Chiral recognition at the heme active site of nitric oxide synthase is markedly enhanced by L-arginine and 5,6,7,8-tetrahydrobiopterin

Local anaesthetics upregulate nitric oxide generation in cord blood and adult human neutrophils

Nitric oxide (NO) generation by systemic neonatal neutrophils is not clarified. It is also not known whether local anaesthetics (LAs) transferred to the fetal systemic circulation following maternal epidural blockade may affect this process. In the present study, NO generation was evaluated in neutrophils from cord blood (CB, n = 11) and adult blood (n = 10) following exposure to bupivacaine (0.0005, 0.005, 1 mM), lidocaine (0.002, 0.02, 4 mM) and ropivacaine (0.0007, 0.007, 1.4 mM) using flow cytometry, as well as indirectly by determining nitrite concentrations in cell incubation media. To determine the role of NO synthase (NOS) isoforms in NO generation following exposure to LAs, experiments were repeated in the presence of the NOS inhibitors, N^G-nitro-L-arginine methyl ester and aminoguanidine; in addition, the expression of NOS isoforms was analysed. CB neutrophils produced less NO than adult neutrophils. LAs, especially ropivacaine and lidocaine, stimulated neutrophil NO generation, but in CB neutrophils this effect was negligible at clinically relevant drug concentrations. A mechanism involving NOS activity was responsible for the observed phenomena. In conclusion, LAs are able to upregulate neutrophil NO production, but in neonates this effect is likely to be clinically insignificant.

Influence of chirality on catalytic generation of nitric oxide and platelet behavior on selenocystine immobilized TiO2 films

As nitric oxide (NO) plays vital roles in the cardiovascular system, incorporating this molecule into cardiovascular stents is considered as an effective method. In the present study, selenocystine with different chirality (i.e., l- and d-selenocystine) was used as the catalytic molecule immobilized on TiO2 films for decomposing endogenous NO donor. The influences of surface chirality on NO release and platelet behavior were evaluated. Results show that although the amount of immobilized l-selenocystine on the surface was nearly the same as that of immobilized d-selenocystine, in vitro catalytic NO release tests showed that l-selenocystine immobilized surfaces were more capable of catalyzing the decomposition of S-nitrosoglutathione and thus generating more NO. Accordingly, l-selenocystine immobilized surfaces demonstrated significantly increased inhibiting effects on the platelet adhesion and activation, when compared to d-selenocystine immobilized ones. Measurement of the cGMP concentration of platelets further confirmed that surface chirality played an important role in regulating NO generation and platelet behaviors. Additionally, using bovine serum albumin and fibrinogen as model proteins, the protein adsorption determined with quartz crystal microbalance showed that the l-selenocystine immobilized surface enhanced protein adsorption. In conclusion, surface chirality significantly influences protein adsorption and NO release, which may have significant implications in the design of NO-generating cardiovascular stents.

Purification and characterization of rat liver enzyme catalyzing stereoselective reduction of acetylpyridines

Acetylpyridines (1-3) are known as aroma components of foods, perfumes, and smoking suppressants, showing several biological activities and constituting part of the structure of some important biologically active compounds. We purified and characterized an enzyme that catalyzes the stereoselective reduction of acetylpyridines so that we could clarify its function. The enzyme participating in the reductive metabolism of 4-acetylpyridine (1) in the rat liver was purified by successively applying ammonium sulfate fractionation, anion-exchange, gel filtration, and affinity chromatography, and it was definitively identified as 3alpha-HSD. It preferentially reduced acetylpyridines (1-3) and acetophenone (7) to their corresponding (S)-alcohols, with high enantioselectivity. Kinetic analyses of the compounds were performed, and the V(max)/K(m) values decreased in the order of 4-, 2-, and 3-acetylpyridine (1, 3, 2), while acetophenone (7) showed almost the same value as 3-acetylpyridine (2). These results suggested that the reduction of the substrates by 3alpha-HSD is affected by the nitrogen atom in the aromatic ring.

Autoxidation rates of neuronal nitric oxide synthase: effects of the substrates, inhibitors, and modulators

Autoxidation rates of the full-length neuronal nitric oxide synthase (nNOS) were analyzed and found to be composed of three phases, 60 s(-1) (28%), 5.5 s(-1) (11%) and 0.048 s(-1) (61%). Addition of L-Arg, N(G)-hydroxy-L-Arg (NHA), and N(G)-monomethyl-L-Arg markedly decreased the rate constants for the first and second phases down to 12-20 s(-1) and 0.32-2.6 s(-1), respectively. Addition of (6R)-5,6,7,8-tetrahydro-L-biopterin (H4B) increased the amplitude of the second phase up to 29% of the total. Addition of NHA decreased the rate of the first phase by 4.4-fold in the presence of H4B, whereas addition of L-Arg and other modulators did not significantly affect the rates under the same conditions. Thus, we deduce that (1) L-Arg stabilizes the O2-bound ferrous complex for efficient O-O bond cleavage to occur; (2) H4B influences the O2-bound ferrous complex in a fashion different from L-Arg; and (3) NHA induces a characteristic distal-site structure in the presence of H4B, reflecting a difference in the mechanism of activation of O2 in the first step (monooxygenation of L-Arg) and the second step (monooxygenation of NHA).