AMPD1 gene polymorphism and the vasodilatory response to ischemia

AMPD1 polymorphism and response to regadenoson

AIMS

 AMPD1 c.34C > T (rs17602729) polymorphism results in AMPD1 deficiency. We examined the association of AMPD1 deficiency and variability of hemodynamic response to regadenoson.

SUBJECTS & METHODS

Genotyping for c.34C>T was performed in 267 patients undergoing regadenoson cardiac stress testing.

RESULTS

Carriers of c.34C >T variant exhibited higher relative changes in systolic blood pressure (SBP) compared with wild-type subjects ([%] SBP change to peak: 12 ± 25 vs 5 ± 13%; p = 0.01) ([%] SBP change to nadir: -3 ± 15 vs -7 ± 11%; p = 0.04). Change in heart rate was similar between groups, but side effects were more common in carriers of the variant (+LR = 4.2; p = 0.04).

CONCLUSION

AMPD1 deficiency may be involved in the modulation of regadenoson's systemic effects.

Gene Expression in Experimental Aortic Coarctation and Repair: Candidate Genes for Therapeutic Intervention?

Coarctation of the aorta (CoA) is a constriction of the proximal descending thoracic aorta and is one of the most common congenital cardiovascular defects. Treatments for CoA improve life expectancy, but morbidity persists, particularly due to the development of chronic hypertension (HTN). Identifying the mechanisms of morbidity is difficult in humans due to confounding variables such as age at repair, follow-up duration, coarctation severity and concurrent anomalies. We previously developed an experimental model that replicates aortic pathology in humans with CoA without these confounding variables, and mimics correction at various times using dissolvable suture. Here we present the most comprehensive description of differentially expressed genes (DEGs) to date from the pathology of CoA, which were obtained using this model. Aortic samples (n=4/group) from the ascending aorta that experiences elevated blood pressure (BP) from induction of CoA, and restoration of normal BP after its correction, were analyzed by gene expression microarray, and enriched genes were converted to human orthologues. 51 DEGs with >6 fold-change (FC) were used to determine enriched Gene Ontology terms, altered pathways, and association with National Library of Medicine Medical Subject Headers (MeSH) IDs for HTN, cardiovascular disease (CVD) and CoA. The results generated 18 pathways, 4 of which (cell cycle, immune system, hemostasis and metabolism) were shared with MeSH ID’s for HTN and CVD, and individual genes were associated with the CoA MeSH ID. A thorough literature search further uncovered association with contractile, cytoskeletal and regulatory proteins related to excitation-contraction coupling and metabolism that may explain the structural and functional changes observed in our experimental model, and ultimately help to unravel the mechanisms responsible for persistent morbidity after treatment for CoA.

Inhibition of AMP deaminase as therapeutic target in cardiovascular pathology

AMP deaminase (AMPD; EC 3.5.4.6) catalyzes hydrolysis of the amino group from the adenine ring of AMP resulting in production of inosine 5'-monophosphate (IMP) and ammonia. This reaction helps to maintain healthy cellular energetics by removing excess AMP that accumulates in energy depleted cells. Furthermore, AMPD permits the synthesis of guanine nucleotides from the larger adenylate pool. This enzyme competes with cytosolic 5'-nucleotidases (c5NT) for AMP. Adenosine, a product of c5NT is a vasodilator, antagonizes inotropic effects of catecholamines and exerts anti-platelet, anti-inflammatory and immunosuppressive activities. The ratio of AMPD/c5NT defines the amount of adenosine produced in adenine nucleotide catabolic pathway. Inhibition of AMPD could alter this ratio resulting in increased adenosine production. Besides the potential effect on adenosine production, elevation of AMP due to inhibition of AMPD could also lead to activation of AMP regulated protein kinase (AMPK) with myriad of downstream events including enhanced energetic metabolism, mitochondrial biogenesis and cytoprotection. While the benefits of these processes are well appreciated in cells such as skeletal or cardiac myocytes its role in protection of endothelium could be even more important. Therapeutic use of AMPD inhibition has been limited due to difficulties with obtaining compounds with adequate characteristics. However, endothelium seems to be the easiest target as effective inhibition of AMPD could be achieved at much lower concentration than in the other types of cells. New generation of AMPD inhibitors has recently been established and its testing in context of endothelial and organ protection could provide important basic knowledge and potential therapeutic tools.

The effect of AMPD1 genotype on blood flow response to sprint exercise

Inherited deficiency of skeletal muscle myoadenylate deaminase (mAMPD) is a genetic disorder characterized primarily by a 34C>T transition in exon 2 of the AMPD1 gene. mAMPD deficient individuals exhibit alterations in ATP catabolic flow, resulting in greater adenosine accumulation during high intensity exercise that may possibly enhance exercise-induced hyperaemia. This study tested the hypothesis that individuals with diminished mAMPD activity due to mutations in the AMPD1 gene develop a greater and faster blood flow response to high intensity exercise than individuals with two AMPD1 normal alleles (NN). Four 34C>T homozygotes, two compound heterozygotes (34C>T in one allele and a recently identified 404delT mutation in the other AMPD1 allele), collectively termed MM, one 34C>T heterozygote (NM) and eight NN males were studied. They performed a 30 s Wingate cycling test with monitoring of power output and other parameters of exercise performance. Common femoral artery blood flow was measured before and after (up to 25 min) exercise, using ultrasonography. Mean power during Wingate cycling was approximately 10% lower in MM/NM than in NN; p<0.01. Blood flow response to exercise also differed between MM/NM and NN individuals (ANOVA; p<0.001). There was also a difference in peak post-exercise blood flow (p<0.05), and the subsequent fall in blood flow during the recovery phase (T1/2) occurred more than twice as fast in MM/NM compared to NN subjects (7.8+/-1.1 min vs. 16.1+/-1.4 min, p<0.001). These results suggest a better circulatory adaptation to exercise in individuals with diminished mAMPD activity, probably due to an AMPD1 genotype-dependent increase in adenosine formation.