Oxalate and Calcium Oxalate (CaOx) Crystal Involvement in Production of Urinary Macromolecules in an Animal Model of Nephrolithiasis

Hyperoxaluria induced CaOx nephrolithiasis is associated with increased production of reactive oxygen species and macromolecules such as osteopontin (OPN), kidney injury molecule (KIM), monocyte chemoattractant-protein-1 (MCP-1) and ED-1. It is however unclear whether oxalate or CaOx crystals are responsible for the increases. We investigated this aspect in hydroxy l proline (HLP) induced hyperoxaluria where after 28 days of consuming HLP, only half of the rats (3 of 6) developed heavy deposition of CaOx crystals in the rat kidneys. Male Sprague-Dawley rats were given 5% HLP in food. Urine was collected on days 7, 14 and 28, when rats were sacrificed. Urinary excretion of oxalate, hydrogen peroxide (H2O2), OPN, MCP-1, KIM-1 was determined using ELISA kits. Renal expression of OPN, MCP-1, ED-1, KIM-1 was examined immunohistochemically. We also looked at the differential expression of genes for the 4 macromolecules using microarray analysis. Comparisons were made between rat kidneys from only hyperoxaluric (Ox) rats and those which were hyperoxaluric and had heavy deposition of CaOx crystals (Ctl). All rats had similar increases in urinary excretion of oxalate and H2O2. Both Ox and Ctl rats showed significant increases in the relative expression of genes as well as excretion of KIM-1, MCP-1, and OPN. But differences between urinary excretion by Ox and Ctl rats were highly significant, particularly MCP-1 and OPN production. Results suggest that hyperoxaluria may start the process which becomes more pronounced with CaOx crystal deposition. Research supported by NIH grant R01 DK 6078602