Cutaneous blood flow during white dermographism in patients with atopic dermatitis

Clinically uninvolved but not healthy-The skin of patients with atopic dermatitis is primed for itch and inflammation

BACKGROUND

Atopic dermatitis (AD) is a highly prevalent inflammatory skin disorder characterized by episodic exacerbations and remissions. Why the clinically healthy skin of AD patients becomes rapidly inflamed and very pruritic is poorly understood.

OBJECTIVE

To investigate cowhage- and histamine-induced itch and skin expression levels of their target receptors in lesional and non-lesional skin of AD, compared to the skin of patients with psoriasis, chronic spontaneous urticaria (CSU) and healthy subjects.

METHODS

Patients with AD, psoriasis and chronic spontaneous urticaria (CSU) as well as healthy control subjects (HC) (n = 20 each) were assessed for differences in itch parameters, neurogenic flare reaction and local blood flow responses to skin provocations with cowhage and histamine. Skin biopsies from 10 AD, 10 psoriasis,11 CSU and 12 HC were obtained to assess expression of protease-activated receptors 2 and 4 (PAR-2, PAR-4), histamine H1 and H4 receptors (H1R, H4R), and mast cells.

RESULTS

Provocation of non-lesional skin of AD patients with cowhage resulted in prolonged itch (p = 0.020), which was not observed in psoriasis and CSU. Significantly prolonged and more intense cowhage- and histamine-induced itch (for duration, peak and overall intensity) was also observed in lesional AD skin. Diminished neurogenic flare reaction and blood flow after histamine provocation were shown in AD and psoriasis patients. Non-lesional AD skin along with lesional AD and psoriasis skin showed an increased expression of PAR-2 and PAR-4, H1R and H4R. Mast cell number was higher in lesional AD and psoriasis skin (p = 0.006 and p = 0.006, respectively).

CONCLUSION

The non-lesional skin of AD patients markedly differs from healthy skin in cowhage-induced itch responses and the expression of receptors for proteases and histamine. Proactive therapeutic interventions that downregulate these receptors may prevent episodic exacerbation in AD.

A mechanistic physiologically based model to assess the effect of study design and modified physiology on formulation safe space for virtual bioequivalence of dermatological drug products

Physiologically based pharmacokinetic (PBPK) models are widely accepted tools utilised to describe and predict drug pharmacokinetics (PK). This includes the use of dermal PBPK models at the regulatory level including virtual bioequivalence (VBE) studies. The current work considers the Topicort® Spray formulation, which contains 0.25% desoximetasone (DSM), as an example formulation. Quantitative formulation composition and in vitro permeation testing (IVPT) data were obtained from the public literature to develop a mechanistic model using the multi-phase, multi-layer (MPML) MechDermA IVPT module in the Simcyp Simulator. In vitro-in vivo extrapolation functionality was used to simulate in vivo PK for various scenarios and predict a 'safe space' for formulation bioequivalence using the VBE module. The potential effect of vasoconstriction, impaired barrier function, and various dosing scenarios on the formulation safe space was also assessed. The model predicted 'safe space' for formulation solubility suggesting that a 50% change in solubility may cause bio-in-equivalence, whereas viscosity could deviate by orders of magnitude and the formulation may still remain bioequivalent. Evaporation rate and fraction of volatile components showed some sensitivity, suggesting that large changes in the volume or composition of the volatile fraction could cause bio-in-equivalence. The tested dosing scenarios showed decreased sensitivity for all formulation parameters with a decreased dose. The relative formulation bioequivalence was insensitive to vasoconstriction, but the safe space became wider with decreased barrier function for all parameters, except viscosity that was unaffected.

KSHV and the pathogenesis of Kaposi sarcoma: listening to human biology and medicine

The linkage of Kaposi sarcoma (KS) to infection by a novel human herpesvirus (Kaposi sarcoma-associated herpesvirus [KSHV]) is one of the great successes of contemporary biomedical research and was achieved by using advanced genomic technologies in a manner informed by a nuanced understanding of epidemiology and clinical investigation. Ongoing efforts to understand the molecular mechanisms by which KSHV infection predisposes to KS continue to be powerfully influenced by insights emanating from the clinic. Here, recent developments in KS pathogenesis are reviewed, with particular emphasis on clinical, pathologic, and molecular observations that highlight the many differences between this process and tumorigenesis by other oncogenic viruses.

Vascular pattern of the palms--a clinical feature of atopic skin diathesis

BACKGROUND

Atopic skin diathesis is a clinical term to describe skin atopics with previous, present or future atopic eczema/dermatitis syndrome (AEDS). In clinical practice, an unequivocal assessment of atopic skin diathesis in non-eczematous patients may be difficult. The majority of the known clinical features included in diagnostic scores are characteristic, but not specific markers of atopy. Especially, the vasoreactivity of atopic skin is disturbed. This is manifested by white dermographism, an irregular vascular response to thermal stimuli, and paradoxic skin reactions to histamine, cholinergic agents, and nicotinates.

OBJECTIVE

The aims of our study were to investigate the clinical morphology of palmar vascular reactions in skin atopic and non-atopic individuals, and to determine whether this abnormal vascular reaction is more pronounced in skin atopic individuals.

METHODS

Forty persons, 20 of them skin atopics, assessed by the Erlangen Atopy Score and an elevated serum IgE level (>150 U/ml), were included in a prospective single-centre study. Standardized digital photographs of the palms were presented in a blinded manner to five dermatologists in random order by means of the computerized imaging analysis system KS400 3.0.

RESULTS

Evaluation of the original rgb (red, green, blue) color images and modified gray-level images showed that a pronounced reticular pattern of erythema of the palms was significantly (P < 0.0001) more common in skin atopics (72% and 69.6%, respectively).

CONCLUSION

The gross vascular pattern of the palm might be an additional diagnostic feature of atopy, and further studies are needed to establish its exact prevalence.

Kinetics of the superficial perfusion and temperature in connection with photodynamic therapy of basal cell carcinomas using esterified and non-esterified 5-aminolaevulinic acid

BACKGROUND

Photodynamic therapy (PDT) is a local treatment modality with increasing indications for various malignant and non malignant diseases. The treatment parameters have not yet been optimized as there is a need for a better understanding of the process. The skin is an important target and serves as a good model for monitoring and evaluating the interaction of light with biological tissue.

OBJECTIVES

The tissue perfusion and the temperature of basal cell carcinomas were measured in connection with PDT in order to investigate the biological mechanisms involved.

METHODS

An infrared camera was used during the treatment to measure skin temperature and a laser Doppler perfusion imaging device was used to image the superficial perfusion before and after treatment. Six hours after topical application of 5-aminolaevulinic acid (ALA) or methyl esterified ALA (ALA-ME), 38 basal cell carcinomas were treated using light from a diode laser at 633 nm.

RESULTS

In the lesions, the perfusion immediately after PDT was similar to that before PDT. One hour after the treatment the perfusion in the lesion was increased 50% compared with before PDT. However, in the skin surrounding the lesions the perfusion was doubled immediately after PDT and was still increasing 1 h after treatment. A temperature increase in the lesions of about 1-3 degrees C was observed for light fluence rates of 100-150 mW cm-2. In all patients treated, a diffuse temperature increase was visible outside the lesions. In some of the patients, the outlines of the blood vessels surrounding the treated lesions became visible in the thermal images. Measurements of temperature on healthy volunteers not administered photosensitizer, but illuminated with light of the same fluence rate, showed a similar increase in temperature in the illuminated spots. However, no temperature increase was observed outside the illuminated area. No statistically significant differences were found between the measurements on patients treated with ALA and ALA-ME.

CONCLUSIONS

The increased perfusion in the area surrounding the lesions after PDT, as seen by perfusion and temperature measurements, is the result of an inflammatory reaction to the PDT process. However, directly after PDT the perfusion in the lesions was the same as before irradiation. The combination of these observations suggests the presence of local blood stasis during and immediately after the treatment. The temperature measurements showed that the increased temperature was well below the temperature limit of hyperthermal damage. Furthermore, the measurements indicate that the increase in temperature was primarily a consequence of the heat absorbed in the tissue.

Prostaglandin E2 induces vasodilation and pruritus, but no protein extravasation in atopic dermatitis and controls

BACKGROUND

Prostaglandin E(2) (PGE(2)) has well-established vasodilatory effects, whereas its effects on protein extravasation and its sensory effects are less clear.

OBJECTIVE

Vasoactive effects of PGE(2) were correlated to its ability to evoke pain or itch in healthy volunteers and patients with atopic dermatitis (AD).

METHODS

Intradermal microdialysis was used to apply PGE(2) (10(-8)-10(-4) M) via microdialysis capillaries in 8 patients and 8 controls. Large pore size membranes (3000 kd) enabled simultaneous analysis of protein extravasation. Itch and pain sensations were measured psychophysically, and superficial blood flow was measured by laser Doppler imaging.

RESULTS

PGE(2) dose dependently provoked intense local vasodilation, weak pruritus, and pain, but no protein extravasation. No differences were found between patients with AD and controls for any parameter.

CONCLUSION

We conclude that PGE(2) is a potent vasodilator and a weak pruritic agent in normal skin and in patients with AD, but does not provoke increased protein extravasation.

Non-invasive measurement of the vascular dynamics of dermographism--comparative study in atopic and non-atopic subjects

There is no dissent about the vascular origin of dermographism (D); however, the microcirculatory events underlying this phenomenon are not yet elucidated sufficiently. In particular, the vascular mechanisms producing the white D pattern in atopics are a matter of divergent hypotheses. In order to quantify the D phenomenon reproducibly, we constructed an easily usable device called "Dermographometer" which enables us to apply constant stretching pressure to the skin. We were able to investigate several parameters of microvascular cutaneous reaction to defined skin stretching pressure by laser-Doppler-microfluxmetry and infrared-thermography. These measurements were performed on 23 patients with atopic eczema (AE) and 21 healthy controls under standardized investigative conditions. Only patients under similar therapeutic regimens (no corticosteroids) with dry or lichenified skin inflammation (lumbar area) were included in the study. The basic values of laser-Doppler-fluxmetry (LDF) showed a significant reduction in the intensity of hyperemia in the patients from those in the normal controls; this reaction depended on the visual degree of the dermographic blanching effect (white, delayed white, indifferent, pale-red). Patients with white or indifferent D had the lowest rises in blood flux; those with delayed white or pale-red D had more elevated blood fluxes, but these were still clearly below the mean levels of normal red D. Infrared-thermography showed a significant diminution of both the rise and plateau phase of the radiating temperature in comparison to the controls. Our results support the hypothesis that white D (including different subtypes of its pallor) depends on the degree of local vasoconstriction, possibly in combination with altered blood flow in cutaneous shunt vessels.

Pharmacophysiology of atopic dermatitis

Atopic dermatitis is clearly characterized by altered cutaneous physiologic responses. There is a tendency to acral vasoconstriction. Rubbing causes skin pallor and white dermographism. Vascular instability is demonstrated by responses to cholinergic agents, histamine, and nicotinates. Psychophysiologic studies demonstrate exaggerated vasodilator responses to emotional stress with consequent pruritus and scratching. The itch threshold is low, duration is prolonged, and nighttime scratching movements may be frequent or almost continuous. Regardless of the inciting trigger factors, the scratching causes the damage and the severe dermatitis. Thermal as well as emotional stimuli to sweating cause severe itching in AD, yet the concept of a miliaria-type, poral occlusion mechanism remains unproven. Some studies suggest actually increased sweating along with erythema and pruritus during acute flares of AD. The concept of sweat-borne allergens causing skin reactions during sweating is interesting but has never been proven. Studies of sweat responses to pharmacologic agents have produced conflicting data, and attempts to link these responses to Szentivanyi's beta-adrenergic blockade theory are not convincing. The numerous variables of climate, season, sex, age, and habitus affect sweating greatly. Future studies must carefully control for each of these factors before pharmacologically induced sweat responses can be interpreted clearly. A number of lines of evidence suggest involvement of histamine and other mediators in the evolution of erythema, pruritus, and scratching in AD. Flares of the condition have been reproducibly evoked by only two incitants: experimental emotional stress interviews and specific food challenge in selected sensitive individuals. In the latter, increased plasma histamine has been demonstrated, presumably generated by antigen/IgE stimulated degranulation of mast cells in the gut and/or skin. The demonstrated increased histamine releasability of basophils from atopic individuals may be the result of defective cellular regulatory mechanisms. Recent studies have demonstrated increased cyclic AMP-phosphodiesterase activity in leukocytes from atopic individuals. The resultant decreased intracellular cyclic AMP removes an inhibitory factor, which in turn causes net cellular hyperresponsiveness. This effect has been shown to account, at least in part, for increased histamine release from leukocytes of patients with AD. These and other studies focused upon cell functional regulation are providing better understanding of basic biochemical abnormalities and may lead to improved diagnostic and therapeutic approaches in managing atopic disease.

Local variation in cutaneous and subcutaneous blood flow measured by CdTe(C1) minidetectors in normal and psoriatic skin

The accuracy of the 133Xe washout method and the validity of newly developed cadmium telluride CdTe(Cl) minisemiconductor detectors were estimated by performing comparative, simultaneous measurements of both cutaneous (CBF) and subcutaneous (SBF) blood flow using 2 conventional scintillation sodium iodide NaI(Tl) and CdTe(Cl) detectors over the same radioactive depot in each of 10 individuals. The accuracy of the 133Xe washout method was found to be 13-15% (C.V.) for the CBF measurements and 9-12% (C.V.) for the SBF measurements. The CdTe(Cl) detectors, which have a weight of 20 g and were attached directly over the radioactive depot, may replace stationary NaI(Tl) detectors placed 20 cm from the depot for measurements of both CBF and SBF. Two CdTe(Cl) detectors were used for estimations of the local variation in CBF and SBF within a distance of 5 cm in normal skin of 10 individuals. The C.V. was 7% for the CBF measurements and 18% for the SBF measurements. Measurements of CBF and SBF were performed in 6 psoriatic patients who, after about 1 week of antipsoriatic treatment with beech tar, developed typical Woronoff rings. The local CBF differed significantly from the center of psoriatic plaques to the margin, in the Woronoff ring, and in nonlesional skin. In contrast, SBF was remarkably equal within the plaque and in the Woronoff ring. The color of the Woronoff ring cannot be ascribed to a local cutaneous vasoconstriction. Cutaneous blood flow in chronic stable, lesional psoriatic skin was significantly lower than previously published values for active lesional psoriatic skin, but significantly higher than CBF in normal individuals. Measurements of CBF in tetrahydrofurfuryl nicotinic acid (Trafuril)-treated skin showed higher values than measurements of CBF in the postischemic hyperemia period both in normal and in lesional psoriatic skin. Trafuril induced a significant increase of CBF in both lesional and nonlesional skin. The high CBF rates in lesional psoriatic skin are not due to a maximally, passively dilated vascular bed.

Dermographism: a review

Urticaria is one of the more common skin conditions seen by physicians. Physical agents are an important cause of urticaria, with pressure or shearing forces being the most common. Dermographism is due to a combination of pressure and shearing forces and is present in a large number of healthy individuals. The purpose of this article is to provide a review of dermographism and its clinical variants.