Unveiling the pharmacological mechanisms of Spirulina platensis in rheumatoid arthritis rats through the integration of serum metabolomics, pathways analysis, and experimental validation

Rheumatoid arthritis (RA) is an autoimmune disease primarily manifested by insistent proliferative synovitis, joint degradation, and bone erosions with no targeted therapy yet. Spirulina platensis serves as a treasure house of bioactive compounds with potential significance against different inflammatory ailments. Inspired by the potentiating biological attributes of S. platensis, the current investigation is concerned with dissecting the mechanistic basis of S. platensis against rheumatoid arthritis (RA) through a series of biochemical and histopathological assessments integrated with a serum metabolomics strategy to explore more efficacious and safe alternative therapies to rectify RA. Firstly, a rat model of RA was established using complete Freund's adjuvant (CFA), and RA-related biochemical and histopathological scores were determined as monitoring indexes for control efficiency of S. platensis against RA. Serum metabolomics was adopted to profile the potential biomarkers and their corresponding metabolic pathways modulated by Spirulina through UPLC-MS/MS analysis integrated with chemometrics and MetaboAnalyst 5.0 pathway analysis. The results demonstrated that Spirulina exerted significantly modulatory effects in the CFA model by reducing systemic manifestations of oxidative stress, inflammation, and impaired liver and kidney functions typically exemplified by catalase (CAT), superoxide dismutase (SOD), reduced glutathione (GSH), rheumatoid factor (RF), monocyte chemotactic protein 1 (MCP-1), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6), as well as alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine, and urea. Histopathological investigations have revealed that Spirulina intervention causes moderately lower inflammatory cells infiltrations, synovial hyperplasia, and cartilage destruction. Regarding serum metabolomics, Spirulina could remarkably reverse disordered RA-associated metabolites, namely glutamic acid, arachidonic acid, 5-hydroxyeicosatetraenoic acid, (20:4/18:0) phosphatidylcholine, and citric acid, to a normal-like state through modulating arachidonic acid metabolism, alanine, aspartate and glutamate metabolism, and citrate cycle pathways putatively implicated in inflammation and joint damage. Our findings provide compelling evidence that S. platensis possesses a broad spectrum of mechanisms to restore the disrupted homeostasis in RA by multi-targeted, synergistic actions.