Reduction in Monocyte Isolevuglandins Associated with High Interstitial Sodium Mirrors Salt‐Sensitivity of Blood Pressure in Patients with Essential Hypertension

Abstract

Salt Sensitivity (SS) of blood pressure (BP) is an independent risk factor for cardiovascular mortality. Sodium (Na+) is stored in skin and muscle interstitium. Antigen presenting cells are activated in response to elevated extracellular Na+ in an ENaC-dependent manner resulting in formation of (isolevuglandin) IsoLG-protein adducts. This leads to T-cell activation, release of inflammatory cytokines, kidney damage, endothelial dysfunction and an increase in BP. We aimed to determine the effect of tissue Na+ storage and immune cell activation on salt-sensitive hypertension. Five subjects with essential hypertension discontinued all anti-hypertensive therapy two weeks before the study. SS was assessed by a rapid inpatient protocol of salt loading (460 mmoL/24 hours) and salt depletion (10 mmoL/24 hours, plus furosemide 40 mg x 3). 23Sodium magnetic resonance imaging was used to measure muscle and skin Na+ contents at baseline (BA). Urine and serum electrolytes, glomerular filtration rate, plasma renin, aldosterone levels, plasma and urine EETs (8-9, 11-12 and 14-15 isoforms) and the percentage of IsoLG adduct-containing CD14+ monocytes via flow cytometry were measured at BA, after salt-loading (HI) and after salt-depletion (LO). All continuous data are displayed as median (interquartile range). Spearman's correlation was used to test associations. 60% of subjects were female, median age was 54 years (44-55), BMI was 35 kg/m2 (30-39), and screening BP was 140/88 mmHg (134-148 / 84-99). The range of the drop in systolic BP from HI to LO (salt-sensitivity index, SSI) was -13.8 to +1.8 mmHg. %isoLG+ CD14+ cells were 48 (27-65) at BA, 55 (31-56) at HI, and 70 (33-72) at LO (p=0.594, by the Kruskal-Wallis test). The correlation between SSI and delta (∆) %isoLGLO minus HI in CD14+ monocytes, was 0.86, [95% confidence interval (CI), -0.07-0.99] (Figure 1A). Skin Na+ content correlated with baseline % IsoLG+ CD14 (r=0.91; 95% CI, 0.12-0.99) (Figure 1B). Higher excretion of urine EETs associated with less IsoLG+ CD14+ cells whereas higher plasma aldosterone per unit urine EET, (a marker of net stimulation of ENaC) associated with a greater number of IsoLG-containing CD14+ cells. No such relationships were observed with plasma EETs. Finally, less stimulation of the aldosterone/urine EET ratio by salt depletion associated with a greater fall in IsoLG+ CD14+ cells (Figure 1C). The change in IsoLG-containing CD14+ monocytes in response to salt depletion appears to be associated with SSBP, which if confirmed in larger number of subjects could constitute a biomarker for SSBP in humans. The association between baseline % of IsoLG-containing CD14+ monocytes and skin Na+ suggests that activation of these cells is due to hyperosmolar Na+ exposure in some interstitial compartment of the body. Relationships between IsoLGs and urine but not plasma EETs suggest that this exposure could be occurring in the hyperosmolar renal medulla.