| 1. |
- Fridén, Markus, et al.
(författare)
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Development of a High-Throughput Brain Slice Method for Studying Drug Distribution in the Central Nervous System
- 2009
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Ingår i: Drug Metabolism And Disposition. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0090-9556 .- 1521-009X. ; 37:6, s. 1226-1233
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Tidskriftsartikel (refereegranskat)abstract
- New, more efficient methods of estimating unbound drug concentrations in the CNS combine the amount of drug in whole brain tissue samples measured by conventional methods with in vitro estimates of the unbound brain volume of distribution (Vu,brain). While the brain slice method is the most reliable in vitro method for measuring Vu,brain, it has not previously been adapted for the needs of drug discovery research. The aim of this study was to increase the throughput and optimize the experimental conditions of this method. Equilibrium of drug between the buffer and the brain slice within the 4-5 hours of incubation is a fundamental requirement. However, it is difficult to meet this requirement for many of the extensively binding, lipophilic compounds in drug discovery programmes. In this study, the dimensions of the incubation vessel and mode of stirring influenced the equilibration time, as did the amount of brain tissue per unit buffer volume. The use of casette experiments for investigating Vu,brain in a linear drug concentration range increased the throughput of the method. The Vu,brain for the model compounds ranged from mL*g brain(-1); the sources of variability are discussed. The optimized set-up of the brain slice method allows precise, robust estimation of Vu,brain for drugs with diverse properties, including highly lipophilic compounds. This is a critical step forward for the implementation of relevant measurements of CNS exposure in the drug discovery setting.
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| 2. |
- Fridén, Markus, et al.
(författare)
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In vitro methods for estimating unbound drug concentrations in the brain interstitial and intracellular fluids
- 2007
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Ingår i: Drug Metabolism And Disposition. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0090-9556 .- 1521-009X. ; 35:9, s. 1711-1719
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of unbound drug in the interstitial fluid of the brain are not rapidly measured in vivo. Therefore, measurement of total drug levels, i.e., the amount of drug per gram of brain, has been a common but unhelpful practice in drug discovery programs relating to central drug effects. This study was designed to evaluate in vitro techniques for faster estimation of unbound drug concentrations. The parameter that relates the total drug level and the unbound interstitial fluid concentration is the unbound volume of distribution in the brain (V(u,brain)). It was measured in vitro for 15 drugs using brain slice uptake and brain homogenate binding methods. The results were validated in vivo by comparison with V(u,brain) microdialysis results. The slice method results were within a 3-fold range of the in vivo results for all but one compound, suggesting that this method could be used in combination with total drug levels to estimate unbound interstitial fluid concentrations within reasonable limits. Although successful in 10 of 15 cases, the brain homogenate binding method failed to estimate the V(u,brain) of drugs that reside predominantly in the interstitial space or compounds that are accumulated intracellularly. Use of the simple methods described in this article will 1) allow quantification of active transport at the blood-brain barrier in vivo, 2) facilitate the establishment of a relationship between in vitro potency and in vivo activity for compounds acting on central nervous system targets, and 3) provide information on intracellular concentrations of unbound drug.
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| 3. |
- Fridén, Markus, et al.
(författare)
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Structure-brain exposure relationships in rat and human using a novel data set of unbound drug concentrations in brain interstitial and cerebrospinal fluids
- 2009
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Ingår i: Journal of Medicinal Chemistry. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 52:20, s. 6233-6243
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Tidskriftsartikel (refereegranskat)abstract
- New experimental methodologies were applied to measure the unbound brain-to-plasma concentration ratio (K(p,uu,brain)) and the unbound CSF-to-plasma concentration ratio (K(p,uu,CSF)) in rats for 43 structurally diverse drugs. The relationship between chemical structure and K(p,uu,brain) was dominated by hydrogen bonding. Contrary to popular understanding based on the total brain-to-plasma concentration ratio (logBB), lipophilicity was not a determinant of unbound brain exposure. Although changing the number of hydrogen bond acceptors is a useful design strategy for optimizing K(p,uu,brain), future improvement of in silico prediction models is dependent on the accommodation of active drug transport. The structure-brain exposure relationships found in the rat also hold for humans, since the rank order of the drugs was similar for human and rat K(p,uu,CSF). This cross-species comparison was supported by K(p,uu,CSF) being within 3-fold of K(p,uu,brain) in the rat for 33 of 39 drugs. It was, however, also observed that K(p,uu,CSF) overpredicts K(p,uu,brain) for highly effluxed drugs, indicating lower efflux capacity of the blood-cerebrospinal fluid barrier compared to the blood-brain barrier.
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| 4. |
- Hammarlund-Udenaes, Margareta, et al.
(författare)
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Methodologies to assess brain drug delivery in lead optimization
- 2009
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Ingår i: Current Topics in Medicinal Chemistry. - : Bentham Science Publishers Ltd.. - 1568-0266 .- 1873-4294. ; 9:2, s. 148-162
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Forskningsöversikt (refereegranskat)abstract
- In the area of lead optimization for potential CNS-active drugs in medicinal chemistry, there is a great need for experimental methodologies that can generate data relevant to estimates of free (unbound) drug exposure within the CNS. The methods chosen have to be efficient and have to measure a pharmacologically relevant entity. The lack of methods for generating such data is probably linked with the lack of successful lead optimization strategies within CNS drug discovery. This article evaluates available methods for estimating drug delivery to the brain, and discusses the relevance of the methods from the perspective of CNS exposure to free drug. It is suggested that the extent of drug delivery is the most important investigative parameter, since permeability (rate of transfer) can vary within a relatively wide range and still allow effects within the CNS. Following this suggestion would shift the focus from the current way of thinking and could lead to the development of less lipophilic compounds than are currently being investigated. It is concluded that an extensive collection of quality data on brain drug delivery, transporter affinities and in vivo behavior is urgently required so as to be able to build relevant predictive in vitro and in silico models for the future. These models need to be much more focused on the asymmetry of active transport across the BBB than on permeability data.
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| 5. |
- Hammarlund-Udenaes, Margareta, et al.
(författare)
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On the rate and extent of drug delivery to the brain
- 2008
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Ingår i: Pharmaceutical research. - : Springer Science and Business Media LLC. - 0724-8741 .- 1573-904X. ; 25:8, s. 1737-1750
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Forskningsöversikt (refereegranskat)abstract
- To define and differentiate relevant aspects of blood-brain barrier transport and distribution in order to aid research methodology in brain drug delivery. Pharmacokinetic parameters relative to the rate and extent of brain drug delivery are described and illustrated with relevant data, with special emphasis on the unbound, pharmacologically active drug molecule. Drug delivery to the brain can be comprehensively described using three parameters: Kp,uu (concentration ratio of unbound drug in brain to blood), CLin (permeability clearance into the brain), and Vu,brain (intra-brain distribution). The permeability of the blood-brain barrier is less relevant to drug action within the CNS than the extent of drug delivery, as most drugs are administered on a continuous (repeated) basis. Kp,uu can differ between CNS-active drugs by a factor of up to 150-fold. This range is much smaller than that for log BB ratios (Kp), which can differ by up to at least 2,000-fold, or for BBB permeabilities, which span an even larger range (up to at least 20,000-fold difference). Methods that measure the three parameters Kp,uu, CLin, and Vu,brain can give clinically valuable estimates of brain drug delivery in early drug discovery programmes.
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| 6. |
- Stridh, Sara, et al.
(författare)
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C-peptide normalizes glomerular filtration rate in hyperfiltrating conscious diabetic rats
- 2009
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Ingår i: Oxygen transport to tissue xxx. - New York : Springer. - 9780387859972 - 0387859977 - 9780387859989 ; , s. 219-225
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Bokkapitel (refereegranskat)abstract
- Tubular electrolyte transport accounts for a major part of the oxygen consumed by the normal kidney. We have previously reported a close association between diabetes and increased oxygen usage, partly due to increased tubular electrolyte transport secondary to glomerular hyperfiltration during the early onset of diabetes. Several studies have shown that acute administration of C-peptide to diabetic rats with glomerular hyperfiltration results in normalized glomerular filtration rate (GFR). In this study, we validated a novel method for precise and repetitive GFR measurements in conscious rats and used C-peptide injection in diabetic rats for evaluation. First, GFR was determined in normoglycemic control rats before and after C-peptide administration. Thereafter, all rats were made diabetic by an i.v. streptozotocin injection. Fourteen days later, GFR was again determined before and after C-peptide administration. GFR was estimated from plasma clearance curves using a single bolus injection of FITC-inulin, followed by serial blood sampling over 155 min. FITC-inulin clearance was calculated using non-compartmental pharmacokinetic data analysis. Baseline GFR in normoglycemic controls was 2.10 +/- 0.18 ml/min, and was unaffected by C-peptide (2.23 +/- 0.14 ml/min). Diabetic rats had elevated GFR (3.06 +/- .034 ml/min), which was normalized by C-peptide (2.35 +/- 0.30 ml/min). In conclusion, the used method for estimation of GFR in conscious animals result in values that are in good agreement with those obtained from traditional GFR measurements on anaesthetized rats. However, multiple measurements from the same conscious subject can be obtained using this method. Furthermore, as previously shown on anaesthetized rats, C-peptide also normalizes GFR in hyperfiltrating conscious diabetic rats.
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