Iodixanol, constriction of medullary descending vasa recta, and risk for contrast medium-induced nephropathy

Molecular mechanisms of renal cellular nephrotoxicity due to radiocontrast media

Modern iodinated radiocontrast media are all based on the triiodinated benzene ring with various chemical modifications having been made over the last few decades in order to reduce their toxicity. However, CIN remains a problem especially in patients with pre-existing renal failure. In vitro studies have demonstrated that all RCM are cytotoxic. RCM administration in vivo may lead to a decrease in renal medullary oxygenation leading to the generation of reactive oxygen species that may cause harmful effects to renal tissue. In addition, endothelin and adenosine release and decreased nitric oxide levels may worsen the hypoxic milieu. In vitro cell culture studies together with sparse in vivo rat model data have shown that important cell signalling pathways are affected by RCM. In particular, the prosurvival and proproliferative kinases Akt and ERK1/2 have been shown to be dephosphorylated (deactivated), whilst proinflammatory/cell death molecules such as the p38 and JNK kinases and the transcription factor NF- κ B may be activated by RCM, accompanied by activation of apoptotic mediators such as caspases. Increasing our knowledge of the mechanisms of RCM action may help to develop future therapies for CIN.

Contrast media viscosity versus osmolality in kidney injury: lessons from animal studies

Iodinated contrast media (CM) can induce acute kidney injury (AKI). CM share common iodine-related cytotoxic features but differ considerably with regard to osmolality and viscosity. Meta-analyses of clinical trials generally failed to reveal renal safety differences of modern CM with regard to these physicochemical properties. While most trials' reliance on serum creatinine as outcome measure contributes to this lack of clinical evidence, it largely relies on the nature of prospective clinical trials: effective prophylaxis by ample hydration must be employed. In everyday life, patients are often not well hydrated; here we lack clinical data. However, preclinical studies that directly measured glomerular filtration rate, intrarenal perfusion and oxygenation, and various markers of AKI have shown that the viscosity of CM is of vast importance. In the renal tubules, CM become enriched, as water is reabsorbed, but CM are not. In consequence, tubular fluid viscosity increases exponentially. This hinders glomerular filtration and tubular flow and, thereby, prolongs intrarenal retention of cytotoxic CM. Renal cells become injured, which triggers hypoperfusion and hypoxia, finally leading to AKI. Comparisons between modern CM reveal that moderately elevated osmolality has a renoprotective effect, in particular, in the dehydrated state, because it prevents excessive tubular fluid viscosity.

Contrast-induced nephropathy in percutaneous coronary interventions: pathogenesis, risk factors, outcome, prevention and treatment

Contrast-induced nephropathy (CIN) is a well-known adverse event of therapeutic and diagnostic procedures requiring the administration of contrast medium (CM). The lack of a universal CIN definition and glomerular filtration rate markers that vary have resulted in a variety of reported incidences. The development of CIN is associated with an increase in the length of hospital stay and the risk of death. Preexisting renal dysfunction, age, diabetes, congestive heart failure and the volume of CM administered are all associated with a risk for developing CIN. The literature suggests the use of low-osmolarity CM and supports volume supplementation before administration. Moreover, other strategies to avoid CIN, including treatment with N-acetylcysteine and sodium bicarbonate have variable levels of evidence. This review examines the main components of the pathogenesis and risk factors of CIN and possible preventive measures and therapies.

Iodinated contrast media cause direct tubular cell damage, leading to oxidative stress, low nitric oxide, and impairment of tubuloglomerular feedback

Iodinated contrast media (CM) have adverse effects that may result in contrast-induced acute kidney injury. Oxidative stress is believed to play a role in CM-induced kidney injury. We test the hypothesis that oxidative stress and reduced nitric oxide in tubules are consequences of CM-induced direct cell damage and that increased local oxidative stress may increase tubuloglomerular feedback. Rat thick ascending limbs (TAL) were isolated and perfused. Superoxide and nitric oxide were quantified using fluorescence techniques. Cell death rate was estimated using propidium iodide and trypan blue. The function of macula densa and tubuloglomerular feedback responsiveness were measured in isolated, perfused juxtaglomerular apparatuses (JGA) of rabbits. The expression of genes related to oxidative stress and the activity of superoxide dismutase (SOD) were investigated in the renal medulla of rats that received CM. CM increased superoxide concentration and reduced nitric oxide bioavailability in TAL. Propidium iodide fluorescence and trypan blue uptake increased more in CM-perfused TAL than in controls, indicating increased rate of cell death. There were no marked acute changes in the expression of genes related to oxidative stress in medullary segments of Henle's loop. SOD activity did not differ between CM and control groups. The tubuloglomerular feedback in isolated JGA was increased by CM. Tubular cell damage and accompanying oxidative stress in our model are consequences of CM-induced direct cell damage, which also modifies the tubulovascular interaction at the macula densa, and may therefore contribute to disturbances of renal perfusion and filtration.

Urinary ET-1 excretion after exposure to radio-contrast media in diabetic patients and patients with preexisting mild impaired renal function

AIMS

Contrast media-induced nephropathy (CIN) is associated with increased morbidity and mortality. The renal endothelin system has been associated with disease progression of various acute and chronic renal diseases. However, robust data coming from adequately powered prospective clinical studies analyzing the short and long-term impacts of the renal ET system in patients with CIN are missing so far. We thus performed a prospective study addressing this topic.

MAIN METHODS

We included 327 patients with diabetes or renal impairment undergoing coronary angiography. Blood and spot urine were collected before and 24 h after contrast media (CM) application. Patients were followed for 90 days for major clinical events like need for dialysis, unplanned rehospitalization or death.

KEY FINDINGS

The concentration of ET-1 and the urinary ET-1/creatinine ratio decreased in spot urine after CM application (ET-1 concentration: 0.91±1.23 pg/ml versus 0.63±1.03 pg/ml, p<0.001; ET-1/creatinine ratio: 0.14±0.23 versus 0.09±0.19, p<0.001). The urinary ET-1 concentrations in patients with CIN decreased significantly more than in patients without CIN (-0.26±1.42 pg/ml vs. -0.79±1.69 pg/ml, p=0.041), whereas the decrease of the urinary ET-1/creatinine ratio was not significantly different (non-CIN patients: -0.05±0.30; CIN patients: -0.11±0.21, p=0.223). Urinary ET-1 concentrations as well as the urinary ET-1/creatinine ratio were not associated with clinical events (need for dialysis, rehospitalization or death) during the 90 day follow-up after contrast media exposure. However, the urinary ET-1 concentration and the urinary ET-1/creatinine ratio after CM application were higher in those patients who had a decrease of GFR of at least 25% after 90 days of follow-up.

SIGNIFICANCE

In general the ET-1 system in the kidney seems to be down-regulated after contrast media application in patients with moderate CIN risk. Major long-term complications of CIN (need for dialysis, rehospitalization or death) are not associated with the renal ET system.

Why is diabetes mellitus a risk factor for contrast-induced nephropathy?

Contrast-induced nephropathy (CIN) remains a leading cause of iatrogenic acute kidney injury, as the usage of contrast media for imaging and intravascular intervention keeps expanding. Diabetes is an important predisposing factor for CIN, particularly in patients with renal functional impairment. Renal hypoxia, combined with the generation of reactive oxygen species, plays a central role in the pathogenesis of CIN, and the diabetic kidney is particularly susceptible to intensified hypoxic and oxidative stress following the administration of contrast media. The pathophysiology of this vulnerability is complex and involves various mechanisms, including a priori enhanced tubular transport activity, oxygen consumption, and the generation of reactive oxygen species. The regulation of vascular tone and peritubular blood flow may also be altered, particularly due to defective nitrovasodilation, enhanced endothelin production, and a particular hyperresponsiveness to adenosine-related vasoconstriction. In addition, micro- and macrovascular diseases and chronic tubulointerstitial changes further compromise regional oxygen delivery, and renal antioxidant capacity might be hampered. A better understanding of these mechanisms and their control in the diabetic patient may initiate novel strategies in the prevention of contrast nephropathy in these susceptible patients.

Iodinated contrast media can induce long-lasting oxidative stress in hemodialysis patients

PURPOSE

Due to their comorbidities, dialysis patients have many chances to undergo radiologic procedures using iodinated contrast media. We aimed to assess time-sequenced blood oxidative stress level after contrast exposure in hemodialysis (HD) patients compared to those in the non-dialysis population.

MATERIALS AND METHODS

We included 21 anuric HD patients [HD-coronary angiography (CAG) group] and 23 persons with normal renal function (nonHD-CAG group) scheduled for CAG, and assessed 4 oxidative stress markers [advanced oxidation protein products (AOPP); catalase; 8-hydroxydeoxyguanosine; and malondialdehyde] before and after CAG, and subsequently up to 28 days.

RESULTS

In the nonHD-CAG group, only AOPP increased immediately after CAG and returned to baseline within one day. However, in the HD-CAG group, all four oxidative stress markers were significantly increased starting one day after CAG, and remained elevated longer than those in the nonHD-CAG group. Especially, AOPP level remained elevated for a month after contrast exposure.

CONCLUSION

Our study showed that iodinated contrast media induces severe and prolonged oxidative stress in HD patients.

Contrast-induced nephropathy: pharmacology, pathophysiology and prevention

Modern iodinated contrast media (CM) consist of one or two tri-iodobenzene rings. They differ from each other in the composition of the side chains, creating different molecules and thus different brand substances. After intravascular administration, all CM are distributed rapidly into intravascular and extracellular fluids. They are eliminated solely by glomerular filtration. In patients with normal renal function, CMs are eliminated within 24 h. The pathophysiology of contrast-induced nephropathy (CIN) is based on three distinct but interacting mechanisms: medullary ischaemia, formation of reactive oxygen species and direct tubular cell toxicity. The contribution of each of these mechanisms to the development of CIN in the individual patient remains unclear. CIN prevention is extensively described in guidelines, such as the recently updated guideline from the Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR). The recent update is briefly discussed. Furthermore, it remains unclear if volume expansion with either NaCl 0.9 % or NaHCO₃ 1.4 % is superior.

Teaching points

• After intravascular injection, CM are distributed over intravascular and extracellular fluids.

• CM are eliminated by glomerular filtration in patients with normal kidney function.

• CIN pathophysiology is based on medullary ischaemia, formation of reactive oxygen species (ROS) and tubular cell toxicity.

• It remains unclear if volume expansion with either NaCl 0.9 % or NaHCO₃1.4 % is superior.

Radiographic contrast-media-induced acute kidney injury: pathophysiology and prophylactic strategies

Contrast-induced acute kidney injury (CI-AKI) is one of the most widely discussed and debated topics in cardiovascular medicine. With increasing number of contrast-media- (CM-) enhanced imaging studies being performed and growing octogenarian population with significant comorbidities, incidence of CI-AKI remains high. In this review, pathophysiology of CI-AKI, its relationship with different types of CM, role of serum and urinary biomarkers for diagnosing CI-AKI, and various prophylactic strategies used for nephroprotection against CI-AKI are discussed in detail.

Intravascular radiocontrast iodixanol increases permeability of proximal tubule epithelium: a possible mechanism of contrast-induced nephropathy

PURPOSE

To investigate the effect of Iodixanol on kidney proximal tubular cell line human kidney 2 (HK-2).

METHODS

The HK-2 cells were treated with Iodixanol. A Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay was used to evaluate apoptosis. Cell viability was measured by proliferation assay kit. Cell permeability changes were assessed by transwell assay and intercellular gaps measurement. Expression of claudin-2 was assessed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and Western blot.

RESULTS

Iodixanol reduced tubule cell viability (P < .01) but did not cause apoptosis. The intercellular gap formation (P < .01) and transwell (P < .05) assays revealed that cell permeability significantly increased after Iodixanol treatment of monolayer cells. Western blot and qRT-PCR showed significant upregulation of claudin-2 protein (P < .05) and messenger RNA expression (P < .01).

CONCLUSIONS

Our in vitro data do not support the hypothesis that direct kidney cell death from Iodixanol is a major mechanism of contrast-induced nephropathy (CIN). However, increased permeability of proximal tubule epithelium caused by Iodixanol may play an important role in CIN.

Early effects of an x-ray contrast medium on renal T(2) */T(2) MRI as compared to short-term hyperoxia, hypoxia and aortic occlusion in rats

AIM

X-ray contrast media (CM) can cause acute kidney injury (AKI). Medullary hypoxia is pivotal in CM-induced AKI, as indicated by invasively and pin-point measured tissue oxygenation. MRI provides spatially resolved blood oxygenation level-dependent data using T2 * and T2 mapping. We studied CM effects on renal T2 */T2 and benchmarked them against short periods of hyperoxia, hypoxia and aortic occlusion (AO).

METHODS

Rats were equipped with carotid artery catheters (tip towards aorta) and supra-renal aortic occluders. T2 */T2 mapping was performed using a 9.4-T animal scanner. CM (1.5 mL iodixanol) was injected into the thoracic aorta with the animal in the scanner followed by 2 h of T2 */T2 mapping. For T2 */T2 assessment, regions of interest in the cortex (C), outer medulla (OM), inner medulla (IM) and papilla (P) were determined according to morphological features.

RESULTS

Hyperoxia increased T2 * in C (by 17%) and all medullary layers (25-35%). Hypoxia decreased T2 * in C (40%) and all medullary layers (55-60%). AO decreased T2 * in C (18%) and all medullary layers (30-40%). Upon injection of CM, T2 * increased transiently, then decreased, reaching values 10-20% below baseline in C and OM and 30-40% below baseline in IM and P.

CONCLUSION

T2 * mapping corroborates data previously obtained with invasive methods and demonstrates that CM injection affects renal medullary oxygenation. CM-induced T2 * decrease in OM was small vs. hypoxia and aortic occlusion. T2 * decrease obtained for hypoxia was more pronounced than for AO. This indicates that T2 * may not accurately reflect blood oxygenation under certain conditions.

Glomerular filtration rate in evaluation of the effect of iodinated contrast media on renal function

OBJECTIVE

The purpose of this study was to use measured glomerular filtration rate (GFR), the reference standard of renal function, to assess the deleterious effect of iodinated contrast media on renal function. Such an effect has been traditionally defined as a greater than 0.5-mg/dL increase in serum creatinine concentration or a 25% or greater increase 24-72 hours after the injection of iodinated contrast medium.

SUBJECTS AND METHODS

This pilot investigation was focused on the consequences of clinically indicated IV injection of iodinated contrast media; intraarterial injection was excluded. One hundred thirteen patients with normal serum creatinine concentrations were enrolled in an approved protocol. At random, as chosen by one of the investigators, patients underwent imaging with one of three monomeric agents (iopamidol 300, iopromide 300, iohexol 300) and one dimeric agent (iodixanol 320). Measured GFR was determined immediately before CT and approximately 3 and 72 hours after the contrast injection for the CT examination. Iodinated contrast medium, a glomerular filtrate with no tubular excretion or reabsorption, was the GFR marker. Measured GFR was determined by x-ray fluorescence analysis with nonisotopic iodinated contrast media.

RESULTS

Monomeric and dimeric contrast agents in diagnostic CT volumes (based on bodyweight and imaging protocol) did not induce a significant change in measured GFR (95% confidence by Wilcoxon test), suggesting that use of the evaluated contrast media will not lead to more than a 12% variation.

CONCLUSION

The three monomeric agents studied and the one dimeric agent were equivalent in terms of lack of a significant effect on measured GFR when administered to patients with a normal GFR.

Functional characterization of isolated, perfused outermedullary descending human vasa recta

AIM

The renal medulla plays an important role in the control of water and salt balance by the kidney. Outer medullary descending vasa recta (OMDVR) are microscopic vessels providing blood flow to the renal medulla. Data on the physiology of human vasa recta are scarce. Therefore, we established an experimental model of human single isolated, perfused OMDVR and characterized their vasoactivity in response to angiotensin II and to pressure changes.

METHODS

Human non-malignant renal tissue was obtained from patients undergoing nephrectomy due to renal cell carcinoma. OMDVR were dissected under magnification and perfused using concentric microscopic pipettes. The response of OMDVR to angiotensin II and pressure changes was quantified in serial pictures. All patients signed a consent form prior to surgery.

RESULTS

Outer medullary descending vasa recta constricted significantly after bolus applications of angiotensin II. OMDVR constriction to angiotensin II was also concentration dependent. Response to luminal pressure changes was different according to the diameter of vessels, with larger OMDVR constricting after pressure increase, while smaller ones did not.

CONCLUSION

Outer medullary descending vasa recta constrict in response to angiotensin II and pressure increases. Our results show that OMDVR may take part in the regulation of medullary blood flow in humans. Our model may be suitable for investigating disturbances of renal medullary circulation in human subjects.

Iodinated contrast media cause endothelial damage leading to vasoconstriction of human and rat vasa recta

Contrast-induced acute kidney injury is an important clinical event with a worldwide increasing number of cases. Medullary hypoperfusion and hypoxia due to constriction of vasa recta are main factors in the pathophysiology of acute kidney injury. However, the mechanism of contrast media (CM)-induced vessel constriction is not known. We tested the hypothesis that vasa recta constriction is a consequence of endothelial dysfunction due to the cytotoxicity of CM. Human and rat descending vasa recta (DVR) were isolated and perfused with CM, and the luminal diameter was analyzed. For morphological analysis of the endothelium, renal arteries were CM perfused and then processed for electron microscopy. Transcellular electrical resistance was used to estimate CM-induced changes in the permeability of human umbilical vein endothelial cell (HUVEC) layers. Perfusion with CM constricted human and rat DRV (to 54.3 and 50.9% of initial diameter, respectively). This was blunted by adrenomedullin (77.7 and 77.1%, respectively). The ANG II response was enhanced by CM in rat DVR (reduction to 15.6 and 35.0% of initial diameter, respectively). Adrenomedullin blunted this effect (67.5%). CM led to endothelial damage of renal arteries characterized by a ragged surface, with sharply protruding intimal folds, spindle-like shape, and bulging in the lumen. These phenomena were reduced by adrenomedullin. The permeability of HUVEC cell layers was increased by CM, and this went along with increased myosin light chain phosporylation. Again, adremonedullin reduced the CM effect. Our study suggests that the constrictor effect of CM on the renal medullary microvasculature is a consequence of endothelial cell damage and the resulting endothelial dysfunction.

Simvastatin attenuates contrast-induced nephropathy through modulation of oxidative stress, proinflammatory myeloperoxidase, and nitric oxide

Contrast media- (CM-) induced nephropathy is a serious complication of radiodiagnostic procedures. Available data suggests that the development of prophylaxis strategies is limited by poor understanding of pathophysiology of CM-induced nephropathy. Present study was designed to determine the role of oxidative stress, myeloperoxidase, and nitric oxide in the pathogenesis of iohexol model of nephropathy and its modification with simvastatin (SSTN). Adult Sprague Dawley rats were divided into seven groups. After 24 h of water deprivation, all the rats except in control and SSTN-only groups were injected (10 ml/kg) with 25% glycerol. After 30 min, SSTN (15, 30, and 60 mg/kg) was administered orally, daily for 4 days. Twenty-four hours after the glycerol injection, iohexol was infused (8 ml/kg) through femoral vein over a period of 2 min. All the animals were sacrificed on day 5 and blood and kidneys were collected for biochemical and histological studies. The results showed that SSTN dose dependently attenuated CM-induced rise of creatinine, urea, and structural abnormalities suggesting its nephroprotective effect. A significant increase in oxidative stress (increased lipid hydroperoxides and reduced glutathione levels) and myeloperoxidase (MPO) and decreased nitric oxide in CM group were reversed by SSTN. These findings support the use of SSTN to combat CM-induced nephrotoxicity.

Medullary thick ascending limb buffer vasoconstriction of renal outer-medullary vasa recta in salt-resistant but not salt-sensitive rats

We have demonstrated previously that paracrine signaling occurs between medullary thick ascending limb (mTAL) and the contractile pericytes of outer-medullary vasa recta (VR), termed "tubular-vascular cross-talk." The aim of the current study was to determine whether tubular-vascular cross-talk has a functional effect on vasoconstrictor responses to angiotensin II and to determine whether this is altered in the Dahl salt-sensitive (SS) rat. Studies were performed on salt-resistant consomic SS.13 Brown Norway (BN) and SS rats using a novel outer medullary tissue strip preparation in which freshly isolated VRs within VR bundles were perfused either alone or in combination with nearby mTAL. In VRs from SS.13BN rats, angiotensin II (1 µmol/L) increased VR bundle intracellular Ca2+ concentration 19±9 nmol/L (n=8) and reduced focal diameter in perfused VRs by -20±7% (n=5). In the presence of nearby mTAL, however, VR bundle intracellular Ca2+ concentration (-9±8 nmol/L; n=8) and VR diameter (-1±4%, n=7) in SS.13BN rats were unchanged by angiotensin II. In contrast, in Dahl SS rats, angiotensin II resulted in rapid and sustained increase in VR bundle intracellular Ca2+ concentration (89±48 nmol/L, n=7; 50±24%, n=8) and a reduction in VR diameter of (-17±7%, n=7; -11±4%, n=5) in both isolated VRs and VRs with nearby mTAL, respectively. In VRs with mTAL from SS13BN rats, inhibiton of purinergic receptors resulted in an increase in VR bundle intracellular Ca2+ concentration, indicating that purinergic signaling buffers vasoconstriction. Importantly, our in vitro data were able to predict medullary blood flow responses to angiotensin II in SS and SS.13BN rats in vivo. We conclude that paracrine signaling from mTAL buffers angiotensin II vasoconstriction in Dahl salt-resistant SS.13BN rats but not SS rats.

Proof of principle: hydration by low-osmolar mannitol-glucose solution alleviates undesirable renal effects of an iso-osmolar contrast medium in rats

OBJECTIVE

Saline infusion is widely used to prevent contrast media (CM)-induced acute kidney injury, because it fosters diuresis. Osmodiuretics have a stronger diuretic effect than saline, yet previous trials indicate that osmodiuretic mannitol tends to promote rather than to prevent CM-induced acute kidney injury. However, these studies used hypertonic mannitol solutions that will result in rebound volume contraction. We hypothesize that combining the osmodiuretic effects of a nonhypertonic mannitol solution with sustained volume expansion alleviates undesirable renal effects of CM.

MATERIALS AND METHODS

Forty-four anesthetized rats were studied by 4 protocols. Urine flow rate, urine viscosity, and glomerular filtration rate (GFR) were measured. Intravenous infusions of hydration solutions were initiated 60 minutes before CM administration and continued throughout the observation period. Hydration by a 3.2% mannitol and 3.2% glucose solution infused at 12 mL/kg per hour (Mannit-Gluc regimen) was compared with a standard regimen of isotonic saline at 4 mL/kg per hour (NaCl regimen); greater infusion rates are required for the Mannit-Gluc regimen because of the profound diuretic effect of mannitol. Two CM were studied: iso-osmolar iodixanol (320 mg I/mL) and low-osmolar iopromide (370 mg I/mL), they were administered as 1.5-mL bolus injection into the thoracic aorta.

RESULTS

The Mannit-Gluc regimen resulted in higher urine flow rates than the standard NaCl regimen, yet maintained a good volume status. By virtue of its stronger diuretic effect, the Mannit-Gluc regimen greatly diminished the increase in urine viscosity and completely prevented the transient decrease in GFR caused by iodixanol with the NaCl regimen. After iopromide, the differences between the hydration regimens were much less, as iopromide increased urine flow rates much more than iodixanol, thus resulting in a much smaller increase in viscosity than iodixanol and no decrease in GFR even with the NaCl regimen.

CONCLUSION

This proof of principle study shows that a hydration regimen that combines the osmodiuretic effect of a low-osmolar mannitol-glucose solution with sustained volume expansion is effective in reducing high urine viscosity and preventing GFR reduction caused by iso-osmolar iodixanol. For low-osmolar CM, the beneficial effects seem negligible, because these compounds per se exert greater osmodiuretic action.

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.

Contrast-induced nephropathy--a review of current literature and guidelines

The use of iodine-based contrast agents always entails the risk of contrast-induced nephropathy (CIN). The recently observed dramatic increase in the number of examinations and therapeutic procedures using iodine-based contrast media led us to conduct a thorough analysis of the growing number of scientific reports and collective works devoted to contrast-induced nephropathy, based on current definitions, epidemiology, pathophysiology, risk factors, successful prophylaxis and guidelines of the European Society of Urogenital Radiology (ESUR).

Radiological contrast agents are the third most common cause of nephropathy among in-patients, accounting for 11–12% of cases. CIN is connected with some clinically significant consequences, including increased morbidity, prolonged hospitalisation, increased risk of complications, potential need for dialysis and increased mortality rate. A significant increase in the number of examinations applying iodine-based contrast media in the course of inpatient procedures requires close cooperation of the clinician and radiologist, supported by knowledge of all CIN issues. In order to protect patients from contrast-induced nephropathy, it is necessary to monitor their renal function, indentify patients with risk factors, refer patients for examinations in a responsible manner, and undertake successful preventive measures.

Pathophysiology of renal tissue damage by iodinated contrast media

1. The present review focuses on the cytotoxic effects of iodinated contrast media (CM) that are shared by all types of CM. 2. Although the clinical nephrotoxicity of CM has been progressively improved, all currently available CM still possess a level of cytotoxicity, which is probably caused by iodine. 3. The toxicity caused by specific CM properties, such as osmolarity, viscosity and ionic strength, can be differentiated from the cytotoxicity common to all CM in studies using cell culture, isolated blood vessels and isolated tubules. 4. The cytotoxicity induced by CM leads to apoptosis and cell death of endothelial and tubular cells and may be initiated by cell membrane damage, together with oxidative stress. 5. Cell damage may be aggravated by factors such as tissue hypoperfusion and hypoxia, properties of individual CM, such as ionic strength, high osmolarity and/or viscosity, and clinically unfavourable conditions. 6. Clinically detectable renal failure may result from the summation of all these factors.

How to reduce the incidence of contrast induced acute kidney injury after cardiac invasive procedures, a review and practical recommendations

BACKGROUND

Contrast induced acute kidney injury is an important complication after cardiac (invasive) procedures and is associated with substantial morbidity and mortality. The aim of the current article is to provide a comprehensive overview of the current knowledge regarding contrast induced acute kidney injury.

METHODS

Current literature was reviewed and relevant articles were selected. Articles were identified through MEDLINE and Pubmed selecting articles, limited between 1980 and 2010.

RESULTS

The pathophysiological process resulting in contrast induced acute kidney injury is not completely understood, nevertheless several mechanisms involved have been proposed. However, the risk factors for contrast induced acute kidney injury and its timing are well known, making it amenable for preventive strategies. In the past decade various preventive strategies have been investigated with different results.

CONCLUSIONS

Currently, only adequate hydration, with saline, is uniformly accepted as a beneficial prophylactic strategy. Furthermore promising results have also been reported for several other prophylactic strategies. These results, however, need to be confirmed in future trials.

Reactive oxygen species and the pathogenesis of radiocontrast-induced nephropathy

Experimental findings in vitro and in vivo illustrate enhanced hypoxia and the formation of reactive oxygen species (ROS) within the kidney following the administration of iodinated contrast media, which may play a role in the development of contrast media-induced nephropathy. Clinical studies indeed support this possibility, suggesting a protective effect of ROS scavenging or reduced ROS formation with the administration of N-acetyl cysteine and bicarbonate infusion, respectively. Furthermore, most risk factors, predisposing to contrast-induced nephropathy are prone to enhanced renal parenchymal hypoxia and ROS formation. In this review, the association of renal hypoxia and ROS-mediated injury is outlined. Generated during contrast-induced renal parenchymal hypoxia, ROS may exert direct tubular and vascular endothelial injury and might further intensify renal parenchymal hypoxia by virtue of endothelial dysfunction and dysregulation of tubular transport. Preventive strategies conceivably should include inhibition of ROS generation or ROS scavenging.

Contrast-induced acute kidney injury (CIAKI)

Injury to the kidney continues to occur following the administration of intravascular iodinated contrast media. In this article, the author reviews the pathophysiology of contrast-induced acute kidney injury (CIAKI), the relationship of CIAKI to long-term adverse outcomes, what type of patients are at risk of CIAKI, and how the diagnosis is made. After discussion of the reported incidence of CIAKI, an approach to prevention is briefly reviewed.