RELEASE PROCESSES IN MAST CELLS AND THEIR ACTIVATION BY INJURY

Inflammatory effects of snake venom myotoxic phospholipases A2

Snake venom phospholipases A2 (PLA2) show a remarkable functional diversity. Among their toxic activities, some display the ability to cause rapid necrosis of skeletal muscle fibers, thus being myotoxic PLA2s. Besides myotoxicity, these enzymes evoke conspicuous inflammatory and nociceptive events in experimental models. Local inflammation and pain are important characteristics of snakebite envenomations inflicted by viperid and crotalid species, whose venoms are rich sources of myotoxic PLA2s. Since the discovery that mammalian PLA2 is a key enzyme in the release of arachidonic acid, the substrate for the synthesis of several lipid inflammatory mediators, much interest has been focused on this enzyme in the context of inflammation. The mechanisms involved in the proinflammatory action of secretory PLA2s are being actively investigated, and part of the knowledge on secretory PLA2 effects has been gained by using snake venom PLA2s as tools, due to their high structural homology with human secretory PLA2s. The inflammatory events evoked by PLA2s are primarily associated with enzymatic activity and to the release of arachidonic acid metabolites. However, catalytically inactive Lys49 PLA2s trigger inflammatory and nociceptive responses comparable to those of their catalytically active counterparts, thereby evidencing that these proteins promote inflammation and pain by mechanisms not related to phospholipid hydrolysis nor to mobilization of arachidonic acid. These studies have provided a boost to the research in this field and various approaches have been used to identify the amino acid residues and the specific sites of interaction of myotoxic PLA2s with cell membranes potentially involved in the PLA2-induced inflammatory and nociceptive effects. This work reviews the proinflammatory and nociceptive effects evoked by myotoxic PLA2s and their mechanisms of action.

Mediators of inflammation and the inflammatory process

A complex interplay of inflammatory cells and chemical mediators is responsible for allergic inflammation. It is now understood that the allergic reaction consists of an early-phase response involving mast cell degranulation with the release of histamine and a late-phase response characterized by the migration of inflammatory cells. This review provides a summary of the early- and late-phase events associated with allergic inflammation and an overview of the principal chemical mediators involved in the inflammatory process.

Histamine H1 receptor-induced Ca2+ mobilization and prostaglandin E2 release in human gingival fibroblasts. Possible role of receptor-operated Ca2+ influx

Stimulation of human gingival fibroblasts with histamine elicited an increase in the intracellular concentration of free calcium ([Ca2+]i) and the formation of inositol 1,4,5-trisphosphate (InsP3) in a concentration- and time-dependent manner. The histamine-induced increase in [Ca2+]i was attenuated completely by chlorpheniramine, an H1 antagonist, but not by cimetidine, an H2 antagonist. The histamine-induced Ca2+ response consisted of an initial transient peak response and a subsequent sustained increase. The transient phase can be largely attributed to Ca2+ release from intracellular InsP3-sensitive stores since the increased [Ca2+]i effect of histamine completely disappeared after depletion of intracellular Ca2+ stores with thapsigargin in the absence of extracellular Ca2+. The sustained phase was due to Ca2+ influx which was attenuated in the absence of extracellular Ca2+. The Ca2+ influx required the continuous binding of histamine to the receptor, since chlorpheniramine attenuated the increase in [Ca2+]i observed when extracellular Ca2+ was re-applied to the cells after stimulation with histamine in the absence of extracellular Ca2+. Pretreatment with the Ca2+ channel blocker SK&F96365 inhibited the Ca2+ influx component, suggesting that histamine stimulates Ca2+ influx through an H1 receptor-operated Ca2+ channel. Histamine also evoked a concentration- and time-dependent release of prostaglandin E2 (PGE2). The histamine-evoked PGE2 release was reduced markedly by exclusion of extracellular Ca2+ or pretreatment with SK&F96365 or an H1 antagonist. These results indicate that histamine stimulates both the intracellular Ca2+ release from InsP3-sensitive stores and the H1 receptor-operated Ca2+ influx from extracellular sites. The increased [Ca2+]i due to the Ca2+ influx causes PGE2 release in human gingival fibroblasts.

Effects of mast cell degranulation on blood-nerve barrier permeability and nerve conduction in vivo

Changes in blood-nerve barrier (BNB) integrity and nerve conduction were assessed in rat tibial nerves in which mast cell degranulation was induced by intraneural injection of Compound 48/80 (C48/80). BNB permeability changes were quantitated by the endoneurial accumulation of Evan's blue-labelled albumin (EBA). Over 24 h following intraneural injections, nerves receiving saline showed a 6-fold increase in endoneurial extravasated EBA compared to non-injected nerves. Injection of 250 ng C48/80 produced a similar level of EBA accumulation as saline injections. Increasing the C48/80 dose to 1 microgram produced twice the EBA accumulation as control saline injections and a 12-fold increase over non-injected nerves. Tibial nerves injected with these C48/80 doses showed completely normal nerve conduction. In contrast, increasing the dose to 5 micrograms C48/80 induced, again, increased EBA accumulation over lower doses, but also significant axonal degeneration indicated by profound decreases in compound muscle action potential amplitudes measured with nerve stimulation distal to the injection site. Co-injection of Leupeptin and neutralizing anti-TNF-alpha antibodies with C48/80 failed to mitigate conduction abnormalities suggesting a direct toxic effect of C48/80 on nerve fibres. Time-kinetic studies showed rapid restoration of BNB integrity 24-48 h after injections in all nerves, but at these timepoints C48/80 injected nerves still showed significantly increased BNB permeability compared to nerves injected with saline. Neural mast cell stimulation in the absence of a primed immune response can produce profound temporary changes in blood-nerve barrier permeability and endoneurial fluid composition without affecting nerve conduction.

Resistance to peritonitis following disruption of peritoneal mast cells

A single ip injection of distilled water osmotically disrupts almost the entire population of peritoneal mast cells in rats. The metachromatic granules released from disrupted mast cells are phagocytosed by peritoneal macrophages increasing their chemotactic and spreading activities. On this basis a study was carried out to determine whether an ip injection of distilled water, by releasing an abundance of these granules for peritoneal macrophage stimulation, protects rats subsequently exposed to peritonitis. We found that a single ip injection of distilled water lowers the mortality in rats exposed to bacterial peritonitis 2-3 weeks later from 80 to 33%.

Mast cells in nerve end neuromas of mice

The volume density of mast cells was estimated in nerve end neuromas at various time-points after transection of the left sciatic nerve of 6-week-old mice. After an initial reduction in the amount of mast cells there was a steady increase with numerous cells in 6-month-old neuromas. The variation in amount of mast cells in the individual animals at each time-point was relatively large. Exposure of neuromas to mild trauma resulted in degranulation of mast cells. Possibly, these numerous mast cells, which can liberate their contents after very light touching, may influence the neuroma.

The role of ascorbic acid deficiency in human gingivitis--a new hypothesis

Periodontal disease is one of the most prevalent health problems in the world and is the major cause of tooth loss in the adult population. Its two major subdivisions are gingivitis where disease is confined to the gingiva, and periodontitis where disease is present both in the gingiva and the supporting periodontal tissues. During the first stage there is a vasculitis of vessels subjacent to the junctional epithelium which is followed by exudation of fluid from the gingival sulcus and migration of leukocytes. There is variable expression of this stage throughout the mouth with new areas of involvement appearing in place of healed areas. Mast cells which are present in the gingival connective tissues may participate in this inflammatory response by liberating histamine. Ascorbic acid deficiency has been shown to be a conditioning factor in the development of gingivitis. When humans are placed on ascorbic acid deficient diets there is increased edema, redness and swelling of the gingiva. These changes have been attributed to deficient collagen production by gingival blood vessels. However, this may be due to an antihistamine role of ascorbic acid. This vitamin may act to directly detoxify histamine or effect a change in the level of enzymes responsible for histamine metabolism. This could occur through the influence of ascorbic acid in altering cyclic AMP (c-AMP) levels. Such changes in the level of this regulatory molecule could result in increased histamine-N-methyl transferase and other enzymes responsible for the breakdown of histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Mast cell degranulation in the evolution of acute eruptive guttate psoriasis vulgaris

Clinically normal psoriatic skin (CNPS) and psoriatic lesions (PLs) were studied for mast cell degranulation (MCD) in patients with acute eruptive guttate psoriasis vulgaris (AEGP) following penicillin-treated acute streptococcal throat infection. The clinically manifest duration of psoriasis at the time of the biopsies was 2, 5, 10, 14, or 21 days. Two types of MCD were distinguished. Type I was characteristic for those portions of the CNPS in which vascular and epidermal changes were detected, while the PLs showed both Type I and Type II MCD. In Type I MCD the extruded granules (MCGs) in the immediate vicinity of the mast cells appeared as intact bodies encased in a distinctly trilaminar membrane. Around subepidermal and subpapillary blood vessels, in stratum papillare without proximity of blood vessels, beneath the epidermal-dermal junction, in lamina lucida, and in intercellular space of strata basale and spinosum the MCGs appeared partly as intact structures and partly in more or less disintegrated form. In Type II MCD the MCGs were extruded without perigranular membranes. The data here presented showed that MCD is an early and constant feature in the evolution of AEGP.

Cation exchange--a common mechanism in the storage and release of biogenic amines stored in granules (vesicles)? III. A possible role of sodium ions in non-exocytotic fractional release of neurotransmitters

The matrices of the amine storing granules in mast cells, chromaffin cells and noradrenergic nerves show properties reminiscent of cation exchanger materials. In vitro, the amines are released from their granule storage sites on exposure of the granules to cations, e.g. sodium ions. The proposal is made that also in vivo the release of transmitter amines is the result of cation exchange Amine+ in equilibrium Na+ ions and that the release of transmitter amines occurs as a nonexocytotic fractional release engaging multiple granules instead of exocytotic emptying of a few. Some physiological and pharmacological implications of a fractional transmitter release are discussed.

Quantitative correlation between histamine and 35S release from isolated rat mast cells due to the beta-adrenergic blocking drug Kö 1124

An attempt was made to explain the mechanism of histamine release from isolated rat mast cells induced by the beta-adrenergic blocking drug Kö 1124. This drug at the highest concentration used released 12 times more histamine than most other investigated beta-blockers. The release of histamine with Kö 1124 was dose and temperature dependent. The maximal histamine release was at pH 8 and in the absence of calcium ions. Increased calcium concentration decreased histamine release significantly. The effect of Kö 1124 on histamine release from mast cells was inhibited only by cocaine and 2,4-dinitrophenol; other metabolic inhibitors were ineffective. The histamine release due to Kö 1124 was not followed by an equal release of 35S. Isoprenaline in equimolar concentration decreased histamine release induced by Kö 1124 significantly. The release of 35S-labelled granules was decreased or blocked by isoprenaline.

Complement-dependent histamine release from rat peritoneal mast cells, induced by lipopolysaccharides from Bacteroides oralis, Fusobacterium nucleatum and Veillonella parvula

The capacity of phenol/water extracted lipopolysaccharides (LPS) from Bacteroides, Fusobacterium and Veillonella to induce histamine release from rat peritoneal mast cells has been evaluated by means of a bioassay using atropinized guinea pig ileum and a fluorescence assay. Histamine release was found to be completely complement dependent. It was also found that LPS of Veillonella have the greatest capacity to induce histamine release and Bacteroides have the weakest.

Characteristics of histamine release evoked by acetylcholine in isolated rat mast cells

1. Histamine secretion from rat mast cells occurs in the presence of nanomolar concentrations of acetylcholine. 2. Intact glycolytic and oxidative metabolism is required for the acetylcholine-induced histamine secretion. Removal of extracellular glucose, hypoxia, cyanide and monoiodoacetate almost completely inhibit the secretion. 3. The secretion of histamine is dependent on the extracellular H ion concentration and is blocked when the cells are exposed to Na-deficient media. 4. The order of potency of cholinrgic agonists in evoking the secretion of histamine is oxotremorine > acetylcholine > choline > carbamycholine > nicotine. 5. Atropine competitively blocks the acetylcholine-induced histamine secretion, indicating the presence of cholinergic muscarinic receptors on mast cells. 6. Dibutyryl cyclic AMP and adrenaline inhibit the acetylcholine-induced histamine secretion, indicating a regulatory function afforded by cyclic nucleotides in the cholinergic histamine release.

Histamine-releasing effect of a corticotrophin derivative. II. Mechanism of action of histamine release by C 44 680-Ba, compared with that of Cpd. 48/80, dextran and triton

The mechanism of the histamine-liberating action of the synthetic polypeptide C 44 680-Ba, an alkyl-prolyl derivative of beta 1-19 corticotrophin, was investigated and compared with those of Compound 48/80, dextran, Melittin and Triton X-100. It was found that the release of histamine from rat peritoneal cells induced by the polypeptide is dependent on temperature, pH, calcium ions and energy-providing processes. In regard to these criteria, the mode of action of this histamine liberator resembles that of Compound 48/80 but is quite distinct from that of the unspecific substance Triton X-100.

Increased uptake and desulphation of heparin by mouse macrophages in the presence of polycations

Heparin uptake and desulphation by cultured macrophages were investigated. Histones, polyamino-acids, protamine and eosinophil-basic protein stimulated both heparin uptake and desulphation, processes found to be non-related. Poly-L-ornithine and poly-DL-lysine increased the heparin uptake by about 33-fold, and histone produced up to 7.5-fold increase in the desulphation. The same polycations inhibited heparin desulphation by macrophage extracts.

Possible involvement of cyclic AMP in inflammation induced by a surfactant

Alkyldimethylbenzylammonium chloride (alkyl-DBAC), a cationic surfactant, produces acute exudative inflammation accompanied by an enhancement of energy metabolism. The mechanism of metabolic changes, consequently the cyclic AMP level and the effects of certain drugs were determined in the gastrocnemius muscles of rats in which acute exudative inflammation had been induced by intramuscular injections of alkyl-DBAC. A transient increase in the cyclic AMP level was noted at 15 to 30 minutes after the injection of alkyl-DBAC, and this elevation was antagonized by chlorpromazine, diphenhydramine, promethazine, aspirin and indomethacin. The time course of increasing tendency in the cyclic AMP level after the injection of histamine closely paralleled that of alkyl-DBAC. These results suggest that cyclic AMP may be involved in the metabolic changes with inflammation induced by alkyl-DBAC.

Crush injury to peripheral nerve. An electron microscope study employing horseradish peroxidase

Electron microscope observations were made of rat peroneal nerve after crushing using intravenously injected horseradish peroxidase (HRP) as a tracer protein to indicate changes in vascular permeability. At 1/2 h and 2 d after the crush there was gross leakage of HRP from damaged capillaries at the site of injury but none from vessels above or below this. Ultrastructurally vessels at the site of crush showed broken and separated endothelial cells. Proximally and distally there was little abnormal in the vessel walls; vesicles containing HRP were absent and tight-junctions between cells remained intact. Twenty-one days after the crush, leakage of HRP was found both at the site of crush and along the distal segment. The only change in vessel walls was an obvious increase in vesicles filled with HRP. Tracer was also found both in perivascular locations and throughout the endoneurial space.

Mast cells and pterygium

A total of thirty pterygia were studied for mast cells using metachromatic dye (toluidine blue) together with routine histological stains. On microscopic examination, the lesion was differentiated and classified into angiomatous, fibrous and mixed varieties based on the vascular and collagenous components. The mast cell counts were undertaken in all types and were found to have significant correlation with the morphological types when compared to normal conjunctiva. 15.1 +/- 3.1, 22.7 +/- 3.8, 9.5 +/- 3.2 mast cell per mm2 were found in the angiomatous, mixed and fibrous types respectively. In the control material, the mast cell count was 12.4 +/- 2.3 per mm2. The results are discussed. It is believed that mast cells are actively involved in the genesis and progress of pterygium.

An ultrastructural study of two different responses of mouse mast cells to transplantation antibodies directed against the same transplantation antigens

The present paper describes an ultrastructural study of two different kinds of behavior of mouse mast cells during two immunological reactions induced by transplantation antibodies: the direct allogeneic anaphylactic degranulation and the serocytotoxicity. In both situations, the same alloantigens, born by the mast cells themselves, are the targets of the reaction, but the first one is mediated by anaphylactic alloantibodies whereas the second one is mediated by cytotoxic alloantibodies in the presence of complement. The comparison of the ultrastructural aspects of the cells in these two systems demonstrated that mast cells can behave in two different ways depending on the nature of the immunological agents utilized. First, a physiological degranulation process with active granule expulsion was observed. This process was shown to be identical to the one induced in classical in vitro anaphylaxis or by histamine releasers such as compound 48/80. A second type of behavior was a lethal, complement-dependent, cell lysis without active granule expulsion.

The effect of Trimepranol on thrombocyte function and histamin release in the rat

Trimepranol a beta adrenergic blocking drug released serotonin from rat isolated and plasma-rich thrombocytes in vitro. The release was time- and dose-dependent. With the same concentrations this drug inhibited the histamine release from isolated rat mast cells. Aggregation of isolated or plasma-rich thrombocytes induced by ADP was inhibited by Trimepranol. The inhibition was dose, time dependent and reversed by calcium ions.

The mast cells of the newborn rat diaphragm and their response to histamine liberators

The mast cell population of rat diaphragm was estimated between birth and adulthood and found to rise with an increase in the age of rat studied. Degranulation of these cells was observed in rats from all age groups, following treatment with compound 48/80 and dextran. The association of mast cells with the blood vessel wall in adult rat diaphragm was not observed in the comparable tissues of newborn rats. These findings are discussed in relationship to the poor vascular permeability reactions exhibited by newborn and young rats.