Aims: Due to its increasing production, durability and multiple applications, plastic is a material we encounter every day. Small plastic particles from the µm to the mm range are classified as microplastics and produced for cosmetic and medical products, but are also a result of natural erosion and decomposition of macroplastics. Although being omnipresent in our environment and already detected in various organisms, less is known about the effects of microplastics on humans in general, or on vascular biology in particular. Here we investigated the effects of carboxylated polystyrene (PS) microplastic particles (1 µm) on murine endothelial and immune cells, which are both crucially involved in vascular inflammation, using in vitro and in vivo approaches.

Methods: Murine monocytic J774A.1 cells and endothelial MyEND cells were stimulated with PS particles for 3 and 6 hours (n=7-10). mRNA and protein levels were analyzed using real-time PCR and ELISA. Adhesion assays were performed incubating confluent MyEND cells with PS particles for 16 hours and Calcein-AM labelled J774A.1 for 1 hour (static and flow). Adherent J774A.1 were detected by fluorescence microscopy (n=6). C57BL/6J wild type mice were injected with TRITC-conjugated PS i.v. (n=6/group). After 3 hours, MPPs were localized in blood and liver using IHC staining.

Results: In J774A.1 cells, PS particles induced Il1-β and Tnf-a mRNA expression and TNF-a protein release. In MyEND cells, PS particles up-regulated Icam-1 and Vcam-1 mRNA expression and sVCAM-1 protein release. Investigating cell adhesion, more adherent J774A.1 cells were detected on endothelial monolayer after PS particle stimulation under static as well as flow conditions. In vivo, PS particles taken up by Ly6G-positive cells were detected in the peripheral blood, identifying neutrophils as PS particles-clearing leukocytes. PS particles accumulated in the liver, accompanied by a strong up-regulation of the acute phase proteins Saa1, Saa2 and Saa3. Moreover, Aortic tissue from mice injected with MPPs showed enhanced Il-1β and Vcam-1 expression.

Conclusion: Our data show that PS are able to activate the endothelium with subsequent monocyte adhesion, representing a hallmark of vascular inflammation. Thus, microplastics need to be evaluated as a potential novel environmental risk factor for endothelial inflammation.