Characterization of diuron N-demethylation by mammalian hepatic microsomes and cDNA-expressed human cytochrome P450 enzymes.

Diuron, a widely used herbicide and antifouling biocide, has been shown to persist in the environment and contaminate drinking water. It has been characterized as a "known/likely" human carcinogen. Whereas its environmental transformation and toxicity have been extensively examined, its metabolic characteristics in mammalian livers have not been reported. This study was designed to investigate diuron biotransformation and disposition because metabolic routes, metabolizing enzymes, interactions, interspecies differences, and interindividual variability are important for risk assessment purposes. The only metabolic pathway detected by liquid chromatography/mass spectometry in human liver homogenates and seven types of mammalian liver microsomes including human was demethylation at the terminal nitrogen atom. No other phase I or phase II metabolites were observed. The rank order of N-demethyldiuron formation in liver microsomes based on intrinsic clearance (V(max)/K(m)) was dog > monkey > rabbit > mouse > human > minipig > rat. All tested recombinant human cytochrome P450s (P450s) catalyzed diuron N-demethylation and the highest activities were possessed by CYP1A1, CYP1A2, CYP2C19, and CYP2D6. Relative contributions of human CYP1A2, CYP2C19, and CYP3A4 to hepatic diuron N-demethylation, based on average abundances of P450 enzymes in human liver microsomes, were approximately 60, 14, and 13%, respectively. Diuron inhibited relatively potently only CYP1A1/2 (IC(50) 4 microM). With human-derived and quantitative chemical-specific data, the uncertainty factors for animal to human differences and for human variability in toxicokinetics were within the range of the toxicokinetics default uncertainty/safety factors for chemical risk assessment.     

Effect of renal impairment on the pharmacokinetics of bupropion and its metabolites

AIMS: To investigate the effect of kidney disease on bupropion pharmacokinetics and on cytochrome P450 (CYP) 2B6 activity as measured by bupropion hydroxylation. METHODS: In an open parallel group study, 17 healthy, nonsmoking subjects and 10 patients with impaired kidney function received a single 150 mg oral dose of sustained release bupropion. Plasma concentrations of bupropion and its metabolites were measured for up to 72 h. Subjects were genotyped for the CYP2B6 SNPs 1459 C>T, 785 A>G and 516 G>T. RESULTS: Bupropion AUC was 126% higher (P < 0.0001, 95% CI +72%, +180%), C(max) 86% higher (P = 0.001, 95% CI +40%, +131%), CL/F 63% lower (P = 0.001, 95% CI -29%, -96%), and t(1/2) 140% longer (P = 0.001, 95% CI +76%, +204%) in renally impaired patients. However, only minor changes were detected in the concentrations of the metabolites. In renally impaired subjects the hydroxybupropion : bupropion AUC ratio was decreased by 66% (P = < 0.0001, 95% CI -19%, -114%) and the hydrobupropion : bupropion AUC ratio by 69% (P = 0.001, 95% CI +8%, -146%) compared with controls. CONCLUSIONS: The CL/F of bupropion was significantly lower in subjects with renal impairment. Because the principal metabolites of bupropion possess similar pharmacological activity to the parent compound, dosage recommendations for patients with renal impairment cannot be given. A direct effect of renal impairment on CYP2B6 activity could not be demonstrated by the present study design.     

Effects of Selective Serotonin Reuptake Inhibitors on Timolol Metabolism in Human Liver Microsomes and Cryo‐Preserved Hepatocytes

Abstract: Timolol has been widely used in the treatment of glaucoma. Topically applied, timolol may cause adverse cardiovascular effects due to systemic absorption through the nasolacrimal duct. Timolol is mainly metabolized by cytochrome P450 2D6 (CYP2D6) in the liver. The aim of the present study was to characterize further the metabolism of timolol in vitro. Especially the effect of several drugs such as selective serotonin reuptake inhibitors on the metabolism of timolol was evaluated. In human liver microsomes, four timolol metabolites were identified, in cryo‐preserved hepatocytes nine. In both in vitro experiments, the hydroxy metabolite M1 was the main metabolite. The in vivo half‐life predicted for timolol was 3.7 hr. in cryo‐preserved hepatocytes, corresponding to the half‐life of timolol in humans in vivo. Fluoxetine, paroxetine, sertraline, citalopram and fluvoxamine inhibited the formation of M1 in microsomes with IC₅₀ values of 1.4, 2.0, 3.5, 21 and 20 μM, respectively. In human cryo‐preserved hepatocytes, the IC₅₀ values for fluoxetine, paroxetine and fluvoxamine were 0.7, 0.5 and 5.9 μM, respectively. In conclusion, compounds known to be potent CYP2D6 inhibitors inhibited timolol metabolism in in vitro experiments. The present results strongly suggest that fluoxetine and paroxetine may significantly affect the metabolism of timolol also in vivo and may thus potentiate the adverse cardiovascular effects of topically administered timolol.     

Parental role in the diagnostics of otitis media: Can parents be taught to use tympanometry reliably?

Objective

Tympanometry can be used to detect middle ear effusion (MEE). As the need for rearrangement of clinical resources at the primary care level increases, it is important to determine whether layman parents could be taught to use the tympanometer reliably, aiming to reduce unnecessary physician visits during respiratory tract infections.

Methods

From our AOM treatment trial we enrolled 78 children (age 6–35 months) who had persistent MEE, parents were voluntary and willing to use a tympanometer at home, the child was sufficiently co-operative, and parents learned technically the use of the tympanometer. At home, parents were asked to perform daily bilateral tympanometry on their child. We included those parental tympanometric examinations, to which the corresponding tympanometric examination, within one day by a study physician was available. Parental tympanometric examinations were compared to the pneumatic otoscopy by a study physician which served as the diagnostic standard.

Results

This study involved 78 children and a total of 432 parental tympanometric examinations. From these 432 examinations, parents obtained an interpretable tympanogram in 83% (359/432) and physicians in 91% (393/432) (absolute rate difference 8%, 95% CI 3–12%). Both obtained an interpretable tympanogram from the same ear in 75% (326/432) of the tympanometric examinations. Of these 326 interpretable examinations, parents and physicians were in accordance with either a peaked or a flat tympanogram in 88% of examinations (288/326) (kappa-value 0.77). When the tympanogram was peaked, pneumatic otoscopy indicated healthy middle ear in 72% (122/169) of parental and in 69% (149/217) of study physicians’ tympanometric examinations (absolute rate difference 4%, 95% CI −6% to 13%). When the tympanogram was flat, pneumatic otoscopy indicated any MEE in 92% of parental (174/190) and in 96% (169/176) of study physicians’ tympanometric examinations (absolute rate difference 4%, 95% CI −9% to 1%).

Conclusion

This study showed that layman parents are able to use tympanometry technically successfully, and that the parental tympanometric examinations are as reliable as those obtained by study physicians.     

Structural brain changes and cognition in relation to markers of vascular dysfunction

The aim was to investigate the relationship between blood markers of vascular dysfunction with brain microstructural changes and cognition. Eighty-six participants from the Barcelona-Asymptomatic Intracranial Atherosclerosis (AsIA) neuropsychology study were included. Subjects were 50-65 years old, free from dementia and without history of vascular disease. We assessed correlations of blood levels of inflammatory biomarkers (C-reactive protein [CRP] and resistin) and fibrinolysis inhibitors (plasminogen activator inhibitor-1 [PAI-1] and A-lipoprotein (Lp (a)) with fractional anisotropy (FA) measurements of diffusion tensor images (DTI), regional gray matter (GM) volumes and performance in several cognitive domains. Increasing levels of C-reactive protein and PAI-1 levels were associated with white matter (WM) integrity loss in corticosubcortical pathways and association fibers of frontal and temporal lobes, independently of age, sex and vascular risk factors. PAI-1 was also related to lower speed and visuomotor/coordination. None of the biomarkers were related to gray matter volume changes. Our findings suggest that inflammation and dysregulation of the fibrynolitic system may be involved in the pathological mechanisms underlying the WM damage seen in cerebrovascular disease and subsequent cognitive impairment.     

Installation of mechanical ventilation in a horse stable: effects on air quality and human and equine airways

Objectives  

To examine the effects of installing a mechanical ventilation system at a riding-school stable on indoor air quality and human and horse airways.     

Are the CSF levels of 24S-hydroxycholesterol a sensitive biomarker for mild cognitive impairment?

There is a need for effective biomarkers showing whether or not a patient with mild cognitive impairment (MCI) will progress to Alzheimer's disease (AD) with dementia. At the present three cerebrospinal fluid (CSF) biomarkers are in general use: total tau, phospho-tau and beta-Amyloid. These markers are regarded to have high capacity to differentiate early AD from normal ageing. We have analysed CSF levels of a new marker for neuronal degeneration, 24S-hydroxycholesterol (24OHC) in patients with MCI. For reasons of comparison, we also analysed these levels in patients with AD. There was a significant correlation between CSF levels of 24OHC and total tau (as well as phospho-tau) in both groups of patients. Fifty percent of the patients contemplated for MCI were found to have elevated levels of 24OHC (using a 95th upper percentile set cut-off). All the MCI patients with normal levels of 24OHC had normal levels of the other markers. In patients with AD, the percentages of those with increased levels of 24OHC, tau and phospho tau were similar (55-67%). In this pilot study, we discuss the possibility that 24OHC may be a sensitive test for MCI.