In Vitro Transport Studies

Aoki, J., Suzuki, H., Sugiyama, Y., Quantitative prediction of in vivo biliary excretion clearance across the bile canalicular membrane from in vitro transport studies with isolated membrane vesicles. Abstract of Millennial World Congress of pharmaceutical Sciences, San Francisco, April 16-20, 2000, p. 92. 

Honeywell-Nguyen, P.L., et al. 2002. Transdermal delivery of pergolide from surfactant-based elastic and rigid vesicles Characterization and in vitro transport studies. Pharm Res 19 991. 

Figure 2 Comparison between the uptake clearance obtained in vivo and that extrapolated from the in vitro transport study of endothelin antagonists. In vivo uptake clearance of endothelin antagonists (BQ-123, BQ-518, BQ-485, compound A) was evaluated by integration plot analysis using the plasma concentration-time profile after intravenous administration (500 nmol/kg) and the amount of drug in the liver and that excreted in the bile. In vitro hepatic uptake clearance was measured using isolated rat hepatocytes and was extrapolated to the in vivo uptake clearance assuming the well-stirred model. Source From Ref. 5.

As mentioned earlier, the underlying mechanisms for many of the transporter-mediated interactions are not fully understood and remain elusive at the present time. With the limited knowledge on the molecular mechanisms of transporter-mediated interaction and the fact that many inhibitors and inducers can simultaneously affect both drug transporters and CYP enzymes, it is difficult to quantitatively differentiate transporter-mediated interactions from CYP-mediated interactions. From the literature, it becomes clear that evidence of transporter-mediated dmg interactions, with few exceptions, is often indirectly derived from in vitro transport studies with cellular culture models and heterologous expression systems. 

Hanisch G, Utter L, Ungell A-L, and Lucas M. Surface pH Measurements During in vitro Transport Studies Across Intestinal Epithelia Thickness of Acid Microclimate. AAPS annual meeting in San Diego, California, 6-10 Nov, 1994. Pharm Res.l994 ,vo 11 10 suppl. 

SNAPs is an acronym for soluble NSF attachment proteins. They were originally discovered as cofactors for NSF that mediate the membrane binding of NSF in in vitro transport assays. Several isoforms of SNAPs exist in mammalian cells. SNAPs are also highly conserved proteins. Crystallographic studies indicated that the proteins form a very stiff and twisted sheet that is formed by a series of antiparallel and tightly packed helices connected by short loops. 

A number of studies have implicated cytoplasmic dynein as playing a role in retrograde axonal transport [11, 39]. In vitro motility studies demonstrate that cytoplasmic dynein generates force towards the minus ends of MTs consistent with a retrograde motor. Dynein immu-noreactivities have been associated with MBOs and... 

The permeability of the drug substance can be determined by different approaches such as pharmacokinetic studies in humans (fraction absorbed or mass balance studies) or intestinal permeability studies (in vivo intestinal perfusion studies in humans or suitable animal models or in vitro permeation studies using excised intestinal tissue or epithelial cell culture monolayers like CaCo-2 cell line). In order to avoid misclassification of a drug subject to efflux transporters such as P-glycoprotein, functional expression of such proteins should be investigated. Low- and high-permeability model... 

Shen Q, Lin Y, Handa T, Doi M, Sugie M, Wakayama K, Okada N, Fujita T, Yamamoto A (2006) Modulation of intestinal P-glycoprotein function by polyethylene glycols and their derivatives by in vitro transport and in situ absorption studies. Int J Pharm 313 49-56. 

For in vitro toxicity studies and assessment of the barrier function, drug transport, cell physiology, and metabolism as well as the development of delivery systems, cell culture models provide powerful systems for scientific research. As the corneal epithelium is the main barrier for ocular penetration, various corneal epithelial cell cultures were established besides the corneal constructs that mimic the whole cornea and serve as reductionist models for the ocular barrier. In general, two types of cell culture models are available primary cell cultures and immortalized, continuous cell lines. 

In vitro permeation studies employ a glass diffusion cell with the buccal tissue mounted between the two halves of the eell whieh may be filled with constantly stirred buffer solutions. The bueeal mueosa is exeised from the eanine, porcine, or rabbit eheek immediately after saerifiee. Permeation studies may provide meaningful results on the simultaneous proeesses of drug transport and metabolism in the tissue... 

A concerted effort is needed to increase our understanding of the transfer and uptake of reactive gases in the lung. A program in this field should involve in vitro model studies, animal experiments, and clinical studies. More information is required on the chemical, physical, and morphologic properties of the mucous layer and the kinetics of the reactions of ozone in the mucous and tissue layers. Experimental data on uptake and dosage for ozone and other oxidants are difficult to obtain for the tracheobronchial and pulmonary regions. Such data for animals and humans will be needed to test the present simple transport models, before further refinements are made. 

FIGURE 22.6 Permeability and permselectivity of vaginal and buccal epithelia in the rabbit, (a) Flux of 6-carboxyfluoroscein, a hydrophilic molecule, by in vitro perfusion studies steady-state flux ( xg/cm2/h x 106), (b) resistance (fl cm2 x 10 2), (c) thickness (p,m x 10-2), and (d) ratio of potassium transport number to chloride transport number, which is calculated from electrical measurements, used as indicative of the epithelium selectivity for positively charged molecules. (Modified from Sayani, A.P. and Chien, Y.W., Crit. Rev. Ther. Drug Carrier Syst. 13, 85, 1996.)... 

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