Betaine, the trimethyl derivative of the amino acid glycine, is a metabolite of plant and animal tissues. In plants, betaine is particularly synthesised and accumulated as an osmoprotectant against salt and temperature stress. In animals, betaine is the product of choline oxidation or it originates from nutritional sources.
Betaine as an osmotic active substance:
In vertebrates, betaine accumulation is stimulated by external hyperosmolarity in the renal cells (Bagnasco et al.1986; Nakanishi et al. 1990; Moeckel & Lien, 1997) and macrophages (Warskulat et al. 1995; Zhang et al. 1996).
Betaine also acts as an organic osmolyte in mouse embryos(Dawson & Baltz, 1997), mouse hybridoma cells (Oyaas et al. 1995), rat liver sinusoidal epithelial cells (Weik et al. 1998; Wettstein et al. 1998), rat hepatic stellate cells (Peters-Regehr et al. 1999) and chick embryo fibroblasts (Tramacere et al. 1984; Petronini et al. 1992). Osmolytes are particularly important in situations of cellular dehydration since these compounds help to minimize water loss against a prevailing osmotic gradient (Klasing et al. 2002).
Betaine exerts an osmoprotective effect by accumulating in cell organelles and cells exposed to osmotic and ionic stress, thereby replacing inorganic ions and protecting enzymes as well as cell membranes from inactivation by inorganic ions (Petronini et al. 1992). Changes in cell water volume are known to affect cell activity. For example, a slight increase in the volume of liver cells directs the cells into a more anabolic state, whereas the reverse may happen with loss of water (Haussinger, 1998). Thus, water homeostasis is an important factor for cells exposed to different osmotic pressures. Furthermore, it is known that endothelial cells exposed to a hyperosmotic media stop cell proliferation and undergo apoptosis (Alfieri et al. 2002). Betaine has been shown to exert anti-apoptotic effects and to promote cell proliferation in a hyperosmotic medium (Alfieri et al. 2002).
Finally, there is some evidence that betaine reduces energy expenditure for ion pumping in cells exposed to hyperosmotic media (Moeckel et al. 2002). The spared energy may promote cell proliferation as well.
Osmotic capacity of betaine in the gut:
Intestinal cells always have to cope with variable osmotic media since the luminal content of the intestine is hyperosmotic in relation to blood plasma (Mongin, 1976). Moreover, the process of nutrient digestion and absorption necessitates osmolytic protection mechanisms since intestinal cells mediate the exchange of water, small solutes such as ions, nutrients and macromolecules between plasma and intestinal fluid. Betaine is thought to be an important organic osmolyte for the control of the osmotic pressure inside the intestinal epithelial cells (Hochachka & Somero, 1984).
Osmotic protection would allow for the maintenance of water balance and intestinal cell volume, thereby facilitating secretion of digestive enzymes. If betaine stimulates cell proliferation in the intestinal tissue, the enlarged gut wall epithelium would provide an increased surface for nutrient absorption. Effects of betaine as an osmotic active substance may be more pronounced in animals exposed to osmotic disorders such as Diarrhea, Heat Stress, coccidiosis in poultry.