ASH choosing wisely

The Choosing Wisely(R) campaign challenges medical societies to identify 5 tests, procedures, or treatments within each specialty's clinical domain that are offered to patients despite an absence of evidence demonstrating benefit or, in some cases, despite evidence demonstrating disutility or harm

Slow amyloid nucleation via α-helix-rich oligomeric intermediates in short polyglutamine-containing huntingtin fragments

The 17-amino-acid N-terminal segment (httNT) that leads into the polyglutamine (polyQ) segment in the Huntington\u27s disease protein huntingtin (htt) dramatically increases aggregation rates and changes the aggregation mechanism, compared to a simple polyQ peptide of similar length. With polyQ segments near or above the pathological repeat length threshold of about 37, aggregation of htt N-terminal fragments is so rapid that it is difficult to tease out mechanistic details. We describe here the use of very short polyQ repeat lengths in htt N-terminal fragments to slow this disease-associated aggregation. Although all of these peptides, in addition to httNT itself, form α-helix-rich oligomeric intermediates, only peptides with QN of eight or longer mature into amyloid-like aggregates, doing so by a slow increase in β-structure. Concentration-dependent circular dichroism and analytical ultracentrifugation suggest that the httNT sequence, with or without added glutamine residues, exists in solution as an equilibrium between disordered monomer and α-helical tetramer. Higher order, α-helix rich oligomers appear to be built up via these tetramers. However, only httNTQN peptides with N=8 or more undergo conversion into polyQ β-sheet aggregates. These final amyloid-like aggregates not only feature the expected high β-sheet content but also retain an element of solvent-exposed α-helix. The α-helix-rich oligomeric intermediates appear to be both on- and off-pathway, with some oligomers serving as the pool from within which nuclei emerge, while those that fail to undergo amyloid nucleation serve as a reservoir for release of monomers to support fibril elongation. Based on a regular pattern of multimers observed in analytical ultracentrifugation, and a concentration dependence of α-helix formation in CD spectroscopy, it is likely that these oligomers assemble via a four-helix assembly unit. PolyQ expansion in these peptides appears to enhance the rates of both oligomer formation and nucleation from within the oligomer population, by structural mechanisms that remain unclear. © 2011 Elsevier Ltd

Polyglutamine Disruption of the Huntingtin Exon 1 N Terminus Triggers a Complex Aggregation Mechanism

Simple polyglutamine (polyQ) peptides aggregate in vitro via a nucleated growth pathway directly yielding amyloid-like aggregates. We show here that the 17-amino-acid flanking sequence (HTTNT) N-terminal to the polyQ in the toxic huntingtin exon 1 fragment imparts onto this peptide a complex alternative aggregation mechanism. In isolation, the HTTNT peptide is a compact coil that resists aggregation. When polyQ is fused to this sequence, it induces in HTTNT, in a repeat-length dependent fashion, a more extended conformation that greatly enhances its aggregation into globular oligomers with HTTNT cores and exposed polyQ. In a second step, a new, amyloid-like aggregate is formed with a core composed of both HTTNT and polyQ. The results indicate unprecedented complexity in how primary sequence controls aggregation within a substantially disordered peptide and have implications for the molecular mechanism of Huntington\u27s disease

Efficacy of Preemptive Dexamethasone versus Methylprednisolone in the Management of Postoperative Discomfort and Pain after Mandibular Third Molar Surgery: A Systematic Review and Meta-Analysis

The corticosteroids have been used for preemptive management of surgical sequelae after mandibular third molar extraction. The aim of this article was to review the efficacy of methylprednisolone versus dexamethasone in the management of postsurgical pain, swelling, and trismus after mandibular third molar surgery. Randomized, double-blinded studies from PubMed, CINAHL, Scopus, DOSS, Cochrane central, and Web of Science were identified by using a search strategy. Randomized controlled trials evaluating the efficacy of use of dexamethasone versus methylprednisolone for mandibular third molar extraction were only considered. The studies involving the use of any other corticosteroid agent were excluded. Outcomes assessed were postoperative pain, the number of rescue analgesics required, swelling, trismus, and adverse events. The search strategy yielded 1046 articles for title and abstract screening, out of which only seven studies were included in the systematic review after full text screening. There was considerable heterogeneity between the studies with regards to the method as well as the parameters assessed. Risk of bias was low in three studies and unclear in other four studies. On pooled analyses, there was no significant difference with respect to pain, rescue analgesics, and swelling in the test and the control group. Forest plot analysis showed that dexamethasone had lesser trismus in early postoperative period (postoperative day 2) as compared to methylprednisolone. None of the included studies reported any adverse effects. Both the corticosteroids have similar efficacy in reducing the postoperative pain and swelling; however, dexamethasone showed statistically significant difference from methylprednisolone in reducing trismus (estimated standardized mean difference of −0.69 mm; 95% CI: −1.01 to −0.38; p<0.0001) in the early postoperative period. However, due to statistical heterogeneity, quality of the evidence for the review was low to moderate. Hence, more studies with larger study sample and low risk of bias are needed to confirm these results

Kinetically Competing Huntingtin Aggregation Pathways Control Amyloid Polymorphism and Properties

In polyglutamine (polyQ) containing fragments of the Huntington’s disease protein huntingtin (htt), the N-terminal 17 amino acid htt^NT segment serves as the core of α-helical oligomers whose reversible assembly locally concentrates the polyQ segments, thereby facilitating polyQ amyloid nucleation. A variety of aggregation inhibitors have been described that achieve their effects by neutralizing this concentrating function of the htt^NT segment. In this paper we characterize the nature and limits of this inhibition for three means of suppressing htt^NT-mediated aggregation. We show that the previously described action of htt^NT peptide-based inhibitors is solely due to their ability to suppress the htt^NT-mediated aggregation pathway. That is, under htt^NT inhibition, nucleation of polyQ amyloid formation by a previously described alternative nucleation mechanism proceeds unabated and transiently dominates the aggregation process. Removal of the bulk of the htt^NT segment by proteolysis or mutagenesis also blocks the htt^NT-mediated pathway, allowing the alternative nucleation pathway to dominate. In contrast, the previously described immunoglobulin-based inhibitor, the antihtt^NT V_L 12.3 protein, effectively blocks both amyloid pathways, leading to stable accumulation of nonamyloid oligomers. These data show that the htt^NT-dependent and -independent pathways of amyloid nucleation in polyQ-containing htt fragments are in direct kinetic competition. The results illustrate how amyloid polymorphism depends on assembly mechanism and kinetics and have implications for how the intracellular environment can influence aggregation pathways