Enhancement of long-term potentiation by a potent nitric oxide-guanylyl cyclase activator, 3-(5-hydroxymethyl-2-furyl)-1-benzyl-indazole

BAY 41‐2272, a potent activator of soluble guanylyl cyclase, stimulates calcium elevation and calcium‐activated potassium current in pituitary GH3cells

The effects of BAY 41-2272, a nitric oxide-independent activator of soluble guanylyl cyclase, on Ca2+ signalling and ion currents were investigated in pituitary GH3 cells. Intracellular Ca2+ concentrations ([Ca2+]i) in these cells were increased by BAY 41-2272. Removing extracellular Ca2+ abolished the BAY 41-2272-induced increase in [Ca2+]i. After [Ca2+]i was elevated by BAY 41-2272 (300 nmol/L), subsequent application of 1-benzyl-3-(5'-hydroxymethyl-2'-furyl) indazole (YC-1; 1 micromol/L) did not increase [Ca2+]i further. In whole-cell recordings, BAY 41-2272 reversibly stimulated Ca2+-activated K+ current (I(K(Ca))) with an EC50 of 225 +/- 8 nmol/L. At 3 micromol/L, BAY 41-2272 slightly and significantly decreased L-type Ca2+ current. In the cell-attached configuration, BAY 41-2272 (300 nmol/L) enhanced the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels. After BK(Ca) channel activity was stimulated by spermine NONOate (30 micromol/L) or YC-1 (10 micromol/L) in cell-attached patches, subsequent application of BAY 41-2272 (300 nmol/L) further increased the channel open probability. In the inside-out configuration, BAY 41-2272 applied to the intracellular surface of excised patches enhanced BK(Ca) channel activity. Unlike 1 micromol/L paxilline, 1H-[1,2,4]oxadiazolol-[4,3a] quinoxalin-1-one (ODQ; 10 micromol/L) or heme (10 micromol/L) had no effect on BAY 41-2272-stimulated channel activity. BAY 41-2272 caused no shift in the activation curve of BK(Ca) channels; however, it did increase the Ca2+ sensitivity of these channels. At 300 nmol/L, BAY 41-2272 reduced the firing rate of spontaneous action potentials stimulated by thyrotropin-releasing hormone (10 micromol/L). The BK(Ca) channel activity was also enhanced by 300 nmol/L BAY 41-2272 in neuroblastoma IMR-32 cells. Therefore, the BAY 41-2272-induced increase in [Ca2+]i is primarily explained by an increase in Ca2+ influx. The BAY 41-2272-mediated simulation of IK(Ca) may result from direct activation of BKCa channels and indirectly as a result of elevated [Ca2+]i.

Induction of Thioredoxin and Mitochondrial Survival Proteins Mediates Preconditioning-Induced Cardioprotection and Neuroprotection

Delayed cardio- and neuroprotection are observed following a preconditioning procedure evoked by a brief and nontoxic oxidative stress due to deprivation of oxygen, glucose, serum, trophic factors, and/or antioxidative enzymes. Preconditioning protection can be observed in vivo and is under clinical trials for preservation of cell viability following organ transplants of liver. Previous studies indicated that ischemic preconditioning increases the expression of heat-shock proteins (HSPs) and nitric oxide synthase (NOS). Our pilot studies indicate that the treatment of neuronal NOS inhibitor (7-nitroindazole) and 6Br-cGMP blocks and mimics, respectively, preconditioning protection in human neuroblastoma SH-SY5Y cells. This minireview focuses on nitric oxide-mediated cellular adaptation and the related cGMP/PKG signaling pathway in a compensatory mechanism underlying preconditioning-induced hormesis. Both preconditioning and 6Br-cGMP increase the induction of human thioredoxin (Trx) mRNA and protein for cytoprotection, which is largely prevented by transfection of cells with Trx antisense but not sense oligonucleotides. Cytosolic Trx1 and mitochondrial Trx2 suppress free radical formation, lipid peroxidation, oxidative stress, and mitochondria-dependent apoptosis; knock out/down of either Trx1 or Trx2 is detrimental to cell survival. Other recent findings indicate that a transgenic increase of Trx in mice increases tolerance against oxidative nigral injury caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Trx1 can be translocated into nucleus and phosphoactivated CREB for a delayed induction of mitochondrial anti-apoptotic Bcl-2 and antioxidative MnSOD that is known to increase vitality and survival of cells in the brain and the heart. In conclusion, preconditioning adaptation or a brief oxidative stress induces a delayed nitric oxide-mediated compensatory mechanism for cell survival and vitality in the central nervous system and the cardiovascular system. Preconditioning-induced adaptive tolerance may be signaling through a cGMP-dependent induction of cytosolic redox protein Trx1 and subsequently mitochondrial proteins such as Bcl-2, MnSOD, and perhaps Trx2 or HSP70.

YC-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] inhibits endothelial cell functions induced by angiogenic factors in vitro and angiogenesis in vivo models

Angiogenesis is a process that involves endothelial cell proliferation, migration, invasion, and tube formation, and inhibition of these processes has implications for angiogenesis-mediated disorders. The purpose of this study was to evaluate the antiangiogenic efficacy of YC-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] in well characterized in vitro and in vivo systems. YC-1 inhibited the ability of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in a dose-dependent manner to induce proliferation, migration, and tube formation in human umbilical vascular endothelial cells; these outcomes were evaluated using [3H]thymidine incorporation, transwell chamber, and Matrigel-coated slide assays, respectively. YC-1 inhibited VEGF- and bFGF-induced p42/p44 mitogen-activated protein kinase and Akt phosphorylation as well as protein kinase C alpha translocation using Western blot analysis. The effect of YC-1 on angiogenesis in vivo was evaluated using the mouse Matrigel implant model. YC-1 administered orally in doses of 1 to 100 mg/kg/day inhibited VEGF- and bFGF-induced neovascularization in a dose-dependent manner over 7 days. These results indicate that YC-1 has antiangiogenic activity at very low doses. Moreover, in transplantable murine tumor models, YC-1 administered orally displayed a high degree of antitumor activity (treatment-to-control life span ratio > 175%) without cytotoxicity. YC-1 may be useful for treating angiogenesis-dependent human diseases such as cancer.

Enhancement of learning behaviour by a potent nitric oxide-guanylate cyclase activator YC-1

Memory is one of the most fundamental mental processes, and various approaches have been used to understand the mechanisms underlying this process. Nitric oxide (NO), cGMP and protein kinase G (PKG) are involved in the modulation of synaptic plasticity in various brain regions. YC-1, which is a benzylindazole derivative, greatly potentiated the response of soluble guanylate cyclase to NO (up to several hundreds fold). We have previously shown that YC-1 markedly enhances long-term potentiation in hippocampal and amygdala slices via NO-cGMP-PKG-dependent pathway. We here further investigated whether YC-1 promotes learning behaviour in Morris water maze and avoidance tests. It was found that YC-1 shortened the escape latency in the task of water maze, increased and decreased the retention scores in passive and active avoidance task, respectively. Administration of YC-1 30 min after foot-shock stimulation did not significantly affect retention scores in response to passive avoidance test. Administration of scopolamine, a muscarinic antagonist, markedly impaired the memory acquisition. Pretreatment of YC-1 inhibited the scopolamine-induced learning deficit. The enhancement of learning behaviour by YC-1 was antagonized by intracerebroventricular injection of NOS inhibitor L-NAME and PKG inhibitors of KT5823 and Rp-8-Br-PET-cGMPS, indicating that NO-cGMP-PKG pathway is also involved in the learning enhancement action of YC-1. YC-1 is thus a good drug candidate for the improvement of learning and memory.

What turns CREB on?

The transactivation domain of the cAMP response element-binding protein (CREB) consists of two major domains. The glutamine-rich Q2 domain, which interacts with the general transcription factor TAFII130/135, is sufficient for the recruitment of a functional RNA polymerase II complex and allows basal transcriptional activity. The kinase-inducible domain, however, mediates signal-induced activation of CREB-mediated transcription. It is generally believed that recruitment of the coactivators CREB-binding protein (CBP) and p300 after signal-induced phosphorylation of this domain at serine-133 strongly enhances CREB-dependent transcription. Transcriptional activity of CREB can also be potentiated by phosphoserine-133-independent mechanisms, and not all stimuli that provoke phosphorylation of serine-133 stimulate CREB-dependent transcription. This review presents an overview of the diversity of stimuli that induce CREB phosphorylation at Ser-133, focuses on phosphoserine-133-dependent and -independent mechanisms that affect CREB-mediated transcription, and discusses different models that may explain the discrepancy between CREB Ser-133 phosphorylation and activation of CREB-mediated transcription.

Nitric oxide signaling: systems integration of oxygen balance in defense of cell integrity

PURPOSE OF REVIEW

Nitric oxide has emerged as a ubiquitous signaling molecule subserving diverse pathophysiologic processes, including cardiovascular homeostasis and its decompensation in atherogenesis. Recent insights into molecular mechanisms regulating nitric oxide generation and the rich diversity of mechanisms by which it propagates signals reveal the role of this simple gas as a principle mediator of systems integration of oxygen balance.

RECENT FINDINGS

The molecular lexicon by which nitric oxide propagates signals encompasses the elements of posttranslational modification of proteins by redox-based nitrosylation of transition metal centers and free thiols. Spatial and temporal precision and specificity of signal initiation, amplification, and propagation are orchestrated by dynamic assembly of supramolecular complexes coupling nitric oxide production to upstream and downstream components in specific subcellular compartments. The concept of local paracrine signaling by nitric oxide over subcellular distances for short durations has expanded to include endocrine-like effects over anatomic spatial and temporal scales. From these insights emerges a role for nitric oxide in integrating system responses controlling oxygen supply and demand to defend cell integrity in the face of ischemic challenge. In this context, nitric oxide coordinates the respiratory cycle to acquire and deliver oxygen to target tissues by regulating hemoglobin function and vascular smooth muscle contractility and matches energy supply and demand by down-regulating energy-requiring functions while shifting metabolism to optimize energy production.

SUMMARY

Insights into mechanisms regulating nitric oxide production and signaling and their integration into responses mediating homeostasis place into specific relief the role of those processes in pathophysiology. Indeed, endothelial dysfunction associated with altered production of nitric oxide regulating tissue integrity contributes to the pathogenesis underlying atherogenesis. Moreover, this central role in pathophysiology identifies nitric oxide signaling as a key target for novel therapeutic interventions to minimize irreversible tissue damage associated with ischemic cardiovascular disease.