Effect of caffeine on SPECT myocardial perfusion imaging during regadenoson pharmacologic stress: rationale and design of a prospective, randomized, multicenter study

The belated US FDA approval of the adenosine A2A receptor antagonist istradefylline for treatment of Parkinson's disease

After more than two decades of preclinical and clinical studies, on August 27, 2019, the US Food and Drug Administration (FDA) approved the adenosine A_2A receptor antagonist Nourianz® (istradefylline) developed by Kyowa Hakko Kirin Inc., Japan, as an add-on treatment to levodopa in Parkinson's disease (PD) with "OFF" episodes. This milestone achievement is the culmination of the decade-long clinical studies of the effects of istradefylline in more than 4000 PD patients. Istradefylline is the first non-dopaminergic drug approved by FDA for PD in the last two decades. This approval also provides some important lessons to be remembered, namely, concerning disease-specific adenosine signaling and targeting subpopulation of PD patients. Importantly, this approval paves the way to foster entirely novel therapeutic opportunities for adenosine A_2A receptor antagonists, such as neuroprotection or reversal of mood and cognitive deficits in PD and other neuropsychiatric diseases.

Effect of caffeine on SPECT myocardial perfusion imaging during regadenoson pharmacologic stress: a prospective, randomized, multicenter study

A multicenter, double-blind, randomized study was conducted to assess the effect of caffeine on regadenoson stress myocardial perfusion imaging (MPI). Subjects with a high likelihood of coronary artery disease underwent a rest single-photon emission computed tomography MPI on day 1 (MPI-1) and a stress MPI with regadenoson on day 3 (MPI-2). Individuals with ≥1 segment with a reversible defect received double-blind caffeine tablets (200 or 400 mg) or placebo 90 min before a repeat regadenoson stress MPI (MPI-3) on day 5. Overall, 207 subjects completed the study (caffeine 200 mg, n = 70; caffeine 400 mg, n = 71; placebo, n = 66). The mean number of segments with reversible defects decreased from MPI-2 to MPI-3 in the caffeine 200 and 400 mg groups versus no significant change in the placebo group [mean ± standard deviation: -0.61 ± 1.097, -0.62 ± 1.367, and 0.12 ± 0.981, respectively (overall treatment effect, P < 0.001)]. The majority of subjects who received caffeine shifted to a lower ischemia size category from MPI-2 to MPI-3, with no clear pattern observed in subjects who received placebo. For caffeine exposed patients with ≥3 segments with reversible defects at MPI-2, 21/23 had fewer detected at MPI-3. Both the 200 and 400 mg doses of caffeine significantly reduced the number of segments with reversible defects detected by regadenoson stress MPI.

Regadenoson: review of its established role in myocardial perfusion imaging and emerging applications

Myocardial perfusion imaging is a well-established noninvasive modality for the diagnosis and prognosis of coronary artery disease. The pharmacologic stress agents adenosine and dipyridamole are widely used in imaging studies, but cause undesirable side effects, like atrioventricular block and bronchospasm, due to their nonselective adenosine receptor activation. Furthermore, the mode of administration of these agents as a bolus infusion is less preferred. Regadenoson, an A2A adenosine receptor selective pharmacologic stress agent was approved in 2008 and is widely used instead of adenosine and dipyridamole. This article reviews regadenosons structure, mechanism of action, advantages over adenosine and dipyridamole, and its role in various patient populations undergoing stress perfusion imaging. Emerging applications where regadenoson could be of potential use are also explored.

Adenosine receptors as drug targets--what are the challenges?

Adenosine signalling has long been a target for drug development, with adenosine itself or its derivatives being used clinically since the 1940s. In addition, methylxanthines such as caffeine have profound biological effects as antagonists at adenosine receptors. Moreover, drugs such as dipyridamole and methotrexate act by enhancing the activation of adenosine receptors. There is strong evidence that adenosine has a functional role in many diseases, and several pharmacological compounds specifically targeting individual adenosine receptors--either directly or indirectly--have now entered the clinic. However, only one adenosine receptor-specific agent--the adenosine A2A receptor agonist regadenoson (Lexiscan; Astellas Pharma)--has so far gained approval from the US Food and Drug Administration (FDA). Here, we focus on the biology of adenosine signalling to identify hurdles in the development of additional pharmacological compounds targeting adenosine receptors and discuss strategies to overcome these challenges.

Effect of caffeine on adenosine-induced reversible perfusion defects assessed by automated analysis

OBJECTIVES

This prospective study investigated the effects of caffeine ingestion on the extent of adenosine-induced perfusion abnormalities during myocardial perfusion imaging (MPI).

METHODS

Thirty patients with inducible perfusion abnormalities on standard (caffeineabstinent) adenosine MPI underwent repeat testing with supplementary coffee intake. Baseline and test MPIs were assessed for stress percent defect, rest percent defect, and percent defect reversibility. Plasma levels of caffeine and metabolites were assessed on both occasions and correlated with MPI findings.

RESULTS

Despite significant increases in caffeine [mean difference 3,106 μg/L (95% CI 2,460 to 3,752 μg/L; P < .001)] and metabolite concentrations over a wide range, there was no statistically significant change in stress percent defect and percent defect reversibility between the baseline and test scans. The increase in caffeine concentration between the baseline and the test phases did not affect percent defect reversibility (average change -0.003 for every 100 μg/L increase; 95% CI -0.17 to 0.16; P = .97).

CONCLUSION

There was no significant relationship between the extent of adenosine-induced coronary flow heterogeneity and the serum concentration of caffeine or its principal metabolites. Hence, the stringent requirements for prolonged abstinence from caffeine before adenosine MPI - based on limited studies - appear ill-founded.

Selective action of metoprolol to attenuate regadenoson-induced tachycardia in conscious dogs

BACKGROUND

Regadenoson is a coronary vasodilator that causes tachycardia via activation of the sympathetic nervous system. We determined whether β(1)-adrenergic blockade can attenuate tachycardia without significantly reducing coronary vasodilation induced by regadenoson.

METHODS AND RESULTS

Hemodynamics and coronary blood flow (CBF) were measured in conscious dogs. Baseline CBF and heart rate (HR) were 42 ± 2 mL/min and 87 ± 8 bpm (mean ± SEM), respectively. Regadenoson (1, 2.5, and 5 μg/kg) increased peak CBF by 129 ± 10, 149 ± 7, and 174 ± 10 mL/min and HR by 48 ± 6, 67 ± 5, and 85 ± 11 bpm, respectively, (all P < .05 vs baseline). In the presence of metoprolol (1.5 mg/kg), the peak increases in CBF caused by these three doses of regadenoson were reduced by only 11 ± 7%, 10 ± 4%, and 21 ± 2% (P = NS, <.05, and <.05 vs regadenoson alone), respectively, whereas the regadenoson-induced tachycardia was significantly reduced by 55 ± 8%, 55 ± 4%, and 52 ± 5% (all P < .05). In the presence of metoprolol, the duration of the regadenoson-induced increase in CBF was reduced, but the duration of the 2-fold increase in CBF caused by 5 μg/kg regadenoson was still nearly 6 minutes.

CONCLUSION

β(1)-Adrenergic blockade with metoprolol attenuated the regadenoson-induced increase in HR more than the increase in CBF.