Biodegradable Polymer (D,L-Lactide-ε-Caprolactone) in Aortic Vascular Prosthesis: Morphological Evaluation in an Animal Model

Biodegradable D,L-Lactide-ε-caprolactone copolymer was used in substitution to bovine collagen to seal porosity in nine Dacron vascular Sorin Carbografts®. One served as control and 8 were implanted in mini-pigs as vascular by-pass in the thoracic aorta. The grafts were explanted at 7 days (4 animals), 30 (2 animals) and at 90 days (2 animals), and submitted to gross examination, X-ray, histology and electron microscopy.

Aim of the study was to assess the safety and the reliability of these polyester vascular prostheses impregnated with the copolymer in terms of containment of the bleeding in the perioperative period, host inflammatory response, copolymer biodegradation and prostheses “healing”.

All the grafts were patent at angiographic and X-ray examination. At 7 days blood infiltration between Dacron and copolymer lining was detected. Inflammatory granulocyte infiltrates and granulomatous reaction with polymer degradation was observed at 30 days and fibrous tissue healing at 90 days. Luminal surface was covered by thin thrombi at 7 and by a neointima at 30 and 90 days.

We conclude that D,L-Lactide-ε-caprolactone copolymer is effective in preventing perigraft bleeding, even though an early hematoma between Dacron and the copolymer coating occurs. Copolymer is degraded through a mild inflammatory reaction, with eventual evolution to fibrous healing.

Warm hepatic ischemia in pigs: effects of L-arginine and oligotide treatment

Reperfusion injury represents a key event leading to graft nonfunction. Maintaining adequate nitric oxide levels and stimulating vasodilator synthesis can probably minimize endothelial damage. The aim of this study was to investigate the effect of L-arginine, a substrate of nitric oxide synthesis, and oligotide, a promoter of prostacyclin synthesis, on liver function and morphology after warm ischemia-reperfusion injury. After constructing a side-to-side portacaval shunt, ischemia was induced by clamping the hepatic hilum for 2 h above the shunt, in 19 female pigs divided into a control group (n = 7), an L-arginine treatment group (n = 6), and an oligotide treatment group (n = 6). Liver function tests and measurements of serum and red blood cell malondialdehyde and plasma nitric oxide levels were performed before reperfusion and at 1, 10, 60, and 120 min after reperfusion. Liver biopsies, taken before reperfusion and at 30 min and 7 days after reperfusion, were analyzed for tissue malondialdehyde, histological-ultrastructural features, and apoptosis evaluation. Thirty minutes after reperfusion, liver malondialdehyde, sinusoidal congestion, necrosis, and apoptosis were significantly lower in the L-arginine group than in the controls (p < .05). On postoperative day 7, tissue malondialdehyde decreased, while plasma nitric oxide and hepatocyte glycogen content were increased in the L-arginine group compared to controls (p < .05). This study demonstrates the protective effect of L-arginine on hepatic lipoperoxidation and liver morphology in a pig model of warm ischemia-reperfusion injury. The increased plasma levels of nitric oxide a week after ischemia-reperfusion injury support the hypothesis that it has a role in preventing liver damage. The same beneficial effect was not confirmed for oligotide.

Is the tricuspid position suitable for testing replacement bioprosthetic valves in the sheep model?

BACKGROUND AND AIM OF THE STUDY

Glutaraldehyde may promote calcification in xenograft tissue by the action of toxic aldehyde group residues involved in the cross-link process. Post-fixation treatment with homocysteic acid (HA) neutralizes this toxicity by bonding aldehyde groups, and enhances biocompatibility on the basis of strongly electronegative sulfonic groups. Previous studies in a rat subcutaneous model showed significant long-term mitigation of mineralization of glutaraldehyde-fixed pericardium treated with HA. This study aimed to assess the anticalcific efficacy of HA in a valvular implant in growing sheep, and establish if the tricuspid position is suitable for testing replacement bioprosthetic valves.

METHODS

Eleven stented 25 mm Pericarbon bioprostheses (seven HA-treated, four standard) were implanted in the tricuspid position of growing sheep. Infective endocarditis occurred in four prostheses. Among the remaining seven, three (two HA-treated, one standard) were explanted at 91 days (mid-term), and four (two HA-treated, two standard) at 140-141 days (long-term). All explants were studied by gross, X-ray, light, transmission and scanning electron microscopy, as well as by atomic absorption spectroscopy.

RESULTS

No histological and ultrastructural difference in tissue preservation were observed between HA-treated and standard Pericarbon bioprostheses, either in the mid or long term. The mean calcium content of mid-term HA-treated explants was 9.55 mg/g compared with 16.26 mg/g in mid-term standard explants. Only one late standard explant failed as a result of severe stenosis caused by massive dystrophic calcification. Among four late explants, two showed significant increase in mineralization (HA-treated, 87.45 mg/g; standard, 181.20 mg/g), while two showed calcium contents similar to those in mid-term explants (HA-treated, 11.96 mg/g; standard, 17.32 mg/g).

CONCLUSION

Post-fixation treatment with HA preserves structural properties after tricuspid implantation in growing sheep. The tricuspid implant in the sheep model failed to reproduce remarkable accelerated progressive calcification in all xenografts so as to demonstrate a significant difference between HA and standard explants. The tricuspid position for testing replacement bioprosthetic valves should be abandoned, and investigations repeated with the prosthesis in the mitral position.

Primary tissue failure of bioprostheses: new evidence from in vitro tests

BACKGROUND

Primary tissue failure, which is mainly caused by calcification, is still the limiting factor in the long-term outcome of heart valve bioprostheses. Even though the precise nature of this process is not fully understood, in vitro tests have been developed to reproduce and predict calcification for individual bioprostheses.

METHODS

In vitro calcification testing was performed by using an accelerated pulsatile valve tester which was adapted for testing stented as well as stentless bioprostheses with physiological fluid dynamics. A total of 84 bioprostheses (porcine, pericardial and stentless porcine of different manufacturers) were cyclically loaded at a test rate of 300/min at 37 degrees C within a rapid calcification fluid with CaxP = 130(mg/dl)2 at pH 7.4. Calcification was assessed by microradiography after 12 x 10(6) cycles. In a previous step, holographic interferometry was performed to identify irregularities of valve leaflets in order to predict later calcification. Selected specimens of calcified bioprostheses underwent histology, transmission (TEM) and scanning (SEM) electron microscopy. Tissue mineralization was investigated by coupling SEM, electron microprobe analysis (EMPA) and X-ray powder diffraction (XRPD) methods.

RESULTS

For all tested bioprostheses, a significant calcification was achieved within 4 to 6 weeks of ongoing testing, and the degree of calcification increased with time. A significant correlation between calcification and leaflet irregularities (detected by holographic interferometry) was found (r = 0.80, p = 0.001). Calcification varied between individual bioprostheses, and significant differences were detected for different groups (calculated as percentage of total leaflet area, mean +/- SD): porcine stented (37.3 +/- 12.0%), bovine stented (23.0 +/- 8.9%), porcine stentless (16.2 +/- 7.6%). Histological and ultrastructural investigation showed intrinsic calcification involving both the spongiosa and fibrosa with collagen fibrils, interfibrillar spaces and cells as early sites of calcification. There was clear evidence of apatite crystallization, and observations made with in vitro calcification were quite similar to those occurring with in vivo implanted bioprostheses.

CONCLUSION

In vitro tests can reproduce intrinsic calcification of bioprostheses even in the absence of viable biologic host factors. Moreover, degree and sites of calcification have become predictable. This enables the development and evaluation of bioprostheses with reduction of animal experiments. From our results obtained with a broad range of available bioprostheses, stented bovine and stentless porcine valves seem to be superior to conventional stented porcine bioprostheses with regard to leaflet calcification.

Dynamic in vitro calcification of bioprosthetic porcine valves: evidence of apatite crystallization

OBJECTIVE

Calcification is the most important cause of structural deterioration of glutaraldehyde-fixed bioprosthetic valves. Devitalization of tissue favors calcium deposits in the shape of apatite crystals. Host factors influence the extent and progression of calcification, but the phenomenon can also occur in vitro in the absence of a viable milieu. Whether calcific deposits obtained in vitro are similar to those found in vivo is unknown.

METHODS

Four porcine frame-mounted bioprostheses (St Jude Medical Bioimplant; St Jude Medical, Inc, St Paul, Minn) were tested in vitro by using a pulsatile accelerated calcification testing device at a frequency of 300 cycles per minute at 37 degrees C for 19 x 10(6) cycles with a rapid synthetic calcification solution (final product [calcium x phosphate], 130 mg/dL(2)). Three of the same type of xenografts explanted from human subjects because of calcific failure (time in place, 108 +/- 25.63 mo) served as control grafts. Each sample underwent gross and x-ray examination, histology, transmission and scanning electron microscopy, atomic absorption spectroscopy, electron microprobe analysis, and x-ray powder diffraction methods.

RESULTS

All in vitro bioprostheses were heavily calcific, with intrinsic Von Kossa stain-positive deposits and a mean calcium content of 205.285 +/- 64.87 mg/g dry weight. At transmission electron microscopy, nuclei of calcification involved mostly collagen fibers and interfibrillar spaces and, more rarely, cell debris and nuclei. Electron microprobe analysis showed a Ca/P atoms ratio of 4.5:3, a value intermediate between hydroxyapatite and its precursor, octacalciumphosphate. X-ray powder diffraction showed a well-separated and sharp peak, which is typical of hydroxyapatite. Aggregates of plate-like crystals up to 8 microm in size were observed at scanning electron microscopy, with a typical tabular hexagonal shape consistent with apatite. The morphologic and chemical findings in human explants were similar.

CONCLUSIONS

Intrinsic calcification of glutaraldehyde-fixed porcine valves was induced in vitro. Electron microprobe analysis and x-ray powder diffraction findings were in keeping with apatite crystallization, such as that occurring in valve xenografts implanted in vivo. The model may be of value to accelerate the screening of anticalcific agents and may reduce the need for animal experiments.

Liver cell apoptosis in chronic hepatitis C correlates with histological but not biochemical activity or serum HCV-RNA levels

In hepatitis C virus (HCV) infection, mechanisms responsible for liver cell damage are still poorly understood and both necrosis and apoptosis may be operative. By using terminal deoxynucleotydil transferase-mediated d-UTP-biotin nick-end labeling (TUNEL) we have evaluated and quantified apoptosis in liver biopsy specimens from 61 patients with chronic hepatitis C. All patients had detectable apoptotic cells in the liver. Presence of increased apoptotic activity was confirmed in selected cases by electron microscopy and by DNA gel electrophoresis. The amount of liver cell apoptosis expressed as apoptotic index, ranged between 0.01% to 0.54% and showed a positive correlation with histological activity grading (P <.0005) and with the amount of infiltrating CD8-positive cells (P =. 01). Apoptosis did not correlate with transaminase levels or with HCV load and genotype. These results support the concept that immune-mediated apoptosis may play a role in the pathogenesis of chronic hepatitis C and indicate that this type of reaction may occur in the absence of significant alanine transaminase (ALT) elevation, thus explaining the lack of correlation between biochemical activity and liver histological damage.

Detoxified glutaraldehyde cross-linked pericardium: tissue preservation and mineralization mitigation in a subcutaneous rat model

BACKGROUND AND AIM OF THE STUDY

Glutaraldehyde is considered a promoter of calcification by the action of toxic aldehyde group residuals from cross-linking. Post-fixation treatment with homocysteic acid (HA), besides bonding aldehyde groups and neutralizing toxicity, should enhance biocompatibility due to the strongly electronegative sulfonic group. The aim of this investigation was to evaluate HA efficacy on tissue preservation and dystrophic calcification mitigation in glutaraldehyde cross-linked bovine pericardium (BP) using a subcutaneous rat model.

METHODS

Four samples of BP, two with glutaraldehyde-HA and two with glutaraldehyde treatment, were implanted in each of 24 male Sprague-Dawley rats. Three rats were killed at 14 days, eight at 28 days, eight at 56 days and five at 84 days. Unimplanted glutaraldehyde-HA- and glutaraldehyde-treated samples served as controls. All samples were studied by gross examination, mammography, light transmission and scanning electron microscopy, and atomic absorption spectroscopy. The nature of mineralization was investigated by coupling techniques of scanning electron microscopy, electron microprobe analysis and X-ray powder diffraction.

RESULTS

No histological and ultrastructural differences were found between glutaraldehyde-HA- and glutaraldehyde-treated BP, whether implanted or unimplanted. In both groups, calcification progressed with time, but significantly less after glutaraldehyde-HA treatment than after glutaraldehyde alone and at all time intervals (14.63 +/- 21.34 versus 43.17 +/- 15.99 at 28 days, p = 0.003; 56.42 +/- 40.20 versus 90.59 +/- 32.90 at 56 days, p = 0.008; 91.68 +/- 67.68 versus 156.23 +/- 17.85 at 84 days, p = 0.01). Differences were evident by mammography and histology (von Kossa stain). Electron microprobe analysis in both groups showed the composition of calcified nuclei to be calcium phosphate, stoichiometrically close to apatite (Ca5(PO4)3(OH)). The occurrence of crystallized apatite was supported by X-ray powder diffraction findings, the amount of crystallized apatite being higher in glutaraldehyde-treated samples.

CONCLUSIONS

Post-fixation treatment with HA preserves BP structural properties and significantly mitigates mineralization of long-term subcutaneous implants.

The protective effects of L-arginine after liver ischaemia/reperfusion injury in a pig model

Hepatic ischaemia/reperfusion is characterized by circulatory and metabolic derangement, liver dysfunction, and tissue damage. To evaluate the role of L-arginine, a substrate of nitric oxide, in ischaemia/reperfusion injury, total liver ischaemia was induced for 120 min in 22 Landrace x Large White female pigs, which were randomly assigned to a treatment group (10 animals) or a control group (12 animals). An L-arginine bolus (540 mg/kg i.v.) was administered to the treatment group 1 h before clamping the hepatic hilum, at clamping, at reperfusion, and at 1 and 2 h after reperfusion. The control animals received normal saline and an i.v. infusion. Liver function tests and analysis of serum, erythrocyte, and tissue malondialdehyde contents were performed at commencement of laparotomy, before reperfusion, and at 30 min and 7 days after reperfusion. Liver biopsies were taken at laparotomy, at 30 min, and at 7 days after reperfusion for histological and ultrastructural examination. Assessment of apoptosis included in situ end-labelling analysis and DNA gel electrophoresis. Survival at 7 days was better in the treated animals than in the controls (9/10 vs. 7/12). Tissue malondialdehyde content, aspartate aminotransferase, and lactate dehydrogenase levels were lower in the treatment group, in which morphological changes were significantly less evident than in the controls 30 min after reperfusion. At 7 days, differences between the groups with respect to cell integrity were apparent only on ultrastructural analysis. Glycogen content, 7 days after reperfusion, was higher in the treatment group than in the controls: 70.25 per cent vs. 21.66 per cent positive hepatocytes (score 3 vs. score 1). Multiparametric analysis showed fewer apoptotic cells in the treatment group at all times. Our data show that the administration of L-arginine reduces damage to liver tissue after ischaemia/reperfusion injury in a pig model. This may be explained not only by the known vasodilator, anti-aggregation, and superoxide inactivation effects of increased nitric oxide release, but possibly also by some other action of L-arginine, such as its influence on cellular metabolism.

3'-5' L-capped-antisense oligodeoxynucleotides targeted at the SV40 T-antigen gene: pharmacological and biological properties

This paper reports on some pharmacological and biological properties of 22-mer antisense oligodeoxynucleotides which contain an L-deoxyribonucleoside at each terminus. Compared with natural compounds, of which they retain the DNA hybridizing ability and the cell uptake mechanism, the L-22-mers exhibited an increased resistance to phosphodiesterase degradation, an apparent higher intracellular concentration and a longer intracellular half life. Antiviral activity was not prominent.