TL1A is an epithelial alarmin that cooperates with IL-33 for initiation of allergic airway inflammation

Epithelium-derived cytokines or alarmins, such as interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP), are major players in type 2 immunity and asthma. Here, we demonstrate that TNF-like ligand 1A (TL1A) is an epithelial alarmin, constitutively expressed in alveolar epithelium at steady state in both mice and humans, which cooperates with IL-33 for early induction of IL-9high ILC2s during the initiation of allergic airway inflammation. Upon synergistic activation by IL-33 and TL1A, lung ILC2s acquire a transient IL-9highGATA3low "ILC9" phenotype and produce prodigious amounts of IL-9. A combination of large-scale proteomic analyses, lung intravital microscopy, and adoptive transfer of ILC9 cells revealed that high IL-9 expression distinguishes a multicytokine-producing state-of-activated ILC2s with an increased capacity to initiate IL-5-dependent allergic airway inflammation. Similar to IL-33 and TSLP, TL1A is expressed in airway basal cells in healthy and asthmatic human lungs. Together, these results indicate that TL1A is an epithelium-derived cytokine and an important cofactor of IL-33 in the airways.

Fibroblasts transfection by electroporation in 3D reconstructed human dermal tissue

The understanding of the mechanisms involved in DNA electrotransfer in human skin remains modest and limits the clinical development of various biomedical applications, such as DNA vaccination. To elucidate some mechanisms of DNA transfer in the skin following electroporation, we created a model of the dermis using a tissue engineering approach. This model allowed us to study the electrotransfection of fibroblasts in a three-dimensional environment that included multiple layers of fibroblasts as well as the self-secreted collagen matrix. With the aim of improving transfection yield, we applied electrical pulses with electric field lines perpendicular to the reconstructed model tissue. Our results indicate that the fibroblasts of the reconstructed skin tissue can be efficiently permeabilized by applied millisecond electrical pulses. However, despite efficient permeabilization, the transfected cells remain localized only on the surface of the microtissue, to which the plasmid was deposited. Second harmonic generation microscopy revealed the extensive extracellular collagen matrix around the fibroblasts, which might have affected the mobility of the plasmid into deeper layers of the skin tissue model. Our results show that the used skin tissue model reproduces the structural barriers that might be responsible for the limited gene electrotransfer in the skin.

Cancer Imaging by Intravital Microscopy: The Dorsal Window Chamber Model

Intravital microscopy allows a direct visualization of cells' behavior in their environment in a living organism with all its complexity. With appropriated models, longitudinal studies of structural and functional changes can be followed in the same animal on long period. In the field of cancer, the dorsal window chamber model is the model of choice for tumor events such as cells migration, vessels growth, and their permeability or interactions between cells and vessels. Coupled with wide-field, confocal, or multiphoton fluorescence microscopes, high spatial and temporal resolutions of the cellular events can be analyzed in vivo.

Gene Electrotransfer Efficiency in 2D and 3D Cancer Cell Models Using Different Electroporation Protocols: A Comparative Study

Electroporation, a method relying on a pulsed electric field to induce transient cell membrane permeabilization, can be used as a non-viral method to transfer genes in vitro and in vivo. Such transfer holds great promise for cancer treatment, as it can induce or replace missing or non-functioning genes. Yet, while efficient in vitro, gene-electrotherapy remains challenging in tumors. To assess the differences of gene electrotransfer in respect to applied pulses in multi-dimensional (2D, 3D) cellular organizations, we herein compared pulsed electric field protocols applicable to electrochemotherapy and gene electrotherapy and different "High Voltage-Low Voltage" pulses. Our results show that all protocols can result in efficient permeabilization of 2D- and 3D-grown cells. However, their efficiency for gene delivery varies. The gene-electrotherapy protocol is the most efficient in cell suspensions, with a transfection rate of about 50%. Conversely, despite homogenous permeabilization of the entire 3D structure, none of the tested protocols allowed gene delivery beyond the rims of multicellular spheroids. Taken together, our findings highlight the importance of electric field intensity and the occurrence of cell permeabilization, and underline the significance of pulses' duration, impacting plasmids' electrophoretic drag. The latter is sterically hindered in 3D structures and prevents the delivery of genes into spheroids' core.

Tumor-associated high endothelial venules mediate lymphocyte entry into tumors and predict response to PD-1 plus CTLA-4 combination immunotherapy

Recruitment of lymphocytes into tumors is critical for anti-tumor immunity and efficacious immunotherapy. We show in murine models that tumor-associated high endothelial venules (TA-HEVs) are major sites of lymphocyte entry into tumors at baseline and upon treatment with anti-PD-1/anti-CTLA-4 immune checkpoint blockade (ICB). TA-HEV endothelial cells (TA-HECs) derive from post-capillary venules, co-express MECA-79⁺ HEV sialomucins and E/P-selectins, and are associated with homing and infiltration into tumors of various T cell subsets. Intravital microscopy further shows that TA-HEVs are the main sites of lymphocyte arrest and extravasation into ICB-treated tumors. Increasing TA-HEC frequency and maturation increases the proportion of tumor-infiltrating stem-like CD8⁺ T cells, and ameliorates ICB efficacy. Analysis of tumor biopsies from 93 patients with metastatic melanoma reveals that TA-HEVs are predictive of better response and survival upon treatment with anti-PD-1/anti-CTLA-4 combination. These studies provide critical insights into the mechanisms governing lymphocyte trafficking in cancer immunity and immunotherapy.

High Power Electromagnetic Waves Exposure of Healthy and Tumor Bearing Mice: Assessment of Effects on Mice Growth, Behavior, Tumor Growth, and Vessel Permeabilization

High power radiofrequencies may transiently or permanently disrupt the functioning of electronic devices, but their effect on living systems remains unknown. With the aim to evaluate the safety and biological effects of narrow-band and wide-band high-power electromagnetic (HPEM) waves, we studied their effects upon exposure of healthy and tumor-bearing mice. In field experiments, the exposure to 1.5 GHz narrow-band electromagnetic fields with the incident amplitude peak value level in the range of 40 kV/m and 150 MHz wide-band electric fields with the amplitude peak value in the range of 200 kV/m, did not alter healthy and tumor-bearing animals' growth, nor it had any impact on cutaneous murine tumors' growth. While we did not observe any noticeable behavioral changes in mice during the exposure to narrow-band signals when wide-band HPEM signals were applied, mice could behave in a similar way as they respond to loud noise signals: namely, if a mouse was exploring the cage prior to signal application, it returned to companion mates when wide-band HPEM signals were applied. Moreover, the effect of wide-band signals was assessed on normal blood vessels permeability in real-time in dorsal-chamber-bearing mice exposed in a pilot study using wide-band signal applicators. Our pilot study conducted within the applicator and performed at the laboratory scale suggests that the exposure to wide-band signals with the amplitude of 47.5 kV/m does not result in increased vessel permeability.

Magnetic Silica-Coated Iron Oxide Nanochains as Photothermal Agents, Disrupting the Extracellular Matrix, and Eradicating Cancer Cells

Cancerous cells and the tumor microenvironment are among key elements involved in cancer development, progression, and resistance to treatment. In order to tackle the cells and the extracellular matrix, we herein propose the use of a class of silica-coated iron oxide nanochains, which have superior magnetic responsiveness and can act as efficient photothermal agents. When internalized by different cancer cell lines and normal (non-cancerous) cells, the nanochains are not toxic, as assessed on 2D and 3D cell culture models. Yet, upon irradiation with near infrared light, the nanochains become efficient cytotoxic photothermal agents. Besides, not only do they generate hyperthermia, which effectively eradicates tumor cells in vitro, but they also locally melt the collagen matrix, as we evidence in real-time, using engineered cell sheets with self-secreted extracellular matrix. By simultaneously acting as physical (magnetic and photothermal) effectors and chemical delivery systems, the nanochain-based platforms offer original multimodal possibilities for prospective cancer treatment, affecting both the cells and the extracellular matrix.

Evaluations of Acute and Sub-Acute Biological Effects of Narrowband and Moderate-Band High Power Electromagnetic Waves on Cellular Spheroids

High power electromagnetic signals can disrupt the functioning of electronic devices. As electromagnetism plays a role in cells homeostasis, such electromagnetic signals could potentially also alter some physiological processes. Herein we report on distinct biological parameters assessment after cellular spheroids exposure to high power electromagnetic signals, such as the ones used for defense applications. Signals effects were assessed in tumor cells spheroids and in normal human dermal fibroblasts spheroids, where macroscopic aspect, growth, plasma membrane integrity, induction of apoptosis, ATP content, and mitochondrial potential were investigated after spheroids exposure to high power electromagnetic signals. No significant effects were observed, indicating that 1.5 GHz narrowband electromagnetic fields with incident amplitude level of 40 kV/m, and 150 MHz moderate-band electric fields with an amplitude of 72.5 to approximately 200 kV/m, do not cause any significant alterations of assessed parameters.

Biodistribution and Biosafety of a Poly(Phosphorhydrazone) Dendrimer, an Anti-Inflammatory Drug-Candidate

Dendrimers are nanosized, arborescent polymers of which size and structure are perfectly controlled. This is one reason why they are widely used for biomedical purposes. Previously, we showed that a phosphorus-based dendrimer capped with anionic azabisphosphonate groups (so-called ABP dendrimer) has immuno-modulatory and anti-inflammatory properties towards human immune cells in vitro. Thereafter, we have shown that the ABP dendrimer has a promising therapeutic efficacy to treat models of chronic inflammatory disorders. On the way to clinical translation, the biodistribution and the safety of this drug-candidate has to be thoroughly assessed. In this article, we present preliminary non-clinical data regarding biodistribution, hematological safety, genotoxicity, maximal tolerated doses, and early cardiac safety of the ABP dendrimer. One of the genotoxicity assays reveals a potential mutagen effect of the item at a concentration above 200 µM, i.e., up to 100 times the active dose in vitro on human immune cells. However, as the results obtained for all the other assays show that the ABP dendrimer has promising biodistribution and safety profiles, there is no red flag raised to hamper the regulatory pre-clinical development of the ABP dendrimer.

Pre-clinical investigation of the synergy effect of interleukin-12 gene-electro-transfer during partially irreversible electropermeabilization against melanoma

BACKGROUND

Melanoma is a very aggressive skin tumor that can be cured when diagnosed and treated in its early stages. However, at the time of identification, the tumor is frequently in a metastatic stage. Intensive research is currently ongoing to improve the efficacy of the immune system in eliminating cancer cells. One approach is to boost the activation of cytotoxic T cells by IL-12 cytokine that plays a central role in the activation of the immune system. In parallel, physical methods such as electropermeabilization-based treatments are currently under investigation and show promising results.

METHODS

In this study, we set electrical parameters to induce a partial-irreversible electropermeabilization (pIRE) of melanoma to induce a sufficient cell death and potential release of tumor antigens able to activate immune cells. This protocol mimics the situation where irreversible electropermeabilization is not fully completed. Then, a peritumoral plasmid IL-12 electrotransfer was combined with pIRE treatment. Evaluation of the tumor growth and survival was performed in mouse strains having a different immunological background (C57Bl/6 (WT), nude and C57Bl6 (TLR9-/-)).

RESULTS

pIRE treatment induced apoptotic cell death and a temporary tumor growth delay in all mouse strains. In C57Bl/6 mice, we showed that peritumoral plasmid IL-12 electrotransfer combined with tumor pIRE treatment induced tumor regression correlating with a local secretion of IL-12 and IFN-γ. This combined treatment induced a growth delay of distant tumors and prevented the emergence of a second tumor in 50% of immunocompetent mice.

CONCLUSIONS

The combination of pIL-12 GET and pIRE not only enhanced survival but could bring a curative effect in wild type mice. This two-step treatment, named Immune-Gene Electro-Therapy (IGET), led to a systemic activation of the adaptive immune system and the development of an anti-tumor immune memory.

Safe and efficient novel approach for non-invasive gene electrotransfer to skin

Gene transfer into cells or tissue by application of electric pulses (i.e. gene electrotransfer (GET)) is a non-viral gene delivery method that is becoming increasingly attractive for clinical applications. In order to make GET progress to wide clinical usage its efficacy needs to be improved and the safety of the method has to be confirmed. Therefore, the aim of our study was to increase GET efficacy in skin, by optimizing electric pulse parameters and the design of electrodes. We evaluated the safety of our novel approach by assaying the thermal stress effect of GET conditions and the biodistribution of a cytokine expressing plasmid. Transfection efficacy of different pulse parameters was determined using two reporter genes encoding for the green fluorescent protein (GFP) and the tdTomato fluorescent protein, respectively. GET was performed using non-invasive contact electrodes immediately after intradermal injection of plasmid DNA into mouse skin. Fluorescence imaging of transfected skin showed that a sophistication in the pulse parameters could be selected to get greater transfection efficacy in comparison to the standard ones. Delivery of electric pulses only mildly induced expression of the heat shock protein Hsp70 in a luminescent reporting transgenic mouse model, demonstrating that there were no drastic stress effects. The plasmid was not detected in other organs and was found only at the site of treatment for a limited period of time. In conclusion, we set up a novel approach for GET combining new electric field parameters with high voltage short pulses and medium voltage long pulses using contact electrodes, to obtain a high expression of both fluorescent reporter and therapeutic genes while showing full safety in living animals.

In Vivo Evaluation of a New Recombinant Hyaluronidase to Improve Gene Electro-Transfer Protocols for DNA-Based Drug Delivery against Cancer

Cancer vaccines based on plasmid DNA represent a good therapeutic perspective, despite their low potency. Animal-derived hyaluronidases (Hyals) are employed in oncological clinical practice. Hyal has been also demonstrated to be a good enhancer of intramuscular Gene Electro-Transfer (GET) efficiency in anti-cancer preclinical protocols, with increased transfected cells and higher expression of the encoded genes. Nevertheless, the use of animal-derived Hyals results limited respect to their potentialities, since such preparations could be affected by low purity, variable potency and uncertain safety. To improve the delivery of intramuscular GET-based protocols in mouse, we investigated a new recombinant Hyal, the rHyal-sk, to assess in vivo safety and activity of this treatment at cellular and biochemical levels. We evaluated the cellular events and the inflammation chemical mediators involved at different time points after rHyal-sk administration plus GET. Our results demonstrated the in vivo safety and efficacy of rHyal-sk when injected once intramuscularly in association with GET, with no toxicity, good plasmid in-take ability, useful inflammatory response activation, and low immunogenicity. Following these findings, we would recommend the use of the new rHyal-sk for the delivery of DNA-based vaccines and immunotherapy, as well as into clinical practice, for tumor disease treatments.

Increased permeability of blood vessels after reversible electroporation is facilitated by alterations in endothelial cell-to-cell junctions

Delivery of electric field pulses, i.e. electroporation (EP), to tissues has been shown to have a blood flow modifying effect. Indeed, the diameter of blood vessels exposed to EP is immediately reduced resulting in blood flow abrogation, followed by an increase in vascular permeability. The main cause of the increased permeability remains unknown. The aim of this study was to determine whether the in vivo effects of EP on permeability of blood vessels are linked to the permeabilization of endothelial cells' membrane (EC) and/or disruption of cell-to-cell junctions. We used a dorsal window chamber model in C57Bl/6 mice coupled with multiphoton microscopy and fluorescently labelled antibodies against PECAM-1 (CD31) to visualize endothelial cell-to-cell junctions. Clinically validated EP parameters were used and behavior of cell-to-cell junctions, in combination with leakage of 70 kDa fluorescein isothiocyanate labelled dextran (FD), was followed in time. After EP, a constriction of blood vessels was observed and correlated with the change in the shape of ECs. This was followed by an increase in permeability of blood vessels for 70 kDa FD and a decrease in the volume of labelled cell-to-cell junctions. Both parameters returned to pre-treatment values in 50% of mice. For the remaining 50%, we hypothesize that disruption of cell-to-cell junctions after EP may trigger the platelet activation cascade. Our findings show for the first time in vivo that alterations in cell-to-cell junctions play an important role in the response of blood vessels to EP and explain their efficient permeabilization.

High power electromagnetic pulse applicators for evaluation of biological effects induced by electromagnetic radiation waves

Micro applicators for real-time observation of electromagnetic radiation waves effects on giant unilamellar vesicles and mammalian cells.

Post-pulse addition of trans-cyclohexane-1,2-diol improves electrotransfer mediated gene expression in mammalian cells

Electric field mediated gene transfer is facing a problem in expression yield due to the poor transfer across the nuclear envelope. Trans-cyclohexane-1,2-diol (TCHD) was shown to significantly increase chemically mediated transfection by collapsing the permeability barrier of the nuclear pore complex. We indeed observed a significant increase in expression by electrotransfer when cells are treated post pulse by a low non toxic concentration of TCHD. This was obtained for different pulsing conditions, cell strains and plasmid constructs. An interesting improvement in cell viability can be obtained. This can significantly enhance the non-viral gene electrical delivery.

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Trans-cyclohexane-1,2-diol (TCHD) collapses the permeability barrier of the nuclear pore complex.

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TCHD improves expression in gene electrotransfer.

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Post pulse TCHD addition is the most effective protocol.

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TCHD does not affect the cell viability when coupled to electrotransfer.

Electrochemotherapy guided by intraoperative fluorescence imaging for the treatment of inoperable peritoneal micro-metastases

Surgery is often the first therapeutic indication in cancer. Patient survival essentially depends on the completeness of tumor resection. This is a major challenge, particularly in patients with peritoneal carcinomatosis (PC), where tumors are widely disseminated in the large peritoneal cavity. These small tumors can be difficult to visualize and are often positioned in delicate locations, further increasing the risk of producing serious tissue/organ damage during their ablation. We propose an innovative therapeutic approach based on intraoperative fluorescence (IF) guided electrochemotherapy (ECT) for the treatment of peritoneal micro-metastases. ECT combines the effects of tissue electro-permeabilization (EP) with the administration of an antimitotic agent (bleomycin) that has poor permeability across intact membranes. IF significantly improves the detection of small tumor lesions. ECT is clinically validated for the treatment of cutaneous tumors in animals and humans, but this is the first time that it has been used along with IF imaging for the targeted treatment of peritoneal metastases in a preclinical model. We set up a murine model of PC that develops secondarily to the resection of a distant primary tumor. Tumor growth and metastasis were finely monitored by non-invasive multimodal imaging (bioluminescence and 3D fluorescence/microCT). Once metastases were detected, mice were randomized into three groups: the ECT group (bleomycin injected intravenously followed by EP) and 2 control groups (bleomycin alone and EP alone). Twenty four hours after the intravenous injection of the tumor targeting agent Angiostamp™700, mice in all groups underwent an abdominal surgery for metastases exploration assisted by fluorescence imaging with the Fluobeam®700 portative device. EP was applied to every nodule detected by IF, except in the bleomycin control group. After surgery, the metastatic invasion was tracked by bioluminescence imaging. In mice treated with bleomycin or EP alone, the metastatic load progressed very rapidly and mice showed no significant difference in lifespan compared to non-operated mice (median lifespan: 27days vs. 25days, respectively). In contrast, the mice treated with ECT displayed a decreased metastatic load and an increased survival rate (median lifespan: 34days). These results provide evidence that IF guided ECT is an effective approach for the treatment of inoperable intraperitoneal micro-metastases.

Abstract 5119: Mechanisms associated with blood flow modifying effects of electric pulses used for electrochemotherapy on normal and tumor blood vessels

Electropermeabilization/electroporation (EP) is a physical method that by applying external electric pulses to cells increases cell membrane permeability and thus enables the introduction of molecules into the cells. Nowadays, it is used in treatment of tumors, where its benefits are exploited in electrochemotherapy (ECT). In vivo EP also modifies blood flow, resulting in a decreased blood flow and increased permeability of blood vessel walls; whereas ECT has a vascular disrupting effect. The aim of our study was to evaluate the effects of EP on normal blood vessels and the effects of EP and ECT with bleomycin on tumor vasculature with the use of in vivo microscopy.

The effects of pulse parameters used for ECT (8 pulses, 1300 V/cm, 100 μs, 1 Hz) on normal blood vessels were determined via a dorsal skinfold window chamber (DWC) with intravital two-photon microscopy after in vivo labelling of CD31 with fluorescently labeled antibodies. Furthermore, 70 kDa fluorescently labeled dextrans was used to visualize the increased permeability of blood vessel walls. Additionally, Fluorescence Lifetime Imaging (FLIM) was used to determine the stability of the used fluorochrome. In tumors the effects of ECT pulse parameters on tumor blood vessels after EP or ECT with bleomycin were determined using 70 kDa fluorescently labeled dextrans either with two-photon or widefield intravital microsocopy via DWC. Solid mouse sarcoma SA-1 tumors were induced by a subcutaneous injection of dense cell suspension into the area of DWC in mice and an intravenous injection of bleomycin (100 μg/mouse) was performed 3 min before the application of electric pulses.

EP resulted in immediate constriction of the affected normal blood vessels and in a rapid increase of vascular permeability. This was accompanied by the change of the endothelial cells’ shape and a decrease of CD31 labelling in the cell-to-cell junctions. In vivo 3D FLIM showed no difference in the lifetime of the used fluorochrome before and after EP. When electric pulses or ECT were applied to tumors the increase in vascular permeability and the constriction of tumor blood vessels were not as pronounced as in normal blood vessels. However, there was a complete vascular lock that lasted for more than 30 min. Furthermore, ECT had a differential vascular disrupting effect on tumor blood vessels, leaving the larger normal blood vessels surrounding the tumors functional after the therapy.

In conclusion, the results of our study provide direct in vivo evidence of the difference in vascular effects of electric pulses used for ECT in normal and tumor blood vessels, show the response of normal endothelial cells to EP with two-photon microscopy and 3D FLIM, and provide evidence of the differential vascular disrupting action of ECT.

Citation Format: Bostjan Markelc, Elisabeth Bellard, Gregor Sersa, Tanja Dolinsek, Justin Teissie, Muriel Golzio, Maja Cemazar. Mechanisms associated with blood flow modifying effects of electric pulses used for electrochemotherapy on normal and tumor blood vessels. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5119. doi:10.1158/1538-7445.AM2015-5119

High accuracy 4D cell tracking into explanted skin using two-photon excitation microscopy

Two-photon excitation microscopy (2PEM) analysis of large explanted organs is still laborious, principally because of tissue movements inducing lateral and axial drifts during extended imaging sessions. Here, we describe a two-step approach to track motile T cells in murine dorsal explanted skin with the best accuracy. First, we compared various explanted skin mounting methods for 2PEM analysis to define the setup allowing for minimal sample drift over time. Second, we developed two algorithms with the ImageJ software (National Institute of Health, Bethesda, MD) to correct the residual drift using lateral and axial registration of the collagen network. Finally, we applied the macro we developed to track fluorescent T cells in explanted skin. We found that our newly developed macro is more efficient than freely or commercially available software for shift correction, leading to more accurate velocity calculations. Our work provides a practical guide for investigators interested to employ skin-imaging approaches and offers a free alternative to commercial software for correcting lateral and axial drifts.

A double-pulse approach for electrotransfection

Gene transfer and expression can be obtained by delivering calibrated electric pulses on cells in the presence of plasmids coding for the activity of interest. The electric treatment affects the plasma membrane and induces the formation of a transient complex between nucleic acids and the plasma membrane. It results in a delivery of the plasmid in the cytoplasm. Expression is only obtained if the plasmid is translocated inside the nucleus. This is a key limit in the process. We previously showed that delivery of a high-field short-duration electric pulse was inducing a structural alteration of the nuclear envelope. This study investigates if the double-pulse approach (first pulse to transfer the plasmid to the cytoplasm, and second pulse to induce the structural alteration of the envelope) was a way to enhance the protein expression using the green fluorescent protein as a reporter. We observed that not only the double-pulse approach induced the transfection of a lower number of cells but moreover, these transfected cells were less fluorescent than the cells treated only with the first pulse.

Membrane disorder and phospholipid scrambling in electropermeabilized and viable cells

Membrane electropermeabilization relies on the transient permeabilization of the plasma membrane of cells submitted to electric pulses. This method is widely used in cell biology and medicine due to its efficiency to transfer molecules while limiting loss of cell viability. However, very little is known about the consequences of membrane electropermeabilization at the molecular and cellular levels. Progress in the knowledge of the involved mechanisms is a biophysical challenge. As a transient loss of membrane cohesion is associated with membrane permeabilization, our main objective was to detect and visualize at the single-cell level the incidence of phospholipid scrambling and changes in membrane order. We performed studies using fluorescence microscopy with C6-NBD-PC and FM1-43 to monitor phospholipid scrambling and membrane order of mammalian cells. Millisecond permeabilizing pulses induced membrane disorganization by increasing the translocation of phosphatidylcholines according to an ATP-independent process. The pulses induced the formation of long-lived permeant structures that were present during membrane resealing, but were not associated with phosphatidylcholine internalization. These pulses resulted in a rapid phospholipid flip/flop within less than 1s and were exclusively restricted to the regions of the permeabilized membrane. Under such electrical conditions, phosphatidylserine externalization was not detected. Moreover, this electrically-mediated membrane disorganization was not correlated with loss of cell viability. Our results could support the existence of direct interactions between the movement of membrane zwitterionic phospholipids and the electric field.

Direct validation of aptamers as powerful tools to image solid tumor

Visualization of cancer cells requires distinguishing malignant from normal cells by objective criteria with high specificity. For several years, tumor markers expressed on the surface of cancer cells have been characterized as cancer signatures, and their labeling with specific imaging probes has revolutionized cancer diagnosis. This specific labeling is also an important tool in surgery tumor ablation. The present study considers the tumor labeling potential of an aptamer that specifically recognizes the epithelial cancer biomarker mucin1 (MUC1). This anti-MUC1 aptamer was investigated in vitro in a three-dimensional (3D) environment and compared to an anti-MUC1 antibody for its capacity to visualize cancer cells. Multicellular spheroids of breast cancer MCF-7 cells were used as tumor models and anti-MUC1 fluorescent aptamer and antibody were visualized by fluorescence imaging. Results showed that the antibodies interacted only with cells located on the surface of the spheroid, whereas the anti-MUC1 aptamers were able to penetrate inside these 3D tumor models and thereafter internalized into the cancer cells. Due to their lack of immunogenicity and their facility to be chemically modified, aptamers may replace advantageously the use of antibodies in diagnosis based on imaging setup thanks to their specific detection of cancer cells without invasive surgical procedures or during clinical intraoperative intervention.

Sub-cellular temporal and spatial distribution of electrotransferred LNA/DNA oligomer

Low biological activity and inefficient targeted delivery in vivo have hindered RNA interference (RNAi)-based therapy from realising its full clinical potential. To overcome these hurdles, progresses have been made to develop new technologies optimizing oligonucleotides chemistry on one hand and achieving its effective delivery on the other hand. In this report, we achieved, by using the electropulsation technique (EP), efficient cellular delivery of chemically-modified oligonucleotide: The locked nucleic acid (LNA)/DNA oligomer. We used single cell level confocal fluorescence microscopy to follow the spatial and temporal distribution of electrotransferred cyanine 5 (Cy5)-labeled LNA/DNA oligomer. We observed that EP allowed LNA/DNA oligomer cellular uptake providing the oligomer a rapid access to the cytoplasm of HeLa cells. Within a few minutes after electrotransfer, Cy5-LNA/DNA oligomers shuttle from cytoplasm to nucleus whereas in absence of pulses application, Cy5-LNA/DNA oligomers were not detected. We then observed a redistribution of the Cy5 fluorescence that accumulated over time into cytoplasmic organelles. To go further and to identify these compartments, we used the HeLa GFP-Rab7 cell line to visualise late endosomes, and lysosomal or mitochondrial specific markers. Our results showed that the EP technique allowed direct entry into the cytoplasm of the Cy5-LNA/DNA oligomer bypassing the endocytosic pathway. However, in absence of pulses application, Cy5-LNA/DNA oligomer were able to enter cells through the endocytosic pathway. We demonstrated that EP is an efficient technique for LNA-based oligonucleotides delivery offering strong advantages by avoiding the endolysosomal compartmentalization, giving a rapid and free access to the cytoplasm and the nucleus where they can find their targets.

In vivo molecular imaging and histological analysis of changes induced by electric pulses used for plasmid DNA electrotransfer to the skin: a study in a dorsal window chamber in mice

Electropermeabilization/electroporation (EP) is a physical method that by application of electric pulses to cells increases cell membrane permeability and enables the introduction of molecules into the cells. One of the uses of EP in vivo is plasmid DNA electrotransfer to the skin for DNA vaccination. EP of tissues induces reduction of blood flow and, in combination with plasmid DNA, induction of an immune response. One of the EP protocols for plasmid DNA electrotransfer to the skin is a combination of high-voltage (HV) and low-voltage (LV) pulses. However, the effects of this pulse combination on skin-vessel blood flow are not known. Therefore, using intravital microscopy in a dorsal window chamber in mice and fluorescently labeled dextrans, the effects of one HV and eight LV pulses on skin vasculature were investigated. In addition, a detailed histological analysis was performed. Image analysis of fluorescence intensity changes demonstrated that EP induces a transient constriction and increased permeability of blood vessels as well as a “vascular lock.” Histological analysis revealed rounding up of endothelial cells and stacking up of erythrocytes at 1 h after EP. In addition, extravasation of erythrocytes and leukocyte infiltration accompanied by edema were determined up to 24 h after EP. In conclusion, our results show that blood flow modifying effects of EP in skin contribute to the infiltration of immune cells in the exposed area. When combined with plasmid DNA for vaccination, this could enable the initial and prolonged contact of immune cells with encoded therapeutic proteins.

LNA-based oligonucleotide electrotransfer for miRNA inhibition

Micro-RNAs (miRNAs) are small regulatory RNAs that play an important role in disease development and progression and therefore represent a potential new class of therapeutic targets. However, an effective and safe clinical approach for miRNA inhibition remains elusive, primarily due to the lack of effective delivery methods. We proposed to inhibit miRNA by electrotransferring an antisense DNA oligomer containing locked nucleic acids (LNAs) (LNA/DNA oligomer). We observed that electropulsation (EP) led to a strong cellular uptake of LNA/DNA oligomer. The LNA/DNA oligomer electrotransfer mechanism and intracellular localization were visually investigated in real time at the single-cell level. Cyanine 5-labeled oligonucleotide entered exclusively during pulse application on the side of the permeabilized cell membrane facing the cathode, driven by electrophoretic forces. Minutes after the electrotransfer, the LNA/DNA oligomer diffused into the nucleus. EP provided the anti-miRNA oligomer with immediate and direct access to its cytoplasmic mature miRNA target and/or its nuclear precursor miRNA target. We then demonstrated using a LNA/DNA oligomer anti-miR34a that LNA/DNA oligomer electrotransfer decreased the level of the miR34a target and induced its functional inhibition. Our findings show that using the electrotransfer technique for LNA-based oligonucleotide delivery is a promising therapeutic strategy to silence deleterious miRNAs overexpressed in diseases.

Giant lipid vesicles under electric field pulses assessed by non invasive imaging

We present experimental results regarding the effects of electric pulses on giant unilamellar vesicles (GUVs). We have used phase contrast and coherent anti-Stokes Raman scattering (CARS) microscopy as relevant optical approaches to gain insight into membrane changes under electropermeabilization. No addition of exogenous molecules (lipid analogue, fluorescent dye) was needed. Therefore, experiments were performed on pure lipid systems avoiding possible artefacts linked to their use. Structural membrane changes were assessed by loss of contrast inside the GUVs due to sucrose and glucose mixing. Our observations, performed at the single vesicle level, indicate these changes are under the control of the number of pulses and field intensity. Larger number of pulses enhances membrane alterations. A threshold value of the field intensity must be applied to allow exchange of molecules between GUVs and the external medium. This threshold depends on the size of the vesicles, the larger GUVs being affected at lower electric field strengths than the smaller ones. Our experimental data are well described by a simple model in which molecule entry is driven by direct exchange. The CARS microscopic study of the effect of pulse duration confirms that pulses, in the ms time range, induce loss of lipids and membrane deformations facing the electrodes.

Drug delivery by electropulsation: Recent developments in oncology

Electro-permeabilisation allows the free access of polar compounds to the cytoplasm by a reversible alteration of the cell membrane. It is now used in clinics for the eradication of cutaneous solid tumors. New developments predict its future applications for other anti-cancer treatments.

Human solid tumors contain high endothelial venules: association with T- and B-lymphocyte infiltration and favorable prognosis in breast cancer

The mechanisms governing infiltration of lymphocytes into tumors remain poorly characterized, in spite of the critical impact of these cells on patient prognosis and therapeutic responses. High endothelial venules (HEV) are blood vessels found in lymphoid tissues, specialized in lymphocyte recruitment, but their implications in human cancer are unknown. In this article, we report the presence of MECA 79(+) blood vessels displaying all the phenotypic characteristics of HEVs in most of the 319 human primary solid tumors, including melanomas, breast, ovarian, colon, and lung carcinomas, analyzed. Tumor HEVs were specifically located within lymphocyte-rich areas, and their density within the tumor stroma was a strong predictor of infiltration by CD3(+) and CD8(+) T cells as well as B cells. Large-scale flow cytometric and quantitative reverse transcriptase-PCR analyses in freshly operated breast tumors revealed that high densities of tumor HEVs correlated with increased naive, central memory and activated effector memory T-cell infiltration and upregulation of genes related to T-helper 1 adaptive immunity and T-cell cytotoxicity. Finally, in a retrospective cohort of 146 invasive breast cancer patients, we found that high densities of tumor HEVs independently conferred a lower risk of relapse and significantly correlated with longer metastasis-free, disease-free, and overall survival rates. Together, our findings suggest that tumor HEVs function as major gateways for lymphocyte infiltration into human tumors, and may represent attractive targets for cancer diagnosis and therapy.

A novel antiangiogenic and vascular normalization therapy targeted against human CD160 receptor

A monoclonal anti-CD160 antibody inhibits the growth of new vessels in pathological ocular and tumor neoangiogenesis but not in healthy tissues.

Angiogenesis plays an essential role in several diseases of the eye and in the growth of solid tumors, but existing antiangiogenic therapies have limited benefits in several cases. We report the antiangiogenic effects of a monoclonal antibody, CL1-R2, in several animal models of neovascularization. CL1-R2 recognizes human CD160, a membrane receptor which is conserved in various mammal species. We show that CD160 is expressed on the endothelial cells of newly formed blood vessels in human colon carcinoma and mouse B16 melanoma but not in vessels of healthy tissues. CL1-R2 reduced fibroblast growth factor 2–induced neovascularization in the rabbit cornea, in a mouse model of oxygen-induced retinopathy, and in a mouse Matrigel plug assay. Treatment of B16 melanoma-bearing mice with CL1-R2 combined with cyclophosphamide chemotherapy caused regression of the tumor vasculature and normalization of the remaining vessels as shown by Doppler ultrasonography, intravital microscopy, and histology. These studies validate CD160 as a potential new target in cases of human pathological ocular and tumor neoangiogenesis that do not respond or become resistant to existing antiangiogenic drugs.

Gene electrotransfer: from biophysical mechanisms to in vivo applications : Part 1- Biophysical mechanisms

Electropulsation is one of the nonviral methods successfully used to deliver genes into living cells in vitro and in vivo. This approach shows promise in the field of gene and cellular therapies. The present review focuses on the processes supporting gene electrotransfer in vitro. In the first part, we will report the events occurring before, during, and after pulse application in the specific field of plasmid DNA electrotransfer at the cell level. A critical discussion of the present theoretical considerations about membrane electropermeabilization and the transient structures involved in the plasmid uptake follows in a second part.

Tracking in vitro and in vivo siRNA electrotransfer in tumor cells

RNA interference-mediated gene silencing offers the potential of targeted inhibition of disease-relevant genes. In vivo delivery of RNAi reagents can be obtained by a variety of approaches. Physical delivery methods appear safer and lack side effects. Electro-permeabilization is one of the non-viral methods successfully used to transfer small interfering RNAs (siRNAs) in vitro and in vivo. A promising approach may be, very little is known about the fundamental processes mediating siRNA transfer. In this study, we have investigated cellular delivery pathways involved in electro-delivery of siRNAs by a direct fluorescence imaging method. An Alexa-labeled siRNA was electro-transferred into murine melanoma cells stably-expressing the enhanced green fluorescent protein (eGFP) target reporter gene. The silencing of eGFP gene expression was quantified by time-lapsed fluorescence microscopy. Fluorescently-labeled siRNAs were found distributed homogeneously in cytoplasm 48 hours after electro-transfer, apparently by diffusion. Furthermore, siRNAs showed homogeneous distribution in vivo 48 hrs after intra-tumoral injection followed by electro- permeabilization. Histological fluorescence microscopy showed that siRNAs were mostly localized in the cytoplasm. Overall, this study shows that electro-permeabilization facilitates cytoplasmic distribution of siRNA, both in cultured cells and in vivo. This method offers a potential therapeutic tool to facilitate direct siRNA penetration into solid tumors.

Cardiovascular variables do not predict head-up tilt test outcome better than body composition

Reflex syncope is a well-recognized phenomenon, but the understanding of its underlying pathophysiology remains limited. We hypothesized that patients with a history of syncope and a positive head-up tilt test (HUTT) outcome are in a "not-yet defined" abnormal state even before the head-up position. We performed a 45 min HUTT on 86 patients with a history of syncope. We assessed 19 variables during the supine period before head-up position. Of these variables, 9 were cardiovascular variables (CV) while 8 were body composition variables (BC). The two remaining variables were age and sex. Forty-five patients (41 +/- 15 years, 22 males) have a positive HUTT outcome and 41 a negative one (46 +/- 15 years, 22 males). Statistical tests applied on each of the 19 variables individually did not discriminate patients with a positive and a negative outcome. We used neural networks to screen the sets of variables that allowed for the best predictions of HUTT outcomes. The sensitivity, specificity, positive and negative predictive values (PPV and NPV, respectively) were determined. The best set of predictive values determined from the 19 variables was 76, 81, 78 and 80% for sensitivity, sensibility, PPV, and NPV, respectively. Unexpectedly, the HUTT outcome prediction performed with cardiovascular variables was not better than the prediction performed with body composition variables only. Patients with a positive HUTT outcome are in an abnormal state that can be detected even before the head-up position. Body composition is an important contributor to this abnormal state.

Increased hydration alone does not improve orthostatic tolerance in patients with neurocardiogenic syncope

In patients with neurocardiogenic syncope, the beneficial effects of increased daily fluid intake, without an accompanying high dose of salt, are unknown. Our aim was to (1) determine whether plasma volume was low in patients with recurrent neurocardiogenic syncope, and (2) determine how recommendation about increased daily fluid intake, without an accompanying high dose of sodium, effects plasma volume and if this potential therapy improves orthostatic tolerance. Eighty-six patients with neurocardiogenic syncope were recruited in a prospective randomized open study. After an initial head-up tilt test, patients were randomly assigned to either the hydration supplementation group (1500 ml of water + 1500 mg of NaCl/day) or the no treatment (control) group. After ten days a second head-up tilt test was performed. Plasma volume, osmolality, and total body water were measured at baseline, and heart rate, arterial blood pressure, and cardiac transthoracic impedance were monitored during tilting. Hydration treatment did not affect the number of positive tilt tests (52% initial day, 54% after treatment, NS). In both groups, the overall number of positive tilt tests decreased between the initial and final head-up tilt test. There was no association between low plasma volume and positive tilt test. Patients with the lowest plasma volume were equally distributed in both positive and negative tilt response groups. An increased daily intake of fluid, without an accompanying high dose of salt, had no measurable beneficial effect on tolerance to head-up tilting in patients with neurocardiogenic syncope. Moreover in this patient group there was no association between a low plasma volume and a reduced tolerance to orthostatic stress.

Comparison of computational algorithms applied on transthoracic impedance waveforms to predict head-up tilt table testing outcome

The goal of the present study was to develop and evaluate new algorithms for the prediction of the outcome of a head-upright tilt test (HUTT). Using transthoracic impedance and its first derivative, we attempted to determine if indexes computed on these waveforms could detect a positive outcome to a 70 degrees -45min HUTT with reliable sensitivity and specificity. The methods were evaluated retrospectively in a group of 70 patients and validated prospectively in a group of 59 patients. The best detector obtained used a neural network. It compares very favorably with published results for other syncope detectors.

Cancer cells regulate lymphocyte recruitment and leukocyte-endothelium interactions in the tumor-draining lymph node

The physiologic function of the secondary lymphoid organs to recruit large numbers of naïve lymphocytes increases the probability that antigens encounter their rare, sometimes unique, specific T lymphocytes and initiate a specific immune response. In peripheral lymph nodes (LNs), this recruitment is a multistep process, initiated predominantly within the high endothelial venules (HEVs), beginning with rolling and chemokine-dependent firm adhesion of the lymphocytes on the venular endothelium surface. We report here that, in C57BL/6 mice, the recruitment of naïve lymphocytes is impaired in LNs draining a B16 melanoma tumor. Intravital microscopy analysis of the tumor-draining LNs revealed that this effect is associated with an important defect in lymphocyte adhesion in the HEVs and a progressive decrease in the expression of the LN chemokine CCL21. In parallel with these effects, the tumor up-regulated, essentially through a P-selectin-dependent mechanism, the rolling and sticking of circulating polymorphonuclear cells within the LN low-order venules where few rolling and sticking events are usually observed. These effects of the tumor were independent of the presence of metastasis into the LN and occurred as long as the tumor developed. Together, these results indicate that the tumor proximity disturbs the LN physiology by modifying the molecular, spatial, and cellular rules that usually control leukocyte-endothelium interactions into the peripheral LNs. In addition, they emphasize a new role for the low-order venules of the peripheral LNs, which compared with the HEVs, seem to be the preferential port of entry for cells linked to inflammatory processes.

Do we need a reflex tachycardia to stand up?

BACKGROUND

Sophisticated atrio-ventricular pacing models are designed to integrate the pacemaker into cardiovascular autonomic control to react appropriately to the cardiovascular demands. Such an approach might be beneficial for patients with vasovagal responses to counterbalance the upright fall in arterial blood pressure by a pacing rate increase. We hypothesized that this approach would improve the cardiovascular response to standing in comparison with a regular pacing mode.

METHODS

Two 5-minute tilt tests were performed in a random order in 5 patients with a pacemaker (CLS-INOS(2)) for sinus node disease and atrio-ventricular block. One tilt test was performed in fixed pacing rate (DDD), the other one was performed in close loop stimulation (CLS), which allowed an upright rate-rise pacing. Heart rate, systolic blood pressure, and cardiac output (modelflow) were recorded on a beat-by-beat basis.

RESULTS

Changes of systolic blood pressure and cardiac output in response to upright posture were not significantly different between DDD and CLS modes (2.7 +/- 13.2 vs 10.1 +/- 12.9 mmHg and -0.8 +/- 0.3 vs -1.1 +/- 0.4 L/min, respectively). But upright posture led to a tachycardia of more than 30 bpm in 3 patients in CLS mode and to a fall in systolic blood pressure greater than 20 mmHg in 3 patients in CLS mode and only in one patient in DDD mode.

CONCLUSION

Systolic blood pressure and cardiac output are not improved by the upright tachycardia and upright blood pressure response is actually worsened when an upright rate-rise pacing is used. Thus, it appears that tachycardia alone cannot compensate for an upright fall in blood pressure.

Late Hemodynamic Changes During a Negative Passive Head-up Tilt Predict the Symptomatic Outcome to a Nitroglycerin Sensitized Tilt

BACKGROUND

Sublingual nitroglycerin is advocated to sensitize the passive 70 degrees head-upright tilt test (HUTT) of patients with unexplained syncope. We hypothesized that a detailed analysis of hemodynamic responses recorded during a negative HUTT could predict the outcome to a subsequent nitroglycerin sensitized HUTT (NTG-HUTT).

METHODS

Thirty-two patients (46 +/- 3 years, 17 males) with recurrent unexplained syncope but a negative HUTT were included. Heart rate, arterial blood pressure, and central hemodynamics assessed by transthoracic impedance (preejection and rapid left ventricular ejection time, slow ejection time, peak amplitude of first derivative, and cardiac index) were recorded during supine rest and 45 minutes HUTT. Changes from supine rest of the variables were retrospectively compared between patients with a negative (n = 15, NTG-HUTT(-)) and positive (n = 17, NTG-HUTT(+)) outcome to 10 minutes subsequent NTG-HUTT.

RESULT

Significant differences between groups were observed during the 15th-20th minutes (Italian protocol) and during the last 5 minutes of passive HUTT (Westminster protocol). The combination of cutoff values, determined by receiver operating curves, on hemodynamic variables changes during the last 5 minutes predicted the outcome to a NTG-HUTT with a sensitivity of 76% and a specificity of 87%. The cutoff values determined during 15th-20th minutes gave an attractive sensitivity (85%) but a too weak specificity (53%) to shorten the 45 minutes passive HUTT at 20 minutes.

CONCLUSION

Outcome to a NTG-HUTT can be reliably predicted by selected criteria determined from multiple hemodynamic variables recorded during a passive 70 degrees HUTT.

Comparison of various techniques used to estimate spontaneous baroreflex sensitivity (the EuroBaVar study)

This study compared spontaneous baroreflex sensitivity (BRS) estimates obtained from an identical set of data by 11 European centers using different methods and procedures. Noninvasive blood pressure (BP) and ECG recordings were obtained in 21 subjects, including 2 subjects with established baroreflex failure. Twenty-one estimates of BRS were obtained by methods including the two main techniques of BRS estimates, i.e., the spectral analysis (11 procedures) and the sequence method (7 procedures) but also one trigonometric regressive spectral analysis method (TRS), one exogenous model with autoregressive input method (X-AR), and one Z method. With subjects in a supine position, BRS estimates obtained with calculations of alpha-coefficient or gain of the transfer function in both the low-frequency band or high-frequency band, TRS, and sequence methods gave strongly related results. Conversely, weighted gain, X-AR, and Z exhibited lower agreement with all the other techniques. In addition, the use of mean BP instead of systolic BP in the sequence method decreased the relationships with the other estimates. Some procedures were unable to provide results when BRS estimates were expected to be very low in data sets (in patients with established baroreflex failure). The failure to provide BRS values was due to setting of algorithmic parameters too strictly. The discrepancies between procedures show that the choice of parameters and data handling should be considered before BRS estimation. These data are available on the web site (http://www.cbi.polimi.it/glossary/eurobavar.html) to allow the comparison of new techniques with this set of results.

Haemodynamic response to peripheral venous congestion in patients with unexplained recurrent syncope

In patients with recurrent unexplained syncope, exaggerated peripheral venous pooling and impaired circulatory adjustment is thought to contribute to the outcome of a head-up tilt (HUT) test. The present study investigated the role of leg volume changes during venous congestion in the haemodynamic response of patients with recurrent unexplained syncope and the ability to predict the outcome of a HUT test. Changes in calf volume (strain gauge plethysmography), heart rate and arterial blood pressure were recorded in 60 patients with history of unexplained syncope (without postural tachycardia symptom) during venous congestion provoked by pneumatic thigh cuffs while supine at rest and during the initial 10 min of a 45 min 70 degrees HUT test. Twenty-seven patients [age (mean+/-S.D.), 39+/-16 years] exhibited symptoms [HUT(+)] and 33 patients (45+/-14 years) were asymptomatic [HUT(-)]. During venous congestion, mean+/-S.E.M. calf volume increased in both groups [HUT(-), 4.5+/-0.2; HUT(+), 4.8+/-0.4 ml x 100 ml(-1), not significant), but significantly less during head-upright tilt [HUT(-), 3.3+/-0.2, P <0.01; HUT(+), 2.6+/-0.3 ml x 100 ml(-1), P <0.001] without differences between the groups. During venous congestion, arterial pressure increased significantly in asymptomatic HUT(-) patients, but not in the HUT(+) patients. Calf volume changes did not correlate with a symptomatic outcome to a 70 degrees HUT. The lack of exaggerated venous pooling during venous congestion and the inability of calf volume changes to predict a positive HUT suggest that excessive venous pooling does not contribute to the outcome of HUT. Attenuated changes in arterial pressure during venous congestion while supine suggest impaired adjustment of peripheral resistance to leg venous occlusion.

Changes in the transthoracic impedance signal predict the outcome of a 70 degrees head-up tilt test

We determined whether early changes in central haemodynamics, as determined by transthoracic impedance, induced by a 70 degrees head-up tilt (HUT) test could predict syncope. Heart rate, arterial blood pressure and central haemodynamics [pre-ejection period and rapid left ventricular ejection time ( T (1)), slow ejection time ( T (2)) and d Z /d t (max) (where Z is thoracic impedance), assessed by the transthoracic impedance technique], were recorded during supine rest and during a 45 min 70 degrees HUT test in 68 patients (40+/-2 years) with a history of unexplained recurrent syncope. We found that 38 patients (42+/-3 years) had a symptomatic outcome to 70 degrees HUT (fainters) and 30 (39+/-2 years) had a negative outcome (non-fainters). When measured between 5 and 10 min of 70 degrees HUT, T (2) had increased significantly only in the fainters, and a change in T (2) of >40 ms from baseline predicted a positive outcome with a sensitivity of 68% and a specificity of 70%. During supine rest prior to 70 degrees HUT, the fainters exhibited a shorter T (2) than non-fainters (183+/-10 compared with 233+/-14 ms; P <0.01), and a T (2) of <199 ms predicted a positive outcome to 70 degrees HUT with a sensitivity of 68% and a specificity of 63%. Incorporation of the changes that occurred from rest to 70 degrees HUT in other haemodynamic variables (heart rate >11 beats/min, systolic pressure <2 mmHg, diastolic pressure <7 mmHg and pulse pressure <-3 mmHg) increased the specificity to 97% and the positive predictive value to 93%. Thus transthoracic impedance could detect differences in central haemodynamics between fainters and non-fainters during supine rest and during the initial period of 70 degrees HUT with a consistent sensitivity and specificity when combined with peripheral haemodynamic variables.