Lipidomic analysis of mussel hemocytes exposed to polystyrene nanoplastics.

Leroux N, Hosseinzadeh M, Katsumiti A, Porte C, and Cajaraville MP. (2022) Lipidomic analysis of mussel hemocytes exposed to polystyrene nanoplastics. Environmental Research

Micro-plastics and nanoplastics are typically formed when plastics enter the environment then are fragmented by solar radiation, temperature, waves, wind, and biotic factors. However, they are also intentionally produced for cosmetics and nanomedicine, then reach the environment through wastewater or through incidents in their production, transport, or recycling. Once these very small plastics reach the environment they can be taken up by aquatic organisms and accumulate in the guts and gills as well as enter their circulatory system and reach other organs. As mussels are sessile filter feeders, they are the best choice when assessing the effects of pollutants in their environment. Uptake of micro-plastics and nanoplastics has a number of negative effects in these bivalves including reduced filtering activity, altering feeding, lipid peroxidation and oxidative damage, neurotoxicity, genotoxicity, and immune responses to name a few. Although these effects are well known, the specific mechanisms behind toxicity are not. Leroux et al were interested in determining how polystyrene nanoplastics alter the lipidome and the resultant immune response using mussel hemocytes, the first line of immune defense in bivalves against pathogens and foreign particles.

Hemocytes were cultured from mussels (Mytilus galloprovincialis) from a clean site in Plentzia Bay of Biscay. The cells were exposed to 10^6 and 10^9 particles/mL of 50 (nanoplastic size) and 500 nm (micro-plastic size) polystyrene plastic for 24 hours since this exposure concentration and time had been shown to cause cellular responses previously. Flow injection analysis was used to determine lipid levels in extracts from both control hemocytes and the plastic-treated cells. The 50 nm and 500 nm treated hemocytes were found to have reduced membrane lipids including phosphatidylcholines, choline plasmalogens, and phosphatidylinositols as well as triglycerides, but only the choline plasmalogens were statistically significant. Interestingly, when they looked for changes in the levels found in the culture medium after treatment, there was a trend towards increased lipid levels after exposure to 500 nm nanoplastics.

With the increase in micro-plastics and nanoplastics being produced and finding their way into the environment, we are slowly learning about the layers of effects this has. It has been previously demonstrated that these plastics are taken up by aquatic organisms and accumulate systemically and this has distinct effects, but the mechanisms behind this toxicity are not well known. Lipid metabolism is known to be affected by the accumulation of nanoplastics, therefore Leroux et al wanted to determine how the uptake of nanoplastics alters the lipidome in mussel hemocytes. In previous work, they showed that both sizes of plastics tested in this study were taken up by the hemocytes, however they did not use column separation and were not able to complete a detailed description of the lipidome in the control or treated hemocytes. Even with this drawback Leroux et al were able to show some differences between the groups, specifically the downregulation of membrane lipids, which could indicate a reorganization of the membrane with exposure to the nanoplastics and potential oxidation of plasmalogens, a class of lipid with a vinyl-ether bond. These findings highlight a real concern with the growing levels of plastics in the environment. Plastic pollution is obviously causing negative effects on the wildlife in these environments and could alter their ability to survive through reducing their immune function and altering host/pathogen interactions. Further work with a more detailed lipid analysis is needed to fully conclude on the effects of micro-plastics and nanoplastics and their exact effects in aquatic animals.