Topical vaginal drug delivery in the guinea pig. I. Effect of estrous cycle on the vaginal membrane permeability of vidarabine

In previous studies, permeability was shown to be one of the most important factors influencing the delivery of vidarabine and its 5'-0-esters in the vaginal membrane of the mouse. The present report describes the results of the extension of these studies to the guinea pig vaginal membrane. By a vaginal smear procedure, the estrous cycle (approx. 16 days in duration) was monitored by dividing it into five stages. The vaginal membrane permeability of vidarabine was measured during each stage in a two-chamber diffusion cell. This study revealed that the permeability coefficients for vidarabine were 5-100 times higher during the early diestrus stage than during the estrus stage. Additional permeation studies on membranes at the estrus stage were performed by separating the upper layer (keratin layer combined with mucous layer) from the rest of the membrane. The low permeability coefficient of vidarabine for the upper layer suggests that this layer may be the major diffusion barrier (mainly keratin layer) for vidarabine when the drug is topically applied during the estrus stage. The immature guinea pig vaginal membranes showed permeability coefficients comparable to those values obtained from the membranes of mature guinea pigs during the early diestrus stage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25677/1/0000230.pd

Topology of factor VIII bound to phosphatidylserine-containing model membranes

AbstractFactor VIII (FVIII), a plasma glycoprotein, is an essential cofactor in the blood coagulation cascade. It is a multidomain protein, known to bind to phosphatidylserine (PS)-containing membranes. Based on X-ray and electron crystallography data, binding of FVIII to PS-containing membranes has been proposed to occur only via the C2 domain. Based on these models, the molecular topology of membrane-bound FVIII can be envisioned as one in which only a small fraction of the protein interacts with the membrane, whereas the majority of the molecule is exposed to an aqueous milieu. We have investigated the topology of the membrane-bound FVIII using biophysical and biochemical techniques. Circular dichroism (CD) and fluorescence studies indicate no significant changes in the secondary and tertiary structure of FVIII associated with the membranes. Acrylamide quenching studies show that the protein is predominantly present on the surface of the membrane, exposed to the aqueous milieu. The light scattering and electron microscopy studies indicate the absence of vesicle aggregation and fusion. Binding studies with antibodies directed against specific epitopes in the A1, A2 and C2 domains suggest that FVIII binds to the membrane primarily via C2 domain including the specific phospholipid binding epitope (2303–2332) and may involve subtle conformational changes in this epitope region