ASSESSMENT OF Ca²⁺ ATPase ACTIVITY AND MARKERS OF OXIDATIVE STRESS IN INDIVIDUALS OCCUPATIONALLY EXPOSED TO LEAD

Abstract

Lead (Ph²⁺) is an environmental toxicant which causes serious occupational diseases that are of major public health significance. Lead intoxication may arise from acute or chronic exposure and may alter calcium homeostasis leading to oxidative stress within human system. There are conflicting reports on the effect of lead on the activities of Ca²⁺ ATPase and oxidative stress. The aim of this study was to purify calcium ATPase, assess Blood Lead Levels (BLL), evaluate the activity of endogenous antioxidant enzymes and the production of reactive oxygen species in the blood of workers occupationally-exposed to lead. Forty consenting occupationally-exposed subjects: Battery chargers (BC, n=20), Spray painters (SP, n=10) and Auto Mechanics (AM, n=10) and fifteen consenting occupationally- unexposed subjects (control) were recruited from lbadan municipality. All subjects were aged between 25 and 55 years and those exposed to lead for at least 10 years. Blood samples (20ml) were collected from all subjects into ethylene diamine tetra- acetic acid tubes. Calmodulin-deficient ghost membranes were prepared from the crytherocytes and Ca²⁺-ATPase activity was assayed spectrophotometrically in the absence and presence of calmodulin. The BLL, biochemical and hematological profiles viz total protein, albumin, cholesterol and C-reactive protein (C-RP), antioxidant biomarkers such as Superoxide Dismutase (SOD), Catalase (CAT). Reduced Glutathione (GSH), Malondialdehyde (MDA), Total Antioxidant status. Total Plasma Peroxide (TPP) and Oxidative Stress Index (OSI) were by assayed by spectrophotometric techniques. Data were analysed using student's t-test and ANOVA at p=0.05. The BLL in BC (51.5±18.8 ug/dL), SP (35.8±10.1 ug/dL), AM (10.6±2.5 ug/dL) were significantly higher relative to control (8.5±4.5 ug/dL). The Ca²⁺-ATPase activities in BC (0.3) ± 0.02 umol/mg/h), SP (0.4± 0.03 umol/mg/h) and AM (0.6 ± 0.02 umol/mg/h) was significantly reduced relative to control (0.9 ± 0.03 umol/mg/h), in the presence of calmodulin, basal ATPase activity was increased by 68.4% in BC, 67.8% in SP and 68.2% in AM relative to control. The C-RP levels were higher in BC (16.0±10.1mg/L). SP (11.3±5.8mg/L) and AM (6.0±2.7mg/L) compared to control (3.1±1.5 mg/L). Cholesterol levels increased significantly only in BC (192.7± 26.4mg/L) when compared to control (160.6±8.0mg/L). The levels of MDA were higher in all lead-exposed workers: BC (9.3±0.8 nM/ml), SP (8.1± 1.2 nM/ml) and AM (7.3±0.5 nM/ml) relative to control (5.1±0.8 nM/ml). The levels of the antioxidant markers: CAT (0.02 ±0.01, 0.03 ±0.00, 0.03 ± 0.00 umol H₂O₂), SOD (0.3± 0.24, 0.2± 0.17, 0.8± 0.30 SOD units) and GSH (51.0 ± 4.39, 42.5± 8.92, 38.2 ± 8.57 umol/g) respectively, were all significantly reduced in BC, SP and AM when compared to the controls. Catalytic activities of the erythrocyte membrane Ca²⁺-ATPase were reduced in subjects occupationally-exposed to lead. Lead toxicity may be due to oxidative damage of the plasma membrane and its interaction with the catalytic cycle and calcium transport mechanism of the pump.