Nitrates Do Not Affect Bone Density or Bone Turnover in Postmenopausal Women: A Randomized Controlled Trial

The multi-faceted nature of age-associated osteoporosis

Age-associated osteoporosis (AAOP) poses a significant health burden, characterized by increased fracture risk due to declining bone mass and strength. Effective prevention and early treatment strategies are crucial to mitigate the disease burden and the associated healthcare costs. Current therapeutic approaches effectively target the individual contributing factors to AAOP. Nonetheless, the management of AAOP is complicated by the multitude of variables that affect its development. Main intrinsic and extrinsic factors contributing to AAOP risk are reviewed here, including mechanical unloading, nutrient deficiency, hormonal disbalance, disrupted metabolism, cognitive decline, inflammation and circadian disruption. Furthermore, it is discussed how these can be targeted for prevention and treatment. Although valuable as individual targets for intervention, the interconnectedness of these risk factors result in a unique etiology for every patient. Acknowledgement of the multifaceted nature of AAOP will enable the development of more effective and sustainable management strategies, based on a holistic, patient-centered approach.

Nitric oxide is associated with fracture risk in Japanese women

Although nitric oxide (NO) is a known factor that regulates the bone physiology, few and discordant results have been obtained in human studies evaluating the effect of nitrates on bone health. We investigated for the relationship between serum NOx level and incident osteoporotic fracture rate prospectively in a cohort consisting of Japanese women. A total of 871 subjects (67.5 ± 10.8 y/o) were analyzed. During the observation period (8.8 ± 7.2 yrs), incident osteoporotic fractures occurred in 267 participants (209 vertebral fractures, 57 long-bone fractures, and 1 both types). Hazard ratio, by the Cox proportional hazards model, of serum NOx for incident fracture was 0.64 (95% confidence interval 0.53-0.78, p < 0.001) after adjustment for baseline age (1.13, 1.06-1.21, p < 0.001), lumbar bone mineral density (L-BMD; 0.85, 0.78-0.92, p < 0.001), presence of prevalent fracture (3.27, 2.49-4.32, p < 0.001), and treatment of osteoporosis (0.70, 0.53-0.92, p = 0.010). The relationships between serum level of NOx and bone-related parameters were examined by multiple regression analysis; body mass index (p < 0.001) and L-BMD (p = 0.011) were significantly associated with serum NOx level. These results suggest that the low circulating NOx is one of the independent predictors for osteoporotic fracture occurrence in postmenopausal women.

Chronic nitrate administration increases the expression the genes involved in the browning of white adipose tissue in female rats

Nitrate, a nitric oxide (NO) donor, has antiobesity effect in female rats. This study hypothesized that the antiobesity effect of nitrate in female rats is due to the browning of white adipose tissue (WAT). Female Wistar rats (aged 8 months) were divided into two groups (n = 10/group): the control group received tap water and the nitrate group received water containing 100 mg/L of sodium nitrate for 9 months. At months 0, 3, 6, and 9, obesity indices were measured. At month 9, gonadal adipose tissue was used to measure messenger RNA (mRNA) and protein levels of peroxisome proliferator-activated receptor-γ (PPAR-γ), PPAR-γ coactivator 1-α (PGC1-α), uncoupling protein 1 (UCP1), and adipocyte density and area. After the 9-month intervention, nitrate-treated rats had lower body weight, body mass index, thoracic circumference, and abdominal circumference by 6.4% (p = .012), 9.1% (p = .029), 6.0% (p = .056), and 5.7% (p = .098), respectively. In addition, nitrate-treated rats had higher PPAR-γ (mRNA: 1.78-fold, p = .016 and protein: 19%, p = .076), PGC1-α (mRNA: 1.69-fold, p = .012 and protein: 68%, p = .001), and UCP1 (mRNA: 2.50-fold, p = .001 and protein: 81%, p = .001) in gonadal adipose tissue. Nitrate also reduced adipocyte area by 35% (p = .054) and increased adipocyte density by 31% (p = .086). In conclusion, antiobesity effect of nitrate in female rats is associated with increased browning of gonadal adipose tissue as indicated by higher expression of PPAR-γ, PGC1-α, and UCP1 and reduced adipocyte area and increased adipocyte density.

The Efficacy of Nitrates for Bone Health: A Systematic Review and Meta-Analysis of Observational and Randomized Controlled Studies

BACKGROUND

Although some studies have found that nitrates were beneficial for bone health, the findings are inconsistent. To assess the efficacy of nitrates for bone health, we conducted a meta-analysis.

METHODS

PubMed, EMBASE databases, Cochrane Library for relevant articles published before December 2021 were searched. All observational and randomized controlled studies that reporting bone mineral density (BMD), fractures with nitrates use were included. A meta-analysis was performed to calculate risk ratios (RRs) for fractures, change differences for bone mineral density.

RESULTS

Four cohort studies and two case-control studies examining the association between nitrates use and fractures were identified. The nitrates use was not associated with any fracture risk (RR = 0.97; 95% CI, 0.94-1.01; I² = 31.5%) and hip fracture (RR = 0.88; 95% CI, 0.76-1.02; I² = 74.5%). Subgroup analyses revealed no differences in fracture risk, whereas two cohort studies revealed a reduced risk of hip fracture (RR = 0.71, 95% CI, 0.58-0.86, I² = 0.0%). There were no statistically significant differences in BMD percent changes at lumbar spine (WMD = -0.07, 95% CI,-0.78-0.65; I² = 0.0%), total hip (WMD = -0.42, 95% CI,-0.88-0.04; I² = 0.0%), femoral neck (WMD = -0.38, 95% CI,-1.02-0.25; I² = 0.0%), or total body (WMD = -0.17, 95% CI,-0.51-0.17; I² = 0.0%) in two randomized controlled trials (RCTs) compared with a placebo. Another two RCTs compared nitrates with alendronate. Nitrates were comparable to alendronate in increasing bone mineral density at lumbar spine (WMD = 0.00, 95% CI,-0.01-0.02; I² = 0.0%). Besides, the most common adverse effect was headache, contributing to low adherence to therapy.

CONCLUSION

Our meta-analysis showed no association between nitrates use and fractures in observational studies. The results of RCTs on the usage of nitrates and their effects on BMD were inconsistent. High-quality, long-term studies are needed to clarify the efficacy of nitrates for bone health.

The NO-cGMP-PKG pathway in skeletal remodeling

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) pathway plays a critical role in skeletal homeostasis. Preclinical data using NO and its donors and genetically modified mice demonstrated that NO was required in bone remodeling and partly mediated the anabolic effects of mechanical stimuli and estrogen. However, the off-target effects and tachyphylaxis of NO limit its long-term use, and previous clinical trials using organic nitrates for osteoporosis have been disappointing. Among the other components in the downstream pathway, targeting cGMP-specific phosphodiesterase to promote the NO-cGMP-PKG signal is a viable option. There are growing in vitro and in vivo data that, among many other PDE families, PDE5A is highly expressed in skeletal tissue, and inhibiting PDE5A using currently available PDE5A inhibitors might increase the osteoanabolic signal and protect the skeleton. These preclinical data open the possibility of repurposing PDE5A inhibitors for treating osteoporosis. Further research is needed to address the primary target bone cell of PDE5A inhibition, the contribution of direct and indirect effects of PDE5A inhibition, and the pathophysiological changes in skeletal PDE5A expression in aging and hypogonadal animal models.