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Biomedical subjects

R Chakrabarti

Publications and source records attributed to R Chakrabarti.

At least 37 records · Page 2Linked to original sources
PubMed1999

Comparison of growth factor expression in fetal and adult fibroblasts: a preliminary report.

BACKGROUND: Fetal wounds can heal without any histological evidence of scarring. Fetal wounds lack the inflammatory infiltrate characteristic of adult wounds, and the fetal environment is not necessary for scarless healing to occur. Recent evidence suggests that fibroblasts are the main effector of scarless healing in fetal tissue. What has not been shown is what profile of growth factors the fibroblast uses to influence wound repair. OBJECTIVE: To determine the expression of growth factors (transforming growth factors beta1, beta2, and beta3; acidic and basic fibroblast growth factors; keratinocyte growth factor; and platelet-derived growth factor AA, BB, and AB) of fetal and adult fibroblasts in vitro. DESIGN: Adult and fetal fibroblasts were grown in culture, and messenger RNA was extracted by standard techniques. Northern hybridization was used to identify messenger RNA transcripts for the aforementioned growth factors. Densitometry was used to compare growth factor messenger RNA expression with that of a ubiquitously expressed control, glyceraldehyde phosphate dehydrogenase. RESULTS: The data suggest that fetal and adult fibroblasts express acidic and basic fibroblast growth factor and transforming growth factor beta1. Adult fibroblasts show twice the relative expression of these growth factors compared with fetal fibroblasts. CONCLUSIONS: The adult fibroblasts demonstrate a relative excess production of cytokines compared with fetal fibroblasts. This is thought to contribute to suboptimal wound healing in adult wounds compared with the scarless healing of fetal wounds.

Adult↗
PubMed1999

Relative roles of T-cell receptor ligands and interleukin-2 in driving T-cell proliferation.

Stimulation of T cells by the T-cell receptor (TCR)/CD3 complex results in interleukin-2 (IL-2) synthesis and surface expression of the IL-2 receptor (IL-2R), which in turn drive T-cell proliferation. However, the significance of the requirement of IL-2 in driving T-cell proliferation, when TCR stimulation itself delivers potential mitogenic signals, is unclear. We show that blocking of IL-2 synthesis by Cyclosporin A (CsA) suppressed both the Concanavalin A (Con A)- and phorbol myristate acetate (PMA)/ionomycin-induced proliferation of T cells. The latter is also inhibited by anti-IL-2R. Kinetic studies showed that T-cell proliferation begins to become resistant to CsA inhibition by about 12 h and became largely resistant by 18 h of stimulation. PMA, the protein kinase C activator, enhanced Con A-induced T-cell proliferation if added only within first 12 h of stimulation, and not after that. Given the fact that, in the present study, TCR is downregulated within 2 h of Con A stimulation and T cells entered the S phase of cell cycle by about 18 h of stimulation, the above results suggest that TCR stimulation provides the initial trigger to the resting T cells, which allows the cells to traverse the first two third portions of G1 phase of cell cycle and become proliferation competent. IL-2 action begins afterward, delivering the actual proliferation signal(s), allowing the cells to traverse the rest of G1 phase and enter the S phase of the cell cycle.

Animals↗
PubMed1999

Studies on the euglycemic and hypolipidemic potentials of the novel indole analogue of thiazolidinedione, DRF 2189.

Euglycemic and hypolipidemic activities of a novel indole analogue of thiazolidinedione, DRF 2189 (CAS 172647-53-9), have been evaluated in different animal models. Compared to troglitazone (CAS 97322-87-7), DRF 2189 exhibited interesting plasma glucose and triglyceride lowering activity in genetically diabetic and obese db/db mice. It also produced a significant reduction in plasma glucose, triglyceride, total cholesterol levels and improvement in oral glucose tolerance in another genetic mouse model, the ob/ob mice. In high-fat diet fed Sprague-Dawley rats, DRF 2189 treatment showed improvement in plasma lipid parameters. Like other thiazolidinediones, this compound also possesses peroxisome proliferator activated receptor gamma (PPAR gamma) transactivation potential. In anaesthetized rat experiment, DRF 2189 produced a transient fall in blood pressure without any change in the ECG pattern. It showed non-specific smooth muscle relaxant activity against acetylcholine, histamine and potassium chloride induced contractions in isolated guinea pig ileum. A twenty-eight-day toxicity study in Wistar rats did not show any signs of treatment related adverse effects. The overall antidiabetic and hypolipidemic activities of DRF 2189 are comparable with rosiglitazone (CAS 155141-29-0) and superior to troglitazone. In conclusion, results from these preclinical studies indicate that DRF 2189, a novel thiazolidinedione, has a marked potential for the management of type-2 diabetes.

Animals↗
PubMed1998

Transcriptional regulation of the rat glutamine synthetase gene by tumor necrosis factor-alpha.

The expression of glutamine synthetase (GS) is induced in rat skeletal muscle cells (L-6) in response to treatment with the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha). This paper reports the regulation of GS expression in rat skeletal muscle which expresses high levels of GS. TNF-alpha treatment leads to a 3-4-fold increase in GS activity in a dose-dependent and time-dependent manner. Northern-blot analysis of GS mRNA revealed an increased mRNA concentration, reaching a peak at 12 h in response to TNF-alpha treatment. To monitor transcriptional activation of GS by TNF-alpha, and to identify a TNF-alpha-responsive element in the GS promoter, L6 cells were treated with TNF-alpha following transfection of GS-chloramphenicol-acetyltransferase (CAT) constructs. The first 251-bp fragment at the GS upstream sequence showed basal promoter activity, but failed to show any TNF-alpha-inducible activity. However, a 2.5-3-fold induction was noted in constructs extending up to 1.1 kb. This data demonstrates that the rat GS gene is transcriptionally regulated by TNF-alpha and identifies a TNF-alpha-responsive region at the 5' flanking sequence of the GS gene.

Animals↗
PubMed1998

Novel euglycemic and hypolipidemic agents. 1.

A series of [[(heterocyclyl)ethoxy]benzyl]-2,4-thiazolidinediones have been synthesized by the condensation of corresponding aldehyde 1 and 2,4-thiazolidinedione followed by hydrogenation. Both unsaturated thiazolidinedione 2 and its saturated counterpart 3 have shown antihyperglycemic activity. Many of these compounds have shown superior euglycemic and hypolipidemic activity compared to troglitazone (CS 045). The indole analogue DRF-2189 (3g) was found to be a very potent insulin sensitizer, comparable to BRL-49653 in genetically obese C57BL/6J-ob/ob and 57BL/KsJ-db/db mice. Pharmacokinetic and tissue distribution studies conducted on BRL-49653 and DRF-2189 (3g) indicate that these drugs are well-distributed in target tissues. On the basis of euglycemic activity as well as enhanced selectivity against reduction of triglycerides in plasma, DRF-2189 (3g) has been selected for further evaluation.

Animals↗
PubMed1998

Deletion mapping of endocrine tumors localizes a second tumor suppressor gene on chromosome band 11q13.

Multiple endocrine neoplasia type 1 syndrome (MEN1, MIM 131100), an autosomal dominant disease, is characterized by parathyroid hyperplasia, pancreatic endocrine tumors, and pituitary adenomas. These tumors also occur sporadically. Both the familial (MEN1) and the sporadic tumors reveal loss of heterozygosity (LOH) for chromosome band 11q13 sequences. Based on prior linkage and LOH analyses, the MEN1 gene was localized between PYGM and D11S460. Recently, the MEN1 gene (menin) has been cloned from sequences 30-kb distal to PYGM. We performed deletion mapping on 25 endocrine tumors (5 MEN1 and 20 sporadic) by using 21 polymorphic markers on chromosome band 11q13. Of these, two (137C7A, 137C7B) were derived from PYGM-containing BAC (bacterial artificial chromosome-137C7) sequences, one from INT2-containing cosmid sequences and the marker D11S4748, a (CA)20 repeat marker that was developed by us. The LOH analysis shows that the markers close to the MEN1 (menin) gene were not deleted in three of the tumors. These tumors, however, showed LOH for distal markers. Thus, the data suggest the existence of a second tumor suppressor gene on chromosome band 11q13.

Chromosome Banding↗
PubMed1997

A transcript map encompassing the multiple endocrine neoplasia type-1 (MEN1) locus on chromosome 11q13.

A transcription map of a 1200-kb region encompassing the MEN1 locus was constructed by direct cDNA selection and mapping ESTs. A total of 29 genes were mapped. Ten transcripts were identified by cDNA selection of a focused 300-kb genomic region telomeric to the MEN1 consensus region. Since many of the sequences cloned by cDNA selection also identified ESTs from the region, 19 additional RH-mapped ESTs were mapped to the entire contig region by PCR amplification of genomic clones. Nine known genes, 2 putative human homologues to mouse genes, and 18 novel transcripts map to the region. Transcripts that map to the MEN1 interval PYGM-D11S449 include SGC35223, IB1256, AA147620, ZFM1, FAU, and CAPN1. The latter 3 known genes have already been excluded as candidate MEN1 genes. The 2 putative human homologues of mouse genes Ltbp2 and Spa-1 may be candidate tumor suppressor genes, but they map telomeric to D11S449. Although both of these genes map outside the MEN1 consensus region they may play a role in sporadic endocrine tumors independent of the MEN1 gene or in other tumors, such as breast cancer, that have loss of heterozygosity within this region.

Blotting, Northern↗
PubMed1997

Alteration of platelet-activating factor-induced signal transduction in macrophages by n-3 fatty acids.

Diets rich in polyunsaturated n-3 fatty acids can alter various macrophage functions. One possible mechanism by which this occurs is through modulation of the physicochemical properties of the cell membrane and the signal transduction pathways associated with macrophage activation. In this study, we investigated how n-3 fatty acids altered the signaling pathway of the lipid-based mediator platelet-activating factor (PAF). Macrophages from mice fed a diet containing n-3 fatty acids showed a greater increase in PAF-induced intracellular Ca2+ mobilization than macrophages from mice fed an n-6 fatty acid-rich diet. Macrophages treated in vitro with the n-3 fatty acids docosahexaenoic and eicosapentaenoic also showed higher intracellular Ca2+ mobilization than untreated or n-6 fatty acid-treated macrophages. Scatchard analysis of PAF binding showed the presence of one type of PAF receptor; their number and affinities were not altered by dietary fat. Mastoparan, which can activate G-protein-linked phosphoinositide (PI)-signaling pathway through the activation of G proteins, stimulated a higher Ca2+ mobilization in macrophages from mice fed n-3 compared to n-6 fatty acids. In addition, the response of macrophages from n-3-fed mice to PAF was less sensitive to phospholipase C inhibition than that of macrophages from those fed n-6 diets. The activity of phospholipase C in macrophages from mice fed n-3 diets was significantly higher than that of macrophages from mice fed diets containing n-6 fatty acids. Collectively, these results showed that n-3 fatty acids can enhance the PAF-signaling pathway in macrophages by increasing the activation potential of phospholipase C, without affecting PAF receptor number and affinity.

Animals↗
PubMed1997

Deletion analysis of the p16/CDKN2 gene in head and neck squamous cell carcinoma using quantitative polymerase chain reaction method.

BACKGROUND: Recently, the p16/CDKN2/MTS1 gene in the 9p21-22 region has been offered as a candidate tumor suppressor gene. We examined the frequency of hemizygous and homozygous deletions of p16/CDKN2 in head and neck squamous cell carcinoma (HNSCC) using a quantitative polymerase chain reaction (PCR) method. DESIGN: Twenty-one HNSCC and 12 corresponding normal DNA samples were examined for deletion of p16/ CDKN2 using PCR amplification and fluorescent quantification of DNA. All tumor and normal DNA samples were also amplified with fluorescein-labeled primers for a control DNA marker on chromosome 8p (D8S265). The ratios of the observed fluorescence of the p16/CDKN2 and 8p PCR products were compared. SETTING AND PARTICIPANTS: Patients with HNSCC scheduled to undergo surgical resection of their tumors were recruited. After the specimen was removed, a portion of the tissue was snap frozen for further DNA extraction. RESULTS: Eight tumors (38%) had p16/CDKN2-D8S265 ratios of greater than 0.75; 8 tumors (38%), from 0.25 to 0.75; and 5 tumors (24%), of less than 0.25, the average ratio in this last group being 0.06. CONCLUSIONS: These ratios suggest a higher rate of homozygous deletion than previously reported and significant probable hemizygous deletion of the p16/CDKN2 gene in HNSCC.

Carcinoma, Squamous Cell↗
PubMed1997

Characterization of glutamine synthetase transcript, protein, and enzyme activity in the human placenta.

This study characterizes the molecular mechanisms necessary for glutamine synthesis in the human placenta. RNA hybridization and protein immunoblotting were used to verify the presence of glutamine synthetase (GS) transcripts and protein, respectively. Additionally, the presence of GS was determined by immunohistochemistry. RNA hybridization demonstrated the presence of 1.8- and 2.8-kB transcripts and protein immunoblotting yielded a single 49-kDa band, characteristics of GS transcripts and protein, respectively. The mean (+/- s.d.) specific activity of placental GS, expressed as mumol gamma-glutamyl hydroxamic acid/mg protein/h was 1.80 +/- 0.59, which is comparable to other organs which are net glutamine producers. Immunohistochemical analysis indicated the presence of GS within the cytotrophoblast and mesenchyme layers of placental villi, but not in the syncytiotrophoblast. Although these results suggest that the human placenta is capable of synthesizing glutamine, the fate of glutamine produced by this organ remains speculative.

Female↗
PubMed1996

A 1.5-megabase physical map encompassing the multiple endocrine neoplasia type-1 (MEN1) locus on chromosome 11q13.

Linkage analysis and loss of heterozygosity studies have shown that the gene responsible for the multiple endocrine neoplasia type-1 (MEN1) syndrome localizes to a small interval between D11S427 and D11S460 on chromosome 11q13. As an initial step to clone this tumor suppressor gene, our group is the first to map the MEN1 region physically using yeast artificial chromosome, bacterial artificial chromosome (BAC), and cosmid contigs. The 1.5-Mb high-resolution, contiguous map extends from PYGM to 300 kb telomeric of D11S460. Of this, the 1.2-Mb interval between PYGM and D11S460 is isolated in cosmids and BACs and will be useful for the development of genomic sequences and transcription maps of this important region. Nine new sequence-tagged sites (STS) are also characterized from this region. The physical map and the STSs will be valuable tools for the cloning of the MEN1 gene.

Chromosome Mapping↗
PubMed1996

Tyrosine kinase but not phospholipid/Ca2+ signaling pathway is involved in interferon-gamma stimulation of Ia expression in macrophages.

The specific signal transduction pathway(s) involved in the induction of the expression of the MHC class II molecule, Ia, on macrophages by interferon-gamma (IFN-gamma) is unclear. In this paper, we assessed the role of several signal transduction pathways including calcium mobilization, phospholipase C, protein kinase C and cyclic nucleotide-dependent protein kinase, and the tyrosine kinase pathways. IFN-gamma was unable to mobilize intracellular calcium, unlike platelet-activating factor, which stimulated a threefold increase in cytosolic Ca2+ concentration in macrophages. Inhibition of the phospholipase C pathway by U73122 or ET-180CH3 and of phosphatidic acid phosphohydrolase by propranolol did not suppress IFN-gamma-induced Ia expression. In addition, inhibition of protein kinase C by calphostin C or cyclic nucleotide-dependent protein kinase by HA1004 did not suppress Ia expression. However, IFN-gamma-induced Ia expression was significantly suppressed when the tyrosine kinase pathway was inhibited with herbimycin A and genestein. In addition, those two inhibitors suppressed tyrosine phosphorylation of several proteins in macrophages that may or may not be involved in the induction of Ia expression. Thus, IFN-gamma used only the tyrosine kinase signaling pathway, but not the phospholipid/Ca2+ signaling pathways, to induce Ia expression in macrophages.

Animals↗
PubMed1996

Dielectric analysis of phosphorylcholine head group mobility in egg lecithin liposomes.

PURPOSE: A knowledge of the interfacial properties of lecithin underpins our understanding of many of the physicochemical characteristics of drug delivery systems such as liposomes and lecithin stabilized microemulsions. In order to further this understanding, a high frequency dielectric study of the interfacial properties of egg lecithin liposomes was undertaken. METHODS: The effect of temperature, lecithin concentration and probe sonication on the interfacial dielectric properties of liposomal suspensions was investigated by high frequency dielectric relaxation spectroscopy between 0.2-6 GHz. RESULTS: The frequency dependent permittivity of each suspension exhibited a dielectric dispersion centred around 100 MHz, corresponding to the relaxation of zwitterionic head groups. The activation energy for head group reorientation was estimated as delta H = 6.3 kJ mol-1. There was an increase in extent of inter-head group interactions on increasing the liposome volume fraction, whereas the effect of probe sonication showed that: (i) head groups in both the outer and inner lamellae contribute to the dielectric response; (ii) the head groups may be less restricted in liposomes of high surface curvature with few lamellae; (iii) the high frequency permittivity of the suspension increased on sonication, as a result of a reduction in the amount of (depolarized) interlamellar water following a reduction in the number of lamellae per liposome. CONCLUSIONS: Dielectric analysis of the zwitterionic head groups of lecithin therefore provides a means for investigating the surface of lecithin liposomes, and may be used to investigate the effect of drugs and other solutes on membranes.

Eggs↗
PubMed1996

Glutamine nutrition and metabolism: where do we go from here ?

Glutamine, a "nonessential" amino acid, is attracting widespread attention because of its relevance to numerous metabolic processes and its potential role in the treatment and prevention of critical illness. In this paper we review some key concepts of glutamine biochemistry, metabolism, and nutrition. We then discuss several studies in the area of glutamine metabolism and nutrition that are primed for further investigation.

Animals↗