Abstract
This study aimed at discriminating with sensitivity the toxicological effects of carbon dots (CDs) with various zeta potential (ζ) and charge density (Qek) in different cellular models of the human respiratory tract. One anionic and three cationic CDs were synthetized as follows: CD-COOH (ζ = −43.3 mV); CD-PEI600 (Qek = 4.70 µmol/mg; ζ = +31.8 mV); CD-PEHA (Qek = 3.30 µmol/mg; ζ = +29.2 mV) and CD-DMEDA (Qek = 0.01 µmol/mg; ζ = +11.1 mV). Epithelial cells (A549) and macrophages (THP-1) were seeded alone or as co-cultures with different A549:THP-1 ratios. The obtained models were characterized, and multiple biological responses evoked by CDs were assessed in the mono-cultures and the best co-culture model. With 14% macrophages, the 2:1 ratio co-culture best mimicked the in vivo conditions and responded to lipopolysaccharides. The anionic CD did not induce any effect in the mono-cultures nor in the co-culture. Among the cationic CDs, the one with the highest charge density (CD-PEI600) induced the most pronounced responses whatever the culture model. The cationic CDs of low charge density (CD-PEHA and CD-DMEDA) evoked similar responses in the mono-cultures, whereas in the co-culture, the three cationic CDs ranked according to their charge density (CD-PEI600 > CD-PEHA > CD-DMEDA), when taking into account their inflammatory effect. Thus, the co-culture system developed in this study appears to be a sensitive model for finely discriminating the toxicological profile of cationic nanoparticles differing by the density of their surface charges.
Highlights
The production of manufactured nanoparticles (NPs) raises genuine concerns about health risks, especially by inhalation [1,2]
The surface charge density of the cationic carbon dots (CDs) increased with the nitrogen content of the passivation agent used for their synthesis, with the Qek value ranging from 0.01 μmol/mg for CD-dimethylethylene diamine (DMEDA) to
If the anionic CD did not induce any cytotoxic effect, we provided a ranking of the toxicity of the three cationic CDs that parallels their positive surface charge density, i.e., CD-PEI600 >> CD-pentaethylene hexamine (PEHA) > CD-DMEDA, with no toxicity of CD-DMEDA
Summary
The production of manufactured nanoparticles (NPs) raises genuine concerns about health risks, especially by inhalation [1,2]. In vivo studies have provided valuable information on NP deposition and toxicological effects in the lung [3,4]. Inhaled NPs were shown to deposit all throughout the airways, and to accumulate in the alveoli [4], where they are internalized by epithelial cells and macrophages [5]. Lung tissue inflammation and remodeling were reported in rodents upon inhalation or lung instillation of NPs [5,6,7]. Animal studies are costly, time-consuming and should be reduced in accordance with the 3R principle. Cellular and molecular mechanisms involved in NP toxicity cannot be studied in vivo [9]. Over the last years, several in vitro models have been developed to investigate on the safety of NPs [10,11]
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