Bone Metabolic Disease Animal Models: Modeling Methods and Experimental Evaluation
Bone Metabolic Disease Animal Models: Modeling Methods and Experimental Evaluation
Bone metabolism is a dynamic process involving continuous coordination among bone formation, bone resorption, and mineralization, thereby maintaining the stability of bone mass, bone microarchitecture, and mechanical properties. Estrogen deficiency, long-term glucocorticoid exposure, aging, reduced mechanical loading, and abnormalities in calcium and phosphorus metabolism can all disrupt the balance of bone remodeling, leading to bone loss, deterioration of bone microarchitecture, or impaired mineralization and giving rise to different types of metabolic bone diseases.
Keywords: metabolic bone disease; osteoporosis; animal model; bone remodeling; Micro-CT; osteogenesis; osteoclast; histology
1 Bone Metabolic Imbalance and Major Diseases
1.1 Bone Formation, Bone Resorption, and Mineralization
Bone remodeling is jointly accomplished by osteoclast-mediated resorption of old bone and osteoblast-mediated formation of new bone. The RANKL–RANK–NFATc1 axis participates in osteoclast differentiation. Mature osteoclasts dissolve hydroxyapatite through local acidification and degrade organic bone matrix such as type I collagen using proteases including CTSK. During osteogenesis, RUNX2 and SP7 participate in osteogenic lineage differentiation, ALPL is associated with establishment of the mineralization environment, COL1A1 reflects formation of the organic bone matrix, and OCN more closely corresponds to the mature osteoblast state. Osteocytes participate in regulation of bone formation and bone resorption through mechanosensing and signaling pathways such as SOST/Wnt and RANKL.
Bone mineralization occurs after osteoid formation and requires an appropriate balance of Ca²⁺, inorganic phosphate, and pyrophosphate. Insufficient bone formation, enhanced bone resorption, and mineralization defects can occur independently or simultaneously and constitute the major pathological basis of different metabolic bone diseases.
1.2 Major Metabolic Bone Diseases
Postmenopausal osteoporosis is mainly associated with estrogen deficiency and increased bone turnover; glucocorticoid-induced osteoporosis is characterized more prominently by suppression of osteogenesis; senile osteoporosis involves reduced osteogenic potential, cellular senescence, and alterations in the bone marrow microenvironment; and disuse osteoporosis mainly results from sustained reduction in mechanical loading. The core feature of osteomalacia is insufficient mineralization of osteoid, whereas chronic kidney disease–mineral and bone disorder (CKD-MBD) involves systemic abnormalities of renal function, phosphate metabolism, PTH, FGF23, and the vitamin D axis.
Table 1 Pathological Characteristics of Common Metabolic Bone Diseases
Disease Type | Major Pathological Basis | Typical Bone Phenotype |
Postmenopausal osteoporosis | Estrogen deficiency, increased bone turnover | Rapid trabecular bone loss |
Glucocorticoid-induced osteoporosis | Suppressed osteogenesis, abnormal bone turnover | Reduced bone mass and bone strength |
Senile osteoporosis | Reduced osteogenic potential, cellular senescence | Trabecular and cortical bone degeneration |
Disuse osteoporosis | Reduced mechanical loading | Bone loss in weight-bearing bones |
Osteomalacia | Impaired osteoid mineralization | Increased unmineralized osteoid |
CKD-MBD | Abnormal mineral metabolism and endocrine regulation | Abnormal bone turnover and mineralization |
2 Postmenopausal Osteoporosis and the OVX Model
2.1 Disease Mechanism
Estrogen deficiency can alter the RANKL/OPG balance in bone marrow and on bone surfaces, enhance osteoclast formation and bone resorption, and simultaneously affect osteoblast and osteocyte functions. Trabecular bone-rich regions such as the distal femur, proximal tibia, and vertebral bodies usually show early reductions in trabecular number and connectivity together with increased trabecular separation.
2.2 Ovariectomy Modeling
(1) Model Establishment
Ovariectomy (OVX) is generally performed in sexually mature female rats or mice. Bilateral ovariectomy is conducted under anesthesia to establish persistent estrogen deficiency. Both dorsal and ventral surgical approaches can be used, but animal age, surgical route, and postoperative treatment conditions should be standardized within the same experiment.
(2) Control Setting
The sham-operated group receives the same anesthesia, incision, and exposure of the ovarian region while retaining the ovaries, thereby controlling for the effects of surgical trauma, anesthesia, and postoperative stress on bone metabolism.
(3) Model Determination
Uterine atrophy or reduced circulating estrogen can confirm loss of ovarian function, whereas the osteoporotic phenotype should also be evaluated using Micro-CT parameters such as BV/TV, Tb.N, and Tb.Sp together with TRAP, CTSK, or other bone-turnover indicators. Structural changes in bone are important evidence that the OVX model has established a stable bone-loss phenotype.
3 Glucocorticoid-Induced Osteoporosis Model
3.1 Disease Mechanism
Persistent glucocorticoid exposure can suppress differentiation of osteogenic precursor cells, mature osteoblast function, and bone-matrix synthesis, while also affecting osteocyte survival and the bone marrow microenvironment. During long-term exposure, insufficient bone formation and abnormal bone turnover are generally more prominent, distinguishing this model from the high-turnover phenotype of the OVX model.
3.2 Drug-Induced Modeling
(1) Modeling Method
Glucocorticoids such as prednisone, prednisolone, or dexamethasone can be administered by continuous oral dosing, repeated administration, or sustained-release approaches to establish chronic exposure. Drug type, dose, route of administration, and treatment duration should be determined according to animal species, age, and the intended bone phenotype.
(2) Experimental Control
Animal strain, sex, and age can influence glucocorticoid sensitivity. Control groups should receive the corresponding vehicle or blank treatment, while basal diet, activity environment, and husbandry conditions should remain consistent.
(3) Model Determination
Micro-CT is used to confirm changes in bone mass and microarchitecture, while RUNX2, ALPL, COL1A1, OCN, and dynamic bone-formation indicators are used to evaluate the extent of osteogenic impairment. Reduced bone mass accompanied by decreased osteogenic indicators and relatively limited changes on the osteoclast side is more consistent with the low-bone-formation phenotype after sustained glucocorticoid exposure.
4 Aging and Disuse Osteoporosis Models
4.1 Natural Aging Model
The natural aging model directly uses rats or mice that have reached the target age, with young adult animals serving as age controls and without additional drug or surgical induction. Aging can simultaneously reduce osteogenic potential of mesenchymal stromal cells, increase bone marrow adiposity, promote osteocyte senescence, and induce chronic inflammatory changes, while both trabecular and cortical bone may undergo degeneration. Experimental strain, sex, age, and husbandry conditions should be strictly controlled to reduce interindividual variability among aged animals.
4.2 Hindlimb Unloading Model
(1) Tail Suspension
Tail suspension keeps the hindlimbs of rodents in a continuous non-weight-bearing state, reducing mechanical stimulation of the femur and tibia while preserving basic forelimb activity. This model is suitable for simulating bone loss associated with microgravity, prolonged bed rest, or sustained immobilization.
(2) Bone Metabolic Changes
Reduced mechanical stimulation can enhance SOST-related inhibition, suppress Wnt-mediated osteogenic signaling, and may be accompanied by increased bone resorption. Trabecular BV/TV, Tb.N, Tb.Sp, cortical thickness, and SOST/Wnt-related indicators can be used to evaluate model changes.
4.3 Immobilization and Denervation Models
Limb immobilization creates a local disuse state by restricting joint motion and weight bearing and can simultaneously cause muscle atrophy. Denervation models such as sciatic nerve transection additionally involve neural injury and muscle disuse and are therefore more suitable for studies of nerve–muscle–bone interactions. In addition to bone structure, muscle mass or functional changes can also be evaluated simultaneously in these models.
5 Osteomalacia and CKD-MBD Models
5.1 Vitamin D Deficiency and Low-Phosphate Models
(1) Vitamin D Deficiency
Continuous feeding of a vitamin D-deficient diet can impair intestinal calcium and phosphorus absorption and systemic mineral homeostasis and, in severe cases, result in insufficient osteoid mineralization. Model evaluation should combine Ca, P, PTH, and vitamin D-related indicators with assessment of unmineralized osteoid and mineralization status.
(2) Low-Phosphate Model
A low-phosphate diet induces hypophosphatemic mineralization defects by limiting the inorganic phosphate required for bone mineralization. Serum phosphate, unmineralized osteoid, mineral apposition rate, and bone mechanics can reflect the severity of mineralization defects more effectively than BMD alone.
5.2 5/6 Nephrectomy Model
The 5/6 nephrectomy model establishes chronic renal dysfunction by markedly reducing the number of functional nephrons. A staged surgical procedure is commonly used, in which part of one kidney is first removed or its functional tissue is reduced, followed by removal of the contralateral kidney. Evaluation includes serum creatinine, blood urea nitrogen, P, Ca, PTH, FGF23, and bone histomorphology to determine whether renal dysfunction has subsequently caused abnormalities in mineral and bone metabolism.
5.3 Adenine and High-Phosphate Diet Models
Continuous administration of adenine-containing feed can cause tubulointerstitial renal injury and chronic renal dysfunction. Combination with a high-phosphate diet can further aggravate hyperphosphatemia and abnormalities of the PTH/FGF23 axis and is suitable for CKD-MBD research. Model determination should simultaneously confirm renal function, mineral metabolism, and bone-tissue phenotypes.
Table 2 Common Metabolic Bone Diseases and Modeling Methods
Disease | Common Model | Major Modeling Method | Major Simulated Process |
Postmenopausal osteoporosis | OVX model | Bilateral ovariectomy | Estrogen deficiency |
Glucocorticoid-induced osteoporosis | GIOP model | Continuous glucocorticoid administration | Suppression of osteogenesis and abnormal bone turnover |
Senile osteoporosis | Natural aging model | Natural aging to the target age | Aging-related bone-remodeling imbalance |
Disuse osteoporosis | Hindlimb unloading model | Tail suspension | Reduced mechanical loading |
Disuse osteoporosis | Immobilization/denervation model | Limb immobilization, sciatic nerve transection | Local disuse |
Osteomalacia | Vitamin D deficiency model | Vitamin D-deficient diet | Calcium/phosphate metabolism and mineralization defects |
Osteomalacia | Low-phosphate model | Low-phosphate diet | Insufficient mineralization substrate |
CKD-MBD | 5/6 nephrectomy model | Reduction in functional nephron mass | Chronic renal dysfunction |
CKD-MBD | Adenine model | Adenine diet, optionally combined with high phosphate | Renal injury and abnormal mineral metabolism |
6 Experimental Evaluation of Bone Metabolic Models
6.1 Micro-CT and Bone Microarchitecture
(1) Trabecular Bone
BV/TV reflects the proportion of bone tissue volume within the ROI, while Tb.N, Tb.Th, and Tb.Sp represent trabecular number, thickness, and separation, respectively. Combined analysis of multiple parameters can determine whether bone loss primarily results from reduced trabecular number, thinning, or increased separation.
(2) Cortical Bone
Ct.Th, cortical bone area, and cross-sectional geometric parameters can be used to evaluate cortical bone changes. Different models affect trabecular and cortical bone with different temporal patterns, so the analysis site and ROI should be predefined during experimental design.
(3) Detection Sequence
Micro-CT depends on X-ray attenuation differences generated by bone mineral and should therefore be performed before decalcification. Scanned samples can subsequently be used for histology, or the left and right bones can be allocated to different assays at the time of tissue collection.
6.2 Histology and Dynamic Bone Formation
(1) HE and TRAP
HE staining is used to observe morphological changes in trabecular bone, bone marrow cavities, cell distribution, and bone marrow adiposity. TRAP histochemistry is used to localize mature osteoclasts on bone surfaces and can quantify the number of TRAP-positive multinucleated cells, osteoclast surface, or positive area.
(2) Dynamic Bone Formation
Calcium-binding fluorescent labels can mark mineralization fronts at different time points, and dynamic bone-formation parameters such as mineral apposition rate can be calculated from the distance between fluorescent labels. This assay requires undecalcified bone tissue.
6.3 Serum Bone Turnover and Bone Mechanics
P1NP, bone-specific ALP, and OCN can reflect systemic bone-formation status, whereas CTX-I and TRAP5b are used to evaluate bone resorption. Serum indicators are suitable for longitudinal monitoring and can be analyzed together with terminal Micro-CT and histological results.
Changes in bone mass do not fully represent bone strength. Long bones can be evaluated using three-point bending to measure parameters such as maximum load and stiffness, whereas vertebral bodies can be assessed by compression testing. These methods are suitable for functional evaluation in glucocorticoid-induced osteoporosis, aging, mineralization disorders, and related models.
7 Bone Tissue Collection and Decalcification
7.1 Micro-CT and Sample Allocation
Bone tissue is often simultaneously used for Micro-CT, decalcified histology, undecalcified histomorphometry, protein detection, and electron microscopy. The intended use of left and right bones or different bone segments should be determined during tissue collection to avoid loss of mineral information caused by decalcification or interference with protein and antigen detection caused by fixation procedures.
7.2 Acid and EDTA Decalcification
(1) Acid Decalcification
Acidic systems such as formic acid achieve decalcification by promoting dissolution of bone mineral. They act relatively rapidly and are suitable for routine paraffin histology. Excessive treatment time can affect nuclear staining, tissue structure, and some protein antigens.
(2) EDTA Decalcification
EDTA gradually removes the mineral phase by chelating Ca²⁺ and is relatively gentle on tissue morphology and some protein antigens. It is more suitable for bone-tissue IHC requiring detection of antigens such as RUNX2, OCN, RANKL, and CTSK.
(3) Other Decalcification Methods
Citrate-based systems can balance tissue softening and morphological preservation. Electrolytic decalcification uses an electric field to promote Ca²⁺ migration and can improve processing efficiency, but current, temperature, and treatment time must be controlled.
7.3 IHC, Undecalcified Sections, and Electron Microscopy Samples
(1) IHC
Both fixation and decalcification can affect antigen epitopes. Antigen retrieval can improve some epitope masking caused by fixation-induced crosslinking but cannot restore target proteins that have already undergone irreversible damage during decalcification.
(2) Undecalcified Sections
Studies of dynamic bone formation, mineralization fronts, and material–bone interfaces require complete preservation of the mineral phase and should therefore use undecalcified embedding and sectioning. Samples that have undergone EDTA or acid decalcification are unsuitable for dynamic histomorphometric measurements such as mineral apposition rate.
(3) Electron Microscopy
Electron microscopy is mainly used to observe ultrastructural features such as bone-cell membranes, mitochondria, organelles, and bone-matrix interfaces and is sensitive to fixation and decalcification damage. Samples should be allocated independently and processed using conditions compatible with electron microscopy fixation, dehydration, and resin embedding.
7.4 Decalcification Endpoint and Post-Treatment
Insufficient decalcification can cause knife marks, section tearing, and local tissue loss, whereas excessive decalcification can affect nuclear staining, tissue structure, and antigen preservation. Comparative experiments should standardize tissue size, decalcification-solution volume, treatment conditions, and endpoint determination methods. After acidic decalcification, samples should undergo sufficient washing, neutralization, or corresponding post-treatment according to the specific system used.
8 Products Related to Animal Models of Metabolic Bone Diseases
8.1 Products Related to Model Establishment and Mechanistic Research
Catalog # | Product Name | Grade & Purity | Mechanism | Research Application |
β-Estradiol | Analytical standard, Moligand™, ≥99.5% | Activates ERα/ERβ and regulates osteogenesis, osteoclast activity, and the RANKL/OPG balance | Quantitative analysis of β-estradiol, methodological controls, and estrogen-related analytical research | |
Dexamethasone | BioReagent, for cell culture, Moligand™, ≥97%, powder | Activates the glucocorticoid receptor; sustained exposure can suppress osteogenesis and matrix formation | Glucocorticoid-related bone-metabolism and osteogenesis-inhibition studies | |
Alendronate sodium trihydrate | 10mM in Water | Inhibits FPPS and protein isoprenylation, reducing osteoclast-mediated bone-resorption function | Antiresorptive mechanism studies and osteoporosis intervention controls | |
Odanacatib (MK-0822) | Moligand™, ≥98% | Selectively inhibits CTSK and reduces osteoclast-mediated collagen-matrix degradation | CTSK-dependent bone-resorption and osteoclast-function studies | |
Recombinant Human RANK/TNFRSF11A Protein | Animal Free, Carrier Free, Bioactive, ActiBioPure™, High Performance, His Tag, Fc Tag, ≥95%(SDS-PAGE) | RANK mediates RANKL-induced NF-κB, MAPK, and NFATc1 signaling | RANKL–RANK binding and osteoclast-differentiation mechanism studies |
8.2 Products Related to Osteogenesis, Osteoclast Activity, and Bone-Turnover Detection
Catalog # | Product Name | Grade & Purity | Mechanism/Detection Principle | Research Application |
Recombinant RUNX2 Antibody | Recombinant, ExactAb™, Validated, See COA | Specifically recognizes RUNX2 to detect proteins associated with early osteogenic differentiation | Evaluation of RUNX2 expression and tissue localization | |
ALPL Mouse mAb | KD Validation | Specifically recognizes ALPL, which participates in bone-matrix mineralization | Detection of proteins related to osteogenic differentiation and mineralization | |
Alkaline Phosphatase (ALP) Activity Assay Kit (DPP, Colorimetric Method) | BioReagent | Detects ALP activity, reflecting osteogenic differentiation and mineralization preparation | ALP activity detection and osteogenesis-related evaluation in tissue and cellular samples | |
Tartrate Resistant Acid Phosphatase (TRAP) Activity Assay Kit (pNPP, Micro Method) | BioReagent | Detects TRAP activity, reflecting osteoclast differentiation and maturation | TRAP activity detection and evaluation of osteoclast differentiation and maturation | |
Alizarin Red S Staining Solution (0.2%) | BioReagent, Biological Stain, for microscopy, 0.2% | Binds calcium salts to visualize calcium deposition in mineralized matrix | Evaluation of osteoblast mineralized nodules and matrix mineralization | |
Calcium Staining Solution (Alizarin Red S Method) | BioReagent, Biological Stain, for microscopy | Binds tissue calcium salts to visualize mineralized regions | Observation of tissue calcium deposition and abnormal mineralization | |
Mouse Osteocalcin (BGP/OCN) ELISA Kit | BioReagent | Quantitatively detects OCN, reflecting mature osteoblasts and later-stage bone formation | Evaluation of bone formation and bone turnover in mice | |
Rat N-terminal Mid-segment Osteocalcin(N-MID-OT) ELISA Kit | BioReagent | Quantitatively detects N-MID osteocalcin, reflecting bone formation and bone-turnover status | Evaluation of bone formation in rat bone-metabolism models | |
Mouse Type Ⅰ collagen (ColⅠ) ELISA Kit | BioReagent | Quantitatively detects type I collagen, reflecting formation of the organic bone matrix | Evaluation of bone-matrix synthesis in mice | |
Rat Procollagen Ⅰ (PCⅠ) ELISA Kit | BioReagent | Detects type I procollagen, reflecting newly synthesized collagen | Evaluation of bone-matrix formation in rats | |
Mouse Runt Related Transcription Factor 2 (RUNX2) ELISA Kit | BioReagent | Quantitatively detects RUNX2, reflecting early osteogenic differentiation status | Evaluation of osteogenic programs in mice |
8.3 Products Related to Bone-Tissue Decalcification and Sample Pretreatment
Catalog # | Product Name | Grade & Purity | Principle | Research Application |
JYBL-ⅠDecalcifying Solution | BioReagent | Removes mineral components from calcified tissue to soften hard tissue | Bone-tissue decalcification, paraffin embedding, and histological section preparation | |
Rapid EDTA Decalcifying Solution (For Immunohistochemistry) | Suitable for Immunohistochemistry(IHC), BioReagent | EDTA chelates Ca²⁺ to remove the mineral phase while relatively preserving antigens | Bone-tissue decalcification before IHC | |
Rapid Decalcifying Solution (for Histopathology) | BioReagent | Rapidly removes tissue mineral components and reduces bone hardness | Routine bone histopathology sectioning and morphological observation | |
Citrate Decalcifying Solution | BioReagent | Promotes removal of the mineral phase through acidification and calcium-ion complexation | Decalcification requiring a balance between tissue softening and morphological preservation | |
Formic Acid Decalcifying Solution | BioReagent | Promotes bone mineral removal through acidic dissolution | Routine bone-tissue decalcification and paraffin section preparation | |
Decalcification Endpoint Detection Kit (Chemical Method) | BioReagent | Determines the extent of calcium-ion removal during decalcification through a chemical reaction | Control of the decalcification endpoint to reduce insufficient or excessive decalcification | |
EDTA Antigen Retrieval Solution (50X) | BioReagent, sterile-filtered, Suitable for Immunohistochemistry(IHC), sterile, 50X | Heat-induced retrieval improves some antigen-epitope masking caused by fixation | Antigen retrieval before IHC of decalcified paraffin sections |
Metabolic bone diseases involve abnormalities in bone resorption, bone formation, mechanical responses, and mineralization, and different animal models therefore correspond to distinct pathological mechanisms and evaluation priorities. Appropriate selection of modeling methods combined with integrated assessment of bone microarchitecture, bone turnover, tissue morphology, and bone mechanics can more accurately distinguish enhanced bone resorption, insufficient bone formation, and mineralization defects while reducing the influence of sample pretreatment on result interpretation.