Detrimental effects of fructose on mitochondria in mouse motor neurons and on C. elegans healthspan

Virtually identical does not mean exactly identical: Discrepancy in energy metabolism between glucose and fructose fermentation influences the reproductive potential of yeast cells

The physiological efficiency of cells largely depends on the possibility of metabolic adaptations to changing conditions, especially on the availability of nutrients. Central carbon metabolism has an essential role in cellular function. In most cells is based on glucose, which is the primary energy source, provides the carbon skeleton for the biosynthesis of important cell macromolecules, and acts as a signaling molecule. The metabolic flux between pathways of carbon metabolism such as glycolysis, pentose phosphate pathway, and mitochondrial oxidative phosphorylation is dynamically adjusted by specific cellular economics responding to extracellular conditions and intracellular demands. Using Saccharomyces cerevisiae yeast cells and potentially similar fermentable carbon sources i.e. glucose and fructose we analyzed the parameters concerning the metabolic status of the cells and connected with them alteration in cell reproductive potential. Those parameters were related to the specific metabolic network: the hexose uptake - glycolysis and activity of the cAMP/PKA pathway - pentose phosphate pathway and biosynthetic capacities - the oxidative respiration and energy generation. The results showed that yeast cells growing in a fructose medium slightly increased metabolism redirection toward respiratory activity, which decreased pentose phosphate pathway activity and cellular biosynthetic capabilities. These differences between the fermentative metabolism of glucose and fructose, lead to long-term effects, manifested by changes in the maximum reproductive potential of cells.

Safety assessment of high fructose corn syrup and fructose used as sweeteners in foods

High Fructose Corn Syrup (HFCS) and Fructose (FR) are widely used sweeteners in many foods and beverages. This study aimed at investigating the cytotoxic effects of HFCS (5%-30%) and FR (62.5-2000 μg/mL) using MTT assay in Human Hepatocellular Carcinoma (HepG2) cells, and genotoxic effects of using Chromosome Aberrations (CAs), Sister Chromatid Exchanges (SCEs), Micronuclei (MN) and comet assays in human lymphocytes. HFCS significantly reduced the cell viability in HepG2 cells at between 7.5% and 30% for 24 and 48 h. 30% HFCS caused a very significant toxic effect. FR had a cytotoxic effect in HepG2 cells at all treatments. However, as fructose concentration decreased, the cell viability decreased. HFCS (10%-20%) and FR (250-2000 μg/mL) decreased the mitotic index at higher concentrations. IC50 value was found to be a 15% for 48 h. IC50 value of FR was detected as 62.5 μg/mL for 24 h and 48 h. HFCS significantly increased CAs frequency at 15% and 20%. FR significantly increased the frequency of CAs at 250, 1000, and 2000 μg/mL for 48 h. Both sweeteners increased the frequency of SCEs at all concentrations. HFCS (15% and 20%) and FR (250, 1000, and 2000 μg/mL) induced MN frequency at higher concentrations. HFCS caused DNA damage in comet assay at 10% -30%. FR increased tail intensity and moment at 125-2000 μg/mL and tail length at 62.5, 250 and 500 μg/mL. Therefore, HFCS and FR are clearly seen to be cytotoxic and genotoxic, especially at higher concentrations.

Chronic high-sugar diet in adulthood protects Caenorhabditis elegans from 6-OHDA-induced dopaminergic neurodegeneration

BACKGROUND

Diets high in saturated fat and sugar, termed "Western diets," have been associated with several negative health outcomes, including increased risk for neurodegenerative disease. Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and is characterized by the progressive death of dopaminergic neurons in the brain. We build upon previous work characterizing the impact of high-sugar diets in Caenorhabditis elegans to mechanistically evaluate the relationship between high-sugar diets and dopaminergic neurodegeneration.

RESULTS

Adult high-glucose and high-fructose diets, or exposure from day 1 to 5 of adulthood, led to increased lipid content, shorter lifespan, and decreased reproduction. However, in contrast to previous reports, we found that adult chronic high-glucose and high-fructose diets did not induce dopaminergic neurodegeneration alone and were protective from 6-hydroxydopamine (6-OHDA) induced degeneration. Neither sugar altered baseline electron transport chain function and both increased vulnerability to organism-wide ATP depletion when the electron transport chain was inhibited, arguing against energetic rescue as a basis for neuroprotection. The induction of oxidative stress by 6-OHDA is hypothesized to contribute to its pathology, and high-sugar diets prevented this increase in the soma of the dopaminergic neurons. However, we did not find increased expression of antioxidant enzymes or glutathione levels. Instead, we found evidence suggesting downregulation of the dopamine reuptake transporter dat-1 that could result in decreased 6-OHDA uptake.

CONCLUSIONS

Our work uncovers a neuroprotective role for high-sugar diets, despite concomitant decreases in lifespan and reproduction. Our results support the broader finding that ATP depletion alone is insufficient to induce dopaminergic neurodegeneration, whereas increased neuronal oxidative stress may drive degeneration. Finally, our work highlights the importance of evaluating lifestyle by toxicant interactions.

Chronic high-sugar diet in adulthood protects Caenorhabditis elegans from 6-OHDA induced dopaminergic neurodegeneration

BACKGROUND

Diets high in saturated fat and sugar, termed western diets, have been associated with several negative health outcomes, including increased risk for neurodegenerative disease. Parkinson s Disease (PD) is the second most prevalent neurodegenerative disease and is characterized by the progressive death of dopaminergic neurons in the brain. We build upon previous work characterizing the impact of high sugar diets in Caenorhabditis elegans to mechanistically evaluate the relationship between high sugar diets and dopaminergic neurodegeneration.

RESULTS

Non-developmental high glucose and fructose diets led to increased lipid content and shorter lifespan and decreased reproduction. However, in contrast to previous reports, we found that non-developmental chronic high-glucose and high-fructose diets did not induce dopaminergic neurodegeneration alone and were protective from 6-hydroxydopamine (6-OHDA) induced degeneration. Neither sugar altered baseline electron transport chain function, and both increased vulnerability to organism-wide ATP depletion when the electron transport chain was inhibited, arguing against energetic rescue as a basis for neuroprotection. The induction of oxidative stress by 6-OHDA is hypothesized to contribute to its pathology, and high sugar diets prevented this increase in the soma of the dopaminergic neurons. However, we did not find increased expression of antioxidant enzymes or glutathione levels. Instead, we found evidence suggesting alterations to dopamine transmission that could result in decreased 6-OHDA uptake.

CONCLUSION

Our work uncovers a neuroprotective role for high sugar diets, despite concomitant decreases in lifespan and reproduction. Our results support the broader finding that ATP depletion alone is insufficient to induce dopaminergic neurodegeneration, whereas increased neuronal oxidative stress may drive degeneration. Finally, our work highlights the importance of evaluating lifestyle by toxicant interactions.

Could Alzheimer's disease be a maladaptation of an evolutionary survival pathway mediated by intracerebral fructose and uric acid metabolism?

An important aspect of survival is to assure enough food, water, and oxygen. Here, we describe a recently discovered response that favors survival in times of scarcity, and it is initiated by either ingestion or production of fructose. Unlike glucose, which is a source for immediate energy needs, fructose metabolism results in an orchestrated response to encourage food and water intake, reduce resting metabolism, stimulate fat and glycogen accumulation, and induce insulin resistance as a means to reduce metabolism and preserve glucose supply for the brain. How this survival mechanism affects brain metabolism, which in a resting human amounts to 20% of the overall energy demand, is only beginning to be understood. Here, we review and extend a previous hypothesis that this survival mechanism has a major role in the development of Alzheimer's disease and may account for many of the early features, including cerebral glucose hypometabolism, mitochondrial dysfunction, and neuroinflammation. We propose that the pathway can be engaged in multiple ways, including diets high in sugar, high glycemic carbohydrates, and salt. In summary, we propose that Alzheimer's disease may be the consequence of a maladaptation to an evolutionary-based survival pathway and what had served to enhance survival acutely becomes injurious when engaged for extensive periods. Although more studies are needed on the role of fructose metabolism and its metabolite, uric acid, in Alzheimer's disease, we suggest that both dietary and pharmacologic trials to reduce fructose exposure or block fructose metabolism should be performed to determine whether there is potential benefit in the prevention, management, or treatment of this disease.

Caenorhabditis elegans as an emerging model in food and nutrition research: importance of standardizing base diet

As a model organism that has helped revolutionize life sciences, Caenorhabditis elegans has been increasingly used in nutrition research. Here we explore the tradeoffs between pros and cons of its use as a dietary model based primarily on literature review from the past decade. We first provide an overview of its experimental strengths as an animal model, focusing on lifespan and healthspan, behavioral and physiological phenotypes, and conservation of key nutritional pathways. We then summarize recent advances of its use in nutritional studies, e.g. food preference and feeding behavior, sugar status and metabolic reprogramming, lifetime and transgenerational nutrition tracking, and diet-microbiota-host interactions, highlighting cutting-edge technologies originated from or developed in C. elegans. We further review current challenges of using C. elegans as a nutritional model, followed by in-depth discussions on potential solutions. In particular, growth scales and throughputs, food uptake mode, and axenic culture of C. elegans are appraised in the context of food research. We also provide perspectives for future development of chemically defined nematode food ("NemaFood") for C. elegans, which is now widely accepted as a versatile and affordable in vivo model and has begun to show transformative potential to pioneer nutrition science.

High Fructose Negatively Impacts Proliferation of NSC-34 Motor Neuron Cell Line

Objectives The main aim of this study is to identify the deleterious effects of indiscriminately consumed high fructose on motor neurons that are critically affected in many neurological conditions causing movement disorders including paralysis.

Materials and Methods Neuroblastoma x mouse spinal cord motor neuron cell line (NSC-34) motor neuron cell lines were treated with high fructose and oxygen supplementation (18.8%) and assayed for cell proliferation/death, reactive oxygen species (ROS) generation, and oxidative stress response induction

Statistical Analysis Mean and standard deviation, significance with and without high fructose (F)-5%, were estimated by t-tests using GraphPad Prism ver. 8.2.1

Results F-5% along with O2 (18.8%) annihilates the cells (∼85%) by day10 and inhibits cell division as observed by the presence of multinucleated cells. Unexpectedly, 1 to 2% of cells that survived, differentiated and displayed progressive neurite extension. Though not healthy, they were viable up to 80 days. F-5% increased ROS levels (∼34%) not accompanied by concomitant enhanced expression of oxidative stress response regulator, the transcription factor, nrf-2, or downstream effector, sod-1.

Conclusion High fructose is extremely harmful to NSC-34 motor neuron cell line.

Effects of High Dietary Carbohydrate and Lipid Intake on the Lifespan of C. elegans

Health and lifespan are influenced by dietary nutrients, whose balance is dependent on the supply or demand of each organism. Many studies have shown that an increased carbohydrate–lipid intake plays a critical role in metabolic dysregulation, which impacts longevity. Caenorhabditis elegans has been successfully used as an in vivo model to study the effects of several factors, such as genetic, environmental, diet, and lifestyle factors, on the molecular mechanisms that have been linked to healthspan, lifespan, and the aging process. There is evidence showing the causative effects of high glucose on lifespan in different diabetic models; however, the precise biological mechanisms affected by dietary nutrients, specifically carbohydrates and lipids, as well as their links with lifespan and longevity, remain unknown. Here, we provide an overview of the deleterious effects caused by high-carbohydrate and high-lipid diets, as well as the molecular signals that affect the lifespan of C. elegans; thus, understanding the detailed molecular mechanisms of high-glucose- and lipid-induced changes in whole organisms would allow the targeting of key regulatory factors to ameliorate metabolic disorders and age-related diseases.

Genes in human obesity loci are causal obesity genes in C. elegans

Obesity and its associated metabolic syndrome are a leading cause of morbidity and mortality. Given the disease's heavy burden on patients and the healthcare system, there has been increased interest in identifying pharmacological targets for the treatment and prevention of obesity. Towards this end, genome-wide association studies (GWAS) have identified hundreds of human genetic variants associated with obesity. The next challenge is to experimentally define which of these variants are causally linked to obesity, and could therefore become targets for the treatment or prevention of obesity. Here we employ high-throughput in vivo RNAi screening to test for causality 293 C. elegans orthologs of human obesity-candidate genes reported in GWAS. We RNAi screened these 293 genes in C. elegans subject to two different feeding regimens: (1) regular diet, and (2) high-fructose diet, which we developed and present here as an invertebrate model of diet-induced obesity (DIO). We report 14 genes that promote obesity and 3 genes that prevent DIO when silenced in C. elegans. Further, we show that knock-down of the 3 DIO genes not only prevents excessive fat accumulation in primary and ectopic fat depots but also improves the health and extends the lifespan of C. elegans overconsuming fructose. Importantly, the direction of the association between expression variants in these loci and obesity in mice and humans matches the phenotypic outcome of the loss-of-function of the C. elegans ortholog genes, supporting the notion that some of these genes would be causally linked to obesity across phylogeny. Therefore, in addition to defining causality for several genes so far merely correlated with obesity, this study demonstrates the value of model systems compatible with in vivo high-throughput genetic screening to causally link GWAS gene candidates to human diseases.