Neutron reflectivity of supported membranes incorporating terminally anchored polymers: Protrusions vs. blisters.

The effect of terminally anchored chains on the structure of lipid bilayers adsorbed at the solid/water interface was characterized by neutron reflectivity. In the studied system, the inner leaflet, closer to the substrate, consisted of head-deuterated 1,2-distearoyl-sn-glycero-3-phosphorylcholine (DSPC) and the outer leaflet comprised a mixture of DSPC and polyethylene glycol (PEG) functionalized 1,2-distearoyl-sn-glycero-3-phosphoethanolamine. The DSPC headgroups were deuterated to enhance sensitivity and demarcate the bilayer/water interface. The effect on the inner and outer headgroup layers was characterized by w(1/2), the width at half-height of the scattering length density profile. The inner headgroup layer was essentially unperturbed while w(1/2) of the outer layer increased significantly. This suggests that the anchored PEG chains give rise to headgroup protrusions rather than to blister-like membrane deformations.

Atomic force microscopy of polymer brushes: colloidal versus sharp tips.

Force versus distance profiles acquired by atomic force microscopy probe the structure and interactions of polymer brushes. An interpretation utilizing the Derjaguin approximation and assuming local compression of the brush is justified when colloidal probes are utilized. The assumptions underlying this approach are not satisfied for sharp tips, and deviations from this model were reported for experiments and simulations. The sharp-tip force law proposed assumes that the free energy penalty of insertion into the brush is due to the osmotic pressure of the unperturbed brush. This static force law is in semiquantitative agreement with the simulation results of Murat and Grest (Murat, M.; Grest, G. S. Macromolecules 1996, 29, 8282).

Ternary protein adsorption onto brushes: strong versus weak.

Attractive interactions between proteins and polyethylene glycol (PEG) give rise to ternary adsorption within PEG brushes. Experimental evidence suggests two ternary adsorption modes: (i) weak, due to nonspecific weak attraction between PEG monomers and the surface of the protein, as exemplified by serum albumin and (ii) strong, due to strong binding of PEG segments to specific protein sites as it occurs for PEG antibodies, which can involve the terminal adsorption of free chain ends or backbone adsorption due to binding to interior chain segments. Ternary adsorption affects the capacity of brushes to repress protein adsorption. The strong adsorption of antibodies can trigger an immune response that may affect the biocompatibility of the surface. Theoretical adsorption isotherms and protein concentration profiles of the three cases are compared for "parabolic" brushes, allowing for the grafting density, 1/Sigma, and degree of polymerization of the PEG chains, N, as well as the volume and surface area of the proteins. The amount of adsorbed protein per unit area, Gamma, exhibits a mode-specific maximum in all three cases. For backbone and weak adsorption, Gamma approximately N, whereas for terminal adsorption, Gamma approximately N0. In every case, the concentration profile of adsorbed proteins, ctern(z), exhibits a maximum at zmax>0 that shifts outward as Sigma decreases; zmax=0 occurs only for weak and backbone adsorption at a high Sigma value.

Primary versus ternary adsorption of proteins onto PEG brushes.

Polyethylene glycol (PEG) brushes are used to reduce protein adsorption at surfaces. Their design needs to allow for two leading adsorption modes at the brush-coated surface. One is primary adsorption at the surface itself. The second is ternary adsorption within the brush as a result of weak PEG-protein attraction. We present a scaling theory of the equilibrium adsorption isotherms allowing for concurrent primary and ternary adsorption. The analysis concerns the weak adsorption limit when individual PEG chains do not bind proteins. It also addresses two issues of special relevance to brushes of short PEGs: the consequences of large proteins at the surface protruding out of a shallow brush and the possibility of marginal solvent conditions leading to mean-field behavior. The simple expressions for the adsorption isotherms are in semiquantitative agreement with experiments.

Are symptoms of peripheral neuropathy more prevalent in patients with Gaucher disease?

BACKGROUND: A previous epidemiological survey from an American referral clinic noted a high incidence of neurological symptoms among patients with type I (non-neuronopathic) Gaucher disease all of whom were treated with specific enzyme replacement. OBJECTIVES: The current study replicates the above in a larger cohort of Ashkenazi Jewish patients with at least one N370S mutation which has been assumed to be protective of neurological involvement. About half the patients had mild disease and were untreated. Methods - Self-reporting questionnaires were sent to patients and their significant others as socio-economically matched controls. RESULTS: There was no significant difference between groups in incidence of concomitant diseases and medications, except patients who reported a significantly higher incidence of vitamin B(12) deficiency and gammopathies. Patients reported significantly higher incidence of virtually all symptoms and signs of peripheral neuropathy and a significantly higher number of symptoms than controls (mean 4.4 vs 2.4). CONCLUSIONS: The conclusion of this study, as of the seminal study, is that the high incidence of neurological complaints in patients with the non-neuronopathic form of Gaucher disease should be viewed in the context of concomitant illnesses, specifically, vitamin B(12) deficiency and gammopathies, regardless of the need for enzyme replacement therapy.

Hybridization at a surface: the role of spacers in DNA microarrays.

Flexible spacer chains are utilized to enhance the hybridization of terminally anchored oligonucleotide probes of DNA microarrays. A polymer physics approach identifies an underlying mechanism and yields guidelines for the optimal spacer length in terms of the effect on the equilibrium state. For low grafting densities, the dominant effect arises because of the decimation in the number of accessible chain configurations due to the impenetrable surface. Opposing trends are found for long targets and for short targets. At higher grafting densities, different brush regimes introduce an extra hybridization penalty. A novel brush regime is obtained for long neutral spacers and short targets at intermediate ionic strength where the chain stretching is due to the electrostatic interactions between the probes.

Brush effects on DNA chips: thermodynamics, kinetics, and design guidelines.

In biology experiments, oligonucleotide microarrays are contacted with a solution of long nucleic acid targets. The hybridized probes thus carry long tails. When the surface density of the oligonucleotide probes is high enough, the progress of hybridization gives rise to a polyelectrolyte brush due to mutual crowding of the nucleic acid tails. The free-energy penalty associated with the brush modifies both the hybridization isotherms and the rate equations: the attainable hybridization is lowered significantly as is the hybridization rate. When the equilibrium hybridization fraction, x(eq), is low, the hybridization follows a Langmuir type isotherm, x(eq)/(1 - x(eq)) = c(t)K where c(t) is the target concentration and K is the equilibrium constant. K is smaller than its bulk value by a factor (n/N)(2/5) due to wall effects where n and N denote the number of bases in the probe and the target. At higher x(eq), when the brush is formed, the leading correction is x(eq)/(1 - x(eq)) = c(t)K exp - const'x(eq)(2/3) - x(B)(2/3) where x(B) corresponds to the onset of the brush regime. The denaturation rate constant in the two regimes is identical. However, the hybridization rate constant in the brush regime is lower, the leading correction being exp -const' x(2/3) - x(B)(2/3).

Effects of stacking on the configurations and elasticity of single-stranded nucleic acids.

Stacking interactions in single-stranded nucleic acids give rise to configurations of an annealed rod-coil multiblock copolymer. Theoretical analysis identifies the following resulting signatures for long homopolynucleotides: a nonmonotonic dependence of size on temperature, the corresponding effects on cyclization and a plateau in the extension force law. Explicit numerical results for polydeoxyadenylate [poly(dA)] and polyriboadenylate [poly(rU)] are presented.

Sensitivity, specificity, and the hybridization isotherms of DNA chips.

Competitive hybridization, at the surface and in the bulk, lowers the sensitivity of DNA chips. Competitive surface hybridization occurs when different targets can hybridize with the same probe. Competitive bulk hybridization takes place when the targets can hybridize with free complementary chains in the solution. The effects of competitive hybridization on the thermodynamically attainable performance of DNA chips are quantified in terms of the hybridization isotherms of the spots. These relate the equilibrium degree of the hybridization to the bulk composition. The hybridization isotherm emerges as a Langmuir isotherm modified for electrostatic interactions within the probe layer. The sensitivity of the assay in equilibrium is directly related to the slope of the isotherm. A simpler description is possible, in terms of c(50) values specifying the bulk composition corresponding to 50% hybridization at the surface. The effects of competitive hybridization are important for the quantitative analysis of DNA chip results, especially when used to study point mutations.

Inhibition of potentially anti-apoptotic proteins by antisense protein kinase C-alpha (Isis 3521) and antisense bcl-2 (G3139) phosphorothioate oligodeoxynucleotides: relationship to the decreased viability of T24 bladder and PC3 prostate cancer cells.

Isis 3521 and G3139 are 20- and 18-mer phosphorothioate oligonucleotides, respectively, targeted to the protein kinase C (PKC)-alpha and bcl-2 mRNAs. Treatment of T24 bladder and PC3 prostate carcinoma cells with full-length and 3'-truncation mutants of Isis 3521 causes down-regulation of PKC-alpha protein and mRNA. However, at the level of a 15-mer and shorter, down-regulation of mRNA expression is no longer observed. Further, no diminution in cellular viability, as measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide assay, in response to increasing concentrations of paclitaxel, can be observed for these shorter oligomers. These observations not only indicate that PKC-alpha protein expression can be down-regulated by both RNase H-dependent and -independent mechanisms but also that down-regulation of PKC-alpha is insufficient by itself to "chemosensitize" cells. G3139, which down-regulates bcl-2 protein and mRNA expression, also down-regulates PKC-alpha protein and mRNA expression but not that of PKC-betaI, -epsilon, or -zeta. However, the down-regulation of PKC-alpha and bcl-2 are not linked. When the carrier Eufectin 5 is employed, only bcl-2 is down-regulated in both T24 and PC3 cells at 50 nM oligonucleotide concentration. At 100 nM, both bcl-2 and PKC-alpha expression are down-regulated, and only at this concentration can "chemosensitization" to paclitaxel and carboplatin be observed. In contrast, the down-regulation of bcl-2 seems to be linked with that of RelA (p65). However, this too is also not sufficient for chemosensitization, even though it leads to the loss of expression of genes under the putative control of nuclear factor-kappaB and to detachment of the cells from plastic surfaces. These results underscore the complexity of the intracellular requirements for the initiation of chemosensitization to anti-neoplastic agents.

The effect of a hospitalist service with nurse discharge planner on patient care in an academic teaching hospital.

PURPOSE: To evaluate the impact of implementing a hospitalist service with a nurse discharge planner in an academic teaching hospital. SUBJECTS AND METHODS: Inpatient medicine service was provided by hospitalists, general internists, and specialists. Service personnel were identical except that the hospitalist service also had a nurse discharge planner. Hospitalists attended 4 months per year (compared with the 1 month by most other attending physicians) and had no outpatient responsibilities during the ward months. Patients were admitted alternately based on resident call schedule. Major outcomes included average costs of hospitalization, length of stay, and resource utilization. Quality measures included inpatient mortality, 30-day readmission rates, and satisfaction of patients, residents and students. RESULTS: Hospitalist-attended services had lower mean (+/- SD) inpatient costs per patient ($4289 +/- $6512) compared with specialist-staffed services ($6066 +/- $7550, P < 0.0001), with a trend toward lower costs when compared with generalist-attended services ($4850 +/- $7027, P = 0.11). Hospitalist services had shorter mean lengths of stay (4.4 +/- 4.0 days), compared with generalists (5.2 +/- 5.2 days) and specialists (6.0 +/- 5.5 days, P < 0.0001 for hospitalists vs. both groups). Readmission rates were similar in all groups. Mortality rates were higher in the specialist group [5.0% (44 of 874)] compared with hospitalists [2.2% (18 of 829)] and generalists [2.6% (20 of 761), P = 0.002 for specialists vs. both groups, P = 0.09 for generalists vs hospitalists]. Satisfaction results were uniformly high in all groups, with no significant differences. CONCLUSION: Hospitalist services with a nurse discharge planner were associated with lower average cost and shorter average length of hospital stay, without any apparent compromise in clinical outcomes or patient satisfaction.

Extension of rod-coil multiblock copolymers and the effect of the helix-coil transition

The extension elasticity of rod-coil mutliblock copolymers is analyzed for two experimentally accessible situations. In the quenched case, when the architecture is fixed by the synthesis, the force law is distinguished by a sharp change in the slope. In the annealed case, where interconversion between rod and coil states is possible, the resulting force law is sigmoid with a pronounced plateau. This last case is realized, for example, when homopolypeptides capable of undergoing a helix-coil transition are extended from a coil state.

Early stages of homopolymer collapse

Interest in the protein folding problem has motivated a wide range of theoretical and experimental studies of the kinetics of the collapse of flexible homopolymers. In this paper, a phenomenological model is proposed for the kinetics of the early stages of homopolymer collapse following a quench from temperatures above to below the straight theta temperature. In the first stage, nascent droplets of the dense phase are formed, with little effect on the configurations of the bridges that join them. The droplets then grow by accreting monomers from the bridges, thus causing the bridges to stretch. During these two stages, the overall dimensions of the chain decrease only weakly. Further growth of the droplets is accomplished by the shortening of the bridges, which causes the shrinking of the overall dimensions of the chain. The characteristic times of the three stages scale as N0, N(1/5), and N(6/5), respectively, where N is the degree of polymerization of the chain.

Grafted poly(ethylene oxide) brushes as nonfouling surface coatings.

The identification of design criteria for the prevention of surface fouling by protein adsorption has been an elusive research goal. The current ideas in this domain assume two different directions. One focuses on correlating protein adsorption with macroscopic surface properties such as the water wettability. The second approach involves tailoring the molecular interactions between the adsorbing proteins and the surface. In this paper, we focus on the experimental results and theoretical ideas concerned with tuning the interfacial forces by means of terminally grafted PEO chains.

Multidisciplinary evidence-based medicine journal clubs: curriculum design and participants' reactions.

BACKGROUND: Evidence-based medicine (EBM) is becoming an accepted educational paradigm in medical education at a variety of levels. It focuses on identifying the best evidence for medical decision making and applying that evidence to patient care. METHODS: Three EBM journal clubs were developed at the West Virginia University School of Medicine. One was for senior medical students, another for residents, and the third for primary care faculty members. In each, the sessions stressed answering clinical questions arising from actual patient-care issues. The curricular structure and development of the journal clubs are described. Participants anonymously evaluated aspects of the journal clubs regarding their educational value with Likert scale questions. RESULTS: Faculty members and residents generally gave high evaluations to all aspects of the EBM journal clubs. Student evaluations were more mixed. For each of the evaluation questions, the student means were lower than those of faculty and residents. However the differences reached statistical significance only in the responses to the usefulness of the sessions in understanding the medical literature (P < 0.01). Residents and faculty rated the EBM sessions more favorably than grand rounds or the resident lecture series. CONCLUSIONS: The establishment of evidence-based medicine journal clubs is feasible, and learners seem to value the sessions. More developed learners may gain more from the experience than those earlier in their medical education.

Appalachian perspective on modifiable risk factors in coronary artery disease: how well are we doing?

BACKGROUND: Despite recognition of modifiable risk factors and available and effective life-style and pharmacologic therapies, many individuals have unrecognized or untreated risk factors for coronary artery disease. METHODS: Using MEDLINE, we searched for relevant review articles and clinical trials related to hypertension, hyperlipidemia, diabetes mellitus, smoking, physical activity, obesity, and psychologic risk factors for coronary artery disease. We carefully reviewed the literature and statistics on modifiable risk factors and identified appropriate physician interventions. RESULTS: A large amount of information is available on coronary artery disease and modifiable risk factors. Much of the data focuses on diagnosis and treatment to goal. CONCLUSIONS: Coronary artery disease remains the number one cause of death in the United States and West Virginia, even though specific guidelines have been established for detection and treatment. The medical community needs to be more aggressive in managing modifiable risk factors.