Development of reporter gene imaging techniques for long-term assessment of human circulating angiogenic cells.

The use of biomaterials and tracking the long-term fate of the transplanted cells is expected to help improve the clinical translation of cell therapies for cardiac regeneration. To this end, reporter gene strategies are promising for monitoring the fate of cells transplanted with or without a delivery biomaterial; however, their application with primary adult progenitor cells (such as human circulating angiogenic cells (CACs)) has not been extensively evaluated. In this study, human CACs were transduced with reporter genes via one of two lentiviral (LV) vectors: LV-GFP-iresTK or LV-Fluc-RFP-tTK. The mean transduction efficiency was 15% (LV-GFP-iresTK) and 13% (LV-Fluc-RFP-tTK) at multiplicities of infection (MOI) of 10 and 50, respectively. Western blot analysis confirmed HSV1-tk protein expression in transduced CACs. There was no significant difference in viability between the transduced CACs and the untreated controls at a MOI of 50 or below. However, a reduction was observed in cell viability of CACs transduced with LV-Fluc-RFP-tTK at an MOI of 100. Cell migration and angiogenic potential were not affected by transduction protocol. After 4 weeks, 80.3 ± 8.4% of the labeled cells continued to express the reporters and could be visualized when embedded within a collagen matrix scaffold. Therefore, quiescent human CACs can be stably transduced to express reporter genes without affecting their function. This reporter gene technique is a promising approach to be further tested for tracking transplanted CACs (±delivery matrix) non-invasively and longitudinally.

Analysis of [11C]methyl-candesartan kinetics in the rat kidney for the assessment of angiotensin II type 1 receptor density in vivo with PET.

INTRODUCTION: Angiotensin II type 1 (AT(1)) receptors play a key role in the regulation of renal and cardiovascular functions and have been implicated in the pathogenesis of many diseases. The aim of this study was to assess binding of the novel radioligand [(11)C]methyl-candesartan to AT(1) receptors in the rat kidney in vivo with PET. METHODS: Dynamic PET images were acquired for 60 min at baseline, with coinjection of candesartan (5 mg/kg), and after injection of PD123,319 (5 mg/kg). Volumes of distribution (R(C)∙V(T)) were estimated with a two-compartment model, by Logan analysis, and by taking the tissue-to-plasma activity ratio at 50-60 min post-injection. RESULTS: The two-compartment model did not describe the kinetics at baseline adequately and the baseline scans were too short to obtain accurate estimates of R(C)∙V(T) with the Logan approach. Based on the tissue-to-plasma ratios, roughly one-third of V(T) at baseline could be attributed to AT(1) receptor binding. There were no indications of AT(2) receptor binding in the rat kidney. CONCLUSION: It may be possible to detect changes in AT(1) receptor density in the rat kidney in vivo with [(11)C]methyl-candesartan and PET. Imaging AT(1) receptors with PET may provide valuable information on the role of these receptors in the pathogenesis of diseases such as hypertension, diabetic nephropathy, ventricular remodeling, and heart failure.

In vivo assessment of myocardial glucose uptake by positron emission tomography in adults with the PRKAG2 cardiac syndrome.

BACKGROUND: The PRKAG2 cardiac syndrome is an inherited metabolic disease of the heart characterized by excessive myocardial glycogen deposition. The biochemical alterations associated with this condition remain controversial and have not previously been studied in affected humans. METHODS AND RESULTS: Positron emission tomography (PET) imaging was used to quantitatively assess myocardial glucose uptake (MGU) in 6 adult subjects with the PRKAG2 cardiac syndrome and 6 healthy, matched control subjects using the glucose analogue (18)F-Fluoro-2-deoxyglucose (FDG). Studies were performed under a euglycemic hyperinsulinemic clamp to ensure stable blood glucose levels. Rubidium-82 perfusion scans were performed to ensure that myocardial differences in myocardial glucose uptake were not the result of significant myocardial scar. In adult patients with phenotypic expression of disease, the median myocardial glucose uptake of the left ventricle was 0.18 mumol/min/g (interquartile range, 0.14, 0.24), compared with 0.40 mumol/min/g (interquartile range, 0.30 to 0.45) in the control group (P=0.01). The median blood glucose during FDG-PET imaging was 4.72 mmol/L (interquartile range, 4.32 to 4.97) in the PRKAG2 group and 4.38 mmol/L (interquartile range, 3.90, 4.79) in the control group (P=NS). The significant decrease observed in myocardial glucose uptake in affected patients occurred in the absence of significant myocardial scar. CONCLUSIONS: The PRKAG2 cardiac syndrome is associated with a reduction of glucose uptake in adult patients affected with this genetic condition. In this pilot study, (18)F-FDG-PET imaging is a useful tool to assess alterations in myocardial glucose transport in this inherited metabolic disease and provide insight into the biochemical pathophysiology of the diseased state.