Determination of Fecal Triglycerides and Fatty Acids of Medium Chain Length by Electrical Capacitance and by Petroleum Ether Extraction

Abstract The extraction method of Friedner and Moberg for determining fecal lipids gave recoveries of medium-chain triglycerides and of octanoic and decanoic acids from stool specimens averaging 103, 97, and 107%, respectively. Fatty acids did not esterify appreciably during extraction. Accordingly, this method is suitable for use in measuring intestinal absorption of triglycerides of medium chain length. The electrical capacitance method of Wolochow et al. is unsuited to the determination of total lipids in a mixture of triglycerides and fatty acids of long and medium chain length because these substances differ widely in capacitance.

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Effects of propionate and carnitine on the hepatic oxidation of short- and medium-chain-length fatty acids

Biochemical Journal ◽

10.1042/bj2500819 ◽

1988 ◽

Vol 250 (3) ◽

pp. 819-825 ◽

Cited By ~ 52

Author(s):

E P Brass ◽

R A Beyerinck

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Organic Acid ◽

Chain Length ◽

Ketone Body ◽

Acetyl Coa ◽

Body Formation ◽

Medium Chain ◽

Medium Chain Length ◽

Hepatic Oxidation

Accumulation of propionate, or its metabolic product propionyl-CoA, can disrupt normal cellular metabolism. The present study examined the effects of propionate, or propionyl-CoA generated during the oxidation of odd-chain-length fatty acids, on hepatic oxidation of short- and medium-chain-length fatty acids. In isolated hepatocytes, ketone-body formation from odd-chain-length fatty acids was slow as compared with even-chain-length fatty acid substrates, and increased as the carbon chain length was increased from five to seven to nine. In contrast, rates of ketogenesis from butyrate, hexonoate and octanoate were all approximately equal. Propionate (10 mM) inhibited ketogenesis from butyrate, hexanoate and octanoate by 81%, 53% and 18% respectively. Addition of carnitine had no effect on ketogenesis from the even-chain-length fatty acids, but increased the rate of ketone-body formation from pentanoate (by 53%), heptanoate (by 28%) and from butyrate or hexanoate in the presence of propionate. The inhibitory effect of propionate could not be explained by shunting acetyl-CoA into the tricarboxylic acid cycle, as CO2 formation from butyrate was also decreased by propionate. Examination of the hepatocyte CoA pool during oxidation of butyrate demonstrated that addition of propionate decreased acetyl-CoA and CoA as propionyl-CoA accumulated. Addition of carnitine decreased propionyl-CoA by 50% (associated with production of propionylcarnitine) and increased acetyl-CoA and CoA. Similar changes in the CoA pool were seen during the oxidation of pentanoate. These results demonstrate that accumulation of propionyl-CoA results in inhibition of short-chain fatty acid oxidation. Carnitine can partially reverse this inhibition. Changes in the hepatocyte CoA pool are consistent with carnitine acting by generating propionylcarnitine, thereby decreasing propionyl-CoA and increasing availability of free CoA. The data provide further evidence of the potential cellular toxicity from organic acid accretion, and supports the concept that carnitine's interaction with the cellular CoA pool can have a beneficial effect on cellular metabolism and function under conditions of unusual organic acid accumulation.

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