diamide and sorbinil

Using isolated rat hepatocytes we have shown that glutathione (GSH) depletion by glutathione-S-transferase (GST)-catalyzed conjugation with 1-bromoheptane or phorone was accompanied by a significant elevation in ascorbate synthesis. Glycogenolysis was also stimulated without a significant rise in glucose synthesis. Furthermore, when glycogenolysis was stimulated in control hepatocytes by increasing intracellular cAMP levels (with glucagon or dibutyryl cAMP), cellular glucose levels, but not ascorbate levels, increased. These data suggest that GSH depletion can stimulate ascorbate synthesis independently of glucose synthesis and that hepatocytes can direct glycogenolysis towards ascorbate synthesis during GSH conjugation.

Topics: Animals; Ascorbic Acid; Bucladesine; Cyclic AMP; Diamide; Dithiothreitol; Fructose; Glutathione; Glutathione Disulfide; Glycogen; Hepatocytes; Heptanes; Imidazoles; Imidazolidines; Ketones; Male; Rats; Rats, Sprague-Dawley; Uridine Diphosphate Glucose

Vitamin C synthesis in rat liver is enhanced by several xenobiotics, including aminopyrine and chloretone. The effect of these agents has been linked to induction of enzymes potentially involved in the formation of glucuronate, a precursor of vitamin C. Using isolated rat hepatocytes as a model, we show that a series of agents (aminopyrine, antipyrine, chloretone, clotrimazole, metyrapone, proadifen, and barbital) induced in a few minutes an up to 15-fold increase in the formation of glucuronate, which was best observed in the presence of sorbinil, an inhibitor of glucuronate reductase. They also caused an approximately 2-fold decrease in the concentration of UDP-glucuronate but little if any change in the concentration of UDP-glucose. Depletion of UDP-glucuronate with resorcinol or d-galactosamine markedly decreased the formation of glucuronate both in the presence and in the absence of aminopyrine, confirming the precursor-product relationship between UDP-glucuronate and free glucuronate. Most of the agents did not induce the formation of detectable amounts of glucuronides, indicating that the formation of glucuronate is not due to a glucuronidation-deglucuronidation cycle. With the exception of barbital (which inhibits glucuronate reductase), all of the above mentioned agents also caused an increase in the concentration of ascorbic acid. They had little effect on glutathione concentration, and their effect on glucuronate and vitamin C formation was not mimicked by glutathione-depleting agents such as diamide and buthionine sulfoximine. It is concluded that the stimulation of vitamin C synthesis exerted by some xenobiotics is mediated through a rapid increase in the conversion of UDP-glucuronate to glucuronate, which does not apparently involve a glucuronidation-deglucuronidation cycle.

Topics: Aminopyrine; Animals; Anti-Inflammatory Agents, Non-Steroidal; Antipyrine; Ascorbic Acid; Barbital; Buthionine Sulfoximine; Cells, Cultured; Chlorobutanol; Chromatography, High Pressure Liquid; Clotrimazole; Diamide; Dose-Response Relationship, Drug; Enzyme Inhibitors; Galactosamine; Glucuronates; Glucuronic Acid; Hepatocytes; Imidazoles; Imidazolidines; Metyrapone; Models, Chemical; Preservatives, Pharmaceutical; Proadifen; Rats; Rats, Wistar; Resorcinols; Time Factors; Xenobiotics; Xylulose