Erythropoietin Mediated Bone Loss in Mice Is Dose-Dependent and Mostly Irreversible

Effects of Erythropoietin-Promoted Fracture Healing on Bone Turnover Markers in Cats

In orthopaedics, erythropoietin (EPO) is applied in the preoperative management of anaemic patients, but also as a stimulating factor to assist bone regeneration due to its angiogenic and osteoinductive potential. Since orthopaedists mainly rely on their clinical experience to assess bone healing, additional and more objective methods such as studying the dynamics of bone markers are needed. Therefore, the aim of this study was to investigate the plasma activity of bone-specific alkaline phosphatase (BALP), the N-terminal propeptide of type I collagen (PINP), the C-terminal telopeptide of type I collagen (CTX), and deoxypyridinoline (DPD) during the first 2 months of healing of comminuted fractures in cats, either non-stimulated or locally stimulated with recombinant human erythropoietin (rhEPO). The study included twelve cats of mixed breeds, aged 7.2 ± 4 months, weighing 2.11 ± 1.1 kg, with comminuted diaphyseal fractures of the femur. Surgical treatment with plate osteosynthesis was performed in all animals. The cats were randomly divided into two groups-a control (n = 6) and an EPO group (n = 6). The locally applied EPO leads to the increased activity of bone formation markers (BALP and PINP) during the second week after the osteosynthesis, preceding the peaks in the control group by two weeks. The studied bone resorption markers (DPD, CTX) varied insignificantly during the studied period. In conclusion, erythropoietin could serve as a promoter of bone healing in comminuted fractures in cats.

Erythropoietin Receptor (EPOR) Signaling in the Osteoclast Lineage Contributes to EPO-Induced Bone Loss in Mice

Erythropoietin (EPO) is a pleiotropic cytokine that classically drives erythropoiesis but can also induce bone loss by decreasing bone formation and increasing resorption. Deletion of the EPO receptor (EPOR) on osteoblasts or B cells partially mitigates the skeletal effects of EPO, thereby implicating a contribution by EPOR on other cell lineages. This study was designed to define the role of monocyte EPOR in EPO-mediated bone loss, by using two mouse lines with conditional deletion of EPOR in the monocytic lineage. Low-dose EPO attenuated the reduction in bone volume (BV/TV) in Cx3cr1^Cre EPOR^f/f female mice (27.05%) compared to controls (39.26%), but the difference was not statistically significant. To validate these findings, we increased the EPO dose in LysM^Cre model mice, a model more commonly used to target preosteoclasts. There was a significant reduction in both the increase in the proportion of bone marrow preosteoclasts (CD115⁺) observed following high-dose EPO administration and the resulting bone loss in LysM^Cre EPOR^f/f female mice (44.46% reduction in BV/TV) as compared to controls (77.28%), without interference with the erythropoietic activity. Our data suggest that EPOR in the monocytic lineage is at least partially responsible for driving the effect of EPO on bone mass.

Hypobaric hypoxia deteriorates bone mass and strength in mice

Mountaineers at high altitude are at increased risk of acute mountain sickness as well as high altitude pulmonary and cerebral edema. A densitometric study in mountaineers has suggested that expeditions at high altitude decrease bone mineral density. Surprisingly, the in vivo skeletal effects of hypobaric hypoxia are largely unknown, and have not been studied using advanced contemporary methods to assess bone microstructure. Eighty-four 22-week-old female mice were divided into seven groups with 12 mice in each group: 1. Baseline; 2. Normobaric, 4 weeks; 3. Hypobaric hypoxia, 4 weeks; 4. Normobaric, 8 weeks; 5. Hypobaric hypoxia, 8 weeks; 6. Normobaric, 12 weeks; and 7. Hypobaric hypoxia, 12 weeks. Hypobaric hypoxia mice were housed in hypobaric chambers at an ambient pressure of 500 mbar (5500 m altitude), while normobaric mice were housed at sea level atmospheric pressure for 4, 8, or 12 weeks, respectively. Hypobaric hypoxia had a profound impact on femoral cortical bone and L4 trabecular bone, while the effect on femoral trabecular bone was less pronounced. Hypobaric hypoxia reduced the bone strength of the femoral mid-diaphysis and L4 at all time-points. At femoral cortical bone, hypobaric hypoxia reduced bone formation through fewer mineralizing surfaces and lower bone formation rate after 2 weeks. In addition, bone strength decreased, and C-terminal telopeptide of type I collagen (CTX-I) increased independently of the duration of exposure to simulated high altitude. At L4, hypobaric hypoxia resulted in a substantial reduction in bone volume fraction, trabecular thickness, and trabecular number after 4 weeks of exposure. Hypobaric hypoxia reduced bone strength and femoral bone mass, while femoral trabecular bone was much less affected, indicating the skeletal response to hypobaric hypoxia differ between cortical and trabecular bone. These findings provide initial preclinical support for future clinical studies in mountaineers to assess bone status and bone strength after exposure to prolonged high altitude exposure.

Association Between Hemoglobin Levels and Osteoporosis in Chinese Patients with Type 2 Diabetes Mellitus: A Cross-Sectional Study

PURPOSE

To explore the relationship between hemoglobin levels and osteoporosis and the risk factors for osteoporosis in patients with type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

A cross-sectional study was conducted in 495 T2DM adults. Medical data were collected from electronic medical records.

RESULTS

T2DM patients with osteoporosis had significant lower hemoglobin levels (P < 0.001). Spearman correlation analysis and logistic regression analysis showed that age, female, body mass index (BMI), smoking, drinking and hemoglobin levels were significantly associated with osteoporosis in T2DM patients (all P < 0.05). After adjustment for BMI, diabetic duration, estimated glomerular filtration rate (eGFR), smoking and drinking, a significant association between hemoglobin levels and osteoporosis was observed in T2DM males aged 50 years and older (odds ratio [OR] = 0.978, 95% confidence interval [CI]: 0.958-0.998, P = 0.030). Compared to Q3 groups with normal hemoglobin levels, Q1 groups with anemia had an odd of osteoporosis increased 2.9-fold in T2DM men after adjustment for age, BMI, diabetic duration, eGFR, smoking and drinking (P = 0.032).

CONCLUSION

Hemoglobin levels were associated with the presence of osteoporosis in T2DM men, especially in those aged 50 years and older.

Effect of Acetazolamide and Zoledronate on Simulated High Altitude-Induced Bone Loss

Exposure to hypobaric hypoxia at high altitude puts mountaineers at risk of acute mountain sickness. The carbonic anhydrase inhibitor acetazolamide is used to accelerate acclimatization, when it is not feasible to make a controlled and slow ascend. Studies in rodents have suggested that exposure to hypobaric hypoxia deteriorates bone integrity and reduces bone strength. The study investigated the effect of treatment with acetazolamide and the bisphosphonate, zoledronate, on the skeletal effects of exposure to hypobaric hypoxia. Eighty 16-week-old female RjOrl : SWISS mice were divided into five groups: 1. Baseline; 2. Normobaric; 3. Hypobaric hypoxia; 4. Hypobaric hypoxia + acetazolamide, and 5. Hypobaric hypoxia + zoledronate. Acetazolamide was administered in the drinking water (62 mg/kg/day) for four weeks, and zoledronate (100 μg/kg) was administered as a single subcutaneous injection at study start. Exposure to hypobaric hypoxia significantly increased lung wet weight and decreased femoral cortical thickness. Trabecular bone was spared from the detrimental effects of hypobaric hypoxia, although a trend towards reduced bone volume fraction was found at the L4 vertebral body. Treatment with acetazolamide did not have any negative skeletal effects, but could not mitigate the altitude-induced bone loss. Zoledronate was able to prevent the altitude-induced reduction in cortical thickness. In conclusion, simulated high altitude affected primarily cortical bone, whereas trabecular bone was spared. Only treatment with zoledronate prevented the altitude-induced cortical bone loss. The study provides preclinical support for future studies of zoledronate as a potential pharmacological countermeasure for altitude-related bone loss.

The Non-Erythropoietic EPO Analogue Cibinetide Inhibits Osteoclastogenesis In Vitro and Increases Bone Mineral Density in Mice

The two erythropoietin (EPO) receptor forms mediate different cellular responses to erythropoietin. While hematopoiesis is mediated via the homodimeric EPO receptor (EPOR), tissue protection is conferred via a heteromer composed of EPOR and CD131. In the skeletal system, EPO stimulates osteoclast precursors and induces bone loss. However, the underlying molecular mechanisms are still elusive. Here, we evaluated the role of the heteromeric complex in bone metabolism in vivo and in vitro by using Cibinetide (CIB), a non-erythropoietic EPO analogue that exclusively binds the heteromeric receptor. CIB is administered either alone or in combination with EPO. One month of CIB treatment significantly increased the cortical (~5.8%) and trabecular (~5.2%) bone mineral density in C57BL/6J WT female mice. Similarly, administration of CIB for five consecutive days to female mice that concurrently received EPO on days one and four, reduced the number of osteoclast progenitors, defined by flow cytometry as Lin⁻CD11b⁻Ly6C^hi CD115⁺, by 42.8% compared to treatment with EPO alone. In addition, CIB alone or in combination with EPO inhibited osteoclastogenesis in vitro. Our findings introduce CIB either as a stand-alone treatment, or in combination with EPO, as an appealing candidate for the treatment of the bone loss that accompanies EPO treatment.

Epo/EpoR signaling in osteoprogenitor cells is essential for bone homeostasis and Epo-induced bone loss

High erythropoietin (Epo) levels are detrimental to bone health in adult organisms. Adult mice receiving high doses of Epo lose bone mass due to suppressed bone formation and increased bone resorption. In humans, high serum Epo levels are linked to fractures in elderly men. Our earlier studies indicated that Epo modulates osteoblast activity; however, direct evidence that Epo acts via its receptor (EpoR) on osteoblasts in vivo is still missing. Here, we created mice lacking EpoR in osteoprogenitor cells to specifically address this gap. Deletion of EpoR in osteoprogenitors (EpoR:Osx-cre, cKO) starting at 5 weeks of age did not alter red blood cell parameters but increased vertebral bone volume by 25% in 12-week-old female mice. This was associated with low bone turnover. Histological (osteoblast number, bone formation rate) and serum (P1NP, osteocalcin) bone formation parameters were all reduced, as were the number of osteoclasts and TRAP serum level. Differentiation of osteoblast precursors isolated from cKO versus control mice resulted in lower expression of osteoblast marker genes including Runx2, Alp, and Col1a1 on day 21, whereas the mineralization capacity was similar. Moreover, the RANKL/OPG ratio, which determines the osteoclast-supporting potential of osteoblasts, was substantially decreased by 50%. Similarly, coculturing cKO osteoblasts with control or cKO osteoclast precursors produced significantly fewer osteoclasts than coculture with control osteoblasts. Finally, exposing female mice to Epo pumps (10 U·d⁻¹) for 4 weeks resulted in trabecular bone loss (−25%) and increased osteoclast numbers (1.7-fold) in control mice only, not in cKO mice. Our data show that EpoR in osteoprogenitors is essential in regulating osteoblast function and osteoblast-mediated osteoclastogenesis via the RANKL/OPG axis. Thus, osteogenic Epo/EpoR signaling controls bone mass maintenance and contributes to Epo-induced bone loss.

Intestinal-derived FGF15 protects against deleterious effects of vertical sleeve gastrectomy in mice

Bariatric surgeries such as the Vertical Sleeve Gastrectomy (VSG) are invasive but provide the most effective improvements in obesity and Type 2 diabetes. We hypothesized a potential role for the gut hormone Fibroblast-Growth Factor 15/19 which is increased after VSG and pharmacologically can improve energy homeostasis and glucose handling. We generated intestinal-specific FGF15 knockout (FGF15^INT-KO) mice which were maintained on high-fat diet. FGF15^INT-KO mice lost more weight after VSG as a result of increased lean tissue loss. FGF15^INT-KO mice also lost more bone density and bone marrow adipose tissue after VSG. The effect of VSG to improve glucose tolerance was also absent in FGF15^INT-KO. VSG resulted in increased plasma bile acid levels but were considerably higher in VSG-FGF15^INT-KO mice. These data point to an important role after VSG for intestinal FGF15 to protect the organism from deleterious effects of VSG potentially by limiting the increase in circulating bile acids.

The mechanisms that mediate the effects of weight loss surgeries such as vertical sleeve gastrectomy (VSG) are incompletely understood. Here the authors show that intestinal FGF15 is necessary to improve glucose tolerance and to prevent the loss of muscle and bone mass after VSG, potentially via protection against bile acid toxicity.