Ultrastructural Studies of the Reaction of Urate Crystals with a Cultured Renal Tubular Cell Line

Abstract

Hypotheses concerning the development of uric acid and gouty nephropathy suggest that the initiating disease mechanism involves an interaction between uric acid or monosodium urate monohydrate (MSUM) crystals and renal tubular epithelial cells. We have studied the interaction of these crystals with Madin-Darby canine kidney (MDCK) cells, which exhibit many of the characteristics of cells of the collecting duct epithelium. Addition of MSUM crystals to monolayer cultures of MDCK cells leads to the formation of reaction sites, localised areas which are raised above the monolayer forming a 3-dimensional structure. These reaction sites are evident within 4-8 h and appear to be initiated by the interaction of a single crystal or small number of crystals with a single cell. With time, both cells and crystals accumulate at the site. By 24 h most reaction sites involve 6-12 cells and numerous crystals. Interaction of MSUM crystals and MDCK cells not only involves the attachment of crystals to cells but, by 8 h, some crystals appear to be completely or partially covered by the cell membrane, and MDCK cells appear to react by growing around the crystals. Transmission electron microscopy shows that crystals are found not only within cells, but also within the intercellular spaces. Within the cells, crystals have been shown in vacuoles containing lysosomal enzymes, indicating the formation of a phagolysosome. Ultimately, enzyme release occurs. These studies support the hypothesis that some interstitial deposits of urate and uric acid in the kidney may be derived from intratubular deposits that react with the tubular epithelium and pass into the interstitium; loss of tubular integrity may not be a prerequisite for crystal migration.