Sirtuin modulators: where are we now? A review of patents from 2015 to 2019

Sirtuins as Potential Targets for Neuroprotection: Mechanisms of Early Brain Injury Induced by Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a prevalent cerebrovascular disease with significant global mortality and morbidity rates. Despite advancements in pharmacological and surgical approaches, the quality of life for SAH survivors has not shown substantial improvement. Traditionally, vasospasm has been considered a primary contributor to death and disability following SAH, but anti-vasospastic therapies have not demonstrated significant benefits for SAH patients' prognosis. Emerging studies suggest that early brain injury (EBI) may play a crucial role in influencing SAH prognosis. Sirtuins (SIRTs), a group of NAD + -dependent deacylases comprising seven mammalian family members (SIRT1 to SIRT7), have been found to be involved in neural tissue development, plasticity, and aging. They also exhibit vital functions in various central nervous system (CNS) processes, including cognition, pain perception, mood, behavior, sleep, and circadian rhythms. Extensive research has uncovered the multifaceted roles of SIRTs in CNS disorders, offering insights into potential markers for pathological processes and promising therapeutic targets (such as SIRT1 activators and SIRT2 inhibitors). In this article, we provide an overview of recent research progress on the application of SIRTs in subarachnoid hemorrhage and explore their underlying mechanisms of action.

Discovery of Novel Thiazole-Based SIRT2 Inhibitors as Anticancer Agents: Molecular Modeling, Chemical Synthesis and Biological Assays

The search and development of effective sirtuin small molecule inhibitors (SIRTIs) continues to draw great attention due to their wide range of pharmacological applications. Based on SIRTs' involvement in different biological pathways, their ligands were investigated for many diseases, such as cancer, neurodegenerative disorders, diabetes, cardiovascular diseases and autoimmune diseases. The elucidation of a substantial number of SIRT2-ligand complexes is steering the identification of novel and more selective modulators. Among them, SIRT2 in the presence of the SirReal2 analog series was the most studied. On this basis, we recently reported structure-based analyses leading to the discovery of thiazole-based compounds acting as SIRT2 inhibitors (T1, SIRT2 IC50 = 17.3 µM). Herein, ligand-based approaches followed by molecular docking simulations allowed us to evaluate in silico a novel small series of thiazoles (3a-3d and 5a, 5d) as putative SIRT2 inhibitors. Results from the computational studies revealed comparable molecular interaction fields (MIFs) and docking positionings of most of these compounds with respect to reference SIRT2Is. Biochemical and biological assays validated this study and pointed to compound 5a (SIRT2 IC50 = 9.0 µM) as the most interesting SIRT2I that was worthy of further development as an anticancer agent.

Maternal Dietary Strategies for Improving Offspring Cardiovascular-Kidney-Metabolic Health: A Scoping Review

Dietary regulation has been recognized for its profound impact on human health. The convergence of cardiovascular, kidney, and metabolic disorders at the pathophysiological level has given rise to cardiovascular-kidney-metabolic (CKM) syndrome, which constitutes a significant global health burden. Maternal dietary nutrients play a crucial role in fetal development, influencing various programmed processes. This review emphasizes the effects of different types of dietary interventions on each component of CKM syndrome in both preclinical and clinical settings. We also provide an overview of potential maternal dietary strategies, including amino acid supplementation, lipid-associated diets, micronutrients, gut microbiota-targeted diets, and plant polyphenols, aimed at preventing CKM syndrome in offspring. Additionally, we discuss the mechanisms mediated by nutrient-sensing signals that contribute to CKM programming. Altogether, we underscore the interaction between maternal dietary interventions and the risk of CKM syndrome in offspring, emphasizing the need for continued research to facilitate their clinical translation.

Activation and inhibition of sirtuins: From bench to bedside

The sirtuin family comprises seven NAD+-dependent enzymes which catalyze protein lysine deacylation and mono ADP-ribosylation. Sirtuins act as central regulators of genomic stability and gene expression and control key processes, including energetic metabolism, cell cycle, differentiation, apoptosis, and aging. As a result, all sirtuins play critical roles in cellular homeostasis and organism wellness, and their dysregulation has been linked to metabolic, cardiovascular, and neurological diseases. Furthermore, sirtuins have shown dichotomous roles in cancer, acting as context-dependent tumor suppressors or promoters. Given their central role in different cellular processes, sirtuins have attracted increasing research interest aimed at developing both activators and inhibitors. Indeed, sirtuin modulation may have therapeutic effects in many age-related diseases, including diabetes, cardiovascular and neurodegenerative disorders, and cancer. Moreover, isoform selective modulators may increase our knowledge of sirtuin biology and aid to develop better therapies. Through this review, we provide critical insights into sirtuin pharmacology and illustrate their enzymatic activities and biological functions. Furthermore, we outline the most relevant sirtuin modulators in terms of their modes of action, structure-activity relationships, pharmacological effects, and clinical applications.

Recent Advances in the Discovery of SIRT1/2 Inhibitors via Computational Methods: A Perspective

Sirtuins (SIRTs) are classified as class III histone deacetylases (HDACs), a family of enzymes that catalyze the removal of acetyl groups from the ε-N-acetyl lysine residues of histone proteins, thus counteracting the activity performed by histone acetyltransferares (HATs). Based on their involvement in different biological pathways, ranging from transcription to metabolism and genome stability, SIRT dysregulation was investigated in many diseases, such as cancer, neurodegenerative disorders, diabetes, and cardiovascular and autoimmune diseases. The elucidation of a consistent number of SIRT-ligand complexes helped to steer the identification of novel and more selective modulators. Due to the high diversity and quantity of the structural data thus far available, we reviewed some of the different ligands and structure-based methods that have recently been used to identify new promising SIRT1/2 modulators. The present review is structured into two sections: the first includes a comprehensive perspective of the successful computational approaches related to the discovery of SIRT1/2 inhibitors (SIRTIs); the second section deals with the most interesting SIRTIs that have recently appeared in the literature (from 2017). The data reported here are collected from different databases (SciFinder, Web of Science, Scopus, Google Scholar, and PubMed) using "SIRT", "sirtuin", and "sirtuin inhibitors" as keywords.

Novel xanthone derivatives as potent sirtuin 2 inhibitors

Six amino derivatives of xanthone were obtained via chemical synthesis. Biochemical studies revealed their SIRT2 inhibitory activity ranging from 48.5 % (compound 4, 5-chloro-2-((4-(3-methoxyphenyl)piperazin-1-yl)methyl)-9H-xanthen-9-one hydrochloride) to 93.2 % (compound 3, 5-chloro-2-(((2-methoxyphenethyl)amino)methyl)-9H-xanthen-9-one hydrochloride). The structure-activity analysis showed favourable properties of secondary amines relative to tertiary piperazine derivatives. The tested compounds do not possess additional SIRT1 activating activity and no antioxidant activity (DPPH in vitro assay). Comprehensive analysis of the lipophilicity of the obtained compounds was also performed. For compound 3 potential molecular targets and similar active compounds were predicted in order to facilitate further research in this group of compounds.

SIRT3 Activation a Promise in Drug Development? New Insights into SIRT3 Biology and Its Implications on the Drug Discovery Process

Sirtuins catalyze deacetylation of lysine residues with a NAD+-dependent mechanism. In mammals, the sirtuin family is composed of seven members, divided into four subclasses that differ in substrate specificity, subcellular localization, regulation, as well as interactions with other proteins, both within and outside the epigenetic field. Recently, much interest has been growing in SIRT3, which is mainly involved in regulating mitochondrial metabolism. Moreover, SIRT3 seems to be protective in diseases such as age-related, neurodegenerative, liver, kidney, heart, and metabolic ones, as well as in cancer. In most cases, activating SIRT3 could be a promising strategy to tackle these health problems. Here, we summarize the main biological functions, substrates, and interactors of SIRT3, as well as several molecules reported in the literature that are able to modulate SIRT3 activity. Among the activators, some derive from natural products, others from library screening, and others from the classical medicinal chemistry approach.

Sirtuins in macrophage immune metabolism: A novel target for cardiovascular disorders

Sirtuins (SIRT1-SIRT7), as a family of NAD+-dependent protein modifying enzymes, have various catalytic functions, such as deacetylases, dealkalylases, and deribonucleases. The Sirtuins family is directly or indirectly involved in pathophysiological processes such as glucolipid metabolism, oxidative stress, DNA repair and inflammatory response through various pathways and assumes an important role in several cardiovascular diseases such as atherosclerosis, myocardial infarction, hypertension and heart failure. A growing number of studies supports that metabolic and bioenergetic reprogramming directs the sequential process of inflammation. Failure of homeostatic restoration leads to many inflammatory diseases, and that macrophages are the central cells involving the inflammatory response and are the main source of inflammatory cytokines. Regulation of cellular metabolism has emerged as a fundamental process controlling macrophage function, but its exact signaling mechanisms remain to be revealed. Understanding the precise molecular basis of metabolic control of macrophage inflammatory processes may provide new approaches for targeting immune metabolism and inflammation. Here, we provide an update of studies in cardiovascular disease on the function and role of sirtuins in macrophage inflammation and metabolism, as well as drug candidates that may interfere with sirtuins, pointing to future prospects in this field.

The role of mitochondrial/metabolic axis in development of tamoxifen resistance in breast cancer

Only a few investigations, to our knowledge, have examined the bioenergetics of Tamoxifen (TMX) resistant individuals and reported altered mitochondrial activity and metabolic profile. The primary cause of TMX resistance is firmly suggested to be metabolic changes. Metabolic variations and hypoxia have also been linked in a bidirectional manner. Increased hypoxic levels correlate with early recurrence and proliferation and have a negative therapeutic impact on breast cancer (BC) patients. Hypoxia, carcinogenesis, and patient death are all correlated, resulting in more aggressive traits, a higher chance of metastasis, and TMX resistance. Consequently, we sought to investigate the possible role of the metabolic/hypoxial axis Long non-coding RNA (LncRNA) Taurine up-regulated 1 (TUG-1), Micro-RNA 186-5p (miR-186), Sirtuin-3 (SIRT3), Peroxisome Proliferator Activator Receptor alpha (PPAR-α), and Hypoxia-Inducible Factor-1 (HIF-1) in the development of TMX resistance in BC patients and to correlate this axis with tumor progression. Interestingly, this will be the first time to explore epigenetic regulation of this axis in BC.

The role of structural biology in the design of sirtuin activators

Sirtuins are NAD+-dependent protein lysine deacylases and mono-ADP-ribosylases whose activity regulates different pathways, including DNA damage repair, cell survival and metabolism, reactive oxygen species (ROS) detoxification, inflammation, cardiac function, and neuronal signaling. Considering the beneficial effects of specific sirtuin isoforms on health and lifespan, the past two decades have seen a mounting interest in the development of sirtuin activators. The availability of enzyme-activator co-crystal structures has proven significant throughout the years for elucidating the mechanisms of action of activators and designing more potent and selective molecules. In this review, we highlight the most interesting examples of sirtuin activators and provide comprehensive coverage of the role that structural biology played in their discovery and characterization.

Deciphering the Allosteric Activation Mechanism of SIRT6 Using Molecular Dynamics Simulations

As a member of the histone deacetylase protein family, the NAD+-dependent SIRT6 plays an important role in maintaining genomic stability and regulating cell metabolism. Interestingly, SIRT6 has been found to have a preference for hydrolyzing long-chain fatty acyls relative to deacetylation, and it can be activated by fatty acids. However, the mechanisms by which SIRT6 recognizes different substrates and can be activated by small molecular activators are still not well understood. In this study, we carried out extensive molecular dynamic simulations to shed light on these mechanisms. Our results revealed that the binding of the myristoylated substrate stabilizes the catalytically favorable conformation of NAD+, while the binding of the acetyl-lysine substrate leads to a loose binding of NAD+ in SIRT6. Based on these observations, we proposed a reasonable allosteric binding mode for myristic acid, which can enhance the catalytic activity of SIRT6 by stabilizing the binding of NAD+ with His131 as well as the acetylated substrate. Furthermore, our molecular dynamics simulations demonstrated that synthetic SIRT6 activators, such as UBCS039, MDL-801, and 12q, block the flipping of ribose in NAD+ and therefore can stabilize substrate-NAD+-His131 interactions in a manner similar to fatty acids. In summary, our newly proposed activation mechanism of SIRT6 highlights the importance of protein-substrate interactions, which would facilitate the rational design of new SIRT6 activators.

Novel Thiazole-Based SIRT2 Inhibitors Discovered via Molecular Modelling Studies and Enzymatic Assays

Recently, the development of sirtuin small molecule inhibitors (SIRTIs) has been gaining attention for the treatment of different cancer types, but also to contrast neurodegenerative disease, diabetes, and autoimmune syndromes. In the search for SIRT2 modulators, the availability of several X-crystallographic data regarding SIRT2-ligand complexes has allowed for setting up a structure-based study, which is herein presented. A set of 116 SIRT2 inhibitors featuring different chemical structures has been collected from the literature and used for molecular docking studies involving 4RMG and 5MAT PDB codes. The information found highlights key contacts with the SIRT2 binding pocket such as Van der Waals and π-π stacking with Tyr104, Phe119, Phe234, and Phe235 in order to achieve high inhibitory ability values. Following the preliminary virtual screening studies, a small in-house library of compounds (1a-7a), previously investigated as putative HSP70 inhibitors, was described to guide the search for dual-acting HSP70/SIRT2 inhibitors. Biological and enzymatic assays validated the whole procedure. Compounds 2a and 7a were found to be the most promising derivatives herein proposed.

Role of sirtuins in hepatocellular carcinoma progression and multidrug resistance: Mechanistical and pharmacological perspectives

Hepatocellular carcinoma (HCC) is the third most common cause of death from cancer worldwide. Therapeutic strategies are still challenging due to the high relapse rate after surgery and multidrug resistance (MDR). It is essential to better understand the mechanisms for HCC progression and MDR for the development of new therapeutic strategies. Mammalian sirtuins (SIRTs), a family of seven members, are related to tumor progression, MDR and prognosis and were proposed as potential prognostic markers, as well as therapeutic targets for treating cancer. SIRT1 is the most studied member and is overexpressed in HCC, playing an oncogenic role and predicting poor prognosis. Several manuscripts describe the role of SIRTs2-7 in HCC; most of them report an oncogenic role for SIRT2 and -7 and a suppressive role for SIRT3 and -4. The scenario is more confusing for SIRT5 and -6, since information is contradictory and scarce. For SIRT1 many inhibitors are available and they seem to hold therapeutic promise in HCC. For the other members the development of specific modulators has just started. This review is aimed to describe the features of SIRTs1-7 in HCC, and the role they play in the onset and progression of the disease. Also, when possible, we will depict the information related to the SIRTs modulators that have been tested in HCC and their possible implication in MDR. With this, we hope to clarify the role of each member in HCC and to shed some light on the most successful strategies to overcome MDR.

Emerging Roles of SIRT5 in Metabolism, Cancer, and SARS-CoV-2 Infection

Sirtuin 5 (SIRT5) is a predominantly mitochondrial enzyme catalyzing the removal of glutaryl, succinyl, malonyl, and acetyl groups from lysine residues through a NAD+-dependent deacylase mechanism. SIRT5 is an important regulator of cellular homeostasis and modulates the activity of proteins involved in different metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, fatty acid oxidation, electron transport chain, generation of ketone bodies, nitrogenous waste management, and reactive oxygen species (ROS) detoxification. SIRT5 controls a wide range of aspects of myocardial energy metabolism and plays critical roles in heart physiology and stress responses. Moreover, SIRT5 has a protective function in the context of neurodegenerative diseases, while it acts as a context-dependent tumor promoter or suppressor. In addition, current research has demonstrated that SIRT5 is implicated in the SARS-CoV-2 infection, although opposing conclusions have been drawn in different studies. Here, we review the current knowledge on SIRT5 molecular actions under both healthy and diseased settings, as well as its functional effects on metabolic targets. Finally, we revise the potential of SIRT5 as a therapeutic target and provide an overview of the currently reported SIRT5 modulators, which include both activators and inhibitors.

In silico screening of small molecule modulators and their binding studies against human sirtuin-6 protein

Sirtuin-6 (SIRT6), class III family of deacetylase regulates several biological functions, including transcriptional repression, telomere maintenance, and DNA repair. It is unique among sirtuin family members with diverse enzymatic functions: mono-ADP-ribosylase, deacetylase and defatty-acylase. The studies so far implicated SIRT6 role in lifespan extension, tumor suppression, and is considered as an attractive drug target for aging-related disease. In this study, we have carried out in silico screening for human SIRT6 modulators using NCI Diversity Set III library, molecular dynamic (MD) simulations to analyze the protein-ligand interaction, and validated their binding-affinity (Kd) using MicroScale Thermophoresis. This study yielded two novel compounds, ((3Z)-3-((4-(dimethylamino)phenyl)methylidene)-5-(5,6,7,8-tetrahydronaphthalen-2-yl)furan-2-one and 5-phenyl-2-(5-phenyl-2,3-dihydro-1,3-benzoxazol-2-yl)-2,3-dihydro-1,3-benzoxazole showing high-affinity interaction for SIRT6. The structural analysis from MD simulation suggests both compounds might act as substrate-analogs or mimic the nicotinamide binding. On considering the uniqueness of SIRT6 substrate binding acyl channel among sirtuin family member, binding of both compounds to the above site suggesting their specificity for SIRT6 isoform. Therefore, it may form the basis for the development of potential modulators for human SIRT6.Communicated by Ramaswamy H. Sarma.

The Pursuit of Enzyme Activation: A Snapshot of the Gold Rush

A range of enzymes drive human physiology, and their activities are tightly regulated through numerous signaling pathways. Depending on the context, these pathways may activate or inhibit an enzyme as a way to ensure proper execution of cellular functions. From a drug discovery and development perspective, pharmacological inhibition of enzymes has been a focus of interest, as many diseases are associated with the upregulation of enzyme function. On the other hand, however, pharmacological activation of enzymes such as kinases and phosphatases has been of increasing interest. In this review, we discuss seven case studies that highlight pharmacological activation strategy, describe the binding modes and pharmacology of the activators, and comment on how this on-demand activation strategy complements the commonly pursued inhibition strategy, thus jointly enabling bidirectional modulation of specific target of interest. Going forward, we expect activators to play important roles as chemical probes and drug leads.

Role of Sirtuins in Diabetes and Age-Related Processes

The practice of intermittent fasting continues to grow as a widely practiced diet trend due to its feasibility and reported high success rate. By practicing intermittent fasting, levels of sirtuin proteins (SIRTs), also known as the longevity protein, rise in the body and bring numerous health benefits. Currently, seven SIRTs have been described in humans in different locations of the cell with a wide variety of corresponding functions including gene transcription, DNA repair, and protection against oxidative damage. SIRT activators, such as resveratrol found in red wine, are also commonly consumed to amplify the health benefits associated with protection against diabetes and age-related disease processes. The purpose of this review is to explore the interaction of intermittent fasting on SIRT levels and how the increase in these proteins impacts age-related disease processes. The understanding of SIRTs is continuously evolving as more interactions and SIRT-specific activators are being revealed. New discoveries are crucial for forming potential therapeutics that delay many common diseases and promote healthy living. 

Virtual Screening in the Identification of Sirtuins’ Activity Modulators

Sirtuins are NAD⁺-dependent deac(et)ylases with different subcellular localization. The sirtuins’ family is composed of seven members, named SIRT-1 to SIRT-7. Their substrates include histones and also an increasing number of different proteins. Sirtuins regulate a wide range of different processes, ranging from transcription to metabolism to genome stability. Thus, their dysregulation has been related to the pathogenesis of different diseases. In this review, we discussed the pharmacological approaches based on sirtuins’ modulators (both inhibitors and activators) that have been attempted in in vitro and/or in in vivo experimental settings, to highlight the therapeutic potential of targeting one/more specific sirtuin isoform(s) in cancer, neurodegenerative disorders and type 2 diabetes. Extensive research has already been performed to identify SIRT-1 and -2 modulators, while compounds targeting the other sirtuins have been less studied so far. Beside sections dedicated to each sirtuin, in the present review we also included sections dedicated to pan-sirtuins’ and to parasitic sirtuins’ modulators. A special focus is dedicated to the sirtuins’ modulators identified by the use of virtual screening.

Targeting Mitochondria as a Therapeutic Approach for Parkinson's Disease

Neurodegeneration is among the most critical challenges that involve modern societies and annually influences millions of patients worldwide. While the pathophysiology of Parkinson's disease (PD) is complicated, the role of mitochondrial is demonstrated. The in vitro and in vivo models and genome-wide association studies in human cases proved that specific genes, including PINK1, Parkin, DJ-1, SNCA, and LRRK2, linked mitochondrial dysfunction with PD. Also, mitochondrial DNA (mtDNA) plays an essential role in the pathophysiology of PD. Targeting mitochondria as a therapeutic approach to inhibit or slow down PD formation and progression seems to be an exciting issue. The current review summarized known mutations associated with both mitochondrial dysfunction and PD. The significance of mtDNA in Parkinson's disease pathogenesis and potential PD therapeutic approaches targeting mitochondrial dysfunction was then discussed.

Therapeutic Potential and Activity Modulation of the Protein Lysine Deacylase Sirtuin 5

Sirtiun 5 (SIRT5) is a NAD+-dependent protein lysine deacylase primarily located in mitochondria. SIRT5 displays an affinity for negatively charged acyl groups and mainly catalyzes lysine deglutarylation, desuccinylation, and demalonylation while possessing weak deacetylase activity. SIRT5 substrates play crucial roles in metabolism and reactive oxygen species (ROS) detoxification, and SIRT5 activity is protective in neuronal and cardiac physiology. Moreover, SIRT5 exhibits a dichotomous role in cancer, acting as context-dependent tumor promoter or suppressor. Given its multifaceted activity, SIRT5 is a promising target in the design of activators or inhibitors that might act as therapeutics in many pathologies, including cancer, cardiovascular disorders, and neurodegeneration. To date, few cellular-active peptide-based SIRT5 inhibitors (SIRT5i) have been described, and potent and selective small-molecule SIRT5i have yet to be discovered. In this perspective, we provide an outline of SIRT5's roles in different biological settings and describe SIRT5 modulators in terms of their mode of action, pharmacological activity, and structure-activity relationships.

Sirtuin modulators: past, present, and future perspectives

Sirtuins are NAD⁺-dependent protein lysine deacylase and mono-ADP ribosylases present in both prokaryotes and eukaryotes. The sirtuin family comprises seven isoforms in mammals, each possessing different subcellular localization and biological functions. Sirtuins have received increasing attention in the past two decades given their pivotal functions in a variety of biological contexts, including cytodifferentiation, transcriptional regulation, cell cycle progression, apoptosis, inflammation, metabolism, neurological and cardiovascular physiology and cancer. Consequently, modulation of sirtuin activity has been regarded as a promising therapeutic option for many pathologies. In this review, we provide an up-to-date overview of sirtuin biology and pharmacology. We examine the main features of the most relevant inhibitors and activators, analyzing their structure-activity relationships, applications in biology, and therapeutic potential.

Value of Serum Sirtuin-1 (SIRT1) Levels and SIRT1 Gene Variants in Periodontitis Patients

Background and Objectives: Periodontitis is a multifactorial inflammatory disease associated with biofilm dysbiosis and is defined by progressive periodontium destruction. Genes largely regulate this entire process. SIRTs are a group of histone deacetylases (HDACs) intimately involved in cell metabolism and are responsible for altering and regulating numerous cell functions. Understanding SIRTs and their functions in periodontitis may be useful for therapeutic treatment strategies in the future. The aim of our study was to investigate the associations amid SIRT1 single-gene nucleotide polymorphisms (rs3818292, rs3758391, and rs7895833) and SIRT1 serum levels for patients affected by periodontitis in the Caucasian population. Materials and Methods: The study included 201 patients affected by periodontitis and 500 healthy controls. DNA extraction from peripheral leukocytes was carried out using commercial kits. The real-time PCR method was selected for the determination of the genotype of the periodontitis patients and the control group. The ELISA method was used to measure the SIRT1 concentration. A statistical data analysis was performed using “BM SPSS Statistics 27.0” software. Results: The SIRT1 rs3818292 AG genotype was associated with a 2-fold and 1.9-fold increase in the development of periodontitis under the codominant and overdominant models (OR = 1.959; CI = 1.239–3.098; p = 0.004; and OR = 1.944; CI = 1.230–3.073; p = 0.004, respectively). The serum SIRT1 levels were not statistically significantly different between subjects in the periodontitis and control groups (0.984 (5.159) ng/mL vs. 0.514 (7.705) ng/mL, p = 0.792). Conclusions: in our study, the genotypes and alleles of SIRT1 rs3818292, rs3758391, and rs7895833 statistically significantly differed between the periodontitis and control groups, exclusively in the male population and subjects older than 60 years.

Flavonoids as Sirtuin Modulators

Sirtuins (SIRTs) are described as NAD+-dependent deacetylases, also known as class III histone deacetylases. So far, seven sirtuin genes (SIRTS 1-7) have been identified and characterized in mammals and also known to occur in bacteria and eukaryotes. SIRTs are involved in various biological processes including endocrine system, apoptosis, aging and longevity, diabetes, rheumatoid arthritis, obesity, inflammation, etc. Among them, the best characterized one is SIRT1. Actually, small molecules seem to be the most effective SIRT modulators. Flavonoids have been reported to possess many positive effects favrable for human health, while a relatively less research has been reported so far on their funcions as SIRT modulation mechanisms. In this regard, we herein aimed to focus on modulatory effects of flavonoids on SIRTs as the most common secondary metabolites in natural products. Our literature survey covering the years of 2006-2021 pointed out that flavonoids frequently interact with SIRT1 and SIRT3 followed by SIRT6. It can be also concluded that some popular flavonoid derivatives, e.g. resveratrol, quercetin, and catechin derivatives came forward in terms of SIRT modulation.

Biochemical Functions and Clinical Characterizations of the Sirtuins in Diabetes-Induced Retinal Pathologies

Diabetic retinopathy (DR) is undoubtedly one of the most prominent causes of blindness worldwide. This pathology is the most frequent microvascular complication arising from diabetes, and its incidence is increasing at a constant pace. To date, the insurgence of DR is thought to be the consequence of the intricate complex of relations connecting inflammation, the generation of free oxygen species, and the consequent oxidative stress determined by protracted hyperglycemia. The sirtuin (SIRT) family comprises 7 histone and non-histone protein deacetylases and mono (ADP-ribosyl) transferases regulating different processes, including metabolism, senescence, DNA maintenance, and cell cycle regulation. These enzymes are involved in the development of various diseases such as neurodegeneration, cardiovascular pathologies, metabolic disorders, and cancer. SIRT1, 3, 5, and 6 are key enzymes in DR since they modulate glucose metabolism, insulin sensitivity, and inflammation. Currently, indirect and direct activators of SIRTs (such as antagomir, glycyrrhizin, and resveratrol) are being developed to modulate the inflammation response arising during DR. In this review, we aim to illustrate the most important inflammatory and metabolic pathways connecting SIRT activity to DR, and to describe the most relevant SIRT activators that might be proposed as new therapeutics to treat DR.

SIRT7 is a Prognostic Biomarker in Kidney Renal Clear Cell Carcinoma That is Correlated with Immune Cell Infiltration

Background

SIRT7 has been shown to be expressed in many cancer types, including clear cell renal cell carcinoma (KIRC), but its functional role in this oncogenic context remains to be firmly defined. This study was designed to explore correlations between SIRT7 and KIRC characteristics using the TCGA database.

Methods

Relationships between SIRT7 expression and KIRC patient clinicopathological characteristics were assessed through Kruskal-Wallis tests, Wilcoxon signed-rank tests, and logistic regression analyses. Area under the ROC curve (AUC) values were used to assess the prognostic value of SIRT7 as a means of classifying clear cell renal cell carcinoma patients. The functional role of SIRT7 in this cancer type was assessed through GO/KEGG enrichment analyses and immune cell infiltration analyses.

Results

In KIRC patients, higher levels of SIRT7 expression were associated with Race, M stage, T stage (all P < 0.05). SIRT7 offered significant diagnostic value in ROC curve analyses (AUC = 0.912), and elevated SIRT7 levels were linked to worse patient overall survival (OS; P < 0.001). The expression of SIRT7 was independently related with KIRC patient OS (HR: 1.827; 95% CI: 1.346-2.481; P<0.001). In GO/KEGG analyses, SIRT7 was found to be associated with ubiquitin-mediated proteolysis and nucleotide excision repair. Higher SIRT7 expression was related to the enhanced infiltration of certain immune cells.

Conclusion

Increased SIRT7 expression was associated with a worse KIRC patient prognosis, and immune infiltrates, suggesting it may offer value as a prognostic biomarker for this cancer type.

Mitochondrial Sirtuins in Chronic Degenerative Diseases: New Metabolic Targets in Colorectal Cancer

Sirtuins (SIRTs) are a family of class III histone deacetylases (HDACs) consisting of seven members, widely expressed in mammals. SIRTs mainly participate in metabolic homeostasis, DNA damage repair, cell survival, and differentiation, as well as other cancer-related biological processes. Growing evidence shows that SIRTs have pivotal roles in chronic degenerative diseases, including colorectal cancer (CRC), the third most frequent malignant disease worldwide. Metabolic alterations are gaining attention in the context of CRC development and progression, with mitochondrion representing a crucial point of complex and intricate molecular mechanisms. Mitochondrial SIRTs, SIRT2, SIRT3, SIRT4 and SIRT5, control mitochondrial homeostasis and dynamics. Here, we provide a comprehensive review on the latest advances on the role of mitochondrial SIRTs in the initiation, promotion and progression of CRC. A deeper understanding of the pathways by which mitochondrial SIRTs control CRC metabolism may provide new molecular targets for future innovative strategies for CRC prevention and therapy.

SIRT2 tyrosine nitration by peroxynitrite in response to renal ischemia/reperfusion injury

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the production of renal ischemia/reperfusion (I/R). The current study is to elucidate a mechanism of SIRT2 tyrosine nitration to accelerate the cell apoptosis induced by peroxynitrite (ONOO‾), the most reactive and deleterious RNS type in renal ischemia/reperfusion (I/R) injury. Our results demonstrate that there is a significant enhancement of the 3-nitrotyrosine levels in renal tissues of Acute Kidney Injury (AKI) patients and rats that underwent renal I/R, and a positive correlation between the 3-nitrotyrosine level and renal function impairment, indicative of an accumulation of peroxynitrite. Notably, peroxynitrite-evoked nitration of SIRT2 destroyed its enzymatic activity and the capability to deacetylate FOXO3a, and enhanced expression of Bim and caspase3, facilitating renal cell apoptosis in renal ischemia/reperfusion and SIN-1(peroxynitrite donor) treatment in vitro, and these effects were reversed by FeTMPyP, a peroxynitrite decomposition scavenger. Importantly, we identified that the tyrosine 86 is responsible for SIRT2 nitration and inactivation using site-mutation assay and Mass Spectrography analysis. Altogether, these findings point to a novel protective mechanism that an inhibition of SIRT2 tyrosine nitration can be a promising strategy to prevent ischemic renal diseases involving AKI.

Redox Homeostasis in Cardiovascular Disease: The Role of Mitochondrial Sirtuins

Cardiovascular disease (CVD) is still the leading cause of death worldwide. Despite successful advances in both pharmacological and lifestyle strategies to fight well-established risk factors, the burden of CVD is still increasing. Therefore, it is necessary to further deepen our knowledge of the pathogenesis of the disease for developing novel therapies to limit even more its related morbidity and mortality. Oxidative stress has been identified as a common trait of several manifestations of CVD and could be a promising target for innovative treatments. Mitochondria are a major source of oxidative stress and sirtuins are a family of enzymes that generate different post-translational protein modifications, thus regulating important cellular processes, including cell cycle, autophagy, gene expression, and others. In particular, three sirtuins, SIRT3, SIRT4, and SIRT5 are located within the mitochondrial matrix where they regulate energy production and antioxidant pathways. Therefore, these sirtuins are strongly involved in the balance between oxidant and antioxidant mechanisms. In this review, we summarize the activities of these sirtuins with a special focus on their role in the control of oxidative stress, in relation to energy metabolism, atherosclerosis, and CVD.

Sirtuins as Potential Therapeutic Targets for Hepatitis B Virus Infection

Sirtuins (SIRTs) are well-known histone deacetylases that are capable of modulating various cellular processes in numerous diseases, including the infection of hepatitis B virus (HBV), which is one of the primary pathogenic drivers of liver cirrhosis and hepatocellular carcinoma. Mounting evidence reveals that HBV can alter the expression levels of all SIRT proteins. In turn, all SIRTs regulate HBV replication via a cascade of molecular mechanisms. Furthermore, several studies suggest that targeting SIRTs using suitable drugs is a potential treatment strategy for HBV infection. Here, we discuss the molecular mechanisms associated with SIRT-mediated upregulation of viral propagation and the recent advances in SIRT-targeted therapy as potential therapeutic modalities against HBV infection.

Diabetes Mellitus and Cardiovascular Diseases: Nutraceutical Interventions Related to Caloric Restriction

Type 2 diabetes (T2DM) and cardiovascular disease (CVD) are closely associated and represent a key public health problem worldwide. An excess of adipose tissue, NAFLD, and gut dysbiosis establish a vicious circle that leads to chronic inflammation and oxidative stress. Caloric restriction (CR) is the most promising nutritional approach capable of improving cardiometabolic health. However, adherence to CR represents a barrier to patients and is the primary cause of therapeutic failure. To overcome this problem, many different nutraceutical strategies have been designed. Based on several data that have shown that CR action is mediated by AMPK/SIRT1 activation, several nutraceutical compounds capable of activating AMPK/SIRT1 signaling have been identified. In this review, we summarize recent data on the possible role of berberine, resveratrol, quercetin, and L-carnitine as CR-related nutrients. Additionally, we discuss the limitations related to the use of these nutrients in the management of T2DM and CVD.

Selective SIRT2 inhibitors as promising anticancer therapeutics: An update from 2016 to 2020

Sirtuin 2 (SIRT2) is a member of the human sirtuins, which regulates various biological processes and is deemed as a novel biomarker for different cancers. Depending on the tumor type, SIRT2 knockout leads to a controversial role in tumorigenesis, however, pharmacological inhibition of SIRT2 results exclusively in growth inhibition of various cancer cells. In this respect, selective SIRT2 inhibitors hold therapeutic promise in a wide range of tumors. The literature has a batch of successful stories of SIRT2 modulators discovery. This review presents our perspective on the up-to-date selective SIRT2 inhibitors and their antiproliferative activity.

Sirtuins as pharmacological targets in neurodegenerative and neuropsychiatric disorders

Histone deacetylases (HDACs) are enzymes that regulate several processes, such as transcription, cell proliferation, differentiation and development. HDACs are classified as either Zn²⁺ -dependent or NAD⁺ -dependent enzymes. Over the years, experimental and clinical evidence has demonstrated that HDAC modulation is a critical process in neurodegenerative and psychiatric disorders. Nevertheless, most of the studies have focused on the role of Zn²⁺ -dependent HDACs in the development of these diseases, although there is growing evidence showing that the NAD⁺ -dependent HDACs, known as sirtuins, are also very promising targets. This possibility has been strengthened by reports of decreased levels of NAD⁺ in CNS disorders, which can lead to alterations in sirtuin activation and therefore result in increased pathology. In this review, we discuss the role of sirtuins in neurodegenerative and neuropsychiatric disorders as well the possible rationale for them to be considered as pharmacological targets in future therapeutic interventions.

Promising drug discovery strategies for sirtuin modulators: what lessons have we learnt?

INTRODUCTION

Sirtuins, NAD-dependent protein deacetylases, require NAD⁺ for enzymatic activity. Recent research has indicated that sirtuins have a key role in the regulation of gene expression, the cell cycle, apoptosis, neurodegeneration and several age-related diseases. In mammals, there are seven sirtuin isoforms (SIRT-1-7) that catalyze specific lysine substrate deacetylation.

AREAS COVERED

This review explains the current information on the structure, function and importance of sirtuin modulators. It also explores the possible therapeutic applications of sirtuin modulators and related small molecules in the context of various diseases.

EXPERT OPINION

Sirtuin's modulators open a new area of research for targeting pathological conditions. Sirtuin modulators, through their targeted function, may provide a possible tool for the amelioration of various diseases. However, the search of activators/inhibitors for sirtuins needs further research. The structural elucidation of sirtuins will create an understanding for the development of isoform-specific selective modulators. This could be a useful tool to determine the functions of individual sirtuins as potential therapeutic agents.

Emerging roles of SIRT6 in human diseases and its modulators

The biological functions of sirtuin 6 (SIRT6; e.g., deacetylation, defatty-acylation, and mono-ADP-ribosylation) play a pivotal role in regulating lifespan and several fundamental processes controlling aging such as DNA repair, gene expression, and telomeric maintenance. Over the past decades, the aberration of SIRT6 has been extensively observed in diverse life-threatening human diseases. In this comprehensive review, we summarize the critical roles of SIRT6 in the onset and progression of human diseases including cancer, inflammation, diabetes, steatohepatitis, arthritis, cardiovascular diseases, neurodegenerative diseases, viral infections, renal and corneal injuries, as well as the elucidation of the related signaling pathways. Moreover, we discuss the advances in the development of small molecule SIRT6 modulators including activators and inhibitors as well as their pharmacological profiles toward potential therapeutics for SIRT6-mediated diseases.

Substrate-Dependent Sensitivity of SIRT1 to Nicotinamide Inhibition

SIRT1 is the most extensively studied human sirtuin with a broad spectrum of endogenous targets. It has been implicated in the regulation of a myriad of cellular events, such as gene transcription, mitochondria biogenesis, insulin secretion as well as glucose and lipid metabolism. From a mechanistic perspective, nicotinamide (NAM), a byproduct of a sirtuin-catalyzed reaction, reverses a reaction intermediate to regenerate NAD+ through "base exchange", leading to the inhibition of the forward deacetylation. NAM has been suggested as a universal sirtuin negative regulator. Sirtuins have evolved different strategies in response to NAM regulation. Here, we report the detailed kinetic analysis of SIRT1-catalyzed reactions using endogenous substrate-based synthetic peptides. A novel substrate-dependent sensitivity of SIRT1 to NAM inhibition was observed. Additionally, SIRT1 demonstrated pH-dependent deacetylation with normal solvent isotope effects (SIEs), consistent with proton transfer in the rate-limiting step. Base exchange, in contrast, was insensitive to pH changes with no apparent SIEs, indicative of lack of proton transfer in the rate-limiting step. Consequently, NAM inhibition was attenuated at a high pH in proteated buffers. Our study provides new evidence for "activation by de-repression" as an effective sirtuin activation strategy.

The ambiguous role of sirtuins in head and neck squamous cell carcinoma

Oral cancer is one of the most leading cancer responsible for significant morbidity and mortality. The sirtuins (SIRTs) are a family of class III histone deacetylases and are known to regulate a variety of molecular signaling associated with different cancer types including oral malignancies. SIRT1 acts as bifunctional in a variety of cancer. In oral cancer, SIRT1 seems to work as a tumor suppressor. The carcinogenic potential of SIRT1 is also reported in oral cancer, and hence, its role is still ambiguous. SIRT2 is also said to play a dual-faced role in different types of cancers. However, in oral cancer, SIRT2 is not studied and its role remains obscure. SIRT3 expression was positively correlated with oral malignancies. However, studies also showed the anti-cancer role of SIRT3 in oral cancer. SIRT7 loss was observed in oral cancer cells, while its overexpression caused the suppression of oral cancer cells proliferation, migration, and invasiveness. The role of other SIRTs in oral cancer was studied meagerly or reports not available. To date, only the roles of SIRT1, SIRT3, and SIRT7 have been reported in oral malignancies. Therefore, understanding the regulatory mechanisms employed by sirtuins to modulate oral cancer is important for developing potential anti-cancer therapeutic strategies.

Targeting Mitochondrial Impairment in Parkinson's Disease: Challenges and Opportunities

The underlying pathophysiology of Parkinson's disease is complex, but mitochondrial dysfunction has an established and prominent role. This is supported by an already large and rapidly growing body of evidence showing that the role of mitochondrial (dys)function is central and multifaceted. However, there are clear gaps in knowledge, including the dilemma of explaining why inherited mitochondriopathies do not usually present with parkinsonian symptoms. Many aspects of mitochondrial function are potential therapeutic targets, including reactive oxygen species production, mitophagy, mitochondrial biogenesis, mitochondrial dynamics and trafficking, mitochondrial metal ion homeostasis, sirtuins, and endoplasmic reticulum links with mitochondria. Potential therapeutic strategies may also incorporate exercise, microRNAs, mitochondrial transplantation, stem cell therapies, and photobiomodulation. Despite multiple studies adopting numerous treatment strategies, clinical trials to date have generally failed to show benefit. To overcome this hurdle, more accurate biomarkers of mitochondrial dysfunction are required to detect subtle beneficial effects. Furthermore, selecting study participants early in the disease course, studying them for suitable durations, and stratifying them according to genetic and neuroimaging findings may increase the likelihood of successful clinical trials. Moreover, treatments involving combined approaches will likely better address the complexity of mitochondrial dysfunction in Parkinson's disease. Therefore, selecting the right patients, at the right time, and using targeted combination treatments, may offer the best chance for development of an effective novel therapy targeting mitochondrial dysfunction in Parkinson's disease.

MDL-800, an allosteric activator of SIRT6, suppresses proliferation and enhances EGFR-TKIs therapy in non-small cell lung cancer

Sirtuin 6 (SIRT6), a member of the sirtuin family, is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that is involved in various physiological and pathological processes. SIRT6 is generally downregulated and linked to tumorigenesis in non-small cell lung carcinoma (NSCLC), thus regarded as a promising therapeutic target of NSCLC. In this study, we investigated whether MDL-800, an allosteric activator of SIRT6, exerted antiproliferation effect against NSCLC cells in vitro and in vivo. We showed that MDL-800 increased SIRT6 deacetylase activity with an EC50 value of 11.0 ± 0.3 μM; MDL-800 (10-50 μM) induced dose-dependent deacetylation of histone H3 in 12 NSCLC cell lines. Treatment with MDL-800 dose dependently inhibited the proliferation of 12 NSCLC cell lines with IC50 values ranging from 21.5 to 34.5 μM. The antiproliferation effect of MDL-800 was significantly diminished by SIRT6 knockout. Treatment with MDL-800 induced remarkable cell cycle arrest at the G0/G1 phase in NSCLC HCC827 and PC9 cells. Furthermore, MDL-800 (25, 50 μM) enhanced the antiproliferation of epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) in osimertinib-resistant HCC827 and PC9 cells as well as in patient-derived primary tumor cells, and suppressed mitogen-activated protein kinase (MAPK) pathway. In HCC827 cell-derived xenograft nude mice, intraperitoneal administration of MDL-800 (80 mg · kg-1 · d-1, for 14 days) markedly suppressed the tumor growth, accompanied by enhanced SIRT6-dependent histone H3 deacetylation and decreased p-MEK and p-ERK in tumor tissues. Our results provide the pharmacological evidence for future clinical investigation of MDL-800 as a promising lead compound for NSCLC treatment alone or in combination with EGFR-TKIs.

A new series of benzoxazole-based SIRT1 modulators for targeted therapy of non-small-cell lung cancer

In an attempt to identify potential anticancer agents for non-small-cell lung cancer (NSCLC) targeting sirtuin 1 (SIRT1), the synthesis of a new series of benzoxazoles (3a - i) was carried out through a facile and versatile synthetic route. The compounds were evaluated for their cytotoxic effects on A549 human lung adenocarcinoma and NIH/3T3 mouse embryonic fibroblast cells using the MTT assay. 2-[(5-Nitro-1H-benzimidazol-2-yl)thio]-N-(2-methylbenzoxazol-5-yl)acetamide (3e) and 2-[(5-chloro-1H-benzimidazol-2-yl)thio]-N-(2-methylbenzoxazol-5-yl)acetamide (3g) were the most potent and selective anticancer agents in this series against the A549 cell line, with IC₅₀ values of 46.66 ± 11.54 and 55.00 ± 5.00 µM, respectively. The flow cytometry-based apoptosis detection assay was performed to determine their effects on apoptosis in A549 cells. Both compounds induced apoptosis in a dose-dependent manner. The effects of compounds 3e and 3g on SIRT1 activity were determined. On the basis of in vitro studies, it was observed that compound 3g caused a significant decrease in SIRT1 levels in a dose-dependent manner, whereas compound 3e increased the SIRT1 levels. According to molecular docking studies, the substantial alteration in the type of action could be attributed to the difference between the interactions of compounds 3e and 3g with the same residues in the active site of SIRT1 (PDB code: 4IG9). On the basis of in silico ADME (absorption, distribution, metabolism, and excretion) studies, these compounds are predicted to possess favorable ADME profiles. According to the in vitro and in silico studies, compounds 3e and 3g, small-molecule SIRT1 modulators, were identified as potential orally bioavailable anticancer agents for the targeted therapy of NSCLC.