Fructose improves the ability of hyperglycemia per se to regulate glucose production in type 2 diabetes

Fructose overconsumption accelerates renal dysfunction with aberrant glomerular endothelial-mesangial cell interactions in db/db mice

For the advancement of DKD treatment, identifying unrecognized residual risk factors is essential. We explored the impact of obesity diversity derived from different carbohydrate qualities, with an emphasis on the increasing trend of excessive fructose consumption and its effect on DKD progression. In this study, we utilized db/db mice to establish a novel diabetic model characterized by fructose overconsumption, aiming to uncover the underlying mechanisms of renal damage. Compared to the control diet group, the fructose-fed db/db mice exhibited more pronounced obesity yet demonstrated milder glucose intolerance. Plasma cystatin C levels were elevated in the fructose model compared to the control, and this elevation was accompanied by enhanced glomerular sclerosis, even though albuminuria levels and tubular lesions were comparable. Single-cell RNA sequencing of the whole kidney highlighted an increase in Lrg1 in glomerular endothelial cells (GECs) in the fructose model, which appeared to drive mesangial fibrosis through enhanced TGF-β1 signaling. Our findings suggest that excessive fructose intake exacerbates diabetic kidney disease progression, mediated by aberrant Lrg1-driven crosstalk between GECs and mesangial cells.

Glucokinase regulatory protein: a balancing act between glucose and lipid metabolism in NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a common liver disease worldwide, affected by both genetics and environment. Type 2 diabetes (T2D) stands as an independent environmental risk factor that precipitates the onset of hepatic steatosis and accelerates its progression to severe stages of liver damage. Furthermore, the coexistence of T2D and NAFLD magnifies the risk of cardiovascular disease synergistically. However, the association between genetic susceptibility and metabolic risk factors in NAFLD remains incompletely understood. The glucokinase regulator gene (GCKR), responsible for encoding the glucokinase regulatory protein (GKRP), acts as a regulator and protector of the glucose-metabolizing enzyme glucokinase (GK) in the liver. Two common variants (rs1260326 and rs780094) within the GCKR gene have been associated with a lower risk for T2D but a higher risk for NAFLD. Recent studies underscore that T2D presence significantly amplifies the effect of the GCKR gene, thereby increasing the risk of NASH and fibrosis in NAFLD patients. In this review, we focus on the critical roles of GKRP in T2D and NAFLD, drawing upon insights from genetic and biological studies. Notably, prior attempts at drug development targeting GK with glucokinase activators (GKAs) have shown potential risks of augmented plasma triglycerides or NAFLD. Conversely, overexpression of GKRP in diabetic rats improved glucose tolerance without causing NAFLD, suggesting the crucial regulatory role of GKRP in maintaining hepatic glucose and lipid metabolism balance. Collectively, this review sheds new light on the complex interaction between genes and environment in NAFLD, focusing on the GCKR gene. By integrating evidence from genetics, biology, and drug development, we reassess the therapeutic potential of targeting GK or GKRP for metabolic disease treatment. Emerging evidence suggests that selectively activating GK or enhancing GK-GKRP binding may represent a holistic strategy for restoring glucose and lipid metabolic balance.

Maternal Fructose Intake, Programmed Mitochondrial Function and Predisposition to Adult Disease

Fructose consumption is now recognised as a major risk factor in the development of metabolic diseases, such as hyperlipidaemia, diabetes, non-alcoholic fatty liver disease and obesity. In addition to environmental, social, and genetic factors, an unfavourable intrauterine environment is now also recognised as an important factor in the progression of, or susceptibility to, metabolic disease during adulthood. Developmental trajectory in the short term, in response to nutrient restriction or excessive nutrient availability, may promote adaptation that serves to maintain organ functionality necessary for immediate survival and foetal development. Consequently, this may lead to decreased function of organ systems when presented with an unfavourable neonatal, adolescent and/or adult nutritional environment. These early events may exacerbate susceptibility to later-life disease since sub-optimal maternal nutrition increases the risk of non-communicable diseases (NCDs) in future generations. Earlier dietary interventions, implemented in pregnant mothers or those considering pregnancy, may have added benefit. Although, the mechanisms by which maternal diets high in fructose and the vertical transmission of maternal metabolic phenotype may lead to the predisposition to adult disease are poorly understood. In this review, we will discuss the potential contribution of excessive fructose intake during pregnancy and how this may lead to developmental reprogramming of mitochondrial function and predisposition to metabolic disease in offspring.

Glycerate from intestinal fructose metabolism induces islet cell damage and glucose intolerance

Dietary fructose, especially in the context of a high-fat western diet, has been linked to type 2 diabetes. Although the effect of fructose on liver metabolism has been extensively studied, a significant portion of the fructose is first metabolized in the small intestine. Here, we report that dietary fat enhances intestinal fructose metabolism, which releases glycerate into the blood. Chronic high systemic glycerate levels induce glucose intolerance by slowly damaging pancreatic islet cells and reducing islet sizes. Our findings provide a link between dietary fructose and diabetes that is modulated by dietary fat.

Hypoglycemic effect of low-sugar juice derived from Hovenia dulcis on type 1 diabetes mellitus rats

BACKGROUND

Fruit juice is usually rich in monosaccharides and disaccharides. A reverse osmosis separation machine was used to remove monosaccharides and disaccharides from Hovenia dulcis fruit juice, leaving behind most of the bioactive substances in a low-sugar fruit juice (LSFJ), so as to provide a more effective treatment for diabetic patients.

METHOD

This study was carried out with type 1 diabetes mellitus model induced with high dose of streptozotocin (60 mg kg^-1 ), and oral administration of LSFJ for 4 weeks.

RESULTS

LSFJ treatment led to significant gain in body weight and increased serum insulin level, insulin-like growth factor-1 level, blood urea nitrogen level, creatinine level, and hepatic glycogen level. Meanwhile, fasting blood glucose, fructosamine level, and glucose tolerance were also observably enhanced. Additional, LSFJ treatment significantly improved lipid metabolism, islet quality, and islet oxidative stress. The messenger RNA levels of glucose metabolism genes in the pancreas of diabetic rats decreased in the diabetes model group, whereas messenger RNA expression of these genes was significantly increased with LSFJ treatment.

CONCLUSION

These findings indicate that LSFJ can improve symptoms associated with type 1 diabetes mellitus. The research also suggests new strategies for diabetes prevention and treatment. © 2021 Society of Chemical Industry.

Metabolic and Appetite Effects of Fructose and Glucose in Subjects with Type 1 Diabetes: A Randomized Crossover Clinical Trial

BACKGROUND

Fructose has been widely used for producing lower post-infusion glucose increase than other carbohydrates, but it seems that it promotes an increase in post-infusion triglycerides.

OBJECTIVE

The present study investigated the effects of fructose and glucose in metabolic variables and appetite sensations in patients with type 1 diabetes mellitus (T1DM).

METHODS

This is a single-blind, randomized, and crossover study (washout of 1-5 weeks), which evaluated 16 adult T1DM patients, accompanied at University Hospital. After eight hours of overnight fasting, there was an assessment of capillary blood glucose, anthropometric variables, appetite sensations, and laboratory tests (glycemia, lipemia, leptin and glucagon) were conducted. Subsequently, they received 200mL of solutions with water and 75g of crystal fructose or glucose. Appetite sensations and capillary blood glucose were evaluated in different post-infusion times. Blood was drawn after 180 minutes for the laboratory tests.

RESULTS

Blood glucose increased after the intake of both solutions, but glucose induced a higher elevation. None of them increased triglycerides or glucagon. Glucagon maintenance was similar among the solutions. Furthermore, both solutions reduced leptin and increased fullness, but only fructose increased the lack of interest in eating sweets.

CONCLUSION

Fructose induced a smaller increase in postprandial blood glucose than glucose, without changes in triglycerides and glucagon. In addition, leptin levels and appetite sensations were similar to glucose. Other studies are needed in order to confirm these findings, especially in the long term, so that their use becomes really reliable.

Fatty Acid Synthase Inhibitor TVB-2640 Reduces Hepatic de Novo Lipogenesis in Males With Metabolic Abnormalities

BACKGROUND AND AIMS

Elevated hepatic de novo lipogenesis (DNL) is a key distinguishing characteristic of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis. In rodent models of NAFLD, treatment with a surrogate of TVB-2640, a pharmacological fatty acid synthase inhibitor, has been shown to reduce hepatic fat and other biomarkers of DNL. The purpose of this phase I clinical study was to test the effect of the TVB-2640 in obese men with certain metabolic abnormalities that put them at risk for NAFLD.

APPROACH AND RESULTS

Twelve subjects (mean ± SEM, 42 ± 2 years, body mass index 37.4 ± 1.2 kg/m² , glucose 103 ± 2 mg/dL, triacylglycerols 196 ± 27 mg/dL, and elevated liver enzymes) underwent 10 days of treatment with TVB-2640 at doses ranging from 50-150 mg/day. Food intake was controlled throughout the study. Hepatic DNL was measured before and after an oral fructose/glucose bolus using isotopic labeling with 1-¹³ C₁ -acetate intravenous infusion, followed by measurement of labeled very low-density lipoprotein palmitate via gas chromatography mass spectometry. Substrate oxidation was measured by indirect calorimetry. Across the range of doses, fasting DNL was reduced by up to 90% (P = 0.003). Increasing plasma concentrations of TVB-2640 were associated with progressive reductions in the percent of fructose-stimulated peak fractional DNL (R²  = -0.749, P = 0.0003) and absolute DNL area under the curve 6 hours following fructose/glucose bolus (R²  = -0.554, P = 0.005). For all subjects combined, alanine aminotransferase was reduced by 15.8 ± 8.4% (P = 0.05). Substrate oxidation was unchanged, and safety monitoring revealed that the drug was well tolerated, without an increase in plasma triglycerides. Alopecia occurred in 2 subjects (reversed after stopping the drug), but otherwise no changes were observed in fasting glucose, insulin, ketones, and renal function.

CONCLUSION

These data support the therapeutic potential of a fatty acid synthase inhibitor, TVB-2640 in particular, in patients with NAFLD and nonalcoholic steatohepatitis.

A Sweet Connection? Fructose's Role in Hepatocellular Carcinoma

Hepatocellular carcinoma is one of few cancer types that continues to grow in incidence and mortality worldwide. With the alarming increase in diabetes and obesity rates, the higher rates of hepatocellular carcinoma are a result of underlying non-alcoholic fatty liver disease. Many have attributed disease progression to an excess consumption of fructose sugar. Fructose has known toxic effects on the liver, including increased fatty acid production, increased oxidative stress, and insulin resistance. These effects have been linked to non-alcoholic fatty liver (NAFLD) disease and a progression to non-alcoholic steatohepatitis (NASH). While the literature suggests fructose may enhance liver cancer progression, the precise mechanisms in which fructose induces tumor formation remains largely unclear. In this review, we summarize the current understanding of fructose metabolism in liver disease and liver tumor development. Furthermore, we consider the latest knowledge of cancer cell metabolism and speculate on additional mechanisms of fructose metabolism in hepatocellular carcinoma.

Aerobic exercise training improves hepatic and muscle insulin sensitivity, but reduces splanchnic glucose uptake in obese humans with type 2 diabetes

BACKGROUND

Aerobic exercise training is known to have beneficial effects on whole-body glucose metabolism in people with type 2 diabetes (T2D). The responses of the liver to such training are less well understood. The purpose of this study was to determine the effect of aerobic exercise training on splanchnic glucose uptake (SGU) and insulin-mediated suppression of endogenous glucose production (EGP) in obese subjects with T2D.

METHODS

Participants included 11 obese humans with T2D, who underwent 15 ± 2 weeks of aerobic exercise training (AEX; n = 6) or remained sedentary for 15 ± 1 weeks (SED; n = 5). After an initial screening visit, each subject underwent an oral glucose load clamp and an isoglycemic/two-step (20 and 40 mU/m²/min) hyperinsulinemic clamp (ISO-clamp) to assess SGU and insulin-mediated suppression of EGP, respectively. After the intervention period, both tests were repeated.

RESULTS

In AEX, the ability of insulin to suppress EGP was improved during both the low (69 ± 9 and 80 ± 6% suppression; pre-post, respectively; p < 0.05) and high (67 ± 6 and 82 ± 4% suppression, respectively; p < 0.05) insulin infusion periods. Despite markedly improved muscle insulin sensitivity, SGU was reduced in AEX after training (22.9 ± 3.3 and 9.1 ± 6.0 g pre-post in AEX, respectively; p < 0.05).

CONCLUSIONS

In obese T2D subjects, exercise training improves whole-body glucose metabolism, in part, by improving insulin-mediated suppression of EGP and enhancing muscle glucose uptake, which occur despite reduced SGU during an oral glucose challenge.

Effect of dried fruit on postprandial glycemia: a randomized acute-feeding trial

Background/Objectives

To investigate the effect of dried fruit in modifying postprandial glycemia, we assessed the ability of 4 dried fruits (dates, apricots, raisins, sultanas) to decrease postprandial glycemia through three mechanisms: a glycemic index (GI) effect, displacement effect, or ‘catalytic’ fructose effect.

Subjects/Methods

We conducted an acute randomized, multiple-crossover trial in an outpatient setting in 10 healthy adults. Participants received 3 white bread control meals and 12 dried fruit test meals in random order. The test meals included each of 4 dried fruits (dates, apricots, raisins, sultanas) alone (GI effect), 4 of the dried fruits displacing half the available carbohydrate in white bread (displacement effect), or 4 of the dried fruits providing a small ‘catalytic’ dose (7.5 g) of fructose added to white bread (‘catalytic’ fructose effect). The protocol followed the ISO method for the determination of GI (ISO 26642:2010). The primary outcome was mean ± SEM GI (glucose scale) for ease of comparison across the three mechanisms.

Results

Ten healthy participants (7 men, 3 women; mean ± SD age and BMI: 39 ± 12 years and 25 ± 2 kg/m²) were recruited and completed the trial. All dried fruit had a GI below that of white bread (GI = 71); however, only dried apricots (GI = 42 ± 5), raisins (GI = 55 ± 5), and sultanas (51 ± 4) showed a significant GI effect (P < 0.05). When displacing half the available carbohydrate in white bread, all dried fruit lowered the GI; however, only dried apricots (GI = 57 ± 5) showed a significant displacement effect (P = 0.025). None of the dried fruits showed a beneficial ‘catalytic’ fructose effect.

Conclusions

In conclusion, dried fruits have a lower GI and reduce the glycemic response of white bread through displacement of half of the available carbohydrate. Longer-term randomized trials are needed to confirm whether dried fruit can contribute to sustainable improvements in glycemic control.

Trial registration

ClinicalTrials.gov identifier, NCT02960373

Food sources of fructose-containing sugars and glycaemic control: systematic review and meta-analysis of controlled intervention studies

OBJECTIVE

To assess the effect of different food sources of fructose-containing sugars on glycaemic control at different levels of energy control.

DESIGN

Systematic review and meta-analysis of controlled intervention studies.

DATA SOURCES

Medine, Embase, and the Cochrane Library up to 25 April 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Controlled intervention studies of at least seven days' duration and assessing the effect of different food sources of fructose-containing sugars on glycaemic control in people with and without diabetes were included. Four study designs were prespecified on the basis of energy control: substitution studies (sugars in energy matched comparisons with other macronutrients), addition studies (excess energy from sugars added to diets), subtraction studies (energy from sugars subtracted from diets), and ad libitum studies (sugars freely replaced by other macronutrients without control for energy). Outcomes were glycated haemoglobin (HbA1c), fasting blood glucose, and fasting blood glucose insulin.

DATA EXTRACTION AND SYNTHESIS

Four independent reviewers extracted relevant data and assessed risk of bias. Data were pooled by random effects models and overall certainty of the evidence assessed by the GRADE approach (grading of recommendations assessment, development, and evaluation).

RESULTS

155 study comparisons (n=5086) were included. Total fructose-containing sugars had no harmful effect on any outcome in substitution or subtraction studies, with a decrease seen in HbA1c in substitution studies (mean difference -0.22% (95% confidence interval to -0.35% to -0.08%), -25.9 mmol/mol (-27.3 to -24.4)), but a harmful effect was seen on fasting insulin in addition studies (4.68 pmol/L (1.40 to 7.96)) and ad libitum studies (7.24 pmol/L (0.47 to 14.00)). There was interaction by food source, with specific food sources showing beneficial effects (fruit and fruit juice) or harmful effects (sweetened milk and mixed sources) in substitution studies and harmful effects (sugars-sweetened beverages and fruit juice) in addition studies on at least one outcome. Most of the evidence was low quality.

CONCLUSIONS

Energy control and food source appear to mediate the effect of fructose-containing sugars on glycaemic control. Although most food sources of these sugars (especially fruit) do not have a harmful effect in energy matched substitutions with other macronutrients, several food sources of fructose-containing sugars (especially sugars-sweetened beverages) adding excess energy to diets have harmful effects. However, certainty in these estimates is low, and more high quality randomised controlled trials are needed.

STUDY REGISTRATION

Clinicaltrials.gov (NCT02716870).

The Effect of Small Doses of Fructose and Its Epimers on Glycemic Control: A Systematic Review and Meta-Analysis of Controlled Feeding Trials

Objective: Contrary to the concerns that fructose may have adverse metabolic effects, an emerging literature has shown that small doses (≤10 g/meal) of fructose and its low-caloric epimers (allulose, tagatose, and sorbose) decrease the glycemic response to high glycemic index meals. Whether these acute reductions manifest as sustainable improvements in glycemic control is unclear. Our objective was to synthesize the evidence from controlled feeding trials that assessed the effect of small doses of fructose and its low-caloric epimers on glycemic control. Methods: We searched MEDLINE, EMBASE, and the Cochrane Library through April 18, 2018. We included controlled feeding trials of ≥1 week that investigated the effect of small doses (≤50 g/day or ≤10% of total energy intake/day) of fructose and its low-caloric epimers on HbA_1c, fasting glucose, and fasting insulin. Two independent reviewers extracted data and assessed risk of bias. Data were pooled using the generic inverse variance method and expressed as mean differences (MDs) with 95% confidence intervals (CIs). Heterogeneity was assessed using the Cochran Q statistic and quantified using the I² statistic. Grading of Recommendations Assessment, Development and Evaluation (GRADE) assessed the certainty of the evidence. Results: We identified 14 trial comparisons (N = 337) of the effect of fructose in individuals with and without diabetes, 3 trial comparisons (N = 138) of the effect of allulose in individuals without diabetes, 3 trial comparisons (N = 376) of the effect of tagatose mainly in individuals with type 2 diabetes, and 0 trial comparisons of the effect of sorbose. Small doses of fructose and tagatose significantly reduced HbA_1c (MD = -0.38% (95% CI: -0.64%, -0.13%); MD = -0.20% (95% CI: -0.34%, -0.06%)) and fasting glucose (MD = -0.13 mmol/L (95% CI: -0.24 mmol/L, -0.03 mmol/L)); MD = -0.30 mmol/L (95% CI: -0.57 mmol/L, -0.04 mmol/L)) without affecting fasting insulin (p > 0.05). Small doses of allulose did not have a significant effect on HbA_1c and fasting insulin (p > 0.05), while the reduction in fasting glucose was of borderline significance (p = 0.05). The certainty of the evidence of the effect of small doses of fructose and allulose on HbA_1c, fasting glucose, and fasting insulin was graded as low. The certainty of the evidence of the effect of tagatose on HbA_1c, fasting glucose, and fasting insulin was graded as moderate. Conclusions: Our results indicate that small doses of fructose and tagatose may improve glycemic control over the long term. There is a need for long-term randomized controlled trials for all four sugars to improve our certainty in the estimates.

The effect of small doses of fructose and allulose on postprandial glucose metabolism in type 2 diabetes: A double-blind, randomized, controlled, acute feeding, equivalence trial

AIM

To assess and compare the effect of small doses of fructose and allulose on postprandial blood glucose regulation in type 2 diabetes.

METHODS

A double-blind, multiple-crossover, randomized, controlled, acute feeding, equivalence trial in 24 participants with type 2 diabetes was conducted. Each participant was randomly assigned six treatments separated by >1-week washouts. Treatments consisted of fructose or allulose at 0 g (control), 5 g or 10 g added to a 75-g glucose solution. A standard 75-g oral glucose tolerance test protocol was followed with blood samples at -30, 0, 30, 60, 90 and 120 minutes. The primary outcome measure was plasma glucose incremental area under the curve (iAUC).

RESULTS

Allulose significantly reduced plasma glucose iAUC by 8% at 10 g compared with 0 g (717.4 ± 38.3 vs. 777.5 ± 39.9 mmol × min/L, P = 0.015) with a linear dose response gradient between the reduction in plasma glucose iAUC and dose (P = 0.016). Allulose also significantly reduced several related secondary and exploratory outcome measures at 5 g (plasma glucose absolute mean and total AUC) and 10 g (plasma glucose absolute mean, absolute and incremental maximum concentration [Cmax ], and total AUC) (P < .0125). There was no effect of fructose at any dose. Although allulose showed statistically significant reductions in plasma glucose iAUC compared with fructose at 5 g, 10 g and pooled doses, these reductions were within the pre-specified equivalence margins of ±20%.

CONCLUSION

Allulose, but not fructose, led to modest reductions in the postprandial blood glucose response to oral glucose in individuals with type 2 diabetes. There is a need for long-term randomized trials to confirm the sustainability of these improvements.

Postprandial Glycaemic Responses of Dried Fruit-Containing Meals in Healthy Adults: Results from a Randomised Trial

The aim of this study was to explore the glycaemic response (GR) patterns of four dried fruits (DF) and the mixed meals containing dried fruits, rice and almonds. Dried apples (DApp), dried jujubes (DJ), raisins (Ra) and dried apricots (DApr) were tested in eleven healthy subjects in random order. Test meals included the following 3 groups: (1) dried fruits containing 50 g available carbohydrates; (2) mixed meals consisting of DF and rice (DF + R), each contributing 25 g available carbohydrates; (3) Group (2) supplemented with 30 g almonds (DF + R + A). The postprandial GR and other characteristics in 240 min were investigated. The GI values of 4 DFs were 43 for DApp, 55 for DJ, 56 for both Ra and DApr. The DApp displayed the smallest amplitude of glycaemic excursion within 240 min (MAGE0⁻240). Compared with rice, the DApp + R meal elicited a significantly reduced GR and a smaller MAGE0⁻240 (GI 81 vs. 65). With the addition of almonds, the GIs and MAGE0⁻240 decreased significantly in all DF + A + R combinations except DApp + R + A. The ratio of total fructose/glucose contents of test meals were negatively correlated to GIs. Dried fruits and nuts may have the potential to mitigate the postprandial GR when jointly introduced into glycaemic management diets.

Insights into the Hexose Liver Metabolism-Glucose versus Fructose

High-fructose intake in healthy men is associated with characteristics of metabolic syndrome. Extensive knowledge exists about the differences between hepatic fructose and glucose metabolism and fructose-specific mechanisms favoring the development of metabolic disturbances. Nevertheless, the causal relationship between fructose consumption and metabolic alterations is still debated. Multiple effects of fructose on hepatic metabolism are attributed to the fact that the liver represents the major sink of fructose. Fructose, as a lipogenic substrate and potent inducer of lipogenic enzyme expression, enhances fatty acid synthesis. Consequently, increased hepatic diacylglycerols (DAG) are thought to directly interfere with insulin signaling. However, independently of this effect, fructose may also counteract insulin-mediated effects on liver metabolism by a range of mechanisms. It may drive gluconeogenesis not only as a gluconeogenic substrate, but also as a potent inducer of carbohydrate responsive element binding protein (ChREBP), which induces the expression of lipogenic enzymes as well as gluconeogenic enzymes. It remains a challenge to determine the relative contributions of the impact of fructose on hepatic transcriptome, proteome and allosterome changes and consequently on the regulation of plasma glucose metabolism/homeostasis. Mathematical models exist modeling hepatic glucose metabolism. Future models should not only consider the hepatic adjustments of enzyme abundances and activities in response to changing plasma glucose and insulin/glucagon concentrations, but also to varying fructose concentrations for defining the role of fructose in the hepatic control of plasma glucose homeostasis.

Rare Sugar Syrup Containing d-Allulose but Not High-Fructose Corn Syrup Maintains Glucose Tolerance and Insulin Sensitivity Partly via Hepatic Glucokinase Translocation in Wistar Rats

Ingestion of high-fructose corn syrup (HFCS) is associated with the risk of both diabetes and obesity. Rare sugar syrup (RSS) has been developed by alkaline isomerization of HFCS and has anti-obesity and anti-diabetic effects. However, the influence of RSS on glucose metabolism has not been explored. We investigated whether long-term administration of RSS maintains glucose tolerance and whether the underlying mechanism involves hepatic glucokinase translocation. Wistar rats were administered water, RSS, or HFCS in drinking water for 10 weeks and then evaluated for glucose tolerance, insulin tolerance, liver glycogen content, and subcellular distribution of liver glucokinase. RSS significantly suppressed body weight gain and abdominal fat mass (p < 0.05). The glucose tolerance test revealed significantly higher blood glucose levels in the HFCS group compared to the water group, whereas the RSS group had significantly lower blood glucose levels from 90 to 180 min (p < 0.05). At 30, 60, and 90 min, the levels of insulin in the RSS group were significantly lower than those in the water group (p < 0.05). The amount of hepatic glycogen was more than 3 times higher in the RSS group than that in the other groups. After glucose loading, the nuclear export of glucokinase was significantly increased in the RSS group compared to the water group. These results imply that RSS maintains glucose tolerance and insulin sensitivity, at least partly, by enhancing nuclear export of hepatic glucokinase.

Controversies about sugars: results from systematic reviews and meta-analyses on obesity, cardiometabolic disease and diabetes

Fructose-containing sugars are a focus of attention as a public health target for their putative role in obesity and cardiometabolic disease including diabetes. The fructose moiety is singled out to be the primary driver for the harms of sugars due to its unique endocrine signal and pathophysiological role. However, this is only supported by ecological studies, animal models of overfeeding and select human intervention studies with supraphysiological doses or lack of control for energy. The highest level of evidence from systematic reviews and meta-analyses of controlled trials has not shown that fructose-containing sugars behave any differently from other forms of digestible carbohydrates. Fructose-containing sugars can only lead to weight gain and other unintended harms on cardiometabolic risk factors insofar as the excess calories they provide. Prospective cohort studies, which provide the strongest observational evidence, have shown an association between fructose-containing sugars and cardiometabolic risk including weight gain, cardiovascular disease outcomes and diabetes only when restricted to sugar-sweetened beverages and not for sugars from other sources. In fact, sugar-sweetened beverages are a marker of an unhealthy lifestyle and their drinkers consume more calories, exercise less, smoke more and have a poor dietary pattern. The potential for overconsumption of sugars in the form of sugary foods and drinks makes targeting sugars, as a source of excess calories, a prudent strategy. However, sugar content should not be the sole determinant of a healthy diet. There are many other factors in the diet-some providing excess calories while others provide beneficial nutrients. Rather than just focusing on one energy source, we should consider the whole diet for health benefits.

Glycemic index, glycemic load and glycemic response: An International Scientific Consensus Summit from the International Carbohydrate Quality Consortium (ICQC)

BACKGROUND AND AIMS

The positive and negative health effects of dietary carbohydrates are of interest to both researchers and consumers.

METHODS

International experts on carbohydrate research held a scientific summit in Stresa, Italy, in June 2013 to discuss controversies surrounding the utility of the glycemic index (GI), glycemic load (GL) and glycemic response (GR).

RESULTS

The outcome was a scientific consensus statement which recognized the importance of postprandial glycemia in overall health, and the GI as a valid and reproducible method of classifying carbohydrate foods for this purpose. There was consensus that diets low in GI and GL were relevant to the prevention and management of diabetes and coronary heart disease, and probably obesity. Moderate to weak associations were observed for selected cancers. The group affirmed that diets low in GI and GL should always be considered in the context of diets otherwise understood as healthy, complementing additional ways of characterizing carbohydrate foods, such as fiber and whole grain content. Diets of low GI and GL were considered particularly important in individuals with insulin resistance.

CONCLUSIONS

Given the high prevalence of diabetes and pre-diabetes worldwide and the consistency of the scientific evidence reviewed, the expert panel confirmed an urgent need to communicate information on GI and GL to the general public and health professionals, through channels such as national dietary guidelines, food composition tables and food labels.

High hydrostatic pressure processing reduces the glycemic index of fresh mango puree in healthy subjects

HHP-MP showed a significantly lower GI than the unprocessed-MP. HHP changes in viscosity and solubility could induce lower AUC values and greater glucose retardation indexes.

Normal roles for dietary fructose in carbohydrate metabolism

Although there are many well-documented metabolic effects linked to the fructose component of a very high sugar diet, a healthy diet is also likely to contain appreciable fructose, even if confined to that found in fruits and vegetables. These normal levels of fructose are metabolized in specialized pathways that synergize with glucose at several metabolic steps. Glucose potentiates fructose absorption from the gut, while fructose catalyzes glucose uptake and storage in the liver. Fructose accelerates carbohydrate oxidation after a meal. In addition, emerging evidence suggests that fructose may also play a role in the secretion of insulin and GLP-1, and in the maturation of preadipocytes to increase fat storage capacity. Therefore, fructose undergoing its normal metabolism has the interesting property of potentiating the disposal of a dietary carbohydrate load through several routes.

Hepatic glucose sensing is impaired, but can be normalized, in people with impaired fasting glucose

OBJECTIVE

Abnormal endogenous glucose production (EGP) is a characteristic feature in people with impaired fasting glucose (IFG). We sought to determine whether impaired hepatic glucose sensing contributes to abnormal EGP in IFG and whether it could be experimentally restored.

METHODS

Glucose production (rate of appearance; Ra) and flux (glucose cycling) were assessed during a hyperglycemic-euinsulinemic somatostatin clamp with an infusion of [6,6-(2)H2-]glucose and [2-(2)H]glucose before and after enhanced hepatic glucokinase activity via an infusion of low-dose fructose in people with IFG and normal glucose tolerance (NGT).

RESULTS

During euglycemia, neither endogenous glucose production [(6,6-(2)H2)-glucose Ra; P = 0.53] or total glucose output (TGO; [2-(2)H]-glucose Ra; P = .12) was different between groups, but glucose cycling ([2-(2)H]glucose Ra to [6,6-(2)H2-]glucose Ra; a surrogate measure of hepatic glucokinase activity in the postabsorptive state) was lower in IFG than NGT (P = .04). Hyperglycemia suppressed EGP more in NGT than IFG (P < .01 for absolute or relative suppression, NGT vs IFG), whereas TGO decreased similarly in both groups (P = .77). The addition of fructose completely suppressed EGP in IFG (P < .01) and tended to do the same to TGO (P = .01; no such changes in NGT, P = .39-.55). Glucose cycling (which reflects glucose-6-phosphatase activity during glucose infusion) was similar in IFG and NGT (P = .51) during hyperglycemia and was unchanged and comparable between groups with the addition of fructose (P = .24).

CONCLUSIONS

In summary, glucose sensing is impaired in IFG but can be experimentally restored with low-dose fructose. Glucokinase activation may prove to be a novel strategy for the prevention of diabetes in this high-risk group.

Sex differences in glucose and insulin trajectories prior to diabetes diagnosis: the Whitehall II study

To examine sex differences in trajectories of glucose and insulin prior to the development of type 2 diabetes. Glucose and insulin levels from oral glucose tolerance tests performed every 5 years in the prospective Whitehall II cohort were analysed using mixed-effects models. Out of 6,712 White participants, 475 men and 177 women developed diabetes during a median follow-up time of 14 years. Men who developed diabetes had higher fasting glucose levels than women over the entire follow-up period (P < 0.001), whereas trajectories of 2-h glucose did not differ between sexes (P = 0.34). Two-hour insulin levels tended to be higher among women than men developing diabetes (P = 0.05), but not after adjustment for height (P = 0.45). Men have higher fasting glucose levels than women many years before the diagnosis of diabetes and at time of diagnosis, indicating that the pathogenesis of diabetes may be different between sexes.

Fructose-containing sugars, blood pressure, and cardiometabolic risk: a critical review

Excessive fructose intake from high-fructose corn syrup (HFCS) and sucrose has been implicated as a driving force behind the increasing prevalence of obesity and its downstream cardiometabolic complications including hypertension, gout, dyslidpidemia, metabolic syndrome, diabetes, and non-alcoholic fatty liver disease (NAFLD). Most of the evidence to support these relationships draws heavily on ecological studies, animal models, and select human trials of fructose overfeeding. There are a number of biological mechanisms derived from animal models to explain these relationships, including increases in de novo lipogenesis and uric acid-mediated hypertension. Differences between animal and human physiology, along with the supraphysiologic level at which fructose is fed in these models, limit their translation to humans. Although higher level evidence from large prospective cohorts studies has shown significant positive associations comparing the highest with the lowest levels of intake of sugar-sweetened beverages (SSBs), these associations do not hold true at moderate levels of intake or when modeling total sugars and are subject to collinearity effects from related dietary and lifestyle factors. The highest level of evidence from controlled feeding trials has shown a lack of cardiometabolic harm of fructose and SSBs under energy-matched conditions at moderate levels of intake. It is only when fructose-containing sugars or SSBs are consumed at high doses or supplement diets with excess energy that a consistent signal for harm is seen. The available evidence suggests that confounding by excess energy is an important consideration in assessing the role of fructose-containing sugars and SSBs in the epidemics of hypertension and other cardiometabolic diseases.

The Role of Fructose, Sucrose and High-fructose Corn Syrup in Diabetes

Concerns are growing regarding the role of dietary sugars in the development of obesity and cardiometabolic diseases, including diabetes. High-fructose corn syrup (HFCS) and sucrose are the most important dietary sweeteners. Both HFCS and sucrose have overlapping metabolic actions with adverse effects attributed to their fructose moiety. Ecological studies have linked the rise in fructose availability with the increases in obesity and diabetes worldwide. This link has been largely underpinned by animal models and select human trials of fructose overfeeding at high levels of exposure. Although prospective cohort studies have shown significant associations comparing the highest with the lowest levels of intake sugar-sweetened beverages, these associations are small, do not hold at moderate levels of intake and are subject to collinearity effects from related dietary and lifestyle factors. Most systematic reviews and meta-analyses from controlled feeding trials have shown that fructose-containing sugars in isocaloric exchange for other carbohydrates do not show evidence of harm and, in the case of fructose, may even have advantages for glycaemic control, especially at small doses. Nevertheless, trials in which fructose-containing sugars supplement diets with excess energy have shown adverse effects, effects that appear more attributable to the excess energy than the sugar. There is no unequivocal evidence that fructose intake at moderate doses is directly related with adverse metabolic effects, although there is potentially cause for concern where fructose is provided at high doses or contributes excess energy to diets. Further investigation is warranted due to the significant knowledge gaps and weaknesses in existing research.

Acute effects of raisin consumption on glucose and insulin reponses in healthy individuals

Raisins are popular snacks with a favourable nutrient profile, being high in dietary fibre, polyphenols and a number of vitamins and minerals, in addition to being rich in fructose. In light of evidence demonstrating improvements in glycaemic control with moderate fructose intake and low-glycaemic index (GI) fruits, our aim was to determine the GI, insulin index (II) and postprandial responses to raisins in an acute feeding setting. A total of ten healthy participants (four male and six female) consumed breakfast study meals on four occasions over a 2- to 8-week period: meal 1: white bread (WB) (108 g WB; 50 g available carbohydrate) served as the control and was consumed on two separate occasions; meal 2: raisins (R50) (69 g raisins; 50 g available carbohydrate); and meal 3: raisins (R20) (one serving, 28 g raisins; 20 g available carbohydrate). Postprandial glucose and insulin were measured over a 2 h period for the determination of GI, glycaemic load (GL) and II. The raisin meals, R50 and R20, resulted in significantly reduced postprandial glucose and insulin responses when compared with WB (P < 0·05). Furthermore, raisins were determined to be low-GI, -GL and -II foods. The favourable effect of raisins on postprandial glycaemic response, their insulin-sparing effect and low GI combined with their other metabolic benefits may indicate that raisins are a healthy choice not only for the general population but also for individuals with diabetes or insulin resistance.

Molecular basis for the role of glucokinase regulatory protein as the allosteric switch for glucokinase

Glucokinase (GK) is a monomeric allosteric enzyme and plays a pivotal role in blood glucose homeostasis. GK is regulated by GK regulatory protein (GKRP), and indirectly by allosteric effectors of GKRP. Despite the critical roles of GK and GKRP, the molecular basis for the allosteric regulation mechanism of GK by GKRP remains unclear. We determined the crystal structure of Xenopus GK and GKRP complex in the presence of fructose-6-phosphate at 2.9 Å. GKRP binds to a super-open conformation of GK mainly through hydrophobic interaction, inhibiting the GK activity by locking a small domain of GK. We demonstrate the molecular mechanism for the modulation of GK activity by allosteric effectors of GKRP. Importantly, GKRP releases GK in a sigmoidal manner in response to glucose concentration by restricting a structural rearrangement of the GK small domain via a single ion pair. We find that GKRP acts as an allosteric switch for GK in blood glucose control by the liver.

ILSI Brazil International Workshop on Functional Foods: a narrative review of the scientific evidence in the area of carbohydrates, microbiome, and health

To stimulate discussion around the topic of ‘carbohydrates’ and health, the Brazilian branch of the International Life Sciences Institute held the 11th International Functional Foods Workshop (1–2 December 2011) in which consolidated knowledge and recent scientific advances specific to the relationship between carbohydrates and health were presented. As part of this meeting, several key points related to dietary fiber, glycemic response, fructose, and impacts on satiety, cognition, mood, and gut microbiota were realized: 1) there is a need for global harmonization of a science-based fiber definition; 2) low-glycemic index foods can be used to modulate the postprandial glycemic response and may affect diabetes and cardiovascular outcomes; 3) carbohydrate type may influence satiety and satiation; glycemic load and glycemic index show links to memory, mood, and concentration; 4) validated biomarkers are needed to demonstrate the known prebiotic effect of carbohydrates; 5) negative effects of fructose are not evident when human data are systematically reviewed; 6) new research indicates that diet strongly influences the microbiome; and 7) there is mounting evidence that the intestinal microbiota has the ability to impact the gut–brain axis. Overall, there is much promise for development of functional foods that impact the microbiome and other factors relevant to health, including glycemic response (glycemic index/glycemic load), satiety, mood, cognition, and weight management.

Meal Replacement Beverage Twice a Day in Overweight and Obese Adults (MDRC2012-001)

This open label, single arm, prospective, interventional, weight loss trial evaluated a meal replacement beverage (Right Size^® Smoothie) used to replace breakfast and lunch each day for 12 weeks (7 clinic visits) as part of a calorie-restricted diet in overweight and obese adults. A total of 155 individuals were screened, 55 enrolled and 28 completed this 12 week study. Subjects were obese (mean weight: 206 pounds and BMI: 32.7 kg/m²) and the mean age was 40 years including 42 (76.4%) female and 13 (23.6%) male volunteers. The modified Intent to Treat and Completer groups lost an average of 10.6 and 13.8 pounds and reduced their average BMI by 1.7 and 2.2 kg/m² respectively during this 12 week trial. The Per Protocol group lost 15.2 pounds and 2.4 kg/m² and the Optimal Weight Loss group lost 18.5 pounds and 2.9 kg/m². Using the Satiety Labeled Intensity Magnitude scale (SLIM) questionnaire, subjects reported feeling relatively hungry before they consumed the beverage, then feeling relatively full 15 minutes following the beverage with the sensation of some fullness lasting more than 2 hours and then feeling relatively hungry again at 3 hours after consuming the beverage. Study subjects reported significant improvements in physical functioning, general health, vitality and mental health as well as increased cognitive restraint of eating, reduced disinhibition and reduced hunger during the trial. The study beverages were well tolerated and no Serious Adverse Events (SAE) reported. This study suggests the study beverage aids in weight loss by helping to curb hunger during a reduced calorie diet program.

'Catalytic' doses of fructose may benefit glycaemic control without harming cardiometabolic risk factors: a small meta-analysis of randomised controlled feeding trials

Contrary to concerns that fructose may have adverse metabolic effects, there is evidence that small, 'catalytic' doses ( ≤ 10 g/meal) of fructose decrease the glycaemic response to high-glycaemic index meals in human subjects. To assess the longer-term effects of 'catalytic' doses of fructose, we undertook a meta-analysis of controlled feeding trials. We searched MEDLINE, EMBASE, CINAHL and the Cochrane Library. Analyses included all controlled feeding trials ≥ 7 d featuring 'catalytic' fructose doses ( ≤ 36 g/d) in isoenergetic exchange for other carbohydrates. Data were pooled by the generic inverse variance method using random-effects models and expressed as mean differences (MD) with 95 % CI. Heterogeneity was assessed by the Q statistic and quantified by I 2. The Heyland Methodological Quality Score assessed study quality. A total of six feeding trials (n 118) met the eligibility criteria. 'Catalytic' doses of fructose significantly reduced HbA1c (MD - 0·40, 95 % CI - 0·72, - 0·08) and fasting glucose (MD - 0·25, 95 % CI - 0·44, - 0·07). This benefit was seen in the absence of adverse effects on fasting insulin, body weight, TAG or uric acid. Subgroup and sensitivity analyses showed evidence of effect modification under certain conditions. The small number of trials and their relatively short duration limit the strength of the conclusions. In conclusion, this small meta-analysis shows that 'catalytic' fructose doses ( ≤ 36 g/d) may improve glycaemic control without adverse effects on body weight, TAG, insulin and uric acid. There is a need for larger, longer ( ≥ 6 months) trials using 'catalytic' fructose to confirm these results.

Effect of fructose on glycemic control in diabetes: a systematic review and meta-analysis of controlled feeding trials

OBJECTIVE

The effect of fructose on cardiometabolic risk in humans is controversial. We conducted a systematic review and meta-analysis of controlled feeding trials to clarify the effect of fructose on glycemic control in individuals with diabetes.

RESEARCH DESIGN AND METHODS

We searched MEDLINE, EMBASE, and the Cochrane Library (through 22 March 2012) for relevant trials lasting ≥7 days. Data were aggregated by the generic inverse variance method (random-effects models) and expressed as mean difference (MD) for fasting glucose and insulin and standardized MD (SMD) with 95% CI for glycated hemoglobin (HbA(1c)) and glycated albumin. Heterogeneity was assessed by the Cochran Q statistic and quantified by the I(2) statistic. Trial quality was assessed by the Heyland methodological quality score (MQS).

RESULTS

Eighteen trials (n = 209) met the eligibility criteria. Isocaloric exchange of fructose for carbohydrate reduced glycated blood proteins (SMD -0.25 [95% CI -0.46 to -0.04]; P = 0.02) with significant intertrial heterogeneity (I(2) = 63%; P = 0.001). This reduction is equivalent to a ~0.53% reduction in HbA(1c). Fructose consumption did not significantly affect fasting glucose or insulin. A priori subgroup analyses showed no evidence of effect modification on any end point.

CONCLUSIONS

Isocaloric exchange of fructose for other carbohydrate improves long-term glycemic control, as assessed by glycated blood proteins, without affecting insulin in people with diabetes. Generalizability may be limited because most of the trials were <12 weeks and had relatively low MQS (<8). To confirm these findings, larger and longer fructose feeding trials assessing both possible glycemic benefit and adverse metabolic effects are required.

Design, synthesis, and pharmacological evaluation of benzamide derivatives as glucokinase activators

A series of benzamide derivatives were assembled by using the privileged-fragment-merging (PFM) strategy and their SAR studies as glucokinase activators were described. Compounds 5 and 16b were identified having a suitable balance of potency and activation profile. They showed EC(50) values of 28.3 and 44.8 nM, and activation folds of 2.4 and 2.2, respectively. However, both compounds displayed a minor reduction in plasma glucose levels on imprinting control region (ICR) mice. Unfavorable pharmacokinetic profiles (PK) were also observed on these two compounds.

The relation of low glycaemic index fruit consumption to glycaemic control and risk factors for coronary heart disease in type 2 diabetes

AIMS/HYPOTHESIS

Sugar has been suggested to promote obesity, diabetes and coronary heart disease (CHD), yet fruit, despite containing sugars, may also have a low glycaemic index (GI) and all fruits are generally recommended for good health. We therefore assessed the effect of fruit with special emphasis on low GI fruit intake in type 2 diabetes.

METHODS

This secondary analysis involved 152 type 2 diabetic participants treated with glucose-lowering agents who completed either 6 months of high fibre or low GI dietary advice, including fruit advice, in a parallel design.

RESULTS

Change in low GI fruit intake ranged from -3.1 to 2.7 servings/day. The increase in low GI fruit intake significantly predicted reductions in HbA(1c) (r = -0.206, p =0.011), systolic blood pressure (r = -0.183, p = 0.024) and CHD risk (r = -0.213, p = 0.008). Change in total fruit intake ranged from -3.7 to 3.2 servings/day and was not related to study outcomes. In a regression analysis including the eight major carbohydrate foods or classes of foods emphasised in the low GI diet, only low GI fruit and bread contributed independently and significantly to predicting change in HbA(1c). Furthermore, comparing the highest with the lowest quartile of low GI fruit intake, the percentage change in HbA(1c) was reduced by -0.5% HbA(1c) units (95% CI 0.2-0.8 HbA(1c) units, p < 0.001).

CONCLUSIONS/INTERPRETATION

Low GI fruit consumption as part of a low GI diet was associated with lower HbA(1c), blood pressure and CHD risk and supports a role for low GI fruit consumption in the management of type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00438698.

Hepatic glycogen supercompensation activates AMP-activated protein kinase, impairs insulin signaling, and reduces glycogen deposition in the liver

OBJECTIVE

The objective of this study was to determine how increasing the hepatic glycogen content would affect the liver's ability to take up and metabolize glucose.

RESEARCH DESIGN AND METHODS

During the first 4 h of the study, liver glycogen deposition was stimulated by intraportal fructose infusion in the presence of hyperglycemic-normoinsulinemia. This was followed by a 2-h hyperglycemic-normoinsulinemic control period, during which the fructose infusion was stopped, and a 2-h experimental period in which net hepatic glucose uptake (NHGU) and disposition (glycogen, lactate, and CO(2)) were measured in the absence of fructose but in the presence of a hyperglycemic-hyperinsulinemic challenge including portal vein glucose infusion.

RESULTS

Fructose infusion increased net hepatic glycogen synthesis (0.7 ± 0.5 vs. 6.4 ± 0.4 mg/kg/min; P < 0.001), causing a large difference in hepatic glycogen content (62 ± 9 vs. 100 ± 3 mg/g; P < 0.001). Hepatic glycogen supercompensation (fructose infusion group) did not alter NHGU, but it reduced the percent of NHGU directed to glycogen (79 ± 4 vs. 55 ± 6; P < 0.01) and increased the percent directed to lactate (12 ± 3 vs. 29 ± 5; P = 0.01) and oxidation (9 ± 3 vs. 16 ± 3; P = NS). This change was associated with increased AMP-activated protein kinase phosphorylation, diminished insulin signaling, and a shift in glycogenic enzyme activity toward a state discouraging glycogen accumulation.

CONCLUSIONS

These data indicate that increases in hepatic glycogen can generate a state of hepatic insulin resistance, which is characterized by impaired glycogen synthesis despite preserved NHGU.

Acute hypoxia and exercise improve insulin sensitivity (S(I) (2*)) in individuals with type 2 diabetes

BACKGROUND

hypoxia has been shown to increase glucose uptake in skeletal muscle using the contraction-stimulated pathway, independent of the actions of insulin. Yet, the same stress has also been linked with causing insulin resistance and hyperglycaemia. The aim of this study was to examine the effects of acute hypoxia with and without exercise on insulin sensitivity (S(I)(2*) in individuals with type 2 diabetes.

METHODS

eight type 2 diabetic patients completed 60 min of the following: (1) normoxic rest; (2) hypoxic rest [O(2) = 14.6 (0.4)%]; (3) normoxic exercise and (4) hypoxic exercise [O(2) = 14.6 (0.4)%]. Exercise trials were set at 90% of lactate threshold. Each condition was followed by a labelled intravenous glucose tolerance test to provide estimations of insulin sensitivity (S(I)(2*) and β-cell function.

RESULTS

Two-compartmental analysis showed that insulin sensitivity (S(I)(2*) was higher following hypoxic rest compared with normoxic rest (p = 0.047). Insulin sensitivity (S(I)(2*) was also higher following hypoxic exercise [4.37 (0.48) × 10(-4) /min (µU/mL)] compared with normoxic exercise [3.24 (0.51) × 10(-4) /min (µU/mL)] (p = 0.048). Acute insulin response to glucose was reduced following hypoxic rest versus normoxic rest (p = 0.014).

CONCLUSIONS

this study demonstrated that (1) hypoxic-induced improvements in glucose tolerance in the 4 h following exposure can be attributed to improvements in peripheral insulin sensitivity (S( I)(2*) and (2) exercise and hypoxia have an additive effect on insulin sensitivity (S(I)(2*) in type 2 diabetic patients. Acute hypoxia may therefore improve short-term glycaemic control in individuals with type 2 diabetes. The application of these findings in the clinic will require further investigation.

Measurement of glucose and fructose in clinical samples using gas chromatography/mass spectrometry

OBJECTIVE

The impact of increased fructose consumption on carbohydrate metabolism is a topic of current interest, but determination of serum level has been hindered due to low concentration and interference from serum glucose. We are reporting a method for the quantification of glucose and fructose in clinical samples using gas chromatography/mass spectrometry (GC/MS). The accuracy and precision of GC/MS and an enzymatic assay were compared.

DESIGN AND METHODS

Mass spectrometry fragmentation patterns of methyloxime peracetate derivatized aldose and ketose were determined. Unique fragments for glucose and fructose were used for quantitative analysis using isotope labeled recovery standards.

RESULTS

Methyloxime peracetate derivatives of glucose and fructose showed characteristic loss of acetate (M-60) or ketene (M-42) under chemical ionization (CI). Under electron impact (EI) ionization, a unique C1-C2 fragment of glucose was formed, while a C1-C3 fragment was formed from keto-hexoses. These unique fragments were used in the quantitative assay of glucose and fructose in clinical samples. In clinical samples, the GC/MS assay has a lower limit of detection than that of the enzymatic assay. In plasma samples from patients evaluated for diabetes the average serum glucose and fructose were 6.19+/-2.72 mM and 46+/- 25.22 microM. Fructose concentrations in many of these samples were below the limit of detection of the enzymatic method.

CONCLUSION

Derivatization of aldose and ketose monosaccharides to their respective O-methyloxime acetates for GC/MS analysis is a facile method for determination of serum/plasma glucose and fructose samples.

Inhibiting gluconeogenesis prevents fatty acid-induced increases in endogenous glucose production

Glucose effectiveness, the ability of glucose per se to suppress endogenous glucose production (EGP), is lost in type 2 diabetes mellitus (T2DM). Free fatty acids (FFA) may contribute to this loss of glucose effectiveness in T2DM by increasing gluconeogenesis (GNG) and impairing the response to hyperglycemia. Thus, we first examined the effects of increasing plasma FFA levels for 3, 6, or 16 h on glucose effectiveness in nondiabetic subjects. Under fixed hormonal conditions, hyperglycemia suppressed EGP by 61% in nondiabetic subjects. Raising FFA levels with Liposyn infusion for > or =3 h reduced the normal suppressive effect of glucose by one-half. Second, we hypothesized that inhibiting GNG would prevent the negative impact of FFA on glucose effectiveness. Raising plasma FFA levels increased gluconeogenesis by approximately 52% during euglycemia and blunted the suppression of EGP by hyperglycemia. Infusion of ethanol rapidly inhibited GNG and doubled the suppression of EGP by hyperglycemia, thereby restoring glucose effectiveness. In conclusion, elevated FFA levels rapidly increased GNG and impaired hepatic glucose effectiveness in nondiabetic subjects. Inhibiting GNG could have therapeutic potential in restoring the regulation of glucose production in type 2 diabetes mellitus.

Glucokinase activators in diabetes management

Type 2 diabetes is a chronic metabolic disease that adversely affects both the quality and longevity of life. The disease is characterised by elevated blood glucose (hyperglycaemia) that is associated with microvascular complications and increased macrovascular risk. Existing oral agents, either alone or in combination, do not exhibit adequate or sustained glucose lowering efficacy in Type 2 diabetics. Consequently, there is an unmet medical need for improved antidiabetic agents which are both more effective at lowering glucose and which display sustained efficacy over a number of years. Such agents would allow present glycaemic treatment targets to be achieved with greater success. Glucokinase activators (GKAs) represent a novel class of glucose-lowering agents. Preclinical data supports the notion that these agents act to lower blood glucose through effects in both the liver and pancreas. It is predicted that this dual compartment mechanism of action of GKAs will translate to robust glucose lowering in diabetic patients. The potential benefits and risks associated with the pharmacological activation of glucokinase are evaluated. The status of GKAs in preclinical and clinical development is assessed are the future prospects of these agents.

Insulin-sensitizing effects of thiazolidinediones are not linked to adiponectin receptor expression in human fat or muscle

Circulating adiponectin levels are increased by the thiazolidinedione (TZD) class of PPARgamma agonists in concert with their insulin-sensitizing effects. Two receptors for adiponectin (AdipoR1 and AdipoR2) are widely expressed in many tissues, but their physiological significance to human insulin resistance remains to be fully elucidated. We examined the expression patterns of AdipoR1 and AdipoR2 in fat and skeletal muscle of human subjects, their relationship to insulin action, and whether they are regulated by TZDs. Expression patterns of both AdipoRs were similar in subcutaneous and omental fat depots, with higher expression in adipocytes than in stromal cells and macrophages. To determine the effects of TZDs on AdipoR expression, subcutaneous fat and quadriceps muscle were biopsied in 14 insulin-resistant subjects with type 2 diabetes mellitus after 45 mg pioglitazone or placebo for 21 days. This duration of pioglitazone improved insulin's suppression of glucose production by 41% and enhanced stimulation of glucose uptake by 27% in concert with increased gene expression and plasma levels of adiponectin. Pioglitazone did not affect AdipoR expression in muscle, whole fat, or cellular adipose fractions, and receptor expression did not correlate with baseline or TZD-enhanced insulin action. In summary, both adiponectin receptors are expressed in cellular fractions of human fat, particularly adipocytes. TZD administration for sufficient duration to improve insulin action and increase adiponectin levels did not affect expression of AdipoR1 or AdipoR2. Although TZDs probably exert many of their effects via adiponectin, changes in these receptors do not appear to be necessary for their insulin-sensitizing effects.

A defect in glucose-induced dissociation of glucokinase from the regulatory protein in Zucker diabetic fatty rats in the early stage of diabetes

Effect of stimulation of glucokinase (GK) export from the nucleus by small amounts of sorbitol on hepatic glucose flux in response to elevated plasma glucose was examined in 6-h fasted Zucker diabetic fatty rats at 10 wk of age. Under basal conditions, plasma glucose, insulin, and glucagon were ∼8 mM, 2,000 pmol/l, and 60 ng/l, respectively. Endogenous glucose production (EGP) was 44 ± 4 μmol·kg−1·min−1. When plasma glucose was raised to ∼17 mM, GK was still predominantly localized with its inhibitory protein in the nucleus. EGP was not suppressed. When sorbitol was infused at 5.6 and 16.7 μmol·kg−1·min−1, along with the increase in plasma glucose, GK was exported to the cytoplasm. EGP (23 ± 19 and 12 ± 5 μmol·kg−1·min−1) was suppressed without a decrease in glucose 6-phosphatase flux (145 ± 23 and 126 ± 16 vs. 122 ± 10 μmol·kg−1·min−1without sorbitol) but increased in glucose phosphorylation as indicated by increases in glucose recycling (122 ± 17 and 114 ± 19 vs. 71 ± 11 μmol·kg−1·min−1), glucose-6-phosphate content (254 ± 32 and 260 ± 35 vs. 188 ± 20 nmol/g liver), fractional contribution of plasma glucose to uridine 5′-diphosphate-glucose flux (43 ± 8 and 42 ± 8 vs. 27 ± 6%), and glycogen synthesis from plasma glucose (20 ± 4 and 22 ± 5 vs. 9 ± 4 μmol glucose/g liver). The decreased glucose effectiveness to suppress EGP and stimulate hepatic glucose uptake may result from failure of the sugar to activate GK by stimulating the translocation of the enzyme.

Glucose toxicity is responsible for the development of impaired regulation of endogenous glucose production and hepatic glucokinase in Zucker diabetic fatty rats

The effect of restoration of normoglycemia by a novel sodium-dependent glucose transporter inhibitor (T-1095) on impaired hepatic glucose uptake was examined in 14-week-old Zucker diabetic fatty (ZDF) rats. The nontreated group exhibited persistent endogenous glucose production (EGP) despite marked hyperglycemia. Gluconeogenesis and glucose cycling (GC) were responsible for 46 and 51% of glucose-6-phosphatase (G6Pase) flux, respectively. Net incorporation of plasma glucose into hepatic glycogen was negligible. Glucokinase (GK) and its inhibitory protein, GK regulatory protein (GKRP), were colocalized in the cytoplasm of hepatocytes. At day 7 of drug administration, EGP was slightly reduced, but G6Pase flux and GC were markedly lower compared with the nontreated group. In this case, GK and GKRP were colocalized in the nuclei of hepatocytes. When plasma glucose and insulin levels were raised during a clamp, EGP was completely suppressed and GC, glycogen synthesis from plasma glucose, and the fractional contribution of plasma glucose to uridine diphosphoglucose flux were markedly increased. GK, but not GKRP, was translocated from the nucleus to the cytoplasm. Glucotoxicity may result in the blunted response of hepatic glucose flux to elevated plasma glucose and/or insulin associated with impaired regulation of GK by GKRP in ZDF rats.

Time-dependent effects of free fatty acids on glucose effectiveness in type 2 diabetes

Impaired effectiveness of glucose to suppress endogenous glucose production (EGP) is an important cause of worsening hyperglycemia in type 2 diabetes. Elevated free fatty acids (FFAs) may impair glucose effectiveness via several mechanisms, including rapid changes in metabolic fluxes and/or more gradual changes in gene expression of key enzymes or other proteins. Thus, we examined the magnitude and time course of effects of FFAs on glucose effectiveness in type 2 diabetes and whether glucose effectiveness can be restored by lowering FFAs. Glucose fluxes ([3-(3)H]-glucose) were measured during 6-h pancreatic clamp studies, at euglycemia (5 mmol/l glucose, t=0-240 min), and hyperglycemia (10 mmol/l, t=240-360 min). We studied 19 poorly controlled subjects with type 2 diabetes (HbA(1c) 10.9 +/- 0.4%, age 50 +/- 3 years, BMI 30 +/- 2 kg/m(2)) on at least two occasions with saline (NA- group) or nicotinic acid (NA group) infusions for 3, 6, or 16 h (NA3h, NA6h, and NA16h groups, respectively) to lower FFAs to nondiabetic levels. As a reference group, glucose effectiveness was also assessed in 15 nondiabetic subjects. There was rapid improvement in hepatic glucose effectiveness following only 3 h of NA infusion (NA3h = 31 +/- 6% suppression of EGP with hyperglycemia vs. NA- = 8 +/- 7%; P<0.01) and complete restoration of glucose effectiveness after 6 h of NA (NA6h = 41 +/- 8% suppression of EGP; P = NS vs. nondiabetic subjects). Importantly, the loss of hepatic glucose effectiveness in type 2 diabetes is completely reversible upon correcting the increased FFA concentrations. A longer duration of FFA lowering may be required to overcome the chronic effects of increased FFAs on hepatic glucose effectiveness.

Catalytic amounts of fructose may improve glucose tolerance in subjects with uncontrolled non-insulin-dependent diabetes

BACKGROUND

It was suggested that acute ingestion of small amounts of fructose can improve glucose homeostasis.

AIM

To study the effect of a long-term tri-daily supplementation of catalytic amounts of fructose on glucose tolerance of subjects with type 2 diabetes (NIDDM).

METHODS

A double-blind, placebo-controlled study. Twenty-six subjects with uncontrolled NIDDM as indicated by high levels of hemoglobin A1C (Hgb(A1c)) and 2-h postprandial glucose levels >200 mg% were assigned to either fructose or maltodextrin supplementation (7.5 g) tri-daily after each main meal. The subjects were challenged with a fixed meal and blood was drawn for determining levels of glucose, insulin and triglycerides before and 2 h after meal at baseline and 1 month after study entry. Blood was drawn for total cholesterol, high-density and low-density lipoprotein cholesterol (LDL-c), fructosamine and Hgb(A1C) before study entry and at 1, 2 and 3 months into the study.

RESULTS

No changes were observed in the difference between postprandial and pre-meal glucose, insulin or triglyceride levels in each group or between groups. No significant statistical differences were found in weight, total cholesterol, LDL-c and high-density lipoprotein cholesterol (HDL-c) in each group or between groups along the study period. After 1 month fructosamin levels decreased in the fructose-supplemented group but not in the maltodextrin-supplemented group (P<0.052). Hgb(A1C) levels decreased with time in both groups but were significantly lower at 2 months in the fructose group as compared to the maltodextrin group (P<0.03).

CONCLUSIONS

Subjects with NIDDM may benefit from daily supplementation of catalytic amounts of fructose in their diet.

Dietary fructose: implications for dysregulation of energy homeostasis and lipid/carbohydrate metabolism

Fructose intake and the prevalence of obesity have both increased over the past two to three decades. Compared with glucose, the hepatic metabolism of fructose favors lipogenesis, which may contribute to hyperlipidemia and obesity. Fructose does not increase insulin and leptin or suppress ghrelin, which suggests an endocrine mechanism by which it induces a positive energy balance. This review examines the available data on the effects of dietary fructose on energy homeostasis and lipid/carbohydrate metabolism. Recent publications, studies in human subjects, and areas in which additional research is needed are emphasized.