Oxidative Stress and Antioxidants PDF

Oxidative stress and antioxidants Dr. Omnia Safwat El-Deeb Assistant Prof. of Medical Biochemistry Faculty of Medicine Tanta University *Free radical: - It is an atom or a molecule that has one or more (unpaired) electron. - It is unstable & highly reactive because it tend...

Oxidative stress and antioxidants Dr. Omnia Safwat El-Deeb Assistant Prof. of Medical Biochemistry Faculty of Medicine Tanta University *Free radical: - It is an atom or a molecule that has one or more (unpaired) electron. - It is unstable & highly reactive because it tends to acquire an electron from other substances *Antioxidant: - It is a molecule stable enough to denote an electron to a free radical to neutralize it, thus reducing its capacity to damage *Pro-oxidant: -They are substances that induce oxidative stress, either by generating reactive oxygen species or by inhibiting antioxidants system  Oxidative stress: Oxidative stress is a phenomenon caused by an imbalance between production and accumulation of oxygen reactive species (ROS) in cells and tissues and the ability of a biological system to detoxify these reactive products.  I-Reactive oxygen species (ROS) & Reactive nitrogen species (RNS): - Reactive oxygen species (ROS) Are reactive chemical species containing oxygen. They include:  Hydroxyl (OH ) ,  Hydrogen peroxide (H2O2)  Superoxide (O2 ),  Peroxyl (RO2 ),  Singlet oxygen (O2). - Reactive nitrogen species (RNS) is a collective term that includes  Nitric oxide radical (NO ),  Nitrogen dioxide radical (NO2 ),  Peroxynitrite (ONOO −) and other oxides of nitrogen and products arising when NO reacts with O2 and other free radicals. II-Sources of free radicals: a- Internally generated sources : 1- Mitochondria. 2- Peroxisomes 3- Phagocytes. 4- Plasma membrane 5- Arachidonate pathways (cyclo- and lipoxygenase). 6- Reactions involving iron and other transitions metals. b- Externally generated sources: 1- Ultraviolet rays & radiation. 2- Environmental pollution. 3- Cigarette smoking. 4- Inflammation, drugs, & industrial solvents. II-Dangerous effects of free radicals:.  *Classifications of antioxidant: The antioxidant defense system consists of I- Enzymatic antioxidants: a- Superoxide dismutase: 1- SOD is an enzyme that dismutates superoxide radicals to form hydrogen peroxide (H2O2) and oxygen (O2). 2- It is considered to be the first line of defense against free radical formation. 3- Three isoforms of it (SOD1, SOD2, SOD3) are present in the mammalian cells. b- Catalase: 1- Catalase is found in nearly all living organisms. It catalyzes the decomposition of hydrogen peroxide to water and oxygen. 2- It is a very important enzyme in protecting the cell from oxidative damage by (ROS). 3- It has one of the highest turnover numbers of all enzymes; one catalase molecule can convert approximately 5 million molecules of hydrogen peroxide to water and oxygen each minutes.  c- Glutathione peroxidase & Glutathione reductase: Glutathione peroxidase is an enzyme that catalyzes the breakdown of hydrogen peroxide and organic hydroperoxides. Glutathione reductase is a crucial enzyme that reduces glutathione disulfide (GSSG) to the sulfhydryl form (GSH) by the NADPH-dependent mechanism. Thank You