Impact of Iron-Enriched Aspergillus oryzae on Iron Bioavailability, Safety, and Gut Microbiota in Rats

Iron deficiency is a leading global nutritional problem. Ferrous sulfate (FeSO₄) is the most common iron source used for supplementation. Because of many side effects associated with its consumption, it is important to identify new forms of iron. The objectives of this study were to assess the bioavailability of iron-enriched Aspergillus oryzae, Aspiron (ASP), evaluate the toxicity of high-dose iron supplementation with ASP, and determine the ASP impact on gut microbiota in rats. In this study, we investigated iron bioavailability using the hemoglobin repletion test. Aspartate aminotransferase, alanine aminotransferase, and blood urea nitrogen levels were determined to evaluate the effect on liver and kidney functions. Protein carbonyls were measured to assess oxidative damage to proteins. Fecal samples at the end of the 14 day repletion period were used for 16S rRNA sequencing for gut microbiota analysis. The slope ratio method using a common intercept linear regression model was used to compare the bioavailability of ASP to FeSO₄. Iron repletion increased hemoglobin concentrations with both ASP and FeSO₄ treatments compared to the control group, except in the lowest ASP group. The slope ratio indicated that relative iron bioavailability of ASP was 60% of that of FeSO₄ when hemoglobin change was compared to iron in the diet. Similar results were obtained when absolute iron intake was compared on the basis of food consumption. In comparison to the control, protein carbonyl concentrations were significantly (p < 0.05) higher in the FeSO₄ group but not with the ASP group. Supplementation with both sources of iron reduced the Enterobacteriaceae population in the gut microbiota of the rats. A higher relative abundance of bacteria from the phylum Verrucomicrobia was also observed with the highest dose of ASP. Iron-enriched A. oryzae with 60% relative bioavailability of FeSO₄ did not show any signs of adverse effects after 14 days of iron supplementation. Future human studies are needed to understand the ASP detailed effect on gut microbiota.