The role of metabolites in the progression of osteoarthritis: Mechanisms and advances in therapy

Osteoarthritis (OA) is a progressive degenerative disease affected by many factors, and there is currently no effective treatment. In recent years, the latest progress in metabolomics in OA research has revealed several metabolic pathways and new specific metabolites involved in OA. Metabolites play significant roles in the identification and management of OA. This review looks back on the development history of metabolomics and the progress of this technology in OA as well as its potential clinical applications. It summarizes the applications of metabolites in the field of OA and future research directions. This understanding will advance the identification of metabolic treatment goals for OA.

The translational potential of this article

The development of metabolomics offers possibilities for the treatment of OA. This article reviews the relationship between metabolites associated with chondrocytes and OA. Selectively altering these three metabolic pathways and their associated metabolites may hold great potential as new focal points for OA treatment.

HDL-C is inversely associated with the incidence of osteoarthritis among the USA: evidence from the NHANES program of 1999-2020

Osteoarthritis (OA) has been the most common arthritis affecting public health all over the world. Previous experimental research reported that increased low-density lipoprotein cholesterol, along with decreased high-density lipoprotein cholesterol may be associated with increased ectopic bone formation and possible knee OA, while clinical evidence is absent. This study aimed to investigate the association between blood high-density lipoprotein cholesterol (HDL-C) and OA. In this cross-sectional study, all the data were acquired from the National Health and Nutrition Examination Survey (NHANES) program from 1999 to 2020. The blood lipid metabolites of each participant were acquired from the laboratory data, using the standard approach. The diagnosis of OA was established through a questionnaire interview. The multivariate logistic regression analysis, subgroup analysis, and smooth curve fitting analysis were applied to investigate the association between the blood lipid metabolites and OA after adjusting with covariates including gender, age, race, BMI, marital status, physical activity, smoking, hypertension, and diabetes. The interaction analysis and Subgroup analysis were also performed. A total of 28,933 participants, including 3710 people with self-reported OA and 25,223 people without arthritis, were finally eligible for inclusion in this study. The multiple logistic regression indicated that in the 3rd and 4th quartiles, the HDL-C level showed a positive association with the risk of OA (Q3: OR = 1.1342, 95% CI 1.0071, 1.2773, p < 0.05; Q4: OR = 1.2354, 95% CI 1.0937, 1.3956, p < 0.001). The smooth curve fitting showed a trend that the OA odds ratio increased with the increase of HDL-C. Subgroup analysis continued to show that increased HDL led to increased OA risk at certain quartiles in different subgroups. This study shows a positive correlation between blood HDL-C levels and osteoarthritis (OA) risk, suggesting HDL-C may be a risk factor. Further research is needed, especially on lipid-lowering drugs like statins, which can affect HDL-C and influence this association.

Associations between hand osteoarthritis, obesity and lipid metabolism: a cross-sectional study of the Halland County Osteoarthritis (HALLOA) cohort

BACKGROUND

To determine whether obesity and markers of lipid metabolism are associated with radiological hand osteoarthritis (OA) in the Halland County Osteoarthritis (HALLOA) cohort.

METHODS

In this cross-sectional study, we included 231 participants aged 30-65 from the HALLOA cohort, which began in 2017 and is ongoing. Hand OA was defined as ≥ 2 joint groups (distal interphalangeal, proximal interphalangeal, and carpometacarpal I) with Kellgren-Lawrence grade ≥ 2. The severity of hand OA was classified in terms of the number of affected joint groups (moderate hand OA 2-4 joint groups, severe hand OA 5-6 joint groups). Metabolic profile, including body mass index (BMI), bioimpedance, waist circumference, blood pressure, serum leptin, total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides, were obtained. Multicollinearity was assessed with Pearson's correlation and associations with logistic regression analyses adjusting for age, HDL-cholesterol, and central obesity.

RESULTS

Two-thirds of the participants were women, and 91 (39%) had hand OA. We found a relationship between LDL-cholesterol and prevalent hand OA in women with an odds ratio of 1.7 (95% CI 1.1-2.6) and an association between LDL-cholesterol and severity of hand OA in women; odds ratio for no hand OA vs. moderate hand OA was 1.6 (95% CI 1.0-2.4) and for no hand OA vs. severe hand OA 2.5 (95% CI 1.2-4.9). There were no significant relationships between hand OA and obesity or serum leptin levels.

CONCLUSION

Circulating LDL-cholesterol levels were associated with the prevalence and severity of hand OA in women but not men.

TRIAL REGISTRATION

ClinicalTrials. Gov (NCT04928170), Date of registration: 2017-12-20.

Trends and Prospects of Low-Density Lipoprotein Cholesterol in Stroke: A Bibliometric Analysis

Management of low-density lipoprotein cholesterol (LDL-C) in stroke is a crucial component of cardiovascular disease care. Recent years have seen substantial progress in understanding and managing LDL-C in the context of stroke. This study utilized bibliometric methods to analyze and synthesize trends in this area over the past decade, incorporating 2,841 publications from the Web of Science database. The analyses included trend topic analysis, co-authorship analysis, and co-citation analysis. The findings indicate that research had predominantly concentrated on epidemiological studies related to pharmacological management strategies. Future research is expected to continue exploring lipid-lowering therapies, including both established treatments like statins and newer drugs such as proprotein convertase subtilisin-kexin type 9 inhibitors. Assessing residual cholesterol and employing Mendelian randomization techniques may become potential research hotspots. The New England Journal of Medicine is the most globally influential journal, while Circulation holds the most influence within the field, and Atherosclerosis ranks as the most prolific. International collaboration in this research area was strong between the USA and England, followed by the USA and China. However, collaboration between productive institutions in the USA and China remains limited, highlighting the need to strengthen partnerships between these institutions to further advance the field.

Daily habits, diseases, drugs and knee osteoarthritis: a two-sample Mendelian randomization analysis

Background

The causal relationship between daily habits, diseases, drugs, and knee osteoarthritis (KOA) remains unclear. This study utilized a two-sample Mendelian randomization (MR) method to investigate the causal links between these factors and KOA, providing new insights for KOA prevention.

Methods

SNPs strongly associated with exposure factors (daily habits, diseases, drugs) were extracted from publicly available genome-wide association study (GWAS) as instrumental variables (IVs). We then selected GWAS of KOA as the outcome, conducting a two-sample MR analysis.

Results

Our findings revealed significant causal relationships between several factors and KOA. There was a notable association with time spent watching TV (OR = 4.038; 95% CI: 1.859-8.770; P = 4.192E-04), frequency of friend/family visits (OR = 0.415; 95% CI: 0.219-0.788; P = 7.174E-03), smoking history (OR = 0.781; 95% CI: 0.663-0.921; P = 3.235E-03), gastroesophageal reflux disease (GERD) (OR = 1.519; 95% CI: 1.244-1.856; P = 4.183E-05), hypercholesterolemia (OR = 0.498; 95% CI: 0.290-0.855; P = 0.011), hypothyroidism (OR = 1.048; 95% CI: 1.013-1.084; P = 6.645E-03), use of antithrombotic agents (OR = 0.892; 95% CI: 0.816-0.976; P = 0.013), statin medication (OR = 0.956; 95% CI: 0.916-0.998; P = 0.041), and thyroid preparations (OR = 1.042; 95% CI: 1.014-1.071; P = 2.974E-03) with KOA. Specifically, KOA was positively associated with longer time spent watching TV, GERD, hypothyroidism and thyroid preparations, however showed a negative correlation with more frequent visits from friends or family, smoking history, hypercholesterolemia, antithrombotic agents and statin medication. Sensitivity analysis indicated no significant pleiotropy in these studies (P > 0.05).

Conclusion

This comprehensive study underscores the significance of modifying certain habits to mitigate the risk of KOA. Additionally, the elevated risk of KOA among individuals with GERD, hypothyroidism, and those using thyroid preparations warrants attention. These results would be beneficial for clinical research and nursing education.

[Relationship between hypercholesterolemia and osteoarthritis (preliminary results)]

AIM

To evaluate the relationship of hypercholesterolemia (HCE) with clinical, instrumental, and laboratory parameters in osteoarthritis (OA) in a multicenter, cross-sectional study.

MATERIALS AND METHODS

The study included 183 patients aged 40-75 years, with a confirmed diagnosis of stage I-III OA (ACR) of the knee joints, who signed an informed consent. The mean age was 55.6±10.7 years (40 to 75), body mass index was 29.3±6.3 kg/m2, and disease duration was 5 [1; 10] years. For each patient, a case record form was filled out, including anthropometric indicators, medical history, clinical examination data, an assessment of knee joint pain according to VAS, WOMAC, KOOS and comorbidities. All patients underwent standard radiography and ultrasound examination of the knee joints and laboratory tests.

RESULTS

HCE was detected in 59% of patients. Depending on its presence or absence, patients were divided into two groups. Patients were comparable in body mass index, waist and hip measurement, and disease duration but differed significantly in age. Individuals with elevated total cholesterol levels had higher VAS pain scores, total WOMAC and its components, an overall assessment of the patient's health, a worse KOOS index, and ultrasound findings (reduced cartilage tissue). HCE patients showed high levels of cholesterol, low-density lipoproteins, triglycerides, STX-II, and COMP (p<0.05). However, after stratification by age, many initial intergroup differences became insignificant, and differences in the WOMAC pain score persisted.

CONCLUSION

The results of the study confirmed the high prevalence of HCE in OA patients (59%). Patients with OA and increased total cholesterol have more intense pain in the knee joints.

The metabolic characteristics and changes of chondrocytes in vivo and in vitro in osteoarthritis

Osteoarthritis (OA) is an intricate pathological condition that primarily affects the entire synovial joint, especially the hip, hand, and knee joints. This results in inflammation in the synovium and osteochondral injuries, ultimately causing functional limitations and joint dysfunction. The key mechanism responsible for maintaining articular cartilage function is chondrocyte metabolism, which involves energy generation through glycolysis, oxidative phosphorylation, and other metabolic pathways. Some studies have shown that chondrocytes in OA exhibit increased glycolytic activity, leading to elevated lactate production and decreased cartilage matrix synthesis. In OA cartilage, chondrocytes display alterations in mitochondrial activity, such as decreased ATP generation and increased oxidative stress, which can contribute to cartilage deterioration. Chondrocyte metabolism also involves anabolic processes for extracellular matrix substrate production and energy generation. During OA, chondrocytes undergo considerable metabolic changes in different aspects, leading to articular cartilage homeostasis deterioration. Numerous studies have been carried out to provide tangible therapies for OA by using various models in vivo and in vitro targeting chondrocyte metabolism, although there are still certain limitations. With growing evidence indicating the essential role of chondrocyte metabolism in disease etiology, this literature review explores the metabolic characteristics and changes of chondrocytes in the presence of OA, both in vivo and in vitro. To provide insight into the complex metabolic reprogramming crucial in chondrocytes during OA progression, we investigate the dynamic interaction between metabolic pathways, such as glycolysis, lipid metabolism, and mitochondrial function. In addition, this review highlights prospective future research directions for novel approaches to diagnosis and treatment. Adopting a multifaceted strategy, our review aims to offer a comprehensive understanding of the metabolic intricacies within chondrocytes in OA, with the ultimate goal of identifying therapeutic targets capable of modulating chondrocyte metabolism for the treatment of OA.

Impact of the Body Composition on Knee Osteoarthritis Assessed Using Bioimpedance Analysis

Osteoarthritis (OA) ranks among the most prevalent inflammatory diseases affecting the musculoskeletal system and is a leading cause of disability globally, impacting approximately 250 million individuals. This study aimed to assess the relationship between the severity of knee osteoarthritis (KOA) and body composition in postmenopausal women using bioimpedance analysis (BIA). The study included 58 postmenopausal females who were candidates for total knee arthroplasty. The control group consisted of 25 postmenopausal individuals with no degenerative knee joint changes. The anthropometric analysis encompassed the body mass index (BMI), mid-arm and mid-thigh circumferences (MAC and MTC), and triceps skinfold thickness (TSF). Functional performance was evaluated using the 30 s sit-to-stand test. During the BIA test, electrical parameters such as membrane potential, electrical resistance, capacitive reactance, impedance, and phase angle were measured. Additionally, body composition parameters, including Total Body Water (TBW), Extracellular Water (ECW), Intracellular Water (ICW), Body Cellular Mass (BCM), Extracellular Mass (ECM), Fat-Free Mass (FFM), and Fat Mass (FM), were examined. The study did not find any statistically significant differences in the electrical parameters between the control (0-1 grade on the K-L scale) and study groups (3-4 grade on the K-L scale). However, statistically significant differences were observed in BMI, fat mass (FM), arm circumference, triceps skinfold thickness, and sit-to-stand test results between the analyzed groups. In conclusion, the association between overweight and obesity with KOA in postmenopausal women appears to be primarily related to the level of adipose tissue and its metabolic activity.

Combination of hyperlipidemia and 17β-Estradiol induces TMJOA-like pathological changes in rats

OBJECTIVE

We explored whether hyperlipidemia or combination of hyperlipidemia and E2 could induce TMJOA.

MATERIALS AND METHODS

Four groups of female rats were treated with normal diet, normal diet with E2, high-fat diet, and high-fat diet with E2 (HFD/E2), respectively, to induce TMJOA till 8 weeks. Another three groups were then used for COX2 inhibitor celecoxib to block the induction of TMJOA. Primary condylar chondrocytes were treated with combination of E2, ox-LDL, and corresponding inhibitors for evaluating expressions of related molecules.

RESULTS

Condylar cartilage proliferation with plenty of chondrocyte apoptosis and increased staining for LOX1, nuclear NF-κB, IL-1β, and COX2 at 4 weeks and decreased condylar cartilage and increased subchondral bone density at 8 weeks were observed only in the HFD/E2 group. Celecoxib significantly alleviated the cartilage proliferation and apoptosis in the HFD/E2 group. Serum ox-LDL increased in both high-fat diet groups, while serum IL-1β increased only in the HFD/E2 group. Combination of E2 and ox-LDL synergistically induced expressions of LOX1, phosphorylated NF-κB, IL-1β, and COX2, while LOX1 inhibitor blocked the induction of phosphorylated NF-κB, and NF-κB inhibitor the induction of IL-1β, and IL-1β inhibitor the induction of COX2.

CONCLUSION

Combination of hyperlipidemia and E2-induced TMJOA-like pathological changes through LOX1/NF-κB/IL-1β/COX2-signaling pathway.

The microbiota-metabolic syndrome axis as a promoter of metabolic osteoarthritis

The relation between obesity and osteoarthritis (OA) development has been traditionally explained as consequence of the excessive joint effort derived of overweight. However, in the last two decades a metabolic OA has been suggested through diverse molecular mechanism implying metabolic syndrome, although more investigation must be conducted to elucidate it. Metabolic syndrome is responsible of the release of diverse inflammatory cytokines, specially the increased adipokine in obesity, causing a chronic low-grade inflammatory status that alters the joint homeostasis. In this scenario, the microbiota dysbiosis contribute by worsening the low-grade chronic inflammation or causing metabolic disorders mediated by endotoxemia generated by an increased lipopolysaccharides intake. This results in joint inflammation and cartilage degradation, which contributes to the development of OA. Also, the insulin resistance provoked by type 2 Diabetes contributes to the OA development. When intake patterns are considered, some coincidences can be pointed between the food patterns associated to the metabolic syndrome and the food patterns associated to OA development. Therefore, these coincidences support the idea of a molecular mechanism of the OA development caused by the molecular mechanism generated under the metabolic syndrome status. This review points the relation between metabolic syndrome and OA, showing the connected molecular mechanisms between both pathologies as well as the shared dietary patterns that promote or prevent both pathologies.

A clinical model to predict the progression of knee osteoarthritis: data from Dryad

BACKGROUND

Knee osteoarthritis (KOA) is a multifactorial, slow-progressing, non-inflammatory degenerative disease primarily affecting synovial joints. It is usually induced by advanced age and/or trauma and eventually leads to irreversible destruction of articular cartilage and other tissues of the joint. Current research on KOA progression has limited clinical application significance. In this study, we constructed a prediction model for KOA progression based on multiple clinically relevant factors to provide clinicians with an effective tool to intervene in KOA progression.

METHOD

This study utilized the data set from the Dryad database which included patients with Kellgren-Lawrence (KL) grades 2 and 3. The KL grades was determined as the dependent variable, while 15 potential predictors were identified as independent variables. Patients were randomized into training set and validation set. The training set underwent LASSO analysis, model creation, visualization, decision curve analysis and internal validation using R language. The validation set is externally validated and F1-score, precision, and recall are computed.

RESULT

A total of 101 patients with KL2 and 94 patients with KL3 were selected. We randomly split the data set into a training set and a validation set by 8:2. We filtered "BMI", "TC", "Hypertension treatment", and "JBS3 (%)" to build the prediction model for progression of KOA. Nomogram used to visualize the model in R language. Area under ROC curve was 0.896 (95% CI 0.847-0.945), indicating high discrimination. Mean absolute error (MAE) of calibration curve = 0.041, showing high calibration. MAE of internal validation error was 0.043, indicating high model calibration. Decision curve analysis showed high net benefit. External validation of the metabolic syndrome column-line graph prediction model was performed by the validation set. The area under the ROC curve was 0.876 (95% CI 0.767-0.984), indicating that the model had a high degree of discrimination. Meanwhile, the calibration curve Mean absolute error was 0.113, indicating that the model had a high degree of calibration. The F1 score is 0.690, the precision is 0.667, and the recall is 0.714. The above metrics represent a good performance of the model.

CONCLUSION

We found that KOA progression was associated with four variable predictors and constructed a predictive model for KOA progression based on the predictors. The clinician can intervene based on the nomogram of our prediction model.

KEY INFORMATION

This study is a clinical predictive model of KOA progression. KOA progression prediction model has good credibility and clinical value in the prevention of KOA progression.

The Value of the Monocyte to High-Density Lipoprotein Cholesterol Ratio in Assessing the Severity of Knee Osteoarthritis: A Retrospective Single Center Cohort Study

Background

Inflammatory responses and metabolic abnormalities play essential roles in the pathophysiology of osteoarthritis (OA). Our study aimed to evaluate the association between monocyte-to-high density lipoprotein-cholesterol ratio (MHR) and OA and compared it with other systemic inflammatory markers.

Methods

This study recruited 323 OA cases and age- and sex-matched 283 control participants during the same period. Demographic, clinical, and imaging data and laboratory indicators were obtained from participants' records. Systemic inflammatory markers were calculated for both cohorts. The diagnostic effectiveness of each index for distinguishing patients with OA was analyzed using receiver operating characteristic (ROC) curves. Spearman's method and ordered logistic regression were used to analyze the association between each indicator and Kellgren and Lawrence (KL) grade.

Results

MHR was significantly higher (0.38±0.18 vs 0.25±0.07, p < 0.0001) in OA patients than healthy controls. MHR had the largest area under the ROC curve for predicting OA. Analysis of ordered logistic regression indicated that MHR was a risk factor for OA radiological severity. Spearman correlation analysis indicated that MHR significantly correlates with the KL grade. Moreover, MHR was significantly higher in early stage patients than in healthy controls.

Conclusion

These results suggest that an elevated MHR could reflect knee OA severity and might be a useful marker for diagnosis and monitoring of OA.

Resveratrol Improves the Progression of Osteoarthritis by Regulating the SIRT1-FoxO1 Pathway-Mediated Cholesterol Metabolism

Osteoarthritis (OA) is considered a metabolic disorder. This study investigated the effect of resveratrol (RES) on cholesterol accumulation in osteoarthritic articular cartilage via the silent information regulator 1 (SIRT1)/forkhead transcription factor (FoxO1) pathway. Interleukin (IL)-1β-treated chondrocytes that mimic OA chondrocytes were used in in vitro experiments. The optimal RES concentration was selected based on the results of chondrocyte proliferation in the Cell Counting Kit-8 assay. Western blotting, immunofluorescence, and reverse transcription-quantitative polymerase chain reaction were performed. For the animal experiments, mice were randomly divided into the RES group (n = 15), medial meniscus destabilization group (n = 15), and sham group (n = 15), and each group received the same dose of RES or saline. Articular cartilage tissue was obtained eight weeks after surgery for relevant histological analysis. Clinical tissue test results suggest that downregulation of the SIRT1/FoxO1 pathway is associated with cholesterol buildup in OA chondrocytes. For the in vitro studies, RES increased the expression of SIRT1 and phosphorylation of FoxO1 in IL-1β-treated chondrocytes, promoted the expression of cholesterol efflux factor liver X receptor alpha (LXRα), and inhibited the expression of cholesterol synthesis-associated factor sterol-regulatory element binding proteins 2 (SREBP2). This reduced IL-1β-induced chondrocytes cholesterol accumulation. SIRT1 inhibition prevented the RES-mediated reduction in cholesterol buildup. Inhibiting FoxO1 but not SIRT1 reduced FoxO1 phosphorylation and increased cholesterol buildup in cultured chondrocytes. Additionally, in vivo experiments have shown that RES can alleviate cholesterol buildup and pathological changes in OA cartilage. Our findings suggest that RES regulates cholesterol buildup in osteoarthritic articular cartilage via the SIRT1/FoxO1 pathway, thereby improving the progression of OA.

FEATURES OF THE CLINICAL COURSE OF OSTEOARTHRITIS IN COMBINATION WITH DIABETES MELLITUS

OBJECTIVE

The aim: To examine the features of the clinical course of osteoarthritis in combination with type 2 diabetes on the background of obesity and hypertension.

PATIENTS AND METHODS

Materials and methods: 116 patients who were in the inpatient stage of treatment in the rheumatology department of the Chernivtsi Regional Clinical Hospital during 2015-2017 were examined. The epidemiological and clinical features of osteoarthritis in patients with type 2 diabetes mellitus were also analyzed.

RESULTS

Results: It was found that the course of osteoarthritis is extremely severe with limited range of motion in the joints, their deformation and significant deteri¬oration of functional capacity, duration of pain, periodic prolonged exacerbations, the predominance of knee and hip injuries (64.8%) and 14.8 persons - small joints. This showed the progression and generalization of processes in various joints, aggravation of the course and prognosis of osteoarthritis, especially in women. Their prevalence was registered at II radiological stage (59.27% and 74.0%, respectively).

CONCLUSION

Conclusions: The authors emphasize that such a clinical course indicates the worst prognosis. This multimorbidity of diseases requires treatment, observation and consultation with a traumatologist, rheumatologist and endocrinologist, due to the multisystem approach to the treatment and rehabilitation of such patients with an emphasis on individual clinical features (including gender) and the course of comorbidities or syndromes.

Activation of circulating monocytes by low-density lipoprotein-a risk factor for osteoarthritis?

Synovial macrophages are key mediators of OA pathology, and skewing of macrophage phenotype in favour of an M1-like phenotype is thought to underlie the chronicity of synovial inflammation in OA. Components of the metabolic syndrome (MetS), such as dyslipidaemia, can affect macrophage phenotype and function, which could explain the link between MetS and OA development. Recently published studies have provided novel insights into the different origins and heterogeneity of synovial macrophages. Considering these findings, we propose an important role for monocyte-derived macrophages in particular, as opposed to yolk-sac derived residential macrophages, in causing a pro-inflammatory phenotype shift. We will further explain how this can start even prior to synovial infiltration; in the circulation, monocytes can be trained by metabolic factors such as low-density lipoprotein to become extra responsive to chemokines and damage-associated molecular patterns. The concept of innate immune training has been widely studied and implicated in atherosclerosis pathology, but its involvement in OA remains uncharted territory. Finally, we evaluate the implications of these insights for targeted therapy directed to macrophages and metabolic factors.

Deletion of ApoE Leads to Intervertebral Disc Degeneration via Aberrant Activation of Adipokines

STUDY DESIGN

Animal experiment: a mouse model of intervertebral disc (IVD) degeneration induced by deletion of apolipoprotein E (apoE).

OBJECTIVE

The aim of this study was to investigate the role and mechanism of apoE on the process of IVD degeneration.

SUMMARY OF BACKGROUND DATA

Abnormal lipid metabolism has been demonstrated to be closely related to IVD degeneration, a common chronic degenerative joint disease. ApoE, a component of apolipoproteins, plays a crucial role in lipid transportation and metabolic balance. But the relationship between apoE and IVD degeneration remains largely unknown.

METHODS

ApoE knockout (KO) mouse was employed to investigate the progressive disc degeneration. The changes of vertebral bone and intervertebral disc space were measured by micro-computed tomography (micro-CT). The histo-morphological changes of cartilage endplate (CEP) and underlying signals were tested using immunohistochemistry and immunofluorescence staining.

RESULTS

The deletion of apoE gene accelerated the lumbar spine degeneration. Compared with WT mice, apoE KO mice showed reduced IVD space and increased vertebral bone mass. The progressive CEP degeneration was further found with cartilage degradation and endplate sclerosis in apoE KO mice. The deletion of apoE stimulated abnormal CEP bone remodeling and activation of adipokines signals.

CONCLUSION

The deletion of apoE gene induced abnormal activation of adipokines signals, thus contribute to the CEP degeneration.

LEVEL OF EVIDENCE

N/A.

Foamy macrophages potentially inhibit tuberculous wound healing by inhibiting the TLRs/NF-κB signalling pathway

To characterise the distribution, classification, and quantity of foamy macrophages (FMs) in tuberculous wound tissue and the relationship between FM and delayed healing of tuberculous wounds. Morphological studies were performed to explore the distribution of FM and Mycobacterium tuberculosis (Mtb) in tuberculous wounds, with acute and chronic wounds included for comparison. Phorbol-12-myristate-13-acetate stimulation-differentiated THP-1 cells were treated with Mtb to induce their differentiation into FM with oxidised low-density lipoprotein treatment serving as a control. Relative cytokine levels were determined by quantitative PCR and Western blotting. Varied co-culture combinations of Mtb, THP-1, FM, and fibroblasts were performed, and proliferation, migration, ability to contract collagen gel, and protein levels of the chemokines in the supernatants of the fibroblasts were assessed. The differentially expressed genes in human skin fibroblasts (HSFs) after co-culture with or without FM were identified using microarray. Many FM were found in the tissues of tuberculous wounds. The FM that did not engulf Mtb (NM-FM) were mainly distributed in tissues surrounding tuberculous wounds, whereas the FM that engulfed Mtb (M-FM) were dominantly located within granulomatous tissues. Co-culture experiments showed that, with the Mtb co-culture, the portions of NM-FM in the total FM grew over time. The migration, proliferation, chemokine secretion, and the ability of fibroblasts to contract collagen gel were inhibited when co-cultured with Mtb, FM, or a combination of the two. Further investigation showed that the TLRs/NF-κB signalling pathway is involved in fibroblast function under the stimulation of FM. TLRs and NF-κB agonists could reverse the phenotypic changes in HSFs after co-culture with FM. The tuberculous wound microenvironment composed of Mtb and FM may affect wound healing by inhibiting the functions of fibroblasts. FM potentially inhibit fibroblasts' function by inhibiting the TLRs/NF-κB signalling pathway in tuberculous wounds.

Association of Serum Low-Density Lipoprotein, High-Density Lipoprotein, and Total Cholesterol With Development of Knee Osteoarthritis

OBJECTIVE

Studies suggest an association between elevated total serum cholesterol, particularly low-density lipoprotein (LDL), and osteoarthritis (OA). The present study was undertaken to evaluate the association between total cholesterol, LDL, and high-density lipoprotein (HDL) and risk of knee OA.

METHODS

We studied participants from the Multicenter Osteoarthritis study (MOST) cohort at risk of developing knee OA. From baseline through 7 years, repeated knee radiographs and magnetic resonance images (MRIs) were obtained, and knee symptoms were queried. From baseline fasting blood samples, lipids and lipoproteins were analyzed using standard assays. After excluding participants with baseline OA, we defined 2 sets of patients: those developing radiographic OA, and those developing symptomatic OA (knee pain and radiographic OA). Controls did not develop these outcomes. Additionally, we examined worsening of cartilage loss and synovitis on MRI and of knee pain using the Western Ontario and McMaster Universities Osteoarthritis Index scale. We carried out logistic regression adjusting for age, sex, body mass index, education, baseline pain, and depressive symptoms, testing total cholesterol and lipoproteins as continuous measures, and we performed sensitivity analyses examining whether commonly used thresholds for high cholesterol, LDL, or low HDL increased risk.

RESULTS

We studied 337 patients with incident symptomatic OA and 283 patients with incident radiographic OA. The mean age at baseline was 62 years (55% women). Neither total cholesterol, LDL, nor HDL showed a significant association with radiographic or symptomatic OA. Additionally, we found no association of these lipid measures with cartilage loss, worsening synovitis, or worsening knee pain.

CONCLUSION

Our data do not support an association between total cholesterol, LDL, or HDL with OA outcomes.

Effect of blood lipids and lipid-lowering therapies on osteoarthritis risk: A Mendelian randomization study

Background

We aimed to investigate the effects of blood lipids and lipid-lowering agents on osteoarthritis (OA) risk.

Materials and methods

We performed Mendelian randomization (MR) analyses to estimate the causal effect of blood low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) levels on knee and hip OA. Single nucleotide polymorphisms (SNPs) were selected from large genome-wide association studies (GWASs) of individuals of European ancestry as genetic instruments for blood lipid levels. The associations of selected genetic instruments with knee and hip OA were estimated in a recent GWAS of the UK Biobank and arcOGEN datasets. Univariate and multivariate MR analyses were performed to detect and adjust for potential pleiotropy. Furthermore, genetic instruments in HMGCR, NPC1L1, and PCSK9 regions were used to mimic LDL-C-lowering effects of statin, ezetimibe, and evolocumab, respectively.

Results

Genetically determined LDL-C increments led to reduced risks of both knee OA (OR = 0.91 per 1-SD increment, 95% CI: 0.86-0.95, P = 6.3 × 10^-5) and hip OA (OR = 0.92, 95% CI: 0.85-0.99, P = 0.027). Multivariate MR analysis proved that the effect was independent of HDL-C, TG, and body mass index. TG increment was associated with reduced risks of hip OA in the univariate MR analysis; however, this was not supported by the multivariate MR analysis. Genetically proxied LDL-C-lowering effects of statins are related to increased risks of knee OA but not hip OA.

Conclusions

The findings suggested that LDL-C increments have independent protective effects on both knee and hip OA. LDL-C-lowering effects of statins may increase the risk of knee OA.

High-Density Lipoprotein Cholesterol and Apolipoprotein A1 in Synovial Fluid: Potential Predictors of Disease Severity of Primary Knee Osteoarthritis

OBJECTIVES

The aim of this study was to detect levels of common lipid species in serum and synovial fluid (SF) of primary knee osteoarthritis (OA) patients and investigate their correlations with disease severity.

MATERIALS AND METHODS

The study enrolled 184 OA patients receiving arthroscopic debridement or total knee arthroplasty and 180 healthy controls between April 2012 and March 2018. Total triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (ApoA1), and apolipoprotein B (ApoB) levels were analyzed in serum and SF of OA patients, and in serum of healthy individuals. The Noyes rating criteria, Kellgren-Lawrence (KL) grading system, and Western Ontario McMaster University Osteoarthritis Index (WOMAC) scores were, respectively, used to assess cartilage damage, radiographic severity, and symptomatic severity of OA.

RESULTS

No significant differences were found in serum TG and ApoB levels between the 2 groups, while OA patients had higher TC and LDL-C levels and lower HDL-C and ApoA1 levels (P < 0.05). Pearson correlation analysis revealed SF HDL-C and ApoA1 levels were negatively correlated with cartilage damage scores, KL grades as well as WOMAC scores (P < 0.05), which were still significant after adjusting for confounding factors (P < 0.05). Receiver operating characteristic curve analysis revealed SF HDL-C (area under the curve [AUC]: 0.816) and ApoA1 (AUC: 0.793) were also good predictors of advanced-stage OA (P < 0.001).

CONCLUSION

SF HDL-C and ApoA1 levels were negatively correlated with cartilage damage, radiographic severity, and symptomatic severity of primary knee OA, emerging as potential biomarkers for radiographic advanced-stage OA, which may serve as predictors of disease severity.

Cholesterol metabolism related genes in osteoarthritis

Cholesterol homeostasis plays a significant role in skeletal development and the dysregulation of cholesterol-related mechanism has been shown to be involved in the development of cartilage diseases including osteoarthritis (OA). Epidemiological studies have shown an association between elevated serum cholesterol levels and OA. Furthermore, abnormal lipid accumulation in chondrocytes as a result of abnormal regulation of cholesterol homeostasis has been demonstrated to be involved in the development of OA. Although, many in vivo and in vitro studies support the connection between cholesterol and cartilage degradation, the mechanisms underlying the complex interactions between lipid metabolism, especially HDL cholesterol metabolism, and OA remain unclear. The current review aims to address this problem and focuses on key molecular players of the HDL metabolism pathway and their role in ΟΑ pathogenesis. Understanding the complexity of biological processes implicated in OA pathogenesis, such as cholesterol metabolism, may lead to new targets for drug therapy of OA patients.

5,7,3',4'-tetramethoxyflavone ameliorates cholesterol dysregulation by mediating SIRT1/FOXO3a/ABCA1 signaling in osteoarthritis chondrocytes

Dyslipidemia has been associated with the development of osteoarthritis. Our previous study found that 5,7,3',4'-tetramethoxyflavone (TMF) exhibited protective activities against the pathological changes of osteoarthritis. Aim: To investigate the roles of TMF in regulating ABCA1-mediated cholesterol metabolism. Methods: Knockdown and overexpression were employed to study gene functions. Protein-protein interaction was investigated by co-immunoprecipitation, and the subcellular locations of proteins were studied by immunofluorescence. Results: IL-1β decreased ABCA1 expression and induced apoptosis. Therapeutically, TMF ameliorated the effects of IL-1β. FOXO3a knockdown expression abrogated the effects of TMF, and FOXO3a overexpression increased ABCA1 expression by interacting with LXRα. TMF promoted FOXO3a nuclear translocation by activating SIRT1 expression. Conclusions: TMF ameliorates cholesterol dysregulation by increasing the expression of FOXO3a/LXRα/ABCA1 signaling through SIRT1 in C28/I2 cells.

Orbitrap-MS-based untargeted metabolomics study on the therapeutic effect of colchicine on myocardial infarction

Myocardial infarction (MI) is one of the most common causes of death worldwide. A metabolomic approach based on an ultra-high performance liquid chromatography-Orbitrap analytical method was established to analyze the metabolites and to investigate the therapeutic mechanism of colchicine. Forty-six biomarkers were significantly changed between the sham group and the MI group. Thirty-five metabolites were increased and 11 were decreased in MI rats, and colchicine reversed all of them. Pathway analysis showed that the TCA cycle, alanine, aspartate and glutamate metabolism, glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, glyoxylate and dicarboxylate metabolism and arginine biosynthesis were altered in the MI group. Ingenuity pathway function and network analysis showed that colchicine improved MI through regulation of cardiac β-adrenergic signaling and cardiac hypertrophy signaling. The present study provided a useful approach for exploring the mechanism of MI and evaluating the efficacy of colchicine.

Modulation of the Inflammatory Process by Hypercholesterolemia in Osteoarthritis

Objective: Several studies have linked metabolic syndrome to the development of osteoarthritis (OA) through hypercholesterolemia, one of its components. However, epidemiological studies showed contradictory results, and it is not clear how hypercholesterolemia itself, or oxidized LDL (oxLDL)-a pathological molecule potentially involved in this relationship-could be affecting OA. The objectives of this study were to investigate the effect of hypercholesterolemia induced by high-fat diet (HFD) in cartilage from OA rabbits, and how oxLDL affect human chondrocyte inflammatory and catabolic responses. Design: New Zealand rabbits were fed with HFD for 18 weeks. On week 6, OA was surgically induced. At the end of the study, cartilage damage and IL-1β, IL-6, MCP-1, MMP-13, and COX-2 expression in articular cartilage were evaluated. In addition, cultured human OA articular chondrocytes were treated with oxLDL at concentrations equivalent to those expected in synovial fluid from HFD rabbits, in the presence of IL-1β and TNFα. The effect of oxLDL on cell viability, nitric oxide production and catabolic and pro-inflammatory gene expression was evaluated. Results: HFD intake did not modify cartilage structure or pro-inflammatory and catabolic gene expression and protein presence, both in healthy and OA animals. OxLDL did not affect human chondrocyte viability, ADAMTS5 and liver X receptor (LXR) α gene expression, but decreased the induction of IL-1β, IL-6, MCP-1, MMP-13, iNOS, and COX-2 gene expression and MMP-13 and COX-2 protein presence, evoked by cytokines. Conclusions: Our data suggest that cholesterol intake per se may not be deleterious for articular cartilage. Instead, cholesterol de novo synthesis and altered cholesterol metabolism could be involved in the associations observed in human disease.

Regulation of gene expression by MF63, a selective inhibitor of microsomal PGE synthase 1 (mPGES1) in human osteoarthritic chondrocytes

Background and Purpose

mPGES1 catalyses the production of PGE₂, the most abundant prostanoid related to inflammation and pain in arthritis. mPGES1 is suggested to be a safer and more selective drug target in inflammatory conditions compared to the COX enzymes inhibited by NSAIDs. In the present study, we investigated the effects of the selective mPGES1 inhibitor MF63 on gene expression in primary human chondrocytes from patients with osteoarthritis (OA).

Experimental Approach

Chondrocytes were isolated from articular cartilage obtained from osteoarthritis patients undergoing knee replacement surgery. The effects of MF63 were studied in the primary chondrocytes with RNA‐sequencing based genome‐wide expression analysis. The main results were confirmed with qRT‐PCR and compared with the effects of the NSAID ibuprofen. Functional analysis was performed with the GO database and interactions between the genes were studied with STRING.

Key Results

MF63 enhanced the expression of multiple metallothionein 1 (MT1) isoforms as well as endogenous antagonists of IL‐1 and IL‐36. The expression of IL‐6, by contrast, was down‐regulated. These genes were also essential in functional and interaction network analyses. The effects of MF63 were consistent in qRT‐PCR analysis, whereas the effects of ibuprofen overlapped only partly with MF63. There were no evident findings of catabolic effects by MF63.

Conclusion and Implications

Metallothionein 1 has been suggested to have anti‐inflammatory and protective effects in cartilage. Up‐regulation of the antagonists of IL‐1 superfamily and down‐regulation of the pro‐inflammatory cytokine IL‐6 also support novel anti‐inflammatory and possibly disease‐modifying effects of mPGES1 inhibitors in arthritis.

Metabolic syndrome, hypertension, and hyperglycemia were positively associated with knee osteoarthritis, while dyslipidemia showed no association with knee osteoarthritis

OBJECTIVE

Metabolic syndrome (MetS) is a clustering of at least three of the following four medical conditions: obesity, hypertension, dyslipidemia, and hyperglycemia. We aimed to discover the relationships between these diseases and osteoarthritis (OA) of the knee.

METHODS

We searched four databases (EMBASE, PubMed, Cochrane Library, and MEDLINE), as well as articles on websites and conference materials. Study effect estimates and their 95% confidence intervals (CIs) were extracted and calculated. Sensitivity analyses were undertaken to determine inter-study heterogeneity. Finally, we tested for publication bias to determine whether the outcome of the meta-analysis was robust.

RESULTS

A total of 1609 articles were identified, 40 of which were included. In radiological studies, the relationships with OA were increased for people with the following diseases: metabolic syndrome (OR 1.418, 95% CI 1.162 to 1.730), hypertension (OR 1.701, 95% CI 1.411 to 2.052), and hyperglycemia (OR 1.225, 95% CI 1.054 to 1.424). In symptomatic studies, the outcomes were similar in metabolic syndrome (OR 1.174, 95% CI 1.034 to 1.332) and hypertension (OR 1.324, 95% CI 1.186 to 1.478) studies, while there were no associations in hyperglycemia (OR 0.975, 95% CI 0.860 to 1.106) studies. There was no correlation between dyslipidemia and OA, whether in radiological studies (OR 1.216, 95% CI 0.968 to 1.529) or symptomatic studies (OR 1.050, 95% CI 0.961 to 1.146).

CONCLUSIONS

In both studies, metabolic syndrome and hypertension were positively associated with knee OA, and dyslipidemia showed no correlations. Hyperglycemia was associated with OA in radiological studies, while results were reversed in symptomatic studies. Key Points • The hypothesis that metabolic syndrome and its components increase the risk for knee osteoarthritis is attractive; thus, this meta-analysis may help us find out the answer. • There were lots of large-scale studies here, and the total participants were considerable; and this meta-analysis was relatively robust because of reasonable heterogeneity and publication bias. • Targeted education and effective management of risk factors may be helpful for reducing the prevalence of knee osteoarthritis.

Can metabolic profiling provide a new description of osteoarthritis and enable a personalised medicine approach?

Osteoarthritis (OA) is a multifactorial disease contributing to significant disability and economic burden in Western populations. The aetiology of OA remains poorly understood, but is thought to involve genetic, mechanical and environmental factors. Currently, the diagnosis of OA relies predominantly on clinical assessment and plain radiographic changes long after the disease has been initiated. Recent advances suggest that there are changes in joint fluid metabolites that are associated with OA development. If this is the case, biochemical and metabolic biomarkers of OA could help determine prognosis, monitor disease progression and identify potential therapeutic targets. Moreover, for focussed management and personalised medicine, novel biomarkers could sub-stratify patients into OA phenotypes, differentiating metabolic OA from post-traumatic, age-related and genetic OA. To date, OA biomarkers have concentrated on cytokine action and protein signalling with some progress. However, these remain to be adopted into routine clinical practice. In this review, we outline the emerging metabolic links to OA pathogenesis and how an elucidation of the metabolic changes in this condition may provide future, more descriptive biomarkers to differentiate OA subtypes.

Osteoarthritis and type 2 diabetes: From pathogenetic factors to therapeutic intervention

Over the last decades, osteoarthritis (OA) and type 2 diabetes (T2D) prevalence increased due to the global ageing population and the pandemic obesity. They currently affect a substantial part of the Western world population and are characterized by enhancing the risk of disability and reduction of quality of life. OA is a multifactorial condition whose development derives from the interaction between individual and environmental factors: The best known primarily include age, female gender, genetic determinants, articular biomechanics, and obesity (OB). Given the high prevalence of OA and T2D and their association with OB and inflammation, several studies have been conducted to investigate the causative role of biological characteristics proper to T2D on the development of OA. This review aims to analyse the relationship between of OA and T2D, in order to explain the pathophysiological drivers of the degenerative process and to delineate possible targets to which appropriate treatments may be addressed in the near future.

Osteoarthritis and inflammation: a serious disease with overlapping phenotypic patterns

Globally, osteoarthritis (OA) is the most prevalent arthritic condition in those aged over 60 years. OA has a high impact on patient disability and is associated with a significant economic burden. Pain is the most common first sign of disease and the leading cause of disability. Data demonstrating the increasing global prevalence of OA, together with a greater understanding of the burden of the disease, have led to a reassessment of the seriousness of OA and calls for the designation of OA as a serious disease in line with the diseases impact on comorbidity, disability, and mortality. While OA was traditionally seen as a prototypical 'wear and tear' disease, it is now more accurately thought of as a disease of the whole joint involving cartilage together with subchondral bone and synovium. As more has become known of the pathophysiology of OA, it has become increasingly common for it to be described using a number of overlapping phenotypes. Patients with OA will likely experience multiple phenotypes during their disease. This review focuses on what we feel are three key phenotypes: post-trauma, metabolic, and aging. A greater understanding of OA phenotypes, particularly at the early stages of disease, may be necessary to improve treatment outcomes. In the future, non-pharmacological and pharmacological treatments could be tailored to patients based on the key features of their phenotype and disease pathway.

Macrophage: A Potential Target on Cartilage Regeneration

Cartilage lesions and osteoarthritis (OA) presents an ever-increasing clinical and socioeconomic burden. Synovial inflammation and articular inflammatory environment are the key factor for chondrocytes apoptosis and hypertrophy, ectopic bone formation and OA progression. To effectively treat OA, it is critical to develop a drug that skews inflammation toward a pro-chondrogenic microenvironment. In this narrative and critical review, we aim to see the potential use of immune cells modulation or cell therapy as therapeutic alternatives to OA patients. Macrophages are immune cells that are present in synovial lining, with different roles depending on their subtypes. These cells can polarize to pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes, being the latter associated with wound-healing by the production of ARG-1 and pro-chondrogenic cytokines, such as IL-10, IL-1RA, and TGF-b. Emerging evidence reveals that macrophage shift can be determined by several stimuli, apart from the conventional in vitro IL-4, IL-13, and IL-10. Evidences show the potential of physical exercise to induce type 2 response, favoring M2 polarization. Moreover, macrophages in contact with oxLDL have effect on the production of anabolic mediators as TGF-b. In the same direction, type II collagen, that plays a critical role in development and maturation process of chondrocytes, can also induce M2 macrophages, increasing TGF-b. The mTOR pathway activation in macrophages was shown to be able to polarize macrophages in vitro, though further studies are required. The possibility to use mesenchymal stem cells (MSCs) in cartilage restoration have a more concrete literature, besides, MSCs also have the capability to induce M2 macrophages. In the other direction, M1 polarized macrophages inhibit the proliferation and viability of MSCs and impair their ability to immunosuppress the environment, preventing cartilage repair. Therefore, even though MSCs therapeutic researches advances, other sources of M2 polarization are attractive issues, and further studies will contribute to the possibility to manipulate this polarization and to use it as a therapeutic approach in OA patients.

The CH25H-CYP7B1-RORα axis of cholesterol metabolism regulates osteoarthritis

Osteoarthritis-the most common form of age-related degenerative whole-joint disease¹-is primarily characterized by cartilage destruction, as well as by synovial inflammation, osteophyte formation and subchondral bone remodelling^2,3. However, the molecular mechanisms that underlie the pathogenesis of osteoarthritis are largely unknown. Although osteoarthritis is currently considered to be associated with metabolic disorders, direct evidence for this is lacking, and the role of cholesterol metabolism in the pathogenesis of osteoarthritis has not been fully investigated^4-6. Various types of cholesterol hydroxylases contribute to cholesterol metabolism in extrahepatic tissues by converting cellular cholesterol to circulating oxysterols, which regulate diverse biological processes^7,8. Here we show that the CH25H-CYP7B1-RORα axis of cholesterol metabolism in chondrocytes is a crucial catabolic regulator of the pathogenesis of osteoarthritis. Osteoarthritic chondrocytes had increased levels of cholesterol because of enhanced uptake, upregulation of cholesterol hydroxylases (CH25H and CYP7B1) and increased production of oxysterol metabolites. Adenoviral overexpression of CH25H or CYP7B1 in mouse joint tissues caused experimental osteoarthritis, whereas knockout or knockdown of these hydroxylases abrogated the pathogenesis of osteoarthritis. Moreover, retinoic acid-related orphan receptor alpha (RORα) was found to mediate the induction of osteoarthritis by alterations in cholesterol metabolism. These results indicate that osteoarthritis is a disease associated with metabolic disorders and suggest that targeting the CH25H-CYP7B1-RORα axis of cholesterol metabolism may provide a therapeutic avenue for treating osteoarthritis.

Hand and knee osteoarthritis are associated with reduced diameters in retinal vessels: the AGES-Reykjavik study

To investigate the association between osteoarthritis (OA) and microvascular pathology, we examined the relationship between retinal microvascular caliber and osteoarthritis of the hand and knee in an elderly population. The AGES-Reykjavik is a population-based, multidisciplinary longitudinal cohort study of aging. Retinal vessel caliber, hand osteoarthritis and total knee joint replacements due to OA were examined in 4757 individuals (mean age 76 ± 5 years; 57% female). Incident knee joint replacements during 5-year follow-up (n = 2961, mean age 75 ± 5 years; 58% female) were also assessed. Logistic regression analysis, adjusting for age, sex, and body mass index, showed an association between narrow arteriolar caliber and hand OA, as well as knee replacement. After adjustment for other covariates, including statin therapy, this association was significant for both hand OA in men and women [OR 1.10(1.03-1.17), p < 0.01] (per unit standard deviation decrease in CRAE) and TKR prevalence [OR 1.15 (1.01-1.32), p = 0.04], especially for men [OR 1.22 (1.00-1.51) p = 0.04] and also for incident TKRs in men [OR 1.50 (1.07-2.10), p = 0.04]. Narrow venular caliber was associated with hand OA in women [OR 1.10 (1.01-1.21), p = 0.03]. Retinal arterial narrowing in hand and knee OA is present in males as well as females. Venular narrowing in hand OA in women was an unexpected finding and is in contrast with the venular widening usually observed in cardiovascular diseases.

What is the evidence for a role for diet and nutrition in osteoarthritis?

As current treatment options in OA are very limited, OA patients would benefit greatly from some ability to self-manage their condition. Since diet may potentially affect OA, we reviewed the literature on the relationship between nutrition and OA risk or progression, aiming to provide guidance for clinicians. For overweight/obese patients, weight reduction, ideally incorporating exercise, is paramount. The association between metabolic syndrome, type-2 diabetes and OA risk or progression may partly explain the apparent benefit of dietary-lipid modification resulting from increased consumption of long-chain omega-3 fatty-acids from oily fish/fish oil supplements. A strong association between OA and raised serum cholesterol together with clinical effects in statin users suggests a potential benefit of reduction of cholesterol by dietary means. Patients should ensure that they meet the recommended intakes for micronutrients such as vitamin K, which has a role in bone/cartilage mineralization. Evidence for a role of vitamin D supplementation in OA is unconvincing.

Association between the severity of symptomatic knee osteoarthritis and cumulative metabolic factors

BACKGROUND

The association between cumulative metabolic syndrome (MS) factors and knee osteoarthritis (KOA) has been highlighted over the past two decades.

AIMS

To clarify the relationship between cumulative MS factors and symptomatic KOA.

METHODS

A cross-sectional survey involving 119 women aged 45-88 years who were scheduled to undergo knee surgery was conducted. They were stratified into tertiles of symptoms as assessed by the Japanese Orthopedic Association score for KOA. Multinomial logistic regressions were performed using the severity of symptomatic KOA as the dependent variable and each MS factor or the cumulative MS factors as the independent variables.

RESULTS

Logistic regression analyses were performed with the upper tertile of stratified symptoms of subjects used as the reference group. After adjustment for confounders, KOA patients who had two (p = 0.004) or three or more (p < 0.0001) MS factors were significantly more likely to have severe symptoms compared to those who had no MS factors. MS factors excluding obesity were similarly analyzed. Even after additional adjustment for body mass index (BMI), KOA patients who had two or more (p = 0.005) MS factors were significantly more likely to have severe symptoms.

CONCLUSION

Among KOA female patients diagnosed using radiographic definition, the severity of symptomatic KOA was significantly associated with hypertension, dyslipidemia, and the number of MS factors after adjustment for age, BMI, strength of the knee extensor, and Kellgren-Lawrence grade. The severity of radiographic KOA was not associated with any MS factor or cumulative MS factors.

Variable cartilage degradation in mice with diet-induced metabolic dysfunction: food for thought

OBJECTIVE

Human cohort studies have demonstrated a role for systemic metabolic dysfunction in osteoarthritis (OA) pathogenesis in obese patients. To explore the mechanisms underlying this metabolic phenotype of OA, we examined cartilage degradation in the knees of mice from different genetic backgrounds in which a metabolic phenotype was established by various dietary approaches.

DESIGN

Wild-type C57BL/6J mice and genetically modified mice (hCRP, LDLr^-/-. Leiden and ApoE*3Leiden.CETP mice) based on C57BL/6J background were used to investigate the contribution of inflammation and altered lipoprotein handling on diet-induced cartilage degradation. High-caloric diets of different macronutrient composition (i.e., high-carbohydrate or high-fat) were given in regimens of varying duration to induce a metabolic phenotype with aggravated cartilage degradation relative to controls.

RESULTS

Metabolic phenotypes were confirmed in all studies as mice developed obesity, hypercholesteremia, glucose intolerance and/or insulin resistance. Aggravated cartilage degradation was only observed in two out of the twelve experimental setups, specifically in long-term studies in male hCRP and female ApoE*3Leiden.CETP mice. C57BL/6J and LDLr^-/-. Leiden mice did not develop HFD-induced OA under the conditions studied. Osteophyte formation and synovitis scores showed variable results between studies, but also between strains and gender.

CONCLUSIONS

Long-term feeding of high-caloric diets consistently induced a metabolic phenotype in various C57BL/6J (-based) mouse strains. In contrast, the induction of articular cartilage degradation proved variable, which suggests that an additional trigger might be necessary to accelerate diet-induced OA progression. Gender and genetic modifications that result in a humanized pro-inflammatory state (human CRP) or lipoprotein metabolism (human-E3L.CETP) were identified as important contributing factors.

Increased synovial lipodystrophy induced by high fat diet aggravates synovitis in experimental osteoarthritis

BACKGROUND

Metabolic syndrome (MetS) may be associated with knee osteoarthritis (OA), but the association between the individual components and OA are not well-understood. We aimed to study the effect of hypercholesterolemia on synovial inflammation in knee OA.

METHODS

OA was surgically induced in rabbits fed with standard diet (OA group, n = 10) or in rabbits fed with high fat diet (OA-HFD, n = 10). Healthy rabbits receiving standard diet (Control, n = 10) or fed with HFD (HFD, n = 6) were also monitored. Twelve weeks after OA induction, synovial membranes were isolated and processed for studies.

RESULTS

Animals fed HFD showed higher levels of total serum cholesterol, triglycerides and C-reactive protein than control rabbits. Twelve weeks after OA induction, synovial membrane inflammation and macrophage infiltration were increased in rabbits with OA, particularly in the OA-HFD group. Extensive decrease of synovial adipose tissue area, adipocyte size and perilipin-1A synthesis were observed in the OA-HFD group in comparison to the OA and control groups. The HFD further increased the proinflammatory mediators IL-1β, IL-6 and TNF in the OA synovium. However, the synovial gene expression of adipokines, such as leptin and adiponectin, were markedly decreased in the rabbits with OA, especially in the OA-HFD group, in correlation with adipose tissue loss. However, circulating leptin was upregulated in the HFD and OA-HFD groups.

CONCLUSION

Our results indicate that a HFD is an aggravating factor worsening synovial membrane inflammation during OA, guided by increased infiltration of macrophages and removal of the adipose tissue, together with a remarkable presence of proinflammatory factors. Synovial adipocytes and dyslipemia could probably play pivotal roles in OA joint deterioration in patients with MetS, supporting that the link between obesity and OA transcends mechanical loading.

Conditional Macrophage Depletion Increases Inflammation and Does Not Inhibit the Development of Osteoarthritis in Obese Macrophage Fas-Induced Apoptosis-Transgenic Mice

OBJECTIVE

To investigate whether short-term, systemic depletion of macrophages can mitigate osteoarthritis (OA) following injury in the setting of obesity.

METHODS

CSF-1R-GFP+ macrophage Fas-induced apoptosis (MaFIA)-transgenic mice that allow conditional depletion of macrophages were placed on a high-fat diet and underwent surgery to induce knee OA. A small molecule (AP20187) was administrated to deplete macrophages in MaFIA mice. The effects of macrophage depletion on acute joint inflammation, OA severity, and arthritic bone changes were evaluated using histology and micro-computed tomography. Immunohistochemical analysis was performed to identify various immune cells. The levels of serum and synovial fluid cytokines were also measured.

RESULTS

Macrophage-depleted mice had significantly fewer M1 and M2 macrophages in the surgically operated joints relative to controls and exhibited decreased osteophyte formation immediately following depletion. Surprisingly, macrophage depletion did not attenuate the severity of OA in obese mice; instead, it induced systemic inflammation and led to a massive infiltration of CD3+ T cells and particularly neutrophils, but not B cells, into the injured joints. Macrophage-depleted mice also demonstrated a markedly increased number of proinflammatory cytokines including granulocyte colony-stimulating factor, interleukin-1β (IL-1β), IL-6, IL-8, and tumor necrosis factor in both serum and joint synovial fluid, although the mice showed a trend toward decreased levels of insulin and leptin in serum after macrophage depletion.

CONCLUSION

Our findings indicate that macrophages are vital for modulating homeostasis of immune cells in the setting of obesity and suggest that more targeted approaches of depleting specific macrophage subtypes may be necessary to mitigate inflammation and OA in the setting of obesity.

Association between osteoarthritis and dyslipidaemia: a systematic literature review and meta-analysis

OBJECTIVES

We aimed to investigate the prevalence of dyslipidemia in patients with osteoarthritis (OA) and whether OA and dyslipidemia are associated.

METHODS

We performed a systematic literature review and a meta-analysis, including cross-sectional, cohort and case-control studies, to assess the number of patients with OA and/or dyslipidemia. We calculated the mean (±SD) prevalence of dyslipidemia in patients with and without OA and the risk of dyslipidemia (OR, 95% CI) among patients with OA.

RESULTS

From 605 articles screened, 48 were included in the analysis (describing 29 cross-sectional, 10 cohort and 9 case-control studies). The mean prevalence of dyslipidemia was 30.2%±0.6% among 14 843 patients with OA and 8.0%±0.1% among 196 168 without OA. The risk of dyslipidemia was greater with than without OA overall (OR 1.98,95% CI 1.43 to 2.75, p<0.0001) and with knee OA (OR 2.27, 1.33 to 3.89, p=0.003) and hand OA (OR 2.12, 1.46 to 3.07), p<0.0001).

CONCLUSION

The risk of dyslipidemia was twofold greater with than without OA, so lipid disturbances could be a risk factor for OA. Such a result supports the individualisation of the metabolic syndrome-associated OA phenotype.

Metabolic syndrome-associated osteoarthritis

PURPOSE OF REVIEW

Interest in the metabolic syndrome-associated osteoarthritis phenotype is increasing. Here, we summarize recently published significant findings.

RECENT FINDINGS

Meta-analyses confirmed an association between type 2 diabetes and osteoarthritis and between cardiovascular diseases and osteoarthritis. Recent advances in the study of metabolic syndrome-associated osteoarthritis have focused on a better understanding of the role of metabolic diseases in inducing or aggravating joint damage. In-vivo models of obesity, diabetes, or dyslipidemia have helped to better decipher this association. They give emerging evidence that, beyond the role of common pathogenic mechanisms for metabolic diseases and osteoarthritis (i.e., low-grade inflammation and oxidative stress), metabolic diseases have a direct systemic effect on joints. In addition to the impact of weight, obesity-associated inflammation is associated with osteoarthritis severity and may modulate osteoarthritis progression in mouse models. As well, osteoarthritis synovium from type 2 diabetic patients shows insulin-resistant features, which may participate in joint catabolism. Finally, exciting data are emerging on the association of gut microbiota and circadian rhythm and metabolic syndrome-associated osteoarthritis.

SUMMARY

The systemic role of metabolic syndrome in osteoarthritis pathophysiology is now better understood, but new avenues of research are being pursued to better decipher the metabolic syndrome-associated osteoarthritis phenotype.

Lysophosphatidylcholine activates the Akt pathway to upregulate extracellular matrix protein production in human aortic valve cells

BACKGROUND

Overproduction of extracellular matrix (ECM) protein by aortic valve interstitial cells (AVICs) plays an important role in valvular sclerosis (thickening) associated with the early pathobiology of aortic stenosis. Accumulation of oxidized low-density lipoprotein (oxLDL) is observed in sclerotic aortic valve and may have a mechanistic role in valvular disease progression. Lysophosphatidylcholine (LysoPC) is a component of oxLDL and has multiple biological activities. This study was to test the hypothesis that oxLDL and LysoPC upregulate ECM protein production in human AVICs.

METHODS AND RESULTS

AVICs were isolated from normal human aortic valves. Cells were treated with oxLDL (40 μg/mL) or LysoPC (40 μmol/L). Immunoblotting was applied to analyze ECM proteins (collagens I and III and biglycan) in cell lysate and Picrosirius red staining was used to examine collagen deposition. Both oxLDL and LysoPC upregulated the production of biglycan and collagen I. The upregulation of ECM proteins by LysoPC was preceded by the phosphorylation of Akt and ERK1/2. Inhibition of Akt markedly reduced the effect of LysoPC on ECM protein production and collagen deposition. However, inhibition of ERK1/2 had no effect.

CONCLUSIONS

LysoPC upregulates the production of biglycan and collagen I in human AVICs and may mediate the effect of oxLDL on ECM protein production. The Akt pathway appears to be critical in mediating the effect of LysoPC. oxLDL accumulation and generation of LysoPC in the aortic valve tissue may contribute to the mechanism of valvular sclerosis associated with the development and progression of aortic stenosis.

Synovial macrophages promote TGF-β signaling and protect against influx of S100A8/S100A9-producing cells after intra-articular injections of oxidized low-density lipoproteins

OBJECTIVE

Low-density lipoproteins (LDL) in inflamed synovium is oxidized and taken-up by synoviocytes. In this study, we investigate whether direct injection of oxidized LDL (oxLDL) into a normal murine knee joint induces joint pathology and whether synovial macrophages are involved in that process.

DESIGN

Synovium was obtained from end-stage osteoarthritis (OA) patients in order to analyze LDL-uptake. Murine knee joints were injected five consecutive days with oxLDL, LDL, or vehicle (phosphate buffered saline (PBS)). This procedure was repeated in mice depleted of synovial macrophages by intra-articular injection of clodronate liposomes 7 days prior to the consecutive injections. Joint pathology was investigated by immunohistochemistry, flow cytometry (FCM) and synovial RNA expression and protein production.

RESULTS

Synovial tissue of OA patients showed extensive accumulation of apolipoprotein B. Multiple injections of oxLDL in murine knee joints significantly increased TGF-β activity in synovial wash-outs, but did not induce catabolic or inflammatory processes. In contrast, repeated injections of oxLDL in macrophage-depleted knee joints led to increased synovial thickening in combination with significantly upregulated protein and RNA levels of CCL2 and CCL3. FCM-analyses revealed increased presence of monocytes and neutrophils in the synovium, which was confirmed by immunohistochemistry. Also protein levels of S100A8/A9 were significantly increased in synovial wash-outs of oxLDL-injected joints, as was expression of aggrecanase-induced neo-epitopes. Interestingly, no raise in TGF-β concentrations was measured in macrophage-depleted joints.

CONCLUSIONS

OxLDL can affect joint pathology, since synovial macrophages promote anabolic processes after oxLDL injections. In absence of synovial macrophages, however, oxLDL induces production of pro-inflammatory mediators and aggrecanase activity combined with increased influx of monocytes and neutrophils.

Emerging role of metabolic signaling in synovial joint remodeling and osteoarthritis

Obesity and associated metabolic diseases collectively referred to as the metabolic syndrome increase the risk of skeletal and synovial joint diseases, including osteoarthritis (OA). The relationship between obesity and musculoskeletal diseases is complex, involving biomechanical, dietary, genetic, inflammatory, and metabolic factors. Recent findings illustrate how changes in cellular metabolism and metabolic signaling pathways alter skeletal development, remodeling, and homeostasis, especially in response to biomechanical and inflammatory stressors. Consequently, a better understanding of the energy metabolism of diarthrodial joint cells and tissues, including bone, cartilage, and synovium, may lead to new strategies to treat or prevent synovial joint diseases such as OA. This rationale was the basis of a workshop presented at the 2016 Annual ORS Meeting in Orlando, FL on the emerging role of metabolic signaling in synovial joint remodeling and OA. The topics we covered included (i) the relationship between metabolic syndrome and OA in clinical and pre-clinical studies; (ii) the effect of biomechanical loading on chondrocyte metabolism; (iii) the effect of Wnt signaling on osteoblast carbohydrate and amino acid metabolism with respect to bone anabolism; and (iv) the role of AMP-activated protein kinase in chondrocyte energetic and biomechanical stress responses in the context of cartilage injury, aging, and OA. Although challenges exist for measuring in vivo changes in synovial joint tissue metabolism, the findings presented herein provide multiple lines of evidence to support a central role for disrupted cellular energy metabolism in the pathogenesis of OA. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2048-2058, 2016.

Metabolic Syndrome Increases the Risk for Knee Osteoarthritis: A Meta-Analysis

Background. Studies revealed that metabolic factors might contribute substantially to osteoarthritis (OA) pathogenesis. There has been an increasing interest to understand the relationship between knee OA and the metabolic syndrome (MetS). The purpose of this study was to explore the association between metabolic syndrome and knee osteoarthritis using meta-analysis. Methods. Databases, including PUBMED, EMBASE, and the Cochrane Library, were searched to get relevant studies. Data were extracted separately by two authors and pooled odds ratio (OR) with 95% confidence interval (CI) was calculated. Results. The meta-analysis was finished with 8 studies with a total of 3202 cases and 20968 controls finally retrieved from the database search. The crude pooled OR is 2.24 (95% CI = 1.38-3.64). Although there was significant heterogeneity among these studies, which was largely accounted for by a single study, the increase in risk was still significant after exclusion of that study. The pooled adjusted OR remained significant with pooled adjusted OR 1.05 (95% CI = 1.03-1.07, p < 0.00001). No publication bias was found in the present meta-analysis. Conclusions. The synthesis of available evidence supports that metabolic syndrome increases the risk for knee osteoarthritis, even after adjustment for many risk factors.