Associations between Lead Exposure and Dose and Protein Kinase C Activation in Erythrocytes Among Lead Workers

Hwang, Kyu Yoon; Hwangbo, Young; Ahn, Hyun Cheol; Kim, Yong Bae; Lee, Gap Soo; Lee, Sung Soo; Ahn, Kyu Dong; Lee, Byung Kook

Abstract

OBJECTIVES
Protein kinase C(PKC), a calcium and phospholipid dependent enzyme, is activated by lead in vitro at picomolar concentrations. However, the effect of lead on PKC has never been studied in a human population. The purpose of the study was to evaluate whether lead exposure was associated with PKC mediated-phosphorylation in erythrocytes among lead workers.
METHODS
Two hundred and twelve lead workers were studied. To determine the levels of phosphorylation in vivo, an in vitro back phosphorylation technique was used by adding PKC and gamma-32P to preparations of erythrocyte membranes. We measured back phosphorylations of erythrocyte membrane proteins, spectrin, and 52 kDa and 48 kDa, as an indirect measure of PKC activation in vivo.
RESULTS
The mean(SD) age and exposure duration was 39.1(10.0) years and 8.1(6.5) years, respectively. Tibial lead ranged from 0.8 to 290.8 microgram Pb/g bone mineral with a mean(SD) of 34.4(35.2) microgram Pb/g bone mineral. The means(SD) of back phosphorylation levels of the three proteins were 540.7(304.1), 198.6(78.2), and 247.7(83.3) photostimulated luminescence units(PSL), respectively, by phosphoimager. After adjustment for potential confounding factors, tibial lead and exposure duration were significantly and inversely associated with back phosphorylation levels. One unit of increase in tibial lead(1 microgram Pb/g bone mineral) is associated with a decline in spectrin, band 4.9 52 kDa, and band 4.9 48 kDa back phosphorylation levels by 1.4(P<0.05), 0.34(P<0.05), and 0.47(P<0.01), respectively. However, there were no associations between the back phosphorylation levels and either blood lead or ZPP levels.
CONCLUSIONS
These findings suggest that the PKC activity in erythrocytes is increased by chronic lead exposure and that erythrocyte membrane protein phosphorylation may be a biomarker of lead exposure.