Effects of pyrroloquinoline quinone (PQQ) and PQQ-oxazole on DNA synthesis of cultured human fibroblasts

The effects of pyrroloquinoline quinone (PQQ) and PQQ-oxazole (PQQ-glycine adduct) on DNA synthesis were examined using cultured human fibroblasts. Confluent fibroblasts were cultured in serum-free Dulbecco's modified Eagle's media, and various concentrations of PQQ and PQQ-oxazole were added to the media. After incubation for 24 h, [3H] thymidine was added to the media as an indicator for DNA synthesis of the cells. The thymidine incorporation into the cells was significantly enhanced even in the presence of very low concentrations of PQQ (0.003–0.03 μM); it remained significantly enhanced, up to 30 μM PQQ. However, the incorporation remarkably decreased at 750–1500 μM of PQQ. In contrast to the results for PQQ, DNA synthesis was not stimulated by addition of 0.003–3 μM PQQ-oxazole, but it was slightly enhanced at concentrations 15–750 μM. In morphological examination of the cultured human fibroblasts, cell density was increased by addition of 0.003–30 μM PQQ when compared with that of the control, supporting the above biochemical data. However, there were no distinct differences in morphological effect between PQQ and PQQ-oxazole.