Characterization of histamine receptor sub-types regulating prostacyclin release from human endothelial cells

Bixa orellana leaf extract suppresses histamine-induced endothelial hyperpermeability via the PLC-NO-cGMP signaling cascade

BACKGROUND

Histamine is established as a potent inflammatory mediator and it is known to increased endothelial permeability by promoting gap formation between endothelial cells. Previous studies have shown that aqueous extract of Bixa orellana leaves (AEBO) exhibits antihistamine activity in vivo, yet the mechanism of its action on endothelial barrier function remains unclear. Therefore, the current study aimed to determine the protective effect of AEBO against histamine-induced hyperpermeability in vitro.

METHODS

The endothelial protective effect of AEBO was assess using an in vitro vascular permeability assay kit. Human umbilical vein endothelial cells (HUVEC) were used in the current study. HUVEC were pre-treated with AEBO for 12 h before histamine induction. Vascular permeability was evaluated by the amount of FITC-dextran leakage into the lower chamber. In order to elucidate the mechanism of action of AEBO, phospholipase C (PLC) activity, intracellular calcium level, nitric oxide (NO) concentration, cyclic guanosine monophosphate (cGMP) production and protein kinase C (PKC) activity were determined following histamine challenge.

RESULTS

Histamine-induced increased HUVEC permeability was significantly attenuated by pretreatment with AEBO in a time- and concentration-dependent manner. Upregulation of PLC activity caused by histamine in HUVEC was suppressed by pretreatment with AEBO. Pretreatment with AEBO also blocked the production of intracellular calcium induced by histamine in HUVEC. In addition, AEBO suppressed the NO-cGMP signaling cascade when HUVEC were challenged with histamine. Moreover, PKC activity was significantly abolished by pretreatment with AEBO in HUVEC under histamine condition.

CONCLUSION

In conclusion, the present data suggest that AEBO could suppress histamine-induced increased endothelial permeability and the activity may be closely related with the inhibition of the PLC-NO-cGMP signaling pathway and PKC activity.

Endotoxin differentially impairs receptor-mediated relaxation in rat isolated pulmonary and thoracic aortic vessels

PURPOSE

The purpose of this study was to determine the effect of endotoxin on vasorelaxation in the pulmonary and systemic circulations in response to the following agonists that require generation of cyclic adenosine monophosphate: (1) beta-adrenergic receptor stimulation with isoproterenol; (2) H2 receptor stimulation with dimaprit; and (3) adenylate cyclase stimulation with forskolin.

METHODS

Male Sprague-Dawley rats weighing 250 to 350 g were injected with endotoxin (20 mg/kg intraperitoneal) or saline. Six hours later, the cumulative dose response to beta-adrenergic receptor stimulation (isoproterenol), H2 receptor stimulation (dimaprit), and adenylate cyclase stimulation (forskolin) was determined in isolated rat pulmonary artery and thoracic aortic rings preconstricted with phenylephrine.

RESULTS

Endotoxin caused significant impairment of relaxation to isoproterenol in the pulmonary artery, but the response in the aorta was not different from the control response. In the pulmonary circulation, endotoxin converted the response to dimaprit from vasorelaxation to vasoconstriction. On the other hand, dimaprit resulted in vasorelaxation in the thoracic aorta after endotoxin; however, the response was impaired compared with the control response. Endotoxin did not affect the dose response to forskolin in either the pulmonary artery or the thoracic aorta.

CONCLUSION

From these data, we conclude that endotoxin causes regional specific changes in vascular reactivity. These changes in vascular reactivity result in preserved vasorelaxation in the systemic circulation and impairment of vasorelaxation in the pulmonary circulation in response to endotoxin.

Histamine H2-receptor-mediated nitric oxide release from porcine endothelial cells

The involvement of histamine-receptor subtypes in histamine-induced release of nitric oxide (NO) from porcine aortic endothelial cells was studied. NO release was measured directly by using an NO electrode and by electron paramagnetic resonance (EPR) spin trapping. NO release induced by histamine (200 microM) was reduced in the presence of 2 microM cimetidine, an H2-receptor antagonist, but not altered by 2 microM pyrilamine, an H1-receptor antagonist. Histamine-induced NO release was significantly reduced by the addition of 20 microM of the Rp diastereomer of adenosine cyclic 3',5'-phosphorothioate (Rp-cAMPS), a membrane-permeable antagonist of cyclic adenosine monophosphate (cAMP). Application of 100 microM forskolin, an activator of adenylate cyclase, induced NO release from porcine aortic endothelial cells. Fura-2 acetoxymethylester (fura-2/AM) studies showed that addition of 100 microM histamine did not produce any significant increase in the use of free concentration of intracellular Ca2+. These results suggest that in porcine aortic endothelial cells, NO-mediated vasodilation might be caused by production of cAMP initiated through the histamine H2-receptor.

Epithelium-derived inhibitory prostaglandins modulate human bronchial smooth muscle responses to histamine

The role of the bronchial epithelium and inhibitory prostaglandins in the induction of histamine tachyphylaxis in human isolated bronchial smooth muscle was investigated using bronchi obtained from 14 patients who had been treated with non-steroidal anti-inflammatory drugs (NSAID) for > 2 months and from 14 untreated patients. Epithelium-intact bronchial strips from untreated patients demonstrated tachyphylaxis to histamine with the maximum response (Emax) reduced by 30 +/- 5% (P < 0.02) and the EC50 increased 1.86-fold (P < 0.02). Tachyphylaxis was not observed in epithelium-denuded strips. In epithelium-intact bronchial preparations from NSAID treated patients, the mean initial maximum tension generated in response to histamine was significantly greater than that for bronchial preparations from untreated patients (P < 0.05). In NSAID-treated patients, both epithelium-intact and denuded preparations failed to demonstrate tachyphylaxis. The generation of prostaglandin E2 and prostacyclin was assessed by radio-immunoassay using bronchi from untreated patients (n = 8). In epithelium-intact bronchial preparations, the generation of both prostaglandin E2 and prostacyclin was significantly increased by histamine exposure (P < 0.05) and was completely inhibited by indomethacin. However, the selective histamine H2 receptor antagonist, ranitidine, selectively inhibited the synthesis of prostaglandin E2 alone. Production of both prostaglandins was not altered by exposure to acetylcholine. These results suggest that prostaglandin E2 and prostacyclin are released primarily from the epithelium in response to histamine and may be specifically involved in inhibiting human bronchial smooth muscle responsiveness to this mediator. Significantly, the release of prostaglandin E2 appears to be selectively controlled by histamine H2 receptors, resident on the epithelium.

Interaction between histamine and adenosine in human cerebromicrovascular endothelial cells: modulation of second messengers

This study demonstrates the presence of histamine H1 and H2 receptors and purinoreceptors A1 and A2 on endothelial cells derived from human brain microvessels (HBEC). Histamine induced formation of both inositol triphosphate (IP3) (EC50 = 10.2 +/- 0.9 microM) and cyclic adenosine monophosphate (cAMP) (EC50 = 5.2 +/- 0.9 microM) in HBEC in a concentration-dependent fashion. IP3 formation was inhibited by H1 receptor antagonists mepyramine maleate and chlorphenyramine, but not by H2 receptor antagonist cimetidine. Production of cAMP was efficiently inhibited by cimetidine. Selective A1 receptor agonists decreased, whereas A2 receptor agonists increased cAMP production in HBEC. When added together with histamine to HBEC cultures, both A1 and A2 receptor agonists diminished histamine-induced IP3 stimulation. This effect was reversed in the presence of specific A1 and A2 receptor antagonists, respectively. Marked augmentation of histamine-induced cAMP production by HBEC was observed in the presence of A2 agonist. This response was dependent on H1 receptors, since it was reduced in the presence of H1-receptor antagonist. It is suggested that interaction between histamine and adenosine modulating induction of second messengers in HBEC may influence endothelium-dependent responses of brain microvascular compartments.