Inhibition of nucleoside transport by nitrobenzylthioformycin analogs

Nitrobenzylthioinosine (NBT), a nucleoside transport inhibitor, protects against Shiga toxin cytotoxicity in human microvascular endothelial cells

Infections with Shiga toxin (Stx)-producing Escherichia coli (STEC) cause microvascular endothelial cell damage, resulting in hemorrhagic colitis and hemolytic uremic syndrome. The prevention of endothelial cell damage is therefore a crucial step in overcoming this disorder. Here, we report that nitrobenzylthioinosine (NBT), a nucleoside transport inhibitor, has a protective effect against the cytotoxicity of Stxs in human microvascular endothelial cells (HMVECs). The relative viability of cells treated with 1.5-15 pM of Stx1 was reduced to 10-20% of that without Stx1. However, the viability of cells treated with NBT (10-100 microM) remained higher than 80%, even in the presence of Stx1. NBT also protected against Stx1 cytotoxicity in sodium butyrate-treated hypersensitive HMVECs. The protective effect of NBT against Stx cytotoxicity may be due to the depletion of ATP in the cells, thereby inhibiting the entry of Stx1.

The synthesis and biological evaluation of 4-p-nitrobenzylthio-v-triazolo[4,5-d]pyridazine and imidazo[4,5-d]pyridazine ribosides as potential nucleoside transport inhibitors

The synthesis of S4-substituted nucleosides possessing the imidazo- and v-triazolo[4,5-d]pyridazine ring systems was undertaken and the compounds prepared were evaluated as inhibitors of nucleoside transport into human erythrocytes. 1-(2,3,5-Tri-O-acetyl-beta-D-ribofuranosyl)-v-triazolo[4,5-d]pyridazine- 4 (5H)-thione and 1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)imidazo[4,5-d]pyridazine-4 (5H)-thione were each synthesized by two different routes and served as precursors for the title analogues. The nitrobenzylmercaptopurine riboside (NBMPR) analogues, 4-(p-nitrobenzylthio)-1-(beta-D-ribofuranosyl)imidazo[4,5-d]pyrida zine and 4-(p-nitrobenzylthio)-1-(beta-D-ribofuranosyl)-v-triazolo[4,5-d]py ridazine, inhibited the transport of adenosine, but were approximately 4- and 28-fold less active, respectively, than NBMPR and nitrobenzylthioformycin, known potent and specific inhibitors of carrier-mediated transport.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.