Analysis of vasodilator responses to novel nitric oxide donors in the hindquarters vascular bed of the cat

Mechanisms underlying maternal venous adaptation in pregnancy

To define the effects of pregnancy on mechanical properties and reactivity, mesenteric veins from late pregnant and virgin control (nonpregnant) rats were pressurized to determine gestational changes in size and distensibility. Reactivity studies used an adrenergic constrictor (norepinephrine) and an endothelium-mediated vasodilator (acetylcholine). The contribution of nitric oxide to endothelial function was evaluated with pharmacologic inhibition of nitric oxide synthase. Roles of nitric oxide and cyclic guanosine monophosphate in smooth muscle vasodilation were determined using an nitric oxide donor with and without cyclic guanosine monophosphate inhibition using ODQ, a selective inhibitor of guanylyl cyclase. In pregnancy, endothelium-dependent vasodilation markedly increased (largely due to endogenous nitric oxide), smooth muscle response to nitric oxide decreased (primarily related to cyclic guanosine monophosphate production), and norepinephrine sensitivity decreased considerably, with no changes in vessel size or distensibility. Our results identify a provasodilatory state in the systemic venous system, which would serve to facilitate the accommodation to plasma volume expansion requisite for normal pregnancy.

Cell-permeable esters of diazeniumdiolate-based nitric oxide prodrugs

Although O(2)-(2,4-dinitrophenyl) derivatives of diazeniumdiolate-based nitric oxide (NO) prodrugs bearing a free carboxylic acid group were activated by glutathione to release NO, these compounds were poor sources of intracellular NO and showed diminished antiproliferative activity against human leukemia HL-60 cells. The carboxylic acid esters of these prodrugs, however, were found to be superior sources of intracellular NO and potent inhibitors of HL-60 cell proliferation.

Nitric oxide promotes caspase-independent hepatic stellate cell apoptosis through the generation of reactive oxygen species

Hepatic stellate cells (HSCs) contribute to portal hypertension through multiple mechanisms that include collagen deposition, vasoconstriction, and regulation of sinusoidal structure. Under normal physiologic conditions, endothelial nitric oxide (NO) synthase-derived NO exerts paracrine effects on HSCs; however, in cirrhosis, NO generation is impaired in association with concomitant HSC activation and changes in sinusoidal structure, events that contribute significantly to the development of portal hypertension. These concepts, in combination with recent evidence that induction of HSC-selective apoptosis may represent a useful target for treatment of chronic liver disease, led us to examine if NO may further limit HSC function through apoptosis. Indeed, both NO donors and endothelial NO synthase overexpression promoted HSC apoptotic pathways. HSC death conferred by NO occurred through mitochondrial membrane depolarization and through a caspase-independent pathway. Furthermore, NO-induced apoptosis of HSC did not occur through the canonical pathways of soluble guanylate cyclase or protein nitration, but rather through the generation of superoxide and hydroxyl radical intermediates. Lastly, HSC isolated from rats after bile duct ligation were more susceptible to NO-induced apoptosis. These data indicate that NO promotes HSC apoptosis through a signaling mechanism that involves mitochondria, is mediated by reactive oxygen species, and occurs independent of caspase activation.

CONCLUSION

We postulate that NO-dependent apoptosis of HSCs may maintain sinusoidal homeostasis, and may represent an additional beneficial effect of NO donors for therapy of portal hypertension.

V-PROLI/NO, a prodrug of the nitric oxide donor, PROLI/NO

The sensitivity to decomposition of the nitric oxide (NO) donor ion, 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO), complicates direct electrophilic substitution to form useful prodrug derivatives. A modified general synthetic approach involving 1-[2-(hydroxymethyl)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate ion (structure A, above) was used to prepare several PROLI/NO prodrugs including the previously inaccessible O2-vinyl derivative, V-PROLI/NO. Metabolism of V-PROLI/NO by liver microsomes enriched in human cytochrome P450 isoforms was demonstrated.

E/Z conformation and the vibrational spectroscopy of Me2NN(O)=NOMe

The simple neutral diazenium diolate, O2-methyl-1-(N, N-dimethylamino)diazen-1-ium-1,2-diolate, [Me2NN(O)=NOMe], was experimentally examined by vibrational spectroscopy and the results compared to the theoretically calculated values in an effort to detect both Z and E conformers which result from the stereochemistry of the N=N multiple bond. Room-temperature Raman and infrared spectra were measured and the results compared with the values calculated theoretically with MP2 and density functional techniques (B3LYP). An analysis of the observed frequencies suggests that, down to a detection limit of about 1/1000, only a small quantity of trans (E) diazeniumdiolate, <0.05%, may be present at room temperature.

Overexpressed beta-catenin blocks nitric oxide-induced apoptosis in colonic cancer cells

Beta-catenin plays an important role in colonic tumorigenesis whereas inducible nitric oxide synthase and nitric oxide are elevated in colonic inflammation. Resistance of colonic epithelial cells to the induction of apoptosis may contribute to tumor development. Nitric oxide can stimulate apoptosis and, paradoxically, is implicated in the development of colon cancer. Our hypothesis was that beta-catenin could increase the resistance of colonic cancer cells to nitric oxide-induced apoptotic cell death. Here we show, using a beta-catenin overexpression system, that increased cytosolic beta-catenin renders colonic epithelial cells more resistant to nitric oxide-induced apoptotic cell death, independently of nitric oxide-induced accumulation of p53. Furthermore, we show that this occurs through inhibition of nitric oxide-induced release of cytochrome c from mitochondria and by blocking both the nitric oxide-induced suppression of the antiapoptotic protein, Bcl-xL, and the phosphorylation of Akt. We contend that increased nitric oxide production, such as that which occurs in chronic colonic inflammation, may select the cells with oncogenic mutant beta-catenin regulatory genes and contribute to human colonic carcinogenesis and tumor progression.

Analysis of nitric oxide donor effectiveness in resistance vessels

Decreased nitric oxide (NO) bioavailability is associated with a number of pathological conditions. Administration of a supplemental source of NO can counter the pathological effects arising from decreased NO bioavailability. A class of NO-nucleophile adducts that spontaneously release NO (NONOates) has been developed, and its members show promise as therapeutic sources of NO. Because the NONOates release NO spontaneously, a significant portion of the NO may be consumed by the myriad of NO reactive species present in the body. Here we develop a model to analyze the efficacy of NO delivery, by membrane-impermeable NONOates, in the resistance arterioles. Our model identifies three features of blood vessels that will enhance NONOate efficacy: 1) the amount of NO delivered to the abluminal region increases with lumen radius; 2) the presence of a flow-induced red blood cell-free zone will augment NO delivery; and 3) extravasation of the NONOate into the interstitial space will increase abluminal NO delivery. These results suggest that NONOates may be more effective in larger vessels and that NONOate efficacy can be altered by modifying permeability to the interstitial space.

JS-K, a novel non-ionic diazeniumdiolate derivative, inhibits Hep 3B hepatoma cell growth and induces c-Jun phosphorylation via multiple MAP kinase pathways

JS-K, a non-ionic diazeniumdiolate derivative, is capable of arylating nucleophiles and spontaneously generating nitric oxide (NO) at physiological pH. This recently synthesized low molecular weight compound is shown here to be an inhibitor of cell growth with concomitant activation of mitogen-activated protein kinase (MAPK) members ERK, JNK, and p38 and their downstream effectors c-Jun and AP-1. Inhibitors of these MAPK pathways abrogated the growth inhibitory actions of JS-K. In addition to the well-described actions of JNK as a kinase for c-Jun, we show that c-Jun is also an ERK target. Furthermore, JS-K generated NO in culture and NO inhibitors antagonized both MAPK induction and the growth inhibitory effects of JS-K. These results suggest two possible mechanisms for the mediation of JS-K growth inhibitory actions, namely NO-induction of MAPK pathway constituents as well as possible arylation reactions. The data support the idea that prolonged MAPK activation by JS-K action is important in mediating its growth-inhibitory actions. JS-K thus represents a promising platform for novel growth inhibitory analog synthesis.

Comparative responses to alpha,beta-methylene-ATP in cat pulmonary, mesenteric, and hindquarter vascular beds

Responses to the P2X-purinoceptor agonist alpha,beta-methylene-ATP (alpha,beta-MeATP) were investigated in the pulmonary, hindquarter, and mesenteric vascular beds in the cat. Under constant-flow conditions, injections of alpha,beta-MeATP caused dose-related increases in perfusion pressure in the pulmonary and hindquarter beds and a biphasic response in the mesenteric circulation. In the pulmonary vascular bed, the order of potency was alpha,beta-MeATP > U-46619 > angiotensin II, whereas, in the hindquarters, the order of potency was angiotensin II > U-46619 > alpha,beta-MeATP. The order of potency was similar in the hindquarter and mesenteric beds when the pressor component of the response to alpha,beta-MeATP was compared with responses to angiotensin II and U-46619. The P2X-receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid attenuated the pressor response to alpha,beta-MeATP in the hindquarter circulation and the pressor component in the mesenteric vascular bed. Pressor responses to alpha,beta-MeATP were not altered by cyclooxygenase, alpha-adrenergic, or angiotensin AT(1) antagonists. These data show that alpha,beta-MeATP has potent pressor activity in the pulmonary circulation, where it was 100-fold more potent than angiotensin II. In contrast, alpha,beta-MeATP had modest pressor activity in the systemic bed, where it was 1,000-fold less potent than angiotensin II. These data suggest that responses to alpha,beta-MeATP are dependent on the vascular bed studied and may be dependent on the density of P2X receptors in the vascular bed.