M. G. Di Bello

Platelets and inflammation: role of platelet-derived growth factor, adhesion molecules and histamine.

Abstract. Despite the fact that the relationship between platelets and the inflammatory and immune responses has been reviewed previously, the allocation of platelets among the inflammatory cells is still at issue. Recent developments in our understanding of platelet-associated signalling events have offered new potential insights into platelet functions in inflammatory and immune-related diseases. In recent years, it has been established that a range of molecules, mainly associated with the platelet surface and/or the platelet granules, regulate the capacity of platelets to cross-talk with other inflammatory cells during the process of inflammation, and of vascular inflammation in particular. This is the case with platelet-derived growth factor (PDGF), secreted from platelet alpha-granules, with P-selectin, expressed on the platelet surface, and with platelet histamine, which is secreted from platelets in response to aggregatory and inflammatory stimuli. The nature and mechanism of action of these r egulatory molecules, physiologically present in platelets and mobilised upon platelet activation and aggregation, is the subject of this review. The participation of platelets, through PDGF, P-selectin and histamine, is also discussed in overtly inflammatory disorders, such as acute respiratory distress syndrome, mesangial glomerulonephritis, chronic inflammatory bowel disease, disseminated intravascular inflammation, and allergic vasculitis, focusing on possible pharmacological interventions specifically active against growth factors, adhesion molecules and platelet histamine.

The role of histamine in platelet aggregation by physiological and immunological stimuli.

Abstract.Background: Platelets participate in allergic and inflammatory processes beside their role in haemostasis and thrombosis. This paper reports the level, the uptake, the metabolism and the release of histamine in human platelets. The effects of exogenous histamine, as well as the receptor and signal transduction of these effects, are also described.¶Methods: Purified suspensions of platelets, prepared from healthy volunteers and from atopic patients, were exposed in vitro to physiological and immunological stimuli. Platelet aggregation was measured by the increase in light transmission; histamine content and release, as well as cytosolic free Ca2+ concentration, were measured fluorimetrically. Platelet histamine forming capacity, and the uptake of exogenous histamine, were measured with a radioisotopic method.¶Results: Human platelets contain 72.5  ± 9.6 pmoles of histamine × 109 platelets, and their capacity to form histamine is 18.7 ± 3.5 pmoles h−1 g−1 protein, which is reduced by α-fluoromethylhistidine (10−5 M) a selective inhibitor of the specific histidine decarboxylase. Human platelets take up the preformed amine by a calcium and energy-dependent process, and the uptake of histamine is reduced by mepyramine, an H1-receptor antagonist, and N,N-diethyl-2-[4-(phenylmethyl) phenoxyl] ethanamine (10−6 M), a blocker of intracellular histamine receptors. Histamine is also metabolized by human platelets. The exposure of platelets to thrombin (10–60 mU ml−1) produced a progressive aggregation, associated with histamine release. The same is observed in platelets isolated from atopic patients exposed to anti-IgE antibodies. Exogenous histamine dose-dependently potentiates the aggregation induced by physiological and immunological stimuli. In resting platelets cytosolic calcium level (207 ± 4.2 nM 108 platelets) is increased by thrombin as well as by anti-IgE; this effect is potentiated by 10−5 M histamine.¶Conclusions: The synergistic effect between histamine and other monoamines on platelet aggregation may explain some aspects of allergic vasculitis in which platelet aggregation is present.

Histamine release from rat mast cells induced by the metabolic activation of drugs of abuse into free radicals

BACKGROUND The metabolic activation of morphine, cocaine and methadone into free radicals could have pathophysiological relevance in the organic injuries of drug addiction. METHODS Isolated purified rat serosal mast cells were incubated with morphine, cocaine and methadone (10(-7) M-10(-4) M) with oxidative enzymes (prostaglandin-H-synthetase, 25 mU; rat liver homogenate fraction S 10-mix, 400 microl), and with the drugs of abuse in the presence of oxidative enzymes. Histamine and lactate dehydrogenase (LDH) were analysed with a fluorimetric and spectrophotometric assay, respectively; the generation of malonyldialdehyde (MDA) was measured by a spectrophotometric assay. RESULTS The release of mast cell histamine and the generation of MDA are present only when mast cells were incubated with the drugs of abuse in the presence of oxidative enzymes. This release was dependent on the concentration of the drug in question and showed a maximum value at 10(-4) M. Moreover, in parallel experiments we demonstrated that, under the same experimental conditions, the release of LDH was always less than 20% of the total, suggesting that this effect is due to a selective exocytotic process. Histamine release and MDA generation were abated by the free radical scavengers: reduced glutathione, 10(-4) M GSH and alpha-tocopherol, 10(-4) M and by the spin trapper 5.5-dimethyl-1-pyrroline-N-oxide, 10(-4) M DMPO. The light and electron microscopic features are consistent with exocytotic secretion in the cases of morphine and methadone and with cell lysis in the case of cocaine. CONCLUSION These results suggest that morphine, cocaine and methadone are activated into free radicals which produce membrane lipid perturbation and histamine release, suggesting that a massive release of mast cell histamine could be an additional risk factor in heroin and cocaine overdoses.

Helicobacter pylori potentiates histamine release from serosal rat mast cells in vitro.

Helicobacter pylori seems, to be involved in the etiology of peptic ulcer and chronic gastritis. Histamine is fundamental in gastric secretion modulation, and some features ofH. pylori-associated gastritis (edema, vasodilatation, inflammatory cell infiltration) are typical of the histamine-mediated response Thisin vitro study has been undertaken as a preliminary step, in order to find a possible link betweenH Pylori and histamine release.H. pylori isolated from gastric biopsies, has been tested as whole washed bacterium, whole formalin-killed bacterium, and crude cell wall preparation with serosal mast cells obtained by density gradient centrifugation or elutriation from peritoneal, and pleural washings of male Wistar albino rats. Histamine release was assayed fluorimetrically. No significant histamine release was obtained by testing the various bacterial preparations alone with mast cells. On the contrary, whole washed cells, whole formalin-killed cells and crude cell walls fromH. pylori have been found to potentiate, compound 48/80 or calcium ionophore A23187-induced histamine release. Crude cell walls showed the highest activity, whereas filtered supernatants from broth cultures constantly appeared inactive. The enhancement in histamine release, differed between the different strains. The presentin vitro study, which shows the potentiating effect ofH. pylori on histamine release, may prove interesting; however, at present, clinical implications cannot be inferred and further studies as well asin vivo demonstrations are needed.

Helicobacter pylori potentiates histamine release from rat serosal mast cells induced by bile acids

In the present study we have experimentally addressed the effects ofHelicobacter pylori on the bile acid capability of histamine release. Bile acids alone were confirmed to be able to inducein vitro histamine release from rat serosal and mucosal mast cells. On the contrary, no significant histamine release was obtained when incubating anyHelicobacter pylori preparations alone with mast cells. However, histamine release induced by bile acids was significantly enhanced, without any significant increase in lactate dehydrogenase activity, when whole washed or formalin-killed bacterial cells or crude cell walls were incubated with mast cells in the presence of cholic (0.3 mM), deoxycholic (0.3 mM), or lithocholic (0.3 mM) acids, chenodeoxycholylglycine (0.3 mM), and deoxycholyltaurine (3 mM). The electron microscopic features of mast cells incubated withHelicobacter pylori were consistent with an exocytotic secretion. The release of histamine induced by 0.3 mM deoxycholic acid in the presence ofHelicobacter pylori was inhibited by the preincubation of the cells with dimaprit (an H2 agonist) and potentiated by the H2 antagonist, ranitidine. The current results suggest a link between humanHelicobacter pylori infection and histamine release and a possible involvement of gastric mucosal mast cells in the pathogenesis ofHelicobacter pylori-associated gastritis.

Interaction between Histamine and Nitric Oxide in Rat Mast Cells and in Isolated Guinea Pig Hearts

BACKGROUND Histamine and nitric oxide (NO) are present in guinea pig hearts and in rat mast cells (MCs) of the serosal phenotype. Histamine and NO are simultaneously released upon immunological challenge of isolated hearts of actively sensitised guinea pigs. MCs release histamine in response to antigen and NO in response to stirring. This has prompted us to study the interaction between histamine and NO in rat MCs and in guinea pig hearts. METHODS The experiments have been carried out in isolated purified rat serosal MCs and in isolated perfused guinea pig hearts. The generation of NO by both preparations has been evaluated as nitrites (NO2-) by means of the Griess reaction. RESULTS Histamine upregulates the generation of NO both in rat MCs and in guinea pig hearts. The effect is abolished by blocking NO synthase and preferentially mimicked by a selective H2-receptor agonist. A selective H3-receptor agonist downregulates the generation of NO in lipopolysaccharide-pretreated MCs and in bradykinin-pretreated guinea pig hearts. CONCLUSION A mutual relationship between histamine and NO in allergic inflammation could be envisaged.

Nitric oxide modulates cardiac and mast cell anaphylaxis

Anaphylaxis in the isolated guinea-pig heart was associated with a sudden release of histamine with a long-lasting release of nitrite (NO2−), an oxidation product of NO.NG-monomethyl-l-arginine (MeArg, 300 μM) increased the severity of cardiac anaphylaxis, as shown by the decrease in the coronary flow and by a prolonged duration of antigen-induced arrhythmias. Concomitantly, MeArg increased the release of histamine while decreasing the release of nitrite. Sodium nitroprusside (NaNP, 10−5–10−4M) reduced the severity of cardiac anaphylaxis by increasing coronary flow and shortening the duration of antigen-induced arrhythmias. Concomitantly, NaNP decreased the release of histamine while increasing the release of nitrite. In mast cells isolated from actively sensitized guinea-pigs, the release of histamine elicited by specific antigen was increased by MeArg and decreased by NaNP.In conclusion, endogenous and exogenous NO antagonizes the effect of vasoconstrictor mediators released after antigen challenge and plays a protective role in anaphylactic reactions “in vitro”,

A regulatory role for carbon monoxide in mast cell function

Beside its exogenous generation in the incomplete oxidation of carbon containing materials, carbon monoxide (CO) is produced endogenously by various cell types as a product of heme catabolism, in which heme-oxygenases (HO) catalyse the degradation of heme to biliverdin [1]. CO is a diatomic gas that shares some of the physicochemical properties of nitric oxide (NO). Like NO, CO has the ability to bind to the iron atom of the heme moiety associated with soluble guanylyl cyclase, thereby activating the enzyme and increasing intracellular cGMP production [2]. Exogenously added CO inhibits platelet aggregation, relaxes vascular smooth muscle cells, and modulates neuronal activity by elevating intracellular levels of cGMP [3]. NO donors and generators have been shown to modulate the secretory activity of mast cells (MC) [4]. The homology between CO and NO prompted us to evaluate the effects of exogenous CO on rat MC activity. We report on the effects of exogenous CO on the biochemical and morphological changes induced by compound 48/80 in rat MC.

Platelet Histamine: Characterization of the Proaggregatory Effect of Histamine in Human Platelets

Minute amounts of histamine and a discrete histamine-forming capacity was present in quiescent human platelets. Aggregation of human platelets induced by thrombin was concomitant with the release of h

A place for free radicals in platelet-derived histamine releasing factor (PDHRF) and evidence that histaminergic receptors modulate platelet aggregation

The release of histamine from rat serosal mast cells induced by coincubation with resting and activated human platelets, or by exposure of mast cells to supernatants obtained from activated platelets, is significantly reduced by anti-free radical interventions, and is coupled with the generation of membrane lipid peroxidation products. These results suggest free radical participation in the activity of PDHRF. Human platelets possess specific binding sites for an H1-receptor antagonist, suggesting that H1-receptors could modulate the intracellular calcium levels in a pro-aggregatory fashion.