Organic osmolytes as compatible, metabolic and counteracting cytoprotectants in high osmolarity and other stresses

Structure and energetics of the hydrogen-bonded backbone in protein folding

We seek to understand the link between protein thermodynamics and protein structure in molecular detail. A classical approach to this problem involves assessing changes in protein stability resulting from added cosolvents. Under any given conditions, protein molecules in aqueous buffer are in equilibrium between unfolded and folded states, U(nfolded) <==> N(ative). Addition of organic osmolytes, small uncharged compounds found throughout nature, shift this equilibrium. Urea, a denaturing osmolyte, shifts the equilibrium toward U; trimethylamine N-oxide (TMAO), a protecting osmolyte, shifts the equilibrium toward N. Using the Tanford Transfer Model, the thermodynamic response to many such osmolytes has been dissected into groupwise free energy contributions. It is found that the energetics involving backbone hydrogen bonding controls these shifts in protein stability almost entirely, with osmolyte cosolvents simply dialing between solvent-backbone versus backbone-backbone hydrogen bonds, as a function of solvent quality. This reciprocal relationship establishes the essential link between protein thermodynamics and the protein's hydrogen-bonded backbone structure.

Metagenomic and stable isotopic analyses of modern freshwater microbialites in Cuatro Ciénegas, Mexico

Ancient biologically mediated sedimentary carbonate deposits, including stromatolites and other microbialites, provide insight into environmental conditions on early Earth. The primary limitation to interpreting these records is our lack of understanding regarding microbial processes and the preservation of geochemical signatures in contemporary microbialite systems. Using a combination of metagenomic sequencing and isotopic analyses, this study describes the identity, metabolic potential and chemical processes of microbial communities from living microbialites from Cuatro Ciénegas, Mexico. Metagenomic sequencing revealed a diverse, redox-dependent microbial community associated with the microbialites. The microbialite community is distinct from other marine and freshwater microbial communities, and demonstrates extensive environmental adaptation. The microbialite metagenomes contain a large number of genes involved in the production of exopolymeric substances and the formation of biofilms, creating a complex, spatially structured environment. In addition to the spatial complexity of the biofilm, microbial activity is tightly controlled by sensory and regulatory systems, which allow for coordination of autotrophic and heterotrophic processes. Isotopic measurements of the intracrystalline organic matter demonstrate the importance of heterotrophic respiration of photoautotrophic biomass in the precipitation of calcium carbonate. The genomic and stable isotopic data presented here significantly enhance our evolving knowledge of contemporary biomineralization processes, and are directly applicable to studies of ancient microbialites.

Resting membrane potentials recorded on-site in intact skeletal muscles from deep sea fish (Sigmops gracile) salvaged from depths up to 1.000 m

The effect of elevated ambient pressures in deep sea fish residing at certain bottom depths or even covering different depth levels during migration is poorly understood. Elevated pressures are known to influence membrane properties of various excitable tissues in many species. Reliable results on membrane properties require freshly isolated living cells and short decompression times. During a scientific cruise south of Japan, deep sea fish were sampled from depths up to 1.000 m by using the intelligent operative net sampling system IONESS. On-site electrophysiological recordings of resting membrane potentials were performed in freshly isolated skeletal muscles from Sigmops gracile. Experiments were conducted at various extracellular K+ concentrations to derive relative membrane ion permeabilities and estimate intracellular K+ concentrations [K+]i in the muscles studied. With increasing sampling depth, a tendency for depolarized resting membrane potentials was observed. This could be explained by an increase in relative Na+ over K+ resting membrane permeabilities. Fish samples from deeper sites also had larger [K+]i values compared with shallower sites. This study represents a first approach to perform sophisticated physiological live-cell experiments on board a fully operating ship. These data are expected to more realistically reflect the physiological state of biological preparations residing in the deep sea.

Ultraviolet A induces transport of compatible organic osmolytes in human dermal fibroblasts

Compatible organic osmolytes, such as betaine, myo-inositol and taurine, are involved in cell protection. Human dermal fibroblasts accumulate these osmolytes and express mRNA specific for their transporting systems betaine-/gamma-amino-n-butyric acid (GABA) transporter (BGT-1), sodium-dependent myo-inositol transporter (SMIT) and taurine transporter (TAUT). Taurine uptake was about sixfold higher than that of betaine and myo-inositol. Compared with normoosmotic (305 mOsm/l) control, hyperosmotic exposure (405 mOsm/l) led to a twofold induction of osmolyte uptake. Ultraviolet A (UVA) upregulated osmolyte transporter mRNA levels and increased osmolyte uptake. Taurine inhibited UVA-induced interleukin-6 (Il-6) mRNA expression by 40%. Furthermore, Il-6 accumulation in the supernatants of UVA-irradiated dermal fibroblasts was much slower when cells were preincubated with taurine. These data indicate that taurine accumulation seems to be part of the fibroblast response to UVA radiation and may protect against UVA-induced Il-6 overexpression.

Pharmacological management of dry eye in the elderly patient

Dry eye disease is a common and increasingly prevalent condition particularly associated with advancing age and postmenopausal women. Epidemiological studies identify prevalence rates ranging from 7% in the US to 33% in the Asian population. Research increasingly identifies risk factors of increasing age, female sex, smoking, use of video display terminals and use of certain medications as well as environmental stresses as aggravating factors for the disease. Basic and clinical investigations provide cumulative evidence of hyperosmolarity of the tear film and ocular surface/lacrimal gland inflammation as pathogenic features of dry eye disease. A decline in systemic and local levels of sex hormones is associated with advancing age and advancing disease. Pharmacological therapeutic interventions include enhanced lubricants and anti-inflammatory drugs such as topical corticosteroids and ciclosporin (cyclosporine A). Secretagogues and hormonal supplementation are potential future therapies. The increased understanding of the contributing and pathogenetic factors responsible for dry eye provides a rationale for multiple therapeutic options for this multi-factorial disease. In the elderly patient it is important to recognize the physical and cognitive limitations that will influence the selection of appropriate topical medication.

Synergism between the chaperone-like activity of the stress regulated ASR1 protein and the osmolyte glycine-betaine

Abiotic stress may result in protein denaturation. To confront protein inactivation, plants activate protective mechanisms that include chaperones and chaperone-like proteins, and low-molecular weight organic molecules, known as osmolytes or compatible solutes. If these protective processes fail, the irreversibly damaged proteins are targeted for degradation. Tomato ASR1 (SlASR1) is encoded by a plant-specific gene. Steady state levels of transcripts and protein are transiently induced by salt and water stress in an ABA-dependent manner. SlASR1 is localized in both the cytosol as unstructured monomers and in the nucleus as structured DNA-bound dimers. We show here that the unstructured form of SlASR1 has chaperone-like activity and can stabilize a number of proteins against denaturation caused by heat and freeze-thaw cycles. The protective activity of SlASR1 is synergistic with that of the osmolyte glycine-betaine, which accumulates under stress conditions. We suggest that the cytosolic pool of ASR1 protects proteins from denaturation.

Lineage selection of functional and cryopreservable human embryonic stem cell-derived neurons

A major prerequisite for the biomedical application of human embryonic stem cells (hESC) is the derivation of defined and homogeneous somatic cell types. Here we present a human doublecortin (DCX) promoter-based lineage-selection strategy for the generation of purified hESC-derived immature neurons. After transfection of hESC-derived neural precursors with a DCX-enhanced green fluorescent protein construct, fluorescence-activated cell sorting enables the enrichment of immature human neurons at purities of up to 95%. Selected neurons undergo functional maturation and are able to establish synaptic connections. Considering that the applicability of purified hESC-derived neurons would largely benefit from an efficient cryopreservation technique, we set out to devise defined freezing conditions involving caspase inhibition, which yield post-thaw recovery rates of up to 83%. Combined with our lineage-selection procedure this cryopreservation technique enables the generation of human neurons in a ready-to-use format for a large variety of biomedical applications.

Glycine betaine uptake by the ProXVWZ ABC transporter contributes to the ability of Mycobacterium tuberculosis to initiate growth in human macrophages

Mycobacterium tuberculosis maintains a large genetic capacity necessary for growth in different environments during infection and survival upon aerosol transmission to new hosts. Screening for bacterial RNAs produced in response to host interactions produced candidate lists where we noted proXVWZ, annotated as encoding a putative glycine betaine or proline transporter. As high surface-to-volume ratios make bacterial cells particularly vulnerable to changes in water availability, we investigated the contributions of this transporter to the ability of M. tuberculosis to colonize macrophages. An H37Rv proXVWZ mutant was impaired for initial survival and intracellular growth and exhibited reduced growth at elevated medium osmolarity. This defect could be complemented by restoring proXVWZ and was attributable to a failure to accumulate the compatible solute glycine betaine. We then demonstrated that ProXVWZ allows M. tuberculosis to obtain betaine from host macrophages and thereby contributes to early steps in colonizing this niche.

Effects of solution crowding on actin polymerization reveal the energetic basis for nucleotide-dependent filament stability

Actin polymerization is a fundamental cellular process involved in cell structure maintenance, force generation, and motility. Phosphate release from filament subunits following ATP hydrolysis destabilizes the filament lattice and increases the critical concentration (C(c)) for assembly. The structural differences between ATP- and ADP-actin are still debated, as well as the energetic factors that underlie nucleotide-dependent filament stability, particularly under crowded intracellular conditions. Here, we investigate the effect of crowding agents on ATP- and ADP-actin polymerization and find that ATP-actin polymerization is largely unaffected by solution crowding, while crowding agents lower the C(c) of ADP-actin in a concentration-dependent manner. The stabilities of ATP- and ADP-actin filaments are comparable in the presence of physiological amounts (approximately 30% w/v) and types (sorbitol) of low molecular weight crowding agents. Crowding agents act to stabilize ADP-F-actin by slowing subunit dissociation. These observations suggest that nucleotide hydrolysis and phosphate release per se do not introduce intrinsic differences in the in vivo filament stability. Rather, the preferential disassembly of ADP-actin filaments in cells is driven through interactions with regulatory proteins. Interpretation of the experimental data according to osmotic stress theory implicates water as an allosteric regulator of actin activity and hydration as the molecular basis for nucleotide-dependent filament stability.

Trimetazidine reduces early and long-term effects of experimental renal warm ischemia: a dose effect study

OBJECTIVE

Renal ischemia reperfusion (IR) injury (IRI) is an important mechanism of acute renal failure (ARF) and a crucial factor of tissue damage during vascular surgery. IR may lead to tissue destruction and influence the early and long-term outcome of organs. The anti-anginal medication trimetazidine (TMZ) is a drug, the protective effects of which have been already assessed during cold preservation and warm ischemia (WI). The objective of this dose-effect study was to assess the role of TMZ in severe renal WI model.

MATERIALS AND METHODS

We have used an established WI pig kidney model associated with a uninephrectomy condition and studied the dose-dependent role of TMZ (1, 5, and 10 mg/Kg, i.v. for 24 hours before WI) against deleterious effects of WI (60 minutes of WI followed by reperfusion) compared with sham-operated (control) and uninephrectomized animals (unif). Direct effect of TMZ was determined using different variables: renal function (creatinine clearance; C(cr)) and indirectly, the consequences on inflammation (cells infiltration), rate of apoptosis, fibrosis development, and renal epithelial cells change into myofibroblast, which defined epithelial to mesenchymal transition (alpha-smooth muscle actin [alpha-SMA] and vimentin expression).

RESULTS

TMZ (5 or 10 mg/Kg) significantly increased C(cr) and reduced the inflammatory response prevalent in ischemic kidney injury and rate of apoptosis expression. In addition, the limitation of initial IRI was correlated with an earlier and greater expression of hypoxia-inducible transcription factor-1alpha (HIF-1alpha), which is a hypoxia marker during kidney regeneration. A reduction of the tubulointerstitial development of fibrosis and a limitation of the alpha-smooth muscle actin expression (alpha-SMA) was observed with TMZ treatment. At 3 months, vimentin expression was increased in WI groups without TMZ or low TMZ dose treatment compared with 5 or 10 mg/Kg treated groups.

CONCLUSION

Collectively, these data suggest that TMZ made the warm ischemic kidneys more resistant to the deleterious impact of a single episode of IR and could have a role in preserving the ischemic kidney from long-term damage.

Protection mechanisms in the resurrection plant Xerophyta viscosa: cloning, expression, characterisation and role of XvINO1, a gene coding for a myo-inositol 1-phosphate synthase

We have used reverse transcription-PCR coupled with 5'- and 3'-RACE to isolate a full length INO1 cDNA (1692 bp with an ORF of 1530) from the resurrection plant Xerophyta viscosa Baker. XvINO1 encodes 510 amino acids, with a predicted MW of 56.7kD and contains four sequence motifs that are highly conserved in plant myo-inositol-1-phosphate synthases (MIPS, EC5.5.1.4), the enzyme that catalyses the first step in the formation of myo-inositol (Ino). Northern and western analyses show that the transcript and protein are constitutively present in leaves but their expression increases, temporarily, in response to both accumulative salt stress (~300 mM NaCl) and desiccation (to 5% relative water content). Leaf Ino concentration increases 40-fold during the first 6 h of salt stress, and levels of this and other carbohydrates (galactinol, sucrose, raffinose, stachyose and hexoses) remain elevated relative to control leaves for the duration of salt stress treatment. The timing and pattern of accumulation of these carbohydrates differ under desiccation stress and we propose that they perform different functions in the respective stresses. These are elaborated in discussion of our data.

Revisiting the Krogh Principle in the post-genome era: Caenorhabditis elegans as a model system for integrative physiology research

Molecular biology drove a powerful reductionist or ;molecule-centric' approach to biological research in the last half of the 20th century. Reductionism is the attempt to explain complex phenomena by defining the functional properties of the individual components that comprise multi-component systems. Systems biology has emerged in the post-genome era as the successor to reductionism. In my opinion, systems biology and physiology are synonymous. Both disciplines seek to understand multi-component processes or 'systems' and the underlying pathways of information flow from an organism's genes up through increasingly complex levels of organization. The physiologist and Nobel laureate August Krogh believed that there is an ideal organism in which almost every physiological problem could be studied most readily (the 'Krogh Principle'). If an investigator's goal were to define a physiological process from the level of genes to the whole animal, the optimal model organism for him/her to utilize would be one that is genetically and molecularly tractable. In other words, an organism in which forward and reverse genetic analyses could be carried out readily, rapidly and economically. Non-mammalian model organisms such as Escherichia coli, Saccharomyces, Caenorhabditis elegans, Drosophila, zebrafish and the plant Arabidopsis are cornerstones of systems biology research. The nematode C. elegans provides a particularly striking example of the experimental utility of non-mammalian model organisms. The aim of this paper is to illustrate how genetic, functional genomic, molecular and physiological methods can be combined in C. elegans to develop a systems biological understanding of fundamental physiological processes common to all animals. I present examples of the experimental tools available for the study of C. elegans and discuss how we have used them to gain new insights into osmotic stress signaling in animal cells.

Metabotyping of Caenorhabditis elegans reveals latent phenotypes

Assigning functions to every gene in a living organism is the next challenge for functional genomics. In fact, 85-90% of the 19,000 genes of the nematode Caenorhabditis elegans genome do not produce any visible phenotype when inactivated, which hampers determining their function, especially when they do not belong to previously characterized gene families. We used (1)H high-resolution magic angle spinning NMR spectroscopy ((1)H HRMAS-NMR) to reveal the latent phenotype associated to superoxide dismutase (sod-1) and catalase (ctl-1) C. elegans mutations, both involved in the elimination of radical oxidative species. These two silent mutations are significantly discriminated from the wild-type strain and from each other. We identify a metabotype significantly associated with these mutations involving a general reduction of fatty acyl resonances from triglycerides, unsaturated lipids being known targets of free radicals. This work opens up perspectives for the use of (1)H HRMAS-NMR as a molecular phenotyping device for model organisms. Because it is amenable to high throughput and is shown to be highly informative, this approach may rapidly lead to a functional and integrated metabonomic mapping of the C. elegans genome at the systems biology level.

The reversal by sulfate of the denaturant activity of guanidinium

Guanidinium (Gdm+) chloride is a powerful protein denaturant, whereas the sulfate dianion (SO42-) is a strong stabilizer of folded protein states; Gdm2SO4 is effectively neutral in its effects on protein stability. While the "neutralizing" effects of protein-stabilizing solutes on the activity of denaturants can be broadly interpreted in terms of additive effects of the solutes, recent experimental and simulation studies support a role for hetero-ion interactions in the effect of sulfate on Gdm+ denaturation [Mason, P. E.; et al. J. Phys. Chem. B 2005, 109, 24185-24196]. Here we describe an experimental strategy for testing this mechanism that involves spectroscopic analysis of the separate effects of alkali metal sulfates (Na2SO4, Rb2SO4), GdmCl, and Gdm2SO4 on the folded populations of several peptides chosen to dissect specific noncovalent contributions to the conformational stability of proteins [alanine-based helical peptides stabilized by hydrogen bonds, tryptophan zipper (trpzip) peptides stabilized largely by cross-strand indole-indole interactions]. While the trpzip peptides are highly sensitive to GdmCl denaturation, they are unaffected by NaCl, Na2SO4, or Gdm2SO4, indicating that the reversal of the denaturant activity of Gdm+ by sulfate in this case is not due to competing stabilizing (sulfate) and destabilizing (Gdm+) interactions. Gdm2SO4 was found to retain considerable denaturant activity against alanine-based alpha-helical peptides. The differences in the effects of Gdm2SO4 on the two peptide types can be understood in terms of the different mechanisms of Gdm+ denaturation of trpzip peptides and helical peptides, respectively, and the specific nature of Gdm+ and SO42- ionic "clustering" that differentially affects the ability of Gdm+ to make the molecular interactions with the peptides that underlie its denaturant activity.

Molecular and genetic characterization of osmosensing and signal transduction in the nematode Caenorhabditis elegans

Osmotic homeostasis is a fundamental requirement for life. In general, the effector mechanisms that mediate cellular and extracellular osmoregulation in animals are reasonably well defined. However, at the molecular level, little is known about how animals detect osmotic and ionic perturbations and transduce them into regulatory responses. The nematode Caenorhabditis elegans provides numerous powerful experimental advantages for defining the genes and integrated gene networks that underlie basic biological processes. These advantages include a fully sequenced and well-annotated genome, forward and reverse genetic and molecular tractability, and a relatively simple anatomy. C. elegans normally inhabits soil environments where it is exposed to repeated osmotic stress. In the laboratory, nematodes readily acclimate to and recover from extremes of hypertonicity. We review recent progress in defining the molecular mechanisms that underlie osmosensing and associated signal transduction in C. elegans. Some of these mechanisms are now known to be highly conserved. Therefore, studies of osmosensing in nematodes have provided, and will undoubtedly continue to provide, new insights into similar processes in more complex organisms including mammals.

Trimethylamine N-oxide counteracts the denaturing effects of urea or GdnHCl on protein denatured state

To understand trimethylamine N-oxide (TMAO) attenuation of the denaturating effects of urea or guanidine hydrochloride (GdnHCl), we have determined the apparent transfer free energies (DeltaG(tr)(')) of cyclic dipeptides (CDs) from water to TMAO, urea or GdnHCl, and also the blends of TMAO and denaturants (urea or GdnHCl) at a 1:2 ratio as well as various denaturant concentrations in the presence of 1M TMAO, through the solubility measurements, at 25 degrees C. The CDs investigated in the present study included cyclo(Gly-Gly), cyclo(Ala-Ala) and cyclo(Val-Val). The observed DeltaG(tr)(') values indicate that TMAO can stabilize the CDs while urea or GdnHCl can destabilize the CDs. Furthermore, the DeltaG(tr)(') values of the blends of TMAO with urea or GdnHCl revealed that TMAO strongly counteracted the denaturating effects of urea on CDs in all instances, however, TMAO partially counteracted the perturbing effects of GdnHCl on CDs. TMAO counteraction ability of the deleterious effects of denaturants depended on the denaturant-CDs pair. The experimental results were further used to estimate the transfer free energies (Deltag(tr)(')) of the various functional group contributions from water to TMAO, urea or GdnHCl individually and to the combinations of TMAO and the denaturants in various ratios.

Seasonal variability of free amino acids in two marine bivalves, Macoma balthica and Mytilus spp., in relation to environmental and physiological factors

The seasonal variability of the intracellular free amino acid (FAA) concentration was studied in 5 Macoma balthica populations and 7 Mytilus spp. populations along their European distribution. Because of the well known physiological role of FAA as organic osmolytes for salinity induced cell volume regulation in marine osmoconformers, FAA variations were compared in bivalve populations that were exposed to high vs. low intraannual salinity fluctuations. In general, seasonal FAA variations were more pronounced in M. balthica than in Mytilus spp. In both bivalve taxa from different locations in the Baltic Sea, highest FAA concentrations were found in autumn and winter and low FAA concentrations were measured in summer. Seasonal patterns were less pronounced in both taxa at locations with constant salinity conditions. In contrast to Baltic Sea populations, Atlantic and Mediterranean bivalves showed high FAA concentrations in summer and low values in winter, regardless of seasonal salinity fluctuations. Significant seasonal FAA variations at locations with constant salinity conditions showed that salinity appeared not to be the main factor in determining FAA concentrations. The seasonal patterns of the main FAA pool components, i.e. alanine, glycine and taurine, are discussed in the context of seasonal variations in environmental factors (salinity, temperature) and physiological state (glycogen content, reproductive stage).

Organic osmolytes in the developing kidney of the Australian brush-tailed possum, Trichosurus vulpecula

Developmental changes in the plasma and urine composition of 120 immature possums, Trichosurus vulpecula, were investigated and correlated with changes in the osmolyte composition of the kidneys. In early life, when the animal is confined in the pouch, the urine is more or less isosmotic with the plasma (300+/-70 mOsm kg(-1)), but rises steeply in animals more than 90 days old, up to 667+/-53 mOsm kg(-1) in the oldest age group. In parallel with this change there are corresponding increases in medullary osmolytes. Measured as mmol kg(-1) wet weight, sorbitol was found to increase from 2.1+/-0.8 to 9.7+/-2.2, myo-inositol from 10.9+/-6.2 to 33.6+/-11.7, while the methylamines glycerophosphorylcholine and betaine rose from 6.2+/-0.5 to 15.3+/-3.1 and 3.9+/-2.2 to 9.4+/-2.5 mmol kg(-1) wet weight respectively. Medullary taurine showed no significant changes with age in young possums, while urea increased from 11+/-4.6 to 49+/-7.1 mmol kg(-1) wet weight. These values are similar to, but less than, those found in adult kidneys, but probably further refinement of the concentrating ability of the kidney occurs after the young animal becomes independent.

Impact of genetics and environment on nutritional and metabolite components of maize grain

The Organization for Economic Co-operation and Development (OECD) recommends the measurement of specific plant components for compositional assessments of new biotechnology-derived crops. These components include proximates, nutrients, antinutrients, and certain crop-specific secondary metabolites. A considerable literature on the natural variability of these components in conventional and biotechnology-derived crops now exists. Yet the OECD consensus also suggests measurements of any metabolites that may be directly associated with a newly introduced trait. Therefore, steps have been initiated to assess natural variation in metabolites not typically included in the OECD consensus but which might reasonably be expected to be affected by new traits addressing, for example, nutritional enhancement or improved stress tolerance. The compositional study reported here extended across a diverse genetic range of maize hybrids derived from 48 inbreds crossed against two different testers. These were grown at three different, but geographically similar, locations in the United States. In addition to OECD analytes such as proximates, total amino acids and free fatty acids, the levels of free amino acids, sugars, organic acids, and selected stress metabolites in harvested grain were assessed. The major free amino acids identified were asparagine, aspartate, glutamate, and proline. The major sugars were sucrose, glucose, and fructose. The most predominant organic acid was citric acid, with only minor amounts of other organic acids detected. The impact of genetic background and location was assessed for all components. Overall, natural variation in free amino acids, sugars, and organic acids appeared to be markedly higher than that observed for the OECD analytes.

Impact of genetics and environment on nutritional and metabolite components of maize grain

The Organization for Economic Co-operation and Development (OECD) recommends the measurement of specific plant components for compositional assessments of new biotechnology-derived crops. These components include proximates, nutrients, antinutrients, and certain crop-specific secondary metabolites. A considerable literature on the natural variability of these components in conventional and biotechnology-derived crops now exists. Yet the OECD consensus also suggests measurements of any metabolites that may be directly associated with a newly introduced trait. Therefore, steps have been initiated to assess natural variation in metabolites not typically included in the OECD consensus but which might reasonably be expected to be affected by new traits addressing, for example, nutritional enhancement or improved stress tolerance. The compositional study reported here extended across a diverse genetic range of maize hybrids derived from 48 inbreds crossed against two different testers. These were grown at three different, but geographically similar, locations in the United States. In addition to OECD analytes such as proximates, total amino acids and free fatty acids, the levels of free amino acids, sugars, organic acids, and selected stress metabolites in harvested grain were assessed. The major free amino acids identified were asparagine, aspartate, glutamate, and proline. The major sugars were sucrose, glucose, and fructose. The most predominant organic acid was citric acid, with only minor amounts of other organic acids detected. The impact of genetic background and location was assessed for all components. Overall, natural variation in free amino acids, sugars, and organic acids appeared to be markedly higher than that observed for the OECD analytes.

A reassessment of the function of the so-called compatible solutes in the halophytic plumbaginaceae Limonium latifolium

The compatible solute hypothesis posits that maintaining osmotic equilibrium under conditions of high salinity requires synthesis of organic compounds, uptake of potassium ions, and partial exclusion of NaCl. To assess whether osmotic adaptation in Limonium latifolium proceeds according to this hypothesis, a comprehensive analysis of solute accumulation during NaCl treatments was conducted. Determination of prevailing inorganic ions and establishment of the metabolic profiles for low M(r) organic substances revealed that contrary to the mentioned hypothesis the major contributors to osmolarity were constituted by inorganic solutes. Independent of salinity, only 25% of this osmolarity resulted from organic solutes such as Suc and hexoses. Proline (Pro), beta-alanine betaine, and choline-O-sulfate were minor contributors to osmolarity. Compatible inositols also occurred, especially chiro-inositol, characterized for the first time in this species, to our knowledge. Principal component analysis showed that only a limited number of metabolic reconfigurations occurred in response to dynamic changes in salinity. Under such conditions only sugars, chiro-inositol, and Pro behave as active osmobalancers. Analysis of metabolic profiles during acclimatization to either mild salinity or nonsaline conditions showed that organic solute accumulation is predominantly controlled by constitutive developmental programs, some of which might be slightly modulated by salinity. Osmolarity provided under such conditions can be sufficient to maintain turgor in salinized seedlings. Compartmental analysis of Pro and beta-alanine betaine in leaf tissues demonstrated that these solutes, mainly located in vacuoles under nonsaline conditions, could be partly directed to the cytosol in response to salinization. Thus they did not conform with the predictions of the compatible solute hypothesis.

Thermal diapirism and the habitability of the icy shell of Europa

Europa's chaos and lenticulae features may have originated by thermal diapirs related to convective plumes. Warm ice plumes could be habitable, since their temperature is close to the ice melting temperature. Moreover, thermal plumes intruding into the lower stagnant lid warm several kilometers of country ice above 230 K for periods of 10(5) years, and hundreds of meters above 240 K for periods of 10(4) years. Diapir coalescence generating chaos areas should provide a large zone with temperature above approximately 240 K for thousands of years. A temperature above approximately 230 K is potentially interesting for astrobiology, since it corresponds to the lowest temperature at which microbial metabolic activity in Antarctic ice has been reported. So, the warming by thermal plumes could cause an aureole of biological activation/reactivation in the country ice. Adaptation of life to either high salinity or low temperature is similar: it requires the synthesis of compatible solutes, like trehalose or glycerol, which are efficient cryoprotectants. We therefore propose that the future astrobiological exploration of Europa should include the search for compatible solutes in chaos and lenticulae features.

Cell volume regulation in the perfused liver of a freshwater air-breathing cat fish Clarias batrachus under aniso-osmotic conditions: roles of inorganic ions and taurine

The roles of various inorganic ions and taurine, an organic osmolyte, in cell volume regulation were investigated in the perfused liver of a freshwater air-breathing catfish Clarias batrachus under aniso-osmotic conditions. There was a transient increase and decrease of liver cell volume following hypotonic (-80 mOsmol/l) and hypertonic (+80 mOsmol/l) exposures,respectively, which gradually decreased/increased near to the control level due to release/uptake of water within a period of 25-30 min. Liver volume decrease was accompanied by enhanced efflux of K+ (9.45 +/- 0.54 micromol/g liver) due to activation of Ba(2+)- and quinidine-sensitive K(+) channel, and to a lesser extent due to enhanced efflux of Cl(-) (4.35+/- 0.25 micromol/g liver) and Na+ (3.68+/- 0.37 micromol/g liver). Conversely, upon hypertonic exposure, there was amiloride-and ouabain-sensitive uptake of K+ (9.78+/- 0.65 micromol/g liver), and also Cl(-) (3.72 +/- 0.25 micromol/g liver).The alkalization/acidification of the liver effluents under hypo-/hypertonicity was mainly due to movement of various ions during volume regulatory processes. Taurine,an important organic osmolyte, appears also to play a very important role in hepatocyte cell volume regulation in the walking catfish as evidenced by the fact that hypo- and hyper-osmolarity caused transient efflux (5.68 +/- 0.38 micromol/g liver) and uptake (6.38 +/- 0.45 micromol/g liver) of taurine, respectively. The taurine efflux was sensitive to 4,4' -di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS, an anion channel blocker), but the uptake was insensitive to DIDS, thus indicating that the release and uptake of taurine during volume regulatory processes are unidirectional. Although the liver of walking catfish possesses the RVD and RVI mechanisms, it is to be noted that liver cells remain partly swollen and shrunken during anisotonic exposures,thereby possibly causing various volume-sensitive metabolic changes in the liver as reported earlier.

Management and Therapy of Dry Eye Disease: Report of the Management and Therapy Subcommittee of the International Dry Eye WorkShop (2007)

The members of the Management and Therapy Subcommittee assessed current dry eye therapies. Each member wrote a succinct evidence-based review on an assigned aspect of the topic, and the final report was written after review by and with consensus of all subcommittee members and the entire Dry Eye WorkShop membership. In addition to its own review of the literature, the Subcommittee reviewed the Dry Eye Preferred Practice Patterns of the American Academy of Ophthalmology and the International Task Force (ITF) Delphi Panel on Dry Eye. The Subcommittee favored the approach taken by the ITF, whose recommended treatments were based on level of disease severity. the recommendations of the Subcommittee are based on a modification of the ITF severity grading scheme, and suggested treatments were chosen from a menu of therapies for which evidence of therapeutic effect had been presented.

Which mechanisms are involved in taurine-dependent granulocytic immune response or amino- and α-keto acid homeostasis?

We examined the effects of beta-alanine (taurine analogue and taurine transport antagonist), taurine (regarding its role in neutrophil (PMN) immunonutrition) and taurine combined either with L-NAME (inhibitor of *NO-synthase), SNAP (*NO donor), DON (glutamine-analogue and inhibitor of glutamine-requiring enzymes), DFMO (inhibitor of ornithine-decarboxylase) and beta-alanine on neutrophil amino- and alpha-keto acid profiles or important PMN immune functions in order to establish whether taurine transport-, nitric oxide-, glutamine- or ornithine-dependent mechanisms are involved in any of the taurine-induced effects. According to the present findings, the taurine-mediated effect appears to be based primarily on a modulation of important transmembraneous transport mechanisms and only secondarily on directly or indirectly induced modifications in intragranulocytic amino- and alpha-keto acid homoeostasis or metabolism. Although a direct relation to the parallel observed immunological modifications can only be presumed, these results show very clearly that compositional modifications in the free intragranulocytic amino- and alpha keto-acid pools coinciding with changes in intragranulocytic taurine levels are relevant metabolic determinants that can significantly influence the magnitude and quality of the granulocytic immune response.

A plastid-localized glycogen synthase kinase 3 modulates stress tolerance and carbohydrate metabolism

Glycogen synthase kinase 3 (GSK-3) was originally identified as a regulator of glycogen synthesis in mammals. Like starch in plants, glycogen is a polymer of glucose, and serves as an energy and carbon store. Starch is the main carbohydrate store in plants. Regulation of starch metabolism, in particular in response to environmental cues, is of primary importance for carbon and energy flow in plants but is still obscure. Here, we provide evidence that MsK4, a novel Medicago sativa GSK-3-like kinase, connects stress signalling with carbon metabolism. MsK4 was found to be a plastid-localized protein kinase that is associated with starch granules. High-salt stress rapidly induced the in vivo kinase activity of MsK4. Metabolic profiling of MsK4 over-expressor lines revealed changes in sugar metabolism, including increased amounts of maltose, the main degradation product of starch in leaves. Plants over-expressing MsK4 showed improved tolerance to salt stress. Moreover, under high-salinity conditions, MsK4-over-expressing plants accumulated significantly more starch and showed modified carbohydrate content compared with wild-type plants. Overall, these data indicate that MsK4 is an important regulator that adjusts carbohydrate metabolism to environmental stress.

Effects of environmental salinity and temperature on osmoregulatory ability, organic osmolytes, and plasma hormone profiles in the Mozambique tilapia (Oreochromis mossambicus)

The Mozambique tilapia, Oreochromis mossambicus, is capable of surviving a wide range of salinities and temperatures. The present study was undertaken to investigate the influence of environmental salinity and temperature on osmoregulatory ability, organic osmolytes and plasma hormone profiles in the tilapia. Fish were acclimated to fresh water (FW), seawater (SW) or double-strength seawater (200% SW) at 20, 28 or 35 degrees C for 7 days. Plasma osmolality increased significantly as environmental salinity and temperature increased. Marked increases in gill Na(+), K(+)-ATPase activity were observed at all temperatures in the fish acclimated to 200% SW. By contrast, Na(+), K(+)-ATPase activity was not affected by temperature at any salinity. Plasma glucose levels increased significantly with the increase in salinity and temperature. Significant correlations were observed between plasma glucose and osmolality. In brain and kidney, content of myo-inositol increased in parallel with plasma osmolality. In muscle and liver, there were similar increases in glycine and taurine, respectively. Glucose content in liver decreased significantly in the fish in 200% SW. Plasma prolactin levels decreased significantly after acclimation to SW or 200% SW. Plasma levels of cortisol and growth hormone were highly variable, and no consistent effect of salinity or temperature was observed. Although there was no significant difference among fish acclimated to different salinity at 20 degrees C, plasma IGF-I levels at 28 degrees C increased significantly with the increase in salinity. Highest levels of IGF-I were observed in SW fish at 35 degrees C. These results indicate that alterations in gill Na(+), K(+)-ATPase activity and glucose metabolism, the accumulation of organic osmolytes in some organs as well as plasma profiles of osmoregulatory hormones are sensitive to salinity and temperature acclimation in tilapia.

Mixed osmolytes: the degree to which one osmolyte affects the protein stabilizing ability of another

Mixtures of organic osmolytes occur in cells of many organisms, raising the question of whether their actions on protein stability are independent or synergistic. To investigate this question it is desirable to develop a system that permits evaluation of the effect of one osmolyte on the efficacy of another to either force-fold or denature a protein. A means of evaluating the efficacy of an osmolyte is provided by its m-value, an experimental quantity that measures the ability of the osmolyte to force a protein to unfold or fold. An experimental system is presented that enables evaluations of the m-values of osmolytes in the presence and absence of a second osmolyte. The experimental system involves use of a marginally stable protein in 10 mM buffer (pH 7, 200 mM salt, and 34 degrees C) that is at the midpoint of its native to denatured transition. These conditions enable determination of m-values for protecting and denaturing osmolytes in the presence and absence of a second osmolyte, permitting assessment of the extent to which the two osmolytes affect each other's efficacy. The two osmolytes investigated in this work are the denaturing osmolyte, urea, and the protecting osmolyte, sarcosine. Results show unequivocally that neither osmolyte alters the efficacy of the other in forcing the protein to fold or unfold-the osmolytes act independently on the protein despite their combined concentrations being in the multi-molar range. These osmolytes avoid altering one another's efficacy at these high concentrations because the number of osmolyte interaction sites on the protein is large and the binding constants are quite small. Consequently, the site occupancies are low enough in number that the two osmolytes neither compete nor cooperate in interacting with the protein.

Effects of Osmolytes on Protein Folding and Aggregation in Cells

Nature has developed many strategies to ensure that the complex and challenging protein folding reaction occurs in vivo with adequate efficiency and fidelity for the success of the organism. Among the strategies widely employed in a huge range of species and cell types is the elaboration of small organic molecules called osmolytes that offset the potentially damaging effects of osmotic stress. While considerable knowledge has been gained in vitro regarding the influence of osmolytes on protein structure and folding, it is of great interest to probe the effects of osmolytes in cells. We have developed an in-cell fluorescent-labeling method that enables the study of protein stability and also protein aggregation in vivo. We utilize a genetically encoded tag called a tetra-Cys motif that binds specifically to a bis-arsenical fluorescein-based dye "FlAsH"; we inserted the tetra-Cys motif into a protein of interest in such a way that the FlAsH signal reported on the state of folding or aggregation of the protein. Then, we designed protocols to assess how various osmolytes influence the stability and propensity to aggregate of our protein of interest. These are described here. Not only are there potential biotechnological applications of osmolytes in the quest to produce greater quantities of well-folded proteins, but also osmolytes may serve as tools and points of departure for therapeutic intervention in protein folding and aggregation diseases. Having in vivo methods to analyze how osmolytes affect folding and aggregation enhances our ability to further these goals greatly.

Maintenance and accumulation of trimethylamine oxide by winter skate (Leucoraja ocellata): reliance on low whole animal losses rather than synthesis

Trimethylamine oxide (TMAO) is typically accumulated as an organic osmolyte in marine elasmobranchs to levels second only to urea (which can reach >400 mM); however, little is known about the whole animal regulation of TMAO in elasmobranchs. In the present study on the winter skate ( Leucoraja ocellata), we determine whether this species can maintain levels of TMAO in the absence of feeding, and if so, is this due to endogenous synthesis or low whole animal losses. Winter skates maintain plasma TMAO levels for up to 45 days without feeding. The liver displays methimazole oxidation, which is consistent with the presence of flavin-containing monooxygenase (E.C. 1.14.13.8 ) activity, the class of enzymes responsible for the physiological oxygenation of trimethylamine (TMA) to TMAO in mammals. However, no evidence for TMA oxygenation by winter skates was found using in vivo or in vitro techniques, indicating no significant capacity for endogenous TMAO synthesis. Fed skates displayed low, but measurable (∼4–13 μmol·kg−1·h−1), efflux of TMAO (plus TMA), whereas fasted skates did not. Using the loss of injected [14C]TMAO, it was determined that whole animal TMAO losses are likely <1% of whole body TMAO per day. These results demonstrate that winter skates utilize low whole animal TMAO losses, rather than endogenous synthesis, to maintain TMAO levels when not feeding.

The effects of cosolutes on protein dynamics: the reversal of denaturant-induced protein fluctuations by trimethylamine N-oxide

The protein stabilizing effects of the small molecule osmolyte, trimethylamine N-oxide, against chemical denaturant was investigated by NMR spin-relaxation measurements and model-free analysis. In the presence of 0.7 M guanidine hydrochloride increased picosecond-nanosecond dynamics are observed in the protein ribonuclease A. These increased fluctuations occur throughout the protein, but the most significant increases in flexibility occur at positions believed to be the first to unfold. Addition of 0.35 M trimethylamine N-oxide to this destabilized form of ribonuclease results in significant rigidification of the protein backbone as assessed by (1)H-(15)N order parameters. Statistically, these order parameters are the same as those measured in native ribonuclease indicating that TMAO reduces the amplitude of backbone fluctuations in a destabilized protein. These data suggest that TMAO restricts the bond vector motions on the protein energy landscape to resemble those motions that occur in the native protein and points to a relation between stability and dynamics in this enzyme.

Role of Na+and K+in Enzyme Function

Metal complexation is a key mediator or modifier of enzyme structure and function. In addition to divalent and polyvalent metals, group IA metals Na+and K+play important and specific roles that assist function of biological macromolecules. We examine the diversity of monovalent cation (M+)-activated enzymes by first comparing coordination in small molecules followed by a discussion of theoretical and practical aspects. Select examples of enzymes that utilize M+as a cofactor (type I) or allosteric effector (type II) illustrate the structural basis of activation by Na+and K+, along with unexpected connections with ion transporters. Kinetic expressions are derived for the analysis of type I and type II activation. In conclusion, we address evolutionary implications of Na+binding in the trypsin-like proteases of vertebrate blood coagulation. From this analysis, M+complexation has the potential to be an efficient regulator of enzyme catalysis and stability and offers novel strategies for protein engineering to improve enzyme function.

Small molecule pharmacological chaperones: From thermodynamic stabilization to pharmaceutical drugs

A great deal of attention has been paid to so-called amyloid diseases, in which the proteins responsible for the cell death and resultant diseases undergo conformational changes and aggregate in vivo, although whether aggregate formation is the cause or the result of the cell death is controversial. Recently, an increasing attention is given to protein folding diseases tightly associated with mutations. These mutations result in temperature-dependent misfolding and hence inactivation of the proteins, leading to loss of function, at physiological temperature; at low so-called permissive temperatures, the mutant proteins correctly fold and acquire functional structure. Alternatively, activation can be induced by use of osmolytes, which restores the folding of the mutant proteins and hence are called chemical chaperones. The osmolytes are compatible with macromolecular function and do stabilize the native protein structure. However, chemical chaperones require high concentrations for effective folding of mutant proteins and hence are too toxic in in-vivo applications. This limitation can be overcome by pharmacological chaperones, whose functions are similar to the chemical chaperones, but occur at much lower concentrations, i.e., physiologically acceptable concentrations. Although the research and clinical importance of pharmacological chaperones has been emphasized, the initial and central concept of osmolytes is largely ignored. Here we attempt to bridge the concept of osmolytes to applications of pharmacological chaperones.

Inhibition of protein aggregation in vitro and in vivo by a natural osmoprotectant

Small organic molecules termed osmolytes are harnessed by a variety of cell types in a wide range of organisms to counter unfavorable physiological conditions that challenge protein stability and function. Using a well characterized reporter system that we developed to allow in vivo observations, we have explored how the osmolyte proline influences the stability and aggregation of a model aggregation-prone protein, P39A cellular retinoic acid-binding protein. Strikingly, we find that the natural osmolyte proline abrogates aggregation both in vitro and in vivo (in an Escherichia coli expression system). Importantly, proline also prevented aggregation of constructs containing exon 1 of huntingtin with extended polyglutamine tracts. Although compatible osmolytes are known to stabilize the native state, our results point to a destabilizing effect of proline on partially folded states and early aggregates and a solubilizing effect on the native state. Because proline is believed to act through a combination of solvophobic backbone interactions and favorable side-chain interactions that are not specific to a particular sequence or structure, the observed effect is likely to be general. Thus, the osmolyte proline may be protective against biomedically important protein aggregates that are hallmarks of several late-onset neurodegenerative diseases including Huntington's, Alzheimer's, and Parkinson's. In addition, these results should be of practical importance because they may enable protein expression at higher efficiency under conditions where aggregation competes with proper folding.