In silico and in vitro inhibition of α- glucosidase and α-amylase by compounds from culinary herbs and spices, for possible treatment of type 2 diabetes

Abstract

Diabetes is one of the largest health challenges of the 21st century and is amongst the top 10 causes of death globally. There is no cure for type 2 diabetes (T2DM) and the search for new and improved treatments is ongoing. Various pharmaceuticals are available to treat T2DM, but with varied success. Many traditional herbal medicines are also used to treat T2DM, but mostly without scientific validation. Alternative treatment strategies, like herbal medicines and associated active compounds, can prove to be more cost-effective and may lack undesirable side-effects. This study aimed to assess the in vitro hypoglycaemic, toxicity and insulin mimicking effects of seven compounds found in commercially available herbs and spices, using in silico and in vitro relationship studies. These herbal compounds were acetyleugenol, apigenin, cinnamic acid, eriodictyol, myrcene, piperine and rosmarinic acid, they were chosen based on scientific reports on pleiotropic effects related to the inhibition of starch hydrolysing enzymes and insulin mimicking effects.

Various in silico physiochemical properties of each compound was evaluated and compared with the antidiabetic drug, acarbose. All the herbal compounds had better drug-like features than acarbose. Candidate compounds were further analysed using the Search Tool for Interactions of Chemicals (STITCH) database to explore drug-target interactions, for possible harmful cross-reactions. The drug-target networks generated on STITCH showed no undesirable cross-reactions and highlighted the anti-carcinogenic and anti-inflammatory properties of the herbal compounds. The enzyme inhibitory nature was evaluated using in silico docking analysis with the Glide algorithm in the Maestro software and was further confirmed by in vitro α-amylase and α-glucosidase colorimetric assays.

Alpha-amylase and α-glucosidase have been identified as important therapeutic targets for the management of T2DM. The inhibition of these enzymes would lead to a decrease in postprandial hyperglycaemia, however most clinically used drugs have undesirable side effects. Herbs and spices such as parsley, cinnamon, pepper, oregano, mint and cloves alleviate flatulence, diarrhoea and abdominal pain, counteracting the side effects commonly caused by α-amylase and α-glucosidase inhibitors. The in silico results identified which herbal compounds had better docking scores (more negative delta G values) than acarbose namely, apigenin, eriodictyol, piperine and rosmarinic acid. The in vitro studies revealed that all compounds, except myrcene, inhibited α-amylase and α-glucosidase in a dose-dependent manner. The Ki value of acarbose, a widely prescribed α-glucosidase inhibitor, and eriodictyol, apigenin and piperine were similar (p > 0.05). For α-amylase inhibition, the Ki value of acarbose and those of rosmarinic acid , apigenin and cinnamic acid were similar (p > 0.05). The relationship between the in silico and in vitro results correlated well, where a more negative docking score translated to a higher in vitro inhibitory activity.

The effect of the herbal compounds on cell viability in C2C12 myotubes and HepG2 hepatocarcinoma cells, using the sulforhodamine B assay, was then determined. Eriodictyol and apigenin displayed noticeable toxicity against HepG2 and C2C12 cells. Acetyleugenol, cinnamic acid, myrcene, piperine and rosmarinic acid had similar (p > 0.05) IC50 values to acarbose in both cell lines.

Fluorescence detection was used to investigate the effects of each herbal compound on glucose uptake in HepG2 and C2C12 cells. All of the compounds significantly increased glucose uptake in these cell lines, compared to the control (p < 0.05), with efficacy in the same order as the positive control, insulin (p > 0.05).

This study provides evidence for the antidiabetic potential of herbal compounds in terms of their ability to prevent post-prandial hyperglycaemia, through the inhibition of starch hydrolysing enzymes, and alleviate hyperglycaemia by mimicking the action of insulin. The most promising compounds were cinnamic acid, piperine and rosmarinic acid. Using herbs and spices would have several advantages, including their widespread availability, easily cultivatable nature, affordability and health benefits. These compounds can easily be consumed through teas or using herbs and spices to flavour food.