Activation of The Phosphatidylcholine to Lysophosphatidylcholine Pathway Is Associated with Osteoarthritis Knee Cartilage Volume Loss Over Time

Exploring predictive molecules of acute adverse events in response to volumetric‑modulated arc therapy for prostate cancer using urinary metabolites

Volumetric-modulated arc therapy (VMAT) is a radiotherapy technique used to treat patients with localized prostate cancer, which is frequently associated with acute adverse events (AEs) that can affect subsequent treatment. Notably, the radiation dose of VMAT can be tailored to each patient. In the present study, a retrospective analysis was performed to predict acute AEs in response to a therapeutic high radiation dose rate based on urinary metabolomic molecules, which are easily collected as noninvasive biosamples. Urine samples from 11 patients with prostate cancer who were treated with VMAT (76 Gy/38 fractions) were collected. The study found that seven patients (~64%) exhibited genitourinary toxicity (Grade 1) and four patients had no AEs. A total of 630 urinary metabolites were then analyzed using a mass spectrometer (QTRAP6500+; AB SCIEX), and 234 relevant molecules for biological and clinical applications were extracted from the absolute quantified metabolite values using the MetaboINDICATOR tool. In the Grade 1 acute AE group, there was a significant negative correlation (rs=-0.297, P<0.05) between the number of VMAT fractions and total phospholipase A2 activity in the urine. Additionally, patients with Grade 1 AEs exhibited a decrease in PC aa C40:1, a phospholipid. These findings suggested that specific lipids found in urinary metabolites may serve as predictive biomarkers for acute AEs in response to external radiotherapy.

Risk of metabolic abnormalities in osteoarthritis: a new perspective to understand its pathological mechanisms

Although aging has traditionally been viewed as the most important risk factor for osteoarthritis (OA), an increasing amount of epidemiological evidence has highlighted the association between metabolic abnormalities and OA, particularly in younger individuals. Metabolic abnormalities, such as obesity and type II diabetes, are strongly linked to OA, and they affect both weight-bearing and non-weight-bearing joints, thus suggesting that the pathogenesis of OA is more complicated than the mechanical stress induced by overweight. This review aims to explore the recent advances in research on the relationship between metabolic abnormalities and OA risk, including the impact of abnormal glucose and lipid metabolism, the potential pathogenesis and targeted therapeutic strategies.

Functional Characterization of Lysophospholipids by Proteomic and Lipidomic Analysis of Fibroblast-like Synoviocytes

Synovial fluid (SF) from human knee joints with osteoarthritis (OA) has elevated levels of lysophosphatidylcholine (LPC) species, but their functional role is not well understood. This in vitro study was designed to test the hypothesis that various LPCs found elevated in OA SF and their metabolites, lysophosphatidic acids (LPAs), modulate the abundance of proteins and phospholipids (PLs) in human fibroblast-like synoviocytes (FLSs), with even minute chemical variations in lysophospholipids determining the extent of regulation. Cultured FLSs (n = 5-7) were treated with one of the LPC species, LPA species, IL-1β, or a vehicle. Tandem mass tag peptide labeling coupled with LC-MS/MS/MS was performed to quantify proteins. The expression of mRNA from regulated proteins was analyzed using RT-PCR. PL synthesis was determined via ESI-MS/MS, and the release of radiolabeled PLs was determined by means of liquid scintillation counting. In total, 3960 proteins were quantified using multiplexed MS, of which 119, 8, and 3 were significantly and reproducibly regulated by IL-1β, LPC 16:0, and LPC 18:0, respectively. LPC 16:0 significantly inhibited the release of PLs and the synthesis of phosphatidylcholine, LPC, and sphingomyelin. Neither LPC metabolite-LPA 16:0 nor LPA 18:0-had any reproducible effect on the levels of each protein. In conclusion, small chemical variations in LPC species can result in the significantly altered expression and secretion of proteins and PLs from FLSs. IL-1β influenced all proteins that were reproducibly regulated by LPC 16:0. LPC species are likely to modulate FLS protein expression only in more advanced OA stages with low IL-1β levels. None of the eight proteins being significantly regulated by LPC 16:0 have been previously reported in OA. However, our in vitro findings show that the CD81 antigen, calumenin, and B4E2C1 are promising candidates for further study, focusing in particular on their potential ability to modulate inflammatory and catabolic mechanisms.

Emerging molecular biomarkers in osteoarthritis pathology

Osteoarthritis (OA) is the most common form of arthritis resulting in joint discomfort and disability, culminating in decline in life quality. Attention has been drawn in recent years to disease-associated molecular biomarkers found in readily accessible biofluids due to low invasiveness of acquisition and their potential to detect early pathological molecular changes not observed with traditional imaging methodology. These biochemical markers of OA have been found in synovial fluid, blood, and urine. They include emerging molecular classes, such as metabolites and noncoding RNAs, as well as classical biomarkers, like inflammatory mediators and by-products of degradative processes involving articular cartilage. Although blood-based biomarkers tend to be most studied, the use of synovial fluid, a more isolated biofluid in the synovial joint, and urine as an excreted fluid containing OA biomarkers can offer valuable information on local and overall disease activity, respectively. Furthermore, larger clinical studies are required to determine relationships between biomarkers in different biofluids, and their impacts on patient measures of OA. This narrative review provides a concise overview of recent studies of OA using these four classes of biomarkers as potential biomarker for measuring disease incidence, staging, prognosis, and therapeutic intervention efficacy.

Determination of lysophosphatidylcholine using peroxidase-mimic PVP/PtRu nanozyme

Lysophosphatidylcholine (LPC) can be used as a biomarker for diseases such as cancer, diabetes, atherosclerosis, and sepsis. In this study, we demonstrated the ability of nanozymes to displace the natural derived enzyme in enzyme-based assays for the measurement of LPC. Synthesized polyvinylpyrrolidone-stabilized platinum-ruthenium nanozymes (PVP/PtRu NZs) had a uniform size of 2.48 ± 0.24 nm and superb peroxidase-mimicking activity. We demonstrated that the nanozymes had high activity over a wide pH and temperature range and high stability after long-term storage. The LPC concentration could be accurately analyzed through the absorbance and fluorescence signals generated by the peroxidation reaction using the synthesized nanozyme with substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) and 10-acetyl-3,7-dihydroxyphenoxazine (Ampliflu™ Red). LPC at a concentration of 0-400 µM was used for the analysis, and the coefficient of determination (R²) was 0.977, and the limit of detection (LOD) was 23.1 µM by colorimetric assay. In the fluorometric assay, the R² was 0.999, and the LOD was 8.97 µM. The spiked recovery values for the determination of LPC concentration in human serum samples were 102-115%. Based on these results, we declared that PVP/PtRu NZs had an ability comparable to that of the native enzyme horseradish peroxidase (HRP) in the enzyme-based LPC detection method.

Lysophosphatidylcholine 16:0 mediates chronic joint pain associated to rheumatic diseases through acid-sensing ion channel 3

ABSTRACT

Rheumatic diseases are often associated to debilitating chronic pain, which remains difficult to treat and requires new therapeutic strategies. We had previously identified lysophosphatidylcholine (LPC) in the synovial fluids from few patients and shown its effect as a positive modulator of acid-sensing ion channel 3 (ASIC3) able to induce acute cutaneous pain in rodents. However, the possible involvement of LPC in chronic joint pain remained completely unknown. Here, we show, from 2 independent cohorts of patients with painful rheumatic diseases, that the synovial fluid levels of LPC are significantly elevated, especially the LPC16:0 species, compared with postmortem control subjects. Moreover, LPC16:0 levels correlated with pain outcomes in a cohort of osteoarthritis patients. However, LPC16:0 do not appear to be the hallmark of a particular joint disease because similar levels are found in the synovial fluids of a second cohort of patients with various rheumatic diseases. The mechanism of action was next explored by developing a pathology-derived rodent model. Intra-articular injections of LPC16:0 is a triggering factor of chronic joint pain in both male and female mice, ultimately leading to persistent pain and anxiety-like behaviors. All these effects are dependent on ASIC3 channels, which drive sufficient peripheral inputs to generate spinal sensitization processes. This study brings evidences from mouse and human supporting a role for LPC16:0 via ASIC3 channels in chronic pain arising from joints, with potential implications for pain management in osteoarthritis and possibly across other rheumatic diseases.

Lipid Metabolism in Cartilage Development, Degeneration, and Regeneration

Lipids affect cartilage growth, injury, and regeneration in diverse ways. Diet and metabolism have become increasingly important as the prevalence of obesity has risen. Proper lipid supplementation in the diet contributes to the preservation of cartilage function, whereas excessive lipid buildup is detrimental to cartilage. Lipid metabolic pathways can generate proinflammatory substances that are crucial to the development and management of osteoarthritis (OA). Lipid metabolism is a complicated metabolic process involving several regulatory systems, and lipid metabolites influence different features of cartilage. In this review, we examine the current knowledge about cartilage growth, degeneration, and regeneration processes, as well as the most recent research on the significance of lipids and their metabolism in cartilage, including the extracellular matrix and chondrocytes. An in-depth examination of the involvement of lipid metabolism in cartilage metabolism will provide insight into cartilage metabolism and lead to the development of new treatment techniques for metabolic cartilage damage.

Antibody-induced pain-like behavior and bone erosion: links to subclinical inflammation, osteoclast activity, and acid-sensing ion channel 3-dependent sensitization

ABSTRACT

Several bone conditions, eg, bone cancer, osteoporosis, and rheumatoid arthritis (RA), are associated with a risk of developing persistent pain. Increased osteoclast activity is often the hallmark of these bony pathologies and not only leads to bone remodeling but is also a source of pronociceptive factors that sensitize the bone-innervating nociceptors. Although historically bone loss in RA has been believed to be a consequence of inflammation, both bone erosion and pain can occur years before the symptom onset. Here, we have addressed the disconnection between inflammation, pain, and bone erosion by using a combination of 2 monoclonal antibodies isolated from B cells of patients with RA. We have found that mice injected with B02/B09 monoclonal antibodies (mAbs) developed a long-lasting mechanical hypersensitivity that was accompanied by bone erosion in the absence of joint edema or synovitis. Intriguingly, we have noted a lack of analgesic effect of naproxen and a moderate elevation of few inflammatory factors in the ankle joints suggesting that B02/B09-induced pain-like behavior does not depend on inflammatory processes. By contrast, we found that inhibiting osteoclast activity and acid-sensing ion channel 3 signaling prevented the development of B02/B09-mediated mechanical hypersensitivity. Moreover, we have identified secretory phospholipase A2 and lysophosphatidylcholine 16:0 as critical components of B02/B09-induced pain-like behavior and shown that treatment with a secretory phospholipase A2 inhibitor reversed B02/B09-induced mechanical hypersensitivity and bone erosion. Taken together, our study suggests a potential link between bone erosion and pain in a state of subclinical inflammation and offers a step forward in understanding the mechanisms of bone pain in diseases such as RA.

Serum Metabolomic Signatures for Knee Cartilage Volume Loss over 10 Years in Community-Dwelling Older Adults

Osteoarthritis (OA) is the most prevalent joint disorder characterized by joint structural pathological changes with the loss of articular cartilage as its hallmark. Tools that can predict cartilage loss would help identify people at high risk, thus preventing OA development. The recent advance of the metabolomics provides a new avenue to systematically investigate metabolic alterations in disease and identify biomarkers for early diagnosis. Using a metabolomics approach, the current study aimed to identify serum metabolomic signatures for predicting knee cartilage volume loss over 10 years in the Tasmania Older Adult Cohort (TASOAC). Cartilage volume was measured in the medial, lateral, and patellar compartments of the knee by MRI at baseline and follow-up. Changes in cartilage volume over 10 years were calculated as percentage change per year. Fasting serum samples collected at 2.6-year follow-up were metabolomically profiled using the TMIC Prime Metabolomics Profiling Assay and pairwise metabolite ratios as the proxies of enzymatic reaction were calculated. Linear regression was used to identify metabolite ratio(s) associated with change in cartilage volume in each of the knee compartments with adjustment for age, sex, and BMI. The significance level was defined at α = 3.0 × 10−6 to control multiple testing. A total of 344 participants (51% females) were included in the study. The mean age was 62.83 ± 6.13 years and the mean BMI was 27.48 ± 4.41 kg/m2 at baseline. The average follow-up time was 10.84 ± 0.66 years. Cartilage volume was reduced by 1.34 ± 0.72%, 1.06 ± 0.58%, and 0.98 ± 0.46% per year in the medial, lateral, and patellar compartments, respectively. Our data showed that the increased ratios of hexadecenoylcarnitine (C16:1) to tetradecanoylcarnitine (C14) and C16:1 to dodecanoylcarnitine (C12) were associated with 0.12 ± 0.02% reduction per year in patellar cartilage volume (both p < 3.03 × 10−6). In conclusion, our data suggested that alteration of long chain fatty acid β-oxidation was involved in patellar cartilage loss. While confirmation is needed, the ratios of C16:1 to C14 and C12 might be used to predict long-term cartilage loss.

Restricting Branched-Chain Amino Acids within a High-Fat Diet Prevents Obesity

Obesity is a global pandemic, but there is yet no effective measure to control it. Recent metabolomics studies have identified a signature of altered amino acid profiles to be associated with obesity, but it is unclear whether these findings have actionable clinical potential. The aims of this study were to reveal the metabolic alterations of obesity and to explore potential strategies to mitigate obesity. We performed targeted metabolomic profiling of the plasma/serum samples collected from six independent cohorts and conducted an individual data meta-analysis of metabolomics for body mass index (BMI) and obesity. Based on the findings, we hypothesized that restriction of branched-chain amino acids (BCAAs), phenylalanine, or tryptophan may prevent obesity and tested our hypothesis in a dietary restriction trial with eight groups of 4-week-old male C57BL/6J mice (n = 5/group) on eight different types of diets, respectively, for 16 weeks. A total of 3397 individuals were included in the meta-analysis. The mean BMI was 30.7 ± 6.1 kg/m2, and 49% of participants were obese. Fifty-eight metabolites were associated with BMI and obesity (all p ≤ 2.58 × 10-4), linked to alterations of the BCAA, phenylalanine, tryptophan, and phospholipid metabolic pathways. The restriction of BCAAs within a high-fat diet (HFD) maintained the mice's weight, fat and lean volume, subcutaneous and visceral adipose tissue weight, and serum glucose and insulin at levels similar to those in the standard chow group, and prevented obesity, adipocyte hypertrophy, adipose inflammation, and insulin resistance induced by HFD. Our data suggest that four metabolic pathways, BCAA, phenylalanine, tryptophan, and phospholipid metabolic pathways, are altered in obesity and restriction of BCAAs within a HFD can prevent the development of obesity and insulin resistance in mice, providing a promising strategy to potentially mitigate diet-induced obesity.

Fundamentals of OA. An initiative of Osteoarthritis and Cartilage. Obesity and metabolic factors in OA

OBJECTIVE

Obesity was once considered a risk factor for knee osteoarthritis (OA) primarily for biomechanical reasons. Here we provide an additional perspective by discussing how obesity also increases OA risk by altering metabolism and inflammation.

DESIGN

This narrative review is presented in four sections: 1) metabolic syndrome and OA, 2) metabolic biomarkers of OA, 3) evidence for dysregulated chondrocyte metabolism in OA, and 4) metabolic inflammation: joint tissue mediators and mechanisms.

RESULTS

Metabolic syndrome and its components are strongly associated with OA. However, evidence for a causal relationship is context dependent, varying by joint, gender, diagnostic criteria, and demographics, with additional environmental and genetic interactions yet to be fully defined. Importantly, some aspects of the etiology of obesity-induced OA appear to be distinct between men and women, especially regarding the role of adipose tissue. Metabolomic analyses of serum and synovial fluid have identified potential diagnostic biomarkers of knee OA and prognostic biomarkers of disease progression. Connecting these biomarkers to cellular pathophysiology will require future in vivo studies of joint tissue metabolism. Such studies will help reveal when a metabolic process or a metabolite itself is a causal factor in disease progression. Current evidence points towards impaired chondrocyte metabolic homeostasis and metabolic-immune dysregulation as likely factors connecting obesity to the increased risk of OA.

CONCLUSIONS

A deeper understanding of how obesity alters metabolic and inflammatory pathways in synovial joint tissues is expected to provide new therapeutic targets and an improved definition of "metabolic" and "obesity" OA phenotypes.

Recent Progress of Nanomedicine on Secreted Phospholipase A2 as a Potential Therapeutic Target

Overexpressed secretory phospholipase A2 (sPLA2) is found in many inflammatory diseases and various types of cancer. sPLA2 can catalyze the hydrolysis of phospholipid sn-2 ester bond to lysophosphatidylcholine and free...

Saroglitazar and Hepano treatment offers protection against high fat high fructose diet induced obesity, insulin resistance and steatosis by modulating various class of hepatic and circulating lipids

Higher global prevalence of non-alcoholic fatty liver disease (NAFLD) is associated with obesity, steatosis, and insulin resistance (IR), and often progresses to steatohepatitis (NASH). Even after more than twenty years of research, there is still no FDA approved therapy for the treatment of fatty liver disease/NASH though, Saroglitazar - a dual PPAR α/γ agonist has been recently approved as a therapeutic option for the fatty liver disease in India. Hepatoprotective Ayurvedic formulations are widely used and are considered safe. In the present study, C57BL/6 male mice on HFHF diet for four weeks were treated with vehicle, Saroglitazar (3 mg/kg/po), and Hepano - a formulation of five herbs (200 mg/kg/po), at the human equivalent therapeutic doses for additional eight weeks. These animals were evaluated after 12 weeks for obesity, body mass index (BMI), systemic insulin resistance, hyperglycaemia, dyslipidaemia, and hepatic lipid accumulation. Differential liquid chromatography-mass spectrometry (LC-MS/MS) based lipidomics analysis demonstrated significant changes in the different class of lipids [phospholipids, sphingolipids, diglycerides and triglycerides (TG)] in HFHF fed group. The protective effects of both Saroglitazar and Hepano were evident against IR, obesity and in the modulation of different class of lipids in the circulation and hepatic tissue. Saroglitazar reduced TG as well as modulated phospholipids levels, while Hepano modulated only phospholipids, ceramides, oxidised lipids, and had no effect on hepatic or circulating TG levels in HFHF fed mice. In addition, in vitro studies using HepG2, THP1 and LX2 cells demonstrated safety of both the test substances where Hepano possess better anti-inflammatory as well as anti-fibrotic potential. Overall, Saroglitazar seems to be more efficacious than Hepano in the regimen used against HFHF induced IR, obesity, and dyslipidaemia.

The development of modulators for lysophosphatidic acid receptors: A comprehensive review

Lysophosphatidic acids (LPAs) are bioactive phospholipids implicated in a wide range of cellular activities that regulate a diverse array of biological functions. They recognize two types of G protein-coupled receptors (LPARs): LPA_1-3 receptors and LPA_4-6 receptors that belong to the endothelial gene (EDG) family and non-endothelial gene family, respectively. In recent years, the LPA signaling pathway has captured an increasing amount of attention because of its involvement in various diseases, such as idiopathic pulmonary fibrosis, cancers, cardiovascular diseases and neuropathic pain, making it a promising target for drug development. While no drugs targeting LPARs have been approved by the FDA thus far, at least three antagonists have entered phase Ⅱ clinical trials for idiopathic pulmonary fibrosis (BMS-986020 and BMS-986278) and systemic sclerosis (SAR100842), and one radioligand (BMT-136088/¹⁸F-BMS-986327) has entered phase Ⅰ clinical trials for positron emission tomography (PET) imaging of idiopathic pulmonary fibrosis. This article provides an extensive review on the current status of ligand development targeting LPA receptors to modulate LPA signaling and their therapeutic potential in various diseases.

Integrated metabolomics coupled with pattern recognition and pathway analysis to reveal molecular mechanism of cadmium-induced diabetic nephropathy

Diabetic nephropathy (DN) is becoming a worldwide public health problem and its pathophysiological mechanism is not well understood. Emerging evidences indicated that cadmium (Cd), an industrial material but also an environmental toxin, may be involved in the development and progression of diabetes and diabetes-related kidney disease. However, the underlying mechanism is still unclear. Herein, a DN animal model was constructed by exposing to Cd, the metabolomic profiling of DN mice were obtained by using ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS), pattern recognition and pathway analysis were performed to screen potential biomarker. Moreover, western blotting was employed to verify the possible mechanism involved in the occurrence of Cd-induced DN. A total of 66 metabolites in serum have been screened out and identified as biomarkers, including free fatty acids, phospholipids, sphingomyelins, glycerides, and others. Significant differences were demonstrated between the metabolic profiles, including decreased levels of phospholipid and increased content of triglyceride, diacylglycerols, ceramide, lysophosphatidylcholine in Cd-induced DN mice compared with control. Protein expression level of p38 MAPK and Wnt/β-catenin were significantly increased. UPLC-Q-TOF/MS-based serum metabolomics coupled with pattern recognition methods and pathway analysis provide a powerful approach to identify potential biomarkers and is a new strategy to predict the underlying mechanism of disease caused by environmental toxicant.

Endotypes of primary osteoarthritis identified by plasma metabolomics analysis

OBJECTIVE

To identify endotypes of osteoarthritis (OA) by a metabolomics analysis.

METHODS

Study participants included hip/knee OA patients and controls. Fasting plasma samples were metabolomically profiled. Common factor analysis and K-means clustering were applied to the metabolomics data to identify the endotypes of OA patients. Logistic regression was utilized to identify the most significant metabolites contributing to the endotypes. Clinical and epidemiological factors were examined in relation to the identified OA endotypes.

RESULTS

Six hundred and fifteen primary OA patients and 237 controls were included. Among the 186 metabolites measured, 162 passed the quality control analysis. The 615 OA patients were classified in three clusters (A, 66; B, 200; and C, 349). Patients in cluster A had a significantly higher concentration of butyrylcarnitine (C4) than other clusters and controls (all P < 0.0002). Elevated C4 is thought to be related to muscle weakness and wasting. Patients in cluster B had a significantly lower arginine concentration than other clusters and controls (all P < 7.98 × 10-11). Cluster C patients had a significantly lower concentration of lysophosphatidylcholine (with palmitic acid), which is a pro-inflammatory bioactive compound, than other clusters and controls (P < 3.79 × 10-6). Further, cluster A had a higher BMI and prevalence of diabetes than other clusters (all P ≤ 0.0009), and also a higher prevalence of coronary heart disease than cluster C (P = 0.04). Cluster B had a higher prevalence of coronary heart disease than cluster C (P = 0.003) whereas cluster C had a higher prevalence of osteoporosis (P = 0.009).

CONCLUSION

Our data suggest three possible clinically actionable endotypes in primary OA: muscle weakness, arginine deficit and low inflammatory OA.

Heterogeneity of Lipid and Protein Cartilage Profiles Associated with Human Osteoarthritis with or without Type 2 Diabetes Mellitus

Osteoarthritis (OA) is a multifactorial pathology and comprises a wide range of distinct phenotypes. In this context, the characterization of the different molecular profiles associated with each phenotype can improve the classification of OA. In particular, OA can coexist with type 2 diabetes mellitus (T2DM). This study investigates lipidomic and proteomic differences between human OA/T2DM- and OA/T2DM+ cartilage through a multimodal mass spectrometry approach. Human cartilage samples were obtained after total knee replacement from OA/T2DM- and OA/T2DM+ patients. Label-free proteomics was employed to study differences in protein abundance and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) for spatially resolved-lipid analysis. Label-free proteomic analysis showed differences between OA/T2DM- and OA/T2DM+ phenotypes in several metabolic pathways such as lipid regulation. Interestingly, phospholipase A2 protein was found increased within the OA/T2DM+ cohort. In addition, MALDI-MSI experiments revealed that phosphatidylcholine and sphingomyelin species were characteristic of the OA/T2DM- group, whereas lysolipids were more characteristic of the OA/T2DM+ phenotype. The data also pointed out differences in phospholipid content between superficial and deep layers of the cartilage. Our study shows distinctively different lipid and protein profiles between OA/T2DM- and OA/T2DM+ human cartilage, demonstrating the importance of subclassification of the OA disease for better personalized treatments.

Identification of a distinct lipidomic profile in the osteoarthritic synovial membrane by mass spectrometry imaging

OBJECTIVE

Synovial inflammation is one of the most characteristic events in different types of arthritis, including Osteoarthritis (OA). Emerging evidence also suggests the involvement of lipids in the regulation of inflammatory processes. The aim of this study was to elucidate the heterogeneity and spatial distribution of lipids in the OA synovial membrane and explore their putative involvement in inflammation.

METHOD

The abundance and distribution of lipids were examined in human synovial membranes. To this end, histological cuts from this tissue were analysed by matrix-assisted laser desorption ionization - mass spectrometry imaging (MALDI-MSI). The lipidomic profile of OA synovium was characterized and compared with healthy and other forms of inflammatory arthropathies as Rheumatoid Arthritis (RA) and Psoriatic Arthritis (PsA) using principal component analysis and discriminant analysis methods. Lipid identification was undertaken by tandem MS analyses and database queries.

RESULTS

Our results reveal differential and characteristic lipidomic profiles between OA and control samples. Specifically, we unveiled that OA synovium presents elevated levels of phosphatidylcholines, fatty acids and lysophosphatidic acids and lower levels of lysophosphatidylcholines compared to control tissues. The spatial distribution of particular glycerophospholipids was also correlated with hypertrophic, inflamed or vascularized synovial areas. Compared with other inflammatory arthritis, the OA tissue showed lower amounts of phosphatidylethanolamine-based plasmalogens.

CONCLUSIONS

This study provides a novel insight into the lipid profiles of synovial membrane and differences in abundance between OA and control tissues. The lipidomic alterations improves understanding of the pathogenic mechanisms of OA and may be important for its diagnosis.

Toll-like receptor 2 induced senescence in intervertebral disc cells of patients with back pain can be attenuated by o-vanillin

BACKGROUND

There is an increased level of senescent cells and toll-like teceptor-1, -2, -4, and -6 (TLR) expression in degenerating intervertebral discs (IVDs) from back pain patients. However, it is currently not known if the increase in expression of TLRs is related to the senescent cells or if it is a more general increase on all cells. It is also not known if TLR activation in IVD cells will induce cell senescence.

METHODS

Cells from non-degenerate human IVD were obtained from spine donors and cells from degenerate IVDs came from patients undergoing surgery for low back pain. Gene expression of TLR-1,2,4,6, senescence and senescence-associated secretory phenotype (SASP) markers was evaluated by RT-qPCR in isolated cells. Matrix synthesis was verified with safranin-O staining and Dimethyl-Methylene Blue Assay (DMMB) confirmed proteoglycan content. Protein expression of p16INK4a, SASP factors, and TLR-2 was evaluated by immunocytochemistry (ICC) and/or by enzyme-linked immunosorbent assay (ELISA).

RESULTS

An increase in senescent cells was found following 48-h induction with a TLR-2/6 agonist in cells from both non-degenerate and degenerating human IVDs. Higher levels of SASP factors, TLR-2 gene expression, and protein expression were found following 48-h induction with TLR-2/6 agonist. Treatment with o-vanillin reduced the number of senescent cells, and increased matrix synthesis in IVD cells from back pain patients. Treatment with o-vanillin after induction with TLR-2/6 agonist reduced gene and protein expression of SASP factors and TLR-2. Co-localized staining of p16INK4a and TLR-2 demonstrated that senescent cells have a high TLR-2 expression.

CONCLUSIONS

Taken together our data demonstrate that activation of TLR-2/6 induce senescence and increase TLR-2 and SASP expression in cells from non-degenerate IVDs of organ donors without degeneration and back pain and in cells from degenerating human IVD of patients with disc degeneration and back pain. The senescent cells showed high TLR-2 expression suggesting a link between TLR activation and cell senescence in human IVD cells. The reduction in senescence, SASP, and TLR-2 expression suggest o-vanillin as a potential disease-modifying drug for patients with disc degeneration and back pain.

The role of metabolism in chondrocyte dysfunction and the progression of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by low-grade inflammation and high levels of clinical heterogeneity. Aberrant chondrocyte metabolism is a response to changes in the inflammatory microenvironment and may play a key role in cartilage degeneration and OA progression. Under conditions of environmental stress, chondrocytes tend to adapt their metabolism to microenvironmental changes by shifting from one metabolic pathway to another, for example from oxidative phosphorylation to glycolysis. Similar changes occur in other joint cells, including synoviocytes. Switching between these pathways is implicated in metabolic alterations that involve mitochondrial dysfunction, enhanced anaerobic glycolysis, and altered lipid and amino acid metabolism. The shift between oxidative phosphorylation and glycolysis is mainly regulated by the AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) pathways. Chondrocyte metabolic changes are likely to be a feature of different OA phenotypes. Determining the role of chondrocyte metabolism in OA has revealed key features of disease pathogenesis. Future research should place greater emphasis on immunometabolism and altered metabolic pathways as a means to understand the pathophysiology of age-related OA. This knowledge will advance the development of new drugs against therapeutic targets of metabolic significance.

Metabolic networks of plasma and joint fluid base on differential correlation

Whether osteoarthritis (OA) is a systemic metabolic disorder remains controversial. The aim of this study was to investigate the metabolic characteristics between plasma and knee joint fluid (JF) of patients with advanced OA using a differential correlation metabolic (DCM) networks approach. Plasma and JF were collected during the joint replacement surgery of patients with knee OA. The biological samples were pretreated with standard procedures for metabolite analysis. The metabolic profiling was conducted by means of liquid mass spectrometry coupled with a AbsoluteIDQ kit. A DCM network approach was adopted for analyzing the metabolomics data between the plasma and JF. The variation in the correlation of the pairwise metabolites was quantified across the plasma and JF samples, and networks analysis was used to characterize the difference in the correlations of the metabolites from the two sample types. Core metabolites that played an important role in the DCM networks were identified via topological analysis. One hundred advanced OA patients (50 men and 50 women) were included in this study, with an average age of 65.0 ± 7.6 years (65.6 ± 7.1 years for females and 64.4 ± 8.1 years for males) and a mean BMI of 32.6 ± 5.8 kg/m² (33.4 ± 6.3 kg/m² for females and 31.7 ± 5.3 kg/m² for males). Age and BMI matched between the male and female groups. One hundred and forty-five nodes, 567 edges, and 131 nodes, 407 edges were found in the DCM networks (p < 0.05) of the female and male groups, respectively. Six metabolites in the female group and 5 metabolites in the male group were identified as key nodes in the network. There was a significant difference in the differential correlation metabolism networks of plasma and JF that may be related to local joint metabolism. Focusing on these key metabolites may help uncover the pathogenesis of knee OA. In addition, the differential metabolic correlation between plasma and JF mostly overlapped, indicating that these common correlations of pairwise metabolites may be a reflection of systemic characteristics of JF and that most significant correlation variations were just a result of "housekeeping” biological reactions.

Metabolomic analysis coupled with extreme phenotype sampling identified that lysophosphatidylcholines are associated with multisite musculoskeletal pain

ABSTRACT

Musculoskeletal pain often occurs simultaneously at multiple anatomical sites. The aim of the study was to identify metabolic biomarkers for multisite musculoskeletal pain (MSMP) by metabolomics with an extreme phenotype sampling strategy. The study participants (n = 610) were derived from the Newfoundland Osteoarthritis Study. Musculoskeletal pain was assessed using a self-reported pain questionnaire where painful sites were circled on a manikin by participants and the total number of painful sites were calculated. Targeted metabolomic profiling on fasting plasma samples was performed using the Biocrates AbsoluteIDQ p180 kit. Plasma cytokine concentrations including tumor necrosis factor-α, interleukin-6, interleukin-1β, and macrophage migration inhibitory factor were assessed by enzyme-linked immunosorbent assay. Data on blood cholesterol profiles were retrieved from participants' medical records. Demographic, anthropological, and clinical information was self-reported. The number of reported painful sites ranged between 0 and 21. Two hundred and five participants were included in the analysis comprising 83 who had ≥7 painful sites and 122 who had ≤1 painful site. Women and younger people were more likely to have MSMP (P ≤ 0.02). Multisite musculoskeletal pain was associated with a higher risk of having incontinence, worse functional status and longer period of pain, and higher levels of low-density lipoprotein and non-high-density lipoprotein cholesterol (all P ≤ 0.03). Among the 186 metabolites measured, 2 lysophosphatidylcholines, 1 with 26 carbons with no double bond and 1 with 28 carbons with 1 double bond, were significantly and positively associated with MSMP after adjusting for multiple testing with the Bonferroni method (P ≤ 0.0001) and could be considered as novel metabolic markers for MSMP.

Phenylalanine Is a Novel Marker for Radiographic Knee Osteoarthritis Progression: The MOST Study

OBJECTIVE

To identify plasma markers associated with an increased risk of radiographic knee osteoarthritis(OA) progression using a metabolomics approach.

METHODS

Study participants were from the Multicenter Osteoarthritis Study (MOST) and were categorized into 2 groups based on the presence of baseline radiographic OA. Subjects in group 1 had unilateral knee OA and subjects in group 2 had bilateral knee OA. Progression was defined as a half-grade or greater worsening in joint space width at 30-month follow-up. For group 1, a participant progressed when their OA knee showed radiographic progression and the contralateral knee developed OA; for group 2, a participant progressed when both knees with OA showed radiographic progression. Metabolomic profiling was performed on plasma samples collected at baseline and logistic regression was performed to test the association between each metabolite and knee OA progression after adjustment for age, sex, BMI, and clinic site. Significance was defined as P ≤ 0.0003 in the combined analysis.

RESULTS

There were 234 progressors (57 in group 1 and 177 in group 2) and 322 nonprogressors (206 in group 1 and 116 in group 2) included in the analyses. Among 157 metabolites studied, we found that odds of progression were 1.46 times higher per SD increase of phenylalanine level (95% CI 1.20-1.77, P = 0.0001) in the combined analysis. Sex-specific analysis showed that an association was seen in women (P = 0.0002) but not in men.

CONCLUSION

Our data suggest that phenylalanine might be a novel plasma marker for higher risk of bilateral radiographic knee OA progression in women.

Evaluation of Early Knee Osteoarthritis Using Biomechanical and Biochemical Markers

Altered cellular mechano-transduction and biochemistry lead to degeneration of articular cartilage in people with knee osteoarthritis. However, the influence of low-moderate exposure to weight-bearing activity such as squatting on cartilage metabolism has not been adequately studied. The current study explored associations between knee adduction moment (KAM) during walking, biochemical markers and daily squat exposure. 3D gait analysis was used to determine external loads acting on the knee as indicators of joint compressive forces whereas biomarkers-Urine type-II-collagen-telopeptide (uCTxII), antioxidant and phospholipase A2 (PLA2) activity reflected on articular cartilage status. Following ethical approval, 66 participants with varying daily squat exposure (non-squatters [n = 21, exposure = 0 min]; activity of daily living [ADL] squatters [n = 16, exposure = 34 min]; occupational squatters [n = 13, exposure = 102 min]) and people with grade 2-3 knee osteoarthritis (n = 16, exposure = 28 min) were evaluated using 3D gait and biomarker analysis. The PLA2 activity was lowest in ADL squatters while occupational squatters demonstrated highest activity (p < 0.05). KAM and urine biomarker were similar among the groups. Moderate-strong positive association was observed between sweat PLA2 activity and age (r = 0.819, p = 0.004), daily squat exposure and biomarker uCTxII (r = 0.604, p = 0.013), antioxidant activity and Right-KAM (r = -0.917, p = 0.001), and Left-KAM (r = -0.767, p = 0.016), in people with knee OA. Healthy people demonstrated weak positive associations between KAM, uCTxII, and BMI. Associations between non-invasive biomechanical and biochemical markers indicate their potential use to identify early knee osteoarthritis. Studies with larger sample size are necessary to support prescription of body weight joint loading activities such as squatting in moderation, to delay functional decline caused by knee OA.

Clinical relevance of biochemical and metabolic changes in osteoarthritis

Osteoarthritis (OA) is a multifactorial disease with huge phenotypic heterogeneity. The disease affects all tissues in the joint, and the loss of articular cartilage is its hallmark. The main biochemical components of the articular cartilage are type II collagen, aggrecan, and water. Transforming growth factor-beta (TGF-β) signaling is one of the signaling pathways that maintains the healthy cartilage. However, the two subpathways of the TGF-β signaling-TGF-β and bone morphogenetic proteins (BMP) subpathways, lose their balance in OA, resulting an increased expression of cartilage degradation enzymes including matrix metallopeptidase 13 (MMP13), cathepsin B (CTSB), and cathepsin K (CTSK) and a decreased expression of aggrecan (ACAN). Thus, restoring the balance of two subpathways might provide a new avenue for treating OA patients. Further, metabolic changes are seen in OA and can be used to distinguish different subtypes of OA patients. Metabolomics studies showed that at least three endotypes of OA can be distinguished: 11% of OA patients are characterized by an elevated blood butyryl carnitine, 33% of OA patients have significant reduced arginine concentration, and 56% with metabolic alteration in phospholipid metabolism. While these findings need to be confirmed, they are promising personalized medicine tools for OA management.

Differential correlation network analysis identified novel metabolomics signatures for non-responders to total joint replacement in primary osteoarthritis patients

INTRODUCTION

Up to one third of total joint replacement patients (TJR) experience poor surgical outcome.

OBJECTIVES

To identify metabolomic signatures for non-responders to TJR in primary osteoarthritis (OA) patients.

METHODS

A newly developed differential correlation network analysis method was applied to our previously published metabolomic dataset to identify metabolomic network signatures for non-responders to TJR.

RESULTS

Differential correlation networks involving 12 metabolites and 23 metabolites were identified for pain non-responders and function non-responders, respectively.

CONCLUSION

The differential networks suggest that inflammation, muscle breakdown, wound healing, and metabolic syndrome may all play roles in TJR response, warranting further investigation.

Interventional effects of the direct application of "Sanse powder" on knee osteoarthritis in rats as determined from lipidomics via UPLC-Q-Exactive Orbitrap MS

BACKGROUND

Our previous clinical evidence suggested that the direct application of "Sanse powder" the main ingredient of "Yiceng" might represent an alternative treatment for knee osteoarthritis. However, the mechanism underlying its effect is poorly understood. In this study, we investigated the mechanism of the effect of direct "Sanse powder" application for the treatment of knee osteoarthritis (KOA) in rats by using lipidomics.

METHODS

KOA rats were established by cutting the anterior cruciate ligament, and the cold pain threshold and mechanical withdrawal threshold (MWT) of seven rats from each group were measured before modelling (0 days) and at 7, 14, 21 and 28 days after modelling. Histopathological evaluation of the synovial tissue was performed by haematoxylin and eosin (H&E) staining after modelling for 28 days. Interleukin-1β (IL-1β), pro-interleukin-1β (pro-IL-1β) and tumor necrosis factor-α (TNF-α) proteins in synovial tissue were measured by western blot, and the mRNA expression levels of IL-1β and TNF-α in synovial tissue were measured using Real-time reverse transcription polymerase chain reaction (qRT-PCR), the levels of IL-1β and TNF-α in rat serum were measured by enzyme-linked immunosorbent assay (ELISA), Serum lipid profiles were obtained by using ultra-performance liquid chromatography combined with quadrupole-Exactive Orbitrap mass spectrometry (UPLC-Q-Exactive Orbitrap MS).

RESULTS

The results confirmed that the direct application of "Sanse powder" had a significant protective effect against KOA in rats. Treatment with "Sanse powder" not only attenuated synovial tissue inflammation but also increased the levels of the cold pain threshold and MWT. In addition, the lipidomics results showed that the levels of diacylglycerol (DAG), triacylglycerols (TAGs), lysophosphatidylcholine (LPC), phosphatidylcholine (PC), fatty acid esters of hydroxy fatty acids (FAHFAs), and phosphatidylethanolamine (PE) were restored almost to control levels following treatment.

CONCLUSIONS

Lipidomics provides a better understanding of the actions of direct application "Sanse powder" therapy for KOA.

Serum lysophosphatidylcholines to phosphatidylcholines ratio is associated with symptomatic responders to symptomatic drugs in knee osteoarthritis patients

BACKGROUND

Identification of the optimal treatment for a given patient is of paramount importance. This is of particular relevance in osteoarthritis (OA) because of the high prevalence of the disease, extensive heterogeneity of the disease, and need for long-term treatment. The aim of the study was to examine whether serum lysophosphatidylcholines (lysoPCs) to phosphatidylcholines (PCs) ratio can predict clinical response to licofelone and naproxen treatments in symptomatic knee OA patients.

METHODS

One hundred fifty-eight OA patients who completed the study according to protocol (ATP) of a previous 24-month clinical trial cohort comparing the effect of licofelone vs. naproxen in symptomatic knee OA patients were included. Symptomatic responses to either treatments were classified according to the OARSI-OMERACT criteria based on the WOMAC scores at 24 months. Total concentrations of PCs and lysoPCs were measured in the serum samples collected before the initiation of the treatments, and the lysoPCs to PCs ratio was calculated. Student's t test was utilized to compare the difference in the ratio of lysoPCs to PCs between the symptomatic responders and non-responders. Logistic regression was utilized to adjust for the potential confounders. Receiver operating characteristic (ROC) analysis was performed to identify the optimal cutoff of the ratio for prediction.

RESULTS

Data showed that 61.4% of the patients symptomatically responded to licofelone and naproxen and 38.6% were deemed as therapeutic failures (non-responders). There was no difference in responders between licofelone and naproxen (p = 0.87). Responders had a significantly higher lysoPCs to PCs ratio than non-responders (0.097 ± 0.003 vs. 0.085 ± 0.003; p = 0.006). Patients with a ratio greater than the optimal cutoff of 0.088 had 2.93 times more likely to respond to licofelone and naproxen (p = 0.002).

CONCLUSIONS

Serum lysoPCs to PCs ratio is a marker for response to licofelone and naproxen and may aid in the personalized treatment to knee OA.