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The effect of the serum corona on interactions between a single nano-object and a living cell

View Article: PubMed Central - PubMed

ABSTRACT

Nanoparticles (NPs) which enter physiological fluids are rapidly coated by proteins, forming a so-called corona which may strongly modify their interaction with tissues and cells relative to the bare NPs. In this work the interactions between a living cell and a nano-object, and in particular the effect on this of the adsorption of serum proteins, are directly examined by measuring the forces arising as an Atomic Force Microscope tip (diameter 20 nm) - simulating a nano-object - approaches and contacts a cell. We find that the presence of a serum protein corona on the tip strongly modifies the interaction as indicated by pronounced increase in the indentation, hysteresis and work of adhesion compared to a bare tip. Classically one expects an AFM tip interacting with a cell surface to be repelled due to cell elastic distortion, offset by tip-cell adhesion, and indeed such a model fits the bare-tip/cell interaction, in agreement with earlier work. However, the force plots obtained with serum-modified tips are very different, indicating that the cell is much more compliant to the approaching tip. The insights obtained in this work may promote better design of NPs for drug delivery and other nano-medical applications.

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Related in: MedlinePlus

Statistical results of (a) Amount of indentation (nm), (b) hysteresis (J) and (c) work of adhesion (J) for Group I measured in M (grey) and Group II measured in ComM (black). The data are presented as mean ± standard error. The results presented for each groups are based on a 100 or more independent force profiles per group (Materials and Methods).
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f6: Statistical results of (a) Amount of indentation (nm), (b) hysteresis (J) and (c) work of adhesion (J) for Group I measured in M (grey) and Group II measured in ComM (black). The data are presented as mean ± standard error. The results presented for each groups are based on a 100 or more independent force profiles per group (Materials and Methods).

Mentions: The average modulus of a cell depends on the particular cell type. While the modulus value can vary locally when the cell is probed with a sharp tip, the average value taken over many cells and many contact points should be similar and constant, within the scatter, for that given cell type. As the modulus is an internal cellular property that depends largely on the cytoskeleton structure, it should not be affected by tip coating such as the serum protein corona. As all cells were cultured under identical conditions, those incubated in serum and those without serum during the measurements should have the same overall modulus; indeed, it has been shown49 that the presence or absence or serum proteins does not affect the overall cell modulus over periods shorter than 3 days. We thus extracted the effective modulus E* = 1.3 kPa of our cells from the Group I results as noted above, and attempted to use this value for fitting the data of group II, as it appears in Fig. 3(B), to Eq. 1 with a single fitting parameter γa (we substitute a value E* = 1.3 kPa into Equation (1).) However, there is no value of the adhesion energy which, taken together with this cell modulus, can fit the observed force profiles. This implies that the picture suggested in the inset to Fig. 3(A) and the corresponding Eq. (1), cannot represent what is happening when proteins are present both on the tip as well as in the surrounding medium. Moreover, we have compared values of: 1. average indentation 2. amount of hysteresis and 3. work of adhesion. These average results (based on over a hundred profiles, Materials and Methods) are presented as histograms in Fig. 6, and in Table S1 in the SI. Comparing groups I and II, the average values of the three parameters are clearly very different, differences which remain highly significant even when the scatter is accounted for (p < 0.001 in the Kruskal-Wallis test, see also Materials and Methods). While the average indentation, amount of hysteresis and the work of adhesion measured in group II are 1179 nm and 7.96 × 10−18 J and 6.18 × 10−17 J respectively, the values for Group I are about 3–4 times smaller. The variance of the results is considered in more detail in SI. The results of all three parameters thus indicate consistently that the presence of serum proteins completely alters the tip-cell interaction.


The effect of the serum corona on interactions between a single nano-object and a living cell
Statistical results of (a) Amount of indentation (nm), (b) hysteresis (J) and (c) work of adhesion (J) for Group I measured in M (grey) and Group II measured in ComM (black). The data are presented as mean ± standard error. The results presented for each groups are based on a 100 or more independent force profiles per group (Materials and Methods).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382918&req=5

f6: Statistical results of (a) Amount of indentation (nm), (b) hysteresis (J) and (c) work of adhesion (J) for Group I measured in M (grey) and Group II measured in ComM (black). The data are presented as mean ± standard error. The results presented for each groups are based on a 100 or more independent force profiles per group (Materials and Methods).
Mentions: The average modulus of a cell depends on the particular cell type. While the modulus value can vary locally when the cell is probed with a sharp tip, the average value taken over many cells and many contact points should be similar and constant, within the scatter, for that given cell type. As the modulus is an internal cellular property that depends largely on the cytoskeleton structure, it should not be affected by tip coating such as the serum protein corona. As all cells were cultured under identical conditions, those incubated in serum and those without serum during the measurements should have the same overall modulus; indeed, it has been shown49 that the presence or absence or serum proteins does not affect the overall cell modulus over periods shorter than 3 days. We thus extracted the effective modulus E* = 1.3 kPa of our cells from the Group I results as noted above, and attempted to use this value for fitting the data of group II, as it appears in Fig. 3(B), to Eq. 1 with a single fitting parameter γa (we substitute a value E* = 1.3 kPa into Equation (1).) However, there is no value of the adhesion energy which, taken together with this cell modulus, can fit the observed force profiles. This implies that the picture suggested in the inset to Fig. 3(A) and the corresponding Eq. (1), cannot represent what is happening when proteins are present both on the tip as well as in the surrounding medium. Moreover, we have compared values of: 1. average indentation 2. amount of hysteresis and 3. work of adhesion. These average results (based on over a hundred profiles, Materials and Methods) are presented as histograms in Fig. 6, and in Table S1 in the SI. Comparing groups I and II, the average values of the three parameters are clearly very different, differences which remain highly significant even when the scatter is accounted for (p < 0.001 in the Kruskal-Wallis test, see also Materials and Methods). While the average indentation, amount of hysteresis and the work of adhesion measured in group II are 1179 nm and 7.96 × 10−18 J and 6.18 × 10−17 J respectively, the values for Group I are about 3–4 times smaller. The variance of the results is considered in more detail in SI. The results of all three parameters thus indicate consistently that the presence of serum proteins completely alters the tip-cell interaction.

View Article: PubMed Central - PubMed

ABSTRACT

Nanoparticles (NPs) which enter physiological fluids are rapidly coated by proteins, forming a so-called corona which may strongly modify their interaction with tissues and cells relative to the bare NPs. In this work the interactions between a living cell and a nano-object, and in particular the effect on this of the adsorption of serum proteins, are directly examined by measuring the forces arising as an Atomic Force Microscope tip (diameter 20&thinsp;nm) - simulating a nano-object - approaches and contacts a cell. We find that the presence of a serum protein corona on the tip strongly modifies the interaction as indicated by pronounced increase in the indentation, hysteresis and work of adhesion compared to a bare tip. Classically one expects an AFM tip interacting with a cell surface to be repelled due to cell elastic distortion, offset by tip-cell adhesion, and indeed such a model fits the bare-tip/cell interaction, in agreement with earlier work. However, the force plots obtained with serum-modified tips are very different, indicating that the cell is much more compliant to the approaching tip. The insights obtained in this work may promote better design of NPs for drug delivery and other nano-medical applications.

No MeSH data available.


Related in: MedlinePlus