A four-dimensional simulation model of tumour response to radiotherapy in vivo: parametric validation considering radiosensitivity, genetic profile and fractionation

The aim of this paper is to present the current state of a four-dimensional simulation model of solid tumour growth and response to radiotherapy developed by our group. The most prominent points of the algorithms describing the fundamental biological phenomena involved are outlined. A specific application of the model to a selected clinical case of glioblastoma multiforme is described and comparative studies are performed, using various exploratory values of the model parameters. Qualitative agreement with clinical observations has been achieved. Special emphasis is laid on the variability of radiosensitivity parameters throughout the cell cycle and on the influence of the genetic profile of the tumour on its radiosensitivity. The results of the simulation are three-dimensionally reconstructed. A valuable tool for getting insight into the biology of tumour growth and response to radiotherapy and at the same time an advanced patient specific decision support system is expected to emerge after the completion of the necessary extensive clinical evaluation.     

The impact of high CO2 concentrations on the structure and function of the photosynthetic apparatus and the role of polyamines

Here we examined the influence of high CO2 concentrations on the structure and functioning of the photosynthetic apparatus in the unicellular green alga Scenedesmus obliquus. Presented in this work are: chlorophyll (Chl) a fluorescence induction kinetics, measurements of photosynthetic and respiration rates, estimation of Chl a/Chl b ratios, isolation and quantitative assessment of the photosynthetic subcomplexes, quantitative analyses of thylakoid bound polyamines, and experiments with exogenously supplied polyamines with cultures grown in low- and high-CO2 concentrations. Together, they indicated that high-CO2 concentrations affect polyamines and, more specifically, increase the thylakoid bound putrescine (PUT) level that leads to an increase of the active reaction center density combined with a decrease in the LHCII-size and the ratio of LHCII-oligomeres/LHCII-monomeres. This reorganization of the photosynthetic apparatus leads to enhanced photosynthetic rates, which in combination with the high-CO2 concentrations, leads to an immense increase of biomass (800%). Further incubation for longer time periods under the same conditions produces, due to an increase in cell density, a self-shading effect and photoadaptation of the photosynthetic apparatus to low light conditions and therefore also results in reduction of the high-CO2 effect. The photoadaptation of the photosynthetic apparatus to high-light conditions (Kotzabasis et al. 1999) and the acclimation to high-CO2 concentrations (present work) lead to the same changes in the structure and function of the photosynthetic apparatus. These changes could be induced or inhibited through the manipulation of intracellular polyamines, especially through the putrescine/spermine ratio. The possibility that polyamines influence the photoadaptation of the photosynthetic apparatus and its acclimation to high-CO2 concentrations through a common mechanism is discussed.     

A theoretical model of nitric oxide transport in arterioles: frequency- vs. amplitude-dependent control of cGMP formation

Nitric oxide (NO) plays many important physiological roles, including the regulation of vascular smooth muscle tone. In response to hemodynamic or agonist stimuli, endothelial cells produce NO, which can diffuse to smooth muscle where it activates soluble guanylate cyclase (sGC), leading to cGMP formation and smooth muscle relaxation. The close proximity of red blood cells suggests, however, that a significant amount of NO released will be scavenged by blood, and thus the issue of bioavailability of endothelium-derived NO to smooth muscle has been investigated experimentally and theoretically. We formulated a mathematical model for NO transport in an arteriole to test the hypothesis that transient, burst-like NO production can facilitate efficient NO delivery to smooth muscle and reduce NO scavenging by blood. The model simulations predict that 1) the endothelium can maintain a physiologically significant amount of NO in smooth muscle despite the presence of NO scavengers such as hemoglobin and myoglobin; 2) under certain conditions, transient NO release presents a more efficient way for activating sGC and it can increase cGMP formation severalfold; and 3) frequency-rather than amplitude-dependent control of cGMP formation is possible. This suggests that it is the frequency of NO bursts and perhaps the frequency of Ca(2+) oscillations in endothelial cells that may limit cGMP formation and regulate vascular tone. The proposed hypothesis suggests a new functional role for Ca(2+) oscillations in endothelial cells. Further experimentation is needed to test whether and under what conditions in silico predictions occur in vivo.     

Carcinosarcoma of the maxilla in a squirrel monkey (Saimiri sciureus)

We present the first, to our knowledge, described case of carcinosarcoma of the maxilla in a squirrel monkey. Carcinosarcomas are rare tumors of the upper aerodigestive tract, and consist of carcinomatous and sarcomatous tissue. Histologic analysis revealed a neoplasm composed of an adenocarcinomatous component (epithelial element) and a mesenchymal component (sarcomatous element). Metastatic growth was documented in the lung tissue and the submandibular lymph node. The histolopathologic findings, the pattern of metastasis, and the clinical progression closely resembled those of carcinosarcoma involving salivary glands in humans.     

Effect of several factors on the mechanical properties of pressure-sensitive adhesives used in transdermal therapeutic systems

The effects of coating thickness, type of adhesive, and type and concentration of enhancer on the mechanical properties of two acrylic pressure-sensitive adhesives (PSAs) were investigated using a 2(4) factorial design and an optimization technique. Sixteen formulations containing 0% or 10% of either caprylic acid or methyl laurate in two different PSAs, namely Duro-Tak 87-2196 and Duro-Tak 87-2097, were prepared. The adhesive properties of these laminates were evaluated by applying the 90 degrees Dynamic Adhesive Strength Peel Test (90 degrees DASPT) and 1800 Release Liner Peel Test (180 degrees RLPT). Coating thickness, concentration of enhancer, and type of adhesive did affect the 90 degrees DASPT. For the 180 degrees RLPT, the most significant factors were coating thickness and concentration of enhancer, with a strong interaction observed between the two. Coating thickness and concentration of enhancer were also used to create mathematical models that correlated these factors with the mechanical properties of the PSAs. For this purpose, the optimization technique 3(2) was applied. It was found that the correlation of the above factors can be adequately described with polynomial equations, which can be used for predicting the mechanical properties of the laminates containing the above PSAs and methyl laurate (0%-10%).     

A shrunken-2 transgene increases maize yield by acting in maternal tissues to increase the frequency of seed development

The maize (Zea mays) shrunken-2 (Sh2) gene encodes the large subunit of the rate-limiting starch biosynthetic enzyme, ADP-glucose pyrophosphorylase. Expression of a transgenic form of the enzyme with enhanced heat stability and reduced phosphate inhibition increased maize yield up to 64%. The extent of the yield increase is dependent on temperatures during the first 4 d post pollination, and yield is increased if average daily high temperatures exceed 33 °C. As found in wheat (Triticum aestivum) and rice (Oryza sativa), this transgene increases maize yield by increasing seed number. This result was surprising, since an entire series of historic observations at the whole-plant, enzyme, gene, and physiological levels pointed to Sh2 playing an important role only in the endosperm. Here, we present several lines of evidence that lead to the conclusion that the Sh2 transgene functions in maternal tissue to increase seed number and, in turn, yield. Furthermore, the transgene does not increase ovary number; rather, it increases the probability that a seed will develop. Surprisingly, the number of fully developed seeds is only ～50% of the number of ovaries in wild-type maize. This suggests that increasing the frequency of seed development is a feasible agricultural target, especially under conditions of elevated temperatures.     

Variation within the Huntington's disease gene influences normal brain structure

Genetics of the variability of normal and diseased brain structure largely remains to be elucidated. Expansions of certain trinucleotide repeats cause neurodegenerative disorders of which Huntington's disease constitutes the most common example. Here, we test the hypothesis that variation within the IT15 gene on chromosome 4, whose expansion causes Huntington's disease, influences normal human brain structure. In 278 normal subjects, we determined CAG repeat length within the IT15 gene on chromosome 4 and analyzed high-resolution T1-weighted magnetic resonance images by the use of voxel-based morphometry. We found an increase of GM with increasing long CAG repeat and its interaction with age within the pallidum, which is involved in Huntington's disease. Our study demonstrates that a certain trinucleotide repeat influences normal brain structure in humans. This result may have important implications for the understanding of both the healthy and diseased brain.     

Role of Plastid Transglutaminase in LHCII Polyamination and Thylakoid Electron and Proton Flow

Transglutaminases function as biological glues in animal cells, plant cells and microbes. In energy producing organelles such as chloroplasts the presence of transglutaminases was recently confirmed. Furthermore, a plastidial transglutaminase has been cloned from maize and the first plants overexpressing tgz are available (Nicotiana tabacum TGZ OE). Our hypothesis is that the overexpression of plastidal transglutaminase will alter photosynthesis via increased polyamination of the antenna of photosystem II. We have used standard analytical tools to separate the antenna from photosystem II in wild type and modified plants, 6 specific antibodies against LHCbs to confirm their presence and sensitive HPLC method to quantify the polyamination level of these proteins. We report that bound spermidine and spermine were significantly increased (～80%) in overexpressors. Moreover, we used recent advances in in vivo probing to study simultaneously the proton and electron circuit of thylakoids. Under physiological conditions overexpressors show a 3-fold higher sensitivity of the antenna down regulation loop (qE) to the elicitor (luminal protons) which is estimated as the ΔpH component of thylakoidal proton motive force. In addition, photosystem (hyper-PSIIα) with an exceptionally high antenna (large absorption cross section), accumulate in transglutaminase over expressers doubling the rate constant of light energy utilization (Kα) and promoting thylakoid membrane stacking. Polyamination of antenna proteins is a previously unrecognized mechanism for the modulation of the size (antenna absorption cross section) and sensitivity of photosystem II to down regulation. Future research will reveal which peptides and which residues of the antenna are responsible for such effects.