[Biosynthesis of fatty acids in mouse brain mitochondria in the presence of malonyl-CoA or acetyl-CoA]

Utilization of high-density lipoprotein sphingomyelin by the developing and mature brain in the rat

Utilization of very long chain saturated fatty acids by brain was studied by injecting 20-day-old and adult rats with high-density lipoprotein containing [stearic or lignoceric acid-14C, (methyl-3H)choline]sphingomyelin. Labeling was followed for 24 h. Very small amounts of 14C were recovered in the brain of all rats, and there was no preferential uptake of lignoceric acid. Approximately 20% of the entrapped 14C was located in the form of unchanged sphingomyelin 24 h after injection. This result shows that the rat brain utilizes very little very long chain fatty acids (greater than or equal to 20 C atoms) from high-density lipoprotein sphingomyelin, even during the myelinating period. The [3H]choline moiety from sphingomyelin was recovered in brain phosphatidylcholine in a higher proportion in comparison with the 14C uptake. The brain 3H increased throughout the studied period in all experiments, but was much higher in the myelinating brain than in the mature brain. From the radioactivity distribution in liver and plasma lipids, it is clear that the choline 3H in the brain originates from either double-labeled phosphatidylcholine of lipoproteins or tritiated lysophosphatidylcholine bound to albumin, both synthesized by the liver.

Fatty acid synthesis in mitochondria from Saccharomyces cerevisiae

The ability of purified mitochondria isolated from S. cerevisiae to synthesize fatty acids and especially very long chain fatty acids (VLCFA) has been investigated. The VLCFA synthesis requires malonyl-CoA as the C2 unit donor and NADPH as the reducing agent. Moreover the yeast mitochondrial elongase is able to accept either exogenous long chain fatty acyl-CoAs as substrates or elongate endogenous substrates. In the latter case, ATP is required for full activity. Besides this important VLCFA formation, the mitochondria from S. cerevisiae were also able to synthesize C16 and C18.

Recovery of altered fatty acid composition induced by a diet devoid of n-3 fatty acids in myelin, synaptosomes, mitochondria, and microsomes of developing rat brain

Rats were fed a semisynthetic diet containing either sunflower oil or soya oil. Half the litter fed with sunflower oil diet was changed to a soya oil diet when the pups were 15 days old (during active myelination). Fatty acid analysis was then performed on subcellular fractions of the animals fed (a) soya oil, (b) sunflower oil, and (c) soya oil replacing sunflower oil from the 15th day, to determine the speed of the recovery. All material from animals fed sunflower oil showed an important reduction in docosahexaenoic acid (22:6 n-3), compensated by an increase in docosapentaenoic acid (22:5 n-6), whereas arachidonic acid (20:4 n-6) was not affected. In all fractions examined, when sunflower oil was replaced by soya oil in 15-day-old pups the recovery started from the very first day but lasted more than 2 months (this recovery was determined by the increase of 22:6 n-3 up to the normal value and decrease of the 22:5 n-6). In addition a delay was found for myelin recovery, starting only from the 25th day.

Distribution of radioactivity in myelin lipids following subcutaneous injection of [14C]stearate

Blood fatty acids are an important parameter for the synthesis of brain myelin as exogenous stearic acid is needed: after subcutaneous injection to 18-day-old mice this labelled stearic acid is transported into brain myelin and incorporated into its lipids. However the acid is partly metabolized in the brain by elongation (thus providing very long chain fatty acids, mainly lignoceric acid) or by degradation to acetate units (utilized for synthesis of medium chain fatty acids as palmitic acid, and cholesterol). These metabolites are further incorporated into myelin lipids. The myelin lipid radioactivity increases up to 3 days; most of the activity is found in phospholipids; their fatty acids are labelled in saturated as well as in polyunsaturated homologues but sphingolipids, especially cerebrosides, contain also large amounts of radioactivity (which is mainly found in very long chain fatty acids, almost all in lignoceric acid). The occurrence of unesterified fatty acids must be pointed out, these molecules unlike other lipids, are found in constant amount (expressed in radioactivity per mg myelin lipid).

Lignoceric acid biosynthesis in the developing brain. Activities of mitochondrial acetyl-CoA-dependent synthesis and microsomal malonyl-CoA chain-elongating system in relation to myelination. Comparison between normal mouse and dysmyelinating mutants (quaking and jimpy)

Age-related changes in the activities of microsomal and mitochondrial elongating systems have been determined in mouse brain from birth to maturity. In microsomes, the components necessary for behenyl-CoA (docosanoly-CoA) elongation have been found to be NADPH and malonyl-CoA. In mitochondria, both NADH and NADPH are used and acetyl-CoA is the only donor of two-carbon-atoms unit. The synthesised fatty acids were identified by thin-layer and gas chromatography. The specific activity is higher in microsomes than in mitochondria. In microsomes, the specific activity for malonyl-Co-A incorporation reached a maximum at 15 - 20 days of age; this peak was not obtained in the Quaking and Jimpy mutants. The increase in enzyme activity (specific activity and total activity per brain) paralleled the myelin deposition. The activity of the mitochondrial system increases regularly during development: it is not correlated to myelination and it is not affected in the Quaking mutant. The interplay between microsomal and mitochondrial elongation systems is studied.