of occupational safety training was not associated with a lower rate of injury or infection. Greater occupational safety knowledge and compliance with infection control management practices contribute to a reduced risk of injury and infection among dentists. More focused and specialized training on infection control and occupational safety is needed for all practicing dentists and dental students.

The present study investigated the effects of applied continuous 2.45 GHz electromagnetic radiation (EMR), which might cause physiopathological or morphological changes in the ovarian, fallopian tubal, and uterine tissues of rats. We proposed that the addition of vitamin C (Vit C) may reduce these severe effects. Eighteen female Sprague Dawley rats were randomly divided into three groups with six animals in each: Sham, EMR (EMR, 1 h/day for 30 days), and EMR + Vit C (EMR, 1 h/day for 30 days 250 mg/kg/daily). Total oxidant status (TOS) and oxidative stress index (OSI) levels increased (p = 0.011 and p = 0.002, respectively) in the EMR-only group in ovarian tissues. In all tissues, TOS and OSI levels significantly decreased in the Vit C-treated group in ovarian, fallopian tubal, and uterine tissues (p < 0.05). Anti-müllerian hormone levels significantly increased in the EMR group (p < 0.05) and decreased in the Vit C-treated groups. Estrogen (E2) levels were unchanged in the EMR group, as the differences were not statistically significant. Immunohistochemical examination of the ovaries revealed significant increases in Caspase-3 expressions in the epithelial cells of the EMR group (p < 0.05). In the EMR group, hyperemia was observed in uterine tissues. Also, Caspase-3 and Caspase-8 were significantly increased in the EMR group (p < 0.001). Caspase-3 was significantly diminished with Vit C application in the ovarian and uterine tissues (p < 0.05). Caspase-8 was significantly diminished only in uterine tissues (p < 0.05). These results indicate that prolonged EMR exposure induced physiopathological changes in the ovarian, fallopian tubal, and uterine tissues due to oxidative damage. Under the conditions of this study, Vit C may have protective effects on female reproductive system against oxidative damage.

Brominated flame retardants (BFRs) and heavy metals (HMs) are two main types of pollutants in electronic waste recycling sites, which are also ubiquitously detectable in environmental media and human tissues. However, the adverse health effects of exposure to the mixture of these types of pollutants are unknown. In this study, we investigated the reproductive toxicity of a mixture of decabromodiphenyl ether (BDE-209), tetrabromobisphenol A, cadmium chloride, and lead acetate (PbAc) at the environmental relevant levels. Zebrafish were waterborne and exposed to chemical mixtures for one generation. The reproductive effects were evaluated for F0 adults and F1 offspring. Chemical residues were also analyzed in the exposed adults and their eggs at the end of exposure. Our findings demonstrated that exposure to the chemical mixture for 150 days had no effect on the survival rate of zebrafish, but it decreased body length and weight in females and increased body weight and condition factor in males. The mixture exposure resulted in a female-biased sex ratio in adults and decreased sperm density and motility in males and egg production in females. For the F1 offspring, decreased fertilization, delayed hatching, and increased malformation were found in all exposure groups. In conclusion, chronic co-exposure to BFRs and HMs at the environmental relevant levels not only affected growth, sex ratio, and sperm quantity/quality and egg production in adults but also reduced the reproductive success in the offspring, implying that multi-pollutants in the environmental media may pose a public health risk to other exposed organisms or human beings.

There is a dearth of information regarding the safety of silver nanoparticles (Ag NPs) and multiwalled carbon nanotubes (MWCNTs) with respect to their impact on human/animal health and the environment. This study aimed to determine the half-maximum inhibitory concentration (IC₅₀) of Ag NPs and MWCNTs by employing different doses and time interval combinations in buffalo bull spermatozoa. Semen samples containing 100 million spermatozoa each were incubated with 1, 10, 25, 50, 75 and 100 µg/mL of Ag NPs and MWCNTs at 37°C for 30, 60 and 120 min. Sperm viability was monitored by the MTT assay and eosin–nigrosin staining followed by estimation of IC₅₀ values using correlation–regression analysis. Spermatozoa treated with IC₅₀ doses of Ag NPs and MWCNTs were also assessed for different sperm functionality parameters including oxidative stress and membrane integrity. These parameters were observed to be significantly affected in treated spermatozoa compared with the controls. We concluded that both nanomaterials showed cytotoxicity, mediated principally via oxidative stress. This work has provided valuable toxicological information that will serve as a benchmark for future studies aimed at safe use of nanomaterials.

Diazinon (DZN) is an organophosphate insecticide that has cytotoxic and pathological effects on the reproductive system. It causes a wide variety of pathological effects on the reproductive system such as testicular atrophy, disturbance in sex hormones, impaired spermatogenesis, low quality of sperm, and fertility problems. However, molecular and cellular mechanisms of its adverse effects are not well understood. General events such as testicular damage, inflammation, mitochondrial deficiency, DNA fragmentation, disintegration of sperm plasma membrane, apoptosis, and cell death are observed in DZN-exposed animals. Oxidative stress (OS) induced by reactive oxygen species may be a main mechanism, which can be associated with sperm DNA fragmentation, reduced integrity of sperm cell membrane, apoptosis, depletion of antioxidants, and subsequently poor sperm quality and male infertility. Therefore, identification of these pathways may provide valuable information regarding the mechanisms of DZN action on the male reproductive system. In this review, we aim to discuss the proposed cellular and molecular mechanisms of DZN action on male reproductive system, the importance of OS and mechanisms by which DZN induces OS and depletion of other antioxidants.