A novel insulin receptor-binding protein from Momordica charantia enhances glucose uptake and glucose clearance in vitro and in vivo through triggering insulin receptor signaling pathway

Momordica charantia Bioactive Components: Hypoglycemic and Hypolipidemic Benefits Through Gut Health Modulation

Momordica charantia (MC), a member of the Cucurbitaceae family, is well known for its pharmacological activities that exhibit hypoglycemic and hypolipidemic properties. These properties are largely because of its abundant bioactive compounds and phytochemicals. Over the years, numerous studies have confirmed the regulatory effects of MC extract on glycolipid metabolism. However, there is a lack of comprehensive reviews on newly discovered MC-related components, such as insulin receptor-binding protein-19, adMc1, and MC protein-30 and triterpenoids 3β,7β,25-trihydroxycucurbita-5,23(E)-dien-19-al, and the role of MC in gut microbiota and bitter taste receptors. This review offers an up-to-date overview of the recently reported chemical compositions of MC, including polysaccharides, saponins, polyphenolics, peptides, and their beneficial effects. It also provides the latest updates on the role of MC in the regulation of gut microbiota and bitter taste receptor signaling pathways. As a result, this review will serve as a theoretical basis for potential applications in the creation or modification of MC-based nutrient supplements.

Molecular Targets and Mechanisms of Casein-Derived Tripeptides Ile-Pro-Pro and Val-Pro-Pro on Hepatic Glucose Metabolism

The objective of this study was to explore the molecular targets and mechanism of Ile-Pro-Pro (IPP) and Val-Pro-Pro (VPP) on regulating glucose metabolism in hepatic cells and their in vivo hypoglycemic activities in mice. Results showed that both IPP and VPP (600 μM) significantly enhanced the glucose consumption in HepG2 cells and primary hepatocytes (p < 0.05). They also regulated activities of glucose metabolizing enzymes and increased the protein expression of p-AKT and GLUT2 in HepG2 cells. IPP directly interacted with the insulin receptor (IR) to activate the insulin/AKT signaling pathway. The activity of VPP on glucose consumption was not attributed to IR binding, and 76 potential antidiabetic targets were predicted by similarity ensemble and shape similarity approaches. Among them, the AKT and MAPK signaling pathway, in which two hub genes AKT1 and MAPK4 existed, were evaluated to make major contributions to the activity of VPP on glucose consumption. Moreover, both IPP and VPP (300 μmol/kg) could significantly reduce the blood glucose levels in mice (p < 0.05), with blood glucose area under the curve dropping by approximately 19% ± 0.09 and 21% ± 0.11%, respectively. This study provides a new theoretical support for the development of IPP and VPP as functional foods to regulate glucose metabolic disorders.

Antioxidant and Hypoglycemic Potential of Essential Oils in Diabetes Mellitus and Its Complications

Since the earliest times, essential oils (EOs) have been utilized for medicinal and traditional purposes. However, in recent decades, an increasing interest has developed due to the need to rediscover herbal remedies and adjuvant therapies for the management of various diseases, particularly chronic ones. The present narrative review examines the potential for EOs to exert hypoglycemic and antioxidant effects in diabetes mellitus, analyzing the main publications having evaluated plant species with potentially beneficial effects through their phytocompounds in diabetes mellitus and its complications. Numerous species have shown promising characteristics that can be used in diabetes management. The hypoglycemic effects of these EOs are attributed to their capacity to stimulate glucose uptake, suppress glucose production, and increase insulin sensitivity. Moreover, EOs can alleviate the oxidative stress by manifesting their antioxidant effects via a variety of mechanisms, including the scavenging of free radicals, the regulation of antioxidant enzymes, and the decreasing of lipid peroxidation, due to their diverse chemical composition. These findings demonstrate the possible benefits of EOs as adjuvant therapeutic agents in the management of diabetes and its complications. The use of EOs in the treatment of diabetes shows good potential for the development of natural and effective strategies to enhance the health outcomes of people with this chronic condition, but additional experimental endorsements are required.

An Insulin Receptor-Binding Multifunctional Protein from Tamarindus indica L. Presents a Hypoglycemic Effect in a Diet-Induced Type 2 Diabetes-Preclinical Study

The objectives of this study were to evaluate the hypoglycemic effect of the trypsin inhibitor isolated from tamarind seeds (TTI) in an experimental model of T2DM and the in silico interaction between the conformational models of TTI 56/287 and the insulin receptor (IR). After inducing T2DM, 15 male Wistar rats were randomly allocated in three groups (n = 5): 1—T2DM group without treatment; 2—T2DM group treated with adequate diet; and 3—T2DM treated with TTI (25 mg/kg), for 10 days. Insulinemia and fasting glucose were analyzed, and the HOMA-IR and HOMA-β were calculated. The group of animals treated with TTI presented both lower fasting glucose concentrations (p = 0.0031) and lower HOMA-IR indexes (p = 0.0432), along with higher HOMA-β indexes (p = 0.0052), than the animals in the other groups. The in silico analyses showed that there was an interaction between TTIp 56/287 and IR with interaction potential energy (IPE) of −1591.54 kJ mol⁻¹ (±234.90), being lower than that presented by insulin and IR: −894.98 kJ mol⁻¹ (±32.16). In addition, the presence of amino acids, type of binding and place of interaction other than insulin were identified. This study revealed the hypoglycemic effect of a bioactive molecule of protein origin from Tamarind seeds in a preclinical model of T2DM. Furthermore, the in silico analysis allowed the prediction of its binding in the IR, raising a new perspective for explaining TTI’s action on the glycemic response.

Momordica charantia L.-Diabetes-Related Bioactivities, Quality Control, and Safety Considerations

Momordica charantia L. (Cucurbitaceae), commonly known as bitter gourd or bitter melon, is widely cultivated in many tropical and subtropical regions of the world, where its unripe fruits are eaten as a vegetable. Apart from its culinary use, M. charantia has a long history in traditional medicine, serving as stomachic, laxative or anthelmintic, and, most notably, for the treatment of diabetes and its complications. Its antidiabetic properties and its beneficial effects on blood glucose and lipid concentrations have been reported in numerous in vitro and in vivo studies, but the compounds responsible for the observed effects have not yet been adequately described. Early reports were made for charantin, a mixture of two sterol glucosides, and the polypeptide p-insulin, but their low concentrations in the fruits or their limited bioavailability cannot explain the observed therapeutic effects. Still, for many decades the search for more reasonable active principles was omitted. However, in the last years, research more and more focused on the particular cucurbitane-type triterpenoids abundant in the fruits and other parts of the plant. This mini review deals with compounds isolated from the bitter gourd and discusses their bioactivities in conjunction with eventual antidiabetic or adverse effects. Furthermore, methods for the quality control of bitter gourd fruits and preparations will be evaluated for their meaningfulness and their potential use in the standardization of commercial preparations.

MC03g0810, an Important Candidate Gene Controlling Black Seed Coat Color in Bitter Gourd (Momordica spp.)

Seed coat color is one of the most intuitive phenotypes in bitter gourd (Momordica spp.). Although the inheritance of the seed coat color has been reported, the gene responsible for it is still unknown. This study used two sets of parents, representing, respectively, the intersubspecific and intraspecific materials of bitter gourd, and their respective F₁ and F₂ progenies for genetic analysis and primary mapping of the seed coat color. A large F_2:3 population comprising 2,975 seedlings from intraspecific hybridization was used to fine-map the seed coat color gene. The results inferred that a single gene, named McSC1, controlled the seed coat color and that the black color was dominant over the yellow color. The McSC1 locus was mapped to a region with a physical length of ∼7.8 Mb and 42.7 kb on pseudochromosome 3 via bulked segregant analysis with whole-genome resequencing (BSA-seq) and linkage analysis, respectively. Subsequently, the McSC1 locus was further fine-mapped to a 13.2-kb region containing only one candidate gene, MC03g0810, encoding a polyphenol oxidase (PPO). Additionally, the variations of MC03g0810 in the 89 bitter gourd germplasms showed a complete correlation with the seed coat color. Expression and PPO activity analyses showed a positive correlation between the expression level of MC03g0810 and its product PPO and the seed coat color. Therefore, MC03g0810 was proposed as the causal gene of McSC1. Our results provide an important reference for molecular marker-assisted breeding based on the seed coat color and uncover molecular mechanisms of the seed coat color formation in bitter gourd.

Bioactives of Momordica charantia as Potential Anti-Diabetic/Hypoglycemic Agents

Momordica charantia L., a member of the Curcubitaceae family, has traditionally been used as herbal medicine and as a vegetable. Functional ingredients of M. charantia play important roles in body health and human nutrition, which can be used directly or indirectly in treating or preventing hyperglycemia-related chronic diseases in humans. The hypoglycemic effects of M. charantia have been known for years. In this paper, the research progress of M. charantia phytobioactives and their hypoglycemic effects and related mechanisms, especially relating to diabetes mellitus, has been reviewed. Moreover, the clinical application of M. charantia in treating diabetes mellitus is also discussed, hoping to broaden the application of M. charantia as functional food.

A gastro-resistant peptide from Momordica charantia improves diabetic nephropathy in db/db mice via its novel reno-protective and anti-inflammatory activities

Diabetic nephropathy (DN), a principal diabetic microvascular complication, is a chronic inflammatory immune disorder. A gastro-resistant peptide mcIRBP-9 from Momordica charantia has shown modulation of blood glucose homeostasis in diabetic mice. Here we conducted a long-term experiment to evaluate the therapeutic effects and mechanisms of mcIRBP-9 on DN. Type 2 diabetic mice (db/db mice) were orally given mcIRBP-9 once daily for 12 consecutive weeks. The amelioration of DN was evaluated by renal function indexes, vascular leakage, and pathological lesions. Possible effective mechanisms of mcIRBP-9 on DN were analyzed by gene expression profiles. A pharmacokinetic study in rats was carried out to evaluate the oral bioavailability of mcIRBP-9. Our data showed that mcIRBP-9 was able to enter systemic circulation in rats after oral administration. In comparison with mock, long-term administration of mcIRBP-9 significantly decreased blood glucose (572.25 ± 1.55 mg dL^-1vs. 213.50 ± 163.39 mg dL^-1) and HbA1c levels (13.58 ± 0.30% vs. 8.23 ± 2.98%) and improved the survival rate (85.7% vs. 100%) in diabetic mice. mcIRBP-9 ameliorated DN by reducing renal vascular leakage and histopathological changes. mcIRBP-9 altered the pathways involved in inflammatory and immune responses, and the nuclear factor-κB played a central role in the regulation of mcIRBP-9-affected pathways. Moreover, mcIRBP-9 improved the inflammatory characteristic of DN in diabetic and non-diabetic mice. In conclusion, mcIRBP-9 displayed a novel anti-inflammatory activity and exhibited a reno-protective ability in addition to controlling the blood glucose and HbA1c levels. These findings suggested the role of mcIRBP-9 from M. charantia as a nutraceutical agent for diabetes and subsequent DN.

A randomized, double-blind, placebo-controlled trial to evaluate the hypoglycemic efficacy of the mcIRBP-19-containing

Background

The fruits of Momordica charantia L., also named as bitter gourd or bitter melon in popular, is a common tropical vegetable that is traditionally used to reduce blood glucose. A peptide derived from bitter gourd, Momordica charantia insulin receptor binding peptid-19 (mcIRBP-19), had been demonstrated to possess an insulin-like effect in vitro and in the animal studies. However, the benefit of the mcIRBP-19-containing bitter gourd extracts (mcIRBP-19-BGE) for lowering blood glucose levels in humans is unknown.

Objective

This aim of this study was to evaluate the hypoglycemic efficacy of mcIRBP-19-BGE in subjects with type 2 diabetes who had taken antidiabetic medications but failed to achieve the treatment goal. Whether glucose lowering efficacy of mcIRBP-19-BGE could be demonstrated when the antidiabetic medications were ineffective was also studied.

Design

Subjects were randomly assigned to two groups: mcIRBP-19-BGE treatment group (N = 20) and placebo group (N = 20), and were orally administered 600 mg/day investigational product or placebo for 3 months. Subjects whose hemoglobin A1c (HbA1c) continued declining before the trial initiation with the antidiabetic drugs were excluded from the subset analysis to further investigate the efficacy for those who failed to respond to the antidiabetic medications.

Results

The oral administration of mcIRBP-19-BGE decreased with a borderline significance at fasting blood glucose (FBG; P = 0.057) and HbA1c (P = 0.060). The subgroup analysis (N = 29) showed that mcIRBP-19-BGE had a significant effect on reducing FBG (from 172.5 ± 32.6 mg/dL to 159.4 ± 18.3 mg/dL, P = 0.041) and HbA1c (from 8.0 ± 0.7% to 7.5 ± 0.8%, P = 0.010).

Conclusion

All of these results demonstrate that mcIRBP-19-BGE possesses a hypoglycemic effect, and can have a significant reduction in FBG and HbA1c when the antidiabetic drugs are ineffective.

The novel anti-inflammatory activity of mcIRBP from Momordica charantia is associated with the improvement of diabetic nephropathy

Diabetic nephropathy is an inflammatory immune disorder accompanying diabetes.

Pharmacological reflection of plants traditionally used to manage diabetes mellitus in Tanzania

ETHNOPHARMACOLOGICAL RELEVANCE

The increasing national prevalence of diabetes mellitus (DM) and its complications have overstretched the health care system in Tanzania and influenced patients to use herbal medicines as alternative therapeutic strategies. Therefore, an urgent need exists to validate the safety and efficacy of plants used locally.

AIM OF THE STUDY

To identify plants used for the management of DM in Tanzania and analyses their pharmacological, phytochemistry, and safety evidence with a special focus on the mechanism of action.

METHODS

Researchers searched Medline, web of science, and Scopus for published articles. Also, specialized herbarium documents of Muhimbili Institute of traditional medicine were reviewed. Articles were assessed for relevance, quality, and taxonomical accuracy before being critically reviewed.

RESULTS

We identified 62 plant species used locally for DM management. Moringa oleifera Lam. and Cymbopogon citratus (D.C) stapf were the most mentioned. Fifty-four phytochemicals from 13 species had DM activities. These were mainly; polyphenolics, phytosterols, and triterpenoids. Extracts, fractions, and pure compounds from 18 species had in vitro antidiabetic activities of which 14 had α-glucosidase and α-amylase inhibition effects. The most studied -Momordica charantia L. increased; glucose uptake and adiponectin release in 3T3-L1 adipocytes, insulin secretion, insulin receptor substrate-1 (IRS-1), GLUT-4 translocation, and GLP-1 secretion; and inhibited protein tyrosine phosphatase 1 B (PTP1B). Preclinical studies reported 30 species that lower plasma glucose with molecular targets in the liver, skeletal muscles, adipose tissues, pancreases, and stomach. While three species; Aspilia mossambiscensis (Oliv.) Willd, Caesalpinia bonduc (L.) Roxb, and Phyllanthus amarus Schumach. & Thonn. had mild toxicity in animals, 33 had no report of their efficacy in DM management or toxicity.

CONCLUSION

Local communities in Tanzania use herbal medicine for the management of DM. However, only a fraction of such species has scientific evidence. A. mossambiscensis, C. bonduc., and P. amarus had mild toxicity in animals. Together, our findings call for future researches to focus on in vitro, in vivo, and phytochemical investigation of plant species for which their use in DM among the local communities in Tanzania have not been validated.

The Effect of Momordica charantia in the Treatment of Diabetes Mellitus: A Review

In recent years, many studies of Momordica charantia (MC) in the treatment of diabetes mellitus (DM) and its complications have been reported. This article reviewed the effect and mechanism of MC against diabetes, including the results from in vitro and in vivo experiments and clinical trials. The common side effects of MC were also summarized. We hope that it might open up new ideas for further mechanism exploration and clinical application as well as provide a scientific theoretical basis for the development of drugs or foods derived from MC.

Exploring the Factors Affecting Bitter Melon Peptide Intake Behavior: A Health Belief Model Perspective

Purpose

Diabetes mellitus (DM) patients need to control their blood sugar level in order to achieve a good quality of life. This study was conducted using the health belief model (HBM), to explore the factors behind the bitter melon peptide (BMP) intake behavior and the role of self-efficacy in the model.

Materials and Methods

The subjects were type 2 diabetes mellitus patients in Taiwan. A structured questionnaire was adopted from the theory of health belief model and modified specifically for this study as an instrument to survey 292 DM patients, of whom 51.03% were female, 75.68% were married, and 49.32% were aged 40 to 64 years old. The data were analyzed using t-tests, one-way ANOVA and regression.

Results

Perceived susceptibility was the most sensitive in the response to the various demographic factors, whereas perceived barrier was the least sensitive. The HBM explained 38.0% of BMP intake behavior. Perceived benefits (β= 0.357) and perceived susceptibility (β= 0.348) were the major predictors. Self-efficacy mediated the relationship between perceived benefits and BMP intake behavior, as well as increased the variance explained to 51.30%.

Conclusion

The perceived benefits of taking BMP and perceived susceptibility to DM complications were the two major drivers acting on BMP intake behavior. The power of perceived benefits was mediated by self-efficacy in driving DM patients to take BMP regularly. Several ways of affecting perceived susceptibility and perceived benefits were suggested.

Insulin-Like Proteins in Plant Sources: A Systematic Review

Type 2 diabetes mellitus (T2DM) is characterized by hyperglycemia. Proteins in plant sources that enable the maintenance of the glycemic profile may be of interest in the context of T2DM. However, their mechanisms of action are unclear, unlike other bioactive compounds. This systematic review identified and described the mechanisms of action of isolated and purified proteins and peptides extracted from vegetables on the reduction of blood glucose in T2DM in experimental studies. The research was done in PubMed, ScienceDirect, Scopus, Web of Science, Embase and Virtual Health Library (VHL) databases in March 2019. The initial search retrieved 916 articles, and, after reading the title, abstract and keywords, 24 articles were eligible for full reading. Then, five articles were eligible to build this systematic review. The evaluation of the evidence and the strength of the recommendations of the studies was evaluated with the SYstematic Review Center for Laboratory animal Experimentation - SYRCLE. Studies with proteins or peptides extracted from soybean (Glycine max), corn (Zea mays), peas (Pisum sativum), costus (Costus igneus) and ginseng (Panax ginseng) were found, and all of them decreased glycemia but not by the same mechanisms. The mechanism of action of proteins extracted from Glycine max, Pisum sativum, Costus igneus were similar, acting in the insulin-mediated pathways. The peptide derived from Zea mays increased GLP-1 expression, and the peptide from Panax ginseng reduced NF-kB signaling, both resulting in stimulating the release of insulin. Therefore, bioactive proteins and peptides of plant sources act through biochemical pathways, in the modulation of insulin resistance and the hyperglycemic state. These compounds are promising in scientific research on T2DM, because there is a probable similarity of these proteins with insulin, which enables them to act as insulin-like molecules.

mcIRBP-19 of Bitter Melon Peptide Effectively Regulates Diabetes Mellitus (DM) Patients' Blood Sugar Levels

This study was conducted to test the effectiveness of a particular bitter melon peptide (BMP), with a specific sequence of 19 amino acids (mcIRBP-19), in regulating diabetic patients' blood glucose. In order to test the product with the specially processed BMP, a total of 142 diabetic patients were solicited as study subjects, of which 64 were assigned to an experiment group and 78 to a control group. Biochemical data were compared with a paired t-test to verify the significance of changes over different time periods. The clinical results showed that BMP started to improve the subjects' glycated hemoglobin (HbA1c) levels at the end of the second month (T2), with mean values being significantly lowered from 7.8 ± 1.4% (T0) to 7.5 ± 1.4% (T2) (p = 0.004). The values reduced continuously, eventually reaching 7.4 ± 1.1% (p = 0.000) at the end of the experiment (T3). HbA1c levels for the control group were 7.5 ± 1.2% in T0 and 7.5 ± 1.1% (T3), and not significantly different (p = 0.852) over the same period. This study provides clinical evidence that helps to verify the effectiveness of the new BMP product in regulating diabetic patients' blood sugar levels.

Nutraceutical Improves Glycemic Control, Insulin Sensitivity, and Oxidative Stress in Hyperglycemic Subjects: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

The aim of this research was to investigate the effects of nutraceuticals including bitter melon, fenugreek, cinnamon, alpha-lipoic acid, zinc, biotin, chromium, and cholecalciferol on glycemic control, insulin sensitivity, lipid profiles, oxidative stress, and inflammatory markers in hyperglycemia. The study design was a randomized, double-blind, placebo-controlled trial. Subjects with hyperglycemia were randomly divided into 2 groups. The treatment group ( n = 52) was given a nutraceutical and the control group ( n = 50) was provided with a placebo for 12 weeks. Fasting blood glucose (FBG), hemoglobin A1c (HbA1C), homeostatic model assessment of insulin resistance (HOMA-IR), lipid profiles, biomarkers of oxidative stress, and inflammation were assessed before and after the intervention at 6 weeks and 12 weeks. Nutraceutical supplementation demonstrated a statistically significant decrease in FBG (13.4% and 18.9%), HbA1C (6.5% and 11.3%), and HOMA-IR (28.9% and 35.2%) compared with the placebo. Moreover, low-density lipoprotein-cholesterol (LDL-C) level was significantly reduced in the nutraceutical group (7.1% and 9.3%). Furthermore, the nutraceutical significantly decreased oxidative stress markers, oxidized LDL-C (14.8% and 18.9%) and malondialdehyde (16.6% and 26.2%) compared with the placebo. In conclusion, this nutraceutical can improve glycemic control, insulin resistance, lipid profiles, and oxidative stress markers in hyperglycemic subjects. Therefore, it has the potential to decrease cardiovascular disease risk factors. Clinical trial registration: TCTR20180907001, www.clinicaltrials.in.th.

Trypsin inhibitors: promising candidate satietogenic proteins as complementary treatment for obesity and metabolic disorders?

The increase in non-communicable chronic diseases has aroused interest in the research of adjuvants to the classic forms of treatments. Obesity and metabolic syndrome are the main targets of confrontation because they relate directly to other chronic diseases. In this context, trypsin inhibitors, molecules with wide heterologous application, appear as possibilities in the treatment of overweight and obesity due to the action on satiety related mechanisms, mainly in the modulation of satiety hormones, such as cholecystokinin. In addition, trypsin inhibitors have the ability to also act on some biochemical parameters related to these diseases, thus, emerging as potential candidates and promising molecules in the treatment of the obesity and metabolic syndrome. Thus, the present article proposes to approach, through a systematic literature review, the advantages, disadvantages and viabilities for the use of trypsin inhibitors directed to the treatment of overweight and obesity.

Tamarind Trypsin Inhibitor in Chitosan-Whey Protein Nanoparticles Reduces Fasting Blood Glucose Levels without Compromising Insulinemia: A Preclinical Study

In vivo studies show the benefits of the trypsin inhibitor isolated from tamarind (Tamarindusindica L.) (TTI) seeds in satiety and obesity. In the present study, TTI nanoencapsulation (ECW) was performed to potentialize the effect of TTI and allow a controlled release in the stomach. The impact on glycemia, insulin, and lipid profile was evaluated in Wistar rats overfed with a high glycemic index diet (HGLI). Characterization of the nanoparticles and in vitro stability in simulated gastrointestinal conditions, monitored by antitrypsin activity and HPLC, was performed. ECW and empty nanoparticles (CW) were administered by gavage, using 12.5 and 10.0 mg/kg, respectively. Both nanoformulations presented a spherical shape and smooth surface, with an average diameter of 117.4 nm (24.1) for ECW and 123.9 nm (11.3) for CW. ECW maintained the antitrypsin activity (95.5%) in the gastric phase, while TTI was completely hydrolyzed. In Wistar rats, the nanoformulations significantly reduced glycemia and HOMA IR, and ECW increased HDL-c compared to CW (p < 0.05).Pancreas histopathology of animals treated with ECW suggested an onset of tissue repair. Thenanoencapsulation provided TTI protection, gradual release in the desired condition, and improvement of biochemical parameters related to carbohydrate metabolism disorders,without compromising insulinemia.

Four new cucurbitane-type triterpenes from Momordica charantia L. with their cytotoxic activities and protective effects on H2O2-damaged pancreatic cells

Four new cucurbitane-type triterpenes were isolated from the fruit of Momordica charantia L. The structures of the new compounds were identified based on HR-ESI-MS and 1D- and 2D-NMR spectroscopic methods. The cytotoxicity of the isolated compounds was evaluated using three human cancer cell lines, HeLa, Caco2, and U87. Compound 3 exhibited significant cytotoxic activity against HeLa cells with an IC₅₀ value of 11.18 μM. Additionally, the cytoprotective activity of these compounds was determined in vitro against H₂O₂-induced pancreatic injury. The results revealed that all the compounds obtained possess cytoprotective effects against H₂O₂-induced injury in MIN6 β-cells at a concentration of 10 μM.

Plasticity in the Glucagon Interactome Reveals Novel Proteins That Regulate Glucagon Secretion in α-TC1-6 Cells

Glucagon is stored within the secretory granules of pancreatic alpha cells until stimuli trigger its release. The alpha cell secretory responses to the stimuli vary widely, possibly due to differences in experimental models or microenvironmental conditions. We hypothesized that the response of the alpha cell to various stimuli could be due to plasticity in the network of proteins that interact with glucagon within alpha cell secretory granules. We used tagged glucagon with Fc to pull out glucagon from the enriched preparation of secretory granules in α-TC1-6 cells. Isolation of secretory granules was validated by immunoisolation with Fc-glucagon and immunoblotting for organelle-specific proteins. Isolated enriched secretory granules were then used for affinity purification with Fc-glucagon followed by liquid chromatography/tandem mass spectrometry to identify secretory granule proteins that interact with glucagon. Proteomic analyses revealed a network of proteins containing glucose regulated protein 78 KDa (GRP78) and histone H4. The interaction between glucagon and the ER stress protein GRP78 and histone H4 was confirmed through co-immunoprecipitation of secretory granule lysates, and colocalization immunofluorescence confocal microscopy. Composition of the protein networks was altered at different glucose levels (25 vs. 5.5 mM) and in response to the paracrine inhibitors of glucagon secretion, GABA and insulin. siRNA-mediated silencing of a subset of these proteins revealed their involvement in glucagon secretion in α-TC1-6 cells. Therefore, our results show a novel and dynamic glucagon interactome within α-TC1-6 cell secretory granules. We suggest that variations in the alpha cell secretory response to stimuli may be governed by plasticity in the glucagon "interactome."

Resveratrol exhibits an effect on attenuating retina inflammatory condition and damage of diabetic retinopathy via PON1

Diabetic retinopathy (DR), an obstacle of the visual microvascular system, is a serious complication of diabetic patients. Paraoxonase 1 (PON1) has been extensively evaluated as a genetic candidate for diabetic microvascular complications, and PON1 is associated with DR. In this study, the biological functions of PON1 and its related proteins were determined via gene ontology (GO) enrichment analysis; we demonstrated that treatment with resveratrol alleviated retinal inflammatory activities to evaluate its protective effects on streptozotocin (STZ)-induced diabetic rats and high-glucose (HG) stimulated rat retinal endothelial cells (RRECs). The GO enrichment analysis suggested that PON1 may regulate inflammatory responses and microvascular complications in DR. In an in vivo study, resveratrol significantly recovered the insulin level and PON1 expression and activity, as well as clearly reduced the retinal vascular permeability, retinal AGEs, LDL, Ox-LDL, caspase3 activity, retinal damage, IL-1β, IL-6, TNFα, VEGF, IFNγ and MCP-1 in STZ-diabetic rats. Moreover, resveratrol reduced the caspase3 activity and Ox-LDL expression in HG stimulated RRECs. However, its protective effect was a deficiency in PON1-silenced RRECs. PON1 is a pivotal modulator in the role of resveratrol in reversing the RREC damage induced by HG. Furthermore, we found that resveratrol exhibits an effect on attenuating the retinal inflammatory condition and damage of DR via PON1. Our study suggests that resveratrol-induced PON1 in the retina may be a promising therapeutic strategy to prevent diabetes-related retinopathy.

Inhibitory Effects of Momordicine I on High-Glucose-Induced Cell Proliferation and Collagen Synthesis in Rat Cardiac Fibroblasts

Diabetes-associated cardiac fibrosis is a severe cardiovascular complication. Momordicine I, a bioactive triterpenoid isolated from bitter melon, has been demonstrated to have antidiabetic properties. This study investigated the effects of momordicine I on high-glucose-induced cardiac fibroblast activation. Rat cardiac fibroblasts were cultured in a high-glucose (25 mM) medium in the absence or presence of momordicine I, and the changes in collagen synthesis, transforming growth factor-β1 (TGF-β1) production, and related signaling molecules were assessed. Increased oxidative stress plays a critical role in the development of high-glucose-induced cardiac fibrosis; we further explored momordicine I's antioxidant activity and its effect on fibroblasts. Our data revealed that a high-glucose condition promoted fibroblast proliferation and collagen synthesis and these effects were abolished by momordicine I (0.3 and 1 μM) pretreatment. Furthermore, the inhibitory effect of momordicine I on high-glucose-induced fibroblast activation may be associated with its activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the inhibition of reactive oxygen species formation, TGF-β1 production, and Smad2/3 phosphorylation. The addition of brusatol (a selective inhibitor of Nrf2) or Nrf2 siRNA significantly abolished the inhibitory effect of momordicine I on fibroblast activation. Our findings revealed that the antifibrotic effect of momordicine I was mediated, at least partially, by the inhibition of the TGF-β1/Smad pathway, fibroblast proliferation, and collagen synthesis through Nrf2 activation. Thus, this work provides crucial insights into the molecular pathways for the clinical application of momordicine I for treating diabetes-associated cardiac fibrosis.

Molecular targets and mechanisms of bioactive peptides against metabolic syndromes

Bioactive peptides are present in all living organisms and have critical roles ranging from protection against infection as the key element of innate immunity, regulating blood pressure and glucose levels, to reducing signs of ageing by killing senescent cells. Bioactive peptides are also encrypted within food protein sequences that can be released during proteolysis or food processing. These specific food protein fragments are reported to have potential for improving human health and preventing metabolic diseases through their impact on inflammation, blood pressure, obesity, and type-2 diabetes. This review mainly focuses on the molecular targets and the underlying mechanisms of bioactive peptides against various metabolic syndromes including inflammation, high blood pressure, obesity, and type-2 diabetes, to provide new insights and perspectives on the potential of bioactive peptides for management of metabolic syndromes.

Revisiting amino acids and peptides as anti-glycation agents

The importance of controlling or preventing protein glycation cannot be overstated and is of prime importance in the treatment of diabetes and associated complications including Alzheimer's disease, cataracts, atherosclerosis, kidney aliments among others. In this respect, simple molecules such as amino acids and peptides hold much promise both in terms of ease and scale-up of synthesis as well as in relation to negligible/low associated toxicity. In view of this, a comprehensive account of literature reports is presented, that documents the anti-glycation activity of natural and non-natural amino acids and peptides. This review also discusses the chemical reactions involved in glycation and the formation of advanced glycation end-products (AGEs) and possible/probable intervention sites and mechanism of action of the reported amino acids/peptides. This aspect of amino acids/peptides adds to their growing importance in medicinal and therapeutic applications.

Satietogenic Protein from Tamarind Seeds Decreases Food Intake, Leptin Plasma and CCK-1r Gene Expression in Obese Wistar Rats

OBJECTIVE

This study evaluated the effect of a protein, the isolated Trypsin Inhibitor (TTI) from Tamarindus indica L. seed, as a CCK secretagogue and its action upon food intake and leptin in obese Wistar rats.

METHODS

Three groups of obese rats were fed 10 days one of the following diets: Standard diet (Labina®) + water; High Glycemic Index and Load (HGLI) diet + water or HGLI diet + TTI. Lean animals were fed the standard diet for the 10 days. Food intake, zoometric measurements, plasma CCK, plasma leptin, relative mRNA expression of intestinal CCK-related genes, and expression of the ob gene in subcutaneous adipose tissue were assessed.

RESULTS

TTI decreased food intake but did not increase plasma CCK in obese animals. On the other hand, TTI treatment decreased CCK-1R gene expression in obese animals compared with the obese group with no treatment (p = 0.027). Obese animals treated with TTI presented lower plasma leptin than the non-treated obese animals.

CONCLUSION

We suggest that TTI by decreasing plasma leptin may improve CCK action, regardless of its increase in plasma from obese rats, since food intake was lowest.

Gastro-Resistant Insulin Receptor-Binding Peptide from Momordica charantia Improved the Glucose Tolerance in Streptozotocin-Induced Diabetic Mice via Insulin Receptor Signaling Pathway

Momordica charantia is a commonly used food and has been used for the management of diabetes. Our previous study has identified an insulin receptor (IR)-binding protein (mcIRBP) from Momordica charantia. Here we identified the gastro-resistant hypoglycemic bioactive peptides from protease-digested mcIRBP. By in vitro digestion and IR kinase activity assay, we found that a 9-amino-acid-residue peptide, mcIRBP-9, was a gastro-resistant peptide that enhanced IR kinase activities. mcIRBP-9 activated IR signaling transduction pathway, which resulted in the phosphorylation of IR, the translocation of glucose transporter 4, and the uptake of glucose in cells. Intraperitoneal and oral administration of mcIRBP-9 stimulated the glucose clearance by 30.91 ± 0.39% and 32.09 ± 0.38%, respectively, in streptozotocin-induced diabetic mice. Moreover, a pilot study showed that daily ingestion of mcIRBP-9 for 30 days decreased the fasting blood glucose levels and glycated hemoglobin (HbA1c) levels by 23.62 ± 6.14% and 24.06 ± 1.53%, respectively. In conclusion, mcIRBP-9 is a unique gastro-resistant bioactive peptide generated after the digestion of mcIRBP. Furthermore, oral administration of mcIRBP-9 improves both the glucose tolerance and the HbA1c levels in diabetic mice via targeting IR signaling transduction pathway.

Draft genome sequence of bitter gourd (Momordica charantia), a vegetable and medicinal plant in tropical and subtropical regions

Bitter gourd (Momordica charantia) is an important vegetable and medicinal plant in tropical and subtropical regions globally. In this study, the draft genome sequence of a monoecious bitter gourd inbred line, OHB3-1, was analyzed. Through Illumina sequencing and de novo assembly, scaffolds of 285.5 Mb in length were generated, corresponding to ∼84% of the estimated genome size of bitter gourd (339 Mb). In this draft genome sequence, 45,859 protein-coding gene loci were identified, and transposable elements accounted for 15.3% of the whole genome. According to synteny mapping and phylogenetic analysis of conserved genes, bitter gourd was more related to watermelon (Citrullus lanatus) than to cucumber (Cucumis sativus) or melon (C. melo). Using RAD-seq analysis, 1507 marker loci were genotyped in an F₂ progeny of two bitter gourd lines, resulting in an improved linkage map, comprising 11 linkage groups. By anchoring RAD tag markers, 255 scaffolds were assigned to the linkage map. Comparative analysis of genome sequences and predicted genes determined that putative trypsin-inhibitor and ribosome-inactivating genes were distinctive in the bitter gourd genome. These genes could characterize the bitter gourd as a medicinal plant.

Corn Silk Extract and Its Bioactive Peptide Ameliorated Lipopolysaccharide-Induced Inflammation in Mice via the Nuclear Factor-κB Signaling Pathway

Bioactive peptides derived from foods have shown beneficial anti-inflammatory potential. Inhibitory κB kinase-β (IKKβ) plays a crucial role in the activation of nuclear factor-κB (NF-κB), a transcription factor involved in inflammation. Here we applied proteomic and bioinformatics approaches to identify anti-inflammatory peptides that target IKKβ from corn silk. Corn silk extract significantly suppressed lipopolysaccharide (LPS)-induced NF-κB activities [(1.7 ± 0.2)-fold vs (3.0 ± 0.6)-fold, p < 0.05] in cells. Trypsin hydrolysate of corn silk also suppressed LPS-induced NF-κB activities [(1.1 ± 0.3)-fold vs 3.3 ± 0.5 fold, p < 0.01]. In addition, both corn silk extract and trypsin hydrolysate significantly inhibited LPS-induced interleukin-1β (IL-1β) production by 58.3 ± 4.5 and 55.1 ± 7.4%, respectively. A novel peptide, FK2, docked into the ATP-binding pocket of IKKβ, was further identified from trypsin hydrolysis of corn silk. FK2 inhibited IKKβ activities, IκB phosphorylation, and subsequent NF-κB activation [(2.3 ± 0.4)-fold vs (5.5 ± 0.4)-fold, p < 0.001]. Moreover, FK2 significantly reduced NF-κB-driven luminescent signals in organs by 5-11-fold and suppressed LPS-induced NF-κB activities and IL-β production in tissues. In conclusion, our findings indicated that corn silk displayed anti-inflammatory abilities. In addition, we first identified an anti-inflammatory peptide FK2 from corn silk. Moreover, the anti-inflammatory effect of FK2 might be through IKKβ-NF-κB signaling pathways.

Hypoglycemic effects of Trichosanthes kirilowii and its protein constituent in diabetic mice: the involvement of insulin receptor pathway

BACKGROUND

Diabetes is a serious chronic metabolic disorder. Trichosanthes kirilowii Maxim. (TK) is traditionally used for the treatment of diabetes in traditional Chinese medicine (TCM). However, the clinical application of TK on diabetic patients and the hypoglycemic efficacies of TK are still unclear.

METHODS

A retrospective cohort study was conducted to analyze the usage of Chinese herbs in patients with type 2 diabetes in Taiwan. Glucose tolerance test was performed to analyze the hypoglycemic effect of TK. Proteomic approach was performed to identify the protein constituents of TK. Insulin receptor (IR) kinase activity assay and glucose tolerance tests in diabetic mice were further used to elucidate the hypoglycemic mechanisms and efficacies of TK.

RESULTS

By a retrospective cohort study, we found that TK was the most frequently used Chinese medicinal herb in type 2 diabetic patients in Taiwan. Oral administration of aqueous extract of TK displayed hypoglycemic effects in a dose-dependent manner in mice. An abundant novel TK protein (TKP) was further identified by proteomic approach. TKP interacted with IR by docking analysis and activated the kinase activity of IR. In addition, TKP enhanced the clearance of glucose in diabetic mice in a dose-dependent manner.

CONCLUSIONS

In conclusion, this study applied a bed-to-bench approach to elucidate the hypoglycemic efficacies and mechanisms of TK on clinical usage. In addition, we newly identified a hypoglycemic protein TKP from TK. Our findings might provide a reasonable explanation of TK on the treatment of diabetes in TCM.

Antidiabetic activities of a cucurbitane‑type triterpenoid compound from Momordica charantia in alloxan‑induced diabetic mice

Momordica charantia has been used to treat a variety of diseases, including inflammation, diabetes and cancer. A cucurbitane‑type triterpenoid [(19R,23E)‑5β, 19‑epoxy‑19‑methoxy‑cucurbita‑6,23,25‑trien‑3 β‑o‑l] previously isolated from M. charantia was demonstrated to possess significant cytotoxicity against cancer cells. The current study investigated the effects of this compound (referred to as compound K16) on diabetes using an alloxan‑induced diabetic mouse model. C57BL/6J mice were intraperitoneally injected with alloxan (10 mg/kg body weight), and those with blood glucose concentration higher than 10 mM were selected for further experiments. Diabetic C57BL/6J mice induced by alloxan were administered 0.9% saline solution, metformine (10 mg/kg body weight), or K16 (25 or 50 mg/kg body weight) by gavage for 4 weeks, followed by analysis of blood glucose level, glucose tolerance, serum lipid levels and organ indexes. The results demonstrated that compound K16 significantly reduced blood glucose (31‑48.6%) and blood lipids (13.5‑42.8%; triglycerides and cholesterol), while improving glucose tolerance compared with diabetic mice treated with saline solution, suggesting a positive improvement in glucose and lipid metabolism following K16 treatment. Furthermore, similarly to metformine, compound K16 markedly upregulated the expression of a number of insulin signaling pathway‑associated proteins, including insulin receptor, insulin receptor substrate 1, glycogen synthase kinase 3β, Akt serine/threonine kinase, and the transcript levels of glucose transporter type 4 and AMP‑activated protein kinase α1. The results of the current study demonstrated that compound K16 alleviated diabetic metabolic symptoms in alloxan‑induced diabetic mice, potentially by affecting genes and proteins involved in insulin metabolism signaling.

Promise of bitter melon (Momordica charantia) bioactives in cancer prevention and therapy

Recently, there is a paradigm shift that the whole food-derived components are not 'idle bystanders' but actively participate in modulating aberrant metabolic and signaling pathways in both healthy and diseased individuals. One such whole food from Cucurbitaceae family is 'bitter melon' (Momordica charantia, also called bitter gourd, balsam apple, etc.), which has gained an enormous attention in recent years as an alternative medicine in developed countries. The increased focus on bitter melon consumption could in part be due to several recent pre-clinical efficacy studies demonstrating bitter melon potential to target obesity/type II diabetes-associated metabolic aberrations as well as its pre-clinical anti-cancer efficacy against various malignancies. The bioassay-guided fractionations have also classified the bitter melon chemical constituents based on their anti-diabetic or cytotoxic effects. Thus, by definition, these bitter melon constituents are at cross roads on the bioactivity parameters; they either have selective efficacy for correcting metabolic aberrations or targeting cancer cells, or have beneficial effects in both conditions. However, given the vast, though dispersed, literature reports on the bioactivity and beneficial attributes of bitter melon constituents, a comprehensive review on the bitter melon components and the overlapping beneficial attributes is lacking; our review attempts to fulfill these unmet needs. Importantly, the recent realization that there are common risk factors associated with obesity/type II diabetes-associated metabolic aberrations and cancer, this timely review focuses on the dual efficacy of bitter melon against the risk factors associated with both diseases that could potentially impact the course of malignancy to advanced stages. Furthermore, this review also addresses a significant gap in our knowledge regarding the bitter melon drug-drug interactions which can be predicted from the available reports on bitter melon effects on metabolism enzymes and drug transporters. This has important implications, given that a large proportion of individuals, taking bitter melon based supplements/phytochemical extracts/food based home-remedies, are also likely to be taking conventional therapeutic drugs at the same time. Accordingly, the comprehensively reviewed information here could be prudently translated to the clinical implications associated with any potential concerns regarding bitter melon consumption by cancer patients.

Effects of D-Pinitol on Insulin Resistance through the PI3K/Akt Signaling Pathway in Type 2 Diabetes Mellitus Rats

D-pinitol, a compound isolated from Pinaceae and Leguminosae plants, has been reported to possess insulin-like properties. Although the hypoglycemic activity of D-pinitol was recognized in recent years, the molecular mechanism of D-pinitol in the treatment of diabetes mellitus remains unclear. In this investigation, a model of type 2 diabetes mellitus (T2DM) with insulin resistance was established by feeding a high-fat diet (HFD) and injecting streptozocin (STZ) to Sprague-Dawley (SD) rats, targeting the exploration of more details of the mechanism in the therapy of T2DM. D-pinitol was administrated to the diabetic rats as two doses [30, 60 mg/(kg·body weight·day)]. The level of fasting blood glucose (FBG) was decreased 12.63% in the high-dosage group, and the ability of oral glucose tolerance was improved in D-pinitol-treated groups. The biochemical indices revealed that D-pinitol had a positive effect on hypoglycemic activity. Western boltting suggested that D-pinitol could promote the expression of the phosphatidylinositol-3-kinase (PI3K) p85, PI3Kp110, as well as the downstream target protein kinase B/Akt (at Ser473). Besides, D-pinitol inhibited the expression of glycogen synthesis kinase-3β (GSK-3β) protein and regulated the expression of glycogen synthesis (GS) protein and then accelerated the glycogen synthesis. Above all, D-pinitol played a positive role in regulating insulin-mediated glucose uptake in the liver through translocation and activation of the PI3K/Akt signaling pathway in T2DM rats.