Joint analysis of ESR lineshapes and 1H NMRD profiles of DOTA-Gd derivatives by means of the slow motion theory

The "Swedish slow motion theory" [Nilsson and Kowalewski, J. Magn. Reson. 146, 345 (2000)] applied so far to Nuclear Magnetic Relaxation Dispersion (NMRD) profiles for solutions of transition metal ion complexes has been extended to ESR spectral analysis, including in addition g-tensor anisotropy effects. The extended theory has been applied to interpret in a consistent way (within one set of parameters) NMRD profiles and ESR spectra at 95 and 237 GHz for two Gd(III) complexes denoted as P760 and P792 (hydrophilic derivatives of DOTA-Gd, with molecular masses of 5.6 and 6.5 kDa, respectively). The goal is to verify the applicability of the commonly used pseudorotational model of the transient zero field splitting (ZFS). According to this model the transient ZFS is described by a tensor of a constant amplitude, defined in its own principal axes system, which changes its orientation with respect to the laboratory frame according to the isotropic diffusion equation with a characteristic time constant (correlation time) reflecting the time scale of the distortional motion. This unified interpretation of the ESR and NMRD leads to reasonable agreement with the experimental data, indicating that the pseudorotational model indeed captures the essential features of the electron spin dynamics.

Influence of high‐frequency electromagnetic fields on different modes of cell death and gene expression

PURPOSE

International thresholds for exposure to non-ionizing radiation leading to non-thermal effects were conservatively set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The aim of this study was to examine whether biological effects such as different modes of cell death and gene expression modifications related to tumorgenesis are detectable above the threshold defined.

MATERIALS AND METHODS

Human leukaemia cells (HL-60) grown in vitro were exposed to electromagnetic fields (EMF; t 1/2(r) about 1 ns; field strength about 25 times higher than the ICNIRP reference levels for occupational exposure) leading to non-thermal effects using a high-voltage-improved GTEM cell 5302 (EMCO) connected to a pulse generator NP20 (C = 1 nF, U(Load) = 20kV). HL-60 cells were harvested at 0, 24, 48 and 72 h after radiation exposure. Micronuclei, apoptosis and abnormal cells (e.g. necrosis) were determined using morphological criteria. In parallel, the expression of 1176 genes was measured using Atlas Human 1.2. Array. Based on high data reproducibility calculated from two independent experiments (> 99%), array analysis was performed.

RESULTS

No significant change in apoptosis, micronucleation, abnormal cells and differential gene expression was found.

CONCLUSIONS

Exposure of HL-60 cells to EMFs 25 times higher than the ICNIRP reference levels for occupational exposure failed to induce any changes in apoptosis, micronucleation, abnormal morphologies and gene expression. Further experiments using EMFs above the conservatively defined reference level set by the ICNIRP may be desirable.

A radiation-induced gene signature distinguishes post-Chernobyl from sporadic papillary thyroid cancers

We investigated selected gene targets to differentiate radiation-induced papillary thyroid cancers (PTCs) from other etiologies. Total RNA was isolated from 11 post-Chernobyl PTCs and 41 sporadic PTCs characterized by a more aggressive tumor type and lacking a radiation exposure history. RNA from 10 tumor samples from both groups was pooled and hybridized separately on a whole genome microarray for screening. Then 92 selected gene targets were examined quantitatively on each tumor sample using an RTQ-PCR-based low-density array (LDA). Screening for more than fivefold differences in gene expression between the groups by microarray detected 646 up-regulated and 677 down-regulated genes. Categorization of these genes revealed a significant (P < 0.0006) over-representation of the number of up-regulated genes coding for oxidoreductases, G-proteins and growth factors, while the number of genes coding for immunoglobulin appeared to be significantly down-regulated. With the LDA, seven genes (SFRP1, MMP1, ESM1, KRTAP2-1, COL13A1, BAALC and PAGE1) made a complete differentiation between the groups possible. Gene expression patterns known to be associated with a more aggressive tumor type in older patients appeared to be more pronounced in post-Chernobyl PTC, thus underlining the known aggressiveness of radiation-induced PTC. Seven genes were found that completely distinguished post-Chernobyl (PTC) from sporadic PTC.

Intercellular adhesion molecule-1: a consistent inflammatory marker of the cutaneous radiation reaction both in vitro and in vivo

BACKGROUND

Radiation damage to skin is a key diagnostic and prognostic parameter for patients accidentally exposed to radiation. Moreover, skin is a target organ for crucial side-effects of routine radiotherapy. The pathophysiology of the cutaneous radiation reaction is in many respects still unknown. The acute inflammatory radiation reaction of skin has been shown to involve alterations in cell-cell and cell-matrix interactions, which are mediated by cellular adhesion molecules.

OBJECTIVES

To evaluate the effect of ionizing radiation on intercellular adhesion molecule-1 (ICAM-1) expression in human skin cells.

METHODS

Dermal monolayer cells, a three-dimensional skin model and skin biopsies were investigated for ICAM-1 expression after ionizing radiation using flow cytometry, quantitative reverse transcription-polymerase chain reaction and immunohistochemistry. ICAM-1 expression in monolayer cells pretreated with protein kinase inhibitors and dexamethasone prior to irradiation was analysed by flow cytometry.

RESULTS

Using different sources of skin cells, we demonstrated a consistent upregulation of both ICAM-1 mRNA and protein expression by ionizing radiation. Blocking experiments revealed that tumour necrosis factor-alpha, another ICAM-1 inducer, does not account for the effect of radiation. Radiation-induced upregulation of ICAM-1 expression was significantly attenuated by inhibitors to protein kinase C, mitogen-activated protein (MAP) ERK kinase, p38 MAP kinase and phosphatidylinositol 3-kinase. The anti-inflammatory agent dexamethasone suppressed the effect of radiation on ICAM-1 expression, suggesting its usefulness to treat the cutaneous radiation reaction.

CONCLUSIONS

Our data suggest that ICAM-1 is a consistent inflammatory parameter of the cutaneous radiation reaction both in vitro and in vivo that might provide new therapeutic options for diagnosis and treatment of effects of radiation.

Apoptosis in Non-Tumorous Adult Human Testis Tissue

INTRODUCTION

Apoptosis seems to play an important role in tumorigenesis, prognosis and therapy of testicular tumors. To understand its biological significance, it is important to quantify the amount of apoptosis and to compare the rate of apoptosis to that of a normal, unaffected reference tissue. Usually tissue from the unaffected site of the testis in patients with testicular cancer or testis tissue from patients who underwent surgical castration due to prostate cancer is used as the reference tissue. However it is not known, if both tissues are equivocal with respect to their apoptotic index. The purpose of the study was to compare the two most often used reference tissues for the quantification of apoptosis in testicular tissues with regard to their apoptotic index.

MATERIALS AND METHODS

The apoptotic indices of both tissues were compared, using two standard apoptosis detection methods, i.e. in situ end labeling and a morphological approach.

RESULTS

The apoptotic index in testis tissue from patients who were surgically castrated for anti-hormonal treatment of prostate cancer was shown to be significantly higher than the apoptotic index of tumor free but tumor-associated testicular tissue of testis cancer patients. There was a strong relationship between the apoptotic index and the age of the patients.

CONCLUSION

Although there might be genetic changes in the tumor-associated testicular tissue influencing the apoptotic index, it seems advisable to use tumor-associated tissue rather than testis tissue of patients with prostate cancer as the reference tissue, due to the significant age dependence of the apoptotic index.

Gene Expression Profiling in Seminoma and Nonseminoma

Purpose

Gene expression profiles of seminoma were compared with nonseminoma to get insights into tumorigenesis.

Materials and Methods

Eleven testicular tumor biopsies (five pure seminoma, six nonseminoma; pT1N0M0 to pT2N2M1) and biopsies from unaffected sites were analyzed once per patient using a macroarray (1,176 genes). On the same patients, six genes were validated using real-time quantitative (RTQ) polymerase chain reaction (PCR). Additionally, in a separate cohort of 19 patients, 24 genes selected from the macroarray were measured using RTQ-PCR.

Results

(1) The agreement in gene expression was 94% between the two methods and two different patient cohorts. (2) Two features in gene expression were independent of the tumor entity: Most changes of gene expression occurred in five functional groups like “cell cycle” and “apoptosis.” Genes within these groups were almost similarly (> 80%) up- or downregulated. (3) Nonseminoma were characterized by downregulated genes (75%), but in seminoma, upregulated genes (64%) prevailed. Furthermore, 64.4% of those genes that were differentially expressed in both tumor entities were usually upregulated in seminoma but downregulated in nonseminoma. A reverse pattern was found in 24.4% of such genes. Eleven percent of these genes showed a similar up- or downregulation in gene expression in both tumor entities.

Conclusion

Seminoma in this preliminary study can be differentiated from nonseminoma due to almost opposing gene expression profiles (89% of the significantly differentially expressed genes) and are in line with the histological discrimination of both tumor entities. Underlying mechanisms and implications regarding the origin and tumor progression of both entities are discussed.

Comparison of the abundance of 10 radiation-induced proteins with their differential gene expression in L929 cells

PURPOSE

To determine whether radiation-induced changes in protein abundance can be correlated with their differential gene expression in a murine fibroblast L929 cell line.

MATERIALS AND METHODS

L929 cells were irradiated with 6 Gy. Cell lysates were collected at different points in time (20 min, 12, 24, 36, 48 and 72 h). The extracted proteins were separated by two-dimensional gel electrophoresis and quantified using computerized image analysis. Proteins exhibiting a differential expression equal to or more than twofold were identified by mass spectrometry following trypsin digestion. From these, 10 proteins characterized by large changes of radiation-induced abundance were selected in order to measure their corresponding gene expression using RTQ-PCR (real-time quantitative polymerase chain reaction).

RESULTS

Up to 15-fold changes in the abundance of these 10 proteins were associated with no detectable changes more than twofold on the gene expression level. However, one gene (VEGF-D) showed a significant (p=0.005) up-regulation (1.8-fold).

CONCLUSIONS

Deducing protein abundance from mRNA expression levels and vice versa appears to be of limited use. Furthermore, examination of transcriptional and translational changes provides different but complementary information.

Significance of apoptosis in metastasizing testis tumors

Testis tumors of embryonal origin (ten metastasized, six non-metastasized) and 17 mixed testis cell carcinomas (eight metastasized, nine non-metastasized) were examined. A triple immunofluorescence microscopic labeling procedure allowed the simultaneous detection of two features of apoptosis, namely morphological changes in the nucleus (DNA condensation visualized by DAPI staining) and the process of DNA fragmentation (TdT-assay) in tumor cells as well as T-cells (recognized by their CD45RO epitope). Both methods for apoptosis detection showed similar apoptotic indices (AI) only in 2.6% of all tumors. Most tumors (81.6%) showed more cells with DNA fragments than condensed chromatin, but in a number of cases (10.5%) the opposite pattern was found. These data add to the few published in vivo examinations of apoptosis using different methods and help to explain differences in the judgment of apoptosis significance for tumor prognosis. With regard to tumorigenesis, non-metastasized testis tumors were characterized by higher AIs of tumor cells and T-cells compared with metastasized tumors, which could be interpreted as a characteristic of tumors in an earlier stage of their development into an apoptosis-resistant phenotype. For the first time, in metastasized tumors a 5 to 25-fold increase of the T-cell's AIs over the corresponding AIs of tumor cells was shown. This suggests a successful counterattack of tumor cells, thus supporting the process of metastasis. However, only ten out of 33 tumors revealed these AI changes, which again highlights that tumor biology cannot be predicted by a single parametric approach. It remains to be seen whether these characteristics might be suitable for a reliable prediction of metastasis.

Radiation-induced gene expression in MCF-7 cells

PURPOSE

Detection of gene targets applicable to biological dosimetry and early detection of radiation-induced cell damage.

MATERIALS AND METHODS

MCF-7 human mammary carcinoma cells were exposed to 2 and 6 Gy X-rays. Expression of 1176 genes was traced with the Atlas Human 1.2 Array (Clontech).

RESULTS

(1) Based on data reproducibility (about 98%), a new and improved analysis was employed. (2) Normalization of data using ubiquitin or total gene expression led to the same results. (3) Dose-dependent gene expression was shown for six genes, which were constantly expressed over 1 day (three genes), 2 days (two) and 3 days (one). Differential gene expression was confirmed by RTQ-PCR. Three of the six genes were novel radiation-induced gene targets. (4) When analysing the expression of all genes, the processes of cell degradation (e.g. cell death and protein catabolism) were activated. Simultaneously, inhibition not only of cell proliferation, but also of other cellular functions (e.g. cell repair) was found. Hence, cell death appears a process of 'active silencing'.

CONCLUSIONS

With the screening method applied, six radiation-induced gene targets were found, three of which were novel genes. Their applicability in other cell models remains to be tested. Different sets of genes have to be considered for dose assessment, owing to their changes in gene expression with time after irradiation. Furthermore, it has to be investigated whether 'active silencing' represents a general principle of radiation-induced cell death.

Physicochemical and biological evaluation of P792, a rapid-clearance blood-pool agent for magnetic resonance imaging

RATIONALE AND OBJECTIVES

To summarize the physicochemical characterization, pharmacokinetic behavior, and biological evaluation of P792, a new monogadolinated MRI blood-pool agent.

METHODS

The molecular modeling of P792 was described. The r1 relaxivity properties of P792 were measured in water and 4% human serum albumin at different magnetic fields (20, 40, 60 MHz). The stability of the gadolinium complex was assessed. The pharmacokinetic and biodistribution profiles were studied in rabbits. Renal tolerance in dehydrated rats undergoing selective intrarenal injection was evaluated. Hemodynamic safety in rats and in vitro histamine and leukotriene B4 release were also tested.

RESULTS

The mean diameter of P792 is 50.5 A and the r1 relaxivity of this monogadolinium contrast agent is 29 L x mmol(-1) x s(-1) at 60 MHz. The stability of the gadolinium complex in transmetallation is excellent. The pharmacokinetic and biodistribution profiles are consistent with that of a rapid-clearance blood-pool agent: P792 is mainly excreted by glomerular filtration, and its diffusion across normal endothelium is limited. Renal and hemodynamic safety is comparable to that of the nonspecific agent gadolinium-tetraazacyclododecane tetraacetic acid. No histamine or leukotriene B4 release was found in RBL-2H3 isolated mastocytes.

CONCLUSIONS

The relaxivity of P792 at clinical field is very high for a monogadolinium complex without protein binding. The pharmacokinetic and biodistribution profiles are consistent with those of a rapid-clearance blood-pool agent. Its initial safety profile is satisfactory. Experimental and clinical studies are underway to confirm the potential of P792 in MRI.

P792: a rapid clearance blood pool agent for magnetic resonance imaging: preliminary results

An original MRI contrast agent, called P792, is described. P792 is a gadolinium macrocyclic compound based on a Gd-DOTA structure substituted by hydrophilic arms. The chemical structure of P792 has been optimized in order to provide (1) a high r(1) relaxivity in the clinical field for MRI: 29 mM(-1)xs(-1) at 60 MHz, (2) a high biocompatibility profile and (3) a high molecular volume: the apparent hydrodynamic volume of P792 is 125 times greater than that of Gd-DOTA. As a result of this high molecular volume, P792 presents an unusual pharmacokinetic profile, as it is a Rapid Clearance Blood Pool Agent (RCBPA) characterized by limited diffusion across the normal endothelium. The original pharmacokinetic properties of this RCBPA are expected to be well suited to MR coronary angiography, angiography, perfusion imaging (stress and rest), and permeability imaging (detection of ischemia and tumor grading). Further experimental imaging studies are ongoing to define the clinical value of this compound.

When is now? Perception of simultaneity

We address the following question: Is there a difference (D) between the amount of time for auditory and visual stimuli to be perceived? On each of 1000 trials, observers were presented with a light-sound pair, separated by a stimulus onset asynchrony (SOA) between -250 ms (sound first) and +250 ms. Observers indicated if the light-sound pair came on simultaneously by pressing one of two (yes or no) keys. The SOA most likely to yield affirmative responses was defined as the point of subjective simultaneity (PSS). PSS values were between -21 ms (i.e. sound 21 ms before light) and +150 ms. Evidence is presented that each PSS is observer specific. In a second experiment, each observer was tested using two observer-stimulus distances. The resultant PSS values are highly correlated (r = 0.954, p = 0.003), suggesting that each observer's PSS is stable. PSS values were significantly affected by observer-stimulus distance, suggesting that observers do not take account of changes in distance on the resultant difference in arrival times of light and sound. The difference RTd in simple reaction time to single visual and auditory stimuli was also estimated; no evidence that RTd is observer specific or stable was found. The implications of these findings for the perception of multisensory stimuli are discussed.

Design and initial evaluation of a low-cost 3-Tesla research system for combined optical and functional MR imaging with interventional capability

A 3-Tesla research system has been developed for functional and interventional magnetic resonance imaging (MRI) procedures on animal models based on a low field niche spectrometer. Use of two stages of fourth harmonic frequency multiplication has allowed us to produce a high-frequency spectrometer with good frequency stability based on a low-frequency direct digital synthesizer. The system has been designed with the ability to introduce interventional tools such as biopsy needles, radiofrequency (RF) electrodes, and fiber optics for optical spectroscopy and thermal ablation as well as drug infusions to allow function to be studied in the presence of external challenges. Full MR-compatible physiologic support capability allows animals to be maintained in a stable condition over extended periods of study. Functional MR images have been acquired by using gradient echoes (TR/TE = 40/12 msec) from the rat whisker barrel cortex using electrical stimulation (5-V, 1.5-mA, 1-msec pulses at 5 Hz via two needle electrodes inserted into the rat whisker pad). Initial results using respiratory gas challenges of 100% N(2), 100% O(2), and 10% CO(2) have shown excellent agreement between single wavelength (633 nm) optical and functional MR time series with subsecond time resolution. The 1-mm copper electrodes for interventional radiofrequency ablation procedures were easily visualized in the superior colliculus by using gradient echo sequences. This novel, low-cost, high field system appears to be a useful research tool for functional and interventional studies of rat brain and allows concurrent optical spectroscopy. J. Magn. Reson. Imaging 2001;13:87-92.

Preclinical profile of the monodisperse iodinated macromolecular blood pool agent P743

RATIONALE AND OBJECTIVES

To summarize the chemical synthesis, physicochemical characterization, pharmacokinetic behavior, and biological evaluation of P743, a new macromolecular iodinated contrast medium.

METHODS

The synthesis and molecular modeling of the iodinated macromolecule P743 are described. The pharmacokinetic profile was established in rabbits and rats. Acute toxicity in mice, renal tolerance in normal rabbits, and renal tolerance in uninephrectomized, dehydrated rats undergoing selective intrarenal injection was evaluated. In vitro permeability effects on isolated mastocytes and on the coagulation pathways were carried out. Computed tomography vascular imaging was performed after intravenous injection of P743 (300 mg I/kg) in rabbits and compared with the nonspecific nonionic agent iobitridol.

RESULTS

P743 is a monodisperse, macromolecular iodinated contrast medium. In both rabbits and rats, P743 showed a pharmacokinetic profile consistent with that of a rapid-clearance blood-pool agent. Its diffusion through the endothelium was found to be low in vitro, thus confirming early confinement of this macromolecule, unlike nonspecific contrast media. In both species, P743 was excreted by glomerular filtration. Acute toxicity disclosed no mortality at the highest volume that could be injected into mice, leading to a median lethal dose greater than 8.9 g I/kg. Renal tolerance was found to be good in both euvolemic rabbits and uninephrectomized, dehydrated rats. No histamine or leukotriene B4 release was found on RBL-2H3 isolated mastocytes. P743 did not interfere with the coagulation pathways. Imaging experiments confirmed that P743 remains in the vascular compartment for a longer time than does iobitridol, thus allowing vascular enhancement that is twice as high as that of iobitridol in the recirculation phase.

CONCLUSIONS

The pharmacokinetic and imaging profiles of P743, a new, monodisperse, macromolecular blood-pool iodinated contrast medium, were consistent with those of a rapid-clearance blood-pool agent. Its initial safety profile is satisfactory. Further experimental imaging studies are required to define the clinical interest in such molecules.

Pharmacokinetics of three gadolinium chelates with different molecular sizes shortly after intravenous injection in rabbits: relevance to MR angiography

RATIONALE AND OBJECTIVES

To mimic an MR angiographic protocol, an experimental model was developed in rabbits to determine gadolinium concentrations in blood early after injection. Contrast agents with different molecular sizes were compared.

METHODS

The influence of injection parameters (injection rate, duration of injection, volume of injection, dose) was assessed, and two blood pool agents (P760, P717) were compared with the low-molecular-weight Gd-DOTA under similar conditions.

RESULTS

Two main phases were identified: bolus and post-bolus. Injection parameters strongly influenced the pattern of the bolus phase, but the postbolus phase was sensitive only to the injected dose. The blood pool agents presented a bolus phase profile similar to that of Gd-DOTA, but 45 seconds after injection, 84% of P717 molecules were still present in the blood compartment, compared with 65% of P760 molecules and only 51% of Gd-DOTA molecules.

CONCLUSIONS

Blood pool agents are useful for MR angiographic protocols involving the postbolus phase. In protocols in which only the bolus phase is imaged, blood pool agents provide similar data to Gd-DOTA, provided that the injection rate, iso-T1 efficiency dose, and volume are similar.

Physical, chemical, and biological evaluations of P760: a new gadolinium complex characterized by a low rate of interstitial diffusion

An original gadolinium chelate, termed P760, which diffuses through the vascular endothelium but at a much lower rate than nonspecific agents (NSA), is described. P760 is a gadolinium macrocyclic compound based on a DOTA structure that is substituted by hydrophilic bulky groups branched on the amino-carboxylic residues. The molecular weight is 5293, and the molecular volume, measured by light scattering, is 30 times higher (11.5 nm3) than that of gadolinium (Gd)-DOTA (0.38 nm3). The increase in molecular volume and weight has two consequences: a) higher relaxivity (r1; 24.7 mM-1.s-1 compared with 3.4 mM-1.s-1 for Gd-DOTA at 20 Mhz, 37 degrees C); and b) a lengthening of its transport rate through the endothelium. P760 presents a peculiar pharmacokinetic profile: at early times post injection, the blood concentrations are higher than those of Gd-DOTA, but after 20 minutes, the blood concentrations are equal for the two compounds. The body clearances of the products are identical (i.e., glomerular filtration rate). P760 molecules are large enough to have a restricted diffusion through the endothelium but, conversely, small enough to pass freely through the glomerular membrane. This limited extravasation has been observed in rabbits by magnetic resonance angiography or in investigations of tumor permeability. Further experimental imaging studies are needed to define the clinical interest of such properties.

Interference of magnetic resonance imaging contrast agents with the serum calcium measurement technique using colorimetric reagents

A possible interaction between either linear (Gd-DTPA-BMA and Gd-DTPA) or macrocyclic (Gd-DOTA) gadolinium complexes used as magnetic resonance imaging (MRI) contrast agents and colorimetric technique reagents for the measurement of serum calcium was evaluated on human serum pools, and its mechanism was investigated by means of UV spectrometry and electro-spray ionization mass spectrometry (ESI-MS). The highest concentration tested was 2.5 mM (corresponding to a putative strictly intravascular distribution of the compound) and the lowest dose was 0.2 mM (i.e. about two elimination half lives). Serum calcium was dosed in duplicate by conventional colorimetric techniques involving o-cresol-phthalein complexone (OCP) or methylthymol blue (MTB) as reagents. No interference was detected when mixing Gd DOTA with serum, whatever the concentration. Gd DTPA (2.5 mM) did not interfere with the colorimetric technique either. Conversely, the Gd DTPA-BMA solution induced a concentration-related variation in apparent calcium levels. In the UV experiments, solutions of 2.5 mM MRI contrast media were mixed with OCP or MTB and UV absorption spectra were recorded between 400 and 800 nm. For Gd-DOTA/OCP and Gd-DOTA/MTB, no significant variations in the absorbance were detected. However, in the presence of Gd DTPA BMA, the absorbance of OCP and MTB showed substantial and immediate variations over time. The ESI-MS studies showed a complete displacement of Gd3+ ion in the case of Gd-DTPA BMA. In the presence of OCP, we observed the disappearance of Gd-DTPA BMA and the formation of the free ligand DTPA BMA and a new complex Gd OCP with an original stoichiometry of 2/2. Such a phenomenon did not occur in the case of Gd DOTA and Gd DTPA. The decomplexation of Gd-DTPA BMA in the presence of OCP can probably be explained by the weaker thermodynamic stability of Gd-DTPA BMA compared to that of Gd-DOTA and Gd DTPA.