Alpha-glucosidase inhibitory aspect and anti-oxidant activity of cinnamon extract niosomes for diabetic treatment

Diabetes has been known as one of four major non-communicable diseases, cardiovascular disease, cancer, chronic respiratory disease and diabetes, which globally caused mortalities in 2012. About 90% of patients are type 2 diabetes that so-called insulin resistant diabetes, which was found to be the major cause of mortalities. Insulin resistance leads to the rising of blood glucose level that can cause seriously damage to the body over time and end up with multiple health problems such as stroke, kidney disease and eye damage causing loss of vision. Carbohydrates are the major energy source for human, which are broken down enzymatically to monosaccharides (glucose, fructose) by alpha-glucosidase, located at brush border of small intestine before being absorbed. The most considering approach in lowering blood glucose level is to inhibit alpha-glucosidase for delaying glucose absorption, resulting in postprandial glucose reduction. Moreover, the roles of oxidative stress in the pathogenesis of diabetes have been reported. It could damage enzymes, cellular machinery and also increase insulin resistance. Cinnamon is one of the traditional folk herbs used in Korea, China and Russia for diabetes mellitus, which has reported about the effect of cinnamon extract in decreasing blood glucose level in human Consequently, the main objectives of this research is to select the most effective extraction method and solvent that could provide the massive bioactive compounds. These cinnamon bioactive compounds could contribute to the inhibition of alpha-glucosidase activity and free radical scavenging. Moreover, this research also demonstrates the enhancing of bioavailability and prolonging the active compounds circulation by preparing and utilizing the niosomal hydrogel. The antioxidant activity of cinnamon extracts was evaluated using DPPH (diphenyl-1-picrythydrazyl) method and Total phenolic content (TPC) assay. Alpha-glucosidase inhibitory activity was assayed and estimated by using p-nitrophenyl glucopyranoside (pNPG) as a substrate. To select the most appropriate extraction method, the powder of cinnamon bark was prepared by carrying on shaking and extracting with Soxhlet method for 24 hours at temperatures of 100°C and 150°C, respectively. The results revealed that the shaking method gave the higher radical scavenging activity against DPPH, total phenolic content and also alpha-glucosidase inhibitory activity, presented in the form of IC50 value. These could be seen as the value of 4.07 ± 0.02 µg/mL, 95.61 ± 2.24 mg GAE / g extract and IC50 of 57.33 ± 0.40 µg/mL, respectively. Conversely, the Soxhlet method, done at 100 and 150°C, showed expressed lesser and the least values of in bioactivity, respectively. It can be seen that degradation or deformation of the bioactive compounds could be caused by the heat applied in the Soxhlet method. As a result, the shaking method was then selected for the extraction process, with the suitable solvent and shaking time.To determine the potential solvent, 95% ethanol (EtOH), methanol (MeOH), Ethyl acetate (EtOAc) and Hexane (HEX) were chosen. Each solvent was conducted in shaking periods of 24, 36 and 48 h. HEX, non-polar solvent, showed the least extraction yield and bioactivities. Among various extracting solvents, shaking cinnamon bark powder for 36 h. with EtOH was found to be the most suitable extraction method by providing high extraction yield of 14.4 ± 0.66 %, high antioxidant activity (IC50) of 2.68 ± 0.10 µg/mL, high total phenolic content of 108.53 ± 0.00 mg GAE/ g extract, and high α-glucosidase inhibitory activity of 34.82 ± 0.25 µg/mL. For enhancing the bioavailability and solubility, the niosomal encapsulation was used in selecting the appropriate composition of noisome by considering size, size distribution and encapsulation efficiency of noisome. Span 60 (sorbitan mono stearate) was used as surfactant for self-assembly of nanovesicles, while cholesterol was used in improving vesicles stability. Niosomes were prepared by sonication method. It was found that 2.0:1.0 molar ratio of Span 60 and Cholesterol expressed the particle size of 182.87 ± 0.93 nm, size distribution (PI) of 0.63 ± 0.08 and encapsulation efficiency of 70.20 ± 2.66 %. Furthermore, the extract-loaded noisomes were formulated with the hydrogel, composed of xanthan gum and citric acid, to obtain the niosomal hydrogel. The high gel fraction of 81.11 ± 0.32 % and swelling ratio of 640.76 %, was prepared with 1.5 % xanthan gum and 2.0 % citric acid. These gels were used in investigating in vitro release profile, where the results revealed that the niosomal hydrogel could prolong the releasing of the extract up to 40 min, in comparing to the extract loaded niosome. In summary, shaking with EtOH is suitable for cinnamon extraction as it was safe and provided the highest values of anti-oxidant activity, total phenolic content and alpha-glucosidase inhibitory activity. The molar ratio of Span 60 and Cholesterol at 2.0:1.0 gave the smallest size and the highest encapsulation efficiency. Besides, xanthan-based hydrogel was then used for preparing the niosomal loaded hydrogel. The extract loaded niosomal hydrogel could prolong the releasing of the extracts much longer than that of the extract loaded noisome alone. This study of the alpha-glucosidase inhibitory activity, anti-oxidant activity and in vitro releasing show the potential to reduce blood glucose levels; however, there is need to elucidate the in vivo mechanisms for an effort to expand treatment options.