Lowering of Circulating Sclerostin May Increase Risk of Atherosclerosis and Its Risk Factors: Evidence From a Genome-Wide Association Meta-Analysis Followed by Mendelian Randomization

A Note on Modelling Bidirectional Feedback Loops in Mendelian Randomization Studies

Structural equation models (SEMs) involving feedback loops may offer advantages over standard instrumental variables estimators in terms of modelling causal effects in the presence of bidirectional relationships. In the following note, we show that in the case of a single "exposure" and "outcome" variable, modelling relationships using a SEM with a simple bidirectional linear feedback loop offers no advantage over traditional instrumental variables estimators in terms of consistency (i.e. both approaches yield consistent estimates of the causal effect, provided that causal estimates are obtained in both directions). In the case of finite samples, traditional IV estimators and SEM exhibited similar power across many of the conditions we examined, although which method performed best depended on the residual correlation between variables and the strength of the instruments. In particular, the power of SEM was insensitive to the residual correlation between variables, whereas the power of the Wald estimator/2SLS improved (deteriorated) relative to SEM as the magnitude of the residual correlation increased (decreased) assuming a positive causal effect of the exposure on the outcome. The power of SEM improved relative to the Wald estimator/2SLS as the instruments explained more residual variance in the "outcome" variable.

A practical approach for anabolic treatment of bone fragility with romosozumab

BACKGROUND

Romosozumab, a fully humanized anti-sclerostin-antibody, is a bone-builder stimulating osteoblasts and inhibiting osteoclast by activation of the canonical Wnt-beta catenin signaling. This unique mechanism of action has the potential to address unmet needs in osteoporosis management.

METHODS

The multifaceted practical clinical issues related to romosozumab are discussed, especially focusing on the rationale of employing a sclerostin inhibitor to target bone fragility as first line or second line treatment in post-menopausal osteoporosis and in males at increased risk of fractures.

RESULTS

Four randomized clinical trials with several post-hoc analyses and more than ten observational studies have consistently demonstrated that romosozumab is effective in rapidly increasing bone mineral density (BMD) and decreasing risk of vertebral, non-vertebral and hip fractures in post-menopausal women at very-high risk of fractures. In male osteoporosis, only data on BMD are available. Noteworthy, romosozumab was shown to be more effective and rapid than teriparatide in improving BMD, bone structure and strength at the hip, especially in women already treated with anti-resorptive drugs. Interestingly, even if romosozumab displays best results in treatment-naïve patients, its favourable effects on BMD were observed even in women previously treated with teriparatide or denosumab, although to a lesser extent.

CONCLUSIONS

Based on the available evidence, romosozumab could be proposed as ideal drug in several clinical settings, such as non-fractured post-menopausal women at very-high risk of fractures, patients with recent hip fracture, patients non responder to bisphosphonates and short-term denosumab therapy.

Identification of Transcripts with Shared Roles in the Pathogenesis of Postmenopausal Osteoporosis and Cardiovascular Disease

Epidemiological evidence suggests existing comorbidity between postmenopausal osteoporosis (OP) and cardiovascular disease (CVD), but identification of possible shared genes is lacking. The skeletal global transcriptomes were analyzed in trans-iliac bone biopsies (n = 84) from clinically well-characterized postmenopausal women (50 to 86 years) without clinical CVD using microchips and RNA sequencing. One thousand transcripts highly correlated with areal bone mineral density (aBMD) were further analyzed using bioinformatics, and common genes overlapping with CVD and associated biological mechanisms, pathways and functions were identified. Fifty genes (45 mRNAs, 5 miRNAs) were discovered with established roles in oxidative stress, inflammatory response, endothelial function, fibrosis, dyslipidemia and osteoblastogenesis/calcification. These pleiotropic genes with possible CVD comorbidity functions were also present in transcriptomes of microvascular endothelial cells and cardiomyocytes and were differentially expressed between healthy and osteoporotic women with fragility fractures. The results were supported by a genetic pleiotropy-informed conditional False Discovery Rate approach identifying any overlap in single nucleotide polymorphisms (SNPs) within several genes encoding aBMD- and CVD-associated transcripts. The study provides transcriptional and genomic evidence for genes of importance for both BMD regulation and CVD risk in a large collection of postmenopausal bone biopsies. Most of the transcripts identified in the CVD risk categories have no previously recognized roles in OP pathogenesis and provide novel avenues for exploring the mechanistic basis for the biological association between CVD and OP.

Efficacy of Osteoporosis Medications in Patients with Type 2 Diabetes

PURPOSE OF THE REVIEW

The purpose of the review is to summarise the current scientific evidence on the efficacy of osteoporosis medications in patients with type 2 diabetes.

RECENT FINDINGS

Type 2 diabetes (T2D) is a growing global epidemic. The highest prevalence is observed in the elderly, the same population affected by osteoporosis. Despite normal or even increased bone mineral density and low bone turnover, T2D is associated with an increased risk of fractures in most skeletal sites. These findings raised concerns over the efficacy of anti-osteoporosis drugs in this population. There is no randomised controlled trial designed specifically for people with T2D. However, observational studies and post-hoc analyses of randomised controlled trials have provided valuable insights into the effects of various anti-osteoporosis treatments in this population. Overall, most anti-osteoporosis drugs seem to have similar efficacy and safety profiles for people with and without type 2 diabetes. However, continued research and long-term safety data are needed to optimise treatment strategies and improve bone health outcomes in this population. The current evidence suggests that most anti-osteoporosis drugs exhibit comparable efficacy in people with and without T2D.

Τhe story of sclerostin inhibition: the past, the present, and the future

Sclerostin inhibits osteoblast activity by hampering activation of the canonical Wnt signaling pathway and simultaneously stimulates osteoclastogenesis through upregulation of the receptor activator of NFκB ligand (RANKL). Thus, antibodies against sclerostin (Scl-Abs), besides promoting bone formation, suppress bone resorption and dissociate bone formation from resorption. This dual action results in remarkable increases of bone mineral density which are of a greater magnitude compared to the other antiosteoporotic treatments and are accompanied by decreases of fracture risk at all skeletal sites. The anabolic effect subsides after the first few months of treatment and a predominantly antiresorptive effect remains after this period, limiting its use to 12 months. Furthermore, these effects are largely reversible upon discontinuation; therefore, subsequent treatment with antiresorptives is indicated to maintain or further increase the bone gains achieved. Romosozumab is currently the only Scl-Ab approved for the treatment of severe postmenopausal osteoporosis. Indications for use in other populations, such as males, premenopausal women, and patients with glucocorticoid-induced osteoporosis, are pending. Additionally, the efficacy of Scl-Abs in other bone diseases, such as osteogenesis imperfecta, hypophosphatasia, X-linked hypophosphatemia, and bone loss associated with malignancies, is under thorough investigation. Cardiovascular safety concerns currently exclude patients at high cardiovascular risk from this treatment.

Wnt16 Promotes Vascular Smooth Muscle Contractile Phenotype and Function via Taz (Wwtr1) Activation in Male LDLR-/- Mice

Wnt16 is expressed in bone and arteries, and maintains bone mass in mice and humans, but its role in cardiovascular physiology is unknown. We show that Wnt16 protein accumulates in murine and human vascular smooth muscle (VSM). WNT16 genotypes that convey risk for bone frailty also convey risk for cardiovascular events in the Dallas Heart Study. Murine Wnt16 deficiency, which causes postnatal bone loss, also reduced systolic blood pressure. Electron microscopy demonstrated abnormal VSM mitochondrial morphology in Wnt16-null mice, with reductions in mitochondrial respiration. Following angiotensin-II (AngII) infusion, thoracic ascending aorta (TAA) dilatation was greater in Wnt16-/- vs Wnt16+/+ mice (LDLR-/- background). Acta2 (vascular smooth muscle alpha actin) deficiency has been shown to impair contractile phenotype and worsen TAA aneurysm with concomitant reductions in blood pressure. Wnt16 deficiency reduced expression of Acta2, SM22 (transgelin), and other contractile genes, and reduced VSM contraction induced by TGFβ. Acta2 and SM22 proteins were reduced in Wnt16-/- VSM as was Ankrd1, a prototypic contractile target of Yap1 and Taz activation via TEA domain (TEAD)-directed transcription. Wnt16-/- VSM exhibited reduced nuclear Taz and Yap1 protein accumulation. SiRNA targeting Wnt16 or Taz, but not Yap1, phenocopied Wnt16 deficiency, and Taz siRNA inhibited contractile gene upregulation by Wnt16. Wnt16 incubation stimulated mitochondrial respiration and contraction (reversed by verteporfin, a Yap/Taz inhibitor). SiRNA targeting Taz inhibitors Ccm2 and Lats1/2 mimicked Wnt16 treatment. Wnt16 stimulated Taz binding to Acta2 chromatin and H3K4me3 methylation. TEAD cognates in the Acta2 promoter conveyed transcriptional responses to Wnt16 and Taz. Wnt16 regulates cardiovascular physiology and VSM contractile phenotype, mediated via Taz signaling.

Cardiac Arrhythmia and Heart Failure Shortly After Starting Romosozumab for Osteoporosis: A Case-Based Review

Romosozumab is a humanized monoclonal antibody that targets the sclerostin protein, which regulates bone formation and resorption. It is a novel therapy in the treatment of post-menopausal women with osteoporosis. The evidence regarding romosozumab's cardiovascular safety is conflicting. We report the first post-marketing case demonstrating cardiac events (i.e., atrial fibrillation and congestive heart failure) in a female patient with osteoporosis likely triggered by romosozumab. A literature review on romosozumab and cardiovascular disease is discussed extensively. For osteoporotic patients with cardiovascular risk factors (e.g., hypertension, coronary artery disease, and stroke), the benefits of fracture prevention should be weighed against potential cardiovascular risks before prescribing romosozumab. Real-world data on post-marketing surveillance will shed light on the potential safety signals of romosozumab.

Sclerostin and Cardiovascular Disease

PURPOSE OF REVIEW

The role of wnt signalling in atherogenesis raises the possibility that the wnt inhibitor, sclerostin, provides a natural defence to this process, and that anti-sclerostin antibodies might increase the risk of atherosclerosis and associated conditions such as CVD. This article aims to triangulate evidence concerning possible adverse effects of sclerostin inhibition on CVD risk.

RECENT FINDINGS

Randomised controlled trials of treatment with the anti-sclerostin antibody, romosozumab, have yielded conflicting evidence with respect to possible adverse effects of sclerostin inhibition on CVD risk. To further examine the causal relationship between sclerostin inhibition and CVD risk, three Mendelian randomisation (MR) studies have examined effects of sclerostin lowering on CVD outcomes, using common genetic variants in the SOST gene which produces sclerostin, to mimic effects of a randomised trial. Concordant findings were seen in two studies, comprising an effect of sclerostin lowering on increased risk of MI and type II diabetes mellitus. One study also suggested that sclerostin lowering increases coronary artery calcification. Triangulation of evidence from different sources provides some suggestion that sclerostin lowering increases MI risk, supporting the need for CVD risk assessment when considering treatment with romosozumab.