Type 2 diabetes is a global health issue characterized by a progressive decline in insulin production that leads to high levels of glucose in the blood — hyperglycemia. The incidence of type 2 diabetes has been steadily rising, and the condition is now estimated to accounts for 90–95% of the 425 million cases of diabetes worldwide1. Untreated, it can lead to a range of serious complications, including cardiovascular disease and kidney failure2.

In this case study, researchers used NMR spectroscopy to study the potential therapeutic effects of various types of Sorbus berries on diabetes.

Treatment of type 2 diabetes aims to lower blood glucose levels in order to prolong the production of insulin by the pancreas and avoid the need for insulin injection. This can be achieved initially by diet modifications to avoid sudden peaks of glucose absorption. Medications, such as metformin, are also available when blood glucose levels cannot be managed effectively by diet alone.

There is a growing interest in identifying effective natural anti-hyperglycemic agents to facilitate blood sugar management in type 2 diabetes.

The digestive enzymes α-amylase and α-glucosidase, which facilitate the digestion of starch, have been identified as important targets for the treatment of type 2 diabetes. Inhibitors of these two enzymes delay the absorption of monosaccharides from the small intestine, thereby lowering post-prandial peak plasma glucose levels3. This improves glycaemic control, which is reflected in a reduced glycosylated hemoglobin concentration.

Berries have been shown to provide effective inhibition of these digestive enzymes and may, therefore, play a valuable role in the management of type 2 diabetes using natural agents.

The anti-diabetic potential of berries
Polyphenols occur naturally in a variety of fruits, vegetables, herbs, and spices. They are effective antioxidants and have been associated with a range of health benefits, such as lowering the risk of cancer and heart disease and reducing inflammation.

Polyphenols also help lower blood sugar levels, and so have been explored as potential treatments for type 2 diabetes. A sub-group of polyphenols known as anthocyanins appear to provide the most potent anti-diabetic effect. These are found in red, purple, and blue foods, such as berries.

Several studies investigating the ability of berry extracts to lower blood glucose levels have reported beneficial anti-diabetic activities for a range of berries, including strawberries, blueberries, and lingonberries4. Indeed, berries have been shown to improve overall glycaemic profiles in clinical studies5.

The efficacy of berry polyphenols in type 2 diabetes has been shown to be the result of inhibition of digestive enzymes involved in carbohydrate breakdown, inhibition of glucose absorption in the gastrointestinal tract, and modification of energy metabolism/energy status5.

Despite the promising glucose-lowering activity of berry polyphenols, the anti-diabetic potential of the widely available rowan (Sorbus) berry has been little studied. Extracts from a variety of Sorbus berries have been used in traditional remedies for diabetes and demonstrate good inhibition of α-amylase and α-glucosidase 6,7.

Investigating the glucose-lowering activity of Sorbus berries
Extracts of several types of Sorbus berry have recently been investigated for inhibitory activity on the digestive enzymes α-amylase and α-glucosidase. The anti-hyperglycemic potential of the Sorbus norvegica berry extract in vivo was also assessed8.

Extracts of 16 species of Sorbus berry were analyzed by 1H-nuclear magnetic resonance (NMR) to evaluate the chemical profiles of the extracts. NMR spectra were recorded at room temperature on a 400 MHz Bruker Avance spectrometer. The anti-hyperglycaemic effect was evaluated in an oral starch tolerance test in STZ-treated C57BL/6 mice.

The active extracts inhibited both α-amylase and α-glucosidase activity. The greatest inhibition of α-amylase and α-glucosidase was achieved with the Sorbus species belonging to the subspecies Aria. These species were also shown to have a difference in chemistry. NMR spectra revealed strong peaks for α-D-glucopyranoside and β-D-glucopyranoside in all active Sorbus extracts.

The species with the most potent glucose-lowering effect, Sorbus norvegica, had anti-hyperglycemic activity at a dose 36 times lower than that of acarbose, which is currently used in the treatment of type 2 diabetes.