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  • The amino acids evaluated in this study

    2024-02-23

    The amino acids evaluated in this study represent proteinogenic (amino acids that are applied in the genetic code) or even essential ones (amino acids that cannot be synthesised by the organism and need to be taken up by nutrition). Tryptophan, phenylalanine, tyrosine, isoleucine, threonine and valine are essential proteinogenic amino acids revealing glycogenic effects, whereas leucin represents an essential ketogenic amino acid. [30,31] Sustaining protein synthesis and inflammation continuously affects the metabolism of especially proteinogenic and essential amino acids, where an increasing demand becomes necessary. [32,33] Proteinogenic amino acids are, except for lysine and leucin, glycogenic because they sustain gluconeogenesis. They also reveal anaplerotic and ketogenic effects, which induce both the tricarboxylic ecopipam cycle and the synthesis of acetoacetate and acetyl CoA, a highly-energetic and main coenzyme of intermediary metabolism. [30,[34], [35], [36]] The estimated Fischer ratio showed a significant decrease, which reflects higher levels of AAA and lowered levels of BCAA at mid-term follow up. It may be speculated whether decreasing BCAA might additionally reflect a higher turnover during ongoing neo-endothelization after LAAC. Beyond LAAC further studies in cardiac diseases are available. Decreased fisher ratios were found in patients with severe stages and symptoms of pulmonary hypertension. [37] Furthermore, the Fischer ratio was significantly decreased in a case-control study in 71 patients with systolic heart failure compared to healthy controls. [38] In the present study only the subgroup of diabetic patients showed a significant change of Fischer ratio at mid-term follow-up, suggesting a potential impact of the presence of diabetes itself, which is line with further studies reporting about BCAA as risk markers for diabetes mellitus. [39,40] The complex steps of neo-endothelization require a high turnover of proteins to maintain cell-cell interaction and synthesis of extracellular matrix. [41,42] Mechanical stretch of myocytes increases protein synthesis and a higher demand for amino acids. [[43], [44], [45]] Experimental in-vitro studies demonstrated that myocardial stretch, e.g. of papillary muscle, leads to an increased protein and amino acid synthesis and oxygen consumption. [43,46] Additionally, local inflammation at the landing zone is developing due to myocardial stretch as well as during neoendothelialization. This comprises the activation of inflammatory cells and secretion of growth factors, cytokines (such as interleukin 6) and chemokines. [27] All of the above said activating pathways require and enhance the demand for increasing amino acid synthesis. [32] Furthermore, tyrosine, phenylanaline and tryptophan may also reflect in part the status of bioenergetic efficacy before and after successful LAAC. The measured aliphatic amino acids phenylalanine and tyrosine are original substrates for the biosynthesis of catecholamines, noradrenalin and adrenalin. [47] Hypothetically, the changes of tyrosine and phenylalanine might reflect the precursors of ongoing catecholamine excess and do therefore additionally sustain myocardial contraction of the LAA after LAAC at mid-term follow-up. Increased levels of tryptophan and kynurenine were also found after successful LAAC. Tryptophan is essential for the synthesis of the water-soluble vitamin nicotinic acid, and kynurenine represents a degradation product at these steps. [48] Experimental studies proved evidence of kynurenine acid (KYNA), the active metabolite of kynurenine, in rat atria and demonstrated that administration of KYNA attenuated the chronotropic effect in response to electrical nerve stimulation as well. [49] Moreover, KYNA reveals inflammatory effects as being observed in patients with atherosclerosis and those undergoing cardiac surgery [48,50,51]. Most noteworthy, nicotinic acid is required for the synthesis of nicotinamide-adenine-dinucleotide (NAD) and nicotinamide-adenine-dinucleotide-phosphate (NADP). [48,52] NAD and NADP represent coenzymes of the intermediary metabolism guaranteeing the transfer of hydride-ions for energy coupling within several metabolomic pathways, including substrate chain-phosphorylation, hexose monophosphate pathway, tricarboxylic acid cycle, glycolysis, fatty acid metabolism and electron transport chain (ETC). [48] The coenzymes NAD/NADP are hereby essential for the ongoing generation of adenosine triphosphate (ATP), the main form of energy storage in human cells, sustaining optimal bioenergetic efficacy. [48,53]