23 Interaction between sugarcane ash-derived silica nanoparticles and pesticides leads to mitochondrial impairment in human proximal tubular kidney cells

Abstract Epidemics of chronic kidney disease of unknown etiology (CKDu) are occurring worldwide with sugarcane workers most at risk potentially due to exposure to heat stress, particulate matter and agrochemicals. Sugarcane stalks contain approximately 80% amorphous silica and burning releases silica rich particulate matter. Previous work in our lab has identified silica nanoparticles in kidney biopsies of sugarcane workers along with high levels of pesticides in urine. We quantified the amount of pesticide found in the urine of Guatemalan sugarcane workers over the harvest season and found average levels of each pesticide present including carbofuran (35.3 nM), metolachlor (1.17 nM), paraquat (769.1 nM), and diquat (29,001 nM). We hypothesize that exposure to silica nanoparticles and pesticides synergistically contributes to kidney damage. We utilized a human proximal convoluted tubule (PCT) cell line (HK-2) and treated cells with 2.5 or 25 µg/mL of sugarcane ash derived silica nanoparticles and pesticide ranging in concentration from 0.25 to 50 µg/mL which included carbofuran, metolachlor, diquat, and paraquat. Following 6 and 24 h of exposure, we measured changes in oxygen consumption rate (OCR) and pH changes using a Seahorse XF Analyzer. Both particle treatment and pesticides decreased OCR in a concentration-dependent manner. Using FCCP to disrupt mitochondrial function, particle treated cells showed reduced mitochondrial respiration after 24 h in a dose-dependent manner, whereas paraquat and diquat-treated cells exhibited significant reductions starting at 12.5 µg/mL concentrations. These findings indicate that combined exposure to sugarcane ash and pesticides may synergistically impair mitochondrial function in human PCT cells.