High Milk Lipase Activity Associated with Breast Milk Jaundice

Abstract

Summary: Human milk samples that inhibit bilirubin-UDP-glucuronyl transferase (UDPGT) activity in vitro have been associated with prolonged unconjugated hyperbilirubinemia in newborn infants. We measured the concentrations of nonesterified fatty acids (total and individual fatty acids), total fat and protein, and lipase activities (with and without bile salt stimulation) in milk samples from two groups of women. Women whose infants had prolonged unconjugated hyperbilirubinemia and whose milk inhibited the activity of UDPGT were in the first group (N = 9). Volunteers with healthy infants acted as controls. Inhibitory milk contained significantly more nonester?fied fatty acids (total, palmitic, and oleic) than did controls. Fat and protein concentrations and bile salt-stimulated lipase activities were similar in the two groups. Unstimulated lipase activity was higher in the inhibitory milks (11.9 ± 0.8 mM±min^-1±ml^-1) than in the controls (6.0 ± 0.2 mM±min^-1±ml^-1) (P ≤0.01). The specific activity (mM±min^-1±mg protein^-1) of unstimulated lipase was also significantly higher in the inhibitory milks (P ≤0.0001). The high nonesterified fatty acid levels in inhibitory milks is accounted for by the elevated unstimulated lipase activities. How these circumstances lead to jaundice in the infants remains to be shown. Speculation: The strong association between high unstimulated lipase activity in human milk and the syndrome of breast milk jaundice leads us to conclude that fat digestion and absorption may have an important efffect on the metabolism of bilirubin in newborn infants. Further studv of the influence of the digestive Drocess on the absorption aid further metabolism of dietaiy lipid ih neonates may help to illuminate the relationship between lipid metabolism and neonatal hyperbilirubinemia.