The β-hydroxybutyrate receptor HCA2 activates a neuroprotective subset of macrophages

BHBA attenuates endoplasmic reticulum stress-dependent neuroinflammation via the gut-brain axis in a mouse model of heat stress

BACKGROUND

Heat stress (HS) commonly occurs as a severe pathological response when the body's sensible temperature exceeds its thermoregulatory capacity, leading to the development of chronic brain inflammation, known as neuroinflammation. Emerging evidence suggests that HS leads to the disruption of the gut microbiota, whereas abnormalities in the gut microbiota have been demonstrated to affect neuroinflammation. However, the mechanisms underlying the effects of HS on neuroinflammation are poorly studied. Meanwhile, effective interventions have been unclear. β-Hydroxybutyric acid (BHBA) has been found to have neuroprotective and anti-inflammatory properties in previous studies. This study aims to explore the modulatory effects of BHBA on neuroinflammation induced by HS and elucidate the underlying molecular mechanisms.

METHODS

An in vivo and in vitro model of HS was constructed under the precondition of BHBA pretreatment. The modulatory effects of BHBA on HS-induced neuroinflammation were explored and the underlying molecular mechanisms were elucidated by flow cytometry, WB, qPCR, immunofluorescence staining, DCFH-DA fluorescent probe assay, and 16S rRNA gene sequencing of colonic contents.

RESULTS

Heat stress was found to cause gut microbiota disruption in HS mouse models, and TM7 and [Previotella] spp. may be the best potential biomarkers for assessing the occurrence of HS. Fecal microbiota transplantation associated with BHBA effectively reversed the disruption of gut microbiota in HS mice. Moreover, BHBA may inhibit microglia hyperactivation, suppress neuroinflammation (TNF-α, IL-1β, and IL-6), and reduce the expression of cortical endoplasmic reticulum stress (ERS) markers (GRP78 and CHOP) mainly through its modulatory effects on the gut microbiota (TM7, Lactobacillus spp., Ruminalococcus spp., and Prevotella spp.). In vitro experiments revealed that BHBA (1 mM) raised the expression of the ERS marker GRP78, enhanced cellular activity, and increased the generation of reactive oxygen species (ROS) and anti-inflammatory cytokines (IL-10), while also inhibiting HS-induced apoptosis, ROS production, and excessive release of inflammatory cytokines (TNF-α and IL-1β) in mouse BV2 cells.

CONCLUSION

β-Hydroxybutyric acid may be an effective agent for preventing neuroinflammation in HS mice, possibly due to its ability to inhibit ERS and subsequent microglia neuroinflammation via the gut-brain axis. These findings lay the groundwork for future research and development of BHBA as a preventive drug for HS and provide fresh insights into techniques for treating neurological illnesses by modifying the gut microbiota.

Adaptive Metabolic Responses Facilitate Blood-Brain Barrier Repair in Ischemic Stroke via BHB-Mediated Epigenetic Modification of ZO-1 Expression

Adaptive metabolic responses and innate metabolites hold promising therapeutic potential for stroke, while targeted interventions require a thorough understanding of underlying mechanisms. Adiposity is a noted modifiable metabolic risk factor for stroke, and recent research suggests that it benefits neurological rehabilitation. During the early phase of experimental stroke, the lipidomic results showed that fat depots underwent pronounced lipolysis and released fatty acids (FAs) that feed into consequent hepatic FA oxidation and ketogenesis. Systemic supplementation with the predominant ketone beta-hydroxybutyrate (BHB) is found to exert discernible effects on preserving blood-brain barrier (BBB) integrity and facilitating neuroinflammation resolution. Meanwhile, blocking FAO-ketogenesis processes by administration of CPT1α antagonist or shRNA targeting HMGCS2 exacerbated endothelial damage and aggravated stroke severity, whereas BHB supplementation blunted these injuries. Mechanistically, it is unveiled that BHB infusion is taken up by monocarboxylic acid transporter 1 (MCT1) specifically expressed in cerebral endothelium and upregulated the expression of tight junction protein ZO-1 by enhancing local β-hydroxybutyrylation of H3K9 at the promoter of TJP1 gene. Conclusively, an adaptive metabolic mechanism is elucidated by which acute lipolysis stimulates FAO-ketogenesis processes to restore BBB integrity after stroke. Ketogenesis functions as an early metabolic responder to restrain stroke progression, providing novel prospectives for clinical translation.

Multiple recent HCAR2 structures demonstrate a highly dynamic ligand binding and G protein activation mode

A surprisingly clear picture of the allosteric mechanism connecting G protein-coupled receptor agonists with G protein binding-and back - is revealed by a puzzle of thirty novel 3D structures of the hydroxycarboxylic acid receptor 2 (HCAR2) in complex with eight different orthosteric and a single allosteric agonist. HCAR2 is a sensor of β-hydroxybutyrate, niacin and certain anti-inflammatory drugs. Surprisingly, agonists with and without on-target side effects bound very similarly and in a completely occluded orthosteric binding site. Thus, despite the many structures we are still left with a pertinent need to understand the molecular dynamics of this and similar systems.

Protein acylations induced by a ketogenic diet demonstrate diverse patterns depending on organs and differ between histones and global proteins

An essential ketone body, β-hydroxybutyrate (BOHB), plays various roles in physiological regulations via protein acylations such as lysine acetylation and β-hydroxybutyrylation. Here, to understand how BOHB systemically regulates acylations from an overarching perspective, we administered a ketogenic diet to mice to increase BOHB concentration and examined acylations. We found that global acetylation and β-hydroxybutyrylation dramatically increase in various organs except for the brains, where the increase was much smaller than in the other organs. Interestingly, we observe no increase in histone acetylation in the organs where significant global protein acetylation occurs despite a substantial rise in histone β-hydroxybutyrylation. Finally, we compared the transcriptome data of the mice's liver after the ketogenic diet to the public databases, showing that upregulated genes are enriched in those related to histone β-hydroxybutyrylation in starvation. Our data indicate that a ketogenic diet induces diverse patterns of acylations depending on organs and protein localizations, suggesting that different mechanisms regulate acylations and that the ketogenic diet is associated with starvation in terms of protein modifications.

Remote Ischemic Postconditioning-Mediated Neuroprotection against Stroke by Promoting Ketone Body-Induced Ferroptosis Inhibition

Neuronal death resulting from ischemic stroke is the primary cause of adult mortality and disability, and effective neuroprotective agents for poststroke intervention are still lacking. Remote ischemic postconditioning (RIPostC) has demonstrated significant protective effects against ischemia in various organs; however, the specific mechanisms are not fully understood. This study investigated the potential neuroprotective mechanisms of RIPostC in the context of ischemic stroke. Using a rat model of middle cerebral artery occlusion, we found that RIPostC mitigated neurological damage, improved movement in the open-field test, and protected against neuronal apoptosis. In terms of energy metabolism, RIPostC enhanced ATP levels, suppressed lactate content, and increased the production of ketone bodies (KBs). In the ferroptosis assay, RIPostC protected against lipoperoxidation, reversed the reduction of glutathione peroxidase 4 (GPX4), and mitigated the excessive expression of long-chain acyl-CoA synthetase family member 4 (ACSL4). In oxygen-glucose deprivation/reoxygenation-treated HT22 cells, KBs maintained GPX4 levels, suppressed ACSL4 expression, and preserved the mitochondrial cristae number. However, the effect of KBs on the expression of GPX4, ACSL4, and the number of mitochondrial cristae was blocked by erastin. Moreover, both RIPostC and KBs reduced total iron and ferrous ion content by repressing iron transporters both in vitro and in vivo. In conclusion, KBs-induced mitigation of ferroptosis could represent a new therapeutic mechanism for RIPostC in treating stroke.

Ketone Bodies after Cardiac Arrest: A Narrative Review and the Rationale for Use

Cardiac arrest survivors suffer the repercussions of anoxic brain injury, a critical factor influencing long-term prognosis. This injury is characterised by profound and enduring metabolic impairment. Ketone bodies, an alternative energetic resource in physiological states such as exercise, fasting, and extended starvation, are avidly taken up and used by the brain. Both the ketogenic diet and exogenous ketone supplementation have been associated with neuroprotective effects across a spectrum of conditions. These include refractory epilepsy, neurodegenerative disorders, cognitive impairment, focal cerebral ischemia, and traumatic brain injuries. Beyond this, ketone bodies possess a plethora of attributes that appear to be particularly favourable after cardiac arrest. These encompass anti-inflammatory effects, the attenuation of oxidative stress, the improvement of mitochondrial function, a glucose-sparing effect, and the enhancement of cardiac function. The aim of this manuscript is to appraise pertinent scientific literature on the topic through a narrative review. We aim to encapsulate the existing evidence and underscore the potential therapeutic value of ketone bodies in the context of cardiac arrest to provide a rationale for their use in forthcoming translational research efforts.

Dietary Influence on Drug Efficacy: A Comprehensive Review of Ketogenic Diet-Pharmacotherapy Interactions

It is widely acknowledged that the ketogenic diet (KD) has positive physiological effects as well as therapeutic benefits, particularly in the treatment of chronic diseases. Maintaining nutritional ketosis is of utmost importance in the KD, as it provides numerous health advantages such as an enhanced lipid profile, heightened insulin sensitivity, decreased blood glucose levels, and the modulation of diverse neurotransmitters. Nevertheless, the integration of the KD with pharmacotherapeutic regimens necessitates careful consideration. Due to changes in their absorption, distribution, metabolism, or elimination, the KD can impact the pharmacokinetics of various medications, including anti-diabetic, anti-epileptic, and cardiovascular drugs. Furthermore, the KD, which is characterised by the intake of meals rich in fats, has the potential to impact the pharmacokinetics of specific medications with high lipophilicity, hence enhancing their absorption and bioavailability. However, the pharmacodynamic aspects of the KD, in conjunction with various pharmaceutical interventions, can provide either advantageous or detrimental synergistic outcomes. Therefore, it is important to consider the pharmacokinetic and pharmacodynamic interactions that may arise between the KD and various drugs. This assessment is essential not only for ensuring patients' compliance with treatment but also for optimising the overall therapeutic outcome, particularly by mitigating adverse reactions. This highlights the significance and necessity of tailoring pharmacological and dietetic therapies in order to enhance the effectiveness and safety of this comprehensive approach to managing chronic diseases.

Our extended microbiome: The human-relevant metabolites and biology of fermented foods

One of the key modes of microbial metabolism occurring in the gut microbiome is fermentation. This energy-yielding process transforms common macromolecules like polysaccharides and amino acids into a wide variety of chemicals, many of which are relevant to microbe-microbe and microbe-host interactions. Analogous transformations occur during the production of fermented foods, resulting in an abundance of bioactive metabolites. In foods, the products of fermentation can influence food safety and preservation, nutrient availability, and palatability and, once consumed, may impact immune and metabolic status, disease expression, and severity. Human signaling pathways perceive and respond to many of the currently known fermented food metabolites, though expansive chemical novelty remains to be defined. Here we discuss several aspects of fermented food-associated microbes and metabolites, including a condensed history, current understanding of their interactions with hosts and host-resident microbes, connections with commercial probiotics, and opportunities for future research on human health and disease and food sustainability.

Strengthening the basics: acids and bases influence vascular structure and function, tissue perfusion, blood pressure, and human cardiovascular disease

Acids and their conjugate bases accumulate in or dissipate from the interstitial space when tissue perfusion does not match the metabolic demand. Extracellular acidosis dilates most arterial beds, but associated acid-base disturbances-e.g., intracellular acidification and decreases in HCO3- concentration-can also elicit pro-contractile influences that diminish vasodilation and even dominate in some vascular beds to cause vasoconstriction. The ensemble activities of the acid-base-sensitive reactions in vascular smooth muscle and endothelial cells optimize vascular resistance for blood pressure control and direct the perfusion towards active tissue. In this review, we describe the mechanisms of intracellular pH regulation in the vascular wall and discuss how vascular smooth muscle and endothelial cells sense acid-base disturbances. We further deliberate on the functional effects of local acid-base disturbances and their integrated cardiovascular consequences under physiological and pathophysiological conditions. Finally, we address how mutations and polymorphisms in the molecular machinery that regulates pH locally and senses acid-base disturbances in the vascular wall can result in cardiovascular disease. Based on the emerging molecular insight, we propose that targeting local pH-dependent effectors-rather than systemic acid-base disturbances-has therapeutic potential to interfere with the progression and reduce the severity of cardiovascular disease.

Drug resistant epilepsy and ketogenic diet: A narrative review of mechanisms of action

Drug-resistant epilepsy (DRE) poses a significant global challenge, impacting the well-being of patients. Anti-epileptic drugs often fail to effectively control seizures in individuals with DRE. This condition not only leads to persistent seizures but also induces neurochemical imbalances, elevating the risk of sudden unexpected death in epilepsy and comorbidities. Moreover, patients experience mood and personality alterations, educational and vocational setbacks, social isolation, and cognitive impairments. Ketogenic diet has emerged as a valuable therapeutic approach for DRE, having been utilized since 1920. Various types of ketogenic diets have demonstrated efficacy in controlling seizures. By having a multimodal mechanism of action, the ketogenic diet reduces neuronal excitability and the frequency of seizure episodes. In our narrative review, we have initially provided a concise overview of the factors contributing to drug resistance in epilepsy. Subsequently, we have discussed the different available ketogenic diets. We have reviewed the underlying mechanisms through which the ketogenic diet operates. These mechanisms encompass decreased neuronal excitability, enhanced mitochondrial function, alterations in sleep patterns, and modulation of the gut microbiome. Understanding the complex mechanisms by which this diet acts is essential as it is a rigorous diet and requires good compliance. Hence knowledge of the mechanisms may help to advance research on achieving similar therapeutic effects through other less stringent approaches.

Immune-Modulating Effects of Low-Carbohydrate Ketogenic Foods in Healthy Canines

Background

Ketogenic foods limit digestible carbohydrates but contain high fat, and have antioxidant and anti-inflammatory effects as well as improving mitochondrial function. β-Hydroxybutyrate (BHB), 1 of the ketone bodies, reduces the proinflammatory NLR family pyrin domain containing 3 inflammasomes, as well as chemokines in cultures.

Objectives

We assessed the immune-modulating effects of 2 low-carbohydrate (LoCHO) foods varying in protein and fat and compared their effects with a food replete with high-carbohydrate (HiCHO) in healthy canines.

Methods

Dogs were fed control food [HiCHO; ketogenic ratio (KR: 0.46) followed by LoCHO_PROT (KR: 0.97), then LoCHO_FAT (KR: 1.63) or LoCHO_FAT followed by LoCHO_PROT. Each food was fed for 5 wk, with collections in the 5th wk; 15 wk feeding total. Gene expression for circulating inflammatory cytokines from 10 dogs was assessed using the Canine RT2 Profiler polymerase chain reaction array, and fold changes were calculated using the ΔΔCt method.

Results

LoCHO_FAT significantly increased circulating β-hydroxybutyrate compared with both HiCHO and LoCHO_PROT. When compared with HiCHO, there was a significant decrease in several proinflammatory cytokines/chemokines in LoCHO_PROT and LoCHO_FAT groups, including chemokine (C-C motif) ligand (CCL)1, CCL8, CCL13, CCL17, CCL24, chemokine (C-X3-C motif) ligand 1, chemokine (C-X-C motif) receptor 1, Interleukin-10 receptor alpha ((IL)-10RA), IL-1 receptor antagonist, IL-5, and secreted phosphoprotein 1 (all P < 0.05). Interestingly, a subset of inflammatory proteins that decreased in LoCHO_PROT but not in LoCHO_FAT included IL-33, IL-6 receptor, IL-7, IL-8, Nicotinamide phosphoribosyltransferase, and tumor necrosis factor (TNF) receptor superfamily member 11B. In contrast, the decrease in inflammatory markers in LoCHO_FAT, but not in LoCHO_PROT, included complement component 5, granulocyte colony-stimulating factor or G-CSF, interferon-γ, IL-3, IL-10RB, IL-17C, Tumor necrosis factor superfamily (TNFSF)13, TNFSF13B, and TNFSF14. Decreased concentrations of selected cytokines indicate that both low-carbohydrate foods exert an anti-inflammatory effect and provide a strong rationale for testing their efficacy in dogs with inflammatory conditions.

Conclusions

Both LoCHO_PROT and LoCHO_FAT foods might be important as part of immune-modulating therapeutic nutritional strategies to reduce inflammation to maintain health in canines. Our study identifies several inflammatory genes that are reduced when fed ketogenic food that were not previously reported.

Dietary approaches for exploiting metabolic vulnerabilities in cancer

Renewed interest in tumor metabolism sparked an enthusiasm for dietary interventions to prevent and treat cancer. Changes in diet impact circulating nutrient levels in the plasma and the tumor microenvironment, and preclinical studies suggest that dietary approaches, including caloric and nutrient restrictions, can modulate tumor initiation, progression, and metastasis. Cancers are heterogeneous in their metabolic dependencies and preferred energy sources and can be addicted to glucose, fructose, amino acids, or lipids for survival and growth. This dependence is influenced by tumor type, anatomical location, tissue of origin, aberrant signaling, and the microenvironment. This review summarizes nutrient dependencies and the related signaling pathway activations that provide targets for nutritional interventions. We examine popular dietary approaches used as adjuvants to anticancer therapies, encompassing caloric restrictions, including time-restricted feeding, intermittent fasting, fasting-mimicking diets (FMDs), and nutrient restrictions, notably the ketogenic diet. Despite promising results, much of the knowledge on dietary restrictions comes from in vitro and animal studies, which may not accurately reflect real-life situations. Further research is needed to determine the optimal duration, timing, safety, and efficacy of dietary restrictions for different cancers and treatments. In addition, well-designed human trials are necessary to establish the link between specific metabolic vulnerabilities and targeted dietary interventions. However, low patient compliance in clinical trials remains a significant challenge.

Ketone bodies as chemical signals for the immune system

Ketone bodies are short-chain fatty acids produced by the liver during periods of limited glucose availability, such as during fasting or low carbohydrate feeding. Recent studies have highlighted important nonmetabolic functions of the most abundant ketone body, β-hydroxybutyrate (BHB). Notably, many of these functions, including limiting specific sources of inflammation, histone deacetylase inhibition, NFκB inhibition, and GPCR stimulation, are particularly important to consider in immune cells. Likewise, dietary manipulations like caloric restriction or ketogenic diet feeding have been associated with lowered inflammation, improved health outcomes, and improved host defense against infection. However, the underlying mechanisms of the broad benefits of ketosis remain incompletely understood. In this Perspective, we contextualize the current state of the field of nonmetabolic functions of ketone bodies specifically in the immune system and speculate on the molecular explanations and broader physiological significance.

Altered HCAR3 expression may underlying the blunted niacin responses of the psychiatric disorders and the risk of schizophrenia

AIM

Blunted niacin response (BNR) was an endophenotype of schizophrenia, but the underlying mechanism remains unclarified. The objective of this study was to verify whether genes associated with BNR pathway constitute the genetic basis and the pathological mechanism of BNR phenotypic psychiatric patients.

METHODS

Two independent sample sets consisting of 971 subjects were enrolled in this study. A total of 62 variants were genotyped in the discovery set, then the related variants were verified in the verification set. The published PGC GWAS data were used to validate the associations between the variants and psychiatry disorders. RT-PCR analysis, eQTL data, and Dual-Luciferase Reporter experiment were used to investigate the potential molecular mechanisms of the variants underlying BNR.

RESULTS

The results showed that two SNPs, rs56959712 in HCAR2 and rs2454721 in HCAR3 were significantly associated with niacin response. The risk allele T of rs2454721 could affect the niacin responses of psychiatric patients through elevated HCAR3 gene expression. These two genes, especially HCAR3, were significantly associated with the risk of schizophrenia, as identified in this study and verified using the published GWAS data.

CONCLUSION

HCAR3 is a novel schizophrenia susceptibility gene which is significantly associated with blunted niacin response in schizophrenia. In-depth investigation of HCAR3 is of great significance for uncovering the pathogenesis and propose new therapeutic targets for psychiatric disorders, especially for the BNR subgroup patients.

L-Lactate Treatment at 24 h and 48 h after Acute Experimental Stroke Is Neuroprotective via Activation of the L-Lactate Receptor HCA1

Stroke is the main cause for acquired disabilities. Pharmaceutical or mechanical removal of the thrombus is the cornerstone of stroke treatment but can only be administered to a subset of patients and within a narrow time window. Novel treatment options are therefore required. Here we induced stroke by permanent occlusion of the distal medial cerebral artery of wild-type mice and knockout mice for the lactate receptor hydroxycarboxylic acid receptor 1 (HCA1). At 24 h and 48 h after stroke induction, we injected L-lactate intraperitoneal. The resulting atrophy was measured in Nissl-stained brain sections, and capillary density and neurogenesis were measured after immunolabeling and confocal imaging. In wild-type mice, L-lactate treatment resulted in an HCA1-dependent reduction in the lesion volume accompanied by enhanced angiogenesis. In HCA1 knockout mice, on the other hand, there was no increase in angiogenesis and no reduction in lesion volume in response to L-lactate treatment. Nevertheless, the lesion volumes in HCA1 knockout mice-regardless of L-lactate treatment-were smaller than in control mice, indicating a multifactorial role of HCA1 in stroke. Our findings suggest that L-lactate administered 24 h and 48 h after stroke is protective in stroke. This represents a time window where no effective treatment options are currently available.

Ketosis prevents abdominal aortic aneurysm rupture through C-C chemokine receptor type 2 downregulation and enhanced extracellular matrix balance

Abdominal aortic aneurysms (AAAs) are prevalent with aging, and AAA rupture is associated with increased mortality. There is currently no effective medical therapy to prevent AAA rupture. The monocyte chemoattractant protein (MCP-1)/C-C chemokine receptor type 2 (CCR2) axis critically regulates AAA inflammation, matrix-metalloproteinase (MMP) production, and extracellular matrix (ECM) stability. We therefore hypothesized that a diet intervention that can modulate CCR2 axis may therapeutically impact AAA risk of rupture. Since ketone bodies (KBs) can trigger repair mechanisms in response to inflammation, we evaluated whether systemic ketosis in vivo could reduce CCR2 and AAA progression. Male Sprague-Dawley rats underwent surgical AAA formation using porcine pancreatic elastase and received daily β-aminopropionitrile to promote AAA rupture. Rats with AAAs received either a standard diet, ketogenic diet (KD), or exogenous KBs (EKB). Rats receiving KD and EKB reached a state of ketosis and had significant reduction in AAA expansion and incidence of rupture. Ketosis also led to significantly reduced aortic CCR2 content, improved MMP balance, and reduced ECM degradation. Consistent with these findings, we also observed that Ccr2-/- mice have significantly reduced AAA expansion and rupture. In summary, this study demonstrates that CCR2 is essential for AAA expansion, and that its modulation with ketosis can reduce AAA pathology. This provides an impetus for future clinical studies that will evaluate the impact of ketosis on human AAA disease.

The effect of a ketogenic diet on inflammation-related markers: a systematic review and meta-analysis of randomized controlled trials

CONTEXT

Despite the important role of inflammation-related factors on the occurrence of chronic diseases, there is still conflicting evidence about the effects of the ketogenic diet (KD) on these factors.

OBJECTIVE

In order to obtain a better viewpoint, this study aimed to comprehensively investigate the effects of a KD on inflammation-related markers.

DATA SOURCES

To find pertinent randomized controlled trials up to August 2023, databases including PubMed/Medline, Web of Science, Scopus, Cochrane Library, and Embase were searched.

DATA EXTRACTION

This study included all randomized controlled trials investigating the effects of a KD on C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-8, and IL-10 levels. Pooled weighted mean difference (WMD) and 95% confidence intervals (CIs) were achieved by random-effects model analysis for the best estimation of outcomes.

DATA ANALYSIS

Forty-four studies were included in this article. The pooled findings showed that a KD has an effect on lowering TNF-α (WMD: -0.32 pg/mL; 95% CI: -0.55, -0.09; P = 0.007) and IL-6 (WMD: -0.27 pg/mL; 95% CI: -0.52, -0.02; P = 0.036) compared with control groups. However, no significant effect was reported for others inflammation marker-related levels. The results of the subgroup analysis showed that, in trials following the KD for ≤8 weeks and in people aged ≤50 years, the reduction in TNF-α levels was significantly higher than in other groups. In addition, in people with a body mass index greater than 30 kg/m2 compared to a body mass index ≤30 kg/m2, IL-6 levels decreased to a greater extent after receiving the KD.

CONCLUSIONS

Consequently, adherence to a KD appears to improve some markers associated with inflammation, including TNF-α and IL-6.

Immunological dimensions of neuroinflammation and microglial activation: exploring innovative immunomodulatory approaches to mitigate neuroinflammatory progression

The increasing life expectancy has led to a higher incidence of age-related neurodegenerative conditions. Within this framework, neuroinflammation emerges as a significant contributing factor. It involves the activation of microglia and astrocytes, leading to the release of pro-inflammatory cytokines and chemokines and the infiltration of peripheral leukocytes into the central nervous system (CNS). These instances result in neuronal damage and neurodegeneration through activated nucleotide-binding domain and leucine-rich repeat containing (NLR) family pyrin domain containing protein 3 (NLRP3) and nuclear factor kappa B (NF-kB) pathways and decreased nuclear factor erythroid 2-related factor 2 (Nrf2) activity. Due to limited effectiveness regarding the inhibition of neuroinflammatory targets using conventional drugs, there is challenging growth in the search for innovative therapies for alleviating neuroinflammation in CNS diseases or even before their onset. Our results indicate that interventions focusing on Interleukin-Driven Immunomodulation, Chemokine (CXC) Receptor Signaling and Expression, Cold Exposure, and Fibrin-Targeted strategies significantly promise to mitigate neuroinflammatory processes. These approaches demonstrate potential anti-neuroinflammatory effects, addressing conditions such as Multiple Sclerosis, Experimental autoimmune encephalomyelitis, Parkinson's Disease, and Alzheimer's Disease. While the findings are promising, immunomodulatory therapies often face limitations due to Immune-Related Adverse Events. Therefore, the conduction of randomized clinical trials in this matter is mandatory, and will pave the way for a promising future in the development of new medicines with specific therapeutic targets.

Liver Metabolism in Ischemic Stroke

Focal brain damage and neurological deficits are the direct consequences of acute ischemic stroke (AIS). In addition, cerebral ischemia causes systemic alterations across peripheral organs. Dysregulation of the autonomic and endocrine systems as well as the release of brain-derived pro-inflammatory mediators trigger a peripheral immune response and systemic inflammation. As a key metabolic organ, the liver contributes not only to post-stroke immunosuppression but also to stress-induced hyperglycemia. At the same time, increased ketogenesis and glutathione production in the liver are likely to combat inflammation and oxidative stress after AIS. The closely linked lipid metabolism could regulate both glucose and glutathione homeostasis. In addition, increased hepatic very low-density lipoprotein (VLDL) secretion may improve the availability of phospholipids, polyunsaturated fatty acids (PUFAs) and glutathione after AIS. This review provides an overview of recent findings concerning ischemic stroke and the liver and discusses the therapeutic potential of targeting the hepatic metabolism to improve patient outcome after stroke.

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.

Impact of ketogenic diet on cardiovascular disease

OBJECTIVES

A comprehensive review of the current literature was conducted to summarize the potential therapeutic and management roles of ketogenic diet (KD) for cardiovascular disease (CVD).

BACKGROUND

Consensus has not been reached on the optimal diet for individuals with cardiovascular risk factors. KDs are characterized by high-fat, low-carbohydrate, and appropriate protein content, and have gained popularity in recent years in the management of various conditions, including cardiovascular and metabolic diseases.

METHODS

Original research, systematic reviews, and meta-analyses available in the PubMed, Web of Science, and Google Scholar databases were reviewed.

RESULTS

The current body of preclinical and clinical evidence on the efficacy of KD in the management of CVD remains limited. Specific applications of KD seem to suggest a positive impact on management of CVD. However, conflicting results and a lack of precise molecular and biochemical mechanisms of action provide ample opportunity for future investigation.

CONCLUSION

More multidisciplinary studies are needed to determine the true clinical benefit of KD in the management of CVD and so justify its expanded clinical use.

Natural Fatty Acid Guards against Brain Endothelial Cell Death and Microvascular Pathology following Ischemic Insult in the Presence of Acute Hyperglycemia

Ischemic stroke is worsened by the presence of sudden high blood sugar levels, even in individuals without pre-existing diabetes. This elevated glucose concentration hampers the ability of energy-starved brain cells to efficiently use it as a source of energy. Consequently, this leads to the production of abundant amounts of toxic glucose metabolites, which trigger oxidative stress in the brain milieu, particularly in the microvasculature of the brain. A prominent feature of this oxidative stress is the demise of endothelial cells, causing detrimental changes in blood vessels, including a reduction in their vascular diameter, a decreased efficiency of vessel proliferation, and the impaired integrity of tight junctions. These vascular pathologies contributed to an increase in the volume of damaged tissues (infarct), an exacerbation of brain swelling (edema), and a decline in cognitive and motor functions. In a mouse model of ischemic stroke with induced acute hyperglycemia, a naturally occurring saturated fatty acid provides protective cover to the microvasculature by preventing damage related to oxidative stress. Our current research revealed that lauric acid (LA) attenuated infarct volume and reduced brain edema by reducing endothelial cell death, enhancing vessels' diameter, promoting vascular angiogenesis, and stabilizing barrier functions. Animals administered with this natural compound showed a significant reduction in 4-HNE-positive vessels. In conclusion, natural saturated fatty acids help to preserve brain microvascular functions following ischemic insults in the presence of acute hyperglycemia.

A ketogenic diet reduces age-induced chronic neuroinflammation in mice Running title: ketogenic diet and brain inflammaging

Beta-hydroxybutyrate (BHB) is a ketone body synthesized during fasting or strenuous exercise. Our previous study demonstrated that a cyclic ketogenic diet (KD), which induces BHB levels similar to fasting every other week, reduces midlife mortality and improves memory in aging mice. BHB actively regulates gene expression and inflammatory activation through non-energetic signaling pathways. Neither of these activities has been well-characterized in the brain and they may represent mechanisms by which BHB affects brain function during aging. First, we analyzed hepatic gene expression in an aging KD-treated mouse cohort using bulk RNA-seq. In addition to the downregulation of TOR pathway activity, cyclic KD reduces inflammatory gene expression in the liver. We observed via flow cytometry that KD also modulates age-related systemic T cell functions. Next, we investigated whether BHB affects brain cells transcriptionally in vitro. Gene expression analysis in primary human brain cells (microglia, astrocytes, neurons) using RNA-seq shows that BHB causes a mild level of inflammation in all three cell types. However, BHB inhibits the more pronounced LPS-induced inflammatory gene activation in microglia. Furthermore, we confirmed that BHB similarly reduces LPS-induced inflammation in primary mouse microglia and bone marrow-derived macrophages (BMDMs). BHB is recognized as an inhibitor of histone deacetylase (HDAC), an inhibitor of NLRP3 inflammasome, and an agonist of the GPCR Hcar2. Nevertheless, in microglia, BHB's anti-inflammatory effects are independent of these known mechanisms. Finally, we examined the brain gene expression of 12-month-old male mice fed with one-week and one-year cyclic KD. While a one-week KD increases inflammatory signaling, a one-year cyclic KD reduces neuroinflammation induced by aging. In summary, our findings demonstrate that BHB mitigates the microglial response to inflammatory stimuli, like LPS, possibly leading to decreased chronic inflammation in the brain after long-term KD treatment in aging mice.

Transcriptomic and metabolomic insights into the roles of exogenous β-hydroxybutyrate acid for the development of rumen epithelium in young goats

Beta-hydroxybutyric acid (BHBA), as one of the main metabolic ketones in the rumen epithelium, plays critical roles in cellular growth and metabolism. The ketogenic capacity is associated with the maturation of rumen in young ruminants, and the exogenous BHBA in diet may promote the rumen development. However, the effects of exogenous BHBA on rumen remain unknown. This is the first study to investigate the mechanisms of BHBA on gene expression and metabolism of rumen epithelium using young goats as a model through multi-omics techniques. Thirty-two young goats were divided into control, low dose, middle dose, and high dose groups by supplementation of BHBA in starter (0, 3, 6, and 9 g/day, respectively). Results demonstrated the dietary of BHBA promoted the growth performance of young goats and increased width and length of the rumen papilla (P < 0.05). Hub genes in host transcriptome that were positively related to rumen characteristics and BHBA concentration were identified. Several upregulated hub genes including NDUFC1, NDUFB4, NDUFB10, NDUFA11 and NDUFA1 were enriched in the gene ontology (GO) pathway of nicotinamide adenine dinucleotide (NADH) dehydrogenase (ubiquinone) activity, while ATP5ME, ATP5PO and ATP5PF were associated with ATP synthesis. RT-PCR revealed the expression of genes (HMGCS2, BDH1, SLC16A3, etc.) associated with lipolysis increased significantly by BHBA supplementation (P < 0.05). Metabolomics indicated that some metabolites such as glucose, palmitic acid, cortisol and capric acid were also increased (P < 0.05). This study revealed that BHBA promoted rumen development through altering NADH balance and accelerating lipid metabolism, which provides a theoretical guidance for the strategies of gastrointestinal health and development of young ruminants.

[Beneficial effects of ketogenic diet for Alzheimer's disease management]

Alzheimer's disease (AD) is a neurodegenerative disease that affects almost 1 million people in France and 55 million in the world. This pathology is a global health preoccupation because of the lack of efficient curative treatment and the increase of its prevalence. During the last decade, the comprehension of pathophysiological mechanisms involved in AD have been improved. Amyloid plaques and neurofibrillary tangles accumulation are characteristic of Alzheimer's brain patients, accompanied by increased brain inflammation and oxidative stress, impaired cerebral metabolism of glucose and mitochondrial function. Treatment of AD includes different approaches, as pharmacology, psychology support, physiotherapy, and speech therapy. However, these interventions do not have a curative effect, but only compensatory on the disease. Ketogenic diet (KD), a low-carbohydrates and high-fat diet, associated with a medium-chain triglycerides intake (MCTs) might induce benefices for Alzheimer disease patients. Carbohydrate restriction and MCTs promotes the production of ketone bodies from fatty acid degradation. These metabolites replacing glucose, serve the brain as energetic substrates, and induce neuroprotective effects. Such a nutritional support might slow down the disease progression and improve cognitive abilities of patients. This review aims to examine the neuroprotective mechanisms of KD in AD progression and describes the advantages and limitations of KD as a therapeutic strategy.

Reversible histone deacetylase activity catalyzes lysine acylation

Starvation and low carbohydrate diets lead to the accumulation of the ketone body, β-hydroxybutyrate (BHB), whose blood concentrations increase more than 10-fold into the millimolar range. In addition to providing a carbon source, BHB accumulation triggers lysine β-hydroxybutyrylation (Kbhb) of proteins via unknown mechanisms. As with other lysine acylation events, Kbhb marks can be removed by histone deacetylases (HDACs). Here, we report that class I HDACs unexpectedly catalyze protein lysine modification with β-hydroxybutyrate (BHB). Mutational analyses of the HDAC2 active site reveal a shared reliance on key amino acids for classical deacetylation and non-canonical HDAC-catalyzed β-hydroxybutyrylation. Also consistent with reverse HDAC activity, Kbhb formation is driven by mass action and substrate availability. This reverse HDAC activity is not limited to BHB but also extends to multiple short-chain fatty acids. The reversible activity of class I HDACs described here represents a novel mechanism of PTM deposition relevant to metabolically-sensitive proteome modifications.

The effects of ketogenic dietary therapies on sleep: A scoping review

Sleep problems are common in neurological conditions for which ketogenic dietary therapies (KDTs) are recognised as an effective intervention (drug-resistant epilepsy, autism spectrum disorder, and migraine). Given the composite framework of action of ketogenic dietary therapies, the prevalence of sleep disturbance, and the importance of sleep regulation, the present scoping review aimed at identifying and mapping available evidence of the effects of ketogenic dietary therapies on sleep. A comprehensive web-based literature search was performed retrieving publications published to June 2023 using PubMed and Scopus, yielding to 277 records. Twenty papers were finally selected and included in the review. Data were abstracted by independent coders. High variability was identified in study design and sleep outcome evaluation among the selected studies. Several changes in sleep quality and sleep structure under ketogenic dietary therapies were found, namely an improvement of overall sleep quality, improvement in the difficulty falling asleep and nighttime awakenings, improvement in daytime sleepiness and an increase of REM sleep. The relevance and possible physiological explanations of these changes, clinical recommendations, and future directions in the field are discussed.

Lauric acid provides neuroprotection against oxidative stress in mouse model of hyperglycaemic stroke

During ischemic stroke, higher glucose level linked worse outcomes were reported even in patients without pre-existing diabetes. Evidence suggest that such worse stroke outcomes were mainly due to production of reactive, toxic glucose metabolites that expands oxidative damage inside the brain. As a consequence of high oxidative stress, microvasculature structures and tight junctions compromised their functionally, infarct volume expands and brain edema exacerbates. In a mouse model of ischemic stroke with induced acute hyperglycaemia, Lauric acid (LA) as a natural saturated fatty acid demonstrated neuroprotection by attenuating infarct volume and brain edema. In addition, in the ipsilateral hyperglycaemic brain, the LA significantly increased the expression of tight junction representative protein (occludin) as well as anti-oxidative markers; Manganese superoxide dismutase (Mn) SOD, Extracellular superoxide dismutase (Ec-SOD) and nuclear factor-erythroid factor 2-related factor 2 (Nrf2) in the ipsilateral region against hyperglycemic ischemic stroke. LA treated animals showed a significant reduction in the production of lipid peroxidation products (4-HNE) in the microvascular structures, maintained the blood brain barrier (BBB) integrity. LA linked neuroprotective outcomes were further confirmed by behavioral tests, where functional outcomes and motor coordination were improved significantly. Furthermore, LA treatment enhanced food intake, decreased mortality rate, and net body weight loss. Conclusively, LA modulated ischemic insult exacerbated by hyperglycemia and provided neuroprotection.

Context-Dependent Effects of the Ketogenic Diet on Retinal Ganglion Cell Survival and Axonal Regeneration After Optic Nerve Injury

Purpose: There is increasing interest in nonpharmacologic approaches to protect retinal ganglion cells (RGCs) after injury and enhance the efficacy of therapeutic molecules. Accumulating evidence demonstrates neuroprotection by the high-fat low-carbohydrate ketogenic diet (KD) in humans and animal models of neurologic diseases. However, no studies to date have examined whether the KD protects RGCs and promotes axonal regrowth after traumatic injury to the optic nerve (ON) or whether it increases efficacy of experimental proregenerative molecules. In this study, we investigated whether the KD promoted RGC survival and axonal regeneration after ON injury in the presence and absence of neuroprotective Wnt3a ligand. Methods: Adult mice were placed on a KD or control diet before ON crush injury and remained on the diet until the end of the experiment. Nutritional ketosis was confirmed by measuring serum beta-hydroxybutyrate levels. Mice were intravitreally injected with Wnt3a ligand or phosphate-buffered saline (PBS), and RGC survival, function, axonal regeneration, and inflammatory responses were measured. Results: Mice fed the KD showed increased RGC survival and reduced inflammatory cells in PBS-injected mice. Also, mice fed the KD had increased RGC functional responses but not increased RGC numbers in the presence of Wnt3a, indicating that the KD did not enhance the prosurvival effect of Wnt3a. The KD did not promote axonal regeneration in the presence or absence of Wnt3a. Conclusions: The KD has a complex protective effect after ON injury and cotreatment with Wnt3a. This work sets the foundation for studies identifying underlying molecular mechanisms.

Structural basis of hydroxycarboxylic acid receptor signaling mechanisms through ligand binding

Hydroxycarboxylic acid receptors (HCA) are expressed in various tissues and immune cells. HCA2 and its agonist are thus important targets for treating inflammatory and metabolic disorders. Only limited information is available, however, on the active-state binding of HCAs with agonists. Here, we present cryo-EM structures of human HCA2-Gi and HCA3-Gi signaling complexes binding with multiple compounds bound. Agonists were revealed to form a salt bridge with arginine, which is conserved in the HCA family, to activate these receptors. Extracellular regions of the receptors form a lid-like structure that covers the ligand-binding pocket. Although transmembrane (TM) 6 in HCAs undergoes dynamic conformational changes, ligands do not directly interact with amino acids in TM6, suggesting that indirect signaling induces a slight shift in TM6 to activate Gi proteins. Structural analyses of agonist-bound HCA2 and HCA3 together with mutagenesis and molecular dynamics simulation provide molecular insights into HCA ligand recognition and activation mechanisms.

Ketogenic diet and β-Hydroxybutyrate alleviate ischemic brain injury in mice via an IRAKM-dependent pathway

Ketogenic diet (KD) is a classical nonpharmacological therapy that has recently been shown to benefit cerebral ischemia, but the mechanism remains unclear. This study investigated the neuroprotective effects of KD pretreatment and β-hydroxybutyrate (BHB, bioactive product of KD) post-treatment in a mouse model of temporary middle cerebral artery occlusion (tMCAO). Neurological function, infarct volume, as well as inflammatory reactions are evaluated 24 h after ischemia. Results showed that both KD pretreatment or BHB post-treatment improved the Bederson score and Grip test score, reduced infarct volume and the extravasation of IgG, suppressed the over-activation of microglia, and modulated the expression of cytokines. Mechanically, we found that both KD pretreatment or BHB post-treatment significantly stimulated the expression of interleukin-1 receptor-associated kinase M (IRAKM) and then inhibited the nuclear translocation of NF-κB. IRAKM deletion (Irakm-/-) exacerbated tMCAO-induced neurovascular injuries, and aggravated neuroinflammatory response. Moreover, KD pretreatment or BHB post-treatment lost their neuroprotection in the tMCAO-treated Irakm-/- mice. Our results support that KD pretreatment and BHB post-treatment alleviate ischemic brain injury in mice, possibly via an IRAKM-dependent way.

Ketone body 3-hydroxybutyrate elevates cardiac output through peripheral vasorelaxation and enhanced cardiac contractility

The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output and myocardial perfusion without affecting blood pressure in humans, but the cardiovascular sites of action remain obscure. Here, we test the hypothesis in rats that 3-OHB acts directly on the heart to increase cardiac contractility and directly on blood vessels to lower systemic vascular resistance. We investigate effects of 3-OHB on (a) in vivo hemodynamics using echocardiography and invasive blood pressure measurements, (b) isolated perfused hearts in Langendorff systems, and (c) isolated arteries and veins in isometric myographs. We compare Na-3-OHB to equimolar NaCl added to physiological buffers or injection solutions. At plasma concentrations of 2-4 mM in vivo, 3-OHB increases cardiac output (by 28.3±7.8%), stroke volume (by 22.4±6.0%), left ventricular ejection fraction (by 13.3±4.6%), and arterial dP/dtmax (by 31.9±11.2%) and lowers systemic vascular resistance (by 30.6±11.2%) without substantially affecting heart rate or blood pressure. Applied to isolated perfused hearts at 3-10 mM, 3-OHB increases left ventricular developed pressure by up to 26.3±7.4 mmHg and coronary perfusion by up to 20.2±9.5%. Beginning at 1-3 mM, 3-OHB relaxes isolated coronary (EC50=12.4 mM), cerebral, femoral, mesenteric, and renal arteries as well as brachial, femoral, and mesenteric veins by up to 60% of pre-contraction within the pathophysiological concentration range. Of the two enantiomers that constitute racemic 3-OHB, D-3-OHB dominates endogenously; but tested separately, the enantiomers induce similar vasorelaxation. We conclude that increased cardiac contractility and generalized systemic vasorelaxation can explain the elevated cardiac output during 3-OHB administration. These actions strengthen the therapeutic rationale for 3-OHB in heart failure management.

Regulation of adult stem cell function by ketone bodies

Adult stem cells play key roles in tissue homeostasis and regeneration. Recent evidence suggests that dietary interventions can significantly impact adult stem cell function. Some of these effects depend on ketone bodies. Adult stem cells could therefore potentially be manipulated through dietary regimens or exogenous ketone body supplementation, a possibility with significant implications for regenerative medicine. In this review we discuss recent findings of the mechanisms by which ketone bodies could influence adult stem cells, including ketogenesis in adult stem cells, uptake and transport of circulating ketone bodies, receptor-mediated signaling, and changes to cellular metabolism. We also discuss the potential effects of ketone bodies on intracellular processes such as protein acetylation and post-transcriptional control of gene expression. The exploration of mechanisms underlying the effects of ketone bodies on stem cell function reveals potential therapeutic targets for tissue regeneration and age-related diseases and suggests future research directions in the field of ketone bodies and stem cells.

MCT-Induced Ketosis and Fiber in Rheumatoid Arthritis (MIKARA)-Study Protocol and Primary Endpoint Results of the Double-Blind Randomized Controlled Intervention Study Indicating Effects on Disease Activity in RA Patients

Fatty acids, such as medium-chain fatty acids (MCFAs) and short-chain fatty acids (SCFAs), both important components of a normal diet, have been reported to play a role in bone-related diseases such as rheumatoid arthritis (RA). However, the role of medium-chain triglycerides (MCTs) has not been investigated in RA to date. The aim of this study was to investigate the effect of supplementation of regular diet with MCT with and without fiber on disease activity as measured with the SDAI (Simplified Disease Activity Index) in RA patients. A total of 61 RA patients on stable drug treatment were randomly assigned to a twice-daily control regimen or to a twice-daily regimen of a formulation containing medium-chain triglycerides (MCTs) 30 g/day for 8 weeks followed by a second twice-daily regimen of combining MCT (30 g/day) plus fiber (30 g/day) for an additional 8 weeks. The control group received a formulation containing long-chain triglycerides (LCTs) instead of MCTs. The preliminary results showed a significant reduction in SDAI from baseline to week 16 in the test group and a significant increase in β-hydroxybutyrate (BHB) levels, while no improvement in SDAI was observed in the control group.

The proteomic effects of ketone bodies: implications for proteostasis and brain proteinopathies

A growing body of evidence supports the beneficial effects of the ketone bodies (KBs), acetoacetate and β-hydroxybutyrate (BHB), on diverse physiological processes and diseases. Hence, KBs have been suggested as therapeutic tools for neurodegenerative diseases. KBs are an alternative fuel during fasting and starvation as they can be converted to Ac-CoA to produce ATP. A ketogenic diet (KD), enriched in fats and low in carbohydrates, induces KB production in the liver and favors their use in the brain. BHB is the most abundant KB in the circulation; in addition to its role as energy fuel, it exerts many actions that impact the set of proteins in the cell and tissue. BHB can covalently bind to proteins in lysine residues as a new post-translational modification (PTM) named β-hydroxybutyrylation (Kbhb). Kbhb has been identified in many proteins where Kbhb sites can be critical for binding to other proteins or cofactors. Kbhb is mostly found in proteins involved in chromatin structure, DNA repair, regulation of spliceosome, transcription, and oxidative phosphorylation. Histones are the most studied family of proteins with this PTM, and H3K9bhb is the best studied histone mark. Their target genes are mainly related to cell metabolism, chromatin remodeling and the control of circadian rhythms. The role of Kbhb on physiological processes is poorly known, but it might link KB metabolism to cell signaling and genome regulation. BHB also impacts the proteome by influencing proteostasis. This KB can modulate the Unfolded Protein Response (UPR) and autophagy, two processes involved in the maintenance of protein homeostasis through the clearance of accumulated unfolded and damaged proteins. BHB can support proteostasis and regulate the UPR to promote metabolism adaptation in the liver and prevent cell damage in the brain. Also, BHB stimulates autophagy aiding to the degradation of accumulated proteins. Protein aggregation is common to proteinopathies like Alzheimer's (AD) and Parkinson's (PD) diseases, where the KD and BHB treatment have shown favorable effects. In the present review, the current literature supporting the effects of KBs on proteome conformation and proteostasis is discussed, as well as its possible impact on AD and PD.

Efficacy, safety and tolerability of very low-calorie ketogenic diet in obese women with fibromyalgia: a pilot interventional study

Introduction

Obesity can worsen fibromyalgia (FM) and very low-calorie ketogenic diet (VLCKD) is a potential therapeutic option for diseases that share clinical and pathophysiological features with FM. In this pilot interventional study, we investigated the effects of VLCKD in obese women with FM.

Methods

Female patients with FM and a body mass index (BMI) ≥ 30  kg/m² were eligible for VLCKD. The ketogenic phase (T0 to T8) was followed by progressive reintroduction of carbohydrates (T8 to T20). Changes in BMI, Fibromyalgia Impact Questionnaire (FIQ), Hospital Anxiety and Depression Scale (HADS), EuroQol 5D (EQ-5D) and 36-item Short Form Health Survey (SF-36) were evaluated. A change of 14% in FIQ was considered clinically relevant. The longitudinal association between BMI and patient-reported outcomes (PROs) was assessed using generalized estimating equations.

Results

Twenty women were enrolled. Two discontinued the intervention. The mean age of the 18 patients who reached T20 was 51.3  years and mean BMI was 37.2  kg/m². All patients lost weight during the first period of VLCKD and this achievement was maintained at T20. Mean BMI decreased from 37.2  kg/m² at T0 to 34.8  kg/m² at T4, 33.5  kg/m² at T8 and 32.1  kg/m² at T20 (p < 0.001). A significant reduction of mean FIQ from 61.7 at T0 to 37.0 at T4 and to 38.7 at T8 (p < 0.001) was observed and it was maintained at T20 with a mean FIQ of 39.1 (p = 0.002). Similar results were obtained for HADS, EQ-5D and SF-36. Analysing each participant, the reduction of FIQ was clinically meaningful in 16 patients (89%) at T4, in 13 (72%) at T8 and in 14 (78%) at T20. No significant association was observed between change in BMI and improvement of the PROs over time. Adverse effects were mild and transient. No major safety concerns emerged.

Conclusion

These are the first data on the efficacy of VLCKD in FM. All patients achieved improvement in different domains of the disease, which was maintained also after carbohydrate reintroduction. Our results suggest that ketosis might exert beneficial effects in FM beyond the rapid weight loss.

Clinical trial registration

This trial is registered on ClinicalTrials.gov, number NCT05848544.

Modulation of the autophagy-lysosomal pathway and endoplasmic reticulum stress by ketone bodies in experimental models of stroke

Ischemic stroke is a leading cause of disability worldwide. There is no simple treatment to alleviate ischemic brain injury, as thrombolytic therapy is applicable within a narrow time window. During the last years, the ketogenic diet (KD) and the exogenous administration of the ketone body β-hydroxybutyrate (BHB) have been proposed as therapeutic tools for acute neurological disorders and both can reduce ischemic brain injury. However, the mechanisms involved are not completely clear. We have previously shown that the D enantiomer of BHB stimulates the autophagic flux in cultured neurons exposed to glucose deprivation (GD) and in the brain of hypoglycemic rats. Here, we have investigated the effect of the systemic administration of D-BHB, followed by its continuous infusion after middle cerebral artery occlusion (MCAO), on the autophagy-lysosomal pathway and the activation of the unfolded protein response (UPR). Results show for the first time that the protective effect of BHB against MCAO injury is enantiomer selective as only D-BHB, the physiologic enantiomer of BHB, significantly reduced brain injury. D-BHB treatment prevented the cleavage of the lysosomal membrane protein LAMP2 and stimulated the autophagic flux in the ischemic core and the penumbra. In addition, D-BHB notably reduced the activation of the PERK/eIF2α/ATF4 pathway of the UPR and inhibited IRE1α phosphorylation. L-BHB showed no significant effect relative to ischemic animals. In cortical cultures under GD, D-BHB prevented LAMP2 cleavage and decreased lysosomal number. It also abated the activation of the PERK/eIF2α/ATF4 pathway, partially sustained protein synthesis, and reduced pIRE1α. In contrast, L-BHB showed no significant effects. Results suggest that protection elicited by D-BHB treatment post-ischemia prevents lysosomal rupture allowing functional autophagy, preventing the loss of proteostasis and UPR activation.

The Promise of Niacin in Neurology

Niacin (vitamin B3) is an essential nutrient that treats pellagra, and prior to the advent of statins, niacin was commonly used to counter dyslipidemia. Recent evidence has posited niacin as a promising therapeutic for several neurological disorders. In this review, we discuss the biochemistry of niacin, including its homeostatic roles in NAD+ supplementation and metabolism. Niacin also has roles outside of metabolism, largely through engaging hydroxycarboxylic acid receptor 2 (Hcar2). These receptor-mediated activities of niacin include regulation of immune responses, phagocytosis of myelin debris after demyelination or of amyloid beta in models of Alzheimer's disease, and cholesterol efflux from cells. We describe the neurological disorders in which niacin has been investigated or has been proposed as a candidate medication. These are multiple sclerosis, Alzheimer's disease, Parkinson's disease, glioblastoma and amyotrophic lateral sclerosis. Finally, we explore the proposed mechanisms through which niacin may ameliorate neuropathology. While several questions remain, the prospect of niacin as a therapeutic to alleviate neurological impairment is promising.

Stimulation of the Hydroxycarboxylic Acid Receptor 2 With the Ketone Body 3-Hydroxybutyrate and Niacin in Patients With Chronic Heart Failure: Hemodynamic and Metabolic Effects

Background The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output (CO) in patients with heart failure through unknown mechanisms. 3-OHB activates the hydroxycarboxylic acid receptor 2 (HCA₂), which increases prostaglandins and suppresses circulating free fatty acids. We investigated whether the cardiovascular effects of 3-OHB involved HCA₂ activation and if the potent HCA₂-stimulator niacin may increase CO. Methods and Results Twelve patients with heart failure with reduced ejection fraction were included in a randomized crossover study and examined by right heart catheterization, echocardiography, and blood sampling on 2 separate days. On study day 1, patients received aspirin to block the HCA₂ downstream cyclooxygenase enzyme, followed by 3-OHB and placebo infusions in random order. We compared the results with those of a previous study in which patients received no aspirin. On study day 2, patients received niacin and placebo. The primary end point was CO. 3-OHB increased CO (2.3 L/min, P<0.01), stroke volume (19 mL, P<0.01), heart rate (10 bpm, P<0.01), and mixed venous saturation (5%, P<0.01) with preceding aspirin. 3-OHB did not change prostaglandin levels, neither in the ketone/placebo group receiving aspirin nor the previous study cohort. Aspirin did not block 3-OHB-induced changes in CO (P=0.43). 3-OHB decreased free fatty acids by 58% (P=0.01). Niacin increased prostaglandin D₂ levels by 330% (P<0.02) and reduced free fatty acids by 75% (P<0.01) but did not affect CO. Conclusions The acute increase in CO during 3-OHB infusion was not modified by aspirin, and niacin had no hemodynamic effects. These findings show that HCA₂ receptor-mediated effects were not involved in the hemodynamic response to 3-OHB. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04703361.

Neurotrophic effects of intermittent fasting, calorie restriction and exercise: a review and annotated bibliography

In the last decades, important progress has been achieved in the understanding of the neurotrophic effects of intermittent fasting (IF), calorie restriction (CR) and exercise. Improved neuroprotection, synaptic plasticity and adult neurogenesis (NSPAN) are essential examples of these neurotrophic effects. The importance in this respect of the metabolic switch from glucose to ketone bodies as cellular fuel has been highlighted. More recently, calorie restriction mimetics (CRMs; resveratrol and other polyphenols in particular) have been investigated thoroughly in relation to NSPAN. In the narrative review sections of this manuscript, recent findings on these essential functions are synthesized and the most important molecules involved are presented. The most researched signaling pathways (PI3K, Akt, mTOR, AMPK, GSK3β, ULK, MAPK, PGC-1α, NF-κB, sirtuins, Notch, Sonic hedgehog and Wnt) and processes (e.g., anti-inflammation, autophagy, apoptosis) that support or thwart neuroprotection, synaptic plasticity and neurogenesis are then briefly presented. This provides an accessible entry point to the literature. In the annotated bibliography section of this contribution, brief summaries are provided of about 30 literature reviews relating to the neurotrophic effects of interest in relation to IF, CR, CRMs and exercise. Most of the selected reviews address these essential functions from the perspective of healthier aging (sometimes discussing epigenetic factors) and the reduction of the risk for neurodegenerative diseases (Alzheimer's disease, Huntington's disease, Parkinson's disease) and depression or the improvement of cognitive function.

Targeting immunometabolism during cardiorenal injury: roles of conventional and alternative macrophage metabolic fuels

Macrophages play critical roles in mediating and resolving tissue injury as well as tissue remodeling during cardiorenal disease. Altered immunometabolism, particularly macrophage metabolism, is a critical underlying mechanism of immune dysfunction and inflammation, particularly in individuals with underlying metabolic abnormalities. In this review, we discuss the critical roles of macrophages in cardiac and renal injury and disease. We also highlight the roles of macrophage metabolism and discuss metabolic abnormalities, such as obesity and diabetes, which may impair normal macrophage metabolism and thus predispose individuals to cardiorenal inflammation and injury. As the roles of macrophage glucose and fatty acid metabolism have been extensively discussed elsewhere, we focus on the roles of alternative fuels, such as lactate and ketones, which play underappreciated roles during cardiac and renal injury and heavily influence macrophage phenotypes.

Ketone bodies promote stroke recovery via GAT-1-dependent cortical network remodeling

Stroke is a leading cause of adult disability worldwide, and better drugs are needed to promote functional recovery after stroke. Growing evidence suggests the critical role of network excitability during the repair phase for stroke recovery. Here, we show that β-hydroxybutyrate (β-HB), an essential ketone body (KB) component, is positively correlated with improved outcomes in patients with stroke and promotes functional recovery in rodents with stroke during the repair phase. These beneficial effects of β-HB depend on HDAC2/HDAC3-GABA transporter 1 (GAT-1) signaling-mediated enhancement of excitability and phasic GABA inhibition in the peri-infarct cortex and structural and functional plasticity in the ipsilateral cortex, the contralateral cortex, and the corticospinal tract. Together with available clinical approaches to elevate KB levels, our results offer a clinically translatable means to promote stroke recovery. Furthermore, GAT-1 can serve as a pharmacological target for developing drugs to promote functional recovery after stroke.

The Role of a Ketogenic Diet in the Treatment of Dementia in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) shares a common molecular mechanism and underlying pathology with dementia, and studies indicate that dementia is widespread in people with T2DM. Currently, T2DM-induced cognitive impairment is characterized by altered insulin and cerebral glucose metabolism, leading to a shorter life span. Increasing evidence indicates that nutritional and metabolic treatments can possibly alleviate these issues, as there is a lack of efficient preventative and treatment methods. The ketogenic diet (KD) is a very high-fat, low-carbohydrate diet that induces ketosis in the body by producing a fasting-like effect, and neurons in the aged brain are protected from damage by ketone bodies. Moreover, the creation of ketone bodies may improve brain neuronal function, decrease inflammatory expression and reactive oxygen species (ROS) production, and restore neuronal metabolism. As a result, the KD has drawn attention as a potential treatment for neurological diseases, such as T2DM-induced dementia. This review aims to examine the role of the KD in the prevention of dementia risk in T2DM patients and to outline specific aspects of the neuroprotective effects of the KD, providing a rationale for the implementation of dietary interventions as a therapeutic strategy for T2DM-induced dementia in the future.

α-Tocopherol Protects Lipopolysaccharide-Activated BV2 Microglia

Microglia, the resident macrophage-like population in the central nervous system, play a crucial role in the pathogenesis of many neurodegenerative disorders by triggering an inflammatory response that leads to neuronal death. Neuroprotective compounds to treat or prevent neurodegenerative diseases are a new field of study in modern medicine. Microglia are activated in response to inflammatory stimuli. The pathogenesis of various neurodegenerative diseases is closely related to the constant activation of microglia due to their fundamental role as a mediator of inflammation in the brain environment. α-Tocopherol, also known as vitamin E, is reported to possess potent neuroprotective effects. The goal of this study was to investigate the biological effects of vitamin E on BV2 microglial cells, as a possible neuroprotective and anti-inflammatory agent, following stimulation with lipopolysaccharide (LPS). The results showed that the pre-incubation of microglia with α-tocopherol can guarantee neuroprotective effects during microglial activation induced by LPS. α-Tocopherol preserved the branched morphology typical of microglia in a physiological state. It also reduced the migratory capacity; the production of pro-inflammatory and anti-inflammatory cytokines such as TNF-α and IL-10; and the activation of receptors such as TRL4 and CD40, which modulate the PI3K-Akt signaling pathway. The results of this study require further insights and research, but they present new scenarios for the application of vitamin E as an antioxidant for the purpose of greater neuroprotection in vivo for the prevention of possible neurodegenerative diseases.

Emerging roles of GPR109A in regulation of neuroinflammation in neurological diseases and pain

Neuroinflammation plays a critical role in the pathological process of multiple neurological disorders and pathological pain conditions. GPR109A, a Gi protein-coupled receptor, has emerged as an important therapeutic target for controlling inflammation in various tissues and organs. In this review, we summarized current data about the role of GPR109A in neuroinflammation. Specifically, we focused on the pharmacological features of GPR109A and signaling pathways used by GPR109A to ameliorate neuroinflammation and symptoms in Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, and pathological pain conditions.

Activation of HCA2 regulates microglial responses to alleviate neurodegeneration in LPS-induced in vivo and in vitro models

BACKGROUND

Previous studies have shown a close association between an altered immune system and Parkinson's disease (PD). Neuroinflammation inhibition may be an effective measure to prevent PD. Recently, numerous reports have highlighted the potential of hydroxy-carboxylic acid receptor 2 (HCA2) in inflammation-related diseases. Notably, the role of HCA2 in neurodegenerative diseases is also becoming more widely known. However, its role and exact mechanism in PD remain to be investigated. Nicotinic acid (NA) is one of the crucial ligands of HCA2, activating it. Based on such findings, this study aimed to examine the effect of HCA2 on neuroinflammation and the role of NA-activated HCA2 in PD and its underlying mechanisms.

METHODS

For in vivo studies, 10-week-old male C57BL/6 and HCA2^-/- mice were injected with LPS in the substantia nigra (SN) to construct a PD model. The motor behavior of mice was detected using open field, pole-climbing and rotor experiment. The damage to the mice's dopaminergic neurons was detected using immunohistochemical staining and western blotting methods. In vitro, inflammatory mediators (IL-6, TNF-α, iNOS and COX-2) and anti-inflammatory factors (Arg-1, Ym-1, CD206 and IL-10) were detected using RT-PCR, ELISA and immunofluorescence. Inflammatory pathways (AKT, PPARγ and NF-κB) were delineated by RT-PCR and western blotting. Neuronal damage was detected using CCK8, LDH, and flow cytometry assays.

RESULTS

HCA2^-/- increases mice susceptibility to dopaminergic neuronal injury, motor deficits, and inflammatory responses. Mechanistically, HCA2 activation in microglia promotes anti-inflammatory microglia and inhibits pro-inflammatory microglia by activating AKT/PPARγ and inhibiting NF-κB signaling pathways. Further, HCA2 activation in microglia attenuates microglial activation-mediated neuronal injury. Moreover, nicotinic acid (NA), a specific agonist of HCA2, alleviated dopaminergic neuronal injury and motor deficits in PD mice by activating HCA2 in microglia in vivo.

CONCLUSIONS

Niacin receptor HCA2 modulates microglial phenotype to inhibit neurodegeneration in LPS-induced in vivo and in vitro models.

Targeting immunometabolism against acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening conditions triggered by multiple intra- and extra-pulmonary injury factors, characterized by complicated molecular mechanisms and high mortality. Great strides have been made in the field of immunometabolism to clarify the interplay between intracellular metabolism and immune function in the past few years. Emerging evidence unveils the crucial roles of immunometabolism in inflammatory response and ALI. During ALI, both macrophages and lymphocytes undergo robust metabolic reprogramming and discrete epigenetic changes after activated. Apart from providing ATP and biosynthetic precursors, these metabolic cellular reactions and processes in lung also regulate inflammation and immunity.In fact, metabolic reprogramming involving glucose metabolism and fatty acidoxidation (FAO) acts as a double-edged sword in inflammatory response, which not only drives inflammasome activation but also elicits anti-inflammatory response. Additionally, the features and roles of metabolic reprogramming in different immune cells are not exactly the same. Here, we outline the evidence implicating how adverse factors shape immunometabolism in differentiation types of immune cells during ALI and summarize key proteins associated with energy expenditure and metabolic reprogramming. Finally, novel therapeutic targets in metabolic intermediates and enzymes together with current challenges in immunometabolism against ALI were discussed.

Ketogenic Diet as a Promising Non-Drug Intervention for Alzheimer’s Disease: Mechanisms and Clinical Implications

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that is mainly characterized by cognitive deficits. Although many studies have been devoted to developing disease-modifying therapies, there has been no effective therapy until now. However, dietary interventions may be a potential strategy to treat AD. The ketogenic diet (KD) is a high-fat and low-carbohydrate diet with adequate protein. KD increases the levels of ketone bodies, providing an alternative energy source when there is not sufficient energy supply because of impaired glucose metabolism. Accumulating preclinical and clinical studies have shown that a KD is beneficial to AD. The potential underlying mechanisms include improved mitochondrial function, optimization of gut microbiota composition, and reduced neuroinflammation and oxidative stress. The review provides an update on clinical and preclinical research on the effects of KD or medium-chain triglyceride supplementation on symptoms and pathophysiology in AD. We also detail the potential mechanisms of KD, involving amyloid and tau proteins, neuroinflammation, gut microbiota, oxidative stress, and brain metabolism. We aimed to determine the function of the KD in AD and outline important aspects of the mechanism, providing a reference for the implementation of the KD as a potential therapeutic strategy for AD.

Ketosis Prevents Abdominal Aortic Aneurysm Rupture Through CCR2 Downregulation and Enhanced MMP Balance

Abdominal aortic aneurysms (AAAs) are common in aging populations, and AAA rupture is associated with high morbidity and mortality. There is currently no effective medical preventative therapy for AAAs to avoid rupture. It is known that the monocyte chemoattractant protein (MCP-1) / C-C chemokine receptor type 2 (CCR2) axis critically regulates AAA tissue inflammation, matrix-metalloproteinase (MMP) production, and in turn extracellular matrix (ECM) stability. However, therapeutic modulation of the CCR2 axis for AAA disease has so far not been accomplished. Since ketone bodies (KBs) are known to trigger repair mechanisms in response to vascular tissue inflammation, we evaluated whether systemic in vivo ketosis can impact CCR2 signaling, and therefore impact AAA expansion and rupture. To evaluate this, male Sprague-Dawley rats underwent surgical AAA formation using porcine pancreatic elastase (PPE), and received daily β-aminopropionitrile (BAPN) to promote AAA rupture. Animals with formed AAAs received either a standard diet (SD), ketogenic diet (KD), or exogenous KB supplements (EKB). Animals that received KD and EKB reached a state of ketosis, and had significantly reduced AAA expansion and incidence of rupture. Ketosis also led to significantly reduced CCR2, inflammatory cytokine content, and infiltrating macrophages in AAA tissue. Additionally, animals in ketosis had improved balance in aortic wall matrix-metalloproteinase (MMP), reduced extracellular matrix (ECM) degradation, and higher aortic media Collagen content. This study demonstrates that ketosis plays an important therapeutic role in AAA pathobiology, and provides the impetus for future studies investigating the role of ketosis as a preventative strategy for individuals with AAAs.

Effect of the Ketone Body, D-β-Hydroxybutyrate, on Sirtuin2-Mediated Regulation of Mitochondrial Quality Control and the Autophagy-Lysosomal Pathway

Mitochondrial activity and quality control are essential for neuronal homeostasis as neurons rely on glucose oxidative metabolism. The ketone body, D-β-hydroxybutyrate (D-BHB), is metabolized to acetyl-CoA in brain mitochondria and used as an energy fuel alternative to glucose. We have previously reported that D-BHB sustains ATP production and stimulates the autophagic flux under glucose deprivation in neurons; however, the effects of D-BHB on mitochondrial turnover under physiological conditions are still unknown. Sirtuins (SIRTs) are NAD⁺-activated protein deacetylases involved in the regulation of mitochondrial biogenesis and mitophagy through the activation of transcription factors FOXO1, FOXO3a, TFEB and PGC1α coactivator. Here, we aimed to investigate the effect of D-BHB on mitochondrial turnover in cultured neurons and the mechanisms involved. Results show that D-BHB increased mitochondrial membrane potential and regulated the NAD⁺/NADH ratio. D-BHB enhanced FOXO1, FOXO3a and PGC1α nuclear levels in an SIRT2-dependent manner and stimulated autophagy, mitophagy and mitochondrial biogenesis. These effects increased neuronal resistance to energy stress. D-BHB also stimulated the autophagic-lysosomal pathway through AMPK activation and TFEB-mediated lysosomal biogenesis. Upregulation of SIRT2, FOXOs, PGC1α and TFEB was confirmed in the brain of ketogenic diet (KD)-treated mice. Altogether, the results identify SIRT2, for the first time, as a target of D-BHB in neurons, which is involved in the regulation of autophagy/mitophagy and mitochondrial quality control.