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 Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 32  |  Issue : 1  |  Page : 20-28

The protective role of vitamin E and angiotensin II receptor blocker in diabetic cardiomyopathy in male albino rats


Department of Physiology, Faculty of Medicine, Benha University, Benha, Egypt

Date of Submission06-May-2015
Date of Acceptance06-May-2015
Date of Web Publication26-Nov-2015

Correspondence Address:
Abeer A Shoman
Department of Physiology, Faculty of Medicine, Benha University, Benha
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-208X.170555

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  Abstract 

Background
Diabetic cardiomyopathy is a common complication of diabetes mellitus. There are many pathophysiological mechanisms of diabetic cardiomyopathy, such as apoptosis and oxidative stress.
Aim
This study was designed to assess the issue of cardiomyocyte apoptosis as a possible cause of diabetic cardiomyopathy and the use of vitamin E as an antioxidant and losartan as an angiotensin II receptor blocker in suppressing this apoptosis.
Materials and methods
Rats were randomly divided into five groups of 10 animals each: group 1 included healthy control rats; group 2, the diabetic group, included rats that were made diabetic with a single injection of streptozotocin; group 3 included diabetic rats treated with losartan; group 4 included diabetic rats treated with vitamin E; and group 5 included diabetic rats treated with losartan and vitamin E. At the end of the experimental period, plasma glucose and serum lipid profile were evaluated. The heart rate and mean systemic arterial blood pressure were measured in all groups. Oxidative stress as assessed with malondialdehyde and reduced glutathione (GSH-PX) concentrations, as well as caspase-3 activity as an index of apoptosis, was determined in cardiac tissue. In addition, cardiac apoptosis was measured with the BCL-X immunohistochemistry technique.
Results
Administration of vitamin E and losartan caused significant decrease in apoptosis. In addition, there was significant decrease in malondialdehyde and caspase-3 and significant increase in GSH in cardiac tissue homogenate, with significant decrease in the serum lipid level. The mean systemic arterial blood pressure was significantly decreased, whereas heart rate increased to normal level.
Conclusion
Vitamin E and losartan have a protective effect on diabetes-induced cardiomyopathy in rats.

Keywords: apoptosis, caspase-3, diabetic cardiomyopathy, losartan, oxidative stress, vitamin E


How to cite this article:
Hussien NI, Shoman AA. The protective role of vitamin E and angiotensin II receptor blocker in diabetic cardiomyopathy in male albino rats. Benha Med J 2015;32:20-8

How to cite this URL:
Hussien NI, Shoman AA. The protective role of vitamin E and angiotensin II receptor blocker in diabetic cardiomyopathy in male albino rats. Benha Med J [serial online] 2015 [cited 2017 Oct 22];32:20-8. Available from: http://www.bmfj.eg.net/text.asp?2015/32/1/20/170555


  Introduction Top


Diabetes represents a serious risk factor for the development of cardiovascular complications such as coronary heart disease, peripheral arterial disease, hypertension, stroke, and cardiomyopathy [1] . Moreover, mortality from cardiac diseases is approximately two-four-fold higher in patients with diabetes than in those who have the same magnitude of vascular diseases without diabetes, and diabetic cardiomyopathy can occur without any vascular pathogenesis [2] .

Diabetic cardiomyopathy is related directly to hyperglycemia. Cell death such as apoptosis plays a critical role in cardiac pathogenesis as hyperglycemia induces myocardial apoptosis [3] . In diabetes, the circulating free radicals may contribute to progression of heart disease and possibly mediate the process of apoptosis [4] . Hyperglycemia-induced myocardial apoptosis is mediated, at least in part, by activation of the cytochrome c-activated caspase-3 pathway, which may be triggered by reactive oxygen species (ROS) derived from high levels of glucose [5] .

Cell death, as a consequence of myocardial abnormalities in diabetes, is an important cause of various cardiomyopathies [6] . In particular, cell death can cause a loss of contractile tissue, compensatory hypertrophy of myocardial cells, and reparative fibrosis [7] . Studies have shown that the incidence of apoptosis increases in the heart of patients with diabetes [8] .

Having diabetes increases the likelihood of high blood pressure and other heart and circulation problems, because diabetes damages arteries and makes them targets for hardening (atherosclerosis). Atherosclerosis can cause high blood pressure, which, if not treated, can lead to blood vessel damage, stroke, heart failure, heart attack, or kidney failure [9] .

It is well recognized that diabetes mellitus (DM) is characterized by enhanced upregulation of the local and systemic Renin-Angiotensin-Aldosterone System (RAAS). Although the basis for dysfunction of the RAAS system in the setting of DM remains incompletely understood, its activation in DM has been demonstrated to be associated with increased oxidative damage, which in turn activates the death pathways implicated in myocardial cell apoptosis and necrosis [10] . These myocyte and nonmyocyte alterations in diabetic hearts resulting from increased activation of RAAS induce impairment of ventricular function. The benefits of RAAS blockade in preventing and reversing diabetic cardiomyopathy in DM patients underscore the importance of dysregulated RAAS in the pathogenesis of diabetic cardiomyopathy [11] .

Renin-angiotensin system (RAS) inhibitors can reduce tissue angiotensin II levels, with beneficial effects on cardiovascular function. Therefore, blockade of the RAS may have a protecting function against diabetic cardiomyopathy through inhibition of excessive activity of RAS. However, this has not been confirmed [12] .

Vitamin E has been shown to increase oxidative resistance in vitro and prevent atherosclerotic plaque formation in mouse models. Consumption of food rich in vitamin E has been associated with lower risk of coronary heart disease in middle-aged to older men and women [13] . Vitamin E is a powerful antioxidant in the body's lipid (fat) phase. It can prevent LDL lipid peroxidation caused by free radical reactions. Its ability to protect cell membranes from oxidation is of crucial importance in preventing and reversing many degenerative diseases. In addition, vitamin E inhibits blood clotting (platelet aggregation and adhesion) and prevents plaque enlargement and rupture [14] .

Thus, the present study was designed to detect the effect of angiotensin II receptor antagonist (losartan) and vitamin E as an antioxidant on blood glucose level, apoptosis, oxidative stress, serum lipid profile level, heart rate, and mean systemic arterial blood pressure (MSBP) in diabetic rats.


  Materials and methods Top


Animals

This study was conducted on 50 adult Wistar albino male rats of 6-8 weeks old, weighing between 170 and 200 g. The animals were housed in the animal laboratory at the medical research center at Benha Faculty of Medicine. They were housed at room temperature (25°C). All rats were fed a standard diet and water.

Groups of the experiment

The animals were randomly divided into five groups of 10 rats each:

  1. Group I (the control group) was injected with a single dose of 1 ml citrate buffer intraperitoneally and with 1 ml saline daily for 8 weeks.
  2. Group II received a single dose of 40 mg/kg streptozotocin (STZ) intraperitoneally.
  3. Group III received losartan potassium at a dose of 1 mg/kg/day. Losartan potassium was dissolved in distilled water and was given orally. It was administered for 8 weeks from the experimental induction of diabetes [15] .
  4. Group IV received vitamin E at a dose of 1 g/kg/day. Vitamin E was dissolved in olive oil and was given daily orally. It was administered for 8 weeks from the experimental induction of diabetes [16] .
  5. Group V received both losartan potassium at a dose of 1 mg/kg/day orally and vitamin E at a dose of 1 g/kg/day. Both were administered for 8 weeks from the experimental induction of diabetes.


Induction and diagnosis of diabetes mellitus

Diabetes was induced with an intraperitoneal injection of a single dose of STZ (40 mg/kg in freshly prepared citrate buffer pH 4.5). The animals were allowed to drink 5% glucose solution overnight to overcome drug-induced hypoglycemia. Control rats were injected with the buffer alone.

Diabetes was verified 72 h later by measuring tail blood glucose levels (after an overnight fasting) using glucose oxidase reagent strips. Rats having a blood glucose level of 250 mg/dl or greater were considered to be diabetic [17] .

Chemicals used

Streptozotocin drug

It was purchased from Sigma-Aldrich Company (USA, http://www.sigmaaldrich.com). It is in powder form, having purity more than 99%, and needs to be dissolved in freshly prepared sodium citrate buffer of pH 4.5.

Sodium citrate buffer pH 4.5

Preparation of 0.1 ml citrate buffer: accurately weigh 10.5 g of citric acid and 14.7 g of sodium citrate. Mix it with 500 ml water, and make up the volume to 1000 ml with distilled water.

Adjust pH to 4.5 using sodium hydroxide [18] .

Vitamin E

It was available in the form of dl-α-tocopheryl acetate soft gelatin capsule (1000 mg) from Pharco.

Losartan potassium

It was available in the form of losartan potassium film-coated tablets (50 mg) from Unipharma (Al-Obour city near Cairo, Egypt).

Procedure of the experiments

Measurement of mean systemic arterial blood pressure (cuff tail blood pressure method)

The rats were placed in the holder for at least 10-15 min before obtaining pressure measurements for acclimatization. Proper animal handling is critical for consistent and accurate blood pressure measurements. A nervous, stressed animal may have diminished circulation in the tail. The animal was allowed to enter the holder freely. After the animal was in the holder, the nose cone was adjusted so that the animal is comfortable but not able to move excessively. The cuff was applied to the tail and connected to the transducer and switched on to record the systolic and diastolic waves. From the charts, the heart rate was calculated. The systolic and diastolic blood pressure values were measured and then MSBP was calculated [19] . Blood pressure was measured at the beginning and at the end of the experiment.

Blood sample collection

At the end of the treatment period, all animals were anesthetized with diethyl ether. The animals were fixed on operating table and the blood samples were taken as follows.

A craniocaudal incision of about 2 cm was made parallel and slightly to the left of the sternum through the skin and pectoral muscles to expose the ribs. A blunt curved forceps was then inserted between the fifth and sixth ribs, through the intercostal muscles. The gap was widened so that the rapidly beating heart becomes visible, and then blood sample was taken from the right ventricle. Blood sample was collected in two tubes:

  1. One tube contained EDTA and was immediately centrifuged for 15 min for separation of plasma and stored at -20°C for estimation of plasma glucose.
  2. In the other tube the blood was left to clot and was centrifuged for 15 min for separation of serum and stored at -20°C for estimation of total cholesterol and triglycerides.


Plasma concentration of glucose, serum triglyceride, and total cholesterol was determined with a standard automated technique using Hitachi Analyzer Model 911 and adequate kits from Roche Company (Switzerland).

Tissue preparation

The heart was dissected and divided into two parts: one part was homogenized for measurement of malondialdehyde (MDA), GSH, and caspase-3 activity, and the remaining was fixed in 10% formalin solution at room temperature. Sections of cardiac tissue were processed for histopathological and immunohistochemical studies.

Assessment of apoptosis

Paraffin-embedded tissue sections of 5 mm were prepared on positively charged slides to be stained with anti-BCL-X antibody using the biotin-streptavidin immunoperoxidase technique [20] .

Interpretation of immunostaining

BCL-X was detected as cytoplasmic brown staining in examined tissue sections. Stained sections were classified as follows: mild intensity of apoptosis for weak brown cytoplasmic stain; moderate intensity for moderate brown cytoplasmic stain; and severe intensity for strong brown cytoplasmic stain [20] .

Measurement of antioxidant activity and apoptosis

The tissues were weighed separately and homogenized in 10 volumes of cold 0.01 mol/l Tris-HCL buffer (pH 7.4) using an automatic homogenizer. The homogenates were then centrifuged at 15 000 rpm for 15 min at 4°C. Clear supernatants were used for MDA assay as an indicator for lipid peroxidation and for glutathione peroxidase (GSH-PX) as an antioxidant enzyme. In addition, the clear supernatants were used for caspase-3 enzymatic assay as an indicator for apoptosis. Tissue MDA level was determined with the thiobarbituric acid method and expressed as nmol/g tissue. GSH-PX activity was measured with NADPH oxidation and expressed as µg/g tissue [21] . Caspase-3 activity was measured with Colorimetric Assay Kit (Bioscience, USA) and expressed as U/mg [3] . The measurements were carried out in the biochemistry analyzing unit at Benha Faculty of Medicine.

Statistical analysis

All data were expressed as mean ± SD. Data were evaluated using the one-way analysis of variance using SPSS version 19 (Hong Kong Ltd. RM).

Difference between groups were compared using Student's t-test, with P less than 0.05 selected as the level of statistical significance.


  Results Top


Mortality rate

No rats died in the control group and in the group that received losartan and vitamin E. However, three rats died in the nontreated STZ group, with a mortality rate of 30%. Among the drug-treated STZ groups, one rat died in the group receiving losartan and one died in the group receiving vitamin E, with a mortality rate of 10% in either group.

Biochemical parameters

[Table 1] showed that there was a significant increase (P < 0.001) in plasma glucose level in group II (the diabetic group) compared with the control group. The serum triglycerides and total cholesterol were significantly increased (P < 0.001) in group II compared with the control group. Losartan administration in diabetic rats (group III) caused significant decrease (P < 0.001) in blood glucose triglycerides and total cholesterol levels compared with untreated diabetic rats. Vitamin E administration in diabetic rats (group IV) caused significant decrease (P < 0.001) in blood glucose, triglycerides, and total cholesterol levels compared with the untreated diabetic rats.
Table 1 Comparison of blood glucose level (mg/dl), triglyceride (mg/dl), and cholesterol level (mg/dl) among the experimental groups (mean ± SD)


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Heart rate and blood pressure changes

[Table 2] showed that there was a significant decrease in the heart rate and a significant increase in MSBP in STZ-induced diabetic rats compared with the control group. Administration of losartan and vitamin E lead to a significant increase in heart rate and a significant decrease in MSBP compared with the untreated diabetic rats (group II).
Table 2 Comparison of the heart rate (beats/min) and mean systemic blood pressure (mmHg) among the experimental groups (mean ± SD)


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Oxidative, antioxidative, and apoptosis changes in cardiac tissue

[Table 3] shows the effect of losartan and vitamin E on antioxidative activity and apoptosis in the cardiac tissue homogenate. There was significant increase in MDA and caspase-3 and significant decrease in GPX level in STZ-induced diabetic rats (group II) compared with the control group (group I). Both losartan and vitamin E treatment caused significant decline (P < 0.001) in MDA and caspase-3, with significant increase in GSH-PX level in cardiac tissue homogenate.
Table 3 Comparison between malondialdehyde (nmol/g), antioxidant enzyme activities glutathione peroxidase (µg/g), and caspase-3 activity (U/mg) among the experimental groups (mean ± SD)


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Apoptosis in cardiac tissue

[Figure 1] shows normal cardiomyocytes with mild brown staining of BCL-X, indicating mild degree of apoptosis (the control group). [Figure 2] shows strong brown staining of cardiomyocytes indicating an increase in apoptotic cell death in the myocardium in untreated diabetic rats (group II). [Figure 3] shows moderate brown staining of cardiac muscle indicating moderate improvement in apoptotic changes in diabetic rats receiving losartan treatment (group III). [Figure 4] shows weak brown staining of the cardiac muscle indicating strong improvement in apoptotic changes in diabetic rats after vitamin E administration (group IV). [Figure 5] also shows weak brown staining of the cardiac muscle indicating marked improvement in apoptotic changes in diabetic rats after combined administration of losartan and vitamin E (group IV).
Figure 1 A section of myocardial muscles of normal (group I) rats showing weak BCL-X expression in the cytoplasm of myocardial muscles (streptavidin– biotin, ×200).



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Figure 2 A section of myocardial muscles of an untreated diabetic rat (group II) showing strong brown BCL-X staining in the cytoplasm of myocardial muscles (streptavidin– biotin, ×200).



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Figure 3 A section of myocardial muscles of a diabetic rat that received losartan (group III) showing moderate brown BCL-X staining in the cytoplasm of myocardial muscles (streptavidin– biotin, ×200).



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Figure 4 A section of myocardial muscles of a diabetic rat that received vitamin E (group IV) showing weak brown BCL-X staining in the cytoplasm of myocardial muscles (streptavidin– biotin, ×200).



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Figure 5 A section of myocardial muscles of a diabetic rat that received vitamin E and losartan (group V) showing weak brown BCL-X staining in the cytoplasm of myocardial muscles (streptavidin– biotin, ×200).



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  Discussion Top


The results obtained from this study demonstrate that apoptosis significantly increased in diabetic myocardium and provide evidence that high levels of glucose directly cause apoptosis. Our study has identified that diabetic myocardial apoptosis is associated with oxidative overactivity as evident by significantly increased MDA level indicating increased lipid peroxidation in the cardiac tissue and significantly decreased GSH-PX level in the cardiac tissue indicating decreased antioxidative activity. This is in agreement with Roy [5] , who suggested that hyperglycemia directly induces apoptotic cell death in the myocardium in vivo. Hyperglycemia-induced myocardial apoptosis is mediated, at least in part, by activation of the cytochrome c-activated caspase-3 pathway, which may be triggered by ROS derived from high levels of glucose. [3] Identified that mitochondrial cytochrome c release and caspase-3 activation are associated with hyperglycemia-induced myocardial apoptosis. Hyperglycemia was also able to induce apoptotic cell death in neuron cells in vivo and in vitro and in endothelial cells in vitro by activating caspase-3, a downstream pivotal step to initiate apoptosis. The correlation between ROS production and mitochondrial cytochrome c release-mediated caspase-3 activation suggests that ROS derived from high levels of glucose may trigger the apoptotic process. Mitochondria are a major source of ROS production. Cellular sources of ROS generation within the heart include cardiac myocytes, endothelial cells, and neutrophils. ROS leads to cellular damage through several mechanisms (oxidation, interference with nitric oxide, and modulation of detrimental intracellular signaling pathways). Therefore, increased ROS causes cardiac dysfunction by direct damage to proteins and DNA, and by inducing apoptosis.

Our finding revealed that STZ-induced diabetic rats have significantly decreased heart rate. This is in agreement with that reported by Yu et al. [20] , who demonstrated that conscious chronic diabetic rats presented lower heart rate variability compared with control rats. In addition, our study showed that diabetes induced by STZ injection leads to significant increase in MSBP. This result was in agreement with that of Stern and Tuck [22] , who revealed that STZ-injected rats tend to be hyperphagic, thus consuming more sodium compared with their nondiabetic control group, and there is evidence that blood pressure in IDDM may be salt sensitive. Another possibility is that the blood pressure increase is due to changes in intravascular volume. Blood volume has been proposed to increase with diabetes because of hyperglycemia-induced osmotic fluid shifts. In addition, Rouyer et al. [23] revealed that diabetes-induced hypertension caused by oxidative stress, inflammation, increased sympathetic nervous activity, and upregulation of rennin angiotensin system, as well as metabolic abnormalities associated with DM, impairs the integrity of elastic fibers in the arterial wall, which translates into increased stiffness of the wall material. The accumulation of advanced glycation end-products is a major pathogenic mechanism contributing to arterial stiffening in DM [10] .

Our results showed that STZ injection leads to a significant increase in blood glucose, triglyceride, and total cholesterol level. This is in accordance with that reported by [24] , who stated that untreated type 1 diabetes shows hypertriglyceridemia. This is mainly due to decreased lipoprotein lipase (LPL) activity, as insulin is a potent activator of the LPL, which promotes the catabolism of triglyceride-rich lipoproteins and reduces as a consequence the plasma triglyceride levels. Insulin not only enhances LPL activity but also has a direct positive effect on the LPL gene in promoting LPL synthesis, whereas hypercholesterolemia in STZ-induced diabetic rats results from increased intestinal absorption and synthesis of cholesterol.

The coincidence between increased triglyceride and cholesterol levels and increased myocardial apoptosis can be explained in terms of hyperlipidemic states, an accumulation of excess lipid in nonadipose tissues leading to cell dysfunction and/or cell death, a phenomenon known as lipotoxicity [25] . Lipoapoptosis is also observed in the heart, in which it leads to the development of heart failure [26] . Studies show that the presence of unsaturated FAs, from endogenous or exogenous sources, promotes triglyceride accumulation, with channeling of excess saturated FA to triglyceride stores and consequent rescue of palmitate-induced apoptosis. There are several mechanisms through which unsaturated fatty acids (FAs) may promote triglyceride cellular accumulation. In one such mechanism the unsaturated FAs serve as ligands for transcription factors such as peroxisome proliferator-activated receptor, which are involved in lipid metabolism [27] . Accumulation of triglyceride in nonadipose tissues likely serves as a barometer of the lipid overload state in human disorders such as hyperlipidemia and lipodystrophies and in animal models such as the Zucker diabetic fatty rat. However, Laura et al. [28] suggeted that cellular triglyceride accumulation itself is not initially toxic. Rather, accumulation of excess FAs in triglyceride pools likely diverts these molecules from pathways that lead to cytotoxicity and may thus serve as a buffer against lipotoxicity. In pathologic states, lipotoxicity may occur over time, despite triglyceride accumulation, when either the cellular capacity for triglyceride storage has exceeded, or when triglyceride pools are hydrolyzed, resulting in increased cellular free FA levels. An additional mechanism through which FA-induced cell death occurs was proposed, stating that long-chain fatty acids can change the dynamics of plasma and mitochondrial membranes by altering phospholipid composition. Detachment of cytochrome c from the mitochondrial inner membrane is a necessary step for cytochrome c release and initiation of apoptosis. The saturated long-chain FA, palmitate, induces apoptosis in rat neonatal cardiomyocytes by diminishing the content of the mitochondrial anionic phospholipid, cardiolipin [29] .

In our experiment, administration of losartan caused significant decrease in blood glucose level. This is in agreement with the findings of Yang and Peng [12] , who demonstrated that the clinical use of angiotensin-converting enzyme inhibitors is associated with increased insulin sensitivity and that angiotensin-converting enzyme inhibitors modulate the early steps of insulin signaling. Another mechanism that explains the hypoglycemic effect of losartan has been reported by Chan et al. [30] , who stated that the treatment with angiotensin receptor blocker (ARB) decreased the plasma glucose level in STZ diabetic rats due to partial inhibition of the sodium-glucose cotransporters in the renal proximal tubular cells leading to decrease in the glucose reabsorbtion in the renal tubules, in addition to enhancing the glucose utilization in peripheral tissues and reduction of hepatic gluconeogenesis through noninsulin mediated mechanisms. Tikellis et al. [31] also reported that there was an increase in β-cell mass of the pancreas after losartan treatment, and this could be due to increased proliferation rates of the residual β-cells that escaped the STZ toxic effect, β-cell differentiation from exocrine progenitors (neogenesis), a reduction in β-cell apoptotic rates, or the combined action of all these three mechanisms.

Our results showed that after losartan administration there was decrease in myocardial apoptosis indexed by significant decrease in caspase-3 activity, decrease in myocardial lipid peroxidation indexed by significant decrease in MDA level, and increased antioxidant enzymes indexed by significant increase in GSH-PX level in cardiac tissue. These results were in agreement with Singh et al. [32] , who reported that ROS generation by exposure to high levels of glucose was found in the myoblast cells and indicated that suppression of angiotensin II can inhibit diabetic cardiomyopathy through inhibition of oxidative stress and myocardial cell death. Another study suggested that myocyte apoptosis occurs by upregulation of any component of the RAS from angiotensinogen to angiotensin receptor level [33] . AT2-linked death cascade requires tyrosine phosphatase that promotes ceramide synthesis. Elevation of intracellular ceramide proceeds to caspase-3 activation. It is noted that apoptosis is mainly mediated through activation of caspase-3 [34] . Moreover, angiotensin II stimulates the release of aldosterone that also stimulates cardiomyocyte apoptosis through caspase-3 activation [35] .

Furthermore, our results showed significantly increased heart rate, compared with the normal level, and significantly decreased MSBP, serum triglyceride, and serum cholesterol level in rats that received losartan. This was in agreement with the findings of Kyvelou and colleagues [36],[37] , who reported that administration of losartan potassium in diabetic rats resulted in decrease in triglycerides and total cholesterol, the lipid-lowering property of ARBs, as they suggested that some ARBs activate peroxisome proliferator-activated receptor-g, which is involved in the regulation of carbohydrate and lipid metabolism.

Our results revealed that administration of vitamin E caused significant decrease in blood glucose, triglycerides, and total cholesterol level. This is in accordance with the findings of Kuhad and Chopra [38] , who reported that vitamin E supplementation (100 IU/day) for 4 weeks helped preserve the body weight and lower plasma glucose concentrations, with no effect on plasma insulin concentrations in STZ-induced diabetic rats [39] . Attributed that to the maintenance of pancreatic islets in diabetes that is mediated by vitamin E, as the oxidative stress caused by hyperglycemia is accompanied by a substantial decrease in the number of insulin-secreting β-cells in the pancreas. In contrast to our results, Haidara et al. [40] showed that treatment with vitamin E at either 300 or 600 mg/kg for 4 weeks did not change blood glucose levels. This controversy could be explained by the difference in doses used and the duration of experiment. In our study, the hypolipidemic effect of vitamin E was in agreement with that reported by Tavares de Almeida et al. [41] , who showed that administration of α-tocopherol acetate once a week at a dose of 440 mg/kg body weight for 30 days resulted in decrease in total cholesterol and triglycerides to near-normal levels. The efficacy of vitamin E as regards reducing serum triglycerides and total cholesterol may be attributed to its protection of membrane-bound LPL against lipid peroxide [42] .

Our study revealed that vitamin E declined myocardial apoptosis with significant decrease in MDA and significant increase in GPX level in cardiac tissue. Furthermore, there was significant increase in heart rate, compared with the normal level, and a significant decrease in MSBP. This coincided with the findings of Bjelakovic et al. [43] , who reported that a vitamin E supplement of 200 IU/day can be effective in mild hypertensive patients in the long term, probably due to nitric oxide, and can improve their blood pressure status. Therefore, vitamin E supplement could be recommended to such patients. Boshtam et al. [44] stated that vitamin E supplements and other antioxidants may help reduce the risk of heart disease and other complications in people with diabetes. Research shows that antioxidants may help control blood sugar levels and lower cholesterol levels in people with type 2 diabetes. The study found that people with type 2 diabetes who took 400 IU of vitamin E daily had reduced risk for heart attack and of dying from heart disease. Recent evidence suggests that vitamin E may have potential benefits only in certain subgroups of the general population. A trial on high-dose vitamin E, for example, showed a marked reduction in coronary heart disease among people with type 2 diabetes who had a common genetic predisposition for greater oxidative stress [45] . Another study reported that vitamin E administration caused significant improvement in the cardiac complications in diabetic rats, along with significant decreases in 8-isoprotane level, and protein carbonyl content and SOD activity were observed after 6 weeks. Structural improvement was also observed as severe reduction of apoptosis in cardiomyocytes [46] .

In our study, combined treatment with vitamin E and losartan lead to more protection compared with each one alone. Thus, cardiac muscle apoptosis represents a novel therapeutic target for the control of diabetic cardiomyopathy in response to therapeutic agents such as losartan, which blocks angiotensin II receptors, and vitamin E, which acts through its antioxidant mechanism.

Acknowledgements

Nil.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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