Pharmacokinetics Study Of Metformin

Metformin is widely used in the treatment of type 2 diabetes. It can not only lower the blood glucose concentration, but also lose body weight and depress food intake. However, little information is available on its pharmacokinetics and distribution in different tissues and organs. And the mechanism of metformin acting in the central nervous system is not very clear yet.In the present study, high performance liquid chromatography was performed to investigate the distribution and pharmacokinetic properties of metformin in rats. Caco-2 cell line was used to study the uptake and transport characteristics of metformin, as well as the relationship of metformin with P-gp. The effect of metformin on CYP450 was also investigated using the methods of hepatic microsome incubations and RT-PCT technology. The central role of metformin in the regulation of appetite, body weight and locomotor in the rats was examined, and the effect of central administration of metformin on POMC and NMU expressions known to be important to the maintenance of energy homeostasis was also analyzed in the hypothalamus of the rats.1. Pharmacokinetics and tissue distribution of metformin in ratsA simple, rapid and accurate HPLC assay was established for quantitative analysis of metformin in rat plasma and organ tissues. The plasma concentration-time curve of metformin revealed that the pharmacokinetics of metformin in vivo fulfills the one-compartment model. The absorption, distribution and clearance of the drug in vivo were all rapid, and the clearance appeared to be mainly via the kidney. Metformin could also across the blood brain barrier. The absolute bioavailability in rats was low.2. Uptake and transport characteristics of metformin in the Caco-2 cell and its relation with P-gpThe uptake and transport of metformin in Caco-2 cells were measured using HPLC. A calcein AM system was used to further evaluate the relation between metformin and P-gp. The results showed that metformin was readily absorbed in a concentration-related manner, and when metformin concentration was stable, the absorption was related with time. Metformin was able to permeate across Caco-2 cells (P_app=2.86×10^-6cm/s) . The uptake and transport characteristics of metformin were not influenced by verapamil which is a specific inhibitor of P-gp. Metformin had no effect on the level of calcein in Caco-2 cells.3. The effects of metformin on CYP3A1 and its metabolism in vitroThe time-related and dose-related effects of metformin on the expression of CYP3A1 mRNA in vivo in the liver of rats were examined. The effect of the drug on CYP3A1 activities at the protein levels was also determined in vivo and in vitro in the rat hepatic microsome incubations using erythromycin as the substrate, rifarnpicin as the inducer and ketoconazole as the inhibitor of CYP3A1. The results showed metfromin could induce CYP3A1 mRNA with a concentration dependent manner. However, metfromin could not induce the enzyme activity of CYP3A1 either in vitro or in vivo. CYP450 might have an overall effect on the metabolism of metformin, although the drug was seemed not to be a substrate specific for CYP3A1.4. Preliminary study of metformin in regulating energy homeostasis in the central nervous systemThe central effects of metformin on the food intake, body weight and the locomotor in the rats intracerebroventricularly administrated with the drug were investigated. The changes in expression of some genes in the hypothalamus involved in energy homeostasis were also determined in the rats with ICV injection of metformin. The results showed that metformin had effects on the reductions of food intake and body weight and the increase of the locomotor in the animals after a single ICV administration; however, the expression results showed that such central anorexigenic and energy expenditure effects of metformin seemed not to be related with either POMC or NMU signaling pathway.