Flow cytometric determination of 5-bromo-2′-deoxyuridine pharmacokinetics in blood serum after intraperitoneal administration to rats and mice

5-Bromo-2'-deoxyuridine (BrdU) is a marker that is widely used to label S-phase cells in neurobiological research in most common doses 50 or 100 mg/kg per single intraperitoneal (i.p.) injection. However, the important data regarding its pharmacokinetics in rodents are still missing. The aim of our study was to investigate the BrdU level in serum after a single i.p. injection to adult rats (doses: 50 or 100 mg/kg) and adult mice (50 mg/kg). The animals were killed at selected time-points after the BrdU injection, and proliferating tumour cells (cell lines HCT-116 and HL-60) were co-cultivated with isolated blood sera. BrdU incorporated in the DNA of the S-phase tumour cells was stained with an anti-BrdU antibody and analysed using flow cytometry. In rats, the efficacies of BrdU labelling of S-phase cells in both in vitro and in vivo conditions were compared in the 50 and 100 mg/kg groups. According to our results, BrdU was in saturated concentration to label almost all S-phase cells for 60 min in both doses and was detectable in blood serum until 120 min after the single i.p. injection. However, the 100 mg/kg dose of BrdU did not provide a prolonged staining period to offset the potentially higher toxicity in comparison with the 50 mg/kg dose. In mice, due to their faster metabolism, the concentration of BrdU in blood serum was sufficient to label the whole population of S-phase cells for only 15 min after the i.p. injection, then dropped rapidly.