Markus T. Grauer

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.

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.

Highly Substituted Hydroxyethyl Starch (HES 200/0.62) Leads to Type-l von Willebrand Syndrome after Repeated Administration

Hydroxyethyl starch (HES) is a frequently used plasma substitute that is popular due to a high degree of therapeutic safety. However, the administration of large volumes of highly substituted, high-molecular-weight starch often leads to iatrogenic von Willebrand syndrome (vWS) with hemorrhagic complications. In patients with cerebral circulatory disturbances we carried out hemodilution therapy during 9-10 days, infusing HES 200/0.62. A von Willebrand factor (vWF) multimeric analysis was carried out in 6 patients using a modified western blot according to the sodium dodecyl sulfate agarose gel electrophoresis method. The vWF multimeric analysis showed that all multimers decreased to the same degree, corresponding to type-I vWS.

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 µg/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.

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

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.

Chronic Fatigue Syndrome in Patients with Lyme Borreliosis

Several authors have reported a chronic fatigue-like syndrome in patients that have suffered from Lyme borreliosis in the past. To further investigate this suspicion of an association without sample bias, we carried out a prospective, double-blind study and tested 1,156 healthy young males for Borrelia antibodies. Seropositive subjects who had never suffered from clinically manifest Lyme borreliosis or neuroborreliosis showed significantly more often chronic fatigue (p = 0.02) and malaise (p = 0.01) than seronegative recruits. Therefore we believe it is worth examining whether an antibiotic therapy should be considered in patients with chronic fatigue syndrome and positive Borrelia serology.

Transcranial Doppler Monitoring of Intracranial Pressure Therapy with Mannitol, Sorbitol and Glycerol in Patients with Acute Stroke

Introduction: The noninvasive management of the conservative therapy for intracranial pressure (ICP) with hyperosmolar substances is a central problem in the treatment of brain edema. Using transcranial Doppler (TCD), a continuous monitoring of ICP is now possible, because the TCD pulsatility index (PI) intraindividually closely correlates with the level of ICP. Patients and Methods: We administered an ICP-lowering treatment 113 times in 10 patients with intracranial bleeding or ischemic stroke who also had signs of elevated ICP in the computer tomogram. The treatment was carried out over a period of 9 days, using 50 g each of intravenous sorbitol (n = 38) and mannitol (n = 32) or oral glycerol (n = 43). Results: PI was significantly lowered between 20.0 and 23.9% (p < 0.01) by all substances in the affected and unaffected sides. The differences between the three substances and the differences between the affected and unaffected sides were not significant. The duration of the therapeutic effect of glycerol (190 ± 41 min) was significantly longer (p < 0.01) than that of sorbitol (150 ± 28 min) or mannitol (130 ± 20 min). The duration of the therapeutic effect was also significantly shorter (p < 0.01) in patients with a high PI (> 1.5). All three substances led to a significant increase (p < 0.01) in minimal (= diastolic) flow velocity (Vmin). The increase was highest for glycerol (56.3 ±72.6%). Summary: The decrease in PI under therapy was caused by an increase in Vmin. This indicates that ICP therapy with hyperosmolar substances improves brain edema and does not suggest a therapy-induced vasoconstriction.

Treatment with anticoagulants in cerebral events (TRACE)

90 patients with acute stroke and a concomitant cardiac embolism source or a symptomatic high-grade stenosis of an extra-or intracranial vessel received in a mulitcenter, randomized, controlled study either Enoxaparin 1 mg/kg BW s.c. b.i.d. or i.v. heparin aPTT-adjusted daily for 8 +/- 2 days as secondary prophylaxis. There were no significant differences between the two groups regarding cerebral and systemic embolic events, bleeding complications, length of hospital stay, number of diagnostic and therapeutic measures and outcome after three months. This suggests that Enoxaparin, which is easier to administer and monitor, is a safe drug in patients with acute cerebral events.

CSF substance P, somatostatin and monoaminergic transmitter metabolites in patients with narcolepsy ☆

We have measured the concentrations of substance P, somatostatin, homovanillic acid (HVA), vanillyl mandelic acid (VMA) and 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF) of six patients suffering from narcolepsy and 12 age- and gender-matched controls using high pressure liquid chromatography (HPLC) and radioimmunoassay (RIA). Substance P and somatostatin were significantly decreased in our patients compared to controls (36.9 +/- 9.1 fmol/ml versus 52.5 +/- 9.9 fmol/ml, P < 0.05 and 30.3 +/- 7.8 fmol/ml versus 43.9 +/- 9.8 fmol/ml, P < 0.05, respectively). 5-HIAA (P < 0.05) and VMA (P < 0.05) were also significantly decreased. HVA was significantly increased (P < 0.01). The CSF concentrations of substance P and somatostatin correlated with the clinical parameters duration of disease (r = -0.68, P < 0.05 and r = -0.72, P < 0.05, respectively) and severity of cataplectic symptoms (r = -0.71, P < 0.05 and r = -0.78, P < 0.01). In addition, substance P correlated with the intensity of sleepiness and the frequency of day-sleep attacks (r = -0.69, P < 0.05 and r = -0.68, P < 0.05, respectively). Substance P affects the amount of dopamine release in the nigra-striatal region, and decreased amounts could contribute to the pathogenesis of narcolepsy. Reduced levels of substance P, which affects serotonin release, may be responsible for diminished release of serotonin which in turn could affect sleep cycles. Because somatostatin affects motor behavior through dopaminergic mechanisms and since the levels of somatostatin correlate with the intensity of cataplectic symptoms, we speculate that an interaction between somatostatin and dopaminergic neurons plays a role in the pathogenesis of narcolepsy.

Influence of Low Molecular Weight Hydroxyethyl Starch (HES 40/0.5-0.55) on Hemostasis and Hemorheology

Hydroxyethyl starch (HES) with a high or medium molecular weight (MW) and a high degree of substitution is difficult to degrade and leads to an accumulation of large molecules. These molecules have a negative effect on hemostasiological parameters. In 10 patients with cerebrovascular diseases, a hemodilution therapy was carried out with low MW HES for 10 days. Due to the low MW of the HES used (56-61 kD), the rheological parameters erythrocyte aggregation and plasma viscosity were significantly lowered (p < 0.01). No coagulation parameters studied were affected beyond the dilution effect, which was measured using the decline in hematocrit. Low MW starch is a volume substitute that is well-suited for repeated infusion or hemodilution therapy, particularly for patients with increased hemorrhagic diathesis, because it does not affect hemostasis. The disadvantage of a relatively short volume effect can be compensated through a continuous infusion of a larger volume.