The induction of plasma leakage in skin by histamine, bradykinin, activated complement, platelet-activating factor and serotonin

Metabolism Regulates Exposure of Pancreatic Islets to Circulating Molecules In Vivo

Pancreatic β-cells modulate insulin secretion through rapid sensing of blood glucose and integration of gut-derived signals. Increased insulin demand during pregnancy and obesity alters islet function and mass and leads to gestational diabetes mellitus and type 2 diabetes in predisposed individuals. However, it is unclear how blood-borne factors dynamically access the islets of Langerhans. Thus, understanding the changes in circulating molecule distribution that accompany compensatory β-cell expansion may be key to developing novel antidiabetic therapies. Here, using two-photon microscopy in vivo in mice, we demonstrate that islets are almost instantly exposed to peaks of circulating molecules, which rapidly pervade the tissue before clearance. In addition, both gestation and short-term high-fat-diet feeding decrease molecule extravasation and uptake rates in vivo in islets, independently of β-cell expansion or islet blood flow velocity. Together, these data support a role for islet vascular permeability in shaping β-cell adaptive responses to metabolic demand by modulating the access and sensing of circulating molecules.

Enhanced vascular permeability facilitates entry of plasma HDL and promotes macrophage-reverse cholesterol transport from skin in mice

Reverse cholesterol transport (RCT) pathway from macrophage foam cells initiates when HDL particles cross the endothelium, enter the interstitial fluid, and induce cholesterol efflux from these cells. We injected [(3)H]cholesterol-loaded J774 macrophages into the dorsal skin of mice and measured the transfer of macrophage-derived [(3)H]cholesterol to feces [macrophage-RCT (m-RCT)]. Injection of histamine to the macrophage injection site increased locally vascular permeability, enhanced influx of intravenously administered HDL, and stimulated m-RCT from the histamine-treated site. The stimulatory effect of histamine on m-RCT was abolished by prior administration of histamine H1 receptor (H1R) antagonist pyrilamine, indicating that the histamine effect was H1R-dependent. Subcutaneous administration of two other vasoactive mediators, serotonin or bradykinin, and activation of skin mast cells to secrete histamine and other vasoactive compounds also stimulated m-RCT. None of the studied vasoactive mediators affected serum HDL levels or the cholesterol-releasing ability of J774 macrophages in culture, indicating that acceleration of m-RCT was solely due to increased availability of cholesterol acceptors in skin. We conclude that disruption of the endothelial barrier by vasoactive compounds enhances the passage of HDL into interstitial fluid and increases the rate of RCT from peripheral macrophage foam cells, which reveals a novel tissue cholesterol-regulating function of these compounds.

Antiedematogenic effects of the polar fractions of Persea cordata Mez. (Lauraceae) on microvascular extravasation in rat skin

ETHNOPHARMACOLOGICAL RELEVANCE

Persea cordata Mez. (Lauraceae) is a medicinal plant used in veterinary ethnopharmacology, which is a popular medicine used as an anti-inflammatory and healing agent, mainly on animal skin diseases, characterized by cutaneous open wounds, in South Brazil.

AIM OF THIS STUDY

The purpose of this study was to investigate a possible antiedematogenic effect of ethyl acetate (EtAc) and butanol (BuOH) polar fractions of Persea cordata on Evans blue dye leakage induced by pro-inflammatory agents in rat skin.

MATERIALS AND METHODS

Male Wistar rats (180-200 g, n=5-6) were pretreated with a single intraperitoneal administration of EtAc or BuOH (1 to 600 mg kg(-1)) fractions followed by intravenous Evans blue dye injection (1%, 30 mg kg(-1), i.v.), 60 min before the injection of phlogistic agents. Animals received intradermal injections (0.05 ml) of carrageenan (CAR, 300 µg/site), 48/80 compound (C4880, 10 µg/site), histamine (HIS, 0.3 µg/site), serotonin (5-HT, 0.01 µg/site), dextran (DEX, 200 µg/site), bradykinin (BK, 0.003 µg/site), capsaicin (CPS, 400 µg/site), substance P (SP, 0.003 µg/site) or prostaglandin E2 (PGE2 10 nmol/site) and they were submitted to euthanasia after 60 min. Skin samples were obtained in the extravasation sites of Evans blue dye. Skin fragments were soaked in formamide at 37°C (during 24h) for Evans blue extraction. The amount of dye leakage in the tissue fragment was determined by a spectrophotometer (620 nm).

RESULTS

In a very similar manner in terms of potency and efficacy, systemic administration of EtAc and BuOH fractions caused dose-dependent inhibition of vascular Evans blue dye leakage induced by phlogistic agents in the rat skin. The results obtained (ID50 values in mgkg(-1) and maximal inhibition in %) with EtAc fraction, as follows were: CAR (34.42 and 63.0), 4880 (8.52 and 59.1), HIS (21.22 and 66.8), 5-HT (32.99 and 73.4), DEX (41.74 and 67.0), BK (34.03 and 68.0), CPS (100.7 and 77), SP (2.1 and 78.9) and PGE2 (133 and 71.0). BuOH fraction significantly inhibited CAR (25.9 and 70)-, 4880 (36.8 and 66)-, HIS (17.6 and 77)-, 5-HT (32.8 and 56)-, DEX (89.6 and 75)-, BK (28.0 and 66)-, CPS (136.37 and 71)-, SP (5.6 and 78)- and PGE2 (109.64 and 56)-induced VE, respectively.

CONCLUSION

Systemic administration of Persea cordata polar fractions exerts a non-specific inhibitory effect on microvascular leakage induced by pro-inflammatory agents in rat skin, probably to interfering with different biological systems involved in the development of the inflammatory process, reinforcing the popular use of Persea cordata as an anti-inflammatory and healing agent for skin.

The cutaneous serotoninergic/melatoninergic system: securing a place under the sun

It was recently discovered that mammalian skin can produce serotonin and transform it into melatonin. Pathways for the biosynthesis and biodegradation of serotonin and melatonin have been characterized in human and rodent skin and in their major cellular populations. Moreover, receptors for serotonin and melatonin receptors are expressed in keratinocytes, melanocytes, and fibroblasts and these mediate phenotypic actions on cellular proliferation and differentiation. Melatonin exerts receptor-independent effects, including activation of pathways protective of oxidative stress and the modification of cellular metabolism. While serotonin is known to have several roles in skin-e.g., pro-edema, vasodilatory, proinflammatory, and pruritogenic-melatonin has been experimentally implicated in hair growth cycling, pigmentation physiology, and melanoma control. Thus, the widespread expression of a cutaneous seorotoninergic/melatoninergic syste,m(s) indicates considerable selectivity of action to facilitate intra-, auto-, or paracrine mechanisms that define and influence skin function in a highly compartmentalized manner. Notably, the cutaneous melatoninergic system is organized to respond to continuous stimulation in contrast to the pineal gland, which (being insulated from the external environment) responds to discontinuous activation by the circadian clock. Overall, the cutaneous serotoninergic/melatoninergic system could counteract or buffer external (environmental) or internal stresses to preserve the biological integrity of the organ and to maintain its homeostasis.-Slominski, A. J., Wortsman, J., Tobin, D. J. The cutaneous serotoninergic/melatoninergic system: securing a place under the sun.

Trends in complete blood count values during acute painful episodes in children with sickle cell disease

Complete blood count (CBC) values are monitored as crude indicators of the hemolytic and inflammatory processes that accompany an acute painful episode in children with sickle cell disease. As part of a larger study that examined the pain experience and pain management of hospitalized children during painful vaso-occlusive episodes, the authors examined trends in CBC values and determined whether there were relationships between these values and pain intensity scores. Children, 5 to 19 years of age, with sickle cell disease whose primary reason for admission was vasoocclusive pain were recruited for participation in the study. Once every evening from the day of admission until the day of discharge, they were asked to rate their worst and least pain using the numeric rating scale of the African American Oucher pain scale. Complete blood count values were obtained from the hospital information system on a daily basis. Parallel changes in CBC values and pain intensity scores were evident within the first 48 hours of hospitalization. However, although the inflammatory and hemolytic processes were resolving, pain persisted at moderate levels throughout the course of hospitalization.

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 Ringer's solution at a constant flow rate of 4 microl/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.Dose-dependent increases in PE could be assessed for all inflammatory mediators tested. Bradykinin (10(-7)M) induced a significant PE, whereas serotonin was effective only at a concentration of 10(-3)M. While serotonin in lower concentrations induced moderate burning pain and an axon reflex flare but no PE, bradykinin provoked PE without pain or axon reflex flare at a concentration of 10(-7)M. Application of histamine similarly evoked PE at lower concentrations as compared to the induction of itch sensation and axon reflex flare. It is concluded that there is no link between nociceptor activation and protein extravasation induced by inflammatory mediators in healthy human skin.

Nonspecific T-cell homing during inflammation in atopic dermatitis: expression of cutaneous lymphocyte-associated antigen and integrin alphaE beta7 on skin-infiltrating T cells

Atopic dermatitis (AD) is a chronic skin disorder, characterized by infiltration of activated memory CD4+ T cells into skin. A model to study the onset of allergic inflammation in a patient with AD is the atopy patch test (APT), in which, by epicutaneous application of aeroallergen, an eczematous reaction is induced in 50% of sensitized patients with AD. Extravasation of T cells into skin is thought to be critically dependent on expression of the surface molecule cutaneous lymphocyte-associated antigen (CLA), which recognizes and binds its ligand E-selectin on endothelium. We studied the dynamics of expression of CLA and the gut homing receptor alphaE beta7 (HML-1) on T cells in the skin of patients with AD and in APT reactions and nickel and sodium lauryl sulfate patch test reactions by means of immunohistochemical double staining of skin biopsy specimens. The results show an increase in the number of CD3+ T cells in the lesional skin of patients with AD, APT reactions, and nickel and sodium lauryl sulfate patch test reactions as compared with nonlesional skin of the same patients and nonatopic individuals. In contrast, the percentages of CLA+ T cells in the lesional skin of patients with AD, in the APT reactions, and in sodium lauryl sulfate and nickel patch test reactions were decreased. In addition, we found a marked expression of alphaE beta7 by T cells present in skin, indicating a nonspecific influx of T cells during allergic skin inflammation. We propose that during allergic skin inflammation CLA expression is not a prerequisite for cutaneous T-cell infiltration. CLA expression may be important for T cells to extravasate from blood into skin during immune surveillance or for retention of allergen-specific T cells in skin.

The effect of immune and inflammatory mediators on growth of Lucilia cuprina larvae in vitro

Immune and inflammatory responses occurring during dermal infestation by larvae of Lucilia cuprina can retard larval growth and development. This study examined the effect of 4 classes of humoral inflammatory mediators on larval growth in an in vitro assay. Mediators of plasma leakage (histamine, bradykinin, platelet-activating factor and serotonin), leucocyte chemotactic agonists (activated complement, leukotriene B4 and interleukin-8), effector molecules of immune responses (interleukin-1 beta, tumour necrosis factor-alpha and interferon-gamma) and endotoxin all failed to inhibit larval growth. In contrast, immunoglobulins isolated from immune serum caused marked retardation of larval growth. The results suggest that humoral mediators of inflammatory and immune responses do not play a role in immune defence against Lucilia cuprina.

Inhibitory influence of sympathetic nerves on afferent nerve-induced extravasation in the rat incisor pulp upon direct electrical stimulation of the tooth

Previous studies have shown that sympathetic nerve stimulation reduces afferent nerve-induced vasodilation by mechanisms unrelated to vasoconstriction in the rat incisor pulp. The present investigation concerned whether similar modulatory mechanisms might also influence neurogenic plasma extravasation in dental pulp. Rat mandibular incisors were electrically stimulated and blood flow reactions in the pulp were recorded by laser Doppler flowmetry. Plasma extravasation in the incisor pulp, gingiva and lip were indirectly assessed by the Evans-blue method. Stimulation of teeth with 50 microA (5 min) did not cause increased dye accumulation in the stimulated pulps whereas stimulation with 100 microA significantly increased the dye content in ipsilateral pulps by 32% as compared to controls; 100 microA stimulation was without effect in unilaterally denervated animals. Tooth stimulation with 50 microA (5 min), in the presence of either the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), or the alpha 1-adrenergic antagonist prazosin (50 micrograms/kg), as well as in chronically sympathectomized animals, significantly increased the Evans-blue content in the stimulated pulps by 47, 83 and 86%, respectively. Application of short trains of impulses (same number of impulses as for the continuous stimulation but producing minimal vasoconstriction) resulted in some dye accumulation, which was enhanced in the ipsilateral pulps in the presence of prazosin (100 micrograms/kg) or after acute resection of the superior cervical sympathetic ganglion by 70 and 64%, respectively. The Evans-blue content in the lip and gingiva was uninfluenced by the tooth stimulation. The results indicate that activation of sympathetic nerves inhibits the afferent nerve-induced plasma extravasation in rat incisor pulp and this effect is mediated by alpha-adrenoceptors not associated with vasoconstriction.

Plasma leakage in skin of sheep selected for resistance or susceptibility to fleece rot and fly strike

The leakage of plasma into skin following injection of histamine, bradykinin, activated complement, platelet-activating factor and serotonin was measured in sheep bred for resistance or susceptibility to fleece rot and fly strike. Genetically susceptible sheep had significantly greater plasma leakage to activated complement than genetically resistant sheep, and for all mediators there was a trend for plasma leakage to be greater in susceptible sheep. Within each genotype there was also a tendency for plasma leakage to be positively correlated with fleece rot score. In a flock of sheep of different genetic background not selected for resistance or susceptibility to fleece rot and fly strike, positive phenotypic correlations were also noted between fleece rot and plasma leakage. Plasma leakage provides nutrition for the first instar larvae of Lucilia cuprina, the major cause of primary blowfly strike in Australia. Diminished leakage of plasma following release of endogenous permeability mediators may be one component of the mechanism that confers resistance in animals bred for resistance to fleece rot and fly strike.

Intradermal and percutaneous transudation of IgG1 and transferrin in sheep

The leakage of [125I]-IgG1 into skin sites following injection of mediators of enhanced vascular permeability and during induction of transudates on the skin surface under negative pressure was examined to determine whether IgG is selectively transported into cutaneous transudates. 111In-transferrin was employed as a marker of plasma leakage unaided by selective transport. The leakage of IgG1 into interstitial spaces of untreated skin, into inflammatory transudates and into transudate fluid drawn to the skin surface under vacuum occurred at a lower rate than did leakage of transferrin. No evidence was found in favour of a selective transport mechanism to aid transport of IgG1 into extravascular skin compartments.