Acetate supplementation reduces microglia activation and brain interleukin-1β levels in a rat model of Lyme neuroborreliosis

Prebiotic inulin enhances gut microbial metabolism and anti-inflammation in apolipoprotein E4 mice with sex-specific implications

Gut dysbiosis has been identified as a crucial factor of Alzheimer's disease (AD) development for apolipoprotein E4 (APOE4) carriers. Inulin has shown the potential to mitigate dysbiosis. However, it remains unclear whether the dietary response varies depending on sex. In the study, we fed 4-month-old APOE4 mice with inulin for 16 weeks and performed shotgun metagenomic sequencing to determine changes in microbiome diversity, taxonomy, and functional gene pathways. We also formed the same experiments with APOE3 mice to identify whether there are APOE-genotype dependent responses to inulin. We found that APOE4 female mice fed with inulin had restored alpha diversity, significantly reduced Escherichia coli and inflammation-associated pathway responses. However, compared with APOE4 male mice, they had less metabolic responses, including the levels of short-chain fatty acids-producing bacteria and the associated kinases, especially those related to acetate and Erysipelotrichaceae. These diet- and sex- effects were less pronounced in the APOE3 mice, indicating that different APOE variants also play a significant role. The findings provide insights into the higher susceptibility of APOE4 females to AD, potentially due to inefficient energy production, and imply the importance of considering precision nutrition for mitigating dysbiosis and AD risk in the future.

Traditional Chinese medicine for the treatment of Alzheimer's disease: A focus on the microbiota-gut-brain axis

Alzheimer's disease (AD), the most frequent cause of dementia, is a neurodegenerative disorder characterised by a progressive decline in cognitive function that is associated with the formation of amyloid beta plaques and neurofibrillary tangles. Gut microbiota comprises of a complex community of microorganisms residing in the gastrointestinal ecosystem. These microorganisms can participate in gut-brain axis activities, thereby affecting cognitive function and associated behaviours. Increasing evidence has indicated that gut dysbiosis can jeopardise host immune responses and promote inflammation, which may be an initiating factor for the onset and evolution of AD. Traditional Chinese medicine (TCM) is a promising resource which encompasses immense chemical diversity and multiple-target characteristics for the treatment of AD. Many TCMs regulate the gut microbiota during treatment of diseases, indicating that gut microbiota may be an important target for TCM efficacy. In this review, we summarised the role of the microbiota-gut-brain axis in the development of AD and the effects of TCM in treating AD by regulating the gut microbiota. We anticipate that this review will provide novel perspectives and strategies for future AD research and treatments.

Glyceryl triacetate feeding in mice increases plasma acetate levels but has no anticonvulsant effects in acute electrical seizure models

INTRODUCTION

Acetate has been shown to have neuroprotective and anti-inflammatory effects. It is oxidized by astrocytes and can thus provide auxiliary energy to the brain in addition to glucose. Therefore, we hypothesized that it may protect against seizures, which is investigated here by feeding glyceryl triacetate (GTA), to provide high amounts of acetate without raising sodium or acid levels.

METHOD

CD1 male mice were fed controlled diets with or without GTA for up to three weeks. Body weights, blood glucose levels, plasma short-chain fatty acid levels, and other hematological parameters were monitored. Seizure thresholds were determined in 6 Hz and maximal electroshock seizure threshold (MEST) tests. Antioxidant capacities were evaluated in the cerebral cortex and plasma using a ferric reducing antioxidant power (FRAP) assay and Trolox equivalent antioxidant capacity assay.

RESULTS

Body weight gain was similar with both diets with and without GTA in two experiments. Glyceryl triacetate-fed groups showed 2-3- and 1.6-fold increased acetate and propionate levels in plasma, respectively. Glucose levels were unaltered in blood collected from the tail tip but increased in trunk blood. No differences were found in the activity of cerebral cortex acetyl-CoA synthetase. In the 6 Hz threshold test, seizure thresholds were lower by 3 mA and 2.4 mA after 8 and 14 days, respectively, in the GTA compared to the control diet-fed group, but showed no difference on day 16, showing that GTA has small, but inconsistent proconvulsant effects in this model. In MEST tests, a slightly increased seizure threshold (1 mA) was found on day 19 in the GTA-fed group, but not in another experiment on day 21. There were no differences in antioxidant capacity in plasma or cortex between the two groups.

CONCLUSION

Glyceryl triacetate feeding showed no antioxidant effects nor beneficial changes in acute electrical seizure threshold mouse models, despite its ability to increase plasma acetate levels.

The role of short-chain fatty acids in central nervous system diseases

Previous studies have found that intracorporal short-chain fatty acids (SCFAs), as the main metabolites of the gut microbiota, play important roles in the intestinal physiology and immune function. Along with the in-depth study of the brain-gut axis, the attention to the roles of SCFAs in central nervous system (CNS) has been raised. It has been found that SCFAs function in CNS diseases by regulating inflammatory response, neuronal apoptosis, oxidative stress, the integrity of the blood-brain barrier (BBB) and so on. Here, the changes, the effects and the mechanisms of different SCFA as individual or mixture in different CNS diseases were summarized. It is expected to lead to increased interest in SCFAs studies as an important regulator in CNS diseases and provide feasible suggestions based on SCFAs for the therapy of CNS diseases in the future.

Gut Microbiota as a Hidden Player in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD), the most common neurodegenerative disorder, is accompanied by cognitive impairment and shows representative pathological features, including senile plaques and neurofibrillary tangles in the brain. Recent evidence suggests that several systemic changes outside the brain are associated with AD and may contribute to its pathogenesis. Among the factors that induce systemic changes in AD, the gut microbiota is increasingly drawing attention. Modulation of gut microbiome, along with continuous attempts to remove pathogenic proteins directly from the brain, is a viable strategy to cure AD. Seeking a holistic understanding of the pathways throughout the body that can affect the pathogenesis, rather than regarding AD solely as a brain disease, may be key to successful therapy. In this review, we focus on the role of the gut microbiota in causing systemic manifestations of AD. The review integrates recently emerging concepts and provides potential mechanisms about the involvement of the gut-brain axis in AD, ranging from gut permeability and inflammation to bacterial translocation and cross-seeding.

The Gut Microbiome as a Regulator of the Neuroimmune Landscape

The gut microbiome influences many host physiologies, spanning gastrointestinal function, metabolism, immune homeostasis, neuroactivity, and behavior. Many microbial effects on the host are orchestrated by bidirectional interactions between the microbiome and immune system. Imbalances in this dialogue can lead to immune dysfunction and immune-mediated conditions in distal organs including the brain. Dysbiosis of the gut microbiome and dysregulated neuroimmune responses are common comorbidities of neurodevelopmental, neuropsychiatric, and neurological disorders, highlighting the importance of the gut microbiome–neuroimmune axis as a regulator of central nervous system homeostasis. In this review, we discuss recent evidence supporting a role for the gut microbiome in regulating the neuroimmune landscape in health and disease.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The dual effect of acetate on microglial TNF-α production

INTRODUCTION

Short-Chain Fatty Acids (SCFA) are products of intestinal microbial metabolism that can reach the brain and alter microglia in health and disease contexts. However, data are conflicting on the effect of acetate, the most abundant SCFA in the blood, in these cells.

OBJECTIVE

The authors aimed to investigate acetate as a modulator of the inflammatory response in microglia stimulated with LPS.

METHOD

The authors used an immortalized cell line, C8-B4, and primary cells for in vitro treatments with acetate and LPS. Cell viability was analyzed by MTT, cytokine by RT-PCR, ELISA, and flow cytometry. The authors also performed in vivo and in silico analyses to study the role of acetate and the TNF-α contribution to the development of Experimental Autoimmune Encephalomyelitis (EAE).

RESULTS

Acetate co-administered with LPS was able to exacerbate the production of pro-inflammatory cytokines at gene and protein levels in cell lines and primary culture of microglia. However, the same effects were not observed when acetate was administered alone or as pretreatment, prior to the LPS stimulus. Additionally, pharmacological inhibition of histone deacetylase concomitantly with acetate and LPS led to decreased TNF-α production. In silico analysis showed a crucial role of the TNF-α pathway in EAE development. Moreover, acetate administration in vivo during the initial phase of EAE led to a better disease outcome and reduced TNF-α production.

CONCLUSION

Treatment with acetate was able to promote the production of TNF-α in a concomitant LPS stimulus of microglia. However, the immune modulation of microglia by acetate pretreatment may be a component in the generation of future therapies for neurodegenerative diseases.

Effects of acetate on cerebral blood flow, systemic inflammation, and behavior in alcohol use disorder

BACKGROUND

Alcohol use disorders (AUDs) are associated with altered regulation of physiological processes in the brain. Acetate, a metabolite of ethanol, has been implicated in several processes that are disrupted in AUDs including transcriptional regulation, metabolism, inflammation, and neurotransmission. To further understand the effects of acetate on brain function in AUDs, we investigated the effects of acetate on cerebral blood flow (CBF), systemic inflammatory cytokines, and behavior in AUD.

METHODS

Sixteen participants with AUD were recruited from a nonmedical, clinically managed detoxification center. Each participant received acetate and placebo in a randomly assigned order of infusion and underwent 3T MR scanning using quantitative pseudo-continuous arterial spin labeling. Participants and the study team were blinded to the infusion. CBF values (ml/100 g/min) extracted from thalamus were compared between placebo and acetate using a mixed effect linear regression model accounting for infusion order. Voxel-wise CBF comparisons were set at threshold of p < 0.05 cluster-corrected for multiple comparisons, voxel-level p < 0.0001. Plasma cytokine levels and behavior were also assessed between infusions.

RESULTS

Fifteen men and 1 woman were enrolled with Alcohol Use Disorders Identification Test (AUDIT) scores between 13 and 38 with a mean of 28.3 ± 9.1. Compared to placebo, acetate administration increased CBF in the thalamus bilaterally (Left: 51.2 vs. 68.8, p < 0.001; Right: 53.7 vs. 69.6, p = 0.001), as well as the cerebellum, brainstem, and cortex. Older age and higher AUDIT scores were associated with increases in acetate-induced thalamic blood flow. Cytokine levels and behavioral measures did not differ between placebo and acetate infusions.

CONCLUSIONS

This pilot study in AUD suggests that during the first week of abstinence from alcohol, the brain's response to acetate differs by brain region and this response may be associated with the severity of alcohol dependence.

Exploring the Role of ATP-Citrate Lyase in the Immune System

Studies over the past decade have revealed that metabolism profoundly influences immune responses. In particular, metabolism causes epigenetic regulation of gene expression, as a growing number of metabolic intermediates are substrates for histone post-translational modifications altering chromatin structure. One of these substrates is acetyl-coenzyme A (CoA), which donates an acetyl group for histone acetylation. Cytosolic acetyl-CoA is also a critical substrate for de novo synthesis of fatty acids and sterols necessary for rapid cellular growth. One of the main enzymes catalyzing cytosolic acetyl-CoA formation is ATP-citrate lyase (ACLY). In addition to its classical function in the provision of acetyl-CoA for de novo lipogenesis, ACLY contributes to epigenetic regulation through histone acetylation, which is increasingly appreciated. In this review we explore the current knowledge of ACLY and acetyl-CoA in mediating innate and adaptive immune responses. We focus on the role of ACLY in supporting de novo lipogenesis in immune cells as well as on its impact on epigenetic alterations. Moreover, we summarize alternative sources of acetyl-CoA and their contribution to metabolic and epigenetic regulation in cells of the immune system.

Acetate Revisited: A Key Biomolecule at the Nexus of Metabolism, Epigenetics, and Oncogenesis - Part 2: Acetate and ACSS2 in Health and Disease

Acetate, the shortest chain fatty acid, has been implicated in providing health benefits whether it is derived from the diet or is generated from microbial fermentation of fiber in the gut. These health benefits range widely from improved cardiac function to enhanced red blood cell generation and memory formation. Understanding how acetate could influence so many disparate biological functions is now an area of intensive research. Protein acetylation is one of the most common post-translational modifications and increased systemic acetate strongly drives protein acetylation. By virtue of acetylation impacting the activity of virtually every class of protein, acetate driven alterations in signaling and gene transcription have been associated with several common human diseases, including cancer. In part 2 of this review, we will focus on some of the roles that acetate plays in health and human disease. The acetate-activating enzyme acyl-CoA short-chain synthetase family member 2 (ACSS2) will be a major part of that focus due to its role in targeted protein acetylation reactions that can regulate central metabolism and stress responses. ACSS2 is the only known enzyme that can recycle acetate derived from deacetylation reactions in the cytoplasm and nucleus of cells, including both protein and metabolite deacetylation reactions. As such, ACSS2 can recycle acetate derived from histone deacetylase reactions as well as protein deacetylation reactions mediated by sirtuins, among many others. Notably, ACSS2 can activate acetate released from acetylated metabolites including N-acetylaspartate (NAA), the most concentrated acetylated metabolite in the human brain. NAA has been associated with the metabolic reprograming of cancer cells, where ACSS2 also plays a role. Here, we discuss the context-specific roles that acetate can play in health and disease.

Borrelia burgdorferi hijacks cellular metabolism of immune cells: Consequences for host defense

Changes in cellular metabolism have proven to be important factors in driving cell behavior. It has been shown that cellular metabolism of immune cells changes when exposed to or infected by several pathogens: while this is often an adaptation of the host cells to the infection, sometimes it represents a mechanism through which the pathogens evade immune activation. Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is a pathogen that highly depends on the host to survive, as the bacterium lacks many central metabolic pathways to generate its own nutrients. It is therefore quite likely that the bacterium interacts with host cells to obtain these metabolites and thereby affects metabolism in the host. Previously, several studies have assessed metabolic pathways in B. burgdorferi s.l. and how it adapts to its different host species. However, few studies have looked into how the interaction with the bacterium might affect the host cell metabolism. In this review we present the major metabolic pathways activated during Lyme borreliosis, viewed from both bacterium and host metabolism, and we discuss how these pathways interact with each other, and how they influence pathogenesis of Lyme borreliosis.

Effects of Alcohol and Acetate on Cerebral Blood Flow: A Pilot Study

BACKGROUND

Acute alcohol produces effects on cerebral metabolism and blood flow. Alcohol is converted to acetate, which serves as a source of energy for the brain and is an agonist at G protein-coupled receptors distributed in different cell types in the body including neurons. Acetate has been hypothesized to play a role in the cerebral blood flow (CBF) response after alcohol ingestion. We tested whether administration of acetate would alter CBF in a pattern similar to or different from that of alcohol ingestion in healthy individuals.

METHODS

Twenty-four healthy participants were assigned by convenience to receive either 0.6 g/kg alcohol orally (n = 12) or acetate intravenously (n = 12). For each participant, CBF maps were acquired using an arterial spin labeling sequence on a 3T magnetic resonance scanner after placebo and after drug administration. Whole-brain CBF maps were compared between placebo and drug using a paired t-test, and set at a threshold of p < 0.05 corrected for multiple comparisons (k ≥ 142 voxels, ≥3.78 cm3 ), voxel-level p < 0.005. Intoxication was measured after placebo and drug administration with a Subjective High Assessment Scale (SHAS-7).

RESULTS

Compared to placebo, alcohol and acetate were associated with increased CBF in the medial thalamus. Alcohol, but not acetate, was associated with increased CBF in the right orbitofrontal, medial prefrontal and cingulate cortex, and hippocampus. Plasma acetate levels increased following administration of alcohol and acetate and did not differ between the 2 arms. Alcohol, but not acetate, was associated with an increase in SHAS-7 scores (p < 0.001).

CONCLUSIONS

Increased thalamic CBF associated with either alcohol or acetate administration suggests that the thalamic CBF response after alcohol could be mediated by acetate. Compared to other brain regions, thalamus may differ in its ability to metabolize acetate or expression of receptors responsive to acetate. Increased prefrontal and limbic CBF associated with alcohol may be linked to alcohol's behavioral effects.

Rhesus Brain Transcriptomic Landscape in an ex vivo Model of the Interaction of Live Borrelia Burgdorferi With Frontal Cortex Tissue Explants

Lyme neuroborreliosis (LNB) is the most dangerous manifestation of Lyme disease caused by the spirochete Borrelia burgdorferi which can reach the central nervous system most commonly presenting with lymphocytic meningitis; however, the molecular basis for neuroborreliosis is still poorly understood. We incubated explants from the frontal cortex of three rhesus brains with medium alone or medium with added live Borrelia burgdorferi for 6, 12, and 24 h and isolated RNA from each group was used for RNA sequencing with further bioinformatic analysis. Transcriptomic differences between the ex vivo model of live Borrelia burgdorferi with rhesus frontal cortex tissue explants and the controls during the progression of the infection were identified. A total of 2249, 1064, and 420 genes were significantly altered, of which 80.7, 52.9, and 19.8% were upregulated and 19.3, 47.1, 80.2% were downregulated at 6, 12, and 24 h, respectively. Gene ontology and KEGG pathway analyses revealed various pathways related to immune and inflammatory responses during the spirochete infection were enriched which is suggested to have a causal role in the pathogenesis of neurological Lyme disease. Moreover, we propose that the overexpressed FOLR2 which was demonstrated by the real-time PCR and western blotting could play a key role in neuroinflammation of the neuroborreliosis based on PPI analysis for the first time. To our knowledge, this is the first study to provide comprehensive information regarding the transcriptomic signatures that occur in the frontal cortex of the brain upon exposure to Borrelia burgdorferi, and suggest that FOLR2 is a promising target that is associated with neuroinflammation and may represent a new diagnostic or therapeutic marker in LNB.

NF‑κB is a key modulator in the signaling pathway of Borrelia burgdorferi BmpA‑induced inflammatory chemokines in murine microglia BV2 cells

Lyme disease, caused by the bacterial spirochete Borrelia burgdorferi, is a tick‑borne zoonosis. Lyme neuroborreliosis is a principal manifestation of Lyme disease and its pathogenesis remains incompletely understood. Recent studies have demonstrated that Borrelia burgdorferi lipoproteins caused similar inflammatory effects as exhibited in Lyme neuroborreliosis. Basic membrane protein A (BmpA) is one of the dominant lipoproteins in the Borrelia burgdorferi membrane. In addition, nuclear factor κ‑B (NF‑κB) modulates the regulation of gene transcription associated with immunity and inflammation; however, in unstimulated cells, NF‑κB is combined with the inhibitor of NF‑κB (IκB‑β). Therefore, it was hypothesized that NF‑κB may be associated with BmpA‑induced inflammation and the occurrence of Lyme neuroborreliosis. Therefore, the aim of the present study was to investigate the role that NF‑κB serves in the signaling pathway of rBmpA‑induced inflammatory chemokines. The present study measured the expression levels of NF‑κB, IκB‑β and inflammatory chemokines following recombinant BmpA (rBmpA) stimulation of murine microglia BV2 cells. Following stimulation with rBmpA, concentrations of pro‑inflammatory cytokines including C‑X‑C motif chemokine 2, C‑C motif chemokine (CCL) 5 and CCL22 were determined by ELISA analysis. Reverse transcription‑quantitative polymerase chain reaction and western blotting were used to detect the expression levels of NF‑κB p65 and IκB‑β. The data demonstrated that concentrations of these chemokines in cell supernatants increased significantly following rBmpA stimulation. NF‑κB was overexpressed, but IκB‑β expression was significantly decreased. In conclusion, these results suggested that NF‑κB serves an important stimulatory role in the signaling pathway of rBmpA‑induced inflammatory chemokines in BV2 cells.

Microbiota in obesity: interactions with enteroendocrine, immune and central nervous systems

Western diets, with high consumption of simple sugars and saturated fats, contribute to the rise in the prevalence of obesity. It now seems clear that high-fat diets cause obesity, at least in part, by modifying the composition and function of the microorganisms that colonize in the gastrointestinal tract, the microbiota. The exact pathways by which intestinal microbiota contribute to obesity remain largely unknown. High-fat diet-induced alterations in intestinal microbiota have been suggested to increase energy extraction, intestinal permeability and systemic inflammation while decreasing the capability to generate obesity-suppressing short-chain fatty acids. Moreover, by increasing systemic inflammation, microglial activation and affecting vagal nerve activity, 'obese microbiota' indirectly influence hypothalamic gene expression and promote overeating. Because the potential of intestinal microbiota to induce obesity has been recognized, multiple ways to modify its composition and function are being investigated to provide novel preventive and therapeutic strategies against diet-induced obesity.

Dietary metabolites derived from gut microbiota: critical modulators of epigenetic changes in mammals

The mammalian gastrointestinal tract harbors trillions of commensal microorganisms, collectively known as the microbiota. The microbiota is a critical source of environmental stimuli and, thus, has a tremendous impact on the health of the host. The microbes within the microbiota regulate homeostasis within the gut, and any alteration in their composition can lead to disorders that include inflammatory bowel disease, allergy, autoimmune disease, diabetes, mental disorders, and cancer. Hence, restoration of the gut flora following changes or imbalance is imperative for the host. The low-molecular-weight compounds and nutrients such as short-chain fatty acids, polyamines, polyphenols, and vitamins produced by microbial metabolism of nondigestible food components in the gut actively participate in various epigenomic mechanisms that reprogram the genome by altering the transcriptional machinery of a cell in response to environmental stimuli. These epigenetic modifications are caused by a set of highly dynamic enzymes, notably histone acetylases, deacetylases, DNA methylases, and demethylases, that are influenced by microbial metabolites and other environmental cues. Recent studies have shown that host expression of histone acetylases and histone deacetylases is important for regulating communication between the intestinal microbiota and the host cells. Histone acetylases and deacetylases influence the molecular expression of genes that affect not only physiological functions but also behavioral shifts that occur via neuroepigenetic modifications of genes. The underlying molecular mechanisms, however, have yet to be fully elucidated and thus provide a new area of research. The present review provides insights into the current understanding of the microbiota and its association with mammalian epigenomics as well as the interaction of pathogens and probiotics with host epigenetic machinery.

Borrelia burgdorferi basic membrane protein A could induce chemokine production in murine microglia cell line BV2

Lyme neuroborreliosis is a nervous system infectious disease caused by Borrelia burgdorferi (B. burgdorferi). It has been demonstrated that cytokines induced by B. burgdorferi are related to Lyme neuroborreliosis. Microglia is known as a key player in the immune responses that occur within the central nervous system. In response to inflammation, it will be activated and generate cytokines and chemokines. Experiments in vitro cells have showed that B. Burgdorferi membrane protein A (BmpA), a major immunogen of B. Burgdorferi, could induce Lyme arthritis and stimulate human and murine lymphocytes to produce inflammatory cytokines. In our study, the murine microglia BV2 cell line was used as a cell model to explore the stimulating effects of recombinant BmpA (rBmpA); Chemokine chip, ELISA and QPCR technology were used to measure the production of chemokines from microglial cells stimulated by rBmpA. Compared with the negative control group, CXCL2, CCL22, and CCL5 concentrations in the cell supernatant increased significantly after the rBmpA stimulation; the concentration of these chemokines increased with rBmpA concentration increasing; the mRNA expression levels of chemokines (CXCL2, CCL22, and CCL5) in murine BV2 cells increased significantly with 10 μg/mL and 20 μg/mL rBmpA stimulation; CXCL13 was not change after the rBmpA stimulation. Our study shows that chemokines, such as CXCL2, CCL22, and CCL5 were up-regulated by the rBmpA in the BV2 cells. The production of chemokines in Lyme neuroborreliosis may be mainly from microglia cells and the rBmpA may be closely related with the development of Lyme neuroborreliosis.

Increasing acetyl-CoA metabolism attenuates injury and alters spinal cord lipid content in mice subjected to experimental autoimmune encephalomyelitis

Acetate supplementation increases brain acetyl-CoA metabolism, alters histone and non-histone protein acetylation, increases brain energy reserves, and is anti-inflammatory and neuroprotective in rat models of neuroinflammation and neuroborreliosis. To determine the impact acetate supplementation has on a mouse model of multiple sclerosis, we quantified the effect treatment had on injury progression, spinal cord lipid content, phospholipase levels, and myelin structure in mice subjected to experimental autoimmune encephalomyelitis (EAE). EAE was induced by inoculating mice with a myelin oligodendrocyte glycoprotein peptide fragment (MOG_35-55 ), and acetate supplementation was maintained with 4 g/kg glyceryl triacetate by a daily oral gavage. Acetate supplementation prevented the onset of clinical signs in mice subject to EAE compared to control-treated mice. Furthermore, acetate supplementation prevented the loss of spinal cord ethanolamine and choline glycerophospholipid and phosphatidylserine in mice subjected to EAE compared to EAE animals treated with water. Treatment increased saturated and monounsaturated fatty acid levels in phosphatidylserine compared to controls suggesting that acetate was utilized to increase spinal cord fatty acid content. Also, acetate supplementation prevented the loss of spinal cord cholesterol in EAE animals but did not change cholesteryl esters. Treatment significantly increased GD3 and GD1a ganglioside levels in EAE mice when compared to EAE mice treated with water. Treatment returned levels of phosphorylated and non-phosphorylated cytosolic phospholipase A₂ (cPLA₂ ) levels back to baseline and based on FluoroMyelin™ histochemistry maintained myelin structural characteristics. Overall, these data suggest that acetate supplementation may modulate lipid metabolism in mice subjected to EAE.

MicroRNA and mRNA Transcriptome Profiling in Primary Human Astrocytes Infected with Borrelia burgdorferi

Lyme disease is caused by infection with the bacterium Borrelia burgdorferi (Bb), which is transmitted to humans by deer ticks. The infection manifests usually as a rash and minor systemic symptoms; however, the bacteria can spread to other tissues, causing joint pain, carditis, and neurological symptoms. Lyme neuroborreliosis presents itself in several ways, such as Bell's palsy, meningitis, and encephalitis. The molecular basis for neuroborreliosis is poorly understood. Analysis of the changes in the expression levels of messenger RNAs and non-coding RNAs, including microRNAs, following Bb infection could therefore provide vital information on the pathogenesis and clinical symptoms of neuroborreliosis. To this end, we used cultured primary human astrocytes, key responders to CNS infection and important components of the blood-brain barrier, as a model system to study RNA and microRNA changes in the CNS caused by Bb. Using whole transcriptome RNA-seq, we found significant changes in 38 microRNAs and 275 mRNAs at 24 and 48 hours following Bb infection. Several of the RNA changes affect pathways involved in immune response, development, chromatin assembly (including histones) and cell adhesion. Further, several of the microRNA predicted target mRNAs were also differentially regulated. Overall, our results indicate that exposure to Bb causes significant changes to the transcriptome and microRNA profile of astrocytes, which has implications in the pathogenesis, and hence potential treatment strategies to combat this disease.

Acetate as a Metabolic and Epigenetic Modifier of Cancer Therapy

Metabolic networks are significantly altered in neoplastic cells. This altered metabolic program leads to increased glycolysis and lipogenesis and decreased dependence on oxidative phosphorylation and oxygen consumption. Despite their limited mitochondrial respiration, cancer cells, nonetheless, derive sufficient energy from alternative carbon sources and metabolic pathways to maintain cell proliferation. They do so, in part, by utilizing fatty acids, amino acids, ketone bodies, and acetate, in addition to glucose. The alternative pathways used in the metabolism of these carbon sources provide opportunities for therapeutic manipulation. Acetate, in particular, has garnered increased attention in the context of cancer as both an epigenetic regulator of posttranslational protein modification, and as a carbon source for cancer cell biomass accumulation. However, to date, the data have not provided a clear understanding of the precise roles that protein acetylation and acetate oxidation play in carcinogenesis, cancer progression or treatment. This review highlights some of the major issues, discrepancies, and opportunities associated with the manipulation of acetate metabolism and acetylation-based signaling in cancer development and treatment.

Acetate supplementation as a means of inducing glioblastoma stem-like cell growth arrest

Glioblastoma (GBM), the most common primary adult malignant brain tumor, is associated with a poor prognosis due, in part, to tumor recurrence mediated by chemotherapy and radiation resistant glioma stem-like cells (GSCs). The metabolic and epigenetic state of GSCs differs from their non-GSC counterparts, with GSCs exhibiting greater glycolytic metabolism and global hypoacetylation. However, little attention has been focused on the potential use of acetate supplementation as a therapeutic approach. N-acetyl-l-aspartate (NAA), the primary storage form of brain acetate, and aspartoacylase (ASPA), the enzyme responsible for NAA catalysis, are significantly reduced in GBM tumors. We recently demonstrated that NAA supplementation is not an appropriate therapeutic approach since it increases GSC proliferation and pursued an alternative acetate source. The FDA approved food additive Triacetin (glyceryl triacetate, GTA) has been safely used for acetate supplementation therapy in Canavan disease, a leukodystrophy due to ASPA mutation. This study characterized the effects of GTA on the proliferation and differentiation of six primary GBM-derived GSCs relative to established U87 and U251 GBM cell lines, normal human cerebral cortical astrocytes, and murine neural stem cells. GTA reduced proliferation of GSCs greater than established GBM lines. Moreover, GTA reduced growth of the more aggressive mesenchymal GSCs greater than proneural GSCs. Although sodium acetate induced a dose-dependent reduction of GSC growth, it also reduced cell viability. GTA-mediated growth inhibition was not associated with differentiation, but increased protein acetylation. These data suggest that GTA-mediated acetate supplementation is a novel therapeutic strategy to inhibit GSC growth.

Acetate supplementation modulates brain adenosine metabolizing enzymes and adenosine A₂A receptor levels in rats subjected to neuroinflammation

Background

Acetate supplementation reduces neuroglia activation and pro-inflammatory cytokine expression in rat models of neuroinflammation and Lyme neuroborreliosis. Because single-dose glyceryl triacetate (GTA) treatment increases brain phosphocreatine and reduces brain AMP levels, we postulate that GTA modulates adenosine metabolizing enzymes and receptors, which may be a possible mechanism to reduce neuroinflammation.

Methods

To test this hypothesis, we quantified the ability of GTA to alter brain levels of ecto-5’-nucleotidase (CD73), adenosine kinase (AK), and adenosine A_2A receptor using western blot analysis and CD73 activity by measuring the rate of AMP hydrolysis. Neuroinflammation was induced by continuous bacterial lipopolysaccharide (LPS) infusion in the fourth ventricle of the brain for 14 and 28 days. Three treatment strategies were employed, one and two where rats received prophylactic GTA through oral gavage with LPS infusion for 14 or 28 days. In the third treatment regimen, an interventional strategy was used where rats were subjected to 28 days of neuroinflammation, and GTA treatment was started on day 14 following the start of the LPS infusion.

Results

We found that rats subjected to neuroinflammation for 28 days had a 28% reduction in CD73 levels and a 43% increase in AK levels that was reversed with prophylactic acetate supplementation. CD73 activity in these rats was increased by 46% with the 28-day GTA treatment compared to the water-treated rats. Rats subjected to neuroinflammation for 14 days showed a 50% increase in levels of the adenosine A_2A receptor, which was prevented with prophylactic acetate supplementation. Interventional GTA therapy, beginning on day 14 following the induction of neuroinflammation, resulted in a 67% increase in CD73 levels and a 155% increase in adenosine A_2A receptor levels.

Conclusion

These results support the hypothesis that acetate supplementation can modulate brain CD73, AK and adenosine A_2A receptor levels, and possibly influence purinergic signaling.

Acetate treatment increases fatty acid content in LPS-stimulated BV2 microglia

Acetate supplementation increases plasma acetate, brain acetyl-CoA, histone acetylation, phosphocreatine levels, and is anti-inflammatory in models of neuroinflammation and neuroborreliosis. Although radiolabeled acetate is incorporated into the cellular lipid pools, the effect that acetate supplementation has on lipid deposition has not been quantified. To determine the impact acetate-treatment has on cellular lipid content, we investigated the effect of acetate in the presence of bacterial lipopolysaccharide (LPS) on fatty acid, phospholipid, and cholesterol content in BV2 microglia. We found that 1, 5, and 10 mM of acetate in the presence of LPS increased the total fatty acid content in BV2 cells by 23, 34, and 14 % at 2 h, respectively. Significant increases in individual fatty acids were also observed with all acetate concentrations tested with the greatest increases occurring with 5 mM acetate in the presence of LPS. Treatment with 5 mM acetate in the absence of LPS increased total cholesterol levels by 11 %. However, neither treatment in the absence of LPS significantly altered the content of individual phospholipids or total phospholipid content. To determine the minimum effective concentration of acetate we measured the time- and concentration-dependent changes in histone acetylation using western blot analysis. These studies showed that 5 mM acetate was necessary to induce histone acetylation and at 10 mM acetate, the histone acetylation-state increased as early as 0.5 h following the start of treatment. These data suggest that acetate increases fatty acid content in LPS-stimulated BV2 microglia that is reflected by an increase in fatty acids esterified into membrane phospholipids.

N-Acetylaspartate reductions in brain injury: impact on post-injury neuroenergetics, lipid synthesis, and protein acetylation

N-Acetylaspartate (NAA) is employed as a non-invasive marker for neuronal health using proton magnetic resonance spectroscopy (MRS). This utility is afforded by the fact that NAA is one of the most concentrated brain metabolites and that it produces the largest peak in MRS scans of the healthy human brain. NAA levels in the brain are reduced proportionately to the degree of tissue damage after traumatic brain injury (TBI) and the reductions parallel the reductions in ATP levels. Because NAA is the most concentrated acetylated metabolite in the brain, we have hypothesized that NAA acts in part as an extensive reservoir of acetate for acetyl coenzyme A synthesis. Therefore, the loss of NAA after TBI impairs acetyl coenzyme A dependent functions including energy derivation, lipid synthesis, and protein acetylation reactions in distinct ways in different cell populations. The enzymes involved in synthesizing and metabolizing NAA are predominantly expressed in neurons and oligodendrocytes, respectively, and therefore some proportion of NAA must be transferred between cell types before the acetate can be liberated, converted to acetyl coenzyme A and utilized. Studies have indicated that glucose metabolism in neurons is reduced, but that acetate metabolism in astrocytes is increased following TBI, possibly reflecting an increased role for non-glucose energy sources in response to injury. NAA can provide additional acetate for intercellular metabolite trafficking to maintain acetyl CoA levels after injury. Here we explore changes in NAA, acetate, and acetyl coenzyme A metabolism in response to brain injury.

Acetate supplementation induces growth arrest of NG2/PDGFRα-positive oligodendroglioma-derived tumor-initiating cells

Cancer is associated with globally hypoacetylated chromatin and considerable attention has recently been focused on epigenetic therapies. N-acetyl-L-aspartate (NAA), the primary storage form of acetate in the brain, and aspartoacylase (ASPA), the enzyme responsible for NAA catalysis to generate acetate and ultimately acetyl-Coenzyme A for histone acetylation, are reduced in oligodendroglioma. The short chain triglyceride glyceryl triacetate (GTA), which increases histone acetylation and inhibits histone deacetylase expression, has been safely used for acetate supplementation in Canavan disease, a leukodystrophy due to ASPA mutation. We demonstrate that GTA induces cytostatic G₀ growth arrest of oligodendroglioma-derived cells in vitro, without affecting normal cells. Sodium acetate, at doses comparable to that generated by complete GTA catalysis, but not glycerol also promoted growth arrest, whereas long chain triglycerides promoted cell growth. To begin to elucidate its mechanism of action, the effects of GTA on ASPA and acetyl-CoA synthetase protein levels and differentiation of established human oligodendroglioma cells (HOG and Hs683) and primary tumor-derived oligodendroglioma cells that exhibit some features of cancer stem cells (grade II OG33 and grade III OG35) relative to an oligodendrocyte progenitor line (Oli-Neu) were examined. The nuclear localization of ASPA and acetyl-CoA synthetase-1 in untreated cells was regulated during the cell cycle. GTA-mediated growth arrest was not associated with apoptosis or differentiation, but increased expression of acetylated proteins. Thus, GTA-mediated acetate supplementation may provide a safe, novel epigenetic therapy to reduce the growth of oligodendroglioma cells without affecting normal neural stem or oligodendrocyte progenitor cell proliferation or differentiation.

Activation of the canonical nuclear factor-κB pathway is involved in isoflurane-induced hippocampal interleukin-1β elevation and the resultant cognitive deficits in aged rats

Although much recent evidence has demonstrated that neuroinflammation contributes to volatile anesthetic-induced cognitive deficits, there are few existing mechanistic explanations for this inflammatory process. This study was conducted to investigate the effects of the volatile anesthetic isoflurane on canonical nuclear factor (NF)-κB signaling, and to explore its association with hippocampal interleukin (IL)-1β levels and anesthetic-related cognitive changes in aged rats. After a 4-h exposure to 1.5% isoflurane in 20-month-old rats, increases in IκB kinase and IκB phosphorylation, as well as a reduction in the NF-κB inhibitory protein (IκBα), were observed in the hippocampi of isoflurane-exposed rats compared with control rats. These events were accompanied by an increase in NF-κB p65 nuclear translocation at 6h after isoflurane exposure and hippocampal IL-1β elevation from 1 to 6h after isoflurane exposure. Nevertheless, no significant neuroglia activation was observed. Pharmacological inhibition of NF-κB activation by pyrrolidine dithiocarbamate markedly suppressed the IL-1β increase and NF-κB signaling, and also mitigated the severity of cognitive deficits in the Morris water maze task. Overall, our results demonstrate that isoflurane-induced cognitive deficits may stem from upregulation of hippocampal IL-1β, partially via activation of the canonical NF-κB pathway, in aged rats.

Acetate reduces PGE2 release and modulates phospholipase and cyclooxygenase levels in neuroglia stimulated with lipopolysaccharide

Acetate supplementation attenuates neuroglial activation, increases histone and non-histone protein acetylation, reduces pro-inflammatory cytokine expression, and increases IL-4 transcription in rat models of neuroinflammation and Lyme's neuroborreliosis. Because eicosanoid signaling is involved in neuroinflammation, we measured the effect acetate treatment had on phospholipase, cyclooxygenase, and prostaglandin E2 (PGE2) levels in BV-2 microglia and primary astrocytes stimulated with lipopolysaccharide (LPS). In BV-2 microglia, we found that LPS increased the phosphorylation-state of cytosolic phospholipase A2 (cPLA2), reduced the levels of phospholipase C (PLC) β1, and increased the levels of cyclooxygenase (Cox)-1 and -2. Acetate treatment returned PLCβ1 and Cox-1 levels to normal, attenuated the increase in Cox-2, but had no effect on cPLA2 phosphorylation. In primary astrocytes, LPS increased the phosphorylation of cPLA2 and increased the levels of Cox-1 and Cox-2. Acetate treatment in these cells reduced secretory PLA2 IIA and PLCβ1 levels as compared to LPS-treatment groups, reversed the increase in cPLA2 phosphorylation, and returned Cox-1 levels to normal. Acetate treatment reduced PGE2 release in astrocytes stimulated with LPS to control levels, but did not alter PGE2 levels in BV-2 microglia. The amount of acetylated H3K9 bound to the promoter regions of Cox-1, Cox-2, IL-1β and NF-κB p65 genes, but not IL-4 in were increased in BV-2 microglia treated with acetate. These data suggest that acetate treatment can disrupt eicosanoid signaling in neuroglia that may, in part, be the result of altering gene expression due chromatin remodeling as a result of increasing H3K9 acetylation.

Acetate supplementation increases brain phosphocreatine and reduces AMP levels with no effect on mitochondrial biogenesis

Acetate supplementation in rats increases plasma acetate and brain acetyl-CoA levels. Although acetate is used as a marker to study glial energy metabolism, the effect that acetate supplementation has on normal brain energy stores has not been quantified. To determine the effect(s) that an increase in acetyl-CoA levels has on brain energy metabolism, we measured brain nucleotide, phosphagen and glycogen levels, and quantified cardiolipin content and mitochondrial number in rats subjected to acetate supplementation. Acetate supplementation was induced with glyceryl triacetate (GTA) by oral gavage (6 g/kg body weight). Rats used for biochemical analysis were euthanized using head-focused microwave irradiation at 2, and 4h following treatment to immediately stop metabolism. We found that acetate did not alter brain ATP, ADP, NAD, GTP levels, or the energy charge ratio [ECR, (ATP+½ ADP)/(ATP+ADP+AMP)] when compared to controls. However, after 4h of treatment brain phosphocreatine levels were significantly elevated with a concomitant reduction in AMP levels with no change in glycogen levels. In parallel studies where rats were treated with GTA for 28 days, we found that acetate did not alter brain glycogen and mitochondrial biogenesis as determined by measuring brain cardiolipin content, the fatty acid composition of cardiolipin and using quantitative ultra-structural analysis to determine mitochondrial density/unit area of cytoplasm in hippocampal CA3 neurons. Collectively, these data suggest that an increase in brain acetyl-CoA levels by acetate supplementation does increase brain energy stores however it has no effect on brain glycogen and neuronal mitochondrial biogenesis.

Modulation of inflammatory cytokines and mitogen-activated protein kinases by acetate in primary astrocytes

Acetate supplementation attenuates neuroglia activation in a rat model of neuroinflammation by a mechanism associated with an increase in brain acetyl-CoA, an alteration in histone acetylation, and reduction of interleukin (IL)-1β expression. We propose that reduced astroglial activation occurs by disrupting astrocyte-derived inflammatory signaling and cytokine release. Using primary astroglial cultures, we found that LPS (0-25 ng/ml, 4 h) increased tumor necrosis factor (TNF-α) and IL-1β in a concentration-dependent manner, which was reduced by treatment with sodium acetate (12 mM). LPS did not alter H3K9 acetylation or IL-6 levels, whereas acetate treatment increased H3K9 acetylation by 2-fold and decreased basal levels of IL-6 by 2-fold. Acetate treatment attenuated the LPS-induced increase in TNF-α mRNA, but did not reverse the mRNA levels of other pro-inflammatory cytokines. By contrast, LPS decreased TGF-β1 and IL-4 protein and TGF-β1 mRNA, all of which was reversed with acetate treatment. Further, we found that acetate treatment completely reversed LPS-induced phosphorylation of MAPK p38 and decreased basal levels of phosphorylated extracellular signal-regulated kinases1/2 (ERK1/2) by 2-fold. Acetate treatment also reversed LPS-elevated NF-κB p65, CCAAT/enhancer-binding protein beta protein levels, and reduced basal levels of phosphorylated NF-κB p65 at serine 536. These results suggest that acetate treatment has a net anti-inflammatory effect in LPS-stimulated astrocytes that is largely associated with a disruption in MAPK and NF-κB signaling.