Density of surface charge is a more predictive factor of the toxicity of cationic carbon nanoparticles than zeta potential

Abstract

Background A positive surface charge has been largely associated with nanoparticle (NP) toxicity. However, by screening a carbon NP library in macrophages, we found that a cationic charge does not systematically translate into toxicity. To get deeper insight into this, we carried out a comprehensive study on 5 cationic carbon NPs (NP2 to NP6) exhibiting a similar zeta (ζ) potential value (from + 20.6 to + 26.9 mV) but displaying an increasing surface charge density (electrokinetic charge, Qek from 0.23 to 4.39 µmol/g). An anionic and non-cytotoxic NP (NP1, ζ-potential = − 38.5 mV) was used as control. Results The 5 cationic NPs induced high (NP6 and NP5, Qek of 2.95 and 4.39 µmol/g, respectively), little (NP3 and NP4, Qek of 0.78 and 1.35 µmol/g, respectively) or no (NP2, Qek of 0.23 µmol/g) viability loss in THP-1-derived macrophages exposed for 24 h to escalating NP dose (3 to 200 µg/mL). A similar toxicity trend was observed in airway epithelial cells (A549 and Calu-3), with less viability loss than in THP-1 cells. NP3, NP5 and NP6 were taken up by THP-1 cells at 4 h, whereas NP1, NP2 and NP4 were not. Among the 6 NPs, only NP5 and NP6 with the highest surface charge density induced significant oxidative stress, IL-8 release, mitochondrial dysfunction and loss in lysosomal integrity in THP-1 cells. As well, in mice, NP5 and NP6 only induced airway inflammation. NP5 also increased allergen-induced immune response, airway inflammation and mucus production. Conclusions Thus, this study clearly reveals that the surface charge density of a cationic carbon NP rather than the absolute value of its ζ-potential is a relevant descriptor of its in vitro and in vivo toxicity.

A Co-Culture Model of the Human Respiratory Tract to Discriminate the Toxicological Profile of Cationic Nanoparticles According to Their Surface Charge Density

“…In the literature, a greater toxicity of positive CDs compared to negative ones was reported [38,49,50]. However, our group also recently demonstrated that a positive zeta potential for NPs does not necessarily translate into toxicity, and that the surface charge density of NPs influences their toxicity as well [39], which is confirmed in this present study. Regarding the cellular models, the viability loss induced by CD-PEI600 and CD-PEHA was greater in THP-1 than in A549 mono-cultures.…”

“…Applied to our safety study on cationic CDs with increasing charge density, this is particularly relevant since only the co-culture model allowed us to find that CDs of medium (CD-PEHA) and low (CD-DMEDA) positive surface charge density could induce a pro-inflammatory response, with a greater effect for CD-PEHA compared to CD-DMEDA. If our previous work had already showed an inflammatory effect for cationic CDs with a high positive charge density [39], we report here for the firsttime a pro-inflammatory potential for cationic CDs of lower charge density. By using the co-culture model developed in this work, we also showed that the inflammatory response induced by cationic CD is hierarchically related to the surface charge density of these NPs.…”

“…Zeta potential was measured by DLS as well and calculated with the Smoluchowski's equation. All measurements were performed in triplicate on fresh samples (1.0 mg/mL in 1.5 mM NaCl pH 7.4) at 25 • C. The surface charge density of CDs was determined by means of polyelectrolyte titration as described elsewhere [39]. In brief, the electrokinetic charge (Q ek ) of the CDs was determined by monitoring zeta potential variation in the sample (1.0 mg/mL, NaCl 1.5 mM pH 7.4) alongside spiking with a solution of poly(acrylic acid) (PAA, MW ± 1800 Da, NaCl 1.5 mM pH 7.4).…”

“…However, our group recently demonstrated that a cationic charge does not systematically confer toxicity to NPs [ 38 ]. In an original way, we have highlighted that the surface charge density of a cationic NP is more predictive of its toxicity than the absolute value of its zeta potential (ζ) [ 39 ]. Thus, in the present work, in order to reinforce these new data concerning the role of surface charge density in the toxicity of cationic NPs, we exposed our mono- and co-culture models to three cationic CDs exhibiting an increasing quantity of amino groups at their periphery, i.e., increasing surface charge density.…”

Characterization and Optimization of Chitosan-Coated Polybutylcyanoacrylate Nanoparticles for the Transfection-Guided Neural Differentiation of Mouse Induced Pluripotent Stem Cells

“…Therefore, taking all these factors together, 0.01% (w/v) HMWC was chosen as the coating agent for PS80 PBCA NP. The effect of chitosan-coating on the cytotoxicity of the PS80 PBCA NP is intriguing, although cationic nanoparticles are known to elicit membrane-permeabilizing effects that can irreversibly lead to cell damage and death [44], the exact structural conformation on the distribution of electric charge in the presence of PS80 PBCA NP, and together with the modification of electric charge by the interacting medium components as the protein corona evolves, may exert a stronger influence on its final cytotoxicity profile [45,46]. Additional factors other than electric charge can augment the cellular responses to nanoparticles, for example, the cytotoxicity of nanoparticles charge-modified by coating with chitosan has been shown to be dependent on the core material and stability of the coated nanoparticle, and the cell type and growth characteristics rather than the electric charge of chitosan alone [47,48].…”