ROS Flashcards
how/why do rose cause damage
• Radicals are the most damaging because they have an unpaired electron in the outer shell, they can attack nearby molecules to capture an electron to gain stability, which mediates redox modification of biomolecules and oxidatively damage the macromolecule (Shama thesis)
o Hydroxy radical
3 electron reductions of O2, formed by the Fenton reaction, (or by decomposition of Peroxynitrite ONOO-).
Very short half life (10^-9) and very highly reactive, as a consequence it cannot diffuse from the site of generation and can very quickly react with and damage surrounding macromolecules,
Diffusion range is calculated to be ~5 nm (the width of 2-3 helcies
o Super oxide
1 electron reduction of O2, relatively unreactive but can react with nitric oxide - peroxynitire ONOO- and can be converted into H2O2 enzymatically by SOD (10^9 /MS) or non-enzymatically (10^6/ MS)
o H2O2
non radical derivative but can still be pro-oxidant. 2 electron reductions of O2 via the dismutation of superoxide (by SOD, non enzymatically, or by direct reduction). Can oxidize the sulfhydryl groups of cystine residues within proteins and cause allosteric changes within the protein to alter its function, however further oxidation of the sulfinic form to the sulphonic form is irreversible
b. Are these all the ROS?
• ROS – peroxyl and alkoxyl, oxides of nitrogen, hypochlorous acid, singlet oxygen (by product in photosynthesis) and ozone
• Other reactive species include reactive nitrogen, chlorine, bromine, iron and sulfur species
o Superoxide can react with nitrox oxide to yield the highly reactive peroxynitire (ONOO-)
c. Which is the most damaging?
- Hydroxyl radical, unpaired electron, very short half life, irreversible covalent bond
- Superoxide radical, has an unpaired electron but it is quickly converted to H2O2 by catalase or non enzymatically
d. Are they membrane permeable?
• Only H2O2, peroxynitrite anion (ONOO−)
e. Where do the majority form? Why?
- MTC
- CYPs in the ER • Super oxide from NOX induction
- Xanthine oxidoreductases
- Autooxidation of molecules
- Reperfusion after cardiac suppression
- Ionizing radiation
- Xenobiotics, bioactivation into electrophilic and free radical intermediates
f. 3 pros for ROS?
- Has a role in memory formation, regulates long-term potentiation (Wikipedia, Shama thesis)
- Participate in cell signaling pathways involved in proliferation, differentiation, and maturation during development
- ROS generation by NOXs have been shown to modulate neuronal development and are required for synaptic plasticity
- Nitric oxide is produced at a low concentration constitutively by nitric oxide synthetases in vascular endothelial cells which can act as a single molecule that mediates vasodilation; but niroic oxide can be produced in high concentrations in the immune system as a toxic oxidant to kill invading microorganisms
g. 3 Consequences?
• Male infertility (Wikipedia)
• Aging (wikipedia)
• Oxidative stress mitochondria dysfunction can lead to apoptosis and programmed cell death
• Altered signal transduction
o H2O2 selectively oxidizes sulfhydryl groups of specific cystine residues, which are reversible and constitute a control mechanism of protein function
H2O2 singal transduction targets
o H2O2 selectively oxidizes sulfhydryl groups of specific cystine residues, which are reversible and constitute a control mechanism of protein function
• Several targets
i. Protein tyrosine phosphatases (inactivates)
ii. Protein tyrosine kinases (activates)
iii. Small g proteins (activates GTPases)
iv. Transcription factor Nrf2 and NF-kB (activates)
k. ROS attack to DNA
o ROS attack to DNA can lead to the generation of more than 20 oxidized base adducts, the most prominent in 8-oxoG, because of its low oxidation potential
o OH attack of the C8 of the guanine leads to the formation for guanine C8-OH adduct radical and (can undergo 3 separate pathways) to form 8-hydroxyguanine, 7-hydro-8-hydroxyguanine, or FAPY-Gua
• 8-oxoG –> reduction, the C8-OH adduct gains an electron
ROS attack to proteins
o can impair the function of signal transduction pathways, receptors, and enzymes, can cause subsequent damage to other cellular macromolecules depending on whether on not the protein was developmentally pathogenic or not
o all amino acid side chains are susceptible to OH.
o Measurement of protein oxidation is through protein carbonyl formation
ROS attacks to lipids
o Polyunsaturated fats within the cellular membrane are common targets of oxidative damage due to the presence of carbon-carbon double bonds
o Lipid peroxidation begins either by the addition of a hydroxy radical across a double bond forcing the electrons to move on the other adjacent carbon carbanion or more commonly by hydrogen abstraction creating a lipid radical. Lipid radicals can stabilize by forming a conjugated diene or react with molecular oxygen to form a peroxy radical abstract a hydrogen from adjacent fatty acid side chain, chain reaction causing propagation, termination of the reaction occurs when two lipid peroxyl radicals combine to produce a non-radical species or when a radial oxidant is halted by binding to antioxidants such as alpha-tocopherol
ROS and teratogenesis
• Reactive intermediate-mediated mechanisms involved the conversion of the parent compound to either an electrophilic reactive intermediate that can covalently bind to cellular macromolecules or to a free radical intermediate which can initiate oxidative stress and the formation of ROS
o Electrophilic reactive intermediate – bioactivation of a drug by CYP enzymes generates a positively charged moiety that can damage protein or DNA with an irreversible covalent bond, if the adduct is on a developmentally important gene or protein altered development or death. Ex. Bezno[a]pyrene
o Free radical intermediate – CYPS, prostaglandin synthase and lipoxygenases can bioactive xenobiotics to free radicals which can react with O2 to form ROS like superoxide, hydrogen peroxide, and hydroxy radial (but CYP expression is low in the embryo, particularly in the mouse) which can oxidatively damage cellular macromolecules or later embryonic signal transduction
