Decreased paraoxonase 1 activity and increased oxidative stress in low lead-exposed workers

Paraoxonase 1 (PON1) has been proposed as an antioxidant enzyme. Although lead-inhibited PON1 activity has been demonstrated mostly based on in vitro experiments, it is uncertain whether this phenomenon is relevant in pathogenesis of lead-induced oxidative stress in the lead exposure. We examined associations of blood lead levels (BLL) and PON1 activity along with oxidative stress parameters in lead exposure workers. We determined malondialdehyde (MDA), conjugated diene (CD), total peroxides (TP), total antioxidant status (TAS), the oxidative stress index (OSI), and PON1 activity in earthenware factory workers (n = 60) and control subjects (n = 65). The lead-exposed group significantly increased lipid peroxidation parameters and OSI compared to the control group (p < 0.001). The lead-exposed group had significantly decreased PON1 activity and TAS levels compared to the control group (p < 0.001). Multiple linear regression analysis revealed that BLL were significantly correlated with decreased TAS (r = -0.496) and PON1 activity (r = -0.434), but with increased CD (r = 0.694), TP (r = 0.614), MDA (r = 0.788), and OSI (r = 0.722). Interestingly, BLL at 10 µg/dL significantly decreased PON1 activity and increased oxidative stress parameters with insignificant changes in other biochemical and hematological parameters. Altogether, the reduction of PON1 activity may associate in an imbalance in pro-oxidants and antioxidants, leading to oxidative damage in lead-exposed workers even at low BLL.