In vitro human nail penetration and kinetics of panthenol.

The in vitro absorption of panthenol into and through the human nail was examined in this study. Panthenol, the alcohol form of pantothenic acid (vitamin B5), is believed to act as a humectant and improve the flexibility and strength of nails. A liquid nail treatment formulated with panthenol (2%) was compared to a solution of panthenol (2%) in water. Fingernail specimens were dosed daily for 7 days with either the nail treatment (non-lacquer film forming) formulation or aqueous solution with sampling performed every 24 h. Panthenol concentrations were determined in the dorsal surface, interior (by drilling and removal) and in the supporting bed under the human nail. Panthenol levels in the dorsal nail (R(2) = 0.87; P < 0.001), nail interior (R(2) = 0.94; P < 0.001) and nail supporting bed (R(2) = 0.79; P < 0.003) showed a significant linear increase with each day of dosing. Significantly more panthenol was delivered into the interior nail and supporting bed by a nail treatment formulation than from an aqueous solution. The film acts not only as a reservoir of panthenol, but also acts to increase the hydration of the nail and the thermodynamic activity of panthenol as well, thereby enhancing diffusion.

Predicted chemical warfare agent VX toxicity to uniformed soldier using parathion in vitro human skin exposure and absorption.

Chemical warfare agents (CWA) are easily and inexpensively produced and are a significant threat to military forces and the public. Most well-known CWAs are organophosphorus compounds, a number or which are used as pesticides, including parathion. This study determined the in vitro percutaneous absorption of parathion as a CWA simulant through naked human skin and uniformed skin (dry and sweated). Parathion percentage dose absorbed through naked skin (1.78 +/- 0. 41) was greater than dry uniformed skin (0.29 +/- 0.17; p = 0.000) and sweated uniformed skin (0.65 +/- 0.16; p = 0.000). Sweated and dry uniformed skin absorption were also different (p = 0.007). These relative dry and sweated uniformed skin absorptions were then applied to VX skin permeability for naked skin (head, neck, arms, and hands) and the remaining uniformed skin over the various regions of the human body. Risk assessment shows VX 50% lethality within the first hour for a soldier wearing a sweated uniform. By 8 h postexposure to naked skin plus trunk area predicted lethality for both dry and sweated uniform, and, at 96 h postexposure, all body regions individually exposed would produce lethality. Military uniform and public clothing provide some immediate protection but absorption through cloth and skin does occur. Immediate safety response to skin and clothing is required.

Assessment of the percutaneous absorption of trichloroethylene in rats and humans using MS/MS real-time breath analysis and physiologically based pharmacokinetic modeling.

The development and validation of noninvasive techniques for estimating the dermal bioavailability of solvents in contaminated soil and water can facilitate the overall understanding of human health risk. To assess the dermal bioavailability of trichloroethylene (TCE), exhaled breath was monitored in real time using an ion trap mass spectrometer (MS/MS) to track the uptake and elimination of TCE from dermal exposures in rats and humans. A physiologically based pharmacokinetic (PBPK) model was used to estimate total bioavailability. Male F344 rats were exposed to TCE in water or soil under occluded or nonoccluded conditions by applying a patch to a clipper-shaved area of the back. Rats were placed in off-gassing chambers and chamber air TCE concentration was quantified for 3-5 h postdosing using the MS/MS. Human volunteers were exposed either by whole-hand immersion or by attaching patches containing TCE in soil or water on each forearm. Volunteers were provided breathing air via a face mask to eliminate inhalation exposure, and exhaled breath was analyzed using the MS/MS. The total TCE absorbed and the dermal permeability coefficient (K(P)) were estimated for each individual by optimization of the PBPK model to the exhaled breath data and the changing media and/or dermal patch concentrations. Rat skin was significantly more permeable than human skin. Estimates for K(P) in a water matrix were 0.31 +/- 0.01 cm/h and 0.015 +/- 0.003 cm/h in rats and humans, respectively. K(P) estimates were more than three times higher from water than soil matrices in both species. K(P) values calculated using the standard Fick's Law equation were strongly affected by exposure length and volatilization of TCE. In comparison, K(P) values estimated using noninvasive real-time breath analysis coupled with the PBPK model were consistent, regardless of volatilization, exposure concentration, or duration.

Understanding percutaneous absorption for occupational health and safety.

Local and systemic toxicity from percutaneous absorption depends on a chemical's penetrating the skin, which is both a barrier to absorption and a primary route to the systemic circulation. The skin's barrier properties are such that fluids and precious chemicals are reasonably retained within the body, while foreign chemicals are restricted from entering the systemic circulation. The skin is a primary body contact with the environment and the route by which many chemicals enter the body. In most instances, the toxicity of the chemical is slight and/or its bioavailability is too low to cause an immediate response. However, some chemicals are toxic when applied to the skin, and more chemicals that come in contact with the skin are being found to be potentially toxic. This article describes percutaneous absorption, methods to determine it, and factors that can affect it.

A real-time in-vivo method for studying the percutaneous absorption of volatile chemicals.

Realistic estimates of percutaneous absorption following exposures to solvents in the workplace, or through contaminated soil and water, are critical to understanding human health risks. A method was developed to determine dermal uptake of solvents under non-steady-state conditions using real-time breath analysis in rats, monkeys, and humans. The exhaled breath was analyzed using an ion-trap mass spectrometer, which can quantitate chemicals in the exhaled breath stream in the 1-5 ppb range. The resulting data were evaluated using physiologically-based pharmacokinetic (PBPK) models to estimate dermal permeability constants (Kp) under various exposure conditions. The effects of exposure matrix (soil versus water), occlusion versus non-occlusion, and species differences on the absorption of methyl chloroform, trichloroethylene, and benzene were compared. Exposure concentrations were analyzed before and at 0.5-hour intervals throughout the exposures. The percentage of each chemical absorbed and the corresponding Kp were estimated by optimization of the PBPK model to the medium concentration and the exhaled-breath data. The method was found to be sufficiently sensitive for animal and human dermal studies at low exposure concentrations over small body surface areas, for short periods, using non-steady-state exposure conditions.

Benzene percutaneous absorption: dermal exposure relative to other benzene sources.

Skin is one of several exposure routes whereby benzene, a widely distributed environmental contaminant that causes leukemia, enters the body, so accurate predictions of its percutaneous absorption are important for risk assessment. Determining benzene's skin-exposure dose and subsequent absorption is difficult because it has a low boiling point and exists as both liquid and vapor. Industrial and environmental benzene is present as a contaminant in other vehicles/solvents, and its percutaneous absorption is in part dependent upon co-solvent volatility. Co-solvents such as benzene in toluene rapidly evaporate from skin, whereas benzene contaminant in water is retained on skin longer due to water's lower volatility. Co-solvents can also affect benzene-skin partition coefficients; thus, permeability coefficients and percentage doses absorbed can vary many-fold. The exposure situation will determine percutaneous absorption, which, if low, can be overwhelmed by benzene intake from the food we eat and the air we breathe.

Utility of real time breath analysis and physiologically based pharmacokinetic modeling to determine the percutaneous absorption of methyl chloroform in rats and humans.

Due to the large surface area of the skin, percutaneous absorption has the potential to contribute significantly to the total bioavailability of some compounds. Breath elimination data, acquired in real-time using a novel MS/MS system, was assessed using a PBPK model with a dermal compartment to determine the percutaneous absorption of methyl chloroform (MC) in rats and humans from exposures to MC in non-occluded soil or occluded water matrices. Rats were exposed to MC using a dermal exposure cell attached to a clipper-shaved area on their back. The soil exposure cell was covered with a charcoal patch to capture volatilized MC and prevent contamination of exhaled breath. This technique allowed the determination of MC dermal absorption kinetics under realistic, non-occluded conditions. Human exposures were conducted by immersing one hand in 0.1% MC in water, or 0.75% MC in soil. The dermal PBPK model was used to estimate skin permeability (Kp) based on the fit of the exhaled breath data. Rat skin K(p)s were estimated to be 0.25 and 0.15 cm/h for MC in water and soil matrices, respectively. In comparison, human permeability coefficients for water matrix exposures were 40-fold lower at 0.006 cm/h. Due to evaporation and differences in apparent Kp, nearly twice as much MC was absorbed from the occluded water (61.3%) compared to the non-occluded soil (32.5%) system in the rat. The PBPK model was used to simulate dermal exposures to MC-contaminated water and soil in children and adults using worst-case EPA default assumptions. The simulations indicate that neither children nor adults will absorb significant amounts of MC from non-occluded exposures, independent of the length of exposure. The results from these simulations reiterate the importance of conducting dermal exposures under realistic conditions.

HPLC-accelerator MS measurement of atrazine metabolites in human urine after dermal exposure.

Metabolites of atrazine were measured in human urine after dermal exposure using HPLC to separate and identify metabolites and accelerator mass spectrometry (AMS) to quantify them. Ring-labeled [14C]atrazine was applied for 24 h with a dermal patch to human volunteers at low (0.167 mg, 6.45 muCi) and high (1.98 mg, 24.7 muCi) doses. Urine was collected for 7 days. The urine was centrifuged to remove solids, and the supernatant was measured by liquid scintillation counting prior to injection on the HPLC to ensure that < 0.17 Bq (4.5 pCi) was injected on the column. A reversed-phase gradient of 0.1% acetic acid in water and 0.1% acetic acid in acetonitrile became less polar with increasing time and separated the parent compound and major atrazine metabolites over 31 min on an octadecylsilane column. Peaks were identified by coelution with known standards. Elution fractions were collected in 1-min increments; half of each fraction was analyzed by AMS to obtain limits of quantitation of 14 amol. Mercapturate metabolites of atrazine and dealkylated atrazine dominated the early metabolic time points, accounting for approximately 90% of the 14C in the urine. No parent compound was detected. The excreted atrazine metabolites became more polar with increasing time, and an unidentified polar metabolite that was present in all samples became as prevalent as any of the known ring metabolites several days after the dose was delivered. Knowledge of metabolite dynamics is crucial to developing useful assays for monitoring atrazine exposure in agricultural workers.

In vivo skin decontamination of methylene bisphenyl isocyanate (MDI): soap and water ineffective compared to polypropylene glycol, polyglycol-based cleanser, and corn oil.

In the home and workplace, decontamination of a chemical from skin is traditionally done with a soap-and-water wash, although some workplaces may have emergency showers. It has been assumed that these procedures are effective, yet workplace illness and even death occur from chemical contamination. Water, or soap and water, may not be the most effective means of skin decontamination, particularly for fat-soluble materials. This study was undertaken to help determine whether there are more effective means of removing methylene bisphenyl isocyanate (MDI), a potent contact sensitizer, from the skin. MDI is an industrial chemical for which skin decontamination, using traditional soap and water and nontraditional polypropylene glycol, a polyglycol-based cleanser (PG-C), and corn oil were all tried in vivo on the rhesus monkey, over 8 h. Water, alone and with soap (5% and 50% soap), were partially effective in the first h after exposure, removing 51-69% of the applied dose. However, decontamination fell to 40-52% at 4 h and 29-46% by 8 h. Thus, the majority of MDI was not removed by the traditional soap-and-water wash; skin tape stripping after washing confirmed that MDI was still on the skin. In contrast, polypropylene glycol, PG-C, and corn oil all removed 68-86% of the MDI in the first h, 74-79% at 4 h, and 72-86% at 8 h. Statistically, polypropylene glycol, PG-C, and corn oil were all better (p < 0.05) than soap and water at 4 and 8 h after dose application. These results indicate that a traditional soap-and-water wash and the emergency water shower are relatively ineffective at removing MDI from the skin. More effective decontamination procedures, as shown here, are available. These procedures are consistent with the partial miscibility of MDI in corn oil and polyglycols.

Diclofenac metabolic profile following in vitro percutaneous absorption through viable human skin.

The extent of metabolism of diclofenac sodium in excised viable human skin was investigated using combination HPLC and radioactivity assay. In an earlier diffusion experiment using an in vitro flow-through diffusion system, radiolabelled diclofenac sodium in either lotion (Pennsaid) or aqueous solution was applied to viable human skin, either as single dose or multiple dose (8 times over 2 days). In this study, the receptor fluid samples from the diffusion experiment were subjected to extraction and the aliquot was analysed using HPLC to separate diclofenac and authentic metabolites. Based on the radioactivity of each HPLC fraction, the collection time of the fractions was compared with the retention time of diclofenac and metabolites in standard solutions. The samples from a single or multiple dose application of lotion showed radioactivity in mainly one fraction, whose retention time corresponded with diclofenac. Other HPLC fractions showed none or only small amounts of radioactivity within the error range of the assay. The same results were obtained with the pooled samples from the application of the lotion or of aqueous solution. The results suggest that diclofenac sodium does not undergo metabolism in viable human epidermis during percutaneous absorption in vitro. Hence, with topical application to human skin in vivo, diclofenac will be delivered with minimal, if any, metabolism.

In vivo percutaneous absorption of boric acid, borax, and disodium octaborate tetrahydrate in humans compared to in vitro absorption in human skin from infinite and finite doses.

Literature from the first half of this century report concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax, and disodium octaborate tetrahydrate (DOT) in biological matrices. This made it possible, in the presence of comparatively large natural dietary boron intakes for the in vivo segment of this study, to quantify the boron passing through skin. Human volunteers were dosed with 10B-enriched boric acid, 5.0%, borax, 5.0%, or disodium octaborate tetrahydrate, 10%, in aqueous solutions. Urinalysis, for boron and changes in boron isotope ratios, was used to measure absorption. Boric acid in vivo percutaneous absorption was 0.226 (SD = 0.125) mean percentage dose, with flux and permeability constant (Kp) calculated at 0.009 microgram/cm2/h and 1.9 x 10(-7) cm/h, respectively. Borax absorption was 0.210 (SD = 0.194) mean percentage of dose, with flux and Kp calculated at 0.009 microgram/cm2/h and 1.8 x 10(-7) cm/h, respectively. DOT absorption was 0.122 (SD = 0.108) mean percentage, with flux and Kp calculated at 0.01 microgram/cm2/h and 1.0 x 10(-7) cm/h, respectively. Pretreatment with the potential skin irritant 2% sodium lauryl sulfate had no effect on boron skin absorption. In vitro human skin percentage of doses of boric acid absorbed were 1.2 for a 0.05% solution, 0.28 for a 0.5% solution, and 0.70 for a 5.0% solution. These absorption amounts translated into flux values of, respectively, 0.25, 0.58, and 14.58 micrograms/cm2/h and permeability constants (Kp) of 5.0 x 10(-4), 1.2 x 10(-4), and 2.9 x 10(-4) cm/h for the 0.05, 0.5, and 5.0% solutions. The above in vitro doses were at infinite, 1000 microliters/cm2 volume. At 2 microliters/cm2 (the in vivo dosing volume), flux decreased some 200-fold to 0.07 microgram/cm2/h and Kp of 1.4 x 10(-6) cm/h, while percentage of dose absorbed was 1.75%. Borax dosed at 5.0%/1000 microliters/cm2 had 0.41% dose absorbed, flux at 8.5 micrograms/cm2/h, and Kp was 1.7 x 10(-4) cm/h. Disodium octaborate tetrahydrate (DOT) dosed at 10%/1000 microliters/cm2 was 0.19% dose absorbed, flux at 7.9 micrograms/cm2/h, and Kp was 0.8 x 10(-4) cm/h. These in vitro results from infinite doses (1000 microliters/cm2) were 1000-fold greater than those obtained in the companion in vivo study. The results from the finite (2 microliters/cm2) dosing were closer (10-fold difference) to the in vivo results. General application of infinite dose percutaneous absorption values for risk assessment is questioned by these results. These in vivo results show that percutaneous absorption of boron, as boric acid, borax, and disodium octaborate tetrahydrate, through intact human skin, is low and is significantly less than the average daily dietary intake. This very low boron skin absorption makes it apparent that, for the borates tested, the use of gloves to prevent systemic uptake is unnecessary. These findings do not apply to abraded or otherwise damaged skin.

In vivo bioavailability and metabolism of topical diclofenac lotion in human volunteers.

PURPOSE: The primary objective of this study was to determine the rate and extent of transdermal absorption for systemic delivery of diclofenac from Pennsaid (Dimethaid Research, Inc.) topical lotion into the systemic circulation after the lotion was applied to human volunteers, in an open treatment, non-blinded, non-vehicle controlled study. In addition, the in vivo metabolism of this topical diclofenac lotion has also been studied. METHODS: Human volunteers were dosed with topical [14C]-diclofenac sodium 1.5% lotion on the knee for 24 h. Sequential time blood and urine samples were taken to determine pharmacokinetics, bioavailability and metabolism. RESULTS: Topical absorption was 6.6% of applied dose. Peak plasma 14C occurred at 30 h after dosing, and peak urinary 14C excretion was at 24-48 h. The urinary 14C excretion pattern exhibits more elimination towards 24 h and beyond, as opposed to early urinary 14C excretion. This suggests a continuous delivery of [14C]-diclofenac sodium from the lotion into and through skin which only ceased when the dosing site was washed. Skin surface residue at 24 h was 26 +/- 9.5% dose (remainder assumed lost to clothing and bedding). Extraction of metabolites from urine amounted to 7.4-22.7% in untreated urine, suggesting substantial diclofenac metabolism to more water soluble metabolites, probably conjugates, which could not be extracted by the method employed. Two Dimensional TLC analysis of untreated urine showed minimal or no diclofenac, again emphasizing the extensive in vivo metabolism of this drug. Treatment of the same urine samples with the enzymes sulfatase and beta-glucuronidase showed a substantial increase in the extractable material. Three spots were consistently present in each sample run, namely diclofenac, 3'hydroxy diclofenac and an intermediate polar metabolite (probably a hydroxylated metabolite). Therefore, there was significant sulfation and glucuronidation of both diclofenac and numerous hydroxy metabolites of diclofenac, but many of the metabolites/conjugates remain unidentified. CONCLUSIONS; There was a continuous delivery of diclofenac sodium from the lotion into and through the skin, which ceased after the dosing site was washed. The majority of the material excreted in the urine were conjugates of hydroxylated metabolites, and not the parent chemical, although further identification is required.

Analytical performance of accelerator mass spectrometry and liquid scintillation counting for detection of 14C-labeled atrazine metabolites in human urine.

Accelerator mass spectrometry (AMS) has been applied to the detection of 14C-labeled urinary metabolites of the triazine herbicide, atrazine, and the analytical performance of AMS has been directly compared to that of liquid scintillation counting (LSC). Ten human subjects were given a dermal dose of 14C-labeled atrazine over 24 h, and urine from the subjects was collected over a 7-day period. Concentrations of 14C in the samples have been determined by AMS and LSC and range from 1.8 fmol/mL to 4.3 pmol/mL. Data from these two methods have a correlation coefficient of 0.998 for a linear plot of the entire sample set. Accelerator mass spectrometry provides superior concentration (2.2 vs 27 fmol/mL) and mass (5.5 vs 54,000 amol) detection limits relative to those of LSC for these samples. The precision of the data provided by AMS for low-level samples is 1.7%, and the day-to-day reproducibility of the AMS measurements is 3.9%. Factors limiting AMS detection limits for these samples and ways in which these can be improved are examined.

Percutaneous absorption of salicylic acid, theophylline, 2, 4-dimethylamine, diethyl hexyl phthalic acid, and p-aminobenzoic acid in the isolated perfused porcine skin flap compared to man in vivo.

Human risk assessment for topical exposure requires percutaneous absorption data to link environmental contamination to potential systemic dose. Human absorption data are not readily available, so absorption models are used. In vitro diffusion systems are easy to use but have proved to be somewhat unreliable and are not validated to man. This study compares percutaneous absorption in the isolated perfused porcine skin flap (IPPSF) system with that in man in vivo. The study design utilized the same compounds and the same dose concentration and vehicle in both systems. Methodology for each system was that which is routinely used ineach system. The skin surface was not protected during the absorption dosing period. Percutaneous absorption values were, for man and the IPPSF system, respectively: salicylic acid (6.5 +/- 5.0%; 7.5 +/- 2.6%), theophylline (16.9 +/- 11.3%; 11.8 +/- 3.8%), 2,4-dimethylamine (1.1 +/- 0.3%; 3.8 +/- 0.6%), diethyl hexyl phthalic acid (1.8 +/- 0.5%; 3.9 +/- 2.4%), and p-aminobenzoic acid (11.5 +/- 6.3%; 5.9 +/- 3.7%) (correlation coefficient was 0.78; p < 0.04). The skin surface wash recovery postapplication was similar for salicylic acid in man (53.4 +/- 6.3%) and the IPPSF system (48.2 +/- 4.9%). With the other compounds the majority of surface chemical was recovered in the surface wash and skin tape strip in the IPPSF system. With man, other than salicylic acid, only a few percent applied dose was recovered with surface washing and tape stripping. Since the wash procedure was effective with pig skin, we can assume that these chemicals in man were lost to adsorption to any clothing or bedding with the volunteers. The absorption in man was not less than that in the IPPSF. Assuming the dose was lost in man, it seems plausible that whatever compound was to penetrate human skin in solvent vehicle did so in the period of time before the chemical was removed. The IPPSF system appears to be a good model for predicting percutaneous absorption relative to man. This study design should be used to validate other systems to humans in vivo.

In vitro cutaneous disposition of a topical diclofenac lotion in human skin: effect of a multi-dose regimen.

PURPOSE: This study determines comparative bioavailability of diclofenac sodium lotion compared to an aqueous solution after topical application to viable human skin in vitro. In addition, the difference between a single dose and multiple doses (8 times) was also determined. METHODS: An in vitro flow-through diffusion cell system was employed, using radiolabelled diclofenac sodium. RESULTS: Multiple doses of lotion (2 microl/cm2 and 5 microl/cm2) delivered a total of 40.1 +/- 17.6 microg and 85.6 micro 41.4 microg diclofenac, respectively, at 48 h, compared to only 9.4 +/- 2.9 microg and 35.7 +/- 19.0 microg absorbed after topical application of diclofenac as an aqueous solution (P < 0.05). A single dose study showed no statistical difference between diclofenac delivered in lotion or an aqueous solution. Over 48 h the total absorption from lotion was 10.2 +/- 6.7 microg and 26.2 +/- 17.6 microg (2 microl/cm2 and 5 microl/cm2, respectively), compared to 8.3 +/- 1.5 microg and 12.5 +/- 5.7 microg from an aqueous solution. Both single doses of lotion and aqueous diclofenac showed decreased diclofenac absorption into the receptor fluid between 12 and 24 h. However, when applied multiple times, absorption from lotion was continually increasing up to 48 h. The total dose accountability ranged from 76.8 +/- 8.2% to 110.6 +/- 15. 1% of the applied dose. CONCLUSIONS: Diclofenac lotion exhibited enhanced diclofenac percutaneous absorption rate through human skin (mass, flux and partition coefficient) when applied a multiple number of times and this enhanced absorption was maintained over 48 h. This suggests that a constituent of the lotion (DMSO) will enhance human skin absorption of diclofenac when used in a multi-dose regimen, but not after a single dose.

Human in vivo and in vitro hydroquinone topical bioavailability, metabolism, and disposition.

Hydroquinone is a ubiquitous chemical readily available as monographed in cosmetic and nonprescription forms for skin lightening, and is an important industrial chemical. The in vivo bioavailability for 24-h application in humans was 45.3+/-11.2% of dose from a 2% cream formulation containing [14C]hydroquinone, with the majority of radioactivity excreted in the first 24 h. Timed skin wash and skin tape-stripping sequences showed a rapid and continuous movement of hydroquinone into the stratum corneum of human volunteers. Plasma levels taken both ipsilateral and contralateral to the topical dosing site contained radioactivity at the first 0.5-h sampling time. Peak plasma radioactivity was at 4 h in the 8-h blood sampling period. In vitro percutaneous absorption with fresh viable human skin gave a bioavailability of 43.3% of dose, and flux was calculated at 2.85 microg/cm2/h. In vitro, some of the skin samples were pretreated with the metabolic inhibitor sodium azide, which had no effect on percutaneous absorption. Receptor fluid accumulations and 24-h skin samples were extracted and the extracts subjected to thin-layer chromatography (TLC). Control [14C]hydroquinone extraction and TLC had one radioactivity peak, hydroquinone. Receptor fluid and skin extraction had a second peak with the same Rf as benzoquinone, which was decreased with azide treatment. No other peaks were found. Ethyl acetate extraction of urine from the in vivo study showed all radioactivity to be only water-soluble, free hydroquinone released following glucuronidase treatment. Risk assessment should not only involve the bioavailability of intact topical hydroquinone, but also consider phase I and phase II metabolism in both humans and any animal for which toxicity potential was assessed.

Human cadaver skin viability for in vitro percutaneous absorption: storage and detrimental effects of heat-separation and freezing.

PURPOSE: For decades, human cadaver skin has been banked and utilized by hospitals for burn wounds and to study percutaneous absorption and transdermal delivery. Skin storage maintenance and confirmation of skin viability is important for both uses, especially for the absorption process where the in vivo situation is simulated. METHODS: Our system uses dermatomed human cadaver skin immediately placed in Eagles MEM-BSS, and refrigerated after donor death, then transferred to the laboratory and placed in Eagles MEM-BSS with 50 micrograms/ml gentamicin at 4 degrees C for storage. RESULTS: Skin viability, determined by anaerobic metabolism where glucose is converted to lactose, was highest (p < 0.000) during the 18 hours of the first day after donor death, decreased some 3-fold by day 2 (p < 0.000), but then maintained steady-state viability through day 8. Viability then decreased by approximately one-half by day 13. Thus, using the above criteria, human skin will sustain viability for 8 days following donor death in this system. Heat-treated (60 degrees C water for one minute) and heat-separated epidermis and dermis lose viability. CONCLUSIONS: Human skin viability can be maintained for absorption studies. It is recommended that this system be used, and that heat-separation and skin freezing not be used, in absorption studies where skin viability and metabolism might be contributing factors to the study.

In vivo percutaneous absorption of boron as boric acid, borax, and disodium octaborate tetrahydrate in humans: a summary.

Literature from the first half of this century reports concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry, which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax, and disodium octaborate tetrahydrate (DOT) in biological matrices. This made it possible, in the presence of comparatively large natural dietary boron intakes for the in vivo segment of this study, to quantify the boron passing through skin. Human volunteers were dosed with 10B-enriched boric acid, 5.0%, borax, 5.0%, or disodium octaborate tetrahydrate, 10% in aqueous solutions. Urinalysis, for boron and changes in boron isotope ratios, was used to measure absorption. Boric acid in vivo percutaneous absorption was 0.226 (SD = 0.125) mean percent dose, with flux and permeability constant (Kp) calculated at 0.009 microg/cm2/h and 1.9 x 10(-7) cm/h, respectively. Borax absorption was 0.210 (SD = 0.194) mean percent dose, with flux and Kp calculated at 0.009 microg/cm2/h and 1.8 x 10(-7) cm/h, respectively. DOT absorption was 0.122 (SD = 0.108) mean percent, with flux and Kp calculated at 0.01 microg/cm2/h and 1.0 x 10(-7) cm/h, respectively. Pretreatment with the potential skin irritant 2% sodium lauryl sulfate had no effect on boron skin absorption. These in vivo results show that percutaneous absorption of boron, as boric acid, borax, and disodium octaborate tetrahydrate, through intact human skin is low and is significantly less than the average daily dietary intake. This very low boron skin absorption makes it apparent that, for the borates tested, the use of gloves to prevent systemic uptake is unnecessary. These findings do not apply to abraded or otherwise damaged skin.

In vitro percutaneous absorption of boron as boric acid, borax, and disodium octaborate tetrahydrate in human skin: a summary.

Literature from the first half of this century reports concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax and disodium octaborate tetrahydrate (DOT) in biological matrices. In vitro human skin percent doses of boric acid absorbed were 1.2 for a 0.05% solution, 0.28 for a 0.5% solution, and 0.70 for a 5.0% solution. These absorption amounts translated into flux values of, respectively, 0.25, 0.58, and 14.58 microg/cm2/h, and permeability constants (Kp) of 5.0 x 10(-4), 1.2 x 10(-4), and 2.9 x 10(-4) cm/h for the 0.05%, 0.5%, and 5.0% solutions. The above in vitro doses were at infinite, 1000 microL/cm2 volume. At 2 microL/cm2 (the in vivo dosing volume), flux decreased some 200-fold to 0.07 microg/cm2/h and Kp of 1.4 x 10(-6) cm/h, while percent dose absorbed was 1.75%. Borax dosed at 5.0%/1000 microL/cm2 had 0.41 percent dose absorbed, flux at 8.5 microg/cm2/h, and Kp was 1.7 x 10(-4) cm/h. Disodium octaborate tetrahydrate (DOT) dosed at 10%/1000 microL/cm2 was 0.19 percent dose absorbed, flux at 7.9 microg/cm2/h, and Kp was 0.8 x 10(-4) cm/h. These in vitro results from infinite doses (1000 microL/cm2) were a 1000-fold greater than those obtained in the companion in vivo study. The results from the finite (2 microL/cm2) dosing were closer (10-fold difference) to the in vivo results. General application of infinite dose percutaneous absorption values for risk assessment is questioned by these results.

Human skin in vitro percutaneous absorption of gaseous ethylene oxide from fabric.

Ethylene oxide, a colourless gas at ordinary room temperature and pressure, is widely used as a fumigant, coming in contact with clothing and human skin. It is genotoxic in somatic and germ cells. [1,2-14C]Ethylene oxide and fabric discs were sealed in a glass container; the fabric discs were then removed and placed on human skin mounted in glass diffusion cells. Percutaneous absorption was 1.3% of the dose when the fabric/skin surface was open to surrounding air, and increased to 46.0% when the surface was occluded with latex glove material. The absorption was rapid, occurring within the first 0-4 hr assay period. Absorbed chemical was confirmed to be unchanged ethylene oxide in the receptor fluid. This study also serves as a model for exposure of fabric/skin to any potentially hazardous gas.