Hydroxyapatite-coated titanium oxide ameliorates dextran sulphate sodium-induced colitis by attenuating both innate and acquired immune reaction

Introduction
Titanium oxide (TiO2) is a widely used oxidizer for environmental management. The power of TiO2 has been demonstrated by its photocatalytic activity. Hydroxyapatite (HA)-coated TiO2 (HA-TiO2) was used to test the in vivo effect on dextran sulphate sodium (DSS)-induced colitis in mice.

Material and methods
Mice were monitored for body weight and then sacrificed on the seventh day, and the colon length was measured. Their faeces were analysed for intestinal microbiota distribution, and colon tissue was subjected to histological examination and immunohistochemical analysis.

Results
Weight loss was significantly lower in HA-TiO2-fed mice than in mice without HA-TiO2. The colon length in the DSS colitis-induced mice was shortened, but HA-TiO2 feeding lessened this effect. Histological and immunohistochemical analyses of the colon revealed that macrophages and CD4+CD8+ T cells were observed in the colitis-occurring site, indicating the involvement of innate and acquired immunity in determining the degree of DSS-induced colitis. Intestinal microbiota analysis in faeces revealed changes in the distribution of multiple bacterial species after DSS colitis induction, and the increase/decrease of 2 Clostridium (sub)clusters moved in response to the colitis phenomenon. All the described effects of HA-TiO2 were photocatalytic activity-dependent because mice that were kept in the dark showed similar results to those treated with DSS alone without HA-TiO2.

Conclusions
HA-coated TiO2 ameliorated DSS-induced colitis through photocatalytic activity, while HA-TiO2 diminished the changes in intestinal microbiota and immune reactions caused by DSS.