Smeared multiscale finite element model for electrophysiology and ionic transport in biological tissue.

Basic functions of living organisms are governed by the nervous system through bidirectional signals transmitted from the brain to neural networks. These signals are similar to electrical waves. In electrophysiology the goal is to study the electrical properties of biological cells and tissues, and the transmission of signals. From a physics perspective, there exists a field of electrical potential within the living body, the nervous system, extracellular space and cells. Electrophysiological problems can be investigated experimentally and also theoretically by developing appropriate mathematical or computational models. Due to the enormous complexity of biological systems, it would be almost impossible to establish a detailed computational model of the electrical field, even for only a single organ (e.g. heart), including the entirety of cells comprising the neural network. In order to make computational models feasible for practical applications, we here introduce the concept of smeared fields, which represents a generalization of the previously formulated multiscale smeared methodology for mass transport in blood vessels, lymph, and tissue. We demonstrate the accuracy of the smeared finite element computational models for the electric field in numerical examples. The electrical field is further coupled with ionic mass transport within tissue composed of interstitial spaces extracellularly and by cytoplasm and organelles intracellularly. The proposed methodology, which couples electrophysiology and molecular ionic transport, is applicable to a variety of biological systems.

Correction function for accuracy improvement of the Composite Smeared Finite Element for diffusive transport in biological tissue systems.

Modeling of drug transport within capillaries and tissue remains a challenge, especially in tumors and cancers where the capillary network exhibits extremely irregular geometry. Recently introduced Composite Smeared Finite Element (CSFE) provides a new methodology of modeling complex convective and diffusive transport in the capillary-tissue system. The basic idea in the formulation of CSFE is in dividing the FE into capillary and tissue domain, coupled by 1D connectivity elements at each node. Mass transport in capillaries is smeared into continuous fields of pressure and concentration by introducing the corresponding Darcy and diffusion tensors. Despite theoretically correct foundation, there are still differences in the overall mass transport to (and from) tissue when comparing smeared model and a true 3D model. The differences arise from the fact that the smeared model cannot take into account the detailed non-uniform pressure and concentration distribution in the vicinity of capillaries. We introduced a field of correction function for diffusivity through the capillary walls of smeared models, in order to have the same mass accumulation in tissue as in case of true 3D models. The parameters of the numerically determined correction function are: ratio of thickness and diameter of capillary wall, ratio of diffusion coefficient in capillary wall and surrounding tissue; and volume fraction of capillaries within tissue domain. Partitioning at the capillary wall - blood interface can also be included. It was shown that the correction function is applicable to complex configurations of capillary networks, providing improved accuracy of our robust smeared models in computer simulations of real transport problems, such as in tumors or human organs.

Progression-dependent transport heterogeneity of breast cancer liver metastases as a factor in therapeutic resistance.

Metastatic disease is a major cause of mortality in cancer patients. While many drug delivery strategies for anticancer therapeutics have been developed in preclinical studies of primary tumors, the drug delivery properties of metastatic tumors have not been sufficiently investigated. Therapeutic efficacy hinges on efficient drug permeation into the tumor microenvironment, which is known to be heterogeneous thus potentially making drug permeation heterogeneous, also. In this study, we have identified that 4 T1 liver metastases, treated with pegylated liposomal doxorubicin, have unfavorable and heterogeneous transport of doxorubicin. Our drug extravasation results differ greatly from analogous studies with 4 T1 tumors growing in the primary site. A probabilistic tumor population model was developed to estimate drug permeation efficiency and drug kinetics of liver metastases by integrating the transport and structural properties of tumors and delivered drugs. The results demonstrate significant heterogeneity in metastases with regard to transport properties of doxorubicin within the same animal model, and even within the same organ. These results also suggest that the degree of heterogeneity depends on the stage of tumor progression and that differences in transport properties can define transport-based tumor phenotypes. These findings may have valuable clinical implications by illustrating that therapeutic agents can permeate and eliminate metastases of "less resistant" transport phenotypes, while sparing tumors with more "resistant" transport properties. We anticipate that these results could challenge the current paradigm of drug delivery into metastases, highlight potential caveats for therapies that may alter tumor perfusion, and deepen our understanding of the emergence of drug transport-based therapeutic resistance.

Multiscale smeared finite element model for mass transport in biological tissue: From blood vessels to cells and cellular organelles.

One of the basic and vital processes in living organisms is mass exchange, which occurs on several levels: it goes from blood vessels to cells and organelles within cells. On that path, molecules, as oxygen, metabolic products, drugs, etc. Traverse different macro and micro environments - blood, extracellular/intracellular space, and interior of organelles; and also biological barriers such as walls of blood vessels and membranes of cells and organelles. Many aspects of this mass transport remain unknown, particularly the biophysical mechanisms governing drug delivery. The main research approach relies on laboratory and clinical investigations. In parallel, considerable efforts have been directed to develop computational tools for additional insight into the intricate process of mass exchange and transport. Along these lines, we have recently formulated a composite smeared finite element (CSFE) which is composed of the smeared continuum pressure and concentration fields of the capillary and lymphatic system, and of these fields within tissue. The element offers an elegant and simple procedure which opens up new lines of inquiry and can be applied to large systems such as organs and tumors models. Here, we extend this concept to a multiscale scheme which concurrently couples domains that span from large blood vessels, capillaries and lymph, to cell cytosol and further to organelles of nanometer size. These spatial physical domains are coupled by the appropriate connectivity elements representing biological barriers. The composite finite element has "degrees of freedom" which include pressures and concentrations of all compartments of the vessels-tissue assemblage. The overall model uses the standard, measurable material properties of the continuum biological environments and biological barriers. It can be considered as a framework into which we can incorporate various additional effects (such as electrical or biochemical) for transport through membranes or within cells. This concept and the developed FE software within our package PAK offers a computational tool that can be applied to whole-organ systems, while also including specific domains such as tumors. The solved examples demonstrate the accuracy of this model and its applicability to large biological systems.

A composite smeared finite element for mass transport in capillary systems and biological tissue.

One of the key processes in living organisms is mass transport occurring from blood vessels to tissues for supplying tissues with oxygen, nutrients, drugs, immune cells, and - in the reverse direction - transport of waste products of cell metabolism to blood vessels. The mass exchange from blood vessels to tissue and vice versa occurs through blood vessel walls. This vital process has been investigated experimentally over centuries, and also in the last decades by the use of computational methods. Due to geometrical and functional complexity and heterogeneity of capillary systems, it is however not feasible to model in silico individual capillaries (including transport through the walls and coupling to tissue) within whole organ models. Hence, there is a need for simplified and robust computational models that address mass transport in capillary-tissue systems. We here introduce a smeared modeling concept for gradient-driven mass transport and formulate a new composite smeared finite element (CSFE). The transport from capillary system is first smeared to continuous mass sources within tissue, under the assumption of uniform concentration within capillaries. Here, the fundamental relation between capillary surface area and volumetric fraction is derived as the basis for modeling transport through capillary walls. Further, we formulate the CSFE which relies on the transformation of the one-dimensional (1D) constitutive relations (for transport within capillaries) into the continuum form expressed by Darcy's and diffusion tensors. The introduced CSFE is composed of two volumetric parts - capillary and tissue domains, and has four nodal degrees of freedom (DOF): pressure and concentration for each of the two domains. The domains are coupled by connectivity elements at each node. The fictitious connectivity elements take into account the surface area of capillary walls which belongs to each node, as well as the wall material properties (permeability and partitioning). The overall FE model contains geometrical and material characteristics of the entire capillary-tissue system, with physiologically measurable parameters assigned to each FE node within the model. The smeared concept is implemented into our implicit-iterative FE scheme and into FE package PAK. The first three examples illustrate accuracy of the CSFE element, while the liver and pancreas models demonstrate robustness of the introduced methodology and its applicability to real physiological conditions.

Accuracy and reproducibility of two scales in causality assessment of unexpected hepatotoxicity.

WHAT IS KNOWN AND OBJECTIVE: There is almost no published information about reliability of scales for causality assessment in hepatotoxicity at pharmacovigilance centres. The aim of this study was to compare two commonly used scales in cases of unexpected hepatotoxicity, in evaluating their accuracy and reproducibility at pharmacovigilance centres (in signal detection). METHODS: Two scales [Council for International Organizations of Medical Sciences or Rousel Uclaf Causality Assessment Method (CIOMS/RUCAM) and NARANJO] were compared in 19 cases of unexpected hepatotoxicity reported during 2004-2009. Data of the cases (with initial clinical assessments) were collected by a network of medical specialists using a structured reporting form. Later, two independent observers assessed each case using both scales. The accuracy and reproducibility of the scales were analysed by Kappa weighted (Kw) test. RESULTS: Both scales (CIOMS/RUCAM vs. NARANJO) showed moderate agreement with the initial clinical assessments (accuracy) for observer A (Kw: 0·56 vs. 0·60) and substantial agreement for observer B (Kw: 0·72 vs. 0·70), with high agreement between observers (Kw: 0·84 vs. 0·67). Both observers (A vs. B) found low agreement between scales (Kw: 0·21 vs. 0·50), with lower scores for the CIOMS/RUCAM scale in 11 and nine cases, respectively. For an early perception of unexpected serious reactions, the scale is more useful if it is not asked for 'previous knowledge' and if it gives higher causality score. WHAT IS NEW AND CONCLUSION: The CIOMS/RUCAM scale showed similar accuracy, but better reproducibility (agreement between observers) than the NARANJO scale, and therefore is recommended for use at pharmacovigilance centres. Fine-tuning of the CIOMS/RUCAM method could contribute to better detection of unexpected hepatotoxicity.

Development of an x-ray imaging system for the Laser Megajoule (LMJ).

This imaging system aims at recording images of the core size and shape of an imploding deuterium-tritium (DT) microballoon on LMJ inertial confinement fusion (ICF) experiments. Image acquisition is difficult due to the harsh surrounding created by the fusion reaction, which affects system specifications. This one is made of a scintillator, an optical relay, and a CCD camera shielded from the surrounding. The system was tested on different facilities at CEA/DIF, where a spatial resolution of 120 µm was achieved and gamma dose up to 20 rad effects were measured. Setup and performed test are described.

HPV-16 E5 oncoprotein upregulates lipid raft components caveolin-1 and ganglioside GM1 at the plasma membrane of cervical cells.

High-risk human papillomaviruses (HPVs), especially HPV-16, play a primary role in the pathogenesis of cervical cancer. HPV-16 encodes the E5, E6 and E7 oncoproteins. Although the biological functions of E5 are poorly understood, recent studies indicate that its expression correlates with papillomavirus oncogenicity. In this study we demonstrate that the HPV-16 E5 oncoprotein increases plasma membrane expression of caveolin-1, which is a constituent of lipid rafts and regulator of cell signaling, and that this phenotype is mediated by the C-terminal 10 amino acids of E5. Moreover, E5 (but not mutant E5) induces a 23- to 40-fold increase in the lipid raft component, ganglioside GM1, on the cell surface and mediates a dramatic increase in caveolin-1/GM1 association. Since gangliosides strongly inhibit cytotoxic T lymphocytes, block immune synapse formation and are expressed at high levels on the surface of many tumor cells, our results suggest a potential mechanism for immune evasion by the papillomaviruses. Additionally, surface gangliosides are known to enhance proliferative signaling by the epidermal growth factor (EGF) receptor, providing a possible mechanistic basis for observations that EGF signaling is enhanced in E5-expressing cells. Finally, the upregulation of caveolin-1 and ganglioside GM1 at the plasma membrane of E5-expressing cervical cells provides potential new therapeutic targets and diagnostic markers for high-risk HPV infections.

[Phantom pain and posttraumatic pain conditions]. / Fantomski bol i posttraumatska bolna stanja.

After limb or body part amputation, three different types of perceptual sensitive phenomena can be recognized. They can be all named posttraumatic neuropathies: painless sensations in phantom limb, painful phantom limb and painful posttraumatic stump. Painless sensations in phantom limb can be seen in 90% of cases in resected body parts as soon as first postoperative day, less often during the first week, and its clinical characteristics are usually stabilized during the first year. Painful posttraumatic stump appears because of pain neuroma existing, that forms at the proximal end of amputational stump as a consequence of physiological nerve regeneration attempt. Frequency of pain significantly varies considering authors from 5-90%, depending on definition of this phenomena and criteria used. It is considered that 5-10% mast be under permanent medicament treatment. Phantom pain appears more often in elderly and people with specific affective personality construction. It can be permanent, burning, nettling, tearing (25%), or intermittent, lancerating, in the shape of electrical discharging (32%), but it can also have bizarre attributes. Phantom pain appearance usually announces its duration in the longer period. After two years it is present at 59% of patients, with decreasing intensity, and only 5-10% suffer severe pain. In our Institute in the period from 1980-2003, 48 patients have been treated, 36 patients with medicamentous treatment, local blockades and chronic stimulations, and 12 patients, who did not react at conservative treatment were operated. In operated group in 10 patients pain disappeared, one patient it was with decreasing intensity, and one patient was without change.

[Transplantation in peripheral nerve injuries]. / Transplantacija kod povreda perifernih nerava.

Autologous nerve grafting is the most commocommnlynly used operative technique in delayed primary, or secondary nerve repair after the peripheral nerve injuries. The aim of this procedure is to overcome nerve gaps that results from the injury itself, fibrous and elastic retraction forces, resection of the damaged parts of the nerve, position of the articulations and mobilisation of the nerve. In this study we analyse the results of operated patients with transections and lacerations of the peripheral nerves from 1979 to 2000 year. Gunshot injuries have not been analyzed in this study. The majority of the injuries were in the upper extremity (more than 87% of cases). Donor for nerve transplantation had usually been sural nerve, and only occasionally medial cutaneous nerve of the forearm was used. In about 93% of cases we used interfascicular nerve grafting, and cable nerve grafting was performed in the rest of them. Most of the grafts were 1 do 5 cm long (70% of cases). Functional recovery was achieved in more than 86% of cases, which is similar to the results of the other authors. Follow up period was minimum 2 years. We analyzed the influence of different factors on nerve recovery after the operation: patient's age, location and the extent (total or partial) of nerve injury, the length of the nerve graft, type of the nerve, timing of surgery, presence of multiple nerve injuries and associated osseal and soft tissue injuries of the upper and lower extremities.

[Reconstructive surgery of facial nerve injuries]. / Rekonstruktivna hirurgija povreda facijalisa.

The facial nerve is main motor nerve of the face and its injury leads to total ipsilateral paralysis. There are several surgical procedures in reconstruction of the facial nerve, and the most frequent one is hypoglosso-facial anastomosis. In this study were analysed a series of 69 patients operated on Institute of neurosurgery from 1981 to 2000 year. The most frequent cause of injury was the operation of cerebellopontine angle tumors, as well as the skull base fractures. Hypoglosso-facial anastomosis was done in 57 patients, in 5 cases we performed nerve grafting in the cerebellopontine angle, and in 7 patients the facial nerve was operated peripherally. Results were analyzed in 27 of 57 patients with hipoglosso-facial nerve anastomosis. Functional recovery was achived in 22 (81.4%) patients.

The efficacy of selenium, WR-2721, and their combination in the prevention of adriamycin-induced cardiotoxicity in rats.

It is known that the antineoplastic drug adriamycin (ADR) can cause cardiotoxic effects. Some data imply that pretreatment with selenium (Se) and the radio- and chemoprotector, amifostine (WR-2721), may confer a protective effect. The aim of this study was to evaluate the efficacy of single doses of Se and WR-2721, alone or in combination, in the prevention of acute ADR-induced cardiotoxicity in male Wistar rats. Se, in the form of sodium selenite (1.6 mg/kg i.p.), and WR-2721 (300 mg/kg i.p.) were given 24 hours and 20 minutes, respectively, before ADR (6 mg/kg i.v.). The cardiotoxicity of ADR was recorded 48 hours after its administration because earlier studies revealed that structural damage of the myocardium occurs within this period. Evaluation of these toxic effects, as well as of the cardioprotective efficacy of the administered drugs, was performed using (1) ECG-records before and during the infusion of the proarrhythmogenic compound, aconitine (8 microg/kg/min i.v.) and (2) the serum activity of creatine kinase (CK), aspartate aminotransferase-(AST), lactate dehydrogenase (LDH), and its isoenzyme alpha-hydroxybutyrate dehydrogenase (alpha-HBDH). The results showed that the arrhythmogenic dose of aconitine was significantly reduced in ADR-treated rats (57.22 vs. 99.65 microg/kg in control; p < 0.05) and that this proarrhythmogenic compound caused a significant increase in heart rate in such animals compared to controls. Pretreatment with Se, WR-2721, and their combination partly reversed the arrhythmogenic dose of aconitine to control (72.09, 82.1, and 88.99 microg/kg, respectively). Se failed to prevent an aconitine-induced increase in heart rate, whereas WR-2721 and their combination successfully counteracted this effect. In addition, ADR produced a significant increase in the serum activity of all monitored enzymes. Pretreatment with Se failed to prevent this increase, whereas pretreatment with WR-2721 did. The best result was obtained with their combination. We conclude that the radio- and chemoprotector, WR-2721, particularly in combination with Se, may provide a significant protective effect against acute ADR-induced cardiotoxicity in rats.

Influence of a radioprotector WR-638 on the lymphoid compartment of the irradiated rat thymus: a flow cytometric analysis.

The T cell composition of the thymus of X-ray irradiated (3.5 Gy) Wistar rat protected with WR-638 was analyzed by flow cytometry using monoclonal antibodies directed to the Thy 1.1, CD43, CD2, CD5, CD4, CD8 and class I and II MHC antigens. It was shown that this dose of X-rays caused cyclic changes in thymic cellularity manifested as: primary involution (until day 2), primary regeneration (from days 2 to 14), secondary involution (from days 14 to 21) and secondary regeneration (from days 21 to 30). WR-638 reduced the magnitude of thymocyte depletion in the primary involutive phase of the irradiated thymi, primarily as a result of protection of Thy 1.1high+ CD2low+ CD5high+ CD4+ CD8+ class I antigen high+ subpopulations of thymocytes. In the early regenerative phase, WR-638 accelerated the regeneration of CD4-CD8- and CD4-CD8+ thymocyte subsets, followed by subsequent increase of CD4+CD8+ and CD4+CD8- thymocyte subsets. Secondary involutive and regenerative phases in protected animals were characterized by higher absolute cell number of almost all thymocyte subpopulations in comparison with those in irradiated, non-protected animals.

Corticosteroid treatment and X-ray irradiation in adult rats induce the reexpression of fetal markers in cortical thymic epithelial cells.

The phenotype of cortical thymic epithelial cells (TEC) following hydrocortisone-treatment and sublethal X-ray irradiation in adult rats was studied by immunohistochemistry. It was found that during thymic regeneration (2-16 days) a TEC subset, predominantly in the outer cortex, transiently expressed cytokeratin (CK) 19 and an antigen defined by PT13D11 monoclonal antibody (mAb). These markers are characteristic for fetal, but not adult cortical TEC. To examine whether regenerating thymocytes may influence the phenotype of cortical TEC we cultivated a rat cortical TEC line (R-TNC 1.1) with thymocytes isolated from the thymuses at day 7 after hydrocortisone treatment. The R-TNC 1.1 TEC line, although established from adult rat thymus, constitutively expresses PT13D11, but not CK19. The appearance of CK19 in the R-TNC 1.1 cells was not inducible neither by coculture of this line with thymocytes, nor by the influence of IL-1, IL-2, IL-6, TNF-alfa and IFN-gamma. These results demonstrated the phenotypic plasticity of cortical TEC in adult rats.

[Radioprotective and therapeutic modulation of thymus gland regeneration in rats after x-ray irradiation]. / Radioprotektivna i terapijska modulacija regeneracije timusa pacova nakon X-zracenja.

There have been studied effects of cystaphos, gammaphos, hydroxyurea, polyadenyl-polyuridinic acids (poly A:poly U) as well as the combination of gammaphos and poly A:poly U, that is, cystaphos and superoxide dismutase on the thymus of Wistar and AO rats irradiated by the hard X-rays in the dose of 5 or 3.5 Gy. Changes were observed up to 30 days after irradiation. The most efficacious protective effect has shown cystaphos (358 mg/kg i.p. 20 min. after irradiation) in Wistar rats irradiated by the dose of 3.5 Gy. It lowered involutive changes and accelerated thymus regeneration. On the basis of phenotypic analysis of thymocytes it can be supposed that such a favourable effect is the consequence of a larger protection of the cortical (strong OX 7+) thymocytes. Differing from cystaphos, transplantation of the syngeneic cells of the bone marrow in AO rats irradiated by the dose of 5 Gy showed favourable effect on thymus regeneration in later phase after irradiation preventing secondary thymus involution.