Phytochemicals and Their Impact on Diabetes

 

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Molecules. 2022 Jul 3;27(13):4278. doi: 10.3390/molecules27134278

Pharmacologically Active Phytomolecules Isolated from Traditional Antidiabetic Plants and Their Therapeutic Role for the Management of Diabetes Mellitus

Prawej Ansari 1,2,*, Samia Akther 1, J M A Hannan 1, Veronique Seidel 3, Nusrat Jahan Nujat 1, Yasser H A Abdel-Wahab 2

Editors: Rudolf Bauer, Jelena S Katanic Stankovic

6. Phytochemicals and Their Impact on Diabetes

Plants are the primary source of biologically active compounds that may ultimately lead to the discovery and development of potential new drugs [238].

 Plants produce both primary and secondary metabolites. Carbohydrates, proteins, and lipids are considered primary metabolites, necessary for the growth and development of plants and involved in essential metabolic pathways,

 such as photosynthesis and glycolysis. Secondary metabolites are not required for the growth and development of plants; rather, they are responsible for interactions between plant species and the environment and have highly specific functions in plants [239].

Over 13,000 secondary metabolites have been purified and isolated from medicinal plants. 

These phytochemicals can be categorized into various chemical classes such as alkaloids, flavonoids, terpenoids, phenolics, tannins, saponins, xanthones, and glycosides [78]. 

Many of these phytochemicals are known to exhibit medicinal properties, including antidiabetic activity [78].

 Several phytochemicals isolated from various plant species have been scientifically validated for their contribution to treating and managing diabetes by exerting antihyperglycemic activity and reducing the complications associated with diabetes [171]. 

For example, the flavonoid rutin, present in the leaves of numerous plants, including Annona squamosa and Azadirachta indica (neem), has been reported to possess many beneficial effects such as anti-inflammatory, anti-cancer, anti-allergic, antiviral, and antioxidative properties [240]. 

Rutin-containing plants have also been shown to protect against heart disease, hepatotoxicity, and diabetes mellitus [240]. 

Rutin exerts its antidiabetic effect by lowering plasma glucose, improving the function of pancreatic β-cells, and enhancing glucose tolerance [10]. 

Two other flavonoids found in the leaves of Annona squamosa, namely quercetin and isoquercetin, have also been reported to possess antihyperglycemic activity by inhibiting α-glucosidase and lowering blood glucose levels [241]. 

Alongside rutin and quercetin, the tetranortriterpenoid meliacinolin, isolated from the leaves of A. indica, has been found to inhibit α-glucosidase and α-amylase in Type 2 diabetic mice [98].

 Nimbidin, extracted from neem seeds, is another phytochemical exhibiting hypoglycemic properties [98].

 Quercetin, allicin, allyl-propyl disulfide, cysteine sulfoxide, and S-allyl cysteine sulfoxide from Allium sativum (garlic) have been reported to stimulate insulin secretion from pancreatic β-cells, increase insulin sensitivity to target cells, and prevent insulin activation triggered by the liver [71].

 Alliin, from garlic, has been reported to mimic the function of glibenclamide and insulin [71].

 Epigallocatechin-3-gallate, epigallocatechin, epicatechin-3-gallate, and epicatechin present in Camellia sinensis (tea) leaves can also lower plasma glucose levels by improving β-cell function, increasing insulin secretion, and enhancing glucose metabolism [117]. 

These phytomolecules may exert their antidiabetic activity in multiple manners, most commonly by being insulinotropic, insulin-mimetic, and by improving β-cell function, increasing insulin sensitivity, improving glucose tolerance and metabolism, as well as inhibiting various enzyme activities. A summary of antidiabetic medicinal plants and their phytochemicals with potential antidiabetic effects is provided in Table 2. The chemical structures of the antidiabetic phytoconstituents of medicinal plants are given in Table 3.