Browsing by Subject "nestekromatografia"

Diseases of the posterior eye segment, such as age-related macular degeneration (AMD), diabetic retinopathy, diabetic macular edema and glaucoma are the leading cause of blindness worldwide. Current therapy to treat these vision-threatening diseases relies on intravitreal injections to maintain a desired therapeutic drug concentration in the back of the eye. Frequent intravitreal injections are uncomfortable with poor patient compliance and causes major burden to the healthcare systems as well as to the patients. Small molecule drugs have shorter half-life in the vitreous and are eliminated rapidly. This requires frequent intravitreal dosing intervals that are not feasible in the clinical settings. Also, intravitreally injected small molecule drugs are often poorly and non-specifically distributed to the ocular tissues causing adverse effects. To address these issues, controlled and sustained drug delivery systems in the form of drug conjugates are desirable. Conjugating small molecule drugs with enzymatically cleavable peptide linkers increases the residence time in the vitreous. The peptide linker gets cleaved by vitreal enzyme and the released drug reaches the target in retina and choroid. Aim of this thesis was to screen a library of 25 peptide linkers for cleavage in the presence of porcine vitreal enzymes. The peptide linkers were chemically synthesized and the in vitro stability of the peptide linkers were studied in freshly isolated porcine vitreous. Ten time point samples were collected over a period of 45 days and the peptide cleavage in porcine vitreous was assessed by LC-MS method. A TQ-S liquid chromatography-mass spectrometer was used to study the linker cleavage. LC-MS method development for the peptide library was carried out using IntelliStart wizard function. Out of the 25 peptide linker in the library, stability of eight linkers were not included in the LC-MS analysis as a mass method could not be developed. Out of 17 peptide linkers studied, 14 were categorized as fast cleaving linkers (>90% of the linker cleaved in porcine vitreous after 5 h). Three linker peptides; P4, P5 and P25 were categorized as slow cleaving linkers. Conjugating slow cleaving peptide linkers to small molecule drugs will increase the half-life and enhance the duration of drug action upon intravitreal injection. In this study, linkers that are hydrolyzed by specific enzymes present in vitreous or ocular tissues are exploited to investigate their potential for delivering small molecule drugs.

Cytochrome P450 (CYP) -enzymes are one of the most important enzymes in the metabolism of xenobiotics. Because many xenobiotics are metabolized with each other by the same CYP-enzymes, it is possible that metabolic interactions will take place. These interactions can be the inhibition or induction of the metabolism of another xenobiotic. The interaction can be harmful e.g. when it causes an accumulation of a toxic metabolite or when it inhibits the metabolism of an active drug substance. The aim of this study was to develop a quantitative method for determining metabolic interactions between drugs and environmental chemicals in human liver microsome (HLM) incubations. HLMs contain high concentrations of CYP-enzymes, enabling the use of CYP-model reactions for observing interactions. The model reactions chosen for this study were O-deethylation of phenacetin (CYP1A2), 7-hydroxylation of coumarin (CYP2A6), 4'-hydroxylation of diclofenac (CYP2C9), 1'-hydroxylation of bufuralol (CYP2D6) and 6β-hydroxylation of testosterone (CYP3A4). Michaelis-Menten constants (Km) and maximal enzymatic activities (Vmax) were determined for each model reaction. The suitability of the model reactions for inhibition studies was assessed with specific inhibitors. The quantitative method was developed for an ultra-high performance liquid chormatograph (UPLC) and for a quadrupole time of flight mass spectrometer (QTOF). Samples were ionized with electrospray ionization (ESI) using positive mode. Device parameters were the same for all the metabolites. The analytical method validation was partly performed according to ICH (International Conference on Harmonisation) guidelines. A sufficient linearity (R2>0,99) and specificity was achieved for the quantitative method. The achieved limits of quantitation (LOQ) were low enough (1-120 nM) for quantitation of the small concentrations of the metabolites formed in the inhibition assays. The measurement reproducibility and the reproducibility and accuracy of the method did not fulfill the acceptance criteria for all the metabolites. Improvement of the results should be tried by e.g. exploring different device parameters. 1'-hydroxydiclofenac was found likely to degrade in the matrix solution because of the acidic conditions, making the reliability of the results poor for this metabolite. The Km value obtained for coumarin differed markedly from literature values, which can be due to a too long incubation time. Therefore, incubation conditions should be optimized for this model reaction in coming studies. The Km values obtained for the model reactions of CYP1A2, CYP2D6 and CYP3A4 were similar to those found in literature. Also the IC50 values were quite well within the range of values reported in literature for the inhibitors of the above mentioned model reactions. The effects of four different polymers, F68, F127, Tetronic 1307 and polyvinyl alcohol (PVA) on the enzyme activities were also studied, at a concentration of 1 mg/ml. In principal, at this concentration the polymers did not cause significant changes in the enzyme activities, although inhibition of the CYP2C9 could have been significant. However, the reliability of CYP2C9 model reaction was found to be poor with the used method. In the future this developed method should be further validated, and the incubation conditions for the model reaction of CYP2A6 should be optimized. After this, the IC50 values for the polymers could be studied to get more reliable information about their potential CYP-inhibition properties.