Nitric oxide synthase (neuronal and endothelial isoforms) (cNOS)

Nitric oxide synthase (NOS) enzymes catalyze the production of nitric oxide (NO), a vital signaling molecule, from L-arginine (Wikipedia, 2024). The neuronal (nNOS or NOS1) and endothelial (eNOS or NOS3) isoforms are collectively known as constitutive NOS (cNOS) because they are typically present in healthy tissues and regulated by calcium/calmodulin (MDPI, 2019). nNOS is primarily expressed in neurons and skeletal muscle, playing key roles in neurotransmission, synaptic plasticity, and neurovascular coupling (NIH, 2020). eNOS is localized to the vascular endothelium, where it maintains cardiovascular homeostasis by promoting vasodilation and inhibiting platelet aggregation (NIH, 2017). Pathologically, nNOS overactivation is linked to neurodegenerative diseases and stroke-induced excitotoxicity, whereas eNOS dysfunction (often due to enzyme uncoupling) is a hallmark of hypertension and atherosclerosis (MDPI, 2025). Pharmacological targeting of these isoforms is challenging; while selective nNOS inhibitors are sought for treating pain and neurological disorders, non-selective inhibition of eNOS can lead to severe side effects such as systemic hypertension and impaired blood flow (NIH, 2023). Consequently, drug development often focuses on achieving high isoform selectivity to avoid the cardiovascular liabilities associated with eNOS inhibition while addressing the neurological pathologies driven by nNOS (Patsnap, 2024).

Other names

nNOS/eNOSConstitutive nitric oxide synthaseNOS1/NOS3Neuronal and endothelial nitric oxide synthase

Inhibition of nitric oxide production through competitive binding at the L-arginine substrate site or the heme/cofactor binding domains (for nNOS), or enhancement of enzyme activity and stability through cofactor supplementation or transcriptional upregulation (for eNOS) (NIH, 2012; NIH, 2023).