Effect of digestion and storage of human milk on free fatty acid concentration and cytotoxicity.
OBJECTIVE
Fat is digested in the intestine into free fatty acids (FFAs), which are detergents and therefore toxic to cells at micromolar concentration. The mucosal barrier protects cells in the adult intestine, but this barrier may not be fully developed in premature infants. Lipase-digested infant formula, but not fresh human milk, has elevated FFAs and is cytotoxic to intestinal cells, and therefore could contribute to intestinal injury in necrotizing enterocolitis (NEC), but even infants exclusively fed breast milk may develop NEC. Our objective was to determine whether stored milk and milk from donor milk (DM) banks could also become cytotoxic, especially after digestion.


METHODS
We exposed cultured rat intestinal epithelial cells or human neutrophils to DM and milk collected fresh and stored at 4°C or -20°C for up to 12 weeks and then treated for 2 hours (37°C) with 0.1 or 1 mg/mL pancreatic lipase and/or trypsin and chymotrypsin.


RESULTS
DM and milk stored 3 days (at 4°C or -20°C) and then digested were cytotoxic. Storage at -20°C for 8 and 12 weeks resulted in an additional increase in cytotoxicity. Protease digestion decreased, but did not eliminate cell death.


CONCLUSIONS
Present storage practices may allow milk to become cytotoxic and contribute to intestinal damage in NEC.
*Departments of Bioengineering †Pediatrics, University of California, San Diego, La Jolla ‡Department of Psychology, University of California, San Diego, La Jolla.
Alexander H
AH
Penn
Angelina E
AE
Altshuler
James W
JW
Small
Sharon F
SF
Taylor
Karen R
KR
Dobkins
Geert W
GW
Schmid-Schönbein
D000818:Animals; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D002918:Chymotrypsin / Q000378:metabolism; D004063:Digestion; D004847:Epithelial Cells; D005230:Fatty Acids, Nonesterified / Q000378:metabolism* / Q000494:pharmacology; D061353:Food Storage; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology; D008049:Lipase / Q000378:metabolism*; D017784:Milk Banks; D008895:Milk, Human / Q000737:chemistry / Q000378:metabolism*; D009504:Neutrophils; D051381:Rats; D013696:Temperature; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism
D005230:Fatty Acids, Nonesterified; D008049:Lipase; D002918:Chymotrypsin; D014357:Trypsin