**5.3 Cytotoxic effects on renal tubular cells**

Investigations performed in vitro on cell lines are used to assess the renal tubular cell function or damage. A porcine cell line of renal proximal tubules, LLC-PK1, was used by Hardiek et al. [55] to investigate the occurrence of CIN. An effect on apoptosis was not elucidated, even though proliferation was impaired. Diminished proliferation will have a hazardous effect on renal function with a delay of hours to days, which may help in explaining the course of CIN. Independent of the contrast media used, tubular cell damage can occur. A more specific distortion of proximal tubular function seems to be a perturbation of mitochondrial enzymatic activity and mitochondrial membrane potential [56]. The degree of mitochondrial enzymatic activity impairment depends mainly on two features of the contrast media: the ionic nature as well as the molecular structure. Remarkably, low-osmolar contrast media had the least observed effects, followed by the iso-osmolar contrast media. Ionic compounds showed the most deleterious effects [56]. In the distal tubule, contrast media may trigger apoptotic effects in the cells, as depicted in the Madin-Darby canine kidney (MDCK) cell line model [57].
