ABSTRACT
OBJECTIVE To investigate and compare the enzyme kinetic characters of psoralen (PRN)and isopsoralen(IPRN)in rat and human liver microsomes. METHODS PRN and IPRN in liver microsomes incubates were determined using LC-MS/MS. The enzyme kinetic and metabolic stability of PRN and IPRN were investigated by employing the optimized rat and human liver microsomes incubations. The Vmax and Km values were calculated using the nonlinear regression method. RESULTS The quanti?tative method showed good linearity within the range of 0.1-50.0 μmol · L-1 and was suitable for the assay in biological samples. The in vitro elimination was linear with the substrate concentrations lower than 1 μmol,the protein concentration within 0.5 g · L-1,and the incubation time within 40 min. The t1/2 values of PRN and IPRN in rat and human liver microsomes were 74.5,95.0,74.5 and 173.3 min, respectively. The Vmax values of PRN in rat and human liver microsomes were(1.140±0.080)μmol·min-1·g-1 protein,(0.620±0.060)μmol·min-1·g-1 protein,while Km values of PRN in rat and human liver microsomes were (12.9 ± 0.3)μmol · L- 1,(7.4 ± 1.3)μmol · L- 1,respectively. The Vmax values of IPRN in rat and human liver microsomes were(0.251±0.012)and(0.103±0.014)μmol·min-1·g-1 protein,while Km values of IPRN in rat and human liver microsomes were (3.0 ± 0.4)μmol · L-1,(3.4 ± 0.7)μmol · L-1,respectively. CONCLUSION The enzyme kinetic characters and metabolic stability of PRN and IPRN show species and chemical structures related differences. Interestingly,the metabolic eliminations of PRN and IPRN are similar in rats. However,the metabolic elimination of IPRN in humans involved in CYP enzymes may be much slower than that of PRN.
ABSTRACT
Objective To develop a steady-state brain distribution model in rats and to assess the blood brain barrier(BBB) penetration of antipyrine, atenolol and a group of ZZB candidate compounds. Methods Antipyrine, atenolol and ZZB compounds were administered to rats by an initial iv bolus dose (loading dose) followed by iv infusion at a constant rate for 30-40 min to reach steady-state plasma kinetics. The blood and brain tissue samples were then collected. The steady-state concentrations of the samples were measured by LC-MS/MS. The steady-state ratio of brain to plasma concentration (Kp) was calculated. The drugs and candidate compounds were also tested with Caco-2 cell model and the apparent bidirectional transport permeability coefficient (Papp) was obtained. Results Antipyrine and atenolol were known as drugs with high and low BBB penetration properties respectively. The mean brain concentrations of antipyrine and atenolol at steady-state were(2561 ± 125) and(20.1±0.8)ng/g with the Kp values of 0.93 ± 0.04 and 0.015 ± 0.002, respectively. The Kp value of antipyrine was about 60 folds higher than that of atenolol. Despite the similar structures of ZZB compounds, the Kp values were varied in the range from 0.044 to 6.41. The Kp values were not correlated with Papp values yielded from Caco-2 cell model. Conclusion The established rat steady-state brain distribution model is simple, reliable and could significantly reduce the animal use. It is a practical in vivo model for assessment of BBB penetration of drugs.