Acute lead (Pb2+) exposure increases calcium oxalate crystallization in the inner medullary collecting duct, and is ameliorated by Ca2+/Mg2+-ATPase inhibition, as well as Capa receptor and SPoCk C knockdown in a Drosophila melanogaster model of nephrolithiasis

Abstract

Calcium oxalate (CaOx) kidney stones accumulate within the renal tubule due to high concentrations of insoluble deposits in the urine. Pb²⁺-induced Ca²⁺ mobilization along with Pb²⁺-induced nephrotoxic effects within the proximal tubule have been well established; however, Pb²⁺ mediated effects within the collecting duct remains insufficiently studied. Thus in vitro and ex vivo model systems were treated with increasing concentrations of lead (II) acetate (PbAc) ± sodium oxalate (Na₂C₂O₄) for 1 h, both individually and in combination. Pb²⁺-mediated solution turbidity increased 2 to 5 times greater post-exposure to 75, 100 and 200 μM Pb²⁺ with the additional co-treatment of 10 mM oxalate in mouse inner medullary collecting duct (mIMCD-3) cells. Additionally, 100 μM and 200 μM Pb²⁺ alone induced significant levels of intracellular Ca²⁺ release. To validate Pb²⁺-mediated effects on the formation of CaOx crystals, alizarin red staining confirmed the presence of CaOx crystallization. Pb²⁺-induced intracellular Ca²⁺ was also observed ex vivo in fly Malpighian tubules with significant increases in CaOx crystal formation via Pb²⁺-induced intracellular Ca²⁺ release significantly increasing the average crystal number, size, and total area of crystal formation, which was ameliorated by tissue-specific SPoCk C transporter and Capa receptor knockdown. These studies demonstrate Pb²⁺-induced Ca²⁺ release likely increases the formation of CaOx crystals, which is modulated by a G_q-linked mechanism with concurrent Ca²⁺ extracellular mobilization.