The effects of corticosteroid therapy on vitamin D and renal tubular function in nephrotic syndrome

Objective: To investigate the effect and possible mechanism of long term high-dose corticosteroid therapy on vitamin D metabolism and renal tubular function in nephrotic syndrome (NS). Methods: Forty-seven NS cases including 28 patients who were given oral prednisone at the dosage of 1mg/Kg/day for 6 weeks, and normal subjects as control. Serum 1,25-(OH)(2)D-3 were measured by RIA while urinary NAG and GAL were also evaluated. Proteinuria was also analyzed by disc electrophoresis. Results: The serum 1,25-(OH)(2)D-3 in NS group was lower than normal control while urinary NAG and GAL were elevated. After oral prednisone therapy the serum 1,25-(OH)(2)D-3 was elevated in comparison with NS group while urinary NAG and GAL were decreased. Conclusions: The reduction in serum 1,25-(OH)(2)D-3 of NS was associated with direct urinary loss of 1,25-(OH)(2)D-3-DBP due to the impaired proximal tubular function and the decreased 1+/--hydroxylase activity. The lesion to the renal tubular epithelial cells in NS was possibly induced by the protein in the urine with a large and middle molecular weight. Serum 1,25-(OH)(2)D-3 may be increased when proximal renal tubular function could be improved on a large-dose corticosteroid treatment. As a marker reflecting proximal renal tubular function, NAG is believed to be more sensitive than GAL.