Applied nutritional investigationGlycerophosphocholine enhances growth hormone secretion and fat oxidation in young adults
Introduction
Choline is crucial for normal cell function and plays several vital roles in the body [1]. It is an important dietary nutrient, which, in humans, is related to neurotransmission (acetylcholine), transmembrane signaling, methyl metabolism, synthesis of phospholipids in the cell membrane, and fat and cholesterol metabolism [2]. Several human studies have demonstrated that a choline-deficient diet induces the development of hepatic steatosis and tissue damage (e.g., in patients receiving total parenteral nutrition), but the effect resolves when a source of dietary choline is provided [3], [4], [5]. In healthy male subjects with normal folate and vitamin B12 levels, average plasma free choline levels were about 10 μmol/L, and a 3-wk diet deficient in choline lowered these levels to about 7 μmol/L, leading to incipient liver dysfunction [1]. Moreover, in rodents and humans, choline deficiency affects brain structure and function [6] and increases the risk of neural tube defects [7], coronary artery disease [8], and cancer [9]. Therefore, the Institute of Medicine of the National Academy of Sciences (USA) recognizes choline as an essential nutrient for humans and has made recommendations for the dietary choline intake [10].
α-Glycerophosphocholine (GPC) is synthesized from beans and is a natural choline compound that has been used in medicines and supplements. In clinical trials, choline supplementation has been found to improve dementia, memory, and cognitive impairments in patients with Alzheimer’s disease [11], [12]. Although it has been shown that GPC supplements may substitute for insufficient dietary choline and protect the liver [1], the effects of a single dose of GPC on hepatic fat metabolism in healthy subjects with sufficient dietary sources of choline are unclear.
Orally administered GPC is effectively absorbed in the intestine [13], and plasma total choline levels increase rapidly after the ingestion of GPC, with high circulating levels of choline maintained for over 24 h in animal models [13], [14]. We hypothesized that GPC administration would increase the fat metabolism in healthy young adults, and that ingested GPC might play a role in the regulation of growth hormone (GH) secretion. We investigated eight young Japanese men to clarify whether acute ingestions of GPC increased resting GH secretion. To confirm the GPC effects on fat metabolism, we examined whether the GPC-induced changes in GH secretion concomitantly affected serum free fatty acid (FFA) and glycerol. Moreover, we measured acetoacetate and 3-hydroxybutyrate, which are indices of fat oxidation in the liver.
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Subjects
Eight healthy males participated in this study (mean ± standard error: age 25.4 ± 1.1 y old, height 171.3 ± 1.9 cm, body mass 66.0 ± 2.2 kg, fat mass 11.4 ± 1.1%). Subjects were informed about the experimental procedures and the potential risks involved, and written consent was obtained. The inclusion criteria were as follows: participants should not be habitual consumers of any fatty acid supplement or medication known to affect lipid metabolism, should have no symptoms of chronic disease, and
Free choline levels
No significant difference was observed in plasma free choline levels at baseline. The average basal plasma free choline concentrations were 8.1 ± 1.4 and 8.5 ± 1.6 μmol/L for the GPC and placebo groups, respectively. In response to ingesting GPC, free choline concentrations increased significantly within 60 min and were maintained for the entire experimental period in the GPC group (Fig. 1). In contrast, no significant changes in plasma free choline concentrations were observed in the placebo
Discussion
In the present study, we observed that the oral ingestion of GPC acutely increased plasma free choline levels by 50% within 60 min and concomitantly increased GH concentrations in young adult male subjects. In addition, serum FFA, acetoacetate, and 3-hydroxybutyrate levels increased significantly, and serum glycerol was modestly increased 120 min after GPC ingestion. However, blood glucose levels were not affected. Thus, acute oral doses of GPC may increase GH secretion and hepatic fat
Conclusion
In response to a single oral dose of GPC, we observed an increase in plasma free choline levels, a concomitant increase in GH secretion, and increased FFA and ketone body levels. These findings suggested that a single dose of GPC may increase GH secretion and fat oxidation in young adults.
Acknowledgments
The authors are grateful to Dr. H. Hibino (NOF Corporation) for informative discussions regarding the report.
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