Abstract-A large body of literature suggest that vascular reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidases are important sources of reactive oxygen species. Many studies, however, relied on data obtained with the inhibitor apocynin (4Ј-hydroxy-3Јmethoxyacetophenone). Because the mode of action of apocynin, however, is elusive, we determined its mechanism of inhibition on vascular NADPH oxidases. In HEK293 cells overexpressing NADPH oxidase isoforms (Nox1, Nox2, or Nox4), apocynin failed to inhibit superoxide anion generation detected by lucigenin chemiluminescence. In contrast, apocynin interfered with the detection of reactive oxygen species in assay systems selective for hydrogen peroxide or hydroxyl radicals. Importantly, apocynin interfered directly with the detection of peroxides but not superoxide, if generated by xanthine/xanthine oxidase or nonenzymatic systems. In leukocytes, apocynin is a prodrug that is activated by myeloperoxidase, a process that results in the formation of apocynin dimers. Endothelial cells and smooth muscle cells failed to form these dimers and, therefore, are not able to activate apocynin. Dimer formation was, however, observed in Nox-overexpressing HEK293 cells when myeloperoxidase was supplemented. As a consequence, apocynin should only inhibit NADPH oxidase in leukocytes, whereas in vascular cells, the compound could act as an antioxidant. Indeed, in vascular smooth muscle cells, the activation of the redox-sensitive kinases p38-mitogen-activate protein kinase, Akt, and extracellular signal-regulated kinase 1/2 by hydrogen peroxide and by the intracellular radical generator menadione was prevented in the presence of apocynin. These observations indicate that apocynin predominantly acts as an antioxidant in endothelial cells and vascular smooth muscle cells and should not be used as an NADPH oxidase inhibitor in vascular systems. Key Words: apocynin Ⅲ NADPH oxidase Ⅲ Nox1 Ⅲ Nox4 Ⅲ leukocytes Ⅲ reactive oxygen species R eactive oxygen species (ROS) have a strong impact on vascular homeostasis. 1 ROS originate from several sources, including xanthine oxidase, cytochrome P450 monooxygenases, mitochondria, and uncoupled NO synthase, as well as from the proteins of the Nox family, the NADPH oxidases. The identification of the individual contribution of these generator systems to oxidative burden has been a focus of an impressive amount of publications. The motivation of these studies is that a site-directed ROS lowering therapy to inhibit individual generator systems should be superior to the presently unsuccessful approaches with antioxidants in preventing ROS-dependent cardiovascular diseases. 2 Although it is generally appreciated that molecular techniques involving antisense oligonucleotides, small-interfering RNA, or transgenic animals are to be preferred to pharmacological inhibitors to characterize the contribution of individual ROS generator systems, the latter studies still represent the majority of scientific contributions in the field.Different from N...

The present study investigated CYP2B6 genetic variability by sequencing genomic DNA samples of African-American, Ghanaian, Taiwanese, Japanese and Korean subjects throughout all exons and exon-intron boundaries. The most common nonsynonymous single nucleotide polymorphisms (SNPs) were 15631G > T (Q172H) and 18053A > G (K262R, together defining allele 2B6*6), both of which had frequencies close to 50% in Ghanaians and 30% in African-Americans. These SNPs have recently been shown to affect efavirenz pharmacokinetics and response in HIV patients. Eight new missense mutations (76A > T [T26S], 83A > G [D28G], 85C > A, 86G > C [both R29T], 15618C>T [T168I], 18038G > A [D257N], 21034C > T [R336C], 21498C > A [P428T]), three new silent mutations and two new intronic SNPs defining six novel alleles (*17A and B, *18, *19, *20, *21) were identified. Heterologous expression in COS-1 cells revealed pronounced reduction in expression and/or bupropion hydroxylase activity for variants T168I, D257N, R336C and P428T, whereas the triple mutant 2B6.17 (T26S, D28G, R29T) appeared to be functionally normal. These data extend the CYP2B6 knowledge base and should be particularly relevant for anti-HIV-therapy with efavirenz.

AA (arachidonic acid) hydroxylation to 20-HETE (20-hydroxyeicosatetraenoic acid) influences renal vascular and tubular function. To identify the CYP (cytochrome P450) isoforms catalysing this reaction in the mouse kidney, we analysed the substrate specificity of Cyp4a10, 4a12a, 4a12b and 4a14 and determined sex- and strain-specific expressions. All recombinant enzymes showed high lauric acid hydroxylase activities. Cyp4a12a and Cyp4a12b efficiently hydroxylated AA to 20-HETE with V(max) values of approx. 10 nmol x nmol(-1) x min(-1) and K(m) values of 20-40 microM. 20-Carboxyeicosatetraenoic acid occurred as a secondary metabolite. AA hydroxylase activities were approx. 25-75-fold lower with Cyp4a10 and not detectable with Cyp4a14. Cyp4a12a and Cyp4a12b also efficiently converted EPA (eicosapentaenoic acid) into 19/20-OH- and 17,18-epoxy-EPA. In male mice, renal microsomal AA hydroxylase activities ranged between approx. 100 (NMRI), 45-55 (FVB/N, 129 Sv/J and Balb/c) and 25 pmol x min(-1) x mg(-1) (C57BL/6). The activities correlated with differences in Cyp4a12a protein and mRNA levels. Treatment with 5alpha-dihydrotestosterone induced both 20-HETE production and Cyp4a12a expression more than 4-fold in male C57BL/6 mice. All female mice showed low AA hydroxylase activities (15-25 pmol x min(-1) x mg(-1)) and very low Cyp4a12a mRNA and protein levels, but high Cyp4a10 and Cyp4a14 expression. Renal Cyp4a12b mRNA expression was almost undetectable in both sexes of all strains. Thus Cyp4a12a is the predominant 20-HETE synthase in the mouse kidney. Cyp4a12a expression determines the sex- and strain-specific differences in 20-HETE generation and may explain sex and strain differences in the susceptibility to hypertension and target organ damage.