Professor Yoo Seung-ah of Catholic University of Korea College of Medicine Confirms World's First Detection of Microplastics in Rheumatoid Arthritis Synovial Fluid and Proves Their Harmfulness

A joint research team led by Professor Yoo Seung-ah of the Department of Biomedical Sciences at Catholic University of Korea College of Medicine, in collaboration with the POSTECH-Catholic University Biomedical Engineering Research Institute and Professor Kim Young-min of Daegu University, has confirmed for the first time worldwide that microplastics are actually present within the joints of rheumatoid arthritis patients. 

 Furthermore, the team scientifically elucidated the process by which these microplastics stimulate the immune system and exacerbate arthritis, drawing significant attention from the international academic community. This research, titled “Polystyrene microplastics activate NF-κB/MAPK signaling in synovial fibroblasts, promoting inflammation and joint destruction in rheumatoid arthritis,” was published in the Journal of Hazardous Materials (Impact Factor 11.3), a highly influential international journal in the field of environment and health.

 This collaborative research involved Professor Yoo Seung-ah (co-corresponding author) and Researcher Lee Soo-hyun (first author), Professor Kim Wan-wook from the POSTECH-Catholic University Bioengineering Research Institute (co-corresponding author), Professor Kim Young-min from the Department of Environmental Technology Engineering at Daegu University. Through a meticulous research strategy linking patient sample analysis, cell experiments, and animal model studies, the team comprehensively elucidated the immunotoxic effects of microplastics.

Rheumatoid arthritis is a representative autoimmune disease where the body's immune system mistakenly attacks its own tissues, causing chronic joint inflammation and damaging cartilage and bone. While research into genetic causes and immune responses has been active, scientific evidence regarding environmental factors that exacerbate the disease has been insufficient. The research team focused precisely on this unresolved area.

 The joint research team successfully conducted a precise analysis of ‘synovial fluid’ (joint fluid secreted by the synovium surrounding the joint) from rheumatoid arthritis patients. Using Py-GC/MS/MS, an advanced instrument capable of decomposing and measuring microplastic components for precise quantification, they successfully detected polystyrene microplastics (PS-MPs) – a plastic material widely used in household goods – in quantifiable amounts. This finding marks the world's first confirmation in rheumatoid arthritis tissue of the previously only-theoretical hypothesis that ‘microplastics can accumulate within bodily tissues’.

 This research goes beyond mere discovery. Using polystyrene microplastics (PS-MPs) – representative plastic particles measuring 5μm (micrometers) in size (significantly smaller than a human hair, which is about 70μm thick, enabling easy penetration into cells) – it systematically and meticulously analyzed how microplastics exacerbate arthritis, extending the investigation to include cell and animal model experiments. 

 In vitro experiments revealed that polystyrene microplastics internalized into rheumatoid arthritis patient-derived synovial fibroblasts (RA-FLS, cells lining the joint interior) activated the NF-κB and MAPK signaling pathways. This induced the expression of inflammatory cytokines (such as IL-6 and IL-8) and tissue-destructive enzymes (MMP3, MMP9), while also increasing cell motility and invasiveness. NF-κB and MAPK are signaling pathways that act as ‘switches’ regulating the inflammatory response; activation of these pathways leads to an explosive increase in inflammation.

 In animal experiments (in vivo), joint inflammation was markedly worsened in arthritis models chronically exposed to polystyrene microplastics. Furthermore, in a xenograft model (a model where cells or tissues from one species are transplanted into a genetically distinct host species, typically immunodeficient mice, to analyze the survival, function, and pathophysiological effects of the transplanted cells) showed significantly increased cartilage erosion and macrophage infiltration.

 In other words, this study is the first to demonstrate that microplastics are not merely ‘present’ but act as a factor that can exacerbate the pathogenesis of autoimmune diseases, going beyond being a simple environmental pollutant. It is regarded as pioneering research that will clarify the link between microplastics and chronic diseases.

 Professor Yoo Seung-ah stated, “This study is an immunotoxicology investigation that elucidates the effects of environmental exposure substances on human immune diseases at the level of immune cells and joint cells,” adding, “It is expected to contribute to developing strategies for removing or blocking microplastics and establishing environmental management guidelines to prevent disease progression.”

 This research is regarded not merely as an academic achievement but as the starting point for a paradigm shift connecting environmental issues and human health. Continued attention and research are needed to understand how the ubiquitous plastics around us, in invisible forms, can affect our bodies and diseases.

△In vitro and in vivo mechanisms by which polystyrene microplastics (PS-MPs) exacerbate rheumatoid arthritis pathology

 :PS-MPs are detected in the synovial fluid of rheumatoid arthritis patients, increase the expression of inflammatory cytokines and MMPs in patient-derived synovial fibroblasts, and promote cell motility and invasiveness. In vivo, prolonged PS-MP exposure exacerbates arthritis, and in a xenograft model using PS-MP-stimulated RA-FLS, increased cartilage destruction and macrophage infiltration occur.