An optimization model for mastication and swallowing in mammals

Mammalian mastication is a process combining simultaneous food comminution and lubrication. The initiation of swallowing, which is voluntary, has been thought to depend on separate thresholds for food particle size and for particle lubrication. Instead of this duality, we suggest that swallowing is initiated when it is sensed that a batch of food particles is binding together under viscous forces so as to form a bolus. Bolus formation ensures that when the food mass is swallowed, it will pass the pharyngeal region safely without risk of inhaling small particles into the lower respiratory tract. Crucial for bolus formation is food particle size reduction by mastication. This allows the tongue to pack particles together tightly by pressure against the hard palate. A major function of salivation is to fill the gradually reducing spaces between particles, so increasing viscous cohesion and promoting bolus formation. If swallowing is delayed, excessive saliva floods the bolus, separating particles and reducing cohesion. Swallowing then becomes more precarious. Our model suggests that there is an optimum moment for a mammal to swallow, defined in terms of a peak cohesive force between food particles. The model is tested on human mastication with two foods, brazil nut and raw carrot, which have very different particle size breakdown rates. The peak cohesive force is much greater with brazil nuts but both foods are predicted to be swallowed after similar numbers of chews despite the very different food particle size reductions achieved at that stage. The predicted number of chews to swallow is in broad agreement with published data.     

Shear-dependent rolling on von Willebrand factor of mammalian cells expressing the platelet glycoprotein Ib-IX-V complex

Mural thrombi form on exposed arterial subendothelium by a two-step process of platelet adhesion and aggregation. At high shear stresses such as are found in stenotic arteries, both steps are mediated by von Willebrand factor (vWF). Platelets initially adhere on vWF affixed to the subendothelial matrix through the glycoprotein (GP) Ib-IX-V complex. To examine the role of the GP Ib-IX-V complex under dynamic conditions, we modeled initial platelet adhesion at shear stresses ranging from 2 to 40 dyn/cm2 using vWF-coated glass slides, mammalian cells expressing full or partial GP Ib-IX-V complexes, and a parallel plate flow chamber with phase contrast video microscopy and digital image processing. Mammalian cells expressing the full complex tethered and rolled on the vWF substrate, whereas control cells did not. The rolling was completely inhibited by the monoclonal GP Ib antibody, AK2, or the vWF antibody, 5D2, both shown previously to block vWF-dependent platelet aggregation. Other GP Ib antibodies, WM23 and SZ2, did not significantly change the number or mean velocity of rolling cells. At low levels of GP Ib surface expression, cells expressing the full complex rolled slower than cells expressing the complex without GP V, indicating that GP V strengthens the interactions with the vWF surface under these conditions. Preshearing vWF for 5 minutes at 40 dyn/cm2 immediately before introducing cells into the chamber did not significantly change the number or the mean velocity of rolling cells. Inhibiting sulfation of the tyrosine residues within the GP Ib subunit reduced the number but did not change the mean velocity of the rolling cells. Our results indicate that, under the conditions of these experiments, bonds between vWF and GP Ib constantly form and break under fluid shear stress. Additionally, our results suggest that GP Ib-IX-V complexes behave like selectin receptors in their ability to mediate smooth rolling while cells maintain continuous surface contact. Such a mechanism, in vivo, would allow platelets to slow down and eventually arrest on the blood vessel wall. The system described provides a valuable approach for investigating the structure-function relationship of individual receptors and ligands in the process of platelet adhesion and thrombosis.     

Synergistic effect and possible mechanisms of tumor necrosis factor and cisplatin cytotoxicity under moderate hyperthermia against gastric cancer cells

Photosensitization induces intracellular free calcium changes ([Ca2+]i) in some eukaryotic cell systems which either contribute to or protect against cell inactivation. We have investigated whether or not similar changes can be induced in prokaryotes. The skin bacterium Propionibacterium acnes was sensitized using protoporphyrin IX (PP IX) or 5-aminolevulinic acid (ALA). Exogenous ALA resulted in either a preferential accumulation of protoporphyrin (ALA-PP) or of coproporphyrin and/or uroporphyrin (ALA-CP/UP) in P. acnes. For PP IX or ALA-PP sensitization, exposure to broad-band red light resulted in an increase in [Ca2+]i. For ALA-PP sensitization, this increase was transient and [Ca2+]i returned to basal levels within 5-10 min after irradiation. However, the elevated [Ca2+]i levels obtained after PP IX sensitization were maintained for at least 1 h after irradiation. In both cases, the reduction in the external calcium concentration led to an enhancement in the cell survival, indicating that induced [Ca2+]i changes may participate in photoinactivation. Sensitization by hydrophilic coproporphyrin and/or uroporphyrin (ALA-CP/UP) did not affect the [Ca2+]i levels, but higher levels of cell inactivation were obtained. It therefore appears that damage to membrane-associated components is at least partly responsible for [Ca2+]i alterations after photosensitization.     

Two-dimensional electrophoresis of precision-cut testis slices: toxicologic application

Advances in tissue slice technology and a recent novel application of this technique to reproductive toxicology using bovine testis have demonstrated the remarkable utility of this approach. The objective of the present study was to combine this in vitro toxicity test system with large-scale two-dimensional polyacrylamide gel electrophoresis (2-DE) to detect and study alterations in testicular-slice protein patterns as molecular correlates of 1,3,5-trinitrobenzene (TNB) and 1,3-dinitrobenzene (DNB) toxicity. Previous studies have shown that testicular slices remain viable for > 24 h and, as measured by protein synthesis inhibition, TNB causes dose-related injury. Tissue-slices were prepared from bovine testicles incubated for 2, 4 or 6 h and exposed to either 100 microM, 500 microM or 1 mM DNB or TNB in the incubation medium. Slices were collected, solubilized, and separated by large scale 2-DE. Resulting protein patterns were then examined by image analysis, which revealed coefficients of variation in protein spot abundance comparable to patterns from fresh rodent tissue samples. Furthermore, specific protein alterations indicated dose-related inductions and declines in protein abundance, some progressive over time. The results of this investigation demonstrate the potential toxicologic utility of combining in vitro tissue-slice technology with high-resolution 2-DE protein mapping. The consolidation of these methods offers a novel approach for toxicity screening and testing, reduces experimental cost, and reduces the use of laboratory animals.     

In unison: regularization of protein secondary structure predictions that makes use of multiple sequence alignments

We present a method whose purpose is to post-process the fuzzy results of secondary structure prediction methods that use multiple sequence alignments, in order to obtain 'realistic' secondary structures, i.e., secondary structure elements whose length is greater than or equal to some predefined minimum length. This regularization helps with interpretation of the secondary structure prediction.     

Hopwood, affirmative action, and deaf education

Leukemic cells of B-lineage acute lymphoblastic leukemia (ALL) are regarded as the malignant counterparts of immature, physiologic B cell precursors (BCPs). To determine whether phenotypic differences exist between these corresponding cell types, we investigated samples of normal pediatric bone marrow (n=30) as well as of B-precursor ALL at diagnosis (n=53; common and pre-B subtype). Using three-color multiparameter flow cytometric analysis, we compared the leukemic populations with the physiologic BCPs of corresponding maturity with respect to the intensity with which they expressed a series of antigens. In some of these antigens, leukemia-associated aberrations were frequently observed. In particular, overexpression of CD10 was displayed by 65% of ALL samples, whereas 58% of leukemic cases aberrantly exhibited very low or no CD45RA expression. Regarding CD11a and CD44, 47% and 35% of ALL populations were aberrant as defined by either the absence or significant overexpression of the antigen. In contrast, antigen densities of CD49d, CD49e, and CD99 on leukemic cells were in the normal range of values for BCPs. Combining the patterns of frequently aberrant markers in a comprehensive analysis, we were able to identify individual phenotypic leukemic cell aberrations in up to 98% of investigated cases. CD10 and/or CD45RA were aberrant in 86% of cases overall, emphasizing the high discriminative potential of these two markers. Using comparative phenotype mapping based on quantitatively aberrant, leukemia-associated antigenic patterns, we were able to detect leukemic blasts among normal bone marrow cells at frequencies as low as 10(-5). We speculate that our approach may have a profound impact on the development of new strategies for minimal residual disease investigations in patients with BCP-ALL.