Generation of nitric oxide from nitrite by carbonic anhydrase: a possible link between metabolic activity and vasodilation

• Published in: American journal of physiology. Heart and circulatory physiology 2009-12, Vol.297 (6), p.H2068-H2074
• Main Authors: Aamand, Rasmus, Dalsgaard, Thomas, Jensen, Frank B, Simonsen, Ulf, Roepstorff, Andreas, Fago, Angela
• Format: Article
• Language: English
• Subjects: Acetazolamide - pharmacology; Animals; Aorta, Thoracic - drug effects; Aorta, Thoracic - enzymology; Bicarbonates - metabolism; Carbon Dioxide - metabolism; Carbonic Anhydrase Inhibitors - pharmacology; Carbonic Anhydrases - metabolism; Catalysis; Chemical reactions; Enzyme kinetics; Hydrogen-Ion Concentration; Hypoxia; In Vitro Techniques; Kinetics; Male; Metabolism; Nitric oxide; Nitric Oxide - metabolism; Nitrites - metabolism; Rats; Rats, Wistar; Sodium Nitrite - metabolism; Sulfonamides - pharmacology; Thiophenes - pharmacology; Tissues; Vasodilation - drug effects
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00525.2009

1 Department of Biological Sciences, 2 Center of Functionally Integrative Neuroscience, and 3 Department of Pharmacology, Aarhus University, Aarhus, Denmark; and 4 Institute of Biology, University of Southern Denmark, Odense, Denmark Submitted June 10, 2009 ; accepted in final form October 6, 2009 In catalyzing the reversible hydration of CO 2 to bicarbonate and protons, the ubiquitous enzyme carbonic anhydrase (CA) plays a crucial role in CO 2 transport, in acid-base balance, and in linking local acidosis to O 2 unloading from hemoglobin. Considering the structural similarity between bicarbonate and nitrite, we hypothesized that CA uses nitrite as a substrate to produce the potent vasodilator nitric oxide (NO) to increase local blood flow to metabolically active tissues. Here we show that CA readily reacts with nitrite to generate NO, particularly at low pH, and that the NO produced in the reaction induces vasodilation in aortic rings. This reaction occurs under normoxic and hypoxic conditions and in various tissues at physiological levels of CA and nitrite. Furthermore, two specific inhibitors of the CO 2 hydration, dorzolamide and acetazolamide, increase the CA-catalyzed production of vasoactive NO from nitrite. This enhancing effect may explain the known vasodilating effects of these drugs and indicates that CO 2 and nitrite bind differently to the enzyme active site. Kinetic analyses show a higher reaction rate at high pH, suggesting that anionic nitrite participates more effectively in catalysis. Taken together, our results reveal a novel nitrous anhydrase enzymatic activity of CA that would function to link the in vivo main end products of energy metabolism (CO 2 /H + ) to the generation of vasoactive NO. The CA-mediated NO production may be important to the correlation between blood flow and metabolic activity in tissues, as occurring for instance in active areas of the brain. acetazolamide; dorzolamide; acidosis; neurovascular coupling Address for reprint requests and other correspondence: A. Fago, Dept. of Biological Sciences, Universitetsparken Bldg. 1131, Aarhus Univ., DK-8000 Aarhus C, Denmark (e-mail: angela.fago{at}biology.au.dk ).