Modulation of cancer cell growth and progression by Caveolin-1 in the tumor microenvironment

Caveolin-1 (Cav-1), a major structural component of cell membrane caveolae, is involved in a variety of intracellular signaling pathways as well as transmembrane transport. Cav-1, as a scaffolding protein, modulates signal transduction associated with cell cycle progression, cellular senescence, cell proliferation and death, lipid homeostasis, etc. Cav-1 is also thought to regulate the expression or activity of oncoproteins, such as Src family kinases, H-Ras, protein kinase C, epidermal growth factor, extracellular signal-regulated kinase, and endothelial nitric oxide synthase. Because of its frequent overexpression or mutation in various tumor tissues and cancer cell lines, Cav-1 has been speculated to play a role as an oncoprotein in cancer development and progression. In contrast, Cav-1 may also function as a tumor suppressor, depending on the type of cancer cells and/or surrounding -stromal cells in the tumor microenvironment as well as the stage of tumors.

Modified pectin structure for targeted divalent cation binding and associated functionalities in food model systems

Extracted pectin is currently widely used as a food additive in plant-based products, particularly in gelling applications, due to its ability to bind divalent cations, especially Ca2+. This pectin functionality has been reported to be largely influenced by its structural properties, in particular the degree and pattern of methylesterification (DM) and blockiness (DBabs), which are a measure for the percentage and distribution of non-methylesterified galacturonic acid units, respectively. Although the role of these structural properties in Ca2+-binding and gelling has been widely explored, fundamental insights into these interactions are limited. Moreover, scarce information is available on the role of the pectin properties in the interaction with other divalent cations, despite the hypothesized ability of pectin to bind these divalent cations yielding specific functionalities. For instance, given that pectin is a dietary fiber and thus not digestible in the small intestine, its interaction with essential divalent cations, such as Zn2+, could result in reduced mineral bioaccessibilities during digestion, potentially contributing to mineral deficiencies. Additionally, binding of Fe2+ has been considered to confer pectin a lipid antioxidant capacity in emulsion-based products, thereby retarding lipid oxidation. Exploring this pectin functionality could promote its use as a natural antioxidant which is more appealing to consumers compared to synthetic additives, such as ethylenediaminetetraacetic acid (EDTA). Therefore, this doctoral thesis aimed to provide fundamental insights into the effect of pectin DM and DBabs on its interaction with Fe2+, Zn2+, or Ca2+ and associated functionalities, particularly the lipid antioxidant capacity and its role in the Zn2+ in vitro bioaccessibility. Pectin samples with comparable methylesterification degrees (DM) but different patterns of methylester distribution (DBabs) were generated through enzymatic (using carrot pectin methylesterase) or alkaline (using NaOH) demethylesterification of high methylesterified citrus pectin. First, the interaction of these pectin samples with Fe2+, Zn2+, or Ca2+ was explored through equilibrium adsorption experiments, followed by generation of adsorption isotherms based on the Langmuir adsorption isotherm model to quantify their maximum binding capacities and associated interaction energies. Results of this study showed that decreasing pectin DM or increasing DBabs promoted the Fe2+-, Zn2+-, or Ca2+-binding capacity of pectin, with the maximum binding capacity being mainly determined by the DM and the interaction energy by DBabs. With regard to cation type, the highest maximum binding capacity and interaction energy were exhibited for Zn2+ compared to Ca2+ and Fe2+. Additionally, insights into the thermodynamics of the pectin-cation interaction, particularly pectin-Zn2+ binding, were obtained using isothermal titration calorimetry (ITC). Results obtained complemented those from the equilibrium adsorption experiment. The binding of Zn2+ to pectin was found to be an endothermic interaction, in which a positive entropy change dominated the unfavorable endothermic enthalpy change. Moreover, the pectin-Zn2+ interaction occurred according to a two-step mechanism involving first monocomplexation and the formation of point-like cross-links, followed by dimerization. The role of pectin DM and DBabs, and associated pectin-Zn2+ interaction, in directing Zn2+ bioaccessibility was subsequently studied through in vitro simulated digestion of Zn2+-enriched pectin solutions. Decreasing DM or increasing DBabs resulted in decreased Zn2+ bioaccessibilities due to higher Zn2+-binding capacities. However, lower amounts of Zn2+ than expected (based on the established maximum Zn2+-binding capacity of pectin) were bioaccessible, suggesting binding of Zn2+ to the bile salts and probably enzymes added during the in vitro simulated digestion. Exploration of the possible competition between Ca2+ and Zn2+ for binding to pectin during digestion revealed that low Ca2+ levels (approximately 0.33 mM) had no clear influence on Zn2+ bioaccessibility. In view of identifying (potential) natural antioxidants to reduce synthetic ones, the lipid antioxidant capacity of the derived pectins in Fe2+-enriched linseed/sunflower oil-in-water (o/w) emulsions (5% w/v) was explored by determination of the peroxide value as a function of storage time. Low DM pectin and increased pectin concentration promoted the lipid antioxidant capacity, due to an increased Fe2+-binding capacity. However, EDTA exhibited still a higher antioxidant capacity compared to low DM pectin. Moreover, pectin was found to destabilize the o/w emulsions by bridging or depletion flocculation. This doctoral thesis clearly demonstrated the role of DM and DBabs in directing pectin cation-binding capacity and associated functionalities. The results obtained provide fundamental insights into the pectin structure-function relation which in turn can contribute to optimization of ex situ pectin functionalities in several applications, including product structure build-up while maintaining the nutritional value of the food product. Moreover, these findings form a basis for potential exploitation of pectin as an antioxidant as well as exploring pectin functionalities in situ.status: publishe

The biology of the sunflower moth, Homoeosoma electellum (Hulst)

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Bibliography: leaves 46-51.Not availabl

Enzymatic hydrolysis of brewers' spent grain proteins and technofunctional properties of the resulting hydrolysates

Brewers' spent grain (BSG) is the insoluble residue of barley malt resulting from the manufacture of wort. Although it is the main byproduct of the brewing industry, it has received little attention as a marketable commodity and is mainly used as animal feed. Our work focuses on one of the main constituents of BSG, i.e., the proteins. The lack of solubility of BSG proteins is one of the limitations for their more extensive use in food processing. We therefore aimed to generate BSG protein hydrolysates with improved technofunctional properties. BSG protein concentrate (BPC) was prepared by alkaline extraction of BSG and subsequent acid precipitation. BPC was enzymatically hydrolyzed in a pH-stat setup by several commercially available proteases (Alcalase, Flavourzyme, and Pepsin) for different times and/or with different enzyme concentrations in order to obtain hydrolysates with different degrees of hydrolysis (DH). Physicochemical properties, such as molecular weight (MW) distribution and hydrophobicity, as well as technofunctional properties, such as solubility, color, and emulsifying and foaming properties, were determined. Enzymatic hydrolysis of BPC improved emulsion and/or foam-forming properties. However, for the hydrolysates prepared with Alcalase and Pepsin, an increasing DH generally decreased emulsifying and foam-forming capacities. Moreover, the type of enzyme impacted the resulting technofunctional properties. Hydrolysates prepared with Flavourzyme showed good technofunctional properties, independent of the DH. Physicochemical characterization of the hydrolysates indicated the importance of protein fragments with relatively high MW (exceeding 14.5 k) and high surface hydrophobicity for favorable technofunctional properties.status: publishe

The effects of malting and mashing on barley protein extractability

Proteins in unmalted and malted barley and in brewers' spent grain (BSG) obtained after mashing were fractionated on the basis of their differential extractability in different media and characterised by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and high-performance liquid chromatography (HPLC). Albumins and globulins were first extracted with 5.0% NaCl and hordeins (barley prolamins) were extracted with 55.0% 1-propanol in the presence, or absence, of 1.0% DTT. Glutelins were then extracted with 2.0% DS/6.()M urea/1.0% DTT or with 55.0% 1-propanol/6.0M urea/1.0% DTT/0.036M Tris-HCl (pH 8.4). Under non-reducing conditions, monomeric C hordeins and some B hordeins were extracted from unmalted barley, whereas most if not all B, C and D hordeins were extracted under reducing conditions. During malting, disulfide bonds are reduced and B and D hordeins are broken down by proteolysis. No D hordeins were extracted from malt and nearly the same levels of malt B hordeins were extracted both under non-reducing and reducing conditions. B hordeins present in BSG proteins were only extractable under reducing conditions. Whereas most of the C hordeins were extracted from BSG under non-reducing conditions, more C hordeins were extracted under reducing conditions. Mashing probably induced disulfide bond formation resulting in aggregation. Although earlier literature suggested the formation of an aggregate composed of B and D hordein (and glutelin) during mashing, the present work suggests the formation of an aggregate composed of B hordeins in which C hordeins are entrapped. (c) 2006 Elsevier Ltd. All rights reserved.status: publishe

Fractionation and Characterization of Brewers' Spent Grain Protein Hydrolysates

Protein hydrolysates with a low and high degree of hydrolysis were enzymatically produced from brewers' spent grain (BSG), the insoluble residue of barley malt resulting from the manufacture of wort in the production of beer. To that end, BSG protein concentrate (BPC), prepared by alkaline extraction of BSG and subsequent acid precipitation, was enzymatically hydrolyzed with Alcalase during both 1.7 and 120 min. Because these hydrolysates contained many different peptides, fractionation of the hydrolysates with graded ammonium sulfate or ethanol precipitation was performed to obtain fractions homogeneous in terms of molecular weight (MW) and hydrophobicity. The emulsifying and foaming capacities of the resultant fractions were determined. MW distributions and surface hydrophobicities of fractions with protein contents exceeding 75% were investigated to determine relationships between technofunctional and physicochemical properties. It was found that the emulsifying and foaming properties are determined by different physicochemical properties of the proteins or peptides. Neither MW nor hydrophobicity alone determines the emulsifying and foaming properties of protein hydrolysates. BSG protein hydrolysates with good emulsifying properties contained less than 40% of fragments with MW exceeding 14500. Moreover, these hydrolysates had a high surface hydrophobicity. BSG protein hydrolysates with good foaming properties contained less than 10% of material with MW lower than 1700. Hydrolysates with good foaming properties showed low surface hydrophobicities, except for protein hydrolysates with higher levels of protein fragments with MW exceeding 14500 than of such fragments with MW in a 1700-14500 range.status: publishe

Foaming properties of tryptic gliadin hydrolysate peptide fractions

A tryptic gliadin hydrolysate was separated into central domain (CD) or terminal domain (TD) related peptide fractions. Whereas the initial foam volume (FV) of CD peptide fractions remained constant as a function of pH, FV of TD peptide fractions increased from acidic to alkaline pH. Foam stability (FS) of CD peptide fractions was maximal near neutral pH. For TD peptide fractions, one fraction showed maximal FS at strongly alkaline pH, while the other showed no clear maximal FS. CD related peptide foams contained higher levels of hydrophobic peptides than the respective solutions, while small differences were observed for TD peptide fractions. Peptide compositions of foams did not vary with pH, indicating that the foaming properties of gliadin peptides are mainly dictated by charges. As the pH dependent foaming properties of TD related peptides resemble best those of gliadin, it was concluded that the pH dependent foaming properties of gliadins are mainly determined by their TDs.status: publishe

Isothermal titration calorimetry to study the influence of citrus pectin degree and pattern of methylesterification on Zn2+ interaction

This work explored the influence of the citrus pectin degree and pattern of methylesterification on its interaction with Zn2+ using isothermal titration calorimetry (ITC). Pectin samples with a comparable degree of methylesterification (DM) but distinct distribution patterns of non-methylesterified carboxylic groups (absolute degree of blockiness, DBabs) were produced through enzymatic (blockwise pattern) or alkaline (random pattern) demethylesterification. The pectin-Zn2+ interaction was found to be endothermic, in which a positive entropy change compensated for the unfavorable endothermic enthalpy change, driving the interaction between pectin and Zn2+. Decreasing pectin DM or increasing DBabs promoted Zn2+ binding, with the estimated binding capacity (mol Zn2+/mol GalA) and binding constant (mM−1) being mainly determined by pectin DBabs, rather than DM. ITC was found to be a useful technique to study the pectin-cation interaction, however, low DM pectin samples are sensitive to gelling and therefore more difficult to study.status: Published onlin

The breakage susceptibility of raw and parboiled rice: A review

Rice (Oryza sativa L.) is one of the most important cereals in the world. Before it is consumed, it is common to remove the hull, bran and germ from the rough rice kernel which is either parboiled or not. During such processing, rice kernels are subjected to mechanical stresses which cause some rice grains to break. A main challenge of the rice industry is to minimize the quantities of broken rice. We here review the factors impacting the breakage susceptibility of rice kernels. Their tendency to break is primarily determined by fissures, chalkiness, immaturity and rice kernel dimensions, properties which are both cultivar and rice grain history dependent. The intensity of processing of any given rice feedstock determines the actual level of broken rice kernels. If performed properly, parboiling, a three-step hydrothermal treatment consisting of soaking, heating and drying of rough rice, substantially reduces the level of broken kernels.status: publishe