Partially bioresorbable vascular grafts in dogs.

Previous studies have shown the effectiveness of partially resorbable arterial prostheses in the rabbit. This study compares these same compound prostheses with commercial graft materials in the dog. Conduits 4 mm inner diameter X 50 mm in length were woven from composite yarns containing 69% polyglactin 910 (PG910)/31% polypropylene or containing 70% polydioxanone/30% polypropylene. Nonresorbable controls were woven Dacron and expanded polytetrafluoroethylene (ePTFE). Baseline platelet aggregometry to 10(-5) mol/L adenosine diphosphate was performed. Seventy prostheses were implanted into the aorto-ilac positions, and the prosthesis/tissue complexes were harvested serially from 2 weeks to 1 year. Explanted specimens were photographed and fixed for light microscopy and for scanning and transmission electron microscopy. Results showed no aneurysms or perigraft hematomas. Overall patency for the PG910/polypropylene grafts was 18 of 20 (90%) and for polydioxanone/polypropylene was 19 of 22 (86%). For Dacron and ePTFE, 13 of 19 (68%) and 6 of 11 (54%) remained patent at time of explantation. The partially resorbable grafts, as a group, had significantly greater patency than the control grafts (p less than 0.03). Platelet aggregometry was not predictive of graft patency. Histologic analysis of the partially bioresorbable groups showed inner capsules (IC) composed of myofibroblasts and collagen beneath confluent endothelialized surfaces by 1 month. Kinetics of IC formation paralleled the rates of resorption of the resorbable components. IC cellularity and thickness were greater than those within Dacron or ePTFE. This study suggests an enhanced transinterstitial endothelial cell and myofibroblast ingrowth into the ICs of partially resorbable grafts and shows the effectiveness of these prostheses in the dog.

Effects of hypercholesterolemia on healing of vascular grafts.

Small-diameter vascular grafts woven from bioresorbable lactide/glycolide copolymers have been successfully interposed into aortas of normal NZW rabbits. The current study examines the histologic and functional reactions to these bioresorbable grafts in severely hypercholesterolemic rabbits, a standard animal model of atherosclerosis. Sixty rabbits were placed on a 2% cholesterol, 6% peanut oil atherogenic diet. Baseline serum cholesterols and triglycerides were measured and repeated at operation 3 months later. Woven polyglactin 910 (PG910) grafts were interposed into infrarenal aortas. Fifty-two rabbits died on the diet or within 3 days of surgery and eight survived operation (normal NZW rabbit operative mortality is less than 10%). Cholesterol levels rose from 63 to 1989, p less than .001. Of the eight survivors, five died after 3 weeks, and one died after 2 1/2 months. Two were sacrificed at 2 and 4 months. Four aortic disruptions with retroperitoneal hematomas, one pseudoaneurysm, and one diffuse aneurysm were observed, greater than in normal rabbits, p less than .001. Inspection revealed severe atherosclerosis. Histologically, 3-week explants showed only small areas of neointima with myofibroblasts and endothelial cells; the outer capsules were infiltrated by lipid-laden macrophages. Graft material in 2- to 4-month explants was replaced by tissue with histologic atherosclerosis. More severe atherosclerosis was observed in native aortas at the perianastomotic areas than the more distant aortic segments. Abundant intracellular lipid was seen also in splenic histiocytes and hepatic cells with evidence of micronodular cirrhosis. Macrophages phagocytizing bioresorbable prostheses may release growth factors mediating the formation of a cellular tissue conduit. Severe hypercholesterolemia may alter monokine release from macrophages resulting in a weakened prosthesis/tissue complex.

The validity of canine platelet aggregometry in predicting vascular graft patency.

Several laboratories have found canine platelet aggregometry predictive of thrombotic potential in vascular grafts. Adenosine diphosphate (ADP) is a frequently used agonist, often at unspecified or differing concentrations. This study was designed to evaluate the predictive value of ADP-induced platelet aggregometry and the validity of the methodology. Platelet aggregometry in response to 2 x 10(-5) M ADP was assayed in 70 dogs. Twenty-six percent were aggregators, 51% were non-aggregators, and 20% were indeterminant. All dogs were then treated with aspirin and dipyridamole. Vascular prostheses were implanted bilaterally (aorto-iliac) and anti-platelet therapy continued for two weeks. Dose-response to ADP was studied at three concentrations in 20 dogs. At 2 x 10(-5) 1/20 aggregated, at 4 x 10(-5) 3/19 aggregated and at 2 x 10(-4) 15/20 aggregated. Time between samples and study was evaluated in 11 dogs, with 2/11 changing from non-aggregator to aggregator at two or three hours. Daily reproducibility was studied in 70 dogs, 14 of which changed aggregation status between days. Patency was 58/68 (85%) for non-aggregators, 23/34 (68%) for aggregators (p = 0.038). Platelet aggregometry has significant predictive value for graft patency but methodology must be specified and standardized.

Prostacyclin production by blood-contacting surfaces of endothelialized vascular prostheses.

This study examines prostacyclin production by blood-contacting surfaces within woven vascular prostheses of polydioxanone (PDS), polyglactin 910 (PG910), or Dacron interposed into rabbit infrarenal aortas. Grafts and normal aortic segments were explanted after 1, 3, and 6 months for pulsatile perfusion with Medium-199 for 60 minutes. Aliquots were removed serially for 6-keto-PGF1 alpha assay. After 30 minutes sodium arachidonate (10 micrograms/ml) was added. Specimens were studied by light microscopy, SEM and TEM. Patency in all three groups exceeded 90%. All three showed re-endothelialization at one month. Normal aorta produced low basal 6-keto-PGF1 alpha with a marked evanescent post arachidonate increase. Dacron did not differ from normal aorta. PG910 and PDS both produced significantly less 6-keto-PGF1 alpha post arachidonate at one month but both increased to normal by three months.

Effects of class I heparin binding growth factor and fibronectin on platelet adhesion and aggregation.

Fibronectin and heparin binding growth factor-type 1 have been affixed to vascular graft surfaces to enhance the attachment and the proliferation of transplanted endothelial cells, respectively. The current study examines the effect of fibronectin and heparin binding growth factor-type 1 on platelet adhesion and activation in vivo and on platelet aggregation in vitro. Expanded polytetrafluoroethylene prostheses (5 cm x 4 mm internal diameter) were treated either with fibronectin (n = 9), fibronectin/heparin/heparin binding growth factor-type 1/heparin (n = 12), or neither (n = 13) and were interposed into canine aortoiliac systems bilaterally. Autogenous radiolabeled (Indium 111 oxine, 650 microCi) platelets were injected intravenously before reestablishment of circulation. Perfusion was maintained for 30 minutes, and prostheses were removed with segments of native aorta and distal iliac arteries bilaterally. Specimens were examined for thrombus-free surface area, by gamma well counting for adherent radiolabeled platelets, and by light microscopy and transmission and scanning electron microscopic techniques. Results showed that both the fibronectin and fibronectin/heparin/heparin binding growth factor-type 1/heparin pretreated prostheses contained significantly greater numbers of platelets and adherent radioactivity than did control graft segments when normalized to their ipsilateral iliac arteries. Fibronectin/heparin/heparin binding growth factor-type 1/heparin pretreated prostheses contained 27 +/- 16 times more radioactivity per square millimeter than ipsilateral iliac arteries, fibronectin pretreated prostheses had 13 +/- 8 times more radioactivity per square millimeter than ipsilateral iliac arteries, and untreated expanded polytetrafluoroethylene had 4 +/- 3 times more radioactivity per square millimeter than ipsilateral iliac arteries. Fibronectin/heparin/heparin binding growth factor-type 1/heparin was more radioactive than fibronectin alone (p = 0.056). Histologic evaluation and thrombus-free surface area determinations corroborated the gamma well counting data. Platelet aggregation in vitro was not activated by either fibronectin (1 to 100 micrograms/100 microliters) or heparin binding growth factor-type 1 (25 to 2500 ng/100 microliters). These data suggest that fibronectin and heparin binding growth factor-type 1 promote platelet adhesion not aggregation.

Plasma polymerized tetrafluoroethylene/polyethylene terephthalate vascular prostheses.

Tetrafluoroethylene (TFE) was discharged onto woven polyethylene terephthalate (PET) prostheses, and the PET prostheses (50 mm long) with or without TFE were implanted into canine carotid arteries and aortas. Additional controls included polytetrafluoroethylene and Dacron. Specimens were explanted after one to 12 months, photographed, and sectioned for light and scanning and transmission electron microscopy, and thrombus-free surface areas calculated by computerized planimetry. Results showed no significant patency differences among carotid or aortic groups. However, both PET carotid groups had significantly greater thrombus-free surface areas. Histologically, both PET groups appeared identical. An endothelialized neointima covered PET carotid specimens by six months, compared with three months in the aortic position, with greater pannus ingrowth in both PET groups. Plasma polymerized TFE offered no additional advantage in these long-term experiments.

Platelet interactions with heparin binding growth factor and fibronectin.

A fibronectin (Fn)/heparin/heparin binding growth factor (HBGF)/heparin (FHHH) complex can be affixed to vascular grafts. This study examines the effect of HBGF, Fn, and FHHH on platelet adhesion and aggregation. Expanded polytetrafluoroethylene (PTFE) grafts (5 cm X 4 mm) were treated with Fn (n = 9), FHHH (n = 9), or neither (n = 10) and interposed into canine aortoiliac systems, using each dog as its own control. Autogenous radiolabeled (111In oxine-650 muCi) platelets were injected IV prior to re-establishment of circulation. Blood flow was determined by electromagnetic flowmetry and perfusion maintained for 30 min. Grafts were removed with native aorta and ipsilateral iliac arteries (IIA). Specimens, excluding anastomoses, were sectioned for gamma counting and computerized planimetry. Results showed that FHHH and Fn treated grafts contained significantly more radioactivity than control segments, when normalized to their IIA. FHHH treated grafts contained 27 +/- 16 times more radioactivity per mm2 than IIA, Fn treated prostheses 12 +/- 8 times more, and untreated PTFE 4 +/- 3 times more. FHHH was significantly more radioactive than Fn alone (p less than or equal to 0.03). Platelet aggregation in response to either Fn or HBGF was studied in vitro. Aggregation was not activated by either Fn (1-100 micrograms/100 microliters) or HBGF (25-2,500 ng/100 microliters). These data suggest that Fn and HBGF promote platelet adhesion but not aggregation.

Hemodynamic effects on endothelial cell monolayer detachment from vascular prostheses.

The establishment of an early blood-contacting endothelialized surface may improve the graft-host relationship. This study evaluated the adherence of indium 111-radiolabeled endothelial cells that were cultured to confluence on fibronectin-treated polyester elastomer (Hytrel) grafts that were perfused for two hours on a pulse duplicator apparatus under high- and low-shear conditions. Perfusate samples were serially assayed for radioactivity. After perfusion, grafts were sectioned into four segments and assayed for retained radioactivity. All graft segments were hematoxylin stained and examined under light microscopy for evaluation of cell density. Excellent endothelial cell adherence (90%) was observed under both hemodynamic conditions at 120 minutes, with most losses occurring within the first 15 minutes. No differences were seen between high- and low-shear conditions or proximal vs distal graft segments.

Polyglactin 910/polydioxanone bicomponent totally resorbable vascular prostheses.

Previous studies from our laboratory have shown that bioresorbable vascular prostheses woven from lactide-glycolide copolymers and implanted into arteries of several animal models become replaced by cellular tissues; the rate of replacement parallels the kinetics of prosthetic resorption. This study evaluates the efficacy of bicomponent resorbable prostheses as a method of augmenting resistance to dilatation during the resorption period of the more rapidly resorbed component. Bicomponent prostheses (n = 37) were woven from compound yarns containing 74% polyglactin 910 (PG910) and 26% polydioxanone (PDS) and were interposed into adult white New Zealand rabbit infrarenal aortas. Resultant prosthesis-tissue complexes were harvested after 2 weeks to 12 months. Specimens were photographed and sectioned for light, scanning, and transmission electron microscopy. Randomly selected fresh explants at 1 and 3 months and control aortic segments from the same rabbits were simultaneously perfused with culture media (37 degrees C, 100/80 mm Hg, 60 ml/min) and perfusates assayed by means of tritiated radioimmunoassay techniques for the stable prostacyclin metabolite 6-keto-PGF1 alpha before and after the addition of sodium arachidonate (10 micrograms/ml) to the media. Results showed 100% patency, no aneurysms, and stenosis in 1 of 37 prostheses (3%). PG910 was totally resorbed by 2 months and PDS by 6 months. By 1 month inner capsule thickness was 303 +/- 30 microns. In contrast to previous reports this was significantly thicker than that within 100% PDS (230 +/- 40 microns) and significantly less thick than in 100% PG910 (530 +/- 62 microns). Inner capsules in all three groups stabilized at similar thicknesses (417 to 502 microns).(ABSTRACT TRUNCATED AT 250 WORDS)

Compound polyglactin 910/polypropylene small vessel prostheses.

This study evaluated morphologic and functional characteristics of tissue reactions to compound prostheses of 69% absorbable polyglactin 910 (PG910) and 31% nonabsorbable polypropylene in the rabbit. Forty-two woven PG910/polypropylene prostheses (24 X 4 mm internal diameter) implanted into rabbit infrarenal aortas were harvested after 2 weeks to 12 months. Each explant was photographed and sectioned for light microscopy and transmission and scanning electron microscopy. Randomly selected explants underwent either compliance and bursting strength measurements or assays of production of prostacyclin and thromboxane metabolites by luminal surfaces of both regenerated conduits and normal control aortas in response to administered sodium arachidonate. Results showed 100% patency with no aneurysms and 2% stenoses (1 of 42 prostheses). Confluent endothelial-like cellular luminal surfaces covering oriented smooth muscle-like myofibroblasts comprised the inner capsules whose thicknesses stabilized at 1 to 2 months. Only residual polypropylene remained in the prostheses after 2 months. Compliance studies reflected a 0.65 mm (14%) change over a pressure range of 0 to 160 mm Hg. All regenerated prosthesis-tissue complexes had bursting strengths greater than the proximal perianastomotic native aortas, which burst between 600 and 2000 mm Hg. At 1 month the rate of production of 6-keto-PGF1 alpha per square millimeter of surface area of experimental segments was normal. Production of 6-keto-PGF1 alpha by experimental segments at 3 months had increased fourfold whereas thromboxane B2 (TxB2) production remained unchanged. The 6-keto-PGF1 alpha/TxB2 ratio increased from 1 to 4 months. This study demonstrates clinically efficacious morphologic, mechanical, and biochemical characteristics of PG910/polypropylene-elicited vascular prosthesis-tissue complexes.

Biomaterial pretreatment with ECGF to augment endothelial cell proliferation.

ECGF, a polypeptide of bovine hypothalamic derivation, is the most potent endothelial cell mitogen known, with mitogenic and chemotactic effects well demonstrated in vitro on human endothelial cells. These effects are synergized by heparin. In vivo re-endothelialization of blood-contacting biomaterials may be enhanced by bonding ECGF and heparin to prosthetic surfaces. Long woven Dacron (24 mm) and woven PDS vascular prostheses were treated first with human plasma fibronectin (10 micrograms/cm2). Porcine sodium heparin (20 micrograms/cm2) was added by means of fibronectin's heparin affinity. Pure 125I-ECGF (95% alpha, 5% beta; 1 ng/cm2) was next fixed by the heparin affinity of ECGF and followed by a second heparin layer (20 micrograms/cm2) to synergize with and stabilize ECGF. 125I-ECGF adherences were determined by scintillation counts. Attachment efficiency averaged 25%. Prostheses were interposed into rabbit aortas and harvested in triplicate from 0 to 30 days to establish in vivo washout curves. After explantation, residual 125I-ECGF was eluted from prostheses, and intact ECGF was identified by SDS gel electrophoresis. Similarly prepared but nonradioiodinated Dacron and PDS prostheses were explanted after 7 days and their ECGF eluted off for in vitro activity documentation. This ECGF retained its mitogenic properties, causing a 1000% to 1200% increase in 3H-thymidine incorporation into newly synthesized DNA in test murine LE-II cells. Fibronectin-heparin-ECGF fixation to blood-contacting biomaterials may enhance spontaneous re-endothelialization and/or hasten the confluence of transplanted endothelial cells.

Serum and organ creatine phosphokinase alterations in exercise.

Rats that swam for 3 h showed a 6-fold increase in serum creatine phosphokinase (SCPK) activity which declined to control values within 7 h after swimming. Of the excess SCPK, 77% was BB isoenzyme; the remainder was mainly MM with traces of MB. Kidney, liver, brain and lung contain mainly BB (50-80%) and only a trace of MB (0-7%). Heart CPK was composed of little BB (8%) and more MB (28%) and MM (64%). Skeletal muscle CPK was almost entirely MM. CPK activity is highest in skeletal muscle, intermediate in heart and brain and lowest in kidney, liver and lung. It is suggested that skeletal muscle and heart are not involved in CPK release in swimming, and kidney, liver and brain may be sites of release.