Antioxidant treatment protects diabetic rats from cardiac dysfunction by preserving contractile protein targets of oxidative stress.

BACKGROUND: Animal studies suggest that reactive oxygen species (ROS) play an important role in the development of diabetic cardiomyopathy. HYPOTHESIS: Matrix metalloproteinase-2 (MMP-2) is activated by ROS and contributes to the acute loss of myocardial contractile function by targeting and cleaving susceptible proteins including troponin I (TnI) and alpha-actinin. METHODS: Using the streptozotocin-induced diabetic rat model, we evaluated the effect of daily in vivo administration of sodium selenate (0.3 mg/kg; DMS group), or a pure omega-3 fish oil with antioxidant vitamin E (omega-3E; 50 mg/kg; DMFA group), which has antioxidant-like effects, for 4 weeks on heart function and on several biochemical parameters related to oxidant stress and MMP-2. RESULTS: Although both treatments prevented the diabetes-induced depression in left ventricular developed pressure (LVDP) as well as the rates of changes in developed pressure (+/-dP/dt) (P<.001), the improvement in LVDP of the DMS group was greater compared to that of the DMFA group (P<.001). Moreover, these treatments reduced the diabetes-induced increase in myocardial oxidized protein sulfhydryl and nitrite concentrations (P<.001). Gelatin zymography and Western blot data indicated that the diabetes-induced changes in myocardial levels of MMP-2 and tissue inhibitor of matrix metalloproteinase-4 (TIMP-4) and the reduction in TnI and alpha-actinin protein levels were improved in both the DMS and DMFA groups (P<.001). CONCLUSIONS: These results suggest that diabetes-induced alterations in MMP-2 and TIMP-4 contribute to myocardial contractile dysfunction by targeting TnI and alpha-actinin and that sodium selenate or omega-3E could have therapeutic benefits in diabetic cardiomyopathy.

Antioxidants but not doxycycline treatments restore depressed beta-adrenergic responses of the heart in diabetic rats.

Reactive oxygen species (ROS) play important roles in the development of diabetic cardiomyopathy. Matrix metalloproteinases (MMPs) can get activated by ROS and contribute to loss of myocardial contractile function in oxidative stress injury. Previously we have shown that either a MMP-2 inhibitor doxycycline or an antioxidant selenium treatment in vivo prevented diabetes-induced cardiac dysfunction significantly. In addition, there is an evidence for impaired cardiac responsiveness to beta-adrenoceptor (beta AR) stimulation in experimental animals with diabetes. The exact nature of linkage between the functional depression in cardiac responses to catecholamines and the variations in uncoupling of beta AR in diabetes has not been clearly defined. Therefore, we aimed to evaluate the effect of in vivo administration of doxycycline on beta AR responses of isolated hearts from diabetic rats and compare these data with two well-known antioxidants; sodium selenate and (n-3) fatty acid-treated diabetic rats. We examined the changes in the basal cardiac function in response to the beta AR stimulation, adenylate cyclase activity, and beta AR affinity to its agonist, isoproterenol. These results showed that antioxidant treatment of diabetic rats could protect the hearts against diabetes-induced depression in beta AR responses, significantly while doxycycline did not have any significant beneficial action on these parameters. As a summary, present data, in part, demonstrate that antioxidants and MMP inhibitors could both regulate MMP function but may also utilize different mechanisms of action in cardiomyocytes, particularly related with beta AR signaling pathway.

Selenium inhibits proliferation signaling and restores sodium/potassium pump function of diabetic rat aorta.

Diabetes is characterized with increased oxidant stress, vasculopathy, and neuropathy. In diabetic vasculopathy, the observed thickening of the media and intima is not only a result of vascular smooth muscle cell proliferation but also due to modification of the extracellular matrix by these cells. Also, there is hampered membrane function and a reduction in sodium pump expression in the vessels of the diabetic animals. Selenium, being a trace element, has both insulinomimetic and antioxidant effects. Thus, we hypothesized that selenium treatment will reduce proliferation, restore physiology, and correct increased proliferation signaling of diabetic aorta. Diabetes was induced by streptozotocin (50 mg/kg body weight), and rats were then treated with sodium selenate (15 mumol/kg body weight/day) for 4 weeks. Our data from diabetic rats showed an increase in proliferation rate and matrix metalloproteinase activity in aortic cell cultures. We observed marked increases in MAPK phosphorylation and caveolin 1 expression but a decrease in Na(+)/K(+) ATPase activity in diabetic rat aorta homogenates. Selenium treatment resulted in complete normalization of the above parameters to control level, while it increased Na(+)/K(+) pump activity by 40%. Our results suggest that selenium treatment of diabetics can play beneficial role in protecting vascular architecture and function against diabetes-induced pathology.

Simvastatin pretreatment reduces the severity of limb ischemia in an experimental diabetes model.

OBJECTIVE: The purpose of this study was to examine the effects of simvastatin pretreatment in the setting of acute limb ischemia-reperfusion injury in an experimental diabetes model that is associated with a high risk for limb loss. METHODS: Adult male Sprague-Dawley rats were randomized into two groups. Diabetes was induced in the first group by intravenous streptozotocin injection. The second group served as the nondiabetic group. Eight weeks after the streptozotocin injection, half of the rats in the diabetic and the nondiabetic groups were further randomized to receive either intraperitoneal simvastatin (1 mg/kg per day) or saline treatment for 6 weeks. Bilateral hind-limb ischemia was induced for 4 hours by the tourniquet method. After 24 hours of reperfusion, tissue samples were collected from the gastrocnemius and anterior tibial muscles bilaterally for measurement of muscle edema, percentage of necrosis, and malondialdehyde (MDA), glutathione, and myeloperoxidase (MPO) levels. RESULTS: Ischemic injury was more prominent in diabetic animals. The diabetic animals with limb ischemia exhibited a 7% increase in tissue edema, a 47% increase in muscle necrosis and MPO level, and a 15% reduction in glutathione levels compared with the nondiabetic animals (P < .05). Simvastatin treatment with 1 mg/kg for 6 weeks reduced the ischemic injury. Simvastatin pretreatment led to a 71% reduction in muscle necrosis in diabetic animals (P < .001). The protective effects of simvastatin pretreatment also correlated with a 23% improvement in tissue edema, a 75% reduction in tissue myeloperoxidase content, and a 71% increase in glutathione levels in diabetic animals (P < .01). Furthermore, skeletal muscle injury, characterized by tissue edema and leucosequestration, was significantly less severe with simvastatin pretreatment compared with the nondiabetic animals (P < .01). CONCLUSION: Simvastatin pretreatment reduced limb ischemia-reperfusion injury in diabetic and nondiabetic animals. We conclude that simvastatin pretreatment may be a potential therapeutic intervention for skeletal muscle ischemia-reperfusion injury in the clinical setting.

Low concentrations of ouabain activate vascular smooth muscle cell proliferation.

In vascular smooth muscle cells the sodium pump complex can act as an intracellular signal transducing complex activated by low ouabain concentrations, which inhibit sufficient pumps to activate a transduction cascade via transactivation of EGFR, but insufficient pumps to alter intracellular ions. Higher concentrations interfere with proliferation. This biphasic ouabain response occurs in human, canine, and rat VSMC at concentrations that reflect the differing ouabain affinities of the alpha1 isoforms of the three species. This supports the proposal that this effect occurs via ouabain binding to the alpha1 subunit of the Na pump. These data suggest a new transducing function of ouabain-Na pump interaction, distinct from the cellular ionic effects resulting from pump inhibition. This transducing function occurs at ouabain concentrations that do not perturb cytoplasmic ion content and requires specific localization of pumps to caveolae.