Genomic Contributors to Esophageal Atresia and Tracheoesophageal Fistula: A 12 Year Retrospective Review

OBJECTIVE

To evaluate genetic testing utilization and diagnostic yield in infants with esophageal atresia (EA)/tracheoesophageal fistula (TEF) over the past 12 years to inform future practices and individualize prognostication and management.

STUDY DESIGN

A retrospective cohort study was performed for all infants with EA or EA/TEF hospitalized between January 2011 and January 2023 at a quaternary children's hospital. For each infant, demographic information, prenatal and postnatal history, and genetic testing were reviewed.

RESULTS

There were 212 infants who were classified as follows: 1) complex/syndromic with EA/TEF plus an additional major anatomic anomaly (n = 114, of which 74 met VACTERL criteria); 2) isolated/nonsyndromic EA/TEF (n = 88) and 3) isolated/nonsyndromic EA (n = 10). A range of genetic tests were sent with varying diagnostic rates including karyotype analysis in 12 (all with complex/syndromic phenotypes and all positive), chromosomal microarray analysis in 189 (114 of whom were complex/syndromic with an overall diagnostic rate of 3/189), single gene testing for CHD7 in 18 (4 positive), and exome analysis in 37 complex/syndromic patients (8 positive).

CONCLUSIONS

EA/TEF with and without additional anomalies is genetically heterogeneous with a broad range of associated phenotypes. While the genetic etiology of EA/TEF with or without VACTERL remains largely unknown, genome wide testing (exome or genome) including copy number analysis is recommended over chromosomal microarray testing. We anticipate that expanded genetic/genomic testing modalities such as RNA sequencing and tissue specific molecular testing are needed in this cohort to improve our understanding of the genomic contributors to EA/TEF.

The Delivery Room Resuscitation of Infants with Congenital Diaphragmatic Hernia Treated with Fetoscopic Endoluminal Tracheal Occlusion: Beyond the Balloon

INTRODUCTION

Randomized controlled trials found that fetoscopic endoluminal tracheal occlusion (FETO) resulted in increased fetal lung volume and improved survival for infants with isolated, severe left-sided congenital diaphragmatic hernia (CDH). The delivery room resuscitation of these infants is particularly unique, and the specific delivery room events are largely unknown. The objective of this study was to compare the delivery room resuscitation of infants treated with FETO to standard of care (SOC) and describe lessons learned.

METHODS

Retrospective single-center cohort study of infants treated with FETO compared to infants who met FETO criteria during the same period but who received SOC.

RESULTS

FETO infants were more likely to be born prematurely with 8/12 infants born <35 weeks gestational age compared to 3/35 SOC infants. There were 5 infants who required emergent balloon removal (2 ex utero intrapartum treatment and 3 tracheoscopic removal on placental bypass with delayed cord clamping) and 7 with prenatal balloon removal. Surfactant was administered in 6/12 FETO (50%) infants compared to 2/35 (6%) in the SOC group. Extracorporeal membrane oxygenation use was lower at 25% and survival was higher at 92% compared to 60% and 71% in the SOC infants, respectively.

CONCLUSION

The delivery room resuscitation of infants treated with FETO requires thoughtful preparation with an experienced multidisciplinary team. Given increased survival, FETO should be offered to infants with severe isolated left-sided CDH, but only in high-volume centers with the experience and capability of removing the balloon, emergently if needed. The neonatal clinical team must be skilled in managing the unique postnatal physiology inherent to FETO where effective interdisciplinary teamwork is essential. Empiric and immediate surfactant administration should be considered in all FETO infants to lavage thick airway secretions, particularly those delivered <48 h after balloon removal.

Prenatal treprostinil improves pulmonary arteriolar hypermuscularization in the rabbit model of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital malformation characterized by pulmonary hypoplasia, pulmonary hypertension, and cardiac dysfunction. Pulmonary hypertension represents the major cause of neonatal mortality and morbidity. Prenatal diagnosis allows assessment of severity and selection of foetal surgery candidates. We have shown that treprostinil, a prostacyclin analogue with an anti-remodelling effect, attenuates the relative hypermuscularization of the pulmonary vasculature in rats with nitrofen-induced CDH. Here we confirm these observations in a large animal model of surgically-created CDH. In the rabbit model, subcutaneous maternal administration of treprostinil at 150 ng/kg/min consistently reached target foetal concentrations without demonstrable detrimental foetal or maternal adverse effects. In pups with CDH, prenatal treprostinil reduced pulmonary arteriolar proportional medial wall thickness and downregulated inflammation and myogenesis pathways. No effect on alveolar morphometry or lung mechanics was observed. These findings provide further support towards clinical translation of prenatal treprostinil for CDH.

Prenatally Diagnosed Large Lung Lesions: Timing of Resection and Perinatal Outcomes

INTRODUCTION

Fetuses with large lung lesions including congenital cystic adenomatoid malformations (CCAMs) are at risk for cardiopulmonary compromise. Prenatal maternal betamethasone and cyst drainage for micro- and macrocystic lesions respectively have improved outcomes yet some lesions remain large and require resection before birth (open fetal surgery, OFS), at delivery via an Ex Utero Intrapartum Treatment (EXIT), or immediately post cesarean section (section-to-resection, STR). We sought to compare prenatal characteristics and outcomes in fetuses undergoing OFS, EXIT, or STR to inform decision-making and prenatal counseling.

METHODS

A single institution retrospective review was conducted evaluating patients undergoing OFS, EXIT, or STR for prenatally diagnosed lung lesions from 2000 to 2021. Specimens were reviewed by an anatomic pathologist. Lesions were divided into "CCAMs" (the largest pathology group) and "all lung lesions" since pathologic diagnosis is not possible during prenatal evaluation when care decisions are made. Prenatal variables included initial, greatest, and final CCAM volume-ratio (CVR), betamethasone use/frequency, cyst drainage, and the presence of hydrops. Outcomes included survival, ECMO utilization, NICU length of stay (LOS), postnatal nitric oxide use, and ventilator days.

RESULTS

Sixty-nine percent (59 of 85 patients) of lung lesions undergoing resection were CCAMs. Among patients with pathologic diagnosis of CCAM, the initial, largest, and final CVRs were greatest in OFS followed by EXIT and STR patients. Similarly, the incidence of hydrops was significantly greater and the rate of hydrops resolution was lower in the OFS group. Although the rate of cyst drainage did not differ between groups, maternal betamethasone use varied significantly (OFS 60.0%, EXIT 100.0%, STR 74.3%; p = 0.0378). Notably, all OFS took place prior to 2014. There was no difference in survival, ventilator days, nitric oxide, NICU LOS, or ECMO between groups. In multiple variable logistic modeling, determinants of survival to NICU discharge among patients undergoing resection with a pathologic diagnosis of CCAM included initial CVR <3.5 and need for <3 maternal betamethasone doses.

CONCLUSION

For CCAMs that remain large despite maternal betamethasone or cyst drainage, surgical resection via OFS, EXIT, or STR are viable options with favorable and comparable survival between groups. In the modern era there has been a shift from OFS and EXIT procedures to STR for fetuses with persistently large lung lesions. This shift has been fueled by the increased use of maternal betamethasone and introduction of a Special Delivery Unit during the study period and the appreciation of similar fetal and neonatal outcomes for STR vs. EXIT and OFS with reduced maternal morbidity associated with a STR. Accordingly, efforts to optimize multidisciplinary perinatal care for fetuses with large lung lesions are important to inform patient selection criteria and promote STR as the preferred surgical approach in the modern era.

LEVEL OF EVIDENCE

Level IV.

Update on Management and Outcomes of Congenital Diaphragmatic Hernia

Infants with congenital diaphragmatic hernia (CDH) benefit from comprehensive multidisciplinary teams that have experience in caring for the unique and complex issues associated with CDH. Despite prenatal referral to specialized high-volume centers, advanced ventilation strategies and pulmonary hypertension management, and extracorporeal membrane oxygenation, mortality and morbidity remain high. These infants have unique and complex issues that begin in fetal and infant life, but persist through adulthood. Here we will review the literature and share our clinical care pathway for neonatal care and follow up. While many advances have occurred in the past few decades, our work is just beginning to continue to improve the mortality, but also importantly the morbidity of CDH.

Ethics Considerations Regarding Artificial Womb Technology for the Fetonate

Since the early 1980's, with the clinical advent of in vitro fertilization resulting in so-called "test tube babies," a wide array of ethical considerations and concerns regarding artificial womb technology (AWT) have been described. Recent breakthroughs in the development of extracorporeal neonatal life support by means of AWT have reinitiated ethical interest about this topic with a sense of urgency. Most of the recent ethical literature on the topic, however, pertains not to the more imminent scenario of a physiologically improved method of neonatal care through AWT, but instead to the remote scenario of "complete ectogenesis" that imagines human gestation occurring entirely outside of the womb. This scoping review of the ethical literature on AWT spans from more abstract concerns about complete ectogenesis to more immediate concerns about the soon-to-be-expected clinical life support of what we term the fetal neonate or fetonate. Within an organizing framework of different stages of human gestational development, from conception to the viable premature infant, we discuss both already identified and newly emerging ethical considerations and concerns regarding AWT and the care of the fetonate.

Neurologic outcomes of the premature lamb in an extrauterine environment for neonatal development

BACKGROUND/PURPOSE

Neurologic injury remains the most important morbidity of prematurity. Those born at the earliest gestational ages can face a lifetime of major disability. Perinatal insults result in developmental delay, cerebral palsy, and other profound permanent neurologic impairments. The EXTracorporeal Environment for Neonatal Development (EXTEND) aims to transition premature neonates through this sensitive period, but it's impact on neurologic development requires analysis.

METHODS

Fetal sheep were maintained in a fluid-filled environment for up to 28 days. Physiologic parameters were measured continuously; tissues were subsequently fixed and preserved for myelin quantification, glial cell staining, and structural assessment via magnetic resonance. Surviving animals were functionally assessed.

RESULTS

No evidence of fetal brain ischemia or white matter tract injury associated with the EXTEND system was detected, and the degree of myelination was regionally appropriate and consistent with age matched controls. No evidence of neurologic injury or immaturity was visible on magnetic resonance; animals that transitioned from the system had no persistent neurologic deficits.

CONCLUSIONS

No evidence of major neurologic morbidity was found in animals supported on the EXTEND system, though more work needs to be done in order to verify its safety during critical periods of neurologic development.

Simple Approach to Increase Donor Hematopoietic Stem Cell Dose and Improve Engraftment in the Murine Model of Allogeneic In Utero Hematopoietic Cell Transplantation

The rationale for in utero hematopoietic cell transplantation (IUHCT) rests on exploitation of normal events during hematopoietic and immunologic ontogeny to allow allogeneic hematopoietic engraftment without myeloablative conditioning.  Host hematopoietic competition is among the primary barriers to engraftment in IUHCT. In the murine model this can be partially overcome by delivery of larger donor cell doses, but volume is limiting. Enrichment of donor hematopoietic stem cells (HSCs) would seem to offer a more efficient approach, but such enriched populations have engrafted poorly in existing models of IUHCT. To increase HSC dose while maintaining the presence of accessory cells, we used a less stringent enrichment protocol of single-step lineage depleted cells alone (lin-) or in combination with whole donor bone marrow mononuclear cells. Our results confirm that increasing doses of HSCs in combination with bone marrow accessory cells can dramatically improve engraftment after IUHCT. This represents a practical and clinically applicable strategy to maximize the engraftment potential of the donor graft without risk of treatment-associated toxicity.

Technical feasibility of umbilical cannulation in midgestation lambs supported by the EXTra-uterine Environment for Neonatal Development (EXTEND)

EXTEND (EXTra-uterine Environment for Neonatal Development) is a novel system for supporting extremely premature infants that replicates in utero conditions by maintaining a sterile fluid environment and providing gas exchange via a pumpless arteriovenous oxygenator circuit connected to the umbilical vessels. Target gestational age (GA) for EXTEND support in human infants is 23-27 weeks, when immature lungs are most susceptible to injury in the setting of air ventilation. We previously demonstrated physiologic support of premature lambs cannulated at 105-117 days GA (lungs developmentally analogous to the 23-27 week GA human infant) for up to 28 days on EXTEND. In the present study, we sought to determine the technical feasibility of umbilical vessel cannulation in 85-96 days GA lambs delivered to EXTEND at weights equivalent to the 23-27 week GA human infant (500-850 g). Five preterm lambs were cannulated at 85-96 days GA (term 145 days) and supported on EXTEND for 4-7 days. All lambs underwent umbilical artery and umbilical vein cannulation. Circuit flows and pressures were monitored continuously, and blood gases were obtained at regular intervals for assessment of oxygen parameters. Systemic pH and lactate were measured at least once daily. Mean body weight at cannulation was 641 ± 71 g (range 480-850 g). All lambs were cannulated successfully (cannula size varied from 8 to 12 Fr), and mean survival on EXTEND was 140 ± 7 hours. Mean circuit flow was 213 ± 15 mL/kg*min, mean pH was 7.37 ± 0.01, and mean lactate was 1.6 ± 0.2 mmol/L. During the initial 120 hours after EXTEND cannulation, there were no significant differences between 85-96 days GA lambs and 105-117 days GA lambs in weight-adjusted circuit flows, oxygen delivery, pH, or lactate levels. This study demonstrates successful umbilical cord cannulation and adequate circuit flows and oxygen delivery in midgestation lambs size-matched to the 23-27 week GA human fetus, which represents an important step in the translation of EXTEND to clinical practice.

Erythropoietin Prevents Anemia and Transfusions in Extremely Premature Lambs Supported by an EXTrauterine Environment for Neonatal Development (EXTEND)

BACKGROUND

We recently developed an EXTrauterine Environment for Neonatal Development (EXTEND) that provides physiologic support for premature lambs. Here, we assess the efficacy of exogenous erythropoietin (EPO) to prevent anemia and transfusions on EXTEND.

MATERIALS AND METHODS

Lambs were cannulated at 0.7 gestation and supported on EXTEND for up to 4 weeks. The lambs were divided into three groups: (1) No EPO, (2) Low EPO (300 U kg-1 per day), and (3) High EPO (800 U kg-1 per day). Daily hematocrit and weekly complete blood count were assessed.

RESULTS

The mean percentage change in hematocrit from baseline was significantly different between the groups (No EPO -23.6 ± 7.8% vs. Low EPO -16.6 ± 6.4% vs. High EPO +2.6 ± 6.6%; p = 0.02). This occurred despite a greater median number of blood transfusions in the No EPO group (5 vs. 1 vs. 0; p = 0.02). EPO administration was associated with a higher mean corpuscular volume (MCV; p < 0.01) and reticulocyte count (p = 0.02). The High EPO group was comparable to in utero control fetuses with respect to hematocrit (p = 0.49), MCV (p = 0.24), and reticulocyte count (p = 0.68).

CONCLUSIONS

EPO (800 U kg-1 per day) prevents anemia, eliminates transfusions, and restores normal red blood cell indices in premature lambs supported by EXTEND.

Pumpless arteriovenous extracorporeal membrane oxygenation: A novel mode of respiratory support in a lamb model of congenital diaphragmatic hernia

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is commonly required in neonates with congenital diaphragmatic hernia (CDH) complicated by pulmonary hypertension (PH). ECMO carries significant risk, and is contraindicated in the setting of extreme prematurity or intracranial hemorrhage. Pumpless arteriovenous ECMO (P-ECMO) may represent an alternative for respiratory support. The present study summarizes our initial experience with P-ECMO in a lamb model of CDH.

STUDY DESIGN

Surgical creation of CDH was performed at 65-75days' gestation. At term (135-145days), lambs were delivered into the P-ECMO circuit. Three animals were maintained on a low-heparin infusion protocol (target ACT 160-180) and three animals were maintained with no systemic heparinization.

RESULTS

Animals were supported by the circuit for 380.7 +/- 145.6h (range, 102-504h). Circuit flow rates ranged from 97 to 208ml/kg/min, with adequacy of organ perfusion demonstrated by stable serum lactate levels (3.0 +/- 1.7) and pH (7.4 +/- 0.3). Necropsy demonstrated no evidence of thrombogenic complications.

CONCLUSION

Pumpless extracorporeal membrane oxygenation achieved support of CDH model lambs for up to three weeks. This therapy has the potential to bridge neonates with decompensated respiratory failure to CDH repair with no requirement for systemic anticoagulation, and may be applicable to patients currently precluded from conventional ECMO support.

Umbilical cannulation optimizes circuit flows in premature lambs supported by the EXTra-uterine Environment for Neonatal Development (EXTEND)

KEY POINTS

Bronchopulmonary dysplasia is a disease of extreme prematurity that occurs when the immature lung is exposed to gas ventilation. We designed a novel 'artificial womb' system for supporting extreme premature lambs (called EXTEND) that obviates gas ventilation by providing oxygen via a pumpless arteriovenous circuit with the lamb submerged in sterile artificial amniotic fluid. In the present study, we compare different arteriovenous cannulation strategies on EXTEND, including carotid artery/jugular vein (CA/JV), carotid artery/umbilical vein (CA/UV) and umbilical artery/umbilical vein (UA/UV). Compared to CA/JV and CA/UV cannulation, UA/UV cannulation provided significantly higher, physiological blood flows to the oxygenator, minimized flow interruptions and supported significantly longer circuit runs (up to 4 weeks). Physiological circuit blood flow in UA/UV lambs made possible normal levels of oxygen delivery, which is a critical step toward the clinical application of artificial womb technology.

ABSTRACT

EXTEND (EXTra-uterine Environment for Neonatal Development) is a novel system that promotes physiological development by maintaining the premature lamb in a sterile fluid environment and providing gas exchange via a pumpless arteriovenous oxygenator circuit. During the development of EXTEND, different cannulation strategies evolved with the aim of improving circuit flow. The present study examines how different cannulation strategies affect EXTEND circuit haemodynamics in extreme premature lambs. Seventeen premature lambs were cannulated at gestational ages 105-117 days (term 145-150 days) and supported on EXTEND for up to 4 weeks. Experimental groups were distinguished by cannulation strategy: carotid artery outflow and jugular vein inflow (CA/JV; n = 4), carotid artery outflow and umbilical vein inflow (CA/UV; n = 5) and double umbilical artery outflow and umbilical vein inflow (UA/UV; n = 8). Circuit flows and pressures were measured continuously. As we transitioned from CA/JV to CA/UV to UA/UV cannulation, mean duration of circuit run and weight-adjusted circuit flows increased (P < 0.001) and the frequency of flow interruptions declined (P < 0.05). Umbilical vessels generally accommodated larger-bore cannulas, and cannula calibre was directly correlated with circuit pressures and indirectly correlated with flow:pressure ratio (a measure of post-membrane resistance). We conclude that UA/UV cannulation in fetal lambs on EXTEND optimizes circuit flow dynamics and flow stability and also supports circuit flows that closely approximate normal placental flow.

An EXTrauterine environment for neonatal development: EXTENDING fetal physiology beyond the womb

Extreme prematurity is a major cause of neonatal mortality and morbidity, and remains an unsolved clinical challenge. The development of an artificial womb, an extrauterine system recreating the intrauterine environment, would support ongoing growth and organ maturation of the extreme preterm fetus and would have the potential to substantially improve survival and reduce morbidity. Previous efforts toward the development of such a system have demonstrated the ability to maintain the isolated fetus for short periods of support, but have failed to achieve the long-term stability required for clinical application. Here we describe our initial experiments demonstrating the stable support of fetal lambs developmentally equivalent to the extreme premature infant for up to four weeks with stable hemodynamics, growth, and development. The achievement of long-term physiologic support of the fetus in an extrauterine system has the potential to fundamentally change the management and clinical outcome of the extreme premature infant.

An extra-uterine system to physiologically support the extreme premature lamb

In the developed world, extreme prematurity is the leading cause of neonatal mortality and morbidity due to a combination of organ immaturity and iatrogenic injury. Until now, efforts to extend gestation using extracorporeal systems have achieved limited success. Here we report the development of a system that incorporates a pumpless oxygenator circuit connected to the fetus of a lamb via an umbilical cord interface that is maintained within a closed 'amniotic fluid' circuit that closely reproduces the environment of the womb. We show that fetal lambs that are developmentally equivalent to the extreme premature human infant can be physiologically supported in this extra-uterine device for up to 4 weeks. Lambs on support maintain stable haemodynamics, have normal blood gas and oxygenation parameters and maintain patency of the fetal circulation. With appropriate nutritional support, lambs on the system demonstrate normal somatic growth, lung maturation and brain growth and myelination.

Right Congenital Diaphragmatic Hernias: Is There a Correlation between Prenatal Lung Volume and Postnatal Survival, as in Isolated Left Diaphragmatic Hernias?

OBJECTIVES

Whereas left-sided congenital diaphragmatic hernias (L-CDH) have been extensively studied and their prognostic parameters delineated, right-sided hernias (R-CDH) have not. Published results remain inconclusive. The aim of this study is to evaluate if proven prognostic indicators of postnatal survival in the fetus with L-CDH apply to the fetus with R-CDH.

METHODS

Retrospective single-center study of R-CDH fetuses with available prenatal studies assessed for fetal lung volume by means of ultrasound-measured observed versus expected (O/E) lung area to head circumference (LHR) and magnetic resonance-calculated O/E total lung volume (TLV) in a 12-year time period. Percentage of herniated liver volume and postnatal use of extracorporeal membrane oxygenation (ECMO) were also evaluated.

RESULTS

In a cohort of 24 patients, O/E LHR, O/E TLV, percentage of herniated liver, and postnatal use of ECMO are not prognostic indicators of survival in the fetus with R-CDH. Cut-off values of O/E LHR of ≤45 or O/E TLV ≤25, known to select a population of severe cases for the L-CDH fetus, do not appear to extrapolate to the R-CDH fetus, as survival in both R-CDH groups is 60%.

CONCLUSION

The findings in this study suggest that L- and R-CDH appear to behave differently, and that factors that make L-CDH fatal (low O/E TLV and O/E LHR, high-volume herniated liver) may not apply to the fetus with R-CDH.

Rate of increase of lung-to-head ratio over the course of gestation is predictive of survival in left-sided congenital diaphragmatic hernia

PURPOSE

Congenital diaphragmatic hernia (CDH) is associated with high postnatal mortality because of pulmonary hypoplasia. The prognostic utility of serial lung-to-head circumference measurements as a marker of lung growth has not been described. Our objective was to examine the relationship between the rate of interval increase of LHR and postnatal survival in left-sided CDH.

METHODS

We retrospectively reviewed charts of all left-sided CDH patients from January 2004 to July 2014. All ultrasound studies performed at our institution (n=473) were reviewed. Categorical and continuous data were analyzed by chi-square and Mann-Whitney t-test, respectively, and slope analysis was performed by linear regression analysis (p<0.05).

RESULTS

A total of 226 patients were studied, with 154 long-term survivors and 72 non-survivors. Established markers of CDH severity, including intrathoracic liver position and requirement for patch repair, were significantly increased in non-survivors (p<0.0001). The rate of LHR increase as measured by linear regression and slope analysis was significantly increased in long-term survivors (p=0.0175).

CONCLUSIONS

Our findings indicate that the interval increase in LHR levels over the course of gestation correlate with survival in left-sided CDH patients. Regular ultrasonographic re-evaluation of LHR throughout gestation following diagnosis of CDH may provide prognostic insight and help guide patient management.

Frequency and complications of inguinal hernia repair in giant omphalocele

PURPOSE

Giant omphalocele (GO) is a challenging problem owing to aberrant anatomy and complex comorbidities. Large inguinal hernias (IH) are known to occur in this population, but have not been well described in the literature. We sought to characterize rates and complications of IH in GO patients.

METHODS

A retrospective chart review was performed on all patients with the diagnosis of GO from 2004 to 2012, with a minimum follow-up period of 12 months. Statistical significance was calculated using Fisher's exact test and Mann-Whitney test (p<0.05).

RESULTS

A total of 51 giant omphalocele patients were born during the 8-year study period, with IH diagnosed in 21 patients (41%). IH was not associated with gestational age, birth weight, or method of GO closure, but was significantly associated with male gender (p<0.0001). Incarceration occurred in 4 patients (19%). Recurrence was noted in 7 cases, with 6/7 recurrences following repair by high ligation of the sac alone. All recurrences were repaired with the Bassini repair. Postoperative complications were noted in 7 patients (33%) and included prolonged ileus following incarceration, testicular tethering, testicular atrophy, persistent hydrocele, and death following acute incarceration.

CONCLUSIONS

Our study suggests a high incidence of IH in GO patients. The prevalance of incarceration and recurrences in these patients support a role for inguinal herniorrhaphy via a Bassini repair prior to initial hospital discharge.

Prenatal diagnosis of esophageal bronchus--first report of a rare foregut malformation in utero

AIM OF THE STUDY

Esophageal bronchus is a rare bronchopulmonary foregut malformation in which an isolated portion of the respiratory system communicates with the esophagus. There are no reports of prenatal diagnosis of an esophageal bronchus in the literature. We present 5 cases of esophageal bronchus and describe unique imaging findings.

METHODS

Following IRB approval, 5 cases of pathologically proven esophageal bronchus were identified from a single center fetal therapy surgical database. Prenatal magnetic resonance and ultrasound studies were scored for the presence of bronchoceles, cysts, vascular feeders, and location. Five control cases were selected from a radiology database, with lesions determined to represent bronchial atresia prenatally and located at the lung bases. All imaging was reviewed blinded to outcome.

MAIN RESULTS

A tubular T2 hyperintense structure (bronchocele) directed from the lung lesion to the gastroesophageal junction was seen in all cases of esophageal bronchus, but in none of the control cases. In all control cases, the bronchocele was directed to the pulmonary hilum. The presence of cysts or vascular feeding vessels was not statistically significant in identifying an esophageal bronchus lesion. All patients were delivered at term and underwent surgical resection between 5 to 19 weeks of age. No postoperative complications occurred.

CONCLUSION

Prenatal diagnosis of an esophageal bronchus can be strongly suggested by the presence of a T2 hyperintense structure arising from a lung lesion and directed towards the GE junction. These findings may be helpful for better counseling of parents and improved surgical planning.

Brain-type natriuretic peptide levels correlate with pulmonary hypertension and requirement for extracorporeal membrane oxygenation in congenital diaphragmatic hernia

PURPOSE

B-type natriuretic peptide (BNP), an established biomarker of ventricular pressure overload, is used in the assessment of children with pulmonary hypertension (PH). PH is commonly observed in congenital diaphragmatic hernia (CDH). However, the use of BNP levels to guide treatment in this patient population has not been well defined. In this study, we investigate BNP levels in a large cohort of CDH patients treated at a single institution.

METHODS

We retrospectively reviewed charts of all CDH patients enrolled in our pulmonary hypoplasia program from 2004-2013. PH was assessed by echocardiography using defined criteria, and patients were further stratified into the following cohorts: no PH, short-term PH (requiring nitric oxide but no additional vasodilatory therapy), long-term PH (requiring continued vasodilatory therapy post-discharge), and ECMO (requiring ECMO therapy).

RESULTS

A total of 132 patients were studied. BNP levels were significantly increased in patients with PH compared to patients with normal pulmonary pressures (P<0.01). BNP levels were not significantly different between the ST-PH, LT-PH, and ECMO cohorts, but all levels in all three cohorts were significantly increased compared to patients who did not develop PH.

CONCLUSION

Our findings indicate that plasma BNP levels correlate with pulmonary hypertension as well as the requirement for ECMO in CDH patients. Monitoring of serial BNP levels may provide a useful prognostic tool in the management of CDH.

Timing of repair of congenital diaphragmatic hernia in patients supported by extracorporeal membrane oxygenation (ECMO)

PURPOSE

The optimal timing of repair for congenital diaphragmatic hernia (CDH) in patients requiring extracorporeal membrane oxygenation (ECMO) is controversial. Repair during ECMO may improve respiratory function by restoring normal anatomy. However, there is increased risk of complications including surgical bleeding. The purpose of this study was to examine the impact of timing of CDH repair on outcomes in a large cohort of patients treated at a single institution.

METHODS

We retrospectively reviewed charts of all CDH patients in our Pulmonary Hypoplasia Program from 2004 to 2013. Categorical variables were analyzed by Fisher's exact test and continuous variables by Mann-Whitney t-test (p<0.05).

RESULTS

A total of 77 CDH patients required ECMO support during the study dates. Of these, 16 patients did not survive to repair, 3 patients were repaired prior to cannulation, 41 patients were repaired during ECMO, and 17 patients were repaired after decannulation. Survival was 67%, 43.9%, and 100% for those repaired prior to, during, or post ECMO, respectively, with statistical significance associated with repair after decannulation (P<0.0001). Operative bleeding requiring transfusion occurred in 12 patients repaired on ECMO, while no significant bleeding occurred in patients repaired after decannulation (P=0.003).

CONCLUSION

Outcomes were improved in CDH patients undergoing surgical repair following ECMO with significantly increased survival, lower rates of surgical bleeding, and decreased total duration of ECMO therapy compared to patients repaired on ECMO. In patients who can be successfully weaned from ECMO, our study supports a role for delayed repair off ECMO with reduced operative morbidity and increased survival.

Pulmonary hypertension in giant omphalocele infants

BACKGROUND

Pulmonary hypoplasia has been described in cases of giant omphalocele (GO), although pulmonary hypertension (PH) has not been extensively studied in this disorder. In the present study, we describe rates and severity of PH in GO survivors who underwent standardized prenatal and postnatal care at our institution.

METHODS

A retrospective chart review was performed for all patients in our pulmonary hypoplasia program with a diagnosis of GO. Statistical significance was calculated using Fisher's exact test and Mann-Whitney test (p<0.05).

RESULTS

Fifty-four patients with GO were studied, with PH diagnosed in twenty (37%). No significant differences in gender, gestational ages, birth weight, or Apgar scores were associated with PH. Patients diagnosed with PH were managed with interventions, including high frequency oscillatory ventilation, and nitric oxide. Nine patients required long-term pulmonary vasodilator therapy. PH was associated with increased length of hospital stay (p<0.001), duration of mechanical ventilation (p=0.008), and requirement for tracheostomy (p=0.0032). Overall survival was high (94%), with significantly increased mortality in GO patients with PH (p=0.0460). Prenatal imaging demonstrating herniation of the stomach into the defect was significantly associated with PH (p=0.0322), with a positive predictive value of 52%.

CONCLUSIONS

In this series, PH was observed in 37% of GO patients. PH represents a significant complication of GO, and management of pulmonary dysfunction is a critical consideration in improving clinical outcomes in these patients.

Incidence and factors associated with sensorineural and conductive hearing loss among survivors of congenital diaphragmatic hernia

PURPOSE

The reported incidence of sensorineural hearing loss (SNHL) in long-term survivors of congenital diaphragmatic hernia varies widely in the literature. Conductive hearing loss (CHL) is also known to occur in CDH patients, but has been less widely studied. We sought to characterize the incidence and risk factors associated with SNHL and CHL in a large cohort of CDH patients who underwent standardized treatment and follow-up at a single institution.

METHODS

We retrospectively reviewed charts of all CDH patients in our pulmonary hypoplasia program from January 2004 through December 2012. Categorical variables were analyzed by Fisher's exact test and continuous variables by Mann-Whitney t-test (p≤0.05).

RESULTS

A total of 112 patients met study inclusion criteria, with 3 (2.7%) patients diagnosed with SNHL and 38 (34.0%) diagnosed with CHL. SNHL was significantly associated with requirement for ECMO (p=0.0130), prolonged course of hospitalization (p=0.0011), duration of mechanical ventilation (p=0.0046), requirement for tracheostomy (p=0.0013), and duration of loop diuretic (p=0.0005) and aminoglycoside therapy (p=0.0003).

CONCLUSIONS

We have identified hearing anomalies in over 30% of long-term CDH survivors. These findings illustrate the need for routine serial audiologic evaluations throughout childhood for all survivors of CDH and stress the importance of targeted interventions to optimize long-term developmental outcomes pertaining to speech and language.

Urologic and anorectal complications of sacrococcygeal teratomas: prenatal and postnatal predictors

PURPOSE

Anorectal and urologic sequelae are observed in long-term survivors of sacrococcygeal teratoma (SCT). In this study we evaluate the incidence and predictors of anorectal and urologic complications in SCT.

METHODS

A retrospective review was performed for all SCT patients who underwent resection at a single institution between 2000 and 2012. Enrollment criteria included a minimum of 12months follow-up. Categorical variables were analyzed by Fisher's exact test and continuous variables by Mann Whitney test (p<0.05).

RESULTS

Forty-five patients were studied. Anorectal complications occurred in 29%, including severe chronic constipation (n=13) and fecal incontinence (n=4). Urologic complications occurred in 33%, including neurogenic bladder (n=12), vesicoureteral reflux (n=5), and urinary incontinence (n=7). Prenatal imaging by fetal MRI demonstrated mass effect with obstruction of the bowel (n=4) or bladder and collecting system (n=7) in a subset of patients with postnatal complications (anorectal 4/4, PPV 100%; urologic 6/7, PPV 86%). Postnatal complications were associated with obstructive findings on prenatal imaging, prenatal therapeutic interventions, Altman classification, perineal reconstruction, and tumor recurrence. No anorectal or urologic complications occurred in patients with Altman type I tumors.

CONCLUSIONS

Urologic and anorectal complications are common in patients with SCT. Higher Altman classification and prenatal imaging suggestive of intestinal or urologic obstruction should prompt focused prenatal counseling and postnatal screening for anorectal and urologic dysfunction.

Maternal-fetal surgery for structural malformations

Although most prenatally diagnosed correctable anatomic abnormalities are best addressed by surgical interventions after birth, the outcomes of a small number of severe structural malformations with predicted fetal demise or devastating sequelae postnatally may be improved by correction before birth. Consideration of maternal-fetal surgical intervention is restricted to those anatomic malformations that interfere with normal organ development and which, if alleviated, may permit normal development to proceed. Advances in prenatal diagnosis and technical innovations in the surgical approach to the fetus have resulted in an increase in the successful clinical application of fetal intervention over the past 3 decades. The purpose of this review is to describe the current status of maternal-fetal surgery, with a focus on the congenital anomalies most commonly treated by intervention before birth, and to highlight the key areas for further research in this evolving surgical specialty.

Metabolic disposition of gefitinib, an epidermal growth factor receptor tyrosine kinase inhibitor, in rat, dog and man

Following oral administration of [14C]-gefitinib to albino and pigmented rats, radioactivity was widely and rapidly distributed, with the highest levels being found in liver, kidney, lung and gastrointestinal tract, but with only low levels penetrating the brain. Levels of radioactivity persisted in melanin-containing tissues (pigmented eye and skin). Binding to plasma proteins was high (86-94%) across the range of species examined and was 91% in human plasma. Substantial binding occurred to both human serum albumin and alpha-1 acid glycoprotein. Following oral and intravenous administration of [14C]-gefitinib, excretion of radioactivity by rat, dog and human occurred predominantly via the bile into faeces, with < 7% of the dose being eliminated in urine. In all three species, gefitinib was cleared primarily by metabolism. In rat, morpholine ring oxidation was the major route of metabolism, leading to the formation of M537194 and M608236 as the main biliary metabolites. Morpholine ring oxidation, together with production of M523595 by O-demethylation of the quinazoline moiety, were the predominant pathways in dog, with oxidative defluorination also occurring to a lesser degree. Pathways in healthy human volunteers were similar to dog, with O-demethylation and morpholine ring oxidation representing the major routes of metabolism.

Pharmacokinetics of gefitinib, an epidermal growth factor receptor tyrosine kinase inhibitor, in rat and dog

The pharmacokinetics of gefitinib and its metabolites in rat and dog were investigated in preclinical studies conducted to support the safety evaluation and clinical development of gefitinib, the first EGFR tyrosine kinase inhibitor approved for the treatment of non-small-cell lung cancer. Following intravenous dosing (5 mg kg(-1), gefitinib plasma half-life was 3-6h in rats and dogs, although studies using a more sensitive HPLC-MS assay produced longer estimates of half-life (7-14h). In these studies, plasma clearance was high (male rat: 25 ml min(-1) kg(-1); female rat: 16 ml min(-1) kg(-1); male dog: 16 ml min(-1) kg(-1)), as was the volume of distribution (8.0-10.41 kg(-1) in rat; 6.31 kg(-1) in dog), and exposure in female rats was double that in males. Following administration of [14C]-gefitinib, concentrations of radioactivity in plasma exceeded gefitinib throughout the profile, indicating the presence of circulating metabolites in both rat and dog. An HPLC-MS assay was developed to measure concentrations of gefitinib and five potential metabolites in plasma. All five metabolites were detected in the rat, but at levels much lower than gefitinib. In the dog, exposure to gefitinib and M523595 was similar, with much lower concentrations of M537194 and only trace levels of the other metabolites. This profile of metabolites is similar to that observed in man.

Plasma membrane domain organization regulates EGFR signaling in tumor cells

Macromolecular complexes exhibit reduced diffusion in biological membranes; however, the physiological consequences of this characteristic of plasma membrane domain organization remain elusive. We report that competition between the galectin lattice and oligomerized caveolin-1 microdomains for epidermal growth factor (EGF) receptor (EGFR) recruitment regulates EGFR signaling in tumor cells. In mammary tumor cells deficient for Golgi β1,6N-acetylglucosaminyltransferase V (Mgat5), a reduction in EGFR binding to the galectin lattice allows an increased association with stable caveolin-1 cell surface microdomains that suppresses EGFR signaling. Depletion of caveolin-1 enhances EGFR diffusion, responsiveness to EGF, and relieves Mgat5 deficiency–imposed restrictions on tumor cell growth. In Mgat5^+/+ tumor cells, EGFR association with the galectin lattice reduces first-order EGFR diffusion rates and promotes receptor interaction with the actin cytoskeleton. Importantly, EGFR association with the lattice opposes sequestration by caveolin-1, overriding its negative regulation of EGFR diffusion and signaling. Therefore, caveolin-1 is a conditional tumor suppressor whose loss is advantageous when β1,6GlcNAc-branched N-glycans are below a threshold for optimal galectin lattice formation.

Distribution of radioactivity and metabolite profiling in tumour and plasma following intravenous administration of a colchicine derivative (14C-ZD6126) to tumour-bearing mice

The main aim of the study was to investigate the distribution of radioactivity in the tissues and tumours using quantitative whole-body autoradiography (QWBA), together with a more detailed investigation of plasma and tumour samples, following administration of a single intravenous dose at 200 mg kg(-1) of 14C-ZD6126 to mice bearing subcutaneous Hras5 tumour xenografts. The study also included an assessment of tumour necrosis following administration of a single intravenous dose of non-labelled ZD6126 at 200 mgkg(-1). QWBA analysis showed that drug-related material was widely distributed to the tissues and tumour. In the majority of tissues, concentrations of radioactivity were highest at 15 min and declined rapidly thereafter. The tumour-to-plasma ratio was 0.6:1 at 0.25 h and increased to 6:1 at 48 h, indicating that drug-related material persisted in the tumour longer than in plasma. ZD6126, a phosphate ester, is rapidly hydrolysed to ZD6126 phenol, the active metabolite. The major metabolite in plasma (36% of the sample radioactivity) and all tumour samples (58-83% of the sample radioactivity) was confirmed as ZD6126 phenol. Extensive tumour necrosis was noted by 24h, which was still evident at 48 h, although there was some evidence of tumour regrowth.

Complex N-glycan number and degree of branching cooperate to regulate cell proliferation and differentiation

The number of N-glycans (n) is a distinct feature of each glycoprotein sequence and cooperates with the physical properties of the Golgi N-glycan-branching pathway to regulate surface glycoprotein levels. The Golgi pathway is ultrasensitive to hexosamine flux for the production of tri- and tetra-antennary N-glycans, which bind to galectins and form a molecular lattice that opposes glycoprotein endocytosis. Glycoproteins with few N-glycans (e.g., TbetaR, CTLA-4, and GLUT4) exhibit enhanced cell-surface expression with switch-like responses to increasing hexosamine concentration, whereas glycoproteins with high numbers of N-glycans (e.g., EGFR, IGFR, FGFR, and PDGFR) exhibit hyperbolic responses. Computational and experimental data reveal that these features allow nutrient flux stimulated by growth-promoting high-n receptors to drive arrest/differentiation programs by increasing surface levels of low-n glycoproteins. We have identified a mechanism for metabolic regulation of cellular transition between growth and arrest in mammals arising from apparent coevolution of N-glycan number and branching.

Metabolic homeostasis and tissue renewal are dependent on beta1,6GlcNAc-branched N-glycans

Golgi beta1,6-N-acetylglucosaminyltransferase V (Mgat5) produces beta1,6GlcNAc-branched N-glycans on glycoproteins, which increases their affinity for galectins and opposes loss from the cell surface to constitutive endocytosis. Oncogenic transformation increases Mgat5 expression, increases beta1,6GlcNAc-branched N-glycans on epidermal growth factor and transforming growth factor-beta receptors, and enhances sensitivities to ligands, cell motility, and tumor metastasis. Here, we demonstrate that Mgat5(-/-) mouse embryonic fibroblasts (MEFs) display reduced sensitivity to anabolic cytokines and reduced glucose uptake and proliferation. Mgat5(-/-) mice are also hypoglycemic, resistant to weight gain on a calorie-enriched diet, hypersensitive to fasting, and display increased oxidative respiration and reduced fecundity. Serum-dependent activation of the extracellular response kinase (growth) and Smad2/3 (arrest) pathways in Mgat5(-/-) MEFs and bone marrow cells reveals an imbalance favoring arrest. Mgat5(-/-) mice have fewer muscle satellite cells, less osteogenic activity in bone marrow, and accelerated loss of muscle and bone mass with aging. Our results suggest that beta1,6GlcNAc-branched N-glycans promote sensitivity to anabolic cytokines, and increase fat stores, tissue renewal, and longevity.

Cytokine sensitivity and N-glycan processing mutations

The EGF and TGF-beta families of cytokines are critical regulators of cell proliferation, morphogenesis, and tissue repair. The signaling pathways downstream of EGF and TGF-beta receptors also contribute to cancer growth and metastasis. Cytokine receptors are glycoproteins, and we have recently shown that GlcNAc-branching of N-glycans enhances their cell surface residency and contributes to the growth autonomy of cancer cells. Ligand-induced dimerization of EGF receptors leads to phosphorylation of Erk1/2, whereas TGF-beta binding to its receptors stimulates phosphorylation of Smad2/3. Activated Erk1/2 and Smad2/3 translocate independently into the nucleus and regulate gene expression. Here we describe a sensitive and robust method to quantify TGF-beta and EGF signaling in cancer cells and primary cells from mice by quantitative fluorescence imaging.

Regulation of cytokine receptors by Golgi N-glycan processing and endocytosis

The Golgi enzyme beta1,6 N-acetylglucosaminyltransferase V (Mgat5) is up-regulated in carcinomas and promotes the substitution of N-glycan with poly N-acetyllactosamine, the preferred ligand for galectin-3 (Gal-3). Here, we report that expression of Mgat5 sensitized mouse cells to multiple cytokines. Gal-3 cross-linked Mgat5-modified N-glycans on epidermal growth factor and transforming growth factor-beta receptors at the cell surface and delayed their removal by constitutive endocytosis. Mgat5 expression in mammary carcinoma was rate limiting for cytokine signaling and consequently for epithelial-mesenchymal transition, cell motility, and tumor metastasis. Mgat5 also promoted cytokine-mediated leukocyte signaling, phagocytosis, and extravasation in vivo. Thus, conditional regulation of N-glycan processing drives synchronous modification of cytokine receptors, which balances their surface retention against loss via endocytosis.

α2HS-glycoprotein, an Antagonist of Transforming Growth Factor β In vivo, Inhibits Intestinal Tumor Progression

Transforming growth factor (TGF)-beta1 is associated with tumor progression and resistance to chemotherapy in established cancers, as well as host immune suppression. Here, we show that the serum glycoprotein alpha2-HS-glycoprotein (AHSG) blocks TGF-beta1 binding to cell surface receptors, suppresses TGF-beta signal transduction, and inhibits TGF-beta-induced epithelial-mesenchymal transition, suggesting that AHSG may play a role in tumor progression. In 66 consecutive sporadic human colorectal cancer specimens, we observed a 3-fold depletion of ASHG in tumor compared with normal tissue, whereas levels of other abundant plasma proteins, albumin and transferrin, were equivalent. Using the Multiple intestinal neoplasia/+ (Min/+) mouse model of intestinal tumorigenesis, we found twice as many intestinal polyps overall, twice as many large polyps (>3 mm diameter), and more progression to invasive adenocarcinoma in Min/+ Ahsg-/- mice than in littermates expressing Ahsg. Phosphorylated Smad2 was more abundant in the intestinal mucosa and tumors of Min/+ mice lacking Ahsg, demonstrating increased TGF-beta signaling in vivo. Furthermore, TGF-beta-mediated suppression of immune cell function was exaggerated in Ahsg-/- animals, as shown by inhibition of macrophage activation and reduction in 12-O-tetradecanoylphorbol 13-acetate-induced cutaneous inflammation. Reconstitution of Ahsg-/- mice with bovine Ahsg suppressed endogenous TGF-beta-dependent signaling to wild-type levels, suggesting that therapeutic enhancement of AHSG levels may benefit patients whose tumors are driven by TGF-beta.

alpha 2-HS glycoprotein/fetuin, a transforming growth factor-beta/bone morphogenetic protein antagonist, regulates postnatal bone growth and remodeling

Soluble transforming growth factor-beta (TGF-beta)/bone morphogenetic protein (BMP)-binding proteins are widely distributed in mammalian tissues and control cytokine access to membrane signaling receptors. The serum and bone-resident glycoprotein alpha2-HS-glycoprotein/fetuin (ASHG) binds to TGF-beta/BMP cytokines and blocks TGF-beta1 binding to cell surface receptors. Therefore, we examined bone growth and remodeling phenotypes in ASHG-deficient mice. The skeletal structure of Ahsg(-/-) mice appeared normal at birth, but abnormalities were observed in adult Ahsg(-/-) mice. Maturation of growth plate chondrocytes was impaired, and femurs lengthened more slowly between 3 and 18 months of age in Ahsg(-/-) mice. However, bone formation was increased in Ahsg(-/-) mice as indicated by greater cortical thickness, accelerated trabecular bone remodeling, and increased osteoblast numbers on bone surfaces. The normal age-related increase in cortical thickness and bone mineral density was accelerated in Ahsg(-/-) mice and was associated with increased energy required to fracture. Bone formation in response to implanted BMP cytokine extended further from the implant in Ahsg(-/-) compared with Ahsg(+/+) mice, confirming the interaction between ASHG and TGF-beta/BMP cytokines in vivo. Our results demonstrate that ASHG blocks TGF-beta-dependent signaling in osteoblastic cells, and mice lacking ASHG display growth plate defects, increased bone formation with age, and enhanced cytokine-dependent osteogenesis.

A comparison of quantitative NMR and radiolabelling studies of the metabolism and excretion of Statil (3-(4-bromo-2-fluorobenzyl)-4-oxo-3H-phthalazin-1-ylacetic acid) in the rat

The identification and quantitation of the metabolites of Statil in rat bile and urine were investigated by 1H- and 19F-NMR spectroscopy and liquid scintillation counting. Male Wistar rats received a single oral dose of 100 mg/kg of radiolabelled Statil. Statil is known to produce glucuronide conjugates which are predominantly excreted into the bile in male rats. The complex multiphasic matrix of bile has been shown to make identification of the resonances by 1H-NMR spectroscopy very difficult as Statil appeared to be micellar bound giving rise to very broad signals. This not only impaired unambiguous signal characterisation but also quantification. The partial separation by SPEC-(1)H-NMR spectroscopy enabled the disruption of the micellar matrices and hence enabled the identification of Statil predominantly as aglycone, and to a lesser extent as glucuronide conjugate. In addition, minor acyl migration products of Statil glucuronide could also be detected as they were separated during the SPEC-process. 19F-NMR spectroscopic measurements on whole bile confirmed their presence as a number of overlapped signals could be observed. The selectivity, simplicity and signal dispersion characteristic of 19F-NMR spectroscopy also enabled the calculation of dose related recoveries of Statil related material in the bile and urine samples without the need for a radiolabel. The aim of this work was to investigate the usefulness and limitations of NMR spectroscopy of intact bile and urine as a means of quantifying levels of drug metabolites. The results obtained from NMR spectroscopy are compared with those obtained using scintillation techniques. Scintillation counting yields unequivocal quantification results, provided the label is preserved in metabolites as has been the case here. In general, quantification by 19F-NMR results similar to those obtained by scintillation counting (in agreement within about 20%). However, discrepancies have been observed with very small and broad 19F-NMR signals in bile. Nevertheless, 19F-NMR spectroscopy of bile is a rapid and facile method for assessing metabolite levels of fluorinated drugs.

The metabolism and excretion of [14c] 2- and 4-chlorobenzoic acids in the rat

The metabolic fate of [14C]-labelled 2 and 4-chlorobenzoic acids (2- and 4-CBA) has been determined in the rat following intraperitoneal (i.p.) administration at 100 mg/kg to male rats. The major route of elimination for both 2-and 4-CBA was urine with > 80%, of the dose recovered in the initial 0-24 h after administration. Glycine conjugation was found to be the dominant metabolic fate for both [14C] 2- and 4-CBA however, the position of chloro substitution had a clear effect on the extent of metabolism via this route with ortho substitution reducing the extent of metabolism via this pathway.