Sirtuins and beta-cell function

The Antioxidant Activities of Betula etnensis Rafin. Ethanolic Extract Exert Protective and Anti-diabetic Effects on Streptozotocin-Induced Diabetes in Rats

Pathophysiological mechanisms correlating diabetes mellitus with associated complications are still not completely clear, even though oxidative stress seems to play a pivotal role. Literature data suggest that cell damages induced by hyperglycemia, although multifactorial, have a common pathway in oxidative/nitrosative stress. The present study evaluated the effects of Betula etnensis Raf. bark extract, a plant belonging to the Betulaceae family endemic to Sicily, on oxidative stress and in preventing and/or retarding diabetes-associated complications in streptozotocin diabetic rats treated with the extract at dose of 0.5 g/kg body weight per day for 28 consecutive days. The extract administration significant decreased food and water intake, fasting blood glucose, weight loss and polyuria, compared with untreated diabetic animals. Furthermore, oxidative stress markers particularly, lipid hydroperoxides (LOOH) and nitrite/nitrate levels, non-proteic thiol groups (RSH), γ-glutamyl-cysteine-synthetase (γ-GCS) activities and expression, heme oxygenase-1 (HO-1), endothelial and inducible nitric oxide synthases (i-NOS e-NOS) expression, significantly changed by streptozocin treatment, were markedly restored both in plasma and tissues together with nuclear sirtuins activity (Sirt1). Results suggested that B. etnensis bark alcoholic extract is able to counteract oxidative stress and to ameliorate some general parameters related to diabetes.

The metabolic sensor Sirt1 and the hypothalamus: Interplay between peptide hormones and pro-hormone convertases

The last decade had witnessed a tremendous progress in our understanding of the causes of metabolic diseases including obesity. Among the contributing factors regulating energy balance are nutrient sensors such as sirtuins. Sirtuin1 (Sirt1), a NAD + - dependent deacetylase is affected by diet, environmental stress, and also plays a critical role in metabolic health by deacetylating proteins in many tissues, including liver, muscle, adipose tissue, heart, endothelium, and in the complexity of the hypothalamus. Because of its dependence on NAD+, Sirt1 also functions as a nutrient/redox sensor, and new novel data show a function of this enzyme in the maturation of hypothalamic peptide hormones controlling energy balance either through regulation of specific nuclear transcription factors or by regulating specific pro-hormone convertases (PCs) involved in the post-translational processing of pro-hormones. The post-translational processing mechanism of pro-hormones is critical in the pathogenesis of obesity as recently shown that metabolic and physiological triggers affect the biosynthesis and processing of many peptides hormones. Specific regulation of pro-hormone processing is likely another key step where final amounts of bioactive peptides can be tightly regulated. Different factors stimulate or inhibit pro-hormones biosynthesis in concert with an increase in the PCs involved in the maturation of bioactive hormones. Adding more complexity to the system, the new studies describe here suggest that Sirt1 could also regulate the fate of peptide hormone biosynthesis. The present review summarizes the recent progress in hypothalamic SIRT1 research with a particular emphasis on the tissue-specific control of neuropeptide hormone maturation. The series of studies done in mouse and rat models strongly advocate for the first time that a deacetylating enzyme could be a regulator in the maturation of peptide hormones and their processing enzymes. These discoveries are the culmination of the first in-depth understanding of the metabolic role of Sirt1 in the brain. It suggests that Sirt1 behaves differently in the brain than in organs such as the liver and pancreas, where the enzyme has been more commonly studied.

In Search of New Therapeutic Targets in Obesity Treatment: Sirtuins

Most of the available non-invasive medical therapies for obesity are non-efficient in a long-term evaluation; therefore there is a constant need for new methods of treatment. Research on calorie restriction has led to the discovery of sirtuins (silent information regulators, SIRTs), enzymes regulating different cellular pathways that may constitute potential targets in the treatment of obesity. This review paper presents the role of SIRTs in the regulation of glucose and lipid metabolism as well as in the differentiation of adipocytes. How disturbances of SIRTs’ expression and activity may lead to the development of obesity and related complications is discussed. A special emphasis is placed on polymorphisms in genes encoding SIRTs and their possible association with susceptibility to obesity and metabolic complications, as well as on data regarding altered expression of SIRTs in human obesity. Finally, the therapeutic potential of SIRTs-targeted strategies in the treatment of obesity and related disorders is discussed.

Antidiabetic Effects of Resveratrol: The Way Forward in Its Clinical Utility

Despite recent advances in the understanding and management of diabetes mellitus, the prevalence of the disease is increasing unabatedly with resulting disabling and life-reducing consequences to the global human population. The limitations and side effects associated with current antidiabetic therapies have necessitated the search for novel therapeutic agents. Due to the multipathogenicity of diabetes mellitus, plant-derived compounds with proven multiple pharmacological actions have been postulated to "hold the key" in the search for an affordable, efficacious, and safer therapeutic agent in the treatment of the disease and associated complications. Resveratrol, a phytoalexin present in few plant species, has demonstrated beneficial antidiabetic effects in animals and humans through diverse mechanisms and multiple molecular targets. However, despite the enthusiasm and widespread successes achieved with the use of resveratrol in animal models of diabetes mellitus, there are extremely limited clinical data to confirm the antidiabetic qualities of resveratrol. This review presents an update on the mechanisms of action and protection of resveratrol in diabetes mellitus, highlights challenges in its clinical utility, and suggests the way forward in translating the promising preclinical data to a possible antidiabetic drug in the near future.

Sirtuins as novel players in the pathogenesis of diabetes mellitus

Diabetes mellitus (DM) is a systemic and complex disease with micro and macrovascular complications that result from impaired metabolic pathways and genetic susceptibilities. DM has been accepted as an epidemic worldwide during the last two decades. A substantial gap in our knowledge exists regarding the pathophysiology of this metabolic disorder despite the improved diagnostic tools and therapeutic approaches. Sirtuins are a group of NAD⁺ dependent enzymes that are involved in cellular homeostasis due to their deacetylating activity. In the present review, we aimed to discuss the role of associated sirtuins in the pathogenesis and treatment of diabetes mellitus.

Novel mitochondrial targets for neuroprotection

Mitochondrial dysfunction contributes to the pathophysiology of acute neurologic disorders and neurodegenerative diseases. Bioenergetic failure is the primary cause of acute neuronal necrosis, and involves excitotoxicity-associated mitochondrial Ca(2+) overload, resulting in opening of the inner membrane permeability transition pore and inhibition of oxidative phosphorylation. Mitochondrial energy metabolism is also very sensitive to inhibition by reactive O(2) and nitrogen species, which modify many mitochondrial proteins, lipids, and DNA/RNA, thus impairing energy transduction and exacerbating free radical production. Oxidative stress and Ca(2+)-activated calpain protease activities also promote apoptosis and other forms of programmed cell death, primarily through modification of proteins and lipids present at the outer membrane, causing release of proapoptotic mitochondrial proteins, which initiate caspase-dependent and caspase-independent forms of cell death. This review focuses on three classifications of mitochondrial targets for neuroprotection. The first is mitochondrial quality control, maintained by the dynamic processes of mitochondrial fission and fusion and autophagy of abnormal mitochondria. The second includes targets amenable to ischemic preconditioning, e.g., electron transport chain components, ion channels, uncoupling proteins, and mitochondrial biogenesis. The third includes mitochondrial proteins and other molecules that defend against oxidative stress. Each class of targets exhibits excellent potential for translation to clinical neuroprotection.

Transient neonatal diabetes mellitus gene Zac1 impairs insulin secretion in mice through Rasgrf1

The biallelic expression of the imprinted gene ZAC1/PLAGL1 underlies ≈ 60% of all cases of transient neonatal diabetes mellitus (TNDM) that present with low perinatal insulin secretion. Molecular targets of ZAC1 misexpression in pancreatic β cells are unknown. Here, we identified the guanine nucleotide exchange factor Rasgrf1 as a direct Zac1/Plagl1 target gene in murine β cells. Doubling Zac1 expression reduced Rasgrf1 expression, the stimulus-induced activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways, and, ultimately, insulin secretion. Normalizing Rasgrf1 expression reversed this phenotype. Moreover, the transplantation of Zac1-overexpressing β cells failed to reinstate euglycemia in experimental diabetic mice. In contrast, Zac1 expression did not interfere with the signaling of the glucagon-like peptide 1 receptor (GLP-1R), and the GLP-1 analog liraglutide improved hyperglycemia in transplanted experimental diabetic mice. This study unravels a mechanism contributing to insufficient perinatal insulin secretion in TNDM and raises new prospects for therapy.

Lysine acetylation in obesity, diabetes and metabolic disease

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) mediate acetylation and deacetylation of histone proteins and transcription factors. There is abundant evidence that these enzymes regulate the acetylation state of many cytoplasmic proteins, including lysine residues in important metabolic enzymes. Lysine acetylation regulates major cellular functions as a common post-transcriptional modification of proteins, conserved from prokaryotes to humans. In this article, we refer to HATs and HDACs broadly as lysine acetyltransferases (KATs) and deacetylases (KDACs). Lysine acetylation is vitally important in both immunological and metabolic pathways and may regulate the balance between energy storage and expenditure. Obesity, type II diabetes and cardiovascular disease (metabolic syndrome) are widely recognised as features of a chronic low-grade inflammatory state, involving significant alterations in primary immunometabolism. Identifying effective therapeutic and preventive options to treat this multi-factorial syndrome has proven to be very challenging, with an emerging focus on developing anti-inflammatory agents that can combat adiposity and metabolic disease. Here, we summarise current evidence and understanding of innate immune and metabolic pathways relevant to adiposity and metabolic disease regulated by lysine acetylation. Developing this understanding in greater detail may facilitate strategic development of novel and enzyme-specific lysine deacetylase modulators that regulate both metabolic and immune systems.

Resveratrol modifies risk factors for coronary artery disease in swine with metabolic syndrome and myocardial ischemia

Resveratrol has been purported to modify risk factors for obesity and cardiovascular disease. We sought to examine the effects of resveratrol in a porcine model of metabolic syndrome and chronic myocardial ischemia. Yorkshire swine were fed either a normal diet (control), a high cholesterol diet (HCD), or a high cholesterol diet with supplemental resveratrol (HCD-R; 100mg/kg/day) for 11 weeks. After 4 weeks of diet modification a baseline cardiovascular MRI was performed and an ameroid constrictor was placed on the left circumflex coronary artery of each animal to induce chronic myocardial ischemia. At 7 weeks, a second cardiovascular MRI was performed and swine were sacrificed and myocardial tissue harvested. Resveratrol supplementation resulted in lower body mass indices, serum cholesterol, and C-reactive protein levels, improved glucose tolerance and endothelial function, and favorably augmented signaling pathways associated with myocardial metabolism. Interestingly, serum tumor necrosis factor-α levels were not influenced by resveratrol treatment. Immunoblotting for markers of metabolism demonstrated that insulin receptor substrate-1, glucose transporters 1 and 4, and phospho-AMPK were increased in the HCD-R group. Peroxisome proliferator-activated receptor γ and retinol binding protein 4 were downregulated in the HCD-R group as compared to the HCD group. Myocardial perfusion and function at rest as assessed with magnetic resonance imaging were not different between groups. By favorably influencing risk factors, resveratrol may decrease the burden of chronic metabolic disease and improve cardiovascular health.

Biological and chemical approaches to diseases of proteostasis deficiency

Many diseases appear to be caused by the misregulation of protein maintenance. Such diseases of protein homeostasis, or "proteostasis," include loss-of-function diseases (cystic fibrosis) and gain-of-toxic-function diseases (Alzheimer's, Parkinson's, and Huntington's disease). Proteostasis is maintained by the proteostasis network, which comprises pathways that control protein synthesis, folding, trafficking, aggregation, disaggregation, and degradation. The decreased ability of the proteostasis network to cope with inherited misfolding-prone proteins, aging, and/or metabolic/environmental stress appears to trigger or exacerbate proteostasis diseases. Herein, we review recent evidence supporting the principle that proteostasis is influenced both by an adjustable proteostasis network capacity and protein folding energetics, which together determine the balance between folding efficiency, misfolding, protein degradation, and aggregation. We review how small molecules can enhance proteostasis by binding to and stabilizing specific proteins (pharmacologic chaperones) or by increasing the proteostasis network capacity (proteostasis regulators). We propose that such therapeutic strategies, including combination therapies, represent a new approach for treating a range of diverse human maladies.