A Fluorescent Polymer Probe with High Selectivity toward Vascular Endothelial Cells for and beyond Noninvasive Two-Photon Intravital Imaging of Brain Vasculature.

A chromophore-engineering strategy that relies on the introduction of a ground-state distortion in a quadrupolar chromophore was used to obtain a quasi-quadrupolar chromophore with red emission and large two-photon absorption (2PA) cross-section in polar solvents. This molecule was functionalized with water-solubilizing polymer chains. It constitutes not only a remarkable contrast agent for intravital two-photon microscopy of the functional cerebral vasculature in a minimally invasive configuration but presents intriguing endothelial staining ability that makes it a valuable probe for premortem histological staining.

Cell imaging by coherent backscattering microscopy using frequency-shifted optical feedback in a microchip laser.

In this work, we present a new development of the laser optical feedback imaging technique for imaging biological structures with a high resolution. The first results obtained on human red blood cells and mice cerebral and muscular tissues slices are shown. The performances of the system and its future developments are also discussed.

Pimonidazole binding in C6 rat brain glioma: relation with lipid droplet detection.

In C6 rat brain glioma, we have investigated the relation between hypoxia and the presence of lipid droplets in the cytoplasm of viable cells adjacent to necrosis. For this purpose, rats were stereotaxically implanted with C6 cells. Experiments were carried out by the end of the tumour development. A multifluorescence staining protocol combined with digital image analysis was used to quantitatively study the spatial distribution of hypoxic cells (pimonidazole), blood perfusion (Hoechst 33342), total vascular bed (collagen type IV) and lipid droplets (Red Oil) in single frozen sections. All tumours (n=6) showed necrosis, pimonidazole binding and lipid droplets. Pimonidazole binding occurred at a mean distance of 114 microm from perfused vessels mainly around necrosis. Lipid droplets were principally located in the necrotic tissue. Some smaller droplets were also observed in part of the pimonidazole-binding cells surrounding necrosis. Hence, lipid droplets appeared only in hypoxic cells adjacent to necrosis, at an approximate distance of 181 microm from perfused vessels. In conclusion, our results show that severe hypoxic cells accumulated small lipid droplets. However, a 100% colocalisation of hypoxia and lipid droplets does not exist. Thus, lipid droplets cannot be considered as a surrogate marker of hypoxia, but rather of severe, prenecrotic hypoxia.

Application of magnetic resonance to animal models of cerebral ischemia.

The present review has been compiled to highlight the role of magnetic resonance imaging (MRI) and MR spectroscopy (MRS) for the investigation of cerebral ischemia in the animal experimental field of basic research. We have focused on stroke investigations analyzing the pathomechanisms of the disease evolution and on new advances in both nuclear MR (NMR) methodology or genetic engineering of transgenic animals for the study of complex molecular relationships and causes of the disease. Furthermore, we have tried to include metabolic and genetic aspects, as well as the application of functional imaging, for the investigation of the disturbance or restitution of functional brain activation under pathological conditions as relates to controlled animal experiments.

Two-voxel localization sequence for in vivo two-dimensional homonuclear correlation spectroscopy.

The combination of localized 2D 1H MR correlation spectroscopy and Hadamard encoding allows the simultaneous acquisition of multiple volumes of interest without an increase in the experimental duration, compared to single-voxel acquisition. In the present study, 2D correlation spectra were acquired simultaneously within 20 to 40 min in two voxels located in each hemisphere of the rat brain. An intervoxel distance of 20% of the voxel size was sufficient to limit spatial contamination. The following cerebral metabolites gave detectable crosspeaks: N-acetylaspartate, the glutamate/glutamine pool, aspartate, phosphoethanolamine, glucose, glutathione, taurine, myo-inositols, lactate, threonine, gamma-aminobutyric acid, and alanine. Most of the metabolites were measured without contamination of other resonances.

Applications of magnetic resonance in model systems: tumor biology and physiology.

A solid tumor presents a unique challenge as a system in which the dynamics of the relationship between vascularization, the physiological environment and metabolism are continually changing with growth and following treatment. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) studies have demonstrated quantifiable linkages between the physiological environment, angiogenesis, vascularization and metabolism of tumors. The dynamics between these parameters continually change with tumor aggressiveness, tumor growth and during therapy and each of these can be monitored longitudinally, quantitatively and non-invasively with MRI and MRS. An important aspect of MRI and MRS studies is that techniques and findings are easily translated between systems. Hence, pre-clinical studies using cultured cells or experimental animals have a high connectivity to potential clinical utility. In the following review, leaders in the field of MR studies of basic tumor physiology using pre-clinical models have contributed individual sections according to their expertise and outlook. The following review is a cogent and timely overview of the current capabilities and state-of-the-art of MRI and MRS as applied to experimental cancers. A companion review deals with the application of MR methods to anticancer therapy.

Noninvasive assessment of the functional neovasculature in 9L-glioma growing in rat brain by dynamic 1H magnetic resonance imaging of gadolinium uptake.

Pathophysiologic parameters of the functional neovasculature and the blood-brain barrier of 9L-glioma in rat brain were measured noninvasively by dynamic 1H magnetic resonance imaging studies of gadolinium (Gd)-DTPA uptake. Changes of apparent [Gd-DTPA] uptake in time (CT[t]) were analyzed in a slice through the center of 10 9L-gliomas using fast T1 measurements. The distribution of the contrast agent was spatially correlated with the distribution of perfused microvessels as determined by immunohistochemical analysis. This method permits a distinction between perfused and nonperfused microvessels with a disrupted blood-brain barrier. In transverse slices of the whole tumor, a spatial correlation was observed between CT maps and the two-dimensional distribution of perfused microvessels. In the next step, Gd-DTPA uptake rates were spatially related to the perfused microvessel density (Np) or vascular surface area (Sp). In tumor voxels with perfused microvessels, a linear correlation was found between Gd-DTPA uptake rate constants (k values) and Np or Sp. No correlation was observed between k values and the total microvessel density. These are the first data that show a relation between Gd-DTPA uptake rates and parameters of the functional neovasculature in 9L-glioma growing in rat brain. Now that Gd-DTPA uptake studies can be related to parameters of the functional neovasculature, they may be used more efficiently as a prognostic tool before or during therapy.

Determination of in vivo rat muscle Gd-DTPA relaxivity at 6.3 T.

For the in vivo relaxivity of Gd-DTPA at 6.3 T in rat muscle a value of 2.7+/-0.5 (mM s)(-1) was found, and for the in vitro value in water 3.00+/-0.56 (mM s)(-1) at 37 degrees C. The temperature dependence of the in vitro relaxivity was -0.087 (mM s degrees C)(-1). The relation between 1/T1 and the tissue Gd-DTPA concentration is linear for the normally used in vivo Gd-DTPA concentration range.

Fast dynamic gadolinium-enhanced MR imaging of urinary bladder and prostate cancer.

Among the noninvasive imaging modalities, contrast enhanced magnetic resonance (MR) imaging is the most powerful tool with which to visualize vascularity. Common pathology only shows microvessel density, whereas dynamic MR imaging is sensitive to the total endothelial surface area of perfused vessels. Therefore, dynamic MR imaging may be of additional value in tumor staging and in evaluating therapies that affect the perfused microvessel density or surface area, such as chemo-, radiation, or anti-angiogenic therapy. In urinary bladder cancer, this technique results in improved local and nodal staging, in improved separation of transurethral granulation tissue and edema from malignant tumor, and in improved evaluation of the effect of chemotherapy. In prostate cancer, dynamic MR imaging may be of help in problematic cases. This technique can assist in determining seminal vesicle infiltration, in depicting of minimal capsular penetration, and in recognizing tumors within the transitional zone. Also, based on very rapid enhancement, very poorly differentiated tumors can be recognized. Evaluation of the effects of therapy is another promising area, however a lot of research remain to be done. This article reviews some basics of fast enhancement techniques, provides practical information, and shows recent developments, in using these fast techniques for staging and grading of bladder and prostate cancer, and for evaluating the effect of therapy.

Global HDO uptake in human glioma xenografts is related to the perfused capillary distribution.

The aim of this study is to evaluate the existence of a possible relationship between global deuterium-labeled water (HDO) uptake rates and the diffusion geometry of human glioma xenografts in nude mice. HDO diffusion times in the whole extravascular tumor volume were estimated by combining quantitative (1)H-MR diffusion imaging and morphometric analysis of intercapillary distances in two tumor lines with a different perfused vascular architecture. HDO uptake was measured independently using (2)H-magnetic resonance spectroscopy. Time constants of HDO-uptake curves (tau) were compared to estimations of maximum HDO diffusion times (t(difmax)). Tumors with a homogeneously perfused capillary distribution showed a mono-exponential HDO uptake. The t(difmax) was comparable to tau values of HDO uptake curves: t(difmax) varied between 74 and 368 sec and the range of tau values was 115-370 sec. Heterogeneously perfused tumors had a bi-exponential HDO uptake with t(difmax) in between the tau values of the fast and slow uptake phase. These findings indicate that the global HDO uptake is related to the perfused capillary distribution in human glioma xenografts. That HDO uptake rates indeed can depend on the perfused capillary distribution was substantiated in experiments with two-dimensional (2D) models. In these models with a diffusion-limited HDO uptake, HDO uptake curves could be approximated by curves derived from 2D HDO diffusion simulations. Magn Reson Med 42:479-489, 1999.

Effect of carbogen breathing on the physiological profile of human glioma xenografts.

The aim of this study was to evaluate the effect of carbogen breathing on the physiological profile of human glioma xenografts. Near infrared spectroscopy was used to investigate changes in oxy- and deoxyhemoglobin concentrations in tumor blood. Oxygen tension changes in tumor tissue were evaluated by (19)F-MR relaxometry, using perfluoro-15-crown-5-ether, and modifications of tumor blood perfusion (TBP) were analyzed by fast dynamic (1)H-MR imaging of Gd-DTPA uptake. Finally, changes of the bioenergetic status and pH of tumor cells were analyzed by (31)P-MRS. After 5 to 8 min of carbogen breathing, the average oxygen tension increase in tumor tissue was 4.6 +/- 1.3 mm Hg, which is in agreement with an increase of the oxyhemoglobin concentration in tumor blood (Delta[O(2)Hb] = 9. 2 +/- 3 microM). However, simultaneously the TBP was reduced, the bioenergetic status was diminished, and pH was decreased. As 100% O(2) breathing alone did not result in a detectable increase of oxyhemoglobin in tumor blood, the increase of the tumor oxygenation by carbogen appears to be mediated by its CO(2) content. This component may cause a nutrient-limited decrease of oxidative energy metabolism, indirectly via a steal-effect and/or by inhibition of the glycolytic rate resulting from tissue acidification. Magn Reson Med 42:490-499, 1999.

Characterization and validation of noninvasive oxygen tension measurements in human glioma xenografts by 19F-MR relaxometry.

PURPOSE: The aim of this study was to characterize and to validate noninvasive 19F-magnetic resonance relaxometry for the measurement of oxygen tensions in human glioma xenografts in nude mice. The following three questions were addressed: 1. When perfluorocarbon compounds (PFCs) are administrated intravenously, which tumor regions are assessed by 19F-MR relaxometry? 2. Are oxygen tension as detected by 19F-MR relaxometry (pO2/relaxo) comparable to Eppendorf O2-electrode measurements (pO2/electrode)? 3. Can 19F-MR relaxometry be used to detect oxygen tension changes in tumor tissue during carbogen breathing? METHODS AND MATERIALS: Slice-selective 19F-MR relaxometry was carried out with perfluoro-15-crown-5-ether as oxygen sensor. The PFC was injected i.v. 3 days before the 19F-MR experiments. Two datasets were acquired before and two after the start of carbogen breathing. The distribution of PFCs and necrotic areas were analyzed in 19F-Spin Echo (SE) density MR images and T2-weighted 1H-SE MR images, respectively. One day after the MR investigations, oxygen tensions were measured by oxygen electrodes in the same slice along two perpendicular tracks. These measurements were followed by (immuno)histochemical analysis of the 2D distribution of perfused microvessels, hypoxic cells, necrotic areas, and macrophages. RESULTS: The PFCs mainly became sequestered in perfused regions at the tumor periphery; thus, 19F-MR relaxometry probed mean oxygen tensions in these regions throughout the selected MR slice. In perfused regions of the tumor, mean PO2/relaxo values were comparable to mean PO2/electrode values, and varied from 0.03 to 9 mmHg. Median pO2/electrode values of both tracks were lower than mean pO2/relaxo values, because low pO2 electrode values that originate from hypoxic and necrotic areas were also included in calculations of median pO2/electrode values. After 8-min carbogen breathing, the average PO2/relaxo increase was 3.3 +/- 0.8 (SEM) mmHg and 2.1 +/- 0.6 (SEM) after 14 min breathing. CONCLUSIONS: We have demonstrated that PFCs mainly became sequestered in perfused regions of the tumor. Here, mean PO2/relaxo values were comparable to mean PO2electrode values. In these areas, carbogen breathing was found to increase the PO2/relaxo values significantly.

Influence of the pharmacokinetic model on the quantification of the Gd-DTPA uptake rate in brain tumours using direct T1 measurements.

After a bolus injection of Gd-DTPA, a fast tracer uptake in rat brain tumours was already observed during the tracer bolus passage. For the quantification of the uptake rate constant, pharmacokinetic models are commonly used. For a good quantification, the changes of the plasma tracer concentration directly after the bolus injection must be incorporated into these models as prior knowledge. The aim of this paper is to investigate whether or not it is necessary to include the bolus passage into the description for the plasma tracer concentration. The result of this study indicates that the best quantification of the uptake rate constant is achieved by using only the data points after the bolus passage. Using all the data points and incorporating the bolus passage in the pharmacokinetic models results in a less accurate estimation.

NMR perfusion and metabolic imaging and some examples on brain tumours.

The potentials and limitations of proton Magnetic Resonance to map the spatial distribution of perfusion parameters and of metabolite concentrations in the brain are demonstrated and discussed. Some examples of applications to brain tumours are given.

In vivo (31)P magnetic resonance spectroscopy and morphometric analysis of the perfused vascular architecture of human glioma xenografts in nude mice.

The relationship between the bioenergetic status of human glioma xenografts in nude mice and morphometric parameters of the perfused vascular architecture was studied using (31)P magnetic resonance spectroscopy (MRS), fluorescence microscopy and two-dimensional digital image analysis. Two tumour lines with a different vascular architecture were used for this study. Intervascular distances and non-perfused area fractions varied greatly between tumours of the same line and tumours of different lines. The inorganic phosphate-nucleoside triphosphate (P(i)/NTP) ratio increased rapidly as mean intervascular distances increased from 100 microm to 300 microm. Two morphometric parameters - the percentage of intervascular distances larger than 200 microm (ivd200) and the non-perfused area fraction at a distance larger than 100 microm from a nearest perfused vessel (area100), - were deduced from these experiments and related to the P(i)/NTP ratio of the whole tumour. It is assumed that an aerobic to anaerobic transition influences the bioenergetic status, i.e. the P(i)/NTP ratio increased linearly with the percentage of ivd200 and the area100.

A two-dimensional 1H-NMR study on Megasphaera elsdenii flavodoxin in the oxidized state and some comparisons with the two-electron-reduced state.

Assignments for the 137 amino acid residues of oxidized Megasphaera elsdenii flavodoxin have been made using the sequential resonance assignment procedure. Great benefit was experienced from assignments of the fully reduced protein. The secondary and tertiary structures of the typical alpha/beta protein remain virtually identical on going from the oxidized to the two-electron-reduced state as judged from two-dimensional NOE spectroscopy. However, functionally important conformation changes in the flavin-binding region do occur on reduction. Considerable reduction-state-dependent chemical shift variations of protons in the immediate vicinity of the isoalloxazine moiety take place. From analysis of these shifts, it can be concluded that ring current effects of the pyrazine part of the flavin diminish on two-electron reduction.