Preservation of membranes in anhydrobiotic organisms: the role of trehalose

Selection of Yeasts for Breadmaking by the Frozen-Dough Method

Eleven yeast strains suitable for frozen dough were selected from over 300 Saccharomyces strains. All of these were identified as Saccharomyces cerevisiae from morphological, cultural, and physiological characteristics. The selected yeast cells accumulated a higher amount of trehalose than did commercial bakers' yeast cells.

Nematodirus battus: development of cold hardiness in dormant eggs

Thermistors and an amplified bridge were used to detect supercooling points of Nematodirus battus eggs weighing ca. 1 microgram wet weight. A cooling rate of about 1 C min-1 was achieved with a manually controlled cold stage using the Peltier effect. The supercooling point of eggs fell during chilling at 5 +/- 1 C for up to 8 weeks from -34.48 +/- 0.49 C to -37.17 +/- 0.76 C. Juveniles freed from these eggs were less cold hardy than intact eggs but chilling improved their supercooling to a greater extent from -19.33 +/- 1.38 C to -32.10 +/- 0.68 C. These results were obtained with eggs showing the characteristic hatching response for this species after transfer from chilling at 5 C to higher temperatures (5-37 +/- 1 C). The results indicate eggs of N. battus acclimate to chilling at a time when previous work had established an increase in their trehalose content.

Solid-state NMR study of trehalose/1,2-dipalmitoyl-sn-phosphatidylcholine interactions

31P and 2H solid-state NMR studies of dry trehalose (TRE) and 1,2-dipalmitoyl-sn-phosphatidylcholine (DPPC) mixtures are reported. 31P spectra are consistent with a rigid head group above and below the calorimetric phase transition for both dry DPPC and a dry 2:1 TRE/DPPC mixture. In addition, 2H spectra of DPPC labeled at the 7-position of the sn-2 chain (2[7,7-2H2]DPPC) show exchange-narrowed line shapes with a width of 120 kHz over the temperature range 25-75 degrees C. These line shapes can be simulated with a model involving two-site jumps of the deuteron. In contrast, the 2H NMR spectrum of a dry 2:1 TRE/2[7,7-2H2]DPPC mixture above the phase transition (Tc = 46 degrees C) is narrowed by a factor of approximately 4 to a width of 29 kHz. Simulation of this spectrum requires a model involving four-site jumps of the deuteron and is indicative of highly disordered lipid acyl chains similar to those found in the L alpha-phases of hydrated lipids. Thus, TRE/DPPC mixtures above their transition temperatures exist in a new type of liquid crystalline like phase, which we term a lambda-phase. The observation of the dynamic properties of this new phase indicates the mechanism by which anhydrobiotic organisms maintain the integrity of their membranes upon dehydration.

The interaction of saccharides with lipid bilayer vesicles: stabilization during freeze-thawing and freeze-drying

The fusion of small unilamellar vesicles of phosphatidylcholines during freeze-thawing and freeze-drying/rehydration, and the suppression of fusion under these conditions by various saccharides, was investigated by gel filtration on Sepharose 4B, quasielastic light scattering, high-resolution 1H-NMR, ESR spin labeling, and differential scanning calorimetry. Freeze-thawing and freeze-drying of aqueous small unilamellar vesicle suspensions in the presence of sufficient sucrose had no significant effect on the average size and size distribution of small unilamellar vesicles. In the presence of sucrose the structural integrity and the permeability properties of the phosphatidylcholine bilayers were retained during freeze-thawing and freeze-drying. A comparison of the stabilizing effect of sucrose with that of trehalose and glucose showed that the stabilization is not sugar-specific but is a general property of saccharides. The fraction of small unilamellar vesicles recovered after freeze-thawing depended on the saccharide/phosphatidylcholine molar ratio. The mechanism of the cryoprotective effect involves binding of the sugar to the phospholipid polar group, probably through hydrogen bonding.

Inhibition of dehydration-induced fusion between liposomal membranes by carbohydrates as measured by fluorescence energy transfer

The relative abilities of a number of naturally occurring carbohydrates to inhibit dehydration-induced fusion between palmitoyloleoylphosphatidylcholine:phosphatidylserine (85:15) large unilamellar vesicles have been studied. Fusion events were quantified using a fluorescence resonance energy transfer technique. Trehalose was most effective at inhibiting fusion (0.4 g/trehalose/g lipid showed 30% probe intermixing), followed by maltose (60% intermixing), fructose (60%), sucrose (70%), glucose (80%), cellobiose, glycerol, raffinose, and myo-inositol (90%). The relative abilities of these carbohydrates to inhibit fusion correlate directly with their abilities to interact with phospholipids, maintain bilayer fluidity, and preserve biological membranes. The results are discussed in relation to the crystalline structure of the carbohydrates and their possible influence on level of interaction with phosphate head groups.

Proliposomes: a novel solution to an old problem

A procedure is described for the preparation of a dry, free-flowing granular product which, on addition of water, disperses/dissolves to form an isotonic liposomal suspension, suitable for administration either intravenously or by other routes. Various parameters have been investigated including the suitability of sorbitol and sodium chloride as carrier materials, the nature of the lipid(s) in the formulation, and the extent of lipid loading onto the carrier. These factors are shown to have a marked effect on both the dry product and the hydrated liposomes.

The metastability of saturated phosphatidylcholines depends on the acyl chain length

We report the peak temperatures and enthalpies of the main (gel to liquid crystal) transitions and 's-transitions' of symmetric saturated PC's (CnPC) with n varying from 12 to 22, where s-transition is defined as the transition between metastable and stable phases. The line for s-transition peak temperature versus n (t = 1.98n -16.0 degrees C) crosses the corresponding pre- and main-transition curves between n = 12 and 14. We also find that the metastability pattern for lipids of n less than 14 is different to that for n greater than 14 (and is similar to that of the phosphatidylethanolamine analogs). For n greater than 14 the enthalpy of the s-transition decreases with increasing n and extrapolates to zero above n = 20, implying that the s-(orthorhombic) and gel (quasi-hexagonal) phases become identical. That simultaneous gel-liquid crystal transition and metastability is restricted to the range n = 12 to 20 may be correlated with the predominance in natural lipids of these acyl chain lengths.

Preservation of freeze-dried liposomes by trehalose

One of the practical difficulties with the frequently proposed use of liposomes for delivery of water-soluble substances to cells in whole organisms is that liposomes are relatively unstable during storage. We have studied the ability of trehalose, a carbohydrate commonly found at high concentrations in organisms capable of surviving dehydration, to stabilize dry liposomes. With trehalose both inside and outside the bilayer, almost 100% of trapped solute was retained in rehydrated vesicles previously freeze-dried with 1.8 g trehalose/g dry phospholipid. Trehalose is very effective at inhibiting fusion between liposomes during drying, as assessed by freeze-fracture and resonance energy transfer between fluorescent probes incorporated into the bilayer. However, inhibition of fusion alone does not account for the preservation of the dry liposomes, since the concentration of trehalose required to prevent leakage is more than 10-fold that required to prevent fusion. We provide evidence that stabilization of the dry liposomes requires depression of transition temperature and consequent maintenance of the constituent lipids in the dry liposomes in a liquid crystalline phase.

Accumulation of alpha,alpha-trehalose by Rhizobium bacteria and bacteroids

Four strains of Rhizobium japonicum (61A76 and USDA 110, 123, and 138) were grown in eight different defined media. Regardless of the carbon or nitrogen source supplied, alpha, alpha-trehalose was the major carbohydrate (among mono- and disaccharides) accumulated by all four strains. After 7 to 9 days of growth, trehalose generally accounted for 90 to 100% of the mono- and disaccharides detected. None of the four strains would grow with trehalose as a carbon source, but the utilization of endogenous trehalose was demonstrated under carbon starvation conditions in water culture or when the carbon supply in a defined medium was exhausted. Under these conditions, a small amount of trehalose was lost from cells to the medium. In a survey of most of the serogroups of R. japonicum and several strains of other Rhizobium species, all strains tested were found to accumulate some trehalose. Trehalose concentrations varied widely; the highest concentration recorded was 41 micrograms/mg of dry weight. In all but six strains trehalose accounted for greater than 80% of the mono- and disaccharides in cells. Fast-growing strains of R. japonicum also accumulated small amounts trehalose. R. japonicum bacteroids also synthesized trehalose; the quantity in nodules varied in approximate correspondence to accumulation of trehalose by cultured bacteria. In young soybean nodules (29 days after planting), 45 to 80% of the trehalose was recovered in the cytosol. There were differences among R. japonicum strains in the retention of trehalose, and the proportion of trehalose retained by bacteroids increased with increasing plant age for all strains.

Membrane stabilization during freezing: the role of two natural cryoprotectants, trehalose and proline

The relative effectiveness of two natural cryoprotectants, proline and trehalose, in preserving membrane structure and function during freezing was studied. Isolated vesicles of sarcoplasmic reticulum (SR) from lobster muscle (Homarus americanus) were employed to study changes in structure and function during rapid freeze-thaw conditions. Both proline and trehalose were shown to effectively preserve the structure (assessed with freeze fracture) and function (assessed by the ability of the membranes to transport calcium) in the frozen vesicles. As a first step toward determining the mechanism of cryoprotection by these compounds, we have investigated their effectiveness in inhibiting freezing induced fusion between phospholipid vesicles. Pamiltoyloleoyl-phosphatidylcholine: phosphatidylserine (85:15 mole ratio) small unilamellar vesicles (SUVs) were made incorporating one of the following fluorescent probes, and energy donor, cholesteryl anthracene-9-carboxylate, or an energy acceptor, nitrobenzo-2-oxa-1,3-diazole phosphatidylethanolamine to investigate the amount of membrane mixing during rapid freeze-thaw cycles, and storage at -20 degrees C. Membrane mixing was measured as an energy transfer from donor to acceptor when donor vesicles and acceptor vesicles were mixed before a particular freezing treatment. Membrane mixing was correlated with structural changes in these membranes by freeze-fracture analysis. Both trehalose and proline were found to be more effective in preventing membrane mixing between SUVs than the standard protectants, glycerol and dimethylsulfoxide.

Protection of large unilamellar vesicles by trehalose during dehydration: retention of vesicle contents

The ability of trehalose and other sugars to maintain the integrity of large unilamellar vesicles subjected to dehydration and rehydration has been investigated. It is shown, employing freeze-fracture techniques, that large unilamellar vesicles prepared in the presence of trehalose at 125 mM or higher concentration do not exhibit significant structural changes during the dehydration-rehydration cycle. Further, up to 90% of entrapped 22Na or [3H]inulin is retained during this process. Other sugars also exhibited similar protective effects where trehalose was most effective, followed by sucrose, maltose, glucose and lactose. It is demonstrated that proton or Na+/K+ electrochemical gradients can be maintained during the dehydration-rehydration process, which can subsequently be used to drive the uptake of lipophilic cationic drugs such as adriamycin. The implications for long-term storage of liposomal systems for use in drug-delivery protocols are discussed.

Degradation of functional integrity during long-term storage of a freeze-dried biological membrane

Trehalose, and to some extent a few other carbohydrates, is capable of stabilizing the structure and function of isolated biological membranes during lyophilization. In this paper the results of investigations into the long-term stability of the lyophilized membrane-carbohydrate mixtures were reported. The effects of varying water content, oxygen level, and light on the rates of oxidation, browning, and degradation of biological activity were reported. The efficiency with which three carbohydrates stabilized membrane structure was also reported, with glucose shown to be less efficient than maltose or trehalose. Increased water content accelerated loss of biological activity, possibly because, under the same conditions, nonenzymatic browning and photooxidation were accelerated also. Glucose-containing samples were especially unstable at elevated humidities. Efficiency of preservation could be maximized by storage under conditions of low oxygen, low humidity, and dark, and by the inclusion of high levels of trehalose.

Ultrastructural changes during recovery from anabiosis in the plant parasitic nematode, Ditylenchus

Ultrastructural changes after desiccation and rehydration of the anabiotic fourth-stage juveniles of the plant parasitic nematode Ditylenchus dipsaci (Kuhn) Filipjev are described and quantified. Anabiotic juveniles retain their structural integrity, although the cuticle decreases in thickness and the muscle cell sarcoplasm condenses. In contrast the structure of the non-anabiotic nematode Panagrellus silusae is completely disorganized by desiccation. Following rehydration of D. dipsaci there is a lag phase of 2-3 hr before the nematodes become active. During this period the juveniles undergo an ordered series of morphological changes. The lipid droplets within the intestinal cells coalesce and the cuticle increases in thickness. The muscle cell sarcoplasm expands, the spacing of the thick myofilaments increases and the mitochondria swell before recovering a more normal appearance. These morphological changes, together with earlier metabolic studies, indicate that repair occurs during the lag phase prior to recovery. This may involve membrane repair and the re-establishment of the ionic gradients essential for normal muscle and nerve function.

Interaction of carbohydrates with dry dipalmitoylphosphatidylcholine

Interactions of six carbohydrates (trehalose, sucrose, glucose, raffinose, inositol, and glycerol) with dry dipalmitoylphosphatidylcholine (DPPC) were studied using differential scanning calorimetry (DSC) and infrared spectroscopy (ir) in order to elucidate the mechanism by which some of these carbohydrates preserve structural and functional integrity of dry membranes. Results with DSC showed that trehalose depressed the main transition temperature (Tmid) of dry DPPC below that of fully hydrated DPPC, and raised the enthalpy of that transition more than did addition of water. Results obtained with ir spectroscopy suggested a potential mechanism for this interaction. In the presence of most of the carbohydrates the ir spectrum for DPPC showed changes similar to those seen when water was added to dry DPPC, and the asymmetric P = O stretching band was diminished in intensity. The degree to which the carbohydrates tested affected the integrated intensity of this band and the Tmid was correlated with the ability of those carbohydrates to preserve dry membranes. Also, bands assigned to -OH deformations in the trehalose and other carbohydrates were depressed in the presence of DPPC. Based on these observations, it is suggested that the mechanism of interaction between the carbohydrate and lipid involves hydrogen bonding between -OH groups on the carbohydrate and the phosphate head group of the phospholipid. The only exceptions to this pattern are glycerol, which depresses Tmid of dry DPPC, and myo-inositol, which has no effect on Tmid or the ir spectrum of DPPC; neither carbohydrate can preserve dry membranes. It is suggested, based on ir spectroscopy and previous results with monolayer preparations, that glycerol interacts with phospholipids by a mechanism different from that shown by the other carbohydrates.

Preservation of functional integrity during long term storage of a biological membrane

Sarcoplasmic reticulum vesicles freeze-dried in the presence of trehalose retain most of their original biological activity for short periods. When the dry vesicles are stored for longer periods in air, Ca2+-transport becomes uncoupled from ATPase activity within a few days. However, when they are stored under vacuum, ATPase activity, Ca2+ transport, and coupling between Ca2+ transport and ATP utilization are maintained essentially intact for at least 110 days.

Microwave dielectric measurements (0.8-70 GHz) on Artemia cysts at variable water content

Dielectric permittivity measurements are reported for cysts of Artemia, a crustacean known as the brine shrimp. Using coaxial and waveguide techniques we examined the frequency range from 0.8 to 70 GHz. Taking advantage of the ability of this system to reversibly lose essentially all intracellular water, we determined the permittivity over the entire range of cyst water contents. Although experimental errors prevent a rigorous treatment of the data, we advance the general conclusion that little of the water in this system behaves dielectrically like pure water, regardless of water content. This conclusion is supported by, and is consistent with, the results of previously published studies that probe the motional properties of water in this system using nuclear magnetic resonance spectroscopy and quasi-elastic neutron scattering.

Infrared spectroscopic studies on interactions of water and carbohydrates with a biological membrane

Infrared spectroscopy was used to investigate the changes in bands assigned to phospholipids and proteins in dehydrated and rehydrated sarcoplasmic reticulum. The changes in CH2 and CH3 stretching bands, amide bands, and phosphate stretching bands are similar to shifts in frequency seen for those bands in phospholipid and protein preparations during thermotropic phase transitions and hydration. IR studies on dry trehalose-sarcoplasmic reticulum mixtures show similar results; with increasing trehalose concentration in the dry mixtures, amide and phosphate bands shift to frequencies characteristic of hydrated samples. Changes in bands assigned to OH deformations in the trehalose suggest that the interaction between the carbohydrate and membrane is by means of hydrogen bonding between these -OH groups and membrane components.