To explore the effect of Auricularia auricula melanin on the physiology and intestinal flora of mice with iron deficiency anemia (IDA).

A total of 45 male Kunming mice aged 24 days were randomly divided into two groups: control (15 animals) and model (30 animals). The control group was given a normal diet and deionized water. The model group was given a low-iron diet and ultrapure water for two weeks to induce IDA, and then was randomly divided into two groups with 15 animals each: IDA and IDA-M. The IDA and IDA-M groups were given the low-iron diet and ultrapure water and gavaged with 0.2 mL of A. auricula melanin solution at a dose of 200 mg/(kg m_b·d) and an equal volume of ultrapure water for another three weeks, respectively. The mice in all groups were weighed every week. At the end of the experiment, routine blood test was carried out and the composition of the intestinal flora in each group of mice were measured by high-throughput sequencing.

After two weeks of feeding, the body mass of mice in the model group decreased significantly compared with that of the mice in the control group (P < 0.05). After three weeks of intervention with melanin, compared with the IDA group, the body mass of the mice in the IDA-M group increased significantly (P < 0.05), and the anemia symptoms such as leukocyte count, erythrocyte count, hemoglobin concentration, hematocrit and mean corpuscular volume returned to the normal level, suggesting that A. auricula melanin alleviates IDA. IDA could cause intestinal flora disorder and significantly change the diversity indices of the intestinal flora (Shannon, Chao1, Ace and Simpson index) (P < 0.05). Compared with the IDA group, the diversity indies and the overall structure of the intestinal flora in the IDA-M group were significantly improved (P < 0.05). At the phylum level, the relative abundance of Bacteroidetes and Proteobacteria decreased significantly, the relative abundance of Firmicutes and Verrucomicrobia increased significantly, and all of them returned to the normal level. At the genus level, A. auricula melanin increased the relative abundance of the dominant bacteria, significantly increased the relative abundance of the beneficial bacteria Alistipes and Akkermansia (P < 0.05) and decreased the relative abundance of the pathogenic bacteria Parabacteroides and Bacteroides (P < 0.05).

A. auricula melanin can alleviate the symptoms of IDA in mice by increasing body mass and improving routine blood indices, and it can also increase the diversity of the intestinal flora and the relative abundance of the dominant microflora and beneficial bacteria, and decrease the relative abundance of pathogenic bacteria.

To explore the protective mechanism of Auricularia auricula melanin (AAM) on iron deficiency anemia (IDA) induced ulcerative colitis (UC) in mice.

Forty-five Kunming male mice were randomly divided into blank control group, model group, and AAM group (n = 15 each). The mice from all groups except the blank control one were provided with a low-iron diet to establish an IDA-induced UC model. After two weeks, AAM was administered by gavage to the mice from the AAM group for three weeks, whereas those from the model group continued receiving the low-iron diet. The effects of AAM on anemia indexes, colonic inflammation characteristics, oxidative stress, inflammatory factor expression levels and inflammatory signaling pathways in UC mice were evaluated.

Compared with the model group, the symptoms of anemia in the AAM group were alleviated. The body mass returned to the normal level, and the colonic pathological score was significantly reduced (P < 0.0001). In addition, the total antioxidant capacity (TAC) and superoxide dismutase (SOD) activity in the colon of mice from the AAM group were significantly enhanced compared with the model group (P < 0.0001), and the levels of malondialdehyde (MDA), hydroxyl radical (·OH), and superoxide anion radical (O₂^-·) were significantly decreased (P < 0.0001, P < 0.01, P < 0.001), indicating that AAM could enhance antioxidant capacity and attenuate oxidative damage in mice. Further mechanistic studies showed that intervention with AAM significantly regulated protein expression associated with Toll-like receptors-4/nuclear factor-kappa B (TLR4/NF-κB) signaling pathway, significantly down-regulated the gene expression of the pro-inflammatory cytokine tumor necrosis factor (TNF-α) (P < 0.01), and significantly increased the gene expression level of the anti-inflammatory cytokine interleukin-10 (IL-10) (P < 0.05).

Auricularia auricula melanin may regulate oxidative stress and inhibit the TLR4/NF-κB signaling pathway, thereby reducing intestinal mucosal ulcer, oxidative stress injury and inflammatory cell infiltration in colon tissue, and finally alleviating IDA-induced UC in mice.