Interaction of Sugacane Ash-Derived Silica Particles and Pesticides on Renal Cell Metabolism and the Thiol Redox Proteome

Chronic kidney disease of unknown etiology (CKDu) is an epidemic which is increasingly prevalent among agricultural workers and nearby communities, particularly those involved in the harvest of sugarcane. CKDu has impacted tens of thousands of individuals worldwide and there is currently no established mechanism of disease pathogenesis.  While CKDu is likely multifactorial, occupational exposure to silica particles, a major constituent within sugarcane ash, has gained increased attention as a potential contributor. In fact, our group has reported the presence of SiNPs in kidney biopsies of individuals with CKDu.  In addition, our group has reported multiple pesticides present in the urine of sugarcane workers.  Importantly, both silica and pesticides have high potential for generation of reactive oxygen species (ROS), and their accumulation in kidney could result in oxidative stress induced kidney damage consistent with CKDu pathology. 

For this study, both silica (derived from sugarcane ash) and pesticides (paraquat, diquat, metalochlor and carbofuran) and their interactions were evaluated using human kidney proximal convoluted tubule (PCT) cells.  In addition, pesticide levels were quantified in urine of sugarcane workers.  HK-2 and primary human PCT cells were evaluated for changes to cellular energy metabolism by Seahorse and redox state were determined. To determine how the cellular redox environment may influence PCT cell function and toxicity, the redox proteome was examined using cysteine-targeted click chemistry proteomics.

Treatment of PCT cells with sugarcane ash derived silica particles (2.5-25 ug/ml) or pesticides (0.5-5 ug/ml) resulted in mitochondrial membrane hyperpolarization, inhibited mitochondrial respiration and increased both cytoplasmic and mitochondrial reactive oxygen species generation.  Importantly, silica exposure induced changes that were associated with redox proteomic trends (oxidation or reduction of thiols) suggesting activation of aryl hydrocarbon receptor (AHR) and other signaling pathways with known roles in mitochondrial inhibition and CKD progression. 

Overall, results suggest that PCT cell exposure to silica particles and pesticides could promote glycolytic and fibrotic shifts consistent with CKDu pathology via oxidative stress-mediated disruption of redox signaling pathways.