α ₁-antitrypsin and antichymotrypsin in human milk: Origin, concentrations, and stability

Background: The protease inhibitors α 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 α ₁-antitrypsin and antichymotrypsin may modulate digestion in the infant gut. Objective: We determined whether the mammary gland expresses α ₁-antitrypsin and antichymotrypsin, measured α ₁-antitrypsin and antichymotrypsin throughout lactation, assessed the resistance of α ₁-antitrypsin to proteolysis, and determined the potential of α 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 α ₁-antitrypsin and antichymotrypsin. α 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 α ₁-antitrypsin against pepsin and pancreatin. Lactoferrin, with α ₁-antitrypsin present, was digested by pancreatin, and the digested proteins were separated. Results: α 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 α ₁-antitrypsin was still intact, whereas many other milk proteins were digested. Much of the lactoferrin was still intact after digestion, but only when α ₁-antitrypsin was added. Conclusions: The results suggest that α ₁-antitrypsin and antichymotrypsin are produced by the mammary gland and are present in milk in relatively high amounts in early lactation. α ₁-Antitrypsin may survive digestion and may affect the survival of other proteins.