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M= Mouse; R=Rat; H=Human; Rb=Rabbit; G=goat; B=Bovine, MO=Monkey; P=pig; CT= near C-terminus; NT=near N-terminus; Internal=Middle of protein. EC=extracellular; CP=cytoplasmic domains *


Malondialdehye (MDA), 4-Hydroxy-2-Nonenal (HNE), Nitrated Tyrosine and 8-hydroxyguanosine (8-OHG), and S-Nitroso-Cys (SNO-Cys) Antibodies-General Information

MDA is a physiological compound produced by peroxidative decomposition of unsaturated lipids as a by-product of arachidonic metabolism. Under normal conditions, MDA is quickly oxidized to acetate or malonate and then to CO2 via TCA cycle. Excessive production of MDA, as a result of tissue injury and DNA-damage, could combine with free amino groups of proteins resulting into MDA-modified protein adducts. Modifications of proteins by MDA could conceivably alter biological properties of proteins. Moreover, MDA-modified protein may serve as an antigen and invoke production of autoantibodies and subsequent destruction of MDA-modified proteins. An uncontrolled diabetes mellitus is known to be associated with high free radical activity. Injections if streptozotocin has been shown to induce MDA-modified proteins in the plasma. MDA-modified LDL shows altered behavior and is entrapped in arterial walls. Autoantibodies to MDA-LDL have been detected in human and rabbits sera. Moreover, alcohol fed rats and alcoholics have autoantibodies to acetaldehyde. Further progress in this field is hampered by the availability of anti-MDA antibodies.

Among the aldehyde which originate from the peroxidation of cellular membrane lipids, 4-hydroxy-2-nonenal (HNE) is the major aldehyde generated by free radical attack on w-6 polyunsaturated fatty acids. HNE is largely responsible for pathogenesis during oxidative stress. HNE is highly reactive towards free sulfydryl groups of proteins producing thioether adducts that further undergo cyclization to form hemiacetals. HNE also reacts with histidine and lysine residues of proteins to form stable Michael addition-type adducts. HNE induces heat shock protein, inhibits cellular proliferation and highly toxic to cells. It exhibits genotoxic and mutagenic effects as well. Elevated levels of HNE modified nigral neurons were also observed in Parkinson disease.

Reactive oxygen species (ROS) are formed at high levels as by-products of the normal cellular metabolism. Both nuclear and Mitochondrial DNA has been shown to accumulate high levels of 8-hydroxy-2'-deoxyguanosine, a very stable and damaging product of hydroxylation of guanine at carbon 8. 8-hydroxyguanosine (8-OHG) induces transversion of G to T, which is potentially mutagenic. The base excision repair (BER) pathway is the most important cellular protection mechanism responding to oxidative DNA damage. They remove modified DNA bases before they are incorporated into DNA during replication. The key enzymes MutT homologs (MutT/MTH) in the BER process are DNA glycosylases, which remove different damaged bases by cleavage of the N-glycosylic bonds between the bases and the deoxyribose moieties of the nucleotide residues. The 8-oxoG glycosylases (Fpg or MutM/OGG) and the MutY homologs (MutY/MYH) glycosylases along with MutT/MTH protect cells from the mutagenic effects of 8-oxoG. 8-hydroxyguanosine (8-OHG) has been used as oxidative stress marker.

Nitric oxide (NO) and reactive oxygen species (ROS) are important mediators to produce harmful or protective functions. NO can react with superoxide anions (O2.-), yielding the toxic oxidizing agent peroxynitrite (ONOO-). Peroxynitrite induces nitration of tyrosine residues leading to changes of protein structure and function, and alterations in signaling pathways. Antibodies to nitrotyrosine have been used to monitor the status of peroxynitrite-induced modification of proteins.

S-nitrosylation of cysteine thiols in proteins by the highly labile NO radical has been identified as a important effectors of NO-related bioactivity both in NOS-containing cells and intercellular signaling. Most cells contain low levels of nitrosylated proteins that are thought to be regulated by S-nitrosylation and denitrosylation. S-nitrosylation of proteins serves as a ubiquitous post-translational modification that dynamically regulates a broad functional spectrum of proteins. The majority of these proteins are regulated by S-nitrosylation on a single critical cysteine residue within an acidic/basic or hydrophobic structural motif that may also be subject to oxygen- or glutathione-dependent modification. NO-sensitive ion channels including the cardiac and skeletal muscle ryanodine receptor (RyR1), N-methyl-D-aspartate receptor (NMDAR) complex, cyclic-nucleotide gated ion channel, are modulated by S-nitrosylation. S-nitrosylation of capsase-3 inhibits apoptosis signaling. S-nitrosylation activates matrix metalloproteinase-9 (MMP-9) and induces neuronal apoptosis. The small G-protein p21Ras and Jun kinase are regulated by S-nitrosylation. The activity of transcription factors such as NF?B, c-jun, and c-fos is modulated by S-nitrosylation. In addition, the formation of S-nitrosylated glutathione (GSNO) has been proposed to be one of the major storage forms of NO in vivo.

 

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