Causal effects of homocysteine levels on the changes of bone mineral density and risk for bone fracture: A two-sample mendelian randomization study

Homocysteine and Multiple Health Outcomes: An Outcome-Wide Umbrella Review of Meta-analyses and Mendelian Randomization Studies

Elevated levels of homocysteine (Hcy) are associated with various health outcomes. We aimed to systematically assess the credibility and certainty of evidence of associations of Hcy and Hcy-lowering therapies with various health outcomes. We retrieved observational meta-analyses examining the associations between Hcy and health outcomes, interventional meta-analyses investigating health outcomes related to Hcy-lowering treatments, and Mendelian randomization (MR) studies exploring the causal associations of Hcy with health outcomes to perform an umbrella review. A total of 135 observational meta-analyses, 106 MR studies, and 26 interventional meta-analyses were included. Among observational studies, 10 associations of diseases/outcomes were classified as highly suggestive; only 1 outcome (digestive tract cancer) was supported by convincing evidence (class I; odd ratio = 1.27, 95% confidence interval = 1.16, 1.40; P = 6.79 × 10-7; I2 = 0, 95% prediction interval excluding null, >1000 cases; P > 0.1 for tests of both small-study effects and excess significance bias). In MR studies, 5 outcomes associated with Hcy presented robust evidence (P < 0.01, power >80%). Among 25 outcomes explored by both observational meta-analyses and MR studies, 7 had consistent results, indicating that elevated Hcy is causally associated with an increased risk of these outcomes. The 3 types of studies collectively suggested that the association of stroke with Hcy was supported by observational studies, causally by MR studies, and further validated by intervention meta-analyses showing that Hcy-lowering with folic acid significantly reduced risk of stroke. For dementia and colorectal cancer, Hcy was significantly associated in meta-analyses of observational studies and folic acid decreased disease risks in interventional meta-analyses. The current umbrella review indicates that convincing evidence for a definitive role of Hcy exposure solely exists in the context of digestive tract cancer excluding bias; however, Hcy may not be causal for this disease. All the 3 types of studies collectively support that Hcy is a key causal risk factor, and Hcy-lowering (specifically with folic acid) may serve as an effective intervention for stroke. This trial was registered at PROSPERO as CRD42024541335.

Endocrine modulation of brain-skeleton axis driven by neural stem cell-derived perilipin 5 in the lipid metabolism homeostasis for bone regeneration

Factors released from the nervous system always play crucial roles in modulating bone metabolism and regeneration. How the brain-driven endocrine axes maintain bone homeostasis, especially under metabolic disorders, remains obscure. Here, we found that neural stem cells (NSCs) residing in the subventricular zone participated in lipid metabolism homeostasis of regenerative bone through exosomal perilipin 5 (PLIN5). Fluorescence-labeled exosomes tracing and histological detection identified that NSC-derived exosomes (NSC-Exo) could travel from the lateral ventricle into bone injury sites. Homocysteine (Hcy) led to osteogenic and angiogenic impairment, whereas the NSC-Exo were confirmed to restore it. Mecobalamin, a clinically used neurotrophic drug, further enhanced the protective effects of NSC-Exo through increased PLIN5 expression. Mechanistically, NSC-derived PLIN5 reversed excessive Hcy-induced lipid metabolic imbalance and aberrant lipid droplet accumulation through lipophagy-dependent intracellular lipolysis. Intracerebroventricular administration of mecobalamin and/or AAV-shPlin5 confirmed the effects of PLIN5-driven endocrine modulations on new bone formation and vascular reconstruction in hyperhomocysteinemic and high-fat diet models. This study uncovered a novel brain-skeleton axis that NSCs in the mammalian brain modulated bone regeneration through PLIN5-driven lipid metabolism modulation, providing evidence for lipid- or bone-targeted medicine development.

Establishment and Verification of a Predictive Nomogram for New Vertebral Compression Fracture Occurring after Bone Cement Injection in Middle-Aged and Elderly Patients with Vertebral Compression Fracture

OBJECTIVE

New vertebral compression fracture (NVCF) occurring after bone cement injection in middle-aged and elderly patients with vertebral compression fracture is very common. Preoperative baseline characteristics and surgical treatment parameters have been widely studied as a risk factor, but the importance of the patients' laboratory indicators has not been thoroughly explored. We aimed to explore the relationship between laboratory indicators and NVCF, and attempt to construct a clinical prediction model of NVCF together with other risk factors.

METHODS

Retrospective analysis was performed for 200 patients who underwent bone cement injection (percutaneous kyphoplasty or vertebroplasty) for vertebral compression fractures between January 2019 and January 2020. We consulted the relevant literature and collated the factors affecting the occurrence of NVCF. Feature selection of patients with NVCF was optimized using the least absolute shrinkage and selection operator regression model, which was used to conduct multivariable logistic regression analysis, to create a predictive model incorporating the selected features. The discrimination, calibration, and clinical feasibility of the predictive model were assessed using the concordance index (C-index), calibration plots, and decision curve analysis. Internal validation was performed using Bootstrap resampling verification.

RESULTS

Time from injury to surgery exceeding 7 days, low osteocalcin levels, elevated homocysteine levels, osteoporosis, mode of operation (percutaneous vertebroplasty), lack of postoperative anti-osteoporosis treatment, and poor diffusion of bone cement were independent risk factors for NVCF in middle-aged and elderly patients with vertebral compression fracture after bone cement injection. The C-index of the nomogram constructed using these seven factors was 0.895, indicating good discriminatory ability. The calibration plot showed that the model was well calibrated. Bootstrap resampling verification yielded a significant C-index of 0.866. Decision curve analysis demonstrated that the greatest clinical net benefit for predicting NVCF after bone cement injection could be achieved with a threshold of 1%-91%.

CONCLUSION

This nomogram can effectively predict NVCF incidence after bone cement injection in middle-aged and elderly patients with vertebral compression fracture, thus aiding clinical decision-making and postoperative management, promoting effective postoperative rehabilitation, and improving the quality of life.

A more accurate indicator to evaluate oxidative stress in rat plasma with osteoporosis

Background: oxidative stress is linked to various human diseases which developed into the idea of "disrupted redox signaling". Osteoporosis (OP) is a chronic skeletal disorder characterized by low bone mineral density and deterioration of bone microarchitecture among which estrogen deficiency is the main cause. Lack of estrogen leads to the imbalance between oxidation and anti-oxidation in patients, and oxidative stress is an important link in the pathogenesis of OP. The ratio of the reduced to the oxidized thiols can characterize the redox status. However, few methods have been reported for the simultaneous determination of reduced forms and their oxidized forms of thiols in plasma. Methods: we developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation and validated a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method to determine two reduced forms of thiols-homocysteine (Hcy), cysteine (Cys) levels and their respective oxidized compounds, homocystine (HHcy) and cystine (Cyss) in rat plasma simultaneously for the first time. Thirty-six female rats were randomly divided into three groups: normal control (NC), oxidative stress (ovariectomy, OVX) and ovariectomy with hydrogen-rich saline administration (OVX + HRS). Results: the validation parameters for the methodological results were within the acceptance criteria. There were both significant differences of Hcy/HHcy (Hcy reduced/oxidized) and Cys/Cyss (Cys reduced/oxidized) in rat plasma between three groups with both p < 0.05 and meanwhile, the p values of malondialdehyde, superoxide dismutase and glutathione peroxidase were all less than 0.01. The value of both Hcy/HHcy and Cys/Cyss were significantly decreased with the change of Micro-CT scan result of femoral neck in OVX group (both the trabecular thickness and trabecular number significantly decreased with a significant increase of trabecular separation) which demonstrate OP occurs. The change of Hcy/HHcy is more obvious and prominent than Cys/Cyss. Conclusions: the Hcy/HHcy and Cys/Cyss could be suitable biomarkers for oxidative stress and especially Hcy/HHcy is more sensitive. The developed method is simple and accurate. It can be easily applied in clinical research to further evaluate the oxidative stress indicator for disease risk factors.

Inferring causal effects of homocysteine and B-vitamin concentrations on bone mineral density and fractures: Mendelian randomization analyses

OBJECTIVES

In the progress of bone metabolism, homocysteine (Hcy) and B vitamins play substantial roles. However, the causal associations of homocysteine, B-vitamin concentrations with bone mineral density (BMD), and fractures remain unclear. Therefore, we employed a two-sample Mendelian randomization (MR) design to infer the causal effects of Hcy and B vitamins on BMD and fractures.

METHODS

We selected instrumental variables from large genome-wide association studies (GWASs). Specifically, the exposures mainly included Hcy (sample size: 44,147), vitamin B12 (sample size: 45,576), folate (sample size: 37,465), and vitamin B6 (sample size: 1,864). The outcome variables included total body BMD (sample size: 66,628), heel BMD (sample size: 142,487), femoral neck BMD (sample size: 32,735), lumbar spine BMD (sample size: 28,498), and forearm BMD (sample size: 8143). Additionally, the total body BMD in several age strata was also included. Furthermore, the fractures of the forearm, femoral neck, lumbar spine, heel corresponding with the BMD regions, and femoral neck and lumbar spine BMD in men and women, separately, were added as additional outcomes. Two-sample MR approaches were utilized in this study. Inverse variance weighting (IVW) was adopted as the main analysis. MR-PRESSO, MR-Egger, the weighted median estimate, and multivariable MR were performed as sensitivity methods.

RESULTS

In the main analysis, Hcy concentrations have an inverse association with heel BMD (Beta = 0.046, 95% confidence interval (CI) -0.073 to -0.019, P = 9.59E-04) per SD unit. In addition, for one SD increase of vitamin B12, the total body BMD decreased 0.083 unit (95%CI -0.126 to -0.040, P = 1.65E-04). The trend was more obvious in age over 45 years (Beta = -0.135, 95%CI -0.203-0.067, P = 9.86E-05 for age 45-60; Beta = -0.074, 95%CI -0.141 to -0.007, P = 0.031 for age over 60 years). No association of B vitamins and Hcy levels with the risk of fractures and femoral neck and lumbar spine BMD in men and women was found in this study. Other sensitivity MR methods elucidated consistent results.

CONCLUSIONS

Our findings indicated that there exist the inversely causal effects of Hcy and vitamin B12 on BMD in certain body sites and age strata. These give novel clues for intervening bone-related diseases in public health and nutrition.

Causal effects of B vitamins and homocysteine on obesity and musculoskeletal diseases: A Mendelian randomization study

OBJECTIVES

Although homocysteine (Hcy) increases the risk of cardiovascular diseases, its effects on obesity and musculoskeletal diseases remain unclear. We performed a Mendelian randomization study to estimate the associations between Hcy and B vitamin concentrations and their effects on obesity and musculoskeletal-relevant diseases in the general population.

METHODS

We selected independent single nucleotide polymorphisms of Hcy (n = 44,147), vitamin B12 (n = 45,576), vitamin B6 (n = 1864), and folate (n = 37,465) at the genome-wide significance level as instruments and applied them to the studies of summary-level data for fat and musculoskeletal phenotypes from the UK Biobank study (n = 331,117), the FinnGen consortium (n = 218,792), and other consortia. Two-sample Mendelian randomization (MR) approaches were utilized in this study. The inverse variance weighting (IVW) was adopted as the main analysis. MR-PRESSO, MR-Egger, the weighted median estimate, bidirectional MR, and multivariable MR were performed as sensitivity methods.

RESULTS

Higher Hcy concentrations were robustly associated with an increased risk of knee osteoarthritis [odds ratio (OR) 1.119; 95% confidence interval (CI) 1.032-1.214; P = 0.007], hospital-diagnosed osteoarthritis (OR 1.178; 95% CI 1.012-1.37; P = 0.034), osteoporosis with pathological fracture (OR 1.597; 95% CI 1.036-2.46; P = 0.034), and soft tissue disorder (OR 1.069; 95% CI 1.001-1.141; P = 0.045) via an inverse variance weighting method and other MR approaches. Higher vitamin B12 levels were robustly associated with decreased body fat percentage and its subtypes (all P < 0.05). Bidirectional analyses showed no reverse causation. Multivariable MR analyses and other sensitivity analyses showed directionally similar results.

CONCLUSIONS

There exist significant causal effects of vitamin B12 in the serum and Hcy in the blood on fat and musculoskeletal diseases, respectively. These findings may have an important insight into the pathogenesis of obesity and musculoskeletal diseases and other possible future therapies.

Plasma homocysteine levels and handgrip strength in postmenopausal women

OBJECTIVE

This study evaluated handgrip strength (HGS), circulating homocysteine levels and related factors in postmenopausal women.

METHODS

This study is a sub-analysis of a prospective cohort of 303 postmenopausal women aged 62.7 ± 6.9 years who had HGS measures with a digital dynamometer as the primary outcome, and plasma homocysteine and creatinine levels and glomerular filtration rate (GFR) measures as the secondary outcomes.

RESULTS

The average HGS was 22.5 ± 4.0 kg, 29.4% of women had dynapenia (HGS < 20 kg), adiposity was 40.3 ± 5.4% and 9.57% of women had hyperhomocysteinemia (homocysteine >15 μmol/l). There were no differences between tertiles of homocysteine and HGS (p = 0.641). Plasma homocysteine levels were unrelated to HGS (r = -0.06) and correlated with age (r = 0.17), GFR (r = -0.28) and creatinine (r = 0.23). Hyperhomocysteinemia was not associated with HGS (odds ratio [OR] = 0.98 [95% confidence interval (CI): 0.89; 1.08]) or dynapenia (OR = 1.10 [95% CI: 0.45; 2.47]). The risk of presenting low HGS were not significantly associated with homocysteine (OR = -0.08 [95% CI: -0.21; 0.06]) and were associated with age (OR = -0.23 [95% CI: -0.29; -0.17]), adiposity (OR = -6.52 [95% CI: -9.53; -3.50]) and creatinine (OR = 6.22 [95% CI: 2.48; 9.97]).

CONCLUSIONS

HGS and dynapenia were unrelated to hyperhomocysteinemia. Age, GFR and creatinine were significantly associated with plasma homocysteine levels.

Associations between Plasma Folate and Vitamin B12, Blood Lead, and Bone Mineral Density among Adults and Elderly Who Received a Health Examination

This study hypothesized that plasma folate and vitamin B₁₂ levels modified the association between blood lead and cadmium and total urinary arsenic levels and bone loss. A total of 447 study subjects who received a physical examination at the Wanfang Hospital Medical Center were recruited. Bone loss was defined as a calcaneus bone mineral density T-score less than -1. Blood cadmium and lead concentrations were measured by ICP-MS. Urinary arsenic species were determined using HPLC-HG-AAS. A SimulTRAC-SNB radioassay was used to measure plasma folate, vitamin B₁₂, and homocysteine levels. Total urinary arsenic and blood lead concentration were positively correlated with the odds ratio (OR) for bone loss in a dose-response manner. The OR and 95% confidence interval (CI) for bone loss in participants with blood lead concentrations > 56.14 versus ≤33.82 μg/dL were 1.82 and 1.10-3.01. No correlation between plasma folate and vitamin B₁₂ levels alone and bone loss was observed. However, this study is the first observational study to find that blood lead concentrations tend to increase the OR of bone loss in a low plasma folate and plasma vitamin B₁₂ group with multivariate ORs (95% CI) of 2.44 (0.85-6.96).

Genetically Predicted Circulating Omega-3 Fatty Acids Levels Are Causally Associated With Increased Risk for Systemic Lupus Erythematosus

Background

Accumulating evidence has demonstrated the associations of omega-3 or omega-6 polyunsaturated fatty acids (PUFAs) with the disease activity and inflammatory mediators of systemic lupus erythematosus (SLE), but the evidence of causal links of omega-3 or omega-6 PUFAs on the risk for SLE remains inconclusive.

Objectives

This study was conducted to evaluate the causal relationships between omega-3/omega-6 PUFAs and SLE by performing the Mendelian randomization (MR) analysis.

Methods

Genome-wide significant single-nucleotide polymorphisms (SNPs) were obtained from genome-wide association studies (GWASs) of circulating omega-3/omega-6 levels (n = up to 13,544) and GWAS meta-analyses of SLE (n = 14,267), respectively. The bidirectional two-sample MR (TSMR) analysis was conducted to infer the causality.

Results

The inverse-variance weighted (IVW) method revealed that genetically determined per SD increase in omega-3 levels were causally associated with an increased risk for SLE (odds ratios [ORs] = 1.49, 95% CI: 1.07, 2.08, p = 0.021), but no causal effect of omega-6 on the risk SLE was observed (IVW OR = 1.06, 95% CI: 0.72, 1.57, p = 0.759). In addition, there were no significantly causal associations in genetic predisposition to SLE with the changes of omega-3 and omega-6 levels, respectively (IVW beta for omega-3: 0.007, 95% CI: −0.006, 0.022, p = 0.299; IVW beta for omega-6: −0.008, 95% CI: −0.023, 0.006, p = 0.255).

Conclusion

The present study revealed the possible causal role of omega-3 on increasing the risk for SLE, it could be the potential implications for dietary recommendations.

The causal association of polyunsaturated fatty acids with allergic disease: A two-sample Mendelian randomization study

Objectives

Previous studies have reported a potential association of polyunsaturated fatty acids (PUFAs) levels with allergic disease risk and the possible benefit of PUFAs supplementation on allergic disease prevention. This study was performed to estimate the genetic association between PUFAs and allergic diseases using the method of both univariable and multivariable two-sample Mendelian randomization (MR).

Methods

As indicators of the PUFAs levels, we included the omega-3, omega-6, docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), linoleic acid (LA), and the ratio of omega-6 to omega-3 (omega-6:3). Summarized statistics of genome-wide association studies (GWASs) for these PUFAs were obtained from the United Kingdom Biobank and the Twins United Kingdom cohort. Genetic data relating to allergic diseases, including atopic dermatitis (AD), allergic rhinitis (AR), allergic conjunctivitis (AC), allergic urticaria (AU) and asthma, were accessed from the FinnGen biobank analysis. Odds ratios and 95% CIs were used to express the impact.

Results

The MR results denoted a genetic association between the genetically determined increase in omega-3 levels and the decreased risk of some allergic diseases including AD (OR: 0.863; 95% CI: 0.785 to 0.949; p = 3.86E-03), AC (OR:0.720; 95% CI: 0.547 to 0.947; p = 1.87E-02) and AU (OR:0.821; 95% CI: 0.684 to 0.985; p = 3.42E-02), while omega-6 and DHA level was only found to have negatively correlation with risk of AC with ORs of 0.655 (95% CI: 0.445 to 0.964; p = 3.18E-02) and 0.671 (95% CI 0.490 to 0.918; p = 1.25E-02), respectively. Omega-6:3 were causally significantly associated with the increased risk of AD (OR:1.171; 95% CI: 1.045 to 1.312; p = 6.46E-03) and AC (IVW: OR:1.341; 95% CI: 1.032 to 1.743; p = 2.83E-02). After adjustment of age, economic level, BMI, smoking and alcohol behaviors in the multivariable MR analysis, a direct causal protective effect of omega-3 on AD and AC, as well as a direct causal association between DHA and AD were observed. Omega-6:3 was also found to be directly associated with an increased risk of AD and AC. No association was found of EPA or LA with allergic diseases.

Conclusion

Higher PUFA concentrations (omega-3, omega-6, DHA) and lower omega-6:3 ratios were genetically associated with a lower risk of some allergic diseases.

Causal effects of homocysteine levels on the components of sarcopenia: A two-sample mendelian randomization study

Background: Currently, it is unclear whether there is a causal association between genetically predicted plasma homocysteine (Hcy) levels and the risk of sarcopenia. We performed a Mendelian randomization (MR) study to assess the association between circulating Hcy levels and the components [grip strength, walking pace, and appendicular lean mass (ALM)] of sarcopenia. Methods: Independent single nucleotide polymorphisms (SNPs) significantly associated with plasma Hcy levels served as instrumental variables. Summary-level data regarding the components of sarcopenia. Were obtained from the UK Biobank. Inverse variance weighted (IVW) as the primary method was used for Mendelian randomization (MR) analysis. We also use four models, weighted median, MR-Egger regression, Maximum likelihood, and Penalised weighted median, as supplementary methods to IVW. The MR-Egger intercept test, Cochran's Q test, and "leave-one-out" sensitivity analysis were performed to evaluate the horizontal pleiotropy, heterogeneities, and stability of the causal association between Hcy levels and the components of sarcopenia. Results: The IVW-MR analysis suggested significant negative associations of increased plasma Hcy levels with grip strength (right: effect = -0.036, SE = 0.032, p = 5.53E-4; left: effect = -0.045, SE = 0.010, p = 1.45E-5), walking pace (effect = -0.038, SE = 0.011, p = 3.18E-4), and ALM (effect = -0.058, 0.013, p = 1.03E-5). However, there were no significant associations of decreased plasma Hcy levels with grip strength (right: effect = 0.005, SE = 0.021, p = 0.82; left: effect = -0.006, SE = 0.014, p = 0.64), walking pace (effect = 0.01, 0.020, p = 0.61), or ALM (effect = -0.034, SE = 0.018, p = 0.06).The accuracy and robustness of these findings were confirmed by sensitivity tests. Conclusion: Increased circulating Hcy levels were associated with lower grip strength, slower walking pace, and decreased ALM.

Relationship Between Serum Amino Acid Levels and Bone Mineral Density: A Mendelian Randomization Study

BACKGROUND

This study aimed to explore the association between serum amino acids (AAs) levels and bone mineral density (BMD).

METHODS

We performed a two-sample Mendelian randomization (MR) analysis to analyze the associations between the levels of eight AAs and BMD values by using summary-level genome-wide association study (GWAS) data. We applied the MR Steiger filtering method and MR Pleiotropy RESidual Sum and Outlier (MR-PRESSO) global test to check for and remove single nucleotide polymorphisms (SNPs) that were horizontally pleiotropic. The associations were estimated with the inverse variance weighted (IVW), MR-Egger, weighted median and MR Robust Adjusted Profile Score (MR.RAPS) methods.

RESULTS

Our study found that genetically increased isoleucine (Ile) [IVW: effect = 0.1601, 95% confidence interval (CI) = 0.0604 ~ 0.2597, p = 0.0016] and valine (Val) levels (IVW: effect = 0.0953, 95% CI = 0.0251 ~ 0.1655, p = 0.0078) were positively associated with total body BMD (TB-BMD). The results also revealed that genetically increased tyrosine (Tyr) levels were negatively associated with TB-BMD (IVW: effect = -0.1091, 95% CI = -0.1863 ~ -0.0320, p = 0.0055).

CONCLUSIONS

In this study, associations between serum AA levels and BMD were established. These findings underscore the important role that serum AAs play in the development of osteoporosis and provide evidence that osteoporosis can be prevented and treated by the intake of certain AAs.