الفهرس 
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Abstract
During the past two decades, dietary consumption of fructose has increased several folds above the amount present in natural foods, because of the use of high fructose corn sweeteners and sucrose in manufactured food. This excessive intake of fructose has been proposed in the etiology of metabolic syndrome whose prevalence is dramatically increasing throughout the world in Western and developing countries. Fructose, unlike glucose, does not directly stimulate insulin secretion. Even though acutely administered fructose does not increase blood insulin concentrations, chronic exposure can indirectly create compensatory hyperinsulinemia associated with insulin resistance.
Several expert groups have published criteria for the diagnosis of metabolic syndrome. These criteria include central components: hyperglycemia, hyperinsulinemia and insulin resistance, dyslipidemia (manifested essentially by elevated triglycerides (TG) and increased low-density lipoprotein cholesterol (LDL-C)), hypertension, and obesity. However, according to the International Diabetes Federation (IDF) and the American Heart Association (AHA) obesity is not considered a mandatory requirement for the diagnosis of metabolic syndrome (MetS).
Important research questions about the metabolic syndrome remain to be addressed including whether the metabolic syndrome is a separate entity that constitutes a viable registrable indication for certain drug therapies. An example of such therapy is the class of so-called “dual peroxisome proliferator-activated receptor (PPAR) agonists”. Simultaneous activation of PPAR-α and PPAR-γ could be a potential therapeutic option to attenuate hyperlipidemia and hyperglycemia in metabolic syndrome. However, previous studies have demonstrated that concomitant activation of PPAR-α and PPAR-γ by using PPAR-α/γ dual agonists such as tesaglitazar and muraglitazar is associated with cardiovascular risks and carcinogenicity due, most probably, to the imbalanced supra-therapeutic activation of PPAR-α and PPAR-γ. Therefore, the aim of the present study was to evaluate the effects of moderate doses of fenofibrate, a commonly used PPAR-α agonist, and pioglitazone, a commonly used PPAR-γ agonist, given alone or in combination on serum and liver tissue biochemical parameters in high fructose-fed rats.
Fenofibrate is a drug of the fibrate class. It is mainly used to reduce elevated serum cholesterol levels in patients at risk of cardiovascular disease. Like other fibrates, it reduces elevated low-density lipoprotein cholesterol (LDL-C) and very low density lipoprotein (VLDL) levels, as well as increases high-density lipoprotein cholesterol (HDL-C) levels and reduces elevated triglyceride levels. Acting as a PPAR-α agonist, fenofibrate activates lipoprotein lipase and reduces apolipoprotein C-III (Apo C-III), which increases lipolysis and elimination of triglyceride-rich particles from plasma. Activation of PPAR-α increases HDL-C containing apolipoprotein A-I (Apo A-I) and A-II (Apo A-II), reduces VLDL and LDL-C containing apolipoprotein B (Apo B).
Pioglitazone is a member of the insulin-sensitizing TZD class and acts as a selective agonist for the nuclear perixosome proliferator-activated receptors of the gamma subfamily (PPAR-γ) which are expressed mainly in fat cells, but also in muscle and other cells. It is an oral antihyperglycemic agent for the treatment of type 2 diabetes. The underlying mechanisms of TZD-mediated improvement of insulin resistance (IR) are not completely understood, but the induction of fat cell differentiation from large insulin resistant adipocytes to smaller, more insulin-sensitive cells seems to be of a particular importance. This differentiation leads to a reduced release of free fatty acids from these cells and diminishes circulating levels of IR-mediating adipocytokines such as TNF-α, leptin and resistin. These changes improve IR in the liver and skeletal muscle.
The present study was performed on 30 adult male albino rats 3-4 month old, weighing between 120-150 g. Insulin resistance was induced, in this study, by feeding rats with a diet containing 60% fructose (HFD) for 10 weeks. The high fructose diet was prepared by adding 600g fructose to 400g normal rat chow. Control rats were fed normal rat chow without fructose.
Animals were divided into 5 groups with 6 rats each:
- group I: (Control group): Rats of this group were allowed to grow on a normal rat chow
balanced diet.
The rest of the rats were fed on the HFD.
-group II: (Fr group, high fructose-fed rats): Rats of this group received the vehicle
(3ml/kg carboxymethyl cellulose (CMC) 0.5% suspension) orally daily starting at
the end of the 4th week and continued for the last 6 weeks of the experimental period.
-group III: (Fr+FF group): the high fructose-fed rats of this group were treated daily orally
with fenofibrate at a dose of 100 mg/kg/day starting at the end of the 4th week and
continued for the last 6 weeks of the experimental period.
-group IV: (Fr+PG group): the high fructose-fed rats of this group were treated daily orally
with pioglitazone at a dose of 15mg/kg/day starting at the end of the 4th week and
continued for the last 6 weeks of the experimental period.
-group V: (Fr+ (FF+PG) group): the high fructose-fed rats of this group were treated daily
orally with both fenofibrate and pioglitazone at the same aforementioned doses
for the last 6 weeks of the experimental period.
Before the beginning of drug (or vehicle) treatment, a blood sample was obtained from the tail vein of each rat for determination of the blood glucose level. At the end of the experimental period, rats were anesthetized and a midline incision was made and blood was collected from the descending aorta. Serum was separated and stored at -20 ºC for determination of:
- Serum glucose level.
- Serum insulin level.
- Lipid profile;
• Serum triglycerides level.
• Serum total cholesterol level.
• Serum LDL-C level.
• Serum HDL-C level.
- Serum uric acid level.
- Serum alanine transaminase (ALT) activity.
Immediately after collection of blood, livers were excised, washed with ice-cold saline blotted dry, weighed and preserved at -80 ºC for the assessment of hepatic tissue parameters:
- Tumor necrosis factor alpha (TNF-α) level.
- Reduced glutathione (GSH) level.
- Superoxide dismutase (SOD) activity.
- Malondialdehyde (MDA) level.
- Nitric oxide (NO) level.
The results of the present study demonstrated that feeding of rats with a high fructose (60%) diet for 10 weeks induced features of metabolic syndrome including hyperuricemia, insulin resistance (manifested by increased serum glucose and insulin levels, a higher HOMA-IR score and a lower QUICKI score), dyslipidemia (manifested by elevated serum triglyceride, total cholesterol and LDL-C levels) and oxidative stress (manifested by reduced hepatic tissue GSH level and SOD activity with elevated MDA level). Also, our results showed that treatment of high fructose-fed rats with fenofibrate, pioglitazone or simultaneously with both drugs resulted in normalization of serum glucose, uric acid and triglyceride levels and ALT activity and hepatic tissue TNF-α, nitrite and MDA levels. Also, treatment with fenofibrate alone or combined with pioglitazone caused attenuation of the changes in serum insulin, HOMA-IR and QUICKI scores and normalization of serum total cholesterol and LDL-C and hepatic tissue GSH level and SOD activity. The results also showed that treatment with pioglitazone alone resulted in elevation of serum HDL-C level and attenuation of hepatic tissue SOD activity, but had no effect on the induced changes in hepatic tissue GSH.
Interestingly, our results showed that treatment of high fructose-fed rats with fenofibrate combined with pioglitazone was more effective than treatment with either drug alone in normalizing serum insulin levels, more effective than treatment with fenofibrate alone in elevating serum HDL-C level and restoring insulin sensitivity, and more effective than treatment with pioglitazone alone in reducing the elevated serum uric acid and total cholesterol levels and improving the decreased hepatic tissue GSH level and SOD activity in high fructose-fed rats. Thus, the present study provides an evidence for a potentiating interaction by the combination therapy with fenofibrate and pioglitazone in ameliorating high fructose-induced metabolic syndrome manifestations in rats.
In conclusion, rats fed with the high fructose (60%) diet for 10 weeks, in the present study, developed several complications observed in human metabolic syndrome including hyperglycemia, hyperinsulinemia with evident insulin resistance, hyperuricemia, hypertriglyceridemia, hypercholesterolemia, increased serum ALT activity and increased hepatic tissue TNF-α, MDA and NO levels in association with decreased hepatic tissue GSH content and SOD activity. Oral treatment of rats with fenofibrate (100mg/kg/day) and/or pioglitazone (15mg/kg/day) from week 5 to week 10 significantly attenuated these high fructose diet-induced serum and hepatic tissue biochemical changes. However, the intensity of improvement of most of these changes was variable depending on the treatment given and
the simultaneous treatment with both fenofibrate and pioglitazone exhibited a higher anti-metabolic syndrome efficacy than treatment with either drug alone. Thus, acting on the two main PPAR subfamilies, a combination of fenofibrate, a PPAR-α agonist, and pioglitazone, a PPAR-γ agonist, may provide beneficial potentiating effects in modulating the metabolic disturbances associated with the fructose rich diet-induced metabolic syndrome.