Comparative assessment of coronary physiology using transthoracic pulsed-wave Doppler and myocardial contrast echocardiography in rats.

BACKGROUND: Coronary physiology assessment in rodents by ultrasound is an excellent noninvasive and easy to perform technique, including pulsed-wave Doppler (PWD) and myocardial contrast echocardiography (MCE). Both techniques and the corresponding calculated parameters were investigated in this study at rest as well as their response to pharmacologically induced stress. METHODS: Left ventricular myocardial function was assessed in eight anaesthetised rats using transthoracic echocardiography. Coronary physiology was assessed by both PWD of the left coronary artery and MCE using a bolus method. Measurements were performed at rest and under stimulation with adenosine and dobutamine. Effects of stimulation on the calculated parameters were evaluated and rated by effect size (η2). RESULTS: Changes could be demonstrated by selected parameters of PWD and MCE. The clearest effect in PWD was found for diastolic peak velocity (η2 = 0.58). It increased from 528 ± 110 mm/s (mean ± standard deviation) at rest to 839 ± 342 mm/s (p = 0.001) with adenosine and 1093 ± 302 mm/s with dobutamine (p = 0.001). The most distinct effect from MCE was found for the normalised wash-in rate (η2 = 0.58). It increased from 1.95 ± 0.35% at rest to 3.87 ± 0.85% with adenosine (p = 0.001) and 3.72 ± 1.03% with dobutamine (p = 0.001). CONCLUSION: Induced changes in coronary physiology by adenosine and dobutamine could successfully be monitored using MCE and PWD in anaesthetised rats. Due to the low invasiveness of the measurements, this protocol could be used for longitudinal animal studies.

Accumbal adenosine A2A receptor inactivation biases for large and costly rewards in the effort- but not delay-based decision making.

The cost-benefit decision-making (CBDM) is critical to normal human activity and a diminished willingness to expend effort to obtain rewards is a prevalent/noted characteristic of neuropsychiatric disorders such as schizophrenia, Parkinson's disease. Numerous studies have identified nucleus accumbens (NAc) as an important locus for CBDM control but their neuromodulatory and behavioral mechanisms remain largely under-explored. Adenosine A2A receptors (A2ARs), which are highly concentrated in the striatopallidal neurons, can integrate glutamate and dopamine signals for controlling effort-related choice behaviors. While the involvement of A2ARs in effort-based decision making is well documented, the role of other decision variables (reward discrimination) in effort-based decision making and the role of A2AR in delay-based decision making are less clear. In this study, we have developed a well-controlled CBDM behavioral paradigm to manipulate effort/cost and reward independently or in combination, allowing a dissection of four behavioral elements: effort-based CBDM (E-CBDM), delay-based CBDM (D-CBDM), reward discrimination (RD), effort discrimination (ED), and determined the effect of genetic knockdown (KD) of NAc A2AR on the four behavioral elements. We found that A2AR KD in NAc increased the choice for larger, more costly reward in the E-CBDM, but not D-CBDM. Furthermore, this high-effort/high-reward bias was attributable to the increased willingness to engage in effort but not the effect of discrimination of reward magnitude. Our findings substantiate an important role of the NAc A2AR in control of E-CBDM and support that pharmacologically targeting NAc A2ARs would be a useful strategy for treating the aberrant effort-based decision making in neuropsychiatric disorders.

Non-Invasive Assessment of Locally Overexpressed Human Adenosine 2A Receptors in the Heart of Transgenic Mice.

A2A adenosine receptors (A2A-AR) have a cardio-protective function upon ischemia and reperfusion, but on the other hand, their stimulation could lead to arrhythmias. Our aim was to investigate the potential use of the PET radiotracer [18F]FLUDA to non-invasively determine the A2A-AR availability for diagnosis of the A2AR status. Therefore, we compared mice with cardiomyocyte-specific overexpression of the human A2A-AR (A2A-AR TG) with the respective wild type (WT). We determined: (1) the functional impact of the selective A2AR ligand FLUDA on the contractile function of atrial mouse samples, (2) the binding parameters (Bmax and KD) of [18F]FLUDA on mouse and human atrial tissue samples by autoradiographic studies, and (3) investigated the in vivo uptake of the radiotracer by dynamic PET imaging in A2A-AR TG and WT. After A2A-AR stimulation by the A2A-AR agonist CGS 21680 in isolated atrial preparations, antagonistic effects of FLUDA were found in A2A-AR-TG animals but not in WT. Radiolabelled [18F]FLUDA exhibited a KD of 5.9 ± 1.6 nM and a Bmax of 455 ± 78 fmol/mg protein in cardiac samples of A2A-AR TG, whereas in WT, as well as in human atrial preparations, only low specific binding was found. Dynamic PET studies revealed a significantly higher initial uptake of [18F]FLUDA into the myocardium of A2A-AR TG compared to WT. The hA2A-AR-specific binding of [18F]FLUDA in vivo was verified by pre-administration of the highly affine A2AAR-specific antagonist istradefylline. Conclusion: [18F]FLUDA is a promising PET probe for the non-invasive assessment of the A2A-AR as a marker for pathologies linked to an increased A2A-AR density in the heart, as shown in patients with heart failure.

High dose escalation of intracoronary adenosine in the assessment of fractional flow reserve: A retrospective cohort study.

Maximal hyperaemia for fractional flow reserve (FFR) may not be achieved with the current recommended doses of intracoronary adenosine. Higher doses (up to 720 µg) have been reported to optimize hyperaemic stimuli in small dose-response studies. Real-world data from a large cohort of patients is needed to evaluate FFR results and the safety of high-dose escalation. This is a retrospective study aimed to evaluate the safety and frequency of FFR ≤0.8 after high-dose escalation of intracoronary adenosine. Data were extracted from the medical databases of two university hospitals. Increasing doses (100, 200, 400, 600, and 800 µg) of adenosine were administered as intracoronary boluses until FFR ≤0.8 was achieved or heart block developed. The percentage of FFR ≤0.8 after higher-dose escalation was compared with those at conventional doses, and the predictors for FFR ≤0.8 after higher doses were analysed. In the 1163 vessels of 878 patients, 402 vessels (34.6%) achieved FFR ≤0.8 at conventional doses and 623 vessels (53.6%) received high-dose escalation. An additional 84 vessels (13.5%) achieved FFR ≤0.8 after high-dose escalation. No major complications developed during high-dose escalation. Borderline FFR (0.81-0.85) at the conventional dose, stenosis >60%, and triple-vessel disease increased the likelihood of FFR ≤0.8 after high-dose escalation, but chronic kidney disease decreased it. For vessels of borderline FFR at conventional doses, 46% achieved FFR ≤0.8 after high-dose escalation. In conclusion, High-dose escalation of intracoronary adenosine increases the frequency of FFR ≤0.8 without major complications. It could be especially feasible for borderline FFR values near the 0.8 diagnostic threshold.

Clinical assessment of adenosine stress and rest cardiac magnetic resonance T1 mapping for detecting ischemic and infarcted myocardium.

Cardiac magnetic resonance (CMR) spin-lattice relaxation time (T1) may be influenced by pathologic conditions due to changes in myocardial water content. We aimed to validate the principle and investigate T1 mapping at rest and adenosine stress to differentiate ischemic and infarcted myocardium from controls. Patients with suspected coronary artery disease who underwent CMR were prospectively recruited. Native rest and adenosine stress T1 maps were obtained using standard modified Look-Locker Inversion-Recovery technique. Among 181 patients included, T1 values were measured from three groups. In the control group, 72 patients showed myocardium with a T1 profile of 1,039 ± 75 ms at rest and a significant increase during stress (4.79 ± 3.14%, p < 0.001). While the ischemic (51 patients) and infarcted (58 patients) groups showed elevated resting T1 compared to controls (1,040 ± 90 ms for ischemic; 1,239 ± 121 ms for infarcted, p < 0.001), neither of which presented significant T1 reactivity (1.38 ± 3.02% for ischemic; 1.55 ± 5.25% for infarcted). We concluded that adenosine stress and rest T1 mapping may be useful to differentiate normal, ischemic and infarcted myocardium.

An intact animal model for the assessment of coronary blood flow regulation "Coronary blood flow regulation".

Coronary blood flow adapts to metabolic demand ("metabolic regulation") and remains relatively constant over a range of pressure changes ("autoregulation"). Coronary metabolic regulation and autoregulation are usually studied separately. We developed an intact animal experimental model to explore both regulatory mechanisms of coronary blood flow. Coronary pressure and flow-velocities were measured in four anesthetized and closed-chest pigs using an intracoronary Doppler wire. Metabolic regulation was assessed by coronary flow reserve defined as the ratio between the maximally vasodilated and the basal flow, with hyperemia achieved using intracoronary administration of adenosine (90 µg) or bradykinin (10-6  M) as endothelium-independent and -dependent vasodilators respectively. For both vasodilators, we found a healthy coronary flow reserve ≥ 3.0 at baseline, which was maintained at 2.9 ± 0.2 after a 6-hr period. Autoregulation was assessed by the lower breakpoint of coronary pressure-flow relationships, with gradual decrease in coronary pressure through the inflation of an intracoronary balloon. We found a lower limit of autoregulation between 42 and 55 mmHg, which was stable during a 6-hr period. We conclude that this intact animal model is adequate for the study of pharmacological interventions on the coronary circulation in health and disease, and as such suitable for preclinical drug studies.

Methodical Challenges and a Possible Resolution in the Assessment of Receptor Reserve for Adenosine, an Agonist with Short Half-Life.

The term receptor reserve, first introduced and used in the traditional receptor theory, is an integrative measure of response-inducing ability of the interaction between an agonist and a receptor system (consisting of a receptor and its downstream signaling). The underlying phenomenon, i.e., stimulation of a submaximal fraction of receptors can apparently elicit the maximal effect (in certain cases), provides an opportunity to assess the receptor reserve. However, determining receptor reserve is challenging for agonists with short half-lives, such as adenosine. Although adenosine metabolism can be inhibited several ways (in order to prevent the rapid elimination of adenosine administered to construct concentration-effect (E/c) curves for the determination), the consequent accumulation of endogenous adenosine biases the results. To address this problem, we previously proposed a method, by means of which this bias can be mathematically corrected (utilizing a traditional receptor theory-independent approach). In the present investigation, we have offered in silico validation of this method by simulating E/c curves with the use of the operational model of agonism and then by evaluating them using our method. We have found that our method is suitable to reliably assess the receptor reserve for adenosine in our recently published experimental setting, suggesting that it may be capable for a qualitative determination of receptor reserve for rapidly eliminating agonists in general. In addition, we have disclosed a possible interference between FSCPX (8-cyclopentyl-N³-[3-(4-(fluorosulfonyl)benzoyloxy)propyl]-N¹-propylxanthine), an irreversible A1 adenosine receptor antagonist, and NBTI (S-(2-hydroxy-5-nitrobenzyl)-6-thioinosine), a nucleoside transport inhibitor, i.e., FSCPX may blunt the effect of NBTI.

In vivo assessment of coronary flow and cardiac function after bolus adenosine injection in adenosine receptor knockout mice.

Bolus injections of adenosine and the A2A adenosine receptor (AR) selective agonist (regadenoson) are used clinically as a substitute for a stress test in people who cannot exercise. Using isolated tissue preparations, our lab has shown that coronary flow and cardiac effects of adenosine are mostly regulated by the AR subtypes A1, A2A, and A2B In this study, we used ultrasound imaging to measure the in vivo effects of adenosine on coronary blood flow (left coronary artery) and cardiac function in anesthetized wild-type, A1 knockout (KO), A2AKO, A2BKO, A3KO, A1, and A3 double KO (A1/3 DKO) and A2A and A2B double KO (A2A/2B DKO) mice in real time. Echocardiographic and Doppler studies were performed using a Visualsonic Vevo 2100 ultrasound system. Coronary blood flow (CBF) baseline data were obtained when animals were anesthetized with 1% isoflourane. Diameter (D) and velocity time integral (VTI) were measured on the left coronary arteries (CBF = ((π/4) × D(2) × VTI × HR)/1000). CBF changes were the highest within 2 min of injection (about 10 mg/kg). Heart rate, cardiac output, and stroke volume were measured by tracing the left ventricle long axis. Our data support a role for the A2 AR in CBF and further support our conclusions of previous studies from isolated tissues. Adenosine-mediated decreases in cardiac output and stroke volume may be A2B and/or A3 AR-mediated; however, the A1 and A2 ARs also play roles in overall cardiac function. These data further provide a powerful translational tool in studying the cardiovascular effects of adenosine in disease states.

Assessment of Coronary Flow Reserve by Adenosine Stress Myocardial Perfusion Imaging in Patients with Hypertension.

In this study, our aim was to assess the coronary flow reserve (CFR) by performing the adenosine stress (99m)Tc-MIBI single-photon computed tomographic (SPECT) myocardial perfusion imaging in patients with hypertension. 47 hypertensive patients with normal coronary angiography were divided into 2 groups, defined by the presence (LVH, n = 22) and absence (non-LVH, n = 25) of left ventricular hypertrophy with 17 normal cases as controls. All patients were administered the adenosine stress-rest (99m)Tc-MIBI scintigraphy. 0.14 mg/kg/min adenosine was administered by continuous infusion for 6 min. We found that adenosine-induced myocardial ischemia was present in 26 cases (55.3 %) with 87 segments (20.6 %) showing abnormal distribution in the hypertensive group versus a single case (5.9 %) (χ (2) = 31.12, P < 0.001) and segment (0.7 %) (χ (2) = 32.90, P < 0.001) in the control group by SPECT perfusion. In the LVH group, 17 cases (77.3 %) and 67 segments (33.8 %) of myocardial ischemia were present. In the non-LVH group, there were 9 cases (36.0 %) (χ (2) = 8.06, P < 0.001), 20 segments (8.9 %) (χ (2) = 40.13, P < 0.001). There was a significant decrease in coronary reserve in the hypertensive groups following adenosine infusion with a fourfold decrease in cases and a sixfold decrease in segments (P < 0.001). Our study suggests that assessing CFR by the (99m)Tc-MIBI adenosine stress by SPECT imaging is a relatively easy, safe, and non-invasive test in patients with hypertension. We noted a decrease in CFR in patients with hypertension. This decrease was especially remarkable for hypertensive patients with LVH. This study shows that administering the (99m)Tc-MIBI adenosine stress by SPECT imaging is a safe, simple, and non-invasive test for detecting CFR in patients with hypertension.

Noninvasive Assessment of Atrioventricular Nodal Function: Effect of Rate-Control Drugs during Atrial Fibrillation.

BACKGROUND: During atrial fibrillation (AF), conventional electrophysiological techniques for assessment of refractory period or conduction velocity of the atrioventricular (AV) node cannot be used. We aimed at evaluating changes in AV nodal properties during administration of tecadenoson and esmolol using a novel ECG-based method. METHODS: Fourteen patients (age 58 ± 8 years, 10 men) with AF were randomly assigned to either 75 or 300 µg intravenous tecadenoson. After tecadenoson wash-out, patients received esmolol continuously (100 µg/kg per min for 10 mins, then 50 µg/kg per min for 50 mins). Atrial fibrillatory rate (AFR) and heart rate (HR) were assessed in 15-min segments. Using the novel method, we assessed the absolute refractory periods of the slow and fast pathways (aRPs and aRPf) of the AV node to produce an estimate of the functional refractory period. RESULTS: During esmolol infusion, AFR and HR were significantly decreased and the absolute refractory period was significantly prolonged in both pathways (aRPs: 387 ± 73 vs 409 ± 62 ms, P < 0.05; aRPf: 490 ± 80 vs 529 ± 58 ms, P < 0.05). During both tecadenoson doses, HR decreased significantly and AFR was unchanged. Both aRPs and aRPf were prolonged for a 75 µg dose (aRPs: 322 ± 97 vs 476 ± 75 ms, P < 0.05; aRPf: 456 ± 102 vs 512 ± 55 ms, P < 0.05) whereas a trend toward prolongation was observed for a 300 µg dose. CONCLUSIONS: The estimated parameters reflect expected changes in AV nodal properties, i.e., slower conduction through the AV node for tecadenoson and prolongation of the AV node refractory period for esmolol. Thus, the proposed approach may be used to assess drug effects on the AV node in AF patients.

Assessment of myocardial reactivity to controlled hypercapnia with free-breathing T2-prepared cardiac blood oxygen level-dependent MR imaging.

PURPOSE: To examine whether controlled and tolerable levels of hypercapnia may be an alternative to adenosine, a routinely used coronary vasodilator, in healthy human subjects and animals. MATERIALS AND METHODS: Human studies were approved by the institutional review board and were HIPAA compliant. Eighteen subjects had end-tidal partial pressure of carbon dioxide (PetCO2) increased by 10 mm Hg, and myocardial perfusion was monitored with myocardial blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging. Animal studies were approved by the institutional animal care and use committee. Anesthetized canines with (n = 7) and without (n = 7) induced stenosis of the left anterior descending artery (LAD) underwent vasodilator challenges with hypercapnia and adenosine. LAD coronary blood flow velocity and free-breathing myocardial BOLD MR responses were measured at each intervention. Appropriate statistical tests were performed to evaluate measured quantitative changes in all parameters of interest in response to changes in partial pressure of carbon dioxide. RESULTS: Changes in myocardial BOLD MR signal were equivalent to reported changes with adenosine (11.2% ± 10.6 [hypercapnia, 10 mm Hg] vs 12% ± 12.3 [adenosine]; P = .75). In intact canines, there was a sigmoidal relationship between BOLD MR response and PetCO2 with most of the response occurring over a 10 mm Hg span. BOLD MR (17% ± 14 [hypercapnia] vs 14% ± 24 [adenosine]; P = .80) and coronary blood flow velocity (21% ± 16 [hypercapnia] vs 26% ± 27 [adenosine]; P > .99) responses were similar to that of adenosine infusion. BOLD MR signal changes in canines with LAD stenosis during hypercapnia and adenosine infusion were not different (1% ± 4 [hypercapnia] vs 6% ± 4 [adenosine]; P = .12). CONCLUSION: Free-breathing T2-prepared myocardial BOLD MR imaging showed that hypercapnia of 10 mm Hg may provide a cardiac hyperemic stimulus similar to adenosine.

Hemodynamic response to intravenous adenosine and its effect on fractional flow reserve assessment: results of the Adenosine for the Functional Evaluation of Coronary Stenosis Severity (AFFECTS) study.

BACKGROUND: We studied the hemodynamic response to intravenous adenosine on calculation of fractional flow reserve (FFR). Intravenous adenosine is widely used to achieve conditions of stable hyperemia for measurement of FFR. However, intravenous adenosine affects both systemic and coronary vascular beds differentially. METHODS AND RESULTS: A total of 283 patients (310 coronary stenoses) underwent coronary angiography with FFR using intravenous adenosine 140 mcg/kg per minute via a central femoral vein. Offline analysis was performed to calculate aortic (Pa), distal intracoronary (Pd), and reservoir (Pr) pressure at baseline, peak, and stable hyperemia. Seven different hemodynamic patterns were observed according to Pa and Pd change at peak and stable hyperemia. The average time from baseline to stable hyperemia was 68.2±38.5 seconds, when both ΔPa and ΔPd were decreased (ΔPa, -10.2±10.5 mm Hg; ΔPd, -18.2±10.8 mm Hg; P<0.001 for both). The fall in Pa closely correlated with the reduction in peripheral Pr (ΔPr, -12.9±15.7 mm Hg; P<0.001; r=0.9; P<0.001). ΔPa and ΔPd were closely related under conditions of peak (r=0.75; P<0.001) and stable hyperemia (r=0.83; P<0.001). On average, 56% (10.2 mm Hg) of the reduction in Pd was because of fall in Pa. FFR lesion classification changed in 9% using an FFR threshold of ≤0.80 and 5.2% with FFR threshold <0.75 when comparing Pd/Pa at peak and stable hyperemia. CONCLUSIONS: Intravenous adenosine results in variable changes in systemic blood pressure, which can lead to alterations in FFR lesion classification. Attention is required to ensure FFR is measured under conditions of stable hyperemia, although the FFR value at this point may be numerically higher.

In vivo assessment of the impact of efflux transporter on oral drug absorption using portal vein-cannulated rats.

The purpose of this study was to evaluate the impact of intestinal efflux transporters on the in vivo oral absorption process. Three model drugs-fexofenadine (FEX), sulfasalazine (SASP), and topotecan (TPT)-were selected as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and P-gp and BCRP substrates, respectively. The drugs were orally administered to portal vein-cannulated rats after pretreatment with zosuquidar (ZSQ), P-gp inhibitor, and/or Ko143, BCRP inhibitor. Intestinal availability (Fa·Fg) of the drugs was calculated from the difference between portal and systemic plasma concentrations. When rats were orally pretreated with ZSQ, Fa·Fg of FEX increased 4-fold and systemic clearance decreased to 75% of the control. In contrast, intravenous pretreatment with ZSQ did not affect Fa·Fg of FEX, although systemic clearance decreased significantly. These data clearly show that the method presented herein using portal vein-cannulated rats can evaluate the effects of intestinal transporters on Fa·Fg of drugs independently of variable systemic clearance. In addition, it was revealed that 71% of FEX taken up into enterocytes underwent selective efflux via P-gp to the apical surface, while 79% of SASP was effluxed by Bcrp. In the case of TPT, both transporters were involved in its oral absorption. Quantitative analysis indicated a 3.5-fold higher contribution from Bcrp than P-gp. In conclusion, the use of portal vein-cannulated rats enabled the assessment of the impact of efflux transporters on intestinal absorption of model drugs. This experimental system is useful for clarifying the cause of low bioavailability of various drugs.

Comparative assessment of rest and post-stress left ventricular volumes and left ventricular ejection fraction on gated myocardial perfusion imaging (MPI) and echocardiography in patients with transient ischaemic dilation on adenosine MPI: myocardial stunning or subendocardial hypoperfusion?

BACKGROUND: Transient ischaemic dilation (TID) on myocardial perfusion imaging (MPI) is an important finding, conveying a high risk of subsequent cardiac events. However, the mechanism leading to TID on MPI is not well elucidated. This study aimed to determine if TID is due to true LV cavity dilation and ventricular stunning, or is due to relative subendocardial hypoperfusion. METHODS: 31 patients undergoing single-day Tc-99m adenosine sestamibi MPI were recruited. All had routine ECG-gated single-day rest-stress adenosine MPI, with transthoracic echocardiograms (echo) acquired concurrently at rest, and both immediately, and 2 hours, post-stress. Echocardiography was performed using a Vivid-7 (GE). LV volumes and LVEF were quantified blinded to MPI results, using biplane Simpson method on echo, and quantitatively (including TID) with QGS(®), on MPI. RESULTS: Patients were divided into quartiles for TID, with the top quartile considered TID positive [TID+ 9/31 (TID ratio 1.3 ± 0.09)], and TID negative [TID- 22/31 (TID ratio 1.01 ± 0.04)]. There was good correlation between resting echo and MPI physical measurements (LVEDV r(2) = 0.79, LVESV r(2) = 0.9, and LVEF r(2) = 0.75). On MPI, a significant drop in LVEF was observed between rest and early stress in the TID+ group (56.6% vs 46.5%, P < .002), as well as an increase in both LVESV (62 vs 79 mls, P < .0001) and LVEDV (113 vs 131 mls, P < .0001). However, no statistically significant change in LVEF, LVESV or LVEDV was identified on concurrent echo imaging (LVEF 57% vs 56%, P < .66; LVESV 48 vs 54 mls, P < .26; LVEDV 87 vs 97 mls, P < .299). No significant change in LVEF or ventricular volumes was noted in the TID- group by either echo or MPI. CONCLUSION: Transient dilation of the left ventricle on adenosine MPI is not related to chamber enlargement and myocardial stunning, but is more likely a function of subendocardial hypoperfusion and impaired coronary flow reserve.

Optimization of adenosine 5'-carboxamide derivatives as adenosine receptor agonists using structure-based ligand design and fragment screening.

Structures of G protein-coupled receptors (GPCRs) have a proven utility in the discovery of new antagonists and inverse agonists modulating signaling of this important family of clinical targets. Applicability of active-state GPCR structures to virtual screening and rational optimization of agonists, however, remains to be assessed. In this study of adenosine 5' derivatives, we evaluated the performance of an agonist-bound A(2A) adenosine receptor (AR) structure in retrieval of known agonists and then employed the structure to screen for new fragments optimally fitting the corresponding subpocket. Biochemical and functional assays demonstrate high affinity of new derivatives that include polar heterocycles. The binding models also explain modest selectivity gain for some substituents toward the closely related A(1)AR subtype and the modified agonist efficacy of some of these ligands. The study suggests further applicability of in silico fragment screening to rational lead optimization in GPCRs.

Ticagrelor: oral reversible P2Y(12) receptor antagonist for the management of acute coronary syndromes.

BACKGROUND: The clinical benefits of dual antiplatelet treatment (aspirin + clopidogrel) in the management of acute coronary syndromes (ACS) are well established. However, clopidogrel is a prodrug that requires hepatic activation. Concerns regarding its delayed onset of action, variability in antiplatelet effects, and prolonged recovery of platelet function after discontinuation have prompted the development of P2Y(12) receptor antagonists. Ticagrelor is the most recently developed P2Y(12) receptor antagonist available in the United States. Ticagrelor is a nonthienopyridine antiplatelet agent and is the first reversible oral antagonist of the P2Y(12) receptors. OBJECTIVE: This article reviews the pharmacology, clinical efficacy, and tolerability of ticagrelor use in management of ACS. METHODS: Peer-reviewed clinical trials, review articles, and relevant treatment guidelines published from 1966 to March 15, 2012, were identified from the MEDLINE and Current Content databases using the search terms ticagrelor, ACS, pharmacokinetics, pharmacodynamics, pharmacoeconomics, and cost-effectiveness. Citations from available articles were also reviewed for additional references. RESULTS: Nine pharmacokinetics/pharmacodynamics studies in humans and 1 clinical study were identified. In addition, the findings from 6 subanalyses based on the clinical study were included. Compared with clopidogrel, ticagrelor was associated with a significantly reduced composite rate of death from cardiovascular causes, myocardial infarction, or stroke (ticagrelor, 9.8%; clopidogrel, 11.7%; hazard ratio [HR] = 0.84; 95% CI, 0.77-0.92; P < 0.001). The difference in the rates of major bleeding was not significant (ticagrelor, 11.6%; clopidogrel, 11.2%). Ticagrelor was associated with a higher rate of non-coronary artery bypass graft surgery related major bleeding (4.5% vs 3.8%; P = 0.03), including fatal intracranial bleeding (0.1% vs 0.01%; P = 0.02), and fewer cases of other types of fatal bleeding (0.1% vs 0.3%; P = 0.03). Other adverse events reported with ticagrelor use included dyspnea (13.8%), headache (6.5%), and bradyarrhythmia (5.8%). The effects of ticagrelor have not been compared to those of other antiplatelet agents, including prasugrel. CONCLUSIONS: Based on the findings from the present review, ticagrelor provides reversible inhibition of adenosine diphosphate-induced platelet aggregation, with a faster onset of action than clopidogrel, and is effective in the treatment of patients with ACS. More data are required to definitively position ticagrelor with respect to other antiplatelet agents, including prasugrel.

Assessment and modulation of forsythiaside absorption with MDCKII cells and validation with in situ intestinal experiment.

Forsythiaside was characterized by low intestinal absorption by in situ rat experiment and Caco-2 cells. The mechanisms behind this low absorption had not yet been elucidated. The purpose of this study was to investigate the role of efflux transporters in the intestinal absorption of forsythiaside as a potential mechanism for its low small-intestinal absorption following oral administration. Polarized MDCKII cell lines stably transfected with human or murine complementary DNA encoding for various efflux transporters (P-gp/MDR1, MRP2 and Bcrp1) were used to study transepithelial transport of forsythiaside and compare results with the MDCKII-Wild type cells. The transportation inhibitors GF120918, MK571 and Ko143 were used to investigate the transport mechanism. The active transport of forsythiaside was found in MDCKII-WT cells. The MDCKII-MRP2 and MDCKII-Bcrp1 cells significantly increased forsythiaside efflux ratio compared with the parental cells due to the apically directed transport by MRP2 and Bcrp1, respectively. The efflux ratios in MRP2 and Bcrp1 transfected cell lines were greatly decreased in the presence of MK-571 and Ko143, respectively, which indicated that forsythiaside efflux by MRP2 and Bcrp1 were significantly inhibited by their selective inhibitors. MDCKII-MDR1 cells did not exhibit a significant reduction in the forsythiaside efflux compared with the parental cells, indicating that it was not a good substrate for MDR1. And the results were then validated by the in situ experiment. This study presents direct evidence that forsythiaside is effluxed by both MRP2 and Bcrp1, which may contribute to its poor oral bioavailability.