27‐Hydroxycholesterol contributes to hypercholesterolemia‐associated aggravation of apical periodontitis in ovariectomized rats and raloxifene counteracts its action

Abstract Aim The influence of hypercholesterolemia on the development of apical periodontitis (AP) is inconclusive. Recent studies revealed that cholesterol metabolite 27‐hydoxycholesterol (27HC) can affect cellular responses to bacterial infections and oestrogen status and raloxifene may influence its action. Herein, we aimed to examine the impact of 27HC on production of inflammatory mediators by macrophages and the regulatory function of raloxifene. The contribution of 27HC to AP development and the therapeutic effect of raloxifene were evaluated in a rat model. Methods Murine macrophages J774 cells were used. The expression of inducible nitric oxide synthase (iNOS) was examined by Western blot. The concentrations of C‐C motif chemokine ligand (CCL) 2 and 27HC were assessed by enzyme‐linked immunosorbent assay. Colorimetric assay was used to evaluate cholesterol levels. Experimental AP was induced in ovariectomized (OVX) or un‐operated rats receiving high‐fat/high‐cholesterol diet (HFHCD) or normal diet (ND). Micro‐computed tomography and immunohistochemistry were employed to evaluate disease severity and the therapeutic effect of raloxifene. Results Cholesterol enhanced 27HC production in macrophages. 27HC induced iNOS and CCL2 synthesis by macrophages and estradiol suppressed the responses. In our animal model of AP, HFHCD plus OVX significantly augmented serum and lesion tissue levels of 27HC ( p < .05 versus the ND group). Lesion size, infiltration of CD68 + cells, and iNOS + monocytes were increased in parallel with 27HC accumulation. Raloxifene inhibited pro‐inflammatory effects of 27HC on macrophages and suppressed AP progression in HFHCD/OVX rats ( p < .05 versus the vehicle control group). Conclusions Our results suggested that 27HC contributes to AP aggravation associated with hypercholesterolemia. Oestrogen deficiency may both enhance 27HC production and exacerbate its downstream action.