The Role of Prostanoids in Microvascular Leak

Victoria C Jones, Sarah A Maher, Mark A Birrell, Mark J Griffiths, Maria G Belvisi. Imperial College, London, UK

Microvascular leak (MVL) is a prominent feature of respiratory diseases such as asthma and Chronic Obstructive Pulmonary Disease (COPD) yet little is known about what drives it (Paredi & Barnes, 2009). Prostanoids, such as PGE2, are known to be present in the diseased airway and could play a role in the MVL. The aim of this study was to determine if prostanoids can cause MVL using a murine model system which uses leakage of i.v. administered Evans blue dye (EB) into the airway tissue.

Male C57bl/6 mice (20-25 gm) were anaesthetised with urethane (2 gm kg-1) prior to delivery of EB (5 mg kg-1 i.v at 4 ml kg-1). One minute later vehicle (1% ethanol in saline) or test compound (i.v. 4 ml kg-1) was injected. Thirty minutes later circulating blood was removed using a saline flush. The trachea, bronchi and intrapulmonary airways (IPA) were dissected and incubated in formamide to extract the EB. The level of MVL was quantified by measuring the level of dye in the airway tissue and expressing the data as ng mg of tissue-1.

PGE2 (0.1, 0.3, 1, 3 and 10 mg kg-1; n = 4) induced a dose related increase in MVL. When a sub-maximal dose of PGE2 (3 mg kg-1) was given to EP receptor deficient mice the data indicated that the EP2 and EP4 receptors were central to the response (Figure 1). Further studies using other prostanoid receptor ligands demonstrated that PGD2, PGF2α, and U46619 could induce MVL (all at 3 mg kg-1) and parallel experiments with prostanoid receptor deficient mice showed that the responses observed appeared to be via the activation of the DP1, FP and TP receptors, respectively. MVL induced by the IP ligand (Iloprost) into the airways did not reach significance under these experimental conditions. In DP knockouts the response was inhibited to PGD2 (trachea: WT 33.16 + 4.183 ng mg-1 KO 19.26 + 3.00 ng mg-1 where KO/Veh was 11.24 + 2.02 ng mg-1 of tissue;n = 6, p<0.05). Similarly the response in FP knockouts to PGF2α (trachea: WT 48.04 + 6.05 ng mg-1 KO 26.25 + 2.23 ng mg-1 where KO/Veh 16.59 + 1.71 ng mg-1 of tissue; n = 6, p<0.05) and the response in TP knockouts to U46619 (trachea: WT 30.60 + 4.64 ng mg-1 KO 14.35 + 2.63 ng mg-1 where KO/Veh was 11.10 + 2.00 ng mg-1 of tissue; n = 6, p<0.05).

The data, so far, suggests that PGE2 is mediating airway MVL via the activation of EP2 and EP4 receptors. In addition, other prostanoids are able to mediate microvascular leak. Identifying the receptor/s mediating prostanoid-induced microvascular leak is an important step in furthering understanding into the role that they play in airway inflammation.

Figure 1. Effect of PGE2 on MVL in the trachea of (A) WT and EP1-3 receptor deficient mice and (B) in WT and EP4 receptor deficient mice. n = 6, **p<0.01 significant decrease from WT, One-Way ANOVA Kruskal-Wallis test with Dunn’s Multiple Comparison test (A) and unpaired t test (B).

Paredi & Barnes (2009) Thorax, 64, 444-450.