α-Melanocyte-stimulating-hormone (α-MSH) modulates human chondrocyte activation induced by proinflammatory cytokines

Bone-brain crosstalk in osteoarthritis: pathophysiology and interventions

Osteoarthritis (OA) is a prevalent articular disorder characterized by joint degeneration and persistent pain; it imposes a significant burden on both individuals and society. While OA has traditionally been viewed as a localized peripheral disorder, recent preclinical and clinical studies have revealed the crucial interconnections between the bone and the brain, highlighting the systemic nature of OA. The neuronal pathway, molecular signaling, circadian rhythms, and genetic underpinnings within the bone-brain axis play vital roles in the complex interplay that contributes to OA initiation and progression. This review explores emerging evidence of the crosstalk between the bone and brain in OA progression, and discusses the potential contributions of the bone-brain axis to the development of effective interventions for managing OA.

Anti-inflammatory treatment using alpha melanocyte stimulating hormone (α-MSH) does not alter osteoblasts differentiation and fracture healing

BACKGROUND

Alpha-melanocyte-stimulating-hormone (α-MSH) has been identified as a new anti-inflammatory treatment compound in rheumatoid arthritis (RA) and other inflammatory diseases. However, its direct effect on bone cell differentiation or on bone regeneration, which is an inflammatory process, too, has not been investigated, yet. Bone tissue is significantly affected in inflammatory joint diseases. Additionally, inflammatory signaling is essential -in bone regeneration during fracture healing. Therefore, we evaluated the impact of α-MSH-treatment on bone forming cells in an inflammatory setting in vitro and as a treatment approach in a murine fracture healing model in vivo.

METHODS

The influence of α-MSH treatment and melanocortin-receptor expression patterns was investigated in vitro in the presence of either IL-1β or/and TNF-α as an inflammatory stimulus. Osteoblast cell function was evaluated by analyzing proliferation and mineralisation capacities. Using quantitative real time PCR, we analyzed mRNA expression of receptors. To explore the impact of α-MSH on bone regeneration in vivo, treatment with α-MSH or NaCl (control) was performed in a murine fracture-healing model using a closed femur fracture stabilized with an intramedullary implant (female, n = 6-8 mice per group).

RESULTS

α-MSH-treatment did not impair either proliferation nor mineralisation of osteoblastic cells under native or inflammatory conditions (no significant differences found). All four melanocortin receptor-molecules were expressed in murine osteoblastic cells but in very limited amounts and this did not change upon treatment with inflammatory cytokines or α-MSH or both at the same time. Callus formation in fractured femurs of α-MSH-treated mice was slightly delayed at day 14 post fracture with regard to less cartilage formation (NaCl: 19.9%; α-MSH: 13.5%) and soft tissue remodeling (NaCl: 15.2%; α-MSH: 19.5%) but these results were not significantly different and fracture healing overall occurred in a regular way.

CONCLUSION

α-MSH has no negative impact on bone or bone-forming cells in native, inflammatory, or regenerative contexts. We can conclude from our results, that treatment of inflammatory diseases using α-MSH does not interfere significantly with bone regeneration in a murine fracture model and therefore treatment with α-MSH could be continued without negative effects on bone formation and bone regeneration in patients.

CLINICAL TRIAL NUMBER

Not applicable.

Inflammation-Driven Secretion Potential Is Upregulated in Osteoarthritic Fibroblast-Like Synoviocytes

Osteoarthritis (OA) is one of the most common joint pathologies and a major cause of disability among the population of developed countries. It manifests as a gradual degeneration of the cartilage and subchondral part of the bone, leading to joint damage. Recent studies indicate that not only the cells that make up the articular cartilage but also the synoviocytes, which build the membrane surrounding the joint, contribute to the development of OA. Therefore, the aim of the study was to determine the response to inflammatory factors of osteoarthritic synoviocytes and to identify proteins secreted by them that may influence the progression of OA. This study demonstrated that fibroblast-like synoviocytes of OA patients (FLS-OA) respond more strongly to pro-inflammatory stimulation than cells obtained from control patients (FLS). These changes were observed at the transcriptome level and subsequently confirmed by protein analysis. FLS-OA stimulated by pro-inflammatory factors [such as lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNFα) were shown to secrete significantly more chemokines (CXCL6, CXCL10, and CXCL16) and growth factors [angiopoietin-like protein 1 (ANGPTL1), fibroblast growth factor 5 (FGF5), and insulin-like growth factor 2 (IGF2)] than control cells. Moreover, the translation of proteolytic enzymes [matrix metalloprotease 3 (MMP3), cathepsin K (CTSK), and cathepsin S (CTSS)] by FLS-OA is increased under inflammatory conditions. Our data indicate that the FLS of OA patients are functionally altered, resulting in an enhanced response to the presence of pro-inflammatory factors in the environment, manifested by the increased production of the previously mentioned proteins, which may promote further disease progression.

Dexamethasone Attenuates the Expression of MMP-13 in Chondrocytes through MKP-1

Mitogen-activated protein kinase phosphatase-1 (MKP-1) is upregulated in inflammation and reduces the activity of proinflammatory mitogen-activated protein kinases (MAP kinases) by dephosphorylation. MAP kinases are intracellular signaling pathways that mediate the cellular effects of proinflammatory cytokines. In the present study, we investigated the effects of the glucocorticoid dexamethasone on the expression of catabolic enzymes in chondrocytes and tested the hypothesis that these effects are mediated through MKP-1. Dexamethasone was found to significantly attenuate the expression of matrix metalloproteinase (MMP)-13 in human OA chondrocytes as well as in chondrocytes from MKP-1 WT mice, but not in chondrocytes from MKP-1 KO mice. Dexamethasone also increased the expression of MKP-1 in murine and human OA chondrocytes. Furthermore, p38 MAP kinase inhibitors significantly attenuated MMP-13 expression in human OA chondrocytes, while JNK MAP kinase inhibitors had no effect. The results indicate that the effect of dexamethasone on MMP-13 expression in chondrocytes was mediated by an MKP-1 and p38 MAP kinase-dependent manner. These findings, together with previous results, support the concept of MKP-1 as a protective factor in articular chondrocytes in inflammatory conditions and as a potential drug target to treat OA.

The causal role of gut microbiota in development of osteoarthritis

OBJECTIVE

There is considerable evidence for relationship between gut microbiota and osteoarthritis (OA), but no studies have investigated their causal relationship.

METHOD

This study utilized large-scale genome-wide association studies (GWAS) summary statistics to evaluate the causal association between gut microbiota and OA risk. Specifically, two-sample Mendelian randomization (MR) approach was used to identify the causal microbial taxa for OA. Comprehensively sensitive analyses were performed to validate the robustness of results and novel multivariable MR analyses were further conducted to ensure the independence of causal association. Reverse-direction MR analyses were performed to rule out the possibility of reverse associations. Finally, enrichment analyses were used to investigate the biofunction.

RESULTS

After correction, three microbial taxa were identified to be causally associated with diverse joint OA (P_FDR < 0.100), namely Methanobacteriaceae family for knee OA (P_FDR = 0.043) and any OA (P_FDR = 0.028), Desulfovibrionales order for knee OA (P_FDR = 0.045) and Ruminiclostridium5 genus for knee OA (P_FDR = 0.063). In addition, we also identified five suggestive microbial taxa that were significant with three different methods under the nominal significance (P < 0.05). Sensitive analysis excluded the influence of heterogeneity and horizontal pleiotropy and multivariable MR analysis ruled out the possibility of horizontal pleiotropy of BMI. GO enrichment analysis illustrates the protective mechanism of the identified taxa against OA.

CONCLUSIONS

This study found that several microbial taxa were causally associated with diverse joint OA. The results enhanced our understanding of gut microbiota in the pathology of OA.

Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player

The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.

Nasal Chondrocyte-Derived Soluble Factors Affect Chondrogenesis of Cocultured Mesenchymal Stem Cells

To investigate the effect of soluble factors released from human nasal chondrocytes (NCs) on cocultured human bone marrow mesenchymal stem cells (MSCs) and NC tissue-engineered constructs. Cartilage engineered from pure NCs on a three-dimensional (3D) porous collagen scaffold was cultured indirectly in a Transwell system with cartilage engineered from a direct coculture of human bone marrow-derived MSCs and NCs on a 3D porous collagen scaffold. The soluble factors were measured in the conditioned media from the different chambers of the Transwell system. Engineered cartilage from cocultures exposed to the pure NC construct exhibited reduced chondrogenic potential relative to control constructs, shown by reduced extracellular matrix deposition and increased expression of hypertrophic markers. Analysis of the soluble factors within the conditioned media showed an increase in inflammatory cytokines in the coculture chamber exposed to the pure NC construct. Principal component analysis revealed that the majority of the data variance could be explained by proinflammatory factors and hypertrophic chondrogenesis. In conclusion, our data suggest that inflammatory cytokines derived from NCs reduce the chondrogenic potential of coculture engineered cartilage through the induction of hypertrophic chondrogenesis. Impact statement The use of engineered cartilage from cocultured nasal chondrocytes (NCs) and mesenchymal stem cells for nasal cartilage reconstruction may be problematic. Our data suggest that the soluble factors from surrounding native NCs in the cartilage to be fixed can compromise the quality of the engineered cartilage if used in reconstructive surgery.

The Role of Inflammation in the Pathogenesis of Osteoarthritis

A joint is the point of connection between two bones in our body. Inflammation of the joint leads to several diseases, including osteoarthritis, which is the concern of this review. Osteoarthritis is a common chronic debilitating joint disease mainly affecting the elderly. Several studies showed that inflammation triggered by factors like biomechanical stress is involved in the development of osteoarthritis. This stimulates the release of early-stage inflammatory cytokines like interleukin-1 beta (IL-1β), which in turn induces the activation of signaling pathways, such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), phosphoinositide 3-kinase/protein kinase B (PI3K/AKT), and mitogen-activated protein kinase (MAPK). These events, in turn, generate more inflammatory molecules. Subsequently, collagenase like matrix metalloproteinases-13 (MMP-13) will degrade the extracellular matrix. As a result, anatomical and physiological functions of the joint are altered. This review is aimed at summarizing the previous studies highlighting the involvement of inflammation in the pathogenesis of osteoarthritis.

Novel anti-inflammatory and chondroprotective effects of the human melanocortin MC1 receptor agonist BMS-470539 dihydrochloride and human melanocortin MC3 receptor agonist PG-990 on lipopolysaccharide activated chondrocytes

Human melanocortin MC1 and MC3 receptors expressed on C-20/A4 chondrocytes exhibit chondroprotective and anti-inflammatory effects when activated by melanocortin peptides. Nearly 9 million people in the UK suffer from osteoarthritis, and bacterial infections play a role in its development. Here, we evaluate the effect of a panel of melanocortin peptides with different selectivity for human melanocortin MC1 (α-MSH, BMS-470539 dihydrochloride) and MC3 ([DTrp⁸]-γ-MSH, PG-990) receptors and C-terminal peptide α-MSH_11-13(KPV), on inhibiting LPS-induced chondrocyte death, pro-inflammatory mediators and induction of anti-inflammatory proteins. C-20/A4 chondrocytes were treated with a panel of melanocortin peptides prophylactically and therapeutically in presence of LPS (0.1 μg/ml). The chondroprotective properties of these peptides determined by cell viability assay, RT-PCR, ELISA for detection of changes in inflammatory markers (IL-6, IL-8 and MMP-1, -3 and -13) and western blotting for expression of the anti-inflammatory protein heme-oxygenase-1. C-20/A4 expressed human melanocortin MC1 and MC3 receptors and melanocortin peptides elevated cAMP. LPS stimulation caused a reduction in C-20/A4 viability, attenuated by the human melanocortin MC1 receptor agonist BMS-470539 dihydrochloride, and MC3 receptor agonists PG-990 and [DTrp⁸]-γ-MSH. Prophylactic and therapeutic regimes of [DTrp⁸]-γ-MSH significantly inhibited LPS-induced modulation of cartilage-damaging IL-6, IL-8, MMPs -1,-3 and -13 mediators both prophylactically and therapeutically, whilst human melanocortin MC1 and MC3 receptor agonists promoted an increase in HO-1 production. In the presence of LPS, activation of human melanocortin MC1 and MC3 receptors provided potent chondroprotection, upregulation of anti-inflammatory proteins and downregulation of inflammatory and proteolytic mediators involved in cartilage degradation, suggesting a new avenue for osteoarthritis treatment.

Synovium stem cell-derived matrix enhances anti-inflammatory properties of rabbit articular chondrocytes via the SIRT1 pathway

Autologous chondrocyte implantation (ACI) is a promising approach to repair cartilage defects; however, the cartilage trauma-induced inflammatory environment compromises its clinical outcomes. Cell-derived decellularized extracellular matrix (DECM) has been used as a culture substrate for mesenchymal stem cells (MSCs) to improve the cell proliferation and lineage-specific differentiation. In this study, DECM deposited by synovium-derived MSCs was used as an in vitro expansion system for rabbit articular chondrocytes and the response of DECM-expanded chondrocytes to pro-inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) was evaluated. Compared with those grown on tissue culture polystyrene (TCPS), the proliferation rate was significantly improved in DECM-expanded chondrocytes. TCPS- and DECM-expanded chondrocytes were isolated and induced to redifferentiation in a high-density pellet culture. DECM-expanded chondrocytes exerted a stronger resistance to 1 ng/mL of IL-1β than TCPS-expanded cells, but the production of cartilage matrix in both groups was inhibited by 5 ng/mL of IL-1β. When exposed to 1 or 5 ng/mL of TNF-α, DECM-expanded chondrocytes showed higher levels of cartilage matrix synthesis than TCPS-expanded cells. In addition, the gene expression of IL-1β- or TNF-α-induced matrix degrading enzymes (MMP3, MMP9, MMP13, and ADAMTS5) was significantly lower in DECM-expanded chondrocytes than TCPS-expanded cells. Furthermore, we found that SIRT1 inhibition by nicotinamide completely counteracted the protective effect of DECM on chondrocytes in the presence of IL-1β or TNF-α, indicating that the SIRT1 signaling pathway was involved in the DECM-mediated enhancement of anti-inflammatory properties of chondrocytes. Taken together, this work suggests that stem cell-derived DECM is a superior culture substrate for in vitro chondrocyte expansion by improving proliferation and enhancing the anti-inflammatory properties of chondrocytes. DECM-expanded chondrocytes with enhanced anti-inflammatory properties hold great potential in clinically ACI-based cartilage repair.

Saxagliptin suppresses degradation of type II collagen and aggrecan in primary human chondrocytes: a therapeutic implication in osteoarthritis

Osteoarthritis (OA) is a major public health concern for which a reliable non-invasive treatment option has yet to be developed. In the present study, we investigated the effects of saxagliptin, a novel dipeptidyl peptidase IV (DPP-4) inhibitor, on several important aspects of the pathophysiology of OA using primary human chondrocytes. The results of real-time PCR and ELISA analyses show that saxagliptin treatment significantly decreased mRNA and protein expression of three key cartilage degrading enzymes: matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13. The results of western blot confirmed that this decrease in MMP-1, -3, and -13 expression prevented degradation of type II collagen. We also found that saxagliptin significantly inhibited expression of a disintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-4 and ADAMTS-5, which was reflected by markedly decreased degradation of aggrecan. Inhibition of DPP-4 by saxagliptin also reduced oxidative stress in human primary chondrocytes as evidenced by decreased production of reactive oxygen species (ROS) and increased glutathione (GSH) levels. Additionally, the results of western blot analysis show that the effects of saxagliptin are mediated through the p38/IκBα/NF-κB pathway, which is considered an important treatment target for OA. These findings suggest a potential role for saxagliptin as a novel treatment against OA.

Effect of BMS-470539 on lipopolysaccharide-induced neutrophil activation

Background

BMS-470539, a recently introduced selective agonist of the melanocortin 1 receptor, is known to have anti-inflammatory properties. In this study, we investigated the effects of BMS-470539 on lipopolysaccharide (LPS)-induced inflammatory responses and delayed apoptosis with its signaling pathways in human neutrophils.

Methods

Isolated human neutrophils were incubated with various concentrations of BMS-470539 (1, 10, and 100 µM) in the presence or absence of LPS (100 ng/ml), and the expression of pro-inflammatory cytokines, such as tumor necrosis factor alpha, interleukin (IL)-6, and IL-1β, were assessed. The effects of BMS-470539 on the expression of mitogen-activated protein kinases (MAPKs), such as p38, extracellular-signal-regulated kinase 1/2, and c-Jun N-terminal kinase, and the expression of nuclear factor kappa B (NF-κB) in LPS-stimulated human neutrophils, were evaluated by enzyme-linked immunosorbent assay. Neutrophil apoptosis was also measured by fluorescence-activated cell sorting (annexin V/propidium iodide) in LPS-stimulated neutrophils under treatment with BMS-470539.

Results

BMS-470539 attenuated LPS-induced expression of pro-inflammatory cytokines, and phosphorylation of MAPKs and NF-κB. LPS stimulation reduced neutrophil apoptosis compared to the controls; however, BMS-470539 significantly inhibited the reduction of neutrophil apoptosis.

Conclusions

BMS-470539 can suppress the inflammatory responses of LPS-stimulated neutrophils by inhibition of MAPK pathways or NF-κB pathway, and it can also inhibit LPS-delayed neutrophil apoptosis.

Transdermal Iontophoretic Delivery of Lysine-Proline-Valine (KPV) Peptide Across Microporated Human Skin

Lysine-proline-valine (KPV) is a C-terminal peptide fragment of α-melanocyte stimulating hormone with potent anti-inflammatory properties. Present study investigates various transdermal enhancement strategies such as iontophoresis (ITP), microneedles (MN), and their combination (ITP + MN) on KPV delivery across dermatomed human skin. KPV attains a positive charge at pH less than 7.0, thus anodal ITP was used. The influence of current strength, KPV concentration, and duration of current application on the KPV delivery was investigated. At defined ITP parameters, the influence of MN on KPV delivery (ITP + MN) across skin was also determined. KPV permeation was less than detectable levels (limit of detection, 0.01 μg/mL) by simple passive diffusion. However, KPV permeation was increased to 4.4 μg/cm²/h by MN treatment. Furthermore, ITP and ITP + MN increased the permeation rate by 8 and 35 fold, respectively, as compared to MN alone. The skin retention levels of KPV by MN, ITP, and ITP + MN were increased by 5, 10, and 10 fold, respectively, as compared to passive diffusion. Confocal studies indicate that fluorescein isothiocyanate-labeled KPV migrated through the stratum corneum, along the microchannels and into the lower epidermal tissue because the fluorescence was observed beyond the depth of 100 μm.