Glycoxidative Stress and Cardiovascular Complications in Experimentally-Induced Diabetes: Effects of Antioxidant Treatment

Diabetes mellitus (DM) is a common metabolic disease, representing a serious risk factor for the development of cardiovascular complications, such as coronary heart disease, peripheral arterial disease and hypertension. Oxidative stress (OS), a feature of DM, is defined as an increase in the steady-state levels of reactive oxygen species (ROS) and may occur as a result of increased free radical generation and/or decreased anti-oxidant defense mechanisms. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage in DM, either through repeated acute changes in cellular glucose metabolism, or through long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs are formed by the Maillard process, a non-enzymatic reaction between ketone group of the glucose molecule or aldehydes and the amino groups of proteins that contributes to the aging of proteins and to the pathological complications of DM. In the presence of uncontrolled hyperglycemia, the increased formation of AGEs and lipid peroxidation products exacerbate intracellular OS and results in a loss of molecular integrity, disruption in cellular signaling and homeostasis, followed by inflammation and tissue injury such as endothelium dysfunction, arterial stiffening and microvascular complications. In addition to increased AGE production, there is also evidence of multiple pathways elevating ROS generation in DM, including; enhanced glucose auto-oxidation, increased mitochondrial superoxide production, protein kinase C-dependent activation of NADPH oxidase, uncoupled endothelial nitric oxide synthase (eNOS) activity, increased substrate flux through the polyol pathway and stimulation of eicosanoid metabolism. It is, therefore, not surprising that the correction of these variables can result in amelioration of diabetic cardiovascular abnormalities. A linking element between these phenomena is cellular redox imbalance due to glycoxidative stress (GOS). Thus, recent interest has focused on strategies to prevent, reverse or retard GOS in order to modify the natural history of diabetic cardiovascular abnormalities. This review will discuss the links between GOS and diabetes-induced cardiovascular disorders and the effect of antioxidant therapy on altering the development of cardiovascular complications in diabetic animal models

Hydrogen Peroxide-Induced Inhibition of Vasomotor Activity: Evaluation of Single and Combined Treatments With Vitamin A and Insulin in Streptozotocin-Diabetic Rats

A positive correlation has been established between increased oxidative stress and cardiovascular diseases in diabetes mellitus. We evaluated the effects of single or combined treatments with vitamin A (retinol acetate, 30 mg/kg/day, for 12-weeks) and insulin (8-10 IU/rat/day for the final 6-week) on vasomotor activity, oxidative stress and retinol metabolism in 12-week streptozotocin diabetic rats. The vasomotor activity was determined by measuring in vitro responsiveness of aorta rings to phenylephrine (PE) and acetylcholine (ACh) in the absence or in the presence of hydrogen peroxide (H2O2). Preincubation with H2O2 (10 μM) produced a significant decrease in PE (1 mM)-induced contraction in untreated-diabetic but not in control rats. Single treatment with insulin counteracted this effect of H2O2 and also reversed the increased contractile response of diabetic aorta to PE, while vitamin A was found to be ineffective. H2O2 (10 μM) also inhibited ACh (1 mM)-stimulated endothelium- dependent relaxation two fold more in diabetic than in control aorta. In the prevention of H2O2-induced inhibition of vascular relaxation to ACh, vitamin A alone was markedly effective while insulin alone was not. The combination of vitamin A plus insulin removed the inhibitory action of H2O2 in diabetic aorta. Diabetic animals displayed an increased level of aorta thiobarbituric acid reactive substance (TBARS) in association with decreased levels of plasma retinol and retinol-binding protein (RBP). Single treatment with insulin, in spite of allowing recovery of normal growth rate and improved glucose and retinol metabolism in diabetic rats, was unable to control TBARS production to the same extent as vitamin A alone. Our findings suggest that the maintenance of ACh-stimulated endothelium-dependent vasorelaxant tone in normal physiological levels depends largely on the prevention and/or inhibition of peroxidative stress, which is achieved by combined treatment with vitamin A plus insulin. The use of vitamin A together with insulin provides a better metabolic control and more benefits than use of insulin alone in the reduction of diabetes-induced vascular complications

Effects of peroxynitrite on the reactivity of diabetic rat aorta. Pharmacology 63: 58–64

Abstract Endogenous nitric oxide (NO) reacts with superoxide to form peroxynitrite, which is capable of either oxidizing or nitrating various biological substrates. We compared the vasodilatory effect of exogenous peroxynitrite with the effects of decomposed peroxynitrite or sodium nitrite in precontracted aorta isolated from streptozotocin-induced diabetic and age-matched control rats. Peroxynitrite (10 nmol/l to 300 Ìmol/l) produced a concentrationdependent relaxation in aortic rings with or without endothelium. Relaxation was also observed with a higher concentration of its decomposition product or sodium nitrite, although these relaxations were considerably slower and with reduced sensitivity. Endothelium-containing rings were less sensitive to the vasorelaxant effect of peroxynitrite than the endothelium-denuded rings in control (pD 2 was 5.19 B 0.06 in rings with endothelium and 5.86 B 0.03 in rings without endothelium, p ! 0.01) but not in diabetic aorta (pD 2 was 5.97 B 0.05 in rings with endothelium and 6.12 B 0.06 in rings without endothelium, p 1 0.05). The maximum relaxation to peroxynitrite also increased in diabetics, but did not change by removal of the endothelium either in diabetic or control rings. Diabetes did not alter the relaxations elicited by both decomposed peroxynitrite and sodium nitrite. Peroxynitrite-induced relaxation was not inhibited by diethylenetriaminepentaacetic acid, an inhibitor of hydroxyl radical formation. Pretreatment with peroxynitrite (1 Ìmol/l, 15 min) significantly suppressed the phenylephrine-induced tone and acetylcholine-stimulated endothelium-dependent relaxation, both effects were more pronounced in diabetic than in control aorta. The increased responsiveness of diabetic vessels to exogenous peroxynitrite seems to be related to depressed basal NO bioavailability and may be considered as a compensatory way against activated contractile mechanisms of diabetic vascular smooth muscle

A pyridoindole antioxidant SMe1EC2 regulates contractility, relaxation ability, cation channel activity, and protein-carbonyl modifications in the aorta of young and old rats with or without diabetes mellitus

WOS: 000444557200004PubMed ID: 30054861We studied the effects of treatment with SMe1EC, a hexahydropyridoindole antioxidant, on vascular reactivity, endothelial function, and oxidonitrosative stress level of thoracic aorta in young and old rats with or without diabetes mellitus. The rats were grouped as young control (YC 3 months old), old control (OC 15 months old), young diabetic (YD), old diabetic (OD), young control treated (YCT), old control treated (OCT), young diabetic treated (YDT), and old diabetic treated (ODT). Diabetes was induced by streptozotocin injection and subsequently SMe1EC2 (10 mg/kg/day, p.o.) was administered to YCT, OCT, YDT, and ODT rats for 5 months. In young and old rats, diabetes resulted in hypertension, weight loss, hyperglycemia, and hypertriglyceridemia, which were partially prevented by SMe1EC2. SMe1EC2 also inhibited the diabetes-induced increase in aorta levels of AGEs (advanced glycosylation end-protein adducts), 4-HNE (4-hydroxy-nonenal-histidine), 3-NT (3-nitrotyrosine), and RAGEs (receptors for AGEs). The contractions of the aorta rings to phenylephrine (Phe) and KCL did not significantly change, but acetylcholine (ACh) and salbutamol relaxations were reduced in OC compared to YC rats. Diabetes induction increased Phe contractions in YC and OC rats, KCL contractions in YC rats, and did not cause further inhibition in already inhibited ACh and salbutamol relaxations in OC rats. We have achieved the lowest levels of ACh relaxation in YD rats compared to other groups. SMe1EC2 did not change the response of aorta to ACh, salbutamol and Phe in YC rats, and ameliorated ACh relaxations in OC and YD but not in OD rats. In YDT and ODT rats, increased Phe and KCL contractions, high blood pressure, and impaired salbutamol relaxations were amended by SMe1EC2. Phe contractions observed in YD and OD rats as well as KCl contractions observed in OC rats were the lowest levels when the rats were treated with SMe1EC2. When the bath solution was shifted to cyclopiazonic acid (CYP) or CYP plus Ca2+-free medium, the contraction induced by a single dose of Phe (3 x 10(-6) M) was more inhibited in YD and OD than in YC but not in OC rats. In SMe1EC2-treated rats, neither the presence of CFM nor CFM plus CYP exhibited a significant change in response of aorta to a single dose of Phe. These findings suggest that alpha 1-adrenergic receptor signaling is activated in both age groups of diabetic rats, diabetes activates K+-depolarization and calcium mobilization via Ca-V especially in the aorta of young rats, and sensitizes the aorta of old rats to the regulating effect of SMe1EC2. ACh relaxations were inhibited in YC rats, increased in OC rats and unchanged in YD and OD rats when aortic rings pretreated with TEA, an inhibitor of calcium-activated K+ channels (K-Ca), or 4-aminopyridine (4-AP), an inhibitor of voltage-sensitive K+ channels (K-V). ACh relaxations were inhibited in YCT, OCT, and YDT rats in the presence of 4-AP or TEA. In ODT rats, 4-AP did not change ACh relaxation but TEA inhibited. These findings suggest that the contribution of K-v and K-Ca to ACh relaxation is likely upregulated by SMe1EC2 when the relaxations were inhibited by aging or diabetes. We conclude that SMe1EC2 might be a promising agent for aging and diabetes related vascular disorders.Research Foundation of Gazi University [01/2010-126]; Research Foundation of Ankara University [10B336002]; COST Action [BM1203]; Slovak Academy of Sciences [APVV-51-017905]This article has been written by Prof. Karasu who is the leader of ADIC study group. We thank Ahmet Cumaolu and Elif Aydn for their technical help during measurement of some biomarkers. This work originally includes a part of the PhD thesis of Dr. Arzu Sakul and was partly supported by the Research Foundations of Gazi and Ankara Universities (GU-Project No. 01/2010-126, AU-Project No. 10B336002), COST Action BM1203 and the Slovak Academy of Sciences (VEGA grant APVV-51-017905)

The ultrastructural analysis of the effects of probucol on endocrin pancreas tissue ın experimentaly induced diabetes mellitus

Bu çalışmada Streptozotosin ile oluşturulan diyabet modellerinde önemli bir antioksidan olan probukolün B hücreleri üzerine koruyucu etkisinin elektron mikroskop düzeyinde incelenmesi amaçlanmıştır. Çalışmada 200 – 250 gr ağırlığında, 7 – 8 haftalık toplam 24 adet erkek sıçan kullanılmış ve 3 grup oluşturulmuştur. 1. grup kontrol (n=8) (sodyum sitrat, i.p., tek doz), 2. grup kronik (8 hafta) diyabet (n=8) (50mg/kg, i.p. tek doz STZ), 3. grup ise diyabet (8 hafta) + probucol tedavisi (300mg/kg/gün, 3 hafta) uygulanan grup (n=8) olarak ayrılmıştır. Süre bitiminde alınan pankreas dokuları LEO 906E Transmission Elektron Mikroskopta değerlendirilmiştir. Yapılan elektron mikroskobik incelemelerde diyabetik grup kontrol grubu ile karşılaştırıldığında, granül sayısının az olduğu, mitokondrion ve Golgi kompleksinde dejeneratif değişikliklerin varlığı gözlenmiştir. Diyabeti izleyen probukol tedavisi sonucunda ise granül sayısının normale yakın olduğu; ancak, organel dejenerasyonunun kısmen de olsa bulunduğu belirlenmiştir. Sonuç olarak, diyabetin B hücrelerinde oluşturduğu dejeneratif değişikliklerin probukol ile azaldığı; ancak, tamamen yok olmadığı belirlenmiştir.The aim of the present study is to investigate the protective effect of probucol, which is an antioxidant agent on beta cells in STZ induced diabetes mellitus model. In this study, 24, 7-8- week -old male rats, weighing 200-250 g were used, and the animals were divided into three groups. The control group received a single dose of sodium citrate (ip, n = 8), the 8 weeks chronic diabetes mellitus group received of a single dose 50 mg/kg STZ (ip, n = 8), the diabetes mellitus group received 300 mg/kg/day probucol for 3 weeks (n = 8). Electron microscopic examination revealed degenerative changes of mitochondria and Golgi complexes in diabetes mellitus group when compared with control group and beta cell granules were relatively decreased. When the samples from the diabetes mellitus group treated with probucol were evaluated, beta cell granule numbers were nearly normal, degeneration in organelle structure was reduced, but still present. As a conclusion probucol decreases the degenerative effects of diabetes mellitus on beta cells, but does not treat them all

Polyphenolic Extracts from Olea europea L. Protect Against Cytokine-Induced beta-Cell Damage Through Maintenance of Redox Homeostasis

Various pancreatic beta-cell stressors, including cytokines, are known to induce oxidative stress, resulting in apoptotic/necrotic cell death and inhibition of insulin secretion. Traditionally, olive leaves or fruits are used for treating diabetes, but the cellular mechanism(s) of their effects are not known. We examined the effects of Olea europea L. (olive) leaf and fruit extracts and their component oleuropein on cytokine-induced beta-cell toxicity. INS-1, an insulin-producing beta-cell line, was preincubated with or without increasing concentrations of olive leaf or fruit extract or oleuropein for 24 hr followed by exposure to a cytokine cocktail containing 0.15 ng/mL interleukin-1 beta (IL-1 beta), 1 ng/mL interferon-gamma (IFN-gamma), and 1 ng/mL tumor necrosis factor-alpha (TNF-alpha) for 6 hr. The cytotoxicity was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) testing. Apoptosis was quantified by detecting acridine orange/ethidium bromide-stained condensed nuclei under a fluorescent microscope. The cells exposed to cytokines had a higher apoptotic rate, a decreased viability (MTT), and an increased caspase 3/7 activity. Both extracts and oleuropein partially increased the proportion of living cells and improved the viability of cells after cytokines. The protective effects of extracts on live cell viability were mediated through the suppression of caspase 3/7 activity. Oleuropein did not decrease the amount of both apoptotic and necrotic cells, whereas extracts significantly protected cells against cytokine-induced death. Cytokines led to an increase in reactive oxygen species (ROS) generation and inhibited glutathione level, superoxide dismutase activity, and insulin secretion in INS-1. Insulin secretion was almost completely protected by leaf extract, but was partially affected by fruit extract or oleuropein. Neither cytokines nor olive derivatives had a significant effect on cellular cytochrome c release and catalase activity. Moreover, the cells incubated with each extract or oleuropein showed a significant reduction in cytokine-induced ROS production and ameliorated abnormal antioxidant defense. The molecular mechanism by which olive polyphenols inhibit cytokine-mediated beta-cell toxicity appears to be involving the maintenance of redox homeostasis

Effects of antioxidant stobadine on protein carbonylation, advanced oxidation protein products and reductive capacity of liver in streptozotocin-diabetic rats: Role of oxidative/nitrosative stress

Background: Increased oxidative/nitrosative stress is important in the pathogenesis of diabetic complications, and the protective effects of antioxidants are a topic of intense research. The purpose of this study was to investigate whether a pyridoindole antioxidant stobadine (STB) have a protective effect on tissue oxidative protein damage represented by the parameters such as protein carbonylation (PC), protein thiol (P-SH), total thiol (T-SH) and non-protein thiol (Np-SH), nitrotyrosine (3-NT), and advanced oxidation protein products (AOPP) in streptozotocin-diabetic rats