Vitamin C uptake and recycling among normal and tumor cells from the central nervous system.
Specialized cells transport vitamin C in its reduced form using sodium-dependent cotransporters (SVCT1 and SVCT2). Additionally, different cells transport the oxidized form of vitamin C, dehydroascorbic acid, through glucose transporters (GLUTs). We have proposed recently a model for vitamin C uptake that resolves the apparent contradiction that although only ascorbic acid is detectable in vivo, there are cells that transport only dehydroascorbic acid. We carried out a detailed kinetic analysis to compare the mechanisms of vitamin C uptake in normal human melanocytes, neurons isolated from brain cortex, hypothalamic ependymal-glial cells, and astrocytes. Uptake of ascorbic acid was also analyzed in the human oligodendroglioma cell line TC620, in human choroid plexus papilloma cells (HCPPC-1), and in the neuroblastoma cell line Neuro-2a. Melanocytes were used to carry out a detailed analysis of vitamin C uptake. Analysis of the transport data by the Lineweaver-Burk plot revealed the presence of one functional component (K(m) 20 microM) involved in ascorbic acid transport by melanocytes. Vitamin C sodium-dependent saturable uptake was also observed in neurons and hypothalamic tanycytes. We confirmed SVCT2 expression in neurons by in situ hybridization; however, SVCT2 expression was not detected in astrocytes in situ. Functional data indicate that astrocytes transport mainly dehydroascorbic acid, using the glucose transporter GLUT1. Our functional uptake analyses support the hypothesis that astrocytes are involved in vitamin C recycling in the nervous system. This recycling model may work as an efficient system for the salvage of vitamin C by avoiding the hydrolysis of dehydroascorbic acid produced by antioxidative protection.
Astuya
Allisson
A
Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, casilla 160C, Concepción, Chile.
Caprile
Teresa
T
Castro
Maite
M
Salazar
Katterine
K
García
María de los Angeles
Mde L
Reinicke
Karin
K
Rodríguez
Federico
F
Vera
Juan Carlos
JC
Millán
Carola
C
Ulloa
Viviana
V
Low
Marcela
M
Martínez
Fernando
F
Nualart
Francisco
F
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D001921:Brain / Q000166:cytology* / Q000378:metabolism; D001932:Brain Neoplasms / Q000473:pathology*; D002478:Cells, Cultured; D002794:Choline / Q000493:pharmacokinetics; D003572:Cytochalasins / Q000494:pharmacology; D003683:Dehydroascorbic Acid / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D051272:Glucose Transporter Type 1; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D008544:Melanocytes / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D008959:Models, Neurological; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009447:Neuroblastoma / Q000473:pathology*; D009457:Neuroglia / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D029363:Organic Anion Transporters, Sodium-Dependent / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012965:Sodium Chloride / Q000494:pharmacology; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
D003572:Cytochalasins; D005904:Glial Fibrillary Acidic Protein; D051272:Glucose Transporter Type 1; D009004:Monosaccharide Transport Proteins; D016376:Oligonucleotides, Antisense; D029363:Organic Anion Transporters, Sodium-Dependent; D012333:RNA, Messenger; C555162:SLC23A1 protein, human; C555163:SLC23A2 protein, human; C495677:SLC2A1 protein, human; C555164:Slc23a1 protein, mouse; C555166:Slc23a1 protein, rat; C555165:Slc23a2 protein, mouse; C555167:Slc23a2 protein, rat; C495678:Slc2a1 protein, mouse; C495679:Slc2a1 protein, rat; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters; D012965:Sodium Chloride; D002794:Choline; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid