In vitro percutaneous absorption of the fragrance ingredient musk xylol

Predicting human skin absorption of chemicals: development of a novel quantitative structure activity relationship

The objective of this study was to construct and validate a quantitative structure-activity relationship model for skin absorption. Such models are valuable tools for screening and prioritization in safety and efficacy evaluation, and risk assessment of drugs and chemicals. A database of 340 chemicals with percutaneous absorption was assembled. Two models were derived from the training set consisting 306 chemicals (90/10 random split). In addition to the experimental Kow values, over 300 2D and 3D atomic and molecular descriptors were analyzed using MDL's QsarIS computer program. Subsequently, the models were validated using both internal (leave-one-out) and external validation (test set) procedures. Using the stepwise regression analysis, three molecular descriptors were determined to have significant statistical correlation with Kp (R2 = 0.8225): logKow, ×0 (quantification of both molecular size and the degree of skeletal branching), and SsssCH (count of aromatic carbon groups). In conclusion, two models to estimate skin absorption were developed. When compared to other skin absorption QSAR models in the literature, our model incorporated more chemicals and explored a large number of descriptors. Additionally, our models are reasonably predictive and have met both internal and external statistical validations. Toxicology and Industrial Health 2007; 23: 39—45.

Absorption of Lawsone Through Human Skin

Lawsone (2-hydroxy-1,4-naphthoquinone) is the principal color ingredient in henna, a color additive approved with limitations for coloring hair by the Food and Drug Administration (FDA) under 21 CFR 73.2190. In 2002, the scientific committee on cosmetics and non-food products (SCCNFP), now known as the scientific committee for consumer products (SCCP), evaluated the safety of lawsone as a coloring agent in hair dye products of the European Union (EU). The SCCNFP concluded that lawsone was mutagenic and not suitable for use as a hair coloring agent. As a result, studies were conducted to measure the extent of lawsone absorption through human skin. Lawsone skin absorption was determined from two hair coloring products and two shampoo products, all containing henna. [(14)C]-Lawsone (sp. act. 22.9 mCi/mmol) was added to each commercial product and the products were applied to dermatomed, nonviable human skin mounted in flow-through diffusion cells perfused with a physiological buffer (HEPES-buffered Hanks' balanced salt solution, pH 7.4). Products remained on the skin for 5 minutes (shampoos) and 1 hour (hair color paste). For the henna hair paste products, 0.3 and 1.3% of the applied dose was absorbed into the receptor fluid in 24 hours while 2.2 and 4.0% remained in the skin. For both henna shampoo products, 0.3% of the applied dose was absorbed into the receptor fluid at 24 hours while 3.6 and 6.8% remained in the skin. For all products, most of the lawsone applied was washed from the surface of the skin (83-102%) at the end of the exposure period. Extended absorption studies were conducted for 72 hours to determine if skin levels of lawsone in the 24 hour studies might eventually be percutaneously absorbed. These studies determined that the majority of the lawsone remained in the skin with only a small but significant increase (for three out of four products) in receptor fluid values. Therefore, it appears that receptor fluid values would give a good estimate of lawsone absorption for an exposure estimate and that skin levels of lawsone need not be included.

Temporal trends of synthetic musk compounds in mother's milk and associations with personal use of perfumed products

We analyzed two nitro musks (musk xylene and musk ketone) and five polycyclic musks (HHCB, AHTN, ADBI, ATII, and AHDI) in mother's milk from primiparae women (N = 101) living in Uppsala County, Sweden, 1996-2003. Possible temporal trends in musk concentrations and associations with lifestyle/medical factors, such as use of perfumed products during pregnancy were studied. HHCB showed the highest median concentration (63.9 ng/g lipid) followed by AHTN (10.4 ng/g) and musk xylene (MX) (9.5 ng/g). Concentrations of the other substances were, in most cases, below the quantification limit (2.0-3.0 ng/g). Women with a high use of perfume during pregnancy had elevated milk concentrations of HHCB, and elevated concentrations of AHTN were observed among women reporting use of perfumed laundry detergent. This strongly suggests that perfumed products are important sources of musk exposure both among the mothers and the nursed infants. Concentrations of AHTN and MX declined significantly between 1996 and 2003, suggesting a decline in the industrial use of the compounds in consumer products, or alterations in the consumer use pattern of perfumed products. No temporal trend in HHCB concentrations was seen. The lack of toxicity data makes it difficult to generalize about the safety of musk exposure of breast-fed infants.

Comparison of the human skin grafted onto nude mouse model with in vivo and in vitro models in the prediction of percutaneous penetration of three lipophilic pesticides

The evaluation of the degree of percutaneous penetration of agrochemicals is a key part of risk assessment for operators. The availability of suitable and predictive experimental models is crucial, in particular in the case of lipophilic compounds which persist in the stratum corneum (SC). Regulatory models (rat in vivo, human and rat in vitro) and the innovative human skin grafted onto nude mice (HuSki) model were compared for their ability to predict the human skin absorption. Radiolabelled malathion, lindane and cypermethrin (4microg/cm(2)) were topically applied to each model. The % of applied dose absorbed and that present in skin and SC were evaluated at 24h. Additionally, the absorption profile of cypermethrin was evaluated in the in vivo rat and HuSki models for up to 11 days. We found that the human in vitro and HuSki models closely predicted the human skin absorption at 24h, while rat models overestimated the human skin absorption. Furthermore, our experiments with cypermethrin indicated that evaluation of % percutaneous absorption over extended periods of time was feasible with the HuSki model. In our studies the HuSki model overcame the limitations of the regulatory models and is promising to realistically refine the dermal absorption assessment of topically applied chemicals.

In vitro human skin penetration of diethanolamine

Concerns about the safety of diethanolamine (DEA) have been raised by the National Toxicology Program (NTP). Therefore, we measured the extent of DEA absorption in human skin relevant to exposures from shampoos, hair dyes and body lotions. Radiolabeled [14C]-DEA was added to two commercial products from each class and applied to excised viable and non-viable human skin in flow-through diffusion cells. The products remained on the skin for 5, 30 and 24 h for shampoos, hair dyes and body lotions, respectively. After 24 h, most of the absorbed dose was found in skin: 2.8% for shampoos, 2.9% for hair dyes and 10.0% for body lotions. Only small amounts were absorbed into the receptor fluid: 0.08%, 0.09% and 0.9% for shampoos, hair dyes and body lotions respectively. There was no significant difference in the absorption of DEA through viable and non-viable skin or from product application doses of 1, 2 or 3 mg lotion/cm2. In 72 h daily repeat dose studies with a lotion, DEA appeared to accumulate in the skin (29.2%) with little diffusing out into the receptor fluid. Therefore, skin levels of DEA should not be included in estimates of systemic absorption used in exposure assessments.

Fate of chemicals in skin after dermal application: does the in vitro skin reservoir affect the estimate of systemic absorption?

Recent international guidelines for the conduct of in vitro skin absorption studies put forward different approaches for addressing the status of chemicals remaining in the stratum corneum and epidermis/dermis at the end of a study. The present study investigated the fate of three chemicals [dihydroxyacetone (DHA), 7-(2H-naphtho[1,2-d]triazol-2-yl)-3-phenylcoumarin (7NTPC), and disperse blue 1 (DB1)] in an in vitro absorption study. In these studies, human and fuzzy rat skin penetration and absorption were determined over 24 or 72 h in flow-through diffusion cells. Skin penetration of these chemicals resulted in relatively low receptor fluid levels but high skin levels. For DHA, penetration studies found approximately 22% of the applied dose remaining in the skin (in both the stratum corneum and viable tissue) as a reservoir after 24 h. Little of the DHA that penetrates into skin is actually available to become systemically absorbed. 7NTPC remaining in the skin after 24 h was approximately 14.7% of the applied dose absorbed. Confocal laser cytometry studies with 7NTPC showed that it is present across skin in mainly the epidermis and dermis with intense fluorescence around hair. For DB1, penetration studies found approximately 10% (ethanol vehicle) and 3% (formulation vehicle) of the applied dose localized in mainly the stratum corneum after 24 h. An extended absorption study (72 h) revealed that little additional DB1 was absorbed into the receptor fluid. Skin levels should not be considered as absorbed material for DHA or DB1, while 7NTPC requires further investigation. These studies illustrate the importance of determining the fate of chemicals remaining in skin, which could significantly affect the estimates of systemically available material to be used in exposure estimates. We recommend that a more conclusive means to determine the fate of skin levels is to perform an extended study as conducted for DB1.

In vitro and in vivo percutaneous absorption of catechol

The Cosmetic Ingredient Review Expert Panel found insufficient data to conclude that catechol could be used safely in permanent hair dye products. Information was lacking on the extent of oxidation and skin absorption of remaining catechol. In vitro percutaneous absorption studies were conducted in human and rat skin using a consumer permanent hair dye spiked with 0.6% catechol. A 30-min application demonstrated 0.4% of the applied dose was absorbed through human skin and 0.2% through rat skin. The minimal absorption observed was due to the short exposure time and to partial oxidation of catechol by the dye developer. The fate of catechol remaining in rat skin after exposure in vitro and in vivo was investigated with additional absorption studies using catechol in ethanol. At 72 h, 24-h application of 4% catechol resulted in skin absorption of 81% of the applied dose in vitro and 53% in vivo. Skin levels measured at 24 h remained unchanged after 72 h. Therefore the skin reservoir did not contribute to the estimated systemic absorption. A deconvolution technique employed to predict skin absorption using plasma levels from intravenous and dermal administration overestimated in vivo skin absorption due to volatility of catechol in an ethanolic vehicle.

Transition of nitro musks and polycyclic musks into human milk

Synthetic musks are widely used in various consumer products. The identification of nitro musks in human milk in the early 1990s in connection with evidence for cancerogenicity in animal experiments have caused public concern. However, the validity of previously reported quantitative data has been questioned. Polycylic musks have hardly been investigated so far. The present study aimed at providing accurate current data on the occurrence of nitro and polycyclic musks in human milk. Samples from 40 healthy breast feeding mothers were analysed under carefully controlled conditions avoiding secondary contamination. As in earlier studies, among the nitro compounds musk xylene and ketone were the most frequently detected substances. However, much lower concentrations (roughly by a factor of 10) were found (musk xylene: median 6.1 ng/kg fat). Among the polycylic musks HHCB was found in most samples (median 64 ng/kg fat). Scientific knowledge on possible routes of exposure and health risk aspects is summarized and discussed.

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.

In vitro percutaneous absorption models

In vitro skin absorption studies are commonly used to estimate in vivo skin absorption in topical safety and efficacy evaluations. In vitro studies are more economical and result in minimization or elimination of the use of animals.

Effects of musk xylene and musk ketone on rat hepatic cytochrome P450 enzymes

The purpose of the present work was to characterize the effect of musk xylene (MX) and musk ketone (MK) treatment on rat hepatic cytochrome P450 enzymes. Male F344 rats were dosed orally with MX (10, 50 or 200 mg/kg) or MK (20, 100 or 200 mg/kg) for 7 days, after which CYP1A, 2B and 3A enzyme activities and protein levels were determined. MX treatment resulted in a two- to four-fold increase in the activity of CYP1A, 2B and 3A enzymes. For CYP1A and 3A, these changes were consistent with small increases in immunoreactive proteins. However, for CYP2B, despite only a three-fold increase in enzyme activity, protein levels were increased nearly 50-fold relative to control. This induction occurred by transcriptional activation of the CYP2B1 gene as evidenced by increased steady state CYP2B1 mRNA levels. In contrast to MX, MK treatment increased CYP2B activity, protein and mRNA levels. However MK treatment also increased CYP1A enzyme activity nearly 30-fold higher than control rats, a profile that was markedly different from MX, and very different from its effects in mice (Stuard, S.B., Caudill, D., Lehman-Mc-Keeman, L.D., 1997. Characterization of the effects of musk ketone on mouse cytochrome P450 enzymes. Fund. Appl. Toxicol. 40, 264-271). These results indicate that in rats, MX is an inducer of CYP2B enzymes, but these enzymes are not functionally active. In contrast, MK also induces CYP2B enzymes, with no concurrent inactivation. MK also exhibits a unique pattern of cytochrome P450 induction by increasing both CYP1A and CYP2B in rats.

The systemic exposure to the polycyclic musks, AHTN and HHCB, under conditions of use as fragrance ingredients: evidence of lack of complete absorption from a skin reservoir

7-Acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN) and 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexa-methylcyclopenta-gamma-2-be nzopyran (HHCB) are two large volume fragrance ingredients widely used in consumer products. As part of the risk evaluation, the systemic exposures to these materials was determined in rats under occlusion and in humans under simulated conditions of exposure. Ring 14C-labeled AHTN or HHCB were applied dermally in alcoholic solutions to rats at doses of 4.5 mg/kg and occluded for 6 h. Urine, feces and air were collected for up to 120 h and analyzed for radioactivity. Pairs of rats were sacrificed periodically for analysis of tissues and organs. The total amount absorbed was approximately 19% for AHTN and 14% for HHCB. In both cases, significant amounts diffused into the skin, most of which was further absorbed but a significant amount of which was lost to surface dressing by reverse diffusion and/or desquamation. Ring 14C-labeled AHTN or HHCB were applied in alcoholic solutions without occlusion to three male volunteers at concentrations approximating that which might be encountered in a typical cologne type product. After a 6-h period, all material was removed from the surface of the skin. Blood, feces and urine were collected over a 5-day period. For both materials, levels in blood and plasma were below limits of detection at all times. Based on excretion, primarily in the urine, the total absorbed dose was approximately 1 and 0.1% for AHTN and HHCB, respectively. However, over the 5-day period, 14.5% of AHTN and 19.5% of HHCB was recovered from the skin in dressings over the site of application indicating that a 'reservoir' had formed in the skin but the material in the reservoir was lost, by desquamation and/or by reverse absorption, and not available systemically. A mean of 24% (AHTN) and 22% (HHCB) was shown to evaporate under the conditions of exposure.

Dermal absorption and disposition of musk ambrette, musk ketone and musk xylene in rats

Dermal doses of carbon-14 labelled musk ambrette (MA), musk ketone (MK) or musk xylene (MX) to male Sprague-Dawley CD rats were applied at a nominal dose level of 0.5 mg/kg (11 microg/cm2 of skin) and excess material removed at 6 h. Means of about 40, 31 and 19% of the applied doses of MA, MK and MX, respectively, were absorbed. Most of the absorbed material was excreted within 5 days with only 1-2% of the applied dose remaining in the animal at this time. Tissue concentrations of radiolabel were similar for all three compounds with peak concentrations occurring at 6-8 h. In general, fat and liver contained the highest concentrations at around 0.2 microg nitromusk equivalents/g but concentrations in fat declined fairly rapidly to around 0.005 microg equiv./g at 120 h. Most of the absorbed dose was eliminated in bile mainly in the form of polar conjugated metabolites. Structural characterisation of the major aglycones for MA and MX indicated that they were hydroxylated analogues formed by oxidation of the ring methyl. Repeated daily dosing for 14 days resulted in little bioaccumulation for musk xylene and accumulation of about three-fold for musk ketone.

Biotransformation and toxicokinetics of musk xylene in humans

Musk xylene (1-tert-butyl-3,5-dimethyl-2,4,6-trinitrobenzene, MX) is widely used as a fragrance ingredient in detergents and toiletries and is an environmental contaminant. High concentrations of MX have been found in fish, and humans are constantly exposed to MX as a result of its stability in the environment. We investigated the biotransformation and toxicokinetics of MX in humans. A single dose of 0.3 mg/kg body wt of 15N-labeled MX (15N-MX) was given to six volunteers (three male and three female) by the oral route and to another six volunteers (three males and three females) by the dermal route. Urine was collected for 96 h after exposure. Blood samples were taken at intervals for up to 140 days after administration. The metabolite 1-tert-butyl-3,5-dimethyl-15N-4-amino-2,6-dinitrobenzene in urine and 15N-MX in plasma were quantified by gas chromatography/electron-capture mass spectrometry (GC-MS/NCI). Peak plasma concentrations of 15N-MX after oral administration were 36-262 and 1.6-5.5 ng/ml plasma after dermal administration. The toxicokinetics of 15N-MX in plasma can be described by a two-compartment kinetic model with an initial rapid decrease, due to the distribution from the blood into a second compartment (likely fat tissue) and a terminal elimination phase with an average half-life of 70 days for both routes of administration. The amount of 1-tert-butyl-3,5-dimethyl-15N-4-amino-2,6-dinitrobenzene (15N-4-A-MX) in recovered urine represented 0.1-0.5% of the oral applied dose of 15N-MX, respectively, 0.02-0.16% of dermal dose. After a short time of invasion the concentrations of 15N-4-A-MX in urine reached a maximum 18-24 h after administration. The further elimination of the metabolite occurred by first-order kinetics with an average elimination half-life of 11.8 h. After the single oral or dermal dose of 15N-MX, 15N-4-A-MX was not detected in hemoglobin. However, hemoglobin samples contained 1-tert-butyl-3, 5-dimethyl-4-amino-2,6-dinitrobenzene (4-A-MX) (11.4-18.9 fmol/mg Hb), likely derived from chronic environmental exposures.

Assessment of organic contaminant fate in waste water treatment plants. I: Selected compounds and physicochemical properties

An extensive and comprehensive literature review has been conducted for compounds which we hypothesise could be present in sludge and maintain their integrity following application to agricultural land. The following compounds have been selected for review; chlorinated paraffins, quintozene, brominated diphenyl ethers, polychlorinated naphthalenes, polydimethylsiloxanes, chloronitrobenzenes, and a range of biologically active and pharmaceutical compounds. All have received interest as a result of their persistence and/or toxicity in environmental media. Physicochemical property information has also been compiled and/or calculated. In this way, an accompanying paper will attempt to predict compound fate in waste water treatment plants (WWTPs) and assess likely transfers from soil/plants to grazing livestock. These papers describe a first attempt to predict the fate of these classes of compounds in the environment and prioritise those of greatest concern.

Bioaccumulation of musk xylene (MX) in developing and adult rats of both sexes

Bioaccumulation of musk xylene (MX) was measured by GC-ECD in adult and developing Long Evans rats. Males and females were fed with MX-containing chow (0.001, 0.01, 0.033, 0.1 g MX/kg food pellets) for 10 weeks before mating. Treatment continued during pregnancy and lactation. Offspring exhibited dose-dependent MX accumulation with 1/2-3/4 of adult female or 3-4 times adult male body fat levels (at 0.1 mg/kg food) at days 1 and 14. Milk levels were comparable to adult female adipose tissue. Data indicate significant transplacental passage and exposure via maternal milk. In rats fed with MX in adulthood, levels were highest in adipose tissue with significant amounts in other organs (ovary, adrenal). Female tissue levels were 3.7-6.8 times higher. This unexplained sex difference was unrelated to lipid content and was absent in offspring.