Development of nitric oxide releasing visible light crosslinked gelatin methacrylate hydrogel for rapid closure of diabetic wounds.

Management of non-healing and slow to heal diabetic wounds is a major concern in healthcare across the world. Numerous techniques have been investigated to solve the issue of delayed wound healing, though, mostly unable to promote complete healing of diabetic wounds due to the lack of proper cell proliferation, poor cell-cell communication, and higher chances of wound infections. These challenges can be minimized by using hydrogel based wound healing patches loaded with bioactive agents. Gelatin methacrylate (GelMA) has been proven to be a highly cell friendly, cell adhesive, and inexpensive biopolymer for various tissue engineering and wound healing applications. In this study, S-Nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO) donor, was incorporated in a highly porous GelMA hydrogel patch to improve cell proliferation, facilitate rapid cell migration, and enhance diabetic wound healing. We adopted a visible light crosslinking method to fabricate this highly porous biodegradable but relatively stable patch. Developed patches were characterized for morphology, NO release, cell proliferation and migration, and diabetic wound healing in a rat model. The obtained results indicate that SNAP loaded visible light crosslinked GelMA hydrogel patches can be highly effective in promoting diabetic wound healing.

S-Nitroso-N-acetylpenicillamine impregnated endotracheal tubes for prevention of ventilator-associated pneumonia.

The chances of ventilator-associated pneumonia (VAP) increases 6-20 folds when an endotracheal tube (ETT) is placed in a patient. VAP is one of the most common hospital-acquired infections and comprises 86% of the nosocomial pneumonia cases. This study introduces the idea of nitric oxide-releasing ETTs (NORel-ETTs) fabricated by the incorporation of the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) into commercially available ETTs via solvent swelling. The impregnation of SNAP provides NO release over a 7-day period without altering the mechanical properties of the ETT. The NORel-ETTs successfully reduced the bacterial infection from a commonly found pathogen in VAP, Pseudomonas aeruginosa, by 92.72 ± 0.97% when compared with the control ETTs. Overall, this study presents the incorporation of the active release of a bactericidal agent in ETTs as an efficient strategy to prevent the risk of VAP.

Nitric oxide-releasing antibacterial albumin plastic for biomedical applications.

Designing innovative materials for biomedical applications is desired to prevent surface fouling and risk of associated infections arising in the surgical care patient. In the present study, albumin plastic was fabricated and nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP), was incorporated through a solvent swelling process. The albumin-SNAP plastic was evaluated in terms of mechanical and thermal properties, and bacterial adhesion to the plastic surface. Thermal and viscoelastic analyses showed no significant difference between albumin-SNAP plastics and pure, water-plasticized albumin samples. Bacteria adhesion tests revealed that albumin-SNAP plastic can significantly reduce the surface-bound viable gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa bacterial cells by 98.7 and 98.5%, respectively, when compared with the traditional polyvinyl chloride medical grade tubing material. The results from this study demonstrate NO-releasing albumin plastic's potential as a material for biomedical device applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1535-1542, 2018.

Intracerebroventricular application of S100B selectively impairs pial arteriolar dilating function in rats.

S100B is an astrocyte-derived protein that can act through the receptor for advanced glycation endproducts (RAGE) to mediate either "trophic" or "toxic" responses. Its levels increase in many neurological conditions with associated microvascular dysregulation, such as subarachnoid hemorrhage (SAH) and traumatic brain injury. The role of S100B in the pathogenesis of microvasculopathy has not been addressed. This study was designed to examine whether S100B alters pial arteriolar vasodilating function. Rats were randomized to receive (1) artificial cerebrospinal fluid (aCSF), (2) exogenous S100B, and (3) exogenous S100B+the decoy soluble RAGE (sRAGE). S100B was infused intracerebroventricularly (icv) using an osmotic pump and its levels in the CSF were adjusted to achieve a concentration similar to what we observed in SAH. After 48 h of continuous icv infusion, a cranial window/intravital microscopy was applied to animals for evaluation of pial arteriolar dilating responses to sciatic nerve stimulation (SNS), hypercapnia, and topical suffusion of vasodilators including acetylcholine (ACh), s-nitroso-N-acetyl penicillamine (SNAP), or adenosine (ADO). Pial arteriolar dilating responses were calculated as the percentage change of arteriolar diameter in relation to baseline. The continuous S100B infusion for 48 h was associated with reduced responses to the neuronal-dependent vasodilator SNS (p<0.05) and the endothelial-dependent vasodilator ACh (p<0.05), compared to controls. The inhibitory effects of S100B were prevented by sRAGE. On the other hand, S100B did not alter the responses elicited by vascular smooth muscle cell-dependent vasodilators, namely hypercapnia, SNAP, or ADO. These findings indicate that S100B regulates neuronal and endothelial dependent cerebral arteriolar dilation and suggest that this phenomenon is mediated through RAGE-associated pathways.

ß-Adrenergic receptor antagonists inhibit vasculogenesis of embryonic stem cells by downregulation of nitric oxide generation and interference with VEGF signalling.

The ß-adrenoceptor antagonist Propranolol has been successfully used to treat infantile hemangioma. However, its mechanism of action is so far unknown. The hypothesis of this research was that ß-adrenoceptor antagonists may interfere with endothelial cell differentiation of stem cells. Specifically, the effects of the non-specific ß-adrenergic receptor (ß-adrenoceptor) antagonist Propranolol, the ß1-adrenoceptor-specific antagonist Atenolol and the ß2-adrenoceptor-specific antagonist ICI118,551 on vasculogenesis of mouse embryonic stem (ES) cells were investigated. All three ß-blockers dose-dependently downregulated formation of capillary structures in ES cell-derived embryoid bodies and decreased the expression of the vascular cell markers CD31 and VE-cadherin. Furthermore, ß-blockers downregulated the expression of fibroblast growth factor-2 (FGF-2), hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor 165 (VEGF165), VEGF receptor 2 (VEGF-R2) and phospho VEGF-R2, as well as neuropilin 1 (NRP1) and plexin-B1 which are essential modulators of embryonic angiogenesis with additional roles in vessel remodelling and arteriogenesis. Under conditions of ß-adrenoceptor inhibition, the endogenous generation of nitric oxide (NO) as well as the phosphorylation of endothelial nitric oxide synthase (eNOS) was decreased in embryoid bodies, whereas an increase in NO generation was observed with the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP). Consequently, vasculogenesis of ES cells was restored upon treatment of differentiating ES cells with ß-adrenoceptor antagonists in the presence of NO donor. In summary, our data suggest that ß-blockers impair vasculogenesis of ES cells by interfering with NO generation which could be the explanation for their anti-angiogenic effects in infantile hemangioma.

Excess nitric oxide impairs LXR(α)-ABCA1-dependent cholesterol efflux in macrophage foam cells.

Excess nitric oxide (NO) promotes the progression of atherosclerosis by increasing the oxidation of low-density lipoprotein (LDL) and inflammatory responses. However, little is known about the impact of NO and its underlying molecular mechanism on lipid metabolism of macrophage foam cells. In this study, Oil-red O staining, cholesterol and triglyceride assay, Dil-oxidized LDL (oxLDL) binding assay, cholesterol efflux assay, real-time RT-PCR and Western blot analysis were used for in vitro experiments. Apolipoprotein E-deficient (apoE(-/-) ) and apoE and inducible nitric oxide synthase-deficient (apoE(-/-) iNOS(-/-) ) mice were as our in vivo models. Treatment with S-nitroso-N-acetyl-D,L-penicillamine (SNAP), an NO donor, exacerbated oxLDL-induced cholesterol accumulation in macrophages, because of reduced efficacy of cholesterol efflux. In addition, SNAP decreased the protein level of ATP-binding cassette transporter A1 (ABCA1) without affecting scavenger receptor type A (SR-A), CD36, ABCG1, or SR-B1 levels. This SNAP-mediated downregulation of ABCA1 was mainly through the effect of NO but not peroxynitrite. Furthermore, the SNAP-downregulated ABCA1 was due to the decrease in the liver X receptor α (LXRα)-dependent transcriptional regulation. Moreover, genetic deletion of iNOS increased the serum capacity of reverse cholesterol efflux and protein expression of LXRα, ABCA1, and SR-BI in aortas and retarded atherosclerosis in apoE(-/-) mice. Our findings provide new insights in the pro-atherogenic effect of excess NO on cholesterol metabolism in macrophages.

Are in situ formulations the keys for the therapeutic future of S-nitrosothiols?

S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) were formulated into in situ forming implants (ISI) and microparticles (ISM) using PLGA and either N-methyl-2-pyrrolidone (NMP) or triacetin. Physicochemical characterization was carried out, including the study of matrix structure and degradation. A strong correlation between drug hydrophobicity and the in vitro release profiles was observed: whatever the formulation, GSNO and SNAP were completely released after ca. 1 day and 1 week, respectively. Then, selected formulations (i.e., SNAP-loaded NMP formulations) demonstrated the ability to sustain the vasodilation effect of SNAP, as shown by monitoring the arterial pressure (telemetry) of Wistar rats after subcutaneous injection. Both ISI and ISM injections resulted in a 3-fold extended decrease in pulse arterial pressure compared with the unloaded drug, without significant decrease in the mean arterial pressure. Hence, the results emphasize the suitability of these formulations as drug delivery systems for S-nitrosothiols, widening their therapeutic potential.

Effect of nitric oxide and TH1/TH2 cytokine supplementation over ectopic endometrial tissue growth in a murine model of endometriosis.

Using a murine model, we evaluated the growth of ectopic endometrial tissue in the presence of T helper 1 (Th1) or Th2 cytokines or a nitric oxide donor (S-nitroso-N-acetyl-penicillamine [SNAP]). Female mice were autografted with endometrial tissue in the peritoneum. Different combinations and concentrations of cytokines or SNAP were injected intraperitoneally for 8 weeks. Implants were recovered, measured, and weighed. Cytokines were determined in plasma. Implants (weight and area) were smaller in mice that received interferon γ plus interleukin 2 (IFN-γ + IL-2) compared to mice treated with IL-2, IL-4 + IL-10 or saline solution, and saline solution compared to different concentrations of SNAP. The IL-2, IFN-γ, and IL-4 concentrations in plasma decreased in accordance with the increase in SNAP concentrations compared to saline solution. The promotion of a Th1 milieu in the peritoneum reduced the weight and area of the implant. Different concentrations of SNAP suppressed Th1 and Th2 cytokines and enabled the growth of the implant in this murine model.

Parthenogenetic activation of pig oocytes using pulsatile treatment with a nitric oxide donor.

The nitric oxide donor (+)-S-nitroso-N-acetylpenicillamine (SNAP) is capable of inducing parthenogenetic activation in pig oocytes matured in vitro. However, quite a long exposure to the nitric oxide donor, exceeding 10 h, is necessary for successful oocyte activation. Repeated short-term treatment with 2 mm SNAP significantly increased the activation rates despite the fact that the overall exposure time to the nitric oxide donor did not exceed 4 h. With regard to the activation rate, 12 repeated treatments lasting 10 min each were found to be the most efficient regimen (63.3%). The continuous exposure to the nitric oxide donor for the same overall time induced parthenogenetic activation in 12.5% oocytes (2-h continuous treatment with 2 mm SNAP). The development of parthenogenetic embryos increased after repeated short-term treatment with SNAP. After continuous treatment with 2 mm SNAP for 10 h, only 6.7% of the oocytes cleaved, and none developed beyond the 4-cell stage. Thirty-minute treatment repeated four times with 2 mm SNAP induced cleavage in 37.5% of the oocytes, 18.3% developed to the morula stage, and 6.7% reached the blastocyst stage. Based on the results, it is concluded that pulsatile treatment can significantly improve parthenogenetic activation rate when compared with the continuous treatment using nitric oxide donors.

Protective mechanisms of NO preconditioning against NO-induced apoptosis in H9c2 cells: role of PKC and COX-2.

Cardiomyocyte apoptosis is involved in several cardiovascular diseases, including ischemia, hypertrophy and heart failure. Nitric oxide (NO) signalling is crucial in the regulation of cardiomyocyte apoptosis, capable of both inducing and preventing apoptosis depending upon the level of NO production. Growing evidence suggests that NO preconditioning has cardioprotective effects, but the mechanism remains unclear. The purpose of this study was to elucidate how NO preconditioning inhibits subsequent NO-induced apoptosis in H9c2 cells. According to the data, preconditioning with a low concentration of sodium nitroprusside (SNP, 0.3 mM) inhibited subsequent high-concentration-SNP (1.5 mM)-induced apoptosis and this effect was reversed by the protein kinase C (PKC) inhibitor chelerythrine and the cyclooxygenase-2 (COX-2) inhibitor rofecoxib. Low-concentration-SNP-mediated protection involved extracellular signal regulated kinase 1/2 (ERK1/2), a signal transducers and activators of transcription 1/3 (STAT1/3) activation and increased COX-2 expression. Activation of ERK1/2 and STAT1/3 was abolished by chelerythrine. However, COX-2 expression was not inhibited, implying that the COX-2-mediated protective effect occurred via a PKC-independent pathway. The results showed that low-concentration-SNP preconditioning suppresses subsequent high-concentration-SNP-induced apoptosis by ERK1/2-STAT 1/3 activation via PKC-dependent mechanisms in H9c2 cells. COX-2 also plays a role in NO-induced preconditioning, but is independent of PKC.

Correlation of in vitro and in vivo kinetics of nitric oxide donors in ocular tissues.

In the eye, nitric oxide (NO) is involved in the regulation of intraocular pressure (IOP) and ocular blood flow. The main purpose of this study was to measure the kinetics of NO release from NO donors in ocular cells and tissues using in vivo and in vitro models and demonstrate the link between the kinetics of NO release with the functional effect, IOP. Nitric oxide release was measured in human ocular cells using a fluorescent dye, diaminofluorescein (DAF), following treatment with short-acting sodium nitroprusside (SNP) and longer-acting S-nitroso-N-acetylpenicillamine (SNAP) NO donors. Both SNP and SNAP were also administered topically to rabbits; IOP was measured and levels of NO and cGMP were assessed as biomarkers over a time course in the aqueous humor (AH) and iris/ciliary body (ICB). Time- and concentration-dependent increases in NO level were produced by SNP and SNAP in human ocular cells. Both NO and cGMP levels appeared to be elevated following treatment with the aforementioned NO donors in rabbit ocular tissues. Transient IOP lowering was accompanied with these biochemical estimations in rabbits, with time of maximal effect being shifted to the right for longer-acting SNAP as compared with short-acting SNP. In vitro and in vivo NO/cGMP assay results displayed a correlation between short- and longer-acting NO donors, discriminating their respective temporal actions in the eye. Due to their translatability, the in vitro DAF assay and in vivo NO fluorometric assay can therefore be potentially useful in screening novel NO donors with different temporal/kinetic profiles.

Nitric oxide enhances expression of raf kinase inhibitor protein in keratinocytes.

Several reports have focused on the potential of nitric oxide (NO) to influence the proliferation and differentiation cascade in a number of mammalian cells. The purpose of this study was to determine the relationship between expression of raf kinase inhibitor protein (RKIP) and proliferation in keratinocyte with NO treatment. Normal human keratinocytes were treated with SNAP (NO donor) doses of 10(-7), 10(-6), 10(-5), 10(-4) and 0 m (control group) separately. Expression of protein and mRNA of RKIP, cell proliferation and apoptosis have been measured. These results showed that elevated expression of RKIP in keratinocyte with NO treatment may contribute to the pathological and physiological features of NO-inhibited proliferation.

Nitric oxide and its modulators in chronic constriction injury-induced neuropathic pain in rats.

This study was conducted to examine the role of nitric oxide (NO) in peripheral neuropathy induced by chronic constriction injury of sciatic nerve of rats by using NO precursor, NO donors and nitric oxide synthase (NOS) inhibitors. Chronic constriction injury of sciatic nerve of rats resulted in peripheral neuropathy as confirmed by nociceptive behavioural tests using mechanical, thermal and cold allodynia. NO precursor, L-arginine and NO donors sodium nitroprusside, S-nitroso-N-acetylpenicillamine potentiated the hyperalgesia and allodynia significantly suggesting proalgesic effect in neuropathic rats. Intracerebroventricular (i.c.v.) administration of rats with NOS inhibitors such as L-N(G)-nitroarginine methyl ester, N-iminoethyl lysine and 7-nitroindazole did not show any effect but i.p. administration of NOS inhibitors aminoguanidine, L-N(G)-nitroarginine methyl ester and 7-nitroindazole caused alleviation of pain. The study confirms the involvement of endogenously synthesized and exogenously administered NO in chronic constriction injury-induced neuropathy in rats. Significant increase in the levels of nitrate and nitrite in ligated sciatic nerve suggest that local up regulation of NO in the production and maintenance of neuropathic pain. In conclusion, initial attempt to manipulate L-arginine: NO pathway is indicative of therapeutic potential of these interventions in the management of neuropathic pain.

Oxidative stress and 8-iso-prostaglandin F(2alpha) induce ectodomain shedding of CD163 and release of tumor necrosis factor-alpha from human monocytes.

CD163 is a membrane glycoprotein of the cysteine-rich scavenger receptor superfamily. Upon an inflammatory stimulus CD163 undergoes ectodomain shedding and the soluble protein has been shown to play a role in downregulation of inflammation. The purpose of the present study was to identify a physiological activator of CD163 shedding that is consistently present under inflammatory conditions. Therefore, we elucidated whether oxidative stress or 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) is involved in shedding of CD163. Oxidative stress induced by H(2)O(2) or a NO donor as well as 8-iso-PGF(2alpha) induced significant shedding of CD163. In contrast, release of CD163 was not stimulated by PGF(2alpha). We identified both calcium and reactive oxygen species as common cellular mediators of CD163 release. Since shedding of both CD163 and tumor necrosis factor-alpha (TNFalpha) is known to be mediated by a TIMP-3-sensitive metalloproteinase we examined whether release of TNFalpha was induced by the same mediators that trigger shedding of CD163. Only oxidative stress generated by H(2)O(2) as well as 8-iso-PGF(2alpha) and PGF(2alpha) enhanced TNFalpha secretion. Thus, we identified novel common and divergent activators of shedding of CD163 and TNFalpha. These inducers of shedding are present in inflammation and might play an important role in membrane protein cleavage.

Control of myocardial oxygen consumption in transgenic mice overexpressing vascular eNOS.

Our objective was to investigate the potential role of selective endothelial nitric oxide (NO) synthase (eNOS) overexpression in coronary blood vessels in the control of myocardial oxygen consumption (MVO2). Transgenic (Tg) eNOS-overexpressing mice (eNOS Tg) (n=22) and wild-type (WT) mice (n=24) were studied. Western blot analysis indicated greater than sixfold increase of eNOS in cardiac tissue. Echocardiography in awake mice indicated no difference in cardiac function between WT and eNOS Tg; however, systolic pressure in eNOS Tg mice decreased significantly (126 +/- 2.3 to 109 +/- 2.3 mmHg; P <0.05), whereas heart rate (HR) was not different. Total peripheral resistance (TPR) was also decreased (9.8 +/- 0.8 to 7.6 +/- 0.4 4 mmHg.ml(-1).min; P <0.05) in eNOS Tg. Furthermore, female eNOS Tg mice showed even lower TPR (7.2 +/- 0.4 mmHg.ml(-1).min) compared with male eNOS mice (8.6 +/- 0.5, mmHg.ml.min(-1); P <0.05). Left ventricular slices were isolated from WT and eNOS Tg mice. With the use of a Clark-type oxygen electrode in an airtight bath, MVO2 was determined as the percent decrease during increasing doses (10(-10) to 10(-4) mol/l) of bradykinin (BK), carbachol (CCh), forskolin (10(-12) to 10(-6) mol/l), or S-nitroso-N-acetyl penicillamine (SNAP; 10(-7) to 10(-4) mol/l). Baseline MVO2 was not different between WT (181 +/- 13 nmol.g(-1).min(-1)) and eNOS Tg (188 +/- 14 nmol.g(-1).min(-1)). BK decreased MVO2 (10(-4) mol/l) in WT by 17% +/- 1.1 and 33% +/- 2.7 in eNOS Tg (P < 0.05). CCh also decreased MVO2, 10(-4) mol/l, in WT by 20% +/- 1.7 and 31% +/- 2.0 in eNOS Tg (P <0.05). Forskolin (10(-6) mol/l) or SNAP (10(-4) mol/l) also decreased MVO2 in WT by 24% +/- 2.8 and 36% +/- 1.8 versus eNOS 31% +/- 1.8 and 37% +/- 3.5, respectively. N-nitro-L-arginine methyl ester (10(-3) mol/l) inhibited the MVO2 reduction to BK, CCh, and forskolin by a similar degree (P <0.05), but not to SNAP. Thus selective overexpression of eNOS in cardiac blood vessels in mice enhances the control of MVO2 by eNOS-derived NO.

Exogenous nitric oxide upregulates p21(waf1/cip1) in pulmonary microvascular smooth muscle cells.

The histopathology of chronic pulmonary hypertension includes microvascular proliferation and neointimal formation. Nitric oxide (NO) has been implicated in the regulation of these mechanisms, but how NO controls microvascular proliferation and its effect on pulmonary microvascular cells is still unclear. In this study, we characterized the in vitro effects of NO on rat pulmonary microvascular smooth muscle cell (PMVSMC) proliferation and investigated the contribution of the p42/44 mitogen-activated protein kinase (MAPK) pathway and p21(waf1/cip1) induction to this response. NO donors inhibited PMVSMC proliferation in a dose-dependent manner. In the presence of hypoxia, the degree of inhibition was significantly enhanced. This inhibition was reversible and independent of apoptosis. The soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) had no impact on proliferation rates, suggesting a cyclic guanosine monophosphate-independent process. Administration of MEK1/2 inhibitors failed to abrogate the antimitotic effect of NO. There was a two- fold induction of the cyclin-dependent kinase inhibitor p21 in PMVSMC treated with NO donors. Under hypoxic conditions, NO caused a three-fold increase in p21 levels. These results demonstrate that NO inhibits PMVSMC proliferation and that this inhibition is not the result of p42/44 MAPK activation. The ability of NO to induce p21 upregulation may be a mechanism by which it exerts antiproliferative effects in PMVSMC.

Superoxide does not mediate the acute vasoconstrictor effects of angiotensin II: a study in human and porcine arteries.

OBJECTIVE: To investigate whether superoxide mediates angiotensin (Ang) II-induced vasoconstriction. METHODS: Human coronary arteries (HCAs), porcine femoral arteries (PFA) and porcine coronary arteries (PCAs) were mounted in organ baths and concentration-response curves to Ang II, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and the NAD(P)H oxidase substrate NADH were constructed in the absence and presence of superoxide inhibiting and activating drugs. Extracellular superoxide was measured using cytochrome c reduction. RESULTS: Ang II constricted both HCAs and PFAs. In HCAs, the NAD(P)H inhibitors diphenyleneiodonium (DPI) and apocynin, and the xanthine oxidase (XO) inhibitor allopurinol, but not the superoxide dismutase (SOD) mimetic tempol or the SOD inhibitor diethyldithiocarbamate (DETCA), reduced this constriction. Catalase potentiated Ang II in HCAs, indicating a vasodilator role for H2O2. DPI, tempol and SOD did not affect Ang II in PFAs. DPI, apocynin and allopurinol relaxed preconstricted HCAs. Although the relaxant effects of the NO donor SNAP in PCAs was reduced by DETCA, indicating that superoxide-induced constrictions depend on NO inactivation, the apocynin-induced relaxations were NO independent. Moreover, NADH relaxed all vessels, and this effect was blocked by KCl but not DPI or NO removal. Xanthine plus XO also relaxed HCAs and PCAs. Incubation of human or porcine arteries with Ang II or NADH did not result in detectable increases of extracellular superoxide within 1 h. CONCLUSIONS: Acute vasoconstriction by Ang II is not mediated via superoxide generated through NAD(P)H oxidase and/or XO activation. Such activation, if occurring, rather results in the generation of the vasodilator H2O2.

Maturation alters cyclic nucleotide and relaxation responses to nitric oxide donors in ovine cerebral arteries.

To examine the hypothesis that maturation modulates nitric oxide (NO)-induced relaxation in cerebral arteries, we quantified concentration-relaxation relations and the corresponding dynamic responses of guanosine 3':5'-cyclic monophosphate (cGMP) and adenosine 3':5'-cyclic monophosphate (cAMP) levels following administration of nitroglycerin and S-nitroso-N-acetyl-penicilamine (SNAP), an NO donor, in posterior communicating and middle cerebral arteries from newborn (3-7 days) and adult sheep. The results offer 5 main observations: (1) the efficacy and potency of NO donors were generally greater in newborn than in adult cerebral arteries; (2) rates of relaxation, and presumably rates of NO release, were faster for equimolar concentrations of SNAP than for nitroglycerin in both newborn and adult arteries; (3) basal concentrations were greater for cAMP than for cGMP, and both were greater in newborn than adult cerebral arteries; (4) in adult cerebral arteries, NO-induced increases in cGMP occurred faster but relaxation developed more slowly than in newborn cerebral arteries, and (5) responses to NO donors involved significant cross-reactivity between cGMP and cAMP, the characteristics of which were age, artery, and agent specific. From these results, we conclude that postnatal changes in reactivity to NO reflect corresponding changes in soluble guanylate cyclase activity and possible decreases in NO half-life. We also conclude that maturation slows the mechanisms mediating NO-induced relaxation, and that this effect is more pronounced in distal than in proximal cerebral arteries. The data also suggest that the rate-limiting step governing rates of response to NO is probably downstream from cGMP synthesis. From the basal cyclic nucleotide levels, we conclude that basal ratios of synthesis to hydrolysis were greater in fetal than adult arteries. Because NO increased both cGMP and cAMP, we speculate that Type III phosphodiesterase has a possible influence upon cerebrovascular responses to NO, and that this influence varies with postnatal age and artery type. Together, these findings emphasize that the cerebrovascular effects of NO are highly age dependent and artery specific, and should be carefully considered when administering NO therapeutically in the neonate.

cDNA microarray analysis of vascular gene expression after nitric oxide donor infusions in rats: implications for nitrate tolerance mechanisms.

Vascular nitrate tolerance is often accompanied by changes in the activity and/or expression of a number of proteins. However, it is not known whether these changes are associated with the vasodilatory properties of nitrates, or with their tolerance mechanisms. We examined the hemodynamic effects and vascular gene expressions of 2 nitric oxide (NO) donors: nitroglycerin (NTG) and S-nitroso-N-acetylpenicillamine (SNAP). Rats received 10 microg/min NTG, SNAP, or vehicle infusion for 8 hours. Hemodynamic tolerance was monitored by the maximal mean arterial pressure (MAP) response to a 30-microg NTG or SNAP bolus challenge dose (CD) at various times during infusion. Gene expression in rat aorta after NTG or SNAP treatment was determined using cDNA microarrays, and the relative differences in expression after drug treatment were evaluated using several statistical techniques. MAP response of the NTG CD was attenuated from the first hour of NTG infusion (P <.001, analysis of variance [ANOVA]), but not after SNAP (P >.05, ANOVA) or control infusion (P >.05, ANOVA). Student t-statistics revealed that 447 rat genes in the aorta were significantly altered by NTG treatment (P <.05). An adjusted t-statistic approach using resampling techniques identified a subset of 290 genes that remained significantly different between NTG treatment vs control. In contrast, SNAP treatment resulted in the up-regulation of only 7 genes and the down-regulation of 34 genes. These results indicate that continuous NTG infusion induced widespread changes in vascular gene expression, many of which are consistent with the multifactorial and complex mechanisms reported for nitrate tolerance.

Gastric nitric oxide synthase expression during endotoxemia: implications in mucosal defense in rats.

BACKGROUND & AIMS: This study was performed to examine expression of gastric nitric oxide synthase (NOS) isoforms during endotoxemia in rats and to assess their role(s) in gastric injury from bile and ethanol. METHODS: Lipopolysaccharide (LPS) enhanced the expression and activity of inducible nitric oxide synthase in gastric mucosa in a dose- and time-dependent manner. RESULTS: Endothelial nitric oxide synthase and neural nitric oxide synthase expression did not significantly change, but constitutive nitric oxide synthase activity decreased over time. LPS alone caused injury to the gastric mucosa and disrupted F-actin filaments in the same cells with enhanced immunostaining for inducible nitric oxide synthase. LPS also exacerbated gastric injury from the mild irritants 5 mmol/L acidified taurocholate and 20% ethanol as did local intra-arterial infusion of the nitric oxide donor S-nitroso-N-acetyl-penicillamine. The selective inducible nitric oxide synthase inhibitor aminoguanidine negated LPS-induced exacerbation of gastric injury from these irritants. The nonselective NOS inhibitor N(G)-nitro-L-arginine methyl ester augmented the deleterious effects of LPS, an effect reversed by L-arginine but not D-arginine. Aminoguanidine, but not N(G)-nitro-L-arginine methyl ester, negated LPS-induced accumulation of gastric luminal nitrates. CONCLUSIONS: These data suggest that increased inducible NOS activity and decreased constitutive nitric oxide synthase activity are primarily responsible for exacerbating gastric injury from luminal irritants during endotoxemia. Moreover, septic patients may be more susceptible to gastric injury from bile during gastrointestinal ileus.