ADF and Cofilin1 Control Actin Stress Fibers, Nuclear Integrity, and Cell Survival

Genetic co-depletion of the actin-severing proteins ADF and CFL1 triggers catastrophic loss of adult homeostasis in multiple tissues. There is impaired cell-cell adhesion in skin keratinocytes with dysregulation of E-cadherin, hyperproliferation of differentiated cells, and ultimately apoptosis. Mechanistically, the primary consequence of depleting both ADF and CFL1 is uncontrolled accumulation of contractile actin stress fibers associated with enlarged focal adhesions at the plasma membrane, as well as reduced rates of membrane protrusions. This generates increased intracellular acto-myosin tension that promotes nuclear deformation and physical disruption of the nuclear lamina via the LINC complex that normally connects regulated actin filaments to the nuclear envelope. We therefore describe a pathway involving the actin-severing proteins ADF and CFL1 in regulating the dynamic turnover of contractile actin stress fibers, and this is vital to prevent the nucleus from being damaged by actin contractility, in turn preserving cell survival and tissue homeostasis.

Critical roles for multiple formins during cardiac myofibril development and repair

Cardiac and skeletal muscle function depends on the proper formation of myofibrils, which are tandem arrays of highly organized actomyosin contractile units called sarcomeres. How the architecture of these colossal molecular assemblages is established during development and maintained over the lifetime of an animal is poorly understood. We investigate the potential roles in myofibril formation and repair of formin proteins, which are encoded by 15 different genes in mammals. Using quantitative real-time PCR analysis, we find that 13 formins are differentially expressed in mouse hearts during postnatal development. Seven formins immunolocalize to sarcomeres in diverse patterns, suggesting that they have a variety of functional roles. Using RNA interference silencing, we find that the formins mDia2, DAAM1, FMNL1, and FMNL2 are required nonredundantly for myofibrillogenesis. Knockdown phenotypes include global loss of myofibril organization and defective sarcomeric ultrastructure. Finally, our analysis reveals an unanticipated requirement specifically for FMNL1 and FMNL2 in the repair of damaged myofibrils. Together our data reveal an unexpectedly large number of formins, with diverse localization patterns and nonredundant roles, functioning in myofibril development and maintenance, and provide the first evidence of actin assembly factors being required to repair myofibrils.

Structure of the inhibitor complex of old yellow enzyme from Trypanosoma cruzi

Old yellow enzyme (OYE) is an NADPH oxidoreductase which contains flavin mononucleotide as prosthetic group. The X-ray structures of OYE from Trypanosoma cruzi (TcOYE) which produces prostaglandin (PG) F(2α) from PGH(2) have been determined in the presence or absence of menadione. The binding motif of menadione, known as one of the inhibitors for TcOYE, should accelerate the structure-based development of novel anti-chagasic drugs that inhibit PGF(2α) production specifically.

Isoform-selective chemical inhibition of mDia-mediated actin assembly

Formins are potent actin assembly factors. Diaphanous formins, including mDia1, mDia2, and mDia3 in mammals, are implicated in mitosis and cytokinesis, but no chemical interactors have been reported. We developed an in vitro screen for inhibitors of actin assembly by mDia1 and identified an inhibitor of mDia1 and mDia2 that does not inhibit mDia3 at the concentrations tested. These results establish the druggability of mDia formins and introduce a first-generation inhibitor.

[Wheat root cells functioning under inhibition of I and II complexes of mitochondrial respiratory chain]

A joint effect of rotenone and malonate on the intensity of respiration, output of K+ and ultrastructure of wheat root cells treated for 6 h was studied. The addition of malonate to rotenone containing solution, in which wheat roots had been incubated for an hour, caused further decrease in respiration intensity and K+ output into external medium. Many mitochondria acquired torus shape in 2h after malonate addition. The increase in respiratory intensity and re-entry of K+ from the incubation medium into the cells were observed during following hours of incubation. We assume that reparation and adaptation processes took place in this case. The observed contacts of endoplasmic reticulum lumens with mitochondria are indicative of possible synthesis of an enzyme able to metabolize malonate to acetyl-CoA and CO2. We propose that torus shape of mitochondria is due to the increase in their outer surfaces, that, in turn, is a result of activation of external NAD(P)H-dehydrogenase. These findings may be evidence of possible adaptation of the root cells to the joint effect of the inhibitors.

Regulation of common carotid arterial blood flow by nitrergic neurons in the medulla of cats

Glutamate stimulation of the dorsal facial area, an area located dorsal to the facial nucleus, increases common carotid arterial blood flow. Nitrergic neurons are important in cardiovascular regulatory areas. We investigated whether the nitrergic neurons might be present and play a role in the dorsal facial area to regulate the arterial blood flow. Injections of L-arginine (an NO precursor) and sodium nitroprusside (an NO donor) into the area caused dose-dependent increases in the arterial blood flow. Injection of N(G)-nitro-arginine methyl ester (L-NAME, an NO synthase inhibitor) or methylene blue (a guanylate cyclase inhibitor) decreased the arterial blood flow. Nitrergic neurons and fibers were found in the dorsal facial area by histochemical staining of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase, a maker of NO synthase. In conclusion, nitrergic neurons are present in the dorsal facial area and appear to release NO tonically in stimulating the area to cause increase in common carotid arterial blood flow.

Menadione-induced reactive oxygen species generation via redox cycling promotes apoptosis of murine pancreatic acinar cells

Oxidative stress may be an important determinant of the severity of acute pancreatitis. One-electron reduction of oxidants generates reactive oxygen species (ROS) via redox cycling, whereas two-electron detoxification, e.g. by NAD(P)H:quinone oxidoreductase, does not. The actions of menadione on ROS production and cell fate were compared with those of a non-cycling analogue (2,4-dimethoxy-2-methylnaphthalene (DMN)) using real-time confocal microscopy of isolated perfused murine pancreatic acinar cells. Menadione generated ROS with a concomitant decrease of NAD(P)H, consistent with redox cycling. The elevation of ROS was prevented by the antioxidant N-acetyl-l-cysteine but not by the NADPH oxidase inhibitor diphenyliodonium. DMN produced no change in reactive oxygen species per se but significantly potentiated menadione-induced effects, probably via enhancement of one-electron reduction, since DMN was found to inhibit NAD(P)H:quinone oxidoreductase detoxification. Menadione caused apoptosis of pancreatic acinar cells that was significantly potentiated by DMN, whereas DMN alone had no effect. Furthermore, bile acid (taurolithocholic acid 3-sulfate)-induced caspase activation was also greatly increased by DMN, whereas DMN had no effect per se. These results suggest that acute generation of ROS by menadione occurs via redox cycling, the net effect of which is induction of apoptotic pancreatic acinar cell death. Two-electron detoxifying enzymes such as NAD(P)H:quinone oxidoreductase, which are elevated in pancreatitis, may provide protection against excessive ROS and exert an important role in determining acinar cell fate.

Detection of NADPH-diaphorase activity in Paramecium primaurelia

Recently, we showed that Paramecium primaurelia synthesizes molecules functionally related to the cholinergic system and involved in modulating cell-cell interactions leading to the sexual process of conjugation. It is known that nitric oxide (NO) plays a role in regulating the release of transmitter molecules, such as acetylcholine, and that the NO biosynthetic enzyme, nitric oxide synthase (NOS), shows nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity. In this work, we detected the presence of NADPH-d activity in P. primaurelia. We characterized this activity histochemically by examining its specificity for beta-NADPH and alpha-NADH co-substrates, and sensitivity both to variations in chemico-physical parameters and to inhibitors of enzymes showing NADPH-d activity. Molecules immunologically related to NOS were recognized by the anti-rat brain NOS (bNOS) antibody. Moreover, bNOS immunoreactivity and NADPH-d activity sites were found to be co-localized. The non-denaturing electrophoresis, followed by exposure to beta-NADPH or alpha-NADH co-substrates, revealed the presence of a band of apparent molecular mass of about 124 kDa or a band of apparent molecular mass of about 175 kDa, respectively. In immunoblot experiments, the bNOS antibody recognized a single band of apparent molecular mass of about 123 kDa.

The Basic Region of the Diaphanous-autoregulatory Domain (DAD) Is Required for Autoregulatory Interactions with the Diaphanous-related Formin Inhibitory Domain

Mammalian diaphanous-related (mDia) formins act as Rho GTPase effectors during cytoskeletal remodeling. Rho binding to mDia amino-terminal GTPase-binding domains (GBDs) causes the adjacent Dia-inhibitory domain (DID) to release the carboxyl-terminal Dia-autoregulatory (DAD) domain that flanks the formin homology-2 (FH2) domain. The release of DAD allows the FH2 domain to then nucleate and elongate nonbranched actin filaments. DAD, initially discovered as a region of homology shared between a phylogenetically divergent set of formin proteins, is comprised of a core motif, MDXLLXL, and an adjacent region is comprised of numerous basic residues, typically RRKR in the mDia family. Here, we show that these specific amino acids within the basic region of DAD contribute to the binding of DID and therefore the maintenance of the mDia autoregulatory mechanism. In addition, expression of full-length versions of mDia2 containing amino acid substitutions in either the DAD core or basic regions causes profound changes in the F-actin architecture, including the formation of filopodia-like structures that rapidly elongate from the cell edge. These studies further refine our understanding of the molecular contribution of DAD to mDia control and the role of mDia2 in the assembly of membrane protrusions.

Extremely potent triterpenoid inducers of the phase 2 response: correlations of protection against oxidant and inflammatory stress

A series of synthetic triterpenoid (TP) analogues of oleanolic acid are powerful inhibitors of cellular inflammatory processes such as the induction by IFN-gamma of inducible nitric oxide synthase (iNOS) and of cyclooxygenase 2 in mouse macrophages. Here, we show that these analogues are also extremely potent inducers of the phase 2 response [e.g., elevation of NAD(P)H-quinone oxidoreductase and heme oxygenase 1], which is a major protector of cells against oxidative and electrophile stress. Moreover, like previously identified phase 2 inducers, the TP analogues use the antioxidant response element-Nrf2-Keap1 signaling pathway. Thus, induction of the phase 2 response and suppression of the iNOS induction was abrogated in nrf2(-/-) and keap1(-/-) mouse embryonic fibroblasts. The high potency of TP analogues in inducing the phase 2 response and blocking inflammation depends on the presence of activated Michael reaction (enone) functions at critical positions in rings A and C. The most potent TP doubles NAD(P)H-quinone oxidoreductase in murine hepatoma cells at 0.28 nM and has an IC(50) for suppression of iNOS induction in primary mouse macrophages of 0.0035 nM. The direct interaction of this TP with thiol groups of the Keap1 sensor for inducers is demonstrated spectroscopically. The antiinflammatory and phase 2 inducer potencies of 18 TP are closely linearly correlated (r(2) = 0.91) over 6 orders of magnitude of concentration. Thus, in addition to blocking inflammation and promoting differentiation, these TP exhibit another very important protective property: the induction of the phase 2 response.

Site-specific inhibitors of NADPH oxidase activity and structural probes of flavocytochrome b: characterization of six monoclonal antibodies to the p22phox subunit

The integral membrane protein flavocytochrome b (Cyt b) is the catalytic core of the human phagocyte NADPH oxidase, an enzyme complex that initiates a cascade of reactive oxygen species important in the elimination of infectious agents. This study reports the generation and characterization of six mAbs (NS1, NS2, NS5, CS6, CS8, and CS9) that recognize the p22(phox) subunit of the Cyt b heterodimer. Each of the mAbs specifically detected p22(phox) by Western blot analysis but did not react with intact neutrophils in FACS studies. Phage display mapping identified core epitope regions recognized by mAbs NS2, NS5, CS6, CS8, and CS9. Fluorescence resonance energy transfer experiments indicated that mAbs CS6 and CS8 efficiently compete with Cascade Blue-labeled mAb 44.1 (a previously characterized, p22(phox)-specific mAb) for binding to Cyt b, supporting phage display results suggesting that all three Abs recognize a common region of p22(phox). Energy transfer experiments also suggested the spatial proximity of the mAb CS9 and mAb NS1 binding sites to the mAb 44.1 epitope, while indicating a more distant proximity between the mAb NS5 and mAb 44.1 epitopes. Cell-free oxidase assays demonstrated the ability of mAb CS9 to markedly inhibit superoxide production in a concentration-dependent manner, with more moderate levels of inhibition observed for mAbs NS1, NS5, CS6, and CS8. A combination of computational predictions, available experimental data, and results obtained with the mAbs reported in this study was used to generate a novel topology model of p22(phox).

Cortical interneurons become activated by deafferentation and instruct the apoptosis of pyramidal neurons

Unlike peripheral nervous system neurons and certain groups of nerve cells in the CNS, cortical projection neurons are tolerant of axonal lesions. This resistance is incongruent with the massive death of pyramidal neurons in age-associated neurodegenerative diseases that proceed along corticocortical connections. Some insights have emerged from our previous work showing that pyramidal cells in piriform cortex undergo classical apoptosis within 24 h after bulbectomy via transsynaptic, but not retrograde, signaling. These findings allow the investigation of cellular and molecular changes that take place in the context of experimental cortical degeneration. In the present study, we show that the transsynaptic death of pyramidal neurons in piriform cortex is a nitric oxide-mediated event signaled by activated interneurons in layer I. Thus, we demonstrate that cortical interneurons play an essential role in transducing injury to apoptotic signaling that selectively targets pyramidal neurons. We propose that this mechanism may be generic to cortical degenerations and amenable to therapeutic interventions.

Homocysteine enhances TIMP-1 expression and cell proliferation associated with NADH oxidase in rat mesangial cells

BACKGROUND

Recent studies in our laboratory demonstrated that chronic hyperhomocysteinemia (hHcys) induced glomerular sclerosis. The mechanism mediating hHcys-induced glomerular damage remains unknown. The present study was designed to test a hypothesis that homocysteine (Hcys) increases the production by nicotinamide adenine dinucleotide (NADH) oxidase and thereby stimulates the formation of tissue inhibitor of metalloproteinase (TIMP-1) in rat mesangial cells, consequently leads to glomerulosclerosis.

METHODS

Rat mesangial cells were incubated with L-homocysteine (L-Hcys) to determine the effects of Hcys on cell proliferation and metabolism of extracellular matrix (ECM). Northern blot, Western blot, oligonucleotide transfection, measurements of NADH oxidase activity and levels, and cell proliferation assay were performed.

RESULTS

In cultured rat mesangial cells, treatment with L-Hcys (40 to 160 micromol/L) markedly increased the mRNA levels of TIMP-1 and Gp91 and led to accumulation of collagen I, which were accompanied by enhanced cell proliferation and NADH oxidase activity in mesangial cells. These Hcys-induced biochemical and functional changes were substantially blocked by a NADH oxidase inhibitor, diphenylene iodonium chloride (DPI) or a superoxide dismutase (SOD) mimetic, hydroxyl-tetramethylpiperidin-oxyl (TEMPOL). Moreover, blockade of NADH oxidase subunit, phox22, by its antisense oligodeoxynucleotide also eliminated the increase in NADH oxidase activity induced by L-Hcys.

CONCLUSION

These results indicate that Hcys-induced alterations of ECM metabolism in mesangial cells are associated with enhanced NADH oxidase activity and that oxidative stress-stimulated up-regulation of TIMP-1 may play an important role in the deposition of collagen or ECM elements in the glomeruli during hHcys.

Flavoenzymes inhibited by indomethacin

The effect of indomethacin on the activity of five different flavoenzymes, three dehydrogenases and six hydrosases, was determined. Indomethacin at concentration 1.0 mM inhibited the activity, in decreasing order of sensitivity, of the following flavoenzymes: D-amino acid oxidase (pig kidney), flavin-containing monooxygenases (pig liver microsomal), cyclohexanone monooxygenase (Acinetobacter), NADPH-quinone reductase (pig liver), and glutathione reductase (yeast), but it had no effect on the activity of glucose oxidase (Aspergillus) or liver microsomal NADPH-cytochrome P-450 reductase. Indomethacin was competitive with D-alanine for the D-amino acid oxidase (Ki=30 microM) and with NADPH for all other flavoenzymes sensitive to this compound (Kis 170-500 microM). While indomethacin also inhibited two of the three NAD(P)+-dependent dehydrogenases tested, the Kis were relatively high (<1, 500 microM), and of the six different hydrolases tested only one, liver microsomal esterase, was inhibited by indomethacin (Ki=600 microM). Indomethacin also inhibited aminopyrine demethylation catalyzed by the liver microsomal P-450 monooxygenase (Ki=1,000 microM). Although the exact mechanism for the inhibition of functionally different flavoenzymes sensitive to indomethacin is not known, the inhibition is probably not due to the detergent properties of this drug.

Post-illumination reduction of the plastoquinone pool in chloroplast transformants in which chloroplastic NAD(P)H dehydrogenase was inactivated

We reported previously that an ndhB gene disruptant, delta ndhB, had the same phenotype as wild-type tobacco plants under normal growth conditions. Two other groups have reported conflicting phenotypes with each other for ndhCKJ operon disruptants. Here, we generated two transformants in which the ndhCKJ operon was disrupted, and found that new transformants had the same phenotype as delta ndhB. After illumination with visible light, all ndh disruptants had higher levels of steady-state fluorescence than wild-type controls when measured under weak light, suggesting that reduction of the plastoquinone pool in ndh disruptants was greater than that in wild-type controls. The weak light itself could not reduce the plastoquinone much, so the reduction in the plastoquinone in the mutant was due to electron donation from stromal reductants generated during illumination with the strong light. These results supported the hypothesis that NAD(P)H dehydrogenase prevents overreduction in chloroplasts and suggested that chlororespiratory oxidase did not function under low light or in the dark.

An NAD(P)H oxidase regulates growth and transcription in melanoma cells

Malignant melanoma cells spontaneously generate reactive oxygen species (ROS) that promote constitutive activation of the transcription factor nuclear factor-kappaB (NF-kappaB). Although antioxidants and inhibitors of NAD(P)H oxidases significantly reduce constitutive NF-kappaB activation and suppress cell proliferation (11), the nature of the enzyme responsible for ROS production in melanoma cells has not been determined. To address this issue, we now have characterized the source of ROS production in melanoma cells. We report that ROS are generated by isolated, cytosol-free melanoma plasma membranes, with inhibition by NAD(P)H oxidase inhibitors. The p22(phox), gp91(phox), and p67(phox) components of the human phagocyte NAD(P)H oxidase and the gp91(phox) homolog NOX4 were demonstrated in melanomas by RT-PCR and sequencing, and protein product for both p22(phox) and gp91(phox) was detected in cell membranes by immunoassay. Normal human epidermal melanocytes expressed only p22(phox) and NOX4. Melanoma proliferation was reduced by NAD(P)H oxidase inhibitors and by transfection of antisense but not sense oligonucleotides for p22(phox) and NOX4. Also, the flavoprotein inhibitor diphenylene iodonium inhibited constitutive DNA binding of nuclear protein to the NF-kappaB and cAMP-response element consensus oligonucleotides, without affecting DNA binding activity to activator protein-1 or OCT-1. This suggests that ROS generated in autocrine fashion by an NAD(P)H oxidase may play a role in signaling malignant melanoma growth.

Sustained, long-lasting inhibition of nitric oxide synthase aggravates the neural damage in some models of excitotoxic brain injury

Brain nitric oxide (NO) can be a mediator of physiological and neuroprotective actions and an effector of neural damage. The effectiveness of acute or chronic inhibition of NO production in in vivo experiments of neurotoxicity/neuroprotection is controversial. We report here on the effects of a chronic, sustained inhibition of nitric oxide synthase (NOS) on the neurodegenerative damage caused by three different excitotoxic lesions. The damage caused by intrastriatal injection of ibotenic or kainic acid was aggravated in rats subjected to chronic NOS inhibition. On the contrary, the drop of cortical cholinergic input consequent to ibotenic acid-mediated degeneration of basal forebrain neurons was not altered by chronic NOS inhibition. The worsening of the damage was not related to any overt differential sensitivity to excitotoxicity of NOS-containing striatal neurons under conditions of NOS inhibition. These results suggest that, contrary to what has been often reported for short-term, mild inhibition of NO production, chronic and sustained NOS inhibition may exacerbate neuropathology. Thus, long-lasting shortage of NO may be detrimental when neuroprotective mechanisms related to the physiological action of this free radical are severely impaired. Although we cannot exclude that inhibition of the endothelial NOS isoform could have contributed to the worsening of neuropathology, differences among the paradigms of neurotoxicity used in the present study suggest a primary involvement of the neuronal NOS isoform. In view of the potential therapeutic use of NOS inhibitors, the effects of a too drastic alteration of the balance between neuroprotective and neurodegenerative actions of NO should be carefully considered.

The ultrastructural localization of NADPH-diaphorase enzymatic activity in the Leydig cells of mouse. effects of ethanol administration

The effects of the chronic ethanol treatment on the NOS-related NADPH-diaphorase activity were described in the mouse Leydig cells by means of transmission electron microscope. The recovery of the Leydig cells was also examined during a period of four weeks. About 10% of the Leydig cells showed various degrees of morphological alterations, consisting in increased number of lipid droplets, rarefaction and vacuolization of the cytoplasmic matrix. Other groups of Leydig cells (about 10%) revealed evident signs of degeneration. The NADPH-d activity was reduced both in apparently normal and injured Leydig cells and a moderate enzymatic reaction was only detected in the smooth endoplasmic reticulum. A week after the treatment an increased number of the degenerating Leydig cells and a further reduction of the enzymatic reaction were observed. Then, the Leydig cells showed a progressive recovery and four weeks after the treatment they exhibited a normal morphology and NADPH-d enzymatic reaction. These results demonstrated for the first time the inhibition of NOS activity in the Leydig cells after chronic ethanol administration.

Characterization of the flavoprotein domain of gp91phox which has NADPH diaphorase activity

A series of truncated forms of gp91phox were expressed in Escherichia coli in which the N-terminal hydrophobic transmembrane region was replaced with a portion of the highly soluble bacterial protein thioredoxin. TRX-gp91phox (306-569), which contains the putative FAD and NADPH binding sites, showed weak NADPH-dependent NBT (nitroblue tetrazolium) reductase activity, whereas TRX-gp91phox (304-423) and TRX-gp91phox (424-569) were inactive. Activity saturated at about a 1:1 molar ratio of FAD to TRX-gp91phox (306-569), and showed the same K(m) for NADPH as that for superoxide generating activity by the intact enzyme. Activity was not inhibited by superoxide dismutase, indicating that it was not mediated by superoxide, but was blocked by an inhibitor of the respiratory burst oxidase, diphenylene iodonium. In the presence of Rac1, the cytosolic regulatory protein p67phox stimulated the NBT reductase activity, but p47phox had no effect. Truncated p67phox containing the activation domain (residues 199-210) [C.-H. Han, J.R. Freeman, T. Lee, S.A. Motalebi, and J.D. Lambeth (1998) J. Biol. Chem. 273, 16663-16668] stimulated activity approximately 2-fold, whereas forms mutated or lacking this region failed to stimulate the activity. Our data indicate that: (i) TRX-gp91phox (306-569) contains binding sites for both pyridine and flavin nucleotides; (ii) this flavoprotein domain shows weak diaphorase activity; and (iii) the flavin-binding domain of gp91phox is the target of regulation by the activation domain of p67phox.

The external calcium-dependent NADPH dehydrogenase from Neurospora crassa mitochondria

We have inactivated the nuclear gene coding for a putative NAD(P)H dehydrogenase from the inner membrane of Neurospora crassa mitochondria by repeat-induced point mutations. The respiratory rates of mitochondria from the resulting mutant (nde-1) were measured, using NADH or NADPH as substrates under different assay conditions. The results showed that the mutant lacks an external calcium-dependent NADPH dehydrogenase. The observation of NADH and NADPH oxidation by intact mitochondria from the nde-1 mutant suggests the existence of a second external NAD(P)H dehydrogenase. The topology of the NDE1 protein was further studied by protease accessibility, in vitro import experiments, and in silico analysis of the amino acid sequence. Taken together, it appears that most of the NDE1 protein extends into the intermembrane space in a tightly folded conformation and that it remains anchored to the inner mitochondrial membrane by an N-terminal transmembrane domain.

Dual effect of oxidized LDL on cell cycle in human endothelial cells through oxidative stress

BACKGROUND

Oxidized low-density lipoprotein (OxLDL) exerts proliferation and apoptosis in vascular cells, depending on its concentration and the exposure time. Various steps in the cell cycle and in the apoptotic signaling cascade are modulated by O2-, and OxLDL stimulates vascular O2- formation. Here we studied the role of NADPH oxidase, a potential source for O2- formation after OxLDL stimulation, in cell proliferation, and we investigated whether OxLDL influences anti-apoptotic genes in cultured human umbilical vein endothelial cells (HUVEC). Methods and Results. OxLDL dose-dependently (10 to 300 microg/mL) stimulated O2- formation in HUVEC (detected by cytochrome c assay and by chemiluminescence of lucigenin). Low OxLDL concentrations (5 to 10 microg/mL) induced proliferation (detected by 3H-thymidine incorporation), while higher concentrations (50 to 300 microg/mL) induced apoptotic cell death (detected by Annexin assay and DNA fragmentation). Proliferation was blocked by the antioxidants SOD and catalase and by diphenyleneiodonium (10 micromol/L), an inhibitor of the O2- generating NADPH oxidase. In addition, cells transfected with antisense oligonucleotides for NADPH oxidase showed a significantly reduced O2- formation after stimulation with OxLDL. The OxLDL effect on apoptosis was also blocked by antioxidants. Since endothelial cells are protected against apoptosis through anti-apoptotic genes, we investigated whether OxLDL overcomes protection against apoptosis through suppression of the anti-apoptotic gene A20, a zinc-finger protein. OxLDL suppressed the expression of A20 in a dose-dependent manner.

CONCLUSION

These data indicate that OxLDL has a dual effect on cell cycle in HUVEC, inducing proliferation at low and apoptosis at higher concentrations. Both effects are mediated by O2- formation, with NADPH oxidase being a major source for O2-. Thus, OxLDL contributes importantly to vascular cellular turnover through the induction of oxidative stress.

Fluorescent imaging of nitric oxide production in neuronal varicosities associated with intraparenchymal arterioles in rat hippocampal slices

The fluorescent indicator 4,5-diaminofluorescein (DAF-2) has been used to investigate the production of nitric oxide in the vicinity of intraparenchymal cerebral blood vessels. Slices of rat hippocampus 300-350 microm thick, were loaded with 5 microM DAF-2 diacetate. On exposure to light of 450-490 nm wavelength, point sources of fluorescence, 1.8+/-0.2 microm in diameter (mean+/-SEM), were observed in close apposition to the outer surface of the vascular smooth muscle wall of 10/15 arterioles. In fixed slices, resectioned and processed for nicotinamide adenine dinucleotide phosphate-dependent diaphorase, stained varicose fibres were also seen in close association with the smooth muscle wall of small arterioles. These findings suggest that tonic activity in perivascular nitrergic nerve fibres lying in close proximity to intraparenchymal microvessels may be a source of dilator tone within the parenchyma.

Acute blockade of nitric oxide synthesis induces disorganization and amplifies lesion-induced plasticity in the rat retinotectal projection

In the rat visual system, the uncrossed retinotectal projection undergoes a topographical refinement within the first two postnatal weeks. We have studied the role of nitric oxide (NO), a retrograde messenger which couples pre- and postsynaptic activation, in the development of the uncrossed retinotectal projection and in the plasticity of this pathway as a result of a restricted retinal lesion in the opposite eye. During development, maximal nitric oxide synthase (NOS) activity was observed in homogenates of tectal tissue at postnatal day 5 (PND 5), followed by a two-step decrease at the end of the topographical fine tuning period (PND 21) and the adult stage (PND 42). We also tested the effects of an acute in vivo blockade of NOS during the development of both animals that had not been operated on, and lesioned animals. Animals ranging from PND 4 to PND 42 were treated either with the NOS inhibitor, L-nitro-arginine (Narg 50 mg/kg ip.) or vehicle (NaCl 0.9%) during 4 days (from PND 4-7 or PND 9-12) or 8 days (from PND 20-27 or PND 34-41). Reduction of NOS activity induced sprouting of the ipsilateral pathway up to the second postnatal week in the animals that had not been operated on. Rats that had been operated on, however, showed an amplification of the lesion-induced plasticity up to the fourth postnatal week under NOS blockade. The data suggest that NO plays a role in the stabilization of retinotectal synapses during the critical period of topographic refinement, and indicate that an acute blockade of retrograde signals enables plastic rearrangements in the visual system within this time window.

On the effect of neonatal nitric oxide synthase inhibition in rats: a potential neurodevelopmental model of schizophrenia

NADPH-d (nicotinamide-adenine dinucleotide phosphate-diaphorase) neurons are thought to migrate improperly during development in the brains of schizophrenic patients. This enzyme is a nitric oxide synthase (NOS). Nitric oxide (NO) is known to affect neurodevelopmental processes in the CNS. Therefore, we hypothesized that interference of NO generation during development may produce some aspects of schizophrenia symptomatology in a rat model. In these experiments, neonatal rats were challenged with a NOS inhibitor (L-nitroarginine 1-100 mg/kg s.c.) daily on post-natal days 3-5. L-Nitroarginine (L-NoArg) treated male rats developed a hypersensitivity to amphetamine in adulthood versus vehicle treated controls, whereas female rats did not. However, L-NoArg treated female rats developed a hypersensitivity to phencyclidine (PCP) at juvenile and adult ages versus vehicle treated controls, whereas male animals did not. L-NoArg treated male rats also had deficits in pre-pulse inhibition of startle whereas adult female rats did not. The results are discussed in terms of a new neurodevelopmental model of schizophrenia and male/female differences inherent in this disease.

Intracellular polyamine levels are involved in NMDA-evoked nitric oxide production in chick retina cells

The NMDA-sensitive glutamate receptor complex can be modulated by numerous drugs and endogenous substances such as polyamines. We studied the pathway of arginine/nitric oxide/cyclic GMP in cultured chick retina cells through NMDA receptor activation, seen as a function of both differentiation stages of culture and intracellular polyamine levels. In our experimental conditions, the nitric oxide synthase activity was stimulated by NMDA from three to four times between embryonic day (E) 8 plus 5 days in vitro (C) and E8C7. The NMDA response was blocked by MK-801 (10 microM) by >60% at stage E8C5. During culture differentiation, the NMDA-induced increase in nitric oxide synthase activity at the E8C5 stage was blocked by preliminary incubation (24 h) of the cells with alpha-difluoromethylornithine, the inhibitor of polyamine biosynthesis. This effect was assessed by a reduction of NMDA-evoked cyclic GMP formation in polyamine-depleted retina cells. Thus, intracellular polyamine levels are involved in NMDA-evoked nitric oxide production. Our results indicate that (a) the developmental pattern of polyamine levels can be associated with the modulation of NMDA-evoked events and (b) the NMDA-mediated effects have been reduced in alpha-difluoromethylornithine-treated cell cultures. These observations provide evidence for a physiological interaction between polyamines and NMDA-sensitive glutamate receptors during differentiation stages of cultured chick retina cells.

Blockade of tetrahydrobiopterin synthesis protects neurons after transient forebrain ischemia in rat: a novel role for the cofactor

The generation of nitric oxide (NO) aggravates neuronal injury. (6R)-5,6,7,8-Tetrahydro-L-biopterin (BH4) is an essential cofactor in the synthesis of NO by nitric oxide synthase (NOS). We attempted to attenuate neuron degeneration by blocking the synthesis of the cofactor BH4 using N-acetyl-3-O-methyldopamine (NAMDA). In vitro data demonstrate that NAMDA inhibited GTP cyclohydrolase I, the rate-limiting enzyme for BH4 biosynthesis, and reduced nitrite accumulation, an oxidative metabolite of NO, without directly inhibiting NOS activity. Animals exposed to transient forebrain ischemia and treated with NAMDA demonstrated marked reductions in ischemia-induced BH4 levels, NADPH-diaphorase activity, and caspase-3 gene expression in the CA1 hippocampus. Moreover, delayed neuronal injury in the CA1 hippocampal region was significantly attenuated by NAMDA. For the first time, these data demonstrate that a cofactor, BH4, plays a significant role in the generation of ischemic neuronal death, and that blockade of BH4 biosynthesis may provide novel strategies for neuroprotection.

Binding and reactivity of Candida albicans estrogen binding protein with steroid and other substrates

In this report recombinant estrogen binding protein (EBP1), isolated originally from Candida albicans as a result of its high affinity for 17beta-estradiol, has been purified extensively using a modified affinity purification scheme originally developed for a homolog of EBP1, old yellow enzyme (OYE). It is shown that like OYE, the protein binds a variety of compounds with a phenolic structure, including 17beta-estradiol, and compounds with an alpha, beta-unsaturated keto or aldehyde structure. In addition, EBP1 exhibits an NADPH oxidoreductase activity, transferring electrons from NADPH to all alpha,beta-unsaturated ketones and aldehydes tested via the tightly bound FMN cofactor. Analysis of the steady-state kinetics of these reactions indicate a tetra uni ping-pong mechanism. Inhibition of the steady-state reaction by 17beta-estradiol gives a Ki = 10 +/- 2 nM, and indicates exclusive binding of this steroid to the enzyme in its oxidized state. In contrast, 19-nortestosterone binds to both oxidized and reduced forms of the enzyme with dissociation constants of 600 +/- 100 and 650 +/- 90 nM, respectively. EBP1 also catalyzes a disproportionation reaction with certain compounds, in which two molecules of a cylic alpha,beta-unsaturated ketone, including the steroid 19-nortestosterone, are individually aromatized and reduced to the corresponding saturated ketone. Despite the extensive similarity in sequence and enzymic activity, notable differences between EBP1 and the OYE family of proteins exist with regard to the binding behavior and reactivity with the two steroids tested here, estradiol and 19-nortestosterone.

Induction of NADPH-diaphorase activity in the forebrain in a model of intracerebral hemorrhage and its inhibition by the traditional Chinese medicine complex Nao Yi An

Induction of NADPH-diaphorase (NDP) activity in the rat cerebral cortex was studied after autologous blood injection into the internal capsule as experimental model of intracerebral hemorrhage. The potential inhibitory effect on NDP induction by Nao Yi An (NYA), a complex derived from materials of animal and plant origin used in the treatment of intracerebral hemorrhage in traditional Chinese medicine, was also investigated. In animals without therapeutic treatment 2 and 4 days after injection of autologous blood, NDP activity was highly induced in pyramidal neurons in the neocortex, piriform, and entorhinal cortices, in astrocytes and in phagocytes in the hematoma and the area surrounding it, as well as in the subcortical white matter, and in endothelial cells in both the cortex and subcortical white matter bilaterally. Oral administration of NYA failed to inhibit NDP induction in endothelial cells but demonstrated a strong inhibitory effect on NDP activity induced in pyramidal neurons and astrocytes. NDP induction in phagocytes was also inhibited by the administration of NYA. Altogether the present results suggest that intracerebral hemorrhage in the internal capsule may induce nitric oxide synthase activity in different cell populations in the cortex and that administration of NYA can selectively inhibit such induction and, thus, potentially play a neuroprotective role.

Nitric oxide synthase, cGMP, and NO-mediated cGMP production in the olfactory bulb of the rat

High levels of nitric oxide synthase and cyclic 3',5'-guanosine monophosphate (cGMP) in the olfactory bulb suggest that nitric oxide, acting as a diffusible intercellular messenger molecule inducing increased synthesis of cGMP, plays an important role in olfaction. The localization of cGMP after sodium nitroprusside stimulation of in vitro slices of rat olfactory bulb was compared with the distribution of nicotinamide adenine dinucleotide phosphatediaphorase, nitric oxide synthase, and glial fibrillary acidic protein. cGMP was detected immunohistochemically in cryostat sections. In the presence of the phosphodiesterase blocker isobutyl methylxanthine, cGMP was present in neurons in the glomerular layer, axons in the external and internal plexiform layers, and in a few somata and axons of the granule cell layer. This staining was blocked by NG-nitro-L-arginine methylester hydrochloride or hemoglobin. After sodium nitroprusside stimulation, the olfactory nerve layer was intensely stained, as were the glomeruli and periglomerular cells. In the external plexiform layer, axonal staining was increased substantially, and there were occasional multipolar cGMP-positive neurons. In the internal plexiform and granule cell layers, axonal staining was greatly increased. Many granule cells were also cGMP positive after sodium nitroprusside stimulation. cGMP and nitric oxide synthase-positive neuronal elements overlapped in the glomerular and granule cell layers, but staining was not colocalized, cGMP was not found in astrocytes. The glutamatergic antagonists D-2-amino-5-phosphonovalerate and 6-cyano-7-nitroquinoxaline caused differential inhibition of cGMP accumulation in layers of the olfactory bulb. These findings support the hypothesis that nitric oxide is an intercellular messenger in the olfactory bulb (Breer and Shepherd [1993] Trends Neurosci. 16:5-9).

Development of NADPH-diaphorase in the avian retina: regulation by calcium ions and relation to nitric oxide synthase

Nitric oxide plays an important role as an intercellular messenger in the CNS. In the present work we measured NADPH-diaphorase activity, which is considered to be a marker of cells producing nitric oxide, in homogenates of the developing chick retina. The enzyme activity can be detected beginning in 8-day-old embryonic retinas with no further quantitative variations throughout development. Arginine analogues inhibit approximately 65% of the activity in embryonic retinas and 50% in posthatched retinas. The enzyme is stimulated 50% by 2 mM calcium chloride in retinas from 8 to 14 embryonic days, but this effect decreases to 20% in 17-day embryonic retinas and practically disappears in posthatched animals. The stimulation by calcium is completely blocked by arginine analogues. The decrease in enzyme activity at posthatched retinas is not due to stimulation by endogenous calcium or the presence of insufficient amounts of calmodulin, because addition of EGTA or calmodulin, respectively, did not restore the stimulation to levels observed at embryonic stages. Inhibition of NADPH-diaphorase activity by NG-nitro-L-arginine or L-NG-(iminoethyl) ornithine is concentration dependent with IC50 values of approximately 1 mM at all stages studied. However, in the presence of calcium, the inhibition by both analogues is shifted to the left and is apparently biphasic at all developmental stages, including in posthatched animals, with IC50 values in the low micromolar range. NADPH-diaphorase was also detected by histochemistry in specific groups of cells in the early embryonic retina and in subsets of amacrine and ganglion cells, as well as in photoreceptors, in more developed retinas. The results indicate that different isoforms of nitric oxide synthase are present in the chick retina and that a calcium-dependent isoform is predominant in early periods of development.

[The effect of L-arginine on the NADPH-diaphorase activity in Drosophila melanogaster homogenates]

It was shown that L-arginine (up to 0.5 mM) competitively inhibits the NADPH-diaphorase activity in drosophila melanogaster. The value of inhibition constant is equal to 103 microM. In the presence of higher concentration of L-arginine total NADPH-diaphorase activity includes not only the L-arginine inhibited component, but also the non-inhibited one.

Direct evidence for the presence of two external NAD(P)H dehydrogenases coupled to the electron transport chain in plant mitochondria

Exogenous NADPH oxidation by purified mitochondria from both potato tuber and Arum maculatum spadix was completely and irreversibly inhibited by sub-micromolar diphenyleneiodonium (DPI), while exogenous NADH oxidation was inhibited to only a small degree. Addition of DPI caused the collapse of the membrane potential generated by NADPH oxidation, while the potential generated by NADH was unaffected. We conclude that there are two distinct enzymes on the outer surface of the inner membrane of plant mitochondria, one specific for NADH, the other relatively specific for NADPH, with both enzymes linked to the electron transport chain.

Protection against ischemic injury by nonvasoactive concentrations of nitric oxide synthase inhibitors in the perfused rabbit heart

BACKGROUND

The functional and metabolic effects of inhibitors of nitric oxide (NO) synthase on ischemic hearts have not been investigated. This work was designed to perform such a study in isolated perfused rabbit hearts submitted to low-flow ischemia.

METHODS AND RESULTS

After a 30-minute equilibration period, the hearts were submitted to low-flow ischemia for 60 minutes followed by reperfusion for 30 minutes. Functional and metabolic parameters were followed in hearts perfused with or without inhibitors of NO synthase or NO precursors, which were added 15 minutes before ischemia but were absent during reperfusion. Ischemic contracture was delayed and reduced in hearts perfused with 1 mumol/L L-N-monomethylarginine (L-NMMA) or 1 mumol/L L-N-arginine methylester, two inhibitors of NO synthase, but not with D-N-monomethylarginine, the inactive enantiomer of L-NMMA. The protection was suppressed by addition to the perfusate containing L-NMMA of 1 mmol/L L-arginine or 0.1 mmol/L sodium nitroprusside but not by addition of 10 mumol/L 8-bromo cGMP, a cGMP analogue. The functional protection by 1 mumol/L L-NMMA was related to a stimulation of glycolysis from exogenous glucose and a preservation of the glycogen stores. This resulted in a better maintenance of high-energy phosphates and a lower acidosis as measured by 31P nuclear magnetic resonance spectroscopy. During reperfusion, functional recovery was more than doubled, and enzyme release was halved in L-NMMA-treated hearts compared with controls. The functional and metabolic protection was maximal at 1 nmol/L to 1 mumol/L L-NMMA, ie, below the vasoactive concentrations of the inhibitor.

CONCLUSIONS

Nonvasoactive concentrations of NO synthase inhibitors protect the heart against ischemic damage; this relates to a stimulation of glycolysis from exogenous glucose.

The toxicity of aromatic nitrocompounds to bovine leukemia virus-transformed fibroblasts: the role of single-electron reduction

Bovine leukemia virus-transformed lamb embryo fibroblasts (line FLK) possess activity of DT-diaphorase of ca. 260 U/mg protein and similar levels of other NADP(H)-oxidizing enzymes: NADH:oxidase, 359 U/mg; NADPH:oxidase, 43 U/mg; NADH:cytochrome-c reductase, 141 U/mg; NADPH:cytochrome-c reductase, 43 U/mg. In general, the toxicity of aromatic nitrocompounds towards FLK cells increases on increase of single-electron reduction potentials (E1(1)) of nitrocompounds or the log of their reduction rate constants by single-electron-transferring enzymes, microsomal NADPH:cytochrome P-450 reductase (EC 1.6.2.4) and mitochondrial NADH:ubiquinone reductase (EC 1.6.99.3). No correlation between the toxicity and reduction rate of nitrocompounds by rat liver DT-diaphorase (EC 1.6.99.2) was observed. The toxicity is not significantly affected by dicumarol, an inhibitor of DT-diaphorase. Nitrocompounds examined were poor substrates for DT-diaphorase, being 10(4) times less active than menadione. Their poor reactivity is most probably determined by their preferential binding to a NADPH binding site, but not to menadione binding site of diaphorase. These data indicate that at comparable activities of DT-diaphorase and single-electron-transferring NAD(P)H dehydrogenases in the cell, the toxicity of nitrocompounds will be determined mainly by their single-electron reduction reactions.

Effects of methylene blue and LY83583 on neuronal nitric oxide synthase and NADPH-diaphorase

Methylene blue and 6-anilino-5,8-quinolinedione (LY83583) have often been used as 'selective' inhibitors of soluble guanylyl cyclase. We report that in in vitro assays, both these compounds were potent inhibitors of rat cerebellar nitric oxide synthase activity. Methylene blue had an apparent Ki of 2.7 microM, while for LY83583 the Ki was 15.8 microM. Furthermore, methylene blue, but not LY83583, inhibited the NADPH-diaphorase histochemical reaction associated with nitric oxide synthase. Our results indicate that many of the effects of these drugs which have been attributed to inhibition of guanylyl cyclase, may derive from their direct inhibition of nitric oxide synthase activity instead.

Acute and chronic effects of cigarette smoking on exhaled nitric oxide

Cigarette smoking is associated with an increased risk of respiratory tract infections, chronic airway disease, and cardiovascular diseases, all of which may be modulated by endogenous nitric oxide (NO). We have investigated whether cigarette smoking reduces the production of endogenous NO. We compared exhalations of 41 current cigarette smokers with normal lung function and 73 age-matched non-smoking controls. Peak exhaled NO levels were measured by a modified chemiluminescence analyzer. The effects of inhaling a single cigarette in smokers were also measured. In control subjects we also measured the effects of inhalation of NO itself and carbon monoxide, both constituents of tobacco smoke. Peak exhaled NO concentrations were significantly reduced in smokers (42 +/- 3.9 compared with 88 +/- 2.7 parts per billion in nonsmokers, p < 0.01), with a significant relation between the exhaled NO and cigarette consumption (r = 0.77, p < 0.001). Smoking a single cigarette also significantly (p < 0.02), but transiently, reduced exhaled NO. Inhalation of carbon monoxide and NO had no effect on exhaled NO in normal subjects. Cigarette smoking decreased exhaled NO, suggesting that it may inhibit the enzyme NO synthase. Since endogenous NO is important in defending the respiratory tract against infection, in counteracting bronchoconstriction and vasoconstriction, and in inhibiting platelet aggregation, this effect may contribute to the increased risks of chronic respiratory and cardiovascular disease in cigarette smokers.

Effects of nitric oxide synthase inhibition on myocardial capillary permeability and reactive hyperaemic response

OBJECTIVE

The aim was to examine the role of nitric oxide (NO) in the myocardial microcirculation.

METHODS

Open chest anaesthetised dogs received intracoronary infusion of NG-monomethyl-L-arginine (L-NMMA; 0.5 mg.kg-1 over 30 min). Myocardial microvascular extraction fraction of a small hydrophilic solute (technetium 99m labelled diethylenetriaminepenta-acetate [99mTc-DTPA]), and the regional myocardial plasma flow rate, were determined by the single injection, residue detection method, and the capillary permeability-surface area product was calculated. The tone in intramyocardial resistance vessels was assessed by the local 133Xe washout method during baseline conditions, in response to intracoronary acetylcholine, and during peak reactive hyperaemia after 10 s or 30 s of myocardial ischaemia, respectively.

RESULTS

In eight open chest dogs, L-NMMA attenuated the increase in myocardial plasma flow rate in response to intracoronary acetylcholine by 32(SEM 7)%, but failed to alter baseline myocardial plasma flow rate significantly, as determined by the local 133Xe washout method. L-NMMA did not influence myocardial microvascular permeability to 99mTc-DTPA. However, intracoronary L-NMMA decreased the peak reactive hyperaemic myocardial plasma flow rate after 10 s, but not 30 s, of coronary occlusion.

CONCLUSIONS

In open chest dogs, microvascular NO synthesis is not a major determinant of baseline myocardial plasma flow rate, and does not appear to influence myocardial microvascular permeability significantly. In this model, NO intervenes in the regulation of the peak reactive hyperaemic plasma flow rate following brief, but not more prolonged, periods of coronary occlusion.

L-NNA inhibits the histochemical NADPH-d reaction in rat spinal cord neurons

In nerve tissue the histochemical nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) reaction is considered a suitable marker for nitric oxide synthase (NOS) activity. We have previously shown that the NOS-specific inhibitor L-nitroarginine (L-NNA) can block NADPH-d staining in intermediolateral (IML) neurons of the rat spinal cord: such a reaction might serve as a control for the presence of a NOS-related catalytic activity, i.e., L-NNA-dependent NO synthesis in these neurons. However, L-NNA inhibition of neuronal NADPH-d is inconsistent and is therefore disputed by others. This prompted us to reinvestigate the reaction conditions to provide a standardized protocol for inhibition experiments. In IML neurons of formaldehyde-fixed spinal cord tissue, inhibition of NADPH-d reaction was tested by preincubation of frozen sections with the flavin-binder diphenylene iodonium chloride (DPI, 10 microM-1 mM) which blocked the NADPH-d reaction in a concentration-dependent way, suggesting an inverse relationship of inhibitor concentration and final reaction product generated. Preincubation with the NOS-specific inhibitor L-NNA in glycine-NaOH buffer (pH 8.5-9.5) but not L-nitroarginine methyl ester (L-NAME) revealed a concentration-dependent blocking effect on neuronal NADPH-d comparable to the effects seen with DPI, suggesting the existence of a L-NNA sensitive NADPH-d activity. Blocking with L-NNA (100 microM-10 mM) was prevented by excess L-arginine (10-100 mM), suggesting competitive binding sites. NADPH-d staining was not inhibited by 7-nitro indazole, another NOS inhibitor. Thus, in formaldehyde-fixed nervous tissue both DPI and L-NNA inhibit the NOS-associated catalytic NADPH-d activity, thereby preventing NADPH-dependent conversion of nitroblue tetrazolium to formazan.

Oxidized lipoproteins induce long-lasting inhibition of nitric oxide synthase from a murine endothelioma cell line (bEnd.4)

BACKGROUND

The vascular endothelium produces nitric oxide, which has vasodilatory properties. It has been postulated that some lipoproteins may increase arterial vascular tone by decreasing the availability of endothelium-derived nitric oxide. The mechanism underlying this effect, however, is still poorly understood.

METHODS

We investigated the effect of native and oxidized human low- and high-density lipoproteins on the nitric oxide synthetic activity of an endothelioma cell line (bEnd.4). Oxidized lipoproteins were obtained by incubation with CuSO4. The production of nitric oxide by the cells was monitored by quantifying the nitrite concentration in the medium using Greiss reagent.

RESULTS

The synthesis of nitric oxide by the bEnd.4 cell line was calcium-dependent and was abolished by a selective inhibitor of the constitutive nitric oxide synthase. Incubation with oxidized lipoproteins caused a time- and dose-dependent inhibition of nitric oxide synthetic activity. At a concentration of 100 micrograms/ml cholesterol, oxidized low- and high-density lipoproteins inhibited the production of nitric oxide by 27 and 51%, respectively, within 6h. The lipid fraction obtained from the native or the oxidized lipoproteins mimicked the effect of the intact lipoproteins.

CONCLUSION

These results support the involvement of oxidized lipoproteins in the modulation of endothelial functions relevant to the pathogenesis of cardiovascular disease.

Aminoguanidine attenuates the delayed circulatory failure and improves survival in rodent models of endotoxic shock

1. We have investigated the effects of aminoguanidine, a relatively selective inhibitor of the cytokine-inducible isoform of nitric oxide synthase (iNOS), on the delayed circulatory failure, vascular hyporeactivity to vasoconstrictor agents, and iNOS activity in a rat model of circulatory shock induced by bacterial endotoxin (E. coli lipopolysaccharide; LPS). In addition, we have evaluated the effect of aminoguanidine on the 24 h survival rate in a murine model of endotoxaemia. 2. Male Wistar rats were anaesthetized and instrumented for the measurement of mean arterial blood pressure (MAP) and heart rate (HR). Injection of LPS (10 mg kg-1, i.v.) resulted in a fall in MAP from 115 +/- 4 mmHg (time 0, control) to 79 +/- 9 mmHg at 180 min (P < 0.05, n = 10). The pressor effect of noradrenaline (NA, 1 microgram kg-1, i.v.) was also significantly reduced at 60, 120 and 180 min after LPS injection. In contrast, animals pretreated with aminoguanidine (15 mg kg-1, i.v., 20 min prior to LPS injection) maintained a significantly higher MAP (at 180 min, 102 +/- 3 mmHg, n = 10, P < 0.05) when compared to rats given only LPS (LPS-rats). Cumulative administration of aminoguanidine (15 mg kg-1 and 45 mg kg-1) given 180 min after LPS caused a dose-related increase in MAP and reversed the hypotension. Aminoguanidine also significantly alleviated the reduction of the pressor response to NA: indeed, at 180 min, the pressor response returned to normal in aminoguanidine pretreated LPS-rats. 3. Thoracic aortae obtained from rats at 180 min after LPS showed a significant reduction in the contractile responses elicited by NA (10-9- 10-6 M). Pretreatment with aminoguanidine (15 mg kg- 1, i.v.,at 20 min prior to LPS) significantly prevented this LPS-induced hyporeactivity to NA ex vivo.4. Endotoxaemia for 180 min resulted in a significant increase in iNOS activity in the lung from 0.6 +/- 0.2 pmol mg-1 min-1 (control, n = 4) to 4.8 +/- 0.3 pmol mg-1 min-1 (P<0.05, n = 6). In LPS-rats treated with aminoguanidine, iNOS activity in the lung was attenuated by 44+/- 5% (n = 6, P <0.05).Moreover, when added in vitro to lung homogenates obtained from LPS-rats, aminoguanidine and N omega-nitro-L-arginine methyl ester (L-NAME; 10-8 to 10-3 M) caused a concentration-dependent inhibition of iNOS activity (n = 3-6, IC50: 30 +/- 12 and 11 +/- 6pEM, respectively P>0.05). In contrast,aminoguanidine was a less potent inhibitor than L-NAME of the constitutive nitric oxide synthase in rat brain homogenates (n = 3-6, IC50 is 140 +/- 10 and 0.6 +/- 0.1 I1M, respectively, P<0.05). In addition, the inhibitory effect of aminoguanidine on iNOS activity showed a slower onset than that of L-NAME(maximal inhibition at 90 min and 30 min, respectively).5. Treatment of conscious Swiss albino (T/O) mice with a high dose of endotoxin (60 mg kg-1, i.p.)resulted in a survival rate of only 8% at 24 h (n = 12). However, therapeutic application of aminoguanidine (15 mg kg-1, i.p. at 2 h and 6 h after LPS) increased the 24 h survival rate to 75%(n = 8), whereas L-NAME (3 mg kg-1, i.p. at 2 h and 6 h after LPS) did not affect the survival rate(11%, n=9).6 Thus, aminoguanidine inhibits iNOS activity and attenuates the delayed circulatory failure caused by endotoxic shock in the rat and improves survival in a murine model of endotoxaemia. Aminoguanidine,or novel, more potent selective inhibitors of iNOS may be useful in the therapy of septic shock.

Assessment of renal dopaminergic system activity in the nitric oxide-deprived hypertensive rat model

1. The present paper reports changes in the urinary excretion of dopamine, 5-hydroxytryptamine and amine metabolites in nitric oxide deprived hypertensive rats during long-term administration of NG-nitro-L-arginine methyl ester (L-NAME). Aromatic L-amino acid decarboxylase (AAAD) activity in renal tissues and the ability of newly-formed dopamine to leave the cellular compartment where the synthesis of the amine has occurred were also determined. 2. Twenty four hours after exposure to L-NAME, both systolic (SBP) and diastolic (DBP) blood pressure were increased by 20 mmHg; heart rate was slightly decreased. During the next 13 days both SBP and DBP increased progressively reaching 170 +/- 3 and 116 +/- 3 mmHg, respectively. 3. Baseline urinary excretion of L-DOPA, dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT) and homovanillic acid (HVA) during the 4 day period of stabilization averaged 4.4 +/- 0.5, 13.8 +/- 0.3, 37.4 +/- 0.8, 180.0 +/- 2.7 and 206.1 +/- 6.7 nmol day-1, respectively. The urinary excretion of L-DOPA, dopamine and DOPAC, but not that of 3-MT and HVA, were increased from day 6-8 of L-NAME administration onwards (L-DOPA, up to 13.4 +/- 2.1; dopamine, up to 23.0 +/- 1.6; DOPAC, up to 62.8 +/- 3.7 nmol day-1). Baseline daily urinary excretion of 5-hydroxytryptamine and 5-hydroxyindolacetic acid (5-HIAA) averaged 73.5 +/- 1.1 and 241.7 +/- 5.4 nmol day-1, respectively. During the first week of L-NAME administration, the urinary excretion of both 5-hydroxytryptamine and 5-HIAA did not change significantly; however, as was found with dopamine and DOPAC, changes in the urinary excretion of 5-hydroxytryptamine were evident during the second week of L-NAME administration. 4. In experiments performed on homogenates of isolated renal tubules, the decarboxylation of L-DOPA to dopamine was dependent on the concentration of L-DOPA used (10 to 5000 microM) and saturable at 1000 microM. AAAD activity as determined in homogenates (Vmax, in nmol mg-1 protein h-1; Km in microM) was significantly (P < 0.01) higher in rats given L-NAME for 14 days (Vmax = 25 +/- 2; Km = 72 +/- 10) than in control rats (Vmax = 14 +/- 1; Km = 63 +/- 7), rats given L-NAME for 7 days (Vmax = 15 +/- 1; Km = 69 +/- 5) and rats given L-NAME plus L-arginine (Vmax = 13 +/- 1; Km = 60 +/- 3) for 14 days. 5. A considerable amount of the total dopamine formed from added L-DOPA in kidney slices escaped into the incubation medium. The application of the Michaelis-Menten equation to the net transport of newly-formed dopamine allowed the identification of a saturable (carrier-mediated transfer) and a non-saturable component (diffusion). No significant differences in the diffusional rate of transfer(0.14 +/- 0.02 micro mol-1) were observed between the four experimental groups. However, the saturable outward transfer of dopamine (Vmax, in micromol mg-1 protein h-1; Km in microM) was higher in control animals(Vmax= 2.3 +/- 0.2; Km = 568 +/- 67) than that in rats treated with L-NAME for 14 days (Vmax = 0.8 +/- 0.02;Km = 241 +/- 21), but similar to that observed in rats receiving L-NAME plus L-arginine (Vmax= 2.4+/- 0.2; Km= 618 +/- 61); the saturable dopamine outward rate of transfer in rats given L-NAME for 7days (Vmax = 3.9 +/- 0.2; Km = 1006 +/- 32) was higher than in controls.6. In conclusion, the present studies show that the hypertensive response resulting from the long-term administration of L-NAME is accompanied by an increased urinary excretion of dopamine and 5-hydroxytryptamine, which appears to follow an enhanced activity of renal AAAD. The observation that the increased AAAD activity can be reversed by the administration of L-arginine to L-NAME treated rats favours the view that the adaptational response which results in an enhanced AAAD activity probably involves a decrease in the generation of nitric oxide.

Antioxidative properties of alcoholic extracts from Fraxinus excelsior, Populus tremula and Solidago virgaurea

Aqueous-ethanolic extracts from Fraxinus excelsior, Populus tremula and Solidago virgaurea inhibit biochemical model reactions representing inflammatory situations to various extents. These model reactions include xanthine oxidase, diaphorase in the presence of the autoxidizable quinone juglone, lipoxygenase and photodynamic reactions driven by riboflavin or rose bengal. The tested extracts are the components of the phytomedicine Phytodolor N (abbreviated as PD) which possesses antipyretic, analgesic, antiinflammatory and antirheumatic activity. Since several reactive oxygen species produced by the mentioned model systems are also involved in inflammatory processes, the beneficial activities of the complete drug may at least in part be due to the reported antioxidative functions of the individual components.

Nitric oxide promotes arteriolar dilation during cortical spreading depression in rabbits

BACKGROUND AND PURPOSE

Pial arterioles transiently dilate during cortical spreading depression (CSD), although the mechanisms are unclear. We tested the hypothesis that increased production of nitric oxide (NO) promotes arteriolar dilation.

METHODS

Urethane-anesthetized rabbits were equipped with cranial windows, and the diameter (reported in micrometers) of a pial arteriole was determined via intravital microscopy. In each rabbit, a baseline CSD was elicited by microapplication of KCl onto the cortex, and resultant pial arteriolar dilation was measured. Either 100 mumol/L N omega-nitro-L-arginine methyl ester (L-NAME) or 50 mumol/L NG-nitro-L-arginine (L-NA), both competitive NO synthase inhibitors, was then applied to the brain surface. A CSD was elicited as before. The L-NAME and L-NA were then removed by artificial cerebrospinal fluid washes. An additional CSD was induced with KCl as before.

RESULTS

Control CSD in the L-NAME group dilated pial arterioles; baseline diameter, 66 +/- 7 mm, with CSD = 106 +/- 8 mm (59% increase). After topically applied L-NAME, CSD dilated pial arterioles less: baseline diameter, 61 +/- 7 mm, with CSD = 77 +/- 6 mm (26% increase), P < .05 compared with control CSD diameter. Topical L-NA had similar effects on CSD: control CSD dilated pial arterioles 51%; after topical L-NA, only 14% (P < .05). After removal of L-NAME or L-NA, CSD-induced pial arteriolar dilation was similar to original control values.

CONCLUSIONS

The reversible inhibition of CSD-induced pial arteriolar dilation by either L-NAME or L-NA suggests that NO contributes to arteriolar dilation observed with CSD.

Nerve-mediated nitric oxide production by opossum lower esophageal sphincter

Antagonists of nitric oxide synthesis inhibit nerve-induced hyperpolarization and relaxation of muscle from the opossum lower esophageal sphincter. These studies test the hypothesis that nitric oxide is released during stimulation of intrinsic esophageal nerves. The intrinsic nerves were stimulated with an electrical field (10-sec trains of 1-msec, 30-V pulses delivered at 10 Hz). Nitric oxide production was measured with a DASIBI model 2108 Chemiluminescence NO Analyzer. NG-Nitro-L-arginine, an inhibitor of NO synthase, antagonized nerve-induced relaxation the lower esophageal sphincter. Nerve stimulation increased NO production from 0.50 +/- 0.04 nmol/min/100 mg tissue to 0.87 +/- 0.07 nmol/min/100 mg tissue (P < 0.01). NG-nitro-L-arginine inhibited both basal (0.030 +/- 0.09 nmol/min/100 mg tissue, P < 0.05 vs baseline) and stimulated (0.38 +/- 0.10 nmol/min/100 mg tissue, P < 0.01 vs stimulated). These studies support the hypothesis that nerve stimulation releases nitric oxide from the lower esophageal sphincter.

Effects of a nitric oxide synthase inhibitor on vasopressin and atrial natriuretic hormone release, thermogenesis and cardiovascular functions in response to interleukin-1 beta in rats

To assess whether nitric oxide (NO) formed by IL-1 beta affects vasopressin (AVP) and atrial natriuretic hormone (ANH) release and the regulation of blood pressure and body temperature, intravenous infusion of either N omega-nitro-L-arginine methyl ester (L-NAME) alone (50 micrograms/kg.body weight.min for 135 min), human recombinant interleukin 1 beta (IL-1 beta) alone (750 ng/kg.body weight.min for 120 min), or L-NAME (50 micrograms/kg.body weight.min for 135 min) with IL-1 beta (750 ng/kg.body weight.min for 120 min), was performed following priming doses of L-NAME (2 mg/kg.body weight) and IL-1 beta (7.5 micrograms/kg.body weight) into conscious rats (n = 6 each). In the control group, saline alone was administered. Plasma AVP and ANH, mean arterial blood pressure (MABP), heart rate (HR) and rectal temperature (RT) were determined. In response to L-NAME, plasma AVP significantly increased, but plasma ANH did not change, despite increases in MABP and decreases in HR. In response to IL-1 beta, both plasma AVP and ANH increased with decreases in MABP and RT without any changes in HR. With L-NAME and IL-1 beta, both plasma AVP and ANH increased, and depressor response to IL-1 beta was partly attenuated by L-NAME, without any changes in RT. With saline alone, none of these parameters changed during the study. These results suggest that NO may directly affect the release of AVP and ANH and the regulation of body temperature and blood pressure, but NO formed by IL-1 beta may not have direct effects on the release of these hormones, and the regulation of blood pressure and temperature.

Effects of flavonoid compounds on the activity of NADPH diaphorase prepared from the mouse brain

The effects of flavonoids on NADPH diaphorase activity were studied in vitro, and we found that the enzyme activity was markedly inhibited by quercetin. This inhibitory action was shown to be accompanied by an increase in the apparent Km value of the enzyme for the cofactor NADPH, with a decrease in the Vmax, and an increase in the apparent Km for the substrate nitro blue tetrazolium, without any significant change in the Vmax. These results indicate that quercetin may directly inhibit NADPH diaphorase, thus suggesting the possibility that this compound may be able to inhibit the production of nitric oxide in the brain.

Nitric oxide synthase inhibitors improve skin flap survival in the rat

The ability of nitric oxide (NO) synthase inhibitors to reduce ischemia-induced skin flap necrosis was assessed using a modified McFarlane flap in the rat. Flap survival was significantly improved in L-NIO treated (86 +/- 2%), L-NAME-treated (84 +/- 2%), and aminoguanidine-treated (76 +/- 2%) animals compared to the saline-treated group (54 +/- 2%), P < 0.005. Inhibition of NO synthase significantly decreased the hyperemia and edema within the flaps at 24 hours post-elevation. These findings suggest that endogenous NO production contributes to ischemic necrosis and that inhibition of NO synthase may prove useful in extending survival of tissues subjected to ischemia.

Nitric oxide synthase inhibitor, nitro-iminoethyl-L-ornithine, reduces ischemia-reperfusion injury in rabbit skeletal muscle

Nitric oxide (NO), originally identified as the mediator of endothelial-dependent relaxation of vascular smooth muscle, is now known to also have cytotoxic effects under certain conditions. Thus, we have investigated the effects of inhibition of NO synthesis on ischemia/reperfusion injury in the rabbit rectus femoris muscle. Three and a half hours of ischemia and 24 hours of reperfusion resulted in a 56% loss of viability. In muscles receiving an infusion of the nitric oxide synthase inhibitor, L-NIO (30 microM), the loss of viability was reduced to 15%. Post-ischemic blood flow was increased in muscles receiving a saline infusion, whereas there was a marked decrease in blood flow for at least the first 60 minutes of reperfusion in muscles treated with L-NIO (30 microM). The increase in myeloperoxidase levels (indicative of neutrophil accumulation) following 24 hours of reperfusion was attenuated with L-NIO infusion by approximately 50% and the reperfusion-induced edema was also attenuated in L-NIO treated muscle. These findings suggest that endogenous NO production during ischemia/reperfusion injury may be deleterious to muscle survival.

An inducible NADP(+)-dependent D-phenylserine dehydrogenase from Pseudomonas syringae NK-15: purification and biochemical characterization

An inducible NADP(+)-dependent D-phenylserine dehydrogenase [EC 1.1.1.-], which catalyzes the oxidation of the hydroxyl group of D-threo-beta-phenylserine, was purified to homogeneity from a crude extract of Pseudomonas syringae NK-15 isolated from soil. The enzyme consisted of two subunits identical in molecular weight (about 31,000). In addition to D-threo-beta-phenylserine, it utilized D-threo-beta-thienylserine, D-threo-beta-hydroxynorvaline, and D-threonine as substrates but was inert towards other isomers of beta-phenylserine and threonine. It showed maximal activity at pH 10.4 for the oxidation of D-threo-beta-phenylserine, and it required NADP+ as a natural coenzyme. NAD+ showed a slight coenzyme activity. The enzyme was inhibited by p-chloromercuribenzoate, HgCl2, and monoiodoacetate but not by the organic acids such as tartronate. The Michaelis constants for D-threo-beta-phenylserine and NADP+ were 0.44 mM and 29 microM, respectively. The N-terminal 27 amino acids sequence was determined. It suggested that the NADP(+)-binding site was located in the N-terminal region of the enzyme.