Studies on CYP2C8-mediated drug interactions

Useiden lääkkeiden yhtäaikainen käyttö on nykyään hyvin yleistä, mikä lisää lääkeaineiden haitallisten yhteisvaikutusten riskiä. Lääkeaineiden poistumisessa elimistöstä ovat tärkeässä osassa niitä hajottavat (metaboloivat) maksan sytokromi P450 (CYP) entsyymit. Vasta aivan viime vuosina on havaittu, että CYP2C8-entsyymillä voi olla tärkeä merkitys mm. lääkeaineyhteisvaikutuksissa. Eräät lääkeaineet voivat estää (inhiboida) CYP2C8-entsyymin kautta tapahtuvaa metaboliaa. Tässä työssä selvitettiin CYP2C8-entsyymiä estävien lääkkeiden vaikutusta sellaisten lääkeaineiden pitoisuuksiin, joiden aikaisemman tiedon perusteella arveltiin metaboloituvan CYP2C8-välitteisesti. Näiden lääkeaineiden metaboliaa tutkittiin myös koeputkiolosuhteissa (in vitro -menetelmillä). Lisäksi CYP2C8-entsyymiä estävän lipidilääke gemfibrotsiilin yhteisvaikutusmekanismia tutkittiin selvittämällä interaktion säilymistä koehenkilöillä gemfibrotsiilin annostelun lopettamisen jälkeen. Yhteisvaikutuksia tutkittiin terveillä vapaaehtoisilla koehenkilöillä käyttäen vaihtovuoroista koeasetelmaa. Koehenkilöille annettiin CYP2C8-entsyymiä estävää lääkitystä muutaman päivän ajan ja tämän jälkeen kerta-annos tutkimuslääkettä. Koehenkilöiltä otettiin useita verinäytteitä, joista määritettiin lääkepitoisuudet nestekromatografisilla tai massaspektrometrisillä menetelmillä. Gemfibrotsiili nosti ripulilääke loperamidin pitoisuudet keskimäärin kaksinkertaiseksi. Gemfibrotsiili lisäsi, mutta vain hieman, kipulääke ibuprofeenin pitoisuuksia, eikä sillä ollut mitään vaikutusta unilääke tsopiklonin pitoisuuksiin toisin kuin aiemman kirjallisuuden perusteella oli odotettavissa. Toinen CYP2C8-estäjä, mikrobilääke trimetopriimi, nosti diabeteslääke pioglitatsonin pitoisuuksia keskimäärin noin 40 %. Gemfibrotsiili nosti diabeteslääke repaglinidin pitoisuudet 7-kertaiseksi ja tämä yhteisvaikutus säilyi lähes yhtä voimakkaana vielä 12 tunnin päähän viimeisestä gemfibrotsiiliannoksesta. Tehdyt havainnot ovat käytännön lääkehoidon kannalta merkittäviä ja ne selvittävät CYP2C8-entsyymin merkitystä useiden lääkkeiden metaboliassa. Gemfibrotsiilin tai muiden CYP2C8-entsyymiä estävien lääkkeiden yhteiskäyttö loperamidin kanssa voi lisätä loperamidin tehoa tai haittavaikutuksia. Toisaalta CYP2C8-entsyymin osuus tsopiklonin ja ibuprofeenin metaboliassa näyttää olevan pieni. Trimetopriimi nosti kohtalaisesti pioglitatsonin pitoisuuksia, ja kyseisten lääkkeiden yhteiskäyttö voi lisätä pioglitatsonin annosriippuvaisia haittavaikutuksia. Gemfibrotsiili-repaglinidi-yhteisvaikutuksen päämekanismi in vivo näyttää olevan CYP2C8-entsyymin palautumaton esto. Tämän vuoksi gemfibrotsiilin estovaikutus ja yhteisvaikutusriski säilyvät pitkään gemfibrotsiilin annostelun lopettamisen jälkeen, mikä tulee ottaa huomioon käytettäessä sitä CYP2C8-välitteisesti metaboloituvien lääkkeiden kanssa.

Common and rare variants of the renin-angiotensin system and their relation to antihypertensive drug responses

Most of the diseases affecting public health, like hypertension, are multifactorial by etiology. Hypertension is influenced by genetic, life style and environmental factors. Estimation of the influence of genes to the risk of essential hypertension varies from 30 to 50%. It is plausible that in most of the cases susceptibility to hypertension is determined by the action of more than one gene. Although the exact molecular mechanism underlying essential hypertension remains obscure, several monogenic forms of hypertension have been identified. Since common genetic variations may predict, not only to susceptibility to hypertension, but also response to antihypertensive drug therapy, pharmacogenetic approaches may provide useful markers in finding relations between candidate genes and phenotypes of hypertension. The aim of this study was to identify genetic mutations and polymorphisms contributing to human hypertension, and examine their relationships to intermediate phenotypes of hypertension, such as blood pressure (BP) responses to antihypertensive drugs or biochemical laboratory values. Two groups of patients were investigated in the present study. The first group was collected from the database of patients investigated in the Hypertension Outpatient Ward, Helsinki University Central Hospital, and consisted of 399 subjects considered to have essential hypertension. Frequncies of the mutant or variant alleles were compared with those in two reference groups, healthy blood donors (n = 301) and normotensive males (n = 175). The second group of subjects with hypertension was collected prospectively. The study subjects (n=313) underwent a protocol lasting eight months, including four one-month drug treatment periods with antihypertensive medications (thiazide diuretic, β-blocker, calcium channel antagonist, and an angiotensin II receptor antagonist). BP responses and laboratory values were related to polymorphims of several candidate genes of the renin-angiotensin system (RAS). In addition, two patients with typical features of Liddle’s syndrome were screened for mutations in kidney epithelial sodium channel (ENaC) subunits. Two novel mutations causing Liddle’s syndrome were identified. The first mutation identified located in the beta-subunit of ENaC and the second mutation found located in the gamma-subunit, constituting the first identified Liddle mutation locating in the extracellular domain. This mutation showed 2-fold increase in channel activity in vitro. Three gene variants, of which two are novel, were identified in ENaC subunits. The prevalence of the variants was three times higher in hypertensive patients (9%) than in reference groups (3%). The variant carriers had increased daily urinary potassium excretion rate in relation to their renin levels compared with controls suggesting increased ENaC activity, although in vitro they did not show increased channel activity. Of the common polymorphisms of the RAS studied, angiotensin II receptor type I (AGTR1) 1166 A/C polymorphism was associated with modest changes in RAS activity. Thus, patients homozygous for the C allele tended to have increased aldosterone and decreased renin levels. In vitro functional studies using transfected HEK293 cells provided additional evidence that the AGTR1 1166 C allele may be associated with increased expression of the AGTR1. Common polymorphisms of the alpha-adducin and the RAS genes did not significantly predict BP responses to one-month monotherapies with hydroclorothiazide, bisoprolol, amlodipin, or losartan. In conclusion, two novel mutations of ENaC subunits causing Liddle’s syndrome were identified. In addition, three common ENaC polymorphisms were shown to be associated with occurrence of essential hypertension, but their exact functional and clinical consequences remain to be explored. The AGTR1 1166 C allele may modify the endocrine phenotype of hypertensive patients, when present in homozygous form. Certain widely studied polymorphisms of the ACE, angiotensinogen, AGTR1 and alpha-adducin genes did not significantly affect responses to a thiazide, β-blocker, calcium channel antagonist, and angiotensin II receptor antagonist.

Anti-TNF treatment in juvenile idiopathic arthritis and associated uveitis : Clinical perspectives on growth, uveitis, and drug survival

Juvenile idiopathic arthritis (JIA) is a heterogeneous group of childhood chronic arthritides, associated with chronic uveitis in 20% of cases. For JIA patients responding inadequately to conventional disease-modifying anti-rheumatic drugs (DMARDs), biologic therapies, anti-tumor necrosis factor (anti-TNF) agents are available. In this retrospective multicenter study, 258 JIA-patients refractory to DMARDs and receiving biologic agents during 1999-2007 were included. Prior to initiation of anti-TNFs, growth velocity of 71 patients was delayed in 75% and normal in 25%. Those with delayed growth demonstrated a significant increase in growth velocity after initiation of anti-TNFs. Increase in growth rate was unrelated to pubertal growth spurt. No change was observed in skeletal maturation before and after anti-TNFs. The strongest predictor of change in growth velocity was growth rate prior to anti-TNFs. Change in inflammatory activity remained a significant predictor even after decrease in glucocorticoids was taken into account. In JIA-associated uveitis, impact of two first-line biologic agents, etanercept and infliximab, and second-line or third-line anti-TNF agent, adalimumab, was evaluated. In 108 refractory JIA patients receiving etanercept or infliximab, uveitis occurred in 45 (42%). Uveitis improved in 14 (31%), no change was observed in 14 (31%), and in 17 (38%) uveitis worsened. Uveitis improved more frequently (p=0.047) and frequency of annual uveitis flares was lower (p=0.015) in those on infliximab than in those on etanercept. In 20 patients taking adalimumab, 19 (95%) had previously failed etanercept and/or infliximab. In 7 patients (35%) uveitis improved, in one (5%) worsened, and in 12 (60%) no change occurred. Those with improved uveitis were younger and had shorter disease duration. Serious adverse events (AEs) or side-effects were not observed. Adalimumab was effective also in arthritis. Long-term drug survival (i.e. continuation rate on drug) with etanercept (n=105) vs. infliximab (n=104) was at 24 months 68% vs. 68%, and at 48 months 61% vs. 48% (p=0.194 in log-rank analysis). First-line anti-TNF agent was discontinued either due to inefficacy (etanercept 28% vs. infliximab 20%, p=0.445), AEs (7% vs. 22%, p=0.002), or inactive disease (10% vs. 16%, p=0.068). Females, patients with systemic JIA (sJIA), and those taking infliximab as the first therapy were at higher risk for treatment discontinuation. One-third switched to the second anti-TNF agent, which was discontinued less often than the first. In conclusion, in refractory JIA anti-TNFs induced enhanced growth velocity. Four-year treatment survival was comparable between etanercept and infliximab, and switching from first-line to second-line agent a reasonable therapeutic option. During anti-TNF treatment, one-third with JIA-associated anterior uveitis improved.

Inhibition of CYP1A2-mediated drug metabolism in vitro and in humans : With special emphasis on rofecoxib and other NSAIDs

The cytochrome P450 1A2 (CYP1A2) is one of the major metabolizing enzymes. The muscle relaxant tizanidine is a selective substrate of CYP1A2, and the non-steroidal anti-inflammatory drug (NSAID) rofecoxib was thought to modestly in-hibit it. Cases suggesting an interaction between tizanidine and rofecoxib had been reported, but the mechanism was unknown. Also other NSAIDs are often used in combination with muscle relaxants. The aims of this study were to investigate the effect of rofecoxib, several other NSAIDs and female sex steroids on CYP1A2 ac-tivity in vitro and in vivo, and to evaluate the predictability of in vivo inhibition based on in vitro data. In vitro, the effect of several NSAIDs, female sex steroids and model inhibitors on CYP1A2 activity was studied in human liver microsomes, without and with preincubation. In placebo controlled, cross-over studies healthy volunteers ingested a single dose of tizanidine after a pretreament with the inhibitor (rofecoxib, tolfenamic acid or celecoxib) or placebo. Plasma (and urine) concentrations of tizanidine and its metabolites were measured, and the pharmacodynamic effects were recorded. A caffeine test was also performed. In vitro, fluvoxamine, tolfenamic acid, mefenamic acid and rofecoxib potently in-hibited CYP1A2. Ethinylestradiol, celecoxib, desogestrel and zolmitriptan were moderate, and etodolac, ciprofloxacin, etoricoxib and gestodene were weak inhibi-tors of CYP1A2. At 100 µM, other tested NSAIDs and steroids inhibited CYP1A2 less than 35%. Rofecoxib was found to be a mechanism-based inhibitor of CYP1A2. In vivo, rofecoxib greatly increased the plasma concentrations (over ten-fold) and the pharmacodynamic effects of tizanidine. Also the metabolism of caf-feine was impaired by rofecoxib. Despite the relatively strong in vitro CYP1A2 inhibitory effects, tolfenamic acid and celecoxib did not have a significant effect on tizanidine and caffeine concentrations in humans. Competitive inhibition model and the free plasma concentration of the inhibitor predicted well the effect of fluvoxam-ine and the lack of effect of tolfenamic acid and celecoxib on tizanidine concentra-tions in humans, and mechanism-based inhibition model explained the effects of rofecoxib. However, the effects of ciprofloxacin and oral contraceptives were un-derestimated from the in vitro data. Rofecoxib is a potent mechanism-based inhibitor of CYP1A2 in vitro and in vivo. This mechanism may be involved in the adverse cardiovascular effects of rofecoxib. Tolfenamic acid and celecoxib seem to be safe in combination with tizanidine, but mefenamic acid might have some effect on tizanidine concentrations in vivo. Con-sidering the mechanism of inhibition, and using the free plasma concentration of the inhibitor, many but not all CYP1A2 interactions can be predicted from in vitro data.

HIV outbreak among injecting drug users in Finland

An HIV outbreak among Finnish injecting drug users (IDUs) occurred in 1998. By the end of 2005, 282 IDUs were in-fected, most of them by recombinant virus CRF01_AE of HIV. After a rapid spread, the outbreak subsided, and the prevalence of HIV among IDUs remained low (<2%). The purpose of the study was to describe the outbreak in order to recognise factors that have influenced the spread and restriction of the outbreak, and thus to find tools for HIV preven-tion. Data on Finnish IDUs newly diagnosed HIV-positive between 1998 and 2005 was collected through interviews and patient documents. Study I compared markers of disease progression between 93 Finnish IDUs and 63 Dutch IDUs. In study II, geographical spread of the HIV outbreak was examined and compared with the spatial distribution of employed males. In study III, risk behaviour data from interviews of 89 HIV-positive and 207 HIV-negative IDUs was linked, and prevalence and risk factors for unprotected sex were evaluated. In study IV, data on 238 newly diagnosed IDUs was combined with data on 675 sexually transmitted HIV cases, and risk factors for late HIV diagnosis (CD4 cell count <200/µL, or AIDS at HIV diagnosis) were analysed. Finnish IDUs infected with CRF01_AE exhibited higher viral loads than did Amsterdam IDUs infected with subtype B, but there was no difference in CD4 development. The Finnish IDU outbreak spread and was restricted socially in a marginalised IDU population and geographically in areas characterised by low proportions of employed males. Up to 40% of the cases in the two clusters outside the city centre had no contact with the centre, where needle exchange services were available since 1997. Up to 63% of HIV-positive and 80% of HIV-negative sexually active IDUs reported inconsistent condom use, which was associated with steady relationships and recent inpatient addiction care. Com-pared to other transmission groups, HIV-positive IDUs were diagnosed earlier in their infection. The proportion of late diagnosed HIV cases in all transmission groups was 23%, but was only 6% among IDUs diagnosed during the first four years of the epidemic. The high viral load in early HIV infection may have contributed to the rapid spread of recombinant virus in the Finnish outbreak. The outbreak was restricted to a marginalised IDU population, and limited spatially to local pockets of pov-erty. To prevent HIV among IDUs, these pockets should be recognised and reached early through outreach work and the distribution of needle exchange and other prevention activities. To prevent the sexual transmission of HIV among IDUs, prevention programmes should be combined with addiction care services and targeted at every IDU. The early detection of the outbreak and early implementation of needle exchange programmes likely played a crucial role in re-versing the IDU outbreak.

Just say no? The influence of personal goals, beliefs, psychosocial adjustment, and parental relationships in drug use by adolescents

The study in its entirety focused on factors related to adolescents decisions concerning drug use. The term drug use is taken here to include the use of tobacco products, alcohol, narcotics, and other addictive substances. First, the reasons given for drug use (attributions) were investigated. Secondly, the influence of personal goals, the beliefs involved in decision making, psychosocial adjustment including body image and involvement with peers, and parental relationships on drug use were studied. Two cohorts participated in the study. In 1984, a questionnaire on reasons for drug use was administered to a sample of adolescents aged 14-16 (N=396). A further questionnaire was administered to another sample of adolescents aged 14-16 (N=488) in 1999. The results for both cohorts were analyzed in Articles I and II. In Articles III and IV further analysis was carried out on the second cohort (N=488). The research report presented here provides a synthesis of all four articles, together with material from a further analysis. In a comparison of the two cohorts it was found that the attributions for drug use had changed considerably over the intervening fifteen-year period. In relation to alcohol and narcotics use an increase was found in reasons involving inner subjective experiences, with mention of the good feeling and fun resulting from alcohol and narcotics use. In addition, the goals of alcohol consumption were increasingly perceived as drinking to get drunk, and for its own sake. The attributions for the adolescents own smoking behavior were quite different from the attributions for smoking by others. The attributions were only weakly influenced by the participants gender or by their smoking habits, either in 1984 or 1999. In relation to participants own smoking, the later questionnaire elicited more mention of inner subjective experiences involving "good feeling. In relation to the perceived reasons for other people s smoking, it elicited more responses connected with the notion of "belonging. In the second sample, the results indicated that the levels of body satisfaction among adolescent girls are lower than those among adolescent boys. Overall, dissatisfaction with one's physical appearance seemed to relate to drug use. Girls were also found to engage in more discussions than boys; this applied to (i) discussion with peers (concerning both intimate and general matters), and (ii) discussion with parents (concerning general matters). However, more than a quarter of the boys (out of the entire population) reported only low intimacy with both parents and peers. If both drinking and smoking were considered, it seemed that girls in particular who reported drinking and smoking also reported high intimacy with parents and peers. Boys who reported drinking and smoking reported only medium intimacy with parents and peers. In addition, having an intimate relationship with one's peers was associated with a greater tendency to drink purely in order to get drunk. Overall, the results seemed to suggest that drug use is connected with a close relationship with peers and (surprisingly) with a close relationship with parents. Nevertheless, there were also indications that to some extent peer relationships can also protect adolescents from smoking and alcohol use. The results, which underline the complexity of adolescent drug use, are taken up in the Discussion section. It may be that body image and/or other identity factors play a more prominent role in all drug use than has previously been acknowledged. It does appear that in the course of planning support campaigns for adolescents at risk of drug use, we should focus more closely on individuals and their inner world. More research on this field is clearly needed, and therefore some ideas for future research are also presented.

Medicalising Prohibition : Harm reduction in Finnish and International Drug Policy

The increase in drug use and related harms in the late 1990s in Finland has come to be referred to as the second drug wave. In addition to using criminal justice as a basis of drug policy, new kinds of drug regulation were introduced. Some of the new regulation strategies were referred to as "harm reduction". The most widely known practices of harm reduction include needle and syringe exchange programmes for intravenous drug users and medicinal substitution and maintenance treatment programmes for opiate users. The purpose of the study is to examine the change of drug policy in Finland and particularly the political struggle surrounding harm reduction in the context of this change. The aim is, first, to analyse the content of harm reduction policy and the dynamics of its emergence and, second, to assess to what extent harm reduction undermines or threatens traditional drug policy. The concept of harm reduction is typically associated with a drug policy strategy that employs the public health approach and where the principal focus of regulation is on drug-related health harms and risks. On the other hand, harm reduction policy has also been given other interpretations, relating, in particular, to human rights and social equality. In Finland, harm reduction can also be seen to have its roots in criminal policy. The general conclusion of the study is that rather than posing a threat to a prohibitionist drug policy, harm reduction has come to form part of it. The implementation of harm reduction by setting up health counselling centres for drug users with the main focus on needle exchange and by extending substitution treatment has implied the creation of specialised services based on medical expertise and an increasing involvement of the medical profession in addressing drug problems. At the same time the criminal justice control of drug use has been intensified. Accordingly, harm reduction has not entailed a shift to a more liberal drug policy nor has it undermined the traditional policy with its emphasis on total drug prohibition. Instead, harm reduction in combination with a prohibitionist penal policy constitutes a new dual-track drug policy paradigm. The study draws on the constructionist tradition of research on social problems and movements, where the analysis centres on claims made about social problems, claim-makers, ways of making claims and related social mobilisation. The research material mainly consists of administrative documents and interviews with key stakeholders. The doctoral study consists of five original articles and a summary article. The first article gives an overview of the strained process of change of drug policy and policy trends around the turn of the millennium. The second article focuses on the concept of harm reduction and the international organisations and groupings involved in defining it. The third article describes the process that in 1996 97 led to the creation of the first Finnish national drug policy strategy by reconciling mutually contradictory views of addressing the drug problem, at the same as the way was paved for harm reduction measures. The fourth article seeks to explain the relatively rapid diffusion of needle exchange programmes after 1996. The fifth article assesses substitution treatment as a harm reduction measure from the viewpoint of the associations of opioid users and their family members.

Drug cultures in Estonia : contexts, meanings and patterns of illicit drug use.

In Estonia, illicit drug use hardly existed before the social changes of the 1990s when, as a result of economic and cultural transformations, the country became part of a world order centred in the West. On the one hand, this development is due to the spread of international youth culture, which many young people have perceived as being associated with drugs; on the other hand, it results from the marginalisation of a part of the population. The empirical part of the study is based mostly on in-depth interviews with different drug users conducted during between 1998 and 2002. Complementary material includes the results of participant observations, interviews with key experts, and the results of previous quantitative studies and statistics. The young people who started experimenting with illicit drugs from the 1990s and onwards perceived them as a part of an attractive lifestyle - a Western lifestyle, a point which is worth stressing in the case of Estonia. Although the reasons for initiation into drug use were similar for the majority of young people, their drug use habits and the impact of the drug use on their lives began to differ. I argue that the potential pleasure and harm which might accompany drug use is offset by the meanings attached to drugs and the sanctions and rituals regulating drug use. In the study both recreational and problem use have been analysed from different aspects in seven articles. I have investigated different types of drug users: new bohemians, cannabis users, in whose case partying and restrictive drug use is positively connected to their lives and goals within established society; stimulant-using party people for whom drugs are a means of having fun but who do not have the same restrictive norms regulating their drug use as the former and who may get into trouble under certain conditions; and heroin users for whom the drug rapidly progressed from a means of having fun to an obligation due to addiction. The research results point at the importance not only of the drug itself and the socio-economic situation of the user, but also of the cultural and social context within which the drug is used. The latter may on occasions be a crucial factor in whether or not initial drug use eventually leads to addiction.

Mass spectrometry and n-in-one analytics in early drug discovery: Combinatorial chemistry libraries, lipophilicity and absorption screening

This thesis describes current and past n-in-one methods and presents three early experimental studies using mass spectrometry and the triple quadrupole instrument on the application of n-in-one in drug discovery. N-in-one strategy pools and mix samples in drug discovery prior to measurement or analysis. This allows the most promising compounds to be rapidly identified and then analysed. Nowadays properties of drugs are characterised earlier and in parallel with pharmacological efficacy. Studies presented here use in vitro methods as caco-2 cells and immobilized artificial membrane chromatography for drug absorption and lipophilicity measurements. The high sensitivity and selectivity of liquid chromatography mass spectrometry are especially important for new analytical methods using n-in-one. In the first study, the fragmentation patterns of ten nitrophenoxy benzoate compounds, serial homology, were characterised and the presence of the compounds was determined in a combinatorial library. The influence of one or two nitro substituents and the alkyl chain length of methyl to pentyl on collision-induced fragmentation was studied, and interesting structurefragmentation relationships were detected. Two nitro group compounds increased fragmentation compared to one nitro group, whereas less fragmentation was noted in molecules with a longer alkyl chain. The most abundant product ions were nitrophenoxy ions, which were also tested in the precursor ion screening of the combinatorial library. In the second study, the immobilized artificial membrane chromatographic method was transferred from ultraviolet detection to mass spectrometric analysis and a new method was developed. Mass spectra were scanned and the chromatographic retention of compounds was analysed using extract ion chromatograms. When changing detectors and buffers and including n-in-one in the method, the results showed good correlation. Finally, the results demonstrated that mass spectrometric detection with gradient elution can provide a rapid and convenient n-in-one method for ranking the lipophilic properties of several structurally diverse compounds simultaneously. In the final study, a new method was developed for caco-2 samples. Compounds were separated by liquid chromatography and quantified by selected reaction monitoring using mass spectrometry. This method was used for caco-2 samples, where absorption of ten chemically and physiologically different compounds was screened using both single and nin- one approaches. These three studies used mass spectrometry for compound identification, method transfer and quantitation in the area of mixture analysis. Different mass spectrometric scanning modes for the triple quadrupole instrument were used in each method. Early drug discovery with n-in-one is area where mass spectrometric analysis, its possibilities and proper use, is especially important.

Understanding Human Drug Conjugating Enzymes; Regio- and Stereoselectivity in Sulfotransferase 1A3 and the UDP-Glucuronosyltransferases

Sulfotransferases (SULTs) and UDP-glucuronosyltransferases (UGTs) are important detoxification enzymes and they contribute to bioavailability and elimination of many drugs. SULT1A3 is an extrahepatic enzyme responsible for the sulfonation of dopamine, which is often used as its probe substrate. A new method for analyzing dopamine-3-O-sulfate and dopamine-4-O-sulfate by high-performance liquid chromatography was developed and the enzyme kinetic parameters for their formation were determined using purified recombinant human SULT1A3. The results show that SULT1A3 strongly favors the 3-hydroxy group of dopamine, which indicates that it may be the major enzyme responsible for the difference between the circulating levels of dopamine sulfates in human blood. All 19 known human UGTs were expressed as recombinant enzymes in baculovirus infected insect cells and their activities toward dopamine and estradiol were studied. UGT1A10 was identified as the only UGT capable of dopamine glucuronidation at a substantial level. The results were supported by studies with human intestinal and liver microsomes. The affinity was low indicating that UGT1A10 is not an important enzyme in dopamine metabolism in vivo. Despite the low affinity, dopamine is a potential new probe substrate for UGT1A10 due to its selectivity. Dopamine was used to study the importance of phenylalanines 90 and 93 in UGT1A10. The results revealed distinct effects that are dependent on differences in the size of the side chain and on the differences in their position within the protein. Examination of twelve mutants revealed lower activity in all of them. However, the enzyme kinetic studies of four mutants showed that their affinities were similar to that of UGT1A10 suggesting that F90 and F93 are not directly involved in dopamine binding in the active site. The glucuronidation of β-estradiol and epiestradiol (α-estradiol) was studied to elucidate how the orientation of the 17-OH group affects conjugation at the 3-OH or the 17-OH of either diastereomer. The results show that there are clear differences in the regio- and stereoselectivities of UGTs. The most active isoforms were UGT1A10 and UGT2B7 demonstrating opposite regioselectivity. The stereoselectivities of UGT2Bs were more complex than those of UGT1As. The amino acid sequences of the human UGTs 1A9 and 1A10 are 93% identical, yet there are large differences in their activity and substrate selectivity. Several mutants were constructed to identify the residues responsible for the activity differences. The results revealed that the residues between Leu86 and Tyr176 of UGT1A9 determine the differences between UGT1A9 and UGT1A10. Phe117 of UGT1A9 participated in 1-naphthol binding and the residues at positions 152 and 169 contributed to the higher glucuronidation rates of UGT1A10. In summary, the results emphasize that the substrate selectivities, including regio- and stereoselectivities, of UGTs are complex and they are controlled by many amino acids rather than one critical residue.