Carbonic anhydrases I and II.

Carbonic anhydrase (CA, EC 4.2.1.1) isoforms I (CA I) and II (CA II) are widespread cytosolic proteins in most vertebrates. They are abundant in the red blood cells and many other tissues, being involved in physiological processes such as pH regulation, CO₂/bicarbonate homeostasis, respiration, and secretion of electrolytes rich in acid or bicarbonate in the stomach, kidneys, cerebrospinal fluid, eyes, and bones. The genetics, biochemistry, expression, localization in tissues and organs, kinetic properties, and catalytic mechanisms of these enzymes are well understood at the molecular level. At least five different inhibition mechanisms were described with more than 50 chemotypes acting as inhibitors. The activation with amine/amino acid activators was also well studied. The physiological role of CA I is poorly understood, whereas CA II is a physiologically dominant isoform, playing crucial functions in a host of tissues/organs. Interfering with its activity by means of inhibitors has been and is currently exploited in therapy for the management of edema, glaucoma, epilepsy, obesity, acute mountain sickness, and idiopathic intracranial hypertension. Promising preclinical data pointed to the potential use of CA II inhibitors for the management of other conditions, such as neuropathic pain, cerebral ischemia, rheumatoid arthritis, Alzheimer's disease, osteoporosis, and obstructive sleep apnea. Many CA inhibitors are in clinical use for the management of such conditions, among which are acetazolamide, thiazides and high-ceiling diuretics, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide, and antiepileptics such as sulthiame, topiramate and zonisamide, whereas SLC-0111 is in clinical development as an antitumor agent. CA activators are not yet used clinically, but they might have pharmacological applications in the management of neurodegeneration, emotional memory disorders, obsessive-compulsive disorders, phobias, generalized anxiety, and post-traumatic stress. Finding novel modulators of activity for these enzymes may lead to innovative therapeutic applications and deepen our understanding of enzymes, their inhibitors, and their activators.