EPR quantification of vascular nitric oxide production in genetically modified mouse models

Combined Raman- and AFM-based detection of biochemical and nanomechanical features of endothelial dysfunction in aorta isolated from ApoE/LDLR-/- mice

Endothelial dysfunction is recognized as a critical condition in the development of cardiovascular disorders. This multifactorial process involves changes in the biochemical and mechanical properties of endothelial cells leading to disturbed release of vasoprotective mediators. Hypercholesterolemia and increased stiffness of the endothelial cortex are independently shown to result in reduced release of nitric oxide and thus endothelial dysfunction. However, direct evidence linking these parameters to each other is missing. Here, a novel method combining Raman spectroscopy for biochemical analysis and Atomic Force Microscopy (AFM) for analyzing the endothelial nanomechanics was established. Using this dual approach, the same areas of native ex vivo aortas were investigated, either derived from mice with endothelial dysfunction (ApoE/LDLR-/-) or wild type mice. In particular an increased intracellular lipid content and elevated cortical stiffness/elasticity were shown in ApoE/LDLR-/- aortas, demonstrating a direct link between endothelial dysfunction, the biochemical composition and the nanomechanical properties of endothelial cells.

M2 Macrophage Polarization Mediates Anti-inflammatory Effects of Endothelial Nitric Oxide Signaling

Endothelial nitric oxide (NO) signaling plays a physiological role in limiting obesity-associated insulin resistance and inflammation. This study was undertaken to investigate whether this NO effect involves polarization of macrophages toward an anti-inflammatory M2 phenotype. Mice with transgenic endothelial NO synthase overexpression were protected against high-fat diet (HFD)-induced hepatic inflammation and insulin resistance, and this effect was associated with reduced proinflammatory M1 and increased anti-inflammatory M2 activation of Kupffer cells. In cell culture studies, exposure of macrophages to endothelial NO similarly reduced inflammatory (M1) and increased anti-inflammatory (M2) gene expression. Similar effects were induced by macrophage overexpression of vasodilator-stimulated phosphoprotein (VASP), a key downstream mediator of intracellular NO signaling. Conversely, VASP deficiency induced proinflammatory M1 macrophage activation, and the transplantation of bone marrow from VASP-deficient donor mice into normal recipients caused hepatic inflammation and insulin resistance resembling that induced in normal mice by consumption of an HFD. These data suggest that proinflammatory macrophage M1 activation and macrophage-mediated inflammation are tonically inhibited by NO → VASP signal transduction, and that reduced NO → VASP signaling is involved in the effect of HFD feeding to induce M1 activation of Kupffer cells and associated hepatic inflammation. Our data implicate endothelial NO → VASP signaling as a physiological determinant of macrophage polarization and show that signaling via this pathway is required to prevent hepatic inflammation and insulin resistance.

Regulation of iNOS function and cellular redox state by macrophage Gch1 reveals specific requirements for tetrahydrobiopterin in NRF2 activation

Inducible nitric oxide synthase (iNOS) is a key enzyme in the macrophage inflammatory response, which is the source of nitric oxide (NO) that is potently induced in response to proinflammatory stimuli. However, the specific role of NO production, as distinct from iNOS induction, in macrophage inflammatory responses remains unproven. We have generated a novel mouse model with conditional deletion of Gch1, encoding GTP cyclohydrolase 1 (GTPCH), an essential enzyme in the biosynthesis of tetrahydrobiopterin (BH4) that is a required cofactor for iNOS NO production. Mice with a floxed Gch1 allele (Gch1(fl/fl)) were crossed with Tie2cre transgenic mice, causing Gch1 deletion in leukocytes (Gch1(fl/fl)Tie2cre). Macrophages from Gch1(fl/fl)Tie2cre mice lacked GTPCH protein and de novo biopterin biosynthesis. When activated with LPS and IFNγ, macrophages from Gch1(fl/fl)Tie2cre mice induced iNOS protein in a manner indistinguishable from wild-type controls, but produced no detectable NO, as judged by L-citrulline production, EPR spin trapping of NO, and by nitrite accumulation. Incubation of Gch1(fl/fl)Tie2cre macrophages with dihydroethidium revealed significantly increased production of superoxide in the presence of iNOS expression, and an iNOS-independent, BH4-dependent increase in other ROS species. Normal BH4 levels, nitric oxide production, and cellular redox state were restored by sepiapterin, a precursor of BH4 production by the salvage pathway, demonstrating that the effects of BH4 deficiency were reversible. Gch1(fl/fl)Tie2cre macrophages showed only minor alterations in cytokine production and normal cell migration, and minimal changes in basal gene expression. However, gene expression analysis after iNOS induction identified 78 genes that were altered between wild-type and Gch1(fl/fl)Tie2cre macrophages. Pathway analysis identified decreased NRF2 activation, with reduced induction of archetypal NRF2 genes (gclm, prdx1, gsta3, nqo1, and catalase) in BH4-deficient Gch1(fl/fl)Tie2cre macrophages. These findings identify BH4-dependent iNOS regulation and NO generation as specific requirements for NRF2-dependent responses in macrophage inflammatory activation.

Measurement of NO in biological samples

Although the physiological regulatory function of the gasotransmitter NO (a diatomic free radical) was discovered decades ago, NO is still in the frontline research in biomedicine. NO has been implicated in a variety of physiological and pathological processes; therefore, pharmacological modulation of NO levels in various tissues may have significant therapeutic value. NO is generated by NOS in most of cell types and by non-enzymatic reactions. Measurement of NO is technically difficult due to its rapid chemical reactions with a wide range of molecules, such as, for example, free radicals, metals, thiols, etc. Therefore, there are still several contradictory findings on the role of NO in different biological processes. In this review, we briefly discuss the major techniques suitable for measurement of NO (electron paramagnetic resonance, electrochemistry, fluorometry) and its derivatives in biological samples (nitrite/nitrate, NOS, cGMP, nitrosothiols) and discuss the advantages and disadvantages of each method. We conclude that to obtain a meaningful insight into the role of NO and NO modulator compounds in physiological or pathological processes, concomitant assessment of NO synthesis, NO content, as well as molecular targets and reaction products of NO is recommended.

Glutathione (GSH) and the GSH synthesis gene Gclm modulate plasma redox and vascular responses to acute diesel exhaust inhalation in mice

CONTEXT

Inhalation of fine particulate matter (PM₂.₅) is associated with acute pulmonary inflammation and impairments in cardiovascular function. In many regions, PM₂.₅ is largely derived from diesel exhaust (DE), and these pathophysiological effects may be due in part to oxidative stress resulting from DE inhalation. The antioxidant glutathione (GSH) is important in limiting oxidative stress-induced vascular dysfunction. The rate-limiting enzyme in GSH synthesis is glutamate cysteine ligase and polymorphisms in its catalytic and modifier subunits (GCLC and GCLM) have been shown to influence vascular function and risk of myocardial infarction in humans.

OBJECTIVE

We hypothesized that compromised de novo synthesis of GSH in Gclm⁻/⁺ mice would result in increased sensitivity to DE-induced lung inflammation and vascular effects.

MATERIALS AND METHODS

WT and Gclm⁻/⁺ mice were exposed to DE via inhalation (300 μg/m³) for 6 h. Neutrophil influx into the lungs, plasma GSH redox potential, vascular reactivity of aortic rings and aortic nitric oxide (NO•) were measured.

RESULTS

DE inhalation resulted in mild bronchoalveolar neutrophil influx in both genotypes. DE-induced effects on plasma GSH oxidation and acetylcholine (ACh)-relaxation of aortic rings were only observed in Gclm⁻/⁺ mice. Contrary to our hypothesis, DE exposure enhanced ACh-induced relaxation of aortic rings in Gclm⁻/⁺ mice.

DISCUSSION AND CONCLUSION

THESE data support the hypothesis that genetic determinants of antioxidant capacity influence the biological effects of acute inhalation of DE. However, the acute effects of DE on the vasculature may be dependent on the location and types of vessels involved. Polymorphisms in GSH synthesis genes are common in humans and further investigations into these potential gene-environment interactions are warranted.

Glutathione (GSH) and the GSH synthesis gene Gclm modulate vascular reactivity in mice

Oxidative stress has been implicated in the development of vascular disease and in the promotion of endothelial dysfunction via the reduction in bioavailable nitric oxide (NO()). Glutathione (GSH) is a tripeptide thiol antioxidant that is utilized by glutathione peroxidase (GPx) to scavenge reactive oxygen species such as hydrogen peroxide and phospholipid hydroperoxides. Relatively frequent single-nucleotide polymorphisms (SNPs) within the 5' promoters of the GSH synthesis genes GCLC and GCLM are associated with impaired vasomotor function, as measured by decreased acetylcholine-stimulated coronary artery dilation, and with increased risk of myocardial infarction. Although the influence of genetic knockdown of GPx on vascular function has been investigated in mice, no work to date has been published on the role of genetic knockdown of GSH synthesis genes on vascular reactivity. We therefore investigated the effects of targeted disruption of Gclm in mice and the subsequent depletion of GSH on vascular reactivity, NO() production, aortic nitrotyrosine protein modification, and whole-genome transcriptional responses as measured by DNA microarray. Gclm(-/+) and Gclm(-/-) mice had 72 and 12%, respectively, of wild-type (WT) aortic GSH content. Gclm(-/+) mice had a significant impairment in acetylcholine (ACh)-induced relaxation in aortic rings as well as increased aortic nitrotyrosine protein modification. Surprisingly, Gclm(-/-) aortas showed enhanced relaxation compared to Gclm(-/+) aortas, as well as increased NO() production. Although aortic rings from Gclm(-/-) mice had enhanced ACh relaxation, they had a significantly increased sensitivity to phenylephrine (PE)-induced contraction. Alternatively, the PE response of Gclm(-/+) aortas was nearly identical to that of their WT littermates. To examine the role of NO() or other potential endothelium-derived factors in differentially regulating vasomotor activity, we incubated aortic rings with the NO() synthase inhibitor L-NAME or physically removed the endothelium before PE treatment. L-NAME treatment and endothelium removal enhanced PE-induced contraction in WT and Gclm(-/+) mice, but this effect was severely diminished in Gclm(-/-) mice, indicating a potentially unique role for GSH in mediating vessel contraction. Whole-genome assessment of aortic mRNA in Gclm(-/-) and WT mice revealed altered expression of genes within the canonical Ca(2+) signaling pathway, which may have a role in mediating these observed functional effects. These findings provide additional evidence that the de novo synthesis of GSH can influence vascular reactivity and provide insights regarding possible mechanisms by which SNPs within GCLM and GCLC influence the risk of developing vascular diseases in humans.

Endothelial NO/cGMP/VASP signaling attenuates Kupffer cell activation and hepatic insulin resistance induced by high-fat feeding

OBJECTIVE

Proinflammatory activation of Kupffer cells is implicated in the effect of high-fat feeding to cause liver insulin resistance. We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.

RESEARCH DESIGN AND METHODS

Effect of NO/cGMP signaling on hepatic inflammation and on isolated Kupffer cells was examined in C57BL/6 mice, eNos(-/-) mice, and Vasp(-/-) mice fed a low-fat or high-fat diet.

RESULTS

We show that high-fat feeding induces proinflammatory activation of Kupffer cells in wild-type mice coincident with reduced liver endothelial nitric oxide synthase activity and NO content while, conversely, enhancement of signaling downstream of endogenous NO by phosphodiesterase-5 inhibition protects against high fat-induced inflammation in Kupffer cells. Furthermore, proinflammatory activation of Kupffer cells is evident in eNos(-/-) mice even on a low-fat diet. Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.

CONCLUSIONS

These results collectively imply a physiological role for endothelial NO to limit obesity-associated inflammation and insulin resistance in hepatocytes and support a model in which Kupffer cell activation during high-fat feeding is dependent on reduced NO signaling. Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

Determination of in vivo nitric oxide levels in animal tissues using a novel spin trapping technology

It has been established that microdialysis ensured by the passage of aqueous solutions of Fe(3+) complexes with N-methyl-D: -glucamine dithiocarbamate (MGDMGD ) through fine dialysis fibers permeable for compounds with molecular weights below 5 kDa. These fibers can be implanted into heart, liver, and kidney tissues, enabling effective binding of Fe(3+)-MGD complexes to nitric oxide generated in interstitial fluids of narcotized rats in vivo. Subsequent treatment of dialyzate samples (60 μL) with sodium dithionite favors conversion of newly formed diamagnetic NO-Fe(3+)-MGD complexes into electron paramagnetic resonance-detectable NO-Fe(2+)-MGD complexes. The basal levels of NO determined from the concentrations of the complexes in the respective tissues are similar (1 μМ). The microdialysis data suggest that treatment of rats with a water-soluble analogue of nitroglycerine or a dinitrosyl iron complex with thiosulfate induces a long-lasting (>1 h) increase in the steady-state level of NO in animal tissues. This novel technology can be used for comparative analyses of production rates of NO and reactive oxygen species when using iron-dithiocarbamate complexes and spin traps for reactive oxygen species, respectively.

Real-time measurement of murine hippocampus NO levels in response to cerebral ischemia/reperfusion

Nitric oxide has been implicated as a mediator of synaptic transmission and a pathological factor in stroke/reperfusion. The purpose of this study was to detect the change of nitric oxide concentration in rat hippocampus during global cerebral ischemia and reperfusion in vivo and to reveal effects of different nitric oxide synthases. In the present study, the real-time record of nitric oxide levels in rat hippocampus was obtained by using a nitric oxide sensor during global cerebral ischemia and the initial stage of reperfusion. We also observed the effects of two inhibitors of nitric oxide synthases on nitric oxide concentration. The two inhibitors were administrated intravenously at the onset of reperfusion and 1 h later. The change of the nitric oxide concentration in the initial stage of reperfusion was 0.768 ± 0.029 μM. 7-Nitroindazole (7-NI7-NI , inhibitor of nNOS) had a strong inhibitive effect on nitric oxide synthesis at both time points, while 1400 W1400 W dihydrochloride (1400 W, inhibitor of iNOSiNOS ) had no significant effect on nitric oxide synthesis. The results showed that during the initial stage of reperfusion, nitric oxide biosynthesis was mainly an nNOS-dependent process.

Helper-dependent adenoviral vectors are superior in vitro to first-generation vectors for endothelial cell-targeted gene therapy

Arterial endothelial cells (EC) are attractive targets for gene therapy of atherosclerosis because they are accessible to hematogenous and catheter-based vector delivery and overlie atherosclerotic plaques. Vector-mediated expression-in EC-of proteins that mediate cholesterol transfer out of the artery wall and decrease inflammation could prevent and reverse atherosclerosis. However, clinical application of this strategy is limited by lack of a suitable gene-transfer vector. First-generation adenovirus (FGAd) is useful for EC gene transfer in proof-of-concept studies, but is unsuitable for atheroprotective human gene therapy because of limited duration of expression and proinflammatory effects. Moreover, others have reported detrimental effects of FGAd on critical aspects of EC physiology including proliferation, migration, and apoptosis. Here, we investigated whether helper-dependent adenovirus (HDAd) either alone or expressing an atheroprotective gene [apolipoprotein A-I (apoA-I)] could circumvent these limitations. In contrast to control FGAd, HDAd did not alter any of several critical EC physiologic functions (including proliferation, migration, apoptosis, metabolic activity, and nitric oxide (NO) production) and did not stimulate proinflammatory pathways [including expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and interleukin-6 (IL-6)]. Expression of apoA-I by HDAd reduced EC VCAM-1 expression. HDAd is a promising vector and apoA-I is a promising gene for atheroprotective human gene therapy delivered via EC.

Electron Paramagnetic Resonance - A Powerful Tool of Medical Biochemistry in Discovering Mechanisms of Disease and Treatment Prospects

In pathophysiological conditions related to oxidative stress, the application of selected antioxidants could have beneficial effects on human health. Electron paramagnetic resonance (EPR) spectroscopy is a technique that provides unique insight into the redox biochemistry, due to its ability to: (i) distinguish and quantify different reactive species, such as hydroxyl radical, superoxide, carbon centered radicals, hydrogen atom, nitric oxide, ascorbyl radical, melanin, and others; (ii) evaluate the antioxidative capacity of various compounds, extracts and foods; (iii) provide information on other important parameters of biological systems. A combination of EPR spectroscopy and traditional biochemical methods represents an efficient tool in the studies of disease mechanisms and antioxidative therapy prospects, providing a more complete view into the redox processes in the human organism.

The dynamic detection of NO during stroke and reperfusion in vivo

PURPOSE

Nitric oxide (NO) has been implicated as a mediator of synaptic transmission and a pathological factor in stroke/reperfusion. The purpose of this study was to detect the change of NO concentration in rat hippocampus during global cerebral ischemia and reperfusion in vivo and to reveal effects of different NO synthases (NOS).

METHOD

In the present study, the real-time record of NO levels in rat hippocampus was obtained by using a NO sensor during the global cerebral ischemia and the initial stage of reperfusion. The effects of two inhibitors of NOS on NO concentration were also observed. The two inhibitors were respectively administrated intravenously at the onset of reperfusion and 1 hour later.

RESULTS

The change of the NO concentration in the initial stage of reperfusion was 0.768 +/- 0.029 microM. 7-nitroindazole (7-NI, inhibitor of nNOS) had a strong inhibitive effect on NO synthesis at both time points, while 1400W dihydrochloride (1400W, inhibitor of iNOS) had no significant effect on the NO synthesis.

CONCLUSIONS

The in vivo detection revealed the real dynamic change of NO concentration, which is much more reliable than the in vitro method. The results showed that, during the initial stage of reperfusion, NO biosynthesis was mainly in an nNOS-dependent manner. Thus, the toxicity of NO in this process had a close relationship with the activity of nNOS but not iNOS.

Multimodality imaging of nitric oxide and nitric oxide synthases

Nitric oxide (NO) and NO synthases (NOSs) are crucial factors in many pathophysiological processes such as inflammation, vascular/neurological function, and many types of cancer. Noninvasive imaging of NO or NOS can provide new insights in understanding these diseases and facilitate the development of novel therapeutic strategies. In this review, we will summarize the current state-of-the-art multimodality imaging in detecting NO and NOSs, including optical (fluorescence, chemiluminescence, and bioluminescence), electron paramagnetic resonance (EPR), magnetic resonance (MR), and positron emission tomography (PET). With continued effort over the last several years, these noninvasive imaging techniques can now reveal the biodistribution of NO or NOS in living subjects with high fidelity which will greatly facilitate scientists/clinicians in the development of new drugs and/or patient management. Lastly, we will also discuss future directions/applications of NO/NOS imaging. Successful development of novel NO/NOS imaging agents with optimal in vivo stability and desirable pharmacokinetics for clinical translation will enable the maximum benefit in patient management.

Electron paramagnetic resonance (EPR) spin trapping of biological nitric oxide

Nitric oxide (NO) is a free radical species with multiple physiological functions. Because of low concentrations and short half-life of NO, its direct measurement in living tissues remains a difficult task. Electron paramagnetic resonance (EPR) spin trapping is probably one of the best suitable platforms for development of new methods for quantification of biological NO. The most reliable EPR-based approaches developed so far are based on the reaction of NO with various iron complexes, both intrinsic and exogenously applied. This review is focused on the current state and perspectives of EPR spin trapping for experimental and clinical NO biology.

Radiochemical HPLC detection of arginine metabolism: measurement of nitric oxide synthesis and arginase activity in vascular tissue

Nitric oxide (NO) plays a key role in vascular homeostasis. Accurate measurement of NO production by endothelial nitric oxide synthase (eNOS) is critical for the investigation of vascular disease mechanisms using genetically modified animal models. Previous assays of NO production measuring the conversion of arginine to citrulline have required homogenisation of tissue and reconstitution with cofactors including NADPH and tetrahydrobiopterin. However, the activity and regulation of NOS in vivo is critically dependant on tissue levels of these cofactors. Therefore, understanding eNOS regulation requires assays of NO production in intact vascular tissue that do not depend on the addition of exogenous cofactors and have sufficient sensitivity and specificity. We describe a novel technique, using radiochemical detection of arginine to citrulline conversion, to measure NO production within intact mouse aortas, without exogenous cofactors. We demonstrate the presence of arginase activity in mouse aortas which has the potential to confound this assay. Furthermore, we describe the use of N-hydroxy-nor-L-arginine (nor-NOHA) to inhibit arginase and permit specific detection of NO production in intact mouse tissue. Using this technique we demonstrate a 2.4-fold increase in NO production in aortas of transgenic mice overexpressing eNOS in the endothelium, and show that this technique has high specificity and high sensitivity for detection of in situ NO synthesis by eNOS in mouse vascular tissue. These results have important implications for the investigation of NOS regulation in cells and tissues.

ESR techniques for the detection of nitric oxide in vivo and in tissues

Plasma levels of nitrite/nitrate may not accurately reflect endothelial nitric oxide synthase (eNOS) function because of interference by dietary nitrates. Nitrosyl hemoglobin (HbNO), a metabolic product of nitric oxide (NO*), may better correlate with bioavailable NO*, but it may depend on the activity of different NOS isoforms and may be affected by dietary nitrite/nitrate. This work examined the correlation between vascular endothelial NO* release and blood levels of HbNO. We measured HbNO in mouse blood using electron spin resonance (ESR) spectrometry, and we quantified vascular production of NO* using colloid Fe(DETC)2 and ESR. C57Blk/6 mice who were fed a high-nitrate diet had levels of plasma HbNO increased 10-fold, whereas those fed a low-nitrate diet had decreased HbNO levels from 0.58 +/- 0.02 to 0.48 +/- 0.01 microM. Therefore, a low-nitrate diet is essential when using HbNO as a marker of eNOS activity. Treatment with L-NAME and the eNOS-specific inhibitor L-NIO halved HbNO formation, which reflects the complete inhibition of NO* release by aorta endothelium. Treatment of mice with the selective inducible NOS (iNOS) inhibitor, 1400W, or the selective neuronal NOS (nNOS) inhibitor N-AANG did not alter either blood HbNO levels or vascular NO*. The relationship between HbNO and NO* production by the endothelium (0.23 microM HbNO to 5.27 microM/h of NO*/mg of dry weight aorta) was found to be identical for both C57Blk/6 mice and mice with vascular smooth muscle-targeted expression of p22phox associated with strong increase in eNOS activity. These results support the important role of eNOS in the formation of circulating HbNO, whereas iNOS and nNOS do not contribute to HbNO formation under normal conditions. These data suggest that HbNO can be used as a noninvasive marker of endothelial NO* production in vivo.

Release and hemodynamic influence of nitro-glycerine-derived nitric oxide in endotoxemic rats

BACKGROUND AND AIM

Nitric oxide released from nitro-glycerine (NG) has been considered to improve the microcirculation. Septic conditions are, however, associated with excessive formation of nitric oxide (NO), which is formed from l-arginine by the inducible NO synthase (iNOS) activity. Since the characteristics and influence of NG-derived NO in sepsis remains unclear, the major aims of the present study were to quantify the release and to determine the effects of NO formed from NG on systemic blood pressure under endotoxemic conditions.

MATERIAL AND METHODS

Four hours following endotoxin challenge (10 mg/kg intraperitoneally), rats received an infusion of NG (0.5 or 5.0 micromol/kg/h) over 45 min. We determined the changes in blood pressure and the NO concentrations generated in brain, heart, intestine, kidney, liver, and lung by means of NO trapping and EPR technique.

RESULTS

NG infusion in control rats and endotoxin challenge decreased systemic blood pressure to the same extent. However, in rats subjected to endotoxin challenge NG infusion did not affect the blood pressure. The endotoxin-induced increase in tissue NO concentrations were found to be 15-folds higher than tissue levels of NO following NG infusion.

CONCLUSION

Our results suggest that under endotoxic shock conditions in rats NG may not additionally affect the systemic blood pressure. This may relate to the excessive tissue NO levels induced by endotoxin that are not further increased by NG.

Endothelial nitric oxide synthase dysfunction in diabetic mice: importance of tetrahydrobiopterin in eNOS dimerisation

AIMS/HYPOTHESIS

Impaired nitric oxide (NO) bioactivity and increased superoxide (SO) production are characteristics of vascular endothelial dysfunction in diabetes. The underlying mechanisms remain unknown. In this regard, we investigated the role of tetrahydrobiopterin (BH4) bioavailability in regulating endothelial nitric oxide synthase (eNOS) activity, dimerisation and SO production in streptozotocin-induced diabetic mice.

METHODS

Mouse aortas were used for assays of the following: (1) aortic function by isometric tension; (2) NO by electronic paramagnetic resonance; (3) SO by lucigenin-enhanced chemiluminescence and dihydroethidine fluorescence; (4) total biopterin and BH4 by high-performance liquid chromatography; and (5) eNOS protein expression and dimerisation by immunoblotting.

RESULTS

In diabetic mouse aortas, relaxations to acetylcholine and NO levels were significantly decreased, but SO production was increased, in association with reductions in total biopterins and BH4. Although total eNOS levels were increased in diabetes, the protein mainly existed in monomeric form. Conversely, specifically augmented BH4 in diabetic endothelium preserved eNOS dimerisation, but the expression remained unchanged.

CONCLUSIONS/INTERPRETATION

Our results demonstrate that BH4 plays an important role in regulating eNOS activity and its functional protein structure, suggesting that increasing endothelial BH4 and/or protecting it from oxidation may be a rational therapeutic strategy to restore eNOS function in diabetes.