Glucuronidation of Entacapone, Nitecapone, Tolcapone, and Some Other Nitrocatechols by Rat Liver Microsomes

Purpose. Nitrocatechol COMT inhibitors are a new class of bioactive compounds, for which glucuronidation is the most important metabolic pathway. The objective was to characterize the enzyme kinetics of nitrocatechol glucuronidation to improve the understanding and predicting of the pharmacokinetic behavior of this class of compounds. Methods. The glucuronidation kinetics of seven nitrocatechols and 4-nitrophenol, the reference substrate for phenol UDP-glucuronosyltrans-ferase activity, was measured in liver microsomes from creosote-treated rats and determined by non-linear fitting of the experimental data to the Michaelis-Menten equation. A new method that combined densitometric and radioactivity measurement of the glucuronides separated by HPTLC was developed for the quantification. Results. Apparent K_m values for the nitrocatechols varied greatly depending on substitution pattern being comparable with 4-nitrophenol (0.11 mM) only in the case of 4-nitrocatechol (0.19 mM). Simple nitrocatechols showed two-fold V_max values compared with 4-nitrophenol (68.6 nmol min^–1 mg^–1), while all disubstituted catechols exhibited much lower glucuronidation rate. V_max/K_m values were about 10 times higher for monosubstituted catechols compared to disubstituted ones. The kinetic parameters for COMT inhibitors were in the following order: K_m nitecapone >> entacapone > tolcapone; V_max nitecapone > entacapone > tolcapone; V_max/K_m tolcapone > nitecapone > entacapone. Conclusions. Nitrocatechols can in principle be good substrates of UGTs. However, substituents may have a remarkable effect on the enzyme kinetic parameters. The different behaviour of nitecapone compared to the other COMT inhibitors may be due to its hydrophilic 5-substituent. The longer elimination half-life of tolcapone in vivo compared to entacapone could not be explained by glucuronidation kinetics in vitro.     

Effects of commercial chlorophenolate, 2,3,7,8-TCDD,and pure phenoxyacetic acids on hepatic peroxisome proliferation,xenobiotic metabolism and sister chromatid exchange in the rat

The induction of hepatic peroxisome proliferation and drug metabolizing enzymes and of sister chromatid exchange (SCE) in lymphocytes was studied in male Han/Wistar rats after exposing them for 2 weeks to a commercial chlorophenolate formulation (Ky-5) (100mg/kg/ day), to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD; 0.05–5 g/kg/wk) and to the pure phenoxyacetic acids, 2,4-dichlorophenoxyacetic acid (2,4-D; 100 mg/kg/day) and 2-chloro-4-methylphenoxyacetic acid (MCPA; 100 mg/kg/day). The chlorophenolate formulation and pure 2,4-D and MCPA caused significant increases in the number of peroxisomes in liver cells, although the average size of peroxisomes was not affected, whereas the effect of even the highest dose of 2,3,7,8-TCDD remained small. This finding indicates that dioxin impurities do not account for the peroxisome proliferation induced by chlorophenolate. The relative weight of the liver increased significantly in rats treated with the chlorophenolate formulation and with 2,3,7,8-TCDD (5.0 and 0.5 g/kg). The pattern of induction of xenobiotic metabolizing enzymes showed some differences between chlorophenolate treatment and 2,3,7,8-TCDD treatment. Furthermore, the effects of pure phenoxyacetic acids were different from that seen with chlorophenolate and 2,3,7,8-TCDD. The highest dose of 2,3,7,8-TCDD increased the frequency of SCE in circulating lymphocytes slightly, but significantly.     

Immunochemical characterization of cytochrome P-450 isozymes responsible for benzene oxidation in the rat liver

The contribution of cytochrome P-450 isozymes to benzene metabolismin liver microsomes from fed, fasted, pyrazole-, pbenobarbital(PB)- and ethanol-treated rats and in respective isocaloriccontrols was investigated using monoclonal antibodies (mAbs).Clone 1-7-1 mAb did not inhibit benzene metabolism, whereasclone 2-66-3 inhibited only in PB-induced microsomes at a highconcentration of benzene (6.26 mM), and clone 1-91-3 mAb inhibitedbenzene metabolism in all cases. The degree of inhibition wasas follows: fed isocaloric control PB < fasted < pyrazole ethanol. The pattern of inhibition was similar with clone 1-91-3for low (0.23 mM) and high concentrations of benzene, exceptin PB-induced mkrosomes. Western blot analysis showed that clone1-7-1 mAb did not bind any liver mkrosomal protein in the regionof cytochrome P-450s, whereas with clone 2-66-3 a clear-cutband was seen only in liver microsomes from PB-treated rats,with clone 1-98-1, a band was detected in mkrosomes from alltreated groups, in the following order: PB = isocaloric control< fed < fasted < pyrazole < ethanol. These resultsindicate that (i) cytochromes P-450b,e and P-450J contributeto benzene metabolism in rat liver; (ii) the former has a lowaffinity to benzene and is induced by PB; and (iii) P-450J hasa high affinity to benzene and is induced by 1-day fasting,pyrazole and ethanol, but decreased by PB treatment.     

Melatonin modulates allergic lung inflammation

Asthma is an inflammatory lung disease characterized by cell migration, bronchoconstriction and hyperresponsiveness, and can be induced, as an experimental model, by ovalbumin sensitization followed by a challenge. In addition to the well-known immunostimulatory effects of melatonin, research has identified some of its anti-inflammatory properties. In this study, we evaluated the influence of pinealectomy and melatonin administration on cell migration in an experimental model of allergic airway inflammation. We evaluated, in pinealectomized rats treated or not with melatonin, cell migration into the bronchoalveolar fluid, the number of cells and their proliferative activity in the bone marrow, and plasma corticosterone levels. Pinealectomy reduces, 24 hr after the challenge, the total cell number count in the lung and bone marrow cell proliferation, without changing the number of cells in the bone marrow or in the peripheral blood. This fact suggests that melatonin is important in the control of cell recruitment from the bone marrow and the migration of those cells to the lung. Melatonin administration to pinealectomized rats seems to restore the ability of cells to migrate from the bone marrow to the bronchoalveolar fluid. So, the development of specific inhibitors of melatonin would benefit patients with asthma.     

Immigrant patients' experiences and reflections pertaining to the consultation: a study on patients from Chile, Iran and Turkey in primary health care in Stockholm, Sweden

Our knowledge of the immigrant patient’s experiences and reflections regarding consultations in primary health care where interpreters are used is limited. Thus, the primary aim was to explore these experiences and reflections. The second aim was to study whether demographic and migration‐related factors are associated with the patient’s satisfaction with the consultation and feeling of consolation given by the general practitioner (GP). The third aim was to analyse whether these feelings are related to the time from the booking to the consultation, to self‐reported health, symptoms and the patient’s experiences. A questionnaire was distributed to 78 consecutive immigrant patients from Chile, Iran and Turkey at 12 primary healthcare centres around Stockholm. The respondents were asked about their background and health status, while open‐ended questions focused on their experiences and comments regarding the consultation and cross‐cultural communication in general. Ethical approval was obtained. The respondents consisted of 52 patients, 16 from Chile, nine from Iran and 27 from Turkey. Most of the answers concerned communication problems because of language and cultural differences between the GP and the patient and the GP’s ability to listen. Therefore, the importance of having a competent interpreter for a satisfactory consultation was stressed. Many of the respondents also felt that the GP’s ability to listen to them and understand them is crucial in the consultation. Background facts, including demographic and migration‐related factors, health status and factors related to the consultation, did not seem to be associated with the patient’s satisfaction and the feeling of consolation. One limitation is that the sample is small and not equally distributed. The use of authorized interpreters during the consultation is essential. The consultation must be based on a patient‐centred strategy and adjusted to the patient’s educational level. Cultural competence is needed when meeting immigrant patients.     

The adoption of dispensing technology: an occasion for restructuring hospital pharmacy work

Objective To understand the ways in which hospital dispensary work is being restructured following the implementation of dispensing technology. We examine the evolving role of pharmacists, technicians and assistants in their use of the technology. Setting The implementation of dispensing robots in two hospital dispensaries in a metropolitan region of the UK were examined over a 2‐year period. Method A qualitative case‐study design was used. Non‐participant observation, interviews and organisational documentary sources were the primary data sources. Analysis of first‐order themes identified common issues. Drawing on literature within organisational studies, second‐order themes were developed iteratively. Key findings Pharmacists render the dispensary less dependent on their physical presence by inscribing key dispensary practices into the robot, enabling them to move into more cognitive work roles. Technicians quickly adapt to the new dispensing process, gaining technical skills and competences through training on the robot and daily maintenance. This modernises the role of technicians and improves their visibility in the dispensary and within the pharmacy profession. Assistants become users of technology and become increasingly dependent on others for technical support. They lose autonomy as their work becomes more interdependent. The robot takes on the role as a team member, christened with a name, and referred to in anthropomorphising terms. Conclusion Dispensary workers and managing pharmacists should go beyond viewing the adoption of new technology at a functional level of efficiency and error rates. Rather, the findings highlight the changing nature of tasks and roles that are evolving with the restructuring of dispensing work. These need to be considered by those managing change processes associated with the implementation of these technologies, as they are shaped by workers' perception of the technology in use.     

Burden and Biochemical Effects of Extended Tetrahydrofuran Vapour Inhalation of Three Concentration Levels

Abstract: Adult male rats exposed to tetrahydrofuran vapour at 8.2 (200 p.p.m.), 41 (1,000 p.p.m.) or 82 μmol/1 (2,000 p.p.m.) for 2 to 18 weeks, five days a week, 6 hrs daily, showed dose-dependent brain and perirenal fat solvent burden linearly correlated to each other. After two weeks of exposure, the body burden of tetrahydrofuran seems to decrease. This might have been caused by increased oxidative metabolism as enhanced 7-ethoxycoumarin O-deethylase activity was detected in liver and kidneys in the 2nd week and onwards. The exposure also caused inhibition of alcohol and formaldehyde dehydrogenase activities in liver at the highest dose. Biochemical effects in the cerebellum were not detected while gluteal muscle specimens showed increased succinate dehydrogenase activity in a dose-related manner. This points to effects on the energy metabolism. Muscle acetylcholine esterase activity was also increased showing possible effects on the myoneural junctions.     

The Effect of Maternally Inhaled Styrene on Embryonal and Foetal Development in Mice and Chinese Hamsters

Abstract: Pregnant mice and Chinese hamsters were exposed to styrene 6 hrs daily during the period of major organogenesis via inhalation in concentrations 250 p.p.m., and 300, 500, 750 and 1000 p.p.m., respectively. Both in mice and in Chinese hamsters embryotoxicity was raised. Some minor skeletal malformations (rib fusions, extra ribs) were noted in mice but not in Chinese hamsters.     

Deleterious effects of subacute carbon disulphide exposure on mouse liver.

Female mice, fed ad lib., were exposed to 1.5 mg of carbon disulphide per liter of air for 4 hr a day, 5 days a week, for approximately 3.5 weeks. During the first week of the experiment the liver changes were similar to those found after acute carbon disulphide intoxication, i.e microsomal cytochropie P-450 content was lowered, the activities of NADPH cytochrome c-reductase and 7-ethoxycoumarin deethylase were decreased and the measurable UDP-glucuronosyltransferase activity was increased. The copper and phospholipid contents of the liver were also increased somewhat. Later on the activities of the microsomal enzymes were either partially or totally restored in spite of continuing exposure. The liver phospholipid content was also restored. The activity of UDP-glucuronosyltransferase was decreased significantly below the control level. The diene conjugation of liver phospholipids was increased, and this finding indicates that the exposure was able to damage the membrane lipids of the liver continuously. It is suggested that the partial or total restoration of the enzyme activities resulted either from their decreased sensitivity to the toxic metabolites of carbon disulphide or from their stimulated synthesis. The increased diene conjugation of the liver phospholipids indicates that the lipid environment of membrane bound enzymes changes during subacute exposure to carbon disulphide.     

Biochemical effects of methyl tertiary-butyl ether in extended vapour exposure of rats

Male Wistar rats exposed to 50, 100 or 300 ppm methyl tertiary-butyl ether vapour for 2–15 weeks, 6 h daily, 5 days a week, showed a dose-dependent blood ether concentration after 2 weeks' exposure. Blood concentrations of teriary-butanol, were also dose dependent indicating metabolic breakdown of the ether in vivo. The blood ether concentrations decreased after 6 weeks of exposure at the 50 ppm dose level and remained unaffected at higher doses while tertiary-butanol concentrations increased after 6 weeks with all doses, and began to decrease thereafter. Exposure caused a transient increase in UDP-glucuronosyltransferase activities in liver and kidney microsomes, almost no effects on hepatic cytochrome P-450 concentrations and a minor induction of kidney microsomal cytochrome P-450 content. Exposure produced almost no effect on brain succinate dehydrogenase, creatine kinase or acetylcholinesterase activities, while early inhibition of muscle creatine kinase activity was noted, accompanied by increased activity at the end of exposure.