Henry T. Akinbi

Early Bubble CPAP and Outcomes in ELBW Preterm Infants

OBJECTIVE: To test whether the introduction of early bubble continuous positive airway pressure (CPAP) results in improved respiratory outcomes in extremely low birth-weight infants.STUDY DESIGN: Outcomes of all infants between 401 and 1000 g born in a level 3 neonatal intensive care units (NICU) between July 2000 and October 2001 (period 2) were compared using historical controls (period 1). Early bubble (CPAP) was prospectively introduced in the NICU during period 1. Univariate and adjusted comparisons were made across time periods.RESULTS: Delivery room intubations, days on mechanical ventilation and use of postnatal steroids decreased (p<0.001) in period 2, while mean days on CPAP, number of babies on CPAP at 24 hours (p<0.001) and mean weight at 36 weeks corrected gestation also increased (p<0.05) after introduction of early bubble CPAP.CONCLUSIONS: Early bubble CPAP reduced delivery room intubations, days on mechanical ventilation, postnatal steroid use and was associated with increased postnatal weight gain with no increased complications.

The peptidoglycan-degrading property of lysozyme is not required for bactericidal activity in vivo

Lysozyme is an abundant, cationic antimicrobial protein that plays an important role in pulmonary host defense. Increased concentration of lysozyme in the airspaces of transgenic mice enhanced bacterial killing whereas lysozyme deficiency resulted in increased bacterial burden and morbidity. Lysozyme degrades peptidoglycan in the bacterial cell wall leading to rapid killing of Gram-positive organisms; however, this mechanism cannot account for the protective effect of lysozyme against Gram-negative bacteria. The current study was therefore designed to test the hypothesis that the catalytic activity (muramidase activity) of lysozyme is not required for bacterial killing in vivo. Substitution of serine for aspartic acid at position 53 (D53S) in mouse lysozyme M completely ablated muramidase activity. Muramidase-deficient recombinant lysozyme (LysMD53S) killed both Gram-positive and Gram-negative bacteria in vitro. Targeted expression of LysMD53S in the respiratory epithelium of wild-type (LysM+/+/LysMD53S) or lysozyme Mnull mice (LysM−/−/LysMD53S) resulted in significantly elevated lysozyme protein in the airspaces without any increase in muramidase activity. Intratracheal challenge of transgenic mice with Gram-positive or Gram-negative bacteria resulted in a significant increase in bacterial burden in LysM−/− mice that was completely reversed by targeted expression of LysMD53S. These results indicate that the muramidase activity of lysozyme is not required for bacterial killing in vitro or in vivo.

Resistance to Mucosal Lysozyme Compensates for the Fitness Deficit of Peptidoglycan Modifications by Streptococcus pneumoniae

The abundance of lysozyme on mucosal surfaces suggests that successful colonizers must be able to evade its antimicrobial effects. Lysozyme has a muramidase activity that hydrolyzes bacterial peptidoglycan and a non-muramidase activity attributable to its function as a cationic antimicrobial peptide. Two enzymes (PgdA, a N-acetylglucosamine deacetylase, and Adr, an O-acetyl transferase) that modify different sites on the peptidoglycan of Streptococcus pneumoniae have been implicated in its resistance to lysozyme in vitro. Here we show that the antimicrobial effect of human lysozyme is due to its muramidase activity and that both peptidoglycan modifications are required for full resistance by pneumococci. To examine the contribution of lysozyme and peptidoglycan modifications during colonization of the upper respiratory tract, competition experiments were performed with wild-type and pgdAadr mutant pneumococci in lysozyme M-sufficient (LysM+/+) and -deficient (LysM−/−) mice. The wild-type strain out-competed the double mutant in LysM+/+, but not LysM−/− mice, indicating the importance of resistance to the muramidase activity of lysozyme during mucosal colonization. In contrast, strains containing single mutations in either pgdA or adr prevailed over the wild-type strain in both LysM+/+ and LysM−/− mice. Our findings demonstrate that individual peptidoglycan modifications diminish fitness during colonization. The competitive advantage of wild-type pneumococci in LysM+/+ but not LysM−/− mice suggests that the combination of peptidoglycan modifications reduces overall fitness, but that this is outweighed by the benefits of resistance to the peptidoglycan degrading activity of lysozyme.

Alterations in the host defense properties of human milk following prolonged storage or pasteurization.

Objectives: Preterm infants are often fed pasteurized donor milk or mothers milk that has been stored frozen for up to 4 weeks. Our objectives were to assess the impact of pasteurization or prolonged storage at −20°C on the immunologic components of human milk and the capability of the different forms of human milk to support bacterial proliferation. Materials and Methods: The concentrations and activities of major host defense proteins in the whey fractions of mothers milk stored for 4 weeks at −20°C or pasteurized human donor milk were compared with freshly expressed human milk. Proliferation of bacteria incubated in the 3 forms of human milk was assessed. Results: Relative to freshly expressed human milk, the concentrations of lysozyme, lactoferrin, lactoperoxidase, and secretory immunoglobulin A were reduced 50% to 82% in pasteurized donor milk and the activities of lysozyme and lactoperoxidase were 74% to 88% lower (P < 0.01). Proliferation of bacterial pathogens in pasteurized donor milk was enhanced 1.8- to 4.6-fold compared with fresh or frozen human milk (P < 0.01). Conclusions: The immunomodulatory proteins in human milk are reduced by pasteurization and, to a lesser extent, by frozen storage, resulting in decreased antibacterial capability. Stringent procedure to minimize bacterial contamination is essential during handling of pasteurized milk.

Maternal and neonatal factors impacting response to methadone therapy in infants treated for neonatal abstinence syndrome.

Objective:To identify maternal and neonatal factors that impact response to methadone therapy for neonatal abstinence syndrome.Study Design:This is a retrospective review of 128 infants that received pharmacotherapy for opiate withdrawal to identify factors associated with favorable response to methadone therapy. Maternal and neonatal data were analyzed with univariate statistics and multivariate logistic regression.Result:Maternal methadone maintenance dose during pregnancy correlated with length of stay (P=0.009). There was an inverse correlation between the amount of mothers breast milk ingested and length of stay (β=−0.03, P=0.02). Methadone was initiated later, tapered more rapidly and was more successful as monotherapy in preterm infants. Five percent of infants were admitted to hospital again for rebound withdrawal following reduction of breast milk intake.Conclusion:Severity of neonatal abstinence syndrome may be mitigated by titrating methadone to the lowest effective dose during pregnancy and by encouraging breast milk feeds, which should be weaned gradually.

Surfactant protein C-deficient mice are susceptible to respiratory syncytial virus infection.

Patients with mutations in the pulmonary surfactant protein C (SP-C) gene develop interstitial lung disease and pulmonary exacerbations associated with viral infections including respiratory syncytial virus (RSV). Pulmonary infection with RSV caused more severe interstitial thickening, air space consolidation, and goblet cell hyperplasia in SP-C-deficient (Sftpc(-/-)) mice compared with SP-C replete mice. The RSV-induced pathology resolved more slowly in Sftpc(-/-) mice with lung inflammation persistent up to 30 days postinfection. Polymorphonuclear leukocyte and macrophage counts were increased in the bronchoalveolar lavage (BAL) fluid of Sftpc(-/-) mice. Viral titers and viral F and G protein mRNA were significantly increased in both Sftpc(-/-) and heterozygous Sftpc(+/-) mice compared with controls. Expression of Toll-like receptor 3 (TLR3) mRNA was increased in the lungs of Sftpc(-/-) mice relative to Sftpc(+/+) mice before and after RSV infection. Consistent with the increased TLR3 expression, BAL inflammatory cells were increased in the Sftpc(-/-) mice after exposure to a TLR3-specific ligand, poly(I:C). Preparations of purified SP-C and synthetic phospholipids blocked poly(I:C)-induced TLR3 signaling in vitro. SP-C deficiency increases the severity of RSV-induced pulmonary inflammation through regulation of TLR3 signaling.

Antimicrobial Activity of Native and Synthetic Surfactant Protein B Peptides

Surfactant protein B (SP-B) is secreted into the airspaces with surfactant phospholipids where it reduces surface tension and prevents alveolar collapse at end expiration. SP-B is a member of the saposin-like family of proteins, several of which have antimicrobial properties. SP-B lyses negatively charged liposomes and was previously reported to inhibit the growth of Escherichia coli in vitro; however, a separate study indicated that elevated levels of SP-B in the airspaces of transgenic mice did not confer resistance to infection. The goal of this study was to assess the antimicrobial properties of native SP-B and synthetic peptides derived from the native peptide. Native SP-B aggregated and killed clinical isolates of Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and group B streptococcus by increasing membrane permeability; however, SP-B also lysed RBC, indicating that the membranolytic activity was not selective for bacteria. Both the antimicrobial and hemolytic activities of native SP-B were inhibited by surfactant phospholipids, suggesting that endogenous SP-B may not play a significant role in alveolar host defense. Synthetic peptides derived from native SP-B were effective at killing both Gram-positive and Gram-negative bacteria at low peptide concentrations (0.15–5.0 μM). The SP-B derivatives selectively lysed bacterial membranes and were more resistant to inhibition by phospholipids; furthermore, helix 1 (residues 7–22) retained significant antimicrobial activity in the presence of native surfactant. These results suggest that the role of endogenous SP-B in host defense may be limited; however, synthetic peptides derived from SP-B may be useful in the treatment of bacterial pneumonias.

Gastrointestinal and renal blood flow velocity profile in neonates with birth asphyxia

Pulsed Doppler ultrasound blood flow profiles were studied, before the initiation of enteral feedings, in 23 neonates with birth asphyxia. We observed a significant direct correlation between the reduction of peak velocity and increased resistance in the renal and superior mesenteric arteries to the severity of asphyxia (r = 0.8; p < 0.05); the changes often persisted up to 3 days of age. Longitudinal evaluation of flow in these vessels might help to time the initiation of enteral nutrition in neonates with asphyxia.

Comparison of the microbicidal and muramidase activities of mouse lysozyme M and P.

Lysozyme is one of the most abundant antimicrobial proteins in the airspaces of the lung. Mice express two lysozyme genes, lysozyme M and P, but only the M enzyme is detected in abundance in lung tissues. Disruption of the lysozyme M locus significantly increased bacterial burden and mortality following intratracheal infection with a Gram-negative bacterium. Unexpectedly, significant lysozyme enzyme activity (muramidase activity) was detected in the airspaces of uninfected lysozyme M-/- mice, amounting to 25% of the activity in wild-type mice. Muramidase activity in lysozyme M-/- mice was associated with increased lysozyme P mRNA and protein in lung tissue and bronchoalveolar lavage fluid respectively. The muramidase activity of recombinant lysozyme P was less than that of recombinant M lysozyme. Recombinant P lysozyme was also less effective in killing selected Gram-negative bacteria, requiring higher concentrations than lysozyme M to achieve the same level of killing. The lower antimicrobial activity of P lysozyme, coupled with incomplete compensation by P lysozyme in lysozyme M-/- mice, probably accounts for the increased susceptibility of null mice to infection. Recombinant lysozyme M and P were equally effective in killing selected Gram-positive organisms. This outcome suggests that disruption of both M and P loci would significantly increase susceptibility to airway infections, particularly those associated with colonization by Gram-positive organisms.

Macrosomic infants of nondiabetic mothers and elevated C-peptide levels in cord blood☆☆☆★★★

C-peptide concentrations in the cord blood of 29 macrosomic neonates born of nondiabetic mothers were higher than in 23 control infants whose birth weight was appropriate for gestational age, and there was a significant direct correlation between birth weight and C-peptide concentration. Six of the macrosomic infants studied (20%) had hypoglycemia in the first 24 hours of life, compared with none of the infants born with appropriate weight. We conclude that chronic fetal hyperinsulinemia may be one of the causes of macrosomia and neonatal hypoglycemia in infants of nondiabetic mothers.