RADIOCONTRAST-INDUCED DNA FRAGMENTATION OF RENAL TUBULAR CELLS IN-VITRO - ROLE OF HYPERTONICITY

Background. Radiocontrast-induced nephropathy is a clinically importan t complication of invasive cardiological procedures. It has been assoc iated with DNA fragmentation of renal tubular cells, which is a hallma rk feature of programmed cell death (apoptosis). We investigated the m echanism of this DNA fragmentation in an in vitro model of radiocontra st cytotoxicity on renal epithelial cells. Methods. Madin Darby canine kidney (MDCK) cell monolayers were incubated (for 2-8 h) with isoiodi ne doses (37-111 mg iodine/ml) of the highly hyperosmolal, ionic radio contrast agent diatrizoate or of the less hyperosmolal, non-ionic subs tance iopamidol. Mannitol, urea, and NaCl control media of correspondi ng hyperosmolality were used to evaluate the contribution of hypertoni city, hyperosmolality and/or ionic strength to radiocontrast toxicity. DNA fragmentation was assessed using fluorescence-activated cell sort ing (FACS), agarose gel electrophoresis and terminal deoxynucleotidyl transferase-mediated deoxyuridine nick end labelling (TUNEL), cell mor phology was analysed in Giemsa-stained cytospins. Results. Diatrizoate induced concentration-and time-dependent DNA fragmentation of MDCK ce lls which was associated with morphological signs of apoptosis. Cycloh eximide (1 mu g/ml) did not prevent diatrizoate-induced DNA fragmentat ion, indicating that it is not dependent on protein synthesis. Diatriz oate-mediated cell death was associated with cell detachment from the tissue culture matrix. However, the DNA fragmentation is not a consequ ence of cell detachment since the prevention of cell attachment on aga rose-coated dishes induced significantly less DNA fragmentation than d iatrizoate. Iopamidol caused no detectable DNA breakdown. In contrast, hypertonic mannitol and sodium chloride, but not hyperosmolal urea, i nduced DNA fragmentation in MDCK cells, albeit less than diatrizoate. Conclusions. The DNA fragmentation of MDCK cells induced by diatrizoat e is related to its hypertonicity in this in vitro model of radiocontr ast cytotoxicity. Nuclear disintegration with subsequent cell death ma y contribute to the pathophysiology of radiocontrast-induced nephropat hy, particularly in the hypertonic/hypoxic environment of the renal me dulla. The present results underscore the importance of avoiding hyper osmolal urine states in patients at high risk of radiocontrast-induced nephropathy.