Biomed Res Int. 2015;2015:214918. doi: 10.1155/2015/214918.
Hypoglycaemic and antidiabetic effect of Pleurotus sajor-caju aqueous extract in normal and streptozotocin-induced diabetic rats.
Sze Han Ng1, Mohd Shazwan Mohd Zain1, Fatariah Zakaria1, Wan Rosli Wan Ishak1,*, Wan Amir Nizam Wan Ahmad2
1Nutrition Program, School of Health Sciences, Universiti Sains Malaysia Health Campus, 16150 Kubang Kerian, Kelantan, Malaysia
2Biomedicine Program, School of Health Sciences, Universiti Sains Malaysia Health Campus, 16150 Kubang Kerian, Kelantan, Malaysia
Objectives: To study the hypoglycaemic and antidiabetic effects of Pleurotus sajor-caju (PSC) aqueous extract in normal and diabetic rats.
Methods: A single dose of PSC extract of (500, 750 or 1000 mg/kg) was given to experimental rats to investigate the effects on blood glucose (BG) and oral glucose tolerance test (OGTT). The effective dose of PSC extract was then repeatedly administrated daily for 21 days (subacute study) in diabetic rats to examine its antidiabetic effects in term of fasting BG, body weight, urine sugar, HbA1c and lipid profiles.
Results: After 6 hours administration in BG study, the dose of 750 mg/kg showed the most significant BG reduction (23.5%) in normal rats. In OGTT study, the same dose produced a maximum BG fall of 41.3% in normal rats and 36.5% in diabetic rats after 3 hours glucose administration. In subacute study, treated diabetic rats showed significant improvement in terms of fasting BG, body weight, urine sugar, HbA1c and lipid profiles as compared to control diabetic rats.
Conclusion: The study evidenced scientifically the beneficial use of PSC as an alternative medicine in diabetes management.
Diabetes is a serious chronic metabolic disorder characterized by high BG levels (ADA, 2005). According to WHO (2008), there are 171 million people worldwide suffering from diabetes in 2000 and is predicted to be double (366 million) by 2030. It is the major cause of morbidity and mortality worldwide as it causes health complications and affects quality of life (Kamarul Imran et al., 2010).
WHO revealed that diets with high dietary fibre (DF) should be recommended to control BG response and reduce risk of developing diabetes (Adam-Perrot et al., 2006). DF is defined as an indigestible portion of plant foods which consists of the structural and storage polysaccharides and lignin in plants (Marlett et al., 2002). It is of late gaining increasing importance in view of its close relationship with reduction of postprandial glucose response and control of diabetes (Iwona, 2009). Studies have repeatedly shown that β-glucans, a type of soluble DF, also give interesting health-promoting properties, such as enhancement of immune function as well as reduction of blood cholesterol and BG levels (Maier et al., 2000; Dongowski, 2003).
Figure 1: Soxhlet apparatus (hot continuous extraction method)
Many oral hypoglycemic drugs, such as biguanides, α-glucosidase inhibitors and sulphonylurea are utilised for the diabetes treatment. These synthetic drugs are not free from harmful side effects such as hepatic toxicity, weight increase, abdomen enlargement, and gastrointestinal discomfort (Li et al., 2004; Lee et al., 2012). Therefore, development of safe and effective oral hypoglycaemic agents from medicinal plants to manage diabetes without side effects is of great interest to ethno-botanical community. In this context, we study PSC which is one of the prominent edible oyster mushroom.
PSC could be naturally found in tropical and subtropical rainforests, as well as can be artificially cultivated in a simple and cheap way. Previously, attention has been focused mainly on its immune modulating, hypotensive, hypocholesterolemic and antitumor properties (Shah et al., 2007). Nevertheless, lack of information is available on its anti-diabetic properties and so it is necessary to find out.
How to obtain PSC aqueous extract? Firstly, Biodehydration drying process of fresh PSC (the secret trade drying process done by Anjaad industry, Malacca, Malaysia) was applied to form PSC powder (yield: 10%w/w). Next, it undergoes hot continuous extraction method (20g of PSC powder was extracted with 250 mL of distilled water) by using Soxhlet apparatus (Figure 1). After the extract was cooled down, it was put into screw cap bottle and freeze-dried to obtain PSC aqueous extract (yield: 30% w/w). Before administered to experimental rats, freeze-dried PSC aqueous extract was diluted with distilled water. The progress of obtaining the PSC aqueous extract was summarized in Figure 2.
Figure 2: The progress in obtaining PSC aqueous extract from fresh bodies of PSC.
A= Fresh fruiting bodies of PSC obtained from local wet market;
B= PSC powder after Bio-dehydration drying technique;
C= Freeze-dried PSC aqueous extract after hot continuous extraction method and freeze-dried at -80oC;
D= Finalised PSC extract after diluted with distilled water
The obtained PSC aqueous extract at dose of 500, 750 and 1000 mg/kg were then given to STZ-induced Sprague-Dawley rats to investigate the effect of PSC aqueous extract by comparing to untreated diabetic rats. Immediate effect (OGTT) and subacute effects (fasting BG, body weight, urine sugar, lipid profiles and HbA1c) was analysed. The effects were evaluated along with the standard drug metformin.
In OGTT study, diabetic rats treated with 750 and 1000 mg/kg of the PSC extract significantly (P < 0.05) exhibited the lower BG level peak compared to vehicle control group and produced no significant difference compared to metformin group (Table 1). After 3 hours of glucose loading, the dose of 750 mg/kg exhibited a maximum fall of 36.5%. This indicated that PSC extract has favourable effects in bringing down the complications such as glucose intolerance and prevent severity of diabetes.
Table 1: Effects of PSC aqueous extract on OGTT in diabetic rats (mean ± SD)
In subacute study, the parameters were measured before and after 7, 14 and 21 days of treatment. Generally, the PSC extract and metformin exhibited gradual FBG reduction in diabetic rats. In the aspect of body weight, there was significant difference (P < 0.05) detected between control and PSC extract-treated group after 21 days of treatment. The results indicated that 21-day treatment of PSC extract maintained body weight of rats which was dropped initially. In addition, PSC extract-treated diabetic group showed lower urine sugar (50% reduction after 14 days of treatment) compared to control diabetic groups. Hence, improvement of these diabetes characteristics indirectly justified the antidiabetic activity of the PSC extract.
After blood was withdrawn by means of cardiac puncture, lipid profiles (total cholesterol, HDL cholesterol, LDL cholesterol and triglyceride) of diabetic rats administrated with PSC extract were reported slight improvement in comparing to control diabetic rats. So, the PSC extract could possibly be the fundamental agent in overcoming complications caused by diabetes. In term of HbA1c, diabetic rats treated with PSC extract documented lower reading with 6.5% reduction observed comparing to control diabetic rats.
Nutritional investigation of PSC reveals the presence of high content of DF (35.6%) including β-glucan (3.57%) (Wan Rosli and Aishah, 2012). They have scientifically proven for its synergistic effects and protective effects against various diseases such as heart disease, stroke and diabetes as they can reduce blood cholesterol and BG levels (Maier et al., 2000). In details, β-glucan is a soluble DF which can form viscous solution, thus resistant to stomach digestive enzyme and delays glucose absorption in intestine as well as gastric emptying rate (Chen and Raymond, 2008). Therefore, it may slow down the rise in BG level after administration of PSC aqueous extract, resulting in controlling of diabetes.
The importance of this study:
- Our data suggest that treatment with PSC aqueous extract can reduce postprandial BG level as well as improve measured parameters such as fasting BG, body weight, urine sugar, lipid profiles and HbA1c.
- These results evidently express the excellent benefits of PSC aqueous extract in controlling diabetes, preventing risk of developing diabetes and the complications caused by diabetes.
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Acknowledgement: The authors acknowledge Research Universiti Grant (Grant no: 1001/PPSK/813057) for giving financial assistance. Our appreciations are also extended to the staff members from Animal Research and Service Centre and nutrition lab in Universiti Sains Malaysia.
| Wan Rosli Wan Ishak, Ph.D.
Nutrition Program, School of Health Sciences,
Universiti Sains Malaysia Health Campus,
16150, Kubang Kerian,