The activation of retinal HCA2 receptors by systemic beta-hydroxybutyrate inhibits diabetic retinal damage through reduction of endoplasmic reticulum stress and the NLRP3 inflammasome

Intermittent fasting and neurodegenerative diseases: Molecular mechanisms and therapeutic potential

Neurodegenerative disorders are straining public health worldwide. During neurodegenerative disease progression, aberrant neuronal network activity, bioenergetic impairment, adaptive neural plasticity impairment, dysregulation of neuronal Ca2+ homeostasis, oxidative stress, and immune inflammation manifest as characteristic pathological changes in the cellular milieu of the brain. There is no drug for the treatment of neurodegenerative disorders, and therefore, strategies/treatments for the prevention or treatment of neurodegenerative disorders are urgently needed. Intermittent fasting (IF) is characterized as an eating pattern that alternates between periods of fasting and eating, requiring fasting durations that vary depending on the specific protocol implemented. During IF, depletion of liver glycogen stores leads to the production of ketone bodies from fatty acids derived from adipocytes, thereby inducing an altered metabolic state accompanied by cellular and molecular adaptive responses within neural networks in the brain. At the cellular level, adaptive responses can promote the generation of synapses and neurons. At the molecular level, IF triggers the activation of associated transcription factors, thereby eliciting the expression of protective proteins. Consequently, this regulatory process governs central and peripheral metabolism, oxidative stress, inflammation, mitochondrial function, autophagy, and the gut microbiota, all of which contribute to the amelioration of neurodegenerative disorders. Emerging evidence suggests that weight regulation significantly contributes to the neuroprotective effects of IF. By alleviating obesity-related factors such as blood-brain barrier dysfunction, neuroinflammation, and β-amyloid accumulation, IF enhances metabolic flexibility and insulin sensitivity, further supporting its potential in mitigating neurodegenerative disorders. The present review summarizes animal and human studies investigating the role and underlying mechanisms of IF in physiology and pathology, with an emphasis on its therapeutic potential. Furthermore, we provide an overview of the cellular and molecular mechanisms involved in regulating brain energy metabolism through IF, highlighting its potential applications in neurodegenerative disorders. Ultimately, our findings offer novel insights into the preventive and therapeutic applications of IF for neurodegenerative disorders.

DAG-MAG-ΒHB: A Novel Ketone Diester Modulates NLRP3 Inflammasome Activation in Microglial Cells in Response to Beta-Amyloid and Low Glucose AD-like Conditions

BACKGROUND

A neuroinflammatory disease such as Alzheimer's disease, presents a significant challenge in neurotherapeutics, particularly due to the complex etiology and allostatic factors, referred to as CNS stressors, that accelerate the development and progression of the disease. These CNS stressors include cerebral hypo-glucose metabolism, hyperinsulinemia, mitochondrial dysfunction, oxidative stress, impairment of neuronal autophagy, hypoxic insults and neuroinflammation. This study aims to explore the efficacy and safety of DAG-MAG-ΒHB, a novel ketone diester, in mitigating these risk factors by sustaining therapeutic ketosis, independent of conventional metabolic pathways.

METHODS

We evaluated the intestinal absorption of DAG-MAG-ΒHB and the metabolic impact in human microglial cells. Utilizing the HMC3 human microglia cell line, we examined the compound's effect on cellular viability, Acetyl-CoA and ATP levels, and key metabolic enzymes under hypoglycemia. Additionally, we assessed the impact of DAG-AG-ΒHB on inflammasome activation, mitochondrial activity, ROS levels, inflammation and phagocytic rates.

RESULTS

DAG-MAG-ΒHB showed a high rate of intestinal absorption and no cytotoxic effect. In vitro, DAG-MAG-ΒHB enhanced cell viability, preserved morphological integrity, and maintained elevated Acetyl-CoA and ATP levels under hypoglycemic conditions. DAG-MAG-ΒHB increased the activity of BDH1 and SCOT, indicating ATP production via a ketolytic pathway. DAG-MAG-ΒHB showed remarkable resilience against low glucose condition by inhibiting NLRP3 inflammasome activation.

CONCLUSIONS

In summary, DAG-MAG-ΒHB emerges as a promising treatment for neuroinflammatory conditions. It enhances cellular health under varying metabolic states and exhibits neuroprotective properties against low glucose conditions. These attributes indicate its potential as an effective component in managing neuroinflammatory diseases, addressing their complex progression.

Exogenous Ketones in Cardiovascular Disease and Diabetes: From Bench to Bedside

Ketone bodies are molecules produced from fatty acids in the liver that act as energy carriers to peripheral tissues when glucose levels are low. Carbohydrate- and calorie-restricted diets, known to increase the levels of circulating ketone bodies, have attracted significant attention in recent years due to their potential health benefits in several diseases. Specifically, increasing ketones through dietary modulation has been reported to be beneficial for cardiovascular health and to improve glucose homeostasis and insulin resistance. Interestingly, although excessive production of ketones may lead to life-threatening ketoacidosis in diabetic patients, mounting evidence suggests that modest levels of ketones play adaptive and beneficial roles in pancreatic beta cells, although the exact mechanisms are still unknown. Of note, Sodium-Glucose Transporter 2 (SGLT2) inhibitors have been shown to increase the levels of beta-hydroxybutyrate (BHB), the most abundant ketone circulating in the human body, which may play a pivotal role in mediating some of their protective effects in cardiovascular health and diabetes. This systematic review provides a comprehensive overview of the scientific literature and presents an analysis of the effects of ketone bodies on cardiovascular pathophysiology and pancreatic beta cell function. The evidence from both preclinical and clinical studies indicates that exogenous ketones may have significant beneficial effects on both cardiomyocytes and pancreatic beta cells, making them intriguing candidates for potential cardioprotective therapies and to preserve beta cell function in patients with diabetes.

A ketogenic diet alleviates the apoptosis of granulosa cells by inhibiting the activation of cGAS-STING signaling pathway in PCOS mice

BACKGROUND

Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility. The ketogenic diet (KD), a diet high in fat and low in carbohydrates, has been applied clinically for the treatment of obese women with PCOS. We have previously demonstrated that KD improved the reproductive phenotype in an androgen-induced PCOS mouse model, yet the underlying molecular mechanisms remain largely unclear. The aim of the present study was to investigate the effect of KD on the reproductive phenotype of a letrozole-induced PCOS mouse model.

METHODS

Female C57BL/6N mice were divided into three groups, designated control, letrozole, and letrozole + KD groups. Mice of control and letrozole groups were fed the control diet, whereas letrozole + KD mice were fed a KD with 89.9% (kcal) fat for 3 weeks after the PCOS mouse model was generated. β-hydroxybutyrate (BHB), the most abundant ketone body in the body, was used to treat KGN cells with testosterone (T) to simulate the KD effect on PCOS mouse ovaries in vitro.

RESULTS

Our data showed that KD treatment significantly increased blood ketone levels and reduced body weight. Ovarian functions were improved in some letrozole + KD mice. Results from in vitro experiments indicated mitochondrial damage owing to high T levels, which resulted in the leakage of cytochrome C and mitochondrial DNA into the cytosol and thus induced the activation of the intracellular caspase cascade and the cGAS-STING-NF-κB pathway, leading to granulosa cell inflammation and apoptosis. BHB exhibited certain protective effects on mitochondria of T-treated KGN cells via inhibiting the cGAS-STING pathway. Moreover, the cGAS-STING pathway was activated in ovaries of letrozole mice and was down-regulated in letrozole + KD mice.

CONCLUSION

These findings, for the first time, revealed that hyperandrogenism induced ovarian dysfunction possibly through activation of the cGAS-STING pathway, which could be partially inhibited by ketone bodies produced from KD administration.

European Association for the Study of Obesity (EASO) Position Statement on Medical Nutrition Therapy for the Management of Individuals with Overweight or Obesity and Cancer

Obesity, a prevalent and multifactorial disease, is linked to a range of metabolic abnormalities, including insulin resistance, dyslipidemia, and chronic inflammation. These imbalances not only contribute to cardiometabolic diseases but also play a significant role in cancer pathogenesis. The rising prevalence of obesity underscores the need to investigate dietary strategies for effective weight management for individuals with overweight or obesity and cancer. This European Society for the Study of Obesity (EASO) position statement aimed to summarize current evidence on the role of obesity in cancer and to provide insights on the major nutritional interventions, including the Mediterranean diet (MedDiet), the ketogenic diet (KD), and the intermittent fasting (IF), that should be adopted to manage individuals with overweight or obesity and cancer. The MedDiet, characterized by high consumption of plant-based foods and moderate intake of olive oil, fish, and nuts, has been associated with a reduced cancer risk. The KD and the IF are emerging dietary interventions with potential benefits for weight loss and metabolic health. KD, by inducing ketosis, and IF, through periodic fasting cycles, may offer anticancer effects by modifying tumor metabolism and improving insulin sensitivity. Despite the promising results, current evidence on these dietary approaches in cancer management in individuals with overweight or obesity is limited and inconsistent, with challenges including variability in adherence and the need for personalized dietary plans.

Inhibition of CYP1A1 expression enhances diabetic wound healing by modulating inflammation and oxidative stress in a rat model

OBJECTIVE

Wound therapies utilizing gene delivery to the skin offer considerable promise owing to their localized treatment benefits and straightforward application. This study investigated the impact of skin electroporation of CYP1A1 shRNA lentiviral particles on diabetic wound healing in a streptozotocin (STZ)-induced rat model.

METHODS

Male Sprague Dawley (SD) rats were made diabetic by injecting STZ and subsequently creating foot skin wounds. The rats were randomly divided into four groups: normal, diabetic foot ulcers (DFU), DFU + control shRNA (electroporation of control shRNA lentiviral particles), and DFU + CYP1A1 shRNA (electroporation of CYP1A1 shRNA lentiviral particles). Wound healing progress was monitored at multiple time points (0, 1, 3, 5, 7, 10, 14 days). On day 14, wound tissue specimens were collected for histological examination. Wound samples collected at days 7 and 14 were used for gene expression analysis via qRT-PCR, assessment of CYP1A1 protein levels using western blotting, and evaluation of oxidative stress markers.

RESULTS

Treatment with CYP1A1 shRNA significantly enhanced diabetic wound healing rates compared to untreated controls over the observation period. Histological analysis revealed improved wound characteristics in the CYP1A1 shRNA-treated group, including enhanced epithelial regeneration, reduced inflammation, and increased collagen deposition, indicative of improved tissue repair. Furthermore, suppression of CYP1A1 corresponded with decreased expression levels of pro-inflammatory cytokines (interleukin-1β, tumor necrosis factor-α, and interleukin-6) and diminished oxidative stress markers (malondialdehyde, superoxide dismutase) within wound tissues.

CONCLUSION

Targeted suppression of CYP1A1 represents a promising therapeutic strategy to enhance diabetic wound healing by modulating inflammation and oxidative stress.

Therapeutic potential of the ketogenic diet: A metabolic switch with implications for neurological disorders, the gut-brain axis, and cardiovascular diseases

The Ketogenic Diet (KD) is a dietary regimen that is low in carbohydrates, high in fats, and contains adequate protein. It is designed to mimic the metabolic state of fasting. This diet triggers the production of ketone bodies through a process known as ketosis. The primary objective of KD is to induce and sustain ketosis, which has been associated with numerous health benefits. Recent research has uncovered promising therapeutic potential for KD in the treatment of various diseases. This includes evidence of its effectiveness as a dietary strategy for managing intractable epilepsy, a form of epilepsy that is resistant to medication. We are currently assessing the efficacy and safety of KD through laboratory and clinical studies. This review focuses on the anti-inflammatory properties of the KD and its potential benefits for neurological disorders and the gut-brain axis. We also explore the existing literature on the potential effects of KD on cardiac health. Our aim is to provide a comprehensive overview of the current knowledge in these areas. Given the encouraging preliminary evidence of its therapeutic effects and the growing understanding of its mechanisms of action, randomized controlled trials are warranted to further explore the rationale behind the clinical use of KD. These trials will ultimately enhance our understanding of how KD functions and its potential benefits for various health conditions. We hope that our research will contribute to the body of knowledge in this field and provide valuable insights for future studies.

Developing poly(ethylene glycol)-b-poly(β-hydroxybutyrate)-based self-assembling prodrug for the management of cisplatin-induced acute kidney injury

Although β-hydroxybutyrate (BHB), one of the endogenous body ketones, possesses high bioactivities, it is rapidly consumed, metabolized, and eliminated from the body. In this study, we designed new self-assembling nanoparticles that sustainably released BHB to improve bioavailability and evaluated their efficacy in in vivo experiments using rodent animal models. Since poly(β-hydroxybutyrate) [poly(BHB)] is regarded as a polymeric prodrug that is hydrolyzed by endogenous enzymes and releases BHB in a sustained manner, our idea was to engineer hydrophobic poly(BHB) in one of the segments in the amphiphilic block copolymer, of which self-assembles in water to form nanoparticles of tens of nanometers in size (abbreviated as NanoBHB). Here, methoxy-poly(ethylene glycol) was employed as the hydrophilic segment of the block copolymer to stabilize the nanoparticles in aqueous environments, thus enabling NanoBHBs to be administrable both orally and through injection. Experimental results showed that NanoBHB has low toxicity and releases free BHB for an extended period in vitro and in vivo. Moreover, NanoBHB exhibits superior nephroprotective effects in cisplatin-induced acute kidney injury mouse models compared to low-molecular-weight (LMW) sodium BHB, suggesting the potential of NanoBHB as a sustainable release formulation to supply BHB for medicinal applications.

Spatial Proteomics Reveals Alcohol-Induced Damages to the Crypts and Villi of the Mouse Small Intestine

Alcohol consumption perturbs the gut immune barrier and ultimately results in alcoholic liver diseases, but little is known about how immune-related cells in the gut are perturbed in this process. In this study, we employed laser capture microdissection and a label-free proteomics approach to investigate the consequences of alcohol exposure to the proteomes of crypts and villi in the proximal small intestine. Intestinal tissues from alcohol-fed and pair-fed mice were microdissected to selectively capture cells in the crypts and villi regions, followed by one-pot protein digestion and data-independent LC-MS/MS analysis. We successfully identified over 3000 proteins from each of the crypt or villi regions equivalent to ∼3000 cells. Analysis of alcohol-treated tissues indicated an enhanced alcohol metabolism and reduced levels of α-defensins in crypts, alongside increased lipid metabolism and apoptosis in villi. Immunofluorescence imaging further corroborated the proteomic findings. Our work provides a detailed profiling of the proteomic changes in the compartments of the mouse small intestine and aids in molecular-level understanding of alcohol-induced tissue damage.

The therapeutic potential of ketones in cardiometabolic disease: impact on heart and skeletal muscle

β-Hydroxybutyrate (βOHB) is the major ketone in the body, and it is recognized as a metabolic energy source and an important signaling molecule. While ketone oxidation is essential in the brain during prolonged fasting/starvation, other organs such as skeletal muscle and the heart also use ketones as metabolic substrates. Additionally, βOHB-mediated molecular signaling events occur in heart and skeletal muscle cells, and via metabolism and/or signaling, ketones may contribute to optimal skeletal muscle health and cardiac function. Of importance, when the use of ketones for ATP production and/or as signaling molecules becomes disturbed in the presence of underlying obesity, type 2 diabetes, and/or cardiovascular diseases, these changes may contribute to cardiometabolic disease. As a result of these disturbances in cardiometabolic disease, multiple approaches have been used to elevate circulating ketones with the goal of optimizing either ketone metabolism or ketone-mediated signaling. These approaches have produced significant improvements in heart and skeletal muscle during cardiometabolic disease with a wide range of benefits that include improved metabolism, weight loss, better glycemic control, improved cardiac and vascular function, as well as reduced inflammation and oxidative stress. Herein, we present the evidence that indicates that ketone therapy could be used as an approach to help treat cardiometabolic diseases by targeting cardiac and skeletal muscles.

Impact of fasting & ketogenic interventions on the NLRP3 inflammasome: A narrative review

Overactivation of the NLRP3 inflammasome is implicated in chronic low-grade inflammation associated with various disease states, including obesity, type 2 diabetes, atherosclerosis, Alzheimer's disease, and Parkinson's disease. Emerging evidence, mostly from cell and animal models of disease, supports a role for ketosis in general, and the main circulating ketone body beta-hydroxybutyrate (BHB) in particular, in reducing NLRP3 inflammasome activation to improve chronic inflammation. As a result, interventions that can induce ketosis (e.g., fasting, intermittent fasting, time-restricted feeding/eating, very low-carbohydrate high-fat ketogenic diets) and/or increase circulating BHB (e.g., exogenous ketone supplementation) have garnered increasing interest for their therapeutic potential. The purpose of the present review is to summarize our current understanding of the literature on how ketogenic interventions impact the NLRP3 inflammasome across human, rodent and cell models. Overall, there is convincing evidence that ketogenic interventions, likely acting through multiple interacting mechanisms in a cell-, disease- and context-specific manner, can reduce NLRP3 inflammasome activation. The evidence supports a direct effect of BHB, although it is important to consider the myriad of other metabolic responses to fasting or ketogenic diet interventions (e.g., elevated lipolysis, low insulin, stable glucose, negative energy balance) that may also impact innate immune responses. Future research is needed to translate promising findings from discovery science to clinical application.

Alleviative effect of poly-β-hydroxybutyrate on lipopolysaccharide-induced oxidative stress, inflammation and cell apoptosis in Cyprinus carpio

In this study, the alleviative effects of poly-β-hydroxybutyrate (PHB) in bioflocs on oxidative stress, inflammation and apoptosis of common carp (Cyprinus carpio) induced by lipopolysaccharide (LPS) were evaluated. Common carp were irregularity divided into 5 groups and fed five diets with 0 % (CK), 2 %, 4 %, 6 % and 8 % PHB. After 8-week feeding trial, LPS challenge was executed. Results showed that appropriate level of PHB enhanced serum immune function by reversing LPS-induced the decrease of C3, C4, IgM, AKP, ACP and LZM in serum, alleviated LPS-induced intestinal barrier dysfunction by decreasing the levels of 5-HT, D-LA, ET-1 and DAO in serum, increasing ZO-1, Occludin, Claudin-3 and Claudin-7 mRNA, improving intestinal morphology. Moreover, dietary PHB reversed LPS-induced the decrease of AST and ALT in hepatopancreas, while in serum exhibited the opposite trend. Suitable level of PHB reversed LPS-induced the reduction of GSH-PX, CAT, T-SOD and T-AOC in intestines and hepatopancreas, whereas MDA showed the opposite result. PHB alleviated LPS-induced the decrease of Nrf2, HO-1, CAT, SOD and GSH-PX mRNA, the increase of Keap1 mRNA. Appropriate level of PHB alleviated LPS-induced inflammation and apoptosis by up-regulating TGF-β, IL-10 and Bcl-2 mRNA, down-regulating NF-κB, TNF-α, IL-6, Bax, Caspase-3, Caspase-8 and Caspase-9 mRNA. Furthermore, PHB inhibited activation of NLRP3 inflammasomes by reducing the levels of NLRP3, Caspase-1, ASC, IL-1β and IL-18 mRNA and protein. In addition, the increases of dietary PHB linearly and quadratically affected LPS-induced adverse effects on common carp. Summary, this study suggested that appropriate level of dietary PHB alleviated LPS-induced oxidative stress, inflammation, apoptosis and the activation of NLRP3 inflammasome in common carp. And the appropriate level of PHB in common carp diets was 4 %.

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.

Protective Effect of Topiramate against Diabetic Retinopathy and Computational Approach Recognizing the Role of NLRP3/IL-1β/TNF-α Signaling

The possible impact of topiramate against diabetic retinopathy (DREN) and its molecular mechanisms in relation to the nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome has not been studied before. Thus, in the present study, we aimed to utilize a computational approach to investigate the possible protective effect of topiramate on experimental DREN and explore its impact on NLRP3/interlukin-1β signaling and brain-derived neurotrophic factor (BDNF) expression. Male albino mice were distributed to four experimental groups and assigned the following categorizations: (i) saline, (ii) diabetic, (iii) diabetic + topiramate 10 mg/kg and (iv) diabetic + topiramate 30 mg/kg. We observed shrinkage of total retinal thickness and elevation in retinal glutamate, malondialdehyde, NLRP3 and interlukin-1β but decreased glutathione (GSH) levels in the diabetic mice. Additionally, retinal ultra-structures in the diabetic group showed abnormalities and vacuolations in the pigmented epithelium, the photoreceptor segment, the outer nuclear layer, the inner nuclear layer and the ganglion cell layer (GCL). Mice treated with topiramate 10 or 30 mg/kg showed downregulation in retinal malondialdehyde, NLRP3 and interlukin-1β levels; improvements in the retinal pathologies; enhanced immunostaining for BDNF and improved ultra-structures in different retinal layers. Overall, the current results suggest topiramate as a neuroprotective agent for DREN, and future studies are warranted to further elucidate the mechanism of its protective action.

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.

Inhibition of Galectins and the P2X7 Purinergic Receptor as a Therapeutic Approach in the Neurovascular Inflammation of Diabetic Retinopathy

Diabetic retinopathy (DR) is the most frequent microvascular retinal complication of diabetic patients, contributing to loss of vision. Recently, retinal neuroinflammation and neurodegeneration have emerged as key players in DR progression, and therefore, this review examines the neuroinflammatory molecular basis of DR. We focus on four important aspects of retinal neuroinflammation: (i) the exacerbation of endoplasmic reticulum (ER) stress; (ii) the activation of the NLRP3 inflammasome; (iii) the role of galectins; and (iv) the activation of purinergic 2X7 receptor (P2X7R). Moreover, this review proposes the selective inhibition of galectins and the P2X7R as a potential pharmacological approach to prevent the progression of DR.

Ketogenic Diet and Ketone Bodies as Clinical Support for the Treatment of SARS-CoV-2-Review of the Evidence

One of the proposed nutritional therapies to support drug therapy in COVID-19 is the use of a ketogenic diet (KD) or ketone bodies. In this review, we summarized the evidence from tissue, animal, and human models and looked at the mechanisms of action of KD/ketone bodies against COVID-19. KD/ketone bodies were shown to be effective at the stage of virus entry into the host cell. The use of β-hydroxybutyrate (BHB), by preventing the metabolic reprogramming associated with COVID-19 infection and improving mitochondrial function, reduced glycolysis in CD4+ lymphocytes and improved respiratory chain function, and could provide an alternative carbon source for oxidative phosphorylation (OXPHOS). Through multiple mechanisms, the use of KD/ketone bodies supported the host immune response. In animal models, KD resulted in protection against weight loss and hypoxemia, faster recovery, reduced lung injury, and resulted in better survival of young mice. In humans, KD increased survival, reduced the need for hospitalization for COVID-19, and showed a protective role against metabolic abnormalities after COVID-19. It appears that the use of KD and ketone bodies may be considered as a clinical nutritional intervention to assist in the treatment of COVID-19, despite the fact that numerous studies indicate that SARS-CoV-2 infection alone may induce ketoacidosis. However, the use of such an intervention requires strong scientific validation.

β-Hydroxybutyric acid upregulated by Suhuang antitussive capsule ameliorates cough variant asthma through GSK3β/AMPK-Nrf2 signal axis

ETHNOPHARMACOLOGICAL RELEVANCE

Cough variant asthma (CVA) is a chronic inflammatory disease characterized by cough as the main symptom. Suhuang antitussive capsule (Suhuang), one of traditional Chinese patent medicines, mainly treats CVA clinically. Previous studies have shown that Suhuang significantly improved CVA, post-infectious cough (PIC), sputum obstruction and airway remodeling. However, the effect of Suhuang on ovalbumin-induced (OVA-induced) metabolic abnormalities in CVA is unknown.

AIM OF THE STUDY

This study aimed to identify potential metabolites associated with efficacy of Suhuang in the treatment of CVA, and determined how Suhuang regulates metabolites, and differential metabolites reduce inflammation and oxidative stress.

MATERIALS AND METHODS

Rats were given 1 mg OVA/100 mg aluminum hydroxide in the 1st and 7th days by intraperitoneal injection and challenged by atomizing inhalation of 1% OVA saline solution after two weeks to establish the CVA model. Rats were intragastrically (i.g.) administrated with Suhuang at 1.4 g/kg and β-hydroxybutyric acid (β-HB) were given with different concentrations (87.5 and 175 mg/kg/day) by intraperitoneal injection for 2 weeks. After 26 days, GC-MS-based metabolomic approach was applied to observe metabolic changes and search differential metabolites. The number of coughs, coughs latencies, enzyme-linked immunosorbent assay (ELISA), histological analysis and quantitative-polymerase chain reaction (Q-PCR) were used to investigate the effects of Suhuang. Then β-HB on CVA rats, NLRP3 inflammasome and GSK3β/AMPK/Nrf2 signalling pathway were detected by western blotting.

RESULTS

The results showed that Suhuang treatment significantly enhanced the serum level of β-HB. Interestingly, exposure to exogenous β-HB was also protective against OVA-induced CVA. β-HB significantly reduced the number of coughs and lengthened coughs latencies, improved lung injury, reduced the secretion of various cytokines, and directly inhibited the NLRP3 inflammasome. In addition, β-HB increased the nuclear accumulation of Nrf2 by activating the GSK3β/AMPK signaling axis, and then inactivating the NF-κB signaling pathway, effectively protecting OVA-induced CVA from oxidative stress and inflammation.

CONCLUSIONS

The results of this study shows that β-HB can reduce inflammation and oxidative stress, the increased production of β-HB in serum might be the crucial factor for Suhuang to exert its effect in the treatment of CVA.

Targeting the NLRP3 inflammasome in diabetic retinopathy: From Pathogenesis to Therapeutic Strategies

Diabetic retinopathy (DR) is a common diabetic microvascular complication and the main cause of vision loss in working-aged people. The NLRP3 inflammasome is a cytosolic multimeric complex that plays a significant role in innate immunity. After sensing injury, the NLRP3 inflammasome induces inflammatory mediator secretion and triggers a form of inflammatory cell death known as pyroptosis. Studies over the past five years have shown increased expression of NLRP3 and related inflammatory mediators in vitreous samples from DR patients at different clinical stages. Many NLRP3-targeted inhibitors have shown great antiangiogenic and anti-inflammatory effects in diabetes mellitus models, suggesting that the NLRP3 inflammasome is involved in the progression of DR. This review covers the molecular mechanisms of NLRP3 inflammasome activation. Furthermore, we discuss the implications of the NLRP3 inflammasome in DR, including the induction of pyroptosis and inflammation and the promotion of microangiopathy and retinal neurodegeneration. We also summarize the research progress on targeting the NLRP3 inflammasome in DR therapeutics with the expectation of providing new insights into DR progression and treatment.

Oral Administration of Vitamin D3 Prevents Corneal Damage in a Knock-Out Mouse Model of Sjögren's Syndrome

BACKGROUND

Vitamin D deficiency has been associated with dry eye development during Sjögren's syndrome (SS). Here, we investigated whether repeated oral vitamin D3 supplementation could prevent the corneal epithelium damage in an SS mouse model.

METHODS

30 female mouse knock-out for the thrombospondin 1 gene were randomized (six per group) in untreated mice euthanized at 6 weeks as negative control (C-) or at 12 weeks as the positive control for dry eye (C+). Other mice were sacrificed after 6 weeks of oral vitamin D3 supplementation in the drinking water (1000, 8000, and 20,000 IU/kg/week, respectively).

RESULTS

The C+ mice showed alterations in their corneal epithelial morphologies and thicknesses (p < 0.01 vs. C-), while the mice receiving 8000 (M) and 20,000 (H) IU/kg/week of vitamin D3 showed preservation of the corneal epithelium morphology and thickness (p < 0.01 vs. C+). Moreover, while the C+ mice exhibited high levels and activity of corneal tumor necrosis factor alpha converting enzyme (TACE), neovascularization and fibrosis markers; these were all reduced in the M and H mice.

CONCLUSIONS

Oral vitamin D3 supplementation appeared to counteract the negative effect of TACE on corneal epithelium in a mouse model of SS-associated dry eye.

Molecular Mechanisms for Ketone Body Metabolism, Signaling Functions, and Therapeutic Potential in Cancer

The ketone bodies (KBs) β-hydroxybutyrate and acetoacetate are important alternative energy sources for glucose during nutrient deprivation. KBs synthesized by hepatic ketogenesis are catabolized to acetyl-CoA through ketolysis in extrahepatic tissues, followed by the tricarboxylic acid cycle and electron transport chain for ATP production. Ketogenesis and ketolysis are regulated by the key rate-limiting enzymes, 3-hydroxy-3-methylglutaryl-CoA synthase 2 and succinyl-CoA:3-oxoacid-CoA transferase, respectively. KBs participate in various cellular processes as signaling molecules. KBs bind to G protein-coupled receptors. The most abundant KB, β-hydroxybutyrate, regulates gene expression and other cellular functions by inducing post-translational modifications. KBs protect tissues by regulating inflammation and oxidative stress. Recently, interest in KBs has been increasing due to their potential for treatment of various diseases such as neurological and cardiovascular diseases and cancer. Cancer cells reprogram their metabolism to maintain rapid cell growth and proliferation. Dysregulation of KB metabolism also plays a role in tumorigenesis in various types of cancer. Targeting metabolic changes through dietary interventions, including fasting and ketogenic diets, has shown beneficial effects in cancer therapy. Here, we review current knowledge of the molecular mechanisms involved in the regulation of KB metabolism and cellular signaling functions, and the therapeutic potential of KBs and ketogenic diets in cancer.

Systemic Beta-Hydroxybutyrate Affects BDNF and Autophagy into the Retina of Diabetic Mice

Background: Diabetic retinopathy (DR) is a neurovascular disease, characterized by a deficiency of brain-derived neurotrophic factor (BDNF), a regulator of autophagy. Beta-hydroxybutyrate (BHB), previously reported as a protective agent in DR, has been associated with BDNF promotion. Here, we investigated whether systemic BHB affects the retinal levels of BDNF and local autophagy in diabetic mice with retinopathy; Methods: C57BL/6J mice were administered with intraperitoneal (i.p.) streptozotocin (STZ) (75 mg/kg) injection to develop diabetes. After 2 weeks, they received i.p. injections of BHB (25−50−100 mg/kg) twice a week for 10 weeks. Retinal samples were collected in order to perform immunofluorescence, Western blotting, and ELISA analysis; Results: BHB 50 mg/kg and 100 mg/kg significantly improved retinal BDNF levels (p < 0.01) in diabetic mice. This improvement was negatively associated with autophagosome−lysosome formations (marked by LC3B and ATG14) and to higher levels of connexin 43 (p < 0.01), a marker of cell integrity. Moreover, BHB administration significantly reduced M1 microglial activation and autophagy (p < 0.01); Conclusions: The systemic administration of BHB in mice with DR improves the retinal levels of BDNF, with the consequent reduction of the abnormal microglial autophagy. This leads to retinal cell safety through connexin 43 restoration.

Spotlight on pyroptosis: role in pathogenesis and therapeutic potential of ocular diseases

Pyroptosis is a programmed cell death characterized by swift plasma membrane disruption and subsequent release of cellular contents and pro-inflammatory mediators (cytokines), including IL‐1β and IL‐18. It differs from other types of programmed cell death such as apoptosis, autophagy, necroptosis, ferroptosis, and NETosis in terms of its morphology and mechanism. As a recently discovered form of cell death, pyroptosis has been demonstrated to be involved in the progression of multiple diseases. Recent studies have also suggested that pyroptosis is linked to various ocular diseases. In this review, we systematically summarized and discussed recent scientific discoveries of the involvement of pyroptosis in common ocular diseases, including diabetic retinopathy, age-related macular degeneration, AIDS-related human cytomegalovirus retinitis, glaucoma, dry eye disease, keratitis, uveitis, and cataract. We also organized new and emerging evidence suggesting that pyroptosis signaling pathways may be potential therapeutic targets in ocular diseases, hoping to provide a summary of overall intervention strategies and relevant multi-dimensional evaluations for various ocular diseases, as well as offer valuable ideas for further research and development from the perspective of pyroptosis.

Potential for Ketotherapies as Amyloid-Regulating Treatment in Individuals at Risk for Alzheimer’s Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative condition characterized by clinical decline in memory and other cognitive functions. A classic AD neuropathological hallmark includes the accumulation of amyloid-β (Aβ) plaques, which may precede onset of clinical symptoms by over a decade. Efforts to prevent or treat AD frequently emphasize decreasing Aβ through various mechanisms, but such approaches have yet to establish compelling interventions. It is still not understood exactly why Aβ accumulates in AD, but it is hypothesized that Aβ and other downstream pathological events are a result of impaired bioenergetics, which can also manifest prior to cognitive decline. Evidence suggests that individuals with AD and at high risk for AD have functional brain ketone metabolism and ketotherapies (KTs), dietary approaches that produce ketone bodies for energy metabolism, may affect AD pathology by targeting impaired brain bioenergetics. Cognitively normal individuals with elevated brain Aβ, deemed “preclinical AD,” and older adults with peripheral metabolic impairments are ideal candidates to test whether KTs modulate AD biology as they have impaired mitochondrial function, perturbed brain glucose metabolism, and elevated risk for rapid Aβ accumulation and symptomatic AD. Here, we discuss the link between brain bioenergetics and Aβ, as well as the potential for KTs to influence AD risk and progression.

Beta-Hydroxybutyrate: A Dual Function Molecular and Immunological Barrier Function Regulator

Ketone bodies are crucial intermediate metabolites widely associated with treating metabolic diseases. Accumulating evidence suggests that ketone bodies may act as immunoregulators in humans and animals to attenuate pathological inflammation through multiple strategies. Although the clues are scattered and untrimmed, the elevation of these ketone bodies in the circulation system and tissues induced by ketogenic diets was reported to affect the immunological barriers, an important part of innate immunity. Therefore, beta-hydroxybutyrate, a key ketone body, might also play a vital role in regulating the barrier immune systems. In this review, we retrospected the endogenous ketogenesis in animals and the dual roles of ketone bodies as energy carriers and signal molecules focusing on beta-hydroxybutyrate. In addition, the research regarding the effects of beta-hydroxybutyrate on the function of the immunological barrier, mainly on the microbiota, chemical, and physical barriers of the mucosa, were outlined and discussed. As an inducible endogenous metabolic small molecule, beta-hydroxybutyrate deserves delicate investigations focusing on its immunometabolic efficacy. Comprehending the connection between ketone bodies and the barrier immunological function and its underlining mechanisms may help exploit individualised approaches to treat various mucosa or skin-related diseases.

Serum Iba-1, GLUT5, and TSPO in Patients With Diabetic Retinopathy: New Biomarkers for Early Retinal Neurovascular Alterations? A Pilot Study

Purpose

This study explored the possibility of highlighting early retinal neurovascular alterations of diabetic retinopathy (DR) by monitoring in DR patients the serum levels of microglial biomarkers ionized calcium-binding adapter molecule 1 (Iba-1), glucose transporter 5 (GLUT5), and translocator protein (TSPO), along with serum changes of the endothelial dysfunction marker arginase-1.

Methods

Serum markers were determined by enzyme-linked immunosorbent assay in 50 patients: 12 non-diabetic subjects, 14 diabetic patients without DR, 13 patients with non-proliferative DR (NPDR), and 11 patients with proliferative DR (PDR). The results were correlated with hyperreflective retinal spots (HRS), observed with optical coherence tomography (OCT).

Results

Although HRS were absent in diabetic patients without DR, NPDR patients showed an average of 4 ± 1 HRS, whereas the highest presence was detected in PDR patients, with 8 ± 1 HRS (P < 0.01 vs. NPDR). HRS were positively correlated (P < 0.01) with serum levels of arginase-1 (r = 0.91), Iba-1 (r = 0.96), GLUT5 (r = 0.94), and TSPO (r = 0.88). Moreover, serum proinflammatory cytokines and chemokines showed a positive correlation (P < 0.01) with HRS number and the serum markers analyzed.

Conclusions

Serum markers of microglial activation positively correlate with retinal HRS in NPDR and PDR patients.

Translational Relevance

These data corroborate the possibility of highlighting early retinal neurovascular changes due to diabetes by monitoring circulating microglial markers.

Possible roles of anti-type II collagen antibody and innate immunity in the development and progression of diabetic retinopathy

The pathogenesis of both diabetic retinopathy (DR) and rheumatoid arthritis (RA) has recently been considered to involve autoimmunity. Serum and synovial fluid levels of anti-type II collagen antibodies increase early after the onset of RA, thus inducing immune responses and subsequent hydrarthrosis and angiogenesis, which resemble diabetic macular edema and proliferative DR (PDR), respectively. We previously reported that DR is also associated with increased serum levels of anti-type II collagen antibodies. Retinal hypoxia in DR may induce pericytes to express type II collagen, resulting in autoantibody production against type II collagen. As the result of blood-retinal barrier disruption, anti-type II collagen antibodies in the serum come into contact with type II collagen around the retinal vessels. A continued loss of pericytes and type II collagen around the retinal vessels may result in a shift of the immune reaction site from the retina to the vitreous. It has been reported that anti-inflammatory M2 macrophages increased in the vitreous of PDR patients, accompanied by the activation of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, a key regulator of innate immunity. M2 macrophages promote angiogenesis and fibrosis, which might be exacerbated and prolonged by dysregulated innate immunity.

Effects of novel SGLT2 inhibitors on cancer incidence in hyperglycemic patients: a meta-analysis of randomized clinical trials

Epidemiological evidence shows that diabetic patients have an increased cancer risk and a higher mortality rate. Glucose could play a central role in metabolism and growth of many tumor types, and this possible mechanism is supported by the high rate of glucose demand and uptake in cancer. Thus, growing evidence suggests that hyperglycemia contributes to cancer progression but also to its onset. Many mechanisms underlying this association have been hypothesized, such as insulin resistance, hyperinsulinemia, and increased inflammatory processes. Inflammation is a common pathophysiological feature in both diabetic and oncological patients, and inflammation linked to high glucose levels sensitizes microenvironment to tumorigenesis, promoting the development of malignant lesions by altering and sustaining a pathological condition in tissues. Glycemic control is the first goal of antidiabetic therapy, and glucose level reduction has also been associated with favorable outcomes in cancer. Here, we describe key events in carcinogenesis focusing on hyperglycemia as supporter in tumor progression and in particular, related to the role of a specific hypoglycemic drug class, sodium-glucose linked transporters (SGLTs). We also discuss the use of SGLT2 inhibitors as a novel potential cancer therapy. Our meta-analysis showed that SGLT-2 inhibitors were significantly associated with an overall reduced risk of cancer as compared to placebo (RR = 0.35, CI 0.33-0.37, P = 0. 00) with a particular effectiveness for dapaglifozin and ertuglifozin (RR = 0. 06, CI 0. 06-0. 07 and RR = 0. 22, CI 0. 18-0. 26, respectively). Network Medicine approaches may advance the possible repurposing of these drugs in patients with concomitant diabetes and cancer.

Ketogenic diet and cancer: Fad or fabulous?

As the prevalence of smoking continues to decline, dietary factors are rapidly becoming the leading preventable cause of disease. Diet and obesity are also leading to a shift in cancer prevalence with increases noted in breast, liver, pancreas, and uterine cancers. Once cancer is detected, obesity is also associated with poorer outcomes with therapy as well as higher morbidity and mortality. Key factors are associated with the link between obesity and cancer including chronic inflammation, change in sex hormones, alteration in insulin-IGF-1 axis, alteration in adipokines, as well as cancer stem cells that are derived from adipose tissue. Because of these associations, a great deal of effort is being placed in implementing lifestyle changes that mitigate obesity-associated factors that contribute to development of cancer, reduce side effects of treatment, and improve survival. Ketogenic diet is emerging as an attractive option in countering obesity-related tumor-promoting factors, as it is associated with weight loss as well as a reduction in insulin resistance and inflammation. Ketogenic diet can also deprive cancer cells of glucose, a fuel source that is predominantly used by many cancer lines through aerobic glycolysis in the setting of dysregulated mitochondria. Current manuscript reviews the theoretical benefits for use of ketogenic diet in cancer as well as the data available from clinical trials.

Fingolimod and Diabetic Retinopathy: A Drug Repurposing Study

This study aimed to investigate the interactions between fingolimod, a sphingosine 1-phosphate receptor (S1PR) agonist, and melanocortin receptors 1 and 5 (MCR1, MCR5). In particular, we investigated the effects of fingolimod, a drug approved to treat relapsing-remitting multiple sclerosis, on retinal angiogenesis in a mouse model of diabetic retinopathy (DR). We showed, by a molecular modeling approach, that fingolimod can bind with good-predicted affinity to MC1R and MC5R. Thereafter, we investigated the fingolimod actions on retinal MC1Rs/MC5Rs in C57BL/6J mice. Diabetes was induced in C57BL/6J mice through streptozotocin injection. Diabetic and control C57BL/6J mice received fingolimod, by oral route, for 12 weeks and a monthly intravitreally injection of MC1R antagonist (AGRP), MC5R antagonist (PG20N), and the selective S1PR1 antagonist (Ex 26). Diabetic animals treated with fingolimod showed a decrease of retinal vascular endothelial growth factor A (VEGFA) and vascular endothelial growth factor receptors 1 and 2 (VEGFR1 and VEGFR2), compared to diabetic control group. Fingolimod co-treatment with MC1R and MC5R selective antagonists significantly (p < 0.05) increased retinal VEGFR1, VEGFR2, and VEGFA levels compared to mice treated with fingolimod alone. Diabetic animals treated with fingolimod plus Ex 26 (S1PR1 selective blocker) had VEGFR1, VEGFR2, and VEGFA levels between diabetic mice group and the group of diabetic mice treated with fingolimod alone. This vascular protective effect of fingolimod, through activation of MC1R and MC5R, was evidenced also by fluorescein angiography in mice. Finally, molecular dynamic simulations showed a strong similarity between fingolimod and the MC1R agonist BMS-470539. In conclusion, the anti-angiogenic activity exerted by fingolimod in DR seems to be mediated not only through S1P1R, but also by melanocortin receptors.

The ketone body β-hydroxybutyrate mitigates the senescence response of glomerular podocytes to diabetic insults

Diabetic kidney disease (DKD) is one of the most common complications of diabetes and clinically featured by progressive albuminuria, consequent to glomerular destruction that involves podocyte senescence. Burgeoning evidence suggests that ketosis, in particular β-hydroxybutyrate, exerts a beneficial effect on aging and on myriad metabolic or chronic diseases, including obesity, diabetes and chronic kidney diseases. Its effect on DKD is largely unknown. In vitro in podocytes exposed to a diabetic milieu, β-hydroxybutyrate treatment substantially mitigated cellular senescence and injury, as evidenced by reduced formation of γH2AX foci, reduced staining for senescence-associated-β-galactosidase activity, diminished expression of key mediators of senescence signaling like p16INK4A and p21, and preserved expression of synaptopodin. This beneficial action of β-hydroxybutyrate coincided with a reinforced transcription factor Nrf2 antioxidant response. Mechanistically, β-hydroxybutyrate inhibition of glycogen synthase kinase 3β (GSK3β), a convergent point for myriad signaling pathways regulating Nrf2 activity, seems to contribute. Indeed, trigonelline, a selective inhibitor of Nrf2, or ectopic expression of constitutively active mutant GSK3β abolished, whereas selective activation of Nrf2 was sufficient for the anti-senescent and podocyte protective effects of β-hydroxybutyrate. Moreover, molecular modeling and docking analysis revealed that β-hydroxybutyrate is able to directly target the ATP-binding pocket of GSK3β and thereby block its kinase activity. In murine models of streptozotocin-elicited DKD, β-hydroxybutyrate therapy inhibited GSK3β and reinforced Nrf2 activation in glomerular podocytes, resulting in lessened podocyte senescence and injury and improved diabetic glomerulopathy and albuminuria. Thus, our findings may pave the way for developing a β-hydroxybutyrate-based novel approach of therapeutic ketosis for treating DKD.

β-Hydroxybutyrate inhibits cardiac microvascular collagen 4 accumulation by attenuating oxidative stress in streptozotocin-induced diabetic rats and high glucose treated cells

Accumulation of collagen 4 (COL4) and thickened basement membrane are features of diabetic cardiac microvascular fibrosis that may be induced by oxidative stress. The ketone body β-hydroxybutyrate exhibits various cardiovascular protective effects, however its mechanism remains to be clarified. In the current study, the effects of β-hydroxybutyrate on cardiac microvascular fibrosis and COL4 accumulation were evaluated in streptozotocin-induced diabetic rats and in high glucose (HG) treated human cardiac microvascular endothelial cells (HCMECs). Generations of inducible nitric oxide synthase (iNOS) and copper-zinc superoxide dismutase (Cu/Zn-SOD), and the amount of nitrotyrosine (NT) were measured in vivo and in vitro. Ten weeks of β-hydroxybutyrate treatment (160, 200 and 240 mg/kg/d) attenuated cardiac microvascular fibrosis and inhibited cardiac COL4 generation and microvascular distribution in diabetic rats. Furthermore, β-hydroxybutyrate promoted cardiac Cu/Zn-SOD generation and reduced NT content, without reducing iNOS generation in diabetic rats. In HCMECs, stimulation with HG induced excess generation of COL4 via peroxynitrite. β-Hydroxybutyrate treatment (2, 4, 6 mM) attenuated HG-stimulated COL4 accumulation in a concentration-dependent manner. Similarly, 4 mM β-hydroxybutyrate promoted Cu/Zn-SOD generation and reduced NT content, without affecting excess iNOS generation in HG-stimulated HCMECs. In conclusion, this study showed that β-hydroxybutyrate promoted Cu/Zn-SOD generation, reduced peroxynitrite and inhibited cardiac microvascular COL4 accumulation in diabetes.

SGLT2 Inhibitor-Induced Low-Grade Ketonemia Ameliorates Retinal Hypoxia in Diabetic Retinopathy-A Novel Hypothesis

Diabetic retinopathy (DR) is a well-recognized microvascular complication of diabetes. Growing evidence suggests that, in addition to retinal vascular damage, there is significant damage to retinal neural tissue in DR. Studies reveal neuronal damage before clinically evident vascular lesions and DR is now classified as a neurovascular complication. Hyperglycemia causes retinal damage through complex metabolic pathways leading to oxidative stress, inflammation, vascular damage, capillary ischemia, and retinal tissue hypoxia. Retinal hypoxia is further worsened by high oxygen consumption in the rods. Persistent hypoxia results in increases in vascular endothelial growth factor (VEGF) and other pro-angiogenic factors leading to proliferative DR/macular edema and progressive visual impairment. Optimal glucose control has favorable effects in DR. Other treatments for DR include laser photocoagulation, which improves retinal oxygenation by destroying the high oxygen consuming rods and their replacement by low oxygen consuming glial tissue. Hypoxia is a potent stimulator of VEGF, and intravitreal anti-VEGF antibodies are effective in regressing macular edema and in some studies, retinal neovascularization. In this review, we highlight the complex pathophysiology of DR with a focus on retinal oxygen/fuel consumption and hypoxic damage to retinal neurons. We discuss potential mechanisms through which sodium-glucose cotransporter 2 (SGLT2) inhibitors improve retinal hypoxia-through ketone bodies, which are energetically as efficient as glucose and yield more ATP per molecule of oxygen consumed than fat, with less oxidative stress. Retinal benefits would occur through improved fuel energetics, less hypoxia and through the anti-inflammatory/oxidative stress effects of ketone bodies. Well-designed studies are needed to explore this hypothesis.

The Role of the Effects of Endoplasmic Reticulum Stress on NLRP3 Inflammasome in Diabetes

Endoplasmic reticulum (ER) is an important organelle for the protein synthesis, modification, folding, assembly, and the transport of new peptide chains. When the folding ability of ER proteins is impaired, the accumulation of unfolded or misfolded proteins in ER leads to endoplasmic reticulum stress (ERS). The nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome, can induce the maturation and secretion of interleukin-1beta (IL-1β) and IL-18 through activating caspase-1. It is associated with many diseases. Studies have shown that ERS can regulate NLRP3 inflammasome in many diseases including diabetes. However, the mechanism of the effects of ERS on NLRP3 inflammasome in diabetes has not been fully understood. This review summarizes the recent researches about the effects of ERS on NLRP3 inflammasome and the related mechanism in diabetes to provide ideas for the relevant basic research in the future.

NLRP3 Inflammasome: Potential Role in Obesity Related Low-Grade Inflammation and Insulin Resistance in Skeletal Muscle

Among multiple mechanisms, low-grade inflammation is critical for the development of insulin resistance as a feature of type 2 diabetes. The nucleotide-binding oligomerization domain-like receptor family (NOD-like) pyrin domain containing 3 (NLRP3) inflammasome has been linked to the development of insulin resistance in various tissues; however, its role in the development of insulin resistance in the skeletal muscle has not been explored in depth. Currently, there is limited evidence that supports the pathological role of NLRP3 inflammasome activation in glucose handling in the skeletal muscle of obese individuals. Here, we have centered our focus on insulin signaling in skeletal muscle, which is the main site of postprandial glucose disposal in humans. We discuss the current evidence showing that the NLRP3 inflammasome disturbs glucose homeostasis. We also review how NLRP3-associated interleukin and its gasdermin D-mediated efflux could affect insulin-dependent intracellular pathways. Finally, we address pharmacological NLRP3 inhibitors that may have a therapeutical use in obesity-related metabolic alterations.

β-Hydroxybutyrate inhibits histone deacetylase 3 to promote claudin-5 generation and attenuate cardiac microvascular hyperpermeability in diabetes

AIMS/HYPOTHESIS

Microvascular endothelial hyperpermeability, mainly caused by claudin-5 deficiency, is the initial pathological change that occurs in diabetes-associated cardiovascular disease. The ketone body β-hydroxybutyrate (BHB) exerts unique beneficial effects on the cardiovascular system, but the involvement of BHB in promoting the generation of claudin-5 to attenuate cardiac microvascular hyperpermeability in diabetes is poorly understood.

METHODS

The effects of BHB on cardiac microvascular endothelial hyperpermeability and claudin-5 generation were evaluated in rats with streptozotocin-induced diabetes and in high glucose (HG)-stimulated human cardiac microvascular endothelial cells (HCMECs). To explore the underlying mechanisms, we also measured β-catenin nuclear translocation, binding of β-catenin, histone deacetylase (HDAC)1, HDAC3 and p300 to the Claudin-5 (also known as CLDN5) promoter, interaction between HDAC3 and β-catenin, and histone acetylation in the Claudin-5 promoter.

RESULTS

We found that 10 weeks of BHB treatment promoted claudin-5 generation and antagonised cardiac microvascular endothelial hyperpermeability in rat models of diabetes. Meanwhile, BHB promoted claudin-5 generation and inhibited paracellular permeability in HG-stimulated HCMECs. Specifically, BHB (2 mmol/l) inhibited HG-induced HDAC3 from binding to the Claudin-5 promoter, although nuclear translocation or promoter binding of β-catenin did not change with BHB treatment. In addition, BHB prevented the binding and co-localisation of HDAC3 to β-catenin in HG-stimulated HCMECs. Furthermore, using mass spectrometry, acetylated H3K14 (H3K14ac) in the Claudin-5 promoter following BHB treatment was identified, regardless of whether cells were stimulated by HG or not. Although reduced levels of acetylated H3K9 in the Claudin-5 promoter were found following HG stimulation, increased H3K14ac was specifically associated with BHB treatment.

CONCLUSIONS/INTERPRETATION

BHB inhibited HDAC3 and caused acetylation of H3K14 in the Claudin-5 promoter, thereby promoting claudin-5 generation and antagonising diabetes-associated cardiac microvascular hyperpermeability. Graphical abstract.

Investigating Ketone Bodies as Immunometabolic Countermeasures against Respiratory Viral Infections

Respiratory viral infections remain a scourge, with seasonal influenza infecting millions and killing many thousands annually and viral pandemics, such as COVID-19, recurring every decade. Age, cardiovascular disease, and diabetes mellitus are risk factors for severe disease and death from viral infection. Immunometabolic therapies for these populations hold promise to reduce the risks of death and disability. Such interventions have pleiotropic effects that might not only target the virus itself but also enhance supportive care to reduce cardiopulmonary complications, improve cognitive resilience, and facilitate functional recovery. Ketone bodies are endogenous metabolites that maintain cellular energy but also feature drug-like signaling activities that affect immune activity, metabolism, and epigenetics. Here, we provide an overview of ketone body biology relevant to respiratory viral infection, focusing on influenza A and severe acute respiratory syndrome (SARS)-CoV-2, and discuss the opportunities, risks, and research gaps in the study of exogenous ketone bodies as novel immunometabolic interventions in these diseases.

Up-regulation of MMP-2 by histone H3K9 β-hydroxybutyrylation to antagonize glomerulosclerosis in diabetic rat

AIMS

Besides energy supply, β-hydroxybutyrate (BHB) acts as a bioactive molecule to play multiple protective roles, even in diabetes and its complications. The aim of this study was to investigate the antagonizing effects of BHB against diabetic glomerulosclerosis and the underlying mechanism.

METHODS

Male Sprague-Dawley rats were intraperitoneally injected with streptozotocin to induce diabetes and then treated with different concentrations of β-hydroxybutyrate. After 10 weeks, body weight, blood glucose, serum creatinine and 24-h urine protein were examined. Glomerular morphological changes and the contents of collagen type IV (COL IV) were evaluated. Then, transforming growth factor (TGF)-β/Smad3 contents and matrix metalloproteinase-2 (MMP-2) generation were detected. Moreover, the total contents of trans-activating histone H3K9 β-hydroxybutyrylation (H3K9bhb) and the contents of H3K9bhb in the Mmp-2 promoter were measured.

RESULTS

It was firstly confirmed that BHB treatments reduced renal biochemical indicators and attenuated glomerular morphological changes of the diabetic rats, with COL IV content decreased in a concentration-dependent manner. Then, BHB treatments were found to up-regulate renal MMP-2 generation of the diabetic rats significantly, while not affecting the increased TGF-β/Smad3 contents. Furthermore, the contents of H3K9bhb in the Mmp-2 promoter were elevated significantly for the middle and high concentrations of BHB treatments, up-regulating MMP-2 generation.

CONCLUSION

BHB treatments could up-regulate MMP-2 generation via causing elevated H3K9bhb in its promoter to antagonize glomerulosclerosis in the diabetic rats.

β-Hydroxybutyrate Oxidation Promotes the Accumulation of Immunometabolites in Activated Microglia Cells

Metabolic regulation of immune cells has arisen as a critical set of processes required for appropriate response to immunological signals. While our knowledge in this area has rapidly expanded in leukocytes, much less is known about the metabolic regulation of brain-resident microglia. In particular, the role of alternative nutrients to glucose remains poorly understood. Here, we use stable-isotope (¹³C) tracing strategies and metabolomics to characterize the oxidative metabolism of β-hydroxybutyrate (BHB) in human (HMC3) and murine (BV2) microglia cells and the interplay with glucose in resting and LPS-activated BV2 cells. We found that BHB is imported and oxidised in the TCA cycle in both cell lines with a subsequent increase in the cytosolic NADH:NAD⁺ ratio. In BV2 cells, stimulation with LPS upregulated the glycolytic flux, increased the cytosolic NADH:NAD⁺ ratio and promoted the accumulation of the glycolytic intermediate dihydroxyacetone phosphate (DHAP). The addition of BHB enhanced LPS-induced accumulation of DHAP and promoted glucose-derived lactate export. BHB also synergistically increased LPS-induced accumulation of succinate and other key immunometabolites, such as α-ketoglutarate and fumarate generated by the TCA cycle. Finally, BHB upregulated the expression of a key pro-inflammatory (M1 polarisation) marker gene, NOS2, in BV2 cells activated with LPS. In conclusion, we identify BHB as a potentially immunomodulatory metabolic substrate for microglia that promotes metabolic reprogramming during pro-inflammatory response.

Chronically Elevating Circulating Ketones Can Reduce Cardiac Inflammation and Blunt the Development of Heart Failure

BACKGROUND

Previous studies have shown beneficial effects of acute infusion of the primary ketone body, β-hydroxybutyrate, in heart failure (HF). However, whether chronic elevations in circulating ketones are beneficial remains unknown.

METHODS

To chronically elevate circulating ketones in mice, we deleted the expression of the ketolytic, rate-limiting-enzyme, SCOT (succinyl-CoA:3-ketoacid-CoA transferase 1; encoded by Oxct1), in skeletal muscle. Tamoxifen-inducible skeletal muscle-specific Oxct1^Muscle-/- knockout (n=32) mice and littermate controls (wild type; WT; n=35) were subjected to transverse aortic constriction (TAC) surgery to induce HF.

RESULTS

Deletion of SCOT in skeletal, but not cardiac muscle resulted in elevated concentrations of fasted circulating β-hydroxybutyrate in knockout mice compared with WT mice (P=0.030). Five weeks following TAC, WT mice progressed to HF, whereas knockout mice with elevated fasting circulating ketones were largely protected from the TAC-induced effects observed in WT mice (ejection fraction, P=0.011; mitral E/A, P=0.012). Furthermore, knockout mice with TAC had attenuated expression of markers of sterile inflammation and macrophage infiltration, which were otherwise elevated in WT mice subjected to TAC. Lastly, addition of β-hydroxybutyrate to isolated hearts was associated with reduced NLRP3 (nucleotide-binding domain-like receptor protein 3)-inflammasome activation, which has been previously shown to play a role in contributing to HF-induced cardiac inflammation.

CONCLUSIONS

These data show that chronic elevation of circulating ketones protects against the development of HF that is associated with the ability of β-hydroxybutyrate to directly reduce inflammation. These beneficial effects of ketones were associated with reduced cardiac NLRP3 inflammasome activation, suggesting that ketones may modulate cardiac inflammation via this mechanism.

A prodrug of epigallocatechin-3-gallate alleviates high glucose-induced pro-angiogenic factor production by inhibiting the ROS/TXNIP/NLRP3 inflammasome axis in retinal Müller cells

Diabetic retinopathy (DR) is a neurovascular complication of diabetes mellitus that leads to blindness in the working-age population. Retinal Müller cells proliferate and produce pro-angiogenic factors, including vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF), via the reactive oxygen species (ROS)/thioredoxin interacting protein (TXNIP)/NACHT, LRR and PYD domain-containing protein 3 (NLRP3) inflammasome axis to promote proliferative DR. Epigallocatechin-3-gallate (EGCG) plays anti-oxidant, anti-inflammatory, anti-proliferative and anti-angiogenic roles in Müller cells. A prodrug of EGCG (pro-EGCG) enhances the bioavailability of EGCG. In an in vitro model of high glucose-stimulated Müller cells, pro-EGCG inhibited proliferation and pro-angiogenic factor production by down-regulating the activity of the ROS/TXNIP/NLRP3 inflammasome axis. In a mouse DR model, pro-EGCG reduced ROS accumulation, NLRP3 inflammasome activation, Müller cell proliferation, and production of the pro-angiogenic factors VEGF and HGF. In summary, pro-EGCG mitigated hyperglycaemia-challenged Müller cell proliferation and pro-angiogenic factor production by inhibiting ROS/TXNIP/NLRP3 inflammasome signalling, implying a potential therapeutic strategy for DR.

The role of microglia in neuroprogressive disorders: mechanisms and possible neurotherapeutic effects of induced ketosis

A comprehensive review of molecular mechanisms involved in the promotion and maintenance of distinct microglia phenotypes is provided. The acquisition and perpetuation of predominantly pro-inflammatory microglial phenotypes have been implicated in the pathophysiology of several neuroprogressive diseases and is associated with reduced ATP production via oxidative phosphorylation, increased ATP generation by glycolysis, elevated oxidative and nitrosative stress and other metabolic, inflammatory and hormonal insults. Microglia can also adopt a predominantly anti-inflammatory phenotypes with neuroprotective properties. Strategies that promote and maintain a predominantly anti-inflammatory phenotype may hold promise as novel therapeutic opportunities for neuroprogressive illness. Induced ketosis may promote a transition towards predominantly anti-inflammatory microglial states/phenotypes by several mechanisms, including inhibition of glycolysis and increased NAD⁺ production; engagement of microglial GPR109A receptors; histone deacetylase inhibition; and elevated n-3 polyunsaturated fatty acids levels. Since microglia activation can now be assessed in vivo, these data provide a clear rationale for the design of transdiagnostic randomized controlled trials of the ketogenic diet and other ketosis-inducing strategies for neuroprogressive diseases, which may also provide mechanistic insights through the assessment of "target engagement".

Ketogenic diet in the treatment of cancer - Where do we stand?

BACKGROUND

Cancer is one of the greatest public health challenges worldwide, and we still lack complementary approaches to significantly enhance the efficacy of standard anticancer therapies. The ketogenic diet, a high-fat, low-carbohydrate diet with adequate amounts of protein, appears to sensitize most cancers to standard treatment by exploiting the reprogramed metabolism of cancer cells, making the diet a promising candidate as an adjuvant cancer therapy.

SCOPE OF REVIEW

To critically evaluate available preclinical and clinical evidence regarding the ketogenic diet in the context of cancer therapy. Furthermore, we highlight important mechanisms that could explain the potential antitumor effects of the ketogenic diet.

MAJOR CONCLUSIONS

The ketogenic diet probably creates an unfavorable metabolic environment for cancer cells and thus can be regarded as a promising adjuvant as a patient-specific multifactorial therapy. The majority of preclinical and several clinical studies argue for the use of the ketogenic diet in combination with standard therapies based on its potential to enhance the antitumor effects of classic chemo- and radiotherapy, its overall good safety and tolerability and increase in quality of life. However, to further elucidate the mechanisms of the ketogenic diet as a therapy and evaluate its application in clinical practice, more molecular studies as well as uniformly controlled clinical trials are needed.

Induced Ketosis as a Treatment for Neuroprogressive Disorders: Food for Thought?

Induced ketosis (or ketone body ingestion) can ameliorate several changes associated with neuroprogressive disorders, including schizophrenia, bipolar disorder, and major depressive disorder. Thus, the effects of glucose hypometabolism can be bypassed through the entry of beta-hydroxybutyrate, providing an alternative source of energy to glucose. The weight of evidence suggests that induced ketosis reduces levels of oxidative stress, mitochondrial dysfunction, and inflammation-core features of the above disorders. There are also data to suggest that induced ketosis may be able to target other molecules and signaling pathways whose levels and/or activity are also known to be abnormal in at least some patients suffering from these illnesses such as peroxisome proliferator-activated receptors, increased activity of the Kelch-like ECH-associated protein/nuclear factor erythroid 2-related factor 2, Sirtuin-1 nuclear factor-κB p65, and nicotinamide adenine dinucleotide (NAD). This review explains the mechanisms by which induced ketosis might reduce mitochondrial dysfunction, inflammation, and oxidative stress in neuropsychiatric disorders and ameliorate abnormal levels of molecules and signaling pathways that also appear to contribute to the pathophysiology of these illnesses. This review also examines safety data relating to induced ketosis over the long term and discusses the design of future studies.

Interleukin-1β is a potential therapeutic target for periodontitis: a narrative review

Interleukin(IL)-1β, a pro-inflammatory cytokine, was elevated and participates in periodontitis. Not only the link between IL-1β and periodontitis was proved by clinical evidence, but also the increased IL-1β triggers a series of inflammatory reactions and promotes bone resorption. Currently, IL-1β blockage has been therapeutic strategies for autoimmune and autoinflammatory diseases such as rheumatoid arthritis, cryopyrin-associated periodic syndromes, gout and type II diabetes mellitus. It is speculated that IL-1β be a potential therapeutic target for periodontitis. The review focuses on the production, mechanism, present treatments and future potential strategies for IL-1β in periodontitis.

Resolvin D1 reduces mitochondrial damage to photoreceptors of primary retinal cells exposed to high glucose

No study has investigated the interaction of Resolvin D1 (RvD1) with mitochondrial damage of retinal cells caused by diabetes. This study aims to investigate the effects of RvD1 (50 nM) on morphological and biochemical indicators of mitochondrial damage in primary retinal cells exposed to 30 mM d-glucose high glucose (HG). HG-cells exhibited photoreceptor damage characterized by short and small mitochondria with prevalent mitochondrial disruption, fragmentation, and aggregation. The cells had low mitochondrial transporters TIMM44 and TOMM40, Connexin 43, NAD/NADH ratio, and ATP levels, whereas increased cytosolic cytochrome c. Moreover, they expressed high cytosolic metalloproteinase matrix metallopeptidase 9 (MMP-9) and MMP-2 activity. HG-cells treated with RvD1 (50 nM) showed reduced reactive oxygen species levels, improved mitochondrial morphology and function, promoted mitochondrial DNA repair by OGG1, and reduced cell apoptosis and metalloproteinase activity. Therefore, RvD1 induces protection from high glucose-load to the retinal cell and promotes their survival by decreasing cytosolic MMP and mitochondrial damage.