An intravital microscopic model for mast cell-dependent inflammation in the hamster cheek pouch

Cutaneous nociception and neurogenic inflammation evoked by PACAP38 and VIP

Pituitary adenylate cyclase-activating peptide-38 (PACAP38) and vasoactive intestinal peptide (VIP) belong to the same secretin–glucagon superfamily and are present in nerve fibers in dura and skin. Using a model of acute cutaneous pain we explored differences in pain perception and vasomotor responses between PACAP38 and VIP in 16 healthy volunteers in a double-blind, placebo-controlled, crossover study. All participants received intradermal injections of 200 pmol PACAP38, 200 pmol VIP and placebo into the volar forearm. Measurements included pain intensity on a visual analog scale (VAS), blood flow by laser Doppler flowmetry, visual flare and wheal. Pain intensities after PACAP38 and VIP were mild and limited to a short time of about 100 s after injection. The area under the VAS-time curve was larger following PACAP38 (P = 0.004) and VIP (P = 0.01) compared to placebo. We found no statistical difference in pain perception between PACAP38 and VIP. Skin blood flow increase, flare and wheal were larger after both PACAP38 (P = 0.011) and VIP (P = 0.001) compared to placebo. VIP induced a considerably larger increase in skin blood flow, flare and wheal than PACAP38 (P = 0.002). In conclusion, we found that peripheral nociceptive cutaneous responses elicited by PACAP38 and VIP are similar in healthy volunteers. This suggests that acute pain and vasomotor responses following intradermal injections of PACAP38 and VIP are primarily mediated by VPAC receptors.

Experimental model in hamster (Mesocricetus auratus) to study heterologous graft of scars and cutaneous diseases in plastic surgery

Syrian golden hamster (Mesocricetus auratus) has in its cheek pouches sub-epithelium an "Immunologically Privileged Site" which allows the integration of homo- and heterologous graft. This paper describes some anatomical and histological characteristics of that site, as well as analyzes aspects related with its immune properties. It also focuses the advantages of this experimental model over other models which are natural or induced carriers of immunodeficiency. Based on both these advantages and literature, this study aims to establish this model, through the performance of heterologous graft, as another option for the investigation of scar disturbances, as keloids and other diseases which may interest Plastic Surgery, as benign cutaneous lesions, and malignant neoplasias such as skin carcinomas and melanomas. The work also addresses perspectives for using this model, which still is a source scarcely known by Brazilian medical class.

Safety of high-dose rofecoxib in patients with aspirin-exacerbated respiratory disease

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is characterized by progressive sinusitis, nasal polyposis, and asthma that begins and continues in the absence of exposure to aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs). Cross-sensitivity to all NSAIDs that inhibit cyclooxygenase-1 (COX-1) occurs in these individuals. Reactions to aspirin and NSAIDs in patients with AERD are largely due to inhibition of COX-1. Despite accumulating data on the safety of COX-2 selective inhibitors in AERD, concern still remains that high doses of a COX-2 inhibitor may be sufficient to induce a cross-reaction.

OBJECTIVE

To determine whether high-dose rofecoxib cross-reacts in patients with AERD and asthma.

METHODS

Sixty asthmatic patients underwent blinded placebo-controlled oral challenges with 50 mg of rofecoxib. Aspirin sensitivity was subsequently confirmed in all patients with the use of single-blinded aspirin challenges.

RESULTS

None of the 60 patients experienced any symptoms, changes in nasal examination results, or declines in lung function during rofecoxib challenge. All 60 patients experienced respiratory reactions to aspirin challenge, with a mean provoking dose of 57 mg. The exact 1-sided 95% confidence interval for the underlying probability of 50 mg of rofecoxib inducing respiratory cross-reactions in patients with AERD is 0 to 0.05, or 0% to 5%.

CONCLUSIONS

These results confirm the lack of cross-reactivity of aspirin and the highly selective COX-2 inhibitors in AERD. We suggest that it is time for the labeling of highly selective COX-2 inhibitors to reflect these data and for the warning that patients with AERD in particular and asthmatic patients in general avoid selective COX-2 inhibitors to be removed.

Investigation into the mechanisms by which nedocromil sodium, frusemide and bumetanide inhibit the histamine-induced itch and flare response in human skin in vivo

BACKGROUND

In a previous study, iontophoresis of nedocromil sodium into human skin in vivo was shown to reduce histamine-induced itch and flare. In asthma, the Na+/K+/2Cl- cotransporter inhibitors, frusemide and bumetanide, have been reported to have many similar actions to nedocromil sodium.

OBJECTIVE

To compare the effects of these drugs in the histamine-induced itch, flare and weal response in human skin in vivo and elucidate their site of action.

METHODS

Nedocromil sodium, frusemide bumetanide and reversed osmosis water (control), were introduced by iontophoresis into the forearm skin of 10 volunteers in each of two single-blind studies. In study 1, histamine (20 microL of 100 microM) or vehicle was injected into the area of iontophoresis 10 min later. In study 2, histamine or vehicle was injected 5 mm outside the area of iontophoresis so the flare developed over the area of iontophoresis. Itch was scored on a visual analogue scale every 20 s for 5 min, flare areas were assessed using scanning laser Doppler imaging up to 10 min and weal was assessed by planimetry at 10 min.

RESULTS

In study 1, nedocromil sodium, frusemide and bumetanide reduced itch scores by 36%, 48% and 34%, respectively, and flare areas by 17%, 26% and 15% respectively (all P<0.05). Weal areas and blood flux in the flare were unaffected. In study 2, itch scores, flare areas and weal areas were not inhibited. Also, blood flux values in areas of drug and water iontophoresis were not different.

CONCLUSION

This study has provided evidence to support the hypothesis that nedocromil sodium, frusemide and bumetanide inhibit sensory nerve activation to reduce the itch and flare responses induced by histamine in human skin in vivo. It is likely that inhibition of a Na+/K+/2Cl- cotransporter in the sensory nerve membrane is a possible mechanism of action.

Mast Cell-Independent Mechanisms of Immediate Hypersensitivity: A Role for Platelets

Mast cells have been implicated as the central effectors in allergic responses, yet a fatal anaphylactic response can be induced in mast cell-deficient mice. In this study, we examined the immediate hypersensitivity response in wild-type (WT) and mast cell-deficient mice (W/W(v)) in two different tissues (skin and skeletal muscle). Vascular permeability and leukocyte recruitment were studied after immediate challenge or 4 h postchallenge in OVA-sensitized mice. In skin, immediate challenge induced a significant increase in vascular permeability (75%) within 30 min and was accompanied by increased leukocyte adhesion 4 h postchallenge. In the absence of mast cells, no changes in vascular permeability or leukocyte recruitment were observed in skin. In WT skeletal muscle, immediate challenge induced a rapid increase (80%) in vascular permeability within 5 min and significant leukocyte recruitment after 4 h. Surprisingly, in W/W(v), a gradual increase in vascular permeability was observed, reaching a maximum (50%) within 30 min. Despite the absence of mast cells, subsequent leukocyte emigration was similar to that observed in WT mice. Pretreatment with anti-platelet serum in W/W(v) returned Ag-induced vascular permeability and leukocyte recruitment to baseline. Platelets were shown to interact with endothelium in skeletal muscle, but not dermal microvasculature. These data illustrate that mast cells play a prominent role in vascular permeability and leukocyte recruitment in skin in response to Ag, however, in skeletal muscle; these changes can occur in the absence of mast cells, and are mediated, in part, by the presence of platelets.

Nedocromil sodium inhibits histamine-induced itch and flare in human skin

This study was designed to test the hypothesis that nedocromil sodium inhibits sensory nerve function to reduce flare and itch in human skin. Nedocromil sodium (2%) or water (control) was introduced into the volar forearm skin of eight non-atopic volunteers by iontophoresis (8 mC) and histamine (20 microl of 1 microM and 300 nM) injected intradermally 10 min later at the same site. Itch was assessed on a visual analogue scale every 20 s for 5 min. Weal and flare areas and mean blood flux within the flare were assessed by scanning laser Doppler imaging at 10 min. The results showed that nedocromil sodium reduced itch scores, totalled over 5 min, by approximately 74.0% (P<0.005) and flare areas by approximately 65% (P<0.03). Neither weal areas nor blood flux within were reduced. These data demonstrate that nedocromil sodium is effective in reducing neurogenic itch and flare in the skin. We suggest that its mechanism of action is modulation of sensory neurone activation or conduction in the skin.

Leukocyte adherence contributes to disruption of the blood-brain barrier during activation of mast cells

The goal of this study was to examine the role of leukocytes in disruption of the blood-brain barrier during activation of mast cells using compound 48/80. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood-brain barrier (clearance of fluorescent-labeled dextran; molecular weight 10000 daltons; FITC-dextran-10 K) was determined while suffusing with vehicle or compound 48/80 (10 or 25 microg/ml). During superfusion with vehicle (saline), clearance of FITC-dextran-10 K from pial vessels was modest and remained relatively constant during the experimental period (0.52+/-0.05 ml/sx10(-6) at 80 min). In addition, diameter of pial arterioles remained constant (32+/-5 microm) while suffusing with vehicle. In contrast, topical application of compound 48/80 produced marked disruption of the blood-brain barrier to FITC-dextran-10 K. For example, suffusion with compound 48/80 (25 microg/ml) increased clearance of FITC-dextran-10 K about 4-fold to 2.26+/-0.25 ml/sx10(-6) at 80 min. In addition, superfusion with compound 48/80 (25 microg/ml) constricted pial arterioles by 26+/-9% at 80 min. To determine a potential role for leukocyte adhesion to endothelium in disruption of the blood-brain barrier during suffusion with compound 48/80, we examined permeability during suffusion with compound 48/80 (25 microg/ml) in the presence of WT.3 (2 mg/kg i.v.), a monoclonal antibody directed against the functional epitope of the leukocyte adhesive glycoprotein (CD18; LFA-1beta). We found that infusion of WT.3 markedly attenuated disruption of the blood-brain barrier to FITC-dextran-10 K in response to compound 48/80. The clearance of FITC-dextran-10 K during superfusion with compound 48/80 in the presence of WT.3 was 1.29+/-0.14 ml/sx10(-6) at 80 min (P<0.05). Thus, the findings of the present study suggest that application of compound 48/80, to degranulate mast cells, activates the adhesion of leukocytes to cerebral venular endothelium which contributes to disruption of the blood-brain barrier.

Human skin mast cells: in vitro and in vivo studies

OBJECTIVE

This short review surveys our current knowledge on the development and heterogeneity of human mast cells, the distribution of mast cells within human skin and the properties of human skin mast cells both in vitro and in vivo. It also examines the effects of antihistamines in the wheal-and-flare response in the skin provoked by bradykinin.

RESULTS

Mast cells derive from mononuclear precursor cells which undergo their final phase of their differentiation in the tissues. In normal skin, mast cells, which are primarily of the MC(TC) subtype, occur in the greatest density in the superficial dermal zone. Like all other mast cells, human skin mast cells bind IgE with high affinity to specific FcepsilonRI receptors, but unlike those from lung, tonsils, adenoids or intestine, they also express the C5a receptor (CD88) and activation sites for substance P, VIP, somatostatin, and compound 48/80. Both IgE-dependent stimulation by activating tyrosine kinases, and non-immunologic stimulation by activating G-proteins induce a characteristic compound exocytosis resulting in the liberation of the preformed mediators. Production of prostaglandin D2 and leukotriene C4, however, occurs only with IgE-dependent stimulation. In vivo, dermal microdialysis and scanning laser Doppler imaging have been used to assess the role of histamine in the wheal-and-flare response. These techniques were also used to show that low concentrations of intradermal bradykinin release negligible quantities of histamine. The results showed that although the resultant flare was inhibitable by antihistamines, low concentrations of bradykinin released negligible quantities of histamine. This suggests a potentially novel mechanism of action of antihistamines that requires further detailed investigation.

Effects of H1 antagonists on the cutaneous vascular response to histamine and bradykinin: a study using scanning laser Doppler imaging

Histamine plays an important part in the cutaneous weal and flare response which underlies many allergic skin conditions. It has a direct effect on the local vasculature to promote vasodilatation and increase microvascular permeability and may also initiate the more widely spread neurogenic flare. Quantification of these responses and studies of the mediator mechanisms underlying them have been limited by the lack of appropriate techniques to investigate them. To address this we have used two relatively new techniques, scanning laser Doppler imaging (LDI) and dermal microdialysis to measure changes in skin blood flow and the release of histamine within the weal and flare, following intradermal injection of histamine or bradykinin. These measurements have been made both in the absence and presence of the H1 receptor blockers cetirizine and loratadine. Scanning LDI of the inflammatory response revealed marked differences in both the development and steady state responses to the intradermal injection of histamine (1-3 mumol/L) and bradykinin (1 mumol/L). The development of the flare and the weal response to both histamine and bradykinin was significantly reduced by cetirizine but not by loratadine. The histamine-induced flare area fell by 57 +/- 4% (mean +/- SEM, n = 10, P < 0.001) after cetirizine and the area of the weal fell by 73 +/- 11% (P < 0.009). Bradykinin-induced inflammatory responses were similarly reduced by cetirizine, the weal by 60 +/- 16% (P < 0.02) and the flare by 61 +/- 4% (P < 0.005). Measurement of histamine concentration in skin using microdialysis, in six subjects, confirmed that histamine levels rose in the dialysate collected from the weal to 310 +/- 16 nmol/L following injection of histamine. Histamine levels also rose following bradykinin injection in some subjects (mean 147 +/- 46 nmol/L, range 18-336). Little increase in histamine concentration was seen in the dialysate from the flare following injection of either histamine or bradykinin. The histamine concentration in dialysate from unprovoked skin was 4.19 +/- 0.75 nmol/L. These data reveal differences in the dermal responses to different mediators when assessed using scanning LDI. They confirm that histamine is released within the weal but not the flare response to the intradermal injection of both histamine and bradykinin and that its effects on the local vasculature to cause the oedematous weal and the axon reflex-mediated flare are significantly attenuated by the H1 antagonist cetirizine and to a lesser extent by the H1 antagonist loratadine.

Mast cell amines and inosineinduced vasoconstriction in the rat hind limb

Under certain circumstances injected inosine causes a net vasoconstrictive effect on the arterioles, which has been attributed to 5-hydroxytryptamine (5HT) released in response to adenosine type 3 (A₃) receptor stimulation of mast cells residing in the adventitia. We have sought further evidence for this hypothesis using blood vessels of the rat hind limb perfused in vitro at constant rate with a gelatin-containing physiological salt solution. Injection of inosine (2.7 mg) caused a rise in perfusion pressure, which was only slightly increased by inclusion of N-nitro-L-arginine methyl ester (100 μM) in the perfusate. Inclusion in the perfusate of cyproheptadine (1 μM), compound 48 80 (1 μg ml), 8-phenyltheophylline (1 μM) or 8-cyclopentyl-1,3 dipropylxanthine (0.1 μM) greatly reduced the pressor response to inosine. The pressor effect of injected 5HT (400 μg) was abolished by pre-treatment with cyproheptadine, but not by pre-treatment with compound 48 80. These results suggest that the net pressor response to injected inosine was mainly the result of an A₁ receptor-mediated release of 5HT, most probably from mast cells. No evidence was found for an involvement of A₃ receptor stimulation.

The effect of cetirizine and loratadine on codeine-induced histamine release in human skin in vivo assessed by cutaneous microdialysis

OBJECTIVE AND DESIGN

To determine whether or not cetirizine and loratadine inhibit codeine- induced histamine release in human skin in vivo, we conducted a placebo-controlled double-blind trial in which histamine release was assessed by dermal microdialysis.

SUBJECTS

A group of ten normal volunteers were studied, each subject visiting the laboratory on three occasions with intervals of at least 2 weeks between visits.

TREATMENT

Cetirizine, loratadine (both 10 mg) or placebo was given orally 4 h before provocation of weal and flare responses in the skin by intradermal injection of 25 microliters of 3 or 10 mg/ml codeine 1 mm from the centre of individual 216 microns diameter microdialysis fibres inserted in the dermis.

METHODS

Dialysate was collected at 2 min intervals for 4 min before and 20 min after codeine injection and histamine assayed spectrofluorometrically. Weal and flare responses to codeine were assessed in the opposite arm.

RESULTS

Histamine concentrations in the microdialysis fibre outflow with 3 and 10 mg/ml codeine were maximal at 2-4 min when 910 +/- 156 and 1194 +/- 304 nM respectively were found in the placebo group. Cetirizine and loratadine did not modify either the kinetics or total histamine release while significantly (p < 0.01) inhibiting weal and flare responses.

CONCLUSIONS

Neither cetirizine nor loratadine inhibited codeine-induced histamine release or modified the time course of its release in human skin in vivo when given in clinically used doses which are sufficient to significantly reduce weal and flare responses.

The hamster cheek pouch: an immunologically privileged site suitable to the study of granulomatous infections

The hamster cheek pouch is an invagination of oral mucosa, characterized histologically as skin-like. In this paper we describe anatomical, histological and embriological features of the pouch and comment on the pouch as an immunologically privileged site since it lacks lymphatic drainage and has few Langerhans cells. We present the review from literature and our observations after inoculation in the pouch of mycobacteriae (BCG, Mycobacterium tuberculosis and Mycobacterium leprae) and a fungus (Paracoccidioides brasiliensis). Lesions in the pouch were granulomatous but smaller and long lasting; even granulomatous, the reaction was inefficient to control the proliferation of agents compared with inoculation in other sites, except for BCG. Appearance of immunity was also delayed or absent and, when it was detected, a sharp decrease in number of agents in pouch lesions was observed. These observations make the pouch an interesting site for the study of the role of immune system in infectious diseases and in granuloma formation.

Short-term exposure to lipopolysaccharide is associated with microvascular contractile dysfunction in vivo

The purpose of this study was to determine whether short-term exposure of resistance arterioles to lipopolysaccharide in situ is associated with changes in vasomotor tone. Using intravital microscopy, we found that suffusion of Escherichia coli lipopolysaccharide (3 micrograms/ml) over hamster cheek pouch arterioles for 1 h was associated with a significant immediate biphasic response: vasoconstriction followed by vasodilation (p < 0.05). The former was attenuated by indomethacin, and the latter by SK&F 108566, a selective, non-peptide angiotension II receptor antagonist (p < 0.05). The nitric oxide synthase inhibitor, NG-L-nitro arginine, had no significant effects on lipopolysaccharide-induced responses. Allopurinol, a scavenger of reactive oxygen species, significantly attenuated lipopolysaccharide-induced vasodilation. Acetylcholine- and nitroglycerin-induced vasodilation were significantly potentiated after lipopolysaccharide. These responses were recorded in the absence of any significant changes in systemic arterial blood pressure. Collectively, these data suggest that short-term exposure of the peripheral microcirculation to lipopolysaccharide in situ is associated with an ischemia-reperfusion-like injury. These changes may contribute to end organ failure observed several hours after exposure to lipopolysaccharide.

Polycations induce microvascular leakage of macromolecules in hamster cheek pouch

The microvascular response to two polycationic proteins, poly-L-lysine (mol wt 104,000) and leukocyte elastase, was studied in the hamster cheek pouch microcirculation model. A 2-min topical application of polylysine (100 micrograms/ml) induced vigorous macromolecular leakage from venules only that declined within 30 min. A second application induced significantly less leakage. The leakage was inhibited by admixing polylysine with dextran sulfate prior to application or by giving hamsters an intravenous injection of dextran sulfate. The histamine antagonist pyrilamine did not interfere with the leakage, and only a few degranulated mast cells were found after polylysine application. No intravascular adhesion of leukocytes could be detected. Elastase (100 micrograms/ml) was deposited adjacent to venules with micropipets. The resulting leakage response was not inhibited by L658,758, an inhibitor of elastase enzymatic activity, but by dextran sulfate. These results may prove significant in light of the numerous polycationic proteins present within neutrophil granules.

Vasodilatation and inhibition of mediator release represent two distinct mechanisms for prostaglandin modulation of acute mast cell-dependent inflammation

1. Intravital microscopy of the hamster cheek pouch was used to examine the influence of vasodilator prostanoids (prostaglandin E2 (PGE2), PGI2), forskolin, and nitroprusside on the microvascular changes during acute inflammation induced by antigen or histamine. The results extend our previous finding that PGE2 modulates allergic inflammation and histamine release in the cheek pouch model. 2. The microvascular actions of arachidonic acid and different cyclo-oxygenase products (PGE2, PGD2, PGI2, PGF2 alpha, and the thromboxane A2 (TXA2)-analogue U-44069) were first compared with respect to their effects on arteriolar tone. Of the prostaglandins, only PGE2 and PGI2 were potent vasodilators and markedly increased local blood flow. Nitroprusside and forskolin also caused vasodilatation and increased blood flow, but were somewhat less potent than PGE2 and PGI2. 3. Topically applied PGE2 and PGI2 in vasodilator concentrations suppressed the antigen-induced plasma leakage. On the other hand, although the antigen response was predominantly mediated by histamine, both prostaglandins enhanced the plasma leakage evoked by exogenous histamine. 4. In contrast, the vasodilator nitroprusside, in a dose causing an increase in blood flow equal to that of PGE2 and PGI2, potentiated both the histamine-induced plasma leakage, as well as the plasma and leukocyte extravasation after antigen challenge, indicating that the anti-inflammatory actions of the prostaglandins were unrelated to their vasodilator properties per se. 5. Because forskolin, a specific activator of adenylate cyclase, mimicked the actions of PGE2 and PGI2, i.e. inhibition of the antigen-induced plasma extravasation and enhancement of the histamine response, it is possible that the observed antiallergic effects of the prostaglandins were related to accumulation of intracellular adenosine 3': 5'-cyclic monophosphate (cyclic AMP). 6. Taken together, there appears to be a competition between pro- and anti-inflammatory effects of PGE2 and PGI2 in reactions involving release of endogeneous inflammatory mediators in vivo, i.e. enhancement of inflammatory mediator target action on one hand ('two mediator synergism'), and suppression of mediator release on the other. Moreover, the observations indicate that vasodilatation and inhibition of mediator release are two distinct actions of PGE2 and PGI2.

Prostaglandin E2 prevents diclofenac-induced enhancement of histamine release and inflammation evoked by in vivo challenge with compound 48/80 in the hamster cheek pouch

Based on observations obtained by the use of intravital microscopy, we report that prostaglandins (PGs) can exert inhibitory effects on mast cell-dependent inflammation. Thus, the PG-synthesis inhibitors diclofenac and indomethacin potentiated extravasation of plasma evoked by challenge with the mast cell secretagogue compound 48/80. Although the plasma leakage induced by compound 48/80 was in large mediated by histamine, neither diclofenac nor indomethacin potentiated the plasma leakage caused by exogenous histamine. These findings indicated that endogenous PGs inhibited the mast cell-dependent reaction at the level of mediator release. This mode of action was confirmed, as diclofenac was found to enhance the in vivo release of histamine that ensued challenge with compound 48/80. Moreover, the enhancement of the response to compound 48/80 observed after diclofenac treatment was prevented by local administration of PGE2 (30 nM). This inhibition included both the histamine release and the plasma leakage. In addition, diclofenac enhanced the leukocyte emigration after compound 48/80 challenge, and PGE2 reversed also this effect, suggesting that endogenous PGs (e.g. PGE2) also inhibited the release of chemotactic mediators.

Dual inhibitory action of nedocromil sodium on antigen-induced inflammation

In human lung tissue in vitro, nedocromil sodium inhibited the release of histamine and leukotrienes induced by anti-IgE, as well as the contraction of isolated bronchi which followed this challenge. In the hamster cheek pouch in vivo, nedocromil sodium inhibited the inflammatory response induced by challenge with either antigen or the individual inflammatory mediators, histamine and leukotriene B4. The findings thus indicate that nedocromil sodium has a dual anti-inflammatory action: inhibition of mediator secretion and antagonism of mediator action.