Sulfaquinoxaline inhibition of vitamin K epoxide and quinone reductase

Sulfaquinoxaline Oxidation and Toxicity Reduction by Photo-Fenton Process

Sulfaquinoxaline (SQX) has been detected in environmental water samples, where its side effects are still unknown. To the best of our knowledge, its oxidation by Fenton and photo-Fenton processes has not been previously reported. In this study, SQX oxidation, mineralization, and toxicity (Escherichia coli and Staphylococcus aureus bacteria) were evaluated at two different setups: laboratory bench (2 L) and pilot plant (15 L). The experimental design was used to assess the influence of the presence or absence of radiation source, as well as different H2O2 concentrations (94.1 to 261.9 mg L-1). The experimental conditions of both setups were: SQX = 25 mg L-1, Fe(II) = 10 mg L-1, pH 2.8 ± 0.1. Fenton and photo-Fenton were suitable for SQX oxidation and experiments resulted in higher SQX mineralization than reported in the literature. For both setups, the best process was the photo-Fenton (178.0 mg L-1 H2O2), for which over 90% of SQX was removed, over 50% mineralization, and bacterial growth inhibition less than 13%. In both set-ups, the presence or absence of radiation was equally important for sulfaquinoxaline oxidation; however, the degradation rates at the pilot plant were between two to four times higher than the obtained at the laboratory bench.

Evaluation of the aquatic toxicity of two veterinary sulfonamides using five test organisms

The aquatic toxicity of sulfaquinoxaline (SQO) and sulfaguanidine (SGD) was evaluated on the following test organisms: Daphnia magna (reproduction test), Pseudokirchneriella subcapitata, Scenedesmus dimorphus, Synecococcus leopoliensis (algal growth inhibition test) and Lemna gibba (duckweed growth inhibition test). Furthermore, the additivity of the two compounds was measured on D. magna (acute immobilisation test) and P. subcapitata (algal growth inhibition test) using the isobologram method. Results show that SQO and SGD are more toxic to green algae and daphnids, respectively, than other veterinary sulfonamides (SAs) and that their mixtures have a less then additive interaction. Taking into account the highest concentrations detected so far in surface waters for SQO (0.112 μg L(-1)) and for SGD (0.145 μg L(-1)) and the lowest NOECs obtained with the five test organisms, divided by an assessment factor of 10, the following PNECs and risk quotients (RQs) were calculated. SQO: PNEC 2 μg L(-1); RQ 0.056. SGD: PNEC 39.5 μg L(-1); RQ 0.004. Consequently, at the concentrations actually detected in the aquatic environment, the two SAs alone should not harm the freshwater organisms. However, it seems advisable, for veterinary mass treatments, the use of other SAs that have a lesser impact on the aquatic environment. Furthermore, considering the high probability of having complex mixtures of different SAs residues in water, each individual contamination should be evaluated by applying to the SAs mixtures the conservative criteria of additivity.

A cellular conformation-based screen for androgen receptor inhibitors

The androgen receptor (AR), a member of the steroid nuclear receptor family of transcription factors, regulates a wide range of physiological processes. Androgen signaling is also associated with numerous human diseases, including prostate cancer. All current antiandrogen therapies reduce ligand access to AR, whether by competitive antagonism or inhibition of androgen production, but are limited by acquired resistance and serious side-effects. Thus, novel antiandrogens that target events subsequent to ligand binding could have important therapeutic value. We developed a high throughput assay that exploits fluorescence resonance energy transfer (FRET) to measure ligand-induced conformation change in AR. We directly compared this assay to a transcription-based assay in a screen of FDA-approved compounds and natural products. The FRET-based screen identified compounds with previously unrecognized antiandrogen activities, with equivalent sensitivity and superior specificity compared to a reporter-based screen. This approach can thus improve the identification of small molecule AR inhibitors.

Bioactivation of lapachol responsible for DNA scission by NADPH-cytochrome P450 reductase

The reduction of the naphthoquinone derivative, lapachol, which is responsible for its bioactivation was examined using microsomal preparations and NADPH-cytochrome P450 reductase (P450 reductase). Phenobarbital (PB) pretreatment resulted in an induction of enzyme activities for cytochrome c reduction (1.54 times) and lapachol reduction (1.20 times) by hepatic microsomal preparation of rats. The specific activity of lapachol reduction by purified P450 reductase showed 56-fold higher than that by untreated liver microsomes. Addition of antibody against P450 reductase (2 mg of IgG/mg of protein) to the microsomal incubation mixture caused an immunoinhibition of cytochrome c (32%) and lapachol (19%) reduction activities, suggesting that P450 reductase catalyzes lapachol reduction. Generation of superoxide anion radical (1321 nmol/mg per min) in approximately equivalent amounts of with NADPH consumption (941 nmol/mg per min) was detected during metabolism of lapachol by P450 reductase. Electron spin resonance (ESR) experiments confirmed generation of superoxide anion radical and hydroxyl radical as these 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) adducts. Incubation of lapachol with P450 reductase caused a cleavage of DNA which was reduced in the presence of Cu,Zn-superoxide dismutase (Cu,Zn-SOD), catalase(1), and hydroxyl radical scavengers such as dimethyl sulfoxide (DMSO) and thiourea. Taken together, these results indicate that lapachol is bioactivated by P450 reductase to reactive species, which promote DNA scission through the redox cycling based generation of superoxide anion radical.

Vitamin K metabolism and nutriture

Vitamin K functions as a co-factor for the post-translational carboxylation of specific glutamate residues to gamma-carboxyglutamate (Gla) residues in several blood coagulation factors (II, VII, IX and X) and coagulation inhibitors (proteins C and S) in the liver; as well as a variety of extrahepatic proteins such as the bone protein osteocalcin. This review outlines some recent advances in our understanding of the metabolism of vitamin K and its role in human nutriture. The introduction of new methodologies to measure the low endogenous tissue concentrations of K vitamins and circulating plasma levels of des-gamma-carboxyprothrombin (PIVKA-II) have provided correspondingly more refined indices for the assessment of human vitamin K status. The assays for vitamin K have also been used to study the sources, intestinal absorption, plasma transport, storage and transplacental transfer of K vitamins and the importance of phylloquinone (vitamin K1) versus menaquinones (vitamins K2) to human needs. The ability to biochemically monitor subclinical vitamin K deficiency has reaffirmed the precarious vitamin K status of the newborn and led to an increased appreciation of the risk factors leading to haemorrhagic disease of the newborn and how this may be prevented. Biochemical studies are leading to an increased knowledge of the mode of action of traditional coumarin anticoagulants and how some unrelated compounds (e.g. antibiotics) may also antagonize vitamin K and cause bleeding. There is also an awareness of the possible deleterious effects of vitamin K antagonism or deficiency on non-hepatic Gla-proteins which may play some subtle role in calcium homeostasis.

Hemorrhagic toxicity of d-alpha-tocopherol in the rat

When male Sprague-Dawley rats were administered d-alpha-tocopherol and butylated hydroxytoluene in the diet or intraperitoneally for 7 days, prolongations of prothrombin time and partial thromboplastin time were observed in those given both chemicals by both routes in a dose-dependent manner. However, intraperitoneal d-alpha-tocopherol was less toxic and the prothrombin and partial thromboplastin time indices were approx. 70% and approx. 60% in rats given 2.91 mmol/kg body weight daily. Rats given d-alpha-tocopherol in the diet at a daily dose of 2.31 mmol/kg body weight were approx. 13% and approx. 16% of the control, and in those dietary groups severe hemorrhages in epididymis and other organs were also observed. Plasma concentrations of total tocopherols were more increased by the dietary than the intraperitoneal route. These results suggest that the great difference in the hemorrhagic effect of d-alpha-tocopherol between dietary and intraperitoneal route administration may largely be due to the differing absorption rates of the drug by these two means.

Vitamin K1 2,3-epoxide and quinone reduction: mechanism and inhibition

The chemical and enzymatic pathways of vitamin K1 epoxide and quinone reduction have been investigated. The reduction of the epoxide by thiols is known to involve a thiol-adduct and a hydroxy vitamin K enolate intermediate which eliminates water to yield the quinone. Sodium borohydride treatment resulted in carbonyl reduction generating relatively stable compounds that did not proceed to quinone in the presence of base. NAD(P)H:quinone oxidoreductase (DT-diaphorase, E.C. 1.6.99.2) reduction of vitamin K to the hydroquinone was a significant process in intact microsomes, but 1/5th the rate of the dithiothreitol (DTT)-dependent reduction. No evidence was found for DT-diaphorase catalyzed reduction of vitamin K1 epoxide, nor was it capable of mediating transfer of electrons from NADH to the microsomal epoxide reducing enzyme. Purified diaphorase reduced detergent- solubilized vitamin K1 10(-5) as rapidly as it reduced dichlorophenylindophenol (DCPIP). Reduction of 10 microM vitamin K1 by 200 microM NADH was not inhibited by 10 microM dicoumarol, whereas DCPIP reduction was fully inhibited. In contrast to vitamin K3 (menadione), vitamin K1 (phylloquinone) did not stimulate microsomal NADPH consumption in the presence or absence of dicoumarol. DTT-dependent vitamin K epoxide reduction and vitamin K reduction were shown to be mutually inhibitory reactions, suggesting that both occur at the same enzymatic site. On this basis, a mechanism for reduction of the quinone by thiols is proposed. Both the DTT-dependent reduction of vitamin K1 epoxide and quinone, and the reduction of DCPIP by purified DT-diaphorase were inhibited by dicoumarol, warfarin, lapachol, and sulphaquinoxaline.