Figure 2.

Intestinal microbiota affects iron metabolism. Microorganisms utilize various mechanisms to obtain different forms of iron (Fe³⁺, Fe²⁺, heme iron). Moreover, the microbiota reduces intestinal pH by producing essential amino acids or SCFAs to optimize dietary iron bioavailability, regulates the expression of hepcidin, transforms inorganic iron into organic forms to lower the toxicity of free iron and modulates the ferritin levels. The microbiota also activates the HO-1/CO pathway or NRF2/HO-1 to strengthen phagocytosis and increase macrophage processing of hemoglobin for iron release. SCFAs, Short-chain fatty acids; HO-1, heme oxygenase-1; CO, carbon monoxide; NRF2, Nuclear factor erythroid 2-related factor 2.