	Mammalian cells are unable to synthesize choline "de novo" and therefore must rely on exogenous sources from the diet. The uptake of choline is accomplished predominantly by the high-affinity, sodium dependent choline transporter (CHT) and requires ATP as an energy source. On the other hand, choline may enter the cell through the activation of low-affinity, sodium-independent organic cation transport proteins (OCTs) and/or carnitine/organic cation transporters (OCTNs), and do not require ATP. Lastly, choline may enter the cell through intermediate-affinity transporters, which include the choline transporter-like protein 1 (CTL1).