SLC22A15 is an organic zwitterion/cation transporter with broad substrate specificity for amino acids and their derivatives 1. It bidirectionally transports zwitterionic compounds including carnitine, acetylcarnitine, ergothioneine, carnosine, and glycine betaine, with lower affinity for cations like thiamine 1. Notably, SLC22A15 functions as a creatine efflux transporter in oligodendrocytes, where it remains inactive by default but becomes activated by external substrates (guanidinoacetic acid, GABA, MPP+) through one-to-one exchange, thereby controlling creatine release to supply neighboring neurons 2. The transport mechanism involves sodium-dependent symport or sodium-allosterically regulated facilitated diffusion 1. SLC22A15 is highly expressed in oligodendrocytes and bone marrow, with expression correlating with creatine synthesis enzyme levels 2. Disease relevance includes associations with bronchodilator response variation in Latino asthma patients, with rare variants identified in lung and bronchial epithelial tissues 3. SLC22A15 promotes hepatocellular carcinoma progression through enhanced cell proliferation, migration, and invasion 4, and facilitates pancreatic cancer epithelial-mesenchymal transition via glutathione accumulation and ROR1 signaling activation 5. These findings establish SLC22A15 as a multifunctional transporter with critical roles in brain creatine metabolism and potential involvement in cancer progression.