Application of dermal microdialysis for the determination of bioavailability of clobetasol propionate applied to the skin of human subjects

Preclinical pharmacokinetic investigation of the bioavailability and skin distribution of HY-072808 ointment, a novel drug candidate for the treatment of atopic dermatitis, in minipigs by a newly LC-MS/MS method

HY-072808 is a novel phosphodiesterase 4 inhibitor clinically used for topical atopic dermatitis treatment. Cytochrome P450 enzymes are involved in transforming it into major metabolite ZZ-24. An efficient UPLC-MS/MS method was established to detect HY-072808 and ZZ-24 in plasma and skin tissues of minipigs.One-step protein precipitation was performed with acetonitrile. Subsequently, elution was served with a methanol and water gradient containing 0.1% formic acid for 3.5 min. The plasma and skin tissue concentrations of HY-072808 and ZZ-24 showed good linearity from 0.200 to 200 ng/mL.The experimental minipigs exhibited low systemic exposure and bioavailability of 3.1-7.6% after transdermal application of 1-4% HY-072808 ointment. Multiple topical administrations over seven consecutive days showed a minor accumulation in systemic exposure, with accumulation factors of 2.3 and 4.0 for HY-072808 and ZZ-24, respectively.The distribution of HY-072808 ointment among different cortical layers in minipigs was studied for the first time. Following transdermal application of 2% HY-072808 ointment, the concentration in plasma and skin tissues in the order of epidermis > dermis > subcutaneous tissue ≈ subcutaneous muscle ≈ plasma; at 48 h after the administration, the epidermis and dermis still had a high concentration of the drug.

Reverse Iontophoresis: Noninvasive Assessment of Topical Drug Bioavailability

Assessing drug disposition in the skin after the application of a topical formulation is difficult. It is hypothesized that reverse iontophoresis (RI), which can extract charged/polar molecules for monitoring purposes, may provide a noninvasive approach for the assessment of local drug bioavailability. The passive and RI extraction of salicylic acid (SA) and nicotine (NIC) from porcine skin in vitro was assessed after a simple solution of the former and a transdermal patch of the latter had been applied for 24 and 8 h, respectively. Immediately after this "passive skin loading", the amount of drug in the stratum corneum (SC) and "viable" tissue (VT) was measured either (a) after tape-stripping and subsequent solvent extraction of both skin layers or (b) following RI extraction over 4 h. Parallel experiments were then performed in vivo in healthy volunteers; in this case, the VT was not sampled and the skin loading period for NIC was only 4 h. RI extraction of both drugs was significantly higher (in vitro and in vivo) than that achieved passively, and the cumulative RI extraction profiles as a function of time were mathematically analyzed using a straightforward compartmental model. Best-fit estimates of drug amounts in the SC and VT (ASC,0 and AVT,0, respectively) at the end of "loading" and two first-order rate constants describing transfer between the model compartments were then determined. The in vitro predictions of ASC,0 and AVT,0 were in excellent agreement with the experimental results, as was the value of the former in vivo. The rate constants derived from the in vitro and in vivo results were also similar. In summary, the results provide proof-of-concept that the RI method has the potential to noninvasively assess relevant metrics of drug bioavailability in the skin.

Bioequivalence Evaluation of Topical Metronidazole Products Using Dermal Microdialysis in New Zealand Rabbits

Comparative assessment of cutaneous pharmacokinetics (cPK) by dermal microdialysis (dMD) appears to be suitable to evaluate the bioequivalence (BE) of topical dermatological drug products applied to the skin (TDDPs). Although dMD studies in the literature have reported inconclusive BE assessments, we have addressed several methodological deficiencies to improve dMD's capability to assess BE between reference (R) and approved generic (referred to as test (T)) gel and cream products of metronidazole (MTZ). The 90% confidence interval (CI) of the geometric mean ratios for the Ln(AUC0-24) and Ln(Cmax) endpoints was centered within the BE limits of 80-125%. The CIs extended outside this range as the proof-of-principle study was not statistically powered to demonstrate BE (N = 7 rabbits). A power analysis suggests that, with the variability observed in this study, 21 rabbits for the cream and 11 rabbits for the gel would be sufficient to support an evaluation of BE with the 2 probe replicates we used, and only 10 and 5 rabbits would be sufficient to power the study for the cream and gel, respectively, if 4 probe replicates are used for each treatment per rabbit. These results indicate that dMD when properly controlling variables can be used to support BE assessments for TDDPs.

Hedgehog Signaling in CNS Remyelination

Remyelination is a fundamental repair process in the central nervous system (CNS) that is triggered by demyelinating events. In demyelinating diseases, oligodendrocytes (OLs) are targeted, leading to myelin loss, axonal damage, and severe functional impairment. While spontaneous remyelination often fails in the progression of demyelinating diseases, increased understanding of the mechanisms and identification of targets that regulate myelin regeneration becomes crucial. To date, several signaling pathways have been implicated in the remyelination process, including the Hedgehog (Hh) signaling pathway. This review summarizes the current data concerning the complicated roles of the Hh signaling pathway in the context of remyelination. We will highlight the open issues that have to be clarified prior to bringing molecules targeting the Hh signaling to demyelinating therapy.

Cutaneous Pharmacokinetic Approaches to Compare Bioavailability and/or Bioequivalence for Topical Drug Products

The evaluation of bioequivalence (BE) involves comparing the test product to its reference product in a study whose fundamental scientific principles allow inferring of the clinical performance of the products. Several test methods have been discussed and developed to evaluate topical bioavailability (BA) and BE. Pharmacokinetics-based approaches characterize the rate and extent to which an active ingredient becomes available at or near its site of action in the skin. Such methodologies are considered to be among the most accurate, sensitive, and reproducible approaches for determining the BA or BE of a product.

Lateral Dermal Penetration is Dependent on the Lipophilicity of Active Ingredients

INTRODUCTION

With its large surface area skin facilitates a topical administration of active ingredients, and thus percutaneous delivery to a specific target site. Due to its high barrier function and different diffusion characteristics skin governs the efficacy of these active ingredients and a bioavailability in the epidermal and dermal tissue.

OBJECTIVE

In order to characterize the vertical and lateral movement of molecules into and inside the skin the diffusivity of active ingredients with different physico-chemical properties and their penetration ability in different dermal skin layers was investigated.

METHODS

A novel lateral dermal microdialysis (MD) penetration setup was used to compare the diffusion characteristics of active ingredients into superficial and deep implanted MD membranes in porcine skin. The corresponding membrane depth was determined via ultrasound and the active ingredients concentration via high-pressure liquid chromatography (HPLC) measurement.

RESULTS

The depth depended penetration of superficial and deep implanted MD membranes and the quantitative diffusivity of two active ingredients was compared. An experimental lateral MD setup was used to determine the influence of percutaneous skin penetration characteristics of an active ingredient with different lipophilic and hydrophilic characteristics. Therefore, hydrophilic caffeine and lipophilic LIP1, which have an identical molecular weight, but different lipophilic characteristics were tested for their penetration ability inside a propylene glycol (PG) and oleic acid (OA) formulation.

CONCLUSION

The vertical and lateral penetration movement of caffeine was found to exceed that of LIP1 through the hydrophilic dermal environment. The findings of this study show that the lipophilicity of active ingredients influence the penetration movement and that skin enables a conical increasing lateral diffusivity and transdermal delivery.

Comparison of Membrane Depth Determination Techniques for Active Ingredient Skin Penetration Studies Using Microdialysis

INTRODUCTION

The skin is a major physical barrier to the environment, and thus, percutaneous delivery of active ingredients to the dermal target site faces a unique set of hurdles. The efficacy of these active ingredients is governed by their release into the underlying epidermal and dermal tissue, especially when administered topically.

OBJECTIVE

The aim of this study was to understand if different physicochemical properties influence the skin penetration of active ingredients and the depth to which they penetrate into the dermis.

METHODS

A microdialysis (MD) setup was used to compare the percutaneous penetration in superficial and deep implanted MD membranes in porcine skin. The precise MD membrane depth was determined using histological sectioning paired with microscopy, ultrasound, and a novel computed tomographic approach.

RESULTS

In study A, the measured depth of the superficial and deep implanted MD membranes was compared using histological sectioning, ultrasound, and computed tomography. Experimental determination of the depth up to which penetration occurs was found to be crucial to percutaneous penetration studies. In study B, the lipophilic differences of the active ingredients and its influences on the penetration was tested using hydrophilic caffeine and lipophilic LIP1 as model compounds, which have an identical molecular weight with different lipophilic characteristics. It is assumed that the lipophilic characteristics of active ingredients influence their penetration and thus governs the concentration of these molecules reaching their target site.

CONCLUSION

The transdermal penetration of caffeine was found to exceed that of LIP1 through the hydrophilic environment of the dermis. Thus, the findings of this study show that the precise MD dermis localization and the physicochemical properties, such as lipophilicity, influence the penetration rate of active ingredients and lay the foundation for creating optimized transdermal delivery systems.

Approaching sites of action of drugs in clinical pharmacology: New analytical options and their challenges

Clinical pharmacology is an important discipline for drug development aiming to define pharmacokinetics (PK), pharmacodynamics (PD) and optimum exposure to drugs, i.e. the concentration-response relationship and its modulators. For this purpose, information on drug concentrations at the anatomical, cellular and molecular sites of action is particularly valuable. In pharmacological assays, the limited accessibility of target cells in readily available samples (i.e. blood) often hampers mass spectrometry-based monitoring of the absolute quantity of a compound and the determination of its molecular action at the cellular level. Recently, new sample collection methods have been developed for the specific capture of rare circulating cells, especially for the diagnosis of circulating tumour cells. In parallel, new advances and developments in mass spectrometric instrumentation now allow analyses to be scaled down to the cellular level. Together, these developments may permit the monitoring of minute drug quantities and show their effect at the cellular level. In turn, such PK/PD associations on a cellular level would not only enrich our pharmacological knowledge of a given compound but also expand the basis for PK/PD simulations. In this review, we describe novel concepts supporting clinical pharmacology at the anatomical, cellular and molecular sites of action, and highlight the new challenges in mass spectrometry-based monitoring. Moreover, we present methods to tackle these challenges and define future needs.

Regulation of Oligodendrocyte Functions: Targeting Lipid Metabolism and Extracellular Matrix for Myelin Repair

Myelin is an essential structure that protects axons, provides metabolic support to neurons and allows fast nerve transmission. Several neurological diseases, such as multiple sclerosis, are characterized by myelin damage, which is responsible of severe functional impairment. Myelin repair requires the timely recruitment of adult oligodendrocyte precursor cells (OPCs) at the lesion sites, their differentiation and maturation into myelinating oligodendrocytes. As a consequence, OPCs undergo profound changes in their morphology, functions, and interactions with other cells and extracellular environment, thus requiring the reorganization of both their lipid metabolism and their membrane composition, which is substantially different compared to other plasma membranes. Despite the growing knowledge in oligodendroglia biology and in the mechanisms involved in OPC-mediated regeneration, the identification of strategies to promote remyelination still remains a challenge. Here, we describe how altered lipid metabolism in oligodendrocytes influences the pathogenesis of demyelination, and we show that several FDA-approved drugs with a previously unknown remyelination potential do act on cholesterol and lipid biosynthetic pathways. Since the interplay between myelin lipids and axons is strictly coordinated by the extracellular matrix (ECM), we also discuss the role of different ECM components, and report the last findings on new ECM-modifiers able to foster endogenous remyelination.

Clobetasol propionate enhances neural stem cell and oligodendrocyte differentiation

Clobetasol propionate (Clo) is a potent topical glucocorticoid and a potential remyelinating agent that has been approved by the U.S. Food and Drug Administration. However, the effect of Clo on neural stem cells (NSCs) remains largely unknown. The aim of the present study was to investigate the effect of Clo on the differentiation of NSCs in vitro. NSCs were isolated from mouse embryonic brain tissues and expanded in vitro. The effect of Clo on NSC viability was examined using an MTT assay. Differentiating NSCs were treated with 5 or 10 µM Clo, or with DMSO control, and the degree of differentiation was examined following culture in stem cell differentiation induction medium for 7 days. The effect of Clo on NSC differentiation was assessed using immunocytochemistry and western blot analyses. The results revealed that Clo significantly increased NSC viability compared with the DMSO control group. Treatment with Clo also significantly increased the number of NSCs that differentiated into growth associated protein 43 positive neurons and corresponding axon lengths were also significantly increased. In addition, treatment with Clo significantly increased the number of myelin basic protein positive oligodendrocytes and decreased the number of glial fibrillary acidic protein positive astrocytes. Furthermore, inhibition of the sonic hedgehog and AMP-activated protein kinase signaling pathways inhibited Clo-induced NSC differentiation, and treatment with Clo upregulated the expression of several neurotrophic factors. In conclusion, the results of the current study suggest that Clo may have a potential therapeutic benefit in neurological disorders affecting oligodendrocytes and neurons.

Skin microdialysis: methods, applications and future opportunities-an EAACI position paper

Skin microdialysis (SMD) is a versatile sampling technique that can be used to recover soluble endogenous and exogenous molecules from the extracellular compartment of human skin. Due to its minimally invasive character, SMD can be applied in both clinical and preclinical settings. Despite being available since the 1990s, the technique has still not reached its full potential use as a tool to explore pathophysiological mechanisms of allergic and inflammatory reactions in the skin. Therefore, an EAACI Task Force on SMD was formed to disseminate knowledge about the technique and its many applications. This position paper from the task force provides an overview of the current use of SMD in the investigation of the pathogenesis of chronic inflammatory skin diseases, such as atopic dermatitis, chronic urticaria, psoriasis, and in studies of cutaneous events during type 1 hypersensitivity reactions. Furthermore, this paper covers drug hypersensitivity, UVB-induced- and neurogenic inflammation, and drug penetration investigated by SMD. The aim of this paper is to encourage the use of SMD and to make the technique easily accessible by providing an overview of methodology and applications, supported by standardized operating procedures for SMD in vivo and ex vivo.

Preparation of mixed monoterpenes edge activated PEGylated transfersomes to improve the in vivo transdermal delivery efficiency of sinomenine hydrochloride

Surfactants generally have been used as edge activators of transfersomes. However, surfactants edge activated transfersomes frequently lead to cutaneous irritation, skin lipid loss and other side effects after dermal administration. In this study, mixed monoterpenes edge activated PEGylated transfersomes (MMPTs) were prepared by ethanol injection process with sinomenine hydrochloride as a model drug. The formulation of MMPTs was optimized by an orthogonal design. We investigated skin permeation/deposition characteristics and pharmacokinetics of sinomenine hydrochloride loaded in MMPTs by comparing with liposomes using in vitro skin tests and in vivo cutaneous microdialysis. In in vitro study, the accumulative skin permeated quantity (ASPQ) and skin permeation rate (SPR) of simonenine (SIN) in the optimized MMPTs were prominently higher than that in the other MMPTs. The optimized MMPTs had a SIN ASPQ of over three times of SIN ASPQ in the liposomes and much larger SPR of SIN compared with the latter. In contrast, the drug deposition of the optimized MMPTs in the stratum corneum was much less than that of the conventional liposomes. It was noteworthy that the drug deposition curve in the whole skin (stratum corneum-stripped skin, either) for the optimized MMPTs increased initially and then decreased with an obvious peak deposition amount at 12h, while, a relatively steady curve was observed for the liposomes. In in vivo cutaneous pharmacokinetic study, the steady state concentration (C_ss) and the area under the curve (AUC_0→t) of SIN from the optimized MMPTs was 8.7 and 8.2 folds higher than those from the liposomes, respectively. Moreover, the MRT_0-inf of SIN from optimal MMPTs got shorter than that from the liposomes. It can be concluded that the optimized MMPTs obviously enhance the percutaneous absorption of sinomenine.

Open Flow Microperfusion as a Dermal Pharmacokinetic Approach to Evaluate Topical Bioequivalence

Background

The availability of generic topical dermatological drug products is constrained by the limited methods established to assess topical bioequivalence (BE). A novel cutaneous pharmacokinetic approach, dermal open-flow microperfusion (dOFM), can continuously assess the rate and extent to which a topical drug becomes available in the dermis, to compare in vivo dermal bioavailability (BA) and support BE evaluations for topical products.

Objective

To evaluate whether dOFM is an accurate, sensitive, and reproducible in vivo method to characterize the intradermal BA of acyclovir from 5 % acyclovir creams, comparing a reference (R) product either to itself or to a different test (T) product.

Methods

In a single-center clinical study, R or T products were applied to six randomized treatment sites on the skin of 20 healthy human subjects. Two dOFM probes were inserted in each treatment site to monitor the intradermal acyclovir concentration for 36 h. Comparative BA (of R vs. R and T vs. R) was evaluated based on conventional BE criteria for pharmacokinetic endpoints (area under the curve and maximum plasma concentration) where the 90 % confidence interval of the geometric mean ratio between the T and R falls within 0.80–1.25.

Results

The positive control products (R vs. R) were accurately and reproducibly confirmed to be bioequivalent, while the negative control products (T vs. R) were sensitively discriminated not to be bioequivalent.

Conclusions

dOFM accurately, sensitively, and reproducibly characterized the dermal BA in a manner that can support BE evaluations for topical acyclovir 5 % creams in a study with n = 40 (20 subjects in this study).

Kinetics of Clobetasol-17-Propionate in Psoriatic Lesional and Non-Lesional Skin Assessed by Dermal Open Flow Microperfusion with Time and Space Resolution

Purpose

To evaluate the kinetics of topically applied clobetasol-17-propionate (CP-17) in lesional and non-lesional psoriatic skin when released from a commercially available low-strength cream using in vivo dermal open-flow microperfusion (dOFM).

Methods

Twelve patients received Dermovate® cream (CP-17, 0.05%) on small lesional and non-lesional skin test sites for 14 days, once daily. On day 1 and 14, dOFM samples were continuously taken in the dermis for 24 h post-dose and analyzed by LC-MS/MS. Probe depths were assessed by 50 MHz ultrasound scanning.

Results

Mixed-effects modelling identified skin condition, treatment duration and probe-depth as kinetics determining variables. The time- and depth-resolved intradermal data revealed (i) slower penetration of CP-17 into lesional than into non-lesional skin, (ii) normalized (faster) skin penetration after repeated dosing, and (iii) no CP-17 accumulation within the dermis independently of the skin condition.

Conclusions

Intradermal investigation of a highly lipophilic drug released from low-strength cream was successfully performed by using dOFM and timely and spatially, i.e., probe-depth dependent, resolved kinetic data were delivered. These data support the assumption that the thickened psoriatic stratum corneum might act as trap compartment which lowers the skin penetration rate for lipophilic topical drugs.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-016-1960-y) contains supplementary material, which is available to authorized users.

Trials and tribulations of skin iontophoresis in therapeutics

Iontophoresis is a method of non-invasive transdermal drug delivery based on the transfer of charged molecules using a low-intensity electric current. Both local and systemic administration are possible; however, the skin pharmacokinetics of iontophoretically delivered drugs is complex and difficult to anticipate. The unquestionable theoretical advantages of the technique make it attractive in several potential applications. After a brief review of the factors influencing iontophoresis, we detail the current applications of iontophoresis in therapeutics and the main potential applications under investigation, including systemic and topical drugs and focusing on the treatment of scleroderma-related ulcerations. Finally, we address the issue of safety, which could be a limitation to the routine clinical use of iontophoresis.

Role of microdialysis in pharmacokinetics and pharmacodynamics: current status and future directions

Diagnostic and therapeutic decisions in medical practice are still generally based on blood concentrations of drugs and/or biomolecules despite the knowledge that biochemical events and pharmacological effects usually take place in tissue rather than in the bloodstream. Microdialysis is a semi-invasive technique that is able to measure concentrations of the free, active drug or endogenous compounds in almost all human tissues and organs. It is currently being used to monitor brain metabolic processes and quantify tissue biomarkers, and determine transdermal drug distribution and tissue pharmacokinetics, confirming its importance as a widely used sampling technique in clinical drug monitoring and drug development as well as therapy and disease follow-up, contributing to rationalizing drug dosing regimens and influencing the clinical decision-making process.

Role of microdialysis in pharmacokinetics and pharmacodynamics: current status and future directions

Diagnostic and therapeutic decisions in medical practice are still generally based on blood concentrations of drugs and/or biomolecules despite the knowledge that biochemical events and pharmacological effects usually take place in tissue rather than in the bloodstream. Microdialysis is a semi-invasive technique that is able to measure concentrations of the free, active drug or endogenous compounds in almost all human tissues and organs. It is currently being used to monitor brain metabolic processes and quantify tissue biomarkers, and determine transdermal drug distribution and tissue pharmacokinetics, confirming its importance as a widely used sampling technique in clinical drug monitoring and drug development as well as therapy and disease follow-up, contributing to rationalizing drug dosing regimens and influencing the clinical decision-making process.

Clinical applicability of dOFM devices for dermal sampling

BACKGROUND

Sampling the dermal interstitial fluid (ISF) allows the pharmacokinetics and pharmacodynamics of dermatological drugs to be studied directly at their site of action. Dermal open-flow microperfusion (dOFM) is a recently developed technique that can provide minimally invasive, continuous, membrane-free (thus unfiltered) access to the dermal ISF. Herein, we evaluate the clinical applicability and reliability of novel wearable dOFM devices in a clinical setting.

METHODS

Physicians inserted 141 membrane-free dOFM probes into the dermis of 17 healthy and psoriatic volunteers and sampled dermal ISF for 25 h by using wearable push-pull pumps. The tolerability, applicability, reproducibility, and reliability of multiple insertions and 25 h continuous sampling was assessed by pain scoring, physician feedback, ultrasound probe depth measurements, and 25 h-drift and variability of the sodium relative recovery.

RESULTS

Insertion pain was moderate and decreased with each additional probe. Probe insertion was precise, although slightly deeper in lesional skin. The wearable push-pull pump enabled uninterrupted ISF sampling over 25 h with low variability. The relative recovery was drift-free and highly reproducible.

CONCLUSION

dOFM sampling devices are tolerable and reliable for prolonged continuous dermal sampling in a multiprobe clinical setting. These devices should enable the study of a wide range of drugs and their biomarkers in the skin.

In vivo microdialysis for the evaluation of transfersomes as a novel transdermal delivery vehicle for cinnamic acid

In this study, cinnamic acid-loaded transfersomes were prepared and dermal microdialysis sampling was used in Sprague-Dawley rats to compare the amount of drug released into the skin using transfersomes as transdermal carriers with that released on using conventional liposomes. The formulation of cinnamic acid-loaded transfersomes was optimized by a uniform design through in vitro transdermal permeation studies. Hydration time was confirmed as a significant factor influencing the entrapment efficiency of transfersomes, further affecting their transdermal flux in vitro. The fluxes of cinnamic acid from transfersomes were all higher than those from conventional liposomes, and the flux from the optimal transfersome formulation was 3.01-fold higher than that from the conventional liposomes (p < 0.05). An in vivo microdialysis sampling method revealed that the dermal drug concentrations from transfersomes applied on various skin regions were much lower than those required with conventional liposomes. After the administration of drug-containing transfersomes and liposomes on abdominal skin regions of rats for a period of 10 h, the Cmax of cinnamic acid from the compared liposomes was 3.21 ± 0.25 μg/mL and that from the transfersomes was merely 0.59 ± 0.02 μg/mL. The results suggest that transfersomes can be used as carriers to enhance the transdermal delivery of cinnamic acid, and that these vehicles may penetrate the skin in the complete form, given their significant deformability.