TKT maintains intestinal ATP production and inhibits apoptosis-induced colitis

Inflammatory bowel disease (IBD) has a close association with transketolase (TKT) that links glycolysis and the pentose phosphate pathway (PPP). However, how TKT functions in the intestinal epithelium remains to be elucidated. To address this question, we specifically delete TKT in intestinal epithelial cells (IECs). IEC TKT-deficient mice are growth retarded and suffer from spontaneous colitis. TKT ablation brings about striking alterations of the intestine, including extensive mucosal erosion, aberrant tight junctions, impaired barrier function, and increased inflammatory cell infiltration. Mechanistically, TKT deficiency significantly accumulates PPP metabolites and decreases glycolytic metabolites, thereby reducing ATP production, which results in excessive apoptosis and defective intestinal barrier. Therefore, our data demonstrate that TKT serves as an essential guardian of intestinal integrity and barrier function as well as a potential therapeutic target for intestinal disorders.

Untargeted metabolomics as an unbiased approach to the diagnosis of inborn errors of metabolism of the non-oxidative branch of the pentose phosphate pathway

Inborn errors of metabolism (IEM) involving the non-oxidative pentose phosphate pathway (PPP) include the two relatively rare conditions, transketolase deficiency and transaldolase deficiency, both of which can be difficult to diagnosis given their non-specific clinical presentations. Current biochemical testing approaches require an index of suspicion to consider targeted urine polyol testing. To determine whether a broad-spectrum biochemical test could accurately identify a specific metabolic pattern defining IEMs of the non-oxidative PPP, we employed the use of clinical metabolomic profiling as an unbiased novel approach to diagnosis. Subjects with molecularly confirmed IEMs of the PPP were included in this study. Targeted quantitative analysis of polyols in urine and plasma samples was accomplished with chromatography and mass spectrometry. Semi-quantitative unbiased metabolomic analysis of urine and plasma samples was achieved by assessing small molecules via liquid chromatography and high-resolution mass spectrometry. Results from untargeted and targeted analyses were then compared and analyzed for diagnostic acuity. Two siblings with transketolase (TKT) deficiency and three unrelated individuals with transaldolase (TALDO) deficiency were identified for inclusion in the study. For both IEMs, targeted polyol testing and untargeted metabolomic testing on urine and/or plasma samples identified typical perturbations of the respective disorder. Additionally, untargeted metabolomic testing revealed elevations in other PPP metabolites not typically measured with targeted polyol testing, including ribonate, ribose, and erythronate for TKT deficiency and ribonate, erythronate, and sedoheptulose 7-phosphate in TALDO deficiency. Non-PPP alternations were also noted involving tryptophan, purine, and pyrimidine metabolism for both TKT and TALDO deficient patients. Targeted polyol testing and untargeted metabolomic testing methods were both able to identify specific biochemical patterns indicative of TKT and TALDO deficiency in both plasma and urine samples. In addition, untargeted metabolomics was able to identify novel biomarkers, thereby expanding the current knowledge of both conditions and providing further insight into potential underlying pathophysiological mechanisms. Furthermore, untargeted metabolomic testing offers the advantage of having a single effective biochemical screening test for identification of rare IEMs, like TKT and TALDO deficiencies, that may otherwise go undiagnosed due to their generally non-specific clinical presentations.

Transketolase Deficiency in Adipose Tissues Protects Mice From Diet-Induced Obesity by Promoting Lipolysis

Obesity has recently become a prevalent health threat worldwide. Although emerging evidence has suggested a strong link between the pentose phosphate pathway (PPP) and obesity, the role of transketolase (TKT), an enzyme in the nonoxidative branch of the PPP that connects PPP and glycolysis, remains obscure in adipose tissues. In this study, we specifically deleted TKT in mouse adipocytes and found no obvious phenotype upon normal diet feeding. However, adipocyte TKT abrogation attenuated high-fat diet-induced obesity, reduced hepatic steatosis, improved glucose tolerance, alleviated insulin resistance, and increased energy expenditure. Mechanistically, TKT deficiency accumulated nonoxidative PPP metabolites and decreased glycolysis and pyruvate input into the mitochondria, leading to increased lipolytic enzyme gene expression and enhanced lipolysis, fatty acid oxidation, and mitochondrial respiration. Therefore, our data not only identify a novel role of TKT in regulating lipolysis and obesity but also suggest that limiting glucose-derived carbon into the mitochondria induces lipid catabolism and energy expenditure.

Transketolase Deficiency Protects the Liver from DNA Damage by Increasing Levels of Ribose 5-Phosphate and Nucleotides

De novo nucleotide biosynthesis is essential for maintaining cellular nucleotide pools, the suppression of which leads to genome instability. The metabolic enzyme transketolase (TKT) in the nonoxidative branch of the pentose phosphate pathway (PPP) regulates ribose 5-phosphate (R5P) levels and de novo nucleotide biosynthesis. TKT is required for maintaining cell proliferation in human liver cancer cell lines, yet the role of TKT in liver injury and cancer initiation remains to be elucidated. In this study, we generated a liver-specific TKT knockout mouse strain by crossing TKT^flox/flox mice with albumin-Cre mice. Loss of TKT in hepatocytes protected the liver from diethylnitrosamine (DEN)-induced DNA damage without altering DEN metabolism. DEN treatment of TKT-null liver increased levels of R5P and promoted de novo nucleotide synthesis. More importantly, supplementation of dNTPs in primary hepatocytes alleviated DEN-induced DNA damage, cell death, inflammatory response, and cell proliferation. Furthermore, DEN and high-fat diet (HFD)-induced liver carcinogenesis was reduced in TKT^flox/floxAlb-Cre mice compared with control littermates. Mechanistically, loss of TKT in the liver increased apoptosis, reduced cell proliferation, decreased TNFα, IL6, and STAT3 levels, and alleviated DEN/HFD-induced hepatic steatosis and fibrosis. Together, our data identify a key role for TKT in promoting genome instability during liver injury and tumor initiation. SIGNIFICANCE: These findings identify transketolase as a novel metabolic target to maintain genome stability and reduce liver carcinogenesis.

Enhanced D-ribose biosynthesis in batch culture of a transketolase-deficient Bacillus subtilis strain by citrate

In this study, the effects of citrate addition on D-ribose production were investigated in batch culture of a transketolase-deficient strain, Bacillus subtilis EC2, in shake flasks and bioreactors. Batch cultures in shake flasks and a 5-l reactor indicated that supplementation with 0.2-0.5 g l(-1) of citrate enhanced D: -ribose production. When B. subtilis EC2 was cultivated in a 15-l reactor in a complex medium, the D: -ribose concentration was 70.9 g l(-1) with a ribose yield of 0.497 mol mol(-1). When this strain was grown in the same medium supplemented with 0.3 g l(-1) of citrate, 83.4 g l(-1) of D-ribose were obtained, and the ribose yield was increased to 0.587 mol mol(-1). Addition of citrate reduced the activities of pyruvate kinase and phosphofructokinase, while it increased those of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Metabolic flux distribution in the stationary phase indicated that citrate addition resulted in increased fluxes in the pentose phosphate pathway and TCA cycle, and decreased fluxes in the glycolysis and acetate pathways.

Metabolic engineering of Saccharomyces cerevisiae for conversion of D-glucose to xylitol and other five-carbon sugars and sugar alcohols

Recombinant Saccharomyces cerevisiae strains that produce the sugar alcohols xylitol and ribitol and the pentose sugar D-ribose from D-glucose in a single fermentation step are described. A transketolase-deficient S. cerevisiae strain accumulated D-xylulose 5-phosphate intracellularly and released ribitol and pentose sugars (D-ribose, D-ribulose, and D-xylulose) into the growth medium. Expression of the xylitol dehydrogenase-encoding gene XYL2 of Pichia stipitis in the transketolase-deficient strain resulted in an 8.5-fold enhancement of the total amount of the excreted sugar alcohols ribitol and xylitol. The additional introduction of the 2-deoxy-glucose 6-phosphate phosphatase-encoding gene DOG1 into the transketolase-deficient strain expressing the XYL2 gene resulted in a further 1.6-fold increase in ribitol production. Finally, deletion of the endogenous xylulokinase-encoding gene XKS1 was necessary to increase the amount of xylitol to 50% of the 5-carbon sugar alcohols excreted.

Transketolase haploinsufficiency reduces adipose tissue and female fertility in mice

Transketolase (TKT) is a ubiquitous enzyme used in multiple metabolic pathways. We show here by gene targeting that TKT-null mouse embryos are not viable and that disruption of one TKT allele can cause growth retardation ( approximately 35%) and preferential reduction of adipose tissue ( approximately 77%). Other TKT(+/-) tissues had moderate ( approximately 33%; liver, gonads) or relatively little ( approximately 7 to 18%; eye, kidney, heart, brain) reductions in mass. These mice expressed a normal level of growth hormone and reduced leptin levels. No phenotype was observed in the TKT(+/-) cornea, where TKT is especially abundant in wild-type mice. The small female TKT(+/-) mice mated infrequently and had few progeny (with a male/female ratio of 1.4:1) when pregnant. Thus, TKT in normal mice appears to be carefully balanced at a threshold level for well-being. Our data suggest that TKT deficiency may have clinical significance in humans and raise the possibility that obesity may be treated by partial inhibition of TKT in adipose tissue.

Production of D-ribose by fermentation

The production of D-ribose by fermentation has received much attention lately, possibly because of the use of this pentose to synthesize antiviral and anticancer drugs. This review briefly outlines the methods that have been used to synthesize D-ribose since it was identified in yeast RNA, and focuses in particular on the latest developments in D-ribose fermentation, which have led to D-ribose yields that exceed 90 g/1. Furthermore, the various transketolase-deficient D-ribose-producing mutants that are used, and the biochemical and genetic rationales applied to select them or to enhance their D-ribose productivities, are dealt with. Attention is also drawn to the unusual pleiotropic characteristics of the mutant strains, as well as to the industrial and academic applications of D-ribose.

Red cell transketolase studies in a private practice specializing in nutritional correction

Erythrocyte transketolase (TKA) and thiamin pyrophosphate percentage uptake, or effect (TPPE) were performed on 1011 patients between 1983 and 1986. The subjects were drawn from a private practice specializing in nutritional correction as a major therapeutic thrust. Either TKA or TPPE or both were abnormal in 283 (28%). Out of the total number of patients with these abnormal studies 36 have been selected as representative. Their clinical presentation is correlated with subsequent laboratory testing in order to draw attention to the practical value of the test in a clinical setting. These data are presented because of the surprisingly high incidence of abnormal tests, that strongly suggests that there is widespread marginal nutritional deficiency in the United States and that it represents a clinical problem that deserves far more attention than it is presently receiving.