The effects of organic nitrates on osteoporosis: a systematic review

Salivary nitrate prevents osteoporosis via regulating bone marrow mesenchymal stem cells proliferation and differentiation

Background

Nitrate, a key component of saliva, has been shown widely physiological functions in the human body. But its function on bone metabolism remains unclear. The aim of this study was to investigate the function and mechanism of saliva nitrate on osteoporosis and the function of bone marrow mesenchymal stem cells (BMSCs).

Methods

Saliva nitrate removal or supplemental interventions were performed for 1 month in ovariectomized (OVX) osteopenia mice. The nitrate levels in saliva and serum were detected. The bone formation and bone microarchitecture in the OVX mouse model were investigated by quantitative Micro--computed tomography imaging, histological staining and serum bone biomarker analysis. The effects of nitrate on the functional homeostasis of BMSCs in OVX mice were explored by Ki67 immunofluorescence staining, Ki67 flow staining, alizarin red staining, qPCR and western blotting. Finally, downstream signaling pathways were screened by proteomics and verified by western blotting.

Results

The results showed that nitrate deficiency exacerbated osteoporosis, while nitrate administration prevent osteoporosis in OVX mice. Nitrate increased the expression of PINP, a biomarker of bone formation, in OVX mice. Besides, nitrate enhanced the proliferative capacity and osteogenic function of BMSCs in OVX mice in vitro and in vivo. In addition, nitrate upregulated the expression levels of osteogenesis-related genes ALP, Run2 and OPN of BMSCs. EGFR and mTOR signaling were screened as the key downstream of nitrate, and phosphorylated protein levels of its subfamily members AKT, ERK and S6K were significantly upregulated by nitrate.

Conclusion

The present results showed saliva nitrate preventively protects against osteoporosis through enhances the proliferation and osteogenic differentiation potential of BMSCs. The effects of nitrate on bone homeostasis are closely related to the EGFR/AKT/ERK and mTOR/S6K signaling axes.

The translational potential of this article

Our study provides experimental evidence for the use of saliva nitrate as an effective candidate for the prevention of osteoporosis and maintenance of bone homeostasis.

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.

Nutritional strategies to optimise musculoskeletal health for fall and fracture prevention: Looking beyond calcium, vitamin D and protein

Falls and osteoporotic fractures are a major public health problem, particularly among older adults. A third of individuals aged 65 years and over fall at least once each year, with up to 20 % of these resulting in serious injury, including fracture. In conjunction with regular exercise, the importance of diet for musculoskeletal health has largely focused upon calcium, vitamin D, and protein, particularly in the context of preventing falls and fractures. Whilst there is evidence for the benefits of these nutrients for musculoskeletal health, other aspects of the diet remain largely underexplored. For example, vegetables are rich sources of macro- and micronutrients that are essential for muscle function and bone health, which are key factors in the prevention of falls and fractures. Recent work has highlighted the importance of nutrients such as vegetable-derived nitrate and vitamin K1 in optimising muscle strength, physical function, and bone quality. In the context of dietary patterns, vegan/plant-based diets have recently gained popularity due to perceived health benefits, animal welfare, or to tackle climate change. The elimination and/or substitution of animal-based products for plant foods (without careful planning and/or expert dietary guidance) could, however, have long-term negative musculoskeletal consequences; a trend uncovered by recent evidence. Within the overarching theme of nutrition for fall and fracture prevention in older populations, the aim of this review is to (i) summarise the current evidence for calcium, vitamin D and protein; (ii) describe the importance of vegetables and selected nutrients, such as nitrate and vitamin K1, for muscle function and bone structural integrity; and (iii) highlight current evidence around different dietary patterns (e.g., plant-based, diet quality, data driven approaches) and their impact on musculoskeletal health.

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

Organic nitrates have been reported to have significant effects on bone mineral density (BMD) and bone turnover in previous clinical trials. However, results are inconsistent and some trials with strikingly positive results have been retracted because of scientific misconduct. As preparation for a potential fracture prevention study, we set out to determine the lowest effective dose and the most effective and acceptable nitrate preparation. We undertook a 1-year, double-blind, randomized, placebo-controlled trial of three different nitrate preparations and two different doses in osteopenic postmenopausal women, with a planned 1-year observational extension. The primary endpoint was change in BMD at the lumbar spine, and secondary endpoints included BMD changes at other sites, changes in bone turnover markers, and adverse events. A total of 240 eligible women who tolerated low-dose oral nitrate treatment in a 2-week run-in period were randomized to five different treatment groups or placebo. Over 12 months, there were no statistically significant between-group differences in changes in BMD at any site and no consistent differences in bone turnover markers. When the active treatment groups were pooled, there were also no differences in changes in BMD or bone turnover markers between nitrate treatment and placebo. Eighty-eight (27%) women withdrew during the run-in phase, with the majority because of nitrate-induced headache, and 41 of 200 (21%) women randomized to nitrate treatment withdrew or stopped study medication during the 1-year study compared with 1 of 40 (2.5%) in the placebo group. In summary, organic nitrates do not have clinically relevant effects on BMD or bone turnover in postmenopausal women and were poorly tolerated. These results call into question the validity of previous clinical research reporting large positive effects of nitrates on BMD and bone turnover. © 2020 American Society for Bone and Mineral Research.

The anabolic action of intermittent parathyroid hormone on cortical bone depends partly on its ability to induce nitric oxide-mediated vasorelaxation in BALB/c mice

There is strong evidence that vasodilatory nitric oxide (NO) donors have anabolic effects on bone in humans. Parathyroid hormone (PTH), the only osteoanabolic drug currently approved, is also a vasodilator. We investigated whether the NO synthase inhibitor L‐NAME might alter the effect of PTH on bone by blocking its vasodilatory effect. BALB/c mice received 28 daily injections of PTH[1–34] (80 µg/kg/day) or L‐NAME (30 mg/kg/day), alone or in combination. Hindlimb blood perfusion was measured by laser Doppler imaging. Bone architecture, turnover and mechanical properties in the femur were analysed respectively by micro‐CT, histomorphometry and three‐point bending. PTH increased hindlimb blood flow by >30% within 10 min of injection (P < 0.001). Co‐treatment with L‐NAME blocked the action of PTH on blood flow, whereas L‐NAME alone had no effect. PTH treatment increased femoral cortical bone volume and formation rate by 20% and 110%, respectively (P < 0.001). PTH had no effect on trabecular bone volume in the femoral metaphysis although trabecular thickness and number were increased and decreased by 25%, respectively. Co‐treatment with L‐NAME restricted the PTH‐stimulated increase in cortical bone formation but had no clear‐cut effects in trabecular bone. Co‐treatment with L‐NAME did not affect the mechanical strength in femurs induced by iPTH. These results suggest that NO‐mediated vasorelaxation plays partly a role in the anabolic action of PTH on cortical bone. © 2016 The Authors. Cell Biochemistry and Function published by John Wiley & Sons, Ltd.

Urinary heavy metals, phthalates, phenols, thiocyanate, parabens, pesticides, polyaromatic hydrocarbons but not arsenic or polyfluorinated compounds are associated with adult oral health: USA NHANES, 2011-2012

Links between environmental chemicals and human health have emerged over the last few decades, but the effects on oral health have been less studied. Therefore, it was aimed to study the relationships of different sets of urinary chemical concentrations and adult oral health conditions in a national and population-based setting. Data was retrieved from the United States National Health and Nutrition Examination Surveys, 2011-2012 including demographics, self-reported oral health conditions and urinary environmental chemical concentrations (one third representative sample of the study population). Chi-square test, t test, and survey-weighted logistic and multi-nominal regression modeling were performed. Of 4566 American adults aged 30-80, 541 adults (11.9 %) reported poor teeth health while 1020 adults (22.4 %) reported fair teeth. Eight hundred fifty-five people (19.1 %) claimed to have gum disease, presented with higher levels of urinary cadmium, cobalt and polyaromatic hydrocarbons. Six hundred three adults (13.3 %) had bone loss around the mouth, presented with higher levels of cadmium, nitrate, thiocyanate, propyl paraben and polyaromatic hydrocarbons. Eight hundred forty-five adults (18.5 %) had tooth loose not due to injury, presented with higher level of cadmium, thiocyanate and polyaromatic hydrocarbons. Eight hundred forty-five adults (18.5 %) with higher levels of lead, uranium, polyaromatic hydrocarbons but lower level of triclosan noticed their teeth did not look right. Three hundred fifty-one adults (7.7 %) often had aching in the mouth and 650 (14.3 %) had it occasionally, presented with higher levels of phthalates, pesticides and polyaromatic hydrocarbons. Benzophenone-3 and triclosan elicited protective effects. Regulation of environmental chemicals in prevention of adult oral health might need to be considered in future health and environmental policies.

NO-Rich Diet for Lifestyle-Related Diseases

Decreased nitric oxide (NO) availability due to obesity and endothelial dysfunction might be causally related to the development of lifestyle-related diseases such as insulin resistance, ischemic heart disease, and hypertension. In such situations, instead of impaired NO synthase (NOS)-dependent NO generation, the entero-salivary nitrate-nitrite-NO pathway might serve as a backup system for NO generation by transmitting NO activities in the various molecular forms including NO and protein S-nitrosothiols. Recently accumulated evidence has demonstrated that dietary intake of fruits and vegetables rich in nitrate/nitrite is an inexpensive and easily-practicable way to prevent insulin resistance and vascular endothelial dysfunction by increasing the NO availability; a NO-rich diet may also prevent other lifestyle-related diseases, including osteoporosis, chronic obstructive pulmonary disease (COPD), and cancer. This review provides an overview of our current knowledge of NO generation through the entero-salivary pathway and discusses its safety and preventive effects on lifestyle-related diseases.

Nitric oxide donors and selective carbonic anhydrase inhibitors: a dual pharmacological approach for the treatment of glaucoma, cancer and osteoporosis

Due to the recognized biological role of nitric oxide (NO) donating derivatives and of selective inhibitors of specific human carbonic anhydrase isoforms (CA, EC 4.2.1.1), promising compounds having an aromatic/heterocyclic primary sulfonamide and functionalized with NO-releasing moieties have been designed. These bifunctional agents have been tested in vitro and in vivo to assess their dual pharmacological activity. According to the encouraging results they could be proposed for the treatment of angle-open glaucoma, cancer regression and osteoporosis, in which both NO and CA activities are involved.

Serum urate levels and the risk of hip fractures: data from the Cardiovascular Health Study

PURPOSE

Uric acid inhibits vitamin D activation experimentally and higher serum urate levels are associated with higher parathyroid hormone levels in humans suggesting a link between uric acid and bone health. We hypothesized that hyperuricemia may increase the risk of fractures in older adults.

METHODS

1963 men and 2729 women ≥65 years of age who participated in the Cardiovascular Health Study and had baseline serum urate levels were included in the study. The primary outcome was incident hip fracture, assessed prospectively through June, 2008 by inpatient and outpatient records. The analysis was stratified by sex a priori.

RESULTS

There was a U-shaped relationship between serum urate levels and hip fractures in men. Men in the lowest and the highest urate quartiles (<4.88 and ≥6.88 mg/dL respectively) had a significantly higher rate of fractures in unadjusted analysis. However, upon multivariate adjustment, only the HR for hip fracture in highest quartile versus the reference remained significant (HR 1.9; 95% C.I. 1.1, 3.1; p value 0.02). High serum urate levels were not associated with hip fractures in women.

CONCLUSION

In this large prospective cohort of community-dwelling older adults, increased serum urate levels were associated with an increased risk of hip fractures in men. Further studies are needed to confirm these findings and to understand the mechanisms that underlie them.

NADPH oxidases in bone homeostasis and osteoporosis

Bone formation and degradation are perfectly coordinated. In case of an imbalance of these processes diseases occur associated with exaggerated formation of new bone or bone loss as in osteoporosis. Most studies investigating osteoporosis either focus on osteoblast or osteoclast function and differentiation. Both processes have been suggested to be affected by reactive oxygen species (ROS). Besides a potentially harmful role of ROS, these small molecules are important second messengers. The family of NADPH oxidases produces ROS in a controlled and targeted manner, to specifically regulate signal transduction. This review will highlight the role of reactive oxygen species in bone cell differentiation and bone-loss associated disease with a special focus on osteoporosis and NADPH oxidases as specialized sources of ROS.

The Key Role of the Blood Supply to Bone

The importance of the vascular supply for bone is well-known to orthopaedists but is still rather overlooked within the wider field of skeletal research. Blood supplies oxygen, nutrients and regulatory factors to tissues, as well as removing metabolic waste products such as carbon dioxide and acid. Bone receives up to about 10% of cardiac output, and this blood supply permits a much higher degree of cellularity, remodelling and repair than is possible in cartilage, which is avascular. The blood supply to bone is delivered to the endosteal cavity by nutrient arteries, then flows through marrow sinusoids before exiting via numerous small vessels that ramify through the cortex. The marrow cavity affords a range of vascular niches that are thought to regulate the growth and differentiation of hematopoietic and stromal cells, in part via gradients of oxygen tension. The quality of vascular supply to bone tends to decline with age and may be compromised in common pathological settings, including diabetes, anaemias, chronic airway diseases and immobility, as well as by tumours. Reductions in vascular supply are associated with bone loss. This may be due in part to the direct effects of hypoxia, which blocks osteoblast function and bone formation but causes reciprocal increases in osteoclastogenesis and bone resorption. Common regulatory factors such as parathyroid hormone or nitrates, both of which are potent vasodilators, might exert their osteogenic effects on bone via the vasculature. These observations suggest that the bone vasculature will be a fruitful area for future research.