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Biomedical subjects

R Sircar

Publications and source records attributed to R Sircar.

At least 19 recordsLinked to original sources
PubMed2005

Thoracoabdominal aortic aneurysm repair: interplay of spinal cord protecting modalities.

BACKGROUND: The purpose of this study was to assess the complementary use of different methods of measuring spinal cord perfusion during thoracoabdominal aortic surgery. METHODS: The spinal cords of 28 patients undergoing surgery on the thoracoabdominal aorta were monitored with transcranial electrical stimulation (tcMEP) and somatosensory-evoked potentials (SSEP). Available approaches of spinal cord-protection included: Moderate systemic hypothermia, constant cerebrospinal fluid (CSF) drainage and pressure monitoring, reimplantation of segmental arteries, cardiopulmonary bypass (CPB), and staged clamping. RESULTS: Fourteen of 19 patients (75%) undergoing open surgical treatment (Group I) exhibited loss of tcMEP after proximal aortic clamping. In nine cases (47%), we observed recovery of tcMEP after intraoperative interventions, while two patients subsequently developed paraplegia and three died. Seventeen of 19 patients showed loss of SSEP, with recovery in 12 cases (63%). During stent-graft implantation (Group II), one of nine patients (11%) demonstrated tcMEP loss with intraoperative, intervention-related recovery. The SSEP-recording course remained stable. CONCLUSIONS: tcMEP/SSEP monitoring has proved to be an excellent means of detecting spinal cord ischaemia during surgery on thoracoabdominal aortic aneurysms. The prognostic value of tcMEP monitoring should be considered superior to that of SSEP measurements, because of its direct and rapid response to spinal malperfusion. Through combined neurophysiological monitoring, vital parameter balancing and intraoperative interventions, spinal cord perfusion improves and recovery of tcMEP and SSEP is achievable, reducing the prevalence of postoperative paraplegia.

Adult↗
PubMed2005

Setup of neurophysiological monitoring with tcMEP/SSEP during thoracoabdominal aneurysm repair.

OBJECTIVES: The article describes a procedure for the intraoperative neurophysiological placement of electrodes to control the spinal cord function during thoracoabdominal aortic aneurysm repair. MATERIAL AND METHODS: Intraoperative monitoring is performed by motor-evoked myogenic potentials after transcranial electric stimulation (tcMEP) and somatosensory-evoked potentials (SSEP). In tcMEP, the stimulating percutaneous needle electrodes are placed at C3 and C4 according to the 10 - 20 system for EEG recordings. TcMEP are recorded from the anterior tibial and gastrocnemius muscles on both sides. The SSEP electrodes are placed laterally and caudally onto the malleolus medialis in order to stimulate the tibial nerve. The stimulus is documented via electrodes attached to the scalp within the sensory cortex region. RESULTS: The application of the electrodes is both easy to learn and can be performed without further difficulties. Once attached, the electrodes provide a quick assessment and interpretation of spinal cord function. The identification of external sources of disturbance during the monitoring (e. g. insufficient impedance, unfavourable electrode positioning, and technical interference caused by medical equipment) enables the supervisor to differentiate between normal and abnormal neurological responses. CONCLUSIONS: TcMEP and SSEP allow an adequate, direct, and reliable intraoperative assessment of spinal cord function, enabling the surgeon to diagnose an impending ischaemia and act accordingly. This measurement technique provides the surgical team with a means of integrating neurological aspects during thoracoabdominal aneurysm repair.

Aortic Aneurysm, Abdominal↗
PubMed2001

Postnatal stress selectively upregulates striatal N-methyl-D-aspartate receptors in male rats.

Early life events have been thought to contribute towards vulnerability to drug addiction later in life. In the present investigation, the effect of daily neonatal maternal isolation stress on NMDA channel activity was studied. [3H]MK-801 binding was measured in several brain regions from neonatally isolated (ISO) and nonhandled (NH) adult male and female rats. Maximal [3H]MK-801 binding in the caudate-putamen of male ISO rats was 58% higher compared to same sex NH rats. Unlike male rats, maximal [3H]MK-801 binding in the caudate-putamen of female ISO rats was lower than female NH rats. No other brain region showed any significant difference in maximal [3H]MK-801 binding between ISO and NH male and female rats, respectively. There was no effect of pup isolation on the binding affinity (K(d) value) in either sex. Repeated maternal isolation is associated with alterations in the NMDA channel activity in the caudate-putamen of adult rats, and may be responsible for the augmentation in the addictive behavior reported.

Animals↗
PubMed2000

Effect of melatonin on cocaine-induced behavioral sensitization.

Melatonin, a pineal hormone and a potent free radical scavenger with neuroprotective actions, has been reported to act as an inhibitor of nitric oxide synthase (NOS). We have earlier shown that inhibitors of NOS (N(omega)-nitro-L-arginine methyl ester [L-NAME], 7-nitroindazole [7-NI]) block cocaine-induced behavioral sensitization. In the present study, the effects of melatonin on cocaine behavior were studied. A single injection of melatonin markedly augmented cocaine-induced locomotor activity. Rats injected daily with melatonin prior to cocaine injections failed to elicit cocaine sensitization. These behavioral effects of melatonin do not completely mimic those of other NOS inhibitors, suggesting that the effects of melatonin on cocaine behavior are mediated by both NOS-dependent as well as NOS-independent mechanisms.

Analysis of Variance↗
PubMed2000

Developmental maturation of the N-methyl-D-aspartic acid receptor channel complex in postnatal rat brain.

The N-methyl-D-aspartate (NMDA) receptor plays an important role in developmental plasticity. Previous studies have reported differences between the NMDA receptor-channel complex in the rat pup brain and the adult brain. In the present study, modulation of the NMDA channel complex as a function of age was measured to determine when the temporal switching of the NMDA receptor from the immature form to the adult mature form takes place. [(3)H]MK-801 binding was measured in the rat forebrain from postnatal day 1 to day 21. Our data suggest the presence of two types of NMDA receptors - an immature type and a mature type. The immature NMDA receptor, seen during the early postnatal period (day 1-day 14) is highly sensitive to spermidine, L-glutamate alone potentiates [(3)H]MK-801 binding, and glycine failed to potentiate an L-glutamate-induced increase in [(3)H]MK-801 binding. During the late postnatal period (after day 14) spermidine alone did not increase [(3)H]MK-801 binding as potently as it did during the early postnatal period, high-affinity [(3)H]MK-801 binding was not seen in the presence of L-glutamate alone, and L-glutamate and glycine or L-glutamate and spermidine or L-glutamate, glycine and spermidine together, significantly increased [(3)H]MK-801 binding in a manner similar to that reported in the adult brain. Together, the pharmacology of the NMDA receptor during the early postnatal period differs from the adult-like receptor seen during the late postnatal period, and that in rats the apparent switching of the NMDA receptor from the immature type to the mature type takes place after the second postnatal week.

Age Factors↗
PubMed1999

A chimeric receptor that selectively targets membrane-bound carcinoembryonic antigen (mCEA) in the presence of soluble CEA.

Chimeric T cell receptors with specificity for tumor-associated antigens are successfully used to target T cells to tumor cells. The efficacy of this approach, however, is reduced by soluble antigen that is frequently present in high serum concentrations. To overcome this situation, we constructed an anti-CEA chimeric receptor whose extracellular moiety is composed of a humanized single chain antibody fragment (scFv) derived from the anti-CEA mAb BW431/26 and the CH2/CH3 constant domains of human IgG. The intracellular moiety consists of the gamma-signaling chain of the human Fc epsilon RI receptor constituting a completely humanized chimeric receptor. After transfection, the humBW431/26 scFv-CH2CH3-gamma receptor is expressed as a homodimer on the surface of MD45 T cells. Co-incubation with CEA+ tumor cells specifically activates grafted MD45 T cells indicated by IL-2 secretion and cytolytic activity against CEA+ tumor cells. Notably, the efficacy of receptor-mediated activation is not affected by soluble CEA up to 25 micrograms/ml demonstrating the usefulness of this chimeric receptor for specific cellular activation by membrane-bound CEA even in the presence of high concentrations of CEA, as found in patients during progression of the disease.

Carcinoembryonic Antigen↗
PubMed1999

Characterization of a chimeric T-cell receptor with specificity for the Hodgkin's lymphoma-associated CD30 antigen.

Recombinant receptors with antibody-like specificity for tumor-associated antigens were shown to direct specifically T cells to target tumor cells. Hodgkin and Reed-Sternberg cells, the malignant cell population in Hodgkin's lymphoma, express high amounts of the cell surface antigen CD30. An anti-CD30 T-cell receptor with cellular activation properties is expected to graft T cells with specificity to Hodgkin cells. Here, the authors characterize a chimeric T-cell receptor with an extracellular domain consisting of the single-chain antibody fragment HRS3-scFv with specificity for the CD30 antigen and intracellular domain of the signal transducing part of the Fc-epsilon-I-gamma receptor. The HRS3-scFv was derived from the monoclonal anti-CD30 antibody HRS3 and retained specificity for the CD30 antigen. The recombinant HRS3-scFv-gamma receptor was expressed under control of the RSV-LTR after transfection into MD45 T-cells. The chimeric receptor protein is detected and analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation. Expression of the chimeric receptor converts MD45 T cells to specificity for CD30+ lymphoma cells. Specific cross-linking of the chimeric receptor with antigen resulted in cytolytic reactivity against CD30+ tumor cells in vitro. The results demonstrate that the chimeric receptor HRS3-scFv-gamma converts T cells to a specific MHC-unrestricted cytolytic response against CD30+ tumor cells offering an alternative strategy in cellular immunotherapy of Hodgkin's disease.

Animals↗
PubMed1999

Female gonadal hormones differentially modulate cocaine-induced behavioral sensitization in Fischer, Lewis, and Sprague-Dawley rats.

Evidence suggests the existence of genetic differences in cocaine sensitization in male rats. The present study was undertaken to investigate cocaine sensitization in female rats of genetically distinct inbred (Fischer 344 and Lewis) and outbred (Sprague-Dawley) strains. All female rats were bilaterally ovariectomized and randomly assigned to one of four experimental groups: 1) estradiol benzoate group, 2) progesterone group, 3) estradiol benzoate-plus-progesterone group, and 4) ovariectomized group. Additional controls included sham-operated female rats, female rats that received a single oil injection, and female rats that received repeated oil injections. To determine gender-related differences in the acute and chronic effects of cocaine, data obtained from female rats were compared with those from strain- and weight-matched male rats. Estradiol benzoate-plus-progesterone female rats showed greater locomotor effect in response to an acute dose of cocaine and had more robust sensitization in response to repeated cocaine than did male rats. The bilateral removal of ovaries abolished cocaine sensitization. In all strains of rats studied, progesterone alone did not alter the ovariectomy-induced attenuation of cocaine behavior, but estrogen alone restored cocaine-induced behavioral sensitization. There were significant strain effects on the degree of gonadal hormonal-induced modulation of cocaine sensitization in female rats. Female Lewis rats were extremely sensitive to repeated-cocaine effects, whereas the Fischer 344 female rats showed only marginal effects. The Sprague-Dawley rats ranked intermediate in their behavioral sensitivity. The present study strongly supports the hypothesis that female rats are more sensitive to both acute and chronic behavioral effects of cocaine than are male rats and that the effects are strain dependent. It also shows that estrogen plays an important role in the increased sensitivity of female rats to cocaine sensitization. Together, these data indicate significant interactions between ovarian steroid hormones and genetic factors in cocaine-induced behavioral effects.

Animals↗
PubMed1998

Isolation of single chain antibody fragments with specificity for cell surface antigens by phage display utilizing internal image anti-idiotypic antibodies.

Recombinant single chain antibody fragments (scFv) with specificity for membrane-bound antigens can be isolated by phage display techniques. The strategy involves selection of recombinant phage antibodies by binding to cells expressing the respective antigen. This results frequently in high nonspecific adherence of phages to cellular membranes. To resolve the problem we have made use of an internal image anti-idiotypic antibody mimicking the membrane-bound CD30 antigen and successfully isolated scFv fragments with specificity for CD30. The cDNA coding for the immunoglobulin heavy and light chain variable regions of the anti-CD30 monoclonal antibody (mAb) HRS3 was expressed by phage display techniques. Recombinant HRS3-scFv phages were efficiently enriched by one cycle of panning on the internal image anti-idiotypic mAb 9G10. The isolated HRS3-scFv clone retained the binding specificity of the parental mAb HRS3 to the internal image anti-idiotypic mAb 9G10 as well as to an anti-idiotypic mAb without the internal image. Furthermore HRS3-scFv reacted with recombinant and cell-bound CD30 antigen, respectively. Binding of scFv fragments to anti-idiotypic mAbs will provide a versatile strategy for the efficient isolation of recombinant antibody fragments.

Antibodies, Anti-Idiotypic↗
PubMed1998

Repeated neonatal phencyclidine treatment impairs performance of a spatial task in juvenile rats.

The present study was designed to determine whether repeated postnatal blockade of N-methyl-D-aspartate (NMDA) channel produces cognitive deficit in juvenile rats. Rats receive phencyclidine (PCP) intraperitoneally (i.p.) from postnatal Day 5 and continued daily till Day 15. On Day 28, saline- and PCP-treated rats were trained in the Morris water maze task. PCP-treated rats performed as well as the saline-treated rats on the first day of testing, but on the second day of testing they did significantly poorly compared to saline-treated controls. These data suggest that chronic postnatal NMDA channel blockade by PCP impairs processes that enable rats to retain spatial information.

Aging↗
PubMed1998

An anti-CD30 chimeric receptor that mediates CD3-zeta-independent T-cell activation against Hodgkin's lymphoma cells in the presence of soluble CD30.

Hodgkin's lymphoma patients fail to establish an efficient cellular response against CD30+ Hodgkin/Reed-Sternberg cells. An impaired T-cell receptor/CD3-zeta-mediated activation of T cells is thought to be involved in this situation. We here present a chimeric anti-CD30 receptor that mediates MHC and T-cell receptor/CD3-zeta-independent T-cell activation against CD30+ lymphoma cells even in the presence of soluble CD30. The receptor consists of the binding domain of the monoclonal antibody HRS3 and the signaling unit of the Fc epsilonRI-receptor gamma-chain. After expression in MD45 T cells, receptor cross-linking with immobilized anti-idiotypic monoclonal antibody and CD30+ cells, respectively, results in increased interleukin 2 secretion and specific cytolysis of CD30+ Hodgkin's lymphoma cells. Soluble CD30 in concentrations up to 6000 units/ml did not interfere with cellular activation induced by membrane-bound antigen. This demonstrates the feasibility of the chimeric anti-CD30-scFv-gamma receptor in CD30+ lymphoma cell targeting, even in the presence of as high concentrations of soluble CD30 as are found in patients during progression of the disease.

CD3 Complex↗
PubMed1998

Chimeric anti-TAG72 receptors with immunoglobulin constant Fc domains and gamma or zeta signalling chains.

We recently described the generation and expression of a chimeric T cell receptor with specificity for the tumor antigen TAG72 consisting of the single chain antibody (scFv) B72.3-scFv and the gamma chain of the FcepsilonRI receptor. The corresponding chimeric receptor containing the zeta chain of the TCR as signalling unit is not functionally expressed reflecting that the requirements for functional expression of chimeric receptors containing the gamma signalling chain are apparently different compared to those containing the CD3zeta signalling chain of the TCR. We describe a novel set of chimeric anti-TAG72 receptors including in their extracellular moiety the constant immunoglobulin CH2/3 domains that allow stable expression of chimeric gamma as well as zeta receptors. We designed anti-TAG72 receptors that consist of a scFv fragment derived from an anti-TAG72 second generation antibody (CC49) and of the CH2/3 domains of the human IgG and intracellularily either of the zeta or gamma signalling chain. The recombinant CC49-CH2/3-zeta and CC49-CH2/3-gamma DNA, respectively, was transfected into MD45 T cells and expressed under control of the RSV LTR. Both receptors were found on the cell membrane of transfected cells as demonstrated by flow cytometry analysis using an anti-human IgG Fc antibody directed to the CH2/3 immunoglobulin domains of the chimeric receptor. Specific cross-linking of the chimeric zeta as well as the gamma receptor by antigen or anti-human Ig antibodies resulted in specific activation of transfected cells. Our results demonstrate that both the gamma chain and the zeta chain++ containing receptor are stably expressed and convert T cells to specificity for the TAG72 antigen. This receptor design will facilitate efficient generation of genetically modified peripheral T cells and may provide valuable tools for the cellular immunotherapy of TAG72+ tumors.

Animals↗
PubMed1998

Generation of the single chain antibody fragment conserves the idiotypic profile of the anti-CD30 monoclonal antibody HRS3.

Recombinant single chain antibody fragments (scFv) derived by combining immunoglobulin VL and VH regions provide valuable antibody-like reagents. A number of them are shown to have retained the antigen specificity of the parental monoclonal antibody (MoAb). Little is known about the idiotypic profile of scFv fragments compared with that of the parental MoAb. To address this question we analysed the idiotypic profile of a scFv that was derived by phage-display techniques from the anti-CD30 MoAb HRS3. We assayed (i) binding of HRS3-scFv to recombinant CD30-Fc antigen and to four different anti-idiotypic MoAbs defining at least three different idiotopes on HRS3, and (ii) cross-competition with the parental MoAb HRS3 and the closely related anti-CD30 MoAb HRS4. The assays revealed that the HRS3-scFv fragment exhibits the same specificity for both CD30 antigen and the tested anti-idiotypic MoAbs compared with the parental MoAb demonstrating that the recombinant scFv fragment has retained the complete idiotope of the parental MoAb.

Animals↗
PubMed1997

Effects of nitric oxide synthase inhibitors on cocaine sensitization.

Behavioral sensitization to cocaine was tested for in rats pretreated with a nitric oxide (NO) synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME) or 7-nitro indazole (7-NI). A 5-day pre-exposure to once daily cocaine (15 mg/kg, i.p.) injections yielded sensitization to cocaine (15 mg/kg)-induced behavioral activation. Pretreatment injections of L-NAME (100 mg/kg) or 7-NI (30 mg/kg), administered 30 min before each cocaine pre-exposure injection, acutely inhibited cocaine-induced behavioral activation. No sensitization was found after L-NAME pretreatment in a protocol with a 3-day withdrawal between pre-exposure and test cocaine injections. With a 10-day withdrawal period, cocaine sensitization was prevented by L-NAME or 7-NI pretreatment. These results after a 10-day withdrawal are unlikely to arise from deficient brain NO synthase activity on the test day. Instead, these findings suggest a role for NO in mechanisms underlying the development of cocaine sensitization. We conclude that NO participates in both the development of sensitization as well as the expression of cocaine-induced behavior in previously drug-naive animals.

Analysis of Variance↗
PubMed1997

Specific activation of resting T cells against tumour cells by bispecific antibodies and CD28-mediated costimulation is accompanied by Th1 differentiation and recruitment of MHC-independent cytotoxicity.

Specific activation of resting lymphocytes for tumour targeting can be achieved by bispecific monoclonal antibodies (bi-MoAbs) with specificity for tumour antigens and T cell-activating antigens in combination with a costimulatory anti-CD28 antibody. In this study we focus on the immunomodulatory function of an anti-CD3/CA19-9 bi-MoAb in combination with a costimulatory anti-CD28 antibody which may result not only in antigen-specific, T cell-mediated tumour cell lysis but also in recruitment of other cellular effector functions. In combination with costimulatory anti-CD28 antibodies, resting peripheral lymphocytes could be activated specifically to secrete high amounts of Th1 cytokines (IL-2, interferon-gamma (IFN-gamma)) characterizing a cellular immune response. In contrast, no IL-4 and only low amounts of IL-10 could be detected. Furthermore, bi-MoAb-mediated CA19-9-specific activation of T cells was accompanied by recruitment of MHC- and CA19-9-independent cytotoxicity, as was determined by lysis of different CA19-9-cell lines. This MHC-independent cytotxicity was mediated at least in part by activated natural killer (NK) cells, as depletion of CD16+ NK cells resulted in substantial decrease of cytotoxicity against CA19-9- targets. Our results indicate that specific activation of resting T cells with CD3-associated bi-MoAbs in combination with an anti-CD28 antibody leads to a Th1 differentiation pathway and is accompanied by recruitment of MHC-independent lymphokine-activated killer (LAK) cell cytotoxicity which can possibly be directed against a heterogeneous tumour.

Antibodies, Bispecific↗
PubMed1997

T cell targeting of TAG72+ tumor cells by a chimeric receptor with antibody-like specificity for a carbohydrate epitope.

BACKGROUND & AIMS: Chimeric receptors with specificity for defined tumor antigens are valuable tools for targeting cytolytic T cells specifically to tumor cells. The aim of this study, for the situation of gastrointestinal cancer, was to investigate the generation of a chimeric T cell receptor that specifically binds the tumor antigen TAG72 (CA72-4) and transmits a signal for cellular activation. METHODS: A single-chain antibody (scFv) was derived from the monoclonal anti-TAG72 antibody B72.3 by phage display techniques (B72.3-scFv) and fused to the signaling unit of the Fc epsilon-RI receptor gamma chain, resulting in a chimeric signaling receptor, B72.3-scFv-gamma. RESULTS: The B72.3-scFv and the chimeric B72.3-scFv-gamma receptor bound specifically to the TAG72 antigen. After transfection, T cells expressing the chimeric B72.3-scFv-gamma specifically recognized TAG72 positive cells. Cross-linking of the chimeric receptor with antigen resulted in interleukin 2 release and cytolytic activity against TAG72 positive tumor cells in vitro. CONCLUSIONS: T cells equipped with the chimeric anti-TAG72 receptor can be specifically activated to target and lyse TAG72 positive gastrointestinal tumor cells.

Animals↗