Transdermal Uptake Research Articles

Rational Design of CPP-based Drug Delivery Systems: Considerations from Pharmacokinetics

Therapeutics are restricted from cellular internalization due to the biological barrier formed by the cell membrane. Especially for therapeutics with high molecular weight, strategies are required to enable delivery to intracellular targets. Cell-penetrating peptides (CPPs) represent a powerful tool to mediate the entry of large cargos such as proteins, siRNA and nanoparticles. The high diversity of CPPs is the prerequisite to use this class of carriers for various applications. However, therapies based on CPPs are hampered by their unfavorable pharmacokinetics, mainly dominated by their rapid renal clearance and their lack of specificity. Rational design is required to overcome these disadvantages and thereby exploits the actual potential of CPPs. We summarize and highlight the current state of knowledge with special emphasis on pharmacokinetics. The unclear internalization pathways of CPPs remain one of the main obstacles and therefore have been in the focus of research. In this review, several promising strategies such as the combination with targeting sequences, activatable CPPs and adjustment of the molecular weight are described. In addition, new absorption pathways such as nasal, pulmonary or transdermal uptake expand the applicability of CPPs and may be a promising prospect for clinical application.

Associations of Filaggrin Gene Loss-of-Function Variants with Urinary Phthalate Metabolites and Testicular Function in Young Danish Men

Background: Filaggrin is an epidermal protein that is crucial for skin barrier function. Up to 10% of Europeans and 5% of Asians carry at least one null allele in the filaggrin gene (FLG). Reduced expression of filaggrin in carriers of the null allele is associated with facilitated transfer of allergens across the epidermis. We hypothesized that these individuals may have increased transdermal uptake of endocrine disruptors, including phthalates.Objectives: We investigated urinary excretion of phthalate metabolites and testicular function in young men with and without FLG loss-of-function variants in a cross-sectional study of 861 young men from the general Danish population.Methods: All men were genotyped for FLG R501X, 2282del4, and R2447X loss-of-function variants. We measured urinary concentrations of 14 phthalate metabolites and serum levels of reproductive hormones. We also evaluated semen quality.Results: Sixty-five men (7.5%) carried at least one FLG-null allele. FLG-null carriers had significantly higher urinary concentrations of several phthalate metabolites, including a 33% higher concentration of MnBP (mono-n-butyl phthalate; 95% CI: 16, 51%). FLG-null variants were not significantly associated with reproductive hormones or semen quality parameters.Conclusion: This study provides evidence that carriers of FLG loss-of-function alleles may have higher internal exposure to phthalates, possibly due to increased transepidermal absorption. FLG loss-of-function variants may indicate susceptible populations for which special attention to transepidermal absorption of chemicals and medication may be warranted.Citation: Joensen UN, Jørgensen N, Meldgaard M, Frederiksen H, Andersson AM, Menné T, Johansen JD, Carlsen BC, Stender S, Szecsi PB, Skakkebæk NE, Rajpert-De Meyts E, Thyssen JP. 2014. Associations of filaggrin gene loss-of-function variants with urinary phthalate metabolites and testicular function in young Danish men. Environ Health Perspect 122:345–350; http://dx.doi.org/10.1289/ehp.1306720

Dermal Uptake of Organic Vapors Commonly Found in Indoor Air

Transdermal uptake directly from air is a potentially important yet largely overlooked pathway for human exposure to organic vapors indoors. We recently reported (Indoor Air 2012, 22, 356) that transdermal uptake directly from air could be comparable to or larger than intake via inhalation for many semivolatile organic compounds (SVOCs). Here, we extend that analysis to approximately eighty organic compounds that (a) occur commonly indoors and (b) are primarily in the gas-phase rather than being associated with particles. For some compounds, the modeled ratio of dermal-to-inhalation uptake is large. In this group are common parabens, lower molecular weight phthalates, o-phenylphenol, Texanol, ethylene glycol, and α-terpineol. For other compounds, estimated dermal uptakes are small compared to inhalation. Examples include aliphatic hydrocarbons, single ring aromatics, terpenes, chlorinated solvents, formaldehyde, and acrolein. Analysis of published experimental data for human subjects for twenty different organic compounds substantiates these model predictions. However, transdermal uptake rates from air have not been measured for the indoor organics that have the largest modeled ratios of dermal-to-inhalation uptake; for such compounds, the estimates reported here require experimental verification. In accounting for total exposure to indoor organic pollutants and in assessing potential health consequences of such exposures, it is important to consider direct transdermal absorption from air.

Effects of water gradients and use of urea on skin ultrastructure evaluated by confocal Raman microspectroscopy

The rather thin outermost layer of the mammalian skin, stratum corneum (SC), is a complex biomembrane which separates the water rich inside of the body from the dry outside. The skin surface can be exposed to rather extreme variations in ambient conditions (e.g. water activity, temperature and pH), with potential effects on the barrier function. Increased understanding of how the barrier is affected by such changes is highly relevant for regulation of transdermal uptake of exogenous chemicals. In the present study we investigate the effect of hydration and the use of a well-known humectant, urea, on skin barrier ultrastructure by means of confocal Raman microspectroscopy. We also perform dynamic vapor sorption (DVS) microbalance measurements to examine the water uptake capacity of SC pretreated with urea. Based on novel Raman images, constructed from 2D spectral maps, we can distinguish large water inclusions within the skin membrane exceeding the size of fully hydrated corneocytes. We show that these inclusions contain water with spectral properties similar to that of bulk water. The results furthermore show that the ambient water activity has an important impact on the formation of these water inclusions as well as on the hydration profile across the membrane. Urea significantly increases the water uptake when present in skin, as compared to skin without urea, and it promotes formation of larger water inclusions in the tissue. The results confirm that urea can be used as a humectant to increase skin hydration.

SVOC exposure indoors: fresh look at dermal pathways

This paper critically examines indoor exposure to semivolatile organic compounds (SVOCs) via dermal pathways. First, it demonstrates that--in central tendency--an SVOC's abundance on indoor surfaces and in handwipes can be predicted reasonably well from gas-phase concentrations, assuming that thermodynamic equilibrium prevails. Then, equations are developed, based upon idealized mass-transport considerations, to estimate transdermal penetration of an SVOC either from its concentration in skin-surface lipids or its concentration in air. Kinetic constraints limit air-to-skin transport in the case of SVOCs that strongly sorb to skin-surface lipids. Air-to-skin transdermal uptake is estimated to be comparable to or larger than inhalation intake for many SVOCs of current or potential interest indoors, including butylated hydroxytoluene, chlordane, chlorpyrifos, diethyl phthalate, Galaxolide, geranyl acetone, nicotine (in free-base form), PCB28, PCB52, Phantolide, Texanol and Tonalide. Although air-to-skin transdermal uptake is anticipated to be slow for bisphenol A, we find that transdermal permeation may nevertheless be substantial following its transfer to skin via contact with contaminated surfaces. The paper concludes with explorations of the influence of particles and dust on dermal exposure, the role of clothing and bedding as transport vectors, and the potential significance of hair follicles as transport shunts through the epidermis. Human exposure to indoor pollutants can occur through dietary and nondietary ingestion, inhalation, and dermal absorption. Many factors influence the relative importance of these pathways, including physical and chemical properties of the pollutants. This paper argues that exposure to indoor semivolatile organic compounds (SVOCs) through the dermal pathway has often been underestimated. Transdermal permeation of SVOCs can be substantially greater than is commonly assumed. Transport of SVOCs from the air to and through the skin is typically not taken into account in exposure assessments. Yet, for certain SVOCs, intake through skin is estimated to be substantially larger than intake through inhalation. Exposure scientists, risk assessors, and public health officials should be mindful of the dermal pathway when estimating exposures to indoor SVOCs. Also, they should recognize that health consequences vary with exposure pathway. For example, an SVOC that enters the blood through the skin does not encounter the same detoxifying enzymes that an ingested SVOC would experience in the stomach, intestines, and liver before it enters the blood.

In vitro study of percutaneous absorption of aluminum from antiperspirants through human skin in the Franz™ diffusion cell

Aluminum salts such as aluminum chlorohydrate (ACH) are known for use as an active antiperspirant agent that blocks the secretion of sweat. A local case report of hyperaluminemia in a woman using an aluminum-containing antiperspirant for 4years raises the problem of transdermal absorption of aluminum (Al). Only a very limited number of studies have shown that the skin is an effective barrier to transdermal uptake of Al. In accordance with our analytical procedure, the aim of this study with an in vitro Franz™ diffusion cell was to measure aluminum uptake from three cosmetic formulations of antiperspirant: the base for an “aerosol” (38.5% of ACH), a “roll-on” emulsion (14.5% ACH), and a “stick” (21.2%), by samples of intact and stripped human skin (5 donors). The Al assays were performed by Zeeman Electrothermal Atomic Absorption Spectrophotometry (ZEAAS). Following contacts lasting 6, 12 and 24h, the Al assays showed only insignificant transdermal absorption of Al (≤0.07% of the quantity of Al deposited) and particularly low cutaneous quantities that varied according to the formulations (1.8μg/cm² for “aerosol base” and “stick” — 0.5μg/cm² for the “roll-on”). On stripped skin, for which only the “stick” formulation was tested, the measured uptake was significantly higher (11.50μg/cm² versus 1.81μg/cm² for normal skin). These results offer reassurance as regards to the use of antiperspirants for topical application of ACH-containing cosmetic formulations on healthy skin over a limited time span (24h). On the other hand, high transdermal Al uptake on stripped skin should compel antiperspirant manufacturers to proceed with the utmost caution.

Simulation of urinary excretion of 1-hydroxypyrene in various scenarios of exposure to polycyclic aromatic hydrocarbons with a generic, cross-chemical predictive PBTK-model

A physiologically based toxicokinetic (PBTK) model can predict blood and urine concentrations, given a certain exposure scenario of inhalation, dermal and/or oral exposure. The recently developed PBTK-model IndusChemFate is a unified model that mimics the uptake, distribution, metabolism and elimination of a chemical in a reference human of 70 kg. Prediction of the uptake by inhalation is governed by pulmonary exchange to blood. Oral uptake is simulated as a bolus dose that is taken up at a first-order rate. Dermal uptake is estimated by the use of a novel dermal physiologically based module that considers dermal deposition rate and duration of deposition. Moreover, evaporation during skin contact is fully accounted for and related to the volatility of the substance. Partitioning of the chemical and metabolite(s) over blood and tissues is estimated by a Quantitative Structure-Property Relationship (QSPR) algorithm. The aim of this study was to test the generic PBTK-model by comparing measured urinary levels of 1-hydroxypyrene in various inhalation and dermal exposure scenarios with the result of model simulations. In the last three decades, numerous biomonitoring studies of PAH-exposed humans were published that used the bioindicator 1-hydroxypyrene (1-OH-pyrene) in urine. Longitudinal studies that encompass both dosimetry and biomonitoring with repeated sampling in time were selected to test the accuracy of the PBTK-model by comparing the reported concentrations of 1-OHP in urine with the model-predicted values. Two controlled human volunteer studies and three field studies of workers exposed to polycyclic aromatic hydrocarbons (PAH) were included. The urinary pyrene-metabolite levels of a controlled human inhalation study, a transdermal uptake study of bitumen fume, efficacy of respirator use in electrode paste workers, cokery workers in shale oil industry and a longitudinal study of five coke liquefaction workers were compared to the PBTK-predicted values. The simulations showed that the model-predicted concentrations of urinary pyrene and metabolites over time, as well as peak-concentrations and total excreted amount in different exposure scenarios of inhalation and transdermal exposure were in all comparisons within an order of magnitude. The model predicts that only a very small fraction is excreted in urine as parent pyrene and as free 1-OH-pyrene. The predominant urinary metabolite is 1-OH-pyrene-glucuronide. Enterohepatic circulation of 1-OH-pyrene-glucuronide seems the reason of the delayed release from the body. It appeared that urinary excretion of pyrene and pyrene-metabolites in humans is predictable with the PBTK-model. The model outcomes have a satisfying accuracy for early testing, in so-called 1st tier simulations and in range finding. This newly developed generic PBTK-model IndusChemFate is a tool that can be used to do early explorations of the significance of uptake of pyrene in the human body following industrial or environmental exposure scenarios. And it can be used to optimize the sampling time and urine sampling frequency of a biomonitoring program.

A Generic, Cross-Chemical Predictive PBTK Model with Multiple Entry Routes Running as Application in MS Excel; Design of the Model and Comparison of Predictions with Experimental Results

Physiologically based toxicokinetic (PBTK) models are computational tools, which simulate the absorption, distribution, metabolism, and excretion of chemicals. The purpose of this study was to develop a physiologically based pharmacokinetic (PBPK) model with a high level of transparency. The model should be able to predict blood and urine concentrations of environmental chemicals and metabolites, given a certain environmental or occupational exposure scenario. The model refers to a reference human of 70 kg. The partition coefficients of the parent compound and its metabolites (blood:air and tissue:blood partition coefficients of 11 organs) are estimated by means of quantitative structure-property relationship, in which five easily available physicochemical properties of the compound are the independent parameters. The model gives a prediction of the fate of the compound, based on easily available chemical properties; therefore, it can be applied as a generic model applicable to multiple compounds. Three routes of uptake are considered (inhalation, dermal, and/or oral) as well as two built-in exercise levels (at rest and at light work). Dermal uptake is estimated by the use of a dermal diffusion-based module that considers dermal deposition rate and duration of deposition. Moreover, evaporation during skin contact is fully accounted for and related to the volatility of the substance. Saturable metabolism according to Michaelis-Menten kinetics can be modelled in any of 11 organs/tissues or in liver only. Renal tubular resorption is based on a built-in algorithm, dependent on the (log) octanol:water partition coefficient. Enterohepatic circulation is optional at a user-defined rate. The generic PBTK model is available as a spreadsheet application in MS Excel. The differential equations of the model are programmed in Visual Basic. Output is presented as numerical listing over time in tabular form and in graphs. The MS Excel application of the PBTK model is available as freeware. The accuracy of the model prediction is illustrated by simulating experimental observations. Published experimental inhalation and dermal exposure studies on a series of different chemicals (pyrene, N-methyl-pyrrolidone, methyl-tert-butylether, heptane, 2-butoxyethanol, and ethanol) were selected to compare the observed data with the model-simulated data. The examples show that the model-predicted concentrations in blood and/or urine after inhalation and/or transdermal uptake have an accuracy of within an order of magnitude. It is advocated that this PBTK model, called IndusChemFate, is suitable for 'first tier assessments' and for early explorations of the fate of chemicals and/or metabolites in the human body. The availability of a simple model with a minimum burden of input information on the parent compound and its metabolites might be a stimulation to apply PBTK modelling more often in the field of biomonitoring and exposure science.

An analytical procedure for the determination of aluminum used in antiperspirants on human skin in Franz™ diffusion cell

A local case report of hyperaluminemia (aluminum concentration: 3.88 µmol/L) in a woman using an aluminum-containing antiperspirant for 4 years raises the question of possible transdermal uptake of aluminum salt as a future public health problem. Prior to studying the transdermal uptake of three commercialized cosmetic formulas, an analytical assay of aluminum (Al) in chlorohydrate form (ACH) by Zeeman Electrothermal Atomic Absorption Spectrophotometer (ZEAAS) in a clean room was optimized and validated. This analysis was performed with different media on human skin using a Franz™ diffusion cell. The detection and quantification limits were set at ≤ 3 µg/L. Precision analysis as within-run (n = 12) and between-run (n = 15–68 days) yield CV ≤ 6%. The high analytic sensitivity (2–3 µg/L) and low variability should allow an in vitro study of the transdermal uptake of ACH.

Aerosols transmit prions to immunocompetent and immunodeficient mice.

Prions, the agents causing transmissible spongiform encephalopathies, colonize the brain of hosts after oral, parenteral, intralingual, or even transdermal uptake. However, prions are not generally considered to be airborne. Here we report that inbred and crossbred wild-type mice, as well as tga20 transgenic mice overexpressing PrPC, efficiently develop scrapie upon exposure to aerosolized prions. NSE-PrP transgenic mice, which express PrPC selectively in neurons, were also susceptible to airborne prions. Aerogenic infection occurred also in mice lacking B- and T-lymphocytes, NK-cells, follicular dendritic cells or complement components. Brains of diseased mice contained PrPSc and transmitted scrapie when inoculated into further mice. We conclude that aerogenic exposure to prions is very efficacious and can lead to direct invasion of neural pathways without an obligatory replicative phase in lymphoid organs. This previously unappreciated risk for airborne prion transmission may warrant re-thinking on prion biosafety guidelines in research and diagnostic laboratories.

Transdermal penetration of topical drugs used in the treatment of acne.

Acne vulgaris is a very common skin disease. Most patients present with mild to moderate acne comedonica or papulopustulosa grade I-II. The first-line treatment for these cases is generally via the topical route, whereas systemic medication is indicated when higher severity grades with small nodes or scarring occur. There are several topical agents available that affect at least one of the main pathogenetic factors responsible for the development of acne: hyperseborrhoea, hyperkeratosis, microbial colonisation and inflammatory and immunological reactions. Topical retinoids have a comedolytic and anticomedogenic activity, and some of them have anti-inflammatory potency. Azelaic acid and benzoyl peroxide have a moderate to strong antibacterial effect without inducing bacterial resistance, which is becoming a significant problem with the increasing use of topical antibacterials. Topical antiandrogens may soon be available for the treatment of the pathogenetic factor hyperseborrhoea. The transdermal penetration and the resulting systemic bioavailability of the various topical agents has not been widely considered. Apart from the retinoids, which can be associated with the risk of embryotoxicity/teratogenicity, and clindamycin, which might cause pseudomembranous colitis, information on the systemic pharmacokinetics of other topical agents is not readily available. There is still no consensus on the safe use of topical retinoids in pregnancy, and the occurrence of pseudomembranous colitis after the topical use of clindamycin does not appear to be of clinical relevance. In general, topical anti-acne agents are well tolerated and, as would be expected from their limited transdermal uptake, other significant safety concerns have not so far arisen.

Distribution and metabolism of topically applied progesterone in a rat model

This study investigated the transdermal uptake and subsequent tissue distribution of [ 3 H ]progesterone applied in a commercially available progesterone cream in a rat model. Concentrations of lipid- and water-soluble metabolites of [ 3 H ]progesterone were also measured in plasma, urine and selected tissues (uterus, liver, kidney, salivary gland) 3 h after its topical application. Female rats were ovariectomized and adrenalectomized to remove all endogenous progesterone, and 4 weeks later were anaesthetized and 150 mg Pro-Feme® cream (containing progesterone 3.2% w/w and 200 μCi [ 3 H ]progesterone) was applied to the abdominal skin. Six arterial blood samples were then obtained from a carotid cannula over the following 3 h, and urine and selected tissue samples were collected after the final blood sample. Plasma progesterone increased progressively until 90 min, then remained relatively stable. Plasma levels of [ 3 H ]progesterone were high by the 15-min sample and increased only slightly thereafter. Water-soluble metabolites were detectable in plasma at 15 min, whereas lipid-soluble metabolites became apparent only by 60 min then increased progressively to 180 min. The tissue:plasma concentration ratio for [ 3 H ]progesterone exceeded 1 in all tissues, most notably in uterus (8.4) and lung (9.6), whereas urinary [ 3 H ]progesterone levels were only half those in plasma. Concentrations of lipid- and water-soluble progesterone metabolites were most prevalent in liver and kidney, and both reached very high concentrations in urine. These results demonstrate that topically applied progesterone is rapidly absorbed transdermally and that its patterns of distribution and metabolism are comparable to those previously reported for intravascularly administered progesterone.

Transdermal absorption of topical anti-acne agents in man; review of clinical pharmacokinetic data.

Apart from oral drug treatment, drug therapy in acne vulgaris comprises topical treatment with agents with a primarily keratolytic action (e.g. tretinoin and benzoylperoxide), and with antibiotics (clindamycin, erythromycin, and erythromycin-zinc complex). The acne grade in the particular patient usually determines the selection of the preferred route of administration, viz. topical or oral, or a combination of both, and topical treatment is usually preferred in mild to moderate acne. The fact that a topically applied compound may also become systemically available to a quantifiable extent, is not generally considered. The present paper reviews the clinical data on transdermal uptake of anti-acne agents in man, also with respect to their relevance for daily clinical practice. The majority of published data on transdermal penetration of topical anti-acne agents focuses on the retinoid tretinoin, and on the antimicrobial agent clindamycin. This interest emerges from the fact that these agents have been associated with embryotoxicity/teratogenicity, and pseudomembranous colitis, respectively. For both compounds the extent of systemic availability after topical application is low, viz. 5-7% and 8%, respectively, at its highest. The height and variability in endogenous retinoid levels is very likely to outweigh any contribution of exogenously applied tretinoin, but a full consensus on the safe use of topical tretinoin in pregnancy is still lacking. With respect to clindamycin, the suggested association between its topical use and the occurrence of pseudomembranous colitis appears not to be of clinical relevance. In order to reduce systemic exposure to clindamycin as much as possible, topical application of clindamycin phosphate is to be preferred over clindamycin hydrochloride salt. Regarding other topical anti-acne agents, it has been suggested that topical zinc-erythromycin is to be preferred over erythromycin, both from clinical efficacy and safety viewpoints. With respect to the currently used compounds like benzoylperoxide, azelaic acid, and adapalene, available clinical pharmacokinetic data are scarce, and significant safety concerns did not emerge as yet. The limited transdermal uptake of topical anti-acne agents underpins their safe use in daily clinical practice. With respect to topical retinoids, formal consensus is lacking regarding their use in pregnancy.

Bioaccumulation of water soluble aluminium chloride in the hippocampus after transdermal uptake in mice.

Normally, only very small amounts of ingested aluminium are absorbed and accumulated. Despite the percutaneous absorption of many drugs and chemicals, the skin has not been considered as a possible site at which aluminium could enter the body. Application of low aqueous concentrations of aluminium chloride (A1C1(3), 6H20) (0.025-0.1 micrograms/cm2) to healthy shaved Swiss mouse skin for 130 days led to a significant increase in urine, serum and whole brain aluminium, especially in the hippocampus, compared to control animals. This percutaneous uptake and accumulation of aluminium in the brain was greater than that caused by dietary exposure to 2.3 micrograms per day in feed and water. In vitro studies demonstrated the passage of aluminium through viable mouse skin. This study shows for the first time that aluminium is absorbed through the skin of mice in vivo and this contributes to a greater body burden than does oral uptake.

A Note on the Trandermal Delivery of Clenbuterol

A modified diffusion/compartmental model has been used to simulate the transdermal uptake of clenbuterol from a matrix-type delivery device. The application of a fresh device every 7 days was found to produce a pseudo-steady state drug plasma profile after approx. three changes of device. Of the matrix properties, only drug loading had substantial effect on the drug plasma profile.

Transdermal uptake of a peptide hormone: Inhibition by calcitonin eardrops of induced osteolysis in guinea-pig ossicles

In view of a recent proposal that calcitonin injections may arrest the bony pathology of otosclerosis, we have tested the possibility of obtaining locally effective concentrations by giving salmon calcitonin in eardrops. Osteolysis of guinea-pig ossicles induced by injecting parathyroid hormone shortly before explantation was markedly inhibited by 3 days prior instillation of the calcitonin in an aqueous vehicle or in dimethyl sulphoxide, but not by a solution in propylene carbonate.