Useful and harmful effects of nitric oxide

Abstract

In living systems synthesis of nitric oxide occurs during metabolism from Larginin, nitrite and ascorbate. Being very significant carrier of information within numerous both physiological and pathological processes in mammals' organisms, nitric oxid could possibly be useful as well as harmful. Nitric oxide synthesis is adjuvant in a healthy organism because it represents the basic molecule for understanding numerous processes in neurology, psychology, immunology and varios related fields. In other words, nitric oxide participate in number of physiological processes, such as: transmission of nerve signals (neurotransmitter role), regulation of smooth muscle tissue relaxation (eg. vasodilatation), peristaltic movements, immunomodulation, mastocyte activation, development of inflammatory response, apoptosis regulation, angiogenesis and glucose metabolism, normal heart functioning and antioxidation role. Besides being useful, nitric oxide can be harmful as well, because it has one unpaired electron, so consequently it is susceptible to oxidation becoming a stable free radical. Being such, it reacts quickly with superoxide-anion radical, givind at first an extremely reactive peroxinitrite anion, and subsequently peroxidnitrite acid. This acid is very dangerous causing thiol groups oxidation, tyrosine and phenylalanine nitrosylation, lipid oxidation, DNK chain splitting, nitrification and nucleic bases deamination. These damages of macromolecules can cause a series of undesirable changes which subsequently disturb functions of molecules, and thus of cells, tissues and even organs.

U živim sistemima sinteza azot-monoksida nastaje tokom metabolizma, od L-arginina, nitrita i askorbata. S obzirom da je važan prenosilac informacija u okviru mnogih fizioloških ali i patoloških procesa u organizmu sisara, azot-monoksid može biti i koristan i štetan. Sinteza azot-monoksida u zdravom organizmu je poželjna jer predstavlja osnovni molekul za razumevanje brojnih procesa u neurologiji, psihologiji, imunologiji i najrazličitijim drugim oblastima. Naime, azotmonoksid učestvuje u nizu fizioloških procesa, među kojima su: prenos nervnih signala (neurotransmiterska uloga), regulacija relaksacije glatkomišićnih tkiva (npr. vazodilatacija), odvijanje peristaltičkih pokreta, imunomodulacija, aktivacija mastocita, razvoj zapaljenske reakcije, regulacija apoptoze, angiogeneze i metabolizma glukoze, normalno funkcionisanje srca i antioksidantna uloga. Osim što je koristan, azot-monoksid može da bude i štetan jer poseduje jedan nespareni elektron, tako da podleže oksidaciji i postaje stabilan slobodni radikal. Kao takav, brzo reaguje sa superoksidanjon radikalom, dajući prvo izuzetno reaktivan peroksinitrit anjon, a potom i peroksinitritnu kiselinu. Ona je vrlo opasna jer dovodi do: oksidacije tiolnih grupa, nitrozilovanja tirozina i fenil-alanina, oksidacije lipida, cepanja lanaca DNK, nitrovanja i dezaminacije nukleinskih baza. Ova oštećenja makromolekula mogu izazvati niz nepoželjnih promena kojima se remeti funkcija molekula a time i ćelije, tkiva pa i organa.