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J M Girardot

Publications and source records attributed to J M Girardot.

15 recordsLinked to original sources
PubMed1997

Refinement of the alpha aminooleic acid bioprosthetic valve anticalcification technique.

BACKGROUND: Aminooleic acid treatment has been demonstrated to prevent porcine valve calcification and to protect valvular hemodynamic function. Initial enthusiasm was tempered by histologic studies of these AOA valves, which showed cuspal hematomas, structural loosening, and surface roughening. This prompted a systematic review of the AOA treatment process. Unsolubilized particles of alpha aminooleic acid present in the treatment solution were identified as the cause of mechanical abrasion of valve cusps during processing. These particles were eliminated with a revamped protocol, which included filtration of the AOA solution before valve preparation. METHODS: Porcine aortic valve cusps treated with this modified AOA protocol (AOA II) were studied in a rat subdermal implant model of mineralization. A juvenile sheep trial was then used to confirm the antimineralization effects of AOA II on glutaraldehyde-fixed porcine aortic roots in a circulatory model of accelerated calcification. RESULTS: Retrieved AOA II-treated cusps from the subdermal model were markedly less calcified than control cusps (AOA II, 1 +/- 0, 17 +/- 4, 23 +/- 6, and 17 +/- 10 versus control, 189 +/- 14, 251 +/- 16, 250 +/- 14, and 265 +/- 10 mg calcium/mg sample at 4, 8, 12, and 16 weeks, respectively; p < 0.0001). Morphologic examination of the AOA II cusps of the valves retrieved from the sheep demonstrated freedom from the structural loosening, surface roughening, and hematoma formation that had limited the utility of the original AOA preparation technique. Cusps from AOA II-treated porcine roots had significantly less calcium than control cusps (AOA II, 5.5 +/- 3.0 mg/g; control, 91.2 +/- 19.5 mg/g; p = 0.0004). The aortic walls had similar levels of calcification (AOA II, 156 +/- 73 mg/g; control, 159 +/- 10 mg/g; p = not significant). CONCLUSIONS: These data suggest that the modified AOA technique warrants further evaluation as an antimineralization treatment for glutaraldehyde-fixed porcine bioprostheses.

Animals↗
PubMed1996

Amide cross-linking: an alternative to glutaraldehyde fixation.

BACKGROUND AND AIMS OF THE STUDY: A new fixation method for bioprosthetic tissues is being developed, which does not utilize the standard glutaraldehyde treatment. This method, referred to as Ultifix, uses a coupler and a coupling enhancer with or without one or more coupling agents. It fixes the tissue by linking the amine and the carboxyl moieties through amide bonds either directly, or indirectly when coupling agents form bridges. The amide bonds thus formed are more stable than the Schiff-base bonds formed by glutaraldehyde. All compounds used during the fixation process and their by-products are water-soluble, and are easily removed by washing. In addition, the by-products are not toxic, as opposed to glutaraldehyde, which induces toxic reactions after implantation. The tests described in the manuscript were specifically aimed at evaluating the cross-linking efficacy of the process on heart valve tissues, as well as their resistance to calcification in the rat model. METHODS: Porcine aortic roots and porcine pericardium were fixed using the coupling agents 1,6-hexane diamine (DIA) and suberic acid (SUA) in the presence of the coupler 1-ethyl-3(-3 dimethyl aminopropyl) carbodiimide hydrochloride (EDC) and the coupling enhancer N-hydroxysulfosuccinimide (sulfo-NHS). The tissues were then evaluated for their resistance to thermal denaturation, to enzymatic digestion, and to calcification when implanted subdermally in rats for two, four, eight and 16 weeks. RESULTS: The results demonstrate that the cusps and the wall of porcine aortic roots, and porcine pericardium, are as well stabilized and as cross-linked by Ultifix as they are by the standard glutaraldehyde method. In addition, the cusps of the porcine aortic root and the porcine pericardium, but not the wall of the porcine aortic root, calcify minimally and significantly less when implanted subdermally for up to 16 weeks in three week old rats than the control material fixed with glutaraldehyde. CONCLUSION: The Ultifix process of cross-linking bioprosthetic heart valves may thus be a good alternative to the standard glutaraldehyde process of fixation, with increased durability and without toxic effects.

Amides↗
PubMed1995

Role of glutaraldehyde in calcification of porcine heart valves: comparing cusp and wall.

Experiments were performed to better understand the relationship between glutaraldehyde and calcification of bioprosthetic heart valves, using both the cusps and the wall of porcine aortic roots. The results of the first experiment, for which 3H-labeled glutaraldehyde solutions were used, indicated that binding of glutaraldehyde in cusps and wall is concentration-dependent, that the wall contains significantly less glutaraldehyde than the cusp, and that glutaraldehyde, which penetrates in the wall at similar rates from the intima and the adventitia, is homogeneously distributed throughout the wall after 7 days of fixation, except for the intima side, where it is significantly lower. The results of the second experiment, for which cusps and 1-cm2 pieces of wall from glutaraldehyde-fixed porcine aortic roots were implanted subdermally in young rats, indicated that for both types of tissue, calcification appears to first initiate predominantly in the cell nuclei before extending to the other structures. After 8 weeks of implantation, whereas the cusps were completely calcified, calcification of the wall was limited to two longitudinal bands 150-300 microns thick, located below the adventitia and intima surfaces. The results of the third experiment indicated that cusp calcification, which decreased significantly after a 12-month storage period, was reset to high levels by reexposing the valves to glutaraldehyde at the end of the 12-month storage period. Wall calcification remained constant under all tested conditions. The results suggest that the mechanism(s) of calcification in the wall and the cusp may be different, and that calcification may be related to a particular molecular configuration resulting from exposure to glutaraldehyde.

Animals↗
PubMed1994

Effect of AOA on glutaraldehyde-fixed bioprosthetic heart valve cusps and walls: binding and calcification studies.

Alpha-aminooleic acid (AOA), a potent, non-toxic and biocompatible anticalcification agent, has been shown to be effective for glutaraldehyde-fixed valves in rat and juvenile sheep models, and is used for the treatment of Medtronic heart valve bioprostheses currently in clinical trials. In the pre-clinical sheep study of a stentless aortic root, the treatment with AOA prevented calcification of the cusps, but not of the wall. The experiments described in this manuscript were designed to investigate a possible relationship between the binding of AOA and the differential treatment efficacy in the cusp and the wall, and to improve the anticalcification effect of the AOA treatment in the wall. Glutaraldehyde-fixed porcine roots were treated with [14C]-AOA for binding studies, and with non-radioactive AOA for calcification studies for rat subdermal implants. The results indicate that a) the AOA treatment did reduce wall calcification, but only temporarily, b) the low efficacy of the AOA treatment on the wall was probably due to the limited penetration of AOA, and c) increasing the volume of the AOA solution during treatment significantly increased the content of AOA in the wall, and significantly decreased wall calcification. This study suggests that AOA efficacy in the wall may be hindered because of the physical characteristics of the wall, and that wall calcification may be prevented by developing methods aimed at increasing AOA penetration into the wall.

Animals↗
PubMed1992

Calcification of porcine valves: a successful new method of antimineralization.

Despite distinct advantages over mechanical cardiac valve prostheses, the use of bioprosthetic valves remains limited due to poor long-term durability, primarily as a result of tissue calcification. A novel anticalcification process, based on treatment of porcine bioprostheses with a derivative of oleic acid, has been developed by one of us (J.M.G.) (US Patent Number 4,976,733). This process employing 2-aminooleic acid (AOA) was tested in a juvenile sheep model. Terminal studies after a 20-week interval included hemodynamic, radiographic, morphologic, and quantitative tissue calcium analyses. All control valves (n = 4) had thickened, immobile, heavily calcified leaflets, whereas all AOA-treated valves (n = 8) were pliable and free of calcium deposits. Calculated valve orifice areas for controls (0.9 +/- 0.2 cm2) (mean +/- standard error of the mean) was less than for AOA-treated valves (2.0 +/- 0.3 cm2) (p less than 0.05). Radiographic calcification scores were greatly elevated in the control (25.5 +/- 5.6) versus AOA-treated valves (0.5 +/- 0.5) (p less than 0.002). In quantitative mineralization studies, the mean calcium content of the control leaflets was 129 +/- 21 milligrams per gram dry weight cusp tissue versus 7.7 +/- 5.8 mg/g for AOA-treated valves (p less than 0.001). Pathologic examination confirmed heavy calcification in the control leaflets, which was essentially absent in the AOA-treated leaflets. However, cuspal hematomas in areas of structural loosening and surface roughening were noted in AOA-treated valves. This anticalcification process dramatically reduced mineralization of porcine valve prostheses in this model.

Animals↗
PubMed1984

Inhibition of vitamin K-dependent carboxylase by metal ions and metal complexes: a reassessment.

The vitamin K-dependent enzymatic carboxylation of glutamyl residues in blood protein precursors and in synthetic peptides is inhibited in vitro by transition metal complexes. Some authors suggested it is a result of metal ions interaction with intermediary oxygenated species. Using an oxygraph we have observed increases in the rate of oxygen utilization in the carboxylating system containing reduced vitamin K after addition of some transition metal ions and complexes. Kinetic studies indicate that, although oxygen utilization is increased by the addition of Cu2+, Fe3+, and hematin, the initial rate of carboxylation is not affected. The rate of carboxylation rapidly decreases at oxygen concentrations below 50 microM and reaches zero when oxygen is depleted. UV spectroscopy revealed simultaneous acceleration of the conversion of vitamin K hydroquinone into the parent quinone. The magnitude of these effects, as well as carboxylation inhibition, depends on the oxidation potential of the complexed ion and its lipophilicity. Addition of stable Mn parallel ion, which has no inhibitory effect on carboxylation, does not increase the rate of oxygen utilization nor the hydroquinone oxidation. The results suggest that inhibition of carboxylation by transition metals is mainly due to depletion of the necessary components (oxygen, vitamin K hydroquinone) of the carboxylating system rather than quenching of activated, oxygen-containing intermediates.

Animals↗
PubMed1983

Role of calmodulin in the effect of guanyl nucleotides on rat hippocampal adenylate cyclase: involvement of adenosine and opiates.

The adenylate cyclase activity of rat hippocampal plasma membranes can be stimulated by vasoactive intestinal polypeptide (VIP). Low concentrations (10(-9) to 19(-7) M) of 5'-guanylyl-imido diphosphate (GppNHp) evoke a transient inhibition of the enzyme, which is followed by stimulation with increasing GppNHp concentrations (10(-6) to 10(-4) M). Inclusion of Inclusion of ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) during incubation abolishes the GppNHp inhibition while preserving GppNHp activation. The stimulation induced by GppNHp is amplified by VIP, but the inhibition is unaffected. Adenosine analogs and opiates are inhibitory ligands in the presence of GTP, and their effects can be reversed by the appropriate receptor antagonists, 3-isobutyl-1-methylxanthine and naloxone. Treatment of membranes with trypsin abolishes the GppNHp-induced inhibition without affecting the GppNHp stimulation. The inhibition induced by GppNHp is also abolished by EGTA treatment followed by washing, which coincides with a reduction in the adenosine- and opiate-mediated, GTP-dependent inhibition. The GppNHp inhibition can be restored in EGTA-treated but not in trypsin-treated membranes by addition of calcium-calmodulin but not by Ca2+ or Mg2+. Calcium-calmodulin-depleted membranes lack calcium stimulation as well as GppNHp-induced inhibition, whereas untreated membranes and calcium-calmodulin-depleted membranes plus exogenous calcium-calmodulin showed calcium stimulation and GppNHp inhibition. These results suggest that calmodulin is involved in both Ca2+ stimulation and guanine nucleotide-mediated inhibition of rat hippocampal adenylate cyclase.

Adenosine↗
PubMed1982

Vitamin K-dependent carboxylase. Partial purification and properties of the enzyme-substrate complex.

The vitamin K-dependent carboxylase extracted from rat liver microsomes by 3-([3-cholamidopropyl] dimethylammoniol)-1-propane sulfonate detergent solution has been partially purified by chromatography on Ultrogel AcA-34 followed by carboxymethyl-Sepharose chromatography and pentapeptide affinity chromatography. The carboxylase appears to be composed of two proteins, the enzyme and endogenous substrate as judged by the incorporation of 14CO2 into trichloroacetic acid insoluble protein. The apparent Km for Phe-Leu-Glu-Glu-Leu as carboxylation substrate is approximately 3 mM. 2,3,5,6-Tetrachloro-4-pyridinol at 10 microM inhibits 90% of the enzyme activity, whereas maximal stimulation (1.7-fold) by pyridoxal 5'-phosphate is obtained at 1 mM and by Mn2+ at 5 mM. The stimulation by pyridoxal 5'-phosphate and by Mn2+ are not additive. The carboxylation of Phe-Leu-Glu-Glu-Leu at 20 degrees C is linear for 90 min. Vitamin K1 plus NADH do not replace vitamin K1 hydroquinone, indicating that vitamin K reductase is not part of this purified carboxylase-substrate complex. Vitamin K epoxidase activity co-elutes with the carboxylase complex. Some 400-fold purification from microsomes has been obtained to yield enzyme preparations with a specific activity of approximately 17,000 pmol of CO2 fixed into peptide/mg of enzyme protein, which is some 15-fold greater than any previously reported enzyme preparation from rat liver microsomes.

Animals↗
PubMed1976

Soluble enzyme system for vitamin K-dependent carboxylation.

The vitamin K-dependent carboxylating system has been solubilized by Lubrol PX or Triton X-100 treatment of vitamin K-deficient rat liver microsomes. As obtained from vitamin K-deficient rat liver, this soluble preparation is dependent upon the in vitro addition of vitamin K1 for carboxylating activity. The enzyme system is complex and is dependent upon NADH and dithiothreitol for maximum activity. While detergents used to solubilize the enzyme complex do markedly inhibit the activity of the system, the solubilized system is still highly responsive to vitamin K addition and can be used for further study of the carboxylating enzyme system. The requirement for dithiothreitol and the inhibition by p-hydroxymercuribenzoate indicate the involvement of an --SH enzyme in the carboxylating system.

Animals↗