Noninvasive monitoring of stem cell transfer for muscle disorders

Abstract

In this study the ability of magnetodendrimers to efficiently label cultured muscle stem cells and allow for subsequent in vivo cell detection was determined. Magnetodendrimer-labeled cells exhibited normal growth rates in culture, and retained their capacity to undergo proliferation and form normal myotubes. Labeled stem cells possessed high in vivo proton relaxivities that enhanced MRI contrast properties and enabled us to noninvasively monitor the stem cells' incorporation into dystrophic muscle. Well defined regions of decreased signal intensity were observed in both T 2 -and T 1 -weighted image sequences. MRI was used to longitudinally follow stem cell dynamics in dystrophic muscle with in-plane resolutions on the order of a single muscle fiber (22 ؋ 43 m 2 ). Regions of decreased signal intensity were well correlated with iron accumulation and other histochemical markers of stem cell incorporation. The monitoring of stem cell transfer efficacy and incorporation (1) in a clinical setting currently necessitates the use of invasive techniques (2,3). This can be problematic in subjects with extensive muscle damage and necrosis, such as children with Duchenne's muscular dystrophy. Although it has been shown that both direct intramuscular (4,5) and intravenous injection of normal muscle stem cells (3,5-7) can lead to the reexpression of dystrophin and the rescue of dystrophic muscle (8), the transfer efficacy is limited and stem cell incorporation may be transient because of the host immune response. Techniques to noninvasively monitor such transplants are essential to accelerate the development of cell therapies by reducing the labor associated with conventional cell-detection strategies, as well as to minimize the risk associated with invasive muscle biopsies. We therefore sought to develop high-resolution MRI techniques capable of detecting and following the fate of exogenous muscle stem cell transplants using magnetodendrimers.Magnetodendrimers are a novel class of MR contrast reagents that are effective for nonspecific in vitro cellular labeling. Magnetodendrimers consist of an iron oxide core coated with carboxylated poly(amidoamine) generation 4.5 dendrimers. Dendrimers function as a "synthetically controllable mesh" or matrix that can be used to encapsulate iron particles (9,10), particularly superparamagnetic iron oxide (SPIO). Dendrimers have been demonstrated to have a high nonspecific affinity for cellular membranes, and thus are an efficient vehicle for facilitating the intracellular accumulation of SPIO by a non-receptor-mediated process. The use of magnetodendrimers eliminates the need for complex cellular labeling strategies that rely on the overexpression of iron-binding receptors or the conjugation of iron oxides to specific ligands. SPIOs have net magnetic moments that are at least 4 orders of magnitude higher than the same number of paramagnetic spins, resulting in large local field gradients that dephase nearby protons and dramatically reduce proton relaxation times. When cells are labeled w...

Discrepancies between the fate of myoblast xenograft in mouse leg muscle and NMR label persistency after loading with Gd-DTPA or SPIOs

“…The ranges of CA concentrations, determined to be safe in vitro, then in vivo in this study, have also been proven non-toxic and effective in other studies using SPIOs 21,28,29 or Gd chelate. 20 …”

Superparamagnetic iron oxide nanoparticles: magnetic nanoplatforms as drug carriers

“…[49][50][51] Carboxylated polyamidoamine dendrimers are commonly used to coat and stabilize iron oxide nanoparticle suspensions. 33 In general, at an elevated temperature and pH in the presence of dendrimers, oxidation of Fe(II) yields highly stable and soluble SPIONs with dendrimers.…”

Labeling of skeletal myoblasts with a novel oxygen-sensing spin probe for noninvasive monitoring of in situ oxygenation and cell therapy in heart

“…In a rat model of coronary occlusion, the efficacy of myoblast implantation was demonstrated by ex vivo histological staining procedures (28). Genetic markers, such as green fluorescent protein and LacZ, have been used as fluorescent labels for cell transplant studies (16,42). Recently, CD34…”

“…Current strategies for cell-tracking use labeling with a thymidine analog [e.g., bromodeoxyuridine (BrdU)], or a transfected gene (e.g., green fluorescent protein or LacZ) for visualization using histochemical methods, optical imaging using bioluminescence and fluorescence, ultrasound, single-photon-emission computed tomography, and magnetic resonance imaging (MRI) using ultrasmall superparamagnetic particulates of iron oxide, have been shown to be useful for noninvasive cell tracking (6,7,9,12,16,42). Unfortunately, the biodegradable nature of the probes limits long-term measurements (44).…”