Cytotoxicity of radiocontrast agents on polarized renal epithelial cell monolayers.

OBJECTIVE: Radiocontrast-induced nephropathy is a clinically important complication of coronary angiography. The cellular mechanisms of radiocontrast-induced renal dysfunction are not clear. Since tubular transport functions depend on the polarity of renal epithelial cells, we investigated the effects of radiocontrast agents on polarized tubular cells in vitro. METHODS: We studied the effects of iso-iodine concentrations (37 and 74 mg iodine/ml) of an ionic (diatrizoate) and a non-ionic (iopamidol) monomeric radiocontrast agent and of hyperosmolal mannitol control solutions on filter-grown renal epithelial cell (MDCK, LLCPK) monolayers in vitro. The cytotoxicity was assayed by measurement of cell viability, transepithelial resistance, inulin permeability and (polarized) cellular enzyme release. The polarized MDCK cell phenotype was assessed by transmission electron microscopy and indirect immunofluorescence microscopy using monoclonal antibodies against specific apical (gp135) and basal (gp60, uvomorulin) MDCK surface markers. RESULTS: The radiocontrast agents reduced cell viability to a greater extent than hyperosmolal mannitol solutions in both cell lines; diatrizoate was more toxic than iopamidol. LLCPK cells were more susceptible to radiocontrast cytotoxicity than MDCK cells. This cytotoxicity was associated with an alteration of MDCK cell polarity as assessed by the redistribution of surface marker proteins. CONCLUSIONS: Diatrizoate is more toxic than iopamidol, which is partly related to its higher osmolality. The cytotoxicity of radiocontrast agents induces a redistribution of polarized membrane proteins which could contribute to the pathophysiology of radiocontrast-induced nephropathy.

Comparative cytotoxicity of ionic and non-ionic radiocontrast agents on MDCK cell monolayers in vitro.

BACKGROUND: Intravascular radiocontrast agents may cause acute renal failure, particularly in patients with pre-existing renal insufficiency. Direct cytotoxic effects of radiocontrast agents on renal tubular cells may contribute to the pathogenesis of radiocontrast-induced nephropathy. METHODS: We analysed the cytotoxicity of the ionic radiocontrast agents diatrizoate (monomeric) and ioxaglate (dimeric), as well as of the non-ionic radiocontrast agents iohexol (monomeric) and iodixanol (dimeric) on the renal epithelial Madin Darby Canine Kidney (MDCK) cell line grown on permeable supports. The toxicity assays assessed cell viability, transmonolayer resistance and inulin permeability between the apical and basal cell culture compartment. In addition, the distribution of the tight-junction-associated membrane proteins ZO-1 and occludin was analysed using immunofluorescence microscopy. RESULTS: In all assays the high osmolal ionic compound diatrizoate had significant cytotoxic effects that included the partial redistribution of the tight-junction-associated membrane proteins into a cytoplasmic compartment. To a lesser extent this redistribution also occurred with the dimeric ionic compound ioxaglate, but not with the non-ionic radiocontrast agents. With regards to cell viability, transmonolayer resistance and inulin permeability the radiocontrast agents with reduced osmolality were significantly less toxic than diatrizoate, independent of their ionic strength. CONCLUSIONS: Physicochemical factors contribute to the cytotoxicity of radiocontrast agents in vitro. The redistribution of tight-junction-associated membrane proteins by the ionic radiocontrast agents corresponds with the loss of the barrier function of the epithelial cell monolayer, which is a major pathophysiological mechanism in acute renal failure. The radiocontrast agents with reduced osmolality are less cytotoxic than diatrizoate, independent of their ionicity. Hyperosmolality appears to be a more important determinant of the cytotoxicity of diatrizoate than ionic strength.

Radiocontrast-induced DNA fragmentation of renal tubular cells in vitro: role of hypertonicity.

BACKGROUND: Radiocontrast-induced nephropathy is a clinically important complication of invasive cardiological procedures. It has been associated with DNA fragmentation of renal tubular cells, which is a hallmark feature of programmed cell death (apoptosis). We investigated the mechanism of this DNA fragmentation in an in vitro model of radiocontrast cytotoxicity on renal epithelial cells. METHODS: Madin Darby canine kidney (MDCK) cell monolayers were incubated (for 2-8 h) with isoiodine doses (37-111 mg iodine/ml) of the highly hyperosmolal, ionic radiocontrast agent diatrizoate or of the less hyperosmolal, non-ionic substance iopamidol. Mannitol, urea, and NaCl control media of corresponding hyperosmolality were used to evaluate the contribution of hypertonicity, hyperosmolality and/or ionic strength to radiocontrast toxicity. DNA fragmentation was assessed using fluorescence-activated cell sorting (FACS), agarose gel electrophoresis and terminal deoxynucleotidyl transferase-mediated deoxyuridine nick end labelling (TUNEL), cell morphology was analysed in Giemsa-stained cytospins. RESULTS: Diatrizoate induced concentration- and time-dependent DNA fragmentation of MDCK cells which was associated with morphological signs of apoptosis. Cycloheximide (1 microg/ml) did not prevent diatrizoate-induced DNA fragmentation, indicating that it is not dependent on protein synthesis. Diatrizoate-mediated cell death was associated with cell detachment from the tissue culture matrix. However, the DNA fragmentation is not a consequence of cell detachment since the prevention of cell attachment on agarose-coated dishes induced significantly less DNA fragmentation than diatrizoate. Iopamidol caused no detectable DNA breakdown. In contrast, hypertonic mannitol and sodium chloride, but not hyperosmolal urea, induced DNA fragmentation in MDCK cells, albeit less than diatrizoate. CONCLUSIONS: The DNA fragmentation of MDCK cells induced by diatrizoate is related to its hypertonicity in this in vitro model of radiocontrast cytotoxicity. Nuclear disintegration with subsequent cell death may contribute to the pathophysiology of radiocontrast-induced nephropathy, particularly in the hypertonic/hypoxic environment of the renal medulla. The present results underscore the importance of avoiding hyperosmolal urine states in patients at high risk of radiocontrast-induced nephropathy.