Diffusion of MRI and CT contrast agents in articular cartilage under static compression.

Cartilage has a limited capacity for self-repair and focal damage can eventually lead to complete degradation of the tissue. Early diagnosis of degenerative changes in cartilage is therefore essential. Contrast agent-based computed tomography and magnetic resonance imaging provide promising tools for this purpose. However, the common assumption in clinical applications that contrast agents reach steady-state distributions within the tissue has been of questionable validity. Characterization of nonequilibrium diffusion of contrast agents rather than their equilibrium distributions may therefore be more effective for image-based cartilage assessment. Transport of contrast agent through the extracellular matrix of cartilage can be affected by tissue compression due to matrix structural and compositional changes including reduced pore size and fluid content. We therefore investigate the effects of static compression on diffusion of three common contrast agents: sodium iodide, sodium diatrizoate, and gadolinium diethylenetriamine-pentaacid (Gd-DTPA). Results showed that static compression was associated with significant decreases in diffusivities for sodium iodide and Gd-DTPA, with similar (but not significant) trends for sodium diatrizoate. Molecular mass of contrast agents affected diffusivities as the smallest one tested, sodium iodide, showed higher diffusivity than sodium diatrizoate and Gd-DTPA. Compression-associated cartilage matrix alterations such as glycosaminoglycan and fluid contents were found to correspond with variations in contrast agent diffusivities. Although decreased diffusivity was significantly correlated with increasing glycosaminoglycan content for sodium iodide and Gd-DTPA only, diffusivity significantly increased for all contrast agents by increasing fluid fraction. Because compounds based on iodine and gadolinium are commonly used for computed tomography and magnetic resonance imaging, present findings can be valuable for more accurate image-based assessment of variations in cartilage composition associated with focal injuries.

On the search for in vitro in vivo correlations in the field of intra-articular drug delivery: administration of sodium diatrizoate to the horse.

Development of suitable in vitro release models for formulation development as well as quality control purposes has to be initiated in the early design phase of injectable depots. Optimally, construction of an in vitro release model may lead to the establishment of in vitro in vivo correlations. By using a model compound (sodium diatrizoate, DTZ), the purpose of this study was to investigate the possibility of establishing in vitro in vivo relations between the DTZ disappearance profile obtained from the donor compartment of the rotating dialysis cell model and the joint disappearance profile following intra-articular administration. In vitro experiments were conducted by applying solutions of DTZ to the donor compartment. In the in vivo experiments, five horses were subjected to both intravenous and intra-articular administration of an aqueous solution of 3.9 mg DTZ/kg. A strong relation (R(2)=0.99) was obtained between the disappearance data from the donor compartment of the in vitro model and the disappearance data from the synovial fluid after intra-articular administration of DTZ. Furthermore, a relation (R(2)=0.91) between the appearance data obtained from the acceptor compartment and the deconvolved appearance serum data upon intra-articular administration of DTZ was obtained. The correlations obtained in this study hold promise that the rotating dialysis cell model has a role in the prediction of the intra-articular fate of drugs injected as solutions.

The pharmacokinetics of the weakly protein-bound anionic compound diatrizoate in serum and synovial fluid of the horse.

PURPOSE: To establish a pharmacokinetic model for the model drug, sodium diatrizoate (DTZ), allowing joint disappearance kinetics to be estimated from serum appearance kinetics following intra-articular administration, and to calculate the relative joint exposure after intravenous and intra-articular DTZ administration (F(iv/IA)). METHODS: Each of five horses received an aqueous solution of 3.9 mg/kg sodium diatrizoate both intravenously and intra-articularly separated by a one-week wash out period. Serum and synovial samples were collected over 7 h and analyzed for content of model compound using inductively coupled plasma mass spectrometry. RESULTS: Differential equations were used for describing the transport of DTZ between the joint and the central compartment. The three-compartment lag-time model obtained demonstrates that the rate of drug appearance in the systemic circulation equals the rate of disappearance from the joint compartment. Following intravenous and intra-articular administration, an average F(iv/IA) of 0.04% (n = 4) was calculated based on the synovial fluid profiles of DTZ. CONCLUSIONS: This study implies that aspects of the intra-articular fate of DTZ can be obtained from serum data in case synovial fluid samplings are limited, for various possible reasons. The low F(iv/IA) may stimulate future research in the field of intra-articular administration of anti-osteoarthritic drugs.

Renal chemoembolization with mitomycin c/Ethibloc: pharmacokinetics and efficacy in an animal model.

BACKGROUND AND PURPOSE: Arterial embolization can be an alternative treatment for kidney malignancy. We investigated the efficacy of renal embolization with a combination of an occlusive agent (Ethibloc) and the cytotoxic substance mitomycin C (MMC) in an animal model. MATERIALS AND METHODS: In 32 rats with implanted Yoshida sarcoma, nephrectomy was carried out 15, 30, 60, or 90 minutes after chemoembolization (1 mg v 2 mg of MMC/mL of Ethibloc) or chemoperfusion (1 mg of MMC/mL of NaCl) of the tumor-bearing kidney. The MMC tissue concentration was measured in the kidney specimens. Six dogs also underwent chemoembolization or chemoperfusion with monitoring of MMC serum concentration at the same intervals. We compared the survival time of rats with Yoshida sarcoma after chemoembolization (N = 15), chemoperfusion (N = 18), embolization (N = 18), nephrectomy (N = 21), and no treatment (N = 25). RESULTS: The MMC tissue concentration in the rat model was much higher after chemoembolization than after chemoperfusion for at least 1.5 hours. The MMC serum concentration in the dogs showed a high initial peak (0.6 mg/L) after chemoperfusion, then dropped quickly to the same level seen 30 minutes after chemoembolization with 1 mg of MMC/mL of Ethibloc (0.15 mg/L). The MMC serum concentration following chemoembolization with 2 mg of MMC/mL of Ethibloc stayed higher (0.3-0.25 mg/L) for 60 minutes. The survival rates after nephrectomy were equal to those after chemoembolization (80% survival after 30 days), with poorer survival being seen after embolization (75%) and chemoperfusion (70%). In the control group, all rats were dead at the 27th day. CONCLUSION: Chemoembolization produces persistently high tissue concentrations of MMC and avoids toxic peak serum levels. It improves the efficacy of organ ablative vasoocclusion in renal malignancies.

Role of NO in endothelin-regulated drug transport in the renal proximal tubule.

We previously demonstrated in intact killifish renal proximal tubules that endothelin (ET), acting through an ET(B) receptor and protein kinase C (PKC), reduced transport mediated by multidrug resistance-associated protein 2 (Mrp2), i.e., luminal accumulation of fluorescein methotrexate (FL-MTX) (Masereeuw R, Terlouw SA, Van Aubel RAMH, Russel FGM, and Miller DS. Mol Pharmacol 57: 59-67, 2000). In the present study, we used confocal microscopy and quantitative image analysis to measure Mrp2-mediated transport of FL-MTX in killifish tubules as an indicator of the status of this ET-fired, intracellular signaling pathway. Exposing tubules to sodium nitroprusside (SNP), a nitric oxide (NO) donor, signaled a reduction in luminal accumulation of FL-MTX, which suggested pathway activation. N(G)-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor, blocked the action of ET-1 on transport. Because SNP effects on transport were blocked by bisindoylmaleide, a PKC-selective inhibitor, but not by RES-701-1, an ET(B)-receptor antagonist, generation of NO occurred after ET(B) receptor signaling but before PKC activation. NO generation was implicated in the actions of several nephrotoxicants, i.e., diatrizoate, gentamicin, amikacin, HgCl(2), and CdCl(2), each of which decreased Mrp2-mediated transport by activating ET signaling. For each nephrotoxicant, decreased FL-MTX transport was prevented when tubules were exposed to L-NMMA. ET-1 and each nephrotoxicant stimulated NO production by the tubules, as determined by a fluorescence-based assay. Together, the data show that NO generation follows ET binding to the basolateral ET(B) receptor and that, in activating the ET-signaling pathway, nephrotoxicants produce NO, a molecule that could contribute to subsequent toxic effects.

Analysis of blood coagulation in the zebrafish.

The zebrafish (Danio rerio) is a unique animal model in which saturation mutagenesis has been used to identify genes involved in vertebrate development. The relevance of the zebrafish as a genetic model for hemostasis depends, in large part, on the degree of similarity between the zebrafish and mammalian systems. The diminutive size of the zebrafish poses technical problems for analysis of coagulation. This study describes methods to obtain citrated whole blood and plasma from the zebrafish, analyze in vitro coagulation in small plasma volumes, obtain uniform dosing of zebrafish with oral anticoagulants, and demonstrate specific factor activities via chromogenic assays. Analysis of the zebrafish system demonstrates the presence of both the intrinsic and extrinsic pathways of coagulation, evidence for prothrombin, factor X, protein C, antithrombin, and heparin cofactor II activity, and a requirement for vitamin K dependent gamma-carboxylation of zebrafish hemostatic proteins. Induction of a morphologically recognizable bleeding phenotype by warfarin treatment is also demonstrated. Characterization of zebrafish coagulation provides evidence that major hemostatic pathways are conserved between zebrafish and man. These similarities indicate that the zebrafish is a relevant genetic model for identification of novel genes involved in hemostasis and thrombosis.

Renal cortical retention of contrast medium after angiography as assessed by delayed CT: a multivariate analysis.

Renal cortical retention (RCR) of contrast medium discovered by delayed X-ray examination is sometimes reported in patients with problems in the urinary system. However, we frequently found RCR even in patients with normal renal function. Therefore, we examined the incidence and factors involved in RCR by delayed computed tomography (CT) 12-24 hours after angiography in 168 patients. RCR was found in 80 of 168 cases (48%). Ioxaglate (60%) and iohexol (60%) showed higher incidences of RCR than diatrizoate (37%) and iopamidol (37%). Multivariate logistic regression analysis was performed to determine the predisposing factors of RCR. Dose of administered contrast medium by body weight (p = 0.004), age (p = 0.009), sex (p = 0.013), type of contrast medium (p = 0.003), serum albumin (p = 0.011), and serum creatinine (p = 0.002) were identified as significant and independent predisposing factors of RCR. We suggest that RCR is not a rare phenomenon if delayed CT is carried out.

Effects of diatrizoate and iopamidol on spermatogenesis.

RATIONALE AND OBJECTIVES: The biological effects of iodinated contrast media were examined by using spermatogenesis in mouse testis as the experimental model. METHODS: Spermhead survival and abnormality assays were used as the biological end points. Diatrizoate meglumine/diatrizoate sodium and iopamidol were administered intravenously at equal rates and concentrations. Testicular uptake and clearance of these contrast agents were examined by high-performance liquid chromatography techniques. Appropriate mannitol solutions were employed as osmolality controls. RESULTS: Intravenous administration of the contrast agent or its respective mannitol control resulted in approximately a 30% decrease in spermhead count. A dose-related experiment with mannitol demonstrated that the spermhead count decreased rapidly until 600 mOsm/kg was reached, beyond which this decrease was minimal. Clearance of both contrast media was complete in approximately 4 hours. No significant increase in the induction of spermhead abnormalities was observed. CONCLUSION: Osmotic substances, such as iodinated contrast agents, affect the process of spermatogenesis.

Pretreatment with steroids before intravenous injection of diatrizoate or iohexol. Effects on urine and serum profiles.

The effects on urine and serum profiles of intravenous injection of diatrizoate, iohexol, or saline were studied in male rats pretreated with steroids or saline. Using urinary albumin, glucose, sodium, and the enzymes lactate dehydrogenase (LDH), gamma-glutamyltransferase (GGT), and N-acetyl-beta-D-glucosaminidase (NAG) as markers of glomerular and tubular function, it was found that diatrizoate caused temporary glomerular and tubular dysfunction; the effect was independent of the kind of pretreatment. Iohexol did not cause increased glomerular permeability in steroid- and saline-pretreated rats. When used following saline, iohexol induced increased excretion of three tubular components, whereas iohexol plus steroids caused increased excretion of all five tubular components. The dysfunctional effect of iohexol plus steroids was less than that of diatrizoate plus steroids. The serum components revealed no abnormalities induced by either contrast media or methylprednisolone. Pretreatment with steroids has no effect on the glomerular or tubular dysfunctional effect of diatrizoate, whereas it worsens the temporary tubular dysfunctional effect of iohexol in rats.

Renal clearance of an ionic high-osmolar and a nonionic low-osmolar contrast medium.

One hundred patients with normal serum creatinine concentration underwent intravenous urography with either an ionic high-osmolar (diatrizoate) or a nonionic low-osmolar (iopamidol) contrast medium after randomization. Before injection of the contrast medium, a blood sample was drawn for determinating serum creatinine concentration, and a urine sample for measurement of urine osmolality. Using x-ray fluorescence, the plasma concentration of iodine (contrast medium) was determined on blood samples drawn approximately 3 and 4 hours after injection of the contrast medium. The glomerular filtration rate was calculated by two different formulas: one requiring only a single sample and one requiring at least two samples (standard). There were poor correlations between the standard contrast medium clearance and the serum creatinine concentration, the estimated creatinine clearance (calculated from a nomogram), as well as the urine osmolality. The 3-hour and the 4-hour single-sample values correlated well with the two-sample values for both contrast media. In patients with normal serum creatinine, the glomerular filtration rate determined by measuring the contrast medium concentration in a single plasma sample obtained at 3 hours, is almost identical to the value determined from two samples. Consequently, two samples are unnecessary.

Factors affecting penetration of retrograde coronary venous injections into normal and ischemic canine myocardium: assessment by contrast echocardiography and digital angiography.

Ths experimental study described myocardial echo contrast enhancement through coronary venous injections. Retrograde administration of renografin was performed in 15 closed-chest dogs. Two-dimensional echocardiography was used to study myocardial echo contrast enhancement before and after coronary artery occlusion. Digital subtraction venography was used to assess delivery, drainage and shunting of the retrograde injectate. Systolic/diastolic blood pressure in the great cardiac vein measured 7 +/- 3/1 +/- 0.6 mm Hg and increased to 29 +/- 11/5 +/- 3 after coronary sinus occlusion and to 55 +/- 2.3/15 +/- 12 mm Hg during coronary sinus contrast injection. Myocardial contrast echo appearance in a midpapillary left ventricular short axis cross-section was limited to the anteroseptal region, extending to 28.4 +/- 11.3% of the section circumference after great cardiac vein injections and 35.3 +/- 17% after coronary sinus injections (difference NS). After occlusion of the left anterior descending coronary artery, great cardiac vein contrast injections resulted in opacification of 36.6 +/- 9.7% of the section circumference (N.S. vs preocclusion control) and opacified most, but not all asynergic segments. After occlusion of the circumflex coronary artery, myocardial echo contrast uptake was restricted to the septum and the anterior wall. The ischemic and asynergic posterolateral myocardial segments were not opacified. Digital subtraction coronary venography revealed rapid drainage of retrogradely injected contrast to the right atrium, in spite of coronary sinus balloon occlusion via venovenous anastomoses. Retrograde coronary venous contrast injections may help define myocardial regions which are accessible with retrograde coronary venous interventions.

Pharmacokinetics of three contrast media in experimental pancreatography.

Diatrizoate, iohexol and ioxaglate were compared in experimental pancreatography in piglets. Outflow of contrast medium (CM) through the pancreatic papilla was permitted (n = 14) or impaired (n = 17) during examination. The CM concentrations were measured in portal and systemic plasma and in lymph to study the absorption of CM. Absorption of diatrizoate and iohexol was similar in both types of experiment, but radiographically, diatrizoate escaped significantly earlier from the pancreatic duct when outflow was permitted (p less than 0.01), suggesting that the CM was absorbed mainly during injection. Ioxaglate concentrations rose more slowly in systemic plasma and lymph, and fell more slowly in the portal plasma than those of diatrizoate and iohexol, which suggests that ioxaglate was absorbed over a longer period. When outflow was impaired, ioxaglate concentrations remained on a lower level, indicating less penetration in the pancreatic parenchyma. CM absorption varied markedly within each group, suggesting that variations in intraductal pressure and flow are more important in absorption than the type of CM used.

Diatrizoate levels in cerebrospinal fluid following intravenous administration. Role of fluid production rate.

The central nervous system (CNS) may be highly susceptible to the toxic effects of conventional contrast media (CM). The current study quantifies levels of diatrizoate in canine cerebrospinal fluid (CSF) following intravenous administration and examines how these levels change as CSF production rate is reduced. Cerebrospinal fluid was collected continuously from the cisterna magna of anesthetized dogs before and after the administration of diatrizoate (1 mL/kg bolus followed by a 12.5 microliters/kg/minute maintenance infusion, IV). The influence of CSF production rate on CSF diatrizoate levels was examined by injecting acetazolamide (30 mg/kg, IV). Diatrizoate levels in CSF were quantified by a high performance liquid chromatography (HPLC) method. Baseline CSF production was 81.5 microliters/minute and dropped to 37.4 microliters/minute following diatrizoate and to 29.5 microliters/minute following acetazolamide. The concentration of diatrizoate in CSF averaged 166 micrograms/mL and increased significantly to 379 micrograms/mL following acetazolamide with no change in serum concentration (1.3 mg/mL). These experimental results suggest that appreciable quantities of intravenously administered diatrizoate may enter the CNS, and that these quantities may increase significantly with reduced CSF production. This may help to explain CSF enhancement and certain CNS toxicity after the intravenous administration of CM.

Lyophilized liposomes: a new method for long-term vesicular storage.

To facilitate acceptance and use of radiopaque liposomes as novel CT contrast agents, we developed a technique that permits their long-term storage at room temperature. This study compares standard storage procedures with the new method. Multilamellar vesicles were prepared with egg lecithin, cholesterol and stearylamine (4:1:1 molar ratio) as well as diatrizoate. After synthesis, the vesicles were separated into batches: one portion was kept frozen (FRO), another was lyophilized and stored at room temperature (LYO-RT), and a third was thawed and stored at room temperature (RT). Size, structure and biodistribution of vesicles in all three groups were assessed over a 6-month period. Freeze-drying the vesicles caused no apparent damage to their membranes The RT group showed marked aggregation after 1 month, while the LYO-RT and FRO vesicles showed only a slight shift to larger particles after 6 months. At this time, there was no significant change in the biodistribution of the LYO-RT vesicles compared to FRO. Uptakes in the reticuloendothelial tissues were 15 per cent and 19 per cent respectively. The LYO-RT materials showed additional advantages in that they were always easy to resuspend. This technique appears to be the most successful and convenient procedure for the long-term storage of liposomes.