Formation of toxic iodinated disinfection by-products from compounds used in medical imaging

Iodinated X-ray contrast media (ICM) were investigated as a source of iodine in the formation of iodo-trihalomethane (iodo-THM) and iodo-acid disinfection byproducts (DBPs), both of which are highly genotoxic and/or cytotoxic in mammalian cells. ICM are widely used at medical centers to enable imaging of soft tissues (e.g., organs, veins, blood vessels) and are designed to be inert substances, with 95% eliminated in urine and feces unmetabolized within 24 h. ICM are not well removed in wastewater treatment plants, such that they have been found at elevated concentrations in rivers and streams (up to 100 μg/L). Naturally occurring iodide in source waters is believed to be a primary source of iodine in the formation of iodo-DBPs, but a previous 23-city iodo-DBP occurrence study also revealed appreciable levels of iodo-DBPs in some drinking waters that had very low or no detectable iodide in their source waters. When 10 of the original 23 cities' source waters were resampled, four ICM were found--iopamidol, iopromide, iohexol, and diatrizoate--with iopamidol most frequently detected, in 6 of the 10 plants sampled, with concentrations up to 2700 ng/L. Subsequent controlled laboratory reactions of iopamidol with aqueous chlorine and monochloramine in the absence of natural organic matter (NOM) produced only trace levels of iodo-DBPs; however, when reacted in real source waters (containing NOM), chlorine and monochloramine produced significant levels of iodo-THMs and iodo-acids, up to 212 nM for dichloroiodomethane and 3.0 nM for iodoacetic acid, respectively, for chlorination. The pH behavior was different for chlorine and monochloramine, such that iodo-DBP concentrations maximized at higher pH (8.5) for chlorine, but at lower pH (6.5) for monochloramine. Extracts from chloraminated source waters with and without iopamidol, as well as from chlorinated source waters with iopamidol, were the most cytotoxic samples in mammalian cells. Source waters with iopamidol but no disinfectant added were the least cytotoxic. While extracts from chlorinated and chloraminated source waters were genotoxic, the addition of iopamidol enhanced their genotoxicity. Therefore, while ICM are not toxic in themselves, their presence in source waters may be a source of concern because of the formation of highly toxic iodo-DBPs in chlorinated and chloraminated drinking water.

Iodinated contrast induced renal vasoconstriction is due in part to the downregulation of renal cortical and medullary nitric oxide synthesis

OBJECTIVES

The loss of renal function continues to be a frequent complication of the iodinated contrast agents used to perform diagnostic angiography and endovascular procedures. This study examined the hypothesis that contrast-induced renal injury is partly due to a decrease in cortical and medullary microvascular blood flow after the downregulation of endogenous renal cortical and medullary nitric oxide (NO) synthesis.

METHODS

Anesthetized male Sprague-Dawley rats (300 g) had microdialysis probes or laser Doppler fibers inserted into the renal cortex to a depth of 2 mm and into the renal medulla to a depth of 4 mm. Laser Doppler blood flow was continuously monitored, and the microdialysis probes were connected to a syringe pump and perfused in vivo at 3 muL/min with lactated Ringer's solution. Dialysate fluid was collected at time zero (basal) and 60 minutes after infusion of either saline or Conray 400 (6 mL/kg). Both groups were treated with saline carrier, N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 30 mg/kg), L-arginine (400 mg/kg), or superoxide dismutase (10,000 U/kg), an oxygen-derived free radical scavenger. Dialysate was analyzed for total NO and eicosanoid synthesis. The renal cortex and medulla were analyzed for inducible NO synthase (iNOS), cyclooxygenase-2 (COX2), prostacyclin synthase, and prostaglandin E(2) (PGE(2)) synthase content by Western blot analysis.

RESULTS

Conray caused a marked decrease in cortical and medullary blood flow with a concomitant decrease in endogenous cortical NO, PGE(2), and medullary NO synthesis. The addition of L-NAME to the Conray further decreased cortical and medullary blood flow and NO synthesis, which were restored toward control by L-arginine. Neither L-NAME nor L-arginine (added to the Conray) altered cortical or medullary eicosanoids release. Medullary PGE(2) synthesis decreased when superoxide dismutase was added to the Conray treatment, suggesting that oxygen-derived free radicals had a protective role in maintaining endogenous medullary PGE(2) synthesis after Conray treatment. Conray did not significantly alter iNOS, COX-2, prostacyclin synthase, or PGE(2) synthase content.

CONCLUSIONS

These findings suggest that the downregulation of renal cortical and medullary NO synthesis contributes to the contrast-induced loss of renal cortical and medullary microvascular blood flow. Preservation of normal levels of renal cortical and medullary NO synthesis may help prevent or lessen contrast-induced renal vasoconstriction and lessen contrast-induced renal injury found after diagnostic and therapeutic endovascular procedures.

Effect of contrast media on vascular smooth muscle cells

PURPOSE

In order to alleviate the adverse effects of contrast media (CMs) on the vascular system, the role of Ca2+ in the viability of vascular smooth muscle cells (VSMCs) was investigated.

MATERIAL AND METHODS

VSMCs were obtained from swine thoracic aorta. The number of VSMCs was counted under a microscope using the trypan blue dye-exclusion method 24 h after culture in RPMI containing physiological saline (SAL) as control, iothalamate (IOT), or iohexol (IOH) at 10% by volume with CaCl2 added at 0 to 2.0 mmol/l. Free Ca2+ in the above media was measured using an ion-selective electrode.

RESULTS

Free Ca2+ was 0.4 to 1.5 mmol/l with ionic IOT and 0.4 to 1.8 mmol/l with non-ionic IOH as well as with control. The ratio of viable cells grown in the presence of CMs to those grown in the control was optimal at approximately 0.60 near 1 mmol/l Ca2+ and decreased markedly to 0.00 at 1.5 mmol/l Ca2+ in the presence of IOT and to 0.39 at 1.8 mmol/l Ca2+ in the presence of IOH, while the ratios decreased gradually to 0.28 in the presence of IOT and 0.53 in the presence of IOH at 0.4 mmol/l Ca2+.

CONCLUSION

Ionic IOT is more cytotoxic to VSMCs than non-ionic IOH. However, the cytotoxicity was minimal and similar between both CMs at 1 mmol/l Ca2+ in accordance with the sodium-calcium balance.

Differential effects of radiocontrast agents on human umbilical vein endothelial cells: cytotoxicity and modulators of thrombogenicity

The endothelium plays a central role in the regulation of blood flow and coagulation. The impact of radiocontrast agents on endothelial cells is therefore potentially clinically important, particularly in percutaneous interventions for acute coronary thrombosis. The effects of radiocontrast agents on endothelial cell viability and determinants of thrombogenicity were studied in human umbilical vein endothelial cells (HUVECs) in vitro. Intercellular tight junctions were assessed using immunofluorescence microscopy and measurement of the transmonolayer electrical resistance (TMR). The concentrations of endothelin-1 (E), von Willebrand factor (vWF), plasminogen activator inhibitor-1 (PAI-1) and thrombomodulin (T) were measured in the cell culture media. The ionic, high osmolal radiocontrast agent diatrizoate induced concentration-dependent cell death and an opening of tight junctions with the attendant abolition of the TMR. The concentration of E decreased, vWF increased in the cell culture media, the concentration of PAI-1 and T was not significantly changed by diatrizoate. Radiocontrast agents with reduced osmolality (ioxaglate: ionic; iopamidol: non-ionic) induced an increase in PAI-1 and vWF, but E and T were not significantly changed.

CONCLUSIONS

Radiocontrast agents have differential effects on endothelial cells in vitro including the secretion of modulators of thrombogenesis. The effects are most pronounced in the markedly hyperosmolal compound diatrizoate suggesting a contributory role of hypertonicity. Ioxaglate and iopamidol both increased the prothrombotic factors vWF and PAI-1 to the same degree indicating a similar risk of thrombogenicity between low-osmolal ionic and non-ionic radiocontrast agents in this in vitro model.

Ionic and non-ionic contrast agent-mediated endothelial injury. Quantitative analysis of cell proliferation during endothelial repair

PURPOSE

To quantitatively evaluate endothelial injury in vivo and to assess the time course of cellular repair after endothelial cell exposure to ionic and non-ionic contrast media.

MATERIAL AND METHODS

Local changes at the cellular level following intraaortic injection of 1 ml of the ionic contrast agent ioxithalamate or 1 ml of the non-ionic contrast agent iomeprol, each with an iodine content of 300 mg/ml, were investigated using rat endothelium as an in vivo model. A sorbitol solution iso-osmolar to iomeprol served as control. Quantitative analysis of endothelial changes by autoradiography of 3H-thymidine-labeled endothelial cells was assessed after 3, 5 and 10 days, determining the 3H-thymidine index and the DNA synthesis rate.

RESULTS

Ioxithalamate showed a clear harmful effect on the endothelium, with an elevated 3H-thymidine index of 7.68% on day 3 and 6.89% on day 5, versus 2.97% on day 3 and 2.55% on day 5 for iomeprol and 2.29% on day 3 and 1.91% on day 5 for the control.

CONCLUSION

Ionic contrast agents lead to reversible transient focal endothelial cell injury. No such side effect was detectable for non-ionic contrast agents.

Changes in intrarenal oxygenation as evaluated by BOLD MRI in a rat kidney model for radiocontrast nephropathy

The pathogenesis of radiocontrast nephropathy is poorly understood. In an animal model, inhibition of the synthesis of nitric oxide and prostaglandins appears to predispose rats to severe renal injury following the administration of radiocontrast. Here we have investigated whether administration of radiocontrast, as well as changes in renal medullary oxygenation following pharmacologic inhibition of nitric oxide and prostaglandin synthesis, might be evaluated by blood oxygenation level-dependent (BOLD) MRI. Nineteen anesthetized (Inactin 100 mg/kg) rats were studied. BOLD MRI measurements were performed following administration of L-NAME (N-nitro-L-arginine methyl ester, 10 mg/kg), Indomethacin (10 mg/kg), and a radiocontrast agent (sodium iothalamate 60%, 6 mL/kg). Marked sequential changes in medullary R(*)(2), presumably reflecting decline in medullary pO(2), were noted after each of the pharmacological interventions employed. These results, obtained by noninvasive MRI, are consistent with prior direct recordings of pO(2) and doppler flow in the rat renal medulla after administration of L-NAME, Indomethacin and iothalamate. Medullary oxygenation in rats was reduced by inhibition of the synthesis of prostaglandins and nitric oxide, as well as by intravenous injection of radiocontrast agents. BOLD MRI can noninvasively evaluate changes in medullary oxygenation in rats that appear to predispose acute renal failure. J. Magn. Reson. Imaging 2001;13:744-747.

The endogenous insulin-like growth factor system in radiocontrast nephropathy

The response of insulin-like growth factor (IGF) I in acute renal failure was evaluated in a model of radiocontrast nephropathy associated with selective necrosis of medullary thick ascending limbs. In brief, rats were administered radiocontrast medium or vehicle injections for controls after combined inhibition of prostanoids and nitric oxide. Twenty-four hours after the insult, tissue mRNAs for IGF-I, the IGF-I receptor, and IGF-binding proteins (IGFBP) 1 and 3 were assayed in cortex, medulla, and liver by solution hybridization-RNase protection assay, and IGFBPs were measured in serum and tissue by Western ligand blotting. Cortical IGF-1 increased, whereas medullary IGF-I mRNA decreased. Renal IGFBPs decreased, whereas IGFBP-1 mRNA increased. The IGF system in the liver was unchanged. We conclude that general changes in renal IGFBPs in this experimental model of acute renal failure might increase the level of cortical IGF-I in a way that could modulate medullary recovery.

Are iodinated contrast agents detrimental in acute cerebral ischemia? An experimental study in rats

PURPOSE

To study the effects of iothalamate sodium and two dosages of iopromide in acute cerebral ischemia on infarction volume, neurologic performance, and mortality in a rat model of middle cerebral artery occlusion.

MATERIALS AND METHODS

Sixty-four rats underwent endovascular occlusion of the middle cerebral artery. Four hours later, 16 animals received iothalamate sodium (588 mg iodine per kilogram); 16, iopromide as a single bolus (518 mg iodine per kilogram); and 16, iopromide as a double bolus (1,036 mg iodine per kilogram). Sixteen animals received equivolumetric saline (control group). Neurologic score and body weight were recorded every 8 hours. Twenty-four hours after occlusion, all animals were killed; brains were stained to assess the infarction size.

RESULTS

Single and double doses of iopromide did not affect infarction volume or neurologic performance. Iothalamate caused an increase in infarction volume and worsening of the neurologic score (p < .05). Mortality rate was 25% in the iothalamate group, 12% in the control group, and 6% in the iopromide groups.

CONCLUSION

Bolus injection of the nonionic iopromide does not statistically significantly affect infarction volume or cerebral ischemia symptoms. Nonionic rather than ionic contrast agents should be preferred during acute cerebral ischemia.

Renal microcirculation and tissue damage during acute ureteral obstruction in the rat: effect of saline infusion, indomethacin and radiocontrast

Radiocontrast agents and nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the diagnosis and treatment of renal colic. We studied their impact during unilateral acute urinary outflow obstruction upon renal microcirculation and parenchymal integrity. Laser-Doppler and ultrasonic regional flow measurements demonstrated selective decline of outer medullary blood flow by 23 +/- 2% during an acute increase of intra-pelvic pressure to 50 to 55 cm H2O (N = 28, X +/- SEM, P < 0.01). In rats preconditioned with indomethacin, this manipulation reduced medullary blood flow by 50 +/- 4% (N = 16, P < 0.01 vs. obstruction alone), with cortical and total renal blood flow declining by 18 +/- 4% and 16 +/- 2%, respectively (P < 0.01). Unilateral obstruction alone for 24 hours in intact rats resulted in injury (hemorrhage and necrosis) to the papilla and fornix (formed laterally by inner stripe and medially by the inner medulla). These changes were detected as early as 30 minutes after ureteral ligature by staining for fragmented nuclear DNA (TUNEL). Mild damage of thick ascending limbs (mTALs) was associated with substantial medial fornix injury. Indomethacin markedly increased mTAL injury in obstructed kidneys, but attenuated inner medullary damage, both in the medial border of the urinary space and at the papilla. This latter protective effect, probably mediated by the decrease in intrapelvic pressure, was blunted by concomitant intravenous fluid load. Contrast media (iothalamate) and L-NAME (N omega nitro-L-arginine methyl ester) both augmented inner stripe and inner medullary damage in hydronephrotic kidneys. In rats concomitantly subjected to radiocontrast, indomethacin and L-NAME (an acute renal failure protocol, J Clin Invest 94:1069, 1994), unilateral obstruction augmented inner stripe hypoxic damage (65 +/- 6% vs. 24 +/- 11% of mTALs in contralateral kidneys, N = 7, P < 0.01). Injury was maximal at the fornix (93 +/- 6% vs. 39 +/- 14% of mTALs in the mid-inner stripe, P < 0.01) and extended to the outer stripe and medullary rays. Thus, in the rat acute ureteral obstruction alters medullary blood flow and within 24 hours produces medullary damage in both forniceal and inner medullary locations, that is exacerbated by concomitant measures which limit medullary oxygenation. Contrast studies, forced hydration and NSAIDs for renal colic are potentially harmful and their use should be re-evaluated.

Failure of insulin-like growth factor 1 to improve radiocontrast nephropathy

Exogenous insulin-like growth factor 1 (IGF-1) has been reported to improve experimental ischemic acute renal failure. We investigated a possible beneficial role of IGF-1 in a model of radiocontrast nephropathy induced by indomethacin, nitro-L-arginine ester and iothalamate. Multiple injections of recombinant human IGF-1 (or its vehicle) at 150 microg/100 g body weight/day were given for 24 h starting 1 h after radiocontrast, or initiated 1 day after the insults and continued for 48 h. IGF-1 prevented neither the fall in creatinine clearance nor medullary thick ascending limb necrosis observed at 24 h. Similarly IGF-1, given for 2 days after renal failure had been established, did not accelerate functional recovery at 72 h, did not ameliorate catabolism and did not alter the morphological evolution of intrarenal damage. In conclusion, IGF-1 had no beneficial effects in this model of radiocontrast nephropathy.

A role for nitric oxide in X-ray contrast material toxicity

RATIONALE AND OBJECTIVES

We assessed the role that nitric oxide (NO) plays in contrast media (CM) toxicity, using 100% lethal dose (LD100) studies in hyperimmune Brown Norway (BN) rats.

METHODS

Ninety-two BN rats and 41 Sprague-Dawley (SD) rats underwent CM LD100 tail vein injections with methylglucamine iothalamate or sodium iothalamate to the point of cessation of respiration. Methylglucamine hydrochloride also was injected. The injections were accompanied by L-arginine (L-Arg) or D-arginine (D-Arg) analogues or by an H1 blocker. L-Arg analogues inhibit NO formation, and D-Arg analogues do not.

RESULTS

An L-Arg analogue, but not a D-Arg analogue, increased the tolerance of BN rats (p < .005) for methylglucamine iothalamate but not for sodium iothalamate. The L-Arg analogue also protected BN rats against methylglucamine chloride injections (p < .002). H1 blockade protected BN rats against methylglucamine iothalamate (p < .0005) and methylglucamine chloride (p < .005) injections. None of these measures altered the CM tolerance of SD rats. In SD rats, injections of either methylglucamine iothalamate or sodium iothalamate along with a D-Arg analogue or normal saline were better tolerated than similar injections in BN rats (p < .01 and .002 for methylglucamine iothalamate and sodium iothalamate, respectively). In SD rats but not BN rats, sodium iothalamate was better tolerated than was methylglucamine iothalamate (p < .0005).

CONCLUSION

NO appears to play a significant role in BN rats LD100 CM toxicity and has been implicated by others in the blood pressure fall characterizing some forms of antigen-induced anaphylaxis [1, 2]. The results of the current study and the literature suggest that methylglucamine-modulated release of histamine from mast cells may underlie the NO production.

[Increase of kidney enzymes in urine after administration of contrast media: comparison of the nephrotoxicity of ionic and nonionic substances]

In a double blind clinical study, 50 patients with healthy kidneys were tested for the discharge of renal marker proteins before and after receiving a high or low osmoloar contrast medium (Meglium-Ioglicinat, Imeprol) using i.v. urography. The renal excretion of the tubular indicator enzymes alanine aminopeptidase, beta-Glutamyltranspeptidase and alkaline phosphatase increased in all patients after administration of the contrast media. The enzymuria was significantly lower with the non-ionic contrast medium with the ionic one, thus demonstrating that the non-ionic contrast medium has a lower nephrotoxic potential than the conventional ionic contrast medium. Three independent investigators evaluated the radiograms with regard to the contrast quality using prearranged criteria in a 5 point system. The diversity of the evaluations clearly favoured the non-ionic contrast medium.

Nitric oxide and prostanoids protect the renal outer medulla from radiocontrast toxicity in the rat

Human radiocontrast nephrotoxicity is predicted by the presence of multiple risk factors, often associated with compromised renal circulation. To produce a simple model of radiocontrast nephropathy, rats were pretreated with indomethacin and N omega-nitro-L-arginine methyl ester (L-NAME, to inhibit nitric oxide synthesis) before the administration of iothalamate. Acute renal failure consistently developed, with a decline in creatinine clearance from 1.05 +/- 0.10 to 0.27 +/- 0.05 ml/min (P < 0.001) associated with selective necrosis of 49 +/- 9% of medullary thick ascending limbs. Hemodynamic studies using laser-Doppler probes revealed that when injected alone, iothalamate increased outer medullary blood flow to 196 +/- 25% of baseline (P < 0.001). Pretreatment by L-NAME or indomethacin both reduced basal medullary blood flow and transformed the medullary vasodilator response to radiocontrast into vasoconstriction, with a prolonged reduction of medullary blood flow to less then half of baseline. Combined administration of indomethacin, L-NAME, and iothalamate lowered medullary blood flow to 12 +/- 4% of baseline. We conclude that prostanoids and nitric oxide have an important protective role in the renal response to radiocontrast material. Reduced synthesis of these vasoactive substances in renal/vascular diseases may predispose patients to radiocontrast nephropathy.

Mechanism of pain induced by radiocontrast media

In lightly-anesthetized dogs, ionic or non-ionic RCM (Iotalamato and iohexol, respectively) when injected by intracarotid route (i.c.), elicit a pain response comparable to that caused by bradykinin (BK) or capsaicin (CAP). This response, which is characterized by vocalization, hyperpnea, bradycardia and neck muscle contraction, was dose dependent and related to the osmolarity of the RCM. In the present study we observed that indomethacin did not interfere with CAP and RCM-induced pain at dose (2 mg/kg i.c.) that reduced BK-elicited responses. In contrast, Ruthenium Red (RR), in dose (1 mg/kg i.c.) that reduced CAP and/or RCM-induced effects did not affect BK-induced phenomena. We also verified that L-NAME (50 mg/kg i.c.) reduced the BK-, but not the CAP- and/or RCM-induced pain responses which suggests that an L-arginine-derived NO or related compound is involved in BK activation of perivascular nociceptors. Indeed, we found that i.c. injection of 20 mg of S-nitrosocysteine, a putative EDRF, caused BK-like responses. On the other hand, RCM and CAP appear to activate the same RR sensitive ionic channels of primary afferent endings. Therefore, RR-analogues could constitute a novel approach to minimizing or eventually abolishing the RCM side effects.

Radiocontrast increases plasma and urinary endothelin

Recent studies indicate that endothelin (ET), a potent endogenous systemic and renal vasoconstrictor peptide, may mediate decreases in GFR in models of acute renal dysfunction. Moreover, in an animal model of radiocontrast-induced nephropathy (RCIN), it was recently demonstrated that early renal hemodynamic responses to radiocontrast are attenuated by intra-arterial atrial natriuretic factor (ANF), which prevents subsequent RCIN. The studies presented here were therefore designed to determine whether i.v. infusion of radiocontrast produces increases in endogenous plasma and urinary ET and whether these responses are modulated by intra-arterial ANF in an animal model of RCIN. In these studies, dogs with pacing-induced heart failure received i.v. radiocontrast in the presence and absence of an intra-aortic infusion of ANF. Significant increases in both plasma and urinary ET were observed during and after radiocontrast. Although coadministration of ANF did not prevent increases in plasma and urinary ET, ANF preserved renal function acutely in this model of RCIN by increasing GFR above baseline levels.

Early renal medullary hypoxic injury from radiocontrast and indomethacin

We evaluated the acute changes in cortical and outer medullary oxygen tension and the alterations in renal function and morphology within the first 90 minutes after the administration of indomethacin and iothalamate to anesthetized Sprague-Dawley rats. Both agents were found to produce marked and protracted outer medullary hypoxia averaging 12 +/- 4 and 9 +/- 2 mm Hg, respectively (mean +/- SE). Given together to salt depleted uninephrectomized rats they produced an early hypoxic injury localized selectively in the outer medulla. This lesion progressed from 3 +/- 1% of medullary thick ascending limbs (mTALs) at 15 minutes to 22 +/- 7% at 24 hours. Condensed "dark" cells were observed at 15 minutes, probably representing a type of early injury. Residual red cell mass, quantified in the outer medullary vasculature of perfusion-fixed kidneys and presumably reflecting stasis, was substantially increased in iothalamate treated rats. Red cell mass in the interbundle zone correlated with mTAL necrosis. Taken together, these results show an early period of medullary hypoxia, accompanied by a selective injury to mTALs in the central interbundle zone with apparent stasis. These findings contrast sharply with the ischemia-reflow pattern of renal damage and emphasize the important role of medullary hypoxia in the genesis of acute renal failure in this model.

Variable effects of radiological contrast media on thrombus growth in a rabbit jugular vein thrombosis model

We studied the effect of an ionic high osmolar contrast medium (Ioxitalamate), an ionic low osmolar contrast medium (Ioxaglate) and various nonionic low osmolar contrast media (Iopamidol, Iopromide and Iohexol) on thrombus growth in a rabbit jugular vein thrombosis model. Thrombus growth was determined by the accretion of 125I-labeled fibrinogen onto autologous preformed thrombi in rabbit jugular veins at various time-intervals from 15 min up to 10 h after infusion of the study solution. The ionic low osmolar contrast medium markedly inhibited thrombus growth whereas all nonionic low osmolar contrast media promoted thrombus growth. The ionic high osmolar, contrast medium inhibited thrombus growth, but less than the ionic low osmolar contrast medium. Within the group of nonionic contrast media, the Iopamidol associated promotion of thrombus growth was significantly higher than the Iopromide or Iohexol associated effects. The simultaneous administration of the apparently most potent thrombus growth promoting contrast medium (i.e. Iopamidol) and heparin resulted in complete abolishment of the increase in thrombus growth. These results support the claims of prothrombotic properties of nonionic as compared to ionic contrast media and could explain the clinically encountered thromboembolic complications after the use of nonionic low osmolar contrast media.

Experimental nephrotoxicity of the radiocontrast agents iohexol, ioxaglate, and iothalamate. An in vitro and in vivo study

The authors compared the renal toxicity of the low osmolality radiocontrast agents, iohexol and ioxaglate, and the ionic agent, iothalamate, at equivalent iodine dose, using experimental models in vitro and in vivo. In isolated perfused rat kidneys, all agents induced comparable biphasic hemodynamic changes, associated with similar declines in glomerular filtration rate (GFR) and tubular necrosis. In two different in vivo models (using multiple insults combined with the administration of radiocontrast), iothalamate appeared to induce more severe morphologic injury. Despite similar nephrotoxic potential in vitro, the newer radiocontrast agents, iohexol and ioxaglate, cause in vivo less renal injury than iothalamate in the experimental models.

Nephrotoxicity of contrast media in high-risk patients with renal insufficiency: comparison of low- and high-osmolar contrast agents

We have compared the renal effects of ioxitalamate, ioxaglate, and iopamidol in patients with chronic renal failure. Sixty consecutive patients with an estimated creatinine clearance (ECRCl) less than 60 ml/min were randomly assigned to receive either ioxitalamate, iopamidol, or ioxaglate. All patients received 500 cm3 isotonic saline before the procedure. Serum creatinine and ECRCl were estimated before, 1 and 2 or 3 days after the procedure. There was no statistical difference between the three groups with respect to age, sex, weight, renal function, amount of iodine, and type of procedure. Mean serum creatinine and ECRCl remained unchanged after administration of contrast media. No patient had nephrotoxicity or acute oliguria requiring dialysis as a result of the administration of contrast material. The number of patients with an increase in the serum creatinine level greater than 10% from the basal value did not differ in the treatment groups. The maximal increases in serum creatinine were 52 mumol/l (29%) in the ioxitalamate group, 56 mumol/l (18%) in the ioxaglate group, and 57 mumol/l (23%) in the iopamidol group (p = NS). Using a population carefully randomized and matched for renal insufficiency, we could not show any differences in nephrotoxicity between these three contrast agents. Clinically serious renal impairment was uncommon in our study, regardless of the contrast agent used. However, the interpretation of these favorable findings requires a cautionary note. All patients in this study were well hydrated before and after uro-/angiography, and none had a recent renal injury or a treatment with a nephrotoxic agent that would predispose to injury from contrast material.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction and prevention of radiocontrast-induced nephropathy in dogs with heart failure

Radiocontrast-induced nephropathy (RCIN) is a clinically important cause of acute renal failure with no effective treatment. Recognizing the high incidence of RCIN in humans with severe congestive heart failure (CHF), this study was designed to test the hypotheses that dogs with experimental CHF are at increased risk for RCIN and that pharmacologic renal levels of atrial natriuretic factor (ANF) can prevent RCIN in this model. In chronic experiments, three groups of five conscious dogs received intravenous radiocontrast (7 ml/kg). One group consisted of normal controls, while the two other groups had experimental CHF induced by eight days of ventricular pacing at 250 beats per minute. One of the CHF groups received an infusion of ANF (30 ng/kg/min) into the suprarenal aorta for one hour before, during and after the infusion of radiocontrast to achieve pharmacologic renal plasma levels. Renal function remained stable in the normal controls in contrast to the consistent decreases in daily creatinine clearance during the five days following radiocontrast in experimental CHF. In addition, ANF prevented radiocontrast-induced reductions in creatinine clearance in dogs with experimental CHF. Additional studies performed in two groups of anesthetized dogs with experimental CHF demonstrated that, in this model of RCIN, the reduction in renal function appears biphasic, and the action of ANF may be to increase glomerular filtration rate prior to radiocontrast, thus allowing a maintenance of renal function during and after radiocontrast.

Experimental tissue damage after subcutaneous injection of water soluble contrast media

Various water soluble contrast media (WSCM) were injected subcutaneously into 970 hind feet of 485 rats. Gross morphologic changes were seen after the injection and analyzed as a function of various physicochemical characteristics of WSCM. The WSCM of larger volume, higher osmolality, higher iodine content, and meglumine salts rather than sodium salts caused more severe tissue damage; younger rats showed more severe tissue damage by WSCM of high osmolality.

[Effect of renovascular roentgen contrast media on the function of the healthy kidney--an individual comparison]

In 50 patients with healthy kidneys the excretion of tubular enzymes was determined quantitatively before and after administration of an ionic and a non-ionic contrast medium and compared intra-individually. Both preparations produced a highly significant increase in enzyme levels to about twice the initial value, the increase being significantly lower with the non-ionic contrast medium. This effect was fully reversible within 24 hours. No noticeable change was seen within the examination period of 48 hours in respect of creatinine and creatinine clearance levels.

Tolerability of hypertonic and isotonic contrast media injected intravenously. A comparative study in the dog

We examined the use of isotonic and hypertonic contrast media injected intravenously in the dog from the standpoint of cardiovascular tolerance after right atrial injections performed at 2.56 and 5.12 g I/second. The parameters measured were lead II of the electrocardiograph, heart rate, pulmonary and abdominal arterial pressure, and aortic flow. Three contrast media, ioxitalamate, ioxaglate, and iopamidol (two ionic and one nonionic), were compared, either concentrated (32% iodine) or dilute and isotonic with plasma (ioxaglate 160 mg I/mL and iopamidol 128 mg I/mL). At an injection rate of 5.12 g I/second, iopamidol-128 showed lower electrophysiologic tolerability and caused a higher increase in aortic flow than ioxitalamate 160 or ioxaglate 160. These effects may explain the lower radiographic efficacy observed with iopamidol-128 in previous digital subtraction angiography studies.

Tissue reaction following endobronchial application of iopamidol and ioxithalamate in rats

Lung tissue reaction to endobronchial application of iopamidol and ioxithalamate were compared by chest radiograph and histological examination in the rat. Radiographs cleared within hours in both groups. Tissue reaction after ioxithalamate application was significantly more pronounced than with iopamidol and included macrophage response, partial atelectasis, and intra-alveolar and interstitial oedema. Different from iopamidol, ioxithalamate induced a significantly stronger reaction than tracheotomy alone. Because no important significant side effects were observed on chest radiographs or in lung histology, iopamidol is recommended for the radiological examination of the gastrointestinal tract in patients with an increased risk of aspiration.

Contrast, coagulation, and fibrinolysis

Some adverse clinical effects of intravascular radiologic contrast agents have been attributed to their interference with the normal hemostatic processes. This study compares the effects of the low osmolality agents with those of the conventional agents by in vitro studies of platelet function, fibrin formation, and fibrinolytic activation. In various degrees, all the contrast agents studied inhibit platelet aggregation and fibrin formation but show virtually no direct activation of fibrinolysis. The new low osmolality agents generally show lesser inhibitory effects on the hemostatic mechanisms. Some clinical implications are discussed.

Effects of radiographic contrast media on monolayer cell cultures

The relationship between iodine concentration, osmolality, and toxicity for nine different contrast media was studied. High osmolal conventional ionic contrast media (Na-metrizoate, Na-iothalamate, meglumine/Na-diatrizoate, meglumine-calcium-metrizoate) and the new low osmolal nonionic (Metrizamide, iopamidol, iohexol) and ionic dimer (Meglumine/Na-ioxaglate) contrast media were tested. Monolayer cell cultures of human cervical carcinoma in situ cells were used as a test system. The toxicity of contrast media on cell cultures was strongly dependent on the osmolality, and different contrast media with the same osmolality had about similar effects on the cell cultures. However, contrast media seem to have some additional and more specific effects since equiosmolal saline and mannitol were better tolerated. When the toxicity was related solely to iodine concentration it emerged that the new low osmolal contrast media were much better tolerated than the high osmolal conventional contrast media.

[Acute cardiac side effects of iodecol, a new nonionic dimer roentgen contrast medium, in intracoronary injection]

The effects of intracoronary injections of Iodecol, a nonionic-dimeric contrast medium (iodine content 350 mg/ml, osmolality 0.34 osmol/kg, viscosity 13.8 mPa X s) on haemodynamics, coronary blood flow, ECG, and cationic content as well as osmolality of coronary sinus blood have been evaluated and compared to those of Iopamidol and Amidotrizoate. Experiments were carried out in 9 closed-chest dogs using heart catheterisation techniques. After Iodecol and Iopamidol only positive inotropism was seen while Amidotrizoate initially had cardiodepressive effects. Iodecol caused less increase of peak velocity of pressure rise and systolic blood pressure than Iopamidol. All contrast media led to an increase in coronary blood flow of the same extent. ECG changes were most marked following Amidotrizoate and only slight after Iodecol. Decrease of cationic content and increase of osmolality in coronary sinus blood were seen after each compound. Changes were only small after Iodecol and always greater after Amidotrizoate. Moreover, an overproportional decrease of coronary sinus calcium content was seen after Amidotrizoate due to calcium binding. Thus, based on these animal experiments, a further slight reduction of acute cardiac side effects during coronary arteriography could be expected from the use of nonionic dimeric compounds, compared to ionic and currently used nonionic contrast media.

Iohexol and ioxithalamate for intravenous urography. A comparative parallel study

Omnipaque (iohexol) 350 mg I/ml has been compared with Telebrix (ioxithalamate) 380 mg I/ml in 48 patients undergoing intravenous urography. The contrast medium dose corresponded to 400 mg I/kg body weight. No cardiovascular reactions (BP and pulse rate) were observed. Subjective reactions occurred somewhat more frequently after Telebrix than after Omnipaque. Sensation of warmth was significantly less with Omnipaque (p less than or equal to 0.05). The overall radiological quality was equally good for the two contrast media.

In vitro testing for the risk of arachnoiditis from myelographic contrast media

The risk of arachnoiditis from aqueous myelographic contrast media has been assayed reliably only in experimental animals. The effect of contrast media on protein and collagen production by fibroblasts in vitro was studied. Iocarmate, metrizamide, and iopamidol added to the culture medium caused cells to produce more protein and collagen. The degree to which the contrast medium stimulated collagen production correlated with the risk of arachnoiditis from the intrathecal use of the contrast medium. In vitro testing appears to be an effective assay for arachnoiditis.

Experimental evaluation of iosefamate meglumine and its derivatives as hepatobiliary CT contrast agents

Iosefamate meglumine has attracted attention as a possible hepatobiliary contrast agent for CT scanning. However, its limited hepatic opacification has prevented clinical acceptance. To find a more efficient agent, the efficacy and toxicity of six derivatives of iosefamate were compared with those of the parent compound in dogs. Twenty dogs received intravenous doses ranging from 150 to 600 mg I/kg of one of these seven water-soluble, ionic, dimeric agents. Three control animals received equivalent amounts of physiologic saline. The CT densities of liver, biliary tract, kidneys, and blood were then measured for up to 3 hr. Toxicity tests of liver and kidney function were performed for up to 3 days. Among the new agents, only MI-294, a previously unreported compound, proved to be a slightly more efficient hepatic opacifier than iosefamate (0.40 vs. 0.34 H per mg I/kg, respectively). MI-294 was also the least toxic. However, transient abnormalities in at least one liver function test were observed with every agent at some dose level. One animal died with hepatic necrosis after receiving iosefamate. No renal impairment was noted in any case. MI-294 has advantages over iosefamate as a CT liver and biliary opacifier in dogs. Potential hepatotoxicity of this class of agents needs to be more fully evaluated.

Iotrol, a new water-soluble non-ionic dimeric contrast medium for intrathecal use

The side effects associated with the use of Iotrol were determined in 100 patients and compared with metrizamide and iopamidol in two double-blind studies. The relevance of the distribution of the contrast medium in the CSF space to the occurrence of headache is discussed. The low persistence of iotrol in the brain parenchyma is demonstrated on CT density profiles, compared with metrizamide and iopamidol. Iotrol seems to be the safest contrast substance for intrathecal use.

Extravascular lung water: effects of intravenous ionic and non-ionic (lopamidol) contrast media during ischemia

Intravenous injections of ionic contrast media increase extravascular lung water in patients with elevated left atrial pressure, particularly in the presence of myocardial ischemia. The authors compared bolus injections of sodium methylglucamine diatrizoate and iopamidol on extravascular lung water at several levels of left atrial pressure in dogs. Methylglucamine increased lung water by a maximum of approximately 25-30% above baseline levels at low (less than 3 mm Hg), moderate (approximately equal to 15 mm Hg), and elevated left atrial pressures (greater than or equal to 25 mm Hg). At matched pressures, the peak change in lung water in the dogs given iopamidol was +4%, +7%, and +6%, respectively. In dogs with myocardial ischemia, the differences were even more pronounced (+45%, +60%, and +70%, respectively, for ionic media, and +7%, +12%, and +21% for iopamidol). The authors caution against using ionic contrast media in patients with left ventricular dysfunction, particularly associated with ischemia. In such cases, non-ionic media appear safer.

Chemotoxicity of contrast media and clinical adverse effects: a review

The clinical effects of contrast agents not only result from high osmolality, but also from their own specific pharmacology, which mediates chemotoxic effects. In this review, the chemotoxic effects of the new nonionic agent, iohexol, are compared with those of standard ionic and other low osmolality contrast agents, ionic and nonionic. Iohexol has the lowest chemotoxicity of any agent yet synthesized. Its low systemic toxicity is the combined result of low chemotoxicity and low osmolality. Mechanisms of severe adverse reactions are reviewed, including the views of Lasser and Lalli, and the view that emphasizes the importance of cardiotoxic and hemodynamic effects. It is concluded that whichever view is taken of the mechanisms of severe adverse reactions, the new nonionic agents are likely to be safer than the ionic agents now in use.

Pathogenesis of postmyelographic arachnoiditis

The causal relationship between a myelogram with an aqueous contrast medium and postmyelographic arachnoiditis has not been clarified. Primates after myelography with metrizamide or meglumine iocarmate were studied with fluorescent microscopy, energy dispersion analysis and with scanning and transmission electron and light microscopy. All controls and, up to the eighth day after myelography, all treated animals had normal-appearing arachnoid membranes by microscopy. After eight days the treated animals had progressively more severe arachnoid fibrosis. Energy dispersive analysis revealed iodine in the arachnoid only up to 24 hours after myelography. Fluorescent microscopy revealed no evidence of immune complexes in the arachnoid. The chronic effects of water-soluble media on the arachnoid are not apparently mediated by contrast medium persisting in the arachnoid or by immune complexes.

Contrast media induced pulmonary edema. Comparison of ionic and nonionic agents in an animal model

High intravenous doses of diatrizoate are known to induce pulmonary edema in the rat. The newer generation of contrast media--nonionics and monovalent dimers--are considered less toxic than diatrizoate. In this study we evaluated the degree of pulmonary edema induced by a high dose (6 g I/kg) of these new agents and found that Ioxaglate produced higher lung weights than Renografin 60 and Iopamidol. Iohexol and Amipaque did not induce a significant degree of edema. The model used in this study demonstrates distinct differences in pulmonary toxicity among these new agents, when given in doses exceedingly higher than given in clinical practice.

Comparative evaluation of the effects of an ionic vs. a nonionic contrast medium on the venous endothelium. Preliminary scanning electron microscopic observations

Isolated segments of the right jugular veins of six mongrel dogs were exposed to solutions of 60% diatrizoate (3 dogs) and 60% iopamidol (3 dogs) in vivo. Normal blood flow was re-established after 3 minutes of exposure to the contrast material. The left jugular veins served as controls. Veins were harvested at 1, 24, and 48 hours and studied by light and scanning electron microscopy. Changes consisting of cellular swelling, denudation, platelet aggregation and fibrin deposition were uniform and prominent with diatrizoate. Response to iopamidol was minimal consisting only of cellular swelling. The study suggests that post-phlebographic thrombophlebitis may be reduced by the use of nonionic contrast materials.

Nephrotoxicity of contrast media assessed by occlusion arteriography

The authors describe an experimental model for the study of nephrotoxicity induced by contrast media, based on a standardized injection combined with occlusion of the renal artery so as to expose the kidney to a high concentration of contrast medium for ten minutes. Iopamidol, ioxaglate, and both isosmolar and hyperosmolar saline were well tolerated, but diatrizoate caused marked radiological and pathological changes. This model may be helpful in studies of the mechanisms underlying contrast medium nephrotoxicity and evaluating differences in toxicity between contrast agents.

Psychopathometric demonstration and quantification of mental disturbances following myelography with metrizamide and iopamidol

Groups each consisting of ten patients underwent lumbar and cervical myelography with metrizamide and iopamidol, together with a control group of ten patients who underwent lumbar punctures only. These groups were studied with a psychopathometric test procedure in order to demonstrate and quantify mental disturbances. It was shown that in contrast to myelography with iopamidol, mild mental disturbances are common after myelography with metrizamide. The severity of the mental disturbances after myelography with metrizamide was dependent on the quantity of contrast medium which diffused into the intracranial space after myelography, suggesting a dose-related neurotoxic effect of this substance. Such a correlation was not found with iopamidol.

Renal toxicity of contrast agents: iopamidol, iothalamate, and diatrizoate

As part of a general safety study of iopamidol, a nonionic iodinated contrast agent, urine N-acetyl-beta-glucosaminidase enzyme assays were done to compare the renal toxicity of iopamidol with that of iothalamate and diatrizoate. In a randomized study of 30 patients for computed body tomography and another 30 patients for angiography, 10 in each group were injected with iopamidol, 10 with iothalamate, and 10 with diatrizoate. After computed tomography or angiography with the three agents, there was no significant difference in urinary enzyme levels among the groups. The nephrotoxicity of iopamidol appears equivalent to that of diatrizoate and iothalamate.

Iopamidol: new, nonionic contrast agent for excretory urography

Iopamidol, a new, nonionic contrast agent, was evaluated in 18 patients undergoing excretory urography. None of the 18 patients experienced any side effects or adverse reactions. No abnormalities were noted in serum chemistries, complete blood cell counts, urinalyses, or electrocardiograms. The half-life of iopamidol in 17 patients with normal renal function was 2.5 hr. The urograms were judged to be of good or excellent quality in 15 of 16 patients using doses of 200 and 250 mg l/kg of iopamidol. Two patients who were studied using a dose of only 120 mg l/kg had urograms rated poor. Fifteen iopamidol urograms (mean iodine dose, 17.4 g) were compared in a blind fashion with 15 meglumine diatrizoate studies (iodine dose, 29 g). No qualitative difference could be detected between the two groups of urograms. Iopamidol may provide equal-quality diagnostic studies with a lower iodine dose and perhaps greater safety than the currently used ionic agents.

Scanning electron microscopic (SEM) studies on the effect of x-ray contrast media on aortic endothelium in the rat

A study comparing the effects of diatrizoate, ioxitalamate, metrizamide, ioxaglate, and a 22% sorbitol on aortic endothelia of the rat was performed. In each case 1 ml of the respective solution was injected in a single dose into the aorta. Endothelial damage was seen after injection of metrizamide, diatrizoate, and ioxitalamate. After injection of ioxaglate or sorbitol, only minor endothelial changes were observed.