A proper balance between synapse assembly and disassembly is crucial for the formation of functional neuronal circuits and synaptic plasticity in the adult brain. During development, synaptogenesis ...generates a vast excess of synapses, which are subsequently eliminated. Importantly, aberrant synaptic disassembly during development underpins many neurological disorders. Wnt secreted proteins are robust synaptogenic factors that regulate synapse assembly and function in the developing and mature brain. Recent studies show that Wnt blockade with the antagonist Dickkopf-1 (Dkk1) induces the rapid disassembly of synapses in mature neurons. Importantly, Dkk1 mediates synaptic loss induced by Amyloid-ß, a key pathogenic molecule in Alzheimer's disease (AD). These findings provide new insights into the potential contribution of dysfunctional Wnt signaling to synaptic loss observed in neurodegenerative diseases. In this review, we discuss the role of Wnt signaling in vertebrate synaptic assembly, function and maintenance, and consider how dysfunction of Wnt signaling could contribute to synaptic disassembly in neurodegenerative diseases such as AD.
1. UK-453,061 is a novel second-generation non-nucleoside reverse transcriptase inhibitor (NNRTI). Following intravenous bolus administration of UK-453,061 in male rat and infusion administration in ...dog, UK-453,061 had the following mean pharmacokinetic properties: elimination T1/2 of 1.6 and 2.4 h, CLp of 26 and 10 ml min−1 kg−1 and Vss of 1.6 and 2 l kg−1, respectively.
2. The half-lives of UK-453,061 disappearance in recombinant human CYPs 2C8, 2C9, 2A6, 2E1, 1A2, 2C19, 2D6 and 3A4 were 71, 100, 56, 101, 61, 34, 60 and 8 min, respectively. The disappearance half-life of UK-453,061 in human liver microsomes in the presence of UDPGA was 90 min.
3. Human clearance values were predicted using single-species scaling from in vivo data and from in vitro data using SimCYP. The human distribution of UK-453,061 was estimated using an in silico physiologically based pharmacokinetics (PBPK) methodology and absorption was predicted from measured physicochemical, permeability, and solubility data using GastroPlus and SimCYP. The Cmax was predicted to be 68, 185, 149% of the actual mean value using rat, dog and in vitro predicted values of human clearance at 30 mg and 53, 150, 29% of actual at 500 mg. The area under the curve (AUC) was predicted to be 73, 285 and 142% of the actual mean value using rat, dog and in vitro predicted values of human clearance at 30 mg and 52, 212 and 35% of actual at 500 mg.
4. This study demonstrates the utility of using in silico PBPK approaches to make predictions of human pharmacokinetics before dosing for the first time in humans.
Campylobacter spp. are a major contaminant of poultry. Eating undercooked chicken and handling raw poultry have been identified as risk factors for campylobacteriosis in humans. Previous studies have ...found Campylobacter spp. on 90% of poultry carcasses. In the present study, pulsed-field gel electrophoresis (PFGE) was used to assess the genetic diversity of strains on retail poultry carcasses. PFGE patterns of isolates from campylobacteriosis cases were compared to those from the poultry isolates. Over a 1-year study period (March 2000 through February 2001), whole fresh young chickens (n = 72) were obtained from three retail outlets in an urban community in the south-central United States. Campylobacter spp. were isolated from 82% of these carcasses. Strains (n = 70) were defined on the basis of their PFGE pattern. Sixty-seven percent of the carcasses from which Campylobacter spp. were isolated were contaminated with more than one PFGE-distinguishable strain. During the 1-year study period, most of the PFGE patterns (59%) were limited to isolates obtained from a single carcass. Forty-one percent of the PFGE-distinguishable strains were recovered from more than one carcass. Ninety-seven percent of the carcasses contaminated with the same strain were purchased at the same time from the same store. To examine the degree of genetic stability, four strains were followed in vitro over an estimated 1,000 doublings. The PFGE pattern of one of these isolates underwent minor changes during in vitro growth. The data indicate extensive variability in the PFGE patterns of Campylobacter spp. isolated from humans and from poultry carcasses. In spite of difficulties caused by such diversity and the fact that some carcasses are contaminated with more than one strain, the pattern variation provides a useful method for linking a particular strain to its source.
Aims The use of multiple probe substrates to evaluate the activity of drug metabolizing enzymes requires that there are no inter–substrate interactions. As part of a series of studies to develop a ...clinically useful collection of probe substrates that could be given alone or in any combination, we observed an interaction between midazolam (MDZ) and another component of the six‐drug cocktail. Published data indicated that the interacting component was likely to be chlorzoxazone. This was investigated as part of a second study. The data relating to the interaction from both studies are reported here.
Methods
Both studies were performed in 16 healthy subjects. All treatments were given orally after an overnight fast. In study 1, which was performed to a four‐period, open, crossover design, subjects received on separate occasions MDZ 5 mg, diclofenac 25 mg, a four drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg and chlorzoxazone 250 mg) and a six drug cocktail (caffeine 100 mg, mephenytoin 100 mg, debrisoquine 10 mg, chlorzoxazone 250 mg, diclofenac 25 mg and MDZ 5 mg). In study 2, which was performed to a two‐period, open, crossover design, subjects received a five drug cocktail (as the six drug cocktail in the first study, but without chlorzoxazone and with diclofenac dose increased to 50 mg) and a six drug cocktail (as five drug cocktail, with chlorzoxazone 250 mg). In both studies, blood samples were taken for measurement of plasma MDZ and 1‐hydroxy MDZ (1‐OH MDZ) concentrations. In study 1, blood samples were taken up to 12 h post‐dose while in study 2 a single sample was taken 2 h after dosing. In study 1, the potential interaction between MDZ and the other components of the six drug cocktail was assessed by comparing AUClast ratios (1‐OH MDZ/MDZ) between the two treatments. Additionally, a single sampling timepoint of 2 h post‐dose for determination of concentration, rather than AUC, ratios was established. The 2 h plasma concentration ratios from studies 1 and 2 were combined and a pooled analysis performed to compare ratios within each study (to determine the change in ratio when MDZ was dosed with and without chlorzoxazone) and between studies (to determine the consistency of the ratios when MDZ was given either as part of the two six drug cocktails or when given alone and as part of the five drug cocktail).
Results
In study 1, both the AUClast ratio and the 2 h post‐dose plasma concentration ratio were reduced when MDZ was given as part of the six drug cocktail in comparison with those for MDZ alone. This was the result of an increase in MDZ, rather than decrease in 1‐OH MDZ, concentrations and was considered to result from a reduction in first pass metabolism of MDZ. The geometric mean AUClast values (with 95% CI) for MDZ were 95.6 (79.0, 115.7) and 160.4 (133.6, 192.6) µg l−1 h when given alone and as part of the six drug cocktail, respectively. The corresponding values for 1‐OH MDZ were 789.6 (697.6, 893.6) and 791.4 (701.7, 892.6) µg l−1 h. The ratio of adjusted geometric mean AUClast ratios for the two treatments was 1.82 (90% CI 1.48, 2.23, P < 0.001). The pooled plasma 1‐OH MDZ/MDZ ratio data from both studies showed that the differences in MDZ metabolism observed in study 1 were replicated in study 2. The adjusted geometric mean 1‐OH MDZ/MDZ ratios when MDZ was given alone and as part of the six drug cocktail were 7.79 and 4.59, respectively, for study 1 (ratio 1.70, 95% CI 1.36, 2.11, P < 0.001) and 7.64 and 4.60 for study 2 (ratio 1.66, 95% CI 1.34, 2.06, P < 0.001). These data indicate that when given orally chlorzoxazone interacts with MDZ, increasing plasma MDZ concentrations. In contrast, there was no difference between the plasma 1‐OH MDZ/MDZ ratios when MDZ was given alone and as part of the five drug cocktail indicating that there were no interactions between MDZ and any of the other components of that cocktail.
Conclusions
Chlorzoxazone appears to significantly influence the pharmacokinetics of oral MDZ, probably through inhibition of first pass metabolism by CYP3A in the GI tract. Data from these studies and literature evidence showing a further interaction between chlorzoxazone and CYP1A2 substrates and questions concerning the specificity of chlorzoxazone as a probe substrate for CYP2E1, indicate that the use of chlorzoxazone in multisubstrate probe cocktails should be avoided.
Induction of cytochromes P450 Dickins, Maurice
Current topics in medicinal chemistry,
01/2004, Letnik:
4, Številka:
16
Journal Article
Recenzirano
The induction of cytochromes P450 (CYPs) has been appreciated for some time but an understanding of the mechanisms involved has been poorly understood until recently. The discovery of the role of ...nuclear receptors such as the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) has provided a major trigger for research in this area. This work has provided an explanation for species differences in hepatic induction. The production of a PXR crystal structure in the presence and absence of known high affinity ligands has offered the possibility of predicting structures which may bind to the receptor and hence act as inducing agents in man. An improvement in the technology of hepatocyte culture, access to good quality human hepatocytes and the miniaturisation of cultured preparations has meant that the potential of this technique to predict induction in man has been realised. Molecular biological techniques have also proved essential in both the science and the quantitation of CYP induction. The use of transient transfection cell based systems coupled with reporter gene assays have meant that dose response curves can be generated for many chemicals. Assays have been developed to measure the increase of the corresponding CYP mRNAs in primary hepatocytes and some cell lines with a high degree of sensitivity and specificity (allowing the quantitation of closely related CYPs). Although CYP induction is not usually considered as a major drawback in drug development, the aim should be to eliminate or reduce the inducing effects of a new drug to a minimum. Thus, it is essential to increase our understanding of the complex mechanisms that regulate induction and to pay attention to both the dose and the physicochemical and structural properties of CYP inducing agents.
The most recent information suggests two periods of glaciation separated by a considerable time interval. The first is found in the Namurian (Early Carboniferous) and may extend into the beginning of ...the Late Carboniferous. Evidence for the Carboniferous glaciation is largely or entirely redeposited, striated clasts known only from the New England area of northeastern New South Wales. These are considered to represent montane type glaciation associated with a developing alpine chain.
After a long interval, glacial deposits are then found in many parts of Australia in the Asselian, the lowest stage of the Permian, and the glaciation may extend into the beginning of the Sakmarian, the following stage. In Western Australia a number of major fluctuations are recorded in the Asselian. The end of the glaciation seems to be associated with a worldwide eustatic rise in sea-level in the Tastubian (the lower stage of the Sakmarian). After the Tastubian no direct, verifiable evidence, indicates glaciation in the Permian in Australia or any other part of the world. In Australia there is no clear evidence on the climate in the interval between the two glacial periods but in South America and other parts of the world, a warm interval is reported at this time. Most of the glacial debris is now found in sedimentary basins which were developing contemporaneously with the glaciation and is of a wet-based type. Glaciers were active on steep hinterland carrying debris in adjacent water-covered basins but how far the ice may have spread over lower lying land areas in not clear. There is no real evidence of a thick dry-based ice-sheet like that of present Antarctica.
After the Tastubian there are a number of major fluctuations in climate during the rest of the Permian. At times seasonal ice and/or perhaps icebergs may have been active, but fluctuations which were cool or warm-temperate or in some places, in Australia, even subtropical or tropical are found in the Sterlitamakian (Upper Sakmarian), beginning and end of the Baighenzhinian (Upper Artinskian), Kungurian, Kazanian and Dzhulfian, all separated probably by colder and in some cases considerably colder periods.
Comparison of the marine faunas of the Carboniferous and Permian suggests that the
Levipustula fauna may not represent as cold sea water as the
Eurydesma fauna.
The structural characteristics of cytochrome P450 substrates are summarised, showing that molecular descriptors can discriminate between chemicals of differing P450 isozyme specificity. Procedures ...for the estimation of P450 substrate binding interaction energies and rates of metabolism are described, providing specific examples in both individual compounds binding to P450s, including those of known crystal structure, and within series of structurally related chemicals. It is demonstrated that binding energy components are primarily hydrophobic/desolvation and electrostatic/hydrogen-bonded in nature, whereas electronic factors are of importance in determining variations in reaction rates. It is thus shown that the prediction of P450 substrate binding affinities and catalytic rates may be feasible, provided that sufficient structural information is available for the relevant enzyme–substrate complex.
Various contributory factors associated with the kinetics of cytochrome P450-mediated catalytic activity and the metabolic clearance of drug substrates are discussed and evaluated, based on ...literature data and physicochemical parameters. Quantitative relationships between molecular structure and biological activity for several series of P450 substrates are presented which point to certain commonalities in P450-catalyzed reactions. In particular, it appears that frontier orbital energies are especially important for the estimation of reaction rates and clearance for many P450 substrates, although occasionally these have to be combined with other descriptors, such as compound lipophilicity (in the form of log
P or log
D
74).
Compound lipophilicity is of key importance to P450 binding affinity and enzyme selectivity. Here, lipophilicity is discussed with reference to the human drug-metabolizing P450 enzymes of families ...CYP1, CYP2 and CYP3. From an extensive compilation of log P values for P450 substrates, and by analysis of relationships between partitioning energy and substrate-binding free energy, the relevance of lipophilicity and other factors pertaining to P450 binding affinity is explained, leading to the formulation of lipophilicity relationships within substrates of each human P450 enzyme involved in drug metabolism. Furthermore, log P values for P450 substrates appear to represent markers for enzyme selectivity. Together with the important roles of hydrogen bonding and π–π stacking interaction energies, the desolvation of the P450 active site makes a major contribution to the overall substrate-binding energy and, consequently, a good agreement with experimental information is reported based on this analysis.
Lipophilicity appears to have a marked bearing on P450 substrate selectivity and metabolism. Substrate binding affinity is well correlated with log P data, and substrates of a given P450 exhibit well-defined ranges of log P values.
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