Investigation of the role and quantitative impact of breast cancer resistance protein on drug distribution into brain and CSF in rats.

Breast cancer resistance protein (BCRP) expressed in the blood-brain barrier plays a major role in limiting drug distribution into the central nervous system (CNS). However, functional involvement of BCRP in drug distribution into the brain and cerebrospinal fluid (CSF) remains unclear. The aim of present study was to reveal the role and quantitative impact of BCRP on CNS distribution. The brain-to-plasma unbound concentration ratio (Kp,uu,brain) and CSF-to-plasma unbound concentration ratio (Kp,uu,CSF) values of BCRP-specific substrates were determined in rats. The Kp,uu,brain values decreased, as the in vitro BCRP corrected flux ratio (CFR) increased. The Kp,uu,CSF values of BCRP-specific substrates were greater than the Kp,uu,brain values. Increase in the Kp,uu,brain values induced by co-administration of BCRP inhibitor correlated with the in vitro BCRP CFR and were greater than the increase in Kp,uu,CSF values induced by BCRP inhibitor except nebicapone. The contribution of BCRP to the brain and CSF distribution of the dual P-glycoprotein/BCRP substrates, imatinib and prazosin, was similar to that of BCRP-specific substrates. Thus, we revealed that the impact of in vivo BCRP on CNS distribution is correlated with in vitro BCRP CFR, and that BCRP limits drug distribution into the brain more strongly than into the CSF.

Multiplatform metabolomic analysis of the R6/2 mouse model of Huntington's disease.

Huntington's disease (HD) is a progressive, neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. To investigate the metabolic alterations that occur in HD, here we examined plasma and whole-brain metabolomic profiles of the R6/2 mouse model of HD. Plasma and brain metabolomic analyses were conducted using capillary electrophoresis-mass spectrometry (CE-MS). In addition, liquid chromatography-mass spectrometry (LC-MS) was also applied to plasma metabolomic analyses, to cover the broad range of metabolites with various physical and chemical properties. Various metabolic alterations were identified in R6/2 mice. We report for the first time the perturbation of histidine metabolism in the brain of R6/2 mice, which was signaled by decreases in neuroprotective dipeptides and histamine metabolites, indicative of neurodegeneration and an altered histaminergic system. Other differential metabolites were related to arginine metabolism and cysteine and methionine metabolism, suggesting upregulation of the urea cycle, perturbation of energy homeostasis, and an increase in oxidative stress. In addition, remarkable changes in specific lipid classes are indicative of dysregulation of lipid metabolism. These findings provide a deeper insight into the metabolic alterations that occur in HD and provide a foundation for the future development of HD therapeutics.

Hippocampal GABAA antagonism reverses the novel object recognition deficit in sub-chronic phencyclidine-treated rats.

BACKGROUND: Abnormalities in prefrontal cortical and hippocampal GABAergic function are postulated to be major causes of the cognitive impairment associated with schizophrenia (CIAS). There are conflicting views on whether diminished or enhanced GABAergic activity contributes to the deficit in short-term novel object recognition (NOR) in the sub-chronic phencyclidine (scPCP) rodent model of CIAS. This study assessed the role of GABAA signaling in the medial prefrontal cortex (mPFC) and ventral hippocampus (vHPC) in NOR in saline (scSAL)- and scPCP-treated rats. METHODS: The effects of local administration of a GABAA agonist (muscimol) into the vHPC or mPFC and an antagonist (bicuculline) or a GABAA/benzodiazepine partial agonist (bretazenil) into the vHPC on NOR in scSAL and scPCP-treated rats were determined. RESULTS: In scSAL-treated rats, injection of muscimol into the vHPC, but not mPFC, induced a deficit in NOR. The scPCP-induced NOR deficit was significantly reversed by intra-vHPC bicuculline, while intra-vHPC bretazenil produced a non-significant trend for reversal (p = .06). scPCP treatment increased mRNA expression of GABAA γ2 in PFC and GABAA α5 and GABAA ß1 in the HPC. However, GABA concentration in the PFC or HPC was not altered. CONCLUSIONS: These findings indicate that the scPCP-induced NOR deficit can be rescued by reducing GABAA receptor stimulation in vHPC, indicating that increased vHPC GABAA inhibition may contribute to the scPCP-induced NOR deficit in rats. These results also indicate that excessive GABAA receptor signalling in the vHPC has a deleterious effect on NOR in normal rats.

Discovery of 3H-imidazo[4,5-c]quinolin-4(5H)-ones as potent and selective dipeptidyl peptidase IV (DPP-4) inhibitors: use of a carboxylate prodrug to improve bioavailability.

We have previously reported a novel series of 3H-imidazo[4,5-c]quinolin-4(5H)-ones with potent dipeptidyl peptidase IV (DPP-4) inhibitory activity. However, these compounds showed poor oral absorption. We attempted in this study esterification of the carboxylic acid moiety to improve the compounds 1-4 plasma concentrations. Our efforts yielded 10h with a 5-methyl-2-oxo-1,3-dioxol-4-yl methyl ester as an S9/plasma-cleavable functionality. Compound 10h showed significantly high oral absorption and potent DPP-4 inhibition in vivo and decreased Zucker fatty rats glucose levels in the oral glucose tolerance test. Optimization of the ester moiety revealed that rapid conversion to the carboxyl form in both liver S9 fractions and serum was important for prodrugs not to be detected in the plasma after oral administration. In particular, lability in the serum was found to be an important characteristic. Through our investigation, we were able to develop a novel efficient synthetic method for construction of 3H-imidazo[4,5-c]quinolin-4(5H)-ones using intramolecular radical cyclization.

Evaluation of factors to decrease plasma concentration of an HIV protease inhibitor, saquinavir in ethanol-treated rats.

Although alcohol consumption is a factor in which the bioavailability of saquinavir (SQV) are retarded, the cause for this phenomenon remains to be uncertain. In the presence study, we examined factors to decrease plasma concentration of SQV in ethanol-treated rats. The ethanol-treated rats were prepared by making them freely access to 15% ethanol solution for 14 d (Day 14 rats). The exsorption clearance of SQV from the blood circulation to the jejunal lumen in the Day 14 rats increased by 6-fold as compared to ethanol non-treated (NT) rats. In the presence of 25 microM ketoconazole (KCZ) or 10 microM cyclosporin A (CsA) in the jejunal lumen, the plasma concentration of SQV in the portal vein increased significantly, and this effect of 10 microM CsA was superior to that of 25 microM KCZ. The biliary excretion clearance of SQV in Day 14 rats also increased by 1.8-fold as compared to that in the NT rats. The metabolic clearance rate (V(max)/K(m)) of SQV in the intestinal microsomes from the Day 14 rats increased significantly, while in the liver microsomes the V(max)/K(m) did not change. The phase II metabolism processes in the Day 14 rats based on UDP-glucuronosyltransferases and gultathion-S-tnrasferase activities were activated, however, they were not likely to be one of factors to decrease the bioavailability of oral SQV, because CYP3A activity in the liver and intestine was not activated to such an extent and SQV itself was not conjugated. These observations suggest that a main possible factor to explain the reducing effect on the SQV oral bioavailability during ethanol consumption is an enhanced efflux of SQV at the intestine and liver, where it is suggested that functional enhancement or excessive expression of P-glycoprotein is caused by ethanol consumption.

Effect of indinavir on the intestinal exsorption of amprenavir, saquinavir and nelfinavir after intravenous administration in rats.

To elucidate drug interaction between human immunodeficiency virus (HIV) protease inhibitors (PIs), the effect of indinavir (IDV) on the intestinal exsorption of other HIV PIs, amprenavir (APV), saquinavir (SQV) and nelfinavir (NFV) was investigated in rats using an in situ single perfusion method. IDV in the intestinal perfusate inhibited the exsorption of rhodamine 123 (Rho123), a known P-glycoprotein (P-gp) substrate, from blood into intestinal lumen in a concentration-dependent manner, and the inhibitory potency of 10 micro M IDV in the perfusate was close to that of 10 micro M cyclosporin A (CsA) in the perfusate. Ten micro M of IDV in the intestinal perfusate also decreased significantly the exsorption clearance of Rho123 after intravenous administration. The IDV concentration in this system was not likely to cause hepatic interaction between HIV PIs, because the plasma IDV concentration was far below its inhibition constants for other HIV PIs in the liver microsomes. Thus, 10 micro M of IDV was chosen to investigate the effect of this inhibition on the exsorption of APV, SQV and NFV. IDV in the intestinal perfusate markedly increased the exsorbed amounts of SQV and NFV but not APV after intravenous administrations. Their exsorption clearances, however, showed only a slight increasing tendency or remained unchanged. These findings suggest that in addition to P-gp inhibition, other factors such as CYP3A inhibition might be important in the drug interaction of IDV with APV, SQV and NFV after intravenous administration in rat small intestine. The results obtained in this study will provide useful information to discuss the interactions among PIs when a double protease therapy is used for in HIV-infected patients.