Michael David Bell

Delivery of ibuprofen to the skin

Ibuprofen (IBU) has been available as a topical skin preparation for more than two decades. Its primary indication is for the relief of pain and inflammation in rheumatic disease and other musculoskeletal conditions. This article reviews the various formulation strategies which have been investigated for percutaneous IBU delivery to date. The focus is on studies which have been conducted with IBU in the free base form on human or porcine skin as data from other species are known to overestimate likely permeation in man. Emerging technologies for enhanced dermal delivery of IBU are considered including methods which require physical disruption of the membrane. The role of biophysical techniques such as Confocal Raman Spectroscopy in the rational development of IBU formulations is also discussed.

A comparative study of the in vitro permeation of ibuprofen in mammalian skin, the PAMPA model and silicone membrane

Human skin remains the membrane of choice when conducting in vitro studies to determine dermal penetration of active pharmaceutical ingredients or xenobiotics. However there are ethical and safety issues associated with obtaining human tissue. For these reasons synthetic membranes, cell culture models or in silico predictive algorithms have been researched intensively as alternative approaches to predict dermal exposure in man. Porcine skin has also been recommended as an acceptable surrogate for topical or transdermal delivery research. Here we examine the in vitro permeation of a model active, ibuprofen, using human or porcine skin, as well as the Parallel Artificial Membrane Permeation Assay (PAMPA) model and silicone membrane. Finite dose studies were conducted in all models using commercial ibuprofen formulations and simple volatile ibuprofen solutions. The dose applied in the PAMPA model was also varied in order to determine the amount of applied formulation which best simulates typical amounts of topical products applied by patients or consumers. Permeation studies were conducted up to 6h for PAMPA and silicone and up to 48h for human and porcine skin. Cumulative amounts permeated at 6h were comparable for PAMPA and silicone, ranging from 91 to 136μg/cm(2) across the range of formulations studied. At 48h, maximum ibuprofen permeation in human skin ranged from 11 to 38μg/cm(2) and corresponding values in porcine skin were 59-81μg/cm(2). A dose of 1μL was confirmed as appropriate for finite dose studies in the PAMPA model. The formulation which delivered the greatest amount of ibuprofen in human skin was also significantly more efficient than other formulations when evaluated in the PAMPA model. The PAMPA model also discriminated between different formulation types (i.e. gel versus solution) compared with other models. Overall, the results confirm the more permeable nature of the PAMPA, silicone membrane and porcine tissue models to ibuprofen compared with human skin. Further finite dose studies to elucidate the effects of individual excipients on the barrier properties of the PAMPA model are needed to expand the applications of this model. The range of actives that are suitable for study using the model also needs to be delineated.

Melanin fate in the human epidermis: a reassessment of how best to detect and analyse histologically

Melanin is the predominant pigment responsible for skin colour and is synthesized by the melanocyte in the basal layer of the epidermis and then transferred to surrounding keratinocytes. Despite its optical properties, melanin is barely detectable in unstained sections of human epidermis. However, identification and localization of melanin is of importance for the study of skin pigmentation in health and disease. Current methods for the histologic quantification of melanin are suboptimal and are associated with significant risk of misinterpretation. The aim of this study was to reassess the existing literature and to develop a more effective histological method of melanin quantification in human skin. Moreover, we confirm that Warthin‐Starry (WS) stain provides a much more sensitive and more specific melanin detection method than the commonplace Fontana‐Masson (FM) stain. For example, WS staining sensitivity allowed the visualization of melanin even in very pale Caucasian skin that was missed by FM or Von Kossa (VK) stains. From our reassessment of the histology‐related literature, we conclude that so‐called melanin dust is most likely an artifact of discoloration due to non‐specific silver deposition in the stratum corneum. Unlike FM and VK, WS was not associated with this non‐specific stratum corneum darkening, misinterpreted previously as ‘degraded’ melanin. Finally, WS melanin particle counts were largely similar to previously reported manual counts by transmission electron microscopy, in contrast to both FM and VK. Together these findings allow us to propose a new histology/Image J‐informed method for the accurate and precise quantification of epidermal melanin in skin.

Age-Related Changes to Human Stratum Corneum Lipids Detected Using Time-of-Flight Secondary Ion Mass Spectrometry Following in Vivo Sampling

This work demonstrates the ability to detect changes in both quantity and spatial distribution of human stratum corneum (SC) lipids from samples collected in vivo. The SC functions as the predominant barrier to the body, protecting against the penetration of xenobiotic substances. Changes to the SC lipid composition have been associated with barrier impairment and consequent skin disorders, and it is therefore important to monitor and quantify changes to this structure. This work demonstrates the first reported use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to assess physiological changes to human SC as a function of depth. This technique provides exceptional sensitivity and chemical specificity, allowing analysis of single tape stripped samples taken from volunteers. Using this methodology we were able to successfully identify chemical differences in human SC resulting from both intrinsic and extrinsic (photo) aging. Samples were collected from women of two age groups (under 27 and postmenopausal) and from two body sites with varying UV exposure (inner forearm and dorsal hand), and differences were identified using multivariate data analysis. The key finding was the significant aged-related increase and change in spatial distribution of the sterol cholesterol sulfate, a membrane stabilizing lipid. Significant changes in the prevalence of both lignoceric acid (C24:0) and hexacosanoic acid (C26:0) were also observed. This work describes previously unreported age-related chemical changes to human SC, providing an insight into aging mechanisms which may improve the design of both pharmaceutical and cosmetic topical products.

Over-the-counter anti-ageing topical agents and their ability to protect and repair photoaged skin.

Ultraviolet radiation (UVR)-induced photoageing of the skin is associated with characteristic clinical features including a sallow complexion, deep, coarse wrinkles and a loss of elasticity. Remodelling of the dermal extracellular matrix (ECM) with changes to fibrillar collagens, elastic fibres and glycosaminoglycans is likely to be a major contributing factor to these particular clinical signs. Over-the-counter (OTC) topical formulations are one popular management strategy for preventing and/or repairing photoaged skin, most commonly targeting wrinkles as these are often the most concerning clinical feature. Due to the cosmetic nature of such formulations, evidence of their clinical efficacy and mechanism of action is often limited. However, these formulations usually contain putative active ingredients which individually have been subject to in vitro and in vivo investigation for efficacy as photoageing interventions. This review highlights commonly found ingredients within OTC formulations and assesses the evidence for: (i) their efficacy in clinically and histologically improving photoaged skin; (ii) the potential mechanisms of action; and (iii) their ability to act synergistically with complementary ingredients to enhance the clinical outcome.

The effects of Sophora angustifolia and other natural plant extracts on melanogenesis and melanin transfer in human skin cells

Skin pigmentation is a multistep process of melanin synthesis by melanocytes, its transfer to recipient keratinocytes and its degradation. As dyspigmentation is a prominent marker of skin ageing, novel effective agents that modulate pigmentation safely are being sought for both clinical and cosmetic use. Here, a number of plant extracts were examined for their effect on melanogenesis (by melanin assay and Western blotting) and melanin transfer (by confocal immunomicroscopy of gp100‐positive melanin granules in cocultures and by SEM analysis of filopodia), in human melanocytes and in cocultures with phototype‐matched normal adult epidermal keratinocytes. Mulberry, Kiwi and Sophora extracts were assessed against isobutylmethylxanthine, hydroquinone, vitamin C and niacinamide. Compared with unstimulated control, all extracts significantly reduced melanogenesis in human melanoma cells and normal adult epidermal melanocytes. These extracts also reduced melanin transfer and reduced filopodia expression on melanocytes, similar to hydroquinone and niacinamide, indicating their effectiveness as multimode pigmentation actives.

A new in vitro assay to test UVR protection of dermal extracellular matrix components by a flat spectrum sunscreen.

The efficacy of topical sunscreens is currently assessed by crude, costly and time consuming in vivo assays. We have previously demonstrated that components of the dermal extracellular matrix (ECM), rich in UV-absorbing amino acids, are susceptible to damage by solar simulated radiation (SSR) in vitro. Here we developed an in vitro method to test the ability of sunscreens to protect fibrillin-rich microfibrils (FRM) and fibronectin, key components of the dermal ECM from UV-induced damage. Solutions of FRM or fibronectin were irradiated without protection, in the presence of a vehicle or a commercially-available flat-spectrum sunscreen. The effect of SSR on molecular structure was determined by atomic force microscopy (FRM) and SDS-PAGE (fibronectin). Following irradiation, FRM periodicity became bi-modally distributed (peaks: 40nm & 59nm) compared to the unimodal distribution in unexposed controls (peak: 50nm). Irradiation in the presence of flat-spectrum sunscreen protected against this change, maintaining the unimodal distribution. SSR induced significant aggregation of fibronectin (p=0.005), which was abrogated by sunscreen. These results demonstrate that this in vitro assay system is sufficiently sensitive to act as an initial/additional screen of sunscreen efficacy. We conclude that sunscreen can reduce UV-mediated damage of key dermal ECM in vitro and thereby prevent remodelling associated with photoageing.

A theoretical and experimental study of the temporal reduction in UV protection provided by a facial day cream

To investigate how the UV protection provided by a facial day cream reduces over the course of a day.

An explanation for the mysterious distribution of melanin in human skin: a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes

Melanin is synthesized by melanocytes in the basal layer of the epidermis. When transferred to surrounding keratinocytes melanin is the key ultraviolet radiation‐protective biopolymer responsible for skin pigmentation. Most melanin is observable in the proliferative basal layer of the epidermis and only sparsely distributed in the stratifying/differentiating epidermis. The latter has been explained as ‘melanin degradation’ in suprabasal layers.

The Skin Extracellular Matrix as a Target of Environmental Exposure: Molecular Mechanisms, Prevention and Repair

The dermal extracellular matrix (ECM) undergoes age-related remodelling which leads to wrinkle formation and increased tissue fragility. In healthy young individuals structural ECM assemblies, such as collagens and elastin, are ordered into larger scale structures (collagen fibril bundles and elastic fibres), which mediate the mechanical properties of the dermis. Equally important however, are the less abundant extracellular accessory molecules that regulate complex processes such as cell migration, wound healing and which also orchestrate complex ECM protein-to-protein interactions. These structures and molecular interactions are perturbed in extrinsically aged skin. Using bioinformatics alongside established molecular investigations opens up exciting new ways to understand skin ageing and may help to identify novel biomarkers. In this chapter we propose a mechanism whereby UVR-induced damage of key ECM molecules drives elastosis. We discuss how: i) the amino acid composition of proteins can be used to predict their susceptibility to damage by ultraviolet radiation (UVR) and ii) other environmental factors, such as smoking and air pollution may contribute towards premature skin ageing. Finally this chapter reviews the latest topical applications and systemic therapies that may be able to reverse the consequences of damage to the ECM in ageing.