Lee Fung Ang

Potent α-glucosidase and α-amylase inhibitory activities of standardized 50% ethanolic extracts and sinensetin from Orthosiphon stamineus Benth as anti-diabetic mechanism

BackgroundIn the present study, we tested a 50% ethanolic extract of Orthosiphon stamineus plants and its isolated bioactive compound with respect to their α-glucosidase and α-amylase inhibitory activities.MethodsBioactive flavonoid sinensetin was isolated from 50% ethanolic extract of Orthosiphon stamineus. The structure of this pure compound was determined on the NMR data and the α-glucosidase and α-amylase inhibitory activities of isolated sinensetin and 50% ethanolic extract of Orthosiphon stamineus were evaluated.ResultsIn vitro studies of a 50% ethanolic extract of O. stamineus and the isolated sinensetin compound showed inhibitory activity on α-glucosidase (IC50: 4.63 and 0.66 mg/ml, respectively) and α-amylase (IC50: 36.70 mg/ml and 1.13 mg/ml, respectively). Inhibition of these enzymes provides a strong biochemical basis for the management of type 2 diabetes via the control of glucose absorption.ConclusionAlpha-glucosidase and α-amylase inhibition could the mechanisms through which the 50% ethanolic extract of O. stamineus and sinensetin exert their antidiabetic activity, indicating that it could have potential use in the management of non-insulin-dependent diabetes.

Orthosiphon stamineus Leaf Extract Protects Against Ethanol-Induced Gastropathy in Rats

Orthosiphon stamineus Benth., which is used as a gastroprotective herbal remedy in Malaysia, was assessed for its anti-ulcerogenic activity against ethanol-induced ulcers in rats. Fifty percent methanol was used to extract the oven-dried O. stamineus leaves. The extract was then lyophilized with a rotary evaporator and freeze-dried. Oral administration of O. stamineus methanolic extract (OSME) (125, 250, 500, and 1,000 mg/kg) was found to significantly decrease the ulcer index (P < .01, P < .001, P < .001, and P < .001, respectively). Histological study of a section of the rat stomach also showed a marked improvement in the gastric mucosal damage in groups receiving OSME. In order to further investigate the gastroprotective mechanism of OSME, mucus secretion and lipid peroxidation level were estimated in vitro and ex vivo. OSME exhibited dose-dependent stimulation of mucus secretion (r = 0.718, P < .001) and inhibition of lipid peroxidation in rat gastric mucosal homogenates (both in vitro [r = 0.819, P < .05] and ex vivo [r = 0.981, P < .05]). It was concluded that the gastroprotective mechanism of OSME was partly due to its ability to inhibit lipid peroxidation and stimulate gastric mucus secretion.

Antidiabetic Properties and Mechanism of Action of Orthosiphon stamineus Benth Bioactive Sub-fraction in Streptozotocin-induced Diabetic Rats

Orthosiphon stamineus is a popular folk medicine widely used to treat many diseases including diabetes. Previous studies have shown that the sub-fraction of chloroform extract was able to inhibit the rise of blood glucose levels in a glucose tolerance test. This study was carried out to evaluate the chronic effect and possible mechanism of action of the bioactive chloroform sub-fraction of O. stamineus using streptozotocin-induced diabetic rats and in vitro methods. Administration of the chloroform extract sub-fraction 2 (Cƒ2-b) at a dose of 1 g/kg twice daily on diabetic rats for 14 days showed a significant lowering (p < 0.05) of the final blood glucose level compared to the pretreatment level. However, there were no significant differences in the plasma insulin levels post-treatment compared to the pretreatment levels for all doses of Cƒ2-b. Conversely, Cƒ2-b at a concentration of 2 mg/mL significantly increased (p < 0.001) the glucose uptake by the rat diaphragm muscle. The increase in glucose uptake was also shown when the muscle was incubated in a solution containing 1 IU/mL of insulin or 1 mg/mL of metformin. Furthermore, the effect of this sub-fraction on glucose absorption in the everted rat jejunum showed that Cƒ2-b at concentrations of 0.5 mg/mL, 1 mg/mL and, 2 mg/mL significantly reduced the glucose absorption of the jejunum (p < 0.05-0.001). Similarly, the absorption of glucose was also inhibited by 1 mg/mL and 2 mg/mL of metformin (p < 0.001). These results suggest that the effect of Cƒ2-b may be due to extra-pancreatic mechanisms. There was no evidence that the plant extract stimulated the release of insulin in order to lower the blood glucose level.

Development of an Amperometric-Based Glucose Biosensor to Measure the Glucose Content of Fruit

An amperometric enzyme-electrode was introduced where glucose oxidase (GOD) was immobilized on chitosan membrane via crosslinking, and then fastened on a platinum working electrode. The immobilized enzyme showed relatively high retention activity. The activity of the immobilized enzyme was influenced by its loading, being suppressed when more than 0.6 mg enzyme was used in the immobilization. The biosensor showing the highest response to glucose utilized 0.21 ml/cm2 thick chitosan membrane. The optimum experimental conditions for the biosensors in analysing glucose dissolved in 0.1 M phosphate buffer (pH 6.0) were found to be 35°C and 0.6 V applied potential. The introduced biosensor reached a steady-state current at 60 s. The apparent Michaelis-Menten constant (KMapp) of the biosensor was 14.2350 mM, and its detection limit was 0.05 mM at s/n > 3, determined experimentally. The RSD of repeatability and reproducibility of the biosensor were 2.30% and 3.70%, respectively. The biosensor was showed good stability; it retained ~36% of initial activity after two months of investigation. The performance of the biosensors was evaluated by determining the glucose content in fruit homogenates. Their accuracy was compared to that of a commercial glucose assay kit. There was no significance different between two methods, indicating the introduced biosensor is reliable.

Anti-inflammatory and Analgesic Effects of Elephantopus tomentosus Ethanolic Extract

Elephantopus tomentosus is widely used in Asia, especially in Malaysia, for the treatment of pain and inflammation. In the present study, the analgesic and anti-inflammatory effects of a 95% ethanol extract of E. tomentosus were investigated in different experimental models. In the anti-inflammation study, 1000 mg/kg of extract significantly reduced carrageenan-induced hind paw edema (p < 0.05) and inhibited abdominal permeability compared with control (p < 0.01). The analgesic activity was assayed in several experimental models in mice: (1) hot plate, (2) tail flick, (3) writhing test; and rats: carrageenan-induced hyperalgesia pain threshold test. However, at the doses tested, no significant activity was found in the hot plate test and the tail flick test. E. tomentosus ethanol extract at 1000 mg/kg significantly (p < 0.05) increased hyperalgesia pain threshold and inhibited writhing activity. The results suggest that E. tomentosus ethanol extract at 1000 mg/kg dose is effective in anti-inflammatory and non-steroidal anti-inflammatory drug type anti-nociception activities.

Study on Different Molecular Weights of Chitosan as an Immobilization Matrix for a Glucose Biosensor

Two chitosan samples (medium molecular weight (MMCHI) and low molecular weight (LMCHI)) were investigated as an enzyme immobilization matrix for the fabrication of a glucose biosensor. Chitosan membranes prepared from acetic acid were flexible, transparent, smooth and quick-drying. The FTIR spectra showed the existence of intermolecular interactions between chitosan and glucose oxidase (GOD). Higher catalytic activities were observed on for GOD-MMCHI than GOD-LMCHI and for those crosslinked with glutaraldehyde than using the adsorption technique. Enzyme loading greater than 0.6 mg decreased the activity. Under optimum conditions (pH 6.0, 35°C and applied potential of 0.6 V) response times of 85 s and 65 s were observed for medium molecular weight chitosan glucose biosensor (GOD-MMCHI/PT) and low molecular weight chitosan glucose biosensor (GOD-LMCHI/PT), respectively. The apparent Michaelis-Menten constant () was found to be 12.737 mM for GOD-MMCHI/PT and 17.692 mM for GOD-LMCHI/PT. This indicated that GOD-MMCHI/PT had greater affinity for the enzyme. Moreover, GOD-MMCHI/PT showed higher sensitivity (52.3666 nA/mM glucose) when compared with GOD-LMCHI/PT (9.8579 nA/mM glucose) at S/N>3. Better repeatability and reproducibility were achieved with GOD-MMCHI/PT than GOD-LMCHI/PT regarding glucose measurement. GOD-MMCHI/PT was found to give the highest enzymatic activity among the electrodes under investigation. The extent of interference encountered by GOD-MMCHI/PT and GOD-LMCHI/PT was not significantly different. Although the Nafion coated biosensor significantly reduced the signal due to the interferents under study, it also significantly reduced the response to glucose. The performance of the biosensors in the determination of glucose in rat serum was evaluated. Comparatively better accuracy and recovery results were obtained for GOD-MMCHI/PT. Hence, GOD-MMCHI/PT showed a better performance when compared with GOD-LMCHI/PT. In conclusion, chitosan membranes shave the potential to be a suitable matrix for the development of glucose biosensors.

HPLC Method for Simultaneous Quantitative Detection of Quercetin and Curcuminoids in Traditional Chinese Medicines

Objectives: Quercetin and curcuminoids are important bioactive compounds found in many herbs. Previously reported high performance liquid chromatography ultraviolet (HPLC-UV) methods for the detection of quercetin and curcuminoids have several disadvantages, including unsatisfactory separation times and lack of validation according the standard guidelines of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. Methods: A rapid, specific, reversed phase, HPLC-UV method with an isocratic elution of acetonitrile and 2% v/v acetic acid (40% : 60% v/v) (pH 2.6) at a flow rate of 1.3 mL/minutes, a column temperature of 35°C, and ultraviolet (UV) detection at 370 nm was developed. The method was validated and applied to the quantification of different types of market available Chinese medicine extracts, pills and tablets. Results: The method allowed simultaneous determination of quercetin, bisdemethoxycurcumin, demethoxycurcumin and curcumin in the concentration ranges of 0.00488 ─ 200 μg/mL, 0.625 ─ 320 μg/mL, 0.07813 ─ 320 μg/mL and 0.03906 ─ 320 μg/mL, respectively. The limits of detection and quantification, respectively, were 0.00488 and 0.03906 μg/mL for quercetin, 0.62500 and 2.50000 μg/mL for bisdemethoxycurcumin, 0.07813 and 0.31250 μg/mL for demethoxycurcumin, and 0.03906 and 0.07813 μg/mL for curcumin. The percent relative intra day standard deviation (% RSD) values were 0.432 ─ 0.806 μg/mL, 0.576 ─ 0.723 μg/mL, 0.635 ─ 0.752 μg/mL and 0.655 ─ 0.732 μg/mL for quercetin, bisdemethoxycurcumin, demethoxycurcumin and curcumin, respectively, and those for intra day precision were 0.323 ─ 0.968 μg/mL, 0.805 ─ 0.854 μg/mL, 0.078 ─ 0.844 μg/mL and 0.275 ─ 0.829 μg/mL, respectively. The intra day accuracies were 99.589% ─ 100.821%, 98.588% ─ 101.084%, 9.289% ─ 100.88%, and 98.292% ─ 101.022% for quercetin, bisdemethoxycurcumin, demethoxycurcumin and curcumin, respectively, and the inter day accuracy were 99.665% ─ 103.06%, 97.669% ─ 103.513%, 99.569% ─ 103.617%, and 97.929% ─ 103.606%, respectively. Conclusion: The method was found to be simple, accurate and precise and is recommended for routine quality control analysis of commercial Chinese medicine products containing the flour flavonoids as their principle components in the extracts.

Antioxidant and Toxicity Studies of 50% Methanolic Extract of Orthosiphon stamineus Benth

The present study evaluated the antioxidant activity and potential toxicity of 50% methanolic extract of Orthosiphon stamineus (Lamiaceae) leaves (MEOS) after acute and subchronic administration in rats. Superoxide radical scavenging, hydroxyl radical scavenging, and ferrous ion chelating methods were used to evaluate the antioxidant properties of the extract. In acute toxicity study, single dose of MEOS, 5000 mg/kg, was administered to rats by oral gavage, and the treated rats were monitored for 14 days. While in the subchronic toxicity study, MEOS was administered orally, at doses of 1250, 2500, and 5000 mg/kg/day for 28 days. From the results, MEOS showed good superoxide radical scavenging, hydroxyl radical scavenging, ferrous ion chelating, and antilipid peroxidation activities. There was no mortality detected or any signs of toxicity in acute and subchronic toxicity studies. Furthermore, there was no significant difference in bodyweight, relative organ weight, and haematological and biochemical parameters between both male and female treated rats in any doses tested. No abnormality of internal organs was observed between treatment and control groups. The oral lethal dose determined was more than 5000 mg/kg and the no-observed-adverse-effect level (NOAEL) of MEOS for both male and female rats is considered to be 5000 mg/kg per day.

Safety assessment of standardised methanol extract of Cinnamomum burmannii

The present study aims to evaluate the safety of methanol extract of Cinnamomum burmannii (MECB) by acute 14-day (single dose) and sub-chronic 28-day (repeated doses) oral administration to Sprague-Dawley rats. Our results showed that no toxicity was found in either acute or sub-chronic toxicity studies. MECB (containing 0.07% and 0.20% (w/w) of coumarin and trans-cinnamaldehyde, respectively), which was given orally at doses of 500, 1000 and 2000 mg/kg caused neither visible signs of toxicity nor mortality. No significant differences were observed in general condition, growth, organ weight, hematological parameters, biochemical values, or the gross and microscopic appearance of the organs from the treatment groups as compared to the control group. In conclusion, MECB did not cause any mortality nor did it cause any abnormalities in the necropsy and histopathology findings of treated rats. The LD50 for the MECB was found to be more than 2000 mg/kg. No adverse effects were observed in the treated rats at all the doses tested. The no-observed-adverse-effect level (NOAEL) for the 28-day study was determined to be 2000 mg/kg body weight/day.

Evaluation of α-Glucosidase Inhibitory Effect of 50% Ethanolic Standardized Extract of Orthosiphon stamineus Benth in Normal and Streptozotocin-Induced Diabetic Rats

In the present study, a 50% ethanolic extract of Orthosiphon stamineus was tested for its α-glucosidase inhibitory activity. In vivo assays of the extract (containing 1.02%, 3.76%, and 3.03% of 3′hydroxy-5,6,7,4′-tetramethoxyflavone, sinensetin, and eupatorin, resp.) showed that it possessed an inhibitory activity against α-glucosidase in normal rats loaded with starch and sucrose. The results showed that 1000 mg/kg of the 50% ethanolic extract of O. stamineus significantly (P < 0.05) decreased the plasma glucose levels of the experimental animals in a manner resembling the effect of acarbose. In streptozotocin-induced diabetic rats, only the group treated with 1000 mg/kg of the extract showed significantly (P < 0.05) lower plasma glucose levels after starch loading. Hence, α-glucosidase inhibition might be one of the mechanisms by which O. stamineus extract exerts its antidiabetic effect. Furthermore, our findings indicated that the 50% ethanolic extract of O. stamineus can be considered as a potential agent for the management of diabetes mellitus.