Chain Blocker Research Articles

On the Shelter of a Poset & Its Algebraic Applications

For a poset \(P = C_a \times C_b\), a subset \(A \subseteq P\) is called a chain blocker for \(P\) if \(A\) is inclusion-wise minimal with the property that every maximal chain in \(P\) contains at least one element of \(A\), where \(C_i\) is the chain \(1 < \cdots < i\). In this article, we define the shelter of the poset \(P\) to give a complete description of all chain blockers of \(C_5 \times C_b\) for \(b \geq 1\).

Impact of Wortmannilactone F and G31P on Clonorchis Sinensis-infected mice

Clonorchis sinensis could induce inflammation, epithelial hyperplasia and fibrosis in the intrahepatic bile duct as a food-borne parasite, which was associated with the development of cholangiocarcinoma (CCA). Praziquantel was the most effective drug on treatment of this kind of parasite. However, new drugs with minimal toxicity to the host were urgently needed due to the side effects of Praziquantel and its CCA risk. In this study, helminth mitochondria respiratory chain blocker Wortmannilatone F (WF) and IL-8 analogue CXCL8 (3–72) K11R/G31P were used to treat BALB/C mice infected by Clonorchis sinensis. We investigated the gross and histopathological morphology of the liver, inflammation-associated cytokine IL-6, lipid peroxidation-related proteins cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX), collagen fiber accumulation and fibroblast-specific protein 1 (FSP1), malignant markers proliferating cell nuclear antigen (PCNA) and cytokeratin 19 (CK19), as well as the disinfection effect on these parasites in vitro. WF inhibited and killed the worms dramatically, and the combination of WF with G31P improved the condition of the hepatobiliary duct tissue greatly. These outcomes indicated that the combination of WF and G31P was a potential therapeutic method to treat the Clonorchis sinensis infection.

Influential Factors in the Synthesis of Polymethylhydrogenosiloxane Obtained via Cationic Ring-Opening Polymerization Using Synthetic Silica-Aluminates as Catalysts

In the ambit of the synthesis of silicon polymers and elastomers, there are a lot of variables that affect the final properties of the material, and consequently, their applications. In this work, we synthetized polymethylhydrogensiloxane using the ring opening polymerization (ROP) with 2,4,6,8-tetramethylcyclotetrasiloxane as monomer (D4H), a synthetic aluminosilicate like catalytic species and hexamethyldisiloxane as chain blocker. We made a set of experiments, in order to find the effect on the reaction yield, the absence of crosslinking, crosslinking degree and the mechanical properties of the final polymers. We found that the factor “chain blocker addition time” is significant for yield reaction and crosslinking degree of the elastomers, obtaining a greater crosslinking degree and reaction yield when is added at the beginning of the reaction. Also, using DSC measurements, we found an endothermal signal in 553 K corresponding to the elastomer’s chains rearrangement to dissipate the heat supplied. We obtained PMHS chains up to 24,270 g/mol indicating the ability of this kind of catalysts to achieve relatively high molecular weight chains.

Chain Blockers and Convoluted Catalan Numbers

We give new interpretations of Catalan and convoluted Catalan numbers in terms of trees and chain blockers. For a poset P we say that a subset A ⊆ P is a chain blocker if it is an inclusionwise minimal subset of P that contains at least one element from every maximal chain. In particular, we study the set of chain blockers for the class of posets P = C a × C b where C i is the chain 1 < ⋯ < i. We show that subclasses of these chain blockers are counted by Catalan and convoluted Catalan numbers.

Inhibition of Nicotinamide Phosphoribosyltransferase (NAMPT) Activity by Small Molecule GMX1778 Regulates Reactive Oxygen Species (ROS)-mediated Cytotoxicity in a p53- and Nicotinic Acid Phosphoribosyltransferase1 (NAPRT1)-dependent Manner

Cancer cells undergo mitosis more frequently than normal cells and thus have increased metabolic needs, which in turn lead to higher than normal reactive oxygen species (ROS) production. Higher ROS production increases cancer cell dependence on ROS scavenging systems to balance the increased ROS. Selectively modulating intracellular ROS in cancers by exploiting cancer dependence on ROS scavenging systems provides a useful therapeutic approach. Essential to developing these therapeutic strategies is to maintain physiologically low ROS levels in normal tissues while inducing ROS in cancer cells. GMX1778 is a specific inhibitor of nicotinamide phosphoribosyltransferase, a rate-limiting enzyme required for the regeneration of NAD(+) from nicotinamide. We show that GMX1778 increases intracellular ROS in cancer cells by elevating the superoxide level while decreasing the intracellular NAD(+) level. Notably, GMX1778 treatment does not induce ROS in normal cells. GMX1778-induced ROS can be diminished by adding nicotinic acid (NA) in a NA phosphoribosyltransferase 1 (NAPRT1)-dependent manner, but NAPRT1 is lost in a high frequency of glioblastomas, neuroblastomas, and sarcomas. In NAPRT1-deficient cancer cells, ROS induced by GMX1778 was not susceptible to treatment with NA. GMX1778-mediated ROS induction is p53-dependent, suggesting that the status of both p53 and NAPRT1 might affect tumor apoptosis, as determined by annexin-V staining. However, as determined by colony formation, GMX1778 long term cytotoxicity in cancer cells was only prevented by the addition of NA to NAPRT1-expressing cells. Exposure to GMX1778 may be a novel way of inducing ROS selectively in NAPRT1-negative tumors without inducing cytotoxic ROS in normal tissue.

In vitro skin permeation and cellular protective effects of flavonoids isolated from Suaeda asparagoides extracts

The objective of this study was to compare astragalin (kaempferol-3-O-glucoside) isolated from Suaeda asparagoides extract with kaempferol, an aglycone of astragalin showing the anti-oxidative activity, the cellular protective effect, and skin permeability. Kaempferol was superior to (+)-α-tocopherol and l-ascorbic acid known as strong antioxidants in the antioxidative activity by DPPH method and chemiluminescence assay. Astragalin and kaempferol exhibited more prominent cellular protective effect than the lipid peroxidation chain blocker, (+)-α-tocopherol. In this in vitro permeation experiment of astragalin and kaempferol through the ICR mouse skin, kaempferol permeated deeper into the skin than astragalin. These results indicate that kaempferol and astragalin can function as antioxidants in biological systems, particularly skin exposed to solar radiation, and protect cellular membranes against reactive oxygen species.

Glutamine effect on cultured granule neuron death induced by glucose deprivation and chemical hypoxia

Using a specific fluorescent probe of mitochondrial membrane potential (tetramethylrhodamine ethyl ester), we have shown that glucose deprivation (GD) of cultured cerebellar granule neurons (CGN) for 3h lowers mitochondrial membrane potential in these cells. Longer glucose starvation (24h) causes CGN death that is not prevented by blockers of ionotropic glutamate receptors (MK-801 (10µM) and NBQX (10µM)). Glutamine or pyruvate (2mM) maintain membrane potential of mitochondria and decrease CGN death under GD conditions. In the presence of glucose the mitochondrial respiratory chain blocker rotenone induces neuron death potentiated by glutamine. The potentiation effect is completely prevented by blockers of ionotropic glutamate receptors. These results show that glutamine under conditions of GD can be utilized by mitochondria as substrate, but at the same time, in the case of mitochondrial function deterioration, metabolism of this amino acid results in glutamate accumulation to toxic level.

Changes in mitochondrial NAD(P)H and glutamate-induced delayed calcium deregulation in cultured rat cerebellar granule neurons

Changes in cytosolic [Ca2+]i, mitochondrial potential (ΔVm), and mitochondrial NAD(P)H autofluorescence were compared in experiments on cultured cerebellar granule cells co-loaded with Ca2+ indicator Fluo-3FF or mitochondrial potential-sensitive probe Rh123. In the majority of neurons (94% of cells, n = 205, 28 experiments) the delayed Ca2+ deregulation (DCD) induced by Glu (100 μM) was preceded by more or less prolonged decrease in NAD(P)H, which in 57% of cells underwent a further (secondary) reduction during DCD development. To clarify the origin of these changes in NAD(P)H production during DCD we examined the effects of the protonophore FCCP on NAD(P)H increase induced by the electron chain blocker CN (3 mM) application. The data suggest that a pronounced lowering of mitochondrial pH during DCD contributed to the mechanism of Glu-induced suppression of NAD(P)H production.

Photocuring of cinnamic carbohydrate esters: Controlling the reaction by monocinnamoylated derivatives

A monofunctional and a polyfunctional monomer were studied for use as potential co-photopolymers. The monomers were the totally cinnamoylated derivatives of p-nitrophenol (PNPCN) and d-manitol (MNTCN), and their structures were characterized by several spectroscopic techniques. The derivatives obtained were cross-linked by irradiation in the ultraviolet region, where the photosensitive monomers showed maximum sensitivity. The thermal properties of these photosensitive monomers and the mixtures prepared with different MNTCN:PNPCN ratios were investigated by differential scanning calorimetry under nitrogen atmosphere, and their photoreactivity was investigated in thin films. Photoreaction products were analyzed by gel permeation chromatography. The effect of PNPCN as a chain blocker in the MNTCN photocrosslinking reaction was evaluated by UV–visible spectroscopy and by 1H NMR.

Inhibitory effect of taurine on veratridine-evoked d-[ 3H]aspartate release from murine corticostriatal slices: Involvement of chloride channels and mitochondria

We have previously shown that the inhibitory neuromodulator taurine attenuates the release of preloaded d-[ 3H]aspartate from murine corticostriatal slices evoked by ischemic conditions or by application of the sodium channel agonist veratridine. The release of d-[ 3H]aspartate (a non-metabolized analog of glutamate) was used as an index of glutamate release. The aim of the present study was to reveal the molecular mechanisms responsible for this inhibitory effect of taurine. It was shown that 10 mM taurine suppresses d-[ 3H]aspartate release evoked by 0.1 mM veratridine, but does not affect the high-K +-(50 mM) or ouabain- (0.1 mM) evoked release. Taurine had no effect in Ca 2+-free medium when the synaptic exocytosis of d-[ 3H]aspartate was inhibited. Nor did it suppress the release from slices preloaded with the competitive glutamate uptake blocker dl-threo-β-hydroxyaspartate (THBA), which inhibits d-[ 3H]aspartate release mediated by the reverse action of glutamate transporters. Omission of Cl − from the incubation medium reduced the effect of taurine, signifying the involvement of a Cl − channel. The glycine receptor antagonist strychnine and the GABA A receptor antagonist bicuculline did not block the taurine effect, although picrotoxin, a less specific blocker of agonist-gated chloride channels, completely prevented the effect of taurine on veratridine-induced d-[ 3H]aspartate release. The respiratory chain blocker rotenone or mitochondrial protonophore carbonyl cyanide 3-chlorophenylhydrazone (CCCP) in combination with the mitochondrial ATPase inhibitor oligomycin, which inhibits the mitochondrial Ca 2+ uniporter, also reduced the effect of taurine. The results obtained in the present study show that taurine acts specifically on the release of preloaded d-[ 3H]aspartate evoked by veratridine, but not on that evoked by other depolarizing agents, and affects the release mediated both by synaptic exocytosis and the reverse action of glutamate transporter. Taurine may attenuate d-[ 3H]aspartate release by regulation of mitochondrial Ca 2+ sequestration and by activation of a chloride channel, but not that governed by GABA A or strychnine-sensitive glycine receptors.

Mitochondrial Production of Reactive Oxygen Species Mediate Dicumarol-induced Cytotoxicity in Cancer Cells

Dicumarol is a naturally occurring anticoagulant derived from coumarin that induces cytotoxicity and oxidative stress in human pancreatic cancer cells (Cullen, J. J., Hinkhouse, M. M., Grady, M., Gaut, A. W., Liu, J., Zhang, Y., Weydert, C. J. D., Domann, F. E., and Oberley, L. W. (2003) Cancer Res. 63, 5513-5520). Although dicumarol has been used as an inhibitor of the two-electron reductase NAD(P)H:quinone oxidoreductase (NQO1), dicumarol is also thought to affect quinone-mediated electron transfer reactions in the mitochondria, leading to the production of superoxide (O2*-) and hydrogen peroxide (H(2)O(2)). We hypothesized that mitochondrial production of reactive oxygen species mediates the increased susceptibility of pancreatic cancer cells to dicumarol-induced metabolic oxidative stress. Dicumarol decreased clonogenic survival equally in both MDA-MB-468 NQO1(-) and MDA-MB-468 NQO1+ breast cancer cells. Dicumarol decreased clonogenic survival in the transformed fibroblast cell line IMRSV-90 compared with the IMR-90 cell line. Dicumarol, with the addition of mitochondrial electron transport chain blockers, decreased clonogenic cell survival in human pancreatic cancer cells and increased superoxide levels. Dicumarol with the mitochondrial electron transport chain blocker antimycin A decreased clonogenic survival and increased superoxide levels in cells with functional mitochondria but had little effect on cancer cells without functional mitochondria. Overexpression of manganese superoxide dismutase and mitochondrial-targeted catalase with adenoviral vectors reversed the dicumarol-induced cytotoxicity and reversed fluorescence of the oxidation-sensitive probe. We conclude mitochondrial production of reactive oxygen species mediates the increased susceptibility of cancer cells to dicumarol-induced cytotoxicity.

Mitochondria-Derived Reactive Oxygen Species Dilate Cerebral Arteries by Activating Ca 2+ Sparks

Mitochondria regulate intracellular calcium (Ca2+) signals in smooth muscle cells, but mechanisms mediating these effects, and the functional relevance, are poorly understood. Similarly, antihypertensive ATP-sensitive potassium (KATP) channel openers (KCOs) activate plasma membrane KATP channels and depolarize mitochondria in several cell types, but the contribution of each of these mechanisms to vasodilation is unclear. Here, we show that cerebral artery smooth muscle cell mitochondria are most effectively depolarized by diazoxide (-15%, tetramethylrhodamine [TMRM]), less so by levcromakalim, and not depolarized by pinacidil. KCO-induced mitochondrial depolarization increased the generation of mitochondria-derived reactive oxygen species (ROS) that stimulated Ca2+ sparks and large-conductance Ca2+-activated potassium (KCa) channels, leading to transient KCa current activation. KCO-induced mitochondrial depolarization and transient KCa current activation were attenuated by 5-HD and glibenclamide, KATP channel blockers. MnTMPyP, an antioxidant, and Ca2+ spark and KCa channel blockers reduced diazoxide-induced vasodilations by >60%, but did not alter dilations induced by pinacidil, which did not elevate ROS. Data suggest diazoxide drives ROS generation by inducing a small mitochondrial depolarization, because nanomolar CCCP, a protonophore, similarly depolarized mitochondria, elevated ROS, and activated transient KCa currents. In contrast, micromolar CCCP, or rotenone, an electron transport chain blocker, induced a large mitochondrial depolarization (-84%, TMRM), reduced ROS, and inhibited transient KCa currents. In summary, data demonstrate that mitochondria-derived ROS dilate cerebral arteries by activating Ca2+ sparks, that some antihypertensive KCOs dilate by stimulating this pathway, and that small and large mitochondrial depolarizations lead to differential regulation of ROS and Ca2+ sparks.

7-Nitroindazole prevents dopamine depletion caused by low concentrations of MPP+ in rat striatal slices

A significant loss of dopamine was found in rat striatal slices incubated with 1–methyl–4–phenylpyridinium ion (MPP+) at a concentration of 2 mM or higher. The addition of 7–nitroindazole, a specific inhibitor of neuronal nitric oxide synthase (nNOS), prevented this effect on dopamine when the concentration of MPP+ was between 2–5 M, but not at higher concentrations. This protection was reproduced with other less specific NOS–inhibitors, such as nitro–arginine and nitro–arginine methylester. 7–nitroindazole did not protect against the dopamine depletion caused by the non–specific mitochondrial chain blocker rotenone. Neither MPP+ nor rotenone significantly increased the nitrite concentration in striatal slices, measured as an index of nitric oxide production. The basal production of nitric oxide may be enough to trigger the dopamine depletion at very low concentrations of MPP+ probably acting synergistically with cytosolic calcium increase. Higher concentrations of MPP+ are toxic by themselves without the mediation of nitric oxide. The inhibition of nNOS may protect against dopamine loss at early stages of a neurodegenerative process, and it could then be considered in the treatment or prevention of neurodegenerative human processes such as Parkinson’s disease. © 1998 Elsevier Science Ltd. All rights reserved.

Protective effects of baicalein against cell damage by reactive oxygen species.

Baicalein (5,6,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one), a naturally occurring flavonoid, was found to prevent human dermal fibroblast cell damage induced by reactive oxygen species such as hydrogen peroxide (H2O2), tert-butyl hydroperoxide (BuOOH) and superoxide anions (.O2-) in a concentration-dependent manner, and was more effective than the iron chelator, deferoxamine, hydroxyl radical (.OH) scavengers such as dimethyl sulfoxide (DMSO) and ethanol (EtOH), the lipid peroxidation chain blocker, alpha-tocopherol (Vit. E) and the xanthine oxidase inhibitor, allopurinol. To probe the mechanism of cell defense, the reaction of baicalein with oxygen free radicals was investigated using electron spin resonance (ESR) spectrometry. Baicalein decreased the signal intensities due to the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin adducts of .OH, .O2- and tert-butyl peroxyl (BuOO.) radicals in a concentration-dependent manner. The IC50 values, which are the 50% inhibition concentrations of baicalein for the free radicals, were 10, 45 and 310 microM, respectively. These results suggested that baicalein possesses free radical scavenging ability which prevents the fibroblast damage induced by these free radical species.

Ischemic preconditioning reduces O 2.- generation and prevents respiratory impairment in the mitochondria of post-ischemic reperfused heart of rat

The present study was performed to test whether the ischemic preconditioning could reduce mitochondrial O 2 .- production and prevent mitochondrial respiratory impairment upon reperfusion of ischemic hearts. The isolated perfused rat hearts were subjected to 30 min of global ischemia and 20 min of reperfusion. Ischemic preconditioning was performed, involving three 5-min periods of ischemia, each followed by a 5-min reperfusion just before a sustained ischemia. Ischemic preconditioning improved the post-ischemic cardiac function and reduced LDH release and malondialdehyde production upon reperfusion. O 2 .- generation of mitochondria isolated from the preconditioned hearts was significantly lower than that of mitochondria from the non-preconditioned hearts, and none of the activities of mitochondrial antioxidant enzymes(SOD, catalase, glutathione peroxidase) was altered as a consequence of the ischemic preconditioning alone. The impairment of mitochondrial state 3 respiration induced by ischemia and reperfusion was prevented by ischémie preconditioning. Amytal, a reversible respiratory chain blocker suppressing O 2 .- production in mitochondria, prevented the ischemia/reperfusion injury. The cardioprotective effect of Amytal could not be distinguished from that of ischemic preconditioning. These results suggest that the cardioprotective effect of ischemic preconditioning against the ischemia/reperfusion injury is attributed partly to the reduction of mitochondrial oxygen radical generation and prevention of the respiratory impairment during ischemia and reperfusion.

Internally Located and Oppositely Oriented Polymerase II Promoters Direct Convergent Transcription of a LINE-Like Retroelement, the Dictyostelium Repetitive Element, from Dictyostelium discoideum

The Dictyostelium discoideum NC4 genome harbors approximately 150 individual copies of a retrotransposable element called the Dictyostelium repetitive element (DRE). This element contains nonidentical terminal repeats (TRs) consisting of conserved building blocks A and B in the left TR and B and C in the right TR. Seven different-sized classes of RNA transcripts from these elements were resolved by Northern (RNA) blot analysis, but their combined abundance was very low. When D. discoideum cells were grown in the presence of the respiratory chain blocker antimycin A, steady-state concentrations of these RNA species increased 10- to 20-fold. The D. discoideum genome contains two DRE subtypes, the full-length 5.7-kb DREa and the internally deleted 2.4-kb DREb. Both subtypes are transcribed, as confirmed by analysis of cloned cDNA. Primary transcripts from the sense strand originate at nucleotide +1 and terminate at two dominant sites, located 21 or 28 nucleotides upstream from the 3' end of the elements. The activity of a reasonably strong polymerase II promoter in the 5'-terminal A module is slightly upregulated by the tRNA gene located 50 +/- 4 nucleotides upstream and drastically reduced by the adjacent B module of the DRE. Transcripts from the opposite DNA strand (complementary-sense transcripts) were also detected, directed by an internally located polymerase II promoter residing within the C module. This latter transcription was initiated at multiple sites within the oligo(dA12) stretch which terminates DREs.

Internally located and oppositely oriented polymerase II promoters direct convergent transcription of a LINE-like retroelement, the Dictyostelium repetitive element, from Dictyostelium discoideum.

The Dictyostelium discoideum NC4 genome harbors approximately 150 individual copies of a retrotransposable element called the Dictyostelium repetitive element (DRE). This element contains nonidentical terminal repeats (TRs) consisting of conserved building blocks A and B in the left TR and B and C in the right TR. Seven different-sized classes of RNA transcripts from these elements were resolved by Northern (RNA) blot analysis, but their combined abundance was very low. When D. discoideum cells were grown in the presence of the respiratory chain blocker antimycin A, steady-state concentrations of these RNA species increased 10- to 20-fold. The D. discoideum genome contains two DRE subtypes, the full-length 5.7-kb DREa and the internally deleted 2.4-kb DREb. Both subtypes are transcribed, as confirmed by analysis of cloned cDNA. Primary transcripts from the sense strand originate at nucleotide +1 and terminate at two dominant sites, located 21 or 28 nucleotides upstream from the 3' end of the elements. The activity of a reasonably strong polymerase II promoter in the 5'-terminal A module is slightly upregulated by the tRNA gene located 50 +/- 4 nucleotides upstream and drastically reduced by the adjacent B module of the DRE. Transcripts from the opposite DNA strand (complementary-sense transcripts) were also detected, directed by an internally located polymerase II promoter residing within the C module. This latter transcription was initiated at multiple sites within the oligo(dA12) stretch which terminates DREs.