Effects of Protein-Derived Amino Acid Modification Products Present in Infant Formula on Metabolic Function, Oxidative Stress, and Intestinal Permeability in Cell Models
Proteins present in infant formulas
are modified by oxidation and glycation during processing. Modified
amino acid residues released from proteins may be absorbed in the
gastrointestinal tract, and pose a health risk to infants. In this
study, the markers of glycation furosine (1.7–3.5 μg
per milligram of protein) and Nε-(carboxymethyl)lysine (28–81 ng per milligram of protein)
were quantitated in infant formulas. The effects of these species,
and other amino acid modifications, at the levels detected in infant
formulas, on 3T3-L1 (murine preadipocyte) and Caco-2 (human intestinal
epithelial) cells were assessed. Incubation of 3T3-L1 cells for 48
h with amino acid side chain oxidation and glycation products (1 and
10 μM) resulted in a loss (up to 40%, p <
0.05) of cell thiols and decreased metabolic activity compared with
those of the controls. In contrast, Caco-2 cells showed a stimulation
(10–50%, p < 0.05) of cellular metabolism
on exposure to these products for 24 or 48 h. A 28% (p < 0.05) increase in protein carbonyls was detected upon incubation
with 200 μM modified amino acids for 48 h, although no alteration
in transepithelial electrical resistance was detected. Oxidation products
were detected in the basolateral compartments of Caco-2 monolayers
when modified amino acids were applied to the apical side, consistent
with limited permeability (up to 3.4%) across the monolayer. These
data indicate that modified amino acids present in infant formulas
can induce effects on different cell types, with evidence of bioavailability
and induction of cellular stress. This may lead to potential health
risks for infants consistently exposed to high levels of infant formulas