Detection of Aspartic Proteinase Activities Using Gel Zymography

Gel zymography is a two-stage process where the proteins from the test sample are first separated by electrophoresis followed by the detection of the activity of hydrolytic enzymes. Many zymography procedures use sodium dodecyl sulfate (SDS) polyacrylamide gels copolymerized with an appropriate substrate. The procedure described here uses native polyacrylamide gel electrophoresis (PAGE) in the absence of both SDS and substrate. In order to visualize aspartic proteinase activity, the gel is impregnated in bovine hemoglobin at pH 3.0 for 15 min after the electrophoresis procedure. Subsequently, the gel is incubated in a humid container in the absence of hemoglobin for 1 h at 37 °C. At the end, the gel is stained with amido black and destained. Clear areas against a dark background corresponding to aspartic proteinase activities can be detected.

Bioassay-guided fractionation and identification of α-amylase inhibitors from Syzygium cumini leaves

CONTEXT

Pancreatic α-amylase and α-glucosidase inhibitors serve as important strategies in the management of blood glucose. Even though Syzygium cumini (L.) Skeels (Myrtaceae) (SC) is used extensively to treat diabetes; scientific evidence on antidiabetic effects of SC leaves is scarce.

OBJECTIVE

SC leaf extract was investigated for α-amylase inhibitory effect and continued with isolation and identification of α-amylase inhibitors.

MATERIALS AND METHODS

Bioassay-guided fractionation was conducted using in vitro α-amylase inhibitory assay (with 20-1000 μg/mL test material) to isolate the inhibitory compounds from ethyl acetate extract of SC leaves. Structures of the isolated inhibitory compounds were elucidated using 1H NMR and 13C NMR spectroscopic analysis and direct TLC and HPLC comparison with authentic samples. Study period was from October 2013 to October 2015.

RESULTS

An active fraction obtained with chromatographic separation of the extract inhibited porcine pancreatic α-amylase with an IC50 of 39.9 μg/mL. Furthermore, it showed a strong inhibition on α-glucosidase with an IC50 of 28.2 μg/mL. The active fraction was determined to be a 3:1 mixture of ursolic acid and oleanolic acid. Pure ursolic acid and oleanolic acid showed IC50 values of 6.7 and 57.4 μg/mL, respectively, against α-amylase and 3.1 and 44.1 μg/mL respectively, against α-glucosidase.

DISCUSSION AND CONCLUSIONS

The present study revealed strong α-amylase and α-glucosidase inhibitory effects of ursolic acid and oleanolic acid isolated from SC leaves for the first time validating the use of SC leaves in antidiabetic therapy.

α-glucosidase and glycation inhibitory effects of costus speciosus leaves

BACKGROUND

Hyperglycaemia is a salient feature of poorly controlled diabetes mellitus. Rate of protein glycation is increased with hyperglycaemia leading to long term complications of diabetes. One approach of controlling blood glucose in diabetes targets at reducing the postprandial spikes of blood glucose. The objectives of this study were to assess the in vitro inhibitory effects of Costus speciosus (COS) leaves on α-amylase and α-glucosidase activities, fructosamine formation, protein glycation and glycation-induced protein cross-linking.

METHODS

Methanol extracts of COS leaves were used. Inhibitory effects on enzyme activities were measured using porcine pancreatic α-amylase and α-glucosidase from Saccharomyces cerevisiae in the presence of COS extract. Percentage inhibition of the enzymes and the IC50 values were determined. In vitro protein glycation inhibitory effect of COS leaves on early and late glycation products were measured using bovine serum albumin or chicken egg lysozyme with fructose. Nitroblue tetrazolium was used to assess the relative concentration of fructosamine and polyacrylamide gel electrophoresis was used to assess the degree of glycation and protein cross-linking in the reaction mixtures.

RESULTS

α-Glucosidase inhibitory activity was detected in COS leaves with a IC50 of 67.5 μg/ml which was significantly lower than the IC50 value of Acarbose (p < 0.01). Amylase inhibitory effects occurred at a comparatively higher concentration of extract with a IC50 of 5.88 mg/ml which was significantly higher than the IC50 value of Acarbose (p < 0.01). COS (250 μg/ml) demonstrated inhibitory effects on fructosamine formation and glycation induced protein cross-linking which were in par with 1 mg/ml aminoguanidine were detected.

CONCLUSION

Methanol extracts of COS leaves demonstrated in vitro inhibitory activities on α-glucosidase, fructosamine formation, glycation and glycation induced protein cross-linking. These findings provide scientific evidence to support the use of COS leaves for hypoglycemic effects with an added advantage in slowing down protein glycation.

Analysis of glycation induced protein cross-linking inhibitory effects of some antidiabetic plants and spices

Background

Protein cross-linking which occurs towards the latter part of protein glycation is implicated in the development of chronic diabetic complications. Glycation induced protein cross-linking inhibitory effects of nine antidiabetic plants and three spices were evaluated in this study using a novel, simple, electrophoresis based method.

Methods

Methanol extracts of thirteen plants including nine antidiabetic plants and three spices were used. Lysozyme and fructose were incubated at 37 °C in the presence or absence of different concentrations of plant extracts up to 31 days. Standard glycation inhibitor aminoguanidine and other appropriate controls were included. A recently established sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE) method was used to detect the products of protein cross-linking in the incubation mixtures.

Results

High molecular weight protein products representing the dimer, trimer and tetramer of lysozyme were detected in the presence of fructose. Among the nine antidiabetic plants, seven showed glycation induced protein cross-linking inhibitory effects namely Ficus racemosa (FR) stem bark, Gymnema sylvestre (GS) leaves, Musa paradisiaca (MP) yam, Phyllanthus debilis (PD) whole plant, Phyllanthus emblica (PE) fruit, Pterocarpus marsupium (PM) latex and Tinospora cordifolia (TC) leaves. Inhibition observed with Coccinia grandis (CG) leaves and Strychnos potatorum (SP) seeds were much low. Leaves of Gymnema lactiferum (GL), the plant without known antidiabetic effects showed the lowest inhibition. All three spices namely Coriandrum sativum (CS) seeds, Cinnamomum zeylanicum (CZ) bark and Syzygium aromaticum (SA) flower buds showed cross-link inhibitory effects with higher effects in CS and SA. PD, PE, PM, CS and SA showed almost complete inhibition on the formation of cross-linking with 25 μg/ml extracts.

Conclusions

Methanol extracts of PD, PE, PM, CS and SA have shown promising inhibitory effects on glycation induced protein cross-linking.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-015-0689-1) contains supplementary material, which is available to authorized users.

A simple method to detect plant based inhibitors of glycation induced protein cross-linking

Background: Glycation induced cross-linking of proteins are associated with chronic diabetic complications. Inhibition of protein glycation is one of the therapeutic approaches to prevent the progression of diabetic complications. Objective: Objective of this study was to establish a simple method to identify medicinal plants which can inhibit glycation induced protein cross-linking. Methods: Lysozyme was incubated at 37°C up to 4 weeks with different concentrations of glucose, fructose and ribose in sodium phosphate buffer (pH 7.4). Appropriate controls and blanks were carried out. Aminoguanidine (AG) was used as the standard inhibitor. Water extracts of Bryophyllum pinnatum leaves, Coriandrum sativum seed and Murraya koenigi leaves were used as potential inhibitors. Aliquots were removed from the incubation mixtures at intervals and analyzed for the presence of AGE induced protein cross-links, using SDS-PAGE. Appearance and the intensity of high molecular weight products were compared. Results: Extent of cross-linking was dependent on the sugar concentration. Cross-linking was slowest in the presence of glucose and fastest in the presence of ribose. AG inhibited glycation induced protein cross-linking in the presence of all three sugars. B. pinnatum leaves, C. sativum seeds and M. koenigi leaves inhibited protein cross-linking in the presence of sugar. This inhibition was greater than that of AG. Conclusions: We have established a simple SDS-PAGE method to identify medicinal plants which inhibit glycation induced protein cross-linking. We also demonstrated the effectiveness of B. pinnatum leaves, C. sativum seed and M. koenigi leaves in inhibiting glycation induced protein cross-linking in vitro. DOI: http://dx.doi.org/10.3126/ajms.v6i1.10181 Asian Journal of Medical Sciences Vol.6(1) 2015 28-33

A novel in vitro method to detect inhibitors of protein glycation

Background: Protein glycation generates advanced glycation end products (AGEs) which are implicated in the pathogenesis of chronic complications associated with diabetes. Identifi cation of medicinal plants with protein glycation inhibitory potential will enhance the opportunity to delay or inhibit diabetic complications with minimum side effects. Techniques available to identify protein glycation inhibitors require expensive specialized equipment. Objective: Objective of this study was to develop a relatively simple in vitro method to identify the protein glycation inhibitory potential of compounds or medicinal plants. Methods: Bovine serum albumin (BSA) was incubated with different concentrations of glucose or fructose or ribose for 31 days at pH 7.4. Standard inhibitor aminoguanidine (AG) was used as a positive control. Effect on the BSA migration under different experimental conditions was compared using polyacrylamide gel electrophoresis under native conditions (PAGE). Murraya koenigii leaf extract was analyzed for its effect on protein glycation. Results: We demonstrated many aspects of protein glycation including the effect of sugar concentration, type of the sugar and incubation period on protein glycation using this comparatively simpler method, which was previously, demonstrated using more sophisticated and expensive equipment. Migration of the BSA band towards the anode was proportionate to the degree of protein glycation. Further, we were innovative in demonstrating the inhibitory effect of AG on protein glycation using PAGE. BSA migration was comparatively slower when AG was included in the presence of sugar, indicating its inhibitory effects. We also revealed the protein glycation inhibitory potential of Murraya koenigii leaf extract, which was greater than that of AG at the concentrations used in the study. Conclusion: We have developed novel simple in vitro method using PAGE to identify inhibitors of protein glycation. Asian Journal of Medical Science, Volume-5(3) 2014: 15-21 http://dx.doi.org/10.3126/ajms.v5i3.8670