Presence of platelet-activating factor-acetylhydrolase in milk.
Human milk contains numerous factors such as immunoglobulins, lactoferrin, lysozyme, macrophages, etc., which serve an immunoprotective role. Platelet-activating factor (PAF) is one of the most proinflammatory agents thus far described. PAF is metabolized to the biologically inactive lysoPAF by the enzyme PAF-acetylhydrolase (PAF-AH). In the present study we have demonstrated that PAF-AH activity is present in human milk. The activity was associated with aqueous phase and was not stimulated by the addition of bile salts or Ca2+. The activity of PAF-AH in human milk was not affected by the addition of propranolol or NaCl. PAF, and 1-acyl-2-acetyl-glycerophosphocholine were the only substrates cleaved by the enzyme. Based on these properties it is concluded that the milk PAF-AH is not the lipoprotein or bile salt-stimulated lipase known to be present in milk. Inhibitor studies revealed that the enzyme in human milk was the plasma type PAF-AH. The activity of PAF-AH was stable at pH 4.0 at 37 degrees C and the activity varied in milk samples obtained from various species. The enzyme was secreted by milk macrophages. The presence of PAF-AH in human milk may explain, in part, the beneficial effects of breast feeding in the prevention of necrotizing enterocolitis by inactivating the potent proinflammatory autacoid, PAF.
Furukawa
M
M
Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas 75235-9051.
Narahara
H
H
Yasuda
K
K
Johnston
J M
JM
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D003600:Cytosol / Q000201:enzymology; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D006041:Goats; D006863:Hydrogen-Ion Concentration; D008264:Macrophages / Q000201:enzymology; D008892:Milk / Q000201:enzymology*; D008895:Milk, Human / Q000201:enzymology*; D010741:Phospholipases A / Q000032:analysis* / Q000502:physiology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D012965:Sodium Chloride / Q000494:pharmacology; D013045:Species Specificity
D001647:Bile Acids and Salts; D012965:Sodium Chloride; D004533:Egtazic Acid; D011433:Propranolol; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D002118:Calcium