Quantitative changes in long-chain fatty acids during fetal and early postnatal development in rats

Linoleic acid-derived metabolites constitute the majority of oxylipins in the rat pup brain and stimulate axonal growth in primary rat cortical neuron-glia co-cultures in a sex-dependent manner

In adult rats, omega-6 linoleic acid (LA, 18:2n-6) serves as a precursor to oxidized LA metabolites (OXLAMs) known to regulate multiple signaling processes in the brain. However, little is known regarding the levels or role(s) of LA and its metabolites during brain development. To address this gap, fatty acids within various brain lipid pools, and their oxidized metabolites (oxylipins) were quantified in brains from 1-day-old male and female pups using gas chromatography and liquid chromatography coupled to tandem mass spectrometry, respectively. Primary neuron-glia co-cultures derived from postnatal day 0-1 male and female rat neocortex were exposed to vehicle (0.1% ethanol), LA, the OXLAM 13-hydroxyoctadecadienoic acid (13-HODE), or prostaglandin E2 at 10-1000 nM for 48 h to test their effects on neuronal morphology. In both male and female pups, LA accounted for 1-3% of fatty acids detected in brain phospholipids and cholesteryl esters. It was not detected in triacylglycerols, and free fatty acids. Unesterified OXLAMs constituted 47-53% of measured unesterified oxylipins in males and females (vs. ~5-7% reported in adult rat brain). Of these, 13-HODE was the most abundant, accounting for 30-33% of measured OXLAMs. Brain fatty acid and OXLAM concentrations did not differ between sexes. LA and 13-HODE significantly increased axonal outgrowth. Separate analyses of cultures derived from male versus female pups revealed that LA at 1, 50, and 1000 nM, significantly increased axonal outgrowth in female but not male cortical neurons, whereas 13-HODE at 100 nM significantly increased axonal outgrowth in male but not female cortical neurons. prostaglandin E2 did not alter neuronal outgrowth in either sex. This study demonstrates that OXLAMs constitute the majority of unesterified oxylipins in the developing rat brain despite low relative abundance of their LA precursor, and highlights a novel role of LA and 13-HODE in differentially influencing neuronal morphogenesis in the developing male and female brain.

Metabolic consequences of hypoxia from birth and dexamethasone treatment in the neonatal rat: comprehensive hepatic lipid and fatty acid profiling

Neonatal hypoxia is a common condition resulting from pulmonary and/or cardiac dysfunction. Dexamethasone therapy is a common treatment for many causes of neonatal distress, including hypoxia. The present study examined the effects of dexamethasone treatment on both normoxic and hypoxic neonatal rats. We performed comprehensive hepatic fatty acid/lipid profiling and evaluated changes in pertinent plasma hormones and lipids and a functional hepatic correlate, i.e. hepatic lipase activity. Rats were exposed to hypoxia from birth to 7 d of age. A 4-d tapering dose regimen of dexamethasone was administered on: postnatal day (PD)3 (0.5 mg/kg), PD4 (0.25 mg/kg), PD5 (0.125 mg/kg), and PD6 (0.05 mg/kg). The most significant finding was that dexamethasone attenuated nearly all hypoxia-induced changes in hepatic lipid profiles. Hypoxia increased the concentration of hepatic triacylglyceride and free fatty acids and, more specifically, increased a number of fatty acid metabolites within these lipid classes. Administration of dexamethasone blocked these increases. Hypoxia alone increased the plasma concentration of cholesterol and triacylglyceride, had no effect on plasma glucose, and only tended to increase plasma insulin. Dexamethasone administration to hypoxic pups resulted in an additional increase in plasma lipid concentrations, an increase in insulin, and a decrease in plasma glucose. Hypoxia and dexamethasone treatment each decreased total hepatic lipase activity. Normoxic pups treated with dexamethasone displayed increased plasma lipids and insulin. The effects of dexamethasone on hepatic function in the hypoxic neonate are dramatic and have significant implications in the assessment and treatment of metabolic dysfunction in the newborn.

Fatty acid composition of late embryonic and early postnatal rat brain

The fatty acid (FA) composition and distribution in a variety of phospholipids (PL) and neutral lipids (NL) at two discrete stages during the embryonic rat brain development were investigated. Over 96% of the FA were acylated into fetal brain PL at embryonic day 17 after the peak of neuronal proliferation and at embryonic day 20, one day prior to delivery. Phosphatidylcholine constituted approximately 60% of the total PL pool, phosphatidylethanolamine (PE) 30%, phosphatidylserine (PS) 6%, and phosphatidylinositol (PI) 4%. The diacylglycerols and triacylglycerols constituted 1-2% of the fetal brain lipids. alpha-Linolenic acid (18:3n-3) and linoleic acid (18:2n-6) were found in very low amounts in all fetal brain PL and NL. The percentage of the n-6 polyunsaturated FA, consisting of arachidonic acid (AA), 22:4n-6 and 22:5n-6, remained unchanged in all the fractions, except in PI, in which the proportion of AA increased. The concentration of docosahexaenoic acid (DHA) increased with age in all the fractions, with the bulk of accumulation accounted for by its increase in PE and, to a lesser extent, in PS. This finding suggests a "DHA accretion spurt" during the last three days of pregnancy.