Use of magnetic nanoparticles to monitor alginate‐encapsulated βTC‐tet cells

Noninvasive monitoring of tissue‐engineered constructs is an important component in optimizing construct design and assessing therapeutic efficacy. In recent years, cellular and molecular imaging initiatives have spurred the use of iron oxide‐based contrast agents in the field of NMR imaging. Although their use in medical research has been widespread, their application in tissue engineering has been limited. In this study, the utility of monocrystalline iron oxide nanoparticles (MIONs) as an NMR contrast agent was evaluated for βTC‐tet cells encapsulated within alginate/poly‐L‐lysine/alginate (APA) microbeads. The constructs were labeled with MIONs in two different ways: 1) MION‐labeled βTC‐tet cells were encapsulated in APA beads (i.e., intracellular compartment), and 2) MION particles were suspended in the alginate solution prior to encapsulation so that the alginate matrix was labeled with MIONs instead of the cells (i.e., extracellular compartment). The data show that although the location of cells can be identified within APA beads, cell growth or rearrangement within these constructs cannot be effectively monitored, regardless of the location of MION compartmentalization. The advantages and disadvantages of these techniques and their potential use in tissue engineering are discussed. Magn Reson Med 61:282–290, 2009. © 2009 Wiley‐Liss, Inc.     

Neurovascular changes measured by time‐of‐flight MR angiography in cholesterol‐fed rabbits with cortical amyloid β‐peptide accumulation

Purpose:

To test the hypothesis that narrowing of cranial blood vessels in cholesterol‐fed rabbits is a function of the duration of the high cholesterol diet. Such neurovascular changes, caused by elevated serum cholesterol, are linked to stroke and Alzheimer's disease risk.

Materials and Methods:

Four groups of New Zealand White rabbits were studied. Six were fed a normal diet, 19 were fed a 2% cholesterol diet with 0.12 ppm copper in the drinking water for 8 weeks, 10 weeks, or 12 weeks. Time‐of‐flight (TOF) MR angiography (MRA) at 3 Tesla was used to measure arterial diameters in 11 vessels. Previously published data for amyloid β‐peptide (Aβ) accumulation in the brains measured postmortem were correlated to vessel diameters. Ventricular volumes of rabbits were measured on group‐averaged data.

Results:

Several vessel diameters decreased with cholesterol diet duration. The posterior communicating arteries showed the largest significant effect. Aβ accumulation was inversely correlated with arterial diameter. Ventricular volumes between the normal diet and 12 weeks cholesterol‐fed groups were not significantly different.

Conclusion:

Reduction in vessel diameter of medium‐sized vessels but not large vessels was measured in these hypercholesterolemic rabbits. The vessel diameter narrowing and cortical Aβ deposition occurred before measurable ventricular enlargement. J. Magn. Reson. Imaging 2010;32:306–314. © 2010 Wiley‐Liss, Inc.     

S‐Gal®, A novel 1H MRI reporter for β‐galactosidase

Reporter genes and associated enzyme activity are becoming increasingly significant for research in vivo. The lacZ gene and β‐galactosidase (β‐gal) expression have long been exploited as reporters of biologic manipulation at the molecular level, and a noninvasive detection strategy based on proton MRI is particularly attractive. 3,4‐Cyclohexenoesculetin β‐D‐galactopyranoside (S‐Gal®) is a commercial histologic stain, which forms a black precipitate in the presence of β‐gal and ferric ions, suggesting potential detectability by MRI. Generation of the precipitate is now shown to cause strong T₂* relaxation, revealing β‐gal activity. A series of tests with the enzyme in vitro and with tumor cells shows that this approach can be used as an assay for β‐gal activity. Proof of principle is shown in human breast tumor xenografts in mice. Upon direct injection of a mixture of 3,4‐cyclohexenoesculetin β‐D‐galactopyranoside and ferric ammonium citrate, intense contrast was observed immediately in MCF7‐lacZ tumors, but not in wild‐type tumors. 3,4‐Cyclohexenoesculetin β‐D‐galactopyranoside activation in combination with ferric ions introduces a novel approach for assaying enzyme activity by MRI in vivo. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Lack of β2‐AR improves exercise capacity and skeletal muscle oxidative phenotype in mice

β₂‐adrenergic receptor (β₂‐AR) agonists have been used as ergogenics by athletes involved in training for strength and power in order to increase the muscle mass. Even though anabolic effects of β₂‐AR activation are highly recognized, less is known about the impact of β₂‐AR in endurance capacity. We presently used mice lacking β₂‐AR [β₂‐knockout (β₂ KO)] to investigate the role of β₂‐AR on exercise capacity and skeletal muscle metabolism and phenotype. β₂ KO mice and their wild‐type controls (WT) were studied. Exercise tolerance, skeletal muscle fiber typing, capillary‐to‐fiber ratio, citrate synthase activity and glycogen content were evaluated. When compared with WT, β₂ KO mice displayed increased exercise capacity (61%) associated with higher percentage of oxidative fibers (21% and 129% of increase in soleus and plantaris muscles, respectively) and capillarity (31% and 20% of increase in soleus and plantaris muscles, respectively). In addition, β₂ KO mice presented increased skeletal muscle citrate synthase activity (10%) and succinate dehydrogenase staining. Likewise, glycogen content (53%) and periodic acid‐Schiff staining (glycogen staining) were also increased in β₂ KO skeletal muscle. Altogether, these data provide evidence that disruption of β₂‐AR improves oxidative metabolism in skeletal muscle of β₂ KO mice and this is associated with increased exercise capacity.