Studying the effect of particle size and coating type on the blood kinetics of superparamagnetic iron oxide nanoparticles

Figures & data

Table 1 Physicochemical characterization of different SPIOs

SPIO sample	dH^a [nm]	PDI^b	dcore^c [nm]	ξ-potential^d [mV]	Ms^e [emu g^−1]	r1^f in water [L mmol^−1 s ^−1]	r2^f in water [L mmol^−1 s ^−1]	r1^f in plasma [L mmol^−1 s ^−1]	r2^f in plasma [L mmol^−1 s ^−1]
CDX–SPIO20	19	0.191	4.5 ± 0.9	−20	75.7 ± 1.5	13.19 ± 0.05	49.4 ± 0.2	10.8 ± 0.1	51 ± 2
CDX–SPIO35	36	0.135	3.8 ± 1.4	−38	76.3 ± 8.2	12.1 ± 0.1	141.5 ± 0.2	9.1 ± 0.1	158 ± 3
CDX–SPIO50	51	0.149	4.1 ± 0.9	−30	84.0 ± 3.8	9.7 ± 0.1	239 ± 1	6.8 ± 0.1	266 ± 9
CDX–SPIO60	61	0.139	4.6 ± 1.4	−30	94.0 ± 4.5	8.8 ± 0.1	303 ± 1	6.5 ± 0.1	314 ± 3
CDX–SPIO65	64	0.136	nd	−34	92.8 ± 8.5	8.80 ± 0.09	320 ± 2	6.6 ± 0.2	339 ± 9
CDX–SPIO70	72	0.125	nd	−27	95.1 ± 5.3	8.24 ± 0.07	318 ± 1	6.0 ± 0.2	325 ± 1
CDX–SPIO85	86	0.137	5.4 ± 1.0	−32	74.9 ± 1.8	7.3 ± 0.04	339 ± 4	6.3 ± 1	276 ± 11
PEG–SPIO50	52	0.13	11.1 ± 3.6	−20	nd	11.9 ± 0.8	262 ± 24	13 ± 2	283 ± 1
Starch–SPIO50	51	0.13	10.7 ± 3.5	−25	nd	11.3 ± 0.4	241 ± 1	10.5 ± 0.7	269 ± 19
PAA–SPIO50	49	0.13	11.0 ± 3.1	−40	nd	18.0 ± 0.3	287 ± 10	14 ± 5	309 ± 16
PAA–SPIO20	17	0.17	10.9 ± 3.2	−13	nd	16.4 ± 1.6	54 ± 4	16 ± 1	73 ± 6

Notes:

a Intensity-weighted hydrodynamic diameter d_H (z average) obtained by dynamic light scattering in triplicate with n = 5;

b polydispersity index (cumulants method);

c iron oxide crystallite core diameter d_core determined by TEM, size of n ≥ 50 cores was measured and given as a mean value and standard deviation;

d mean zeta potential obtained in water at pH 6 with n = 6 of 30 runs;

e saturation magnetization calculated from SQIUD data by a bifunctional Langevin fit;

f relaxivity obtained at 40°C and 1.41 T with standard deviation.

Abbreviations: emu, electromagnetic unit; H, magnetic field strength; M, magnetization; nd, not determined; PDI, poly dispersity index; r, relaxivity; SQUID, superconducting quantum interference device.

Figure 1 SPIO core diameters were determined by transmission electron microscopy. (A) Representative TEM images of CDX–SPIO20, CDX–SPIO50, CDX–SPIO85, PEG–SPIO50, starch–SPIO50, PAA–SPIO50. White bars represent 100-nm scale, gray bars 30-nm scale. Crystallite core diameter distributions for the different sized CDX–SPIOs are shown in the upper plot and distributions for the differently coated SPIOs in the lower plot. Distribution was determined by measuring n ≥ 50 cores per SPIO type. Mean core diameter and standard deviation of all SPIO types are also presented in Lohrke et al.¹¹ FTIR spectra of all 50 nm SPIOs are shown in (B).

Abbreviations: CDX, carboxydextran; FTIR, fourier transform infrared spectroscopy; PAA, polyacrylic acid; PEG, polyethylene glycol; SPIO, superparamagnetic iron oxide nanoparticle.

Figure 2 Size and coating dependency of proton relaxivity and magnetic characteristics. Longitudinal (A) and transversal (B) relaxivity are shown to be dependent on particle size. Relaxivities were determined at 40°C and 1.41 T. M/H hysteresis curves (C) represent the change of magnetization (emu g⁻¹ iron) at increasing field strengths for the different CDX fractions at 300 K in aqueous solution as measured by SQUID.

Abbreviations: CDX, carboxydextran; emu, electromagnetic unit; H, magnetic field strength; M, magnetization; PAA, polyacrylic acid; PEG, polyethylene glycol; SPIO, superparamagnetic iron oxide nanoparticle; SQUID, superconducting quantum interference device; r, relaxivity.

Figure 3 Dose dependency of blood kinetics. CDX–SPIO20 was injected into rats (n ≥ 3 per group) at doses of 12.5, 25, 50, and 100 μmol kg⁻¹. Plasma samples were taken at indicated time points to determine the plasma iron concentration (A). Mean half-lives are summarized in (B).

Note: Error bars represent standard deviations of the mean.

Abbreviations: CDX, carboxydextran; SPIO, superparamagnetic iron oxide nanoparticle.

Table 2 Comparison of selected SPIO blood half-lives in rats determined by different methods

Method	Fe conc in plasma	r2 in plasma	MR signal in aorta
SPIO sample	t1/2 [minutes]
CDX–SPIO20	49 ± 10	25 ± 3	38 ± 10
CDX–SPIO50	5.0 ± 0.5	nd	9 ± 1
CDX–SPIO70	2.9 ± 0.4	2.8 ± 0.4	5 ± 2
PAA–SPIO50	4.5 ± 0.4	3.8 ± 0.2	nd
PAA–SPIO20	25 ± 1	21 ± 3	nd

Note: Errors are given as standard deviations of the mean.

Abbreviations: CDX, carboxydextran; MR, magnetic resonance; PAA, polyacrylic acid; r, relaxivity; SPIO, superparamagnetic iron oxide nanoparticle.

Figure 4 Comparison of different methods to determine the CDX–SPIO20 blood half-life. (A) T₂*-weighted transversal MR images were acquired pre and post injection of CDX–SPIO20 application iv in rats and are shown here at representative time points. (B) Signal intensities pre (SI₀) and post injection (SI) of the aorta (white circles in A) were analyzed to obtain blood clearance. The first values (white spheres) with constant low signal intensities were not used for the fit. (C) R₂ relaxation rates of plasma samples taken from 3 minutes to 360 minutes were determined at 40°C and 1.41 T in a time-domain NMR. (D) The iron concentrations in the same plasma samples were measured by ICP–OES.

Note: The values were plotted versus time and fitted by single-order kinetics.

Abbreviations: CDX, carboxydextran; ICP-OES, inductively coupled plasma optical emission spectroscopy; iv, intravenous; MR, magnetic resonance; R, relaxation rate; SI, signal intensity; SPIO, superparamagnetic iron oxide nanoparticle.

Table 3 Plasma kinetics in rats for all SPIO types

Parameter	t1/2 [minutes]	cmax [mmol L^−1]	Clearance [mL minute^−1 kg^−1]	Vss [L kg^−1]
SPIO sample
CDX–SPIO20	49 ± 9	1.4 ± 0.4	1.1 ± 0.5	0.074 ± 0.02
CDX–SPIO35	16 ± 3	1.0 ± 0.02	4.3 ± 0.6	0.096 ± 0.002
CDX–SPIO50	5.0 ± 0.5	0.98 ± 0.06	14.4 ± 0.6	0.103 ± 0.006
CDX–SPIO60	4.0 ± 0.8	1.0 ± 0.1	18 ± 6	0.097 ± 0.012
CDX–SPIO70	2.9 ± 0.4	0.54 ± 0.11	47 ± 16	0.19 ± 0.04
CDX–SPIO85	2.8 ± 0.9	1.0 ± 0.2	27 ± 8	0.10 ± 0.02
PEG–SPIO50	28 ± 3	2.7 ± 0.5	1.0 ± 0.2	0.041 ± 0.008
Starch–SPIO50	12.8 ± 1.4	2.6 ± 0.2	2.7 ± 0.4	0.049 ± 0.004
PAA–SPIO50	4.5 ± 0.4	2.25 ± 0.06	8.3 ± 0.8	0.054 ± 0.001
PAA–SPIO20	25 ± 1	3.1 ± 0.9	1.1 ± 0.4	0.04 ± 0.01

Notes: Plasma samples were collected at time points of 1 to 360 minutes post injection of 100 μmol Fe kg⁻¹ in rats. Values were calculated based on the iron concentrations in the plasma samples. Errors are given as standard deviations of the mean (n ≥ 3).

Abbreviations: CDX, carboxydextran; PAA, polyacrylic acid; PEG, polyethylene glycol; SPIO, superparamagnetic iron oxide nanoparticle.

Figure 5 The blood half-life is dependent on the particle size and coating material.

Notes: SPIOs were injected at a dose of 100 μmol kg⁻¹, and blood samples were taken pre and post injection up to 360 minutes. The iron concentration was determined in plasma by ICP–OES and used to calculate the half-life. Values represent mean of n ≥ 3 rats.

Abbreviations: CDX, carboxydextran; ICP-OES, inductively coupled plasma optical emission spectroscopy; PAA, polyacrylic acid; PEG, polyethylene glycol; SPIO, superparamagnetic iron oxide nanoparticle.

Figure 6 Size- and coating-dependent uptake by macrophages. P388D1 cells were incubated with 300 μmol L⁻¹ SPIO solution for 4 hours at 37°C. (A) Prussian blue stain of phagocytized SPIOs. Representative images of cells incubated with CDX–SPIO20, CDX–SPIO50, and CDX–SPIO85 are shown exemplarily. Cells incubated without SPIOs served as control as well as cells incubated with CDX–SPIO50 at 4°C. (B) SPIO uptake was obtained by iron determination in the washed cells.

Note: Values represent means of at least four experiments.

Abbreviations: CDX, carboxydextran; PAA, polyacrylic acid; PEG, polyethylene glycol; SPIO, superparamagnetic iron oxide nanoparticle.

LohrkeJBrielAMäderKCharacterization of superparamagnetic iron oxide nanoparticles by asymmetrical flow-field-flow-fractionationNanomedicine20083443745218694306

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