PGE2 deficiency predisposes to anaphylaxis by causing mast cell hyperresponsiveness.

BACKGROUND: Reduced levels of prostaglandin E2 (PGE2) contribute to aspirin-induced hypersensitivity. COX inhibitors are also frequent cofactors in anaphylaxis. Whether alterations in the PGE2 system contribute to anaphylaxis independently of COX inhibitor intake is unclear. OBJECTIVE: Our aim was to test the hypothesis that relative PGE2 deficiency predisposes to anaphylaxis. METHODS: Sera from 48 patients with anaphylaxis and 27 healthy subjects were analyzed for PGE2 levels and correlated against severity; 9α,11ß-PGF2 and PGI2 metabolites were measured for control purposes. PGE2 stabilization by 15-hydroxyprostaglandin dehydrogenase inhibitor or EP2 or EP4 receptor agonists were used in a murine model of passive systemic anaphylaxis. FcεRI-triggered mediator release was determined in bone marrow-derived cultured mast cells (MCs) and human skin-derived MCs. Signaling was studied by Western blot analysis. RESULTS: Patients with anaphylaxis were characterized by markedly reduced PGE2 levels vis-à-vis healthy subjects, whereas prostacyclin metabolite levels were diminished only weakly, and 9α,11ß-PGF2 levels conversely increased. PGE2 was negatively correlated with severity. Lower PGE2 levels and higher susceptibility to anaphylaxis were also found in C57BL/6 mice vis-à-vis in Balb/c mice. Stabilization of PGE2 level by 15-hydroxyprostaglandin dehydrogenase inhibitor protected mice against anaphylaxis. Exogenous PGE2 attenuated bone marrow-derived cultured MC activation through EP2 and EP4 receptors. EP2 and EP4 agonism also curbed FcεRI-mediated degranulation of human MCs. Mechanistically, PGE2 interfered with the phosphorylation of phospholipase C gamma-1 and extracellular signal-regulated kinase. CONCLUSIONS: Homeostatic levels of PGE2 attenuate MC activation via EP2/EP4 and protect against anaphylaxis. Relative deficiency of PGE2 predisposes to anaphylaxis in humans and mice, whereas PGE2 stabilization protects against anaphylactic reactions.

Ramipril and metoprolol intake aggravate human and murine anaphylaxis: evidence for direct mast cell priming.

BACKGROUND: Cofactors contribute to the elicitation of anaphylaxis. ß-Blockers and angiotensin-converting enzyme (ACE) inhibitors are widely used cardiovascular drugs. We specially designed a mouse model to further analyze the cofactor potential of these drugs. OBJECTIVE: We sought to test the hypothesis that ß-blockers and ACE inhibitors alter the risk for severe anaphylaxis and to pinpoint the associated mechanism. METHODS: The risk factor potency of cardiovascular drugs on the severity of anaphylaxis in patients from German-speaking countries was analyzed. In vivo interaction of the cardiovascular drugs metoprolol (ß-blocker) and ramipril (ACE inhibitor) with the anaphylactic response was determined. Mast cell (MC) mediators (histamine, serotonin, leukotriene C4, prostaglandin D2, and mouse mast cell protease 1) were quantified in serum. Bone marrow-derived cultured MCs served to identify whether the therapeutics targeted MCs directly. RESULTS: Our anaphylaxis database indicated a higher risk of severe anaphylaxis after monotherapy with ß-blockers or ACE inhibitors, which was more pronounced when both drugs were combined. This was confirmed in our mouse model. While single therapeutics had either no significant (ramipril) or a modestly aggravating (metoprolol) effect, their combined administration exacerbated anaphylactic symptoms potently and simultaneously enhanced MC mediators, hinting at MCs as direct targets. In fact, FcεRI-mediated MC histamine release was synergistically increased by metoprolol/ramipril or metoprolol/bradykinin (the latter increased after ACE inhibitor intake), whereas the substances had no significant effect on their own. MC priming was particularly pronounced when FcεRI aggregation was in the suboptimal range, reflecting common clinical settings. CONCLUSION: ß-Blockers and ACE inhibitors synergistically aggravate anaphylaxis at least partly by decreasing the threshold of MC activation.