Myocarditis Following Coronavirus Disease 2019 mRNA Vaccine: A Case Series and Incidence Rate Determination

BACKGROUND

Myocarditis following coronavirus disease 2019 (COVID-19) mRNA vaccines (Pfizer-BioNTech and Moderna) has been increasingly reported. Incidence rates in the general population are lacking, with pericarditis rather than myocarditis diagnostic codes being used to estimate background rates. This comparison is critical for balancing the risk of vaccination with the risk of no vaccination.

METHODS

A retrospective case series was performed using the Mayo Clinic COVID-19 Vaccine Registry. We measured the incidence rate ratio (IRR) for myocarditis temporally related to COVID-19 mRNA vaccination compared with myocarditis in a comparable population from 2016 through 2020. Clinical characteristics and outcomes of the affected patients were collected. A total of 21 individuals were identified, but ultimately 7 patients met the inclusion criteria for vaccine-associated myocarditis.

RESULTS

The overall IRR of COVID-19-related myocarditis was 4.18 (95% confidence interval [CI], 1.63-8.98), which was entirely attributable to an increased IRR among adult males (IRR, 6.69; 95% CI, 2.35-15.52) compared with females (IRR 1.41; 95% CI, .03-8.45). All cases occurred within 2 weeks of a dose of the COVID-19 mRNA vaccine, with the majority occurring within 3 days (range, 1-13) following the second dose (6 of 7 patients, 86%). Overall, cases were mild, and all patients survived.

CONCLUSIONS

Myocarditis is a rare adverse event associated with COVID-19 mRNA vaccines. It occurs in adult males with significantly higher incidence than in the background population. Recurrence of myocarditis after a subsequent mRNA vaccine dose is not known at this time.

Performance of cardiac PET/CT with and without phase analysis for detection of scar in cardiac sarcoidosis: Comparison to cardiac magnetic resonance imaging

BACKGROUND

The presence of myocardial scar in CS patients results in poor prognosis and worse outcomes. 18F-fluorodeoxyglucose (18F-FDG) PET/CT excels at visualizing inflammation but is suboptimal at detecting scar. We evaluated PET/CT sensitivity to detect scar and investigated the incremental diagnostic value of automated PET-derived data.

METHODS

176 patients who underwent cardiac magnetic resonance (CMR) and N-13 ammonia/18F-FDG cardiac PET/CT for suspected CS within 3 months were enrolled. Scar was defined as late gadolinium enhancement (LGE) on CMR without concordant 18F-FDG uptake on 18F-FDG PET/CT. Accuracy of cardiac PET/CT at detecting scar (perfusion defect without concordant 18F-FDG uptake) was assessed before and after addition of automated PET-derived data.

RESULTS

Sensitivity of PET/CT for scar detection was 45.3% (specificity 88.9%). Addition of PET-derived LV volumes and function in a logistic regression model improved sensitivity to 57.0% (specificity: 80.0%, AUC 0.72). Addition of phase analysis maximum segmental onset of myocardial contraction > 61 improved AUC to 0.75, correctly relabeling 16.3% of patients as scar (net reclassification index 8.2%).

CONCLUSION

Sensitivity of gated PET MPI alone for scar detection in CS is suboptimal. Adding PET-derived volumes/function and phase analysis data results in improved detection and characterization of scar.

The Myocardial Microenvironment Modulates the Biology of Transplanted Mesenchymal Stem Cells

PURPOSE

The maximal efficacy of cell therapy depends on the survival of stem cells, as well as on the phenotypic and biologic changes that may occur on these cells after transplantation. It has been hypothesized that the post-ischemic myocardial microenvironment can play a critical role in these changes, potentially affecting the survival and reparative potential of mesenchymal stem cells (MSCs). Here, we use a dual reporter gene sensor for the in vivo monitoring of the phenotype of MSCs and study their therapeutic effect on cardiac function.

PROCEDURES

The mitochondrial sensor was tested in cell culture in response to different mitochondrial stressors. For in vivo testing, MSCs (3 × 10⁵) were delivered in a murine ischemia-reperfusion (IR) model. Bioluminescence imaging was used to assess the mitochondrial biology and the viability of transplanted MSCs, while high-resolution ultrasound provided a non-invasive analysis of cardiac contractility and dyssynchrony.

RESULTS

The mitochondrial sensor showed increased activity in response to mitochondrial stressors. Furthermore, when tested in the living subject, it showed a significant increase in mitochondrial dysfunction in MSCs delivered in IR, compared with those delivered under sham conditions. Importantly, MSCs delivered to ischemic hearts, despite their mitochondrial stress and poor survival, were able to induce a significant improvement in cardiac function, through decreased collagen deposition and resynchronization/contractility of left ventricular wall motion.

CONCLUSIONS

The ischemic myocardium induces changes in the phenotype of transplanted MSCs. Despite their limited survival, MSCs still elicit a certain therapeutic response, as evidenced by improvement in myocardial remodeling and cardiac function. Maximization of the survival and reparative efficacy of stem cells remains a key for the success of stem cell therapies.

Senolytic agents lessen the severity of abdominal aortic aneurysm in aged mice

Age is a major risk factor for abdominal aortic aneurysm (AAA), for which treatment options are limited to surgical intervention for large AAA and watchful waiting for small aneurysms. However, the factors that regulate the expansion of aneurysms are unclear. Development of new therapeutic strategies to prevent or treat small aneurysms awaits a more thorough understanding of the etiology of AAA formation and progression with aging. A variety of structural and functional changes have been reported in aging vasculature, but emerging evidence implicates senescent cells in the formation of AAA through their paracrine effects on vascular wall cell populations. Here we show that aging is associated with transcriptional changes in abdominal aortic tissue consistent with loss of smooth muscle cells, leukocyte adhesion, inflammation, and accumulation of senescent cells in the vascular wall and surrounding perivascular adipose tissue. Furthermore, aged mice demonstrated anatomical and histopathological features of AAA development in response to administration of angiotensin II over 28 days. Importantly, in our study we sought to determine if reducing senescent cells could lessen the severity of AAA in aged mice. We find that pretreatment of aged mice with oral senolytic agents (dasatinib + quercetin) reduced senescent cell abundance in the arterial walls and surrounding tissues and lessened the severity of AAA in response to angiotensin II administration. These data provide important preliminary evidence supporting a role of senescent cells in age-related AAA formation and progression and suggest that strategies to reduce senescent cell burden hold promise to lessen AAA severity.

Cardio Phenotypic Potential of Mesenchymal Stem Cells

Cell therapy is being investigated as a powerful intervention to ameliorate the consequences of coronary artery disease. Among the different stem cell options, mesenchymal stem cells (MSCs) are particularly attractive due to their high availability, as well as immune-privileged status. However, it is still unclear whether mesenchymal stem cells can acquire cardiomyogenic characteristics after they are transplanted to the myocardium. In this article, we outline protocols that illustrate the plasticity of MSCs and their ability to acquire cardiogenic characteristics when they are in an ischemic-like environment, as typically encountered after transplantation into the ischemic heart. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Isolation of mesenchymal stem cells (MSCs) Support Protocol 1: Characterization of MSCs by flow cytometry Basic Protocol 2: Isolation of neonatal cardiomyoctes (NCMs) Support Protocol 2: Characterization of NCMs Basic Protocol 3: Cardiogenic plasticity of MSCs under ischemic-like conditions Support Protocol 3: Characterization of the cardiomyogenic potential of MSCs.

Stem Cell-Laden Coaxially Electrospun Fibrous Scaffold for Regenerative Engineering Applications

Stem cell-based therapies for various ailments have attracted significant attention for over a decade. However, low retention of transplanted cells at the damaged site has hindered their potential for use in therapy. Tissue engineered grafts with fibrillar structures mimicking the extracellular matrix (ECM) can be potentially used to increase the retention and engraftment of stem cells at the damaged site. Moreover, these grafts may also provide mechanical stability at the damaged site to enhance function and regeneration. Among all the methods to produce fibrillar structures developed in recent years, electrospinning is a simple and versatile method to produce fibrous structures ranging from a few nanometers to micrometers. Coaxial electrospinning enables production of a mechanically stable core with a cell-binding sheath for enhanced cell adhesion and proliferation. Furthermore, this process provides an alternative to functionalized engineered scaffolds with specific compositions. The present article describes the protocol for developing a polycaprolactone (PCL) core and gelatin/gelatin methacrylate (GelMA) sheath laden with stem cells for various regenerative engineering applications. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Uniaxial PCL electrospinning Basic Protocol 2: Coaxial electrospinning Support Protocol 1: Scaffold characterization for Basic Protocols 1 and 2 Basic Protocol 3: Cell seeding on uniaxial and coaxial electrospun scaffolds and MTS assay Support Protocol 2: Preparation of scaffold with cells for scanning electron microscopy.

Delayed Intramyocardial Delivery of Stem Cells after Ischemia Reperfusion Injury in a Murine Model

There is significant interest in the use of stem cells (SCs) for the recovery of cardiac function in individuals with myocardial injuries. Most commonly, cardiac stem cell therapy is studied by delivering SCs concurrently with the induction of myocardial injury. However, this approach presents two significant limitations: the early hostile pro-inflammatory ischemic environment may affect the survival of transplanted SCs, and it does not represent the subacute infarction scenario where SCs will likely be used. Here we describe a two-part series of surgical procedures for the induction of ischemia-reperfusion injury and delivery of mesenchymal stem cells (MSCs). This method of stem cell administration may allow for the longer viability and retention around damaged tissue by circumventing the initial immune response. A model of ischemia reperfusion injury was induced in mice accompanied by the delivery of mesenchymal stem cells (3.0 x 10⁵), stably expressing the reporter gene firefly luciferase under the constitutively expressed CMV promoter, intramyocardially 7 days later. The animals were imaged via ultrasound and bioluminescent imaging for confirmation of injury and injection of cells, respectively. Importantly, there was no added complication rate when performing this two-procedure approach for SC delivery. This method of stem cell administration, collectively with the utilization of state-of-the-art reporter genes, may allow for the in vivo study of viability and retention of transplanted SCs in a situation of chronic ischemia commonly seen clinically, while also circumventing the initial pro-inflammatory response. In summary, we established a protocol for the delayed delivery of stem cells into the myocardium, which can be used as a potential new approach in promoting regeneration of the damaged tissue.

Pathway-specific reporter genes to study stem cell biology

Little is known on the phenotypic characteristics of stem cells (SCs) after they are transplanted to the myocardium, in part due to lack of noninvasive platforms to study SCs directly in the living subject. Reporter gene imaging has played a valuable role in the noninvasive assessment of cell fate in vivo. In this study, we validated a pathway-specific reporter gene that can be used to noninvasively image the phenotype of SCs transplanted to the myocardium. Rat mesenchymal SCs (MSCs) were studied for phenotypic evidence of myogenic characteristics under in vitro conditions. After markers of myogenic characteristics were identified, we constructed a reporter gene sensor, comprising the firefly luciferase (Fluc) reporter gene driven by the troponin T (TnT) promoter (cardio MSCs had threefold expression in polymerase chain reaction compared to control MSCs) using a two-step signal amplification strategy. MSCs transfected with TnT-Fluc were studied and validated under in vitro conditions, showing a strong signal after MSCs acquired myogenic characteristics. Lastly, we observed that cardio MSCs had higher expression of the reporter sensor compared to control cells (0.005 ± 0.0005 vs 0.0025 ± 0.0008 Tnt-Fluc/ubiquitin-Fluc, P < .05), and that this novel sensor can detect the change in the phenotype of MSCs directly in the living subject. Pathway-specific reporter gene imaging allows assessment of changes in the phenotype of MSCs after delivery to the ischemic myocardium, providing important information on the phenotype of these cells. Imaging sensors like the one described here are critical to better understanding of the changes that SCs undergo after transplantation.

A Metabolic Intravascular Platform to Study FDG Uptake in Vascular Injury

PURPOSE

Metabolic alterations underlie many pathophysiological conditions, and their understanding is critical for the development of novel therapies. Although the assessment of metabolic changes in vivo has been historically challenging, recent developments in molecular imaging have allowed us to study novel metabolic research concepts directly in the living subject, bringing us closer to patients. However, in many instances, there is need for sensors that are in close proximity to the organ under investigation, for example to study vascular metabolism.

METHODS

In this study, we developed and validated a metabolic detection platform directly in the living subject under an inflammatory condition. The signal collected by a scintillating fiber is amplified using a photomultiplier tube and decodified by an in-house tunable analysis platform. For in vivo testing, we based our experiments on the metabolic characteristics of macrophages, cells closely linked to inflammation and avid for glucose and its analog ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). The sensor was validated in New Zealand rabbits, in which inflammation was induced by either a) high cholesterol (HC) diet for 16 weeks or b) vascular balloon endothelial denudation followed by HC diet.

RESULTS

There was no difference in weight, hemodynamics, blood pressure, or heart rate between the groups. Vascular inflammation was detected by the metabolic sensor (Inflammation: 0.60 ± 0.03 AU vs. control: 0.48 ± 0.03 AU, p = 0.01), even though no significant inflammation/atherosclerosis was detected by intravascular ultrasound, underscoring the high sensitivity of the system. These findings were confirmed by the presence of macrophages on ex vivo aortic tissue staining.

CONCLUSION

In this study, we validated a tunable very sensitive metabolic sensor platform that can be used for the detection of vascular metabolism, such as inflammation. This sensor can be used not only for the detection of macrophage activity but, with alternative probes, it could allow the detection of other pathophysiological processes.

Molecular Imaging of Stem Cells

Regenerative medicine with the use of stem cells has appeared as a potential therapeutic alternative for many disease states. Despite initial enthusiasm, there has been relatively slow transition to clinical trials. In large part, numerous questions remain regarding the viability, biology and efficacy of transplanted stem cells in the living subject. The critical issues highlighted the importance of developing tools to assess these questions. Advances in molecular biology and imaging have allowed the successful non-invasive monitoring of transplanted stem cells in the living subject. Over the years these methodologies have been updated to assess not only the viability but also the biology of transplanted stem cells. In this review, different imaging strategies to study the viability and biology of transplanted stem cells are presented. Use of these strategies will be critical as the different regenerative therapies are being tested for clinical use.

The impact of combined cardiopulmonary exercise testing and SPECT myocardial perfusion imaging on downstream evaluation and management

OBJECTIVE

The diagnostic yield of combined cardiopulmonary exercise testing (CPET) and myocardial perfusion imaging (MPI) in patients referred for stress testing has received limited study.

METHODS

We evaluated consecutive patients who underwent combined CPET-MPI at a single tertiary referral center between 2011 and 2015. An abnormal CPET was defined as any of the following: reduced oxygen consumption, cardiac output impairment, or pulmonary impairment. Normal MPI was defined as the absence of resting or stress perfusion defect. The primary study outcome was change in clinical decision-making after CPET-MPI including management of pulmonary disease, management of deconditioning, heart failure management, and referral for cardiac catheterization. Outcomes of patients with normal and abnormal MPI were presented based on the specific CPET abnormality.

RESULTS

415 patients were included in the study. Of the 269 patients that had normal MPI, 206 (77%) had abnormal CPET. Patients with abnormal CPET and normal MPI, compared with patients that had normal CPET and normal MPI, were more frequently diagnosed with pulmonary disease (11.7% vs 3.2%, P = .04) and deconditioning (33.5% vs 17.4%, P = .01). Of the 146 patients that had abnormal MPI, 128 (88%) had abnormal CPET. Patients with abnormal CPET and abnormal MPI, compared with patients that had normal CPET and abnormal MPI, did not statistically differ with regard to the study outcome.

CONCLUSION

An abnormal CPET, if the MPI was normal, prompted further evaluation and led to management of pulmonary disease and deconditioning.

Phase analysis single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) detects dyssynchrony in myocardial scar and increases specificity of MPI

BACKGROUND

Myocardial perfusion imaging (MPI) with single-photon emission computed tomography (SPECT) is commonly used to assess patients with cardiovascular disease. However, in certain scenarios, it may have limited specificity in the identification of hemodynamically significant coronary artery disease (e.g., false positive), potentially resulting in additional unnecessary testing and treatment. Phase analysis (PA) is an emerging, highly reproducible quantitative technology that can differentiate normal myocardial activation (synchrony) from myocardial scar (dyssynchrony). The objective of this study is to determine if PA can improve the specificity SPECT MPI.

METHODS

An initial cohort of 340 patients (derivation cohort), referred for SPECT-MPI, was prospectively enrolled. Resting MPI studies were assessed for resting perfusion defects (scar). These were utilized as the reference standard for scar. Subsequently, we collected a second independent validation cohort of 138 patients and tested the potential of PA to reclassify patients for the diagnosis of "scar" or "no scar." Patients were assigned to three categories depending upon their pre-test probability of scar based on multiple clinical and imaging parameters: ≤ 10% (no scar), 11-74% (indeterminate), and ≥ 75% (scar). The ability of PA variables to reclassify patients with scar to a higher group and those without scar to a lower group was then determined using the net reclassification index (NRI).

RESULTS

Entropy (≥ 59%) was independently associated with scar in both patient cohorts with an odds ratio greater than five. Furthermore, when added to multiple clinical/imaging variables, the use of entropy significantly improved the area under the curve for assessment of scar (0.67 vs. 0.59, p = 0.04). The use of entropy correctly reclassified 24% of patients without scar, by clinical model, to a lower risk category (as determined by pre-test probability) with an overall NRI of 18% in this validation cohort.

DISCUSSION

The use of PA entropy can improve the specificity of SPECT MPI and may serve as a useful adjunctive tool to the interpreting physician. The current study determined the optimal PA parameters to detect scar (derivation cohort) and applied these parameters to a second, independent, patient group and noted that entropy (≥ 59%) was independently associated with scar in both patient cohorts. Therefore, PA, which requires no additional imaging time or radiation, enhances the diagnostic capabilities of SPECT MPI.

CONCLUSION

The use of PA entropy significantly improved the specificity of SPECT MPI and could influence the labeling of a patient as having or not having myocardial scar and thereby may influence not only diagnostic reporting but also potentially prognostic determination and therapeutic decision-making.

Noninvasive Monitoring of the Mitochondrial Function in Mesenchymal Stromal Cells

PURPOSE

Mitochondria are a gatekeeper of cell survival and mitochondrial function can be used to monitor cell stress. Here we validate a pathway-specific reporter gene to noninvasively image the mitochondrial function of stem cells.

PROCEDURES

We constructed a mitochondrial sensor with the firefly luciferase (Fluc) reporter gene driven by the NQO1 enzyme promoter. The sensor was introduced in stem cells and validated in vitro and in vivo, in a mouse model of myocardial ischemia/reperfusion (IR).

RESULTS

The sensor activity showed an inverse relationship with mitochondrial function (R (2) = -0.975, p = 0.025) and showed specificity and sensitivity for mitochondrial dysfunction. In vivo, NQO1-Fluc activity was significantly higher in IR animals vs. controls, indicative of mitochondrial dysfunction, and was corroborated by ex vivo luminometry.

CONCLUSIONS

Reporter gene imaging allows assessment of the biology of transplanted mesenchymal stromal cells (MSCs), providing important information that can be used to improve the phenotype and survival of transplanted stem cells.

How to Develop a Cardio-Oncology Clinic

Cardiovascular demands to the care of cancer patients are common and important given the implications for morbidity and mortality. As a consequence, interactions with cardiovascular disease specialists have intensified to the point of the development of a new discipline termed cardio-oncology. As an additional consequence, so-called cardio-oncology clinics have emerged, in most cases staffed by cardiologists with an interest in the field. This article addresses this gap and summarizes key points in the development of a cardio-oncology clinic.

Noninvasive Assessment of Cell Fate and Biology in Transplanted Mesenchymal Stem Cells

Recently, molecular imaging has become a conditio sine qua non for cell-based regenerative medicine. Developments in molecular imaging techniques, such as reporter gene technology, have increasingly enabled the noninvasive assessment of the fate and biology of cells after cardiovascular applications. In this context, bioluminescence imaging is the most commonly used imaging modality in small animal models of preclinical studies. Here, we present a detailed protocol of a reporter gene imaging approach for monitoring the viability and biology of Mesenchymal Stem Cells transplanted in a mouse model of myocardial ischemia reperfusion injury.

Intravascular Delivery of Biologics to the Rat Kidney

The renal microvascular compartment plays an important role in the progression of kidney disease and hypertension, leading to the development of End Stage Renal Disease with high risk of death for cardiovascular events. Moreover, recent clinical studies have shown that renovascular structure and function may have a great impact on functional renal recovery after surgery. Here, we describe a protocol for the delivery of drugs into the renal artery of rats. This procedure offers significant advantages over the frequently used systemic administration as it may allow a more localized therapeutic effect. In addition, the use of rodents in pharmacodynamic analysis of preclinical studies may be cost effective, paving the way for the design of translational experiments in larger animal models. Using this technique, infusion of rat recombinant Vascular Endothelial Growth Factor (VEGF) protein in rats has induced activation of VEGF signaling as shown by increased expression of FLK1, pAKT/AKT, pERK/ERK. In summary, we established a protocol for the intrarenal delivery of drugs in rats, which is simple and highly reproducible.

Association between coronary microvascular function and the vasa vasorum in patients with early coronary artery disease

BACKGROUND AND AIMS

The vasa vasorum (VV) plays a role in the initial phase of atherosclerosis, and abnormalities in microvascular function may be sensitive measures of the early development of atherosclerosis. The current study was designed to access the association between coronary microvascular function and VV density in patients undergoing cardiac catheterization.

METHODS

Twenty-four patients with early coronary artery disease underwent endothelium-dependent (coronary blood flow, CBF) and endothelium-independent (coronary flow velocity reserve, CFVR) coronary microvascular function testing, and optical coherence tomography (OCT) imaging of the left anterior descending coronary artery (LAD). Using an intracoronary Doppler guidewire, CBF was examined by evaluating changes in blood flow in response to acetylcholine and CFVR in response to adenosine. VV density (VV volume/vessel volume × 100, %VV) of the proximal 10 mm of the LAD was quantified by OCT.

RESULTS

The median values (Q1, Q3) of CFVR, % changes in CBF in response to acetylcholine, and the %VV were 2.70 (2.30, 2.90), -16.82 (-42.34, 54.52), and 2.62 (2.35, 3.35), respectively. %VV correlated inversely with CBF (r = -0.614, p = 0.001) and directly with CFVR (r = 0.423, p = 0.040). Multivariate analysis showed that only %VV was significantly correlated with CBF and the association was independent of other clinical variables, Framingham risk score, body mass index, and a family history of coronary heart disease.

CONCLUSIONS

This study demonstrates that VV density has negative correlation with endothelium-dependent microvascular function in patients with early coronary atherosclerosis. These observations link adventitial VV structure and function to microvascular dysfunction in early coronary atherosclerosis.

Evaluation of coronary adventitial vasa vasorum using 3D optical coherence tomography--animal and human studies

Objectives

This study sought to evaluate adventitial vasa vasorum (VV) in vivo with novel imaging technique of optical coherence tomography (OCT).

Methods

To verify OCT methods for quantification of VV, we first studied 2 swine carotid arteries in a model of focal angiogenesis by autologous blood injection, and compared microchannel volume (MCV) by OCT and VV by m-CT, and counts of those. In OCT images, adventitial MC was identified as signal-voiding areas which were located within 1 mm from the lumen-intima border. After manually tracing microchannel areas and the boundaries of lumen-intima and media-adventitial in all slices, we reconstructed 3D images. Moreover, we performed with OCT imaging in 8 recipients referred for evaluation of cardiac allograft vasculopathy at 1 year after heart transplantation. MCV and plaque volume (PV) were assessed with 3D images in each 10-mm-segment.

Results

In the animal study, among the 16 corresponding 1-mm-segments, there were significant correlations of count and volume between both the modalities (count r²=0.80, P<0.01; volume r² =0.50, P<0.01) and a good agreement with a systemic bias toward underestimation with m-CT. In the human study, there was a significant positive correlation between MCV and PV (segment number=24, r² =0.63, P<0.01).

Conclusion

Our results suggest that evaluation of MCV with 3D OCT imaging might be a novel method to estimate the amount of adventitial VV in vivo, and further has the potential to provide a pathophysiological insight into a role of the VV in allograft vasculopathy.

Mesenchymal Stromal Cells Improve Renovascular Function in Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure, for which there is no accepted treatment. Progenitor and stem cells have been shown to restore renal function in a model of renovascular disease, a disease that shares many features with PKD. The objective of this study was to examine the potential of adult stem cells to restore renal structure and function in PKD. Bone marrow-derived mesenchymal stromal cells (MSCs, 2.5 × 10(5)) were intrarenally infused in 6-week-old PCK rats. At 10 weeks of age, PCK rats had an increase in systolic blood pressure (SBP) versus controls (126.22 ± 2.74 vs. 116.45 ± 3.53 mmHg, p < 0.05) and decreased creatinine clearance (3.76 ± 0.31 vs. 6.10 ± 0.48 µl/min/g, p < 0.01), which were improved in PKD animals that received MSCs (SBP: 114.67 ± 1.34 mmHg, and creatinine clearance: 4.82 ± 0.24 µl/min/g, p = 0.001 and p = 0.003 vs. PKD, respectively). MSCs preserved vascular density and glomeruli diameter, measured using microcomputed tomography. PCK animals had increased urine osmolality (843.9 ± 54.95 vs. 605.6 ± 45.34 mOsm, p < 0.01 vs. control), which was improved after MSC infusion and not different from control (723.75 ± 56.6 mOsm, p = 0.13 vs. control). Furthermore, MSCs reduced fibrosis and preserved the expression of proangiogenic molecules, while cyst size and number were unaltered by MSCs. Delivery of exogenous MSCs improved vascular density and renal function in PCK animals, and the benefit was observed up to 4 weeks after a single infusion. Cell-based therapy constitutes a novel approach in PKD.

Noninvasive imaging of hypoxia-inducible factor-1α gene therapy for myocardial ischemia

Hypoxia-inducible factor-1 alpha (HIF-1α) gene therapy holds great promise for the treatment of myocardial ischemia. Both preclinical and clinical evaluations of this therapy are underway and can benefit from a vector strategy that allows noninvasive assessment of HIF-1α expression as an objective measure of gene delivery. We have developed a novel bidirectional plasmid vector (pcTnT-HIF-1α-VP2-TSTA-fluc), which employs the cardiac troponin T (cTnT) promoter in conjunction with a two-step transcriptional amplification (TSTA) system to drive the linked expression of a recombinant HIF-1α gene (HIF-1α-VP2) and the firefly luciferase gene (fluc). The firefly luciferase (FLuc) activity serves as a surrogate for HIF-1α-VP2 expression, and can be noninvasively assessed in mice using bioluminescence imaging after vector delivery. Transfection of cultured HL-1 cardiomyocytes with pcTnT-HIF-1α-VP2-TSTA-fluc led to a strong correlation between FLuc and HIF-1α-dependent vascular endothelial growth factor expression (r(2)=0.88). Intramyocardial delivery of pcTnT-HIF-1α-VP2-TSTA-fluc into infarcted mouse myocardium led to persistent HIF-1α-VP2 expression for 4 weeks, even though it improved neither CD31+ microvessel density nor echocardiographically determined left ventricular systolic function. These results lend support to recent findings of suboptimal efficacy associated with plasmid-mediated HIF-1α therapy. The imaging techniques developed herein should be useful for further optimizing HIF-1α-VP2 therapy in preclinical models of myocardial ischemia.

Safety and efficacy of extracorporeal shock wave myocardial revascularization therapy for refractory angina pectoris

OBJECTIVE

To assess the safety and efficacy of extracorporeal shockwave myocardial revascularization (ESMR) therapy in treating patients with refractory angina pectoris.

PATIENTS AND METHODS

A single-arm multicenter prospective trial to assess safety and efficacy of the ESMR therapy in patients with refractory angina (class III/IV angina) was performed. Screening exercise treadmill tests and pharmacological single-photon emission computed tomography (SPECT) were performed for all patients to assess exercise capacity and ischemic burden. Patients were treated with 9 sessions of ESMR to ischemic areas over 9 weeks. Efficacy end points were exercise capacity by using treadmill test as well as ischemic burden on pharmacological SPECT at 4 months after the last ESMR treatment. Safety measures included electrocardiography, echocardiography, troponin, creatine kinase, and brain natriuretic peptide testing, and pain questionnaires.

RESULTS

Fifteen patients with medically refractory angina and no revascularization options were enrolled. There was a statistically significant mean increase of 122.3±156.9 seconds (38% increase compared with baseline; P=.01) in exercise treadmill time from baseline (319.8±157.2 seconds) to last follow-up after the ESMR treatment (422.1±183.3 seconds). There was no improvement in the summed stress perfusion scores after pharmacologically induced stress SPECT at 4 months after the last ESMR treatment in comparison to that at screening; however, SPECT summed stress score revealed that untreated areas had greater progression in ischemic burden vs treated areas (3.69±6.2 vs 0.31±4.5; P=.03). There was no significant change in the mean summed echo score from baseline to posttreatment (0.4±5.1; P=.70). The ESMR therapy was performed safely without any adverse events in electrocardiography, echocardiography, troponins, creatine kinase, or brain natriuretic peptide. Pain during the ESMR treatment was minimal (a score of 0.5±1.2 to 1.1±1.2 out of 10).

CONCLUSION

In this multicenter feasibility study, ESMR seems to be a safe and efficacious treatment for patients with refractory angina pectoris. However, larger sham-controlled trials will be required to confirm these findings.

Endothelial dysfunction occurs prior to clinical evidence of polycystic kidney disease

OBJECTIVE

Polycystic kidney disease (PKD), a monogenic disease with an autosomal dominant or an autosomal recessive form of inheritance (ARPKD), is the most common genetic cause of renal dysfunction and end-stage renal failure. In addition to the development of cysts, the autosomal form of PKD is associated with vascular endothelial dysfunction, a marker of vascular disease. Whether vascular endothelial dysfunction is also present in ARPKD, and its relationship with renal dysfunction remain to be determined.

METHODS

ARPKD rats (PCK model) and controls were studied at 6 and 10 weeks of age, and mean arterial pressure and renal function were measured. Aortic endothelial function was assessed using organ chamber techniques. Aortic endothelial cells (ECs) were isolated, characterized and their function studied.

RESULTS

Compared to controls, ARPKD animals had a decrease in the vasorelaxation to endothelium-dependent vasodilators, even prior to changes in mean arterial pressure or renal function. The abnormal vasoreactivity was corrected with L-arginine (a precursor of nitric oxide, NO), while the expression of endothelial NO synthase (eNOS) was unchanged. Furthermore, isolated ECs from 6-week-old ARPKD animals showed increased oxidative stress, with preserved eNOS expression and abnormal patterns of migration and angiogenic capacity (measured by the scratch and tube formation assays, respectively).

CONCLUSION

ARPKD leads to impairments in aortic vascular function and ECs at an early stage, which can have significant functional consequences, potentially representing a novel therapeutic target in this disease.

Polycystic kidneys have decreased vascular density: a micro-CT study

OBJECTIVE

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure and many of these patients suffer vascular dysfunction and hypertension. It remains unclear whether PKD is associated with abnormal microvascular structure. Thus, this study examined the renovascular structure in PKD.

METHODS

PKD rats (PCK model) and controls were studied at 10 weeks of age, and mean arterial pressure (MAP), renal blood flow, and creatinine clearance were measured. Microvascular architecture and cyst number and volume were assessed using micro-computed tomography, and angiogenic pathways evaluated.

RESULTS

Compared with controls, PKD animals had an increase in MAP (126.4 ± 4.0 vs. 126.2 ± 2.7 mmHg) and decreased clearance of creatinine (0.39 ± 0.09 vs. 0.30 ± 0.05 mL/min), associated with a decrease in microvascular density, both in the cortex (256 ± 22 vs. 136 ± 20 vessels per cm2) and medullar (114 ± 14 vs. 50 ± 9 vessels/cm2) and an increase in the average diameter of glomeruli (104.14 ± 2.94 vs. 125.76 ± 9.06 mm). PKD animals had increased fibrosis (2.2 ± 0.2 fold vs. control) and a decrease in the cortical expression in hypoxia inducible factor 1-α and vascular endothelial growth factor.

CONCLUSIONS

PKD animals have impaired renal vascular architecture, which can have significant functional consequences. The PKD microvasculature could represent a therapeutic target to decrease the impact of this disease.

Non-invasive assessment of cardiac function in a mouse model of renovascular hypertension

Hypertension continues to be a significant cause of morbidity and mortality, underscoring the need to better understand its early effects on the myocardium. The aim of this study is to determine the feasibility of in vivo longitudinal assessment of cardiac function, particularly diastolic function, in a mouse model of renovascular hypertension. Renovascular hypertension (RVH) was induced in 129S1/SvImJ male mice (n=9). To assess left ventricular (LV) systolic and diastolic function, M-mode echocardiography, pulsed-wave Doppler echocardiography and tissue Doppler imaging were performed at baseline, 2 and 4 weeks after the induction of renal artery stenosis. Myocardial tissue was collected to assess cellular morphology, fibrosis, extracellular matrix remodeling and inflammation ex vivo. RVH led to a significant increase in systolic blood pressure after 2 and 4 weeks (baseline: 99.26±1.09 mm Hg; 2 weeks: 140.90±7.64 mm Hg; 4 weeks: 147.52±5.91 mm Hg, P<0.05), resulting in a significant decrease in LV end-diastolic volume, associated with a significant elevation in ejection fraction and preserved cardiac output. Furthermore, the animals developed an abnormal diastolic function profile, with a shortening in the E velocity deceleration time as well as increases in the E/e' and the E/A ratio. The ex vivo analysis revealed a significant increase in myocyte size and deposition of extracellular matrix. Non-invasive high-resolution ultrasonography allowed assessment of the diastolic function profile in a small animal model of renovascular hypertension.

Noninvasive monitoring of oxidative stress in transplanted mesenchymal stromal cells

OBJECTIVES

The goal of this study was to validate a pathway-specific reporter gene that could be used to noninvasively image the oxidative status of progenitor cells.

BACKGROUND

In cell therapy studies, reporter gene imaging plays a valuable role in the assessment of cell fate in living subjects. After myocardial injury, noxious stimuli in the host tissue confer oxidative stress to transplanted cells that may influence their survival and reparative function.

METHODS

Rat mesenchymal stromal cells (MSCs) were studied for phenotypic evidence of increased oxidative stress under in vitro stress. On the basis of their up-regulation of the pro-oxidant enzyme p67(phox) subunit of nicotinamide adenine dinucleotide phosphate (NAD[P]H oxidase p67(phox)), an oxidative stress sensor was constructed, comprising the firefly luciferase (Fluc) reporter gene driven by the NAD(P)H p67(phox) promoter. MSCs cotransfected with NAD(P)H p67(phox)-Fluc and a cell viability reporter gene (cytomegalovirus-Renilla luciferase) were studied under in vitro and in vivo pro-oxidant conditions.

RESULTS

After in vitro validation of the sensor during low-serum culture, transfected MSCs were transplanted into a rat model of myocardial ischemia/reperfusion (IR) and monitored by using bioluminescence imaging. Compared with sham controls (no IR), cardiac Fluc intensity was significantly higher in IR rats (3.5-fold at 6 h, 2.6-fold at 24 h, 5.4-fold at 48 h; p < 0.01), indicating increased cellular oxidative stress. This finding was corroborated by ex vivo luminometry after correcting for Renilla luciferase activity as a measure of viable MSC number (Fluc:Renilla luciferase ratio 0.011 ± 0.003 for sham vs. 0.026 ± 0.004 for IR at 48 h; p < 0.05). Furthermore, in IR animals that received MSCs preconditioned with an antioxidant agent (tempol), Fluc signal was strongly attenuated, substantiating the specificity of the oxidative stress sensor.

CONCLUSIONS

Pathway-specific reporter gene imaging allows assessment of changes in the oxidative status of MSCs after delivery to ischemic myocardium, providing a template to monitor key biological interactions between transplanted cells and their host environment in living subjects.

Circulating humanin levels are associated with preserved coronary endothelial function

Humanin is a small endogenous antiapoptotic peptide, originally identified as protective against Alzheimer's disease, but subsequently also found on human endothelium as well as carotid artery plaques. Endothelial dysfunction is a precursor to the development of atherosclerotic plaques, which are characterized by a highly proinflammatory, reactive oxygen species, and apoptotic milieu. Previous animal studies demonstrated that humanin administration may improve endothelial function. Thus the aim of this study was to test the hypothesis that patients with coronary endothelial dysfunction have reduced systemic levels of humanin. Forty patients undergoing coronary angiography and endothelial function testing were included and subsequently divided into two groups based on coronary blood flow (CBF) response to intracoronary acetylcholine (normal ≥ 50% increase from baseline, n = 20 each). Aortic plasma samples were obtained at the time of catheterization for the analysis of humanin levels and traditional biomarkers of atherosclerosis including C-reactive protein, Lp-Pla(2), and homocysteine. Baseline characteristics were similar in both groups. Patients with coronary endothelial dysfunction (change in CBF = -33 ± 25%) had significantly lower humanin levels (1.3 ± 1.1 vs. 2.2 ± 1.5 ng/ml, P = 0.03) compared with those with normal coronary endothelial function (change in CBF = 194 ± 157%). There was a significant and positive correlation between improved CBF and humanin levels (P = 0.0091) not seen with changes in coronary flow reserve (P = 0.76). C-reactive protein, Lp-Pla(2), and homocysteine were not associated with humanin levels. Thus we observed that preserved human coronary endothelial function is uniquely associated with higher systemic humanin levels, introducing a potential diagnostic and/or therapeutic target for patients with coronary endothelial function.

Cell tracking and the development of cell-based therapies: a view from the Cardiovascular Cell Therapy Research Network

Cell-based therapies are being developed for myocardial infarction (MI) and its consequences (e.g., heart failure) as well as refractory angina and critical limb ischemia. The promising results obtained in preclinical studies led to the translation of this strategy to clinical studies. To date, the initial results have been mixed: some studies showed benefit, whereas in others, no benefit was observed. There is a growing consensus among the scientific community that a better understanding of the fate of transplanted cells (e.g., cell homing and viability over time) will be critical for the long-term success of these strategies and that future studies should include an assessment of cell homing, engraftment, and fate as an integral part of the trial design. In this review, different imaging methods and technologies are discussed within the framework of the physiological answers that the imaging strategies can provide, with a special focus on the inherent regulatory issues.

Humanin, a cytoprotective peptide, is expressed in carotid atherosclerotic [corrected] plaques in humans

OBJECTIVE

The mechanism of atherosclerotic plaque progression leading to instability, rupture, and ischemic manifestation involves oxidative stress and apoptosis. Humanin (HN) is a newly emerging endogenously expressed cytoprotective peptide. Our goal was to determine the presence and localization of HN in carotid atherosclerotic plaques.

METHODS AND RESULTS

Plaque specimens from 34 patients undergoing carotid endarterectomy were classified according to symptomatic history. Immunostaining combined with digital microscopy revealed greater expression of HN in the unstable plaques of symptomatic compared to asymptomatic patients (29.42±2.05 vs. 14.14±2.13% of plaque area, p<0.0001). These data were further confirmed by immunoblot (density of HN/β-actin standard symptomatic vs. asymptomatic 1.32±0.14 vs. 0.79±0.11, p<0.01). TUNEL staining revealed a higher proportion of apoptotic nuclei in the plaques of symptomatic patients compared to asymptomatic (68.25±3.61 vs. 33.46±4.46% of nuclei, p<0.01). Double immunofluorescence labeling revealed co-localization of HN with macrophages (both M1 and M2 polarization), smooth muscle cells, fibroblasts, and dendritic cells as well as with inflammatory markers MMP2 and MMP9.

CONCLUSIONS

The study demonstrates a higher expression of HN in unstable carotid plaques that is localized to multiple cell types within the plaque. These data support the involvement of HN in atherosclerosis, possibly as an endogenous response to the inflammatory and apoptotic processes within the atheromatous plaque.

Emerging roles for integrated imaging modalities in cardiovascular cell-based therapeutics: a clinical perspective

Despite preclinical promise, the progress of cell-based therapy to clinical cardiovascular practice has been slowed by several challenges and uncertainties that have been highlighted by the conflicting results of human trials. Most telling has been the revelation that current strategies fall short of achieving sufficient retention and engraftment of cells to meet the ambitious objective of myocardial regeneration. This has sparked novel research into the refinement of cell biology and delivery to overcome these shortcomings. Within this context, molecular imaging has emerged as a valuable tool for providing noninvasive surveillance of cell fate in vivo. Direct and indirect labelling of cells can be coupled with clinically relevant imaging modalities, such as radionuclide single photon emission computed tomography and positron emission tomography, and magnetic resonance imaging, to assess their short- and long-term distributions, along with their viability, proliferation and functional interaction with the host myocardium. This review details the strengths and limitations of the different cell labelling and imaging techniques and their potential application to the clinical realm. We also consider the broader, multifaceted utility of imaging throughout the cell therapy process, providing a discussion of its considerable value during cell delivery and its importance during the evaluation of cardiac outcomes in clinical studies.

Molecular imaging of cell therapy for gastroenterologic applications

Stem cell therapy has appeared as a possible therapeutic alternative for numerous diseases. Furthermore, cancer stem cells are a focus of significant interest as they may allow for a better understanding of the genesis of different malignancies. The ultimate goal of stem cell therapeutics is to ensure the viability and functionality of the transplanted cells. Similarly, the ultimate goal of understanding cancer stem cells is to understand how they behave in the living subject. Until recently, the efficacy of stem cell therapies has been assessed by overall organ function recovery. Understanding the behavior and biology of stem cells directly in the living subject can also lead to therapy optimization. Thus, there is a critical need for reliable and accurate methods to understand stem cell biology in vivo. Recent advances in both imaging and molecular biology have enabled transplanted stem cells to be successfully monitored in the living subject. The use of molecular imaging modalities has the capability to answer these questions and may one day be translated to patients. In this review, we will discuss the potential imaging strategies and how they can be utilized, depending on the questions that need to be answered.

Role of oxidative stress in hypoxia preconditioning of cells transplanted to the myocardium: a molecular imaging study

AIM

Cell-based therapies are a potential therapeutic alternative for the treatment of coronary artery disease (CAD). However, transplanted cells undergo significant death in the living subject. Hypoxic preconditioning (HPC) is a potential intervention to increase transplanted cell survival. However, the biological mechanisms of this benefit remain unclear. We hypothesize that the beneficial effect of HPC on stem cell survival is in part due to preservation of oxidant status, an effect that will be monitored using state-of-the-art molecular imaging.

METHODS

H9c2 rat cardiomyoblasts expressing the construct CMV-firefly luciferase (h9c2-fluc), with and without HPC, were exposed to hypoxia, and oxidative stress and cell survival were measured. Subsequently, H9c2-fluc cells, with and without HPC, were injected into the myocardium of rats and cell survival was monitored daily with Bioluminescence (BLI) using a CCD camera.

RESULTS

Compared to controls, cells exposed to hypoxia had increased amount of reactive oxygen species (ROS, control: 14.1±0.9 vs. hypoxia: 19.5 ± 2.0 RFU/µg protein, P=0.02) and decreased cell survival (control: 0.29 ± 0.005 vs. hypoxia: 0.24 ± 0.005 OD, P<0.001). HPC treatment decreased the amount of hypoxia-induced ROS (HPC: 11.5 ± 0.7RFU/µg protein, P=0.002 vs. hypoxia and P=0.11 vs. control), associated with improved survival (HPC: 0.27 ± 0.004OD/µg protein, P=0.002 vs. hypoxia and P=0.005 vs. control). Most importantly, compared to un-conditioned cells, HPC-cells had increased cell survival after transplantation to the myocardium (C: 34.7 ± 6.7% vs. HPC: 83.4 ± 17.5% at day 5 compared to day 1, P=0.01).

CONCLUSION

The beneficial effect of HPC is in part due to preservation of oxidant status. Molecular imaging can assess changes in cell survival in the living subject and has the potential to be applied clinically.

Improved survival of mesenchymal stromal cell after hypoxia preconditioning: role of oxidative stress

AIMS

To investigate the mechanisms underlying the beneficial effect of hypoxia preconditioning (HPC) on mesenchymal stromal cells (MSCs) and optimize novel non-invasive methods to assess the effect of biological interventions aimed to increased cell survival.

MAIN METHODS

MSCs from rat femur, with or without HPC, were exposed to hypoxic conditions in cell culture (1% O(2) for 24h) and cell survival (by the LDH release assay and Annexin-V staining) was measured. Oxidant status (conversion of dichloro-fluorescein-DCF- and dihydro-ethidium-DHE-, protein expression of oxidant enzymes) was characterized, together with the mobility pattern of cells under stress. Furthermore, cell survival was assessed non-invasively using state-of-the-art molecular imaging.

KEY FINDINGS

Compared to controls, Hypoxia resulted in increased expression of the oxidative stress enzyme NAD(P)H oxidase (subunit 67(phox): 0.05 ± 0.01AU and 0.48 ± 0.02AU, respectively, p<0.05) and in the amount of ROS (DCF: 13 ±1 and 42 ± 3 RFU/μg protein, respectively, p<0.05) which led to a decrease in stem cell viability. Hypoxia preconditioning preserved cell biology, as evidenced by preservation of oxidant status (16 ± 1 RFU/μg protein, p<0.05 vs. hypoxia), and cell viability. Most importantly, the beneficial effect of HPC can be assessed non-invasively using molecular imaging.

SIGNIFICANCE

HPC preserves cell viability and function, in part through preservation of oxidant status, and its effects can be assessed using state-of-the-art molecular imaging. Understanding of the mechanisms underlying the fate of stem cells will be critical for the advancement of the field of stem cell therapy.

Indirect imaging of cardiac-specific transgene expression using a bidirectional two-step transcriptional amplification strategy

Transcriptional targeting for cardiac gene therapy is limited by the relatively weak activity of most cardiac-specific promoters. We have developed a bidirectional plasmid vector, which uses a two-step transcriptional amplification (TSTA) strategy to enhance the expression of two optical reporter genes, firefly luciferase (fluc) and Renilla luciferase (hrluc), driven by the cardiac troponin T (cTnT) promoter. The vector was characterized in vitro and in living mice using luminometry and bioluminescence imaging to assess its ability to mediate strong, correlated reporter gene expression in a cardiac cell line and the myocardium, while minimizing expression in non-cardiac cell lines and the liver. In vitro, the TSTA system significantly enhanced cTnT-mediated reporter gene expression with moderate preservation of cardiac specificity. After intramyocardial and hydrodynamic tail vein delivery of an hrluc-enhanced variant of the vector, long-term fluc expression was observed in the heart, but not in the liver. In both the cardiac cell line and the myocardium, fluc expression correlated well with hrluc expression. These results show the vector's ability to effectively amplify and couple transgene expression in a cardiac-specific manner. Further replacement of either reporter gene with a therapeutic gene should allow non-invasive imaging of targeted gene therapy in living subjects.

Antioxidants improve early survival of cardiomyoblasts after transplantation to the myocardium

PURPOSE

We tested the hypothesis that modulation of the microenvironment (using antioxidants) will increase stem cell survival in hypoxia and after transplantation to the myocardium.

PROCEDURES

Rat cardiomyoblasts were stably transfected with a reporter gene (firefly luciferase) for bioluminescence imaging (BLI). First, we examined the role of oxidative stress in cells under hypoxic conditions. Subsequently, stem cells were transplanted to the myocardium of rats using high-resolution ultrasound, and their survival was monitored daily using BLI.

RESULTS

Under hypoxia, oxidative stress was increased together with decreased cell survival compared to control cells, both of which were preserved by antioxidants. In living subjects, oxidative stress blockade increased early cell survival after transplantation to the myocardium, compared to untreated cells/animals.

CONCLUSION

Modulation of the local microenvironment (with antioxidants) improves stem cell survival. Increased understanding of the interaction between stem cells and their microenvironment will be critical to advance the field of regenerative medicine.

Noninvasive evaluation of immunosuppressive drug efficacy on acute donor cell survival

PURPOSE

The therapeutic benefits of cell transplantation may depend on the survival of sufficient numbers of grafted cells. We evaluate four potent immunosuppressive medications aimed at preventing acute donor cell death.

PROCEDURES AND RESULTS

Embryonic rat H9c2 myoblasts were stably transduced to express firefly luciferase reporter gene (H9c2-Fluc). H9c2-Fluc cells (3x10(6)) were injected into thigh muscles of Sprague-Dawley rats (N=30) treated with cyclosporine, dexamethasone, mycophenolate mofetil, tacrolimus, or saline from day -3 to day +14. Longitudinal optical bioluminescence imaging was performed over two weeks. Fluc activity was 40.0+/-12.1% (dexamethasone), 30.5+/-12.5% (tacrolimus), and 21.5+/-3.5% (mycophenolate) vs. 12.0+/-5.0% (control) and 8.3+/-5.0% (cyclosporine) at day 4 (P<0.05). However, by day 14, cell signals had decreased drastically to <10% for all groups despite drug therapy.

CONCLUSION

This study demonstrates the ability of optical molecular imaging for tracking cell survival noninvasively and raises important questions with regard to the overall efficacy of immunosuppressives for prolonging transplanted cell survival.

Imaging gene expression in human mesenchymal stem cells: from small to large animals

PURPOSE

To evaluate the feasibility of reporter gene imaging in implanted human mesenchymal stem cells (MSCs) in porcine myocardium by using clinical positron emission tomography (PET)-computed tomography (CT) scanning.

MATERIALS AND METHODS

Animal protocols were approved by the Institutional Administrative Panel on Laboratory Animal Care. Transduction of human MSCs by using different doses of adenovirus that contained a cytomegalovirus (CMV) promoter driving the mutant herpes simplex virus type 1 thymidine kinase reporter gene (Ad-CMV-HSV1-sr39tk) was characterized in a cell culture. A total of 2.25 x 10(6) transduced (n = 5) and control nontransduced (n = 5) human MSCs were injected into the myocardium of 10 rats, and reporter gene expression in human MSCs was visualized with micro-PET by using the radiotracer 9-(4-[fluorine 18]-fluoro-3-hydroxymethylbutyl)-guanine (FHBG). Different numbers of transduced human MSCs suspended in either phosphate-buffered saline (PBS) (n = 4) or matrigel (n = 5) were injected into the myocardium of nine swine, and gene expression was visualized with a clinical PET-CT. For analysis of cell culture experiments, linear regression analyses combined with a t test were performed. To test differences in radiotracer uptake between injected and remote myocardium in both rats and swine, one-sided paired Wilcoxon tests were performed. In swine experiments, a linear regression of radiotracer uptake ratio on the number of injected transduced human MSCs was performed.

RESULTS

In cell culture, there was a viral dose-dependent increase of gene expression and FHBG accumulation in human MSCs. Human MSC viability was 96.7% (multiplicity of infection, 250). Cardiac FHBG uptake in rats was significantly elevated (P < .0001) after human MSC injection (0.0054% injected dose [ID]/g +/- 0.0007 [standard deviation]) compared with that in the remote myocardium (0.0003% ID/g +/- 0.0001). In swine, myocardial radiotracer uptake was not elevated after injection of up to 100 x 10(6) human MSCs (PBS group). In the matrigel group, signal-to-background ratio increased to 1.87 after injection of 100 x 10(6) human MSCs and positively correlated (R(2) = 0.97, P < .001) with the number of administered human MSCs.

CONCLUSION

Reporter gene imaging in human MSCs can be translated to large animals. The study highlights the importance of co-administering a "scaffold" for increasing intramyocardial retention of human MSCs.

Comparison of optical bioluminescence reporter gene and superparamagnetic iron oxide MR contrast agent as cell markers for noninvasive imaging of cardiac cell transplantation

PURPOSE

In this study, we compared firefly luciferase (Fluc) reporter gene and superparamagnetic iron oxide (Feridex) as cell markers for longitudinal monitoring of cardiomyoblast graft survival using optical bioluminescence imaging (BLI) and magnetic resonance imaging (MRI), respectively.

PROCEDURES

Rats (n = 31) underwent an intramyocardial injection of cardiomyoblasts (2 x 10(6)) labeled with Fluc, Feridex, or no marker (control) or an injection of Feridex alone (75 microg). Afterward, rats were serially imaged with BLI or MRI and killed at different time points for histological analysis.

RESULTS

BLI revealed a drastically different cell survival kinetics (half-life = 2.65 days over 6 days) than that revealed by MRI (half-life = 16.8 days over 80 days). Injection of Feridex alone led to prolonged tissue retention of Feridex (> or =16 days) and persistent MR signal (> or =42 days).

CONCLUSIONS

Fluc BLI reporter gene imaging is a more accurate gauge of transplanted cell survival as compared to MRI of Feridex-labeled cells.

Imaging of VEGF receptor in a rat myocardial infarction model using PET

Myocardial infarction (MI) leads to left ventricular (LV) remodeling, which leads to the activation of growth factors such as vascular endothelial growth factor (VEGF). However, the kinetics of a growth factor's receptor expression, such as VEGF, in the living subject has not yet been described. We have developed a PET tracer (64Cu-DOTA-VEGF121 [DOTA is 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid]) to image VEGF receptor (VEGFR) expression after MI in the living subject.

METHODS

In Sprague-Dawley rats, MI was induced by ligation of the left coronary artery and confirmed by ultrasound (n = 8). To image and study the kinetics of VEGFRs, 64Cu-DOTA-VEGF121 PET scans were performed before MI induction (baseline) and on days 3, 10, 17, and 24 after MI. Sham-operated animals served as controls (n = 3).

RESULTS

Myocardial origin of the 64Cu-DOTA-VEGF121 signal was confirmed by CT coregistration and autoradiography. VEGFR specificity of the 64Cu-DOTA-VEGF121 probe was confirmed by in vivo use of a 64Cu-DOTA-VEGFmutant. Baseline myocardial uptake of 64Cu-DOTA-VEGF121 was minimal (0.30 +/- 0.07 %ID/g [percentage injected dose per gram of tissue]); it increased significantly after MI (day 3, 0.97 +/- 0.05 %ID/g; P < 0.05 vs. baseline) and remained elevated for 2 wk (up to day 17 after MI), after which time it returned to baseline levels.

CONCLUSION

We demonstrate the feasibility of imaging VEGFRs in the myocardium. In summary, we imaged and described the kinetics of 64Cu-DOTA-VEGF121 uptake in a rat model of MI. Studies such as the one presented here will likely play a major role when studying pathophysiology and assessing therapies in different animal models of disease and, potentially, in patients.