Urinary enzyme activities in patients treated with gold and other antirheumatic drugs

We have studied 48 rheumatoid arthritis (RA) patients treated with nonsteroidal antiinflammatory drugs (NSAIDs), except salicylates, in 31 of whom parenteral gold was associated as therapeutic agent. In order to assess initial tubular involvement, the activities of some urinary enzymes were measured: N-acetylglucosaminidase (NAG, EC 3.2.1.30), microsomal amino-peptidase (MAP, EC 3.4.11.2) and gamma-glutamyltransferase (GGT; EC 2.3.2.2). Results were compared with a control group of 51 subjects of similar age, with no rheumatic symptoms and normal renal function. Both groups of patients (31 with gold therapy and 17 without) showed a significantly increased activity of NAG in urine, but the increase was greater in those treated with gold. MAP and GGT were not elevated significantly in either group. There was no correlation, however, between the increase of NAG and the cumulative dose of gold. NAG, MAP and GGT activities in serum yielded no relevant information. All the usual tests of renal function were also normal. Determination of NAG in urine may be regarded as a sensitive test, capable of detecting selective involvement of renal tubular cells, whose final diagnostic and prognostic significance merits further evaluation.