Quantitative evaluation of biliary elimination of gadoxetate, a magnetic resonance imaging contrast agent, via geometrical isomer-specific transporting system in rats.

Gadoxetate, a magnetic resonance imaging contrast agent, is eliminated into bile. Gadoxetate geometrical isomers are chromatographically classified into two groups by differences between their ionic states (GIs-I and GIs-II; 65:35 w/w); however, the elimination mechanism of each isomer in vivo remains controversial. Thus, the contribution of carrier-mediated transport systems on the biliary elimination of gadoxetate was examined. Gadoxetate was injected intravenously into rats, and the time courses of the plasma concentrations and biliary elimination of GIs-I and GIs-II were examined by high-performance liquid chromatography techniques. The results showed that 34.7% of GIs-I (GIs-I(s); 22.6% of gadoxetate) was quickly eliminated into bile within 30 min after injection. The contents of the residual GIs-I (GIs-I(r)) and GIs-II in plasma similarly decreased according to a first-order elimination process (t1/2=23-27 min), and 64.0% of GIs-I(r) and GIs-II (49.6% of gadoxetate) was eliminated into the bile within 2 h after injection. There was no significant difference between the elimination half-lives of GIs-I(r) and GIs-II in rats. In conclusion, the geometrical isomer with specific conformation corresponding to 22.6% of gadoxetate was eliminated into bile in rats via a carrier-mediated transport system no later than 30 min after intravenous injection.

Sensitive and simple determination of bromate in foods disinfected with hypochlorite reagents using high performance liquid chromatography with post-column derivatization.

A novel analytical method for the quantification of bromate in fresh foods using high performance liquid chromatography (HPLC) with a post-column reaction has been developed. The fresh food sample solutions were pretreated with homogenization, centrifugal ultrafiltration and subsequent solid phase extraction using a strong anion-exchange resin. After separation on a strong anion-exchange chromatography column using a highly concentrated NaCl solution (0.3M) as the eluent, the bromate was quantified by detection using a post-column reaction with a non-carcinogenic reagent (tetramethylbenzidine). The developed HPLC technique made it possible to quantify bromate in salt-rich fresh foods. The recoveries from fresh foods spiked with bromate at low levels (2 or 10 ng/g) satisfactorily ranged from 75.3 to 90.7%. The lowest quantification limit in fresh foods was estimated to be 0.6 ng/g as bromic acid. The method should be helpful for the quantification of bromate in fresh foods disinfected with hypochlorite solutions.

Nitric oxide converts fatty acid alkoxyl radicals into fatty acid allyl radicals.

Nitric oxide (()NO) is thought to react with fatty acid alkoxyl radical, which is generated from fatty acid hydroperoxide via one-electron reduction. However, detail in the reaction remains obscure. In the present study, we examined the reaction of nitric oxide with fatty acid alkoxyl radical generated in the lipoxygenase/linoleate/13-hydroperoxyoctadecadienoate (13-HpODE) system under anaerobic conditions via HPLC equipped with mass spectrometry and photodiode array detections. In this reaction system, nitric oxide can scavenge linoleate alkoxyl radical, producing 13-ONO-9Z,11E-ODE. However, instead of 13-ONO-9Z,11E-ODE, 13-NO-9E,11E-ODE and 9-NO-10E,12E-ODE were alternatively detected in the reaction solution. To explain this contradiction, we proposed a mechanism as follows: (1) 13-ONO-9E/11Z-ODE undergoes homolytic cleavage at >CHONO bond into the linoleate allyl radical and nitrogen dioxide, (2) the allyl radical undergoes resonance stabilization into the E/E-form, and (3) nitric oxide scavenges the E/E-pentadiene radical at C9 or C13 position. Consequently, we concluded that nitric oxide immediately converts fatty acid alkoxyl radical into allyl radical.

Trapping of fatty acid allyl radicals generated in lipoxygenase reactions in biological fluids by nitroxyl radical.

Nitroxyl radicals can trap fatty acid allyl radicals on ferric-lipoxygenases at lower oxygen content, which are an intermediate in the lipoxygenase reaction. In the present study, we examined whether nitroxyl radical-trapping of fatty acid allyl radicals on the enzyme proceeds in biological fluids with abundant antioxidants. The fatty acid allyl radical-nitroxyl radical adducts were quantified by HPLC with electrochemical detection (HPLC-ECD); the adducts in eluate degraded into nitroxyl radical by passing through heating coil at 100 degrees C, and then nitroxyl radical was detected by electrochemical detector. Soybean 15-lipoxygenase and nitroxyl radical (3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-N-oxyl, CmDeltaP) were mixed with rat serum prepared from fresh venous blood, and the solution was stood at 37 degrees C for 1 h. One volume of the solution was mixed with 5 vols of cold acetonitrile. After centrifugation, the supernatant was subjected to HPLC-ECD. Arachidonate allyl radical-CmDeltaP adducts as well as linoleate allyl radical-CmDeltaP adducts were detected in the solution, and the content of these adducts remarkably increased in the presence of phospholipase A(2). It is proved for the first time that nitroxyl radical traps fatty acid allyl radicals generated in the lipoxygenase reaction in biological fluid without competition from endogenous antioxidants.