Cationic amino acid transporter-1 (CAT-1) promotes fibroblast-like synoviocyte proliferation and cytokine secretion by taking up L-arginine in rheumatoid arthritis

Surface saturation of drug-loaded hollow manganese dioxide nanoparticles with human serum albumin for treating rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease accompanied by energy depletion and accumulation of reactive oxygen species (ROS). Inorganic nanoparticles (NPs) offer great promise for the treatment of RA because they mostly have functions beyond being drug carriers. However, conventional nanomaterials become coated with a protein corona (PC) or lose their cargo prematurely in vivo, reducing their therapeutic efficacy. To avoid these problems, we loaded methotrexate (MTX) into hollow structured manganese dioxide nanoparticles (H-MnO2 NPs), then coated them with a 'pseudo-corona' of human serum albumin (HSA) at physiological concentrations to obtain HSA-MnO2@MTX NPs. Efficacy of MTX, MnO2@MTX, and HSA-MnO2@MTX NPs was compared in vitro and in vivo. Compared to MnO2@MTX, HSA-coated NPs were taken up better by lipopolysaccharide-activated RAW264.7 and were more effective at lowering levels of pro-inflammatory cytokines and preventing ROS accumulation. HSA-MnO2@MTX NPs were also more efficient at blocking the proliferation and migration of fibroblast-like synoviocytes from rats with collagen-induced arthritis. In this rat model, HSA-MnO2@MTX NPs showed better biodistribution than other treatments, specifically targeting the ankle joint. Furthermore, HSA-MnO2@MTX NPs reduced swelling in the paw, regulated pro-inflammatory cytokine production, and limited cartilage degradation and signs of inflammation. These results establish the therapeutic potential of HSA-MnO2@MTX NPs against RA.

Comprehensive review of amino acid transporters as therapeutic targets

The solute carrier (SLC) family, with more than 400 membrane-bound proteins, facilitates the transport of a wide array of substrates such as nutrients, ions, metabolites, and drugs across biological membranes. Amino acid transporters (AATs) are membrane transport proteins that mediate transfer of amino acids into and out of cells or cellular organelles. AATs participate in many important physiological functions including nutrient supply, metabolic transformation, energy homeostasis, redox regulation, and neurological regulation. Several AATs have been found to significantly impact the progression of human malignancies, and dysregulation of AATs results in metabolic reprogramming affecting tumor growth and progression. However, current clinical therapies that directly target AATs have not been developed. The purpose of this review is to highlight the structural and functional diversity of AATs, the molecular mechanisms in human diseases such as tumors, kidney diseases, and emerging therapeutic strategies for targeting AATs.

Metabolic changes in fibroblast-like synoviocytes in rheumatoid arthritis: state of the art review

Fibroblast-like synoviocytes (FLS) are important components of the synovial membrane. They can contribute to joint damage through crosstalk with inflammatory cells and direct actions on tissue damage pathways in rheumatoid arthritis (RA). Recent evidence suggests that, compared with FLS in normal synovial tissue, FLS in RA synovial tissue exhibits significant differences in metabolism. Recent metabolomic studies have demonstrated that metabolic changes, including those in glucose, lipid, and amino acid metabolism, exist before synovitis onset. These changes may be a result of increased biosynthesis and energy requirements during the early phases of the disease. Activated T cells and some cytokines contribute to the conversion of FLS into cells with metabolic abnormalities and pro-inflammatory phenotypes. This conversion may be one of the potential mechanisms behind altered FLS metabolism. Targeting metabolism can inhibit FLS proliferation, providing relief to patients with RA. In this review, we aimed to summarize the evidence of metabolic changes in FLS in RA, analyze the mechanisms of these metabolic alterations, and assess their effect on RA phenotype. Finally, we aimed to summarize the advances and challenges faced in targeting FLS metabolism as a promising therapeutic strategy for RA in the future.

L-arginine metabolism inhibits arthritis and inflammatory bone loss

OBJECTIVES

To investigate the effect of the L-arginine metabolism on arthritis and inflammation-mediated bone loss.

METHODS

L-arginine was applied to three arthritis models (collagen-induced arthritis, serum-induced arthritis and human TNF transgenic mice). Inflammation was assessed clinically and histologically, while bone changes were quantified by μCT and histomorphometry. In vitro, effects of L-arginine on osteoclast differentiation were analysed by RNA-seq and mass spectrometry (MS). Seahorse, Single Cell ENergetIc metabolism by profilIng Translation inHibition and transmission electron microscopy were used for detecting metabolic changes in osteoclasts. Moreover, arginine-associated metabolites were measured in the serum of rheumatoid arthritis (RA) and pre-RA patients.

RESULTS

L-arginine inhibited arthritis and bone loss in all three models and directly blocked TNFα-induced murine and human osteoclastogenesis. RNA-seq and MS analyses indicated that L-arginine switched glycolysis to oxidative phosphorylation in inflammatory osteoclasts leading to increased ATP production, purine metabolism and elevated inosine and hypoxanthine levels. Adenosine deaminase inhibitors blocking inosine and hypoxanthine production abolished the inhibition of L-arginine on osteoclastogenesis in vitro and in vivo. Altered arginine levels were also found in RA and pre-RA patients.

CONCLUSION

Our study demonstrated that L-arginine ameliorates arthritis and bone erosion through metabolic reprogramming and perturbation of purine metabolism in osteoclasts.

Regulated Arginine Metabolism in Immunopathogenesis of a Wide Range of Diseases: Is There a Way to Pass between Scylla and Charybdis?

More than a century has passed since arginine was discovered, but the metabolism of the amino acid never ceases to amaze researchers. Being a conditionally essential amino acid, arginine performs many important homeostatic functions in the body; it is involved in the regulation of the cardiovascular system and regeneration processes. In recent years, more and more facts have been accumulating that demonstrate a close relationship between arginine metabolic pathways and immune responses. This opens new opportunities for the development of original ways to treat diseases associated with suppressed or increased activity of the immune system. In this review, we analyze the literature describing the role of arginine metabolism in the immunopathogenesis of a wide range of diseases, and discuss arginine-dependent processes as a possible target for therapeutic approaches.

PINK1/Parkin-Mediated Mitochondrial Autophagy Participates in H2O2-Induced Abnormal Proliferation of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis

Introduction

To explore the role of PINK1/Parkin-mediated mitochondrial autophagy in H₂O₂-induced abnormal proliferation of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS).

Methods

Firstly, we isolated fibroblast like synoviocytes (RA-FLS) from RA patients. H₂O₂-induced oxidative stress, and NAC (a ROS inhibitor) or FCCP (a mitochondrial autophagy activator) treatment inhibited ROS level or activate mitochondrial autophagy in RA-FLS. MitoSOX Red, JC-1 kit, DCFH-DA kit and CCK8 kit were used to evaluate mitochondrial redox status, mitochondrial membrane potential, intracellular ROS level and cell activity, respectively. Western blot was used to detect the protein expression. The rat model of Freund's complete adjuvant arthritis (AA) was established and treated with NAC and FCCP, respectively. The pathological changes of synovium and the percentage of apoptotic cells in synovium were detected by H&E and TUNEL staining, respectively.

Results

We have successfully isolated synovial cells from RA patients. Using 5μM H₂O₂ to stimulate RA-FLS could induce mitochondrial abnormalities of RA-FLS and inhibit RA-FLS autophagy. FCCP could reverse the effect of H₂O₂ on RA-FLS cell proliferation and apoptosis. NAC could reverse the effect of H₂O₂ on PINK1/Parkin. Overexpression of PINK1 or Parkin reversed the effect of H₂O₂ on RA-FLS mitochondrial autophagy, proliferation and apoptosis. The in vivo experiment results showed that both NAC and FCCP could prevent the pathogenesis of RA, reduce RA-FLS cell viability and increase RA-FLS cell apoptosis.

Conclusion

The PINK1/Parkin-mediated mitochondrial autophagy participates in H₂O₂-induced abnormal proliferation of RA-FLS, and targeting of PINK1/Parkin-mediated mitochondrial autophagy may be the key mechanism in the treatment of RA.