Objectives: Under oxidative stress conditions, hydroxyl radicals can oxidize the phenyl ring of phenylalanine (Phe), which then produces various abnormal tyrosine (Tyr) isomers (meta-, ortho- and para-tyrosine; m-, o- and p-Tyr). These Tyr isomers different depending on the location of hydroxyl group on benzyl ring. This study aimed to compare patients with ST-segment elevation myocardial infarction (STEMI) and non ST-segment elevation myocardial infarction (NSTEMI) as well as to compare serum levels of Tyr isomers and Phe at the aortic root and after culprit lesion in both groups.

Methods: The study was performed on 44 patients diagnosed with acute coronary syndrome (ACS), who were admitted into the cardiac catheterization laboratory (Department of Interventional Cardiology, Heart Institute, University of Pécs Clinical Centre) during the period from January 1, 2017 to March 3, 2017. Arterial blood samples were taken from the aortic root through the guiding catheter, and from the culprit vessel segment with aspiration catheter, distally from the primary lesion during the percutaneous coronary intervention. Serum levels of Phe, p-, m- and o-Tyr were determined using a reverse phase- high performance liquid chromatography method.

Results: Serum Phe level was significantly higher after the culprit lesion than at the aortic root of STEMI patients (44.74 vs. 35.56 𝜇mol/L, P= 0.002). Serum p-Tyr/Phe and m-Tyr/Phe ratios were significantly lower after the culprit lesion than at the aortic root of STEMI patients (0.738 vs. 0.940 𝜇mol/𝜇mol, P= 0.024) and (0.188 vs. 0.404 nmol/𝜇mol, P= 0.018), respectively. There were no statistically significant differences with respect to changes of serum Phe and Tyr isomers after the culprit lesion compared to at the aortic root in patients with NSTEMI.

Conclusions: Our data suggest that changes of serum levels of different Tyr isomers could, in fact, represent mediators of the effects of oxidative stress during the heart attack.