α1-antitrypsin and antichymotrypsin in human milk: Origin, concentrations, and stability

Abstract

Background: The protease inhibitors α1-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 α1-antitrypsin and antichymotrypsin may modulate digestion in the infant gut. Objective: We determined whether the mammary gland expresses α1-antitrypsin and antichymotrypsin, measured α1-antitrypsin and antichymotrypsin throughout lactation, assessed the resistance of α1-antitrypsin to proteolysis, and determined the potential of α1-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 α1-antitrypsin and antichymotrypsin. α1-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 α1-antitrypsin against pepsin and pancreatin. Lactoferrin, with α1-antitrypsin present, was digested by pancreatin, and the digested proteins were separated. Results: α1-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 α1-antitrypsin was still intact, whereas many other milk proteins were digested. Much of the lactoferrin was still intact after digestion, but only when α1-antitrypsin was added. Conclusions: The results suggest that α1-antitrypsin and antichymotrypsin are produced by the mammary gland and are present in milk in relatively high amounts in early lactation. α1-Antitrypsin may survive digestion and may affect the survival of other proteins.