β‐Oxidation of 5‐hydroxydecanoate, a Putative Blocker of Mitochondrial ATP‐Sensitive Potassium Channels

Abstract

5‐Hydroxydecanoate (5‐HD) inhibits ischaemic and pharmacological preconditioning of the heart. Since 5‐HD is thought to inhibit specifically the putative mitochondrial ATP‐sensitive K+ (KATP) channel, this channel has been inferred to be a mediator of preconditioning. However, it has recently been shown that 5‐HD is a substrate for acyl‐CoA synthetase, the mitochondrial enzyme which ‘activates’ fatty acids. Here, we tested whether activated 5‐HD, 5‐hydroxydecanoyl‐CoA (5‐HD‐CoA), is a substrate for medium‐chain acyl‐CoA dehydrogenase (MCAD), the committed step of the mitochondrial β‐oxidation pathway. Using a molecular model, we predicted that the hydroxyl group on the acyl tail of 5‐HD‐CoA would not sterically hinder the active site of MCAD. Indeed, we found that 5‐HD‐CoA was a substrate for purified human liver MCAD with a Km of 12.8 ± 0.6 μm and a kcat of 14.1 s−1. For comparison, with decanoyl‐CoA (Km∼3 μm) as substrate, kcat was 6.4 s−1. 5‐HD‐CoA was also a substrate for purified pig kidney MCAD. We next tested whether the reaction product, 5‐hydroxydecenoyl‐CoA (5‐HD‐enoyl‐CoA), was a substrate for enoyl‐CoA hydratase, the second enzyme of the β‐oxidation pathway. Similar to decenoyl‐CoA, purified 5‐HD‐enoyl‐CoA was also a substrate for the hydratase reaction. In conclusion, we have shown that 5‐HD is metabolised at least as far as the third enzyme of the β‐oxidation pathway. Our results open the possibility that β‐oxidation of 5‐HD or metabolic intermediates of 5‐HD may be responsible for the inhibitory effects of 5‐HD on preconditioning of the heart.

Cardioprotection of Interleukin-2 Is Mediated via κ-Opioid Receptors

“…Blockade of cardioprotection with IL-2 by 5-HD was interpreted as indication of a mediatory role of the mito-K ATP channel. There is, however, a recent report that suggested that ␤-oxidation or metabolites of 5-HD may be responsible for abolition of cardioprotection of preconditioning (Hanley et al, 2003).…”

Structural Basis for Substrate Fatty Acyl Chain Specificity

“…Therefore, the lack of this hydrogen bond to the loop between ␤-strands 4 and 5 in VLCAD offsets the tighter binding of the fatty acyl chain and allows for longer chain length products to be more easily released, resulting in a more efficient catalytic turnover. Indeed, it has been shown with MCAD that the weaker binding 5-hydroxydecanoyl-CoA actually has a higher V max than the tighter binding decanoyl-CoA (44). This absence of a hydrogen bond (between the CoA moiety and the polypeptide) in VLCAD may also be the cause of higher mobility of the CoA moiety, which results in the weak electron density observed in this region.…”

Interaction of Cardiovascular Risk Factors with Myocardial Ischemia/Reperfusion Injury, Preconditioning, and Postconditioning

“…Diazoxide/Pinacidil Its uncoupling effect in isolated rat heart mitochondria respiring on pyruvate and malate was markedly reduced by inhibitors of the adenine nucleotide translocase, which also affected mitochondrial matrix volume regulation Kopustinskiene et al (2003), Das et al (2003) 5-HD As 5-HD is metabolized in the first 3 steps of the betaoxidation, its metabolic intermediates, rather than blockade of K ATP , could be involved in the inhibitory effect of 5-HD on preconditioning; 5-HD did not affect mitochondrial matrix volume in rat heart mitochondria Hanley et al (2003), Das et al (2003) CARDIOPROTECTION AND RISK FACTORS Connexin-43 is another protein implicated in classic preconditioning. The protein forms the multimeric hemichannel structure of gap junctions in myocardium and appears to be obligatory for classic preconditioning, as hearts (Schwanke et al, 2002(Schwanke et al, , 2003 or cardiomyocytes obtained from connexin-43 heterozygous knockout mice display no preconditioning response .…”