Protective Effect of Curcumin on Bone Trauma in a Rat Model via Expansion of Myeloid Derived Suppressor Cells

Abstract

BACKGROUND Bone fracture, a common injury to bones leads to various biophysiological changes and pathological responses in the body. The current study investigated curcumin for treatment of bone fracture in a rat model of bone trauma, and evaluated the related mechanism. MATERIAL AND METHODS The rats were separated randomly into 3 groups; sham, model, and curcumin treatment groups. The fracture rat model was established by transverse osteotomy in the right femur bone at the mid-shaft. The osteoblast count was determined using hematoxylin and eosin staining. Vascular endothelial growth factor (VEGF) and proliferating cell nuclear antigen (PCNA) expression were measured by western blotting. RESULTS The rpS6-phosphorylation was suppressed and light chain 3 (LC3II) expression elevated in the curcumin treated group of the fracture rat model. In the curcumin-treated group, mineralization of fracture calluses was markedly higher on day 14 of fracture. The formation of osteoblasts was observed at a greater rate in the curcumin treated group compared to the model rat group. Treatment of rats with curcumin significantly (P<0.05) promoted expression of PCNA and VEGF. The decrease in CD11b+/Gr-1+ cell expansion in rats with bone trauma was alleviated significantly by curcumin treatment. A marked increase in arginase-1 expression in rats with bone trauma was caused by curcumin treatment. CONCLUSIONS In summary, curcumin activates autophagy and inhibits mTOR activation in bone tissues of rats with trauma. The curcumin promoted myeloid-derived suppressor cell (MDSC) proliferation and increased expansion of MDSCs in a rat model of trauma. Therefore, curcumin may have beneficial effect in patients with bone trauma and should be evaluated further for development of treatment.

Figure 1

(A, B) Effect of curcumin on rpS6-phosphorylation in fracture rat model. The rat calluses from curcumin treated or untreated groups were collected on day 14, 28, and 42 after fracture. Immunohistochemical analysis was performed for detection of rpS6-phosphorylation. * P<0.05, ** P<0.02 versus model (control) group. Magnification, 200×.

Figure 2

(A, B) Effect of curcumin on LC3-II expression in fracture rat model. The rat calluses from curcumin treated or untreated groups were collected on day 14, 28, and 42 after fracture. The LC3-II expression in the bone tissues was detected using immunofluorescence. * P<0.05, ** P<0.02 versus model (control) group. Magnification, 200×.

Figure 3

Effect of curcumin on fracture repair in rats. The callus mineralization as well as size in fracture rat model was observed on day 14, 28, and 42 of fracture using x-ray imaging. * P<0.05, ** P<0.02 versus model (control) group.

Figure 4

Effect of curcumin on osteoblast proliferation. The callus sections of sham, model, and curcumin treatment groups were analyzed for osteoblast proliferation on day 14, 28, and 42 after fracture using hematoxylin and eosin dyes. * P<0.05, ** P<0.02 versus model (control) group.

Figure 5

Curcumin promotes PCNA and VEGF expression. (A) The PCNA and VEGF levels in calluses of rats were assessed by western blotting on day 14, 28, and 42 post fractures. (B) The quantification of PCNA and VEGF levels was made taking GAPDH as loading control. * P<0.05, ** P<0.02 versus model (control) group. PCNA – proliferating cell nuclear antigen; VEGF – vascular endothelial growth factor; GAPHD – glyceraldehyde 3-phosphate dehydrogenase.

Figure 6

Effect of curcumin on expansion of CD11b+/Gr1+ cells. The rats with bone trauma were treated with curcumin or left untreated. The expansion of CD11b+/Gr1+ cells to (A) spleen, (B) bone marrow, and (C) blood was detected by flow cytometry. * P<0.5 and ** P<0.02 versus model (control).

Figure 7

Effect of curcumin on expression of arginase-1 in Gr-1+ cells. The rats were treated with curcumin immediately following trauma. (A) The expression of arginase-1 was measured by western blotting. (B) Quantification of western blotting data. * P<0.05 and ** P<0.02 versus model (control).