On abnormal microvascular phenotypes in a mouse model of glioblastoma and the effect of vessel compression on blood flow

Cancer is a major healthcare concern in the world, accounting for one in six deaths. Despite this, cancer patient survival rates have increased over the past decades as a result of healthcare improvement reforms and advances in medical research. Among the numerous areas of research in cancer, studying the tumour microenvironment and the physics of cancer has shown promising results for patient benefit, and will be the focus of this thesis. A tumour is an abnormal cell growth, and is cancerous when it has the potential to metastasise. Tumours have their own microenvironment which presents numerous abnormalities compared to healthy tissue. In particular, as tumours grow they develop their own microvascular system to transport nutrients and oxygen to the cells. However, the tumour vasculature is abnormal and inefficient, leading to an abnormal microenvironment, with traits such as hypoxia. Hypoxia leads to more aggressive tumours and is a barrier to treatment, making it an undesirable trait. A better understanding of the causes of tumour hypoxia could thus benefit patient care. One tumour vessel abnormality is vessel compression, which is the result of high solid stress in tumours. Studies have shown that vessel compression correlates with reduced survival rates, and increased hypoxia and oxygen heterogeneity. However, the biophysical mechanism which links compressed vessels to hypoxia is not clear. In addition, vessel compression has not been characterised in glioblastoma multiforme brain tumours, despite the correlation between vessel compression and reduced survival rates, and the low survival rates of glioblastoma patients. As red blood cells transport oxygen in blood, the central hypothesis of this thesis is that vessel compression leads to abnormal transport of red blood cells, contributing to tissue hypoxia. Therefore, the aim of this work is to find a mechanistic link between vessel compression and abnormal red blood cell transport in compressed vascular networks and contextualise it to glioblastoma. The first results chapter investigates the effect of a compression on the partitioning of red blood cells at a downstream bifurcation. The numerical experiment shows that, with a compressed parent branch, the higher flowing child branch is enriched in red blood cells compared to a control simulation. The abnormal partitioning of red blood cells is the result of a narrowing of the red blood cell cross-sectional distribution as they enter the compression. Indeed, in the compression the red blood cells undergo cross-streamline migration to more central streamlines as a result of the increased shear rate and shear rate gradient in the compression. The results further show that the abnormal partitioning of red blood cells is present over a wide range of flow ratios to the child branches. The abnormal partitioning of red blood cells becomes less pronounced as the parent branch haematocrit increases, up to a critical threshold of around 30%, above which abnormal partitioning no longer occurs. The second results chapter builds on to the first one and numerically investigates how the abnormal partitioning of red blood cells at a single bifurcation propagates at a network level. To do so, it adapts and validates an existing reduced-order model to accurately and efficiently calculate the abnormal partitioning of red blood cells when parent branches are compressed. At a network level, and compared to a control, vessel compression increases haematocrit heterogeneity, reduces the average haematocrit, and increases the number of plasma channels present. The mechanisms for these findings are investigated and show that both the increased resistance to flow and the abnormal partitioning of red blood cells at a bifurcation contribute to lowering the haematocrit in the networks, but that haematocrit heterogeneity is only the result of the abnormal partitioning of red blood cells. Finally, it is shown that the reduction in average haematocrit in the networks occurs over a wide range of inlet haematocrits, and that only a relatively small number of vessels need to be compressed for the reduction to be present. The final results chapter phenotypes and compares the microvasculature in a mouse model of a glioblastoma to control mice. A pipeline is developed and validated to reconstruct the threedimensional vessel surfaces from multiphoton microscopy images of the vasculature. The data show that the non-dimensional interbifurcation distance and the mean tissue-vessel distance are significantly lower in tumours, but that other phenotypes are not different. Notably, the tumour vessels were not compressed. Furthermore, the results show that there is a correlation between the mean tissue-vessel distance in a region of interest and the distance of the region of interest from the tumour core. Taken together, these findings address the aim of this thesis and provide a mechanism for abnormal transport of red blood cells in compressed vessel networks. Due to the importance of red blood cells in the transport of oxygen, this work contributes to the knowledge of the causes of hypoxia in tumours with vessel compression. As hypoxia is an important trait adversely affecting patient prognosis, understanding the mechanisms leading to hypoxia has the potential, in the long term, to inform patient care

Compressed vessels bias red blood cell partitioning at bifurcations in a hematocrit-dependent manner:implications in tumor blood flow

The tumor microenvironment is abnormal and associated with tumor tissue hypoxia, immunosuppression, and poor response to treatment. One important abnormality present in tumors is vessel compression. Vessel decompression has been shown to increase survival rates in animal models via enhanced and more homogeneous oxygenation. However, our knowledge of the biophysical mechanisms linking tumor decompression to improved tumor oxygenation is limited. In this study, we propose a computational model to investigate the impact of vessel compression on red blood cell (RBC) dynamics in tumor vascular networks. Our results demonstrate that vessel compression can alter RBC partitioning at bifurcations in a hematocrit-dependent and flow rate–independent manner. We identify RBC focusing due to cross-streamline migration as the mechanism responsible and characterize the spatiotemporal recovery dynamics controlling downstream partitioning. Based on this knowledge, we formulate a reduced-order model that will help future research to elucidate how these effects propagate at a whole vascular network level. These findings contribute to the mechanistic understanding of hemodilution in tumor vascular networks and oxygen homogenization following pharmacological solid tumor decompression

Influence of DC electric field upon the production of oil-in-water-in-oil double emulsions in upwards mm-scale channels at low electric field strength

AbstractA novel approach to create O/W/O is developed and described to achieve uniform oil drop size coated with thin layers of water. Drops were created using a test cell where the DC field is applied between different internal diameter (ID) needles (from which the O/W emulsion emits upwards into a continuous oil phase) and a grounded metal ring which was located at selected distances from the needle top. The advantages compared to the previous techniques consist of possibility of control on drop size and coating layer of the water using low electric field. A high speed imaging technique has been applied to determine drop size under different flow and electric field conditions. Without the electric field, several flow regimes were observed; stable formation of both the O/W/O emulsion and the O/W emulsion upstream of the cell was possible over a range of Reynolds numbers from 80 to 100. The effect of the electric field was found to be reverse below electric field strength of 60kVm−1, beyond this critical value there was significant impact upon the flow regime, drop size and emulsion structure. The impact of the electric field strength upon flow pattern and emulsion structure and a quantitative analysis of droplet size are presented. The work shows the results for the controlled creation of complex emulsion droplets combining electric field and mm scale channels. The differences with the other physical processes reported in the literature are discussed

Combined collision-induced dissociation and photo-selected reaction monitoring mass spectrometry modes for simultaneous analysis of coagulation factors and estrogens

AbstractOral estrogens are directly associated with changes in plasma levels of coagulation proteins. Thus, the detection of any variation in protein concentrations due to estrogen contraceptives, by a simultaneous analysis of both coagulation proteins and estrogens, would be a very informative tool. In the present study, the merit of photo-selected reaction monitoring (SRM), a new analytical tool, was evaluated towards estrogens detection in plasma. Then, SRM and photo-SRM detection modes were combined for the simultaneous analysis of estrogen molecules together with heparin co-factor and factor XIIa, two proteins involved in the coagulation cascade. This study shows that photo-SRM could open new multiplexed analytical routes

Development of a combined solver to model transport and chemical reactions in catalytic wall-flow filters

none5siIn this work, we develop a non-isothermal model for diesel particulate filters including exothermic and competing chemical reactions. We begin with an isothermal, single-reaction model and we gradually increase its complexity. By comparing various models, we aim at establishing the minimum degree of complexity required to effectively model the system under investigation. Based on the numerical simulations, we conclude that isothermal models are adequate only if the temperature of the catalyst is, at all times, completely below or completely above a critical temperature. However, if the goal is to predict the critical temperature, only non-isothermal models should be used. The results with competing reactions, on the other hand, show that the presence of competing reactions does not affect significantly the overall conversion in the filter.noneAllouche M.H.; Enjalbert R.; Alberini F.; Ariane M.; Alexiadis A.Allouche M.H.; Enjalbert R.; Alberini F.; Ariane M.; Alexiadis A

Abnormal morphology biases haematocrit distribution in tumour vasculature and contributes to heterogeneity in tissue oxygenation

Oxygen heterogeneity in solid tumors is recognized as a limiting factor for therapeutic efficacy. This heterogeneity arises from the abnormal vascular structure of the tumor, but the precise mechanisms linking abnormal structure and compromised oxygen transport are only partially understood. In this paper, we investigate the role that red blood cell (RBC) transport plays in establishing oxygen heterogeneity in tumor tissue. We focus on heterogeneity driven by network effects, which are challenging to observe experimentally due to the reduced fields of view typically considered. Motivated by our findings of abnormal vascular patterns linked to deviations from current RBC transport theory, we calculated average vessel lengths L⎯⎯ and diameters d⎯⎯ from tumor allografts of three cancer cell lines and observed a substantial reduction in the ratio λ=L⎯⎯/d⎯⎯ compared to physiological conditions. Mathematical modeling reveals that small values of the ratio λ (i.e., λ<6 ) can bias hematocrit distribution in tumor vascular networks and drive heterogeneous oxygenation of tumor tissue. Finally, we show an increase in the value of λ in tumor vascular networks following treatment with the antiangiogenic cancer agent DC101. Based on our findings, we propose λ as an effective way of monitoring the efficacy of antiangiogenic agents and as a proxy measure of perfusion and oxygenation in tumor tissue undergoing antiangiogenic treatment

Effect of vessel compression on blood flow in microvascular networks and its implications for tumour tissue hypoxia

Abstract The tumour microenvironment is abnormal and one of its consequences is that blood vessels are compressed. Vessel compression correlates with reduced survival rates, while decompression of vessels improves tissue oxygenation as well as increases survival rates. Vessel compression contributes, at a single vascular bifurcation, to the increase of heterogeneity of red blood cell (RBC) transport. However, the effect that vessel compression has at a network level is unknown. This work numerically investigates the effect of vessel compression on RBC transport in microvascular networks. The key findings are that vessel compression both reduces the average haematocrit, and increases haematocrit heterogeneity, in vessels in the network. The mechanisms for these changes in haematocrit distribution are unravelled, and a parameter sweep shows that networks with lower inlet haematocrits are more susceptible to haemodilution from vessel compression over a wide range of compressed fraction of a network. These findings provide a theoretical underpinning for the link between vessel compression and tumour tissue hypoxia

Evaluation of hydrophilic interaction chromatography (HILIC) versus C-18 reversed-phase chromatography for targeted quantification of peptides by mass spectrometry

International audienceHydrophilic-interaction liquid chromatography (HILIC) is a widely used technique for small polar molecule analysis and offers the advantage of improved sensitivity in mass spectrometry. Although HILIC is today frequently employed as an orthogonal fractionation method for peptides during the proteomic discovery phase, it is still seldom considered for quantification. In this study, the performances in terms of peak capacity and sensitivity of 3 HILIC columns were compared to traditional reversed phase liquid C-18 column in the context of targeted quantification of proteotypic peptides using selected reaction monitoring mode (SRM). The results showed that the maximum sensitivity in HILIC chromatography was achieved by using an amide column without salt buffer and that the signal increased compared to classic reversed phase chromatography. However, the intensity improvement is quite low compared to the one obtained for small molecules. This is due on one hand to a higher matrix effect in HILIC and on the other hand to a change of charge states of peptides in organic solvent (doubly charged to monocharged). The doubly charged ions can be more readily dissociated than singly charged ions, making them ideal for SRM peptide quantification. As a result "supercharging" reagents are added to the mobile phase to shift from predominant singly charged ions to the more favorable doubly charged species. Using such optimized conditions, peptide signal is improved by a factor of between two and ten for 88% of the peptides of the 81 peptides investigate

A 3D wheat model to study competition for light via the prediction of tillering dynamics

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