Cryoprotective properties of vasoconstriction

In standardized freezing experiments made on depilated rat skin, it was found that vasconstriction gives some cryoprotection, but, only if tissue temperatures do not drop below ?30 °C.It is suggested that vasoconstriction, which is a well-known sequel to more moderate drops in tissue temperature, is in fact a physiological temperature defense mechanism. This mechanism is probaly only of minor importance in connection with cryosurgical procedures. It would, however, be worthwhile to look into the cryoprotective effect of vasoconstriction from a purely physiological point of view, but this has been beyond the scope of the present study.In the course of the experiments it was found that when edema persists in frozen skin beyond 24 to 48 hr after the cryoinsult, then the edema can be taken as a sign of viability of the tissue.     

Analysis of mixtures of pectins and amidated pectins

Amidated pectins and non-amidated pectins are transformed by saponification into amidated pectic acid and pectic acid. By heat treatment under alkaline conditions only amidated pectic acid is depolymerized and can be separated from the high-molecular pectic acid by gel-filtration. On this basis the composition of mixtures can be analysed.     

Structure of citrus pectins and viscometric study of their solution properties

Citrus pectins with degrees of methylation between 30 and 72% were carefully characterized in order to determine their charge density and molecular weight distribution, the content in galacturonic acid and in neutral sugars, the degree of methylation and acetylation. Using enzymic degradation it has been found that pectin molecules consist mainly of long homogalacturonan regions with some regions of neutral sugars as side chains attached on rhamnose residues. The viscometric behaviour of the different samples indicates that 0.1 M NaCl, at 25 degrees C, is a good solvent of sodium pectinates. From the evolution of the Huggins parameter, it appears that pectins with 50% of methylated galacturonic groups exhibit a maximum flexibility. A Mark-Houwink exponent of 0.8 has been found in good agreement with theoretical predictions for flexible polymers in a good solvent.     

Comparison of the in vitro bifidogenic properties of pectins and pectic-oligosaccharides

AIMS: To compare the in vitro fermentation properties of pectins and oligosaccharides derived from them in pure and mixed faecal cultures. METHODS AND RESULTS: Specific growth rates of selected bacterial genera were calculated in pure culture. Bifidobacterium angulatum, B. infantis and B. adolescentis had higher growth rates on pectic oligosaccharides (POS I) derived from high methylated pectin (HMP) than on HMP and B. pseudolongum and B. adolescentis on pectic oligosaccharides (POS II) derived from low methylated pectin than on HMP. Controlled pH batch mixed faecal cultures were then carried out and a prebiotic index was calculated as a mean to compare the fermentation properties of the different substrates. In general, greater fermentation selectivity was obtained with lower degrees of methylation (PI24(-HMP) = -0.11, PI24(-LMP) = 0.033; PI24(-POS I) = 0.071 and PI24(-POS II) = 0.092). An effect of size on prebiotic potential was observed, with the oligosaccharides having more selective fermentation properties than the pectins they derived from. CONCLUSIONS: The degree of methylation plays an important role in the fermentation properties of pectins. Pectic-oligosaccharides are a better prebiotic candidate than the pectins, although their bifidogenic effect is low compared to oligofructose. SIGNIFICANCE AND IMPACT OF THE STUDY: The effect of size on prebiotic potential was demonstrated. Non-selectively fermented polysaccharides like pectin can have their bifidogenic properties improved by partial hydrolysis.     

Gelation properties of extruded lemon cell walls and their water-soluble pectins

The amount of water-soluble pectins was largely increased after extrusion-cooking of lemon fibres. These pectins showed the ability to form a gel in the presence of sucrose and at acidic pH. The gels obtained with the water-extracted pectins after extrusion-cooking and with pectins acid-extracted on a laboratory scale were softer than those prepared with commercial citrus pectins. The water-extracted pectins after extrusion-cooking and the pectins acid-extracted on a laboratory scale contained long neutral side-chains and required a higher sucrose concentration to gel than the commercial citrus pectins. The extruded lemon fibres showed the ability to form gels in the presence of sucrose and at acidic pH. The gels obtained with the extruded fibres containing some water-solube pectins of high molecular weight were stronger than those obtained with the extruded fibres containing higher amounts of more depolymerised water-soluble pectins. The extruded fibres containing 12.5–14.9% of water-soluble pectins of high molecular weight (intrinsic viscosity: 413–504 mL/g) were those showing the better gelation properties.     

Effects of some oxidising agents,especially ammonium peroxysulfate,on sugar-beet pectins

Sugar-beet pectins contain feruloyl groups linked to the side chains of the rhamnogalacturonan backbone. Coupling reactions may cross-link these macro-molecules. Of several oxidising agents, only hydrogen peroxide-peroxidase and ammonium peroxysulfate were effective, indicating the involvement of free radicals. The effects of peroxysulfate and pectin concentrations, temperature, and the presence of some additives have been investigated mainly by viscometry and chromatography on Sepharose CL-2B. Depending on the concentration of the pectin, the reaction may be used to obtain either water-soluble products of increased molecular weight or gels.     

Cryoprotective properties of water in the Earth cryolithosphere and its role in exobiology

In permanently frozen rocks, water occurs in all the three phases and plays a dual role from the biological point of view. About 93–98% of it is in the solid state. This, alongside with negative temperatures, contributes to cell cryoconservation. The remaining 2–7% is in the unfrozen state and represents thin films enveloping organic-mineral particles. These films play the role of cryoprotectors against cell damage by ice crystals during geologically significant time. Electron microscope examinations of prokaryotes revealed the well preserved outer cell structures, specifically strong envelopes and capsules. The cells are resistant to water phase transitions through 0 °C, i.e. to the freezing-thawing stress. The exobiolocial implication of this phenomenon is determined by the fact that the Earth permafrost at first approximation can be considered as a model of e.g. the Mars one. The latter protects the cells against radiation and simultaneously serves as a cryoconservant. However, most important is the possible presence of unfrozen (=liquid) water as prerequisite for the development of microbial life forms.Presented at the Session Water in the Solar System and Its Role in Exobiology during the 26th General Assembly of the European Geophysical Society, 22–26 April 1991 in Wiesbaden, Germany.Corresponding author.     

Cryoprotective leaf proteins.

Leaves of frost-resistant plants contain a number of soluble proteins which are capable of protecting isolated biomembranes against inactivation during freezing. Such proteins have not been found in non-hardy summer material. The pattern of protective proteins was not uniform in hardy material of different origin and appeared to change with the season. Cryoprotective proteins were isolated by preparative gel electrophoresis. Molecular weights of different proteins as determined by their electrophoretic mobility in sodium dodecyl sulfate gels were between 10000 and 20000. Circular dichroism measurements failed to indicate helical structures. The amino acid composition of 2 active proteins revealed a high content of polar amino acids. The proteins were heat-stable. They were, on a molar basis, more than 1000 times as effective in protecting thylakoid membranes against freezing damage as low-molecular-weight cryoprotectants such as sucrose, glycerol or dimethylsulfoxide. Very low concentrations of the proteins increased cryoprotection provided by sucrose. Of a number of oligopeptides of known composition, only a few were cryoprotective. Their activity was very small as compared with that of the active proteins. The concentration of the cryoprotective proteins in hardy leaves appeared to be high enough for a significant contribution of the proteins to the frost tolerance of resistant plants.     

Cryoprotective activity of phosphorus-containing phenol

The antioxidant and cryoprotective efficiencies of a 3,5-di-tert-butyl-4-hydroxyphenyl)methylenediphosphonic acid (MDPA) differ significantly for sperm cells of various species of sturgeon fish (Russian sturgeon, beluga and Stellate sturgeon). The ability of phosphorus-containing phenol MDPA to decrease the level of lipid peroxidation of sperm, beneficial effect on the activity indicators of the sperm of native sturgeon and of the defrosted one after deep freezing as well as on the fertility of sperm cells was shown.     

Cryoprotective and contraceptive properties of egg yolk as an additive in rooster sperm diluents

The addition of chicken egg yolk to semen extenders is thought to reduce the fertilizing potential of rooster spermatozoa - but not (or at least not as much) that of other avian species. The aim of the present study was to determine whether quail egg yolk, a novel extender additive, provides advantages over chicken egg yolk in the cryopreservation of rooster spermatozoa. Experiments were also performed to determine whether the harmful effect of egg yolk occurs during cryopreservation or during fertilization after artificial insemination. Heterospermic rooster semen samples were divided into aliquots and cooled in a polyvinylpyrrolidone-based medium containing 15% chicken egg yolk, 15% quail egg yolk or no egg yolk at all. The viability of spermatozoa of cooled samples (5 °C) without egg yolk were less viable (P < 0.01) than those of samples containing either type of egg yolk. The same aliquots were then cryopreserved for 15 days. Thawed spermatozoa preserved without egg yolk showed lower motility (P < 0.001) and viability (P < 0.001) than those in samples diluted with either type of egg yolk extender. No eggs were fertilized when hens were inseminated with semen that had been diluted with chicken egg yolk. The fertilization rate was only slightly higher when sperm diluted with quail egg yolk was used (1.5%). The best results were obtained when no egg yolk was used (13.8%). These results show that the addition of egg yolk of either type protects rooster sperm cells against cold shock and during freezing and thawing, but exerts a contraceptive effect in the genital tract of the hen.     

Cryoprotective and contraceptive properties of egg yolk as an additive in rooster sperm diluents

The addition of chicken egg yolk to semen extenders is thought to reduce the fertilizing potential of rooster spermatozoa - but not (or at least not as much) that of other avian species. The aim of the present study was to determine whether quail egg yolk, a novel extender additive, provides advantages over chicken egg yolk in the cryopreservation of rooster spermatozoa. Experiments were also performed to determine whether the harmful effect of egg yolk occurs during cryopreservation or during fertilization after artificial insemination. Heterospermic rooster semen samples were divided into aliquots and cooled in a polyvinylpyrrolidone-based medium containing 15% chicken egg yolk, 15% quail egg yolk or no egg yolk at all. The viability of spermatozoa of cooled samples (5 °C) without egg yolk were less viable (P < 0.01) than those of samples containing either type of egg yolk. The same aliquots were then cryopreserved for 15 days. Thawed spermatozoa preserved without egg yolk showed lower motility (P < 0.001) and viability (P < 0.001) than those in samples diluted with either type of egg yolk extender. No eggs were fertilized when hens were inseminated with semen that had been diluted with chicken egg yolk. The fertilization rate was only slightly higher when sperm diluted with quail egg yolk was used (1.5%). The best results were obtained when no egg yolk was used (13.8%). These results show that the addition of egg yolk of either type protects rooster sperm cells against cold shock and during freezing and thawing, but exerts a contraceptive effect in the genital tract of the hen.     

Enzymic degradation of apple pectins

Purified apple pectins extracted under mild conditions were degraded by purified pectin lyase (EC 4.2.2.10) and pectate lyase (EC 4.2.2.2). The degraded pectins were fractionated by gel permeation chromatography and the degree of esterification and the sugar composition determined for each fraction. More than 90% of the uronic acid residues can be isolated as homogalacturonan chains. The neutral sugar residues can be detected in the column eluates as high molecular weight fragments. Models of the apple pectin molecules are presented. In the models the neutral sugars are present as side chains, arranged in blocks (in so-called ‘hairy regions’). The galacturonate residues in the hairy regions are esterified with methanol.     

Properties of cellulose/pectins composites: Implication for structural and mechanical properties of cell wall

The primary cell wall of dicotyledonous plants can be considered as a concentrated polymer assembly, containing in particular polysaccharides among which cellulose and pectins are known to be the major components. In order to understand and control the textural quality of plant-derived foods, it is highly important to elucidate the rheological and microstructural properties of these components, individually and in mixture, in order to define their implication for structural and mechanical properties of primary plant cell wall. In this study, the rheological and microstructural properties of model systems composed of sugar-beet microfibrillated cellulose and HM pectins from various sources, with varied degrees of methylation and containing different amounts of neutral sugar side chains, were investigated. The influence of the presence of calcium and/or sodium ions and the biopolymer concentrations on the properties of the mixed systems were also studied. The characterizations of the mixed system, considered as a simplified model of primary plant cell wall, showed that whatever the structural characteristics of the pectins, the ionic conditions of the medium and the biopolymer concentrations, the gelation of the composite was mainly controlled by cellulose. Thus, the cellulose network would be the principal component governing the mechanical properties of the cell walls. However, the neutral sugar side chains of the pectins seem to play a part in the interactions with cellulose, as shown by the interesting viscoelastic properties of cellulose/apple HM pectins systems. The rigidity of cellulose/pectins composite was strongly influenced by the structural characteristics of pectins. The particular properties of primary plant cell walls would thus result from the solid viscoelastic properties of cellulose, its interactions with pectins according to their structural characteristics (implication of the neutral sugar side chains and the specific potential calcic interactions) and of the distribution of the components in separate phases.     

Cryoprotective effects of D-allose on mammalian cells

D-allose, an aldo-hexose, is a rare sugar whose biological functions remain largely unclear. Recently, we demonstrated a novel inhibitory effect of D-allose on production of reactive oxygen species (ROS). Here, we focused on investigating cryoprotective effects of D-allose on cell viability. Mammalian cell lines including OVCAR-3 (human ovarian cancer), HeLa (human cervical cancer), HaCaT (human skin keratinocytes), HDF (human dermal fibroblasts) and NIH3T3 (murine fibroblasts) cells were frozen at -80 degrees C in culture media with various D-allose concentrations. Cells were allowed to recover for 24 h, 1 week or 1 month prior to survival assessment using the trypan blue dye exclusion test, when cell proliferation was evaluated by MTT assay. A beneficial protective role of D-allose on cell survival was found, similar to that of trehalose (disaccharide of glucose), a recognized cryoprotectant. The results suggest that D-allose as a sole additive may provide effective protection for mammalian cells during freezing. Practical studies now need to be performed with D-allose, for example to determine optimal freezing protocols and explore potential for preservation of tissues or organs at non-freezing temperatures.     

Growth control by cell wall pectins

Plant cell growth is controlled by the balance between turgor pressure and the extensibility of the cell wall. Several distinct classes of wall polysaccharides and their interactions contribute to the architecture and the emergent features of the wall. As a result, remarkable tensile strength is achieved without relinquishing extensibility. The control of growth and development does not only require a precisely regulated biosynthesis of cell wall components, but also constant remodeling and modification after deposition of the polymers. This is especially evident given the fact that wall deposition and cell expansion are largely uncoupled. Pectins form a functionally and structurally diverse class of galacturonic acid-rich polysaccharides which can undergo abundant modification with a concomitant change in physicochemical properties. This review focuses on homogalacturonan demethylesterification catalyzed by the ubiquitous enzyme pectin methylesterase (PME) as a growth control module. Special attention is drawn to the recently discovered role of this process in primordial development in the shoot apical meristem.     

Polypotency of the immunomodulatory effect of pectins

Pectins are the major component of plant cell walls, and they display diverse biological activities including immunomodulation. The pectin macromolecule contains fragments of linear and branched regions of polysaccharides such as homogalacturonan, rhamnogalacturonan-I, xylogalacturonan, and apiogalacturonan. These structural features determine the effect of pectins on the immune system. The backbones of pectic macromolecules have immunosuppressive activity. Pectins containing greater than 80% galacturonic acid residues were found to decrease macrophage activity and inhibit the delayed-type hypersensitivity reaction. Branched galacturonan fragments result in a biphasic immunomodulatory action. The branched region of pectins mediates both increased phagocytosis and antibody production. The fine structure of the galactan, arabinan, and apiogalacturonan side chains determines the stimulating interaction between pectin and immune cells. This review summarizes data regarding the relationship between the structure and immunomodulatory activity of pectins isolated from the plants of the European north of Russia and elucidates the concept of polypotency of pectins in native plant cell walls to both stimulate and suppress the immune response. The possible mechanisms of the immunostimulatory and anti-inflammatory effects of pectins are also discussed.