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P-glycoprotein and chiral antidepressant drugs: Pharmacokinetic, pharmacogenetic and toxicological aspects
Linköping University, Department of Medical and Health Sciences, Clinical Pharmacology. Linköping University, Faculty of Health Sciences.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The blood-brain barrier (BBB) is formed by the capillary endothelial cells, joined together by tight junctions, with transporter proteins. BBB acts to regulate the brain concentrations of substances including many drugs. Transport across the cells is necessary for a drug to ensure that the drug reaches the site of action and transport proteins such as P-glycoprotein (P-gp; ABCB1) can limit the entrance into various tissues, including the brain.

Molecules that are not superimposable on their mirror images and thus exist in two enantiomeric forms (enantiomers) are said to be chiral. A racemic compound is one composed of a 50:50 mixture of two enantiomers, S- and R-enantiomers. Two examples of frequently prescribed racemic drugs are the chiral antidepressants venlafaxine (VEN) and citalopram (CIT). The enantiomers of VEN possess different pharmacodynamic profiles where the R-enantiomer is a potent inhibitor of both serotonin and noradrenaline reuptake (SNRI), while the S-enantiomer is more selective in inhibiting serotonin reuptake (SSRI). The SSRI effect of CIT resides in the S-enantiomer, whereas the R-enantiomer is considered to be therapeutically inactive, or even that it counteracts the effects. The S-enantiomer of CIT is now available as a separate SSRI (escitalopram, EsCIT). VEN and CIT are also among the most commonly found drugs in forensic autopsy cases.

Few previous studies have examined a possible enantioselective activity of P-gp. Thus, the general aim of this thesis was to study the enantiomeric distribution of chiral antidepressant drugs, focusing on the role of P-gp in the BBB. For this purpose, a mouse model disrupted of the genes coding for P-gp (abcb1ab (-/-) mice) was used. Brain and serum concentrations of the enantiomers of VEN and CIT, and their major metabolites, were compared to the corresponding wild-type mice (abcb1ab (+/+) mice). The open-field locomotor and rearing activities were examined after chronic VEN administration. In addition to the animal studies, genetic and toxicological aspects of P-gp were studied in a forensic autopsy material, where intoxication cases were compared with cases that were not related to intoxications.

The brain to serum concentration ratios for VEN, CIT and EsCIT differed between knockout mice and wild-type mice, with 2-3 fold higher brain concentrations in mice with no expression of P-gp. Hence, all studied drugs, and their major metabolites, were substrates for P-gp. There was no evidence for a stereoselective P-gp mediated transport. The P-gp substrate properties were reflected in the open-field behavior test where the knockout mice displayed increased center activity compared with wild-type mice following chronic VEN exposure. The genotype distribution of ABCB1 SNPs C1236T, G2677T and C3435T in VEN positive cases was significantly (or borderline) different between the intoxication cases and the non-intoxication cases. This difference in genotype distribution was not observed for the CIT positive cases.

To conclude, the present work has led to an increased knowledge about how the enantiomers of VEN and CIT are affected by the BBB transporter P-gp. Using an animal model, VEN and CIT have proved to be actively transported out of the brain by P-gp and no difference was observed for the enantiomers with regard to P-gp transport. Further, the ABCB1 genotype distribution was different in intoxication cases compared with non-intoxication cases. Taken together, these findings offer the possibility that the expression of P-gp in humans may be a contributing factor for limited treatment response and increased risk of side-effects following antidepressant drug treatment.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 80 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1283
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-76126ISBN: 978-91-7393-003-1 (print)OAI: oai:DiVA.org:liu-76126DiVA: diva2:512541
Public defence
2012-04-13, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2012-03-28 Created: 2012-03-28 Last updated: 2012-03-28Bibliographically approved
List of papers
1. Blood-brain barrier penetration of the enantiomers of venlafaxine and its metabolites in mice lacking P-glycoprotein
Open this publication in new window or tab >>Blood-brain barrier penetration of the enantiomers of venlafaxine and its metabolites in mice lacking P-glycoprotein
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2010 (English)In: European Neuropsychopharmacology, ISSN 0924-977X, E-ISSN 1873-7862, Vol. 20, no 9, 632-640 p.Article in journal (Refereed) Published
Abstract [en]

According to in vitro studies the enantiomers of venlafaxine display different degrees of serotonin and noradrenaline reuptake inhibition. Therefore, clarification of the enantiomeric drug distribution between serum and brain is highly warranted. To elucidate if P-glycoprotein (P-gp) in a stereoselective manner transports venlafaxine and its metabolites out of the brain we used abcb1ab double-knockout mice that do not express P-gp. A single dose of racemic venlafaxine (10 mg/kg bw) was intraperitoneally injected to knockout (-/-) and wildtype (+/+) mice. Serum and brain samples were collected 1, 3, 6 and 9 h following drug administration for analysis by LC/MS/MS. One to six hours post-dose, the brain concentrations of venlafaxine, O-desmethylvenlafaxine and N-desmethylvenlafaxine were 2-3, 2-6 and 3-12 times higher in abcb1ab (-/-) mice compared to abcb1ab (+/+) mice, respectively. No major differences in the serum and brain disposition of the S- and R-enantiomers of venlafaxine and its metabolites were found between the groups. We conclude that P-gp decreases the penetration of the S- and R-enantiomers of venlafaxine and its major metabolites into the brain. No evidence of a stereoselective P-gp mediated transport of these substances was observed.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-58805 (URN)10.1016/j.euroneuro.2010.04.004 (DOI)20466523 (PubMedID)
Note
Original Publication: Louise Karlsson, Ulrich Schmitt, Martin Josefsson, Björn Carlsson, Johan Ahlner, Finn Bengtsson, Fredrik C Kugelberg and Christoph Hiemke, Blood-brain barrier penetration of the enantiomers of venlafaxine and its metabolites in mice lacking P-glycoprotein, 2010, European Neuropsychopharmacology, (20), 9, 632-640. http://dx.doi.org/10.1016/j.euroneuro.2010.04.004 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-08-27 Created: 2010-08-27 Last updated: 2017-12-12
2. Effects on enantiomeric drug disposition and open-field behavior after chronic treatment with venlafaxine in the P-glycoprotein knockout mice model
Open this publication in new window or tab >>Effects on enantiomeric drug disposition and open-field behavior after chronic treatment with venlafaxine in the P-glycoprotein knockout mice model
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2011 (English)In: Psychopharmacology, ISSN 0033-3158, E-ISSN 1432-2072, Vol. 215, no 2, 367-377 p.Article in journal (Refereed) Published
Abstract [en]

Our results show that P-gp at the blood-brain barrier plays an important role in limiting brain entry of the enantiomers of venlafaxine and its metabolites after chronic dosing. Taken together, the present pharmacokinetic and pharmacodynamic findings offer the possibility that the expression of P-gp in patients may be a contributing factor for limited treatment response.

Place, publisher, year, edition, pages
Springer, 2011
Keyword
abcb1ab . Blood–brain barrier . Knockout mice . P-glycoprotein . Pharmacodynamic . Pharmacokinetic .Venlafaxine
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-68038 (URN)10.1007/s00213-010-2148-5 (DOI)000289985700016 ()21191569 (PubMedID)
Note
The original publication is available at www.springerlink.com: Louise Karlsson, Christoph Hiemke, Björn Carlsson, Martin Josefsson, Johan Ahlner, Finn Bengtsson, Ulrich Schmitt and Fredrik C Kugelberg, Effects on enantiomeric drug disposition and open-field behavior after chronic treatment with venlafaxine in the P-glycoprotein knockout mice model., 2011, Psychopharmacology, (215), 2, 367-377. http://dx.doi.org/10.1007/s00213-010-2148-5 Copyright: Springer Science Business Media http://www.springerlink.com/Available from: 2011-05-06 Created: 2011-05-06 Last updated: 2017-12-11
3. Altered brain concentrations of citalopram and escitalopram in P-glycoprotein deficient mice after acute and chronic treatment
Open this publication in new window or tab >>Altered brain concentrations of citalopram and escitalopram in P-glycoprotein deficient mice after acute and chronic treatment
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2013 (English)In: European Neuropsychopharmacology, ISSN 0924-977X, E-ISSN 1873-7862, Vol. 23, no 11, 1636-1644 p.Article in journal (Refereed) Published
Abstract [en]

Background: According to both in vitro and in vivo data P-glycoprotein (P-gp) may restrict the uptake of several antidepressants into the brain, thus contributing to the poor success rate of current antidepressant therapies. The therapeutic activity of citalopram resides in the Senantiomer, whereas the R-enantiomer is practically devoid of serotonin reuptake potency. To date, no in vivo data are available that address whether the enantiomers of citalopram and its metabolites are substrates of P-gp.

Methods: P-gp knockout (abcb1ab (-/-)) and wild-type (abcb1ab (+/+)) mice underwent acute (single-dose) and chronic (two daily doses for 10 days) treatment with citalopram (10 mg/kg) or escitalopram (5 mg/kg). Serum and brain samples were collected 1-6 h after the first or last i.p. injection for subsequent drug analysis by an enantioselective HPLC method. Results: In brain, 3-fold higher concentrations of S- and R-citalopram, and its metabolites, were found in abcb1ab (-/-) mice than in abcb1ab (+/+) mice after both acute and chronic citalopram treatments. After escitalopram treatment, the S-citalopram brain concentration was 3-5 times higher in the knockout mice than in controls.

Conclusions: The results provide novel evidence that the enantiomers of citalopram are substrates of P-gp. Possible clinical and toxicological implications of this finding need to be further elucidated.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Citalopram, enantiomers, escitalopram, mice knockout, P-glycoprotein
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-76122 (URN)10.1016/j.euroneuro.2013.01.003 (DOI)000328014700033 ()
Available from: 2012-03-28 Created: 2012-03-28 Last updated: 2017-12-07Bibliographically approved
4. ABCB1 gene polymorphisms in forensic autopsy cases positive for citalopram and venlafaxine
Open this publication in new window or tab >>ABCB1 gene polymorphisms in forensic autopsy cases positive for citalopram and venlafaxine
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

P-glycoprotein (P-gp), encoded by the ABCB1/MDR1 gene, is a drug transporter expressed on e.g. the endothelial cells of the blood-brain barrier which regulates the efflux of many drugs. Several polymorphisms in the ABCB1 gene are known to affect the activity and/or expression of P-gp, thereby influencing the treatment response and toxicity of P-gp substrates. It has previously been shown that the antidepressant drugs citalopram and venlafaxine are actively transported out of the brain by P-gp using a mouse model. In the present study we aimed to investigate the frequency of ABCB1 genotypes in forensic autopsy cases positive for these two antidepressants. Further, the distribution of ABCB1 genotypes in deaths related to intoxication was compared to cases not associated to drug intoxication. The present study included 228 forensic autopsy cases positive for venlafaxine and citalopram with different causes of deaths. The ABCB1 single nucleotide polymorphisms (SNPs) G1199A, C1236T, C3435T and G2677T/A for these individuals were determined by Pyrosequencing. The SNPs C1236T, G2677T and C3435T in venlafaxine positive cases were significantly different between the intoxication cases and non-intoxications. The latter novel finding should, however, be confirmed in future studies with larger number of cases.

Keyword
ABCB1, citalopram, forensic material, genotype, postmortem, venlafaxine
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-76125 (URN)
Available from: 2012-03-28 Created: 2012-03-28 Last updated: 2013-09-03Bibliographically approved

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