LC/MS/MS equipment substitution: singlet molecular oxygen and peroxides in chemical and biological systems

• Grant number: 07/00144-1
• Support Opportunities: Regular Research Grants
• Start date: August 01, 2007
• End date: July 31, 2009
• Field of knowledge: Biological Sciences - Biochemistry - Metabolism and Bioenergetics
• Principal Investigator: Paolo Di Mascio
• Grantee: Paolo Di Mascio
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Our studies focus on providing the mechanism by which 1O2 and other reactive oxygen species play their physiological and pathological roles. We have been devoted to develop suitable 1O2 generators based on the thermolysis of endoperoxides. These compounds are chemically inert and have been employed as versatile sources of 1O2. This approach has been used in our studies for the detection of 1O2-induced damage in cells (DNA, lipids and proteins) and for screening of biologically occurring compounds for quenching 1O2.Evidence has been accumulated during the last three decades on the strong implication of reactive oxygen species and one-electron oxidants in the generation of hydroperoxides from several nucleobases, amino acids and unsaturated lipid components. Singlet oxygen is also a major source of peroxidation of several key cellular components. The breakdown products of the rather unstable hydroperoxide (ROOH) precursors thus produced from exposure to endogenous or exogenous oxidizing agents may be implicated in deleterious biological effects such as cellular lethality, aging, mutagenesis and carcinogenesis. It may be added that oxidative processes to biomolecules are also involved in the etiology of other diseases including arteriosclerosis, arthritis, cataract and diabetes. The purpose of the present project is to extend our understanding of the reactions between reactive oxygen species, specifically 1O2 and ROOH with biomolecules in vitro and in vivo emphasizing the following aspects. Description of the main peroxidation reactions initiated by 1O2 and ROOH within key cellular targets including pyrimidine and purine nucleobases, several lipid components and amino acids. Studies on the molecular effects of the initial formation of the above hydroperoxides within cellular components. Search of stable degradation products of biomolecules (ex. nucleobase) hydroperoxides that may be considered as the chemical signature of the formation of the latter unstable compounds that can be measured within cellular structure (ex. DNA, lipids, proteins). Indicators of lipid peroxidation that may involve cholesterol hydroperoxides and several degradation products including aldehydes. Measurement of adducts between amino substituted nucleobases and reactive compounds as aldehydes arise from the breakdown of initially generated unstable peroxides. Measurement of several side-chain altered amino residues that often arise from the fate of initially generated peroxides is used as bio-indicators of protein oxidation within cells.Major efforts have been devoted to the elucidation of the mechanisms of peroxidation of major cellular biomolecules including nucleic acids, lipids and proteins. Relevant peroxidation pathways are now available at least for the main components of the key cellular biomolecules although there is still a need of further studies, particularly for isolating and characterizing putative hydroperoxides. Attempts should also be made to validate in the whole biomolecules the mechanisms of formation of hydroperoxides that were inferred from model studies. Another relevant major topic deals with the search of molecular signature of the peroxide/1O2 formation in targeted biomolecules within cells upon exposure to oxidative conditions. It may be anticipated that gentle and sensitive mass spectrometric methods such as tandem mass spectrometry (MS/MS) in association with HPLC and the use of 18O-labeled peroxide/1O2 should constitute powerful tools for this purpose. (AU)