Research ReportSynaptic proteins and phospholipids are increased in gerbil brain by administering uridine plus docosahexaenoic acid orally
Introduction
The synthesis in brain of phosphatidylcholine (PtdCho) and other membrane phosphatides can utilize, besides glucose, three compounds obtained from the circulation (Kennedy and Weiss, 1956): choline; a pyrimidine like uridine; and a polyunsaturated fatty acid (PUFA) like docosahexaenoic acid (DHA) (Rapoport, 2001, Marszalek and Lodish, 2005); all three readily cross the blood–brain barrier (Cornford et al., 1978, Li et al., 2001, Spector, 2001, Hashimoto et al., 2002). The choline is phosphorylated to form phosphocholine through the action of choline kinase (CK), a low-affinity enzyme that is unsaturated with choline at normal brain choline levels (Spanner and Ansell, 1979, Millington and Wurtman, 1982). The uridine is phosphorylated by uridine–cytidine kinase (Suzuki et al., 2004) to uridine triphosphate (UTP), which is further transformed by the enzyme CTP synthetase (Genchev and Mandel, 1974) to cytidine triphosphate (CTP), the rate-limiting precursor in PtdCho synthesis (Ross et al., 1997). Both of these latter enzymes are also low affinity, hence giving a single oral dose of uridine-5′-monophosphate (UMP), a uridine source sequentially increases brain uridine, UTP and CTP (Cansev et al., 2005). The phosphocholine and CTP combine to form cytidine-5′-diphosphocholine (CDP-choline), which then combines with diacylglycerol (DAG), including species containing DHA or another PUFA, to yield the PtdCho. The Kennedy cycle similarly synthesizes phosphatidylethanolamine (PtdEtn) from uridine and PUFA like DHA, but starting with ethanolamine, instead of choline.
Although DHA is found in PtdCho, PtdEtn and other brain membrane phosphatides (Marszalek and Lodish, 2005, Knapp and Wurtman, 1999), apparently no information is available concerning the effects of DHA's oral administration on brain phosphatide levels in vivo. Moreover, while a single dose of UMP has been shown to increase brain CDP-choline levels (Cansev et al., 2005), suggesting that it also accelerates PtdCho synthesis (Lopez-Coviella et al., 1995), no direct evidence is available that any treatment regimen involving uridine also affects brain PtdCho levels. We now show that oral administration of DHA or UMP, given alone for several weeks to animals consuming a choline-containing diet, can increase brain PtdCho and other major membrane phosphatides. Moreover, the effect of giving both DHA and UMP tends to be greater (P < 0.01 for SM) than the sum of the effects observed when each is given separately. This increase may include synaptic membranes inasmuch as the treatment also increases levels of presynaptic and postsynaptic proteins.
Section snippets
Effects of UMP and/or DHA on brain phosphatides
Animals received just the control diet or one of the three experimental treatments for 4 weeks; brain samples were assayed as described in Experimental Procedures, and phosphatide levels were given as nmol/mg protein. Addition of UMP to the standard diet without concurrent DHA treatment significantly increased brain levels of PtdCho, PtdEtn and PtdIns by 13%, 29% and 48%, respectively (Table 1A). Administration of DHA, without UMP, also significantly increased brain levels of these phosphatides
Discussion
These data show that administering DHA by gavage or UMP via the diet, daily for 4 weeks, significantly increases brain membrane PtdCho levels (Table 1A) among gerbils consuming a standard, choline-containing diet. These effects are observed whether the PtdCho is expressed per mg protein or per cell (DNA), indicating that each brain cell, on average, contains more of the membrane phosphatide. Moreover, when all three of the potentially limiting circulating precursors (i.e., choline, uridine and
Drugs and chemicals
DHA was purchased from Nu-Chek Prep, Inc. (Elysian, MN, USA). UMP was kindly provided by Numico Research (Wageningen, Netherlands). Control and UMP-containing diets were prepared by Harlan-Teklad (Madison, WI, USA). Standards for phospholipids were purchased from Sigma Chemicals (St. Louis, MO, USA). Mouse anti-NF-70, mouse anti-tubulin beta III subunit, and rabbit anti-NF-M were purchased from Chemicon (Temecula, CA, USA); mouse anti-PSD-95 from Upstate (Lake Placid, NY, USA); and mouse
Acknowledgments
The authors thank Dr. Mark Vangel for his help with statistical analyses. This work was supported by grants from the National Institutions of Health (Grant MH-28783), the Center for Brain Sciences and Metabolism Charitable Trust and the Turkish Academy of Sciences (IH Ulus).
References (43)
- et al.
Oral choline increases choline metabolites in human brain
Psychiatry Res.
(2004) - et al.
Oral uridine 5′ monophosphate (UMP) increases brain CDP-choline levels in gerbils
Brain Res.
(2005) - et al.
A simple method for the isolation and purification of total lipides from animal tissues
J. Biol Chem.
(1957) - et al.
SAP family proteins
Biochem. Biophys. Res. Commun.
(2000) - et al.
The function of cytidine coenzymes in the biosynthesis of phospholipids
J. Biol. Chem.
(1956) - et al.
Enhancement of free fatty acid incorporation into phospholipids by choline plus cytidine
Brain Res.
(1999) - et al.
A simple, rapid and sensitive DNA assay procedure
Anal. Biochem.
(1980) - et al.
Induction of neurofilament triplet proteins in PC12 cells by nerve growth factor
Brain Res.
(1982) - et al.
Long-chain acyl-Coa synthetase 6 preferentially promotes DHA metabolism
J. Biol. Chem.
(2005) - et al.
Is docosahexaenoic acid, an n-3 long-chain polyunsaturated fatty acid, required for development of normal brain function? An overview of evidence from cognitive and behavioral tests in humans and animals
Am. J. Clin. Nutr.
(2005)