Biomedical subjects

David Allara

Publications and source records attributed to David Allara.

5 recordsLinked to original sources

PubMed2006

Characterization of human breast epithelial cells by confocal Raman microspectroscopy.

BACKGROUND: The past decade has seen an explosion of interest in utilizing Raman spectroscopy in cancer diagnosis, due to its capability to probe changes in the biochemical composition of tissue that accompany disease progression. However, most of the existing methods used multivariate statistical analysis/chemometrics to differentiate normal and diseased tissues, which did not identify the compositional and chemical changes associated with the tumorigenic transition explicitly; also the sub-cellular level spatial resolution achievable through Confocal Raman microscopy was not fully utilized. METHODS: Confocal Raman microspectroscopy was used to characterize normal and transformed human breast epithelial cell lines. Key molecular components (DNA, RNA, and proteins) were extracted from cell nuclei and their Raman spectra were measured and used as a basis set to fit the spectra of cell nuclei. Contributions of each component and their relative contents were evaluated based on the fitting coefficients. RESULTS: Spectrum-fitting revealed that DNA duplication activities in tumorigenic cell nuclei are significantly higher than in normal cells. The fitting coefficients could serve as good spectral markers for disease state identification. CONCLUSIONS: A spectroscopic approach that yields compositional information of cell nuclei could be a powerful tool for rapid cell characterization and assessment of cellular activities at the sub-cellular level.

Breast↗

PubMed2006

Interfacial energetics of globular-blood protein adsorption to a hydrophobic interface from aqueous-buffer solution.

Adsorption isotherms of nine globular proteins with molecular weight (MW) spanning 10-1000 kDa confirm that interfacial energetics of protein adsorption to a hydrophobic solid/aqueous-buffer (solid-liquid, SL) interface are not fundamentally different than adsorption to the water-air (liquid-vapour, LV) interface. Adsorption dynamics dampen to a steady-state (equilibrium) within a 1 h observation time and protein adsorption appears to be reversible, following expectations of Gibbs' adsorption isotherm. Adsorption isotherms constructed from concentration-dependent advancing contact angles theta(a) of buffered-protein solutions on methyl-terminated, self-assembled monolayer surfaces show that maximum advancing spreading pressure, Pi(a)max, falls within a relatively narrow 10 < Pi(a)max < 20 mN m(-1) band characteristic of all proteins studied, mirroring results obtained at the LV surface. Furthermore, Pi(a) isotherms exhibited a 'Traube-rule-like' progression in MW similar to the ordering observed at the LV surface wherein molar concentrations required to reach a specified spreading pressure Pi(a) decreased with increasing MW. Finally, neither Gibbs' surface excess quantities [Gamma(sl)-Gamma(sv)] nor Gamma(lv) varied significantly with protein MW. The ratio {[Gamma(sl)-Gamma(sv)]/Gamma(lv)} approximately 1, implying both that Gamma(sv) approximately 0 and chemical activity of protein at SL and LV surfaces was identical. These results are collectively interpreted to mean that water controls protein adsorption to hydrophobic surfaces and that the mechanism of protein adsorption can be understood from this perspective for a diverse set of proteins with very different composition.

Adsorption↗

PubMed2006

Interfacial energetics of blood plasma and serum adsorption to a hydrophobic self-assembled monolayer surface.

Interfacial energetics of blood plasma and serum adsorption to a hydrophobic, methyl-terminated self-assembled monolayer (SAM) surface (solid-liquid SL interface) are shown to be essentially the same as to the buffer-air interface (liquid-vapor LV interface). Specifically, spreading pressure (Pia) isotherms scaled on a w/v concentration basis constructed from advancing contact angles (thetaa) of serially diluted plasma/serum derived from four different mammalian species (bovine, equine, human, and ovine) on the SAM surface are not resolvable at the 99% confidence level and furthermore are found to be strikingly similar to isotherms of purified human-blood proteins. Maximum advancing spreading pressures Piamax for protein mixtures fall within a relatively narrow 17<Piamax<26 mN/m band, mirroring results obtained at the LV surface. These observations lead to the conclusion that neither depletion of coagulation proteins in the conversion of plasma to serum nor variation in the plasma proteome among species has a substantial affect on adsorption energetics to these test hydrophobic surfaces. Experimental results are rationalized on the basis that there is a generic mechanism controlling adsorption of globular-blood proteins to test hydrophobic surfaces. We conclude that this generic mechanism is the hydrophobic effect by which proteins are expelled from aqueous solution in order to increase hydrogen-bonding (self-association) among water molecules at the expense of less favorable water-protein interactions. Expelled protein readily displaces water within the hydrophobic-surface region and becomes adsorbed. The amount of water displaced per gram of adsorbed protein does not vary greatly among globular proteins because the partial specific volume v0 of globular proteins is quite conserved (0.70<or=v0<or=0.75 cm3/g protein). Any single blood protein or mixture of proteins consequently displaces nearly an equivalent amount of interfacial water and hence adsorption is observed to scale similarly with solution concentration expressed in w/v units.

Adsorption↗

PubMed2005

Scaled interfacial activity of proteins at a hydrophobic solid/aqueous-buffer interface.

Contact-angle goniometry confirms that interfacial energetics of protein adsorption to the hydrophobic solid/aqueous-buffer (solid-liquid, SL) surface is not fundamentally different than adsorption to the aqueous-buffer/air (liquid-vapor, LV) interface measured by pendant-drop tensiometry. Adsorption isotherms of 9 globular blood proteins with molecular weight (MW) spanning from 10 to 1000 kDa on methyl-terminated self-assembled monolayer surfaces demonstrate that (i) proteins are weak surfactants, reducing contact angles by no more than about 15 degrees at maximum solution concentrations ( approximately 10 mg/mL); (ii) the corresponding dynamic range of spreading pressure Pi(a) < 20 mN/m; and (iii) the maximum spreading pressure Pi(max) (a) for these diverse proteins falls within a relatively narrow 5 mN/m band. As with adsorption to the LV interface, we find that concentration scaling substantially alters perception of protein interfacial activity measured by Pi(a). Proteins appear more similar than dissimilar on a weight/volume basis whereas molarity scaling reveals a systematic ordering by MW, suggesting that adsorption is substantially driven by solution concentration rather than diversity in protein amphilicity. Scaling as a ratio-to-physiological-concentration demonstrates that certain proteins exhibit Pi(max)(a) at-and-well-below physiological concentration whereas others require substantially higher solution concentration to attain Pi(max)(a). Important among this latter category of proteins is blood factor XII, assumed by the classical biochemical mechanism of plasma coagulation to be highly surface active, even in the presence of overwhelming concentrations of other blood constituents such as albumin and immunoglobulin that are shown by this work to be among the class of highly surface-active proteins at physiologic concentration. The overarching interpretation of this work is that water plays a dominant, controlling role in the adsorption of globular-blood proteins to hydrophobic surfaces and that energetics of hydration control the amount of protein adsorbed to poorly water-wettable biomaterials.

Adsorption↗

PubMed2005

An evaluation of methods for contact angle measurement.

A systematic comparison of Wilhelmy-balance tensiometry (WBT), tilting-plate goniometry (TPG) and captive-drop goniometry (CDG), using a variety of silane-treated glass surfaces of variable wetting characteristics is reported. WBT was assumed to be the benchmark of comparison (gold standard). Advancing angles measured by TPG and CDG were in statistical agreement with corresponding WBT measurements. In contrast, receding angles from both goniometric techniques were systematically higher than WBT.

Chemistry, Physical↗