Induction of morphological changes in the urothelium of cultured adult rat bladder by sodium saccharin and sodium cyclamate

The direct effects of sodium saccharin and sodium cyclamate on the morphology of organ cultures of normal rat bladder have been studied by histology and scanning electron microscopy (SEM). Untreated cultures retained histologically normal urothelia up to 89 days with cell surface features characteristic of mature, fully differentiated superficial cells and maturing intermediate cells. Continuous treatment with either sodium saccharin (6 or 12 mM) or sodium cyclamate (12 or 24 mM) induced progressive abnormalities in the cultured urothelium. Acute toxicity was not seen but focal necrosis was observed with the higher dose of each compound and histological abnormalities were more severe with the higher doses. Sodium saccharin induced mild hyperplasia of the urothelium on the surface of the culture and foci of altered epithelial polarity from 14 days; abnormal nuclear staining plus changes in the basal lamina were evident from 28 days and were pronounced from 56 days onwards. Hyperplasia of the urothelium over the explants was mild but there were extensive epithelial outgrowths onto the culture support. In general, sodium cyclamate induced more severe changes than did sodium saccharin, with alterations in epithelial cell polarity plus basal cell changes from 14 days and focal nodular urothelial hyperplasia over the explant and gross hyperplasia between the explant and culture support and in the outgrowth from 28 days. The severe and rapid surface changes, evident by SEM, were similar both in saccharin-treated and in cyclamate-treated cultures. There was some early loss of superficial cells to reveal underlying immature cells which, together with the remaining mature cells, developed abnormal blebs and processes. From 14 days small immature cells were located at the culture surface between the mature cells. These were covered by a variety of membrane protrusions including long pleomorphic microvilli. Sodium cyclamate-treated cultures mostly had fewer small membrane protrusions than sodium saccharin-treated cultures but more pleomorphic microvilli. These morphological changes induced in the rat urothelium in vitro by direct treatment with sodium saccharin and sodium cyclamate are thus similar to those described previously in association with in vivo long-term feeding studies of sodium saccharin to rats and with both in vivo and in vitro treatment of the rat urothelium with the bladder carcinogen N-methyl-N-nitrosourea (MNU).