International journal of pharmaceutics, Jan 9, 2004
Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesti... more Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption...
In this study the intestinal degradation and absorption of a synthetic pentapeptide, metkephamid,... more In this study the intestinal degradation and absorption of a synthetic pentapeptide, metkephamid, were investigated in the rat by determination of its wall permeabilities in the small and large intestine and the extent and mechanism of its intestinal degradation. The peptide was metabolized in the gut wall through contact with membrane-bound enzymes in the brush border membrane. The extent of
The former general belief that all peptides and proteins are entirely decomposed in the gastroint... more The former general belief that all peptides and proteins are entirely decomposed in the gastrointestinal tract before absorption occurs turns out to be a misconception. Today several lines of evidence suggest that some proteins and peptides are capable of traversing the intestinal epithelium in intact form, however with yet unpredictable and often insufficient bioavailability, due to severe presystemic degradation in
Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implant... more Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implants, providing a biologically active template for tissue (re)-generation. The goal of this study is to evaluate the feasibility of controlled insulin-like growth factor I (IGF-I) releasing silk fibroin (SF) scaffolds in the context of cartilage repair. The impact of manufacturing parameters (pH, methanol treatment and drug load)
To gain more insights into the human intestinal absorption of alkamides from Echinacea species, t... more To gain more insights into the human intestinal absorption of alkamides from Echinacea species, transport studies were performed with the human adenocarcinoma colonic cell line Caco-2 (ATCC) as a model to assess the epithelial transport of dodeca-2 E,4 E,8 Z,10 E/ Z-tetraenoic acid isobutylamides (1/ 2). 30 minutes after apical loading of 25 microg/ml 1/ 2, about 15 % of these alkamides were detectable on the basolateral side. Close monitoring of the transport during 6 hours revealed a nearly complete transport to the basolateral side after 4 hours and no significant metabolism was observable. Transport experiments performed at 4 degrees C showed only a slight decrease in transport, which is a strong hint that dodeca-2 E,4 E,8 Z,10 E/ Z-tetraenoic acid isobutylamides (1/ 2) cross biological membranes by passive diffusion. Nearly the same results were obtained after preincubation of the Caco-2 cells with lipopolysaccharides (LPS) or phorbol 12-myristate-13-acetate (PMA) to mimic an inflammatory status. These results support the assumption that the alkamides can be easily transported from the intestinum and hence may contribute to the in vivo effects of Echinacea preparations.
European Journal of Pharmaceutics and Biopharmaceutics, 2004
Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is abou... more Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is about to gain important potential as a future therapeutic tool. Depending on the targeted cell type and its state of differentiation, growth factors can activate or regulate a variety of cellular functions. Therefore, strictly localized delivery regimens at well-defined kinetics appear to be logical prerequisites
Purpose. The objective of this study was to evaluate nanoparticle uptake by the Caco-2 monolayer ... more Purpose. The objective of this study was to evaluate nanoparticle uptake by the Caco-2 monolayer model in vitro. Special emphasis was placed on the localization and the quantification of the uptake of fluorescently labeled polystyrene and poly(lactic-co-glycolic acid) (PLGA) nanoparticles.
The purpose of this study was to demonstrate specific receptor-mediated targeting of phagocytes b... more The purpose of this study was to demonstrate specific receptor-mediated targeting of phagocytes by functional surface coatings of microparticles, shielding from nonspecific phagocytosis and allowing ligand-specific interactions via molecular recognition. Coatings of the comb polymer poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) were investigated for potential to inhibit 1) nonspecific spreading of human blood-derived macrophages (MOs) and dendritic cells (DCs) on glass and 2) nonspecific phagocytosis of PLL-g-PEG-coated, carboxylated polystyrene (PS) or biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microspheres. Coating was performed by adsorption of positively charged PLL-g-PEG on negatively charged microparticles or plasma-cleaned glass through electrostatic interaction. The feasibility of ligand-specific interactions was tested with a model ligand, RGD, conjugated to PEG chains of PLL-g-PEG to form PLL-g-PEG-RGD and compared with inactive ligand conjugate, PLL-g-PEG-RD...
With the aim of developing multivalent vaccines for single-injection, we examined the feasibility... more With the aim of developing multivalent vaccines for single-injection, we examined the feasibility of combining antigens in biodegradable microspheres. Such vaccines are expected to improve vaccination coverage by reducing the number of vaccination sessions required to generate immunity. Mono- and multivalent vaccines of Haemophilus influenzae type b (Hib) conjugate, diphtheria toxoid (DT), tetanus toxoid (TT), and pertussis toxin (PT) in poly (lactic acid) and poly(lactic-coglycolic acid) microspheres were prepared by spray drying, and the influence of coencapsulated antigens and excipients on antigen loading, release, and stability was examined. Two tetravalent formulations were tested in guinea pigs. Monovalent Hib and PT vaccines showed loading efficiencies of 10% (Hib) and 30% (PT) in both polymers. The loading efficiencies increased upon addition of trehalose and, even more, when the antigens were coencapsulated in di- and trivalent combinations. Highest loading efficiencies (&...
Vaccination techniques do not always stimulate immunity because of the inappropriate mobilization... more Vaccination techniques do not always stimulate immunity because of the inappropriate mobilization of immune responses, and the frequency of vaccinations required is impractical in many developing countries. Such limitations have spurred the development of new vaccine-delivery approaches. Microparticles made of poly(lactide-co-glycolide) can induce adaptive immunity after a single administration of a vaccine. However, the preclinical assessment of such vaccines is not standardized, making it difficult to compare pharmaceutical with immunological data. The relevance of and the ambiguity in the assessment of microparticulate vaccines with respect to the current knowledge on immunity are discussed, in addition to the application of this knowledge to rational vaccine design.
The formation of succinimide intermediates at Asp-Gly sites and their hydrolysis products, e.g., ... more The formation of succinimide intermediates at Asp-Gly sites and their hydrolysis products, e.g., isoAsp isomers, represents a common source of microheterogeneity in therapeutic proteins. Here we report on the stabilization effect of a zinc chloride induced precipitation of recombinant hirudin HV1 (rHir), an anticoagulant protein. rHir was precipitated by zinc chloride at neutral pH to form a Zn-rHir suspension. An Arrhenius-type study (at 50, 40, 30, and 25 degrees C) and a 4 degrees C stability study were performed. Monitoring of rHir, rHir succinimides at Asp33-Gly34 (Q5) and Asp53-Gly54 (Q4), and further side products was by capillary electrophoresis (CE). The activation energies of rHir degradation in both aqueous rHir solution and Zn-rHir suspension were similar, i.e. 104.5 and 110.3 kJ/mol, respectively. Zn-rHir suspension demonstrated improved shelf-life stability (t90%, 95% confidence limit) versus rHir solution, i.e., 23 versus 3 days at 25 degrees C and 292 versus 147 days...
To gain information on the chemical stability pattern and the kinetics of the degradation of reco... more To gain information on the chemical stability pattern and the kinetics of the degradation of recombinant hirudin variant HV1 (rHir), a thrombin-specific inhibitor protein of 65 amino acids, in aqueous solution as a function of pH. Stability of rHir was monitored at 50 degrees C in the framework of a classical pH-stability study in aqueous buffers pH 1-9.5. Two capillary electrophoresis (CE) protocols were used: one for the kinetics of succinimide formation at Asp53-Gly54 (C-terminal tail) and Asp33-Gly34 (loop section), the other for the kinetics of rHir degradation. To check for potential effects of conformational changes by thermal denaturation, circular dichroism (CD) measurements were performed between 25 and 80 degrees C. Throughout the pH range studied no effect of thermal denaturation on rHir confirmation at 50 degrees C was observed. rHir was most stable at a neutral pH whereas, at slightly acidic pH, an intermediate stability plateau was found. Both, strongly acidic and alk...
Our goals are to establish an in vitro screening system and to evaluate a new approach in improvi... more Our goals are to establish an in vitro screening system and to evaluate a new approach in improving oral absorption of peptides and peptide-like drugs by overexpression of the human intestinal oligopeptide transporter (hPepT1). This study characterizes the expression of hPepT1 in human intestinal Caco-2 cells, rat intestinal epithelial cells (IEC-18), and human cervix epithelial cells (Hela) after adenoviral transduction. A recombinant replication-deficient adenovirus carrying the hPepT1 gene was made and used as a vector for the expression of hPepT1. The increase in the uptake permeability of cephalexin and Gly-Sar was determined. The effects of time, dose, apical pH, and substrate specificity were evaluated. A significant increase in the uptake permeability of Gly-Sar and cephalexin was found in all three cell lines after viral transduction. The increase of Gly-Sar permeability in Hela. IEC-18, and Caco-2 cells was 85-, 46-, and 15-fold respectively. Immunoblotting using an antibo...
Tetanus toxoid (Ttxd) encapsulated in polyester microspheres (MS) for single injection immunizati... more Tetanus toxoid (Ttxd) encapsulated in polyester microspheres (MS) for single injection immunization have so far given pulsatile in vitro release and strong immune response in animals, but no boosting effect. This has been ascribed to insufficient toxoid stability within the MS exposed to in vivo conditions over a prolonged time period. This study examined the effect of co-encapsulated putative stabilizing additives. Two different Ttxd were encapsulated in poly(D,L-lactic-co-glycolic acid) (PLGA 50:50) and poly(D,L-lactic acid) (PLA) MS by spray-drying. The influence of co-encapsulated additives on toxoid stability, loading in and release from the MS, was studied by fluorimetry and ELISA. Co-encapsulated albumin, trehalose and gamma-hydroxypropyl cyclodextrin all improved the toxoid encapsulation efficiency in PLGA 50:50 MS. Albumin increased the encapsulation efficiency of antigenic Ttxd by one to two orders of magnitude. Further, with albumin or a mixture of albumin and trehalose E...
Two calcitonins, i.e. human calcitonin (hCT) and, for comparison, salmon calcitonin (sCT), were c... more Two calcitonins, i.e. human calcitonin (hCT) and, for comparison, salmon calcitonin (sCT), were chosen as peptide models to investigate nasal mucosal metabolism. The susceptibility of hCT and sCT to nasal mucosal enzymes was assessed by in-and-out reflection kinetics experiments in an in vitro model based on the use of freshly excised bovine nasal mucosa, with the mucosal surface of the mucosa facing the peptide solution. The kinetics of CT degradation in the bulk solution was monitored by HPLC. Peptide sequences of the main nasal metabolites of hCT were analyzed by using both liquid secondary ionization mass spectrometry (LSIMS), following HPLC fractionation of the metabolites, and matrix-assisted laser desorption ionization mass (MALDI) spectrometry. For sCT, the molecular weights of two major metabolites were determined by LC-MS with electrospray ionization. Both CTs were readily metabolized by nasal mucosal enzymes. In the concentration range studied metabolic rates were higher ...
European Journal of Pharmaceutics and Biopharmaceutics, 1997
The intestinal absorption mechanism, permeability and bioavailability of the parasympatholytic tr... more The intestinal absorption mechanism, permeability and bioavailability of the parasympatholytic trospium chloride has been investigated in vitro and in vivo in rats, in order to gain a better mechanistic explanation for the underlying cause leading to low bioavailability of quaternary compounds following peroral dosing. Permeability determinations were done in Ussing-type chambers with rat jejunum and human Caco-2 cells. In vivo
International journal of pharmaceutics, Jan 9, 2004
Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesti... more Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption...
In this study the intestinal degradation and absorption of a synthetic pentapeptide, metkephamid,... more In this study the intestinal degradation and absorption of a synthetic pentapeptide, metkephamid, were investigated in the rat by determination of its wall permeabilities in the small and large intestine and the extent and mechanism of its intestinal degradation. The peptide was metabolized in the gut wall through contact with membrane-bound enzymes in the brush border membrane. The extent of
The former general belief that all peptides and proteins are entirely decomposed in the gastroint... more The former general belief that all peptides and proteins are entirely decomposed in the gastrointestinal tract before absorption occurs turns out to be a misconception. Today several lines of evidence suggest that some proteins and peptides are capable of traversing the intestinal epithelium in intact form, however with yet unpredictable and often insufficient bioavailability, due to severe presystemic degradation in
Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implant... more Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implants, providing a biologically active template for tissue (re)-generation. The goal of this study is to evaluate the feasibility of controlled insulin-like growth factor I (IGF-I) releasing silk fibroin (SF) scaffolds in the context of cartilage repair. The impact of manufacturing parameters (pH, methanol treatment and drug load)
To gain more insights into the human intestinal absorption of alkamides from Echinacea species, t... more To gain more insights into the human intestinal absorption of alkamides from Echinacea species, transport studies were performed with the human adenocarcinoma colonic cell line Caco-2 (ATCC) as a model to assess the epithelial transport of dodeca-2 E,4 E,8 Z,10 E/ Z-tetraenoic acid isobutylamides (1/ 2). 30 minutes after apical loading of 25 microg/ml 1/ 2, about 15 % of these alkamides were detectable on the basolateral side. Close monitoring of the transport during 6 hours revealed a nearly complete transport to the basolateral side after 4 hours and no significant metabolism was observable. Transport experiments performed at 4 degrees C showed only a slight decrease in transport, which is a strong hint that dodeca-2 E,4 E,8 Z,10 E/ Z-tetraenoic acid isobutylamides (1/ 2) cross biological membranes by passive diffusion. Nearly the same results were obtained after preincubation of the Caco-2 cells with lipopolysaccharides (LPS) or phorbol 12-myristate-13-acetate (PMA) to mimic an inflammatory status. These results support the assumption that the alkamides can be easily transported from the intestinum and hence may contribute to the in vivo effects of Echinacea preparations.
European Journal of Pharmaceutics and Biopharmaceutics, 2004
Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is abou... more Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is about to gain important potential as a future therapeutic tool. Depending on the targeted cell type and its state of differentiation, growth factors can activate or regulate a variety of cellular functions. Therefore, strictly localized delivery regimens at well-defined kinetics appear to be logical prerequisites
Purpose. The objective of this study was to evaluate nanoparticle uptake by the Caco-2 monolayer ... more Purpose. The objective of this study was to evaluate nanoparticle uptake by the Caco-2 monolayer model in vitro. Special emphasis was placed on the localization and the quantification of the uptake of fluorescently labeled polystyrene and poly(lactic-co-glycolic acid) (PLGA) nanoparticles.
The purpose of this study was to demonstrate specific receptor-mediated targeting of phagocytes b... more The purpose of this study was to demonstrate specific receptor-mediated targeting of phagocytes by functional surface coatings of microparticles, shielding from nonspecific phagocytosis and allowing ligand-specific interactions via molecular recognition. Coatings of the comb polymer poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) were investigated for potential to inhibit 1) nonspecific spreading of human blood-derived macrophages (MOs) and dendritic cells (DCs) on glass and 2) nonspecific phagocytosis of PLL-g-PEG-coated, carboxylated polystyrene (PS) or biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microspheres. Coating was performed by adsorption of positively charged PLL-g-PEG on negatively charged microparticles or plasma-cleaned glass through electrostatic interaction. The feasibility of ligand-specific interactions was tested with a model ligand, RGD, conjugated to PEG chains of PLL-g-PEG to form PLL-g-PEG-RGD and compared with inactive ligand conjugate, PLL-g-PEG-RD...
With the aim of developing multivalent vaccines for single-injection, we examined the feasibility... more With the aim of developing multivalent vaccines for single-injection, we examined the feasibility of combining antigens in biodegradable microspheres. Such vaccines are expected to improve vaccination coverage by reducing the number of vaccination sessions required to generate immunity. Mono- and multivalent vaccines of Haemophilus influenzae type b (Hib) conjugate, diphtheria toxoid (DT), tetanus toxoid (TT), and pertussis toxin (PT) in poly (lactic acid) and poly(lactic-coglycolic acid) microspheres were prepared by spray drying, and the influence of coencapsulated antigens and excipients on antigen loading, release, and stability was examined. Two tetravalent formulations were tested in guinea pigs. Monovalent Hib and PT vaccines showed loading efficiencies of 10% (Hib) and 30% (PT) in both polymers. The loading efficiencies increased upon addition of trehalose and, even more, when the antigens were coencapsulated in di- and trivalent combinations. Highest loading efficiencies (&...
Vaccination techniques do not always stimulate immunity because of the inappropriate mobilization... more Vaccination techniques do not always stimulate immunity because of the inappropriate mobilization of immune responses, and the frequency of vaccinations required is impractical in many developing countries. Such limitations have spurred the development of new vaccine-delivery approaches. Microparticles made of poly(lactide-co-glycolide) can induce adaptive immunity after a single administration of a vaccine. However, the preclinical assessment of such vaccines is not standardized, making it difficult to compare pharmaceutical with immunological data. The relevance of and the ambiguity in the assessment of microparticulate vaccines with respect to the current knowledge on immunity are discussed, in addition to the application of this knowledge to rational vaccine design.
The formation of succinimide intermediates at Asp-Gly sites and their hydrolysis products, e.g., ... more The formation of succinimide intermediates at Asp-Gly sites and their hydrolysis products, e.g., isoAsp isomers, represents a common source of microheterogeneity in therapeutic proteins. Here we report on the stabilization effect of a zinc chloride induced precipitation of recombinant hirudin HV1 (rHir), an anticoagulant protein. rHir was precipitated by zinc chloride at neutral pH to form a Zn-rHir suspension. An Arrhenius-type study (at 50, 40, 30, and 25 degrees C) and a 4 degrees C stability study were performed. Monitoring of rHir, rHir succinimides at Asp33-Gly34 (Q5) and Asp53-Gly54 (Q4), and further side products was by capillary electrophoresis (CE). The activation energies of rHir degradation in both aqueous rHir solution and Zn-rHir suspension were similar, i.e. 104.5 and 110.3 kJ/mol, respectively. Zn-rHir suspension demonstrated improved shelf-life stability (t90%, 95% confidence limit) versus rHir solution, i.e., 23 versus 3 days at 25 degrees C and 292 versus 147 days...
To gain information on the chemical stability pattern and the kinetics of the degradation of reco... more To gain information on the chemical stability pattern and the kinetics of the degradation of recombinant hirudin variant HV1 (rHir), a thrombin-specific inhibitor protein of 65 amino acids, in aqueous solution as a function of pH. Stability of rHir was monitored at 50 degrees C in the framework of a classical pH-stability study in aqueous buffers pH 1-9.5. Two capillary electrophoresis (CE) protocols were used: one for the kinetics of succinimide formation at Asp53-Gly54 (C-terminal tail) and Asp33-Gly34 (loop section), the other for the kinetics of rHir degradation. To check for potential effects of conformational changes by thermal denaturation, circular dichroism (CD) measurements were performed between 25 and 80 degrees C. Throughout the pH range studied no effect of thermal denaturation on rHir confirmation at 50 degrees C was observed. rHir was most stable at a neutral pH whereas, at slightly acidic pH, an intermediate stability plateau was found. Both, strongly acidic and alk...
Our goals are to establish an in vitro screening system and to evaluate a new approach in improvi... more Our goals are to establish an in vitro screening system and to evaluate a new approach in improving oral absorption of peptides and peptide-like drugs by overexpression of the human intestinal oligopeptide transporter (hPepT1). This study characterizes the expression of hPepT1 in human intestinal Caco-2 cells, rat intestinal epithelial cells (IEC-18), and human cervix epithelial cells (Hela) after adenoviral transduction. A recombinant replication-deficient adenovirus carrying the hPepT1 gene was made and used as a vector for the expression of hPepT1. The increase in the uptake permeability of cephalexin and Gly-Sar was determined. The effects of time, dose, apical pH, and substrate specificity were evaluated. A significant increase in the uptake permeability of Gly-Sar and cephalexin was found in all three cell lines after viral transduction. The increase of Gly-Sar permeability in Hela. IEC-18, and Caco-2 cells was 85-, 46-, and 15-fold respectively. Immunoblotting using an antibo...
Tetanus toxoid (Ttxd) encapsulated in polyester microspheres (MS) for single injection immunizati... more Tetanus toxoid (Ttxd) encapsulated in polyester microspheres (MS) for single injection immunization have so far given pulsatile in vitro release and strong immune response in animals, but no boosting effect. This has been ascribed to insufficient toxoid stability within the MS exposed to in vivo conditions over a prolonged time period. This study examined the effect of co-encapsulated putative stabilizing additives. Two different Ttxd were encapsulated in poly(D,L-lactic-co-glycolic acid) (PLGA 50:50) and poly(D,L-lactic acid) (PLA) MS by spray-drying. The influence of co-encapsulated additives on toxoid stability, loading in and release from the MS, was studied by fluorimetry and ELISA. Co-encapsulated albumin, trehalose and gamma-hydroxypropyl cyclodextrin all improved the toxoid encapsulation efficiency in PLGA 50:50 MS. Albumin increased the encapsulation efficiency of antigenic Ttxd by one to two orders of magnitude. Further, with albumin or a mixture of albumin and trehalose E...
Two calcitonins, i.e. human calcitonin (hCT) and, for comparison, salmon calcitonin (sCT), were c... more Two calcitonins, i.e. human calcitonin (hCT) and, for comparison, salmon calcitonin (sCT), were chosen as peptide models to investigate nasal mucosal metabolism. The susceptibility of hCT and sCT to nasal mucosal enzymes was assessed by in-and-out reflection kinetics experiments in an in vitro model based on the use of freshly excised bovine nasal mucosa, with the mucosal surface of the mucosa facing the peptide solution. The kinetics of CT degradation in the bulk solution was monitored by HPLC. Peptide sequences of the main nasal metabolites of hCT were analyzed by using both liquid secondary ionization mass spectrometry (LSIMS), following HPLC fractionation of the metabolites, and matrix-assisted laser desorption ionization mass (MALDI) spectrometry. For sCT, the molecular weights of two major metabolites were determined by LC-MS with electrospray ionization. Both CTs were readily metabolized by nasal mucosal enzymes. In the concentration range studied metabolic rates were higher ...
European Journal of Pharmaceutics and Biopharmaceutics, 1997
The intestinal absorption mechanism, permeability and bioavailability of the parasympatholytic tr... more The intestinal absorption mechanism, permeability and bioavailability of the parasympatholytic trospium chloride has been investigated in vitro and in vivo in rats, in order to gain a better mechanistic explanation for the underlying cause leading to low bioavailability of quaternary compounds following peroral dosing. Permeability determinations were done in Ussing-type chambers with rat jejunum and human Caco-2 cells. In vivo
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Papers by Hans Merkle