Hydroxyurea Augments Nitric Oxide Bioavailability in Humanized Sickle Cell Mice

Abstract

Sickle cell disease (SCD) is an inherited hemoglobinopathy that affects millions of people across the world. Despite advancements in disease management, sickle cell nephropathy (SCN), a major contributor to mortality and morbidity in patients, has limited therapeutic options. Only one of two FDA‐approved therapies for the treatment of SCD, hydroxyurea (HU) has been shown to improve renal injury but the mechanism is elusive. Studies have shown that many of the therapeutic benefits of HU may be due to its ability to improve nitric oxide (NO) bioavailability. Thus, we hypothesized that HU treatment would improve NO bioavailability in the humanized sickle cell mouse. Male 12‐week old sickle (HbSS) and genetic control (HbAA) mice were treated with HU or vehicle for two weeks before renal and systemic NO bioavailability as well as renal injury were assessed. Vehicle treated HbSS mice exhibited significant renal injury compared to vehicle treated HbAA mice, indicated by increased proteinuria (4.7 ± 0.6 vs. 2.2 ± 0.3 mg/day, respectively, p=0.002), elevated plasma endothelin‐1 (ET‐1) (1.6 ± 0.1 vs. 0.9 ± 0.1 pg/ml, respectively, p<0.001), and reduced urine concentrating ability (1380 ± 89 vs. 2481 ± 93 mOsmol/kg, respectively, p< 0.0001). HU treatment reduced renal injury in HbSS mice indicated by reduced proteinuria (2.3 ± 0.3 vs.4.7 ± 0.6 mg/day, respectively, p<0.01) and lower plasma ET‐1 levels (1.2 ± 0.1 vs. 1.6 ±0.1 pg/ml, respectively, p=0.04). While HU treatment improved urine concentrating ability, this effect was not statistically significant (1623 ± 73 vs.1380 ± 89 mOsmol/kg, respectively, p=0.05). Vehicle treated HbSS mice showed signs of impaired systemic NO bioavailability compared to HbAA mice, indicated by elevated plasma arginase activity (347 ± 48 vs. 52.9 ± 4.6 units/L, respectively, p<0.001). NO bioavailability impairments were improved with HU treatment as seen by reduced plasma arginase activity (150 ± 33 vs. 347±48 units/L, respectively, p=0.01) and increased plasma nitrite levels (1.1 ± 0.3 vs. 0.04 ± 0.02 mM, respectively, p=0.01) compared to HbSS vehicle treated mice. Renal vessels isolated from HbSS mice also had elevated nitric oxide synthase 3 (NOS3) expression (2.5 ± 0.4 vs.1.0 ± 0.1 arbitrary units (A.U.), respectively, p=0.04) compared to vehicle treated HbAA mice detected by Western blot analysis. HU treatment did not alter renal vascular NOS3 expression (0.9 ± 0.2 vs. 1.0 ± 0.1 A.U., respectively, p=0.94), however, renal vascular arginase 2 expression was reduced by HU (0.07± 0.01 vs. 1.0 ± 0.1 A.U., respectively, p<0.0001). These data support the hypothesis that HU treatment augments renal and systemic NO bioavailability possibly via reducing arginase activity as a potential mechanism for the improvement on renal injury seen in sickle cell mice with HU.Support or Funding InformationSupport provided by an APS Porter Fellowship to CT, American Society of Nephrology Ben J. Lipps Research Fellowship for MK, F31 DK111067 to RS, T32 GM109780 to LSD, and a U01 HL117684 to JSP, CD, and DMP.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.