Materials. Histones from calf thymus, bovine serum albumin, N-isopropylacrylamide (NIPAm), sodium dodecyl sulfate (SDS), fluoresceinamine isomer and poly(ethylene glycol) methyl ether methacrylate (average Mn 500, 1500 and 4000) were purchased from Sigma Aldrich. N,N’-methylenebisacrylamide (BIS) was from Fluka; N-t-butylacrylamide (TBAm) was from ACROS ORGANICS. [2,3-14C]-Acrylamide was purchased from GE Healthcare UK Ltd (Buckinghamshire, UK). Histone H1, H2A, H2B, H3.3 and H4 (Human, Recombinant) were purchased form New England Biolabs, Inc., (MA, USA). Sulfo-Cy5 NHS ester was purchased from Lumiprobe (FL, USA). 5-(and 6)-carboxytetramethylrhodamine, succinimidyl ester (NHS-Rhodamine) was purchased from Thermo Fisher Scientific, Inc.
Preparation of HNPs. HNPs were synthesized by free-radical copolymerization of N-isopropylacrylamide (NIPAm), N,N’-methylenebisacrylamide (Bis), N-t-butylacrylamide (TBAm), acrylic acid (AAc) and N-(3-aminopropyl)methacrylamide hydrochloride (APM). SDS (10 mg) were dissolved in water (50 mL). The solutions were filtered through a no. 2 Whatman filter paper (total monomer concentration; 65 mM). TBAm was dissolved in ethanol before the addition. Poly(ethylene glycol) methacrylates was added to the initial solution. Nitrogen was bubbled before the reaction for 30 min. Following the addition of ammonium persulfate aqueous solution (30 mg), the polymerization was carried out at 65 °C for 3 h under. The polymerized solutions were purified by dialysis.
Characterization of HNPs. The hydrodynamic diameter of HNPs was determined by dynamic light scattering (DLS) (Zetasizer Nano ZS). The temperature of the HNP samples was controlled via Peltier device at 25 ± 0.1 °C. Yield and concentration of HNPs was determined by measuring weight of HNP after lyophilization of an aliquot.
Quantification of functional monomers in HNPs by 1H-NMR. To determine the incorporation ratio of TBAm, NIPAm, and Peg in the polymer, 1H NMR spectroscopy was demonstrated (acquisition time; 30 sec). NMR spectra were acquired in CD3OD and the chemical shifts are reported in ppm on the δ scale reference to residual CD2HOD (δ 3.31 ppm). The incorporation ratio of Peg and TBAm to NIPAm in the polymer was calculated from the integration of the methyl proton resonances at 1.36 (Tp), 1.16 ppm (Np), 3.63 ppm (Pp) using equation 1.
TBAm :NIPAm :Peg =(Tp/9):(Np/6):(Pp/4) (1)
We used this relationship to approximate the incorporation of Peg in all of the HNPs synthesized in this study.
Transmission electron microscopy image. HNPs (1 mg/ml) in a volume of 5 µL were placed on a grid (Nisshin EM, Tokyo, Japan) and dried with a stream of warm air 3 times. Then, each sample was negatively stained with 10 µL of 1 w/v% ammonium molybdate for 1 min and imaged with an HT7700 TEM System (Hitachi High-Technologies, Tokyo, Japan). The images were recorded with a CCD camera at 1024 x 1024 pixels (Advanced Microscopy Techniques, Woburn, MA, USA).
Quartz crystal microbalance (QCM) analysis. An Affinix Q4 and Q8 QCM instruments (Alvac Co. Ltd., Kanagawa, Japan) were used to quantify interactions between the HNPs and histones. Gold electrodes of the QCM cell were cleaned with piranha solution for 5 min, twice. 3,3’-Dithiodipropionic acid (1 mM, 0.1 mL) was added to the QCM cells and incubated for overnight. Then, the QCM cells were washed with water and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (100 mg/ml, 50 µL) and N-hydroxysuccinimide (100 mg/mL, 50 µL) were added to the cell to form N-hydroxysuccinimidyl esters. Histones (30 µg/mL) were added onto the QCM gold surface (10 µL) and incubated for 1 h at 37°C. The QCM cells were washed with water 2 times, and blocked with 1 mg/mL BSA solution for 1 h. HNPs were added into the cells at concentrations of 100 µg/ml. Interactions between HNPs and proteins were observed at (37±0.1) °C in PBS (pH 7.4).
Apparent equilibrium dissociation constant (Kd). An Affinix Q8 QCM instruments (Alvac Co. Ltd., Kanagawa, Japan) was used. Histones were immobilized in the QCM cells by amino coupling as described above. After washing the cells twice, HNPs were added into the cells until the saturation. Then, the QCM cells were washed with PBS 2 times. Purified histone subtypes were added to the cell to measure the affinity of HNPs for the histone subtypes at (37±0.1)°C in PBS (pH 7.4). The apparent dissociation constant of HNPs to protein was calculated under the assumption that all particles have the same average affinity to the protein.
Binding capacity of HNPs for histone subtypes. The capacity of histones captured by HNPs was quantified by an Affinix Q4 QCM instrument. Histones were immobilized on the QCM cells by amino coupling as described above. After washing the cells twice, 800±100 Hz of HNPs were immobilized on the surface. Then, the QCM cells were washed with PBS twice. Purified histone subtypes were added to measure the binding affinity and capacity. Frequency change was plotted against concentration of histones and fitted to the Langmuir isotherm. Maximum absorption amount of histone was determined from the saturation point of the fitted curves. Binding capacity was determined by dividing the saturated amount of histone by the amount of immobilized HNPs. Here, the effect of water surrounding proteins and HNPs on the frequency change observed by the QCM have to be considered55. Thus, the effect of water on the frequency change was determined for histones and HNPs prior to the experiments as reported55.
Histone capture rate by HNPs. Histone (600 µg/ml) and HNPs (3 mg/ml) were incubated for 30 min at 37°C. Histones which were not captured by HNPs were measured by UV visible spectroscopy (280 nm) of the supernatant after ultracentrifugation (235,000 × g , 37ºC , 30 min).
Cell culture. 2H-11 murine endothelial cells (ATCC, Virginia, USA) were cultured in DME/high-glucose medium (Wako Pure Chemical Industries, Ltd., Osaka, Japan) supplemented 10% FBS, 100 U/mL penicillin, and 100 μg/mL streptomycin at 37°C in a humidified atmosphere of 5% CO2 in the air.
Histone toxicity neutralization preincubation of HNPs and histones. 2H-11 cells were seeded onto the 24-well plate at 6.0 × 103 cells/well and incubated overnight. Then, the cells were treated with HNPs (20 µg/mL) and histones (45 µg/mL) after the preincubation of HNPs and histones for 30 min. Twenty-four h after the addition, the viable cells were determined by using a Cell Counting Kit-8 (Dojindo, Kumamoto, Japan) in accordance with the manufacturer’s instructions. For the measurement of HNP toxicity, cells were incubated with HNPs for 24 h and the viability was determined. Absorbance was measured with an Infinite® M200 (Tecan Group, Männedorf, Switzerland) at a test wavelength of 450 nm and a reference wavelength of 630 nm.
Neutralization of cell surface-bound histone toxicity. 2H-11 cells were seeded onto the 24-well plate at 2.0 × 104 cells/well and incubated overnight. The cells were treated with histones (500 µg/mL) for 1 min. Several concentrations of HNPs were added after washing the cells with PBS 3 times to remove histone in the medium. At 24 h after the histone addition, the viable cells were detected by using a Cell Counting Kit-8 in accordance with the manufacturer’s instructions.
Preparation of sulfo-Cy5- or rhodamine-conjugated histones. Sulfo-Cy5 NHS ester or rhodamine NHS diluted with DMSO was incubated with histones (histones: sulfo-Cy5 NHS ester or rhodamine NHS = 1: 2 as a molar ratio) for 45 min at 25°C. After the reaction, the solution was dialyzed against PBS for 2 days by use of a Float-A-Lyzer G2 Dialysis Device (MWCO: 3 kDa).
Removal of cell surface-bound histones by HNPs washing. 2H-11 cells were seeded onto the 24-well plate at 2.0 × 104 cells/well and incubated overnight. The cells were treated with Cy5-histones (100 µg/mL) for 10 sec. Then, the cells were washed with HNPs (400 µg/mL) or PBS for 3 times. The cells were lysed with 1 w/v% noctyl-β-D-glucoside containing the following protease inhibitors: 1 mM phenylmethylsulfonyl fluoride, 2 μg/mL leupeptin, 2 μg/mL aprotinin, and 2 μg/mL pepstatin A. The fluorescence intensity of Cy5-histone was determined with a Tecan Infinite M200 microplate reader (ex. 640 nm, em. 670 nm).
Localization of Cy5-histone and FITC-HNPs in vitro. 2H-11 cells were seeded onto a glass bottom 24-well plate (AGC Techno Glass Co., Ltd., Shizuoka, Japan) at 2.0 × 104 cells/well and incubated overnight. The cells were treated with Cy5-histones (100 µg/mL) for 10 sec. Then, FITC-HNPs (400 µg/mL) were added after washing the cells with PBS 3 times to remove histone in the medium. At 30 min and 24 h after the histone addition, localization of Cy5-histone and FITC-HNPs were observed by confocal laser-scanning microscopy.
Selectivity of HNPs to histones. PegHNP12 were incubated in 50% plasma (25 mg/ml protein concentration) or 50% plasma (25 mg/ml) containing histones (6 mg/ml) for 1 h at 37 °C. Then, HNPs were purified by gel filtration chromatography and protein quantities in the HNP fraction (fraction No. 22-27, 1 mL in each fraction) were measured by BCA assay.
Experimental animals. Five-week-old BALB/c male mice were purchased from Japan SLC Inc. (Shizuoka, Japan). The animals were cared for according to the Animal Facility Guidelines of the University of Shizuoka. All animal experiments were approved by the Animal and Ethics Review Committee of the University of Shizuoka.
Biodistribution of HNPs in mice. HNPs were radiolabeled by the inclusion of small amount of [14C]-acrylamide. Mice were injected with [14C]-labeled HNPs (74 kBq/mouse [n=6]) via a tail vein. For the measurement of the biodistribution of HNPs and histone complex, mice were intravenously injected with [14C]-labeled HNPs at 20 sec after the intravenous injection of histones. Three or twenty-four hours after the administration, the mice were sacrificed under deep anesthesia with isoflurane for the collection of blood. Then, the blood was heparinized and separated by centrifugation (700 x g, 15 min, 4 °C) to obtain the plasma. After the mice had been bled from a carotid artery, their heart, lungs, liver, spleen, and kidneys were removed and weighed. The radioactivity in plasma and each organ was determined with a liquid scintillation counter (LSC-3100, Aloka, Tokyo, Japan). The total radioactivity in the plasma was calculated based on the average body weight of the mice, where the average plasma volume was assumed to be 4.27% of the body weight based on the data on total blood volume.
Biodistribution of histone in mice. Mice were injected with HNP (10 mg/kg) via a tail vein 20 sec after Cy5-histone (50 mg/kg) injection. Then, in vivo imaging was performed by in vivo imaging system. One h after the histone injection, the mice were sacrificed under deep anesthesia with isoflurane. Then, ex vivo imaging was performed using heart, lungs, liver, spleen, kidneys and intestine.
In vivo real time imaging of FITC-HNPs and Rhodamine-histone. For the in vivo real time imaging of HNP and histones in the bloodstream, mice were anesthetized with 2.5 % isoflurane and the ear was set on the cover glass. The mice were intravenously injected with FITC-HNPs (600 µg/mouse). At 1 h after the injection, rhodamine-histone (180 µg/mouse) was intravenously injected into the mice. Bloodstream in ear (every 8 sec) was observed 10 min before and after the rhodamine-histone injection under an A1R+ confocal laser-scanning microscope (Nikon, Tokyo, Japan). FITC channel: Ex=488 nm, Em=520 nm. FRET channel: Ex=488 nm, Em=570 nm
HNPs treatment after intravenous injection of histones. Mice were intravenously injected with histones at the concentration of 75 mg/kg. Twenty sec later, PBS or HNPs (10 mg/kg) was intravenously injected into the animals.
HNPs treatment before intravenous injection of histones. Mice were intravenously injected with PBS or HNPs (10 mg/kg). One h later, histone (75 mg/kg) was intravenously injected into the animals.
Inhibition of platelets and histone interaction by HNPs. Blood was collected from the hearts with 0.38% citric acid (pH=5.5) under deep anesthesia with isoflurane. The blood was centrifuged (80 x g, 10 min, 4 °C) to collect platelet rich plasma. Then, 1 volume of the platelet rich plasma added to 1 volume of Tyroad buffer containing prostaglandin E1 (5 µg/ml) and apyrase (2 U/ml) and centrifuged (400 x g, 5 min, 4 °C). The platelets were stained with CellTraceTM Violet (Invitrogen, Rockville, MD) according to manufacturer’s instructions. Then, FITC-PegHNP12 (1 mg/ml) and Cy5-histone (1 mg/ml) were added to the platelets (1x107 cells). The platelets, Cy5-histone and FITC-HNPs were observed by confocal laser-scanning microscopy.
Measurement of the number of platelets in the blood and bleeding time. Mice were intravenously injected with histones (40 mg/kg) 1 h after the PegHNP12 injection (10 mg/kg). Twenty min after the histone injection, the blood was collected from the hearts with 0.38% citric acid (pH=5.5) under deep anesthesia with isoflurane. Then, the number of platelets was measured with Celltac α (NIHON KOHDEN CORPORATION, Japan, Tokyo). For the measurement of bleeding time, 3 mm of the distal mouse tail was cut and immersing the tail in PBS (37°C) 20 min after the histone injection. Then, bleeding time was measured. Importantly, measurement of bleeding time was stopped at 900 seconds.
Localization of histone, platelets and HNPs in the lung. Mice were intravenously injected with Cy5-histones (40 mg/kg) 1 h after the FITC-PegHNP12 injection (10 mg/kg). Thirty min after the histone injection, frozen section of lungs (20 µm) were incubated with mouse integrin alpha 2b/CD41 alexa fluor® 594-conjugated antibody (USA, Minneapolis, MN) for 1 h at room temperature after the blocking with 1% BSA-PBS for 1 h at room temperature. Then, the sample was fixed with 4% paraformaldehyde for 30 minutes at room temperature. Localization of platelets, Cy5-histone and FITC-HNPs were observed by confocal laser-scanning microscopy.
Therapeutic effect of HNPs on sepsis model mice. Mice were intravenously injected with LPS at the concentration of 15 mg/kg. Thirty min later, PBS or HNPs (10 mg/kg) was intravenously injected into the mice for 4 times every 2 h.