Decrease of fatty acid oxidation, ketogenesis and gluconeogenesis in isolated perfused rat liver by phenylalkyl oxirane carboxylate (B 807‐27) due to inhibition of CPT I (EC 2.3.1.21)

Abstract

Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (B 807-27 or POCA) inhibits ketogenesis from endogenous and exogenous long-chain fatty acids and 14C02 production from [U-'4C]palmitate, but not from [U-'4C]palmitoylcarnitine or octanoate, and inhibits gluconeogenesis from lactate and pyruvate in perfused livers of starved rats.2. Inhibition of ketogenesis, 14C02 production and gluconeogenesis was complete at concentrations of 10 pmol/l POCA, but onset was more rapid for inhibition of ketogenesis and C 0 2 production than for gluconeogenesis. Infusion of octanoate abolished inhibition of all three processes.3. Experiments with isolated rat liver mitochondria showed that carnitine palmitoyltransferase I (EC 2.3.1.21) is inhibited by POCA-CoA.The inhibitory process is dependent on time and concentration, and more pronounced in mitochondria from fed than from fasted rats. Concentrations required for 50% inhibition after 20 min preincubation with POCACoA are 0.02, 0.06 and 0.1 pmol/l in liver mitochondria from fed, 24-h-fasted and 48-h-fasted rats, respectively. The inhibitor appears to be tightly bound to the enzyme.4. The extent of inhibition of carnitine palmitoyltransferase I correlates well with the hypoglycaemic and hypoketonaemic effects of the compounds in fasted rats. We conclude that specific inhibition of the enzyme leads, due to inhibition of long-chain fatty acid utilization, to depressed ketogenesis and gluconeogenesis and, in consequence, to hypoglycaemic and hypoketonaemia in vivo under gluconeogenic and ketogenic conditions.Several cr-modified fatty acids are able to inhibit fatty acid oxidation, ketogenesis and gluconeogenesis [l -71. Since the consequence of these effects are a lowering of glucose and ketone body concentrations in the blood, the compounds were discussed as potential drugs in antidiabetic therapy [7].A few years ago, 2-tetradecylglycidate (McN-3802) was shown to exert these effects via a specific inhibition of carnitine palmitoyltransferase I (CPT I) [8], an enzyme located at the outer side of the inner mitochondria1 membrane which is involved in the transport of long-chain acyl-CoA into the mitochondria [9]. More recently, we found a new class of hypoglycaeimc compounds which shows similarities to McN-3802 as well as to the physiological inhibitor of CPT I, malonyl-CoA [lo, 1 I]. , inhibits oxidation of long-chain fatty acids in rat hepatocytes [12], rat liver and muscle mitochondria [13], perfused rat hearts [14, 151 and human fibroblasts [16]. A specific inhibition of CPT I has been shown in mitochondria of several rat organs [14,17, 181. The purpose of the present study was to provide further experimental evidence that POCA inhibits long-chain fatty acid oxidation at the site of CPT I and to investigate how this affects ketogenesis and gluconeogenesis in isolated perfused rat liver as well as blood concentrations of ketones and glucose in vivo. Sodium-2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate MATERIALS AND METHODSSodium-2-[ 5-(4-chlorophenyl)-pentyl]-oxirane...

The dependence of electrophysiological derangements on accumulation of endogenous long-chain acyl carnitine in hypoxic neonatal rat myocytes.

“…By inhibiting fatty acid oxidation, POCA may diminish metabolism through 'oxygenwasting' pathways that may accelerate membrane damage. Alternatively, POCA may prevent the electrophysiological alterations by increasing uptake and metabolism of glucose (Wolf et al, 1982(Wolf et al, , 1985. Several observations (McDonald and MacLeod, 1973;Higgins et al, 1981;Hasin and Barry, 1984) suggest that ATP produced through glycolysis preferentially subserves maintenance of membrane function.…”

“…In some experiments, sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (POCA, 10 MM, 97% pure, kindly provided by Dr. Ludwig, ByK Gulden Pharmazeutika) was used to inhibit carnitine acyltransferase I activity (Bartlett et al, 1981;Wolf et al, 1982Wolf et al, , 1985. Thioesterificarion of this compound is required for expression of its inhibitory activity (Wolf and Engel, 1985).…”

“…Thioesterificarion of this compound is required for expression of its inhibitory activity (Wolf and Engel, 1985).…”

The Use of Partial Fatty Acid Oxidation Inhibitors for Metabolic Therapy of Angina Pectoris and Heart Failure

“…Etomoxir has been developed for treating non-insulindependent diabetes mellitus [54,147]. This CPT-1 inhibitor has no acute cardiovasuclar effects in rats as shown by an unaltered heart rate ( Figure 2) and blood pressure (not shown).…”

Structural insight into function and regulation of carnitine palmitoyltransferase

“…Phenylalkyl oxirane carboxylates (POCA) exert their full efficacy as CPT-1 inhibitors when converted to POCACoA [87][88][89]. Besides inhibiting CPT-1, POCA stimulates peroxisome proliferation similar to fibrates and thereby increases lipid catabolism via peroxisomal oxidation.…”