Cellular Uptake of Pyrroloquinoline Quinone in Its Intact and Derivatized Forms from the Cell Culture Medium of 3T3-L1.

Following a growing interest in the physiological effects of pyrroloquinoline quinone (PQQ), more cell culture experiments have begun to elucidate its mechanism of action. However, to our knowledge, no reports have used instrumental analysis, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS), to study cellular uptake of PQQ. In addition, despite the propensity of PQQ to react with amino acids and other compounds, only a handful of cell culture experiments have been conducted on PQQ derivatives. In the present study, we prepared PQQ derivatives by reacting PQQ with various amino acids and used them as reference standards for optimizing the LC-MS/MS analysis conditions to detect PQQ and its derivatives. Using this method, we evaluated the uptake of PQQ into mouse 3T3-L1 cells and found that most PQQ added to the medium was taken up by the cells in its unchanged form, while some PQQ reacted with amino acids in the medium and was taken up by the cells as PQQ derivatives. These results suggest that PQQ derivatives may contribute to the physiological effects of PQQ. To further elucidate the function of PQQ, it is necessary for future studies to clarify the activity of PQQ derivatives and to evaluate the types of PQQ present in food, animal, and cell samples in more detail.