PEGylated Polyethylenimine as Enhanced T₁ Contrast Agent for Efficient Magnetic Resonance Imaging

Currently used small molecular magnetic resonance (MR) imaging contrast agents (CAs) in clinics have relatively short half-lives, which has limited the acquisition of high-resolution organ and angiographic images. Therefore, development of a facile strategy for the synthesis of long-circulating CAs with the transforming potential for MR imaging still remains a great challenge. Here we communicate the design and synthesis of PEGylated polyethylenimine (PEI) and its application as enhanced T₁ CA for the long-circulating blood pool as well as efficient organ and tumor imaging. In this study, PEI was covalently grafted with gadolinium (Gd^III) chelator and <i>m</i>PEG-NHS, followed by acetylation of the remaining amines to improve biocompatibility and prolong circulation time. With the relatively long circulation time (3.8 h), the formed multifunctional PEI (PEI.NHAc-DTPA­(Gd^III)-<i>m</i>PEG) can be used as an enhanced T₁ CA for blood pool and major organ imaging, and could be cleared from the body 96 h post administration through the urinary system. Importantly, the PEI.NHAc-DTPA­(Gd^III)-<i>m</i>PEG complexes displayed a strong T₁ contrast effect for tumor imaging through the enhanced permeation and retention effect. These findings suggest that the synthesized PEI.NHAc-DTPA­(Gd^III)-<i>m</i>PEG may be used as a promising CA for T₁ MR imaging of various biological systems

A 54-years-old man, diagnosed as LDH and left foot drop.

<p>(A) Preoperative radiography. (B) Preoperative mid-sagittal MRI showed LDH on L4-S1. (C) Preoperative axial MRI of L4-5 showed the left L5 nerve root compression. (D) Preoperative axial MRI of L5-S1 showed the left S1 nerve root compression. (E) Postoperative radiography.</p

Compressed nerve roots in patients with foot drop.

<p>L5 nerve root was most frequently affected. Double or triple roots compression was a common condition.</p

Additional file 1 of Integrin αVβ3 antagonist-c(RGDyk) peptide attenuates the progression of ossification of the posterior longitudinal ligament by inhibiting osteogenesis and angiogenesis

Supplementary Material

Increased expression of PUMA correlates with apoptosis of spinal cord cells.

<p>(A) The expression of PUMA in spinal cord (SC), cauda equina (CE) and dorsal root ganglion (DRG) was examined using immunohistochemistry (IHC) before (day -3) or after surgery (day 3). (B) 5 independent fields of PUMA IHC staining were counted and the average numbers of PUMA-positive cells were shown. (C) Double staining of Tuj1 (Red) and PUMA (Green) in spinal cord before or after surgery. In the lower panel, TUNEL assay and sequential PUMA staining (Green) were performed in the same specimens from spinal cord region before or after surgery. (D) qRT-PCR analysis of PUMA mRNA level at different time points before (day 0) or after surgery (day 1, 3, 7, 14, 28) in spinal dorsal, cauda equina, and dorsal root ganglion.</p

Confirmed expression patterns in spinal cord by Western Blot.

<p>(A–B) The expression of PUMA, p53, SirT2 were determined at indicated time points by western blot before or after surgery and β-actin served as loading control. Quantitation of relative band densities was performed and shown in B. (C–D) The expression level of PUMA, p53, SirT2 and MDM2 were evaluated by western blot under Methylprednisolone (Methy) protection in 3 groups: sham-operated group (n = 25); Methylprednisolone (30 mg/kg) combined compression group (n = 36); Modified cauda equina compression group (n = 50). Quantitation of relative protein level was shown in D.</p

Surgical procedure of modified cauda equina compression.

<p>After exposure of L4 and L5 vertebral plates, a piece of trapezoid-shaped silicon rubber (10.0×1.0×1.1 to 10.0×1.0×1.3 mm) was inserted into the epidural space under the L5 and L6 vertebral plate.</p

p53 upregulation and SirT2 decrease in compression treated spinal cord.

<p>(A) The expression of p53 and SirT2 in spinal dorsal and ventral horn regions was determined by immunohistochemistry (IHC) before (day -3) or after surgery (day 3) in MCC group. (B) At least 5 independent fields of IHC staining were counted and the average numbers of p53- and SirT2-positive cells were shown.</p

Compression caused apoptosis in spinal cord cells.

<p>(A) The apoptosis of cells in spinal cord (SC), cauda equina (CE) and dorsal root ganglion (DRG) were analyzed by TUNEL method in three groups: before surgery; sham-operated; MCC group. (B) TUNEL positive cells were counted in >5 fields and the average numbers were shown in different groups. (C) qRT-PCR analysis of the expression of Bcl-2, Bcl-xl, Bax, Bak and Bad in three experimental groups. (D) The expression level of pro-caspase-3 (pro-casp-3) and active caspase-3 (active caspase-3) was determined by western blot in indicated 3 groups.</p

Behavioral Assessment of the Animal Model.

<p>(A–C) BBB scores (A), paw withdrawal threshold (PWL) under thermal stimulation (B) and tactile withdrawal threshold (C) were determined at different time points before or after surgery (day −3/−1, 1, 3, 7, 14, 28) in sham-operated group (SHAM), classic cauda equina compression group (CCC) and modified cauda equina compression group (MCC). (D–E) Forced running (D) or free running (E) distances were tested in SHAM, CCC and MCC group rats.</p