Limitations in the use of 3-hydroxy fatty acid analysis to determine endotoxin in mammalian samples.

3-Hydroxy fatty acids (3-OH FAs) of 10-18-carbon chain lengths are constituents of the lipopolysaccharide of Gram-negative bacteria. These acids are used as chemical markers for determining endotoxin in environmental samples. The present communication addresses the question whether this type of analysis also would be applicable to mammalian samples. Low levels (6.1+/-1.6-94.0+/-23.2 pmol/ml) of the studied 3-OH FAs were detected in blood from both conventional and germ-free rats. The levels were considerably higher (0.0-1.06+/-0.17 nmol/mg) in livers. The amounts of the 3-OH FAs did not differ between the two groups of rats. All analyses were made by gas chromatography-tandem mass spectrometry (GC-MSMS) for unequivocal identification. The results illustrate a limitation in using 3-OH FA analysis to determine endotoxin in mammalian samples since these acids may represent not only endotoxin but also products from mammalian mitochondrial fatty acid beta-oxidation.