P2X7 Receptor Signaling Inhibition by Melatonin Prevent Vascular Hyporeactivity of LPS-treated aorta

Sepsis is a life-threatening condition characterized by organ dysfunction due to a dysregulated immune response, often resulting in vascular hyporeactivity mediated by LPS/TLR4, with limited treatment options (JAMA (2016) 315: 801; J Innate Immun. (2021) 13:323). In addition, there is evidence that internalized LPS interacts with the P2X7 receptor (P2X7R) (J Immunol. (2001) 167: 1871).  Melatonin is a hormone with pleiotropic effects and has been investigated in clinical trials due to its anti-inflammatory effects (J Pineal Res. 2009;46:268; J Matern Fetal Neonatal Med. 2018;31:2299). This study investigated the contribution of TLR4/P2X7R signaling to vascular hypocontractility and evaluated the protective effects of melatonin. Aortic rings from male Wistar rats (2–3 months; CEUA 001/24) were mounted in organ baths for isometric tension recording. After assessing endothelial integrity, concentration-response curves to phenylephrine (0.01–10 µM) were obtained in the absence (control) or presence of LPS (1 µg/mL), the P2X7R agonist BzATP (10 µM), the P2X7R antagonist A740003 (50 nM), melatonin (10 µM). Maximal contraction (E_max) and EC₅₀ values were determined by nonlinear regression. In the presence of intact endothelium, BzATP and melatonin did not alter E_max values of phenylephrine, while LPS reduced the E_max value by 20% when compared to the control group (n=10; p<0.01). Meanwhile, treatment with the LPS+BzATP combination reduced further aorta reactivity by 35% (n=9; p<0,01). This effect was inhibited by A740003 (n=9; p<0,01). Finally, treatment with melatonin inhibited the LPS+BzATP-induced reduction in aortic contractility (n= 7, p<0,01). These findings suggest that P2X7R activation contributes to LPS-induced vascular hyporeactivity and that melatonin preserves vascular contractility.

Support: CAPES, FAPERJ, CNPq, INCT "Sinalização Purinérgica: Desafios para a Saúde do Século XXI", CNPq 409156/2024-8.