Modeling gas phase nitric oxide release in lung epithelial cells

Area of Science:

• Biochemistry
• Physiology
• Computational Biology

Background:

• Exhaled nitric oxide (NO) is a key noninvasive biomarker for airway inflammation, particularly in asthma.
• Nitric oxide synthase (NOS) produces NO from L-arginine, but arginase also utilizes L-arginine and is upregulated in asthma.
• Competition for L-arginine between NOS and arginase may affect NO production, impacting asthma monitoring.

Purpose of the Study:

• To develop and validate a computational model simulating L-arginine metabolism and NO release in lung epithelial cells.
• To investigate the impact of varying NOS and arginase activity on intracellular L-arginine levels and gas-phase NO release.
• To determine the relative contribution of NOS and arginase to NO production under inflammatory conditions.

Main Methods:

• Developed a steady-state computational model for L-arginine transport, NO synthesis, diffusion, and release.
• Validated the model using experimental data on gas-phase NO and intracellular L-arginine in A549 cells.
• Performed sensitivity analysis to assess the influence of NOS and arginase activity on NO production.

Main Results:

• The model accurately predicted NO release and L-arginine concentrations across a range of extracellular L-arginine levels.
• Sensitivity analysis revealed that increased arginase activity minimally affects L-arginine availability for NOS.
• Nitric oxide synthase (NOS) activity was identified as the dominant factor influencing gas-phase NO release.

Conclusions:

• Computational modeling provides insights into the complex interplay of enzymes in NO production.
• Arginase upregulation in asthma does not significantly limit substrate availability for NOS-mediated NO production.
• Nitric oxide synthase activity is the primary determinant of exhaled NO levels, reinforcing its role as an asthma biomarker.