The biomechanics of pedicle screw-based instrumentation

There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision. A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability. Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity.

Sweetening the pot: adding glycosylation to the biomarker discovery equation

BACKGROUND

Cancer has profound effects on gene expression, including a cell's glycosylation machinery. Thus, tumors produce glycoproteins that carry oligosaccharides with structures that are markedly different from the same protein produced by a normal cell. A single protein can have many glycosylation sites that greatly amplify the signals they generate compared with their protein backbones.

CONTENT

In this article, we survey clinical tests that target carbohydrate modifications for diagnosing and treating cancer. We present the biological relevance of glycosylation to disease progression by highlighting the role these structures play in adhesion, signaling, and metastasis and then address current methodological approaches to biomarker discovery that capitalize on selectively capturing tumor-associated glycoforms to enrich and identify disease-related candidate analytes. Finally, we discuss emerging technologies--multiple reaction monitoring and lectin-antibody arrays--as potential tools for biomarker validation studies in pursuit of clinically useful tests.

SUMMARY

The future of carbohydrate-based biomarker studies has arrived. At all stages, from discovery through verification and deployment into clinics, glycosylation should be considered a primary readout or a way of increasing the sensitivity and specificity of protein-based analyses.

Glycoproteomics of plasma based on narrow selectivity lectin affinity chromatography

Lectin affinity chromatography using concanavalin A (Con A), Helix pomatia agglutinin (HPA), Lycopersicon esculentum lectin (LEL), Aleuria aurantia lectin (AAL) and Lens culinaris agglutinin (LCA) was used to investigate the utility of narrow selectivity lectins in the characterization of plasma glycoproteome diversity and to recognize cancer associated aberrations in glycosylation. Following affinity chromatographic selection, proteins were tryptically digested, the peptide fragments separated by reversed phase chromatography (RPC), and fractions from RPC identified by tandem mass spectrometry. The diversity of glycosylation found with narrow selectivity lectins was generally 2/3 that of Con A and not related to protein abundance. Small groups of proteins were found with each of the affinity columns, HPA, LEL, AAL, and LCA, that changed 3-fold or more in concentration between normal and breast cancer patient plasma. Although the number of cancer patients examined was too small to validate cancer marker candidates, they are clearly worth examining in a larger, more diverse patient population.

Use of glycan targeting antibodies to identify cancer-associated glycoproteins in plasma of breast cancer patients

Immunoaffinity chromatography (IAC) was used to isolate and identify potential cancer biomarker glycoproteins by targeting disease-associated glycans. Glycoproteins were selected from plasma of disease-free and breast cancer patients with an anti-Lewis x (Le(x)) IAC column. After extensive washing of the IAC column to remove abundant proteins, the selected proteins were eluted with an acidic mobile phase and identified in two ways. The protocol used in route A involved the steps of tryptic digestion, reversed-phase chromatographic fractionation of the digest, and identification of peptides in collected RPC fractions by MALDI-MS/MS. Route B differed in that IAC-selected proteins were further fractionated by reversed-phase chromatography before proteolysis of individual chromatographic fractions and identification by MALDI-MS/MS. Route A was the more efficacious of the two protocols in total number of proteins identified. Of the 26 proteins identified, 9 were found to be potential breast cancer marker candidates based on their elevation in breast cancer patients. The potential of these candidates as cancer markers remains to be validated in much larger, more diverse populations of breast cancer patients.

Differential phase-contrast BioCD biosensor

Common-path differential phase-contrast interferometry measures the spatial gradient of surface dipole density on a bio-optical compact disk (BioCD) and is sensitive to small changes in dipole density following molecular binding of target molecules out of solution. The recognition molecules are antibody IgG proteins that are deposited in periodic patterns on the BioCD using soft lithography or photolithography on the silanized silica surfaces of dielectric mirrors. Spatial carrier-wave sideband demodulation extracts the slowly varying protein envelope that modulates the protein carrier frequency. The experimental interferometric profilometry has surface height sensitivity down to 20 pm averaged over a lateral scale of 70 microm with a corresponding scaling mass sensitivity limit of 1.5 pg/mm. Under the conditions of an IgG immunoassay with background changes caused during incubation, the scaling mass sensitivity is approximately 7 pg/mm. A saturated reverse immunoassay performed with IgG at 100 ng/ml showed false positive and false negative rates of 0.2%.

Adaptive interferometry of protein on a BioCD

Adaptive spinning-disk interferometry is capable of measuring surface profiles of a thin biolayer with subnanometer longitudinal resolution. High-speed phase modulation in the signal beam arises from the moving surface height profile on the spinning disk and is detected as a homodyne signal via dynamic two-wave mixing. A photorefractive quantum-well device performs as an adaptive mixer that compensates disk wobble and vibration while it phase-locks the signal and reference waves in the phase quadrature condition (pi/2 relative phase between the signal and local oscillator). We performed biosensing of immobilized monolayers of antibodies on the disk in both transmission and reflection detection modes. Single- and dual-analyte adaptive spinning-disk immunoassays were demonstrated with good specificity and without observable cross-reactivity. Reflection-mode detection enhances the biosensing sensitivity to one-twentieth of a protein monolayer, creates a topographic map of the protein layer, and can differentiate monolayers of different species by their effective optical thicknesses.

Center of pressure (COP) during the Postural Balance Control of High-Heeled Woman

This study addressed the effect of balance control problems of the high-heeled women. Clinical relationships have been proposed linking foot ailments or pain to wearing high heels, yet little quantitative research has been done on the relationship between bare foot and high feeled foot. The purposes of this study were to objectively quantify the displacements and velocities of center-of- pressure (COP) of body during two-way waist pulling and to compare the differences between barefooted and high-heeled situations. We used a waist pulling system which has three different magnitudes to sway the subjects. We found that the kinematic information of barefooted and high-heeled women's COP is very important in understanding the mechanism of postural balance control of women in every-day life. In the high-heeled's case, the displacement of COP increases in 200% as against bare footed. Also the velocity variation of COP grows two times than the bare footed.

Hydrolysis of minor glycerophospholipids of plasma lipoproteins by human group IIA, V and X secretory phospholipases A2

We investigated the hydrolysis of the minor glycerophospholipids of human HDL(3), total HDL and LDL using human group IIA, V and X secretory phospholipases A(2) (sPLA(2)s). For this purpose we employed the enzyme and substrate concentrations and incubation times optimized for hydrolysis of phosphatidylcholine (PtdCho), the major glycerophospholipid of plasma lipoproteins. In contrast to PtdCho, which was readily hydrolyzed by group V and X sPLA(2)s, and to a lesser extent by group IIA sPLA(2), the minor ethanolamine, inositol and serine glycerophospholipids exhibited marked resistance to hydrolysis by all three sPLA(2)s. Thus, when PtdCho was hydrolyzed about 80%, the ethanolamine and inositol glycerophospholipids reached a maximum of 40% hydrolysis. The hydrolysis of phosphatidylserine (PtdSer), which was examined to a more limited extent, showed similar resistance to group IIA, V and X sPLA(2)s, although the group V sPLA(2) attacked it more readily than group X sPLA(2) (52% versus 39% hydrolysis, respectively). Surprisingly, the group IIA sPLA(2) hydrolysis remained minimal at 10-15% for all minor glycerophospholipids, and was of the order seen for the PtdCho hydrolysis by group IIA sPLA(2) at the 4-h digestion time. All three enzymes attacked the oligo- and polyenoic species in proportion to their mole percentage in the lipoproteins, although there were exceptions. There was evidence of a more rapid destruction of the palmitoyl compared to the stearoyl arachidonoyl glycerophospholipids. Overall, the characteristics of hydrolysis of the molecular species of the lipoprotein-bound diradyl GroPEtn, GroPIns and GroPSer by group V and X sPLA(2)s differed significantly from those observed with lipoprotein-bound PtdCho. As a result, the acidic inositol and serine glycerophospholipids accumulated in the digestion residues of both LDL and HDL, and presumably increased the acidity of the residual particles. An accumulation of the ethanolamine glycerophospholipids in the sPLA(2) digestion residues also had not been previously reported. These results further emphasize the diversity in the enzymatic activity of the group IIA, V and X sPLA(2)s. Since these sPLA(2)s possess comparable tissue distribution, their combined activity may exacerbate their known proinflammatory and proatherosclerotic function.

High-Speed Interferometric Detection of Label-Free Immunoassays on the Biological Compact Disc

Background: We describe a direct-detection immunoassay that uses high-speed optical interferometry on a biological compact disc (BioCD).

Methods: We fabricated phase-contrast BioCDs from 100-mm diameter 1.1-mm thick borosilicate glass disks coated with a 10-layer dielectric stack of Ta2O5/SiO2 that serves as a mirror with a center wavelength at 635 nm. The final layer is a λ/4 layer of SiO2 onto which protein patterns are immobilized through several different chemical approaches. Protein on the disc is scanned by a focused laser spot as the disc spins. Interaction of the light with the protein provides both a phase-modulated signal and a local reference that are combined interferometrically to convert phase into intensity. A periodic pattern of protein on the spinning disc produces an intensity modulation as a function of time that is proportional to the surface-bound mass. The binding of antigen or antibodies is detected directly, without labels, by a change in the interferometric intensity. The technique is demonstrated with a reverse assay of immobilized rabbit and mouse IgG antigen incubated against anti-IgG antibody in a casein buffer.

Results: The signal increased with increased concentration of analyte. The current embodiment detected a concentration of 100 ng/L when averaged over ∼3000 100-micron-diameter protein spots.

Conclusions: High-speed interferometric detection of label-free protein assays on a rapidly spinning BioCD is a high-sensitivity approach that is amenable to scaling up to many analytes.

Differential hydrolysis of molecular species of lipoprotein phosphatidylcholine by groups IIA, V and X secretory phospholipases A2

Human groups IIA, V and X secretory phospholipases A2 (sPLA2s) were incubated with human HDL3, total HDL and LDL over a range of enzyme and substrate concentrations and exposure times. The residual phosphatidylcholines (PtdChos) were assayed by high performance liquid chromatography with electrospray ionization mass spectrometry (LC/ESI-MS). The enzymes varied markedly in their rates of hydrolysis of the different molecular species and in the production of lysoPtdCho. The sPLA2s were compared at a concentration of 1 microg/ml and an incubation time of 4 h, when all three enzymes showed significant activity. The groups V and X sPLA2 were up to 20 times more reactive than group IIA sPLA2. Group X sPLA2 hydrolyzed arachidonate and linoleate containing species preferentially, while group V hydrolyzed the linoleates in preference to polyunsaturates. In all instances, the arachidonoyl and linoleoyl palmitates were hydrolyzed in preference to the corresponding stearates by group X sPLA2. The group IIA enzyme appeared to hydrolyze randomly all diacyl molecular species. The minor alkylacyl and alkenylacyl glycerophosphocholines (GroPChos) were poor substrates for groups V and X sPLA2s and these phospholipids tended to accumulate. The present study demonstrates a preferential release of arachidonate from plasma lipoprotein PtdCho by group X sPLA2, as well as a relative resistance of polyunsaturated PtdChos to hydrolysis by group V enzyme, which had not been previously documented. The use of lipoprotein PtdCho as substrate with LC/ESI-MS identification of hydrolyzed molecular species eliminates much of the uncertainty about sPLA2 specificity arising from past analyses of fatty acid release from unknown or ill-defined sources.

Absolute electronic excitation cross sections for low-energy electron (5–12eV) scattering from condensed thymine

The absolute cross sections for electronic excitations of thymine by electron impact between 5 and 12 eV are determined by means of electron-energy loss (EEL) spectroscopy for the molecule deposited at submonolayer coverage on an inert Ar substrate. The lowest EEL features at 3.7 and 4.0 eV are attributed to the excitation of the triplet 1 3A'(pi --> pi*) and 1 3A''(n --> pi*) valence states of the molecule. The higher EEL features located at 4.9, 6.3, 7.3, and 9 eV with a weak shoulder around 6 eV are ascribed mostly to triplet valence (pi --> pi*) excitation manifold of the molecule. The energy dependence of the cross section for both the lowest triplet valence excitations shows essentially a peak at about 5 eV reaching a value of 2.9 x 10(-17) cm2. The cross sections for the higher EEL features are generally characterized by a common broad maximum around 8 eV. The latter reaches a value of 1.36 x 10(-16) cm2 for the combined 6 and 6.3 eV excitation region. The maxima in the present cross sections are found to correspond to the resonances that have been reported at about the same energies in the O- yield from electron impact on thymine in the gas phase.