The impact of complexation or complex coacervation of lactoferrin and osteopontin on simulated infant gastrointestinal digestion, intestinal inflammation, and in vivo bone development

Lactoferrin (LF) and osteopontin (OPN) are bioactive milk proteins which can form heteroprotein complexes and complex coacervates. This research studied the effect of LF-OPN complexation and complex coacervation on the simulated infant gastrointestinal digestion of LF with subsequent examination of gut and bone health bioactivities in preclinical models. In an infant digestion model, the proteolytic profile of LF was unaltered by the pre-association of LF and OPN. Gastric proteolysis of LF was increased when the model gastric pH was reduced from 5.3 to 4.0, but less so when complexed with OPN. In a model of intestinal inflammation, undigested (79% inhibition) and gastric digestates (26% inhibition) of LF, but not gastrointestinal digestates, inhibited lipopolysaccharide (LPS)-induced NF-κB activation in intestinal epithelial cells. LF-OPN complexation sustained the inhibitory effect (21-43% of the undigested effect, depending on the type of complex) of LF after gastrointestinal digestion, suggesting that the peptides produced were different. In a neonatal rodent model used to study bone development, coacervating LF and OPN improved bone structures with a significant increase of trabecular proportion (BV/TV increase by 21.7%). This resulted in an 11.3% increase in stiffness of bones. Feeding the LF and OPN proteins in coacervate format also increased the levels of OPN, P1NP and M-CSF in blood, signifying a more pronounced impact on bone development. This research demonstrated that LF-OPN complexation and complex coacervation can delay simulated infant gastrointestinal digestion of LF and protect or improve the bioactivity of the proteins.