Higher Urinary Levels of 8-Hydroxy-2'-deoxyguanosine Are Associated with a Worse RANKL/OPG Ratio in Postmenopausal Women with Osteopenia

Associations of global biomarkers of oxidative stress with osteoporosis, bone microstructure and bone turnover: Evidence from human and animal studies

PURPOSE

Human evidence on the association between oxidative stress and osteoporosis is inconsistent. Fluorescent Oxidation Products (FlOPs) are global biomarkers of oxidative stress. We examined the associations of FlOPs (excitation/emission wavelengths 320/420 nm for FlOP_320, 360/420 nm for FlOP_360, and 400/475 nm for FlOP_400) with osteoporosis, bone microstructure, and bone turnover markers in humans and rats.

METHODS

In humans, we conducted a 1:2 age, sex, hospital, and specimen-matched case-control study to test the association between FlOPs and osteoporosis diagnosed from dual-energy X-ray absorptiometry. In eight-week-old male Wistar rats, we administrated D-galactose and 0.9 % saline for 90 days in treatment and control groups (n = 8/group); micro-CT was used to determine bone microstructure.

RESULTS

In humans, higher levels of FlOP_320 (OR for per 1 SD increase = 1.49, 95 % CI: 1.01-2.20) and FlOP_360 (OR for per 1 SD increase = 1.59, 95 % CI: 1.07-2.37) were associated with increased odds of osteoporosis. FlOP_400 were not associated with osteoporosis. D-galactose treated rats, as compared with control rats, showed higher levels of FlOP_320 and MDA, and lower P1NP levels during 90 days of experiment (all P < 0.05). The D-galactose group had lower trabecular bone volume fraction (0.07 ± 0.03 vs. 0.13 ± 0.05; P = 0.008) and volumetric BMD (225.4 ± 13.8 vs. 279.1 ± 33.2 mg HA/cm3; P = 0.001) than the control group.

CONCLUSION

In conclusion, higher FlOP_320 levels were associated with increased odds of osteoporosis, impaired bone microstructure and decreased bone formation.

Oxidative stress as a key modulator of cell fate decision in osteoarthritis and osteoporosis: a narrative review

During aging and after traumatic injuries, cartilage and bone cells are exposed to various pathophysiologic mediators, including reactive oxygen species (ROS), damage-associated molecular patterns, and proinflammatory cytokines. This detrimental environment triggers cellular stress and subsequent dysfunction, which not only contributes to the development of associated diseases, that is, osteoporosis and osteoarthritis, but also impairs regenerative processes. To counter ROS-mediated stress and reduce the overall tissue damage, cells possess diverse defense mechanisms. However, cellular antioxidative capacities are limited and thus ROS accumulation can lead to aberrant cell fate decisions, which have adverse effects on cartilage and bone homeostasis. In this narrative review, we address oxidative stress as a major driver of pathophysiologic processes in cartilage and bone, including senescence, misdirected differentiation, cell death, mitochondrial dysfunction, and impaired mitophagy by illustrating the consequences on tissue homeostasis and regeneration. Moreover, we elaborate cellular defense mechanisms, with a particular focus on oxidative stress response and mitophagy, and briefly discuss respective therapeutic strategies to improve cell and tissue protection.

Oxidative Stress and Natural Antioxidants in Osteoporosis: Novel Preventive and Therapeutic Approaches

This review reports in detail the cellular and molecular mechanisms which regulate the bone remodeling process in relation to oxidative stress (OS), inflammatory factors, and estrogen deficiency. OS is considered an important pathogenic factor of osteoporosis, inducing osteocyte apoptosis and varying levels of specific factors, such as receptor activator κB ligand (RANKL), sclerostin, and, according to recent evidence, fibroblast growth factor 23, with consequent impairment of bone remodeling and high bone resorption. Bone loss increases the risk of fragility fractures, and the most commonly used treatments are antiresorptive drugs, followed by anabolic drugs or those with a double effect. In addition, recent data show that natural antioxidants contained in the diet are efficient in preventing and reducing the negative effects of OS on bone remodeling and osteocytes through the involvement of sirtuin type 1 enzyme. Indeed, osteocytes and some of their molecular factors are considered potential biological targets on which antioxidants can act to prevent and reduce bone loss, as well as to promote bone anabolic and regenerative processes by restoring physiological bone remodeling. Several data suggest including antioxidants in novel therapeutic approaches to develop better management strategies for the prevention and treatment of osteoporosis and OS-related bone diseases. In particular, anthocyanins, as well as resveratrol, lycopene, oleuropein, some vitamins, and thiol antioxidants, could have protective and therapeutic anti-osteoporotic effects.

Ameliorative Effect of Tocotrienols on Perimenopausal-Associated Osteoporosis-A Review

Osteoporosis, or bone loss, is a disease that affects many women globally. As life expectancy increases, the risk of osteoporosis in women also increases, too, and this will create a burden on the healthcare and economic sectors of a country. Osteoporosis was once thought to be a disease that would occur only after menopause. However, many studies have shown that osteoporosis may develop even in the perimenopausal stage. Due to the erratic levels of estrogen and progesterone during the perimenopausal stage, studies suggest that women are exposed to the risk of developing osteoporosis even at this stage. The erratic hormonal changes result in the production of proinflammatory mediators and cause oxidative stress, which leads to the progressive loss of bone-building activities. Tocotrienols, members of vitamin E, have many health-promoting properties. Due to their powerful anti-oxidative and anti-inflammatory properties, tocotrienols have shown positive anti-osteoporotic properties in post-menopausal studies. Hence, we propose here that tocotrienols could also possibly alleviate perimenopausal osteoporosis by discussing in this review the connection between inflammatory mediators produced during perimenopause and the risk of osteoporosis. Tocotrienols could potentially be an anti-osteoporotic agent, but due to their low bioavailability, they have not been as effective as they could be. Several approaches have been evaluated to overcome this issue, as presented in this review. As the anti-osteoporotic effects of tocotrienols were mostly studied in post-menopausal models, we hope that this review could pave the way for more research to be done to evaluate their effect on peri-menopausal models so as to reduce the risk of osteoporosis from an earlier stage.

Superoxide Dismutase and Glutathione Reductase as Indicators of Oxidative Stress Levels May Relate to Geriatric Hip Fractures' Survival and Walking Ability: A Propensity Score Matching Study

Background

Oxidative stress status may affect bone metabolism and regeneration. However, few studies reported whether oxidative stress could impact the outcomes of hip fractures. This study aimed to explore if superoxide dismutase and glutathione reductase, the critical antioxidant enzymes, correlated with the prognosis of hip fractures.

Methods

Patients with hip fractures were extracted from our database, and those who met the inclusion criteria were analyzed. Propensity score matching was used to reduce the influence of confounding factors, and ROC curves based on matched populations were created to determine the optimal cutoff points of SOD and GR. Then, outcomes between SOD or GR and outcomes of hip fractures were compared.

Results

Out of 301 patients enrolled in this study, 50 patients died within one year. After a 1:1 PSM, the patients with less than 1-year survival had significantly lower SOD (p = 0.026) and GR (p = 0.021) than those who were still alive at one year. Logistics analysis showed that low SOD and low GR may be independent risk factors for 6-month survival, 1-year survival, 6-month free walking ability, and 1-year free walking ability.

Conclusion

SOD and GR may be the independent risk factors for survival and walking abilities of hip fractures.

Treatment of fibrous dysplasia: focus on denosumab

INTRODUCTION

Fibrous dysplasia (FD) is a rare bone disease that is associated with various endocrine conditions, such as McCune Albright syndrome. It manifests as abnormal osteolysis, multiple fractures, or deformities that are reported during disease course. The receptor activator of nuclear factor-kappa B (RANK)/RANK ligand (RANKL) pathway is upregulated in FD and can be targeted with denosumab, a blocking monoclonal antibody.

AREAS COVERED

Preclinical and clinical data on the scientific rationale for using denosumab in FD and on the efficacy and safety of this therapy for this condition have been reviewed, in addition to other therapies.

EXPERT OPINION

Denosumab is a potential therapeutic agent against FD. A combined synergic approach involving theranostics might increase its therapeutic potential.

The relationship between bone marrow adipose tissue and bone metabolism in postmenopausal osteoporosis

Postmenopausal osteoporosis (PMOP) is a prevalent skeletal disorder associated with menopause-related estrogen withdrawal. PMOP is characterized by low bone mass, deterioration of the skeletal microarchitecture, and subsequent increased susceptibility to fragility fractures, thus contributing to disability and mortality. Accumulating evidence indicates that abnormal expansion of marrow adipose tissue (MAT) plays a crucial role in the onset and progression of PMOP, in part because both bone marrow adipocytes and osteoblasts share a common ancestor lineage. The cohabitation of MAT adipocytes, mesenchymal stromal cells, hematopoietic cells, osteoblasts and osteoclasts in the bone marrow creates a microenvironment that permits adipocytes to act directly on other cell types in the marrow. Furthermore, MAT, which is recognized as an endocrine organ, regulates bone remodeling through the secretion of adipokines and cytokines. Although an enhanced MAT volume is linked to low bone mass and fractures in PMOP, the detailed interactions between MAT and bone metabolism remain largely unknown. In this review, we examine the possible mechanisms of MAT expansion under estrogen withdrawal and further summarize emerging findings regarding the pathological roles of MAT in bone remodeling. We also discuss the current therapies targeting MAT in osteoporosis. A comprehensive understanding of the relationship between MAT expansion and bone metabolism in estrogen deficiency conditions will provide new insights into potential therapeutic targets for PMOP.

Changes in Adipose Tissue Distribution and Association between Uric Acid and Bone Health during Menopause Transition

Despite convincing experimental evidence, epidemiological studies on the effects of serum uric acid (SUA) on bone health are still conflicting since factors influencing SUA bioavailability have not been adequately considered. To shed some light on this issue, we investigated the impact of adiposity and menopause status on the relationship between SUA and bone health. We examined SUA in relation to bone mineral density (BMD) at different skeletal sites and with markers of bone metabolism in 124 pre-menopausal and 234 post-menopausal women and assessed whether adiposity, evaluated by anthropometry and dual x-ray absorptiometry (DXA), might have a discriminant role. After conservative adjustment (covariates: age, hormones treatment, smoking and time since menopause), SUA showed a significant and positive association with total hip BMD (β = 0.220, p < 0.01) among postmenopausal women, maintained also after adjustment for legs adiposity. Notably, stratification for waist circumference quartiles revealed that the correlation between SUA and total hip BMD was significant (r = 0.444, p = 0.001) in the highest quartile (91–100 cm). Our results suggest that SUA might be beneficial for bone health in postmenopausal women being characterized by a more android fat distribution, ascribing to SUA a discriminant role during menopause transition, potentially relevant also for men.

N-acetylcysteine prevents orchiectomy-induced osteoporosis by inhibiting oxidative stress and osteocyte senescence

Oxidative stress is associated with many diseases and has been found to induce DNA damage and cellular senescence. Numerous evidences support the detrimental effects of oxidative stress or cellular senescence on skeletal homeostasis. N-acetylcysteine (NAC) is a powerful antioxidant. However, it is unclear whether NAC can suppress orchiectomy (ORX)-induced osteoporosis by inhibiting oxidative stress and osteocyte senescence. In this study, ORX mice were supplemented with/without NAC, and were compared with each other and with sham-operated mice. Our results showed that NAC could prevent ORX-induced osteoporosis by inhibiting oxidative stress, DNA damage, osteocyte senescence and senescence-associated secretory phenotype (SASP), subsequently stimulating osteoblastic bone formation and inhibiting osteoclastic bone resorption. The results from this study suggest that NAC could be considered as a potential therapeutic agent for prevention and treatment of osteoporosis caused by testosterone deficiency.

Oxidative stress as a possible pathogenic cofactor of post-menopausal osteoporosis: Existing evidence in support of the axis oestrogen deficiency-redox imbalance-bone loss

Post-menopausal osteoporosis (PO) is one of the major health issues associated with menopause-related oestrogen withdrawal. Despite the intense research and the relevant progress achieved in the last two decades, the pathogenic mechanism underlying PO is still poorly understood. As a consequence of this gap in the knowledge, such disorder and the related complications are still difficult to be effectively prevented. A wealth of experimental and epidemiological/clinical evidence suggests that the endocrine change associated to menopausal transition might lead to a derangement of redox homeostasis, that is, the prelude to the health-threaten condition of oxidative stress (OxS). In turn, this (bio)chemical stress has been widely hypothesized to contribute, most likely in synergy with inflammation, to the development of menopause-related diseases, including PO. The main aim of this review is to discuss the current literature evidence on the association between post-menopausal oestrogen withdrawal, OxS and PO. It is also aimed to provide a critical overview of the most significant epidemiological studies on the effects of dietary antioxidants on bone health and to devise a strategy to overcome the limitations emerged and controversial results.

Tocotrienol supplementation suppressed bone resorption and oxidative stress in postmenopausal osteopenic women: a 12-week randomized double-blinded placebo-controlled trial

Tocotrienols have shown bone-protective effect in animals. This study showed that a 12-week tocotrienol supplementation decreased concentrations of bone resorption biomarker and bone remodeling regulators via suppressing oxidative stress in postmenopausal osteopenic women.

INTRODUCTION

Tocotrienols (TT) have been shown to benefit bone health in ovariectomized animals, a model of postmenopausal women. The purpose of this study was to evaluate the effect of 12-week TT supplementation on bone markers (serum bone-specific alkaline phosphatase (BALP), urine N-terminal telopeptide (NTX), serum soluble receptor activator of nuclear factor-kappaB ligand (sRANKL), and serum osteoprotegerin (OPG)), urine calcium, and an oxidative stress biomarker (8-hydroxy-2'-deoxyguanosine (8-OHdG)) in postmenopausal women with osteopenia.

METHODS

Eighty-nine postmenopausal osteopenic women (59.7 ± 6.8 year, BMI 28.7 ± 5.7 kg/m²) were randomly assigned to three groups: (1) placebo (430 mg olive oil/day), (2) low TT (430 mg TT/day, 70% purity), and (3) high TT (860 mg TT/day, 70% purity). TT, an extract from annatto seed with 70% purity, consisted of 90% delta-TT and 10% gamma-TT. Overnight fasting blood and urine samples were collected at baseline, 6, and 12 weeks for biomarker analyses. Eighty-seven subjects completed the 12-week study.

RESULTS

Relative to the placebo group, there were marginal decreases in serum BALP level in the TT-supplemented groups over the 12-week study period. Significant decreases in urine NTX levels, serum sRANKL, sRANKL/OPG ratio, and urine 8-OHdG concentrations and a significant increase in BALP/NTX ratio due to TT supplementation were observed. TT supplementation did not affect serum OPG concentrations or urine calcium levels throughout the study period. There were no significant differences in NTX level, BALP/NTX ratio, sRANKL level, and sRANKL/OPG ratio between low TT and high TT groups.

CONCLUSIONS

Twelve-week annatto-extracted TT supplementation decreased bone resorption and improved bone turnover rate via suppressing bone remodeling regulators in postmenopausal women with osteopenia. Such osteoprotective TT's effects may be, in part, mediated by an inhibition of oxidative stress.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02058420.

TITLE

Tocotrienols and bone health of postmenopausal women.

VDR, RANKL and OPG polymorphisms as possible predisposing cofactors of postmenopausal osteoporosis: explorative study in Italian population

Postmenopausal osteoporosis (PO) has a strong genetic component. Presently, the published evidence on the association between the main single-nucleotide polymorphisms (SNPs) of the receptor activator of nuclear factor-kb ligand (RANKL), osteoprotegerin (OPG) and vitamin D receptor (VDR) and bone mass density (BMD) are scarce, mostly considering Italian population. This study sought to determine whether OPG (rs2073618), RANKL (rs9525641) and the VDR (rs2228570) SNPs were associated with BMD in a sample of 139 North-Italian postmenopausal women. The allelic distribution of rs9525641 in women with PO or osteopenia (OP + OPE group) differed from controls (p < 0.05), suggesting that this allele might confer a greater susceptibility to bone resorption. Concerning rs2228570, CC genotype was associated with OP + OPE women, with a worst total hip BMD. Notably, the combined genotype RANK (CT)-VDR (TT) was significantly associated to spine BMD (p < 0.05). In conclusion, this pilot study showed that rs9525641 and rs2228570 polymorphisms might contribute, separately or in combination, in determining BMD phenotype in selected postmenopausal populations.

Risk assessment of environmental exposure to heavy metals in mothers and their respective infants

Exposure to heavy metals can cause renal injury, which has been well documented in occupational exposure. Studies of low exposure in the general population, however, are still scarce, particularly for vulnerable populations such as mothers and young children. This study evaluated exposure to heavy metals, and biomarkers of renal function and oxidative stress in 944 lactating mothers and their infants and investigated the role of the interaction between heavy metals and oxidative stress in altering renal function. Mother and infant urine samples were analyzed to measure mercury (Hg), cadmium (Cd), and lead (Pb) concentrations for determining body-burden exposure; N-acetyl-β-d-glucosaminidase (NAG), α₁-microglobulin (α₁-MG), albumin (ALB), and creatinine (Cr) concentrations for determining early renal injury; and 8-hydroxy-2-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) concentrations for determining oxidative stress. The median concentrclearlyations in mothers presented as μg/g Cr (infants as μg/l) for Hg, Cd, and Pb were 0.695 (0.716), 0.322 (0.343), and 3.97 (5.306) respectively. The mothers and their infants had clearly been exposed to heavy metals and had levels higher than the reference values reported for the general populations of USA, Germany, and Canada. Multiple regression analyses clearly demonstrated associations between urinary heavy metals in quartiles and several renal and oxidative biomarkers in mothers and to a lesser extent their infants. ß coefficients for urinary excretions of MDA, 8-OHdG, ALB, α₁-MG, NAG, and Cr in mothers were high in the highest quartile of Hg (1.183-51.29μg/g Cr or 1.732-106.95μg/l), Cd (0.565-765.776μg/g Cr or 0.785-1347.0μg/l), and Pb (6.606-83.937μg/g Cr or 9.459-80.826μg/l), except Pb was not associated with ALB. Infants in the highest Pb quartile (9.293-263.098μg/l) had the highest ß coefficients of urinary excretion of MDA, 8-OHdG, ALB, NAG, and Cr. Significant increasing trend in biomarkers across the quartiles of the three metals was seen in both mothers and infants (p_trend <0.001). A receiver operating characteristic analysis supported the predictive abilities of the four renal biomarkers in discriminating between low versus high metal quartiles. The interaction between heavy metals and oxidative stress contributed to the high excretions of renal biomarkers, but the mechanism remains unclear. These findings add to the limited evidence that low exposure to heavy metals in the general population is associated with alterations in renal function that could eventually progress to renal damage if exposure continues and that children are more susceptible due to the immaturity of their body organs.