Inactivation of bacterial respiratory chain enzymes by singlet oxygen

To distinguish the bactericidal action of singlet oxygen (1O2) from hypohalous acids, wild-type and lycopene transformant E. coli strains were exposed to each of the oxidants and then bacterial viability was investigated. 1O2 was generated by chemical and enzymatic systems at pH 4.5. ExpoSure of wild-type E. coli to 1O2 caused a significant loss of E. coli viability due to inactivation of membrane respiratory chain enzymes by 1O2. This action of 1O2 could be attenuated by lycopene in the bacterial cell membrane. In the lycopene transformant strain of E. coli, inactivation of NADH oxidase and succinate oxidase by hypohalous acids were significantly suppressed, but E. coli viability was unaffected. Based on these findings, we suggest that phagocytic leukocytes produce 1O2 as a major bactericidal oxidant in the phagosome.

Useful 1O2 (1delta g) generator, 3-(4'-methyl-1'-naphthyl)-propionic acid, 1',4'-endoperoxide (NEPO), for dioxygenation of squalence (a skin surface lipid) in an organic solvent and bacterial killing in aqueous medium

3-(4'-Methyl-1'-naphthyl)-propionic acid, 1',4'-endoperoxide (NEPO) provides singlet state of oxygen (1O2, 1delta g) at 37 degrees C in sodium phosphate buffer (pH 7.2), acetate buffer (pH 4.5), methanol or chloroform, through the retro-Diels-Alder reaction. The total amount of 1O2 generated by NEPO was calculated using the following equation: [1O2]= [NEPO]0[1-exp(-kt)], where [1O2], [NEPO]0 and k are the total amount of 1O2 produced during the time t, initial concentration of NEPO and the first-order reaction rate constant, respectively. When squalene was exposed to 1O2 which was generated thermolytically from NEPO, it was oxidized to three hydroperoxides, mono-, di- and tri-hydroperoxides, in amounts proportional to the dose of NEPO. The oxidizability of squalene was much more extensive compared with unsaturated phospholipids. Additionally, when wild-type E. coli and lycopene-producing mutant E. coli were exposed to NEPO-derived 1O2, there was significant loss of viability of wild-type E. coli but no significant loss of viability in lycopene-producing strain, suggesting that lycopene by scavenging 1O2 protected E. coli against 1O2 toxicity.

Preferential hydrolysis of oxidized phosphatidylcholine in cholesterol-containing phosphatidylcholine liposome by phospholipase A2

Hydrolysis of 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC) hydroperoxide (PLPC-OOH) in PLPC liposomal membrane by Crotalus adamanteus venom phospholipase A2 (PLA2) was studied by measuring the decay of PLPC and PLPC-OOH and the formation of linoleate and linoleate hydroperoxide. We demonstrate that PLA2 has a preference to hydrolyze PLPC-OOH over PLPC when more than 25 mole % of cholesterol is incorporated into the PLPC liposomal membrane. Similar results were obtained for PLPC hydroxide (PLPC-OH). These results suggest that cholesterol displaces the hydrophilic hydroperoxyl and hydroxyl moieties of PLPC-O(O)H to the surface interface of the liposomal membrane where they are more accessible to PLA2 hydrolysis.

A study of medical emergency workflow

In this paper, the authors introduce a workflow model. The development of computer network technology enables us to share the distributed data in real time. It is a considerable significance in the practical application of network capabilities not only to office work but also to the medical environment. In order to construct a well-connected, managed post (environment, scene), a model is needed to design the workflow. Here we propose a workflow model to cope with the scene of unforeseen events that we usually encounter in daily clinical activities. We give careful consideration to the ability of this model to manage dynamic changes within the workflow and describe its application to a medical scene (triage) and then carry out simulations based on this model. The authors are able to demonstrate the validity of this model through this simulation.

1,2-Diacylglycerol hydroperoxides induce the generation and release of superoxide anion from human polymorphonuclear leukocytes

We examined the effect of 1-palmitoyl-2-linoleoylglycerol (PLG), PLG hydroxide (PLG-OH), and PLG hydroperoxide (PLG-OOH) on the release of superoxide anion from human PMNs monitored by the chemiluminescence generated by the superoxide anion-sensitive reagent, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin++ +-3-one (MCLA). PLG-OOH at low micromolar concentrations stimulated human PMNs whereas PLG and PLG-OH did not. 1,3-Dilinoleoylglycerol hydroperoxide, 1-palmitoyl-2-linoleoylphosphatidylcholine hydroperoxide, and linoleic acid hydroperoxide were much less efficient in stimulating human PMNs than PLG-OOH. The PKC inhibitors, chelerythrine chloride and staurosporine, inhibited the stimulation of PMNs. Possible pathophysiological role of 1,2-diacylglycerol hydroperoxides is discussed.

Oxidation of rat liver phospholipids: comparison of pathways in homogeneous solution, in liposomal suspension and in whole tissue homogenates

The oxidation of equivalent concentrations of phospholipids in homogeneous solution, in multilamellar liposomal suspension, and in rat liver homogenate was carried out under aerobic conditions at 37 degrees C in order to examine the biochemical fate of oxidized phospholipids. Rat liver phospholipids were extracted with chloroform and methanol, and oxidation in this homogeneous solution was initiated with a lipid-soluble radical initiator. The oxidation products were phosphatidylcholine hydroperoxide (PC-OOH) and phosphatidylethanolamine hydroperoxide (PE-OOH), which were quantified by HPLC separation using a hydroperoxide-specific chemiluminescence detector. Co-extracted alpha-tocopherol and ubiquinol-9 suppressed the formation of PC-OOH and PE-OOH until oxidatively exhausted. The oxidation of extracted rat liver phospholipids in multilamellar liposomal suspension initiated with the lipid-soluble initiator gave similar results, but with slower rates of antioxidant depletion and phospholipid hydroperoxide formation due to a lower efficiency of free radical production in liposomal membranes. In contrast, the oxidation of rat liver homogenate containing active tissue enzymes initiated by the addition of either free radical initiators or tert-butyl hydroperoxide gave phosphatidylcholine hydroxide, phosphatidylethanolamine hydroxide, and free fatty acid hydroxides as oxidation products. Exogenous PC-OOH added to the rat liver homogenate was reduced to phosphatidylcholine hydroxide with subsequent hydrolysis to its free fatty acid hydroxide. These results suggest that peroxidase and phospholipase enzymes play important roles in the repair of oxidatively damaged phospholipids in biomembranes.

Insulin and insulin-like growth factors induce expression of angiotensin type-2 receptor in vascular-smooth-muscle cells

Angiotensin type-2 receptor (AT2) is abundant in fetal tissues, including aorta, and its expression level declines after birth. In the present study, the regulation of its expression was studied in cultured vascular-smooth-muscle cells (VSMC). The maximum number of binding sites of AT2 increased in VSMC after they were cultured without serum in the presence of insulin, which was essential for its expression. AT2 expression was inhibited by treatment with phorbol ester. Northern blot analyses revealed that insulin-dependent expression is due to elevation of mRNA level of AT2. Similar induction was observed when insulin-like growth factor (IGF)-I or IGF-II was used instead of insulin. The study on the dose dependencies of these factors revealed that the induction of AT2 expression was mediated through the activation of IGF-I receptors. The insulin-induced expression of AT2 was detected in the aorta of genetically obese (fa/fa) Zucker rats, which reportedly have approximately tenfold-higher plasma concentrations of insulin than their lean littermates. The insulin-dependence seems characteristic of VSMC, because it was not observed for pheochromocytoma cells or adrenal glands. These results suggest that the expression of AT2 is regulated by at least two mechanisms, that is, IGF-I receptor dependent and IGF-I receptor independent, and that the former may play an important role in the expression of AT2 in VSMC.

Differential inducibility of angiotensin II AT2 receptor between SHR and WKY vascular smooth muscle cells

Although the fetal aorta expresses a substantial amount of angiotensin II type 2 receptors, the expression level of angiotensin II type 2 receptors in the adult aorta and cultured vascular smooth muscle cells is very low or even absent. Prolonged serum depletion (6 to 8 days) with a supplement of insulin, transferrin and sodium selenite induced angiotensin II type 2 receptors and mRNA in cultured vascular smooth muscle cells from Wistar Kyoto rats. Insulin was found to be essential for the induction of the receptor. However, these receptors could not be induced in cultured vascular smooth muscle cells from spontaneously hypertensive rats. These results suggest that: (1) insulin plays an important role for the expression of the angiotensin II type 2 receptor gene; and (2) the type 2 receptor gene expression is differentially regulated between cultured vascular smooth muscle cells of Wistar Kyoto rats and spontaneously hypertensive rats.

Transcription of the rat angiotensin II type 2 receptor gene

The promoter region of the rat angiotensin II type 2 receptor gene was cloned and the nucleotide sequences were determined. A computer homology search for a 1.2 Kb promoter region showed that there are several consensus cis DNA elements such as C/EBP, NF-IL6, GRE and AP1 in this region. Primer extension experiments showed that there is one transcription initiation site 15 bp-downstream of the TATA box. Deletion mutants of the 1.2 Kb segment were prepared and fused to a luciferase reporter gene. These type 2 receptor promoter-luciferase constructs were introduced into PC12W cells, a pheochromocytoma cell line expressing the type 2 receptor, and luciferase activity was measured. It showed that (1) a DNA segment between -1208 bp and -749 bp suppresses the promoter activity of type 2 receptor gene, (2) a positive regulatory element is present in a DNA segment between -749 bp and -216 bp; and (3) a DNA segment between -44 bp +58 bp is important for the basal promoter activity of the type 2 receptor gene.

Activation of protein kinase C by oxidized diacylglycerols

The effects of 1,2-diacylglycerol hydroperoxide (DAG-OOH), its alcohol (DAG-OH), "unoxidized" 1,2-diacylglycerol (DAG), 1,2-dioleoylglycerol (DOG), and phorbol 12-myristate acetate (PMA) on the activity of protein kinase C (PKC) isolated from rat brain were examined in the presence and absence of phosphatidylserine (PS) and calcium ion. Both DAG-OOH and DAG-OH stimulated the activity of PKC dose- and time-dependently. The ability of additives for PKC activation increased in the order of DOG, DAG << DAG-OOH, DAG-OH < PMA. DAG-OOH and DAG-OH activated PKC even in the absence of PS and calcium ion as PMA does. If DAG-OOH and DAG-OH are released from the oxidized biomembranes by the action of phospholipase C, these components may act like PMA and serve to activate the PKC-dependent signal transduction system.

Multiple growth factors modulate mRNA expression of angiotensin II type-2 receptor in R3T3 cells

Previous studies showed that angiotensin II type-2 receptor (AT2) sites were increased when R3T3 cells were growth arrested and decreased when they were stimulated with fibroblast growth factor or serum. We examined the effects of several other growth factors on the expression of AT2 mRNA to clarify the relation between the AT2 receptor and growth factors. R3T3 cells were cultured in the medium containing 10% FCS until they were confluent and then serum was removed. AT2 mRNA was increased after serum was depleted, and the expression level reached a plateau after 2 days of serum depletion. The presence of serum (10%), fibroblast growth factor (10 ng/mL), or lysophosphatidic acid (1 mumol/L) reduced the AT2 mRNA expression. Phorbol ester (1 to 100 nmol/L) also suppressed the AT2 mRNA expression in a dose-dependent manner. Interleukin-1 beta (1 ng/mL) enhanced the AT2 mRNA expression 1.6-fold and the AT2 receptor number 1.4-fold. Insulin (100 nmol/L) enhanced AT2 mRNA expression 1.4-fold and the AT2 receptor number 1.6-fold. These results suggest that AT2 mRNA expression is modulated by multiple growth factors in both positive and negative directions. The presence of potential cis DNA elements that respond to interleukin-1 beta (CCAAT enhancer binding protein site), insulin [insulin response sequence of phospho(enol)pyruvate carboxykinase gene], and phorbol ester (AP-1 site) in the promoter region of the mouse AT2 gene suggests that the effects of these growth factors and phorbol ester may be mediated via these cis DNA elements.

Adrenomedullin stimulates two signal transduction pathways, cAMP accumulation and Ca2+ mobilization, in bovine aortic endothelial cells

The biological action of adrenomedullin, a novel hypotensive peptide, on bovine aortic endothelial cells, was examined. The specific binding of adrenomedullin to these cells was observed, and adrenomedullin was found to induce intracellular cAMP accumulation in a dose-dependent manner. EC50 for the cAMP accumulation was about 100 times lower than the apparent IC50 for the binding assay. Adrenomedullin also induced increase of intracellular free Ca2+ in endothelial cells in a dose-dependent manner. The Ca2+ response to adrenomedullin was biphasic with an initial transient increase due to the release from thapsigargin-sensitive intracellular Ca2+ storage and a prolonged increase by influx through the ion channel on the plasma membrane. This intracellular free Ca2+ increase resulted from phospholipase C activation and inositol 1,4,5-trisphosphate formation, and seemed to cause nitric oxide synthase activation by monitoring intracellular cGMP accumulation. Both cAMP accumulation and Ca2+ increased responses to adrenomedullin were mediated by cholera toxin-sensitive G protein, but the two signal transduction pathways were independent. Thus, the results suggest that adrenomedullin elicits the hypotensive effect through at least two mechanisms, a direct action on vascular smooth muscle cells to increase intracellular cAMP and an action on endothelial cells to stimulate nitric oxide release, with both leading to vascular relaxation.

Cloning and expression of protein tyrosine phosphatase-like protein derived from a rat pheochromocytoma cell line

A novel protein [designated protein tyrosine phosphatase-like protein (PTPLP)] which is distantly related to receptor-type protein tyrosine phosphatases (PTPases) was cloned from a rat pheochromocytoma cell line. The PTPLP was detected exclusively in the brain. Overexpression of the PTPLP decreased the basal PTPase activity of COS-7 cells for Raytide. These results suggest that PTPLP may function as a negative regulator of PTPases in neuronal tissues.

Cloning, expression and regulation of angiotensin II receptors

Complementary DNAs for angiotensin II type 1 receptor isoforms AT1A and AT1B were cloned by expression cloning from bovine adrenal and rat vascular smooth muscles. Human AT1 receptor was also cloned. Seven transmembrane structures emerged. The AT1 type receptor interacted with more than one type of G-proteins. The ligand binding site of AT1 involving Arg167, Lys199, and Asp263 has been identified by site directed mutagenesis. The regulation of the receptors occur at many stages. The isoform, AT2, was also expression cloned from rat pheochromocytoma cells. Although its ligand binding is not affected by stable GTP analogs, it is a seven transmembrane domain receptor. It mediates the modulations of phosphotyrosine phosphatase by angiotensin II and AT2 specific CGP42112A. The modulation was abolished by pertussis toxin. Thus, AT2 belongs to a new class of angiotensin receptors with unique signalling and regulatory mechanisms. AT1 mediates cellular growth. Interestingly, AT2 expression is inversely related to the mitogenic activity of cells.

Molecular structure and function of angiotensin type 2 receptor

More than two isoforms have been identified for angiotensin receptors based on their ligand selectivity. The objective of this study is to determine the molecular structure of angiotensin type 2 receptor (AT2), whose physiological functions are still an enigma despite extensive studies on its distribution in fetal tissues. We expression-cloned a cDNA of an affinity-purified AT2 from rat pheochromocytoma cells (PC12w). The AT2 cDNA clone comprises 2,868 nucleotides and encodes a 363 amino acid protein with seven putative transmembrane domains. The dissociation constant for its binding to 125I-CGP42112A, an AT2-specific ligand, was 0.11 +/- 0.01 nM. Its binding to 0.5 nM 125I-[Sar1,Ile8]-Ang II was not inhibited by Dup 753 but by PD123319 (IC50 = 1.7 +/- 0.2 nM). These binding features are characteristic of angiotensin type 2 receptor. The amino acid sequence analysis of the purified AT2 corroborated the amino terminus of the deduced primary structure of AT2. Angiotensin type 1 receptor (AT1) is the most closely related to AT2 but with only 32% amino acid sequence identity. Angiotensin II attenuated membrane-associated protein tyrosine phosphatase activity in the COS-7 cells stably expressing AT2 through a pertussis toxin-sensitive G protein. However, the physiological function of AT2 in the fetal kidney is still unresolved.

Cloning, expression and regulation of angiotensin II receptors

Angiotensin II isoform 1 (AT1) receptor cDNAs were cloned by expression cloning from bovine adrenal and rat vascular smooth muscles. Human AT1 receptor was also cloned. Seven transmembrane structures emerged. A single type of receptor seems to interact with more than one type of G-protein. AT1 consists of subtypes AT1A and AT1B, and the regulation of the receptors occurs at many stages. The isoform AT2 was also expression cloned from rat pheochromocytoma cells. Although its ligand binding is not affected by GTP analogs, it is a seven transmembrane domain receptor. It mediates the inhibition of phosphotyrosine phosphatase by angiotensin II and AT2 specific CGP42112A; the inhibition was abolished by pertussis toxin. Thus, AT2 belongs to a new class of angiotensin receptors with unique signalling and regulatory mechanisms.

Angiotensin II receptors: cloning and expression

To identify the mechanisms of action of isoforms angiotensin II receptors (AT1A, AT1B, and AT2) and to overcome the difficulties encountered in attempts to purify the receptors, we have expression-cloned their cDNAs from bovine and rat sources and isolated human cDNA and rat and human genomic DNA. The AT1A and AT1B cDNAs were found to encode respective receptor proteins with 359 amino acid residues, whereas, AT2 encodes a 363 amino acid residue receptor protein. Both AT1 and AT2 were found to conform with the seven transmembrane receptor structural motif, but showed only 32% amino acid residue identity to each other. The AT1 receptor was shown to be coupled to, at least, three different G proteins activating phospholipase C, inhibiting adenylyl cyclase and opening an L-type Ca(2+)-channel, whereas, AT2 was found to inhibit a phosphotyrosine phosphatase activity without affecting guanylyl cyclase by a pertussis-toxin-sensitive, presumably G-protein-mediated mechanism.

Cloning of the cDNA and the genomic DNA of the mouse angiotensin II type 2 receptor

Of the two major isoforms of the angiotensin II receptors, type 1 (AT1) and type 2 (AT2), little is known about the structure and features of AT2. We cloned a mouse AT2 cDNA from a mouse fetus cDNA library and an AT2 genomic DNA from a 129SV mouse genomic DNA library. The amino acid sequence of the mouse AT2 (363 residues) deduced from a mouse cDNA clone showed seven membrane-spanning domains. Amino acid identity of the mouse AT2 with mouse AT1 is 37%, and 98% with rat AT2. The genomic DNA (4.4 kb) contained three exons and two introns and the entire coding region was contained in the third exon.

Protein tyrosine phosphatase inhibition by angiotensin II in rat pheochromocytoma cells through type 2 receptor, AT2

Two major isoforms of angiotensin II receptors, AT1 and AT2, have been defined on the basis of their ligand selectivity. While AT1 is known to mediate typical biological actions of angiotensin II as a cardiovascular regulator, the biological function of AT2 has not yet been established. In the present study using a rat pheochromocytoma cell line, which expresses AT2 exclusively, we found that angiotensin II inhibits phosphotyrosine phosphatase activity in vivo as measured by the inhibition of hydrolysis of [32P]-phosphate from the 32P-labeled synthetic peptide substrate, Raytide. This phosphotyrosine phosphatase inhibition was completely reversed by pertussis toxin, which indicates a G-protein coupled mechanism. In SDS-polyacrylamide gel electrophoresis we found that the phosphotyrosine group of an 85 kDa protein was a substrate mainly preserved, presumably as a consequence of the plausible intracellular phosphotyrosine phosphatase inhibition by angiotensin II.

Molecular cloning of a novel angiotensin II receptor isoform involved in phosphotyrosine phosphatase inhibition

There are two major isoforms of the angiotensin II receptor, type 1 (AT1) and type 2 (AT2). AT2 is distinguished from AT1 with respect to its ligand selectivity, its insensitivity to non-hydrolyzable GTP analogues, and its as yet unidentified biological functions. In the present study we have expression-cloned AT2 cDNA from a cDNA library of a rat pheochromocytoma cell line (PC12w). Rat AT2 cDNA encodes a 363-amino acid protein that has seven transmembrane domains. AT1 is the closest in homology to AT2 but with only a 32% identity of amino acid sequence. Stably expressed in COS-7 cells, the receptor showed selective binding to AT2-specific ligands PD123319 and CGP42112A but not to the AT1-specific ligand, losartan. Northern blot analysis revealed that the mRNA of rat AT2 was expressed not only in PC12w cells but also in the adrenal glands and in the inferior olive of the brain, both of which are known to contain AT2 type binding sites. The expressed AT2 receptor mediated angiotensin II-induced inhibition of protein tyrosine phosphatase, an action that was dependent on a pertussis toxin-sensitive G-protein-coupled mechanism in COS-7 cells. The AT2-specific ligand CGP42112A was an agonist rather than antagonist in the inhibition of phosphotyrosine phosphatase. AT2 did not cause a decrease in cGMP in PC12w or COS-7 cells expressing AT2 stably. These results indicate that the AT2 receptor is structurally and functionally different from AT1 and suggest novel functional roles of the renin-angiotensin system in cross-talk with phosphotyrosine signaling by modulating protein phosphotyrosine levels.

Peptide growth factors markedly decrease the ligand binding of angiotensin II type 2 receptor in rat cultured vascular smooth muscle cells

Of two major isoforms of angiotensin II receptors, AT1 and AT2, biological roles of AT2 remain unclear. Using vascular smooth muscle cells, we investigated the regulation of expression of AT2 by growth factors in comparison with that of AT1. The cultured rat aorta smooth muscle cells had detectable AT2 binding sites, which were reduced significantly by treatment with platelet derived growth factor-BB. On the other hand, AT1 binding sites were increased under the same conditions. Other growth factors, such as epidermal growth factor and endothelin-1, also suppressed AT2 receptors to varying extents. A negative correlation between DNA synthesis promoted by these growth factors and the binding capacity of AT2 sites was observed. This study indicated that the expression of AT2 is downregulated in cultured vascular smooth muscle cells by growth factors in contrast to that of AT1, which was slightly upregulated.

Receptor selectivity of natriuretic peptide family, atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide

To elucidate the ligand-receptor relationship of the natriuretic peptide system, which comprises at least three endogenous ligands, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), and three receptors, the ANP-A receptor or guanylate cyclase-A (GC-A), the ANP-B receptor or guanylate cyclase-B (GC-B), and the clearance receptor (C-receptor), we characterized the receptor preparations from human, bovine, and rat tissues and cultured cells with the aid of the binding assay, Northern blot technique, and the cGMP production method. Using these receptor preparations, we examined the binding affinities of ANP, BNP, and CNP for the C-receptor and their potencies for cGMP production via the ANP-A receptor (GC-A) and the ANP-B receptor (GC-B). These analyses revealed the presence of a marked species difference in the receptor selectivity of the natriuretic peptide family, especially among BNPs. Therefore, we investigated the receptor selectivity of the natriuretic peptide family using the homologous assay system with endogenous ligands and receptors of the same species. The rank order of binding affinity for the C-receptor was ANP greater than CNP greater than BNP in both humans and rats. The rank order of potency for cGMP production via the ANP-A receptor (GC-A) was ANP greater than or equal to BNP much greater than CNP, but that via the ANP-B receptor (GC-B) was CNP greater than ANP greater than or equal to BNP. These findings on the receptor selectivity of the natriuretic peptide family provide a new insight into the understanding of the physiological and clinical implications of the natriuretic peptide system.

Biological characterization of human brain natriuretic peptide (BNP) and rat BNP: species-specific actions of BNP

We examined the diuretic-natriuretic activities of rat BNP and human BNP in anesthetized rats in vivo and their vasorelaxant activities for rat thoracic aorta and porcine coronary artery in vitro. Rat BNP was almost equipotent to rat ANP in diuresis and natriuresis with relative potencies of 1.6 and 2.5, respectively, while human BNP exerted no significant activity. Rat ANP, rat BNP and human BNP relaxed PGF2 alpha-contracted rat aortic strips with IC50 values of 0.62, 0.64 and 12.1 nM, respectively, while they relaxed PGF2 alpha-contracted porcine coronary arteries with IC50 values of 0.04, 1.10 and 0.02 nM, respectively. These results strongly suggest that the biological action of BNP is species-specific.