Abstract MP51: Isolevuglandins In Antigen-presenting Cells, A Biomarker For Salt Sensitivity Of Blood Pressure In Humans?

Abstract

Background: High Na+ stimulates antigen-presenting cells (APCs) in an ENaC dependent manner, with formation of isolevuglandin (isoLG) adducts (neoantigen peptides) that promote T cell activation and salt sensitive (SS) hypertension in rodents. Methods: We studied this pathway in 9 subjects with essential hypertension who discontinued anti-hypertensive therapy for 2 weeks. Their SS was assessed by 24-hrs of salt loading (460 mmoL) and salt depletion (10 mmoL/24 hr, plus furosemide 40 mg x 3). Muscle and skin Na + were measured at baseline (BA) by 23 Na magnetic resonance imaging (NaMRI). The % of APCs containing isoLG adducts (flow cytometry), urine and serum electrolytes and epoxyeicosatrienoic acids (EETs 8-9, 11-12 and 14-15) were measured at BA, after salt-loading (HI) and after salt-depletion (LO). Results: Age was 54 years (48-56), with 23% female, BMI 30 kg/m 2 (28-40) and screening SBP 136 mmHg (120-144), and DBP 85 mmHg (75-99). BA 24-hr urine Na + excretion was 178 (143-212) mmoL, Hi 392 (229-421) and LO 27 (25-29). SBP response to salt-depletion varied from -13.8 to +5.6 mmHg. Muscle Na+ correlated with duration of hypertension (r=0.73, p<0.03) and with SBP, DBP and mean arterial pressure (MAP) during BA, HI and LO (r=0.66 to 0.87). Mean %isoLGs in APCs were not different among the three stages of the protocol but ΔisoLGs due to HI or LO had positive correlations with ΔSBP, ΔDBP and ΔMAP produced by the same interventions (r=0.46 to 0.70). A 10% change in dendritic cell isoLGs predicted a 1.45 mmHg change of SBP in the same direction. Urine (not plasma) EETs (sum of three isoforms) showed negative correlations with isoLGs on the three phases of the protocol (r=0.57 to 0.69), and ΔEETs by HI and LO correlated negatively with ΔisoLGs produced by the same interventions (r=0.58 to 0.77). Conclusions: Muscle Na+ increases with duration of hypertension and correlates with severity of BP elevation. Changes in APC isoLGs due to Na+ loading or depletion seem to be a biomarker of SS of BP in humans. Relations between urine EETs and ΔEETs with APC isoLGs and ΔisoLGs suggest that EETs might be inhibitors of APC ENaC as they are of renal ENaC. Relationships between isoLGs and urine but not plasma EETs suggest that activation of APCs by high salt may occur in the hyperosmolar renal medulla.