We investigated the in vitro metabolism of two (nitrooxy)butyl ester nitric oxide (NO) donor derivatives of flurbiprofen and ferulic acid, [1,1Ј-biphenyl]-4-acetic acid-2-fluoro-␣-methyl-4-(nitrooxy)butyl ester (HCT 1026) and 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid 4-(nitrooxy)butyl ester (NCX 2057), respectively, in rat blood plasma and liver subcellular fractions compared with (nitrooxy)butyl alcohol (NOBA) and glyceryl trinitrate (GTN). HCT 1026 and NCX 2057 undergo rapid ubiquitous carboxyl ester hydrolysis to their respective parent compounds and NOBA. The nitrate moiety of this latter is subsequently metabolized to inorganic nitrogen oxides (NOx), predominantly in liver cytosol by glutathione S-transferase (GST) and to a lesser extent in liver mitochondria. If, however, in liver cytosol, the carboxyl ester hydrolysis is prevented by an esterase inhibitor, the metabolism at the nitrate moiety level does not occur.In blood plasma, HCT 1026 and NCX 2057 are not metabolized to NOx, whereas a slow but sustained NO generation in deoxygenated whole blood as detected by electron paramagnetic resonance indicates the involvement of erythrocytes in the bioactivation of these compounds. Differently from NOBA, GTN is also metabolized in blood plasma and more quickly metabolized by different GST isoforms in liver cytosol. The cytosolic GST-mediated denitration of these organic nitrates in liver limits their interaction with other intracellular compartments to possible generation of NO and/or their subsequent availability and bioactivation in the systemic circulation and extrahepatic tissues. We show the possibility of modulating the activity of hepatic cytosolic enzymes involved in the metabolism of (nitrooxy)butyl ester compounds, thus increasing the therapeutic potential of this class of compounds.The therapeutic potential of organic nitrates has been known for more than 120 years since the use of glyceryl trinitrate (GTN) in the treatment of angina pectoris. Moreover, the pharmaceutical development of organic nitrates containing adjunct pharmacophores was reported over 40 years ago, and these were observed to manifest biological properties beyond those of the parent compound (Hodosan et al., 1969). However, there has been an explosion of activity in the area of hybrid nitrates over the past decade, stimulated by a growing realization that nitrates may represent new therapeutic agents in different areas (Keeble and Moore, 2002). Despite this, the metabolism of several organic nitrates is still to be elucidated. The exact mechanism whereby nitric oxide (NO) is generated from organic nitrates is still unknown, and several mechanisms have been proposed and rejected. Although nonenzymatic pathways involving endogenous sulfhydryl groups (Ignarro et al., 1980) or hemoglobin (Bennett et al., 1986;Cosby et al., 2003) have been suggested to mediate the biotransformation to NO, the attention has also shifted to an enzyme-catalyzed mechanism (Needleman, 1976). Several enzymes have been proposed to be directly or i...

No abstract

Reboxetine, (RS)-2-[(RS)-alpha-(2-ethoxyphenoxy)benzyl]morpholine methanesulphonate, is a racemic compound and consists of a mixture of the (R,R)- and (S,S)-enantiomers. In this study, brain and plasma levels of both enantiomers were determined in mice and rats after oral administration of reboxetine at doses (1.1 mg/kg, mouse; 20 mg/kg, rat) twice the respective ED50 values in the antireserpine test. Plasma and brain concentrations of each enantiomer were measured up to 6 h postdosing using an HPLC method with fluorimetric detection after derivatization with a chiral agent (FLEC). In mice and rats, brain and plasma levels of the (R,R)-enantiomer were always higher than those of the (S,S)-enantiomer. After normalization for dose, the mean AUC0-tz values of both the (R,R)- and (S,S)-enantiomers in mouse brain were about 23 and 32 times higher than in rat brain, respectively. In plasma, the corrected mean AUC0-tz values were about 5 (R,R) and 10 (S,S) times higher in mice than in rats. These results provide evidence for the higher bioavailability and/or lower clearance of both enantiomers in mice than in rats, and for a higher penetration of both enantiomers into mouse brain compared to rat brain.

Portal hypertension, a life threatening complication of liver cirrhosis, results from increased intrahepatic resistance and increased portal blood inflow through a hyperdynamic splanchnic system. The increased intrahepatic vascular tone is the result of an enhanced activity of endogenous vasoconstrictors and a deficiency of nitric oxide (NO) release by sinusoidal endothelial cells. These pathophysiological events provide the rational basis for using NO-based therapies for the treatment of portal hypertension. Clinical studies have demonstrated that nitrate therapy results in a significant reduction of portal pressure as assessed by hepatic venous portal gradient but causes vasodilation in both systemic arterial and venous vascular beds, aggravating the progression of the vasodilatory syndrome of cirrhotic patients. For this reason, the ideal drug for the treatment of portal hypertension should act by decreasing intrahepatic vascular resistance, without worsening the splanchnic/systemic vasodilatation. NCX-1000 is the prototype of a family of NO-releasing derivatives of ursodeoxycholic acid (UDCA). These compounds are releasing selectively, from parenchymal and non-parenchymal hepatic cells, biologically active NO into the liver microcirculation with no detectable effect on systemic circulation. Preclinical studies have shown that long- and short-term administration of NCX-1000 to rodents with chronic liver injury protects against the development of portal hypertension and reduces the intrahepatic hyperreactivity to alpha1-adrenoceptor agonists. The finding of increased liver nitrite/nitrate content in NCX-1000-treated animals together with an increase in cGMP levels in their liver homogenates suggests that this nitro-compound behaves as a liver-selective NO donor. In contrast to conventional NO-donors such as isosorbide mono- and di-nitrate, which are also used for primary and secondary prevention of gastrointestinal bleeding, NCX-1000 has no effect on mean arterial pressure in either normal or cirrhotic animals indicating the absence of adverse systemic effect. In summary, these data suggest that NCX-1000 may provide a novel therapy for the treatment of patients with portal hypertension.

Hepatic veno-occlusive disease, also called sinusoidal obstruction syndrome (VOD/SOS), is an unpredictable, potentially life-threatening complication of hematopoietic stem cell transplant conditioning. Severe VOD/SOS, generally associated with multiorgan dysfunction (pulmonary or renal dysfunction), may be associated with >80% mortality. Defibrotide, recently approved in the US, has demonstrated efficacy treating hepatic VOD/SOS with multiorgan dysfunction. Because renal impairment is prevalent in patients with VOD/SOS, this Phase I, open-label, two-part study in adults examined the effects of hemodialysis and severe or end-stage renal disease (ESRD) on defibrotide pharmacokinetics (PK). Part 1 compared defibrotide PK during single 6.25 mg/kg doses infused with and without dialysis. Part 2 assessed defibrotide plasma PK after multiple 6.25 mg/kg doses in nondialysis-dependent subjects with severe/ESRD versus healthy matching subjects. Among six subjects enrolled in Part 1, percent ratios of least-squares mean and 90% confidence intervals (CIs) on dialysis and nondialysis days were 109.71 (CI: 97.23, 123.78) for maximum observed plasma concentration (Cmax); 108.39 (CI: 97.85, 120.07) for area under the concentration–time curve to the time of the last quantifiable plasma concentration (AUC0–t); and 109.98 (CI: 99.39, 121.70) for AUC extrapolated to infinity (AUC0–∞). These ranges were within 80%–125%, indicating no significant effect of dialysis on defibrotide exposure/clearance. In Part 2, defibrotide exposure parameters in six subjects with severe/ESRD after multiple doses (AUC0–t, 113 µg·h/mL; AUC over dosing interval, 113 µg·h/mL; Cmax, 53.8 µg/mL) were within 5%–8% of parameters after the first dose (AUC0–t, 117 µg·h/mL; AUC0–∞, 118 µg·h/mL; Cmax, 54.9 µg/mL), indicating no accumulation. Defibrotide peak and extent of exposures in those with severe/ESRD were ~35%–37% and 50%–60% higher, respectively, versus controls, following single and multiple doses. One adverse event (vomiting, possibly drug-related) was reported. These findings support defibrotide prescribing guidance stating no dose adjustment is necessary for hemodialysis or severe/ESRD.