Biomedical subjects

R Kinget

Publications and source records attributed to R Kinget.

At least 37 records · Page 2Linked to original sources

PubMed2000

Toxicological investigations of the effects carboxymethylcellulose on ciliary beat frequency of human nasal epithelial cells in primary suspension culture and in vivo on rabbit nasal mucosa.

The objective of this study was to investigate the safety of a mucoadhesive carboxymethylcellulose (CMC) formulation for intranasal administration of apomorphine. The effect of different concentrations of CMC on ciliary beat frequency (CBF) was studied using a human nasal epithelial suspension cell culture system. The CBF was determined by computerized microscope photometry. The in vivo rabbit nasal mucosal tolerance of the mucoadhesive polymer was investigated using light microscopy. Twice daily, six rabbits received CMC powder in one nostril and CMC/apomorphine powder in the alternate nostril for 4 weeks. Two control rabbits received air puffs in one nostril and nothing in the alternate nostril. The rabbits were subsequently sacrificed and the stained nasal sections examined microscopically. CMC showed both concentration- and time-dependent inhibitory effects on the CBF. Only mild-to-moderate cilio-inhibition was recorded with the different concentrations of the polymer. CMC (both with and without apomorphine) caused mild-to-moderate inflammation after 4 weeks. Necrosis, squamous metaplasia or ciliary degeneration was not observed. Based on: (1) the mild-to-moderate cilio-inhibition induced by different concentrations of CMC; and (2) the mild-to-moderate nasal mucosal inflammation caused by CMC with and without apomorphine, we conclude that this polymer can be considered as a safe carrier for short-term intranasal administration. However, further investigations are required for its use in the treatment of chronic diseases such as with apomorphine in Parkinson's disease.

Animals↗

PubMed2000

Species-dependent and site-specific intestinal metabolism of ester prodrugs.

In order to select a species for drug absorption studies of ester prodrugs and to identify a possible absorption window with low esterase activity and hence increased absorption of the ester prodrug, the esterase activity was investigated in homogenates from various intestinal segments of different species. p-Nitrophenyl acetate and tenofovir disoproxil [bis(POC)-PMPA] were used as substrates for esterases. p-Nitrophenyl acetate is a model substrate for esterase activity, while tenofovir disoproxil (fumarate salt) is an ester prodrug of the potent antiviral nucleoside phosphonate analogue tenofovir. As esterase-mediated degradation during transepithelial transport may be a limiting factor for its oral absorption, targeting the prodrug to a region of the intestine with lower esterase activity may lead to an increase in oral absorption of the prodrug. The results obtained with p-nitrophenyl acetate and tenofovir disoproxil showed both a site-specific (duodenum > or = jejunum > ileum > or = colon) and species-dependent (rat > man > pig) degradation in intestinal homogenates. Degradation of tenofovir disoproxil in homogenates from Caco-2 monolayers (0.016+/-0.003 nmol. s(-1). mg protein(-1)) was low compared to its degradation in homogenates from human ileum (0.177+/-0.052 nmol. s(-1). mg protein(-1)). Rat ileum appears to be a suitable model to evaluate the influence of esterase activity on the oral absorption of the ester prodrug, as the degradation rate for tenofovir disoproxil (0.245+/-0.054 nmol. s(-1). mg protein(-1)) in rat ileum was similar to degradation in human ileum. The results also suggest that colon targeting may be a useful strategy to reduce the esterase-mediated degradation of ester prodrugs, hence resulting in a possible increase in their oral absorption.

Animals↗

PubMed2000

Scintigraphic evaluation in rabbits of nasal drug delivery systems based on carbopol 971p((R)) and carboxymethylcellulose.

The residence time of apomorphine mucoadhesive preparations incorporating 99mTc labeled colloidal albumin in rabbit nasal cavity was evaluated by gamma scintigraphy. This technique was used to compare the nasal clearance of preparations based either on Carbopol 971P((R)) or lactose (control), each with and without apomorphine, or carboxymethylcellulose with apomorphine. The planar 1-min images showed an excipient-dependent progressive migration of radioactivity with time from the nasal cavity to the stomach and intestine. Thirty minutes post insufflation, the percentages of the formulations cleared from the nasal cavity were 47% for lactose, 26% for lactose/apomorphine, 10% for Carbopol 971P((R)), and 3% for both Carbopol 971P((R))/apomorphine and carboxymethylcellulose/apomorphine. Three hours post insufflation, the percentages of the formulations cleared from the nasal cavity were 70% for lactose, 58% for lactose/apomorphine, 24% for Carbopol 971P((R)), 12% for Carbopol 971P((R))/apomorphine, and 27% for carboxymethylcellulose/apomorphine. Apomorphine inhibited nasal mucociliary clearance since migration of the radioactivity administered with apomorphine containing preparations was in all cases slower than that of the corresponding powder without apomorphine. The peak plasma concentration of apomorphine was attained while all the formulations were still within the nasal cavity. The use of mucoadhesive polymers such as Carbopol 971P((R)) or carboxymethylcellulose in nasal dosage forms increases their residence time within the nasal cavity and provides the opportunity for sustained nasal drug delivery.

Acrylic Resins↗

PubMed2000

Intranasal bioavailability of apomorphine from carboxymethylcellulose-based drug delivery systems.

Carboxymethyl cellulose (CMC) powder formulation of apomorphine was prepared by lyophilization and characterized with respect to the in vitro and intranasal in vivo release of apomorphine in rabbits. This was compared to apomorphine release from degradable starch microspheres (DSM) and lactose, as well as in vivo absorption after subcutaneous injection. In vitro apomorphine release from CMC was sustained, unlike that of DSM and lactose. Changing the drug loading of CMC from 15 to 30% (w/w) influenced drug release rate, which increased with increased drug loading. In vivo absorption of apomorphine from lactose, DSM and subcutaneous injection were rapid and not sustained. Slower absorption rates of apomorphine occurred from CMC. The fastest absorption rate was obtained with lactose and the slowest with CMC of 15% (w/w) drug loading. The T(max) from the CMC dosage forms were significantly prolonged compared to the immediate release forms. Plasma drug levels were sustained with CMC. The plasma concentration was maintained within 50% of the C(max), longer (15% (w/w), 70 min; 30% (w/w), 40 min) compared to the rest (lactose, 20 min; DSM, 25 min, subcutaneous injection, 35 min). The sustained plasma level of apomorphine by CMC was achieved with relative bioavailabilities equivalent to subcutaneous injection.

Administration, Intranasal↗

PubMed2000

Safety assessment of selected cyclodextrins - effect on ciliary activity using a human cell suspension culture model exhibiting in vitro ciliogenesis.

The objective of this study was to assess the cilio-inhibitory effect of a series of cyclodextrins using a human cell suspension culture system exhibiting in vitro ciliogenesis. Enzymatically released human nasal epithelial cells were cultured as sequential monolayer-suspension culture showing in vitro ciliogenesis. Ciliary beat frequency (CBF) was determined by computerized microscope photometry. Among the cyclodextrins investigated (gamma-cyclodextrin, hydroxypropyl-beta-cyclodextrin, anionic-beta-cyclodextrin polymer, dimethyl-beta-cyclodextrin and alpha-cyclodextrin), it was shown that after 30 min of exposure, gamma-cyclodextrin (10% w/v), hydroxypropyl-beta-cyclodextrin (10.0% w/v) and anionic-beta-CD polymer (8.0% w/v) were not significantly cilio-inhibitory (P0.05). Similarly, CBF remained stable upon cell exposure to alpha-cyclodextrin (2.0% w/v) and dimethyl-beta-cyclodextrin (1.0% w/v). However, higher concentrations of alpha-cyclodextrin and dimethyl-beta-cyclodextrin resulted in mild to severe cilio-inhibition after 45 min of exposure. The effect of alpha-cyclodextrin (5.0% w/v; 54+/-4% cilio-inhibition) was partially reversible while dimethyl-beta-cyclodextrin (10% w/v; 36+/-4% cilio-inhibition) was irreversible. The cilio-inhibition observed in this model was lower than reported for chicken trachea model. Given the fact that (1) irreversible cilio-inhibition observed in this study occurred only at concentrations exceeding those used in pharmaceutical formulations and/or at an unusual exposure time (45 min) and that (2) in an in vivo situation, dilution and mucociliary clearance contribute to further decrease in local concentrations of the applied compound, the results of this study confirm the safety of the cyclodextrins investigated as nasal absorption enhancers.

Cells, Cultured↗

PubMed2000

In vitro, ex vivo, and in situ intestinal absorption characteristics of the antiviral ester prodrug adefovir dipivoxil.

Caco-2 monolayers (in vitro), rat intestinal sheets mounted in modified Ussing Chambers (ex vivo), and in situ intestinal perfusion of rat ileum were used as models to determine and compare the absorption characteristics of the antiviral agent 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA, adefovir) and its bis(pivaloyloxymethyl)-ester prodrug [bis(POM)-PMEA, adefovir dipivoxil]. Although metabolism of adefovir dipivoxil was more pronounced in the ex vivo and in situ models than in the Caco-2 system, the transport of 'total adefovir' [= adefovir dipivoxil and its metabolites mono(POM)-PMEA and adefovir] was comparable in the three models. Compared with transport of the parent compound (adefovir), use of adefovir dipivoxil resulted in a significant increase in transport of total adefovir in the in vitro ( approximately 100-fold) and the in situ ( approximately 10-fold) models; in contrast, the ex vivo method failed to demonstrate a remarkable transport enhancement when using the ester prodrug. Similar to the results obtained in the Caco-2 model, the inclusion of the P-glycoprotein inhibitor verapamil resulted in transport enhancement during in situ perfusion of rat ileum with adefovir dipivoxil; however, no effect of verapamil could be observed in the ex vivo model. The results of this study confirm the utility of both the in vitro and in situ models to assess intestinal transport and metabolism of adefovir dipivoxil. The ex vivo model appeared to be less appropriate because of its inability to discriminate transport following administration of adefovir or adefovir dipivoxil and because of the absence of an effect of verapamil on transport when using adefovir dipivoxil.

Adenine↗

PubMed2000

Physicochemical characterization of solid dispersions of the antiviral agent UC-781 with polyethylene glycol 6000 and Gelucire 44/14.

The purpose of this study was to prepare and characterize solid dispersions of the antiviral thiocarboxanilide UC-781 with PEG 6000 and Gelucire 44/14 with the intention of improving its dissolution properties. The solid dispersions were prepared by the fusion method. Evaluation of the properties of the dispersions was performed using dissolution studies, differential scanning calorimetry, Fourier-transform infrared spectroscopy and X-ray powder diffraction. To investigate the possible formation of solid solutions of the drug in the carriers, the lattice spacings [d] of PEG 6000 and Gelucire 44/14 were determined in different concentrations of UC-781. The results obtained showed that the rate of dissolution of UC-781 was considerably improved when formulated in solid dispersions with PEG 6000 and Gelucire 44/14 as compared to pure UC-781. From the phase diagrams of PEG 6000 and Gelucire 44/14 it could be noted that up to approximately 25% w/w of the drug was dissolved in the liquid phase in the case of PEG 6000 and Gelucire 44/14. The data from the X-ray diffraction showed that the drug was still detectable in the solid state below a concentration of 5% w/w in the presence of PEG 6000 and Gelucire 44/14, while no significant changes in the lattice spacings of PEG 6000 or Gelucire 44/14 were observed. Therefore, the possibility of UC-781 to form solid solutions with the carriers under investigation was ruled out. The results from infrared spectroscopy together with those from X-ray diffraction and differential scanning calorimetry showed the absence of well-defined drug-polymer interactions.

Anilides↗

PubMed2000

Nasal toxicological investigations of Carbopol 971P formulation of apomorphine: effects on ciliary beat frequency of human nasal primary cell culture and in vivo on rabbit nasal mucosa.

OBJECTIVE: The objective of this study was to investigate the nasal toxicity of a mucoadhesive Carbopol 971P formulation of apomorphine. MATERIALS AND METHODS: The effects of different concentrations of Carbopol 971P and apomorphine on ciliary beat frequency (CBF) were studied in suspension cultures of human nasal epithelial cells. The rabbit nasal mucosal tolerance of the formulation and its components were investigated using light microscopy. Different groups of the rabbits received twice daily, air puffs, glucose, glucose/apomorphine, Carbopol 971P or Carbopol 971P/apomorphine for 1 week (glucose-treated rabbits) or 1, 2 and 4 weeks (other treatments). RESULTS: Both Carbopol 971P and apomorphine showed both concentration- and time-dependent inhibitory effects on the CBF. The effects on CBF were: apomorphine, 1.0% w/v, irreversible ciliostasis; 0.1 and 0.5% w/v, reversible cilio-inhibition; 0.01%w/v, irreversible cilio-stimulation; and Carbopol 971P, 0.1 and 0.25% w/v, partially-reversible cilio-inhibition. Glucose and glucose/apomorphine physical mixture caused mild inflammation. Carbopol 971P (both with and without apomorphine) caused severe inflammation, which increased with duration of treatment. Necrosis, squamous metaplasia or ciliary degeneration was not observed. CONCLUSIONS: Due to the severe inflammation caused by Carbopol 971P with and without apomorphine, we conclude that this polymer is not a suitable carrier for intranasal administration of apomorphine. This is in spite of the reversible effects of Carbopol 971P (0.1 and 0. 25% w/v) and apomorphine (0.1 and 0.5% w/v) on CBF.

Acrylates↗

PubMed2000

Increased absorption of the antiviral ester prodrug tenofovir disoproxil in rat ileum by inhibiting its intestinal metabolism.

Previous studies have shown that strawberry extract increases the transepithelial transport of tenofovir disoproxil, an esterase-sensitive prodrug of the antiviral compound tenofovir (formerly PMPA), across Caco-2 monolayers. This increase in transport was at least partially due to inhibition of its intestinal metabolism. To further study the feasibility of this absorption enhancing strategy, the influence of various concentrations of strawberry extract (0-2%) on the intestinal absorption of tenofovir disoproxil (100 microM) was assessed using an in situ perfusion model with immediate blood sampling from the mesenteric vein, a model closer to the in vivo situation than the in vitro Caco-2 system. Inclusion of strawberry extract (1%) resulted in a 7-fold increase in the appearance of tenofovir equivalents. The metabolism of tenofovir disoproxil in the intestinal perfusate was significantly lower in the presence of strawberry extract (1%), showing that the metabolism of tenofovir disoproxil is reduced by the flavoring extract.

Adenine↗

PubMed1999

Evaluation of the potential of ion pair formation to improve the oral absorption of two potent antiviral compounds, AMD3100 and PMPA.

9-(2-phosphonyomethoxypropyl)adenine (PMPA) and AMD3100 are highly potent and selective antiretroviral agents. Since PMPA is negatively charged and AMD3100 positively charged at physiological pH, their transepithelial transport and their potential for oral drug delivery is very low. In this study, ion pair formation was evaluated as a possible strategy to enhance transepithelial transport of PMPA and AMD3100. Positively charged counter ions such as t-hexyl-, t-heptyl-, t-octylammonium bromide and dodecyl-, tetradecyl-, hexadecyltrimethylammonium bromide were used to form ion pairs with PMPA, while sodium taurodeoxycholate (in vitro experiments) and sodium taurocholate (in vivo experiments) were used as counter ions for AMD3100. The effect of counter ions on transepithelial transport of PMPA (1 mM) and AMD3100 (1 mM) was investigated by measuring the flux across Caco-2 monolayers. An enhancement in drug transport could be observed at a concentration of 2 mM of hexadecyltrimethylammonium bromide (counter ion for PMPA) and 10 mM of sodium taurodeoxycholate (counter ion for AMD3100), but at the concentrations used, the absorption enhancing effect could be attributed to a reduction of the integrity of the monolayers. When AMD3100 transport was tested at a concentration of 200 microM, no flux was observed, even in the presence of relatively high concentrations of counter ion (20 times the concentration of AMD3100). Results obtained from partitioning studies of the drugs in the presence or absence of counter ion revealed that competition by other ions was responsible for the absence of an effect: when pure water was used as the aqueous phase, a reduction up to 24.4+/-1.4% and 17.0+/-1.3% of the initial aqueous concentration was observed for PMPA and AMD3100, respectively; however, as soon as other ions were present in the aqueous phase, the effect of the counter ion was diminished (25-50 mOsm) or completely abolished (270-305 mOsm). The absorption enhancing effect of counter ions was also studied in vivo: pharmacokinetic studies in rabbits showed that the oral bioavailability of AMD3100 in the presence of 4 equivalents of taurocholic acid remained very low and was only 3.2-fold better (i.e. 3.6%) in comparison to pure AMD3100. In view of the results obtained in the Caco-2 system, this absorption enhancement can be attributed to an effect on monolayer integrity rather than to the potential to form ion pairs. We can conclude that the formation of ion pairs may not be very efficient as a strategy to enhance transepithelial transport of charged hydrophilic compounds, as competition by other ions may abolish the beneficial effect of counter ions.

Adenine↗

PubMed1999

Nasal mucoadhesive delivery systems of the anti-parkinsonian drug, apomorphine: influence of drug-loading on in vitro and in vivo release in rabbits.

Lyophilized polyacrylic acid powder formulations loaded with apomorphine HCl were prepared and the influence of drug loading on in vitro release and in vivo absorption studied after intranasal administration in rabbits. These formulations prepared with Carbopol 971P, Carbopol 974P and polycarbophil sustained apomorphine release both in vitro and in vivo. The in vitro release rate and mechanism were both influenced by the drug loading. There was no large influence of drug loading on the time to achieve the peak (Tmax) for a particular polymer, but Tmax differed between different polymers. For a particular drug loading, the Tmax from Carbopol 971P was the slowest compared with that for Carbopol 974P and polycarbophil; however, only the Tmax from Carbopol 971P loaded with 15% w/w of apomorphine was significantly longer than polycarbophil of similar drug loading (P=0.0386). The trend further observed was that increasing drug loading led to increased peak plasma concentration and area under the curve (AUC). In the second part of this study, a mixture containing an immediate release component and sustained release formulation was administered in an attempt to increase the initial plasma level, as this could be therapeutically beneficial. Only one peak plasma concentration was observed and the initial plasma concentrations were no higher than those obtained with solely sustained release formulation. The Tmax, the peak plasma drug concentration (Cmax) and AUC from the lactose-containing formulation were lower than the formulation without lactose but the differences were only marginally statistically significant for Cmax (P=0.0911) and AUC (P=0.0668), but not Tmax (P=0.2788).

Absorption↗

PubMed1999

Bioavailability of apomorphine following intranasal administration of mucoadhesive drug delivery systems in rabbits.

PURPOSE: The purpose of this study was to investigate both the in vitro and in vivo release of apomorphine from mucoadhesive powder formulations of Carbopol 971P and polycarbophil. METHODS: The in vitro drug release from the mucoadhesive formulations was studied using a modified USP XXII rotating basket. The pharmacokinetics of apomorphine given as a solution was determined after subcutaneous and intranasal administrations to rabbits. The animals also received intranasally the mucoadhesive dosage forms and immediate release lactose powder mixture. Comparisons were made between the salient pharmacokinetic parameters of the different dosage forms. RESULTS: Sustained in vitro drug release was obtained from the mucoadhesive formulations. Apomorphine was absorbed more rapidly in rabbits when administered intranasally than as a subcutaneous injection. The mucoadhesive formulations both gave sustained plasma drug concentrations and bioavailabilities comparable to subcutaneous injections. The times taken to achieve peak plasma drug concentrations from these mucoadhesive formulations were more than three-fold that of lactose. With these mucoadhesive formulations apomorphine lasted longer in the blood. It could be detected for up to 6-8 h compared to approximately 3 h for the other forms of administration. CONCLUSIONS: The nasal bioavailability of powders is higher than that of solutions. Drug release from the mucoadhesive powders was sustained and there was no significant difference between Carbopol 971P and polycarbophil.

Acrylic Resins↗

PubMed1999

In vitro biodegradation study of acetyl and methyl inulins by Bifidobacteria and inulinase.

The purpose of this study was to investigate if acetylated and methylated inulins can be degraded by inulinase from Aspergillus niger and by Bifidobacteria, in order to determine their potential in colonic drug delivery. Methyl and acetyl inulins were synthesized by the reaction of inulin (Raftiline HP) with methyl sulfate and acetic anhydride, respectively. The degree of substitution (DS) and the structure of the reaction products were confirmed by 13C-NMR. Degradation by inulinase was investigated in a citrate buffer (0.05 M, pH 4) or with a mixture of citrate buffer and DMSO at 37 degrees C. Biodegradation by Bifidobacteria was investigated under anaerobic conditions using an in-house prepared broth at 37 degrees C for 2 days. The resulting products were analyzed chromatographically; the formation of short chain fatty acids was followed by measuring the pH of the incubation media. The results obtained suggest that acetylated and methylated inulins are not biodegradable, since no degradation product could be detected after incubation; a decrease in pH was clearly observed in control samples (pure fructose and inulin), but not in the derivatized inulin samples. The results can probably be explained by a change in conformation of inulin due to derivatization.

Acetylation↗

PubMed1999

Stability prediction of amorphous benzodiazepines by calculation of the mean relaxation time constant using the Williams-Watts decay function.

The enthalpic relaxation of three amorphous benzodiazepines, diazepam, temazepam and triazolam was studied using differential scanning calorimetry for ageing temperatures which were below the glass transition temperature, and ageing times up to 16 h. Experimental determination of the relaxation enthalpy and the heat capacity change, both accompanying the glass transition, enabled us to calculate the extent of relaxation of the amorphous drugs at specific ageing conditions. Fitting of the relaxation function to the Williams-Watts two parameter decay function led to calculation of the mean relaxation time constant tau and the molecular relaxation time distribution parameter beta. The mean relaxation time constants for the three drugs increased from approximately ten h at the glass transition temperature with more than eight orders of magnitude at 66 K below the glass transition temperature. It was found that the benzodiazepines exhibited significant molecular mobility until approximately 50 K below the glass transition temperature; below this temperature molecular mobility becomes unimportant with respect to the shelf life stability. Hence the presented procedure provides the formulation scientist with a tool to set storage conditions for amorphous drugs and glassy pharmaceutical products.

Benzodiazepines↗

PubMed1999

Inulin hydrogels as carriers for colonic drug targeting. Rheological characterization of the hydrogel formation and the hydrogel network.

Free radical polymerization converts aqueous solutions of methacrylated inulin into cross-linked hydrogels. The purpose of this work was to study the hydrogel formation and to characterize the fully cured hydrogels. The gelation process of aqueous solutions of methacrylated inulin was monitored as a function of time by means of linear oscillatory shear measurements, at a fixed frequency and amplitude. The fully cured inulin hydrogels were characterized by measurement of the frequency-dependency of the linear elastic modulus G'. The effects of the degree of substitution and feed concentration of methacrylated inulin on both the gelation kinetics and the rigidity of the obtained hydrogels were determined. The effect of the concentration of the initiators of the radical polymerization reaction has been studied as well. The weight fraction of polymer which was not incorporated in the hydrogel networks was determined using the anthrone reaction, and physical chain entanglements were determined by solution viscosity measurements. The gelation kinetics and the elastic modulus were proportional to the degree of substitution and feed concentration of methacrylated inulin. Increasing concentrations of radical-forming compounds also accelerated the hydrogel formation, but lowered the elastic modulus of the obtained hydrogels. The amount of polymer chains incorporated in the hydrogel network seemed to be especially influenced by the degree of substitution of the derivatized inulin, and for a feed concentration of 27% w/w of methacrylated inulin, entanglements have to be accounted for. The gelation kinetics and the elastic modulus of inulin hydrogels are not only affected by the degree of substitution and the feed concentration of methacrylated inulin, but also by the concentration of the initiators of the free radical polymerization reaction.

Algorithms↗

PubMed1999

Inhibition of intestinal metabolism of the antiviral ester prodrug bis(POC)-PMPA by nature-identical fruit extracts as a strategy to enhance its oral absorption: an in vitro study.

PURPOSE: To explore the usefulness of fruit extracts as enhancers of the oral absorption of esterase-sensitive prodrugs. METHODS: Inhibition of esterase-mediated degradation by nature-identical fruit extracts was evaluated using 1) p-nitrophenylacetate (model substrate for esterase-activity) in rat intestinal homogenates and 2) bis(isopropyloxycarbonyloxymethyl)-(R)-9-[(2-phosphonomethoxy++ +)propyl]adenine [bis(POC)-PMPA] (esterase-sensitive prodrug of the antiviral agent PMPA) in Caco-2 cell homogenates and in intestinal homogenates from rat, pig and man. Subsequently, transport of the ester prodrug was studied across Caco-2 monolayers in the presence or absence of fruit extracts. RESULTS: In homogenates from rat ileum, the esterase activity could be reduced significantly by the inclusion of fruit extracts (1%): the initial enzymatic degradation of p-nitrophenylacetate was inhibited by 77% (strawberry), 16% (passion fruit) and 57% (banana). A similar inhibition of bis(POC)-PMPA metabolism by fruit extracts was observed in intestinal homogenates from several species and in homogenates from Caco-2 cells. Transport of total PMPA across Caco-2 monolayers was enhanced 3-fold by co-incubation with strawberry extract (1%). The fraction of intact prodrug appearing in the acceptor compartment increased from virtually zero to 67%. CONCLUSIONS: The results suggest that co-incubation with nature-identical fruit extracts might be useful as a strategy to enhance the transepithelial transport of esterase-sensitive prodrugs through inhibition of intracellular metabolism of the prodrug.

Absorption↗

PubMed1999

Effects of pharmaceutical compounds on ciliary beating in human nasal epithelial cells: a comparative study of cell culture models.

PURPOSE: To test two in vitro human nasal epithelial cell culture systems for their ability to screen the effects of pharmaceutical compounds on ciliary beating. METHODS: Human nasal epithelial cells were cultured as monolayer and in a sequential monolayer-suspension culture with in vitro ciliogenesis. The influence of reference cilio-stimulatory compounds (glycocholate, isoprenaline), reference cilio-inhibitory compounds (chlorocresol, diphenhydramine) and pH on ciliary beating was investigated using computerized microscope photometry. RESULTS: Sodium glycocholate (0.5% w/v) maximally and reversibly increased CBF of the cells in both culture systems by 26 +/- 4% (monolayer) and 18 +/- 6% (suspension). Similarly, isoprenaline (10(-3) M) maximally, but irreversibly increased CBF of the cells by 14 +/-3% (monolayer) and 17 +/- 4% (suspension). Chlorocresol (0.005% w/ v) reversibly reduced the CBF of the cells by 50 +/- 6% (monolayer) and 34 +/- 4% (suspension); at a higher concentration (0.1% w/v) it resulted in instantaneous and irreversible ciliostasis. Diphenhydramine (0.1% w/v) reversibly reduced CBF in both culture systems by 45 +/- 13% (monolayer) and 69 +/- 5% (suspension); irreversible cilio-stasis occurred in less than 2 minutes in both culture systems upon cell exposure to diphenhydramine (1.0% w/v). In the monolayer culture system, CBF was stable only within the physiological pH range of 6.5-8.0; ciliary beating in the suspension culture remained stable within a pH range of 4.0-10.0. CONCLUSIONS: Both cell culture systems are suitable for screening the effects of pharmaceutical compounds on ciliary beating. Especially the sequential monolayer-suspension culture appears to be very promising as ciliary activity can be preserved for as long as 6 months.

Anti-Allergic Agents↗

PubMed1998

Comparison of the disposition of ester prodrugs of the antiviral agent 9-(2-phosphonylmethoxyethyl)adenine [PMEA] in Caco-2 monolayers.

PURPOSE: To evaluate the potential of several bis-ester prodrugs of the antiviral agent 9-(2-phosphonylmethoxyethyl)adenine (PMEA, adefovir) to enhance the oral absorption of PMEA. METHODS: Caco-2 monolayers were used to estimate intestinal transport and metabolism of the bis(pivaloyloxymethyl)-ester [bis(POM)-] and a series of bis(S-acyl-2-thioethyl)-esters [bis(SATE)-] of PMEA. An LC-MS method was used for the identification of unknown metabolites which were formed from the SATE-esters. RESULTS: During transport across Caco-2 monolayers, all esters were extensively degraded as could be concluded from the appearance of the mono-ester and free PMEA in apical as well as basolateral compartments. Incubation of SATE-esters with the monolayers resulted in the formation of two additional metabolites, which were identified as 2-thioethyl-PMEA and its dimerisation product. All ester prodrugs resulted in enhanced transepithelial transport of total PMEA (i.e. the bis-esters and their corresponding metabolites, including PMEA), but significant differences could be observed between the various esters. Transport of total PMEA ranged from 0.4 +/- 0.1% for the bis[S(methyl) ATE]-ester to 15.3 +/- 0.9% for the more lipophilic bis[S(phenyl)ATE]-PMEA. A relationship between total transport of the esters and their lipophilicity (as estimated by their octanol/water partition coefficient) was established (r2 = 0.87). Incubation of prodrug esters with homogenates from Caco-2 cells showed large differences in susceptibility of the compounds to esterases, the half-lives of the bis-esters varying from 4.3 +/- 0.3 min for the bis[S(phenyl)ATE]-PMEA to 41.5 +/- 0.8 min for its methyl analogue. In addition, intracellularly formed PMEA was observed to be further converted by the cells to the diphosphorylated PMEA (PMEApp). CONCLUSIONS: Several SATE-esters of PMEA can be considered as potential alternatives to bis(POM)-PMEA, due to enhanced epithelial transport, sufficient chemical and enzymatic stability and adequate release of PMEA. Toxicological studies as well as in vivo experiments are required in order to further explore the potential of those SATE-esters as prodrugs for oral delivery of PMEA.

Adenine↗