Regional particle size dependent deposition of inhaled aerosols in rats and mice.

CONTEXT: The current data analysis tools in nuclear medicine have not been used to evaluate intra organ regional deposition patterns of pharmaceutical aerosols in preclinical species. OBJECTIVE: This study evaluates aerosol deposition patterns as a function of particle size in rats and mice using novel image analysis techniques. MATERIALS AND METHOD: Mice and rats were exposed to radiolabeled polydisperse aerosols at 0.5, 1.0, 3.0, and 5.0 µm MMAD followed by SPECT/CT imaging for deposition analysis. Images were quantified for both macro deposition patterns and regional deposition analysis using the LRRI-developed Onion Model. RESULTS: The deposition fraction in both rats and mice was shown to increase as the particle size decreased, with greater lung deposition in rats at all particle sizes. The Onion Model indicated that the smaller particle sizes resulted in increased peripheral deposition. DISCUSSION: These data contrast the commonly used 10% deposition fraction for all aerosols between 1.0 and 5.0 µm and indicate that lung deposition fraction in this range does change with particle size. When compared to historical data, the 1.0, 3.0, and 5.0 µm particles result in similar lung deposition fractions; however, the 0.5 µm lung deposition fraction is markedly different. This is probably caused by the current aerosols that were polydisperse to reflect current pharmaceutical aerosols, while the historical data were generated with monodisperse aerosols. CONCLUSION: The deposition patterns of aerosols between 0.5 and 5.0 µm showed an increase in both overall and peripheral deposition as the particle size decreased. The Onion Model allows a more complex analysis of regional deposition in preclinical models.

A phenotypic model recapitulating the neuropathology of Parkinson's disease.

This study was undertaken to develop a phenotypic model recapitulating the neuropathology of Parkinson's disease (PD). Such a model would show loss of dopamine in the basal ganglia, appearance of Lewy bodies, and the early stages of motor dysfunction. The model was developed by subcutaneously injecting biodegradable microspheres of rotenone, a complex I inhibitor in 8-9 month old, ovariectomized Long-Evans rats. Animals were observed for changes in body weight and motor activity. At the end of 11-12 weeks animals were euthanized and the brains examined for histopathological changes. Rotenone treated animals gain weight and appear normal and healthy as compared to controls but showed modest hypokinesia around 5-6 weeks posttreatment. Animals showed loss of dopaminergic (DA) neurons and the appearance of putative Lewy bodies in the substantia nigra. Neuroinflammation and oxidative stress were evidenced by the appearance of activated microglia, iron precipitates, and 8-oxo-2'-deoxyguanosine a major product of DNA oxidation. The dorsal striatum, the projection site of midbrain DA neurons, showed a significant reduction in tyrosine hydroxylase immunostaining, together with an increase in reactive astrocytes, an early sign of DA nerve terminal damage. Levels of vesicular monoamine transporter 2 (VMAT2) were significantly reduced in the dorsal striatum; however, there was an unexpected increase in dopamine transporter (DAT) levels. Old, ovariectomized females treated with rotenone microspheres present with normal weight gain and good health but a modest hypokinesia. Accompanying this behavioral phenotype are a constellation of neuropathologies characteristic of PD that include loss of DA neurons, microglia activation, oxidative damage to nuclear DNA, iron deposition, and appearance of putative Lewy bodies. This phenotypic model recapitulating the neuropathology of Parkinson's disease could provide insight into early mechanisms of pathogenesis and could aid in the identification of biomarkers to identify patients in early stage, PD.

Evaluation of a candidate anti-arthritic drug using the mouse collagen antibody induced arthritis model and clinically relevant biomarkers.

The most rigorous scenario for testing a candidate rheumatoid arthritis therapeutic would be to use clinically relevant biomarkers and readouts to monitor disease development in an animal model that has a mechanism of disease that reflects the human condition. Treatment should begin when the full spectrum of arthritic processes, including bone damage, is present. We have tried to take this approach to evaluate a novel EP4 receptor antagonist (ER-886046) for its anti-arthritic potential. This work aimed not only to test a potential drug, but to also demonstrate a strategy for performing a more clinically relevant evaluation of future candidate arthritis treatments. A variety of biomarkers including: radiographic evaluation, clinical scoring, histology analysis, F4/80 macrophage immunohistochemistry, luminol bioluminescent imaging and (99m)Tc-MDP-SPECT imaging were evaluated as disease readouts in the mouse anti-collagen antibody induced arthritis model (CAIA). CAIA mice were treated either prophylactically or therapeutically with ER-886046 and the compound's efficacy was probed using the various biomarkers and compared to the reference drugs prednisolone and celecoxib. The various biomarkers effectively measured different aspects of arthritis pathology and consistently demonstrated the efficacy of ER-886046. The compound was found to be effective even when dosed therapeutically after bone damaging processes had initiated. The results presented herein demonstrate how biomarkers and a clinically relevant experimental design can be used to evaluate a candidate therapeutic. Utilization of clinically relevant biomarkers may provide a means for more translatable pre-clinical testing of candidate therapeutics and may provide information on their mechanism of action.

Metastatic melanoma imaging with an (111)In-labeled lactam bridge-cyclized alpha-melanocyte-stimulating hormone peptide.

INTRODUCTION: The purpose of this study was to examine whether a novel lactam bridge-cyclized (111)In-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-Gly-Glu-c[Lys-Nle-Glu-His-d-Phe-Arg-Trp-Gly-Arg-Pro-Val-Asp] {DOTA-GlyGlu-CycMSH} could be an effective imaging probe for metastatic melanoma detection. METHODS: (111)In-DOTA-GlyGlu-CycMSH was prepared and purified by reverse-phase high-performance liquid chromatography (RP-HPLC). The internalization and efflux of (111)In-DOTA-GlyGlu-CycMSH were examined in B16/F10 melanoma cells. The biodistribution of (111)In-DOTA-GlyGlu-CycMSH was determined in B16/F10 pulmonary metastatic melanoma-bearing and normal C57 mice. Pulmonary metastatic melanoma imaging was performed by small-animal single-photon emission computed tomography (SPECT)/CT (Nano-SPECT/CT) using (111)In-DOTA-GlyGlu-CycMSH as an imaging probe and compared with 2-[(18)F]fluoro-2-deoxy-d-glucose ([(18)F]FDG) positron emission tomography (PET) imaging. RESULTS: (111)In-DOTA-GlyGlu-CycMSH was readily prepared with greater than 95% radiolabeling yield. (111)In-DOTA-GlyGlu-CycMSH displayed rapid internalization and extended efflux in B16/F10 cells. (111)In-DOTA-GlyGlu-CycMSH exhibited significantly (P<.05) higher uptakes (2.00+/-0.74%ID/g at 2 h post-injection and 1.83+/-0.12%ID/g at 4 h post-injection) in metastatic melanoma-bearing lung than that in normal lung (0.08+/-0.08%ID/g and 0.05+/-0.05%ID/g at 2 and 4 h post-injection, respectively). The activity accumulation in normal organs was low (<0.5%ID/g) except for the kidneys 2 and 4 h post-injection. B16/F10 pulmonary melanoma metastases were clearly visualized with (111)In-DOTA-GlyGlu-CycMSH 2 h post-injection rather than with [(18)F]FDG 1 h post-injection. CONCLUSIONS: (111)In-DOTA-GlyGlu-CycMSH exhibited favorable metastatic melanoma-targeting and -imaging properties, highlighting its potential as an effective imaging probe for metastatic melanoma detection.

Evaluating Estimation Techniques in Medical Imaging Without a Gold Standard: Experimental Validation.

Imaging is often used for the purpose of estimating the value of some parameter of interest. For example, a cardiologist may measure the ejection fraction (EF) of the heart to quantify how much blood is being pumped out of the heart on each stroke. In clinical practice, however, it is difficult to evaluate an estimation method because the gold standard is not known, e.g., a cardiologist does not know the true EF of a patient. An estimation method is typically evaluated by plotting its results against the results of another (more accepted) estimation method. This approach results in the use of one set of estimates as the pseudo-gold standard. We have developed a maximum-likelihood approach for comparing different estimation methods to the gold standard without the use of the gold standard. In previous works we have displayed the results of numerous simulation studies indicating the method can precisely and accurately estimate the parameters of a regression line without a gold standard, i.e., without the x-axis. In an attempt to further validate our method we have designed an experiment performing volume estimation using a physical phantom and two imaging systems (SPECT,CT).

SemiSPECT: A Small-animal Imaging System Based on Eight CdZnTe Pixel Detectors.

We have constructed a SPECT system for small animals that utilizes eight CdZnTe pixel detectors. The eight detectors are arranged in a single octagonal ring, where each views the object to be imaged through a single pinhole. Additional projections are obtained via rotation of the animal. Each CdZnTe detector is approximately 2 mm in thickness and is patterned on one surface into a 64×64 array of pixels with 380 micron pitch. We have designed an electronic readout system capable of collecting data from the eight detectors in listmode. In this scheme each event entry for a gamma-ray hit includes the pulse height of the pixel with the largest signal and the pulse height for each of its eight nearest neighbors. We present details of the overall design, the electronics, and system performance.