Design and synthesis of benzoxazole derivatives as novel melatoninergic ligands

A novel series of benzoxazole derivatives was synthesized and evaluated as melatoninergic ligands. The binding affinity of these compounds for human MT(1) and MT(2) receptors was determined using 2-[(125)I]-iodomelatonin as the radioligand. The results of the SAR studies in this series led to the identification of compound 28, which exhibited better MT(1) and MT(2) receptor affinities than melatonin itself. This work also established the benzoxazole nucleus as a melatoninergic pharmacophore, which served as an isosteric replacement to the previously established alkoxyaryl core.     

Nitric oxide regulation of myocardial O2 consumption and HEP metabolism

NO and O(2) compete at cytochrome-c oxidase, thus potentially allowing NO to modulate mitochondrial respiration. We previously observed a decrease of myocardial phosphocreatine (PCr)/ATP during very high cardiac work states, corresponding to an increase in cytosolic free ADP. This study tested the hypothesis that NO inhibition of respiration contributes to this increase of ADP. Infusion of dobutamine + dopamine (DbDp, each 20 microg.kg(-1).min(-1) iv) to more than double myocardial oxygen consumption (MVo(2)) in open-chest dogs caused a decrease of myocardial PCr/ATP measured with (31)P NMR from 2.04 +/- 0.09 to 1.85 +/- 0.08 (P < 0.05). Inhibition of NO synthesis with N(omega)-nitro-L-arginine (L-NNA), while catecholamine infusion continued, caused PCr/ATP to increase to the control value. In a second group of animals, L-NNA administered before catecholamine stimulation (reverse intervention of the first group) increased PCr/ATP during basal conditions. In these animals L-NNA did not prevent a decrease of PCr/ATP at the high cardiac work state but, relative to MVo(2), PCr/ATP was significantly higher after L-NNA. In a third group of animals, pharmacological coronary vasodilation with carbochromen was used to prevent changes in coronary flow that might alter endothelial NO production. In these animals L-NNA again restored depressed myocardial PCr/ATP during catecholamine infusion. The finding that inhibition of NO production increased PCr/ATP suggests that during very high work states NO inhibition of mitochondrial respiration requires ADP to increase to drive oxidative phosphorylation.     

Increased superoxide production causes coronary endothelial dysfunction and depressed oxygen consumption in the failing heart

This study examined whether increased superoxide (O(2)(-).) production contributes to coronary endothelial dysfunction and decreased coronary blood flow (CBF) in congestive heart failure (CHF). To test this hypothesis, the effects of the low-molecular-weight SOD mimetic M40401 on CBF and myocardial oxygen consumption (MVo(2)) were examined in dogs during normal conditions and after CHF was produced by 4 wk of rapid ventricular pacing. The development of CHF was associated with decreases of left ventricular (LV) systolic pressure, maximum first derivative of LV pressure, MVo(2), and CBF at rest and during treadmill exercise as well as endothelial dysfunction with impaired vasodilation in response to intracoronary acetylcholine. M40401 increased CBF (18 +/- 5%, P < 0.01) and MVo(2) (14 +/- 6%, P < 0.01) in CHF dogs and almost totally reversed the impaired CBF response to acetylcholine. M40401 had no effect on acetylcholine-induced coronary vasodilation, CBF, or MVo(2) in normal dogs. Western blot analysis demonstrated that extracellular SOD (EC-SOD) was significantly decreased in CHF hearts, whereas mitochondrial Mn-containing SOD was increased. Cytosolic Cu/Zn-containing SOD was unchanged. Both increased O(2)(-). production and decreased vascular O(2)(-). scavenging ability by EC-SOD could have contributed to endothelial dysfunction in the failing hearts.     

Current Status of Heart Replacement

A review of heart replacement involves discussion of the artificial heart and the cardiac homograft. The mechanical substitute shows destruction of blood cellular elements and clot formation, regardless of the type of pump used. Significant postoperative survival remains as the major goal. Animals having homograft substitutions show prolonged survival and good cardiac function. Philosophical and legal problems rank above the rejection phenomenon in curtailing clinical isotopic replacement.     

Cilia and coordination of signaling networks during heart development

Primary cilia are unique sensory organelles that coordinate a wide variety of different signaling pathways to control cellular processes during development and in tissue homeostasis. Defects in function or assembly of these antenna-like structures are therefore associated with a broad range of developmental disorders and diseases called ciliopathies. Recent studies have indicated a major role of different populations of cilia, including nodal and cardiac primary cilia, in coordinating heart development, and defects in these cilia are associated with congenital heart disease. Here, we present an overview of the role of nodal and cardiac primary cilia in heart development.     

Neuregulin and BDNF Induce a Switch to NMDA Receptor-Dependent Myelination by Oligodendrocytes

Myelination is essential for rapid impulse conduction in the CNS, but what determines whether an individual axon becomes myelinated remains unknown. Here we show, using a myelinating coculture system, that there are two distinct modes of myelination, one that is independent of neuronal activity and glutamate release and another that depends on neuronal action potentials releasing glutamate to activate NMDA receptors on oligodendrocyte lineage cells. Neuregulin switches oligodendrocytes from the activity-independent to the activity-dependent mode of myelination by increasing NMDA receptor currents in oligodendrocyte lineage cells 6-fold. With neuregulin present myelination is accelerated and increased, and NMDA receptor block reduces myelination to far below its level without neuregulin. Thus, a neuregulin-controlled switch enhances the myelination of active axons. In vivo, we demonstrate that remyelination after white matter damage is NMDA receptor-dependent. These data resolve controversies over the signalling regulating myelination and suggest novel roles for neuregulin in schizophrenia and in remyelination after white matter damage.     

A novel post-translational modification in nerve terminals: O-linked N-acetylglucosamine phosphorylation

Protein phosphorylation and glycosylation are the most common post-translational modifications observed in biology, frequently on the same protein. Assembly protein AP180 is a synapse-specific phosphoprotein and O-linked beta-N-acetylglucosamine (O-GlcNAc) modified glycoprotein. AP180 is involved in the assembly of clathrin coated vesicles in synaptic vesicle endocytosis. Unlike other types of O-glycosylation, O-GlcNAc is nucleocytoplasmic and reversible. It was thought to be a terminal modification, that is, the O-GlcNAc was not found to be additionally modified in any way. We now show that AP180 purified from rat brain contains a phosphorylated O-GlcNAc (O-GlcNAc-P) within a highly conserved sequence. O-GlcNAc or O-GlcNAc-P, but not phosphorylation alone, was found at Thr-310. Analysis of synthetic GlcNAc-6-P produced identical fragmentation products to GlcNAc-P from AP180. Direct O-linkage of GlcNAc-P to a Thr residue was confirmed by electron transfer dissociation MS. A second AP180 tryptic peptide was also glycosyl phosphorylated, but the site of modification was not assigned. Sequence similarities suggest there may be a common motif within AP180 involving glycosyl phosphorylation and dual flanking phosphorylation sites within 4 amino acid residues. This novel type of protein glycosyl phosphorylation adds a new signaling mechanism to the regulation of neurotransmission and more complexity to the study of O-GlcNAc modification.     

Effects of exercise on VLDL-triglyceride oxidation and turnover

Lipids are important substrates for oxidation at rest and during exercise. Aerobic exercise mediates a delayed onset decrease in total and VLDL-triglyceride (TG) plasma concentration. However, the acute effects of exercise on VLDL-TG oxidation and turnover remain unclear. Here, we studied the acute effects of 90 min of moderate-intensity exercise in healthy women and men. VLDL-TG kinetics were assessed using a primed constant infusion of ex vivo labeled [1-(14)C]triolein VLDL-TG. Fractional VLDL-TG-derived fatty acid oxidation was measured from (14)CO(2) specific activity in expired air. VLDL-TG concentration was unaltered during exercise and early recovery, whereas non-VLDL-TG concentration decreased significantly.VLDL-TG secretion rate decreased significantly during exercise and remained suppressed during recovery. Total VLDL-TG oxidation rate was unaffected by exercise. However, the contribution of VLDL-TG oxidation to total energy expenditure fell from 14 ± 9% at rest to 3 ± 4% during exercise. We conclude that VLDL-TG fatty acids are quantitatively important oxidative substrates under basal postabsorptive conditions but remain unaffected during 90-min moderate-intensity exercise and, thus, become relatively less important during exercise. Lower VLDL secretion rate during exercise may contribute to the decrease in TG concentrations during and after exercise.