Biomedical subjects

N Lange

Publications and source records attributed to N Lange.

At least 19 recordsLinked to original sources

PubMed2003

Photodynamic diagnosis of ovarian cancer using hexaminolaevulinate: a preclinical study.

The unfailing detection of micrometastases during surgery of patients suffering from ovarian cancer is mandatory for the optimal management of this disease. Thus, the present study aimed at determining the feasibility of detecting micrometastases in an ovarian cancer model using the intraperitoneal administration of the photosensitiser precursor hexaminolaevulinate (HAL). For this purpose, HAL was applied intraperitoneally at different concentrations (4-12 mM) to immunocompetent Fischer 344 rats bearing a syngeneic epithelial ovarian carcinoma. The tumours were visualised laparoscopically using both white and blue light (D-light, Karl Storz, Tuttlingen, Germany), and the number of peritoneal micrometastases detected through HAL-induced photodiagnosis (PD) was compared to standard white light visualisation. Fluorescence spectra were recorded with an optical fibre-based spectrofluorometer and the fluorescence intensities were compared to the protoporphyrin IX (PpIX) fluorescence induced by 5-aminolevulinic acid under similar conditions. The number of metastases detected by the PD blue light mode was higher than when using standard white light abdominal inspection for all applied concentrations. Twice as many cancer lesions were detected by fluorescence than by white light inspection. The hexyl-ester derivative produced higher PpIX fluorescence than its parent substance aminolevulinic acid at the same concentration and application time. Fluorescence contrast between healthy and cancerous tissue was excellent for both compounds. To overcome poor diagnostic efficiency and to detect peritoneal ovarian carcinoma foci in the large surface area of the human peritoneal cavity, HAL fluorescence-based visualisation techniques may acquire importance in future and lead to a more correct staging of early ovarian cancer.

Aminolevulinic Acid↗

PubMed2003

Dynorphinergic GABA neurons are a target of both typical and atypical antipsychotic drugs in the nucleus accumbens shell, central amygdaloid nucleus and thalamic central medial nucleus.

Administration of typical and atypical antipsychotic drugs leads to activation of cells in the nucleus accumbens shell, central amygdaloid nucleus, and midline thalamic central medial nucleus, implicating important shared effects of these drugs. However, the exact cell types responding to antipsychotic drugs in the nucleus accumbens shell, central amygdaloid nucleus, and midline thalamic central medial nucleus are unclear. We report here that, in a rat model, the results of studies using double immunofluorescence labeling with antibodies directed against markers specific to candidate cell types suggest that the cells responding to haloperidol and clozapine in all three sites are: 1) neurons, rather than astrocytes; 2) inhibitory GABA neurons, but not acetylcholinergic neurons; and 3) dynorphin-containing GABA neurons, but not M-enkephalin-containing GABA neurons. The present study provides pharmacological evidence, at the cellular level in vivo, that the shared effects of antipsychotic drugs, whether typical and atypical, is activation of dynorphinergic GABA neurons in the nucleus accumbens shell, central amygdaloid nucleus, and midline thalamic central medial nucleus. Alternative ways to modulate dynorphinergic GABA neuronal activity or its target receptors might present an important new avenue for the treatment of schizophrenia and other psychotic disorders.

Acetylcholine↗

PubMed2003

Endoscopic fluorescence detection of intraepithelial neoplasia in Barrett's esophagus after oral administration of aminolevulinic acid.

BACKGROUND AND STUDY AIMS: Barrett's esophagus is strongly associated with adenocarcinoma. Early malignant transformation of the Barrett's mucosa is often not visible endoscopically and may remain undetected until the invasive adenocarcinoma stage. Endoscopic surveillance is currently carried out on random four-quadrant biopsies at 1-2 cm intervals. Endoscopic fluorescence detection of protoporphyrin IX induced by 5-aminolevulinic acid can identify premalignant lesions. This study evaluates endoscopic fluorescence detection in patients having Barrett's esophagus and compares the results to those of standard endoscopy with random four-quadrant biopsies. PATIENTS AND METHODS: The study included 30 examinations in 28 patients (22 men, 6 women; age range 37-78 years, mean age 60 years,), with five patients having known intraepithelial neoplasia. A dose of 20 mg/kg of 5-aminolevulinic acid was given orally 5 hours before examination. Random four-quadrant biopsies were performed 4-6 weeks before endoscopic fluorescence detection. RESULTS: Of the biopsies taken during the endoscopic fluorescence detection procedure, 28 % (23/81) were true positives. More than one-third of the false-positive results were due to inflammation. None of the 97 control biopsies taken on nonfluorescing areas during endoscopic fluorescence detection were dysplastic. Endoscopic fluorescence detection showed low-grade intraepithelial neoplasia in five patients which was not diagnosed with random four-quadrant biopsies, while random four-quadrant biopsies alone showed three low-grade intraepithelial neoplasias that were invisible during endoscopic fluorescence detection. All high-grade intraepithelial neoplasias or adenocarcinomas (2/2) were detected with both methods. CONCLUSIONS: Fluorescence detection achieved a similar performance when compared with four-quadrant random biopsy, but resulted in fewer biopsies (81 for endoscopic fluorescence detection vs 531 for random four-quadrant biopsies).

Administration, Oral↗

PubMed2003

Dissociations of cerebral cortex, subcortical and cerebral white matter volumes in autistic boys.

High-functioning autistic and normal school-age boys were compared using a whole-brain morphometric profile that includes both total brain volume and volumes of all major brain regions. We performed MRI-based morphometric analysis on the brains of 17 autistic and 15 control subjects, all male with normal intelligence, aged 7-11 years. Clinical neuroradiologists judged the brains of all subjects to be clinically normal. The entire brain was segmented into cerebrum, cerebellum, brainstem and ventricles. The cerebrum was subdivided into cerebral cortex, cerebral white matter, hippocampus-amygdala, caudate nucleus, globus pallidus plus putamen, and diencephalon (thalamus plus ventral diencephalon). Volumes were derived for each region and compared between groups both before and after adjustment for variation in total brain volume. Factor analysis was then used to group brain regions based on their intercorrelations. Volumes were significantly different between groups overall; and diencephalon, cerebral white matter, cerebellum and globus pallidus-putamen were significantly larger in the autistic group. Brain volumes were not significantly different overall after adjustment for total brain size, but this analysis approached significance and effect sizes and univariate comparisons remained notable for three regions, although not all in the same direction: cerebral white matter showed a trend towards being disproportionately larger in autistic boys, while cerebral cortex and hippocampus-amygdala showed trends toward being disproportionately smaller. Factor analysis of all brain region volumes yielded three factors, with central white matter grouping alone, and with cerebral cortex and hippocampus-amygdala grouping separately from other grey matter regions. This morphometric profile of the autistic brain suggests that there is an overall increase in brain volumes compared with controls. Additionally, results suggest that there may be differential effects driving white matter to be larger and cerebral cortex and hippocampus-amygdala to be relatively smaller in the autistic than in the typically developing brain. The cause of this apparent dissociation of cerebral cortical regions from subcortical regions and of cortical white from grey matter is unknown, and merits further investigation.

Autistic Disorder↗

PubMed2003

Comparison of aminolevulinic acid and hexylester aminolevulinate induced protoporphyrin IX distribution in human bladder cancer.

PURPOSE: Successful photodynamic therapy of epithelial cancer requires a specific photosensitization of malignant tissue. We evaluate the intensity and localization of protoporphyrin IX (PpIX) in superficial transitional cell carcinoma and nonmalignant cells of the human bladder following topical administration of its precursor, either aminolevulinic acid (ALA) or hexylester aminolevulinate (HAL). MATERIALS AND METHODS: Solutions of ALA or HAL were instilled into the bladder of 18 patients presenting with recurrent transitional cell carcinoma. The distribution of PpIX through the bladder wall was studied on frozen biopsies using fluorescence microscopy and correlated with pathological findings. RESULTS: Topical bladder instillation with 180 mmol (3%) ALA administered for 6 hours or 8 mmol (0.2%) HAL administered for 4 hours gave similar results regarding intensity and tissue distribution of PpIX fluorescence, whereas 8 mmol HAL administered for 2 hours followed by 2 hours of resting time (2+2 hours concept) induced a PpIX fluorescence twice as high. The fluorescence remained limited to cancer cells. Only a trace of PpIX fluorescence was observed in suburothelial connective tissue, that is chorion, but none in the bladder smooth muscle regardless of experiment conditions. CONCLUSIONS: HAL is an excellent precursor for PpIX synthesis in bladder cancer. With the 2+2 hour topical administration condition it yielded the highest PpIX fluorescence intensity and fluorescence contrast between normal and malignant urothelial cells. This approach allows us to optimize PpIX tissue distribution for photodynamic therapy in superficial bladder cancer.

Administration, Intravesical↗

PubMed2002

Production of protoporphyrin IX from 5-aminolevulinic acid and two of its esters in cells in vitro and tissues in vivo.

5-Aminolevulinic acid (ALA) and two of its esters were studied in cells in vitro and in vivo on skin of healthy hairless mice. In vitro, both esters, which are more lipophilic than ALA, induced higher PpIX fluorescence at lower concentrations compared with ALA. In vivo, ALA induced PpIX fluorescence more efficiently than the esters. The difference between ALA and the esters may be related to structures in the stratum corneum or to rate of penetration through this skin layer. The stratum corneum may bind the esters temporarily, and slow down their penetration into the living cells where PpIX is formed.

Aminolevulinic Acid↗

PubMed2001

Test-retest reliability of DSC MRI CBV mapping in healthy volunteers.

Dynamic susceptibility contrast magnetic resonance imaging (DSC MRI) can be used to generate high resolution maps of cerebral blood volume (CBV). To determine the test-retest reliability, CBV was measured in eight volunteers on two occasions, separated by 4 weeks. The mean ratio (scan 2/scan 1) for 72 cortical regions of interest (ROIs) was 1.03, with a coefficient of variation of 14%. The correlation between the first and second scans was 0.73 (p < 0.0001; 95%). In five hand-drawn ROIs, the mean ratio was 1.08, with a coefficient of variation of 12%. The correlation between scans was 0.84 (p < 0.0001). The data presented here support the hypothesis that DSC MRI CBV mapping has acceptable test-retest reliability.

Adult↗

PubMed2001

Consensus inference in neuroimaging.

We introduce model averaging in neuroimaging. We show that model summary images can be directly compared and averaged after histogram equalization. We demonstrate that averaging enhances the ROC curve in a simulation study. The averaging procedure is applied to a fMRI study of motor cortex.

Brain Mapping↗

PubMed2001

Two-dimensional versus three-dimensional cell counting: a practical perspective.

In recent years, it has been argued by some neuroanatomists that three-dimensional (3-D) counting approaches must be used in studies of neural systems, so that 'unbiased' counts of neurons can be obtained. By contrast, two-dimensional (2-D) cell-counting methods are said to be 'assumption-based' and to yield inaccurate results. Working from the premise that all scientific methodologies are assumption-based and suffer from inherent biases, the current review considers the relative strengths and weaknesses of 2-D versus 3-D counting approaches. This comparison is from the standpoint of predictive performance with respect to bias, variance and fidelity to the actual spatial arrangements of cells in the tissue under study. When these considerations are taken, together with the human resources that are required in using either methodology, 2-D methods offer more practical alternatives that might even provide more scientifically accurate estimates compared with their 3-D counterparts.

Animals↗

PubMed2001

Influence of baseline hematocrit and hemodilution on BOLD fMRI activation.

Current understanding of blood oxygenation level dependent (BOLD) fMRI physiology predicts a close relationship between BOLD signal and blood hematocrit level. However, neither this relationship nor its effect on BOLD percent activation (BPA) has been empirically examined in man. To that end, BPA in primary visual cortex in response to photic stimulation was determined in a group of 24 normal subjects. A positive linear relationship between BPA and hematocrit was seen, particularly in men. To evaluate the effect of change in hematocrit on BPA, 9 men were studied before and following isotonic saline hemodilution, resulting in an average 6% reduction in hematocrit and an 8-31% reduction in BPA. No significant change in the number of activated pixels was seen. A model of predicted BPA as a function of hematocrit and vessel size was developed, and results from this model closely mirrored the empiric data. These results suggest that hematocrit significantly influences the magnitude of BPA and that such baseline factors should be accounted for when comparing BOLD data across groups of subjects, particularly in the many instances in which hematocrit may vary systematically. Such instances include several disease states as well as studies involving sex differences, drug administration, stress and other factors. Finally, the robust agreement between predicted and empiric data serves to validate a semiquantitative approach to the analysis of BOLD fMRI data.

Brain↗

PubMed2001

Effects of noradrenergic activity on temporal information processing in humans.

Temporal processing of durations in the range of seconds or more is mediated by working-memory mechanisms whereas processing of brief durations in the range of milliseconds appears to be beyond cognitive control and modulated by dopaminergic activity in the basal ganglia. In the present study, the effects of the selective noradrenaline reuptake inhibitor reboxetine on temporal information processing were evaluated. In a double-blind crossover design, either placebo or 2 or 4 mg of reboxetine were administered to 24 healthy male volunteers. Performance on temporal discrimination of longer durations, as indicated by 75%-difference thresholds in relation to a 1,000-ms standard interval, was significantly improved by 2 mg of reboxetine as compared to placebo, whereas the improvement observed with the 4-mg dose just failed to reach statistical significance. There was, however, no effect of reboxetine on temporal discrimination of extremely brief durations, as indicated by threshold values in relation to a 50-ms standard interval. Findings provided additional evidence for the notion that temporal processing of durations in the range of seconds is based on working-memory processes including aspects of directed attention. In timing of brief durations in the range of milliseconds, however, noradrenergic activity did not seem to play a critical role.

Adrenergic Uptake Inhibitors↗

PubMed2001

Automated identification of Fos expression.

The concentration of Fos, a protein encoded by the immediate-early gene c-fos, provides a measure of synaptic activity that may not parallel the electrical activity of neurons. Such a measure is important for the difficult problem of identifying dynamic properties of neuronal circuitries activated by a variety of stimuli and behaviours. We employ two-stage statistical pattern recognition to identify cellular nuclei that express Fos in two-dimensional sections of rat forebrain after administration of antipsychotic drugs. In stage one, we distinguish dark-stained candidate nuclei from image background by a thresholding algorithm and record size and shape measurements of these objects. In stage two, we compare performance of linear and quadratic discriminants, nearest-neighbour and artificial neural network classifiers that employ functions of these measurements to label candidate objects as either Fos nuclei, two touching Fos nuclei or irrelevant background material. New images of neighbouring brain tissue serve as test sets to assess generalizability of the best derived classification rule, as determined by lowest cross-validation misclassification rate. Three experts, two internal and one external, compare manual and automated results for accuracy assessment. Analyses of a subset of images on two separate occasions provide quantitative measures of inter- and intra-expert consistency. We conclude that our automated procedure yields results that compare favourably with those of the experts and thus has potential to remove much of the tedium, subjectivity and irreproducibility of current Fos identification methods in digital microscopy.

Journal Article↗

PubMed2001

Routine experimental system for defining conditions used in photodynamic therapy and fluorescence photodetection of (non-) neoplastic epithelia.

A common method to induce enhanced short-term endogenous porphyrin synthesis and accumulation in cell is the topical, systemic application of 5-aminolevulinic acid or one of its derivatives. This circumvents the intravenous administration of photosensitizers normally used for photodynamic therapy (PDT) of fluorescence photodetection. However, in the majority of potential medical indications, optimal conditions with respect to the porphyrin precursor or its pharmaceutical formulation have not yet been found. Due to ethical restrictions and animal right directives, the number of available test objects is limited. Hence, definition and use of nonanimal test methods are needed. Tissue and organ cultures are a promising approach in replacing cost intensive animal models in early stages of drug development. In this paper, we present a tissue culture, which can among others be used routinely to answer specific questions emerging in the field of photodynamic therapy and fluorescence photodetection. This technique uses mucosae excised from sheep paranasal sinuses or pig bladder, which is cultured under controlled conditions. It allows quasiquantitative testing of different protoporphyrin IX precursors with respect to dose-response curves and pharmacokinetics, as well as the evaluation of different incubation conditions and/or different drug formulations. Furthermore, this approach, when combined with the use of electron microscopy and fluorescence-based methods, can be used to quantitatively determine the therapeutic outcome following protoporphyrin IX-mediated PDT.

Aminolevulinic Acid↗

PubMed2001

A new drug-screening procedure for photosensitizing agents used in photodynamic therapy for CNV.

PURPOSE: Because vascular occlusion has been observed as a consequence of photodynamic therapy (PDT), this method has been successfully used for the treatment of choroidal neovascularization (CNV) in age-related macular degeneration (AMD). However, most conventional photosensitizers, primarily developed for tumor PDT, lack selectivity for the targeting of neovascularization. An experimental model has been developed for drug screening of new photosensitizers for the treatment of CNV associated with AMD. It consists of intravenous (IV) injection of photosensitizers and fluorescent dyes into the chick's chorioallantoic membrane (CAM), followed by measurement of fluorescence pharmacokinetics, leakage from the vascular system, and photothrombic efficacy. METHODS: Fertilized chicken eggs were placed under a fluorescence microscope. After intravenous injection of different dyes, time-dependent fluorescence angiography was performed. The effect of PDT parameters was assessed by fluorescence angiography 24 hours after PDT. RESULTS: Although fluorescence of lipophilic benzoporphyrin derivative monoacid ring A (BPD-MA) remained intravascular during 2 hours, hydrophilic dyes tended to leak through the fenestrated neovascularization. By variation of PDT parameters, vascular damage could be directed toward closure of vessels with a diameter smaller than 10 microm, as measured 24 hours after PDT. High photosensitizer concentrations and high light doses resulted in blood flow stasis within 60 minutes, confirmed by fluorescence angiography. CONCLUSIONS: Fluorescence angiography and PDT after IV injection into the CAM showed strong similarities to results obtained in clinical tests of PDT in CNV associated with AMD. Thus, this model can provide valuable information about PDT mechanisms and can be used for drug-screening purposes in development of improved sensitizers for the PDT of CNV.

Allantois↗

PubMed2000

5-Aminolevulinic acid and its derivatives: physical chemical properties and protoporphyrin IX formation in cultured cells.

Protoporphyrin IX (PpIX) is used as a fluorescence marker and photosensitizing agent in photodynamic therapy (PDT). A temporary increase of PpIX in tissues can be obtained by administration of 5-aminolevulinic acid (ALA). Lipophilicity is one of the key parameters defining the bioavailability of a topically applied drug. In the present work, octanol-water partition coefficients of ALA and several of its esters have been determined to obtain a parameter related to their lipophilicity. The influence of parameters such as lipophilicity, concentration, time, and pH value on PpIX formation induced by ALA and its esters is then investigated in human cell lines originating from the lung and bladder. ALA esters are found to be more lipophilic than the free acid. The optimal concentration (c(opt), precursor concentration at which maximal PpIX accumulation is observed) is then measured for each precursor. Long-chained ALA esters are found to decrease the c(opt) value by up to two orders of magnitude as compared to ALA. The reduction of PpIX formation observed at higher concentrations than c(opt) is correlated to reduced cell viability as determined by measuring the mitochondrial activity. Under optimal conditions, the PpIX formation rate induced by the longer-chained esters is higher than that of ALA or the shorter-chained esters. A biphasic pH dependence on PpIX generation is observed for ALA and its derivatives. Maximal PpIX formation is measured under physiological conditions (pH 7.0-7.6), indicating that further enhancement of intracellular PpIX content may be achieved by adjusting the pharmaceutical formulation of ALA or its derivatives to these pH levels.

Aminolevulinic Acid↗

PubMed1999

Generalizable patterns in neuroimaging: how many principal components?

Generalization can be defined quantitatively and can be used to assess the performance of principal component analysis (PCA). The generalizability of PCA depends on the number of principal components retained in the analysis. We provide analytic and test set estimates of generalization. We show how the generalization error can be used to select the number of principal components in two analyses of functional magnetic resonance imaging activation sets.

Algorithms↗

PubMed1999

Plurality and resemblance in fMRI data analysis.

We apply nine analytic methods employed currently in imaging neuroscience to simulated and actual BOLD fMRI signals and compare their performances under each signal type. Starting with baseline time series generated by a resting subject during a null hypothesis study, we compare method performance with embedded focal activity in these series of three different types whose magnitudes and time courses are simple, convolved with spatially varying hemodynamic responses, and highly spatially interactive. We then apply these same nine methods to BOLD fMRI time series from contralateral primary motor cortex and ipsilateral cerebellum collected during a sequential finger opposition study. Paired comparisons of results across methods include a voxel-specific concordance correlation coefficient for reproducibility and a resemblance measure that accommodates spatial autocorrelation of differences in activity surfaces. Receiver-operating characteristic curves show considerable model differences in ranges less than 10% significance level (false positives) and greater than 80% power (true positives). Concordance and resemblance measures reveal significant differences between activity surfaces in both data sets. These measures can assist researchers by identifying groups of models producing similar and dissimilar results, and thereby help to validate, consolidate, and simplify reports of statistical findings. A pluralistic strategy for fMRI data analysis can uncover invariant and highly interactive relationships between local activity foci and serve as a basis for further discovery of organizational principles of the brain. Results also suggest that a pluralistic empirical strategy coupled formally with substantive prior knowledge can help to uncover new brain-behavior relationships that may remain hidden if only a single method is employed.

Brain↗

PubMed1999

Photodetection of early human bladder cancer based on the fluorescence of 5-aminolaevulinic acid hexylester-induced protoporphyrin IX: a pilot study.

Exogenous administration of 5-aminolaevulinic acid (ALA) is becoming widely used to enhance the endogenous synthesis of protoporphyrin IX (PpIX) in photodynamic therapy (PDT) and fluorescence photodetection (PD). Recently, results have shown that the chemical modification of ALA into its more lipophilic esters circumvents limitations of ALA-induced PpIX like shallow penetration depth into deep tissue layers and inhomogeneous biodistribution and enhances the total PpIX formation. The present clinical pilot study assesses the feasibility and the advantages of a topical ALA ester-based fluorescence photodetection in the human bladder. In this preliminary study 5-aminolaevulinic acid hexylester (h-ALA) solutions, containing concentrations ranging from 4 to 16 mM, were applied intravesically to 25 patients. Effects of time and drug dose on the resulting PpIX fluorescence level were determined in vivo with an optical fibre-based spectrofluorometer. Neither local nor systemic side-effects were observed for the applied conditions. All conditions used yielded a preferential PpIX accumulation in the neoplastic tissue. Our clinical investigations indicate that with h-ALA a twofold increase of PpIX fluorescence intensity can be observed using 20-fold lower concentrations as compared to ALA.

Aged↗