A fluorescence-based method for measuring nitric oxide in extracts of skeletal muscle

Effect of endogenous hydrogen sulfide on the transwall gradient of the mouse colon circular smooth muscle

A transwall gradient in resting membrane potential (RMP) exists across the circular muscle layer in the mouse colon. This gradient is dependent on endogenous generation of CO. H2S is also generated in muscle layers of the mouse colon. The effect of endogenously generated H2S on the transwall gradient is not known. The aim was to investigate the role of endogenous H2S. Our results showed that the CSE inhibitor dl-propargylglycine (PAG, 500 μm) had no effect on the transwall gradient. However, in preparations pretreated with the nitric oxide synthase inhibitor N-nitro-l-arginine (l-NNA, 200 μm) and in nNOS-knockout (KO) mouse preparations, PAG shifted the transwall gradient in the depolarizing direction. In CSE-KO-nNOS-KO mice, the gradient was shifted in the depolarizing direction. Endogenous generation of NO was significantly higher in muscle preparations of CSE-KO mice compared to wild-type (WT) mice. The amplitude of NO-mediated slow inhibitory junction potentials (S-IJPs) evoked by electric field stimulation was significantly higher in CSE-KO mouse preparations compared to the amplitude of S-IJPs in wild-type mouse preparations. CSE was present in all submucosal ganglion neurons and in almost all myenteric ganglion neurons. Eleven per cent of CSE positive neurons in the submucosal plexus and 50% of CSE positive neurons in the myenteric plexus also contained nNOS. Our results suggest that endogenously generated H2S acts as a stealth hyperpolarizing factor on smooth muscle cells to maintain the CO-dependent transwall gradient and inhibits NO production from nNOS.

Passive stretch reduces calpain activity through nitric oxide pathway in unloaded soleus muscles

Unloading in spaceflight or long-term bed rest induces to pronounced atrophy of anti-gravity skeletal muscles. Passive stretch partially resists unloading-induced atrophy of skeletal muscle, but the mechanism remains elusive. The aims of this study were to investigate the hypotheses that stretch tension might increase protein level of neuronal nitric oxide synthase (nNOS) in unloaded skeletal muscle, and then nNOS-derived NO alleviated atrophy of skeletal muscle by inhibiting calpain activity. The tail-suspended rats were used to unload rat hindlimbs for 2 weeks, at the same time, left soleus muscle was stretched by applying a plaster cast to fix the ankle at 35° dorsiflexion. Stretch partially resisted atrophy and inhibited the decreased protein level and activity of nNOS in unloaded soleus muscles. Unloading increased frequency of calcium sparks and elevated intracellular resting and caffeine-induced Ca(2+) concentration ([Ca(2+)]i) in unloaded soleus muscle fibers. Stretch reduced frequency of calcium sparks and restored intracellular resting and caffeine-induced Ca(2+) concentration to control levels in unloaded soleus muscle fibers. The increased protein level and activity of calpain as well as the higher degradation of desmin induced by unloading were inhibited by stretch in soleus muscles. In conclusion, these results suggest that stretch can preserve the stability of sarcoplasmic reticulum Ca(2+) release channels which prevents the elevated [Ca(2+)]i by means of keeping nNOS activity, and then the enhanced protein level and activity of calpain return to control levels in unloaded soleus muscles. Therefore, stretch can resist in part atrophy of unloaded soleus muscles.

Effects of 4',7-dimethoxyflavanone on cell cycle arrest and apoptosis in human breast cancer MCF-7 cells

The present study was designed to investigate the anticancer activity of 4,7-dimethoxyflavanone in vitro. When human breast cancer MCF-7 cells were treated with 4',7-dimethoxyflavanone at various concentrations (1-200 μM) for 24 h, antiproliferative effects were first observed at 1 μM and the IC(50) was 115.62 μM. Conversely, 4',7-dimethoxyflavanone was not cytotoxic (measured as lactate dehydrogenase release in CHO-K1 cells) under the same conditions. MCF-7 cells exposed to the 4',7-dimethoxyflavanone at the IC(50) concentration showed cell cycle arrest and apoptosis. Compared to the respective control level, exposure to 4',7-dimethoxyflavanone resulted in a remarkable increase of small DNA fragments at the sub-G1 phase and an increase in the G2/M phase cell population. Moreover, when 4',7-dimethoxyflavanone treatment caused G2/M phase arrest, an increase in CDK1 together with an increase in cyclin B was observed. Based on these results, 4',7-dimethoxyflavanone may be a useful anticancer agent.

Suppressive effects on the biosynthesis of inflammatory mediators by Aralia elata extract fractions in macrophage cells

The aim of this study is to elucidate the anti-inflammatory effects of Aralia elata extract fractions (AEEFs). A. elata-ethyl acetate fraction (AEEF) had the strongest antioxidant activity. A. elata-chloroform fraction (AECF) and A. elata-butanol fraction (AEBF) inhibited potently LPS-induced nitrite production from RAW 264.7 macrophage cells. The inhibition of nitric oxide (NO) production by AEEFs was partially due to chemical scavenge of NO and the suppression of inducible NOS (iNOS) transcription level in LPS-induced macrophage cells. In addition, AEEFs inhibited significantly the biosynthesis of Prostaglandin E(2) (PGE(2)), and cyclooxygenase-2, which regulates the synthesis of PGE(2), was attenuated partially by the treatment of AEEFs in LPS-induced macrophage cells. Also, A. elata-methanolic extract (AEME) suppressed remarkably IL-1β and IL-6 level to the basal (more than 99% inhibition) in concentration-dependant manners. Its anti-inflammatory actions might be related with inhibition of NF-κB activation in LPS-stimulated macrophage cells. It is concluded that AEEFs may be useful as a functional food material and an alternative medicine for the relief and retardation of immunological inflammatory responses.

A novel method of measuring nitric-oxide-dependent fluorescence using 4,5-diaminofluorescein (DAF-2) in the isolated Langendorff-perfused rabbit heart

4,5-Diaminofluorescein (DAF-2) has been used to measure nitric oxide (NO) activity from a variety of preparations. The aim of this study was to develop a method to assess changes in NO fluorescence using DAF-2 in isolated rabbit hearts (2.0-2.5 kg, n = 8). Hearts were perfused in constant flow Langendorff mode and instrumented to record aortic perfusion pressure, left ventricular pressure and left ventricular epicardial fluorescence using a bifurcated light guide at excitation wavelengths of 470 +/- 10, 480 +/- 10, 490 +/- 10 and 500 +/- 10 nm collected at 535 nm. DAF-2 DA was loaded using a single bolus 150-microl (1 micromol) injection. Changes in NO-dependent fluorescence were determined using the NO donor sodium nitroprusside (SNP: 100 microM), NO-dependent vasodilator bradykinin (BK: 100 microM) and non-specific NO synthase inhibitor NG-nitro-L-arginine (LNA: 200 microM) before and after loading hearts with DAF-2 DA. Before loading, these agents did not alter epicardial fluorescence. After loading, SNP, BK and LNA produced a consistent change in each excitation wavelength. Together, this suggests that change in fluorescence represents changes in the level of NO. SNP and BK increased whilst LNA significantly decreased left ventricular epicardial NO-dependent fluorescence. At the excitation wavelength of 490 nm, SNP and BK increased fluorescence by 104.7 +/- 18.7 mV (1.1 +/- 0.2%) and 150.7 +/- 26.1 mV (1.5 +/- 0.3%) respectively, whilst LNA significantly decreased fluorescence by 90.3 +/- 17.0 mV (-0.9 +/- 0.2%). Changing the rate of aortic perfusion did not alter fluorescence suggesting that changes in aortic perfusion pressure per se do not contribute to the changes in DAF-2 fluorescence seen with SNP, BK or LNA. Our data suggest that DAF-2 DA is a useful fluorescence indicator for measuring NO activity in isolated hearts.

FK506 binding protein 12/12.6 depletion increases endothelial nitric oxide synthase threonine 495 phosphorylation and blood pressure

Chronic treatment with the immunosuppressive drug rapamycin leads to hypertension; however, the mechanisms are unknown. Rapamycin binds FK506 binding protein 12 and its related isoform 12.6 (FKBP12/12.6) and displaces them from intracellular Ca2+ release channels (ryanodine receptors) eliciting a Ca2+ leak from the endoplasmic/sarcoplasmic reticulum. We tested whether this Ca2+ leak promotes conventional protein kinase C-mediated endothelial NO synthase phosphorylation at Thr495, which reduces production of the vasodilator NO. Rapamycin treatment of control mice for 7 days, as well as genetic deletion of FKBP12.6, increased systolic arterial pressure significantly compared with controls. Untreated aortas from FKBP12.6-/- mice and in vitro rapamycin-treated control aortas had similarly decreased endothelium-dependent relaxation responses and NO production and increased endothelial NO synthase Thr495 phosphorylation and protein kinase C activity. Inhibition of either conventional protein kinase C or ryanodine receptor restored endothelial NO synthase Thr495 phosphorylation and endothelial function to control levels. Rapamycin induced a small increase in basal intracellular Ca2+ levels in isolated endothelial cells, and rapamycin or FKBP12.6 gene deletion decreased acetylcholine-induced intracellular Ca2+ release, all of which were reversed by ryanodine. These data demonstrate that displacement of FKBP12/12.6 from ryanodine receptors induces an endothelial intracellular Ca2+ leak and increases conventional protein kinase C-mediated endothelial NO synthase Thr495 phosphorylation leading to decreased NO production and endothelial dysfunction. This molecular mechanism may, in part, explain rapamycin-induced hypertension.

Inactivation of oxidized and S-nitrosylated mitochondrial proteins in alcoholic fatty liver of rats

Increased oxidative/nitrosative stress is a major contributing factor to alcohol-mediated mitochondrial dysfunction. However, which mitochondrial proteins are oxidatively modified under alcohol-induced oxidative/nitrosative stress is poorly understood. The aim of this study was to systematically investigate oxidized and/or S-nitrosylated mitochondrial proteins and to use a biotin-N-maleimide probe to evaluate their inactivation in alcoholic fatty livers of rats. Binge or chronic alcohol exposure significantly elevated nitric oxide, inducible nitric oxide synthase, and ethanol-inducible CYP2E1. The biotin-N-maleimide-labeled oxidized and/or S-nitrosylated mitochondrial proteins from pair-fed controls or alcohol-fed rat livers were subsequently purified with streptavidin-agarose. The overall patterns of oxidized and/or S-nitrosylated proteins resolved by 2-dimensional polyacrylamide gel electrophoresis were very similar in the chronic and binge alcohol treatment groups. Seventy-nine proteins that displayed differential spot intensities from those of control rats were identified by mass spectrometry. These include mitochondrial aldehyde dehydrogenase 2 (ALDH2), ATP synthase, acyl-CoA dehydrogenase, 3-ketoacyl-CoA thiolase, and many proteins involved in chaperone activity, mitochondrial electron transfer, and ion transport. The activity of 3-ketoacyl-CoA thiolase involved in mitochondrial beta-oxidation of fatty acids was significantly inhibited in alcohol-exposed rat livers, consistent with hepatic fat accumulation, as determined by biochemical and histological analyses. Measurement of activity and immunoblot results showed that ALDH2 and ATP synthase were also inhibited through oxidative modification of their cysteine or tyrosine residues in alcoholic fatty livers of rats. In conclusion, our results help to explain the underlying mechanism for mitochondrial dysfunction and increased susceptibility to alcohol-mediated liver damage.

Performance of diamino fluorophores for the localization of sources and targets of nitric oxide

An emergent approach to the detection of nitric oxide (NO) in tissues relies on the use of fluorescence probes that are activated by products of NO autoxidation. Here we explore the performance of the widely used NO probe 4,5-diaminofluorescein diacetate (DAF-2 DA) for the localization of sources of NO in rat aortic tissue, either from endogenous NO synthesis or from chemically or photolytically released NO from targets of nitrosation/nitrosylation. Of importance toward understanding the performance of this probe in tissues is the finding that, with incubation conditions commonly used in the literature (10 microM DAF-2 DA), intracellular DAF-2 accumulates to concentrations that approach the millimolar range. Whereas such high probe concentrations do not interfere with NO release or signaling, they help to clarify why DAF-2 nitrosation is possible in the presence of endogenous nitrosation scavengers (e.g., ascorbate and glutathione). The gain attained with such elevated concentrations is, however, mitigated by associated high levels of background autofluorescence from the probe. This, together with tissue autofluorescence, limits the sensitivity of the probe to low-micromolar levels of accumulated DAF-2 triazole (DAF-2 T), the activated form of the probe, which is higher than the concentrations of most endogenous nitrosation/nitrosylation products found in tissues. We further show that the compartmentalization of DAF-2 around elastic fibers further limits its potential to characterize the site of NO production at the subcellular level. Moreover, we find that reaction of DAF-2 with HgCl(2) and other commonly employed reagents is associated with spectral changes that may be misinterpreted as NO signals. Finally, UV illumination can lead to high levels of nitrosating species that interfere with NO detection from enzymatic sources. These findings indicate that while DAF-2 may still represent an important tool for the localization of NO synthesis, provided important pitfalls and limitations are taken into consideration, it is not suited for the detection of basally generated nitrosation/nitrosylation products.

Direct evidence that induced nitric oxide production in hepatocytes prevents liver damage during lipopolysaccharide tolerance in rats

BACKGROUND

The role of nitric oxide (NO) in lipopolysaccharide (LPS) tolerance in the liver has been investigated in a number of previous studies, but it is still not clear whether NO is cytotoxic or cytoprotective. The aims of this study were to investigate whether low-dose LPS (LLPS)-induced hepatic production of NO is beneficial and to clarify the origins of cytoprotective NO-producing cells in the liver during LPS tolerance.

MATERIALS AND METHODS

Male Wistar rats received saline or LLPS intraperitoneally (i.p.; 0.01-1000 microg/kg) followed by a high dose of LPS (HLPS, 5 mg/kg) at various time intervals (4-16 h). NG-nitro-L-arginine methyl ester (L-NAME) was used to investigate the effects of inhibition of NOS. 4,5-Diaminofluorescein (DAF-2) was used to identify NO-producing cells in isolated liver cells in vitro. At various time points (4-16 h) after saline or LLPS (1 microg/kg, i.p.) injection, hepatocytes and Kupffer cells were isolated, incubated in 7 microm DAF-2 diacetate, and perfused with Krebs solution. Illumination at 495 nm revealed DAF-fluorescence (515 nm) in isolated cells under confocal laser fluorescence microscopy. The NO production in hepatocytes and Kupffer cells was assessed by the number of labeled cells per 1000 cells or per 100 cells, respectively.

RESULTS

Pretreatment with LLPS (0.1-100 microg/kg) resulted in a significant reduction (maximal at 8 h) of the HLPS-induced liver damage. L-NAME abolished the LLPS-induced protection. The NO production in hepatocytes was significantly increased and reached a maximum of 84% of all cells 8 h after LLPS administration. By contrast, the NO production in Kupffer cells remained constant at 95%, even following preinjection of LLPS.

CONCLUSION

LLPS-induced NO in hepatocytes, but not in Kupffer cells, exhibits cytoprotective effects on HLPS-induced liver damage, suggesting that NO has a beneficial role in the induction of the early phase of LPS tolerance.

Impaired nitric oxide production of the myenteric plexus in colitis detected by a new bioimaging system

Direct measurement of the release of nitric oxide (NO) from the myenteric plexus has been extremely difficult to date, due to the lack of suitable methodologies. We have developed a new bioimaging system to visualize the nitrergic neurons of the myenteric plexus and investigated whether NO production is impaired in dextran sulfate sodium (DSS)-induced colitis. Longitudinal muscle layers with the myenteric plexus intact were obtained from the rat colon and were incubated with 4,5-diaminofluorescein-2-diacetate (DAF-2DA) (7 microm) for 30 min. Illumination at 450-490 nm revealed the fluorescence in the myenteric plexus. Confocal laser microscopy and three-dimensional reconstruction techniques were used to quantify the changes in the amount of NO production by the myenteric plexus. Fluorescent double-labeled immunostaining for nNOS was performed to confirm the colocalization of nNOS in 4,5-diaminofluorescein (DAF-2)-positive cells. DAF-2 fluorescence was abolished by pretreatment with N(G)-nitro-l-arginine methyl ester (l-NAME; a nonselective NOS inhibitor), 1-(2-trifluoromethylphenyl) imidazole (TRIM; a selective neuronal NOS inhibitor), and omega-conotoxin GVIA (an N-type Ca(2+) channel blocker), but not by nifedipine (an l-type Ca(2+) channel blocker). Fluorescent double-labeled immunostaining showed that DAF-2-positive cells colocalized with nNOS-positive cells. Oral administration of 5% DSS for 7 days induced distal colitis and the number of DAF-2-positive neurons were significantly reduced to 55 +/- 17% of control. DAF-2 offers a sensitive indicator for visualizing production of NO with high spatial resolution. This new system may contribute to the study of the pathophysiological role of the nitrergic pathway in the gastrointestinal tract.

4,5-diaminofluoroscein imaging of nitric oxide synthesis in crayfish terminal ganglia

We have analyzed the synthesis of nitric oxide in the terminal abdominal ganglion of the crayfish using the fluorescent probe 4,5-Diaminofluoroscein diacetate, DAF-2 DA. Following DAF-2 loading, ganglia showed cell-specific patterns of fluorescence in which the occurrence of strongly fluorescent cell bodies was highest in specific anterior, central, and posterior regions. We found that preincubation with the nitric oxide synthase (NOS) inhibitor L-NAME prevented much of the initial development of DAF-2 fluorescence, whereas the inactive isomer D-NAME had no effect. Washout of preincubated L-NAME caused increased cell-specific fluorescence due to endogenous NOS activity. Application of the NOS substrate L-arginine also resulted in an increase of DAF-2 fluorescence in a cell-specific manner. We bath applied the NO donor SNAP to increase exogenous NO levels which resulted in DAF-2 fluorescence increases in most cells. We therefore presume that the cell-specific pattern of DAF-2 fluorescence indicates the distribution of neurones actively synthesizing NO. The similarity between the DAF-2 staining pattern and previously published studies of NOS activity are discussed.