α-Tocopherols modify the membrane dipole potential leading to modulation of ligand binding by P-glycoprotein.

α-Tocopherol (vitamin E) has attracted considerable attention as a potential protective or palliative agent. In vitro, its free radical-scavenging antioxidant action has been widely demonstrated. In vivo, however, vitamin E treatment exhibits negligible benefits against oxidative stress. α-Tocopherol influences lipid ordering within biological membranes and its derivatives have been suggested to inhibit the multi-drug efflux pump, P-glycoprotein (P-gp). This study employs the fluorescent membrane probe, 1-(3-sulfonatopropyl)-4-[ß[2-(di-n-octylamino)-6-naphthyl]vinyl] pyridinium betaine, to investigate whether these effects are connected via influences on the membrane dipole potential (MDP), an intrinsic property of biological membranes previously demonstrated to modulate P-gp activity. α-Tocopherol and its non-free radical-scavenging succinate analog induced similar decreases in the MDP of phosphatidylcholine vesicles. α-Tocopherol succinate also reduced the MDP of T-lymphocytes, subsequently decreasing the binding affinity of saquinavir for P-gp. Additionally, α-tocopherol succinate demonstrated a preference for cholesterol-treated (membrane microdomain enriched) cells over membrane cholesterol-depleted cells. Microdomain disruption via cholesterol depletion decreased saquinavir's affinity for P-gp, potentially implicating these structures in the influence of α-tocopherol succinate on P-gp. This study provides evidence of a microdomain dipole potential-dependent mechanism by which α-tocopherol analogs influence P-gp activity. These findings have implications for the use of α-tocopherol derivatives for drug delivery across biological barriers.

Rational targeting of subclasses of intermolecular interactions: elimination of nonspecific binding for analyte sensing.

The ability to target and control intermolecular interactions is crucial in the development of several different technologies. Here we offer a tool to rationally design liquid media systems that can modulate specific intermolecular interactions. This has broad implications in deciphering the nature of intermolecular forces in complex solutions and offers insight into the forces that govern both specific and nonspecific binding in a given system. Nonspecific binding still continues to be a problem when dealing with analyte detection across a range of different detection technologies. Here, we exemplify the problem of nonspecific binding on model membrane systems and when dealing with low-abundance protein detection on commercially available SPR technology. A range of different soluble reagents that target specific subclasses of intermolecular interactions have been tested and optimized to virtually eliminate nonspecific binding while leaving specific interactions unperturbed. Thiocyanate ions are used to target nonpolar interactions, and small reagents such as glycylglycylglycine are used to modulate the dielectric constant, which targets charge-charge and dipole interactions. We show that with rational design and careful modulation these reagents offer a step forward in dissecting the intermolecular forces that govern binding, alongside offering nonspecific binding elimination in detection systems.

Evidence for sodium metasilicate receptors on the human osteoblast cell surface; spatial localization and binding properties.

We report details of the interaction of sodium metasilicate with osteoblast cellular membranes using Fluoresceinphosphatidylethanolamine (FPE) as a fluorescent indicator of membrane interactions. Fluorescence imaging studies of the FPE-based indicator system revealed areas of localized binding that would be consistent with the presence of a structure with 'receptor-like' properties. From these results, it seems unlikely that silica binds 'non-specifically' to the osteoblast surface. Moreover, the receptors are localized into membrane domains. Such regions of the cell membrane could well be structures such as 'rafts' or other such localized domains within the membrane. The binding profile of silica with the osteoblast cell surface takes place with all the characteristics of a receptor-mediated process best represented by a cooperativity (sigmoidal) binding model with a Hill coefficient of 3.6.

Rationalising the role of Keratin 9 as a biomarker for Alzheimer's disease.

Keratin 9 was recently identified as an important component of a biomarker panel which demonstrated a high diagnostic accuracy (87%) for Alzheimer's disease (AD). Understanding how a protein which is predominantly expressed in palmoplantar epidermis is implicated in AD may shed new light on the mechanisms underlying the disease. Here we use immunoassays to examine blood plasma expression patterns of Keratin 9 and its relationship to other AD-associated proteins. We correlate this with the use of an in silico analysis tool VisANT to elucidate possible pathways through which the involvement of Keratin 9 may take place. We identify possible links with Dickkopf-1, a negative regulator of the wnt pathway, and propose that the abnormal expression of Keratin 9 in AD blood and cerebrospinal fluid may be a result of blood brain barrier dysregulation and disruption of the ubiquitin proteasome system. Our findings suggest that dysregulated Keratin 9 expression is a consequence of AD pathology but, as it interacts with a broad range of proteins, it may have other, as yet uncharacterized, downstream effects which could contribute to AD onset and progression.

Practical detection of a definitive biomarker panel for Alzheimer's disease; comparisons between matched plasma and cerebrospinal fluid.

Previous mass spectrometry analysis of cerebrospinal fluid (CSF) has allowed the identification of a panel of molecular markers that are associated with Alzheimer's disease (AD). The panel comprises Amyloid beta, Apolipoprotein E, Fibrinogen alpha chain precursor, Keratin type I cytoskeletal 9, Serum albumin precursor, SPARC-like 1 protein and Tetranectin. Here we report the development and implementation of immunoassays to measure the abundance and diagnostic capacity of these putative biomarkers in matched lumbar CSF and blood plasma samples taken in life from individuals confirmed at post-mortem as suffering from AD (n = 10) and from screened 'cognitively healthy' subjects (n = 18). The inflammatory components of Alzheimer's disease were also investigated. Employment of supervised learning techniques permitted examination of the interrelated expression patterns of the putative biomarkers and identified inflammatory components, resulting in biomarker panels with a diagnostic accuracy of 87.5% and 86.7% for the plasma and CSF datasets respectively. This is extremely important as it offers an ideal high-throughput and relatively inexpensive population screening approach. It appears possible to determine the presence or absence of AD based on our biomarker panel and it seems likely that a cheap and rapid blood test for AD is feasible.