Desynchronization: a novel model to induce heart failure

BACKGROUND

Previous large animal heart failure models led to inhomogeneous results. Therefore, we developed a novel model combining rapid pacing with forced ventricular desynchronization.

METHODS

Heart failure was induced in 20 pigs during a pacing period of 21 days. Group A (n = 10) received one right ventricular lead (220 bpm). In group B (n = 10), two leads were implanted in different right ventricular regions with beat-to-beat alternation of activation sites (each lead 110 bpm). Sham-operated pigs (n = 6) served as controls. Hemodynamics were invasively evaluated and tissue was analyzed by immunohistochemistry and zymography.

RESULTS

Hemodynamics were significantly more impaired in group B with an increase of pulmonary capillary wedge and central venous pressure and a reduction of cardiac index (control 4.3 +/- 0.1 l/min/m (2); A 3.6 +/- 0.2; B 2.9 +/- 0.2, P < 0.05). Heart-to-body weight ratio was significantly higher in group B. Histological analyses showed a significant increase of cell diameters and interstitial fibrosis with significantly higher collagen contents in group B.

CONCLUSION

The new model with a combination of rapid pacing and forced desynchronization of the ventricular contraction is superior to traditional heart failure models induced solely by rapid pacing.

Classically and alternatively activated macrophages contribute to tissue remodelling after myocardial infarction

An important goal in cardiology is to minimize myocardial necrosis and to support a discrete but resilient scar formation after myocardial infarction (MI). Macrophages are a type of cells that influence cardiac remodelling during MI. Therefore, the goal of the present study was to investigate their transcriptional profile and to identify the type of activation during scar tissue formation. Ligature of the left anterior descending coronary artery was performed in mice. Macrophages were isolated from infarcted tissue using magnetic cell sorting after 5 days. The total RNA of macrophages was subjected to microarray analysis and compared with RNA from MI and LV-control. mRNA abundance of relevant targets was validated by quantitative real-time PCR 2, 5 and 10 days after MI (qRT-PCR). Immunohistochemistry was performed to localize activation type-specific proteins. The genome scan revealed 68 targets predominantly expressed by macrophages after MI. Among these targets, an increased mRNA abundance of genes, involved in both the classically (tumour necrosis factor α, interleukin 6, interleukin 1β) and the alternatively (arginase 1 and 2, mannose receptor C type 1, chitinase 3-like 3) activated phenotype of macrophages, was found 5 days after MI. This observation was confirmed by qRT-PCR. Using immunohistochemistry, we confirmed that tumour necrosis factor α, representing the classical activation, is strongly transcribed early after ligature (2 days). It was decreased after 5 and 10 days. Five days after MI, we found a fundamental change towards alternative activation of macrophages with up-regulation of arginase 1. Our results demonstrate that macrophages are differentially activated during different phases of scar tissue formation after MI. During the early inflammatory phase, macrophages are predominantly classically activated, whereas their phenotype changes during the important transition from inflammation to scar tissue formation into an alternatively activated type.

Effects of 2-Deoxy-d-Glucose on Proliferation of Vascular Smooth Muscle Cells and Endothelial Cells

2-Deoxy-d-glucose (2-DG) is a glucose analogue that has been proposed for cancer therapy due to its cytostatic properties. Its effect on the proliferation of smooth muscle cells and endothelial cells has not been fully clarified. The aims of this study were to investigate the effects of 2-DG on the proliferation of porcine aortic endothelial cells (PAEC) and porcine smooth muscle cells (PSMC), to establish an overview of its dose-dependent inhibitory capacity and to examine whether the short-term incubation of cells with 2-DG has an impact on cell proliferation in culture. Our results showed a dose-dependent significant inhibitory effect on proliferation, which was more pronounced in PSMC than in PAEC. Even after short-term incubation of cells with 2-DG, relevant inhibition of proliferation was documented. The clinical application of 2-DG might be a promising concept by inhibiting cells that show a potentially rapid proliferation in response to non-malignant stimuli, such as smooth muscle cells after intracoronary stenting.

Negative Inotropic Effect of Rapamycin on Isolated Human Cardiomyocytes

Rapamycin is an increasingly important immunosuppressive drug and reduces restenosis after coronary stenting, but its effects on cardiac contractility are largely unknown. We investigated the acute inotropic effects of rapamycin on isolated human cardiomyocytes. Cardiomyocytes were enzymatically isolated from right atrial appendages obtained during routine coronary artery bypass surgery. Cell morphology was examined by confocal microscopy. Cell contraction was recorded after electrical stimulation. Rapamycin elicited a concentration-dependent decrease in fractional cell shortening ranging from 14.3 ± 2.6% at 10−8 M rapamycin to 26.4 ± 4.2% at 10−5 M. Rapamycin also caused a concentration-dependent decrease in diastolic cell length. Contractile performance of isolated cardiomyocytes was well preserved, as evidenced by the profound positive inotropic effects of high extracellular calcium concentration and the β-adrenoreceptor agonist isoproterenol. The acute negative inotropic effect of rapamycin on human cardiomyocytes might be due to altered calcium homeostasis through the binding of rapamycin to FKBP12.6 and its regulatory function on the ryanodine receptor, with increased calcium leakage from the sarcoplasmic reticulum.

Left Ventricular Tamponade - A Clinical Chameleon

We present a 45-year-old patient who had to undergo aortocoronary bypass surgery after acute posterior myocardial infarction. On day twelve, the patient suddenly developed the classic signs of cardiogenic shock including angina, tachycardia, and hypotension. ECG displayed significant ST-elevations and troponin T was positive. Echocardiography suspected relevant pericardial effusion. However, the typical clinical signs of acute pericardial tamponade(distension of jugular veins, paradoxical pulse) were absent. Therefore, a computed tomography was carried out, which confirmed an isolated left ventricular tamponade resulting in severe diastolic and systolic dysfunction with profoundly impaired left ventricular filling. Immediate operative drainage was necessary since percutaneous pericardiocentesis was impossible given the untypical localization. This case demonstrates that clearcut signs of myocardial infarction can be misleading and may represent the untypical presentation of left ventricular tamponade,particularly in the setting after open-heart surgery.

Treatment of in-stent restenosis with sirolimus-eluting-stents—

Treatment of in-stent restenosis (ISR) remains a therapeutic challenge since many pharmacological and mechanical approaches have shown disappointing results except for brachytherapy. Drug-eluting stents (DES) have been reported to effectively reduce ISR in de novo lesions. We studied 55 consecutive patients with ISR in native coronary arteries and 7 with ISR in saphenous vein grafts (SVG) with elective indication for percutaneous coronary intervention (PCI), who underwent successful implantation with DES. No in-hospital postprocedural major adverse cardiac events were observed. All but one patient (n=61) underwent an angiographic follow-up at 183+/-30 days. Grade of stenosis was assessed by quantitative coronary angiography (QCA) at index procedure and at control angiography. Restenosis (>50%) occurred in 5 patients (8.2%). Target vessel revascularization was performed in an additional 4 patients. Minimal intimal hyperplasia was observed in all segments covered by DES (late loss 0.08+/-0.37 mm, loss index 0.11+/-0.47). One patient suffered from subacute stent thrombosis due to discontinuation of clopidogrel medication. At six month follow-up two patients had died. Death was not related to a restenosis in the treated segment. Conclusion Our experiences with DES treatment of ISR lesions show good angiographic and clinical results at index procedure and at the 6 month follow-up with low sub acute thrombosis rate as compared with existing treatment modalities. Restenosis rate seems to be at least as low as reported for brachytherapy.

Transcatheter closure of a ruptured ventricular septum after myocardial infarction using a venous approach

A 65-year old patient was admitted after having sustained a ventricular septum rupture 18 days after an anterior myocardial infarction. He developed acute heart failure. Given the extremely high perioperative risk in surgical approaches in this setting, we decided for a transcatheter closure of the defect with an exclusively venous approach. After a complete recovery, the patient underwent open heart surgery with aorto coronary bypass, aneurysmectomy, and removal of the closure device. This case demonstrates that transcatheter closure of a post infarction ventricular septum rupture is a technically feasible and suitable method.

Clopidogrel in acute coronary syndrome: when, how much, how long?

An important part of the therapy management of acute coronary syndrome (ACS) consists of antiplatelet drugs. Whereas the administration of acetylsalicylic acid (ASA) is well established, the guidelines recommend the additive use of clopidogrel in patients with ACS without persisting ST-elevation. Clopidogrel should be added to ASA as soon as possible in patients with a non-invasive treatment strategy and continued for more than 1 month (class 1A) and up to 9 months (class 1B). In patients for whom a percutaneous coronary intervention (PCI) is planned, an additional loading-dose of 300 mg clopidogrel should be given on top of ASA (100 mg). These recommendations are based on data recently published in the CURE and CREDO trials, which however should be critically discussed: In these trials, an absolute risk reduction of only 2% could be documented by additive use of clopidogrel. The combined endpoint of cardiovascular death, myocardial infarction and stroke is significantly reduced, but there was no improvement taken the individual endpoints alone. In additional, the data for duration of clopidogrel therapy were determined by taken the mean follow-up of these studies. The efficacy of the dual antiplatelet therapy should be discussed in the context of an increased frequency of major bleedings (in total 1%) and should be considered against a reasonable cost effective background. An adequate therapy with clopidogrel in patients presenting ACS should be confirmed by further trials. Until more detailed data are available, the guideline recommendations should be implemented based on of patient's individual risk.

Interpretation of absorption rate data for inhaled fluticasone propionate obtained in compartmental pharmacokinetic modeling

OBJECTIVE

Reports characterizing the pharmacokinetics of inhaled fluticasone propionate (FP) using compartmental approaches have suggested that the absorption of FP into the systemic circulation is rapid with a half-life of approximately 10 min. We believe that this is a classical case of misassignment of the pharmacokinetic parameter estimates, a problem often encountered while modeling pharmacokinetic data. The objective of this study was to illustrate and analyze this problem using actual blood level data of FP obtained in 14 healthy subjects.

MATERIALS AND METHODS

Serum concentration-time data of FP were obtained from a double-blind, randomized study involving single and multiple twice-daily inhalations of 500 microg via a dry powder device, Diskus. The profiles were fitted using one- and two-compartment pharmacokinetic models with first order absorption. Various permutations of the resulting exponential rate constants were analyzed to determine the combination that was most consistent with the underlying physical process.

RESULTS

The two-compartment body model with first order absorption gave excellent fits for the observed FP concentrations after both single and multiple dosing. Even though peak levels were reached relatively early (30 - 90 min) after inhalation, the combination that most appropriately described the underlying process was alpha > Ka > beta, i.e. slow absorption, rapid distribution and slower elimination kinetics. The absorption, distribution and elimination half-lives resulted to be 3.8 h, 9.9 min and 13.6 h, respectively, consistent with the high lipophilicity and sustained dissolution characteristics observed in vitro.

CONCLUSIONS

Analysis of FP pharmacokinetics after inhalation represents a classical case of potential misassignment of the exponential rate constants, which if ignored, could lead to erroneous interpretations regarding the underlying process. The study also elucidates the pitfall of using t(max) to calculate absorption rate.

Population pharmacokinetics of methylprednisolone in accident victims with spinal cord injury

OBJECTIVE

High-dose methylprednisolone (MP) is used to treat acute spinal cord injury (ASCI). The objective of the present study was to determine the pharmacokinetics of the pro-drug methylprednisolone hemisuccinate (MPHS) and MP in accident victims with ASCI.

METHODS

The patients (n = 26) were treated with a bolus intravenous loading dose of 30 mg/kg MPHS within 2 h after injury and this was followed by a maintenance infusion of 5.4 mg/kg/h up to 24 h. Blood, CSF and saliva samples were collected up to 48 h after the initial dose and the samples were analyzed by HPLC. Concentration-time data of MPHS and MP were analyzed using population pharmacokinetic analysis with NONMEM software.

RESULTS

MPHS and MP could be monitored in plasma and CSF. MP but not MPHS was present in saliva. High variability was seen in the MPHS levels in CSF. The pharmacokinetics of the pro-drug and the metabolite were adequately described by a 2-compartment model with exponential distribution models assigned to the interindividual and the residual variability. At steady state, the average measured MP concentration in plasma was 12.3+/-7.0 microg/ml and 1.74+/-0.85 microg/ml in CSF. The CSF levels of MP could be modeled as a part of the peripheral compartment.

CONCLUSION

This study demonstrated that CSF concentrations of MP were sufficiently high after i.v. administration and reflected the concentrations of unbound drug in plasma. Salivary levels of MP were about 32% of the plasma level and may serve as an easily accessible body fluid for drug level monitoring.

Single-dose and steady-state pharmacokinetic and pharmacodynamic evaluation of therapeutically clinically equivalent doses of inhaled fluticasone propionate and budesonide, given as Diskus or Turbohaler dry-powder inhalers to healthy subjects

Direct comparisons of the pharmacokinetic (PK) and systemic pharmacodynamic (PD) properties of inhaled corticosteroids after single and multiple dosing in the same subjects are scarce. The objective of this study was to compare thePK/PDproperties of clinically equivalent, single, and multiple doses of dry-powder formulations of inhaled fluticasone propionate (FP 200 and 500 microg via Diskus) and budesonide (BUD, 400 and 1,000 microg via Turbohaler). Fourteen healthy subjects completed a double-blind, double-dummy, randomized, placebo-controlled, five-way crossover study consisting of a single dose administered at 8 a.m. on day 1 followed by 4 days of twice-daily dosing at 8 a.m. and 8 p.m. on days 2 to 5. Serum concentrations of FP and BUD were measured using validated liquid chromatography/ mass spectrometry assays. The 24-hour cumulative cortisol suppression (CCS) in serum was monitored as the pharmacodynamic surrogate marker. Peak serum concentrations following single and multiple dosing were observed 10 to 30 minutes after inhalation for BUD and 30 to 90 minutes afterinhalation of FP with no influence of dose ordosingregimen. After a single dose of 1000 microg BUD and 500 microg FP the median estimates of terminal half-life and mean residence time were 3.5 and 3.9 hours for BUD and 10.1 and 12.0 hours for FP, respectively. Using previously reported intravenous data, the mean absorption times (MAT) were calculated to be around 2 hours and 7 hours for BUD and FP respectively. On average, the area under the curve (A UC) at steady state (day 5) was up to 30% higher for BUD compared to that over a 12-hour period following the first dose on day 1, whereas A UC estimates were 50% to 80% higherforFP at steady state, indicating accumulation. However, the steady-state Cmax values were seven to eight times and AUC values three to four times higher for BUD than for FP. Comparison of active treatment data with placebo showed that CCS after a single dose was not pronounced for any of the doses/drugs studied. On day 5, both doses of BUD caused statistically significant suppression (CCS of 19% for the 400 microg dose and 36% for the 1,000 microg dose). For FP only the high dose had a statistically significant effect on serum cortisol (CCS of 14% for the 200 microg dose and 27% for the 500 microg dose). Compared to BUD, FP has slower pulmonary absorption and slower elimination kinetics. However, following inhalation of therapeutically equipotent, multiple twice-daily doses in healthy subjects, the systemic effects of FP delivered via Diskus on AUC24 serum cortisol were relatively low and similar to those of BUD delivered via Turbohaler.

Evaluation of pulmonary absorption using pharmacokinetic methods

When assessing inhaled drug absorption, standard pharmacokinetic analyses cannot differentiate drug that reaches the systemic circulation from the lungs from that of the gut. Pulmonary absorption kinetics can be assessed for drugs with negligible gastrointestinal absorption or for drugs that are eliminated via first-pass metabolism. For other drugs, pulmonary absorption kinetics can be studied by blocking gastrointestinal absorption with charcoal, or by studying absorption during the first 30 minutes post inhalation before appreciable oral absorption has occurred. Pharmacokinetic data generally agree well with pulmonary deposition data derived by measuring inhaled radiotracer-labelled drug using gamma-scintigraphy. Monitoring pulmonary and oral absorption also provides information on total systemic exposure and therefore safety. Furthermore, the duration of action of different inhaled drugs and the degree of pulmonary targeting can be obtained by determining the corticosteroid occupancy of lung and systemic glucocorticoid receptors. Pharmacokinetic data from healthy volunteers cannot be extrapolated to patients with asthma, as systemic exposure to inhaled drugs can be markedly less in patients than in healthy volunteers. This correlates with the observed differences in side effects in these two groups. Although pharmacokinetic methods do not provide information on regional deposition, they do generate data on systemic and pulmonary exposure, and so play a role in the development of delivery systems.

Pharmacokinetics and pharmacodynamics of dexamethasone sodium-m-sulfobenzoate (DS) after intravenous and intramuscular administration: a comparison with dexamethasone phosphate (DP)

The pharmacokinetics (PK) and pharmacodynamics (effects on blood lymphocytes) of dexamethasone (D) after intravenous (i.v.) administration of dexamethasone phosphate (DP, 10 mg, equivalent to 8.3 mg of dexamethasone) and after intravenous and intramuscular (i.m.) administration of dexamethasone sulfobenzoate sodium (DS, 9.15 mg, equivalent to 6 mg of dexamethasone) were assessed. Only 25% of DS was converted into dexamethasone with a half-life for DS of 5.4 hours and 7.4 hours after i.v. and i.m. administration, respectively. Consequently, the mean residence time of D after both i.m. and i.v. administration of DS (10.4-11.6 h) was longer than that after DP administration (6.1 h). The smaller lymphocyte suppression induced by DS (50% of that after DP administration) was shown to be related to differences in the pharmacokinetics. This study revealed significant differences in the pharmacokinetics of D after administration of DS and DP and stresses the importance of the prodrug for the pharmacological response. Because of the slow and incomplete conversion of DS into dexamethasone, its use in emergency medicine situations should be critically evaluated.

Optimized therapeutic ratio of inhaled corticosteroids using retrometabolism

During recent years, the treatment of pulmonary diseases could be significantly improved due to the introduction of modern retrometabolism-based corticosteroids with improved therapeutic ratio. It is the goal of all inhaled corticosteroids to produce long lasting therapeutic effects at the pulmonary target site and to minimize systemic side effects by rapid clearance of the absorbed drug and low oral bioavailability. The development of PK/PD models allows predictions of drug effects based on the administered dose. For example, the cumulative suppression of endogenous cortisol release (CCS) as one of the major systemic side effects of inhaled corticosteroid therapy can be described with an integrated Emax based PK/PD model. In order to assess the predictive power of this model, a study was conducted to compare the PK/PD-based predictions with CCS data obtained from actual clinical trials for flunisolide, fluticasone propionate, budesonide and triamcinolone acetonide. CCS was predicted for different single doses from different inhaler devices for each drug and a good correlation was observed. Thus, the presented PK/PD model proved to be a valid tool for predicting CCS of inhaled corticosteroids. By fully understanding the underlying mechanisms it will be possible to further improve their therapeutic index.

A sensitive LC-MS/MS method for the quantification of fluticasone propionate in human plasma

A sensitive and selective LC-(APCI) MS/MS method capable of quantifying fluticasone propionate (FP) at levels down to 10 pg ml(-1) in human plasma is reported. The method was validated over a linear range from 10 to 1000 pg ml(-1) using a previously published solid-phase extraction procedure with a 13C3-labeled internal standard. The inter and intra batch precision (coefficient of variation) and accuracy (% bias) of the quality controls samples (20, 25, 50, 100, 200, 500 and 1000 pg ml(-1)) were less than 15 and 11%, respectively. The method is robust, rapid (analysis time of 2 min), selective and hence is ideally suited for pharmacokinetic investigations involving inhalation of therapeutic doses of FP.

Mechanism-based PK/PD model for the lymphocytopenia induced by endogenous and exogenous corticosteroids

OBJECTIVE

Lymphocytopenia is a sensitive surrogate marker for the immunological effects of corticosteroids. This pharmacokinetic/pharmacodynamic (PK/PD) study investigated whether the circadian variation of blood lymphocytes observed after placebo is secondary to the circadian rhythm of endogenous cortisol, and developed based on this relationship an improved PK/PD model for a more sensitive description of the effect of low-dose corticosteroid therapy on blood lymphocytes considering the net activity of the exogenous corticosteroid budesonide and endogenous cortisol.

METHODS

In an open, parallel study design, 3 mg oral budesonide or placebo were given at 8.00 a.m., 4.00 p.m. and midnight to two groups of 12 volunteers. Lymphocyte counts and serum concentrations of budesonide and cortisol were monitored for 24 hours. A mechanism-based PK/PD model which considered the non-linear protein binding of cortisol and the budesonide-induced cortisol suppression was employed to relate changes in blood lymphocytes to free cortisol levels after placebo and to the net activity of free budesonide and free endogenous cortisol after active treatment.

RESULTS

The circadian rhythm of blood lymphocytes observed after placebo could inversely be related to the circadian rhythm of serum cortisol. After budesonide administration, lymphocyte counts could accurately be linked to the net activity of budesonide and endogenous cortisol. The resulting EC50 values for the effect of budesonide on cortisol, budesonide on lymphocytes and cortisol on lymphocytes were 0.063 +/- 0.034, 0.22 +/- 0.13 and 26.3 +/- 15.0 ng/ml (placebo group 15.4 +/- 3.4 ng/ml), respectively.

CONCLUSIONS

The presented mechanism-based PK/PD model suggests that blood lymphocytes are under physiological control of cortisol. It further indicates that endogenous and exogenous corticosteroids and their pharmacological interaction need to be considered for modeling the effects of low doses of exogenous corticosteroids on the immune system.

A pharmacokinetic/pharmacodynamic approach to predict the cumulative cortisol suppression of inhaled corticosteroids

The suppression of endogenous cortisol release is one of the major systemic side effects of inhaled corticosteroids in the treatment of asthma. The circadian rhythm of the endogenous cortisol release and the resulting plasma concentrations as well as the release suppression during corticosteroid therapy could previously be described with an integrated PK/PD model. Based on this model, a PK/PD approach was developed to quantify and predict the cumulative cortisol suppression (CCS) as a surrogate marker for the systemic activity of inhaled corticosteroid therapy. The presented method was applied to predict CCS after single doses and during short-term multiple dosing of the inhaled corticosteroids flunisolide (FLU), fluticasone propionate (FP), and triamcinolone acetonide (TCA), and after oral methylprednisolone as systemic reference therapy. Drug-specific PK and PD parameters were obtained from previous single-dose studies and extrapolated to the multiple-dose situation. For single dosing, a similar CCS within the range of 16-21% was predicted for FP 250 micrograms, FLU 500 micrograms, and TCA 1000 micrograms. For multiple dosing, a respective CCS of 28-33% was calculated for FLU 500 micrograms bid, FP 250 micrograms, bid, and TCA 1000 micrograms bid. Higher cortisol suppression compared to these single and multiple dosing regimens of the inhaled corticosteroids was predicted after oral doses of only 1 mg and 2 mg methylprednisolone, respectively. The predictive power of the approach was evaluated by comparing the PK/PD-based simulations with data reported previously in clinical studies. The predicted CCS values were in good correlation with the clinically observed results. Hence, the presented PK/PD approach allows valid predictions of CCS for single and short-term multiple dosing of inhaled corticosteroids and facilitates comparisons between different dosing regimens and steroids.