A fluorescence method for the determination of photochemically generated peroxynitrite in seawater

A near-infrared fluorescent probe for imaging peroxynitrite levels in paw edema mice and drug evaluation

A near-infrared fluorescent probe (TX-P) for detecting peroxynitrite is constructed. The probe has a near-infrared emission (725 nm), large Stokes shift (125 nm) and excellent sensitivity and selectivity. In addition, TX-P can be used to visualize ONOO- in living cells, image ONOO- in paw edema mice and evaluate anti-inflammatory drugs.

Pro-fluorescent probe with morpholine moiety and its reactivity towards selected biological oxidants

Biological oxidants participate in many processes in the human body. Their excessive production causes organelle damage, which may result in the accumulation of cytotoxic mediators and cell degradation and may manifest itself in various diseases. Peroxynitrite (ONOO- ), hypochlorous acid (HOCl), hydrogen peroxide (H2 O2 ), and peroxymonocarbonate (HOOCO2 - ) are important oxidants in biology, toxicology, and various pathologies. Derivatives of coumarin, containing an oxidant-sensitive boronate group, have been recently developed for the fluorescent detection of inflammatory oxidants. Here, we report the synthesis and characterization of 4-[2-(morpholin-4-yl)-2-oxoethyl]-2-oxo-2H-chromen-7-yl boronic acid (MpC-BA) as a fluorescent probe for the detection of oxidants, with better solubility in water, high stability and fast response time toward peroxynitrite and hypochlorous acid. The effectiveness of the MpC-BA probe for the detection of peroxynitrite was measured by adding bolus ONOO- or using the co-generating superoxide and nitrogen oxide system. MpC-BA is oxidized by ONOO- to 7-hydroxy-4-[2-(morpholin-4-yl)-2-oxoethyl]-2H-chromen-2-one (MpC-OH). However, peroxynitrite-specific product (MpC-H) is formed in the minor reaction pathway. MpC-OH is also yielded in the reaction of MpC-BA with HOCl, and the subsequent formation of a chlorinated MpC-OH gives a specific product for HOCl (MpC-OHCl). H2 O2 slowly oxidizes MpC-BA. However, the addition of NaHCO3 increased the MpC-OH formation rate. We conclude that MpC-BA is potentially an improved fluorescent probe detecting peroxynitrite and hypochlorite in biological settings. Complementation of the fluorescence measurements by HPLC-based identification of chlorinated and reduced coumarin(s) will help identify the oxidants detected.

A mitochondria-targeted dual-response sensor for monitoring viscosity and peroxynitrite in living cells with distinct fluorescence signals

Viscosity and peroxynitrite (ONOO-) are two significant indicators to affect and evaluate the mitochondrial functional status, which are nearly relational with pathophysiological process in many diseases. Developing suitable analytical methods for monitoring mitochondrial viscosity changes and ONOO- is thus of great importance. In this research, a new mitochondria-targeted sensor DCVP-NO2 for the dual determination of viscosity and ONOO- was exploited based on the coumarin skeleton. DCVP-NO2 displayed a red fluorescence "turn-on" response toward viscosity along with about 30-fold intensity increase. Meanwhile, it could be used as ratiometric probe for detection of ONOO- with excellent sensitivity and extraordinary selectivity for ONOO- over other chemical and biological species. Moreover, thanks to its good photostability, low cytotoxicity and ideal mitochondrion-targeting capability, DCVP-NO2 was successfully utilized for fluorescence imaging of viscosity variations and ONOO- in mitochondria of living cells through different channels. In addition, the results of cell imaging revealed that ONOO- would lead to the increase of viscosity. Taken together, this work provides a potential molecular tool for researching biological functions and interactions of viscosity and ONOO- in mitochondria.

Photochemically generated nitric oxide in seawater: The peroxynitrite sink and its implications for daytime air quality

In this study, we experimentally investigated the magnitude of the peroxynitrite sink: a radical-radical consumption mechanism for photochemically generated nitric oxide (NO) in surface seawater that describes NO reactions with co-generated superoxide (O₂^-) to yield peroxynitrite (ONOO^-). Measurements of photochemically generated NO, O₂^- and ONOO^- were conducted on seawater samples obtained from the Seto Inland Sea, Japan. Nitrite, dissolved organic carbon, chromophoric dissolved organic matter and pH were also measured in the same samples using standard analytical methods. The average photoformation rates of NO, O₂^- and ONOO^- were: 1.78 × 10^-12 M s^-1, 7.19 × 10^-10 M s^-1 and 9.0 × 10^-10 M s^-1, respectively, and the average steady-state concentrations were: 67.28 × 10^-12 M, 2.69 × 10^-12 M and 2.26 × 10^-11 M, respectively. Further evaluation of the experimental data indicated that the existence of ONOO^- in seawater strongly depends on, and is limited by, photoformed NO. Seawater alkalinity favored the consumption of photoformed NO· via the peroxynitrite sink. The magnitude of average sinks (%) calculated from kinetic estimates and experimental data were: 0.17% and 0.11%, respectively. These results show that the consumption of photochemically generated NO· via the peroxynitrite sink is not significant in surface seawater. Therefore, we propose that sea-to-air efflux across the marine boundary layer is the major sink of photochemical NO· and can be regarded as a non-anthropogenic contributor to daytime atmospheric NO_x concentrations.