Blood-brain barrier penetration and pharmacokinetics of amitriptyline and its metabolites in p-glycoprotein (abcb1ab) knock-out mice and controls.

In earlier studies with P-gp (abcb1) knock-out mice, we showed that P-gp exports the antidepressants citalopram, paroxetine, venlafaxine and amitriptyline and its metabolites across the blood-brain barrier, thereby reducing cerebral bioavailability of some substances up to 9 times. The present study investigated the pharmacokinetics of amitriptyline and whether abcb1ab double knock-out mice metabolize amitriptyline and its metabolites differently. P-gp knock-out mice and controls received a s.c. injection of 10mug amitriptyline/g of body weight. The animals were sacrificed after 30, 60, 120 and 240min and concentrations of amitriptyline and its metabolites were measured with HPLC in brain, plasma, liver, kidney, spleen, lung, muscle, fat and ovaries. Cerebral concentrations of amitriptyline and its metabolites were higher in P-gp-deficient mice compared to controls. No significant group effect was found for spleen, liver, lung, kidney and fat tissue. The results of our study indicate that amitriptyline and its metabolites are substrates of P-gp. Overall pharmacokinetics between knock-outs and controls were very similar. This confirms the validity of the P-gp knock-out model and allows for a continued research of the interactions between P-gp, the blood-brain barrier and CNS substances such as antidepressants, neuroleptics and others.

The anti-Parkinson drug budipine is exported actively out of the brain by P-glycoprotein in mice.

P-glycoprotein, a product of the ABCB1 gene, is a plasma membrane transporter that exports certain drugs as well as endogenous substances against a concentration gradient in the intestines, kidney and testes. It also constitutes an important part of the blood-brain barrier, where it exports its substrates out of the brain back into the circulation. To investigate whether the uptake of the anti-Parkinson drug budipine into the brain is mediated by P-glycoprotein, abcb1ab(-/-) double knock-out mice and wild-type control mice received budipine continuously over 11 days via implanted osmotic infusion pumps at the rate of 30ug over 24h. Concentrations of the drug in plasma, brain, and organs were measured with HPLC. Budipine concentrations in the abcb1ab knock-out animals were 3.1 times higher than in control mice. This study confirms the important role P-gp plays at the blood-brain barrier and shows that budipine is a substrate of P-gp.

P-glycoprotein is a factor in the uptake of dextromethorphan, but not of melperone, into the mouse brain: evidence for an overlap in substrate specificity between P-gp and CYP2D6.

In this study, the role of P-glycoprotein (P-gp) for the pharmacokinetics of dextromethorphan, a CYP2D6 substrate, and of melperone, a CYP2D6 inhibitor, was investigated. The substances were administered subcutaneously near the nape of the neck of wild-type mice and of abcb1ab (-/-) mice. One hour after injection, concentrations of the two drugs in cerebrum, plasma and in different organs were measured by high-performance liquid chromatography. No significant differences between wild-type mice and abcb1ab (-/-) mice were observed for melperone, suggesting that P-gp is not involved in the uptake of melperone into the brain or other organs of mice. The concentration of dextromethorphan in the brain was more than twice as high in abcb1ab (-/-) mice compared to wild-type mice. Therefore, P-gp appears to be a factor in the uptake of dextromethorphan into the mouse brain, and abcb1-polymorphisms need to be considered for CYP2D6 phenotyping experiments with this drug. There is an overlap in substrate specificity between P-gp and CYP2D6. P-gp is a factor in the uptake of dextromethorphan, but not of melperone.

P-glycoprotein reduces the ability of amitriptyline metabolites to cross the blood brain barrier in mice after a 10-day administration of amitriptyline.

P-glycoprotein (P-gp) is a 170-kDa membrane protein and the gene product of the multiple drug resistance (MDR1 or ABCB1) gene. It constitutes an important part of the blood-brain barrier and actively exports a number of molecules across the blood-brain barrier back into the vascular space, subsequently reducing central nervous system (CNS) bioavailability of these substances. The aim of the present study was to investigate the pharmacokinetics of amitriptyline and its metabolites in P-gp (also called mdr1ab or abcb1ab) knockout mice and controls after a long-term adminstration for 10 days. Knockout mice and controls received s.c. injections of amitriptyline (10 microg/g bodyweight) twice daily for 10 days. After 10 days, the animals were sacrificed and the concentrations of amitriptyline and nortriptyline and both their E-10-OH and Z-10-OH metabolites were measured with high-performance liquid chromatography in the cerebrum, plasma, spleen, kidney, testes, lung, liver, muscle and fat. Except for amitriptyline, the brain concentrations of all other examined substances were significantly higher in the P-gp knockout mice. Compared to controls, concentrations of nortriptyline were 2.6-fold higher, E-10-OH-nortriptyline 10-fold higher, Z-10-OH-nortriptyline seven-fold higher, E-10-OH-amitriptyline two-fold higher and Z-10-OH-amitriptyline five-fold higher. The present study confirms that P-gp plays an important role in the interaction between CNS drugs and the blood-brain barrier. Without P-gp at the blood-brain barrier, the brain concentrations of the substances were up to 10-fold higher, showing that P-gp plays an active role in exporting CNS drugs out of the brain. Recent clinical studies showing different side-effects in patients with P-gp polymorphisms confirm the clinical importance of these findings.

Differential enhancement of antidepressant penetration into the brain in mice with abcb1ab (mdr1ab) P-glycoprotein gene disruption.

BACKGROUND: Mice with a genetic disruption (knockout) of the multiple drug resistance (abcb1ab) gene were used to examine the effect of the absence of the drug-transporting P-glycoprotein (P-gp) at the blood-brain barrier on the uptake of the antidepressants venlafaxine, paroxetine, mirtazapine, and doxepin and its metabolites into the brain. METHODS: One hour after subcutaneous injection of venlafaxine, paroxetine, mirtazapine, or doxepin, knockout and wildtype mice were sacrificed, and the drug concentrations in brain, spleen, kidney, liver, and plasma were measured. RESULTS: The cerebrum concentrations of doxepin, venlafaxine, and paroxetine were higher in knockout mice, demonstrating that these substances are substrates of P-gp and that abcb1ab activity at the level of the blood-brain barrier reduces the penetration of these substances into the brain. In contrast, brain distribution of mirtazapine was indistinguishable between the groups. CONCLUSIONS: The differences reported here in brain penetration of antidepressant drugs that depend on the presence of the abcb1ab gene may offer an explanation for poor or nonresponse to antidepressant treatment. Furthermore, they may be able to explain in part the discrepancies between plasma levels of an antidepressant and its clinical effects and side effects.

Influence of long-term volume therapy with hydroxyethyl starch on leukocytes in patients with acute stroke.

A repeated administration of hydroxyethyl starch affects hemostasiological and rheological factors such as the concentration of factor VIII/von Willebrand factor, platelet volume and plasma viscosity. An earlier study showed that HES also lowers the concentration of fibronectin, a molecule important in the reticuloendothelial system (RES). RES has a "clearing function" and is a part of the non-immune-specific defense mechanisms of the body. It is involved in the elimination of HES from the blood. Since leukocytes are another important part of the unspecific defense system, the goal of the present study was to investigate whether HES affects leukocytes. After giving their informed consent, 20 patients with cerebral perfusion disorders were randomized and underwent a double-blind 10-day hypervolemic hemodilution with HES 200/0.5/13 or HES 70/0.5/4. The numbers of leukocytes, percentage of lymphocytes, percentage of neutrophilic granulocytes and hemoglobin concentration were measured. The absolute number of leukocytes did not change significantly, but the share of neutrophilic granulocytes increased. The increase in neutrophilic granulocytes reflects an increase in phagocytic activity. HEs 200/0.5/13, which has the larger in vivo molecular weight (MW = 95 kD), caused a larger increase in neutrophilic granulocytes than HES 70/0.5/4, which has an in vivo MW of 58 kD.

abcb1ab P-glycoprotein is involved in the uptake of citalopram and trimipramine into the brain of mice.

The phenomenon of a heterogeneous response to the same drug in different patients is well-known. An important reason is that, even at equal concentrations, the bioavailability of a drug depends on the interaction of the drug with the blood-brain barrier (BBB). In part, this is due to the drug-transporting P-glycoprotein (P-gp), a product of the multiple drug resistance gene (ABCB1), which can transport drugs against a concentration gradient across the BBB back into the plasma and thereby reduce the bioavailability in the brain. In the present study, we have examined the uptake of the antidepressants citalopram and trimipramine into the brain of abcb1ab knockout mice compared with controls. One hour after s.c. injection of the drugs, concentrations of the two drugs and of the metabolite d-trimipramine in brain, spleen, kidney, liver and plasma were measured with HPLC. Significantly higher brain concentrations in knockout mice, showing that these drugs are substrates of P-gp and that the presence of P-gp reduces the effective bioavailability of these substances in the brain. The results of our study contradict an earlier report that citalopram is not actively transported from endothelial cells. These results were derived from an in vitro study, showing that due to the complexity of the BBB-drug interaction, it is difficult to transfer results from in vitro studies to the in vivo situation. We hypothesize that inter-individual differences in the activity of the ABCB1 gene can account in part for the great variation in clinical response to antidepressants in psychiatric patients, even at comparable plasma levels.

Influence of a long-term, high-dose volume therapy with 6% hydroxyethyl starch 130/0.4 or crystalloid solution on hemodynamics, rheology and hemostasis in patients with acute ischemic stroke. Results of a randomized, placebo-controlled, double-blind study.

BACKGROUND: This study was performed to investigate the clinical effects of a 4-day volume therapy with a newly developed, 6% hydroxyethyl starch (HES) 130/0.4 versus crystalloid solution, with particular regard to systemic and cerebral hemodynamics, rheology and safety. METHODS: In a randomized, double-blind study, 40 patients suffering from an acute ischemic stroke received either 6% HES 130/0.4 or crystalloid solution as continuous infusion over 4 days with a total dose of 6.5 liters. Efficacy parameters studied included hemodynamics (cardiac output, blood pressure, flow velocity with transcranial Doppler) and rheology (hematocrit and plasma viscosity). Safety parameters examined included laboratory, hemostaseology (including factor VIII) and an adverse event questionnaire (including pruritus). RESULTS: In both groups, a small, but not significant increase in cardiac output was observed. There were no significant changes regarding the remaining efficacy or safety parameters, except for the well-known increase in serum alpha-amylase through the infusion of HES. CONCLUSION: In our study with patients suffering from acute ischemic stroke, continuous infusion (1 ml/min) of HES 130/0.4 or crystalloid solution did not differ regarding safety or hemodynamic efficacy.