Lipases in Preterm Human Milk

Abstract

SummaryTerm human milk contains two lipases: Bile salt stimulated lipase (BSSL—this lipase also has bile salt stimulated esterolytic activity, BSSE) and lipoprotein lipase (LPL). We have measured the activity of these lipases in preterm (25–36 weeks' gestation) and term (37–40 weeks' gestation) human milk collected from the time of parturition until 3 months of lactation. BSSL levels are similar in preterm and term milk and do not vary significantly as a function of length of lactation. In the three groups of women who delivered at 26–30, 31–36, and 37–40 weeks of gestation, BSSL levels were 22.5 ± 6.6, 21.0 ± 3.6. and 32.3 ± 7.6 U/ml in colostrum and 26.3 ± 1 1.4, 31.1 ± 3.4, and 33.3 ± 10.7 U/ml in milk collected at 3 months of lactation, respectively. These observations suggest that preterm milk has the same fat digesting potential as term milk. BSSE activity decreased as a function of length of gestation and lactation, 61.2 ± 8.78, 44.4 ± 4.6, and 44.9 ± 13.3 U/ml in colostrum and 40.8 ± 5.0, 35.6 ± 9.5, and 23.3 ± 3.4 U/ml in milk collected after 3 months of lactation in the three groups studied. In all milks examined, the esterase lost its bile salt dependency upon storage at ‐ 10°C for periods of 2 weeks, suggesting that spontaneous hydrolysis of milk fat and accumulation of free fatty acids can occur in milk stored at ‐ 10°C. LPL activity increased as a function of length of gestation and lactation. LPL activity increased from 12.2 ± 3.3 U/ml in colostrum to 101.6 ± 12.6 U/ml in milk collected at 6 weeks of lactation from the preterm mothers and from 17.0 ± 9.7 U/ml in colostrum to 270 ± 15.5 U/ml in milk collected at 3 weeks of lactation from mothers of term infants. Our data suggest: (a) Milk secreted by women who deliver premature infants (26–36 weeks' gestation) has the same fat digesting potential as milk secreted by mothers of term infants, (b) The esterolytic component of the BSSL develops earlier than the lipolytic activity, (c) “Drip ” milk has higher LPL activity than milk pumped concomitantly from the other breast, suggesting that there is no relationship between mammary cell damage and LPL release, (d) Since BSSL and BSSE activities are 200− to 3,000‐fold higher in human milk than LPL activity, and since BSSE loses its bile salt dependency during storage at −10°C, the rise in free fatty acid levels in banked milks could be related to BSSE rather than to LPL.