title: 3,4-Dihydroxy-l-phenylalanine as a biomarker of oxidative damage in proteins: improved detection using cloud-point extraction and HPLC.
abstract: Oxidized protein adducts are formed under conditions of oxidative stress and may represent a valuable biomarker for a variety of diseases which share this common aetiology. A suitable candidate biomarker for oxidized proteins is protein-bound 3,4-dihydroxyl-l-phenylalanine (l-DOPA), which is formed on 3'-hydroxylation of tyrosine residues by hydroxyl radicals. Existing methodologies to measure protein-bound l-DOPA employ lengthy acid hydrolysis steps (ca. 16h) which may cause artifactual protein oxidation, followed by HPLC with detection based on the intrinsic fluorescence of l-DOPA. We report a novel method for the measurement of protein-bound l-DOPA which involves rapid hydrolysis followed by pre-column concentration of 6-aminoquinolyl-derivatives using cloud-point extraction. The derivatized material is resolved by reversed-phase HPLC in less than 30min and has derivatization chemistry compatible with both UV and fluorescent detection, providing detection down to the femtomole level. The method provides identical results to those found with highly specific ELISA-based techniques and requires only basic instrumentation. The stability of the 6-aminoquinolyl-derivatives together with the fast and sensitive nature of the assay will be appealing to those who require large sample throughput.
authors.affiliation: School of Applied Science, Belfast Metropolitan College, Belfast, UK. Electronic address: pmcpherson@belfastmet.ac.uk.
authors.forename: Peter A C
authors.initials: PA
authors.lastname: McPherson
authors.affiliation: School of Applied Science, Belfast Metropolitan College, Belfast, UK.
authors.forename: Bryn T
authors.initials: BT
authors.lastname: Türemen
mesh_terms: D000578:Amidines / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry*; D001798:Blood Proteins / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D006868:Hydrolysis; D007963:Leukocytes, Mononuclear / Q000737:chemistry*; D007980:Levodopa / Q000032:analysis*; D059627:Liquid Phase Microextraction; D010084:Oxidation-Reduction; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000737:chemistry*
chemical_list: D000578:Amidines; D000596:Amino Acids; D001798:Blood Proteins; D012710:Serum Albumin, Bovine; D007980:Levodopa; C046728:2,2'-azobis(2-amidinopropane)
keywords: 6-Aminoquinolyl-N-hydroxyl-succinimidyl carbamate; Biomarker; Protein hydrolysis; Protein oxidation