A promising novel aquatic model for assessing cellular and physiological response to personal care product additives

Originating from the Pacific Ocean, the pearl oyster Pinctada imbricata (Röding, 1798) stands as one of the first “Lessepsian migrants” to reach the Mediterranean Sea via Suez. Since the 2000s, the species has established a successful population in the transitional waterways of the “Capo Peloro Lagoon natural reserve”, exhibiting exceptional abundance owing to its remarkable adaptability across various hydrological, climatic, environmental, and pollution conditions. With reference to recent studies1,2 and considering its biological traits, P. imbricata appears to embody the qualities of an effective bioindicator and model organism for ecotoxicological investigations. The relevance of the availability of suitable bioindicators and model organisms stems from the growing awareness of identifying and addressing stress conditions that affect aquatic ecosystems, primarily due to human-induced pressures. Effectively, aquatic ecosystems are among the main target environments for biomonitoring strategies, as they represent one of the main receptors of pollutants. For instance, the COVID-19 pandemic has increased the use of personal hygiene products, containing compounds, e.g. preservatives, that may threaten aquatic ecosystems. Preservatives include various categories including quaternary ammonium compounds (QACs), recognized for their ability to withstand metabolic degradation and persistence in wastewater due to their lipophilic nature. Among QACs is quaternium-15, which is widely incorporated in various personal care products (PCPs). Therefore, this study aims to assess the physiological and cellular responses of P. imbricata's haemocytes to different concentrations of quaternium-15 (0.1 and 1 mg L-1) in vitro, to determine the suitability of the species as an experimental model in ecotoxicological studies and the toxicity of the substance. The investigation included cell viability and phagocytosis assays, along with modulation of γ-actin (γAct) and oxidative stress-related gene expression (Cat, MnSod, Zn/CuSod, GPx). Findings revealed a significant reduction in haemocyte viability and phagocytosis activity after exposure to both concentrations. The decreasing phagocytosis activity was also supported by the gene expression modulation of γAct, which is involved in cytoskeleton rearrangement. The qPCR data revealed significant alterations in the antioxidant response, resulting in the upregulation of Cat and GPx and the downregulation of MnSod and Zn/CuSod. These data indicate that exposure to quaternium-15 caused harmful effects on the immune-mediated response of haemocytes, which act as the primary defence mechanism for bivalve molluscs against xenobiotics. Additionally, there is evidence of a time and dose-dependent response, highlighting the importance of exploring sustainable alternatives to replace harmful additives in PCPs and promoting P. imbricata as a valuable model for future ecotoxicological studies. 1Kuchel, R.P., et al. (2010). Haemocyte morphology and function in the Akoya pearl oyster, Pinctada imbricata. J. Invertebr. Pathol., 105(1), 36-48. 2Pagano, M., et al. (2023). A first insight into haemocytes of Pinctada imbricata radiata: A morpho‐functional characterization. Micros. Res. Techniq., 86(3), 368-377.