vitamin-k-semiquinone-radical and sodium-arsenite

This study demonstrates the menadione-dependent reduction of imipramine N-oxide, a tertiary amine N-oxide, to imipramine by rat liver cytosol in the presence of NADH or NADPH. A mechanism for the cytosolic reduction of the tertiary amine N-oxide is proposed. Menadione is converted to its reduced form by a menadione-reducing enzyme such as DT-diaphorase and the reduced pyridine nucleotide, followed by reduction of the tertiary amine N-oxide to the amine by the heme group of catalytic hemoproteins in the presence of reduced menadione as an electron donor.

Topics: Animals; Arsenites; Carbon Monoxide; Catalase; Cytosol; Dicumarol; Hemin; Hemoglobins; Imipramine; Liver; Male; Myoglobin; NAD; NADP; Oxidation-Reduction; Potassium Cyanide; Rats; Rats, Wistar; Sodium Compounds; Vitamin K

To study the genetic changes that generate resistance to oxidants in mammalian cells, we isolated cell lines that are resistant to the naphthoquinone, menadione, from a Chinese hamster ovary cell line (CHO-K1). Corss-resistance to other oxidants (H2O2 and sodium arsenite) was observed. The IC50 of menadione (measured using a clonogenic assay) was 7.8-fold greater for one menadione-resistant cell line (MRc40) than for CHO-K1. Acquisition of resistance was associated with elevations of 2- and 3.2-fold in the low molecular weight thiols, glutathione and cysteine, respectively. Further, characterization demonstrated significant changes in the expression of enzymes associated with the oxidative stress response and with protection against oxidizing agents. The expressions of glutathione S-transferase pi (GST pi), glutathione peroxidase (GPX) and heme oxygenase mRNAs were all increased. Accompanying these changes the enzyme activity of GST pi, GPX and gamma-glutamyl transpeptidase (gamma-GT) were also elevated. Interestingly, in a revertant cell line heme oxygenase overexpression approached wild-type levels. Intriguingly, similar changes in gene expression seen in the menadione-resistant cells were also observed in wild-type cells following transient oxidative stress, indicating that the observed changes in the resistant line may be due to the immortalization of a normally transient adaptive stress response.

Topics: Animals; Arsenites; CHO Cells; Cricetinae; Drug Resistance; Hydrogen Peroxide; Oxidants; Oxidative Stress; Sodium Compounds; Vitamin K

PCR and Southern blot analyses demonstrate that mRNA for heme oxygenase (HO), a well known "stress protein" in a number of tissues, is present in human retina. Western and northern blots show that the protein and mRNA are also expressed in human Y-79 retinoblastoma cells in culture and that the HO enzyme is rapidly induced by its substrate, heme. Moreover, HO is also induced by two chemicals, sodium arsenite and menadione, that act as agents of oxidative stress. HO is the regulatory enzyme in the heme degradative pathway and an increase in its activity could lead to the accumulation of bilirubin, an antioxidant, in the cell at the expense of heme, a prooxidant. The HO pathway may thus be of importance in protecting the retina against oxidative stress in vivo. Moreover, the Y-79 culture system should provide an excellent model for use in examining stress mechanisms in retinal cells at a molecular level.

Topics: Arsenic; Arsenites; Bilirubin; Eye Neoplasms; Heme; Heme Oxygenase (Decyclizing); Humans; Immunoblotting; Models, Biological; Polymerase Chain Reaction; Retina; Retinoblastoma; RNA, Messenger; Sodium Compounds; Tumor Cells, Cultured; Vitamin K

Topics: Arsenic; Arsenic Poisoning; Arsenites; Blood Coagulation; Factor V; Factor VII; Humans; Prothrombin; Sodium Compounds; Thioctic Acid; Vitamin K; Vitamins