Toxicity of acetaminophen,salicylic acid,and caffeine for first-passage rat renal inner medullary collecting duct cells

Chronic excess ingestion of nonsteroid anti-inflammatory drugs causes renal medullary necrosis. Previously, using an immortalized line of mouse inner medullary collecting ducts cells (mIMCD3), we found that acetaminophen, salicylic acid, and caffeine are toxic, and the effects of acetaminophen and caffeine are strongly additive. Furthermore, toxicity was greater in proliferating than in nonproliferating cells. Important limitations were that mIMCD3 cells do not readily tolerate the high concentrations of salt and urea normally present in renal inner medullas and proliferate much more rapidly than inner medullary cells in vivo. Thus, these cells may not serve as an appropriate model for the in vivo IMCD. The present studies address these limitations by using passage-1 rat inner medullary collecting duct (p1rIMCD) cells, which tolerate high salt and urea and become contact inhibited when confluent. At 640 mOsmol/kg (the lowest normal inner medullary osmolality), the drugs, singly and in combination, reduce the number of proliferating (i.e., subconfluent) p1rIMCD cells more than they do confluent cells. Effects of acetaminophen and caffeine are strongly additive. Addition of as little as 0.1 mM caffeine significantly enhances the toxicity of acetaminophen plus salicylic acid. With confluent cells at 640 mOsmol/kg and very slowly growing cells at 1370 mOsmol/kg, combinations of drugs that include acetaminophen increase proliferation, accompanied by DNA damage and apoptosis. We conclude that these drugs are toxic to renal inner medullary collecting duct cells under the conditions of high osmolality normally present in the inner medulla, that combinations of the drugs are more toxic than are the drugs individually, and that the toxicity includes induction of proliferation of these cells that are otherwise quiescent in the presence of high osmolality.