[Non-unions. From diagnosis to healing]. / Pseudarthrosen. Von der Diagnose bis zur Ausheilung.

Non-unions are a relevant medical and socio-economic problem. Hyper-, oligo- and atrophic non-unions as well as septic and aseptic non-unions are differentiated. Correct classification is essential for the selected therapy. The "diamond concept" describes five pillars, on which bone healing is based and that have to be considered in the treatment of non-unions: osteogenic cells (mesenchymal stem cells), osteoinduction (growth factors), osteoconduction (scaffolds), mechanical stability, and vascularization. Factors that predispose to non-union also influence fracture healing. The gold standard of therapy are still resection of the non-union, decortication and autologous bone grafting. No advantage could be proven for any of the numerous procedures in monotherapy. But the combination of various procedures - polytherapy - seems to be promising. The aim is to optimize these concepts.

Studying the deformation of arachnid slit sensilla by a fracture mechanical approach.

Slit sensilla are sensory organs which measure strains in the exoskeleton of arachnids. They occur as isolated slits, in loose groups and in close parallel arrangements known as lyriform organs or compound slit sensilla. The deformations of the slits' faces induced by far-field strains acting on groups of slits are studied using Kachanov's analytical approximations for the opening displacements of cracks, a method developed within the framework of fracture mechanics. The accuracy of the approach is assessed by comparisons with results obtained by finite element analysis. The limits of its applicability to slit sensilla are found to be reached when the lateral spacing between interacting slits is less than half their length, i.e., the method is suitable for studying single slits and loose groups but not lyriform organs. The influence of a number of geometrical parameters of slit sensilla on the deformation patterns of the faces of parallel slits in generic arrangements is studied, viz., spacing between slits, longitudinal shifts between slits, and slit length. The results are presented as opening distances along the length of the cracks and in terms of normalized diagrams that relate the opening distances at mid-length of the slits to the geometrical parameters. In addition, Kachanov's method is used to find a set of slit lengths that give rise to prescribed opening distances.

Structure-based library design: molecular modelling merges with combinatorial chemistry.

Recent advances in both computational and experimental techniques now allow a very fruitful interplay of computational and combinatorial chemistry in the structure-based design of combinatorial libraries.

Combinatorial docking and combinatorial chemistry: design of potent non-peptide thrombin inhibitors.

A computational algorithm was used to design automatically novel thrombin inhibitors that are available from a single-step chemical reaction. The compounds do not contain amide bonds, are achiral and have a molecular weight below 400. Of the 10 compounds that were synthesized, five bind to thrombin with a Ki in the nanomolar range. Subsequent X-ray structure determination of the thrombin-inhibitor complex for the best compound (Ki = 95 nM) confirms the predicted binding mode. The novel algorithm is applicable to a broad range of chemical reactions.

Prediction of binding constants of protein ligands: a fast method for the prioritization of hits obtained from de novo design or 3D database search programs.

A dataset of 82 protein-ligand complexes of known 3D structure and binding constant Ki was analysed to elucidate the important factors that determine the strength of protein-ligand interactions. The following parameters were investigated: the number and geometry of hydrogen bonds and ionic interactions between the protein and the ligand, the size of the lipophilic contact surface, the flexibility of the ligand, the electrostatic potential in the binding site, water molecules in the binding site, cavities along the protein-ligand interface and specific interactions between aromatic rings. Based on these parameters, a new empirical scoring function is presented that estimates the free energy of binding for a protein-ligand complex of known 3D structure. The function distinguishes between buried and solvent accessible hydrogen bonds. It tolerates deviations in the hydrogen bond geometry of up to 0.25 A in the length and up to 30 degrees in the hydrogen bond angle without penalizing the score. The new energy function reproduces the binding constants (ranging from 3.7 x 10(-2) M to 1 x 10(-14) M, corresponding to binding energies between -8 and -80 kJ/mol) of the dataset with a standard deviation of 7.3 kJ/mol corresponding to 1.3 orders of magnitude in binding affinity. The function can be evaluated very fast and is therefore also suitable for the application in a 3D database search or de novo ligand design program such as LUDI. The physical significance of the individual contributions is discussed.

Development of filter functions for protein-ligand docking.

Current docking methods can generate bound conformations of a ligand close to the experimentally observed structure of a protein-ligand complex. However, the scoring functions used to evaluate the potential solutions are not yet reliable enough at giving the highest ranks to the best structure predictions. One approach to this problem is the use of filter functions that are applied to all docked conformations to remove structures with certain energetically unfavorable properties. We present a computationally efficient scheme for such a postprocessing of docking results. For each of the conformations generated for a given protein-ligand complex, four properties are calculated: the fraction of the ligand volume buried inside the binding pocket, the size of lipophilic cavities along the protein-ligand interface, the solvent-accessible surface (SAS) of nonpolar parts of the ligand, and the number of close contacts between nonhydrogen-bonded polar atoms of the ligand and the protein. These four terms were used to filter out the majority of the calculated solutions and to rescore the remaining ones. On a test set of 32 protein-ligand complexes, this protocol significantly improves the accuracy of the structure predictions.

Energetic and entropic factors determining binding affinity in protein-ligand complexes.

Understanding of non-covalent interactions in protein-ligand complexes is essential in modern biochemistry and should contribute toward the discovery of new drugs. The affinity of a ligand toward its receptor falls into a range of 10-80 kJ/mol. It is related to the binding constant and corresponds to a free energy. Accordingly enthalpic and entropic effects determine binding affinity. Hydrogen bonds and lipophilic contacts are the most important contributions to protein-ligand interactions. They are governed by changes in entropy and enthalpy. Solvation and desolvation effects either of the ligand and the protein binding site play a key role in the binding process. Prerequisite for a quantitative description and subsequently for a prediction of protein-ligand interactions is a partitioning in additive group contributions. In many cases, this additivity seems to be a good approximation, however, phenomena such as conformational pre-organizations give rise for a non-additive behavior. Flexibility and mobility of the bound ligand influence binding affinity. The rare experiments separating enthalpic and entropic contributions to the binding affinity sometimes reveal surprisings results, e.g. the loss of a hydrogen bond parallels with a loss in entropy.

Towards the automatic design of synthetically accessible protein ligands: peptides, amides and peptidomimetics.

The computer program LUDI for the de novo design of protein ligands was extended so that it is now able to take into account the synthetic accessibility of the constructed molecules. As an example, the design of peptides, amides and peptidomimetics using amino acids as building blocks is described. Two new libraries containing natural and non-natural amino acids were constructed for this purpose. Conformational flexibility is taken into account by using multiple conformers for each amino acid. The program was applied to the design of ligands for the enzymes elastase, renin and thermolysin.

Current computational tools for de novo ligand design.

Several new algorithms have been proposed recently for computational de novo ligand design. Empirical scoring functions are now available to prioritize the suggested structures. The first successful applications have been reported.

Discovery and optimization of a novel class of orally active nonpeptidic endothelin-A receptor antagonists.

A novel class of endothelin-A receptor ligands was discovered by high-throughput screening. Lead structure optimization led to highly potent antagonists which can be synthesized in a short sequence. The compounds are endothelin-A-selective, are orally available, and show a long duration of action.

[Dynamic skin suture for secondary skin closure and treatment of skin defects]. / Dynamische Hautnaht zum sekundären Hautverschluss und zur Behandlung von Hautdefekten.

Dynamic skin suture exerts progressive traction to the wound margins which allows a stepwise closure of a defect. It consists of interrupted sutures with two additional plastic tubes lying parallel to the wound margins on the surface of the skin. The extracuticular slopes of the sutures and the knots pass over these tubes. This decreases local pressure on the skin. The knots are performed in a way that, once they have been tied, permits further tightening without opening them. A viscoelastic property of the skin--stress-relaxation- reduces the tension on the sutures over time and allows a further tightening. As an example for the use of this technique, the results of closures of fasciotomies in compartment syndromes are presented. In 1993, 50 fasciotomies in 35 patients were treated with dynamic suture. In 42 defects (84%) a complete obliteration was possible. In the residual 8 defects reduction of size was significant. The mean time until obliteration was 11.5 days, in average sutures were tightened 4 times. The results suggest that dynamic suture is a useful technique for repair in fasciotomies. It helps avoiding tissue transplantations. The operative procedure itself is speedy and simple. Possible indications in limited excisional defects are demonstrated in a case report.

Design, synthesis and biological activity of novel rigid amidino-phenylalanine derivatives as inhibitors of thrombin.

(3S)-(Naphthalene-2-sulfonylamino)-1-[2R-(4-amidinophenyl)-1- piperidinocarbonylethyl]-2-pyrrolidinone (1a) is a potent inhibitor of thrombin with an IC50 value by 112 times lower than that of NAPAP (racemate). The selectivity versus trypsin can be improved by incorporation of substituents on the naphthyl ring. The mode of binding of the compound was determined by X-ray crystallography.

On the use of LUDI to search the Fine Chemicals Directory for ligands of proteins of known three-dimensional structure.

It is shown that the computer program LUDI can be used to search large database of three-dimensional structures for putative ligands of proteins with known 3D structure. As an example, a subset of approximately 30,000 small molecules (with less than 40 atoms and 0-2 rotatable bonds) from the Fine Chemicals Directory has been used in the search for possible novel ligands for four different proteins (trypsin, streptavidin, purine nucleoside phosphorylase and HIV protease). For trypsin and streptavidin, known ligands or substructures of known ligands are retrieved as top-scoring hits. In addition, a number of new interesting structures are found in all considered cases. Therefore, the method holds promise to retrieve automatically protein ligands from a 3D database if the 3D structure of the target protein is known.

[Dynamic skin suture for closure of the incision defect after compartment incision]. / Dynamische Hautnaht zum Verschluss des Inzisionsdefektes nach Kompartmentspaltung.

Dynamic skin suture consists of a technique that diminishes local pressure on skin and permits progressive tightening of the sutures for stepwise incisional closure. A clinical series of 28 repairs after release of compartment syndromes shows complete closure in 22 incisions, the other 6 defects could be reduced in size. Technique, results and biological basics are discussed.

The development of a simple empirical scoring function to estimate the binding constant for a protein-ligand complex of known three-dimensional structure.

A new simple empirical function has been developed that estimates the free energy of binding for a given protein-ligand complex of known 3D structure. The function takes into account hydrogen bonds, ionic interactions, the lipophilic protein-ligand contact surface and the number of rotatable bonds in the ligand. The dataset for the calibration of the function consists of 45 protein-ligand complexes. The new energy function reproduces the binding constants (ranging from 2.5.10(-2) to 4.10(-14) M, corresponding to binding energies between -9 and -76 kJ/mol) of the dataset with a standard deviation of 7.9 kJ/mol, corresponding to 1.4 orders of magnitude in binding affinity. The individual contributions to protein-ligand binding obtained from the scoring function are: ideal neutral hydrogen bond: -4.7 kJ/mol; ideal ionic interaction: -8.3 kJ/mol; lipophilic contact: -0.17 kJ/mol A2; one rotatable bond in the ligand: +1.4 kJ/mol. The function also contains a constant contribution (+5.4 kJ/mol) which may be rationalized as loss of translational and rotational entropy. The function can be evaluated very fast and is therefore also suitable for application in a 3D database search or de novo ligand design program such as LUDI.