Disposition of irbesartan, an angiotensin II AT1-receptor antagonist, in mice, rats, rabbits, and macaques.

Metabolism and disposition of irbesartan, an angiotensin II AT(1) receptor antagonist, were investigated in mice, rats, rabbits, and macaques. In both rats and macaques, irbesartan was characterized by a rapid oral absorption, a large volume of distribution, a low plasma clearance, and a long terminal half-life. The oral bioavailability in macaques was notably higher than in rats. Irbesartan was highly protein bound in rats and macaques. A lower binding rate was found in mice and rabbits. In distribution studies performed in rats, mice, and rabbits, irbesartan was rapidly distributed into most organs and tissues including brain, intrauterine area, and milk. No retention of radioactivity in tissues other than liver and kidney was noted. Irbesartan was the main circulating compound in rats, rabbits, and macaques representing a maximum of 67, 68, and 80% of plasma radioactivity, respectively. The drug was metabolized mainly by glucuronidation (primarily on the tetrazole ring), hydroxylation, and additional oxidation. The overall pathways within the different species generated 18 metabolites identified from bile, urine, and feces samples. Irbesartan did not significantly induce or inhibit most of the isoenzymes commonly associated with drug metabolism in either rats or macaques after oral administration for 1 month. In most species irbesartan and its metabolites were mainly excreted in feces with more than 80% of a radioactive dose recovered within 24 or 48 h. Enterohepatic circulation was demonstrated in rats and macaques.

Disposition of tiludronate (Skelid) in animals.

The disposition of tiludronate in mouse, rat, rabbit, dog and monkey has been studied after oral and intravenous doses. Like other bisphosphonates, tiludronate was characterized by poor absorption from the gastrointestinal tract. Peak plasma concentrations appeared shortly (0.5-1 h) after dosing, except for the baboon (4.5 h). Food intake highly impaired intestinal absorption The affinity of tiludronate for bone and the slow release from this deep compartment could account for the large volume of distribution and the low plasma clearance found in all species. Tiludronate has low affinity for red blood cells and binds moderately to serum proteins, mainly to serum albumin. Calcified tissues appeared to be the main target for deposition. Distribution into bone was not homogenous, with higher levels in the trabecular bone than in the corticol part of the long bones. The uptake of tiludronate into bone was unequivocally less in the older animal. No metabolism occurred in the tested animal species. The major route of elimination of the absorbed drug is urine. Preclinical observations made with tiludronate, like with other bisphosphonates, were predictive of results obtained in clinical investigation.

Functional upregulation of granulocytes labeled with technetium-99m-HMPAO and indium-111-oxinate.

UNLABELLED: Indium-111-oxinate-labeled granulocytes have been used in vivo for several years for the detection of abscesses. Technetium-99-m-hexamethylpropyleneamine oxime (99mTc-HMPAO) labeling has more recently been described. METHODS: The influence of radiolabeling by both radiotracers on adhesion glycoprotein CD11b quantification was studied in quiescent and formyl-methionylleucylphenylalanine (fMLP)-activated neutrophils (PMN). Adhesion was assessed on human umbilical endothelial cells (HUVEC) as well as the repercussion of the granulocyte labeling on HUVEC viability (neutral red) and metabolic activity (MTT). Chemotaxis of PMN was evaluated by measuring migration under agarose with fMLP as chemoattractant. We also measured phagocytosis and the production of hydrogen peroxide induced by staphylococcus aureus. RESULTS: Whereas whole functional integrity is maintained after labeling, most of the functions (CD11b expression, adhesion, HUVEC metabolic activity) are up-regulated while chemotaxis is decreased in the presence of both radiotracers. Indium-111-oxinate induces larger alterations than 99mTc-HMPAO. CONCLUSION: These data were obtained in normal volunteers. In patients, alterations due to the in vitro labeling procedure, in addition to potential functional alterations caused by the underlying pathology, should be taken into account during image interpretation.

An ex vivo original test using radiotracers for evaluating haemocompatibility of tubular biomaterials.

The haemocompatibility of a vascular prosthesis can be estimated as the result of its interaction with blood components. The authors describe an ex vivo canine shunt for evaluating isotopic haemocompatibility in blood-wall interactions. Methods employing radioisotopic tracers can be used to dynamically monitor the adsorption of labelled blood cells and proteins on different biomaterial surfaces. This ex vivo test should enable materials to be assessed for quality according to two thrombogenic criteria: (i) number of adhered platelets mm-2 s-1; (ii) quantity of adsorbed fibrinogen expressed as microgram mm-2 s-1, which would provide the basis for a scale of haemocompatibility.

A canine ex vivo shunt for isotopic hemocompatibility evaluation of a NHLBI DTB primary reference material and of a IUPAC reference material.

Factors determining the thrombogenic response to particular artificial surfaces were investigated ex vivo in a canine shunt model. Methods using radioisotopic tracers made it possible to dynamically monitor the deposition of labelled blood cells and proteins on a NHLBI.DTB primary reference material polydimethylsiloxane (PRM.PDMS) and on a IUPAC reference material polyvinyl chloride (IUPAC.PVC). On the one hand, leukocyte affinity tau s(leu) (number of deposited leukocytes mm-2s-1) was not significantly different between IUPAC.PVC (tau s(leu) = 1.2-2.5) and PRM.PDMS (tau s(leu) = 1.5-3.4) and the fibrinogen adsorption rate varied from 33 to 48.10(-5) micrograms mm-2s-1 for both these materials. On the other hand, platelet affinity tau s(plat) (number of deposited platelets mm-2s-1) was significantly different (p < 0.05) for IUPAC.PVC and PRM.PDMS (tau s(plat)PVC = 683 +/- 200 > tau s(plat)PDMS = 327 +/- 80). Scanning electron micrographs of adherent platelets, red cells and leukocytes after blood contact ex vivo were performed after each experiment. This preliminary work contributes not only to quantify the adsorption of different radiotracers, but also to evaluate the superficial distribution of the labelled biological species on the inner surface of the tested biomaterials.

Ex vivo leucocyte adhesion and protein adsorption on TiN.

Titanium nitride (TiN) is regarded as a potential biomaterial for blood-contact applications. Its in vitro haemocompatibility has been evaluated already and gave promising results. The purpose of this study was to continue studying its 'biological' behaviour through an ex vivo evaluation. The material was a physical vapour deposition elaborated TiN coating and the phenomena observed were leucocyte adhesion and albumin and fibrinogen adsorption. These ex vivo results were compared with in vitro results obtained previously. Two reference medical grade silicone elastomer and three TiN arterio-arterial extra-corporeal circuits were tested. No leucocyte was retained by TiN, as in in vitro experiments; the ex vivo fibrinogen adsorbed quantity was higher and albumin adsorption was about the same in in vitro and in ex vivo situations. TiN can be considered as a suitable blood-contacting material.

Compliance and effects of nutritional treatment on progression and metabolic disorders of chronic renal failure.

Low-protein, low-phosphorus diets (LPD) are prescribed to patients with chronic renal failure (CRF) to slow down the rate of progression of CRF and to control uraemic symptoms. A satisfactory adherence of patients to the prescribed diet is needed to meet these two goals. We studied the compliance of CRF patients to a LPD providing daily (per kg body weight) 0.3 g protein, 3-5 mg phosphorus, 35 kcal, and supplemented with essential amino-acids and keto-analogues. Forty CRF patients were studied for 23.3 +/- 10.8 months (range 12-45). Compliance to LPD was evaluated by dietary inquiry and protein intake estimated from urinary urea excretion. According to compliance to LPD, patients were retrospectively assigned to the compliant (n = 27) or the non-compliant (n = 13) group. GFR measured by the urinary clearance of [51Cr]-EDTA was identical in the two groups at the start of the study: compliant patients 15.7 +/- 5.3 ml/mn, non-compliant patients 15.4 +/- 5.9 ml/mn. The decrease of GFR was -0.08 +/- 0.22 ml/min per month in compliant patients versus -0.31 +/- 0.37 ml/min per month in non-compliant patients (P < 0.02). These results were not demonstrated if the progression of CRF was assessed by the linear regressions over time of creatinine clearance or the reciprocal of creatinine. Serum bicarbonate, serum phosphorus and PTH levels were corrected by LPD in compliant patients (P < 0.005 for all parameters) but not in non-compliant patients. These results suggest that evaluation of compliance is necessary to assess the response of CRF patients to LPD, whether the aim is to slow the progression of CRF or to control its metabolic consequences. A beneficial effect of compliance to LPD was demonstrated upon these two goals.

Cytocompatibility study of NHLBI primary reference materials using human endothelial cells.

Four different materials, low density polyethylene (LDPE), polydimethylsiloxane (PDMS), polyvinylcholoride (PVC) and cellulose, were selected by the Devices and Technology Branch of the National Heart Lung and Blood Institute (NHLBI) as primary reference materials for blood contacting. Among the wide variety of tests proposed to assess hemocompatibility of short-term blood contacting catheters, it was desirable to rule out whether these materials could release toxics for vascular cells of the physiological environment. Thus, the cytocompatibility of these materials have been checked towards human umbilical vein endothelial cells: the method used avoids direct contact between cells and materials but evaluates the effect of possible toxic substances leached from materials. These substances were obtained under defined conditions according to a standard. The results show that the extracts of cellulose and LDPE provoke an important cytotoxic effect on the endothelial cell cultures, while the extracts of PDMS and PVC allow the obtention of endothelial cell lining of the reference surface, with a correct global metabolic activity and the intracellular presence of von Willebrand factor.

Improvement of leucocytic Na+ K+ pump activity in uremic patients on low protein diet.

Leucocytic Na+ K+ pump activity was assessed in 20 patients with advanced renal failure. Na+ K(+)-ATPase activity was reduced when compared with the values obtained from normal subjects (101.8 +/- 48.6 versus 165.13 +/- 8.9 microM of Pi hr-1.g-1; P less than 0.001) and the mean 86Rb uptake by U 937 cells was depressed by 38% after the addition of patients' sera. Subsequently, patients were put on a diet providing 0.3 g protein/kg body weight daily and supplemented with ketoacids. After three months of dietary treatment Na+ K(+)-ATPase activity increased to 142 +/- 48.3 (P less than 0.01) and reached normal values at the sixth month (162.8 +/- 54.70 microM of Pi hr-1.g-1; P less than 0.001) whereas 86Rb uptake increased by 23 percent when compared to initial values. These data suggest that among the different mechanisms which have been advanced to explain the defects in the Na+ pump observed in uremic patients, circulating inhibitors deriving from alimentary protein intake may affect cation transport.

Rationale for the design of biomaterials and the evaluation of their biocompatibility.

The biocompatibility of a material can be considered as the ideally expectable result of its interactions with living tissues with which it is interfaced. This property determines the ability of devices involving this material in their constitution, to correctly assume their ascribed function; reciprocally a bad fitting, between devices and their intended use, coming from a non-optimized design or from an inappropriate prescription, may alter the original biocompatibility of constitutive materials. Accordingly, the actual biocompatibility of a biomaterial depends upon both its intrinsic properties and the application in which it is involved. Such considerations must be taken into account by specialists who try to design more performant biomaterials, or new assist devices, should they be implantable or not; but they draw also methodological guidelines for the evaluation of the biocompatibility of these biomedical products.

In vitro diffusion in polyacrylamide embedded agarose microbeads.

125I Sodium iodide, 125I insulin, 125I albumin, and 111indium IGG were employed to investigate release from, and penetration of different sized molecules into agarose/polyacrylamide microcapsules. The microcapsules were formed by photopolymerization of an acrylamide solution round agarose beads. The indium-chelated antibody gave a particular low background count. The different release times were explained in terms of differences in diffusion coefficient. By retarding in vitro penetration of antibodies, these microcapsules could be of value for the encapsulation of living cells in bioartificial organs.

Biocompatibility of carbon-carbon materials: blood tolerability.

Carbon-carbon composites are well known in the field of aerospace technology. Such composites have been proposed to be used as biomaterials, particularly in contact with blood. To evaluate their haemocompatibility, samples were tested in vivo and in vitro, using radiotracers. In vivo study showed the accumulation of platelets on the exposed surface material with any surface morphology, whereas platelet concentration in blood remained constant. In vitro study allowed us to distinguish, among entrapped platelets, active adhering platelets from those mechanically retained and it appeared that the bulk structure of materials influenced the adhesion mechanism of platelets.

Experimental evaluation of a gelatin-coated polyester graft used as an arterial substitute.

Protein coating and endothelial cell preseeding have been proposed and studied as improvements to arterial prostheses. In this paper, an impervious polyester vascular graft which had been coated with cross-linked gelatin was compared to a porous one over a period of up to 8 months in dogs. This evaluation involved in vivo methods using radio tracers to study patency and thrombogenicity and in vitro controls of the healing processes. The main advantages offered by coated grafts over uncoated include the absence of preclotting and better biointegration.

Control and isotopic quantification of affinity of antithrombin III for heparin-like surfaces.

Heparin-like materials, characterized by a defined superficial density of functional groups which activate antithrombin III (AT III), when in contact with blood specifically inhibit thrombin as soon as it appears. This paper describes an isotopic method to estimate this density and to visualize the distribution of the affinity sites concerned, both directly with AT III labelled with 125Iodine and indirectly with an anti AT III monoclonal antibody labelled with 111Indium.

Conditions for radioiodination of antithrombin III retaining its biological properties.

In order to obtain a radioiodinated antithrombin III (AT III) with a good labelling yield and optimal biological properties towards heparin, thrombin and its anti-AT III monoclonal antibodies, we compared the classical labelling methods and found them wanting. Thus, we perfected a new labelling procedure which fulfils the above requirements.

Topographic and dynamic radioisotopic investigations of interactions between biomaterials and blood components.

Functional investigations using radionuclides to study protein adsorption and platelet adhesion onto biomaterials are described. The authors' novel methods use radiotracers with a dynamic technique. This allows direct observation of the interaction between blood, or simpler biological substances, and artificial materials. Several radiotracers were used in this study, including 111In-platelets, 123I-fibrinogen, 123I-antithrombin III, and 99mTc-tagged red blood cells. The detectors employed were a semiconductor diode or gamma-camera equipped with special collimators. The acquisition and treatment of data were performed with an original device. These methods allowed precise comparisons, especially between platelet adhesion upon different materials in the form of tubes and also protein adsorption and desorption. The results are discussed in terms of materials to be used for work in vivo.