Intestinal metabolite xylulose inhibits colorectal cancer by inducing apoptosis through the MAPK signalling pathway.

BACKGROUND: The intestinal metabolites are involved in the initiation, progression and metastasis of colorectal cancer (CRC). They are a potential source of agents for cancer therapy. Our previous study identified altered faecal metabolites between CRC patients and healthy volunteers. However, no specific metabolite was clearly illustrated for CRC therapy. RESULTS: We found that the level of xylulose was lower in the stools of CRC patients than in those of healthy volunteers. Xylulose inhibited cell growth without affecting the cell cycle by inducing apoptosis in CRC cells, which was evidenced by increased expression of the proapoptotic proteins C-PARP and C-Caspase3 and decreased expression of the antiapoptotic protein BCL-2 in CRC cells. Mechanistically, xylulose reduced the activity of the MAPK signalling pathway, represented by reduced phosphorylation of JNK, ERK, and P38. Furthermore, an ALI model was used to show the tumour killing ability of xylulose on human CRC spheres, as well as human colorectal adenoma (AD) spheres. CONCLUSION: Xylulose inhibits CRC growth by inducing apoptosis through attenuation of the MAPK signalling pathway. These results suggest that xylulose may serve as an effective agent for CRC therapy.

Investigation of the effect of oligo-xylulose on the intestinal flora under pressure overload in mice based on 16S rRNA gene sequencing.

The relationship between gut microbiota dysbiosis and heart failure has been drawing increasing attention. This study aimed to investigate the effects of oligo-xylulose (XOS) on the gut microbiota of mice with heart failure induced by pressure overload. A chronic heart failure mouse model was constructed by pressure overload, and XOS were administered in their diet. The gut microbiota was analyzed using 16S rRNA gene sequencing, and the effects of XOS on the microbiota composition were evaluated. . XOS supplementation improved the balance of intestinal microbiota in mice under pressure overload, increasing the abundance of beneficial bacteria, such as Bifidobacterium and Lactobacillus, while decreasing the abundance of harmful bacteria, such as Desulfovibrio and Enterococcus. XOS has potential as a dietary supplement to improve the balance of intestinal microbiota and benefit individuals with heart failure. The findings of this study suggest that modulating the gut microbiota could be a novel strategy for treating heart failure.

Advances in applications, metabolism, and biotechnological production of L-xylulose.

L-Xylulose is an intermediate in certain metabolic pathways and is classified as a rare sugar. It shows important physiological effects such as acting as an inhibitor of α-glucosidase and decreasing blood glucose, and it can be employed to produce other significant rare sugars, such as L-ribose and L-xylose which contribute to the production of antiviral drugs. Chemical synthesis of L-xylulose was performed, but it is difficult and low yielding. The biotransformation from xylitol to L-xylulose by xylitol 4-dehydrogenase was studied intensively. This review describes the occurrence of L-xylulose in certain metabolic pathways, its bioproduction, and application potential.

Coordination of gene expression and growth-rate in natural populations of budding yeast.

Cells adapt to environmental changes through genetic mutations that stabilize novel phenotypes. Often, this adaptation involves regulatory changes which modulate gene expression. In the budding yeast, ribosomal-related gene expression correlates with cell growth rate across different environments. To examine whether the same relationship between gene expression and growth rate is observed also across natural populations, we measured gene expression, growth rate and ethanol production of twenty-four wild type yeast strains originating from diverse habitats, grown on the pentose sugar xylulose. We found that expression of ribosome-related genes did not correlate with growth rate. Rather, growth rate was correlated with the expression of amino acid biosynthesis genes. Searching other databases, we observed a similar correlation between growth rate and amino-acid biosyntehsis genes in a library of gene deletions. We discuss the implications of our results for understanding how cells coordinate their translation capacity with available nutrient resources.

[Xylose isomerase constitutive biosynthesis in Arthrobacter nicotianae].

The specific features of biosynthesis of the cell-bound xylose isomerase by the actinobacterium Arthrobacter nicotianae BIM V-5 were studied. It was demonstrated that the constitutive synthesis of this enzyme in the studied bacteria, not subject to catabolite repression, was inhibited by xylulose, an intermediate product ofxylose utilization and the final product of its enzymatic isomerization. Short-term experiments demonstrated that xylulose at a concentration of 0.005% almost completely repressed the xylose isomerase synthesis in A. nicotianae. This effect was independent of the time moment when the repressor was added to the cultivation medium and was not associated with its influence on the catalytic activity of the enzyme.

Effects of terpenoid precursor feeding on Catharanthus roseus hairy roots over-expressing the alpha or the alpha and beta subunits of anthranilate synthase.

Among the pharmacologically important terpenoid indole alkaloids produced by Catharanthus roseus are the anti-cancer drugs vinblastine and vincristine. These two drugs are produced in small yields within the plant, which makes them expensive to produce commercially. Metabolic engineering has focused on increasing flux through this pathway by various means such as elicitation, precursor feeding, and introduction of genes encoding specific metabolic enzymes into the plant. Recently in our lab, a feedback-resistant anthranilate synthase alpha subunit was over-expressed in C. roseus hairy roots under the control of a glucocorticoid inducible promoter system. Upon induction we observed a large increase in the indole precursors, tryptophan, and tryptamine. The current work explores the effects of over-expressing the anthranilate synthase alpha or alpha and beta subunits in combination with feeding with the terpenoid precursors 1-deoxy-D-xylulose, loganin, and secologanin. In feeding 1-deoxy-D-xylulose to the hairy root line expressing the anthranilate synthase alpha subunit, we observed an increase of 125% in hörhammericine levels in the induced samples, while loganin feeding increased catharanthine by 45% in the induced samples. Loganin feeding to the hairy root line expressing anthranilate synthase alpha and beta subunits increases catharanthine by 26%, ajmalicine by 84%, lochnericine by 119%, and tabersonine by 225% in the induced samples. These results suggest that the terpenoid precursors to the terpenoid indole alkaloids are important factors in terpenoid indole alkaloid production.

Cross-talk between the cytosolic mevalonate and the plastidial methylerythritol phosphate pathways in tobacco bright yellow-2 cells.

In plants, two pathways are utilized for the synthesis of isopentenyl diphosphate, the universal precursor for isoprenoid biosynthesis. The key enzyme of the cytoplasmic mevalonic acid (MVA) pathway is 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR). Treatment of Tobacco Bright Yellow-2 (TBY-2) cells by the HMGR-specific inhibitor mevinolin led to growth reduction and induction of apparent HMGR activity, in parallel to an increase in protein representing two HMGR isozymes. Maximum induction was observed at 24 h. 1-Deoxy-d-xylulose (DX), the dephosphorylated first precursor of the plastidial 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway, complemented growth inhibition by mevinolin in the low millimolar concentration range. Furthermore, DX partially re-established feedback repression of mevinolin-induced HMGR activity. Incorporation studies with [1,1,1,4-2H4]DX showed that sterols, normally derived from MVA, in the presence of mevinolin are synthesized via the MEP pathway. Fosmidomycin, an inhibitor of 1-deoxy-d-xylulose-5-phosphate reductoisomerase, the second enzyme of the MEP pathway, was utilized to study the reverse complementation. Growth inhibition by fosmidomycin of TBY-2 cells could be partially overcome by MVA. Chemical complementation was further substantiated by incorporation of [2-13C]MVA into plastoquinone, representative of plastidial isoprenoids. Best rates of incorporation of exogenous stably labeled precursors were observed in the presence of both inhibitors, thereby avoiding internal isotope dilution.

Contribution of the mevalonate and methylerythritol phosphate pathways to the biosynthesis of gibberellins in Arabidopsis.

Gibberellins (GAs) are diterpene plant hormones essential for many developmental processes. Although the GA biosynthesis pathway has been well studied, our knowledge on its early stage is still limited. There are two possible routes for the biosynthesis of isoprenoids leading to GAs, the mevalonate (MVA) pathway in the cytosol and the methylerythritol phosphate (MEP) pathway in plastids. To distinguish these possibilities, metabolites from each isoprenoid pathway were selectively labeled with (13)C in Arabidopsis seedlings. Efficient (13)C-labeling was achieved by blocking the endogenous pathway chemically or genetically during the feed of a (13)C-labeled precursor specific to the MVA or MEP pathways. Gas chromatography-mass spectrometry analyses demonstrated that both MVA and MEP pathways can contribute to the biosyntheses of GAs and campesterol, a cytosolic sterol, in Arabidopsis seedlings. While GAs are predominantly synthesized through the MEP pathway, the MVA pathway plays a major role in the biosynthesis of campesterol. Consistent with some crossover between the two pathways, phenotypic defects caused by the block of the MVA and MEP pathways were partially rescued by exogenous application of the MEP and MVA precursors, respectively. We also provide evidence to suggest that the MVA pathway still contributes to GA biosynthesis when this pathway is limiting.

(-)-2C-methyl-D-erythrono-1,4-lactone is formed after application of the terpenoid precursor 1-deoxy-D-xylulose.

Application of [1,2-14C]1-deoxy-D-xylulose, the committed precursor of terpenoids, thiamine and pyridoxol, to a variety of plant species resulted in the labelling of an unknown metabolite. The isolation and purification of this metabolite from Ipomoea purpurea plants fed with 1-deoxy-D-xylulose (DX), followed by NMR analysis, resulted in the identification of its structure as (-)-2C-methyl-D-erythrono-1,4-lactone (MDEL). MDEL has been previously isolated as a stress metabolite of certain plants. A hypothetical biosynthetic scheme is given.

Inhibition of glycoprotein processing by L-fructose and L-xylulose.

A number of unusual and rare carbohydrates were tested as potential inhibitors of various glycosidases, as well as inhibitors of N-linked oligosaccharide processing. The best inhibitors of several arylglycosidases and of glucosidase I were L-xylulose and L-fructose. Both of these sugars showed some inhibitory activity towards yeast alpha-glucosidase but were inactive against beta-glucosidase and other arylglycosidases. The inhibition of yeast alpha-glucosidase by L-xylulose was of a competitive nature and required a concentration of 1 x 10(-5) M for 50% inhibition. Both L-xylulose and L-fructose also inhibited the purified soybean glucosidase I, with 50% inhibition occurring at about 1 x 10(-4) M, but showed no inhibitory activity against soybean glucosidase II. When influenza virus-infected MDCK cells were raised in the presence of L-xylulose, there was a dose-dependent inhibition in the formation of complex types of oligosaccharides on the viral glycoproteins consistent with the inhibition of the processing glucosidase I. This inhibition resulted in the occurrence of oligosaccharides on the viral glycoproteins that were characterized as Glc3Man9(GlcNAc)2 structures. L-Fructose also inhibited glycoprotein processing in cell culture, and the inhibition resulted in the formation of similar oligosaccharides to those seen with L-xylulose. However, L-fructose was a poorer inhibitor than L-xylulose and required much higher concentrations for the same degree of inhibition. Neither of these compounds inhibited protein synthesis or the formation of lipid-linked saccharides in culture MDCK cells, even when tested at concentrations of 5 mg/ml (about 30 mM) of culture media.

D-xylulose-induced depletion of ATP and Pi in isolated rat hepatocytes.

Xylitol is known to cause hepatic ATP catabolism by inducing the trapping of Pi in the form of glycerol 3-P as a consequence of an increase in the NADH:NAD+ ratio, resulting from the oxidation of xylitol to D-xylulose. The question was therefore raised whether D-xylulose also depletes hepatic ATP. In isolated rat hepatocytes, 5 mM D-xylulose decreased ATP by 80% within 5 min compared to 40% with 5 mM xylitol. Intracellular Pi decreased by 70% within the same time interval with both compounds, but was restored three-fold faster with D-xylulose. The rate of utilization of D-xylulose reached 5 mumol.min-1.g-1 of cells, as compared with 1.5 for xylitol, indicating that reduction of xylitol into D-xylulose is a rate-limiting step in the metabolism of the polyol. D-Xylulose barely modified the concentration of glycerol 3-P but increased xylulose 5-P from 0.02 to 0.5 mumol/g within 5 min. The main cause of the ATP- and Pi-depleting effects of D-xylulose was found to be an accumulation of sedoheptulose 7-P from a basal value of 0.1 to 5 mumol/g of cells after 10 min. Ribose 5-P increased from 0.03 to 0.5 mumol/g at 5 min. Ribose 1-P also accumulated, albeit outside of the cells. This extracellular accumulation can be explained by the release of intracellular purine nucleoside phosphorylase from damaged hepatocytes acting on inosine that had diffused out of the cells. Smaller increases in the concentrations of sedoheptulose 7-P and pentose phosphates were recorded after incubations of the cells with xylitol.

Increase in phosphoribosyl pyrophosphate induced by ATP and Pi depletion in hepatocytes.

A series of compounds that induce depletion of ATP and Pi when added to isolated rat hepatocytes were found to cause a remarkable, although transient, elevation in the concentration of phosphoribosyl pyrophosphate (PRPP) in these cells. After the addition of 5 mM fructose, xylitol, tagatose, or D-xylulose, PRPP increased from a basal value of 6 +/- 1 nmol/g of cells to, respectively, 68 +/- 11, 42 +/- 11, 67 +/- 22, and 530 +/- 50 nmol/g of cells (means +/- SEM of 3-9 experiments). In each case, the increase in PRPP was preceded by a latency period of 5-10 min. PRPP reached maximal levels 15 min after the addition of fructose and 30 min after that of xylitol and D-xylulose, but continued to increase for as long as 60 min after the addition of tagatose. Most striking was that the increase in PRPP closely paralleled the restoration of intracellular Pi. Ribose 5-P increased about two- to fivefold after the addition of fructose, xylitol, and tagatose, and approximately 12-fold after D-xylulose. The mechanism by which ATP- and Pi-depleting compounds stimulate the activity of PRPP synthetase in isolated rat hepatocytes is discussed.

Inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase by xylulose 1,5-bisphosphate.

Xylulose 1,5-bisphosphate is a potent inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase. The enzyme was inhibited 50% at a xylulose 1,5-bisphosphate concentration of 0.56 micrometer and an enzyme concentration of 0.14 micrometer. When both ribulose 1,5-bisphosphate and xylulose 1,5-bisphosphate were added simultaneously to the enzyme, this inhibition appeared to be competitive. A preincubation of 20 to 30 min was needed for maximum inhibition. The inhibitory effect of this compound is probably exerted through its binding at the ribulose 1,5-bisphosphate active site, since both the carboxylase and oxygenase activities were inhibited similarly.