Browsing by Author "Pfeiffer, M."

Halorhodopsin (HR) was investigated with atomic force microscopic techniques (AFM) in aqueous solution. Two-dimensional (2D) crystals of HR were obtained by purifying an HR membrane fraction with the same buoyant density as the purple membrane (HR-PM) from the overexpressing strain Halobacterium salinarum D2. The membrane patches of HR were immobilized on mica. Images with a resolution up to 14 Angstrom were recorded. Crystals showed an orthogonal structure and the orientation of the molecules showed p42(1)2 symmetry; thus, alternate tetramers are inverted in the membrane. The crystal surface was found to display different structures depending on the imaging force used, indicating that some parts of the HR molecule are more rigid but others more compressible. From samples with single tetramers missing in the crystalline patches dimensions of the unit cell could be determined. Helix-connecting loops in single molecules of halorhodopsin were assigned. The images indicate that the large extracellular BC loop covers the whole molecule and is very flexible. (C) 2001 Academic Press.

Prospectively, with randomized segment-treatment assignment, and with blinded evaluators, lumbar motion segments in Cercopithecus monkeys were analyzed for macroscopic and radiological changes 24 weeks after nucleotomy and nucleotomy with additional intradiscal application of different hyaluronic acid formulations versus untreated control segments. The objective was to find out whether hyaluronic acid is able to influence the degenerative cascade in nonhuman primates after nucleotomy. In a similar procedure, hyaluronic acid has proven to decrease degeneration after nucleotomy in a Minipig model. This is the first such study ever undertaken in primates, thus trying to overcome the known limitations of non-primate spine models. Twenty monkeys with four segments each obtained nucleotomy in three segments and solely exposure of another control segment. Nucleotomy was performed from a transpsoatic retroperitoneal approach. Preoperative radiographs and follow-up radiographs, magnetic resonance imaging (MRI), computed tomography (CT), Q-CT with bone mineral density measurements and three-dimensional reconstruction were obtained and analyzed qualitatively and quantitatively. Segments with high-molecular-weight hyaluronic acid (Hylan G-F 20) application proved to be significantly superior over those with a standard nucleotomy in radiographs, MR images, CT scans, and macroscopic appearance at follow-up. Control segments remained unaffected. Interdependence between the different methods validated the utilized methods of quantitative radiological assessment of degeneration. Hylan G-F 20 appears to be a possible adjunct in reducing postoperative degeneration in an animal nucleotomy model. It deserves further evaluation, despite the fact that the mechanisms of its effects are still speculative.