Silica Nephropathy and Chronic Kidney Disease of Unknown Etiology

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Project Summary Epidemics of chronic kidney disease of unknown etiology (CKDu) have emerged along the Pacific Coast of Central America (Mesoamerican Nephropathy), in northern Sri Lanka (Sri Lankan nephropathy), in Andhra Pradesh and other regions of India (Uddanam Nephropathy), and in Veracruz, Mexico. In all cases, the primary histologic finding is chronic interstitial nephritis with variable degrees of glomerulosclerosis. To date a variety of causes have been considered, including heavy metals, agrochemicals, infectious diseases, and recurrent heat stress and dehydration. Here we evaluate the novel hypothesis that amorphous silica, released into the air during the burning of sugarcane and rice, may be a primary cause. The evidence supporting this hypothesis consists of the following: 1. Amorphous silica is present in sugarcane and rice and is released when sugarcane is burned or rice husks are burned each season. 2. The particular matter fraction (PM2.5) of burned sugarcane and rice contains 80-90 percent amorphous, nanoparticle sized silica. 3. Both PM2.5 and exposure to silica is associated with risk for CKD, and records show that the amount of burning of sugarcane in Central America and of rice in Sri Lanka parallel the epidemics in these countries. 4. Rats administered amorphous nanoparticle sized silica develop CKD with minimal respiratory signs and the biopsies show chronic interstitial nephritis with silica particles in tubules. 5. Human biopsies of subjects with Mesoamerican Nephropathy, Sri Lankan Nephropathy, and Uddanam nephropathy show dramatic presence of amorphous nano-sized silica particles in tubules compared to controls by darkfield spectral microscopy and confirmed by ICP-mass spectrometry of the kidney tissues. Given these findings, we propose to 1) Identify the Route(s) and Mechanisms by which nanoparticle silica may cause kidney injury in a rat model, evaluating both oral and intranasal approaches; varying the nanoparticle size, and doing both a time and dose response; evaluating the potentially synergistic effect of heat; determining if the mechanism involves lysosomal uptake and inflammasome activation; evaluating if other organs (such as the lung) are involved, and testing the therapeutic potential of mycophenolate and allopurinol. 2) To characterize the silica in the kidney biopsy tissue and urine using ICP-MS, Raman spectroscopy, electron microscopy and enhanced darkfield hyperspectral imaging. 3) To identify the Impact of Silica Nephropathy in both Epidemic CKDu and Other Renal Diseases by better characterizing silica nephropathy in kidney biopsies from known epidemic areas, predicting and testing for silica nephropathy in other regions where sugarcane is burned (or not); and 4) Evaluating previously collected kidney biopsies in Denver and Stockholm, and other areas of the world to determine if silica is increased in CKDu compared to other renal diseases. These studies will characterize silica nephropathy, possibly one of the first major kidney diseases associated with air pollution, and with major implications for nephrology, public health, environmental safety, and human and animal health.