Glycation marker glucosepane increases with the progression of osteoarthritis and correlates with morphological and functional changes of cartilage in vivo

AGE-RAGE Axis and Cardiovascular Diseases: Pathophysiologic Mechanisms and Prospects for Clinical Applications

Advanced glycation end products (AGE), a diverse array of molecules generated through non-enzymatic glycosylation, in conjunction with the receptor of advanced glycation end products (RAGE), play a crucial role in the pathogenesis of diabetes and its associated complications. Recent studies have revealed that the AGE-RAGE axis potentially accelerated the progression of cardiovascular diseases, including heart failure, atherosclerosis, myocarditis, pulmonary hypertension, hypertension, arrhythmia, and other related conditions. The AGE-RAGE axis is intricately involved in the initiation and progression of cardiovascular diseases, independently of its engagement in diabetes. The mechanisms include oxidative stress, inflammation, alterations in autophagy flux, and mitochondrial dysfunction. Conversely, inhibition of AGE production, disruption of the binding between RAGE and its ligands, or silencing of RAGE expression could effectively impair the function of AGE-RAGE axis, thereby delaying or ameliorating the aforementioned diseases. AGE and the soluble receptor for advanced glycation end products (sRAGE) have the potential to be novel predictors of cardiovascular diseases. In this review, we provide an in-depth overview towards the biosynthetic pathway of AGE and elucidate the pathophysiological implications in various cardiovascular diseases. Furthermore, we delve into the profound role of RAGE in cardiovascular diseases, offering novel insights for further exploration of the AGE-RAGE axis and potential strategies for the prevention and management of cardiovascular disorders.

Naturally Occurring Osteoarthritis Features and Treatments: Systematic Review on the Aged Guinea Pig Model

To date, several in vivo models have been used to reproduce the onset and monitor the progression of osteoarthritis (OA), and guinea pigs represent a standard model for studying naturally occurring, age-related OA. This systematic review aims to characterize the guinea pig for its employment in in vivo, naturally occurring OA studies and for the evaluation of specific disease-modifying agents. The search was performed in PubMed, Scopus, and Web of Knowledge in the last 10 years. Of the 233 records screened, 49 studies were included. Results showed that within a relatively short period of time, this model develops specific OA aspects, including cartilage degeneration, marginal osteophytes formation, and subchondral bone alterations. Disease severity increases with age, beginning at 3 months with mild OA and reaching moderate–severe OA at 18 months. Among the different strains, Dunkin Hartley develops OA at a relatively early age. Thus, disease-modifying agents have mainly been evaluated for this strain. As summarized herein, spontaneous development of OA in guinea pigs represents an excellent model for studying disease pathogenesis and for evaluating therapeutic interventions. In an ongoing effort at standardization, a detailed characterization of specific OA models is necessary, even considering the main purpose of these models, i.e., translatability to human OA.

The repair effect and mechanism of continuous passive motion on osteoarthritis in a rabbit model

OBJECTIVE

To observe the effect of continuous passive motion (CPM) on osteoarthritis in a rabbit model and explore its mechanism.

METHODS

Thirty healthy rabbits with a total of 60 knee joints were randomized into three groups. Group A had CPM for 8 h daily, starting on postoperative day 1 and free movement in the cage, group B received CPM for 2 h daily, starting on postoperative day 1 and free movement in the cage, and group C only had free movement in the cage. Mankin's score was used to compare the gross morphology of the rabbit's knee joint. Malondialdehyde (MDA) and superoxide dismutase (SOD) were measured by RT-PCR and western blot method before and after intervention.

RESULTS

The Mankin's scores of rabbits in groups A and B were significantly lower than those in group C, and those in group A were lower than those in group B at week 4 and week 12 of intervention (P<0.05). At week 4 of the CPM intervention, the gross morphological scores were the highest in group A, followed by group B, and the lowest in group C (P<0.05). At week 12 of CPM intervention, the gross morphological scores of the knee joints in groups A and B were increased again, which were the highest in group A, followed by group B, and the lowest in group C (P<0.05). At week 12 of intervention, MDA levels in group A were lower than those in groups B and C, whereas SOD levels in group A were higher than those in groups B and C.

CONCLUSION

CPM can effectively improve the symptoms of knee osteoarthritis in rabbits and increase the mobility of the joints, and the mechanism may be related to the ability of CPM to reduce the overproduction of peroxide at the lesion site.

AGEomics Biomarkers and Machine Learning-Realizing the Potential of Protein Glycation in Clinical Diagnostics

Protein damage by glycation, oxidation and nitration is a continuous process in the physiological system caused by reactive metabolites associated with dicarbonyl stress, oxidative stress and nitrative stress, respectively. The term AGEomics is defined as multiplexed quantitation of spontaneous modification of proteins damage and other usually low-level modifications associated with a change of structure and function—for example, citrullination and transglutamination. The method of quantitation is stable isotopic dilution analysis liquid chromatography—tandem mass spectrometry (LC-MS/MS). This provides robust quantitation of normal and damaged or modified amino acids concurrently. AGEomics biomarkers have been used in diagnostic algorithms using machine learning methods. In this review, I describe the utility of AGEomics biomarkers and provide evidence why these are close to the phenotype of a condition or disease compared to other metabolites and metabolomic approaches and how to train and test algorithms for clinical diagnostic and screening applications with high accuracy, sensitivity and specificity using machine learning approaches.

AGE/Non-AGE Glycation: An Important Event in Rheumatoid Arthritis Pathophysiology

Rheumatoid arthritis (RA) is a chronic inflammatory, autoimmune disease that gradually affects the synovial membrane and joints. Many intrinsic and/or extrinsic factors are crucial in making RA pathology challenging throughout the disease. Substantial enzymatic or non-enzymatic modification of proteins driving inflammation has gained a lot of interest in recent years. Endogenously modified glycated protein influences disease development linked with AGEs/non-AGEs and is reported as a disease marker. In this review, we summarized current knowledge of the differential abundance of glycated proteins by compiling and analyzing a variety of AGE and non-AGE ligands that bind with RAGE to activate multi-faceted inflammatory and oxidative stress pathways that are pathobiologically associated with RA-fibroblast-like synoviocytes (RA-FLS). It is critical to comprehend the connection between oxidative stress and inflammation generation, mediated by glycated protein, which may bind to the receptor RAGE, activate downstream pathways, and impart immunogenicity in RA. It is worth noting that AGEs and non-AGEs ligands play a variety of functions, and their functionality is likely to be more reliant on pathogenic states and severity that may serve as biomarkers for RA. Screening and monitoring of these differentially glycated proteins, as well as their stability in circulation, in combination with established pre-clinical characteristics, may aid or predict the onset of RA.

Soluble biological markers in osteoarthritis

In recent years, markers research has focused on the structural components of cartilage matrix. Specifically, a second generation of degradation markers has been developed against type II collagen neoepitopes generated by specific enzymes. A particular effort has been made to measure the degradation of minor collagens III and X of the cartilage matrix. However, because clinical data, including longitudinal controlled studies, are very scarce, it remains unclear whether they will be useful as an alternative to or in combination with current more established collagen biological markers to assess patients with osteoarthritis (OA). In addition, new approaches using high-throughput technologies allowed to detect new types of markers and improve the knowledge about the metabolic changes linked to OA. The relative advances coming from phenotype research are a first attempt to classify the heterogeneity of OA, and several markers could improve the phenotype characterization. These phenotypes could improve the selection of patients in clinical trials limiting the size of the studies by selecting patients with OA characteristics corresponding to the metabolic pathway targeted by the molecules evaluated. In addition, the inclusion of rapid progressors only in clinical trials would facilitate the demonstration of efficacy of the investigative drug to reduce joint degradation. The combination of selective biochemical markers appears as a promising and cost-effective approach to fulfill this unmet clinical need. Among the various potential roles of biomarkers in OA, their ability to monitor drug efficacy is probably one of the most important, in association with clinical and imaging parameters. Biochemical markers have the unique property to detect changes in joint tissue metabolism within a few weeks.

A Hypothesis: Fructosamine-3-Kinase-Related-Protein (FN3KRP) Catalyzes Deglycation of Maillard Intermediates Directly Downstream from Fructosamines

Non-enzymatic glycation (a.k.a. Maillard reaction) is a series of random spontaneous reactions between reducing sugars and amines, resulting in the formation of irreversible advanced glycation endproducts (AGE's). In food chemistry, this process is beneficial by contributing to the flavor, aroma, texture, and appearance of cooked foods. In vivo, however, Maillard reaction is deleterious because uncontrolled modification and crosslinking of biological macromolecules impairs their function. Consequently, chronic hyperglycemia of diabetes mellitus, for instance, leads to increased non-enzymatic glycation and diverse, multi-organ pathologies of diabetic complications. Based on the fact that toxic compounds, such as free radicals, are detoxified in vivo by specific defense mechanisms, one would expect to find mechanisms to control glucose toxicity as well. Thus far, only one such enzyme, fructosamine-3-kinase (FN3K), has been characterized. It operates intracellularly by catalyzing ATP-dependent removal of Maillard adducts, D-fructoselysines, from proteins, thereby reducing the Maillard reaction flux from glucose to AGE's. When FN3K was isolated, a closely related but distinct protein copurified with it. Unlike FN3K, however, this enzyme, fructosamine-3-kinase-related protein (FN3KRP), does not phosphorylate D-fructoselysines but it does phosphorylate several other (non-physiological) substrates. Interestingly, the distribution of FN3KRP in nature appears to be nearly universal whereas that of FN3K is limited to endotherms. In this article, it is suggested that the function of FN3KRP is deglycation of Maillard adducts downstream from fructoselysines. Such a mechanism, if proven correct, would be valuable given reports on apparent correlations between FN3KRP and some chronic conditions and/or diseases, such as a recent publication which proposes that the FN3KRP gene may be a longevity gene.

Protein glycation - biomarkers of metabolic dysfunction and early-stage decline in health in the era of precision medicine

Protein glycation provides a biomarker in widespread clinical use, glycated hemoglobin HbA1c (A1C). It is a biomarker for diagnosis of diabetes and prediabetes and of medium-term glycemic control in patients with established diabetes. A1C is an early-stage glycation adduct of hemoglobin with glucose; a fructosamine derivative. Glucose is an amino group-directed glycating agent, modifying N-terminal and lysine sidechain amino groups. A similar fructosamine derivative of serum albumin, glycated albumin (GA), finds use as a biomarker of glycemic control, particularly where there is interference in use of A1C. Later stage adducts, advanced glycation endproducts (AGEs), are formed by the degradation of fructosamines and by the reaction of reactive dicarbonyl metabolites, such as methylglyoxal. Dicarbonyls are arginine-directed glycating agents forming mainly hydroimidazolone AGEs. Glucosepane and pentosidine, an intense fluorophore, are AGE covalent crosslinks. Cellular proteolysis of glycated proteins forms glycated amino acids, which are released into plasma and excreted in urine. Development of diagnostic algorithms by artificial intelligence machine learning is enhancing the applications of glycation biomarkers. Investigational glycation biomarkers are in development for: (i) healthy aging; (ii) risk prediction of vascular complications of diabetes; (iii) diagnosis of autism; and (iv) diagnosis and classification of early-stage arthritis. Protein glycation biomarkers are influenced by heritability, aging, decline in metabolic, vascular, renal and skeletal health, and other factors. They are applicable to populations of differing ethnicities, bridging the gap between genotype and phenotype. They are thereby likely to find continued and expanding clinical use, including in the current era of developing precision medicine, reporting on multiple pathogenic processes and supporting a precision medicine approach.

An implementation study of periarticular knee osteotomy in the treatment of knee osteoarthritis

OBJECTIVE

To analyze the clinical effects of periarticular knee osteotomy (PKO) in the treatment of knee osteoarthritis (KOA).

METHODS

A total of 180 patients with KOA admitted to our hospital were selected as the study subjects, and were divided into study group (90 cases) and control group (90 cases) in accordance with different intervention measures. The study group was treated with PKO, while the control group was treated with joint replacement. The perioperative indices, and postoperative pain degrees, knee joint function, quality of life, inflammatory factors and complications were compared between the two groups.

RESULTS

The control group was superior to the study group regarding the amount of preoperative bleeding, surgical duration, and incidence rate of complications, while the study group was superior to the control group regarding the long-term (over 2 years) knee joint function and quality of life (P < 0.05). There was no marked difference in the postoperative pain degrees and preoperative and postoperative levels of inflammatory factors between the two groups (P < 0.05).

CONCLUSION

PKO, exhibiting a high safety profile, can remarkably improve the joint pain symptoms, knee joint function, quality of life and symptoms of KOA in patients with KOA. Therefore, PKO is worthy of clinical promotion and implementation.

Quantitative measures of bone shape, cartilage morphometry and joint alignment are associated with disease in an ACLT and MMx rat model of osteoarthritis

Multi-scale, subject-specific quantitative methods to characterize and monitor osteoarthritis in animal models and therapeutic treatments could help reveal causal relationships in disease development and distinguish treatment strategies. In this work, we demonstrate a reproducible and sensitive quantitative image analysis to characterize bone, cartilage and joint measures describing a rat model of post-traumatic osteoarthritis. Eleven 3-month-old male Wistar rats underwent medial anterior cruciate ligament (ACL) transection and medial meniscectomy on the right knee to destabilise the right tibiofemoral joint. They were sacrificed 6 weeks post-surgery and a silicon-based micro-bead contrast agent was injected in the joint space, before scanning with micro-computed tomography (microCT). Subsequently, 3D quantitative morphometric analysis (QMA), previously developed for rabbit joints, was performed. This included cartilage, subchondral cortical and epiphyseal bone measures, as well as novel tibiofemoral joint metrics. Semi-quantitative evaluation was performed on matching two-dimensional (2D) histology and microCT images. Reproducibility of the QMA was tested on eleven age-matched additional joints. The results indicate the QMA method is accurate and reproducible and that microCT-derived cartilage measurements are valid for the analysis of rat joints. The pathologic changes caused by transection of the ACL and medial meniscectomy were reflected in measurements of bone shape, cartilage morphology, and joint alignment. Furthermore, we were able to identify model-specific predictive parameters based on morphometric parameters measured with the QMA.

A low cartilage formation and repair endotype predicts radiographic progression of symptomatic knee osteoarthritis

Background

Osteoarthritis (OA) is a disease with multiple endotypes. A hallmark of OA is loss of cartilage; however, it is evident that the rate of cartilage loss differs among patients, which may partly be attributed to differential capacity for cartilage repair. We hypothesize that a low cartilage repair endotype exists and that such endotypes are more likely to progress radiographically. The aim of this study is to examine the associations of level of cartilage formation with OA severity and radiographic OA progression. We used the blood-based marker PRO-C2, reflecting type II collagen formation, to assess levels of cartilage formation.

Materials and methods

The type II collagen propeptide PRO-C2 was measured in the serum/plasma of knee OA subjects from New York University (NYU, n = 106) and a subcohort of the phase III oral salmon calcitonin (sCT) trial SMC021-2301 (SMC, n = 147). Risk of radiographic medial joint space narrowing (JSN) over 24 months was compared between quartiles (very low, low, moderate, and high) of PRO-C2. Associations were adjusted for age, gender, BMI, race, baseline pain levels, and baseline joint space width.

Results

In both the NYU and SMC cohorts, subjects with low PRO-C2 levels had greater JSN compared with subjects with high PRO-C2. Mean difference in JSN between subjects with very low and high levels of PRO-C2 was 0.65 mm (p = 0.002), corresponding to a 3.4 (1.4–8.6)-fold higher risk of progression. There was no significant effect of sCT treatment, compared with placebo, on JSN over 2 years before stratification based on baseline PRO-C2. However, there were proportionately fewer progressors in the sCT arm of the very low/low PRO-C2 group compared with the moderate/high group (Chi squared = 6.5, p = 0.011).

Conclusion

Serum/plasma level of type II collagen formation, PRO-C2, may be an objective indicator of a low cartilage repair endotype, displaying radiographic progression and superior response to a proanabolic drug.

Level of evidence

Level III post hoc exploratory analysis of one longitudinal cohort and a sub-study from one phase III clinical trial.

Reading patterns of proteome damage by glycation, oxidation and nitration: quantitation by stable isotopic dilution analysis LC-MS/MS

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) provides a high sensitivity, high specificity multiplexed method for concurrent detection of adducts formed by protein glycation, oxidation and nitration, also called AGEomics. Combined with stable isotopic dilution analysis, it provides for robust quantitation of protein glycation, oxidation and nitration adduct analytes. It is the reference method for such measurements. LC-MS/MS has been used to measure glycated, oxidized and nitrated amino acids - also called glycation, oxidation and nitration free adducts, with a concurrent quantitation of the amino acid metabolome in physiological fluids. Similar adduct residues in proteins may be quantitated with prior exhaustive enzymatic hydrolysis. It has also been applied to quantitation of other post-translation modifications, such as citrullination and formation of Nε-(γ-glutamyl)lysine crosslink by transglutaminases. Application to cellular and extracellular proteins gives estimates of the steady-state levels of protein modification by glycation, oxidation and nitration, and measurement of the accumulation of glycation, oxidation and nitration adducts in cell culture medium and urinary excretion gives an indication of flux of adduct formation. Measurement of glycation, oxidation and nitration free adducts in plasma and urine provides for estimates of renal clearance of free adducts. Diagnostic potential in clinical studies has been enhanced by the combination of estimates of multiple adducts in optimized diagnostic algorithms by machine learning. Recent applications have been in early-stage detection of metabolic, vascular and renal disease, and arthritis, metabolic control and risk of developing vascular complication in diabetes, and a blood test for autism.

Molecular taxonomy of osteoarthritis for patient stratification, disease management and drug development: biochemical markers associated with emerging clinical phenotypes and molecular endotypes

PURPOSE OF REVIEW

This review focuses on the molecular taxonomy of osteoarthritis from the perspective of molecular biomarkers. We discuss how wet biochemical markers may be used to understand disease pathogenesis and progression and define molecular endotypes of osteoarthritis and how these correspond to clinical phenotypes.

RECENT FINDINGS

Emerging evidence suggests that osteoarthritis is a heterogeneous and multifaceted disease with multiple causes, molecular endotypes and corresponding clinical phenotypes. Biomarkers may be employed as tools for patient stratification in clinical trials, enhanced disease management in the primary care centres of the future and for directing more rational and targeted osteoarthritis drug development. Proximal molecular biomarkers (e.g synovial fluid) are more likely to distinguish between molecular endotypes because there is less interference from systemic sources of biomarker noise, including comorbidities.

SUMMARY

In this review, we have focused on the molecular biomarkers of four distinct osteoarthritis subtypes including inflammatory, subchondral bone remodelling, metabolic syndrome and senescent age-related endotypes, which have corresponding phenotypes. Progress in the field of osteoarthritis endotype and phenotype research requires a better understanding of molecular biomarkers that may be used in conjunction with imaging, pain and functional assessments for the design of more effective, stratified and individualized osteoarthritis treatments.

Glucosepane is associated with changes to structural and physical properties of collagen fibrils

Collagen glycation, and in particular the formation of advanced glycation end-product (AGE) crosslinks, plays a central role in the ageing process and in many of the long-term complications of diabetes. Glucosepane, the most abundant and relevant AGE crosslink, has been suggested to increase the stiffness of tissue and reduce its solubility, although no evidence is available concerning the mechanisms. We have used a combination of computational and experimental techniques to study a collagen-rich tissue with a relatively simple organisation to further our understanding of the impact of glucosepane on the structural and physical properties of collagen fibrils. Our work shows that glucosepane levels increase dramatically in aged tendon tissue and are associated with the reduced density of collagen packing and increased porosity to water molecules. Our studies provide the basis to understand many of the tissue dysfunctions associated with ageing and diabetes across a range of different tissues types.

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Levels of the advanced glycation end-product glucosepane increase in human tendon with increasing chronological age.

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Glucosepane results in a less tightly held helical structure in the collagen molecule and increased porosity to water.

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Water content is higher in Achilles and anterior tibialis tendon tissue from older individuals compared to young people.

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The denaturation temperature of collagen increases in the older age group suggesting a more highly cross-linked structure.

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The enthalpy of collagen denaturation decreases in older donors suggesting molecules are less confined within the fibril.

7,8-Dihydroxyflavone activates Nrf2/HO-1 signaling pathways and protects against osteoarthritis

The aim of the present study was to investigate the effect of 7,8-dihydroxyflavone (7,8-DHF) against osteoarthritis (OA) and examine its regulatory role in the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway in chondrocytes. Primary mouse chondrocytes were treated with 7,8-DHF to examine the expression of Nrf2 and downstream heme oxygenase 1 (HO-1). The surgical destabilization of the medial meniscus model was used to assess the effectiveness of 7,8-DHF in protecting the cartilage from damage, with knee cartilage harvested from mice for histological analysis. The results revealed that 7,8-DHF activated the Nrf2 signaling pathway in primary chondrocytes. Cartilage degradation in the 7,8-DHF-treated group was reduced significantly compared with that in the vehicle-treated group, according to histological evaluation. The gene expression of matrix metalloproteinase (MMP)1, MMP3, MMP13, interleukin (IL)-1β, IL-6 and tumor necrosis factor-α were reduced in the cartilage of OA mice following 7,8-DHF treatment. Genetic and protein analyses indicated that the expression levels of HO-1 were upregulated in the cartilage of the knee with OA, and 7,8-DHF treatment further promoted the induction of HO-1. These results suggest that 7,8-DHF may serve as a potential therapeutic agent in OA.

Impairment of glyoxalase-1, an advanced glycation end-product detoxifying enzyme, induced by inflammation in age-related osteoarthritis

BACKGROUND

Accumulation of advanced glycation end-products (AGEs) is involved in age-related osteoarthritis (OA). Glyoxalase (Glo)-1 is the main enzyme involved in the removal of AGE precursors, especially carboxymethyl-lysine (CML). We aimed to investigate the expression of several AGEs and Glo-1 in human OA cartilage and to study chondrocytic Glo-1 regulation by inflammation, mediated by interleukin (IL)-1β.

METHODS

Ex vivo, we quantified AGEs (pentosidine, CML, methylglyoxal-hydroimidazolone-1) in knee cartilage from 30 OA patients. Explants were also incubated with and without IL-1β, and we assessed Glo-1 protein expression and enzymatic activity. In vitro, primary cultured murine chondrocytes were stimulated with increasing concentrations of IL-1β to assess Glo-1 enzymatic activity and expression. To investigate the role of oxidative stress in the IL-1β effect, cells were also treated with inhibitors of mitochondrial oxidative stress or nitric oxide synthase.

RESULTS

Ex vivo, only the human cartilage CML content was correlated with patient age (r = 0.78, p = 0.0031). No statistically significant correlation was found between Glo-1 protein expression and enzymatic activity in human cartilage and patient age. We observed that cartilage explant stimulation with IL-1β decreased Glo-1 protein expression and enzymatic activity. In vitro, we observed a dose-dependent decrease in Glo-1 mRNA, protein quantity, and enzymatic activity in response to IL-1β in murine chondrocytes. Inhibitors of oxidative stress blunted this downregulation.

CONCLUSION

Glo-1 is impaired by inflammation mediated by IL-1β in chondrocytes through oxidative stress pathways and may explain age-dependent accumulation of the AGE CML in OA cartilage.