Phosphorus Bioaccessibility Measured in Four Amino Acid–based Formulas Using In-Vitro Batch Digestion Translates Well into Phosphorus Bioavailability in Mice

Objective: The aim of this study was to quantify the bioaccessibility of phosphorus from amino acid-based formulas (AAFs) under different digestive conditions. Methods: We developed in-vitro batch digestion models with stomach digestion at different pH mimicking the normal digestive condition and conditions representing use of acid-suppressive medication. To validate bioaccessibility findings, we devised a low phosphorus murine model to test phosphorus bioavailability under compromised digestive conditions using proton pump inhibitors (PPIs) to neutralize stomach pH. Results: In vitro phosphorus bioaccessibility of AAFs Neocate (R) Infant and Neocate Junior ranged between 57% and 65% under normal digestive conditions for infants (stomach pH 3.5) and between 38% and 46% under conditions that simulated bypass of stomach acidification, which is comparable to control diet and two EleCare (R) AAFs. In vivo bioavailability analysis showed that both Neocate formulas were able to normalize plasma phosphorus levels when administered to low phosphorus mice along with PPIs (control diet + PPI 8 +/- 0.4; Neocate Infant 10.1 +/- 0.9; Neocate Junior 9.2 +/- 0.6; EleCare Infant 8.6 +/- 0.4; EleCare Junior 8.7 +/- 0.5; n = 8-10; P < 0.0001 versus baseline 3.4 +/- 0.2 mg/dL). In comparison, plasma phosphorus levels remained lower on the low phosphorus diet (5.7 +/- 0.2 mg/dL). Furthermore, urinary phosphorus/creatinine and intact fibroblast growth factor 23 were significantly lowered by low phosphorus diet. In contrast, intact parathyroid hormone and 1,25-dihydroxy vitamin D decreased and increased, respectively, and these parameters likewise normalized in mice administered AAFs. Conclusion: The present findings indicated that phosphorus bioaccessibility in the in-vitro batch digestion model translates well into phosphorus bioavailability in mice even under compromised digestive conditions that bypass gastric acidification. (C) 2021 The Author( s). Published by Elsevier Inc.