Effective rational humanization of a PASylated anti-galectin-3 Fab for the sensitive PET imaging of thyroid cancer in vivo

The lack of a non-invasive test for malignant thyroid nodules makes the diagnosis of thyroid cancer (TC) challenging. Human galectin-3 (hGal3) has emerged as a promising target for medical TC imaging and diagnosis because of its exclusive overexpression in malignant thyroid tissues. We previously developed a human-chimeric αhGal3 Fab fragment derived from the rat monoclonal antibody (mAb) M3/38 with optimized clearance characteristics using PASylation technology. Here, we describe the elucidation of the hGal3 epitope recognized by mAb M3/38, X-ray crystallographic analysis of its complex with the chimeric Fab and, based on the three-dimensional structure, the rational humanization of the Fab by CDR grafting. Four CDR-grafted versions were designed using structurally most closely related fully human immunoglobulin VH/VL regions of which one-employing the acceptor framework regions of the HIV-1 neutralizing human antibody m66-showed the highest antigen affinity. By introducing two additional back-mutations to the rodent donor sequence, an affinity toward hGal3 indistinguishable from the chimeric Fab was achieved (KD = 0.34 ± 0.02 nM in SPR). The PASylated humanized Fab was site-specifically labelled with the fluorescent dye Cy7 and applied for the immuno-histochemical staining of human tissue sections representative for different TCs. The same protein was conjugated with the metal chelator Dfo, followed by radiolabelling with 89Zr(IV). The resulting protein tracer allowed the highly sensitive and specific PET/CT imaging of orthotopic tumors in mice, which was confirmed by quantitative analysis of radiotracer accumulation. Thus, the PASylated humanized αhGal3 Fab offers clinical potential for the diagnostic imaging of TC.

Development of a Chimeric Antigen-Binding Fragment Directed Against Human Galectin-3 and Validation as an Immuno-Positron Emission Tomography Tracer for the Sensitive In Vivo Imaging of Thyroid Cancer

Background: The lack of facile methods for the specific characterization of malignant thyroid nodules makes the diagnosis of thyroid cancer (TC) challenging. Due to its restricted expression in such nodules, the cell-associated lectin galectin-3 (Gal3) has emerged as a marker for TC with growing interest for in vivo imaging as well as targeted radionuclide therapy. To accelerate translation into clinical application, we have developed a cognate chimeric human antigen-binding fragment (Fab) derived from the rat anti-Gal3 monoclonal antibody M3/38. Methods: The variable immunoglobulin (Ig) light and heavy chain sequences were cloned from the hybridoma cell line, and the corresponding Fab carrying human IgG1/κ constant genes was functionally produced in the periplasm of Escherichia coli and purified to homogeneity. To moderately prolong its plasma half-life and, thus, increase tumor uptake, the recombinant Fab was fused with a long disordered amino acid chain comprising in total 200 Pro, Ala, and Ser residues (PASylation). This novel tracer was subjected to in vitro characterization and in vivo validation by using two thyroid cancer orthotopic murine models. To this end, the αGal3-Fab-PAS₂₀₀ was conjugated with deferoxamine (Dfo), labeled with ⁸⁹Zr under mild conditions and tested for binding on TC cell lines. Athymic nude mice were inoculated either with FRO82-1 or with CAL62 tumor cells into the left thyroid lobe. After intravenous injection with ∼3.0 MBq of ⁸⁹Zr-Dfo-PAS₂₀₀-Fab, these mice were subjected to positron emission tomography (PET)/computed tomography imaging followed by quantification of tumor accumulation and immunohistochemical analysis. Results: The αGal3-Fab-PAS₂₀₀ revealed high affinity toward the recombinant Gal3 antigen, with a dissociation constant ≤1 nM as measured via enzyme-linked immunosorbent assay, surface plasmon resonance spectroscopy, and radioactive cell binding assay. The in vivo Gal3-targeting by the ⁸⁹Zr(IV)-labeled protein tracer, as investigated by immuno-PET, demonstrated highly selective and fast accumulation in orthotopically implanted tumors, with strong contrast images achieved 24 hours postinjection, and no uptake in the tumor-free thyroid lobe, as also confirmed by biodistribution studies. Conclusions: The chimeric αGal3 ⁸⁹Zr-Dfo-PAS₂₀₀-Fab tracer exhibits selective accumulation in the tumor-bearing thyroid lobe of xenograft mice. Thus, this novel radioactive probe offers potential to change TC management, in addition to current diagnostic procedures, and to reduce unnecessary thyroidectomies.

Development of a high affinity Anticalin® directed against human CD98hc for theranostic applications

Enhanced amino acid supply and dysregulated integrin signaling constitute two hallmarks of cancer and are pivotal for metastatic transformation of cells. In line with its function at the crossroads of both processes, overexpression of CD98hc is clinically observed in various cancer malignancies, thus rendering it a promising tumor target.

Methods: We describe the development of Anticalin proteins based on the lipocalin 2 (Lcn2) scaffold against the human CD98hc ectodomain (hCD98hcED) using directed evolution and protein design. X-ray structural analysis was performed to identify the epitope recognized by the lead Anticalin candidate. The Anticalin - with a tuned plasma half-life using PASylation^® technology - was labeled with ⁸⁹Zr and investigated by positron emission tomography (PET) of CD98-positive tumor xenograft mice.

Results: The Anticalin P3D11 binds CD98hc with picomolar affinity and recognizes a protruding loop structure surrounded by several glycosylation sites within the solvent exposed membrane-distal part of the hCD98hcED. In vitro studies revealed specific binding activity of the Anticalin towards various CD98hc-expressing human tumor cell lines, suggesting broader applicability in cancer research. PET/CT imaging of mice bearing human prostate carcinoma xenografts using the optimized and ⁸⁹Zr-labeled Anticalin demonstrated strong and specific tracer accumulation (8.6 ± 1.1 %ID/g) as well as a favorable tumor-to-blood ratio of 11.8.

Conclusion: Our findings provide a first proof of concept to exploit CD98hc for non-invasive biomedical imaging. The novel Anticalin-based αhCD98hc radiopharmaceutical constitutes a promising tool for preclinical and, potentially, clinical applications in oncology.

Room Temperature Al18 F Labeling of 2-Aminomethylpiperidine-Based Chelators for PET Imaging

Positron emission tomography (PET) is a non-invasive molecular imaging technology that is constantly expanding, with a high demand for specific antibody-derived imaging probes. The use of tracers based on temperature-sensitive molecules (i. e. Fab, svFab, nanobodies) is increasing and has led us to design a class of chelators based on the structure of 2-aminomethylpiperidine (AMP) with acetic and/or hydroxybenzyl pendant arms (2-AMPTA, NHB-2-AMPDA, and 2-AMPDA-HB), which were investigated as such for {Al¹⁸ F}²⁺ -core chelation efficiency. All the compounds were characterized by HPLC-MS analysis and NMR spectroscopy. The AlF-18 labeling reactions were performed under various conditions (pH/temperature), and the radiolabeled chelates were purified and characterized by radio-TLC and radio-HPLC. The stability of labeled chelates was investigated up to 240 min in human serum (HS), EDTA 5 mM, PBS and 0.9 % NaCl solutions. The in vivo stability of [Al¹⁸ F(2-AMPDA-HB)]^- was assessed in healthy nude mice (n=6). Radiochemical yields between 55 % and 81 % were obtained at pH 5 and room temperature. High stability in HS was measured for [Al¹⁸ F(2-AMPDA-HB)]^- , with 90 % of F-18 complexed after 120 min. High stability in vivo, rapid hepatobiliary and renal excretion, with low accumulation of free F-18 in bones were measured. Thus, this new Al¹⁸ F-chelator may have a great impact on immuno-PET radiopharmacy, by facilitating the development of new fluorine-18-labeled heat-sensitive biomolecules.

Reproducibility and Comparability of Preclinical PET Imaging Data: A Multicenter Small-Animal PET Study

The standardization of preclinical imaging is a key factor to ensure the reliability, reproducibility, validity, and translatability of preclinical data. Preclinical standardization has been slowly progressing in recent years and has mainly been performed within a single institution, whereas little has been done in regards to multicenter standardization between facilities. This study aimed to investigate the comparability among preclinical imaging facilities in terms of PET data acquisition and analysis. In the first step, basic PET scans were obtained in 4 different preclinical imaging facilities to compare their standard imaging protocol for ¹⁸F-FDG. In the second step, the influence of the personnel performing the experiments and the experimental equipment used in the experiment were compared. In the third step, the influence of the image analysis on the reproducibility and comparability of the acquired data was determined. Distinct differences in the uptake behavior of the 4 standard imaging protocols were determined for the investigated organs (brain, left ventricle, liver, and muscle) due to different animal handling procedures before and during the scans (e.g., fasting vs. nonfasting, glucose levels, temperature regulation vs. constant temperature warming). Significant differences in the uptake behavior in the brain were detected when the same imaging protocol was used but executed by different personnel and using different experimental animal handling equipment. An influence of the person analyzing the data was detected for most of the organs, when the volumes of interest were manually drawn by the investigators. Coregistration of the PET to an MR image and drawing the volume of interest based on anatomic information yielded reproducible results among investigators. It has been demonstrated that there is a huge demand for standardization among multiple institutions.

Galectin-3 Targeting in Thyroid Orthotopic Tumors Opens New Ways to Characterize Thyroid Cancer

Preoperative characterization of thyroid nodules is challenging since thyroid scintigraphy fails to distinguish between benign and malignant lesions. Galectin-3 (gal-3) is expressed in well-differentiated and in undifferentiated thyroid cancer types but not in normal thyrocytes and benign thyroid lesions. Herein, we aimed to validate gal-3 targeting as a specific method to detect non-radioiodine-avid thyroid cancer in thyroid orthotopic tumor models. Methods: Papillary (BcPAP) and anaplastic (CAL62 and FRO82-1) thyroid carcinoma cell lines were characterized via Western blot and polymerase chain reaction for gal-3 and sodium-iodide symporter (NIS) expression. An ⁸⁹Zr-labeled F(ab')₂ antigal-3 was generated and characterized for binding versus ¹²⁵I on 2- and 3-dimensional cell cultures. The thyroid carcinoma cells were inoculated into the left thyroid lobe of athymic nude mice, and the orthotopic tumor growth was monitored via ultrasound and fluorescence molecular tomography. Head-to-head PET/CT comparison of ¹²⁴I versus ⁸⁹Zr-deferoxamine (DFO)-F(ab')₂ antigal-3 was performed, followed by biodistribution studies and immunohistochemical analysis for gal-3 and NIS expression. Results: The thyroid carcinoma cells investigated were invariably gal-3-positive while presenting low or lost NIS expression. ⁸⁹Zr-DFO-F(ab')₂ antigal-3 tracer showed high affinity to gal-3 (dissociation constant, ∼3.9 nM) and retained immunoreactivity (>75%) on 2-dimensional cell cultures and on tumor spheroids. ¹²⁵I internalization in FRO82-1, BcPAP, and CAL62 was directly dependent on NIS expression, both in 2-dimensional and tumor spheroids. PET/CT imaging showed ⁸⁹Zr-DFO-F(ab')₂ antigal-3 signal associated with the orthotopically implanted tumors only; no signal was detected in the tumor-free thyroid lobe. Conversely, PET imaging using ¹²⁴I showed background accumulation in tumor-infiltrated lobe, a condition simulating the presence of non-radioiodine-avid thyroid cancer nodules, and high accumulation in normal thyroid lobe. Imaging data were confirmed by tracer biodistribution studies and immunohistochemistry. Conclusion: A specific and selective visualization of thyroid tumor by targeting gal-3 was demonstrated in the absence of radioiodine uptake. Translation of this method into the clinical setting promises to improve the management of patients by avoiding the use of unspecific imaging methodologies and reducing unnecessary thyroid surgery.

Preclinical Evaluation of the Hsp70 Peptide Tracer TPP-PEG24-DFO[89Zr] for Tumor-Specific PET/CT Imaging

High precision in vivo PET/CT imaging of solid tumors improves diagnostic credibility and clinical outcome of patients. An epitope of the oligomerization domain of Hsp70 is exclusively exposed on the membrane of a large variety of tumor types, but not on normal cells, and thus provides a universal tumor-specific target. Here we developed a novel PET tracer TPP-PEG₂₄-DFO[⁸⁹Zr] based on the tumor cell-penetrating peptide probe TPP, which specifically recognizes membrane Hsp70 (mHsp70) on tumor cells. The implemented PEG₂₄ moiety supported tracer stability and improved biodistribution characteristics in vivo The K _d of the tracer ranged in the low nanomolar range (18.9 ± 11.3 nmol/L). Fluorescein isothiocyanate (FITC)-labeled derivatives TPP-[FITC] and TPP-PEG₂₄-[FITC] revealed comparable and specific binding to mHsp70-positive 4T1, 4T1⁺, a derivative of the 4T1 cell line sorted for high Hsp70 expression, and CT26 tumor cells, but not to mHsp70-negative normal fibroblasts. The rapid internalization kinetics of mHsp70 into the cytosol and the favorable biodistribution of the peptide-based tracer TPP-PEG₂₄-DFO[⁸⁹Zr] in vivo enabled a tumor-specific accumulation with a high tumor-to-background contrast and renal body clearance. The tumor-specific enrichment of the tracer in 4T1⁺ (6.2 ± 1.1%ID/g), 4T1 (4.3 ± 0.7%ID/g), and CT26 (2.6 ± 0.6%ID/g) mouse tumors with very high, high, and intermediate mHsp70 densities, respectively, reflected mHsp70 expression profiles of the different tumor types, whereas benign mHsp70-negative fibroblastic hyperplasia showed no tracer accumulation (0.2 ± 0.03%ID/g). The ability of our chemically optimized peptide-based tracer TPP-PEG₂₄-DFO[⁸⁹Zr] to detect mHsp70 in vivo suggests its broad applicability in targeting and imaging with high specificity for any tumor type that exhibits surface expression of Hsp70.Significance: A novel peptide-based PET tracer against the oligomerization domain of Hsp70 has potential for universal tumor-specific imaging in vivo across many tumor type. Cancer Res; 78(21); 6268-81. ©2018 AACR.

In-depth Characterization of a TCR-specific Tracer for Sensitive Detection of Tumor-directed Transgenic T Cells by Immuno-PET

A number of different technologies have been developed to monitor in vivo the distribution of gene-modified T cells used in immunotherapy. Nevertheless, in-depth characterization of novel approaches with respect to sensitivity and clinical applicability are so far missing. We have previously described a novel method to track engineered human T cells in tumors using ⁸⁹Zr-Df-aTCRmu-F(ab')₂ targeting the murinized part of the TCR beta domain (TCRmu) of a transgenic TCR. Here, we performed an in-depth in vitro characterization of the tracer in terms of antigen affinity, immunoreactivity, influence on T-cell functionality and stability in vitro and in vivo. Of particular interest, we have developed diverse experimental settings to quantify TCR-transgenic T cells in vivo. Local application of ⁸⁹Zr-Df-aTCRmu-F(ab')₂-labeled T cells in a spot-assay revealed signal detection down to approximately 1.8x10⁴ cells. In a more clinically relevant model, NSG mice were intravenously injected with different numbers of transgenic T cells, followed by injection of the ⁸⁹Zr-Df-aTCRmu-F(ab')₂ tracer, PET/CT imaging and subsequent ex vivo T-cell quantification in the tumor. Using this setting, we defined a comparable detection limit of 1.0x10⁴ T cells. PET signals correlated well to total numbers of transgenic T cells detected ex vivo independently of the engraftment rates observed in different individual experiments. Thus, these findings confirm the high sensitivity of our novel PET/CT T-cell tracking method and provide critical information about the quantity of transgenic T cells in the tumor environment suggesting our technology being highly suitable for further clinical translation.

Comparison of 18F-Labeled Fluoroalkylphosphonium Cations with 13N-NH3 for PET Myocardial Perfusion Imaging

Despite substantial advances in the diagnosis of cardiovascular disease, there is a need for 18F-labeled myocardial perfusion agents for the diagnosis of ischemic heart disease because current PET tracers for myocardial perfusion imaging have a short half-life that limits their widespread clinical use in PET. Thus, 18F-labeled fluoroalkylphosphonium derivatives (18F-FATPs), including (5-18F-fluoropentyl)triphenylphosphonium cation (18F-FPTP), (6-18F-fluorohexyl)triphenylphosphonium cation (18F-FHTP), and (2-(2-18F-fluoroethoxy)ethyl)triphenylphosphonium cation (18F-FETP), were synthesized. The myocardial extraction and image quality of the 18F-FATPs were compared with those of 13N-NH3 in rat models.

METHODS

The first-pass extraction fraction (EF) values of the 18F-FATPs (18F-FPTP, 18F-FHTP, 18F-FETP) and 13N-NH3 were measured in isolated rat hearts perfused with the Langendorff method (flow velocities, 0.5, 4.0, 8.0, and 16.0 mL/min). Normal and myocardial infarction rats were imaged with small-animal PET after intravenous injection of 37 MBq of 18F-FATPs and 13N-NH3. To determine pharmacokinetics, a region of interest was drawn around the heart, and time-activity curves of the 18F-FATPs and 13N-NH3 were generated to obtain the counts per pixel per second. Defect size was analyzed on the basis of polar map images of 18F-FATPs and 13N-NH3.

RESULTS

The EF values of 18F-FATPs and 13N-NH3 were comparable at low flow velocity (0.5 mL/min), whereas at higher flows EF values of 18F-FATPs were significantly higher than those of 13N-NH3 (4.0, 8.0, and 16.0 mL/min, P<0.05). Myocardium-to-liver ratios of 18F-FPTP, 18F-FHTP, 18F-FETP, and 13N-NH3 were 2.10±0.30, 4.36±0.20, 3.88±1.03, and 0.70±0.09, respectively, 10 min after injection, whereas myocardium-to-lung ratios were 5.00±0.25, 4.33±0.20, 7.98±1.23, and 2.26±0.14, respectively. Although 18F-FATPs and 13N-NH3 sharply delineated myocardial perfusion defects, defect size on the 13N-NH3 images was significantly smaller than on the 18F-FATP images soon after tracer injection (0-10 min, P=0.027).

CONCLUSION

18F-FATPs exhibit higher EF values and more rapid clearance from the liver and lung than 13N-NH3 in normal rats, which led to excellent image quality in a rat model of coronary occlusion. Therefore, 18F-FATPs are promising new PET radiopharmaceuticals for myocardial perfusion imaging.

Assessment of the 18F-labeled PET tracer LMI1195 for imaging norepinephrine handling in rat hearts

A novel (18)F-labeled tracer, LMI1195 (N-[3-bromo-4-(3-(18)F-fluoro-propoxy)-benzyl]-guanidine), is being developed for sympathetic nerve imaging; its high specificity for neural uptake-1 mechanism has previously been demonstrated in cell associative studies and in rabbit and nonhuman primate studies assessing heart uptake. The aim of this study was to investigate the mechanisms of (18)F-LMI1195 cardiac uptake in the rat, which is known to contain norepinephrine uptake mechanisms beyond uptake-1.

METHODS

Tracer accumulation in the heart was studied over time after intravenous administration of (18)F-LMI1195 in healthy male Wistar rats by quantitative in vivo PET imaging. The uptake mechanism was assessed by pretreatment with the nonselective norepinephrine uptake-1 and norepinephrine uptake-2 inhibitor phenoxybenzamine (50 mg/kg intravenously; n = 4), the selective norepinephrine uptake-1 inhibitor desipramine (2 mg/kg intravenously; n = 4), or saline control (intravenously; n = 4).

RESULTS

(18)F-LMI1195 produced high and sustained heart uptake allowing clear delineation of the left ventricular wall over 60 min after tracer administration. Pretreatment with phenoxybenzamine markedly reduced the (18)F-LMI1195 cardiac uptake when compared with controls. In contrast, there was preserved (18)F-LMI1195 uptake after desipramine pretreatment.

CONCLUSION

In rats, cardiac uptake of (18)F-LMI1195 was significantly inhibited by phenoxybenzamine but not desipramine, suggesting (18)F-LMI1195 is a substrate for the uptake-2 mechanism and is consistent with the rat heart having a dominant level of the mechanism.

Small-animal PET imaging of amyloid-beta plaques with [11C]PiB and its multi-modal validation in an APP/PS1 mouse model of Alzheimer's disease

In vivo imaging and quantification of amyloid-β plaque (Aβ) burden in small-animal models of Alzheimer's disease (AD) is a valuable tool for translational research such as developing specific imaging markers and monitoring new therapy approaches. Methodological constraints such as image resolution of positron emission tomography (PET) and lack of suitable AD models have limited the feasibility of PET in mice. In this study, we evaluated a feasible protocol for PET imaging of Aβ in mouse brain with [¹¹C]PiB and specific activities commonly used in human studies. In vivo mouse brain MRI for anatomical reference was acquired with a clinical 1.5 T system. A recently characterized APP/PS1 mouse was employed to measure Aβ at different disease stages in homozygous and hemizygous animals. We performed multi-modal cross-validations for the PET results with ex vivo and in vitro methodologies, including regional brain biodistribution, multi-label digital autoradiography, protein quantification with ELISA, fluorescence microscopy, semi-automated histological quantification and radioligand binding assays. Specific [¹¹C]PiB uptake in individual brain regions with Aβ deposition was demonstrated and validated in all animals of the study cohort including homozygous AD animals as young as nine months. Corresponding to the extent of Aβ pathology, old homozygous AD animals (21 months) showed the highest uptake followed by old hemizygous (23 months) and young homozygous mice (9 months). In all AD age groups the cerebellum was shown to be suitable as an intracerebral reference region. PET results were cross-validated and consistent with all applied ex vivo and in vitro methodologies. The results confirm that the experimental setup for non-invasive [¹¹C]PiB imaging of Aβ in the APP/PS1 mice provides a feasible, reproducible and robust protocol for small-animal Aβ imaging. It allows longitudinal imaging studies with follow-up periods of approximately one and a half years and provides a foundation for translational Alzheimer neuroimaging in transgenic mice.

Simplified quantification of myocardial flow reserve with flurpiridaz F 18: validation with microspheres in a pig model

The novel PET flow tracer flurpiridaz F 18 shows high myocardial extraction and slow washout. flurpiridaz F 18 PET data analysis with tracer kinetic modeling provides accurate absolute myocardial blood flow (MBF) measurements but requires in-scanner injection and complex processing. We evaluated the hypothesis that myocardial retention and standardized uptake values (SUVs) based on late uptake provide accurate estimates of myocardial flow reserve (MFR) and, thus, might allow simplified quantification after tracer injection outside the scanner.

METHODS

Nine pigs had dynamic PET scans after repeated injections of flurpiridaz F 18 at rest and combined adenosine and dobutamine stress. flurpiridaz F 18 PET with a 3-compartment model and coinjected radioactive microspheres were used to delineate MBF. These quantitative measurements were compared with myocardial retention (%/min) and SUV of flurpiridaz F 18 after summing data over 5-10, 5-12, 5-15, 10-15, and 10-20 min after tracer injection.

RESULTS

MBF ranged from 0.5 to 2.8 mL/min/g. There was a good correlation between both flurpiridaz F 18 retention and SUVs from 5 to 12 min after injection and MBF measured using 3-compartment model- or microsphere-derived MBF (r = 0.73, P < 0.05, and r = 0.68, P < 0.05, respectively, for retention; r = 0.88, P < 0.001, and r = 0.92, P < 0.001, respectively, for SUV). At later time points, retention and SUV underestimated stress microsphere flow (at 10-20 min: r = 0.41, P = not significant, and r = 0.46, P = not significant, respectively, for retention; r = 0.41, P = not significant, and r = 0.65, P < 0.05, respectively, for SUV). When measured 5-12 min after injection, there was a close agreement between MFR measured with either flurpiridaz F 18 retention or SUV and MFR measured using microspheres (mean difference, -0.08 ± 0.36 and -0.18 ± 0.25, respectively).

CONCLUSION

Myocardial retention and SUVs of the (18)F-labeled flow tracer flurpiridaz F 18 accurately reflect the MFR. These simplified analysis methods may facilitate the combination of quantitative assessment of perfusion reserve and rapid clinical imaging protocols.

Assessment of alphavbeta3 integrin expression after myocardial infarction by positron emission tomography

AIMS

The purpose of this study was to determine the feasibility of a new positron emission tomography (PET) imaging approach using an (18)F-labelled alpha(v)beta(3) integrin antagonist ((18)F-Galacto-RGD) to monitor the integrin expression after myocardial infarction.

METHODS AND RESULTS

Male Wister rats were subjected to 20 min transient left coronary artery occlusion followed by reperfusion. Autoradiographic analysis and in vivo PET imaging were used to determine myocardial (18)F-Galacto-RGD uptake at different time points following reperfusion.

RESULTS

PET imaging and autoradiography demonstrated no significant focal myocardial (18)F-Galacto-RGD uptake in non-operated control rats and at day 1 after reperfusion. However, focal accumulation in the infarct area started at day 3 (uptake ratio = 1.91 +/- 0.22 vs. remote myocardium), peaked between 1 (3.43 +/- 0.57) and 3 weeks (3.43 +/- 0.95), and decreased to 1.96 +/- 0.40 at 6 months after reperfusion. Pretreatment with alpha(v)beta(3) integrin antagonist c(-RGDfV-) significantly decreased tracer uptake, indicating the specificity of tracer uptake. The time course of focal tracer uptake paralleled vascular density as measured by CD31 immunohistochemical analysis.

CONCLUSION

Regional (18)F-Galacto-RGD accumulation suggests up-regulation of alpha(v)beta(3) integrin expression after myocardial infarction, which peaks between 1 and 3 weeks and remains detectable until 6 months after reperfusion. This new PET tracer is promising for the monitoring of myocardial repair processes.

Characterization of normal and infarcted rat myocardium using a combination of small-animal PET and clinical MRI

The combination of small-animal PET and MRI data provides quantitative in vivo insights into cardiac pathophysiology, integrating information on biology and morphology. We sought to determine the feasibility of PET and MRI for the quantification of ischemic injury in the rat model.

METHODS

Fourteen healthy male Wistar rats were studied with 18F-FDG PET and cine MRI. Myocardial viability was determined in a transmural myocardial infarction model in 12 additional rats, using 18F-FDG PET and delayed-enhancement MRI with gadolinium-diethylenetriaminepentaacetic acid. All PET was acquired with a dedicated small-animal PET system. MRI was performed on a 1.5-T clinical tomograph with a dedicated small-animal electrocardiographic triggering device and a small surface coil.

RESULTS

In normal rats, 18F-FDG uptake was homogeneous throughout the left ventricle. The lowest mean uptake of the 18F-FDG was found in the apical regions (79% +/- 6.0% of maximum) and the highest uptake was in the anterior wall (93% +/- 4.3 % of maximum). Myocardial infarct size as determined by histology correlated well with defects of glucose metabolism obtained with 18F-FDG PET (r = 0.89) and also with delayed-enhancement MRI (r = 0.91). Left ventricular ejection fraction in normal rats measured by cine MRI was 57% +/- 5.4% and decreased to 38% +/- 12.9% (P < 0.001) in the myocardial infarction model.

CONCLUSION

Integrating information from small-animal PET and clinical MRI instrumentation allows for the quantitative assessment of cardiac function and infarct size in the rat model. The MRI measurements of scar can be complemented by metabolic imaging, addressing the extent and severity of ischemic injury and providing endpoints for therapeutic interventions.

Performance evaluation of the Philips MOSAIC small animal PET scanner

PURPOSE

In this study an evaluation of the performance of the Philips MOSAIC small animal PET scanner is presented, with special emphasis on the ability of the system to provide quantitatively accurate PET images.

METHODS

The performance evaluation was structured according to NEMA-like procedures.

RESULTS

The transaxial spatial resolution of the system (radial component) ranged between 2.7 mm FWHM at the centre and 3.2 mm FWHM at a radial offset of 45 mm from the centre. The axial spatial resolution of the system ranged between 3.4 mm FWHM at the centre and 5.8 mm FWHM at a radial offset of 45 mm from the centre. The scatter fraction was determined for a mouse- as well as for a rat-sized phantom, and the values obtained were 9.6% and 16.8%, respectively. For the mouse phantom, the maximum count rate measured was 560 kcps at 93 MBq; the maximum NEC rate equalled 308 kcps at 1.7 MBq/ml. For the rat phantom, these values were 400 kcps at 100 MBq and 129 kcps at 0.24 MBq/ml, respectively. The sensitivity of the system was derived to be 0.65%. An energy window between 410 and 665 keV was used in all experiments.

CONCLUSION

The MOSAIC system exhibits moderate spatial resolution and sensitivity values, but good NEC performance. In combination with its relatively large field of view, the system allows for high-throughput whole-body imaging of mice and rats. The accurate measurement of relative changes in radiotracer distributions is feasible.

Noninvasive Characterization of Myocardial Molecular Interventions by Integrated Positron Emission Tomography and Computed Tomography

OBJECTIVES

We sought to investigate the usefulness of integrated positron emission tomography (PET) and computed tomography (CT) for in vivo characterization of an angiogenesis-directed molecular intervention.

BACKGROUND

Controversies about the effectiveness of molecular therapies for cardiovascular disease have prompted the need for more powerful noninvasive imaging techniques.

METHODS

In a model of regional adenoviral transfer of the VEGF(121) gene to myocardium of healthy pigs, PET-CT using multiple molecular-directed radiotracers was employed.

RESULTS

Two days after gene transfer, successful transgene expression was noninvasively confirmed by a reporter probe targeting co-expressed HSV1-sr39tk reporter gene. The CT-derived ventricular function and morphology remained unaltered (left ventricular ejection fraction 57 +/- 5% in adenovirus-injected animals vs. 53 +/- 5% in controls; p = 0.36). Increased regional perfusion was identified in areas overexpressing VEGF (myocardial blood flow during adenosine-induced vasodilation 1.47 +/- 0.49 vs. 1.14 +/- 0.27 ml/g/min in remote areas; p = 0.01), corroborating in vivo effects on microvascular tone and permeability. Finally, regional angiogenesis-associated alpha(v)beta3 integrin expression was not enhanced, suggesting little contribution to the perfusion increase. Fusion of CT morphology and tracer-derived molecular signals allowed for accurate regional localization of biologic signals. Findings were validated by control vectors, sham-operated animals, and ex vivo tissue analysis.

CONCLUSIONS

Integrated PET-CT has the potential to dissect cardiovascular biologic mechanisms from gene expression to physiologic function and morphology. The VEGF overexpression in healthy myocardium increases myocardial perfusion without significant up-regulation of alpha(v)beta3 integrin adhesion molecules early after the intervention.

Comparison of three instructional methods for teaching cardiopulmonary resuscitation and use of an automatic external defibrillator to high school students

OBJECTIVE

To evaluate new instructional methods for teaching high school students cardiopulmonary resuscitation (CPR) and automated external defibrillator (AED) knowledge, actions and skills.

METHODS

We conducted a cluster-controlled trial of 3 instructional interventions among Seattle area high school students, with random allocation based on classrooms, during 2003-04. We examined two new instructional methods: interactive-computer training and interactive-computer training plus instructor-led (hands-on) practice, and compared them with traditional classroom instruction that included video, teacher demonstration and instructor-led (hands-on) practice, and with a control group. We assessed CPR and AED knowledge, performance of key AED and CPR actions, and essential CPR ventilation and compressions skills 2 days and 2 months after training. All outcomes were transformed to a scale of 0-100%.

RESULTS

For all outcome measures mean scores were higher in the instructional groups than in the control group. Two days after training all instructional groups had mean CPR and AED knowledge scores above 75%, with use of the computer program scores were above 80%. Mean scores for key AED actions were above 80% for all groups with training, with hands-on practice enhancing students' positive outcomes for AED pad placement. Students who received hands-on practice more successfully performed CPR actions than those in the computer program only group. In the 2 hands-on practice groups the scores for 3 of the outcomes ranged from 57 to 74%; they were 32 to 54% in the computer only group. For the outcome of continuing CPR until the AED was available scores were high, 89 to 100% in all 3 training groups. Mean CPR skill scores were low in all groups. The highest mean score for successful ventilations was 15% and for compressions, 29%. The pattern of results was similar after 2 months.

CONCLUSIONS

We found evidence that interactive computer based self instruction alone was sufficient to teach CPR and AED knowledge and AED actions to high school students. All forms of instruction were highly effective in teaching AED use. In contrast to AED skills, CPR remains a set of difficult psychomotor skills that is challenging to teach to high school students as well as other members of the lay public.

Myocardial kinetics of reporter probe 124I-FIAU in isolated perfused rat hearts after in vivo adenoviral transfer of herpes simplex virus type 1 thymidine kinase reporter gene

Reporter gene imaging holds promise for noninvasive monitoring of cardiac gene therapy. We recently demonstrated that (124)I-labeled 2'-fluoro-2'-deoxy-5'-iodo-1beta-d-arabinofuranosyluracil ((124)I-FIAU) is suitable for PET of myocardial expression of herpes simplex virus type 1 thymidine kinase reporter gene (HSV1-tk). In contrast to previous studies in tumors, early specific uptake was followed by rapid washout. Myocardial kinetics of (124)I-FIAU are still poorly understood. This study aimed at a further investigation under controlled conditions using an isolated heart perfusion model.

METHODS

Male Wistar rats underwent transthoracic regional injection of replication-defective adenovirus (2.5 x 10(9) plaque-forming units) containing either HSV1-tk (n = 16) or LacZ reporter gene (n = 15) into the inferior wall. Nonmanipulated rats (n = 5) served as further controls. Hearts were excised 2 d later and perfused according to the Langendorff technique with (124)I-FIAU-containing buffer (15 min, followed by 30 min of nonradioactive perfusion). Experiments were performed under baseline conditions and in the presence of thymidine (competitive substrate) or fludarabine (in vitro inhibitor of 5'-nucleotidase). Time-activity curves were acquired by external coincident detectors. The myocardial rate of (124)I-FIAU uptake (K(i)), clearance rate (K(o)), and volume of distribution (V(d) = K(i)/K(o)) were calculated. Subsequently, hearts were subjected to gamma-counting, followed by microtome slicing and autoradiography.

RESULTS

The V(d) from Langendorff perfusion significantly correlated with final whole-heart tracer retention (r = 0.88, P = 0.019) and the autoradiographic area of regional myocardial activity (r = 0.89, P = 0.016). HSV1-tk hearts showed higher K(i) and V(d) of (124)I-FIAU compared with that of controls (P < 0.001) and detectable but slower washout compared with that of the LacZ group (P < 0.01). Addition of thymidine to the perfusate inhibited myocardial uptake of (124)I-FIAU by reducing V(d) and K(i) in HSV1-tk and LacZ hearts compared with the baseline. Addition of fludarabine did not result in the expected reduction of washout in HSV1-tk hearts due to inhibition of 5'-nucleotidases (which may dephosphorylate (124)I-FIAU monophosphate). It acted as an uptake inhibitor similar to thymidine, reducing V(d) in HSV1-tk hearts.

CONCLUSION

Assessment of specific reporter probe kinetics after regional in vivo reporter gene transfer is feasible using the isolated perfused rat heart preparation. This model allows one to study the effects of pharmacologic interventions and may refine understanding of the reporter probe signal for in vivo imaging. Different nucleoside analogs significantly inhibit (124)I-FIAU uptake, emphasizing the importance of transporter mechanisms for reporter probe kinetics.

PET of cardiac transgene expression: comparison of 2 approaches based on herpesviral thymidine kinase reporter gene

PET of reporter gene expression holds promise for noninvasive monitoring of gene therapy. Previously, 2 approaches based on the herpes simplex virus type 1 thymidine kinase gene (HSV1-tk) have been successfully applied to the heart. Wild-type HSV1-tk was imaged with (124)I-labeled 2'-fluoro-2'-deoxy-5-iodo-1-beta-D-arabinofuranosyl-5-iodouracil (FIAU), and a mutant HSV1-tk (HSV1-sr39tk) was imaged with (18)F-labeled 9-[4-fluoro-3-(hydroxymethyl)butyl]guanine (FHBG). The aim of this study was to compare these 2 combinations with regard to specificity, imaging contrast, and reporter probe kinetics using dynamic PET in small and large animals.

METHODS

Similar titers of adenovirus-expressing wild-type HSV1-tk (Ad(tk)), mutant HSV1-sr39tk (Ad(sr39tk)), or control genes were directly injected into the myocardium of 24 rats and 8 pigs. Two days later, dynamic PET was performed with a clinical scanner during the 120 min after injection of (124)I-FIAU (Ad(tk) animals and controls) or (18)F-FHBG (Ad(sr39tk) animals and controls). Imaging with (13)N-ammonia was performed to identify cardiac regions of interest.

RESULTS

In rats, significant cardiac (124)I-FIAU accumulation occurred in images obtained early (10-30 min) after Ad(tk) injection. Because of tracer washout, however, no difference between Ad(tk)-injected animals and controls was seen in the images obtained later. For (18)F-FHBG, specific myocardial accumulation greater than background levels was detected in Ad(sr39tk)-injected animals at early imaging and, in contrast to (124)I-FIAU accumulation, increased over time until the latest imaging (105-120 min). At maximum, cardiac (18)F-FHBG concentration showed a 4.15 +/- 1.65-fold increase compared with controls (105-120 min), and cardiac (124)I-FIAU concentration reached a maximal increase of 1.34 +/- 0.38-fold compared with controls (10-30 min, P = 0.0014). Global cardiac reporter probe kinetics in rats were confirmed by regional myocardial analysis in pig hearts. Transgene expression was specifically visualized by both approaches. The highest target-to-background ratio of (124)I-FIAU in Ad(tk)-infected pig myocardium was 1.50 +/- 0.20, versus 2.64 +/- 0.49 for (18)F-FHBG in Ad(sr39tk)-infected areas (P = 0.01). In vivo results were confirmed by ex vivo counting and autoradiography.

CONCLUSION

Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression in different species. Specific probe kinetics suggest different myocardial handling of pyrimidine (FIAU) and acycloguanosine (FHBG) derivatives. The results favor (18)F-FHBG with mutant HSV1-sr39tk because of continuous accumulation over time and higher imaging contrast.

Coexpression of herpesviral thymidine kinase reporter gene and VEGF gene for noninvasive monitoring of therapeutic gene transfer: an in vitro evaluation

Coexpression of a reporter gene and a therapeutic gene may allow for noninvasive monitoring of cardiac gene therapy. We sought to evaluate the usefulness of an adenoviral vector expressing mutant herpesviral thymidine kinase reporter gene (HSV1-sr39tk) and vascular endothelial growth factor (VEGF) 121 in independent expression cassettes (Ad4tk).

METHODS

Accumulation of 14C-2'-fluoro-5-methyl-1-beta-D-arabinofuranosyluracil (FIAU) and 9-(4-18F-fluoro-3-hydroxymethylbutyl)guanine (FHBG) as reporter probes, and secretion of VEGF into medium, were determined for Ad4tk-infected H9c2 rat cardiac cells in vitro.

RESULTS

In vitro tracer uptake increased with increasing vector concentration and over time. It was comparable to cells infected with adenovirus expressing only wild-type HSV1-tk (reporter probe: 14C-FIAU) or mutant HSV1-sr39tk (reporter probe: 18F-FHBG). No significant uptake was observed in cells infected with adenovirus expressing VEGF alone. With increasing vector concentration, Ad4tk-infected cells increasingly released VEGF into medium. VEGF production correlated significantly with cellular reporter probe uptake (r = 0.93; P = 0.0003).

CONCLUSION

The usefulness of a vector coexpressing HSV1-tk and VEGF for noninvasive imaging of expression of a therapeutic transgene has been demonstrated in vitro. This approach may allow for future in vivo monitoring of cardiac angiogenesis gene therapy.

Delayed response of insulin-stimulated fluorine-18 deoxyglucose uptake in glucose transporter-4-null mice hearts

OBJECTIVES

We sought to evaluate the time course of insulin-stimulated myocardial glucose uptake (MGU) in mice that had undergone ablation of glucose transporter-4 (GLUT4).

BACKGROUND

The relative importance of GLUT4, the most abundant insulin-responsive glucose transporter, to modulate myocardial glucose metabolism is not well defined.

METHODS

Myocardial glucose uptake was assessed at various time points after glucose (1 mg/g) and insulin (8 mU/g) injection in GLUT4-null (G4N) (n = 48) and wild-type (WT) (n = 48) mice with (18)F-2-deoxy-2-fluoro-d-glucose (FDG) using in vivo positron emission tomography (PET), in vitro gamma-counter biodistribution, and isolated, perfused hearts.

RESULTS

Baseline assessment with PET imaging showed comparable MGU in G4N (0.66 +/- 0.12) and WT (0.67 +/- 0.11, p = 0.70) mice. Early after insulin injection, WT mice demonstrated a 3.5-fold increase in MGU (2.45 +/- 0.45, p = 0.03), whereas G4N mice presented no increase (1.11 +/- 0.24, p = 0.28). At 60 min, MGU was comparable in G4N (3.19 +/- 0.60) and WT (2.66 +/- 0.47, p = 0.28) mice. In vitro gamma-counter biodistribution evaluation confirmed in G4N mice a lack of MGU increase early after insulin, but a slow response over 120 min. The isolated, perfused hearts of G4N mice during short-term (15 min) insulin stimulation displayed no increase in MGU (0.08 +/- 0.01 ml/g/min), whereas WT mice presented a threefold increase (0.22 +/- 0.01 ml/g/min, p < 0.01). With long-term (60 min) insulin stimulation, similar MGU was found in G4N (0.31 +/- 0.02 ml/g/min) and WT (0.33 +/- 0.04 ml/g per min, p = 0.04) mice.

CONCLUSIONS

The G4N mice displayed an increase of MGU in response to insulin similar to that of controls, but with a markedly delayed time response. Our findings underscore the important role of GLUT4 in the rapid adaptive response of myocardial glucose metabolism.

Evaluation of cardiac beta-adrenoreceptors in the isolated perfused rat heart using (S)-11C-CGP12388

(S)-(11)C-CGP12388 ((11)C-CGP12388) was recently developed as an in vivo PET tracer for the evaluation of cardiac beta-adrenergic receptors. The purpose of this study was to evaluate the myocardial kinetics of (11)C-CGP12388 using the perfused rat heart model.

METHODS

Normal rat hearts were cannulated for retrograde perfusion according to the Langendorff method. Studies were performed using constant coronary flow rates of 12 mL/min (high flow: n = 6) and 6 mL/min (low flow: n = 6). Beta-adrenergic-blocking studies were also done using propranolol (blocking: n = 6). Two bolus injections of (11)C-CGP12388 were administered at a 25-min interval, and time-activity curves were measured using bismuth germanate detectors. The beta-adrenergic receptor density (B(max)) and total distribution volume (DV(tot)) were estimated using compartmental modeling. After the experiment, B(max) in vitro was measured for all hearts using (3)H-CGP12177, and the values were compared with the B(max) estimated in isolated hearts.

RESULTS

DV(tot) was significantly lower in the blocking group than in the high-flow group (P < 0.01), and there was no significant difference in DV(tot) between the high- and the low-flow groups. B(max) values estimated from (11)C-CGP12388 kinetics were 5.05 +/- 0.90 pmol/g under the high-flow model and 5.20 +/- 0.63 pmol/g under the low-flow model. The B(max) results in isolated hearts correlated significantly with the measured in vitro B(max) values (r(2) = 0.69; P < 0.001).

CONCLUSION

Beta-adrenoreceptor density in the isolated rat heart can be quantified using (11)C-CGP12388 and a 2-injection protocol. The binding of the tracer was flow independent, with low nonspecific binding. These results suggest that (11)C-CGP12388 is a promising PET tracer that may be applicable to human studies.

Simultaneous multi-analyte determination of estrone, isoproturon and atrazine in natural waters by the RIver ANAlyser (RIANA), an optical immunosensor

In most medical and environmental applications of biosensors, only single analytes are determined. However, the monitoring of several analytes is obviously preferable in order to gather more information about the sample under analysis. In line with this, different technologies are being developed to obtain multi-analyte sensors. In this paper, an analytical method for the simultaneous determination of three different contaminants-atrazine, isoproturon, and estrone-in natural waters by using an optical immunosensor prototype, the so-called "RIver ANAlyser" (RIANA), is described. RIANA is based on a rapid solid-phase fluoroimmunoassay that takes place at an optical transducer chip. The transducer surface is chemically modified with three analytes derivatives placed in different discrete locations. The sensor surface can be regenerated thus allowing the performance of several measurements with the same transducer. Each test cycle, including one regeneration step, is accomplished in 15 min. Detection limits achieved were 0.155, 0.046, and 0.084 microg/l, for atrazine, isoproturon, and estrone, respectively. Satisfactory repetition, with relative standard deviations between 1.06 and 6.98%, was obtained. Excluding a minor non-specifical binding of the isoproturon antibodies, no cross-reactivity effects were observed. Matrix effects were significant only in the case of wastewater samples. Biosensor measurements were validated using conventional liquid chromatography-mass spectrometry. The results obtained with both techniques were in good agreement.

Noninvasive Imaging of Transgene Expression by Use of Positron Emission Tomography in a Pig Model of Myocardial Gene Transfer

BACKGROUND

Radionuclide imaging of reporter gene expression may be useful for noninvasive monitoring of clinical cardiac gene therapy. Experience until now, however, has been limited to small animals.

METHODS AND RESULTS

To evaluate feasibility in a clinically applicable setting, pigs were studied by conventional positron emission tomography (PET) 2 days after regional intramyocardial injection of control adenovirus or adenovirus carrying herpesviral thymidine kinase reporter gene (HSV1-tk). Myocardial blood flow was quantified by use of [13N]ammonia. Subsequently, kinetics of the reporter substrate [124I]-2'-fluoro-2'-deoxy-5-iodo-1-beta-d-arabino-furanosyluracil (FIAU) were assessed over a period of 2 hours. Areas infected with adenovirus expressing HSV1-tk showed significantly elevated FIAU retention during the first 30 minutes after injection. At later times, washout was observed, and retention was not different from that in areas infected with control virus or remote myocardium. Early in vivo FIAU uptake correlated with ex vivo images, autoradiography, and immunohistochemistry for reporter gene product after euthanasia. After intramyocardial injection of both adenoviruses, myocardial blood flow was mildly elevated compared with that in remote areas, consistent with histological signs of regional inflammation.

CONCLUSIONS

In vivo quantification of regional myocardial transgene expression is feasible with clinical PET methodology, the radioiodinated reporter probe FIAU, and the HSV1-tk reporter gene. Radioactivity efflux after specific initial uptake was not observed previously in tumor studies, suggesting that tissue-specific differences in nucleoside metabolism influence reporter probe kinetics. By coregistering reporter gene expression with additional biological parameters such as myocardial blood flow, PET allows for noninvasive characterization of the success of cardiac gene transfer along with its functional correlates.

Comparison of two fluorescence immunoassay methods for the detection of endocrine disrupting chemicals in water

We describe two fluorescence immunoassays capable of detecting endocrine disrupting compounds in waste water. The first fluorescence method is a heterogeneous assay using total internal reflection fluorescence (TIRF) detection. The second method is a homogeneous assay that utilizes energy transfer (ETIA). Both fluorescence immunoassays are compared with respect to detection principle and ability to quantify the model analytes estrone, estradiol, and ethinylestradiol in a complex matrix regarding recovery rates and limits of detection. Calibrations were performed for the three analytes using both fluorescence methods. Limits of detection between 0.01 and 0.85 microg/l are achieved. In addition, measurements in synthetic waste water spiked with the analytes were performed. Both immunoassays allow the detection in waste water with recovery rates in the range of 70-112%.

Using a dual method needs assessment to evaluate the training needs of public health professionals

A dual method research approach was used to identify the training needs of the public health professionals in Washington. A mail questionnaire was implemented, followed by focus groups with Washington State Department of Health (DOH) and local health department (LHD) professionals. Focus groups were used successfully to enhance and clarify the survey findings by identifying the specific content of the highest rated training needs (interpersonal communication, cross-culture and cross-age communication, participatory teaching/training skills, and electronic communication) and by pinpointing preference for different modes of training delivery for different training needs.

[Effects of dehydration on functional parameters of fluid balance as well as effectiveness of rehydration using crystalline or colloidal infusion drips in calves]

Studies were conducted on 57 calves (aged 3-23 d) to elucidate the effects of diarrhoeal and experimentally induced dehydration upon functional parameters of the fluid balance and of renal functionality. Aggravating intensity and length of diarrhoea was found to be accompanied by decline in intravasal and extracellular fluid compartments. Ante mortem dehydration of the animals with diarrhoea was close to 20% relative to body weight. This was paralleled by life-threatening drop of glomerular filtration rates to < 10% of original physiological values. Administration of a diuretic, associated with reduction by 50% of daily liquid uptake, proved helpful in generating dehydration of 5 to 6% relative to body weight. Evidence was provided to the effect that isooncotic colloid-electrolyte solution was superior to pure isotonic electrolyte solution for rehydration of calves dehydrated in the first place in the way described. Colloidal infusion, in particular, produced favourable therapeutic effects in terms of optimization of blood plasma volume and renal ultrafiltration.

[Diagnostic and pathophysiological aspects of the determination of kidney function in animals]

Early diagnosis of loss in renal function (< 60-70%) is not possible either by resorting to the parameters of plasma urea and creatinine concentrations (responsive to functional loss by > 75% or by reference to urine concentration capacity (urine density: sensitive to concentrations > 60%). However, clearance techniques for determination of the glomerular filtration rate (GFR) have proved suitable for quantitative assessment of renal function. Endogenous creatinine clearance is one of the most common clinical approaches in GFR determination. Criticism of results obtainable from endogenous creatinine clearance appears to be justified by pharmacokinetic aspects of creatinine as an indicator, as well as by some of its analytical peculiarities. The tediousness of the procedure is another counterproductive aspect pertaining to large-scale use of endogenous creatinine clearance in veterinary medicine. Total blood-plasma clearance of exogenous creatinine (T-Clexo.Creatinine) would provide vets with an accurate (diagnostic validity) and practical method for carrying out clinical kidney-function diagnostics. However, more research on a number of related issues will be required before the general introduction of the procedure.

[Diagnostic and pathophysiological aspects of the determination of kidney function in animals]

Early diagnosis of loss in renal function (< 60-70%) is not possible either by resorting to the parameters of plasma urea and creatinine concentrations (responsive to functional loss by > 75% or by reference to urine concentration capacity (urine density: sensitive to concentrations > 60%). However, clearance techniques for determination of the glomerular filtration rate (GFR) have proved suitable for quantitative assessment of renal function. Endogenous creatinine clearance is one of the most common clinical approaches in GFR determination. Criticism of results obtainable from endogenous creatinine clearance appears to be justified by pharmacokinetic aspects of creatinine as an indicator, as well as by some of its analytical peculiarities. The tediousness of the procedure is another counterproductive aspect pertaining to large-scale use of endogenous creatinine clearance in veterinary medicine. Total blood-plasma clearance of exogenous creatinine (T-Clexo.Creatinine) would provide vets with an accurate (diagnostic validity) and practical method for carrying out clinical kidney-function diagnostics. However, more research on a number of related issues will be required before the general introduction of the procedure.

Regulation of the beta-adrenoceptor-cAMP-system during dynamic exercise in patients with primary hypertension after acute beta-blockade

Beta-adrenoceptors on lymphocytes are acutely increased after dynamic exercise in normotensive subjects, but not in hypertensives. It was thus of interest to evaluate the acute regulation of the lymphocyte beta-adrenoceptor-adenylate-cyclase-cAMP-system (BAAS) in patients with primary hypertension during dynamic stress after acute beta-blockade. Density and affinity of beta 2-adrenoceptors, and intracellular cAMP concentrations (baseline and isoprenaline stimulated values) were measured on the peripheral mononuclear cells in 8 male patients with primary hypertension before and immediately after dynamic exercise on a bicycle (50-200 W) at baseline and after acute beta-blockade (2 h following 100 mg atenolol). Dynamic exercise causes no significant changes in receptor density and affinity, nor in basal cAMP values. After acute beta-blockade the dynamic stress-induced rise in mean arterial blood pressure was significantly (p < 0.01) reduced from 33 to 24 mmHg, and beta-adrenoceptor density significantly (p < 0.05) increased from 1320 to 2102 molecules/cell, whereas affinity remained unchanged. Baseline and stimulated cAMP concentrations increased significantly (p < 0.05) from 5.3 to 7.0 and from 2.1 to 3.5 pmol/10(6) cells, respectively. These findings suggest that in primary hypertension the regulation of the beta 2-adrenoceptor-adenylate-cyclase-cAMP-system is impaired on exercise and can be normalised by acute beta-blockade. Since atenolol predominantly blocks beta 1-adrenoceptors, the observed normalisation of the lymphocyte BAAS may reflect only an unspecific effect of antihypertensive therapy per se.

Beta-adrenergic blood pressure regulation in Shy-Drager syndrome and pheochromocytoma

Both Shy-Drager syndrome and pheochromocytoma are characterized by an abnormal catecholamine secretion, e.g. a reduced secretion in Shy-Drager syndrome, and an excessive stimulation in pheochromocytoma resulting in adrenergic dysfunction and in adrenergic hyperactivity, respectively. The relationship between extreme variations in circulating catecholamines and beta-adrenergic receptor activity was studied in two patients with severe orthostatic hypotension (Shy-Drager syndrome) and in a patient with pheochromocytoma with excessive spontaneous catecholamine increases using the lymphocyte beta 2-adrenoceptor assay. In both patients with Shy-Drager syndrome, basal plasma concentrations of epinephrine and dopamine were low under resting conditions and could not be stimulated in the upright position. Norepinephrine was low in the first patient, and could not be stimulated; whereas the second patient had a normal basal concentration of norepinephrine, which could be moderately stimulated. There was no beta-adrenoceptor abnormality in the first patient: however, in the second patient, there were no measurable beta-adrenoceptors on membrane fractions, whereas a population of receptors only in the low affinity state could be identified on intact cells. Alpha-adrenoceptor density on thrombocyte membranes was slightly increased in both patients with Shy-Drager syndrome and showed no substantial change during upright posture. Catecholamine increases in the pheochromocytoma patient were accompanied by a rise in blood pressure, bradycardia, and an acute up-regulation of beta-adrenoceptors. Plasma concentrations of cAMP paralleled the increase in receptor density and blood pressure. The findings in pheochromocytoma add support to the theory that an acute catecholamine stimulation gives rise to an acute beta-adrenergic sensitization leading to blood pressure elevation.(ABSTRACT TRUNCATED AT 250 WORDS)