Barrier Biological

Currently, the only biological barrier registered as a biochemical pest control agent is kaolin, a clay mineral [47]. Kaolin is a ubiquitous clay substance found in soils worldwide and consists of a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra [Al2Si205(0H)4]. 

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N. Washington, C. G. Wilson, and C. Washington, Physiological Pharmaceutics Biological Barriers to DrugAbsorption, Ellis Horwood Ltd., Chichester, England, 1989, pp. 155-178. 

K. L. Audus and T. J. Raub, Biological Barriers to Protein Delivery, Plenum Press, New York, 1993. 

P-glycoprotein, a plasma membrane transport protein, is present in the gut, brain, liver, and kidneys 42 This protein provides a biologic barrier by eliminating toxic substances and xenobiotics that may accumulate in these organs. P-glycoprotein plays an important role in the absorption and distribution of many medications. Medications that are CYP3A4 substrates, inhibitors, or inducers are also often affected by P-glycoprotein therefore, the potential for even more DDIs exists in transplant recipients.42... 

J. C. Lang and M. M. Stiemke, Biological barriers to ocular delivery in Ocular Therapeutics and Drug Delivery, A Multidisciplinary Approach (I. K. Reddy, ed.), Technomic Publishing Company, 1996, pp. 51-132. 

Most drug-like molecules dissolved in water form hydrogen bonds with the solvent. When such a molecule transfers from water into a phospholipid bilayer, the solute-water hydrogen bonds are broken (desolvation), as new solute-lipid H bonds form in the lipid phase. The free-energy difference between the two states of solvation has direct impact on the ability of the molecules to cross biological barriers. 

Ghosh, R., Novel membranes for simulating biological barrier transport, J. Membr. Sci. 192, 145-154 (2001). 

The identification and characterization of cell culture systems (e.g., Caco-2-cells) that mimic in vivo biological barriers (e.g., intestinal mucosa) have afforded pharmaceutical scientists the opportunity to rapidly and efficiently assess the permeability of drugs through these barriers in vitro. The results generated from these types of in vitro studies are generally expressed as effective permeability coefficients (Pe). If Pe is properly corrected to account for the barrier effects of the filter (PF) and the aqueous boundary layer (PAbl) as previously described in Section II.C, the results provide the permeability coefficient for the cell monolayer... 

Although obviously occurring in practice, macromolecules absorbed via the pulmonary route must cross a number of biological barriers to get into the blood. These are ... 

No matter what their composition, such synthetic gene delivery systems also meet various biological barriers to efficient cellular gene delivery. Viral vector-based systems are far less prone to such problems, as the viral carrier has evolved in nature to overcome such obstacles. Obstacles relate to ... 

Boudou, A., Delnomdedieu, M., Georgescauld, D., Ribeyre, F. and Saouter, E. (1991). Fundamental roles of biological barriers in mercury accumulation and transfer in freshwater ecosystems (analysis at organism, organ, cell and molecular levels), Wat. Air, Soil Poll., 56, 807-822. 

P. Calvo, J. L. Vila-Jato, and M. J. Alonso, Corneal penetration of 14C-indomethacin-loaded nanocapsules, in Methods to Overcome Biological Barriers in Drug Delivery, Kuopio, Finland, 1993, Kuopio University, Department of Pharmaceutical Technology, p. 93. 

Uptake is the process by which chemicals (either dissolved in water or sorbed onto sediment and/or suspended solids) are transferred into and onto an organism. For surfactants, this generally occurs in a series of steps a rapid initial step controlled by sorption, where the surface phenomenon is especially relevant then a diffusion step, when the chemical crosses biological barriers, and later steps when it is transported and distributed among the tissues and organs. 

Tukker JJ (2002) Characterization of transport over epithelial barriers. In Lehr CM (Ed) Cell Culture Models of Biological Barriers. In-vitro Test Systems for Drug Absorption and Delivery. Taylor and Francis, London, pp 52-61. 

When a drug has dissolved in the GI fluids and is present in solution at the site of absorption it has to pass a biological barrier, that is, the enterocytes lining the gut wall, in order to be absorbed into the body. The absorptive flux (J) can be described as a function of the permeability of the intestinal mucosa to the drug (Peff), the surface area available for absorption (SA), and the concentration gradient (AC) across the mucosa (e.g., [6], Eq. 2)... 

The successful application of in vitro models of intestinal drug absorption depends on the ability of the in vitro model to mimic the relevant characteristics of the in vivo biological barrier. Most compounds are absorbed by passive transcellular diffusion. To undergo tran-scellular transport a molecule must cross the lipid bilayer of the apical and basolateral cell membranes. In recent years, there has been a widespread acceptance of a technique, artificial membrane permeation assay (PAMPA), to estimate intestinal permeability.117118 The principle of the PAMPA is that, diffusion across a lipid layer, mimics transepithelial permeation. Experiments are conducted by applying a drug solution on top of a lipid layer covering a filter that separates top (donor) and bottom (receiver) chambers. The rate of drug appearance in the bottom wells should reflect the diffusion across the lipid layer, and by extrapolation, across the epithelial cell layer. 

Neutra, M. and Kraehenhuhl, J.P., Transepithelial transport of proteins by intestinal epithelial cells, in Biological Barriers to Protein Delivery, Audus, K.L. and Raub, T.J., Eds., Plenum Press, New York, 1993, pp. 107-129. 

Wilson, C.G., and Washington, N., Physiological Pharmaceutics, Biological Barriers to Drug Absorption, Ellis Harwood Ltd, Chichester, UK, 1989. 

Wilson CG, Washington N. Physiological Pharmaceutics Biological Barriers to Drug Absorption, 2nd edn. Chichester Ellis Horwood, 2001. 

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