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₁-Antitrypsin and antichymotrypsin in human milk: origin, concentrations, and stability^1,2,3

¹ From the Department of Nutrition, the University of California, Davis.

Background: The protease inhibitors ₁-antitrypsin and antichymotrypsin are present in human milk, but little is known about their roles in protein digestion during infancy. It has been hypothesized that ₁-antitrypsin and antichymotrypsin may modulate digestion in the infant gut.

Objective: We determined whether the mammary gland expresses ₁-antitrypsin and antichymotrypsin, measured ₁-antitrypsin and antichymotrypsin throughout lactation, assessed the resistance of ₁-antitrypsin to proteolysis, and determined the potential of ₁-antitrypsin to affect the survival of other milk proteins.

Design: A pool of complementary DNA from the human mammary gland was analyzed with polymerase chain reaction to detect genes for ₁-antitrypsin and antichymotrypsin. ₁-Antitrypsin and antichymotrypsin concentrations were measured in milk samples obtained longitudinally (days 4–47) from 8 women. An in vitro model of infant digestion was used to assess the digestive stability of ₁-antitrypsin against pepsin and pancreatin. Lactoferrin, with ₁-antitrypsin present, was digested by pancreatin, and the digested proteins were separated.

Results: ₁-Antitrypsin and antichymotrypsin concentrations were high in early milk and decreased throughout lactation. Polymerase chain reaction products were detected for both genes. After in vitro digestion, much of the ₁-antitrypsin was still intact, whereas many other milk proteins were digested. Much of the lactoferrin was still intact after digestion, but only when ₁-antitrypsin was added.

Conclusions: The results suggest that ₁-antitrypsin and antichymotrypsin are produced by the mammary gland and are present in milk in relatively high amounts in early lactation. ₁-Antitrypsin may survive digestion and may affect the survival of other proteins.

Key Words: ₁-Antitrypsin • antichymotrypsin • human milk • milk proteins • mammary gland • infant digestion • breast milk • protease inhibitors • breast-feeding

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