Discovery of pyridoxal reductase activity as part of human vitamin B6 metabolism.

•Pyridoxine strongly accumulates in CSF of PLP-treated patients, thus suggesting the existence of a PN-forming enzyme;•Our in vitro studies show that all mammalian cell lines tested reduce PL to PN in a time- and dose-dependent manner;•We expand the number of enzymes with a role in human vitamin B6 metabolism;•PL reductase(s) may play an important role in limiting the intracellular accumulation of PL and PLP.