A novel flavonoid C-glucoside from Ulmus wallichiana preserves bone mineral density, microarchitecture and biomechanical properties in the presence of glucocorticoid by promoting osteoblast survival: a comparative study with human parathyroid hormone

Abstract

Purpose: 6-C-β-D-glucopyranosyl-(2S,3S)-(+)-5,7,3',4'-tetrahydroxydihydroflavonol (GTDF) is a novel compound isolated from Ulmus wallichiana, reported to have bone anabolic action in ovariectomized rats. Here, we studied the effect of GTDF in glucocorticoid (GC)-induced bone loss and its mode of action.

Methods: Osteoblasts were cultured from rat calvaria or bone marrow to study apoptosis and differentiation by dexamethasone (Dex), methylprednisolone (MP), GTDF, quercetin and rutin. Female Sprague Dawley rats were treated with Dex or MP with or without GTDF or PTH. Efficacy was evaluated by bone microarchitecture using microcomputed tomography, determination of new bone formation by fluorescent labeling of bone and osteoblast apoptosis by co-labeling bone sections with Runx-2 and TUNEL. Serum osteocalcin was determined by ELISA.

Results: GTDF preserved trabecular and cortical bones in the presence of Dex and MP and mitigated the MP-mediated suppression of serum osteocalcin. Co-administration of GTDF to MP rats increased mineral apposition, bone formation rates, bone biomechanical strength, reduced osteoblast apoptosis and increased osteogenic differentiation of bone marrow stromal cells compared to MP group, suggesting in vivo osteogenic effect of GTDF. These effects of GTDF were to a great extent comparable to PTH. GTDF prevented GC-induced osteoblast apoptosis by inhibiting p53 expression and acetylation, and activation of AKT but did not influence transactivation of GC receptor (GR).

Conclusions: GTDF protects against GC-induced bone loss by promoting osteoblast survival through p53 inhibition and activation of AKT pathways but not as a GR antagonist. GTDF has the potential in the management of GC-induced osteopenia.

Keywords: 6-C-β-d-glucopyranosyl-(2S,3S)-(+)-5,7,3′,4′- tetrahydroxydihydroflavonol; AKT pathway; B.Ar; BFR/BS; BMD; BV/TV; Bone anabolic; Bone histomorphometry; Conn.D; Cs.Th; DA; Dex; Dox; GR; GTDF; Glucocorticoid-induced osteoporosis; MAR; MP; Quercetin; Runx-2; SMI; TFSP; TUNEL; Tb.N; Tb.pf; Tb.sp; Tb.th; bone and mineral density; bone forming rate/bone surface; bone volume/trabecular volume; connection density; cortical mean cross-sectional area; cortical thickness; degree of anisotropy; dexamethasone; doxorubicin; glucocorticoids receptor; methyl prednisolone; microcomputed tomography; mineral appositional rate; runt related transcription factor2; structure model index; terminal deoxynucleotidyl transferase dUTP nick end labeling; tibia-fibular separation point; trabecular number; trabecular pattern factor; trabecular separation; trabecular thickness; μCT.