rifamycin-sv and thiobarbituric-acid

The effect of rifamycin SV on metabolic performance and cell viability was studied using isolated hepatocytes from fed, starved and glutathione (GSH) depleted rats. The relationships between GSH depletion, nutritional status of the cells, glucose metabolism, lactate dehydrogenase (LDH) leakage and malondialdehyde (MDA) production in the presence of rifamycin SV and transition metal ions was investigated. Glucose metabolism was impaired in isolated hepatocytes from both fed and starved animals, the effect is dependent on the rifamycin SV concentration and is enhanced by copper (II). Oxygen consumption by isolated hepatocytes from starved rats was also increased by copper (II) and a partial inhibition due to catalase was observed. Cellular GSH levels which decrease with increasing the rifamycin SV concentration were almost depleted in the presence of copper (II). A correlation between GSH depletion and LDH leakage was observed in fed and starved cells. Catalase induced a slight inhibition of the impairment of gluconeogenesis, GSH depletion and LDH leakage in starved hepatocytes incubated with rifamycin SV, iron (II) and copper (II) salts. Lipid peroxidation measured as MDA production by isolated hepatocytes was also augmented by rifamycin SV and copper (II), especially in hepatic cells isolated from starved and GSH depleted rats. Higher cytotoxicity was observed in isolated hepatocytes from fasted animals when compared with fed or GSH depleted animals. It seems likely that in addition to GSH level, there are other factors which may have an influence on the susceptibility of hepatic cells towards xenobiotic induced cytotoxicity.

Topics: Animals; Catalase; Cell Survival; Copper; Gluconeogenesis; Glutathione; Iron; L-Lactate Dehydrogenase; Lipid Peroxidation; Liver; Male; Malondialdehyde; Oxidation-Reduction; Oxygen Consumption; Rats; Rats, Inbred Strains; Rifamycins; Thiobarbiturates

The hydroquinone moiety of the antibiotic rifamycin SV reacts with molecular oxygen to form reduced oxygen intermediates such as superoxide (O2-.) and hydrogen peroxide (H2O2). The antibiotic semiquinone is also formed. Rifamycin SV in the presence of iron and copper salts can lead to the formation of the highly reactive hydroxyl radical (OH) which degrades the sugar deoxyribose. This damage is substantially inhibited by the enzyme catalase and scavengers of the hydroxyl radical such as formate, mannitol and thiourea. When linear duplex DNA is substituted for deoxyribose only rifamycin SV and copper ions substantially degrade DNA with release from the DNA molecule of thiobarbituric acid-reactive products. Damage to DNA by rifamycin and copper ions is significantly inhibited by catalase but poorly inhibited by scavengers of the hydroxyl radical consistent with a site-specific radical reaction of the DNA molecule. Several biological properties of rifamycin SV are known to resemble those of the metal chelating agent 1,10-phenanthroline. Here, we show that similarities extend to an unusual chemical property whereby thiobarbituric acid-reactive material is released from DNA in the presence of a copper salt.

Topics: Copper; DNA; DNA Damage; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; Rifamycins; Thiobarbiturates