Renal effects of iodixanol in healthy volunteers and patients with severe renal failure

Urine metabolomic analysis to detect metabolites associated with the development of contrast induced nephropathy

Objective

Contrast induced nephropathy (CIN) is a result of injury to the proximal tubules. The incidence of CIN is around 11% for imaging done in the acute care setting. We aim to analyze the metabolic patterns in the urine, before and after dosing with intravenous contrast for computed tomography (CT) imaging of the chest, to determine if metabolomic changes exist in patients who develop CIN.

Methods

A convenience sample of high risk patients undergoing a chest CT with intravenous contrast were eligible for enrollment. Urine samples were collected prior to imaging and 4 to 6 hours post imaging. Samples underwent gas chromatography/mass spectrometry profiling. Peak metabolite values were measured and data was log transformed. Significance analysis of microarrays and partial least squares was used to determine the most significant metabolites prior to CT imaging and within subject. Analysis of variance was used to rank metabolites associated with temporal change and CIN. CIN was defined as an increase in serum creatinine level of ≥ 0.5 mg/dL or ≥ 25% above baseline within 48 hours after contrast administration.

Results

We sampled paired urine samples from 63 subjects. The incidence of CIN was 6/63 (9.5%). Patients without CIN had elevated urinary citric acid and taurine concentrations in the pre-CT urine. Xylulose increased in the post CT sample in patients who developed CIN.

Conclusion

Differences in metabolomics patterns in patients who do and do not develop CIN exist. Metabolites may be potential early identifiers of CIN and identify patients at high-risk for developing this condition prior to imaging.

Urinary metabolomic analysis to detect changes after intravenous, non-ionic, low osmolar iodinated radiocontrast for computerized tomographic imaging

Introduction

Contrast-induced nephropathy is a result of injury to the proximal tubules caused by oxidative stress and ischemia. Metabolomics is a novel technique that has been used to identify renal damage from drug toxicities. The objective of this study is to analyze the metabolic changes in the urine after dosing with intravenous (IV) contrast for computed tomograph (CT) of the chest

Methods

A convenience sample of patients undergoing a chest CT with IV contrast who had at least one of the following: age ≥50 years, diabetes, heart failure, chronic kidney disease, coronary artery disease, or diastolic blood pressure >90 mmHg -- were eligible for enrollment. Urine samples were collected prior to imaging and 4–6 hours post imaging. Samples underwent gas chromography/mass spectrometry profiling. We measured peak metabolite values and log transformed data. Paired T tests were calculated. We used significance analysis of microarrays (SAM) to determine the most significant metabolites.

Results

The cohort comprised 14 patients with matched samples; 9/14 (64.3) were males, and the median age was 61 years (IQR 50–68). A total of 158 metabolites were identified. Using SAM we identified 9 metabolites that were identified as significant using a delta of 1.6.

Conclusion

Changes in urinary metabolites are present soon after contrast administration. This change in urinary metabolites may be potential early identifiers of contrast-induced nephropathy and could identify patients at high-risk for developing this condition.

Mechanisms for an effect of acetylcysteine on renal function after exposure to radio-graphic contrast material: study protocol

Background

Contrast-induced nephropathy is a common complication of contrast administration in patients with chronic kidney disease and diabetes. Its pathophysiology is not well understood; similarly the role of intravenous or oral acetylcysteine is unclear. Randomized controlled trials to date have been conducted without detailed knowledge of the effect of acetylcysteine on renal function. We are conducting a detailed mechanistic study of acetylcysteine on normal and impaired kidneys, both with and without contrast. This information would guide the choice of dose, route, and appropriate outcome measure for future clinical trials in patients with chronic kidney disease.

Methods/Design

We designed a 4-part study. We have set up randomised controlled cross-over studies to assess the effect of intravenous (50 mg/kg/hr for 2 hrs before contrast exposure, then 20 mg/kg/hr for 5 hrs) or oral acetylcysteine (1200 mg twice daily for 2 days, starting the day before contrast exposure) on renal function in normal and diseased kidneys, and normal kidneys exposed to contrast. We have also set up a parallel-group randomized controlled trial to assess the effect of intravenous or oral acetylcysteine on patients with chronic kidney disease stage III undergoing elective coronary angiography. The primary outcome is change in renal blood flow; secondary outcomes include change in glomerular filtration rate, tubular function, urinary proteins, and oxidative balance.

Discussion

Contrast-induced nephropathy represents a significant source of hospital morbidity and mortality. Over the last ten years, acetylcysteine has been administered prior to contrast to reduce the risk of contrast-induced nephropathy. Randomized controlled trials, however, have not reliably demonstrated renoprotection; a recent large randomized controlled trial assessing a dose of oral acetylcysteine selected without mechanistic insight did not reduce the incidence of contrast-induced nephropathy. Our study should reveal the mechanism of effect of acetylcysteine on renal function and identify an appropriate route for future dose response studies and in time randomized controlled trials.

Trial registration

Clinical Trials.gov: NCT00558142; EudraCT: 2006-003509-18.

Contrast-induced kidney injury: mechanisms, risk factors, and prevention

In general, iodinated contrast media (CM) are tolerated well, and CM use is steadily increasing. Acute kidney injury is the leading life-threatening side effect of CM. Here, we highlight endpoints used to assess CM-induced acute kidney injury (CIAKI), CM types, risk factors, and CIAKI prevention. Moreover, we put forward a unifying theory as to how CIAKI comes about; the kidney medulla's unique hyperosmolar environment concentrates CM in the tubules and vasculature. Highly concentrated CM in the tubules and vessels increases fluid viscosity. Thus, flow through medullary tubules and vessels decreases. Reducing the flow rate will increase the contact time of cytotoxic CM with the tubular epithelial cells and vascular endothelium, and thereby damage cells and generate oxygen radicals. As a result, medullary vasoconstriction takes place, causing hypoxia. Moreover, the glomerular filtration rate declines due to congestion of highly viscous tubular fluid. Effective prevention aims at reducing the medullary concentration of CM, thereby diminishing fluid viscosity. This is achieved by generous hydration using isotonic electrolyte solutions. Even forced diuresis may prove efficient if accompanied by adequate volume supplementation. Limiting the CM dose is the most effective measure to diminish fluid viscosity and to reduce cytotoxic effects.

Persistent renal enhancement after intra-arterial versus intravenous iodixanol administration

PURPOSE

To examine the clinical significance of persistent renal enhancement after iodixanol administration.

METHODS

We retrospectively studied 166 consecutive patients who underwent non-enhanced abdominopelvic CT within 7 days after receiving intra-arterial (n=99) or intravenous (n=67) iodixanol. Renal attenuation was measured for each non-enhanced CT scan. Persistent renal enhancement was defined as CT attenuation>55 Hounsfield units (HU). Contrast-induced nephropathy (CIN) was defined as a rise in serum creatinine>0.5 mg/dL within 5 days after contrast administration.

RESULTS

While the intensity and frequency of persistent renal enhancement was higher after intra-arterial (mean CT attenuation of 73.7 HU, seen in 54 of 99 patients, or 55%) than intravenous contrast material administration (51.8 HU, seen in 21 of 67, or 31%, p<0.005), a multivariate regression model showed that the independent predictors of persistent renal enhancement were a shorter time interval until the subsequent non-enhanced CT (p<0.001); higher contrast dose (p<0.001); higher baseline serum creatinine (p<0.01); and older age (p<0.05). The route of contrast administration was not a predictor of persistent renal enhancement in this model. Contrast-induced nephropathy was noted in 9 patients who received intra-arterial (9%) versus 3 who received intravenous iodixanol (4%), and was more common in patients with persistent renal enhancement (p<0.01).

CONCLUSION

Persistent renal enhancement at follow-up non-contrast CT suggests a greater risk for contrast-induced nephropathy, but the increased frequency of striking renal enhancement in patients who received intra-arterial rather than intravenous contrast material also reflects the larger doses of contrast and shorter time to subsequent follow-up CT scanning for such patients.

Iodixanol Versus Low-Osmolar Contrast Media for Prevention of Contrast Induced Nephropathy

Background—

Contrast-induced nephropathy (CIN) is associated with significant morbidity and mortality. The objective of our meta-analysis was to assess the efficacy of iodixanol compared with low-osmolar contrast media (LOCM) for prevention of CIN.

Methods and Results—

We searched MEDLINE, the Cochrane Central Register of Controlled Trials, and internet sources of cardiology trial results for individual and relevant reviews of randomized, controlled trials, for the terms contrast media, contrast nephropathy, renal failure, iodixanol, Visipaque, and low-osmolar contrast media. All studies reported an incidence rate of CIN for each study group; there was no restriction on the definition of CIN. There were no restrictions on journal type or patient population. Overall, 36 trials were identified for analysis of aggregated summary data on 7166 patients; 3672 patients received iodixanol and 3494 patients received LOCM. Overall, iodixanol showed no statistically significant reduction in CIN incidence below that observed with heterogeneous comparator agents ( P =0.11). Analysis of patient subgroups revealed that there was a significant benefit of iodixanol when compared with iohexol alone (odds ratio, 0.25; 95% confidence interval, 0.11 to 0.55; P <0.001) but not when compared with LOCM other than iohexol or with other ionic dimers or among patients receiving intra-arterial contrast injections or among patients undergoing coronary angiography with or without percutaneous intervention.

Conclusions—

Analysis of aggregated summary data from multiple randomized, controlled trials of iodixanol against diverse LOCMs for heterogeneous procedures and definitions of CIN show an iodixanol-associated reduction that is suggestive but statistically nonsignificant.

Renal effects of contrast media in diabetic patients undergoing diagnostic or interventional coronary angiography

BACKGROUND

The use of safe iodinated contrast media (CM) to prevent contrast-induced nephropathy (CIN) is an important consideration among renally impaired diabetic patients during coronary angiography.

HYPOTHESIS

Diabetic patients with normal or mild renal dysfunction are less likely to receive renal protective measures during angiography, yet they may also be at risk for CIN. We compared the renal effects of iopamidol and iodixanol in diabetic patients who were referred for angiography.

METHODS

Diabetic patients (N=122) with a serum creatinine (SCr) level of < or = 2 mg/dl were double-blind randomized to receive nonionic CM: iopamidol-370 (low osmolar, monomeric) or iodixanol-320 (iso-osmolar, dimeric). Renal stability was evaluated at baseline and at Days 1, 3, and 7 post-angiography. The primary endpoint was a > or = 25% increase in SCr.

RESULTS

Seventeen (10 iopamidol, 7 iodixanol; P=NS) patients had an increase in SCr > or = 25% over baseline. Over all days, analysis revealed nonsignificant differences in the incidence of CIN between the two study groups regardless of how CIN was defined.

CONCLUSIONS

Diabetic patients with normal or mild renal dysfunction are at risk for CIN. No significant difference in renal response was observed for these CM in this at-risk population.

Pathophysiology of contrast-induced nephropathy

Contrast-induced nephropathy (CIN) is the third leading cause of acute kidney injury in hospitalized patients and is associated with significant patient morbidity. The pathogenesis of CIN is complex and not fully understood, but iodinated contrast agents induce intense and prolonged vasoconstriction at the corticomedullary junction of the kidney. Moreover, high-osmolar dyes directly impair the autoregulatory capacity of the kidney through a loss of nitric oxide production. These effects, coupled with direct tubular toxicity of contrast media, lead to overt acute tubular necrosis and the syndrome of CIN.

Uroangiographic Contrast Media-Induced Nephropathy: Correlations between Their Physicochemical Properties and Renal Damage

Contrast media-induced nephropathy (CN) is an important cause of hospital-acquired acute renal failure. Patients with both diabetes mellitus and renal impairment are at high risk. CN pathophysiology involves activation of the tubulo-glomerular feedback and vasoactive mediators such as renin-angiotensin 2, endothelin, adenosine, ADH, etc. The risk of CN can be minimized by the use of non-ionic, low or isoosmolar, contrast material, adequate hydration and prophylactic pharmacological measures. In patients with chronic renal failure who are undergoing arteriography (e.g. coronary angiography and angioplasty), periprocedural hemofiltration appears effective in preventing further renal damage due to contrast agents.

Using a dopamine type 1A receptor agonist in high-risk patients to ameliorate contrast-associated nephropathy

OBJECTIVE

The objective of our study was to evaluate the effects of fenoldopam mesylate, a dopamine type 1A receptor agonist and a potent renal vasodilator that markedly increases renal blood flow, on kidney function of patients who were receiving iodinated contrast material for an interventional procedure and thought to be at high risk of contrast-associated nephropathy.

MATERIALS AND METHODS

We retrospectively reviewed the records of all patients who received fenoldopam mesylate to determine the acute and, when possible, the longer term effects on kidney function.

RESULTS

Twenty-nine cases were reviewed. The average serum creatinine value before contrast administration was 2.55 mg/dL (range, 1.3-5.8 mg/dL) [corrected]. Twenty-four hours after contrast administration, serum creatinine was measured in 28 of the 29 patients. The serum creatinine values had decreased in 16 of the 28 patients by an average of 0.55 mg/dL [corrected]. In nine patients, the serum creatinine value had not changed. Two of the three increases in the serum creatinine value appear to have been caused primarily by problems that did not involve the contrast material.

CONCLUSION

The use of fenoldopam mesylate at appropriate doses offers patients at high risk for contrast-associated nephropathy a chance to avoid this complication. To learn the extent and true nature of the effect of fenoldopam mesylate in this patient population requires a rigorous scientific trial, which is currently underway.

Renal artery stenosis in minority patients undergoing diagnostic cardiac catheterization: prevalence and risk factors

BACKGROUND

Atherosclerotic renal artery stenosis (RAS) is a frequently overlooked clinical entity that can cause progressive renal failure and uncontrolled hypertension. Revascularization of a stenosed renal artery is associated with improved clinical outcomes including the prevention of renal failure. Thus, it is important to recognize all potential candidates for renal artery revascularization. In a general population referred for diagnostic cardiac catheterization, RAS of any severity was found in 30% of patients and significant stenosis (> or = 50% diameter narrowing) was found in 15% of patients. The number of minority groups is increasing in the US population, and RAS in this population is not well investigated. Our purpose was to determine the prevalence and risk factors associated with RAS in minority patients referred for diagnostic cardiac catheterization.

METHODS

Abdominal aortography was performed in 171 consecutive minority patients referred for diagnostic cardiac catheterization (hispanics = 115, African Americans = 56). The association of clinical and angiographic variables with RAS was examined using univariate and multivariate logistic regression analyses.

RESULTS

Renal artery stenosis of any severity was identified in 13.5% of patients (unilateral 7.7%, bilateral 5.8%). Significant RAS was found in 7.7% of patients (unilateral 4.8%, bilateral 2.9%). Independent predictors of RAS included age (mean +/-1SD, 68 +/-10 vs 57 +/-12 yr, P < 0.001, for patients with vs without RAS), coronary artery disease, and elevated serum creatinine levels (> 115 micromol/L). Race/ethnicity (hispanics vs African Americans), sex, smoking, congestive heart failure, diabetes mellitus, peripheral vascular disease, and hypertension were not independent predictors.

CONCLUSIONS

Renal artery stenosis in minority patients undergoing diagnostic cardiac catheterization is less common than reported in white patients, is similar in hispanics and African Americans, and is similar in women and men. The clinical and angiographic features are helpful in predicting its presence.

Renal cortical retention on delayed CT after angiography and contrast associated nephropathy

The aim of this study was to examine the relationship between renal cortical retention (RCR) of contrast media observed on delayed CT (median delay: 20 h) and contrast associated nephropathy (CAN). We investigated the incidence of both phenomena in 270 patients. CAN was defined as an increase in the creatinine level > 0.5 mg dl-1 (44 mumol l-1) and > 25% on day 1, 3 or 7, while RCR was recognized when CT values for the renal cortex showed either mild RCR (CT value > 50) or severe RCR (CT value > 100). RCR was demonstrated in 127 patients (47%), mild in 78 (29%) and severe in 49 (18%), on delayed CT after angiography. CAN was found in eight patients (3%). Patients with severe RCR showed a higher CAN rate (8%) than other patients (mild RCR: 4%, RCR (-): 1%) (p = 0.02). The type of contrast medium was independently associated with the incidence of RCR (p = 0.0001). Although severe RCR was associated with a higher frequency of CAN than the milder forms of RCR, RCR as such was not always associated with CAN.