iabetes mellitus (DM) is considered as one of the most important clinical risk factors involved in some disorders like nephropathy, retinopathy, neuropathy, and cardiovascular diseases, which its prevalence is predicted to be increased daily (1). DM prevalence in Iran is about 5-6%, and at the present, about 4 million Iranians are living with DM or prone to become diabetic (2). Although the most common treatment is insulin and drugs with hypoglycemic effects, but their side effects such as increasing body fat storages, body wasting at the injection site, and hypoglycemic shock are worth to mention; however, these drugs do not have many impact on long term debilitating morbidities. Regarding our daily increasing knowledge about the disease, it is really needed to seek for new medications with fewer side effects (3). Herbal medication usage is of great importance in traditional medicine and such plants have been used for the treatment of many diseases for a long time, whereas there are not still enough scientific evidences about the
Mohammadhassan Ghosian Moghaddam
Faculty of Medicine, Shahed University, Tehran, Iran.
effects of most of them (4). From the plants used for diabetes, olive (Olea europia) is of great importance.
Olive is a shrub from oleace species with permanent green leaves, which grows wild with about 5m or more height. Used parts of the tree include the fruit and leaves. This plant has been mentioned in traditional medicine as having the following effects; antihypertensive, anti-atherosclerotic, laxative, giving strength, effective on urinary tracts infection, headache treatment, and antioxidant (5). Also, there are some reports available about the effects of olive leaves in the treatment of malaria (6).
In this study, rats were treated with olive leaves to investigate its anti-diabetic effects. For this purpose, serum glucose level and lipid profile were measured during the study.
2. Materials and Methods
2.1. Collection, identification and preparation of the plant
Olea europia leaves were collected and identified by Karaj Agriculture Faculty taxonomists. Plant leaves were dried at 25°C under shade, then powdered with mechanical grinder. Olive leaves powder was mixed with rats food at a ratio of 6.25%, and the mixture was used as the food for rats under treatment (7).
This investigation was an experimental study, in which 30 adult male Wistar rats (weight range from 200 to 250 g) were used (Razi Institute). Rats were kept at animal room, and water and food were provided ad libitum.
In this study, only male Wistar rats with a serum glucose level lower than 250 mg/dl at normal conditions without fasting were used (8). Rats were randomly divided into 4 groups including control, control under treatment, diabetic and diabetic under treatment. Control and diabetic groups used only standard food, while control group under treatment and diabetic group under treatment used standard food in combination with the olive leaves powder. Treatment lasted for six weeks. Streptozocin at a dose of 60 mg/kg (single dose) dissolved in normal saline was used intraperitoneally to induce diabetes in rats (8). Diabetes signs including weight loss, polydipsia, and polyuria appeared after 5-7 days. More assurance was obtained after detecting glucosuria and serum glucose level of more than 250 mg/dl.
Blood samples were taken 3 times from rats, the first and second times were performed using capillary tubes from retroorbital capillary vessels, and the third time was performed from the heart. Samples were kept in microtubes at -70°C to measure glucose, cholesterol, triglyceride, HDL and LDL using available commercial kits (ZistChem Co., Tehran).
2.4. Statistical analysis
Data were expressed as positive and negative mean standard deviation. ANOVA test with repeated measures was used to compare each parameter in each group before and after the treatment. Also, one-way ANOVA and Tukey’s post-test were used to compare groups with each other. In addition, p
3.1. Serum glucose level
Serum glucose level significantly increased in diabetic rats as compared to control rats (p
3.2. Serum lipids
Serum triglyceride level was higher in diabetic group (p
Moreover, diabetes caused significant elevation of cholesterol and olive leaves consumption led to a significant decrease of cholesterol level in diabetic group under treatment as compared to those without treatment (p
Figure 1. The effect of long-term oral consumption of olive leaves on serum glucose level of control and diabetic rats. ** p
Figure 2. The effect of long-term oral consumption of olive leaves on serum triglyceride in control and diabetic rats. * P
Figure 3. The effect of long-term oral consumption of olive leaves on serum cholesterol in control and diabetic rats. ** p
Figure 4. The effect of long-term oral consumption of olive leaves on serum HDL cholesterol level in control and diabetic rats. $ p
Figure 5. The effect of long-term oral consumption of olive leaves on the LDL cholesterol level in diabetic and control rats. * p
The results of the present study indicated that oral consumption of olive leaves powder for 6 weeks in diabetic rats has hypoglycemic effect and causes beneficial changes of cholesterol, HDL and LDL levels.
Streptozocin-induced diabetes leads to some changes at metabolic enzymes level due to absence or very low levels of insulin, therefore causes hyperglycemia. Diabetes causes some inappropriate changes of plasma lipids and lipoproteins, in which some body tissues especially liver have a significant role with absorption of serum free fatty acids, then oxidation and metabolic changes of these fatty acids to other undesired molecules, cholesterol and phospholipids synthesis, and secretion of some proteins into the plasma (9). Furthermore, an increase in triglyceride and cholesterol levels in this study is in line with the existing evidence (10). Moreover, increased levels of serum glucose in diabetic rats can increase triglyceride, LDL, VLDL and indirectly decreases HDL (10).
The hypoglycemic effect of olive leaves powder is presumably due to an increase in glucose consumption by the peripheral tissues (11). Olive leaves powder causes glucose consumption maintenance, probably due to continuing the response to insulin and inhibition of intestinal absorption of glucose (12). Eidi et al results showed that olive leaves alcoholic extract leads to a decrease in serum glucose level and an increase in serum insulin level in diabetic rats, but no effect was seen on healthy animals (13).
Moreover, komeyli et al study indicated the hypoglycemic effect of aqueous extract of olive leaves in diabetic rats, blood cholesterol and triglyceride also decreased and HDL cholesterol increased, which is in accordance with our results (14). Although Jamae et al evaluated the effects of some other extracts of olive leaves on alloxan-induced diabetic rats, they concluded that serum glucose and cholesterol levels significantly decreased and this effect is due to antioxidant properties of olive leaves (15). In an investigation conducted by Alazavi et al on healthy and alloxan-induced diabetic rabbits for 16 weeks, hypoglycemic and antioxidant properties of olive leaves were approved and long-term administration of olive leaves led to a decrease in lipid peroxidation products like MDA (16).
In conclusion, long-term oral consumption of olive leaves by streptozocin-induced diabetic rats has hypoglycemic effect, decreases serum triglyceride, total cholesterol and LDL cholesterol and increases HDL level.
The present study was the results of a MD thesis project that was financially supported by Shahed University.