Accumulation of intracellular ascorbate from dehydroascorbic acid by astrocytes is decreased after oxidative stress and restored by propofol

Abstract

Primary rat astrocyte cultures absorbed dehydroascorbic acid from the medium and reduced it to intracellular ascorbate. Uptake of dehydroascorbic acid (5-200 microM) was inhibited only partially by glucose (10 mM). The remaining glucose-insensitive component of dehydroascorbic acid uptake was inhibited reversibly by sulfinpyrazone (IC(50) = 80 microM). Dehydroascorbic acid uptake was not mediated by Na(+)-ascorbate cotransporters or volume-sensitive anion channels because it was neither Na(+)-dependent nor blocked by the channel antagonist, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. Oxidative stress, induced in astrocytes by the lipophilic radical generator tert-butyl hydroperoxide, decreased intracellular glutathione concentration and inhibited accumulation of intracellular ascorbate from dehydroascorbic acid. Subsequent administration of either the native antioxidant alpha-tocopherol (200 microM) or anesthetic concentrations of the antioxidant sedative propofol (1-8 microM, administered 30 min after tert-butyl hydroperoxide), did not change glutathione concentration but restored the ability of astrocytes to accumulate intracellular ascorbate from dehydroascorbic acid. These results are consistent with a novel mechanism of astrocytic ascorbate accumulation that is inhibited by lipophilic radicals and protected by lipophilic antioxidants such as propofol.

Impact of Oxidative Stress on Ascorbate Biosynthesis in Chlamydomonas via Regulation of the VTC2 Gene Encoding a GDP-l-galactose Phosphorylase

“…5B). The observation that tBuOOH treatment depletes cellular ascorbate has been made previously in rat hepatocytes (44) and rat astrocytes (45). Altogether, our results indicate a correlation between the VTC2 mRNA levels and L-ascorbic acid content in C. reinhardtii cells exposed to oxidative stress.…”

Decreased Tissue Accumulation of 6-Deoxy-6-[18F]fluoro-L-ascorbic Acid in Glutathione-Deficient Rats Induced by Administration of Diethyl Maleate

“…22) In an environment in which cellular GSH is depleted, a profound reduction in the ability to reduce DHA to AA has been suggested to take place in some cells such as endothelial cells and erythrocytes. 23,24) Moreover, it has been reported that, in adult mice with GSH depletion, the levels of DHA in tissues increased markedly.…”

Vitamin C Transporter (SVCT2) Distribution in Developing and Adult Brains

“…However, today we know that astrocytes perform critical physiological activities, such as (1) the uptake of extracellular glutamate for recycling into glutamine to avoid neuronal excitotoxicity; (2) the release of lactate to be used by neurons for energy production; (3) the release of interleukin-6 (IL-6) and tumor growth factor-beta (TGF-beta) neuroprotective cytokines; (4) the synthesis of apolipoprotein E for axonal growth; and (5) the release of trophic factors, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and ciliary neurotrophic factor (CNTF), among others [40]. Moreover, astrocytes are required for vitamin C recycling in the CNS due to their ability to uptake DHA from the extracellular space and, in virtue of its elevated reducing power, to efficiently reduce it back into AA [41,42]. After that, astrocytes release AA to the extracellular space to maintain stable AA concentrations [43].…”