Novel in vitro dynamic metabolic system for predicting the human pharmacokinetics of tolbutamide.

Liver metabolism is commonly considered the major determinant in drug discovery and development. Many in vitro drug metabolic studies have been developed and applied to understand biotransformation. However, these methods have disadvantages, resulting in inconsistencies between in vivo and in vitro experiments. A major factor is that they are static systems that do not consider the transport process in the liver. Here we developed an in vitro dynamic metabolic system (Bio-PK metabolic system) to mimic the human pharmacokinetics of tolbutamide. Human liver microsomes (HLMs) encapsulated in a F127'-Acr-Bis hydrogel (FAB hydrogel) were placed in the incubation system. A microdialysis sampling technique was used to monitor the metabolic behavior of tolbutamide in hydrogels. The measured results in the system were used to fit the in vitro intrinsic clearance of tolbutamide with a mathematical model. Then, a PBPK model that integrated the corresponding in vitro intrinsic clearance was developed to verify the system. Compared to the traditional incubation method, reasonable PK profiles and the in vivo clearance of tolbutamide could be predicted by integrating the intrinsic clearance of tolbutamide obtained from the Bio-PK metabolic system into the PBPK model. The predicted maximum concentration (Cmax), area under the concentration-time curve (AUC), time to reach the maximum plasma concentration (Tmax) and in vivo clearance were consistent with the clinically observed data. This novel in vitro dynamic metabolic system can compensate for some limitations of traditional incubation methods; it may provide a new method for screening compounds and predicting pharmacokinetics in the early stages, supporting the development of compounds.

[Role mechanism of extracellular polymeric substances in the formation of aerobic granular sludge].

During the aerobic granulation of activated sludge in SBR, the changes in the key components of sludge EPS (extracellular polymeric substances) and surface characteristics, and the correlation between them were analyzed. The SDS-PAGE results of exopolymeric protein for different sludge samples indicated that the distribution of bands for protein molecular weight was in the range of 31.0 x 10(3) - 97.4 x 10(3). Compared with seed sludge, some new protein bands increased with the aerobic granulation, and the color of the bands were enhanced, indicating the species and contents of exopolymeric protein gradually increased with the granulation. Moreover the quantitative determination indicated that the protein excreted increased from 49.4 mg x g(-1) to 148.3 mg x g(-1) with the granulation. There was no obvious increase in the polysaccharide content. The PN/PS ratio was increased from to 2.3 to 4.9 accordingly. The cell hydrophobicity of aerobic granular sludge was 1 time higher than that of seed sludge. The changes in cell hydrophobicity were positively correlated with PN/PS values, and the related coefficient was 0.969. The average Zeta potential of seed sludge and granular sludge was -28.5 mV and -13.2 mV, respectively. Obviously, the surface negative charges of granular sludge decreased. From the protein characteristics, we speculate the increase in exopolymeric protein content may enhance cell relative hydrophobicity and reduce negative surface charges, thus contributing to aerobic granulation.