Some immunological parameters in workers occupationally exposed to n-hexane

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.

Urinary 2,5-hexanedione excretion in cryptogenic polyneuropathy compared to the general Swedish population

Background

2,5-hexanedione (2,5-HD) is the main neurotoxic metabolite of methyl-n-butyl ketone (MBK) and n-hexane, and known to cause polyneuropathy. The aim of our study was to compare the urinary levels of 2,5-HD between cases with cryptogenic polyneuropathy and the general Swedish population, and to elucidate the role of certain external factors.

Methods

Morning urine samples were collected from 114 cases with cryptogenic polyneuropathy (77 men and 37 women) and 227 referents (110 men and 117 women) randomly selected from the population registry. None had any current occupational exposure to n-hexane or MBK. The urine samples were analysed by a gas chromatographic method based on acidic hydrolysis.

Results

Cases had statistically higher urinary levels of 2,5-HD (0.48 mg/L) than the general population (0.41 mg/L) and men higher excretion than women (0.48 mg/L and 0.38 mg/L, respectively). There was no difference in 2,5-HD levels between current smokers and non-smokers. Occupational exposure to xylene, alcohol consumption and ever exposed to general anaesthesia were associated with lower excretion in men while for occupational exposure to nitrous oxide in women higher excretion was seen. Higher excretion of 2,5 HD was inversely related to increasing age.

Conclusions

Significantly higher levels of urinary 2,5-HD were seen in men and cryptogenic polyneuropathy cases seemingly unexposed to n-hexane. Hypothetically, this might be due to either differences in metabolic patterns or some concealed exposure. The difference in means between cases and the general population is small and can therefore not allow any firm conclusions of the causality, however.

In vitro exposure of jurkat T-cells to industrially important organic solvents in binary combination: interaction analysis

Humans are frequently exposed to mixtures of environmental pollutants at low levels over prolonged periods of time yet most toxicity studies deal with acute exposure to high concentrations of single chemicals. Investigation of the biological effects and possible toxic interactions during long-term exposure to such mixtures is warranted. Here Jurkat T-cells were exposed to toluene, n-hexane and methyl ethyl ketone in binary combination. Concentration ranges were centered on thresholds at which the individual agents caused cell toxicity under otherwise similar conditions, and concentrations were confirmed by headspace gas chromatography. After 5 days cells were harvested and toxicity measured in terms of membrane damage (lactate dehydrogenase [LDH] leakage), perturbations in [Ca(2+)](i) and changes in glutathione redox status. Data for all three endpoints were subjected to isobolographic analysis to test for interaction between components of the solvent mixture. Almost all combinations of toluene and n-hexane elicited greater than additive toxicity in terms of each of the three endpoints, as did methyl ethyl ketone (MEK)/n-hexane and MEK/toluene combinations for the LDH and glutathione endpoints. The main exceptions were the two combinations involving MEK, which caused less than additive effects on perturbations of [Ca(2+)](i). It is concluded that toxicity in immune-derived T cells may exhibit greater than additive effects when there is coexposure to organic solvents. This may have implications for risk assessment of environmental exposure to these agents.

Validation of a method for acute and subchronic exposure of cells in vitro to volatile organic solvents

In vitro assessment of organic solvents can be problematic as the volatile nature of these compounds makes maintaining a constant exposure level difficult. However, a stable exposure level must be maintained if reliable dose response data are to be obtained. Here we describe a gas-tight glass exposure system which allows prolonged exposure of cultured cells to constant concentrations of volatile organic solvents. The system permits convenient sampling of gas and liquid phases for reliable quantification of solvent concentration. We determined medium/air partition coefficients (K) for toluene, n-hexane and methyl ethyl ketone which can be used to calculate liquid phase solvent exposure levels in an in vitro system specifically designed for organic solvent exposure. Cultured cells were exposed to these compounds for five days and toxicity assessed by trypan blue exclusion. Headspace gas chromatography was used to determine K in RPMI-1640 and EMEM tissue culture medium at 37 degrees C. The presence of cells in the system at levels normally used in in vitro exposure systems did not significantly alter solvent partitioning. Equilibrium liquid phase solvent concentrations were measured by gas chromatography for two of the compounds to confirm that exposure levels calculated using K were correct. Results show that sub-chronic exposure to volatile organic solvents causes a dose dependent decrease in Jurkat T-cells and SH-SY5Y viability. Solvent potency increased with lipophilicity (n-hexane>toluene>MEK).

Involvement of the extracellular signal regulated kinase pathway in hydrocarbon-induced reactive oxygen species formation in human neutrophil granulocytes

In the present study we have examined the effects of hydrocarbons on the formation of reactive oxygen species (ROS) in human neutrophil granulocytes in vitro. We found that hydrocarbons induce ROS formation in a concentration-dependent manner and that the ROS-inducing potency increases with increasing number of carbon atoms in the structure. In general, aromatic hydrocarbons were less potent inducers of ROS than aliphatic and cyclic hydrocarbons. The most potent compound in each group, t-butylcyclohexane, n-decane, and n-butylbenzene, were chosen for mechanistic studies. ROS formation was inhibited by the MEK1/2 inhibitor U0126, the tyrosine kinase inhibitor erbstatin-A, and the phosphatidylinositol-3 kinase inhibitor wortmannin. The involvement of the ERK1/2 pathway was confirmed by Western blot analysis of phosphorylated ERK1/2. The study revealed only small differences in the mechanisms involved for the three compounds. The responses were not affected by Pertussis toxin, indicating that Gi-protein coupled receptors are not involved in neutrophil activation after hydrocarbon exposure. Based on these findings we propose a mechanism involving tyrosine kinases, PI3 kinase, and the ERK1/2 pathway, leading to activation of the NADPH oxidase and production of ROS in neutrophils stimulated by organic solvents.

Proliferative response of peripheral blood lymphocytes and lymphocyte subpopulations in n-Hexane, toluen, and methyl ethyl ketone co-exposed workers

To estimate the quantitative relation between chronic co-exposure to airborne n-hexane, toluen, methyl ethyl ketone (MEK) and various markers of immune function such as proliferative response of peripheral blood lymphocytes and lymphocyte subpopulations, a group of workers employed in a shoe factory were examined and compared with the unexposed controls. A significant increase was observed in the proliferative response of the peripheral lymphocytes to 2.5 and 5 μg PHA in the exposed group compared with that of the control group. There was no significant change in the percentage of circulating CD3(+), CD4(+), CD8(+), CD19(+), CD16(+) lymphocytes even in those workers with 3.3-fold higher mean levels of urine 2,5-hexanedione (2,5-Hxdn) and approximately twofold higher mean levels of urine hippuric acid (HA) as compared to controls. No difference was also observed between the mean granulocyte, monocyte, lymphocyte percentages of the groups, but a significant increase was observed in mean serum C3 level of the workers. Our results suggest that while lymphocyte subpopulations and leucocyte percentages are not affected, the proliferative response of the peripheral lymphocytes is stimulated after chronic co-exposure to n-hexane, toluen and MEK at the defined levels.

Effects of occupational chronic co-exposure to n-hexane, toluen, and methyl ethyl ketone on NK cell activity and some immunoregulatory cytokine levels in shoe workers

1. To evaluate the effects of occupational long-term co-exposure to n-hexane, toluen, and methyl ethyl ketone (MEK) on NK cell activity and serum IL-2, gamma-IFN levels, we studied a group of workers employed in a shoe factory where the jobs include use of glues and adhesives containing mainly n-hexane, and at low concentrations, toluen and MEK. 2. No differences were found in these parameters even in those workers with 3.3-fold higher mean levels of urine, 2,5-Hxdn and approximately twofold higher mean levels of urine hippuric acid as compared to controls. 3. We conclude that chronic co-exposure to n-hexane, toluen, and MEK at these levels is not associated with an impairment on either NK cell activity or serum IL-2 and gamma-IFN levels.

Relationship between 2,5-hexanedione concentrations in nerve, serum, and urine alone or under co-treatment with different doses of methyl ethyl ketone, acetone, and toluene

To ascertain the relationship among 2,5-hexanedione (2,5-HD) concentrations in nerve, serum and urine, rats were injected subcutaneously with 2.6 mmol/kg 2,5-HD alone, or together with 2.6 or 13.0 mmol/kg of methyl ethyl ketone, acetone and toluene. 2,5-HD concentrations in sciatic nerve (NC), serum (SC) and urine (UC) were determined, and the linear regression between each two of NC, SC, and UC were calculated. There was good correlation between NC and SC, SC and UC in the 2,5-HD alone group, and good correlation between NC and SC in the co-treated groups. Co-treatment solvent had little effect on the relationship between SC and NC. 13.0 mmol/kg co-treated solvent tended to decrease the regression coefficients compared with 2.6 mmol/kg co-treated solvent. These results show that SC can be used in estimating NC in the 2,5-HD alone or co-treated groups, and UC can be used in estimating SC in the 2,5-HD alone group.