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Formation of sorbitol 6-phosphate by bovine and human lens aldose reductase, sorbitol dehydrogenase and sorbitol kinase.

Formation of sorbitol 6-phosphate by bovine and human lens aldose reductase and sorbitol dehydrogenase by the reduction of glucose 6-phosphate and fructose 6-phosphate, respectively, has been demonstrated. The reaction product has been identified by Dowex-formate column chromatography, gas chromatography and mass spectrometry. Sorbitol 6-phosphate can also be formed by the phosphorylation of sorbitol by lens sorbitol kinase in the presence of ATP.

Aldehyde Reductase↗

Sorbitol-6-phosphate dehydrogenase expression in transgenic tobacco. High amounts of sorbitol lead to necrotic lesions

We analyzed transgenic tobacco (Nicotiana tabacum L.) expressing Stpd1, a cDNA encoding sorbitol-6-phosphate dehydrogenase from apple, under the control of a cauliflower mosaic virus 35S promoter. In 125 independent transformants variable amounts of sorbitol ranging from 0.2 to 130 &mgr;mol g-1 fresh weight were found. Plants that accumulated up to 2 to 3 &mgr;mol g-1 fresh weight sorbitol were phenotypically normal, with successively slower growth as sorbitol amounts increased. Plants accumulating sorbitol at 3 to 5 &mgr;mol g-1 fresh weight occasionally showed regions in which chlorophyll was partially lost, but at higher sorbitol amounts young leaves of all plants lost chlorophyll in irregular spots that developed into necrotic lesions. When sorbitol exceeded 15 to 20 &mgr;mol g-1 fresh weight, plants were infertile, and at even higher sorbitol concentrations the primary regenerants were incapable of forming roots in culture or soil. In mature plants sorbitol amounts varied with age, leaf position, and growth conditions. The appearance of lesions was correlated with high sorbitol, glucose, fructose, and starch, and low myo-inositol. Supplementing myo-inositol in seedlings and young plants prevented lesion formation. Hyperaccumulation of sorbitol, which interferes with inositol biosynthesis, seems to lead to osmotic imbalance, possibly acting as a signal affecting carbohydrate allocation and transport.

Journal Article↗

In vivo measurements of sulcal plaque pH after topical applications of sorbitol and sucrose in rats fed sorbitol or sucrose.

To test whether adaptation to sorbitol could be observed in rat plaque, we made pH measurements of rat sulcal plaque in vivo, following topical application of 10% sorbitol solution. Rat pups were inoculated orally with S. mutans 6715 and fed diet MIT 305 (5% sucrose) for 16 days. Baseline sulcal plaque pH response of these rats to topical application of 10% sorbitol solution was measured. One group of 16 rats was then fed 20% sucrose in the diet, and a second group 20% sorbitol. After 13 days' feeding of the experimental diets (four days were used for accommodation to dose, and nine days at the 20% level for sorbitol), there was a significantly greater (p less than 0.01) drop in pH following topical application of 10% sorbitol in this group than in the sucrose-fed group. There was no difference in the pH response of the two groups to topical application of a 10% sucrose solution when tested six days later. The sulcal enamel caries score was significantly higher (p less than 0.001) in the sucrose group, but buccal enamel scores were similar in both groups. Adaptation in rat plaque took place, and could be measured in vivo as an increased drop in sulcal plaque pH following topical application of sorbitol. It is not clear whether this adaptation was primarily due to selection of sorbitol-fermenting micro-organisms, or, more likely, by induction of sorbitol-specific enzymes. Relative to the sucrose-containing diet, the sorbitol diet was hypocariogenic, even under experimental conditions.

Administration, Topical↗

Human erythrocyte sorbitol metabolism and the role of sorbitol dehydrogenase.

Rapid fluctuation of erythrocyte sorbitol in response to the changes in plasma glucose concentration has been reported from clinical evidence. We performed more extensive in vitro and in vivo studies focussing on how fast sorbitol was accumulated and how fast the accumulated sorbitol was oxidised in response to the changes in ambient glucose concentration. Incubation studies of intact erythrocytes from healthy subjects and diabetic patients showed that erythrocyte sorbitol increased rapidly in response to increased ambient glucose concentration and the accumulated sorbitol easily decreased according to the rapid reduction of ambient glucose concentration. In addition, the higher the glucose concentration in the medium, the more erythrocytes could accumulate sorbitol. The rapid response of sorbitol levels to ambient glucose concentration was further confirmed by the results of a 75 g oral glucose tolerance test in non-diabetic subjects and diabetic patients with gastrectomy, who showed marked early hyperglycaemia caused by rapid absorption of ingested glucose and subsequent rapid reduction of plasma glucose concentration (erythrocyte sorbitol levels changed concomitantly). These findings strongly indicate that the measurement of erythrocyte sorbitol is not useful as an index of medium or long term glycaemic control.

Adult↗

[Effect of the intravenous administration of a sorbitol solution on the blood plasma content of sorbitol, fructose, glucose, insulin and free fatty acids as well as on the sorbitol half-life in calves, young and adult cattle].

Average sorbite half-life values were 11.8 minutes in two fasting calves, 18.7 minutes in three calves after drinking, 16.4 minutes in five heads of young cattle, and 16.6 minutes in two heads of adult cattle, following intravenous injection of 0.5 g/kg live weight of sorbite solution. Sorbite conversion thus proved adequate and better than glucose conversion. Fructose levels in the blood plasma of fasting calves as well as of young and adult cattle underwent statistically significant rises, following sorbite infusion, the steepest rise being recorded from adult cattle. Significant glucose and insulin increases following sorbite infusion were recordable only from blood plasma of adult cattle. Concentrations of free fatty acids in blood plasma were quite irregular.

Animals↗

Sorbitol concentrations in plasma in connection with transurethral resection of the prostate using sorbitol solution as an irrigating fluid.

20 patients undergoing transurethral resection of the prostate (TURP) using 5% sorbitol (N = 13) or Cytosol (N = 7) (5% sorbitol and 0.25% acetic acid) as an irrigating fluid were studied. The sorbitol concentration was determined in serum (plasma), as were sodium, prostatic acid phosphatase protein (PAP) and osmolality, as possible indicators of absorption of irrigating fluid. The plasma level of sorbitol immediately postoperatively, the increase in serum PAP and the decrease in serum sodium all reflect the amount of irrigating fluid absorbed during TURP. The three variables are intercorrelated. The plasma osmolality was not significantly changed. The maximum sorbitol concentration immediately postoperatively in any patient was 6.0 g/l (33.5 mmol/l). The mean for the series was 1.2 g/l (6.8 mmol/l). The mean serum PAP increase was 31 micrograms/l. The serum sodium decrease ranged between 0 and 14 mmol/l, mean 5.0 mmol/l. The mean half-life of sorbitol in plasma was short: 35 min, reflecting rapid metabolism. An estimate of the volume of fluid absorbed was made from the plasma sorbitol levels observed. A fluid absorption up to 2.3 l (mean 0.6 l) was found. A marked diuretic effect up to 14.1 ml/min (mean 7.8 ml/min) was observed in some cases when irrigation with sorbitol was combined with intravenous furosemide given postoperatively.

Aged↗

Three-generation reproduction study of rats ingesting up to 10% sorbitol in the diet--and a brief review of the toxicological status of sorbitol.

Groups of 12 male and 24 female 5-wk-old Charles River CD (SD) BR rats (F0) were fed a sucrose-containing ground cereal-based diet in which 0, 2.5, 5.0 and 10.0% (w/w) sorbitol was included at the expense of sucrose. The rats were first mated after 14 wk on the diet. F1a litters were born 19 wk after the start of the study and F1b litters at wk 30. Groups of 12 male and 24 female F1b rats were first mated when 18 wk old. They gave rise to F2a litters after 3 wk and to F2b litters 10 wk later. Likewise, groups of 12 male and 24 female F2b rats were first mated when 18 wk old, producing F3a and F3b litters 3 wk and 10 wk later, respectively. F0 rats were killed 33 wk after the start of the study, F1a in wk 22, F1b in wk 68, F2a in wk 57, F2b in wk 92 and F3a in wk 96. Apart from slight reductions in food consumption in sorbitol-fed F1b males and in body-weight gain in sorbitol-fed F0, F1b and F2b rats of both sexes, treatment was associated with no clinically observed effects. There were no deaths attributable to treatment and no adverse effects on mating performance or pregnancy rates in the parent animals of any generation. Treatment was associated with no consistent adverse effect on any measure of reproductive performance or behaviour during gestation or lactation. No abnormal pups were observed in any generation. Not unexpectedly, caecal enlargement was consistently observed at necropsy of sorbitol-treated rats of all generations and significant rises in serum calcium were observed in F0 males and females exposed to 10% sorbitol and in F1b males exposed to either 5 or 10% sorbitol. Differences between treated and control F3a rats in respect of T3 and TSH levels were probably spurious as they followed no consistent pattern. Similarly, between-group variations in gonadal weight were considered to have no toxicological significance because they lacked consistency and were not accompanied by any histologically-evident changes. Microscopic examination of lesions from F1a and F2a animals, of gonads from F1b and F2b and of selected tissues from the F3a generation revealed no changes of toxicological significance.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Medulla↗

Functional bowel disease: malabsorption and abdominal distress after ingestion of fructose, sorbitol, and fructose-sorbitol mixtures.

Twenty-five patients with functional bowel disease were given fructose, sorbitol, fructose-sorbitol mixtures, and sucrose. The occurrence of malabsorption was evaluated by means of hydrogen breath tests and the gastrointestinal symptoms, if any, were recorded. One patient could not be evaluated because of lack of H2 production. Based on a cut-off level of 10 ppm rise of H2 concentration, malabsorption was apparent in 13 patients, in 7 of which the calculated absorption capacities were below 15 g. In contrast, in patients given 50 g of sucrose, malabsorption could not be detected. Ingestion of fructose caused marked abdominal distress in patients with demonstrable malabsorption. Ingestion of sucrose in these patients gave less pronounced symptoms of abdominal distress. Malabsorption of a 5-g dose of sorbitol could be detected in 8 of 13 patients. Mixtures of 25 g of fructose and 5 g of sorbitol caused significantly increased abdominal distress, and more than additive malabsorption was found in several cases. The present study shows that pronounced gastrointestinal distress may be provoked by malabsorption of small amounts of fructose, sorbitol, and fructose-sorbitol mixtures in patients with functional bowel disease. The findings may have direct influence on the dietary guidance given to a major group of patients with functional bowel disease and may make it possible to define separate entities in this disease complex.

Adult↗

Sorbitol synthesis in transgenic tobacco with apple cDNA encoding NADP-dependent sorbitol-6-phosphate dehydrogenase.

The apple (Malus domestica) cDNA encoding NADP-dependent sorbitol-6-phosphate dehydrogenase (S6PDH) was stably integrated and expressed in transgenic tobacco (Nicotiana tabacum cv. SR1). Expression of the cDNA in either a sense or antisense orientation was accomplished using cauliflower mosaic virus regulatory sequences (CaMV35S). Sorbitol synthesis was confirmed by gas-chromatography-mass-spectroscopy (GC-MS). Sorbitol concentration in the leaves of the transgenic plants expressing the sense orientation varied from 186 to 446 nmol (g fr wt)-1. The concentration positively correlates with S6PDH activity in leaves. Neither sorbitol nor S6PDH activity was detected in the extracts of nontransformed tobacco or transgenic tobacco expressing the antisense orientation. These results provide key genetic evidence that S6PDH expression is sufficient for the synthesis of sorbitol in tobacco, implicating it as a key enzyme in the sorbitol biosynthetic pathway in apple and perhaps other members of the woody Rosaceae.

Base Sequence↗

Sorbitol-fermenting predominant cultivable flora of human dental plaque in relation to sorbitol adaptation and salivary secretion rate.

The sorbitol-fermenting predominant flora of human dental plaque was studied in 12 people with low and 11 with normal salivary secretion rates before and after a period of frequent mouth rinses with sorbitol solution. A total of 277 sorbitol-fermenting isolates are described by their morphological and physiological characteristics. The flora was almost exclusively composed of gram-positive bacteria belonging to the genera Streptococcus, Lactobacillus and Actinomyces in people with low secretion rates and Streptococcus and Actinomyces in those with normal salivation. At the species level, Streptococcus mutans predominated in all. The frequent use of sorbitol resulted in an increase of the streptococcal species mainly and particularly of Streptococcus sanguis I in people with normal salivation. The counts of lactobacilli and Actinomyces remained unaffected. Almost all isolates appeared to belong to the resident plaque flora. Succession of new sorbitol-fermenting genera to the plaque community could not be observed as a result of the frequent exposure of the mouth to sorbitol.

Adaptation, Biological↗

Does the presence of xylitol in a sorbitol-containing chewing gum affect the adaptation to sorbitol by dental plaque?

It is known that xylitol inhibits sorbitol metabolism in some bacteria in vitro. The effect of xylitol/sorbitol-containing chewing gum on sorbitol adaptation of dental plaque was therefore examined. Ten subjects used this chewing gum for 12 wk, and plaque was collected before (control plaque) and after (test plaque) the exposure to sorbitol/xylitol. The metabolism of sorbitol by the plaque was examined with 14C-labeled sorbitol, and the radioactive metabolites were detected by high-performance liquid chromatography (HPLC). A considerable individual variation in acid formation was found. The mean values of total acids in the test plaque increased, as compared with the control plaque. An adaptation of dental plaque to sorbitol thus occurred in spite of the presence of xylitol in the chewing gum. The concentration of acetic acid predominated over other acids in both the control and test plaques. The proportions of acids expressed in percentage of total acids differed only slightly. Thus, long-term use of xylitol/sorbitol-containing chewing gum did not eliminate the adaptation of dental plaque to sorbitol.

Acetates↗

The sorbitol pathway: effect of streptozotocin induced diabetes and the feeding of a sucrose-rich diet on glucose, sorbitol and fructose in the retina, blood and liver of rats.

The sorbitol, fructose and glucose content of the retina, blood and liver from normal and streptozotocin diabetic rats fed either a starch- or sucrose-rich diet for 15 days has been determined. The sorbitol and fructose level in the retina was much higher than that in either the liver or blood and was significantly increased in diabetes on either diet. Such increases in the sorbitol concentration did not occur in either the liver or the blood during diabetes, and the possibility that the sorbitol pathway can play an important metabolic role in the diabetic retina has been discussed. The feeding of a sucrose- as opposed to a starch-rich diet did not significantly alter the concentrations of glucose, sorbitol or fructose in the normal rat retina but caused a marked elevation in the diabetic state.

Animals↗

Redox state-dependent and sorbitol accumulation-independent diabetic albuminuria in mice with transgene-derived human aldose reductase and sorbitol dehydrogenase deficiency.

AIMS/HYPOTHESIS: We investigated the role played by sorbitol accumulation in the kidney in the development of diabetic albuminuria. METHODS: We created mice ( hAR-Tg:SDH null) with transgene-derived human aldose reductase and sorbitol dehydrogenase (SDH) deficiency, and analysed (i). the contribution of accumulated sorbitol to urinary albumin excretion rate, and (ii). the effect of the aldose reductase inhibitor, epalrestat, on the diabetic redox state, including decreased renal reduced glutathione concentrations or increased lactate to pyruvate ratios in the diabetic kidney. RESULTS: Compared to littermates, non-diabetic transgenic mice had a 2.6-fold increase in aldose reductase mRNA. In a diabetic group, aldose reductase mRNA in hAR-Tg mice was 2.7-fold higher than in littermates. In the diabetic and non-diabetic groups, hAR-Tg:SDH null mice had the highest sorbitol content among all four genetic types including hAR-Tg:SDH null, SDH null, hAR-Tg and littermates. The urinary albumin excretion rate in non-diabetic groups was similar in the four genetic types of mouse. In diabetic groups it was greater than in non-diabetic groups, but did not correlate with the sorbitol content among the four genetic types of mouse. When aldose reductase inhibitor and streptozotocin were given simultaneously at 6 weeks of age, epalrestat prevented diabetic increases in urinary albumin excretion rate and completely prevented diabetic decreases in reduced glutathione concentrations and diabetic increases in lactate to pyruvate ratios, even in the presence of transgenic aldose reductase. CONCLUSIONS/INTERPRETATION: The degree of diabetic albuminuria in genetically modified mice is dependent on the redox state and independent of polyol accumulation; aldose reductase inhibitor can prevent diabetic albuminuria by normalising diabetic redox changes.

Albuminuria↗

Sorbitol synthesis by an engineered Lactobacillus casei strain expressing a sorbitol-6-phosphate dehydrogenase gene within the lactose operon.

Sorbitol is claimed to have important health-promoting effects and Lactobacillus casei is a lactic acid bacterium relevant as probiotic and used as a cheese starter culture. A sorbitol-producing L. casei strain might therefore be of considerable interest in the food industry. A recombinant strain of L. casei was constructed by the integration of a d-sorbitol-6-phosphate dehydrogenase-encoding gene (gutF) in the chromosomal lactose operon (strain BL232). gutF expression in this strain followed the same regulation as that of the lac genes, that is, it was repressed by glucose and induced by lactose. (13)C-nuclear magnetic resonance analysis of supernatants of BL232 resting cells demonstrated that, when pre-grown on lactose, cells were able to synthesize sorbitol from glucose. Inactivation of the l-lactate dehydrogenase gene in BL232 led to an increase in sorbitol production, suggesting that the engineered route provides an alternative pathway for NAD(+) regeneration.

Gene Expression Regulation, Bacterial↗

[Simultaneous analysis of aspartic acid and sorbitol in potassium magnesium aspartate and sorbitol injection by ion-exclusion chromatography with evaporative light-scattering detection].

An ion-exclusion chromatographic (IEC) method with evaporative light-scattering detector (ELSD) was established for the simultaneous analysis of the aspartic acid and sorbitol in Potassium Magnesium Aspartate and Sorbitol Injection. This procedure eliminates the need for complex derivatization schemes since ELSD can detect aspartic acid and sorbitol directly. An ion exclusion column (TSKgel OApak-A column, 7.8 mm i.d. x 300 mm, 5 microns, Tosho, Japan) was used for separation. The mobile phase was a mixture of aqueous solution (containing 0.1% (volume fraction) trifluoroacetic acid)-methanol (9:1, volume ratio). Under the above conditions aspartic acid and sorbitol were separated to baseline in 12 min. Regression equations revealed linear relationship (correlation coefficient: 0.999) between the concentrations of the analytes injected and the peak areas of the analytes detected by ELSD. The detection limits of ELSD (S/N = 3) were about 30 mg/L and 20 mg/L for aspartic acid and sorbitol, respectively.

Aspartic Acid↗

[Influence in vivo of sorbitol on sorbitol dehydrogenase activity].

Previous researches carried out on the metabolism of sorbitol in the rat showed the influence of this polyalcohol on the activity of some dehydrogenases NAD and NADP-dependent and on lacate/pyruvate, NADH/NAD and NADPH/NADP ratios. Since sorbitol dehydrogenase (SDH, EC 1.1.1.14) is an enzyme with a great affinity for sorbitol, it seemed interesting to investigate the effect of a sorbitol-enriched diet on SDH activity in the rat liver after different periods of dietary treatment (20, 40, 60 days). SDH was assayed by a continuous optical test according to Bücher et al. The data obtained show a repressive action on SDH activity by a sorbitol-enriched diet. In fact, whilst after 20 days of treatment SDH activity decreased of about 18% in respect of the controls, after 60 days a decrease of 80% was observed. This result is so interesting to stimulate other investigations in vitro on the kinetics of such metabolic reaction in the attempt to explain the relation between the enzyme and its substrate.

Animals↗

High pressure liquid chromatographic determination of sorbitol in bulk sorbitol.

An HPLC procedure for determining sorbitol in bulk sorbitol is described. An Aminex HPX-87 column (Bio-Rad) is used with water as a mobile phase and with a refractive index detector to monitor column eluate. Sorbitol is separated from pentaerythritol, erythritol, ribitol, ethylene glycol, propylene glycol, arabitol, galactitol, mannitol, iditol, and other carbohydrates. The precision of the sorbitol determination, characterized by a 95% confidence interval, corresponds to +/- 1.22%.

Chromatography, High Pressure Liquid↗