Seminaphthofluorescein-Based Fluorescent Probes for Imaging Nitric Oxide in Live Cells

Fluorescent turn-on probes for nitric oxide based on seminaphthofluorescein scaffolds were prepared and spectroscopically characterized. The Cu(II) complexes of these fluorescent probes react with NO under anaerobic conditions to yield a 20–45-fold increase in integrated emission. The seminaphthofluorescein-based probes emit at longer wavelengths than the parent FL1 and FL2 fluorescein-based generations of NO probes, maintaining emission maxima between 550 and 625 nm. The emission profiles depend on the excitation wavelength; maximum fluorescence turn-on is achieved at excitations between 535 and 575 nm. The probes are highly selective for NO over other biologically relevant reactive nitrogen and oxygen species including NO3–, NO2–, HNO, ONOO–, NO2, OCl–, and H2O2. The seminaphthofluorescein-based probes can be used to visualize endogenously produced NO in live cells, as demonstrated using Raw 264.7 macrophages.National Science Foundation (U.S.) (CHE-0611944)National Institutes of Health (U.S.) (K99GM092970

Dynamics and diagnostic relevance of kynurenine serum level after kidney transplantation

BACKGROUND: Inflammatory events after kidney transplantation (Tx) may lead to activation of the tryptophane-catabolizing enzyme indoleamine 2,3-dioxygenase followed by the formation of kynurenine (KYN). Post-transplant KYN serum levels in kidney allograft recipients were analyzed for their diagnostic value. MATERIAL AND METHODS: This was a retrospective analysis of KYN levels (normal value: 2.7±0.6 nmol/ml) measured in 4083 blood samples collected from 355 kidney graft recipients in connection with uncomplicated courses, acute rejections (ARs), infections, and type of immunosuppression. We performed descriptive data analysis and analysis of variance. RESULTS: In 212 recipients with immediately functioning grafts, the KYN levels dropped from pre-Tx 13.3±5.9 nmol/ml to nearly normal values at day 5 (5.8±3.0 nmol/ml). In patients with delayed graft function, the KYN reduction started only after the last hemodialysis treatment. With respect to ARs in recipients with creatinine values <300 µmol/l pre-AR, the increase of KYN levels depended on the severity of ARs (steroid-sensitive ARs: from 4.5±1.4 to 6.0±6.1 nmol/ml; steroid-resistant ARs: from 6.1±3.1 to 12.9±7.1 nmol/ml; vascular rejections: from 5.8±3.0 to 16.9±9.1 nmol/ml). In patients with creatinine values ≥300 µmol/l pre-AR, a further increase of the KYN level (from 10.1 to 13.2 nmol/ml) was only observed in severe, steroid-resistant ARs. With respect to infections evaluated, the KYN levels before diagnosis/start of treatment were 5.7±3.4 nmol/ml in asymptomatic CMV infections, 7.5±4.4 nmol/ml in CMV diseases, 8.3±3.3 nmol/ml in pneumonia, and 10.4±6.5 nmol/ml in bacterial sepsis. CONCLUSIONS: Serum KYN seems to be a reliable diagnostic tool for the assessment of post-transplant inflammatory complications, already in an early stage, and for monitoring the efficacy of therapeutic interventions. Prospective studies are recommended

Mechanism of transfer of NO from extracellular S-nitrosothiols into the cytosol by cell-surface protein disulfide isomerase

N-dansylhomocysteine (DnsHCys) is quenched on S-nitrosation. The product of this reaction, N-dansyl-S-nitrosohomocysteine, is a sensitive, direct fluorogenic substrate for the denitrosation activity of protein disulfide isomerase (PDI) with an apparent K(M) of 2 μM. S-nitroso-BSA (BSA-NO) competitively inhibited this reaction with an apparent K(I) of 1 μM. The oxidized form of DnsHCys, N,N-didansylhomocystine, rapidly accumulated in cells and was reduced to DnsHCys. The fluorescence of DnsHCys-preloaded human umbilical endothelial cells and hamster lung fibroblasts were monitored as a function of extracellular BSA-NO concentration via dynamic fluorescence microscopy. The observed quenching of the DnsHCys fluorescence was an indirect measure of cell surface PDI (csPDI) catalyzed denitrosation of extracellular S-nitrosothiols as decrease or increase in the csPDI levels in HT1080 fibrosarcoma cells correlated with the rate of quenching and the PDI inhibitors, 5,5′-dithio-bis-3-nitrobenzoate and 4-(N-(S-glutathionylacetyl) amino)phenylarsenoxide inhibited quenching. The apparent K(M) values for denitrosation of BSA-NO by csPDI ranged from 12 μM to 30 μM. Depletion of membrane N(2)O(3) with the lipophylic antioxidant, vitamin E, inhibited csPDI-mediated quenching rates of DnsHCys fluorescence by ≈70%. The K(M) for BSA-NO increased by ≈3-fold and V(max) decreased by ≈4-fold. These findings suggest that csPDI catalyzed NO released from extracellular S-nitrosothiols accumulates in the membrane where it reacts with O(2) to produce N(2)O(3). Intracellular thiols may then be nitrosated by N(2)O(3) at the membrane-cytosol interface