ARTIFACTS IN HPLC DETECTION OF 3-NITROTYROSINE IN HUMAN BRAIN-TISSUE

An HPLC method was used for quantification of 3-nitrotyrosine (3-NT) i n human postmortem brain tissue. A peak with similar retention time to 3-NT was detected in brain tissue from patients with Parkinson's dise ase, Huntington's chorea, multiple system atrophy, and Alzheimer's dis ease but not in control tissue. The peak was lost on reduction with di thionite, a criterion often used to identify 3-NT. Tissue from the sam e neurodegenerative diseases was analysed by HPLC using a photodiode a rray detector in series with an amperometric electrochemical detector, but the peak was found not to be 3-NT. The absorbance spectrum, fragm entation pattern on mass spectroscopy, and electrochemical profile of this peak do not match authentic 3-NT. A search of the mass spectrosco py databases failed to reveal its identity. The presence of this close ly eluting, dithionite-reducible peak could confound analysis of human tissues for 3-NT. In vitro experiments showed that high concentration s of peroxynitrite were needed to achieve detectable levels of 3-NT in human brain tissue.