Dehydroascorbate transport in human chondrocytes is regulated by hypoxia and is a physiologically relevant source of ascorbic acid in the joint.
OBJECTIVE
To evaluate the dehydroascorbate (DHA) transport mechanisms in human chondrocytes.


METHODS
The transport of L-(14)C-DHA in human chondrocytes was analyzed under various conditions, including the use of RNA interference (RNAi), to determine the role of glucose transporter 1 (GLUT-1) and GLUT-3 in L-14C-DHA transport and to evaluate the effects of physiologically relevant oxygen tensions on L-14C-DHA transport. In order to estimate the contributions of reduced ascorbic acid (AA) and DHA to intracellular ascorbic acid (Asc), the quantities of AA and DHA were measured in synovial fluid samples from osteoarthritis (OA) patients and compared with the reported levels in rheumatoid arthritis (RA) patients.


RESULTS
DHA transport in human chondrocytes was glucose-sensitive, temperature-dependent, cytochalasin B-inhibitable, modestly stereoselective for L-DHA, and up-regulated by low oxygen tension. Based on the RNAi results, GLUT-1 mediated, at least in part, the uptake of DHA, whereas GLUT-3 had a minimal effect on DHA transport. DHA constituted a mean 8% of the total Asc in the synovial fluid of OA joints, in contrast to 80% of the reported total Asc in RA joints.


CONCLUSIONS
We provide the first evidence that chondrocytes transport DHA via the GLUTs and that this transport mechanism is modestly selective for L-DHA. In the setting of up-regulated DHA transport at low oxygen tensions, DHA would contribute 26% of the total intracellular Asc in OA chondrocytes and 94% of that in RA chondrocytes. These results demonstrate that DHA is a physiologically relevant source of Asc for chondrocytes, particularly in the setting of an inflammatory arthritis, such as RA.
McNulty
Amy L
AL
Duke University Medical Center, Durham, North Carolina 27710, USA.
Stabler
Thomas V
TV
Vail
Thomas P
TP
McDaniel
Gary E
GE
Kraus
Virginia B
VB
D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D001205:Ascorbic Acid / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism*; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002851:Chromatography, High Pressure Liquid; D003683:Dehydroascorbic Acid / Q000378:metabolism*; D015870:Gene Expression; D007719:Knee Joint / Q000378:metabolism* / Q000473:pathology; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D020370:Osteoarthritis, Knee / Q000378:metabolism* / Q000473:pathology; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation
D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid