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. 2016 Jun 9;7:11770.
doi: 10.1038/ncomms11770.

Dynamic Protein Coronas Revealed as a Modulator of Silver Nanoparticle Sulphidation in Vitro

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Dynamic Protein Coronas Revealed as a Modulator of Silver Nanoparticle Sulphidation in Vitro

Teodora Miclăuş et al. Nat Commun. .
Free PMC article

Abstract

Proteins adsorbing at nanoparticles have been proposed as critical toxicity mediators and are included in ongoing efforts to develop predictive tools for safety assessment. Strongly attached proteins can be isolated, identified and correlated to changes in nanoparticle state, cellular association or toxicity. Weakly attached, rapidly exchanging proteins are also present at nanoparticles, but are difficult to isolate and have hardly been examined. Here we study rapidly exchanging proteins and show for the first time that they have a strong modulatory effect on the biotransformation of silver nanoparticles. Released silver ions, known for their role in particle toxicity, are found to be trapped as silver sulphide nanocrystals within the protein corona at silver nanoparticles in serum-containing cell culture media. The strongly attached corona acts as a site for sulphidation, while the weakly attached proteins reduce nanocrystal formation in a serum-concentration-dependent manner. Sulphidation results in decreased toxicity of Ag NPs.

Figures

Figure 1
Figure 1. Silver sulphide forms close to the surface of Ag NPs.
TEM image with arrows highlighting nano-Ag2S (a, scale bar 50 nm), X-rays elemental mapping of Ag (red), S (blue, with white rings marking the approximate contour of the Ag NPs) and overlaid Ag and S (b), EDS spectrum—with arrows pointing at the peaks corresponding to each element—(c) and diffraction pattern—arrow pointing at the diffraction line corresponding to monoclinic Ag2S—(d) of silver nanocubes after 7 days incubation in RPMI-1640 supplemented with 1% FBS and formation of Ag2S at the surface of the Ag NPs.
Figure 2
Figure 2. Protein coronas modulate sulphide formation.
Proposed mechanism of protein corona-modulated nano-Ag2S formation at Ag NPs, with hard corona proteins trapping Ag+ released from the nanoparticle surface and soft corona proteins transporting said ions away from the sulphide-formation centres in the long-lived corona (a); TEM images of silver nanocubes after 24 h in RPMI-1640 cell culture medium supplemented with 1% FBS (b), followed by 6 days incubation in RPMI-1640 with 0% FBS (inset cartoon showing only hard corona around Ag NPs) (c), 1% FBS (d) or 10% FBS (e; common inset cartoon showing hard and soft coronas, as well as free bulk proteins around Ag NPs); TEM images of silver nanocubes after 7 days incubation in RPMI-1640 with 0.4 mg ml−1 BSA (f) or 4 mg ml−1 BSA (g) (common inset cartoon showing hard corona and free bulk proteins around Ag NPs); Ultraviolet–visible spectra of cubic (h) and quasi-spherical (i) Ag NPs after 24 h incubation in RPMI-1640 cell culture medium supplemented with 1, 10 or 50% FBS; TEM images of silver nanocubes after 24 h in RPMI-1640 supplemented with 1% FBS (j), 10% FBS (k) and 50% FBS (l). Scale bars are 100 nm (b, jl) or 50 nm (cg).
Figure 3
Figure 3. Silver nanoparticle dissolution is involved in nano-Ag2S formation.
Ultraviolet–visible full spectra of quasi-spherical Ag NPs (a) and quadrupole peak detail of nanocubes (b) incubated (1 day: blue or 7 days: pink) in RPMI-1640 cell culture medium supplemented with 1% FBS, with or without added extra 10% (by mass) Ag+ ions from AgNO3; EDS spectra of the supernatant obtained after centrifugation of Ag NPs incubated for 7 days in RPMI-1640 with 1% FBS, before (c) and after (d) spiking with 5 nm PVP-coated Ag NPs, with dotted red line highlighting the presence of a silver signal only in the spiked sample.
Figure 4
Figure 4. Sulphur sources and the Ag:S ratio influence Ag2S formation.
TEM images of Ag NPs after 7 days incubation in PBS (a), PBS supplemented with 1% FBS (b) and PBS supplemented with L-cysteine and L-methionine at the same concentrations of amino acids as those found in RPMI-1640 (c) and corresponding EDS spectra (d); TEM images and corresponding EDS spectra (insets) of Ag NPs after 7 days incubation in RPMI-1640 supplemented with 1% FBS, with initial silver concentrations of 2 μg ml−1 (e), 10 μg ml−1 (f) and 100 μg ml−1 (g), with elemental mapping images provided in Supplementary Fig. 26. Scale bars are 100 nm (ac) or 50 nm (eg).
Figure 5
Figure 5. Corona-mediated sulphidation of Ag NPs impacts particle toxicity.
TEM images of partially sulphidated Ag NPs after pre-incubation in RPMI-1640 with 10% FBS (a) and completely sulphidated Ag NPs after pre-incubation in RPMI-1640 with 1% FBS (b); scale bars are 50 nm; Viability of J774 murine macrophages (as measured with MTT assays) after 24 h exposure to various concentrations (2, 5, 10, 15, 25, 50 and 100 μg ml−1) of Ag+ ions (black diamonds), pristine Ag NPs (red triangles), partially sulphidated Ag NPs (blue squares) and completely sulphidated Ag NPs (orange circles); error bars are provided as standard deviation; statistically significant differences (two-tailed t-test, with all data sets showing normal distribution and similar variance values) as compared with the control are marked with **P<0.005 or ***P<0.0005 (n=6), with all the P values available in Supplementary Table 7 (c); release profiles of TNFα (d) and MIP-2 (e) after 24 h exposure of J774 macrophages to various concentrations (2, 5, 10, 15, 25, 50 and 100 μg ml−1) of pristine (red), partially sulphidated (blue) and completely sulphidated (orange) Ag NPs; the missing concentrations of TNFα and MIP-2 after exposure to pristine Ag NPs are above the measuring limit (see calibration curves in Supplementary Fig. 29).

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