Molecular dynamics simulations and neutron reflectivity as an effective approach to characterize biological membranes and related macromolecular assemblies.

In combination with other spectroscopy, microscopy, and scattering techniques, neutron reflectivity is a powerful tool to characterize biological systems. Specular reflection of neutrons provides structural information at the nanometer and subnanometer length scales, probing the composition and organization of layered materials. Currently, analysis of neutron reflectivity data involves several simplifying assumptions about the structure of the sample under study, affecting the extraction and interpretation of information from the experimental data. Computer simulations can be used as a source of structural and dynamic data with atomic resolution. We present a novel tool to compare the structural properties determined by neutron reflectivity experiments with those obtained from molecular simulations. This tool allows benchmarking the ability of molecular dynamics simulations to reproduce experimental data, but it also promotes unbiased interpretation of experimentally determined quantities. Two application examples are presented to illustrate the capabilities of the new tool. The first example is the generation of reflectivity profiles for a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayer from molecular dynamics simulations using data from both atomistic and coarse-grained models, and comparison with experimentally measured data. The second example is the calculation of lipid volume changes with temperature and composition from all atoms simulations of single and mixed 1,2-di-palmitoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine (DPPC) bilayers.

Antimicrobial peptide dendrimer interacts with phosphocholine membranes in a fluidity dependent manner: A neutron reflection study combined with molecular dynamics simulations.

The interaction mechanism of a novel amphiphilic antimicrobial peptide dendrimer, BALY, with model lipid bilayers was explored through a combination of neutron reflection and molecular dynamics simulations. 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phos-phocholine (DPPC) lipid bilayers were examined at room temperature to extract information on the interaction of BALY with fluid and gel phases, respectively. Furthermore, a 1:4 mixture of POPC and DPPC was used as a model of a phase-separated membrane. Upon interaction with fluid membranes, BALY inserted in the distal leaflet and caused thinning and disordering of the headgroups. Membrane thinning and expansion of the lipid cross-sectional area were observed for gel phase membranes, also with limited insertion to the distal leaflet. However, dendrimer insertion through the entire lipid tail region was observed upon crossing the lipid phase transition temperature of DPPC and in phase separated membranes. The results show clear differences in the interaction mechanism of the dendrimer depending on the lipid membrane fluidity, and suggest a role for lipid phase separation in promoting its antimicrobial activity.

Efficacy of periodontal treatment on glycaemic control in diabetic patients: A meta-analysis of interventional studies.

AIM: There is growing evidence that periodontal disease may favour the incidence or aggravation of diabetes and its complications. To investigate the issue, we conducted a meta-analysis of the effect of periodontal therapy on glycaemic control in diabetic patients. METHODS: A literature search was carried out using seven databases (Medline, EMBASE, LILACS, The Cochrane Library, Pascal, IADR Abstracts and Current Contents), with no language restrictions. We followed the QUOROM-recommended standards for improving the quality of reporting meta-analyses of interventional studies. RESULTS: Twenty-five studies, involving 976 subjects altogether, were included in the present systematic review. Of these, nine studies, involving a total of 485 patients, were controlled trials and were included in the meta-analysis. The standardized mean difference in HbA(1c) with the treatment of periodontal disease was 0.46 (95% CI: 0.11, 0.82). These findings suggest that periodontal treatment could lead to a significant 0.79% (95% CI: 0.19, 1.40) reduction in HbA(1c) level. CONCLUSION: The present meta-analysis represents the best information available to date that addresses this issue, and suggests that periodontal treatment could improve glycaemic control. Nevertheless, these results need to be viewed with caution because of a lack of robustness, and deficiencies in the design of some of the studies included. A randomized controlled trial with sufficient statistical power would help to confirm the results of this meta-analysis.