In vitro inhibitory activities of selected Australian medicinal plant extracts against protein glycation, angiotensin converting enzyme (ACE) and digestive enzymes linked to type II diabetes

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Background There is a need to develop potential new therapies for the management of diabetes and hypertension. Australian medicinal plants collected from the Kuuku I’yu (Northern Kaanju) homelands, Cape York Peninsula, Queensland, Australia were investigated to determine their therapeutic potential. Extracts were tested for inhibition of protein glycation and key enzymes relevant to the management of hyperglycaemia and hypertension. The inhibitory activities were further correlated with the antioxidant activities. Methods Extracts of five selected plant species were investigated: Petalostigma pubescens, Petalostigma banksii, Memecylon pauciflorum, Millettia pinnata and Grewia mesomischa. Enzyme inhibitory activity of the plant extracts was assessed against α-amylase, α-glucosidase and angiotensin converting enzyme (ACE). Antiglycation activity was determined using glucose-induced protein glycation models and formation of protein-bound fluorescent advanced glycation endproducts (AGEs). Antioxidant activity was determined by measuring the scavenging effect of plant extracts against 1, 1-diphenyl-2-picryl hydrazyl (DPPH) and using the ferric reducing anti-oxidant potential assay (FRAP). Total phenolic and flavonoid contents were also determined. Results Extracts of the leaves of Petalostigma banksii and P. pubescens showed the strongest inhibition of α-amylase with IC50 values of 166.50 ± 5.50 μg/mL and 160.20 ± 27.92 μg/mL, respectively. The P. pubescens leaf extract was also the strongest inhibitor of α-glucosidase with an IC50 of 167.83 ± 23.82 μg/mL. Testing for the antiglycation potential of the extracts, measured as inhibition of formation of protein-bound fluorescent AGEs, showed that P. banksii root and fruit extracts had IC50 values of 34.49 ± 4.31 μg/mL and 47.72 ± 1.65 μg/mL, respectively, which were significantly lower (p < 0.05) than other extracts. The inhibitory effect on α-amylase, α-glucosidase and the antiglycation potential of the extracts did not correlate with the total phenolic, total flavonoid, FRAP or DPPH. For ACE inhibition, IC50 values ranged between 266.27 ± 6.91 to 695.17 ± 15.38 μg/mL. Conclusions The tested Australian medicinal plant extracts inhibit glucose-induced fluorescent AGEs, α-amylase, α-glucosidase and ACE with extracts of Petalostigma species showing the most promising activity. These medicinal plants could potentially be further developed as therapeutic agents in the treatment of hyperglycaemia and hypertension

Influence of the methanolic extract from Abutilon indicum leaves in normal and streptozotocin-induced diabetic rats

The methanolic leaf extract of Abutilon indicum (AI) was investigated for hypoglycemic effect in normal and streptozotocin-induced diabetic rats. The chemical screening of the extract showed that phenoliccompounds and flavonoid contents were 1.04 ± 0.01 mg/g and 59.92 ± 3.88 g/g extract, respectively. A single oral administration of the extract at a dose of 500 mg/kg significantly decreased the bloodglucose concentrations in both normal and diabetic rats after 2 h administration. Metformin was used as the reference drug and reduced the blood glucose only in diabetic rats. To clarify the involvedmechanism, normal rats were orally administered with sucrose and maltose at a dose of 3 g/kg with or without AI extract. The postprandial elevation in the blood glucose concentrations at 30 min after theadministration of sucrose with the extract was significantly suppressed when compared with the control group. No significant change in blood glucose concentrations was observed in maltose-loading rats. An in vitro study indicated that AI extract inhibited -glucosidases, the disaccharide-digesting enzyme in the small intestine. The extract showed a potent sucrase inhibitory activity with IC50 of 2.45 ±0.13 mg/ml while the extract was less potent on the maltase inhibition. The results suggested that the extract from AI extract would be effective for lowering and suppressing elevation of blood glucose