Carnosine Alleviates Knee Osteoarthritis and Promotes Synoviocyte Protection via Activating the Nrf2/HO-1 Signaling Pathway: An In-Vivo and In-Vitro Study

Acetyl-11-keto-β-boswellic acid restrains the progression of synovitis in osteoarthritis via the Nrf2/HO-1 pathway

Synovial inflammation plays a key role in osteoarthritis (OA) pathogenesis. Fibroblast-like synoviocytes (FLSs) represent a distinct cell subpopulation within the synovium, and their unique phenotypic alterations are considered significant contributors to inflammation and fibrotic responses. The underlying mechanism by which acetyl-11-keto-β-boswellic acid (AKBA) modulates FLS activation remains unclear. This study aims to assess the beneficial effects of AKBA through both in vitro and in vivo investigations. Network pharmacology evaluation is used to identify potential targets of AKBA in OA. We evaluate the effects of AKBA on FLSs activation in vitro and the regulatory role of AKBA on the Nrf2/HO-1 signaling pathway. ML385 (an Nrf2 inhibitor) is used to verify the binding of AKBA to its target in FLSs. We validate the in vivo efficacy of AKBA in alleviating OA using anterior cruciate ligament transection and destabilization of the medial meniscus (ACLT+DMM) in a rat model. Network pharmacological analysis reveals the potential effect of AKBA on OA. AKBA effectively attenuates lipopolysaccharide (LPS)-induced abnormal migration and invasion and the production of inflammatory mediators, matrix metalloproteinases (MMPs), and reactive oxygen species (ROS) in FLSs, contributing to the restoration of the synovial microenvironment. After treatment with ML385, the effect of AKBA on FLSs is reversed. In vivo studies demonstrate that AKBA mitigates synovial inflammation and fibrotic responses induced by ACLT+DMM in rats via activation of the Nrf2/HO-1 axis. AKBA exhibits theoretical potential for alleviating OA progression through the Nrf2/HO-1 pathway and represents a viable therapeutic candidate for this patient population.

PEGylation renders carnosine resistant to hydrolysis by serum carnosinase and increases renal carnosine levels

Carnosine's protective effect in rodent models of glycoxidative stress have provided a rational for translation of these findings in therapeutic concepts in patient with diabetic kidney disease. In contrast to rodents however, carnosine is rapidly degraded by the carnosinase-1 enzyme. To overcome this hurdle, we sought to protect hydrolysis of carnosine by conjugation to Methoxypolyethylene glycol amine (mPEG-NH2). PEGylated carnosine (PEG-car) was used to study the hydrolysis of carnosine by human serum as well as to compare the pharmacokinetics of PEG-car and L-carnosine in mice after intravenous (IV) injection. While L-carnosine was rapidly hydrolyzed in human serum, PEG-car was highly resistant to hydrolysis. Addition of unconjugated PEG to carnosine or PEG-car did not influence hydrolysis of carnosine in serum. In mice PEG-car and L-carnosine exhibited similar pharmacokinetics in serum but differed in half-life time (t1/2) in kidney, with PEG-car showing a significantly higher t1/2 compared to L-carnosine. Hence, PEGylation of carnosine is an effective approach to prevent carnosine degradations and to achieve higher renal carnosine levels. However, further studies are warranted to test if the protective properties of carnosine are preserved after PEGylation.

Lipoxin A4 ameliorates knee osteoarthritis progression in rats by antagonizing ferroptosis through activation of the ESR2/LPAR3/Nrf2 axis in synovial fibroblast-like synoviocytes

BACKGROUND

Our previous studies have shown that lipoxin A4 (LXA4) can serve as a potential biomarker for assessing the efficacy of exercise therapy in knee osteoarthritis (KOA), and fibroblast-like synoviocytes (FLSs) may play a crucial role in KOA pain as well as in the progression of the pathology.

OBJECTIVE

By analyzing the GSE29746 dataset and collecting synovial samples from patients with different Kellgren-Lawrence (KL) grades for validation, we focused on exploring the potential effect of LXA4 on ferroptosis in FLSs through the ESR2/LPAR3/Nrf2 axis to alleviate pain and pathological advancement in KOA.

METHODS

The association between FLSs ferroptosis and chondrocyte matrix degradation was explored by cell co-culture. We overexpressed and knocked down LPAR3 in vitro to explore its potential mechanism in FLSs. A rat model of monosodium iodoacetate (MIA)-induced KOA was constructed and intervened with moderate-intensity treadmill exercise and intraperitoneal injection of PHTPP to investigate the effects of the LXA4 intracellular receptor ESR2 on exercise therapy.

RESULTS

ESR2, LPAR3, and GPX4 levels in the synovium decreased with increasing KL grade. After LXA4 intervention in the co-culture system, GPX4, LPAR3, and ESR2 were upregulated in FLSs, collagen II was upregulated in chondrocytes, and MMP3 and ADAM9 were downregulated. LPAR3 overexpression upregulated the expression of GPX4, Nrf2, and SOD1 in FLSs, while downregulating the expression of MMP13 and MMP3; LPAR3 knockdown reversed these changes. Moderate-intensity platform training improved the behavioral manifestations of pain in KOA rats, whereas PHTPP treatment partially reversed the improvement in synovial and cartilage pathologies induced by platform training.

CONCLUSION

LXA4 inhibited FLSs ferroptosis by activating the ESR2/LPAR3/Nrf2 axis, thereby alleviating the pain and pathological progression of KOA. This study brings a new target for the treatment of KOA and also leads to a deeper understanding of the potential mechanisms of exercise therapy for KOA.

Apoptotic body-inspired nanotherapeutics efficiently attenuate osteoarthritis by targeting BRD4-regulated synovial macrophage polarization

Bromodomain-containing protein 4 (BRD4) is the most well-studied BET protein that is important for the innate immune response. We recently revealed that targeting BRD4 triggers apoptosis in tumor-associated macrophages, but its role in synovial macrophages and joint inflammation is largely unknown. Herein, we demonstrated that BRD4 was highly expressed in the iNOS-positive M1 macrophages in the human and mouse osteoarthritis (OA) synovium, and conditional knockout of BRD4 in the myeloid lineage using Lyz2-cre; BRD4flox/flox mice significantly abolished anterior cruciate ligament transection (ACLT)-induced M1 macrophage accumulation and synovial inflammation. Accordingly, we successfully constructed apoptotic body-inspired phosphatidylserine-containing nanoliposomes (PSLs) loaded with the BRD4 inhibitor JQ1 to regulate inflammatory macrophages. JQ1-loaded PSLs (JQ1@PSLs) exhibited a higher cellular uptake by macrophages than fibroblast-like synoviocytes (FLSs) in vitro and in vivo, as well as the reduction in proinflammatory M1 macrophage polarization. Intra-articular injections of JQ1@PSLs showed prolonged retention within the joint, and remarkably reduced synovial inflammation and joint pain via suppressing M1 polarization accompanied by reduced TRPA1 expression by targeted inhibition of BRD4 in the macrophages, thus attenuating cartilage degradation during OA development. The results show that BRD4-inhibiting JQ1@PSLs can targeted-modulate macrophage polarization, which opens a new avenue for efficient OA therapy via a "Trojan horse".

Anti-Osteoarthritis Mechanism of the Nrf2 Signaling Pathway

Osteoarthritis (OA) is a chronic degenerative disease and the primary pathogenic consequence of OA is inflammation, which can affect a variety of tissues including the synovial membrane, articular cartilage, and subchondral bone. The development of the intra-articular microenvironment can be significantly influenced by the shift of synovial macrophages between pro-inflammatory and anti-inflammatory phenotypes. By regulating macrophage inflammatory responses, the NF-κB signaling route is essential in the therapy of OA; whereas, the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway appears to manage the relationship between oxidative stress and inflammation. Additionally, it has been demonstrated that under oxidative stress and inflammation, there is a significant interaction between transcriptional pathways involving Nrf2 and NF-κB. Studying how Nrf2 signaling affects inflammation and cellular metabolism may help us understand how to treat OA by reprogramming macrophage behavior because Nrf2 signaling is thought to affect cellular metabolism. The candidates for treating OA by promoting an anti-inflammatory mechanism by activating Nrf2 are also reviewed in this paper.

Carnosine, Zinc and Copper: A Menage a Trois in Bone and Cartilage Protection

Dysregulated metal homeostasis is associated with many pathological conditions, including arthritic diseases. Osteoarthritis and rheumatoid arthritis are the two most prevalent disorders that damage the joints and lead to cartilage and bone destruction. Recent studies show that the levels of zinc (Zn) and copper (Cu) are generally altered in the serum of arthritis patients. Therefore, metal dyshomeostasis may reflect the contribution of these trace elements to the disease's pathogenesis and manifestations, suggesting their potential for prognosis and treatment. Carnosine (Car) also emerged as a biomarker in arthritis and exerts protective and osteogenic effects in arthritic joints. Notably, its zinc(II) complex, polaprezinc, has been recently proposed as a drug-repurposing candidate for bone fracture healing. On these bases, this review article aims to provide an overview of the beneficial roles of Cu and Zn in bone and cartilage health and their potential application in tissue engineering. The effects of Car and polaprezinc in promoting cartilage and bone regeneration are also discussed. We hypothesize that polaprezinc could exchange Zn for Cu, present in the culture media, due to its higher sequestering ability towards Cu. However, future studies should unveil the potential contribution of Cu in the beneficial effects of polaprezinc.

Carnosine alleviates kidney tubular epithelial injury by targeting NRF2 mediated ferroptosis in diabetic nephropathy

Diabetic nephropathy (DN) can promote the occurrence of end-stage renal disease (ESRD). The injury of renal tubular epithelial cells is a significant reason for the occurrence of ESRD. A recent research demonstrated that ferroptosis was associated with renal tubular injury in DN. Ferroptosis is a kind of cell death brought on by the buildup of iron ions and lipid peroxidation brought on by ROS. Because carnosine (CAR) is a scavenger of iron ions and reactive oxygen species, we investigated whether CAR can improve DN by regulating ferroptosis. The results show that both CAR and Fer-1 significantly reduced kidney damage and inhibited ferroptosis in STZ mice. In addition, ferroptosis caused by HG or erastin (an inducer of ferroptosis) in human kidney tubular epithelial cell (HK2) was also rescued by CAR treatment. It was discovered that the protective effect of CAR against HG-induced ferroptosis was abolished when NRF2 was specifically knocked down in HK2 cells.

Copper(II) Complexes with Carnosine Conjugates of Hyaluronic Acids at Different Dipeptide Loading Percentages Behave as Multiple SOD Mimics and Stimulate Nrf2 Translocation and Antioxidant Response in In Vitro Inflammatory Model

A series of copper(II) complexes with the formula [Cu2+Hy(x)Car%] varying the molecular weight (MW) of Hyaluronic acid (Hy, x = 200 or 700 kDa) conjugated with carnosine (Car) present at different loading were synthesized and characterized via different spectroscopic techniques. The metal complexes behaved as Cu, Zn-superoxide dismutase (SOD1) mimics and showed some of the most efficient reaction rate values produced using a synthetic and water-soluble copper(II)-based SOD mimic reported to date. The increase in the percentage of Car moieties parallels the enhancement of the I50 value determined via the indirect method of Fridovich. The presence of the non-functionalized Hy OH groups favors the scavenger activity of the copper(II) complexes with HyCar, recalling similar behavior previously found for the copper(II) complexes with Car conjugated using β-cyclodextrin or trehalose. In keeping with the new abilities of SOD1 to activate protective agents against oxidative stress in rheumatoid arthritis and osteoarthritis diseases, Cu2+ interaction with HyCar promotes the nuclear translocation of erythroid 2-related factor that regulates the expressions of target genes, including Heme-Oxigenase-1, thus stimulating an antioxidant response in osteoblasts subjected to an inflammatory/oxidative insult.

The Role of Genetics and Epigenetic Regulation in the Pathogenesis of Osteoarthritis

Osteoarthritis (OA) is progressive disease characterised by cartilage degradation, subchondral bone remodelling and inflammation of the synovium. The disease is associated with obesity, mechanical load and age. However, multiple pro-inflammatory immune mediators regulate the expression of metalloproteinases, which take part in cartilage degradation. Furthermore, genetic factors also contribute to OA susceptibility. Recent studies have highlighted that epigenetic mechanisms may regulate the expression of OA-associated genes. This review aims to present the mechanisms of OA pathogenesis and summarise current evidence regarding the role of genetics and epigenetics in this process.

Vitamin D reduces pain and cartilage destruction in knee osteoarthritis animals through inhibiting the matrix metalloprotease (MMPs) expression

Aim of the study

In this study, we investigated the therapeutic potential of vitamin D (VITD) in OA Wistar rats induced by anterior cruciate ligament transection combined with medial meniscectomy (ACLT + MMx). In ACLT + MMx-induced OA rats, pain severity, cartilage destruction, inflammatory cytokines, and MMPs were all measured.

Materials and methods

ACLT + MMx methods were used to induce OA, and pain behavioral studies such as the weight bearing test and paw withdrawal test were performed while the knee width and body weights were also measured. Furthermore, Hematoxylin and Eosin (H&E) staining was used to determine knee histopathological studies, as well as OARSI scoring, cartilage thickness, cartilage width, and cartilage degradation scores. The enzyme-linked immunosorbent assay (ELISA) studies were used to check the serum levels of VITD, C-telopeptide of Type II collagen (CTX-II), and pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and anti-inflammatory cytokines interleukin-10 (IL-10), and MMPs (MMP-3, MMP-9, and MMP-13). Finally, the reverse transcription polymerase chain reaction (RT-PCR) test was used to determine the levels of MMPs, nuclear factor-kappa B (NF-κB), TNF-α, IL-6, and IL-10 in IL-1β stimulated chondrocytes.

Results

The oral VITD supplement significantly reduced OA pain, inflammation, cartilage destruction, and MMPs levels. Furthermore, serum VITD levels increased while CTX-II levels decreased, indicating that VITD reduced cartilage degradation effectively. Moreover, VITD supplementation reduced the expression of pro-inflammatory TNF-α, IL-1β, and IL-6 cytokines while increasing the expression of anti-inflammatory IL-10. The elevation of MMPs after ACLT + MMx surgery contributed to articular cartilage destruction, which was reduced by VITD supplementation. Finally, VITD supplementation significantly reduces serum levels of MMPs, IL-1β, TNF-α, and IL-6 while increasing IL-10 levels. Then, using the in-vitro cytotoxicity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) MTT assay, examine the cytotoxicity profile of VITD in rat chondrocytes after stimulated with IL-1β, which shows no toxicity in the dose range of VITD 0-500 IU. Finally, RT-PCR studies in IL-1β stimulated rat chondrocytes revealed that VITD (50, 100, and 500 IU) significantly reduced the mRNA levels of MMPs, NF-κB, TNF-α, and IL-6, while increasing IL-10 levels, indicating that VITD reduced chondrocyte destruction and overcame harsh conditions in a dose-dependent manner.

Conclusion

Overall, the in vivo and in vitro findings show that VITD effectively reduces OA pain, inflammation, and chondrocyte destruction by lowering MMPs levels specifically.