Metallothionein suppresses angiotensin II-induced nicotinamide adenine dinucleotide phosphate oxidase activation, nitrosative stress, apoptosis, and pathological remodeling in the diabetic heart

Anti-inflammatory and anti-coagulatory activities of caffeic acid and ellagic acid in cardiac tissue of diabetic mice

Background

Caffeic acid (CA) and ellagic acid (EA) are phenolic acids naturally occurring in many plant foods. Cardiac protective effects of these compounds against dyslipidemia, hypercoagulability, oxidative stress and inflammation in diabetic mice were examined.

Methods

Diabetic mice were divided into three groups (15 mice per group): diabetic mice with normal diet, 2% CA treatment, or 2% EA treatment. One group of non-diabetic mice with normal diet was used for comparison. After 12 weeks supplement, mice were sacrificed, and the variation of biomarkers for hypercoagulability, oxidative stress and inflammation in cardiac tissue of diabetic mice were measured.

Results

The intake of CA or EA significantly increased cardiac content of these compounds, alleviated body weight loss, elevated plasma insulin and decreased plasma glucose levels in diabetic mice (p < 0.05). These treatments also significantly enhanced plasma antithrombin-III and protein C activities (p < 0.05); and decreased triglyceride content in cardiac tissue and plasma (p < 0.05), in which the hypolipidemic effects of EA were significantly greater than that of CA (p < 0.05). CA or EA significantly lowered cardiac levels of malondialdehyde, reactive oxygen species, interleukin (IL)-beta, IL-6, tumor necrosis factor (TNF)-alpha and monocyte chemoattractant protein (MCP)-1 (p < 0.05); and retained cardiac activity of glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (p < 0.05). These compounds also significantly up-regulated cardiac mRNA expression of GPX1, SOD and catalase; and down-regulated IL-1beta, IL-6, TNF-alpha and MCP-1 mRNA expression in diabetic mice (p < 0.05).

Conclusion

These results support that CA and EA could provide triglyceride-lowering, anti-coagulatory, anti-oxidative, and anti-inflammatory protection in cardiac tissue of diabetic mice. Thus, the supplement of these agents might be helpful for the prevention or attenuation of diabetic cardiomyopathy.

Dimethylthiourea normalizes velocity-dependent, but not force-dependent, index of ventricular performance in diabetic rats: role of myosin heavy chain isozyme

Hydroxyl radicals and hydrogen peroxide are involved in the pathogenesis of systolic dysfunction in diabetic rats, but the precise mechanisms and the effect of antioxidant therapy in diabetic subjects have not been elucidated. We aimed to evaluate the effects of dimethylthiourea (DMTU), a potent hydroxyl radical scavenger, on both force-dependent and velocity-dependent indexes of cardiac contractility in streptozotocin (STZ)-induced early and chronic diabetic rats. Seventy-two hours and 8 wk after STZ (55 mg/kg) injection, diabetic rats were randomized to either DMTU (50 mg x kg(-1) x day(-1) ip) or vehicle treatment for 6 and 12 wk, respectively. All rats were then subjected to invasive hemodynamic studies. Maximal systolic elastance (E(max)) and maximum theoretical flow (Q(max)) were assessed by curve-fitting techniques in terms of the elastance-resistance model. Both normalized E(max) (E(maxn)) and afterload-adjusted Q(max) (Q(maxad)) were depressed in diabetic rats, concomitant with altered myosin heavy chain (MHC) isoform composition and its upstream regulators, such as myocyte enhancer factor-2 (MEF-2) and heart autonomic nervous system and neural crest derivatives (HAND). In chronic diabetic rats, DMTU markedly attenuated the impairment in Q(maxad) and normalized the expression of MEF-2 and eHAND and MHC isoform composition but exerted an insignificant benefit on E(maxn). Regarding preventive treatment, DMTU significantly ameliorated both E(maxn) and Q(maxad) in early diabetic rats. In conclusion, our study shows that DMTU has disparate effects on Q(maxad) and E(maxn) in chronic diabetic rats. The advantage of DMTU in chronic diabetic rats might involve normalization of MEF-2 and eHAND, as well as reversal of MHC isoform switch.

Diabetes- and angiotensin II-induced cardiac endoplasmic reticulum stress and cell death: metallothionein protection

We have shown cardiac protection by metallothionein (MT) in the development of diabetic cardiomyopathy (DCM) via suppression of cardiac cell death in cardiac-specific MT-overexpressing transgenic (MT-TG) mice. The present study was undertaken to define whether diabetes can induce cardiac endoplasmic reticulum (ER) stress and whether MT can prevent cardiac cell death via attenuating ER stress. Diabetes was induced by streptozotocin in both MT-TG and wild-type (WT) mice. Two weeks, and 2 and 5 months after diabetes onset, cardiac ER stress was detected by expression of ER chaperones, and apoptosis was detected by CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) and cleaved caspase-3 and caspase-12. Cardiac apoptosis in the WT diabetic mice, but not in MT-TG diabetic mice, was significantly increased 2 weeks after diabetes onset. In parallel with apoptotic effect, significant up-regulation of the ER chaperones, including glucose-regulated protein (GRP)78 and GRP94, cleaved ATF6 and phosporylated eIF2alpha, in the hearts of WT, but not MT-TG diabetic mice. Infusion of angiotensin II (Ang II) also significantly induced ER stress and apoptosis in the hearts of WT, but not in MT-TG mice. Direct administration of chemical ER stress activator tunicamycin significantly increased cardiac cell death only in WT mice. Pre-treatment with antioxidants completely prevented Ang II-induced ER stress and apoptosis in the cultured cardiac cells. These results suggest that ER stress exists in the diabetic heart, which may cause the cardiac cell death. MT prevents both diabetes- and Ang II-induced cardiac ER stress and associated cell death most likely via its antioxidant action, which may be responsible for MT's prevention of DCM.

Metallothionein alleviates oxidative stress-induced endoplasmic reticulum stress and myocardial dysfunction

Oxidative stress and endoplasmic reticulum (ER) stress have been implicated in cardiovascular diseases although the interplay between the two is not clear. This study was designed to examine the influence of oxidative stress through glutathione depletion on myocardial ER stress and contractile function in the absence or presence of the heavy metal scavenger antioxidant metallothionein (MT). FVB and MT overexpression transgenic mice received the GSH synthase inhibitor buthionine sulfoximine (BSO, 30 mM) in drinking water for 2 weeks. Oxidative stress, ER stress, apoptosis, cardiac function and ultrastructure were assessed using GSH/GSSG assay, reactive oxygen species (ROS), immunoblotting, caspase-3 activity, Langendorff perfused heart function (LVDP and +/-dP/dt), and transmission electron microscopy. BSO led to a robust decrease in the GSH/GSSG ratio and increased ROS production, consolidating oxidative stress. Cardiac function and ultrastructure were compromised following BSO treatment, the effect of which was obliterated by MT. BSO promoted overt ER stress as evidenced by upregulated BiP, calregulin, phospho-IRE1 alpha and phospho-eIF2 alpha without affecting total IRE1 alpha and eIF2 alpha. BSO treatment led to apoptosis manifested as elevated expression of CHOP/GADD153, caspase-12 and Bax as well as caspase-3 activity, reduced Bcl-2 expression and JNK phosphorylation, all of which was ablated by MT. Moreover, both antioxidant N-acetylcysteine and the ER stress inhibitor tauroursodeoxycholic acid reversed the oxidative stress inducer menadione-elicited depression in cardiomyocyte contractile function. Taken together, these data suggested that ER stress occurs likely downstream of oxidative stress en route to cardiac dysfunction.

Stable overexpression of human metallothionein-IIA in a heart-derived cell line confers oxidative protection

Metallothionein (MT) is a metal binding protein and cardioprotective. In order to understand the molecular mechanisms underlying the role of MT in the heart, in the current study we established a stable MT-IIA over-expressing cardiac cell line, and evaluated its anti-oxidative property. Rat heart-derived H9c2 cell line was stably transfected with a vector in which the human MT-IIA gene was placed under the control of the constitutively active beta-actin promoter. The transfected cell line (H9c2MT7) exhibited similar growth kinetics and morphology. Western blotting analysis showed that H9c2MT7 had a remarkable increased MT protein level compared with the parent cell line H9c2. Addition of 25 microM ZnSO(4) had an undetectable effect on the induction of endogenous MT, but it likely stabilized the MT protein that is expressed only in H9c2MT7 cells. H9c2MT7 cells showed marked reduction in reactive oxygen species production when exposed to hydrogen peroxide or subjected to hypoxia/reoxygenation challenge evaluated by dihydroethidium staining. In addition, transfection of MT conferred cellular resistance to cadmium toxicity. In summary, we have established a stable human MT-IIA over-expressing cardiac cell line; and this cell line showed a markedly increased oxidative protection and would be useful for dissection of the mechanisms of MT in the cardiac protection.