Effects of recombinant human keratinocyte growth factor on surfactant, plasma, and liver phospholipid homeostasis in hyperoxic neonatal rats

Development of a blood proteins-based model for bronchopulmonary dysplasia prediction in premature infants

BACKGROUND

Bronchopulmonary dysplasia (BPD) is the most common chronic pulmonary disease in premature infants. Blood proteins may be early predictors of the development of this disease.

METHODS

In this study, protein expression profiles (blood samples during their first week of life) and clinical data of the GSE121097 was downloaded from the Gene Expression Omnibus. Weighted gene co-expression network analysis (WGCNA) and differential protein analysis were carried out for variable dimensionality reduction and feature selection. Least absolute shrinkage and selection operator (LASSO) were conducted for BPD prediction model development. The performance of the model was evaluated by the receiver operating characteristic (ROC) curve, calibration curve, and decision curve.

RESULTS

The results showed that black module, magenta module and turquoise module, which included 270 proteins, were significantly correlated with the occurrence of BPD. 59 proteins overlapped between differential analysis results and above three modules. These proteins were significantly enriched in 253 GO terms and 11 KEGG signaling pathways. Then, 59 proteins were reduced to 8 proteins by LASSO analysis in the training cohort. The proteins model showed good BPD predictive performance, with an AUC of 1.00 (95% CI 0.99-1.00) and 0.96 (95% CI 0.90-1.00) in training cohort and test cohort, respectively.

CONCLUSION

Our study established a reliable blood-protein based model for early prediction of BPD in premature infants. This may help elucidate pathways to target in lessening the burden or severity of BPD.

Choline Kinetics in Neonatal Liver, Brain and Lung-Lessons from a Rodent Model for Neonatal Care

Choline requirements are high in the rapidly growing fetus and preterm infant, mainly serving phosphatidylcholine (PC) synthesis for parenchymal growth and one-carbon metabolism via betaine. However, choline metabolism in critical organs during rapid growth is poorly understood. Therefore, we investigated the kinetics of D9-choline and its metabolites in the liver, plasma, brain and lung in 14 d old rats. Animals were intraperitoneally injected with 50 mg/kg D9-choline chloride and sacrificed after 1.5 h, 6 h and 24 h. Liver, plasma, lungs, cerebrum and cerebellum were analyzed for D9-choline metabolites, using tandem mass spectrometry. In target organs, D9-PC and D9-betaine comprised 15.1 ± 1.3% and 9.9 ± 1.2% of applied D9-choline at 1.5 h. D9-PC peaked at 1.5 h in all organs, and decreased from 1.5-6 h in the liver and lung, but not in the brain. Whereas D9-labeled PC precursors were virtually absent beyond 6 h, D9-PC increased in the brain and lung from 6 h to 24 h (9- and 2.5-fold, respectively) at the expense of the liver, suggesting PC uptake from the liver via plasma rather than local synthesis. Kinetics of D9-PC sub-groups suggested preferential hepatic secretion of linoleoyl-PC and acyl remodeling in target organs. D9-betaine showed rapid turnover and served low-level endogenous (D3-)choline synthesis. In conclusion, in neonatal rats, exogenous choline is rapidly metabolized to PC by all organs. The liver supplies the brain and lung directly with PC, followed by organotypic acyl remodeling. A major fraction of choline is converted to betaine, feeding the one-carbon pool and this must be taken into account when calculating choline requirements.

Intratracheal Keratinocyte Growth Factor Enhances Surfactant Protein B Expression in Mechanically Ventilated Preterm Pigs

Bronchopulmonary dysplasia (BPD) is a devastating disease of prematurity that is associated with mechanical ventilation and hyperoxia. We used preterm pigs delivered at gestational day 102 as a translational model for 26-28-week infants to test the hypothesis administering recombinant human keratinocyte growth factor (rhKGF) at initiation of mechanical ventilation will stimulate type II cell proliferation and surfactant production, mitigate ventilator induced lung injury, and reduce epithelial to mesenchymal transition considered as a precursor to BPD. Newborn preterm pigs were intubated and randomized to receive intratracheal rhKGF (20 μg/kg; n = 6) or saline (0.5 ml 0.9% saline; control; n = 6) before initiating 24 h of ventilation followed by extubation to nasal oxygen for 12 h before euthanasia and collection of lungs for histopathology and immunohistochemistry to assess expression of surfactant protein B and markers of epithelial to mesenchymal transition. rhKGF pigs required less oxygen during mechanical ventilation, had higher tidal volumes at similar peak pressures indicative of improved lung compliance, and survival was higher after extubation (83% vs. 16%). rhKGF increased surfactant protein B expression (p < 0.05) and reduced TGF-1β (p < 0.05), that inhibits surfactant production and is a prominent marker for epithelial to mesenchymal transition. Our findings suggest intratracheal administration of rhKGF at initiation of mechanical ventilation enhances surfactant production, reduces ventilator induced lung injury, and attenuates epithelial-mesenchymal transition while improving pulmonary functions. rhKGF is a potential therapeutic strategy to mitigate pulmonary responses of preterm infants that require mechanical ventilation and thereby reduce the incidence and severity of bronchopulmonary dysplasia.

Fatty acid composition of adipose tissue at term indicates deficiency of arachidonic and docosahexaenoic acid and excessive linoleic acid supply in preterm infants

BACKGROUND

Arachidonic (ARA) and docosahexaenoic acid (DHA) are constitutive to membrane phospholipids, and essential for brain and overall development. ARA/DHA pools in term infants (TI) are built during the third trimester, stored as adipose tissue triglycerides and predominantly distributed via plasma phosphatidylcholine (PC). In preterm infants (PTI), placental ARA/DHA supply is replaced by linoleic-acid (LA)-enriched nutrition. This study aimed to investigate the impact of PTI nutrition, compared to placental supply, on fatty acid composition in adipose tissue and blood.

METHODS

Prospective observational study (4/2017-3/2019) in 12 PTI and 3 PTI with enterostomy (PTI/E) (gestational age (GA) < 32 weeks) with surgical intervention at term (± 6 weeks) and 14 TI (GA ≥ 34 weeks, surgical intervention < 2 weeks postnatally). PTI/E were analyzed descriptively only. PC and triglyceride fatty acids were analyzed with tandem mass spectrometry and gas chromatography, respectively. Results were compared between TI and PTI with Wilcoxon Test and shown as median [25th percentile-75th percentile] mol%.

RESULTS

PTI had less ARA in adipose tissue TG (0.77[0.67-0.87]% vs. 1.04[0.95-1.14]%, p = 0.0003) and plasma PC (20.7[18.7-22.8]% vs. 28.3[22.7-33.5]%, p = 0.011) than TI. PTI also had less DHA in adipose tissue TG (0.6[0.4-0.8]% vs. 1.1[0.8-1.4]%, p = 0.006) and plasma PC (6.4[5.6-7.1]% vs. 8.4[7.8-13.1]%, p = 0.002). LA was increased in PTI's adipose tissue TG (10.0[8.8-12.3]% vs. 3.0[2.5-3.6]%, p < 0.0001) and plasma PC (48.4[44.6-49.6]% vs. 30.6[24.9-35.6]%, p = 0.0002). Similar differences were observed in erythrocyte PC.

CONCLUSION

In PTI, LA is increased and ARA/DHA decreased in adipose tissue, plasma and erythrocyte lipids as proxies for other tissues, likely caused by PTI nutrition. This may contribute to impaired PTI development.

Phosphatidylcholine kinetics in neonatal rat lungs and the effects of rhuKGF and betamethasone

Surfactant, synthesized by type II pneumocytes (PN-II), mainly comprises phosphatidylcholine (PC) and is essential to prevent neonatal respiratory distress. Furthermore, PC is essential to lung tissue growth and maintenance as a membrane component. Recent findings suggest that the lung contributes to systemic lipid homeostasis via PC export through ABC-A1 transporter expression. Hence it is important to consider pharmacological interventions in neonatal lung PC metabolism with respect to such export. Five-day-old rats were treated with carrier (control), intraperitoneal betamethasone, subcutaneous recombinant human keratinocyte growth factor (rhuKGF), or their combination for 48 h. Animals were intraperitoneally injected with 50 mg/kg [D9-methyl]choline chloride 1.5, 3.0, and 6.0 h before death at day 7, and lung lavage fluid (LLF) and tissue were harvested. Endogenous PC, D9-labeled PC species, and their water-soluble precursors (D9-)choline and (D9-)phosphocholine were determined by tandem mass spectrometry. Treatment increased secreted and tissue PC pools but did not change equilibrium composition of PC species in LLF. However, all treatments increased specific surfactant components in tissue. In control rats, peak D9-PC in lavaged lung was reached after 3 h and was decreased at 6 h. Only 13% of this net loss in lavaged lung was found in LLF. Such decrease was not present in lungs treated with betamethasone and/or with rhuKGF. D9-PC loss at 3–6 h and PC synthesis calculated from D9 enrichment of phosphocholine indicated that daily synthesis rate is higher than total pool size. We conclude that lung tissue contributes to systemic PC homeostasis in neonatal rats, which is altered by glucocorticoid and rhuKGF treatment.

The Effects of Lung Protective Ventilation or Hypercapnic Acidosis on Gas Exchange and Lung Injury in Surfactant Deficient Rabbits

Background

Permissive hypercapnia has been shown to reduce lung injury in subjects with surfactant deficiency. Experimental studies suggest that hypercapnic acidosis by itself rather than decreased tidal volume may be a key protective factor.

Objectives

To study the differential effects of a lung protective ventilatory strategy or hypercapnic acidosis on gas exchange, hemodynamics and lung injury in an animal model of surfactant deficiency.

Methods

30 anesthetized, surfactant-depleted rabbits were mechanically ventilated (FiO₂ = 0.8, PEEP = 7cmH₂O) and randomized into three groups: Normoventilation-Normocapnia (NN)-group: tidal volume (Vt) = 7.5 ml/kg, target PaCO₂ = 40 mmHg; Normoventilation-Hypercapnia (NH)-group: Vt = 7.5 ml/kg, target PaCO₂ = 80 mmHg by increasing FiCO₂; and a Hypoventilation-Hypercapnia (HH)-group: Vt = 4.5 ml/kg, target PaCO₂ = 80 mmHg. Plasma lactate and interleukin (IL)-8 were measured every 2 h. Animals were sacrificed after 6 h to perform bronchoalveolar lavage (BAL), to measure lung wet-to-dry weight, lung tissue IL-8, and to obtain lung histology.

Results

PaO₂ was significantly higher in the HH-group compared to the NN-group (p<0.05), with values of the NH-group between the HH- and NN-groups. Other markers of lung injury (wet-dry-weight, BAL-Protein, histology-score, plasma-IL-8 and lung tissue IL-8) resulted in significantly lower values for the HH-group compared to the NN-group and trends for the NH-group towards lower values compared to the NN-group. Lactate was significantly lower in both hypercapnia groups compared to the NN-group.

Conclusion

Whereas hypercapnic acidosis may have some beneficial effects, a significant effect on lung injury and systemic inflammatory response is dependent upon a lower tidal volume rather than resultant arterial CO₂ tensions and pH alone.

Surface tension of airway aspirates withdrawn during neonatal resuscitation reflects lung maturity

The indications for treatment of neonates with exogenous pulmonary surfactant are still discussed controversially. Some premature neonates are sufficiently treated by CPAP, others need conventional ventilation and/or surfactant. The available lung maturity tests have limitations. The captive bubble surfactometer (CBS) provides measurement of surface activity from rather small amounts of surfactant. This study aimed to determine surface activity from small volume aspirates of the upper airways of neonates by means of the CBS and to correlate the results with clinical data. Small upper airway aspirates from 159 neonates (gestational age 25-42 weeks) were withdrawn and concentrated 16.7-fold by ultracentrifugation and resuspension in saline. Surface activities after 5 min of adsorption were determined in the CBS and correlated to the perinatal data (e.g., gestational age, birth weight, gender), airway interventions (like CPAP, conventional ventilation) and surfactant treatment. Additionally, 27 samples were analyzed for surfactant specific phosphatidylcholine concentrations by using electrospray ionization tandem mass-spectroscopy. Surface activities show a significant correlation to gestational age, birth weight, and the need for airway interventions. Comparing the need for airway interventions versus surface activity, a receiver operating characteristic calculated a sensitivity of 0.77 and a specificity of 0.72 at a "cut off" of 44 mN/m. Surface activity correlates significantly with the phosphatidylcholine concentrations and the latter one correlates with the gestational age. Determination of surface activity from upper airway aspirates is feasible. Further clinical studies are needed to prove the predictive value of the method.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Plasma phospholipids indicate impaired fatty acid homeostasis in preterm infants

BACKGROUND

During fetal development, docosahexaenoic (DHA) and arachidonic acid (ARA) are particularly enriched in brain phospholipids. After preterm delivery, fetal enrichment of DHA and ARA via placental transfer is replaced by enteral and parenteral nutrition, which is rich in linoleic acid (LA) instead. Specific DHA and ARA enrichment of lipoproteins is reflected by plasma phosphatidylcholine (PC) species, whereas plasma phosphatidylethanolamine (PE) composition reflects hepatic stores.

OBJECTIVE

We profiled PC and PE species in preterm infant plasma, compared with cord and maternal blood, to assess whether current feeding practice meets fetal conditions in these patients.

DESIGN

Preterm infant plasma (N = 171, 23-35 w postmenstrual age (PMA), postnatal day 1-103), cord plasma (N = 194) and maternal serum (N = 121) (both 24-41 w PMA) were collected. After lipid extraction, PC and PE molecular species were analyzed using tandem mass spectrometry.

RESULTS

Phospholipid concentrations were higher in preterm infant than in cord plasma after correction for PMA. This was mainly due to postnatal increases in LA-containing PC and PE, resulting in decreased fractions of their DHA- and ARA-containing counterparts. These changes in preterm infant plasma phospholipids occurred during the time of transition to full enteral feeds (day 0-10 after delivery). Thereafter, the fraction of ARA-containing phospholipids further decreased, whereas that of DHA slowly reincreased but remained at a level 50% of that of PMA-matched cord blood.

CONCLUSIONS

The postnatal increase in LA-PC in preterm infant plasma results in decreased fractions of DHA-PC and ARA-PC. These changes are also reflected by PE molecular composition as an indicator of altered hepatic fatty acid homeostasis. They are presumably caused by inadequately high LA, and low ARA and DHA supply, at a stage of development when ARA-PC and DHA-PC should be high, probably reducing the availability of DHA and ARA to the developing brain and contributing to impaired neurodevelopment of preterm infants.