Double-sink

Avdeef, A., Artursson, P., NeuhofF, S., Lazorova, L., Grasjo, J., Tavelin, S. Caco-2 permeability of weakly basic drugs predicted with the double-sink PAM PA pKl method. Eur.J. Pharm. Sci. 2005, 24, 333-349. 

In the BBB-PAMPA lipid formulation illustrated in Fig. 3.4, the diff values, defined as the difference log Pq-log Pi, range from 2.9 (morphine) to 4.2 (warfarin), somewhat similar to the values observed in the octanol-water system. However, it is premature to propose a pdiffi-A approximation, given the limited amount of data reported. With other lipid formulations, larger differences are usually observed. In Double-Sink PAM PA, and especially in hexadecane-PAMPA, transport of ionized drugs has not been reported [84]. 

DERIVATION OF MEMBRANE-RETENTION PERMEABILITY EQUATIONS (ONE-POINT MEASUREMENTS, PHYSICAL SINKS, IONIZATION SINKS, BINDING SINKS, DOUBLE SINKS)... 

In this chapter we use the term sink to mean any process that can significantly lower the concentration of the neutral form of the sample molecule in the acceptor compartment. Under the right conditions, the ionization and the binding sinks serve the same purpose as the physically maintained sink often used in Caco-2 measurements. We will develop several transport models to cover these chemical sink conditions. When both of the chemical sink conditions (ionization and binding) are imposed, we will use the term double sink in this chapter. 

Double Sink Eq. (7.34) in the Presence of Serum Protein or Sink in Acceptor Wells... 

For ionizable lipophilic molecules, the right pH gradients can drive the solute in the acceptor compartment to the charged (impermeable) form the uncharged fraction is then further diminished in concentration by binding to the serum protein or surfactant, in the double-sink assay. 

Figure 7.41 Gradient pH profiles for three weak bases with double-sink conditions, 20% wt/vol soy lecithin in dodecane (a) verapamil (pKa 9.07) (b) propranolol (pKa 9.53) (c) metoprolol (pKa 9.56).

DOUBLE-SINK (Soy Lecithin 20% wt/vol in Dodecane, SINK in Acceptor)... 

Figure 7.43 Gradient pH profiles for two nonionizable molecules double-sink conditions, 20% wt/vol soy lecithin in dodecane.

TABLE 7.18 Interpolated Apparent and Membrane Permeabilities Determined from Double-Sink Conditions 20% Soy Lecithin in Dodecane... 

TABLE 7.22 In Vitro Double-Sink PAMPA Models for GIT and BBB Targets... 

In Vivo GIT In Vivo BBB In Vitro Double-Sink GIT Model (20% Soy Lecithin) In Vitro Double-Sink BBB Model (20% Soy Lecithin)... 

The best correlations were observed under gradient pH and sink conditions ( double-sink set at the bottom of Table 7.23), with the donor pH 5 and acceptor pH 7.4 producing r2 0.97. The r2/donor pH plot is shown in Fig. 7.62. The data represented by the solid line corresponds to P, values (Pe corrected for the... 

Figure 7.62 Correlation between human jejunal permeabilities [vs. PAMPA (double-sink)] and soy lecithin models under gradient pH conditions.

Figure 7.63 Human jejunal permeabilities compared to pION s double-sink sum-Pe PAM PA GIT model.

The pION double-sink GIT model, with donor pH 5, predicts the human jejunal permeabilities as well as the best reported Caco-2 model (Artursson s), and a lot better than the rest of the reported Caco-2 models, as shown in Fig. 7.63. 

Figure 7.67 Human intestinal absorption compared to (a) pION s double-sink sum-P, PAMPA GIT model and (b) human jejunal permeabilities [56],...

In conclusion, the double-sink su m-P, PAMPA in vitro GIT assay seems to predict human absorption as well as in vivo human permeability measurements (see Figs. 7.66a,b) and in vitro Caco-2 permeability measurements (see Figs. 7.60 and 7.63), but at a lower cost and higher speed. 

The lengthy permeability chapter (Chapter 7) recounts the study of many different artificial membrane formulations, comparing transport results of each to human jejunal permeabilities. A very promising in vitro screening system was described the double-sink sum-Pe PAMPA GIT model. It is most applicable to molecules that are classified as soluble in the BCS scheme. 

Composition of the PAM PA membrane varies from a purely organic solvent membrane to a purely phospholipid membrane. At the first international conference of PAM PA in 2002 (www.pampa2002.com/), it was agreed that these variations would be notated as initials or a short adjective at the head of PAMPA (e.g., BM-PAMPA for biomimetic PAMPA). The original PAMPA (Egg-PAMPA) [47], hexadecane membrane PAMPA (HDM-PAMPA) [48], BM-PAMPA [49], double sink PAMPA (DS-PAMPA) and blood-brain barrier PAMPA (BBB-PAMPA) [51] are reviewed elsewhere [3]. 

ThepION Inc. method uses double-sink conditions, both ionization and binding maintained. 

Also in the PAMPAmodel, alternatives to BSAhave been explored to improve the biorelevance of the model. To overcome the adsorption and/or absence of sink conditions, different additives that do not require an additional step of sample preparation as compared with the addition of albumin, have been proposed. Recently, the use of Double-Sink PAMPA (DS-PAMPA) was proposed as biorelevant alternative to the classic PAMPA methodology (Avdeef, 2003). In DS-PAMPA, a non-specific binding agent (lipophilic sink) was included in the receiver compartment to create sink conditions. 

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