Anti-diabetic polysaccharides from natural sources: A review

Highlights

• A large amount of natural polysaccharides have anti-diabetic activities.

• Polysaccharides show their effects by different ways.

• The anti-diabetic polysaccharides in the past 5 years were summarized.

• The chemical characters of these polysaccharides were also summarized.

Abstract

Diabetes mellitus (DM) is a metabolic disease attracted worldwide concerns, which severely impairs peoples’ quality of life and is attributed to several life-threatening complications, including atherosclerosis, nephropathy and retinopathy. The current therapies for DM include mainly oral anti-diabetic drugs and insulin. However, continuous use of these causes insulin resistance and side-effects, and the demand of effective, nontoxic and affordable drugs for DM patients is eager. Several previous studies have shown that non-toxic biological macromolecules, mainly polysaccharides, possess prominent efficacies on DM. Based on these encouraging observations, a great deal of efforts have been focused on discovering anti-diabetic polysaccharides for the development of effective therapeutics for DM. This review focuses on the advancements in the anti-diabetic efficacy of various natural polysaccharides and polysaccharide complexes from 2010 to 2015.

Introduction

The statistics from International Diabetes Federation (IDF) in 2013 indicates that over 382 million individuals worldwide are suffered from diabetes mellitus (DM), the number of which has increased more than 13-fold since 1980, and will achieve 600 million by 2030 through following projected trends analysis (Kokil, Veedu, Ramm, Prins, & Parekh, 2015). In patients with DM, atherosclerosis is the main reason for impaired life expectancy, and diabetic nephropathy and retinopathy are the largest contributors to end-stage renal disease and blindness, respectively (Rask-Madsen & King, 2013). On the other hand, DM places immense financial pressures on already overstretched healthcare budgets in the developed as well as developing world, putting estimated global expenditure at a staggering US $548 billion in 2013 alone (Morales & Morris, 2015).

DM is a group of metabolic disease characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both (Steck & Winter, 2011). Generally, DM is classified into two types: type 1 (T1DM) and type 2 (T2DM), with the latter accounting for ∼90% of cases, and it is therefore the focus of this review (Skyler & Oddo, 2002). For T2DM, insulin resistance (IR) and pancreatic β-cell failure are the key drivers, with a complex interrelationship responsible for initiating its pathogenesis (Polonsky, 2015, Thorens, 2011). T2DM develops when pancreatic β cells fail to secrete sufficient amounts of insulin to meet the metabolic demand. An increased metabolic demand for insulin due to insulin resistance in several tissues usually precedes the development of hyperglycemia. There is thus a period of normal or near-normal glycemia in which pancreatic β cells compensate for insulin resistance by hypersecretion of insulin. At some point, however, this period of β cell compensation is followed by β cell failure, in which the pancreas fails to secrete sufficient insulin and diabetes ensues (Kasuga, 2006). Additionally, genetic predisposition, increasing age, and obesity are three leading and well-reported exacerbators of IR and pancreatic β-cell failure (Emerging Risk Factors Collaboration, 2011). The relationship between insulin resistance and β-cell failure is seen in Fig. 1.

For DM therapy, there have been a series of agents, including sulfonylureas, thiazolidinedione, α-glucosidase inhibitors and Biguanide, whose commercial products have been used for decades of years. As seen in Table 1, however, the adverse effects are existed in these drugs, more or less. Considering the long-term course of DM treatment, it is a serious issue should be considering. Currently, several new drugs with new targets have been developed to market, like DPP-4 inhibitors, GLP-1 analogs, GPR 119 agonists and SGLT-2 inhibitors (Zhang, Zhou, & Li, 2009), however, the high price as well as the indistinct safety property of them cause the huge demand of effective, nontoxic and affordable drugs for DM.

The new tendency of DM patients has led to the use of functional foods and complementary or alternative medicine. Some patients have been using medicinal plants, mushrooms and other sources preparations to complement DM treatment. Scientists have found out a great variety of active molecules from these natural products, and their polysaccharides have been the subject of intense research, taking into view its high potential for application in DM treatment (Huang, Wang, Zhou, Yang, & Wang, 2015). Actually, in China, several polysaccharides products have been used alternative medicine to treat DM in clinic, among them astragalus polysaccharide, konjac glucomannan, ginseng polysaccharide, pumpkin polysaccharide and so on (Diao, Jiang, Zhu, Meng, & Shan, 2011). Thus, it is a promising direction to find effective anti-diabetic drugs focused on natural polysaccharides.