Ketone Bodies and SIRT1, Synergic Epigenetic Regulators for Metabolic Health: A Narrative Review

Metabolic Effects of Ketogenic Diets: Exploring Whole-Body Metabolism in Connection with Adipose Tissue and Other Metabolic Organs

The ketogenic diet (KD) is characterized by minimal carbohydrate, moderate protein, and high fat intake, leading to ketosis. It is recognized for its efficiency in weight loss, metabolic health improvement, and various therapeutic interventions. The KD enhances glucose and lipid metabolism, reducing triglycerides and total cholesterol while increasing high-density lipoprotein levels and alleviating dyslipidemia. It significantly influences adipose tissue hormones, key contributors to systemic metabolism. Brown adipose tissue, essential for thermogenesis and lipid combustion, encounters modified UCP1 levels due to dietary factors, including the KD. UCP1 generates heat by uncoupling electron transport during ATP synthesis. Browning of the white adipose tissue elevates UCP1 levels in both white and brown adipose tissues, a phenomenon encouraged by the KD. Ketone oxidation depletes intermediates in the Krebs cycle, requiring anaplerotic substances, including glucose, glycogen, or amino acids, for metabolic efficiency. Methylation is essential in adipogenesis and the body's dietary responses, with DNA methylation of several genes linked to weight loss and ketosis. The KD stimulates FGF21, influencing metabolic stability via the UCP1 pathways. The KD induces a reduction in muscle mass, potentially involving anti-lipolytic effects and attenuating proteolysis in skeletal muscles. Additionally, the KD contributes to neuroprotection, possesses anti-inflammatory properties, and alters epigenetics. This review encapsulates the metabolic effects and signaling induced by the KD in adipose tissue and major metabolic organs.

SIRT1 and ZNF350 as novel biomarkers for osteoporosis: a bioinformatics analysis and experimental validation

BACKGROUND

Osteoporosis (OP) is characterized by bone mass decrease and bone tissue microarchitectural deterioration in bone tissue. This study identified potential biomarkers for early diagnosis of OP and elucidated the mechanism of OP.

METHODS

Gene expression profiles were downloaded from Gene Expression Omnibus (GEO) for the GSE56814 dataset. A gene co-expression network was constructed using weighted gene co-expression network analysis (WGCNA) to identify key modules associated with healthy and OP samples. Functional enrichment analysis was conducted using the R clusterProfiler package for modules to construct the transcriptional regulatory factor networks. We used the "ggpubr" package in R to screen for differentially expressed genes between the two samples. Gene set variation analysis (GSVA) was employed to further validate hub gene expression levels between normal and OP samples using RT-PCR and immunofluorescence to evaluate the potential biological changes in various samples.

RESULTS

There was a distinction between the normal and OP conditions based on the preserved significant module. A total of 100 genes with the highest MM scores were considered key genes. Functional enrichment analysis suggested that the top 10 biological processes, cellular component and molecular functions were enriched. The Toll-like receptor signaling pathway, TNF signaling pathway, PI3K-Akt signaling pathway, osteoclast differentiation, JAK-STAT signaling pathway, and chemokine signaling pathway were identified by Kyoto Encyclopedia of Genes and Genomes pathway analysis. SIRT1 and ZNF350 were identified by Wilcoxon algorithm as hub differentially expressed transcriptional regulatory factors that promote OP progression by affecting oxidative phosphorylation, apoptosis, PI3K-Akt-mTOR signaling, and p53 pathway. According to RT-PCR and immunostaining results, SIRT1 and ZNF350 levels were significantly higher in OP samples than in normal samples.

CONCLUSION

SIRT1 and ZNF350 are important transcriptional regulatory factors for the pathogenesis of OP and may be novel biomarkers for OP treatment.

Twice-Weekly 36-Hour Intermittent Fasting Practice Attenuates Hunger, Quadruples ß-Hydroxybutyrate, and Maintains Weight Loss: A Case Report

Intermittent fasting (IF) approach to weight loss obviates the inconvenience of calorie counting required in daily caloric restriction (DCR). A metabolic defense mechanism (MDM) obstructs weight loss and facilitates weight regain possibly by increasing hunger and efficiency of exercise energy expenditure (EEf), and by reducing resting metabolic rate (RMR) and energy expenditure (EE) including physical activity (PA). IF may test whether its paradigm can better counteract MDM than DCR. A knowledge gap exists about whether the duration of weekly uninterrupted fasts (UFs), when the IF protocols are isocaloric, affects the MDM. The aim and objective of this 82-week study were to determine whether 36 hours of near-absolute twice-weekly UF will exacerbate MDM but generate similar rates of weight and fat losses compared to four IF studies featuring 20 hours of weekly UF with both IF protocols matched for weekly hours of fast (108) and free access to food (60), a fasting-to-eating (F/E) ratio of 1.8. This case report presents results of twice-weekly fasting on non-consecutive days (5:2-NC) and compares them to results from a 4:3-NC protocol with a 20-hour UF caused by a modification of providing a 500-600 kcal meal on three fasting days (M4:3-NC). Because the large meal raises insulin concentration for four hours at the start of the fasting day, the 20-hour UF consists of the remaining eight hours on the fasting day, followed by 12 additional nocturnal hours of fasting. The hypotheses were that (1) because of their matched F/E ratio, the rates of weight and fat losses will be similar in both protocols, and (2) because of its longer UF period, hunger will be higher and RMR and EE will be lower, in 5:2-NC than in M4:3-NC protocol. The main findings were that the 5:2-NC protocol produced (1) slower rates of weight and fat losses, (2) modest reduction in the sensation of hunger and substantial decline in fullness, (3) no change in RMR and EE, and (4) fourfold post-fast increase in the circulating concentration of the ketone body ß-hydroxybutyrate (BHB), 2.5 greater than in the M4:3-NC protocol. The absence of increased hunger and changes in EE, the variability of the rate of weight loss in the 5:2-NC protocol, plus increased EEf in one M4:3-NC study, suggest that IF does not mitigate MDM, but that shortened UF period in M4:3-NC reduces the rise in BHB. Thus, the addition of a large meal on fasting days is unnecessary for the prevention of hunger and is counterproductive for increases in BHB and its potential health benefits. Continuous practice of the 5:2-NC protocol allows sustained weight loss and maintenance of lost weight with diminished hunger for as long as it is implemented.

Effect of calorie restriction on redox status during chemically induced estropause in female mice

In females, there is a continuous decline of the ovarian reserve with age, which results in menopause in women or estropause in mice. Loss of ovarian function results in metabolic alterations in mice and women. Based on this, we aimed to evaluate the effect of caloric restriction (CR) on redox status and metabolic changes in chemically induced estropause in mice. For this, mice were divided into four groups (n = 10): cyclic ad libitum (AL), cyclic 30% CR, AL estropause, and estropause 30% CR. Estropause was induced using 4-vinylcyclohexene diepoxide (VCD) for 20 consecutive days in 2-month-old females. The CR protocol started at 5 months of age and the treatments lasted for 4 months. The CR females gained less body weight than AL females (p < 0.001) and had lower glycemic curves in response to glucose tolerance test (GTT). The AL estropause females had the highest body weight and body fat, despite having lower food intake. However, the estropause females on 30% CR lost the most body weight and had the lowest amount of body fat compared to all groups. The effect of 30% CR on redox status in fat and liver tissue was similar for cyclic and estropause females. Interestingly, estropause decreased ROS in adipose tissue, while increasing it in the liver. No significant effects of CR on redox status were observed. Chemically induced estropause did not influence the response to 30% CR on glucose tolerance and redox status; however, weight loss was exarcebated compared to cyclic females.

Helpful to Live Healthier? Intermittent Hypoxic/Ischemic Training Benefits Vascular Homeostasis and Lipid Metabolism with Activating SIRT1 Pathways in Overweight/Obese Individuals

INTRODUCTION

The present study aimed to investigate whether and how normobaric intermittent hypoxic training (IHT) or remote ischemic preconditioning (RIPC) plus normoxic training (RNT) has a synergistic protective effect on lipid metabolism and vascular function compared with normoxic training (NT) in overweight or obese adults.

METHODS

A total of 37 overweight or obese adults (36.03 ± 10.48 years) were randomly assigned to 3 groups: NT group (exercise intervention in normoxia), IHT group (exercise intervention in normobaric hypoxic chamber), and RNT group (exercise intervention in normoxia + RIPC twice daily). All participants carried out the same 1-h exercise intervention for a total of 4 weeks, 5 days per week. Physical fitness parameters were evaluated at pre- and postexercise intervention.

RESULTS

After training, all three groups had a significantly decreased body mass index (p < 0.05). The IHT group had reduced body fat percentage, visceral fat mass (p < 0.05), blood pressure (p < 0.01), left ankle-brachial index (ABI), maximal heart rate (HRmax) (p < 0.05), expression of peroxisome proliferator-activated receptor-γ (PPARγ) (p < 0.01) and increased expression of SIRT1 (p < 0.05), VEGF (p < 0.01). The RNT group had lowered waist-to-hip ratio, visceral fat mass, blood pressure (p < 0.05), and HRmax (p < 0.01).

CONCLUSION

IHT could effectively reduce visceral fat mass and improve vascular elasticity in overweight or obese individuals than pure NT with the activation of SIRT1-related pathways. And RNT also produced similar benefits on body composition and vascular function, which were weaker than those of IHT but stronger than NT. Given the convenience and economy of RNT, both intermittent hypoxic and ischemic training have the potential to be successful health promotion strategies for the overweight/obese population.

Molecular Mechanisms of Neuroprotection by Ketone Bodies and Ketogenic Diet in Cerebral Ischemia and Neurodegenerative Diseases

Ketone bodies (KBs), such as acetoacetate and β-hydroxybutyrate, serve as crucial alternative energy sources during glucose deficiency. KBs, generated through ketogenesis in the liver, are metabolized into acetyl-CoA in extrahepatic tissues, entering the tricarboxylic acid cycle and electron transport chain for ATP production. Reduced glucose metabolism and mitochondrial dysfunction correlate with increased neuronal death and brain damage during cerebral ischemia and neurodegeneration. Both KBs and the ketogenic diet (KD) demonstrate neuroprotective effects by orchestrating various cellular processes through metabolic and signaling functions. They enhance mitochondrial function, mitigate oxidative stress and apoptosis, and regulate epigenetic and post-translational modifications of histones and non-histone proteins. Additionally, KBs and KD contribute to reducing neuroinflammation and modulating autophagy, neurotransmission systems, and gut microbiome. This review aims to explore the current understanding of the molecular mechanisms underpinning the neuroprotective effects of KBs and KD against brain damage in cerebral ischemia and neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease.

Editorial for "The Role of Ketogenic Diet in Human Health and Diseases": The Multifaceted Impact of Ketogenic Diets on Health and Disease

The ketogenic diet (KD), characterized by a very low carbohydrate intake and variable protein, fat and calorie intake, has long been in the spotlight for its potential therapeutic applications [...].

Pterostilbene Enhances Thermogenesis and Mitochondrial Biogenesis by Activating the SIRT1/PGC-1α/SIRT3 Pathway to Prevent Western Diet-Induced Obesity

SCOPE

Sirtuin 1/peroxisome proliferator-activated receptor gamma co-activator 1 alpha (SIRT1/PGC-1α) pathway activation is known to promote thermogenesis and mitochondrial biogenesis. Pterostilbene (PSB) and pinostilbene (PIN), the methylated analogs of resveratrol, are potential candidates to enhance thermogenesis and mitochondrial biogenesis.

METHOD AND RESULTS

A model of Western diet-induced obesity in mice is designed. Either PSB or PIN is supplemented in the diet for 16 weeks. Both samples can significantly reduce body weight gain but only PSB can decrease inguinal adipose tissue weight. Besides, both samples can promote lipolysis but only PSB supplementation activates the SIRT1/PGC-1α/SIRT3 pathway to enhance mitochondrial biogenesis and thermogenesis in the inguinal adipose tissue. In addition, although both samples exert a modulatory effect on gut microbiota but significant increments in fecal isobutyric acid, valeric acid, and isovaleric acid are only observed in the PSB group, functioning as gut microbial metabolites.

CONCLUSION

Overall, these findings suggest PSB and PIN as potential candidates for the improvement of obesity and gut microbiota dysbiosis. With its higher stability, PSB exerts a greater effect than PIN by promoting thermogenesis and mitochondrial biogenesis via SIRT1 activation.

1,3-Butanediol Administration Increases β-Hydroxybutyrate Plasma Levels and Affects Redox Homeostasis, Endoplasmic Reticulum Stress, and Adipokine Production in Rat Gonadal Adipose Tissue

Ketone bodies (KBs) are an alternative energy source under starvation and play multiple roles as signaling molecules regulating energy and metabolic homeostasis. The mechanism by which KBs influence visceral white adipose tissue physiology is only partially known, and our study aimed to shed light on the effects they exert on such tissue. To this aim, we administered 1,3-butanediol (BD) to rats since it rapidly enhances β-hydroxybutyrate serum levels, and we evaluated the effect it induces within 3 h or after 14 days of treatment. After 14 days of treatment, rats showed a decrease in body weight gain, energy intake, gonadal-WAT (gWAT) weight, and adipocyte size compared to the control. BD exerted a pronounced antioxidant effect and directed redox homeostasis toward reductive stress, already evident within 3 h after its administration. BD lowered tissue ROS levels and oxidative damage to lipids and proteins and enhanced tissue soluble and enzymatic antioxidant capacity as well as nuclear erythroid factor-2 protein levels. BD also reduced specific mitochondrial maximal oxidative capacity and induced endoplasmic reticulum stress as well as interrelated processes, leading to changes in the level of adipokines/cytokines involved in inflammation, macrophage infiltration into gWAT, adipocyte differentiation, and lipolysis.

Caloric restriction prevents inflammation and insulin dysfunction in middle-aged ovariectomized mice

BACKGROUND

Loss of ovarian function is associated with increased visceral fat. In this study, we aimed to study the effects of caloric restriction (CR) on metabolism in ovariectomized mice.

METHODS AND RESULTS

Female, 8-12-month-old mice were divided into three groups: OVX (ovariectomized mice), OVXR (40% CR) and Sham. CR increased insulin sensitivity and glucose tolerance. AMPK phosphorylation was observed in the liver of OVXR mice. CR also increased hepatic cholesterol and triglyceride levels. The reductions in the level of TBARS in the serum and liver and of H2O2 in the liver of OVXR mice suggested alterations in the redox state of the liver. Although expression of catalase protein was reduced by CR, expression of superoxide dismutase was not altered by CR. Although interleukin IL-6 and IL-10 levels in OVXR mice were similar to those in Sham mice, macrophage infiltration was reduced in OVXR mice. OVXR mice had increased sirtuin1 levels and decreased sirtuin3 levels in the liver.

CONCLUSIONS

In conclusion, CR improved the condition of ovariectomized mice by reducing adiposity and increasing insulin sensitivity and glucose tolerance through a mechanism that may involve AMPK.

Investigating the Link between Ketogenic Diet, NAFLD, Mitochondria, and Oxidative Stress: A Narrative Review

Together with the global rise in obesity and metabolic syndrome, the prevalence of individuals who suffer from nonalcoholic fatty liver disease (NAFLD) has risen dramatically. NAFLD is currently the most common chronic liver disease and includes a continuum of liver disorders from initial fat accumulation to nonalcoholic steatohepatitis (NASH), considered the more severe forms, which can evolve in, cirrhosis, and hepatocellular carcinoma. Common features of NAFLD includes altered lipid metabolism mainly linked to mitochondrial dysfunction, which, as a vicious cycle, aggravates oxidative stress and promotes inflammation and, as a consequence, the progressive death of hepatocytes and the severe form of NAFLD. A ketogenic diet (KD), i.e., a diet very low in carbohydrates (<30 g/die) that induces "physiological ketosis", has been demonstrated to alleviate oxidative stress and restore mitochondrial function. Based on this, the aim of the present review is to analyze the body of evidence regarding the potential therapeutic role of KD in NAFLD, focusing on the interplay between mitochondria and the liver, the effects of ketosis on oxidative stress pathways, and the impact of KD on liver and mitochondrial function.

Intermittent fasting with ketogenic diet: A combination approach for management of chronic diseases

Intermittent Fasting (IF) is the consumption of food and drinks within a defined time, while the ketogenic diet (KD) switches the metabolism from glucose to fats. Continuation of intermittent fasting leads to the generation of ketones, the exact mechanism for a ketogenic diet. This article discusses the types of IF and KD, the monitoring required, and the mechanisms underlying IF and KD, followed by disorders in which the combination strategy could be applied. The strategies for successfully applying combination therapy are included, along with recommendations for the primary care physicians (PCP) which could serve as a handy guide for patient management. This opinion article could serve as the baseline for future clinical studies since there is an utmost need for developing new wholesome strategies for managing chronic disorders.

Ketones and the Heart: Metabolic Principles and Therapeutic Implications

The ketone bodies beta-hydroxybutyrate and acetoacetate are hepatically produced metabolites catabolized in extrahepatic organs. Ketone bodies are a critical cardiac fuel and have diverse roles in the regulation of cellular processes such as metabolism, inflammation, and cellular crosstalk in multiple organs that mediate disease. This review focuses on the role of cardiac ketone metabolism in health and disease with an emphasis on the therapeutic potential of ketosis as a treatment for heart failure (HF). Cardiac metabolic reprogramming, characterized by diminished mitochondrial oxidative metabolism, contributes to cardiac dysfunction and pathologic remodeling during the development of HF. Growing evidence supports an adaptive role for ketone metabolism in HF to promote normal cardiac function and attenuate disease progression. Enhanced cardiac ketone utilization during HF is mediated by increased availability due to systemic ketosis and a cardiac autonomous upregulation of ketolytic enzymes. Therapeutic strategies designed to restore high-capacity fuel metabolism in the heart show promise to address fuel metabolic deficits that underpin the progression of HF. However, the mechanisms involved in the beneficial effects of ketone bodies in HF have yet to be defined and represent important future lines of inquiry. In addition to use as an energy substrate for cardiac mitochondrial oxidation, ketone bodies modulate myocardial utilization of glucose and fatty acids, two vital energy substrates that regulate cardiac function and hypertrophy. The salutary effects of ketone bodies during HF may also include extra-cardiac roles in modulating immune responses, reducing fibrosis, and promoting angiogenesis and vasodilation. Additional pleotropic signaling properties of beta-hydroxybutyrate and AcAc are discussed including epigenetic regulation and protection against oxidative stress. Evidence for the benefit and feasibility of therapeutic ketosis is examined in preclinical and clinical studies. Finally, ongoing clinical trials are reviewed for perspective on translation of ketone therapeutics for the treatment of HF.

Ketone Bodies and Cardiovascular Disease: An Alternate Fuel Source to the Rescue

The increased metabolic activity of the heart as a pump involves a high demand of mitochondrial adenosine triphosphate (ATP) production for its mechanical and electrical activities accomplished mainly via oxidative phosphorylation, supplying up to 95% of the necessary ATP production, with the rest attained by substrate-level phosphorylation in glycolysis. In the normal human heart, fatty acids provide the principal fuel (40-70%) for ATP generation, followed mainly by glucose (20-30%), and to a lesser degree (<5%) by other substrates (lactate, ketones, pyruvate and amino acids). Although ketones contribute 4-15% under normal situations, the rate of glucose use is drastically diminished in the hypertrophied and failing heart which switches to ketone bodies as an alternate fuel which are oxidized in lieu of glucose, and if adequately abundant, they reduce myocardial fat delivery and usage. Increasing cardiac ketone body oxidation appears beneficial in the context of heart failure (HF) and other pathological cardiovascular (CV) conditions. Also, an enhanced expression of genes crucial for ketone break down facilitates fat or ketone usage which averts or slows down HF, potentially by avoiding the use of glucose-derived carbon needed for anabolic processes. These issues of ketone body utilization in HF and other CV diseases are herein reviewed and pictorially illustrated.

The Ketogenic Diet and Neuroinflammation: The Action of Beta-Hydroxybutyrate in a Microglial Cell Line

The ketogenic diet (KD), a diet high in fat and protein but low in carbohydrates, is gaining much interest due to its positive effects, especially in neurodegenerative diseases. Beta-hydroxybutyrate (BHB), the major ketone body produced during the carbohydrate deprivation that occurs in KD, is assumed to have neuroprotective effects, although the molecular mechanisms responsible for these effects are still unclear. Microglial cell activation plays a key role in the development of neurodegenerative diseases, resulting in the production of several proinflammatory secondary metabolites. The following study aimed to investigate the mechanisms by which BHB determines the activation processes of BV2 microglial cells, such as polarization, cell migration and expression of pro- and anti-inflammatory cytokines, in the absence or in the presence of lipopolysaccharide (LPS) as a proinflammatory stimulus. The results showed that BHB has a neuroprotective effect in BV2 cells, inducing both microglial polarization towards an M2 anti-inflammatory phenotype and reducing migratory capacity following LPS stimulation. Furthermore, BHB significantly reduced expression levels of the proinflammatory cytokine IL-17 and increased levels of the anti-inflammatory cytokine IL-10. From this study, it can be concluded that BHB, and consequently the KD, has a fundamental role in neuroprotection and prevention in neurodegenerative diseases, presenting new therapeutic targets.

Ketogenic Diet Increases Serum and White Adipose Tissue SIRT1 Expression in Mice

Overnutrition and its sequelae have become a global concern due to the increasing incidence of obesity and insulin resistance. A ketogenic diet (KD) is widely used as a dietary treatment for metabolic disorders. Sirtuin1 (SIRT1), a metabolic sensor which regulates fat homeostasis, is modulated by dietary interventions. However, the influence of nutritional ketosis on SIRT1 is still debated. We examined the effect of KD on adipose tissue, liver, and serum levels of SIRT1 in mice. Adult C57BL/6J male mice were randomly assigned to two isocaloric dietary groups and fed with either high-fat KD or normal chow (NC) for 4 weeks. Serum SIRT1, beta-hydroxybutyrate (βHB), glucose, and triglyceride levels, as well as SIRT1 expression in visceral (VAT), subcutaneous (SAT), and brown (BAT) adipose tissues, and in the liver, were measured. KD-fed mice showed an increase in serum βHB in parallel with serum SIRT1 (r = 0.732, p = 0.0156), and increased SIRT1 protein expression in SAT and VAT. SIRT1 levels remained unchanged in BAT and in the liver, which developed steatosis. Normal glycemia and triglycerides were observed. Under a KD, serum and white fat phenotypes show higher SIRT1, suggesting that one of the molecular mechanisms underlying a KD's potential benefits on metabolic health involves a synergistic interaction with SIRT1.