Biomedical subjects

A Pramanik

Publications and source records attributed to A Pramanik.

At least 37 records · Page 2Linked to original sources

PubMed2000

Clustering of apoptotic cells via bystander killing by peroxides.

Clustering of apoptotic cells is a characteristic of many developing or renewing systems, suggesting that apoptotic cells kill bystanders. Bystander killing can be triggered experimentally by inducing apoptosis in single cells and may be based on the exchange of as yet unidentified chemical cell death signals between nearby cells without the need for cell-to-cell communication via gap junctions. Here we demonstrate that apoptotic cell clusters occurred spontaneously, after serum deprivation or p53 transfection in cell monolayers in vitro. Clustering was apparently induced through bystander killing by primary apoptotic cells. Catalase, a peroxide scavenger, suppressed bystander killing, suggesting that hydrogen peroxide generated by apoptotic cells is the death signal. Although p53 expression increased the number of apoptoses, clustering was found to be similar around apoptotic cells whether or not p53 was expressed, indicating that there is no specific p53 contribution to bystander killing. Bystander killing through peroxides emitted by apoptotic cells may propagate tissue injury in different pathological situations and be relevant in chemo-, gamma-ray, and gene therapy of cancer.

Apoptosis↗

PubMed2000

Role of C-peptide in human physiology.

The C-peptide of proinsulin is important for the biosynthesis of insulin but has for a long time been considered to be biologically inert. Data now indicate that C-peptide in the nanomolar concentration range binds specifically to cell surfaces, probably to a G protein-coupled surface receptor, with subsequent activation of Ca(2+)-dependent intracellular signaling pathways. The association rate constant, K(ass), for C-peptide binding to endothelial cells, renal tubular cells, and fibroblasts is approximately 3. 10(9) M(-1). The binding is stereospecific, and no cross-reaction is seen with insulin, proinsulin, insulin growth factors I and II, or neuropeptide Y. C-peptide stimulates Na(+)-K(+)-ATPase and endothelial nitric oxide synthase activities. Data also indicate that C-peptide administration is accompanied by augmented blood flow in skeletal muscle and skin, diminished glomerular hyperfiltration, reduced urinary albumin excretion, and improved nerve function, all in patients with type 1 diabetes who lack C-peptide, but not in healthy subjects. The possibility exists that C-peptide replacement, together with insulin administration, may prevent the development or retard the progression of long-term complications in type 1 diabetes.

Amino Acid Sequence↗

PubMed1999

Specific binding of proinsulin C-peptide to human cell membranes.

Recent reports have demonstrated beneficial effects of proinsulin C-peptide in the diabetic state, including improvements of kidney and nerve function. To examine the background to these effects, C-peptide binding to cell membranes has been studied by using fluorescence correlation spectroscopy. Measurements of ligand-membrane interactions at single-molecule detection sensitivity in 0.2-fl confocal volume elements show specific binding of fluorescently labeled C-peptide to several human cell types. Full saturation of the C-peptide binding to the cell surface is obtained at low nanomolar concentrations. Scatchard analysis of binding to renal tubular cells indicates the existence of a high-affinity binding process with K(ass) > 3.3 x 10(9) M(-1). Addition of excess unlabeled C-peptide is accompanied by competitive displacement, yielding a dissociation rate constant of 4.5 x 10(-4) s(-1). The C-terminal pentapeptide also displaces C-peptide bound to cell membranes, indicating that the binding occurs at this segment of the ligand. Nonnative D-C-peptide and a randomly scrambled C-peptide do not compete for binding with the labeled C-peptide, nor were crossreactions observed with insulin, insulin-like growth factor (IGF)-I, IGF-II, or proinsulin. Pretreatment of cells with pertussis toxin, known to modify receptor-coupled G proteins, abolishes the binding. It is concluded that C-peptide binds to specific G protein-coupled receptors on human cell membranes, thus providing a molecular basis for its biological effects.

Binding, Competitive↗

PubMed1999

Amyloid beta-peptide polymerization studied using fluorescence correlation spectroscopy.

BACKGROUND: The accumulation of fibrillar deposits of amyloid beta-peptide (Abeta) in brain parenchyma and cerebromeningeal blood vessels is a key step in the pathogenesis of Alzheimer's disease. In this report, polymerization of Abeta was studied using fluorescence correlation spectroscopy (FCS), a technique capable of detecting small molecules and large aggregates simultaneously in solution. RESULTS: The polymerization of Abeta dissolved in Tris-buffered saline, pH 7.4, occurred above a critical concentration of 50 microM and proceeded from monomers/dimers into two discrete populations of large aggregates, without any detectable amount of oligomers. The aggregation showed very high cooperativity and reached a maximum after 40 min, followed by an increase in the amount of monomers/dimers and a decrease in the size of the large aggregates. Electron micrographs of samples prepared at the time for maximum aggregation showed a mixture of an amorphous network and short diffuse fibrils, whereas only mature amyloid fibrils were detected after one day of incubation. The aggregation was reduced when Abeta was incubated in the presence of Abeta ligands, oligopeptides previously shown to inhibit fibril formation, and aggregates were partly dissociated after the addition of the ligands. CONCLUSIONS: The polymerization of Abeta is a highly cooperative process in which the formation of very large aggregates precedes the formation of fibrils. The entire process can be inhibited and, at least in early stages, partly reversed by Abeta ligands.

Alzheimer Disease↗

PubMed1997

Cloning, characterization and identification of the gene encoding phosphatidylinositol 4-kinase.

The vast majority of AIDS-related deaths are associated with opportunistic infections. For fungal infections, there are few effective antifungals, particularly for systemic use. The discovery that very low doses of the bleomycin family of anticancer chemical congeners compromise the integrity of fungal cell walls led to our approach to identify genes that complement-cell wall defects, and develop methods to facilitate the identification of new antifungals targeted to fungal cell walls. This report describes one of the genes cloned by complementation of the blm1-1 mutation of S. cerevisiae using a YCp50-based yeast genomic library. Characterization and identification of the gene were carried out using drug screening tests, Southern hybridization analyses, DNA sequencing and DNA sequence similarity searches in databases. The gene STT4, is essential for viability and encodes a phosphatidylinositol 4-kinase that plays an important role in the phosphatidylinositol-mediated signal transduction pathway required for cell wall integrity. Like blm1-1 mutant strains, stt4 cells arrest mostly in the G2/M phase of the cell cycle. Further studies using this approach should help us understand the role of PI4-K in maintaining fungal cell-wall integrity, identify additional genes affecting potential target structures in cell walls of opportunistic fungal pathogens in AIDS patients, and assist in drug discovery and antifungal drug design.

1-Phosphatidylinositol 4-Kinase↗

PubMed1996

Omega amino acids in peptide design: incorporation into helices.

Incorporation of easily available achiral omega-amino acid residues into an oligopeptide results in substitution of amide bonds by polymethylene units of an aliphatic chain, thereby providing a convenient strategy for constructing a peptidomimetic. The central Gly-Gly segment of the helical octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe(1) has been replaced by delta-amino-valeric acid (delta-Ava) residue in the newly designed peptide Boc-Leu-Aib-Val-delta-Ava-Leu-Aib-Val-OMe(2). 1H-nmr results clearly suggest that in the apolar solvent CDCl3, the delta-Ava residue is accommodated into a folded helical conformation, stabilized by successive hydrogen bonds involving the NH groups of Val(3), delta-Ava(4), and Leu(5). The delta-Ava residue must adopt a gauche-gauche-trans-gauche-gauche conformation along the central polymethylene unit of the aliphatic segment, a feature seen in an energy-minimized model conformation based on nmr parameters. The absence of hydrogen bonding functionalities, however, limits the elongation of the helix. In fact, in CDCl3, the folded conformation consists of an N-terminal helix spanning residues 1-4, followed by a Type II beta-turn at residues 5 and 6, whereas in strongly solvating media like (CD3)2SO, the unfolding of the N-terminal helix results in beta-turn conformations at Leu(1)-Aib(2). The Type II beta-turn at the Leu(5)-Aib(6) segment remains intact even in (CD3)2SO.CD comparisons of peptides 1 and 2 reveal a "nonhelical" spectrum for 2 in 2,2,2-trifluoroethanol.

Amino Acids↗

PubMed1996

Candida parapsilosis bloodstream infections in neonatal intensive care unit patients: epidemiologic and laboratory confirmation of a common source outbreak.

BACKGROUND: Candida parapsilosis is a common cause of sporadic and epidemic infections in neonatal intensive care units (NICUs). When a cluster of C. parapsilosis bloodstream infections occurred in NICU patients in a hospital in Louisiana, it provided us with the opportunity to conduct an epidemiologic investigation and to apply newly developed molecular typing techniques. METHODS: A case-patient was defined as any NICU patient at Louisiana State University Medical Center, University Hospital, with a blood culture positive for C. parapsilosis during July 20 to 27, 1991. To identify risk factors for C. parapsilosis bloodstream infection, a cohort study of all NICU infants admitted during July 17 to 27, 1991, was performed. Electrophoretic karyotyping was used to assess the relatedness of C. parapsilosis isolates. RESULTS: The receipt of liquid glycerin given as a suppository was identified as a risk factor (relative risk, 31.2; 95% confidence intervals, 4.3 to 226.8). Glycerin was supplied to the NICU in a 16-oz multidose bottle. Bottles used at the time of the outbreak were not available for culture. All six available isolates from four case-patients had identical chromosomal banding patterns; six University Hospital non-outbreak isolates had different banding patterns. CONCLUSIONS: This study demonstrates the utility of combined epidemiologic and laboratory techniques in identifying a novel common source for a C. parapsilosis bloodstream infection outbreak and illustrates that extreme caution should be exercised when using multidose medications in more than one patient.

Candida↗

PubMed1996

The efficacy and safety of KL4-surfactant in preterm infants with respiratory distress syndrome.

The present study was undertaken to determine if a synthetic peptide, KLLLLKLLLLKLLLLKLLLLK (KL4), in which K = lysine and L = leucine, in an aqueous dispersion of phospholipids (DPPC and POPG), would expand pulmonary alveoli and improve gas exchange in premature human infants with respiratory distress syndrome (RDS). The KL4 peptide was synthesized to resemble the amino acid pattern of surfactant protein B (SP-B). Forty-seven infants with RDS were treated within 4 h of birth with the KL4-peptide/phospholipid mixture, called KL4-Surfactant. The average arterial-to-alveolar oxygen tension ratios (a/A O2) of 39 patients included in efficacy analyses rose from pretreatment values of 0.14 +/- 0.02 (mean +/- SEM) to 0.40 +/- 0.04 (normal value > or = 0.40) by 12 h of age. Mean airway pressures and oxygenation index values fell concomitantly, and expansion of the lungs was observed on radiographs. The median duration of mechanical ventilation was 5.0 d. Of the 39 included infants, 29 required only a single dose. Radiographic data indicate that those patients requiring a second instillation of KL4-Surfactant but not showing a sustained rise in a/A O2 ratios did, in fact, exhibit expansion of alveoli in the lung. There were no RDS-related deaths; the incidence of complications was no higher than found in other comparable published studies. The data demonstrate that the synthetic peptide, KL4, which mimics the hydrophobic and hydrophilic pattern of SP-B, when formulated in an aqueous dispersion with the phospholipids DPPC and POPG, creates a strong and durable surfactant activity as judged by expansion of pulmonary alveoli and improvement of gas exchange in infants with RDS.

Age Factors↗

PubMed1995

Genetic changes and bioassays in bleomycin- and phleomycin-treated cells, and their relationship to chromosomal breaks.

The recombinogenicity of damaged chromosomes in diploid Saccharomyces cerevisiae cells treated with bleomycin and structurally related phleomycin was measured, along with aneuploidy and mutation events. Phleomycin was substantially (up to 26-fold) more effective than bleomycin in producing genetic changes at all concentrations, even when colony-forming abilities of cells growing in the presence of bleomycin or phleomycin were similar. These results suggest that the DNA lesions produced by the two structurally related analogs could differ in their nature or frequency, or could be processed differently by the cells. Bioassays were developed and used to compare the cytotoxicities of freshly dissolved bleomycin and phleomycin with the cytotoxicities of lysates prepared from bleomycin- and phleomycin-treated cells. Unexpectedly, lysates prepared from bleomycin-treated cells were 1.5-3.5 times more cytotoxic than freshly dissolved bleomycin after 45-min treatments (3-33 x 10(-6) M). In contrast, lysates prepared from phleomycin-treated cells were 3-38 times less cytotoxic than freshly dissolved phleomycin (0.5-6.4 x 10(-6) M). Cytotoxicities of all lysates were higher after 36-h treatments than after 45-min treatments. At 3.3 x 10(-6) M, this increase was eightfold for bleomycin and 15-fold for phleomycin. Nevertheless, lysates from phleomycin-treated cells were considerably more cytotoxic than lysates from bleomycin-treated cells or freshly prepared bleomycin, consistent with the higher effectiveness of phleomycin than bleomycin in producing chromosomal breaks, genetic changes, and cell killing.

Aneuploidy↗

PubMed1995

A mutant approach and molecular strategy to study fungal cell walls.

The current study describes recombinant plasmids which complement the hypersusceptibility to killing bleomycin of blm1-1 mutant cells of Saccharomyces cerevisiae, and a strategy developed and used to recover active clones from a stable yeast genomic library. The resistance of a spontaneous revertant isolated from the original blm1-1 mutant strain and of mutant cells transformed with each of several recombinant plasmids which complemented the recessive blm1-1 mutation was comparable to the resistance of the parental (non-mutant) strain from which the original blm1-1 mutant was derived. The strategy for cloning S. cerevisiae DNA was based on complementation and in situ hybridization. This strategy employed 32P-labelled 6.6-kb BamHI and 3.8-kb BamHI-ClaI probes from a cloned DNA fragment to recover clones which either fully or partially complemented the hypersensitivity of mutant cells to killing by bleomycin. This method considerably reduced the time and effort required to recover biologically active clones from a genomic library.

Bleomycin↗

PubMed1994

Nosocomial Malassezia pachydermatis bloodstream infections in a neonatal intensive care unit.

Malassezia pachydermatis, a lipophilic yeast, has been described to cause sporadic nosocomial bloodstream infections (BSI). Nosocomial outbreaks of M. pachydermatis BSI have never been described. A cluster of M. pachydermatis BSIs in the neonatal intensive care unit at Louisiana State University Medical Center, University Hospital provided the opportunity to investigate the epidemiology of this organism and apply molecular epidemiologic typing techniques. A case-patient was defined as any neonatal intensive care unit patient in University Hospital with a blood culture positive for M. pachydermatis from January 1, 1989, through August 15, 1991. Five patients met the case definition. Case-patients were premature as estimated by gestational age and required prolonged hospitalization. Case-patients received parenteral nutrition and intravenous lipids for twice as many days as randomly selected controls. No environmental source of M. pachydermatis was identified; however, infants on each side of a previously identified M. pachydermatis-colonized infant became colonized with M. pachydermatis during a 20-day period. Chromosomal analysis of five M. pachydermatis blood isolates from two case-patients had identical banding patterns. These data show that M. pachydermatis can cause nosocomial BSI outbreaks, that premature infants receiving parenteral nutrition and/or lipids may be at greatest risk and that transmission is most likely from person to person, probably via the hands of medical personnel.

Cross Infection↗

PubMed1993

Differential effects of the putative galanin receptor antagonists M15 and M35 on striatal acetylcholine release.

The putative galanin receptor antagonists M15 and M35 were examined for their effects on the basal and the galanin-evoked release of acetylcholine in the striatum. Extracellular concentrations of acetylcholine were measured in male rats using in vivo microdialysis and high pressure liquid chromatography techniques. Galanin (300 microM or 3 nmol/10 microliters), perfused through the microdialysis membrane into the striatum, enhanced (100% increase) basal acetylcholine release. M35 (300 microM or 3 nmol/10 microliters) also stimulated the basal acetylcholine release to some extent (about 50%) while M15 at the same concentration failed to do so. When M15 and M35 were coinfused with galanin, the galanin-evoked acetylcholine release was blocked completely by M15 (300 microM or 3 nmol/10 microliters) but only partially by M35 (300 microM or 3 nmol/10 microliters). The increase in acetylcholine release induced by M35 (300 microM) was blocked by M15 (300 microM). It is concluded that M15 is a full galanin receptor antagonist while M35 behaves as a mixed agonist-antagonist in vivo in the rat striatum. Both M15 and M35 fully displaced 0.2 nM [125I]galanin from its binding sites in the striatal membranes. The Hill coefficient of these [125I]galanin displacement curves with M15 and M35 was 0.4-0.5 compared to unity in the case of galanin. Analysis of the displacement curves suggested that both M15 and M35 recognized two classes of galanin binding sites in striatal membranes of the rat. To explain the difference between M15 and M35 it is suggested that there may exist a putative subtype of galanin receptor in the striatum, which is differentially affected by M15 and M35.

Acetylcholine↗

PubMed1993

Galanin stimulates striatal acetylcholine release via a mechanism unrelated to cholinergic receptor stimulation.

The effect of galanin (GAL) on the basal and the muscarinic agonist/antagonist mediated release of acetylcholine (ACh) in the striatum was investigated in male rats using in vivo microdialysis and HPLC techniques. GAL (300 microM or 3 nmol/10 microliters), perfused through the microdialysis membrane into the striatum, was found to enhance basal ACh release. The GAL evoked ACh release was completely prevented by bupivacaine, a sodium channel blocker (1.5 mM) when coperfused with GAL. This suggests that the effect of GAL depends on intact neuronal activity and thus derives from impulse-dependent release. The muscarinic agonists oxotremorine (0.3 mg/kg, i.p.) or carbachol (100 microM, infusion) reduced ACh release and reduced the stimulation of ACh release by GAL with a magnitude corresponding to that of oxotremorine or carbachol alone. Thus, the resultant effect of GAL on ACh release remained unchanged. When GAL was given at a threshold dose (30 microM), which by itself did not stimulate ACh release, it was unable to attenuate the muscarinic agonist induced inhibition of ACh releases. Furthermore, GAL given in combination with scopolamine (0.25 mg/kg, i.p.) or pirenzepine (1 microM, infusion) added to the stimulating effect by the two muscarinic antagonists. In contrast to the GAL (300 microM) evoked ACh release, the scopolamine (0.25 mg/kg, i.p.) stimulated ACh release was not blocked by M15, a putative GAL antagonist, indicating that the mechanisms behind GAL and scopolamine evoked striatal ACh release differ. These results suggest that the mechanisms behind GAL evoked release do not involve direct interactions with pre- or postsynaptic muscarinic receptor mediated events. It is concluded that the stimulation of the basal ACh release by GAL in the striatum occurs via occupation of GAL receptors located on cholinergic interneurons and that the release process is dependent on intact neuronal activity.

Acetylcholine↗

PubMed1992

Galanin-evoked acetylcholine release in the rat striatum is blocked by the putative galanin antagonist M15.

The effect of the putative galanin (GAL) antagonist M15 on the Gal-evoked release of acetylcholine (ACh) was investigated in the rat striatum using microdialysis and HPLC techniques. GAL (3 nmol/10 microliters), applied in the lateral ventricle (i.c.v.) or perfused through the microdialysis membrane into the striatum, was found to enhance basal ACh release. The GAL-evoked release of striatal ACh was completely blocked by M15 (3 nmol/10 microliters), administered either i.c.v. or into the straitum. This finding suggests that GAL stimulates the basal ACh release in the rat striatum by a direct action of the peptide on striatal GAL receptors.

Acetylcholine↗

PubMed1992

Controlled trial of a single dose of synthetic surfactant at birth in premature infants weighing 500 to 699 grams. The American Exosurf Neonatal Study Group I.

In a multicenter, double-blind, placebo-controlled trial conducted at 23 hospitals in the United States, a single prophylactic 5 ml/kg dose of a synthetic surfactant (Exosurf Neonatal) or air placebo was administered shortly after birth to 215 infants with birth weights of 500 to 699 gm. Despite stratification at entry by birth weight and gender, by chance female infants predominated in the air placebo group and male infants predominated in the surfactant group. Among infants receiving synthetic surfactant, improvements in oxygen requirements were significant at 2 hours after birth (p = 0.014) and persisted for 3 days (p = 0.001); improvements in the alveolar-arterial partial pressure of oxygen gradient were significant at 6 hours after birth (p = 0.01) and persisted for 3 days (p = 0.008). Improvements in mean airway pressure were not significant at 2 or at 6 hours after birth (p = 0.622 and 0.083, respectively), but became significant thereafter and persisted for 3 days (p = 0.002). Pneumothorax was reduced by slightly more than half (25 vs 11; p = 0.014); death from respiratory distress syndrome (RDS) was also reduced (26 vs 15; p = 0.046). Overall neonatal mortality, however, was not significantly reduced (58 vs 46; p = 0.102). Other complications of RDS and prematurity were not altered, except that pulmonary hemorrhage occurred significantly more frequently in infants receiving synthetic surfactant (2 vs 12; p = 0.006). These findings indicate that a single prophylactic dose of synthetic surfactant in infants weighing 500 to 699 gm at birth improves lung function, incidence of air leak, and death from RDS but not overall mortality. The only safety problem identified was an increase in pulmonary hemorrhage.

Bronchopulmonary Dysplasia↗

PubMed1992

Lesions and preferential initial localization of [S-methyl-3H]bleomycin A2 on Saccharomyces cerevisiae cell walls and membranes.

Extensive lesions were produced in cell walls of Saccharomyces cerevisiae by the bleomycin family of anticancer antibiotics (30 min to 4 h). Electron micrographs revealed that the alterations were most frequently large breaks and small interruptions or holes in cell walls, which sometimes extended into cell membranes. Large portions of cell walls were sometimes lost. Cell walls were frequently ruptured in one or more positions. More than 75% of bud scar regions in single-plane sections and all bud scars in serial sections exhibited many interruptions and breaks after 3 or 4 h of treatment. The discovery of extensive damage to cell walls was consistent with the preferential (approximately 70%) association of radiolabeled bleomycin with cell walls and perimeters of bud scar regions after short exposures (30 min). After longer exposures, the distribution of silver grains changed from a predominant association with cell walls (30 min) to an increased association with the cell cytoplasm (1 to 4 h). This correlated with increased ultrastructural damage, since damage to cell walls was generally more frequent and more severe with increasing length of treatment (30 min to 4 h) or dose (25 to 100 micrograms/ml). Although DNA lesions are believed to be the lethal properties of bleomycins, the lesions produced in cell walls are also lethal properties of the antibiotics. The distributions of lesions on cell walls suggested a generalized interaction of the antibiotic with a cell wall component. These results led us to hypothesize a mechanism of effective antifungal action for the bleomycin family of antibiotics.

Autoradiography↗

PubMed1991

Galanin stimulates acetylcholine release in the rat striatum.

The effect of the neuropeptide galanin (GAL) on the basal and the evoked release of acetylcholine (ACh) was investigated in the rat striatum using microdialysis and HPLC techniques. GAL (0.3, 1 and 3 nmol), applied in the lateral ventricle (10 microliters), was found to cause a dose-dependent stimulation of the basal ACh release. The stimulating effect of GAL on ACh release was longlasting (greater than 90 min) and reached its peak 30 min after i.c.v. administration. GAL failed to affect the scopolamine (0.25 and 0.5 mg/kg, i.p.) stimulated release of ACh. Possible mechanisms behind the GAL-stimulated ACh release in the rat striatum are discussed. It may involve effects on GAL receptors in the striatum or indirect effects via stimulation of GAL receptors in the substantia nigra resulting in inhibition of striatal dopamine (DA) transmission.

Acetylcholine↗

PubMed1988

Some characteristics of cyclic photophosphorylation in maize bundle sheath chloroplasts.

PMS-dependent photophosphorylation in bundle sheath chloroplasts isolated from Zea mays was monitored by using a continuous method. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and venturicidin were shown to inhibit the ATP-synthesis. Venturicidin has been shown to inhibit ATP-formation in both mesophyll and bundle sheath chloroplasts. In contrast to the case in mesophyll chloroplasts, FMN was not able to promote photophosphorylation in bundle sheath chloroplasts. The effects of other cofactors and inhibitors on the ATP-synthesis in bundle sheath chloroplasts are shown. No photoinduced synthesis of inorganic pyrophosphate was seen, neither in bundle sheath chloroplasts, nor in mesophyll chloroplasts.

Adenosine Triphosphate↗