Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
Heme oxygenase 1 (Hmox1), a ubiquitous enzyme degrading heme to carbon monoxide, iron, and biliverdin, is one of the\ncytoprotective enzymes induced in response to a variety of stimuli, including cellular oxidative stress. Gangliosides, sialic acidcontaining\nglycosphingolipids expressed in all cells, are involved in cell recognition, signalling, and membrane stabilization.\nTheir expression is often altered under many pathological and physiological conditions including cell death, proliferation, and\ndifferentiation. The aim of this study was to assess the possible role of Hmox1 in ganglioside metabolism in relation to oxidative\nstress. The content of liver and brain gangliosides, their cellular distribution, and mRNA as well as protein expression of key\nglycosyltransferases were determined in Hmox1 knockout mice as well as their wild-type littermates. To elucidate the possible\nunderlying mechanisms between Hmox1 and ganglioside metabolism, hepatoblastoma HepG2 and neuroblastoma SH-SY5Y cell\nlines were used for in vitro experiments. Mice lacking Hmox1 exhibited a significant increase in concentrations of liver and\nbrain gangliosides and in mRNA expression of the key enzymes of ganglioside metabolism. A marked shift of GM1 ganglioside\nfrom the subsinusoidal part of the intracellular compartment into sinusoidal membranes of hepatocytes was shown in Hmox1\nknockout mice. Induction of oxidative stress by chenodeoxycholic acid in vitro resulted in a significant increase in GM3, GM2,\nand GD1a gangliosides in SH-SY5Y cells and GM3 and GM2 in the HepG2 cell line. These changes were abolished with\nadministration of bilirubin, a potent antioxidant agent. These observations were closely related to oxidative stress-mediated\nchanges in sialyltransferase expression regulated at least partially through the protein kinase C pathway. We conclude that\noxidative stress is an important factor modulating synthesis and distribution of gangliosides in vivo and in vitro which might\naffect ganglioside signalling in higher organisms....
The binding site for DETQ [2-(2,6-dichlorophenyl)-1-((1S,3R)-\n3-(hydroxymethyl)-5-(2-hydroxypropan-2-yl)-1-methyl-3,4-\ndihydroisoquinolin-2(1H)-yl)ethan-1-one], a positive allosteric\nmodulator (PAM) of the dopamine D1 receptor, was identified\nand compared with the binding site for CID 2886111 [N-(6-tert-butyl-\n3-carbamoyl-4,5,6,7-tetrahydro-1-benzothiophen-2-yl)pyridine-4-\ncarboxamide], a reference D1 PAM. From D1/D5 chimeras, the\nsite responsible for potentiation by DETQ of the increase in cAMP\nin response to dopamine was narrowed down to the N-terminal\nintracellular quadrant of the receptor; arginine-130 in intracellular\nloop 2 (IC2) was then identified as a critical amino acid based on a\nhuman/rat species difference. Confirming the importance of IC2, a\nb2-adrenergic receptor construct in which the IC2 region was\nreplaced with its D1 counterpart gained the ability to respond to\nDETQ. A homology model was built from the agonist-state\nb2-receptor structure, and DETQ was found to dock to a cleft\ncreated by IC2 and adjacent portions of transmembrane helices\n3 and 4 (TM3 and TM4). When residues modeled as pointing into\nthe cleft were mutated to alanine, large reductions in the potency of\nDETQ were found for Val119 and Trp123 (flanking the conserved\nDRY sequence in TM3), Arg130 (located in IC2), and Leu143 (TM4).\nThe D1/D5 difference was found to reside in Ala139; changing this\nresidue to methionine as in the D5 receptor reduced the potency\nof DETQ by approximately 1000-fold. None of these mutations\naffected the activity of CID 2886111, indicating that it binds to a\ndifferent allosteric site. When combined, DETQ and CID 2886111 elicited\na supra-additive response in the absence of dopamine,\nimplying that bothPAMscan bind to the D1 receptor simultaneously....
Several studies showed that [11C]ABP688 binding is altered following drug-induced\nperturbation of glutamate levels in brains of humans, non-human primates and rats. We evaluated\nwhether the fluorinated derivative [18F]PSS232 can be used to assess metabotropic glutamate receptor\n5 (mGluR5) availability in rats after pharmacological challenge with ketamine, known to increase\nglutamate, or ceftriaxone, known to decrease glutamate. In vitro autoradiography was performed on\nrat brain slices with [18F]PSS232 to prove direct competition of the drugs for mGluR5. One group\nof rats were challenged with a bolus injection of either vehicle, racemic ketamine, S-ketamine or\nceftriaxone followed by positron emission tomography PET imaging with [18F]PSS232. The other\ngroup received an infusion of the drugs during the PET scan. Distribution volume ratios (DVRs) were\ncalculated using a reference tissue model. In vitro autoradiography showed no direct competition of\nthe drugs with [18F]PSS232 for the allosteric binding site of mGluR5. DVRs of [18F]PSS232 binding\nin vivo did not change in any brain region neither after bolus injection nor after infusion. We conclude\nthat [18F]PSS232 has utility for measuring mGluR5 density or occupancy of the allosteric site in vivo,\nbut it cannot be used to measure in vivo fluctuations of glutamate levels in the rat brain....
According to current views, oxidation of aldehyde dehydrogenase-2\n(ALDH2) during glyceryltrinitrate (GTN) biotransformation is essentially\ninvolved in vascular nitrate tolerance and explains the dependence\nof this reaction on added thiols. Using a novel fluorescent\nintracellular nitric oxide (NO) probe expressed in vascular smooth\nmuscle cells (VSMCs), we observed ALDH2-catalyzed formation of\nNO from GTN in the presence of exogenously added dithiothreitol\n(DTT), whereas only a short burst of NO, corresponding to a single\nturnover of ALDH2, occurred in the absence of DTT. This short burst\nof NO associated with oxidation of the reactive C302 residue in the\nactive site was followed by formation of low-nanomolar NO, even\nwithout added DTT, indicating slow recovery of ALDH2 activity by an\nendogenous reductant. In addition to the thiol-reversible oxidation of\nALDH2, thiol-refractive inactivation was observed, particularly under\nhigh-turnover conditions. Organ bath experiments with rat aortas\nshowed that relaxation by GTNlasted longer than that caused by the\nNO donor diethylamine/NONOate, in line with the long-lasting\nnanomolar NO generation from GTN observed in VSMCs. Our\nresults suggest that an endogenous reductant with low efficiency\nallows sustained generation of GTN-derived NO in the lownanomolar\nrange that is sufficient for vascular relaxation. On a\nlonger time scale, mechanism-based, thiol-refractive irreversible\ninactivation of ALDH2, and possibly depletion of the endogenous\nreductant, will render blood vessels tolerant to GTN. Accordingly, full\nreactivation of oxidizedALDH2may not occur in vivo and may not be\nnecessary to explain GTN-induced vasodilation....
This study investigated the potential hepatoprotective effect of oligoribonucleotides-D\n-mannitol complexes (ORNs-D-M) against thioacetamide (TAA)-induced hepatotoxicity in mice.\nThe hepatoprotective activity of ORNs-D-M was evaluated in thioacetamide (TAA)-treated C57BL/6J.\nResults indicate that treatment with ORNs-D-M displayed a protective effect at the TAA-induced\nliver injury. Treatment with ORNs-D-M, starting at 0 h after the administration of TAA, decreased\nTAA-elevated serum alanine aminotransferase (ALT) and \n-glutamyl transpeptidase (GGT). Activities\nof glutathione S-transferase (GST) and glutathione peroxidase (GPx), and levels of glutathione (GSH),\nwere enhanced with ORNs-D-M administration, while the hepatic oxidative biomarkers (TBA-reactive\nsubstances, protein carbonyl derivatives, protein-SH group) and myeloperoxidase (MPO) activity\nwere reduced. Furthermore, genetic analysis has shown that the ORNs-D-M decreases the expression\nof mRNA pro-inflammatory cytokines, such as tumor necrosis factor (TNF-) and interleukin-6\n(IL-6), profibrogenic cytokine-transforming growth factor 1 (TGF-1), as well as the principal protein\nof the extracellular matrixâ??collagen I. The present study demonstrates that ORNs-D-M exerts a\nprotective effect against TAA-induced liver injury, which may be associated with its anti-inflammatory\neffects, inhibition of overexpression of mRNA cytokines, and direct effects on the metabolism of\nthe toxin....
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