Accumulation Of Sugar Alcohols Research Articles

Metabolic response induced by parasitic plant-fungus interactions hinder amino sugar and nucleotide sugar metabolism in the host.

Infestation by the biotrophic pathogen Gymnosporangium asiaticum can be devastating for plant of the family Rosaceae. However, the phytopathology of this process has not been thoroughly elucidated. Using a metabolomics approach, we discovered the intrinsic activities that induce disease symptoms after fungal invasion in terms of microbe-induced metabolic responses. Through metabolic pathway enrichment and mapping, we found that the host altered its metabolite levels, resulting in accumulation of tetrose and pentose sugar alcohols, in response to this fungus. We then used a multiple linear regression model to evaluate the effect of the interaction between this abnormal accumulation of sugar alcohol and the group variable (control/parasitism). The results revealed that this accumulation resulted in deficiency in the supply of specific sugars, which led to a lack of amino sugar and nucleotide sugar metabolism. Halting this metabolism could hamper pivotal functions in the plant host, including cell wall synthesis and lesion repair. In conclusion, our findings indicate that altered metabolic responses that occur during fungal parasitism can cause deficiency in substrates in pivotal pathways and thereby trigger pathological symptoms.

Identification of structural alerts for substances with PBT/vPvB potential

Rats fed a high-galactose diet develop marked thickening of their retinal capillary basement membranes. The effect is prevented if the animals also receive the aldose reductase inhibitor sorbinil. The effect does not appear to be due to aldose reductase itself, since immunoreactive aldose reductase has not been found in the retinal microvasculature of the rat but rather to a related enzyme with similar substrate specificity. The detailed biochemical mechanism for basement membrane thickening is obscure, involving an alteration of the extracellular matrix, where aldose reductase and similar enzymes have not been described; osmotic damage to the microvascular cells, such as has been described following aldose reductase-induced sugar alcohol accumulation in lens epithelial cells, is not apparent in diabetic or galactosemic animals. It is possible that concentrations of intracellular sugar alcohols that do not substantially change the osmolarity of the cell cytosol alter intracellular enzyme activities. This, in turn, could affect the biosynthesis of extracellular matrix macromolecules, as suggested, for example, by the hypothesis of Rohrbach et al, based on studies of a basement membrane-producing tumor implanted in diabetic mice, which proposes that the hyperglycemia of diabetes mellitus causes a reduced synthesis of the heparan sulfate BM-1 proteoglycan with a subsequent overproduction of type IV collagen. This and other hypotheses of basement membrane thickening can be tested in diabetic or galactosemic rats, some of which receive aldose reductase inhibitors, or in retinal microvascular pericytes and endothelial cells grown in culture.

Maternal control of cold and desiccation tolerance in eggs of the band‐legged ground cricket Dianemobius nigrofasciatus in relation to embryonic diapause

AbstractCold and desiccation tolerance was investigated in the eggs of the band‐legged ground cricket Dianemobius nigrofasciatus in relation to embryonic diapause. Diapause eggs were more tolerant to both desiccation and cold than non‐diapause eggs. In addition, diapause‐destined eggs on day zero (0–12 h after being laid) already showed high tolerance to these stresses before entering diapause. This clearly indicates that stress tolerance, like diapause, is controlled by photoperiod, but is not directly associated with diapause itself. Because the acquisition of stress tolerance predates the onset of diapause, it is plausible that diapause programming during some period before the onset of diapause is involved in the acquisition of stress tolerance. Weights and sizes were nearly identical in short‐day and long‐day eggs until day five. Sorbitol, a major sugar alcohol in eggs of D. nigrofasciatus, was accumulated at the same level in short‐day and long‐day eggs on days zero and five. These results indicate that the surface‐to‐volume ratio as well as the accumulation of sugar alcohol is not involved in the acquisition of stress tolerance. Maternal factors are clearly involved in the acquisition of stress tolerance in D. nigrofasciatus eggs, but the physiological mechanisms underlying the tolerance are still unclear.

The Inhibitory Effect of Aldose Reductase Inhibitor on Proliferation in the Lens Epithelial Cells of Rat Sugar Cataract

To evaluate the inhibitory effect of aldose reductase inhibitor (ARI) for the accumulation of sugar alcohol and the enhanced proliferation of lens epithelial cells of rats fed a galactose diet. Sprague-Dawley rats were fed a diet containing 50% galactose with or without ARI (SNK-860). Histological changes in the lenses were observed by light microscopy, and the amount of galactitol accumulated in the lens epithelium was measured by liquid-gas chromatography. Immuno-histochemical staining of proliferating cell nuclear antigen (PCNA) in whole-mount preparations was performed to assay the proliferative ability of the lens epithelial cells. The amount of galactitol in the lens epithelium and the number of PCNA positive cells in rats administered ARI were less than in rats fed the galactose diet. Multi-layered epithelium was observed in advanced cataract of rats fed the galactose diet, but not in the rats given ARI. The administration of ARI can prevent cataractous changes and aberrant proliferation of lens epithelial cells.

Apoptotic cell death in the lens epithelium of rat sugar cataract

Apoptosis of lens epithelial cells (LECs) is implicated in the pathogenesis of several types of cataract formation. The high intracellular levels of polyol induce histological change in the LECs, which is considered the earliest event in sugar cataractogenesis. This study was designed to investigate whether high galactose exposure induces apoptosis in LECs during the development of sugar cataract. The effect of an aldose reductase inhibitor, SNK-860, was also examined. We induced sugar cataract in Sprague-Dawley rats by feeding them a 50% galactose-containing diet with or without SNK-860. The percentage of LECs undergoing apoptosis was measured by the terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL) method, and DNA fragmentation analyses were performed. Galactitol levels in the lens epithelium were quantified by gas chromatography. The number of TUNEL-positive cells gradually increased throughout the period of galactose exposure, up to 5 days. DNA fragmentation analysis in LECs of rats fed a galactose-rich diet demonstrated an apparent ladder pattern. SNK-860 reduced the percentage of TUNEL-positive cells, the amount of intracellular galactitol, and the levels of DNA laddering. To explore the mechanism of the apoptotic process, the expression of p53, a potent mediator of apoptosis, was examined. Based on Western blot and real-time reverse transcription-polymerase chain reaction results, the amount of p53-expression increased at both the protein and mRNA levels after galactose exposure, and the increase in p53-expression was inhibited by SNK-860. Based on these results, we concluded that apoptosis occurs in rat lens epithelial cells following galactose exposure. Furthermore, the reduction of apoptosis by aldose reductase inhibitor suggests that this apoptosis is associated with the accumulation of sugar alcohols. It is probable that the mechanism of apoptosis during sugar cataract formation involves the increased expression of p53.

The effect of drought on mycorrhizas of beech (Fagus sylvatica L.): changes in community structure, and the content of carbohydrates and nitrogen storage bodies of the fungi.

In a water-exclusion experiment, five different ecotypes of beech (Fagus sylvatica L.; representing regions of different environmental and climatic conditions in Baden-Württemberg, Germany) were subjected to drought conditions of different severity between July and September of two consecutive years. Drought stress as characterised by the water content and the pre-dawn water potential of the leaves was related to the degree of mycorrhization, the type of ectomycorrhiza, and the physiological properties of individual fungus/plant interactions at the fine roots of different beech ecotypes. Our data show that decreased soil water availability did not significantly change either the degree of fungal colonisation of beech roots (measured by the amount of ergosterol) or the number of ectomycorrhizal types per root system. Drought did, however, have an influence on the composition of the ectomycorrhizal community, and different mycorrhizal types responded to drought differently in terms of their patterns of occurrence/abundance. While the abundance of the dominant mycorrhizal types, formed with Byssocorticium atrovirens and Lactarius subdulcis, was not affected, drought increased the abundance of mycorrhiza formed between beech and Xerocomus chrysenteron. A detailed analysis of plant and fungal carbohydrates in mycorrhizas indicated that different drought intensities led to distinguishable responses. In plants exhibiting a pre-dawn water potential of down to -1.96 MPa, drought caused the accumulation of sucrose, glucose and fructose, and of fungus-specific compounds such as mannitol and arabitol in mycorrhizal roots at the expense of, e.g. trehalose. The accumulation of sugar alcohols, which constitute compatible solutes known to counteract drought stress, was species-specific. Mycorrhizas with X. chrysenteron formed large amounts of arabitol, while those with L. subdulcis accumulated mannitol. Sustained partitioning of carbon towards the mycorrhizal fungi under drought was also reflected by an increase of nitrogen storage in the fungal vacuoles. In treatments where the pre-dawn water potential reached values of as low as -2.4 MPa, such alterations were no longer found. In such plants, the starch and soluble sugars content was generally reduced, which also resulted in a lack of increase in protective, fungus-specific sugar alcohols. In summary, the data show that, within certain limits, an increase in drought causes a shift in plant/fungus communities. The shift in the pattern of fungus-specific compounds could possibly be used as a sensitive measure of physiological stress imposed on this symbiosis.

The role of aldose reductase in sugar cataract formation: aldose reductase plays a key role in lens epithelial cell death (apoptosis)

Since aldose reductase is localized primarily in lens epithelial cells, osmotic insults induced by the accumulation of sugar alcohols occur first in these cells. To determine whether the accumulation of sugar alcohols can induce lens epithelial cell death, galactose-induced apoptosis has been investigated in dog lens epithelial cells. Dog lens epithelial cells were cultured in Dulbecco's modified Eagle's mimimum essential medium (DMEM) supplemented with 20% fetal calf serum (FCS). After reaching confluence at fifth passage, the medium was replaced with the same DMEM medium containing 50 mM d-galactose and the cells were cultured for an additional 2 weeks. Almost all of the cells cultured in galactose medium were stained positively for apoptosis with the terminal deoxynucleotidyl transferance-mediated biotin-dUTP nick end labeling (TUNEL) technique. Agarose gel electrophoresis of these cells displayed obvious DNA fragmentation, known as a ladder formation. All of these apoptotic changes were absent in similar cells cultured in galactose medium containing 1 μM of the aldose reductase inhibitor AL 1576. Addition of AL 1576 also reduced the cellular galactitol levels from 123±10 μg/10 6 cells ( n=5) to 3.9±1.9 μg/10 6 cells ( n=5). These observations confirm that galactose induced apoptosis occurs in dog lens epithelial cells. Furthermore, the prevention of apoptosis by an aldose reductase inhibitor suggests that this apoptosis is linked to the accumulation of sugar alcohols.

Polyol pathway and NADPH-dependent reductases in dog leukocytes

Recent reports suggest that excess amounts of sugar alcohol are linked to leukocyte dysfunctions associated with diabetes. As the polyol pathway has not been firmly established in leukocytes, we have investigated NADPH-dependent reductases and sugar alcohol formation in dog leukocytes. NADPH-dependent reductase activity was observed with DL-glyceraldehyde as substrate in both mononuclear and polymorphonuclear leukocytes isolated from dog. By chromatofocusing, this activity corresponded primarily to aldehyde reductase rather than aldose reductase. The enzymatic conversion of glucose to the sugar alcohol sorbitol in leukocytes was confirmed in vitro by 19F nuclear magnetic resonance (NMR) spectroscopy using 3-deoxy-3-fluoro-D-glucose as substrate. The NMR spectrum obtained after incubation with 10 Mm 3-deoxy-3-fluoro-D-glucose at 37 °C for 24 h displayed newly formed 3-deoxy-3-fluoro-D-sorbitol and 3-deoxy-3-fluoro-D-fructose peaks with both mononuclear and polymorphonuclear leukocytes. Sugar alcohol production in leukocytes from galactose-fed dogs was also observed in vivo. Galactitol accumulation was consistently observed by gas chromatography to occur in mononuclear cells while only trace amounts of galactitol were observed in polymorphonuclear leukocytes. Activation of NADPH oxidase activity in neutrophils isolated from galactose-fed dogs by zymosan was also significantly reduced compared to that of nongalactosemic control dogs. These results indicate that glucose is converted to fructose through sorbitel in both mononudear and polymorphonuclear leukocytes despite the observations that these cells primarily contain aldehyde reductase rather than aldose reductase. In vivo, sugar alcohol accumulation in mononuclear cells is greater than in polymorphonuclear leukocytes.

Accumulation of sugar alcohols by filamentous fungi

Five hundred isolates of different xerophilic and non-xerophilic fungi belonging to 10 genera and 74 species were screened for alditol (sugar alcohol) accumulation. Ninety-two of the isolates failed to grow on a salt medium, most of the isolates (408) produced alditols; 348,44 and 16 of them produced low, moderate and high levels of alditols, respectively. The high alditol producers belonged to five species ofAspergillus, six species ofEurotium andFennellia flavipes. Glycerol andd-mannitol were the main constituents of alditol pools of the 16 high alditol producers.d-Arabinitol andmeso-erythritol were also formed but at low concentrations by several of the tested isolates.

The lens in diabetes.

This paper reviews the changes which occur in the human lens in diabetes. They include refractive changes and cataract and age-related increases in thickness, curvatures, light scattering, autofluorescence and yellowing. The incidence of cataract is greatly increased over the age of 50 years, slightly more so in women, compared with non-diabetics. Experimental models of sugar cataract provide some evidence for the mechanism of the uncommon, but morphologically distinct, juvenile form of human diabetic cataract, where an osmotic mechanism due to sugar alcohol accumulation has been thoroughly studied in diabetic or galactose-fed rats. The discrepancy between the ready accumulation of sugar alcohol in the lens in model systems and the very slow kinetics of aldose reductase (AR) has not been satisfactorily explained and suggests that the mechanism of polyol formation is not yet fully understood in mammalian systems. The activity of AR in the human lens lies mainly in the epithelium and there appears to be a marginal expectation that sufficient sorbitol accumulates in cortical lens fibres to explain the lens swelling and cataract on an osmotic basis. This is even more so in the cataracts of adult diabetics, which resemble those of age-related non-diabetic cataracts in appearance. The very low levels of sorbitol in adult diabetic lenses make an osmotic mechanism for the increased risk of cataract even less likely. Other mechanisms, including glycation and oxidative stress, are discussed. The occurrence of cataract is a predictor for increased mortality in the diabetic.

Stress Protection of Transgenic Tobacco by Production of the Osmolyte Mannitol

The accumulation of sugar alcohols and other low molecular weight metabolites such as proline and glycine-betaine is a widespread response that may protect against environmental stress that occurs in a diverse range of organisms. Transgenic tobacco plants that synthesize and accumulate the sugar alcohol mannitol were engineered by introduction of a bacterial gene that encodes mannitol 1 -phosphate dehydrogenase. Growth of plants from control and mannitol-containing lines in the absence and presence of added sodium chloride was analyzed. Plants containing mannitol had an increased ability to tolerate high salinity.

Galactitol is not a cause of senile cataract.

It has been postulated that the accumulation of sugar alcohol, galactitol, from milk induces cataract in the eye lens through an osmotic mechanism. In this study the concentrations of galactitol and other sugar alcohols (sorbitol, mannitol and inositol) were measured by sensitive gas chromatography in the lenses of 15 patients operated on for senile idiopathic cataracts and in 14 clear lenses removed at autopsy. Large amounts of inositol (mean +/- SD, 4.1 +/- 3.1 vs 4.7 +/- 3.0 mumol/g lens wet weight) and small amounts of mannitol and sorbitol were detected in both study groups. Galactitol levels remained clearly below the detection limit (2 nmol/g) in all lenses. It seems unlikely that senile cataract is a result of the accumulation of galactitol in the eye lens.

In vitrostudy of aldose reductase inhibitor concentrations in the lens and inhibitory effect on sugar alcohol accumulation

Rat lenses were cultured in a medium containing either 30mM xylose or 30mM glucose. Inhibitory effects of two aldose reductase inhibitors, AD-5467 and CT-112, on the accumulation of sugar alcohols and the concentrations of the drugs in the lens were measured. Inhibitory effect of lens opacification by the drugs were also observed. Lens opacification was apparently inhibited in a medium containing each of the drugs. Inhibition rates for sugar alcohol accumulation by AD-5467 and CT-112 were unrelated to the kinds of added sugars. 50% inhibition-concentration in the medium was 0.82-1.02 x 10(-7) M for AD-5467 and 3.78-5.92 x 10(-7) M for CT-112, and the resulting concentration of drug in the lens was 2.33-3.08 nmole/g lens for AD-5467 vs. 21.19-24.63 nmole/g lens for CT-112. The results above indicated that the concentration of CT-112 should be 4.6-5.8 times of that of AD-5467 in the medium to attain the same inhibitory effect on sugar alcohol accumulation, and 8.0-9.1 times more CT-112 is needed in the lens. A linear correlation was found on a bilogarithmic graph of concentrations in the medium and in the lens for both drugs. This correlation is an empirical adsorption isotherm shown by Freundrich. So this suggested that both drugs were adsorbed into the lens. The rate of adsorption varied with the drugs. Even when the drug concentrations in the medium were the same, the concentration of CT-112 in the lens was 2-4 times higher than that of AD-5467.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldose reductase activity and basement membrane thickening

Rats fed a high-galactose diet develop marked thickening of their retinal capillary basement membranes. The effect is prevented if the animals also receive the aldose reductase inhibitor sorbinil. The effect does not appear to be due to aldose reductase itself, since immunoreactive aldose reductase has not been found in the retinal microvasculature of the rat but rather to a related enzyme with similar substrate specificity. The detailed biochemical mechanism for basement membrane thickening is obscure, involving an alteration of the extracellular matrix, where aldose reductase and similar enzymes have not been described; osmotic damage to the microvascular cells, such as has been described following aldose reductase-induced sugar alcohol accumulation in lens epithelial cells, is not apparent in diabetic or galactosemic animals. It is possible that concentrations of intracellular sugar alcohols that do not substantially change the osmolarity of the cell cytosol alter intracellular enzyme activities. This, in turn, could affect the biosynthesis of extracellular matrix macromolecules, as suggested, for example, by the hypothesis of Rohrbach et al, based on studies of a basement membrane-producing tumor implanted in diabetic mice, which proposes that the hyperglycemia of diabetes mellitus causes a reduced synthesis of the heparan sulfate BM-1 proteoglycan with a subsequent overproduction of type IV collagen. This and other hypotheses of basement membrane thickening can be tested in diabetic or galactosemic rats, some of which receive aldose reductase inhibitors, or in retinal microvascular pericytes and endothelial cells grown in culture.

Endoneurial blood flow and oxygen tension in the sciatic nerves of rats with experimental diabetic neuropathy.

Endoneurial hypoxia has been postulated to be important in the pathogenesis of diabetic peripheral neuropathy and may be due to reduced nerve blood flow. Neither blood flow nor oxygen tension have previously been measured in peripheral nerve in diabetic neuropathy. We have therefore measured both nerve blood flow and endoneurial oxygen tension in the sciatic nerves of 8 rats with streptozotocin-induced diabetes for four months, and in 8 age-matched controls. In 7 of the diabetic animals mean nerve blood flow was 8.7 +/- 1.3 ml X min-1 X 100 g-1 which is significantly less than mean nerve blood flow in the controls (13.08 +/- 0.8 ml X min-1 X 100 g-1; P less than 0.01). In one diabetic animal, nerve blood flow was too low to be accurately measured. The reduction in nerve blood flow in diabetic neuropathy is due to an increase in resistance to flow which may be due to microangiopathy and to blood hyperviscosity. Endoneurial oxygen tension was also significantly reduced in experimental diabetic neuropathy in which 60 per cent of the oxygen measurements were less than 25 mmHg, compared with 19 per cent in the controls. Nerve blood flow was also measured in rats with experimental galactose neuropathy in which there is more marked sugar-alcohol accumulation, endoneurial oedema and elevation of endoneurial fluid pressure than in experimental diabetic neuropathy. The results obtained in this neuropathy suggest that the reduction in nerve blood flow which occurs in experimental diabetic neuropathy is due largely to factors other than sugar-alcohol accumulation in nerve. We postulate that endoneurial hypoxia may produce many of the observed morphological and biochemical changes in experimental diabetic neuropathy.

Peripheral nerve conduction studies in galactose-poisoned rats: Demonstration of increased resistance to ischemic conduction associated with endoneurial edema due to sugar alcohol accumulation

Edematous nerves of galactose-poisoned rats had an increased resistance to ischemic conduction block when compared with control animals. Ischemia was caused by cardiac arrest due to intracardiac air embolism in 1 group and by occlusion of the abdominal aorta in another. In these 2 groups of galactose-fed rats, time to 50% conduction block was increased by 27 and 42%, respectively and the difference between control and galactose rats was significant ( P < 0.01 and P < 0.001).

Glucose-induced membrane permeability changes in the lens

The effect of glucose and other hexose sugars on the electrical conductance of the amphibian lens was investigated using voltage-clamp techniques. Perifusing the lens with a Ringers solution made hyperosmotic by the addition of 40 m m-glucose to the control solution caused a steady increase in the conductance with the voltage clamped at the resting value ( ∼ −80 mV). Return to the control solution did not establish the original control conductance, but rather a further increase was observed. Perifusion with an isosmotic glucose-containing solution (40 m m-glucose added and 20 m m-NaCl removed) also caused the voltage-clamped conductance to increase and on return to the control solution a steady, raised baseline conductance was obtained. Similar conductance changes were observed in the presence of galactose, fructose and 3- o-methyl glucose and as the latter is not metabolized by the lens it is unlikely that the conductance changes are due to an accumulation of sugar alcohol. They are in fact interpreted in terms of a swelling of the lens in the presence of a permeant solute. Small fluctuations in external glucose levels, such as occur in diabetes, thus cause marked changes in membrane permeability and these changes are likely to impose an additional strain on lens volume regulation. Phloretin, which is an inhibitor of glucose transport, also significantly increased the lens conductance in concentrations as low as 10 −5 m. As there was a concomitant hyperpolarization of the lens membrane potential, the conductance change was probably due to an increase in potassium permeability. Similar changes have also been reported in nervous tissue in the presence of low concentrations of phloretin.

Sugar metabolism in the crystalline lens

Research on the sugar metabolism of the crystalline lens, past and present, is reviewed. The chief energy source in the lens is the Embden-Meyerhof pathway; respiration and oxidative phosphorylation become more important as the lens ages. The function of the α-glycerophosphate cycle is not fully understood. The mechanisms involved in cataract formation, including those of hypoglycemic cataract and osmotic cataracts, are discussed. Sugar cataracts can be delayed or prevented with such aldose reductase inhibitors as flavonoids. By inhibiting aldose reductase, the formation and accumulation of sugar alcohols is stopped. This approach may be useful as a medical therapy for human diabetic senile cataracts.

The absence of cataracts in mice with congenital hyperglycemia

Investigations were conducted to determine the biochemical basis of the absence of cataracts in genetically diabetic mice. The resistance of these mice to cataracts appears to be due to the low activity of aldose reductase in the lens. Consequently only low amounts of polyols accumulate even after persistent hyperglycemia. The finding thus lends further support to the polyol theory of sugar cataractogenesis. The accumulation of sugar alcohols in galactosemic mice lenses was also much lower as compared to that in the lenses of galactosemic rats. A study was made of the enzymes that influence the polyol level in the lenses of various mouse strains. The activities of aldose reductase, polyol dehydrogenase, hexokinase and glucose-6-phosphate and 6-phosphogluconate dehydrogenases in the mouse and rat lenses were determined. The activities of all the enzymes except that of aldose reductase were similar in the lenses of both species. The aldose reductase activity in the mouse lens was only one tenth of that present in the rat lens.

Nerve Conduction Defect in Galactose-fed Rats

Dulcitol accumulation associated with swelling occurs in the peripheral nerves of rats fed a 40 per cent galactose diet. These alterations are associated with a motor nerve conduction velocity defect which is reversible on withdrawal of galactose from the diet. These findings suggest that the accumulation of sugar alcohol plays an important role in the etiology of galactosemic neuropathy.