Current Pharmaceutical Design - Volume 20, Issue 22, 2014

The regulation of endothelial NO synthase (eNOS) employs multiple different cellular control mechanisms impinging on level and activity of the enzyme. This review aims at summarizing the current knowledge on the posttranslational modifications of eNOS, including acylation, nitrosylation, phosphorylation, acetylation, glycosylation and glutathionylation. Sites, mediators and impact on enzyme localization and activity of the single modifications will be discussed. Moreover, interdependence, cooperativity and competition between the different posttranslational modifications will be elaborated with special emphasis on the susceptibility of eNOS to metabolic cues.

Endothelial nitric oxide synthase (eNOS) is expressed in vascular endothelial cells and plays an important role in the regulation of vascular tone, platelet aggregation and angiogenesis. Protein-protein interactions represent an important posttranslational mechanism for eNOS regulation. eNOS has been shown to interact with a variety of regulatory and structural proteins which provide fine tuneup of eNOS activity and eNOS protein trafficking between plasma membrane and intracellular membranes in a number of physiological and pathophysiological processes. eNOS interacts with calmodulin, heat shock protein 90 (Hsp90), dynamin-2, β-actin, tubulin, porin, high-density lipoprotein (HDL) and apolipoprotein AI (ApoAI), resulting in increases in eNOS activity. The negative eNOS interacting proteins include caveolin, G protein-coupled receptors (GPCR), nitric oxide synthase-interacting protein (NOSIP), and nitric oxide synthase trafficking inducer (NOSTRIN). Dynamin-2, NOSIP, NOSTRIN, and cytoskeleton are also involved in eNOS trafficking in endothelial cells. In addition, eNOS associations with cationic amino acid transporter-1 (CAT-1), argininosuccinate synthase (ASS), argininosuccinate lyase (ASL), and soluble guanylate cyclase (sGC) facilitate directed delivery of substrate (L-arginine) to eNOS and optimizing NO production and NO action on its target. Regulation of eNOS by protein-protein interactions would provide potential targets for pharmacological interventions in NO-compromised cardiovascular diseases.

Numerous epidemiological studies indicate that consumption of polyphenol-rich food and beverages is associated with a protective effect on the cardiovascular system. The beneficial effect has been attributable to several mechanisms including the improvement of the vascular function. Indeed, polyphenols have been shown to be potent stimulators of endothelial vasoprotective mechanisms including the formation of nitric oxide (NO) and the induction of endothelium-derived hyperpolarization (EDH). The aim of this review is to provide a non-exhaustive analysis of the literature regarding polyphenols-rich sources capable of activating endothelial NO synthase and the characterization of the underlying mechanism as well as the beneficial effects of polyphenols on the endothelial function in both experimental models of cardiovascular diseases and in Humans.

The methylarginines asymmetric dimethylarginine (ADMA) and monomethylarginine (L-NMMA) are endogenously formed inhibitors of nitric oxide synthases (NOS), which have extensively been investigated as risk markers and used as pharmacological tools to study the L-arginine-nitric oxide (NO) pathway in vitro and in vivo. It is the aim of the present review to summarize the clinical and experimental data on the pharmacological properties that are of relevance when planning and conducting experiments and clinical studies involving methylarginines. Key pharmacodynamic and pharmacokinetic data including IC50 values of ADMA and L-NMMA for NOS isoforms and transport proteins, as well as metabolism by dimethylarginine dimethylaminohydrolases (DDAH1 and DDAH2) and alanine-glyoxylate aminotransferase 2 (AGXT2) are discussed.

Nitric oxide (NO) is a gaseous signaling molecule and effector in various biological processes. In mammalian cells, NO is produced by a family of NO synthases (NOS). Three NOS isoforms have been identified as: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). In addition to NO, NOS also produces superoxide anion. This phenomenon is named NOS uncoupling as superoxide generation mainly occurs when NOS is not coupled with its cofactor or substrate. nNOS was first found to produce superoxide under L-arginine depletion condition. Further studies demonstrated that superoxide production is a general feature of all three NOS isoforms. In particular, superoxide generated from uncoupled eNOS has been found to play critical roles in the process of various cardiovascular diseases. Although NOS was first found to produce superoxide only when uncoupled with its cofactor or substrate, recent studies reveal that oxygen reduction to superoxide is an intrinsic process amid NO synthesis. Tetrahydrobiopterin plays a controlling role in preventing superoxide release from the eNOS oxygenase domain. Besides tetrahydrobiopterin, the regulation of eNOS uncoupling by the interactions with other proteins, protein phosphorylation, S-glutathionylation, and endogenous L-arginine derivatives, will be discussed in this review.

Tetrahydrobiopterin (BH4) is an essential cofactor of nitric oxide synthase (NOS). In the cardiovascular system, endothelial NOS (eNOS) has a major role in maintaining vascular tone and endothelial function, as well as in mediating many other vascular protective properties. Evidence from humans and animals have demonstrated that decreased BH4 bioavailability, with subsequent uncoupling of eNOS, has significant effects on the pathogenesis of endothelial dysfunction, which is a hallmark of vascular injury in cardiovascular disorders, including hypertension, hyperlipidemia, and diabetes. In this review, we discuss the synthesis of BH4, its molecular mechanisms regulating eNOS coupling, the pathophysiologic roles of decreased BH4 bioavailability in cardiovascular diseases, and the potential therapeutic application of BH4 in clinics.

Cardiovascular disease remains the number one killer in the United States and many other countries. Each year, there are enormous research efforts on its pathogenesis, prevention and treatment led by scientists worldwide. One of the most significant research areas is the impact and mechanisms of existing or new cardiovascular risk factors on the vascular system. The current review provides the most updated research advances in the area of the regulation of the endothelial nitric oxide synthase-nitric oxide (eNOS-NO) system by several cardiovascular risk factors. There are many exciting discoveries made from the studies of several major cardiovascular risk factors such as hypertension, cigarette smoking, dyslipidemia and diabetes mellitus as well as emerging risk factors such as HIV infection, antiretroviral therapy, genomic variability, and cytokines. In general, cardiovascular risk factors could impair the eNOS-NO system with a variety of molecular mechanisms including decrease in NO bioavailability by excess reactive oxygen species, inhibition of eNOS expression and activity, and deficiency of eNOS cofactors. Special attention is paid to the impact of several new or emerging risk factors on cardiovascular disease and the eNOS-NO system. These mechanistic studies are clinically significant because they may lead towards new and effective strategies for the prevention and treatment of cardiovascular disease.

Many cardiovascular diseases and drug-induced complications are associated with - or even based on - an imbalance between the formation of reactive oxygen and nitrogen species (RONS) and antioxidant enzymes catalyzing the break-down of these harmful oxidants. According to the “kindling radical” hypothesis, the formation of RONS may trigger in certain conditions the activation of additional sources of RONS. According to recent reports, vascular dysfunction in general and cardiovascular complications such as hypertension, atherosclerosis and coronary artery diseases may be connected to inflammatory processes. The present review is focusing on the uncoupling of endothelial nitric oxide synthase (eNOS) by different mechanisms involving so-called “redox switches”. The oxidative depletion of tetrahydrobiopterin (BH4), oxidative disruption of the dimeric eNOS complex, S-glutathionylation and adverse phosphorylation as well as RONS-triggered increases in levels of asymmetric dimethylarginine (ADMA) will be discussed. But also new concepts of eNOS uncoupling and state of the art detection of this process will be described. Another part of this review article will address pharmaceutical interventions preventing or reversing eNOS uncoupling and thereby normalize vascular function in a given disease setting. We finally turn our attention to the inflammatory mechanisms that are also involved in the development of endothelial dysfunction and cardiovascular disease. Inflammatory cell and cytokine profiles as well as their interactions, which are among the kindling mechanisms for the development of vascular dysfunction will be discussed on the basis of the current literature.

Under physiological conditions, nitric oxide (NO) is produced in the vasculature mainly by the endothelial NO synthase (eNOS). This endothelium-derived NO is a protective molecule with antihypertensive, antithrombotic and anti-atherosclerotic properties. Cardiovascular risk factors such as hypertension, hypercholesterolemia, cigarette smoking and diabetes mellitus induce oxidative stress mostly by stimulation of the NADPH oxidase. Overproduction of reactive oxygen species leads to oxidation of tetrahydrobiopterin (BH4), the essential cofactor of eNOS. In BH4 deficiency, oxygen reduction uncouples from NO synthesis, thereby converting eNOS to a superoxide- producing enzyme. Consequently, NO production is reduced and the pre-existing oxidative stress is enhanced, which contribute significantly to cardiovascular pathology. Therefore, pharmacological approaches that prevent eNOS uncoupling are of therapeutic interest. Among the drugs currently in clinical use, the renin inhibitor aliskiren, angiotensin-converting enzyme inhibitors, AT1 receptor blockers, the selective aldosterone antagonist eplerenone, statins, nebivolol and pentaerithrityl tetranitrate have been shown to have the potential to prevent or reverse eNOS uncoupling under experimental conditions. Resveratrol, BH4, sepiapterin, folic acid and AVE3085 have also been shown to recouple eNOS and improve endothelial function. The long-term benefit of these compounds, however, is still controversial.

Response to anti-diabetic medications is not always predictable or favourable even in phenotypically similar type-2 diabetes (T2D) cases. This is not only due to patient’s compliance and access to care but is also considered to be an effect of idiosyncratic differences among individuals, stemming from the combination of their unique genetic background and environmental exposures. In this systematic review, we aimed to summarise the available evidence on pharmacogenetic and pharmacogenomic studies of oral agents for T2D that are currently in the market and describe the agents studied, the targeted loci in regards to the efficacy and the toxicity profile of the agents included. We included 53 studies published between 2003-2012, which examined the following anti-diabetic classes: sulphonylureas, metformin, metiglinides and thiazolidenediones. There were no published studies on newer agents (e.g. incretin based treatments). Forty-nine studies (92.5%) examined the therapeutic response to oral antiglycaemic agents. Outcomes assessed included changes in metabolic markers (fasting or postprandial blood glucose, fasting or postprandial insulin, HbA1c), Homeostasis Assessment Model (HOMA)-Insulin Resistance (IR) or HOMA-B-cell function (HOMA-B), and time to monotherapy failure. Regarding side effects, hypoglycaemia and TZD-related oedema were the most commonly assessed. In the vast majority of the studies included (n=38, 71.7%), more than one outcomes (n=27, 50.9%) and/or more than one SNPs (n=21, 39.6%) were evaluated in the same publication, but most studies examined one drug (n=50, 94.3%). A considerable number of the proposed genes seem to be related to beta-cell development and function, but there are several genes whose underlying pathway linked to diabetes pharmacotherapy remains poorly understood. Pharmacogenomics are still not in pace with the wealth of information provided by GWAS in the genetics of T2D and related traits and the proposed associations need further validation in well-characterized large studies of varying ancestral origins.

It is currently estimated that over 370 million individuals have diabetes, making diabetes a major public health issue contributing significantly to global morbidity and mortality. The steep rise in diabetes prevalence over the past decades is attributable, in a large part, to lifestyle changes, with dietary habits and behaviour as significant contributors. Despite the relatively wide availability of antidiabetic medicine, it is lifestyle approaches that still remain the cornerstone of diabetes prevention and treatment. Glycemic index (GI) is a nutritional tool which represents the glycemic response to carbohydrate ingestion. In light of the major impact of nutrition on diabetes pathophysiology, with the rising need to combat the escalating diabetes epidemic, this review will focus on the role of GI in glycemic control, the primary target of diabetic treatment and beyond. The review will present the evidence relating GI and diabetes treatment and prevention, as well as weight loss, weight maintenance and cardiovascular disease risk factors.

The recent increase in the prevalence of obesity seems to be responsible for the increase in T2 Diabetes Mellitus (T2DM). At present around 50 % of T2DM patients are obese and this percentage appears set to increase in the near future. Successful management of T2DM in obese patients is a complicated task, as many parameters such as blood pressure, LDL-cholesterol levels have to be adequately controlled along with HbA1c levels. There is a substantial amount of evidence showing that bariatric surgery achieves long term remission of diabetes in the majority of obese patients and improves significantly comorbidities associated with DM such as dyslipidemia, hypertension, and obstructive sleep apnea. It seems that early surgical intervention before irreversible b-cell damage has occurred, increases the chances of long term T2DM resolution. However, at present a very small percentage (< 2%) of obese patients with T2DM is treated surgically. The present review focuses on the efficacy and safety of the main bariatric procedures. It also emphasizes the mechanism with which bariatric surgery exerts its therapeutic effect and on the long term results on T2DM remission.

Sodium-glucose co-transporters (SGLT2) are mainly expressed in the kidneys and are responsible for the renal handling of glucose load. SGLT2 inhibitors represent the latest oral agents for diabetes treatment. Their unique mechanism of action, which practically spares the insulin secretion or insulin utilization, differentiates the SGLT2 inhibitors from any existing antidiabetic agent. Thus, it is hypothesized that SGLT2 inhibitors can be effectively (and probably safely) combined with any existing antidiabetic agent (including insulin), either as monotherapy, or in dual or triple combinations. All these hypotheses are currently tested in many clinical trials. Currently dapagliflozin, one of the three most advanced SGLT2 inhibitors in the development (along with canagliflozin and empagliflozin), is already in the market in few European countries and canagliflozin has been approved from the Food and Drug Administration (FDA) in US. The evidence so far shows that SGLT2 inhibitors are equally effective to established antidiabetic agents such as metformin or sulfonylureas in their ability to lower HbA1c. On the other hand, SGLT2 inhibitors increase the possibility of genitourinary infections in type 2 diabetic individuals. Their potency in different populations and with different background therapy, but more importantly their short and long term safety remains to be seen.

Statins are highly efficacious lipid modifying agents that reduce the risk for cardiovascular (CV) events in both primary and secondary prevention settings. However, statins affect molecular mechanisms which adversely impact on insulin sensitivity and β-cell function, thereby increasing risk for new onset diabetes mellitus (NOD). Defining the mechanisms involved is the focus of considerable current investigation. The statins reduce the risk for CV events in normoglycemic patients as well as in those with diabetes mellitus (DM) and their benefits outweigh the risk of inducing NOD. We review the clinical evidence for NOD with statin treatment, as well as the potential mechanisms involved. Our literature search was based on PubMed and Scopus listings. Further large studies are needed to elucidate both the association between NOD and statin use and the underlying mechanisms.

The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide. T2DM is associated with both microvascular (neuropathy, nephropathy and retinopathy) and macrovascular complications [coronary artery disease (CAD), stroke, carotid artery disease and peripheral artery disease (PAD)]. Apart from acting on diabetic dyslipidemia, statins were shown to exert beneficial effects on several diabetic complications as well as other cardiovascular (CVD) risk predictors such as endothelial dysfunction, inflammation, oxidative stress, chronic kidney disease (CKD), non-alcoholic fatty liver disease (NAFLD), metabolic syndrome (MetS), obstructive sleep apnea syndrome (OSAS) and hyperuricemia. Several clinical trials involving T2DM patients have reported significant reductions in coronary and cerebrovascular events following statin treatment. However, a modest statin-related risk of new-onset diabetes (NOD) has been reported but that did outweigh the benefit of CVD risk reduction in high-risk individuals. Overall, statin use is beneficial and should be recommended in diabetic patients to target their increased CVD risk.

Diabetics are regarded a special category of patients known to experience higher rates of cardiovascular complications as compared to the non-diabetic ones. Despite substantial efforts to minimize these risks, with aggressive antiplatelet and lipid lowering therapy, some of the diabetic patients still have a considerable residual risk for cardiovascular adverse events. Important preclinical data with potent lipid-lowering agents, like fibrates, omega-3-fatty acids, and niacin, have shown that they can provide sufficient help in reducing rates of cardiovascular events. In the present review, we are aim to explain their basic mechanisms of action, to present all the available clinical data regarding the efficacy of those agents, and to identify specific diabetic patients’ subsets, in whom supplementary therapy with those agents could provide substantial benefit in terms of clinical outcome and not only lipid profile improvement.

Diabetic neuropathy is a common complication of diabetes mellitus affecting 30-50% of patients and is a major cause for increased costs, morbidity and mortality. Strict diabetes control prevents this complication and may restore neurologic deficits in the early stages. Several efforts have been undertaken to alter the natural history of this complication, including the use of aldose reductase and protein kinase-C inhibitors, as well as antioxidants. Available data so far do not support the use of aldose reductase inhibitors due to safety issues and efficacy. Protein kinase-C inhibitors have provided encouraging initial results but their development has been halted. Antioxidants, like a-lipoic acid, improve some neurological deficits and painful symptoms. There are effective and safe medications such as anticonvulsants, antidepressants and opioids for the management of patients with painful symptoms. In this revew we present standard and emerging treatment modalities for the etiologic and symptomatic treatment of diabetic neuropathy.

The aim of this review is to examine the evidence on the role of antidiabetic agents in patients with type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD). In particular, metformin does not seem to have significant effects on liver histology. Glitazones improve steatosis and necro-inflammation, delay progression of fibrosis, and ameliorate glucose and lipid metabolism and subclinical inflammation. However, there is now evidence that prolonged treatment with these agents may offer no additional histological benefit and that metabolic improvement does not necessarily parallel histological improvement. Moreover, the long-term safety and efficacy of glitazones is an issue of continuing concern. Injectable glucagon-like peptide 1 (GLP-1) agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors are more recent antidiabetic agents with some promising preliminary resulst in NFLD. However, experience with their use is still very limited. In conclusion, no antidiabetic agent has hitherto been shown to exert a beneficial effect on hepatic fibrosis. However, pharmacological treatment could be considered in patients with non-alcoholic steatohepatitis (NASH) not responding to lifestyle intervention. Finally, larger long-term studies are needed to shed more light on the effect of antidiabetic treatment on NAFLD.