Does a selective adenosine A(1) receptor agonist protect against exercise induced ischaemia in patients with coronary artery disease?

Involvement of adenosine signaling pathway in migraine pathophysiology: a systematic review of preclinical studies

Background

Adenosine is a purinergic signaling molecule with a wide range of physiological functions including anti- and pronociceptive properties. Adenosine receptors are expressed in the trigeminovascular system, and adenosine receptor antagonist, caffeine, relieves migraine headache. We performed a systematic review of the literature of preclinical data addressing the role of adenosine in migraine pathophysiology.

Methods

PubMed and EMBASE were searched for pre-clinical studies on the role of adenosine in migraine pathophysiology on September 5^th, 2021.

Results

A total of 2510 studies were screened by title and abstract. Of these, thirteen pre-clinical studies evaluating adenosine, adenosine A1, A2A and A3 receptors were included.

These studies showed that adenosine signaling pathway is involved in controlling vascular tone. Furthermore, electrical stimulation of the trigeminal ganglion modulates the expression of adenosine A₁ and A_2A receptors in the trigeminal ganglion and trigeminal nucleus caudalis implicating adenosine signaling pathway in pain transmission.

Conclusion

Preclinical studies showed that adenosine has a dual effect on vasodilation and trigeminal pain pathway due to different receptor activation, suggesting a possible role of adenosine in migraine pathophysiology. Studies investigating pharmacological characteristics of subtypes of adenosine receptors are needed to further elucidate their role as a potential target for migraine treatment.

Involvement of adenosine signaling pathway in migraine pathophysiology: A systematic review of clinical studies

OBJECTIVE

To systematically review clinical studies investigating the involvement of adenosine and its receptors in migraine pathophysiology.

BACKGROUND

Adenosine is a purinergic signaling molecule, clinically used in cardiac imaging during stress tests. Headache is a frequent adverse event after intravenous adenosine administration. Migraine headache relief is reported after intake of adenosine receptor antagonist, caffeine. These findings suggest a possible involvement of adenosine signaling in migraine pathophysiology and its potential as a drug target.

METHODS

A search through PubMed and EMBASE was undertaken for clinical studies investigating the role of adenosine and its receptors in migraine, published until September 2021.

RESULTS

A total of 2510 studies were screened by title and abstract. Of these, seven clinical studies were included. The main findings were that adenosine infusion induced headache, and plasma adenosine levels were elevated during ictal compared to interictal periods in migraine patients.

CONCLUSION

The present systematic review emphasizes a potentially important role of adenosine signaling in migraine pathogenesis. Further randomized and placebo-controlled clinical investigations applying adenosine receptors modulators in migraine patients are needed to further understand the adenosine involvement in migraine.

Diabetes and the heart: could the diabetic myocardium be protected by preconditioning?

Both type 1 and type 2 diabetes (insulin-dependent and non-insulin dependent diabetes, respectively) are associated with increased risk for microvascular and macrovascular complications including retinopathy, neuropathy, nephropathy and atherosclerosis. Type 2 diabetes markedly increases the risk for cardiovascular morbidity and mortality, which has major public health implications. In this review, molecular mechanisms pertaining to diabetes-induced heart pathology are addressed.

Multicentre evaluation of the adenosine agonist GR79236X in patients with dental pain after third molar extraction

BACKGROUND

Adenosine is analgesic in humans, and the selective adenosine A1 receptor agonist GR79236X has significant anti-nociceptive activity in an animal pain model of inflammatory pain.

METHODS

Seventy-nine patients with moderate pain after third molar extraction under general anaesthesia were randomized to receive a 15 min double-blind infusion containing either GR79236X 4 microg kg-1, GR79236X 10 microg kg-1, diclofenac 50 mg, or saline placebo. Rescue analgesia was promptly available to all patients.

RESULTS

Meaningful pain relief (mild or no pain) was attained by 9 (47%) patients in the placebo group, 12 (63%) patients in the GR79236 4 microg kg-1 group, 10 (48%) patients in the 10 microg kg-1 group, and 16 (80%) patients in the diclofenac 50 mg group. Neither dose of GR79236 produced a significant improvement over placebo, but diclofenac was superior to both placebo (P=0.036) and GR79236 10 microg kg-1 (P=0.034). Median times to rescue or additional analgesia were 62, 100, 60, and 363 min for patients receiving placebo, GR79236 4 microg kg-1, 10 microg kg-1, and diclofenac 50 mg, respectively (diclofenac significantly longer than placebo, P=0.002 log-rank test). Pain control was poor in the placebo group and in both GR79236 groups, with between 79 and 86% of patients having good pain control (i.e. mild or no pain) for <20% of the time compared with only 30% of patients who received diclofenac.

CONCLUSION

We found no evidence of efficacy of GR79236 compared with placebo, but the active control diclofenac was effective. It is possible that a higher dose of GR79236 might have been effective or that i.v. administration of this drug does not achieve appropriate concentrations in the brain or peripheral nerves.

Effects of pharmacological modulation of the ATP-sensitive potassium channels on the development of warm-up angina pectoris

The aim of this study was to examine the effect of pharmacological modulation of the ATP-sensitive potassium channels in the development of warm-up angina pectoris. Thirty-one patients with stable angina pectoris, a positive exercise test and angiographically documented coronary artery disease underwent three exercise tests 90 min after receiving either glibenclamide 10.5 mg (an ATP-sensitive potassium channel blocker), pinacidil 25 mg (an ATP-sensitive potassium channel opener) or placebo in a blinded fashion. There was a 30-min recovery period between the first and the second test and 60 min between the second and the third test. The rate-pressure product at 1-mm ST-segment depression (ischemic threshold) and the maximum ST-segment depression (STD) adjusted to the highest rate-pressure product common to the three tests were analyzed. In the placebo group, there was a significant increase in the ischemic threshold during the second and third test and a significant decrease in the maximum adjusted STD during the second test which was lost during the third test. This apparent adaptation to exercise-induced ischemia was not seen in the glibenclamide-treated patients. In the pinacidil-treated patients, there was a paradoxical decrease in ischemic threshold during the second test with no change in maximum adjusted STD which tended to be lower than in the placebo-treated patients on each exercise test. This study confirms that the warm-up phenomenon can be induced during repeated exercise testing. The blockade of this phenomenon by glibenclamide suggests that the ATP-sensitive potassium channels may be involved in this potential protective mechanism. At the same time, the paradoxical response in the pinacidil-treated patients flags a warning that drugs acting on the sarcolemmal ATP-sensitive potassium channels may have a direct effect on the ST-segment that may interfere with the interpretation of the electrocardiogram.

Adenosine receptor agonists: from basic medicinal chemistry to clinical development

Adenosine is a physiological nucleoside which acts as an autocoid and activates G protein-coupled membrane receptors, designated A(1), A(2A), A(2B) and A(3). Adenosine plays an important role in many (patho)physiological conditions in the CNS as well as in peripheral organs and tissues. Adenosine receptors are present on virtually every cell. However, receptor subtype distribution and densities vary greatly. Adenosine itself is used as a therapeutic agent for the treatment of supraventricular paroxysmal tachycardia and arrhythmias and as a vasodilatatory agent in cardiac imaging. During the past 20 years, a number of selective agonists for A(1), A(2A) and A(3) adenosine receptors have been developed, all of them structurally derived from adenosine. Several such compounds are currently undergoing clinical trials for the treatment of cardiovascular diseases (A(1)and A(2A)), pain (A(1)), wound healing (A(2A)), diabetic foot ulcers (A(2A)), colorectal cancer (A(3)) and rheumatoid arthritis (A(3)). Clinical evaluation of some A(1) and A(2A) adenosine receptor agonists has been discontinued. Major problems include side effects due to the wide distribution of adenosine receptors; low brain penetration, which is important for the targeting of CNS diseases; short half-lifes of compounds; or a lack of effects, in some cases perhaps due to receptor desensitisation or to low receptor density in the targeted tissue. Partial agonists, inhibitors of adenosine metabolism (adenosine kinase and deaminase inhibitors) or allosteric activators of adenosine receptors may be advantageous for certain indications, as they may exhibit fewer side effects.

The effect of an angiotensin-converting enzyme inhibitor and a K+(ATP) channel opener on warm up angina

AIMS

In various models, angiotensin-converting enzyme (ACE) inhibitors and K+(ATP) channel openers can potentiate and mimic ischaemic preconditioning, respectively. Our aim was to determine whether these characteristics are shared by the phenomenon of warm up in angina, often regarded as a surrogate of ischaemic preconditioning.

METHODS AND RESULTS

Twenty patients with ischaemic heart disease were assigned in a double blind, randomized cross-over design to equivalent pressor doses of nicorandil 20 mg bid, enalapril 10 mg bid, losartan 25 mg bid, or placebo for 3 days. Patients underwent three consecutive exercise tolerance tests on each medication separated by a 1-week interval. Each patient underwent 12 exercise tests in total and 13 patients completed the study. On each medication the second exercise was separated from the first by 15 min of rest and the third exercise was performed 90 min after the second to control for training. The time to 0.1 mV ST depression and rate pressure product at 0.1 mV ST depression increased significantly in all groups during exercise two compared with exercise one. Nicorandil reduced angina but did not attenuate this warm up effect. This benefit of first exercise waned by test three with placebo, losartan, and nicorandil, but not with enalapril.

CONCLUSION

In contrast to predictions based on ischaemic preconditioning the magnitude of the warm up was apparently unaltered by nicorandil, losartan, or enalapril, however its duration seemed to be extended by enalapril. Thus ischaemic preconditioning and warm up angina are likely to have differing pharmacological profiles suggesting a diverse underlying mechanism.