P2X₇ receptor activation contributes to an initial upstream mechanism of lipopolysaccharideinduced vascular dysfunction

Pro-inflammatory cytokines, chemokines and ROS (reactive oxygen species) are excessively produced in endotoxaemia. However, attempting to inhibit all of these inflammatory signalling pathways at the same time in order to prevent endotoxaemia is difficult. In a previous study we observed that activation of P2X₇ receptors elicited the release of IL (interleukin)-1β from LPS (lipopolysaccharide)-incubated vessels. In the present study, we hypothesize that P2X₇ receptor activation is the initial event leading to vascular dysfunction following LPS treatment. LPS-induced decreases in MAP (mean arterial pressure) and pressor responses to NE (noradrenaline) were attenuated in P2X₇KO (P2X₇-knockout) mice. Hyporeactivity in response to PE (phenylephrine) in isolated mesenteric arteries by LPS treatment was also observed in C57BL/6 [WT (wild-type)] mice, which was prevented by IL1ra (IL-1 receptor antagonist), L-NAME (N^G-nitro-L-arginine methyl ester) and indomethacin and in P2X₇KO mice. In addition, treatment with IL1ra plus L-NAME produced an additive inhibition of LPS-induced vascular hyporeactivity, suggesting different signalling pathways between IL-1β and NOS (NO synthase). LPS-induced plasma levels of IL-1β, TNFα (tumour necrosis factor α), IL-10, vascular eNOS (endothelial NOS) and COX2 (cyclo-oxygenase 2) protein expression, as determined by ELISA and Western blot, observed in WT mice were inhibited by IL1ra and in P2X₇KO mice. These results suggest that P2X₇ receptor activation involves an initial upstream mechanism of LPS-induced vascular dysfunction, which is associated with IL-1β-mediated eNOS, COX2 activation and TNFα release.