Multiple enzyme inhibitions by histamine H3 receptor antagonists as potential procognitive agents

Novel highly affine histamine H3 receptor ligands with additional inhibitory effects on the main histamine metabolizing enzyme in the brain, N-methyltransferase, chemically show structural elements of the acetylcholinesterase inhibitor tacrine. H3 receptor antagonism, inhibition of metabolisation of neuronal histamine as well as inhibition of hydrolysis of acetylcholine are each one believed to improve reduced cognitive functions, which is useful for symptomatic treatment of Alzheimer's disease. Some of the new compounds proved in a slightly modified colorimetric Ellmann's assay to be potent inhibitors of acetylcholinesterase and of butyrylcholinesterase which is another catalytic enzyme hydrolysing acetylcholine. Some compounds with (sub)nanomolar activities on the histamine-related targets are also active in the nanomolar concentration range on both cholinesterase targets being 5- to 40-times more potent than tacrine. Preliminary structure-activity relationships could already be drawn from the small number of compounds. The compounds acting as hybrid drugs simultaneously on four different targets to enhance cognitive functions via different pathways are promising lead structures for a new approach in the treatment of Alzheimer's disease.

Poisson bracket approach to the dynamics of nematic liquid crystals: the role of spin angular momentum

Nematic liquid crystals are well modeled as a fluid of rigid rods. Starting from this model, we use a Poisson-bracket formalism to derive the equations governing the dynamics of nematic liquid crystals. We treat the spin angular momentum density arising from the rotation of constituent molecules about their centers of mass as an independent field and derive equations for it, the mass density, the momentum density, and the nematic director. Our equations reduce to the original Leslie-Ericksen equations, including the inertial director term that is neglected in the hydrodynamic limit, only when the moment of inertia for angular momentum parallel to the director vanishes and when a dissipative coefficient favoring locking of the angular frequencies of director rotation and spin angular momentum diverges. Our equations reduce to the equations of nematohydrodynamics in the hydrodynamic limit but with dissipative coefficients that depend on the coefficient that must diverge to produce the Leslie-Ericksen equations.

Effects of prosthetic treatment for shortened dental arches on oral health-related quality of life, self-reports of pain and jaw disability: results from the pilot-phase of a randomized multicentre trial

A multi-centre randomized clinical trial is under way at 14 university dental schools in Germany to compare prosthodontic treatments for the shortened dental arch (SDA). One of the aims of this pilot-study was to measure the effect of two treatment options of the SDA on oral health-related quality of life and on the Research Diagnostic Criteria (RDC) for temporomandibular disorders (TMD). Thirty-four patients participated in the pilot-study. Inclusion criteria were: all molars were missing and the presence of at least both canines and one premolar in each quadrant. Participants were randomly assigned to receive either removable partial dentures including molar replacement (RPD_group) or retain a premolar occlusion (PROC_group). The Oral Health Impact Profile (OHIP-49) and the RDC for TMD were completed by participants before treatment (pre-treatment), 6 weeks (6 wks), 6 months (6m) and 12 months (12 m) after treatment. At the 12-month follow up, data of 10 women and 11 men (mean age: 62 +/- 10 years) were available. Medians of the OHIP total-scores were as follows: RPD (n = 10), 43.5 (pre-treatment), 18.2 (6 wks), 13.3 (6m), 14.7 (12 m). PROC (n = 11): 31.8 (pre-treatment), 27.1 (6 wks), 8.8 (6m), 8.3 (12 m). Significant differences were shown for RPD_group between pre-treatment and 6m/12 m and for PROC_group between pre-treatment and 6m. There were no significant differences between treatment groups at any time. Within each group, an improvement of life-quality was observed. No significant difference could be reported between the two therapy concepts. This may be due to the low sample size within the pilot study.

Advantages of CCD detectors for de novo three-dimensional structure determination in single-particle electron microscopy

For three-dimensional (3D) structure determination of large macromolecular complexes, single-particle electron cryomicroscopy is considered the method of choice. Within this field, structure determination de novo, as opposed to refinement of known structures, still presents a major challenge, especially for macromolecules without point-group symmetry. This is primarily because of technical issues: one of these is poor image contrast, and another is the often low particle concentration and sample heterogeneity imposed by the practical limits of biochemical purification. In this work, we tested a state-of-the art 4 k x 4 k charge-coupled device (CCD) detector (TVIPS TemCam-F415) to see whether or not it can contribute to improving the image features that are especially important for structure determination de novo. The present study is therefore focused on a comparison of film and CCD detector in the acquisition of images in the low-to-medium ( approximately 10-25 A) resolution range using a 200 kV electron microscope equipped with field emission gun. For comparison, biological specimens and radiation-insensitive carbon layers were imaged under various conditions to test the image phase transmission, spatial signal-to-noise ratio, visual image quality and power-spectral signal decay for the complete image-processing chain. At all settings of the camera, the phase transmission and spectral signal-to-noise ratio were significantly better on CCD than on film in the low-to-medium resolution range. Thus, the number of particle images needed for initial structure determination is reduced and the overall quality of the initial computed 3D models is improved. However, at high resolution, film is still significantly better than the CCD camera: without binning of the CCD camera and at a magnification of 70 kx, film is better beyond 21 A resolution. With 4-fold binning of the CCD camera and at very high magnification (> 300 kx) film is still superior beyond 7 A resolution.

Photon channelling in foams

Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction epsilon. We then construct two-dimensional Voronoi foams, replace the cell edges by channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling only occurs in a finite range of epsilon.

Synchronization of rotating helices by hydrodynamic interactions

Some types of bacteria use rotating helical flagella to swim. The motion of such organisms takes place in the regime of low Reynolds numbers where viscous effects dominate and where the dynamics is governed by hydrodynamic interactions. Typically, rotating flagella form bundles, which means that their rotation is synchronized. The aim of this study is to investigate whether hydrodynamic interactions can be at the origin of such a bundling and synchronization. We consider two stiff helices that are modelled by rigidly connected beads, neglecting any elastic deformations. They are driven by constant and equal torques, and they are fixed in space by anchoring their terminal beads in harmonic traps. We observe that, for finite trap strength, hydrodynamic interactions do indeed synchronize the helix rotations. The speed of phase synchronization decreases with increasing trap stiffness. In the limit of infinite trap stiffness, the speed is zero and the helices do not synchronize.

Pathogenesis of levodopa-induced dyskinesia: focus on D1 and D3 dopamine receptors

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa therapy for Parkinson's disease. Taking advantage of a monkey brain bank constituted to study the pathophysiology of levodopa-induced dyskinesia, we here report the changes affecting D1, D2 and D3 dopamine receptors within the striatum of four experimental groups of non-human primates: normal, parkinsonian, parkinsonian treated with levodopa without or with dyskinesia. We also report the possible role of arrestin and G protein-coupled receptor kinases.

Piperidine-containing histamine H3 receptor antagonists of the carbamate series: the alkyl derivatives

A series of N-alkyl urethanes, potential histamine H3 receptor antagonists, was prepared. Carbamate derivatives were synthesized from appropriate isocyanates and N-piperidinoalkan-1-ols. The novel compounds were evaluated for histamine H3 receptor activity in vitro on the guinea pig ileum. Some selected compounds were tested in vivo after p.o. application to mice and in vitro for selectivity towards other histamine receptors (H1, H2) in functional assays in the guinea pig. The most potent H3 receptor antagonist in vitro was compound 14 (pA2 = 7.2). Compound 14 was equipotent at M3 receptors and lacked H3 receptor activity in vivo. Predictions of octanol-water partition coefficient (Pallas) and metabolic fate (MetabolExpert, METEOR) were used to explore potential reasons for this absence of in vivo activity.

Traumatic brain injury results in mast cell increase and changes in regulation of central histamine receptors

Experimental fluid-percussion models produce brain injury by rapidly injecting saline into the closed cranium of rats. In this study our purpose was to determine how the central histaminergic system, which controls excitability and neurotransmitter release through G-protein coupled receptors, is affected by the pathophysiology of traumatic brain injury. We found that mast cell infiltration, as a result of the trauma, occurred primarily in the injured cortex and did not proceed beyond the fimbria of the hippocampus. In comparing injured animals with controls we found that H3 receptor binding densities are significantly decreased bilaterally in the cortex but are significantly increased bilaterally in the thalamus. H3 receptor binding densities may well be affected by mast cell secretion of mediators (i.e. histamine, heparin, leukotrienes), evidenced by detection of a cosecreted enzyme (mast cell tryptase) in the extracellular region. Moreover, we detected significant decreases in H1 and H3 receptor mRNA as well as Cu/Zn-dependent superoxide dismutase (SOD) mRNA in the thalamic region closest to the trauma. These significant decreases delineate the extent of cellular damage because of trauma and may underlie sustained cognitive and motor deficits displayed by these animals.

Search for histamine H3 receptor antagonists with combined inhibitory potency at Ntau-methyltransferase: ether derivatives

With the recent development of new hybrid compounds having histamine H3 receptor antagonist with combined histamine Ntau-methyltransferase (HMT) inhibitory potency an innovative approach was described in the research of novel lead compounds modulating histaminergic neurotransmission. Several compounds containing an ether moiety derived from the recently published 4-(3-piperidinopropoxy)phenylaminoquinoline derivatives (like FUB 836), were synthesized in this study and tested for their affinity at cloned human histamine H3 (hH3) receptors and on the inhibition of rat HMT. Besides different heterocycles, e.g. nitro- or amino-substituted pyridines, quinolines, benzothiazole or pyrroline, three classes of compounds were produced: heteroaromatic 3-piperidinopropyl ethers, keto- or imino-substituted 4-(3-piperidinopropyl)phenyl ethers and 4-(3-piperidinopropyl)phenyl ethers with substituted (alkyl)aminopyridines. Whereas the (3-piperidinopropoxy)heterocycles showed only moderate activities on both test models, the 4-(3-piperidinopropoxy)phenyl derivatives were identified as potent histamine H3 receptor ligands and/or HMT inhibitors. Ki values up to 0.42 nM were found for the affinity to the hH3 receptor. HMT inhibitory potency was identified with IC50 values about 0.3 microM for the most potent compounds in this series. Comparison of the pyridine-containing derivatives to recently published quinoline analogues showed a decrease in potencies for the pyridines. The dual activity, H3 receptor affinity and HMT inhibition, was moderate to good. For all compounds affinities at hH3 receptors were higher than their inhibitory HMT potencies. The described new histamine H3 receptor antagonists with an ether moiety represent a further promising step in our investigations for a dual activity.

Unexpected partial H1-receptor agonism of imidazole-type histamine H3-receptor antagonists lacking a basic side chain

OBJECTIVE AND DESIGN

The putative partial H1-receptor agonism of some H3-receptor antagonists belonging to the proxifan series was characterized in a functional in-vitro assay using guinea-pig ileum.

METHODS

Whole segments of guinea-pig ileum were mounted in Tyrode's solution under isotonic conditions in the presence of atropine (10(-7) M) and were cumulatively treated with histamine as an internal reference. After washout, the putative H1-receptor agonists were added cumulatively to determine agonist potency (pEC50) and intrinsic activity (Emax) relative to histamine. Maximal or supramaximal concentrations of partial agonists, or sufficient concentrations of H1-receptor antagonists were incubated for 3-15 min prior to construction of a second concentration-effect curve to histamine in order to calculate partial agonist or antagonist affinity for the H1 receptor (pKP or pA2 value, respectively).

RESULTS

Several analogues of FUB 372 displayed low H1-receptor affinities (pA2 or pKP 4.2-5.5) except for a methyl benzoate derivative (pA2 = 6.81, Schild plot slope unity). FUB 372, four ortho-substituted derivatives (R = F, CH3, OCH3, CF3), and ciproxifan were weak contractile agents (Emax 9-38%, pEC50 4.73-5.68, histamine: 6.70) susceptible to antagonism by the H1-antihistaminergic drug mepyramine (2.10(-9)-10(-7) M). Agonist potency and H1-receptor affinity of these compounds did not correlate with the data of a set of H1-histaminergic 2-phenylhistamines bearing the same substituents.

CONCLUSIONS

A specific subset of proxifans related to FUB 372 and ciproxifan represent a unique type of H1-receptor agonists lacking a basic side chain.

Corrim-based alignment for improved speed in single-particle image processing

The technique of single-particle electron cryomicroscopy is currently making possible the 3D structure determination of large macromolecular complexes at constantly increasing levels of resolution. Work at resolution now attainable requires many thousands of individual images to be processed computationally. The most time-consuming step of the image-processing procedure is usually the iterative alignment of individual particle images against a set of reference images derived from a preliminary 3-D structure. We have developed an improved multireference alignment procedure based on interpolated cross-correlation images (corrims) that results in an approximately 8-fold acceleration of the iterative alignment steps. These corrims can be used to restrict the number of image-alignment calculations by narrowing down the set of reference images. Another improvement in alignment speed has been achieved by optimising the software and its implementation on many parallel processors. This new corrim-based refinement has been found to work well with two different alignment algorithms, the commonly used "fast alignment by separate translational/rotational searches" and "exhaustive alignment by polar coordinates."

Aufbau und Erprobung eines neuartigen Meßsystems für die dentale Biomechanik – Meßprinzip und Beispielmessungen des Hexapod-Meß-Systems / Design and Testing of a Novel Measuring Set-up for Use in Dental Biomechanics – Measuring Principle and Exemplary Measurements with the Hexapod Measuring System

A novel measuring set-up based on a hexapod system for use in dental biomechanics is described. It was specially developed to measure force/deflection characteristics of different dental materials and devices. The functionability and suitability of the system for use in experimental biomechanics were investigated in two different studies. In a first study the micro mobility of prosthetic telescopic crowns prior to and after simulated wear was determined to investigate the influence of wear processes on the stability of the anchorage elements and thus of prostheses. This study investigated the ability of the setup to load a specimen with high forces or torques of up to 100 Newton. The second study looked at the force/deflection characteristics of orthodontic anchorage pins used in orthodontics to additionally stabilize the anchorage unit, for example during molar movement. In this study specimens were loaded with small forces of less than 10 Newton, as are typically used in orthodontics. Using the setup, the deflection behaviour of these devices under high and low loading was measured at a resolution of approximately one micrometer or one angular second.

Learning a new behavioral strategy in the shuttle-box increases prefrontal dopamine

Using microdialysis from medial prefrontal cortex of gerbils during aversive auditory conditioning in the shuttle-box we have previously shown a transient increase of dopamine efflux correlated with the establishment of avoidance behavior. We hypothesized that the acquisition of a new behavioral strategy is generally accompanied by this extra prefrontal dopamine release. The present experiment aimed at further testing this hypothesis. In a pre-training period in the shuttle-box the gerbils acquired an active avoidance response by generalizing two different tone signals to a GO-meaning (change of shuttle-box compartment). Thereafter, they were subjected in relearning sessions to differentially associate the known tone stimuli with GO- and NOGO- (no change of shuttle-box compartment) conditions, respectively. The following formation of discrimination behavior led to a similar extra dopamine increase as found during establishment of the avoidance strategy. This significant enhancement was limited to rapidly relearning individuals. Furthermore, the dopamine increase attenuated in these animals with increasing performance during the course of the discrimination training, similar to the retrieval stage of the avoidance strategy. Therefore, the dopamine system seems to be critically involved in the initial formation of associations for new behavioral strategies, i.e. learning. We assume that the prefrontal dopamine increase during initial learning of the complex discrimination behavior indicates an involvement of working memory principles and a goal-directed formation of a behavioral strategy.

Therapeutic implications of constitutive activity of receptors: the example of the histamine H3 receptor

Some G-protein-coupled receptors display constitutive activity, that is spontaneous activity in the absence of agonist: a proportion of the receptor population adopts a conformation that can bind and activate G proteins. Whereas this was mainly shown to occur with recombinant or pathologically mutated receptors, the physiological relevance of the process has remained debated. We have adressed this question in the case of the histamine H3 receptor, a presynaptic inhibitory receptor regulating histamine release in brain. Having identified a neutral antagonist and inverse agonists with variable intrinsic activity, we show that the native H3 receptor in brain displays high constitutive activity in vitro and, in vivo, controls the release of endogenous histamine. This implies that inverse agonists with high intrinsic activity should be preferred for therapeutic application as "cognitive enhancers" in several psychiatric disorders.

Poisson-bracket approach to the dynamics of nematic liquid crystals

We use the general Poisson-bracket formalism for obtaining stochastic dynamical equations for slow macroscopic fields to derive the equations that govern the dynamics of nematic liquid crystals in both their nematic and isotropic phases. For uniaxial molecules, we calculate the Poisson bracket between the tensorial nematic order parameter Q and the momentum density g, as well as those between all pairs of conserved quantities. We show that the full nonlinear hydrodynamical equations for the nematic phase derived in this formalism are identical to the nonlinear Ericksen-Leslie equations. We also obtain the complete dynamical equations for the slow dynamics of the tensorial nematic order parameter Q valid both in the isotropic and the nematic phase. They differ from those obtained by other techniques only in the values of kinetic coefficients and in the number of nonlinear terms in Q, which are present.

Automatic CTF correction for single particles based upon multivariate statistical analysis of individual power spectra

Three-dimensional electron cryomicroscopy of randomly oriented single particles is a method that is suitable for the determination of three-dimensional structures of macromolecular complexes at molecular resolution. However, the electron-microscopical projection images are modulated by a contrast transfer function (CTF) that prevents the calculation of three-dimensional reconstructions of biological complexes at high resolution from uncorrected images. We describe here an automated method for the accurate determination and correction of the CTF parameters defocus, twofold astigmatism and amplitude-contrast proportion from single-particle images. At the same time, the method allows the frequency-dependent signal decrease (B factor) and the non-convoluted background signal to be estimated. The method involves the classification of the power spectra of single-particle images into groups with similar CTF parameters; this is done by multivariate statistical analysis (MSA) and hierarchically ascending classification (HAC). Averaging over several power spectra generates class averages with enhanced signal-to-noise ratios. The correct CTF parameters can be deduced from these class averages by applying an iterative correlation procedure with theoretical CTF functions; they are then used to correct the raw images. Furthermore, the method enables the tilt axis of the sample holder to be determined and allows the elimination of individual poor-quality images that show high drift or charging effects.

[Development of a periodontium-approximated specimen holder for attrition studies of telescopic crowns]

To enable attritional studies on telescopic crowns, a specimen holder has been constructed that is intended to simulate, in zero approximation, the biomechanical properties of abutments bearing telescopic crowns. The specimen holder consists essentially of a system with two metal "concertinas" with different elasticity constants reflecting the different biomechanical parameters for periodontium and bone. The biomechanical processes in the periodontium are too complex to be simulated accurately in vitro. Nevertheless, the specimen holder described here enables the forces acting during insertion and removal of a partial denture to be accommodated elastically in the angular and axial directions, to simulate the possible degrees of freedom of the abutments in situ. In this way, the unavoidable errors of specimen fixation are rendered tolerable, so that local preferential wear is decisively reduced.

Piperidine-containing histamine H3 receptor antagonists of the carbamate series: the influence of the additional ether functionality

Recently novel leads for histamine H3 receptor antagonists of the non-imidazole type have been described. As a continuation of this research eleven new carbamate derivatives possessing an additional ether functionality were prepared. The compounds were evaluated in vitro for their antagonist activity on isolated organs of guinea-pig (GP) H3 as well as H2, H1, and M3 receptors, respectively. All compounds investigated possessed moderate antagonist affinities at guinea-pig histamine H3 receptors (pA2 6.11-6.76). An ether functionality introduced in different places of the lipophilic part of carbamates differently influenced activity and selectivity toward H3, M3, and other histamine receptors tested.