SRT2104 attenuates diabetes-induced aortic endothelial dysfunction via inhibition of P53

Research progress on Sirtuins (SIRTs) family modulators

Sirtuins (SIRTs) represent a class of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that exert a crucial role in cellular signal transduction and various biological processes. The mammalian sirtuins family encompasses SIRT1 to SIRT7, exhibiting therapeutic potential in counteracting cellular aging, modulating metabolism, responding to oxidative stress, inhibiting tumors, and improving cellular microenvironment. These enzymes are intricately linked to the occurrence and treatment of diverse pathological conditions, including cancer, autoimmune diseases, and cardiovascular disorders. Given the significance of histone modification in gene expression and chromatin structure, maintaining the equilibrium of the sirtuins family is imperative for disease prevention and health restoration. Mounting evidence suggests that modulators of SIRTs play a crucial role in treating various diseases and maintaining physiological balance. This review delves into the molecular structure and regulatory functions of the sirtuins family, reviews the classification and historical evolution of SIRTs modulators, offers a systematic overview of existing SIRTs modulation strategies, and elucidates the regulatory mechanisms of SIRTs modulators (agonists and inhibitors) and their clinical applications. The article concludes by summarizing the challenges encountered in SIRTs modulator research and offering insights into future research directions.

Fenugreek extract improves diabetes-induced endothelial dysfunction via the arginase 1 pathway

Endothelial dysfunction (ED) is an initiating trigger and key factor in vascular complications, leading to disability and mortality in individuals with diabetes. The research concerning therapeutic interventions for ED has gained considerable interest. Fenugreek, a commonly used edible plant in dietary consumption, has attracted significant attention due to its management of diabetes and its associated complications. The research presented in this study examines the potential therapeutic benefits of fenugreek in treating ED and investigates the underlying mechanism associated with its effects. The analysis on fenugreek was performed using 70% ethanol extract, and its chemical composition was analyzed using ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). In total, we identified 49 compounds present in the fenugreek extract. These compounds encompass flavonoids, saponins, and phospholipids. Then, the models of ED in streptozotocin-induced diabetic mice and high glucose-induced isolated rat aortas were established for research. Through vascular function testing, it was observed that fenugreek extract effectively improved ED induced by diabetes or high glucose. By analyzing the protein expression of arginase 1 (Arg1), Arg activity, Arg1 immunohistochemistry, nitric oxide (NO) level, and the protein expression of endothelial nitric oxide synthase (eNOS), p38 mitogen-activated protein kinase (p38 MAPK), and p-p38 MAPK in aortas, this study revealed that the potential mechanism of fenugreek extract in anti-ED involves the downregulation of Arg1, leading to enhanced NO production. Furthermore, analysis of serum exosomes carrying Arg activity indicates that fenugreek may decrease the activity of Arg transported by serum exosomes, potentially preventing the increase in Arg levels triggered by the uptake of serum exosomes by vascular endothelial cells. In general, this investigation offers valuable observations regarding the curative impact of fenugreek extract on anti-ED in diabetes, revealing the involvement of the Arg1 pathway in its mechanism.

Emerging roles of SIRT1 activator, SRT2104, in disease treatment

Silent information regulator 1 (SIRT1) is a NAD+-dependent class III deacetylase that plays important roles in the pathogenesis of numerous diseases, positioning it as a prime candidate for therapeutic intervention. Among its modulators, SRT2104 emerges as the most specific small molecule activator of SIRT1, currently advancing into the clinical translation phase. The primary objective of this review is to evaluate the emerging roles of SRT2104, and to explore its potential as a therapeutic agent in various diseases. In the present review, we systematically summarized the findings from an extensive array of literature sources including the progress of its application in disease treatment and its potential molecular mechanisms by reviewing the literature published in databases such as PubMed, Web of Science, and the World Health Organization International Clinical Trials Registry Platform. We focuses on the strides made in employing SRT2104 for disease treatment, elucidating its potential molecular underpinnings based on preclinical and clinical research data. The findings reveal that SRT2104, as a potent SIRT1 activator, holds considerable therapeutic potential, particularly in modulating metabolic and longevity-related pathways. This review establishes SRT2104 as a leading SIRT1 activator with significant therapeutic promise.

Identification of hub genes and pathways associated with cellular senescence in diabetic foot ulcers via comprehensive transcriptome analysis

This research aimed to find important genes and pathways related to cellular senescence (CS) in diabetic foot ulcers (DFU) and to estimate the possible pathways through which CS affects diabetic foot healing. The GSE80178 dataset was acquired from the Gene Expression Omnibus (GEO) database, containing six DFU and three diabetic foot skin (DFS) samples. The limma package was used to identify differentially expressed genes (DEGs). At the same time, DEGs associated with CS (CS-DEGs) were found using the CellAge database. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted on the CS-DEGs. A protein-protein interaction (PPI) network was built using the String database, and the cytoHubba plug-in within Cytoscape helped identify hub genes. Lastly, the miRNA-TF-mRNA regulatory network for these hub genes was established. In total, 66 CS-DEGs were obtained. These genes mainly focus on CS, Kaposi sarcoma-associated herpesvirus infection and Toll-like receptor signalling pathway. Eight hub genes were identified to regulate cell senescence in DFU, including TP53, SRC, SIRT1, CCND1, EZH2, CXCL8, AR and CDK4. According to miRNA-TF-mRNA regulatory network, hsa-mir-132-3p/SIRT1/EZH2 axis is involved in senescence cell accumulation in DFU.

The Impact of SRT2104 on Skeletal Muscle Mitochondrial Function, Redox Biology, and Loss of Muscle Mass in Hindlimb Unloaded Rats

Mechanical unloading during microgravity causes skeletal muscle atrophy and impairs mitochondrial energetics. The elevated production of reactive oxygen species (ROS) by mitochondria and Nox2, coupled with impairment of stress protection (e.g., SIRT1, antioxidant enzymes), contribute to atrophy. We tested the hypothesis that the SIRT1 activator, SRT2104 would rescue unloading-induced mitochondrial dysfunction. Mitochondrial function in rat gastrocnemius and soleus muscles were evaluated under three conditions (10 days): ambulatory control (CON), hindlimb unloaded (HU), and hindlimb-unloaded-treated with SRT2104 (SIRT). Oxidative phosphorylation, electron transfer capacities, H₂O₂ production, and oxidative and antioxidant enzymes were quantified using high-resolution respirometry and colorimetry. In the gastrocnemius, (1) integrative (per mg tissue) proton LEAK was lesser in SIRT than in HU or CON; (2) intrinsic (relative to citrate synthase) maximal noncoupled electron transfer capacity (E_CI+II) was lesser, while complex I-supported oxidative phosphorylation to E_CI+II was greater in HU than CON; (3) the contribution of LEAK to E_CI+II was greatest, but cytochrome c oxidase activity was lowest in HU. In both muscles, H₂O₂ production and concentration was greatest in SIRT, as was gastrocnemius superoxide dismutase activity. In the soleus, H₂O₂ concentration was greater in HU compared to CON. These results indicate that SRT2104 preserves mitochondrial function in unloaded skeletal muscle, suggesting its potential to support healthy muscle cells in microgravity by promoting necessary energy production in mitochondria.

Cellular and molecular biology of sirtuins in cardiovascular disease

Sirtuins (SIRTs) are a nicotinic adenine dinucleotide (+) -dependent histone deacetylase that regulates critical signaling pathways in prokaryotes and eukaryotes. Studies have identified seven mammalian homologs of the yeast SIRT silencing message regulator 2, namely, SIRT1-SIRT7. Recent in vivo and in vitro studies have successfully demonstrated the involvement of SIRTs in key pathways for cell biological function in physiological and pathological processes of the cardiovascular system, including processes including cellular senescence, oxidative stress, apoptosis, DNA damage, and cellular metabolism. Emerging evidence has stimulated a significant evolution in preventing and treating cardiovascular disease (CVD). Here, we review the important roles of SIRTs for the regulatory pathways involved in the pathogenesis of cardiovascular diseases and their molecular targets, including novel protein post-translational modifications of succinylation. In addition, we summarize the agonists and inhibitors currently identified to target novel specific small molecules of SIRTs. A better understanding of the role of SIRTs in the biology of CVD opens new avenues for therapeutic intervention with great potential for preventing and treating CVD.

The activation of histone deacetylases 4 prevented endothelial dysfunction: A crucial mechanism of HuangqiGuizhiWuwu Decoction in improving microcirculation dysfunction in diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

The regulation of epigenetic factors is considered a crucial target for solving complex chronic diseases such as cardio-cerebrovascular diseases. HuangqiGuizhiWuwu Decoction (HGWWD), a classic Chinese prescription, is mainly used to treat various vascular diseases. Although our previous studies reported that HGWWD could effectively prevent vascular dysfunction in diabetic rodent models, the precise mechanism is still elusive.

AIM OF THE STUDY

In this study, we investigated the epigenetic mechanisms of modulating the damage of vascular endothelial cells in diabetes by HGWWD.

METHODS

We first analyzed common active components of HGWWD by using HPLC-Q-TOF-MS/MS analysis, and predicted the isoforms of histone deacetylase (HDAC) that can potentially combine the above active components by systems pharmacology. Next, we screened the involvement of specific HDAC isoforms in the protective effect of HGWWD on vascular injury by using pharmacological blockade combined with the evaluation of vascular function in vivo and in vitro.

RESULTS

Firstly, HDAC1, HDAC2, HDAC3, HDAC4, HDAC6, HDAC7, SIRT2, and SIRT3 have been implicated with the possibility of binding to the thirty-one common active components in HGWWD. Furthermore, the protective effect of HGWWD is reversed by both TSA (HDAC inhibitor) and MC1568 (class II HDAC inhibitor) on vascular impairment accompanied by reduced aortic HDAC activity in STZ mice. Finally, inhibition of HDAC4 blocked the protective effect of HGWWD on microvascular and endothelial dysfunction in diabetic mice.

CONCLUSIONS

These results prove the key role of HDAC4 in diabetes-induced microvascular dysfunction and underlying epigenetic mechanisms for the protective effect of HGWWD in diabetes.

The role of p53 in the alternation of vascular functions

Ageing is a risk factor for many degenerative diseases. Cardiovascular diseases (CVDs) are usually big burdens for elderly, caregivers and the health system. During the aging process, normal functions of vascular cells and tissue progressively lost and eventually develop vascular diseases. Endothelial dysfunction, reduced bioavailability of endothelium-derived nitric oxide are usual phenomena observed in patients with cardiovascular diseases. Myriad of studies have been done to investigate to delay the vascular dysfunction or improve the vascular function to prolong the aging process. Tumor suppressor gene p53, also a transcription factor, act as a gatekeeper to regulate a number of genes to maintain normal cell function including but not limited to cell proliferation, cell apoptosis. p53 also crosstalk with other key transcription factors like hypoxia-inducible factor 1 alpha that contribute to the progression of cardiovascular diseases. Therefore, in recent three decades, p53 has drawn scientists’ attention on its effects in vascular function. Though the role of tumor suppressor gene p53 is still not clear in vascular function, it is found to play regulatory roles and may involve in vascular remodeling, atherosclerosis or pulmonary hypertension. p53 may have a divergent role in endothelial and vascular muscle cells in those conditions. In this review, we describe the different effects of p53 in cardiovascular physiology. Further studies on the effects of endothelial cell-specific p53 deficiency on atherosclerotic plaque formation in common animal models are required before the therapeutic potential can be realized.

Progesterone Attenuates SIRT1-Deficiency-Mediated Pre-Eclampsia

Pre-eclampsia is a severe hypertensive disorder of pregnancy (HDP), mainly characterized by new-onset hypertension with proteinuria after 20-week gestation. Sirtuin1 (SIRT1), a class III histone deacetylase, is associated with the regulation of various pathophysiological processes, including inflammation, immune response, metabolism, and autophagy. However, the effect of SIRT1 in the pathogenesis of pre-eclampsia remains to be elucidated. In this study, we found that the expression of SIRT1 was relatively lower in the placentas and serum samples of pre-eclampsia patients. Typical pre-eclampsia-like symptoms, such as hypertension, proteinuria, fetal growth restriction, kidney injury, and a narrow placental labyrinth layer, were observed in SIRT1 knockdown (SIRT1^+/−) mice. Of note, these performances could be improved after the intraperitoneal injection of SIRT1 agonist SRT2104. More importantly, we found that the efficacy of progesterone on attenuating symptoms of PE was profoundly better than that of metformin in SIRT1^+/− mice. In addition, our results suggested that progesterone can promote the invasion and inhibit the apoptosis of trophoblasts. These data suggest that SIRT1 plays an important role in pre-eclampsia and that progesterone alleviates pre-eclampsia-like symptoms mediated by SIRT1 deficiency.

p53 regulated senescence mechanism and role of its modulators in age-related disorders

Multiple co-morbidities are associated with age, and there is a need for the broad-spectrum drug to prevent multiple regimens that may cause an adverse effect in the geriatric population. Cellular senescence is a primary mechanism for ageing in various tissues. p53, a tumor suppressor protein, plays a significant role in forming DNA damage foci and post different stress responses. DNA damage foci can be transient or persistent that can progress to DNA-SCARS inducing senescence. p53 also plays a role in apoptosis and negative regulation of SASP. Few upstream targets like FOXO4, MDM2, MDM4, USP7 control the availability of p53 for apoptosis. Hence, the senolytic therapies, modulating p53 upstream targets, can be a good approach for preventing age-related disorders. This review discusses the insights on the role of p53 in the formation of DNA-SCARS, various upstream target proteins, and pathways involved in p53 regulation. Further, the review aimed to include recently discovered small molecules acting on these upstream targets, and those can be modified using medicinal chemistry approaches to give successful senotherapeutics.

The Emerging Role of HDACs: Pathology and Therapeutic Targets in Diabetes Mellitus

Diabetes mellitus (DM) is one of the principal manifestations of metabolic syndrome and its prevalence with modern lifestyle is increasing incessantly. Chronic hyperglycemia can induce several vascular complications that were referred to be the major cause of morbidity and mortality in DM. Although several therapeutic targets have been identified and accessed clinically, the imminent risk of DM and its prevalence are still ascending. Substantial pieces of evidence revealed that histone deacetylase (HDAC) isoforms can regulate various molecular activities in DM via epigenetic and post-translational regulation of several transcription factors. To date, 18 HDAC isoforms have been identified in mammals that were categorized into four different classes. Classes I, II, and IV are regarded as classical HDACs, which operate through a Zn-based mechanism. In contrast, class III HDACs or Sirtuins depend on nicotinamide adenine dinucleotide (NAD+) for their molecular activity. Functionally, most of the HDAC isoforms can regulate β cell fate, insulin release, insulin expression and signaling, and glucose metabolism. Moreover, the roles of HDAC members have been implicated in the regulation of oxidative stress, inflammation, apoptosis, fibrosis, and other pathological events, which substantially contribute to diabetes-related vascular dysfunctions. Therefore, HDACs could serve as the potential therapeutic target in DM towards developing novel intervention strategies. This review sheds light on the emerging role of HDACs/isoforms in diabetic pathophysiology and emphasized the scope of their targeting in DM for constituting novel interventional strategies for metabolic disorders/complications.

Design, Synthesis and Pharmacological Evaluation of Naphthofuran Derivatives as Potent SIRT1 Activators

Diabetic nephropathy (DN) is one of the most important medical complications in diabetic patients, which is an essential cause of end-stage renal disease in diabetic patients and still lacks effective medicines. Silent information regulator 1 (SIRT1) is closely related to the occurrence and development of DN. Activation of SIRT1 could significantly improve the symptoms of DN, while the activities of SIRT1 activators need to be further improved. Based on the crystal structure of SIRT1, structure and ligand-based approaches were carried out, and a lead compound 4,456–0661 (renamed as M1) was identified. Moreover, seven M1 analogues (6a-6g) were designed using a structure-based drug design strategy followed by bioactivity evaluation with SRTR2104 used as positive drugs. Among the target molecules, compounds M1, 6b, and 6d were proved to be potent SIRT1 activators, the activities of which are comparable to SRT2104. More importantly, compounds M1, 6b, and 6d could resist high glucose-induced apoptosis of HK-2 cells by activating SIRT1 and deacetylation of p53. Apart from the beneficial effect on apoptosis of DN, these compounds also alleviated high glucose stimulating inflammation response in HK-2 cells through SIRT1/NF-κB (p65) pathway. Consequently, M1, 6b, and 6d could be promising drug candidates for SIRT1 related diseases.

Sirt1 activator SRT2104 protects against oxygen-glucose deprivation/reoxygenation-induced injury via regulating microglia polarization by modulating Sirt1/NF-κB pathway

Cerebral ischemic/reperfusion injury is the most common neurological disorder and the second leading cause of death worldwide. Modulating microglia polarization from pro-inflammatory M1 phenotype to anti-inflammatory M2 state has been suggested as a potential therapeutic approach in the treatment of this injury. SRT2104, a novel activator of histone deacetylase Sirtuin-1 (Sirt1), has recently been shown to have anti-inflammation properties. However, the effect of SRT2104 on cerebral ischemic/reperfusion injury has not been elucidated. Here, we found that SRT2104 inhibited neuron and microglia death directly and indirectly through microglia condition medium from an oxygen glucose deprivation/reoxygenation (OGD/R) -induced cell injury models. Moreover, SRT2104 treatment modulated the microglia polarization shift from the M1 phenotype and skewed toward the M2 phenotype. Additionally, we found that SRT2104 could significant inhibit the activation of NF-κB and enhanced Sirt1 expression in microglia. Mechanism studies using the BV2 microglial cell line confirmed that knockdown Sirt1 significantly reduced the effect of SRT2104 on the activation of NF-κB pathway and microglial phenotype shift. Altogether, our result shows SRT2104 protect OGD/R-induced injury through shifting microglia phenotype, which may have potential in further studies as a novel neuroprotective agent for cerebral ischemic/reperfusion injury therapy.

The Endothelium as a Target for Anti-Atherogenic Therapy: A Focus on the Epigenetic Enzymes EZH2 and SIRT1

Endothelial cell inflammatory activation and dysfunction are key events in the pathophysiology of atherosclerosis, and are associated with an elevated risk of cardiovascular events. Yet, therapies specifically targeting the endothelium and atherosclerosis are lacking. Here, we review how endothelial behaviour affects atherogenesis and pose that the endothelium may be an efficacious cellular target for antiatherogenic therapies. We discuss the contribution of endothelial inflammatory activation and dysfunction to atherogenesis and postulate that the dysregulation of specific epigenetic enzymes, EZH2 and SIRT1, aggravate endothelial dysfunction in a pleiotropic fashion. Moreover, we propose that commercially available drugs are available to clinically explore this postulation.

Therapeutic Effects of SRT2104 on Lung Injury in Rats with Emphysema via Reduction of Type II Alveolar Epithelial Cell Senescence

Chronic obstructive pulmonary disease (COPD) is one of the most prevalent and severe diseases worldwide with high societal and health care costs. The pathogenesis of COPD is very complicated, and no curative treatment is available. Cellular senescence promotes the development of COPD. Type II alveolar epithelial cells (AECII) play a momentous role in lung tissue repair and maintenance of alveolar homeostasis. Sirtuin 1 (SIRT1), an antiaging molecule involved in the response to chronic inflammation and oxidative stress, regulates many pathophysiological changes including stress resistance, apoptosis, inflammation, and cellular senescence. This study aimed to investigate whether the pharmacological SIRT1 activator SRT2104 protects against AECII senescence in rats with emphysema. Our findings confirmed that SRT2104 administration reduced the pathological characteristics of emphysema and improved lung function parameters, including pulmonary resistance, pulmonary dynamic compliance, and peak expiratory flow. Moreover, SRT2104 treatment upregulated the expression of surfactant proteins A and C, SIRT1, and forkhead box O 3a (FoxO3a), decreased senescence-associated-β-galactosidase (SA-β-gal) activity, increased SIRT1 deacetylase activity, and downregulated the levels of p53 and p21. Therefore, SRT2104 administration protected against AECII senescence in rats with emphysema via SIRT1/FoxO3a and SIRT1/p53 signaling pathways and may provide a novel potential therapeutic strategy for COPD.

Protective role of NRF2 in macrovascular complications of diabetes

Macrovascular complications develop in over a half of the diabetic individuals, resulting in high morbidity and mortality. This poses a severe threat to public health and a heavy burden to social economy. It is therefore important to develop effective approaches to prevent or slow down the pathogenesis and progression of macrovascular complications of diabetes (MCD). Oxidative stress is a major contributor to MCD. Nuclear factor (erythroid‐derived 2)‐like 2 (NRF2) governs cellular antioxidant defence system by activating the transcription of various antioxidant genes, combating diabetes‐induced oxidative stress. Accumulating experimental evidence has demonstrated that NRF2 activation protects against MCD. Structural inhibition of Kelch‐like ECH‐associated protein 1 (KEAP1) is a canonical way to activate NRF2. More recently, novel approaches, such as activation of the Nfe2l2 gene transcription, decreasing KEAP1 protein level by microRNA‐induced degradation of Keap1 mRNA, prevention of proteasomal degradation of NRF2 protein and modulation of other upstream regulators of NRF2, have emerged in prevention of MCD. This review provides a brief introduction of the pathophysiology of MCD and the role of oxidative stress in the pathogenesis of MCD. By reviewing previous work on the activation of NRF2 in MCD, we summarize strategies to activate NRF2, providing clues for future intervention of MCD. Controversies over NRF2 activation and future perspectives are also provided in this review.

The road ahead for health and lifespan interventions

Aging is a modifiable risk factor for most chronic diseases and an inevitable process in humans. The development of pharmacological interventions aimed at delaying or preventing the onset of chronic conditions and other age-related diseases has been at the forefront of the aging field. Preclinical findings have demonstrated that species, sex and strain confer significant heterogeneity on reaching the desired health- and lifespan-promoting pharmacological responses in model organisms. Translating the safety and efficacy of these interventions to humans and the lack of reliable biomarkers that serve as predictors of health outcomes remain a challenge. Here, we will survey current pharmacological interventions that promote lifespan extension and/or increased healthspan in animals and humans, and review the various anti-aging interventions selected for inclusion in the NIA's Interventions Testing Program as well as the ClinicalTrials.gov database that target aging or age-related diseases in humans.

Axonal protection by a small molecule SIRT1 activator, SRT2104, with alteration of autophagy in TNF-induced optic nerve degeneration

PURPOSE

To examine the effects of SRT2104, an SIRT1 activator, in optic nerve degeneration induced by TNF and to investigate whether it affects the autophagic status after induction of axonal degeneration.

STUDY DESIGN

Experimental.

METHODS

Adult male Wistar rats received intravitreal injection of TNF alone, concomitant injection of SRT2104 and TNF, or injection of SRT2104 alone. The autophagic status in the optic nerve was evaluated to examine p62 and LC3-II expression by immunoblot analysis. The effect of SRT2104 on TNF-induced axon loss was determined by counting the number of axons.

RESULTS

Intravitreal injection of SRT2104 showed a modest protective tendency in the 2-pmol-treated groups against TNF-induced axon loss, although the tendency was not significant on quantitative analysis. However, significant protective effects were found in the 20- or 200-pmol-treated groups. Injection of SRT2104 alone significantly decreased the p62 levels and increased the LC3-II levels as compared with the basal levels. Similarly, concomitant injection of SRT2104 and TNF significantly decreased the p62 levels and increased the LC3-II levels as compared with the TNF-treated group. Upregulation of SIRT1 expression was observed in the optic nerve after SRT2104 treatment.

CONCLUSION

The SIRT1 activator SRT2104 exerts axonal protection in TNF-induced optic nerve degeneration. This effect may be associated with upregulated autophagic status in the optic nerve.

Two novel SIRT1 activators, SCIC2 and SCIC2.1, enhance SIRT1-mediated effects in stress response and senescence

SIRT1, a NAD⁺-dependent deacetylase, is the most well-studied member of class III histone deacetylases. Due to its wide range of activities and substrate targets, this enzyme has emerged as a major regulator of different physiological processes. However, SIRT1-mediated alterations are also implicated in the pathogenesis of several conditions, including metabolic and neurodegenerative disorders, and cancer. Current evidence highlights the potential role of SIRT1 as an attractive therapeutic target for disease prevention and treatment strategies, thus propelling the development of new pharmacological agents. By high-throughput screening of a large library of compounds, we identified SCIC2 as an effective SIRT1 activator. This small molecule showed enzymatic activity of 135.8% at 10 μM, an AC₅₀ value of 50 ± 1.8 µM, and bound SIRT1 with a K_D of 26.4 ± 0.6 μM. In order to potentiate its SIRT1-activating ability, SCIC2 was subjected to modelling studies, leading to the identification of a more potent derivative, SCIC2.1. SCIC2.1 displayed higher SIRT1 activity (175%; AC₅₀ = 36.83 ± 2.23 µM), stronger binding to SIRT1, and greater cell permeability than SCIC2. At cellular level, both molecules did not alter the cell cycle progression of cancer cells and normal cells, and were able to strengthen SIRT1-mediated effects in stress response. Finally, SCIC2 and SCIC2.1 attenuated induction of senescence by reducing senescence-associated β-galactosidase activity. Our findings warrant further investigation of these two novel SIRT1 activators in in vivo and human studies.

P53/NRF2 mediates SIRT1's protective effect on diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end stage renal disease, posing a severe threat to public health. Previous studies reported the protective role of sirtuin 1 (SIRT1) in DN, encouraging the investigation of more potent and specific SIRT1 activators. SRT2104 is a novel, first-in-class, highly selective small-molecule activator of SIRT1, with its effect and mechanism unknown on DN. To this end, streptozotocin-induced C57BL/6 wild-type (WT) diabetic mice were treated with SRT2104, for 24 weeks. To determine whether SRT2104 acted through inhibition of P53 - a substrate of SIRT1, the P53 activator nutlin3a was administered to the WT diabetic mice in the presence of SRT2104. In order to test whether nuclear factor erythroid 2-related factor 2 (NRF2) - the master of cellular antioxidants - mediated SIRT1 and P53's actions, WT and Nrf2 gene knockout (KO) diabetic mice were treated with SRT2104 or the P53 inhibitor pifithrin-α (PFT-α). In the WT mice, SRT2104 enhanced renal SIRT1 expression and activity, deacetylated P53, and activated NRF2 antioxidant signaling, providing remarkable protection against the DM-induced renal oxidative stress, inflammation, fibrosis, glomerular remodeling and albuminuria. These effects were completely abolished in the presence of nutlin3a. Deletion of the Nrf2 gene completely abrogated the efficacies of SRT2104 and PFT-α in elevating antioxidants and ameliorating DN, despite their abilities to activate SIRT1 and inhibit P53 in the Nrf2 KO mice. The present study reports the beneficial effects of SRT2104 on DN, uncovering a SIRT1/P53/NRF2 pathway that modulates the pathogenesis of DN.

Inhibition of P53/miR-34a improves diabetic endothelial dysfunction via activation of SIRT1

Endothelial dysfunction contributes to diabetic macrovascular complications, resulting in high mortality. Recent findings demonstrate a pathogenic role of P53 in endothelial dysfunction, encouraging the investigation of the effect of P53 inhibition on diabetic endothelial dysfunction. Thus, high glucose (HG)‐treated endothelial cells (ECs) were subjected to pifithrin‐α (PFT‐α)—a specific inhibitor of P53, or P53‐small interfering RNA (siRNA), both of which attenuated the HG‐induced endothelial inflammation and oxidative stress. Moreover, inhibition of P53 by PFT‐α or P53‐siRNA prohibited P53 acetylation, decreased microRNA‐34a (miR‐34a) level, leading to a dramatic increase in sirtuin 1 (SIRT1) protein level. Interestingly, the miR‐34a inhibitor (miR‐34a‐I) and PFT‐α increased SIRT1 protein level and alleviated the HG‐induced endothelial inflammation and oxidative stress to a similar extent; however, these effects of PFT‐α were completely abrogated by the miR‐34a mimic. In addition, SIRT1 inhibition by EX‐527 or Sirt1‐siRNA completely abolished miR‐34a‐I's protection against HG‐induced endothelial inflammation and oxidative stress. Furthermore, in the aortas of streptozotocin‐induced diabetic mice, both PFT‐α and miR‐34a‐I rescued the inflammation, oxidative stress and endothelial dysfunction caused by hyperglycaemia. Hence, the present study has uncovered a P53/miR‐34a/SIRT1 pathway that leads to endothelial dysfunction, suggesting that P53/miR‐34a inhibition could be a viable strategy in the management of diabetic macrovascular diseases.

Dimethyl fumarate accelerates wound healing under diabetic condition

Impaired wound healing is a common complication among patients with diabetes mellitus (DM), resulting in high rates of disability and mortality. Recent findings highlighted the critical role of nuclear factor erythroid 2-related factor 2 (NRF2) - a master of cellular antioxidants scavenging excessive DM-induced free radicals - in accelerating diabetic wound healing. Dimethyl fumarate (DMF) is a potent NRF2 activator used for the treatment of multiple sclerosis. However, the effect of DMF on wound healing has not been determined. The present study investigated the effect of DMF on the diabetic and the non-diabetic wound healing in streptozotocin-induced diabetic mice and non-diabetic control mice. DMF activated NRF2 signaling under both conditions. Interestingly, DMF attenuated oxidative damage and inflammation, and accelerated wound closure in the diabetic mice. However, this effect was not observed in non-diabetic mice. Keratinocytes were treated with normal glucose (NG), high glucose (HG), or hydrogen peroxide (H2O2), in the presence or absence of DMF to assess the role of reactive oxygen species (ROS) - inducible in DM - in mediating DMF-induced protection. Both HG and H2O2 elevated ROS, oxidative damage, and inflammation, the effects of which were similarly blunted by DMF. However, in spite of the activation of NRF2, DMF lost this capability under the NG condition. The findings of this study demonstrate that ROS activate the protective effect of DMF on the diabetic wound healing.

Sodium butyrate attenuates diabetes-induced aortic endothelial dysfunction via P300-mediated transcriptional activation of Nrf2

Oxidative stress and inflammation are major contributors to diabetes-induced endothelial dysfunction which is the critical first step to the development of diabetic macrovascular complications. Nuclear factor erythroid 2-related factor 2 (NRF2) plays a key role in combating diabetes-induced oxidative stress and inflammation. Sodium butyrate (NaB) is an inhibitor of histone deacetylase (HDAC) and an activator of NRF2. However, NaB's effect on diabetes-induced aortic injury was unknown. It was also not known whether or to what extent NRF2 is required for both self-defense and NaB's protection in the diabetic aorta. Additionally, the mechanism by which NaB activates NRF2 was unclear. Therefore, C57BL/6 Nrf2 knockout (KO) and wild type (WT) mice were induced to diabetes by streptozotocin, and were treated in the presence or absence of NaB, for 20 weeks. The KO diabetic mice developed more severe aortic endothelial oxidative stress, inflammation and dysfunction, as compared with the WT diabetic mice. NaB significantly attenuated these effects in the WT, but not the KO, mice. In high glucose-treated aortic endothelial cells, NaB elevated Nrf2 mRNA and protein without facilitating NRF2 nuclear translocation, an effect distinct from that of sulforaphane. NaB inhibited HDAC activity, and increased occupancy of the transcription factor aryl hydrocarbon receptor and the co-activator P300 at the Nrf2 gene promoter. Further, the P300 inhibitor C646 completely abolished NaB's efficacies. Thus, NRF2 is required for both self-defense and NaB's protection against diabetes-induced aortic endothelial dysfunction. Other findings suggest that P300 mediates the transcriptional activation of Nrf2 by NaB.

MDM2 controls NRF2 antioxidant activity in prevention of diabetic kidney disease

Oxidative stress and P53 contribute to the pathogenesis of diabetic kidney disease (DKD). Nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of cellular antioxidant defense system, is negatively regulated by P53 and prevents DKD. Recent findings revealed an important role of mouse double minute 2 (MDM2) in protection against DKD. However, the mechanism remained unclear. We hypothesized that MDM2 enhances NRF2 antioxidant signaling in DKD given that MDM2 is a key negative regulator of P53. The MDM2 inhibitor nutlin3a elevated renal P53, inhibited NRF2 signaling and induced oxidative stress, inflammation, fibrosis, DKD-like renal pathology and albuminuria in the wild-type (WT) non-diabetic mice. These effects exhibited more prominently in nutlin3a-treated WT diabetic mice. Interestingly, nutlin3a failed to induce greater renal injuries in the Nrf2 knockout (KO) mice under both the diabetic and non-diabetic conditions, indicating that NRF2 predominantly mediates MDM2's action. On the contrary, P53 inhibition by pifithrin-α activated renal NRF2 signaling and the expression of Mdm2, and attenuated DKD in the WT diabetic mice, but not in the Nrf2 KO diabetic mice. In high glucose-treated mouse mesangial cells, P53 gene silencing completely abolished nutlin3a's inhibitory effect on NRF2 signaling. The present study demonstrates for the first time that MDM2 controls renal NRF2 antioxidant activity in DKD via inhibition of P53, providing MDM2 activation and P53 inhibition as novel strategies in the management of DKD.