Effect of JP-8 jet fuel on molecular and histological parameters related to acute skin irritation

Percutaneous absorption and skin irritation upon low-level prolonged dermal exposure to nonane, dodecane and tetradecane in hairless rats

Even though the dermal toxicity of hydrocarbon fuels has been well established in the literature, there is little information available on the dermal penetration kinetics and irritation potential of the individual hydrocarbons. The penetration and skin retention of nonane, dodecane and tetradecane was assessed in vitro using hairless rats’ skin. The effects of unocclusive dermal exposures of these chemicals (15 mL every 2 h for 8 h a day for four days) on the transepidermal water loss (TEWL) and erythema were measured in CD hairless rats. The expression of interleukin 1a (IL-1a) and TNF-a in the skin and blood were measured at the end of dermal exposures. The flux of dodecane was 3- and 77-fold higher than nonane and tetradecane. The retention of chemicals in stratum corneum (SC) was in the order of tetradecane-dodecane-nonane, and directly correlated to the log Kp (r2-0.9900) and molecular weight of the chemicals (r2-0.8782). The TEWL and erythema data indicate that irritation was in the following order: tetradecane-dodecane-nonane. Likewise, the expression of IL-1a in the blood and TNF-a in the skin after dermal exposures was higher for tetradecane followed by dodecane and nonane compared to control. In conclusion, the aliphatic hydrocarbon chemicals of the present study induced cumulative irritation upon low-level repeat exposures for a four-day period. The affinity of the chemicals to SC and their gradual accumulation in the skin in the present study is the probable cause for the differences in the skin irritation profiles of different aliphatic chemicals. The findings of the present study will be helpful in understanding the skin irritation response of the chemicals in humans; indeed the reality check arises from dermal exposures in humans and human experience in occupational handling of these chemicals.

In Vitro Pro-inflammatory Regulatory role of Substance P in Alveolar Macrophages and Type II Pneumocytes after JP-8 Exposure

The effects of JP-8 on pro-inflammatory cytokine interleukin (IL)-1alpha,beta and nitric oxide (NO) secretion as well as the role of substance P (SP) in these processes were examined in cultured alveolar macrophages (AM), type II epithelial cells (AIIE), and AM/AIIE co-cultures. Exposure of AM to JP-8 for 24 hr exhibited release of IL-1alpha,beta, whereas exposure to AIIE showed a concentration-dependent NO overproduction. Data indicate that there are cell-dependent inflammatory mechanisms responsible for the actual level of JP-8 exposure in alveoli. However, treatment with substance P significantly attenuated JP-8 induced the IL-1alpha,beta secretion. This finding was confirmed by using [Sar(9) Met (O(2))(11)] SP (10(- 10) M), an agonist of substance P, suggesting that substance P may have signal pathway(s) to AM in the inflammatory response mediated by IL-1. Moreover, AM/AIIE co-culture obviously reduced NO overproduction observed in AIIE alone, suggesting that there may be cell interactions or communications between AM and AIIE in response to the JP-8 exposure.

IL-6 deficiency exacerbates skin inflammation in a murine model of irritant dermatitis

Contact dermatitis is the second most reported occupational injury associated with workers compensation. Inflammatory cytokines are closely involved with the development of dermatitis, and their modulation could exacerbate skin damage, thus contributing to increased irritancy. IL-6 is a pro-inflammatory cytokine paradoxically associated with both skin healing and inflammation. To determine what role this pleiotropic cytokine plays in chemically-induced irritant dermatitis, IL-6 deficient (KO), IL-6 over-expressing transgenic (TgIL6), and corresponding wild-type (WT) mice were exposed to acetone or the irritants JP-8 jet fuel or benzalkonium chloride (BKC) daily for 7 days. Histological analysis of exposed skin was performed, as was tissue mRNA and protein expression patterns of inflammatory cytokines via QPCR and multiplex ELISA. The results indicated that, following JP-8 exposure, IL-6KO mice had greatly increased skin IL-1β, TNFα, CCL2, CCL3, and CXCL1 mRNA and corresponding product protein expression when compared to that of samples from WT counterparts and acetone-exposed control mice. BKC treatment induced the expression of all cytokines examined as compared to acetone, with CCL2 significantly higher in skin from IL-6KO mice. Histological analysis showed that IL-6KO mice displayed significantly more inflammatory cell infiltration as compared to WT and TgIL6 mice in response to jet fuel. Analysis of mRNA for the M2 macrophage marker CD206 indicated a 4-fold decrease in skin of IL-6KO mice treated with either irritant as compared to WT. Taken together, these observations suggest that IL-6 acts in an anti-inflammatory manner during irritant dermatitis, and these effects are dependent on the chemical nature of the irritant.

Systemic molecular and cellular changes induced in rats upon inhalation of JP-8 petroleum fuel vapor

Limited information is available regarding systemic changes in mammals associated with exposures to petroleum/hydrocarbon fuels. In this study, systemic toxicity of JP-8 jet fuel was observed in a rat inhalation model at different JP-8 fuel vapor concentrations (250, 500, or 1000 mg/m(3), for 91 days). Gel electrophoresis and mass spectrometry sequencing identified the alpha-2 microglobulin protein to be elevated in rat kidney in a JP-8 dose-dependent manner. Western blot analysis of kidney and lung tissue extracts revealed JP-8 dependent elevation of inducible heat shock protein 70 (HSP70). Tissue changes were observed histologically (hematoxylin and eosin staining) in liver, kidney, lung, bone marrow, and heart, and more prevalently at medium or high JP-8 vapor phase exposures (500-1000 mg/m(3)) than at low vapor phase exposure (250 mg/m(3)) or non-JP-8 controls. JP-8 fuel-induced liver alterations included dilated sinusoids, cytoplasmic clumping, and fat cell deposition. Changes to the kidneys included reduced numbers of nuclei, and cytoplasmic dumping in the lumen of proximal convoluted tubules. JP-8 dependent lung alterations were edema and dilated alveolar capillaries, which allowed clumping of red blood cells (RBCs). Changes in the bone marrow in response to JP-8 included reduction of fat cells and fat globules, and cellular proliferation (RBCs, white blood cells-WBCs, and megakaryocytes). Heart tissue from JP-8 exposed animals contained increased numbers of inflammatory and fibroblast cells, as well as myofibril scarring. cDNA array analysis of heart tissue revealed a JP-8 dependent increase in atrial natriuretic peptide precursor mRNA and a decrease in voltage-gated potassium (K+) ion channel mRNA.

Expression Profiling of Human Epidermal Keratinocyte Response Following 1-Minute JP-8 Exposure

The cDNA microarray analysis of 9600 expressed sequence tags was performed to examine the gene expression changes in human epidermal keratinocytes after 1-minute JP-8 exposure; 151 genes were identified as JP-8 responsive and classified into 8 clusters by self organization map. Genes involved in basal transcription and translations were up-regulated, whereas genes related to DNA repair, metabolism, and keratin were mostly down-regulated. Genes encoded for growth factors, apoptosis, signal transduction, and adhesion were also altered. These results indicated that human keratinocyte responds to a single dose of JP-8 insult and revealed several cellular processes previously not associated with jet fuel exposure.

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.

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.

Assessment of skin absorption and irritation potential of arachidonic acid and glyceryl arachidonate using in vitro diffusion cell techniques

Arachidonic acid (AA), a precursor of pro-inflammatory mediators, and its glycerin ester, glyceryl arachidonate (GA), are reportedly used in cosmetic products. In vitro skin penetration of AA and GA and GA's ester hydrolysis was determined in flow-through diffusion cells. AA penetration with human and rat skin was 19.5% and 52.3% of the applied dose respectively, a substantial amount of which remained in the skin at 24h. Similar penetration results were obtained with GA in human skin. However, GA penetration through cultured skin (EpiDerm) was 51% of the applied dose, almost all of which appeared in the receptor fluid. At least 27.8% of GA penetrating skin was hydrolyzed to AA. In vitro methods were used to assess skin irritation in diffusion cells. Skin irritation of AA, sodium lauryl sulfate (SLS), and Tween 80 was determined by changes in transepidermal water loss (TEWL), skin viability (3-(4,5-dimethylthiaxol-2-yl)-2,5-diphenyltetrazolium bromide, MTT, formation), and cytokine release (IL-1alpha). SLS irritation was much less pronounced in an emulsion versus an aqueous vehicle. No significant irritation was observed in vitro from AA in an emulsion. This work predicts that AA would penetrate human skin in vivo and that it could be formed in skin from topically applied GA.

Estimation of proinflammatory biomarkers of skin irritation by dermal microdialysis following exposure with irritant chemicals

The aim of the present study was to quantify the release of proinflammatory biomarkers by dermal microdialysis after topical exposure with irritant chemicals, Jet fuel (JP-8) and xylene in rat skin. Occlusive dermal exposure (2h) was carried out with 230microl of JP-8 or xylene using Hill top chambers((R)). Linear microdialysis probes (10mm) were inserted in the dermis under urethane anesthesia. The dialysis fluid was pumped at a flow rate of 2microl/min and the dialysate was collected for 7h following probe insertion. The expression of substance P (SP), calcitonin-gene related peptide (CGRP) and prostaglandin E(2) (PGE(2)) in the dialysate following microdialysis was measured by enzyme immunoassay (EIA). The effect of pretreatment with an SP antagonist (SR-140333) and a PGE(2) inhibitor (celecoxib), 6 and 18h before the application of JP-8 was also assessed to further establish the sensitivity of the microdialysis set up. On similar lines, untreated and capsaicin treated control experiments were performed to compare with the SP release following JP-8 treatment. Further, we also investigated the SP release following topical application of xylene. The mean concentrations of SP after the application of JP-8 (90.01+/-3.31) and 3h after its removal (58.66+/-9.36) indicated that JP-8 induced significantly higher release of SP as compared to the baseline value (P<0.05). The release of SP following JP-8 treatment (58.66+/-9.36pg/ml) was comparable to capsaicin (58.18+/-11.29pg/ml). JP-8 exposure resulted in a significant increase (P<0.001) in PGE(2) levels over the baseline control at the end of 1 and 2h of exposure. JP-8 treatment also produced significant increase (P<0.001) in PGE(2) levels as compared to the untreated control during occlusion and 1h following its removal. There was a significant drop (P<0.05) in the PGE(2) levels by the end of 3h following exposure. Pretreatment with SR-140333 and celecoxib significantly reduced (P<0.05) SP and PGE(2) release induced by JP-8. The mean concentrations of SP following xylene exposure (25.50+/-8.80pg/ml) and 3h after its removal (34.37+/-5.61pg/ml) indicated its skin irritation potential. Unlike JP-8, xylene produced a significant increase in SP release only after the removal of occlusion. Pretreatment with SR-140333 significantly blocked the xylene induced SP release. CGRP was not detected in any of the samples. This study demonstrates that dermal microdialysis can be used to quantify skin irritation potential of JP-8 and related irritant chemicals.

Gene expression and target tissue dose in the rat epidermis after brief JP-8 and JP-8 aromatic and aliphatic component exposures

Exposures of jet propulsion fuel 8 (JP-8) to human and laboratory animal skin have resulted in skin irritation. JP-8 is a mixture of aromatic and aliphatic hydrocarbons, which in some cases have also been shown to be irritating to the skin. In an attempt to determine if aromatic or aliphatic components could mimic the JP-8-induced gene expression response, we exposed rats to JP-8, undecane (UND), tetradecane (TET), trimethylbenzene (TMB), and dimethylnaphthalene (DMN) for 1 h and examined the epidermis to characterize the gene expression response. We also measured the concentrations of the JP-8 components in the epidermis with gas chromatography/mass spectrometry after 1-h exposures to JP-8 and pure components to determine if differences in potency could be identified. Changes in gene expression, compared to sham treatment, were studied with microarray techniques and analyzed for changes in gene ontology categories. UND and TMB exposures caused the greatest number of changes in transcript levels compared to DMN and TET. When only the specific functional and signaling pathways that were changed by JP-8 were considered, these pathways were nearly all activated by the components, but to different extents. After pure component exposures, the epidermal concentrations of the components showed no significant differences, although the differences in magnitude of either total or pathway-specific gene expression differed by a factor of 10-fold. We conclude that no single component that we studied mimicked the gene expression resulting from the JP-8 exposure but that UND had the most similar responses. These data suggest that there are differences in potency between the four components studied.

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.

In vitro and in vivo comparison of dermal irritancy of jet fuel exposure using EpiDerm (EPI-200) cultured human skin and hairless rats

The purpose of this study was to evaluate an in vitro EpiDerm human skin model (EPI-200) to study the irritation potential of jet fuels (JP-8 and JP-8+100). Parallel in vivo studies on hairless rats on the dermal irritancy of jet fuels were also conducted. Cytokines are an important part of an irritation and inflammatory cascade, which are expressed in upon dermal exposures of irritant chemicals even when there are no obvious visible marks of irritation on the skin. We have chosen two primary cytokines (IL-1alpha and TNF-1alpha) as markers of irritation response of jet fuels. Initially, the EPI-200 was treated with different quantities of JP-8 and JP-8+100 to determine quantities which did not cause significant cytotoxicity, as monitored using the MTT assay and paraffin embedded histological cross-sections. Volumes of 2.5-50 microl/tissue (approximately 4.0-78 microl/cm2) of JP-8 and JP-8+100 showed a dose dependent loss of tissue viability and morphological alterations of the tissue. At a quantity of 1.25 microl/tissue (approximately 2.0 microl/cm2), no significant change in tissue viability or morphology was observed for exposure time extending to 48 h. Nonetheless, this dose induced significant increase in IL-1alpha and TNF-alpha release versus non-treated controls after 24 and 48 h. In addition, IL-1alpha release for JP-8+100 was significantly higher than that observed for JP-8, but TNF-alpha release after 48 h exposure to these two jet fuels was the same. These findings parallel in vivo studies on hairless rats, which indicated higher irritation levels due to JP-8+100 versus JP-8. In vivo, transepidermal water loss (TEWL) and IL-1alpha expression levels followed the order JP-8+100 > JP-8 > control. Further, in vivo TNF-alpha levels for JP-8 and JP-8+100 were also elevated but not significantly different from one another. In aggregate, these findings indicate that EPI-200 tissue model can be utilized as an alternative to the use of animals in evaluating dermal irritation.

Toxicity of jet fuel aliphatic and aromatic hydrocarbon mixtures on human epidermal Keratinocytes: evaluation based on in vitro cytotoxicity and interleukin-8 release

Jet fuels are complex mixtures of aliphatic (ALI) and aromatic (ARO) hydrocarbons that vary significantly in individual cytotoxicity and proinflammatory activity in human epidermal keratinocytes (HEK). In order to delineate the toxicological interactions among individual hydrocarbons in a mixture and their contributions to cutaneous toxicity, nine ALI and five ARO hydrocarbons were each divided into five (high/medium/low cytotoxic and strong/weak IL-8 induction) groups and intra/inter-mixed to assess for their mixture effects on HEK mortality and IL-8 release. Addition of single hydrocarbon to JP-8 fuel was also evaluated for their changes in fuel dermatotoxicity. The results indicated that when hydrocarbons were mixed, HEK mortality and IL-8 release were not all predictable by their individual ability affecting these two parameters. The lowest HEK mortality (7%) and the highest IL-8 production were induced with mixtures including high cytotoxic and weak IL-8 inductive ARO hydrocarbons. Antagonistic reactions not consistently correlated with ALI carbon chain length and ARO structure were evident and carried different weight in the overall mixture toxicities. Single addition of benzene, toluene, xylene or ethylbenzene for up to tenfold in JP-8 did not increase HEK mortality while single addition of ALI hydrocarbons exhibited dose-related differential response in IL-8. In an all ALI environment, no single hydrocarbon is the dominating factor in the determination of HEK cytotoxicity while deletion of hexadecane resulted in a 2.5-fold increase in IL-8 production. Overall, decane, undecane and dodecane were the major hydrocarbons associated with high cytotoxicity while tetradecane, pentadecane and hexadecane were those which had the greatest buffering effect attenuating dermatotoxicity. The mixture effects must be considered when evaluating jet fuel toxicity to HEK.

Effect of methyl substitution of benzene on the percutaneous absorption and skin irritation in hairless rats

The permeation rate and skin retention of benzene and methylbenzenes were assessed in vitro using hairless rat skin. The effects of unocclusive dermal exposures of these chemicals (15 microl every 2h for 8h a day for 4 days) on the transepidermal water loss (TEWL), erythema and skin histopathology were measured in CD hairless rats. The expression of IL-1 alpha and TNF-alpha in the skin and blood were measured at the end of dermal exposures. The flux of benzene was about 1.5-, 2.5- and 80-fold higher than toluene, xylene and tetramethyl benzene isomers (TMB), respectively, and the values were inversely correlated with molecular weight (r(2)=0.7455) and logoctanol-water partition coefficient (r(2)=0.7831). The retention of chemicals in stratum corneum (SC) was in the order of TMB>xylene>toluene approximately benzene. The TEWL and erythema data demonstrated that the irritation was in the following order: TMB>xylene>benzene. The histo-pathological examination showed that xylene and TMB induced granulocyte infiltration, swelling of the epidermis, and extensive disruption and damage of stratum corneum. Likewise, the expression of IL-1 alpha in the blood and TNF-alpha in the skin after dermal exposures was higher for TMB followed by xylene and benzene compared to control. In conclusion, the aromatic hydrocarbon chemicals induced cumulative irritation upon low-level repeat exposures for a 4-day period and the irritation increased with the number of methyl groups of benzene. The affinity of the chemical to SC and their gradual accumulation in the skin in the present study is the reason for the differences in the skin irritation profiles of different aromatic chemicals. Our ultimate goal is to develop a biologically based model that connects skin retention of chemical to the skin irritation response. The findings of the present study will be helpful in understanding the role of these chemicals in the jet fuel and various petroleum based fuels in inducing skin irritation response.

Stress induced in heart and other tissues by rat dermal exposure to JP-8 fuel

Limited information is available regarding the development of systemic organ stress by dermal exposure to JP-8 fuel. In this study, the systemic stress potential of this fuel is evaluated in a rat model subjected to dermal applications of JP-8 for 7 days at 300 microl per day. Tissue histology indicated that JP-8 induces morphological alterations that suggest that tissue stress in the heart is more substantial than stress in the kidney and liver. Immunoblot analysis of tissues revealed increased levels of the inducible heat shock protein 70 (HSP70) in the heart, kidney, and liver after this dermal JP-8 exposure. This exposure also leads to increased levels of heme oxygenase-1 (HO-1/HSP3) in the liver. Additionally during this exposure, a negative regulator of inflammation, IkappaBalpha (inhibitor of NF-kappaB), was increased in the liver, slightly increased in the kidney, and not increased in the heart. Two regions of the rat brain were also examined and HSP70 and IkappaBalpha were increased in the cerebellum but not significantly increased in the cortex. This study indicates dermal JP-8 exposure causes systemic alterations that are associated with cytoprotective activities (e.g., in the liver) as well as potentially toxic mechanisms (heart and kidney).

The effect of occlusive and unocclusive exposure to xylene and benzene on skin irritation and molecular responses in hairless rats

Aromatic hydrocarbons readily penetrate the skin on dermal exposure, leading to irritation, inflammation and cytotoxicity. The effects of short-term occlusive and long-term unocclusive dermal exposure to benzene and xylene on the skin irritation response (transepidermal water loss (TEWL), skin moisture content and erythema) and cytokine/chemokine expression (interleukin-1alpha (IL-1alpha), tumor necrosis factor-alpha (TNF-alpha) and monocyte chemoattractant protein-1 (MCP-1)) were investigated in hairless rats. Occlusive dermal exposure was carried out with 230 microL of the chemicals for 1 h using Hill top chambers. In unocclusive dermal exposure, 15 microL of the chemicals were applied to the skin every 2 h, for 8 h a day, for 4 days. The occlusive dermal exposure revealed a clear difference in the TEWL and erythema response of these chemicals (xylene>benzene) whereas unocclusive exposure revealed similar TEWL and erythema scores for both benzene and xylene. The expression of IL-1alpha was elevated 2.5- and 3.8-fold in response to occlusive and unocclusive exposure, respectively, vs control (P<0.01) for both the chemicals (benzene and xylene). Similarly, TNF-alpha levels were elevated about 2.4- and 6.0-fold as a result of occlusive and unocclusive exposure, respectively, vs control (P<0.01). These results show that unocclusive exposure induced significantly higher TNF-alpha expression than occlusive exposure (P<0.05). The MCP-1 expression in blood was slightly elevated compared with the control group, but this increase was not statistically significant (P>0.05). Similarly, MCP levels in skin were increased approximately 1.7- and 1.8-fold by occlusive and unocclusive exposure, respectively, compared with the control group (P<0.05). Our study demonstrates that the skin irritation profiles of benzene and xylene are similar and unocclusive long-term exposure to small amounts of these chemicals can induce more skin irritation and cytokine response than occlusive exposure.

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.

Acute and subacute dermal toxicity of Break-Free CLP®: a weapons cleaning and maintenance compound

Break-Free CLP((R)) is a commercial cleaning, lubricating and preserving compound used in both the military and civilian sectors for maintenance of small- and large-caliber weapons. Like many commercial mixtures, there is very little information available on the toxicity of Break-Free CLP. Studies were conducted to characterize the biological effects of single or repeat dermal application of Break-Free CLP to the clipped backs of CD-1 mice. Break-Free CLP was applied neat, 50 microl three times of week for up to 2 weeks. Foci of epithelial ulceration were observed in skin sections from 22% of Break-Free CLP-treated animals in conjunction with markedly thickened epithelium suggesting that robust epithelial regeneration was occurring in these animals. Skin histopathology of Break-Free CLP-treated animals closely matched the histopathology from mice treated repeatedly with 2% croton oil in acetone (dermal irritation positive control). Serum alkaline phosphatase activity was significantly (P < 0.05) lower for mice treated with Break-Free CLP, 2% croton oil or 7,12-dimethylbenz[a]anthracene (DMBA) compared with negative and vehicle control mice. Skin nitric oxide (NO) levels were not significantly elevated for mice treated with Break-Free CLP but were significantly elevated for mice treated with dermal irritation positive control compound DMBA. The cumulative skin changes in Break-Free CLP-treated animals support conducting a subchronic dermal application study. The observed decreases in serum alkaline phosphatase activity suggest that future studies should include the liver and bone as possible target organs. Additionally, dermal penetration studies could provide key health risk assessment information for characterizing the potential health risks associated with chronic dermal exposure to Break-Free CLP.

Assessment of skin irritation and molecular responses in rat skin exposed to nonane, dodecane and tetradecane

Aliphatic hydrocarbons constitute a major portion of jet fuels, kerosene and other solvents. This study investigated the effects of dermal exposures of selected aliphatic hydrocarbons (nonane, dodecane and tetradecane) on the skin irritation (erythema), transepidermal waterloss (TEWL) and expression of interleukin-1alpha (IL-1alpha), tumor necrosis factor (TNF-alpha) and monocyte chemoattractant protein-1 (MCP-1) in the skin and blood of hairless rats. Dermal exposures were carried out by occlusive application of chemicals (230 microl for 1 h, using Hill Top Chambers) for 1 h. The expression of IL-1alpha, TNF-alpha and MCP-1 was measured by enzyme immunoassay (EIA), and the regulatory proteins NFkappaB and IkappaBalpha were measured by Western blot analysis. The skin irritation and TEWL data indicate that the irritation was in the following decreasing order: nonane > dodecane > tetradecane. Likewise, nonane significantly increased the expression of IL-1alpha, TNF-alpha and MCP-1 in skin and blood as compared to control at different time points. Dodecane and tetradecane did not show any increase in the expression of IL-1alpha and MCP-1 as compared to control (P > 0.05), but the expression of TNF-alpha by dodecane and tetradecane was significantly higher than control at all time points. The release of cytokines by nonane exposure was further supported by activation of NFkappaB p65 and corresponding degradation of IkappaBalpha in the skin. In conclusion, this study demonstrates that the biophysical parameters (TEWL and erythema scores) were correlated to the biomarker expressions after dermal exposures with nonane but not with dodecane and tetradecane. Dodecane produced only mild irritation in response to experimental conditions of the present study and further did not show significant differences in IL-1alpha and MCP-1 levels in skin and blood. However, TNF-alpha was well expressed in response to all the chemicals. Tetradecane did not show any visible signs of skin irritation and also did not produce any significant difference in IL-1alpha and MCP-1 release profiles as compared with control. The expression of TNF-alpha in skin due to tetradecane support the fact that visually indistinguishable skin irritation reactions can induce significant changes in the biological marker profile.

Evaluation of gene expression profile of keratinocytes in response to JP-8 jet fuel

The skin is the principal barrier against any environmental insult. Therefore, there is a high risk for a large number of military and civilian personnel exposed to jet fuel JP-8 to suffer percutaneous absorption of this fuel. This paper reports the use of cDNA microarray to identify the gene expression profile in normal human epidermal keratinocytes exposed to JP-8 for 24-h and 7-day periods. The effects of JP-8 exposure on keratinocytes at these two different periods induced a set of genes with altered expression in response to this type of insult. Microarray data were visualized using a novel algorithm based on simple statistical analyses to reduce data dimensionality and identify subsets of discriminant genes. Predictive neural networks were built using a multiplayer perceptron to carry out a proper classification task in microarray data in the untreated versus JP-8-treated samples. The pattern of expressions in response to JP-8 provides evidences that detoxificant-related and cell growth regulator genes with the most variability in the level of expression may be useful genetic markers in adverse health effects of personnel exposed to JP-8. The approaches in our analysis provide a simple, safe, novel, and effective method that is reliable in identifying and analyzing gene expression in samples treated with JP-8 or over potential toxic agents. Gene expression data from these studies can be used to build accurate predictive models that separate different molecular profiles. The data establish the use and effectiveness of these approaches for future prospective studies.

Gene expression in rat skin induced by irritating chemicals

Occupational skin disease is the second most significant cause of occupational disease, after accidents. Irritation from occupational chemicals such as solvents, hydrocarbons, and surfactants are one cause of this disease. Gene expression studies provide useful information about normal processes in the skin and responses of the skin to exogenous chemicals. We exposed rats, cutaneously, to sodium lauryl sulfate (SLS, 1% and 10% aqueous solution), m-xylene (pure liquid), and d-limonene (pure liquid) for 1 h and measured transcriptional responses at the end of the exposure and 3 h later for comparison with untreated skin samples. Total skin RNA was isolated and analyzed using the Affymetrix RatTox U34 array. Using the Affymetrix software, we found that 234 of approximately 850 genes were detected as present in at least 80% of the normal skin samples. The largest number of these genes was related to metabolism, oxidative/cellular stress, and signal transduction. Limonene caused the largest change in mRNA levels with a total of 34 increased transcripts and 4 decreased transcripts. Xylene treatment resulted in 6 increased transcripts and 14 decreased transcripts, while 10% SLS caused 5 transcripts to increase and 17 to decrease. Only two transcripts were observed to change in skin following a 1% SLS exposure. Sodium lauryl sulfate transcript changes increased with dose and were maximum at 4 h. Limonene transcript changes were more numerous at 1 h than at 4 h. The observed differences may reflect different mechanisms of irritation.

The cytotoxicity of volatile JP-8 jet fuel components in keratinocytes

In vitro models are being used to evaluate the toxic and irritating effects of JP-8, a kerosene-based jet fuel. JP-8 components are volatile, which makes in vitro studies difficult to evaluate dose-response relationships due to changes in chemical dosimetry caused by evaporation from the exposure medium. An in vitro approach testing volatile chemical toxicity that we have recently developed was used to evaluate the toxicity of the JP-8 components m-xylene, 1-methylnaphthalene (1-MN), and n-nonane in keratinocytes. Partition coefficients were measured and used to estimate the chemical concentration in the keratinocytes. The EC50 for m-xylene and 1-MN decreased significantly (P < or = 0.05) at 1, 2, and 4h. For n-nonane, no significant decreases in the EC50 values were observed over time; marginal cytotoxicity of n-nonane in keratinocytes was observed at 1h. Within 4h, about 75-90% of each volatile chemical was observed to be lost from the exposure medium when tissues were exposed in unsealed 24-well plates. This decrease resulted in significantly higher medium chemical concentrations needed to obtain EC50 values when compared to tissues exposed in sealed vials. This study demonstrates that chemical evaporation during in vitro exposures can significantly affect toxicological endpoint measurements. Ultimately, relating target cell chemical concentration to cellular responses in vitro could be used in determining an equivalent external dose using a biologically-based mathematical model.

Dermal toxicity and microscopic alterations by JP-8 jet fuel components in vivo in rabbit

In this study, we investigated the skin irritation, macroscopic and microscopic barrier alteration in vivo in rabbits from aliphatic and aromatic components of jet propellant-8 (JP-8) jet fuel. Macroscopic barrier properties were evaluated by measuring transepidermal water loss (TEWL), skin capacitance, and skin temperature; microscopic changes were observed by light microscopy. Draize visual scoring system was used to measure skin irritation. We found significant (P<0.05) increase in temperature at the site of all chemically saturated patches immediately after patch removal in comparison to the control site. Tridecane (TRI) produced a greater increase in temperature and capacitance at all time points than all the other components of JP-8. Both the aliphatic and aromatic components increased the TEWL at all time points. Tridecane produced greater increase in TEWL followed by naphthalene (NAP), 1-methylnaphthalene (1-MN), 2-metylnaphthalene (2-MN), tetradecane (TET), and dodecane (DOD). All of the above components of JP-8 caused moderate to severe erythema and edema, which were not resolved to the baseline even after 24h of patch removal. Light microscopy revealed an increase in epidermal thickness (ET), and decrease in length and thickness of collagen fibers' bundle by the above components of JP-8. These results suggest potential dermatotoxicity from the JP-8 components.

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.

Molecular and histological responses in rat skin exposed to m-xylene

Solvents, surfactants, cutting fluids, hydrocarbons, and oils cause skin irritation by incompletely understood mechanisms. This study examined histological and molecular changes in rodent skin caused by brief topical exposures to m-xylene. At 0, 1, 2, 4, and 6 h after 1-h exposure, skin samples were removed and analyzed for histopathological changes and interleukin-1 alpha (IL-1 alpha) and inducible nitric oxide synthase (iNOS) protein levels. Histopathological changes (epidermal-dermal separation and granulocyte infiltration) and increases in IL-1 alpha and iNOS protein expression occurred during our observation period. IL-1 alpha levels increased by 80% immediately after exposure and iNOS levels increased about 60% 4 hours after exposure. Our study demonstrates that dermal exposure to m-xylene promotes IL-1 alpha and iNOS production in skin and these proteins may serve as early indicators of skin irritation.

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.

Gulf War related exposure factors influencing topical absorption of 14C-permethrin

Topical exposure to permethrin has often been implicated as a mitigating factor in the illnesses reported in Gulf War veterans. These studies were designed to assess the effect of co-exposure to low level sulfur mustard, JP-8 jet fuel, N,N-diethyl-m-toluamide (DEET) and fabric occlusion on the percutaneous absorption and skin disposition of topically applied 14C-permethrin (40 microg/cm(2)) in the isolated perfused porcine skin flap (IPPSF) model. Extent of dermal absorption in vehicle controls in the IPPSF was comparable to literature values for humans. These studies demonstrated a two-fold increased 14C-permethrin percutaneous absorption and almost three-fold increased penetration when JP-8 was present, compared to a one-third decreased permethrin flux in the presence of sulfur mustard. Complete occlusion slightly increased 14C-permethrin absorption, while occlusion with fabric showed no significant effect. A previously noted effect of DEET to inhibit permethrin absorption was still seen in the presence of sulfur mustard exposure. These studies suggest that co-exposure to JP-8 or sulfur mustard may modulate transdermal flux of 14C-permethrin. However, the JP-8 increase in absorption and penetration was less than the five-fold increase previously seen with arterial infusion of pyridostigmine bromide and diisopropylfluorophosphate in the IPPSF. The toxicologic significance of this moderate increase in permethrin absorption remains unclear.

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.

Assessment of dermal absorption and penetration of components of a fuel mixture (JP-8)

Occupational and environmental multi-chemical exposures are extremely common. Methods for assessment of the risks from dermal exposures to complex mixtures vary depending on the information available. The composition of a volatile mixture (such as JP-8 jet fuel) can change radically, depending on the phase of the mixture - vapor, liquid or aerosol. Assessing the absorption (into the skin) and penetration (through the skin) of components of the mixture can reduce uncertainty in the risk assessment process. Permeability coefficients of the 12 individual components that could be detected to penetrate the skin could be used to assess the toxicity of each individual component in the JP-8. The penetration of each of these components is related to and can be predicted from molecular weight and octanol water partition coefficients of that component. The composition of the components that penetrate the skin would be different from the composition of JP-8 because the permeability of the components differs by two orders of magnitude. Concentrations of the aliphatic chemicals found in the skin correlated well with carbon number. The JP-8 jet fuel is used as an example of how component data on absorption and penetration can be integrated into an assessment (McDougal et al., Toxicol Sci 2000; 55: 247-255). The component approach shows promise for estimating systemic toxicity of mixtures. Local toxicity (irritation, sensitization, etc.) may be better understood in the future when quantitative information becomes available about the duration and magnitude of chemical exposures required to cause local effects.

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.

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.