Vitamin B6 (pyridoxal 5’ phosphate) antagonizes carotid body P2X3 receptors in hypertension

Abstract

Aims ATP acting on P2X3R within carotid bodies (CBs) underpins chemoreflex-mediated sympathetic overactivity in Spontaneously Hypertensive rats (SHR). Pyridoxal 5’phosphate (PLP), the active form of vitamin B6, is reported as being a non-selective P2X receptor blocker. Hence, we hypothesized that PLP antagonism of P2X3R in the CB would treat hypertension. Methods and Results Herein, we employed a multipronged approach to investigate PLP’s capability to attenuate CB hyperexcitability in hypertension. First, PLP inhibited Ca2+ responses evoked by α, β-methylene ATP in cells lines expressing human (h) P2X3R with IC50 of 8.7µM. Next, in-silico data predicted that PLP binds to the same site of Gefapixant, supporting an allosteric antagonism. Using an isolated perfused carotid artery bifurcation-CB preparation, arterial infusion of PLP (50 µM; 15 min) attenuated CBs sensory firing in SHR (P=0.012). Using the in situ working-heart brainstem preparation, carotid artery injections of PLP (1-5mM) attenuated the chemoreflex-evoked sympathetic (P=0.023) but not phrenic (P=0.62) responses; the CB was stimulated with potassium cyanide (KCN,50 µL; 0.04%). In awake telemetered SHR (n=6), intravenous infusion of PLP (48 mg/Kg/h; 30 min) attenuated KCN-evoked chemoreflex responses and reduced systolic, diastolic, and mean blood pressures (ΔMBP = -15.6 mmHg; P=0.025). Translating our results, we performed a small double-blind randomized clinical trial. In volunteers with hypertension (n=14), oral supplementation with pyridoxine hydrochloride (600 mg) attenuated the hypoxic ventilatory response only in patients with high peripheral chemoreflex sensitivity (P=0.021). Conclusion Our findings suggest that PLP binds to and antagonizes P2X3R and is a viable candidate for larger clinical trials to treat CB dysregulation in cardiovascular diseases.