Gene manipulated peritoneal cell patch repairs infarcted myocardium

A gene manipulated cell patch using a homologous peritoneum substrate was developed and applied after myocardial infarction to repair scarred myocardium. We genetically engineered male rat mesenchymal stem cells (MSC) using adenoviral transduction to over-express CXCR4/green fluorescent protein (GFP) (MSC(CXCR4)) or MSC(Null) or siRNA targeting CXCR4 (MSC(siRNA)). Gene expression was studied by real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). Cells were cultured on excised peritoneum for 9 days. Two weeks after left anterior descending (LAD) coronary artery ligation in female hearts, the peritoneum patch was applied over the scarred myocardium, cell side down. Efficacy of engraftment was determined by presence of GFP positive cells. One month after cell implantation, echocardiography was performed and hearts were harvested for histological analysis. Left ventricle (LV) fibrosis, LV anterior wall thickness (AWT) and blood vessel density at the margins of the graft were measured. There was significant up-regulation of the chemokines in the MSC(CXCR4) group cultured under normoxic conditions when compared to the MSC(Null) group and a further increase was observed after exposure to hypoxia. One month after cell transplantation with the peritoneum patch, substantial numbers of GFP-positive cells were observed in and around the infarcted myocardium in MSC(CXCR4) group. LV AWT, LV fibrosis and LV function were significantly improved in the MSC(CXCR4) group as compared to these same variables in the MSC(Null) control. These salutary effects were absent in MSC(siRNA) group. The gene manipulated MSC-seeded peritoneum patch promotes tissue nutrition (angiogenesis), reduces myocardial remodeling, and enhances heart function after myocardial infarction.

Stem cell homing and angiomyogenesis in transplanted hearts are enhanced by combined intramyocardial SDF-1alpha delivery and endogenous cytokine signaling

We used a heterotopic transplanted working heart model to probe the collaborative role of bone marrow-derived progenitor cells (BPCs) and stromal cell-derived factor (SDF)-1alpha in attenuating tissue remodeling in recipient and transplanted hearts. BPCs from male transgenic rats expressing green fluorescent protein (GFP(+) BPCs, 2 x 10(6) cells) were injected intravenously into myeloablated female rats. One month later, heterotopic heart transplantation was performed. The left anterior descending coronary artery (LAD) of the recipient heart was occluded permanently. Mesenchymal stem cells (MSCs; 2 x 10(6) cells) with a null gene (null group) or overexpressing SDF-1alpha (SDF-1alpha group) were injected intramyocardially in the LAD perfusion region of both recipient and transplanted hearts. Recipient and transplanted hearts (n = 10 hearts/group) were harvested 21 days later for analysis. The survival of transplanted hearts was assessed daily by palpation in additional animals (n = 7). Five days after LAD occlusion, subpopulations of GFP(+) BPCs in the circulation were significantly higher in the SDF-1alpha group. Y chromosome, 5-bromo-2'-deoxyuridine, Ki67-positive nuclei, newly formed vessels, and GFP(+) cells significantly increased in transplanted hearts of the SDF-1alpha group at 21 days after the injection of MSCs overexpressing SDF-1alpha, whereas fewer TUNEL-positive nuclei were found. The survival of transplanted hearts was also markedly increased in the SDF-1alpha group (P < 0.05). Supplementation of endogenous cytokines released from the ischemic myocardium with exogenous MSCs overexpressing SDF-1alpha significantly increased BPC homing to acutely ischemic recipient and progressively ischemic transplanted hearts. BPC recruitment resulted in the regeneration of new cardiomyocytes and blood vessels and extended survival of the transplanted hearts.

Functional and anatomical diagnosis of coronary artery stenoses

BACKGROUND

Functional/physiological evaluation of coronary artery stenoses may be more important than anatomical measurements of severity. Optimization of thresholds for stenosis intervention and treatment endpoints depend on coupling functional hemodynamic and anatomical data. We sought to develop a single prognostic parameter correlating stenosis-specific anatomy, pressure gradient, and velocities that could be measured during catheterization.

MATERIALS AND METHODS

In vivo Experiments were performed in six swine (41 +/- 3 kg). The lumen area of the left anterior descending coronary artery was measured with intravascular ultrasound. An angioplasty balloon was inflated to create the desired intraluminal area obstructions. Fractional flow reserve (FFR), coronary flow reserve (CFR), and hyperemic-stenosis-resistance index were measured distal to the balloon at peak hyperemia with 10 mg intracoronary papaverine. A functional index:pressure drop coefficient (CDP) and a combined functional and anatomical index:lesion flow coefficient (LFC) were calculated from measured hyperemic pressure gradient, velocity, and percentage area stenosis. P < 0.05 was considered statistically significant.

RESULTS

The CDP and LFC correlated linearly and significantly with FFR and CFR. The CDP (R(2) = 0.72, P < 0.0001) correlated better than LFC (R(2) = 0.19, P < 0.003) with hyperemic-stenosis-resistance index. When LFC was correlated simultaneously with FFR and CFR, R(2) improved to 0.82 (P < 0.0001). Inclusion of percentage area stenoses concurrently with FFR and CFR marginally improved the correlation with LFC.

CONCLUSIONS

A dimensionless parameter combining measured pressure gradient, velocity, and area reduction data can optimally define the severity of coronary stenoses based on our preliminary results and could prove useful clinically.

Characterizing momentum change and viscous loss of a hemodynamic endpoint in assessment of coronary lesions

Myocardial fractional flow reserve (FFR(myo)) and coronary flow reserve (CFR), measured with guidewire, and quantitative angiography (QA) are widely used in combination to distinguish ischemic from non-ischemic coronary stenoses. Recent studies have shown that simultaneous measurements of FFR(myo) and CFR are recommended to dissociate conduit epicardial coronary stenoses from distal resistance microvascular disease. In this study, a more comprehensive diagnostic parameter, named as lesion flow coefficient, c, is proposed. The coefficient, c, which accounts for mean pressure drop, Delta p, mean coronary flow, Q, and percentage area stenosis, can be used to assess the hemodynamic severity of a coronary artery stenoses. Importantly, the contribution of viscous loss and loss due to momentum change for several lesion sizes can be distinguished using c. FFR(myo), CFR and c were calculated for pre-angioplasty, intermediate and post-angioplasty epicardial lesions, without microvascular disease. While hyperemic c decreased from 0.65 for pre-angioplasty to 0.48 for post-angioplasty lesion with guidewire of size 0.35 mm, FFR(myo) increased from 0.52 to 0.87, and CFR increased from 1.72 to 3.45, respectively. Thus, reduced loss produced by momentum change due to lower percentage area stenosis decreased c. For post-angioplasty lesion, c decreased from 0.55 to 0.48 with the insertion of guidewire. Hence, increased viscous loss due to the presence of guidewire decreased c compared with a lesion without guidewire. Further, c showed a linear relationship with FFR(myo), CFR and percentage area stenosis for pre-angioplasty, intermediate and post-angioplasty lesion. These baseline values of c were developed from fluid dynamics fundamentals for focal lesions, and provided a single hemodynamic endpoint to evaluate coronary stenosis severity.

Effect of simulated microgravity on oxidation-sensitive gene expression in PC12 cells

Oxygen utilization by and oxygen dependence of cellular processes may be different in biological systems that are exposed to microgravity (micro-g). A baseline in which cellular changes in oxygen sensitive molecular processes occur during micro-g conditions would be important to pursue this question. The objective of this research is to analyze oxidation-sensitive gene expression in a model cell line [rat pheochromocytoma (PC12)] under simulated micro-g conditions. The PC12 cell line is well characterized in its response to oxygen, and is widely recognized as a sensitive model for studying the responses of oxygen-sensitive molecular and cellular processes. This study uses the rotating wall vessel bioreactor (RWV) designed at NASA to simulate micro-g. Gene expression in PC12 cells in response to micro-g was analyzed by DNA microarray technology. The microarray analysis of PC12 cells cultured for 4 days under simulated micro-g under standardized oxygen environment conditions revealed more than 100 genes whose expression levels were changed at least twofold (up-regulation of 65 genes and down-regulation of 39 genes) compared with those from cells in the unit gravity (unit-g) control. This study observed that genes involved in the oxidoreductase activity category were most significantly differentially expressed under micro-g conditions. Also, known oxidation-sensitive transcription factors such as hypoxia-inducible factor-2alpha, c-myc, and the peroxisome proliferator-activated receptor-gamma were changed significantly. Our initial results from the gene expression microarray studies may provide a context in which to evaluate the effect of varying oxygen environments on the background of differential gene regulation of biological processes under variable gravity conditions.

Evaluation of coupled convective-diffusive transport of drugs administered by intravitreal injection and controlled release implant

A 3-dimensional finite element model was developed to simulate pharmacokinetics in the eye following drug administration by intravitreal injection and implant for the treatment of retinal disease. The contributions of (1) convection to the transport of drug through the vitreous and aqueous humor and (2) diffusion of drug in the vitreous were varied to study the drug elimination from a normal and diseased eye. Drug distribution achieved by intravitreal injection was compared to that for the same dose released at a constant rate over 15 h from an implant. The model was constructed for a rabbit eye and validated with experimental data for intravitreal injection of fluorescein. The implant reduced peak concentration by 43% and increased residence time by 71% for the baseline (6x10(-6) cm2/s drug diffusivity in vitreous and 0.1 microL/min vitreous outflow), when compared with that of intravitreal injection. Therefore, the implant could be beneficial in reducing the peak concentration and sustaining release of the drug for a longer duration. Convection has a relatively small influence in the normal eye for high diffusivity drugs (1x10(-5) cm2/s), but could have a significant effect for low diffusivity drugs (1x10(-7) cm2/s) in pathophysiologically elevated fluid outflow across the retina. By interpolating the results of this benchmark study, one could estimate the distributions for drugs of different molecular weight, and assess the effect of variable vitreous outflows associated with different pathophysiological conditions.

Delineating the guide-wire flow obstruction effect in assessment of fractional flow reserve and coronary flow reserve measurements

Hemodynamic analysis was conducted to determine uncertainty in clinical measurements of coronary flow reserve (CFR) and fractional flow reserve (FFR) over pathophysiological conditions in a patient group with coronary artery disease during angioplasty. The vasodilation-distal perfusion pressure (CFR-p(rh)) curve was obtained for 0.35- and 0.46-mm guide wires. Our hypothesis is that a guide wire spanning the lesions elevates the pressure gradient and reduces the flow during hyperemic measurements. Maximal CFR-p(rh) was uniquely determined by the intersection of measured CFR and calculated p(rh) of native and residual epicardial lesions in patients without microvascular disease, during angioplasty. Extrapolation of the linear curve gave a zero-coronary flow mean pressure (p(zf)) of approximately 20 mmHg and a corresponding p(rh) of 55 mmHg in the native lesions, which coincided with the level that causes ischemia in human hearts. On this linear curve, values of CFR and FFRmyo (pathophysiological condition) and CFRg and FFRmyog (in the presence of the guide wire) were obtained in native and residual lesions. A strong linear correlation was found between CFR and CFRg [CFR = CFRg x 0.689 + 1.271 (R2= 0.99) for 0.46 mm and CFR = CFRg x 0.757 + 1.004 (R2= 0.99) for 0.35 mm] and between FFRmyo and FFRmyog [FFRmyo = FFRmyog x 0.737 + 0.263 (R2= 0.99) for 0.46 mm and FFRmyo = FFRmyog x 0.790 + 0.210 (R2= 0.99) for 0.35 mm]. This study establishes a strong correlation between CFR and CFRg and between FFRmyo and FFRmyog, which could be used to obtain the true state of occlusion in the coronary artery during angioplasty.

Potential research participants' views regarding researcher and institutional financial conflicts of interest

BACKGROUND

Financial conflict of interest in clinical research is an area of active debate. While data exist on the perspectives and roles of academic institutions, investigators, industry sponsors, and scientific journals, little is known about the perspectives of potential research participants.

METHODS

The authors surveyed potential research participants over the internet, using the Harris Interactive Chronic Illness Database. A potential research participant was defined by: (1) self report of diagnosis by a health care professional and (2) willingness to participate in clinical trials. Email invitations were sent to 20 205 persons with coronary artery disease, breast cancer, or depression; a total of 6363 persons were screened; of these, 86% or 5478 met inclusion criteria and completed the survey. The outcome measures were respondents' ratings on: importance of knowing conflict of interest information, whether its disclosure ought to be required, and its effect on willingness to participate-across seven widely discussed scenarios of financial conflicts of interest (ranging from commercial funding to equity ownership).

RESULTS

Majority responded that knowing conflict of interest information was "extremely" or "very" important; a larger majority felt financial conflicts of interest should be disclosed as part of informed consent (64% to 87%). In all seven scenarios, a majority was still willing to participate but in some scenarios a sizable minority would be wary of participation. Respondents were more wary of individual than institutional conflicts of interest. Illness group and sociodemographic factors had modest effects and did not affect the main trends.

CONCLUSIONS

The prevailing practice of non-disclosure of financial conflicts of interest in clinical research appears contrary to the values of potential research participants.

A study of the pharmacodynamic differences between immediate and extended release bumetanide formulations

Optimized bumetanide extended (ER) and immediate release (IR) formulations were developed using fluid bed layering and coating techniques. We postulated that the ER bumetanide formulation would have more effective and sustained diuretic and saluretic effects than IR. The diuretic/saluretic effects of both formulations were measured in rabbits (n=8) for two days after dosing with 1mg/kg bumetanide. During the first day, both formulations produced 2-3 times more urine volume and sodium excretion than baseline. In the first 24h, despite less bumetanide excretion from the ER formulation (101+/-13.9microg/kg compared to 146+/-14.6microg/kg for the IR formulation; P<0.04); the ER formulation produced diuresis and natriuresis that was equivalent to that of the IR formulation. In contrast, urine production in the IR formulation group fell below that of placebo controls on day 2. During the second day, the ER formulation was noted to produce persistent bumetanide excretion; the diuretic and natriuretic effects were not statistically significant from baseline control. We speculate that the decrease in response to bumetanide observed especially for the IR formulation during the second day may be due to the activation of compensatory counter-regulatory homeostatic mechanism(s). We conclude that the ER formulation had similar diuretic/saluretic effects but better drug excretion to urine production efficiencies than the IR formulation in the healthy rabbit model. The ER formulation, while providing comparable diuretic/saluretic effect to the IR formulation, offers the advantage of avoiding the initial, rapid and robust diuretic effect experienced with the IR formulations. Taken together, the data provide sufficient basis to warrant further investigation and refinement of our ER bumetanide formulation in humans.

Associations between patient report of symptoms and anatomic impairment visible on lumbar magnetic resonance imaging

STUDY DESIGN

A cross-sectional study comparing the relationship of symptoms with anatomic impairment visible on lumbar magnetic resonance imaging in 408 symptomatic subjects.

OBJECTIVE

To determine how various anatomic impairments, including the magnitude and location of nerve compression visible on lumbar magnetic resonance imaging, are associated with patient reports of pain, weakness, and dysesthesia.

SUMMARY AND BACKGROUND DATA

Anatomic impairments of the intervertebral disc, radicular canal, and associated soft tissues are prevalent in people with and those without low back pain or lower extremity radiculopathy. This has led to confusion in differentiating between symptom generators and benign variation visible on lumbar magnetic resonance imaging. Recent literature has suggested that the presence of nerve compression is an important finding in the prediction of symptoms. However, the threshold for meaningful nerve compression has not been described.

METHODS

In this study, 408 participants undergoing a diagnostic workup for low back pain, radiculopathy, and/ or completed a survey and pain drawing. Participants underwent standardized lumbar magnetic resonance imaging using a 1.5-T scanner. Two classification systems describing the spatial distribution of symptoms were developed. An additional system to quantify the magnitude of nerve and thecal sac compression was created. All systems were assessed for reliability, after which comparisons among variables were performed using Chi2 as well as simple and multiple logistic regression analysis.

RESULTS

The reliability coefficients for categorizing patients on the basis of pain drawing ranged from 0. 75 to 0.88. The S1-S2 segmental distribution was the most commonly reported location of symptoms, followed by L4-L5. The most common magnetic resonance imaging diagnosis was "unremarkable," followed by "disc impairment without nerve compression." Disc extrusion was present in 10.8% of participants. The reliability of classifying nerve compression visible on magnetic resonance imaging ranged from 0.27 to 1. Nerve compression was present in 37% of participants, and 18% had severe nerve compression. There were no significant associations between segmental distribution of symptoms and the presence of anatomic impairment. However, according to a collapsed classification scale, severe nerve compression and disc extrusion were predictive of pain distal to the knee (odds ratios, 2.72 and 3. 34). The self-report of weakness was associated mildly with severe nerve compression and disc extrusion, but not with other findings. Magnetic resonance imaging findings did not predict self-reports of dysesthesia.

CONCLUSIONS

The presence of disc extrusion and/or ipsilateral, severe nerve compression at one or multiple sites is strongly associated with distal leg pain. Mild to moderate nerve compression, disc degeneration or bulging, and central spinal stenosis are not significantly associated with specific pain patterns. Although segmental distributions of pain can be determined reliably from pain drawings, this finding alone is of little use in predicting lumbar impairment. The self-report of lower extremity weakness or dysesthesia is not significantly related to any specific lumbar impairments. [Key words: back pain, diagnosis, magnetic resonance imaging, nerve compression, pain drawing, pathology]

Myocardial kinetics of 99m technetium-Q agents: studies in isolated cardiac myocyte, isolated perfused rat heart, and canine regional myocardial ischemia models

OBJECTIVE

Based on reports of high cellular uptake and low plasma binding of nonreducible mixed ligand Tc(III) cations (Q complexes) and high linear uptake versus blood flow of 99mTc-Q3 in canine hearts, the authors hypothesized that the two Q complexes, 99mTc-Q63 and 99mTc-Q64, would have high cell uptake and better differentiation between ischemic and nonischemic myocardium compared with other 99mTc-based compounds.

METHODS

Uptake and retention kinetics of 99mTc-Q63 and 99mTc-Q64 were measured in isolated rat cardiac myocytes, isolated perfused rat hearts, and intact canines and compared with previously reported Q-based compounds, a clinically available 99mTc perfusion agent (sestamibi), and 201Tl.

RESULTS

Uptake of Q63, Q64, and sestamibi by isolated cardiac myocytes was similar. Maximum extraction (Emax) of Q64 by isolated perfused rat hearts was greatest among the 99mTc agents (P < 0.02), but net extraction (Enet) of Q64 was not different from Q63 or sestamibi 3 minutes after tracer injection. By 15 minutes, 201Tl Enet was lower than Q63, Q64, and sestamibi (P < 0.05). Among 99mTc agents, the uptake versus flow of Q3, Q63, and Q64 by canine heart was superior to Q12 and sestamibi (P < 0.05).

CONCLUSIONS

The activity of Q63 and Q64 in the myocardium is related to actual myocardial blood flow over a broad, clinically relevant range of flows. The ischemic-to-normal zone activity distributions of Q63 and Q64 approximate actual flow in a manner more like that of 201Tl than sestamibi or Q12. These results provide a rational foundation in support of further evaluation of Q63 and Q64 in humans.

Uptake of seven myocardial tracers during increased myocardial blood flow by dobutamine infusion

RATIONALE AND OBJECTIVES

Direct comparison of myocardial perfusion tracers has been made difficult by variability in experimental models, and by a virtual absence of data comparing tracer uptake to myocardial blood flow under conditions of increased myocardial oxygen consumption, similar to what occurs with dynamic exercise.

METHODS

Tracer uptake versus myocardial blood flow was evaluated for thallium-201 (201TI) and six technetium-99m (99mTc) myocardial-imaging agents in 24 open-chest canines with an occluded left-anterior descending coronary artery during dobutamine infusion. Data were fitted to the exponential model y = ax(1 - exp[-PSc/x]), where y is the tissue tracer/g normalized to normal (activity at 1 mL/minute/g) and x is the blood flow measured by the radioactive microsphere method.

RESULTS

With dobutamine, myocardial tracer uptake was linear across a wide range of ischemic and hyperemic flows for each tracer. Based on the permeability surface area product, 201TI and 99mTc Q3 provided the best tracer estimate of myocardial blood flow (5.30+/-0.86 mL/minute/g, r = 0.91; 5.46+/-0.58 mL/minute/g, r = 0.94, respectively). Correlation coefficient (r) values for other tracers studied were 99mTc Q4 (r =0.93), 99mTc Q12 (r = 0.93), 99mTc sestamibi (r = 0.90), 99mTc tetrofosmin (r = 0.96), and 99mTc-N-Noet (r = 0.82).

CONCLUSIONS

Of the 99mTc tracers examined under conditions of dobutamine-altered myocardial contractility, the myocardial uptake properties of 99mTc Q3 were most similar to those of 201TI.

Cross-sectional comparison of live and interactive voice recognition administration of the SF-12 health status survey

OBJECTIVE

To compare interactive voice recognition (IVR) and live telephone methods for administering the SF-12 health status survey (SF-12).

STUDY DESIGN

Patients with low back pain received either IVR or live interviews in a cross-sectional design with partial randomization. The interviews consisted of the SF-12 and some additional questions specific to low back pain.

PATIENTS AND METHODS

Complete findings were obtainable from 229 patients. Summary scales were compared by using multivariate analysis of variance with mean comparisons for continuously scored items. Response frequencies for categorically scored items were compared by using the chi-square test.

RESULTS

The 2 methods produced similar results on the Physical Component Summary scale but not the Mental Component Summary scale. Compared with patients who had a live telephone interview, the patients using IVR acknowledged significantly greater overall mental interference, greater general emotional concerns, and poorer mood and overall health.

CONCLUSIONS

Because IVR eliminates the demand characteristics of responding to a personal interviewer, it may be a desirable way to evaluate sensitive topics. It also may reduce costs of data entry, labor, and measurement error.

Effect of congestive heart failure on in vivo canine aortic elastic properties

OBJECTIVES

The aim of this study was to characterize fully in vivo aortic compliance over a wide range of passive distending pressures, and to study pharmacologically induced alterations in compliance using an intravascular ultrasound-based technique in the canine model of heart failure.

BACKGROUND

Altered aortic compliance may influence considerably the function of the failing heart. Although some studies demonstrate that patients with heart failure have decreased aortic compliance, data from other studies are conflicting.

METHODS

Aortic pressures and dimensions in seven dogs were determined both before and after pacing-induced congestive heart failure (CHF) using simultaneous micromanometer and intravascular ultrasound transducers. Decreases in aortic pressure were produced at baseline and after nitroprusside and dobutamine infusions. Inner and outer aortic circumferences were drawn at the lumen-intimal and media-adventitial borders.

RESULTS

Aortic pressure-dimension (chamber) stiffness constants were greater after heart failure was produced (10.0+/-1.5 vs. 6.7+/-1.5, p < 0.05), but stress-strain stiffness (material) constants were similar (11.4+/-1.8 vs. 11.3+/-1.0, p=NS). Equivasodilating doses of nitroprusside and 10 microg/kg/min dobutamine decreased pressure-dimension stiffness constants after pacing-induced heart failure but not beforehand. The aortic wall thickness to diameter ratio was significantly greater in CHF than in the control condition (0.30+/-0.08 vs. 0.16+/-0.03, p < 0.01).

CONCLUSIONS

Aortic compliance is decreased in this model of CHF, and this change is attributable primarily to vessel geometry rather than material properties. Equivasodilating doses of nitroprusside and equivalent doses of dobutamine increase aortic chamber compliance in dogs with CHF, but not in normal dogs. These data suggest that the beneficial effects of nitroprusside and dobutamine in CHF occur in part from improvement in aortic compliance.

Flow versus uptake comparisons of thallium-201 with technetium-99m perfusion tracers in a canine model of myocardial ischemia

We investigated the myocardial flow kinetics of six putative radioperfusion agents (99mTc-Q3, 99mTc-Q4, 99mTc-Q12, 99mTc-sestamibi, 99mTc-tetrofosmin and 99mTcN-NOET) and 201Tl in a canine model of myocardial ischemia with pharmacologic coronary artery vasodilation.

METHODS

In 31 open-chest dogs with acute coronary occlusion, dipyridamole (approximately 0.56 mg/kg) was infused intravenously, followed by a perfusion tracer injection and radioactive microspheres for myocardial blood flow (MBF) measurement. The paired data were normalized using three techniques; average, normal or maximum myocardial tracer activity and MBF.

RESULTS

The upper limit of MBF obtained for the group of tracers ranged from 4.2 ml/min/g to 8.2 ml/min/g. There was a statistically significant (p < 0.0001) linear correlation (r = 0.87-0.98) between the normalized myocardial activity and the normalized MBF values of each of the tracers. The slope of the curve normalized by average for 201Tl (0.83) was greater than those for the 99mTc tracers, and the intercept (0.07) was lower than those for the 99mTc tracers. Slopes and intercepts for the 99mTc agents were as follows: 99mTc-Q3, 0.81 and 0.18; 99mTc-Q4, 0.61 and 0.41; 99mTc-Q12, 0.63 and 0.39; 99mTc-sestamibi, 0.62 and 0.34; 99mTc-tetrofosmin, 0.68 and 0.32; and 99mTcN-NOET, 0.71 and 0.29, respectively.

CONCLUSION

In an anesthetized open-chest canine model of regional myocardial ischemia with dipyridamole induced hyperemia, 201Tl shows a more ideal relationship between tracer uptake and MBF than do the 99mTc-based agents. Of the various 99mTc-based imaging agents studied, the myocardial flow kinetics of 99mTc-Q3 appear to be closest to ideal. This relationship is maintained regardless of the normalization technique used. This may, in theory, imply a higher sensitivity in discerning ischemic from normal myocardium and a role in diagnostic nuclear imaging for 99mTc-Q3.

Extraction and retention of technetium-99m Q12, technetium-99m sestamibi, and thallium-201 in isolated rat heart during coronary acidemia

Technetium-99m Q12 and 99mTc-sestamibi are cationic lipophilic myocardial perfusion imaging tracers. Because myocardium in areas of ischemia becomes acidotic, experiments were designed to differentiate the effects of myocardial perfusate pH on radiotracer extraction and retention independent of substrate availability. We hypothesized that 99mTc-Q12 and 99mTc-sestamibi single-pass uptake and retention would be unaffected by a modest reduction in coronary perfusate pH. Isolated rat hearts were perfused at constant flow with Krebs-Henseleit buffer enriched with bovine red blood cells (20%). The indicator dilution method was used to measure the maximum extraction (Emax) and net extraction (Enet) of thallium-201 and 99mTc-Q12 (n = 8) or 201Tl and 99mTc sestamibi (n = 7) during baseline perfusion (pH = 7.4), during acidemic (pH = 6.7) perfusion, and during a restitution period with normal perfusate (pH = 7.4). 201Tl Emax (0.71+/-0.03) was greater than either 99mTc-Q12 or 99mTc-sestamibi Emax (0.27+/-0.02 and 0.26+/-0.01 respectively, P<0.0001). Acidemia significantly reduced 201Tl Emax (0.65+/-0.03, P<0.02) but not 99mTc-Q12 or 99mTc-sestamibi Emax (0.25+/-0.02 and 0.24+/-0.02 respectively). During control perfusion Enet of 201Tl was greater than that of 99mTc-Q12 at 3 and 5 min and greater than that of 99mTc-sestamibi at 3 min. 99mTc-Q12 Enet was less than 99mTc-sestamibi Enet at 3, 5, and 10 min. Acidemia decreased 201Tl and 99mTc-sestamibi Enet at 3, 5, and 10 min but had no effect on 99mTc-Q12 Enet. It is concluded that Emax of 99mTc-Q12 is less than that of 201Tl but is not different from that of 99mTc-sestamibi. Enet of 99mTc-Q12 is less than that of 99mTc-sestamibi.

Perfluorocarbon compound aerosols for delivery to the lung as potential 19F magnetic resonance reporters of regional pulmonary pO2

RATIONALE AND OBJECTIVES

Perfluorocarbon (PFC) aerosols present the opportunity for simultaneous analysis of lung structure and pulmonary oxygenation patterns. The authors investigated techniques to nebulize neat liquid PFCs for inhalation as a new method of PFC administration and tested the hypothesis that PFC aerosols may be developed for efficient delivery to the lung in an experimental rat model allowing the potential for sequential monitoring of pulmonary status via quantitative fluorine-19 (19F) magnetic resonance (MR) partial pressure of oxygen (pO2) imaging.

METHODS

Pneumatic aerosol generators were configured to produce a neat liquid PFC perfluorotributylamine (FC-43) aerosol. Perfluorocarbon inhalation breathing protocols for the rat model included: spontaneous direct breathing from an aerosol chamber, and use of a tracheotomy tube to bypass nasal breathing. The PFC aerosol delivery into the rat lung was documented through 19F MR imaging in correlation with high-resolution anatomic proton MR images. Theoretical model calculations for PFC mass deposition were compared with experimental results.

RESULTS

The pneumatic generator produced a PFC aerosol droplet within the theoretically targeted range (geometric mean particle diameter of 1.2 microns; concentration of approximately 4 x 10(7) droplets per cm3). No measurable aerosol reached the lungs during spontaneous breathing because of the efficient filtering capabilities of the turbinated nasal passages. With tracheotomy, aerosol depositions within the lung were achieved in mass quantities consistent with theoretical expectations; however, the distribution patterns were nonuniform and unpredictable. Oxygen-enhanced 19F imaging was demonstrated.

CONCLUSIONS

Perfluorocarbon aerosols of controlled size distribution can be produced at sufficient concentration with pneumatic generators for distribution to the terminal pulmonary architecture and visualization using 19F MR imaging. The potential exists for in vivo oxygen-sensitive imaging in the pulmonary system and development of sophisticated experimental animal models of systemic oxygen transport as a function of pulmonary status.

Effects of ouabain on technetium-99m-Q12 and thallium-201 extraction and retention by isolated rat heart

The mechanisms of myocardial extraction and retention of the new cationic lipophilic radionuclide imaging agent 99mTc-Q12 are currently unknown. We hypothesized that 99mTc-Q12 has satisfactory single-pass extraction independent of active transport processes and longer cellular retention than 201Tl for rapid and sustained cardiac imaging to differentiate perfusion defects.

METHODS

Isolated rat hearts were perfused at constant flow with Krebs-Henseleit buffer enriched with bovine red blood cells (30%-40%). The indicator dilution method was used to measure the single-pass maximum extraction (Emax) and net extraction (Enet(t)) of 201Tl and 99mTc-Q12 over 15 min during control perfusion (n = 11) and during normal (1 microM, n = 6) and high cardiotoxic (50 microM, n = 11) dose infusions of the digitalis glycoside, ouabain.

RESULTS

The Emax of 201Tl was greater than 99mTc-Q12 Emax (0.73 +/- 0.01 and 0.29 +/- 0.01, respectively). At 3 min of perfusion, 201Tl Enet was greater than 99mTc-Q12 Enet (0.40 +/- 0.01 and 0.11 +/- 0.00, respectively). Between 3 and 15 min, 201Tl Enet was decreasing by a rate of 2% per minute while 99mTc-Q1 2 Enet was decreasing by less than 0.1 % per minute. Ouabain decreased 201TI Emax but did not change 99mTc-Q12 Emax. High-dose ouabain decreased 201Tl Enet at 3 min and 99-Tc-Q12 Enet at 10 and 15 min.

CONCLUSION

Ouabain reduced 201Tl Emax but not 99mTc-Q12 Emax. Therefore, the cellular extraction process for 99mTc-Q12 is different from that of 201Tl. Since the Enet(t) of 99mTc-Q12 was reduced in the presence of high doses of ouabain while Emax was unchanged, 99mTc-Q12 extraction and retention appear to be controlled by different processes. Extraction and release kinetics of 99mTc-Q12 were not changed with a low dose analogous to the human therapeutic levels of ouabain.

In vivo PO2 imaging in the porcine model with perfluorocarbon F-19 NMR at low field

Quantitative pO2 imaging in vivo has been evaluated utilizing F-19 NMR in the porcine model at 0.14 T for the lungs, liver, and spleen following i.p. administration of the commercial perfluorotributylamine (FC-43)-based perfluorocarbon (PFC) emulsion, Oxypherol-ET. Calculated T1 maps obtained from a two spin-echo saturation recovery/inversion recovery (SR/IR) pulse protocol are converted into quantitative pO2 images through a temperature-dependent calibration curve relating longitudinal relaxation rate (1/T1) to pO2. The uncertainty in pO2 for a T1 measurement error of +/- 5% as encountered in establishing the calibration curves ranges from +/- 10 torr (+/- 40%) at 25 torr to +/- 16 torr (+/- 11%) at 150 torr for FC-43 (37 degrees C). However, additional uncertainties in T1 dependent upon the signal-to-noise ratio may be introduced through the SR/IR calculated T1 pulse protocol, which might severely degrade the pO2 accuracy. Correlation of the organ image calculated pO2 with directly measured pO2 in airway or blood pools in six pigs indicate that the PFC resident in lung is in near equilibrium with arterialized blood and not with airway pO2, suggesting a location distal to the alveolar epithelium. For the liver, the strongest correlation implying equilibrium was evident for venous blood (hepatic vein). For the spleen, arterial blood pO2 (aorta) was an unreliable predictor of pO2 for PFC resident in splenic tissue. The results have demonstrated the utility and defined the limiting aspects quantitative pO2 imaging in vivo using F-19 MRI of sequestered PFC materials.

Myocardial uptake and kinetic properties of technetium-99m-Q3 in dogs

We postulated that 99mTc-Q3, a cationic imaging agent, produces myocardial activity related to myocardial blood flow during myocardial ischemia and pharmacologic coronary artery vasodilation, and shows little or no myocardial redistribution over 4 hr after intravenous injection.

METHODS

In six Group 1 dogs, the chest was opened, the left circumflex coronary artery was acutely ligated, and dipyridamole (0.32, 0.56 or 0.84 mg/kg) was infused into the right atrium, followed by 10 mCi of 99mTc-Q3. Myocardial blood flow was measured by radiolabeled microspheres. The animals were euthanized and 357 myocardial samples were assayed in a well counter for 99mTc activity. One week later, radiolabeled microsphere activity was counted and myocardial blood flow calculated. In nine Group 2 dogs, a variable occluder was placed around the left circumflex coronary artery and an ischemic level of circumflex blood flow was maintained constant over 4 hr as measured by an ultrasonic flow meter. Dipyridamole (0.56 mg/kg) was then infused into the right atrium followed by 10 mCi of 99mTc-Q3. Gamma camera images were acquired at 5, 15, 30, 60, 120 and 240 min following 99mTc-Q3 injection. Microsphere blood flow and endocardial biopsies (n = 6 dogs) were performed at 30, 60, 120 and 240 min following 99mTc-Q3 injection.

RESULTS

In the Group 1 animals, 99mTc activity (y) was related to myocardial blood flow (x) from 0 to 6.1 ml/min/g by the relationship y = 0.83X + 0.18, r = 0.95, p = 0.0001. The scintigraphic ratio of myocardial perfusion defect zone counts-to-normal myocardial zone counts (0.54 +/- 0.05 at 30 min) remained constant over 4 hr, as did technetium counts from direct endocardial sampling. Scintigraphic count ratios allowed discrimination between perfusion defect and normal myocardial regions beginning at 5 min following 99mTc-Q3 injection.

CONCLUSIONS

Over a range of myocardial blood flows from 0 to 6.1 ml/min/g, 99mTc-Q3 myocardial activity is related to myocardial flow at the time of tracer injection. Technetium-99m-Q3 shows no evidence of myocardial redistribution over a 4-hr period.

Evaluation of the influence of the aqueous phase bioconstituent environment on the F-19 T1 of perfluorocarbon blood substitute emulsions

Oxygen-sensitive F-19 magnetic resonance imaging of perfluorocarbon compounds requires that fluorocarbon T1 changes correlate with the local PO2 and not with the composition of the surrounding aqueous phase. The influence of various bioconstituents and paramagnetic ions within the aqueous phase on the F-19 fluorocarbon phase T1 for PFC emulsions was evaluated at 0.14 and 0.66 T. T1 was measured for FC-43, perflubron, and a fluorinated surfactant. Controlled variables introduced in the aqueous phase included annex solution constituents, blood, pH changes, and Gd-DTPA. For a constant PO2, the F-19 T1s were independent of the emulsion constituents, blood concentration, and pH. For FC-43 and perflubron, F-19 T1 was independent of the Gd-DTPA concentration, while the aqueous phase T1 decreased by more than an order of magnitude. XMO-10 (smallest emulsion particle size) showed a slight decrease in F-19 T1 with increasing Gd-DTPA concentration at 0.66 T.