SIRT-3 Modulation by Resveratrol Improves Mitochondrial Oxidative Phosphorylation in Diabetic Heart through Deacetylation of TFAM

Background and Purpose: Mitochondrial dysfunction remains the crucial cause for many heart diseases including diabetic cardiomyopathy (DCM). Sirtuin-3 (SIRT-3) is a protein deacetylase localized in the mitochondria and regulates mitochondrial function. Being a noteworthy mitochondrial protein deacetylase enzyme, the role of SIRT-3 in DCM is yet to be explored. Experimental Approach: Diabetes mellitus (Type-I, T1DM) was induced using streptozotocin (STZ, 50 mg/kg) in male Sprague Dawley (SD) rats. Rats with >200 mg/dL blood glucose levels were then divided randomly into two groups, DIA and DIA + RESV, where vehicle and resveratrol (25 mg/kg/day) were administered orally in both groups, respectively. Cardiac oxidative stress, fibrosis, and mitochondrial parameters were evaluated. H9c2 cells were transfected with SIRT-3 siRNA and shRNA, and ORF plasmid for silencing and overexpression, respectively. Key Results: After eight weeks, diabetic rat heart showed reduced cardiac cell size, increased oxidative stress and reduction of the activities of enzymes involved in mitochondrial oxidative phosphorylation (OXPHOS). There was reduced expression and activity of SIRT-3 and mitochondrial transcription factor (TFAM) in diabetic heart. Reduced SIRT-3 expression is also correlated with increased acetylation, decreased mitochondrial DNA (mtDNA) binding activity of TFAM, and reduced transcription of mitochondrial DNA encoded genes. Administration of resveratrol prevented the decrease in SIRT-3 and TFAM activity, which was corresponding to the reduced acetylation status of TFAM. Silencing SIRT-3 using siRNA in H9C2 cells showed increased acetylation of TFAM. Conclusion and Implications: Together our data shows that resveratrol activates SIRT-3, regulates the acetylation status of TFAM and preserves the mitochondrial function along with cellular size in diabetic rat heart

Sirt1 and Sirt3 Activation Improved Cardiac Function of Diabetic Rats via Modulation of Mitochondrial Function

In the present study, we aimed to evaluate the effect of Sirt1, Sirt3 and combined activation in high fructose diet-induced insulin resistance rat heart and assessed the cardiac function focusing on mitochondrial health and function. We administered the Sirt1 activator; SRT1720 (5 mg/kg, i.p.), Sirt3 activator; Oroxylin-A (10 mg/kg i.p.) and the combination; SRT1720 + Oroxylin-A (5 mg/kg and 10 mg/kg i.p.) daily from 12th week to 20th weeks of study. We observed significant perturbations of most of the cardiac structural and functional parameters in high fructose diet-fed animals. Administration of SRT1720 and Oroxylin-A improved perturbed cardiac structural and functional parameters by decreasing insulin resistance, oxidative stress, and improving mitochondrial function by enhancing mitochondrial biogenesis, OXPHOS expression and activity in high fructose diet-induced insulin-resistant rats. However, we could not observe the synergistic effect of SRT1720 and Oroxylin-A combination. Similar to in-vivo study, perturbed mitochondrial function and oxidative stress observed in insulin-resistant H9c2 cells were improved after activation of Sirt1 and Sirt3. We observed that Sirt1 activation enhances Sirt3 expression and mitochondrial biogenesis, and the opposite effects were observed after Sirt1 inhibition in cardiomyoblast cells. Taken together our results conclude that activation of Sirt1 alone could be a potential therapeutic target for diabetes-associated cardiovascular complications

Allylmethylsulfide, a Sulfur Compound Derived from Garlic, Attenuates Isoproterenol-Induced Cardiac Hypertrophy in Rats

Allylmethylsulfide (AMS) is a novel sulfur metabolite found in the garlic-fed serum of humans and animals. In the present study, we have observed that AMS is safe on chronic administration and has a potential antihypertrophic effect. Chronic administration of AMS for 30 days did not cause any significant differences in the body weight, electrocardiogram, food intake, serum biochemical parameters, and histopathology of vital organs. Single-dose pharmacokinetics of AMS suggests that AMS is rapidly metabolized into Allylmethylsulfoxide (AMSO) and Allylmethylsulfone (AMSO2). To evaluate the efficacy of AMS, cardiac hypertrophy was induced by subcutaneous implantation of ALZET® osmotic minipump containing isoproterenol (~5 mg/kg/day), cotreated with AMS (25 and 50 mg/kg/day) and enalapril (10 mg/kg/day) for 2 weeks. AMS and enalapril significantly reduced cardiac hypertrophy as studied by the heart weight to body weight ratio and mRNA expression of fetal genes (ANP and β-MHC). We have observed that TBARS, a parameter of lipid peroxidation, was reduced and the antioxidant enzymes (glutathione, catalase, and superoxide dismutase) were improved in the AMS and enalapril-cotreated hypertrophic hearts. The extracellular matrix (ECM) components such as matrix metalloproteinases (MMP2 and MMP9) were significantly upregulated in the diseased hearts; however, with the AMS and enalapril, it was preserved. Similarly, caspases 3, 7, and 9 were upregulated in hypertrophic hearts, and with the AMS and enalapril treatment, they were reduced. Further to corroborate this finding with in vitro data, we have checked the nuclear expression of caspase 3/7 in the H9c2 cells treated with isoproterenol and observed that AMS cotreatment reduced it significantly. Histopathological investigation of myocardium suggests AMS and enalapril treatment reduced fibrosis in hypertrophied hearts. Based on our experimental results, we conclude that AMS, an active metabolite of garlic, could reduce isoproterenol-induced cardiac hypertrophy by reducing oxidative stress, apoptosis, and stabilizing ECM components

Sirt1 and Sirt3 Activation Improved Cardiac Function of Diabetic Rats via Modulation of Mitochondrial Function

In the present study, we aimed to evaluate the effect of Sirt1, Sirt3 and combined activation in high fructose diet-induced insulin resistance rat heart and assessed the cardiac function focusing on mitochondrial health and function. We administered the Sirt1 activator; SRT1720 (5 mg/kg, i.p.), Sirt3 activator; Oroxylin-A (10 mg/kg i.p.) and the combination; SRT1720 + Oroxylin-A (5 mg/kg and 10 mg/kg i.p.) daily from 12th week to 20th weeks of study. We observed significant perturbations of most of the cardiac structural and functional parameters in high fructose diet-fed animals. Administration of SRT1720 and Oroxylin-A improved perturbed cardiac structural and functional parameters by decreasing insulin resistance, oxidative stress, and improving mitochondrial function by enhancing mitochondrial biogenesis, OXPHOS expression and activity in high fructose diet-induced insulin-resistant rats. However, we could not observe the synergistic effect of SRT1720 and Oroxylin-A combination. Similar to in-vivo study, perturbed mitochondrial function and oxidative stress observed in insulin-resistant H9c2 cells were improved after activation of Sirt1 and Sirt3. We observed that Sirt1 activation enhances Sirt3 expression and mitochondrial biogenesis, and the opposite effects were observed after Sirt1 inhibition in cardiomyoblast cells. Taken together our results conclude that activation of Sirt1 alone could be a potential therapeutic target for diabetes-associated cardiovascular complications

Design and Synthesis of Amino Acid Derivatives of Substituted Benzimidazoles and Pyrazoles as Selective Sirt1 Inhibitors

Owing to its presence in several biological processes Sirt1 served as a potential therapeutic target for many diseases. Here we report the synthesis of two distinct series of novel Sirt1 selective inhibitors, benzimidazole monopeptides and 5-pyrazolyl methylidene rhodanine carboxylic acid derived amino acids, constructed using structure-guided computational approaches. Furthermore, compounds were evaluated, against human Sirt1-3 for in-vitro inhibitory activity compared to Ex527 (reported Sirt1-selective inhibitor), in liver and breast cancer cell lines for cytotoxicity. The tryptophan conjugates 13h (IC50 = 0.66 µM) and 7d (IC50 = 0.77 µM) demonstrated maximum efficacy to inhibit Sirt1. Molecular dynamics simulations unveil the interaction map and electrostatic complementarity at substrate binding site, could be a cause of selective Sirt1 inhibition. Furthermore, the Sirt1 inhibition was monitored via increased p53 acetylation status checked in HepG2 cells. These findings will pave the pathway for developing novel selective Sirt1-inhibitors in cancer therapeutics

GCN5L1 impairs diastolic function in mice exposed to a high fat diet by restricting cardiac pyruvate oxidation

Abstract Left ventricular diastolic dysfunction is a structural and functional condition that precedes the development of heart failure with preserved ejection fraction (HFpEF). The etiology of diastolic dysfunction includes alterations in fuel substrate metabolism that negatively impact cardiac bioenergetics, and may precipitate the eventual transition to heart failure. To date, the molecular mechanisms that regulate early changes in fuel metabolism leading to diastolic dysfunction remain unclear. In this report, we use a diet‐induced obesity model in aged mice to show that inhibitory lysine acetylation of the pyruvate dehydrogenase (PDH) complex promotes energetic deficits that may contribute to the development of diastolic dysfunction in mouse hearts. Cardiomyocyte‐specific deletion of the mitochondrial lysine acetylation regulatory protein GCN5L1 prevented hyperacetylation of the PDH complex subunit PDHA1, allowing aged obese mice to continue using pyruvate as a bioenergetic substrate in the heart. Our findings suggest that changes in mitochondrial protein lysine acetylation represent a key metabolic component of diastolic dysfunction that precedes the development of heart failure