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Lipoprotein lipase, hepatic lipase, and carnitine in premature infants
L M Rovamo1, E A Nikkilä, K O Raivio
1Children's Hospital, University of Helsinki, Finland.
Insights
Preterm infants show higher lipoprotein lipase activity than adults, suggesting low activity doesn't explain slow fat elimination. Carnitine levels and excretion patterns differ significantly in preterm infants, especially those small for gestational age.
Area of Science:
- Biochemistry
- Neonatology
- Pediatrics
Background:
- Preterm infants exhibit unique metabolic profiles compared to term infants and adults.
- Understanding lipid metabolism and carnitine homeostasis is crucial for neonatal care.
Purpose of the Study:
- To investigate lipoprotein lipase and hepatic lipase activity in preterm infants.
- To assess carnitine concentrations and excretion in relation to gestational age and birth weight.
- To determine factors influencing fat elimination in preterm neonates.
Main Methods:
- Studied 26 preterm infants at 2, 7, and 26 days of age.
- Measured plasma lipoprotein lipase and hepatic lipase activity post-heparin administration.
- Quantified serum and urinary carnitine concentrations.
Main Results:
- Lipoprotein lipase activity was higher in preterm infants (especially appropriate weight for gestational age) than in very low birth weight or small for gestational age infants.
- Preterm infants had lower serum carnitine than term infants.
- Urinary carnitine excretion increased with age and was higher in small for gestational age infants, with a lower acyl/free carnitine ratio.
Conclusions:
- Low lipoprotein lipase activity is unlikely to explain the slow fat elimination observed in preterm infants (<32 weeks gestation).
- Carnitine metabolism is significantly altered in preterm infants, particularly those who are small for gestational age.
- Further research is needed to fully elucidate fat metabolism and carnitine regulation in neonates.
Abstract:
Twenty six preterm infants were studied at the age of 2, 7, and 26 days. The activities of lipoprotein and hepatic lipase in plasma taken 15 minutes after a heparin bolus of 100 IU/kg had been given and the concentrations of carnitine in serum and urine were measured. The mean gestational age was 31 weeks (range 26-35 weeks) and birth weight 1580 g (range 840-2280 g). Thirteen infants weighed under 1500 g at birth (very low birth weight), 20 were of appropriate weight for gestational age and six were small for gestational age. Lipoprotein lipase activity was higher in the preterm infants of appropriate weight than in the infants of very low birth weight and those who were small for gestational age. At the age of 2 or 7 days the activity of lipoprotein lipase in the preterm infants (mean (SEM) 46.2 (4.3) mumol free fatty acid/ml/hour) was, however, higher than in term infants and adults. Multivariate regression analyses showed that weight and relative birth weight together explained 58% of the variance of lipoprotein lipase activity but only 3% of the variance of hepatic lipase activity. Serum carnitine concentration was lower in the preterm infants than in term infants. Urinary excretion of carnitine increased progressively with age but was independent of serum concentration and carnitine intake. Urinary excretion of total carnitine was significantly greater in the infants who were small for gestational age (mean (SEM) 754 (203) nmol/mg of creatinine, n = 6) than in the infants of appropriate weight (161 (22.0) nmol/mg of creatinine, n = 12) but acyl/free carnitine ratio was smaller in the infants who were small for gestational age than in infants of appropriate weight (0.56 v 5.5). The results indicate that the slow elimination of fat from the circulation in preterm infants less mature than 32 weeks of gestation can hardly be explained by low lipoprotein lipase activity.