Biomedical subjects

Aaron Hamvas

Publications and source records attributed to Aaron Hamvas.

At least 19 recordsLinked to original sources

PubMed2006

Surfactant composition and function in patients with ABCA3 mutations.

Mutations in the gene encoding the ATP binding cassette transporter member A3 (ABCA3) are associated with fatal surfactant deficiency. ABCA3 lines the limiting membrane of lamellar bodies within alveolar type-II cells, suggesting a role in surfactant metabolism. The objective of this study was to determine the surfactant phospholipid composition and function in patients with mutations in the ABCA3 gene. Bronchoalveolar lavage (BAL) fluid was analyzed from three groups of infants: 1) Infants with ABCA3 mutations, 2) infants with inherited surfactant protein-B deficiency (SP-B), and 3) patients without parenchymal lung disease (CON). Surfactant phospholipid profile was determined using two-dimensional thin-layer chromatography, and surface tension was measured with a pulsating bubble surfactometer. Phosphatidylcholine comprised 41 +/- 19% of the total phospholipid in the BAL fluid of the ABCA3 group compared with 78 +/- 3% and 68 +/- 18%, p = 0.008 and 0.05, of the CON and SP-B groups, respectively. Surface tension was 31.5 +/- 9.3 mN/m and was significantly greater than CON but no different from SP-B. We conclude that mutations in ABCA3 are associated with surfactant that is deficient in phosphatidylcholine and has decreased function, suggesting that ABCA3 plays an important role in pulmonary surfactant phospholipid homeostasis.

ATP-Binding Cassette Transporters↗

PubMed2006

Long-term outcomes after infant lung transplantation for surfactant protein B deficiency related to other causes of respiratory failure.

OBJECTIVE: To determine if the outcomes of lung transplantation for infants with surfactant protein-B (SP-B) deficiency are unique. STUDY DESIGN: From a prospective analysis to identify infants with genetic causes of surfactant deficiency, we identified 33 SP-B-deficient infants from 1993 to 2005, and, among those undergoing lung transplantation (n = 13), compared their survival, pulmonary function, and developmental progress with infants who underwent transplantation at <1 year of age for parenchymal lung disease (n = 13) or pulmonary vascular disease (n = 11). RESULTS: Five-year survival rates ( approximately 50%, P = .3) and causes of death were similar for all three groups once the infants underwent transplantation. However, significant pretransplantation mortality decreased 5-year survival from listing to approximately 30% (P = .17). Pulmonary function, development of bronchiolitis obliterans, and school readiness were similar among the three groups. We detected anti SP-B antibody in serum of 3 of 7 SP-B-deficient infants and none of 7 SP-B-sufficient infants but could not identify any associated adverse outcomes. CONCLUSIONS: Long-term outcomes after infant lung transplantation for SP-B-deficient infants are similar to those of infants transplanted for other indications. These outcomes are important considerations in deciding to pursue lung transplantation for infants with disorders of alveolar homeostasis.

Female↗

PubMed2006

Surfactant phosphatidylcholine metabolism in neonates with meconium aspiration syndrome.

OBJECTIVE: Because meconium directly inhibits surfactant function, we sought to determine the effect of meconium on endogenous surfactant synthesis and clearance. STUDY DESIGN: We studied surfactant phosphatidylcholine kinetics with the use of stable isotopes in 11 newborn infants with meconium aspiration syndrome (MAS) who required extracorporeal membrane oxygenation (ECMO). For comparison we studied 6 neonates with persistent pulmonary hypertension (PPHN) on ECMO and 10 term neonates ventilated for non-pulmonary indications and not on ECMO. All patients received a 24-hour [U- 13C]glucose infusion as precursor for the palmitic acid in surfactant phosphatidylcholine. RESULTS: In the meconium group, the maximal 13C-incorporation in phosphatidylcholine (PC) was half of that in controls (0.09 +/- 0.01 vs 0.18 +/- 0.03 atom percent excess [APE], P = .027). There was a trend toward lower surfactant synthesis in the MAS group (3.3 +/- 0.7%/day) and PPHN group (2.6 +/- 0.3%/day) compared with controls 8.0 +/- 2.4%/day, P = .058). Significantly lower PC concentrations in tracheal aspirates were found in the MAS group (4.4 +/- 2.6 mg/mL) and PPHN group (3.6 +/- 2.0 mg/mL) compared with controls (12.8 +/- 2.6 mg/mL, P = .01). Endogenously synthesized surfactant had a similar half-life in all groups, ranging from 63 to 98 hours. CONCLUSION: We conclude that surfactant synthesis is disturbed and that surfactant PC concentrations are low in infants with MAS on ECMO.

Analysis of Variance↗

PubMed2006

Defects in surfactant synthesis: clinical implications.

Since the original description of deficiency of the pulmonary surfactant in premature newborn infants by Avery and Mead in 1959, respiratory distress syndrome has most commonly been attributed to developmental immaturity of surfactant production. Studies of different ethnic groups, gender, targeted gene ablation in murine lineages, and recent clinical reports of monogenic causes of neonatal respiratory distress syndrome have demonstrated that genetic defects disrupt pulmonary surfactant metabolism and cause respiratory distress syndrome, especially in term or near-term infants and in older infants, children, and adults. In contrast to developmental causes of respiratory distress, which may improve as infants and children mature, genetic causes result in both acute and chronic (and potentially irreversible) respiratory failure.

Humans↗

PubMed2006

Inherited surfactant protein-B deficiency and surfactant protein-C associated disease: clinical features and evaluation.

The pulmonary surfactant is a mixture of phospholipids and proteins synthesized, packaged, and secreted by alveolar type II cells that lowers surface tension and prevents atelectasis at end-expiration. A tightly regulated, complex metabolic cycle involves all components of the pulmonary surfactant. Disorders of surfactant metabolism that have a genetic basis are rare, but causes of respiratory dysfunction in infants and children emerge. Recessive loss of function mutations in surfactant protein-B (SP-B) gene lead to respiratory failure that is lethal in the newborn period while single allelic mutations in the surfactant protein-C (SP-C) gene cause interstitial lung disease of varying severity and age of onset. The genetic basis, mechanisms, clinical presentation and outcome, diagnostic approach and limited therapeutic options for disease due to mutations the SP-B and SP-C genes will be described in detail in this article. These disorders provide insights into some of the distinct mechanisms that disrupt the surfactant metabolic cycle and cause respiratory disease in infants and children.

Adolescent↗

PubMed2005

Metabolic kinetics of pulmonary surfactant in newborn infants using endogenous stable isotope techniques.

We compared kinetic indices of pulmonary surfactant metabolism in premature infants (n = 41) with respect to i) tracer ([1-(13)C1]acetate, [U-(13)C6]glucose, and [1,2,3,4-(13)C4] palmitate), ii) phospholipid (PL) pool (total PLs or disaturated PLs), or iii) instrumentation [gas chromatography/mass spectrometry (GC/MS) or GC-combustion-isotope ratio mass spectometry (GC-C-IRMS)]. Tracer incorporation was measured in PLs extracted from serial tracheal aspirates after a 24 h tracer infusion. The fractional catabolic rate (FCR), representing the total fractional turnover from all sources of surfactant production, was independent of tracer. The fractional synthesis rate of surfactant PL from plasma palmitate was significantly higher than that from palmitate synthesized de novo from acetate, and these two sources of palmitate together accounted for only half of the total surfactant production in preterm infants. [U-(13)C6]glucose showed significant recycling of the (13)C label in intermediary metabolism, distinguishable by GC-MS but not by GC-C-IRMS, resulting in a slower apparent FCR when GC-C-IRMS was used. The extracted PL pool did not affect the surfactant metabolic indices. We suggest that FCR should be used as a primary measure of surfactant turnover kinetics and that tracers labeling both de novo synthesis (acetate and glucose) and preformed pathways (plasma palmitate) can be used to partition the fractional contribution of each pathway to total production.

Acetates↗

PubMed2005

Genetic variant characterization in intron 4 of the surfactant protein B gene.

Genetic variants in intron 4 of the surfactant protein B gene SFTPB have been associated with pulmonary morbidity in newborn infants and adults. Genetic variant discovery in intron 4 requires high fidelity polymerase amplification due to a variable number of intermotif dinucleotide repeats and reliable characterization of alleles genetically distinct due to insertion, deletion, or both of 11 conserved sequence motifs. To optimize genetic variant discovery, we selected a high fidelity polymerase enzyme by replicate amplification and compared automated sequencing with agarose gel electrophoresis for all variant alleles (N=68) in a cohort of Missouri infants with (N=187) and without (N=53) respiratory distress. We identified and characterized six new alleles based on sequence motifs and two pairs of variant alleles with similar mobilities by agarose gel electrophoresis but distinct motif sequences. We confirmed uniformity of invariant alleles by sequencing (N=77). Logistic regression using race and intron 4 genotype for infants > or = 35 weeks gestation suggested that the invariant allele was independently associated with increased risk of respiratory distress (OR for the invariant allele 2.7, 95% CI 1.0-7.2). Reliable characterization of genetic variants in intron 4 requires both a high fidelity polymerase and sequencing of variant alleles.

Base Sequence↗

PubMed2005

A common mutation in the surfactant protein C gene associated with lung disease.

OBJECTIVE: To determine the contribution of the surfactant protein C (SP-C) I73T mutation to lung disease. STUDY DESIGN: Genomic DNA was obtained from 116 children with interstitial lung disease (ILD) or chronic lung disease of unclear cause and from 166 control subjects and was screened for the I73T mutation using an allele-specific polymerase chain reaction assay. RESULTS: The I73T mutation was found on 7 of 232 SP-C alleles from 7 unrelated children with ILD but was not found on 332 control SP-C alleles ( P < .01, Fisher exact test). The I73T mutation segregated with lung disease in one kindred with familial ILD. The I73T mutation was found in an asymptomatic parent from two different families with affected children consistent with variable penetrance, but it was not found in either asymptomatic parent of two other unrelated affected children consistent with a de novo mutation. Analysis of single nucleotide polymorphisms indicated diverse genetic backgrounds of the I73T alleles. Immunohistochemical analysis of lung tissue from an infant with the I73T mutation demonstrated normal staining patterns for proSP-B, SP-B, and proSP-C. CONCLUSIONS: These findings support the hypothesis that the I73T mutation predisposes to or causes lung disease.

Alleles↗

PubMed2005

Substrate utilization and kinetics of surfactant metabolism in evolving bronchopulmonary dysplasia.

OBJECTIVES: To use stable isotopically labeled precursors of pulmonary surfactant phospholipids to measure precursor utilization and surfactant turnover in premature infants who required mechanical ventilation at birth, 2 weeks, and >4 weeks of age. STUDY DESIGN: Infants of < or =28 weeks' gestation received simultaneous 24-hour intravenous infusions of [1,2,3,4-13C4] palmitate and [1-13C1] acetate at birth, 2 weeks, and > or =4 weeks of life. Disaturated phospholipids were extracted from sequential tracheal aspirate samples obtained over a period of 2 weeks. Fractional catabolic rate (a measure of total turnover) and the fractional synthetic rates from plasma palmitate and de novo synthesis (acetate) were measured. RESULTS: The fractional catabolic rate increased from 25.3% +/- 7.0% per day at birth to 53.8% +/- 14.4% per day at 4 weeks (P=.001). The combined contribution from plasma palmitate and de novo synthesis to total synthesis increased from 44.2% +/- 19.8% at birth to 85.2% +/- 32.8% at 4 weeks (P=.03). CONCLUSIONS: Total surfactant turnover increased in premature infants with evolving bronchopulmonary dysplasia. The increasing contributions from acetate and plasma palmitate suggest a decrease in surfactant phospholipid recycling.

Acetic Acid↗

PubMed2005

Sialidosis presenting as severe nonimmune fetal hydrops is associated with two novel mutations in lysosomal alpha-neuraminidase.

Sialidosis is a lysosomal storage disease characterized by accumulation of sialylated oligosaccharides in tissues, blood and urine and is caused by mutations in the gene for lysosomal alpha-neuraminidase (NEU1). There is wide variability in the age of onset and severity of symptoms in sialidosis. We report here a case of sialidosis due to novel mutations in NEU1 presenting as severe nonimmune hydrops fetalis.

Codon, Nonsense↗

PubMed2004

The N-terminal propeptide of lung surfactant protein C is necessary for biosynthesis and prevents unfolding of a metastable alpha-helix.

The lung surfactant-associated protein C (SP-C) consists mainly of a polyvaline alpha-helix, which is stable in a lipid membrane. However, in agreement with the predicted beta-strand conformation of a polyvaline segment, helical SP-C unfolds and transforms into beta-sheet aggregates and amyloid fibrils within a few days in aqueous organic solvents. SP-C fibril formation and aggregation have been associated with lung disease. Here, we show that in a recently isolated biosynthetic precursor of SP-C (SP-Ci), a 12 residue N-terminal propeptide locks the metastable polyvaline part in a helical conformation. The SP-Ci helix does not aggregate or unfold during several weeks of incubation, as judged by hydrogen/deuterium exchange and mass spectrometry. Hydrogen/deuterium exchange experiments further indicate that the propeptide reduces exchange in parts corresponding to mature SP-C. Finally, in an acidic environment, SP-Ci unfolds and aggregates into amyloid fibrils like SP-C. These data suggest a direct role of the N-terminal propeptide in SP-C biosynthesis.

Circular Dichroism↗

PubMed2004

N-terminally extended surfactant protein (SP) C isolated from SP-B-deficient children has reduced surface activity and inhibited lipopolysaccharide binding.

In both humans and mice, a deficiency of surfactant protein B (SP-B) is associated with a decreased concentration of mature SP-C and accumulation of a larger SP-C peptide, denoted SP-C(i), which is not observed under normal conditions. Isolation of hydrophobic polypeptides from the lungs of children who died with two different SP-B mutations yielded pure SP-C(i) and showed only trace amounts of mature SP-C. Determination of the SP-C(i) covalent structure revealed a 12-residue N-terminal peptide segment, followed by a 35-residue segment that is identical to mature SP-C. The SP-C(i) structure determined herein is similar to that of a proposed late intermediate in the processing of proSP-C, suggesting that SP-C(i) is the immediate precursor of SP-C. In bronchoalveolar lavage fluid from transgenic mice with a focal deficiency of SP-B, SP-C(i) was detected in the biophysically active, large aggregate fraction and was associated with membrane structures that are typical for a large aggregate surfactant. However, unlike SP-C, SP-C(i) exhibited a very poor ability to promote phospholipid adsorption, gave high surface tension during cyclic film compression, and did not bind lipopolysaccharide in vitro. SP-C(i) is thus capable of associating with surfactant lipids, but its N-terminal dodecapeptide segment must be proteolytically removed to generate a biologically functional peptide. The results of this study indicate that the early postnatal fatal respiratory distress seen in SP-B-deficient children is combined with the near absence of active variants of SP-C.

Amino Acid Sequence↗

PubMed2004

Informed consent for genetic research.

BACKGROUND: Rapid technological advances in genetic research and public concern about genetic discrimination have led to anticipatory safeguards in the informed consent process in the absence of legal examples of proven discrimination. Despite federal and state regulations to restrict access to personal health information, including genetic information, institutional review boards have required the addition of language to informed consent documents that warns about the risks of discrimination with participation in genetic research. OBJECTIVE: To determine the reasons that families refused consent for their infant's participation in a study evaluating a genetic cause of respiratory distress syndrome. DESIGN: Survey conducted between February 1, 2002, and March 31, 2003. SETTING: Academic, tertiary free-standing children's hospital. PARTICIPANTS: A convenience sample of 465 families were approached for consent. The 135 families who refused consent were surveyed. MAIN OUTCOME MEASURES: Reasons for refusal. RESULTS: Of the nonconsenting families, 79% spontaneously and specifically identified institutionally required language in our consent form concerning the risk of denial of access to health insurance and employment as the primary reason for refusal; 97% indicated that their fears resulted directly from language in our consent form. Only 20% of families who refused consent cited inadequate time to consider the study. CONCLUSIONS: The institutionally required description of risk of genetic discrimination due solely to participation in genetic research was the primary reason for refusal to consent in this cohort. Information about federally and institutionally mandated protections for confidentiality of participants in genetic research should be included in the informed consent document to balance the description of hypothetical risks and more accurately inform subjects.

Employment↗

PubMed2004

Antimicrobial use and the influence of inadequate empiric antimicrobial therapy on the outcomes of nosocomial bloodstream infections in a neonatal intensive care unit.

OBJECTIVE: To evaluate antimicrobial use and the influence of inadequate empiric antimicrobial therapy on the outcomes of nosocomial bloodstream infections (BSIs). DESIGN: Prospective cohort study with nested case-control analysis. SETTING: Neonatal intensive care unit (NICU). METHODS: All patients weighing 2,000 g or less were enrolled. Data collection included risk factors for nosocomial BSI, admission severity of illness, microbiology, antimicrobial therapy, and outcomes. Inadequate empiric antimicrobial therapy was defined as the use of antibiotics for more than 48 hours after the day that blood cultures were performed that did not cover the microorganisms causing the bacteremia or administration of antibiotics that failed to cover resistant microorganisms. RESULTS: Two hundred twenty-nine patients were enrolled. Forty-five developed nosocomial BSIs. The BSI rates were 11.2, 2.8, and 0 per 1,000 catheter-days for patients weighing 1,000 g or less, between 1,001 and 1,500 g, and between 1,501 and 2,000 g, respectively. After adjustment for severity of illness, the mortality in patients with nosocomial BSI receiving inadequate empiric antimicrobial therapy was higher than in those receiving adequate therapy (adjusted odds ratio [AOR], 5.3; 95% confidence interval [CI95], 1.2-23.2). By multivariate analysis, nosocomial BSI attributed to Candida species (AOR, 6.3; CI95, 1.4-28.0) and invasive procedure prior to onset of BSI (AOR, 6.4; CI95, 1.0-39.0) were associated with administration of inadequate empiric antimicrobial therapy. CONCLUSIONS: Administration of inadequate empiric antimicrobial therapy among NICU patients with nosocomial BSI was associated with higher mortality. Additional studies on the role of inadequate empiric antimicrobial therapy and the outcomes of BSIs among NICU patients are needed.

Anti-Infective Agents↗

PubMed2003

Progressive lung disease and surfactant dysfunction with a deletion in surfactant protein C gene.

Mutations in the surfactant protein (SP)-C gene are responsible for familial and sporadic interstitial lung disease (ILD). The consequences of such mutations on pulmonary surfactant composition and function are poorly understood. To determine the effects of a mutation in the SP-C gene on surfactant, we obtained lung tissue at the time of transplantation from a 14-mo-old infant with progressive ILD. An in-frame 9-bp deletion spanning codons 91-93 in Exon 3 of the SP-C gene was present on one allele; neither parent carried this deletion. SP-C mRNA was present in normal size and amount. By immunofluorescence, proSP-C was aggregated within alveolar Type II cells in a compartment separate from SP-B. In airway surfactant, there was little or no mature SP-B or SP-C; SP-A content was increased. Minimum surface tension was increased (20 mN/m, normal < 5 mN/m). Type II cells contained normal and disorganized appearing lamellar bodies by electron microscopy. This spontaneous deletion on one allele of the SP-C gene was associated with sporadic ILD and abnormalities in surfactant composition and function. We propose that a dominant negative effect on surfactant protein metabolism and function results from aggregation of misfolded proSP-C and subsequent cell injury and inflammation.

Adult↗

PubMed2003

Endogenous surfactant metabolism in newborn infants with and without respiratory failure.

Studies using stable isotopically labeled glucose and palmitate as precursors of pulmonary surfactant synthesis have demonstrated slow surfactant turnover in premature infants with respiratory distress syndrome (RDS). However, only limited data about surfactant turnover are available for term infants. Because acetate is a direct precursor of de novo synthesized surfactant fatty acid, we measured [1-13C1]acetate incorporation into surfactant of term infants without respiratory dysfunction (control group), preterm infants with RDS, and term infants with primary respiratory failure to determine whether stable isotopically labeled acetate would yield similar results to previous studies of preterm infants with RDS and, furthermore, would distinguish normal from abnormal surfactant turnover. Despite similar amounts of phospholipids and acetate precursor enrichment, the control group had higher fractional synthetic rate and shorter half-life of clearance than preterm infants with RDS, (fractional synthetic rate, 15.4 +/- 2.4 versus 2.2 +/- 0.4%/d, p < 0.001; half-life of clearance, 27 +/- 3 versus 105 +/- 11 h, p < 0.001). Term infants with severe respiratory failure had a lower fractional synthetic rate than those with mild disease (2.9 +/- 0.6 versus 13.8 +/- 3.5%/d, p = 0.014) and a reduced amount of phospholipids recovered from tracheal aspirates (54 +/- 17 versus 300 +/- 28 nmol, severe versus mild disease, respectively, p < 0.001). The amount of phospholipids in tracheal aspirates correlated inversely with disease severity, (r = -0.75, p = 0.01). We conclude that normal surfactant turnover in term infants is faster than in preterm infants with RDS. Surfactant turnover in term infants with severe respiratory failure is similar to that of preterm infants with RDS, suggesting either delayed maturity of the surfactant system or disruption from the underlying disease process.

Acetates↗

PubMed2003

Ventilator-associated pneumonia in extremely preterm neonates in a neonatal intensive care unit: characteristics, risk factors, and outcomes.

OBJECTIVE: To determine the rates, characteristics, risk factors, and outcomes of ventilator-associated pneumonia (VAP) in extremely preterm neonates in a neonatal intensive care unit (NICU). METHODS: A prospective cohort study was conducted at the St Louis Children's Hospital on all patients who had birth weight or=48 hours from October 2000 to July 2001. Extremely preterm neonates were defined as neonates with estimated gestational age (EGA) <28 weeks. The primary outcome was the development of VAP. Secondary outcomes were death and NICU length of stay (LOS). Multiple logistic regression was performed to determine independent predictors for VAP and mortality. RESULTS: A total of 229 patients were enrolled. Sixty-seven (29%) had EGA <28 weeks. Nineteen episodes of VAP occurred in 19 (28.3%) of 67 mechanically ventilated patients. VAP rates were 6.5 per 1000 ventilator days for patients with EGA <28 weeks and 4 per 1000 ventilator days for EGA >or=28 weeks. By multivariate analysis, bloodstream infection before VAP (adjusted odds ratio: 3.5; 95% confidence interval [CI]: 1.2-10.8) was an independent risk factor for VAP after adjustment for the duration of endotracheal intubation. Ventilator-associated pneumonia (adjusted odds ratio: 3.4; 95% CI: 1.2-12.3) was an independent predictor of mortality. A strong association between VAP and mortality was observed in neonates who stayed in the NICU >30 days (relative risk: 8.0; 95% CI: 1.9-35.0). Patients with VAP also had prolonged NICU LOS (median: 138 vs 82 days). CONCLUSIONS: VAP occurred at high rates in extremely preterm neonates and was associated with increased mortality. Additional studies are needed to develop interventions to prevent VAP in NICU patients.

Cohort Studies↗

PubMed2002

Endogenous pulmonary surfactant metabolism is not affected by mode of ventilation in premature infants with respiratory distress syndrome.

OBJECTIVE: To determine if high frequency oscillatory ventilation (HFOV) decreases surfactant production in premature infants with respiratory distress syndrome (RDS). STUDY DESIGN: We randomized 19 infants <28 weeks of gestation to either HFOV (n = 8) or conventional ventilation (CV, n = 11) at 24 hours of life. After a 24-hour continuous infusion of uniformly labeled carbon 13 glucose (U-(13)C(6)) glucose, we measured (13)C enrichment in surfactant phosphatidylcholine (PC) in tracheal aspirate samples using gas chromatography/mass spectrometry. We calculated the fractional synthetic rate (FSR) of surfactant PC from labeled glucose and its half-life of clearance (T(1/2)). RESULTS: FSR did not differ between groups (4.7% +/- 2.7%/day CV vs 4.2% +/- 3.1%/day HFOV, P =.7). T(1/2) was 79 +/- 18 hours in the CV group and 76 +/- 23 hours in the HFOV group (P =.7). Neither degree of ventilatory support nor supplemental oxygen exposure correlated with surfactant metabolic indices. Three of 4 infants who died from RDS within the first month of life had a shorter T(1/2) than 14 of 15 infants who survived. CONCLUSION: Surfactant metabolism is similar in preterm infants ventilated with HFOV and CV. Shortened surfactant half-life may characterize a subset of preterm infants with lethal RDS.

Body Fluids↗