Chalupsky Karel, Kračun Damir, Kanchev Ivan, Bertram Katharina, Görlach Agnes
1 Experimental and Molecular Pediatric Cardiology, German Heart Center Munich at the Technical University Munich , Munich, Germany .
2 DZHK (German Centre for Cardiovascular Research) , Partner Site Munich Heart Alliance, Munich, Germany .
Antioxid Redox Signal. 2015 Nov 10;23(14):1076-91. doi: 10.1089/ars.2015.6329. Epub 2015 Nov 5.
Nitric oxide (NO) derived from endothelial NO synthase (eNOS) has been implicated in the adaptive response to hypoxia. An imbalance between 5,6,7,8-tetrahydrobiopterin (BH4) and 7,8-dihydrobiopterin (BH2) can result in eNOS uncoupling and the generation of superoxide instead of NO. Dihydrofolate reductase (DHFR) can recycle BH2 to BH4, leading to eNOS recoupling. However, the role of DHFR and eNOS recoupling in the response to hypoxia is not well understood. We hypothesized that increasing the capacity to recycle BH4 from BH2 would improve NO bioavailability as well as pulmonary vascular remodeling (PVR) and right ventricular hypertrophy (RVH) as indicators of pulmonary hypertension (PH) under hypoxic conditions.
In human pulmonary artery endothelial cells and murine pulmonary arteries exposed to hypoxia, eNOS was uncoupled as indicated by reduced superoxide production in the presence of the nitric oxide synthase inhibitor, L-(G)-nitro-L-arginine methyl ester (L-NAME). Concomitantly, NO levels, BH4 availability, and expression of DHFR were diminished under hypoxia. Application of folic acid (FA) restored DHFR levels, NO bioavailability, and BH4 levels under hypoxia. Importantly, FA prevented the development of hypoxia-induced PVR, right ventricular pressure increase, and RVH.
FA-induced upregulation of DHFR recouples eNOS under hypoxia by improving BH4 recycling, thus preventing hypoxia-induced PH.
FA might serve as a novel therapeutic option combating PH.
内皮型一氧化氮合酶（eNOS）产生的一氧化氮（NO）参与了对缺氧的适应性反应。5,6,7,8-四氢生物蝶呤（BH4）与7,8-二氢生物蝶呤（BH2）之间的失衡会导致eNOS解偶联，并生成超氧化物而非NO。二氢叶酸还原酶（DHFR）可将BH2循环转化为BH4，从而使eNOS重新偶联。然而，DHFR和eNOS重新偶联在缺氧反应中的作用尚未完全明确。我们推测，增强从BH2循环利用BH4的能力，将改善NO的生物利用度，以及改善作为缺氧条件下肺动脉高压（PH）指标的肺血管重塑（PVR）和右心室肥厚（RVH）。
在暴露于缺氧环境的人肺动脉内皮细胞和小鼠肺动脉中，一氧化氮合酶抑制剂L-（G）-硝基-L-精氨酸甲酯（L-NAME）存在时超氧化物生成减少，表明eNOS发生了解偶联。同时，缺氧条件下NO水平、BH4可用性和DHFR表达均降低。应用叶酸（FA）可恢复缺氧条件下的DHFR水平、NO生物利用度和BH4水平。重要的是，FA可预防缺氧诱导的PVR、右心室压力升高和RVH的发生。
FA诱导的DHFR上调通过改善BH4循环利用，使缺氧条件下的eNOS重新偶联，从而预防缺氧诱导的PH。
FA可能成为对抗PH的一种新型治疗选择。
