The cytotoxicity of iodinated radiocontrast agents on renal cells in vitro

A deterioration of renal function is one preoccupying complication of iodinated radiocontrast agents in clinical practice. These compounds have direct toxic effects on renal cells, which are only in part related to their physicochemical properties. The hyperosmolal monomeric ionic radiocontrast agents, like diatrizoate, have the highest toxicity, whereas renal cells are less affected by (nonionic) compounds with reduced osmolality. The toxic effects include cellular energy failure, a disruption of calcium homeostasis, a disturbance of tubular cell polarity and programmed cell death (apoptosis). The molecular mechanisms of the direct cytotoxicity are still unclear, although oxidative stress has been implicated. Radiocontrast cytotoxicity has been demonstrated in glomerular mesangial cells and in renal epithelial cells in vitro. In vivo, the direct cellular toxicity of radiocontrast agents is compounded with alterations in blood flow and/or viscosity, ultimately resulting in renal medullary hypoxia, which is a hallmark feature of the complex clinical syndrome of radiocontrast nephropathy.     

Radiocontrast-induced renal tubular cell apoptosis: hypertonic versus oxidative stress

RATIONALE AND OBJECTIVES: Radiocontrast-induced nephropathy (RCIN) is a major complication of intravascular radiocontrast administration. Renal tubular cell apoptosis is a feature of RCIN, which is related to hypertonicity of contrast agents. Because a hyperosmolal extracellular environment induces oxidative stress via reactive oxygen species, we tested the hypothesis that antioxidants decrease hypertonicity-induced apoptosis of renal epithelial cells. We analyzed the effects of the antioxidants N-acetylcysteine (NAC) and taurine on hypertonicity-induced apoptosis of renal epithelial cells in vitro. METHODS: Madin Darby Canine Kidney (MDCK) cells were incubated with the highly hyperosmolal, ionic radiocontrast agent diatrizoate (20% vol/vol, 6 hours) or with equally hyperosmolal (640 mOsm/kg) NaCl solutions. DNA fragmentation, which is a hallmark feature of apoptosis, was assessed quantitatively using flow cytometry after propidium iodide staining and qualitatively using agarose gel electrophoresis. RESULTS: Both diatrizoate and NaCl induced DNA fragmentation in MDCK cells. Taurine (10 mmol/L) reduced DNA degradation in both diatrizoate- [79.5 +/- 2.3% versus 72.2 +/- 3.0%; P = 0.0088] and NaCl- [49.5 +/- 4.0% versus 39.4 +/- 1.0%; P = 0.0271] treated cells. In contrast, NAC (10 mmol/L) failed to reduce the DNA breakdown in this model of hypertonicity-induced renal tubular cell apoptosis. CONCLUSIONS: The radiocontrast/hypertonicity-induced DNA fragmentation of MDCK cells is attenuated by taurine but not by NAC. Because both agents are antioxidants, the antioxidant property is not sufficient for the observed cytoprotective effect. Hence, the antiapoptotic effect of taurine has to be attributed to other, yet to be defined mechanisms. Our results suggest that pharmacological doses of taurine may be particularly protective against RCIN.     

High on clopidogrel treatment platelet reactivity is frequent in acute and rare in elective stenting and can be functionally overcome by switch of therapy

The benefit of adjusted antiplatelet therapy in patients with myocardial infarction after primary percutaneous coronary intervention is not well elucidated. We aimed to identify patients with high on treatment platelet reactivity and to gradually adjust antiplatelet therapy.     

Predictors of high on-clopidogrel platelet reactivity in patients with acute coronary syndrome

High on-clopidogrel platelet reactivity (HPR) is a predictor of ischemic events after percutaneous coronary intervention. We conducted a prospective cohort study to identify variables related to HPR in acute coronary syndrome patients who are at high thrombotic risk. We enrolled 463 patients undergoing urgent coronary angiography. Platelet reactivity was measured 12–36 hours after 600?mg clopidogrel loading with multiple electrode aggregometry (Multiplate® analyzer, Roche, Basel, Switzerland, 6.4?µM ADP). HPR was defined by the consensus cut-off area under the curve >46?U. The rate of HPR was 16.0%. We analyzed simple clinical and laboratory parameters with backward multivariate logistic regression and identified the following predictors of HPR: platelet count (per G/L, OR: 1.0073, 95% CI: 1.0035–1.0112, p?=?0.0002), CRP level (per mg/L, OR: 1.0077, 95% CI: 1.0016–1.01372, p?=?0.01), and active smoking (OR: 0.51, 95% CI: 0.29–0.89, p?=?0.02). We developed and internally validated a risk prediction model demonstrating moderate discriminative capacity (area-under-the-receiver operating characteristic curve?=?0.67). In conclusion, we found a relatively low rate of high on-clopidogrel platelet reactivity (16.0%) even in an acute patient cohort. HPR measured by Multiplate was associated with high platelet count and CRP level on admission and was inversely related to active smoking. The model with rapidly available simple parameters might help to identify individuals at risk for HPR in the acute setting.     

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 (27-111 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 &mgr;g/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 diatrizioate 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. Key words: apoptosis; cytotoxicity; hypertonicity; MDCK; radiocontrast; renal failure