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The functional properties of egg white (EW) glycated with a rare D-psicose and two alimentary sugars (D-fructose and D-glucose) were investigated. The results indicate that psicose-EW as a food ingredient might have the ability to improve gelling behavior and decrease oxidation reactions during food processing and storage.

D-Psicose (D-ribo-2-hexulose), a C-3 epimer of D-fructose, is a "rare sugar" present in small quantities in commercial mixtures of D-glucose and D-fructose obtained from the hydrolysis of sucrose or isomerization of D-glucose. Because of the very small amounts of D-psicose in natural products, few studies of D-psicose metabolism in mammals have been conducted. Recently, we developed a new method to produce D-psicose enzymatically on a large scale, making it possible to conduct scientific studies. In this study, we examined (1) the metabolic effects of D-psicose, (2) the available energy of D-psicose and (3) acute and subchronic toxicity to gather basic data regarding the safety of using as a new sugar substitute. (Experiment 1) We investigated the absorption and excretion of D-psicose when orally administrated (5g/kg body weight) to Wistar rats, and the fermentation of D-psicose was measured as cecal short-chain fatty acids (SCFA) when fed to rats in controlled diets (0-30%). Urinary and fecal excretions of D-psicose over the 24 h were 11- 15% of dosage for the former and 8-13% of dosage for the latter. Rats fed on D-psicose diets showed SCFA production. (Experiment 2) Wistar rats received 7 g daily of a basal diet to which fixed amounts of D-psicose (0.5-2.0 g) were added for 20 days. Body energy gain did not increase with D-psicose. One gram of D-psicose produced a net energy gain of 0.007 kcal and the energy value of D- psicose was effectively zero. (Experiment 3) Wistar rats were orally given Dpsicose in dose of 8-20 g/kg. The calculated LD50 value was 16.3 g/kg. Another Wistar rats were fed diets containing 0- 40% of D-psicose for 34 days. Body weight gain and food intake were more extensively suppressed by the higher Dpsicose diets. These results suggest that D-psicose displays nutritional characteristics unlike other monosaccharides such as D-glucose or D-fructose and provides no energy for growth. D-Psicose is not a toxic sugar but should be used carefully, if at all, as a dietary fiber-like substance or sweetener in food manufacturing. [ABSTRACT FROM AUTHOR]

To find out the mechanism of action of Dallose researchers tried to trace whether D-allose has an effect on the inhibition of neutrophil adherence to endothelial cells after reperfusion. Researchers administered D-allose or vehicle intraperitoneally to a rat model of 70% partial ischemia for 90 min followed by reperfusion. The effect of D-allose on the expression of adhesion molecule, ICAM-1 was analyzed by immunohistochemistry in the liver tissues taken 3 h after reperfusion. Liver enzymes from hepatic venous blood were estimated. Histological examination was performed in the injured liver.

D-Psicose (D-ribo-2-hexulose), a C-3 epimer of D-fructose, is present in small quantities in commercial carbohydrate complexes or agricultural products. Wistar male rats were fed experimental diets which consisted of 5% D-psicose, cellulose, D-fructose or D-glucose for 28 days. Abdominal adipose tissue weight was significantly lower (P < 0.05) in rats fed the D-psicose diet than in rats fed a D-fructose and D-glucose diets, even though the four dietary groups were offered the same amount throughout the experimental period. Fatty acid synthase and glucose 6-phosphate dehydrogenase activities in the liver were significantly lower (P < 0.05) in rats fed the D-psicose diet than in rats fed the D-fructose and D-glucose diets. However, lipoprotein lipase activities in the heart, soleus muscle and perirenal adipose tissue were the same. These results suggest that a supplement of D-psicose in the diet suppresses hepatic lipogenic enzyme activities. The lower abdominal fat accumulation in rats fed a D-psicose diet might result from lower lipogenesis in the liver. [ABSTRACT FROM AUTHOR]

L-rhamnose isomerase (L-RhI) plays a key role in the microbial L-rhamnose metabolism by catalyzing the reversible isomerization of L-rhamnose to L-rhamnulose. Additionally, the enzyme exhibits activity on various other aldoses and ketoses, and its broad substrate specificity has attracted attention for its potential application in the production of rare sugars; however, improvement of the enzyme properties is desirable, such as thermal stability, enzymatic activity, and a pH optimum suitable for industrial usage. This review summarizes our current insights into L-RhIs with respect to their substrate recognition mechanism and their relationship with D-xylose isomerase (D-XI) based on structural and phylogenetic analyses. These two enzymes are inherently different, but recognize distinctly different substrates, and share common features that may be phylogenetically related. For example, they both have a flexible loop region that is involved in shaping active sites, and this region may also be responsible for various enzymatic properties of L-RhIs, such as substrate specificity and thermal stability. KEY POINTS: •L-RhIs share structural features with D-XI. •There are two types of L-RhIs: E. coli L-RhI-type and D-XI-type. •Flexible loop regions are involved in the specific enzyme properties., (© 2024. The Author(s).)

A recombinant L-rhamnose isomerase (L-RhI) from probiotic Lactobacillus rhamnosus Probio-M9 (L. rhamnosus Probio-M9) was expressed. L. rhamnosus Probio-M9 was isolated from human colostrum and identified as a probiotic lactic acid bacterium, which can grow using L-rhamnose. L-RhI is one of the enzymes involved in L-rhamnose metabolism and catalyzes the reversible isomerization between L-rhamnose and L-rhamnulose. Some L-RhIs were reported to catalyze isomerization not only between L-rhamnose and L-rhamnulose but also between D-allulose and D-allose, which are known as rare sugars. Those L-RhIs are attractive enzymes for rare sugar production and have the potential to be further improved by enzyme engineering; however, the known crystal structures of L-RhIs recognizing rare sugars are limited. In addition, the optimum pH levels of most reported L-RhIs are basic rather than neutral, and such a basic condition causes non-enzymatic aldose-ketose isomerization, resulting in unexpected by-products. Herein, we report the crystal structures of L. rhamnosus Probio-M9 L-RhI (LrL-RhI) in complexes with L-rhamnose, D-allulose, and D-allose, which show enzyme activity toward L-rhamnose, D-allulose, and D-allose in acidic conditions, though the activity toward D-allose was low. In the complex with L-rhamnose, L-rhamnopyranose was found in the catalytic site, showing favorable recognition for catalysis. In the complex with D-allulose, D-allulofuranose and ring-opened D-allulose were observed in the catalytic site. However, bound D-allose in the pyranose form was found in the catalytic site of the complex with D-allose, which was unfavorable for recognition, like an inhibition mode. The structure of the complex may explain the low activity toward D-allose. KEY POINTS: • Crystal structures of LrL-RhI in complexes with substrates were determined. • LrL-RhI exhibits enzyme activity toward L-rhamnose, D-allulose, and D-allose. • The LrL-RhI is active in acidic conditions., (© 2024. The Author(s).)

Recent studies have shown that D-allose, a rare sugar, elicits antitumor effects on different types of solid cancers, such as hepatocellular carcinoma, non-small-cell lung cancer, and squamous cell carcinoma of the head and neck. In this study, we examined the effects of D-allose on the proliferation of human glioblastoma (GBM) cell lines (i.e., U251MG and U87MG) in vitro and in vivo and the underlying mechanisms. D-allose treatment inhibited the proliferation of U251MG and U87MG cells in a dose-dependent manner (3-50 mM). However, D-allose treatment did not affect cell cycles or apoptosis in these cells but significantly decreased the cell division frequency in both GBM cell lines. In a subcutaneous U87MG cell xenograft model, intraperitoneal injection of D-allose (100 mg/kg/day) significantly reduced the tumor volume in 28 days. These data indicate that D-allose-induced reduction in cell proliferation is associated with a subsequent decrease in the number of cell divisions, independent of cell-cycle arrest and apoptosis. Thus, D-allose could be an attractive additive to therapeutic strategies for GBM., (© 2023. The Author(s).)

Allitol is a hexitol produced by reducing the rare sugar D-allulose with a metal catalyst under hydrogen gas. To confirm the safe level of allitol, we conducted a series of safety assessments. From the results of Ames mutagenicity assay using Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537, Escherichia coli strain WP2uvrA, and an in vitro chromosomal aberration test on cultured Chinese hamster cells, allitol did not show any significant genotoxic effect. No significant effects on general condition, urinalysis, hematology, physiology, histopathology, or at necropsy were observed at a dose of 1500 mg/kg body weight of allitol in the acute and 90-day subchronic oral-toxicity assessments for rats. A further study performed on healthy adult humans showed that the acute use level of allitol for diarrhea was 0.2 g/kg body weight for both men and women. The results of current safety assessment studies suggest that allitol is safe for human consumption., (© The Author(s) 2023. Published by Oxford University Press on behalf of Japan Society for Bioscience, Biotechnology, and Agrochemistry.)

d-Aldotetroses are rare sugars that are obtained via chemical synthesis in low yield. In this study, we demonstrated that d-aldotetroses could be produced using 3 isomerases. First, l-erythrulose was epimerized using d-tagatose 3-epimerase from Pseudomonas cichorii ST-24. The specific optical rotation of the reaction solution gradually decreased to zero, indicating that approximately 50% of the l-erythrulose was converted to d-erythrulose. d, l-Erythrulose mixture was isomerized with d-arabinose isomerase from Klebsiella pneumoniae 40bXX to produce d-threose, resulting in a conversion rate of 9.35%. d-Erythrose production using l-rhamnose isomerase from Pseudomonas stutzeri LL172 resulted in a conversion rate of 12.9%. Because of the low purity of the purchased d-erythrose, the product was reduced by the Raney nickel catalyst compared with authentic erythritol. We confirmed the products using HPLC and 13C-NMR spectra. This is the first report of d-aldotetrose production using an enzymatic reaction., (© The Author(s) 2023. Published by Oxford University Press on behalf of Japan Society for Bioscience, Biotechnology, and Agrochemistry.)