Use of Berlin EXCOR cannulas in both venovenous and venoarterial central extracorporeal membrane oxygenation configurations overcomes the problem of cannula instability while bridging infants and young children to lung transplant.

Objectives: Infants and young children awaiting lung transplantation present challenges that often preclude successful extracorporeal membrane oxygenation support as a bridge to transplantation. Instability of neck cannulas often results in the need for intubation, mechanical ventilation, and muscle relaxation creating a worse transplant candidate. With the use of Berlin Heart EXCOR cannulas (Berlin Heart, Inc) in both venoarterial and venovenous central cannulation configurations, 5 pediatric patients were successfully bridged to lung transplant. Methods: We performed a single-center retrospective case review of central extracorporeal membrane oxygenation cannulation used as a bridge to lung transplantation cases performed at Texas Children's Hospital between 2019 and 2021. Results: Six patients, 2 with pulmonary veno-occlusive disease (15-month-old male and 8-month-old male), 1 with ABCA3 mutation (2-month-old female), 1 with surfactant protein B deficiency (2-month-old female), 1 with pulmonary arterial hypertension in the setting of D-transposition of the great arteries after repair as a neonate (13-year-old male), and 1 with cystic fibrosis and end-stage lung disease, were supported for a median of 56.3 days on extracorporeal membrane oxygenation while awaiting transplantation. All patients were extubated after initiation of extracorporeal membrane oxygenation, participating in rehabilitation until transplant. No complications due to central cannulation and use of the Berlin Heart EXCOR cannulas were observed. One patient with cystic fibrosis developed fungal mediastinitis and osteomyelitis resulting in discontinuation of mechanical support and death. Conclusions: Novel use of Berlin Heart EXCOR cannulas for central cannulation eliminates the problem of cannula instability allowing extubation, rehabilitation, and bridge to lung transplant for infants and young children.

Asthma outcomes in pediatric patients with 30-day follow-up after an asthma hospitalization in a Medicaid-managed care program.

BACKGROUND: National asthma guidelines recommend an outpatient follow-up after hospitalization for asthma. Our aim is determine if a follow-up visit within 30 days after an asthma hospitalization impacts risk for re-hospitalization and emergency department visits for asthma within the following year. METHODS: This was a retrospective cohort study of claims data of Texas Children's Health Plan (a Medicaid managed care program) members age 1 to <18 years and hospitalized for asthma between January 1, 2012, and December 31, 2018. Primary outcomes were days to re-hospitalization and emergency department visit between 30 days and 365 days following the index hospitalization. RESULTS: We identified 1,485 children age 1 to <18 years hospitalized for asthma. Comparing those with a 30 day follow-up to those without, there was no difference in days to re-hospitalization (adjusted hazard ratio 1.23, 95% Confidence Interval (CI) 0.74-2.06) or emergency department visit for asthma (aHR 1.08, 95% CI 0.88-1.33). Inhaled corticosteroid and short acting beta agonist dispensing were greater in the group completing the 30 day follow-up (means of 2.8 and 4.8 respectively for those with follow-up, 1.6 and 3.5 respectively for those without, p < 0.0001). CONCLUSION: Having a follow-up outpatient visit within 30 days of an asthma hospitalization is not associated with a decrease in asthma re-hospitalization or emergency department visit in the 30-365 day period following the index hospitalization. Non-adherence to regular use of inhaled corticosteroid medication was high in both groups. These findings suggest need for improvement in the quality and quantity of post hospital asthma follow-up.

Application of organ dysfunction assessment scores following pediatric lung transplantation.

OBJECTIVE: Organ dysfunction (OD) after lung transplantation can reflect preoperative organ failure, intraoperative acute organ damage and post-operative complications. We assessed two OD scoring systems, both the PEdiatric Logistic Organ Dysfunction (PELOD) and the pediatric Sequential Organ Failure Assessment (pSOFA) scores, in recognizing risk factors for morbidity as well as recipients with prolonged post-transplant morbidity. DESIGN: Medical records of recipients from January 2009 to March 2016 were reviewed. PELOD and pSOFA scores were calculated on post-transplant days 1-3. Risk factors assessed included cystic fibrosis (CF), prolonged surgical time and worst primary graft dysfunction (PGD) score amongst others. Patients were classified into three groups based on their initial scores (group A) and subsequent trends either uptrending (group B) or downtrending (group C). Morbidity outcomes were compared between these groups. RESULTS: Total 98 patients were enrolled aged 0-20 years. Risk factors for higher pSOFA scores ≥ 5 on day 1 included non-CF diagnosis and worst PGD scores (p = .0006 and p = .03, respectively). Kruskal Wallis analysis comparing pSOFA group A versus B versus C scores showed significantly prolonged ventilatory days (median 1 vs. 4 vs. 2, p = .0028) and ICU days (median 4 vs. 10 vs. 6, p = .007). Similarly, PELOD group A versus B versus C scores showed significantly prolonged ventilatory days (1 vs. 5 vs. 2, p = < .0001). CONCLUSION: Implementing pSOFA scores bedside is a more effective tool compared to PELOD in identifying risk factors for worsened OD post-lung transplant and can be valuable in providing direction on morbidity outcomes in the ICU.

Children with Near-Fatal Asthma: The Use of Inhaled Volatile Anesthetics and Extracorporeal Membrane Oxygenation.

Background and Purpose: The use of extracorporeal membrane oxygenation (ECMO) has been described for near-fatal asthma that continues to be refractory despite maximal medical therapy. Methods: Patients admitted to the pediatric intensive care unit at Texas Children's Hospital from 2012 to 2020 with the diagnosis of asthma who were supported on ECMO or isoflurane were included in the study. Patient demographics, medication usage, and complications were compared between the case group (ECMO, n = 12) and the control group (isoflurane only, n = 8). Results: All patients survived to discharge. ECMO patients received shorter durations of albuterol (12 versus 104 h, P = 0.0002) and terbutaline (13.3 versus 31.5 h, P = 0.0250). There were no differences in complication rates between the 2 groups. Conclusion: ECMO is a reasonable and safe support method for patients with near-fatal asthma and may lead to less bronchodilator medication exposure when compared with inhaled volatile anesthetic use.

Diagnosis and treatment of cryptococcal osteomyelitis in a pediatric lung transplant patient.

BACKGROUND: Asymptomatic pulmonary nodules may appear at any point after lung transplantation. The differential diagnosis is broad and includes serious life-threatening disease entities. METHODS: A retrospective case report of a single patient who developed a pulmonary nodule after lung transplantation. RESULTS: At 2 years post-transplant, an 11-year-old with cystic fibrosis was asymptomatic and had normal lung function. A single nodule was noted on surveillance chest CT scan. Initial evaluation was negative, but subsequently, he was diagnosed with cryptococcal osteomyelitis in a thoracic rib. He responded well to an extended course of antifungal therapy without loss of allograft function or infectious complications. CONCLUSION: Pulmonary nodules after lung transplantation may be a harbinger of serious complications. A systematic approach to evaluation and follow-up is recommended.

Evaluation of a Theory-Informed Pediatric Rapid Response Training Program Using the Logic Model.

BACKGROUND AND OBJECTIVES: The activators of rapid-response (RR) events tasked with recognition of clinical decompensation, initial management, and response activation seldom receive RR training. RR activators often experience negative emotions of "failure to rescue" that can compromise team performance during RRs. We used the logic model framework for development and evaluation of an educational program grounded in self-determination theory for pediatric RR activators. METHODS: The program unfolded in a large quaternary pediatric hospital to impart knowledge and skills; foster autonomy, competence, and relatedness; and improve participants' satisfaction with performance in RRs. Logic model-guided inputs-activities-outputs-outcomes-context for program evaluation. Preintervention-postintervention follow-up surveys and interviews generated data to determine outcomes and impact of the program. The evaluation instruments were tested for validity and internal consistency. RESULTS: Over 4 years, 207 multidisciplinary RR activators were trained. Iterative modifications yielded a workshop that incorporated multiple learning modalities, a standardized learner-centered case bank, formalized evaluation tools, and a database to track participation. Significant improvements in RR-related knowledge, self-efficacy, and self- determination were noted. Workshop evaluation yielded a mean score of 4.85 (0.27) on a 5-point scale. At 6-months follow-up survey and interviews, participants reported application of the knowledge and increased confidence with participation in real-life RR events. The workshop gained traction across the hospital, was associated with improved RR clinical outcomes, and contributed to professional advancement of the educators. CONCLUSIONS: We successfully implemented a self-determination theory-informed RR training program for pediatric RR activators, and the logic model framework was used to facilitate comprehensive evaluation.

Influence of early extubation on post-operative outcomes after pediatric lung transplantation.

Lung transplantation has become an accepted therapeutic option for a select group of children with end-stage lung disease. We evaluated the impact of early extubation in a pediatric lung transplant population and its post-operative outcomes. Single-center retrospective study. PICU within a tertiary academic pediatric hospital. Patients <22 years after pulmonary transplant between January 2011 and December 2016. A total of 74 patients underwent lung transplantation. The primary pretransplantation diagnoses included cystic fibrosis (58%), pulmonary fibrosis (9%), and surfactant dysfunction disorders (10%). Of 60 patients, 36 (60%) were extubated within 24 hours and 24 patients after 24 hours (40%). A total of seven patients (11.6%) required reintubation within 24 hours. Median length of stay for the early extubation group was shorter at 3 days ([(IQR) 2.2-4.7]) compared to 5 days (IQR, 3-7) (P = .02) in the late extubation group. Median costs were lower for the early extubation group with 13,833 US dollars (IQR, 9980-22,822) vs 23 671 US dollars (IQR, 16 673-39 267) (P = .043). Fourteen patients were in the PICU prior to their transplantation; this did not affect their early extubation success. Neither did the fact of requiring invasive or non-invasive mechanical ventilation before transplantation. Early extubation appears to be safe in a pediatric population after lung transplantation and is associated with a shorter LOS and decreased hospital costs. It may prevent known complications associated with mechanical ventilation.

Infections Within the First Month After Pediatric Lung Transplantation: Epidemiology and Impact on Outcomes.

BACKGROUND: Despite successes in lung transplantation, with infection as the leading cause of death in the first year following lung transplantation, there remains a lag in survival compared with other solid organ transplants. Infections that occur early after transplantation may impact short- and long-term outcomes in pediatric lung transplant recipients (LTRs). METHODS: We performed a retrospective review of pediatric LTRs at a large quaternary-care hospital from January 2009 to March 2016 to evaluate both epidemiologic features of infection in the first 30 days post-transplantation and mortality outcomes. The 30 days were divided into early (0-7 days) and late (8-30 days) periods. RESULTS: Among the 98 LTRs, there were 51 episodes of infections. Cystic fibrosis (CF) was associated with early bacterial infections (P = .004) while non-CF was associated with late viral (P = .02) infections. Infection after transplantation was associated with worse survival by Kaplan-Meier analysis (P value log rank test = .007). Viral infection in the late period was significantly associated with 3-year mortality after multivariable analysis (P = .02). CONCLUSIONS: Infections in pediatric LTRs were frequent in the first 30 days after transplant, despite perioperative antimicrobial coverage. The association of 3-year mortality with late viral infections suggests a possible important role in post-transplant lung physiology and graft function. Understanding the epidemiology of early post-lung transplant infections can help guide post-operative management and interventions to reduce their incidence and the early- and long-term impact in this population.

Clinico-radiologic features of pleuroparenchymal fibroelastosis in children.

BACKGROUND: Pleuroparenchymal fibroelastosis (PPFE) may be underdiagnosed clinically and radiographically in children with a remote history of cancer, leading to a delay in care and unnecessary lung biopsies. OBJECTIVE: To describe the characteristic clinical and radiologic findings of PPFE in a cohort of children to facilitate recognition and noninvasive diagnosis. MATERIALS AND METHODS: Clinical presentation, history of chemotherapy or radiation therapy, lung or bone marrow transplantation, and lung function testing and outcome were retrospectively extracted from the electronic medical records of eight children treated at our institution's pulmonary medicine clinic with histopathology confirmation of PPFE from 2008 to 2018. Two pediatric radiologists evaluated the chest imaging studies for the presence or absence of published radiologic findings of PPFE in adults, including platythorax, pneumothorax, upper lobe predominant pleural and septal thickening, and bronchiectasis. Platythorax indices were calculated from the normal chest CT exams of eight age- and gender-matched individuals obtained via the radiology search engine. RESULTS: The mean presentation age was 12.9 years (range: 7-16 years). Seven of the eight had a history of chemotherapy and radiation therapy for cancer. Three of the eight had undergone bone marrow transplantation and none had undergone lung transplantation. The mean time between chemotherapy, radiation therapy, and/or bone marrow transplantation and the presentation of PPFE was 8.4 years (range: 5.6-12.1 years). Most of the patients presented with dyspnea (63%), cough (50%) and/or pneumothorax (38%). The mean percentage of predicted FEV1 (forced expiratory volume in one second) was 14.1 (range: 7.7-27.5). All eight patients demonstrated platythorax, bronchiectasis, pleural and septal thickening (upper lobes in four, upper and lower lobes in four) and six had pneumothorax. Five underwent lung biopsies, four of whom developed pneumothoraces. CONCLUSION: Clinical and radiologic findings of pediatric PPFE are similar to those in adults, although a majority of the former have a history of treated cancer. Clinical presentation of restrictive lung disease, dyspnea, cough or spontaneous pneumothorax years after treatment for childhood cancer combined with platythorax, upper lobe pleural and septal thickening and traction bronchiectasis on chest CT establishes a presumptive diagnosis of PPFE.

Risk factors for infection after pediatric lung transplantation.

Although infection is the leading cause of death in the first year following pediatric lung transplantation, there are limited data on risk factors for early infection. Sepsis remains under-recognized and under-reported in the early post-operative period for lung transplant recipients (LTR). We evaluated the incidence of infection and sepsis, and identified risk factors for infection in the early post-operative period in pediatric LTRs. A retrospective review of medical records of LTRs at a large quaternary-care hospital from January 2009 to March 2016 was conducted. Microbiology results on days 0-7 after transplant were obtained. Sepsis was defined using the 2005 International Pediatric Consensus Conferencecriteria. Risk factors included history of recipient and donor infection, history of multi-drug resistant (MDR) infection, nutritional status, and surgical times. Among the 98 LTRs, there were 22 (22%) with post-operative infection. Prolonged donor ischemic time ≥7 hours, cardiopulmonary bypass(CPB) time ≥340 minutes, history of MDR infection and diagnosis of cystic fibrosis were significantly associated with infection. With multivariable regression analysis, only prolonged donor ischemic time remained significant (OR 4.4, 95% CI: 1.34-14.48). Further research is needed to determine whether processes to reduce donor ischemic time could result in decreased post-transplant morbidity.

Intermittent bolus feeding promotes greater lean growth than continuous feeding in a neonatal piglet model.

Background: Orogastric tube feeding is indicated in neonates with an impaired ability to ingest food normally and can be administered with an intermittent bolus or continuous feeding schedule. Objectives: The objectives were to 1) compare the long-term effect of continuous with intermittent feeding on growth using the newborn pig as a model, 2) determine whether feeding frequency alters lean tissue and fat mass gain, and 3) identify the signaling mechanisms by which protein deposition is controlled in skeletal muscle in response to feeding frequency. Design: Neonatal pigs were fed the same amount of a balanced formula by orogastric tube either as an intermittent bolus meal every 4 h (INT) or as a continuous infusion (CON). Body composition was assessed at the start and end of the study by dual-energy X-ray absorptiometry, and hormone and substrate profiles, muscle mass, protein synthesis, and indexes of nutrient and insulin signaling were measured after 21 d. Results: Body weight, lean mass, spine length, and skeletal muscle mass were greater in the INT group than in the CON group. Skeletal muscle fractional protein synthesis rates were greater in the INT group after a meal than in the CON group and were associated with higher circulating branched-chain amino acid and insulin concentrations. Skeletal muscle protein kinase B (PKB) and ribosomal protein S6 kinase phosphorylation and eukaryotic initiation factor (eIF) 4E-eIF4G complex formation were higher, whereas eIF2α phosphorylation was lower in the INT group than in the CON group, indicating enhanced activation of insulin and amino acid signaling to translation initiation. Conclusions: These results suggest that when neonates are fed the same amounts of nutrients as intermittent meals rather than continuously there is greater lean growth. This response can be ascribed, in part, to the pulsatile pattern of amino acids, insulin, or both induced by INT, which enables the responsiveness of anabolic pathways to feeding to be sustained chronically in skeletal muscle.

Viscera and muscle protein synthesis in neonatal pigs is increased more by intermittent bolus than by continuous feeding.

BACKGROUND: Continuous and intermittent bolus orogastric feedings are strategies used in infants unable to tolerate normal feeds. METHODS: To determine the effects of feeding modality on protein synthesis in different tissues, neonatal pigs received a balanced formula by orogastric tube as an intermittent bolus feed every 4 h or as a continuous infusion, or were fasted overnight. RESULTS: As compared with fasting, protein synthesis in gastrocnemius, masseter, and soleus muscles; left ventricle; liver; pancreas; jejunum; and kidney increased in bolus- and continuously fed pigs, but the greatest increase occurred after a bolus meal. Tuberous sclerosis complex (TSC2), the proline-rich AKT substrate of 40 kDa (PRAS40), eukaryotic initiation factor (eIF) 4E binding protein (4EBP1), and ribosomal protein S6 kinase 1 (S6K1) phosphorylation in all tissues, and the proportion of ribosomal protein S4 in liver polysomes were enhanced 90 min following the bolus meal but not immediately before the meal or during continuous feeding. Eukaryotic elongation factor 2 (eEF2) and eIF2α phosphorylation were unaffected by feeding. CONCLUSION: These results suggest that intermittent bolus feeding increases protein synthesis in muscles of different fiber types and visceral tissues to a greater extent than continuous feeding by stimulating translation initiation.

Enteral leucine supplementation increases protein synthesis in skeletal and cardiac muscles and visceral tissues of neonatal pigs through mTORC1-dependent pathways.

INTRODUCTION: Leucine (Leu) activates mammalian target of rapamycin (mTOR) to upregulate protein synthesis (PS). RESULTS: PS in skeletal muscles, heart, liver, pancreas, and jejunum, but not kidney, were greater in low protein supplemented with Leu (LP+L) than LP, but lower than high protein (HP). In longissimus dorsi muscle, protein kinase B phosphorylation was similar in LP and LP+L, but lower than HP. Although less than HP, p70 ribosomal S6 kinase 1 (S6K1) and eukaryotic initiation factor (eIF) 4E binding protein 1 (4EBP1) association with regulatory associated protein of mammalian target of rapamycin was greater in LP+L than LP, resulting in higher S6K1 and 4EBP1 phosphorylation. Feeding LP+L vs. LP decreased 4EBP1·eIF4E and increased eIF4E·eIF4G formation, but not to HP. Similar results were obtained for S6K1 and 4EBP1 phosphorylation in gastrocnemius, masseter, heart, liver, pancreas, and jejunum, but not kidney. eIF2α and elongation factor 2 phosphorylation was unaffected by treatment. DICUSSION: Our results suggest that enteral Leu supplementation of a low protein diet enhances PS in most tissues through mTOR complex 1 pathways. METHODS: To examine enteral Leu effects on PS and signaling activation, 5-d-old piglets were fed for 24 h diets containing: (i) LP, (ii) LP+L, or (iii) HP.

Anabolic signaling and protein deposition are enhanced by intermittent compared with continuous feeding in skeletal muscle of neonates.

Orogastric tube feeding is indicated for neonates with impaired ability to ingest and can be administered by intermittent bolus or continuous schedule. Our aim was to determine whether feeding modalities affect muscle protein deposition and to identify mechanisms involved. Neonatal pigs were overnight fasted (FAS) or fed the same amount of food continuously (CON) or intermittently (INT; 7 × 4 h meals) for 29 h. For 8 h, between hours 20 and 28, pigs were infused with [(2)H(5)]phenylalanine and [(2)H(2)]tyrosine, and amino acid (AA) net balances were measured across the hindquarters. Insulin, branched-chain AA, phenylalanine, and tyrosine arterial concentrations and whole body phenylalanine and tyrosine fluxes were greater for INT after the meal than for CON or FAS. The activation of signaling proteins leading to initiation of mRNA translation, including eukaryotic initiation factor (eIF)4E·eIF4G complex formation in muscle, was enhanced by INT compared with CON feeding or FAS. Signaling proteins of protein degradation were not affected by feeding modalities except for microtubule-associated protein light chain 3-II, which was highest in the FAS. Across the hindquarters, AA net removal increased for INT but not for CON or FAS, with protein deposition greater for INT. This was because protein synthesis increased following feeding for INT but remained unchanged for CON and FAS, whereas there was no change in protein degradation across any dietary treatment. These results suggest that muscle protein accretion in neonates is enhanced with intermittent bolus to a greater extent than continuous feeding, mainly by increased protein synthesis.

Development aggravates the severity of skeletal muscle catabolism induced by endotoxemia in neonatal pigs.

Accretion rates of muscle protein are elevated in normal neonates, but this anabolic drive decreases with maturation. As this change occurs, it is not known whether development also influences muscle protein catabolism induced by sepsis. We hypothesize that protein degradation in skeletal muscle induced by endotoxemia becomes more severe as the neonate develops. Fasted 7- and 26-day-old pigs were infused for 8 h with LPS (0 and 10 µg·kg(-1)·h(-1)), while plasma amino acids (AA), 3-methylhistidine (3-MH), and α-actin concentrations and muscle protein degradation signal activation were determined (n = 5-7/group/age). Plasma full-length α-actin was greater in 7- than 26-day-old pigs, suggesting a higher baseline protein turnover in neonatal pigs. LPS increased plasma total AA, 3-MH, and full-length and cleaved α-actin in 26- than in 7-day-old pigs. In muscle of both age groups, LPS increased AMPK and NF-κB phosphorylation, the abundances of activated caspase 3 and E-3 ligases MuRF1 and atrogin1, as well as the abundance of cleaved α-actin, suggesting activation of muscle proteolysis by endotoxin in muscle. LPS decreased Forkhead box 01 (Fox01) and Fox04 phosphorylation and increased procaspase 3 abundance in muscle of 26-day-old pigs despite the lack of effect of LPS on PKB phosphorylation. The results suggest that skeletal muscle in healthy neonatal pigs maintains high baseline degradation signal activation that cannot be enhanced by endotoxin, but as maturation advances, the effect of LPS on muscle protein catabolism manifests its severity.

Intermittent bolus feeding has a greater stimulatory effect on protein synthesis in skeletal muscle than continuous feeding in neonatal pigs.

Orogastric tube feeding, using either continuous or intermittent bolus delivery, is common in infants for whom normal feeding is contraindicated. To compare the impact of different feeding strategies on muscle protein synthesis, after withholding food overnight, neonatal pigs received a complete formula orally as a bolus feed every 4 h or were continuously fed. Protein synthesis rate and translational mechanisms in skeletal muscle were examined after 0, 24, and 25.5 h. Plasma amino acid and insulin concentrations increased minimally and remained constant in continuously fed compared to feed-deprived pigs; however, the pulsatile meal feeding pattern was mimicked in bolus-fed pigs. Muscle protein synthesis was stimulated by feeding and the greatest response occurred after a bolus meal. Bolus but not continuous feeds increased polysome aggregation, the phosphorylation of protein kinase B, tuberous sclerosis complex 2, proline-rich Akt substrate of 40 kDa, eukaryotic initiation factor (eIF) 4E binding protein (4EBP1), and rp S6 kinase and enhanced dissociation of the 4EBP1 ·eIF4E complex and formation of the eIF4E ·eIF4G complex compared to feed deprivation (P < 0.05). Activation of insulin receptor substrate-1, regulatory associated protein of mammalian target of rapamycin, AMP-activated protein kinase, eukaryotic elongation factor 2, and eIF2α phosphorylation were unaffected by either feeding modality. These results suggest that in neonates, intermittent bolus feeding enhances muscle protein synthesis to a greater extent than continuous feeding by eliciting a pulsatile pattern of amino acid- and insulin-induced translation initiation.

Differential regulation of protein synthesis and mTOR signaling in skeletal muscle and visceral tissues of neonatal pigs after a meal.

Protein synthesis (PS) increases after a meal in neonates, but the time course of the changes in PS in different tissues after a meal is unknown. We aimed to evaluate the changes in tissue PS, mammalian target of rapamycin complex 1 (mTORC1) activation, and proportion of ribosomal protein (rp) mRNAs in polysomes over 4 h after a bolus meal in neonatal pigs (n = 6/group; 5- to 7-d-old). The results show a more sustained increase in PS in glycolytic compared with mixed fiber type muscles and no changes in oxidative muscles. PS increased in liver, jejunum, and pancreas but not in kidney and heart. Feeding did not affect AMP-activated protein kinase or RAS-related GTP binding B activation. Phosphorylation of tuberous sclerosis complex 2, proline-rich Akt substrate of 40 kD, mTOR, eukaryotic initiation factor 4E binding protein, and rp S6 kinase 1 increased in all tissues after feeding. The proportion of mRNAs encoding rp S4 and S8 in liver polysomes increased within 30 min postfeeding. These results suggest that feeding stimulates mTORC1 signaling in muscle and viscera, but mTORC1 activation alone is not sufficient to stimulate PS in all tissues.

Sepsis and development impede muscle protein synthesis in neonatal pigs by different ribosomal mechanisms.

In muscle, sepsis reduces protein synthesis (MPS) by restraining translation in neonates and adults. Even though protein accretion decreases with development as neonatal MPS rapidly declines by maturation, the changes imposed by development on the sepsis-associated decrease in MPS have not been described. Pigs at 7 and 26 d of age were infused for 8 h with lipopolysaccharide (LPS, endotoxin, 0 and 10 µg · kg⁻¹ · h⁻¹). Fractional MPS rates and translation eukaryotic initiation factor (eIF) activation in muscle were examined (n = 5-7/group). The LPS-induced decrease in MPS was associated with reduced ribosomal and translational efficiency, whereas the age-induced decrease in MPS occurred by decreasing ribosome number. Abundances of mammalian target of rapamycin (mTOR) and S6 decreased, and that of the repressor eIF4E · 4E-binding protein 1 (4EBP1) association increased in 26-d-old pigs--compared with 7-d-old pigs. LPS decreased the abundance of the active eIF4E ·eIF4G association and the phosphorylation of eIF4G across ages, whereas the abundance of eIF4G declined and eIF2α phosphorylation increased with age. Therefore, when lacking anabolic stimulation, the decrease in MPS induced by LPS is associated with reduced ribosomal efficiency and decreased eIF4E ·eIF4G assembly, whereas that induced by development involves reduced ribosomal number, translation factor abundance, and increased eIF2α phosphorylation.

Differential effects of long-term leucine infusion on tissue protein synthesis in neonatal pigs.

Leucine is unique among the amino acids in its ability to promote protein synthesis by activating translation initiation via the mammalian target of rapamycin (mTOR) pathway. Previously, we showed that leucine infusion acutely stimulates protein synthesis in fast-twitch glycolytic muscle of neonatal pigs but this response cannot be maintained unless the leucine-induced fall in amino acids is prevented. To determine whether leucine can stimulate protein synthesis in muscles of different fiber types and in visceral tissues of the neonate in the long-term if baseline amino acid concentrations are maintained, overnight fasted neonatal pigs were infused for 24 h with saline, leucine (400 micromol kg(-1) h(-1)), or leucine with replacement amino acids to prevent the leucine-induced hypoaminoacidemia. Changes in the fractional rate of protein synthesis and activation of mTOR, as determined by eukaryotic initiation factor 4E binding protein (4E-BP1) and S6 kinase 1 (S6K1) phosphorylation, in the gastrocnemius and masseter muscles, heart, liver, jejunum, kidney, and pancreas were measured. Leucine increased mTOR activation in the gastrocnemius and masseter muscles, liver, and pancreas, in both the absence and presence of amino acid replacement. However, protein synthesis in these tissues was increased only when amino acids were infused to maintain baseline levels. There were no changes in mTOR signaling or protein synthesis in the other tissues we examined. Thus, long-term infusion of leucine stimulates mTOR signaling in skeletal muscle and some visceral tissues but the leucine-induced stimulation of protein synthesis in these tissues requires sustained amino acid availability.

Leucine supplementation of a low-protein meal increases skeletal muscle and visceral tissue protein synthesis in neonatal pigs by stimulating mTOR-dependent translation initiation.

Protein synthesis and eukaryotic initiation factor (eIF) activation are increased in skeletal muscle of neonatal pigs parenterally infused with amino acids. Leucine appears to be the most effective single amino acid to trigger these effects. To examine the response to enteral leucine supplementation, overnight food-deprived 5-d-old pigs were gavage fed at 0 and 60 min a: 1) low-protein diet (LP); 2) LP supplemented with leucine (LP+L) to equal leucine in the high-protein diet (HP); or 3) HP diet. Diets were isocaloric and equal in lactose. Fractional protein synthesis rates and translation initiation control mechanisms were examined in skeletal muscles and visceral tissues 90 min after feeding. Protein synthesis rates in longissimus dorsi, gastrocnemius, and masseter muscles, heart, jejunum, kidney, and pancreas, but not liver, were greater in the LP+L group compared with the LP group and did not differ from the HP group. Feeding LP+L and HP diets compared with the LP diet increased phosphorylation of mammalian target of rapamycin (mTOR), 4E-binding protein 1, ribosomal protein S6 kinase-1, and eIF4G and formation of the active eIF4E·eIF4G complex in longissimus dorsi muscle. In all tissues except liver, activation of mTOR effectors increased in pigs fed LP+L and HP vs. LP diets. Our results suggest that leucine supplementation of a low-protein meal stimulates protein synthesis in muscle and most visceral tissues to a rate similar to that achieved by feeding a high-protein meal and this stimulation involves activation of mTOR downstream effectors.