Cross section of a pION 96-well microtitre plate PAMPA sandwich assembly in .NET framework

Generate Data Matrix 2d barcode in .NET framework Cross section of a pION 96-well microtitre plate PAMPA sandwich assembly
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PARALLEL ARTIFICIAL-MEMBRANE PERMEABILITY ASSAY (PAMPA)
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Figure 710 Absorption% versus PAMPA ux [547]: (a) pH 65; (b) pH 74 [Reprinted from Kansy, M; Senner, F; Gubernator, K J Med Chem, 41, 1070 1110 (1998), with permission from the American Chemical Society]
screening [48,82,91,97,108 110,510 515,551 553] The outliers in their assays, inset in Fig 710, were molecules known to be actively transported Since the arti cial membranes have no active transport systems and no metabolizing enzymes, the assay would not be expected to model actively transported molecules What one sees with PAMPA is pure passive diffusion, principally of the uncharged species More recently, several publications have emerged, describing PAMPA-like systems [25 28,509, 554 565] The PAMPA method has attracted a lot of favorable attention, and has spurred the development of a commercial instrument, [25 28,556] and the organization of the rst international symposium on PAMPA in 2002 [565] 732 Hexadecane PAMPA Model (Novartis Model)
Faller and Wohnsland [509,554] developed the PAMPA assay using phospholipidfree hexadecane, supported on 10-mm thick polycarbonate lters(20% porosity,
PERMEABILITY
03 cm2 cross-sectional area), and were able to demonstrate interesting predictions Their PAMPA method appeared to be a satisfactory substitute for obtaining alkanewater partition coef cients, which are usually very dif cult to measure directly, due to the poor solubility of drug molecules in alkanes They applied the pH-based methods of Walter and Gutknecht [537] to extract the intrinsic permeability coef cients, P0, of the molecules they studied A plot of log P0 vs hexadecane-water log Kd is a straight line with a slope of 086 (r2 096), as shown in Fig 711 Apparently, membrane retention was not measured in the original version of the method A later measurement in our laboratory, where retention was considered, indicated a slope of 100, albeit with a slightly poorer t (r 2 092), as shown by the open circles in Fig 711 733 Brush-Border Lipid Membrane (BBLM) PAMPA Model (Chugai Model) Sugano et al [561,562] explored the lipid model containing several different phospholipids, closely resembling the mixture found in reconstituted brush border lipids [433,566] and demonstrated dramatically improved property predictions The bestperforming lipid composition consisted of a 3% wt/vol lipid solution in 1,7-octadiene (lipid consisting of 33% wt/wt cholesterol, 27% PC, 27% PE, 7% PS, 7% PI) The donor and acceptor compartments were adjusted in the pH interval between 50 and 74 [562] With such a mixture, membrane retention is expected to be extensive when lipophilic drugs are assayed The use of 1,7-octadiene in the assay was noted to require special safety precautions
2 log Po = -269 + 086 log Kp (r = 0961, s=034, n=16)
Wohnsland &Faller [554] pION Wohnsland & Faller [554] pION
log Po
-1 -2 -3 -4 -1
2 logPo = -361 + 100 log Kp (r = 0916, s=055, n=7)
log Kp (hexadecane-water)
Figure 711 Intrinsic permeabilities versus alkane water partition coef cients for drugs: PAMPA lters soaked with alkane [509]
PARALLEL ARTIFICIAL-MEMBRANE PERMEABILITY ASSAY (PAMPA)
Hydrophilic Filter Membrane PAMPA Model (Aventis Model)
Zhu et al [563] found the use of hydrophilic lters (low-protein-binding PVDF) as an advantage in lowering the permeation time to 2 h Egg lecithin, 1% wt/vol in dodecane, was used as the membrane medium Over 90 compounds were characterized at pH 55 and 74 For each molecule, the greater Pe value of the two measured at different pH [509,554] was used to compare to Caco-2 permeabilities reported in the literature It is noteworthy that many ionizable molecules did not follow the permeability-pH dependency expected from the pH partition hypothesis It may be that water channels were contributing to the unexpected permeability-pH trends Solute retention by the membrane was not considered They tried using the Chugai ve-component model, but found dif culties in depositing the lipid mixture on hydrophilic lters Human intestinal absorption (HIA) values were compared to PAMPA measurements, Caco-2 permeabilities, partition coef cients (log Kp / log Kd), polar surface area (PSA) and quantitative structure-property relations (QSPRs) developed by Winiwarter et al [56] It was concluded that PAMPA and Caco-2 measurements best predicted HIA values 735 Permeability Retention Gradient Sink PAMPA Models (pION Models) The system reported by Avdeef and co-workers [25 28,556 560] is an extension of the Roche approach, with several novel features described, including a way to assess membrane retention [25 28,556,557] and a way to quantify the effects of iso-pH [558] and gradient pH [559] conditions applied to ionizable molecules A highly pure synthetic phospholipid, dioleoylphosphatidylcholine (DOPC), was initially used to coat the lters (2% wt/vol DOPC in dodecane) Other lipid mixtures were subsequently developed, and are described in detail in this chapter 736 Structure of Phospholipid Membranes
The structure of the lter-immobilized arti cial membranes is not known with certainty Thompson et al [543] hypothesized that polycarbonate lters had a single bilayer per pore, based largely on the behavior of amphotericin B in the poreforming oligomerization reaction Hennesthal and Steinem [568], using scanning force microscopy, estimated that a single bilayer spans exterior pores of porous alumina These observations may be incomplete, as there is considerable complexity to the spontaneous process of the formation of BLMs (Section 721) When 2% phosphatidylcholine (PC) dodecane solution is suspended in water, where the water exceeds 40 wt%, the lipid solution takes on the inverted hexagonal (HII) structure, where the polar head groups of the PC face water channels in a cylindrical structure [569] Such structures can alter transport properties, compared to those of normal phases [570] (It may be possible to model the paracellular transport mechanism, should the presence of aqueous pores be established) Suspensions