Mendelian randomization analysis to examine for a causal effect of urate on bone mineral density

Mining Candidate Genes and Identifying Risk Factors for Leg Disease in Broilers: A Mendelian Randomization Study

Clinical investigations have highlighted disruptions in bone metabolic processes and abnormal fluctuations in serum indicator levels during the onset of leg disease (LD) in broilers. However, the presence of a genetic causal relationship for this association remains undetermined. Therefore, the aim of this study is to discern the risk factors underlying LD development using 1235 sequenced white-feathered broilers. We employed Mendelian randomization (MR) analysis to assess the associations of bone strength (BS), bone mineral density (BMD), tibial bone weight (TBW), tibial bone length (TBL), tibial bone diameter (TBD), bone ash (BA), ash calcium (Ash Ca), ash phosphorus (Ash P), serum calcium (Ca), serum phosphorus (P), serum alkaline phosphatase (ALP), and serum osteoprotegerin (OPG) with the incidence of LD. Compelling evidence underscores a causal link between the risk of developing LD and decreased BMD (odds ratio (OR) = 0.998; 95% CI: 0.983, 0.993; P < 0.001) and narrower TBD (OR = 0.985, 95% CI: 0.975, 0.994, P = 0.002). Additionally, serum OPG concentrations (OR: 0.995, 95% CI: 0.992, 0.999, P = 0.008) were associated with BMD (OR = 0.0078, 95% CI = 0.0043 to 0.0140, P < 0.001), indicating a robust genetic relationship between ALP concentrations (OR: 0.988, 95% CI: 0.984, 0.993, P < 0.001) and TBD (OR = 0.0046, 95% CI = 0.0026, 0.0083, P < 0.001). Moreover, elevated serum Ca (OR: 0.564, 95% CI: 0.487, 0.655, P < 0.001) and P (OR: 0.614, 95% CI: 0.539, 0.699, P < 0.001) levels were associated with a narrower TBD. Elevated serum levels of Ca, P, ALP, and OPG contribute to disturbances in bone metabolism, while decreased BMD and narrower TBD are associated with a greater risk of developing LD in broilers. This discovery elucidates the metabolic risk factors for LD in broilers and could provide information on LDs, such as osteoporosis, in humans.

Influence of serum uric acid on bone and fracture risk in postmenopausal women

AIMS

Uric acid has been associated with several metabolic conditions, including bone diseases. Our objective here was to consider the relationship between serum uric acid levels and various bone parameters (bone mineral density, ultrasonographic parameters, vitamin D, PTH and serum calcium), as well as the prevalence and risk of fragility fracture.

METHODS

An observational and cross-sectional study carried out on 679 postmenopausal women, classified into 3 groups according to their serum uric acid levels, in whom bone densitometry, calcaneus ultrasounds, PTH, vitamin D and serum calcium analysis were done. Bone fractures were collected through the clinical history and lateral spinal X-ray.

RESULTS

Higher uric acid levels were found in women with older age, high BMI, diabetes, and high blood pressure. Higher levels of PTH and serum calcium were also observed, but did not effect on vitamin D. Serum uric acid was positively related to densitometric and ultrasonic parameters and negatively associated with vertebral fractures.

CONCLUSIONS

In the population of postmenopausal women studied, sUA levels were correlated with BMD, BUA, and QUI-Stiffness, and this correlation was independent of age and BMI. In addition, sUA was associated with a decrease in vertebral fractures. These results imply a beneficial influence of sUA on bone metabolism, with both a quantitative and qualitative positive effect, reflected in the lower prevalence of vertebral fractures.

BMI mediates the association of serum uric acid with bone health: a cross-sectional study of the National Health and Nutrition Examination Survey (NHANES)

BACKGROUND

The associations between serum uric acid and osteoporosis or osteopenia remain controversial, and few studies have explored whether BMI acts as a mediators in the association between the SUA and OP/ osteopenia.

OBJECTIVE

To explore the relationship between serum uric acid and osteoporosis or osteopenia among US adults.

METHODS

A cross-sectional study was conducted to examine the association between serum uric acid and osteoporosis or osteopenia from four cycles of NHANES. Binary logistic regression models and restricted cubic spline models were used to evaluate the association between serum uric acid and osteoporosis or osteopenia, and interaction analysis was used to test the differences between subgroups. Mediation analysis was utilized to investigate whether BMI acts as a mediator in the association between SUA and OP/ osteopenia.

RESULTS

12581 participants aged ≥ 18 years were included. A U-shape nonlinear relationship between SUA and osteoporosis or osteopenia in all people was found (P < 0.0001, P for nonlinear = 0.0287). There were significant interactions in age subgroups (P for interaction = 0.044), sex subgroups (P for interaction = 0.005), and BMI subgroups (P for interaction = 0.017). We further assessed the subgroups and found the optimal range of serum uric acid levels with a lower risk of osteoporosis or osteopenia was 357-535 µmol/L in males, 327-417 µmol/L in people aged ≥ 50 years, above 309 µmol/L in people aged < 50 years, 344-445 µmol/L in people with BMI ≥ 30, and above 308 µmol/L in people with BMI < 30. BMI fully mediated the association of SUA and OP/osteopenia, with a value of -0.0024(-0.0026--0.0021). These results were robust in sensitivity analyses.

CONCLUSIONS

A complicated relationship between SUA and bone health in different populations was observed. Maintaining SUA within a specific range may be beneficial to bone health. In addition, BMI may play an important role in the association between SUA and bone health, but considering the limitations of this study, further prospective research is required.

Inferring Causal Relationships Between Metabolites and Polycystic Ovary Syndrome Using Summary Statistics from Genome‑Wide Association Studies

Polycystic ovary syndrome (PCOS) is a disorder characterized by hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology. Previous studies have suggested that metabolites may play a pivotal mediating role in the progression of phenotypic variations. Although several metabolites had been identified as potential markers for PCOS, the relationship between blood metabolites and PCOS was not comprehensively explored. Previously, Pickrell et al. designed a robust approach to infer evidence of a causal relationship between different phenotypes using independently putative causal SNPs. Our previous paper extended this approach to make it more suitable for cases where only a few independently putative causal SNPs were identified to be significantly associated with the phenotypes (i.e., metabolites). When the most significant SNPs in each independent locus (the independent lead SNPs) with p-values of < 1 × 10-5 were used, 3 metabolites (2-tetradecenoyl carnitine, threitol, 1-docosahexaenoylglycerophosphocholine) causally influencing PCOS and 2 metabolites (asparagine and phenyllactate) influenced by PCOS were identified, (relative likelihood r < 0.01). Under a less stringent threshold of r < 0.05, 7 metabolites (trans-4-hydroxyproline, glutaroyl carnitine, stachydrine, undecanoate, 7-Hoca, N-acetylalanine and 2-hydroxyisobutyrate) were identified. Taken together, this study can provide novel insights into the pathophysiological mechanisms underlying PCOS; whether these metabolites can serve as biomarkers to predict PCOS in clinical practice warrants further investigations.

Causal association between depression and intracranial aneurysms: a bidirectional two-sample Mendelian randomization study

Background

Although observational studies have suggested a bidirectional relation between depression and intracranial aneurysms (IAs), their causal relations remain unclear. Thus we aimed to assess the causal association between depression and IAs.

Methods

We conducted a bidirectional two-sample Mendelian randomization (MR) study using summary-level data from publicly available genome-wide association studies of depression (n = 500,199), IAs (n = 79,429), unruptured intracranial aneurysm (uIA) (n = 74,004), and subarachnoid hemorrhage (SAH) (n = 77,074). MR analyses included the inverse-variance weighted (IVW) method as the primary analytic, plus weighted-median, simple mode, weighted mode, MR-Egger, and MR PRESSO.

Results

Genetically predicted depression was strongly positively related to IAs (odds ratio [OR] = 1.69, 95% confidence interval [CI] 1.19-2.39, p = 0.003), uIA (OR = 1.96, 95% CI 1.06-3.64, p = 0.032), and SAH (OR = 1.73, 95% CI 1.14-2.61, p = 0.009). Reverse MR analyses showed that while genetically predicted uIA was positively related to depression (OR = 1.02, 95% CI 1.00-1.05, p = 0.044), no causal relations were observed for either IAs or SAH for depression.

Conclusion

Our findings provide evidence of a causal effect of depression on IAs, uIA, and SAH. For the reverse MR analyses, we found a causal impact of uIA on depression, but no causal influence of either IAs or SAH for depression.

Exploring the causal relationship between inflammatory cytokines and inflammatory arthritis: A Mendelian randomization study

OBJECTIVES

Previous studies have reported an association between inflammatory cytokines and inflammatory arthritis, including Ankylosing spondylitis (AS), rheumatoid arthritis (RA), and psoriatic arthritis (PsA). This study aims to explore the causal relationship between inflammatory cytokines and AS, RA, and PsA using Mendelian randomization (MR).

METHODS

We conducted a bidirectional two-sample MR analysis using genetic summary data from a publicly available genome-wide association study (GWAS) that included 41 genetic variations of inflammatory cytokines, as well as genetic variant data for AS, RA, and PsA from the FinnGen consortium. The main analysis method used was Inverse variance weighted (IVW) to investigate the causal relationship between exposure and outcome. Additionally, other methods such as MR Egger, weighted median (WM), simple mode, and weighted mode were employed to strengthen the final results. Sensitivity analysis was also performed to ensure the reliability of the findings.

RESULTS

The results showed that macrophage colony-stimulating factor (MCSF) was associated with an increased risk of AS (OR = 1.163, 95 % CI = 1.016-1.33, p = 0.028). Conversely, high levels of TRAIL and beta nerve growth factor (β-NGF) were associated with a decreased risk of AS (OR = 0.892, 95 % CI = 0.81-0.982, p = 0.002; OR = 0.829, 95 % CI = 0.696-0.988, p = 0.036). Four inflammatory cytokines were found to be associated with an increased risk of PsA: vascular endothelial growth factor (VEGF) (OR = 1.161, 95 % CI = 1.057-1.275, p = 0.002); Interleukin 12p70 (IL12p70) (OR = 1.189, 95 % CI = 1.049-1.346, p = 0.007); IL10 (OR = 1.216, 95 % CI = 1.024-1.444, p = 0.026); IL13 (OR = 1.159, 95 % CI = 1.05-1.28, p = 0.004). Interleukin 1 receptor antagonist (IL-1rα) was associated with an increased risk of seropositive RA (OR = 1.181, 95 % CI = 1.044-1.336, p = 0.008). Similarly, genetic susceptibility to inflammatory arthritis was found to be causally associated with multiple inflammatory cytokines. Lastly, the sensitivity analysis supported the robustness of these findings.

CONCLUSIONS

This study provides additional insights into the relationship between inflammatory cytokines and inflammatory arthritis, and may offer new clues for the etiology, diagnosis, and treatment of inflammatory arthritis.

Causal influence of muscle weakness on cardiometabolic diseases and osteoporosis

The causal roles of muscle weakness in cardiometabolic diseases and osteoporosis remain elusive. This two-sample Mendelian randomization (MR) study aims to explore the causal roles of muscle weakness in the risk of cardiometabolic diseases and osteoporosis. 15 single nucleotide polymorphisms (SNPs, P < 5 × 10-8) associated with muscle weakness were used as instrumental variables. Genetic predisposition to muscle weakness led to increased risk of coronary artery disease (inverse variance weighted [IVW] analysis, beta-estimate: 0.095, 95% confidence interval [CI]: 0.023 to 0.166, standard error [SE]:0.036, P-value = 0.009) and reduced risk of heart failure (weight median analysis, beta-estimate: - 0.137, 95% CI - 0.264 to - 0.009, SE:0.065, P-value = 0.036). In addition, muscle weakness may reduce the estimated bone mineral density (eBMD, weight median analysis, beta-estimate: - 0.059, 95% CI - 0.110 to - 0.008, SE:0.026, P-value = 0.023). We found no MR associations between muscle weakness and atrial fibrillation, type 2 diabetes or fracture. This study provides robust evidence that muscle weakness is causally associated with the incidence of coronary artery disease and heart failure, which may provide new insight to prevent and treat these two cardiometabolic diseases.

The causal relationship between autoimmune diseases and osteoporosis: a study based on Mendelian randomization

Objective

The relationship between different autoimmune diseases and bone mineral density (BMD) and fractures has been reported in epidemiological studies. This study aimed to explore the causal relationship between autoimmune diseases and BMD, falls, and fractures using Mendelian randomization (MR).

Methods

The instrumental variables were selected from the aggregated statistical data of these diseases from the largest genome-wide association study in Europe. Specifically, 12 common autoimmune diseases were selected as exposure. Outcome variables included BMD, falls, and fractures. Multiple analysis methods were utilized to comprehensively evaluate the causal relationship between autoimmune diseases and BMD, falls, and fractures. Additionally, sensitivity analyses, including Cochran's Q test, MR-Egger intercept test, and one analysis, were conducted to verify the result's reliability.

Results

Strong evidence was provided in the results of the negatively association of ulcerative colitis (UC) with forearm BMD. UC also had a negatively association with the total body BMD, while inflammatory bowel disease (IBD) depicted a negatively association with the total body BMD at the age of 45-60 years. Horizontal pleiotropy or heterogeneity was not detected through sensitivity analysis, indicating that the causal estimation was reliable.

Conclusion

This study shows a negative causal relationship between UC and forearm and total body BMD, and between IBD and total body BMD at the age of 45-60 years. These results should be considered in future research and when public health measures and osteoporosis prevention strategies are formulated.

Causal Relationship Between Inflammation and Preeclampsia: Genetic Evidence from a Mendelian Randomization Study

Preeclampsia (PE) is a hypertensive disorder of pregnancy. PE patients were reported to have higher serum levels of C-reactive protein (CRP), interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α) than those in healthy controls. However, whether the expressions of these inflammation biomarkers have a causal relationship with PE is unspecified. We applied the Mendelian randomization method to infer the causal relationship between inflammation biomarkers (e.g., CRP, IL-6, interleukin 1 receptor antagonist [IL-1ra] and TNF-α) and PE. Single nucleotide polymorphisms (SNPs) strongly related to inflammation biomarkers were used as instrumental variables. CRP, IL-1ra and IL-6 levels showed no significant effect on PE progression, while the genetic predicted higher level of TNF-α significantly increased the risk of PE (OR per 1-SD increase in TNF-α: 4.33; 95% CI [1.99, 9.39]; p = .00021). The findings suggest that pro-inflammatory activity of TNF-α could be a determinant for PE progression. More antenatal care should be given to those pregnant women with higher level of inflammation biomarkers, especially TNF-α.

Causal roles of circulating adiponectin in osteoporosis and cancers

Circulating adiponectin has some association with the risk of osteoporosis and cancers, but their causal relationships remains elusive. Mendelian randomization (MR) study was used to explore the causal roles of circulating adiponectin in osteoporosis and cancers by using genome-wide association studies (GWASs) associated with circulating adiponectin, osteoporosis and cancers. Fifteen single nucleotide polymorphisms (SNPs) were used as instrumental variables for circulating adiponectin. Genetic predisposition to high circulating adiponectin was strongly associated with low femoral neck bone mineral density (FN-BMD, beta-estimate: -0.015, 95% CI: -0.023 to -0.006, SE: 0.004, P-value = 0.001), low forearm BMD (FA-BMD, beta-estimate: -0.027, 95% CI: -0.050 to -0.004, SE: 0.012, P-value = 0.023) and increased risk of breast cancer (beta-estimate: 0.011, 95% CI: 0.001 to 0.022, SE: 0.005, P-value = 0.031). There was limited evidence of the associations between circulating adiponectin and other outcomes (i.e. lumbar spine BMD [LS-BMD], colorectal cancer, liver cancer, lung cancer, bone cancer and prostate cancer). This study provides robust evidence that high circulating adiponectin is causally associated with low FN-BMD, low FA-BMD and increased risk of breast cancer, which may provide new insight to prevent and treat osteoporosis and breast cancer.

Causal Roles of Sleep Duration in Osteoporosis and Cardiometabolic Diseases: A Mendelian Randomization Study

Sleep duration suggests some association with osteoporosis and cardiometabolic diseases, but it is unknown if these associations are causal or confounded. In this two-sample Mendelian randomization (MR) study, we included the largest genome-wide association studies (GWASs) associated with sleep duration and the outcome measures of osteoporosis and cardiometabolic diseases. Finally, 25 single nucleotide polymorphisms (SNPs) associated with short sleep duration and 7 SNPs associated with long sleep duration obtained the genome-wide significance (P < 5 × 10^-8) and were used as instrumental variables. Genetic predisposition to short sleep duration was strongly associated with increased risk of coronary artery disease (beta-estimate: 0.199, 95% confidence interval CI: 0.081 to 0.317, standard error SE:0.060, P value = 0.001) and heart failure (beta-estimate: 0.145, 95% CI: 0.025 to 0.264, SE:0.061, P value = 0.017), which were both confirmed by the sensitivity analyses. Both short and long sleep duration may reduce the estimated bone mineral density (eBMD, beta-estimate: -0.086, 95% CI: -0.141 to -0.031, SE:0.028, P value = 0.002 for short sleep duration; beta-estimate: -0.080, 95% CI: -0.120 to -0.041, SE:0.020, P value < 0.0001 for long sleep duration). There was limited evidence of associations between sleep duration and fracture, type 2 diabetes, atrial fibrillation, fasting glucose, fasting insulin, or HbA1c. This study provides robust evidence that short sleep duration is causally associated with high risk of coronary artery disease and heart failure and suggests that short sleep duration should be avoided to prevent these two cardiovascular diseases. Short and long sleep duration show some MR association with reduced eBMD, which indicates that both short and long sleep duration may be prevented to reduce the incidence of osteoporosis.

Depression and Osteoporosis: A Mendelian Randomization Study

Observational studies suggest a link between depression and osteoporosis, but these may be subject to confounding and reverse causality. In this two-sample Mendelian randomization analysis, we included the large meta-analysis of genome-wide association studies for depression among 807,553 individuals (246,363 cases and 561,190 controls) of European descent, the large meta-analysis to identify genetic variants associated with femoral neck bone mineral density (FN-BMD), forearm BMD (FA-BMD) and lumbar spine BMD (LS-BMD) among 53,236 individuals of European ancestry, and the GWAS summary data of heel BMD (HE-BMD) and fracture among 426,824 individuals of European ancestry. The results revealed that genetic predisposition towards depression showed no causal effect on FA-BMD (beta-estimate: 0.091, 95% confidence interval [CI] - 0.088 to 0.269, SE:0.091, P value = 0.320), FN-BMD (beta-estimate: 0.066, 95% CI - 0.016 to 0.148, SE:0.042, P value = 0.113), LS-BMD (beta-estimate: 0.074, 95% CI - 0.029 to 0.177, SE:0.052, P value = 0.159), HE-BMD (beta-estimate: 0.009, 95% CI - 0.043 to 0.061, SE:0.027, P value = 0.727), or fracture (beta-estimate: 0.008, 95% CI - 0.071 to 0.087, SE:0.041, P value = 0.844). These results were also confirmed by multiple sensitivity analyses. Contrary to the findings of observational studies, our results do not reveal a causal role of depression in osteoporosis or fracture.

Association between higher serum uric acid levels within the normal physiological range and changes of lumbar spine bone mineral density in healthy Chinese postmenopausal women: a longitudinal follow-up study

OBJECTIVES

The aim of this study was to investigate whether higher serum uric acid (SUA) levels within the physiological range were associated with changes in lumbar spine bone mineral density (LBMD) in postmenopausal women without existing lumbar spine osteoporosis after a longitudinal follow-up of 3.09 years, and to further confirm the relationship between SUA and bone mineral density (BMD) in other sites such as femoral neck, total hip, and trochanter at follow-up.

METHODS

A longitudinal study of 175 healthy postmenopausal women without osteoporosis was conducted in Shenyang, China. BMD of the lumbar spine, femoral neck, total hip, and trochanter were measured using dual-energy x-ray absorptiometry at each visit. Pearson's correlation analysis and regression analyses were performed to determine any associations.

RESULTS

There were positive correlations between baseline SUA and BMD of the lumbar spine (P = 0.03), total hip (P = 0.04), and trochanter (P = 0.04). Moreover, higher baseline SUA levels were independently associated with LBMD decline and the odds ratio of the baseline SUA of the third quartile group was 0.12 (95% confidence interval, 0.02-0.70, P < 0.05), with P = 0.23 for the trend in baseline SUA when compared with participants in the lowest, first quartile group after adjustment for many potential confounding variables.

CONCLUSIONS

Higher SUA levels within the normal physiological range were independently associated with decreased LBMD, and SUA levels were positively related to the BMD of the lumbar spine, total hip, and trochanter in healthy Chinese postmenopausal women.

Analyses of the relationship between hyperuricemia and osteoporosis

The aim of the present study was to evaluate the association between hyperuricemia and osteoporosis in a Korean population. Data from participants of the Korean Genome and Epidemiology Study who were ≥ 40 years old were collected from 2004 to 2016. Among 173,209 participants, 11,781 with hyperuricemia (> 7.0 mg/dL in men and > 6.0 mg/dL in women) and 156,580 controls were selected based on serum measurements. Odds ratios (ORs) of osteoporosis between individuals with hyperuricemia and controls were analyzed using a logistic regression model. In the adjusted model, age, sex, income group, body mass index, smoking, alcohol consumption, hypertension, diabetes mellitus, hyperlipidemia history and nutritional intake were adjusted. The adjusted OR (aOR) of osteoporosis was 0.79 [95% confidence interval (CI) = 0.71–0.87, P < 0.001]. In subgroup analyses according to age and sex, statistical significance was observed in men > 60 years old and in women > 50 years old. In another subgroup analysis according to past medical history, significant differences were found according to hypertension (aOR = 0.83, 95% CI = 0.73–0.94, and 0.75, 95% CI = 0.64–0.87), diabetes mellitus (aOR = 0.77, 95% CI = 0.69–0.86), and hyperlipidemia (aOR = 0.74, 95% CI = 0.61–0.89, and 0.81, 95% CI = 0.72–0.91). This study demonstrated that hyperuricemia was associated with a decreased risk of osteoporosis.

Twelve years of GWAS discoveries for osteoporosis and related traits: advances, challenges and applications

Osteoporosis is a common skeletal disease, affecting ~200 million people around the world. As a complex disease, osteoporosis is influenced by many factors, including diet (e.g. calcium and protein intake), physical activity, endocrine status, coexisting diseases and genetic factors. In this review, we first summarize the discovery from genome-wide association studies (GWASs) in the bone field in the last 12 years. To date, GWASs and meta-analyses have discovered hundreds of loci that are associated with bone mineral density (BMD), osteoporosis, and osteoporotic fractures. However, the GWAS approach has sometimes been criticized because of the small effect size of the discovered variants and the mystery of missing heritability, these two questions could be partially explained by the newly raised conceptual models, such as omnigenic model and natural selection. Finally, we introduce the clinical use of GWAS findings in the bone field, such as the identification of causal clinical risk factors, the development of drug targets and disease prediction. Despite the fruitful GWAS discoveries in the bone field, most of these GWAS participants were of European descent, and more genetic studies should be carried out in other ethnic populations to benefit disease prediction in the corresponding population.

Serum uric acid is associated with incident hip fractures in women and men - Results from a large Austrian population-based cohort study

OBJECTIVES

Serum markers that can be used to estimate the risk of bone fractures are rare, and findings for one candidate marker, uric acid, are heterogeneous. Our aim was to investigate the potential of serum uric acid (SUA) to predict hip fractures occurring in people aged 50 years and over.

STUDY DESIGN

During a medical prevention program over the period 1985-2005 in Vorarlberg, baseline data were collected on SUA levels and covariates (age, BMI, blood pressure, smoking status, diabetes, triglycerides and cholesterol) from 185,397 individuals, of whom 42,488 women and 35,908 men met the inclusion criteria of this population-based cohort study. Information on incident cancer and end-stage kidney disease was acquired from registries.

MAIN OUTCOME MEASURE

Incident hip fracture occurring in participants aged 50 years and over during the observation period 2003-2013.

RESULTS

SUA was associated with a rise in female hip fracture risk by 6% per unit increase (HR 1.06, 95 %-CI 1.01-1.10), and risk in the highest vs. lowest SUA quartile was significantly increased (HR 1.17, 95 %-CI 1.01-1.35), but not at hyperuricemic (>5.7 mg/dl) vs. normouricemic (≤5.7 mg/dl) levels. In men, hip fracture risk rose by 15 % per unit increase (HR 1.15, 95 %-CI 1.08-1.22), and risk was significantly higher in the highest vs. lowest SUA quartile (HR 1.50, 95 %-CI 1.17-1.91) as well as at hyperuricemic (>7.0 mg/dl) vs. normouricemic (≤7.0 mg/dl) levels (HR 1.48, 95 %-CI 1.19-1.84).

CONCLUSIONS

Our results link SUA with increased risk of hip fractures, particularly in men.

Elevated Urate Levels Do Not Alter Bone Turnover Markers: Randomized Controlled Trial of Inosine Supplementation in Postmenopausal Women

OBJECTIVE

Observational studies have consistently demonstrated that serum urate level positively correlates with bone mineral density (BMD). We undertook this study to determine whether moderate hyperuricemia induced by inosine supplements influences bone turnover markers in postmenopausal women over a 6-month period.

METHODS

One hundred twenty postmenopausal women were recruited for a 6-month randomized, double-blind, placebo-controlled trial. Key exclusion criteria were osteoporosis, previous fragility fracture, bisphosphonate therapy, gout, kidney stones, and a urine pH level of ≤5.0. Participants were randomized in a 1:1 ratio to receive placebo or inosine. The coprimary end points were change in levels of N-propeptide of type I procollagen (PINP) and change in levels of β-C-telopeptide of type I collagen (β-CTX). Change in BMD, as measured by dual x-ray absorptiometry, was an exploratory end point.

RESULTS

Administration of inosine led to a significant increase in serum urate concentration over the study period (P < 0.0001 for all follow-up time points). At week 26, the mean change in serum urate concentration was +0.13 mmoles/liter (+2.2 mg/dl) in the inosine group and 0.00 mmoles/liter (0 mg/dl) in the placebo group. There was no difference in PINP or β-CTX levels between groups over the 6 months. There were no significant changes in bone density between groups over the 6 months. Adverse events and serious adverse events were similar between the 2 groups.

CONCLUSION

This clinical trial shows that although inosine supplementation leads to sustained increases in serum urate levels over a 6-month period, it does not alter markers of bone turnover in postmenopausal women. These findings do not support the concept that urate has direct biologic effects on bone turnover.

Systematic Influence of Circulating Bilirubin Levels on Osteoporosis

Observational studies report some association between circulating bilirubin levels and osteoporosis, but it is unknown if this association is causal or confounded. In this two-sample Mendelian randomization (MR) study, we included a large genome-wide association study (GWAS) associated with total bilirubin levels among 317,639 people, a large meta-analysis to identify genetic variants associated with bone mineral density (BMD) estimated by heel quantitative ultrasound (eBMD) among 426,824 individuals and fracture among 1.2 million individuals. The results revealed that circulating bilirubin levels had no causal influence on eBMD (beta-estimate: 0.004, 95% confidence interval [CI]: -0.019 to 0.028, SE:0.012, P-value=0.705) or the risk of fracture (beta-estimate: -0.009, 95% CI: -0.035 to 0.017, SE:0.013, P-value=0.488), which were both confirmed by multiple sensitivity analyses. Our results confirm that circulating bilirubin levels have no causal role in eBMD or the incidence of fracture, indicating that circulating bilirubin levels is unlikely to be a causal risk factor for osteoporosis or fracture.

Causal Effect of Blood Pressure on Bone Mineral Density and Fracture: A Mendelian Randomization Study

BACKGROUND

Hypertension may have some association with osteoporosis. This Mendelian randomization (MR) study aimed to explore the causal effect of blood pressure (BP) on bone mineral density (BMD), fall, and fracture.

METHODS

We used the genome-wide association study (GWAS) summary data among 330,956 European-descent individuals to identify 107 single-nucleotide polymorphisms (SNPs) as the instrumental variables of BP. MR analyses of these instruments were performed on 53,236 European individuals for the association with forearm BMD (FA-BMD), femoral neck BMD (FN-BMD), and lumbar spine BMD (LS-BMD); 451,179 European individuals for fall susceptibility; and up to 1.2 million individuals from European descent for fracture. Conventional inverse variance weighted (IVW) method was adopted to obtain the causal estimates of BP on different outcomes, while weighted median, MR-egger, and MR pleiotropy residual sum and outlier (MR-PRESSO) test were used for sensitivity analyses.

RESULTS

Genetically high pulse pressure (PP) could significantly improve FA-BMD (beta-estimate: 0.038, 95% confidence interval [CI]: 0.013 to 0.063, SE:0.013, P-value=0.003<Bonferroni correction P) in the IVW analysis, indicating that 1-SD increase in PP was associated with the improvement in FA-BMD levels by 0.038 g/cm² (95% CI: 0.013 to 0.063). This positive finding was also confirmed by weighted-median analysis (beta-estimate: 0.034, 95% CI: 0.000 to 0.067, SE:0.017, P-value=0.046) and MR-Egger analysis (beta-estimate: 0.117, 95% CI: 0.026 to 0.208, SE:0.046, P-value=0.011). However, there was no remarkable MR association between BP and other outcomes (i.e., FN-BMD, LS-BMD, fall, and fracture).

CONCLUSIONS

Our findings reveal a potentially causal relationship between high PP and improved FA-BMD, which may provide new sights for the treatment of osteoporosis.

Association between the metabolome and bone mineral density in a Chinese population

BACKGROUND

Osteoporosis is a common metabolic bone disease, which always leads to osteoporotic fractures. Biomarkers of bone mineral density (BMD) are helpful for prevention and early diagnosis of osteoporosis. This study aims to identify metabolomic biomarkers of low BMD.

METHODS

We included 701 participants who had BMD measures by dual-energy X-ray absorptiometry scans and donated fasting plasma samples from three clinical centres as a discovery set and another 278 participants from the fourth centre as an independent replication set. We used a liquid chromatography-mass spectrometry-based metabolomics approach to profile the global metabolites of fasting plasma.

FINDINGS

Among the 265 named metabolites identified in our study, six were associated with low BMD (FDR-adjusted P<0.05) in the discovery set and were successfully validated in the independent replication set. The circulating levels of five metabolites, i.e., inosine, hypoxanthine, PC (O-18:0/22:6), SM (d18:1/21:0) and isoleucyl-proline were associated with decreased odds of low BMD, and PC (16:0/18:3) level was associated with increased odds of low BMD. Per 1-SD increase in a composite metabolite score of these six metabolites was associated with about half decreased odds of low BMD (odds ratio 0.59, 95% confidence interval: 0.52-0.68). Furthermore, introduction of a panel of metabolites selected by elastic net regression to a prediction model of classical risk factors and plasma biomarker of bone resorption substantially improved the prediction performance for low BMD (AUCs: 0.782 vs. 0.698, P=0.002).

INTERPRETATION

Metabolomics profiling may help identify novel biomarkers of low BMD and be helpful for early diagnosis of osteoporosis beyond the current clinical index.

FUNDING

This study was supported by the National Key R&D Program of China [2018YFC2001500 to J.S.], Shanghai Municipal Science and Technology Major Project [2017SHZDZX01], the National Natural Science Foundation of China [Key Program, 91749204 to J.S.], the National Natural Science Foundation of China [General Program, 81771491 to J.S.], the Project of Shanghai Subject Chief Scientist [2017BR011 to J.S.], Grants from the TCM Supported Project [18431902300 to J.S.] from the Science and Technology Commission of Shanghai Municipality, and the National Natural Science Foundation of China [General Program, 81972089 to Z.X.]. Y.Z. was supported by the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and the National Natural Science Foundation of China [81973032].

Relationships between serum uric acid concentrations, uric acid lowering medications, and vertebral fracture in community-dwelling elderly Japanese men: Fujiwara-kyo Osteoporosis Risk in Men (FORMEN) Cohort Study

PURPOSE

The association between serum concentrations of uric acid (UA), a potent endogenous antioxidant, and fracture risk has not yet been examined for morphometric vertebral fracture (VF). This study aimed to determine whether serum UA concentrations are associated with risks of clinical osteoporotic fracture (OPF) and morphometric VF after adjusting for confounding factors including UA-lowering medications (ULMs).

MATERIALS AND METHODS

A total of 2012 Japanese men aged ≥65 years completed the baseline study, which included serum UA measurement and X-ray absorptiometry-based VF assessment. We conducted a follow-up study five years later to identify incident OPFs and VFs. OPF was identified through interviews. Incident VF was defined as a vertebra which showed reduction in any of its anterior, central, or posterior heights by ≥20% during follow-up, and satisfied grade one or higher fracture criteria in Genant's method on follow-up images. Bone mineral density (BMD) of the hip and spine was measured by dual-energy X-ray absorptiometry at baseline and follow-up.

RESULTS

We identified 45 clinical OPFs from 2000 men and 39 VFs from 1530 men during a mean follow-up period of 4.3 years. Hip BMD was significantly higher in higher UA concentration groups after adjusting for age and body mass index. A significantly decreased multivariate-adjusted odds ratio (OR) of incident VF was observed for the highest quartile groups of serum UA concentrations compared with the lowest quartile group (OR: 0.17, 95% confidence interval: 0.05-0.62). This OR remained significant after further adjusting for ULM use. ULM users in the lowest quartile group of serum UA concentrations had a significantly higher incidence rate of VF compared to the other quartile groups.

CONCLUSIONS

Higher serum UA concentrations were associated with a lower risk of morphometric VF independently of ULM in Japanese elderly men. Excessive reduction of serum UA concentrations by ULM might increase VF risk.

Genetic Pleiotropy of Bone-Related Phenotypes: Insights from Osteoporosis

PURPOSE OF REVIEW

We summarize recent evidence on the shared genetics within and outside the musculoskeletal system (mostly related to bone density and osteoporosis).

RECENT FINDINGS

Osteoporosis is determined by an interplay between multiple genetic and environmental factors. Significant progress has been made regarding its genetic background revealing a number of robustly validated loci and respective pathways. However, pleiotropic factors affecting bone and other tissues are not well understood. The analytical methods proposed to test for potential associations between genetic variants and multiple phenotypes can be applied to bone-related data. A number of recent genetic studies have shown evidence of pleiotropy between bone density and other different phenotypes (traits, conditions, or diseases), within and outside the musculoskeletal system. Power benefits of combining correlated phenotypes, as well as unbiased discovery, make these studies promising. Studies in humans are supported by evidence from animal models. Drug development and repurposing should benefit from the pleiotropic approach. We believe that future studies should take into account shared genetics between the bone and related traits.

Bone microstructure and volumetric bone mineral density in patients with hyperuricemia with and without psoriasis

We analyzed volumetric bone mineral density (vBMD) and bone microstructure using HR-pQCT in subjects with normouricemia (NU) and subjects with hyperuricemia (HU) with and without psoriasis (PSO). HU was associated with higher cortical vBMD and thickness. Differences in average and trabecular vBMD were found between patients with PSO + HU and NU.

INTRODUCTION

Hyperuricemia (HU) and gout are co-conditions of psoriasis and psoriatic arthritis. Current data suggest a positive association between HU and areal bone mineral density (BMD) and a negative influence of psoriasis on local bone, even in the absence of arthritis. However, the influence of the combination of HU and psoriasis on bone is still unclear. The aim of this study was to assess the impact of HU with and without psoriasis on bone microstructure and volumetric BMD (vBMD).

METHODS

Healthy individuals with uric acid levels within the normal range (NU), with hyperuricemia (HU), patients with hyperuricemia and psoriasis (PSO + HU), and patients with uric acid within the normal range and psoriasis (PSO + NU) were included in our study. Psoriasis patients had no current or past symptoms of arthritis. Average, trabecular, and cortical vBMD (mgHA/cm³); trabecular number (Tb.N, 1/mm) and thickness (Tb.Th, mm); inhomogeneity of the network (1/N.SD, mm); and cortical thickness (Ct.Th., mm) were carried out at the ultradistal radius using high-resolution peripheral quantitative computed tomography. In addition, bone turnover markers such as DKK-1, sclerostin, and P1NP were analyzed.

RESULTS

In total, 130 individuals were included (44 NU participants (34% female), 50 HU (24%), 16 PSO + HU (6%), 20 PSO + NU (60%)). Subjects were aged: NU 54.5 (42.8, 62.1), HU 57.5 (18.6, 65.1), PSO + HU 52.0 (42.3, 57.8), and PSO + NU 42.5 (34.8, 56.8), respectively. After adjusting for age, sex, BMI, and diabetes, patients in the HU group revealed significantly higher values of cortical vBMD (p < 0.001) as well as cortical thickness (p = 0.04) compared to the NU group. PSO + NU showed no differences to NU, but PSO + HU demonstrated both lower average (p = 0.03) and trabecular vBMD (p = 0.02). P1NP was associated with average, cortical, and trabecular vBMD as well as cortical thickness while sclerostin levels were related to trabecular vBMD.

CONCLUSION

Hyperuricemia in otherwise healthy subjects was associated with a better cortical vBMD and higher cortical thickness. However, patients with both psoriasis and hyperuricemia revealed a lower vBMD.

The Association between Serum Uric Acid and Bone Mineral Density in Older Adults

OBJECTIVES

Uric acid has been found to be potentially protective in bone metabolism. We investigated the relationship between serum uric acid (sUA) and lumbar bone mineral density (BMD) among 4156 participants aged 60 years and over from the National Health and Nutrition Examination Survey (NHANES).

METHODS

To estimate the association between sUA and lumbar BMD, multivariate logistic regression analyses were conducted. Fitted smoothing curves and generalized additive models were also performed.

RESULTS

We found sUA positively correlated with lumbar BMD after adjusting for other confounders. On subgroup analyses, stratified by sex and race/ethnicity, the positive correlation of sUA with lumbar BMD remained in both men and women, as well as in whites and Mexican Americans, but not in blacks. In blacks, the association of sUA with lumbar BMD was an inverted U-shaped curve (inflection point: 7.5 mg/dL).

CONCLUSIONS

Our study revealed a positive relationship between sUA and lumbar BMD among most old adults. This association followed an inverted U-shaped curve among blacks.

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.

Osteoporosis in Rheumatic Diseases

Osteoporosis is a chronic disease characterized by an increased risk of fragility fracture. Patients affected by rheumatic diseases are at greater risk of developing osteoporosis. The purpose of the present review is to discuss the pathogenesis, epidemiology, and treatment of osteoporosis in patients affected by rheumatic diseases with special focus for rheumatoid arthritis, psoriatic arthritis, spondyloarthritis, systemic lupus erythematosus, systemic sclerosis, vasculitides, Sjogren syndrome, and crystal-induced arthritis.

Use of Mendelian Randomization to Examine Causal Inference in Osteoporosis

Epidemiological studies have identified many risk factors for osteoporosis, however it is unclear whether these observational associations reflect true causal effects, or the effects of latent confounding or reverse causality. Mendelian randomization (MR) enables causal relationships to be evaluated, by examining the relationship between genetic susceptibility to the risk factor in question, and the disease outcome of interest. This has been facilitated by the development of two-sample MR analysis, where the exposure and outcome are measured in different studies, and by exploiting summary result statistics from large well-powered genome-wide association studies that are available for thousands of traits. Though MR has several inherent limitations, the field is rapidly evolving and at least 14 methodological extensions have been developed to overcome these. The present paper aims to discuss some of the limitations in the MR analytical framework, and how this method has been applied to the osteoporosis field, helping to reinforce conclusions about causality, and discovering potential new regulatory pathways, exemplified by our recent MR study of sclerostin.

Mendelian randomization in the bone field

Identification of causative risk factors amenable for modification is essential for the prevention and treatment of osteoporosis. Observational studies have identified associations between several potentially modifiable risk factors and osteoporosis. However, observational studies are susceptible to confounding, reverse causation bias, and measurement error, all of which limit their ability to provide causal estimates of the effect of exposures on outcomes, thereby reducing their ability to inform prevention and treatment strategies against bone loss and fractures. In addition, not all risk factors are suitable for an analysis in a randomized clinical trial. Mendelian randomization is a genetic epidemiological method that exploits genetic variants as unbiased proxies for modifiable exposures (e.g., biomarkers, adiposity measures, dietary factors, and behaviors) to determine the causal relationships between exposures and health outcomes. This technique has been used to provide evidence of causal associations of serum estradiol concentrations, smoking, body mass index, and type 2 diabetes with bone mineral density and the lack of associations of serum thyroid stimulating hormone, urate, C-reactive protein, and 25‑hydroxyvitamin D concentrations with bone mineral density in generally healthy populations. This review will briefly explain the concept of Mendelian randomization, the advantages and potential limitations of this study design, and give examples of how Mendelian randomization has been used to investigate questions relevant to osteoporosis.

Examining the causal role of leptin in bone mineral density: A Mendelian randomization study

Leptin, a small polypeptide hormone secreted by the adipocytes, controls body weight and gonadal function by binding to a special receptor located in the hypothalamus. Observational studies have demonstrated a controversial association between leptin and bone mineral density (BMD), and functional studies of the relationship between leptin and BMD still largely vary by different studies. Using SNPs strongly associated with leptin levels in 52,140 individuals, we conducted a two-sample Mendelian randomization study to identify whether genetically lowered leptin levels were associated with BMD by using an inverse-variance weighted method, a weighted median method, MR-Egger and Robust Adjusted Profile Score. We found that circulating leptin levels may causally decrease lumbar spine BMD (effect size = -0.45, 95% CI: -0.82, -0.083; p value = 0.016). The association estimates of circulating leptin levels on femoral neck, forearm and total body BMD were not significant. Our study suggests that genetically predicted higher circulating leptin was associated with lower LS-BMD.

Review of the Literature Examining the Association of Serum Uric Acid with Osteoporosis and Mechanistic Insights into Its Effect on Bone Metabolism

Background And Objective:

Osteoporosis is a common bone disorder that increases susceptibility to fragility bone fractures. The clinical and public health repercussions of osteoporosis are huge due to the morbidity, mortality, and cost of medical care linked with fragility fractures. Clinical assessment of osteoporotic risk factors can help to identify candidates at an early stage that will benefit from medical intervention and potentially lowering the morbidity and mortality seen with fractures and complications. Given this, research is ongoing to evaluate the association of osteoporosis with some novel or less well-studied risk factors/bio-markers such as uric acid (UA).

Discussion:

Uric acid’s antioxidant activity has been proposed to be one of the factors responsible for increasing longevity and lowering rates of age-related cancers during primate evolution, the level of which increased markedly due to loss of uricase enzyme activity (mutational silencing). Accumulated evidence shows that oxidative stress is the fundamental mechanism of age-related bone loss and acts via enhancing osteoclastic activity and increasing bone resorption. Antioxidant substances such as ascorbic acid scavenge free radicals are positively related to bone health. Thus, it is hypothesized that uric acid holds bone-protective potential owing to its potent antioxidative property. Several correlation studies have been conducted globally to investigate the relationship between serum uric acid with bone mineral density and osteoporosis. Few pre-clinical studies have tried to investigate the interaction between uric acid and bone mineral density and reported important role played via Runt-related transcription factor 2 (RUNX2)/core-binding factor subunit alpha-1 (CBF-alpha-1), Wingless-related integration site (Wnt)-3a/β-catenin signaling pathway and 11β Hydroxysteroid Dehydrogenase type 1.

Conclusion:

In this review, the authors provided a comprehensive summary of the literature related to association studies reported in humans as well work done until date to understand the potential cellular and molecular mechanisms that interplay between uric acid and bone metabolism.

Higher serum uric acid is associated with higher lumbar spine bone mineral density in male health-screening examinees: a cross-sectional study

Bone health has been associated with oxidative stress and antioxidants have received interest to this end. Serum uric acid (SUA), an end product of purine metabolism in humans, has recently shown antioxidant properties regarding bone health, but there are conflicting results. The aim of this study was to investigate the relationship between SUA levels and lumbar spine bone mineral density (BMD) in clinically apparently healthy males aged 40-60 years. We performed a cross-sectional study of 6588 Korean males who completed a health-screening program from January 2011 to December 2014. Of the study participants, the mean age was 48.2 ± 10.7 years. Multiple regression analyses resulted in a significant positive association with lumbar spine BMD across SUA quintiles in a dose-response manner after adjusting for various confounding factors (p = 0.013); for each 1 mg/dl increase of SUA, BMD rose by 0.0054 g/cm² (p = 0.004). Stratified analyses revealed that this association between SUA and lumbar spine BMD was consistently observed across all clinically relevant subgroups. The present study demonstrated a positive association in males between SUA and lumbar spine BMD, suggesting that SUA could have a profitable effect on bone metabolism.

Using Mendelian Randomization to Decipher Mechanisms of Bone Disease

PURPOSE OF REVIEW

This review summarizes the basic principles of Mendelian randomization (MR) and provides evidence for the causal effect of multiple modifiable factors on bone outcomes.

RECENT FINDINGS

Several studies using MR approach have provided support for the causal effect of obesity on bone mineral density (BMD). Strikingly, studies have failed to prove a causal association between elevated 25(OH) D concentrations and higher BMD in community-dwelling individuals. The MR approach has been successfully used to evaluate multiple factors related to bone mineral density variation and/or fracture risk. The MR approach avoids some of the classical observational study limitations and provides more robust causal evidence, ensuring bigger success of the clinical trials. The selection of interventions based on genetic evidence could have a substantial impact on clinical practice.

Inferring causal relationships between phenotypes using summary statistics from genome-wide association studies

Genome-wide association studies (GWAS) have successfully identified numerous genetic variants associated with diverse complex phenotypes and diseases, and provided tremendous opportunities for further analyses using summary association statistics. Recently, Pickrell et al. developed a robust method for causal inference using independent putative causal SNPs. However, this method may fail to infer the causal relationship between two phenotypes when only a limited number of independent putative causal SNPs identified. Here, we extended Pickrell's method to make it more applicable for the general situations. We extended the causal inference method by replacing the putative causal SNPs with the lead SNPs (the set of the most significant SNPs in each independent locus) and tested the performance of our extended method using both simulation and empirical data. Simulations suggested that when the same number of genetic variants is used, our extended method had similar distribution of test statistic under the null model as well as comparable power under the causal model compared with the original method by Pickrell et al. But in practice, our extended method would generally be more powerful because the number of independent lead SNPs was often larger than the number of independent putative causal SNPs. And including more SNPs, on the other hand, would not cause more false positives. By applying our extended method to summary statistics from GWAS for blood metabolites and femoral neck bone mineral density (FN-BMD), we successfully identified ten blood metabolites that may causally influence FN-BMD. We extended a causal inference method for inferring putative causal relationship between two phenotypes using summary statistics from GWAS, and identified a number of potential causal metabolites for FN-BMD, which may provide novel insights into the pathophysiological mechanisms underlying osteoporosis.

Lack of Evidence that Soluble Urate Directly Influences Bone Remodelling: A Laboratory and Clinical Study

INTRODUCTION

Numerous observational studies have reported that serum urate concentration positively correlates with bone density and reduced risk of fractures. The aim of this study was to examine whether soluble urate directly influences bone remodelling.

METHODS

In laboratory studies, the in vitro effects of soluble urate were examined in osteoclast, osteoblast and osteocyte assays at a range of urate concentrations consistent with those typically observed in humans (up to 0.70 mmol/L). The clinical relevance of the in vitro assay findings was assessed using serial procollagen-1 N-terminal propeptide (P1NP) and Month 12 bone density data from a randomised controlled trial of allopurinol dose escalation in people with gout.

RESULTS

Addition of urate in the RAW264.7 cell osteoclastogenesis assay led to small increases in osteoclast formation (ANOVA p = 0.018), but no significant difference in bone resorption. No significant effects on osteoclast number or activity were observed in primary cell osteoclastogenesis or resorption assays. Addition of urate did not alter viability or function in MC3T3-E1 pre-osteoblast, primary human osteoblast, or MLO-Y4 osteocyte assays. In the clinical trial analysis, reducing serum urate over a 12 month period by allopurinol dose escalation did not lead to significant changes in P1NP or differences in bone mineral density.

CONCLUSION

Addition of soluble urate at physiological concentrations does not influence bone remodelling in vitro. These data, together with clinical trial data showing no effect of urate-lowering on P1NP or bone density, do not support a direct role for urate in influencing bone remodelling.

Elevated serum urate is a potential factor in reduction of total bilirubin: a Mendelian randomization study

Aim

A Mendelian randomization study (MRS) can be linked to a "natural" randomized controlled trial in order to avoid potential bias of observational epidemiology. We aimed to study the possible association between serum urate (SU) and total bilirubin (TBIL) using MRS.

Materials and Methods

An observational epidemiological study using ordinary least squares (OLS) regression and MRS using two-stage least square (TLS) regression was conducted to assess the effect of SU on TBIL. The comparison between the OLS regression and the TLS regression was analyzed by the Durbin-Hausman test. If the p value is significant, it suggests that the OLS regression cannot evaluate the relationship between exposure and outcome, and the TLS regression is precise; while if the p value is not significant, there would be no significant difference between the two regressions.

Results

A total of 3,753 subjects were analyzed. In OLS regression, there was no significant association between SU and TBIL in all subjects and subgroup analysis (all p > 0.05). However, MRS revealed a negative correlation between SU and TBIL after adjustment for confounders (beta = -0.021, p = 0.010). Further analysis was conducted in different SU subgroups, and results show that elevated SU was associated with a significant reduction in TBIL after adjustment for hyperuricemic subjects (beta = -0.053, p = 0.027). In addition, the results using the Durbin-Hausman test further confirmed a negative effect of SU on TBIL (p = 0.002 and 0.010, respectively).

Conclusions

This research shows for the first time that elevated SU was a potential causal factor in the reduction of TBIL and it provides strong evidence to resolve the controversial association between SU and TBIL.

Serum uric acid levels and multiple health outcomes: umbrella review of evidence from observational studies, randomised controlled trials, and Mendelian randomisation studies

Objective To map the diverse health outcomes associated with serum uric acid (SUA) levels.Design Umbrella review.Data sources Medline, Embase, Cochrane Database of Systematic Reviews, and screening of citations and references.Eligibility criteria Systematic reviews and meta-analyses of observational studies that examined associations between SUA level and health outcomes, meta-analyses of randomised controlled trials that investigated health outcomes related to SUA lowering treatment, and Mendelian randomisation studies that explored the causal associations of SUA level with health outcomes.Results 57 articles reporting 15 systematic reviews and144 meta-analyses of observational studies (76 unique outcomes), 8 articles reporting 31 meta-analyses of randomised controlled trials (20 unique outcomes), and 36 articles reporting 107 Mendelian randomisation studies (56 unique outcomes) met the eligibility criteria. Across all three study types, 136 unique health outcomes were reported. 16 unique outcomes in meta-analyses of observational studies had P<10-6, 8 unique outcomes in meta-analyses of randomised controlled trials had P<0.001, and 4 unique outcomes in Mendelian randomisation studies had P<0.01. Large between study heterogeneity was common (80% and 45% in meta-analyses of observational studies and of randomised controlled trials, respectively). 42 (55%) meta-analyses of observational studies and 7 (35%) meta-analyses of randomised controlled trials showed evidence of small study effects or excess significance bias. No associations from meta-analyses of observational studies were classified as convincing; five associations were classified as highly suggestive (increased risk of heart failure, hypertension, impaired fasting glucose or diabetes, chronic kidney disease, coronary heart disease mortality with high SUA levels). Only one outcome from randomised controlled trials (decreased risk of nephrolithiasis recurrence with SUA lowering treatment) had P<0.001, a 95% prediction interval excluding the null, and no large heterogeneity or bias. Only one outcome from Mendelian randomisation studies (increased risk of gout with high SUA levels) presented convincing evidence. Hypertension and chronic kidney disease showed concordant evidence in meta-analyses of observational studies, and in some (but not all) meta-analyses of randomised controlled trials with respective intermediate or surrogate outcomes, but they were not statistically significant in Mendelian randomisation studies.Conclusion Despite a few hundred systematic reviews, meta-analyses, and Mendelian randomisation studies exploring 136 unique health outcomes, convincing evidence of a clear role of SUA level only exists for gout and nephrolithiasis.

Uric acid and bone mineral density in postmenopausal osteoporotic women: the link lies within the fat

The association between serum uric acid (SUA) levels and bone mineral density (BMD) is controversial. Fat accumulation is linked to SUA and BMD, thus possibly explaining the mixed results. We found that adiposity drives part of the association between SUA and BMD in women with postmenopausal osteoporosis.

INTRODUCTION

Both positive and negative associations between SUA and BMD have been reported. SUA levels and BMD increase with higher body weight and other indices of adiposity; hence, the association between SUA and BMD might be a consequence of the confounding effect of adiposity. We investigated in this cross-sectional study whether the association between SUA and BMD is independent of measures of fat accumulation and other potential confounders.

METHODS

SUA levels, femur BMD, markers of bone metabolism, body mass index (BMI), fat mass (FM), waist circumference (WC), and abdominal visceral fat area were measured in 180 treatment-naive postmenopausal osteoporotic women (mean age 66.3 ± 8.5 years, age range 48-81 years).

RESULTS

Women with higher SUA levels (third tertile) had significantly higher femur BMD and lower cross-linked C-terminal telopeptide of type I collagen (CTX) and bone alkaline phosphatase (bALP) levels. SUA levels were positively associated with all indices of adiposity. In multivariable analysis with femur BMD as dependent variable, the association between logarithmic (LG)-transformed SUA levels and BMD (beta = 0.42, p < 0.001) was lessened progressively by the different indices of adiposity, like LG-BMI (beta = 0.22, p = 0.007), LG-WC (beta = 0.21, p = 0.01), LG-FM (beta = 0.18, p = 0.01), and LG-abdominal visceral fat area (beta = 0.12, p = 0.05). The association between SUA levels and markers of bone metabolism was dependent on the effect of confounders.

CONCLUSION

In postmenopausal osteoporotic women, the strong univariable association between SUA levels and femur BMD is partly explained by the confounding effect of indices of adiposity.

Gout and the Risk of Non-vertebral Fracture

Prior studies suggest an association between osteoporosis, systemic inflammation, and pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6. Conflicting findings exist on the association between hyperuricemia and osteoporosis. Furthermore, it remains unknown whether gout, a common inflammatory arthritis, affects fracture risk. Using data from a US commercial health plan (2004-2013), we evaluated the risk of non-vertebral fracture (ie, forearm, wrist, hip, and pelvis) in patients with gout versus those without. Gout patients were identified with ≥2 diagnosis codes and ≥1 dispensing for a gout-related drug. Non-gout patients, identified with ≥2 visits coded for any diagnosis and ≥1 dispensing for any prescription drugs, were free of gout diagnosis and received no gout-related drugs. Hip fracture was the secondary outcome. Fractures were identified with a combination of diagnosis and procedure codes. Cox proportional hazards models compared the risk of non-vertebral fracture in gout patients versus non-gout, adjusting for more than 40 risk factors for osteoporotic fracture. Among gout patients with baseline serum uric acid (sUA) measurements available, we assessed the risk of non-vertebral fracture associated with sUA. We identified 73,202 gout and 219,606 non-gout patients, matched on age, sex, and the date of study entry. The mean age was 60 years and 82% were men. Over the mean 2-year follow-up, the incidence rate of non-vertebral fracture per 1,000 person-years was 2.92 in gout and 2.66 in non-gout. The adjusted hazard ratio (HR) was 0.98 (95% confidence interval [CI] 0.85-1.12) for non-vertebral fracture and 0.83 (95% CI 0.65-1.07) for hip fracture in gout versus non-gout. Subgroup analysis (n = 15,079) showed no association between baseline sUA and non-vertebral fracture (HR = 1.03, 95% CI 0.93-1.15), adjusted for age, sex, comorbidity score, and number of any prescription drugs. Gout was not associated with a risk of non-vertebral fracture. Among patients with gout, sUA was not associated with the risk of non-vertebral fracture. © 2016 American Society for Bone and Mineral Research.

Hyperuricemia protects against low bone mineral density, osteoporosis and fractures: a systematic review and meta-analysis

BACKGROUND

Serum uric acid (SUA) accounts for about 50% of extracellular antioxidant activity, suggesting that hyperuricemia may have a protective role in diseases characterized by high levels of oxidative stress, such as osteoporosis. We aimed to meta-analyse data regarding bone mineral density (BMD), osteoporosis and fractures in people with higher SUA vs. lower SUA concentrations.

MATERIALS AND METHODS

Two investigators conducted a literature search using PubMed and Scopus, without language restrictions. Standardized mean differences (SMDs) and 95% confidence intervals (CIs) were used for BMD; risk ratios (RRs) and adjusted odds ratios (ORs) for cross-sectional data. Most possible adjusted hazard ratios (HRs) were used to assess the association between baseline SUA and incident fractures.

RESULTS

Of 1405 initial hits, 19 studies were eligible including a total of 55 859 participants. Subjects with higher SUA levels had significantly higher BMD values for the spine (six studies; SMD = 0·29; 95% CI: 0·22-0·35; I² = 47%), total hip (seven studies; SMD = 0·29; 95% CI: 0·24-0·34; I² = 33%) and femoral neck (six studies; SMD = 0·25; 95% CI: 0·16-0·34; I² = 71%). Simple correlation analyses substantially confirmed these findings. An increase of one standard deviation in SUA levels reduced the number of new fractures at follow-up (three studies; HR = 0·83; 95% CI: 0·74-0·92; I² = 0%). No significant differences between men and women emerged, although data about women were limited.

CONCLUSIONS

Hyperuricemia was found independently associated with BMD and fractures, supporting a protective role for uric acid in bone metabolism disorders.

Genetically Low Vitamin D Levels, Bone Mineral Density, and Bone Metabolism Markers: a Mendelian Randomisation Study

Low serum 25-hydroxyvitamin D (25OHD) is associated with osteoporosis and osteoporotic fracture, but it remains uncertain whether these associations are causal. We conducted a Mendelian randomization (MR) study of 1,824 postmenopausal Chinese women to examine whether the detected associations between serum 25OHD and bone mineral density (BMD) and bone metabolism markers were causal. In observational analyses, total serum 25OHD was positively associated with BMD at lumbar spine (P = 0.003), femoral neck (P = 0.006) and total hip (P = 0.005), and was inversely associated with intact parathyroid hormone (PTH) (P = 8.18E-09) and procollagen type 1 N-terminal propeptide (P1NP) (P = 0.020). By contract, the associations of bioavailable and free 25OHD with all tested outcomes were negligible (all P > 0.05). The use of four single nucleotide polymorphisms, GC-rs2282679, NADSYN1-rs12785878, CYP2R1-rs10741657 and CYP24A1-rs6013897, as candidate instrumental variables in MR analyses showed that none of the two stage least squares models provided evidence for associations between serum 25OHD and either BMD or bone metabolism markers (all P > 0.05). We suggest that after controlling for unidentified confounding factors in MR analyses, the associations between genetically low serum 25OHD and BMD and bone metabolism markers are unlikely to be causal.

Gout increases risk of fracture: A nationwide population-based cohort study

There is still debate on whether high uric acid increases bone mineral density (BMD) against osteoporotic fracture or bone resorption caused by gout inflammation. This study aimed to evaluate whether gout offers a protective effect on bone health or not. We conducted a nationwide population-based retrospective cohort study to evaluate the association between gout history and risk factors of fracture.A retrospective cohort study was designed using the claim data from Longitudinal Health Insurance Database (LHID). A total of 43,647 subjects with gout and a cohort of 87,294 comparison subjects without gout were matched in terms of age and sex between 2001 and 2009, and the data were followed until December 31, 2011. The primary outcome of the study was the fracture incidence, and the impacts of gout on fracture risks were analyzed using the Cox proportional hazards model.After an 11-year follow-up period, 6992 and 11,412 incidents of fracture were reported in gout and comparison cohorts, respectively. The overall incidence rate of fracture in individuals with gout was nearly 23%, which was higher than that in individuals without gout (252 vs 205 per 10,000 person-years) at an adjusted hazard ratio of 1.17 (95% confidence interval = 1.14-1.21). Age, sex, and fracture-associated comorbidities were adjusted accordingly. As for fracture locations, patients with gout were found at significant higher fracture risks for upper/lower limbs and spine fractures. In gout patient, the user of allopurinol or benzbromarone has significantly lower risk of facture than nonusers.Gout history is considered as a risk factor for fractures, particularly in female individuals and fracture sites located at the spine or upper/lower limbs.

Relationship Between Changes in Serum Urate and Bone Mineral Density During Treatment with Thiazide Diuretics: Secondary Analysis from a Randomized Controlled Trial

In observational studies, serum urate concentrations associate with bone mineral density (BMD) and reduced risk of fractures. Thiazide diuretics slow the bone loss in healthy older adults, are associated with reduced incidence of fracture and also increase serum urate. We hypothesized that changes in serum urate are associated with changes in BMD during treatment with thiazide diuretics. We analysed data from a double-blind randomized controlled trial of hydrochlorothiazide (50 mg per day) and placebo in normal post-menopausal women. The relationship between change in serum urate and change in BMD after 2 years of treatment was examined using Spearman correlation and multiple linear regression models. Total body BMD increased in the hydrochlorothiazide group by 0.52 % and reduced in the placebo group by 0.29 % over 2 years (between group difference P = 0.0034). Serum urate increased in the hydrochlorothiazide group by 0.038 mmol/L and reduced in the placebo group by 0.004 mmol/L (between group difference P < 0.0001). At Year 2, there was a positive relationship between the change in serum urate and change in total body BMD for entire study population (r = 0.32, P = 0.0002) and for the hydrochlorothiazide group (r = 0.29, P = 0.023). The association between change in serum urate and change in total body BMD persisted after adjusting for treatment allocation, and change in weight, serum calcium, urinary calcium and serum creatinine (P change in serum urate = 0.043). These data raise the possibility that the effects of hydrochlorothiazide on BMD may be mediated, in part, by changes in serum urate concentrations.

The Influence of Serum Uric Acid on Bone Mineral Density, Hip Geometry, and Fracture Risk: The Rotterdam Study

CONTEXT

The role of uric acid (UA) in skeletal metabolism remains to be unraveled.

OBJECTIVE

We prospectively investigated the association between UA, bone mineral density at the femoral neck (FN-BMD), hip bone geometry parameters, and incident fracture risk and examined whether the associations were modified by age and vitamin C intake.

PARTICIPANTS AND SETTING

Data of 5074 participants of The Rotterdam Study, a prospective population-based cohort.

EXPOSURE

Serum UA was assessed at baseline.

MAIN OUTCOMES AND MEASURES

FN-BMD was measured at baseline, and at second, third, and fourth visits of the Rotterdam Study. Hip bone geometry parameters were measured at baseline and at the second and third visits.

RESULTS

Serum UA levels (per SD increase) were positively associated with FN-BMD (β = 0.007 g/cm(2); 95% confidence interval [CI] = 0.002-0.01), thicker cortices (β = 0.002 cm; 95% CI = 0.0003-0.002), lower bone width (β = -0.013 cm; 95% CI = -0.23 to -0.003), and lower cortical buckling ratio (β = -0.19; 95% CI = -0.33 to -0.06). The effects of UA on FN-BMD and cortical buckling ratio tended to become stronger over time. Hazard ratios and 95% CIs per SD increase of baseline UA levels for the development of any type of incident fractures, nonvertebral fractures, and osteoporotic fractures were 0.932 (0.86-0.995), 0.924 (0.856-0.998), and 0.905 (0.849-0.982), respectively. These associations were more prominent in older individuals (age, >65 y) and in participants with high intakes of vitamin C (> median).

CONCLUSIONS

Higher levels of serum UA are associated with higher BMD (at the expense of thicker cortices and narrower bone diameters) and may be a protective factor in bone metabolism. However, interactions with age and vitamin C may be present.

No causal effect of serum urate on bone-related outcomes among a population of postmenopausal women and elderly men of Chinese Han ethnicity--a Mendelian randomization study

SUMMARY

We conducted a Mendelian randomization analysis to assess the effect of serum uric acid on bone-related outcomes using a weighted urate transporter genetic risk score as the instrumental variable. The results showed no significance. Our study identified no evidence of a causal role between uric acid and bone-related outcomes.

INTRODUCTION

Observational studies have associated elevated levels of serum uric acid (SUA) with increasing bone mineral density (BMD) and a lowered prevalence of osteoporotic fractures (OFs) in postmenopausal women and elderly men. However, due to unmeasured confounding variables, these observational studies have not provided insight into the causal relationship between SUA and bone-related outcomes. Our aim was to evaluate the effect of SUA on bone-related outcomes using Mendelian randomization.

METHODS

We recruited 1322 Chinese Han individuals (214 elderly men and 1108 postmenopausal women) from the Shanghai area in China. Mendelian randomization using a two-stage least-squares regression method was conducted with SUA as the exposure variable, a weighted urate transporter genetic risk score as the instrumental variable, and all-site BMD, bone turnover markers, and levels of 25-hydroxyvitamin D3 [25(OH)D], serum calcium (Ca), serum phosphorus (P), and parathyroid hormone (PTH) as outcome variables.

RESULTS

Strong associations between SUA and bone-related outcomes were observed in an ordinary observational analysis (lumbar spine: beta = 0.122, p < 0.0001; hip: beta = 0.104, p < 0.0001; femoral neck: beta = 0.108, p < 0.0001). However, the Mendelian randomization analysis showed no evidence for a causal association of SUA with BMD (lumbar spine: beta = 0.385, p = 0.257; hip: beta = 0.191, p = 0.499; femoral neck: beta = 0.194, p = 0.533). Similar results were found between SUA and other bone-related phenotypes.

CONCLUSIONS

Our study identified no evidence of a causal role between SUA and bone-related outcomes, although strong associations in an observational analysis were observed in a population of postmenopausal women and elderly men.