Mechanism of biosynthesis of trimethylamine oxide from choline in the teleost tilapia, Oreochromis niloticus, under freshwater conditions

The mechanism of biosynthesis of trimethylamine oxide (TMAO) from dietary precursors in the teleost tilapia (Oreochromis niloticus) was investigated. Diets supplemented with quaternary ammonium choline, glycine betaine, carnitine or phosphatidylcholine were administered and significant increases in TMAO levels in the muscle were only observed with choline. Methyl-14C] and 1,2-14C] cholines were given through dietary and intraperitoneal injection routes, but 14C-TMAO was detected only in fish with dietary administration of methyl-14C] choline. Dietary treatment with 15N] choline resulted in the formation of 15N] TMAO in the muscle. The incorporation of radioactivity into TMAO was also observed both following dietary administration and intraperitoneal injection of 14C] trimethylamine (TMA). When choline was introduced into the isolated intestine, marked increases in TMA levels occurred. These increases were significantly suppressed in the presence of penicillin. 14C]-TMA derived from methyl-14C] choline was detected in the cavity of the isolated intestine. The introduction of 15N] choline into the intestinal cavity resulted in the formation of 15N] TMA. TMA mono-oxygenase activities were detected in the liver and kidney. We conclude that tilapia possess the ability to produce TMAO from choline, which is related to intestinal microorganisms and tissue mono-oxygenase under freshwater conditions.