Comparative Effects of Fructose and Glucose on Lipogenic Gene Expression and Intermediary Metabolism in HepG2 Liver Cells

Consumption of large amounts of fructose or sucrose increases lipogenesis and circulating triglycerides in humans. Although the underlying molecular mechanisms responsible for this effect are not completely understood, it is possible that as reported for rodents, high fructose exposure increases expression of the lipogenic enzymes fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC-1) in human liver. Since activation of the hexosamine biosynthesis pathway (HBP) is associated with increases in the expression of FAS and ACC-1, it raises the possibility that HBP-related metabolites would contribute to any increase in hepatic expression of these enzymes following fructose exposure. Thus, we compared lipogenic gene expression in human-derived HepG2 cells after incubation in culture medium containing glucose alone or glucose plus 5 mM fructose, using the HBP precursor 10 mM glucosamine (GlcN) as a positive control. Cellular metabolite profiling was conducted to analyze differences between glucose and fructose metabolism. Despite evidence for the active uptake and metabolism of fructose by HepG2 cells, expression of FAS or ACC-1 did not increase in these cells compared with those incubated with glucose alone. Levels of UDP-N-acetylglucosamine (UDP-GlcNAc), the end-product of the HBP, did not differ significantly between the glucose and fructose conditions. Exposure to 10 mM GlcN for 10 minutes to 24 hours resulted in 8-fold elevated levels of intracellular UDP-GlcNAc (P<0.001), as well as a 74–126% increase in FAS (P<0.05) and 49–95% increase in ACC-1 (P<0.01) expression above controls. It is concluded that in HepG2 liver cells cultured under standard conditions, sustained exposure to fructose does not result in an activation of the HBP or increased lipogenic gene expression. Should this scenario manifest in human liver in vivo, it would suggest that high fructose consumption promotes triglyceride synthesis primarily through its action to provide lipid precursor carbon and not by activating lipogenic gene expression

Temporal metabolomic responses of cultured HepG2 liver cells to high fructose and high glucose exposures

High fructose consumption has been implicated with deleterious effects on human health, including hyperlipidemia elicited through de novo lipogenesis. However, more global effects of fructose on cellular metabolism have not been elucidated. In order to explore the metabolic impact of fructose-containing nutrients, we applied both GC-TOF and HILIC-QTOF mass spectrometry metabolomic strategies using extracts from cultured HepG2 cells exposed to fructose, glucose, or fructose + glucose. Cellular responses were analyzed in a time-dependent manner, incubated in media containing 5.5 mM glucose + 5.0 mM fructose in comparison to controls incubated in media containing either 5.5 mM glucose or 10.5 mM glucose. Mass spectrometry identified 156 unique known metabolites and a large number of unknown compounds, which revealed metabolite changes due to both utilization of fructose and high-carbohydrate loads independent of hexose structure. Fructose was shown to be partially converted to sorbitol, and generated higher levels of fructose-1-phosphate as a precursor for glycolytic intermediates. Differentially regulated ratios of 3-phosphoglycerate to serine pathway intermediates in high fructose media indicated a diversion of carbon backbones away from energy metabolism. Additionally, high fructose conditions changed levels of complex lipids toward phosphatidylethanolamines. Patterns of acylcarnitines in response to high hexose exposure (10.5 mM glucose or glucose/fructose combination) suggested a reduction in mitochondrial beta-oxidation

Associations between dairy foods, diabetes, and metabolic health: Potential mechanisms and future directions

Epidemiological evidence supports an inverse relationship between adequate intake of dairy foods and susceptibility to type 2 diabetes (T2D). The biological mechanisms responsible for this association remain to be established. This review provides a current perspective on proposed mechanisms that may underlie these effects, and highlights how randomized clinical trials can be applied to investigate these relationships. Results from epidemiological studies generally support that consumption of milk and dairy products is associated with a lower incidence of T2D or improvements in glucose homeostasis indices, and studies of animal and cell models support a positive effect of dairy-rich diets or components on metabolic and inflammation factors relevant to T2D and insulin resistance. Emerging evidence indicates that dairy components that alter mitochondrial function (e.g., leucine actions on silent information regulator transcript 1 (SIRT1)-associated pathways), promote gut microbial population shifts, or influence inflammation and cardiovascular function (e.g., Ca-regulated peptides calcitonin gene-related peptide [CGRP] or calcitonin) should be considered as possible mechanistic factors linking dairy intake with lower risk for T2D. The possibility that dairy-derived trans-palmitoleic acid (tC16:1) has metabolic bioactivities has also been proposed. Pre-clinical and clinical studies focusing specifically on these parameters are needed to validate hypotheses regarding the potential roles of dairy products and their components on the determinants of glucose tolerance, particularly insulin sensitivity, pancreatic endocrine function, and inflammation in individuals at-risk for T2D development. Such experiments would complement epidemiological studies and add to the evidence base for recommendations regarding consumption of dairy products and their individual components

Cumulative average dietary pattern scores in young adulthood and risk of incident type 2 diabetes: the CARDIA study.

Aims/hypothesisThe evidence for the role of contemporary dietary patterns, trends and predominant aspects of energy intake in a typical American diet and in type 2 diabetes risk is limited. Therefore, we examined the association between dietary pattern scores created to reflect the 2015 Dietary Guidelines for Americans (DGA) Scientific Report, a Palaeolithic (Palaeo) diet, a diet high in 'empty calories', and the A Priori Diet Quality Score (APDQS) (cohort reference) and type 2 diabetes risk over time.MethodsWe carried out a prospective analysis of 4719 young adult black and white men and women from the Coronary Artery Risk Development in Young Adults (CARDIA) study with repeated dietary histories collected at study years 0, 7 and 20. Using multivariable Cox proportional hazards regression models, we examined the association between time-dependent cumulative average dietary pattern scores and incident type 2 diabetes.ResultsDuring the 30 year follow-up period, 680 (14.4%) incident cases of type 2 diabetes occurred. There was no association between the 2015 DGA, Palaeo or empty calorie scores and type 2 diabetes risk in the overall population. Participants in the fourth quartile of the APDQS, reflecting a more healthful dietary pattern, had a 45% lower risk of type 2 diabetes compared with those in the lowest quartile (HR 0.55 [95% CI 0.41, 0.74]). In stratified analyses there was an inverse association for the 2015 DGA in non-smokers per SD (HR 0.86 [95% CI 0.74, 0.99]) and an inverse association for the empty calorie score in white women (HR 0.76 [95% CI 0.60, 0.96]) as well as in a subgroup analysis of the Palaeo index of participants who maintained a high score over 20 years (per SD, HR 0.59 [95% CI 0.39, 0.88]).Conclusions/interpretationHigher levels of the APDQS, which largely aligns with the 2015 DGA, were strongly inversely associated with 30 year type 2 diabetes risk in the CARDIA cohort; the results from the other patterns were nuanced and need to be considered in the context of the study and potential biases

Dairy Foods and Dairy Fats: New Perspectives on Pathways Implicated in Cardiometabolic Health

Low-fat and nonfat dairy products have been promoted as part of a healthy dietary pattern by both US dietary guidelines and professional organizations for several decades. The basis for this recommendation stems in part from the putative negative cardiometabolic effects associated with saturated fat consumption. However, as nutrition research has shifted from a single nutrient to a whole-food/dietary pattern approach, the role of dairy foods and dairy fat in the diet-disease relationship is being reexamined. Most observational and experimental evidence does not support a detrimental relationship between full-fat dairy intake and cardiometabolic health, including risks of cardiovascular disease and type 2 diabetes. Indeed, an expanded understanding of the dairy food matrix and the bioactive properties of dairy fats and other constituents suggests a neutral or potentially beneficial role in cardiometabolic health. To consider how consuming dairy foods, including full-fat dairy, is associated with cardiometabolic health, this review provides an innovative perspective on mechanisms that link dairy consumption to 3 main biological systems at the core of metabolic health, the gastrointestinal, hepatic, and vascular systems