Leptin in osteoarthritis: Focus on articular cartilage and chondrocytes

Metabolism-Related Adipokines and Metabolic Diseases: Their Role in Osteoarthritis

Osteoarthritis (OA) affects several joints but tends to be more prevalent in those that are weight-bearing, such as the knees, which are the most heavily loaded joints in the body. The incidence and disability rates of OA have continued to increase and seriously jeopardise the quality of life of middle-aged and older adults. However, OA is more than just a wear and tear disease; its aetiology is complex, and its pathogenesis is poorly understood. Metabolic syndrome (MetS) has emerged as a critical driver of OA development. This condition contributes to the formation of a distinct phenotype, termed metabolic syndrome-associated osteoarthritis (MetS-OA),which differs from other metabolically related diseases by its unique pathophysiological mechanisms and clinical presentation. As key mediators of MetS, metabolic adipokines such as leptin, lipocalin, and resistin regulate inflammation and bone metabolism through distinct or synergistic signaling pathways. Their modulation of inflammatory responses and bone remodeling processes plays a critical role in the pathogenesis and progression of OA. Due to their central role in regulating inflammation and bone remodeling, metabolic adipokines not only deepen our understanding of MetS-OA pathogenesis but also represent promising targets for novel therapeutic strategies that could slow disease progression and improve clinical outcomes in affected patients.

Leptin protects chondrocytes by inhibiting autophagy via phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway

Leptin has been widely studied and found to have a significant impact on the development of osteoarthritis (OA). However, there are conflicting findings regarding the impact of leptin on chondrocytes. The study aimed to examine the impact of leptin on human chondrocytes and rats with OA. In the in vitro experiment, cartilage tissue obtained from patients hospitalized for knee replacement due to OA was collected for primary culture of chondrocytes. The proliferation and apoptosis of chondrocytes were assessed using cell counting kit-8 and flow cytometry. Autophagy levels were evaluated through monodansylcadaverine staining, mRFP-GFP-LC3 fluorescence, and transmission electron microscopy. Additionally, the expression of autophagy-related genes and proteins was analyzed using qRT-PCR and western blotting. In the in vivo experiment, an OA rat model was established. Following treatment with leptin and leptin antagonists, the cartilage tissues were examined using histology analysis (hematoxylin-eosin and Safranin O/fast green staining) and immunohistochemical. Mankin's score was utilized to assess the severity of OA, while qRT-PCR and western blotting were employed to detect the expression of autophagy-related genes and proteins in the cartilage. The ability of leptin to protect chondrocytes is achieved through the inhibition of autophagy via phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway.

Osteoarthritis, adipokines and the translational research potential in small animal patients

Osteoartritis (OA) is a debilitating disease affecting both humans and animals. In the early stages, OA is characterized by damage to the extracellular matrix (ECM) and apoptosis and depletion of chondrocytes. OA progression is characterized by hyaline cartilage loss, chondrophyte and osteophyte formation, thickening of the joint capsule and function loss in the later stages. As the regenerative potential of cartilage is very limited and osteoarthritic changes are irreversible, prevention of OA, modulation of existing osteoarthritic joint inflammation, reducing joint pain and supporting joint function are the only options. Progression of OA and pain may necessitate surgical intervention with joint replacement or arthrodesis as end-stage procedures. In human medicine, the role of adipokines in the development and progression of OA has received increasing interest. At present, the known adipokines include leptin, adiponectin, visfatin, resistin, progranulin, chemerin, lipocalin-2, vaspin, omentin-1 and nesfatin. Adipokines have been demonstrated to play a pivotal role in joint homeostasis by modulating anabolic and catabolic balance, autophagy, apoptosis and inflammatory responses. In small animals, in terms of dogs and cats, naturally occurring OA has been clearly demonstrated as a clinical problem. Similar to humans, the etiology of OA is multifactorial and has not been fully elucidated. Humans, dogs and cats share many joint related degenerative diseases leading to OA. In this review, joint homeostasis, OA, adipokines and the most common joint diseases in small animals leading to naturally occurring OA and their relation with adipokines are discussed. The purpose of this review is highlighting the translational potential of OA and adipokines research in small animal patients.

Injection of kaolin/carrageenan in the rat knee joint induces progressive experimental knee osteoarthritis

ABSTRACT

Osteoarthritis (OA), the most common joint disorder worldwide, is characterized by progressive degeneration of articular and periarticular structures, leading to physical and emotional impairments that greatly affect the quality of life of patients. Unfortunately, no therapy has been able to halt the progression of the disease. Owing to the complexity of OA, most animal models are only able to mimic a specific stage or feature of the human disorder. In this work, we demonstrate the intraarticular injection of kaolin or carrageenan leads to the progressive degeneration of the rat's knee joint, accompanied by mechanical hyperalgesia and allodynia, gait impairments (reduced contact area of the affected limb), and radiological and histopathological findings concomitant with the development of human grade 4 OA. In addition, animals also display emotional impairments 4 weeks after induction, namely, anxious and depressive-like behaviour, important and common comorbidities of human OA patients. Overall, prolonging kaolin or carrageenan-induced monoarthritis mimics several important physical and psychological features of human OA in both male and female rodents and could be further applied in long-term studies of OA-associated chronic pain.

Acupuncture improves immunity and fatigue after chemotherapy in breast cancer patients by inhibiting the Leptin/AMPK signaling pathway

OBJECTIVE

Acupuncture has become a popular complementary treatment in oncology. This study is based on RNA-Seq transcriptome sequencing technology to investigate the molecular mechanisms underlying the effect of acupuncture-mediated regulation of the Leptin/AMPK signaling pathway on mitochondrial dysfunction-induced fatigue in breast cancer patients after chemotherapy.

METHODS

Peripheral blood samples from 10 patients with post-operative chemotherapy for breast cancer were selected for transcriptome sequencing to screen the key molecular pathways involved in fatigue after chemotherapy in breast cancer patients. Besides, peripheral blood samples were collected from 138 post-operative chemotherapy patients with breast cancer to study the composite fatigue and quality of life scores. Flow cytometry was used to detect T lymphocyte subsets in peripheral blood-specific immune cells. In addition, a blood cell analyzer was used to measure peripheral blood leukocyte counts, and MSP-PCR was used to detect mitochondrial DNA mutations in peripheral blood leukocytes.

RESULTS

Transcriptome bioinformatics analysis screened 147 up-regulated mRNAs and 160 down-regulated mRNAs. Leptin protein was confirmed as the key factor. Leptin was significantly higher in the peripheral blood of breast cancer patients who developed fatigue after chemotherapy. Acupuncture treatment effectively improved post-chemotherapy fatigue and immune status in breast cancer patients, suppressed the expression of Leptin/AMPK signaling pathway-related factor and leukocyte counts, and significantly reduced the rate of mitochondrial DNA mutations in peripheral blood leukocytes.

CONCLUSION

The Leptin/AMPK signaling pathway may be the key molecular pathway affecting the occurrence of fatigue after chemotherapy in breast cancer patients. Leptin may improve post-chemotherapy fatigue in breast cancer patients by activating AMPK phosphorylation and alleviating mitochondrial functional impairment.

Cartilage-Related Collagens in Osteoarthritis and Rheumatoid Arthritis: From Pathogenesis to Therapeutics

Collagens serve essential mechanical functions throughout the body, particularly in the connective tissues. In articular cartilage, collagens provide most of the biomechanical properties of the extracellular matrix essential for its function. Collagen plays a very important role in maintaining the mechanical properties of articular cartilage and the stability of the ECM. Noteworthily, many pathogenic factors in the course of osteoarthritis and rheumatoid arthritis, such as mechanical injury, inflammation, and senescence, are involved in the irreversible degradation of collagen, leading to the progressive destruction of cartilage. The degradation of collagen can generate new biochemical markers with the ability to monitor disease progression and facilitate drug development. In addition, collagen can also be used as a biomaterial with excellent properties such as low immunogenicity, biodegradability, biocompatibility, and hydrophilicity. This review not only provides a systematic description of collagen and analyzes the structural characteristics of articular cartilage and the mechanisms of cartilage damage in disease states but also provides a detailed characterization of the biomarkers of collagen production and the role of collagen in cartilage repair, providing ideas and techniques for clinical diagnosis and treatment.

Circulating leptin level in osteoarthritis and associations between leptin receptor polymorphisms and disease susceptibility: A meta-analysis

OBJECTIVE

This study aimed to systemically review the evidence on the relationship between the circulating leptin levels and osteoarthritis (OA), and the association between leptin and leptin receptor (LEPR) polymorphisms and OA susceptibility.

METHODS

To find relevant papers (up to February 2023) examining the association between circulating leptin levels, LEPR polymorphisms, and OA, the PUBMED, EMBASE, and Cochrane databases were searched. We performed a meta-analysis to examine the levels of synovial and serum/plasma leptin in OA patients compared with healthy controls, as well as the relationship between OA and LEPR polymorphisms.

RESULTS

Data from 15 investigations, totaling 2197 patients with OA and 2546 controls, were included in the meta-analysis. There were statistically significant differences in the levels of circulating leptin between the OA and control groups (standardized mean difference [SMD] 2.178, 95% confidence interval [CI] 1.208-3.139, P = 0.001). Leptin levels were also substantially greater in European, Asian, and Arab groups among OA patients. After adjusting for age, sex, and/or body mass index, the leptin levels of patients with OA were significantly higher. Similarly, regardless of sample size (n < 100 and n ≥ 100) or year of publication, leptin levels were considerably higher in the OA group. In addition, the synovial leptin level was greater in the OA group than in the control group (SMD 0.783; 95% CI 0.247-1.319, P = 0.004). In the LEPR rs1137101 polymorphism, the OA and AA genotypes were significantly associated (odds ratio 0.282, 95% CI 0.126-0.629, P = 0.002), according to the meta-analysis. Ethnic stratification revealed an association between OA and the LEPR rs1137101 AA genotype in Asian and Arab populations.

CONCLUSION

The results of this meta-analysis indicate that patients with OA had considerably greater levels of circulating leptin than did control individuals. In addition, synovial leptin levels were greater in OA patients than in healthy individuals, and the LEPR rs1137101 polymorphism was linked to an increased risk of developing OA. These results imply that leptin participates in the onset and progression of OA.

Sex-dependent variation in cartilage adaptation: from degeneration to regeneration

Despite acknowledgement in the scientific community of sex-based differences in cartilage biology, the implications for study design remain unclear, with many studies continuing to arbitrarily assign demographics. Clinically, it has been well-established that males and females differ in cartilage degeneration, and accumulating evidence points to the importance of sex differences in the field of cartilage repair. However, a comprehensive review of the mechanisms behind this trend and the influence of sex on cartilage regeneration has not yet been presented. This paper aims to summarize current findings regarding sex-dependent variation in knee anatomy, sex hormones' effect on cartilage, and cartilaginous degeneration and regeneration, with a focus on stem cell therapies. Findings suggest that the stem cells themselves, as well as their surrounding microenvironment, contribute to sex-based differences. Accordingly, this paper underscores the contribution of both stem cell donor and recipient sex to sex-related differences in treatment efficacy. Cartilage regeneration is a field that needs more research to optimize strategies for better clinical results; taking sex into account could be a big factor in developing more effective and personalized treatments. The compilation of this information emphasizes the importance of investing further research in sex differences in cartilage biology.

Association of general and central obesity, and their changes with risk of knee osteoarthritis: a nationwide population-based cohort study

In this study, we aimed to evaluate the association between general and central obesity, and their changes with risk of knee osteoarthritis (OA) using retrospective cohort data collected from the Korean National Health Insurance Service. We studied 1,139,463 people aged 50 and over who received a health examination in 2009. To evaluate the association between general and/or central obesity and knee OA risk, a Cox proportional hazard models were used. Additionally, we investigate knee OA risk according to the change in obesity status over 2 years for subjects who had undergone health examinations for 2 consecutive years. General obesity without central obesity (HR 1.281, 95% CI 1.270-1.292) and central obesity without general obesity (HR 1.167, 95% CI 1.150-1.184) were associated with increased knee OA risk than the comparison group. Individuals with both general with central obesity had the highest risk (HR 1.418, 95% CI 1.406-1.429). This association was more pronounced in women and younger age group. Remarkably, the remission of general or central obesity over two years was associated with decreased knee OA risk (HR 0.884; 95% CI 0.867-0.902; HR 0.900; 95% CI 0.884-0.916, respectively). The present study found that both general and central obesity were associated with increased risk of knee OA and the risk was highest when the two types of obesity were accompanied. Changes in obesity status have been confirmed to alter the risk of knee OA.

Berberine inhibits carcinogenesis through antagonizing the ATX-LPA-LPAR2-p38-leptin axis in a mouse hepatoma model

Chemoprevention of hepatocellular carcinoma (HCC) is highly desirable in clinic. Berberine (BBR) is reported to play potential roles in cancer treatment and prevention. We studied the chemopreventive effect of BBR on hepatocellular carcinogenesis in an inflammation-driven mouse model, as it was enriched in liver after oral administration. Oral BBR significantly decreased the number and volume of visible nodular tumors, and prolonged the median overall survival by 9 and 8 weeks in the diethylnitrosamine (DEN)-injected male and female mice respectively. The nodular tumors were induced through activation of the lysophosphatidic acid (LPA) pathway in liver. LPA stimulated the abnormal leptin transcription through interacting with LPA receptor-2 (LPAR2) followed by p38 activation, and BBR inhibited carcinogenesis by suppressing the bioactivity of LPA. Specifically, BBR significantly reduced the expression of the LPA synthetase autotaxin (ATX) and LPAR2 in the nodular tumors of DEN-injected mice. Subsequently, BBR repressed the abnormal transcription of leptin stimulated by LPA-induced phosphorylation of p38 in hepatoma cells. In fact, BBR reduced the abnormal expression of leptin in livers of DEN-injected male mice throughout the course of an 8-month experiment. BBR might be a preventive agent for HCC, working at least partially through antagonizing the ATX-LPA-LPAR2-p38-leptin axis in liver.

Evidence for causal effects of sleep disturbances on risk for osteoarthritis: a univariable and multivariable Mendelian randomization study

OBJECTIVE

To disentangle whether sleep disturbances have a causal effect on the risk of osteoarthritis (OA) using genetically based approaches.

METHOD

We performed univariable and multivariable Mendelian randomization (MR) analyses using publicly released genome-wide association studies summary statistics to estimate the causal associations of sleep disturbances with OA risk. The inverse-variance weighted (IVW) method was utilized as primary MR analysis, whereas complementary methods including weighted median, weighted mode, MR-Egger regression, and MR pleiotropy residual sum and outlier (MR-PRESSO) were applied to detect and correct for the presence of pleiotropy.

RESULTS

There were 228 independent instrumental variables (IVs) for insomnia and 78, 27 and 8 IVs for sleep duration, short sleep duration and long sleep duration, respectively. Univariable MR analysis suggested that genetically determined insomnia or short sleep duration exerted a causal effect on overall OA in an unfavorable manner (Insomnia: OR = 1.22, 95%CI = 1.15-1.30, P = 8.05 × 10^-10; Short sleep duration: OR = 1.04, 95%CI = 1.02-1.07, P = 2.20 × 10^-3). More compelling, increasing genetic liability to insomnia or short sleep duration was also associated with OA risk, after accounting for effects of insomnia or short sleep duration on body mass index, type 2 diabetes and depression individually, and in a combined model considering all three confounders.

CONCLUSIONS

Findings suggested consisted evidence for an adverse effect of increased insomnia or short sleep duration on OA risk. Strategies to mitigate sleep disturbances may be one of the cornerstones protects against OA.

Co-occurrence of Blount's disease and Legg-Calvé-Perthes disease: is obesity a factor?

Legg-Calvé-Perthes disease (LCPD) and Blount's disease share a similar presenting age in addition to similar symptoms such as limp or knee pain. A little overlap is mentioned about both diseases. We sought to present cases of children having both conditions to discuss the implications of this co-occurrence on diagnosis and management. After institutional review board approval, we retrospectively reviewed records of four children who developed both Blount's disease and LCPD. Patient details and outcomes were analyzed. Radiographs were evaluated for the lateral pillar classification, Stulberg classification, tibial metaphyseal-diaphyseal angle and tibiofemoral angle. Two of the cases were initially diagnosed with Blount's disease and subsequently developed Perthes, one case presented initially with both disorders and the final case had Perthes followed by Blount's. Three children were obese and one was overweight. The common symptom to all patients was an abnormal gait, which was painless in two children and painful in two. Blount's disease required surgery in three children. Radiographs showed Lateral Pillar B, B/C border and C hips, and the final Stulberg was stage II (n = 2) or stage IV (n = 2). Obesity is associated with Blount's disease and LCPD, so obese children can be at an increased risk of developing both disorders. Therefore, a child with Blount's disease who has persistent, recurrent or worsening symptoms such as gait disturbance or thigh or knee pain might benefit from a careful physical exam of the hips to prevent a delayed or even missed LCPD diagnosis.

Associations between adipokines gene polymorphisms and knee osteoarthritis: a meta-analysis

Background

Adipokines gene polymorphisms are speculated to be associated with the risk of knee osteoarthritis (OA), but evidence remains conflicting. This study therefore aimed to examine whether associations exist between adipokines gene polymorphisms and knee OA by considering the evidence collected from eligible studies through a meta-analysis.

Methods

A systematic search was performed on PubMed, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), and Wanfang up to March 31, 2020. Meta-analysis was carried out by focusing on the associations between adipokines gene polymorphisms and knee OA with the allele model, dominant model, and recessive model.

Results

The present meta-analysis included 5 eligible studies for ADIPOQ rs1501299 with 1,021 cases and 1,097 controls, 3 eligible studies for ADIPOQ rs2241766 with 549 cases and 544 controls, 3 eligible studies for LEPR rs1137101 with 808 cases and 856 controls, 2 eligible studies for VISFATIN rs4730153 with 339 cases and 680 controls and 2 eligible studies for VISFATIN rs16872158 with 339 cases and 680 controls. Significant association was observed between LEPR rs1137101 and knee OA in the overall population (recessive: OR = 0.40, 95% CI 0.21–0.79). Limited data revealed that associations may exist between ADIPOQ rs2241766 and knee OA in Asians (dominant: OR = 1.35, 95% CI 1.03–1.78), between VISFATIN rs4730153 and knee OA in Asians (allele: OR = 0.58, 95% CI 0.41–0.83; dominant: OR = 0.57, 95% CI 0.39–0.83), and between VISFATIN rs16872158 and knee OA in Asians (allele: OR = 1.84, 95% CI 1.26–2.68; dominant: OR = 1.94, 95% CI 1.31–2.89).

Conclusions

Adipokines gene polymorphisms may be associated with knee OA. The association was observed in LEPR rs1137101 in the present study. In addition, limited data revealed that associations may also exist in ADIPOQ rs2241766, VISFATIN rs4730153 and VISFATIN rs16872158.

Prospero registration

CRD42020187664.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05111-4.

Exploring Diagnostic Biomarkers and Comorbid Pathogenesis for Osteoarthritis and Metabolic Syndrome via Bioinformatics Approach

BACKGROUND

Metabolic syndrome (MS) has grown in recognition to contribute to the pathogenesis of osteoarthritis (OA), which is the most prevalent arthritis characterized by joint dysfunction. However, the specific mechanism between OA and MS remains unclear.

METHODS

The gene expression profiles and clinical information data of OA and MS were retrieved from the Gene Expression Omnibus (GEO) database. The genes in the key module of MS were identified by weighted gene co-expression network analysis (WGCNA), which intersected with the differentially expressed genes (DEGs) between control and MS samples to obtain hub genes for MS. The potential functions and pathways of hub genes were detected through the Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) analyses. The genes involved in the different KEGG pathways between the control and OA samples overlapped with the DEGs between the two groups via the Venn analysis to gain the hub genes for OA affected by MS (MOHGs). Additionally, the least absolute shrinkage and selection operator (LASSO) was performed on the MOHGs to establish a diagnostic model for each disease.

RESULTS

A total of 61 hub genes for MS were identified that significantly enriched in platelet activation, complement and coagulation cascades, and hematopoietic cell lineage. Besides, 4 candidate genes (ELOVL7, F2RL3, GP9, and ITGA2B) were screened among the 6 MOHGs to construct a diagnostic model, showing good performance for distinguishing controls from patients with MS and OA. GSEA suggested that these diagnostic genes were closely associated with immune response, adipocytokine signaling, fatty acid metabolism, cell cycle, and platelet activation.

CONCLUSION

Taken together, we identified 4 potential gene biomarkers for diagnosing MS and OA patients, providing a theoretical basis and reference for the diagnostics and treatment targets of MS and OA.

Nesfatin-1 facilitates IL-1β production in osteoarthritis synovial fibroblasts by suppressing miR-204-5p synthesis through the AP-1 and NF-κB pathways

The progression of osteoarthritis (OA) is mediated by adipokines, one of which is nesfatin-1, which is responsible for the production of inflammatory cytokines. However, how this molecule may affect the synthesis of the proinflammatory cytokine interleukin 1 beta (IL-1β) in OA is unclear. Our analyses of records from the Gene Expression Omnibus (GEO) dataset and clinical specimens of synovial tissue revealed higher levels of nesfatin-1 and IL-1β in OA samples compared with normal healthy tissue. We found that nesfatin-1 facilitates IL-1β synthesis in human OA synovial fibroblasts (OASFs) and suppresses the generation of micro-RNA (miR)-204-5p, as the miR-204-5p levels in OA patients were lower than those in healthy controls. Nesfatin-1-induced stimulation of IL-1β in human OASFs occurred via the suppression of miR-204-5p synthesis by the PI3K, Akt, AP-1 and NF-κB pathways. We suggest that nesfatin-1 is worth targeting in OA treatment.

Leptin Induced TLR4 Expression via the JAK2-STAT3 Pathway in Obesity-Related Osteoarthritis

Obesity is considered as a risk factor of osteoarthritis (OA), but the precise relationship is still poorly understood. Leptin, one of the most relevant factors secreted by adipose tissues, plays an important role in the pathogenesis of OA. Our aim was to investigate the regulation and molecular mechanism of the leptin signaling pathway in obesity-related OA. SD rats were fed with a high-fat diet (HFD) for 5, 15, and 27 weeks. The levels of leptin in serum increased from W5, while in the synovial fluid increased from W15. The histological evaluation showed that the pathological changes of OA occurred at 27 weeks rather than 5 or 15 weeks. We also found that leptin induced CD14/TLR4 activation by the JAK2-STAT3 signaling pathway to promote OA. Moreover, silencing SOCS3 enhanced leptin-induced JAK2-STAT3-CD14/TLR4 activation in rat primary chondrocytes. Our findings indicated that leptin may be one of the initiating factors of obesity-related OA. TLR4 is at least partially regulated by leptin through the JAK2-STAT3-CD14 pathway. Meanwhile, SOCS3 acting as a negative feedback inhibitor of leptin signaling presented a potential therapeutic prospect for obesity-related OA. Our study provided new evidence suggesting the key role of leptin in mediating obesity-related OA process and its underlying mechanisms.

Causal association of adipokines with osteoarthritis: a Mendelian randomization study

OBJECTIVE

This two-sample Mendelian randomization study aimed to delve into the effects of genetically predicted adipokine levels on OA.

METHODS

Summary statistic data for OA originated from a meta-analysis of a genome-wide association study with an overall 50 508 subjects of European ancestry. Publicly available summary data from four genome-wide association studies were exploited to respectively identify instrumental variables of adiponectin, leptin, resistin, chemerin and retinol-blinding protein 4. Subsequently, Mendelian randomization analyses were conducted with inverse variance weighted (IVW), weighted median and Mendelian randomization-Egger regression. Furthermore, sensitivity analyses were then conducted to assess the robustness of our results.

RESULTS

The positive causality between genetically predicted leptin level and risk of total OA was indicated by IVW [odds ratio (OR): 2.40, 95% CI: 1.13-5.09] and weighted median (OR: 2.94, 95% CI: 1.23-6.99). In subgroup analyses, evidence of potential harmful effects of higher level of adiponectin (OR: 1.28, 95% CI: 1.01-1.61 using IVW), leptin (OR: 3.44, 95% CI: 1.18-10.03 using IVW) and resistin (OR: 1.18, 95% CI: 1.03-1.36 using IVW) on risk of knee OA were acquired. However, the mentioned effects on risk of hip OA were not statistically significant. Slight evidence was identified supporting causality of chemerin and retinol-blinding protein 4 for OA. The findings of this study were verified by the results from sensitivity analysis.

CONCLUSIONS

An association between genetically predicted leptin level and risk of total OA was identified. Furthermore, association of genetically predicted levels of adiponectin, leptin and resistin with risk of knee OA were reported.

The Effect of Platelet-Rich Plasma on the Intra-Articular Microenvironment in Knee Osteoarthritis

Knee osteoarthritis (KOA) represents a clinical challenge due to poor potential for spontaneous healing of cartilage lesions. Several treatment options are available for KOA, including oral nonsteroidal anti-inflammatory drugs, physical therapy, braces, activity modification, and finally operative treatment. Intra-articular (IA) injections are usually used when the non-operative treatment is not effective, and when the surgery is not yet indicated. More and more studies suggesting that IA injections are as or even more efficient and safe than NSAIDs. Recently, research to improve intra-articular homeostasis has focused on biologic adjuncts, such as platelet-rich plasma (PRP). The catabolic and inflammatory intra-articular processes that exists in knee osteoarthritis (KOA) may be influenced by the administration of PRP and its derivatives. PRP can induce a regenerative response and lead to the improvement of metabolic functions of damaged structures. However, the positive effect on chondrogenesis and proliferation of mesenchymal stem cells (MSC) is still highly controversial. Recommendations from in vitro and animal research often lead to different clinical outcomes because it is difficult to translate non-clinical study outcomes and methodology recommendations to human clinical treatment protocols. In recent years, significant progress has been made in understanding the mechanism of PRP action. In this review, we will discuss mechanisms related to inflammation and chondrogenesis in cartilage repair and regenerative processes after PRP administration in in vitro and animal studies. Furthermore, we review clinical trials of PRP efficiency in changing the OA biomarkers in knee joint.

Serum levels of leptin, osteopontin, and sclerostin in patients with and without knee osteoarthritis

OBJECTIVE

To investigate the relationship between leptin, osteopontin (OPN), sclerostin (SOST) and severity of knee osteoarthritis (KOA).

METHODS

The study included 148 consecutive patients with knee OA and 101 non-KOA subjects enrolled in this cross-sectional study. All patients fulfilled the American College of Rheumatology criteria for primary knee OA. Severity of the disease was assessed using plain radiography of the affected knee, according to the Kellgren and Lawrence classification. Fasting blood samples were obtained from all patients and controls; the serum samples were kept at - 80 °C before assessment of leptin, OPN, and SOST using a multiplex particle-based flow cytometric assay.

RESULTS

KOA patients group compared with the control group, serum leptin (KOA, 26581.7 ± 2011.5 pg/ml, vs control,6936.4 ± 702.2 pg/ml),OPN (KOA, 4908.3 ± 769.4 pg/ml, vs control, 2182.5 ± 217.8 pg/ml), and SOST (KOA, 2481.9 ± 543.5 pg/ml, vs control, 1288.9 ± 267.7 pg/ml) in the KOA group were higher than control group; there were also differences in three bone metabolic factors between male and female in the KOA group; meanwhile, there was correlation between each factor and the incidence of KOA.

CONCLUSION

Our study of 249 serum samples was conducted. Serum leptin, OPN, and SOST were significantly increased in KOA patients, and there was an internal correlation; these findings could, at best, contribute to the identification of novel targets for medical interventions. Key Points • The aim of this study was to assess the relationships of radiographic knee OA with altered serum levels of leptin, OPN, and SOST. Our study of 249 serum samples was conducted. Serum leptin, OPN, and SOST were significantly increased in KOA patients compared with control group. There were gender differences in the concentration of three serum bone turnover factors in KOA group and control group. Serum SOST concentration increased with Kellgren-Lawrence (K-L) grading. We found that serum leptin, OPN, and SOST were significantly increased in KOA patients, and there was an internal correlation. Leptin had a remarkable diagnostic value in the incidence of KOA.

Mediterranean Diet and Osteoarticular Diseases

Background:

Besides the well-known positive effect on the reduction of the risk of cardiovascular diseases, in the latest decades growing evidence has accumulated on the beneficial effects of MD on various aspects of health outcomes. Nevertheless, data concerning the existence of a direct positive effect of MD, irrespective of its beneficial effect on body weight, in osteo-articular diseases, are still controversial. In osteo-articular diseases, a pro-inflammatory environment is highlighted, with an increased systemic levels of pro-inflammatory cytokines.

Objective:

Our objective is to investigate the effects of adherence to the Mediterranean diet and osteo-articular diseases.

Conclusion:

Many foods included in MD, have anti-inflammatory properties, due to the presence of nutrients, such as polyunsaturated (PUFA) and monounsaturated (MUFA) fats. The two types of polyunsaturated fatty acids, omega-3 and omega-6, have opposing effects on the inflammatory process. Omega-6 stimulates the production of pro-inflammatory cytokines, while omega-3 fatty acids exert anti-inflammatory effects, including significant reductions in the release of pro-inflammatory cytokines. Some studies have shown that the dietary pattern of MD consumption has an important role in the prevention and development of inflammatory arthritis. Nevertheless, the possible influence of MD on chronic osteo-articular diseases is very limited, this review updates the main experimental and clinical evidences concerning the potential beneficial effects of the Mediterranean Diet on the most diffuse osteo-articular chronic and degenerative joint disease.

Fang-Ji-Huang-Qi-Tang Attenuates Degeneration of Early-Stage KOA Mice Related to Promoting Joint Lymphatic Drainage Function

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the breakdown of articular cartilage, subchondral bone remodeling, and inflammation of the synovium. In this study, we investigated whether Fang-Ji-Huang-Qi-Tang (FJHQT) decoction improved the joint structure of OA or delayed the process of knee joint degeneration in OA mice by promoting lymphatic drain function. The mice were randomly divided into four groups, the sham group, the PBS group, the FJHQT-treated group, and the Mobic-treated group. The mice in each group were tested for lymphatic draining function at 4, 6, 8, and 10 weeks postsurgery (WPS), then sacrificed (N = 10/group). Using a near-infrared indocyanine green (NIR-ICG) lymphatic imaging system, we found that the lymphatic drain function was significantly reduced in the PBS group compared with the sham group. After treatment with the FJHQT decoction, the lymphatic draining function improved at 4 wps and 6 wps. The results of the analysis indicated a strong correlation between lymphatic draining function (ICG clearance) and the degree of joint structural damage (OARSI score). By Alcian blue/orange G (ABOG) staining of the paraffin sections, the FJHQT-treated group exhibited less cartilage destruction and lower OARSI scores. Moreover, the result of immunohistochemical staining (IHC) shows that FJHQT decoction increased the content of type II collagen in knee joints of OA mice at 4 wps and 6 wps. By the double immunofluorescence staining of podoplanin and smooth muscle actin in the paraffin sections, the capillaries and mature lymphatics in the FJHQT group increased at 4 wps. In conclusion, the FJHQT decoction can increase lymphatic vessel number, promote joint lymphatic draining function, and postpone knee osteoarthritis pathologic progression in the early stage of a collagen-induced mouse model. Therefore, the application of sufficient lymphatic drainage in the knee joint may be a new treatment method for knee joint osteoarthritis (KOA).

Novel adipokine associated with OA: retinol binding protein 4 (RBP4) is produced by cartilage and is correlated with MMPs in osteoarthritis patients

Objective

Retinol binding protein 4 (RBP4) is a member of the lipocalin family and a vitamin A carrier in the blood. More recently, RBP4 has been described as an adipokine that is involved in insulin resistance and metabolic syndrome (MetS). As obesity, MetS and some adipokines contribute to the pathogenesis of osteoarthritis (OA), we investigated RBP4 in patients with OA.

Materials and methods

Cartilage, synovial fluid and blood samples were collected from 100 OA patients undergoing total knee replacement surgery. Primary chondrocytes and cartilage tissue were cultured to measure the RBP4 expression. The concentrations of RBP4, other adipokines (adipsin, adiponectin, leptin and resistin) and biomarkers of OA (COMP, MMP-1, MMP-3 and YKL-40) were measured by immunoassay, and gene expression was measured by next-generation RNA sequencing.

Results

The OA cartilage samples released RBP4 into the culture medium, and the levels correlated positively with the expression of the adipokines adipsin, adiponectin, leptin and resistin. RBP4 was the most prominently expressed of these adipokines in the OA chondrocytes, and the expression of the RBP4 receptors STRA6 (stimulated by retinoic acid gene homologue 6) and TLR4 (Toll-like receptor 4) was also detected. Within the cartilage culture medium, RBP4 showed a positive correlation with MMP-1, MMP-3 and YKL-40. RBP4 was also present in the synovial fluid from the OA patients and correlated positively with the concentrations of RBP4 found in the plasma and the cartilage culture medium. Plasma RBP4 concentrations also showed a positive correlation with MMP-3 and adipsin.

Conclusions

We show here, for the first time, that RBP4 is produced within OA joints and that it is associated with increased levels of adipokines and MMPs. The results suggest a role for RBP4 in the pathogenesis of OA and as a possible target for the disease-modifying drugs for the treatment of OA.

An update on the association between metabolic syndrome and osteoarthritis and on the potential role of leptin in osteoarthritis

Metabolic syndrome (MetS) has been associated with osteoarthritis (OA). Leptin, which is one of the markers of MetS, has been associated with OA pathophysiology. This study aimed to provide an update on the association between MetS and OA and on the potential role of leptin in OA. In this review, we summarized the current knowledge of the association between MetS and OA and updated the evidence on the potential role of leptin in OA. Clinical studies have investigated the epidemiologic association between MetS or its components and OA. Results suggested strong epidemiologic associations between MetS and OA, especially in the Asian population. Animal studies also indicated that metabolic dysregulation may lead to OA pathogenesis. The systemic role of MetS in OA pathophysiology is associated with obesity-related inflammation, the beneficial role of n-3 polyunsaturated fatty acids and deleterious role of cholesterol, physical inactivity, hypertension-induced subchondral ischemia, dyslipidemia-induced ectopic lipid deposition in chondrocytes, hyperglycemia-induced local effects of oxidative stress and advanced glycation end-products, low-grade systemic inflammation, and obesity-related adipokines by inducing the expression of proinflammtory factors. Leptin levels in serum/plasma and synovial fluid were associated with joint pain, radiographic progression, bone formation biomarkers, cartilage volume, knee OA incidence, and total joint arthroplasty in OA patients. Elevated leptin expression and increased effect of leptin on infrapatellar fat pad, synovium, articular cartilage, and bone were also involved in the pathogenesis of OA. Current knowledge indicates a convincing epidemiologic association between MetS and OA, especially in the Asian population. Animal studies have also shown that metabolic dysregulation may lead to OA pathogenesis. Accumulating evidence suggests that leptin may play a potential role in OA pathogenesis. Therefore, leptin and its receptor may be an emerging target for intervention in metabolic-associated OA.

Association of Circulating COMP and YKL-40 as Markers of Metabolic Changes of Cartilage with Adipocytokines in Juvenile Idiopathic Arthritis

The aim of this study was to evaluate the association of circulating cartilage oligomeric matrix protein (COMP) and human cartilage glycoprotein-39 (YKL-40) as markers of metabolic changes of cartilage, with leptin, adiponectin, and resistin in juvenile idiopathic arthritis (JIA) patients before and after treatment. A significant decrease of COMP and an increase of YKL-4 were found in blood of untreated patients. JIA treatment leading to clinical improvement resulted in normalization of COMP levels only. Concentrations of both markers in treated patients, while showing no clinical improvement, differed from those in controls and patients with remission. The leptin level decreased (p < 0.05) in untreated patients; however, concentrations of adiponectin and resistin increased (p < 0.05) as compared to controls. JIA treatment resulted in normalization of adipocytokine levels in remissive patients but not those with active JIA. Untreated patients showed a correlation between COMP and leptin, adiponectin, and body mass index (BMI) and between YKL-40 and leptin, adiponectin, BMI, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR). In inactive JIA, a correlation between YKL-40 and leptin was shown. Treated patients with an active JIA demonstrated a correlation between COMP and adiponectin and between YKL-40 and leptin, adiponectin, BMI, CRP, and ESR. The results of this work indicate that leptin and adiponectin but not resistin may be involved in the development and progression of joint dysfunction in JIA. Additionally, we suggest that YKL-40 may be a useful biomarker of disease activity and may be used to assess treatment towards remission, as compared to COMP.

Leptin in the regulation of the immunometabolism of adipose tissue-macrophages

Obesity is a pandemic disease affecting around 15% of the global population. Obesity is a major risk factor for other conditions, such as type 2 diabetes and cardiovascular diseases. The adipose tissue is the main secretor of leptin, an adipokine responsible for the regulation of food intake and energy expenditure. Obese individuals become hyperleptinemic due to increased adipogenesis. Leptin acts through the leptin receptor and induces several immunometabolic changes in different cell types, including adipocytes and Mϕs. Adipose tissue resident Mϕs (ATMs) are the largest leukocyte population in the adipose tissue and these ATMs are in constant contact with the excessive leptin levels secreted in obese conditions. Leptin activates both the JAK2-STAT3 and the PI3K-AKT-mTOR pathways. The activation of these pathways leads to intracellular metabolic changes, with increased glucose uptake, upregulation of glycolytic enzymes, and disruption of mitochondrial function, as well as immunologic alterations, such as increased phagocytic activity and proinflammatory cytokines secretion. Here, we discuss the immunometabolic effects of leptin in Mϕs and how hyperleptinemia can contribute to the low-grade systemic inflammation in obesity.

Glucocorticoid signaling and osteoarthritis

Glucocorticoids are steroid hormones synthesized and released by the adrenal cortex. Their main function is to maintain cell homeostasis through a variety of signaling pathways, responding to changes in an organism's environment or developmental status. Mimicking the actions of natural glucocorticoids, synthetic glucocorticoids have been recruited to treat many diseases that implicate glucocorticoid receptor signaling such as osteoarthritis. In osteoarthritis, synthetic glucocorticoids aim to alleviate inflammation and pain. The variation of patients' response and the possibility of complications associated with their long-term use have led to a need for a better understanding of glucocorticoid receptor signaling in osteoarthritis. In this review, we performed a literature search in the molecular pathways that link the osteoarthritic joint to the glucocorticoid receptor signaling. We hope that this information will advance research in the field and propose new molecular targets for the development of more optimized therapies for osteoarthritis.

Future Cell and Gene Therapy for Osteoarthritis (OA): Potential for Using Mammalian Protein Production Platforms, Irradiated and Transfected Protein Packaging Cell Lines for Over-Production of Therapeutic Proteins and Growth Factors

In this paper I provide a personal perspective on future prospects for cell and gene therapy for osteoarthritis (OA) and how mammalian protein production platforms, virally transfected and irradiated protein packaging cell lines may be used as "cellular factories" for over-production of therapeutic proteins and growth factors, particularly in the context of intra-articular regenerative therapies. I will also speculate on future opportunities and challenges in this area of research and how new innovations in biotechnology will impact on the field of cell and gene therapy for OA, related osteoarticular disorders and the broader discipline of regenerative medicine for musculoskeletal disorders. Mammalian protein production platforms are likely to have a significant impact on synovial joint diseases that are amenable to cell and gene therapy using therapeutic proteins and growth factors. Future cell and gene therapy for OA will need to re-consider the current strategies that employ primary, aged and senescent cells with feeble regenerative properties and seriously consider the use of mammalian protein production platforms.

The effects of metabolic syndrome, obesity, and the gut microbiome on load-induced osteoarthritis

OBJECTIVE

Metabolic syndrome is characterized by obesity, hyperglycemia, hypertension, insulin resistance, and dyslipidemia. Metabolic syndrome is associated with osteoarthritis (OA), but it is unclear if the association is attributable to increased mechanical loading on joints caused by obesity or other aspects of metabolic syndrome. Here we examined the effects of altered metabolism, obesity, and the gut microbiome on load-induced OA.

DESIGN

Cartilage damage was induced through cyclic compressive loading in four groups of adult male mice: Toll-like receptor-5 deficient (TLR5KO) mice that develop metabolic syndrome due to alterations in the gut microbiome, TLR5KO mice submitted to chronic antibiotics to prevent metabolic syndrome (TLR5KOΔMicrobiota), C57BL/6J mice fed a high fat diet to cause obesity (HFD), and untreated C57BL/6J mice (WT). Loading was applied for 2 weeks (n = 10-11/group) or 6 weeks (n = 10-11/group).

RESULTS

After 2 weeks of loading, cartilage damage (OARSI score) was not different among groups. After 6 weeks of loading, HFD mice had increased load-induced cartilage damage, while TLR5KO mice had cartilage damage comparable to WT mice. TLR5KOΔMicrobiota mice had less cartilage damage than other groups. HFD mice had elevated serum inflammatory markers. Each group had a distinct gut microbiome composition.

CONCLUSIONS

Severe obesity increased load-induced cartilage damage, while milder changes in adiposity/metabolic syndrome seen in TLR5KO mice did not. Furthermore, the effects of systemic inflammation/obesity on cartilage damage depend on the duration of mechanical loading. Lastly, reduced cartilage damage in the TLR5KOΔMicrobiota mice suggests that the gut microbiome may influence cartilage pathology.

Roles and mechanisms of leptin in osteogenic stimulation in cervical ossification of the posterior longitudinal ligament

Background

Hyperleptinemia is a common feature of obese people, and leptin, an adipocyte-derived cytokine, is believed to be an important factor in the pathogenesis of cervical ossification of the posterior longitudinal ligament(C-OPLL). So this research was to identify the relation between the serum leptin and bone metabolic markers and how the leptin induced osteogenic effect in C-OPLL.

Methods

Sixty-four samples were selected to determine the concentration of leptin, insulin, and alkaline phosphatase. And the association of leptin with these factors was also examined. We also evaluate the effect of leptin on the development of C-OPLL and further explored the possible underlying mechanism in vitro.

Results

We found that serum leptin concentrations were higher in females than in males. Serum leptin and ALP concentrations were increased significantly in C-OPLL females compared to non-OPLL females. In OPLL subjects, the serum leptin concentration corrected for body mass index correlated negatively with the ALP concentrations. In C-OPLL cells, leptin treatment led to a significant increase in mRNA expressions of ALP and OCN and formation of mineralized nodule. Our experiments reported here that osteogenic effect of leptin in C-OPLL cells could be mediated via ERK1/2, p38 MAPK, and/or JNK signaling pathways.

Conclusions

From this research, we got that leptin treatment led to a significant increase in mRNA expressions of ALP and OCN and formation of mineralized nodule. And the osteogenic effect of leptin in C-OPLL cells could be mediated via ERK1/2, p38 MAPK, and/or JNK signaling pathways.

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.

Leptin induces osteocalcin expression in ATDC5 cells through activation of the MAPK-ERK1/2 signaling pathway

Both leptin and osteocalcin have been found to affect growth-plate cartilage development through regulation of the physiologic processes of endochondral bone formation. Leptin mediates bone development and osteocalcin secreted in the late stage of osteoblast differentiation. The relationship between leptin and osteocalcin expression in the chondrogenic cells line is still not clear. Thus, the aim of this study was to explore the effect of leptin on the expression of osteocalcin in chondrocytes. We used clonal mouse chondrogenic ATDC5 cells to investigate the relationship between leptin and osteocalcin. We found that both leptin and osteocalcin expression were dynamically expressed during ATDC5 cell differentiation from 4 to 21 days. We also found that leptin significantly upregulated osteocalcin mRNA and protein levels 24 h after leptin stimulation. However, different concentrations and exposure times of osteocalcin did not affect the levels of leptin protein. Furthermore, we confirmed that leptin augmented the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in a time-dependent manner but not p38 or AKT. Inhibition of pERK1/2 expression by a specific ERK1/2 inhibitor U0126 and a special small interfering RNA attenuated levels of leptin-induced osteocalcin expression, indicating that ERK1/2 mediates, in part, the effects of leptin on osteocalcin. Taken together, our results suggest that leptin regulates the expression of osteocalcin in growth plate chondrocytes via the ERK1/2 signaling pathway, while there is no effect on the phosphorylation of either p38 or AKT.

Isolation and biological characteristic evaluation of a novel type of cartilage stem/progenitor cell derived from Small‑tailed Han sheep embryos

Cartilage stem/progenitor cells (CSPCs) are a novel stem cell population and function as promising therapeutic candidates for cell‑based cartilage repair. Until now, numerous existing research materials have been obtained from humans, horses, cows and other mammals, but rarely from sheep. In the present study, CSPCs with potential applications in repairing tissue damage and cell‑based therapy were isolated from 45‑day‑old Small‑tailed Han Sheep embryos, and examined at the cellular and molecular level. The expression level of characteristic surface markers of the fetal sheep CSPCs were also evaluated by immunofluorescence, reverse transcription‑polymerase chain reaction analysis and flow cytometric assays. Biological growth curves were drawn in accordance with cell numbers. Additionally, karyotype analysis showed no marked differences in the in vitro cultured CSPCs and they were genetically stable among different passages. The CSPCs were also capable of adipogenic, osteogenic and chondrogenic lineage progression under the appropriate induction medium in vitro. Together, these findings provide a theoretical basis and experimental evidence for cellular transplant therapy in tissue engineering.

Emerging Players at the Intersection of Chondrocyte Loss of Maturational Arrest, Oxidative Stress, Senescence and Low-Grade Inflammation in Osteoarthritis

The prevalence of Osteoarthritis (OA) is increasing because of the progressive aging and unhealthy lifestyle. These risk factors trigger OA by removing constraints that keep the tightly regulated low turnover of the extracellular matrix (ECM) of articular cartilage, the correct chondrocyte phenotype, and the functionality of major homeostatic mechanisms, such as mitophagy, that allows for the clearance of dysfunctional mitochondria, preventing increased production of reactive oxygen species, oxidative stress, and senescence. After OA onset, the presence of ECM degradation products is perceived as a “danger” signal by the chondrocytes and the synovial macrophages that release alarmins with autocrine/paracrine effects on the same cells. Alarmins trigger innate immunity in the joint, with important systemic crosstalks that explain the beneficial effects of dietary interventions and improved lifestyle. Alarmins also boost low-grade inflammation: the release of inflammatory molecules and chemokines sustained by continuous triggering of NF-κB within an altered cellular setting that allows its higher transcriptional activity. Chemokines exert pleiotropic functions in OA, including the recruitment of inflammatory cells and the induction of ECM remodeling. Some chemokines have been successfully targeted to attenuate structural damage or pain in OA animal models. This represents a promising strategy for the future management of human OA.

Biomechanics, obesity, and osteoarthritis. The role of adipokines: When the levee breaks

Osteoarthritis is a high-incidence painful and debilitating disease characterized by progressive degeneration of articular joints, which indicates a breakdown in joint homeostasis favoring catabolic processes. Biomechanical loading, associated with inflammatory and metabolic imbalances of joint, strongly contributes to the initiation and progression of the disease. Obesity is a primary risk factor for disease onset, and mechanical factors increased the risk for disease progression. Moreover, inflammatory mediators, in particular, adipose tissue-derived cytokines (better known as adipokines) play a critical role linking obesity and osteoarthritis. The present article summarizes the knowledge about the role of adipokines in cartilage and bone function, highlighting their contribution to the imbalance of joint homeostasis and, consequently, pathogenesis of osteoarthritis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:594-604, 2018.

Dexamethasone Down-regulates Osteocalcin in Bone Cells through Leptin Pathway

Glucocorticoid therapy, especially at higher doses, is associated with significant adverse side effects including osteoporosis. Leptin, secreted from adipose tissue, has diverse effects on bone tissue regulation. As glucocorticoids stimulate leptin synthesis and secretion directly in adipose tissue we hypothesised that dexamethasone (DEX) induced osteoporosis may, in part, be mediated by an osteoblast dependent leptin-leptin receptor pathway. Human bone cells expressed leptin and leptin receptors (Ob-Ra and Ob-Rb). DEX increased leptin, Ob-Ra and Ob-Rb expression in a dose-dependent manner while decreasing expression of osteocalcin. In the presence of leptin, Cbfa1 and osteonectin expression showed no significant change, whereas osteocalcin expression was decreased. Recombinant human quadruple antagonist leptin suppressed DEX-induced osteocalcin downregulation. The signaling pathway involved up-regulation of JAK2. In conclusion, upregulation of leptin and Ob-Rb in human bone cells by DEX is associated with down-regulation of osteocalcin expression. The down regulation of osteocalcin by DEX was partially through a leptin autocrine/paracrine loop. Adverse effects of DEX on the skeleton may be modified by targeting leptin signaling pathways.

Saturated fatty acids induce development of both metabolic syndrome and osteoarthritis in rats

The predominant saturated fatty acids (SFA) in human diets are lauric acid (LA, C12:0), myristic acid (MA, C14:0), palmitic acid (PA, C16:0) and stearic acid (SA, C18:0). The aim of this study was to investigate whether diets containing individual SFA together with excess simple carbohydrates induce osteoarthritis (OA)-like changes in knee joints and signs of metabolic syndrome in rats. Rats were given either a corn starch diet or a diet composed of simple carbohydrates together with 20% LA, MA, PA, SA or beef tallow for 16 weeks. Rats fed beef tallow, SA, MA or PA diets developed signs of metabolic syndrome, and also exhibited cartilage degradation and subchondral bone changes similar to OA. In contrast, replacement of beef tallow with LA decreased signs of metabolic syndrome together with decreased cartilage degradation. Furthermore, PA and SA but not LA increased release of matrix sulphated proteoglycans in cultures of bovine cartilage explants or human chondrocytes. In conclusion, we have shown that longer-chain dietary SFA in rats induce both metabolic syndrome and OA-like knee changes. Thus, diets containing SFA are strongly relevant to the development or prevention of both OA and metabolic syndrome.

Protective effects of aucubin on osteoarthritic chondrocyte model induced by hydrogen peroxide and mechanical stimulus

Background

During the onset of osteoarthritis (OA), certain biochemical events have been shown to accelerate cartilage degradation, including the dysregulation of cartilage ECM anabolism, abnormal generation of reactive oxygen species (ROS) and overproduction of proteolytic enzymes and inflammatory cytokines. The potency of aucubin in protecting cellular components against oxidative stress, inflammation and apoptosis effects are well documented, which makes it a potential candidate for OA treatment. In this study, we aimed to evaluate the protective benefits of aucubin against OA using H₂O₂ and compression induced OA-like chondrocyte models.

Methods

The effects of aucubin were studied in porcine chondrocytes after 1 mM H₂O₂ stimulation for 30 min or sustained compression for 24 h. Effects of aucubin on cell proliferation and cytotoxicity of chondrocytes were measured with WST-1 and LDH assays. ROS production was evaluated by the Total ROS/Superoxide Detection Kit. Caspase-3 activity was evaluated by the CaspACE assay system. The levels of apoptosis were evaluated by the Annexin V-FITC apoptosis detection kit. OA-related gene expression was measured by reverse transcription quantitative polymerase chain reaction (RT-qPCR). Total DNA quantification was evaluated by the DNeasy Blood and Tissue kit. Sulfated-glycosaminoglycans (sGAGs) production and content were evaluated by DMMB assay and Alcian blue staining.

Results

The results showed that the ROS scavenge effects of aucubin appeared after 1 h of pretreatment. Aucubin could reduce the caspase-3 activity induced by H₂O₂, and reduced the apoptosis cell population in flowcytometry. In RT-qPCR results, aucubin could maintain ACAN and COL2A1 gene expressions, and prevent IL6 and MMP13 gene up-regulation induced by H₂O₂ and compression stimulations. In the DMMB assay and Alcian blue staining, aucubin could maintain the sGAG content and protect chondrocytes against compressive stress, but not oxidative stress from H₂O₂.

Conclusions

These results indicated that aucubin has protective effects in an osteoarthritic chondrocyte model induced by H₂O₂ and mechanical stimulus.

Leptin in the interplay of inflammation, metabolism and immune system disorders

Leptin is one of the most relevant factors secreted by adipose tissue and the forerunner of a class of molecules collectively called adipokines. Initially discovered in 1994, its crucial role as a central regulator in energy homeostasis has been largely described during the past 20 years. Once secreted into the circulation, leptin reaches the central and peripheral nervous systems and acts by binding and activating the long form of leptin receptor (LEPR), regulating appetite and food intake, bone mass, basal metabolism, reproductive function and insulin secretion, among other processes. Research on the regulation of different adipose tissues has provided important insights into the intricate network that links nutrition, metabolism and immune homeostasis. The neuroendocrine and immune systems communicate bi-directionally through common ligands and receptors during stress responses and inflammation, and control cellular immune responses in several pathological situations including immune-inflammatory rheumatic diseases. This Review discusses the latest findings regarding the role of leptin in the immune system and metabolism, with particular emphasis on its effect on autoimmune and/or inflammatory rheumatic diseases, such as rheumatoid arthritis and osteoarthritis.

Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.

Chemically defined serum-free conditions for cartilage regeneration from human embryonic stem cells

AIMS

The aim of this study was to improve a method that induce cartilage differentiation of human embryoid stem cells (hESCs) in vitro, and test the effect of in vivo environments on the further maturation of hESCs derived cells.

MAIN METHODS

Embryoid bodies (EBs) formed from hESCs, with serum-free KSR-based medium and mesodermal specification related factors, CHIR, and Noggin for first 8days. Then cells were digested and cultured as micropellets in serum-free KSR-based chondrogenic medium that was supplemented with PDGF-BB, TGF β3, BMP4 in sequence for 24days. The morphology, FACS, histological staining as well as the expression of chondrogenic specific genes were detected in each stage, and further in vivo experiments, cell injections and tissue transplantations, further verified the formation of chondrocytes.

KEY FINDINGS

We were able to obtain chondrocyte/cartilage from hESCs using serum-free KSR-based conditioned medium. qPCR analysis showed that expression of the chondroprogenitor genes and the chondrocyte/cartilage matrix genes. Morphology analysis demonstrated we got PG+COL2+COL1-particles. It indicated we obtained hyaline cartilage-like particles. 32-Day differential cells were injected subcutaneous. Staining results showed grafts developed further mature in vivo. But when transplanted in subrenal capsule, their effect was not good as in subcutaneous. Microenvironment might affect the cartilage formation.

SIGNIFICANCE

The results of this study provide an absolute serum-free and efficient approach for generation of hESC-derived chondrocytes, and cells will become further maturation in vivo. It provides evidence and technology for the hypothesis that hESCs may be a promising therapy for the treatment of cartilage disease.

An update on the pathophysiology of osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is one of the most common forms of arthritis. There is accumulating evidence to suggest that OA is an inflammatory disease of the entire synovial joint and has multiple phenotypes. This presents the OA research community with new challenges and opportunities. The main challenge is to understand the root cause of the disease and identify differences and similarities between OA phenotypes. The key opportunity is the possibility of developing personalized and individualized prevention and treatment strategies for OA patients with different phenotypes of the disease. Indeed, it has been suggested that this is the era of 'personalized prevention' for OA. The aim of this mini-review paper is to focus on the pathophysiological aspects of OA development and progression, review the current concepts and discuss the future of personalized medicine for OA.

METHOD

The PubMed/MEDLINE bibliographic database was searched using the keywords 'pathophysiology' and 'osteoarthritis'.

RESULTS

The PubMed/MEDLINE search yielded more than 12,000 relevant papers. A selection of these papers is reviewed here.

CONCLUSION

There has been slow but steady progress in our understanding of the pathophysiology of OA over the last two decades. However, large gaps remain in our knowledge of OA pathogenesis and this impacts negatively on patients and drug development pipeline. In the absence of new pharmaceutical agents and disease modifying osteoarthritis drugs (DMOADs) it is clear that lifestyle modification and physical activity are important and may delay the need for surgical intervention.

Pollutants make rheumatic diseases worse: Facts on polychlorinated biphenyls (PCBs) exposure and rheumatic diseases

BACKGROUND

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that bioaccumulate in adipose tissue, disturbing its metabolism and the balance of adipokines, related to obesity. The altering secretion pattern of adipokines from the adipose tissue and the increasing mechanical load in weight-bearing joints presented in obesity condition, are risk factors for osteoarthritis development. The most prevalent rheumatic diseases, osteoarthritis and rheumatoid arthritis, are chronic conditions that target the whole joints, leading to increasing disability and health care cost. The goal of this focused review is to summarize the current knowledge on the role of PCBs in osteoarthritis and rheumatoid arthritis pathogenesis.

SEARCH STRATEGY

A PubMed search was managed using keywords as "rheumatic diseases", "polychlorinated biphenyls", "obesity" and "endocrine disruption".

MAIN RESULTS OF THE REVIEW

The incidence of rheumatoid arthritis has been reported to be increased especially in urban areas in industrialized countries, emphasizing the importance of environment in the pathogenesis of rheumatic diseases. Analysis of two cohorts exposed to PCBs food contamination showed high incidence of arthritis. In addition, PCBs in serum correlated positively with the prevalence of self-reported arthritis. Few studies support the hypothesis that osteoarthritis development could be related to PCBs induction of chondrocytes apoptosis.

CONCLUSION

Evidences have emerged for a relationship between PCBs and development of several types of arthritis. Further research is encouraged to determine the correlation between PCBs exposure and the development of rheumatic diseases.

Leptin promotes apoptosis and inhibits autophagy of chondrocytes through upregulating lysyl oxidase-like 3 during osteoarthritis pathogenesis

OBJECTIVE

Leptin has been found highly expressed in human osteoarthritis. We aimed to explore the possible effects and mechanisms of leptin on the apoptosis and autophagy of chondrocytes during osteoarthritis pathogenesis.

METHODS

Gene expression profile from osteoarthritis affected and preserved cartilage were downloaded from NCBI's Gene Expression Omnibus database (GSE57218). Lysyl oxidase-like 3 (LOXL3) mRNA expression in cartilage tissues and leptin concentration in joint synovial fluid (SF) was measured in samples from 45 osteoarthritis patients and 25 healthy donors by real-time PCR and radioimmunoassay, respectively. Rat osteoarthritis model was induced by anterior cruciate ligament transection (ACLT). The expression of apoptosis regulators and autophagy markers were detected by Western blot. Cell survival and cell apoptosis were identified by CCK-8 and flow cytometry, respectively.

RESULTS

Re-analysis on GSE57218 indicated that LOXL3 mRNA was upregulated in osteoarthritis affected cartilage. LOXL3 mRNA was upregulated in osteoarthritis patients, which was positively correlated with SF leptin concentration. Similar results were obtained in rat osteoarthritis model. Moreover, ACLT surgery led to a significant increase in the protein levels of cleaved caspase 3, and a notable decrease in the protein levels of Bcl-2, LC3 II/LC3 I and Beclin1. Silencing of LOXL3 in ACLT and leptin treated primary chondrocytes significantly inhibited cell apoptosis, and promoted cell proliferation and autophagy. Moreover, overexpression of LOXL3 remarkably inhibited autophagy of chondrocytes via activating mTORC1.

CONCLUSIONS

LOXL3, a downstream of leptin, stimulated the apoptosis, but inhibited the autophagy of chondrocytes. LOXL3 is a potential therapy target for osteoarthritis.

Inflammatory mediators in osteoarthritis: A critical review of the state-of-the-art, current prospects, and future challenges

Osteoarthritis (OA) has traditionally been defined as a prototypical non-inflammatory arthropathy, but today there is compelling evidence to suggest that it has an inflammatory component. Many recent studies have shown the presence of synovitis in a large number of patients with OA and demonstrated a direct association between joint inflammation and the progression of OA. Pro-inflammatory cytokines, reactive oxygen species (ROS), nitric oxide, matrix degrading enzymes and biomechanical stress are major factors responsible for the progression of OA in synovial joints. The aim of this review is to discuss the significance of a wide range of implicated inflammatory mediators and their contribution to the progression of OA. We also discuss some of the currently available guidelines, practices, and prospects. In addition, this review argues for new innovation in methodologies and instrumentation for the non-invasive detection of inflammation in OA by modern imaging techniques. We propose that identifying early inflammatory events and targeting these alterations will help to ameliorate the major symptoms such as inflammation and pain in OA patients.

Reduction of body fat and improved lipid profile associated with daily consumption of a Puer tea extract in a hyperlipidemic population: a randomized placebo-controlled trial

OBJECTIVE

The goal for this study was to evaluate the effects of daily consumption of Puer tea extract (PTE) on body weight, body-fat composition, and lipid profile in a non-Asian population in the absence of dietary restrictions.

MATERIALS AND METHODS

A randomized, double-blind, placebo-controlled study design was used. A total of 59 overweight or mildly obese subjects were enrolled upon screening to confirm fasting cholesterol level at or above 220 mg/dL (5.7 mmol/dL). After giving informed consent, subjects were randomized to consume PTE (3 g/day) or placebo for 20 weeks. At baseline and at 4-week intervals, blood lipids, C-reactive protein, and fasting blood glucose were evaluated. A dual-energy X-ray absorptiometry scan was performed at baseline and at study exit to evaluate changes to body composition. Appetite and physical and mental energy were scored at each visit using visual analog scales (0-100).

RESULTS

Consumption of PTE was associated with statistically significant weight loss when compared to placebo (P<0.05). Fat loss was seen for arms, legs, and the gynoid region (hip/belly), as well as for total fat mass. The fat reduction reached significance on within-group analysis, but did not reach between-group significance. Consumption of PTE was associated with improvements to lipid profile, including a mild reduction in cholesterol and the cholesterol:high-density lipoprotein ratio after only 4 weeks, as well as a reduction in triglycerides and very small-density lipoproteins, where average blood levels reached normal range at 8 weeks and remained within normal range for the duration of the study (P<0.08). No significant changes between the PTE group and the placebo group were seen for fasting glucose or C-reactive protein. A transient reduction in appetite was seen in the PTE group when compared to placebo (P<0.1).

CONCLUSION

The results from this clinical study showed that the daily consumption of PTE was associated with significant weight loss, reduced body mass index, and an improved lipid profile.