URINARY NEUTRAL ENDOPEPTIDASE IN WORKERS EXPOSED TO CADMIUM - INTERACTION WITH CIGARETTE-SMOKING

Objectives-Structural impairment of the renal proximal tubular epithel ium induced by cadmium (Cd) was investigated by measuring the concentr ation of neutral endopeptidase 24.11 (NEP), an ectoenzyme of the apica l brush border, in the urine of 106 male workers employed in a Cd smel ter (among whom 52 were occupationally exposed to Cd), and by comparin g it with other tubular markers (low molecular weight proteins, lysoso mal enzymes). Methods-NEP (EC 3.4.24.11), beta-N-acetyl-glucosaminidas e (NAG) (EC 3.2.1. 30), and NAG-B isoenzyme activities were measured b y fluorimetric assays, whereas the concentrations of retinol binding p rotein (RBP), beta(2)-microglobulin (beta(2)M), and Clara cell protein (CC16) were measured by automated latex agglutination techniques. Res ults-An increased urinary excretion of NEP as well as microproteins wa s found only in subjects excreting more than 5 mu g Cd/g creatinine. I n this group, NEP concentrations were significantly higher in the subj ects who smoked. This significant interaction could not be found for a ny other marker tested. Conclusions-The data suggest that NEP enzymuri a is high even at low exposures to Cd (with a threshold of urinary cad mium excretion (U-Cd) at 5 mu g/g creatinine), indicating early struct ural alterations. Moreover, its particular sensitivity to smoking coul d be useful in the detection of new population clusters potentially mo re susceptible to development of nephrotoxic insult.