Piperazine modification in 2,4,6-triaminopyrimidine derivatives as histamine H4 receptor ligands

The human histamine H4 receptor (hH4R) is a promising new target in the therapy of inflammatory and immunomodulatory diseases. The 2,4,6-triaminopyrimidine structure has been established as a potent hH4R affinity scaffold. By using the inverse agonist ST-1012 as reference ligand, piperazine modifications were performed to get larger structural variations. Therefore, different spacers were introduced into the lead structure and the influence on affinity of this basic element was evaluated. While a short distance between aminopyrimidine and basic moiety is beneficial, a lipophilic group in the eastern part is necessary to maintain hH4R affinity.

Rectification of self-propelled particles by symmetric barriers

The motion of self-propelled particles can be rectified by asymmetric or ratchetlike periodic patterns in space. Here we show that a nonzero average drift can already be induced in a periodic potential with symmetric barriers when the self-propulsion velocity is also symmetric and periodically modulated but phase-shifted against the potential. In the adiabatic limit of slow rotational diffusion we determine the mean drift analytically and discuss the influence of temperature. In the presence of asymmetric barriers, modulating the self-propulsion can largely enhance the mean drift or even reverse it.

Brief report: first identification of H₄ histamine receptor in healthy salivary glands and in focal sialadenitis in Sjögren's syndrome

OBJECTIVE

The conventional H(1) and H(2) histamine receptors have >10,000-fold lower avidity for histamine than H(4) histamine receptor, which has been implicated in autoimmune diseases. This study was undertaken to compare H(4) histamine receptor levels in the salivary glands (SGs) of healthy controls with those in the SGs of patients with primary Sjögren's syndrome (SS).

METHODS

H(4) histamine receptor messenger RNA (mRNA) was analyzed using real-time quantitative polymerase chain reaction, and the receptor protein was examined using immunostaining. Effects of the H(4) histamine receptor agonist ST-1006 on cytokine synthesis by human SG (HSG) cells were analyzed using xMAP technology and enzyme-linked immunosorbent assay.

RESULTS

Healthy SGs contained H(4) histamine receptor mRNA. The receptor protein was localized to the acinar and ductal epithelial cells. H(4) histamine receptor agonist stimulated HSG cells to produce the cytokines interleukin-8 and vascular endothelial growth factor. SS patients had low H(4) histamine receptor levels.

CONCLUSION

H(1) and H(2) histamine receptor antagonists are not effective in the treatment of autoimmune diseases. However, such antagonists do not affect the newly discovered H(4) histamine receptor. Dendritic cells and lymphocytes are nonprofessional histamine-producing cells, which produce histamine at 100-1,000-fold lower rates than mast cells do. Saliva contains only 0.31-12.4 ng/ml histamine, which is too low to stimulate H(1) or H(2) histamine receptor, but stimulates H(4) histamine receptor half maximally. Our findings show that H(4) histamine receptor is strongly expressed in tubuloacinar SG cells, which emphasizes the role of these cells in the pathogenesis of SS.

Inertial microfluidics with multi-particle collision dynamics

Using the method of multi-particle collision dynamics (MPCD), we investigate inertial focussing in microfluidic channels that gives rise to the Segré-Silberberg effect. At intermediate Reynolds numbers, we model the motion of a spherical colloid in a circular microchannel under pressure-driven flow. We determine the radial distribution function and show how its width and the location of its maximum are strongly influenced by the colloid size and the Reynolds number of the Poiseuille flow. We demonstrate that MPCD is well suited for calculating mean values for the lift force acting on the colloid in the cross-sectional plane and for its mean axial velocity. We introduce a Langevin equation for the cross-sectional motion whose steady state is the Boltzmann distribution that contains the integrated lift force as potential energy. It perfectly coincides with the simulated radial distribution function.

Molecular pharmacological profile of a novel thiazolinone-based direct and selective 5-lipoxygenase inhibitor

BACKGROUND AND PURPOSE

The potency of many 5-lipoxygenase (5-LOX) inhibitors depends on the cellular peroxide tone and the mechanism of 5-LOX enzyme activation. Therefore, new inhibitors that act regardless of the mode of enzyme activation need to be developed. Recently, we identified a novel class of thiazolinone-based compounds as potent 5-LOX inhibitors. Here, we present the molecular pharmacological profile of (Z)-5-(4-methoxybenzylidene)-2-(p-tolyl)-5H-thiazol-4-one, compound C06.

EXPERIMENTAL APPROACH

Inhibition of 5-LOX product formation was determined in intact cells [polymorphonuclear leukocytes (PMNL), rat basophilic leukaemia-1, RAW264.7] and in cell-free assays [homogenates, 100, 000×g supernatant (S100), partially purified 5-LOX] applying different stimuli for 5-LOX activation. Inhibition of peroxisome proliferator-activated receptor (PPAR), cytosolic phospholipase A(2) (cPLA(2) ), 12-LOX, 15-LOX-1 and 15-LOX-2 as well as cyclooxygenase-2 (COX-2) were measured in vitro.

KEY RESULTS

C06 induced non-cytotoxic, direct 5-LOX inhibition with IC(50) values about 0.66 µM (intact PMNL, PMNL homogenates) and approximately 0.3 µM (cell-free PMNL S100, partially purified 5-LOX). Action of C06 was independent of the stimulus used for 5-LOX activation and cellular redox tone and was selective for 5-LOX compared with other arachidonic acid binding proteins (PPAR, cPLA(2) , 12-LOX, 15-LOX-1, 15-LOX-2, COX-2). Experimental results suggest an allosteric binding distinct from the active site and the C2-like domain of 5-LOX.

CONCLUSIONS AND IMPLICATIONS

C06 was identified as a potent selective direct 5-LOX inhibitor exhibiting a novel and unique mode of action, different from other established 5-LOX inhibitors. This thiazolinone may possess potential for intervention with inflammatory and allergic diseases and certain types of cancer.

The Randomized Shortened Dental Arch Study

The scientific evidence concerning prosthodontic care for the shortened dental arch (SDA) is sparse. This randomized multicenter study aimed to compare two common treatment options: removable partial dental prostheses (RPDPs) for molar replacement vs. no replacement (SDA). One of the hypotheses was that the follow-up treatment differs between patients with RPDPs and patients with SDAs during the 5-year follow-up period.

Two hundred and fifteen patients with complete molar loss in one jaw were included in the study. Molars were either replaced by RPDPs or not replaced according to the SDA concept.

A mean number of 4.2 (RPDP) and 2.8 (SDA) treatments for biological or technical reasons occurred during the 5-year observation time per patient. Concerning the biological aspect, no significant differences between the groups could be shown, whereas treatment arising from technical reasons was significantly more frequent for the RPDP group. When the severity of treatment was analyzed, a change over time was evident. When, at baseline, only follow-up treatment with minimal effort is required, over time there is a continuous increase to moderate and extensive effort observed for both groups ( Controlled-trials.com number ISRCTN97265367).

Numerical investigations of the loading behaviour of a prefabricated non-rigid bar system

The aim of this study has been to systematically evaluate the loading behaviour of a novel pre-fabricated chair-side SFI-Bar(®) bar system supported by two implants using finite element (FE) analysis. Two series of FE models were created of the bar placed on two idealised implants and embedded in idealised bone segments using CAD data. In the first series, the inter-implant distance varied from 10 to 26mm; the second series consisted of a bar with a fixed implant distance of 26mm and varying horizontal fitting inaccuracy from 0.0 to 0.3mm. The bar was loaded vertically at 500 N. In all simulations, the regions with the greatest amount of stress were concentrated on the connecting elements of the bar and the bar itself. A slight increase in stress was observed with decreasing inter-implant distance. With a non-zero fitting inaccuracy, no clear correlation was observed between the amount of play and the stress distribution in the system. For a perfect fit, an obvious increase in stress was found in the implant and strain in the implant bed. With respect to the excessive static loading performed in our simulations and the resulting loading behaviour, we conclude that the SFI-Bar is a system suitable for clinical application.

[Preventive strategies in prosthetic dentistry]

Despite the success in preventing oral diseases, the prevalence of tooth loss in the German population remains high and increases with age. Today, the advances in prosthetic dentistry allow necessary tooth replacement following preventive strategies-after considering benefits and risks. Modern treatment options improve the overall prognosis of the stomatognathic system and the quality of life of the affected patients significantly. Hereby, adverse iatrogenic effects can be minimized or even completely avoided by extending the traditional treatment spectrum, e.g., using adhesively fixed restorations and implant-supported restorations, and refraining from placing restorations that are unnecessary from the medical point of view. Generally, patients benefit greatly from prosthetic treatment and the achieved health gain is remarkably high. It encompasses not only the recovery of the impaired oral functions but also extends to the whole human organism, including nutrition, digestion, musculoskeletal system, as well as mental and social well-being.

Motor-driven bacterial flagella and buckling instabilities

Many types of bacteria swim by rotating a bundle of helical filaments also called flagella. Each filament is driven by a rotary motor and a very flexible hook transmits the motor torque to the filament. We model it by discretizing Kirchhoff's elastic-rod theory and develop a coarse-grained approach for driving the helical filament by a motor torque. A rotating flagellum generates a thrust force, which pushes the cell body forward and which increases with the motor torque. We fix the rotating flagellum in space and show that it buckles under the thrust force at a critical motor torque. Buckling becomes visible as a supercritical Hopf bifurcation in the thrust force. A second buckling transition occurs at an even higher motor torque. We attach the flagellum to a spherical cell body and also observe the first buckling transition during locomotion. By changing the size of the cell body, we vary the necessary thrust force and thereby obtain a characteristic relation between the critical thrust force and motor torque. We present a elaborate analytical model for the buckling transition based on a helical rod which quantitatively reproduces the critical force-torque relation. Real values for motor torque, cell body size, and the geometry of the helical filament suggest that buckling should occur in single bacterial flagella. We also find that the orientation of pulling flagella along the driving torque is not stable and comment on the biological relevance for marine bacteria.

Dynamics of semi-flexible tethered sheets : a simulation study using stochastic rotation dynamics

The dynamics of a semi-flexible sheet or tethered membrane in a solvent is studied using the method of stochastic rotation dynamics. Hydrodynamic interactions between different parts of the sheet are naturally included in this method. We confirm the scaling law for the radius of gyration versus sheet size predicted for a self-avoiding tethered membrane. The mean-square displacement shows both sub-diffusive and diffusive behavior similar to linear polymers. In the intermediate scattering function the sub-diffusive behavior appears as stretched exponential which we reproduce in our simulations. Thereby, we confirm an early prediction between the roughness and the sub-diffusion exponent derived from Zimm dynamics (E. Frey, D.R. Nelson, J. Phys. I 1, 1715 (1991)). Finally, we show that the diffusion coefficient of the square sheet is inversely proportional to the edge length of the sheet again in good agreement with theoretical predictions.

A colloidal model system with tunable disorder: solid-fluid transition and discontinuities in the limit of zero disorder

We study a colloidal model system where disorder can be continuously tuned from no disorder--corresponding to a system that can crystallize--to large disorder where geometrical frustration occurs. The model system consists of colloidal particles with screened electrostatic repulsion. They can only move on single lines which are parallel and equidistant to each other. We introduce disorder by modulating the particle line density. The system exhibits a solid-to-fluid transition which we study by the structure factor and the temporal evolution of the mean-square distance of nearest neighbors on neighboring lines. A determining feature is the occurrence of discontinuities when disorder is tuned to zero. We observe that the peak height of the pair correlation function in the solid phase does not extrapolate to the value of the perfect crystal. Similarly, the mean interaction energy and the screening length at which the solid-fluid transition occurs seem to be discontinuous when the limit of zero disorder is approached.

Histamine H1, H3 and H4 receptors are involved in pruritus

Histamine has long been recognised as a classical inducer of pruritus. However, the specific mechanism of histamine-induced itch has still not been fully understood. The H1 and H4 receptor appear to be key components in the induction of itch. The specific role of the H3 receptor in histamine-induced itch remains unclear. The aim of our study was to investigate the role of the four known histamine receptors (H1-4) in acute itch in mice. Intradermal injection of the selective H3R inverse agonist pitolisant induced strong itch in mice. Pitolisant (50 nmol/injection)-induced pruritus could be completely blocked by a combined treatment with the H1R antagonist cetirizine (15 mg/kg) and the H4R antagonist JNJ 7777120 (15 mg/kg), whereas the H2R antagonist ranitidine (15 mg/kg) failed to inhibit the scratch response. Next, expression and function of histamine receptors on sensory neurons isolated from dorsal root ganglia of mice were investigated. As the itch sensation results from the excitation of sensory nerves in the skin, we further focused on skin specific sensory neurons. Therefore, neurons were retrograde labelled from the skin by means of a fluorescent tracer. Expression of H1R, H3R and H4R on skin innervating sensory neurons was detected. By single-cell calcium imaging, it was demonstrated that histamine induces a calcium increase in a subset of (skin-specific) sensory neurons via activation of the H1R and H4R as well as inhibition of the H3R. It is assumed that the decreased threshold in response to H3R antagonism activates H1R and H4R on sensory neurons, which in turn results in the excitation of histamine-sensitive afferents and therefore elicits the sensation of itch.

Metachronal waves in a chain of rowers with hydrodynamic interactions

Hair-like appendages called cilia on the surface of a microorganism such as Paramecium or Opalina beat highly synchronized and form so-called metachronal waves that travel along the surfaces. In order to study under what principal conditions these waves form, we introduce a chain of beads, called rowers, each periodically driven by an external force on a straight line segment. To implement hydrodynamic interactions between the beads, they are considered point-like. Two beads synchronize in antiphase or in phase depending on the positive or negative curvature of their driving-force potential. Concentrating on in-phase synchronizing rowers, we find that they display only transient synchronization in a bulk fluid. On the other hand, metachronal waves with wavelengths of 7-10 rower distances emerge, when we restrict the range of hydrodynamic interactions either artificially to nearest neighbors or by the presence of a bounding surface as in any relevant biological system.

Force-extension curves of bacterial flagella

Bacterial flagella assume different helical shapes during the tumbling phase of a bacterium but also in response to varying environmental conditions. Force-extension measurements by Darnton and Berg explicitly demonstrate a transformation from the coiled to the normal helical state (N.C. Darnton, H.C. Berg, Biophys. J. 92, 2230 (2007)). We here develop an elastic model for the flagellum based on Kirchhoff's theory of an elastic rod that describes such a polymorphic transformation and use resistive force theory to couple the flagellum to the aqueous environment. We present Brownian-dynamics simulations that quantitatively reproduce the force-extension curves and study how the ratio Γ of torsional to bending rigidity and the extensional rate influence the response of the flagellum. An upper bound for Γ is given. Using clamped flagella, we show in an adiabatic approximation that the mean extension, where a local coiled-to-normal transition occurs first, depends on the logarithm of the extensional rate.

Lead identification and optimization of diaminopyrimidines as histamine H4 receptor ligands

BACKGROUND

The human histamine H(4) receptor (hH(4)R) is a promising new target in the therapy of inflammatory or immune system diseases.

METHODS

For the development of new hH(4)R ligands, a broad virtual screening was performed and two hits were identified. Their annelated heterocyclic core was optimized with regard to affinity and potency.

RESULTS

Pharmacological characterization of the resulting diaminopyrimidines revealed different agonist and antagonist properties within the same scaffold.