Comparison of the effects of genistein and zoledronic acid on the bone loss in OPG-deficient mice.
Using osteoprotegerin (OPG)-knockout mice, we demonstrated that in vivo the effects of both genistein and 17beta-estradiol (E2) on bone metabolism were completely abolished. In contrast, zoledronic acid could effectively suppress bone resorption and prevent bone loss.


BACKGROUND
The anti-resorptive effects of E2 on bone metabolism are considered to be mediated via modulation of the osteoblast-derived paracrine factor OPG. Recently, the phytoestrogen genistein was found to suppress bone resorption by enhancing osteoblastic production of OPG. However, the mechanism underlying the in vivo effects of E2 and genistein on bone is not entirely understood, and a central question in this regard is whether E2 regulates bone metabolism via an OPG-dependent pathway.


METHODS
After mating heterozygous (OPG+/-) mice, homozygous (OPG-/-) and wild-type (WT) with a mixed C57BL/6J x 129/SV background were obtained. The study involved 6-week-old female OPG-/- (n=40) and WT mice (n=8). The OPG-/- mice were randomly divided into 5 groups (n=8 per group) as follows: (1) genistein-treated mice (Gen) that were subcutaneously injected with genistein at a maximal dose (0.8 mg/day); (2) E2-treated mice (E2) that were subcutaneously injected with E2 at a dose (0.03 microg/day); (3) DMSO control mice (DMSO) that were subcutaneously injected with a mixture of dimethylsulfoxide (DMSO) and polyethyleneglycol-300; (4) zoledronic acid-treated mice (Zol) that were subcutaneously injected with zoledronic acid at a dose of (150 microg/kg) twice per week; and (5) H2O control mice that were subcutaneously injected with sterilized water twice per week. The doses of genistein, estrogen and zoledronic acid were selected based on the results of dose-response effect of agents on bone versus uterus in OPG-/- mice. The mice were sacrificed 6 weeks after this intervention. The microarchitecture of the trabecular and cortical bone was assessed by performing microcomputed tomography (micro-CT) for the right proximal tibia. The bone mineral density (BMD) of the left femur was measured by dual-energy X-ray absorptiometry (DXA). The biomechanical parameters of the right femur were determined by a three-point bend testing. Serum levels of bone alkaline phosphatase (B-ALP), tartarate-resistant acid phosphatase-5b (TRACP-5b), and receptor activator of nuclear factor kappaB ligand (RANKL) were determined by performing ELISA.


RESULTS
DXA analysis revealed that the total BMD of the femur was not significantly altered in the Gen, E2, H2O, and DMSO groups. The three-point bending test revealed no significant differences in the biomechanical parameters, including ultimate loading, ultimate stress, stiff index, and elastic modulus, and micro-CT analysis revealed that the microarchitectural parameters of the trabecular bone (vBMD, tBMD, BVF, BSF, SMI, Tb.N, Conn.D, Tb.Sp, and Tb.Th) and cortical bone (Ct.Th, Mm, In.Pm, Ot.Pm, Ma.Ar, Ct.Ar, Tt.Ar, Ct.BMD, and Ct.BMC) did not differ among the groups. Genistein and E2 treatment did not alter the serum TRACP-5b, B-ALP, or RANKL levels. However, in addition to increasing the bone mass, zoledronic acid could effectively improve biomechanical parameters and could completely prevent deterioration of the bone architecture in the OPG-/- mice.


CONCLUSIONS
The effects of genistein and E2 on bone metabolism in vivo were lost completely in OPG-deficient mice, suggesting that the effect of these agents on bone metabolism seems to be entirely dependent on OPG. In contrast, zoledronic acid could effectively suppress bone resorption and completely prevent the bone loss in the OPG-/- mice--an effect that is likely to be independent of the OPG pathway.
Liu
Jianghua
J
Institute of Metabolism and Endocrinology, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, PR China.
Xu
Kang
K
Wen
Gebo
G
Guo
Hui
H
Li
San
S
Wu
Xianping
X
Dai
Ruchun
R
Sheng
Zhifeng
Z
Liao
Eryuan
E
D000135:Acid Phosphatase / Q000097:blood; D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D001696:Biomechanical Phenomena; D001835:Body Weight / Q000187:drug effects; D015519:Bone Density / Q000187:drug effects; D016723:Bone Remodeling / Q000187:drug effects; D001862:Bone Resorption / Q000097:blood / Q000188:drug therapy* / Q000235:genetics; D004164:Diphosphonates / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004717:Endometrium / Q000187:drug effects / Q000473:pathology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005269:Femur / Q000737:chemistry / Q000187:drug effects; D019833:Genistein / Q000494:pharmacology*; D005838:Genotype; D007093:Imidazoles / Q000494:pharmacology*; D007527:Isoenzymes / Q000097:blood; D008099:Liver / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D053244:Osteoprotegerin / Q000235:genetics* / Q000378:metabolism; D053245:RANK Ligand / Q000097:blood; D000071681:Tartrate-Resistant Acid Phosphatase; D013977:Tibia / Q000187:drug effects / Q000473:pathology; D014599:Uterus / Q000187:drug effects / Q000473:pathology; D000077211:Zoledronic Acid
D004164:Diphosphonates; D007093:Imidazoles; D007527:Isoenzymes; D053244:Osteoprotegerin; D053245:RANK Ligand; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; D004958:Estradiol; D000077211:Zoledronic Acid; D019833:Genistein; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase