Chronological age affects the permeation of fentanyl through human skin in vitro

Revisiting the Effect of Aging on the Transport of Molecules through the Skin

Both intrinsic and extrinsic aging lead to a series of morphological changes in the skin including the flattening of the dermal-epidermal junction, increased stratum corneum dryness, reduction in sebaceous gland activity and enzyme activity as well as atrophy of blood vessels. In this study, the impact of these changes on the transport of molecules through the skin was revised. The increase in the number of transdermal formulations on the market in recent decades and life expectancy represent the main reasons for an in-depth discussion of this topic. Furthermore, elderly subjects have often been excluded from clinical trials due to polypharmacy, raising concerns in terms of efficacy and safety. In this way, ex vivo and in vivo studies comparing the transport of molecules through the mature and young skin were analyzed in detail. The reduced water content in mature skin had a significant impact on the transport rate of hydrophilic molecules. The lower enzymatic activity in aged skin, in turn, would explain changes in the activation of prodrugs. Interestingly, greater deposition of nanoparticles was also found in mature skin. In vivo models should be prioritized in future experimental studies as they allow to evaluate both absorption and metabolism simultaneously, providing more realistic information.

Methods for the characterisation of dermal uptake: Progress and perspectives for organophosphate esters

Organophosphate esters (OPEs) are a group of pollutants that are widely detected in the environment at high concentrations. They can adversely affect human health through multiple routes of exposure, including dermal uptake. Although attention has been paid to achieving an accurate and complete quantification of the dermal uptake of OPEs, existing evaluation methods and parameters have obvious weaknesses. This study reviewed two main categories of methodologies, namely the relative absorption (RA) model and the permeability coefficient (PC) model, which are widely used to assess the dermal uptake of OPEs. Although the PC model is more accurate and is increasingly used, the most important parameter in this model, the permeability coefficient (Kp), has been poorly characterised for OPEs, resulting in considerable errors in the estimation of the dermal uptake of OPEs. Thus, the detailed in vitro methods for the determination of Kp are summarised and sorted. Furthermore, the commonly used skin membranes are identified and the factors affecting Kp and corresponding mechanisms are discussed. In addition, the experimental conditions, conclusions, and available data on Kp values of the OPEs are thoroughly summarised. Finally, the corresponding knowledge gaps are proposed, and a more accurate and sophisticated experimental system and unknown Kp values for OPEs are suggested.

A review of the success and challenges in characterizing human dermal exposure to flame retardants

Since organic flame retardants (FRs) have several industrial applications, they have been largely detected in environmental and biological samples, and humans have been highly exposed to them. Although the effects of oral and inhaled FRs have been well studied, dermal exposure to them has only recently been pointed out as a potential route of human exposure. Consequently, the effects of FRs on the skin and secondary target organs have been poorly investigated. This review article summarizes the main findings regarding dermal exposure to FRs, points the limitation of the published studies, and suggests future perspectives for better understanding of how dermal exposure to FRs impacts the human health. This review lists some gaps that must be filled in future studies, including characterization of the bioavailable fraction and assessment of exposure for new FRs, to establish their physiological significance and to improve the development of 3D dermal tissue for more reliable results to be obtained.

Calcium, magnesium and aluminium ions as decontaminating agents against dermal fluoride absorption following hydrofluoric acid exposure

The fluoride ions of the industrially largely irreplaceable, locally corrosive hydrofluoric acid (HF) can scavenge cations in biological tissues, which explains their high toxic potential, and also leads to local acidification through proton release. The influence of three complexing agents, calcium (Ca²⁺) gluconate (as 2.5% Ca²⁺gel and individually (2.84%) or commercially (10%) formulated Ca²⁺solution), magnesium (Mg²⁺) gluconate (2.84%) solution and aluminium (Al³⁺) solution (Hexafluorine®, pure and diluted) on the absorption of fluoride following HF exposure (1-3 min, 100 μl, 30%/0.64 cm²) through human skin was investigated in an ex-vivo diffusion cell model. Fluoride absorption was assessed over 6-24 h and analysed with a fluoride electrode. Decreasing the contamination time reduced the fluoride absorption distinctly which was further reduced by the application of fluoride-binding decontamination agents (Ca²⁺, Mg²⁺, Al³⁺) or water alone without being significantly different. Ca²⁺ appeared slightly more effective than Mg²⁺ in reducing fluoride absorption. Moreover, the addition of pH adjusting buffer promoted the decontamination efficacy. Fluoride-binding agents can facilitate the decontamination of dermal HF exposure. However, prompt decontamination appeared to be the key to successful limitation of fluoride absorption and pushes the choice of decontamination agent almost into the background.

Impact of physiologically relevant temperatures on dermal absorption of active substances - an ex-vivo study in human skin

Skin temperature plays a certain role in the dermal absorption of substances, but the extent and mechanisms of skin temperatures-induced modulation in ranges caused by physiological thermoregulation or environmental conditions are largely unknown. The influence of dermal temperature on the absorption of the model lipophilic compound (anisole) and the model hydrophilic compounds (1,4-dioxane, ethanol) through human skin was investigated at three dermal temperatures (25, 32 and 39 °C) in an ex-vivo diffusion cell model. The substances were applied to the skin and transdermal penetration was monitored. All substances showed temperature dependent variations in their penetration behavior (3 h: 25-39 °C: 202-275% increase in cumulative, transdermally penetrated amounts). The relative differences in absorption in relation to temperature were greatest within 45 min after exposure (25-39 °C: 347-653% rise in cumulated penetration), although absolute amounts absorbed were small (45 min vs. 3 h: 4.5-14.5%). Regardless of blood circulation, skin temperature significantly influences the amount and kinetics of dermal absorption. Substance-dependent, temperature-related changes of the lipid layer order or the porous pathway may facilitate penetration. The early-stage modulation of transdermal penetration indicates transappendageal absorption, which may be relevant for short-term exposures. For both, toxicological evaluation and perfusion cell studies, it is important to consider the thermal influence on absorption or to perform the latter at a standardized temperature (32±1 °C).

Optimizing skin pharmacotherapy for older patients: the future is at hand but are we ready for it?

Age-related changes affect both the local pharmacotherapy of skin diseases and the transdermal administration of drugs. The development of aged skin models disregards the highly individual process of aging, facilitating general conclusions for older patients. Nevertheless, 'omics technology, high-content screening, and non-invasive imaging, as well as bioprinting, CRISPR-Cas, and, patients-on-a-chip, can retrieve personalized information for the generation of in vitro models. Herein, we suggest a strategy to optimize pharmacotherapy for older patients. The technology for relevant human cell-based models is at hand and the consideration of patient heterogeneity is required to unlock their full potential.

Fibroblast origin shapes tissue homeostasis, epidermal differentiation, and drug uptake

Preclinical studies frequently lack predictive value for human conditions. Human cell-based disease models that reflect patient heterogeneity may reduce the high failure rates of preclinical research. Herein, we investigated the impact of primary cell age and body region on skin homeostasis, epidermal differentiation, and drug uptake. Fibroblasts derived from the breast skin of female 20- to 30-year-olds or 60- to 70-year-olds and fibroblasts from juvenile foreskin (<10 years old) were compared in cell monolayers and in reconstructed human skin (RHS). RHS containing aged fibroblasts differed from its juvenile and adult counterparts, especially in terms of the dermal extracellular matrix composition and interleukin-6 levels. The site from which the fibroblasts were derived appeared to alter fibroblast-keratinocyte crosstalk by affecting, among other things, the levels of granulocyte-macrophage colony-stimulating factor. Consequently, the epidermal expression of filaggrin and e-cadherin was increased in RHS containing breast skin fibroblasts, as were lipid levels in the stratum corneum. In conclusion, the region of the body from which fibroblasts are derived appears to affect the epidermal differentiation of RHS, while the age of the fibroblast donors determines the expression of proteins involved in wound healing. Emulating patient heterogeneity in preclinical studies might improve the treatment of age-related skin conditions.

Dermal uptake and percutaneous penetration of ten flame retardants in a human skin ex vivo model

The dermal uptake and percutaneous penetration of ten organic flame retardants was measured using an ex vivo human skin model. The studied compounds were DBDPE, BTBPE, TBP-DBPE, EH-TBB, BEH-TEBP, α, β and γ-HBCDD as well as syn- and anti-DDC-CO. Little or none of the applied flame retardants was recovered in either type of the receptor fluids used (physiological and worst-case). However, significant fractions were recovered in the skin depot, particularly in the upper skin layers. The primary effect of the worst-case receptor fluid was deeper penetration into the skin. The recovered mass was used to calculate lower- and upper-bound permeability coefficients kp. Despite large structural variation between the studied compounds, a clear, significant decreasing trend of kp was observed with increasing log Kow. The results indicate that the dermis may provide a significant barrier for these highly lipophilic compounds. However, based on our results, dermal uptake should be considered in exposure assessments, though it may proceed in a time-lagged manner compared to less hydrophobic compounds.

The Opioid Rotation Ratio From Transdermal Fentanyl to "Strong" Opioids in Patients With Cancer Pain

CONTEXT

One-third of cancer patients require opioid rotation (OR) to treat uncontrolled pain or opioid-induced neurotoxicity. Although fentanyl is the most frequently rotated opioid in cancer patients, the accurate opioid rotation ratio (ORR) from transdermal fentanyl (TDF) to other so-called "strong" opioids is unknown.

OBJECTIVES

We aimed to determine the ORR of TDF to strong opioids, as measured by morphine equivalent daily dose (MEDD).

METHODS

We reviewed 2471 consecutive patient visits (938 patients) to our supportive care center for an OR from TDF to strong opioids. Information regarding demographics, symptoms, and MEDD was collected in patients who followed up within six weeks. Linear regression analysis was used to estimate the ORR between TDF dose and net MEDD (MEDD after OR minus MEDD of the breakthrough opioid used along with TDF before OR).

RESULTS

Among 47 eligible patients, the median age was 54 years, 53% were male, and 77% had advanced cancer. The median time to follow-up was 14 days. Uncontrolled pain (83%) was the most common reason for OR. In patients with OR and no worsening of pain at follow-up (n = 41), the median ORR (range) from TDF mg/day to net MEDD mg/day was 100 (12.5-217) and from TDF mcg/hour to net MEDD was 2.4 (0.3-5.2); the correlation of TDF dose to net MEDD was 0.60 (P < 0.0001).

CONCLUSION

The median ORR from TDF mg/day to MEDD is 100 and from TDF mcg/hour to MEDD is 2.4, suggesting that TDF 100 mcg/hour is equivalent to an MEDD of 240 mg.

Identifying present challenges to reliable future transdermal drug delivery products

Transdermal systems have become an accepted means of drug delivery, offering clinical benefits over other dosage forms. Although transdermal delivery has been very successful as a controlled release technology platform, there are a number of challenges that prevent this delivery route from achieving its fullest commercial potential. Additionally, beginning in 1997, transdermal drug delivery companies aligned with life science industries to deliver large molecules, peptides and proteins through the skin, which is difficult due to the skin barrier properties. A number of methods and technologies have been conceived to overcome the skin barrier. Among these are mechanical, chemical and thermal permeation enhancement techniques. These methods are briefly discussed as well as future directions for transdermal therapies.

Effect of Skin Protection and Skin Irritation on the Internal Exposure to Carbon Disulfide in Employees of the Viscose Industry

INTRODUCTION

Occupational exposure to carbon disulfide (CS2) leads to inhalative and dermal uptake and thereby to internal exposure. In order to prevent occupational contact dermatitis, gloves and skin protection creams are used at the workplace. The aim of the study was the evaluation of the influence of personal skin protection and irritation on the internal exposure to CS2 of employees in the viscose industry.

METHODS

One hundred and eighty-two male CS2-exposed employees were included in the study and were examined regarding working conditions, use of personal protective measures und skin status. Personal air monitoring and biological monitoring was performed and the 'relative internal exposure' (RIE, internal exposure in relation to external exposure) calculated. A multiple regression analysis calculated the influence of skin protection and irritation on CS2 uptake.

RESULTS

Usage of skin protection creams and gloves (and both in combination) while working was associated with a significantly higher RIE indicating a higher dermal penetration of CS2. Equally, irritated skin and younger age was associated with a higher internal burden.

CONCLUSIONS

Gloves and skin protection creams are useful for preventing occupational skin diseases. However, when handling skin-resorptive substances like CS2, they can increase internal exposure or skin irritation. Therefore, we recommend the careful consideration of benefits and risks of protective creams and gloves at the workplace.