NEPHROTOXICITY TESTING IN-VITRO - WHAT WE KNOW AND WHAT WE NEED TO KNOW

The kidney is affected by many chemicals. Some of the chemicals may ev en contribute to endstage renal disease and thus contribute considerab ly to health care costs. Because of the large functional reserve oi th e kidney, which masks signs of dysfunction, early diagnosis of renal d isease is often difficult. Although numerous studies aimed at understa nding the mechanisms underlying chemicals and drugs that target variou s renal cell types have delivered enough understanding for a reasonabl e risk assessment, there is still an urgent need to better understand the mechanisms leading to renal cell injury and organ dysfunction. The increasing use of in vitro techniques using isolated renal cells, nep hron fragments, or cell cultures derived from specific renal cell type s has improved our insight into the molecular mechanisms involved in n ephrotoxicity. A short overview is given on the various in vitro syste ms currently used to clarify mechanistic aspects leading to sublethal or lethal injury of the functionally most important nephron epithelial cells derived from various species. Whereas freshly isolated cells an d nephron fragments appear to represent a sufficient basis to study ac ute effects (hours) of nephrotoxins, e.g., on cell metabolism, primary cultures of these cells are more appropriate to study long-term effec ts. In contrast to isolated cells and fragments, however, primary cult ures tend to first lose several of their in vivo metabolic properties during culture, and second to have only a limited life span (days to w eeks). Moreover, establishing such primary cultures is a lime-consumin g and laborious procedure. For that reason many studies have been carr ied out on renal cell lines, which are easy to cultivate in large quan tities and which have an unlimited life span. Unfortunately none of th e lines display a slate of differentiation comparable to that of fresh ly isolated cells or their primary cultures. Most often they lack expr ession of key functions (e.g., gluconeogenesis or organic anion transp ort) of their in vivo correspondents. Therefore, the use of cell lines for assessment of nephrotoxic mechanisms will be limited to those fun ctions the lines express. Upcoming molecular biology approaches such a s the transduction of immortalizing genes into primary cultures and th e utilization of cells from transgenic animals may in the near future result in the availability of highly differentiated renal cells with m arkedly extended life spans and near in vivo characteristics that may facilitate the use of renal cell culture for routine screening of neph rotoxins.