Effects of short-term JP-8 jet fuel exposure on cell-mediated immunity

Toxicity and human health assessment of an alcohol-to-jet (ATJ) synthetic kerosene developed under an international agreement with Sweden

Alcohol-to-jet (ATJ) Synthetic Kerosene with Aromatics (SKA) fuels are produced by dehydration and refining of alcohol feed stocks. ATJ SKA fuel known as SB-8 was developed by Swedish Biofuels as a cooperative agreement between Sweden and AFRL/RQTF. SB-8 including standard additives was tested in a 90-day toxicity study with male and female Fischer 344 rats exposed to 0, 200, 700, or 2000 mg/m³ fuel in an aerosol/vapor mixture for 6 hr/day, 5 days/week. Aerosols represented 0.04 and 0.84% average fuel concentration in 700 or 2000 mg/m³ exposure groups. Examination of vaginal cytology and sperm parameters found no marked changes in reproductive health. Neurobehavioral effects were increased rearing activity (motor activity) and significantly decreased grooming (functional observational battery) in 2000 mg/m³ female rats. Hematological changes were limited to elevated platelet counts in 2000 mg/m³ exposed males. Minimal focal alveolar epithelial hyperplasia with increased number of alveolar macrophages was noted in some 2000 mg/m³ males and one female rat. Additional rats tested for genotoxicity by micronucleus (MN) formation did not detect bone marrow cell toxicity or alterations in number of MN; SB-8 was not clastogenic. Inhalation results were similar to effects reported for JP-8. Both JP-8 and SB fuels were moderately irritating under occlusive wrapped conditions but slightly irritating under semi-occlusion. Exposure to SB-8, alone or as 50:50 blend with petroleum-derived JP-8, is not likely to enhance adverse human health risks in the military workplace.

Biological effects of inhaled crude oil. VI. Immunotoxicity

Crude oil is an unrefined petroleum product that is a mixture of hydrocarbons and other organic material. Studies on the individual components of crude oil and crude oil exposure itself suggest it has immunomodulatory potential. As investigations of the immunotoxicity of crude oil focus mainly on ingestion and dermal exposure, the effects of whole-body inhalation of 300 ppm crude oil vapor [COV; acute inhalation exposure: (6 h × 1 d); or a 28 d sub-chronic exposure (6 h/d × 4 d/wk. × 4 wks)] was investigated 1, 28, and 90 d post-exposure in Sprague-Dawley rats. Acute exposure increased bronchoalveolar lavage (BAL) fluid cellularity, CD4+ and CD8+ cells, and absolute and percent CDllb+ cells only at 1 d post-exposure; additionally, NK cell activity was suppressed. Sub-chronic exposure resulted in a decreased frequency of CD4+ T-cells at 1 d post-exposure and an increased number and frequency of B-cells at 28 d post-exposure in the lung-associated lymph nodes. A significant increase in the number and frequency of B-cells was observed in the spleen at 1 d post-exposure; however, NK cell activity was suppressed at this time point. No effect on cellularity was identified in the BALF. No change in the IgM response to sheep red blood cells was observed. The findings indicate that crude oil inhalation exposure resulted in alterations in cellularity of phenotypic subsets that may impair immune function in rats.

Immunopathology of the Respiratory System

Respiratory immunity is accomplished using multiple mechanisms including structure/anatomy of the respiratory tract, mucosal defense in the form of the mucociliary apparatus, innate immunity using cells and molecules and acquired immunity. There are species differences of the respiratory immune system that influence the response to environmental challenges and pharmaceutical, industrial and agricultural compounds assessed in nonclinical safety testing and hazard identification. These differences influence the interpretation of respiratory system changes after exposure to these challenges and compounds in nonclinical safety assessment and hazard identification and their relevance to humans.

Rat Tissue and Blood Partition Coefficients for n-Alkanes (C8 to C12)

Rat tissue:air and blood:air partition coefficients (PCs) for octane, nonane, decane, undecane, and dodecane (n-C8 to n-C12 n-alkanes) were determined by vial equilibration. The blood:air PC values for n-C8 to n-C12 were 3.1, 5.8, 8.1, 20.4, and 24.6, respectively. The lipid solubility of n-alkanes increases with carbon length, suggesting that lipid solubility is an important determinant in describing n-alkane blood:air PC values. The muscle:blood, liver: blood, brain:blood, and fat:blood PC values were octane (1.0, 1.9, 1.4, and 247), nonane (0.8, 1.9, 3.8, and 274), decane (0.9, 2.0, 4.8, and 328), undecane (0.7, 1.5, 1.7, and 529), and dodecane (1.2, 1.9, 19.8, and 671), respectively. The tissue:blood PC values were greatest in fat and the least in muscle. The brain:air PC value for undecane was inconsistent with other n-alkane values. Using the measured partition coefficient values of these n-alkanes, linear regression was used to predict tissue (except brain) and blood:air partition coefficient values for larger n-alkanes, tridecane, tetradecane, pentadecane, hexadecane, and heptadecane (n-C13 to n-C17).Good agreement between measured and predicted tissue:air and blood:air partition coefficient values for n-C8 to n-C12 offer confidence in the partition coefficient predictions for longer chain n-alkanes.

JP-8 jet fuel exposure rapidly induces high levels of IL-10 and PGE2 secretion and is correlated with loss of immune function

The US Air Force has implemented the widespread use of JP-8 jet fuel in its operations, although a thorough understanding of its potential effects upon exposed personnel is unclear. Previous work has demonstrated that JP-8 exposure is immunosuppressive. In the present study, the potential mechanisms for the effects of JP-8 exposure on the immune system were investigated. Exposure of mice to JP-8 for 1 h/day resulted in immediate secretion of two immunosuppressive agents; namely, interleukin-10 (IL-10) and prostaglandin E2 (PGE2). JP-8 exposure rapidly induced a persistently high level of serum IL-10 and PGE2 at an exposure concentration of 1000 mg/m3. IL-10 levels peaked at 2h post-JP-8 exposure and then stabilized at significantly elevated serum levels, while PGE2 levels peaked after 2—3 days of exposure and then stabilized. Elevated IL-10 and PGE2 levels may at least partially explain the effects of JP-8 exposure on immune function. Elevated IL-10 and PGE2 levels, however, cannot explain all of the effects due to JP-8 exposure (e.g., decreased organ weights and decreased viable immune cells), as treatment with a PGE2 inhibitor did not completely reverse the immunosuppressive effects of jet fuel exposure. Thus, low concentration JP-8 jet fuel exposures have significant effects on the immune system, which can be partially explained by the secretion of immunosuppressive modulators, which are cumulative over time.

Jet fuel kerosene is not immunosuppressive in mice or rats following inhalation for 28 days

Previous reports indicated that inhalation of JP-8 aviation turbine fuel is immunosuppressive. However, in some of those studies, the exposure concentrations were underestimated, and percent of test article as vapor or aerosol was not determined. Furthermore, it is unknown whether the observed effects are attributable to the base hydrocarbon fuel (jet fuel kerosene) or to the various fuel additives in jet fuels. The present studies were conducted, in compliance with Good Laboratory Practice (GLP) regulations, to evaluate the effects of jet fuel kerosene on the immune system, in conjunction with an accurate, quantitative characterization of the aerosol and vapor exposure concentrations. Two female rodent species (B6C3F1 mice and Crl:CD rats) were exposed by nose-only inhalation to jet fuel kerosene at targeted concentrations of 0, 500, 1000, or 2000 mg/m(3) for 6 h daily for 28 d. Humoral, cell-mediated, and innate immune functions were subsequently evaluated. No marked effects were observed in either species on body weights, spleen or thymus weights, the T-dependent antibody-forming cell response (plaque assay), or the delayed-type hypersensitivity (DTH) response. With a few exceptions, spleen cell numbers and phenotypes were also unaffected. Natural killer (NK) cell activity in mice was unaffected, while the NK assessment in rats was not usable due to an unusually low response in all groups. These studies demonstrate that inhalation of jet fuel kerosene for 28 d at levels up to 2000 mg/m(3) did not adversely affect the functional immune responses of female mice and rats.

The influence of hydrocarbon composition and exposure conditions on jet fuel-induced immunotoxicity

Chronic jet fuel exposure could be detrimental to the health and well-being of exposed personnel, adversely affect their work performance and predispose these individuals to increased incidences of infectious disease, cancer and autoimmune disorders. Short-term (7 day) JP-8 jet fuel exposure has been shown to cause lung injury and immune dysfunction. Physiological alterations can be influenced not only by jet fuel exposure concentration (absolute amount), but also are dependent on the type of exposure (aerosol versus vapor) and the composition of the jet fuel (hydrocarbon composition). In the current study, these variables were examined with relation to effects of jet fuel exposure on immune function. It was discovered that real-time, in-line monitoring of jet fuel exposure resulted in aerosol exposure concentrations that were approximately one-eighth the concentration of previously reported exposure systems. Further, the effects of a synthetic jet fuel designed to eliminate polycyclic aromatic hydrocarbons were also examined. Both of these changes in exposure reduced but did not eliminate the deleterious effects on the immune system of exposed mice.

Jet fuel toxicity: skin damage measured by 900-MHz MRI skin microscopy and visualization by 3D MR image processing

The toxicity of jet fuels was measured using noninvasive magnetic resonance microimaging (MRM) at 900-MHz magnetic field. The hypothesis was that MRM can visualize and measure the epidermis exfoliation and hair follicle size of rat skin tissue due to toxic skin irritation after skin exposure to jet fuels. High-resolution 900-MHz MRM was used to measure the change in size of hair follicle, epidermis thickening and dermis in the skin after jet fuel exposure. A number of imaging techniques utilized included magnetization transfer contrast (MTC), spin-lattice relaxation constant (T1-weighting), combination of T2-weighting with magnetic field inhomogeneity (T2*-weighting), magnetization transfer weighting, diffusion tensor weighting and chemical shift weighting. These techniques were used to obtain 2D slices and 3D multislice-multiecho images with high-contrast resolution and high magnetic resonance signal with better skin details. The segmented color-coded feature spaces after image processing of the epidermis and hair follicle structures were used to compare the toxic exposure to tetradecane, dodecane, hexadecane and JP-8 jet fuels. Jet fuel exposure caused skin damage (erythema) at high temperature in addition to chemical intoxication. Erythema scores of the skin were distinct for jet fuels. The multicontrast enhancement at optimized TE and TR parameters generated high MRM signal of different skin structures. The multiple contrast approach made visible details of skin structures by combining specific information achieved from each of the microimaging techniques. At short echo time, MRM images and digitized histological sections confirmed exfoliated epidermis, dermis thickening and hair follicle atrophy after exposure to jet fuels. MRM data showed correlation with the histopathology data for epidermis thickness (R(2)=0.9052, P<.0002) and hair root area (R(2)=0.88, P<.0002). The toxicity of jet fuels on skin structures was in the order of tetradecane>hexadecane>dodecane. The method showed a sensitivity of 87.5% and a specificity of 75%. By MR image processing, different color-coded skin structures were extracted and 3D shapes of the epidermis and hair follicle size were compared. In conclusion, high-resolution MRM measured the change in skin epidermis and hair follicle size due to toxicity of jet fuels. MRM offers a three-dimensional spatial visualization of the change in skin structures as a method of toxicity evaluation and for comparison of jet fuels.

Characterization of a nose-only inhalation exposure system for hydrocarbon mixtures and jet fuels

A directed-flow nose-only inhalation exposure system was constructed to support development of physiologically based pharmacokinetic (PBPK) models for complex hydrocarbon mixtures, such as jet fuels. Due to the complex nature of the aerosol and vapor-phase hydrocarbon exposures, care was taken to investigate the chamber hydrocarbon stability, vapor and aerosol droplet compositions, and droplet size distribution. Two-generation systems for aerosolizing fuel and hydrocarbons were compared and characterized for use with either jet fuels or a simple mixture of eight hydrocarbons. Total hydrocarbon concentration was monitored via online gas chromatography (GC). Aerosol/vapor (A/V) ratios, and total and individual hydrocarbon concentrations, were determined using adsorbent tubes analyzed by thermal desorption-gas chromatography-mass spectrometry (TDS-GC-MS). Droplet size distribution was assessed via seven-stage cascade impactor. Droplet mass median aerodynamic diameter (MMAD) was between 1 and 3 mum, depending on the generator and mixture utilized. A/V hydrocarbon concentrations ranged from approximately 200 to 1300 mg/m(3), with between 20% and 80% aerosol content, depending on the mixture. The aerosolized hydrocarbon mixtures remained stable during the 4-h exposure periods, with coefficients of variation (CV) of less than 10% for the total hydrocarbon concentrations. There was greater variability in the measurement of individual hydrocarbons in the A-V phase. In conclusion, modern analytical chemistry instruments allow for improved descriptions of inhalation exposures of rodents to aerosolized fuel.

JP-8 jet fuel exposure suppresses the immune response to viral infections

The US Air Force has implemented the widespread use of JP-8 jet fuel in its operations, although a thorough understanding of its potential effects upon exposed personnel is unclear. Previous work has reported that JP-8 exposure is immunosuppressive. Exposure of mice to JP-8 for 1A h/day resulted in immediate secretion of two immunosuppressive agents, namely, interleukin-10 and prostaglandin E2. Thus, it was of interest to determine if jet fuel exposure might alter the immune response to infectious agents. The Hong Kong influenza model was used for these studies. Mice were exposed to 1000A mg/m(3) JP-8 (1A h/day) for 7A days before influenza viral infection. Animals were infected intra-nasally with virus and followed in terms of overall survival as well as immune responses. All surviving animals were killed 14A days after viral infection. In the present study, JP-8 exposure increased the severity of the viral infection by suppressing the anti-viral immune responses. That is, exposure of mice to JP-8 for 1A h/day for 7A days before infection resulted in decreased immune cell viability after exposure and infection, a greater than fourfold decrease in immune proliferative responses to mitogens, as well as an overall loss of CD3(+), CD4(+), and CD8(+) T cells from the lymph nodes, but not the spleens, of infected animals. These changes resulted in decreased survival of the exposed and infected mice, with only 33% of animals surviving as compared with 50% of mice infected but not jet fuel-exposed (and 100% of mice exposed only to JP-8). Thus, short-term, low-concentration JP-8 jet fuel exposures have significant suppressive effects on the immune system which can result in increased severity of viral infections.

JP-8 induces immune suppression via a reactive oxygen species NF-kappabeta-dependent mechanism

Applying jet fuel (JP-8) to the skin of mice induces immune suppression. JP-8-treated keratinocytes secrete prostaglandin E(2), which is essential for activating immune suppressive pathways. The molecular pathway leading to the upregulation of the enzyme that controls prostaglandin synthesis, cyclooxygenase (COX)-2, is unclear. Because JP-8 activates oxidative stress and because reactive oxygen species (ROS) turn on nuclear factor kappa B (NF-kappabeta), which regulates the activity of COX-2, we asked if JP-8-induced ROS and NF-kappabeta contributes to COX-2 upregulation and immune suppression in vivo. JP-8 induced the production of ROS in keratinocytes as measured with the ROS indicator dye, aminophenyl fluorescein. Fluorescence was diminished in JP-8-treated keratinocytes overexpressing catalase or superoxide dismutase (SOD) genes. JP-8-induced COX-2 expression was also reduced to background in the catalase and SOD transfected cells, or in cultures treated with N-acetylcysteine (NAC). When NAC was injected into JP-8-treated mice, dermal COX-2 expression, and JP-8-induced immune suppression was inhibited. Because ROS activates NF-kappabeta, we asked if this transcriptional activator played a role in the enhanced COX-2 expression and JP-8-induced immune suppression. When JP-8-treated mice, or JP-8-treated keratinocytes were treated with a selective NF-kappabeta inhibitor, parthenolide, COX-2 expression, and immune suppression were abrogated. Similarly, when JP-8-treated keratinocytes were treated with small interfering RNA specific for the p65 subunit of NF-kappabeta, COX-2 upregulation was blocked. These data indicate that ROS and NF-kappabeta are activated by JP-8, and these pathways are involved in COX-2 expression and the induction of immune suppression by jet fuel.

JP-8 jet fuel exposure potentiates tumor development in two experimental model systems

The US Air Force has implemented the widespread use of JP-8 jet fuel in its operations, although a thorough understanding of its potential effects upon exposed personnel is unclear. Previous work has reported that JP-8 exposure is immunosuppressive. Exposure of mice to JP-8 for 1 h/day resulted in immediate secretion of two immunosuppressive agents; namely, interleukin-10 (IL-10) and prostaglandin E2 (PGE2). Thus, it was of interest to determine if jet fuel exposure might promote tumor growth and metastasis. The syngeneic B16 tumor model was used for these studies. Animals were injected intravenously with tumor cells, and lung colonies were enumerated. Animals were also examined for metastatic spread of the tumor. Mice were either exposed to 1000 mg/m3 JP-8 (1 h/ day) for 7 days before tumor injection or were exposed to JP-8 at the time of tumor injection. All animals were killed 17 days after tumor injection. In the present study, JP8 exposure potentiated the growth and metastases of B16 tumors in an animal model. Exposure of mice to JP-8 for 1 h/day before tumor induction resulted in an approximately 8.7-fold increase in tumors, whereas those mice exposed to JP8 at the time of tumor induction had a 5.6-fold increase in tumor numbers. Thus, low concentration JP-8 jet fuel exposures have significant immune suppressive effects on the immune system that can result in increased tumor formation and metastases. We have now extended the observations to an experimental subcutaneous tumor model. JP8 exposure at the time of tumor induction in this model did not affect the growth of the tumor. However, JP8-exposed, tumor-bearing animals died at an accelerated rate as compared with air-exposed, tumor-bearing mice.

Human Metabolism and Metabolic Interactions of Deployment-Related Chemicals

It has been suggested that chemicals and, more specifically, chemical interactions, are involved as causative agents in deployment-related illnesses. Unfortunately, this hypothesis has proven difficult to test, because toxicological investigations of deployment-related chemicals are usually carried out on surrogate animals and are difficult to extrapolate to humans. Other parts of the problem, such as the definition of variation within human populations and the development of methods for designating groups or individuals at significantly greater risk, cannot be carried out on surrogate animals, and the data must be derived from humans. The relatively recent availability of human cell.fractions, such as microsomes, cytosol, etc., human cells such as primary hepatocytes, recombinant human enzymes, and their isoforms and polymorphic variants has enabled a significant start to be made in developing the human data needed. These initial studies have examined the human metabolism by cytochrome P450, other phase I enzymes, and their isoforms and, in some cases, their polymorphic variants of compounds such as chlorpyrifos, carbaryl, DEET, permethrin, and pyridostigmine bromide, and, to a lesser extent, other chemicals from the same chemical and use classes, including solvents, jet fuel components, and sulfur mustard metabolites. A number of interactions at the metabolic level have been described both with respect to other xenobiotics and to endogenous metabolites. Probably the most dramatic have been seen in the ability of chlorpyrifos to inhibit not only the metabolism of other xenobiotics such as carbaryl and DEET but also to inhibit the metabolism of steroid hormones.

Effects of in utero JP-8 jet fuel exposure on the immune systems of pregnant and newborn mice

The US Air Force has implemented the widespread use of JP-8 jet fuel in its operations, although a thorough understanding of its potential effects upon exposed personnel is unclear. Previous work has reported that JP-8 exposure is immunosuppressive. In the present study, the effects of in-utero JP-8 jet fuel exposure in mice were examined to ascertain any potential effects of jet fuel exposure on female personnel and their offspring. Exposure by the aerosol route (at 1000 mg/m3 for 1 h/day; similar to exposures incurred by flight line personnel) commencing during the first (d7 to birth) or last (d15 to birth) trimester of pregnancy was analyzed. It was observed that even 6-8 weeks after the last jet fuel exposure that the immune system of the dams (mother of newborn mice) was affected (in accordance with previous reports on normal mice). That is, thymus organ weights and viable cell numbers were decreased, and immune function was depressed. A decrease in viable male offspring was found, notably more pronounced when exposure started during the first trimester of pregnancy. Regardless of when jet fuel exposure started, all newborn mice (at 6-8 weeks after birth) reported significant immunosuppression. That is, newborn pups displayed decreased immune organ weights, decreased viable immune cell numbers and suppressed immune function. When the data were analyzed in relation to the respective mothers of the pups the data were more pronounced. Although all jet fuel-exposed pups were immunosuppressed as compared with control pups, male offspring were more affected by jet fuel exposure than female pups. Furthermore, the immune function of the newborn mice was directly correlated to the immune function of their respective mothers. That is, mothers showing the lowest immune function after JP-8 exposure gave birth to pups displaying the greatest effects of jet fuel exposure on immune function. Mothers who showed the highest levels of immune function after in-utero JP-8 exposure gave birth to pups displaying levels of immune function similar to controls animals that had the lowest levels of immune function. These data indicated that a genetic component might be involved in determining immune responses after jet fuel exposure. Overall, the data showed that in-utero JP-8 jet fuel exposure had long-term detrimental effects on newborn mice, particularly on the viability and immune competence of male offspring.

Inhibition of jet fuel aliphatic hydrocarbon induced toxicity in human epidermal keratinocytes

Jet propellant (JP)-8, the primary jet fuel used by the U.S. military, consists of hydrocarbon-rich kerosene base commercial jet fuel (Jet-A) plus additives DC1-4A, Stadis 450 and diethylene glycol monomethyl ether. Human epidermal keratinocytes (HEK) were exposed to JP-8, aliphatic hydrocarbon (HC) fuel S-8 and aliphatic HC pentadecane (penta), tetradecane (tetra), tridecane (tri) and undecane (un) for 5 min. Additional studies were conducted with signal transduction pathway blockers parthenolide (P; 3.0 microm), isohelenin (I; 3.0 microm), SB 203580 (SB; 13.3 microm), substance P (SP; 3.0 microm) and recombinant human IL-10 (rHIL-10; 10 ng ml(-1)). In the absence of inhibitors, JP-8 and to a lesser extent un and S-8, had the greatest toxic effect on cell viability and inflammation suggesting, as least in vitro, that synthetic S-8 fuel is less irritating than the currently used JP-8. Each inhibitor significantly (P < 0.05) decreased HEK viability. DMSO, the vehicle for P, I and SB, had a minimal effect on viability. Overall, IL-8 production was suppressed at least 30% after treatment with each inhibitor. Normalizing data relative to control indicate which inhibitors suppress HC-mediated IL-8 to control levels. P was the most effective inhibitor of IL-8 release; IL-8 was significantly decreased after exposure to un, tri, tetra and penta but significantly increased after JP-8 exposure compared with controls. Inhibitors were not effective in suppressing IL-8 release in JP-8 exposures to control levels. This study shows that inhibiting NF-kappa B, which appears to play a role in cytokine production in HC-exposed HEK in vitro, may reduce the inflammatory effect of HC in vivo.

Immunotoxicity evaluation of jet a jet fuel in female rats after 28-day dermal exposure

The potential for jet fuel to modulate immune functions has been reported in mice following dermal, inhalation, and oral routes of exposure; however, a functional evaluation of the immune system in rats following jet fuel exposure has not been conducted. In this study potential effects of commercial jet fuel (Jet A) on the rat immune system were assessed using a battery of functional assays developed to screen potential immunotoxic compounds. Jet A was applied to the unoccluded skin of 6- to 7-wk-old female Crl:CD (SD)IGS BR rats at doses of 165, 330, or 495 mg/kg/d for 28 d. Mineral oil was used as a vehicle to mitigate irritation resulting from repeated exposure to jet fuel. Cyclophosphamide and anti-asialo GM1 were used as positive controls for immunotoxic effects. In contrast to reported immunotoxic effects of jet fuel in mice, dermal exposure of rats to Jet A did not result in alterations in spleen or thymus weights, splenic lymphocyte subpopulations, immunoglobulin (Ig) M antibody-forming cell response to the T-dependent antigen, sheep red blood cells (sRBC), spleen cell proliferative response to anti-CD3 antibody, or natural killer (NK) cell activity. In each of the immunotoxicological assays conducted, the positive control produced the expected results, demonstrating the assay was capable of detecting an effect if one had occurred. Based on the immunological parameters evaluated under the experimental conditions of the study, Jet A did not adversely affect immune responses of female rats. It remains to be determined whether the observed difference between this study and some other studies reflects a difference in the immunological response of rats and mice or is the result of other factors.

Dermal exposure to jet fuel suppresses delayed-type hypersensitivity: a critical role for aromatic hydrocarbons

Dermal exposure to military (JP-8) and/or commercial (Jet-A) jet fuel suppresses cell-mediated immune reactions. Immune regulatory cytokines and biological modifiers, including platelet activating factor (PAF), prostaglandin E(2), and interleukin-10, have been implicated in the pathway of events leading to immune suppression. It is estimated that approximately 260 different hydrocarbons are found in jet fuel, and the exact identity of the active immunotoxic agent(s) is unknown. The recent availability of synthetic jet fuel (S-8), which is refined from natural gas, and is devoid of aromatic hydrocarbons, made it feasible to design experiments to address this problem. Here we tested the hypothesis that the aromatic hydrocarbons present in jet fuel are responsible for immune suppression. We report that applying S-8 to the skin of mice does not upregulate the expression of epidermal cyclooxygenase-2 (COX-2) nor does it induce immune suppression. Adding back a cocktail of seven of the most prevalent aromatic hydrocarbons found in jet fuel (benzene, toluene, ethylbenzene, xylene, 1,2,4-trimethlybenzene, cyclohexylbenzene, and dimethylnaphthalene) to S-8 upregulated epidermal COX-2 expression and suppressed a delayed-type hypersensitivity (DTH) reaction. Injecting PAF receptor antagonists, or a selective cycloozygenase-2 inhibitor into mice treated with S-8 supplemented with the aromatic cocktail, blocked suppression of DTH, similar to data previously reported using JP-8. These findings identify the aromatic hydrocarbons found in jet fuel as the agents responsible for suppressing DTH, in part by the upregulation of COX-2, and the production of immune regulatory factors and cytokines.

Methods for the characterization of Jet Propellent-8: vapor and aerosol

Jet Propellant-8 (JP-8) has been responsible for the majority of reported chemical exposures by the US Department of Defense. Concerns related to human exposure to JP-8 are relatively new; therefore, there is a lack of literature data. Additionally, health effects related to the composition of the exposure have only recently been considered. Two major questions exist: (1) what is the compositional difference between the aerosol and vapor portions of JP-8 under controlled conditions and (2) what is the most representative method to sample JP-8 aerosol and vapor? Thirty-seven standards, representing more than 40% of the mass of JP-8, were used for characterization of the neat fuel, vapor and aerosol portions. JP-8 vapor samples at a concentration of 1600 mg/m(3) were prepared in Tedlar bags. A portion of the vapor samples was adsorbed on charcoal, Tenax and custom mixed phase sorbents. These samples were then extracted using organic solvent and analyzed using gas chromatography/mass spectrometry. The vapor samples extracted from the sorbent tubes were directly compared with a vapor bag. The samples collected using Tenax sorbent tubes were found to be most representative of the composition of the vapor bags. In another set of experiments, aerosolized JP-8 was generated using a collision nebulizer. Aerosol samples were collected and the chemical composition was characterized. The entire aerosol distribution was collected on a glass filter, extracted into solvent, and analyzed by GC-MS. Finally, the composition of the vapor and aerosol was compared. The vapor was found to represent the lower molecular weight components of JP-8, while the aerosol was composed of higher molecular weight components. Therefore, the vapor and aerosol should be treated as two discrete forms of exposure to JP-8.

Effects of brief cutaneous JP-8 jet fuel exposures on time course of gene expression in the epidermis

The jet fuel jet propulsion fuel 8 (JP-8) has been shown to cause an inflammatory response in the skin, which is characterized histologically by erythema, edema, and hyperplasia. Studies in laboratory animal skin and cultured keratinocytes have identified a variety of changes in protein levels related to inflammation, oxidative damage, apoptosis, and cellular growth. Most of these studies have focused on prolonged exposures and subsequent effects. In an attempt to understand the earliest responses of the skin to JP-8, we have investigated changes in gene expression in the epidermis for up to 8 h after a 1-h cutaneous exposure in rats. After exposure, we separated the epidermis from the rest of the skin with a cryotome and isolated total mRNA. Gene expression was studied with microarray techniques, and changes from sham treatments were analyzed and characterized. We found consistent twofold increases in gene expression of 27 transcripts at 1, 4, and 8 h after the beginning of the 1-h exposure that were related primarily to structural proteins, cell signaling, inflammatory mediators, growth factors, and enzymes. Analysis of pathways changed showed that several signaling pathways were increased at 1 h and that the most significant changes at 8 h were in metabolic pathways, many of which were downregulated. These results confirm and expand many of the previous molecular studies with JP-8. Based on the 1-h changes in gene expression, we hypothesize that the trigger of the JP-8-induced, epidermal stress response is a physical disruption of osmotic, oxidative, and membrane stability which activates gene expression in the signaling pathways and results in the inflammatory, apoptotic, and growth responses that have been previously identified.

Expression of JP-8–Induced Inflammatory Genes in AEII Cells Is Mediated by NF-κB and PARP-1

Lung epithelial cells are critical in the regulation of airway inflammation in response to environmental pollutants. Altered activation of NF-kappaB is associated with expression of several proinflammatory factors in respiratory epithelial cells in response to an insult. Here we show that a low threshold dose (8 microg/ml) of the jet fuel JP-8 induces in a rat alveolar epithelial cell line (RLE-6TN) a prolonged activation of NF-kappaB as well as the increased expression of the proinflammatory cytokines TNF-alpha and IL-8, which are regulated by NF-kappaB. The up-regulation of IL-6 mRNA in cells exposed to JP-8 appears to be a reaction of RLE-6TN cells to reduce the enhancement of proinflammatory mediators in response to the fuel. Moreover, lung tissues from rats exposed to occupational levels of JP-8 by nasal aerosol also showed dysregulated expression of TNF-alpha, IL-8, and IL-6, confirming the in vitro data. The poly(ADP-ribosyl)ation of PARP-1, a coactivator of NF-kappaB, was coincident with the prolonged activation of NF-kappaB during JP-8 treatment. These results evidenced that a persistent exposure of the airway epithelium to aromatic hydrocarbons may have deleterious effects on pulmonary function.

Occupational exposure in airport personnel: characterization and evaluation of genotoxic and oxidative effects

Airport personnel can be exposed to several polycyclic aromatic hydrocarbons (PAHs) from jet fuel vapours, jet fuel combustion products and diesel exhaust. The aim of this study was to characterize the exposure and to evaluate genotoxic and oxidative effects in airport personnel (n=41) in comparison with a selected control group (n=31). Environmental monitoring of exposure was carried out analysing 23 PAHs on air samples collected from airport apron, airport building and terminal/office area during 5 working days. The urinary 1-hydroxy-pyrene (1-OHP) following 5 working days, was used as biomarker of exposure. Genotoxic effects and early direct-oxidative DNA damage were evaluated by micronucleus (MN) and Fpg-modified comet assay on lymphocytes and exfoliated buccal cells, and by chromosomal aberrations (CA) and sister chromatid exchange (SCE) analyses. For comet assay, tail moment (the product of comet relative tail intensity and length) values from Fpg-enzyme treated cells (TMenz) and from untreated cells (TM) were used as parameters of oxidative and direct DNA damage, respectively. We found 27,703 microg/m(3) total PAHs in airport apron, 17,275 microg/m(3) in airport building and 9,494 microg/m(3) in terminal/office area. Urinary OH-pyrene did not show differences between exposed and controls. The exposed group showed a higher mean value of SCE frequency in respect to controls (4.6 versus 3.8) and an increase (1.3-fold) of total structural CA in particular breaks (up to 2.0-fold) and fragments (0.32% versus 0.00%), whereas there were no differences of MN frequency in both cellular types. Comet assay evidenced in the exposed group a higher value in respect to controls of mean TM and TMenz in both exfoliated buccal cells (TM 118.87 versus 68.20, p=0.001; TMenz 146.11 versus 78.32, p<0.001) and lymphocytes (TM 43.01 versus 36.01, p=0.136; TMenz 55.86 versus 43.98, p=0.003). An oxidative DNA damage was found, for exfoliated buccal cells in the 9.7% and for lymphocytes in the 14.6% of exposed in respect to the absence in controls. Our findings furnish a useful contribution to the characterization of civil airport exposure and suggest the use of comet assay on exfoliated buccal cells to assess the occupational exposure to mixtures of inhalable pollutants at low doses since these cells represent the target tissue for this exposure and are obtained by non-invasive procedure.

A review of analytical methods for the identification and quantification of hydrocarbons found in jet propellant 8 and related petroleum based fuels

Jet propellant 8 (JP-8) is a complex mixture of compounds that varies from batch to batch. Quantification of various compound classes of JP-8, including BTEX, PAHs and VOCs, has been accomplished. Very few papers have tackled total JP-8 quantification because of its complexity. The components in JP-8 tend to co-elute and present at low concentrations, often nondetectable. JP-8 is the major source of chemical exposure for Department of Defense personnel and a potential hazard for civilians and marine animals. Some components of JP-8 have been identified as possible human carcinogens and have been studied extensively. Development of analytical methods to analyze the components of this fuel are essential to measure the extent of exposure, as well as the short-term and long-term exposure in rodents, humans and marine life. To date, JP-8 has been examined in urine, blood, contaminated water and fish tissue. This paper reviews methods currently utilized in the literature for the analysis of JP-8 and its components. This paper also discusses extraction methods and detectors commonly used in JP-8 and hydrocarbon analysis in general. Finally, the effects of exposure and the future of JP-8 and petroleum analysis with respect to human health are discussed.

Validation of a gas chromatography/mass spectrometry method for the quantification of aerosolized Jet Propellant 8

Jet Propellant 8 (JP-8) jet fuel is a kerosene-based fuel containing hundreds of hydrocarbons used by the military in NATO countries. Previous rodent inhalation studies carried out with aerosolized JP-8 never evaluated the exposure chamber atmosphere. For this reason, our laboratory developed an analytical method, with an accuracy of better than 80% and precision of better than 20%, for JP-8 aerosol and vapor samples using gas chromatography/mass spectrometry (GC/MS). A method was developed for quantification of selected individual components of JP-8 and for the total amount of JP-8 in aerosolized fuel. A 34 component surrogate hydrocarbon mixture (SHM) was developed and used for simultaneous analysis of the individual components. Three separate runs containing a standard curve and five replicates each at the selected concentrations were analyzed for both the SHM and neat JP-8. The resulting interday accuracy (100-percent relative error) and precision (relative standard deviation) values for the SHM were 86.5% or better and 8.0% or better, respectively. The intraday accuracy and precision values ranged from 99.29% to 84.50% and 0.97% to 12.4%, respectively. For the total amount of JP-8 in aerosol and vapor, the interday accuracy was 83.7% or better and interday precision was 7.0% or better. The intraday accuracy and precision values ranged from 94.8% to 80.4% and 2.4% to 10.5%, respectively. We then used this method to analyze samples collected from an inhalation chamber. From the data obtained, we are able to account for approximately 40-44% of the mass of the aerosol portion and 68-70% of the mass of the vapor portion. The aerosol represented 6-10% of the total mass of the aerosolized JP-8 fuel with the remaining portion being the vapor. From these experiments individual components were identified for further in vivo and in vitro toxicological testing.

Comparative in vivo toxicity of topical JP-8 jet fuel and its individual hydrocarbon components: identification of tridecane and tetradecane as key constituents responsible for dermal irritation

Despite widespread exposure to military jet fuels, there remains a knowledge gap concerning the actual toxic entities responsible for irritation observed after topical fuel exposure. The present studies with individual hydrocarbon (HC) constituents of JP-8 jet fuel shed light on this issue. To mimic occupational scenarios, JP-8, 8 aliphatic HC (nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane) and 6 aromatic HC (ethyl benzene, o-xylene, trimethyl benzene, cyclohexyl benzene, naphthalene, dimethyl naphthalene) soaked cotton fabrics were topically exposed to pigs for 1 day and with repeated daily exposures for 4 days. Erythema, epidermal thickness, and epidermal cell layers were quantitated. No erythema was noted in 1-day in vivo HC exposures but significant erythema was observed in 4-day tridecane, tetradecane, pentadecane, and JP-8 exposed sites. The aromatic HCs did not produce any macroscopic lesions in 1 or 4 days of in vivo exposures. Morphological observations revealed slight intercellular and intracellular epidermal edema in 4-day exposures with the aliphatic HCs. Epidermal thickness and number of cell layers significantly increased (p < 0.05) in tridecane, tetradecane, pentadecane, and JP-8-treated sites. No significant differences were observed in the aromatic HC-exposed sites. Subcorneal microabscesses containing inflammatory cells were observed with most of the long-chain aliphatic HCs and JP-8 in 4-day exposures. Ultrastructural studies depicted that jet fuel HC-induced cleft formation within intercellular lipid lamellar bilayers of the stratum corneum. The degree of damage to the skin was proportional to the length of in vivo HC exposures. These data coupled with absorption and toxicity studies of jet fuel HC revealed that specific HCs (tridecane and tetradecane) might be the key constituents responsible for jet fuel-induced skin irritation.

Effect of in vivo jet fuel exposure on subsequent in vitro dermal absorption of individual aromatic and aliphatic hydrocarbon fuel constituents

The percutaneous absorption of topically applied jet fuel hydrocarbons (HC) through skin previously exposed to jet fuel has not been investigated, although this exposure scenario is the occupational norm. Pigs were exposed to JP-8 jet fuel-soaked cotton fabrics for 1 and 4 d with repeated daily exposures. Preexposed and unexposed skin was then dermatomed and placed in flow-through in vitro diffusion cells. Five cells with exposed skin and four cells with unexposed skin were dosed with a mixture of 14 different HC consisting of nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, ethyl benzene, o-xylene, trimethyl benzene (TMB), cyclohexyl benzene (CHB), naphthalene, and dimethyl naphthalene (DMN) in water + ethanol (50:50) as diluent. Another five cells containing only JP-8-exposed skin were dosed solely with diluent in order to determine the skin retention of jet fuel HC. The absorption parameters of flux, diffusivity, and permeability were calculated for the studied HC. The data indicated that there was a two-fold and four-fold increase in absorption of specific aromatic HC like ethyl benzene, o-xylene, and TMB through 1- and 4-dJP-8 preexposed skin, respectively. Similarly, dodecane and tridecane were absorbed more in 4-d than 1-dJP-8 preexposed skin experiments. The absorption of naphthalene and DMN was 1.5 times greater than the controls in both 1- and 4-d preexposures. CHB, naphthalene, and DMN had significant persistent skin retention in 4-d preexposures as compared to 1-d exposures that might leave skin capable of further absorption several days postexposure. The possible mechanism of an increase in HC absorption in fuel preexposed skin may be via lipid extraction from the stratum corneum as indicated by Fourier transform infrared (FTIR) spectroscopy. This study suggests that the preexposure of skin to jet fuel enhances the subsequent in vitro percutaneous absorption of HC, so single-dose absorption data for jet fuel HC from naive skin may not be optimal to predict the toxic potential for repeated exposures. For certain compounds, persistent absorption may occur days after the initial exposure.

Comparative mixture effects of JP-8(100) additives on the dermal absorption and disposition of jet fuel hydrocarbons in different membrane model systems

Jet fuel are complex mixtures of hydrocarbon fuel components and performance additives. Three different membrane systems, silastic, porcine skin and the isolated perfused porcine skin flap (IPPSF) were used to gain insight into the possible mechanism for additive interactions on hydrocarbon component absorption. Influence of JP-8(100) additives on the dermal kinetics of 14C-naphthalene and 14C/3H-dodecane as markers of hydrocarbon absorption, were evaluated using analysis of means (ANOM) and analysis of variance (ANOVA). This study indicated that the naphthalene absorption through silastic membrane was significantly different with JP-8 plus individual additives as compared to controls, i.e. JP-8 and JP-8(100). The porcine skin data indicated that neither individual nor combinations of additives affected naphthalene absorption. The third membrane system (IPPSF) showed that only MDA and BHT were important additives altering naphthalene absorption. MDA was a significant suppressor while BHT was a significant enhancer of naphthalene absorption. MDA significantly decreased dodecane absorption in skin flaps. All individual and combinations of two additives with JP-8 affected naphthalene and dodecane surface retention in silastic membrane. The IPPSF indicated that only 8Q405 is a significant modulator of surface retention for both marker hydrocarbons. The 8Q405 significantly reduced naphthalene contents in dosed silastic and skin indicating a direct interaction between additive and marker hydrocarbons. The MDA and BHT, which significantly retained naphthalene in the stratum corneum of porcine skin individually, led to a statistical decrease in its retention in the stratum corneum when in combination (MDA + BHT) suggesting a potential biological interaction. These observations demonstrate that the single membrane system may not be suitable for the final prediction of complex additive interactions in jet fuels. Rather a combination of different membrane systems may provide the insight to elucidate the possible mechanism for additive interactions. Finally, it is important to assess all components of a chemical mixture since the effects of single components administered alone or as pairs may be confounded when all are present in the complete mixture.

Altered Expression of γ-Synuclein and Detoxification-Related Genes in Lungs of Rats Exposed to JP-8

Many military personnel are at risk of lung damage or systemic toxicity as a result of exposure to the jet fuel JP-8. We have now used microarray analysis to characterize changes in the gene expression profile of lung tissue induced by exposure of rats to JP-8 at a concentration of 171 or 352 mg/m(3) for 1 h/d for 7 d, with the higher dose estimated to mimic the level of occupational exposure in humans. The expression of 56 genes was significantly affected by a factor of </= 0.6 or >/= 1.5 by JP-8 at the low dose. Eighty-six percent of these genes were downregulated by JP-8. The expression of 66 genes was similarly affected by JP-8 at the higher dose, with the expression of 42% of these genes being upregulated. Prominent among the latter genes was that for the centrosome-associated protein gamma-synuclein, whose expression was consistently increased. The expression of various genes related to antioxidant responses and detoxification, including those for glutathione S-transferases and cytochrome P450 proteins, were also upregulated. The microarray data were confirmed by quantitative RT-PCR analysis. Our extensive data set may thus provide important insight into the pulmonary response to occupational exposure to JP-8 in humans.

JP-8 jet fuel exposure induces inflammatory cytokines in rat skin

The Department of Defense (DoD) has identified that one of the main complaints of personnel exposed to JP-8 jet fuel is irritant dermatitis. The purpose of this investigation is to describe the JP-8-induced inflammatory cytokine response in skin. JP-8 jet fuel or acetone control (300 microl) was applied to the denuded skin of rats once a day for 7 days. Skin samples from the exposed area were collected 2 and 24 h after the final exposure. Histological examination of skin biopsies showed neutrophilic inflammatory infiltrate. Reverse transcription-polymerase chain reaction (RT-PCR) was performed utilizing skin total RNA to examine the expression of various inflammatory cytokines. The CXC chemokine GROalpha was significantly upregulated at both time points, whereas GRObeta was only increased 2 h post final exposure. The CC chemokines MCP-1, Mip-1alpha, and eotaxin were induced at both time points, whereas Mip-1beta was induced only 24 h post exposure. Interleukins-1beta and -6 (IL-1beta and IL-6) mRNAs were significantly induced at both time points, while TNFalpha was not significantly different from control. Enzyme-linked immunosorbent assay (ELISA) of skin protein confirmed that MCP-1, TNFalpha, and IL-1beta were modulated as indicated by PCR analysis. However, skin IL-6 protein content was not increased 2 h post exposure, whereas it was significantly upregulated by jet fuel after 24 h. Data from the present study indicate that repeated (7 days) JP-8 exposure induces numerous proinflammatory cytokines in skin. The increased expression of these cytokines and chemokines may lead to increased inflammatory infiltrate in exposed skin, resulting in JP-8-induced irritant dermatitis.

The metabolism of nonane, a JP-8 jet fuel component, by human liver microsomes, P450 isoforms and alcohol dehydrogenase and inhibition of human P450 isoforms by JP-8

Nonane, a component of jet-propulsion fuel 8 (JP-8), is metabolized to 2-nonanol and 2-nonanone by pooled human liver microsomes (pHLM). Cytochrome P450 (CYP) isoforms 1A2, 2B6 and 2E1 metabolize nonane to 2-nonanol, whereas alcohol dehydrogenase, CYPs 2B6 and 2E1 metabolize 2-nonanol to 2-nonanone. Nonane and 2-nonanol showed no significant effect on the metabolism of testosterone, estradiol or N,N-diethyl-m-toluamide (DEET), but did inhibit carbaryl metabolism. JP-8 showed modest inhibition of testosterone, estradiol and carbaryl metabolism, but had a more significant effect on the metabolism of DEET. JP-8 was shown to inhibit CYPs 1A2 and 2B6 mediated metabolism of DEET, suggesting that at least some of the components of JP-8 might be metabolized by CYPs 1A2and/or 2B6.

Immunological and hematological effects observed in B6C3F1 mice exposed to JP-8 jet fuel for 14 days

JP-8 is the primary jet fuel used by the U.S. Air Force and NATO allies. Exposure is likely to be widespread and to include both military and aviation industry personnel as well as residents living near fuel contaminated sites. This study examines the effects of JP-8 on humoral and cell-mediated and hematological parameters. A suite of immunotoxicological endpoints was evaluated in adult female B6C3F1 mice gavaged with JP-8 (in an olive oil carrier) ranging from 250-2500 mg/kg/d for 14 d. One day following the last exposure, significant increases in liver mass were detected beginning at exposure levels of 1000 mg/kg/d, while thymic mass was decreased at exposure levels of 1500 mg/kg/d and above. Decreases in thymic cellularity, however, were only observed at exposure levels of 2000 mg/kg/d and above. Mean corpuscular volume was increased (1500-2500 mg/kg/d), while the hematocrit, hemoglobin concentration, and red blood cell count were decreased only at the 2500 mg/kg/d exposure level. Natural killer cell (NK) activity and T- and B-cell proliferation were not altered. Decreases in the plaque-forming cell (PFC) response were dose responsive at levels of 500 mg/kg/d and greater, while unexpectedly, serum levels of anti-SRBC immunoglobulin M (IgM) were not altered. Alterations were detected in thymic and splenic CD4/8 subpopulations, and proliferative responses of bone marrow progenitor cells were enhanced in mice exposed to 2000 mg/kg/d of JP-8. This study establishes that humoral immune function is impaired with lower exposure levels of JP-8 than are required to affect primary and secondary immune organ weights and cellularities, CD4/8 subpopulations, and hematological endpoints.

Probability estimates for the unique childhood leukemia cluster in Fallon, Nevada, and risks near other U.S. Military aviation facilities

A unique cluster of childhood leukemia has recently occurred around the city of Fallon in Churchill County, Nevada. From 1999 to 2001, 11 cases were diagnosed in this county of 23,982 people. Exposures related to a nearby naval air station such as jet fuel or an infectious agent carried by naval aviators have been hypothesized as potential causes. The possibility that the cluster could be attributed to chance was also considered. We used data from the Surveillance, Epidemiology, and End Results Program (SEER) to examine the likelihood that chance could explain this cluster. We also used SEER and California Cancer Registry data to evaluate rates of childhood leukemia in other U.S. counties with military aviation facilities. The age-standardized rate ratio (RR) in Churchill County was 12.0 [95% confidence interval (CI), 6.0-21.4; p = 4.3 times symbol 10(-9)]. A cluster of this magnitude would be expected to occur in the United States by chance about once every 22,000 years. The age-standardized RR for the five cases diagnosed after the cluster was first reported was 11.2 (95% CI, 3.6-26.3). In contrast, the incidence rate was not increased in all other U.S. counties with military aviation bases (RR = 1.04; 95% CI, 0.97-1.12) or in the subset of rural counties with military aviation bases (RR = 0.72; 95% CI, 0.48-1.08). These findings suggest that the Churchill County cluster was unlikely due to chance, but no general increase in childhood leukemia was found in other U.S. counties with military aviation bases.

Platelet activating factor receptor binding plays a critical role in jet fuel-induced immune suppression

Applying military jet fuel (JP-8) or commercial jet fuel (Jet-A) to the skin of mice suppresses the immune response in a dose-dependent manner. The release of biological response modifiers, particularly prostaglandin E2 (PGE2), is a critical step in activating immune suppression. Previous studies have shown that injecting selective cyclooxygenase-2 inhibitors into jet fuel-treated mice blocks immune suppression. Because the inflammatory phospholipid mediator, platelet-activating factor (PAF), up-regulates cyclooxygenase-2 production and PGE2 synthesis by keratinocytes, we tested the hypothesis that PAF-receptor binding plays a role in jet fuel-induced immune suppression. Treating keratinocyte cultures with PAF and/or jet fuel (JP-8 and Jet-A) stimulates PGE2 secretion. Jet fuel-induced PGE2 production was suppressed by treating the keratinocytes with specific PAF-receptor antagonists. Injecting mice with PAF, or treating the skin of the mice with JP-8, or Jet-A, induced immune suppression. Jet fuel-induced immune suppression was blocked when the jet fuel-treated mice were injected with PAF-receptor antagonists before treatment. Jet fuel treatment has been reported to activate oxidative stress and treating the mice with anti-oxidants (Vitamins C, or E or beta-hydroxy toluene), before jet fuel application, interfered with immune suppression. These findings confirm previous studies showing that PAF-receptor binding can modulate immune function. Furthermore, they suggest that PAF-receptor binding may be an early event in the induction of immune suppression by immunotoxic environmental agents that target the skin.

Skin toxicity of jet fuels: ultrastructural studies and the effects of substance P

Topical exposure to jet fuel is a significant occupational hazard. Recent studies have focused on dermal absorption of fuel and its components, or alternatively, on the biochemical or immunotoxicological sequelae to exposure. Surprisingly, morphological and ultrastructural analyses have not been systematically conducted. Similarly, few studies have compared responses in skin to that of the primary target organ, the lung. The focus of the present investigation was 2-fold: first, to characterize the ultrastructural changes seen after topical exposure to moderate doses (335 or 67 microl/cm2) of jet fuels [Jet A, Jet Propellant (JP)-8, JP-8+100] for up to 4 days in pigs, and secondly, to determine if co-administration of substance P (SP) with JP-8 jet fuel in human epidermal keratinocyte cell cultures modulates toxicity as it does to pulmonary toxicity in laboratory animal studies. The primary change seen after exposure to all fuels was low-level inflammation accompanied by formation of lipid droplets in various skin layers, mitochondrial and nucleolar changes, cleft formation in the intercellular lipid lamellar bilayers, as well as disorganization in the stratum granulosum-stratum corneum interface. An increased number of Langerhans cells were also noted in jet fuel-treated skin. These changes suggest that the primary effect of jet fuel exposure is damage to the stratum corneum barrier. SP administration decreased the release of interleukin (IL)-8 normally seen in keratinocytes after JP-8 exposure, a response similar to that reported for SP's effect on JP-8 pulmonary toxicity. These studies provide a base upon which biochemical and immunological data collected in other model systems can be compared.

Macroarray analysis of the effects of JP-8 jet fuel on gene expression in Jurkat cells

The jet fuel JP-8 is widely used and a large number of military and civilian personnel is, therefore, exposed to it. Treatment of several cell lines, including human Jurkat cells, with JP-8 induces cell death that exhibits various biochemical and morphological characteristics of apoptosis. The molecular mechanism of JP-8 cytotoxicity, however, has remained unclear. The effects of exposure of Jurkat cells to JP-8 (1/10,000 dilution) for 4 h on gene expression have now been examined by cDNA macroarray analysis. We had previously shown in these cells that under the above conditions, JP-8 causes significant apoptosis, based upon the observation that caspase-3 activation occurs at approximately 4 h and consequently most of the other classical apoptotic biochemical and morphological alterations progress until apoptotic cell death at 24 h. Of the 439 apoptosis- or stress response-related genes examined, the expression of 16 genes was up-regulated and that of ten genes was down-regulated by a factor of > or =2. The changes in the expression of 11 of these 26 genes were confirmed by reverse transcription and polymerase chain reaction analysis. These results provide insight into the mechanism of JP-8 toxicity and the associated induction of apoptosis.

Biological and health effects of exposure to kerosene-based jet fuels and performance additives

Over 2 million military and civilian personnel per year (over 1 million in the United States) are occupationally exposed, respectively, to jet propulsion fuel-8 (JP-8), JP-8 +100 or JP-5, or to the civil aviation equivalents Jet A or Jet A-1. Approximately 60 billion gallon of these kerosene-based jet fuels are annually consumed worldwide (26 billion gallon in the United States), including over 5 billion gallon of JP-8 by the militaries of the United States and other NATO countries. JP-8, for example, represents the largest single chemical exposure in the U.S. military (2.53 billion gallon in 2000), while Jet A and A-1 are among the most common sources of nonmilitary occupational chemical exposure. Although more recent figures were not available, approximately 4.06 billion gallon of kerosene per se were consumed in the United States in 1990 (IARC, 1992). These exposures may occur repeatedly to raw fuel, vapor phase, aerosol phase, or fuel combustion exhaust by dermal absorption, pulmonary inhalation, or oral ingestion routes. Additionally, the public may be repeatedly exposed to lower levels of jet fuel vapor/aerosol or to fuel combustion products through atmospheric contamination, or to raw fuel constituents by contact with contaminated groundwater or soil. Kerosene-based hydrocarbon fuels are complex mixtures of up to 260+ aliphatic and aromatic hydrocarbon compounds (C(6) -C(17+); possibly 2000+ isomeric forms), including varying concentrations of potential toxicants such as benzene, n-hexane, toluene, xylenes, trimethylpentane, methoxyethanol, naphthalenes (including polycyclic aromatic hydrocarbons [PAHs], and certain other C(9)-C(12) fractions (i.e., n-propylbenzene, trimethylbenzene isomers). While hydrocarbon fuel exposures occur typically at concentrations below current permissible exposure limits (PELs) for the parent fuel or its constituent chemicals, it is unknown whether additive or synergistic interactions among hydrocarbon constituents, up to six performance additives, and other environmental exposure factors may result in unpredicted toxicity. While there is little epidemiological evidence for fuel-induced death, cancer, or other serious organic disease in fuel-exposed workers, large numbers of self-reported health complaints in this cohort appear to justify study of more subtle health consequences. A number of recently published studies reported acute or persisting biological or health effects from acute, subchronic, or chronic exposure of humans or animals to kerosene-based hydrocarbon fuels, to constituent chemicals of these fuels, or to fuel combustion products. This review provides an in-depth summary of human, animal, and in vitro studies of biological or health effects from exposure to JP-8, JP-8 +100, JP-5, Jet A, Jet A-1, or kerosene.

Percutaneous absorption, biophysical, and macroscopic barrier properties of porcine skin exposed to major components of JP-8 jet fuel

JP-8 has been associated with toxicity in animal models and humans. There is a great potential for human exposure to JP-8. Quantitation of percutaneous absorption of JP-8 is necessary for assessment of health hazards involved in its occupational exposure. In this study, we selected three aliphatic (dodecane, tridecane, and tetradecane) and two aromatic (naphthalene and 2-methylnaphthalene) chemicals, which are major components of JP-8. We investigated the changes in skin lipid and protein biophysics, and macroscopic barrier perturbation from dermal exposure of the above five chemicals. Fourier transform infrared (FTIR) spectroscopy was employed to investigate the biophysical changes in stratum corneum (SC) lipid and protein. FTIR results showed that all of the above five components of JP-8 significantly (P<0.05) extracted SC lipid and protein. Macroscopic barrier perturbation was determined by measuring the rate of transepidermal water loss (TEWL). All of the five JP-8 components studied, caused significant (P<0.05) increase in TEWL in comparison to control. We quantified the amount of chemicals absorbed assuming 0.25 m(2) body surface area exposed for 8 h. Our findings suggest that tridecane exhibits greater permeability through skin among aliphatic and naphthalene among aromatic JP-8 components. Amount of chemicals absorbed suggests that tridecane, naphthalene and its methyl derivatives should be monitored for their possible systemic toxicity.

In vivo percutaneous absorption, skin barrier perturbation, and irritation from JP-8 jet fuel components

JP-8 jet fuel has been reported to cause systemic and dermal toxicities in animal models and humans. There is a great potential for human exposure to JP-8. In this study, we determined percutaneous absorption and dermal toxicity of three components of JP-8 (i.e., xylene, heptane, and hexadecane) in vivo in weanling pigs. In vivo percutaneous absorption results suggest a greater absorption of hexadecane (0.43%) than xylene (0.17%) or heptane (0.14%) of the applied dose after 30 min exposure. Transepidermal water loss (TEWL) provides a robust method for assessing damage to the stratum corneum. Heptane showed greater increase in TEWL than the other two chemicals. No significant (p < 0.05) increase in temperature was observed at the chemically treated site than the control site. Heptane showed greater TEWL values and erythema score than other two chemicals (xylene and hexadecane). We did not observe any skin reactions or edema from these chemicals. Erythema was completely resolved after 24 h of the patch removal in case of xylene and hexadecane.

The role of calpains in apoptotic changes in isolated hepatocytes after attack by Natural Killer cells

Previously, we showed that interleukin-2 activated Natural Killer cells (A-NK cells) in vitro rapidly induced apoptosis in freshly isolated rat hepatocytes (Blom et al., 1999. Hepatology 29 (3): 785-792) which was caused by a rapid decrease in the mitochondrial membrane potential and activation of caspases. In the present study we investigated the involvement of calpains in A-NK cell-induced apoptosis in isolated hepatocytes. When NK cells and hepatocytes were incubated in the presence of a calpain inhibitor the number of apoptotic cells decreased from 46 to 36%. However, more hepatocytes became necrotic (48 vs. 30%) as compared to the uninhibited situation. Inhibition of the calpains alone could not prevent the induction of the nuclear and cytoskeletal disruptions occurring in the hepatocytes. Inhibition of both calpains and caspases increased the number of necrotic cells as compared to incubation with a single inhibitor. However, the damage to the cytoskeleton of the surviving cells was completely inhibited. We conclude that calpains play a role in induction of apoptosis by NK cells. However, their role is limited as compared to caspases.

Dermal application of jet fuel suppresses secondary immune reactions

Applying military jet fuel (JP-8) to the skin of mice activates systemic immune suppression. In all of our previous experiments, JP-8 was applied to immunologically naïve mice. The effect of jet fuels on established immune reactions, such as immunological memory, is unknown. The focus of the experiments presented here was to test the hypothesis that jet fuel exposure [both JP-8 and commercial jet fuel (Jet-A)] suppresses established immune reactions. Mice were immunized with the opportunistic fungal pathogen Candida albicans and, at different times after immunization (10 to 30 days), various doses of undiluted JP-8 or Jet-A were applied to their skin. Both the elicitation of delayed-type hypersensitivity (DTH) (mice challenged 10 days after immunization) and immunological memory (mice challenged 30 days after immunization) were significantly suppressed in a dose-dependent manner. Dermal exposure to either multiple small doses (50 microl over 4 days) or a single large dose (approximately 200-300 microl) of JP-8 and/or Jet-A suppressed DTH to C. albicans. The mechanism by which dermal application of JP-8 and Jet-A suppresses immunological memory involves the release of immune biologic response modifiers. Blocking the production of prostaglandin E(2) by a selective cyclooxygenase-2 inhibitor (SC 236) significantly reversed jet fuel-induced suppression of immunologic memory. These findings indicate, for the first time, that dermal exposure to commercial jet fuel (Jet-A) suppresses the immune response. In addition, the data reported here expand on previous findings by suggesting that jet fuel exposure may depress the protective effect of prior vaccination.

JP-8 jet fuel exposure results in immediate immunotoxicity, which is cumulative over time

The US Air Force has implemented the widespread use of JP-8 jet fuel in its operations, although a thorough understanding of its potential effects upon exposed personnel is unclear. In the present study, the immediate effects of JP-8 exposure on the immune system were analyzed. Exposure of mice once to a single 1000 mg/m3 concentration of JP-8 for one hour resulted in significant immune organ weight loss and loss of viable immune cells from the spleen within two hours post-exposure. Although a similar exposure had no effect on thymus organ weight, it did result in significant losses of viable immune cells at one hour post-exposure. It was also observed that a loss of viable bone marrow cells could be seen at four hours post-exposure, with a return to baseline levels by 24 hours post-exposure. In terms of peripheral blood immune cells, a significant loss of viable immunecells was observed within one hour post-exposure, which became more pronounced with time. Further, it was observed that a single one-hour JP-8 exposure resulted in an immediate loss of immune function at one hour post-exposure that did not recover within 24 hours. An extension of the above experiments revealed that each additional one hour/day of exposure to 1000 mg/m3 of JP-8 promulgates the significant immunotoxicity described above. That is, spleenic organ weights, as well as viable cell numbers, continued to decline with additional days of short-term exposure. Thymic organ weights were significantly reduced at three to four days of one-hour exposures, with a continuing loss of viable cell numbers. Significantly, functional immune responses continued to deteriorate with each additional day of JP-8 exposure. Thus, low concentration JP-8 jet fuel exposures have significant effects on the immune system, these effects occur rapidly and these effects are cumulative over time.

Effects of repeated exposure to JP-8 jet fuel vapor on learning of simple and difficult operant tasks by rats

Groups of 16 Sprague-Dawley rats each were exposed by whole-body inhalation methods to JP-8 jet fuel at the highest vapor concentration without formation of aerosol (1,000 +/- 10% mg/m3); to 50% of this concentration (500 +/- 10% mg/m3); or to treated room air (70 +/- 81 L/min) for 6 h/d, 5 d/wk, for 6 wk (180 h). Although two subjects died of apparent kidney complications during the study, no other change in the health status of exposed rats was observed, including rate of weight gain. Following a 65-d period of rest, rats were evaluated for their capacity to learn and perform a series of operant tasks. These tasks ranged in difficulty from learning of a simple food-reinforced lever pressing response, to learning a task in which subjects were required to emit up to four-response chains of pressing three different levers (e.g., press levers C, R, L, then C). It was shown that repeated exposure to 1,000 mg/m3 JP-8 vapor induced significant deficits in acquisition or performance of moderately difficult or difficult tasks, but not simple learning tasks, as compared to those animals exposed to 500 mg/m3. Learning/performance of complex tasks by the 500-mg/m3 exposure group generally exceeded the performance of control animals, while learning by the 1,000-mg/m3 group was nearly always inferior to controls, indicating possible "neurobehavioral" hormesis. These findings appear consistent with some previously reported data for operant performance following acute exposure to certain hydrocarbon constituents of JP-8 (i.e., toluene, xylenes). There has, however, been little previously published research demonstrating long-term learning effects for repeated hydrocarbon fuel exposures. Examination of regional brain tissues from vapor-exposed rats indicated significant changes in levels of dopamine in the cerebral cortex and DOPAC in the brainstem, measured as long as 180 d postexposure, as compared to controls.

Effects of short-term high-dose and low-dose dermal exposure to Jet A, JP-8 and JP-8 + 100 jet fuels

Occupational and environmental exposures to jet fuel recently have become a source of public and regulatory concern. This study investigates the cutaneous toxicity of three fuels used in both civilian and military aircraft. Pigs, an accepted animal model for human skin, were exposed to low-dose (25 microl or 7.96 microl cm(-2)) or high-dose (335 microl or 67 microl cm(-2)) Jet A, JP-8 and JP-8 + 100 under occluded (Hill Top) chamber or cotton fabric) and non-occluded conditions for 5 h, 24 h and 5 days. To mimic occupational exposure, fuel-soaked fabric (high dose) was used. Erythema, edema, transepidermal water loss (TEWL) and epidermal thickness were quantified. High-dose fabric occluded sites had slight erythema at 5 h with increased erythema at 5 days. No erythema was noted in any of the occluded (Hill Top) or non-occluded sites at any of the time points. Morphological assessments depicted slight intracellular epidermal edema at all time points. An increase in change in TEWL (DeltaTEWL) was observed at the 5-h and 24-h fabric and Hill Top occluded treatments and a decrease at the 5-day fabric and Hill Top occluded sites. In all 5-day JP-8 + 100 fabric sites, intracorneal microabscesses filled with inflammatory cells were observed. Epidermal thickening was significant (P < 0.05) in all three jet fuels at the high-dose fabric sites, with JP-8 + 100 being the thickest. The epidermal rete peg depth increased significantly (P < 0.05) at 24 h and 5 days with Jet A, JP-8, and JP-8 + 100 in the fabric sites. No significant differences were noted in the 5-day non-occluded fabric and Hill Top occluded and non-occluded sites. Jet fuel JP-8 + 100 tended to have the greatest proliferative response. In conclusion, the high-dose fabric-soaked exposure at 5 days to Jet A, JP-8 and JP-8 + 100 fuels caused the greatest increase in cutaneous erythema, edema, epidermal thickness and rete peg depth compared with high-dose non-occluded or low-dose exposure under Hill Top occluded and non-occluded conditions.

Detection of oxidative species and low-molecular-weight DNA in skin following dermal exposure with JP-8 jet fuel

Dermal absorption of JP-8 jet fuel can lead to skin irritation within hours after exposure. This study detected the formation of oxidative species and low-molecular-weight DNA in rat skin as potential indicators of JP-8-induced skin injury. At 0, 1, 2, 4 and 6 h after the beginning of a 1-h exposure, skin samples were removed and analyzed for oxidative species formation and low-molecular-weight DNA analysis. At 1, 2 and 4 h, mean oxidative species levels increased significantly (P < 0.05) above unexposed samples. Significantly higher (P < 0.05) low-molecular-weight DNA values were observed at 4 and 6 h compared with unexposed controls. These results demonstrate significant increases in oxidative species and low-molecular-weight DNA levels in the skin following dermal exposure to JP-8. These responses may serve as indicators of skin injury following exposure to JP-8 jet fuel and other volatile chemicals or mixtures.

Mixture effects of JP-8 additives on the dermal disposition of jet fuel components

Aliphatic and aromatic components in formulated jet fuels can cause occupational dermatitis. However, the influence of JP-8 performance additives (DIEGME, 8Q21, and Stadis450) on the dermal disposition of fuel components is not well understood. These additives are formulated with commercial Jet-A to form military JP-8 fuel. The purpose of this study is to assess the influence of these additives on the dermal disposition of marker aromatic and aliphatic components, naphthalene and dodecane, respectively. Porcine skin sections in an in vitro system were used to characterize chemical-biological interactions that modulate diffusion of jet fuel components and isolated perfused porcine skin flaps (IPPSFs) were used to evaluate diffusion in a viable skin model with an intact microvasculature. In these 5-h studies, Jet-A, Jet-A + DIEGME, Jet-A + 8Q21, and Jet-A + Stadis450, Jet-A + DIEGME + 8Q21, Jet-A + DIEGME + Stadis450, Jet-A + 8Q21 + Stadis450, and JP-8 mixtures were tested. In general, naphthalene absorption (0.76-2.39% dose) was greater than dodecane absorption (0.10-0.84% dose), while the IPPSFs alone demonstrated that dodecane absorption was significantly greater in JP-8 than in Jet-A. Synergistic interactions with 8Q21 + Stadis450 appear to enhance systemic absorption of either naphthalene or dodecane, while DIEGME + Stadis450 increased naphthalene (1.88% dose) and dodecane (2.02% dose) penetration into the skin and fat tissues of IPPSFs. These findings were supported by the fact that 8Q21 + Stadis450 significantly increased dodecane flux and permeability in porcine skin sections, but 8Q21 alone reduced marker diffusion in both membrane systems. Furthermore, dodecane is more likely than naphthalene to remain in the stratum corneum and skin surface at 5 h, and DIEGME mixtures played a significant role in skin and surface retention of both markers. In summary, the data suggest that various combinations of these three performance additives in JP-8 can potentially alter the dermal disposition of aromatic and aliphatic fuel components in skin. More importantly, products of two-factor interactions were not predictable from single-factor exposures and, by extension, cannot be extrapolated to three-factor interactions.

Identification of target genes responsive to JP-8 exposure in the rat central nervous system

Concern for the health risk associated with occupational exposure to jet fuel has emerged in the Department of Defense. Jet propulsion fuel-8 (JP-8) is the fuel used in most US and North Atlantic Treaty Organization (NATO) jet aircraft, and will be the predominant fuel both for military land vehicles and aircraft into the twenty-first century. JP-8 exhibits reduced volatility and lower benzene content as compared to JP-4, the predominant military aircraft fuel before 1992, possibly suggesting greater occupational exposure safety. However, the higher rates of occupational exposure through fueling and maintenance of increasingly larger numbers of aircraft/vehicles raise concerns with respect to toxicity. Clinical studies of workers experiencing long-term exposure to certain jet fuels demonstrated deficits in CNS function, including fatigue, neurobehavioral changes, psychiatric disorders, and abnormal electroencephalogram (EEG). In the present study, cDNA nylon arrays (Atlas Rat 1.2 Array, Clontech Laboratories, Palo Alto, CA) were utilized to measure changes in gene expression in whole brain tissue of rats exposed repeatedly to JP-8, under conditions that simulated possible real-world occupational exposure (6 h/day for 91 days) to JP-8 vapor at 1,000 mg/m3. Gene expression analysis of the exposure group compared to the control group revealed a modulation of several genes, including glutathione S-transferase Yb2 subunit (GST Yb2); cytochrome P450 IIIAl (CYP3A1); glucose-dependent insulinotropic peptide (GIP); alpha1-proteinase inhibitor (alpha1-AT); polyubiquitin; GABA transporter 3 (GAT-3); and plasma membrane Ca2+-transporting ATPase (brain isoform 2) (PMCA2). The implications of these vapor-induced changes in gene expression are discussed.

Cytokine induction as a measure of cutaneous toxicity in primary and immortalized porcine keratinocytes exposed to jet fuels, and their relationship to normal human epidermal keratinocytes

The purpose of this study was to identify biomarkers of toxicity in primary porcine keratinocytes (PKC) and an immortalized porcine keratinocyte cell line (MSK3877) exposed to jet fuels Jet A, JP-8, and JP-8+100. Cells were exposed to 0.1% jet fuels and assayed for interleukin-8 (IL-8) and tumor necrosis factor alpha (TNF-alpha) mRNA using the TaqMan real time quantitative reverse transcriptase PCR assay. IL-8 and TNF-alpha protein release was measured using an ELISA. PKC exposed to jet fuels caused a slight upregulation of TNF-alpha mRNA at early time points, but no significant differences in TNF-alpha protein production were detected. IL-8 mRNA was increased at 4 h following exposure, and IL-8 protein was increased at 8 h. In MSK 3877 cells, jet fuels were shown to increase the production and expression of TNF-alpha mRNA and protein at 30 min and 1 h following exposure, respectively. IL-8 mRNA was only slightly induced compared to control. IL-8 protein release was suppressed by jet fuel exposure. These results were compared with those of a previous study in our laboratory to evaluate the utility of using porcine cells in lieu of normal human epidermal keratinocytes (NHEK). Similarities exist between PKC and NHEK with respect to both TNF-alpha and IL-8 production. The expression profile of TNF-alpha in MSK3877 cells mimics that of NHEK. In contrast, the profile of IL-8 expression opposes that of PKC and NHEK. These results suggest that porcine keratinocytes are susceptible to jet fuel toxicity. However, the responses of immortalized cells may vary from those of PKC and NHEK necessitating cautious interpretation of such data.