The effects of visceral obesity and androgens on bone: trenbolone protects against loss of femoral bone mineral density and structural strength in viscerally obese and testosterone-deficient male rats

The obesity paradox in osteoporosis risk among older adults is mostly driven by women: a population-based prospective study

OBJECTIVES

The obesity paradox is common among older adults at risk for various diseases. Although this paradox has also been observed in the association between obesity and osteoporosis, the available evidence remains controversial. This study aimed to investigate the association between obesity and OP risk in an older population.

METHODS

A cross-sectional and prospective study was conducted using data from 177,734 participants in the UK Biobank. The association of body mass index (BMI), waist circumference (WC), and fat percentage with BMD was examined using Spearman correlation analysis with baseline BMD data. Cox proportional hazards regression analysis was used to investigate the association between obesity and OP risk. Restricted cubic spline (RCS) were used to assess the nonlinear associations of BMI, WC, and fat percentage with OP.

RESULTS

Baseline cross-sectional analyses revealed a significant positive association between BMI, WC, and fat percentage with BMD in women, whereas this association was very weak in men. A total of 8,998 OP patients were identified during a median follow-up period of 13.7 years. Cox analyses showed that obesity as defined by BMI, WC, and fat percentage was associated with a 33%, 23%, and 31% reduction in the risk of OP in older women but not in men, respectively. Conjoint analysis showed that lower BMI was associated with increased risk of OP in older adults, whereas the lowest risk was observed in women with higher BMI and higher body fat. RCS revealed an inverse J-shaped nonlinear association between obesity metrics and OP risk in women.

CONCLUSION

Lower BMI is an independent risk factor for OP in older adults, and the obesity paradox for OP risk exists only in women.

CD4+ T-cell activation of bone marrow causes bone fragility and insulin resistance in type 2 diabetes

Type 2 diabetes mellitus (T2DM) causes an increased risk of bone fractures. However, the pathophysiology of diabetic bone fragility is not completely understood. It has been proposed that an inflammatory microenvironment in bone could be a major mechanism by inducing uncontrolled bone resorption, inadequate bone formation and consequently more porous bones. We propose that activated T-cells in the bone marrow cause a pro-inflammatory microenvironment in bone, and cause bone fragility in T2DM. We induced T2DM in C57BL/6 male mice through a hypercaloric diet rich in carbohydrates and low doses of streptozocin. In T2DM mice we inhibited systemic activation of T-cells with a fusion protein between the extracellular domain of Cytotoxic T-Lymphocyte Antigen 4 and the Fc domain of human immunoglobulin G (CTLA4-Ig). We analysed the effects of T2DM or CTLA4-Ig in lymphocyte cell subsets and antigen-presenting cells in peripheral blood and femoral bone marrow; and their effect on the metabolic phenotype, blood and bone cytokine concentration, femoral bone microarchitecture and biomechanical properties, and the number of osteoblast-like cells in the femoral endosteum. We performed a Pearson multiple correlation analysis between all variables in order to understand the global mechanism. Results demonstrated that CTLA4-Ig decreased the number of activated CD4⁺ T-cells in the femoral bone marrow and consequently decreased TNF-α and RANK-L concentration in bone, notably improved femoral bone microarchitecture and biomechanical properties, increased the number of osteoblast-like cells, and reduces osteoclastic activity compared to T2DM mice that did not receive the inhibitor. Interestingly, we observed that blood glucose levels and insulin resistance may be related to the increase in activated CD4⁺ T-cells in the bone marrow. We conclude that bone marrow activated CD4⁺ T-cells cause poor bone quality and insulin resistance in T2DM.

Design, synthesis and characterization of a PEGylated stanozolol for potential therapeutic applications

Stanozolol (STZ) is a drug used to treat serious disorders like aplastic anemia and hereditary angioedema. It is also indicated as an adjunct therapy for the treatment of vascular disorders and growth failures. Encouraging results obtained using animal models demonstrated that STZ increases bone formation and mineralization, thus improving both density and biomechanical properties. Like natural androgens, such as TST and 5α-dihydrotestosterone (5α-DHT), STZ binds androgen receptor (AR) to activate AR-mediated signaling. Despite its therapeutic effects, this synthetic anabolic-androgenic steroid (AAS), or 5α-DHT derivative, due to its high lipophilicity, is poor soluble in water. Thus, to increase the water solubility and stability of STZ, as well as its bioavailability and efficacy, an innovative PEGylated STZ (STZ conjugated with (MeO-PEG-NH₂)_10kDa, (MeO-PEG-NH)_10kDa-STZ) was synthesized. As confirmed by chromatography (RP-HPLC) and spectrometry (ATR-FTIR, ¹H NMR, elemental CHNS(O) analysis, MALDI-TOF/TOF) analyses, a very pure, stable and soluble compound was obtained. Acetylcholinesterase (AChE) competitive ELISA demonstrated that the resulting PEGylated STZ competes against biological TST, especially at lower concentrations. Cytotoxicity of increasing concentrations (1, 10, 25 or 50 µM) of STZ and/or (MeO-PEG-NH)_10kDa-STZ was also evaluated for up 80 h by performing the MTT assay on human osteosarcoma Saos-2 cells, which express AR and are responsive to STZ. PEGylation mitigated cytotoxicity of STZ, by increasing the cell viability values, especially at higher drug concentrations. Furthermore, these results suggest that (MeO-PEG-NH)_10kDa-STZ is a promising and reliable drug to be used in clinical conditions in which TST is required.

Stanozolol promotes osteogenic gene expression and apposition of bone mineral in vitro

Stanozolol (ST) is a synthetic androgen with high anabolic potential. Although it is known that androgens play a positive role in bone metabolism, ST action on bone cells has not been sufficiently tested to support its clinical use for bone augmentation procedures. Objective: This study aimed to assess the effects of ST on osteogenic activity and gene expression in SaOS-2 cells. Material and Methods: SaOS-2 deposition of mineralizing matrix in response to increasing doses of ST (0-1000 nM) was evaluated through Alizarin Red S and Calcein Green staining techniques at 6, 12 and 24 days. Gene expression of runt-related transcription factor 2 (RUNX2), vitamin D receptor (VDR), osteopontin (SPP1) and osteonectin (ON) was analyzed by RT-PCR. Results: ST significantly influenced SaOS-2 osteogenic activity: stainings showed the presence of rounded calcified nodules, which increased both in number and in size over time and depending on ST dose. RT-PCR highlighted ST modulation of genes related to osteogenic differentiation. Conclusions: This study provided encouraging results, showing ST promoted the osteogenic commitment of SaOS-2 cells. Further studies are required to validate these data in primary osteoblasts and to investigate ST molecular pathway of action.

FGF-2 Gene Polymorphism in Osteoporosis among Guangxi's Zhuang Chinese

Osteoporosis is a complex multifactorial disorder of gradual bone loss and increased fracture risk. While previous studies have shown the importance of many genetic factors in determining peak bone mass and fragility fractures and in suggesting involvement of fibroblast growth factor-2 (FGF-2) in bone metabolism and bone mass, the relationship of FGF-2 genetic diversity with bone mass/osteoporosis has not yet been revealed. The current study investigated the potential relevance of FGF-2 gene polymorphism in osteoporosis among a Zhuang ethnic Chinese cohort of 623, including 237 normal bone mass controls, 227 osteopenia, and 159 osteoporosis of different ages. Bone density was examined by calcaneus ultrasound attenuation measurement, and single nucleotide polymorphisms (SNPs) and linkage disequilibrium analyses were performed on five SNP loci of FGF-2 gene. Significant differences were found in bone mass in males between the 45-year-old and ≥70-year-old groups (p < 0.01), and in females among 55, 60, 65 and 70-year-old groups (p < 0.05). Males had higher bone mass values than females in the same age (over 55-year-old) (p < 0.05). The proportions of individuals with normal bone mass decreased with age (65.2% to 40% in males, and 50% to 0% in females), whereas prevalence of osteoporosis increased with age (15.4% to 30% in men, and 7.7% to 82% in women). Out of five FGF-2 SNP loci, the TA genotype of rs308442 in the osteoporosis group (40.2%) was higher than in the control group (29.5%) (p < 0.05). The TA genotype was significantly correlated with the risk of osteoporosis (odds ratio OR = 1.653), 95% confidence interval (CI): 1.968-1.441). Strong linkage disequilibrium in FGF-2 gene was also detected between rs12644427 and rs3747676, between rs12644427 and rs3789138, and between rs3747676 and rs3789138 (D' > 0.8, and r² > 0.33). Thus, the rs308442 locus of FGF-2 gene is closely correlated to osteoporosis in this Zhuang ethnic Chinese cohort, and the TA may be the risk genotype of osteoporosis.

Obesity is a concern for bone health with aging

Accumulating evidence supports a complex relationship between adiposity and osteoporosis in overweight/obese individuals, with local interactions and endocrine regulation by adipose tissue on bone metabolism and fracture risk in elderly populations. This review was conducted to summarize existing evidence to test the hypothesis that obesity is a risk factor for bone health in aging individuals. Mechanisms by which obesity adversely affects bone health are believed to be multiple, such as an alteration of bone-regulating hormones, inflammation, oxidative stress, the endocannabinoid system, that affect bone cell metabolism are discussed. In addition, evidence on the effect of fat mass and distribution on bone mass and quality is reviewed together with findings relating energy and fat intake with bone health. In summary, studies indicate that the positive effects of body weight on bone mineral density cannot counteract the detrimental effects of obesity on bone quality. However, the exact mechanism underlying bone deterioration in the obese is not clear yet and further research is required to elucidate the effect of adipose depots on bone and fracture risk in the obese population.

Obesity does not aggravate osteoporosis or osteoblastic insulin resistance in orchiectomized rats

The present study aimed to test the hypothesis that testosterone deprivation impairs osteoblastic insulin signaling, decreases osteoblast survival, reduces bone density, and that obesity aggravates those deleterious effects in testosterone-deprived rats. Twenty four male Wistar rats underwent either a bilateral orchiectomy (O, n=12) or a sham operation (S, n=12). Then the rats in each group were further divided into two subgroups fed with either a normal diet (ND) or a high-fat diet (HF) for 12 weeks. At the end of the protocol, blood samples were collected to determine metabolic parameters and osteocalcin ratios. The tibiae were collected to determine bone mass using microcomputed tomography and for osteoblast isolation. The results showed that rats fed with HF (sham-operated HF-fed rats (HFS) and ORX HF-fed rats (HFO)) developed peripheral insulin resistance and had decreased trabecular bone density. In ND-fed rats, only the ORX ND-fed rats (NDO) group had decreased trabecular bone density. In addition, osteoblastic insulin resistance, as indicated by a decrease in tyrosine phosphorylation of the insulin receptor and Akt, were observed in all groups except the sham-operated ND-fed rats (NDS) rats. Those groups, again with the exception of the NDS rats, also had decreased osteoblastic survival. No differences in the levels of osteoblastic insulin resistance and osteoblastic survival were found among the NDO, HFS, and HFO groups. These findings suggest that either testosterone deprivation or obesity alone can impair osteoblastic insulin signaling and decrease osteoblastic survival leading to the development of osteoporosis. However, obesity does not aggravate those deleterious effects in the bone of testosterone-deprived rats.