Influence of Flavonoids on Mechanism of Modulation of Insulin Secretion

Anti-obesity and anti-diabetic bioactive peptides: A comprehensive review of their sources, properties, and techno-functional challenges

The scourge of obesity arising from obesogens and poor dieting still ravages our planet as half of the global population may be overweight and obese by 2035. This metabolic disorder is intertwined with type 2 diabetes (T2D), both of which warrant alternative therapeutic options other than clinically approved drugs like orlistat with their tendency of abuse and side effects. In this review, we comprehensively describe the global obesity problem and its connection to T2D. Obesity, overconsumption of fats, the mechanism of fat digestion, obesogenic gut microbiota, inhibition of fat digestion, and natural anti-obesity compounds are discussed. Similar discussions are made for diabetes with regard to glucose regulation, the diabetic gut microbiota, and insulinotropic compounds. The sources and production of anti-obesity bioactive peptides (AOBPs) and anti-diabetic bioactive peptides (ADBPs) are also described while explaining their structure-function relationships, gastrointestinal behaviors, and action mechanisms. Finally, the techno-functional applications of AOBPs and ADBPs are highlighted.

Endoplasmic reticulum stress in pancreatic β-cell dysfunction: The potential therapeutic role of dietary flavonoids

Diabetes mellitus (DM) is a global health burden that is characterized by the loss or dysfunction of pancreatic β-cells. In pancreatic β-cells, endoplasmic reticulum (ER) stress is a fact of life that contributes to β-cell loss or dysfunction. Despite recent advances in research, the existing treatment approaches such as lifestyle modification and use of conventional therapeutics could not prevent the loss or dysfunction of pancreatic β-cells to abrogate the disease progression. Therefore, targeting ER stress and the consequent unfolded protein response (UPR) in pancreatic β-cells may be a potential therapeutic strategy for diabetes treatment. Dietary phytochemicals have therapeutic applications in human health owing to their broad spectrum of biochemical and pharmacological activities. Flavonoids, which are commonly obtained from fruits and vegetables worldwide, have shown promising prospects in alleviating ER stress. Dietary flavonoids including quercetin, kaempferol, myricetin, isorhamnetin, fisetin, icariin, apigenin, apigetrin, vitexin, baicalein, baicalin, nobiletin hesperidin, naringenin, epigallocatechin 3-O-gallate hesperidin (EGCG), tectorigenin, liquiritigenin, and acacetin have shown inhibitory effects on ER stress in pancreatic β-cells. Dietary flavonoids modulate ER stress signaling components, chaperone proteins, transcription factors, oxidative stress, autophagy, apoptosis, and inflammatory responses to exert their pharmacological effects on pancreatic β-cells ER stress. This review focuses on the role of dietary flavonoids as potential therapeutic adjuvants in preserving pancreatic β-cells from ER stress. Highlights of the underlying mechanisms of action are also presented as well as possible strategies for clinical translation in the management of DM.

Protective effects of cardamom aqueous extract against tamoxifen-induced pancreatic injury in female rats

Tamoxifen (TAM) is a commonly used drug for breast cancer treatment. Although effective, TAM has deleterious effects on many organs. The toxic effects of TAM on the pancreas and the underlying mechanisms however, have not fully investigated. In the present study, we investigated the effects of TAM on the pancreatic tissue in female rats. We also examined whether cardamom aqueous extract (CAE) protects against TAM-induced pancreatic injury. TAM-intoxicated rats were injected with 45 mg/kg of TAM for 10 days, whereas rats in the CAE-treated group were administered 10 mL/kg of CAE for 20 days, starting 10 days prior to TAM administration. Treatment with TAM resulted in severe degeneration of the pancreatic acini and marked increases in the serum levels of pancreatic lipase, α-amylase, glucose, fatty acids and triglycerides along with decreased insulin serum levels. TAM led to oxidative stress as evident from a significant increase in the pancreatic levels of lipid peroxides and nitric oxide along with the depletion of reduced glutathione, glutathione peroxidase, and superoxide dismutase. Moreover, inflammation was indicated by a significant increase in tumor necrosis factor-α and interleukin-6 levels, enhanced expression of the macrophage recruitment marker; CD68 as well as up-regulated protein levels of toll-like receptor 4 and nuclear factor kappa B and increased p-p38/MAPK ratio; which are important signals in the production of inflammatory cytokines. TAM also markedly increased the pancreatic levels of caspase-3 and BAX reflecting its apoptotic effects. The CAE treatment ameliorated all the biochemical and histological changes induced by TAM. The present study revealed, for the first time, that TAM has toxic effects on the pancreatic tissue through oxidative stress, inflammation and apoptotic effects. The present study also provides evidence that CAE exerts cytoprotective effects against these deleterious effects induced by TAM in the pancreatic tissue.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00198-w.

Effects of silibinin on apoptosis and insulin secretion in rat RINm5F pancreatic β-cells

We investigated whether silibinin, a flavonoid, might be useful for treating diabetes mellitus by treating five groups of rat RINm5F β-insulinemia cells as follows: control streptozotocin (STZ) group administered citrate buffer and dimethyl sulfoxide; STZ group administered 20 mM STZ; silibinin group administered 50 µM silibinin; pre-silibinin group administered 50 µM silibinin 5 h before administering 20 mM STZ; simultaneous group administered 50 µM silibinin at the same time as 20 mM STZ. For all groups, MTT assay and flow cytometry were used to evaluate cell viability and necrosis, respectively. Glucose-stimulated insulin secretion (GSIS) and insulin cell content were determined using enzyme-linked immunosorbent assay. Also, expression of genes, pancreatic and duodenal homeobox 1 (pdx1), neuronal differentiation 1 (neurod1), v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog A (mafa), glucose transporter 2 (glut2)) was determined using the real-time polymerase chain reaction. We found that silibinin improved the viability of RINm5F cells and increased GSIS and cellular insulin under glucotoxic conditions. Silibinin increased the expression of neurod1, mafa and glut2, but reduced pdx1 expression. Our findings suggest that silibinin might increase glucose sensitivity and insulin synthesis under glucotoxic conditions, which could be useful for diabetes treatment.

A systematic review on anti-diabetic plant essential oil compounds: Dietary sources, effects, molecular mechanisms, and safety

Type 2 diabetes mellitus (T2DM) is a multifaceted metabolic syndrome defined through the dysfunction of pancreatic β-cells driven by a confluence of genetic and environmental elements. Insulin resistance, mediated by interleukins and other inflammatory elements, is one of the key factors contributing to the progression of T2DM. Many essential oils derived from dietary plants are beneficial against various chronic diseases. We reviewed the anti-diabetic properties of dietary plant-derived essential oil compounds, with a focus on their molecular mechanisms by modulating specific signaling pathways and other critical inflammatory mediators involved in insulin resistance. High-quality literature published in the last 12 years, from 2010 to 2022, was collected from the Scopus, Web of Science, PubMed, and Embase databases using the search terms "dietary plants," "essential oils," "anti-diabetic," "insulin resistance," "antihyperglycemic," "T2DM," "anti-diabetic essential oils," and anti-diabetic mechanism." According to the results, the essential oil compounds, including cinnamaldehyde, carvacrol, zingerone, sclareol, zerumbone, myrtenol, thujone, geraniol, citral, eugenol, thymoquinone, thymol, citronellol, α-terpineol, and linalool have been demonstrated to contain strong anti-diabetic effects via modulating various signal transduction pathways linked to glucose metabolism. Additionally, in diabetes-related animal models, they can also considerably reduce the expression of TNF-α, IL-1β, IL-4, IL-6, iNOS, and COX-2. The main signaling molecules regulated by these compounds include AMPK, GLUT4, Caspase-3, PPARγ, PPARα, NF-κB, p-IκBα, MyD88, MCP-1, SREBP-1c, AGEs, RAGE, VEGF, Nrf2/HO-1, and SIRT-1. They can also significantly inhibit the generation of TBARS and MDA, reduce oxidative stress, increase insulin levels, adiponectin, and glycoprotein enzymes, boost antioxidant enzymes like SOD, CAT, and GPx, as well as reduce glutathione and vital glycolytic enzymes. Besides, they can significantly lower the levels of liver enzymes and lipid profile markers. Moreover, most essential oil compounds are generally safe based on animal studies. In conclusion, dietary plant-derived essential oil compounds have potential anti-diabetic effects by influencing different signaling pathways and molecular targets linked to glucose metabolism, and should be safe and beneficial against diabetes and related complications.

Scopoletin stimulates the secretion of insulin via a KATP channel-dependent pathway in INS-1 pancreatic β cells

OBJECTIVES

In this study, we investigated whether scopoletin stimulated the secretion of insulin in pancreatic β cells as well as the underlying mechanism involved in this process.

METHODS

We incubated the INS-1 pancreatic β cells with various concentrations of glucose (1.1, 5.6 or 16.7 mM) in the presence or absence of scopoletin. We then analysed the secretion of insulin in the cells treated with insulin secretion inhibitors or secretagogues. The intracellular influx of calcium induced by scopoletin was also analysed using the Fluo-2 AM dye.

KEY FINDINGS

We found that scopoletin (1-20 µM) markedly induced the secretion of insulin in a glucose concentration-dependent manner compared with the control. At depolarizing concentrations of potassium chloride (KCl), scopoletin markedly enhanced the insulin secretion compared with the cells which were treated only with KCl. Moreover, the treatment with diazoxide-opening K+ATP channel and verapamil blocking Ca2+ channel significantly decreased the scopoletin-induced increase in insulin secretion. After the pre-treatment of cells with a Ca2+ fluorescent dye, treatment with 20 µM scopoletin resulted in a significant increase in the influx of intracellular Ca2+, exhibiting fluorescence changes in various spectra.

CONCLUSIONS

Scopoletin stimulates the secretion of insulin via a K+ATP channel-dependent pathway in the INS-1 pancreatic β cells.

Comparative effects of metformin and Cistus laurifolius L. extract in streptozotocin-induced diabetic rat model: oxidative, inflammatory, apoptotic, and histopathological analyzes

Interest in phytochemical therapy methods in the treatment of diabetes is increasing day by day. Although the antidiabetic and antioxidant effects of Cistus laurifolius L. (CL) have been mentioned, the systemic effects remain unknown. The present study aims at evaluating the antidiabetic effects of the CL aqueous extract via metformin on streptozotocin (STZ)-induced diabetic rats. Forty male Wistar albino rats were divided into five groups of eight animals each: control, diabetic group (55mg/kg STZ), STZ+125mg/kg CL, STZ+250mg/kg CL, and STZ+100mg/kg metformin. The effects of CL and metformin on oxidative, apoptotic, and inflammatory pathways were comparatively investigated. In addition, nuclear factor-κB (NFκB), tumor necrosis factor-alpha (TNF-α), and interleukin (IL)-1β expressions analysis were carried out. CL treatment resulted in a significant improvement in blood glucose levels, lipid profile, pancreatic markers, and liver and kidney function tests. A 250mg/kg CL treatment decreased by 67.9%, 31.6%, 66.8%, 28.3%, and 31.4% in the total oxidant capacity, NFκB, TNF-α, IL-1β, caspase3, and cytochrome c levels, respectively, compared to the diabetic group. Additionally, CL treatments showed a dose-dependent reduction in NFκB, TNF-α, and IL-1β expression levels. A 250mg/kg CL treatment exhibited a greater increase (by 9.6%) in total antioxidant capacity than metformin. CL treatment provided histologically more improvement in the brain, heart, pancreas, spleen, liver, kidney, and testicular tissues compared to the metformin group. Our results suggest that the single treatment of CL aqueous extract at the low doses may have stronger short-term anti-diabetic effects than metformin. Therefore, further studies are needed regarding the long-term hypoglycemic effect or treatment of CL aqueous extract.

Schisandrin C Affects Glucose-Stimulated Insulin Secretion in Pancreatic β-Cells and Glucose Uptake in Skeletal Muscle Cells

The aim of our study was to investigate the effect of three lignans (schisandrol A, schisandrol B, and schisandrin C) on insulin secretion in rat INS-1 pancreatic β-cells and glucose uptake in mouse C2C12 skeletal muscle cells. Schisandrol A and schisandrin C enhanced insulin secretion in response to high glucose levels with no toxic effects on INS-1 cells. The effect of schisandrin C was superior to that of gliclazide (positive control), a drug commonly used to treat type 2 diabetes (T2D). In addition, western blot analysis showed that the expression of associated proteins, including peroxisome proliferator-activated receptor γ (PPARγ), pancreatic and duodenal homeobox 1 (PDX-1), phosphatidylinositol 3-kinase (PI3K), Akt, and insulin receptor substrate-2 (IRS-2), was increased in INS-1 cells after treatment with schisandrin C. In addition, insulin secretion effect of schisandrin C were enhanced by the Bay K 8644 (L-type Ca²⁺ channel agonist) and glibenclamide (K⁺ channel blocker), were abolished by the nifedipine (L-type Ca²⁺ channel blocker) and diazoxide (K⁺ channel activator). Moreover, schisandrin C enhanced glucose uptake with no toxic effects on C2C12 cells. Western blot analysis showed that the expression of associated proteins, including insulin receptor substrate-1 (IRS-1), AMP-activated protein kinase (AMPK), PI3K, Akt, glucose transporter type 4 (GLUT-4), was increased in C2C12 cells after treatment with schisandrin C. Schisandrin C may improve hyperglycemia by enhancing insulin secretion in pancreatic β-cells and improving glucose uptake into skeletal muscle cells. Our findings may provide evidence that schisandrin C may be beneficial in devising novel anti-T2D strategies.

Caesalpinia bonduc (L.) Roxb. as a promising source of pharmacological compounds to treat Poly Cystic Ovary Syndrome (PCOS): A review

ETHNOPHARMACOLOGICAL RELEVANCE

Caesalpinia bonduc (L.) Roxb. [Family: Fabaceae (Caesalpiniaceae)], known as bonduc nut or fever nut, has been used in India for many years to treat fever, inflammation, diabetes, cardiovascular disorder, cancer and also for birth control. In recent years, the seeds of this plant are consumed to regulate the menstrual disorders in PCOS. Poly cystic ovary syndrome (PCOS) is one of the most common endocrinological disorders faced by women of reproductive-age in several countries.

AIM OF THE REVIEW

This review is aimed at providing the updates on the potential of Caesalpinia bonducella in treating the major symptoms of PCOS and also highlights the future research needs.

MATERIALS AND METHODS

All the data pertaining to the plant was collected from multiple databases like Google, Science Direct, Springer, PubMed, Reaxys, Sci Finder, Wiley Online library and Taylor and Francis without any language restrictions. Moreover, information related to PCOS treatment was obtained from native medicine practitioners and from Ayurvedic pharmacopeia of India.

RESULTS

More than 50 compounds have been identified in the seed kernels of C. bonducella so far. Seed kernel extracts rich in active compounds like bonducellin, caesalpinin, cassane furanoditerpenes, terpernoids, flavonoids and sterols are studied for their anti-diabetic, anti-hyperlipidemic, anti-cancer, anti-pyretic, and anti-oxidant properties. Recent literature has also attributed anti-androgenic and anti-estrogenic potential to this plant which might be helpful in regulating hyperandrogenism, the major predisposing factor contributing to various other clinical symptoms of PCOS.

CONCLUSION

Phytochemicals in C. bonducella are effective against several ailments attributed to PCOS. However, there are no experiments done in PCOS animal models to claim the direct application of C. bonducella in PCOS treatment. Hence, further dose dependent toxicity studies are warranted in animal PCOS models and in PCOS patients to support the traditional evidence of the plants' potential to treat PCOS.

Potential Effects of Sweet Potato (Ipomoea batatas) in Hyperglycemia and Dyslipidemia-A Systematic Review in Diabetic Retinopathy Context

Hyperglycemia is a condition with high glucose levels that may result in dyslipidemia. In severe cases, this alteration may lead to diabetic retinopathy. Numerous drugs have been approved by officials to treat these conditions, but usage of any synthetic drugs in the long term will result in unavoidable side effects such as kidney failure. Therefore, more emphasis is being placed on natural ingredients due to their bioavailability and absence of side effects. In regards to this claim, promising results have been witnessed in the usage of Ipomoea batatas (I. batatas) in treating the hyperglycemic and dyslipidemic condition. Thus, the aim of this paper is to conduct an overview of the reported effects of I. batatas focusing on in vitro and in vivo trials in reducing high glucose levels and regulating the dyslipidemic condition. A comprehensive literature search was performed using Scopus, Web of Science, Springer Nature, and PubMed databases to identify the potential articles on particular topics. The search query was accomplished based on the Boolean operators involving keywords such as (1) Beneficial effect OR healing OR intervention AND (2) sweet potato OR Ipomoea batatas OR traditional herb AND (3) blood glucose OR LDL OR lipid OR cholesterol OR dyslipidemia. Only articles published from 2011 onwards were selected for further analysis. This review includes the (1) method of intervention and the outcome (2) signaling mechanism involved (3) underlying mechanism of action, and the possible side effects observed based on the phytoconstiuents isolated. The comprehensive literature search retrieved a total of 2491 articles using the appropriate keywords. However, on the basis of the inclusion and exclusion criteria, only 23 articles were chosen for further review. The results from these articles indicate that I. batatas has proven to be effective in treating the hyperglycemic condition and is able to regulate dyslipidemia. Therefore, this systematic review summarizes the signaling mechanism, mechanism of action, and phytoconstituents responsible for those activities of I. batatas in treating hyperglycemic based on the in vitro and in vivo study.

Formulation and characterization of rutin loaded chitosan-alginate nanoparticles: Antidiabetic and cytotoxicity studies

BACKGROUND

The rutin loaded chitosan-alginate nanoparticles (RCANP) were prepared using an ion gelation method. The optimized RCANP4 formulation composed of rutin: alginate: chitosan with the ratio of 1.24:5:2. The particle size, zeta potential, and entrapment efficiency of RCANP4 formulation were found to be 168.4 ± 11.23 nm, -24.7 ± 1.5 mV, and 91.23 ± 1.1%, respectively. The in vitro drug release of RCANP4 formulation was found to be 88.89 ± 2.9% within 24 h. The Fourier transform infrared spectroscopy (FT-IR) of RCANP4 revealed all characteristic groups of rutin, confirming the successful loading of rutin into the nanoparticles. <P> Background: The rutin loaded chitosan-alginate nanoparticles (RCANP) were prepared using an ion gelation method. The optimized RCANP4 formulation composed of rutin: alginate: chitosan with the ratio of 1.24:5:2. The particle size, zeta potential, and entrapment efficiency of RCANP4 formulation were found to be 168.4 ± 11.23 nm, -24.7 ± 1.5 mV, and 91.23 ± 1.1%, respectively. The in vitro drug release of RCANP4 formulation was found to be 88.89 ± 2.9% within 24 h. The Fourier transform infrared spectroscopy (FT-IR) of RCANP4 revealed all characteristic groups of rutin, confirming the successful loading of rutin into the nanoparticles. <P> Results: The results obtained for glucose uptake in HepG2 cells, the RCANP4 caused a significant (P < 0.05) increase in glucose uptake in contrast to rutin. In vitro cytotoxicity results explained that RCANP4 could significantly (P < 0.05) reduce the cells viability rate compared with rutin. It may be due to the internalization of RCANP4 formulations in systemic circulation. <P> Conclusion: The results also showed that RCANP4 could significantly reduce cell viability over 24 h and 48 h compared to free rutin.

Syzygium jambos extract mitigates pancreatic oxidative stress, inflammation and apoptosis and modulates hepatic IRS-2/AKT/GLUT4 signaling pathway in streptozotocin-induced diabetic rats

The protective effect of Syzygium jambos (SJ) bark extract against streptozotocin-induced diabetes was tested in rats. Animals were treated with 100 or 200 mg/kg of the extract or glibenclamide, 0.5 mg/kg per os, once daily: started 2 days before streptozotocin (STZ) injection and lasted for 14 days after STZ injection. The effect of the extract was also evaluated on normal rats in comparison with glibenclamide. Diabetic animals showed an elevated blood glucose level, positive glycosuria, elevated fructosamine, pancreatic malondialdehyde, pancreatic TNF-a, and pancreatic caspase-3 levels and decreased serum insulin, pancreatic IL-10, pancreatic BCL-2, reduced glutathione (GSH), liver insulin substrate-2, liver phosphorylated protein kinase B (p-AKT) and liver glucose transporter 4 (GLUT4) levels. Histopathological examination of diabetic rats revealed islets destruction and vacuolation and collagen fibers deposition. All these changes were mitigated dose dependently by the extract. The high dose of the extract exerted comparable effects with glibenclamide in most studied parameters. These results indicated the protective role of SJ against the STZ diabetogenic action. In the pancreatic and hepatic tissue of diabetic rats, SJ effectively recovered pancreatic cells by reducing hyperglycemia through activating endogenous antioxidants, dynamic insulin production, and suppressing inflammation and apoptosis. The observed results might be attributed to the existence of 10 secondary metabolites as annotated by LC-MS. Taken together, S. jambos is a potential candidate for further studies to confirm its activities as a therapeutic agent for diabetic patients.

Antihyperglycemic and hypoglycemic activity of Mayan plant foods in rodent models

BACKGROUND

Postprandial hyperglycemia and decreased insulin secretion are relevant to risk factors in the development of type 2 diabetes and its complications. Plant foods with antidiabetic properties could be an affordable alternative in the prevention and treatment of this disease. In the present study, the antihyperglycemic and hypoglycemic activity of Bixa orellana, Psidium guajava L., Cucurbita moschata, Raphanus sativus L. and Brassica oleracea var. capitata - Mayan plant foods - were evaluated at doses of 5 and 10 mg kg^-1 . Antihyperglycemic activity was measured in healthy Wistar rats and those with obesity induced by high-sucrose diet (group HSD) (20%). The hypoglycemic activity was measure in healthy CD1 mice.

RESULTS

Fasting glucose, Lee index and the body weight of HSD rats increased significantly (P ≤ 0.05) after 12 weeks of induction compared to healthy rats. In healthy rats, P. guajava and Bixa orellana (10 mg kg^-1 ) demonstrated higher and statistically different (P ≤ 0.05) antihyperglycemic activity compared to control acarbose (0.5 mg kg^-1 ). In the HSD rat group, all Mayan plant foods (10 mg kg^-1 ) demonstrated antihyperglycemic activity statistically equal (P ≤ 0.05) to control acarbose. However, Brassica oleracea and R. sativus registered the highest antihyperglycemic activity. Bixa orellana and P. guajava (5 mg kg^-1 ) showed similar hypoglycemic activity (P ≤ 0.05) to glibenclamide (0.5 mg kg^-1 ) but was not significant (P ≤ 0.05) compared to insulin (5 UI kg^-1 ).

CONCLUSION

The present study provides valuable evidence on the possible health benefits of Mayan plant foods. These foods could contribute to the development of therapeutic diet strategies for the prevention and treatment of diabetes. © 2021 Society of Chemical Industry.

The optimization of ultrasonic-microwave assisted synergistic extraction of Lotus plumule extract rich in flavonoids and its hypoglycemic activity

Lotus (Nelumbo nucifera Gaertn), a kind of perennial aquatic plant, is widely cultivated and consumed by people in Asian countries. Lotus plumule flavonoids (LPF) have been recognized as a hypoglycemic agent. LPF was optimally obtained using novel ultrasonic-microwave assisted synergistic extraction (UMSE) method by response surface methodology (RSM) on the basis of the results of single-factor experiments. Furthermore, the hypoglycemic activity of LPF was investigated by measuring the body weight, fasting blood glucose (FBG) level, and oral glucose tolerance test (OGTT) and analyzing the physiological indexes in streptozotocin-diabetic mice model. The optimum extraction conditions consisted of microwave power 355 W, ultrasonic power 423 W, extraction time 15 min, solid-liquid ratio 1:40, ultrasound/interval time 1/0, and ethanol concentration 70% with the maximum LPF yield of 2.62%. LPF supplementation significantly decreased the body weight, FBG, OGTT, serum total cholesterol (TC), serum total triglycerides (TG), and insulin levels, indicating the antidiabetic activity of LPF. This research verified that the UMSE technique was highly efficient to extract LPF to the maximum extent and the flavonoids from L. plumule exhibited hypoglycemic activity, which showed broad development and application prospects.

Natural Polyphenols in Metabolic Syndrome: Protective Mechanisms and Clinical Applications

Metabolic syndrome (MetS) is a chronic disease, including abdominal obesity, dyslipidemia, hyperglycemia, and hypertension. It should be noted that the occurrence of MetS is closely related to oxidative stress-induced mitochondrial dysfunction, ectopic fat accumulation, and the impairment of the antioxidant system, which in turn further aggravates the intracellular oxidative imbalance and inflammatory response. As enriched anti-inflammatory and antioxidant components in plants, natural polyphenols exhibit beneficial effects, including improving liver fat accumulation and dyslipidemia, reducing blood pressure. Hence, they are expected to be useful in the prevention and management of MetS. At present, epidemiological studies indicate a negative correlation between polyphenol intake and MetS incidence. In this review, we summarized and discussed the most promising natural polyphenols (including flavonoid and non-flavonoid drugs) in the precaution and treatment of MetS, including their anti-inflammatory and antioxidant properties, as well as their regulatory functions involved in glycolipid homeostasis.

Chemical Profile, In Vitro Antioxidant, Pancreatic Lipase, and Alpha-Amylase Inhibition Assays of the Aqueous Extract of Elettaria cardamomum L. Fruits

Phytochemical and pharmacological investigations of Elettaria cardamomum L. were mostly focused on its essential oil and organic crude extracts with little attention on its aqueous extracts. Therefore, the current study aimed to investigate the phytochemical profile, in vitro antiobesity, and antidiabetic activities of the aqueous extract of Elettaria cardamomum L. family Zingiberaceae. UPLC-ESI-MS/MS analysis is used for the aqueous extract characterization in both ionization modes. The analysis revealed the tentative identification of forty-seven compounds based on their MS/MS fragmentation pattern and comparison with the reported data. The identified compounds include eight flavones, thirteen phenolic and nonphenolic acids, one coumarin, and nineteen anthocyanins. Moreover, the in vitro antiobesity and antidiabetic activities were also studied. The results showed that E. cardamomum L. aqueous extract inhibits pancreatic lipase and α-amylase enzyme in a concentration-dependent manner, as 1 mg/mL extract was able to inhibit pancreatic lipase and α-amylase by 62.25% ± 0.58 (IC50 = 288.75 ± 1.3 µg/mL) and 70.42% ± 1.5 (IC50 = 220.5 ± 1.3 µg/mL), respectively. Conclusively, the current study indicated that the investigated biological activities of Elettaria cardamomum aqueous extract were attributed to the existence of biologically active metabolites such as flavones, phenolic and nonphenolic acids, coumarins, and anthocyanins. Moreover, it proposed that the aqueous cardamom extract can be used as a natural potential source in different pharmaceutical preparations to protect against variable chronic disorders, especially obesity and diabetes. Deeper in vivo investigations, isolation, purification, and structural elucidation of the major active metabolites from cardamom are recommended.

(-)-Leucophyllone, a Tirucallane Triterpenoid from Cornus walteri, Enhances Insulin Secretion in INS-1 Cells

Phytochemical examination of the MeOH extract from the stems and stem bark of Cornus walteri (Cornaceae) led to the isolation and verification of a tirucallane triterpenoid, (-)-leucophyllone, as a major component. Its structure was elucidated using NMR spectroscopy and liquid chromatography-mass spectrometry. The effect of (-)-leucophyllone on insulin secretion in INS-1 cells was investigated. (-)-Leucophyllone increased glucose-stimulated insulin secretion (GSIS) at concentrations showing no cytotoxic effect in rat INS-1 pancreatic β-cells. Moreover, we attempted to determine the mechanism of action of (-)-leucophyllone in the activation of insulin receptor substrate-2 (IRS-2), phosphatidylinositol 3-kinase (PI3K), Akt, and pancreatic and duodenal homeobox-1 (PDX-1). Treatment of INS-1 cells with (-)-leucophyllone markedly increased the expression of these proteins. Our findings indicate the potential of (-)-leucophyllone as an antidiabetic agent.

A comprehensive review on the antidiabetic activity of flavonoids targeting PTP1B and DPP-4: a structure-activity relationship analysis

Type 2 diabetes (T2D) is an expanding global health problem, resulting from defects in insulin secretion and/or insulin resistance. In the past few years, both protein tyrosine phosphatase 1B (PTP1B) and dipeptidyl peptidase-4 (DPP-4), as well as their role in T2D, have attracted the attention of the scientific community. PTP1B plays an important role in insulin resistance and is currently one of the most promising targets for the treatment of T2D, since no available PTP1B inhibitors were still approved. DPP-4 inhibitors are among the most recent agents used in the treatment of T2D (although its use has been associated with possible cardiovascular adverse events). The antidiabetic properties of flavonoids are well-recognized, and include inhibitory effects on the above enzymes, although hitherto not therapeutically explored. In the present study, a comprehensive review of the literature of both synthetic and natural isolated flavonoids as inhibitors of PTP1B and DPP-4 activities is made, including their type of inhibition and experimental conditions, and structure-activity relationship, covering a total of 351 compounds. We intend to provide the most favorable chemical features of flavonoids for the inhibition of PTP1B and DPP-4, gathering information for the future development of compounds with improved potential as T2D therapeutic agents.

Mormodica charantia L. fruit and Genistein ameliorates type 2 diabetes in rats by preventing lipid accumulation, insulin resistance and enhancing beta cell function

PURPOSE

The present study was aimed at evaluating the role of Momordica charantia L. fruit and Genistein on beta cell, insulin resistance/sensitivity and lipid profile in type 2 diabetic rats.

METHODS

Thirty-five (35) albino rats were divided into seven (7) groups of 5 rats each comprising of five (5) non-diabetic and thirty (30) diabetic rats. Groups 1 and 2 served as the normal control and diabetic control groups respectively and received distill water, groups 3 and 4 received Mormodica charantia L. at 250 mg/kg and 500 mg/kg respectively. Groups 5 and 6 received Genistein at 10 mg/kg and 20 mg/kg respectively while group 7 received Metformin at 500 mg/kg the experiment lasted for four weeks. All the rats were euthanized at the end of the fourth week.

RESULTS

Lipid profile, glucose and insulin levels were determined from the analysis of serum parameters and the histology of the pancreas. A significant reduction (p < 0.05) in blood glucose levels was noticed in rats that received Momordica charantia L. (MC) and genistein when compared with diabetic control rats. A significant decrease (p < 0.05) in cholesterol, triglyceride, low density lipoprotein (LDL) and very low density lipoprotein (VLDL) levels were also noted in rats that received MC and Genistein when compared with the diabetic control rats. MC and Genistein significantly increased (P < 0.05) serum insulin level compared to the diabetic control rats. MC and Genistein significantly decreased (p < 0.05) homeostatic model assessment-insulin resistance (HOMA-IR) level compared with the diabetic control group. Pancreas of rats that received MC and Genistein showed regenerating beta-cells.

CONCLUSION

Momordica charantia L. fruit and Genistein were able to enhance beta cell function and prevent lipid accumulation and insulin resistance in type 2 diabetic rats.

Effects of Rutin on Wound Healing in Hyperglycemic Rats

Long-term poor glycemic control negatively affects macrovascular and microvascular diseases, as well as wound restoration. Buckwheat is a good source of rutin (quercetin-3-O-rutoside) and has benefits in regulating blood sugar. This study was to evaluate the antioxidant and anti-inflammatory effects of rutin on wound healing in streptozotocin-induced hyperglycemic rats. Eighteen male Wistar rats were randomly divided into three groups: normal (NDM), hyperglycemic (DM), and hyperglycemic with rutin (DMR). After induction of hyperglycemia for 2 days, a 15 × 15 mm wound was induced on the back of each rat. Intraperitoneal injection of rutin significantly ameliorated diabetes-induced body weight loss and improved metabolic dysfunctions of hyperglycemic rats. Based on appearance and histopathological staining, rutin promotes wound healing and inhibits production of inflammatory cells. The immunoblotting data indicated that rutin promotes production of antioxidant enzymes induced by nuclear factor erythroid 2-related factor 2 (NRF2), inhibits the expression of matrix metalloproteinases (MMPs) regulated by NF-κB, and decreases the expression of vascular endothelial growth factor (VEGF). It also promotes the expression of neurogenic-related protein (UCH-L1). The aforementioned results indicated that rutin reduces oxidative stress and inflammatory response in hyperglycemic rats, promoting wound healing and subsequently reducing the risk of wound ulcers.

Constituents of Coreopsis lanceolata Flower and Their Dipeptidyl Peptidase IV Inhibitory Effects

A new polyacetylene glycoside, (5R)-6E-tetradecene-8,10,12-triyne-1-ol-5-O-β-glucoside (1), was isolated from the flower of Coreopsis lanceolata (Compositae), together with two known compounds, bidenoside C (10) and (3S,4S)-5E-trideca-1,5-dien-7,9,11-triyne-3,4-diol-4-O-β-glucopyranoside (11), which were found in Coreopsis species for the first time. The other known compounds, lanceoletin (2), 3,2'-dihydroxy-4-3'-dimethoxychalcone-4'-glucoside (3), 4-methoxylanceoletin (4), lanceolin (5), leptosidin (6), (2R)-8-methoxybutin (7), luteolin (8) and quercetin (9), were isolated in this study and reported previously from this plant. The structure of 1 was elucidated by analyzing one-dimensional and two-dimensional nuclear magnetic resonance and high resolution-electrospray ionization-mass spectrometry data. All compounds were tested for their dipeptidyl peptidase IV (DPP-IV) inhibitory activity and compounds 2-4, 6 and 7 inhibited DPP-IV activity in a concentration-dependent manner, with IC₅₀ values from 9.6 to 64.9 μM. These results suggest that C. lanceolata flower and its active constituents show potential as therapeutic agents for diseases associated with type 2 diabetes mellitus.

Cyclohexane extract of walnut leaves improves indices of oxidative stress, total homocysteine and lipids profiles in streptozotocin-induced diabetic rats

This study aimed to evaluate the effect of two doses of cyclohexane extract of walnut leaves on total homocysteine, lipids profiles, and indices of oxidative stress including superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and malondialdehyde (MDA) in diabetic rats. Diabetes was induced by a single intraperitoneal (IP) injection of streptozotocin (50 mg/kg BW). Twenty-eight male Sprague Dawley rats were randomly divided into four groups, group I: control (received sesame oil as vehicle), group II: diabetic control (received sesame oil), group III and IV: diabetic rats treated by 150 and 250 mg/kg body weight (BW) per day extract of walnut leaves, respectively. All groups were treated for 28 days via oral gavage. Fasting blood glucose (FBG) level and body weight measured before injection, 3 days after injection, and on days 0, 7, 14, 21, and 28 of treatment. At the end the 28th day of the experiment, blood samples collected via heart puncture and the sera were used for estimation of the above-mentioned parameters. The results showed a decrease in FBS, TC, TG, LDL-c, VLDL-c, homocysteine, and MDA level and increase in the level of HDL-c in diabetics treated by walnut leave extracts in a dose-dependent manner after 28 days. The activity of antioxidant enzymes significantly increased in treated groups compared with diabetic control. It can be concluded that cyclohexane extract of walnut leaves has an overall beneficial effect on body weight, fasting blood glucose, lipids profile, antioxidant enzyme activities, and homocysteine.

Eugenol Improves Insulin Secretion and Content of Pancreatic Islets from Male Mouse

Glucose homeostasis is required for control of insulin secretion. Phenolic compounds improved glucose-stimulated insulin secretion (GSIS). Eugenol is a phenolic compound that may increase GSIS. So, it was decided to investigate the effect of eugenol on the insulin secretion and content of pancreatic islets from the male mice. In this experimental study, 3-month-old NMRI mice (20-25 g) were prepared. The pancreatic islets of Langerhans were isolated using the collagenase digestion method and divided into 12 groups: glucose 2.8, 5.6, and 16.7 mM, glucose 2.8 mM + eugenol 50, 100, and 200 µM, glucose 5.6 mM + eugenol 50, 100, and 200 µM, and glucose 16.7 mM + eugenol 50, 100, and 200 µM. The islet's insulin secretion and content were measured after 1 hour and 24 hours incubation at 37°C, respectively, by the ELISA assays method and related commercial kit. Present results showed that all doses of eugenol increased islet's insulin secretion and content in the medium containing glucose concentrations 2.8, 5.6, and 16.7 mM (P < 0.05). In conclusion, eugenol as a phenolic compound increased insulin secretion and content of pancreatic islets. The moderate dose of this compound enhanced insulin secretion during hypo- and hyperglycemic conditions, as well as a high dose of eugenol, increased insulin content. Finally, present research suggested that the administration of eugenol 100 µM was suitable for the early stage of T2DM as well as eugenol 200 µM for the advanced stage of this disease.

Astragalin augments basal calcium influx and insulin secretion in rat pancreatic islets

Astragalin is a flavonol glycoside with several biological activities, including antidiabetic properties. The objective of this study was to investigate the effects of astragalin on glycaemia and insulin secretion, in vivo, and on calcium influx and insulin secretion in isolated rat pancreatic islets, ex vivo. Astragalin (1 and 10 mg / kg) was administered by oral gavage to fasted Wistar rats and serum glucose and plasma insulin were measured. Isolated pancreatic islets were used to measure basal insulin secretion and calcium influx. Astragalin (10 mg/ kg) decreased glycaemia and increased insulin secretion significantly at 15-180 min, respectively, in the glucose tolerance test. In isolated pancreatic cells, astragalin (100 μM) stimulated calcium influx through a mechanism involving ATP-dependent potassium channels, L-type voltage-dependent calcium channels, the sarcoendoplasmic reticulum calcium transport ATPase (SERCA), PKC and PKA. These findings highlight the dietary coadjuvant, astragalin, as a potential insulin secretagogue that may contribute to glucose homeostasis.

Methylation and Acetylation Enhanced the Antidiabetic Activity of Some Selected Flavonoids: In Vitro, Molecular Modelling and Structure Activity Relationship-Based Study

Flavonoids have been reported to exert antihyperglycemic effects and have potential to enhance the current therapy options against type 2 diabetes mellitus. However, the structure activity relationships (SAR) studies of flavonoids against this disease have not been thoroughly comprehended. Hence, in the present study, 14 structurally related flavonoids viz. wogonin, techtochrysin, norwogonin, isoscutellarein, hypolaetin, kaempferol, quercetin, methyl ether of wogonin, acetate of wogonin, acetate of norwogonin, 8-hydroxy-7-methoxyflavone, chrysin, (+)-catechin and (-)-epicatechin were taken into account for in vitro antidiabetic evaluation. Cell viability of RIN-5F pancreatic cells and 3T3-L1 pre-adipocyte cells was initially tested, then an insulin secretion assay of RIN-5F as well as adipogenesis and glucose uptake measurements of adipocyte were investigated. Subsequently, protein expressions study through adipokines measurement (leptin, adiponectin, TNF-α, RBP-4) via enzyme-linked immunosorbent assay (ELISA) kit, Western blotting analysis against GLUT4 and C/EBP-α as well as molecular docking against GLUT1 were analyzed. The results from cell culture antidiabetic assays (insulin secretion, adipogenesis, and glucose uptake), protein expressions and molecular docking pointed that the methoxy group at position C-8 is responsible for antidiabetic property of selected flavonoids via glucose uptake mechanism indicated by up regulation of GLUT4 and C/EBP-α expressions. The mechanism could be enhanced by the addition of an acetate group at C-5 and C-7 of the flavone skeleton.

Protective effects of rutin on liver injury in type 2 diabetic db/db mice

The aim of this study was to evaluate the protective effect of rutin on the liver of type 2 diabetic mice and explore the correlation mechanism. The db/db mice, selected as the type 2 diabetes mellitus (T2DM) models, have random blood glucose (RBG) and glucose level after 2 h of oral glucose loading of more than 16.7 mmol/L. After administration of 120 mg/kg or 60 mg/kg rutin, to T2DM mice, RBG, oral glucose tolerance, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in serum, and advanced glycation end products (AGEs) in vivo and vitro of different groups were detected. The liver pathological changes were observed under light and electron microscopy. Western blotting was used to detect the protein expression of insulin receptor substrate 2 (IRS-2) and phosphorylation of phosphatidylinositol 3 kinase (PI3K) on p85, Akt on Ser473, glycogen synthase kinase 3β (GSK-3β) on Ser9, real-time quantitative PCR was used to detect IRS-2 mRNA expression. Moreover, dynamically observing the effect of rutin on the generation of AGEs in non-enzymatic protein glycosylated system, Cell Counting Kit-8 (CCK-8) method was used to detect the effect of rutin on proliferation activity of HepG2 liver cells. The results showed that RBG and glucose levels of oral glucose tolerance test (OGTT) of mice in model group were significantly higher than that of normal group, which were significantly reduced after the rutin treatment. Rutin could reduce the ALT, AST activities and AGEs level in serum and potentiate the expression of IRS-2, P-PI3K (p85), P-Akt (Ser473), P-GSK-3β (Ser9) protein and IRS-2 mRNA in the liver tissue of db/db mice. Moreover, rutin could significantly alleviate the structure disorder of liver, reduce the degeneration and necrosis of liver cells and formation of collagen fibers of db/db mice. The results in vitro also showed that rutin could obviously inhibit the generation of AGEs, and promoted the proliferation activity of high glucose-stimulating HepG2 cells. In general, the protective effect of rutin on the liver of T2DM may be mediated by facilitating signal transduction and activated state of insulin IRS-2/PI3K/Akt/GSK-3β signal pathway, promoting hepatocyte proliferation, reducing blood glucose level and generation of AGEs.

Ethanolic Extract of Caesalpinia bonducella f. Seed Ameliorates Diabetes Phenotype of Streptozotocin- Nicotinamide-Induced Type 2 Diabetes Rat

Caesalpinia bonducella F. (Leguminosae) is widely used medicinal plant which contains flavonoid, tannin, saponin, and a potent antioxidant activity. However, the antihyperglycemic effect of the seed of C. bonducella is remained to be evaluated. This study used 24 male Wistar albino rats that were induced for type 2 diabetes with streptozotocin (STZ) and nicotinamide (NA). The rats were divided into three groups: the distilled water-treated group (NC group), glibenclamide-treated group (10 mg/kg/d, oral; PC group), and C. bonducella seed extract-treated group (500 mg/kg/d, oral; T group). Blood glucose and plasma insulin measurements were done after 14 days of treatment. The results showed that the postprandial blood glucose (PPBG) level of both PC and T groups were decreased significantly (p < 0.01 for both), whereas in NC group, the PPBG level was rising (p < 0.01). Glibenclamide was found to be more effective to decrease the PPBG level than C. bonducella seed extract (p < 0.01). The post-test fasting insulin level of T group was higher than other groups (p < 0.05). In summary, our results suggest that ethanolic extract of C. bonducella seed possesses antidiabetic activity against experimentally-induced type 2 diabetes.