Fructose toxicity: is the science ready for public health actions?

PURPOSE OF REVIEW: The assumption that fructose may be toxic and involved in the pathogenesis of noncommunicable diseases such as obesity, diabetes mellitus, dyslipidemia, and even cancer has resulted in the call for public health action, such as introducing taxes on sweetened beverages. This review evaluates the scientific basis for such action. RECENT FINDINGS: Although some studies hint towards some potential adverse effects of excessive fructose consumption especially when combined with excess energy intake, the results from clinical trials do not support a significant detrimental effect of fructose on metabolic health when consumed as part of a weight-maintaining diet in amounts consistent with the average-estimated fructose consumption in Western countries. However, definitive studies are missing. SUMMARY: Public health policies to eliminate or limit fructose in the diet should be considered premature. Instead, efforts should be made to promote a healthy lifestyle that includes physical activity and nutritious foods while avoiding intake of excess calories until solid evidence to support action against fructose is available. Public health is almost certainly to benefit more from policies that are aimed at promoting what is known to be good than from policies that are prohibiting what is not (yet) known to be bad.

Lipoprotein lipase and leptin are accumulated in different secretory compartments in rat adipocytes.

Adipose cells produce and secrete several physiologically important proteins, such as lipoprotein lipase (LPL), leptin, adipsin, Acrp30, etc. However, secretory pathways in adipocytes have not been characterized, and vesicular carriers responsible for the accumulation and transport of secreted proteins have not been identified. We have compared the intracellular localization of two proteins secreted from adipose cells: leptin and LPL. Adipocytes accumulate large amounts of both proteins, suggesting that neither of them is targeted to the constitutive secretory pathway. By means of velocity centrifugation in sucrose gradients, equilibrium density centrifugation in iodixanol gradients, and immunofluorescence confocal microscopy, we determined that LPL and leptin were localized in different membrane structures. LPL was found mainly in the endoplasmic reticulum with a small pool being present in low density membrane vesicles that may represent a secretory compartment in adipose cells. Virtually all intracellular leptin was localized in these low density secretory vesicles. Insulin-sensitive Glut4 vesicles did not contain either LPL or leptin. Thus, secretion from adipose cells is controlled both at the exit from the endoplasmic reticulum as well as at the level of "downstream" secretory vesicles.

Target Molecular Size and Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis Analysis of the ATP-and Pyrophosphate-Dependent Proton Pumps from Maize Root Tonoplast.

Tonoplast-enriched membranes were prepared from maize (Zea mays L. cv LG 11) primary roots, using sucrose nonlinear gradients. The functional molecular size of the tonoplast ATP-and PPi-dependent proton pumps were analyzed by radiation inactivation. Glucose-6-phosphate dehydrogenase (G6PDH) was added as an internal standard. Frozen samples (-196 degrees C) of the membranes were irradiated with (60)Co for different periods of time. After thawing the samples, the activities of G6PDH, ATPase, and PPase were tested. By applying target theory, the functional sizes of the ATPase and PPase in situ were found to be around 540 and 160 kilodaltons, respectively. The two activities were solubilized and separated by gel filtration chromatography. The different polypeptides copurifying with the two pumps were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two bands (around 59 and 65 kilodaltons) were associated with the ATPase activity, whereas a double band (around 40 kilodaltons) was recovered with the PPase activity.

Experimental endocarditis following dental extractions in rats with periodontitis.

This study analyzed the development of bacterial endocarditis following dental extraction in rats with periodontal disease. Periodontal disease was produced in rats by tying silk ligatures around the two maxillary first molars, and placing the animals on a high sucrose diet. Sterile aortic valve vegetations were produced by means of a transaortic catheter, and 24 hours later the maxillary first molars were extracted. The animals were killed 72 hours after the extractions. In rats with periodontal disease induced for 10 and 14 weeks, extractions resulted in an incidence of bacterial endocarditis of 24% and 50%, respectively, most of which were due to streptococcal species (two were caused by Staphylococcus [corrected] aureus). The difference, though not statistically significant (p = 0.10, chi 2 with Yates correction), shows a trend toward increased incidence of endocarditis with increasing severity of periodontal disease. This model demonstrates that one can reliably induce bacterial endocarditis after dental extractions in rats with periodontal disease.

In vitro effect of malachite green on Candida albicans involves multiple pathways and transcriptional regulators UPC2 and STP2.

In this study, we show that a chemical dye, malachite green (MG), which is commonly used in the fish industry as an antifungal, antiparasitic, and antibacterial agent, could effectively kill Candida albicans and non-C. albicans species. We have demonstrated that Candida cells are susceptible to MG at a very low concentration (MIC that reduces growth by 50% [MIC(50)], 100 ng ml(-1)) and that the effect of MG is independent of known antifungal targets, such as ergosterol metabolism and major drug efflux pump proteins. Transcriptional profiling in response to MG treatment of C. albicans cells revealed that of a total of 207 responsive genes, 167 genes involved in oxidative stress, virulence, carbohydrate metabolism, heat shock, amino acid metabolism, etc., were upregulated, while 37 genes involved in iron acquisition, filamentous growth, mitochondrial respiration, etc., were downregulated. We confirmed experimentally that Candida cells exposed to MG resort to a fermentative mode of metabolism, perhaps due to defective respiration. In addition, we showed that MG triggers depletion of intracellular iron pools and enhances reactive oxygen species (ROS) levels. These effects could be reversed by the addition of iron or antioxidants, respectively. We provided evidence that the antifungal effect of MG is exerted through the transcription regulators UPC2 (regulating ergosterol biosynthesis and azole resistance) and STP2 (regulating amino acid permease genes). Taken together, our transcriptome, genetic, and biochemical results allowed us to decipher the multiple mechanisms by which MG exerts its anti-Candida effects, leading to a metabolic shift toward fermentation, increased generation of ROS, labile iron deprivation, and cell necrosis.

Voluntary alcohol consumption is controlled via the neuropeptide Y Y1 receptor.

We have shown previously that voluntary ethanol consumption and resistance to ethanol-induced sedation are inversely related to neuropeptide Y (NPY) levels in NPY-knock-out (NPY(-/-)) and NPY-overexpressing mice. In the present report, we studied knock-out mice completely lacking the NPY Y1 receptor (Y1(-/-)) to further characterize the role of the NPY system in ethanol consumption and neurobiological responses to this drug. Here we report that male Y1(-/-) mice showed increased consumption of solutions containing 3, 6, and 10% (v/v) ethanol when compared with wild-type (Y1(+/+)) control mice. Female Y1(-/-) mice showed increased consumption of a 10% ethanol solution. In contrast, Y1(-/-) mice showed normal consumption of solutions containing either sucrose or quinine. Relative to Y1(+/+) mice, male Y1(-/-) mice were found to be less sensitive to the sedative effects of 3.5 and 4.0 gm/kg ethanol as measured by more rapid recovery from ethanol-induced sleep, although plasma ethanol levels did not differ significantly between the genotypes. Finally, male Y1(-/-) mice showed normal ethanol-induced ataxia on the rotarod test after administration of a 2.5 gm/kg dose. These data suggest that the NPY Y1 receptor regulates voluntary ethanol consumption and some of the intoxicating effects caused by administration of ethanol.

Effects of fructose-containing caloric sweeteners on resting energy expenditure and energy efficiency: a review of human trials.

Epidemiological studies indicate that the consumption of fructose-containing caloric sweeteners (FCCS: mainly sucrose and high-fructose corn syrup) is associated with obesity. The hypothesis that FCCS plays a causal role in the development of obesity however implies that they would impair energy balance to a larger extent than other nutrients, either by increasing food intake, or by decreasing energy expenditure. We therefore reviewed the literature comparing a) diet-induced thermogenesis (DIT) after ingestion of isocaloric FCCS vs glucose meals, and b) basal metabolic rate (BMR) or c) post-prandial energy expenditure after consuming a high FCCS diet for > 3 days vs basal,weight-maintenance low FCCS diet. Nine studies compared the effects of single isocaloric FCCS and glucose meals on DIT; of them, six studies reported that DIT was significantly higher with FCCS than with glucose, 2 reported a non-significant increase with FCCS, and one reported no difference. The higher DIT with fructose than glucose can be explained by the low energy efficiency associated with fructose metabolism. Five studies compared BMR after consumption of a high FCCS vs a low FCCS diet for > 3 days. Four studies reported no change after 4-7 day on a high FCCS diet, and only one study reported a 7% decrease after 12 week on a high FCCS diet. Three studies compared post-prandial EE after consumption of a high FCCS vs a low FCCS diet for > 3 days, and did not report any significant difference. One study compared 24-EE in subjects fed a weight-maintenance diet and hypercaloric diets with 50% excess energy as fructose, sucrose and glucose during 4 days: 24-EE was increased with all 3 hypercaloric diets, but there was no difference between fructose, sucrose and glucose. We conclude that fructose has lower energy efficiency than glucose. Based on available studies, there is presently no hint that dietary FCCS may decrease EE. Larger, well controlled studies are however needed to assess the longer term effects of FCCS on EE.

Metabolic effects of fructose and the worldwide increase in obesity.

While virtually absent in our diet a few hundred years ago, fructose has now become a major constituent of our modern diet. Our main sources of fructose are sucrose from beet or cane, high fructose corn syrup, fruits, and honey. Fructose has the same chemical formula as glucose (C(6)H(12)O(6)), but its metabolism differs markedly from that of glucose due to its almost complete hepatic extraction and rapid hepatic conversion into glucose, glycogen, lactate, and fat. Fructose was initially thought to be advisable for patients with diabetes due to its low glycemic index. However, chronically high consumption of fructose in rodents leads to hepatic and extrahepatic insulin resistance, obesity, type 2 diabetes mellitus, and high blood pressure. The evidence is less compelling in humans, but high fructose intake has indeed been shown to cause dyslipidemia and to impair hepatic insulin sensitivity. Hepatic de novo lipogenesis and lipotoxicity, oxidative stress, and hyperuricemia have all been proposed as mechanisms responsible for these adverse metabolic effects of fructose. Although there is compelling evidence that very high fructose intake can have deleterious metabolic effects in humans as in rodents, the role of fructose in the development of the current epidemic of metabolic disorders remains controversial. Epidemiological studies show growing evidence that consumption of sweetened beverages (containing either sucrose or a mixture of glucose and fructose) is associated with a high energy intake, increased body weight, and the occurrence of metabolic and cardiovascular disorders. There is, however, no unequivocal evidence that fructose intake at moderate doses is directly related with adverse metabolic effects. There has also been much concern that consumption of free fructose, as provided in high fructose corn syrup, may cause more adverse effects than consumption of fructose consumed with sucrose. There is, however, no direct evidence for more serious metabolic consequences of high fructose corn syrup versus sucrose consumption.

Fermentative 2-carbon metabolism produces carcinogenic levels of acetaldehyde in Candida albicans.

Acetaldehyde is a carcinogenic product of alcohol fermentation and metabolism in microbes associated with cancers of the upper digestive tract. In yeast acetaldehyde is a by-product of the pyruvate bypass that converts pyruvate into acetyl-Coenzyme A (CoA) during fermentation. The aims of our study were: (i) to determine the levels of acetaldehyde produced by Candida albicans in the presence of glucose in low oxygen tension in vitro; (ii) to analyse the expression levels of genes involved in the pyruvate-bypass and acetaldehyde production; and (iii) to analyse whether any correlations exist between acetaldehyde levels, alcohol dehydrogenase enzyme activity or expression of the genes involved in the pyruvate-bypass. Candida albicans strains were isolated from patients with oral squamous cell carcinoma (n = 5), autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) patients with chronic oral candidosis (n = 5), and control patients (n = 5). The acetaldehyde and ethanol production by these isolates grown under low oxygen tension in the presence of glucose was determined, and the expression of alcohol dehydrogenase (ADH1 and ADH2), pyruvate decarboxylase (PDC11), aldehyde dehydrogenase (ALD6) and acetyl-CoA synthetase (ACS1 and ACS2) and Adh enzyme activity were analysed. The C. albicans isolates produced high levels of acetaldehyde from glucose under low oxygen tension. The acetaldehyde levels did not correlate with the expression of ADH1, ADH2 or PDC11 but correlated with the expression of down-stream genes ALD6 and ACS1. Significant differences in the gene expressions were measured between strains isolated from different patient groups. Under low oxygen tension ALD6 and ACS1, instead of ADH1 or ADH2, appear the most reliable indicators of candidal acetaldehyde production from glucose.

Expression analyses of three members of the AtPHO1 family reveal differential interactions between signaling pathways involved in phosphate deficiency and the responses to auxin, cytokinin, and abscisic acid.

The PHO1 protein is involved in loading inorganic phosphate (Pi) to the root xylem. Ten genes homologous to AtPHO1 are present in the Arabidopsis thaliana (L.) Heyn genome. From this gene family, transcript levels of only AtPHO1, AtPHO1;H1 and AtPHO1;H10 were increased by Pi-deficiency. While the up-regulation of AtPHO1;H1 and AtPHO1;H10 by Pi deficiency followed the same rapid kinetics and was dependent on the PHR1 transcription factor, phosphite only strongly suppressed the expression of AtPHO1;H1 and had a minor effect on AtPHO1;H10. Addition of sucrose was found to increase transcript levels of both AtPHO1 and AtPHO1;H1 in Pi-sufficient or Pi-deficient plants, but to suppress AtPHO1:H10 under the same conditions. Treatments of plants with auxin or cytokinin had contrasting effect depending on the gene and on the Pi status of the plants. Thus, while both hormones down-regulated expression of AtPHO1 independently of the plant Pi status, auxin and cytokinin up-regulated AtPHO1;H1 and AtPHO1;H10 expression in Pi-sufficient plants and down-regulated expression in Pi-deficient plants. Treatments with abscisic acid inhibited AtPHO1 and AtPHO1;H1 expression in both Pi-sufficient and Pi-deficient plants, but increased AtPHO1;H10 expression under the same conditions. The inhibition of expression by abscisic acid of AtPHO1 and AtPHO1;H1, and of the Pi-starvation responsive genes AtPHT1;1 and AtIPS1, was dependant on the ABI1 type 2C protein phosphatase. These results reveal that various levels of cross talk between the signal transduction pathways to Pi, sucrose and phytohormones are involved in the regulation of expression of the three AtPHO1 homologues.

Regulation of inflammatory responses by the commensal microbiota.

It is well established that dysregulation of the interactions between the immune system and commensal bacteria is one factor that underpins the development and chronicity of a number of inflammatory diseases. Certain phyla of bacteria within the microbiota have been associated with 'health', but the mechanisms by which the presence of these bacteria supports a healthy environment are still being unravelled. Recent evidence indicates that one such mechanism involves the anti-inflammatory properties of fermentation products of fibre, short-chain fatty acids and their signalling through the G-protein coupled receptor GPR43. Recent findings also indicate that, even in health, bacterial communities harbour in the airways, indicating that direct exposure to bacterial products at this site may provide a further explanation for how commensal bacteria can regulate chronic airway inflammation.

Optimization of preservation conditions of As (III) bioreporter bacteria.

Long-term preservation of bioreporter bacteria is essential for the functioning of cell-based detection devices, particularly when field application, e.g., in developing countries, is intended. We varied the culture conditions (i.e., the NaCl content of the medium), storage protection media, and preservation methods (vacuum drying vs. encapsulation gels remaining hydrated) in order to achieve optimal preservation of the activity of As (III) bioreporter bacteria during up to 12 weeks of storage at 4 degrees C. The presence of 2% sodium chloride during the cultivation improved the response intensity of some bioreporters upon reconstitution, particularly of those that had been dried and stored in the presence of sucrose or trehalose and 10% gelatin. The most satisfying, stable response to arsenite after 12 weeks storage was obtained with cells that had been dried in the presence of 34% trehalose and 1.5% polyvinylpyrrolidone. Amendments of peptone, meat extract, sodium ascorbate, and sodium glutamate preserved the bioreporter activity only for the first 2 weeks, but not during long-term storage. Only short-term stability was also achieved when bioreporter bacteria were encapsulated in gels remaining hydrated during storage.

Simple-sugar meals target GLUT2 at enterocyte apical membranes to improve sugar absorption: a study in GLUT2-null mice.

The physiological significance of the presence of GLUT2 at the food-facing pole of intestinal cells is addressed by a study of fructose absorption in GLUT2-null and control mice submitted to different sugar diets. Confocal microscopy localization, protein and mRNA abundance, as well as tissue and membrane vesicle uptakes of fructose were assayed. GLUT2 was located in the basolateral membrane of mice fed a meal devoid of sugar or containing complex carbohydrates. In addition, the ingestion of a simple sugar meal promoted the massive recruitment of GLUT2 to the food-facing membrane. Fructose uptake in brush-border membrane vesicles from GLUT2-null mice was half that of wild-type mice and was similar to the cytochalasin B-insensitive component, i.e. GLUT5-mediated uptake. A 5 day consumption of sugar-rich diets increased fructose uptake fivefold in wild-type tissue rings when it only doubled in GLUT2-null tissue. GLUT5 was estimated to contribute to 100 % of total uptake in wild-type mice fed low-sugar diets, falling to 60 and 40 % with glucose and fructose diets respectively; the complement was ensured by GLUT2 activity. The results indicate that basal sugar uptake is mediated by the resident food-facing SGLT1 and GLUT5 transporters, whose mRNA abundances double in long-term dietary adaptation. We also observe that a large improvement of intestinal absorption is promoted by the transient recruitment of food-facing GLUT2, induced by the ingestion of a simple-sugar meal. Thus, GLUT2 and GLUT5 could exert complementary roles in adapting the absorption capacity of the intestine to occasional or repeated loads of dietary sugars.

Enhanced kangaroo mother care for heel lance in preterm neonates: a crossover trial.

OBJECTIVE: To test if enhancing maternal skin-to-skin contact, or kangaroo mother care (KMC) by adding rocking, singing and sucking is more efficacious than simple KMC for procedural pain in preterm neonates. STUDY DESIGN: Preterm neonates (n=90) between 32 0/7 and 36 0/7 weeks' gestational age participated in a single-blind randomized crossover design. The infant was held in KMC with the addition of rocking, singing and sucking or the infant was held in KMC without additional stimulation. The Premature Infant Pain Profile was the primary outcome with time to recover as the secondary outcome. A repeated-measures analysis of covariance was employed for analyses. RESULT: There were no significant differences in any of the 30 s time periods over the 2 min of blood sampling nor in time to return to baseline. Compared to historical controls of the same age in incubator, the pain scores were lower and comparable to other studies of KMC. There were site differences related to lower scores with the use of sucrose in one site and higher scores in younger, sicker infants in another site. CONCLUSION: The sensorial stimulations from skin-to-skin contact that include tactile, olfactory sensations from the mother are sufficient to decrease pain response in premature neonates. Other studies showing that rocking, sucking and music were efficacious were independent of skin-to-skin contact, which, when used alone has been shown to be effective as reported across studies.