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Biomedical subjects

G Ramakrishnan

Publications and source records attributed to G Ramakrishnan.

At least 19 recordsLinked to original sources
PubMed2001

Amebiasis and mucosal IgA antibody against the Entamoeba histolytica adherence lectin in Bangladeshi children.

Amebiasis is the third leading parasitic cause of death worldwide, and it is not known whether immunity is acquired from a previous infection. An investigation was done to determine whether protection from intestinal infection correlated with mucosal or systemic antibody responses to the Entamoeba histolytica GalNAc adherence lectin. E. histolytica colonization was present in 0% (0/64) of children with and 13.4% (33/246) of children without stool IgA anti-GalNAc lectin antibodies (P= .001). Children with stool IgA lectin-specific antibodies at the beginning of the study had 64% fewer new E. histolytica infections by 5 months (3/42 IgA(+) vs. 47/227 IgA(-); P= .03). A stool antilectin IgA response was detected near the time of resolution of infection in 67% (12/18) of closely monitored new infections. It was concluded that a mucosal IgA antilectin antibody response is associated with immune protection against E. histolytica colonization. The demonstration of naturally acquired immunity offers hope for a vaccine to prevent amebiasis.

Animals↗
PubMed2001

Reduced cardiotoxicity and preserved antitumor efficacy of liposome-encapsulated doxorubicin and cyclophosphamide compared with conventional doxorubicin and cyclophosphamide in a randomized, multicenter trial of metastatic breast cancer.

PURPOSE: To determine whether Myocet (liposome-encapsulated doxorubicin; The Liposome Company, Elan Corporation, Princeton, NJ) in combination with cyclophosphamide significantly reduces doxorubicin cardiotoxicity while providing comparable antitumor efficacy in first-line treatment of metastatic breast cancer (MBC). PATIENTS AND METHODS: Two hundred ninety-seven patients with MBC and no prior chemotherapy for metastatic disease were randomized to receive either 60 mg/m(2) of Myocet (M) or conventional doxorubicin (A), in combination with 600 mg/m(2) of cyclophosphamide (C), every 3 weeks until disease progression or unacceptable toxicity. Cardiotoxicity was defined by reductions in left-ventricular ejection fraction, assessed by serial multigated radionuclide angiography scans, or congestive heart failure (CHF). Antitumor efficacy was assessed by objective tumor response rates (World Health Organization criteria), time to progression, and survival. RESULTS: Six percent of MC patients versus 21% (including five cases of CHF) of AC patients developed cardiotoxicity (P =.0002). Median cumulative doxorubicin dose at onset was more than 2,220 mg/m(2) for MC versus 480 mg/m(2) for AC (P =.0001, hazard ratio, 5.04). MC patients also experienced less grade 4 neutropenia. Antitumor efficacy of MC versus AC was comparable: objective response rates, 43% versus 43%; median time to progression, 5.1% versus 5.5 months; median time to treatment failure, 4.6 versus 4.4 months; and median survival, 19 versus 16 months. CONCLUSION: Myocet improves the therapeutic index of doxorubicin by significantly reducing cardiotoxicity and grade 4 neutropenia and provides comparable antitumor efficacy, when used in combination with cyclophosphamide as first-line therapy for MBC.

Adult↗
PubMed2000

Entamoeba histolytica: deletion of the GPI anchor signal sequence on the Gal/GalNAc lectin light subunit prevents its assembly into the lectin heterodimer.

Adherence and cytotoxicity of Entamoeba histolytica require the function of a heterodimeric galactose and N-acetylgalactosamine (Gal/GalNAc)-specific lectin. The lectin heavy subunit (Hgl) contains a carbohydrate recognition domain and mediates inside-out cell signaling via its cytoplasmic tail. The function of the lectin light subunit (Lgl) is unknown. The lectin has a unique mechanism of membrane association: Hgl is transmembrane but Lgl is glycosylphosphatidylinositol (GPI) anchored. The role of the GPI anchor signal sequence in heterodimer assembly was tested. Epitope-tagged Lgl with or without the GPI anchor addition signal was expressed in E. histolytica trophozoites. Tagged Lgl did not assemble with Hgl into a lectin heterodimer in the absence of the GPI addition signal. Consistent with previous results that only the Hgl subunit mediates adherence, the monomeric Lgl without the GPI anchor signal lacked Gal/GalNAc-binding activity.

Animals↗
PubMed1998

A randomized comparison of the efficacy and toxicity of epirubicin and doxorubicin in the treatment of patients with non-Hodgkin's lymphoma.

BACKGROUND: Combination chemotherapy consisting of methotrexate, doxorubicin, cyclophosphamide, vincristine, prednisolone, and bleomycin (MACOP-B) has been frequently used for the treatment of non-Hodgkin's lymphoma. This randomized study was undertaken to assess the efficacy and toxicity of this regimen when either doxorubicin or epirubicin was used as the anthracycline drug. METHODS: Between April 1989 and December 1993, 211 previously untreated patients with intermediate grade and high grade non-Hodgkin's lymphoma were randomized to receive either doxorubicin (n=106) or epirubicin (n=105) with the MACOP-B regimen. These patients were followed through December 1996. Numerous clinical features predictive of response and survival were analyzed. Cardiac and noncardiac toxicity in the two treatment arms were compared. RESULTS: The median age of the patients was 48 years. Complete remission was experienced by 122 patients (58.3%); 62 patients (58.5%) achieved complete remission in the doxorubicin arm and 60 (58.1%) in the epirubicin arm. Response rates, time to treatment failure, relapse data, and overall survival were comparable between the two arms. Morbidity due to mucositis, vomiting, peripheral neuropathy, and cardiotoxicity were also comparable. The overall mortality was 10%. Mortality due to neutropenic sepsis was considerably higher among patients who received epirubicin (10 patients) than among those who received doxorubicin (5 patients). Cardiac evaluation revealed no difference in toxicity between the two arms. CONCLUSIONS: Epirubicin was as effective as doxorubicin in terms of patients' responses to therapy. There was no difference in cardiotoxicity between the two treatment arms. However, in this study, the mortality due to neutropenic sepsis was significantly higher among patients treated with epirubicin.

Adolescent↗
PubMed1998

Regulation of adherence and virulence by the Entamoeba histolytica lectin cytoplasmic domain, which contains a beta2 integrin motif.

Killing of human cells by the parasite Entamoeba histolytica requires adherence via an amebic cell surface lectin. Lectin activity in the parasite is regulated by inside-out signaling. The lectin cytoplasmic domain has sequence identity with a region of the beta2 integrin cytoplasmic tail implicated in regulation of integrin-mediated adhesion. Intracellular expression of a fusion protein containing the cytoplasmic domain of the lectin has a dominant negative effect on extracellular lectin-mediated cell adherence. Mutation of the integrin-like sequence abrogates the dominant negative effect. Amebae expressing the dominant negative mutant are less virulent in an animal model of amebiasis. These results suggest that inside-out signaling via the lectin cytoplasmic domain may control the extracellular adhesive activity of the amebic lectin and provide in vivo demonstration of the lectin's role in virulence.

Amino Acid Sequence↗
PubMed1997

A tetracycline-inducible gene expression system in Entamoeba histolytica.

We have developed an episomal inducible gene expression system in Entamoeba histolytica based on the TetR repressor. The tetR gene was placed under control of 5' and 3' ferredoxin (fdx) regulatory sequences on a plasmid encoding the hygromycin resistance gene directed by 5' and 3' hgl sequences. The reporter luciferase constructs were introduced on a second episome bearing the neomycin resistance gene controlled by 5' and 3' actin sequences. The reporter constructs were driven by the hgl5 promoter in which the tetO sequence was introduced. We found that the optimal tetO location for induction by tetracycline was +4 from the start of transcription. The efficiency of repression and the induction ratio could be improved by increasing hygromycin levels, presumably by increasing tetR plasmid levels. Under these conditions, maximal induction of reporter luciferase could be effected with 5 micrograms/ml tetracycline in 18 h. This system permits regulated expression of the reporter gene over two orders of magnitude and should be useful in the analysis of gene function.

Animals↗
PubMed1996

Physical mapping and expression of gene families encoding the N-acetyl D-galactosamine adherence lectin of Entamoeba histolytica.

Adherence of the enteric protozoan parasite Entamoeba histolytica is mediated by an N-acetyl D-galactosamine (GalNAc)-specific lectin, a heterodimer of heavy (170 kDa) and light (35/31 kDa) subunits. The gene families encoding the lectin subunits were characterized using clamped homogeneous electric field (CHEF) gel electrophoresis in the strain HM1:IMSS. The heavy subunit was shown to be encoded by a family of five hgl genes, which were physically mapped to five distinct HindIII restriction fragments. The light subunit was shown to be encoded by a family of lgl genes located at six loci in the genome. Heavy and light subunit genes did not appear to be linked. Partial sequences of new members of the hgl and lgl gene families were obtained. Several different strains of E. histolytica were found to contain multiple hgl loci in their genomes. Expression of hgl and lgl genes in HM1:IMSS trophozoites was examined under different growth conditions using the reverse transcription-polymerase chain reaction (RT-PCR). mRNA transcripts were detected from three hgl genes and three lgl genes, with no significant differences between cultured amoebae and amoebae from liver abscesses. The complexity of GalNAc lectin gene expression observed suggests distinct biological functions for the products of the individual genes during pathogenesis.

Acetylgalactosamine↗
PubMed1994

The Caulobacter crescentus FlbD protein acts at ftr sequence elements both to activate and to repress transcription of cell cycle-regulated flagellar genes.

The flagellar genes (fla genes) in Caulobacter crescentus are organized into a regulatory hierarchy of four levels, I-IV, in which transcription of the class III and class IV genes late in the cell cycle from sigma 54-dependent promoters depends on expression of the class II genes above them. Timing of fla gene expression has been attributed to sequential activation and repression by specific transcription factors. Here we report that purified FlbD activates transcription in vitro from the sigma 54-dependent class III flbG promoter and repress transcription from the class II fliF promoter by binding to ftr (flagellar transcription regulator) sequence elements required for their transcriptional regulation in vivo. The FlbD protein makes symmetrical base-specific contacts at three highly conserved guanine nucleotides in each half site of ftr1 and ftr1* at flbG and the single ftr4 site at fliF. The dual function of FlbD in activation of class III genes and repression of the class II fliF promoter is consistent with a central role of FlbD as a switch protein mediating the transition from level II to level III fla gene expression.

Bacterial Proteins↗
PubMed1994

Multiple structural proteins are required for both transcriptional activation and negative autoregulation of Caulobacter crescentus flagellar genes.

The periodic and sequential expression of flagellar (fla) genes in the Caulobacter crescentus cell cycle depends on their organization into levels I to IV of a regulatory hierarchy in which genes at the top of the hierarchy are expressed early in the cell cycle and are required for the later expression of genes below them. In these studies, we have examined the regulatory role of level II fliF operon, which is located near the top of the hierarchy. The last gene in the fliF operon, flbD, encodes a transcriptional factor required for activation of sigma 54-dependent promoters at levels III and IV and negative autoregulation of the level II fliF promoter. We have physically mapped the fliF operon, identified four new genes in the transcription unit, and determined that the organization of these genes is 5'-fliF-fliG-flbE-fliN-flbD-3'. Three of the genes encode homologs of the MS ring protein (FliF) and two switch proteins (FliG and FliN) of enteric bacteria, and the fourth encodes a predicted protein (FlbE) without obvious similarities to known bacterial proteins. We have introduced nonpolar mutations in each of the open reading frames and shown that all of the newly identified genes (fliF, fliG, flbE, and fliN) are required in addition to flbD for activation of the sigma 54-dependent flgK and flbG promoters at level III. In contrast, fliF, fliG, and flbE, but not fliN, are required in addition to flbD for negative autoregulation of the level II fliF promoter. The simplest interpretation of these results is that the requirements of FlbD in transcriptional activation and repression are not identical, and we speculate that FlbD function is subject to dual or overlapping controls. We also discuss the requirement of multiple structural genes for regulation of levels II and III genes and suggest that fla gene expression in C. crescentus may be coupled to two checkpoints in flagellum assembly.

Amino Acid Sequence↗
PubMed1992

Cisplatin-based (PVB+M) chemotherapy in good-risk and poor-risk nonseminomatous germ cell tumors.

Twenty-seven patients with metastatic nonseminomatous germ cell tumors were treated with Cisplatin, vinblastine, bleomycin, and low-dose methotrexate (PVB+M) combinations. Patients were divided into good-risk and poor-risk groups. All seven patients (100%) with good-risk factors achieved complete response, and all are alive disease free at a median of 70 months. In the poor-risk group, only 10 of 20 patients (50%) achieved complete response, and seven (35%) are alive disease free at a median of 58 months. Eight patients, 4 in each group, were required to undergo surgery for removal of postchemotherapy residual masses. The results confirm that Cisplatin-based chemotherapy protocols are adequate to cure most patients with good-risk factors, and newer approaches are needed for patients at poor risk.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

The cell cycle-regulated flagellar gene flbF of Caulobacter crescentus is homologous to a virulence locus (lcrD) of Yersinia pestis.

We have characterized flbF, a key locus located at the top of the flagellar gene hierarchy of Caulobacter crescentus. This gene is required for transcription from sigma 54 promoters of fla genes expressed late in the cell cycle. We have determined the nucleotide sequence of the gene, mapped the 5' end of the flbF RNA, and examined the pattern of expression in the cell cycle. Our results show that flbF is expressed earlier in the cell cycle than other fla genes, that it is expressed at a low level throughout the stalked cell cycle, and that its 5' regulatory region contains sequences that can be aligned with the sigma 28 promoter consensus reported for enteric bacteria. flbF contains an open reading frame of 700 residues with an amino-terminal half rich in hydrophobic residues that could correspond to six to eight transmembrane domains. The translated flbF sequence is very similar to LcrD (low calcium response) encoded by virulence plasmids of pathogenic Yersinia spp. (G. Plano, S. Barve, and S. Straley, J. Bacteriol. 173:7293-7303, 1991). LcrD and FlbF can be aligned over the entire length of the proteins with the greatest degree of sequence identity (45%) in the hydrophobic amino-terminal region. The high degree of sequence homology of proteins derived from widely differing organisms, including Caulobacter and Yersinia species, suggests that FlbF and LcrD may be representatives of a larger family of regulatory proteins with a common sensor mechanism for modifying responses to appropriate stimuli.

Amino Acid Sequence↗
PubMed1990

FlbD of Caulobacter crescentus is a homologue of the NtrC (NRI) protein and activates sigma 54-dependent flagellar gene promoters.

The periodic transcription of flagellar genes in the Caulobacter crescentus cell cycle is controlled, in part, by their organization in a regulatory hierarchy. The flbG (hook operon), flaN, and flagellin gene operons, which are at the lowest levels of the hierarchy and expressed late in the cell cycle, contain Ntr-like promoters. We report that flbD, one of the early genes required in trans for expression of these operons, codes for a 52-kDa protein homologous to the transcriptional activators NtrC (NRI), NifA, DctD, HydG, and XylR. Our results show that in Escherichia coli flbD partially complements glnG (ntrC) mutations and stimulates transcription of the C. crescentus sigma 54 RNA polymerase-dependent flbG gene. Additionally, the sequence predicts that FlbD protein, along with NtrC, DctD, and HydG proteins, is structurally related at the amino-terminal domain to a larger family of response regulators that mediate cellular responses to environmental stimuli. FlbD may be a singular member of this large protein family in that its function is tied to an internal cell-cycle signal. FlbD is also unusual in that its amino-terminal domain contains only one of the three residues conserved in previously described members of this family of response regulators.

Amino Acid Sequence↗
PubMed1989

Intermediate-dose methotrexate and cisplatin in the treatment of advanced epidermoid esophageal carcinoma. Response rate and disease-free survival.

Seventeen patients with inoperable locoregional disease (epidermoid carcinoma of the esophagus) were treated only with two courses of intermediate-dose methotrexate (200 mg/m2 on day 1) and cisplatin (20 mg/m2/d for 5 days). According to the response criteria, 14 (82.4%) achieved a good response (GR) and 3 (17.6%) showed no response (NR). The median recurrence-free survival time was 5 months (range, 2 to 16 months) in seven patients with regular follow-up. Three patients are still alive and disease-free at 37+, 44+, and 51+ months. No patient received radiotherapy or surgery after chemotherapy until recurrence. This combination schedule appears to be effective in advanced esophageal carcinoma.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1989

Epidemic iatrogenic Acinetobacter spp. meningitis following administration of intrathecal methotrexate.

We report the first outbreak of Acinetobacter species meningitis in a group of children with acute leukaemia following the administration of intrathecal chemotherapy. Eight of twenty patients receiving methotrexate injections on a single day developed signs and symptoms of meningitis within 18 h of treatment, and cases were clustered by time of administration. A cohort study comparing case and non-case patients did not identify any specific host factor associated with meningitis. Acinetobacter calcoaceticus var anitratus was isolated from the cerebrospinal fluid (CSF) of five patients; three patients died. Our investigation determined that the methotrexate was extrinsically contaminated by reused needles, used for reconstitution and administration, which had been inadequately sterilized. Acinetobacter calcoaceticus var anitratus was isolated from an autoclaved needle and a vial of methotrexate used for chemotherapy; these and the clinical isolates had similar antibiograms. After introduction of single-use disposable needles no subsequent cases occurred.

Acinetobacter Infections↗