Arginase Inhibition Reverses Endothelial Dysfunction, Pulmonary Hypertension, and Vascular Stiffness in Transgenic Sickle Cell Mice

Abstract

Background In sickle cell disease (SCD), hemolysis results in the release and activation of arginase, an enzyme that reciprocally regulates nitric oxide (NO) synthase activity and thus, NO production. However, simply supplementing the common substrate L-arginine fails to improve NO bioavailability. In this study, we tested the hypothesis that arginase inhibition would improve NO bioavailability and thereby attenuate systemic and pulmonary vascular endothelial dysfunction in transgenic mice with SCD. Methods and Results We studied 5 month-old transgenic sickle cell (SC) mice and age-matched wild-type (WT) controls. SC mice were treated with the arginase inhibitor, 2(S)-Amino-6-BoronoHexanoic acid (ABH; ~400 μg/d) for four weeks or left untreated. Vascular arginase activity was significantly higher at baseline in untreated SC mice compared to WT controls (SC vs. WT, 346 ±69.3 vs. 69 ±17.3 pmol urea/mg protein/minute; p=0.0043; n = 4–5 animals per group). ABH treatment may significantly decrease arginase activity to levels near WT controls (SC + ABH 125.2 ±17.3 pmol urea/mg protein/minute, p=0.0213). Aortic strips from untreated SC mice showed decreased nitric oxide (NO) and increased reactive oxygen species (ROS) production (NO: fluorescence rate 0.76 ±0.14 vs. 1.34 ±0.17 RFU/s, p = 0.0005 and ROS: fluorescence rate 3.96 ±1.70 vs. 1.63 ±1.20 RFU/s, p = 0.0039; n = 3–5 animals per group). SC animals treated with ABH for 4 weeks demonstrated NO (fluorescence rate: 1.16 ±0.16) and ROS (fluorescence rate: 2.02 ±0.45) levels comparable to age-matched WT controls (n = 3–5 animals per group). The maximal endothelial-dependent vasorelaxation response to acetylcholine was impaired in aortic rings from SC mice compared to WT (57.7 ±8.4% vs. 80.3 ±11.0%; p=0.02; n = 6 animals per group). The endothelial-independent response was not different between groups. In SC mice, the right ventricular cardiac output index, and end-systolic elastance were similar (4.60 ±0.51 vs 2.9 ±0.85 ml/min/100g and 0.89 ±0.48 vs 0.58 ±0.11 mmHg/μl), while the pulmonary vascular resistance index and right ventricular end systolic pressure were higher (2.9 ±0.28 vs 5.5 ±2.0 mmHg×min/μl/100g and 18.9 ±1.1 vs 23.1 ±4.0 mmHg; n = 8 animals per group). Pulse wave velocity (a measure of arterial stiffness) was higher in SC mice compared to WT (3.74 ±0.54 vs. 3.25 ±0.21 m/s; n = 20 animals per group), arginase inhibition for four weeks significantly reduced the vascular SC phenotype to one similar to WT animals (p=0.0009). Conclusion Arginase inhibition improves NO bioavailability and thereby attenuates systemic and pulmonary vascular endothelial dysfunction in transgenic mice with SCD. Therefore, arginase is a potential therapeutic target in the treatment of cardiovascular dysfunction in SCD.

Acquired Amino Acid Deficiencies: A Focus on Arginine and Glutamine

“…Very recently, an oral arginase inhibitor has been developed for human use with anticipated phase 1 clinical trials for solid tumors recruiting soon. The potential benefits of arginase inhibitors for arginine deficiency syndromes remain to be determined, but a promising recent study demonstrated that arginase inhibition improved NO bioavailability and attenuated systemic and pulmonary vascular endothelial dysfunction in transgenic mice with SCD 159 . Therefore, arginase represents a potential therapeutic target in the treatment of cardiovascular dysfunction in hemolytic anemias.…”

An arginase-1 SNP that protects against the development of pulmonary hypertension in bronchopulmonary dysplasia enhances NO-mediated apoptosis in lymphocytes

“…; Steppan et al. ). We have previously shown that NOS and arginase compete for their common substrate, l ‐arginine, such that greater expression and/or activity of one results in lower activity of the other due to limitations in l ‐arginine bioavailability (Nelin et al.…”

Arginine Therapy Shows Promise for Treatment of Sickle Cell Disease Clinical Subphenotypes of Hemolysis and Arginine Deficiency

“…I read with interest “Arginase Inhibition Reverses Endothelial Dysfunction, Pulmonary Hypertension, and Vascular Stiffness in Transgenic Sickle Cell Mice” 1 . Alterations in the arginine metabolome have been extensively studied in sickle cell disease (SCD), in humans as well as in SCD-transgenic mice 2 .…”

“…Alterations in the arginine metabolome have been extensively studied in sickle cell disease (SCD), in humans as well as in SCD-transgenic mice 2 . Although Steppan and colleagues suggest that supplementing L-arginine does not improve nitric oxide (NO) bioavailability 1 , a more comprehensive review of the literature suggests benefits resulting from L-arginine therapy that are likely NO-related 2 . Pulmonary hypertension (PH), leg ulcers and vaso-occlusive pain are SCD-clinical subphenotypes of arginine deficiency that are reversed with arginine supplementation 2 .…”

“…Steppan and colleagues report promising results, as arginase inhibition improved NO bioavailability and attenuated systemic and pulmonary vascular endothelial dysfunction in SCD-transgenic mice 1 . Therefore, arginase represents a potential therapeutic target in the treatment of SCD-related cardiovascular dysfunction in addition to arginine therapy.…”