Current applications of nanotechnology for magnetic resonance imaging of apoptosis

Magnetic resonance imaging characteristics of hepatocyte apoptosis (induced by right portal vein ligation) and necrosis (induced by combined right portal vein and right hepatic artery ligation) in rats

Objective

Using magnetic resonance imaging (MRI), this study aimed to demonstrate the appearance of hepatocytes following ligation of the right portal vein or combined ligation of the right portal vein and right hepatic artery, in a rat model.

Methods

Ninety adult Sprague–Dawley rats (body weight 250–300 g) were divided into three groups ( n = 30 per group): ligation of the right portal vein (Group A); combined ligation of the right portal vein and right hepatic artery (Group B); no intervention to obstruct blood supply (control group). Rats were then randomly subdivided into five groups that underwent examination at 3 h and 1, 3, 7 and 14 days postprocedure ( n = 6 per group). Livers were examined by routine MRI, diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS). After examination, each group of rats was sacrificed. Right hepatic lobes were removed and examined by pathology in six rats per timepoint; transmission electron microscopy (TEM) was undertaken in up to three rats per timepoint.

Results

Hepatocyte apoptosis and necrosis, by right portal vein ligation and combined right portal vein and right hepatic artery ligation respectively, were confirmed by pathology and TEM. In Group A, there were slight increases in intensity of T1- and T2-weighted images and in the apparent diffusion coefficient (ADC). In addition there were larger areas under the lactic acid and lipid peaks on MRS. In Group B, there were increased T1 and T2 signals, a decrease in the ADC and an increase of the area under the lactic acid peaks on MRS.

Conclusions

Hepatocyte apoptosis and necrosis induced by ligation procedures exhibited specific changes that were evident on MRI, DWI and MRS, and could be detected in vivo by MRI, in a rat model.

Development of a Magnetic Resonance Imaging Protocol for the Characterization of Atherosclerotic Plaque by Using Vascular Cell Adhesion Molecule-1 and Apoptosis-Targeted Ultrasmall Superparamagnetic Iron Oxide Derivatives

Objective—

Acute ischemic events are often caused by the disruption of lipid-rich plaques, which are frequently not angiographically visible. Vascular cell adhesion molecule-1 and apoptotic cell-targeted peptides studied during our previous work were conjugated to ultrasmall superparamagnetic iron oxide (USPIO) (USPIO-R832 for vascular cell adhesion molecule-1 targeting; USPIO-R826 for apoptosis targeting) and assessed by magnetic resonance imaging.

Methods and Results—

Apolipoprotein E knockout mice were injected with 0.1 mmol Fe/kg body weight and were imaged on a 4.7-T Bruker magnetic resonance imaging until 24 hours after contrast agent administration. Aortic samples were then harvested and examined by histochemistry, and the magnetic resonance images and histological micrographs were analyzed with ImageJ software. The plaques enhanced by USPIO-R832 contained macrophages concentrated in the cap and a large necrotic core, whereas USPIO-R826 produced a negative enhancement of plaques rich in macrophages and neutral fats concentrated inside the plaque. Both USPIO derivatives colocalized with their target on histological sections and were able to detect plaques with a vulnerable morphology, but each one is detecting a specific environment.

Conclusion—

Our vascular cell adhesion molecule-1 and apoptotic cell targeted USPIO derivatives seem to be highly promising tools for atherosclerosis imaging contributing to the detection of vulnerable plaques. They are able to attain their target in low doses and as fast as 30 minutes after administration.

Engineered nanoparticles for biomolecular imaging

In recent years, the production of nanoparticles (NPs) and exploration of their unusual properties have attracted the attention of physicists, chemists, biologists and engineers. Interest in NPs arises from the fact that the mechanical, chemical, electrical, optical, magnetic, electro-optical and magneto-optical properties of these particles are different from their bulk properties and depend on the particle size. There are numerous areas where nanoparticulate systems are of scientific and technological interest, particularly in biomedicine where the emergence of NPs with specific properties (e.g. magnetic and fluorescence) for contrast agents can lead to advancing the understanding of biological processes at the biomolecular level. This review will cover a full description of the physics of various imaging methods, including MRI, optical techniques, X-rays and CT. In addition, the effect of NPs on the improvement of the mentioned non-invasive imaging methods will be discussed together with their advantages and disadvantages. A detailed discussion will also be provided on the recent advances in imaging agents, such as fluorescent dye-doped silica NPs, quantum dots, gold- and engineered polymeric-NPs, superparamagnetic iron oxide NPs (SPIONs), and multimodal NPs (i.e. nanomaterials that are active in both MRI and optical methods), which are employed to overcome many of the limitations of conventional contrast agents (e.g. gadolinium).

Imaging of apoptosis in the heart with nanoparticle technology

Apoptosis plays an important role in the loss of cardiomyocytes in both ischemic injury and heart failure. Pioneering work with single photon emission computed tomography imaging of (99)Tc-annexin showed that cell death in the heart could be imaged in vivo. Over the last 5 years a significant amount of experience with annexin-labeled magnetic nanoparticles, principally AnxCLIO-Cy5.5, has also been gained. Here, we review the experience with AnxCLIO-Cy5.5 in the heart and compare this experience to that of earlier studies with (99)Tc-annexin. The imaging of apoptosis with AnxCLIO-Cy5.5 provides valuable insights not only into molecular imaging in the heart but, more broadly, into the use of nanoparticle technology for molecular imaging in general.