The Identification of a SIRT6 Activator from Brown Algae Fucus distichus

Opportunities and challenges of fucoidan for tumors therapy

The large-scale collections, screening and discovery of biologically active and pharmacologically significant marine-derived natural products have garnered tremendous attraction. Edible brown algae are rich in fucoidan. Importantly, fucoidan has been reported to inhibit carcinogenesis and metastasis mainly through the regulation of deregulated cell signaling pathways. This review summarizes the structural features of fucoidan, including monosaccharide type, sulfate content, and main chain structure. We have set spotlight on fucoidan-mediated tumor suppressive effects in cell cultures studies and tumor-bearing rodent models. Fucoidan exerts anti-tumor effects primarily through the inhibition of tumor cell viability, proliferation and metastatic dissemination of cancer cells from primary tumor sites to distant secondary sites. Fucoidan not only promotes immunological responses in tumor microenvironment but also induces apoptotic death in cancer cells. In addition, fucoidan can be used as a dietary supplement for preventive purposes, in combination with other drugs as complementary and alternative medicine or with nanoparticle modifications will be the future of fucoidan use. Cutting-edge research related to fucoidan has catalyzed the transition of fucoidan from preclinical studies to different phases of clinical trials. Rationally designed clinical trials for the critical evaluation of fucoidan against different cancers will be valuable to reap full benefits.

Underlying Mechanisms of Brain Aging and Neurodegenerative Diseases as Potential Targets for Preventive or Therapeutic Strategies Using Phytochemicals

During aging, several tissues and biological systems undergo a progressive decline in function, leading to age-associated diseases such as neurodegenerative, inflammatory, metabolic, and cardiovascular diseases and cancer. In this review, we focus on the molecular underpinning of senescence and neurodegeneration related to age-associated brain diseases, in particular, Alzheimer's and Parkinson's diseases, along with introducing nutrients or phytochemicals that modulate age-associated molecular dysfunctions, potentially offering preventive or therapeutic benefits. Based on current knowledge, the dysregulation of microglia genes and neuroinflammation, telomere attrition, neuronal stem cell degradation, vascular system dysfunction, reactive oxygen species, loss of chromosome X inactivation in females, and gut microbiome dysbiosis have been seen to play pivotal roles in neurodegeneration in an interactive manner. There are several phytochemicals (e.g., curcumin, EGCG, fucoidan, galangin, astin C, apigenin, resveratrol, phytic acid, acacetin, daucosterol, silibinin, sulforaphane, withaferin A, and betulinic acid) that modulate the dysfunction of one or several key genes (e.g., TREM2, C3, C3aR1, TNFA, NF-kb, TGFB1&2, SIRT1&6, HMGB1, and STING) affected in the aged brain. Although phytochemicals have shown promise in slowing down the progression of age-related brain diseases, more studies to identify their efficacy, alone or in combinations, in preclinical systems can help to design novel nutritional strategies for the management of neurodegenerative diseases in humans.

SIRT6: A potential therapeutic target for diabetic cardiomyopathy

The abnormal lipid metabolism in diabetic cardiomyopathy can cause myocardial mitochondrial dysfunction, lipotoxicity, abnormal death of myocardial cells, and myocardial remodeling. Mitochondrial homeostasis and normal lipid metabolism can effectively slow down the development of diabetic cardiomyopathy. Recent studies have shown that SIRT6 may play an important role in the pathological changes of diabetic cardiomyopathy such as myocardial cell death, myocardial hypertrophy, and myocardial fibrosis by regulating mitochondrial oxidative stress and glucose and lipid metabolism. Therefore, understanding the function of SIRT6 and its role in the pathogenesis of diabetic cardiomyopathy is of great significance for exploring and developing new targets and drugs for the treatment of diabetic cardiomyopathy. This article reviews the latest findings of SIRT6 in the pathogenesis of diabetic cardiomyopathy, focusing on the regulation of mitochondria and lipid metabolism by SIRT6 to explore potential clinical treatments.

Design, synthesis, and biological screening of a series of pyrazolo [1,5-a]quina-zoline derivatives as SIRT6 activators

SIRT6 has emerged as a novel therapeutic target for a variety of diseases. In this study, a total of 102 pyrazolo [1,5-a]quinazoline derivatives were designed and synthesized. The result revealed that 2-methyl-N-(4-phenoxy-phenyl)pyrazolo [1,5-a]quinazoline-5-amine (21q) was the most active compound by structure-activity relationship study, which significantly enhanced SIRT6 defatty-acylation activity with an EC_1.5 value of 1.85±0.41 μM and EC₅₀ value of 11.15±0.33 μM. The biological activity of 21q was further verified by differential scanning fluorimetry assay (DSF) and surface plasmon resonance assay (SPR). Molecular docking showed that the pyrazolo [1,5-a]quinazoline of 21q formed a hydrogen bond with Val115 and four π- π interactions with Phe64, Phe82 and Phe86. 21q can significantly improve the thermal stability of SIRT6 protein and inhibit the PI3K/Akt signaling pathway in mouse embryonic fibroblasts (MEFs), thereby inhibiting the proliferation of MEFs. Collectively, we discovered a new potent SIRT6 activator, which can be taken as a lead compound for later studies.

DNA damage and repair in age-related inflammation

Genomic instability is an important driver of ageing. The accumulation of DNA damage is believed to contribute to ageing by inducing cell death, senescence and tissue dysfunction. However, emerging evidence shows that inflammation is another major consequence of DNA damage. Inflammation is a hallmark of ageing and the driver of multiple age-related diseases. Here, we review the evidence linking DNA damage, inflammation and ageing, highlighting how premature ageing syndromes are associated with inflammation. We discuss the mechanisms by which DNA damage induces inflammation, such as through activation of the cGAS-STING axis and NF-κB activation by ATM. The triggers for activation of these signalling cascades are the age-related accumulation of DNA damage, activation of transposons, cellular senescence and the accumulation of persistent R-loops. We also discuss how epigenetic changes triggered by DNA damage can lead to inflammation and ageing via redistribution of heterochromatin factors. Finally, we discuss potential interventions against age-related inflammation.

SIRT6 in Vascular Diseases, from Bench to Bedside

Aging is a key risk factor for angiogenic dysfunction and cardiovascular diseases, including heart failure, hypertension, atherosclerosis, diabetes, and stroke. Members of the NAD+-dependent class III histone deacetylase family, sirtuins, are conserved regulators of aging and cardiovascular and cerebrovascular diseases. The sirtuin SIRT6 is predominantly located in the nucleus and shows deacetylase activity for acetylated histone 3 lysine 56 and lysine 9 as well as for some non-histone proteins. Over the past decade, experimental analyses in rodents and non-human primates have demonstrated the critical role of SIRT6 in extending lifespan. Recent studies highlighted the pleiotropic protective actions of SIRT6 in angiogenesis and cardiovascular diseases, including atherosclerosis, hypertension, heart failure, and stroke. Mechanistically, SIRT6 participates in vascular diseases via epigenetic regulation of endothelial cells, vascular smooth muscle cells, and immune cells. Importantly, SIRT6 activators (e.g., MDL-800/MDL-811) have provided therapeutic value for treating age-related vascular disorders. Here, we summarized the roles of sirtuins in cardiovascular diseases; reviewed recent advances in the understanding of SIRT6 in vascular biology, cardiovascular aging, and diseases; highlighted its therapeutic potential; and discussed future perspectives.

Sirtuin 6 Is a Critical Epigenetic Regulator of Cancer

Sirtuin 6 (SIRT6) is a member of the mammalian sirtuin family with deacetylase, deacylase, and mono-ADP-ribosyl-transferase activities. It is a multitasking chromatin-associated protein regulating different cellular and physiological functions in cells. Specifically, SIRT6 dysfunction is implicated in several aging-related human diseases, including cancer. Studies indicate that SIRT6 has a tumor-specific role, and it is considered a tumor suppressor as well as a tumor growth inducer, depending on the type of cancer. In this chapter, we review the role of SIRT6 in metabolism, genomic stability, and cancer. Further, we provide an insight into the interplay of the tumor-suppressing and oncogenic roles of SIRT6 in cancer. Additionally, we discuss the use of small-molecule SIRT6 modulators as potential therapeutics.

Sirtuin 6: linking longevity with genome and epigenome stability

Sirtuin 6 (SIRT6) has been in the spotlight of aging research because progeroid phenotypes are associated with SIRT6 deficiency. SIRT6 has multiple molecular functions, including DNA repair and heterochromatin regulation, which position SIRT6 as a hub that regulates genome and epigenome stability. Genomic instability caused by persistent DNA damage and accumulating mutations, together with alterations in the epigenetic landscape and derepression of repetitive genetic elements, have emerged as mechanisms driving organismal aging. Enhanced levels of SIRT6 expression or activity provide avenues for rejuvenation strategies. This review focuses on the role of SIRT6 in the maintenance of genome and epigenome stability and its link to longevity. We propose a model where SIRT6 together with lamins control aging and rejuvenation by maintaining epigenetic silencing of repetitive elements.

Advantages of Hyaluronic Acid and Its Combination with Other Bioactive Ingredients in Cosmeceuticals

This study proposes a review on hyaluronic acid (HA) known as hyaluronan or hyaluronate and its derivates and their application in cosmetic formulations. HA is a glycosaminoglycan constituted from two disaccharides (N-acetylglucosamine and D-glucuronic acid), isolated initially from the vitreous humour of the eye, and subsequently discovered in different tissues or fluids (especially in the articular cartilage and the synovial fluid). It is ubiquitous in vertebrates, including humans, and it is involved in diverse biological processes, such as cell differentiation, embryological development, inflammation, wound healing, etc. HA has many qualities that recommend it over other substances used in skin regeneration, with moisturizing and anti-ageing effects. HA molecular weight influences its penetration into the skin and its biological activity. Considering that, nowadays, hyaluronic acid has a wide use and a multitude of applications (in ophthalmology, arthrology, pneumology, rhinology, aesthetic medicine, oncology, nutrition, and cosmetics), the present study describes the main aspects related to its use in cosmetology. The biological effect of HA on the skin level and its potential adverse effects are discussed. Some available cosmetic products containing HA have been identified from the brand portfolio of most known manufacturers and their composition was evaluated. Further, additional biological effects due to the other active ingredients (plant extracts, vitamins, amino acids, peptides, proteins, saccharides, probiotics, etc.) are presented, as well as a description of their possible toxic effects.

Emerging Therapeutic Potential of SIRT6 Modulators

Sirtuin 6 (SIRT6) is an NAD⁺-dependent protein deacylase and mono-ADP-ribosyltransferase of the sirtuin family with a wide substrate specificity. In vitro and in vivo studies have indicated that SIRT6 overexpression or activation has beneficial effects for cellular processes such as DNA repair, metabolic regulation, and aging. On the other hand, SIRT6 has contrasting roles in cancer, acting either as a tumor suppressor or promoter in a context-specific manner. Given its central role in cellular homeostasis, SIRT6 has emerged as a promising target for the development of small-molecule activators and inhibitors possessing a therapeutic potential in diseases ranging from cancer to age-related disorders. Moreover, specific modulators allow the molecular details of SIRT6 activity to be scrutinized and further validate the enzyme as a pharmacological target. In this Perspective, we summarize the current knowledge about SIRT6 pharmacology and medicinal chemistry and describe the features of the activators and inhibitors identified so far.

Fucoidan: a promising agent for brain injury and neurodegenerative disease intervention

Brain injury and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis are urgent medical problems, which severely threaten the life quality of patients and their carers. However, there are currently no effective therapies. Fucoidan is a natural compound found in brown algae and some animals, which has multiple biological and pharmacological activities, such as antioxidant, anti-tumor, anti-coagulant, anti-thrombotic, immunoregulatory, anti-viral, and anti-inflammatory effects. A growing number of studies have shown that fucoidan also exerts a neuroprotective function. Particularly, recent findings have indicated that fucoidan could slow down the neurodegenerative processes and show protective effects against brain injury, which might be of therapeutic value for intervening in brain injury and neurodegenerative diseases. In this review, we have discussed the pharmacokinetics of fucoidan as well as the molecular mechanisms by which fucoidan exerts its neuroprotective effect on some neurological disorders. Along with this, we have also summarized the potential benefits of fucoidan in combination with other drugs in the treatment of neurodegenerative diseases and brain injury. Although the extraction process of fucoidan has been improved well, more efforts should be devoted to the translational research and clinical trials of fucoidan in the near future.

Modulation of the ubiquitin-proteasome system by marine natural products

The ubiquitin-proteasome system (UPS) is a key player in the maintenance of cellular protein homeostasis (proteostasis). Since proteasome function declines upon aging leading to the acceleration of its progression and the manifestation of age-related pathologies, many attempts have been performed towards proteasome activation as a strategy to promote healthspan and longevity. The marine environment hosts a plethora of organisms that produce a vast array of primary and secondary metabolites, the majority of which are unique, exhibiting a wide spectrum of biological activities. The fact that these biologically important compounds are also present in edible marine organisms has sparked the interest for elucidating their potential health-related applications. In this review, we focus on the antioxidant, anti-aging, anti-aggregation and anti-photoaging properties of various marine constituents. We further discuss representatives of marine compounds classes with regard to their potential (direct or indirect) action on UPS components that could serve as UPS modulators and exert beneficial effects on conditions such as oxidative stress, aging and age-related diseases.

A Comprehensive Analysis into the Therapeutic Application of Natural Products as SIRT6 Modulators in Alzheimer's Disease, Aging, Cancer, Inflammation, and Diabetes

Natural products have long been used as drugs to treat a wide array of human diseases. The lead compounds discovered from natural sources are used as novel templates for developing more potent and safer drugs. Natural products produce biological activity by binding with biological macromolecules, since natural products complement the protein-binding sites and natural product-protein interactions are already optimized in nature. Sirtuin 6 (SIRT6) is an NAD+ dependent histone deacetylase enzyme and a unique Sirtuin family member. It plays a crucial role in different molecular pathways linked to DNA repair, tumorigenesis, glycolysis, gluconeogenesis, neurodegeneration, cardiac hypertrophic responses, etc. Thus, it has emerged as an exciting target of several diseases such as cancer, neurodegenerative diseases, aging, diabetes, metabolic disorder, and heart disease. Recent studies have shown that natural compounds can act as modulators of SIRT6. In the current review, a list of natural products, their sources, and their mechanisms of SIRT6 activity modulation has been compiled. The potential application of these naturally occurring SIRT6 modulators in the amelioration of major human diseases such as Alzheimer's disease, aging, diabetes, inflammation, and cancer has also been delineated. Natural products such as isoquercetin, luteolin, and cyanidin act as SIRT6 activators, whereas vitexin, catechin, scutellarin, fucoidan, etc. work as SIRT6 inhibitors. It is noteworthy to mention that quercetin acts as both SIRT6 activator and inhibitor depending on its concentration used. Although none of them were found as highly selective and potent modulators of SIRT6, they could serve as the starting point for developing selective and highly potent scaffolds for SIRT6.

Screening of SIRT6 inhibitors and activators: A novel activator has an impact on breast cancer cells

Sirtuin 6 (SIRT6), a member of sirtuin family (SIRT1-7), regulates a variety of cellular processes involved in aging, metabolism, and cancer. Dysregulation of SIRT6 is widely observed in different breast cancer subtypes; however, the role and function of SIRT6 in cancer development remain largely unexplored. The aim of this study was to identify novel compounds targeting SIRT6 which may provide a new approach in development of anti-cancer therapy for breast cancer. Virtual screening was utilized to discover potential compounds targeting SIRT6 for in vitro screening. In addition, novel 1,4-dihydropyridine derivatives were synthetized and further subjected for the screening. The impact of the compounds on the deacetylation activity of SIRT6 was determined with HPLC method. The anti-cancer activities were screened for a panel of breast cancer cells. A set of 1,4-dihydropyridine derivatives was identified as SIRT6 inhibitors. A SIRT6 activating compound, (2,4-dihydroxy-phenyl)-2-oxoethyl 2-(3-methyl-4-oxo-2-phenyl-4H-chromen-8-yl)acetate (later called as 4H-chromen), was discovered and it provided 30-40-fold maximal activation. 4H-chromen was proposed to bind similarly to quercetin and place to previously reported SIRT6 activator sites. 4H-chromen was investigated in various breast cancer cells, and it decreased cell proliferation in all cells as well as arrested cell cycle in triple negative cells. Overall, this study describes a highly potent SIRT6 activator and new inhibitors that represent a novel tool to study the mechanism of SIRT6 function.

Potential Anti-Aging Substances Derived from Seaweeds

Aging is a major risk factor for many chronic diseases, such as cancer, cardiovascular disease, and diabetes. The exact mechanisms underlying the aging process are not fully elucidated. However, a growing body of evidence suggests that several pathways, such as sirtuin, AMP-activated protein kinase, insulin-like growth factor, autophagy, and nuclear factor erythroid 2-related factor 2 play critical roles in regulating aging. Furthermore, genetic or dietary interventions of these pathways can extend lifespan by delaying the aging process. Seaweeds are a food source rich in many nutrients, including fibers, polyunsaturated fatty acids, vitamins, minerals, and other bioactive compounds. The health benefits of seaweeds include, but are not limited to, antioxidant, anti-inflammatory, and anti-obese activities. Interestingly, a body of studies shows that some seaweed-derived extracts or isolated compounds, can modulate these aging-regulating pathways or even extend lifespans of various animal models. However, few such studies have been conducted on higher animals or even humans. In this review, we focused on potential anti-aging bioactive substances in seaweeds that have been studied in cells and animals mainly based on their anti-aging cellular and molecular mechanisms.

Statin suppresses sirtuin 6 through miR-495, increasing FoxO1-dependent hepatic gluconeogenesis

Rationale: Statin, the most widely used medication in lowering cholesterol, is also associated with increased risk of type 2 diabetes, but its molecular basis remains unclear.

Methods: Mice were injected intraperitoneally with statins alone or in combination with sirtuin (Sirt) 6 activator, and blood glucose levels were measured. Liver tissues from patients with statin use were analyzed for the expression of Sirt6.

Results: Statin treatment up-regulated the hepatic expression of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, which was prevented by Sirt6 overexpression. Mechanistically, statin directly repressed Sirt6 expression by induction of microRNA (miR)-495, a novel inhibitor of Sirt6. Pathway analysis for predicted target genes of miR-495 recognized forkhead box protein (Fox)O1 as a key downstream signaling of Sirt6. Statin treatment increased the acetylation and protein stability of FoxO1, which was suppressed by Sirt6 overexpression. Inhibiting miR-495 recovered Sirt6 levels, blocking the ability of statin to increase FoxO1 mediated gluconeogenesis, and thus confirming the role of the miR-495/Sirt6/FoxO1 pathway in controlling gluconeogenesis. Moreover, the Sirt6 activator MDL801 prevented gluconeogenesis and hyperglycemia induced by statin in mice. Equally noteworthy was that human liver tissues obtained from statin users showed a significant decrease in Sirt6 protein levels compared to those of non-users.

Conclusion: Statin induces miR-495 to suppress Sirt6 expression, which leads to enhancement of FoxO1-mediated hepatic gluconeogenesis. Thus, Sirt6 activation may offer a promising strategy for preventing statin-induced hyperglycemia.

Effects of galloflavin and ellagic acid on sirtuin 6 and its anti-tumorigenic activities

Sirtuin 6 (SIRT6), a member of sirtuin family (SIRT1-7), regulates distinct cellular functions; genome stability, DNA repair, and inflammation related diseases. Recently, we demonstrated that anthocyanidins in berries induce the catalytic activity of SIRT6. In this study, we explored the effects of Galloflavin and Ellagic acid, the most common polyphenols in berries, on SIRT6. SIRT6 deacetylation was investigated using HPLC and immunoblotting assays. The expression levels of SIRT6, glycolytic proteins and cellular metabolism were studied on human colon adenocarcinoma cells (Caco2). Molecular docking studies were carried out to study possible interactions of the compounds with sirtuins. Ellagic acid increased the deacetylase activity of SIRT6 by up to 50-fold; it showed moderate inhibition of SIRT1-3. Galloflavin and Ellagic acid showed anti-proliferative effects on Caco2. The compounds also upregulated SIRT6 expression whereas key proteins in glycolysis were downregulated. Galloflavin decreased glucose transporter 1 (GLUT1) expression, and Ellagic acid affected the expression of protein dehydrogenase kinase 1 (PDK1). Interestingly, both compounds caused reduction in glucose uptake and lactate production. Both Galloflavin and Ellagic acid were able to form hydrogen bonds with Asp188 and Gly6 in SIRT6. In this study, we showed that Galloflavin and Ellagic acid increased SIRT6 activity and decreased the expression of SIRT6 associated proteins involved in cancer development. Taken together, Galloflavin and Ellagic acid targeting SIRT6 activity may provide a new insight in the development of anti-cancer therapy.

Biological and catalytic functions of sirtuin 6 as targets for small-molecule modulators

Sirtuin 6 (SIRT6) is a nuclear NAD⁺-dependent deacetylase of histone H3 that regulates genome stability and gene expression. However, nonhistone substrates and additional catalytic activities of SIRT6, including long-chain deacylation and mono-ADP-ribosylation of other proteins, have also been reported, but many of these noncanonical roles remain enigmatic. Genetic studies have revealed critical homeostatic cellular functions of SIRT6, underscoring the need to better understand which catalytic functions and molecular pathways are driving SIRT6-associated phenotypes. At the physiological level, SIRT6 activity promotes increased longevity by regulating metabolism and DNA repair. Recent work has identified natural products and synthetic small molecules capable of activating the inefficient in vitro deacetylase activity of SIRT6. Here, we discuss the cellular functions of SIRT6 with a focus on attributing its catalytic activity to its proposed biological functions. We cover the molecular architecture and catalytic mechanisms that distinguish SIRT6 from other NAD⁺-dependent deacylases. We propose that combining specific SIRT6 amino acid substitutions identified in enzymology studies and activity-selective compounds could help delineate SIRT6 functions in specific biological contexts and resolve the apparently conflicting roles of SIRT6 in processes such as tumor development. We further highlight the recent development of small-molecule modulators that provide additional biological insight into SIRT6 functions and offer therapeutic approaches to manage metabolic and age-associated diseases.

Mechanism of activation for the sirtuin 6 protein deacylase

The histone deacetylase sirtuin 6 (SIRT6) regulates numerous biological functions, including transcriptional repression, DNA repair, and telomere maintenance. Recombinant SIRT6 displays catalytic efficiencies 2 orders of magnitude greater for long-chain deacylation than deacetylation against peptide substrates; however, deacetylation can be enhanced by allosteric small-molecule activators. Here, we investigated the mechanisms of activated lysine deacetylation and enhanced long-chain acyl-group removal by SIRT6. Activity-based screening identified compounds that activated histone peptide deacetylation 18-48-fold. Chemical optimization based on structure-activity relationships yielded an activator with improved potency and selectivity for SIRT6. Using this novel activator, we conducted biochemical and kinetic analyses revealing that SIRT6 is activated via acceleration of a catalytic step occurring after substrate binding but before NAD⁺ cleavage. We identified a SIRT6 variant, R65A, that maintains basal deacetylase activity but cannot be activated and failed to enhance long-chain deacylation. Additional biochemical studies revealed that Arg-65 is critical for activation by facilitating a conformational step that initiates chemical catalysis. This work suggests that SIRT6 activation of deacetylation involves a similar mechanism to improved catalysis as that of long-chain deacylation. The identification of novel SIRT6 activators and the molecular insights into activation and catalysis presented here provide a foundational understanding for physiological SIRT6 activation and for rational design of activating molecules.

Deacetylation of XBP1s by sirtuin 6 confers resistance to ER stress-induced hepatic steatosis

The active spliced form of X-box-binding protein 1 (XBP1s) is a key modulator of ER stress, but the functional role of its post-translational modification remains unclear. Here, we demonstrate that XBP1s is a deacetylation target of Sirt6 and that its deacetylation protects against ER stress-induced hepatic steatosis. Specifically, the abundance of acetylated XBP1s and concordant hepatic steatosis were increased in hepatocyte-specific Sirt6 knockout and obese mice but were decreased by genetic overexpression and pharmacological activation of Sirt6. Mechanistically, we identified that Sirt6 deacetylated a transactivation domain of XBP1s at Lys257 and Lys297 and promoted XBP1s protein degradation through the ubiquitin-proteasome system. Overexpression of XBP1s, but not its deacetylation mutant 2KR (K257/297R), in mice increased lipid accumulation in the liver. Importantly, in liver tissues obtained from patients with nonalcoholic fatty liver disease (NAFLD), the extent of XBP1s acetylation correlated positively with the NAFLD activity score but negatively with the Sirt6 level. Collectively, we present direct evidence supporting the importance of XBP1 acetylation in ER stress-induced hepatic steatosis.

Activating a protein that regulates cellular health could protect against fat accumulation during the onset of non-alcoholic fatty liver disease (NAFLD). A high-fat diet disrupts the endoplasmic reticulum (ER), a cellular membrane network responsible for synthesizing and processing proteins and fats, and can lead to NAFLD development. Previous studies found that a protein called XBP1s activates fat-related genes during NAFLD. Byung-Hyun Park and Eun Ju Bae at Chonbuk National University in Jeonbuk, South Korea, and co-workers, recently demonstrated that high levels of a regulatory protein called Sirt6 limits liver inflammation and ER stress during high-fat diets. Now, in experiments on mouse models and human liver cells, Park’s team have shown that Sirt6 reduces liver ER stress by modifying XBP1s. Encouraging Sirt6 activation may help protect against NAFLD progression.

Targeting epigenetics and non-coding RNAs in atherosclerosis: from mechanisms to therapeutics

Atherosclerosis, the principal cause of cardiovascular death worldwide, is a pathological disease characterized by fibro-proliferation, chronic inflammation, lipid accumulation, and immune disorder in the vessel wall. As the atheromatous plaques develop into advanced stage, the vulnerable plaques are prone to rupture, which causes acute cardiovascular events, including ischemic stroke and myocardial infarction. Emerging evidence has suggested that atherosclerosis is also an epigenetic disease with the interplay of multiple epigenetic mechanisms. The epigenetic basis of atherosclerosis has transformed our knowledge of epigenetics from an important biological phenomenon to a burgeoning field in cardiovascular research. Here, we provide a systematic and up-to-date overview of the current knowledge of three distinct but interrelated epigenetic processes (including DNA methylation, histone methylation/acetylation, and non-coding RNAs), in atherosclerotic plaque development and instability. Mechanistic and conceptual advances in understanding the biological roles of various epigenetic modifiers in regulating gene expression and functions of endothelial cells (vascular homeostasis, leukocyte adhesion, endothelial-mesenchymal transition, angiogenesis, and mechanotransduction), smooth muscle cells (proliferation, migration, inflammation, hypertrophy, and phenotypic switch), and macrophages (differentiation, inflammation, foam cell formation, and polarization) are discussed. The inherently dynamic nature and reversibility of epigenetic regulation, enables the possibility of epigenetic therapy by targeting epigenetic "writers", "readers", and "erasers". Several Food Drug Administration-approved small-molecule epigenetic drugs show promise in pre-clinical studies for the treatment of atherosclerosis. Finally, we discuss potential therapeutic implications and challenges for future research involving cardiovascular epigenetics, with an aim to provide a translational perspective for identifying novel biomarkers of atherosclerosis, and transforming precision cardiovascular research and disease therapy in modern era of epigenetics.

Cell-membrane coated iron oxide nanoparticles for isolation and specific identification of drug leads from complex matrices

The lack of suitable tools for the identification of potential drug leads from complex matrices is a bottleneck in drug discovery. Here, we report a novel method to screen complex matrices for new drug leads targeting transmembrane receptors. Using α3β4 nicotinic receptors as a model system, we successfully demonstrated the ability of this new tool for the specific identification and effective extraction of binding compounds from complex mixtures. The formation of cell-membrane coated nanoparticles was confirmed by transmission electron microscopy. In particular, we have developed a direct tool to evaluate the presence of functional α3β4 nicotinic receptors on the cell membrane. The specific ligand binding to α3β4 nicotinic receptors was examined through ligand fishing experiments and confirmed by high-performance liquid chromatography coupled with diode-array detection and electrospray ionization mass spectrometry. This tool has a great potential to transform the drug discovery process focusing on identification of compounds targeting transmembrane proteins, as more than 50% of all modern pharmaceuticals use membrane proteins as prime targets.

Quercetin based derivatives as sirtuin inhibitors

Polyphenols synthesized by plants and fungi have various pharmacological effects. The ability of polyphenols to modulate sirtuins has gained considerable interest due to the role of sirtuins in aging, insulin sensitivity, lipid metabolism, inflammation, and cancer. In particular, sirtuin 6 (SIRT6) has gained importance in regulating a variety of cellular processes, including genomic stability and glucose metabolism. On the other hand, quercetin has been demonstrated to modulate sirtuins and to protect against several chronic diseases. In this study, two quercetin derivatives, diquercetin and 2-chloro-1,4-naphtoquinone-quercetin, were identified as promising SIRT6 inhibitors with IC₅₀ values of 130 μM and 55 μM, respectively. 2-Chloro-1,4-naphtoquinone-quercetin also showed potent inhibition against SIRT2, with an IC₅₀ value of 14 μM. Diquercetin increased the Km value of NAD⁺, whereas 2-chloro-1,4-naphthoquinone-quercetin increased the Km value of the acetylated substrate. Molecular docking studies suggest that diquercetin prefers the binding site of the nicotinamide (NAM) moiety, whereas 2-chloro-1,4-naphtoquinone-quercetin prefers to dock into the substrate binding site. Overall, the results of in vitro studies and molecular modeling indicate that diquercetin competes with nicotinamide adenine dinucleotide (NAD⁺), whereas 2-chloro-1,4-naphthoquinone-quercetin competes with the acetylated substrate in the catalytic site of SIRT6. Natural polyphenolic compounds targeting sirtuins show promise as a new approach in the search for novel and effective treatments for age-related diseases.

Natural polyphenols as sirtuin 6 modulators

Flavonoids are polyphenolic secondary metabolites synthesized by plants and fungus with various pharmacological effects. Due to their plethora of biological activities, they have been studied extensively in drug development. They have been shown to modulate the activity of a NAD+-dependent histone deacetylase, SIRT6. Because SIRT6 has been implicated in longevity, metabolism, DNA-repair, and inflammatory response reduction, it is an interesting target in inflammatory and metabolic diseases as well as in cancer. Here we show, that flavonoids can alter SIRT6 activity in a structure dependent manner. Catechin derivatives with galloyl moiety displayed significant inhibition potency against SIRT6 at 10 µM concentration. The most potent SIRT6 activator, cyanidin, belonged to anthocyanidins, and produced a 55-fold increase in SIRT6 activity compared to the 3-10 fold increase for the others. Cyanidin also significantly increased SIRT6 expression in Caco-2 cells. Results from the docking studies indicated possible binding sites for the inhibitors and activators. Inhibitors likely bind in a manner that could disturb NAD+ binding. The putative activator binding site was found next to a loop near the acetylated peptide substrate binding site. In some cases, the activators changed the conformation of this loop suggesting that it may play a role in SIRT6 activation.