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D Sidiropoulos

Publications and source records attributed to D Sidiropoulos.

At least 19 recordsLinked to original sources
PubMed1992

Stimulation of phospholipase C by guanine-nucleotide-binding protein beta gamma subunits.

We have previously shown that soluble fractions obtained from human HL-60 granulocytes contain a phospholipase C which is markedly stimulated by the stable GTP analogue guanosine 5'-[3-O-thio]triphosphate (Camps, M., Hou, C., Jakobs, K. H. and Gierschik, P. (1990) Biochem. J. 271, 743-748]. To investigate whether this stimulation was due to a soluble alpha subunit of a heterotrimeric guanine-nucleotide-binding protein or a soluble low-molecular-mass GTP-binding protein, we have examined the effect of purified guanine-nucleotide-binding protein beta gamma dimers on the phospholipase-C-mediated formation of inositol phosphates by HL-60 cytosol. We found that beta gamma subunits, purified from bovine retinal transducin (beta gamma t), markedly stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate by this phospholipase C preparation. The stimulation of phospholipase C by beta gamma t was not secondary to a phospholipase-A2-mediated generation of arachidonic acid, was prevented by the GDP-liganded transducin alpha subunit and was additive to activation of phospholipase C by guanosine 5'-[3-O-thio]triphosphate. Beta gamma t also stimulated soluble phospholipase C from human and bovine peripheral neutrophils, as well as membrane-bound, detergent-solubilized phospholipase C from HL-60 cells. Stimulation of soluble HL-60 phospholipase C was not restricted to beta gamma t, but was also observed with highly purified beta gamma subunits from bovine brain. Fractionation of HL-60 cytosol by anion-exchange chromatography revealed the existence of at least two distinct forms of phospholipase C in HL-60 granulocytes. Only one of these forms was sensitive to stimulation by beta gamma t, demonstrating that stimulation of phospholipase C by beta gamma subunits is isozyme specific. Taken together, our results suggest that guanine-nucleotide-binding protein beta gamma subunits may play an important and active role in mediating the stimulation of phospholipase C by heterotrimeric guanine-nucleotide-binding proteins.

Animals↗
PubMed1989

Two distinct Gi-proteins mediate formyl peptide receptor signal transduction in human leukemia (HL-60) cells.

In membranes of myeloid differentiated HL-60 cells, the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine stimulates phospholipase C via a pertussis toxin-sensitive G-protein but does not inhibit adenylyl cyclase. In these membranes, the chemotactic peptide markedly stimulates the cholera toxin-dependent [32P]ADP-ribosylation of two proteins with approximate molecular masses of 40 and 41 kDa, respectively. The radiolabeled proteins comigrate on sodium dodecyl sulfate-polyacrylamide gels with the two pertussis toxin substrates present in HL-60 membranes, alpha i2 and alpha i3. The effect of the chemotactic peptide is blocked by treatment of intact HL-60 cells with pertussis toxin. Peptide mapping studies using Staphylococcus aureus protease V8 reveal that the two radiolabeled proteins are structurally distinct. Thus, the agonist-activated formyl peptide receptor functionally interacts with two distinct pertussis toxin substrates, most likely with Gi2 and Gi3. As the third Gi protein, Gi1, appears to be absent from both HL-60 cells and from systems that clearly reveal hormonal inhibition of adenylyl cyclase, the results strongly suggest that primary structure alone does not suffice to determine which effector mechanism is regulated by a given Gi-protein.

Adenosine Diphosphate Ribose↗
PubMed1989

Na+ regulation of formyl peptide receptor-mediated signal transduction in HL 60 cells. Evidence that the cation prevents activation of the G-protein by unoccupied receptors.

In neutrophils and several other phagocytes, a pertussis and cholera toxin-sensitive guanine nucleotide-binding protein (G-protein) couples the receptors for formyl methionine-containing chemotactic peptides to stimulation of phospholipase C. We used membranes of myeloid-differentiated HL 60 cells to study the role of Na+ in regulating both the interaction of the formyl peptide receptor with the chemotactic agonist, N-formyl-methionyl-leucyl-phenylalanine (FMLP), and the receptor-mediated activation of the G-protein. Monovalent cations (Na+ greater than Li+ greater than K+ greater than choline+) markedly inhibited the binding of the radiolabeled oligopeptide [3H]FMLP by specifically reducing the number of receptors in the high-affinity state. Half-maximal and maximal inhibition of peptide binding were seen at cation concentrations of approximately 20 and 200 mM, respectively. Inhibition of peptide binding by Na+ was observed in the presence and absence of divalent cations and was strictly additive to inhibition by the poorly hydrolyzable GTP analogue, guanosine-5'-O-(3-thiotriphosphate), or to ADP ribosylation of G-proteins by pertussis toxin. The inhibitory effect of Na+ on peptide binding coincided with a marked reduction of the potency of FMLP to stimulate a high-affinity GTPase. In contrast, the degree of FMLP-stimulated GTPase activity was markedly enhanced in the presence of Na+. This was largely due to the fact that Na+ reduced the agonist-independent basal GTPase activity in the same way but less so than pertussis toxin treatment. The results show that monovalent cations, Na+ in particular, regulate the interaction of the formyl peptide receptor with both the chemotactic agonist and the G-protein by acting on a single site, possibly located on the receptor itself. The observation that basal GTPase activity is markedly reduced by both Na+ and pertussis toxin treatment also suggests (a) that G-proteins interact with and are activated by receptors even in the absence of agonists and (b) that Na+ uncouples unoccupied receptors from G-protein interaction and activation.

Cell Line↗
PubMed1989

Mechanism of noradrenaline-induced heterologous desensitization of adenylate cyclase stimulation in rat heart muscle cells: increase in the level of inhibitory G-protein alpha-subunits.

The mechanism of heterologous desensitization of adenylate cyclase stimulation was studied in cultured neonatal rat heart muscle cells. After culturing of the cells for 3 days in the presence of 1 microM noradrenaline there was in addition to a 52% decrease in isoproterenol-stimulated adenylate cyclase activity, a lessening of the stimulation of beta-adrenoceptor-independent adenylate cyclase by guanosine-5'-O-(thiotriphosphate) and forskolin by 24 and 34%, respectively. The decrease in receptor-independent adenylate cyclase stimulation by forskolin, but not the attenuation of isoproterenol-stimulated adenylate cyclase activity, was abolished by pertussis toxin (PTX) pretreatment of the cells. Gi, the inhibitory G-protein of adenylate cyclase was therefore quantitated. Labelling of the Mr approximately 40 kDa PTX substrates in membranes of noradrenaline-treated cells was increased by 70% as shown by pertussis toxin-catalyzed ADP ribosylation of heart cell membranes. This increase was also seen in the presence of an excess of purified beta gamma-subunits of transducin and of GTP, suggesting that the increased labelling was not due to elevation of the level of beta gamma-subunits or increase in the concentration of GTP in the membranes of noradrenaline-treated cells. Analysis of the PTX substrates on high resolution urea/SDS-polyacrylamide gels revealed that at least two distinct PTX substrates (40 and 41 kDa) were present in rat heart cell membranes. The labelling of both substrates was increased in membranes of desensitized cells. Immunoblotting of heart cell membranes with anti-Gi alpha-antibodies demonstrated a marked increase in the amount of Gi alpha in membranes of noradrenaline-treated cells. In contrast, immunoblotting with anti-beta-antibodies showed that the level of the beta-subunit of G-proteins (36 kDa) was unchanged after noradrenaline exposure. The data indicate that prolonged treatment of rat heart muscle cells with noradrenaline leads to an increase in the level of alpha-subunits of Gi-proteins. This suggests that this increase is responsible for the observed heterologous desensitization of adenylate cyclase stimulation.

Adenosine Diphosphate↗
PubMed1989

Dual Mg2+ control of formyl-peptide-receptor--G-protein interaction in HL 60 cells. Evidence that the low-agonist-affinity receptor interacts with and activates the G-protein.

In neutrophils and several other phagocytic cell types, a pertussis- and cholera-toxin-sensitive form of the guanine-nucleotide-binding protein (G-protein) Gp couples receptors for N-formylmethionine-containing chemotactic peptides to stimulation of phospholipase C. Using membranes of myeloid differentiated HL 60 cells, we have examined the role of Mg2+ and guanine nucleotides in regulating (a) the interaction of the formyl-peptide receptor with the chemotactic agonist N-formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe) and (b) the receptor-mediated activation of Gp. Mg2+ markedly enhanced the number of receptors with high affinity for the radiolabeled oligopeptide fMet-Leu-[3H]Phe. At the same time, Mg2+ largely increased the potency of guanosine-5'-(3-O-thio)triphosphate, but not of GDP or guanosine-5'-(2-O-thio)diphosphate, to inhibit binding of the peptide. Comparison of the potency of Mg2+ in eliciting these two effects and analysis of the specificities of the relevant divalent cation sites revealed that Mg2+ interacts with at least two independent sites on the receptor-Gp complex. One site is specific for Mg2+ and exhibits affinity in the micromolar range, the other site interacts with millimolar concentrations of several divalent cations in a non-selective fashion. It is suggested that the former site is located on Gp and that interaction of Mg2+ with this site is necessary for the receptor-mediated G-protein activation, whereas interaction of divalent cations with the latter site is necessary for high affinity agonist binding. The regulation of the formyl-peptide receptor binding properties by guanine nucleotides is independent of Gp activation, since inhibition of peptide binding is achieved by addition of both guanine nucleoside diphosphates and triphosphates and is readily seen both in the presence and in the absence of Mg2+. The latter finding, together with the observation that, at micromolar concentrations of Mg2+, high-affinity GTPase activity is stimulated by fMet-Leu-Phe primarily via low affinity receptors, suggests that, contrary to widely held opinions, (a) divalent cations are not required for a functional receptor--G-protein interaction and (b) high-affinity agonist binding is not a prerequisite for the receptor-mediated activation of the G-protein.

Binding Sites↗
PubMed1989

Evidence that activation of a common G-protein by receptors for leukotriene B4 and N-formylmethionyl-leucyl-phenylalanine in HL-60 cells occurs by different mechanisms.

Differentiated HL-60 cells were found to respond to the chemoattractants leukotriene B4 (LTB4) and N-formylmethionyl-leucyl-phenylalanine (FMLP), in a manner similar to neutrophils. Membranes of myeloid differentiated HL-60 cells were used (a) to examine the ability of LTB4 receptors to interact with a guanine-nucleotide-binding protein (G-protein), and (b) to compare this G-protein with that which is coupled to the FMLP receptor. LTB4 stimulated a dose-dependent increase in GTP hydrolysis and guanosine 5'-[gamma-thio]triphosphate (GTP[S]) binding, demonstrating that LTB4 receptors on HL-60 cells are coupled to a G-protein. Both pertussis toxin and cholera toxin inhibited stimulation of GTPase activity and GTP[S] binding by either LTB4 or FMLP, indicating that both receptors are coupled to a G-protein containing a 40 kDa alpha-subunit. That the two receptors share a common G-protein was shown by FMLP enhancement of cholera-toxin-induced inhibition of GTPase activity stimulated by either FMLP or LTB4. However, LTB4 did not enhance cholera-toxin-induced inhibition of GTPase activity, suggesting that the receptors interacted differently with this G-protein. This difference was confirmed by showing that FMLP, but not LTB4, stimulated receptor-specific [32P]ADP-ribosylation of the 40 kDa alpha-subunit. Concentrations of LTB4 and FMLP which produced maximal responses produced enhanced stimulation in both assays. This additive effect was not abolished by inactivation of up to 80% of G-protein activity by N-ethylmaleimide or cholera toxin. We conclude that LTB4 and FMLP receptors in HL-60 cells are coupled to a common G-protein. The receptor--G-protein interaction is different for the two receptors, and G-proteins not coupled to both receptors may account for the additive response.

Cell Line↗
PubMed1989

Outcome of fetuses with abnormal biophysical profile.

Sonographic observation of fetal behavior as a possible indicator for the state of fetal health was quantified with a modified biophysical profile (BPP). The observation time was extended to 40 min, as the fetal rest-activity cycle implies that inactivity may last that long. Gestational age ranged 27-43 weeks. Cardiotocography (CTG) was performed subsequent to an abnormal BPP (ultrasound score 0-4). Reactivity, indicating favorable fetal outcome, was more common in near-term fetuses, suggesting that BPP should be interpreted in relation to gestational age. Therefore, fetuses with an abnormal BPP (n = 29) were each matched and compared with 2 fetuses of same gestational age but normal BPP (ultrasound score 6-8; n = 58). The perinatal mortality and morbidity were significantly higher in infants with abnormal score than in infants with normal score (p less than 0.01). BPP by third trimester sonography helps to diagnose acutely endangered fetuses, and an abnormal fetal movement pattern should lead to further evaluation, i.e. CTG. While BPP scoring, as compared to CTG, is less favorable as a primary surveillance technique and not superior for identifying the hypoxic fetus, additional information is obtained with BPP by diagnosing the growth-retarded and/or malformed fetus.

Cardiotocography↗
PubMed1988

[Hepatitis B screening in late pregnancy and results of immunization in newborn infants].

Screening for hepatitis Bs antigen in late pregnancy was introduced in mid-1983 at the University Women's Hospital, Berne. 4118 pregnant women had been investigated by the end of 1986, of whom 26 (0.63%) turned out to be HBsAg positive. The prevalence of HBsAg carriers was 0.12% in Swiss women, 0.65% in other European women, 12.5% in women from the Far East and 5.6% and 4.9% in women from the Near East and Africa respectively. Newborns of HBsAg positive mothers simultaneously received hepatitis B immunoglobulin (400 IU anti-HBs) and a first injection of hepatitis B vaccine (Hevac B 5 mg) in the first hours of life, followed by vaccinations after two, three and twelve months. Of 18 children investigated after the first year of life none was HBsAg positive. 14 children (78%) were shown to have HBs antibodies. Two of the four anti-HBs-negative unfortunately received only the first vaccine injection after birth. Taking this fact into account, the "success rate" of the immunoprophylaxis is 88%.

Female↗
PubMed1988

Single umbilical artery: prenatal findings.

In 450 patients with pregnancy at high risk for fetal malformation and/or intrauterine growth retardation, the umbilical cord was investigated sonographically for the presence of a single umbilical artery. A single umbilical artery was diagnosed in four fetuses between 23 and 33 weeks of gestation and suspected in two. Three cases were overlooked at sonography. All seven surviving fetuses had growth retardation at delivery and four also showed severe malformations. Whenever a single umbilical artery is found at sonography, further work-up is required to rule out associated anomalies, intrauterine growth retardation, or chromosomal abnormality.

Female↗
PubMed1988

Prenatal and postnatal prophylaxis of infections in preterm neonates.

Administration of gamma-globulin for intravenous administration (IVIG) to preterm neonates (0.3 g/day in neonates below 1000 g; 0.5 g/day in neonates over 1000 g for 6 consecutive days) led to a significant rise in circulating serum IgG levels. After 6 days of IVIG administration, the IgG serum levels reached an average of 11 to 12 g/liter, values usually seen in normal term infants. The mortality rate of the preterm infants with septicemia decreased from 44% in the infants receiving only antibiotics to 8% in the infants treated by IVIG together with the same antibiotic. The IVIG preparation was well-tolerated by all newborns. Blood gas analysis, clinical examination, monitoring of respiration, pulse and body temperature revealed no untoward reactions attributable to IVIG. Follow-up at an average age of 2.5 years showed no evidence of harmful effects of IVIG treatment in the neonatal period. In a recently concluded study no differences in the levels of various liver enzymes in infants treated with IVIG and in untreated infants was found 6 weeks after administration of IVIG. In another group of preterm infants with perinatal infections who received IVIG after birth, the serum IgG levels were determined at 3 to 4 and 6 to 8 weeks of age. At 3 to 4 weeks no difference was found in the serum IgG levels in infants with or without recurrent infections. At 6 to 8 weeks the serum IgG levels were slightly decreased in infants with recurrent as compared to those without recurrent infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1987

Purification and immunochemical characterization of the major pertussis-toxin-sensitive guanine-nucleotide-binding protein of bovine-neutrophil membranes.

Bovine peripheral neutrophils contain high levels of a 40-kDa pertussis toxin substrate, which was found highly enriched in a light membrane fraction upon subcellular fractionation of neutrophil homogenates. The 40-kDa pertussis toxin substrate, referred to as alpha n, was purified to near homogeneity from this fraction by sequential ion-exchange, gel-filtration and hydrophobic chromatography. Purified alpha n was shown to interact with beta gamma subunits, undergo ADP-ribosylation by pertussis toxin, and bind guanine nucleotides with high affinity. The mobility of purified alpha n on SDS/polyacrylamide gels was intermediate between those of the alpha subunits of Gi and Go, purified from bovine brain, and slightly lower than the mobility of the alpha subunit of transducin (Gt). Several polyclonal antisera against the alpha subunits of bovine Gt and Go did not react with alpha n on immunoblots. CW 6, a polyclonal antiserum reactive against the bovine alpha i, reacted only minimally with alpha n. These results suggest that the major pertussis toxin substrate of bovine neutrophils, designated Gn, is structurally different from previously identified pertussis toxin substrates and may represent a novel guanine-nucleotide-binding protein.

Adenosine Diphosphate Ribose↗
PubMed1986

Transplacental passage of intravenous immunoglobulin in the last trimester of pregnancy.

Immunoglobulin G was given intravenously (IVIgG) to pregnant women (27 to 36 weeks gestation) with signs of chorioamnionitis who were at risk for preterm delivery. Twenty-four patients received antibiotics alone (control group). Twenty-seven patients received the same antibiotics in combination with IVIgG, either 12 gm in 12 hours (low IVIgG dosage) or 24 gm on each of 5 consecutive days (high IVIgG dosage). Transplacental passage of IVIgG was shown to be a function of gestational age and of dose. Up to the thirty-second week of gestation, IgG infusions had no effect on IgG concentrations in cord sera. After that time, cord serum IgG levels were significantly higher in the high-dose group compared with the low-dose and control groups. All four subclasses of IgG, and two different antibodies present in the IVIgG preparation passed from the mother to the fetus. Thus the infused IgG mimicked the transplacental passage of endogenous IgG.

Chorioamnionitis↗
PubMed1986

Experience with intravenous immunoglobulin treatment in neonates and pregnant women.

Results of 2 methods to treat infection in the neonate are reported. One study demonstrates a decrease in mortality and recurrent infection when neonates with septicemia were given intravenous immunoglobulin (IVIG). In another study, IVIG was administered to pregnant women with symptoms of infection and at risk for preterm delivery. IVIG infused at high doses after 32 weeks of gestation significantly decreased infection in newborns without affecting term.

Dose-Response Relationship, Drug↗
PubMed1986

IgG subclasses and antibodies to group B streptococci, pneumococci, and tetanus toxoid in preterm neonates after intravenous infusion of immunoglobulin to the mothers.

High doses of intravenous immunoglobulin were given to seven pregnant women between the 27th and 36th wk of gestation who were at risk for preterm delivery. Determinations of IgG subclasses and of antibodies against group B streptococcal serotypes, pneumococcal polysaccharides, and tetanus toxoid were done in maternal serum before and after intravenous IgG infusion and after delivery in cord serum. Substantial transplacental passage of the infused material could be observed in five cases where delivery occurred at the 34th wk or later. After the 36th wk of gestation, IgG subclass and antibody concentrations in cord serum were increased up to the levels in the maternal serum.

Antibodies↗
PubMed1984

Plasma ammonia concentrations in newborns and children.

Many, mostly congenital, hyperammonemic syndromes may occur in the first days of life. For the diagnosis of these disorders plasma ammonia levels physiologically present in neonates and early childhood should be known, preferably by the use of an enzymatic method. Full-term newborns had higher capillary ammonia concentrations on the first day of life (30-144 mumol/l) than on the fifth day (31-104 mumol/l). In the same individuals the arterial (38-89 mumol/l) are lower than the capillary concentrations (69-112 mumol/l). The venous concentrations in school children were not higher than in adults. The scatter of capillary values, however, is great. For diagnostic purposes of disorders of ammonia detoxication sampling of arterial or venous blood is preferable.

Adult↗
PubMed1984

The treatment of neonatal isoimmune thrombocytopenia with intravenous immunoglobin (IgG i.v.).

We present a report of the use of IgG i.v. to treat clinically manifest neonatal immune thrombocytopenia. The IgG i.v. was administered at a daily dosage of 0.4 g/kg body weight for 5 days. Treatment was started when the child was 3 days old and had a platelet count of 2 X 10(9)/l. Four days later the platelet count had risen to 200 X 10(9)/l. The diagnosis of immune thrombocytopenia was confirmed by platelet typing of the mother's and child's platelets and identification of anti-platelet antibodies in maternal serum.

Blood Group Incompatibility↗
PubMed1984

Comparison of the fat content and fat globule size distribution of breast milk from mothers delivering term and preterm.

The fat content and the fat globule size distribution of human preterm milk samples were analyzed and compared with data of previously analyzed samples of term milk. A negative correlation was found between the fat content and the gestational age. In both term and preterm milk three subpopulations of fat globules could be observed. The subpopulations of small (1 to 15 microns) and large globules (8 to 13 microns) were larger in preterm milk, but decreased slower throughout lactation. The average diameter was identical in both milks and increased with advancing lactation. The fat surface, which also depends on the fat content, increased with decreasing gestational age. However, no correlation between the specific fat surface area and the gestational age was found. Compared to human milk, commercial infant formulas have a smaller average fat globule diameter and a larger specific fat surface area.

Chemical Phenomena↗