Biomedical subjects

S Sankar

Publications and source records attributed to S Sankar.

At least 19 recordsLinked to original sources

PubMed2003

Antifertility activity of Derris brevipes variety coriacea.

Traditional physicians in and around Kotagiri village near Ootacamund, use a mixture of powdered roots of Cassia occidentalis, Derris brevipes variety coriacea and Justicia simplex to control female fertility. A mixture of powdered roots of these three plants, powdered root of Derris brevipes variety coriacea and its ethanolic extract were screened for antifertility activity in proven fertile female rats at 200 and 600 mg/kg body weight, respectively and given orally on D(1-7) of pregnancy. Both doses of the root powder of Derris brevipes variety coriacea showed 50% anti-implantation activity and also a significant reduction in the number of litters born. The ethanolic extract exhibited 40% anti-implantation activity when given orally at 600 mg/kg body weight. The rats, which continued their pregnancy, did not deliver any litters after their full term. Hence, the combined antifertility (anti-implantation and abortifacient) activity of the ethanolic extract was 100%. The results suggest that the ethanolic extract possesses more abortifacient type effect than the anti-implantation activity. The ethanolic extract also exhibited weak estrogenic activity when given alone and tested in immature ovariectomised female albino rats. But, when given along with ethinyl estradiol, it exhibited slight antiestrogenic activity. Histological and biochemical estimations were carried out to confirm this.

Abortifacient Agents↗

PubMed2002

pH-sensitive liposomes: mechanism of triggered release to drug and gene delivery prospects.

A growing amount of literature describes the development and applications of novel targeting and/or release triggering schemes to improve the therapeutic index of drugs encapsulated within liposomes. The composition of liposomal systems can be modified to facilitate site specific release in response to environmental conditions, namely at the gross anatomical level, at the cellular or sub-cellular level. They are designed in order to release their contents in response to acidic pH within the endosomal system while remaining stable in plasma thus improving the cytoplasmic delivery of various polar materials and macromolecules such as anti-tumor drugs, toxins, proteins and DNA. This review covers various aspect of research on pH-sensitive liposomes.

Animals↗

PubMed2001

Late presentation of congenital factor V deficiency--a case report.

Congenital factor deficiency is a rare coagulation disorder, which is inherited in an autosomal recessive manner. The severity of bleeding symptoms in general is only partially related to the degree of factor V deficiency in plasma. In this report, a boy presenting with hemarthrosis in his late adolescence due to congenital factor V deficiency is reported.

Adolescent↗

PubMed2000

Studies on the structure of the complex of the boron neutron capture therapy drug, L-p-boronophenylalanine, with fructose and related carbohydrates: chemical and 13C NMR evidence for the beta-D-fructofuranose 2,3,6-(p-phenylalanylorthoboronate) structure.

The complex of L-L-boronophenylalanine (L-p-BPA) with fructose has been used for the past 5 years in clinical trials of boron neutron capture therapy to treat both melanoma and glioblastoma multiforme. However, the structure of this complex in water buffered at physiologic pH has not been established. In the (1)H NMR spectra (D(2)O buffered at pD 7.4) of the complex of L-p-BPA with various carbohydrates, the upfield chemical shifts of the aromatic protons of L-p-BPA confirm that the boron atom is negatively charged and tetrahedral. In the (13)C NMR spectrum of the complex of L-p-BPA with U-(13)C labeled fructose, the chemical shifts and (1)J(CC) coupling constants are consistent with fructose adopting the beta-D-fructofuranose form. In addition, the (1)J(CC) coupling constants along with the binding constants measured for L-p-BPA with a series of monosaccharides and disaccharides seem to suggest that the beta-D-fructofuranose 2,3,6-(p-phenylalanylorthoboronate) structure strongly predominates, with free L-p-BPA and fructose the only other species detected.

Boron Compounds↗

PubMed1999

HCPTPA, a protein tyrosine phosphatase that regulates vascular endothelial growth factor receptor-mediated signal transduction and biological activity.

Angiogenesis is a tightly controlled process in which signaling by the receptors for vascular endothelial growth factor (VEGF) plays a key role. In order to define signaling pathways downstream of VEGF receptors (VEGFR), the kinase domain of VEGFR2 (Flk-1) was used as a bait to screen a human fetal heart library in the yeast two-hybrid system. One of the signaling molecules identified in this effort was HCPTPA, a low molecular weight, cytoplasmic protein tyrosine phosphatase. Although HCPTPA possesses no identifiable phosphotyrosine binding domains (i.e. SH2 or phosphotyrosine binding domains), it bound specifically to active, autophosphorylated VEGFR2 but not to a mutated, kinase-inactive VEGFR2. Recombinant VEGFR2 and endogenous VEGFR2 were substrates for recombinant HCPTPA, and HCPTPA was co-expressed with VEGFR2 in endothelial cell lines, suggesting that HCPTPA may be a negative regulator of VEGFR2 signal transduction. To pursue this possibility, an adenovirus directing the expression of HCPTPA was constructed. When used to infect cultured endothelial cells, this adenovirus directed high level expression of HCPTPA that resulted in impairment of VEGF-mediated VEGFR2 autophosphorylation and mitogen-activated protein kinase activation. Adenovirus-mediated overexpression of HCPTPA also inhibited VEGF-induced cellular responses (endothelial cell migration and proliferation) and inhibited angiogenesis in the rat aortic ring assay. Taken together, these findings indicate that HCPTPA may be an important regulator of VEGF-mediated signaling and biological activity. Potential interactions with other signaling pathways and possible therapeutic implications are discussed.

Animals↗

PubMed1998

Expression of Tie2/Tek in breast tumour vasculature provides a new marker for evaluation of tumour angiogenesis.

Endothelial receptor tyrosine kinases may play important roles in pathological vascular growth, particularly in tumours. In this study, immunohistochemistry was used to evaluate the expression of a novel endothelial receptor tyrosine kinase, Tie2/Tek, in the endothelium of vascular 'hotspots' in normal breast tissue (n = 10), benign breast lesions (n = 10) and in breast tumours (n = 123). Tie2 expression was detected in the endothelium of all breast tissues examined. However, the strongest expression of Tie-2 was seen in vascular 'hot spots' within the inflammatory infiltrate at the periphery of invasive tumours. Moreover, the proportion of Tie2-positive vessels (Tie2 counts/CD31 counts) was significantly higher in breast tumours than the proportion of Tie2-positive vessels in either normal breast tissue or benign breast lesions (P = 0.004 and 0.0001 respectively). These data are consistent with a role for Tie2 in tumour angiogenesis and demonstrate the potential use of Tie2 expression as a novel marker of the tumour vasculature.

Antibodies, Monoclonal↗

PubMed1998

Training environment for inferior vena caval filter placement.

This paper describes a Virtual Environment system designed to aid in training interventional radiologists in inferior vena cava filter placement. It is being developed as part of a VE simulator for a number of surgical and interventional radiology procedures at the Laboratory for Advanced Computer Applications in Medicine at the George Washington University. In this procedure a filter is placed in the inferior vena cava to prevent blood clots from the lower portion of the body from reaching the lungs and causing a pulmonary embolus. The simulation is designed to provide both tutorial and testing modes for the filter placement procedure.

Algorithms↗

PubMed1998

Inhibition of tumor growth by targeting tumor endothelium using a soluble vascular endothelial growth factor receptor.

Vascular endothelial growth factor (VEGF) is a leading candidate for an endogenous mediator of tumor angiogenesis. Recently, two endothelial cell surface receptors, flk-1 and flt-1, have been shown to mediate the angiogenic activities of VEGF. In this study, we have evaluated whether a soluble VEGF receptor could suppress tumor angiogenesis and thereby inhibit tumor growth. A soluble VEGF receptor was constructed by fusing the entire extracellular domain of murine flk-1 to a six-histidine tag at the COOH terminus (ExFlk.6His). In vitro, recombinant ExFlk.6His protein bound VEGF with high affinity (Kd, 16 nM) and blocked receptor activation in a dose-dependent manner and inhibited VEGF-induced endothelial cell proliferation and migration. ExFlk.6His bound to endothelial cells only in the presence of VEGF, and cell surface cross-linking yielded a high molecular weight complex consistent with the VEGF-mediated formation of a heterodimer between ExFlk.6His and the endogenous VEGF receptor. In vivo, ExFlk.6His potently inhibited corneal neovascularization induced by conditioned media from a rat mammary carcinoma cell line (R3230AC). Moreover, when ExFlk.6His protein was administered into a cutaneous tumor window chamber concomitantly with R3230AC carcinoma transplants, tumor growth was inhibited by 75% (P < 0.005) and vascular density was reduced by 50% (P < 0.002) compared with control-treated tumors. These results demonstrate the potential of ExFlk.6His to inhibit VEGF action by a potent "dominant-negative" mechanism and suggest that targeting VEGF action using a soluble receptor may be an effective antiangiogenic therapy for cancer and other "angiogenic" diseases.

Animals↗

PubMed1996

Modulation of transforming growth factor beta receptor levels on microvascular endothelial cells during in vitro angiogenesis.

Microvascular endothelial cells (RFCs) cultured in two-dimensional (2D) cultures proliferate rapidly and exhibit an undifferentiated phenotype. Addition of transforming growth factor beta1 (TGFbeta1) increases fibronectin expression and inhibits proliferation. RFCs cultured in three-dimensional (3D) type I collagen gels proliferate slowly and are refractory to the anti-proliferative effects of TGF beta1. TGF beta1 promotes tube formation in 3D cultures. TGF beta1 increases fibronectin expression and urokinase plasminogen activator (uPA) activity and plasminogen activator inhibitor-1 (PAI-1) levels in 3D cultures. Since the TGF beta type I and II receptors have been reported to regulate different activities induced by TGF beta1, we compared the TGF beta receptor profiles on cells in 2D and 3D cultures. RFCs in 3D cultures exhibited a significant loss of cell surface type II receptor compared with cells in 2D cultures. The inhibitory effect of TGF beta1 on proliferation is suppressed in transfected 2D cultures expressing a truncated form of the type II receptor, while its stimulatory effect on fibronectin production is reduced in both 2D and 3D transfected cultures expressing a truncated form of the type I receptor. These data suggest that the type II receptor mediates the antiproliferative effect of TGF beta1 while the type I receptor mediates the matrix response of RFCs to TGF beta1 and demonstrate that changes in the matrix environment can modulate the surface expression of TGF beta receptors, altering the responsiveness of RFCs to TGF beta1.

Animals↗

PubMed1995

Expression of transforming growth factor type III receptor in vascular endothelial cells increases their responsiveness to transforming growth factor beta 2.

Bovine aortic endothelial cells (BAECs) express both type I and type II receptors for transforming growth factor beta (TGF beta). These cells respond to TGF beta 1 but are relatively refractory to another isoform of TGF beta, termed TGF beta 2. TGF beta s are thought to signal through receptor complexes composed of type I and/or type II receptors, both of which appear to be functional serine-threonine kinases. The TGF beta type III receptor, on the other hand, does not seem to have any direct signaling capacity. We have now stably transfected BAECs with the type III receptor cDNA. These cells displayed surface expression of the type III receptor protein, as determined by cross-linking with iodinated TGF beta 1 and immunoprecipitation with antibodies to the type III receptor protein. Transfected BAECs exhibit increased responsiveness to TGF beta 2 by several different criteria including an increase in plasminogen activator inhibitor-1 protein and inhibition of migration and proliferation. Thus, the type III receptor protein may play a role in presenting TGF beta 2 to the type II receptor and increase responsiveness to TGF beta 2 to a level comparable to that of TGF beta 1.

Animals↗

PubMed1995

Modulation of cell spreading and migration by pp125FAK phosphorylation.

We provide evidence for both matrix-dependent and pp60v-src tyrosine kinase-dependent modulation of cell migration via tyrosine phosphorylation of pp125FAK, a focal adhesion kinase, thought to be involved in integrin-mediated signaling. Enhanced pp125FAK tyrosine phosphorylation and cell spreading was associated with decreased migration. Cells plated on type I collagen were less spread and exhibited lower levels of pp125FAK tyrosine phosphorylation and faster migration rates compared with cells on fibronectin that were well spread, which exhibited enhanced levels of pp125FAK tyrosine phosphorylation and slower migration rates. Inside-out signaling via expression of pp60v-src or its kinase-negative mutant caused a decrease in cell migration by changing the extent of pp125FAK tyrosine phosphorylation to above or below the levels obtained with control cells plated on fibronectin. Hence, pp125FAK tyrosine phosphorylation appears to play a role in the signaling cascade pathway involved in regulation of extracellular matrix-modulated, integrin-mediated cell migration.

3T3 Cells↗

PubMed1993

Binding of encephalomyocarditis virus RNA polymerase to the 3'-noncoding region of the viral RNA is specific and requires the 3'-poly(A) tail.

An in vitro RNA bandshift assay has been developed to demonstrate the binding of purified recombinant encephalomyocarditis (EMC) virus RNA-dependent RNA polymerase (3Dpol) to the 3'-noncoding region (NCR) and 30 nucleotides of the adjacent 3'-terminal poly(A) tail (3'-NCR(A)) of EMC virus RNA. The binding of 3Dpol to the 3'-NCR(A) fragment was specific since four other unrelated proteins including an RNA polymerase did not bind, and unlabeled 3'-NCR(A), but not alpha-globin mRNA, tRNA, or pure poly(A), competed with radiolabeled 3'-NCR(A) for binding. Surprisingly, 3Dpol failed to bind to the 3'-NCR of EMC virus RNA lacking the poly(A) tail. The results together show that EMC virus RNA template specificity depends only on 3Dpol, the 3'-NCR, and the poly(A) tail. This suggests that 3'-poly(A) is essential for viral RNA template selection by the EMC virus RNA polymerase.

Base Sequence↗

PubMed1992

Point mutations which drastically affect the polymerization activity of encephalomyocarditis virus RNA-dependent RNA polymerase correspond to the active site of Escherichia coli DNA polymerase I.

The inhibitor sensitivity and functional domains of recombinant encephalomyocarditis (EMC) virus RNA-dependent RNA polymerase (3Dpol) have been extensively analyzed. The inhibitor profiles of EMC virus 3Dpol and Escherichia coli DNA-dependent RNA polymerase are distinct, and experiments with substrate analogs indicate that EMC virus 3Dpol lacks reverse transcriptase activity. Twenty amino acid substitutions were engineered in EMC virus 3Dpol based on sequence alignments of viral RNA-dependent RNA polymerases that identified conserved amino acid residues within motifs. Ten out of 17 conservative substitutions within the four most conserved motifs reduced the RNA polymerase activity of the mutants to 0-6% of the activity of the wild-type enzyme, demonstrating the importance of these amino acids in the structure and/or function of EMC virus 3Dpol. Remarkably, 5 of the 10 mutations in EMC virus 3Dpol which had the most drastic effect on its RNA polymerase activity (D240E, S293T, N302Q, G332A, and D333E) were found to correspond to active site residues in E. coli DNA-dependent DNA polymerase I (Klenow). Our results reveal that a basic structural and functional framework is conserved in the most distantly related classes of nucleic acid polymerases and demonstrate the validity of modeling the active site of an RNA-dependent RNA polymerase on the known structure of a DNA polymerase.

Amino Acid Sequence↗

PubMed1991

Proton nuclear magnetic resonance study of the solution distal histidine orientation in monomeric Chironomus thummi thummi cyanomet hemoglobins. Dynamic stability of the heme pocket as monitored by labile proton exchange.

The 1H nuclear magnetic resonance spectral characteristics of the cyano-Met form of Chironomus thummi thummi monomeric hemoglobins I, III and IV in 1H2O solvent are reported. A set of four exchangeable hyperfine-shifted resonances is found for each of the two heme-insertion isomers in the hyperfine-shifted region downfield of ten parts per million. An analysis of relaxation, exchange rates and nuclear Overhauser effects leads to assignments for all these resonances to histidine F8 and the side-chains of histidine E7 and arginine FG3. It is evident that in aqueous solution, the side-chain from histidine E7 does not occupy two orientations, as found for the solid state, rather the histidine E7 side-chain adopts a conformation similar to that of sperm whale myoglobin or hemoglobin A, oriented into the heme pocket and in contact with the bound ligand. Evidence is presented to show that the allosteric transition in the Chironomus thummi thummi hemoglobins arises from the "trans effect". An analysis of the exchange with bulk solvent of the assigned histidine E7 labile proton confirms that the group is completely buried within the heme pocket in a manner similar to that found for sperm whale cyano-Met myoglobin, and that the transient exposure to solvent is no more likely than in mammalian myoglobins with the "normal" distal histidine orientation. Finally, a comparison of solvent access to the heme pocket of the three monomeric C. thummi thummi hemoglobins, as measured from proton exchange rates of heme pocket protons, is made and correlated to binding studies with the diffusible small molecules such as O2.

Animals↗

PubMed1991

Expression, purification, and properties of recombinant encephalomyocarditis virus RNA-dependent RNA polymerase.

Encephalomyocarditis (EMC) virus RNA-dependent RNA polymerase was expressed in Escherichia coli as a fusion protein with glutathione S-transferase (GST), which allowed easy purification of the fusion protein by affinity chromatography on immobilized glutathione. Inclusion of a thrombin cleavage site between the GST carrier and the viral enzyme facilitated the release of purified mature EMC virus RNA polymerase from the GST carrier by proteolysis with thrombin. The purified recombinant enzyme has a molecular mass of about 52 kDa and is recognized by polyclonal immune serum raised against a peptide sequence corresponding to the C-terminal region of the protein. The recombinant enzyme comigrates with immunoprecipitated EMC virus RNA polymerase from infected mouse L929 cell extracts when run in parallel lanes on a sodium dodecyl sulfate-polyacrylamide gel. The enzyme exhibits rifampin-resistant, poly(A)-dependent poly(U) polymerase activity and RNA polymerase activity, which are both oligo(U) dependent. Template-size products are synthesized in in vitro reactions with EMC virus genomic RNA or globin mRNA. The availability of recombinant EMC virus RNA polymerase in a purified form will allow biochemical analysis of its role in the replication of the virus as well as structure-function studies of this unique class of enzyme.

Amino Acid Sequence↗

PubMed1989

Antisense oligonucleotide inhibition of encephalomyocarditis virus RNA translation.

We report the inhibition of encephalomyocarditis virus (EMCV) RNA translation in cell-free rabbit reticulocyte lysates by antisense oligonucleotides (13-17-base oligomers) complementary to (a) the viral 5' non-translated region, (b) the AUG start codon and (c) the coding sequence. Our results demonstrate that the extent of translation inhibition is dependent on the region where the complementary oligonucleotides bind. Non-complementary and 3'-non-translated-region-specific oligonucleotides had no effect on translation. A significant degree of translation inhibition was obtained with oligonucleotides complementary to the viral 5' non-translated region and AUG initiation codon. Digestion of the oligonucleotide:RNA hybrid by RNase H did not significantly increase translation inhibition in the case of 5'-non-translated-region-specific and initiator-AUG-specific oligonucleotides; in contrast, RNase H digestion was necessary for inhibition by the coding-region-specific oligonucleotide. We propose that (a) 5'-non-translated-region-specific oligonucleotides inhibit translation by affecting the 40S ribosome binding and/or passage to the AUG start codon, (b) AUG-specific oligonucleotides inhibit translation initiation by inhibiting the formation of an active 80S ribosome and (c) the coding-region-specific oligonucleotide does not prevent protein synthesis because the translating 80S ribosome can dislodge the oligonucleotide from the EMCV RNA template.

Animals↗

PubMed1988

Expression and processing of human rhinovirus type 14 polypeptide precursors in Escherichia coli maxicells.

Human rhinovirus serotype-14 (HRV-14) cDNA, encompassing 87.9% of the coding region, was subcloned in an Escherichia coli expression vector, generating plasmid pKCC101. HRV-14 polypeptides encoded by pKCC101 were synthesized in E. coli maxicells. Pulse-chase experiments with pKCC110, a smaller derivative of pKCC101 containing the protease 3C coding region, have clearly demonstrated the proteolysis of a 55-kDa precursor to several polypeptides, including a doublet with the expected size of protease 3C (20 kDa). The proteolysis of the 55-kDa precursor polypeptide was prevented by ZnCl2, a known inhibitor of picornavirus 3C proteases. Results with a derivative of pKCC110 (pKCC115) which is partially deleted for the protease 3C sequence, support the idea that the doublet proteins are specified by the protease 3C coding region. Taken together, our investigations indicate that the precursor form of protease 3C must be responsible for its own cleavage.

Amino Acid Sequence↗

PubMedDate not supplied

Sinonasal carcinoma masquerading as fungal sinusitis.

A 26-year-old man presented with swelling of his face and nose of three months duration. He had multiple hyperpigmented, hyperkeratotic plaques over the swelling, of one-month duration and an erythematous indurated plaque below the left nostril for two weeks. Based on a biopsy taken from the antral mass with special stain for fungus, he was treated as fungal sinusitis with intravenous amphotericin-B, but the lesion did not regress. Later a skin biopsy from the indurated lesion showed moderately differentiated squamous cell carcinoma. A diagnosis of sinonasal carcinoma was made and chemotherapy was started.

Adult↗