OP45 - Sulphur and selenium species as targets and protective species in inflammatory diseases: Why speed matters: understanding key mechanisms of protein modification

Abstract

Activated leukocytes generate multiple oxidants to kill invading pathogens including O 2 -• , H 2 O 2 , NO • , peroxynitrous acid (ONOOH) and hypohalous acids (HOCl, HOBr, HOSCN) via the activity of NADPH oxidases, nitric oxide synthases (e.g. iNOS) and myeloperoxidase (MPO). Inappropriate generation can however result in tissue damage, with this associated with multiple human inflammatory pathologies (e.g. cardiovascular disease, some cancers, rheumatoid arthritis, asthma, cystic fibrosis, neurodegenerative conditions). Sulphur residues in peptides and proteins are key targets. Competition kinetic methods have yielded rate constants, k, for reaction of HOCl with Cys and GSH of 3.6 x 10 8 and 1.2x10 8 M- 1 s- 1 , respectively. These values are ~10-fold higher than reported previously, and are some of the fastest reactions of non-radical oxidants, emphasizing the key role of thiols in protection. N-Ac-methionine also reacts very rapidly (k 1.7x10 8 M- 1 s- 1 ). ONOOH reacts rapidly with Cys and Met with k ~ 2x10 3 and 2x10 2 M- 1 s- 1 respectively. Selenium compounds should react faster than the sulphur analogues. Seleno-compounds, including novel seleno sugars react with HOCl with k ~10 8 M- 1 s- 1 and ~ 100-fold faster than the sulphur analogues. A similar rate enhancement is seen with ONOOH, with k for ONOOH and selenocysteine ~2x10 5 M- 1 s- 1 . The selenoxides formed on oxidation of these species, can be readily reduced by thiols (e.g. GSH) and some enzyme systems, making these catalytic protective agents. The seleno-sugars decrease oxidant-mediated damage to isolated proteins and human plasma at low concentrations. Examination of these seleno sugars in an animal model of wound healing has shown that topical application markedly enhances wound closure in both normal and diabetic animals. These studies demonstrate that novel selenium-containing molecules may be potent modulators of damage at sites of acute and chronic inflammation, and be beneficial in multiple human pathologies.