High Bone Mass is associated with bone-forming features of osteoarthritis in non-weight bearing joints independent of body mass index

Revealing the mediating mechanisms between BMI and osteoarthritis: a Mendelian randomization and mediation analysis

BACKGROUND

Despite well-documented associations between Body mass index (BMI) and Osteoarthritis (OA), the specific biological pathways and mediators involved remain poorly understood. This study aims to explore mediators through which BMI influences OA risk, particularly knee osteoarthritis (KOA), using Mendelian Randomization (MR) and mediation analysis.

METHODS

We used a two-step MR approach with data from the IEU OpenGWAS and FinnGen version 7 databases. BMI (N = 322,154) was the primary exposure, with knee disorders (KD), total bone mineral density (TBMD), metabolic disorders (MD), and anxiety disorders (AD) as potential mediators. Outcomes included KOA (N = 22,347), hip OA (HOA) (N = 11,989), and all OA (AllOA) (N = 50,508). Univariate MR evaluated causal relationships, followed by multivariate MR to quantify mediation effects. Multiple sensitivity analyses were conducted to validate robustness, while horizontal pleiotropy and heterogeneity were assessed using MR-Egger intercept and Cochran's Q statistic.

RESULTS

BMI significantly increased the risk of KOA (odds ratio [OR]: 2.00, 95% confidence interval [CI]: 1.56-2.56), HOA (OR: 2.05, 95% CI: 1.40-2.98), and AllOA (OR: 1.66, 95% CI: 1.41-1.95). KD and TBMD significantly mediated the effect on KOA, with mediation proportions of 20.89% and 3.59%, respectively. MD and AD showed no significant effects. Sensitivity analyses supported the robustness of these findings. Horizontal pleiotropy and heterogeneity tests indicated minimal evidence of bias, supporting the reliability of our results.

CONCLUSIONS

BMI increases OA risk, with KD and TBMD partially mediating the effect, particularly for KOA. The direct impact of BMI remains predominant, emphasizing the importance of weight reduction, joint protection, and physical activity as preventive measures.

A pH-responsive novel delivery system utilizing carbon quantum dots loaded with PT2385 for targeted inhibition of HIF-2α in the treatment of osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a progressive joint disorder marked by the degradation of cartilage. Elevated concentrations of hypoxia-inducible factor-2α (HIF-2α) are intricately linked to the pathological development of OA. PT2385 has demonstrated effective inhibition of HIF-2α, thereby potentially impeding the initial advancement of OA. Nevertheless, challenges persist, including limited penetration into the deeper layers of cartilage, issues related to charge rejection, and a heightened rate of clearance from the joint. These constraints necessitate further consideration and exploration.

METHODS

It has been demonstrated that PT2385 exhibits efficient inhibition of HIF-2α expression, thereby contributing to the delay in the progression of osteoarthritis. The pH-responsive attributes of carbon quantum dots, specifically those employing m-phenylenediamine (m-CQDs) coated with bovine serum albumin (BSA), have been systematically evaluated. In both in vitro settings involving cartilage explants and in vivo experiments, the efficacy of BSA-m-CQDs-PT2385 (BCP) has been confirmed in facilitating the transport of PT2385 to the middle and deep layers of cartilage. Furthermore, the BCP system demonstrates controlled drug release contingent upon alterations in environmental pH.

RESULTS

While the use of PT2385 alone provides protective effects on chondrocytes within an inflamed environment, there exists an opportunity for further enhancement in its efficacy when administered via intra-articular injection. The BCP formulation, characterized by appropriate particle size and charge, facilitates seamless penetration into cartilage tissue. Additionally, BCP demonstrates the capability to release drugs in response to changes in environmental pH. In vitro experiments reveal that BCP effectively inhibits Hif-2α expression and catabolic factors in chondrocytes. Notably, cartilage explants and in vivo experiments indicate that BCP surpasses PT2385 alone in inhibiting the expression of HIF-2α and matrix metalloproteinase 13, particularly in the middle and deep layers.

CONCLUSIONS

The BCP drug delivery system exhibits selective release of PT2385 in response to pH changes occurring during the progression of osteoarthritis (OA), thereby inhibiting HIF-2α expression deep within the cartilage. The use of BCP significantly augments the capacity of PT2385 to retard both cartilage degeneration and the progression of osteoarthritis. Consequently, BCP as an innovative approach utilizing m-CQDs to deliver PT2385 into articular cartilage, shows potential for treating osteoarthritis.This strategy opens new avenues for osteoarthritis treatment.

High bone mass and cam morphology are independently related to hip osteoarthritis: findings from the High Bone Mass cohort

BACKGROUND

High bone mass (HBM, BMD Z-score ≥  + 3.2) and cam morphology (bulging of lateral femoral head) are associated with greater odds of prevalent radiographic hip osteoarthritis (rHOA). As cam morphology is itself a manifestation of increased bone deposition around the femoral head, it is conceivable that cam morphology may mediate the relationship between HBM and rHOA. We therefore aimed to determine if individuals with HBM have increased odds of prevalent cam morphology. In addition, we investigated whether the relationship between cam and prevalent and incident osteoarthritis was preserved in a HBM population.

METHODS

In the HBM study, a UK based cohort of adults with unexplained HBM and their relatives and spouses (controls), we determined the presence of cam morphology using semi-automatic methods of alpha angle derivation from pelvic radiographs. Associations between HBM status and presence of cam morphology, and between cam morphology and presence of rHOA (or its subphenotypes: osteophytes, joint space narrowing, cysts, and subchondral sclerosis) were determined using multivariable logistic regression, adjusting for age, sex, height, weight, and adolescent physical activity levels. The association between cam at baseline and incidence of rHOA after an average of 8 years was determined. Generalised estimating equations accounted for individual-level clustering.

RESULTS

The study included 352 individuals, of whom 235 (66.7%) were female and 234 (66.5%) had HBM. Included individuals contributed 694 hips, of which 143 had a cam deformity (20.6%). There was no evidence of an association between HBM and cam morphology (OR = 0.97 [95% CI: 0.63-1.51], p = 0.90) but a strong relationship was observed between cam morphology and rHOA (OR = 3.96 [2.63-5.98], p = 5.46 × 10-11) and rHOA subphenotypes joint space narrowing (OR = 3.70 [2.48-5.54], p = 1.76 × 10-10), subchondral sclerosis (OR = 3.28 [1.60-6.60], p = 9.57 × 10-4) and osteophytes (OR = 3.01 [1.87-4.87], p = 6.37 × 10-6). Cam morphology was not associated with incident osteoarthritis (OR = 0.76 [0.16-3.49], p = 0.72).

CONCLUSIONS

The relationship between cam morphology and rHOA seen in other studies is preserved in a HBM population. This study suggests that the risk of OA conferred by high BMD and by cam morphology are mediated via distinct pathways.

The nature of coxofemoral joint pathology across family Canidae

We evaluated coxofemoral joints from museum specimens of: Vulpes lagopus; Vulpes vulpes; Vulpes velox; Nyctereutes procyonoides; Urocyon cinereoargenteus; Aenocyon [Canis] dirus; Canis latrans; Canis lupus lupus; Canis lupus familiaris; C. l. familiaris × latrans; and Canis dingo. Acetabular components included: fossa; articular surface; medial and lateral articular margins; and periarticular surfaces. Acetabular components variably revealed: osteophyte-like features; varying appearance of articular margin rims (especially contour changes); rough bone surfaces (especially fossa and articular surface); and surface wear. Proximal femoral components included: articular surface; articular margin; periarticular surfaces; and joint capsule attachment. Femoral components variably revealed: rough bone surface; bone loss; articular margin osteophyte-like features; caudal post-developmental mineralized prominence; and enthesophytes along the joint capsule attachment. Non-metric multidimensional scaling was used to analyze right-left asymmetric relationships between observed traits, across taxa. Significantly different acetabular trait asymmetry involved only C. latrans-C. l. familiaris; V. vulpes-N. procyonoides, and U. cinereoargenteus-N. procyonoides. There were no significant lateralized differences in proximal femoral traits involving modern canids, ancient and modern C. l. familiaris, or modern vulpines. Thus, the observations were strongly bilateral. We hypothesized high similarity of traits across taxa. The data confirm the hypothesis and strongly suggest broad and deep morphological and mechanistic conservation that almost certainly pre-existed (at least) all modern canids. Further zoological studies are needed to evaluate phylogenic implications in greater detail.

Dysbiosis of the gut microbiome is a risk factor for osteoarthritis in older female adults: a case control study

Background

Osteoarthritis (OA) is a multifactorial joint degenerative disease with low-grade inflammation. The gut microbiome has recently emerged as an pathogenic factor of OA, and prebiotics supplementation could alleviate OA symptoms in animal models. However, the relationship between the gut microbiome and OA in the older female adults is hitherto not clear.

Results

Here we studied the gut microbiome of 57 OA patients and their healthy controls by metagenome-wide association study based on previously published data. A significant reduction in the richness and diversity of gut microbiome were observed in OA patients. Bifidobacterium longum and Faecalibacterium prausnitzii were decreased while Clostridium spp. was increased in the OA group. The functional modules, particularly the energetic metabolism and acetate production were also decreased in the OA patients. To evaluate the diagnostic value of identified species for elderly patients with OA, we constructed a set of random forest disease classifiers based on species differences between the two groups. Among them, 9 species reached the lowest classification error in the random forest cross validation, and the area under ROC of the model was 0.81.

Conclusions

Significant alterations in the gut microbial composition and function were observed between the older patients with OA and their controls, and a random forest classifier model for OA were constructed based on the differences in our study. Our study have identified several potential gut microbial targets in the elderly females with OA, which will facilitate the treatment of OA based on gut microbiota, is of great value in alleviating pain and improving the quality of life for them.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-021-04199-0.

Osteoarthritis: Insights Offered by the Study of Bone Mass Genetics

PURPOSE OF REVIEW

This paper reviews how bone genetics has contributed to our understanding of the pathogenesis of osteoarthritis. As well as identifying specific genetic mechanisms involved in osteoporosis which also contribute to osteoarthritis, we review whether bone mineral density (BMD) plays a causal role in OA development.

RECENT FINDINGS

We examined whether those genetically predisposed to elevated BMD are at increased risk of developing OA, using our high bone mass (HBM) cohort. HBM individuals were found to have a greater prevalence of OA compared with family controls and greater development of radiographic features of OA over 8 years, with predominantly osteophytic OA. Initial Mendelian randomisation analysis provided additional support for a causal effect of increased BMD on increased OA risk. In contrast, more recent investigation estimates this relationship to be bi-directional. However, both these findings could be explained instead by shared biological pathways. Pathways which contribute to BMD appear to play an important role in OA development, likely reflecting shared common mechanisms as opposed to a causal effect of raised BMD on OA. Studies in HBM individuals suggest this reflects an important role of mechanisms involved in bone formation in OA development; however further work is required to establish whether the same applies to more common forms of OA within the general population.

Prognostic factors for finger interphalangeal joint osteoarthritis: a systematic review

OBJECTIVE

Radiographic hand OA affects one in five adults. Symptomatic hand OA can result in functional impairment, pain and reduced quality of life. A prevalent form of hand OA is IP joint OA, however prognostic factors for IP joint OA remain poorly understood. This systematic review aimed to identify prognostic factors for IP joint OA, and to summarize the diagnostic criteria for IP joint OA in prognostic studies.

METHODS

EMBASE, MEDLINE, Scopus and The Cochrane Library were searched from inception until 19 February 2020 (PROSPERO CRD42019116782). Eligible studies described diagnostic criteria defining IP joint OA, and assessed potential prognostic factors for IP joint OA. Risk of bias was assessed using a modified Quality in Prognosis Studies (QUIPS) tool and a best evidence synthesis was used.

RESULTS

Eighteen studies were included (risk of bias: eight high, three moderate, seven low). All defined OA radiographically, and three studies incorporated clinical symptoms into their definition of OA. Forty-nine potential prognostic factors were assessed. Eight were prognostic: older age in women, female gender (both moderate evidence); family history of Heberden's nodes, Kashin-Beck disease, older age in men, dental occupation in men, finger fracture, parity (all limited evidence). Higher BMI in women (limited evidence) was prognostic for symptomatic radiographic OA. No prognostic factors for symptomatic OA were identified.

CONCLUSION

IP joint OA is most commonly defined radiographically, yet criteria were heterogeneous. Eight prognostic factors for radiographic IP joint OA and one for symptomatic radiographic IP joint OA were identified, all with limited or moderate evidence. Further studies on causality and on prognostic pathways are needed.

The Genetic Architecture of High Bone Mass

The phenotypic trait of high bone mass (HBM) is an excellent example of the nexus between common and rare disease genetics. HBM may arise from carriage of many 'high bone mineral density [BMD]'-associated alleles, and certainly the genetic architecture of individuals with HBM is enriched with high BMD variants identified through genome-wide association studies of BMD. HBM may also arise as a monogenic skeletal disorder, due to abnormalities in bone formation, bone resorption, and/or bone turnover. Individuals with monogenic disorders of HBM usually, though not invariably, have other skeletal abnormalities (such as mandible enlargement) and thus are best regarded as having a skeletal dysplasia rather than just isolated high BMD. A binary etiological division of HBM into polygenic vs. monogenic, however, would be excessively simplistic: the phenotype of individuals carrying rare variants of large effect can still be modified by their common variant polygenic background, and by the environment. HBM disorders-whether predominantly polygenic or monogenic in origin-are not only interesting clinically and genetically: they provide insights into bone processes that can be exploited therapeutically, with benefits both for individuals with these rare bone disorders and importantly for the many people affected by the commonest bone disease worldwide-i.e., osteoporosis. In this review we detail the genetic architecture of HBM; we provide a conceptual framework for considering HBM in the clinical context; and we discuss monogenic and polygenic causes of HBM with particular emphasis on anabolic causes of HBM.

Thumb base osteoarthritis: A hand osteoarthritis subset requiring a distinct approach

Hand osteoarthritis (OA) is usually a polyarticular disease, preferentially affecting the thumb base (TB) and interphalangeal joints. TB OA alone is generally not addressed separately, but as a part of hand OA. Studies have shown that OA in the TB joints clusters together, as does OA in the interphalangeal joints, supporting it as a distinct subset. Further support for this view comes from a specific risk profile, influence on clinical burden, impact of synovial inflammation on local joint pain, and specific treatment interventions. Therefore, clinical care and future hand OA research should not only address hand OA in general but also should focus on the different subsets separately, including TB OA.

Epidemiology of osteoarthritis: literature update

PURPOSE OF REVIEW

The purpose of this review is to highlight recent studies of osteoarthritis epidemiology, including research on prevalence, disease impact, and potential risk factors.

RECENT FINDINGS

Osteoarthritis is highly prevalent in the United States and around the globe. It is a leading cause of disability and can negatively impact people's physical and mental well being. Healthcare resources and costs associated with managing the disease can be substantial. There is increasing evidence that there are different osteoarthritis phenotypes that reflect different mechanisms of the disease. Various person-level risk factors are recognized, including sociodemographic characteristics (e.g. female sex, African-American race), genetic predispositions, obesity, diet-related factors, and high bone density/mass. Joint-level risk factors include specific bone/joint shapes, thigh flexor muscle weakness, joint malalignment, participation in certain occupational/sports activities, and joint injury. Recent studies have enhanced our understanding of preradiographic lesions associated with osteoarthritis.

SUMMARY

Application of these new findings may allow us to develop innovative strategies and novel therapies with the purpose of preventing new disease onset and minimizing disease progression.