Pyruvate Kinase Activity and δ-Aminolevulinic Acid Dehydratase Activity as Biomarkers of Toxicity in Workers Exposed to Lead

Abstract

Lead (Pb(2+)) is a heavy metal that has long been used by humans for a wide range of technological purposes, which is the main reason for its current widespread distribution. Pb(2+) is thought to enter erythrocytes through anion exchange and to remain in the cell by binding to thiol groups. Pyruvate kinase (PK) is a thiol-containing enzyme that plays a key role in erythrocyte cellular energy homeostasis. δ-aminolevulinic acid dehydratase (δ-ALAD) is the second enzyme in the heme biosynthetic pathway and plays a role in the pathogenesis of Pb poisoning. Our primary objective was to investigate the effect of Pb(2+) on the activity of the thiolenzymes δ-ALAD and PK and on the concentration of glutathione (GSH), a nonenzymatic antioxidant defense, in erythrocytes from Pb-exposed workers. The study sample comprised 22 male Pb workers and 21 normal volunteers (15 men and 6 women). The Pb-exposed workers were employed in manufacturing and recycling of automotive batteries. Basic red-cell parameters were assayed and total white blood cell counts performed. PK and δ-ALAD activity and blood Pb (BPb) concentrations were determined in all subjects. Pb-exposed individuals had significantly greater BPb levels than controls. Both PK and δ-ALAD activity levels were significantly lower in Pb-exposed individuals than in controls. Pb significantly inhibited PK and δ-ALAD activity in a dose-dependent manner. We found that erythrocyte GSH levels were lower in Pb-exposed individuals than normal volunteers. Pb-exposed individuals had lower values than controls for several red cell parameters (hemoglobin, hematocrit, red blood cell count, mean corpuscular volume). These results suggest that Pb inhibits δ-ALAD and PK activity by interacting with their thiol groups. It is therefore possible that Pb disrupts energy homeostasis and may be linked with decreased glucose metabolism because it affects the heme synthesis pathway in erythrocytes, contributing to the cell dysfunction observed in these in Pb-exposed individuals. These results indicate an apparent dose-effect relationship between PK activity and BPb. PK activity in human erythrocytes can be used for biological monitoring of Pb exposure. Study of the mechanisms by which Pb acts may contribute to greater understanding of the symptoms caused by Pb.

Association between Blood Lead Levels and Delta-Aminolevulinic Acid Dehydratase in Pregnant Women

“…They concluded that the possible threshold value of blood lead for ALAD activity is around 10 µg/dL, and thus, ALAD activity may be usedas a biomarker for evaluation of lead toxicity in humans. Similar results were reported by Fecsa et al; who analyzed lead dose-dependent effects for 18 lead exposed individuals and 12 normal volunteers [21]. Jasim et al also reported a decrease of ALAD activity in battery manufacturing factory workers compared to non-exposed group; furthermore, this decrease became even more evident with increased duration of exposure [28].…”

“…For that reason, some researchers have recommended use of ALAD inhibition as an indicator of lead intoxication [12,21,29]. In our study, ALAD activity was significantly lower in women with BLLs ≥ 5 µg/dL compared with those with BLLs below 5 µg/dL.…”

“…Studies reporting high levels of lead in blood revealed significant negative correlations between blood lead concentrations and ALAD activity [12,21,22]. However, some authors have demonstrated that ALAD inhibition occurs at levels of lead in blood around 5 µg/dL [15,16,23].…”

Lead Exposure and Oxidative Stress: A Systematic Review

“…In 3 studies, GSH levels decreased in the exposed group (Mohammad et al 2008 ;Feksa et al 2012 ;Kasperczyk et al 2013b ) and were negatively correlated with BLLs in the Lead Exposure and Oxidative Stress: A Systematic Review 226 other study ( r = −0.423; p < 0.001) (Roels et al 1975 ). However, GSH levels increased in the exposed group and were also negatively correlated with ALAD levels in another study (Gurer-Orhan et al 2004 ;Conterato et al 2013 ).…”

Synergistic protective effect of Beta vulgaris with meso-2,3-dimercaptosuccinic acid against lead-induced neurotoxicity in male rats

“…The reduction in Hb may be related to inhibition of its biosynthesis through the inhibition of δ-aminolevulinic acid synthase, δ-ALA dehydratase and ferrochelatase by Pb 40 . Additionally, Pb can bind with RBCs and inhibits pyruvate kinase "keeps cellular energy homeostasis" 42 and pyrimidine 5′-nucleotidase (essential for RBCs www.nature.com/scientificreports/ maturation) 43 . The inhibition of these enzymes destabilizes the RBCs membrane and decreases its fluidity leading to a shortage of the erythrocyte life span, hemolytic anemia, and ROS generation 42,43 .…”