Inhibition of RNA synthesis, a possible mode of the embryotoxic action of hydroxyurea

Effects of hydroxyurea on postnatal growth and behaviour of rats

Hydroxyurea was administered intraperitoneally to pregnant albino rats in a single dose of 2000 mg/kg on day 14 of gestation. Both the perinatal and postnatal mortality rates of the progeny were increased and their weight gain reduced. Exploratory locomotion of 32-day-old rats, calculated by means of an 'activity index', was significantly reduced. The treatment had no effect on the brain weight. The fertility of the progeny was not impaired.

Cell death and free radicals: a mechanism for hydroxyurea teratogenesis

Hydroxyurea is a drug which causes birth defects in a variety of animals. Its pharmacologic actions include rapid killing of proliferating cells and profound inhibition of the synthesis of DNA. The mechanism whereby hydroxyurea produces teratogenesis is unresolved although it is related to the pharmacologic actions. Careful reading of the scientific literature discloses several putative mechanisms for the teratogenic action of hydroxyurea, which account for the inhibited synthesis of DNA, but do not explain the rapid onset of cell death. This paper presents a hypothesis that hydroxyurea causes rapid cell death through the initiation of uncontrolled free radical chain reactions. In vitro biochemical experiments have demonstrated the ability of compounds containing a hydroxylamine group (such as hydroxyurea) to form H2O2 and intermediate free radicals in biological fluids. Free radicals propagate themselves through chain reactions and can react swiftly and indiscriminately with the macromolecules quickly by inactivating enzymes, cross-linking DNA, and altering membrane functions through lipid auto-oxidation. Preliminary experiments utilizing an antioxidant to counteract the free radical effects appear to support the hypothesis that the rapid cell death is caused by aberrant free radical reactions.

Investigation of the effect of hydroxyurea on the cell cycle and the development of necrosis in the embryonic CNS of mice

On day 10 of gestation pregnant mice (strain NMRI) were given an intravenous injection of 500 mg/kg Hydroxyurea (HU). Simultaneously either 5 muCi/g or 10 muCi/g 3H-thymidine (3H-Tdr; specific activity 5Ci/mmol) was administered to the animals. At various times after treatment embryos and electron microscopy. Two hours after administration of HU condensations of the chromatin structure could be detected electron microscopically in some cells. Thirty minutes later the nucleolus became smaller and denser, the cytoplasm shrank, and the cell organelles moved closer together. Three hours after application of the drug break-down of the involved cells set in. As in the autoradiograms about 98% of the counted necroses were labelled, and since labelled thymidine is almost exclusively incorporated during the S-phase, it can be stated the HU influences only metabolic processes which take place during the S-phase. From the morphological findings it can be concluded that in the case of the S-phase-specific metabolic pathway, which is influenced by HU, we are primarily dealing with DNA synthesis.