Marianne Zeller

Diabetes, oxidative stress and therapeutic strategies

BACKGROUND Diabetes has emerged as a major threat to health worldwide. SCOPE OF REVIEW The exact mechanisms underlying the disease are unknown; however, there is growing evidence that excess generation of reactive oxygen species (ROS), largely due to hyperglycemia, causes oxidative stress in a variety of tissues. Oxidative stress results from either an increase in free radical production, or a decrease in endogenous antioxidant defenses, or both. ROS and reactive nitrogen species (RNS) are products of cellular metabolism and are well recognized for their dual role as both deleterious and beneficial species. In type 2 diabetic patients, oxidative stress is closely associated with chronic inflammation. Multiple signaling pathways contribute to the adverse effects of glucotoxicity on cellular functions. There are many endogenous factors (antioxidants, vitamins, antioxidant enzymes, metal ion chelators) that can serve as endogenous modulators of the production and action of ROS. Clinical trials that investigated the effect of antioxidant vitamins on the progression of diabetic complications gave negative or inconclusive results. This lack of efficacy might also result from the fact that they were administered at a time when irreversible alterations in the redox status are already under way. Another strategy to modulate oxidative stress is to exploit the pleiotropic properties of drugs directed primarily at other targets and thus acting as indirect antioxidants. MAJOR CONCLUSIONS It appears important to develop new compounds that target key vascular ROS producing enzymes and mimic endogenous antioxidants. GENERAL SIGNIFICANCE This strategy might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated with vascular diseases.

Nitric oxide synthase inhibition and oxidative stress in cardiovascular diseases: Possible therapeutic targets?

Nitric oxide (NO) is synthetized enzymatically from l-arginine (l-Arg) by three NO synthase isoforms, iNOS, eNOS and nNOS. The synthesis of NO is selectively inhibited by guanidino-substituted analogs of l-Arg or methylarginines such as asymmetric dimethylarginine (ADMA), which results from protein degradation in cells. Many disease states, including cardiovascular diseases and diabetes, are associated with increased plasma levels of ADMA. The N-terminal catalytic domain of these NOS isoforms binds the heme prosthetic group as well as the redox cofactor, tetrahydrobiopterin (BH(4)) associated with a regulatory protein, calmodulin (CaM). The enzymatic activity of NOS depends on substrate and cofactor availability. The importance of BH(4) as a critical regulator of eNOS function suggests that BH(4) may be a rational therapeutic target in vascular disease states. BH(4) oxidation appears to be a major contributor to vascular dysfunction associated with hypertension, ischemia/reperfusion injury, diabetes and other cardiovascular diseases as it leads to the increased formation of oxygen-derived radicals due to NOS uncoupling rather than NO. Accordingly, abnormalities in vascular NO production and transport result in endothelial dysfunction leading to various cardiovascular disorders. However, some disorders including a wide range of functions in the neuronal, immune and cardiovascular system were associated with the over-production of NO. Inhibition of the enzyme should be a useful approach to treat these pathologies. Therefore, it appears that both a lack and excess of NO production in diseases can have various important pathological implications. In this context, NOS modulators (exogenous and endogenous) and their therapeutic effects are discussed.

Combining Body Mass Index With Measures of Central Obesity in the Assessment of Mortality in Subjects With Coronary Disease : Role of “Normal Weight Central Obesity”

OBJECTIVES This study sought to assess the mortality risk of patients with coronary artery disease (CAD) based ona combination of body mass index (BMI) with measures of central obesity. BACKGROUND In CAD patients, mortality has been reported to vary inversely with BMI (“obesity paradox”). In contrast,central obesity is directly associated with mortality. Because of this bidirectionality, we hypothesized that CAD patients with normal BMI but central obesity would have worse survival compared to individuals with other combinations of BMI and central adiposity. METHODS We included 15,547 participants with CAD who were part of 5 studies from 3 continents. Multivariate stratifiedCox-proportional hazard models adjusted for potential confounders were used to assess mortality risk according to different patterns of adiposity that combined BMI with measures of central obesity. RESULTS Mean age was 66 years, 60% were men. There were 5,507 deaths over a median follow-up of 2.4 years (IQR: 0.5 to 7.4 years). Individuals with normal weight central obesity had the worst long-term survival: a person with BMI of 22 kg/m2 and waist circumference (WC) of 101 cm had higher mortality than a person with similar BMI but WC of 85 cm (HR: 1.10[95% CI: 1.05 to 1.17]), than a person with BMI of 26 kg/m2 and WC of 85 cm (HR: 1.20 [95% CI: 1.09 to 1.31]), than a person with BMI of 30 kg/m2 and WC of 85 cm (HR: 1.61 [95% CI: 1.39 to 1.86]) and than a person with BMI of 30kg/m2 and WC of 101 cm (HR: 1.27 [95% CI: 1.18 to 1.39), p < 0.0001 for all). CONCLUSIONS In patients with CAD, normal weight with central obesity is associated with the highest risk of mortality [corrected].

Relation Between Body Mass Index, Waist Circumference, and Death After Acute Myocardial Infarction

Background— An elevated body mass index (BMI) has been reported to be associated with a lower rate of death after acute myocardial infarction (AMI). However, waist circumference (WC) may be a better marker of cardiovascular risk than BMI. We used data from a contemporary French population-based cohort of patients with AMI to analyze the impact of WC and BMI on death rates. Methods and Results— We evaluated 2229 consecutive patients with AMI. Patients were classified according to BMI as normal, overweight, obese, and very obese (BMI <25, 25 to 29.9, 30 to 34.5, and >35 kg/m2, respectively) and as increased waistline (WC >88/102 cm for women/men) or normal. Half of the patients were overweight (n=1044), and one quarter were obese (n=397) or very obese (n=128). Increased WC was present in half of the patients (n=1110). Increased BMI was associated with a reduced death rate, with a 5% risk reduction for each unit increase in BMI (hazard ratio, 0.95; 95% CI, 0.93 to 0.98; P<0.001). In contrast, WC as a continuous variable had no impact on all-cause death (P=0.20). After adjustment for baseline predictors of death, BMI was not independently predictive of death. The group of patients with high WC but low BMI had increased 1-year death rate. Conclusions— Neither BMI nor WC independently predicts death after AMI. Much of the inverse relationship between BMI and the rate of death after AMI is due to confounding by characteristics associated with survival. This study emphasizes the need to measure both BMI and WC because patients with a high WC and low BMI are at high risk of death.

Antioxidative properties of pyruvate and protection of the ischemic rat heart during cardioplegia.

Formation of oxygen free radicals during heart transplantation seems to be related to the alterations occurring during ischemia and reperfusion and could explain the short preservation time of donor hearts. The aim of our study was (a) to analyze the protective effects of pyruvate during cold cardioplegia and ischemia/reperfusion sequence, and (b) to investigate in vitro the radical scavenging properties of this compound. After 30 min of perfusion, isolated working rat hearts were arrested by cardioplegic solution, stored 4 h in B21 solutions at 4 degrees C, and reperfused with Krebs-Henseleit buffer for 45 min. Pyruvate (2 mM) was added to Krebs-Henseleit, cardioplegic, and storage solutions, and functional parameters were recorded throughout the experiments. In a second part, control hearts and hearts treated with pyruvate were cannulated via the aorta and perfused for 30 min by the Langendorff method, arrested by cardioplegic solution, stored 4 h in B21 solutions at 4 degrees C, and reperfused for 45 min by the Langendorff method. Malonedialdehyde and alpha-tocopherol levels were determined on heart homogenate. In situ detection of apoptotic cells also was performed on tissue samples (left ventricle) at the end of the ischemia/reperfusion sequence. To demonstrate in vitro the antioxidant effects of pyruvate, we monitored (a) its hydroxyl radical scavenging properties by using electron paramagnetic resonance (EPR) spectroscopy, and (b) the decrease of fluorescence of allophycocyanin, in the presence of a Fenton system (H2O2/Cu2+). Ischemia for 4 h, followed by myocardial reperfusion, resulted in substantially reduced mechanical function. Hearts subjected to this ischemia and pretreated with pyruvate showed a significant improvement in the function recovery. After the ischemia/reperfusion protocol, no significant decrease of malonedialdehyde levels was shown on hearts treated with pyruvate. However, alpha-tocopherol levels were higher in the pyruvate group compared with the control group. At the end of the reperfusion period, levels of apoptotic cells were significantly lower in hearts treated with pyruvate compared with control hearts. EPR studies showed that pyruvate was an efficient hydroxyl scavenger, with a median inhibitory concentration (IC50) of 8 mM. The allophycocyanin assay also showed a dose-dependent effect of pyruvate against hydroxyl radicals. In conclusion, these findings showed that pyruvate could prevent reperfusion injuries in the isolated heart, probably by its antioxidative properties. The application of pyruvate may contribute to the preservation of hearts for organ transplantation.

Impact of Type of Preadmission Sulfonylureas on Mortality and Cardiovascular Outcomes in Diabetic Patients with Acute Myocardial Infarction

BACKGROUND The impact of antidiabetic medications on clinical outcomes in patients developing acute myocardial infarction (MI) is controversial. We sought to determine whether in-hospital outcomes in patients who were on sulfonylureas (SUs) when they developed their MIs differed from that of diabetic patients not receiving SUs and whether clinical outcomes were related to the pancreatic cells specificity of SUs. METHODS AND RESULTS We analyzed the outcomes of the 1310 diabetic patients included in the nationwide French Registry of Acute ST-Elevation and Non-ST-Elevation Myocardial Infarction in 2005. Medications used before the acute episode were recorded. In-hospital complications were analyzed according to prior antidiabetic treatment. Mortality was lower in patients previously treated with SUs (3.9%) vs. those on other oral medications (6.4%), insulin (9.4%), or no medication (8.4%) (P = 0.014). Among SU-treated patients, in-hospital mortality was lower in patients receiving pancreatic cells-specific SUs (gliclazide or glimepiride) (2.7%), compared with glibenclamide (7.5%) (P = 0.019). Arrhythmias and ischemic complications were also less frequent in patients receiving gliclazide/glimepiride. The lower risk in patients receiving gliclazide/glimepiride vs. glibenclamide persisted after multivariate adjustment (odds ratio 0.15; 95% confidence interval 0.04-0.56) and in propensity score-matched cohorts. CONCLUSION In this nationwide registry of patients hospitalized for acute MI, no hazard was associated with the use of SUs before the acute episode. In addition, patients previously receiving gliclazide/glimepiride had improved in-hospital outcomes, compared with those on glibenclamide.

Direct and indirect antioxidant properties of α-lipoic acid and therapeutic potential

Diabetes has emerged as a major threat to worldwide health. The exact mechanisms underlying the disease are unknown; however, there is growing evidence that the excess generation of reactive oxygen species (ROS) associated with hyperglycemia, causes oxidative stress in a variety of tissues. In this context, various natural compounds with pleiotropic actions like α-lipoic acid (LA) are of interest, especially in metabolic diseases such as diabetes. LA, either as a dietary supplement or a therapeutic agent, modulates redox potential because of its ability to match the redox status between different subcellular compartments as well as extracellularly. Both the oxidized (disulfide) and reduced (di-thiol: dihydro-lipoic acid, DHLA) forms of LA show antioxidant properties. LA exerts antioxidant effects in biological systems through ROS quenching but also via an action on transition metal chelation. Dietary supplementation with LA has been successfully employed in a variety of in vivo models of disease associated with an imbalance of redox status: diabetes and cardiovascular diseases. The complex and intimate association between increased oxidative stress and increased inflammation in related disorders such as diabetes, makes it difficult to establish the temporal sequence of the relationship.

Antioxidant properties of an endogenous thiol: alpha-lipoic acid, useful in the prevention of cardiovascular diseases.

In the past few years, a growing interest has been given to the possible antioxidant functions of a natural acid, synthesized in human tissues: alpha-lipoic acid (ALA). Both the oxidized (disulfide) and reduced (dithiol: dihydrolipoic acid, DHLA) forms of ALA show antioxidant properties. ALA administered in the diet accumulates in tissues, and a substantial part is converted to DHLA via a lipoamide dehydrogenase. Commercial ALA is usually a racemic mixture of the R and S forms. Chemical studies have indicated that ALA scavenges hydroxyl radicals, hypochlorous acid, and singlet oxygen. ALA exerts antioxidant effects in biological systems not only through direct ROS quenching but also via transition metal chelation. ALA has been shown to possess a number of beneficial effects both in the prevention and treatment of diabetes in experimental conditions. ALA presents beneficial effects in the management of symptomatic diabetic neuropathy and has been used in this context in Germany for more than 30 years. In cardiovascular disease, dietary supplementation with ALA has been successfully employed in a variety of in vivo models: ischemia-reperfusion, heart failure, and hypertension. More mechanistic and human in vivo studies are needed to determine whether optimizing the dietary intake of ALA can help to decrease cardiovascular diseases. A more complete understanding of cellular biochemical events that influence oxidative damage is required to guide future therapeutic advances.

Carbon monoxide: mechanisms of action and potential clinical implications

Small amounts of carbon monoxide (CO) are continuously produced in mammals. The intracellular levels of CO can increase under stressful conditions following the induction of HO-1 (heme oxygnase-1), a ubiquitous enzyme responsible for the catabolism of heme. Unlike nitric oxide, which is a free radical, CO does not contain free electrons but may be involved in oxidative stress. The carbonate radical has been proposed to be a key mediator of oxidative damage resulting from peroxynitrite production, likewise, the precursor of the carbonate radical anion being bicarbonate and carbon dioxide. We report herein some of the transcription factors and protein kinases involved in the regulation of vascular HO-1 expression. Beyond its widely feared toxicity, CO has revealed a very important biological activity as a signaling molecule with marked protective actions namely against apoptosis and endothelial oxidative damage. Abnormal metabolism and function of CO contribute to the pathogenesis and development of cardiovascular diseases. Important results have been reported in which CO and CO-releasing molecules (CO-RMs) prevent intimal hyperplasia by arresting hyperproliferative vascular smooth muscle cells and increased mobilization and recruitment of bone-marrow-derived progenitor cells. Clinical studies have demonstrated beneficial properties of CO-RMs in transplantation. The anti-inflammatory properties of CO and CO-RMs have been demonstrated in a multitude of animal models of inflammation, suggesting a possible therapeutic application for inflammatory diseases. The development of a technology concerning CO-RMs that controls the delivery and action of CO under different pathological conditions represents a major step forward in the development of CO-based pharmaceuticals with therapeutic applications.

Impact of Asymmetric Dimethylarginine on Mortality After Acute Myocardial Infarction

Objective—Asymmetrical dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide (NO) synthases. From a prospective cohort of patients with acute myocardial infarction (MI), we aimed to analyze the predictive value of circulating ADMA concentrations on prognosis. Methods and Results—Blood samples from 249 consecutive patients hospitalized for acute MI <24 hours were taken on admission. Serum levels of ADMA and its stereoisomer, symmetrical dimethylarginine (SDMA), were determined using high-performance liquid chromatography. The independent predictors of ADMA were glomerular filtration rate, female sex, and SDMA (R2=0. 25). Baseline ADMA levels were higher in patients who had died than in patients who were alive at 1 year follow-up (1.23 [0.98 to 1.56] versus 0.95 [0.77 to 1.20] &mgr;mol/L, P<0.001). By Cox multivariate analysis, the higher tertile of ADMA (median [interquartile range]: 1.45 [1.24 to 1.70] &mgr;mol/L) was a predictor for mortality (Hazard Ratio [95% CI], 4.83 [1.59 to 14.71]), when compared to lower tertiles, even when adjusted for potential confounders, such as acute therapy, biological, and clinical factors. Conclusion—Our study suggests that the baseline ADMA level has a strong prognostic value for mortality after MI, beyond traditional risk factors and biomarkers.