Multiphasic modeling of charged solute transport across articular cartilage: Application of multi-zone finite-bath model.

Charged and uncharged solutes penetrate through cartilage to maintain the metabolic function of chondrocytes and to possibly restore or further breakdown the cartilage tissue in different stages of osteoarthritis. In this study the transport of charged solutes across the various zones of cartilage was quantified, taken into account the physicochemical interactions between the solute and the cartilage constituents. A multiphasic finite-bath finite element (FE) model was developed to simulate equine cartilage diffusion experiments that used a negatively charged contrast agent (ioxaglate) in combination with serial micro-computed tomography (micro-CT) to measure the diffusion. By comparing the FE model with the experimental data both the diffusion coefficient of ioxaglate and the fixed charge density (FCD) were obtained. In the multiphasic model, cartilage was divided into multiple (three) zones to help understand how diffusion coefficient and FCD vary across cartilage thickness. The direct effects of charged solute-FCD interaction on diffusion were investigated by comparing the diffusion coefficients derived from the multiphasic and biphasic-solute models. We found a relationship between the FCD obtained by the multiphasic model and ioxaglate partitioning obtained from micro-CT experiments. Using our multi-zone multiphasic model, diffusion coefficient of the superficial zone was up to ten-fold higher than that of the middle zone, while the FCD of the middle zone was up to almost two-fold higher than that of the superficial zone. In conclusion, the developed finite-bath multiphasic model provides us with a non-destructive method by which we could obtain both diffusion coefficient and FCD of different cartilage zones. The outcomes of the current work will also help understand how charge of the bath affects the diffusion of a charged molecule and also predict the diffusion behavior of a charged solute across articular cartilage.

Effect of radiologic contrast material on cell volume regulation in proximal renal tubules from trout (Salmo trutta).

RATIONALE AND OBJECTIVES: Most radiographic contrast media (CM) are hyperosmotic and pose an osmotic threat to cells they are in contact with. To study these effects at the cellular level, cell volume regulatory mechanisms were observed in proximal renal tubules following exposure to the CM iohexol, ioxaglate, and iodixanol. MATERIALS AND METHODS: Isolated renal tubules from trout (Salmo trutta) were exposed to 5% vol/vol iohexol (326 mOsm), ioxaglate (314 mOsm), or iodixanol (300 mOsm) or mannitol (to achieve the same osmolalities), and cell volume changes were observed videometrically. RESULTS: Iohexol and ioxaglate solutions induced a rapid shrinkage (12%-13%) not followed by cell volume regulation. Without CM (same osmolality), the cells shrank 11% but then showed a 77%-88% volume recovery. This reswelling was inhibited by 55% with the Na+, K+, Cl- symporter inhibitor bumetanide (50 micromol/L). Iodixanol did not significantly affect cell volume. Tubules preincubated with CM or mannitol were then stimulated with a hypoosmotic Ringer solution (160 mOsm) resulting in a 26%-36% cellular volume increase. Compared with results of experiments without mannitol and CM, preexposure to iohexol or ioxaglate almost completely inhibited the expected regulatory shrinkage phase, while previous exposure to hyperosmotic solutions with mannitol reduced the shrinkage response by 40%-53%. CONCLUSION: In this system, the hyperosmotic iohexol and ioxaglate cause cell shrinkage followed by an impaired cell volume regulatory response. Exposure to these two CM also inhibits cell volume regulation on hypoosmotic stimulation. The isosmotic iodixanol has no such effects. These changes appear to some extent to be a result of the CM's degree of hyperosmolality, but this property alone does not explain these findings.

In vitro comparison of the effects of contrast media on coagulation and platelet activation.

The aim of this study was to compare the in vitro effects of different classes of contrast media on both the blood coagulation system and on platelet function. Global tests (APTT, TT) and FpA and F1 + 2 generation measurements showed that ioxaglate (ionic dimer) presents the highest anticoagulant potential. The anticoagulant effects of nonionic agents were less marked, iodixanol (nonionic dimer) being significantly less anticoagulant than iohexol (nonionic monomer). Major platelet activation was observed with release of PF4, serotonin and PDGF-AB when iohexol was incubated for 1 min in whole blood. Iodixanol showed no effect over the same period, while moderate platelet activation was observed after 30 min. Under the same experimental conditions, ioxaglate had no effect on platelets even after incubation for 30 min, whereas activation was observed with 9 g/l saline control at this time. Prevention of thrombin formation and platelet activation is only achieved with ioxaglate, the ionic dimer. These findings may be clinically important in the thrombotic environment of radiological procedures and may explain the increased thrombotic risks observed with nonionic agents in interventional procedures.

Electric modification of kidney function. The excretion of radiographic contrast media and adriamycin.

The body consists of systems of conductive pathways for ionic flow of current induced by metabolic or injury potentials among tissues and cells. In vivo electrophoresis in biologically closed electric circuits (BCEC) are coupled to the mechanical transports of blood and lymph. Connections also exist with conductive media such as cerebrospinal fluid, bile, and urine. Artificial induction of current was applied over the kidneys in order to study modification of kidney function. It is thought that studies of this kind will increase our understanding of kidney function from a new angle of view and possibly add new therapeutic possibilities. In anesthetized pigs, one kidney was made anodic (electropositive) and the other cathodic (electronegative). Current was applied between electrodes in each ureter. Intravascularly injected, electronegatively charged aminotrizoate and ioxaglate were excreted mainly by the anodic kidney. Nonionic iohexol was urographically excreted by both kidneys. Excretion of electropositively charged Adriamycin by the cathodic kidney was identified macroscopically and by chemical analysis. Functional effects on the kidneys can be induced electrophoretically without causing injury.

Oxygen saturation of the low osmolar contrast media iohexol, ioxaglate and iodixanol. Effects on contractile force and frequency of ventricular fibrillation in the isolated rabbit heart.

During coronary angiography the exchange of blood with a contrast medium solution causes a period of hypoxia. To investigate whether oxygen saturation of the contrast medium could be beneficial, low osmolar contrast media were infused without and with oxygen saturation into the coronary arteries of the isolated rabbit heart. Iohexol (150-300 mg I/ml, without NaCl or with 20-30 mM NaCl), iodixanol (320 mg I/ml, contains 24 mM NaCl) and ioxaglate (160 mg I/ml, contains 75 mM Na+) were infused without and with oxygen saturation. The decrease in contractile force (CF) of the heart, from the contrast medium solutions, was reduced when the solutions were saturated with oxygen. Oxygen saturation of iohexol (350 mg I/ml, without or with 10 mM NaCl) did not change the frequency of ventricular fibrillations (VF). Low osmolar contrast media, when saturated with oxygen, thus caused a reduced decrease in CF without changing the frequency of VF. This might be beneficial in clinical cardioangiography by reducing the adverse effects from the media.

Intracellular penetration and accumulation of radiographic contrast media in the rat kidney.

Radiographic iodine-containing contrast media (meglumine calcium metrizoate, iohexol and meglumine sodium ioxaglate) were injected intravenously in rats. At various intervals after exposure, in situ cryofixation of kidneys was performed. Thin, freeze-dried cryosections were examined by electron microscopy and X-ray microanalysis. In endothelial cells, erythrocytes and tubular cells high dry weight concentrations of iodine were found. Twenty-four hours after iohexol was injected, no trace of iodine was found in the plasma, microvilli or the nuclei of the tubular cells. Small organelle-like compartments in the cytoplasm of the proximal tubular cells contained high concentrations of iodine, whereas no iodine was found in the surrounding cytoplasm. Since no metabolism of contrast medium has been demonstrated, the iodine signals must be emitted from contrast medium molecules. Other elements were also measured, with the concentrations being always within the ranges found in tubular cells of control animals. The detection of intracellular contrast thus does not seem to be an artifact due to cell injury, but rather represents a physiological event in healthy cells in the rat kidney. Our results are in contradiction to the prevailing opinion that contrast media do not enter healthy cells. However, previous conclusions have been based on the use of conventional preparation methods, and the highly water soluble contrast molecules may have been lost during the different steps of fixation and processing.

Incorporation of contrast media in cultured cells.

Monolayer cultures of human prostatic (PC-3) and cervical (NHIK 3025) carcinoma cells were grown on formvar film and exposed to moderate concentrations of contrast agents for 30 minutes to 4 hours. After the exposure period, the monolayers were quickly frozen, and cryosections were examined by electron microscopy and X-ray microanalysis. Iodine was not detected in control cells, but was found in the cells that had been exposed to iodine-containing contrast media. The amount of intracellular iodine increased with increasing exposure dose and time. Because the cells mostly presented no sign of membrane damage, our findings support the view that contrast media have the ability to enter intact cells.