A Stable Isotope Study to Evaluate the Bioavailability of an Oat Protein-based Iron Delivery System

Iron (Fe) deficiency is the most common nutrient deficiency present worldwide. Alternative solutions are needed for better absorption due to drawbacks that are associated with gastrointestinal side effects from Fe salt supplements. Additionally, Fe is difficult to add as a fortificant to foods due to the organoleptic changes that it causes. Reducing the particle size of iron salts improves their absorption, and submicron-sized Fe compounds are a promising solution in food matrices, although their tendency to oxidize and rapidly aggregate in solution limits their use in fortification.

A novel β-lactoglobulin (BLG) fibrils-Fe compound for use in Fe fortification was developed from milk proteins, and its evaluation in both in vitro digestion and in vivo (rat) bioavailability studies has been reported. It was observed that the material's reducing effect, colloidal stability, improved sensory performance and high bioavailability, making it promising for nutritional applications.

In the current study, a similar strategy is used to isolate amyloid fibrils from a vegan and more sustainable source, namely, oat protein. The reducing ability of the amyloid fibrils on the Fe salt - FeCl3 in the presence of sodium ascorbate (SA) or sodium hydroxide (NaOH), both food grade reagents, has shown the formation of a mixture of Fe2+ and Fe3+ particles with no observed aggregation. A previous human study showed that Fe3+ ions from submicron-sized ferric phosphate had a similar fractional Fe absorption (FIA) compared to that of ferrous sulfate (FeSO4), the current standard of care. The amyloid fibril systems by milk protein as efficient carriers for iron fortification. The evaluation in vitro digestion and in vivo bioavailability showed that β-lactoglobulin (β-lg) fibrils by milk protein disappeared 4 hours after providing this amyloid-rich supplement in the intestinal tract immediately. Moreover, the brain section of the mice supplemented with β-lg amyloid fibril showed no amyloid plague after 1 month of feeding. The β-lactoglobulin (β- lg) fibrils and plant-based oat share the same structure in the amyloid by milk protein. From these results, fibrils by oat are understood to be safe for nutrition.

Additionally, a recent study showed the possibility to produce amyloid fibrils from oat in full analogy to those obtained by BLG. In the current study, the OAT fibril - Fe SA (Fe-oat 1) and OAT fibril - Fe NaOH (Fe-oat 2) will both be studied in vivo, alone are oat fibril powder add iron supplement is soluble in water and oat fibril powder add iron supplement is soluble in water in a food matrix (acai puree and honey) to assess their promise as Fe food fortificants.

This first in human study to short-term food safety assessment and adverse effect of the OAT fibril - Fe SA (Fe-oat 1), OAT fibril - Fe NaOH (Fe-oat 2) and in a food matrix to assess their promise as Fe food fortificants.

The study will be a single-center, prospective cross-over study in which each subject receives 6 test conditions. The study will be conducted at the Institute of Nutrition, Mahidol University, Nakhon Pathom, Thailand. The study has been approved by the Ethical Board of Mahidol University and will be registered at www.clinicaltrials.gov. All subjects will provide written informed consent before any study procedures take place. During the screening, about 2 weeks before the start of the study, women will be assessed for eligibility. The study procedures will be explained to them in detail in a local language and following obtaining informed consent, a venipuncture blood sample (6 mL) will be collected for the determination of hemoglobin (Hb), serum ferritin (SF), c-reactive protein (CRP), thalassemia and pregnancy. Weight will be measured to the nearest 0.1 kg and height to the nearest 0.5 cm, to calculate BMI. An interview will be conducted to assess other inclusion and exclusion criteria. Women will be invited to screen until 52 eligible women have been enrolled to participate in the study. Each subject will complete the six iron absorption studies in which they will receive supplemental iron doses of 4 mg iron from the six products: (i) Fe-oat 1 alone, (ii) Fe-oat 1 with 30 mL acai puree with honey, (iii) Fe-oat 2 alone, (iv) Fe-oat 2 with 30 mL acai puree with honey, (v) FeSO4 alone, (vi) FeSO4 with 30 mL acai puree and honey. Polyphenol content of the acai puree will be measured at the Human Nutrition Laboratory.

The experimental phase will last for 37 days. The first three labeled iron doses will be administered on days 1, 3 and 5 between 07:00 and 09:00 in the morning after an overnight fast. After the third intervention, there will be a wait period of 14 days to allow for incorporation of the labeled iron into erythrocytes. On day 19, 21 and 23, the fourth, fifth and sixth intervention products will be given to the participants. It will be made sure that the randomization of the intervention products is done in such a manner that no two interventions with the same stable isotope are given to participants in the same week. Products 1, 3, and 5 from the list will be given in one week, and 2, 4 and 6 in the second week. There will be three blood sampling points excluding the screening: a baseline sampling on Day 1, sampling on day 17 and a final sampling 14 days after the fourth intervention product, on day 37, the last day of the study. These venous blood samples will be collected to determine Hb, SF and CRF, and erythrocyte isotopic enrichment.

Women will be randomized for the intervention administration order using a Python code. The participants will consume the labeled interventional products in the form of a solution under supervision of the investigators with or without the acai puree depending on the intervention type for the day. After consuming the test products, participants will refrain from eating or drinking for 3 h.

The Fe-oat 1 and Fe-oat 2 solutions will be produced at ETH Zurich at the Laboratory of Food and Soft Materials with food grade or pharmacopoeia grade chemicals and using 57Fe or 58Fe enriched elemental iron powders (Chemgas, Boulogne, France), and considering Good Manufacturing Practice regulations. The SOP for the preparation of the Fe-oat 1 and 2 will be provided upon request. The labelled FeSO4 solutions will be prepared at the Human Nutrition Laboratory (HNL) from 54Fe enriched elemental iron powders (Chemgas, Boulogne, France). The iron powders will be dissolved at room temperature in 1.7 M sulfuric acid (1.21 ml/100 mg Fe) in 100 ml HDPE bottles (Semadeni, Ostermundingen, Switzerland) flushed with argon. The resulting solutions will be brought to a concentration of 4 mg Fe/g solution with sterile pure water. The solutions will be divided into 1 g portions in PFA vials. The vials will be flushed with argon, tightly closed and kept at 4-8°C until use. The reagents will be of European Pharmacopoeia reagent grade (sulfuric acid 95-97%, Sigma-Aldrich, Buchs, Switzerland; Aqua ad iniect. B. Braun, Kantonsapotheke Zürich).