Reaction between Peroxynitrite and Triphenylphosphonium-Substituted Arylboronic Acid Isomers: Identification of Diagnostic Marker Products and Biological Implications

Aromatic boronic acids react rapidly with peroxynitrite (ONOO^–) to yield phenols as major products. This reaction was used to monitor ONOO^– formation in cellular systems. Previously, we proposed that the reaction between ONOO^– and arylboronates (PhB­(OH)₂) yields a phenolic product (major pathway) and a radical pair PhB­(OH)₂O^•–···^•NO₂ (minor pathway). [Sikora, A. et al. (2011) Chem. Res. Toxicol. 24, 687−697]. In this study, we investigated the influence of a bulky triphenylphosphonium (TPP) group on the reaction between ONOO^– and mitochondria-targeted arylboronate isomers (<i>o</i>-, <i>m</i>-, and <i>p</i>-MitoPhB­(OH)₂). Results from the electron paramagnetic resonance (EPR) spin-trapping experiments unequivocally showed the presence of a phenyl radical intermediate from <i>meta</i> and <i>para</i> isomers, and not from the <i>ortho</i> isomer. The yield of <i>o</i>-MitoPhNO₂ formed from the reaction between <i>o</i>-MitoPhB­(OH)₂ and ONOO^– was not diminished by phenyl radical scavengers, suggesting a rapid fragmentation of the <i>o</i>-MitoPhB­(OH)₂O^•– radical anion with subsequent reaction of the resulting phenyl radical with ^•NO₂ in the solvent cage. The DFT quantum mechanical calculations showed that the energy barrier for the dissociation of the <i>o</i>-MitoPhB­(OH)₂O^•– radical anion is significantly lower than that of <i>m</i>-MitoPhB­(OH)₂O^•– and <i>p</i>-MitoPhB­(OH)₂O^•– radical anions. The nitrated product, <i>o</i>-MitoPhNO₂, is not formed by the nitrogen dioxide radical generated by myeloperoxidase in the presence of the nitrite anion and hydrogen peroxide, indicating that this specific nitrated product may be used as a diagnostic marker product for ONOO^–. Incubation of <i>o-</i>MitoPhB­(OH)₂ with RAW 264.7 macrophages activated to produce ONOO^– yielded the corresponding phenol <i>o-</i>MitoPhOH as well as the diagnostic nitrated product, <i>o-</i>MitoPhNO₂. We conclude that the <i>ortho</i> isomer probe reported here is most suitable for specific detection of ONOO^– in biological systems

Bioavailability of ticagrelor and AR-C124910XX over time in patients with STEMI and NSTEMI.

<p>Plasma concentrations of (A) ticagrelor and (B) AR-C124910XX during the first 6 h after oral administration of a 180 mg ticagrelor loading dose in patients with STEMI and NSTEMI. NSTEMI: non-ST-elevation myocardial infarction, STEMI: ST-elevation myocardial infarction.</p

Baseline characteristics of study participants.

<p>Baseline characteristics of study participants.</p

Platelet reactivity over time in STEMI and NSTEMI patients.

<p>Platelet reactivity evaluated with (A) the VASP assay and (B) Multiplate at baseline, and at 0.5 h, 1 h, 2 h, 3 h, 4 h, 6 h, and 12 h after administration of a 180 mg ticagrelor loading dose in patients with STEMI and NSTEMI. NSTEMI: non-ST-elevation myocardial infarction, STEMI: ST-elevation myocardial infarction, VASP: vasodilator-stimulated phosphoprotein.</p

Prevalence of high platelet reactivity over time in STEMI and NSTEMI patients.

<p>Proportion of patients with high platelet reactivity assessed with (A) the VASP assay and Multiplate (B) at baseline, and at 0.5 h, 1 h, 2 h, 3 h, 4 h, 6 h, and 12 h after administration of a 180 mg ticagrelor loading dose in patients with STEMI and NSTEMI. HPR: high platelet reactivity, NSTEMI: non-ST-elevation myocardial infarction, STEMI: ST-elevation myocardial infarction, VASP: vasodilator-stimulated phosphoprotein.</p