Heme oxygenases (HO) catalyze the degradation of heme into biliverdin, carbon monoxide (CO) and free iron. The two major isoforms, HO-2 (constitutive) and HO-1 (inducible by various stressors such as heavy metals and reactive oxygen species) are involved in a variety of physiological functions, including anti-inflammation, antiapoptosis, neuromodulation, and vascular regulation. Major tools used in exploring these actions have been metalloporphyrin analogs of heme that inhibit the HOs. However, these tools are limited by their lack of selectivity; they affect other heme-dependent enzymes, such as cytochromes P450 (CYPs), soluble guanylyl cyclase (sGC), and nitric oxide synthase (NOS). Our laboratory has been able to successfully synthesize a series of small molecule non-porphyrin HO inhibitors (QC-xx) that have had little or no effect against sGC and NOS; however, their effects on various CYP isoforms has yet to be fully elucidated. In order to determine the effects on CYP enzyme activity, microsomal preparations of two CYP isoforms (2E1 and 3A1/3A2) were incubated with varying concentrations of HO inhibitor and the activity was determined via spectrophotometric analysis. Results indicated that some QC compounds demonstrated little to no inhibition of CYP2E1 and/or CYP3A1/2, while some others did inhibit these CYP isoforms. Four regions of interest were analyzed further and several structural changes were identified as conferring increased HO inhibition and decreased effect on both CYP2E1 and 3A1/2. Based on the information obtained, three putative compounds were designed and it is hypothesized that these compounds will be selective inhibitors for HO-1 over HO-2 and will display little effect on either CYP2E1 or 3A1/2 activities. / Thesis (Master, Pharmacology & Toxicology) -- Queen's University, 2008-11-20 11:19:48.841

Most administered drugs are metabolised in the liver by Phase I enzymes and more importantly by the cytochrome P450 (CYP) system. The extent of first-pass metabolism is important in determining whether the drug will have therapeutic or adverse effects after being administered to a patient. To date the CYP family has been shown to consist of 74 families denoted as CYPl to CYP118, and only a few families are significantly involved in drug metabolism. CYP3A4 is the most important isoenzyme followed by CYP2D6, CYP2C9, and CYP2C19 with a small contribution by CYP2E1, CYP2A6, and CYPlA4. CYP2D6 and CYP3A4 enzyme isoforms have been well established to exhibit interethnic and interindividual variability with regard to drug metabolising capacity. Mutation on the gene coding for a metabolising enzyme is a major cause of variation in drug metabolism. This mutation gives rise to allelic variants producing enzymes with altered metabolising activity. The presence of an allele with decreased metabolic activity in an individual gives rise to the poor metabolising (PM) phenotype. When the PM phenotype occurs at a frequency of more than 1% within a given population, then the term genetic polymorphism applies. The aberrant metabolic capacity translates into variable drug responses of more than 20-fold, leading to different susceptibility to sub-therapeutic effects or adverse drug reactions. A significant number of drugs, such as the B-adrenergic blockers, antidepressants, antipsychotic and antiarrhythmic agents, are entirely or partly metabolised by CYP2D6 and CYP3A4. Genetic polymorphism is especially important for drugs with a narrow therapeutic/toxicity window. Phenotyping involves the use of a probe drug that is administered to the subject, followed by determination of the parent drug and its metabolites in the urine. The aim of this study was to develop and validate an HPLC method for phenotypic determination of the CYP3A4 and CYP2D6 enzymes, followed by the application of the assay in a random heterogeneous population of males. Dextromethorphan (DXM) was used as an in vivo probe for simultaneous determination of the phenotypic expression of CYP2D6 and CYP3A4. An HPLC method coupled with a fluorescence detector was developed for the phenotypic determination of CYP2D6 and CYP3A4 iso-enzymes as determined by the concentration of dextromethorphan/dextrophan (DXM/DX) and dextromethorphan/3methoxy-morphinan (DXM/3MM) metabolic ratios respectively. The compounds were separated on a phenyl column (150 x 4,6 mm, 5-um particle size) serially connected to nitrile column (250 x 4,6 mm, 5-um particle size) using mobile phase of 80% (1.5% glacial acetic acid and 0.1% triethyl amine in distilled water) and 20% acetonitrile. Solid phase extraction was used to extract the analytes from urine samples using silica cartridges. The suitability of the method was demonstrated in a preliminary study with sixteen healthy Caucasian males. After a single oral 30 mg DXM dose, the volunteers were required to collect all urine samples voided 8 hours post oral dose. DXM/3HM and DXM/DX metabolic ratios were determined from collected urine samples. The method was validated for DXM and DX at a concentration range of 0.25 - 30 ug/ml, and at 0.025 - 3 ug/ml for 3MM. Calibration curves were linear with R2 values of at-least 0.999 for all compounds of interest. Recoveries were 97%, 93%, and 65% for DX, DXM and 3MM, respectively. The method was reproducible with intra-day precision having coefficients of variation percentage (CV%) of less than 17% for all analytes. Inter-day precision had a CV% of less than 14% for all analytes. The limit of detection was 30 ug/ml for all compounds. All volunteers were classified with an extensive metaboliser (EM) phenotype. In conclusion the method described is suitable for polymorphic determination of CYP2D6 and CYP3A4 in a population study, and may have value in further studies planned at investigating the critical issue of racial genetic polymorphism in ethnic groups in South Africa. / Thesis (M.Sc. (Pharm.))--North-West University, Potchefstroom Campus, 2004.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2002. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2002. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 242-263).

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 174 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 164-174).

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves 138-141).