1521-009X/44/5/624–633$25.00 http://dx.doi.org/10.1124/dmd.115.068932 DRUG METABOLISM AND DISPOSITION Drug Metab Dispos 44:624–633, May 2016 Copyright ª 2016 by The American Society for Pharmacology and Experimental Therapeutics Development of a Rat Plasma and Brain Extracellular Fluid Pharmacokinetic Model for Bupropion and Hydroxybupropion Based on Microdialysis Sampling, and Application to Predict Human Brain Concentrations Thomas I.F.H. Cremers, Gunnar Flik, Joost H.A. Folgering, Hans Rollema, and Robert E. Stratford, Jr. Brains On-Line BV, Groningen, The Netherlands (T.I.F.H.C., G.F. J.H.A.F.); Rollema Biomedical Consulting, Mystic, Connecticut (H.R.); and Division of Pharmaceutical Sciences, Mylan School of Pharmacy, Duquesne University, Pittsburgh, Pennsylvania (R.E.S.) Received December 11, 2015; accepted February 24, 2016 Downloaded from ABSTRACT Administration of bupropion [(6)-2-(tert-butylamino)-1-(3-chlorophenyl) concentration ratio at early time points was observed with propan-1-one] and its preformed active metabolite, hydroxybupropion bupropion; this was modeled as a time-dependent uptake clear- [(6)-1-(3-chlorophenyl)-2-[(1-hydroxy-2-methyl-2-propanyl)amino]- ance of the drug across the blood–brain barrier. Translation of the 1-propanone], to rats with measurement of unbound concentrations model was used to predict bupropion and hydroxybupropion dmd.aspetjournals.org by quantitative microdialysis sampling of plasma and brain extra- exposure in human brain extracellular fluid after twice-daily cellular fluid was used to develop a compartmental pharmacoki- administration of 150 mg bupropion. Predicted concentrations netics model to describe the blood–brain barrier transport of both indicate that preferential inhibition of the dopamine and norepi- substances. The population model revealed rapid equilibration of nephrine transporters by the metabolite, with little to no contribu- both entities across the blood–brain barrier, with resultant steady- tion by bupropion, would be expected at this therapeutic dose. state brain extracellular fluid/plasma unbound concentration ratio Therefore, these results extend nuclear imaging studies on dopa- estimates of 1.9 and 1.7 for bupropion and hydroxybupropion, mine transporter occupancy and suggest that inhibition of both at ASPET Journals on September 25, 2021 respectively, which is thus indicative of a net uptake asymmetry. transporters contributes significantly to bupropion’s therapeutic An overshoot of the brain extracellular fluid/plasma unbound efficacy. Introduction bupropion-related plasma exposure, with one of its metabolites, 6 Bupropion [(6)-2-(tert-butylamino)-1-(3-chlorophenyl)propan-1- hydroxybupropion [( )-1-(3-chlorophenyl)-2-[(1-hydroxy-2-methyl- one] was originally introduced as an effective medication for the 2-propanyl)amino]-1-propanone], representing the predominant circu- treatment of depression (Wellbutrin). Among antidepressants, its lating entity (Ascher et al., 1995; Jefferson et al., 2005). The relative mechanism is considered atypical in that it has no effects on the systemic exposure of this metabolite to bupropion in repeated dosing serotonergic system; rather, its efficacy in depression has been ranges from 5- to 15-fold (Johnston et al., 2001; Learned-Coughlin attributed to its ability to increase dopaminergic and noradrenergic et al., 2003; Benowitz et al., 2013). Given this significant difference, tone, presumably via blockade of the respective synaptic reuptake it has been suggested that hydroxybupropion, which has similar transporters: the dopamine reuptake transporter (DAT) and the inhibitory activity at the DAT, but is a more potent NET inhibitor than norepinephrine reuptake transporter (NET) (Fava et al., 2005). After bupropion, contributes significantly to bupropion’s efficacy (Ascher its approval for depression, bupropion was also marketed as a smoking et al., 1995; Bondarev et al., 2003; Damaj et al., 2004; Lukas et al., cessation aid (Zyban). In addition to its effects on the DAT and NET, it 2010). Moreover, the higher exposure to hydroxybupropion may also has been suggested that bupropion’s efficacy in nicotine dependence be contributing to the side effects and adverse events associated with may be associated with alteration of central nicotinic acetylcholine bupropion therapy, particularly seizures observed at higher doses receptor function (Slemmer et al., 2000; Damaj et al., 2004). (Wooltorton, 2002). Single and repeat administration of therapeutic doses of bupropion in Use of animal models, particularly mice and rats, to understand the humans indicate that bupropion represents a minor fraction of the total complex pharmacology of bupropion is hampered by the very different disposition of bupropion in animals versus humans. In these rodent This research was sponsored by Brains On-Line (South San Francisco, CA). species, hydroxybupropion contributes approximately 10% to the total dx.doi.org/10.1124/dmd.115.068932. systemic and whole brain exposure observed (Suckow et al., 1986), ABBREVIATIONS: 22LL, 22 Â log likelihood; AIC, Akaike information criterion; AUC, area under the curve; BAV, between-animal variability; BBB, blood–brain barrier; CL, clearance; DAT, dopamine reuptake transporter; ECF, extracellular fluid; HPLC, high-performance liquid chromatography; Kp,uu, concentration ratios of brain ECF to plasma; MS/MS, tandem mass spectrometry; NET, norepinephrine reuptake transporter; OFV, objective function value; PD, pharmacodynamics; PET, positron emission tomography; PK, pharmacokinetics; SPECT, single photon emission computed tomography; SR, extended-release; Vb, brain distribution volume. 624 Bupropion and Hydroxybupropion Brain Pharmacokinetics 625 which is in complete reversal to the already-noted relative exposures 2181; ABDiets, Woerden, The Netherlands) and domestic-quality mains water observed in humans. Thus, superimposed upon remaining uncertainty were available ad libitum. regarding bupropion pharmacodynamics, either directly via inhibition Surgery for implantation of the microdialysis guide cannula was conducted of transporter-mediated reuptake of dopamine and norepinephrine or by under isoflurane anesthesia (2% with 400 ml/min N2O and 400 ml/min O2), indirect effects on these two neurotransmitter systems (Cooper et al., using bupivacaine/epinephrine for local analgesia and finadyne for perioperative/postoperative analgesia. One guide cannula was inserted into the 1994; Dong and Blier, 2001), or via effects on nicotinic acetylcholine medial prefrontal cortex to achieve the following probe tip coordinates: receptors (Slemmer et al., 2000; Damaj et al., 2004), the different anteroposterior, +3.4 mm from bregma; lateral, –0.8 mm from midline; and metabolic disposition in rodents complicates the ability to extrapolate to ventral, –5.0 mm from dura. A second 4.2-cm indwelling cannula was inserted humans. Although application of brain imaging modalities, such as into the jugular vein. Guide cannulae were exteriorized through an incision at the positron emission tomography (PET) and single photon emission top of the head. Animals were allowed at least 2 days to recover from surgery. computed tomography (SPECT), has received considerable attention MetaQuant Ultra-Slow Flow microdialysis probes (regenerated cellulose (Meyer et al., 2002; Learned-Coughlin et al., 2003; Árgyelán et al., membrane, 4-mm open membrane surface; BrainLink, Groningen, The Nether- 2005), these approaches cannot distinguish the contributions of lands) were inserted 1 day before the experiments. bupropion and hydroxybupropion to measured receptor occupancy. Drug Administration and Sample Collection. On the day of an experiment, Previous studies have shown that a translational pharmacokinetics probes were connected with flexible PEEK tubing to a CMA 102 microdialysis pump (CMA Microdialysis, Solna, Sweden) and perfused with a filtered (PK)/pharmacodynamics (PD) approach can be of great value to Ringer’s buffer containing 147 mM NaCl, 3.0 mM KCl, 1.2 mM CaCl , and increase understanding of the pharmacology of central nervous system 2 1.2 mM MgCl2 at a flow rate of 0.12 ml/min (CMA 142 pump). The slow flow Downloaded from drugs, particularly those with multiple targets and/or with active design of this probe maximizes sample recovery (Cremers et al., 2009), which metabolites. This approach describes plasma-to-brain transfer [blood– was 91% for bupropion and 100% for hydroxybupropion, as determined from in brain barrier (BBB) transport], using compartmental or physiologically vitro recovery experiments. Ultrapurified water was perfused through the based pharmacokinetic modeling in animals, with subsequent coupling dilution inlet of the probe at a flow rate of 0.8 ml/min; thus, the total dialysate of measured human systemic PK with the human brain disposition flow rate was 0.92 ml/min. After initiating flow, probes were allowed to stabilize derived from weight-based allometric scaling of the corresponding for 2 hours prior to administration of a single subcutaneous dose of bupropion animal parameters (de Lange, 2013). The method has been used to (10 mg/kg, n = 7 with partial overlap for each matrix) or hydroxybupropion dmd.aspetjournals.org predict atomoxetine and duloxetine exposure in human brain extracel- (2 mg/kg, n = 4), both dissolved in 0.9% NaCl at 2 mg/ml. Dialysates from the brain and jugular vein were collected every 30 minutes starting 1 hour prior to lular fluid (ECF) (Kielbasa and Stratford, 2012), risperidone and its administration