UPTAKE MECHANISMS FOR ASCORBATE AND DEHYDROASCORBATE IN LYMPHOBLASTS FROM DIABETIC NEPHROPATHY AND HYPERTENSIVE PATIENTS

In diabetic nephropathy and hypertension, a major cause of mortality i s from cardiovascular disease, Since low levels of antioxidants such a s vitamin C have been associated with such complications, we have exam ined the uptake mechanisms for ascorbic acid (AA) and dehydroascorbic acid (DHA) in lymphoblasts from normal control subjects (CON), normoal buminuric insulin-dependent diabetic (IDDM) patients (DCON), patients with IDDM and nephropathy (DN) and hypertensive patients (HT) using ma ss assays of uptake and measuring AA using high-performance liquid chr omatography. Precautions were taken to prevent oxidation of AA and to take into account the instability of DHA in buffers. DHA uptake was th e major mechanism in all four groups of subjects, and the V-max (maxim al uptake rate) was significantly lower in the DN cells (24.7 +/- 1.0 nmol [95 % confidence intervals CI 22.5, 26.3] 10(6) cells(-1) h(-1)) compared to CON and DCON cells (33.9 +/- 2.1 [95 % CI 29.4, 38.4] and 37.0 +/- 2.2 [95 % CI 32.2, 41.8] nmol 10(6) cells(-1) h(-1), respecti vely, p < 0.001 for both). DHA V-max was also lower in the HT group (2 3.2 +/- 1.1 [95 % CI 20.7, 25.7] nmol 10(6) cells(-1) h(-1)) compared to the CON group (p < 0.001). There were no significant differences in the K-m or passive membrane permeability for DHA or the AA uptake. DH A uptake showed a negative correlation to systolic blood pressure (r(s ) = -0.49, p < 0.001). These findings suggest that impaired DHA uptake may be one component of the phenotype expressed by DN cells that may persist in culture, Impaired DHA uptake in vivo, especially in the pre sence of hyperglycaemia, leads to impaired regeneration of AA and depl etion of anti-oxidant defences, exposing such individuals to increased risk of cardiovascular disease.