Effects of fructose and xylitol on the urinary excretion of adenosine, uridine, and purine bases

Excess dietary fructose does not alter gut microbiota or permeability in humans: A pilot randomized controlled study

Introduction:

Non-alcoholic fatty liver disease (NAFLD) is an increasing cause of chronic liver disease that accompanies obesity and the metabolic syndrome. Excess fructose consumption can initiate or exacerbate NAFLD in part due to a consequence of impaired hepatic fructose metabolism. Preclinical data emphasized that fructose-induced altered gut microbiome, increased gut permeability, and endotoxemia play an important role in NAFLD, but human studies are sparse. The present study aimed to determine if two weeks of excess fructose consumption significantly alters gut microbiota or permeability in humans.

Methods:

We performed a pilot double-blind, cross-over, metabolic unit study in 10 subjects with obesity (body mass index [BMI] 30–40 mg/kg/m²). Each arm provided 75 grams of either fructose or glucose added to subjects’ individual diets for 14 days, substituted isocalorically for complex carbohydrates, with a 19-day wash-out period between arms. Total fructose intake provided in the fructose arm of the study totaled a mean of 20.1% of calories. Outcome measures included fecal microbiota distribution, fecal metabolites, intestinal permeability, markers of endotoxemia, and plasma metabolites.

Results:

Routine blood, uric acid, liver function, and lipid measurements were unaffected by the fructose intervention. The fecal microbiome (including Akkermansia muciniphilia), fecal metabolites, gut permeability, indices of endotoxemia, gut damage or inflammation, and plasma metabolites were essentially unchanged by either intervention.

Conclusions:

In contrast to rodent preclinical findings, excess fructose did not cause changes in the gut microbiome, metabolome, and permeability as well as endotoxemia in humans with obesity fed fructose for 14 days in amounts known to enhance NAFLD.

Consumption of High-Fructose Corn Syrup Compared with Sucrose Promotes Adiposity and Increased Triglyceridemia but Comparable NAFLD Severity in Juvenile Iberian Pigs

BACKGROUND

Fructose consumption has been linked to nonalcoholic fatty liver disease (NAFLD) in children. However, the effect of high-fructose corn syrup (HFCS) compared with sucrose in pediatric NAFLD has not been investigated.

OBJECTIVES

We tested whether the isocaloric substitution of dietary sucrose by HFCS would increase the severity of NAFLD in juvenile pigs, and whether this effect would be associated with changes in gut histology, SCFA production, and microbial diversity.

METHODS

Iberian pigs, 53-d-old and pair-housed in pens balanced for weight and sex, were randomly assigned to receive a mash diet top-dressed with increasing amounts of sucrose (SUC; n = 3 pens; 281.6-486.8 g/kg diet) or HFCS (n = 4; 444.3-724.8 g/kg diet) during 16 wk. Diets exceeded the animal's energy requirements by providing sugars in excess, but met the requirements for all other nutrients. Animals were killed at 165 d of age after blood sampling, and liver, muscle, and gut were collected for histology, metabolome, and microbiome analyses. Data were analyzed by multivariate and univariate statistics.

RESULTS

Compared with SUC, HFCS increased subcutaneous fat, triacylglycerides in plasma, and butyrate in colon (P ≤ 0.05). In addition, HFCS decreased UMP and short-chain acyl carnitines in liver, and urea nitrogen and creatinine in serum (P ≤ 0.05). Microbiome analysis showed a 24.8% average dissimilarity between HFCS and SUC associated with changes in SCFA-producing bacteria. Body weight gain, intramuscular fat, histological and serum markers of liver injury, and circulating hormones, glucose, and proinflammatory cytokines did not differ between diets.

CONCLUSIONS

Fructose consumption derived from HFCS promoted butyrate synthesis, triglyceridemia, and subcutaneous lipid deposition in juvenile Iberian pigs, but did not increase serum and histological markers of NAFLD compared with a sucrose-enriched diet. Longer studies could be needed to observe differences in liver injury among sugar types.

Metabolic effects of the natural sweeteners xylitol and erythritol: A comprehensive review

Xylitol and erythritol are widely used in a variety of food and oral care products as sugar substitutes. Although a number of studies have been conducted on the health benefits of xylitol since the 1960s, erythritol only attracted the attention of researchers during the early 1990s. Historically, researchers mainly focused on the effects of xylitol and other sugar alcohols on oral and dental healthcare while the anti-diabetic or antihyperglycemic effects have only been revealed recently. Though a few reviews have been published on the health benefits of sugar alcohols in the last few decades, none of them closely evaluated the antihyperglycemic potential and underlying mechanisms, particularly with a focus on xylitol and erythritol. The current review thoroughly analyzes the anti-diabetic and antihyperglycemic effects as well as other metabolic effects of xylitol and erythritol using articles published in PubMed since the 1960s, containing research done on experimental animals and humans. This review will help researchers ascertain the controversies surrounding sugar alcohols, investigate further beneficial effects of them as well as aid food industries in exploring the possibilities of using sugar alcohols as anti-diabetic supplements in diabetic foods and food products.

Metabolomics reveals the protective of Dihydromyricetin on glucose homeostasis by enhancing insulin sensitivity

Dihydromyricetin (DMY), an important flavanone found in Ampelopsis grossedentata, possesses antioxidative properties that ameliorate skeletal muscle insulin sensitivity and exert a hepatoprotective effect. However, little is known about the effects of DMY in the context of high-fat diet (HFD)-induced hepatic insulin resistance. Male Sprague-Dawley(SD) rats were fed a HFD(60% fat) supplemented with DMY for 8 weeks. The administration of DMY to the rats with HFD-induced insulin resistance reduces hyperglycemia, plasma levels of insulin, and steatosis in the liver. Furthermore, DMY treatment modulated 24 metabolic pathways, including glucose metabolism, the TCA cycle. DMY significantly enhanced glucose uptake and improved the translocation of glucose transporter 1. The specificity of DMY promoted the phosphorylation of AMP-activated protein kinase (AMPK). In addition, the exposure of HepG2 cells to high glucose concentrations impaired the insulin-stimulated phosphorylation of Akt2 Ser474 and insulin receptor substrate-1 (IRS-1) Ser612, increased GSK-3β phosphorylation, and upregulated G6Pase and PEPCK expression. Collectively, DMY improved glucose-related metabolism while reducing lipid levels in the HFD-fed rats. These data suggest that DMY might be a useful drug for use in type 2 diabetes insulin resistance therapy and for the treatment of hepatic steatosis.

The Flower Tea Coreopsis tinctoria Increases Insulin Sensitivity and Regulates Hepatic Metabolism in Rats Fed a High-Fat Diet

An infusion of Coreopsis tinctoria (CT) flowering tops is traditionally used in Portugal to control hyperglycemia; however, the effects of CT protection against high-fat diet (HFD)-induced hepatic insulin resistance have not been systematically studied and the precise mechanism of action is not clear. The metabolomic profiles of insulin-resistant rats fed a HFD and a CT-supplemented diet (HFD supplemented with CT drinking) for 8 weeks were investigated. Serum samples for clinical biochemistry and liver samples for histopathology and liquid chromatography-mass spectrometry-based metabolomic research were collected. Western blot and quantitative real-time PCR analyses were further used to measure the expression of several relevant enzymes together with perturbed metabolic pathways. Using analysis software, the CT treatment was found to significantly ameliorate the disturbance in 10 metabolic pathways. Combined metabolomic, Western blot, and quantitative real-time PCR analyses revealed that CT treatment significantly improved the glucose homeostasis by, on the one hand, through inhibiting the expression of gluconeogenic pathway key proteins glucose-6-phosphatase and phosphoenolpyruvate carboxykinase and, on the other hand, via regulating the mRNA or protein levels of the Krebs cycle critical enzymes (citrate synthase, succinate dehydrogenase complex, subunit A, flavoprotein, and dihydrolipoamide S-succinyltransferase). These results provide metabolic evidence of the complex pathogenic mechanism involved in hepatic insulin resistance and that the supplementation with CT improves insulin resistance at a global scale. Liquid chromatography-mass spectrometry-based metabolomics approaches are helpful to further understand diabetes-related mechanisms.

Effect of fruit and vegetable antioxidants on total antioxidant capacity of blood plasma

For a long time, the increased consumption of fruits and vegetables was considered critical in protecting humans against a number of diseases, such as cancer, diabetes, neurodegenerative diseases, and heart and brain vascular diseases. Presently, it is thought that the protective properties of these foods result from the presence of low-molecular antioxidants that protect the cells and their structures against oxidative damage. The alleged effect of reducing the risk for many diseases is not only due to the effect of individual antioxidants, such as α-tocopherol, ascorbic acid, or β-carotene, but also may be the result of antioxidant compounds not yet known or synergy of several different antioxidants present in fruits and vegetables. Studies on macromolecules (DNA, nucleotides, proteins) free-radical-related damage showed that diets enriched with extra servings of fruits and vegetables rich in β-carotene, tocopherols, and ascorbic acid had only limited effect on the inhibition of oxidation processes. A number of studies have shown, however, that consuming less common fruits and vegetables contribute much more to the reduction of free-radical processes, most likely because they contain a large amount of non-vitamin antioxidants, such as polyphenols and anthocyanins.

Biochemistry of uridine in plasma

Uridine is a pyrimidine nucleoside that plays a crucial role in synthesis of RNA, glycogen, and biomembrane. In humans, uridine is present in plasma in considerably higher quantities than other purine and pyrimidine nucleosides, thus it may be utilized for endogenous pyrimidine synthesis. Uridine has a number of biological effects on a variety of organs with or without disease, such as the reproductive organs, central and peripheral nervous systems, and liver. In addition, it is used in clinical situations as a rescue agent to protect against the adverse effects of 5-fluorouracil. Since the biological actions of uridine may be related to its plasma concentration, it is important to examine factors that have effects on that concentration. Factors associated with an increase in plasma concentration of uridine include enhanced ATP consumption, enhanced uridine diphosphate (UDP)-glucose consumption via glycogenesis, inhibited uridine uptake by cells via the nucleoside transport pathway, increased intestinal absorption, and increased 5-phosphribosyl-1-pyrophosphate and urea synthesis. In contrast, factors that decrease the plasma concentration of uridine are associated with accelerated uridine uptake by cells via the nucleoside transport pathway and decreased pyrimidine synthesis.

Uridine correlates with the concentration of fructosamine and HbA1c in children with type 1 diabetes

AIM

Treating uridine as a product of UTP degradation and hypoxanthine as a degradation product of ATP, we assessed the concentration of uridine and hypoxanthine in the blood of children with newly diagnosed type 1 diabetes. We also sought to define the relationship between indicators of the degree of metabolic control of diabetes (fructosamine, HbA1c) and the concentration of the tested catabolites.

METHODS

This study was carried out on 33 children aged 12.26 ± 4.49 with newly diagnosed type 1 diabetes during their first hospitalization. The concentration of uridine and hypoxanthine was determined by high-performance liquid chromatography (HPLC).

RESULTS

The results showed significantly elevated levels of hypoxanthine and uridine in the blood. We further show that blood uridine level is associated with purine metabolism and hyperglycaemia, and we demonstrate a significant positive correlation between the concentration of uridine and (i) the percentage of HbA1c and (ii) fructosamine levels, which indicate the role of hyperglycaemia in the pathogenesis of pyrimidine nucleotide metabolism in type 1 diabetes prior to diagnosis.

CONCLUSION

The results confirm the existence of a relationship between the degree of metabolic control of diabetes and pyrimidine metabolism. Presumably, the analysis of uridine could be used as an adjunct marker of the severity of diabetic complications in newly diagnosed patients.

Beyond glucose: metabolic shifts in responses to the effects of the oral glucose tolerance test and the high-fructose diet in rats

High-fructose diet-fed rats as one of the insulin resistant models was used widely for understanding the mechanisms of type 2 diabetes mellitus. Systems-level metabolic profiling of the rat model, however, has not been deciphered clearly. To address this issue, mass spectrometry-based metabolomics was employed to unlock the metabolic snapshots of the oral glucose tolerance test (oGTT) effect in either healthy or diabetic rats, as well as to delineate the metabolic signatures in tissues of rats fed with high-fructose diet. Several differentiating metabolites were highlighted to reveal the metabolic perturbation of the oGTT effects in healthy and diabetic rats, which involved amino acid biosynthesis, polyunsaturated fatty acids, phospholipids and purine metabolism. Surprisingly, the patterns of relationships for the metabolic phenotypes by using data mining revealed that glucose ingestion might induce the healthy group to display its trajectory towards diabetic status, while only a very slight influence was observed on the high-fructose diet-fed rats 120 min after glucose ingestion. The data treatment for liver, skeletal muscle and brain tissues suggested that oxidative stress, such as lipid peroxidation and the declined antioxidant, the elevated amino acids and the perturbation of fatty acids, were caused by the high-fructose diet in liver and skeletal muscle tissues. On the other hand, the up-regulation in purine biosynthesis and the decreased concentrations for amino acids were observed in the cerebral cortex and hippocampus tissues. Collectively, the obtained results might provide a new insight not only for the impairment of glucose tolerance but also for the dietary style in rats.

Effect of quinoa seeds (Chenopodium quinoa) in diet on some biochemical parameters and essential elements in blood of high fructose-fed rats

The effect of Chenopodium quinoa seeds on lipid profile, glucose level, protein metabolism and selected essential elements (Na, K, Ca, Mg) level was determined in high-fructose fed male Wistar rats. Fructose decreased significantly LDL [42%, p<0.01] and activity of alkaline phosphatase [20%, p<0.05], and increased triglycerides level [86%, p<0.01]. The analysis of blood of rats fed quinoa indicated, that these seeds effectively reduced serum total cholesterol [26%, p<0.05], LDL [57%, p<0.008] and triglycerides [11%, p<0.05] when compared to the control group. Quinoa seeds also significantly reduced the level of glucose [10%, p<0.01] and plasma total protein level [16%, p<0.001]. Fructose significantly decreased HDL [15%, p<0.05] level in control group but when the quinoa seeds were added into the diet the decrease of HDL level was inhibited. Quinoa seeds did not prevent any adverse effect of increasing triglyceride level caused by fructose. It was shown in this study that quinoa seeds can reduce most of the adverse effects exerted by fructose on lipid profile and glucose level.

Plasma antioxidant capacity changes following a meal as a measure of the ability of a food to alter in vivo antioxidant status

OBJECTIVE

Determine 1) if consumption of a meal of different fruits or berries increases plasma hydrophilic (H-) or lipophilic (L-) antioxidant capacity (AOC) measured as Oxygen Radical Absorbance Capacity (ORAC(FL)); 2) if including macronutrients in the meal alters postprandial changes in AOC; and 3) if preliminary recommendations can be developed for antioxidant intake.

METHODS

Changes in plasma AOC following consumption of a single meal of berries/fruits (blueberry, dried plum, dried plum juice, grape, cherry, kiwifruit and strawberry) were studied in 5 clinical trials with 6-10 subjects per experiment. In two studies with blueberry or grape, additional macronutrients (carbohydrate, fat, protein) were included in the control and treatment meals. Blood samples collected before and after the meal were analyzed for AOC.

RESULTS

Consumption of dried plums or dried plum juice did not alter either the H- or L-AOC area under the curve (AUC). Consumption of blueberry in 2 studies and of mixed grape powder [12.5 (Study #1), 39.9 (Study #4) and 8.6 (Study #5) mmole Trolox Equivalents (TE) AOC, respectively] increased hydrophilic AOC AUC. L-AOC increased following a meal of blueberry containing 12.5 mmole TE AOC (Study #1). Consumption of 280 g of cherries (4.5 mmol TE AOC) increased plasma L-AOC but not H-AOC. The AOC in the control groups in which additional macronutrients (Studies #4 and #5) were added decreased from the postprandial baseline AOC measurement.

CONCLUSION

We have demonstrated that consumption of certain berries and fruits such as blueberries, mixed grape and kiwifruit, was associated with increased plasma AOC in the postprandial state and consumption of an energy source of macronutrients containing no antioxidants was associated with a decline in plasma AOC. However, without further long term clinical studies, one cannot necessarily translate increased plasma AOC into a potential decreased risk of chronic degenerative disease. Preliminary estimates of antioxidant needs based upon energy intake were developed. Consumption of high antioxidant foods with each meal is recommended in order to prevent periods of postprandial oxidative stress.

Effect of ethanol on metabolism of purine bases (hypoxanthine, xanthine, and uric acid)

There are many factors that contribute to hyperuricemia, including obesity, insulin resistance, alcohol consumption, diuretic use, hypertension, renal insufficiency, genetic makeup, etc. Of these, alcohol (ethanol) is the most important. Ethanol enhances adenine nucleotide degradation and increases lactic acid level in blood, leading to hyperuricemia. In beer, purines also contribute to an increase in plasma uric acid. Although rare, dehydration and ketoacidosis (due to ethanol ingestion) are associated with the ethanol-induced increase in serum uric acid levels. Ethanol also increases the plasma concentrations and urinary excretion of hypoxanthine and xanthine via the acceleration of adenine nucleotide degradation and a possible weak inhibition of xanthine dehydrogenase activity. Since many factors such as the ALDH2*1 gene and ADH2*2 gene, daily drinking habits, exercise, and dehydration enhance the increase in plasma concentration of uric acid induced by ethanol, it is important to pay attention to these factors, as well as ingested ethanol volume, type of alcoholic beverage, and the administration of anti-hyperuricemic agents, to prevent and treat ethanol-induced hyperuricemia.

Effect of branched-chain amino acids on the plasma concentration of uridine does not occur via the action of glucagon or insulin

To examine whether branched-chain amino acids affect the plasma concentration of uridine, we administered branched-chain amino acids (L-isoleucine, 2.85 g, L-leucine 5.71 g, and L-valine, 3.43 g) orally to 6 healthy subjects. Plasma uridine and glucose decreased by 44% and 12%, respectively, together with an increase in plasma isoleucine, leucine, and valine 90 minutes after administration. However, branched-chain amino acids did not affect the plasma concentration and urinary excretion of purine bases (hypoxanthine, xanthine, and uric acid) and uridine or the plasma concentration of insulin, glucagon, and cyclic adenosine monophosphate (cAMP). Since small amounts of regular insulin, which were found to decrease plasma glucose more than the amino acids, did not decrease the plasma concentration of uridine, these results suggest that plasma uridine was decreased by a direct effect of the branched-chain amino acids on the cellular uptake and/or release of uridine.