Biomedical subjects

P N Khalil

Publications and source records attributed to P N Khalil.

5 recordsLinked to original sources

PubMed2001

Dynamics of extracellular matrix production and turnover in tissue engineered cardiovascular structures.

Appropriate matrix formation, turnover and remodeling in tissue-engineered small diameter vascular conduits are crucial requirements for their long-term patency and function. This complex process requires the deposition and accumulation of extracellular matrix molecules as well as the remodeling of this extracellular matrix (ECM) by matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs). In this study, we have investigated the dynamics of ECM production and the activity of MMPs and TIMPs in long-term tissue-engineered vascular conduits using quantitative ECM analysis, substrate gel electrophoresis, radiometric enzyme assays and Western blot analyses. Over a time period of 169 days in vivo, levels of elastin and proteoglycans/glycosaminoglycans in tissue-engineered constructs came to approximate those of their native tissue counter parts. The kinetics of collagen deposition and remodeling, however, apparently require a much longer time period. Through the use of substrate gel electrophoresis, proteolytic bands whose molecular weight was consistent with their identification as the active form of MMP-2 (approximately 64--66 kDa) were detected in all native and tissue-engineered samples. Additional proteolytic bands migrating at approximately 72 kDa representing the latent form of MMP-2 were detected in tissue-engineered samples at time points from 5 throughout 55 days. Radiometric assays of MMP-1 activity demonstrated no significant differences between the native and tissue-engineered samples. This study determines the dynamics of ECM production and turnover in a long-term tissue-engineered vascular tissue and highlights the importance of ECM remodeling in the development of successful tissue-engineered vascular structures.

Animals↗

PubMed2000

Tissue-engineered valved conduits in the pulmonary circulation.

OBJECTIVE: Bioprosthetic and mechanical valves and valved conduits are unable to grow, repair, or remodel. In an attempt to overcome these shortcomings, we have evaluated the feasibility of creating 3-leaflet, valved, pulmonary conduits from autologous ovine vascular cells and biodegradable polymers with tissue-engineering techniques. METHODS: Endothelial cells and vascular medial cells were harvested from ovine carotid arteries. Composite scaffolds of polyglycolic acid and polyhydroxyoctanoates were formed into a conduit, and 3 leaflets (polyhydroxyoctanoates) were sewn into the conduit. These constructs were seeded with autologous medial cells on 4 consecutive days and coated once with autologous endothelial cells. Thirty-one days (+/-3 days) after cell harvesting, 8 seeded and 1 unseeded control constructs were implanted to replace the pulmonary valve and main pulmonary artery on cardiopulmonary bypass. No postoperative anticoagulation was given. Valve function was assessed by means of echocardiography. The constructs were explanted after 1, 2, 4, 6, 8, 12, 16, and 24 weeks and evaluated macroscopically, histologically, and biochemically. RESULTS: Postoperative echocardiography of the seeded constructs demonstrated no thrombus formation with mild, nonprogressive, valvular regurgitation up to 24 weeks after implantation. Histologic examination showed organized and viable tissue without thrombus. Biochemical assays revealed increasing cellular and extracellular matrix contents. The unseeded construct developed thrombus formation on all 3 leaflets after 4 weeks. CONCLUSION: This experimental study showed that valved conduits constructed from autologous cells and biodegradable matrix can function in the pulmonary circulation. The progressive cellular and extracellular matrix formation indicates that the remodeling of the tissue-engineered structure continues for at least 6 months.

Animals↗

PubMed2000

Results of Norwood stage I operation: comparison of hypoplastic left heart syndrome with other malformations.

OBJECTIVE: We compared the Norwood stage I operation for hypoplastic left heart syndrome and other complex malformations with ductus-dependent systemic circulation. METHODS: A retrospective study of 194 patients who underwent a Norwood stage I palliation between 1990 and 1998 was conducted. Malformations in 131 patients were classified as hypoplastic left heart syndrome, defined as aortic and mitral atresia or severe stenosis, normal segmental anatomy, intact ventricular septum, and hypoplasia of the left ventricle. Sixty three patients had other lesions: hypoplastic left ventricle with ventricular septal defect (n = 18), unbalanced complete atrioventricular canal (n = 9), complex double-outlet right ventricle (n = 14), double-inlet left ventricle (n = 11), tricuspid atresia with transposition of the great arteries (n = 6), and others (n = 5), including heterotaxia. RESULTS: Operative (>30 days) and 1-year survivals were lower for patients with hypoplastic left heart syndrome than for those with other lesions (63.4% vs 81%, P =.008, and 51.2% vs 71.4%, P =.02, respectively). The presence of a nonhypoplastic left ventricle (n = 27) was associated with higher operative and 1-year survivals (96.3% vs 64.7%, P =.002; 88.9% vs 52. 7%, P <.001). A restrictive atrial septal defect and prematurity tended to increase mortality across both groups. Cox proportional hazards regression indicated that a single right ventricle was the most important independent predictor of death (P <.001). Operative mortality for all patients undergoing the stage I procedure decreased from 38.5% (1990-1994) to 21.4% after 1994 (P =.02). CONCLUSIONS: The survival of patients with malformations other than hypoplastic left heart syndrome after the Norwood procedure is greater than for those with hypoplastic left heart syndrome. Staged palliation is valid surgical therapy in these patients, with good results in intermediate follow-up.

Abnormalities, Multiple↗

PubMed2000

Patch augmentation of the pulmonary artery with bioabsorbable polymers and autologous cell seeding.

OBJECTIVE: In recent years bioabsorbable synthetic or biologic materials have been used to augment the pulmonary artery or the right ventricular outflow tract. However, each of these polymers has one or more shortcomings. None of these patch materials has been seeded with cells. Thus, we have tested a fast-absorbing biopolymer, poly-4-hydroxybutyric acid, with autologous cell seeding for patch augmentation of the pulmonary artery in a juvenile sheep model. METHODS: Vascular cells were isolated from ovine peripheral veins (n = 6). Bioabsorbable porous poly-4-hydroxybutyric acid patches (porosity > 95%) were seeded on 3 consecutive days with a mixed vascular cell suspension (21.3 +/- 1.3 x 10(6) cells). Forty-five (+/- 2) days after the vessel harvest, 1 unseeded and 6 autologously seeded control patches were implanted into the proximal pulmonary artery. The animals received no postoperative anticoagulation. Follow-up was performed with echocardiography after 1 week and before explantation after 1, 7, and 24 weeks (2 animals each) for the seeded control patches and after 20 weeks for the nonseeded control patch. RESULTS: All animals survived the procedure. Postoperative echocardiography of the seeded patches demonstrated a smooth surface without dilatation or stenosis. Macroscopic appearance showed a smooth internal surface with increasing tissue formation. Histology at 169 days demonstrated a near-complete resorption of the polymer and formation of organized and functional tissue. Biochemical assays revealed increasing cellular and extracellular matrix contents. The control patch showed a slight bulging, indicating a beginning dilatation. CONCLUSION: This experiment showed that poly-4-hydroxybutyric acid is a feasible patch material in the pulmonary circulation.

Absorbable Implants↗

PubMed1999

Repair of tetralogy of Fallot in neonates and young infants.

BACKGROUND: The timing of repair of tetralogy of Fallot (TOF) remains controversial. Advantages to early complete repair include removal of right ventricular outflow tract obstruction, alleviation of systemic hypoxia, and avoidance of palliation with an arteriopulmonary shunt. METHODS AND RESULTS: This is a retrospective review of 99 children with TOF pulmonary stenosis (TOF/PS) or TOF pulmonary atresia (TOF/PA) who were <90 days of age undergoing early complete repair. Fifty-nine were prostaglandin E dependent, and 91% of neonates were symptomatic at the time of repair. Univariate and multivariate analyses of patient characteristics, anatomic features, and operative management showed the diagnosis of TOF/PA and smaller body surface area to be the only independent risk factors for death. Early mortality was 3% (3 of 99), and actuarial survival rates were 94% at 1 year and 91.6% at 5 years. Freedom from catheterization was 86% at 1 year and 73% at 5 years. Patients repaired for TOF/PA had a significantly lower freedom from reoperation than did those repaired for TOF/PS. CONCLUSIONS: Early complete TOF repair can be accomplished with a low mortality. Children with TOF/PA repaired had a lower freedom from reoperation that did those with TOF/PS. Longer follow-up, with emphasis on arrhythmias and right ventricular function, is required to define the long-term benefits of early repair.

Cardiac Surgical Procedures↗