Most of the medicinal researches have aimed to evaluate the therapeutic value of plants and to identify the related active ingredients extracted. The active ingredients from flavonoids (e.g. quercetin and kaempferol), alkaloids such as dieckol, etc which are potential for diabetes treatment have been discovered and their therapeutic functions have been described in . Besides that, some polysaccharides[
25,
26] from plants are also beneficial to humans in fighting diabetes.
| Table 3Potential anti diabetic active compounds extracted from plants in the study |
In this study, the anti diabetic acting mechanisms of the active ingredients are categorized into 6 groups for the ease of compilation as shown in . The acting mechanisms are namely: alteration of glucose metabolism; hypolipidemic effect; pancreatic effect; antioxidative effect; diabetes complication treatment; and, insulin-like effect. gives an overall picture on the trend of plant research for anti diabetic treatment based on the information gathered for the past 20 years. The figure indicates the percentage distribution of anti diabetic acting mechanisms possessed by herbal plant extracts in descending order.
show that 28% of the anti diabetic researches emphasized on the alteration of glucose metabolism. By altering the glucose metabolism, it helps to regulate the blood sugar levels to normal and thus prevent diabetes, whereas other anti diabetic mechanisms assist in treating diabetes and its complications. Several active ingredients belonging to this category are: bassic acid, an active compound isolated from
Bumelia sartorum; and, natural flavonoids such as quercetin and kaempferol as they can promote hypoglycemia through increase glucose uptake and glycogen synthesis.[
27,
33,
38] Recently, researchers found that dieckol, a compound isolated from
Ecklonia cava, is a potential inhibitor for α -glucosidase and α-amylase. It exhibits hypoglycaemia by reducing the impact of carbohydrates on blood sugar and is claimed to be comparable to Acarbose, a medical anti diabetic drug.[
45] In addition, the effect of enhancing glucose tolerance and homeostasis have been reported in the root extracts of
Berberis aristata and in comatin, an active ingredient extracted from
Coprinus comatus broth. Both extracts can prevent diabetes by reducing the severity of insulin resistance.[
43,
64]
The second, third and forth categories of the acting mechanisms respectively focus on hypolipidemic effect, pancreatic effect and antioxidative effect. The interactions among them are important focal points for anti diabetic research; for instance, a common secondary cause of hyperlipidemia is associated with diabetes. On one hand, some herbal plants extract such as guggulsterone isolated from
Commiphora mukul and isoorientin obtained from
Gentiana olivieri possess hypoglycemic and hypolipidemic properties which are suitable for obese diabetes patients;[
50,
53] on the other, herbal plants extract with pancreatic effect helps to enhance insulin secretion through insulin sensitizing mechanism. Furthermore, it has been reported that mangiferin and procyanidins, the natural compounds found in several plants like apple, grape and mango, exhibit hypoglycaemic activity through enhancing insulin signaling pathway.[
65,
66] As for antioxidative effect, plant extracts such as green tea,
Ajuga iva aqueous extract and Chlorogenic acid from
Cecropia pachystachya are capable of reducing oxidative stress and protecting against tissue damage in diabetes.[
41,
57,
67] Another acting mechanism based on antioxidants such as kinsenoside, gymnemic acid and quercetin are helpful in preventing and treating Type I diabetes as they can regenerate the beta cells in islets of Langerhans in pancreas.[
29,
52,
54,
68]
The last two acting mechanisms associate with diabetic complication treatment and insulin-like active ingredients administration. There are a lot of diabetic complications; however, only a few are involved in research attributing to their severity. For example,
Pterocarpus marsupium extract is more effective compared to
Ocimum sanctum extract as it exhibits better anti cataract effect for diabetic complication treatment.[
69] Moreover, some extracts, i.e. garlic and ginger extracts, can be used to prevent and attenuate the development of nephropathy.[
70] In addition, extracts isolated from Syzigium plants, i.e.
S. cumini and
S. aromaticum, are potential active ingredients for insulin substitutes.[
71,
72]