Cardiolipin, Perhydroxyl Radicals, and Lipid Peroxidation in Mitochondrial Dysfunctions and Aging

Mitochondrial dysfunctions caused by oxidative stress are currently regarded as the main cause of aging. Accumulation of mutations and deletions of mtDNA is a hallmark of aging. So far, however, there is no evidence that most studied oxygen radicals are directly responsible for mutations of mtDNA. Oxidative damages to cardiolipin (CL) and phosphatidylethanolamine (PEA) are also hallmarks of oxidative stress, but the mechanisms of their damage remain obscure. CL is the only phospholipid present almost exclusively in the inner mitochondrial membrane (IMM) where it is responsible, together with PEA, for the maintenance of the superstructures of oxidative phosphorylation enzymes. CL has negative charges at the headgroups and due to specific localization at the negative curves of the IMM, it creates areas with the strong negative charge where local pH may be several units lower than in the surrounding bulk phases. At these sites with the higher acidity, the chance of protonation of the superoxide radical (O2•), generated by the respiratory chain, is much higher with the formation of the highly reactive hydrophobic perhydroxyl radical (HO2•). HO2• specifically reacts with the double bonds of polyunsaturated fatty acids (PUFA) initiating the isoprostane pathway of lipid peroxidation. Because HO2• is formed close to CL aggregates and PEA, it causes peroxidation of the linoleic acid in CL and also damages PEA. This causes disruption of the structural and functional integrity of the respirosomes and ATP synthase. We provide evidence that in elderly individuals with metabolic syndrome (MetS), fatty acids become the major substrates for production of ATP and this may increase several-fold generation of O2• and thus HO2•. We conclude that MetS accelerates aging and the mitochondrial dysfunctions are caused by the HO2•-induced direct oxidation of CL and the isoprostane pathway of lipid peroxidation (IPLP). The toxic products of IPLP damage not only PEA, but also mtDNA and OXPHOS proteins. This results in gradual disruption of the structural and functional integrity of mitochondria and cells.

Mitochondria: Aging, Metabolic Syndrome and Cardiovascular Diseases. Formation of a New Paradigm

Cardiovascular diseases are among the major causes of mortality among aged people in most developed countries. Oxidative stress, which causes mutations of mitochondrial DNA and mitochondrial dysfunctions, was considered as the main mechanism of heart failure and other pathologies of old age. However, in recent years the prior paradigm of mechanisms of aging, oxidative stress and antioxidative defense was questioned and in some aspects even turned out to be wrong. In this review, we discuss the new data that led to the need to reconsider paradigms. We show that although the mitochondrial free radical theory of aging remains valid, the radical responsible for the aging is the protonated form of the superoxide radical, namely perhydroxyl radical, which was largely ignored all previous years. Perhydroxyl radical initiates the isoprostane pathway of lipid peroxidation (IPLP) of polyunsaturated fatty acids, which are part of the phospholipid core of the mitochondrial inner membrane. IPLP was discovered 30 years ago by Roberts and Morrow at the Vanderbilt University, but the mechanism of its initiation remained unknown. The IPLP causes formation of the racemic mixture of hundreds of biologically active products, named isoprostanes, and highly toxic molecules, first of all isolevuglandins. We distinguish two types of damages caused by IPLP during aging. The first one is associated with oxidative damages to cardiolipin and phosphatidylethanolamine (PEA), which result in disruption of polyenzymatic complexes of the oxidative phosphorylation system. The second type of dysfunctions is caused by the direct actions of toxic products on the lysine-containing proteins and PEA. To this type of mitochondrial damages evidently belongs the oxidative damage of the mitochondrial DNA polymerase, which results in a 20-fold increase in mutations of mitochondrial mtDNA.

Cytosolic Fe-superoxide dismutase safeguardsTrypanosoma cruzifrom macrophage-derived superoxide radical

Trypanosoma cruzi, the causative agent of Chagas disease (CD), contains exclusively Fe-dependent superoxide dismutases (Fe-SODs). DuringT. cruziinvasion to macrophages, superoxide radical (O2•−) is produced at the phagosomal compartment toward the internalized parasite via NOX-2 (gp91-phox) activation. In this work,T. cruzicytosolic Fe-SODB overexpressers (pRIBOTEX–Fe-SODB) exhibited higher resistance to macrophage-dependent killing and enhanced intracellular proliferation compared with wild-type (WT) parasites. The higher infectivity of Fe-SODB overexpressers compared with WT parasites was lost in gp91-phox−/−macrophages, underscoring the role of O2•−in parasite killing. Herein, we studied the entrance of O2•−and its protonated form, perhydroxyl radical [(HO2•); pKa= 4.8], toT. cruziat the phagosome compartment. At the acidic pH values of the phagosome lumen (pH 5.3 ± 0.1), high steady-state concentrations of O2•−and HO2•were estimated (∼28 and 8 µM, respectively). Phagosomal acidification was crucial for O2•−permeation, because inhibition of the macrophage H+-ATPase proton pump significantly decreased O2•−detection in the internalized parasite. Importantly, O2•−detection, aconitase inactivation, and peroxynitrite generation were lower in Fe-SODB than in WT parasites exposed to external fluxes of O2•−or during macrophage infections. Other mechanisms of O2•−entrance participate at neutral pH values, because the anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid decreased O2•−detection. Finally, parasitemia and tissue parasite burden in mice were higher in Fe-SODB–overexpressing parasites, supporting the role of the cytosolic O2•−-catabolizing enzyme as a virulence factor for CD.

Detection of Hydroxyl and Perhydroxyl Radical Generation from Bleaching Agents with Nuclear Magnetic Resonance Spectroscopy

Objective: Children/adolescent's orodental structures are different in anatomy and physiology from that of adults, therefore require special attention for bleaching with oxidative materials. Hydroxyl radical (OH.) generation from bleaching agents has been considered directly related to both its clinical efficacy and hazardous effect on orodental structures. Nonetheless bleaching agents, indirectly releasing hydrogen peroxide (H2O2), are considered safer yet clinically efficient. Apart from OH., perhydroxyl radicals (HO2.) too, were detected in bleaching chemistry but not yet in dentistry. Therefore, the study aims to detect the OH. and HO2. from bleaching agents with their relative integral value (RIV) using 31P nuclear magnetic resonance (31PNMR) spectroscope. Study design: Radicals were generated with UV light in 30% H2O2, 35% carbamide peroxide (CP), sodium perborate tetrahydrate (SPT) and; neutral and alkaline 30% H2O2. Radicals were spin-trapped with DIPPMPO in NMR tubes for each test agents as a function of time (0, 1, 2, 3min) at their original pH. Peaks were detected for OH. and HO2. on NMR spectrograph. RIV were read and compared for individual radicals detected. Results: Only OH. were detected from acidic and neutral bleaching agent (30% acidic and neutral H2O2, 35%CP); both HO2. and OH. from 30% alkaline H2O2; while only HO2. from more alkaline SPT. RIV for OH. was maximum at 1min irradiation of acidic 30%H2O2 and 35%CP and minimum at 1min irradiation of neutral 30%H2O2. RIV for HO2.was maximum at 0min irradiation of alkaline 30%H2O2 and minimum at 2min irradiation of SPT. Conclusion: The bleaching agents having pH- neutral and acidic were always associated with OH.; weak alkaline with both OH. and HO2.; and strong alkaline with HO2. only. It is recommended to check the pH of the bleaching agents and if found acidic, should be made alkaline to minimize oxidative damage to enamel itself and then to pulp/periodontal tissues. Abbreviations: H2O2: hydrogen peroxide CP: carbamide peroxide SP: sodium perborate SPT: sodium perborate tetrahydrate ROS: reactive oxygen species 31PNMR: 31P nuclear magnetic resonance spectroscope RIV: relative integral value OH2.: hydroxyl radical HO2 .: perhydroxyl radical O2 .: super oxide radical DIPPMPO: 5-(Diisopropoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide DEPMPO: 5-diethoxyphosphoryl-5-methyl-1-pyrroline-n-oxide DMPO: 5,5-dimethyl-1-pyrroline-N-oxide D2O: heavy water EDTA: ethylene diamine tetra acetic acid

Free-radical redox reactions of uranium ions in sulphuric acid solutions

The radiolytic reduction of uranyl ions in degassed sulphuric acid solutions containing various organic solutes was studied. It was shown that while ĊOOH, CO2−, and α-hydroxy-alkyl radicals reduced uranyl ions, the β-hydroxy-alkyl radicals and those derived from gluconic acid could not affect the reduction. The oxidation of uranium(IV) by hydrogen peroxide at pH 0.7 involves hydroxyl radicals in a chain mechanism but at pH 2.0 the oxidation proceeds by a non-radical reaction pathway. From the enhancement of the rate of oxidation of uranium(IV) by oxygen in the presence of 2-propanol, a mechanism involving the perhydroxyl radical, which reconciles earlier published data on kinetics and oxygen tracer studies, is proposed for the oxygen-uranium(IV) reactions.