Procyanidin A2, an anti-diabetic condensed tannin extracted from Wendlandia glabrata, reduces elevated G-6-Pase and mRNA levels in diabetic mice and increases glucose uptake in CC1 hepatocytes and C1C12 myoblast cells

A-type proanthocyanidins: Sources, structure, bioactivity, processing, nutrition, and potential applications

A-type proanthocyanidins (PAs) are a subgroup of PAs that differ from B-type PAs by the presence of an ether bond between two consecutive constitutive units. This additional C-O-C bond gives them a more stable and hydrophobic character. They are of increasing interest due to their potential multiple nutritional effects with low toxicity in food processing and supplement development. They have been identified in several plants. However, the role of A-type PAs, especially their complex polymeric form (degree of polymerization and linkage), has not been specifically discussed and explored. Therefore, recent advances in the physicochemical and structural changes of A-type PAs and their functional properties during extraction, processing, and storing are evaluated. In addition, discussions on the sources, structures, bioactivities, potential applications in the food industry, and future research trends of their derivatives are highlighted. Litchis, cranberries, avocados, and persimmons are all favorable plant sources. Α-type PAs contribute directly or indirectly to human nutrition via the regulation of different degrees of polymerization and bonding types. Thermal processing could have a negative impact on the amount and structure of A-type PAs in the food matrix. More attention should be focused on nonthermal technologies that could better preserve their architecture and structure. The diversity and complexity of these compounds, as well as the difficulty in isolating and purifying natural A-type PAs, remain obstacles to their further applications. A-type PAs have received widespread acceptance and attention in the food industry but have not yet achieved their maximum potential for the future of food. Further research and development are therefore needed.

Condensed tannins-Their content in plant foods, changes during processing, antioxidant and biological activities

Condensed tannins are considered nutritionally undesirable, because they precipitate proteins, inhibit digestive enzymes, and can affect the absorption of vitamins and minerals. From the consumer's point of view, they impart astringency to foods. Yet, they are viewed as a double-edged sword, since they possess antioxidant and anti-inflammatory activities. Intake of a small quantity of the right kind of tannins may in fact be beneficial to human health. This chapter reports on the chemical structure of condensed tannins, their content in plants and food of plant origin, how they are extracted, and methods for their determination. A description of the effects of processing on condensed tannins is discussed and includes soaking, dehulling, thermal processing (i.e., cooking, boiling, autoclaving, extrusion), and germination. The astringency of condensed tannins is described in relation to their interactions with proteins. Finally, details about the biological properties of condensed tannins, including their antimicrobial, anti-inflammatory, anticancer, anti-diabetic, and anti-obesity activities, are reviewed.

Natural Products and Diabetes: (-)-Epicatechin and Mechanisms Involved in the Regulation of Insulin Sensitivity

Type 2 diabetes (T2D) is a disease that occurs when cells do not respond normally to insulin, a condition called insulin resistance, which leads to high blood glucose levels. Although it can be treated pharmacologically, dietary habits beyond carbohydrate restriction can be highly relevant in the management of T2D. Emerging evidence supports the possibility that natural products (NPs) could contribute to managing blood glucose or counteract the undesirable effects of hyperglycemia and insulin resistance. This chapter summarizes the relevant preclinical evidence involving the flavonoid (-)-epicatechin (EC) in the optimization of glucose homeostasis, reducing insulin resistance and/or diabetes-associated disorders. Major effects of EC are observed on (i) intestinal functions, including digestive enzymes, glucose transporters, microbiota, and intestinal permeability, and (ii) redox homeostasis, including oxidative stress and inflammation. There is still a need for further clinical studies to confirm the in vitro and rodent data, allowing recommendations for EC, particularly in prediabetic and T2D patients. The collection of similar data and the lack of clinical evidence for EC is also applicable to other NPs.

Free radical scavenging polyphenols isolated from Phyllanthus niruri L. ameliorates hyperglycemia via SIRT1 induction and GLUT4 translocation in in vitro and in vivo models

Type 2 diabetes milletus (T2DM) is a complex multifaceted disorder characterized by insulin resistance in skeletal muscle. Phyllanthus niruri L. is well reported sub-tropical therapeutically beneficial ayurvedic medicinal plant from Euphorbiaceae family used in various body ailments such as metabolic disorder including diabetes. The present study emphasizes on the therapeutic potential of Phyllanthus niruri L. and its phytochemical(s) against insulin resistance conditions and impaired antioxidant activity thereby aiding as an anti-hyperglycemic agent in targeting T2DM. Three compounds were isolated from the most active ethyl acetate fraction namely compound 1 as 1-O-galloyl-6-O-luteoyl-β-D-glucoside, compound 2 as brevifolincarboxylic acid and compound 3 as ricinoleic acid. Compounds 1 and 2, the two polyphenols enhanced the uptake of glucose and inhibited ROS levels in palmitate induced C2C12 myotubes. PNEAF showed the potent enhancement of glucose uptake in palmitate-induced insulin resistance condition in C2C12 myotubes and significant ROS inhibition was observed in skeletal muscle cell line. PNEAF treated IR C2C12 myotubes and STZ induced Wistar rats elevated SIRT1, PGC1-α signaling cascade through phosphorylation of AMPK and GLUT4 translocation resulting in insulin sensitization. Our study revealed an insight into the efficacy of marker compounds isolated from P. niruri and its enriched ethyl acetate fraction as ROS scavenging agent and helps in attenuating insulin resistance condition in C2C12 myotubes as well as in STZ induced Wistar rat by restoring glucose metabolism. Overall, this study can provide prospects for the marker-assisted development of P. niruri as a phytopharmaceutical drug for the insulin resistance related diabetic complications.

Natural Inhibitors of Mammalian α-Amylases as Promising Drugs for the Treatment of Metabolic Diseases

α-Amylase is a generally acknowledged molecular target of a distinct class of antidiabetic drugs named α-glucosidase inhibitors. This class of medications is scarce and rather underutilized, and treatment with current commercial drugs is accompanied by unpleasant adverse effects. However, mammalian α-amylase inhibitors are abundant in nature and form an extensive pool of high-affinity ligands that are available for drug discovery. Individual compounds and natural extracts and preparations are promising therapeutic agents for conditions associated with impaired starch metabolism, e.g., diabetes mellitus, obesity, and other metabolic disorders. This review focuses on the structural diversity and action mechanisms of active natural products with inhibitory activity toward mammalian α-amylases, and emphasizes proteinaceous inhibitors as more effective compounds with significant potential for clinical use.

Phytochemical analysis, antioxidant, antimicrobial, and anti-enzymatic properties of Alpinia coriandriodora (sweet ginger) rhizome

Alpinia coriandriodora, also known as sweet ginger, is a medicinal and edible plant. A. coriandriodora rhizome is popularly utilized in traditional Chinese medicine and as flavouring spices, but there are few reports on its constituents and bioactivities. This study analyzed the phytochemical components of A. coriandriodora rhizome by GC-MS and UHPLC-Q-Orbitrap-MS and evaluated its antioxidant, antimicrobial, and anti-enzymatic properties. According to the GC-FID/MS data, its rhizome essential oil (EO) consisted mainly of (E)-2-decenal (53.8%), (E)-2-decenyl acetate (24.4%), (Z)-3-dodecenyl acetate (3.5%), and (E)-2-octenal (3.5%). Its water extract (WE) and 70% ethanol extract (EE) showed high total phenolic content (TPC, 52.99-60.49 mg GAEs/g extract) and total flavonoid content (TFC, 260.69-286.42 mg REs/g extract). In addition, the phytochemicals of WE and EE were further characterized using UHPLC-Q-Orbitrap-MS, and a total of sixty-three compounds were identified, including fourteen phenolic components and twenty-three flavonoid compounds. In the antioxidant assay, WE and EE revealed a potent scavenging effect on DPPH (IC50: 6.59 ± 0.88 mg/mL and 17.70 ± 1.15 mg/mL, respectively), surpassing the BHT (IC50: 21.83 ± 0.89 mg/mL). For the antimicrobial activities, EO displayed excellent antibacterial capabilities against Proteus vulgaris, Enterococcus faecalis, Bacillus subtilis, Escherichia coli, and Staphylococcus aureus with DIZ (12.60-22.17 mm), MIC (0.78-1.56 mg/mL), and MBC (3.13 mg/mL) and significantly inhibited Aspergillus flavus growth (MIC = 0.313 mg/mL, MFC = 0.625 mg/mL, respectively). In addition to weak tyrosinase and cholinesterase inhibition, EE and WE had a prominent inhibitory effect against α-glucosidase (IC50: 0.013 ± 0.001 mg/mL and 0.017 ± 0.002 mg/mL), which was significantly higher than acarbose (IC50: 0.22 ± 0.01 mg/mL). Hence, the rhizome of A. coriandriodora has excellent potential for utilization in the pharmaceutical and food fields as a source of bioactive substances.

Exploring plant-based alpha-glucosidase inhibitors: promising contenders for combatting type-2 diabetes

Objective: This systematic review aimed to provide comprehensive details on the α-G inhibitory potential of various bioactive compounds derived from natural sources.Methods: A comprehensive literature search was conducted using various databases and search engines, including Science Direct, Google Scholar, SciFinder, Web of Science, and PubMed until May, 2023.Results and conclusions: The enzyme alpha-glucosidase (α-G) is found in the brush border epithelium of the small intestine and consists of duplicated glycoside hydrolase (GH31) domain. It involves the conversion of disaccharides and oligosaccharides into monosaccharides by acting on alpha (1 → 4) and (1 → 6) linked glucose residue. Once absorbed, glucose enters the bloodstream and elevates postprandial glucose, which is associated with the development of type 2 Diabetes (T2D). Epidemic obesity, cardiovascular disease, and nephropathy are linked to T2D. Traditional medicinal plants with α-G inhibitory potential are commonly used to treat T2D due to the adverse effects of currently used α-G inhibitors miglitol, acarbose, and voglibose. Various bioactive compounds derived from natural sources, including lupenone, Wilforlide A, Baicalein, Betulinic acid, Ursolic acid, Oleanolic acid, Katononic acid, Carnosol, Hypericin, Astilbin, lupeol, betulonic acid, Fagomine, Lactucaxanthin, Erythritol, GP90-1B, Procyanidins, Galangin, and vomifoliol retain α-G inhibitory potential for regulating hyperglycaemia.

Procyanidins: A promising anti-diabetic agent with potential benefits on glucose metabolism and diabetes complications

Diabetes mellitus (DM) is a complex disease with alarming worldwide health implications and high mortality rates, largely due to its complications such as cardiovascular disease, nephropathy, neuropathy, and retinopathy. Recent research has shown that procyanidins (PC), a type of flavonoid, have strong antioxidant and free radical elimination effects, and may be useful in improving glucose metabolism, enhancing pancreatic islet cell activity, and decreasing the prevalence of DM complications. This review article presents a systematic search for peer-reviewed articles on the use of PC in the treatment of DM, without any language restrictions. The article also discusses the potential for PC to sensitise DM medications and improve their efficacy. Recent in vivo and in vitro studies have demonstrated promising results in improving the biological activity and bioavailability of PC for the treatment of DM. The article concludes by highlighting the potential for novel materials and targeted drug delivery methods to enhance the pharmacokinetics and bioactivity of PC, leading to the creation of safer and more effective anti-DM medications in the future.

Recent Updates on Phytoconstituent Alpha-Glucosidase Inhibitors: An Approach towards the Treatment of Type Two Diabetes

Diabetes is a common metabolic disorder marked by unusually high plasma glucose levels, which can lead to serious consequences such as retinopathy, diabetic neuropathy and cardiovascular disease. One of the most efficient ways to reduce postprandial hyperglycemia (PPHG) in diabetes mellitus, especially insulin-independent diabetes mellitus, is to lower the amount of glucose that is absorbed by inhibiting carbohydrate hydrolyzing enzymes in the digestive system, such as α-glucosidase and α-amylase. α-Glucosidase is a crucial enzyme that catalyzes the final stage of carbohydrate digestion. As a result, α-glucosidase inhibitors can slow D-glucose release from complex carbohydrates and delay glucose absorption, resulting in lower postprandial plasma glucose levels and control of PPHG. Many attempts have been made in recent years to uncover efficient α-glucosidase inhibitors from natural sources to build a physiologic functional diet or lead compound for diabetes treatment. Many phytoconstituent α-glucosidase inhibitors have been identified from plants, including alkaloids, flavonoids, anthocyanins, terpenoids, phenolic compounds, glycosides and others. The current review focuses on the most recent updates on different traditional/medicinal plant extracts and isolated compounds' biological activity that can help in the development of potent therapeutic medications with greater efficacy and safety for the treatment of type 2 diabetes or to avoid PPHG. For this purpose, we provide a summary of the latest scientific literature findings on plant extracts as well as plant-derived bioactive compounds as potential α-glucosidase inhibitors with hypoglycemic effects. Moreover, the review elucidates structural insights of the key drug target, α-glucosidase enzymes, and its interaction with different inhibitors.

Iridoid glycoside isolated from Wendlandia glabrata and the role of its enriched fraction in regulating AMPK/PEPCK/G6Pase signaling pathway of hepatic gluconeogenesis

Phytochemical investigation of W. glabrata and antihyperglycemic potential of isolated novel iridoid glycoside enriched fraction in CC1 hepatocytes and STZ-induced diabetic mice.

A review of alpha-glucosidase inhibitors from plants as potential candidates for the treatment of type-2 diabetes

Diabetes mellitus is a multifactorial global health disorder that is rising at an alarming rate. Cardiovascular diseases, kidney damage and neuropathy are the main cause of high mortality rates among individuals with diabetes. One effective therapeutic approach for controlling hyperglycemia associated with type-2 diabetes is to target alpha-amylase and alpha-glucosidase, enzymes that catalyzes starch hydrolysis in the intestine. At present, approved inhibitors for these enzymes are restricted to acarbose, miglitol and voglibose. Although these inhibitors retard glucose absorption, undesirable gastrointestinal side effects impede their application. Therefore, research efforts continue to seek novel inhibitors with improved efficacy and minimal side effects. Natural products of plant origin have been a valuable source of therapeutic agents with lesser toxicity and side effects. The anti-diabetic potential through alpha-glucosidase inhibition of plant-derived molecules are summarized in this review. Eight molecules (Taxumariene F, Akebonoic acid, Morusin, Rhaponticin, Procyanidin A2, Alaternin, Mulberrofuran K and Psoralidin) were selected as promising drug candidates and their pharmacokinetic properties and toxicity were discussed where available.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11101-021-09773-1.

Omnifarious fruit polyphenols: an omnipotent strategy to prevent and intervene diabetes and related complication?

Diabetes mellitus is a metabolic syndrome which cannot be cured. Recently, considerable interest has been focused on food ingredients to prevent and intervene in complications of diabetes. Polyphenolic compounds are one of the bioactive phytochemical constituents with various biological activities, which have drawn increasing interest in human health. Fruits are part of the polyphenol sources in daily food consumption. Fruit-derived polyphenols possess the anti-diabetic activity that has already been proved either from in vitro studies or in vivo studies. The mechanisms of fruit polyphenols in treating diabetes and related complications are under discussion. This is a comprehensive review on polyphenols from the edible parts of fruits, including those from citrus, berries, apples, cherries, mangoes, mangosteens, pomegranates, and other fruits regarding their potential benefits in preventing and treating diabetes mellitus. The signal pathways of characteristic polyphenols derived from fruits in reducing high blood glucose and intervening hyperglycemia-induced diabetic complications were summarized.