Role of thiol homeostasis and adenine nucleotide metabolism in the protective effects of fructose in quinone-induced cytotoxicity in rat hepatocytes.
Freshly-isolated rat hepatocytes were exposed in glucose (15 mM) or fructose (5 mM) medium to menadione (2-methyl-1,4-naphthoquinone) (85 microM) or 1,4-naphthoquinone (NQ) (50 microM). Menadione and NQ are closely related quinones and have an approximately equal potential to induce redox cycling. However, NQ has a higher potential to arylate and is more toxic than menadione. During 2 hr of incubation, cell viability, thiol status, adenine nucleotide level and lactate production were determined. LDH-leakage was used as a measure of cell viability. In glucose medium, exposure of hepatocytes to menadione or NQ resulted in a faster excretion rate of oxidized glutathione as compared to those cells in fructose medium. As a result, quinone-exposed hepatocytes in fructose medium retained higher amounts of oxidized glutathione. Menadione-exposed hepatocytes in fructose medium exhibited a diminished rate of transthiolation of protein thiols with oxidized glutathione as compared to those cells in glucose medium. The adenine nucleotide level of hepatocytes in glucose medium was markedly higher than in fructose medium. This was caused by an ATP decrease in hepatocytes in fructose medium resulting in a low energy charge (E.C.) (0.6) as compared to hepatocytes in glucose medium (0.9). Only menadione caused a decrease in the E.C. in glucose medium while NQ caused a decrease of all three adenine nucleotides. In fructose medium, quinone-exposed hepatocytes showed no change in their adenine nucleotides as compared to control cells. Despite the higher oxidized glutathione content and the lower ATP level of NQ-exposed hepatocytes in fructose medium, they had a better viability than those cells in glucose medium. From our results we conclude that a high ATP content is not always beneficial for cell survival.
Toxopeus
C
C
Research Institute of Toxicology (RITOX), Utrecht University, The Netherlands.
van Holsteijn
I
I
de Winther
M P
MP
van den Dobbelsteen
D
D
Horbach
G J
GJ
Blaauboer
B J
BJ
Noordhoek
J
J
D000227:Adenine Nucleotides / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D005978:Glutathione / Q000032:analysis; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009285:Naphthoquinones / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D014812:Vitamin K / Q000633:toxicity*
D000227:Adenine Nucleotides; D009285:Naphthoquinones; D013438:Sulfhydryl Compounds; D014812:Vitamin K; D005632:Fructose; D000255:Adenosine Triphosphate; D005978:Glutathione; D005947:Glucose; C035342:1,4-naphthoquinone