1-3-dihydroxy-4-4-5-5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole and Hypoxia

Adequate perfusion of the placental vasculature is essential to meet the metabolic demands of fetal growth and development. Lacking neural control, local tissue metabolites, circulating and physical factors contribute significantly to blood flow regulation. Nitric oxide (NO) is a key regulator of fetoplacental vascular tone. Nitrite, previously considered an inert end-product of NO oxidation, has been shown to provide an important source of NO. Reduction of nitrite to NO may be particularly relevant in tissue when the oxygen-dependent NO synthase (NOS) activity is compromised, e.g. in hypoxia. The contribution of this pathway in the placenta is currently unknown. We hypothesised that nitrite vasodilates human placental blood vessels, with enhanced efficacy under hypoxia. Placentas were collected from uncomplicated pregnancies and the vasorelaxant effect of nitrite (10

Topics: Adult; Arteries; Benzoates; Chorion; Cyclic GMP; Dose-Response Relationship, Drug; Female; Humans; Hypoxia; Imidazoles; Nitrites; Placenta; Pregnancy; Sodium Nitrite; Vasodilation; Veins

Hypoxia stimulates excessive growth of vascular smooth muscle cells (VSMCs) contributing to vascular remodelling. Recent studies have shown that histone deacetylase inhibitors (HDIs) suppress VSMC proliferation and activate eNOS expression. However, the effects of HDI on hypoxia-induced VSMC growth and the role of activated eNOS in VSMCs are unclear. Using an EdU incorporation assay and flow cytometry analysis, we found that the HDIs, butyrate (Bur) and suberoylanilide hydroxamic acid (SAHA) significantly suppressed the proliferation of hypoxic VSMC lines and induced apoptosis. Remarkable induction of cleaved caspase 3, p21 expression and reduction of PCNA expression were also observed. Increased eNOS expression and enhanced NO secretion by hypoxic VSMC lines were detected using Bur or SAHA treatment. Knockdown of eNOS by siRNA transfection or exposure of hypoxic VSMCs to NO scavengers weakened the effects of Bur and SAHA on the growth of hypoxic VSMCs. In animal experiments, administration of Bur to Wistar rats exposed to hypobaric hypoxia for 28 days ameliorated the thickness and collagen deposition in pulmonary artery walls. Although the mean pulmonary arterial pressure (mPAP) was not obviously decreased with Bur in hypoxic rats, right ventricle hypertrophy index (RVHI) was decreased and the oxygen partial pressure of arterial blood was elevated. Furthermore, cell viability was decreased and eNOS and cleaved caspase 3 were induced in HDI-treated rat pulmonary arterial SMCs. These findings imply that HDIs prevent hypoxia-induced VSMC growth, in correlation with activated eNOS expression and activity in hypoxic VSMCs.

Topics: Animals; Apoptosis; Benzoates; Butyrates; Cell Hypoxia; Cell Proliferation; Histone Deacetylase Inhibitors; Hydroxamic Acids; Hypoxia; Imidazoles; Male; Models, Biological; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Nitric Oxide; Nitric Oxide Synthase Type III; Pulmonary Artery; Rats, Wistar; Vascular Remodeling; Vorinostat

To determine whether retinal neurons become more susceptible to injury by nitric oxide (NO) under hypoxic conditions.. Cells from the RGC-5 line were exposed to different concentrations (0.1-100 microM) of S-nitroso-N-acetyl-penicillamine (SNAP), an NO donor, under normoxic and hypoxic (1.0% O(2)) conditions with 5.5 mM glucose or with no glucose. In some experiments, carboxy-PTIO, a scavenger of NO, was added with SNAP. The SNAP-induced cell injury was determined by the WST-8 assay and by the assessment of phosphatidylserine externalization and changes in hypodiploid DNAs. Alterations of mitochondrial membrane potential, superoxide anion formation, cellular adenosine triphosphate (ATP) contents, and caspase activity were also determined after exposure to SNAP.. Exposure of RGC-5 cells to SNAP (100 microM) significantly decreased the number of living cells cultured under hypoxic conditions with or without glucose. Coadministration of carboxy-PTIO (1.0 microM) suppressed SNAP-induced cell death. SNAP-induced cell death of cells cultured under hypoxia with glucose was accompanied by increased expression of phosphatidylserine and hypodiploid DNAs. These findings indicated that death was mediated in part by apoptosis. In addition, loss of mitochondrial membrane potential, increase of superoxide formation, and activation of caspase was observed. Cyclosporine A, TEMPOL, and Z-VAD-FMK suppressed cell death. On the other hand, SNAP depleted the ATP contents of cells cultured under hypoxia without glucose, causing mainly necrotic cell death.. These results indicate that RGC-5 cells become susceptible to SNAP under hypoxic conditions in which NO may have greater impact on mitochondrial function.

Topics: Adenosine Triphosphate; Apoptosis; Benzoates; Caspase Inhibitors; Caspases; Cell Line; Diploidy; DNA; Enzyme Inhibitors; Flow Cytometry; Glucose; Humans; Hypoxia; Imidazoles; Membrane Potential, Mitochondrial; Nitric Oxide Donors; Peroxynitrous Acid; Phosphatidylserines; Retinal Ganglion Cells; S-Nitroso-N-Acetylpenicillamine; Superoxides

The effects of agents which affect the action of nitric oxide (NO) were studied intracellularly on the ischemia-induced changes in membrane potential of single CA1 pyramidal neurons of the rat hippocampal slice preparations. The N-methyl-D-aspartate (NMDA) receptor antagonists, (+/-)-2-amino-5-phosphonopentanoic acid (AP5, 250 microM) or Co2 (2 mM) restored the membrane potential in more than 80% of the neurons. In about 60% of the neurons, the membrane potential was partially recovered as a result of exposure to the NO synthase inhibitor, NG-nitro-L-arginine (100 microM). The NO scavengers, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO, 300 microM) and hemoglobin (10 microM) restored the membrane potential in all neurons examined. Superoxide dismutase (50 U/ml) protected about 75% of the neurons from irreversible membrane dysfunction. It is concluded that the release of NO induced by experimental ischemia may result in the irreversible membrane dysfunction, and that a NO scavenger, carboxy-PTIO, prevents the ischemic changes in membrane potential. With respect to ischemic brain damage, the neuroprotection provided by carboxy-PTIO may have clinical relevance in the management of a variety of neurological conditions.

Topics: 2-Amino-5-phosphonovalerate; Animals; Benzoates; Cell Membrane; Cobalt; Glucose; Hemoglobins; Hippocampus; Hypoxia; Imidazoles; In Vitro Techniques; Ischemic Attack, Transient; Male; Membrane Potentials; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pyramidal Cells; Rats; Rats, Wistar; Reaction Time; Receptors, N-Methyl-D-Aspartate; Superoxide Dismutase

Nitric oxide (NO) has been shown to be a mediator of hypoxic injury in rat renal proximal tubules (PT). However, the role of NO in hypoxic injury to mouse. PT has not been examined. The aim of the present study was to determine the effect of knockout of nitric oxide synthase (NOS) isoforms on hypoxic injury in mouse PT. Mouse PTs were isolated by collagenase digestion and Percoll centrifugation. The nonselective NOS inhibitor, N-nitro-L-arginine methyl ester (L-NAME, 10 mM), but not its inactive stereoisomer D-NAME, protected against hypoxic injury as assessed by LDH release. Carboxy-imidazolineoxyl N-oxide (carboxy-PTIO, 100 microM), a stable NO scavenger, also afforded cytoprotection against hypoxic injury. To determine the role of the different NOS isoforms in the hypoxic injury, we examined the effect of hypoxia on PT isolated from knockout mice in which either the inducible NOS (iNOS) endothelial NOS (eNOS) or neuronal NOS (nNOS) gene was lacking. PT isolated from iNOS knockout mice were resistant to hypoxic injury compared to wild-type controls. In contrast, PT isolated from both nNOS and eNOS knockout mice were not protected against hypoxic injury. In conclusion, the present study demonstrates that NO is a mediator of hypoxic PT injury in the mouse and that knockout of the iNOS gene is cytoprotective against this hypoxic PT injury.

Topics: Animals; Benzoates; Enzyme Inhibitors; Gene Deletion; Hypoxia; Imidazoles; In Vitro Techniques; Kidney Tubules, Proximal; L-Lactate Dehydrogenase; Mice; Mice, Knockout; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III