Tissue antioxidant status in streptozotocin-induced diabetes in rats. Effects of dietary manganese deficiency

Role of catecholamines in the pathogenesis of diabetic cardiomyopathy 1

Although the sympathetic nervous system plays an important role in the regulation of cardiac function, the overactivation of the sympathetic nervous system under stressful conditions including diabetes has been shown to result in the excessive production of circulating catecholamines as well as an increase in the myocardial concentration of catecholamines. In this brief review, we provide some evidence to suggest that the oxidation products of catecholamines such as aminochrome and oxyradicals, lead to metabolic derangements, Ca²⁺-handling abnormalities, increase in the availability of intracellular free Ca²⁺, as well as activation of proteases and changes in myocardial gene expression. These alterations due to elevated levels of circulatory catecholamines are associated with oxidative stress, subcellular remodeling, and the development of cardiac dysfunction in chronic diabetes.

Selenium-Dependent Antioxidant Enzymes: Actions and Properties of Selenoproteins

Unlike other essential trace elements that interact with proteins in the form of cofactors, selenium (Se) becomes co-translationally incorporated into the polypeptide chain as part of 21st naturally occurring amino acid, selenocysteine (Sec), encoded by the UGA codon. Any protein that includes Sec in its polypeptide chain is defined as selenoprotein. Members of the selenoproteins family exert various functions and their synthesis depends on specific cofactors and on dietary Se. The Se intake in productive animals such as chickens affect nutrient utilization, production performances, antioxidative status and responses of the immune system. Although several functions of selenoproteins are unknown, many disorders are related to alterations in selenoprotein expression or activity. Selenium insufficiency and polymorphisms or mutations in selenoproteins' genes and synthesis cofactors are involved in the pathophysiology of many diseases, including cardiovascular disorders, immune dysfunctions, cancer, muscle and bone disorders, endocrine functions and neurological disorders. Finally, heavy metal poisoning decreases mRNA levels of selenoproteins and increases mRNA levels of inflammatory factors, underlying the antagonistic effect of Se. This review is an update on Se dependent antioxidant enzymes, presenting the current state of the art and is focusing on results obtained mainly in chicken.

Age-dependent sensitivity of the mouse kidney to chronic nicotine exposure

BackgroundMany adolescents are exposed to nicotine via smoking, e-cigarette use, or second-hand smoke. Nicotine-induced renal oxidative stress and its long-term consequences may be higher in adolescents than in adults because of intrinsic factors in the adolescent kidney.MethodsAdolescent and adult male C57Bl/6J mice were subjected to 2 or 200 μg/ml nicotine, which closely emulates passive or active smoking, respectively, for 4 weeks. Extent of nicotine exposure (cotinine content), oxidative stress (HNE), renal function (creatinine), tubular injury (KIM-1), and pretreatment renal levels of select pro-oxidant (p66shc) and antioxidant (Nrf2/MnSOD) genes were determined. Impact of p66shc overexpression or Nrf2/MnSOD knockdown on low-/high-dose nicotine-induced oxidative stress was determined in cultured renal proximal tubule cells.ResultsDespite similar plasma/renal cotinine levels, renal HNE and KIM-1 contents were higher in adolescents compared with those in adults, whereas renal function was unaltered after passive or active smoking-equivalent nicotine exposure. Pretreatment levels of p66shc were higher, whereas Nrf2/MnSOD levels were lower in the adolescent kidney. In agreement with this, overexpression of p66shc or knockdown of Nrf2/MnSOD augmented nicotine-induced ROS production in renal proximal tubule cells.ConclusionChronic nicotine exposure incites higher oxidative stress in the adolescent than in adult kidney because of a pre-existent pro-oxidant milieu.

Ischemia-reperfusion injury and hypoglycemia risk in insulin-treated T1DM rats following different modalities of regular exercise

While regular exercise is known to improve cardiovascular function, individuals with type 1 diabetes mellitus (T1DM) have an increased risk for exercise-induced hypoglycemia. Clinical data suggest that higher intensities of acute exercise may alleviate the onset of hypoglycemia; however, the cardiovascular benefit from these forms of exercise in patients with T1DM has yet to be established. The purpose of this study was to investigate the cardiovascular benefit of different regular exercise regimes, while monitoring blood glucose concentrations during the post-exercise period. Fifty rats (8-week-old Sprague-Dawley male) were equally divided into the following groups: nondiabetic sedentary (C), diabetic sedentary (DS), diabetic low-intensity aerobic exercise (DL), diabetic high-intensity aerobic exercise (DH) or diabetic resistance exercise (DR). Diabetes was induced using multiple streptozotocin injections (5×; 20 mg/kg) while subcutaneous insulin pellets maintained glycemia in a range typical for individuals that exercise with T1DM. Exercise consisted of six weeks of treadmill running (DL and DH) or weighted ladder climbs (DR). The cardiovascular benefit of each exercise program was determined by the myocardial recovery from ischemia-reperfusion injury. Exercise-related cardiovascular protection was dependent on the exercise modality, whereby DH demonstrated the greatest protection following an ischemic-reperfusion injury. Each exercise modality caused a significant decline in blood glucose in the post-exercise period; however, blood glucose levels did not reach hypoglycemic concentrations (<3.0 mmol/L) throughout the exercise intervention. These results suggest that elevating blood glucose concentrations prior to exercise allows patients with T1DM to perform exercise that is beneficial to the myocardium without the accompanying risk of hypoglycemia.

Administration of chromium(III) and manganese(II) as a potential protective approach against daunorubicin-induced cardiotoxicity: in vitro and in vivo experimental evidence

Daunorubicin (DNR) is a widely used antitumor drug, but its application is limited because of its cardiotoxic side effects. The present study was designed to investigate the interaction between DNR and cardiac myosin (CM) in the presence of chromium(III) (Cr(3+)) and manganese(II) (Mn(2+)) using fluorescence spectrometry under simulative physiological conditions with the aim of exploring the influence of metal ion on DNR-CM complex and finding out an aggressive approach to abrogate of DNR-induced cardiotoxicity. In detail, the quenching and binding constant of ternary system, including metal ion, DNR, and CM, were measured and compared with the DNR-CM. The data from in vitro experiments indicate that the presence of Cr(3+) or Mn(2+) distinctly decreased the binding force between DNR and CM, and alleviated the cardiac toxicity caused by DNR. In addition, the variations in mice body weight and myocardial enzyme level were examined by in vivo experiments. Animals receiving Cr(3+) or Mn(2+) supplementation of DNR showed preservation of the normal pattern of the heart, especially 2.0 mg Cr(3+)/kg body wt or 50.0 mg Mn(2+)/kg body wt exhibited an obviously protective effect accompanied with body weight raise when compared with the mice treated with DNR alone, decreased the ratio of heart to body weight (BW) and the ratio of left ventricular mass to BW to the normal levels, and inhibited the leak of myocardial enzyme caused by DNR. As a result, this study suggests that pretreatment of lower dose of Cr(3+) (2 mg/kg wt) and moderate dose of Mn(2+) (50 mg/kg wt) might be useful and play an important role in ameliorating the cardiotoxicity of DNR treatment in cancer patients.

Reduction of liver manganese concentration in response to the ingestion of excess zinc: identification using metallomic analyses

To date, minerals of interest have been analyzed individually to understand mineral dynamics and metabolism. Our recent development of metallomic analyses enabled us to evaluate minerals in an unbiased and global manner. Here, we evaluated the effects of ingestion of excess zinc to plasma and tissue concentrations of minerals in growing rats. A total of 26 minerals were simultaneously evaluated by metallomic analyses using inductively coupled plasma-mass spectrometry (ICP-MS) in semi-quantification mode; the concentrations of several minerals exhibited consistent changes in response to the concentrations of dietary zinc. Manganese concentrations in plasma and femur increased, while concentrations in the liver and pancreas decreased with increasing dietary zinc concentrations. Because the interaction between zinc and manganese is not known, we further focused our analysis on liver manganese. Quantitative analyses also indicated that the hepatic concentration of manganese decreased in response to the ingestion of diets containing excess zinc, a result that is partly explained by the decreased expression of hepatic Zip8, a manganese transporter. The present study reveals mineral interaction by using metallomic analyses and proposes a possible mechanism that underlies this novel interaction.

The effect of dietary methionine and white tea on oxidative status of gilthead sea bream (Sparus aurata)

Free radicals are continuously generated during an organism's lifetime. In order to understand the involvement in the oxidative status of fish, methionine and white tea were assayed as antioxidant supplements in diets for gilthead sea bream (Sparus aurata). For the purpose of this study, four isonitrogenous and isolipidic diets were formulated to contain 45 % of protein and 18 % lipid and 0·3 % methionine (Met diet), 2·9 % white tea dry leaves (Tea diet) and 2·9 % of white tea dry leaves + 0·3 % methionine (Tea + Met diet). An unsupplemented diet was used as the control. Key enzymatic antioxidant defences, superoxide dismutase (SOD) isoenzyme profile, total, reduced and oxidised glutathione and oxidative damage markers were determined. The results showed that dietary methionine supplementation increased liver SOD activity, while white tea induced higher hepatic catalase activity. Dietary white tea induced a notable increase in Mn-SOD isoenzyme. This is the first study to provide evidence that dietary tea inclusion in fish feeding could be an important source of Mn with metabolic repercussions on antioxidant mechanisms.

Manganese regulates manganese-containing superoxide dismutase (MnSOD) expression in the primary broiler myocardial cells

Previous studies showed that dietary manganese can increase the MnSOD mRNA expression in a dose-dependent manner in the heart of broilers. In order to explore the specific mechanism of the MnSOD expression induced by manganese, a model of MnSOD expression was developed with primary cultured broiler myocardial cells. The objective of the present study was to investigate whether the model was working or not and to determine how manganese affects the expression of the enzyme in broiler myocardial cells in vitro. In experiment 1, various amount of manganese (0, 0.25, 0.5, 1, 2, and 4 mM) were added into the cultures for 24-h incubation to investigate MnSOD expression and for 0-, 6-, 12-, 24-, 36-, and 48-h incubation to measure the cell viability. In experiment 2, the most suitable Mn supplementation based on the results of experiment 1 was added into cultures for 6-, 12-, 24-, and 48-h incubation. The results showed that MnSOD mRNA, MnSOD protein, and MnSOD activity were induced by manganese in dose- and time-dependent manner. Manganese regulates MnSOD expression not only at transcriptional level but also at translational and/or posttranslational levels.

Influence of tea drinking on manganese intake, manganese status and leucocyte expression of MnSOD and cytosolic aminopeptidase P

OBJECTIVE

Since black tea contains high levels of manganese (Mn), we investigated the relationship between dietary Mn intake, circulating Mn levels and leucocyte expression of two Mn-dependent enzymes in tea drinkers and non-tea drinkers.

DESIGN

We assessed Mn intakes (food frequency questionnaire), fasting whole blood and plasma Mn levels, and quantitative expression of peripheral blood mononuclear cell Mn-dependent superoxide dismutase (MnSOD) and cytosolic aminopeptidase-P (cAP-P).

SETTING AND SUBJECTS

In total, 24 tea drinkers (> or = 1 l black tea/day) and 28 non-tea drinkers were recruited from the staff and students of King's College London by circular email.

RESULTS

Dietary Mn intakes (mean (range)) were significantly lower (P < 0.0001) in non tea drinkers (3.2 mg/day (0.5-6.5)) than tea drinkers (5.5 mg/day (2-12) or 10 mg/day (5-20) depending upon the value used for Mn levels of black tea). Whole blood, plasma Mn levels and expression of MnSOD and cAP-P did not differ between the groups. In a continuous analysis, whole blood Mn levels and expression of MnSOD correlated inversely but no other parameters associated with each other.

CONCLUSIONS

Tea drinking is a major source of dietary Mn and intakes commonly exceed proposed adequate intake values of 1.8-2.3 mg Mn/day and, on occasion, exceed upper limits of 10-11 mg/day. Dietary Mn intake has little influence on markers of Mn status or expression of Mn-dependent enzymes. Fasting whole blood Mn levels and leucocyte expression of MnSOD could, together, be further investigated as markers of Mn status.

The Role of Antioxidant Micronutrients in the Prevention of Diabetic Complications

Diabetes mellitus is associated with an increased production of reactive oxygen species and a reduction in antioxidant defenses. This leads to oxidative stress, which is partly responsible for diabetic complications. Tight glycemic control is the most effective way of preventing or decreasing these complications. Nevertheless, antioxidant micronutrients can be proposed as adjunctive therapy in patients with diabetes. Indeed, some minerals and vitamins are able to indirectly participate in the reduction of oxidative stress in diabetic patients by improving glycemic control and/or are able to exert antioxidant activity. This article reviews the use of minerals (vanadium, chromium, magnesium, zinc, selenium, copper) and vitamins or cofactors (tocopherol [vitamin E], ascorbic acid [vitamin C], ubidecarenone [ubiquinone; coenzyme Q], nicotinamide, riboflavin, thioctic acid [lipoic acid], flavonoids) in diabetes, with a particular focus on the prevention of diabetic complications. Results show that dietary supplementation with micronutrients may be a complement to classical therapies for preventing and treating diabetic complications. Supplementation is expected to be more effective when a deficiency in these micronutrients exists. Nevertheless, many clinical studies have reported beneficial effects in individuals without deficiencies, although several of these studies were short term and had small sample sizes. However, a randomized, double-blind, placebo-controlled, multicenter trial showed that thioctic acid at an oral dosage of 800 mg/day for 4 months significantly improved cardiac autonomic neuropathy in type 2 diabetic patients. Above all, individuals with diabetes should be educated about the importance of consuming adequate amounts of vitamins and minerals from natural food sources, within the constraints of recommended sugar and carbohydrate intake.

Platelet dopamine receptors and oxidative stress parameters as markers of manganese toxicity

The present study has been undertaken to investigate whether neurotoxic effects of manganese (Mn) are reflected in platelets in rats to monitor the usefulness of platelet as peripheral model. Exposure of rats to Mn (10 or 15 mg/kg bw, i.p.) for 45 days caused a significant increase in membrane fluidity as evidenced by decrease in fluorescence polarisation in platelets (11% and 14%) and striatum (9% and 13%). These rats exhibited a significant increase in superoxide dismutase activity both in platelets (24% and 37%) and striatum (31% and 42%), respectively, in comparison to controls. Exposure of rats to Mn for 45 days (15 mg/kg bw, i.p.) caused a significant decrease in reduced glutathione content (platelets 20%, striatum 24%) and catalase activity (platelets 35%, striatum 44%) compared to control rats. Rats exposed to Mn (10 or 15 mg/ kg bw, i.p.) for 15 days exhibited a significant increase in dopamine receptors both in platelets (55% and 40%) and striatum (38% and 31%). The results suggest that exposure to Mn may alter the membrane functions and impair the anti-oxidant defense mechanism both in platelets and brain. The study also suggests that dopaminergic mechanisms are impaired following Mn exposure and such changes are reflected in platelets. Interestingly, parallel changes both in striatum and platelets, as observed in the present study, strengthen the usefulness of platelets as a peripheral neuronal model.

Induction of superoxide dismutase and cytotoxicity by manganese in human breast cancer cells

MnCl2 induced manganese-containing superoxide dismutase (MnSOD) expression (mRNA, immunoreactive protein, and enzyme activity) in human breast cancer Hs578T cells. The induction of MnSOD immunoreactive protein in Hs578T cells was inhibited by tiron (a metal chelator and superoxide scavenger), pyruvate (a hydrogen peroxide scavenger), or 2-deoxy-d-glucose (DG, an inhibitor of glycolysis and the hexose monophosphate shunt), but not by 5,5-dimethyl-1-pyrroline-1-oxide (a superoxide scavenger), N-acetyl cysteine (a scavenger for reactive oxygen species and precursor of glutathione), diphenylene iodonium (an inhibitor of flavoproteins such as NADPH oxidase and nitric oxide synthase), or SOD (a superoxide scavenger). Northern blotting demonstrated that tiron or DG affected at the mRNA level, while pyruvate affected Mn-induced MnSOD expression at both the mRNA and protein levels. These results demonstrate that Mn can induce MnSOD expression in cultured human breast cancer cells. Mn also induced apoptosis and necrosis in these cells. Since inhibitors of Mn-induced MnSOD induction did not affect cell viability, MnSOD induction is probably not the cause of the Mn-induced cell killing.

Protective effects of Gingko biloba extract EGb 761 on myocardium of experimentally diabetic rats. I: ultrastructural and biochemical investigation on cardiomyocytes

Chronic diabetes in man and animal models develops cardiomyopathic alterations which cannot be absolutely avoided by insuline therapy. Since diabetic damage is partly attributed to oxidative stress antioxidative treatment could be able to reduce the alterations. Aim of this study was to investigate the cardioprotective effects of EGb 761, known as a radical scavenger, against diabetic alterations in rats. The diabetes was induced by i.p. injection of 60 mg/kg body weight streptozotocin. Duration of diabetes was 4 months, the protected group received 100 mg/kg body weight EGb 761 with the drinking water over 3 months. Electron and light microscopic morphometry of left-ventricular samples revealed typical diabetic alterations consisting in decrease of volume fraction of myofibrils, SR and t-tubules and diminishing of cardiomyocyte diameter, increase of interstitial volume, mitochondrial size and volume fraction, and of vacuoles and of lipid drops. EGb treatment could gradually prevent the loss of myofibrils and reduction of myocyte diameter but has only little influence on interstitial and mitochondria volume. The diabetic-induced increase of lipid and vacuoles and the decrease of SR and t-tubules were not influenced. Biochemical parameters of oxidative stress: malondialdehyde (MDA) was only insignificantly altered by diabetes and EGb. The superoxide dismutase (SOD) activity was increased by diabetes and more increased by EGb treatment. Creatine kinase (CK) activity was diminished by diabetes but slightly increased by EGb. The polymerase chain reaction (PCR) of i-NOS was not different between the diabetic and protected diabetic groups.

Lipoperoxidation in hepatic subcellular compartments of diabetic rats

It is known that an accumulation of lipoperoxidative aldehydes malondialdehyde (MDA) and 4-hydroxynonenal (HNE) takes place in liver mitochondria during aging. The existence and role of an increased extra- and intra-cellular oxidative stress in diabetes, an aging-accelerating disease, is currently under discussion. This report offers evidence that lipoperoxidative aldehydes accumulate in liver microsomes and mitochondria at a higher rate in spontaneously diabetic BB/WOR rats than in control non-diabetic animals (HNE content, diabetes vs. control: microsomes 80.6+/-19.9 vs. 25.75+/-3.6 pmol/mg prot, p = .024; mitochondria 77.4+/-15.4 vs. 26.5+/-3.5 pmol/mg prot, p = .0103). Liver subcellular fractions from diabetic rats, when exposed to the peroxidative stimulus ADP/Fe, developed more lipoperoxidative aldehydes than those from non diabetic rats (HNE amount, diabetes vs. control: microsomes 3.60+/-0.37 vs. 2.33+/-0.22 nmol/mg prot, p = .014; mitochondria 3.62+/-0.26 vs. 2.30+/-0.17 nmol/mg prot, p = .0009). Liver subcellular fractions of diabetic rats developed more fluorescent chromolipids related to HNE-phospholipid adducts, either after in vitro peroxidation (microsomes: p = .0045; mitochondria: p = .0023) or by exposure to exogenous HNE (microsomes: p = .049; mitochondria: p = .0338). This higher susceptibility of diabetic liver membranes to the non-enzymatic attack of HNE may be due to an altered phospholipid composition. Moreover, a decreased activity of the HNE-metabolizing systems can be involved: diabetic liver mitochondria and microsomes were unable to consume exogenous HNE at the same rate as non-diabetic membranes; the difference was already significant after 5' incubation (microsomes p<.001; mitochondria p<.001). These data show an increased oxidative stress inside the hepatocytes of diabetic rats; the impairment of the HNE-metabolizing systems can play a key role in the maintenance and propagation of the damage.

Manganese scavenges superoxide and hydroxyl radicals: an in vitro study in rats

The present study was designed to investigate the role of manganese (Mn) as an antioxidant element. In vitro experiments have been conducted to evaluate the ability of Mn in scavenging oxygen free radicals. Superoxide (O*-) and hydroxyl (OH*-) radicals were generated in vitro by using xanthine and xanthine oxidase system and fenton reactions respectively. Different concentrations of Mn (II) and Mn (III) were used in the reaction mixture to evaluate free radical scavenging ability of Mn. The results indicated that Mn scavenged superoxide radicals at nanomolar concentrations whereas hydroxyl radicals were scavenged at micromolar concentrations. In addition, Mn-superoxide dismutase (SOD) activity was measured in different regions of brain in adult male rats treated with MnCl2. The results showed that Mn-SOD activity increased in Mn treated animals. Therefore, the data support the hypothesis that Mn is one of the essential elements which can protect against oxidative damage, however, at higher concentrations Mn can be neurotoxic by generating the free radicals.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Trace metals and metalloenzymes in placenta after oral administration of lead acetate

The present study was carried out to find the effects of Pb acetate (10-50 mg/kg body wt) after oral administration on: 1. The distribution of elements, such as Fe, Cu, Zn, and Mn; 2. The activity of 6-amino levulenic acid dehydratase (delta-ALAD) and alkaline phosphatase (PAP); and 3. On the level of reduced glutathione (GSH) in murine placenta. Pb toxicity expressed on a dry-wt basis was reflected in terms of deficiency of delta-ALAD and PAP and enhanced content of GSH. Analysis of trace elements following Pb exposure showed low levels of Mn and Cu. Although Fe composition of placenta remained within normal range with increasing load of endogeneous Pb, Zn decline was not consistent after oral feeding of Pb acetate. Deficiency of PAP after Pb exposure did not correlate with the endogeneous levels of Pb or Zn therein, but correlated with endogeneous levels of Mn. Placental deficiencies of Cu and Mn have been related to the disturbed placental functions by Pb accumulation.

Tissue manganese concentrations and antioxidant enzyme activities in rats given total parenteral nutrition with and without supplemental manganese

BACKGROUND

Manganese is an essential but potentially toxic mineral. Parenteral administration of manganese via total parenteral nutrition (TPN) bypasses homeostatic mechanisms (intestinal absorption and presystemic hepatic elimination). Our objective in this study was to determine the effect of supplemental manganese in TPN solutions on manganese status in a rat model.

METHODS

Male Sprague-Dawley rats underwent jugular catheterization and were given 61.0 +/- 0.4 g/d TPN solution providing 0.5 +/- 0.2 nmol manganese/g (Mn-; n = 6) or 16 +/- 3 nmol manganese/g (Mn+; n = 7) for 7 days. Reference rats (RF; n = 8) were fed a purified diet containing 1.3 mmol manganese/g.

RESULTS

Liver manganese decreased in both TPN groups, but tibia, spleen, and pancreas manganese concentrations were greater in Mn+ rats than in Mn- or RF rats. Although no treatment differences were seen in heart or liver manganese superoxide dismutase activity, heart copper-zinc superoxide dismutase activity was lower in the Mn+ rats than in Mn- or RF rats (p < .05). Glutathione peroxidase activity was depressed in livers of both Mn- and Mn+ rats relative to RF rats (p < .0001), which was not due to selenium deficiency.

CONCLUSIONS

Supplemental parenteral manganese is taken up to a greater extent by peripheral tissues than the liver. In this first report of antioxidant enzyme activities in animals maintained with TPN, we found that TPN as well as supplemental manganese can influence antioxidant enzyme activities. We conclude that it is generally unnecessary and potentially toxic to supplement TPN solutions with manganese during short-term usage.