31.
Sköld, Anna-Carin
(författare)
Teratogenicity as a consequence of drug-induced embryonic cardiac arrhythmia : Common mechanism for almokalant, sotalol, cisapride, and phenytoin via inhibition of IKr
2000
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
During the last years, drugs that prolong the repolarisation phase of the myocardial action potential, due to inhibition of the rapid component of the delayed-rectifying potassium channel (IKr) have been in focus. In addition to arrhythmogenic potential, selective Ikr-blockers have also been shown to be embryotoxic and teratogenic in animal studies. The aim of this thesis was to investigate a theory that these developmental toxic results from pharmacologically induced episodes of embryonic cardiac arrhythmias leading to hypoxia related damage in the embryo. Almokalant (ALM) was used as a model compound for selective Ikr-blockers. ALM induced embryonic cardiac arrhythmia, and in similarity with results obtained by maternal hypoxia, ALM induced embryonic death and growth retardation in both rats, and mice. The theory of a hypoxia-related mechanism was strengthened by the results that ALM induce phase specific external and visceral defects (e.g. cleft lip/palate, distal digital, cardiovascular, and urogenital defects), and that the skeletal defects (not shown before) showed a clear trend; the later the treatment the more caudal was the site of the defect, which is in accordance with results from maternal hypoxia induced by e.g. lowering of the O2 content in the air. The spin trapping agent PBN decreased almokalant induced malformations, suggesting that the defects mainly are caused by reoxygenation damage after episodes of severe embryonic dysrhythmia, rather than "pure hypoxia".Sotalol was tested in a third species, the rabbit who expresses functional IKr channels both in the embryo and in the adult, where it induced developmental toxicity, and indicating that the embryo is more sensitive than the adult towards arrhythmia caused by IKr-blockers.
32.
Svensson, Ulrika Sigrid Helena
(författare)
Pharmacokinetics, drug metabolism and clinical effects of the antimalarial artemisinin : Time-dependencies and modeling aspects
2000
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The mechanism behind artemisinin time-dependent bioavailability was investigated using a rat in-situ single-pass jejunal perfusion technique. The consequence for drug combination therapy was studied in healthy volunteers and in patients with Plasmodium falciparum. In the latter, parasite versus time data was modelled using NONMEM and a pharmacodynamic model based on the parasite life cycle was developed. In addition, the hepatic in vitro metabolism of artemisinin in human and rat was assessed using microsomal preparations.The work in this thesis demonstrates that artemisinin pharmacokinetics in healthy subjects exhibit marked time-dependency with a five-fold increase in attemisinin oral clearance after seven days of administration. The absence of a corresponding change in artemisinin's half-life is compatible with that alterations in hepatic intrinsic clearance will primarily affect the bioavailability. It is unlikely that the reduced bioavailability of artemisinin can be explained by induction of P-glycoprotein or a general decrease in jejunal transport, since there was no difference in the effective permeability of rat jejunum to artemisinin after pretreatment withartemisinin. The inductive capacity by artemisinin was demonstrated by its ability to increase the CYP2C19 mediated elimination of omeprazole. The results do not indicate that CYP2C19 induction is the cause of the time-dependent pharmacokinetics of artemisinin, since the decrease in artemisinin AUC was independent of CYP2C19 phenotype. The in vitro metabolism studies supported this finding in that CYP2C19 was shown not be an enzyme of importance in artemisinin metabolism. Instead, CYP2B6 was found to be the primary enzyme with secondary contribution by CYP3A4 and CYP2A6. Artemisinin was shown not to be an inducer of CYP3A4 in humans at clinical concentrations, which is why it is unlikely that induction of gut metabolismis the cause of the time-dependent pharmacokinetics in man.In conclusion, artemisinin time-dependent bioavailability is most likely an (auto)-induction of drug metabolism phenomenon and as such can influence the pharmacokinetics of drugs given simultaneously.
33.
Tuvendal, Paulina
(författare)
Short-chain retinol dehydrogenases/reductases : Involvement in retinoid metabolism and expression in embryonic and adult mouse
2000
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Retinoids are needed in the embryo to ensure proper development and in the adult forvision, maintenance of epithelia and sperm production. Retinol is oxidised within the cell generating retinal and, irreversibly, retinoic acid. In the eye, the biologically active retinoidis 11 -cis-retinal, whereas all -trans-retinoic and 9 -cis-retinoic acid are active in extra-ocular tissues. The retinoic acid receptor (RAR) and the retinoid X receptor (RXR) act as ligand-dependent transcription factors by binding to retinoic acid responsive elements (RAREs), regulating the transcription of target genes.Some microsomal members of the short-chain dehydrogenase/reductase family (SDR) are thought to be responsible for the in vivo oxidation of retinol to retinal. This work describes the cloning and characterisation of a 32 kDa membrane-bound SDR, designated RDH4.RDH4 oxidises both 9 -cis-retinol and 11 -cis-retinol in vitro, suggesting that RDH4 has a dual role in retinoid metabolism; as an 11 -cis-retinol dehydrogenase in the eye, and as a 9 -cis-retinol dehydrogenase in extra-ocular tissues.The expression pattern of RDH4 in the embryonic and adult mouse was investigated using in situ hybridisation and immunohistochemistry. RDH4 was first detected at 8.5 dpc, in the heart and in anterior mesenchyme. Later,RDH4 was detected in the myotome of the somites, in the notochord, in endothelial cells, in the retinal pigment epithelium and in thebronchi.RDH4 was expressed in the CNS;in the roof plate of the hindbrain, and in the floor plate of the hindbrain and caudal midbrain. In the adult, RDH4 was expressed in the liver, kidney, lung and epidermis. In conclusion,RDH4 was expressed during embryogenesisin several tissues known to synthesise, or to depend on, regulated amounts of retinoic acid for normal development. Another SDR,CRAD1, co-localised with RDH4 in the embryo, with the exception of the adrenal glands and cells in the rhombomeres, suggesting functional redundancy. When studying the co-localisation of RDH4 and retinal dehydrogenases, few sites of co-localisation were found, indicating that other, yet to be identified, aldehyde dehydrogenases exist in the embryo.
34.
Wallentin, Niklas
(författare)
Posterior capsule opacification : An experimental study in vitro and in vivo
2000
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The clinical and economic significance of posterior capsule opacification (PCO) makes it an important public health problem. A better understanding of the pathogenesis in order to reduce/prevent PCO is needed. For this purpose an experimental model in the rabbit was used and further developed in thisthesis. The model involves experimental cataract surgery and analysis of aqueous humor (AqH) inflammatory cells and mediators as well as growth factors and analysis of the after cataract weight, cell content and extracellular matrix content. Further, rabbit lens epithelial cells (LECs) were isolated andcultured in vitro. Using these cells the activity of proliferative factors in AqH after cataract surgery was analyzed at different time points after anti-inflammatory treatment and after the use of different surgical techniques. The same components that are reported to exist in human PCO, e.g. inflammation,cell proliferation, fibrosis and extracellular matrix production, have in this thesis also been shown to be components of PCO in the rabbit.No effect of anti-inflammatory treatments was observed on either AqH proliferative effect or after-cataract development despite a reduction in the early postoperative inflammatory response, as measured by AqH leukocytes, prostaglandin E2 (PGE2) and protein leakage. The AqH LEC proliferativeactivity as well as the AqH concentration of basic fibroblast growth factor (bFGF) increased after cataract surgery and the inhibitory transforming growth factor-β (TGF-β) decreased. Further, it was shown that both the early inflammatory response and LEC proliferation are to a great extent caused by the incision in the cornea during cataract surgery and no differences were found between the two surgical techniques, extracapsular cataract extraction and phacoemulsification.It is concluded that the rabbit model reflects human PCO development and is relevant for studying the pathogenesis of this postoperative complication. Furthermore, it is strongly suggested that reduction of the early postoperative inflammatory response does not reduce the development of PCO.Rather the corneal wound healing process and/or the release of growth factors seem to be important for this postoperative complication.
35.
Xie, Rujia
(författare)
Pharmacokinetic aspects of the blood-brain barrier transport and equilibration of opioids studied with microdialysis in rats and mice
2000
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The blood-brain barrier (BBB) transport and equilibration of opioids with different physico-chemical properties and similar structures - codeine, morphine, morphine3-glucuronide (M3G) and morphine-6-glucuronide (M6G) - were investigated in rats and mice using microdialysis. The influences of active efflux pumps, P-glycoprotein (Pgp) and multidrug resistance protein (MRP1), on the BBB transport of morphine and M3G were studied. Modeling of the BBB transport was performed in NONMEM to estimate the intlux and efflux clearances (CLin and CLout). Simulations were performed on the different possible transport processes at the BBB: passive diffusion, influx hindrance, active efflux, or a combination of influx hindrance and active efflux.Codeine was rapidly transported into the brain and quickly reached BBB equilibration with an unbound area under the concentration-time curve (AUC) ratio of brain extracellular fluid (ECF) to blood of 1.0 ± 0.2. The unbound morphine concentration ratio of brain ECF to blood at the end of infusion was 0.5 ± 0.4 in mdrla (+/+) mice and 0.9 ± 0.4 in mdrla (-/-) mice lacking Pgp. The brain ECF-to-blood unbound steady-state concentration ratio of M6G was 0.22± 0.09, while it was 0.10 ± 0.04 for M3G. The ratio for M3G was increased to 0.16 ± 0.05 during co-administration of probenecid, an inhibitor of MRP1. From the modeling analysis, it was shown that CLout of M3G and M6G (1.15 and 2.17 μl/min*g-brain, respectively) were significantly higher than the CLin (0.11 and 0.35 μl/min*g-brain, respectively). These results indicate that the BBB transport of codeine is dominated by passive diffusion, that Pgp contributes to lower the brain concentration of morphine, that MRP1 is involved in the BBB transport of M3G. and that one or both active efflux pumps are active on M6G.All studied opioids had similar half-lives in blood (20-24 min). Longer half-lives were found in brain ECF for M6G (58 ± 17 min) and M3G (81 ± 25 min). Codeine's half-life was similar to that in blood (brain 24 ± 5 min VS. blood 26 ± 3 min. Together with the need for two compartments in the modeling to describe the concentration-time profiles in the brain for M3G and M6G, this indicates that the redistribution within the brain is the rate-limiting step for the elimination of M3G and M6G from the. brain, not the BBB transport itself.Simulations showed that influx hindrance is mom efficient in restraining the drug transport into the brain than active efflux, and it does not affect the half-life in brain. The most powerful mechanism to lower brain concentration is a combination of influx hindrance and active efflux processes, which is the most physiologically plausible process.
36.
37.
Zygmunt, Peter M., et al.
(författare)
The anandamide transport inhibitor AM404 activates vanilloid receptors
2000
Ingår i: European Journal of Pharmacology. - 0014-2999. ; 396:1, s. 39-42
Tidskriftsartikel (refereegranskat) abstract
The possibility that the anandamide transport inhibitor N-(4-hydroxyphenyl)-5,8,11,14-eicosatetraenamide (AM404), structurally similar to the vanilloid receptor agonists anandamide and capsaicin, may also activate vanilloid receptors and cause vasodilation was examined. AM404 evoked concentration-dependent relaxations in segments of rat isolated hepatic artery contracted with phenylephrine. Relaxations were abolished in preparations pre-treated with capsaicin. The calcitonin-gene related peptide (CGRP) receptor antagonist CGRP-(8-37) also abolished relaxations. The vanilloid receptor antagonist capsazepine inhibited vasodilation by AM404 and blocked AM404-induced currents in patch-clamp experiments on Xenopus oocytes expressing the vanilloid subtype 1 receptor (VR1). In conclusion, AM404 activates native and cloned vanilloid receptors. Copyright (C) 2000 Elsevier Science B.V.
38.
Österberg, Thomas
(författare)
Modelling and prediction of drug transport processes with experimental and calculated molecular properties : A multivariate approach
2000
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Less than 2% of the lead compounds generated by the pharmaceutical industry enter the exploratory drug-development phase, from which point they stand only a 10% chance of becoming a commercial medicine. A large proportion of the compounds fail due to poor biopharmaceutical properties, such as permeability and solubility. The main theme of this thesis is, therefore, the development of better experimental and computational methods for modelling and predicting the biopharmaceutical properties of drug candidates. Immobilised liposome chromatography (ILC) was used for studying drug-membrane interactions and for the prediction of passive drug transport. For the drugs studied in this thesis, ILC and octanol/water partitioning showed a similar performance with regard to the prediction of passive drug transport.The theoretical work was directed at the modelling and prediction of drag transport processes using calculated molecular properties and PLS analysis. In the initial studies, the molecular properties were calculated with an advanced computational tool (MolSurf) that takes the three-dimensional structural information and electronic properties of the compound into consideration. Statistical models well suited to the prediction of drug transport processes such as Caco-2 cell permeability, intestinal absorption and CNS penetration were derived.This approach was also successfully applied to the modelling of the interaction of drugs with P-glycoprotein. Subsequently, rapidly calculated descriptors based on two-dimensional structural information and PLS analysis were also found to give good predictive models of drug transport properties. The preferred use of the latter models is for screening compound collections and virtual libraries. It can be concluded that calculated molecular properties in conjunction with PLS analysis are well suited to the modelling and prediction of drug transport processes and to identifying compounds with potential biopharmaceutical problems at an early stage of the drug-development process.
