The use of technetium Tc 99m annexin V for in vivo imaging of apoptosis during cardiac allograft rejection

Modulators of radiation-induced cardiopulmonary toxicities for non-small cell lung cancer: Integrated cytokines, single nucleotide variants, and HBP systems imaging

Radiation therapy (RT)-induced cardiopulmonary toxicities remain dose-limiting toxicities for patients receiving radiation dosages to the thorax, especially for lung cancer. Means of monitoring and predicting for those receiving RT or concurrent chemoradiation therapy before treatment begins in individual patients could benefit early intervention to prevent or minimize RT-induced side effects. Another aspect of an individual's susceptibility to the adverse effects of thoracic irradiation is the immune system as reflected by phenotypic factors (patterns of cytokine expressions), genotypic factors (single nucleotide variants SNVs; formerly single nucleotide polymorphisms [SNPs]), and aspects of quantitative cellular imaging. Levels of transcription, production, and functional activity of cytokines are often influenced by SNVs that affect coding regions in the promoter or regulatory regions of cytokine genes. SNVs can also lead to changes in the expression of the inflammatory cytokines, interferons, interleukins (IL-6, IL-17) and tumor necrosis factors (TNF-α) at the protein level. RT-induced cardiopulmonary toxicities could be quantified by the uptake of ¹⁸F-fluorodeoxyglucose (FDG), however, FDG is a sensitive but not specific biomarker in differential diagnosis between inflammation/infection and tumor recurrence. FDG is suitable for initial diagnosis of predisposed tissue injuries in non-small cell lung cancer (NSCLC). ^99mTc-ethylenedicysteine-glucosamine (^99mTc-EC-G) was able to measure tumor DNA proliferation and myocardial ischemia via hexosamine biosynthetic pathways (HBP). Thus, ^99mTc-EC-G could be an alternative to FDG in the assessment of RT doses and select patients in HBP-directed targets for optimal outcomes. This article reviewed correlative analyses of pro-inflammatory cytokines, genotype SNVs, and cellular imaging to improve the diagnosis, prognosis, monitoring, and prediction of RT-induced cardiopulmonary toxicities in NSCLC.

Targeting phosphatidylserine for radionuclide-based molecular imaging of apoptosis

One major characteristic of programmed cell death (apoptosis) results in the increased expression of phosphatidylserine (PS) on the outer membrane of dying cells. Consequently, PS represents an excellent target for non-invasive imaging of apoptosis by single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Annexin V is a 36 kDa protein which binds with high affinity to PS in the presence of Ca²⁺ ions. This makes radiolabeled annexins valuable apoptosis imaging agents for clinical and biomedical research applications for monitoring apoptosis in vivo. However, the use of radiolabeled annexin V for in vivo imaging of cell death has been met with a variety of challenges which have prevented its translation into the clinic. These difficulties include: complicated and time-consuming radiolabeling procedures, sub-optimal biodistribution, inadequate pharmacokinetics leading to poor tumour-to-blood contrast ratios, reliance upon Ca²⁺ concentrations in vivo, low tumor tissue penetration, and an incomplete understanding of what constitutes the best imaging protocol following induction of apoptosis. Therefore, new concepts and improved strategies for the development of PS-binding radiotracers are needed. Radiolabeled PS-binding peptides and various Zn(II) complexes as phosphate chemosensors offer an innovative strategy for radionuclide-based molecular imaging of apoptosis with PET and SPECT. Radiolabeled peptides and Zn(II) complexes provide several advantages over annexin V including better pharmacokinetics due to their smaller size, better availability, simpler synthesis and radiolabeling strategies as well as facilitated tissue penetration due to their smaller size and faster blood clearance profile allowing for optimized image contrast. In addition, peptides can be structurally modified to improve metabolic stability along with other pharmacokinetic and pharmacodynamic properties. The present review will summarize the current status of radiolabeled annexins, peptides and Zn(II) complexes developed as radiotracers for imaging apoptosis through targeting PS utilizing PET and SPECT imaging.

Noninvasive Whole-Body Imaging of Phosphatidylethanolamine as a Cell Death Marker Using 99mTc-Duramycin During TNF-Induced SIRS

Systemic inflammatory response syndrome (SIRS) is an inflammatory state affecting the whole body. It is associated with the presence of pro- and antiinflammatory cytokines in serum, including tumor necrosis factor (TNF). TNF has multiple effects and leads to cytokine production, leukocyte infiltration, and blood pressure reduction and coagulation, thereby contributing to tissue damage and organ failure. A sterile mouse model of sepsis, TNF-induced SIRS, was used to visualize the temporal and spatial distribution of damage in susceptible tissues during SIRS. For this, a radiopharmaceutical agent, ^99mTc-duramycin, that binds to exposed phosphatidylethanolamine on dying cells was longitudinally visualized using SPECT/CT imaging. Methods: C57BL/6J mice were challenged with intravenous injections of murine TNF or vehicle, and necrostatin-1 was used to interfere with cell death. Two hours after vehicle or TNF treatment, mice received ^99mTc-duramycin intravenously (35.44 ± 3.80 MBq). Static whole-body ^99mTc-duramycin SPECT/CT imaging was performed 2, 4, and 6 h after tracer injection. Tracer uptake in different organs was quantified by volume-of-interest analysis using PMOD software and expressed as SUV_mean After the last scan, ex vivo biodistribution was performed to validate the SPECT imaging data. Lastly, terminal deoxynucleotidyl-transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining was performed to correlate the obtained results to cell death. Results: An increased ^99mTc-duramycin uptake was detected in mice injected with TNF, when compared with control mice, in lungs (0.55 ± 0.1 vs. 0.34 ± 0.05), intestine (0.75 ± 0.13 vs. 0.56 ± 0.1), and liver (1.03 ± 0.14 vs. 0.64 ± 0.04) 4 h after TNF and remained significantly elevated until 8 h after TNF. The imaging results were consistent with ex vivo γ-counting results. Significantly increased levels of tissue damage were detected via TUNEL staining in the lungs and intestine of mice injected with TNF. Interestingly, necrostatin-1 pretreatment conferred protection against lethal SIRS and reduced the ^99mTc-duramycin uptake in the lungs 8 h after TNF (SUV, 0.32 ± 0.1 vs. 0.51 ± 0.15). Conclusion: This study demonstrated that noninvasive ^99mTc-duramycin SPECT imaging can be used to characterize temporal and spatial kinetics of injury and cell death in susceptible tissues during TNF-induced SIRS, making it useful for global, whole-body assessment of tissue damage during diseases associated with inflammation and injury.

Association Between a Polymorphism in CASP3 and CASP9 Genes and Ischemic Stroke

Objective

To investigate whether the polymorphisms of CASP3 gene (rs4647602, intron A/C and rs1049216, UTR C/T) and CASP9 gene (rs1052576, Gln/Arg G/A and rs1052571, Ser/Val T/C) were associated with the development, and clinical severity of ischemic stroke and functional consequences after stroke.

Methods

Genomic DNA from 121 ischemic stroke patients and 201 healthy control subjects were extracted, and polymerase chain reaction products were sequenced. To investigate the association of polymorphisms and the development, and National Institutes of Health Stroke Scale (K-NIHSS), logistic regression models were analyzed.

Results

Polymorphism of the untranslational region of CASP3 (rs1049216, UTR C/T) has been associated with the development of ischemic stroke—in codominant1 model (odds ratio [OR], 0.51; 95% confidence interval [CI], 0.29–0.88; p=0.017), in dominant model (OR, 0.57; 95% CI, 0.34–0.97; p=0.034), and in the overdominant model (OR, 0.50; 95% CI, 0.29–0.87; p=0.011). A missense SNP of CASP9 gene (rs1052571, Ser/Val T/C) was associated with the development of ischemic stroke (OR, 1.93; 95% CI, 1.05–3.55; p=0.034 in recessive model).

Conclusion

These results indicate the possibility that CASP3 and CASP9 genes are markers for the development of ischemic stroke.

Emerging imaging techniques after cardiac transplantation

Improvements in survival after cardiac transplantation have in part been driven by improved graft surveillance. Graft surveillance relies mainly on 3 techniques: coronary angiography, endomyocardial biopsy and echocardiography. Developments in invasive and non-invasive imaging technology have revolutionized assessment of the heart in both health and disease, offering new insights into tissue composition and myocardial metabolism. Herein we aim to review the strengths and weaknesses of these techniques, and summarize the evidence in the following 5 fields of cardiac imaging after transplantation: cardiovascular magnetic resonance; computed tomography; positron emission tomography; single-photon emission computed tomography; and optical coherence tomography and molecular imaging techniques.

Radiolabeled apoptosis imaging agents for early detection of response to therapy

Since apoptosis plays an important role in maintaining homeostasis and is associated with responses to therapy, molecular imaging of apoptotic cells could be useful for early detection of therapeutic effects, particularly in oncology. Radiolabeled annexin V compounds are the hallmark in apoptosis imaging in vivo. These compounds are reviewed from the genesis of apoptosis (cell death) imaging agents up to recent years. They have some disadvantages, including slow clearance and immunogenicity, because they are protein-based imaging agents. For this reason, several studies have been conducted in recent years to develop low molecule apoptosis imaging agents. In this review, radiolabeled phosphatidylserine targeted peptides, radiolabeled bis(zinc(II)-dipicolylamine) complex, radiolabeled 5-fluoropentyl-2-methyl-malonic acid (ML-10), caspase-3 activity imaging agents, radiolabeled duramycin, and radiolabeled phosphonium cation are reviewed as promising low-molecular-weight apoptosis imaging agents.

⁹⁹mTc-N4amG: synthesis biodistribution and imaging in breast tumor-bearing rodents

(99m)Tc-N4-guanine ((99m)Tc-N4amG) was synthesized and evaluated in this study. Cellular uptake and cellular fraction studies were performed to evaluate the cell penetrating ability. Biodistribution and planar imaging were conducted in breast tumor-bearing rats. Up to 17%ID uptake was observed in cellular uptake study with 40% of (99m)Tc-N4amG was accumulated in the nucleus. Biodistribution and scintigraphic imaging studies showed increased tumor/muscle count density ratios as a function of time. Our results demonstrate the feasibility of using (99m)Tc-N4amG in tumor specific imaging.

Adverse cardiovascular effects of anabolic steroids: pathophysiology imaging

BACKGROUND

  Anabolic-androgenic steroids (AAS) are widely abused for enhancing muscle mass, strength, growth and improving athletic performance.

MATERIALS AND METHODS

  In recent years, many observational and interventional studies have shown important adverse cardiovascular effects of AAS abuse.

CONCLUSIONS

  This review discusses established and future perspectives of novel molecular imaging techniques that may serve as potential tools for early detection of AAS-associated cardiovascular disorders.

Noninvasive monitoring the biology of atherosclerotic plaque development with radiolabeled annexin V and matrix metalloproteinase inhibitor in spontaneous atherosclerotic mice

OBJECTIVES

To compare the ability of (99m)Tc-labeled broad-based matrix metalloproteinase inhibitor (RP805) (MPI) and (99m)Tc-annexin V to identify more advanced atherosclerotic disease in apolipoprotein E-null (apoE(-/-)) mice.

BACKGROUND

Both MMP expression and apoptotic cell death occur in both early and in advanced atherosclerotic plaques.

METHODS

Eight 6-9-week-old apoE(-/-) mice, 10 apoE(-/-) mice at 20 weeks, and 12 apoE(-/-) at 40 weeks were injected with both tracers in alternating sequence separated by 48 h, underwent planar imaging and were killed. Radiotracer uptake was quantified from the scans as percent whole body and from tissue as percent injected dose per gram (%ID/g). Quantitative immunohistopathology of the aorta and carotids for macrophages, MMPs, and caspase was performed.

RESULTS

At 6 weeks, mice showed no tracer uptake in the chest or neck and had minimal lesion. At 20 weeks, uptake of annexin V as %ID was borderline higher than MPI (1.10 ± .48% vs .77 ± .31%, P = .09), between 20 and 40 weeks aortic lesion area increased from 37.4 ± 12.0% to 46.2 ± 7.4% and at 40 weeks MPI was significantly greater than annexin V uptake (1.11 ± .66% vs .70 ± .16%, P = .05). On histology there were greater increases in % MMP-2 and -9 than % caspase positive cells. Carotid uptake of MPI was greater than annexin V at both 20 and 40 weeks (1.25 ± .48% vs .78 ± .25%, P = .02 and 3.70 ± 1.45% vs 2.25 ± .66%, P = .005). The carotid lesion area at 40 weeks was 74 ± 9% with greater % cells positive for MMP's than caspase. %ID/g annexin V correlated significantly with % macrophages and with caspase-3 positive cells and %ID/g MPI correlated significantly with % macrophages and with MMP-2 and -9 positive cells.

CONCLUSIONS

In apoE(-/-) mice, MMP expression is greater than apoptosis as the disease progresses and MPI may be a better imaging agent for more advanced disease.

Speckle-tracking 2-dimensional strain echocardiography: a new noninvasive imaging tool to evaluate acute rejection in cardiac transplantation

BACKGROUND

There remains no reliable non-invasive method to detect cardiac transplant rejection. Recently, speckle-tracking 2-dimensional strain echocardiography (2DSE) was shown to be sensitive in the early detection of myocardial dysfunction in various models of cardiomyopathy. We aim to determine if 2DSE-derived functional indices can detect cardiac transplant rejection.

METHODS

Heterotopic rat cardiac transplantation was performed in histocompatible isografts or histoincompatible allografts. Histologic rejection scores were determined. Short-axis, mid-left ventricular (LV) echocardiography was performed on Day 6 after transplantation. Conventional measures of function were measured, (including LV fractional shortening and ejection fraction) as well as 2DSE parameters.

RESULTS

Despite class IIIB rejection in allografts and no rejection in isografts, there was no difference between isografts vs allografts in fractional shortening (15% +/- 3% vs 12% +/- 3%) or ejection fraction (36% +/- 5% vs 26% +/- 6%; both not significant). In contrast, 2DSE revealed decreases between isografts and allografts in global radial strain (12.6% +/- 5.6% vs 1.1% +/- 0.2%, p < 0.05), peak radial systolic strain rate (3.10 +/- 0.74/s vs 0.54 +/- 0.13/s, p < 0.001), and peak circumferential systolic strain rate (-1.99 +/- 0.55 vs -0.43 +/- 0.11/s; p < 0.01).

CONCLUSIONS

Systolic strain imaging using 2DSE differentiates myocardial function between experimental cardiac transplant rejection in allografts and non-rejection in isografts. Therefore, 2DSE may be useful in early non-invasive detection of transplant rejection.

Efficient site-specific radiolabeling of a modified C2A domain of synaptotagmin I with [99mTc(CO)3]+: a new radiopharmaceutical for imaging cell death

We describe the design and synthesis of a new Tc-99m labeled bioconjugate for cell-death imaging, based on C2A, the phosphatidylserine (PS)-binding domain of rat synaptotagmin I. Since several lysine residues in this protein are critical for PS binding, we engineered a new protein, C2AcH, to include the C-terminal sequence CKLAAALEHHHHHH, incorporating a free cysteine (for site-specific covalent modification) and a hexahistidine tag (for site-specific radiolabeling with [99mTc(CO)3(OH2)3]+). We also engineered a second derivative, C2Ac, in which the C-terminal sequence included only the C-terminal cysteine. These proteins were characterized by electrospray mass spectrometry, SDS/PAGE, and size exclusion chromatography and radiolabeled with [99mTc(CO)3(OH2)3]+. Conjugates of the proteins with the rhenium analogue [Re(CO)3(OH2)3]+ were also synthesized. Site-specific labeling was confirmed by performing a tryptic digest of rhenium tricarbonyl-labeled C2AcH, and only peptides containing the His-tag contained the [Re(CO)3]+. The labeled proteins were tested for binding to red blood cells (RBC) with exposed PS in a calcium dependent manner. Labeling 100 microg of C2AcH with [99mTc(CO)3(OH2)3]+ at 37 degrees C for 30 min gave a radiochemical yield of > 96%. However, C2AcH that had first been conjugated with fluorescein maleimide or iodoacetamide via the Cys residue gave only 50% and 83% radiochemical yield, respectively, after incubation for 30 min at 37 degrees C. Serum stability results indicated that >95% of radiolabeled C2AcH remained stable for at least 18 h at 37 degrees C. Site-specifically labeled C2AcH exhibited calcium-dependent binding to the PS on the RBC, whereas a nonspecifically modified derivative, C2AcH-B, in which lysines had been modified with benzyloxycarbonyloxy, did not. We conclude that (i) the combination of Cys and a His-tag greatly enhances the rate and efficiency of labeling with [99mTc(CO)3(OH2)3]+ compared to either the His-tag or the Cys alone, and this sequence deserves further evaluation as a radiolabeling tag; (ii) non-site-specific modification of C2A via lysine residues impairs target binding affinity; (iii) 99mTc-C2AcH has excellent radiolabeling, stability and PS binding characteristics and warrants in vivo evaluation as a cell-death imaging agent.

Radionuclide noninvasive evaluation of heart failure beyond left ventricular function assessment

The management of patients with heart failure (HF) is challenging and requires the integration of clinical skills and accurate ancillary tests for the correct diagnosis and estimation of individual prognosis. Although the basic characterization of patients with HF is supported primarily by echocardiographic assessment of the left ventricular function, other noninvasive imaging procedures are being developed, including those involved in the processes of myocardial perfusion, metabolism, cellular injury, intersticial dysregulation, and neurohormonal receptor function. Nuclear techniques for molecular imaging of the myocardium may provide valuable insights into the pathophysiology, severity, management (medical/mechanical/surgical), response to treatment, and prognosis of HF patients. This will permit individualized management decisions and hopefully facilitate better clinical outcomes for patients with HF.

Prevalence of different gadolinium enhancement patterns in patients after heart transplantation

OBJECTIVES

Transplant coronary artery disease (TCAD) limits long-term survival after heart transplantation (HTX). We hypothesized that contrast-enhanced magnetic resonance imaging (CE-MRI) detects chronic TCAD-related myocardial infarctions (MIs), even in patients with angiographically classified mild TCAD.

BACKGROUND

Coronary angiography underestimates the TCAD-degree, subsequently missing occluded small coronary arteries and resulting MI. CE-MRI as a noninvasive imaging technique identifies infarct-typical MI and myocardial fibrosis.

METHODS

CE-MRI (gadolinium: 0.2 mmol/kg/bw) was performed in 53 HTX patients on a 1.5-T MRI scanner (Philips, Best, the Netherlands). Infarct-typical CE-MRI areas were classified as: I=<or=25%, II=25% to 50%, III=50% to 75% and IV=>or=75%. Infarct-atypical forms were divided into diffuse, spotted, intramural, and infero-septal. Coronary angiography results were reviewed qualitatively with the TCAD score (TCAD I=mild evidence; II=30% to 75%, III=>or=75% stenosis). Groups were compared with analysis of variance (statistically significant p values<or=0.05).

RESULTS

Infarct-typical CE-MRI was already present in TCAD I+II, increased significantly between groups (I=23%, II=33%, III=84%, p<0.05), and involved only single coronary territories in TCAD I but multiple vessels in TCAD II+III. Infarct-atypical CE-MRI was equally distributed across all TCAD stages (I=50% vs. II=58% vs. III=42%, p=NS) without relation to a coronary territory. Patients with only infarct-atypical CE-MRI were associated with significantly better left ventricular function compared with patients with infarct-typical or combined CE-MRI patterns (ejection fraction=66+/-6% vs. 45+/-16% or 60+/-13%; end-diastolic volume=139+/-32 ml vs. 148+/-27 ml or 164+/-43 ml; end-systolic volume=47+/-15 ml vs. 81+/-27 ml or 69+/-38 ml, p<or=0.05).

CONCLUSIONS

CE-MRI allows identification of silent MI in apparently event-free HTX patients and is able to disclose myocardial fibrosis already in patients with absent or mild angiographic TCAD. CE-MRI might be helpful to establish an earlier TCAD diagnosis and to intensify medical treatment. Future studies are necessary to test prognostic implications associated with CE-MRI patterns.

Translational imaging: imaging of apoptosis

Since its original description in 1972, apoptosis or programmed cell death has been recognized as the major pathway by which the body precisely regulates the number and type of its cells as part of normal embryogenesis, development, and homeostasis. Later it was found that apoptosis was also involved in the pathogenesis of a number of human diseases, cell immunity, and the action of cytotoxotic drugs and radiation therapy in cancer treatment. As such, the imaging of apoptosis with noninvasive techniques such as with radiotracers, including annexin V and lipid proton magnetic resonance spectroscopy, may have a wide range of clinical utility in both the diagnosis and monitoring therapy of a wide range of human disorders. In this chapter we review the basic biochemical and morphologic features of apoptosis and the methods developed thus far to image this complex process in humans.

Assessment of neuroprotection in the retina with DARC

Currently, assessment of new drug efficacy in glaucoma relies on conventional perimetry to monitor visual field changes. However, visual field defects cannot be detected until 20-40% of retinal ganglion cells (RGCs), the key cells implicated in the development of irreversible blindness in glaucoma, have been lost. We have recently developed a new, noninvasive real-time imaging technology, which is named DARC (detection of apoptosing retinal cells), to visualize single RGC undergoing apoptosis, the earliest sign of glaucoma. Utilizing fluorescently labeled annexin 5 and confocal laser scanning ophthalmoscopy, DARC enables evaluation of treatment effectiveness by monitoring RGC apoptosis in the same living eye over time. Using DARC, we have assessed different neuroprotective therapies in glaucoma-related animal models and demonstrated DARC to be a useful tool in screening neuroprotective strategies. DARC will potentially provide a meaningful clinical end point that is based on the direct assessment of the RGC death process, not only being useful in assessing treatment efficacy, but also leading to the early identification of patients with glaucoma. Clinical trials of DARC in glaucoma patients are due to start in 2008.

Cardiovascular molecular imaging of apoptosis

Introduction

Molecular imaging strives to visualise processes at the molecular and cellular level in vivo. Understanding these processes supports diagnosis and evaluation of therapeutic efficacy on an individual basis and thereby makes personalised medicine possible.

Apoptosis and molecular imaging

Apoptosis is a well-organised mode of cell suicide that plays a role in cardiovascular diseases (CVD). Apoptosis is associated with loss of cardiomyocytes following myocardial infarction, atherosclerotic plaque instability, congestive heart failure and allograft rejection of the transplanted heart. Thus, apoptosis constitutes an attractive target for molecular imaging of CVD. Our current knowledge about the molecular players and mechanisms underlying apoptosis offers a rich palette of potential molecular targets for molecular imaging. However, only a few have been successfully developed so far.

Aims

This review highlights aspects of the molecular machinery and biochemistry of apoptosis relevant to the development of molecular imaging probes. It surveys the role of apoptosis in four major areas of CVD and portrays the importance and future perspectives of apoptosis imaging. The annexin A5 imaging protocol is emphasised since it is the most advanced protocol to measure apoptosis in both preclinical and clinical studies.

(99m)Tc-Annexin-V uptake in a rat model of variable ischemic severity and reperfusion time

BACKGROUND

To determine whether mild to moderate ischemia that is not severe enough to induce myocardial infarction will cause myocardial cell damage or apoptosis, the (99m)Tc-Annexin-V (Tc-A) uptake was studied in groups of rats with various intervals of coronary occlusion and reperfusion times.

METHODS AND RESULTS

After left coronary artery occlusion for 15 min (n=23), 10 min (n=23), or 5 min (n=12), Tc-A (80-150 MBq) was injected at 0.5, 1.5, 6, or 24 h after reperfusion. One hour later, to verify the area at risk, (201)Tl (0.74 MBq) was injected just after left coronary artery re-occlusion and the rats were killed 1 min later. Dual tracer autoradiography was performed to assess Tc-A uptake and area at risk. In all 5-min occlusion and reperfusion models, no significant Tc-A uptake was observed in the area at risk. Tc-A uptake ratios in the 15-min and 10-min ischemia models were 4.46+/-3.16 and 2.02+/-0.47 (p=0.078) at 0.5 h after reperfusion, 3.49+/-1.78 and 1.47+/-0.11 (p<0.05) at 1.5 h after reperfusion, 1.60+/-0.43 and 1.34+/-0.23 (p=0.24) at 6 h after reperfusion, 1.50+/-0.33 and 1.28+/-0.33 (p=0.099) at 24 h after reperfusion, respectively. With 15-min ischemia, in 3 of the 5 rats there were a few micro-foci of myocardial cell degeneration and cell infiltration in less than 1% of the ischemic area at 24 h after reperfusion. No significant histological change was observed in rats with 10-min or 5-min ischemia.

CONCLUSION

The data indicate that Tc-A binding depends on the severity of ischemia even without a significant amount of histological change or infarction.

Influence of mast cells on outcome after heterotopic cardiac transplantation in rats

Correlative data suggest that mast cells adversely affect cardiac transplantation. This study uses a mast cell-deficient rat model to directly address the role of mast cells in cardiac allotransplantation. Standardized cardiac heterotopic transplantation with cyclosporine immunosuppression was performed in mast cell-deficient and mast cell-competent rats. Rejection, ischemia, fibrosis, fibrin deposition, numbers of T-cell receptor alpha/beta positive cells, expression of transforming growth factor-beta (TGF-beta), and of endothelin-1 (ET-1) and its receptors ETA and ETB were assessed. Differences in baseline cardiac gene expression were quantified by real-time PCR in a separate group of untransplanted animals. Baseline cardiac gene expression levels of all investigated growth factors, cytokines, ET-1, ETA, and ETB were similar in mast cell-deficient and mast cell-competent rats. Surprisingly, upon heterotopic transplantation, donor heart survival was significantly reduced in mast cell-deficient rats. Moreover, in mast cell-deficient donor hearts rejection was more severe, although nonsignificant, and extracellular matrix associated TGF-beta immunoreactivity was significantly lower than in mast cell-competent donor hearts. Fibrin immunoreactive area, on the other hand, was only increased in mast cell-deficient donor hearts, but not in mast cell-competent donor hearts. Histopathological changes in all donor hearts were accompanied by increased immunoreactivity for ET-1. In conclusion, this study shows that mast cells play a protective role after cardiac transplantation.

Purification of recombinant annexins without the use of phospholipids

Due to their involvement in a variety of physiological and pathological processes, different isoforms of annexins are being utilized as markers of some human diseases and bio-imaging of tissue injury (due to apoptosis), and have been proposed as drug delivery vehicles. These, in addition to extensive biophysical studies on the role of annexins in organizing lipid domains in biological membranes, have necessitated development of an efficient protocol for producing annexins in bulk quantities. In this paper, we report a one-step purification protocol for annexin a5 without using lipid vesicles or involving any column chromatographic step. Depending on the growth and expression condition, a fraction of recombinant annexin a5 (cloned in pET3d vector) was sequestered into inclusion bodies. When these inclusion bodies were dissolved in 6 M urea, subjected to a 10-fold snap dilution in the presence of 5 mM Ca(2+) and stored overnight at 4 degrees C, annexin a5 was precipitated as a homogenous protein as judged by SDS-PAGE. This one-step purification protocol produced about 35 mg of highly purified annexin a5 per liter of bacterial culture. The annexin a5 purified from inclusion bodies exhibited similar properties to that obtained from the soluble fraction using the conventional lipid-partitioning approach. Our purification protocol for annexin a5 elaborated herein is equally effective for purification of annexin A2, and we believe, will serve as general protocol for purifying other annexins in bulk quantities for diagnostic as well as detailed biophysical studies.

In vivo imaging of apoptosis in patients with acute stroke: correlation with blood-brain barrier permeability

BACKGROUND

We wished to determine the ability of radiolabeled annexin V to concentrate at sites of ischemic injury in patients with acute cerebral stroke. Secondly, we sought to correlate annexin V imaging in these patients with the degree of blood-brain barrier (BBB) breakdown.

METHODS

Twelve patients with acute stroke had a complete neurological examination, including the National Institutes of Health (NIH) stroke scale and the Glasgow Coma Score (GCS). A non-contrast CT scan was performed on all patients. A SPECT of the brain was obtained 2 h after injection of annexin V. The integrity of the BBB was evaluated in seven patients using Tc-99m-DTPA brain SPECT.

RESULTS

All patients had an infarct in the MCA territory. Eight patients had abnormal increased annexin V activity, which was more common in patients with cortical strokes (P = 0.01). The concentration of annexin had no correlation to the volume of stroke, but it was significantly and inversely related to the GCS on admission (r = -0.7, P = 0.02). Foci of apoptosis were noted contralateral to the affected hemisphere as well. All seven patients who underwent DTPA SPECT showed breakdown of the BBB. DTPA uptake was significantly and positively associated with NIH score (r = 0.80, P = 0.01) and inversely associated with GCS (r = -0.89, P = -0.03).

CONCLUSION

This study shows that it is possible to identify in vivo regions of ischemic neuronal injury using radiolabeled annexin V in patients with acute stroke. Annexin imaging can play a major role in the selection of therapy in the initial period following stroke in adults.

Targeted molecular imaging in oncology

Improvement of scintigraphic tumor imaging is extensively determined by the development of more tumor specific radiopharmaceuticals. Thus, to improve the differential diagnosis, prognosis, planning and monitoring of cancer treatment, several functional pharmaceuticals have been developed. Application of molecular targets for cancer imaging, therapy and prevention using generator-produced isotopes is the major focus of ongoing research projects. Radionuclide imaging modalities (positron emission tomography, PET; single photon emission computed tomography, SPECT) are diagnostic cross-sectional imaging techniques that map the location and concentration of radionuclide-labeled radiotracers. 99mTc- and 68Ga-labeled agents using ethylenedicysteine (EC) as a chelator were synthesized and their potential uses to assess tumor targets were evaluated. 99mTc (t1/2 = 6 hr, 140 keV) is used for SPECT and 68Ga (t1/2 = 68 min, 511 keV) for PET. Molecular targets labeled with Tc-99m and Ga-68 can be utilized for prediction of therapeutic response, monitoring tumor response to treatment and differential diagnosis. Molecular targets for oncological research in (1) cell apoptosis, (2) gene and nucleic acid-based approach, (3) angiogenesis (4) tumor hypoxia, and (5) metabolic imaging are discussed. Numerous imaging ligands in these categories have been developed and evaluated in animals and humans. Molecular targets were imaged and their potential to redirect optimal cancer diagnosis and therapeutics were demonstrated.

New reagents for phosphatidylserine recognition and detection of apoptosis

The phospholipid bilayer surrounding animal cells is made up of four principle phospholipid components, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and sphingomyelin (SM). These four phospholipids are distributed between the two monolayers of the membrane in an asymmetrical fashion, with PC and SM largely populating the extracellular leaflet and PE and PS restricted primarily to the inner leaflet. Breakdown in this transmembrane phospholipid asymmetry is a hallmark of the early to middle stages of apoptosis. The consequent appearance of PS on the extracellular membrane leaflet is commonly monitored using dye-labeled Annexin V, a 36 kDa, Ca2+-dependent PS binding protein. Substitutes for Annexin V are described, including small molecules, nanoparticles, cationic liposomes, and other proteins that can recognize PS in a membrane surface. Particular attention is given to the use of these reagents for detecting apoptosis.

Cyclosporine mitigates graft coronary artery disease in murine cardiac allografts: Description and validation of a novel fully allogeneic model

BACKGROUND

The effect of cyclosporine (CsA) on the development of graft coronary artery disease (GCAD) is controversial. We developed a novel allogeneic mouse model of heart transplantation and investigated the effect of CsA on acute rejection and GCAD.

METHODS

Hearts of FVB mice (H-2(q)) were heterotopically transplanted into 60 C57BL/6 mice (H-2(b)). CsA was administered to recipients at 10, 20 or 30 mg/kg/day for 10 or 30 days after transplantation. Untreated recipients as well as isograft recipients served as controls. Viability of the grafts was assessed daily by palpation. Parenchymal rejection was scored in grafts surviving 30 days in the 30-day treatment groups. GCAD was evaluated by the percentage of luminal narrowing, intima/media ratio and percentage of diseased vessels. Blood CsA and creatinine levels were also evaluated. Results were evaluated statistically.

RESULTS

All groups except the untreated control group and the allograft groups treated with 10 or 20 mg for 10 days showed significant graft survival (>/=33% survival for 30 days). An inverse correlation was observed between CsA treatment dose, parenchymal rejection score and degree of GCAD in the 30-day treatment groups. However, graft survival in the 20-mg/kg/day group was significantly better than that in the 30-mg/kg/day group. Serum creatine levels showed no nephrotoxicity.

CONCLUSIONS

Relatively high-dose CsA mitigated parenchymal rejection and GCAD of the mouse cardiac allografts. In addition, a valuable mouse model mimicking the clinical course of GCAD was achieved with CsA treatment of 20 mg/kg/day for 30 days.

Nuclear medicine in the era of genomics and proteomics: lessons from annexin V

In the past decade, genomics and proteomics have begun to develop many new targets for potential diagnostic and therapeutic agents. Among the life sciences, nuclear medicine is also deeply involved in the field of clinical investigation. Experience with radiolabeled annexin V highlights the many steps required to translate a good basic-science concept into the clinical setting. This model also emphasizes the value of synergy between basic and medical specialties in developing and optimizing a clinically useful product initially derived from basic investigation.

Molecular imaging in breast cancer

Since the 1960s, bone scanning has played a major role in the management of breast cancer. In the last decade, however, the role of radionuclide molecular imaging has expanded significantly in the clinical management of breast cancer because of fluorodeoxyglucose positron emission tomography, mammoscintigraphy, and sentinel lymph node techniques. Molecular imaging also is instrumental in drug development,gene therapy, and in basic science research of breast cancer. This article provides a comprehensive review of the role of molecular imaging of breast cancer in clinical practice and reports on the current state of research in this field.

Assessment of Therapeutic Tumor Response Using 99mTc-Ethylenedicysteine-Glucosamine

PURPOSE

The aim of this study was to evaluate 99mTc-ethylenedicysteine-glucosamine (EC-DG) for the assessment of tumor growth.

METHOD

To evaluate whether 99mTc-EC-DG is involved in cell nuclei activity, in vitro thymidine incorporation, and cell-cycle assays of EC-DG were conducted using lung and breast cancer cells. Biodistribution of 99mTc-EC-DG in lung tumor-bearing mice (0.5-4 hours, 1 Ci/mouse, i. v.) was used to estimate the radiation-absorbed dose. Autoradiograms of 99mTc-EC-DG and 18F-FDG were compared in nude mice bearing uterine sarcoma. Rabbits inoculated with VX-2 cells were imaged with 99mTc-EC-DG and 99mTc-EC. For therapeutic assessment studies, scintigraphic imaging studies with 99mTc-EC-DG in mammary tumor-bearing rats were conducted at various days after treatment with paclitaxel and cisplatin. The imaging findings were correlated immunohistochemical assays (mRNA expression, apoptosis, and cell-cycle changes in tumor), and flow cytometry analysis was performed.

RESULTS

In vitro cellular uptake assays indicated that cell nuclei activity could be assessed by 99mTc-EC-DG. Scintigraphy and autoradiograms in animal models demonstrated that the tumor could be clearly visualized by 99mTc-EC-DG. The efficacy of paclitaxel and cisplatin treatment in rodent models could be assessed using tumor/muscle ratios. Immunohistochemical staining indicated a reduced expression of bFGF and an increased apoptosis and cell-cycle changes after paclitaxel and cisplatin treatment.

CONCLUSION

99mTc-EC-DG is involved in cell nuclei activity and could assess the therapeutic tumor response.

In vivo imaging of radiation-induced apoptosis in follicular lymphoma patients

PURPOSE

To evaluate (99m)Tc-Annexin-V (TAV) scintigraphy in monitoring radiation-induced apoptotic cell death in follicular lymphoma (FL) patients.

PATIENTS AND METHODS

Eleven FL patients (7 female and 4 male; median age, 58 years; range, 42-80 years) with recurrent disease underwent TAV imaging before and 24 hours after the last fraction of the 2 x 2 Gy involved field radiotherapy regimen. Fine-needle aspiration cytology was performed on 5 consecutive days to determine the optimal time window for apoptosis detection and to confirm the apoptotic nature of the response. The TAV scintigraphy (total body studies and SPECT of the irradiated sites) was performed 4 hours after the administration of the radiopharmaceutical. Tumor uptake was scored in a semiquantitative manner as absent (-) weak (+/-), present (+), or intense (++) with corresponding categories for the cytologic slides. Response evaluation was performed after 1 week and 4 weeks both in terms of completeness and speed of remission.

RESULTS

Baseline TAV uptake was absent in 6 and weak in 5 patients. Sequential cytology indicated that the optimal time period for apoptosis assessment was between 24 and 48 hours after the last fraction of the 2 x 2 Gy regimen. Baseline cytology was concordant with baseline TAV in all patients. Apoptotic feature appearance (nuclear chromatin condensation, margination and apoptotic body formation) after low-dose irradiation matched the irradiation response in all patients. In all but 1 patient the posttreatment TAV uptake matched the posttreatment cytology. In these 10 patients the cytology and TAV results correlated with the type and onset of the clinical response.

CONCLUSION

Tumor (99m)Tc-Annexin-V uptake can be increased after 2 x 2 Gy involved field radiotherapy. This increase was concordant with the appearance of apoptotic morphology as determined by cytology, and correlated with the clinical outcome. Apoptotic cell death can be observed on Day 4 of this regimen and if so predicts a complete remission within 1 week.

Measurement of the affinity and cooperativity of annexin V–membrane binding under conditions of low membrane occupancy

We developed a method for measuring the binding affinity of annexin V for phospholipid vesicles and cells at very low levels of membrane occupancy. The annexin V-117 mutant was labeled with fluorescein iodoacetamide on its single N-terminal cysteine residue; binding to phospholipid vesicles containing phosphatidylserine (PS) and 2% rhodamine-phosphatidylethanolamine was measured by fluorescence quenching due to resonance energy transfer; binding to cells with exposed PS was measured by fluorometry after elution of bound protein. The equilibrium constant was calculated as a function of the midpoint of the calcium titration curve, the Hill coefficient, and the concentration of membrane binding sites. Calcium titrations at very low ratios of protein to membrane revealed Hill coefficients of approximately 8 for both vesicles and cells, far higher than previously measured, but as the protein-membrane ratio was increased above 3% of maximum membrane occupancy, the value of the Hill coefficient progressively decreased to a limiting value of about 2. High Hill coefficients were also observed for measurements performed at different ionic strengths and with membrane PS content varied over the range from 20 to 50%. This method allows the accurate determination of the affinity and cooperativity of annexin V-membrane binding and will be useful for the evaluation of modified annexin V derivatives intended for diagnostic and therapeutic applications.

18F-labelled annexin V: a PET tracer for apoptosis imaging

Annexin V can be used to detect apoptotic cells in vitro and in vivo, based on its ability to identify extracellular phosphatidylserine, which arises during apoptosis. In the present study, we examined the synthesis of fluorine-18 labelled annexin V as a positron emission tomography tracer for apoptosis imaging. The distribution of [18F]annexin V and technetium-99m labelled annexin V, a well-characterised SPET tracer for apoptosis imaging, was compared. [18F]annexin V was synthesised using N-succinimidyl 4-[18F]fluorobenzoate as an 18F labelling reagent. Synthesised and purified [18F]annexin V was confirmed by SDS-PAGE. In an ex vivo imaging experiment, [18F]annexin V was intravenously injected into rats 24 h after the induction of myocardial ischaemia, and accumulation in the left ventricle was examined. [18F]annexin V accumulated in the infarct area of the left ventricle, where apoptotic cells were observed. In separate experiments, [18F]annexin V or [(99m)Tc]annexin V was intravenously injected into ischaemic or normal animals, and the distribution of the tracers was compared. In ischaemic animals, accumulation of [18F]annexin V and [(99m)Tc]annexin V in the infarct area was about threefold higher than in the non-infarct area. Furthermore, the ratio of accumulation in the normal heart to the blood radioactivity was not significantly different between the tracers. In normal animals, however, the uptake of [18F]annexin V in the liver, spleen and kidney was much lower than that of [(99m)Tc]annexin V. The low uptake of [18F]annexin V in these organs might represent an advantage over [(99m)Tc]annexin V.

Sustained apoptosis in human cardiac allografts despite histologic resolution of rejection1

BACKGROUND

We investigated the occurrence of apoptosis during and after resolution of cardiac allograft rejection. Apoptosis could play different roles in graft survival depending on the target cells; thus, we also determined the cell types involved.

METHODS

Endomyocardial biopsy specimens were evaluated during the first 6 months after transplantation as follows: group I, no current or prior rejection; group II, during an episode of moderate rejection; and group III, histologic resolution after an episode of moderate rejection.

RESULTS

Groups II and III showed significantly increased apoptotic activity, indicated by increased caspase-8 and caspase-3 activity; however, activated caspase-3 was undetectable in group I. Activated caspase-3 was detected only in groups II and III. Terminal deoxynucleotide transferase-mediated dUTP nick-end labeling was detected in groups II and III but not group I and predominantly in inflammatory cells.

CONCLUSIONS

Increased caspase activity and apoptosis of infiltrating cells not only occurs during acute cardiac allograft rejection but persists after histologic resolution. Thus, programmed cell death occurs beyond the period of histologic resolution and may play a role in regulation of the rejection process.

Bcl-2-mediated inhibition of apoptosis in rat cardiac allografts worsens development of graft coronary artery disease

BACKGROUND

We hypothesized that adenovirally mediated Bcl-2 transfection of donor hearts would reduce the apoptosis that occurs during acute rejection while worsening the development of chronic graft coronary artery disease (GCAD).

METHODS

PVG donor hearts were treated with either AdvBcl-2 or AdvNull virus before heterotopic transplantation into ACI rats. Bcl-2 expression was assessed on post-operative day 4 (POD) 4 by western blot. Apoptosis was measured using (99m)Technetium-bound-annexin V imaging and caspase 3 activity assay. Allograft survival was determined in a separate cohort of animals. Long-term-treated animals were then assessed for measures of GCAD on POD 90.

RESULTS

Western blot analysis showed upregulation of Bcl-2 expression in AdvBcl-2-treated hearts. (99m)Tc-annexin V images demonstrated decreased uptake in the AdvBcl-2 group (1.41 +/- 0.33% vs 1.94 +/- 0.37%, p = 0.026). Caspase 3 activity was also significantly lower in this treatment group (0.112 +/- 0.032 vs 0.204 +/- 0.096, p = 0.049). Allograft survival was similar in both groups, respectively (7.7 +/- 1.2 vs 6.8 +/- 1.5 days, p = 0.340). GCAD, as determined by percent luminal narrowing (5.9 +/- 6.1% vs 1.6 +/- 1.5%, p = 0.039), intima-to-media ratio (5.1 +/- 5.1% vs 1.5 +/- 1.7%, p = 0.040) and percent of affected vessels (15.1 +/- 9.9% vs 5.3 +/- 4.4%, p = 0.009), was higher for the AdvBcl-2 group.

CONCLUSION

Treatment of cardiac allografts with AdvBcl-2 resulted in a reduction of apoptosis that did not significantly improve short-term graft survival, but worsened chronic GCAD.

Non-invasive in vivo imaging of myocardial apoptosis and necrosis

Myocardial necrosis plays an important role in the pathogenesis of various cardiovascular disorders and can result from different myocardial insults. Its non-invasive identification and localisation therefore may help in the diagnosis of these disorders, as well as in prognosis and assessment of treatment response. Apoptosis, or programmed cell death, is important in the spectrum of myocardial damage since it is gradually becoming more apparent that cell death may begin as apoptosis and not as necrosis. First attempts to directly visualise the area of myocardial necrosis were based on recognition of myocardial infarction with "hot spot imaging agents" in patients with chest pain. Since then, the study of myocardial necrosis with gamma imaging agents has gone beyond the detection of myocardial infarction, and attempts have been made to diagnose other cardiovascular disorders associated with cardiac cell death such as heart transplant rejection, myocarditis, cardiotoxicity and cardiomyopathies. Traditionally, two hot spot imaging agents have been used for the detection of myocardial necrosis, (99m)Tc-pyrophosphate and (111)In-antimyosin. In addition, preliminary studies have demonstrated promising results with (99m)Tc-glucarate. Recently, (99m)Tc-annexin V has been successfully used for non-invasive gamma imaging of apoptosis after acute myocardial infarction, acute myocardial ischaemia, acute cardiac allograft rejection and malignant intracardiac tumours. This review article focusses on the characteristics of these different myocardial necrotic and apoptotic markers and compares their role in the assessment of myocardial damage.

Imaging with 99mTc ECDG targeted at the multifunctional glucose transport system: feasibility study with rodents

PURPOSE

To evaluate the feasibility of technetium 99m ((99m)Tc) ethylenedicysteine-deoxyglucose (ECDG) imaging in tumor-bearing rodents.

MATERIALS AND METHODS

ECDG was synthesized by means of reacting ethylenedicysteine with glucosamine, with carbodiimide as the coupling agent. Hexokinase assays were performed at an ultraviolet wavelength of 340 nm. To determine whether blood glucose level could be altered, ECDG or glucosamine was injected into six rats. In a separate study, ECDG followed by insulin was administered to three rats. To determine biodistribution, lung tumor cells were intramuscularly injected into the hind legs of 18 nude mice. The animals were then injected with (99m)Tc ECDG or fluorine 18 ((18)F) fluorodeoxyglucose (FDG) (0.037-0.074 MBq per mouse). Radioactivity was measured in tissue excised from the animals. Scintigraphy was performed in three groups: in group 1 to demonstrate that different-sized tumors could be imaged after (99m)Tc ECDG administration, in group 2 to ascertain whether tumor uptake of (99m)Tc ECDG was perfusion related, and in group 3 to demonstrate that tumor uptake of (99m)Tc ECDG occurred by means of a glucose-mediated process.

RESULTS

ECDG was positive for phosphorylation at hexokinase assay. Blood glucose level increased with ECDG injection and decreased with insulin administration. Tumor-to-brain tissue and tumor-to-muscle tissue ratios of (99m)Tc ECDG uptake were higher than those of (18)F FDG uptake. Scintigraphic results demonstrated the feasibility of (99m)Tc ECDG imaging.

CONCLUSION

There are similarities between (99m)Tc ECDG uptake and (18)F FDG uptake in tumors, and study findings supported the potential use of (99m)Tc ECDG as a functional imaging agent.

The use of (99m)technetium-labeled MCP-1 to assess graft coronary artery disease in rat cardiac allografts

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) is associated with the development of graft coronary artery disease (GCAD) following cardiac transplantation. This study assessed whether technetium 99m ((99m)Tc)-labeled MCP-1 binds its receptors in chronic cardiac transplants and thereby provides a potential modality to assess GCAD.

METHODS

Allogeneic (PVG-->ACI, n = 9) and syngeneic (ACI-->ACI, n = 9) rat heterotopic heart transplants were performed. Allograft recipients were treated with 7.5 mg/kg per day of Cyclosporin A for 10 days until tolerance was achieved. After 90 days, animals were injected intravenously with (99m)Tc-MCP-1 and killed after 1 hour. Radioactivity of heart tissues was measured and standardized to uptake in the overall blood pool. Two-dimensional (99m)Tc-MCP-1 uptake (autoradiographs) was imaged by exposing 50-microm sections on a phosphoimager overnight. ED-1 staining of monocyte/macrophages was performed on serial sections. Additional sections were stained with elastin von Gieson and hematoxylin. Hearts were scored for luminal narrowing and intima/media ratio (I/M) with computerized image analysis.

RESULTS

Allografts exhibited significantly more luminal narrowing (22.5 +/- 10.7% vs 2.6 +/- 4.6, p = 0.0005) and higher I/M (0.173 +/- 0.151 vs 0.015 +/- 0.029, p = 0.0088) than isografts. The ratio of (99m)Tc-MCP-1 uptake in allografts (1.04 +/- 0.4) was greater than that of isograft controls (0.72 +/- 0.11, p = 0.03). Pixel counts of autoradiographs and ED-1-stained sections demonstrated a modest correlation between the two (R(2) = 0.50). No significant differences were seen in acute rejection scores.

CONCLUSION

(99m)Tc-MCP-1 uptake was higher in allografts vs isografts and was consistent with a greater degree of GCAD. These data demonstrating increased radiopharmaceutical uptake in hearts with GCAD provide a foundation for the development of a potentially non-invasive imaging assay of this disease process in heart transplantation.

Development of annexin V mutants suitable for labeling with Tc(i)-carbonyl complex

(99m)Tc-annexin V can be used to image organs undergoing cell death during cancer chemotherapy and organ transplant rejection. We investigated whether the novel Tc-carbonyl labeling method would be suitable for annexin V. Two mutant molecules of annexin V, called annexin V-122 and annexin V-123, were constructed with N-terminal extensions containing either three or six histidine residues. These molecules were expressed cytoplasmically in E. coli and purified with a final yield of 33 mg of protein/L of culture. Analysis by SDS-PAGE, isoelectric focusing, gel filtration chromatography, and mass spectrometry confirmed the purity and homogeneity of the protein preparations. Both mutant proteins retained full binding affinity for cell membranes with exposed phosphatidylserine. Using the Tc-carbonyl reagent, both proteins could be labeled with (99m)Tc to specific activities of at least 10-20 microCi/microg with full retention of bioactivity. The radiolabeled proteins were stable when incubated with phosphate-buffered saline or serum in vitro, and there was no transchelation of label to serum proteins during in vitro incubation. In conclusion, annexin V can be modified near its N-terminus to incorporate sequences that form specific chelation sites for (99m)Tc-carbonyl without altering its high affinity for cell membranes.

Zinc chloride-mediated reduction of apoptosis as an adjunct immunosuppressive modality in cardiac transplantation

BACKGROUND

Zinc (Zn) blocks caspase-3 activation in cardiac allografts and therefore may synergistically decrease apoptosis along with cyclosporine (CsA), which inhibits mitochondrial release of cytochrome c. Simultaneous treatment of rat recipients of heterotopic heart transplants with zinc chloride (ZnCl(2)) thus may allow lower doses of CsA for immunosuppression.

METHODS

PVG (RT1(c)) rat hearts were transplanted heterotopically into the abdomen of ACI (RT1(a)) rats. Group 1 (n = 15) rats received no treatment. Group 2 rats (n = 8) received 2 mg/kg/day CsA (sub-therapeutic dose) by oral gavage. Group 3 rats (n = 9) received 2 mg/kg/day oral CsA in addition to 1 mg/kg/day sub-cutaneous ZnCl(2) delivered by osmotic pump. All rats were imaged using Annexin V-bound (99m)Technetium ((99m)Tc-Annexin V) on post-operative Day 4 and subsequently killed. Annexin V avidly binds apoptotic cells in vivo. Region of interest per whole body (WB) data were calculated using the images. The allograft survival study was conducted with n = 11, 6, and 5 in control, CsA, and CsA+Zn groups, respectively. Finally, percentages of allografts that reached tolerance were measured in both CsA-only and CsA+Zn groups (n = 8 each).

RESULTS

Zinc chloride had an additive effect with CsA on apoptotic blockade and graft survival. The regions of interest per WB uptake of (99m)Tc-Annexin V were 2.43% +/- 0.37%, 2.08% +/- 0.52%, and 1.49% +/- 0.29%*, and acute survivals were 6.4 +/- 1.7, 7.2 +/- 2.1, and 11.2 +/- 2.5* days for control, CsA, and CsA+Zn groups, respectively (*p < 0.001 vs controls). In addition, 87.5% of allografts became tolerant and survived for 90 days in the CsA+Zn group compared with only 37.5% in the CsA-only group (p = 0.049).

CONCLUSION

Zinc-mediated reduction of apoptosis served as an effective adjunct immunosuppressive therapy to CsA in a rat model of cardiac transplantation.

In vivo imaging of acute cardiac rejection in human patients using (99m)technetium labeled annexin V

Annexin V binds phosphatidylserine moieties on apoptotic cells. This study reports the initial experience at Stanford University Medical Center with 99mTc-labeled annexin V imaging as a noninvasive measure of apoptosis in acute cardiac rejection. Ten cardiac transplant patients had 99mTc Annexin V imaging and endomyocardial biopsy (EMB) performed within 24 h. No complications related to 99mTc annexin V administration occurred. Eight patients had ISHLT grade of acute rejection of 1A or less. Five patients had two or more areas of uptake noted in the right ventricle on imaging studies. Two of these patients had positive biopsies: one patient had grade 2 rejection with two focal uptake areas and another had grade 3A rejection with three foci. An additional five patients had either one or zero hot spot areas and corresponding negative EMBs. 99mTc-annexin V appears to be well tolerated and may identify patients with acute cardiac rejection.

In vivo and in vitro measurement of apoptosis in breast cancer cells using 99mTc-EC-annexin V

OBJECTIVE

The purpose of this study was to develop an imaging technique to measure and monitor tumor cells undergoing programmed death caused by radiation and chemotherapy using 99mTc-EC-annexin V. Annexin V has been used to measure programmed cell death both in vitro and in vivo. Assessment of apoptosis would be useful to evaluate the efficacy and mechanisms of therapy and disease progression or regression.

METHODS

Ethylenedicysteine (EC) was conjugated to annexin V using sulfo-N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl as coupling agents. The yield of EC-annexin V was 100%. In vitro cellular uptake, pre- and post-radiation (10-30 Gy) and paclitaxel treatment, was quantified using 99mTc-EC-annexin V. Tissue distribution and planar imaging of 99mTc-EC-annexin V were determined in breast tumor-bearing rats at 0.5, 2, and 4 hrs. To demonstrate in vivo cell apoptosis that occurred during chemotherapy, a group of rats was treated with paclitaxel and planar imaging studies were conducted at 0.5-4 hrs. Computer outlined region of interest (ROI) was used to quantify tumor uptake on day 3 and day 5 post-treatment.

RESULTS

In vitro cellular uptake showed that there was significantly increased uptake of 99mTc-EC-annexin V after irradiation (10-30 Gy) and paclitaxel treatment. In vivo biodistribution of 99mTc-EC-annexin in breast tumor-bearing rats showed increased tumor-to-blood, tumor-to-lung and tumor-to-muscle count density ratios as a function of time. Conversely, tumor-to-blood count density ratios showed a time-dependent decrease with 99mTc-EC in the same time period. Planar images confirmed that the tumors could be visualized clearly with 99mTc-EC-annexin. There was a significant difference of ROI ratios between pre- and post-paclitaxel treatment groups at 2 and 4 hrs post injection.

CONCLUSION

The results indicate that apoptosis can be quantified using 99mTc-EC-annexin and that it is feasible to use 99mTc-EC-annexin to image tumor apoptosis.

Noninvasive strategies to image cardiovascular apoptosis

Apoptosis consists of a complex set of biochemical events initiated by an array of different stimuli and enzymatic pathways. There is a set of common morphologic and biochemical features of apoptosis that could be exploited as hot or cold targets to image cardiovascular apoptosis. First, the authors review the potential array of targets that can be used to identify apoptosis. Then, the authors examine the history and current status of radiolabeled annexin V, the agent currently used to image apoptosis.

Development and characterization of annexin V mutants with endogenous chelation sites for (99m)Tc

[(99m)Tc]Annexin V can be used to image organs undergoing cell death during cancer chemotherapy and organ transplant rejection. To simplify the preparation and labeling of annexin V for nuclear-medicine studies, we have investigated the addition of peptide sequences that will directly form endogenous chelation sites for (99m)Tc. Three mutant molecules of annexin V, called annexin V-116, -117, and -118, were constructed with N-terminal extensions of seven amino acids containing either one or two cysteine residues. These molecules were expressed cytoplasmically in Escherichia coli and purified to homogeneity with a final yield of 10 mg of protein/L of culture. Analysis in a competitive binding assay showed that all three proteins retained full binding affinity for erythrocyte membranes with exposed phosphatidylserine. Using SnCl(2) as reducing agent and glucoheptonate as exchange agent, all three proteins could be labeled with (99m)Tc to specific activities of at least 50-100 microCi/microg. The proteins retained membrane binding activity after the radiolabeling procedure, and quantitative analysis indicated a dissociation constant (K(d)) of 7 nmol/L for the annexin V-117 mutant. The labeling reaction was rapid, reaching a maximum after 40 min at room temperature. The radiolabeled proteins were stable when incubated with phosphate-buffered saline or serum in vitro. Proteins labeled to a specific activity of 25-100 microCi/microg were injected intravenously in mice at a dose of 100 microg/kg, and biodistribution of radioactivity was determined at 60 min after injection. Uptake of radioactivity was highest in kidney and liver, consistent with previous results obtained with wild-type annexin V. Cyclophosphamide-induced apoptosis in vivo could be imaged with [(99m)Tc]annexin V-117. In conclusion, annexin V can be modified near its N-terminus to incorporate sequences that form specific chelation sites for (99m)Tc without altering its high affinity for cell membranes. These annexin V derivatives may be useful for in vivo imaging of cell death.

99mTc annexin V imaging of neonatal hypoxic brain injury

BACKGROUND AND PURPOSE

Delayed cell loss in neonates after cerebral hypoxic-ischemic injury (HII) is believed to be a major cause of cerebral palsy. In this study, we used radiolabeled annexin V, a marker of delayed cell loss (apoptosis), to image neonatal rabbits suffering from HII.

METHODS

Twenty-two neonatal New Zealand White rabbits had ligation of the right common carotid artery with reduction of inspired oxygen concentration to induce HII. Experimental animals (n=17) were exposed to hypoxia until an ipsilateral hemispheric decrease in the average diffusion coefficient occurred. After reversal of hypoxia and normalization of average diffusion coefficient values, experimental animals were injected with (99m)Tc annexin V. Radionuclide images were recorded 2 hours later.

RESULTS

Experimental animals showed no MR evidence of blood-brain barrier breakdown or perfusion abnormalities after hypoxia. Annexin images demonstrated multifocal brain uptake in both hemispheres of experimental but not control animals. Histology of the brains from experimental animals demonstrated scattered pyknotic cortical and hippocampal neurons with cytoplasmic vacuolization of glial cells without evidence of apoptotic nuclei by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Double staining with markers of cell type and exogenous annexin V revealed that annexin V was localized in the cytoplasm of scattered neurons and astrocytes in experimental and, less commonly, control brains in the presence of an intact blood-brain barrier.

CONCLUSIONS

Apoptosis may develop after HII even in brains that appear normal on diffusion-weighted and perfusion MR. These data suggest a role of radiolabeled annexin V screening of neonates at risk for the development of cerebral palsy.