Gernot Seebacher

Early failure of the tissue engineered porcine heart valve SYNERGRAFT in pediatric patients.

OBJECTIVESnThe first tissue engineered decellularized porcine heart valve, Synergraft (Cryolife Inc., USA) was introduced in Europe as an alternative to conventional biological valves. This is the first report of the rapid failure of these new grafts in a small series.nnnMATERIALS AND METHODSnIn 2001, 2 model 500 and 2 model 700 Synergraft valves were implanted in four male children (age 2.5-11 years) in the right ventricular outflow tract as a root. Two patients had a Ross operation and two had a homograft replacement.nnnRESULTSnThe cryopreserved Synergraft valves appeared macroscopically unremarkable at implantation. Recovery from surgery was uneventful and good valve function was demonstrated postoperatively. Three children died, two suddenly with severely degenerated Synergraft valves 6 weeks and 1 year after implantation. The third child died on the 7th day due to Synergraft rupture. Subsequently the fourth graft was explanted prophylactically 2 days after implantation. Macroscopically all four grafts showed severe inflammation starting on the outside (day 2 explant) leading to structural failure (day 7 explant) and severe degeneration of the leaflets and wall (6 weeks and 1 year explant). Histology demonstrated severe foreign body type reaction dominated by neutrophil granulocytes and macrophages in the early explants and a lymphocytic reaction at 1 year. In addition significant calcific deposits were demonstrated at all stages. Surprisingly pre-implant samples of the Synergraft revealed incomplete decellularization and calcific deposits. No cell repopulation of the porcine matrix occurred.nnnCONCLUSIONnThe xenogenic collagen matrix of the Synergraft valve elicits a strong inflammatory response in humans which is non-specific early on and is followed by a lymphocyte response. Structural failure or rapid degeneration of the graft occurred within 1 year. Calcific deposits before implantation and incomplete decellularization may indicate manufacturing problems. The porcine Synergraft treated heart valves should not be implanted at this stage and has been stopped.

Comparison of different decellularization procedures of porcine heart valves

Background Tissue engineering of heart valves should avoid the disadvantages of conventional prostheses. In this study we tested different decellularization procedures for their potential of cell removal and their ability to preserve the matrix. Methods Specimens of porcine aortic and pulmonary roots were treated with either trypsin or sodium-dodecyl-sulfate (SDS) or Triton-X 100® and sodium-deoxycholate with a range of concentrations. Tissue samples were then processed for scanning electron microscopy and laser scanning microscopy. Results Trypsin achieved only incomplete decellularization and caused severe structural alterations of the matrix. In contrast SDS removed cells completely but caused strong structural alterations. Treatment with Triton-X100® and sodium-deoxycholate achieved both complete decellularization and preservation of the matrix structure. Conclusion Techniques of decellularization are highly variable in efficiency and matrix preservation and was best achieved in our study with Triton-X100® and sodium deoxycholate.

Dilatation of the autograft root after the Ross operation.

OBJECTIVEnStructural differences of the pulmonary root may predispose it to progressive dilatation in the systemic circulation after the Ross operation. We identified the incidence and risk factors of pulmonary autograft root dilatation.nnnMETHODSnOne hundred and seven adult patients (mean age of 36+/-11 years) were followed after the Ross operation since 1991 including an echocardiogram within 3 months of surgery and yearly clinical assessment and echocardiography. The autograft was measured at the maximum diameter of the sinus (SV) and aortic insufficiency (AI) assessed. A SV of >37 mm was considered as root dilatation and the incidence over time was calculated using the Kaplan-Meier method. Clinically relevant dilatation was defined as a root diameter of >42 mm. In addition, we determined the percentage change of the sinus diameter between the early and latest echocardiogram. Furthermore we tested the influence of patient variables and risk factors on dilatation.nnnRESULTSnBy 1 year, dilatation was found in 21 patients (20%). The SV was >42 mm in eight patients (7%). By 7 years, only 45% of patients were free of dilatation. Eleven patients (10%) had a SV of >42 mm. Increase in SV was time related and linear. However, 90% of patients showed <25% dilatation during follow-up. Time from operation, early SV diameter, male gender and surgical technique were identified as significant risk factors of dilatation. However, dilatation has not lead to reoperation due to aneurysm formation or development of significant AI.nnnCONCLUSIONSnWe conclude that time dependent autograft root dilation occurs but does not cause an increase in AI and need for reoperation up to 7 years. These findings warrant the pursuit of the concept of the Ross operation in young patients who regain excellent functional status and life style without anticoagulation.

PHARMACOKINETICS OF MYCOPHENOLATE MOFETIL IN HEART TRANSPLANT RECIPIENTS

Mycophenolate Mofetil (MMF) is an ester prodrug of the immunosuppressant myco-phenolic acid (MPA), which selectively inhibits the inosine monophosphate dehydrogenase (IMPDH). IMPDH converts inosine monophosphate (IMP) into xanthosine monophosphate (XMP) which will further be metabolized to ATP and GTP.

GUANOSINE-5'-TRIPHOSPHATE INCREASES IN RED BLOOD CELLS OF HEART TRANSPLANT RECIPIENTS TREATED WITH MYCOPHENOLATE MOFETIL

The present study clearly shows that long-term administration of MMF is associated with increasing whole blood GTP levels obviously due to an induction of IMPDH and HGPRT activities in erythrocytes. First hints for an induction of IMPDH under MMF therapy were recently published for a very few kidney transplanted patients3,4. Moreover, Montero et al.5 reported from a 30-fold elevation of normal pretreatment IMPDH activity following an antiviral therapy with ribavirin, another IMPDH inhibitor.

One and a half years of experience with mycophenolate mofetil (Cellcept) in cardiac transplantation: a prospective, randomized study.

HEART transplantation is an established treatment for patients with end-stage heart failure. Optimal pharmacologic immunosuppression is needed to prevent morbidity and mortality associated with allograft rejection with a minimum of side effects associated with the immunosuppressive drug. Acute graft failure is a problem that apparently was overcome but, unfortunately, chronic rejection and the severe side effects of immunosuppressive drugs are the complications of organ transplantation which need a solution. Mycophenolate mofetil (MMF) is a new immunosuppressive drug with promising results, but long-term experience is still awaited. We have used MMF for more than 1.5 years in combination with cyclosporine A (CyA) and prednisone after cardiac transplantation. MMF is the morpholinethylester of the immunosuppressive agent mycophenolic acid (MPA). This new antimetabolite shows specific activity in lymphocytes where the target enzyme inosine monophosphate dehydrogenase (IMPDH) is blocked and therefore the production of guanosine triphosphate (GTP) inside the cell is reduced. In this way T and B lymphocytes are inhibited in differentiation and proliferation. The drug also reduces antibody production of plasma cells and production of GTP dependent ligands as endothelial adhesion molecules. MPA is glucuronidated to its single metabolite mycophenolic acid glucuronide (MPAG), which was shown to be immunosuppressive by itself. This new immunosuppressive drug is considered to have several advantages in comparison to azathioprine (AZA). Although there is a lot of experience with MMF in renal transplantation, scanty information is available in cardiac transplantation. This prospective, randomized study was designed to evaluate the clinical outcome of patients after heart transplantation under this novel regimen of immunosuppressive therapy and to reduce CyA whole-blood levels in the study group.

Cystic fibrosis and lung transplantation--determination of the survival benefit.

ZusammenfassungEinleitungZystische Fibrose (CF) ist eine anerkannte Indikation zur Lungentransplantation, jedoch ist der optimale Zeitpunkt für die Transplantation noch diskutabel. Liou et al. haben einen Score beschrieben, mit dem die 5-Jahres-Überlebenswahrscheinlichkeit für CF Patienten errechnet werden kann. Er schlussfolgerte, dass nur Patienten mit einer errechneten 5-Jahres-Überlebenswahrscheinlichkeit <30% einen Überlebensvorteil durch die Lungentransplantation haben. Jene zwischen 30% und 50% haben identische Überlebensraten und jene >50% haben schlechtere Überlebensraten mit Transplantation. Ziel dieser Studie ist es, die Gültigkeit und Anwendbarkeit dieses Models zu evaluieren.MethodikEs wurden die Daten von CF Patienten, welche von Jänner 1995 bis Juli 2001 transplantiert wurden, retrospektiv analysiert. Der Score nach Liou wurde anhand von Daten, welche vor der Transplantation erhoben wurden, errechnet. Die Patienten wurden anhand der errechneten 5 Jahresüberlebenswahrscheinlichkeit eingeteilt (Gruppe 1: <30%, Gruppe 2: 30–50%, Gruppen 3–5: >50%). Die Überlebensraten wurden für alle Gruppen ermittelt und mit der errechneten Überlebenswahrscheinlichkeit verglichen.ErgebnisseWährend des Beobachtungszeitraumes wurden 27 CF Patienten lungentransplantiert. 3 Patienten mussten aufgrund inkompletter Daten aus der Analyse ausgeschlossen werden. 15 Patienten fielen in Gruppe 1 und 9 Patienten in Gruppe 2. Kein Patient fiel in die Gruppen 3–5. In Gruppe 1 waren 9 weibliche und 6 männliche Patienten mit einem Durchschnittsalter von 22,1±4,9 Jahren. Durchschnittliche Überlebenszeit waren 918±787 Tage. 1-, 3- und 5-Jahres-Überlebensrate war 66,6%. 3 männliche und 6 weibliche Patienten fielen in Gruppe 2, Altersdurchschnitt waren 26,2±12,2 Jahre. Durchschnittliche Überlebenszeit in dieser Gruppe waren 701±617 Tage. 1-, 3- und 5-Jahres-Überlebensrate war 66,6%.SchlussfolgerungenIm Beobachtungszeitraum wurden nur Patienten mit einer errechneten 5-Jahres-Überlebenswahrscheinlichkeit <50% lungentransplantiert. Sowohl Patienten der Gruppe 1 als auch Gruppe 2 hatten eine 5-Jahres-Überlebensrate von 66,6%. Unserer Erfahrung nach haben demnach sowohl Patienten mit einer 5-Jahres-Überlebenswahrscheinlichkeit <30% als auch jene <50% einen klaren Überlebensvorteil durch die Lungentransplantation.SummaryIntroductionCystic fibrosis is a well acknowledged indication for lung transplantation; however, the optimal timing for transplantation remains debatable. Liou et al. described a score for calculating 5-year probability of survival for patients with cystic fibrosis and concluded that only patients with a probability of survival <30% gained a survival benefit from transplantation; those between 30% and 50% had equivocal survival effects from transplantation and those >50% suffered negative effects. The aim of the present study was to determine the validity and applicability of this model.MethodsData from patients with cystic fibrosis transplanted between January 1995 and July 2001 were retrospectively reviewed. Survival score according to Liou was calculated from data collected before transplantation. Patients were classified according to 5-year probability of survival (group 1: <30%, group 2: 30%–50%, groups 3–5: >50%). Actuarial survival rates were calculated separately for each group and compared with the predicted probability of survival.ResultsDuring the observation period 27 patients were transplanted for cystic fibrosis. Three patients had to be excluded from further analysis because of incomplete pretransplant data. Fifteen patients were classified as group 1 and nine patients as group 2. No patients were eligible for groups 3 to 5. There were nine female patients and six males in group 1, mean age 22.1±4.9 years. Mean survival time was 918±787 days; 1-, 3- and 5-year survival rates were 66.6%. Three male patients and six females were classified as group 2, mean age 26.2±12.2 years. Mean survival time for this group was 701±617 days, and 1-, 3- and 5-year survival rates were 66.6%.ConclusionWe found that only patients with a 5-year probability of survival <50% had been transplanted. For patients in groups 1 and 2 we report identical 5-year survival rates of 66.6%. According to our experience, cystic fibrosis patients with a 5-year probability of survival <30% and also those between 30% and 50% gain a clear survival benefit from bilateral lung transplantation.

Mycophenolic acid influences the expression of ICAM-1 on human endothelial cells.

Mycophenolic acid (MPA) is a potent immunosuppressive agent, which selectively decreases the intracellular guanine nucleotide pools by inhibiting the inosine-5′-mono-phosphate dehydrogenase (IMP-DH) thereby suppressing the proliferation of rapidly proliferating cells e.g. alloantigen stimulated lymphocytes (1,2).

Cystic fibrosis and lung transplantation - determination of the survival benefit

Introduction nCystic fibrosis is a well acknowledged indication for lung transplantation; however, the optimal timing for transplantation remains debatable. Liou et al. described a score for calculating 5-year probability of survival for patients with cystic fibrosis and concluded that only patients with a probability of survival 50% suffered negative effects. The aim of the present study was to determine the validity and applicability of this model.