The 500 Dalton rule for the skin penetration of chemical compounds and drugs

Human skin has unique properties of which functioning as a physicochemical barrier is one of the most apparent. The human integument is able to resist the penetration of many molecules. However, especially smaller molecules can surpass transcutaneously. They are able to go by the corneal layer, which is thought to form the main deterrent. We argue that the molecular weight (MW) of a compound must be under 500 Dalton to allow skin absorption. Larger molecules cannot pass the corneal layer. Arguments for this "500 Dalton rule" are; 1) virtually all common contact allergens are under 500 Dalton, larger molecules are not known as contact sensitizers. They cannot penetrate and thus cannot act as allergens in man; 2) the most commonly used pharmacological agents applied in topical dermatotherapy are all under 500 Dalton; 3) all known topical drugs used in transdermal drug-delivery systems are under 500 Dalton. In addition, clinical experience with topical agents such as cyclosporine, tacrolimus and ascomycins gives further arguments for the reality of the 500 Dalton rule. For pharmaceutical development purposes, it seems logical to restrict the development of new innovative compounds to a MW of under 500 Dalton, when topical dermatological therapy or percutaneous systemic therapy or vaccination is the objective.

Fucoxanthin, a marine carotenoid present in brown seaweeds and diatoms: metabolism and bioactivities relevant to human health

The marine carotenoid fucoxanthin can be found in marine brown seaweeds, the macroalgae, and diatoms, the microalgae, and has remarkable biological properties. Numerous studies have shown that fucoxanthin has considerable potential and promising applications in human health. In this article, we review the current available scientific literature regarding the metabolism, safety, and bioactivities of fucoxanthin, including its antioxidant, anti-inflammatory, anticancer, anti-obese, antidiabetic, antiangiogenic and antimalarial activities, and its protective effects on the liver, blood vessels of the brain, bones, skin, and eyes. Although some studies have shown the bioavailability of fucoxanthin in brown seaweeds to be low in humans, many studies have suggested that a dietary combination of fucoxanthin and edible oil or lipid could increase the absorption rate of fucoxanthin, and thus it might be a promising marine drug.

Glucocorticoid therapy-induced skin atrophy

Glucocorticoids (GCs) are highly effective for the topical treatment of inflammatory skin diseases. Their long-term use, however, is often accompanied by severe and partially irreversible adverse effects, with atrophy being the most prominent limitation. Progress in the understanding of GC-mediated molecular action as well as some advances in technologies to determine the atrophogenic potential of compounds has been made recently. It is likely that the detailed mechanisms of GC-induced skin atrophy will be discovered and in vitro models for the reliable prediction of atrophy will be established in the foreseeable future. This knowledge will not only facilitate safety profiling of established drugs but will also foster further drug discovery by improving compound characterization processes. New insights into GC modes of action will guide optimization strategies aiming at novel GC receptor ligands with improved effect/side effect profile.

The in vitro absorption of microfine zinc oxide and titanium dioxide through porcine skin

Microfine metallic oxides such as titanium dioxide or zinc oxide have been found to be highly protective against harmful UV rays. Because their long-term use could potentially lead to health effects if significant amounts of these microfine metallic oxides would be absorbed through the skin, the in vitro absorption of microfine zinc oxide and titanium oxide in cosmetic formulations through porcine skin was investigated. In the experiments with a microfine zinc oxide formulation, the mean total recoveries of Zn were in the range from 102% to 107% of the total Zn applied. Virtually the total amount of applied Zn was recovered in the first five tape strips. The amounts of Zn found in the skin membrane and the receptor fluid were comparable in untreated, vehicle treated or test substance treated skin preparations. The absorption-time plots from diffusion cells treated with the vehicle did not differ from those treated with the ZnO containing formulation. In the experiments with microfine titanium dioxide formulations T-Lite SF-S and T-Lite SF, mean total recoveries of Ti ranged from 98% to 100% and 86% to 93% of the total Ti applied, respectively. Virtually the total amount of applied Ti could be removed from the skin surface by washing. The amounts of titanium found in the tape strips and skin preparations were in the order of the analytical determination limit. No Ti was found in the receptor fluid at any sampling time. The results show that neither zinc or titanium ions nor microfine zinc oxide or titanium dioxide particles were able to penetrate porcine stratum corneum. Therefore, from the absence of internal exposure we conclude that their use in sunscreens does not pose a health risk.

Site-specific drug delivery to pilosebaceous structures using polymeric microspheres

In order to improve the therapeutic index of adapalene, a new drug under development for the treatment of acne, site-specific delivery to the hair follicles using 50:50 poly(DL-lactic-co-glycolic acid) microspheres as particulate carriers was investigated in vitro and in vivo. The percutaneous penetration pathway of the microspheres was shown to be dependent on their mean diameter. Thus, after topical application onto hairless rat or human skin, adapalene-loaded microspheres (5-microns diameter) were specifically targeted to the follicular ducts and did not penetrate via the stratum corneum. The in vitro release of adapalene from the microspheres into artificial sebum at 37 degrees C was controlled and faster than the in vivo sebum excretion in humans. Aiming to reduce either the applied dose of drug or the frequency of administration, different formulations of adapalene-loaded microspheres were evaluated in vivo in the rhino mouse model. A dose-related comedolytic activity of topical formulations of adapalene-loaded microspheres was observed in this model. Furthermore, by applying a site-specific drug delivery system (0.1% adapalene) every other day or by administering a 10-fold less concentrated targeted formulation (0.01%) every day, a pharmacological activity equivalent to a daily application of an aqueous gel containing drug crystals (0.1% adapalene) was observed. Since an aqueous gel containing 10% adapalene-loaded microspheres was not irritating in a rabbit skin irritancy test, this formulation was applied onto forearms of human volunteers. Site-specific drug delivery was further evidenced by follicular biopsy. Since an aqueous gel containing 10% adapalene-loaded microspheres was not irritating in a rabbit skin irritancy test, this formulation was applied onto forearms of human volunteers. Site-specific drug delivery was further evidenced by follicular biopsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Transdermal delivery of methotrexate: iontophoretic delivery from hydrogels and passive delivery from microemulsions

In vitro assays were performed to investigate the effectiveness of transdermal administration of methotrexate (MTX) by iontophoretic delivery from two types of hydrogel and passive delivery from two types of microemulsion. Both iontophoretic delivery of MTX from hydrogels and passive delivery from microemulsions were more effective than passive delivery from aqueous solutions of the drug. In the iontophoretic delivery assays, the type of hydrogel used and the concentration of the drug in the loading solution had little influence on effectiveness of delivery. In the passive delivery assays, we used both water/oil (w/o) and oil/water (o/w) microemulsions: effectiveness of delivery was higher from o/w systems. At the end of all assays, significant amounts of MTX were detected in the skin. These results suggest that both hydrogels and microemulsions may be of value for the topical administration of MTX in the treatment of psoriasis.

Infliximab monotherapy provides rapid and sustained benefit for plaque-type psoriasis

BACKGROUND

Effective, rapid-acting, safe therapies are needed for the long-term treatment of psoriasis.

OBJECTIVE

We sought to evaluate infliximab monotherapy in maintaining clinical benefit in psoriasis.

METHODS

A total of 33 patients received 3 doses of 5 or 10 mg/kg of infliximab or placebo at weeks 0, 2, and 6 (double-blind phase). During the open-label phase (weeks 10-26), responding patients were evaluated for relapse (loss of at least half of the improvement in the Psoriasis Area Severity Index score at week 10) and retreated with open-label infliximab (5 or 10 mg/kg) as needed. Placebo nonresponders were treated with an induction regimen of infliximab (5 or 10 mg/kg) and followed up through week 26.

RESULTS

In all, 29 patients received either 5 or 10 mg/kg of infliximab in the open-label extension. At week 26, psoriasis area severity index response was maintained in 40% and 73% of patients receiving 5 and 10 mg/kg of infliximab, respectively.

CONCLUSION

Infliximab produced a rapid, effective, and sustainable (through week 26) effect in patients with moderate to severe psoriasis.

Dermal drug delivery by liposome encapsulation: clinical and electron microscopic studies

The fate of liposomes and the encapsulated drug was studied after topical application on the skin. Lidocaine applied on the forearm of human volunteers produced greater local anaesthetic effect in the liposomal form than in the cream form (p less than or equal to 0.001 after 1 h application). Autoradiography demonstrated higher concentration (p less than or equal to 0.01) of 14C-lidocaine in the epidermis and dermis of guinea pigs treated with liposome-encapsulated lidocaine as opposed to lidocaine in Dermabase cream. Electron microscopic observations, using colloidal iron as an electrodense marker, indicated that intact liposomes penetrated into the skin and deposited in the dermis where they acted as a slow release depot system. On the basis of results in the human volunteers and animals, a hypothetical model for liposome-skin interaction is proposed.

Azelaic acid. A review of its pharmacological properties and therapeutic efficacy in acne and hyperpigmentary skin disorders

Azelaic acid is a naturally occurring saturated dicarboxylic acid which, on topical application (usually as a 20% cream), has been shown to be effective in the treatment of comedonal acne and inflammatory (papulopustular, nodular and nodulocystic) acne, as well as various cutaneous hyperpigmentary disorders characterised by hyperactive/abnormal melanocyte function, including melasma and, possibly, lentigo maligna. In addition, azelaic acid has an antiproliferative and cytotoxic effect on the human malignant melanocyte, and preliminary findings indicate that it may arrest the progression of cutaneous malignant melanoma. The mechanism of this selective cytotoxic action of azelaic acid is unclear, but may possibly be related to its inhibition of mitochondrial oxidoreductase activity and DNA synthesis. In controlled studies, topical azelaic acid demonstrated comparable anti-acne efficacy to topical tretinoin, benzoyl peroxide, erythromycin and oral tetracycline, while in patients with melasma azelaic acid proved at least as effective as topical hydroquinone. On topical application azelaic acid is well tolerated, with adverse effects apparently limited to a generally mild and transient local cutaneous irritation. Thus, topical azelaic acid, employed either as monotherapy or in combination with other treatments, is likely to prove of value in the management of acne and several hyperpigmentary disorders, most notably melasma.

Clinical Pharmacokinetics and Pharmacodynamics of Infliximab in the Treatment of Inflammatory Bowel Disease

Infliximab was the first monoclonal antibody to be approved for the treatment of pediatric and adult patients with moderately to severely active Crohn's disease (CD) and ulcerative colitis (UC). It has been shown to induce and maintain both clinical remission and mucosal healing in pediatric and adult patients with inflammatory bowel disease (IBD) who are unresponsive or refractory to conventional therapies. The administration of infliximab is weight-based and the drug is administered intravenously. The volume of distribution of infliximab is low and at steady state ranges from 4.5 to 6 L. Therapeutic monoclonal antibodies, such as immunoglobulins, are cleared from the circulation primarily by catabolism. Median infliximab half-life is approximately 14 days. Infliximab concentration-time data in patients with CD and UC have been shown to be highly variable within an individual patient over time and between individuals by multiple population pharmacokinetic models. Covariates that have been identified to account for a part of the observed inter- and intra-individual variability in clearance are the presence of antidrug antibodies, use of concomitant immunomodulators, degree of systemic inflammation, serum albumin concentration, and body weight, which can affect the pharmacodynamic response. This article provides a comprehensive review of the clinical pharmacokinetics and pharmacodynamics of infliximab, as well as the role of therapeutic drug monitoring in the treatment of IBD.

Safety and tolerability of 1% pimecrolimus cream among infants: experience with 1133 patients treated for up to 2 years

Pimecrolimus is a calcineurin inhibitor developed for the topical treatment of atopic dermatitis. During the clinical development of 1% pimecrolimus cream, 1133 patients 3 to 23 months of age with mild to severe atopic dermatitis were treated for up to 2 years. The objective of this review is to discuss the safety and tolerability of 1% pimecrolimus cream among infants, on the basis of the combined results from all studies (4 pharmacokinetic studies and 6 clinical trials) conducted among these patients. Pimecrolimus blood concentrations measured for 35 patients were consistently low (< or =1 ng/mL in >80% of samples), irrespective of the disease severity and extent, and remained low during intermittent treatment for up to 1 year. The level of systemic exposure to pimecrolimus among infants was comparable to that observed for older pediatric patients enrolled in the same studies and treated in the same way with 1% pimecrolimus cream, which indicated that young pediatric patients are not at higher risk of significant percutaneous absorption of topically applied pimecrolimus, despite their large skin surface area/body mass ratio. The 6 clinical trials included a total of 1098 infants, who were treated for periods ranging from 4 weeks to 2 years. Most of these patients (60%) had moderate to severe disease at baseline. The most frequently reported adverse events were common childhood disorders such as nasopharyngitis, pyrexia, upper respiratory tract infections, ear infections, and bronchitis. During the double-blind (DB) studies or DB phases of studies, the incidence rates for the most frequently reported adverse events were similar for patients who received 1% pimecrolimus cream and patients who received the vehicle, except for the incidence of teething, which was higher among the pimecrolimus-treated infants (relative risk: 2.02; 95% confidence interval: 1.32-3.27). Treatment with 1% pimecrolimus cream was not associated with an increase in the overall incidence of nonskin infections, compared with the vehicle (relative risk: 1.015; 95% confidence interval: 0.88-1.18). The incidence density (ID) rates for total bacterial, fungal, parasitic, and viral skin infections during the DB studies or DB phases of studies were comparable for patients treated with 1% pimecrolimus cream and patients who received the vehicle. The ID rate of herpes simplex virus infections was 0.8 cases per 1000 patient-months of follow-up monitoring among patients treated with 1% pimecrolimus cream and 1.7 cases per 1000 patient-months of follow-up monitoring among patients who received the vehicle. Considering all 1098 infants treated with 1% pimecrolimus cream in DB trials and open-label studies, the ID rate of clinically diagnosed eczema herpeticum was 1.3 cases per 1000 patient-months of follow-up monitoring. Burning and erythema were the most frequently reported application site reactions, with ID rates of 2.0 and 1.2 cases per 1000 patient-months of follow-up monitoring, respectively. No sign of immunosuppression was found among infants treated intermittently with 1% pimecrolimus cream for up to 2 years; they demonstrated normal immune responses to vaccinations and did not show increases in the incidence of systemic infections or skin infections over time.

Atopic dermatitis: Role of the skin barrier, environment, microbiome, and therapeutic agents

Atopic dermatitis (AD) is a chronic, inflammatory skin disorder characterized by eczematous and pruritic skin lesions. In recent decades, the prevalence of AD has increased worldwide, most notably in developing countries. The enormous progress in our understanding of the complex composition and functions of the epidermal barrier allows for a deeper appreciation of the active role that the skin barrier plays in the initiation and maintenance of skin inflammation. The epidermis forms a physical, chemical, immunological, neuro-sensory, and microbial barrier between the internal and external environment. Not only lesional, but also non-lesional areas of AD skin display many morphological, biochemical and functional differences compared with healthy skin. Supporting this notion, genetic defects affecting structural proteins of the skin barrier, including filaggrin, contribute to an increased risk of AD. There is evidence to suggest that natural environmental allergens and man-made pollutants are associated with an increased likelihood of developing AD. A compromised epidermal barrier predisposes the skin to increased permeability of these compounds. Numerous topical and systemic therapies for AD are currently available or in development; while anti-inflammatory therapy is central to the treatment of AD, some existing and novel therapies also appear to exert beneficial effects on skin barrier function. Further research on the skin barrier, particularly addressing epidermal differentiation and inflammation, lipid metabolism, and the role of bacterial communities for skin barrier function, will likely expand our understanding of the complex etiology of AD and lead to identification of novel targets and the development of new therapies.

Transdermal drug delivery: from micro to nano

Delivery across skin offers many advantages compared to oral or intravenous routes of drug administration. Skin however is highly impermeable to most molecules on the basis of size, hydrophilicity, lipophilicity and charge. For this reason it is often necessary to temporarily alter the barrier properties of skin for effective administration. This can be done by applying chemical enhancers, which alter the lipid structure of the top layer of skin (the stratum corneum, SC), by applying external forces such as electric currents and ultrasounds, by bypassing the stratum corneum via minimally invasive microneedles or by using nano-delivery vehicles that can cross and deliver their payload to the deeper layers of skin. Here we present a critical summary of the latest technologies used to increase transdermal delivery.

Potential of Curcumin in Skin Disorders

Curcumin is a compound isolated from turmeric, a plant known for its medicinal use. Recently, there is a growing interest in the medical community in identifying novel, low-cost, safe molecules that may be used in the treatment of inflammatory and neoplastic diseases. An increasing amount of evidence suggests that curcumin may represent an effective agent in the treatment of several skin conditions. We examined the most relevant in vitro and in vivo studies published to date regarding the use of curcumin in inflammatory, neoplastic, and infectious skin diseases, providing information on its bioavailability and safety profile. Moreover, we performed a computational analysis about curcumin's interaction towards the major enzymatic targets identified in the literature. Our results suggest that curcumin may represent a low-cost, well-tolerated, effective agent in the treatment of skin diseases. However, bypass of limitations of its in vivo use (low oral bioavailability, metabolism) is essential in order to conduct larger clinical trials that could confirm these observations. The possible use of curcumin in combination with traditional drugs and the formulations of novel delivery systems represent a very promising field for future applicative research.

Transepidermal water loss does not correlate with skin barrier function in vitro

The purpose of this study was to investigate the relationship between transepidermal water loss and skin permeability to tritiated water (3H2O) and the lipophilic penetrant sulfur mustard in vitro. No correlation was found between basal transepidermal water loss rates and the permeability of human epidermal membranes to 3H2O (p = 0.72) or sulfur mustard (p = 0.74). Similarly, there was no correlation between transepidermal water loss rates and the 3H2O permeability of full-thickness pig skin (p = 0.68). There was no correlation between transepidermal water loss rate and 3H2O permeability following up to 15 tape strips (p = 0.64) or up to four needle-stick punctures (p = 0.13). These data indicate that transepidermal water loss cannot be unconditionally ascribed to be a measure of skin barrier function. It is clear that further work should be conducted to interpret the significance of measuring transepidermal water loss by evaporimetry.

Absorption of sunscreens and other compounds through human skin in vivo: derivation of a method to predict maximum fluxes

PURPOSE

The goal of this study was to quantify the transdermally absorbed amounts of the sunscreens octyl dimethyl p-aminobenzoic acid, oxybenzone, 4-isopropyl-dibenzoylmethane, 3-(4-methylbenzylidene)-camphor, isoamyl-4-methoxycinnamate, the repellent and plasticizer dibutyl phthalate, the antioxidant 3.5-di-t-butyl-4-hydroxyanisol, and the antimicrobial compounds butyl-4-hydroxybenzoate, biphenyl-2-ol, and 2,4,4'-tri-chlor-2'-hydroxydiphenylether (triclosane). Permeabilities PB and maximum fluxes Jmax should be correlated with relevant physicochemical properties.

METHODS

Saturated solutions of the above-mentioned compounds in a propylene glycol/water mixture were applied to the skin using glass chambers which were fixed to the upper arms of volunteers. Maximum fluxes were calculated from concentration decreases in the vehicle.

RESULTS

A linear relationship between the logarithms of permeabilities PB of the penetrants (0.02-0.28 cm h-1) and the corresponding octanol/vehicle partition coefficients PCOct/V (166-186,208) was found. Consequently, the influence of aqueous boundary layers could be neglected. However, the slope of the resulting straight line of 0.38 is considerably smaller than unity indicating that PCOct/V does not represent the lipophilicity of the stratum corneum adequately. Maximum fluxes range from 0.5 to 130 micrograms cm-2 h-1. A general equation for the calculation of Jmax was derived based on experimental data taking into account the PCOct/V and the solubilities CsV of the respective penetrants in the vehicle.

Teratogenicity of isotretinoin revisited: species variation and the role of all-trans-retinoic acid

This paper reviews the teratogenicity of isotretinoin in regard to aspects of species variation, toxicokinetics, and metabolism. Particular emphasis is given to the hypothesis that most effects of isotretinoin (13-cis-retinoic acid) are mediated by isomerization to the all-trans-retinoic acid. This mechanism of action would provide a basis for the understanding of species differences and the extrapolation of experimental results to the human situation and thus improve drug development. The insensitive species (rat, mouse) eliminate the drug rapidly through detoxification to the beta-glucuronide; also, placental transfer is limited in these species. On the other hand, in sensitive species (primates), the drug is predominantly metabolized to the active 13-cis-4-oxo-retinoic acid; placental transfer is more extensive here. The beta-glucuronides showed limited placental transfer in all species examined; these metabolites exhibited very low, if any, measurable concentrations in the human. The 13-cis-retinoic acid is not appreciably bound to cellular retinoid-binding proteins or nuclear receptors and exhibits low tissue distribution and placental transfer. Its access to the nucleus may be extensive. Because of the long half life of 13-cis-retinoic acid, continuous isomerization results in significant area under the concentration-time curve levels of all-trans-retinoic acid in the mouse, monkey and the human; the all-trans-retinoic acid formed is extensively distributed across the placenta and may be an important factor that contributes to the teratogenic potency of 13-cis-retinoic acid. Isomerization cannot explain the teratogenic effects of 13-cis-retinoic acid in the rat and rabbit. It is concluded that the high teratogenic activity of isotretinoin in sensitive species (human, monkey) is related to slow elimination of the 13-cis-isomer, to metabolism to the 4-oxo-derivative, to increased placental transfer, to continuous isomerization and significant exposure of the target tissue to all-trans-retinoic acid; and to lack of binding to cytoplasmic retinoid binding proteins that could possibly result in ready access to the nucleus.

Microdialysis in clinical drug delivery studies

The introduction of in vivo microdialysis (MD) to clinical pharmacological studies has opened the opportunity to obtain previously inaccessible information about the drug distribution process to the clinically relevant target site. The aim of this review is to provide a comprehensive overview of the current literature about MD in drug delivery studies from a clinical perspective. In particular the application of MD in clinical--antimicrobial, oncological and transdermal--and neurological research will be described and the scope of MD in pharmacokinetic-pharmacodynamic (PK-PD) studies will be discussed. It is concluded that MD has a great potential for both academic and industrial research, and may become the method of choice for drug distribution studies in humans.

Systematic understanding the mechanisms of vitiligo pathogenesis and its treatment by Qubaibabuqi formula

ETHNOPHARMACOLOGICAL RELEVANCE

Vitiligo is a depigmentation disorder, which results in substantial cosmetic disfigurement and poses a detriment to patients' physical as well as mental. Now the molecular pathogenesis of vitiligo still remains unclear, which leads to a daunting challenge for vitiligo therapy in modern medicine. Herbal medicines, characterized by multi-compound and multi-target, have long been shown effective in treating vitiligo, but their molecular mechanisms of action also remain ambiguous.

MATERIALS AND METHODS

Here we proposed a systems pharmacology approach using a clinically effective herb formula as a tool to detect the molecular pathogenesis of vitiligo. This study provided an integrative analysis of active chemicals, drug targets and interacting pathways of the Uygur medicine Qubaibabuqi formula for curing Vitiligo.

RESULTS

The results show that 56 active ingredients of Qubaibabuqi interacting with 83 therapeutic proteins were identified. And Qubaibabuqi probably participate in immunomodulation, neuromodulation and keratinocytes apoptosis inhibition in treatment of vitiligo by a synergistic/cooperative way.

CONCLUSIONS

The drug-target network-based analysis and pathway-based analysis can provide a new approach for understanding the pathogenesis of vitiligo and uncovering the molecular mechanisms of Qubaibabuqi, which will also facilitate the application of traditional Chinese herbs in modern medicine.

Clinical pharmacokinetics and drug metabolism of tazarotene: a novel topical treatment for acne and psoriasis

Tazarotene (AGN 190168) is a new acetylenic retinoid which is effective for the topical treatment of patients with stable plaque psoriasis and mild to moderate acne vulgaris. Topical gel application provides direct delivery of tazarotene into the skin. At 10 hours after a topical application of 0.1% tazarotene gel to the skin of healthy individuals and patients with psoriasis, approximately 4 to 6% of the dose resided in the stratum corneum and 2% of the dose distributed to the viable epidermis and dermis. Tazarotene is rapidly hydrolysed by esterases to its active metabolite, tazarotenic acid. Tazarotenic acid does not accumulate in adipose tissue, but undergoes further metabolism to its sulfoxide and to other polar metabolites and is rapidly eliminated via both urinary and faecal pathways with a terminal half-life of about 18 hours. Percutaneous absorption is similar between healthy individuals and patients with facial acne, leading to plasma concentrations below 1 microg/L. The systemic bioavailability of tazarotene (measured as tazarotenic acid) is low, approximately 1% after single and multiple topical applications to healthy skin. In patients with psoriasis under typical conditions of use, systemic bioavailability increased during the initial 2 weeks of treatment from 1% (single dose) to 5% or less (steady state). The increased bioavailability is probably related to decreases in plaque elevation and scaling due to successful treatment, resulting in a less effective skin penetration barrier to tazarotene. Steady-state concentrations of tazarotenic acid are achieved within 2 weeks of topical treatment in both healthy and psoriatic skin types. The large variability in plasma concentrations observed in patients with psoriasis is probably because of the large differences in lesional skin condition, the amount of drug applied and the surface area of application. There was no significant drug accumulation in the body with long term treatment of patients with psoriasis. Topical administration of tazarotene requires dosages much smaller than those usually required for oral retinoids, such as isotretinoin, acitretin and etretinate, and it delivers the drug directly into the target skin tissues. The low systemic absorption and rapid systemic elimination of tazarotene and tazarotenic acid results in limited systemic exposure. Thus, topical tazarotene has a low potential for systemic adverse effects and is effective in the treatment of patients with acne and psoriasis.

Cellular metabolism and actions of 13-cis-retinoic acid

Retinoids (vitamin A and its derivatives) are potent substances for regulating the expression of many different genes within the body. The gene regulatory activities of retinoids are mediated primarily by the all-trans and 9-cis isomers of retinoic acid. Although 13-cis-retinoic acid (isotretinoin) does not have the potent gene regulatory activity of the other two isomers, it is an effective pharmacologic agent for treating a variety of dermatologic conditions. Because 13-cis-retinoic acid is also a naturally occurring retinoid that is present in the circulation, question is raised as to the biochemical mechanism(s) responsible for its pharmacologic efficacy. Some of this efficacy likely arises from the ability of 13-cis-retinoic acid to undergo isomerization to the significantly more active all-trans and 9-cis isomers; however, this does not account for all of the pharmacologic effects observed upon use of this retinoid. Some recent studies suggest that 13-cis-retinoic acid may act by inhibiting the actions of enzymes that are needed to metabolize steroids, while other recent studies indicate that 13-cis-retinoic acid acts through membrane receptors present on the surface of cells. At the present, it is not possible to rule out still other possible biochemical actions of 13-cis-retinoic acid in the body. It is clear, however, that if we are to fully understand the basis for the clinical efficacy of 13-cis-retinoic acid, a better understanding of such biochemical actions is needed.

Calcipotriol delivery into the skin with PEGylated liposomes

The D-vitamin analogue calcipotriol is commonly used for topical treatment of psoriasis, but skin penetration is required for calcipotriol to reach its pharmacological target: the keratinocytes in the lower epidermis. Liposomes can enhance the delivery of drugs into the skin, but a major challenge for the development of dosage forms containing liposomes is to maintain the colloidal stability in the formulation. The purpose of this study was to investigate the effect of stabilising liposomes with the lipopolymer poly(ethylene glycol)-distearoylphosphoethanolamine (PEG-DSPE) on the physicochemical properties of the liposomes and the ability to deliver membrane-intercalated calcipotriol into the skin. Inclusion of 0.5, l and 5 mol% PEG-DSPE in the membrane enhanced the colloidal stability of the liposomes without compromising the delivery of calcipotriol from the vehicle into excised pig skin. Calcipotriol-loaded liposomes with 1 mol% PEG-DSPE did even provide for a significantly increased deposition of calcipotriol into the stratum corneum. The size of the liposomes affected the penetration of calcipotriol into the stratum corneum since small unilamellar vesicles enhanced calcipotriol penetration as compared to large multilamellar vesicles, indicating that the liposomes to some extent migrate as intact vesicles into the stratum corneum. However, calcipotriol penetrated the skin better than the lipid component of the liposomes, suggesting that at least a fraction of the drug is released from the liposomes during skin migration. In conclusion, PEGylation is therefore a promising approach for stabilising calcipotriol-containing liposomal dispersions without compromising their favourable skin accumulation properties.

Potent and selective nonpeptidic inhibitors of procollagen C-proteinase

6-Cyclohexyl-N-hydroxy-3-(1,2,4-oxadiazol-5-yl)hexanamides were previously disclosed as inhibitors of procollagen C-proteinase (PCP) culminating in the identification of amide 1. Our objective was to discover a second inhibitor that would have improved affinity for PCP and to optimize properties for transepidermal delivery (TED) to intact skin. Further investigation of this template identified a number of potent PCP inhibitors (IC50 values of 2-6 nM) with improved TED flux. Sulfonamide 56 had excellent PCP enzyme activity when measured with a peptide substrate (Ki 8.7 nM) or with the endogenous substrate procollagen (IC50 3.4 nM) and demonstrates excellent selectivity over MMPs involved in wound healing (>10 000-fold). In the fibroplasia model, 56 inhibited deposition of insoluble collagen by 76 +/- 2% at 10 microM and was very effective at penetrating human skin in vitro with a TED flux of 1.5 microg/cm2/h, which compares favorably with values for agents that are known to penetrate skin well in vivo. Based on this profile, 56 (UK-421,045) was selected as a candidate for further preclinical evaluation as a topically applied, dermal anti-scarring agent.

Effect of benzoyl peroxide on antioxidant status, NF-kappaB activity and interleukin-1alpha gene expression in human keratinocytes

Benzoyl peroxide (BP) is used as a topical treatment for acne. Besides its anti-bacterial activity, the exact molecular mechanisms underlying its mode of action are not fully understood. In the current study, the effects of BP on cell viability, antioxidant status and, IL-1 and IL-8 gene expression were investigated in HaCaT keratinocytes. Keratinocytes incubated for 24 h with BP exhibited a dose-dependent cytotoxicity at concentrations above 250 microM. Furthermore, in the presence of 300 microM BP about 50% of the cellular vitamin E was depleted within the first 30 min. The intracellular ratio of oxidized to reduced glutathione (GSSG/GSH) was increased significantly starting 6 h after BP treatments indicating that BP reacts rapidly with targets in the cell membrane and more slowly with those in the cytosol. NF-kappaB transactivation was not significantly affected by BP. However, BP treatment of HaCaT keratinocytes resulted in a dose-dependent increase in IL-1alpha gene expression whereas no changes in IL-8 mRNA levels were observed. These results demonstrate that BP induces an inflammatory reaction mediated by oxidative stress by a pathway independent of the redox-sensitive transcription factor NF-kappaB.

First-in-human study to assess guselkumab (anti-IL-23 mAb) pharmacokinetics/safety in healthy subjects and patients with moderate-to-severe psoriasis

PURPOSE

The purpose of this study is to evaluate the pharmacokinetics, immunogenicity, safety, and tolerability of guselkumab, a human monoclonal antibody with high affinity and specificity for binding to interleukin-23.

METHODS

In this first-in-human, phase 1, randomized study, a single intravenous (IV; 0.03-10 mg/kg) or subcutaneous (SC; 10-300 mg) dose of guselkumab was administered to 47 healthy subjects, and a single SC dose (placebo, 10, 30, 100, 300 mg) was administered to 24 patients with moderate-to-severe psoriasis.

RESULTS

Mean maximum observed serum concentration and area under the zero-to-infinity serum concentration-time curve of guselkumab increased in an approximately dose-proportional manner over the dose range of 0.03-10 mg/kg following a single IV administration or 10-300 mg following a single SC administration. Mean clearance and volume of distribution ranged from 3.62-6.03 mL/day/kg and 99.38-123.22 mL/kg, respectively. Mean half-life ranged from 12 to 19 days in healthy subjects and patients with psoriasis. Among guselkumab-treated subjects/patients, 1/30 (3.3 %) healthy subjects in the IV group, 0/6 healthy subjects in the SC group, and 1/20 (5.0 %) patients with psoriasis tested positive for antibodies to guselkumab. No clinically significant adverse events were identified in this study.

CONCLUSION

Guselkumab pharmacokinetic profiles were generally comparable between healthy subjects and patients with psoriasis. Guselkumab, administered as an IV infusion or SC injection, was well tolerated in healthy subjects and patients with psoriasis.