Daniel R. Duncan

Vascular tissue engineering: towards the next generation vascular grafts.

The application of tissue engineering technology to cardiovascular surgery holds great promise for improving outcomes in patients with cardiovascular diseases. Currently used synthetic vascular grafts have several limitations including thrombogenicity, increased risk of infection, and lack of growth potential. We have completed the first clinical trial evaluating the feasibility of using tissue engineered vascular grafts (TEVG) created by seeding autologous bone marrow-derived mononuclear cells (BM-MNC) onto biodegradable tubular scaffolds. Despite an excellent safety profile, data from the clinical trial suggest that the primary graft related complication of the TEVG is stenosis, affecting approximately 16% of grafts within the first seven years after implantation. Continued investigation into the cellular and molecular mechanisms underlying vascular neotissue formation will improve our basic understanding and provide insights that will enable the rationale design of second generation TEVG.

A critical role for macrophages in neovessel formation and the development of stenosis in tissue-engineered vascular grafts

The primary graft‐related complication during the first clinical trial evaluating the use of tissue‐engineered vascular grafts (TEVGs) was stenosis. We investigated the role of macrophages in the formation of TEVG stenosis in a murine model. We analyzed the natural history of TEVG macrophage infiltration at critical time points and evaluated the role of cell seeding on neovessel formation. To assess the function of infiltrating macrophages, we implanted TEVGs into mice that had been macrophage depleted using clodronate liposomes. To confirm this, we used a CD11b‐diphtheria toxin‐receptor (DTR) transgenic mouse model. Monocytes infiltrated the scaffold within the first few days and initially transformed into M1 macrophages. As the scaffold degraded, the macrophage infiltrate disappeared. Cell seeding decreased the incidence of stenosis (32% seeded, 64% unseeded, P= 0.024) and the degree of macrophage infiltration at 2 wk. Unseeded TEVGs demonstrated conversion from M1 to M2 phenotype, whereas seeded grafts did not. Clodronate and DTR inhibited macrophage infiltration and decreased stenosis but blocked formation of vascular neotissue, evidenced by the absence of endothelial and smooth muscle cells and collagen. These findings suggest that macrophage infiltration is critical for neovessel formation and provides a strategy for predicting, detecting, and inhibiting stenosis in TEVGs.—Hibino, N., Yi, T., Duncan, D. R., Rathore, A., Dean, E., Naito, Y., Dardik, A., Kyriakides, T., Madri, J., Pober, J. S., Shinoka, T., Breuer, C. K. A critical role for macrophages in neovessel formation and the development of stenosis in tissue‐engineered vascular grafts. FASEB J. 25, 4253–4263 (2011). www.fasebj.org

Characterization of the Natural History of Extracellular Matrix Production in Tissue-Engineered Vascular Grafts during Neovessel Formation

Background: The extracellular matrix (ECM) is a critical determinant of neovessel integrity. Materials and Methods: Thirty-six (polyglycolic acid + polycaprolactone and poly lactic acid) tissue-engineered vascular grafts seeded with syngeneic bone marrow mononuclear cells were implanted as inferior vena cava interposition grafts in C57BL/6 mice. Specimens were characterized using immunohistochemical staining and qPCR for representative ECM components in addition to matrix metalloproteinases (MMPs). Total collagen, elastin, and glycosaminoglycan (GAG) contents were determined. MMP activity was measured using zymography. Results: Collagen production on histology demonstrated an initial increase in type III at 1 week followed by type I production at 2 weeks and type IV at 4 weeks. Gene expression of both type I and type III peaked at 2 weeks, whereas type IV continued to increase over the 4-week period. Histology demonstrated fibrillin-1 deposition at 1 week followed by elastin production at 4 weeks. Elastin gene expression significantly increased at 4 weeks, whereas fibrillin-1 decreased at 4 weeks. GAG demonstrated abundant production at each time point on histology. Gene expression of decorin significantly increased at 4 weeks, whereas versican decreased over time. Biochemical analysis showed that total collagen production was greatest at 2 weeks, and there was a significant increase in elastin and GAG production at 4 weeks. Histological characterization of MMPs showed abundant production of MMP-2 at each time point, while MMP-9 decreased over the 4-week period. Gene expression of MMP-2 significantly increased at 4 weeks, whereas MMP-9 significantly decreased at 4 weeks. Conclusions: ECM production during neovessel formation is characterized by early ECM deposition followed by extensive remodeling.

Challenges in translating vascular tissue engineering to the pediatric clinic

The development of tissue-engineered vascular grafts for use in cardiovascular surgery holds great promise for improving outcomes in pediatric patients with complex congenital cardiac anomalies. Currently used synthetic grafts have a number of shortcomings in this setting but a tissue engineering approach has emerged in the past decade as a way to address these limitations. The first clinical trial of this technology showed that it is safe and effective but the primary mode of graft failure is stenosis. A variety of murine and large animal models have been developed to study and improve tissue engineering approaches with the hope of translating this technology into routine clinical use, but challenges remain. The purpose of this report is to address the clinical problem and review recent advances in vascular tissue engineering for pediatric applications. A deeper understanding of the mechanisms of neovessel formation and stenosis will enable rational design of improved tissue-engineered vascular grafts.

TGFβR1 Inhibition Blocks the Formation of Stenosis in Tissue-Engineered Vascular Grafts

We previously developed a tissue-engineered vascular graft (TEVG), created by seeding a biodegradable scaffold with autologous bone marrow–derived mononuclear cells, specifically designed for use in congenital heart surgery. We demonstrated in a clinical trial that this approach is safe and

A novel mutation in two families with limb-girdle muscular dystrophy type 2C

The authors present three unrelated North American patients with limb-girdle muscular dystrophy type 2C. Muscle biopsies suggested γ-sarcoglycan deficiencies for all three patients. Patients 1 and 2 had a novel homozygous E263K missense mutation on exon 8 of γ-sarcoglycan (SGCG). Patient 3 had del521T on her maternal allele and an exon 6 deletion on her paternal allele. Patients 1 and 2 are of Puerto Rican ancestry, suggesting the presence of a founder mutation in that population.

Oropharyngeal Dysphagia is Strongly Correlated With Apparent Life-Threatening Events.

Objectives: The aim of the present study was to investigate the prevalence of oropharyngeal dysfunction with resultant aspiration in patients admitted after apparent life-threatening events (ALTE) and to determine whether historical characteristics could predict this oropharyngeal dysphagia and aspiration risk. Methods: We retrospectively reviewed the records of all patients admitted to Boston Childrens Hospital between 2012 and 2015 with a diagnosis of ALTE to determine the frequency of evaluation for oropharyngeal dysphagia using video fluoroscopic swallow studies (VFSS) and clinical feeding evaluations, to determine the prevalence of swallowing dysfunction in subjects admitted after ALTE and to compare presenting historical characteristics to swallow study results. Results: A total of 188 children were admitted with a diagnosis of ALTE of which 29% (n = 55) had an assessment of swallowing by VFSS. Of those who had a VFSS, 73% (n = 40) had evidence of aspiration or penetration on VFSS. Of all of the diagnostic tests ordered on patients with ALTEs, the VFSS had the highest rate of abnormalities of any test ordered. None of the historical characteristics of ALTE predicted which patients were at risk for aspiration. In patients who had both clinical feeding evaluations and VFSS, observed clinical feedings incorrectly identified 26% of patients as having no oropharyngeal dysphagia when in fact aspiration was present on VFSS. Conclusions: Oropharyngeal dysphagia with aspiration is the most common diagnosis identified in infants presenting with ALTEs. The algorithm for ALTE should be revised to include an assessment of VFSS as clinical feeding evaluations are inadequate to assess for aspiration.

Presenting Signs and Symptoms do not Predict Aspiration Risk in Children.

Objectives To determine if any presenting symptoms are associated with aspiration risk, and to evaluate the reliability of clinical feeding evaluation (CFE) in diagnosing aspiration compared with videofluoroscopic swallow study (VFSS). Study design We retrospectively reviewed records of children under 2 years of age who had evaluation for oropharyngeal dysphagia by CFE and VFSS at Boston Childrens Hospital and compared presenting symptoms, symptom timing, and CFE and VFSS results. We investigated the relationship between symptom presence and aspiration using the Fisher exact test and stepwise logistic regression with adjustment for comorbidities. CFE and VFSS results were compared using the McNemar test. Intervals from CFE to VFSS were compared using the Student t test. Results A total of 412 subjects with mean (±SD) age 8.9 ± 6.9 months were evaluated. No symptom, including timing relative to meals, predicted aspiration on VFSS. This lack of association between symptoms and VFSS results persisted even in the adjusted multivariate model. The sensitivity of CFE for predicting aspiration by VFSS was 44%. Patients with a reassuring CFE waited 28.2 ± 8.5 days longer for confirmatory VFSS compared with those with a concerning CFE (P < .05). Conclusions Presenting symptoms are varied in patients with aspiration and cannot be relied upon to determine which patients have aspiration on VFSS. The CFE does not have the sensitivity to consistently diagnose aspiration so a VFSS should be performed in persistently symptomatic patients.

Gastroesophageal Reflux Burden, Even in Children That Aspirate, Does Not Increase Pediatric Hospitalization.

Objectives: Gastroesophageal reflux is common but remains a controversial disease to diagnose and treat and little is known about the role of reflux testing in predicting clinical outcomes, particularly in children at risk for extraesophageal reflux complications. The aim of this study was to determine if rates of hospitalization were affected by reflux burden even after adjusting for aspiration risk. Methods: We prospectively recruited, between 2009 and 2014, a cohort of pediatric patients with suspected extraesophageal reflux disease who were referred for reflux testing and underwent both multichannel intraluminal impedance with pH (pH-MII) and modified barium swallow studies. A subset of patients also underwent bronchoalveolar lavage with pepsin analysis. We determined their rates of hospitalization for a minimum of 1 year following pH-MII testing. Results: We prospectively enrolled 116 pediatric patients who presented for care at Boston Childrens Hospital and underwent both pH-MII and modified barium swallow studies. There was no statistically significant relationship between reflux burden measured by pH-MII or bronchoalveolar pepsin and total number of admissions or number of admission nights even after adjusting for aspiration status (P > 0.2). There were no statistically significant relationships between reflux burden by any method and the number or nights of urgent pulmonary admissions before or after adjusting for aspiration risk (P > 0.08). Conclusions: Even in aspirating children, reflux burden did not increase the risk of hospitalization. Based on these results, routine reflux testing cannot be recommended even in aspirating children, because the results do not impact clinically significant outcomes.

Association of Proton Pump Inhibitors With Hospitalization Risk in Children With Oropharyngeal Dysphagia

Importance Proton pump inhibitors (PPI) are commonly prescribed to children with oropharyngeal dysphagia and resultant aspiration based on the assumption that these patients are at greater risk for reflux-related lung disease. There is little data to support this approach and the potential risk for increased infections in children treated with PPI may outweigh any potential benefit. Objective The aim of this study was to determine if there is an association between hospitalization risk in pediatric patients with oropharyngeal dysphagia and treatment with PPI. Design, Setting, and Participants We performed a retrospective cohort study to compare the frequency and length of hospitalizations for children who had abnormal results on videofluoroscopic swallow studies that were performed between January 1, 2015, and December 31, 2015, and who were or were not treated with PPI, with follow-up through December 31, 2016. Records were reviewed for children who presented for care at Boston Children’s Hospital, a tertiary referral center. Participants included 293 children 2 years and younger with evidence of aspiration or penetration on videofluoroscopic swallow study. Exposures Groups were compared based on their exposure to PPI treatment. Main Outcomes and Measures The primary outcomes were hospital admission rate and hospital admission nights and these were measured as incident rates. Multivariable analyses were performed to determine predictors of hospitalization risk after adjusting for comorbidities. Kaplan-Meier curves were created to determine the association of PPI prescribing with time until first hospitalization. Results A total of 293 patients with a mean (SD) age of 8.8 (0.4) months and a mean (SD) follow-up time of 18.15 (0.20) months were included in the analysis. Patients treated with PPI had higher admission rates (Incidence rate ratio [IRR], 1.77; 95% CI, 1.16-2.68) and admission nights (IRR, 2.51; 95% CI, 1.36-4.62) even after adjustment for comorbidities. Patients with enteral tubes who were prescribed PPIs were at the highest risk for admission (hazard ratio [HR], 2.31; 95% CI, 1.24-4.31). Conclusions and Relevance Children with aspiration who are treated with PPI have increased risk of hospitalization compared with untreated patients. These results support growing concern about the risks of PPI use in children.