ROS - Free Radicals Flashcards
Oxygen toxicity results from what?
It results from reactive oxygen species and free radicals.
What are the two faces of oxygen
It supports life, but also bears toxicity
What are free radicals and why are they harmful?
Free radicals are atomic or molecular species which are extremely reactive because they have an unpaired electron.
What do ROS and free radicals initiate?
Cell injury
Detoxification mechanisms overlap with what system?
The antioxidant system. Detoxification is one of the biggest generators of ROS.
How are ROS generated?
One-electron transfers generate ROS
Why don’t we want free iron floating around in the blood?
Iron (Fe2+) and also copper (Cu1+) combine with H2O2 to create OH* (hydroxyl radical: the “bad actor”) and OH-. This is the Fenton reaction.
Where is the superoxide anion (O2-)produced?
It is produced in the electron transport chain, among other sites. It generates other ROS, but CAN NOT diffuse far from the site of origin.
Hydrogen peroxide (H2O2) is NOT a free radical, so how is harmful?
It can generate free radicals by reaction with a transitional metal (i.e. Fe3+ or Cu1+). It can also diffuse into and through cell membranes.
What is the most reactive species in attacking biological molecules and how is produced?
OH* (Hydroxyl radicals). They are produced by H2O2 in the presence of Fe2+
What is produced by bacteria during the respiratory burst to destroy invading organisms?
HOCl (Hypochlorous acid)
What are endogenous sources of free radicals in the body?
COX, LOX, Cytochrome P450, desaturases, xanthine oxidase - from enzyme activity, electron transport chain, and phagocytic respiratory burst.
What are exogenous sources of free radicals?
UV radiation, drugs (doxorubin), and air pollutants
Why is CoQ10 the biggest offender of free radical formation?
It is abundant, it is small, and unprotected.
What other area of the ETC is a potential source of interaction for ROS?
The complexes that utilize metals (Fe, Cu)
What is the key enzyme that creates HOCl, and causes destruction of the surface of bacteria through the respiratory burst? And which phagocytic cell secretes this enzyme?
Myeloperoxidase; neutrophil
Lipids are susceptible to free radical damage. Oxidation involves the removal of _________ _________ from a/an _____________ fatty acid.
hydrogen radicals; unsaturated
Which type of unsaturated fatty acids are the MOST susceptible to oxidative damage and why?
Polyunsaturated fatty acids (PUFA); because they have more double bonds
Oxidation products form with what two other biosynthetic products?
amino acid residues and DNA
Free radical damage to PUFA can involve what two reactions?
- ) decomposition to bifunctional aldehydes and/or a,B-unsaturated aldehydes which can form adducts or crosslink other biomolucules (this gives more binding sites).
- ) reacting with sulfhydryl groups on enzymes
What are the four stages of the mechanisms for free radical damage of lipids?
Initiation, propagation, degradation, and termination
What is the reaction taking place during initiation?
LH reacts with OH* (the bad actor) and creates a L* and H2O
What is the reaction taking place during propagation and where will it go next?
The L* reacts with O2 to create LOO* which can continue on to either termination or propagation/degradation.
If the LOO* interacts with antioxidants, it will follow which path and ultimately become what?
It will follow the termination pathway to become non-radical products or stable radicals.
If the LOO* follows the propagation pathway, what other pathway will it interact with and what will be the outcomes?
LOO* will interact with LH leaving the L* to continue back through the cycle of propagation, and the LOOH will degrade to 4-HNE, malondialdehyde, ethane/pentane and other products.
How do cells protect themselves against free radical damage/oxygen toxicity (the first line of defense).
Antioxidant enzymes: glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT).
What are the other free radical scavengers (the second line of defense)?
Endogenous: Uric acid & CoQ10
Exogenous: Vitamin E & Vitamin C
What is the third line of defense that mediates oxidative damage?
Repair de novo excision
What is the fourth line of defense leading to diseases and aging?
Adaptation
How do ROS/RNS/ROCl lead to oxidative stress?
They cause disturbance of redox balance
How does oxidative stress lead to oxidative damage?
There is an oxidation of biological molecules
What are the cellular and tissue locations of antioxidants?
Cellular: mitochondria, peroxisomes, and cytosol
Tissue: liver, adrenals, and kidneys
What metal is associated with cytosolic SOD?
Cooper and Zinc
What metal is associated with mitochondrial SOD?
Manganese
What metal is associated with GSH peroxidase?
Selenium
Absorption of Vit C occurs where and by what means?
Distal small intestine; through a sodium dependent ascorbate transporter (SVCT1)
How do other cells acquire Vit C?
They use either SVCT2 or GLUT 1 & GLUT 3 transporters.
What is the primary scavenger/antioxidant that neutralizes radical oxygen and nitrogen species, peroxides, and superoxide?
Ascorbate
Ascorbate is a free radical, why is it okay to have in the body?
It is free to move around the body, but it is VERY stable.
What is required for the regeneration of the reduced form of Vit C?
Reducing agents: NADH, glutathione and an enzyme (NADH reductase, dehydroascorbate reductase, or thioredoxin reductase)
Any antioxidant taken in too high of quantities can lead to pro-oxidant, what is an instance of this with Vit C?
High dose Vit C can lead to kidney stones and diarrhea as a result of oxalic acid.
Where does Vit E come from?
It refers to a mixture of tocopherols and tocotrienols (vitamer). It is made from isoprenes and is an intermediate in biosynthesis of cholesterol.
What specific part of Vit E is selectively extracted in the liver?
a-tocopherol
How does Vit E function as an anti-oxidant?
It accumulates in membranes and lipoproteins for protection, and it donates electrons to free radical species to neutralize them (terminates membrane lipid oxidation through single electron transfers, forming a stable tocopherol species).
How does a redox cycle regenerate reduced Vit E from reduced Vit C?
Vit E gets exposed to Vit C on the surface of membranes and a thiol cycle resets the radical scavengers to their reduced form.
Maintaining RBC membranes depends upon the production of what two products?
NADPH and ATP from glycolysis.
What is the purpose of NADPH in the removal of ROS?
NADPH reduces glutathione which ultimately removes the ROS
What is an action of ROS?
It creates cross-linked hemoglobins, which shortens RBC life cycles.
What enzymatic deficiency is the MOST COMMON genetic enzyme deficiency? And with which condition does it co-localize?
Glucose-6-phosphate dehydrogenase; it co-localizes with malaria
What is the danger with having a G-6-P dehydrogenase deficiency?
It produces anemia and excessive destruction of RBCs
What are some oxidant stressors that increase ROS in RBCs?
Infection, drugs (primaquine - anti-Malaria drug), and fava beans (vicine)
What are the 3 isoforms of NOS?
eNOS - endothelial, nNO - nervous system, and iNOS - inducible by WBC
How are NOS damaging of tissues?
Nitric oxide (NO) diffused through membranes (much like H2O2), HONO2 targets thiols and aromatic residues in proteins, and it reacts slowly with Vit C.
