Dietary Linolenic and Docosahexaenoic Acid Influence the Docosahexaenoic Acid Content of Brain Membrane Lipids and Function in Developing Rats

Raffick Amid Razzakk Bowen, Ph.D., Thesis defended 2001.

Thesis Abstract

One of the debates in infant nutrition concerns whether or not dietary C18:3n-3 can provide for accretion of C22:6n-3 in neonatal tissues. The functional significance of C22:6n-3 in brain has not been fully elucidated.

The objectives of this study were to investigate if:

(1) increasing maternal dietary linolenic acid (C18:3n-3) increases the docosahexaenoic acid (C22:6n-3) content in neuronal cell phospholipids in two-week-old rat pups; (2) increasing maternal dietary C18:3n-3 increases the C18:3n-3 and C22:6n-3 content of different tissues of two-week-old rat pups;

(3) maternal dietary C22:6n-3 is more effective than high C18:3n-3 at increasing the C22:6n-3 content in neuronal and glial cell phospholipids in rat pups at two weeks of age;

(4) maternal dietary C20:4n-6 and C22:6n-3 increases synaptic plasma membrane (SPM) phospholipid and cholesterol content, SPM phospholipid C20:4n-6 and C22:6n-3 content, and SPM sodium-potassium adenosine triphosphatase (Na, K-ATPase) activity in rat pups at two and five weeks of age;

(5) C20:4n-6 and C22:6n-3 are present in gangliosides of SPM;

(6) C20:4n-6 and C22:6n-3 content in SPM gangliosides can be altered by diet fat; and

(7) alkaline ceramidase (CDase) activity is present in the SPM in two-week-old rat pups.

The stomach fatty acid composition of the rat pups reflected the diets of their respective dams.

Objective (1) established that phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) of neuronal cells showed no significant increase in C22:6n-3 content with high levels of C18:3n-3 in maternal diet;

objective (2) showed that C18:3n-3 content in the whole body, brain, liver, skin, epididymal fat pads, and muscles was significantly greater in rat pups fed high compared to low C18:3n-3 diet but the C22:6n-3 content in these tissues was not quantitatively different;

objective (3) showed that the C22:6n-3 content in PE and PS of both neuronal and glial cell was higher when rat pups were fed C22:6n-3 compared C18:3n-3 diet (p<0.05);

and objective (4) demonstrated that rats fed a maternal diet with C20:4n-6 and C22:6n-3 from two to five weeks of age: a) does not increase SPM cholesterol and phospholipid content, b) increases the C20:4n-6 (mainly PS) and C22:6n-3 content of SPM phospholipids, c) increases the SPM Na, K-ATPase Vmax (activity) (~2-fold) but not Km compared to a low C18:3n-3 diet;

objective (5) showed by gas-liquid chromatography (GC) and GC-mass spectrometry that C20:4n-6 and C22:6n-3 are present in gangliosides of SPM of two-week-old rats;

objective (6) suggest that the C20:4n-6 and C22:6n-3 content of SPM gangliosides of two-week-old rats can be altered by diet fat;

and objective (7) showed that alkaline CDase activity is present in the rat SPM and is approximately 15-fold greater than brain homogenate.

It is concluded that dietary C22:6n-3 but not C18:3n-3 supports accretion of C22:6n-3 in neonatal tissues and that increasing the C22:6n-3 content of brain membrane phospholipid increases the activity of SPM Na, K-ATPase. It is also concluded that the presence of alkaline CDase activity in the SPM with the changes in C20:4n-6 and C22:6n-3 content of SPM gangliosides by diet fat may alter the activity of SPM alkaline CDase. Thus, dietary C18:3n-3 and C22:6n-3 can influence the structure and function of brain membrane lipids. This study supports the rationale for providing C20:4n-6 and C22:6n-3 in infant formulas.