High-Fructose Consumption Impairs the Redox System and Protein Quality Control in the Brain of Syrian Hamsters: Therapeutic Effects of Melatonin

The Association of Fructose Metabolism With Anesthesia/Surgery-Induced Lactate Production

BACKGROUND

In elderly individuals, excessive lactate levels in the brain may be associated with the development of cognitive impairment after surgery, including delayed neurocognitive recovery (dNCR). Since the origin of this increased lactate is unknown, here we assessed associations between metabolic pathways and postoperative dNCR.

METHODS

This study included 43 patients (≥60 years old) who had surgery under general anesthesia. We also used a mouse model in which 20-month-old mice were exposed to sevoflurane to induce postoperative dNCR, while control mice were exposed to 40% oxygen. Mice in the control group and anesthesia/surgery group were injected with fructose or glucose intracerebroventricularly, or fructose metabolism inhibitor intraperitoneally. Barnes maze test and Y maze were used to measure cognitive function in mice. Metabolomics was used to measure metabolites in the serum of patients and the brains of mice after anesthesia/surgery. Isotope labeling and metabolic flux were used to analyze flow and distribution of specific metabolites in metabolic pathways.

RESULTS

Among 43 patients, 17 developed dNCR. Metabolomics showed significantly decreased postoperative serum fructose 1-phosphate levels in dNCR compared to nondNCR patients (mean difference [×10 4 ] = -0.164 ± 0.070; P = .024). Similar results were found in the brains of mice (mean difference = -1.669 ± 0.555; * P = .014). Isotope labeling and metabolic flux experiments in mice showed fructose but not glucose entered glycolysis, increasing lactate levels in the brain after anesthesia/surgery ( P < .05). Administration of intraperitoneal fructose inhibitors to mice effectively inhibited increased lactate levels in the brain (mean difference =96.0 ± 4.36, P = .0237) and cognitive dysfunction after anesthesia/surgery (mean difference =69.0 ± 3.94, P = .0237). In a small subsample, we also found anesthesia/surgery increased interleukin-6 (IL-6) levels in the brains of mice (mean difference =88.3 ± 3.44, P = .0237) and that IL-6 may function upstream in fructose activation.

CONCLUSIONS

These results suggest that anesthesia/surgery activates fructose metabolism, producing excessive lactate in the brain that is associated with postoperative cognitive impairment. Fructose metabolism is thus a potential therapeutic target for dNCR.

Melatonin regulates endoplasmic reticulum stress in diverse pathophysiological contexts: A comprehensive mechanistic review

The endoplasmic reticulum (ER) is crucial for protein quality control, and disruptions in its function can lead to various diseases. ER stress triggers an adaptive response called the unfolded protein response (UPR), which can either restore cellular homeostasis or induce cell death. Melatonin, a safe and multifunctional compound, shows promise in controlling ER stress and could be a valuable therapeutic agent for managing the UPR. By regulating ER and mitochondrial functions, melatonin helps maintain cellular homeostasis via reduction of oxidative stress, inflammation, and apoptosis. Melatonin can directly or indirectly interfere with ER-associated sensors and downstream targets of the UPR, impacting cell death, autophagy, inflammation, molecular repair, among others. Crucially, this review explores the mechanistic role of melatonin on ER stress in various diseases including liver damage, neurodegeneration, reproductive disorders, pulmonary disease, cardiomyopathy, insulin resistance, renal dysfunction, and cancer. Interestingly, while it alleviates the burden of ER stress in most pathological contexts, it can paradoxically stimulate ER stress in cancer cells, highlighting its intricate involvement in cellular homeostasis. With numerous successful studies using in vivo and in vitro models, the continuation of clinical trials is imperative to fully explore melatonin's therapeutic potential in these conditions.

Differential Cellular Interactome in Schizophrenia and Bipolar Disorder-Discriminatory Biomarker Role

Schizophrenia (SCH) and bipolar disorder (BD) are two of the most important psychiatric pathologies due to their high population incidence and disabling power, but they also present, mainly in their debut, high clinical similarities that make their discrimination difficult. In this work, the differential oxidative stress, present in both disorders, is shown as a concatenator of the systemic alterations-both plasma and erythrocyte, and even at the level of peripheral blood mononuclear cells (PBMC)-in which, for the first time, the different affectations that both disorders cause at the level of the cellular interactome were observed. A marked erythrocyte antioxidant imbalance only present in SCH generalizes to oxidative damage at the plasma level and shows a clear impact on cellular involvement. From the alteration of protein synthesis to the induction of death by apoptosis, including proteasomal damage, mitochondrial imbalance, and autophagic alteration, all the data show a greater cellular affectation in SCH than in BD, which could be linked to increased oxidative stress. Thus, patients with SCH in our study show increased endoplasmic reticulum (ER)stress that induces increased proteasomal activity and a multifactorial response to misfolded proteins (UPR), which, together with altered mitochondrial activity, generating free radicals and leading to insufficient energy production, is associated with defective autophagy and ultimately leads the cell to a high apoptotic predisposition. In BD, however, oxidative damage is much milder and without significant activation of survival mechanisms or inhibition of apoptosis. These clear differences identified at the molecular and cellular level between the two disorders, resulting from progressive afflictions in which oxidative stress can be both a cause and a consequence, significantly improve the understanding of both disorders to date and are essential for the development of targeted and preventive treatments.

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.

Integrating the effects of sucrose intake on the brain and white adipose tissue: Could autophagy be a possible link?

Excess dietary sucrose is associated with obesity and metabolic diseases. This relationship is driven by the malfunction of several cell types and tissues critical for the regulation of energy balance, including hypothalamic neurons and white adipose tissue (WAT). However, the mechanisms behind these effects of dietary sucrose are still unclear and might be independent of increased adiposity. Accumulating evidence has indicated that dysregulation of autophagy, a fundamental process for maintenance of cellular homeostasis, alters energy metabolism in hypothalamic neurons and WAT, but whether autophagy could mediate the detrimental effects of dietary sucrose on hypothalamic neurons and WAT that contribute to weight gain is a matter of debate. In this review, we examine the hypothesis that dysregulated autophagy in hypothalamic neurons and WAT is an adiposity-independent effect of sucrose that contributes to increased body weight gain. We propose that excess dietary sucrose leads to autophagy unbalance in hypothalamic neurons and WAT, which increases caloric intake and body weight, favoring the emergence of obesity and metabolic diseases.

Removal of Environmental Nanoparticles Increases Protein Synthesis and Energy Production in Healthy Humans

Currently, industrial activity causes the environmental release of nanoparticles that have multiple adverse effects on population health. There is a clear correlation between the increase in particulate air pollution and the increases in mortality and morbidity rates in both adults and children, which demonstrates the toxic effects of these particles. However, the effect of particle removal on healthy individuals is unknown. Thus, in this preliminary study, we showed, for the first time, how the filtering equipment that we used significantly reduced a large amount of nanoparticles in a minimum time and induced a reduction of oxidative damage in healthy individuals of both sexes after 25, 50 and 100 days of exposure. These effects led to increased protein synthesis and enhanced mitochondrial efficiency, thus resulting in a highly significant triggering of ATP synthesis. These results not only provide insight into the chronic effects that environmental nanoparticles have on individuals prior to the development of pathologies but also demonstrate a system capable of reversing nanoparticle toxicity and allowing cellular energy recovery.

Diabetes mellitus and melatonin: Where are we?

Diabetes mellitus (DM) and diabetes-related complications are amongst the leading causes of mortality worldwide. The international diabetes federation (IDF) has estimated 592 million people to suffer from DM by 2035. Hence, finding a novel biomolecule that can effectively aid diabetes management is vital, as other existing drugs have numerous side effects. Melatonin, a pineal hormone having antioxidative and anti-inflammatory properties, has been implicated in circadian dysrhythmia-linked DM. Reduced levels of melatonin and a functional link between melatonin and insulin are implicated in the pathogenesis of type 2 diabetes (T2D) Additionally, genomic studies revealed that rare variants in melatonin receptor 1b (MTNR1B) are also associated with impaired glucose tolerance and increased risk of T2D. Moreover, exogenous melatonin treatment in cell lines, rodent models, and diabetic patients has shown a potent effect in alleviating diabetes and other related complications. This highlights the role of melatonin in glucose homeostasis. However, there are also contradictory reports on the effects of melatonin supplementation. Thus, it is essential to explore if melatonin can be taken from bench to bedside for diabetes management. This review summarizes the therapeutic potential of melatonin in various diabetic models and whether it can be considered a safe drug for managing diabetic complications and diabetic manifestations like oxidative stress, inflammation, ER stress, mitochondrial dysfunction, metabolic dysregulation, etc.

Melatonin induces the rejuvenation of long-term ex vivo expanded periodontal ligament stem cells by modulating the autophagic process

Background

Stem cells that have undergone long-term ex vivo expansion are most likely functionally compromised (namely cellular senescence) in terms of their stem cell properties and therapeutic potential. Due to its ability to attenuate cellular senescence, melatonin (MLT) has been proposed as an adjuvant in long-term cell expansion protocols, but the mechanism underlying MLT-induced cell rejuvenation remains largely unknown.

Methods

Human periodontal ligament stem cells (PDLSCs) were isolated and cultured ex vivo for up to 15 passages, and cells from passages 2, 7, and 15 (P2, P7, and P15) were used to investigate cellular senescence and autophagy change in response to long-term expansion and indeed the following MLT treatment. Next, we examined whether MLT could induce cell rejuvenation by restoring the autophagic processes of damaged cells and explored the underlying signaling pathways. In this context, cellular senescence was indicated by senescence-associated β-galactosidase (SA-β-gal) activity and by the expression of senescence-related proteins, including p53, p21, p16, and γ-H2AX. In parallel, cell autophagic processes were evaluated by examining autophagic vesicles (by transmission electronic microscopy), autophagic flux (by assessing mRFP-GFP-LC3-transfected cells), and autophagy-associated proteins (by Western blot assay of Atg7, Beclin-1, LC3-II, and p62).

Results

We found that long-term in vitro passaging led to cell senescence along with impaired autophagy. As expected, MLT supplementation not only restored cells to a younger state but also restored autophagy in senescent cells. Additionally, we demonstrated that autophagy inhibitors could block MLT-induced cell rejuvenation. When the underlying signaling pathways involved were investigated, we found that the MLT receptor (MT) mediated MLT-related autophagy restoration by regulating the PI3K/AKT/mTOR signaling pathway.

Conclusions

The present study suggests that MLT may attenuate long-term expansion-caused cellular senescence by restoring autophagy, most likely via the PI3K/AKT/mTOR signaling pathway in an MT-dependent manner. This is the first report identifying the involvement of MT-dependent PI3K/AKT/mTOR signaling in MLT-induced autophagy alteration, indicating a potential of autophagy-restoring agents such as MLT to be used in the development of optimized clinical-scale cell production protocols.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02322-9.

Dietary fructose as a model to explore the influence of peripheral metabolism on brain function and plasticity

High consumption of fructose has paralleled an explosion in metabolic disorders including obesity and type 2 diabetes. Even more problematic, sustained consumption of fructose is perceived as a threat for brain function and development of neurological disorders. The action of fructose on peripheral organs is an excellent model to understand how systemic physiology impacts the brain. Given the recognized action of fructose on liver metabolism, here we discuss mechanisms by which fructose can impact the brain by interacting with liver and other organs. The interaction between peripheral and central mechanisms is a suitable target to reduce the pathophysiological consequences of neurological disorders.

Sweet but Bitter: Focus on Fructose Impact on Brain Function in Rodent Models

Fructose consumption has drastically increased during the last decades due to the extensive commercial use of high-fructose corn syrup as a sweetener for beverages, snacks and baked goods. Fructose overconsumption is known to induce obesity, dyslipidemia, insulin resistance and inflammation, and its metabolism is considered partially responsible for its role in several metabolic diseases. Indeed, the primary metabolites and by-products of gut and hepatic fructolysis may impair the functions of extrahepatic tissues and organs. However, fructose itself causes an adenosine triphosphate (ATP) depletion that triggers inflammation and oxidative stress. Many studies have dealt with the effects of this sugar on various organs, while the impact of fructose on brain function is, to date, less explored, despite the relevance of this issue. Notably, fructose transporters and fructose metabolizing enzymes are present in brain cells. In addition, it has emerged that fructose consumption, even in the short term, can adversely influence brain health by promoting neuroinflammation, brain mitochondrial dysfunction and oxidative stress, as well as insulin resistance. Fructose influence on synaptic plasticity and cognition, with a major impact on critical regions for learning and memory, was also reported. In this review, we discuss emerging data about fructose effects on brain health in rodent models, with special reference to the regulation of food intake, inflammation, mitochondrial function and oxidative stress, insulin signaling and cognitive function.

Rheostatic Balance of Circadian Rhythm and Autophagy in Metabolism and Disease

Circadian rhythms are physical, behavioral and environmental cycles that respond primarily to light and dark, with a period of time of approximately 24 h. The most essential physiological functions of mammals are manifested in circadian rhythm patterns, including the sleep-wake cycle and nutrient and energy metabolism. Autophagy is a conserved biological process contributing to nutrient and cellular homeostasis. The factors affecting autophagy are numerous, such as diet, drugs, and aging. Recent studies have indicated that autophagy is activated rhythmically in a clock-dependent manner whether the organism is healthy or has certain diseases. In addition, autophagy can affect circadian rhythm by degrading circadian proteins. This review discusses the interaction and mechanisms between autophagy and circadian rhythm. Moreover, we introduce the molecules influencing both autophagy and circadian rhythm. We then discuss the drugs affecting the circadian rhythm of autophagy. Finally, we present the role of rhythmic autophagy in nutrient and energy metabolism and its significance in physiology and metabolic disease.

Oxidative stress and metabolic parameters are differently affected by fructose when rats were kept sedentary or underwent swimming exercise

The current study evaluated whether fructose supplementation affects oxidative stress and metabolic parameters in the liver and gastrocnemius muscle of rats subjected to swimming exercise. Male adult Wistar rats received a fructose solution (10%) or water during 1 h before exercise and during the rest interval by the intragastric route. The swimming protocol consisted of 6 days: each day, rats underwent 3 sessions of 17 min each, with a load of 5% of body mass, and rest intervals of 3 min. Fructose supplementation changed metabolic and oxidative parameters in the liver and gastrocnemius muscle of sedentary rats. Swimming exercise counteracted the increase of triglyceride levels in plasma and liver induced by fructose supplementation. It also reduced thiobarbituric acid reactive species levels in the liver, and catalase and superoxide dismutase activities in the gastrocnemius muscle of supplemented rats. However, fructose supplementation worsened metabolic (hepatic triglyceride levels) and oxidative parameters (thiobarbituric acid reactive species levels) in the liver and gastrocnemius of exercised rats. This study demonstrates that oxidative stress and metabolic parameters were differently affected by fructose supplementation when rats were kept sedentary or underwent swimming exercise. The present results indicate the need of a new insight of the role of fructose supplementation during physical exercise.

Therapeutic potential of melatonin related to its role as an autophagy regulator: A review

There are several pathologies, syndromes, and physiological processes in which autophagy is involved. This process of self-digestion that cells trigger as a survival mechanism is complex and tightly regulated, according to the homeostatic conditions of the organ. However, in all cases, its relationship with oxidative stress alterations is evident, following a pathway that suggests endoplasmic reticulum stress and/or mitochondrial changes. There is accumulating evidence of the beneficial role that melatonin has in the regulation and restoration of damaged autophagic processes. In this review, we focus on major physiological changes such as aging and essential pathologies including cancer, neurodegenerative diseases, viral infections and obesity, and document the essential role of melatonin in the regulation of autophagy in each of these different situations.