Search PubMed⌕ Search

Biomedical subjects

S Ramakrishnan

Publications and source records attributed to S Ramakrishnan.

At least 109 records · Page 6Linked to original sources
PubMed1996

Prevention of postoperative adhesions by an antibody to vascular permeability factor/vascular endothelial growth factor in a murine model.

OBJECTIVE: Our purpose was to test the ability of an antiserum to vascular permeability factor/vascular endothelial growth factor to inhibit postoperative adhesion formation in a murine model. STUDY DESIGN: After a standardized peritoneal injury, 28 Balb/c mice were randomized and treated intraperitoneally with either vascular permeability factor antiserum (n = 14) or preimmune serum (n = 14) at the time of abdominal closure. Mice were killed on postoperative day 14, and the development of intraabdominal adhesions was determined. Adhesion scoring was based on an overall assessment of the extent, location, and type of adhesions present. Statistical analyses were performed with the Mann-Whitney and Fisher's exact tests. RESULTS: The mice treated with the vascular permeability factor antiserum had significantly lower adhesion scores than did the control group (mean +/- SD 1.5 +/- 0.9, median 1.0, vs control 2.5 +/- 0.7, median 3.0). When the groups were analyzed for the presence of grade 2 or 3 adhesions, the group treated with vascular permeability factor antiserum had a significantly lower incidence of advanced adhesions (38%, vs control 92%). CONCLUSION: This study demonstrates that the intraperitoneal administration of a neutralizing antiserum to vascular permeability factor/vascular endothelial growth factor limits postoperative adhesion formation. These observations, to the best of our knowledge, are the first to suggest a role for vascular permeability factor in the pathogenesis of adhesion formation.

Abdomen↗
PubMed1996

Preoperative evaluation of macrophage colony-stimulating factor levels in patients with endometrial cancer.

OBJECTIVE: Our purpose was to examine the relationship between preoperative serum levels of macrophage colony-stimulating factor, alone and in combination with CA 125, and the presence of prognostic clinicopathologic factors and subclinical metastases in women with endometrial cancer. STUDY DESIGN: Ninety-two women who underwent primary exploration for endometrial adenocarcinoma had preoperative serum samples evaluated for macrophage colony-stimulating factor and CA 125 levels. Multivariate analysis was used to determine the associations of surgicopathologic findings with macrophage colony-stimulating factor and CA 125 levels. Logistic regression analysis was used to identify factors associated with the risk of extrauterine disease. The association of macrophage colony-stimulating factor and CA 125 levels with stage, grade, and depth of myometrial invasion and histologic characteristics were analyzed with Fisher's two-tailed exact test. RESULTS: Elevated levels of macrophage colony-stimulating factor were not associated with depth of myometrial invasion, histologic grade, or histologic cell type; however, advanced stage (p = 0.02) and the presence of lymph node metastases (p = 0.04) were associated with elevated levels. Sensitivity and specificity of macrophage colony-stimulating factor for predicting extrauterine disease were 42% and 89%, respectively. If either an elevated macrophage colony-stimulating factor or an elevated CA 125 level was used to predict extrauterine disease, the sensitivity was increased to 67% but the specificity was decreased to 78%. Macrophage colony-stimulating factor elevations predicted lymph node metastases with a sensitivity of 50% and a specificity of 86%. A multivariate regression model showed CA 125 to be the most significant predictor of extrauterine disease; macrophage colony-stimulating factor also contributed prognostic information (p = 0.02). The sensitivity and specificity of the multivariate model for predicting extrauterine disease were 75% and 73%, respectively. CONCLUSION: Macrophage colony-stimulating factor and CA 125 are neither sensitive nor specific enough to be used as predictors of the presence or absence of extrauterine disease in patients with endometrial cancer.

Adenocarcinoma↗
PubMed1996

Effect of cotrimoxazole (Bactrim) on cholesterol metabolism.

Male albino rats when treated with antimicrobial cotrimoxazole (trimethoprim+sulphamethaoxazole) showed an elevation of plasma high density lipoprotein (HDL) cholesterol and lecithin cholesterol acyl transferase activity (LCAT). Very low density lipoprotein and low density lipoprotein (VLDL+S4, 5LDL) cholesterol levels were decreased. However, total blood cholesterol and aortic cholesterol levels were normal. There was decreased synthesis of cholesterol and its content in the liver. Intestinal cholesterol mobilisation (studied using [U-14C]glucose) towards lymph was normal in spite of decreased synthesis by intestines. Decreased fecal excretion of bile acids and neutral sterols and normal intestinal contribution may be mainly involved in the blood cholesterol homeostasis.

Animals↗
PubMed1996

Expression and purification of recombinant toxicshock-syndrome toxin I.

Toxic-shock-syndrome toxin I (TSSTI), an exotoxin produced by certain strains of Staphylococcus aureus, has been closely associated with the pathogenesis of toxic shock syndrome. Outside the context of its staphylococcal host, TSSTI may offer therapeutic uses. We report here a strategy for high-level expression and simplified purification of TSSTI. We have subcloned the coding region for TSSTI into a vector containing an inducible T7 promoter sequence and expressed the protein in an Escherichia coli host strain. The recombinant TSSTI protein contained ten sequential histidine residues (Histag) at its N-terminus, which enabled its efficient purification using nickel-agarose-affinity resin. Histag-TSSTI (H-TSSTI) was further purified to homogeneity using a size-exclusion column. By this system, 80 mg of highly purified H-TSSTI can be consistently obtained per litre of culture in under 3 days. H-TSSTI retained biological activity and was unaffected by the presence of the Histag, as measured in lymphocyte proliferation assays.

Animals↗
PubMed1996

Activation of rat thymocytes selectively upregulates the expression of somatostatin receptor subtype-1.

Somatostatin and other neuropeptides are known to modulate the proliferative capacity of immune cells. In the present study, we investigated the expression of Somatostatin receptor (SSTR) subtypes on rat thymocytes. RT-PCR analysis of fresh thymocytes showed significant levels of transcripts for the SSTR2 whereas transcripts for the SSTR1 and SSTR3 were not detectable. Interestingly, when the thymocytes were activated with low concentration of Phytohemagglutinin and interleukin 1, the transcript for SSTR1 was markedly increased. Lymphokine induced activation of thymocytes selectively upregulated the SSTR1 since, transcripts for SSTR2 remained the same after activation and SSTR3 was not detectable. PCR amplified fragment of SSTR1 from the activated thymocytes showed identical sequence to the rat brain receptor. The physiological significance of the increase of SSTR1 mRNA in thymocytes after activation remains to be elucidated but it may be possible that these two different subsets of receptors (SSTR1 and SSTR2) are involved in the modulation of thymocyte proliferation and differentiation.

Amino Acid Sequence↗
PubMed1995

Investigation of the structural requirements of the troponin C central helix for function.

The two globular Ca(2+)-binding domains of troponin C are connected by a three-turn, exposed central helix. The requirements of this helical linker for regulatory function are not fully understood. In the present work we investigated the structural requirement of the linker using a series of insertion mutations that differ in predicted flexibility. TnCinrc has a nine-residue flexible random coil insert, TnCinpp has a nine-residue rigid polyproline insert (three turns), and TnCin alpha h has a seven-residue insert with high potential of forming alpha-helix. TnCinrc and TnCinpp were defective in the activation of the regulated actomyosin ATPase activity in the presence of Ca2+ when compared to wild type or TnCin alpha h, suggesting that altering the flexibility of the central helix impairs the regulatory function of troponin C. TnCin alpha h, TnCinrc, and TnCinpp had 87% +/- 3, 62% +/- 3, and 58% +/- 2 of the wild type activity, respectively (n = 6). All insertions in the central helix resulted in elongation of molecule compared to wild type TnC as determined by Stokes' radius. The Ca(2+)-affinity, the Ca(2+)-dependence of the actomyosin ATPase, and the stability of the insertion mutants were similar to wild type. Deletions of up to two turns of the central helix have little effect on troponin C function [Dobrowolski, Z., Xu, G-Q., & Hitchcock-DeGregori, S. E. (1991) J. Biol. Chem. 266, 5703-5710]. In another mutant (TnCd11) the entire central helix, 87KEDAKGKSEEE97, was deleted. With TnCd11, activation of the actomyosin ATPase activity in the presence of Ca2+ was normal, but inhibition in the absence of Ca2+ was less effective. Interaction of TnCd11 with TnI was altered. There was a 2-fold excess of TnCd11 in reconstituted Tn complex, consistent with another report [Babu, A., Rao, V. G, Su, H., & Gulati, J. (1993) J. Biol. Chem. 268, 19232-19238]. Our results suggest that the native length and structure of the central helix are optimal for normal regulatory function and that connectivity alone is insufficient for TnC function.

Amino Acid Sequence↗
PubMed1995

A novel method to purify recombinant vascular endothelial growth factor (VEGF121) expressed in yeast.

VEGF is a potent mitogen for vascular endothelial cells in vitro and acts as an angiogenic factor in vivo. VEGF121 differs from the other isoforms in that it lacks the heparin-binding domain. To study the potential differences in biological functions of the VEGF isoforms, we cloned and expressed VEGF121 in a yeast expression system. VEGF121 was secreted from the yeast cells as a homodimer with a molecular weight of 34-36 kDa. By taking advantage of the consecutive histidine residues present at position 11 and 12 in VEGF, a novel method of purification using Nickel affinity chromatography was developed. Since all the isoforms of VEGF have an identical amino terminal end, this method can be used to purify not only VEGF121 but also the other forms of VEGF. The level of expression achieved using this system was as high as 40 mg/L. The recombinant protein was biologically active in stimulating the in vitro proliferation of vascular endothelial cells and positively reacted to an antiserum made against recombinant VEGF165.

Cell Division↗
PubMed1995

A novel method to purify immunotoxins from free antibodies using modified recombinant toxins.

Monoclonal antibodies linked to toxin polypeptides (immunotoxins) are developed for clinical application against cancer and graft rejection. Immunotoxins prepared by many conventional methods often contain a trace amount of free antibody. Present studies describe a method to purify immunotoxins from free antibody in conjugation mixtures. Recombinant ricin A chain and a truncated form of diphtheria toxin (385 residues) containing ten consecutive histidine residues at the amino terminus were prepared. The modified toxin polypeptides retaining full biological activity were chemically linked to monoclonal antibodies (317G5 and 454C11) reactive to breast cancer cells. The high affinity of consecutive histidine residues for nickel-based resin (Ni-NTA) was exploited to purify immunotoxins from unreacted free antibodies. SDS-PAGE analysis of conjugates eluted from nickel column contained trace amounts of detectable free antibody whereas conjugates purified by other conventional methods using phenyl Sepharose or Cibacron blue Sepharose chromatography contained significant amounts of unconjugated antibody. Furthermore, the immunotoxin fraction containing predominantly two toxin molecules linked to one antibody can be separated from stoichiometric conjugates by Ni-NTA column. Cytotoxicity experiments showed that the complex of two toxin molecules linked to an antibody was more cytotoxic to tumor cells in vitro than the fraction enriched with immunotoxin containing equimolar stoichiometry.

Animals↗
PubMed1995

Genetic construction of a phosphorylation site in ricin A chain: specific radiolabeling of recombinant proteins for localization and degradation studies.

Ricin A chain was modified by the addition of the heptapeptide LRRASLG (Kemptide) and a histidine tag for bacterial expression. The mutagenized toxin was purified by nickel column and could be phosphorylated in vitro by protein kinase A as demonstrated by labeling with [gamma-32P] ATP. Kemptide-A chain could be labeled even after reassociation with ricin B chain or disulfide linkage to antibody to form an immunotoxin. The 32P label in all cases was associated only with the A chain; ricin B chain and antibody were not kinase substrates alone or after conjugation. Kemptide-immunotoxin was tested in cytotoxicity assays and used to monitor internalization of the toxin moiety after [32P] phosphorylation.

Amino Acid Sequence↗
PubMed1995

Complementary DNA cloning of a mu-opioid receptor from rat peritoneal macrophages.

Treatment with opioid agonists in vitro and in vivo has been shown to affect the function of the immune system. Several investigators have suggested that immune cells may express opioid receptors, but it had been very difficult to demonstrate their presence on these cells by direct binding assays. Our earlier studies have shown that macrophage progenitor cells are highly sensitive to morphine treatment in vitro and in vivo. In the current investigation, we determined, unequivocally, the expression of mu-opioid receptor related transcripts in rat peritoneal macrophages by reverse transcriptase-polymerase chain reaction (RT-PCR) studies. In order to further characterize the transcript, the RT-PCR product was cloned and sequenced. The sequence analyses indicate that the transcripts from rat peritoneal macrophages are identical to those for the mu-opioid receptor described in the rat brain. To further confirm the presence of mu-opioid receptors, immunoreactivity to an antiserum raised against the carboxyl terminal fifteen amino acid residues of the mu-opioid receptor was determined. These studies show for the first time that rat peritoneal macrophages express a mu-opioid receptor.

Amino Acid Sequence↗
PubMed1995

Cytotoxic effects of ricin without an interchain disulfide bond: genetic modification and chemical crosslinking studies.

Ricin is a toxic glycoprotein made of two polypeptide chains (A and B) linked by a disulfide bond. Ricin binds to cells by the B chain and is then internalized. The interchain disulfide bond is believed to be reduced in endosomes, and the A chain is then subsequently translocated to cytoplasm where it inactivates ribosomes. To understand the role of the disulfide bond in ricin toxicity, we prepared two types of ricin molecules. First, cysteine 259 of the A chain was mutated to an alanine residue. The mutant A chain was then reassociated with the native B chain to determine whether ricin is biologically active in the absence of an interchain disulfide bond. Reassociated mutant ricin showed a 40-fold reduction in biological activity. Binding studies using a hydrophobic fluorescence probe indicated that the associated complex was stable only at neutral pH and became highly unstable at a lower pH characteristic of the endosomal milieu. In the second construct, the interchain disulfide bond was replaced with a non-reducible bond by chemical derivatization. Interestingly, the non-reducible ricin molecule was equally cytotoxic as native ricin. These results show: (i) that the interchain disulfide bond is necessary to hold the A chain and the B chain together at endosomal pH, and (ii) that intact ricin may be transported to the cytoplasm where proteolysis or hydrolysis may occur to release the biologically active moiety.

Alanine↗