title: Generation of reactive oxygen species undergoing redox cycle of nostocine A: a cytotoxic violet pigment produced by freshwater cyanobacterium Nostoc spongiaeforme.
abstract: Nostocine A (1) is an extracellular cytotoxic violet pigment produced by the freshwater cyanobacterium, Nostoc spongiaeforme TISTR 8169. Treatment with 1 was found to accelerate the generation of reactive oxygen species (ROS) in the green alga, Chlamydomonas reinhardtii, in the light. In vitro analysis revealed that 1 specifically eliminated superoxide radical anion (O(2)(-)) among several ROS tested. During the course of the reaction, oxygen (O(2)) was simultaneously synthesized and the O(2) synthesizing rate increased with the amount of 1 added. In contrast, O(2)(-) generation occurred when NADPH or NADH was added to a solution of 1 under aerobic condition. The reduction potential of 1 is very similar to that of O(2) indicating that 1 and O(2) can easily exchange electrons depending on the mass balance between their oxidized and reduced forms. Based on these results, the following hypothesis is formulated for the mechanism of intracellular ROS generation by treatment with 1: 1 taken into the target cells is reduced specifically by intracellular reductants such as NAD(P)H. When the O(2) level is sufficiently higher than that of 1, the reduced product of 1 is immediately oxidized by O(2). This is accompanied by the synthesis of O(2)(-) from O(2). The generation of O(2)(-) successively occurs, undergoing repeated redox cycles of 1, when the levels of the reductant and O(2) are still dominant to promote these reactions. This similar intracellular ROS generation mechanism to that of paraquat may cause the cytotoxicity.
authors.affiliation: Environmental Biotechnology Laboratory, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita, Osaka 565-0871, Japan. hirata@phs.osaka-u.ac.jp
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Hirata
authors.forename: Sayaka
authors.initials: S
authors.lastname: Yoshitomi
authors.forename: Susilaningsih
authors.initials: S
authors.lastname: Dwi
authors.forename: Osamu
authors.initials: O
authors.lastname: Iwabe
authors.forename: Aparat
authors.initials: A
authors.lastname: Mahakant
authors.forename: Jirapatch
authors.initials: J
authors.lastname: Polchai
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Miyamoto
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism; D003603:Cytotoxins / Q000378:metabolism / Q000494:pharmacology; D005618:Fresh Water; D046937:Nostoc / Q000378:metabolism*; D010084:Oxidation-Reduction; D010860:Pigments, Biological / Q000096:biosynthesis / Q000737:chemistry; D047069:Pyrazolones / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014227:Triazines / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D003603:Cytotoxins; D010860:Pigments, Biological; D047069:Pyrazolones; D017382:Reactive Oxygen Species; D014227:Triazines; C495434:nostocine A