Roman Rukwied

Mast cell mediators other than histamine induce pruritus in atopic dermatitis patients: a dermal microdialysis study

While histamine is the crucial mediator of pruritus in type 1 allergic reactions, its role in atopic dermatitis (AD) is unclear. In this study, the role of mast cell mediators in protein extravasation and pruritus was evaluated using intradermal microdialysis. The microdialysis capillaries were used to apply the mast cell degranulating substance compound 48/80 (C48/80; 0·05%) or histamine (0·01%) and also to deliver H1‐blockers (cetirizine, 200 μg mL−1) in nine AD patients and nine controls. Large pore size membranes (3000 kDa) enabled simultaneous analysis of protein extravasation. Itch sensation was measured psychophysically and weal and flare reaction were evaluated planimetrically. Protein extravasation induced by histamine and C48/80 was significantly reduced in AD patients. Blockade of H1‐receptors by cetirizine significantly reduced C48/80‐induced protein extravasation in AD patients and controls to an identical level. C48/80‐induced pruritus was abolished by cetirizine in controls, whereas pruritus in AD patients was unchanged after H1 blockade. We conclude that mast cell mediators others than histamine are involved in C48/80‐induced pruritus in AD patients. Whether the reduced capacity of AD patients to induce protein extravasation is of pathophysiological relevance for pruritus remains to be established.

Histamine induced responses are attenuated by a cannabinoid receptor agonist in human skin

Abstract:Objective and Design: In the present study we examined the effects of the cannabinoid receptor agonist HU210 on histamine-evoked somatosensory and vascular responses in humans. Subjects: Two sets of experiments were performed, in which twelve (Study 1, iontophoresis) and six participants (Study 2, microdialysis) were recruited. Treatment: HU210 was administered peripherally by skin patch (50 mM) or dermal microdialysis (5 mM), whereas histamine was applied by iontophoresis (50 μAmps) or dermal microdialysis (5 μM). Methods: Skin blood flow was monitored by laser Doppler, widespread flare reaction was evaluated planimetrically, extravasation of plasma proteins was measured in the dialysate and perceived itch was recorded using a visual analogue scale. Data were evaluated by analysis of variance. Results: Experimentally induced itch was significantly reduced by peripheral administration of HU210 (p < 0.05). Additionally, skin blood flow and neurogenic mediated flare responses were attenuated (p < 0.003 and p < 0.03, respectively), whereas protein extravasation due to histamine was enhanced by co-administration of HU210, as investigated by dermal microdialysis. Conclusions: In humans peripheral administration of a cannabinoid receptor agonist attenuates histamine-induced itch. The observation that protein extravasation was not decreased demonstrates that the alleviation of itch is not due to an anti-histaminergic property of HU210. The reduced neurogenic flare reaction indicates an attenuated antidromic nerve fibre activation and neuropeptide release.

Nociceptor activation and protein extravasation induced by inflammatory mediators in human skin.

Protein extravasation (PE) is known to play an important role in inflammatory conditions. In this study we used dermal microdialysis to apply inflammatory mediators (histamine, bradykinin, serotonin) to human skin. Locally induced PE was compared to pain ratings and axon reflex erythema measured simultaneously. Linear microdialysis capillaries (outer diameter 0.4 mm; cut‐off 3000 kDa) were inserted intracutaneously at a length of 1.5 cm in the volar forearm of healthy volunteers. The capillaries were perfused with Ringers solution at a constant flow rate of 4 μ l/min. The perfusate was sampled at 15‐min intervals and was analysed for total protein concentration. After a baseline of 60 min, the perfusion was switched to inflammatory mediators for 30 min and then back to vehicle again. Sensations evoked by the stimulation were assessed on a visual analogue scale and visible axon reflex erythema was measured planimetrically.

Administration of acetylcholine and vasoactive intestinal polypeptide to atopic eczema patients

Abstract: Responses to acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) were investigated in atopic eczema (AE) patients. To elucidate the involvement of histamine to ACh‐provoked vasoreactions and sensations, we applied a selective H1‐antagonist (cetirizine) 3 h prior to the ACh‐administration. Solutions of acetylcholine (ACh, 0.55 M) and vasoactive intestinal polypeptide (VIP, 1.5x10−5 M) were injected (10 μl) intracutaneously into the volar forearm of 14 healthy subjects and 14 atopic eczema (AE) patients. The substances were applied as single stimulus as well as in combination. Sensations evoked by the stimulation were recorded using 2 visual analog scales (VAS). Vasoreactions were analyzed with the new technique of computer assisted video image analysis. With this method we measured the dynamics of the flare development and the extension of the final flare size independent of the observers assessment. In control subjects the development and extension of the observers assessment. In control subjects the development and extension of the final flare size was almost similar, regardless whether ACh and VIP were applied in combination or separately. Compared to healthy controls, after injection of ACh, VIP and the combination of VIP and ACh smaller flare sizes were recorded in AE patients. After VIP was given, the control subjects reported pruritus, which was significantly augmented compared to AE patients. In contrast, controls reported a burning pain after the injection of ACh, whereas AE patients felt predominantly pruritus. Itch sensation after the combined application of VIP and ACh was significantly elevated in AE patients. Consequently, we assume that mediators of sudomotor neurons, i.e., VIP and ACh meet in AE patients apparently sensitized nociceptive primary afferents and induce exaggerated itch, pain and flare responses. When pretreated with the selective H1‐antagonist cetirizine before ACh was injected, pain and erythema due to ACh was diminished in healthy controls. In contrast, cetirizine did not influence the size of erythema and the magnitude of sensation in AE patients. We conclude, that the release of histamine is not involved in ACh‐induced erythema and pruritus in AE. These data provide evidence that pruritus can be elicited in atopic eczema by a cholinergic, histamine independent mechanism.

Neurogenic components of trypsin- and thrombin-induced inflammation in rat skin, in vivo

Abstract:  Activation of protease‐activated receptors (PAR) can induce vasodilation (VD) and increase of vascular permeability either directly by stimulating endothelial cells or indirectly via activation of nociceptors and subsequent release of neuropeptides (neurogenic inflammation). We aimed to estimate the relative contribution of the two pathways for stimulation with endogenous activators of PAR‐2 (trypsin) and of PAR‐1, 3 and 4 (thrombin) using in vivo dermal microdialysis in rats. Protein extravasation (PE) was assessed by increase of protein concentration in the dialysate, and VD was quantified by laser Doppler scanning. Both trypsin (10−8−10−4 M) and thrombin (10−6, 10−5.5 and 10−5 M) provoked PE and local VD in a dose‐dependent manner. Trypsin (10−4 M)‐induced PE was inhibited by 87.2 ± 21% due to the substance P (SP) NK1 receptor antagonist SR140333. VD was blocked by 58.15 ± 10.1% in response to the calcitonin gene‐related peptide (CGRP) receptor antagonist CGRP8‐37. By contrast, CGRP8‐37 did not affect thrombin‐induced VD, while blockade of SP receptors prevented the PE elicited only by low doses of thrombin (10−6 M), being ineffective at higher thrombin concentrations. In conclusion, intradermal trypsin elicits a neurogenic inflammation in rat, probably mediated via PAR‐2 activation on nociceptors and subsequent SP and CGRP release. Thrombin‐induced PE and VD are mediated mainly by a non‐neurogenic mechanism.

Flare responses of atopic eczema patients analysed with true colour images

Abstract.Objective and Design: Attenuated flare responses of atopic eczema (AE) patients to histamine are well documented, but their origin is still unknown.¶Subjects and Methods: Here we studied the development of erythema after histamine iontophoresis in 12 AE patients and 12 healthy volunteers by means of a RGB-camera for recording true colour images.¶Treatment: 10 mg cetirizine or placebo was administered orally 3 h before the experiment in a crossover design.¶Results: The flare reaction was found to develop after termination of histamine iontophoresis in two phases: a first phase lasting 1–2 min in which the flare increased by about 10 mm2/s and a second phase lasting another 10–15 min characterized by a slower growth in the range of 1 mm2/s.¶Conclusions: Flare size was diminished in AE patients, mainly due to a slower or absent growth in the second phase. Oral application of the H1-antagonist cetirizine (Zyrtec®) reduced the flare reaction in both groups of volunteers significantly, indicating that the reaction is dependent on the activation of chemosensitive nerve fibres via H1-receptors.