Two Dimensional Oblique Molecular Packing within a Model Peptide Ribbon Aggregate.

A10 K (A=alanine, K=lysine) model peptides self-assemble into ribbon-like ß-sheet aggregates. Here, we report an X-ray diffraction investigation on a flow-aligned dispersion of these self-assembly structures. The two-dimensional wide-angle X-ray scattering pattern suggests that peptide pack in a two-dimensional oblique lattice, essentially identical to the crystalline packing of polyalanine, An (for n>4). One side of the oblique unit cell, corresponding to the anti-parallel ß-sheet, is oriented along the ribbon's axis. Together with recently published small angle X-ray scattering data of the same system, this work thus yields a detailed description of the self-assembled ribbon aggregates, down to the molecular length scale. Notably, our results highlight the importance of the crystalline peptide packing within its self-assembly aggregates, which is often neglected.

Self-Assembly of Model Amphiphilic Peptides in Nonaqueous Solvents: Changing the Driving Force for Aggregation Does Not Change the Fibril Structure.

Within the homologous series of amphiphilic peptides AnK, both A8K and A10K self-assemble in water to form twisted ribbon fibrils with lengths around 100 nm. The structure of the fibrils can be described in terms of twisted ß-sheets extending in the direction of the fibrils, laminated to give a constant cross section of 4 nm by 8 nm. The finite width of the twisted ribbons can be reasonably explained within a simple thermodynamic model, considering a free energy penalty for the stretching of hydrogen bonds along the twisted ß-sheets and an interfacial free energy gain for the lamination of the hydrophobic ß-sheets. In this study, we characterize the self-assembly behavior of these peptides in nonaqueous solutions as a route to probe the role of hydrophobic interaction in fibril stabilization. Both peptides, in methanol and N,N-dimethylformamide, were found to form fibrillar aggregates with the same ß-sheet structure as in water but with slightly smaller cross-sectional sizes. However, the gel-like texture, the slow relaxation in dynamic light scattering experiments, and a correlation peak in the small-angle X-ray scattering pattern highlighted enhanced interfibril interactions in the nonaqueous solvents in the same concentration range. This could be ascribed to a higher effective volume of the aggregates because of enhanced fibril growth and length, as suggested by light scattering and cryogenic transmission electron microscopy analyses. These effects can be discussed considering how the solvent properties affect the different energetic contributions (hydrophobic, electrostatic, and hydrogen bonding) to fibril formation. In the analyzed case, the decreased hydrogen bonding propensity of the nonaqueous solvents makes the hydrogen bond formation along the fibril a key driving force for peptide assembly, whereas it represents a nonrelevant contribution in water.

Arrested dynamics in a model peptide hydrogel system.

We report here on a peptide hydrogel system, which in contrast to most other such systems, is made up of relatively short fibrillar aggregates, discussing resemblance with colloidal rods. The synthetic model peptides A8K and A10K, where A denotes alanine and K lysine, self-assemble in aqueous solutions into ribbon-like aggregates having an average length 〈L〉 on the order of 100 nm and with a diameter d≈ 6 nm. The aggregates can be seen as weakly charged rigid rods and they undergo an isotropic to nematic phase transition at higher concentrations. Translational motion perpendicular to the rod axis gets strongly hindered when the concentration is increased above the overlap concentration. Similarly, the rotational motion is hindered, leading to very long stress relaxation times. The peptide self-assembly is driven by hydrophobic interactions and due to a net peptide charge the system is colloidally stable. However, at the same time short range, presumably hydrophobic, attractive interactions appear to affect the rheology of the system. Upon screening the long range electrostatic repulsion, with the addition of salt, the hydrophobic attraction becomes more dominant and we observe a transition from a repulsive glassy state to an attractive gel-state of the rod-like peptide aggregates.

Tube to ribbon transition in a self-assembling model peptide system.

Peptides that self-assemble into ß-sheet rich aggregates are known to form a large variety of supramolecular shapes, such as ribbons, tubes or sheets. However, the underlying thermodynamic driving forces for such different structures are still not fully understood, limiting their potential applications. In the AnK peptide system (A = alanine, K = lysine), a structural transition from tubes to ribbons has been shown to occur upon an increase of the peptide length, n, from 6 to 8. In this work we analyze this transition by means of a simple thermodynamic model. We consider three energy contributions to the total free energy: an interfacial tension, a penalty for deviating from the optimal ß-sheet twist angle, and a hydrogen bond deformation when the ß-sheets adopt a specific self-assembled structure. Whilst the first two contributions merely provide similar constant energy offsets, the hydrogen bond deformations differ depending on the studied structure. Consequently, the tube structure is thermodynamically favored for shorter AnK peptides, with a crossover at n≈ 13. This qualitative agreement of the model with the experimental observations shows, that we have achieved a good understanding of the underlying thermodynamic features within the self-assembling AnK system.

Slow Dissolution Kinetics of Model Peptide Fibrils.

Understanding the kinetics of peptide self-assembly is important because of the involvement of peptide amyloid fibrils in several neurodegenerative diseases. In this paper, we have studied the dissolution kinetics of self-assembled model peptide fibrils after a dilution quench. Due to the low concentrations involved, the experimental method of choice was isothermal titration calorimetry (ITC). We show that the dissolution is a strikingly slow and reaction-limited process, that can be timescale separated from other rapid processes associated with dilution in the ITC experiment. We argue that the rate-limiting step of dissolution involves the breaking up of inter-peptide ß-sheet hydrogen bonds, replacing them with peptide-water hydrogen bonds. Complementary pH experiments revealed that the self-assembly involves partial deprotonation of the peptide molecules.

Twisted Ribbon Aggregates in a Model Peptide System.

The model peptides A8K and A10K self-assemble in water into ca. 100 nm long ribbon-like aggregates. These structures can be described as ß-sheets laminated into a ribbon structure with a constant elliptical cross-section of 4 by 8 nm, where the longer axis corresponds to a finite number, N ≈ 15, of laminated sheets, and 4 nm corresponds to a stretched peptide length. The ribbon cross-section is strikingly constant and independent of the peptide concentration. High-contrast transmission electron microscopy shows that the ribbons are twisted with a pitch λ ≈ 15 nm. The self-assembly is analyzed within a simple model taking into account the interfacial free energy of the hydrophobic ß-sheets and a free energy penalty arising from an increased stretching of hydrogen bonds within the laminated ß-sheets, arising from the twist of the ribbons. The model predicts an optimal value N, in agreement with the experimental observations.

Ultratrace Detection of Histamine Using a Molecularly-Imprinted Polymer-Based Voltammetric Sensor.

Rapid and cost-effective analysis of histamine, in food, environmental, and diagnostics research has been of interest recently. However, for certain applications, the already-existing biological receptor-based sensing methods have usage limits in terms of stability and costs. As a result, robust and cost-effective imprinted polymeric receptors can be the best alternative. In the present work, molecularly-imprinted polymers (MIPs) for histamine were synthesized using methacrylic acid in chloroform and acetonitrile as two different porogens. The binding affinity of the MIPs with histamine was evaluated in aqueous media. MIPs synthesized in chloroform displayed better imprinting properties for histamine. We demonstrate here histamine MIPs incorporated into a carbon paste (CP) electrode as a MIP-CP electrode sensor platforms for detection of histamine. This simple sensor format allows accurate determination of histamine in the sub-nanomolar range using an electrochemical method. The sensor exhibited two distinct linear response ranges of 1 × 10-10-7 × 10-9 M and 7 × 10-9-4 × 10-7 M. The detection limit of the sensor was calculated equal to 7.4 × 10-11 M. The specificity of the proposed electrode for histamine is demonstrated by using the analogous molecules and other neurotransmitters such as serotonin, dopamine, etc. The MIP sensor was investigated with success on spiked serum samples. The easy preparation, simple procedure, and low production cost make the MIP sensor attractive for selective and sensitive detection of analytes, even in less-equipped laboratories with minimal training.

Partial weightbearing is not necessary after cementless total hip arthroplasty: a two-year prospective randomized study on 100 patients.

The purpose of this study was to evaluate the effects of partial and full weightbearing after cementless total hip arthroplasty over a two year follow-up period. Fifty-nine women and 41 men (average age 61 years) received an uncemented Spotorno stem and were randomised into a full and a partial weightbearing group. No significant difference was found between the groups with regard to the Merle d' Aubigne hip score, VAS pain level, shaft migration or radiographic signs of bony ingrowth. All femoral components seemed radiologically well-fixed and showed bone ingrowth at 24 months. Provided that solid initial fixation is obtained full weightbearing immediately after cementless total hip arthroplasty using a hydroxyapatite-coated Spotorno-type femoral shaft component can be recommended.

SAXS/WAXS Investigation of Amyloid-ß(16-22) Peptide Nanotubes.

This brief report presents an X-ray scattering investigation of self-assembled nanotubes formed by a short peptide. X-ray scattering methods enable multiscale structural elucidation of these nanotubes in solution under the same conditions involved in the self-assembly process. In particular, the dimensions of nanotubes and the crystalline organization within their walls can be determined quantitatively. This is illustrated in the case of amyloid-ß(16-22) peptide nanotubes.

Multiscale Structural Elucidation of Peptide Nanotubes by X-Ray Scattering Methods.

This mini-review presents the structural investigations of the self-assembled peptide nanotubes using X-ray scattering techniques. As compared to electron microscopy, scattering methods enable studies of nanotubes in solution under the appropriate physicochemical conditions and probe their formation mechanism. In addition, a combination of X-ray scattering methods allow the elucidation of structural organization from the molecular scale to the dimension of nanotubes.

Decreasing glenoid inclination improves function in shoulders with simulated massive rotator cuff tears.

BACKGROUND: A massive rotator cuff tear leads to poor shoulder function as evidenced by diminished glenohumeral abduction and superior translation of the humeral head compared to its normal position. The inclination angle of the glenoid has been associated with rotator cuff tears. The objective of this study was to quantify the effect of a decreased glenoid inclination angle on glenohumeral kinematics during active abduction in shoulders with a simulated, massive rotator cuff tear. METHODS: Eight fresh-frozen full upper extremities were tested using a dynamic shoulder testing apparatus. After recording the kinematics of the intact shoulder, a massive rotator cuff tear was surgically simulated. An osteotomy of the glenoid was then performed and the inclination angle was decreased by 30 degrees . The translation of the humeral head during abduction and the maximum abduction angle were recorded. FINDINGS: With an intact rotator cuff minimal humeral head translation on the glenoid occurred and the maximum abduction angle was mean 85.5 degrees (SD 7.4 degrees ). A massive rotator cuff tear resulted in superior translation of the humeral head with impingement on the acromion. The maximum abduction angle was mean 15.5 degrees (SD 9.4 degrees ). Decreasing the inclination angle of the glenoid resulted in a significant reduction of superior humeral head translation during abduction and there was no impingement on the acromion. The maximum abduction achieved was mean 28.5 degrees (SD 17.0 degrees ). INTERPRETATION: From a clinical perspective the reduced superior translation may decrease shoulder pain since the humeral head no longer impinges on the acromion. Further investigations are necessary to assess if the improvement in abduction is clinically significant.

Recombinant human bone morphogenetic protein-2 for treatment of open tibial fractures: a prospective, controlled, randomized study of four hundred and fifty patients.

BACKGROUND: The treatment of open fractures of the tibial shaft is often complicated by delayed union and nonunion. The objective of this study was to evaluate the safety and efficacy of the use of recombinant human bone morphogenetic protein-2 (rhBMP-2; dibotermin alfa) to accelerate healing of open tibial shaft fractures and to reduce the need for secondary intervention. METHODS: In a prospective, randomized, controlled, single-blind study, 450 patients with an open tibial fracture were randomized to receive either the standard of care (intramedullary nail fixation and routine soft-tissue management [the control group]), the standard of care and an implant containing 0.75 mg/mL of rhBMP-2 (total dose of 6 mg), or the standard of care and an implant containing 1.50 mg/mL of rhBMP-2 (total dose of 12 mg). The rhBMP-2 implant (rhBMP-2 applied to an absorbable collagen sponge) was placed over the fracture at the time of definitive wound closure. Randomization was stratified by the severity of the open wound. The primary outcome measure was the proportion of patients requiring secondary intervention because of delayed union or nonunion within twelve months postoperatively. RESULTS: Four hundred and twenty-one (94%) of the patients were available for the twelve-month follow-up. The 1.50-mg/mL rhBMP-2 group had a 44% reduction in the risk of failure (i.e., secondary intervention because of delayed union; relative risk = 0.56; 95% confidence interval = 0.40 to 0.78; pairwise p = 0.0005), significantly fewer invasive interventions (e.g., bone-grafting and nail exchange; p = 0.0264), and significantly faster fracture-healing (p = 0.0022) than did the control patients. Significantly more patients treated with 1.50 mg/mL of rhBMP-2 had healing of the fracture at the postoperative visits from ten weeks through twelve months (p = 0.0008). Compared with the control patients, those treated with 1.50 mg/mL of rhBMP-2 also had significantly fewer hardware failures (p = 0.0174), fewer infections (in association with Gustilo-Anderson type-III injuries; p = 0.0219), and faster wound-healing (83% compared with 65% had wound-healing at six weeks; p =0.0010). CONCLUSIONS: The rhBMP-2 implant was safe and, when 1.50 mg/mL was used, significantly superior to the standard of care in reducing the frequency of secondary interventions and the overall invasiveness of the procedures, accelerating fracture and wound-healing, and reducing the infection rate in patients with an open fracture of the tibia.

Low-intensity ultrasound enhances maturation of callus after segmental transport.

The purpose of this study was to determine whether low-intensity ultrasound can be used to enhance callus maturation. Fifteen-millimeter bone defects at the metatarsal bones of sheep were treated with a segmental bone transport for 16 days. The callus formations in the bone defects were allowed to mature for 63 days before the animals were sacrificed. Eighteen sheep were operated on and divided into two groups. One group was treated with low-intensity ultrasound for 20 minutes per day, whereas the other group served as an untreated control group. Biomechanical tests after removal of the metatarsals showed significantly higher axial compression stiffness and significantly higher indentation stiffness of callus tissue in the healing zone in the group treated with ultrasound. Also, histologic analysis of the cortical defect zone showed significantly more callus formation and more active zones of endochondral ossification in the group treated with ultrasound. Stimulation of callus maturation by ultrasound is possible, similar to stimulation of fresh fracture healing, and may be used to shorten clinical treatment times.

Tourniquets may increase postoperative swelling and pain after internal fixation of ankle fractures.

UNLABELLED: Tourniquets frequently are used in orthopaedic surgery to provide a bloodless field. There is still controversy among authors regarding the benefits and potential risks of using a tourniquet. The objective of this prospective randomized study was to quantify the effect of tourniquet use on postoperative swelling, pain, and range of motion after open reduction and internal fixation of ankle fractures. Fifty-four patients with closed ankle fractures were treated surgically; 26 patients were operated on using a thigh tourniquet (Group A), and 28 patients had surgery without the use of a tourniquet (Group B). The groups of patients were similar for age, gender, fracture types, and operative procedures. There was no difference in operation time. Using a tourniquet during open reduction and internal fixation of ankle fractures did increase postoperative swelling and postoperative pain at Day 5 and at Week 6 after surgery. We found a trend for a better range of motion in the ankle until the 6-week followup in the nontourniquet group compared with the group in which the tourniquet was inflated. According to these results we do not recommend using a tourniquet for osteosynthesis of ankle fractures. LEVEL OF EVIDENCE: Therapeutic study, Level I-1 (randomized controlled trial). See the Guidelines for Authors for a complete description of levels of evidence.