Langerhans cells, keratinocytes, nitric oxide and psoriasis

More than skin deep: using polymers to facilitate topical delivery of nitric oxide

Skin, the largest organ in the human body, provides several important functions, including providing protection from mechanical impacts, micro-organisms, radiation and chemicals; regulation of body temperature; the sensations of touch and temperature; and the synthesis of several substances including vitamin D, melanin, and keratin. Common dermatological disorders (CDDs) include inflammatory or immune-mediated skin diseases, skin infection, skin cancer, and wounds. In the treatment of skin disorders, topical administration has advantages over other routes of administration, and polymers are widely used as vehicles to facilitate the delivery of topical therapeutic agents, serving as matrices to keep therapeutic agents in contact with the skin. Nitric oxide (NO), a cellular signalling molecule, has attracted significant interest in treating a broad spectrum of diseases, including various skin disorders. However, there are a number of challenges in effectively delivering NO. It must be delivered in a controlled manner at sufficient concentrations to be efficacious and the delivery system must be stable during storage. The use of polymer-based systems to deliver NO topically can be an effective strategy to overcome these challenges. There are three main approaches for incorporating NO with polymers in topical delivery systems: (i) physical incorporation of NO donors into polymer bases; (ii) covalent attachment of NO donors to polymers; and (iii) encapsulation of NO donors in polymer-based particles. The latter two approaches provide the greatest control over NO release and have been used by numerous researchers in treating CDDs, including chronic wounds and skin cancer.

Picea mariana polyphenolic extract inhibits phlogogenic mediators produced by TNF-α-activated psoriatic keratinocytes: Impact on NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Picea mariana ((Miller) Britton, Sterns, and Poggenburg; Pinaceae) bark has been traditionally used by North American natives for treating topical inflammations. It has been also suggested to improve various inflammatory skin disorders like Psoriasis vulgaris. Extracts from this bark storage protein contain polyphenolic compounds which have well-known antiinflammatory activities. Based on the capacity of polyphenolic compounds to modulate functions of normal human keratinocytes, this study was set up to decipher the mechanisms of action of a chemically characterized polyphenolic extract from Picea mariana bark (BS-EAcf) on lesional keratinocytes of skin with psoriasis vulgaris, a disease driven by the immune system in which TNF-α plays a significant role.

MATERIALS AND METHODS

BS-EAcf corresponds to the ethyl acetate soluble fraction from the hot water extract of Picea mariana bark. BS-EAcf effects were evaluated in normal human (NHK) and psoriatic (PK) keratinocytes stimulated by TNF-α. Cell viability was assessed by lactate deshydrogenase release and propidium iodide (PI) staining. The mechanisms of action of BS-EAcf in keratinocytes were investigated by flow cytometry, ELISAs, RT-PCR and western blot analyses.

RESULTS

PK exhibited a higher response to TNF-α than NHK regarding the ICAM-1 expression and the production of NO, IL-6, IL-8, fractalkine and PGE2, whereas BS-EAcf significantly inhibited this TNF-α-induced increase at concentrations without causing keratinocyte toxicity. Additionally, this extract significantly inhibited the TNF-α-induced release of elafin and VEGF by PK and NHK. Since TNF-α activation of most of these factors is dependent on the NF-κB pathway, this latter was studied in TNF-α-activated PK. BS-EAcf inhibited the TNF-α-induced phosphorylation and degradation of total IκBα as well as phosphorylation of NF-κB p65.

CONCLUSIONS

The ethyl acetate fraction from Picea mariana bark extract showed inhibitory effects of cytokines, chemokines, adhesion molecules, nitric oxide and prostaglandins produced by keratinocytes under TNF-α activation through down-regulating the NF-κB pathway. This study demontrated that this extract could be a potential antiinflammatory agent capable of improving psoriatic skin.

The tumour necrosis factor-alpha inhibitor adalimumab rapidly reverses the decrease in epidermal Langerhans cell density in psoriatic plaques

BACKGROUND

The pathophysiology of psoriasis is poorly understood, and the mechanism of action of biological agents interfering with tumour necrosis factor (TNF)-alpha that improve psoriatic plaques is completely unknown.

OBJECTIVES

To begin to unravel the mechanism of action, cellular changes occurring in plaques following administration of adalimumab, a humanized monoclonal antibody against TNF-alpha, were investigated.

METHODS

Thirteen different patients underwent sequential biopsies as part of a clinical trial. Each biopsy was immunostained and evaluated to calculate the relative density of epidermal Langerhans cells (LCs) before and after treatment (days 2, 7, 28, 84). To explore the basis for reduced epidermal LC densities in plaques, a SCID-Hu animal model was utilized. Acute psoriatic lesions were created within 2 weeks by injection of superantigen-activated CD4+ T cells into engrafted symptomless skin.

RESULTS

Compared with symptomless skin, untreated plaques had a significantly reduced density of epidermal LCs. There was a rapid increase in density of epidermal LCs in plaques following treatment with adalimumab beginning as early as day 7. The paucity of epidermal LCs in plaques was contrasted to the prominent density of LCs in other skin disorders with chronic inflammation and alterations in keratinization, including lichen planus and inflamed seborrhoeic keratosis. Rapid creation of plaques using the SCID-Hu model was accompanied by loss of epidermal LCs, indicating that diminished LC density occurs at an early stage of lesion formation.

CONCLUSIONS

These data shed light on a new immunopathological perspective highlighting a rapid loss of epidermal LCs in acute psoriatic lesions, with sustained decreased density of LCs in chronic plaques. Furthermore, an unexpected insight into the mechanism of action was uncovered for adalimumab, in which rapid restoration of epidermal LC density was observed.