Determination of total urinary 2,5-hexanedione in the Chinese general population

Application of multiple occupational health risk assessment models in the prediction of occupational health risks of n-Hexane in the air-conditioned closed workshop

Background

n-Hexane (NH) poisoning is a common occupational poisoning in the hardware and electronics industries. However, there is few research data on risk assessment of positions using NH in enclosed workshops. It is very important to assess the risk level of these positions and put forward effective measures and suggestions.

Methods

The information of selected companies and air samples were collected through on-site investigation, and data collation and sample testing were carried out according to the requirements of Chinese standards. The Control of Substances Hazardous to Health (COSHH) Essential, the EPA non-carcinogenic risk assessment model, the Singapore exposure index method and the Chinese semi-quantitative risk assessment models were used to assess the risks of NH.

Results

The working hours of the exposure groups, printing groups and packing groups all exceeded 9 h per day, less than 30% of each similar exposure groups (SEG) was equipped with the local exhaust ventilation, and 11.1% of the cleaning group and 8.3% of the printing group had NH concentrations in the air that exceeded the Chinese occupational exposure limit (OEL). In the EPA non-carcinogenic risk assessment model, each SEG was evaluated at high risk. In the Chinese semi-quantitative risk assessment models, all of the work groups of exposure groups, 91.7% of the work groups of printing groups, 77.8% of the work groups of printing groups, and 57.1% of the work groups of printing groups were evaluated at unacceptable risk. More than 40.0% of the work groups of printing groups and cleaning groups and over 20.0% of the work groups of exposure groups and packing groups were evaluated at high risk in the Chinese semi-quantitative risk assessment models.

Conclusions

The Chinese exposure index method and the synthesis index method may have a stronger practicability. Some work groups that use NH in air-conditioned enclosed workshops in China, especially the cleaning groups, are still in a high-risk state. It is necessary to increase protective measures and strengthen occupational hygiene management to reduce risks.

Towards Substitution of Hexane as Extraction Solvent of Food Products and Ingredients with No Regrets

Hexane is a solvent used extensively in the food industry for the extraction of various products such as vegetable oils, fats, flavours, fragrances, colour additives or other bioactive ingredients. As it is classified as a "processing aid", it does not have to be declared on the label under current legislation. Therefore, although traces of hexane may be found in final products, especially in processed products, its presence is not known to consumers. However, hexane, and in particular the n-hexane isomer, has been shown to be neurotoxic to humans and has even been listed as a cause of occupational diseases in several European countries since the 1970s. In order to support the European strategy for a toxic-free environment (and toxic-free food), it seemed important to collect scientific information on this substance by reviewing the available literature. This review contains valuable information on the nature and origin of the solvent hexane, its applications in the food industry, its toxicological evaluation and possible alternatives for the extraction of natural products. Numerous publications have investigated the toxicity of hexane, and several studies have demonstrated the presence of its toxic metabolite 2,5-hexanedione (2,5-HD) in the urine of the general, non-occupationally exposed population. Surprisingly, a tolerable daily intake (TDI) has apparently never been established by any food safety authority. Since hexane residues are undoubtedly found in various foods, it seems more than necessary to clearly assess the risks associated with this hidden exposure. A clear indication on food packaging and better information on the toxicity of hexane could encourage the industry to switch towards one of the numerous other alternative extraction methods already developed.

2,5-Hexanedione induced apoptosis in rat spinal cord neurons and VSC4.1 cells via the proNGF/p75NTR and JNK pathways

Increasing evidence suggests that n-hexane induces nerve injury via neuronal apoptosis induced by its active metabolite 2,5-hexanedione (HD). However, the underlying mechanism remains unknown. Studies have confirmed that pro-nerve growth factor (proNGF), a precursor of mature nerve growth factor (mNGF), might activate apoptotic signaling by binding to p75 neurotrophin receptor (p75NTR) in neurons. Therefore, we studied the mechanism of the proNGF/p75NTR pathway in HD-induced neuronal apoptosis. Sprague-Dawley (SD) rats were injected with 400 mg/kg HD once a day for 5 weeks, and VSC4.1 cells were treated with 10, 20, and 40 mM HD in vitro. Results showed that HD effectively induced neuronal apoptosis. Moreover, it up-regulated proNGF and p75NTR levels, activated c-Jun N-terminal kinase (JNK) and c-Jun, and disrupted the balance between B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein (Bax). Our findings revealed that the proNGF/p75NTR signaling pathway was involved in HD-induced neuronal apoptosis; it can serve as a theoretical basis for further exploration of the neurotoxic mechanisms of HD.

The Role of Protein Adduction in Toxic Neuropathies of Exogenous and Endogenous Origin

The peripheral (axonal) neuropathy associated with repeated exposure to aliphatic and aromatic solvents that form protein-reactive γ-diketones shares some clinical and neuropathological features with certain metabolic neuropathies, including type-II diabetic neuropathy and uremic neuropathy, and with the largely sub-clinical nerve damage associated with old age. These conditions may be linked by metabolites that adduct and cross-link neuroproteins required for the maintenance of axonal transport and nerve fiber integrity in the peripheral and central nervous system.

2,5-Hexanedione influences primordial follicular development in cultured neonatal mouse ovaries by interfering with the PI3K signaling pathway via miR-214-3p

The mechanisms by which 2,5-hexanedione (2,5-HD) exposure adversely affects reproduction are unclear. In the present study, whole neonatal mouse ovaries were exposed to 2,5-HD in vitro and then assessed for progesterone levels to determine the effects of this compound on ovary function. Ovarian histomorphological analyses were performed to assess the effects of 2,5-HD on follicular development, and PI3K signaling pathway was evaluated to elucidate the molecular mechanisms of 2,5-HD-mediated toxicity on follicular development. The results showed that after ovarian exposure to 2,5-HD in vitro, the percentage of secondary follicles decreased, while the progesterone levels and the percentage of unhealthy follicles increased, with oocytes identified as the target of damage. The 2,5-HD treatment significantly decreased the of the gene encoding the apoptosis-related protein caspase-8, and PI3K/AKT/FOXO3 pathway signaling was also altered. Furthermore, the effects of 2,5-HD on the gene expression of the PI3K/AKT/FOXO3 and follicular development were blocked by 740Y-P (a PI3K activator), miR-214-3p was abnormally expressed, and luciferase reporter assay results demonstrated that the 3' untranslated region of PI3K was a direct target of miR-214-3p. Overall, the results of the present study indicate that 2,5-HD exposure inhibits follicular development, and the underlying mechanism may involve interference with miR-214-3p-mediated regulation of the PI3K signaling pathway.

Diabetes mellitus is associated with elevated urinary pyrrole markers of γ-diketones known to cause axonal neuropathy

INTRODUCTION

Progressive distal symmetrical axonal neuropathy, a complication of diabetes mellitus (DM), has an unknown cause. Normal physiological metabolism and diabetic dysmetabolism are associated with the generation of γ-diketones. γ-Diketones form pyrroles with protein amines, notably with axonal proteins required for the maintenance of nerve fiber integrity, especially elongate, large-diameter peripheral nerve fibers innervating the extremities. We tested the hypothesis that neuropathy-associated γ-diketone pyrroles are elevated in DM.

RESEARCH DESIGN AND METHODS

We measured the urinary concentration of γ-diketone pyrroles in age-matched and gender-matched elderly (60-84 years) persons with (n=267) or without (n=267) indicators of DM based in a community population (9411 community older adults aged ≥60 years) in Shenzhen city, Guangdong, China. We used statistical methods, including a generalized linear model, multivariate logistic regression analysis and restricted cubic splines, to assess linear and nonlinear relationships between urinary γ-diketone pyrroles and indicators of DM.

RESULTS

Compared with healthy controls, those with DM had significantly higher levels of fasting blood glucose, glycated hemoglobin A1c, urinary ketone bodies and urinary γ-diketone pyrroles. The median concentration of urinary γ-diketone pyrrole adducts was significantly higher (p<0.0001) in individuals with DM (7.5 (5.4) μM) compared with healthy controls (5.9 (4.3) μM). Both linear and non-linear relations were found between urinary γ-diketone pyrroles and indicators of DM.

CONCLUSIONS

Diabetic dysmetabolism includes increased generation and excretion of neuropathy-associated γ-diketone pyrroles. These findings form the foundation for studies to test whether γ-diketone pyrrole concentration correlates with quantitative sensory (vibration and temperature) and electrodiagnostic testing.

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.

Proapoptotic effects of 2,5‑hexanedione on pheochromocytoma cells via oxidative injury

N‑hexanes are prominent environmental pollutants that are able to cause neurotoxicity in vivo and in vitro. Central and peripheral neuropathies induced by n‑hexane exposure are a major health concern. 2,5‑Hexanedione (2,5‑HD) is the most significant neurotoxic metabolite of n‑hexane; however, little is known regarding the underlying mechanism of its neurotoxicity. Thus, the aim of the present study was to investigate the damaging effects of 2,5‑HD on pheochromocytoma PC12 cells, and to explore the underlying mechanism. Cell viability was tested using a Cell Counting Kit‑8 method, and the leakage of lactate dehydrogenase (LDH) from cells was measured using an LDH assay kit. Glutathione peroxidase (GSHPx) and superoxide dismutase (SOD) activities, and the level of malondialdehyde (MDA) were determined using corresponding assay kits. Apoptotic cells were detected using an annexin V‑fluorescein isothiocyanate/propidium iodide (PI) apoptosis kit, and were subsequently observed by fluorescence microscopy. The relative expression levels of cleaved‑caspase‑3, Bcl‑associated‑X protein (Bax) and Bcl‑2 were identified by western blotting. The results revealed that 2,5‑HD was able to decrease the viability of PC12 cells and promoted the leakage of LDH in a concentrationdependent manner. Further analysis demonstrated that 2,5‑HD decreased the activity of the antioxidative enzymes, SOD and GSHPx, and led to an increase in the levels of MDA in the supernatant of cultured PC12 cells. The annexin V/PI staining results revealed that the numbers of apoptotic cells were increased following treatment with 2,5‑HD. In addition, 2,5‑HD (5 and 10 mmol/l) led to significant increases in the expression levels of caspase‑3 and Bax, with the concomitant downregulation of Bcl‑2. The antioxidant N‑acetylcysteine was identified to antagonize 2,5‑HD‑stimulated cleaved‑caspase‑3 and Bax upregulation, and Bcl‑2 downregulation. Collectively, the results of the present study suggested that 2,5‑HD exerts proapoptotic effects on PC12 cells via oxidative injury. These findings may be applied in the development of novel therapeutic strategies to treat neurological disorders associated with nhexane exposure.