Abir L. Banerjee

5‐Hydroxydecanoate is metabolised in mitochondria and creates a rate‐limiting bottleneck for β‐oxidation of fatty acids

5‐Hydroxydecanoate (5‐HD) blocks pharmacological and ischaemic preconditioning, and has been postulated to be a specific inhibitor of mitochondrial ATP‐sensitive K+ (KATP) channels. However, recent work has shown that 5‐HD is activated to 5‐hydroxydecanoyl‐CoA (5‐HD‐CoA), which is a substrate for the first step of β‐oxidation. We have now analysed the complete β‐oxidation of 5‐HD‐CoA using specially synthesised (and purified) substrates and enzymes, as well as isolated rat liver and heart mitochondria, and compared it with the metabolism of the physiological substrate decanoyl‐CoA. At the second step of β‐oxidation, catalysed by enoyl‐CoA hydratase, enzyme kinetics were similar using either decenoyl‐CoA or 5‐hydroxydecenoyl‐CoA as substrate. The last two steps were investigated using l‐3‐hydroxyacyl‐CoA dehydrogenase (HAD) coupled to 3‐ketoacyl‐CoA thiolase. Vmax for the metabolite of 5‐HD (3,5‐dihydroxydecanoyl‐CoA) was fivefold slower than for the corresponding metabolite of decanoate (l‐3‐hydroxydecanoyl‐CoA). The slower kinetics were not due to accumulation of d‐3‐hydroxyoctanoyl‐CoA since this enantiomer did not inhibit HAD. Molecular modelling of HAD complexed with 3,5‐dihydroxydecanoyl‐CoA suggested that the 5‐hydroxyl group could decrease HAD turnover rate by interacting with critical side chains. Consistent with the kinetic data, 5‐hydroxydecanoyl‐CoA alone acted as a weak substrate in isolated mitochondria, whereas addition of 100 μm 5‐HD‐CoA inhibited the metabolism of decanoyl‐CoA or lauryl‐carnitine. In conclusion, 5‐HD is activated, transported into mitochondria and metabolised via β‐oxidation, albeit with rate‐limiting kinetics at the penultimate step. This creates a bottleneck for β‐oxidation of fatty acids. The complex metabolic effects of 5‐HD invalidate the use of 5‐HD as a blocker of mitochondrial KATP channels in studies of preconditioning.

Uncorking of liposomes by matrix metalloproteinase-9

A triggered release methodology of liposomal contents via the enzyme MMP-9 is described.