Fatty acid ethyl esters are present in human serum after ethanol ingestion

The aim of the study was to determine whether fatty acid ethyl esters, nonoxidative products of ethanol metabolism selectively present in organs damaged by ethanol abuse, are detectable in the serum after ethanol ingestion. Serum samples of hospital emergency room patients with positive (n = 32) and negative (n = 5) blood ethanol levels were assayed for fatty acid ethyl esters. In a separate study, five healthy subjects received an ethanol dose based on body weight mixed with fruit juice in a 1:2 ratio and administered by measured ingestion. Fatty acid ethyl esters were found in the serum of hospital emergency room patients with positive blood ethanol levels. The concentration of fatty acid ethyl esters in these patients correlated with the concentration of blood ethanol (r = 0.57; 95% confidence interval 0.28 to 0.77; P = 0.0002). In the controlled ethanol ingestion study with five healthy subjects, it was also determined that the serum fatty acid ethyl ester concentration began to decrease within 2 h of the time ethanol ingestion had been stopped. The fatty acid ethyl esters in the serum were bound to lipoprotein and albumin, and there was a higher percentage of saturated fatty acids in the FAEE pool than in the serum free fatty acid and triglyceride pools. These studies indicate that fatty acid ethyl esters, which have been implicated as mediators of ethanol-induced organ toxicity, are present in serum after ethanol ingestion.

Use of acetyl chloride/methanol for assumed selective methylation of plasma nonesterified fatty acids results in significant methylation of esterified fatty acids

The albumin-bound nonesterified fatty acid pool in plasma, which represents a very small percentage of total plasma fatty acids, has previously been quantitated by a variety of methods. In the present study we determined that the nonesterified fatty acid concentrations in the plasma, quantitated by a popular method using acetyl chloride and methanol which is reported to be specific for methylation of nonesterified fatty acids in the presence of esterified fatty acids (i.e., without prior isolation of the plasma nonesterified fatty acids), were significantly overestimated due to cleavage and methylation of esterified fatty acids. Quantitation of the contaminating fatty acid from the esterified pool demonstrated that the amount of fatty acid cleaved from the esterified pool was enough to exceed the entire mass of nonesterified fatty acids. As an established method for comparison, we isolated nonesterified fatty acids from the plasma by thin-layer chromatography prior to methylation, using a number of simple precautions to limit oxidation. By performing all thin-layer chromatography steps in an atmosphere of nitrogen and by including fatty acid standards in the plasma with 0, 1, 2 or 4 double bonds, we were able to accurately and reproducibly determine the concentration of nonesterified fatty acids in the plasma, including arachidonate. We demonstrated that no oxidation occurred in the thin-layer chromatographic isolation of nonesterified fatty acids and that the coefficients of variation for repeat measurements of the same sample were < 11% using our reference method. Our data indicate that the use of acetyl chloride and methanol for assumed selective methylation of plasma nonesterified fatty acids results in significant methylation of esterified fatty acids.

Complexity of ethanolamine phosphate addition in the biosynthesis of glycosylphosphatidylinositol anchors in mammalian cells

Biosynthetic intermediates for the mammalian glycosylphosphatidylinositol (GPI) anchor have been described. The earliest GPI anchor precursor is N-acetylglucosaminylphosphatidylinositol, which is deacetylated to give glucosaminylphosphatidylinositol. This is followed by fatty acylation of the inositol ring, sequential addition of mannose residues donated by dolichyl mannosyl phosphate, and finally addition of ethanolamine phosphate. Here, we show that the final steps of GPI anchor biosynthesis are more complex than we have previously reported. Six distinct GPI anchor precursors were found to contain at least 1 ethanolamine phosphate residue. The headgroups of these glycolipids were purified and analyzed by a combination of Bio-Gel P4 chromatography and high resolution thin-layer chromatography. The sizes of neutral glycans were determined following HF dephosphorylation. The position of the ethanolamine phosphate residue was inferred from results of alpha-mannosidase treatment. Finally, the number of negative charges on the headgroups were determined by Mono Q chromatography. Our results show that the addition of ethanolamine phosphate is controlled by at least two different genes. Thus, the class F mutant, though unable to add ethanolamine phosphate to the third mannose residue, does incorporate ethanolamine phosphate into the first and second mannose residues. Only the wild type cells are capable of incorporating ethanolamine phosphate into the third mannose residue. Furthermore, the GPI core contains up to 3 ethanolamine phosphate residues. These results should facilitate the elucidation of the biochemical defects in paroxysmal nocturnal hemoglobinuria.

Inhibition of glycosylphosphatidylinositol anchor formation by mannosamine

Many eucaryotic cell surface proteins are anchored to the plasma membrane via a glycosylphosphatidylinositol (GPI), of which the core region is highly conserved from protozoa to mammalian cells. Previous studies (Lisanti, M. P., Field, M. C., Caras, I. W., Menon, A. K., and Rodiguez-Boulan, E. (1991) EMBO J. 10, 1969-1977) showed that mannosamine blocked the expression of a recombinant GPI-anchored protein in Madin-Darby canine kidney cells and converted this protein to an unpolarized secretory product. In the present study, we examined the effect of mannosamine on the formation of the glycan portion of the GPI anchor precursors. This amino sugar inhibited the incorporation of mannose into the glycan portion, and the inhibition was dose-dependent. Mannosamine was shown to be incorporated into the glycan as mannosamine, probably mostly in the second mannose position and thereby to block the further addition of mannose and other anchor components. The products formed in the presence of this drug were characterized by gel filtration and high resolution TLC both before and after deamination with nitrous acid and dephosphorylation by HF. Galactosamine and trehalosamine were inactive in this system, whereas glucosamine also inhibited mannose incorporation into GPI intermediates.