Hypoxanthine decreases equilibrative type of adenosine transport in lymphocytes from Lesch-Nyhan patients

Background Lesch-Nyhan (LN) syndrome is associated with deficient hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity, but the connection between the aberrant purine metabolism and the neurological symptoms remains largely unknown. The aim of this study was to determine adenosine transporter subtypes affected by HPRT deficiency and by the associated hypoxanthine excess. Materials and methods Nucleoside transporter types (depending on their sodium dependence and 10 mu M nitrobenzylthioinosine, NBTI, sensitivity) involved in adenosine transport were compared between peripheral blood lymphocytes (PBL) obtained from nine LN patients, PBLLN (2-21 years) and from nine controls, PBLC (2-23 years) under basal conditions and after 25 mu M hypoxanthine incubation. Results We found four types of adenosine transporters in PBL: equilibrative and concentrative transporters that are either sensitive (ENT1 or cs) or insensitive (ENT2 or ci) to NBTI. Adenosine ENT1 uptake was the predominant transporter in both PBLC (55%) and PBLLN (46%). Under basal conditions no significant differences were found in adenosine transport between PBLC and PBLLN. Incubation of PBL with 25 mu M hypoxanthine markedly decreased total adenosine transport in both cell types. Hypoxanthine affected equilibrative transport (mainly ENT2 type) in PBLLN and PBLC. Only in PBLC was concentrative transport affected by hypoxanthine. Expressions of human (h) ENT1 and hENT2 mRNA were not significantly modified by hypoxanthine incubation in PBLC. Conclusions This study contributes to further knowledge of the defective adenosine transport found in PBLLN. Increased hypoxanthine levels, similar to those reported in HPRT deficient patients, reduced adenosine uptake by 32% in PBLLN as compared to normal transport.