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Biomedical subjects

T Kissel

Publications and source records attributed to T Kissel.

At least 73 records · Page 4Linked to original sources
PubMed1998

Pharmacokinetics of the transdermal reservoir membrane system delivering beta-estradiol: in vitro/in vivo-correlation.

PURPOSE: The aim of our study was to investigate the high fluctuations of Estradiol (E2) plasma levels transdermally delivered in postmenopausal women by a commercially available membrane controlled reservoir system (MCRS). METHODS: The transdermal E2 flux either out of a complete MCRS or across its membrane out of defined ethanol water mixtures was determined, as well as E2 plasma profiles in 6 postmenopausal women produced by a MCRS. RESULTS: The transdermal in vitro E2 flux rate out of a complete MCRS, claimed to deliver 25 microg/day, increased steadily, reaching a maximum value of 2.06 +/- 0.58 microg/h at 30 to 40 hours and decreased to a rate of about 0.5 microg/h from 60 to 90 hours. No statistically significant differences between plasma profiles calculated from the in vitro investigation and derived from a clinical study could be identified. The E2 flux in defined ethanol/water mixtures across MCRS-membrane, adhesive and skin layer increased with increasing ethanol concentrations up to a maximum of 227 +/- 34 ng/cm2/h at an ethanol concentration of 62.5% (V/V) and decreased with further increase in the volume fraction of ethanol. CONCLUSIONS: In vitro as well as in vivo investigations showed high fluctuation of E2 plasma profiles in postmenopausal women produced by the MCRS. These fluctuations are caused by a non-constant input rate of E2 which may be due to changing ethanol concentrations in the reservoir of the MCRS.

Administration, Cutaneous↗
PubMed1998

Biotransformation of estradiol in the human keratinocyte cell line HaCaT: metabolism kinetics and the inhibitory effect of ethanol.

PURPOSE: The aim of our study was to investigate the kinetics of beta-estradiol (E2) metabolism in the human keratinocyte cell line HaCaT and to estimate the effect of the potential inhibitor ethanol on the biotransformation reaction. METHODS: The formation rates of estrone (E1) in dependence on substrate concentrations were determined in HaCaT cells using tritium labelled E2. Experiments were conducted with and without addition of dehydroepiandrosterone (DHEA) and ethanol. Possible toxic effects on the cells due to ethanol were investigated by cytotoxicity tests. RESULTS: The metabolism of E2 in HaCaT cells exhibited Michaelis-Menten kinetics with Km and Vmax values of 3.5 microM and 216 pmol x mg(-1) protein x h(-1), respectively. The reaction was inhibited by DHEA and ethanol. The alcohol showed a reversible competitive inhibition mechanism for concentrations of 4 to 8% (v/v). Lower ethanol concentrations had no effect, whereas levels > or =10% significantly decreased cell viability leading to a different inhibition mechanism. CONCLUSIONS: The HaCaT cell line seems to be a suitable model for studying enzyme kinetics equivalent to the human skin. The concentration dependent inhibitory effect of ethanol observed in this cell line may be relevant for the transdermal E2 application in patients.

Biotransformation↗
PubMed1998

Growth effects of alpha-interferon but not of bombesin or angiotensin II are mediated by activation of STAT proteins.

BACKGROUND: The recently discovered Jak/STAT signal transduction pathway is associated with cytokine or growth factor receptors; whether members of the G protein-coupled receptor superfamily also activate this pathway is not yet clear. As a first member, the angiotensin (AT)1A receptor has been demonstrated to phosphorylate Jak and STAT proteins. Bombesin, a neurotransmitter and growth factor in many cells and tissues, activates its G protein-coupled receptor and in addition phosphorylates proteins that might be members of the Jak/STAT family. This study investigated whether bombesin- or angiotensin-mediated growth effects are associated with STAT protein activation. METHODS: Functional receptors were characterized using ligand-binding studies, second-messenger activation and determination of ligand-mediated growth effects. STAT protein activation was analysed by electrophoretic mobility shift assay (EMSA) using labelled DNA response elements recognizing all known STAT proteins. RESULTS: Functional bombesin receptors mediating mitogenic effects were demonstrated on Swiss 3T3 fibroblasts, human melanoma cells (A375-6) and primary human lung fibroblasts; however, bombesin-related STAT protein activation was not observed by EMSA. Interferon-alpha typically activated a STAT1-STAT2-p48 heterotrimer, as well as STAT1-3 hetero- and homodimers in human melanoma cells and significantly inhibited growth of this cell line in vitro. Functional AT1A receptors on primary rat cardiac fibroblasts mediated angiotensin-stimulated growth effects but, in contrast to recently published data, did not activate any known STAT protein. CONCLUSION: Interferon alpha-stimulated growth inhibition is mediated by activation of the Jak/STAT pathway, whereas bombesin or AT1A receptor-mediated effects on cellular proliferation do not involve phosphorylation of STAT proteins.

3T3 Cells↗
PubMed1997

Effects of peptide structure on transport properties of seven thyrotropin releasing hormone (TRH) analogues in a human intestinal cell line (Caco-2).

We conclude that TRH and its analogues permeate mainly via paracellular routes in this particular clone of Caco-2 cells because variation in lipophilicity, polar surface properties, or hydrogen bonding potential-all influencing the transcellular pathway-do not give meaningful relationships. On the other hand, the variations in molecular size of the TRH analogues were too small to detect any influence on the paracellular transport properties. Further studies concerning the solution conformation and the hydrodynamical radii of the molecules probably give more information about the structure-permeability relationship of TRH transport across Caco-2 cell monolayers. The influence of the structural variations of these 7 TRH analogues on the binding affinity to the di- and tripeptide transporter, using another Caco-2 cell clone, are currently under investigation in our laboratory.

Biological Transport↗
PubMed1997

Microencapsulation of antigens using biodegradable polyesters: facts and phantasies.

New vaccination approaches and new delivery systems have been subject of intensive research activities recently. Controlled release vaccine delivery systems depend on the microencapsulation of antigens into biodegradable polymers, yielding small spherical polymeric particles, in the size range of 1-100 microns. By manipulating the micromorphology of the microparticles and degradation properties of the polymer either continuous or pulsatile release patterns can be adjusted. As biodegradable polymers mainly copolymers of lactic- and glycolic acid have been utilized, since these materials are known to be biocompatible and non-toxic. Apart from modulation of antigen release, an improvement of the adjuvant effect and an increase of in vitro (shelf-life) and in vivo stability of the antigen are issues of general interest with respect to parenteral vaccine delivery systems. Using different microparticles that release antigens in a pulsatile pattern at predetermined timepoints one hopes to induce protective immunity by a single administration of the vaccine delivery system. Using tetanus toxoid (TT) as a model antigen we have examined the stability during preparation, in vitro release and storage of TT microparticles. TT is a complex protein mixture sensitive to changes in pH conditions (pH < 5) and to thermal stress. TT microparticles can be prepared by a W/O/W double emulsion technique with satisfactory encapsulation efficiencies in good yields. In accordance with other investigators we observe an adjuvant effect of TT microspheres in mice upon sc administration leading to a long-lasting antibody response. In challenge experiments we could demonstrate a protective effect. The issue of an ideal release pattern remains open, since a boosting of the antibody titers during the bioerosion of the TT microspheres was not observed, possibly due to desactivation of TT in the degrading microspheres.

Animals↗
PubMed1996

In vivo biocompatibility study of ABA triblock copolymers consisting of poly(L-lactic-co-glycolic acid) A blocks attached to central poly(oxyethylene) B blocks.

Films of three ABA-block copolymers composed of lactic-co-glycolic acid A blocks and poly(oxyethylene) (PEO) B blocks and one random lactic-co-glycolic acid copolymer (PLG) were studied to investigate the influence of different polymer compositions and molecular weights on the tissue reaction, appearance of toxic degradation products, and swelling behavior in the cage implant system in rats. The inflammatory tissue reaction was followed over a 21-day implantation period by monitoring the leukocyte concentration, the extracellular acid, and alkaline phosphatase activities in a quantitative manner. Size and density of adherent macrophages and foreign body giant cells on the film surfaces were determined. The ABA and PLG implants caused only a minimal inflammatory reaction, as characterized by a low concentration of leukocytes during the implantation period when compared to empty cage controls. The content of PEO had an influence on the density of the adherent cells on the surface of the polymer film. An increase in PEO content and molecular weight decreased the cellular density during the implantation period. As demonstrated by scanning electron microscopy, no degradation was observed for all polymers during the implantation period. Our results demonstrate that the ABA block copolymers and PLG copolymer, are equally well tolerated in the cage implant test system.

Alkaline Phosphatase↗
PubMed1996

Effects of permeation enhancers on the transport of a peptidomimetic thrombin inhibitor (CRC 220) in a human intestinal cell line (Caco-2).

PURPOSE: The effects of five different permeation enhancer systems on the transport properties of a peptidomimetic thrombin inhibitor. CRC 220, were investigated in monolayers of a human intestinal cell line (Caco-2). METHODS: The transepithelial transport rates and additionally the cytotoxic properties of these enhancers were characterized using the following tests: measurement of the transepithelial electrical resistance (TEER), the MTT-transformation, the protein content and the release of cytosolic lactate dehydrogenase (LDH), as well as FITC-phalloidin and propidium iodide staining. RESULTS: All permeation enhancer systems showed concentration-dependent effects on cell permeability and toxicity. The most prominent effects on peptide transport were seen at the highest concentration (40 mM), yielding the rank order, NaTC > NaTC/Cholesterol > Solulan C24 > NaTC/Oleic acid > NaTC/PC18. Using the TEER after 120 min exposure as the most sensitive parameter describing cytotoxicity, the following order was obtained: Solulan C24 > NaTC > NaTC/PC18 = NaTC/Cholesterol > NaTC/Oleic acid > NaTC/PC. Generally, efficient enhancement of peptide transport was associated with a noticeable influence on cell viability under in-vitro conditions. CONCLUSIONS: Taking into account permeation and cytotoxicity as a function of concentration, both NaTC at 15 mM and the mixed micellar system NaTC/oleic acid at 0.75 mM offer interesting enhancement properties, showing an 18-fold increase in CRC 220 transport rates. The effects on cell viability and cytotoxicity were comparatively low and of reversible nature.

Antithrombins↗
PubMed1996

In-vitro cell culture models of the nasal epithelium: a comparative histochemical investigation of their suitability for drug transport studies.

PURPOSE: To evaluate different in-vitro cell culture models for their suitability to study drug transport through cell monolayers. METHODS: Bovine turbinate cells (BT; ATCC CRL 1390), human nasal septum tumor cells (RPMI, 2650; ATCC CCL 30), and primary cell cultures of human nasal epithelium were characterized morphologically and histochemically by their lectin binding properties. The development of tight junctions in culture was monitored by actin staining and transepithelial electrical resistance measurements. RESULTS: The binding pattern of thin-sections of excised human nasal respiratory epithelium was characterized using a pannel of fluorescently-labelled lectins. Mucus in goblet cells was stained by PNA, WGA and SBA, demonstrating the presence of terminal N-acetylglucosamine, N-acetylgalactosamine and galactose residues respectively in the mucus of human nasal cells. Ciliated cells revealed binding sites for N-acetylglucosamine, stained by WGA, whereas Con A, characteristic for mannose moieties, labelled the apical cytoplasm of epithelial cells. Binding sites for DBA were not present in this tissue. Comparing three different cell culture models: BT, RPMI 2650, and human nasal cells in primary culture using three lectins (PNA, WGA, Con A) as well as intracellular actin staining and transepithelial electrical resistance measurements we found, that only human nasal epithelial cells in primary culture showed differentiated epithelial cells, ciliated nasal cells and mucus producing goblet cells, which developed confluent cell monolayers with tight junctions. CONCLUSIONS: Of the in-vitro cell culture models studied, only human nasal cells in primary culture appears to be suitable for drug transport studies.

Actins↗
PubMed1996

Albumin nanospheres as carriers for passive drug targeting: an optimized manufacturing technique.

PURPOSE: The purpose of this study was to develop a new method to produce albumin particles in the sub-200-nanometer range with a narrow size distribution and in a controlled and reproducible manner. METHODS: A new emulsion crosslinking method was developed using ultrasound and static mixing as homogenization steps and a central composite design was used to evaluate the influence of different process parameters on particle size, polydispersity and yield. RESULTS: Response surface analysis allowed the location of the most important factors. Of all the factors investigated, only the albumin concentration and the aqueous phase volume showed a significant influence on response parameters. Albumin nanospheres with sizes below 200 nm in diameter and very narrow size distributions were obtained in high yields ( > 80%). CONCLUSIONS: This study describes a new preparation method for albumin nanoparticles which are suitable for future drug targeting studies.

Cross-Linking Reagents↗
PubMed1996

Permeation enhancement of octreotide by specific bile salts in rats and human subjects: in vitro, in vivo correlations.

1. The potential of bile salts to improve the enteral absorption of octreotide, an orally active somatostatin analogue, was investigated by a combination of in vitro, in situ and in vivo experiments. 2. Incorporation of octreotide into lipid monolayers (as measured by area increase of the monolayer at constant surface pressure using a Langmuir-Blodgett trough set-up) depended on the type of bile salt used for monolayer pre-treatment. Addition of 20 microM octreotide to the subphase containing 20 microM of the dihydroxylated bile salt ursodeoxycholate (UDCA) causes a 9% increase in area, whereas addition of octreotide to the subphase containing the 7 alpha-enantiomer of UDCA, chenodeoxycholate (CDCA), resulted in an area increase of the lipid monolayer of 20%. Area increase by octreotide alone was not significantly different from the increase of octreotide and UDCA in combination. 3. CDCA and UDCA in combination with octreotide increased the permeability of liposomal membranes for rubidium ions, whereas octreotide alone did not significantly change the permeability. This indicates membrane distortion as a possible cause for the enhanced absorption of octreotide by bile salts. 4. In polarized Caco-2 cell monolayers octreotide exhibited a permeation coefficient of 0.008 +/- 0.004 cm h-1. Addition of 0.2-1% of UDCA to the apical incubation medium had no significant effect upon the permeation coefficient. In contrast, 0.2-1% CDCA in the incubation medium resulted in a significant increase (P < 0.05) of the monolayer permeability of octreotide (0.015-0.037 cm h-1). 5. Octreotide was absorbed as the intact peptide from the gastrointestinal tract in rats with an absorption efficiency of 0.26%. Coadministration of bile salt resulted in a dose-dependent increase in absorption efficiency of the peptide up to 20.2%. The observed effect was more pronounced for CDCA than for UDCA. 6. The effect of CDCA and UDCA on octreotide absorption in vivo was assessed in a pharmacokinetic study with healthy volunteers. After oral administration of 4 mg octreotide in the presence of 100 mg bile salt, an average bioavailability of the peptide of 1.26% was achieved in the presence of CDCA, whereas in the presence of UDCA a bioavailability of only 0.13% was reached. This difference was statistically significant (P < 0.01). 7. In conclusion, the co-administration of CDCA is able to enhance the enteral absorption of octreotide. The in vitro and in situ experiments were predictive for the observed effect in human subjects.

Adult↗
PubMed1995

Development of a human nasal epithelial cell culture model and its suitability for transport and metabolism studies under in vitro conditions.

A human nasal epithelial cell culture model has been adapted to observe transport and metabolism of drugs, e.g., peptides. Human nasal epithelial cells, isolated by protease treatment of human nasal conchae, grew to confluency after 6-8 days using DMEM supplemented with 1% nonessential amino acids, 1% glutamine, 10% FCS and 1% antibiotics. These cultures expressed microvilli and actively beating cilia as documented by light microscopy and scanning electron microscopy (SEM). Tight junctions were confirmed by dome formation and positive actin staining using FITC-labelled phalloidin. Preliminary transport studies, carried out with FITC-labelled Dextran (FD 4, MW 4400) and Sulforhodamine (SR 101, MW 607), demonstrated the intact barrier function of the cultured monolayer, grown on filter membranes. In addition, the cultured cells metabolized Leu-Enkephalin to Des-Tyr-Leu-Enkephalin demonstrating the presence of aminopeptidase, a naturally occurring enzyme in the human nasal mucosa.

Actins↗
PubMed1995

Transepithelial transport properties of peptidomimetic thrombin inhibitors in monolayers of a human intestinal cell line (Caco-2) and their correlation to in vivo data.

Peptidomimetic thrombin inhibitors (TI), derived from L-Asp-D-Phe were examined in confluent monolayers of a human colon carcinoma cell line (Caco-2) to elucidate their transepithelial transport properties. Effect availabilities, based on activated partial thromboplastin time (aPTT) measurements in rats, after peroral administration of five TI correlated reasonably well with permeability coefficients obtained from in vitro transport studies in Caco-2 monolayers, whereas physicochemical properties, such as molecular mass, solubilities, pKa and octanol-buffer partition coefficients failed to yield meaningful relationships. Substitution of the beta-carboxylic group of L-Asp leads to analogues which are mainly transported by passive diffusion, while an unsubstituted carboxylic group favours carrier-mediated active transport. The effects of concentration, temperature, competitive inhibitors and direction dependence on in vitro transport were investigated. The results obtained are compatible with a saturable carrier-mediated transport, operating parallel to a passive paracellular route. The Michaelis-Menten parameters for the active transport component (Km = 1.67 mM, Vmax = 26.5 pmol min-1 mg protein-1) indicate an involvement of the intestinal di/tripeptide transport system for one of the TI. The Caco-2 transport model may be helpful for the design of perorally active peptidomimetics.

Biological Availability↗
PubMed1994

Transepithelial transport and metabolism of thyrotropin-releasing hormone (TRH) in monolayers of a human intestinal cell line (Caco-2): evidence for an active transport component?

Cell culture models for gastrointestinal transport and metabolism are important mechanistic tools. Our studies of Caco-2 monolayers demonstrate heterogeneity in transport characteristics depending on passage number and origin of the cells. In accordance with data obtained in animals and humans, TRH shows a carrier-mediated, saturable transport component, which operates parallel to a passive pathway in Caco-2 cells at passage number 89-99. At low TRH concentrations (< 3 mM) active transport becomes prominent, as demonstrated by the temperature dependence of TRH transport and inhibition experiments. The Michaelis-Menten parameters of the active, saturable transport component are: Km = 1.59 mM and Vmax = 1.84 microM/min. The pH optimum was determined to be at pH 6.0. On the other hand an exclusively paracellular passive route was found with Caco-2 cells at passage number 30-34. These results are also in agreement with observations made by others in cell culture experiments. The aspect of rigorously characterizing the specific Caco-2 clone under investigation is emphasized, especially when active transport mechanisms are suspected.

Amino Acid Sequence↗
PubMed1993

Therapeutic angiogenesis.

We have proposed the term "therapeutic angiogenesis" to describe the induction or stimulation of neovascularization for the treatment or prevention of pathological clinical situations characterized by local hypovascularity. Evidence also shows that "clinically normal" healing and tissue regeneration can be improved or accelerated by therapeutic angiogenesis. Traditionally, therapeutic angiogenesis has been achieved by surgical methods, ie, the transposition of autologous tissues with uncompromised vasculature and high angiogenic potential such as omentum majus flaps and muscle flaps. Recent advances in the understanding of the biological process of neovascularization as well as the discovery and cloning of angiogenic cytokines may add a new clinical tool: therapeutic angiogenesis by pharmaceutical methods. Based on the results of animal studies and preliminary clinical trials, this review is aimed to give a state-of-the-art compilation of (1) those angiogenesis factors that appear promising in clinical application for therapeutic angiogenesis and (2) the surgical indication fields with near-term potential for therapeutic angiogenesis by use of angiogenic cytokines.

Angiogenesis Inducing Agents↗
PubMed1992

Parameters affecting the immunogenicity of microencapsulated tetanus toxoid.

The immunogenic potential of tetanus toxoid (TT) was compared when either adsorbed to aluminium hydroxide (TT-alum) or entrapped in microparticles consisting of poly(D,L-lactic-co-glycolic acid) (PLA:PGA, 55:45) derived polymers. Furthermore, the effect of administering the microparticles in an aqueous buffer or water-in-oil emulsion on the TT immunogenicity was also investigated. When mice were immunized with the different formulations, similar levels of anti-TT antibodies were observed during the primary IgG response. The choice of the carrier seemed to play an important role for both the level and maintenance of the secondary IgG response, attained as a consequence of a booster immunization with TT-alum. The strongest secondary antibody response was obtained by priming with TT-containing microparticles, resuspended in water-in-oil emulsions. As expected, incomplete Freund's adjuvant (IFA) proved to be a more potent adjuvant than peanut oil, whereas resuspension of the microparticles in aqueous solution induced a relatively less efficient antibody response. Overall, microencapsulated TT primed the mice more effectively, since the secondary antibody response was higher and persisted longer compared with TT-alum priming. These results indicate that in addition to TT maintaining its antigenicity after microencapsulation, the microparticles also potentiate its immunogenic properties. This approach should prove very useful for designing more effective vaccines.

Adjuvants, Immunologic↗
PubMed1992

Tolerability and absorption enhancement of intranasally administered octreotide by sodium taurodihydrofusidate in healthy subjects.

Nasal sprays containing different concentrations of the somatostatin analogue octreotide and sodium tauro-24,25-dihydrofusidate (STDHF) as an absorption promoter were evaluated in two consecutive pharmacokinetic studies in healthy volunteers to characterize their bioavailability and local tolerability. The concentrations of STDHF were selected on the basis of a phase diagram generated by a dynamic laser light-scattering technique to ensure that the mixture was above the critical micellar concentrations. Compared to a 50-micrograms subcutaneous injection, the nasal spray formulation without STDHF had a mean relative bioavailability of 17.9%. For nasal formulations containing 3 and 1.65% (w/v) of STDHF, the bioavailability increased to 29.0 and 25.7%, respectively. The enhancement of nasal absorption was dependent on the STDHF concentrations as shown by decreasing the amounts to 1.2 and 0.8% (w/v) for tolerability reasons; the bioavailability was reduced to 15.3 and 20.5% in these cases, respectively. The local tolerability of all STDHF-containing sprays was poor, leading to stinging sensations and lacrimation. The poor local tolerability of the octreotide nasal spray containing different concentrations of STDHF required for effective nasal absorption enhancement appears to be impractical for further clinical development. These findings clearly stress the necessity to investigate tolerability and safety issues of new drug delivery systems in early developmental phases.

Administration, Intranasal↗
PubMed1992

The absorption site of cyclosporin in the human gastrointestinal tract.

1. An emulsion preparation of cyclosporin was administered locally to different parts of the small and large intestine by gavage: to the duodenum (opposite to the papilla of Vater), jejunum (150 cm distal to the teeth), ileum (300 cm distal to the teeth), and to the colon descendens (30 cm proximal to the anus). 2. The bioavailability of cyclosporin after these instillations was compared with that after oral administration of a hard gelatine capsule formulation. 3. Cyclosporin was found to be absorbed predominantly in the small intestine. This may have implications for dosage in patients with reduced absorptive surface area.

Adult↗