Effect of carnitine acetyltransferase inhibition on rat hepatocyte metabolism.
Carnitine acetyltransferase (CAT) catalyzes the reversible transfer of short chain (less than six carbons in length) acyl groups from acyl-CoA thioesters to form the corresponding acylcarnitines. This reaction has been suggested to be of importance in decreasing cellular content of acyl-CoA under conditions characterized by accumulation of poorly metabolized, potentially toxic acyl-CoAs. To study the importance of the CAT reaction, the effect of CAT inhibitors on rat hepatocyte metabolism in the presence of propionate was examined. Acetyl-DL-aminocarnitine inhibited [14C]propionylcarnitine accumulation by isolated hepatocytes incubated with [14C]propionate (1.0-10.0 mM). Inhibition of propionylcarnitine formation by acetyl-DL-aminocarnitine was concentration dependent and was not due to non-specific cellular toxicity as [14C]glucose formation from [14C]propionate, and [1-14C]pyruvate oxidation were unaffected by the CAT inhibitor. Inhibition of propionylcarnitine formation was increased by preincubating hepatocytes with acetyl-DL-aminocarnitine, suggesting competition for cellular uptake between carnitine and the inhibitor. Hemiacetylcartinium (HAC) and meso-2,6-bis(carboxymethyl)4,4-dimethylmorpholinium bromide (CMDM), potent inhibitors of CAT in broken cell systems, did not inhibit hepatocyte propionylcarnitine formation under the conditions evaluated. Propionate (5 mM) inhibited hepatocyte pyruvate (10 mM) oxidation, and this inhibition was partially reversed by 5 mM carnitine. Addition of 5.0 mM acetyl-DL-aminocarnitine abolished the stimulatory effect of carnitine on pyruvate oxidation in the presence of propionate. These studies establish that acetyl-DL-aminocarnitine inhibits intact hepatocyte CAT activity, and thus provide a useful probe of the role of CAT in cellular metabolism. CAT activity appears to be critical for carnitine-mediated reversal of propionate-induced inhibition of pyruvate oxidation.
Brass
E P
EP
Department of Medicine, Case Western Reserve University, Cleveland, OH 44106.
Gandour
R D
RD
Griffith
O W
OW
D000108:Acetylcarnitine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002331:Carnitine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D002332:Carnitine O-Acetyltransferase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002469:Cell Separation; D008099:Liver / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D009025:Morpholines / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011422:Propionates / Q000378:metabolism / Q000494:pharmacology; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D051381:Rats; D011919:Rats, Inbred Strains
D009025:Morpholines; D011422:Propionates; D011773:Pyruvates; C049831:hemiacetylcarnitinium; C071520:2,6-bis(carboxymethyl)-4,4-dimethylmorpholinium; C003223:propionylcarnitine; D000108:Acetylcarnitine; D019289:Pyruvic Acid; C049138:3-acetylaminocarnitine; D002332:Carnitine O-Acetyltransferase; D002331:Carnitine