Assessment of cell-signaling pathways in the regulation of mammalian target of rapamycin (mTOR) by amino acids in rat adipocytes.

Enhanced phosphorylation of the ribosomal protein s6 kinase, p70(s6k), and the translational repressor, 4E-BP1, are associated with either insulin-induced or amino acid-induced protein synthesis. Hyperphosphorylation of p70(s6k) and 4E-BP1 in response to insulin or amino acids is mediated through the mammalian target of rapamycin (mTOR). In several cell lines, mTOR or its downstream targets can be regulated by phosphatidylinositol (PI) 3-kinase; protein kinases A, B, and C; heterotrimeric G-proteins; a PD98059-sensitive kinase or calcium; as well as by amino acids. Regulation by amino acids appears to involve detection of levels of charged t-RNA or t-RNA synthetase activity and is sensitive to inhibition by amino acid alcohols. In the present article, however, we show that the rapamycin-sensitive regulation of 4E-BP1 and p70(s6k) in freshly isolated rat adipocytes is not inhibited by either L-leucinol or L-histidinol. This finding is in agreement with other recent studies from our laboratory suggesting that the mechanism by which amino acids regulate mTOR in freshly isolated adipocytes may be different than the mechanism found in a number of cell lines. Therefore we investigated the possible role of growth factor-regulated and G-protein-regulated signaling pathways in the rapamycin-sensitive, amino acid alcohol-insensitive actions of amino acids on 4E-BP1 phosphorylation. We found, in contrast to previously published results using 3T3-L1 adipocytes or other cell lines, that the increase in 4E-BP1 phosphorylation promoted by amino acids was insensitive to agents that regulate protein kinase A, mobilize calcium, or inhibit protein kinase C. Furthermore, amino acid-induced 4E-BP1 phosphorylation was not blocked by pertussis toxin nor was it mimicked by the G-protein agonists fluoroaluminate or MAS-7. However, amino acids failed to activate either PI 3-kinase, protein kinase B, or mitogen-activated protein kinase and failed to promote tyrosine phosphorylation of cellular proteins, similar to observations made using cell lines. In summary, amino acids appear to use an amino acid alcohol-insensitive mechanism to regulate mTOR in freshly isolated adipocytes. This mechanism is independent of cell-signaling pathways implicated in the regulation of mTOR or its downstream targets in other cells. Overall, our study emphasizes the need for caution when extending results obtained using established cell lines to the differentiated nondividing cells found in most tissues.

Resting energy expenditure and nitrogen balance in critically ill pediatric patients on mechanical ventilation.

Nutritional support is important in critically ill patients, with variable energy and nitrogen requirements (e.g., sepsis, trauma, postsurgical state) in this population. This study investigates how age, severity of illness, and mechanical ventilation are related to resting energy expenditure (REE) and nitrogen balance. Nineteen critically ill children (mean age, 8 +/- 6 [SD] y and range 0.4-17.0 y) receiving total parenteral nutrition (TPN) were enrolled. We used indirect calorimetry to measure REE. Expected energy requirements (EER) were obtained from Talbot tables. Pediatric Risk of Mortality (PRISM) and Therapeutic Intervention Scoring System (TISS) score were calculated. Total urinary nitrogen was measured using the Kjeldahl method. PRISM and TISS scores were 9 +/- 5 and 31 +/- 6 points, respectively. REE was 62 +/- 25 kcal.kg-1.d-1, EER was 42 +/- 11 kcal.kg-1. d-1, and caloric intake was 49 +/- 22 kcal.kg-1.d-1. Nitrogen intake was 279 +/- 125 mg.kg-1.d-1, total urinary nitrogen was 324 +/- 133 mg.kg-1.d-1, and nitrogen balance was -120 +/- 153 mg.kg-1.d-1. The protein requirement in this population was approximately 2.8 g.kg-1.d-1. These critically ill children were hypermetabolic, with REE 48% higher (20 kcal.kg-1.d-1) than expected. Nitrogen balance significantly correlated with caloric and protein intake, urinary nitrogen, and age, but not with severity of illness scores or ventilatory parameters.

Resting energy expenditure in children in a pediatric intensive care unit: comparison of Harris-Benedict and Talbot predictions with indirect calorimetry values.

The use of prediction equations has been recommended for calculating energy expenditure. We evaluated two equations that predict energy expenditure, each of which were corrected for two different stress factors, and compared the values obtained with those calculated by indirect calorimetry. The subjects were 55 critically ill children on mechanical ventilation. Basal metabolic rates were calculated with the Harris-Benedict and Talbot methods. Measured resting energy expenditure was 4.72 +/- 2.53 MJ/d. The average difference between measured resting energy expenditure and the Harris-Benedict prediction with a stress factor of 1.5 was -0.98 MJ/d, with an SD delta of 1.56 MJ/d and limits of agreement from -4.12 to 2.15; for a stress factor of 1.3 the average difference was -0.22 MJ/d, with an SD delta of 1.57 MJ/d and limits of agreement from -3.37 to 2.93. The average difference between measured resting energy expenditure and the Talbot prediction with a stress factor of 1.5 was -0.23 MJ/d, with an SD delta of 1.36 MJ/d and limits of agreement from -2.95 to 2.48; for a stress factor of 1.3, it was 0.42 MJ/d, with an SD delta of 1.24 MJ/d and limits of agreement from -2.04 to 2.92. These limits of agreement indicate large differences in energy expenditure between the measured value and the prediction estimated for some patients. Therefore, neither the Harris-Benedict nor the Talbot method will predict resting energy expenditure with acceptable precision for clinical use. Indirect calorimetry appears to be the only useful way of determining resting energy expenditure in these patients.

Resource consumption and the extent of futile care among patients in a pediatric intensive care unit setting.

OBJECTIVES: To estimate resource consumption and the extent of futile care among patients admitted to the pediatric intensive care unit (PICU). STUDY DESIGN: A prospective cohort study of 353 consecutive admissions followed for 1334 patient-days during the PICU stay at the Texas Children's Hospital in Houston, Texas. Participants were 353 children and adolescents who were hospitalized in the PICU during September and October 1993. Three broad operational definitions of futility were developed to capture the maximum extent of resource consumption related to medical futility. Definition 1 (imminent demise futility) was developed by an objective, validated, severity of illness measure (Pediatric Risk of Mortality Score) to identify patients with high mortality risks. Definition 2 (lethal condition futility) was used to identify patients in the PICU whose long-term survival was unlikely. Definition 3 (qualitative futility) was used to identify patients with high morbidity. Resource consumption was measured according to the number of patient-days in the PICU and the Therapeutic Intervention Scoring System. RESULTS: Twenty-three (6.5%) patients representing 36 (2.7%) patient-days met at least one of the definitions of medical futility for some of the days when they were in the PICU. None of the patient-days that met any of the definitions of medical futility were associated with high resource consumption compared with non-futile care patient-days. CONCLUSIONS: Despite our use of broad definitions of medical futility, relatively small amounts of resources were used in futile PICU care. This suggests that attempts to reduce resource consumption in the PICU by focusing on medical futility are unlikely to be successful.

Effects of availability of patient-related charges on practice patterns and cost containment in the pediatric intensive care unit.

OBJECTIVE: To investigate the effects of the availability of daily patient-related charges to healthcare providers on practice patterns and cost containment in the pediatric intensive care unit (ICU) setting. DESIGN: Prospective, nonrandomized, controlled trial. SETTING: Pediatric ICU. PATIENTS: All patients admitted to the pediatric ICU during the study period. This number included a prospective control group (n=325) and an intervention group (n=273). These 598 patients spent 2,274 patient days in the pediatric ICU. INTERVENTIONS: The daily itemized patient charges related to diagnostic studies ordered in the pediatric ICU were made available to healthcare providers during the intervention period of the study. MEASUREMENTS AND MAIN RESULTS: Information was collected prospectively on patients in the control group before the intervention period. This information included data on demographics, daily severity of illness measures, daily resource consumption, intensity of nursing and medical interventions, and daily patient-related charges. Outcome information on survival and length of pediatric ICU stay was also collected. The same data were collected prospectively during the intervention period of the study. Measurements on quality assurance and morbidity were made to ensure that there was no compromise in patient care. There were no significant differences in patient demographics and diagnoses between the control and intervention groups. There was a reduction in the average daily laboratory (16.7%), radiology (9.1%) computerized axial tomography (8.5%), and pharmacy (25.1%) charges in the intervention group as compared with controls. The decreases in laboratory and pharmacy charges were statistically significant (p<.0001). The decreases in laboratory and pharmacy charges remained significant even after adjustment for severity of illness. CONCLUSIONS: The availability of patient-related charges to healthcare providers can result in changes in practice patterns, producing a decrease of patient charges and an improvement in cost containment in the pediatric ICU.

Home negative pressure ventilation: report of 20 years of experience in patients with neuromuscular disease.

Twenty years of experience using negative pressure devices (NPD) at home to ventilate 40 patients with neuromuscular disease is presented. The purpose of the study was to determine the costs, complications, and clinical outcome of this form of respiratory support, and to ascertain the reasons for failure to institute effective negative pressure ventilation (NPV) in nine patients. Emerson tank respirators, used mainly to rest respiratory muscles at night, and intermittent positive pressure breathing machines were used by 98% of patients at an average equipment cost of +2,700 annually. Patients in whom NPV was initiated on an elective rather than emergent basis saved an average of +12,000 during their initial hospitalization. Life table analysis shows a five-year survival of 76%, and a 10-year survival of 61%. Complications were minor and occurred at an average rate of less than one per year per patient at home on NPV. Failure to achieve satisfactory NPV in nine patients was associated with age (six patients were younger than 3 years of age), or severe thoracocervical scoliosis, which prevented proper fitting of the NPD. For reasons of safety, economy, and quality of life, NPV at home is the preferred treatment for patients having neuromuscular disease who need respiratory assistance.