Impaired cardiac contractile function in arginine:glycine amidinotransferase knockout mice devoid of creatine is rescued by homoarginine but not creatine.

Kiterie M E Faller,Sevasti Zervou,Dorothee Atzler,Jurgen E Schneider,Hannah J Whittington,Debra J Mcandrew,Craig A Lygate,Dirk Isbrandt,Dunja Aksentijevic,Jillian N Simon,Barbara Casadei,Chi-Un Choe,Stefan Neubauer,Michiel Ten Hove

doi:10.1093/cvr/cvx242

Abstract

AimsCreatine buffers cellular adenosine triphosphate (ATP) via the creatine kinase reaction. Creatine levels are reduced in heart failure, but their contribution to pathophysiology is unclear. Arginine:glycine amidinotransferase (AGAT) in the kidney catalyses both the first step in creatine biosynthesis as well as homoarginine (HA) synthesis. AGAT-/- mice fed a creatine-free diet have a whole body creatine-deficiency. We hypothesized that AGAT-/- mice would develop cardiac dysfunction and rescue by dietary creatine would imply causality.Methods and resultsWithdrawal of dietary creatine in AGAT-/- mice provided an estimate of myocardial creatine efflux of ∼2.7%/day; however, in vivo cardiac function was maintained despite low levels of myocardial creatine. Using AGAT-/- mice naïve to dietary creatine we confirmed absence of phosphocreatine in the heart, but crucially, ATP levels were unchanged. Potential compensatory adaptations were absent, AMPK was not activated and respiration in isolated mitochondria was normal. AGAT-/- mice had rescuable changes in body water and organ weights suggesting a role for creatine as a compatible osmolyte. Creatine-naïve AGAT-/- mice had haemodynamic impairment with low LV systolic pressure and reduced inotropy, lusitropy, and contractile reserve. Creatine supplementation only corrected systolic pressure despite normalization of myocardial creatine. AGAT-/- mice had low plasma HA and supplementation completely rescued all other haemodynamic parameters. Contractile dysfunction in AGAT-/- was confirmed in Langendorff perfused hearts and in creatine-replete isolated cardiomyocytes, indicating that HA is necessary for normal cardiac function.ConclusionsOur findings argue against low myocardial creatine per se as a major contributor to cardiac dysfunction. Conversely, we show that HA deficiency can impair cardiac function, which may explain why low HA is an independent risk factor for multiple cardiovascular diseases.

Highlights

The heart has a constant requirement for large amounts of energy in the form of adenosine triphosphate (ATP) and must maintain the ability to instantly respond to elevated workloads
Arginine:glycine amidinotransferase knockout mice (AGAT-/-) have a homozygous knockout of the Gatmtm1.1Isb allele created by homologous recombination.[22]
Creatine withdrawal study: Since arginine:glycine amidinotransferase (AGAT)-/- mice are dependent on dietary creatine, we hypothesized that changing to a creatine-free diet in adulthood would lead to a gradual reduction in myocardial creatine levels to demonstrate whether low creatine, as observed in the failing heart, can cause cardiac dysfunction per se

Summary

Introduction

The heart has a constant requirement for large amounts of energy in the form of adenosine triphosphate (ATP) and must maintain the ability to instantly respond to elevated workloads. Intracellular ATP levels do not change in the healthy heart, which implies a tight match between ATP demand and supply via glycolysis and oxidative phosphorylation.[1] The creatine kinase (CK) phosphagen system is considered key to this by buffering ATP levels via rapid and reversible transfer of the phosphoryl group of ATP onto creatine (Cr) to form phosphocreatine (PCr)[2]: Cr þ ATP $ PCr þ ADP þ Hþ. In animal models and patients with heart failure, a decrease in total creatine levels and CK enzymatic activity is consistently observed, regardless of aetiology.[3] For example, in patients with dilated cardiomyopathy, the ratio of PCr/ATP is reduced at an early stage of pathology and correlates with ejection fraction and survival.[4] despite decades of research, the exact contribution (i.e. cause or effect) of reduced creatine to cardiac pathophysiology remains controversial

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