Orotic acid and its salts chronically administered have been shown to significantly improve cardiac function in pathological settings associated with ischemia-reperfusion (I/R) injury. The aim of our study was to investigate the effect of magnesium orotate (Mg-Or) administration at the onset of post-ischemic reperfusion on myocardial function and infarct size (IS). Ex-vivo experiments performed on isolated perfused rat hearts were used to compare Mg-Or administration with a control group (buffer treated), ischemic post-conditioning, orotic acid treatment, and MgCl2 treatment. Mg-Or administration was also investigated in an in-vivo model of regional I/R performed in rats undergoing reversible coronary ligation. The effect of Mg-Or on mitochondrial permeability transition pore (mPTP) opening after I/R was investigated in vitro to gain mechanistic insights. Both ex-vivo and in-vivo experiments showed a beneficial effect from Mg-Or administration at the onset of reperfusion on myocardial function and IS. In-vitro assays showed that Mg-Or significantly delayed mPTP opening after I/R. Our data suggest that Mg-Or administered at the very onset of reperfusion may preserve myocardial function and reduce IS. This beneficial effect may be related to a significant reduction of mPTP opening, a usual trigger of cardiac cell death following I/R.

Metabolic therapy involves the administration of a substance normally found in the human body to enhance cellular reactions involved in the pathogenesis of disease. Myocardial ischaemia/reperfusion injury represents a leading cause of morbidity and mortality, also in cardiovascular disease. Therapeutic strategies aimed at limiting cardiomyocyte death during the postischaemic reperfusion and in the perioperative settings are nowadays extensively studied. Conceived originally as a dietary constituent (known as vitamin B13) only, it is now apparent that most orotic acid is synthesized in the human body where it arises as an intermediate in the biosynthetic pathway of pyrimidine nucleotides. Previous investigations in the heart suggest that orotate and its derivatives could be of significant clinical benefit in the treatment of heart disease. The present brief review is concerned with the current knowledge of the major effects of these compounds in both experimental and clinical cardiology. The potential mechanisms and biochemical pathways responsible for cardioprotection are highlighted.

Acute administration of magnesium orotate (Mg-Or) at reperfusion has been previously shown to elicit significant protection in isolated rat hearts. Since recovery of mitochondrial function is mandatory for cardioprotection, the present study was aimed at characterising the effects of Mg-Or on mitochondrial respiration. Isolated male adult rat hearts (n=6/group) subjected to 30 min global ischaemia and 120 min reperfusion were randomised to receive: (i) no additional intervention (Ctrl); (ii) Mg-Or at 28 min of ischaemia (Mg-Or-28I) and (iii) Mg-Or at 3 min of reperfusion (Mg-Or-3R). Mitochondria were isolated at 15 min of reperfusion and oxygen consumption was measured at 37°C by polarographic oxymetry in the presence of NAD and FAD-linked substrates, respectively. Basal (state 2) and ADP-stimulated (state 3) respiratory rates were recorded and expressed as nanoatoms oxygen/min/mg mitochondrial protein and respiratory control ratio (RCR) was calculated. In mitochondria respiring on glutamate/malate a statistically significant increase in state 3 respiratory rates was observed in the Mg-Or-28I group but not in Mg-Or-3R when compared to the ischaemic Ctrl (514±29 and 386±17 vs 350±13, respectively, p<0.001). Subsequently, RCR increased from 6.2±0.38 in Ctrl group to 8±0.28 in Mg-Or-28I group (p<0.05). In the presence of complex II-dependent substrate (succinate+amytal) both administration protocols elicited an important increase in state 3 respiration (Mg-Or-28I: 488±25, Mg-Or-3R: 463±20 vs Ctrl: 355±15, respectively, p<0.001). In isolated rat hearts, magnesium 355+orotate elicited a protocol-dependent improvement of mitochondrial respiration at reperfusion that may contribute to its cardioprotective effect against reperfusion injury.