AB1529 MICROPLASTIC POLLUTION IN SYNOVIAL FLUID SAMPLES FROM SWOLLEN JOINTS ANALYZED WITH RAMAN SPECTROSCOPY

<h3>Background</h3> Microplastics (MPs) have been identified in different types of tissue, including lung, bowel, placenta and as well in human whole blood [1]. During analysis of synovial fluid samples with Raman spectroscopy with the purpose of identification of crystals related to crystallopathies, presence of multiple types of MPS have been identified. Due to the recent interest in the effect of plastic pollution on human health, the noticed presence of these particles in synovial fluid samples is concerning and worthy of our attention. <h3>Objectives</h3> The objective of this study was to characterize deposited MPs in samples drawn from arthritis patients presenting to our rheumatology outpatient clinic, with the aim of calculating their prevalence and estimate the significance of their presence against blank control samples as we are using a novel and highly sensitive technique of integrated Raman spectroscopy with Polarized light microscopy in routine clinical practice. <h3>Methods</h3> This is an analysis of Raman spectroscopic data retrieved from 156 synovial fluid samples drawn from a consecutive series of patients visiting our outpatient clinic. Data was compared against a series of blank samples of MiliQ processed in similar fashion. The number of required blank samples was calculated with the formula of Rosner (2011, [2]), the study population was compared against the controls with a Chi-Square test. <h3>Results</h3> A total of 96 MPs were identified, in 4 distinct types; polyethylene (PE), polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET). A total of 44 samples (28.2%) were positive for one or more particle (Figure 1). 19 (12.2%) samples had one identified MP, 15 (9.6%) had two identified MP, and 10 (6.4%) had three or more identified MPs (Figure 3). Combinations of MPs were present in 7 of 22 samples (31.8%) with more than one MP. Most MPs were identified extracellular, although one case of intracellular polyethylene particles was identified. The incidence in MPs in the study population was 30.8%. With an alpha (significance level) of 0.05 and a power of 90%, 10 blanks control samples would be enough to find a significant difference if in none of these samples particles are identified. However, we identified one or more microplastics in 4 (40%) of the 10 samples. Polyethylene was identified in 3 samples (30%), polypropylene in 1 (10%), and polyethylene terephthalate in 1 (10%). 1 (10%) sample had a combination of plastic types. With a threshold of 1 or more identified MPs considered positive, there is no significant difference (p = 0.542) between the blank controls and the patient sample population. <h3>Conclusion</h3> Due to numeric presence of extracellular microplastics in both patient material as the blank control samples we define that the presence of one or two MPs in a synovial fluid sample from a swollen joint is not significant and probably of no clinical importance. For the determination whether a higher number of extracellular MPs can be significant and of potential clinical relevance, more control samples are to be measured. The interpretation of the presence of intracellular microplastics needs further investigation. <h3>References</h3> [1]Leslie, H.A., M.J.M. van Velzen, S.H. Brandsma, et al., Discovery and quantification of plastic particle pollution in human blood. Environment International, 2022. 163: p. 107199. [2]Rosner, B., Fundamentals of biostatistics. 2011: Seventh edition. Boston: Brooks/Cole, Cengage Learning, [2011] ©2011. <h3>Acknowledgements</h3> We want to thank ReumaNederland for funding our research. <h3>Disclosure of Interests</h3> Tom Niessink: None declared, Matthijs Janssen Shareholder of: Human Crystal Research B.V., Tim Jansen Shareholder of: Human Crystal Research B.V., Cees Otto Shareholder of: Hybriscan Technologies B.V.