Erythrophagocytosis of lead-exposed erythrocytes by renal tubular cells: Possible role in lead-induced nephrotoxicity

Background: Nephrotoxicity associated with lead poisoning has been frequently reported in epidemiological studies, but the underlying mechanisms have not been fully described. oBjectives: We examined the role of erythrocytes, one of the major lead reservoirs, in leadassociated nephrotoxicity. Methods and results: Co-incubation of lead-exposed human erythrocytes with HK-2 human renal proximal tubular cells resulted in renal tubular cytotoxicity, suggesting a role of erythro cytes in lead-induced nephrotoxicity. Morphological and flow cytometric analyses revealed that HK-2 cells actively phagocytized lead-exposed erythro cytes, which was associated with phosphatidylserine (PS) externalization on the erythro cyte membrane and generation of PS-bearing microvesicles. Increased oxidative stress and up-regulation of nephrotoxic biomarkers, such as NGAL, were observed in HK-2 cells undergoing erythrophagocytosis. Moreover, TGF-β, a marker of fibrosis, was also significantly up-regulated. We examined the significance of erythro phago cytosis in leadinduced nephrotoxicity in rats exposed to lead via drinking water for 12 weeks. We observed iron deposition and generation of oxidative stress in renal tissues of lead-exposed rats, as well as the histopathological alterations such as tubulo interstitial lesions, fibrosis, and up-regulation of KIM-1, NGAL, and TGF-β. conclusions: Our data strongly suggest that erythrophagocytosis and subsequent iron deposition in renal tubular cells could significantly enhance nephrotoxicity following lead exposure, providing insight on lead-associated kidney damages.