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Protein turnover, lipolysis, and endogenous hormonal secretion in critically ill children
Paola E Cogo1, Virgilio P Carnielli, Federica Rosso
1Department of Pediatrics, Azienda Ospedaliera of Padova, Italy. paolac@child.pedi.unipd.it
Insights
Protein turnover, not lipid metabolism, correlates with critical illness severity in infants. This finding links protein breakdown to longer intensive care unit stays and specific biomarkers like prealbumin and retinol-binding protein (RBP).
Area of Science:
- Metabolic research in critical care
- Endocrinology of critical illness
- Pediatric intensive care
Background:
- The catabolic state significantly contributes to critical illness morbidity and mortality.
- Endocrine changes are implicated in the catabolic state of critically ill patients.
Purpose of the Study:
- To investigate the correlation between protein and lipid turnover and plasma levels of key hormones in critically ill infants.
- To understand the metabolic and endocrine adaptations during critical illness in pediatric patients.
Main Methods:
- A prospective clinical study was conducted in a pediatric intensive care unit.
- Protein and lipid turnover were measured using stable isotope infusions (13C-palmitic acid, 2H3-leucine, 2H5-glycerol).
- Hormone levels (insulin, growth hormone, thyroid hormones) and serum proteins (albumin, RBP, prealbumin) were simultaneously measured.
Main Results:
- Protein turnover positively correlated with pediatric intensive care unit (PICU) admission duration, prealbumin, and retinol-binding protein (RBP) levels.
- Insulin-like growth factor binding protein (IGFBP)-2 was elevated, and IGFBP-3 was reduced in critically ill children compared to recovery.
- Lipid turnover did not correlate with hormone levels or illness duration; serum albumin was significantly lower in sick children.
Conclusions:
- Protein turnover, unlike lipolysis, is associated with the persistence of critical illness.
- Biomarkers such as prealbumin, RBP, and IGFBP-1 are linked to protein turnover in critically ill infants.
Objectives:
The catabolic state is a major contributor to morbidity and mortality of critical illness and may be related to endocrine changes. We studied whether protein and lipid turnover correlate with insulin and growth and thyroid hormone plasma levels in critically ill infants.
Design:
Prospective clinical study.
Setting:
Pediatric intensive care unit.
Patients:
Twelve critically ill children and ten age-matched controls.
Measurements:
We measured lipolysis and protein turnover by infusing albumin-bound uniformly 13C palmitic acid and 2H3-leucine for 3 hrs and 2H5-glycerol for 5 hrs to critically ill infants. Simultaneously, we measured serum growth hormones, insulin, C-peptide, thyroid-stimulating hormone, T4, T3, albumin, retinol binding protein (RBP), and prealbumin. Hormone and serum protein levels were also measured in six children when recovered from critical illness. Ten healthy age-matched children served as controls for hormone serum levels comparison.
Results:
Palmitic acid and glycerol turnover were 5.6 +/- 2.2 micromol/kg/min and 12.2 +/- 7.3 micromol/kg/min, respectively, whereas alpha-ketoisocaproic turnover was 4.9 +/- 2.8 micromol/kg/min. Alpha-ketoisocaproic turnover positively correlated (R = 0.7, p = .03) with duration of pediatric intensive care unit admission and with prealbumin and RBP serum levels (R = 0.9, p = .001). Insulin-like growth factor binding protein (IGFBP)-2 was significantly higher and IGFBP-3 was significantly lower in critically ill children (p = .03 and p = .04 vs. recovery phase, respectively). No other hormonal differences were found. Serum albumin was significantly lower in sick children. We found a significant correlation between prealbumin and RBP and IGFBP-3 (R = 0.6, p = 0.03 and R = 0.6, p = .04, respectively). Alpha-ketoisocaproic turnover positively correlated with IGFBP-1 (R = 0.79, p = .01) and did not correlate with insulin-like growth factor I (R = -0.5, p = .15 [not significant]) No other correlations were found. Lipid turnover measurements did not correlate with any endogenous hormone levels or with duration of critical illness.
Conclusion:
Protein turnover but not lipolysis correlated with a persisting critically ill condition, serum prealbumin, RBP, and plasma IGFBP-1.