Nonionic iodinated contrast media: potential renal damage assessed with enzymuria

Iodixanol in Abdominal Digital Subtraction Angiography

The safety, tolerability and efficacy of iodixanol 270 mg I/ml were compared to those of iohexol 300 mg I/ml in a double-blind, randomized, parallel abdominal intra-arterial DSA phase III trial. Fifty-nine patients were included in the trial; 39 patients received iodixanol and 20 received iohexol. The mean volume of iodixanol administered was 235.8 ml (0.93 g I/kg b.w.) while the mean volume of iohexol was 254.7 ml (1.10 g I/kg b.w.). No differences in diagnostic information and radiographic density were apparent in spite of the difference in the concentration of iodine. No serious adverse events occurred. Four patients (10%) in the iodixanol group and 2 (10%) in the iohexol group experienced adverse events. Eight percent of the injections of iodixanol promoted discomfort, compared to 12%) of the injections of iohexol. An increase in S-urea and S-creatinine was seen with both agents the first day after injection, but appeared to be less pronounced with iodixanol than with iohexol. Other serum tests revealed no changes of clinical importance. Both iodixanol and iohexol were found to be effective, safe and well tolerated contrast media for abdominal intra-arterial DSA.

Effect of theophylline on contrast material-nephropathy in patients with chronic renal insufficiency: controlled, randomized, double-blinded study

PURPOSE

To investigate whether the adenosine antagonist theophylline reduces the incidence of contrast material-induced nephropathy (serum creatinine level increase of at least 0.5 mg/dL [44.2 micromol/L] in 48 hours) in high-risk patients who have chronic renal insufficiency and have received at least 100 mL of contrast medium.

MATERIALS AND METHODS

One hundred patients with serum creatinine levels of 1.3 mg/dL (114.3 micromol/L) or greater were randomly assigned to intravenously receive 200 mg theophylline or saline 30 minutes before administration of 100 mL or more of low-osmolarity contrast medium arterially (72 [72%] patients) or intravenously (28 [28%] patients).

RESULTS

Patients receiving theophylline and control subjects were comparable with regard to risk factors for contrast-induced nephropathy such as mean serum creatinine level before contrast medium administration (2.07 mg/dL +/- 0.94 [SD] [182.9 micromol/L +/- 83.1] vs 1.92 mg/dL +/- 0.76 [169.7 micromol/L +/- 67.2], respectively), amount of contrast medium (196.5 mL +/- 84.1 vs 216.6 mL +/- 95.0, respectively), and diabetes prevalence. Theophylline prophylaxis significantly reduced the incidence of contrast material-induced nephropathy (4% vs 16%; P =.046). With theophylline, the mean serum creatinine level decreased nonsignificantly 12 (1.98 mg/dL +/- 0.77 [175.0 micromol/L +/- 68.1]; P =.09), 24 (1.97 mg/dL +/- 0.75 [174.1 micromol/L +/- 68.1]; P =.99), and 48 (1.94 mg/dL +/- 0.77 [171.5 micromol/L +/- 68.1]; P =.99)(1.94 mg/dL +/- 0.77 [171.5 micromol/L +/- 68.1]; P =.99) hours after contrast medium administration. With a placebo, serum creatinine level significantly increased 24 hours after contrast medium administration (2.01 mg/dL +/- 0.89 [177.7 micromol/L +/- 78.7]; P =.006). Urinary N-acetyl-beta-glucosaminidase level did not change with theophylline administration but significantly (P =.034) increased 24 hours after contrast medium administration with the placebo.

CONCLUSION

Prophylactic administration of 200 mg theophylline reduces the incidence of contrast material-induced nephropathy in patients with chronic renal insufficiency.

Neuroimaging: do we really need new contrast agents for MRI?

The use of exogenous contrast media in magnetic resonance imaging of the brain has brought dramatic improvement in the sensitivity of detection and delineation of pathological structures, such as primary and metastatic brain tumors, inflammation and ischemia. Disruption of the blood brain barrier leads to accumulation of the intravenously injected contrast material in the extravascular space, leading to signal enhancement. Magnetic resonance angiography benefits from T(1)-shortening effects of contrast agent, improving small vessel depiction and providing vascular visualization even in situations of slow flow. High speed dynamic MRI after bolus injection of contrast media allows tracer kinetic modeling of cerebral perfusion. Progressive enhancement over serial post-contrast imaging allows modeling of vascular permeability and thus quantitative estimation of the severity of blood brain barrier disruption. With such an array of capabilities and ever improving technical abilities, it seems that the role of contrast agents in MR neuroimaging is established and the development of new agents may be superfluous. However, new agents are being developed with prolonged intravascular residence times, and with in-vivo binding of ever-increasing specificity. Intravascular, or blood pool, agents are likely to benefit magnetic resonance angiography of the carotid and cerebral vessels; future agents may allow the visualization of therapeutic drug delivery, the monitoring of, for example, gene expression, and the imaging evaluation of treatment efficacy. So while there is a substantial body of work that can be performed with currently available contrast agents, especially in conjunction with optimized image acquisition strategies, post processing, and mathematical analysis, there are still unrealized opportunities for novel contrast agent introduction, particularly those exploiting biological specificity. This article reviews the current use of contrast media in magnetic resonance neuroimaging, discusses some of the developing strategies for new applications of imaging with these agents and finally offers some views and indications for contrast agents currently under development, as well as some speculation on unsolved problems in neuroimaging, and opportunities for novel contrast agents.

Gamma-glutamyltransferase is a reliable marker for tubular effects of contrast media

The aim of this study was to evaluate the usefulness of the measurement of urinary excretion of the brush-border enzyme gamma glutamyl-transferase (GGT), in comparison with that of alanine aminopeptidase (AAP), as a marker for tubular toxicity due to contrast media (CM). Urinary activities of AAP and GGT were measured prior to the administration of CM and 1, 3 and 5 days after in forty-nine adult renal patients undergoing a radiological examination with intravascular administration of CM. The behavior of GGT was similar to that of AAP. In fact, urinary activities of both AAP and GGT increased greatly after CM. This effect was maximal on the 1st day and statistically significant for both enzymes. Furthermore, on the 1st day a relevant increase of enzyme activity (at least +50% over the basal value) was observed in the same number of patients (67%) for AAP and GGT. The concordance between GGT and AAP variations was high and statistically significant. Finally, different variables (osmolarity, dose of CM, and baseline renal function of the patients) had a similar effect on urinary excretion of AAP and GGT. The repeatability of duplicated determinations of GGT resulted better than that of AAP. In conclusion, the good concordance of the results of GGT with those of AAP justifies the use of GGT as a marker for tubular effects due to CM. Furthermore, the measurement of GGT has a better repeatability than that of AAP.

Tubular toxicity is the main renal effect of contrast media

The aim of this study is to evaluate the effects of contrast media on both tubular and glomerular function. Different parameters of tubular and glomerular function were determined before and at 1, 3, and 5 days after the intravascular administration of contrast media in 100 adult renal patients (plasma creatinine 0.6-10.8 mg/dL, mean: 1.3). Urinary activities of five tubular enzymes (alanine aminopeptidase, gamma-glutamyltransferase, alkaline phosphatase, lactate dehydrogenase, N-acetyl-beta-D-glucosaminidase) increased significantly on the first day after the administration of contrast media, indicating a tubular damage. Glomerular filtration rate and the conventional tests of glomerular function (plasma creatinine, creatinine clearance, and urinary proteins) presented only slight variations after the administration of contrast media. In conclusion, contrast media principally affected the renal tubule (as demonstrated by enzymuria), while their effects on glomerular function were very mild.

Biochemical and morphological effects of contrast media on the kidney

The intravenous use of roentgen contrast media (CM) is associated with a low incidence of renal impairment. This paper considers the intravascular handling and retention of CM in relation to effects on renal function - specifically the ability of the kidney to reabsorb and catabolise low molecular weight proteins. Renal morphology following experimental administration of a high dose of an isotonic dimeric CM (iodixanol at 3 g I/kg) in rats showed numerous, large, protein-containing vacuoles or droplets in the cells of the proximal convoluted tubule. These were fully formed within 3.5 hours. The process of vacuole-formation involving the uptake of CM appears to be analogous to dextran uptake that occurs via fluid phase endocytosis. These vacuoles or CM droplets are abundant for 7 days but then slowly decline over several weeks. The quantitative recovery of (14)C iodixanol (3g I/kg) from the kidneys between 3.5 hours to 7 days after administration was about 1% of the dose, with some 0.2% of the original dose still present at 28 days. Subcellular analysis to determine the site of the radiolabel showed that the (14)C was associated with lysosomal marker enzymes. The CM-induced vacuoles/droplets are most probably giant lysosomes, which contain the intracellularly retained CM. Co-administration of tracer doses of (125)I-labelled cytochrome C with iodixanol showed some impairment of low molecular weight protein reabsorption, but remarkably this process was not effected when the vacuoles were fully formed. The conspicuous morphology of the vacuoles, the CM retention and the transient proteinuria and enzymuria cannot presently be associated with any functionally significant impairment of tubular or cellular processes.

Contrast nephrotoxicity: predictive value of urinary enzyme markers in a rat model

RATIONALE AND OBJECTIVES

We tested whether urinary enzymes are an accurate and useful marker of renal damage in a rat model of contrast media nephrotoxicity.

METHODS

Thirty rats were pretreated with a combination of salt depletion, indomethacin, and contrast material. Alanine aminopeptidase (AAP), gamma-glutamyltranspeptidase (GGT), and N-acetyl-beta-D-glucosaminidase (NAG) were measured before and 24 hr after injection of contrast material. Enzyme concentrations were correlated with glomerular filtration rate (GFR) and histology.

RESULTS

Decreasing GFR and histopathologic changes were found only in rats treated with all three variables. NAG levels increased from baseline for both diatrizoate meglumine- and ioversol-treated animals (from 83.9 +/- 48.6 to 145.5 +/- 55.4 and from 69.41 +/- 43.6 to 123.1 +/- 50.7, respectively; P < 0.05 from baseline for ioversol) and declined in other groups. GGT and AAP levels did not correlate well with structural and functional changes.

CONCLUSIONS

In this model of contrast nephrotoxicity, NAG concentration appears to correlate with structural and functional changes associated with contrast media nephrotoxicity. However, the large range of baseline values makes this of dubious clinical use. AAP and GGT levels appear less helpful in detecting renal damage.