Fructose Diet-Associated Molecular Alterations in Hypothalamus of Adolescent Rats: A Proteomic Approach.

BACKGROUND: The enhanced consumption of fructose as added sugar represents a major health concern. Due to the complexity and multiplicity of hypothalamic functions, we aim to point out early molecular alterations triggered by a sugar-rich diet throughout adolescence, and to verify their persistence until the young adulthood phase. METHODS: Thirty days old rats received a high-fructose or control diet for 3 weeks. At the end of the experimental period, treated animals were switched to the control diet for further 3 weeks, and then analyzed in comparison with those that were fed the control diet for the entire experimental period. RESULTS: Quantitative proteomics identified 19 differentially represented proteins, between control and fructose-fed groups, belonging to intermediate filament cytoskeleton, neurofilament, pore complex and mitochondrial respiratory chain complexes. Western blotting analysis confirmed proteomic data, evidencing a decreased abundance of mitochondrial respiratory complexes and voltage-dependent anion channel 1, the coregulator of mitochondrial biogenesis PGC-1α, and the protein subunit of neurofilaments α-internexin in fructose-fed rats. Diet-associated hypothalamic inflammation was also detected. Finally, the amount of brain-derived neurotrophic factor and its high-affinity receptor TrkB, as well as of synaptophysin, synaptotagmin, and post-synaptic protein PSD-95 was reduced in sugar-fed rats. Notably, deregulated levels of all proteins were fully rescued after switching to the control diet. CONCLUSIONS: A short-term fructose-rich diet in adolescent rats induces hypothalamic inflammation and highly affects mitochondrial and cytoskeletal compartments, as well as the level of specific markers of brain function; above-reported effects are reverted after switching animals to the control diet.

Long-Lasting Impact of Sugar Intake on Neurotrophins and Neurotransmitters from Adolescence to Young Adulthood in Rat Frontal Cortex.

The detrimental impact of fructose, a widely used sweetener in industrial foods, was previously evidenced on various brain regions. Although adolescents are among the highest consumers of sweet foods, whether brain alterations induced by the sugar intake during this age persist until young adulthood or are rescued returning to a healthy diet remains largely unexplored. To shed light on this issue, just weaned rats were fed with a fructose-rich or control diet for 3 weeks. At the end of the treatment, fructose-fed rats underwent a control diet for a further 3 weeks until young adulthood phase and compared with animals that received from the beginning the healthy control diet. We focused on the consequences induced by the sugar on the main neurotrophins and neurotransmitters in the frontal cortex, as its maturation continues until late adolescence, thus being the last brain region to achieve a full maturity. We observed that fructose intake induces inflammation and oxidative stress, alteration of mitochondrial function, and changes of brain-derived neurotrophic factor (BDNF) and neurotrophin receptors, synaptic proteins, acetylcholine, dopamine, and glutamate levels, as well as increased formation of the glycation end-products Nε-carboxymethyllysine (CML) and Nε-carboxyethyllysine (CEL). Importantly, many of these alterations (BDNF, CML, CEL, acetylcholinesterase activity, dysregulation of neurotransmitters levels) persisted after switching to the control diet, thus pointing out to the adolescence as a critical phase, in which extreme attention should be devoted to limit an excessive consumption of sweet foods that can affect brain physiology also in the long term.

Skeletal muscle insulin resistance and adipose tissue hypertrophy persist beyond the reshaping of gut microbiota in young rats fed a fructose-rich diet.

To investigate whether short term fructose-rich diet induces changes in the gut microbiota as well as in skeletal muscle and adipose tissue physiology and verify whether they persist even after fructose withdrawal, young rats of 30 d of age were fed for 3 weeks a fructose-rich or control diet. At the end of the 3-weeks period, half of the rats from each group were maintained for further 3 weeks on a control diet. Metagenomic analysis of gut microbiota and short chain fatty acids levels (faeces and plasma) were investigated. Insulin response was evaluated at the whole-body level and both in skeletal muscle and epididymal adipose tissue, together with skeletal muscle mitochondrial function, oxidative stress, and lipid composition. In parallel, morphology and physiological status of epididymal adipose tissue was also evaluated. Reshaping of gut microbiota and increased content of short chain fatty acids was elicited by the fructose diet and abolished by switching back to control diet. On the other hand, most metabolic changes elicited by fructose-rich diet in skeletal muscle and epididymal adipose tissue persisted after switching to control diet. Increased dietary fructose intake even on a short-time basis elicits persistent changes in the physiology of metabolically relevant tissues, such as adipose tissue and skeletal muscle, through mechanisms that go well beyond the reshaping of gut microbiota. This picture delineates a harmful situation, in particular for the young populations, posed at risk of metabolic modifications that may persist in their adulthood.

Gut and liver metabolic responses to dietary fructose - are they reversible or persistent after switching to a healthy diet?

The link between increased fructose intake and induction of gut and liver dysfunction has been established, while it remains to be understood whether this damage is reversible, particularly in the young population, in which the intake of fructose has reached dramatic levels. To this end, young (30 days old) rats were fed a fructose-rich or control diet for 3 weeks to highlight the early response of the gut and liver to increased fructose intake. After this period, fructose-fed rats were returned to a control diet for 3 weeks and compared to the rats that received the control diet for the entire period to identify whether fructose-induced changes in the gut-liver axis persist or not after switching back to a control diet. Glucose transporter 5 and the tight junction protein occludin were assessed in the ileum and colon. Markers of inflammation and redox homeostasis as well as fructose and uric acid levels were also evaluated in the ileum, colon and liver. From the whole data, it is seen that metabolic derangement elicited by a fructose-rich diet, even after a brief period of intake, is fully reversed in the liver by a period of fructose withdrawal, while the alterations persist in the gut, especially in the ileum. In conclusion, given the increasing consumption of fructose-rich foods in young populations, the present results highlight the risk arising from gut persistent alterations even after the end of a fructose-rich diet. Therefore, dietary recommendations of reducing the intake of this simple sugar is mandatory to avoid not only the related metabolic alterations but also the persistence of these detrimental changes.

Fructose Removal from the Diet Reverses Inflammation, Mitochondrial Dysfunction, and Oxidative Stress in Hippocampus.

Young age is often characterized by high consumption of processed foods and fruit juices rich in fructose, which, besides inducing a tendency to become overweight, can promote alterations in brain function. The aim of this study was therefore to (a) clarify brain effects resulting from fructose consumption in juvenile age, a critical phase for brain development, and (b) verify whether these alterations can be rescued after removing fructose from the diet. Young rats were fed a fructose-rich or control diet for 3 weeks. Fructose-fed rats were then fed a control diet for a further 3 weeks. We evaluated mitochondrial bioenergetics by high-resolution respirometry in the hippocampus, a brain area that is critically involved in learning and memory. Glucose transporter-5, fructose and uric acid levels, oxidative status, and inflammatory and synaptic markers were investigated by Western blotting and spectrophotometric or enzyme-linked immunosorbent assays. A short-term fructose-rich diet induced mitochondrial dysfunction and oxidative stress, associated with an increased concentration of inflammatory markers and decreased Neurofilament-M and post-synaptic density protein 95. These alterations, except for increases in haptoglobin and nitrotyrosine, were recovered by returning to a control diet. Overall, our results point to the dangerous effects of excessive consumption of fructose in young age but also highlight the effect of partial recovery by switching back to a control diet.

Effects of Late-Life Caloric Restriction on Age-Related Alterations in the Rat Cortex and Hippocampus.

BACKGROUND: A major problem of aging is the disruption of metabolic homeostasis. This is particularly relevant in the brain where it provokes neurodegeneration. Caloric restriction is a physiologic intervention known to delay the deleterious consequences of aging in several species ranging from yeast to mammals. To date, most studies on experimental models have started this dietary intervention from weaning, which is very difficult to be translated to human beings. Here, we study the effects of a more realistic dietary regimen in rats, starting at an advanced age and lasting for six months. METHODS: we analyzed in the cortex and hippocampus, the proteins involved in the energetic balance of the cells, cholesterol metabolism, oxidative stress response, inflammation, synaptic impairment, and brain trophism. RESULTS: our results suggest that caloric restriction in late life can revert only some age-related changes studied here.

Adipose Tissue and Brain Metabolic Responses to Western Diet-Is There a Similarity between the Two?

Dietary fats and sugars were identified as risk factors for overweight and neurodegeneration, especially in middle-age, an earlier stage of the aging process. Therefore, our aim was to study the metabolic response of both white adipose tissue and brain in middle aged rats fed a typical Western diet (high in saturated fats and fructose, HFF) and verify whether a similarity exists between the two tissues. Specific cyto/adipokines (tumor necrosis factor alpha (TNF-α), adiponectin), critical obesity-inflammatory markers (haptoglobin, lipocalin), and insulin signaling or survival protein network (insulin receptor substrate 1 (IRS), Akt, Erk) were quantified in epididymal white adipose tissue (e-WAT), hippocampus, and frontal cortex. We found a significant increase of TNF-α in both e-WAT and hippocampus of HFF rats, while the expression of haptoglobin and lipocalin was differently affected in the various tissues. Interestingly, adiponectin amount was found significantly reduced in e-WAT, hippocampus, and frontal cortex of HFF rats. Insulin signaling was impaired by HFF diet in e-WAT but not in brain. The above changes were associated with the decrease in brain derived neurotrophic factor (BDNF) and synaptotagmin I and the increase in post-synaptic protein PSD-95 in HFF rats. Overall, our investigation supports for the first time similarities in the response of adipose tissue and brain to Western diet.