Pharmacokinetics and metabolism of infused versus inhaled iloprost in isolated rabbit lungs

In Vitro Monitoring of the Mitochondrial Beta-Oxidation Flux of Palmitic Acid and Investigation of Its Pharmacological Alteration by Therapeutics

BACKGROUND AND OBJECTIVE

The present study was designed to validate the functional assay that enables rapid screening of therapeutic candidates for their effect on mitochondrial fatty acid oxidation.

METHODS

The two whole-cell systems (tissue homogenates and hepatocytes) have been evaluated to monitor the total beta-oxidation flux of physiologically important ³H-palmitic acid by measurement of tritiated water enrichment in incubations using UPLC coupled on-line to radioactivity monitoring and mass spectrometry.

RESULTS

Our results with several known inhibitors of fatty acid oxidation showed that this simple assay could correctly predict a potential in alteration of mitochondrial function by drug candidates. Since the beta-oxidation of palmitic acid takes place almost exclusively in mitochondria of human hepatocytes, this model can be also utilized to distinguish between the mitochondrial and peroxisomal routes of this essential metabolic pathway in some cases.

CONCLUSIONS

The present work offers a new in vitro screen of changes in mitochondrial beta-oxidation by xenobiotics as well as a model to study the mechanism of this pathway.

Clinical pharmacology and efficacy of inhaled iloprost for the treatment of pulmonary arterial hypertension

Similar to other prostanoids, iloprost is a potent vasodilator with considerable antiproliferative and anti-thrombotic properties, although the relevance of its ability to affect platelet aggregation in this subset of patients is unrecognized. The pathogenesis of pulmonary arterial hypertension (PAH) is a multifactorial and complex process secondary to an innate deficiency of substances that induce vasodilation and an overproduction of substances producing vasoconstriction. The production of endothelial vasoactive mediators such as nitric oxide, prostacyclin, endothelin-1, thromboxane and serotonin affect the growth of smooth muscle cells, which facilitate the development of structural remodeling changes that are characteristic of PAH. There have been remarkable advances in understanding the pathologic processes that are responsible for increasing pulmonary vascular resistance and that result in elevated pulmonary artery pressures in order to reverse and prevent progression of the disease process. The goals of treatment in these patients are to alleviate the patients' symptoms, to improve functional capacity and to prevent the progression of the disease. The prostacyclin analogs, such as iloprost, have given hope to these patients who struggle under the burdens of this complex disease.

[Effect of nebulised iloprost combined with inhaled nitric oxide and oral sildenafil on lung transplant patients. Therapeutic efficacy in pulmonary hypertension during surgery]

OBJECTIVES

There is a high incidence of pulmonary hypertension during the lung transplant peri-operative period, and could lead to a haemodynamic deterioration that may require the need of extracorporeal circulation. Our aim was to study the haemodynamic effects on the pulmonary and systemic circulation of the combination of inhaled nitric oxide and iloprost and oral sildenafil in patients with severe pulmonary hypertension during lung transplant surgery.

PATIENTS AND METHODS

Seventeen patients received 10μg of nebulised iloprost during the peri-operative period of the lung transplant when their mean pulmonary pressure exceeded 50mmHg. AU the patients received 50mg of oral sildenafil 30min before anaesthetic induction, 20ppm of inhaled nitric oxide after tracheal intubation. The haemodynamic and respiratory variables were recorded at baseline (after anaesthetic induction), prior to the administering of iloprost, and at 5 and 30min after it was given.

RESULTS

The administering of iloprost significantly reduced the pulmonary arterial pressure and significantly increases the cardiac Índex and the right ventrícular ejection fractíon. There were no signíficant changes occurred in the systemic arterial pressure.

CONCLUSIONS

The triple combination significantly reduces the pulmonary pressures in the lung transplant peri-operative and should be considered when there is severe pulmonary hypertension during the surgery or during the immediate post-operative period of lung transplantation.

Inhaled iloprost for therapy in pulmonary arterial hypertension

Iloprost (Ventavis, Bayer Schering Pharma, Germany) is a synthetic prostacyclin that is used in its inhalative form for the therapy of pulmonary arterial hypertension. Long-term therapy can increase exercise capacity and quality of life. The use of modern nebulizers especially designed for the administration of iloprost guarantees the pulmonary deposition of the required doses and systematically minimizes side effects. Regarding existing data, inhalative iloprost acts in effective and safe combination with other classes of medication; indeed, such combination therapy is frequently necessary in pulmonary arterial hypertension.

Inhaled iloprost for the control of pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by an elevated pulmonary arterial pressure and vascular resistance with a poor prognosis. Various pulmonary and extrapulmonary causes are now recognized to exist separately from the idiopathic form of pulmonary hypertension. An imbalance in the presence of vasoconstrictors and vasodilators plays an important role in the pathophysiology of the disease, one example being the lack of prostacyclin. Prostacyclin and its analogues are potent vasodilators with antithrombotic, antiproliferative and anti-inflammatory qualities, all of which are important factors in the pathogenesis of precapillary pulmonary hypertension. Iloprost is a stable prostacyclin analogue available for intravenous and aerosolized application. Due to the severe side effects of intravenous administration, the use of inhaled iloprost has become a mainstay in PAH therapy. However, owing to the necessity for 6 to 9 inhalations a day, oral treatment is often preferred as a first-line therapy. Numerous studies proving the efficacy and safety of inhaled iloprost have been performed. It is therefore available for a first-line therapy for PAH. The combination with endothelin-receptor antagonists or sildenafil has shown encouraging effects. Further studies with larger patient populations will have to demonstrate the use of combination therapy for long-term treatment of pulmonary hypertension.

Evaluation of pulmonary vascular response to inhaled iloprost in heart transplant candidates with pulmonary venous hypertension

OBJECTIVE

Chronic left-heart failure is often associated with the development of pulmonary venous hypertension. In heart transplant candidates this is of great significance because the healthy donor heart has to compensate the increased right-ventricular afterload. Right-ventricular dysfunction is still responsible for 19% of all early deaths after orthotopic heart transplantation. Careful preoperative assessment of pulmonary vascular resistance by right-heart catheterization is essential. Reversibility testing is generally carried out to clarify therapeutic options for the post-transplant period. The objective of this case series is to report our institutional experience with inhaled iloprost compared to the common used oxygen/nitroglycerin method for reversibility testing.

METHODS

Right-heart catheterization was performed in 23 patients with severely impaired left-ventricular function (EF < or = 25%, pVO2 < or = 14 ml/kg/min, NYHA III or IV) with combined pulmonary venous hypertension (TPG > 12 mm Hg and or PVR > 250 dyn x s x cm(-5)). An intraindividual comparison was performed between of the hemodynamic effect with oxygen/nitroglycerin s.l. and inhaled iloprost.

RESULTS

The transpulmonary gradient fell significantly from an initial 16 mm Hg to 13 mm Hg on oxygen/nitroglycerin s.l. compared to 10 mm Hg on inhaled iloprost. Pulmonary vascular resistance fell significantly from an initial 344 dyn x s x cm(-5) to 270 dyn x s x cm(-5) on oxygen/nitroglycerin s.l. compared to 209 dyn x s x cm(-5) on inhaled iloprost. On inhaled iloprost a moderate systemic effect was noticed.

CONCLUSION

In heart transplant candidates with pulmonary venous hypertension reversibility testing with inhalation of iloprost is a save method and significantly more effective than the combination of inhaled oxygen plus nitroglycerin s.l.

Comparison of Pharmacokinetics and Vasodilatory Effect of Nebulized and Infused Iloprost in Experimental Pulmonary Hypertension: Rapid Tolerance Development

Aerosolized iloprost has been suggested for selective pulmonary vasodilatation in severe pulmonary hypertension, but its pharmacokinetic profile is largely unknown. In perfused rabbit lungs, continuous infusion of the thromboxane mimetic U46619 was employed for establishing stable pulmonary hypertension. Delivery of a total amount of 75, 300, and 900 ng of iloprost to the bronchoalveolar space by a 10 min-aerosolization maneuver caused a dose-dependent pulmonary vasodilatation. Similarly, dose-dependent appearance of iloprost in the recirculating perfusate was noted, with maximum intravascular concentrations of iloprost ranging at 140, 510, and 1163 pg/mL at the same time period. Comparing pharmacokinetics and pharmacodynamics in a more detailed fashion, the following aspects were of interest. (i) The bioavailability (i.e., the percentage of aerosolized iloprost appearing intravascularly) decreased from 76% at the lowest to 33% at the highest iloprost dosage. (ii) The pulmonary vasodilatory response commenced already during the nebulization maneuver and preceded the perfusate entry of iloprost. (iii) After 3-3.5 h, the pulmonary vasodilatory response to aerosolized iloprost had virtually completely leveled off, whereas approximately two-thirds of the maximum iloprost perfusate levels were still detectable. A corresponding loss of vasodilatory response was also noted in experiments with continuous iloprost perfusion for clamping of the intravascular concentration of this prostanoid. We conclude that aerosolized iloprost causes dose-dependent vasodilatation and iloprost entry into the vascular space in a pulmonary hypertension model. Limited bioavailability in the higher dose range may suggest active prostanoid transport processes, and the early pulmonary vasodilatory response appears to be independent of prostanoid entry into the vessel lumen. Surprisingly, rapid tolerance development to the vasodilatory effect of iloprost is noted, occurring even with fully maintained perfusate levels of this agent.

Fully Stereocontrolled Total Syntheses of the Prostacyclin Analogues 16S-Iloprost and 16S-3-Oxa-Iloprost by a Common Route, Using Alkenylcopper-Azoalkene Conjugate Addition, Asymmetric Olefination, and Allylic Alkylation

In this article we describe fully stereocontrolled total syntheses of 16S-iloprost (16S-2), the most active component of the drugs Ilomedin and Ventavis, and of 16S-3-oxa-iloprost (16S-3), a close analogue of 16S-2 having the potential for a high oral activity, by a new and common route. The key steps of this route are (1) the establishment of the complete C13-C20 omega side chain of the target molecules through a stereoselective conjugate addition of the alkenylcopper derivative 9 to the bicyclic C6-C12 azoalkene 10 with formation of hydrazone 8, (2) the diastereoselective olefination of ketone 7 with the chiral phosphoryl acetate 39, and (3) the regio- and stereoselective alkylation of the allylic acetate 43 with cuprate 42. These measures allowed the 5E,15S,16S-stereoselective synthesis of 16S-2 and 16S-3, a goal which had previously not been achieved. Azoalkene 10 was obtained from the achiral bicyclic C6-C12 ketone 11 as previously described by using as key step an enantioselective deprotonation. The configuration at C16 of omega-side chain building block 9 has been installed with high stereoselectivity by the oxazolidinone method and that at C15 by a diastereoselective oxazaborolidine-catalyzed reduction of the C13-C20 ketone 23 with catecholborane. Surprisingly, a high diastereoselectivity in the reduction of 23 was only obtained by using 2 equiv of oxazaborolidine 24. Application of substoichiometric amounts of 24 resulted in irreproducible diastereoselectivities ranging from very high to nil.

Lung vasodilatory response to inhaled iloprost in experimental pulmonary hypertension: amplification by different type phosphodiesterase inhibitors

Inhaled prostanoids and phosphodiesterase (PDE) inhibitors have been suggested for treatment of severe pulmonary hypertension. In catheterized rabbits with acute pulmonary hypertension induced by continuous infusion of the stable thromboxane analogue U46619, we asked whether sildenafil (PDE1/5/6 inhibitor), motapizone (PDE3 inhibitor) or 8-Methoxymethyl-IBMX (PDE1 inhibitor) synergize with inhaled iloprost. Inhalation of iloprost caused a transient pulmonary artery pressure decline, levelling off within <20 min, without significant changes in blood gases or systemic hemodynamics. Infusion of 8-Methoxymethyl-IBMX, motapizone and sildenafil caused each a dose-dependent decrease in pulmonary artery pressure, with sildenafil possessing the highest efficacy and at the same time selectivity for the pulmonary circulation. When combining a per se ineffective dose of each PDE inhibitor (200 μg/kg × min 8-Methoxymethyl-IBMX, 1 μg/kg × min sildenafil, 5 μg/kg × min motapizone) with subsequent iloprost nebulization, marked amplification of the prostanoid induced pulmonary vasodilatory response was noted and the area under the curve of P_PA reduction was nearly threefold increased with all approaches, as compared to sole iloprost administration. Further amplification was achieved with the combination of inhaled iloprost with sildenafil plus motapizone, but not with sildenafil plus 8MM-IBMX. Systemic hemodynamics and gas exchange were not altered for all combinations. We conclude that co-administration of minute systemic doses of selective PDE inhibitors with inhaled iloprost markedly enhances and prolongs the pulmonary vasodilatory response to inhaled iloprost, with maintenance of pulmonary selectivity and ventilation perfusion matching. The prominent effect of sildenafil may be operative via both PDE1 and PDE5, and is further enhanced by co-application of a PDE3 inhibitor.

Inhaled iloprost: in primary pulmonary hypertension

Iloprost is a stable prostacyclin analogue with a pharmacokinetic profile allowing nebulised administration in patients with primary pulmonary hypertension (PPH). Inhaled iloprost is a potent acute pulmonary vasodilator with a duration of action of about 60 minutes. It may exert additional long-term benefit through antiproliferative and antithrombotic effects. Inhaled iloprost 2.5 or 5 microg six or nine times daily for 12 weeks (n = 101) significantly (p < 0.01) improved a combined clinical endpoint of a > or =10% increase in distance walked in 6 minutes and an improvement of > or =1 class in New York Heart Association functional class without clinical deterioration or death (16.8 versus 4.9% of placebo recipients, n = 102) in patients with severe PPH or selected forms of nonprimary pulmonary hypertension. Statistical analysis of the response for the PPH subgroup (20.8 versus 5.5% with placebo; n = 51 and 51) was not reported. Improvements from baseline in exercise capacity and haemodynamic/gas exchange variables have been reported in patients with PPH with continued use of inhaled iloprost. In addition, improvement in preinhalation vascular resistance occurred after 12 weeks of inhaled iloprost (p < 0.01 versus placebo) in a large randomised trial. Increased cough, headache, flushing and an influenza-like syndrome were the most common adverse events in the largest trial of patients receiving inhaled iloprost. Headache, flushing and jaw pain occurred significantly more frequently with inhaled iloprost than with placebo.

Pharmacodynamics and Pharmacokinetics of Inhaled Iloprost, Aerosolized by Three Different Devices, in Severe Pulmonary Hypertension

BACKGROUND

Inhalation of iloprost, a stable prostacyclin analog, is an effective therapy for pulmonary hypertension with few side effects. This approach may, however, be handicapped by limitations of currently available nebulization devices. We assessed whether the physical characterization of a device is sufficient to predict drug deposition and pharmacologic effects.

METHODS

We investigated the effects of a standardized iloprost aerosol dose (5 micro g; inhaled within approximately 10 min) in 12 patients with severe pulmonary hypertension in a crossover design employing three well-characterized nebulizers. The nebulizers use different techniques to increase efficiency and alveolar targeting (Ilo-Neb/Aerotrap [Nebu-Tec; Elsenfeld, Germany], Ventstream [MedicAid; Bognor Regis, UK], and HaloLite [Profile Therapeutics; Bognor Regis, UK]). Measurements were performed using a Swan-Ganz catheter and determination of arterial iloprost plasma levels.

RESULTS

During inhalation of iloprost, the pulmonary vascular resistance decreased substantially (baseline, approximately 1,250 dyne.s.cm(-5); decrease, - 35.5 to - 38.0%) and pulmonary artery pressure decreased substantially (baseline, approximately 58 mm Hg; decline, - 18.4 to -21.8%), whereas the systemic arterial pressure was largely unaffected. Cardiac output and mixed venous and arterial oxygen saturation displayed a marked increase. The pharmacodynamic profiles with the three devices were superimposable. Moreover, rapid entry of iloprost into the systemic circulation was noted, peaking immediately after termination of the inhalation maneuver, with very similar maximum serum concentrations (158 pg/mL, 155 pg/mL, and 157 pg/mL), and half-lives of serum levels (6.5 min, 9.4 min, and 7.7 min) for the three nebulizers, respectively. Interestingly, the "half-life" of the pharmacodynamic effects in the pulmonary vasculature (eg, decrease in pulmonary vascular resistance, ranging between 21 and 25 min) clearly outlasted this serum level-based pharmacokinetic half-life.

CONCLUSIONS

A standardized dose of aerosolized iloprost delivered by different nebulizer types induces comparable pharmacodynamic and pharmacokinetic responses. Pulmonary vasodilation, persisting after disappearance of the drug from the systemic circulation, supports the hypothesis that local drug deposition largely contributes to the preferential pulmonary vasodilation in response to inhaled iloprost.