PAMPA

PAMPA (parallel artificial membrane permeability assay) is a method which determines the permeability of substances from a donor compartment, through a lipid-infused artificial membrane into an acceptor compartment. A multi-well microtitre plate is used for the donor and a membrane/acceptor compartment is placed on top; the whole assembly is commonly referred to as a “sandwich”. At the beginning of the test, the drug is added to the donor compartment, and the acceptor compartment is drug-free. After an incubation period which may include stirring, the sandwich is separated and the amount of drug is measured in each compartment. Mass balance allows calculation of drug that remains in the membrane. To date, PAMPA models have been developed that exhibit a high degree of correlation with permeation across a variety of barriers, including Caco-2 cultures,^[1][2] the gastrointestinal tract,^[3] blood-brain barrier^[4] and skin.^[5]

The donor and/or acceptor compartments may contain solubilizing agents, or additives that bind the drugs as they permeate. To improve the in vitro - in vivo correlation and performance of the PAMPA method, the lipid, pH and chemical composition of the system is often designed with biomimetic considerations in mind.

The popularity of PAMPA in ADME screening attests to its utility as an early stage, low-cost alternative to cellular models for research compounds. Although active transport is not modeled by the artificial PAMPA membrane, up to 95% of known drugs are absorbed by passive transport.^[6] Some experts support a lower figure, so the amount is open to some interpretation. Microtiter plates with 96 wells can be used for the assay which increases the speed and lowers the per sample cost.

Since the first publication by Kansy and coworkers,^[7] several companies developed their own versions of the assay. Early models incorporated iso-pH conditions in the compartments separated by a simple lipid membrane; subsequently, commercial products were introduced which incorporated more sophisticated lipid membranes^[8]. The commercial products helped ensure that medicinal chemists across different corporate labs within a worldwide organization used the same standardized methodology, reagents and obtained equivalent system performance as demonstrated with a set of test compounds. This has proved very useful as various operational activities have been outsourced to other countries.

As financial and other factors in pharmaceutical development continue to strain timelines and resources, PAMPA will most likely continue to play an ever-increasing role in laboratories wishing to increase their operating efficiencies and success rate.

See also

• Drug development
• Drug Discovery
• Lipid bilayer
• Caco-2 cell-based permability

Further reading

• Avdeef, Alex (2003). Absorption and Drug Development. Hoboken, N.J: Wiley-Interscience/J. Wiley. ISBN 0-471-42365-3. 

External links

• pION INC The first commercial supplier of complete PAMPA systems.
• BD Biosciences Pre-coated PAMPA Plate System.

References

1. ^ Bermejo, M. et al. (2004). PAMPA – a drug absorption in vitro model 7. Comparing rat in situ, Caco-2, and PAMPA permeability of fluoroquinolones. Pharm. Sci., 21: 429-441.
2. ^ Avdeef, A. et al. (2005). Caco-2 permeability of weakly basic drugs predicted with the Double-Sink PAMPA pKaflux method. Pharm. Sci., 24: 333-349.
3. ^ Avdeef, A. et al. (2004). PAMPA – a drug absorption in vitro model 11. Matching the in vivo unstirred water layer thickness by individual-well stirring in microtitre plates. Pharm. Sci., 22: 365-374.
4. ^ Dagenais, C. et al. (2009). P-glycoprotein deficient mouse in situ blood-brain barrier permeability and its prediction using an in combo PAMPA model. Eur. J. Phar. Sci., 38(2): 121-137.
5. ^ Sinkó, B. et al. (2009). A PAMPA Study of the Permeability-Enhancing Effect of New Ceramide Analogues. Chemistry & Biodiversity, 6: 1867-1874.
6. ^ Artursson, P. Application of physicochemical properties of molecules to predict intestinal permeability. AAPS Workshop on Permeability Definitions and Regulatory Standards, Arlington, VA, USA (1998) 17-19 Aug.
7. ^ Kansy M, Senner F, Gubernator K. (1998) Physicochemical high throughput screening: parallel artificial membrane permeability assay in the description of passive absorption processes. J. Med. Chem. 41: 1007-1010.
8. ^ Chen, X. et al. (2008) A Novel Design of Artificial Membrane for Improving the PAMPA Model. Pharmaceutical Research, 25: 1511.