Differential effects of low-level lead exposure on the natural isozymes of erythrocyte 5'-nucleotidase.
OBJECTIVE
Erythrocyte pyrimidine 5'-nucleotidase (Pyr-5'-N) is highly sensitive to heavy metal inactivation in vitro and in vivo, and a number of studies have verified its usefulness as a biomarker of acute and chronic lead exposures. Retrospective and prospective studies attempted to determine whether the known linearity of Pyr-5'-N inhibition by lead concentrations above 40 microg/dL whole blood might continue into the lowest range of exposures now considered to be toxic in children (<10-20 microg/dL), thereby extending its value as a biomarker of lead exposure.


METHODS
Activities of Pyr-5'-N and a lead-insensitive isozyme, deoxyribonucleotidase (d-5'-N), were compared to blood lead and free erythrocyte protoporphyrin (FEP) concentrations.


RESULTS
Pyr-5'-N activities in erythrocytes from 70 children displayed an inverse linear correlation with whole blood lead of 1-35 microg/dL, whereas d-5'-N did not correlate. There was no apparent minimum threshold for Pyr-5'-N inhibition by lead.


CONCLUSIONS
Linearity of Pyr-5'-N inhibition by lead extends throughout the range of clinical concern in pediatric cases. Pyr-5'-N/d-5'-N activity ratios may provide an even more sensitive, internally controlled biomarker of low-level lead overburden, since both isozymes vary comparably in activity as a function of reticulocytosis and mean red cell age.
Paglia
D E
DE
Department of Pathology and Laboratory Medicine, UCLA School of Medicine, Los Angeles, California, USA 90095-1732, USA. dpaglia@pathology.medsch.ucla.edu
Renner
S W
SW
Bhambhani
K
K
D015720:5'-Nucleotidase / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D007223:Infant; D007527:Isoenzymes / Q000097:blood*; D007855:Lead Poisoning / Q000097:blood / Q000201:enzymology*; D012189:Retrospective Studies
D007527:Isoenzymes; D015720:5'-Nucleotidase