Apple polyphenol extract improves insulin sensitivity in vitro and in vivo in animal models of insulin resistance

Indian lychee honey ameliorates hepatic glucose uptake by regulating the ChREBP/Glut4 axis under insulin-resistant conditions

Many traditional treatments include honey owing to its magnificent health beneficiary effects. Recent studies have demonstrated the potent anti-diabetic activity of honey. However, its actual mechanism of action remains elusive. Moreover, being rich in sugar (75%-80%), its role in maintaining glucose homeostasis remains questionable. Although the polyphenol content of honey aids its hypoglycaemic activity, the small quantity of bioactive compounds in honey (0.5%-1.0%) may not be solely responsible for this. In the current study, an attempt was made to understand the role of Indian lychee honey (LyH) in regulating blood glucose levels under diabetic conditions. This study investigated whether LyH, although rich in sugars, can be used as an alternative to regulate glucose and lipid homeostasis under insulin-resistant conditions by regulating the ChREBP/Glut4 signalling pathway. This study was first performed in vitro in palmitic acid-induced insulin-resistant HepG2 cells. Various assays, such as FACS, GCMS, qRT-PCR, immunoblot and ChIP-qPCR, were performed to establish the anti-hyperglycaemic role of LyH in vitro. The in vitro results were subsequently confirmed in vivo using a high-fat diet-induced diabetic C57BL/6 mice model. The in vivo study was supported by several experiments, such as examining blood parameters, histopathology, double-immunohistochemistry and ELISA. Finally, the finding was validated by comparing it with a couple of GEO datasets from the NCBI database. This study found that LyH is an excellent choice for regulating blood sugar levels under diabetic conditions without significant harmful side effects. Moreover, LyH showed excellent hepatic glucose uptake activity in an insulin-independent manner. This activity is mainly governed by sugars as its main ingredient. LyH treatment also regulates hepatic lipid homeostasis by maintaining a balance between saturated and unsaturated fatty acids in insulin-resistant HepG2 cells. Further, sugar, when supplemented individually, caused severe inflammation, which was validated through histopathology, ELISA and IHC. Collectively, the findings of this study indicate that Indian LyH provides a better food matrix (the right proportion of sugars and different bioactive compounds), which significantly improves hyperglycemia and inflammation under diabetic conditions by regulating the hepatic ChREBP/Glut4 axis.

Small Phenolic Metabolites at the Nexus of Nutrient Transport and Energy Metabolism

Over time, human metabolism evolved to accommodate the challenges and benefits of plant foods that contain high amounts of carbohydrates and polyphenols. The latter are typically metabolized into small phenolic metabolites, including phenolic acids and their endogenous and microbial derivatives, that influence interconnected metabolic pathways involved in nutrient transport, energy metabolism, and neurotransmitter balance. Unlike other natural products, their biological effects arise from weak interactions with multiple molecular pathways rather than a single high-affinity receptor, making them versatile regulators of metabolic health. These compounds also modulate glucose transporters and carbohydrate metabolism, playing a crucial role in postprandial glucose and insulin responses. This review addresses the critical role of phenolic metabolites in metabolic health, with a focus on glucose homeostasis, insulin sensitivity, and carbohydrate metabolism. Incorporating polyphenols and phenolic acids into dietary strategies offers significant potential for improving insulin sensitivity, reducing metabolic disorder risks, and promoting whole-body glucose homeostasis. Furthermore, understanding how phenolic metabolites interact with metabolic pathways is essential for developing future effective nutritional strategies to support metabolic health.

Dietary Polyphenols as Potential Therapeutic Agents in Type 2 Diabetes Management: Advances and Opportunities

Poor dietary intake or unhealthy lifestyle contributes to various health disorders, including postprandial hyperglycemia, leading to type 2 diabetes mellitus (T2DM). Reduction of postprandial glucose concentrations through diet is a key strategy for preventing and managing T2DM. Thus, it is essential to understand how dietary components affect glycemic regulation. Dietary polyphenols (DPs), such as anthocyanins and other phenolics found in various fruits and vegetables, are often recommended for their potential health benefits, although their systemic effectiveness is subject to ongoing debate. Therefore, this review assesses the current and historical evidence of DPs bioactivities, which regulate crucial metabolic markers to lower postprandial hyperglycemia. Significant bioactivities such as modulation of glucose transporters, activation of AMP kinase, and regulation of incretins are discussed, along with prospects for diet-induced therapeutics to prevent the onset of T2DM.

Microbiota-gut-brain axis: Natural antidepressants molecular mechanism

BACKGROUND

Major depressive disorder (MDD) is a severe mental health condition characterized by persistent depression, impaired cognition, and reduced activity. Increasing evidence suggests that gut microbiota (GM) imbalance is closely linked to the emergence and advancement of MDD, highlighting the potential significance of regulating the "Microbiota-Gut-Brain" (MGB) axis to impact the development of MDD. Natural products (NPs), characterized by broad biological activities, low toxicity, and multi-target characteristics, offer unique advantages in antidepressant treatment by regulating MGB axis.

PURPOSE

This review was aimed to explore the intricate relationship between the GM and the brain, as well as host responses, and investigated the mechanisms underlying the MGB axis in MDD development. It also explored the pharmacological mechanisms by which NPs modulate MGB axis to exert antidepressant effects and addressed current research limitations. Additionally, it proposed new strategies for future preclinical and clinical applications in the MDD domain.

METHODS

To study the effects and mechanism by which NPs exert antidepressant effects through mediating the MGB axis, data were collected from Web of Science, PubMed, ScienceDirect from initial establishment to March 2024. NPs were classified and summarized by their mechanisms of action.

RESULTS

NPs, such as flavonoids,alkaloids,polysaccharides,saponins, terpenoids, can treat MDD by regulating the MGB axis. Its mechanism includes balancing GM, regulating metabolites and neurotransmitters such as SCAFs, 5-HT, BDNF, inhibiting neuroinflammation, improving neural plasticity, and increasing neurogenesis.

CONCLUSIONS

NPs display good antidepressant effects, and have potential value for clinical application in the prevention and treatment of MDD by regulating the MGB axis. However, in-depth study of the mechanisms by which antidepressant medications affect MGB axis will also require considerable effort in clinical and preclinical research, which is essential for the development of effective antidepressant treatments.

Review on the Role of Polyphenols in Preventing and Treating Type 2 Diabetes: Evidence from In Vitro and In Vivo Studies

Type 2 diabetes (T2D) is one of the leading causes of death globally. There was a 70% increase in diabetes-related deaths between 2000 and 2020, particularly among males. This non-communicable disease is characterized by increased insulin resistance, leading to elevated blood sugar levels and, if untreated, resulting in complications such as nerve damage, kidney disease, blindness, and poor wound healing. T2D management includes dietary intervention, physical exercise, and the administration of blood sugar-lowering medication. However, these medications often have side effects related to intestinal discomfort. Therefore, natural alternatives to standard diabetes medications are being sought to improve the quality of life for individuals with this condition. Polyphenols, which are naturally occurring plant metabolites, have emerged as strong candidates for T2D control. Various phenolic acids (e.g., chlorogenic acid), flavonoids (e.g., quercetin), proanthocyanidins (e.g., procyanidin B2), gallotannins (e.g., monogalloyl hexoside), and ellagitannins (e.g., ellagic acid hexoside) can enhance insulin sensitivity in tissues, reduce chronic inflammation, scavenge free radicals, improve insulin secretion, inhibit enzymes involved in carbohydrate digestion, regulate glucose transport across cell membranes, and modulate gut microbiota. This contribution compiles up-to-date evidence from in vitro and in vivo studies on the role of polyphenols in the prevention and management of T2D, emphasizing the mechanisms of action underlying these effects.

A comprehensive in-vitro/in-vivo screening toolbox for the elucidation of glucose homeostasis modulating properties of plant extracts (from roots) and its bioactives

Plant extracts are increasingly recognized for their potential in modulating (postprandial) blood glucose levels. In this context, root extracts are of particular interest due to their high concentrations and often unique spectrum of plant bioactives. To identify new plant species with potential glucose-lowering activity, simple and robust methodologies are often required. For this narrative review, literature was sourced from scientific databases (primarily PubMed) in the period from June 2022 to January 2024. The regulatory targets of glucose homeostasis that could be modulated by bioactive plant compounds were used as search terms, either alone or in combination with the keyword "root extract". As a result, we present a comprehensive methodological toolbox for studying the glucose homeostasis modulating properties of plant extracts and its constituents. The described assays encompass in-vitro investigations involving enzyme inhibition (α-amylase, α-glucosidase, dipeptidyl peptidase 4), assessment of sodium-dependent glucose transporter 1 activity, and evaluation of glucose transporter 4 translocation. Furthermore, we describe a patch-clamp technique to assess the impact of extracts on KATP channels. While validating in-vitro findings in living organisms is imperative, we introduce two screenable in-vivo models (the hen's egg test and Drosophila melanogaster). Given that evaluation of the bioactivity of plant extracts in rodents and humans represents the current gold standard, we include approaches addressing this aspect. In summary, this review offers a systematic guide for screening plant extracts regarding their influence on key regulatory elements of glucose homeostasis, culminating in the assessment of their potential efficacy in-vivo. Moreover, application of the presented toolbox might contribute to further close the knowledge gap on the precise mechanisms of action of plant-derived compounds.

Apple polyphenol extract ameliorates sugary-diet-induced depression-like behaviors in male C57BL/6 mice by inhibiting the inflammation of the gut-brain axis

To explore whether apple polyphenol extract (APE) ameliorates sugary-diet-induced depression-like behaviors, thirty male C57BL/6 mice (3-4 weeks old) were assigned to three groups randomly to receive different treatments for 8 consecutive weeks: (1) control group (CON), (2) S-HSD group (60% high sucrose diet feeding with 0.1 mg mL-1 sucralose solution as drinking water), and (3) S-APE group (S-HSD feeding with 500 mg per (kg bw day) APE solution gavage). The S-HSD group showed significant depression-like behaviors compared with the CON group, which was manifested by an increased number of buried marbles in the marble burying test, prolonged immobility time in both the tail suspension test and forced swimming test, and cognitive impairment based on the Morris water maze test. However, APE intervention significantly improved the depression-like behaviors by reducing serum levels of corticosterone and adrenocorticotropic hormone, and increasing the serum level of IL-10. Moreover, APE intervention inhibited the activation of the NF-κB inflammatory pathway, elevated colonic MUC-2 protein expression, and elevated the colonic and hippocampal tight junction proteins of occludin and ZO-1. Furthermore, APE intervention increased the richness and diversity of gut microbiota by regulating the composition of microbiota, with increased relative abundance of Firmicutes and Bacteroidota, decreased relative abundance of Verrucomicrobiota at the phylum level, significantly lowered relative abundance of Akkermansia at the genus level, and rebalanced abnormal relative abundance of Muribaculaceae_unclassified, Coriobacteriaceae_UCG-002, and Lachnoclostridium induced by S-HSD feeding. Thus, our study supports the potential application of APE as a dietary intervention for ameliorating depression-like behavioral disorders.

Anti-Diabetic Potential of Polyphenol-Rich Fruits from the Maleae Tribe-A Review of In Vitro and In Vivo Animal and Human Trials

The Maleae tribe consists of over one thousand species, including many well-known polyphenol-containing fruit crops with wide-ranging biological properties, e.g., apples (Malus), chokeberries (Aronia), pears (Pyrus), quinces (Cydonia, Chaenomeles), saskatoon (Amelanchier), loquats (Eriobotrya), medlars (Mespilus), rowans (Sorbus), and hawthorns (Crataegus). Considering the current interest in the concept of functional foods and the still-insufficient methods of diabetes management, the anti-diabetic potential of fruits has been studied intensively, including those of the Maleae tribe. This paper is the first comprehensive overview of this selected topic, covering articles published from 2000 to 2023 (131 articles in total). The first part of this review focuses on the potential mechanisms of action of fruits investigated so far (46 species), including their effects on tissue-specific glucose transport and the expression or activity of proteins in the insulin signalling pathway. The second part covers the phytocompounds responsible for particular fruits' activity-primarily polyphenols (e.g., flavonols, dihydrochalcones, proanthocyanidins, anthocyanins, phenolic acids), but also polysaccharides, triterpenes, and their additive and synergistic effects. In summary, fruits from the Maleae tribe seem promising as functional foods and anti-diabetic agents; however, their prospects for more expansive pro-health application require further research, especially more profound in vivo trials.

Potential Hypoglycemic and Antilipidemic Activity of Polyphenols from Passiflora ligularis (Granadilla)

The consumption of fruits or by-products from plants of the Passifloraceae family has been associated with multiple health and nutritional benefits, due to their phenolic compound content. Likewise, the effects of polyphenols from Camellia sinensis (green tea) have been explored and are considered a reference for different biological actions of these bioactive substances. This study compared the hypoglycemic and antilipemic activity of polyphenol-rich extracts of Passiflora ligularis Juss (passion fruit) and Camellia sinensis (green tea) given to a group of Wistar rats induced to be overweight. The individuals were subjected to three doses of supplementation of both sources of polyphenols in the drinking water. An additional group without polyphenol supplementation served as a control group. Water consumption, weight gain, glycemia, cholesterol, serum triglycerides and percentage of fecal ethereal extracts were analyzed. Although Passiflora ligularis Juss had five times less polyphenol content than Camellia sinensis, rats fed doses of 2.5 and 3.0 g/L Passiflora ligularis Juss showed reduced glycemia by 16%, suggesting an antiglycemic activity similar to that of Camellia sinensis. On the other hand, higher doses of polyphenols from Passiflora ligularis Juss and Camellia sinensis significantly reduced triglyceride levels (p = 0.05) by more than 17% compared to the unsupplemented control group. The polyphenol-rich extracts produced effective inhibitory activity of lipemic metabolites with a reduction in the percentage of fecal lipids (p < 0.05), with no side effects on liver tissue. The 3.0 g/L dose produced the best result on signs of metabolic syndrome associated with excess weight. Polyphenols extracted from fresh Colombian passion fruit showed the potential to decrease metabolic syndrome risk factors in a murine model.

Metabolic and Cardiovascular Benefits of Apple and Apple-Derived Products: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background

Quantitative evidence of the metabolic and cardiovascular effects of apples (Malus domestica) is lacking in interventional studies. This study aimed to summarize the available evidence of the beneficial effects of apples and apple-derived products (ADPs) on metabolic and cardiovascular markers.

Methods

Peer-reviewed randomized controlled trials (RCTs) were identified from four databases on May 3, 2021 and regularly updated until the end of May 2021. Demographic characteristics, intervention types, and evaluation parameters were extracted. A meta-analysis on the mean difference of change scores was conducted on commonly presented outcomes in the RCTs.

Results

The metabolic and cardiovascular effects of diverse regimens, including whole apple, apple extract, and apple juice, were examined in 18 eligible RCTs. Nine common evaluation outcomes were eventually introduced to the meta-analysis, including total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride, glucose, insulin, C-reactive protein, and systolic/diastolic blood pressures. The levels of TC (-2.69 mg/dL; 95% CI: -5.43, 0.04 mg/dL) and LDL (-2.80 mg/dL; 95% CI: -5.78, 0.17 mg/dL) showed a non-significant decreasing tendency after at least a week of apple consumption. Further subgroup analysis, particularly, a comparison with placebo as a control, showed a significant reduction in TC and LDL levels. When stratified by the baseline level, subjects with high TC and LDL level were shown to have more benefits from the apple intake. Intriguingly, apple and ADPs significantly reduced HDL levels to a small extent (-1.04 mg/dL; 95% CI: -1.79, -0.29 mg/dL). The other markers were mostly unaffected by the intervention.

Conclusion

Our investigation revealed that apples could improve blood cholesterol levels.

Systematic Review Registration

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42020215977].

Preventive Effect of Apple Polyphenol Extract on High-Fat Diet-Induced Hepatic Steatosis in Mice through Alleviating Endoplasmic Reticulum Stress

In this work, the protective effect of apple polyphenol extract (APE) on hepatic steatosis was investigated. Thirty-two C57BL/6J mice were assigned randomly to control group, hepatic steatosis group, lovastatin group, and APE group. After 8 weeks of intervention, APE supplementation markedly decreased the body weight gain, liver weight, liver index, epididymal adipose weight, epididymal adipose index, serum, and hepatic lipid levels. Hematoxylin and eosin staining revealed that APE supplementation alleviated histopathological changes of hepatic steatosis. Western blot revealed that APE downregulated the protein levels of GRP78, IRE1α, p-IRE1α, XBP1, PERK, p-PERK, p-eIF2α, ATF6, PPAR-γ, SREBP-1c, FAS, and ACC1. In conclusion, this study found that APE inhibited IRE1α-XBP1, PERK-eIF2α, and ATF6 signaling pathways to alleviate endoplasmic reticulum stress, thereby improving HFD-induced hepatic steatosis.

Red-Fleshed Apples Rich in Anthocyanins and White-Fleshed Apples Modulate the Aorta and Heart Proteome in Hypercholesterolaemic Rats: The AppleCOR Study

The impact of a red-fleshed apple (RFA) rich in anthocyanins (ACNs), a white-fleshed apple (WFA) without ACNs, and an extract infusion from Aronia fruit (AI) equivalent in dose of cyanidin-3-O-galactoside (main ACN) as RFA was determined by the proteome profile of aorta and heart as key cardiovascular tissues. Hypercholesterolaemic Wistar rats were separated into six groups (n = 6/group; three males and three females) and the proteomic profiles were analyzed using nanoliquid chromatography coupled to mass spectrometry. No adverse events were reported and all products were well tolerated. RFA downregulated C1QB and CFP in aorta and CRP in heart. WFA downregulated C1QB and CFP in aorta and C9 and C3 in aorta and heart, among other proteins. AI downregulated PRKACA, IQGAP1, and HSP90AB1 related to cellular signaling. Thus, both apples showed an anti-inflammatory effect through the complement system, while RFA reduced CRP. Regardless of the ACN content, an apple matrix effect was observed that involved different bioactive components, and inflammatory proteins were reduced.

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

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

Insight in the Recent Application of Polyphenols From Biomass

Biomass polyphenols are bio-active macromolecules with distinct chemical structures in a variety of biomass. In recent years, the study of biomass polyphenols and their application in food and medicine fields has become a research hotspot, which predominantly focuses on the preparation, purification, structural identifications, and measurements of biological activities. Many studies describe methodologies for extraction and application of polyphenols, but comprehensive work to review its physiological activities like drugs and health products are lacking. This paper comprehensively unlocks the bioactivities of antioxidant, antibacterial, antitumor, anticancer, neuroprotection, control of blood sugar, regulation of blood fat, and promotion of gastrointestinal health functions of polyphenols from different biomass sources. This review will serve as an illuminating resource for the global scientific community, especially for those who are actively working to promote the advances of the polyphenols research field.

Effect of apple peel extract on diabetes-induced peripheral neuropathy and wound injury

PURPOSE

Diabetic peripheral neuropathy (DPN) affects up to 50 % diabetic patients. Moreover, uncontrolled diabetes associated with impaired wound healing. The present study was aimed at exploring the effect of apple peel extract (APE) on type 2 diabetes (T2D)-induced DPN and delayed wound healing.

METHODS

In adult male Sprague-Dawley rats on high-fat diet, a single low dose streptozotocin (STZ, 35 mg/kg) was administered via intraperitoneal route to induce T2D. Plantar test using Hargreaves apparatus was used to evaluate the DPN. Six different groups of rats were treated orally with saline (naïve control and DPN control), APE (100, 200 and 400 mg/kg) and gabapentin (30 mg/kg) daily for 7 consecutive days and thermal paw withdrawal latency (PWL) was measured. To elucidate the underlying antioxidant effect of APE, the catalase (CAT), glutathione (GSH) and malonaldehyde (MDA) levels were measured. To evaluate the wound healing potential of APE, excision ischemic open wound model was used. Six different groups of rats were applied with 2 % gum acacia (naïve control and diabetic control), 1 % silver sulfadiazine (SSD) cream and APE cream (5, 10 and 20 %) twice daily for 28 days. Dry connective tissue parameters like hydroxyproline and hexosamine were also measured to further confirm the wound healing activity.

RESULTS

Diabetes produced thermal hyperalgesia in rats with a significant decrease in PWL as compared to naive controls indicating induction of DPN. APE and gabapentin significantly improved PWL in diabetic animals. Biochemical analysis revealed a significant improvement in oxidative stress parameters such as catalase, GSH and MDA. Wound closure was significantly more after day 15 of topical application of APE and SSD as compared to control group. APE significantly increased hydroxyproline and hexosamine levels as compared to standard cream. Moreover, histopathology revealed that, topical application of APE cream showed an enhanced healing process.

CONCLUSIONS

On the basis of the findings, we conclude that APE has a potential to be used as a therapeutic intervention for the management of DPN and delayed wound healing in the diabetic condition.

Co-ingested vinegar-soaked or preloaded dried apple mitigated acute postprandial glycemia of rice meal in healthy subjects under equicarbohydrate conditions

This study investigated 2 possible approaches to dietary control of acute postprandial responses to a rice-based meal under equicarbohydrate conditions: (1) a dried apple (DA) preload and (2) co-ingestion of vinegar-soaked DA. We hypothesized that both approaches would counteract hyperglycemia with no negative effect on satiety, possibly explained by an inhibitory effect on digestive enzyme activity and/or the effect of the sugar component of the DA. Fifteen healthy female subjects consumed (1) rice, (2) co-ingestion of DA and rice (DA + R), (3) DA preload and rice (PDA + R), (4) rice with sugar solution (same sugar profile as in DA) preloaded (PSS + R), or (5) co-ingestion of rice with vinegar-soaked DA (VDA + R) in a randomized crossover trial. Acute postprandial glycemic response tests and subjective satiety tests were conducted for each test meal. Compared with rice reference, the PA + R and PSS + R achieved 31.4% and 36.3% reduction of the incremental area under the curve_0-120, 24.3% and 27.0% decreases in the average glucose peak, along with 21.6% and 27.0% decreases in glycemic excursion in 240 minutes, whereas the VDA + R resulted 42.4%, 27.0%, and 29.7% reductions in the incremental area under the curve_0-120, peak, and glycemic excursion, respectively. The DA-containing meals had no effect or a favorable effect on satiety. The in vitro assay found larger resistant starch and smaller rapid digestible starch fractions in DA + R and VDA + R meals compared to those of the rice reference (P < .001). The result of this study supported the research hypothesis, and the DA-containing meals could be considered as a potential dietary approach for glycemic management.

Dietary apple polyphenols promote fat browning in high-fat diet-induced obese mice through activation of adenosine monophosphate-activated protein kinase α

BACKGROUND

Promoting brown and beige adipogenesis contributes to adaptive thermogenesis, which provides a defense against obesity and related disorders. Apple polyphenols (APs) play a significant role in treating variety of metabolic diseases. This study was conducted to determine the effects of APs on the development of brown and beige adipocytes and thermogenesis and investigate whether these effects are mediated by adenosine monophosphate-activated protein kinase (AMPK). High-fat diet (HFD)-induced obese mice and differentiated 3T3-L1 adipocytes were subjected to APs treatment. The thermogenic program and associated regulatory factors, and the involvement of AMPKα was assessed.

RESULTS

Dietary APs supplementation reduced adiposity and improved insulin sensitivity in HFD-induced obese mice. Moreover, APs increased the oxygen consumption and heat production and decreased respiratory exchange ratio, which were accompanied by the upregulation of thermogenic genes expression and the activation of AMPKα in brown fat and inguinal white fat. Further, APs treatment directly increased expression of brown adipogenic markers and induced phosphorylation of AMPKα in differentiated 3T3-L1 adipocytes, whereas the beneficial effects of APs were reversed by AMPK inhibition.

CONCLUSION

Our results provide new insights into the function of APs in regulating brown/beige adipogenesis and adaptive thermogenesis and suggest the potential application of APs in the prevention and therapeutics of obesity and associated metabolic diseases. © 2020 Society of Chemical Industry.

Natural Products Derived from the Mediterranean Diet with Antidiabetic Activity: from Insulin Mimetic Hypoglycemic to Nutriepigenetic Modulator Compounds

BACKGROUND

The Mediterranean diet is a healthy eating pattern that protects against the development of Type 2 diabetes mellitus (T2DM), a metabolic disease characterized by elevated blood sugar levels due to pancreatic beta-cell functional impairment and insulin resistance in various tissues. Inspired by the ancient communities, this diet emphasizes eating primarily plant-based foods, including vegetables, legumes, fruits, cereals, and nuts. Importantly, virgin olive oil is used as the principal source of fat. Red meat is consumed in low amounts while wine and fish are consumed moderately.

OBJECTIVE

Here, we review the most beneficial components of the Mediterranean Diet and tentative mechanisms of action for prevention and/or management of T2DM, based on research conducted within the last decade.

METHODS

The references over the last five years have been reviewed and they have been selected properly according to inclusion/ exclusion criteria.

RESULTS

Several bioactive diet components were evaluated to prevent inflammation and cytokine-induced oxidative damage, reduce glucose concentration, carbohydrate absorption and increase insulin sensitivity and related gene expression.

CONCLUSION

The adherence to a healthy lifestyle, including diet, exercise and habits remains the best approach for the prevention of diabetes as well as frequent check-ups and education. Though diabetes has a strong genetic component, in recent years many reports strongly point to the critical role of lifestyle specific epigenetic modifications in the development of T2DM. It remains to be established how different components of the Mediterranean Diet interact and influence the epigenetic landscape to prevent or treat the disease.

Reduction of blood glucose by plant extracts and their use in the treatment of diabetes mellitus; discrepancies in effectiveness between animal and human studies

ETHNOPHARMACOLOGICAL RELEVANCE

The global problem of diabetes, together with the limited access of large numbers of patients to conventional antidiabetic medicines, continues to drive the search for new agents. Ancient Asian systems such as traditional Chinese medicine, Japanese Kampo medicine, and Indian Ayurvedic medicine, as well as African traditional medicine and many others have identified numerous plants reported anecdotally to treat diabetes; there are probably more than 800 such plants for which there is scientific evidence for their activity, mostly from studies using various models of diabetes in experimental animals.

AIM OF THE REVIEW

Rather than a comprehensive coverage of the literature, this article aims to identify discrepancies between findings in animal and human studies, and to highlight some of the problems in developing plant extract-based medicines that lower blood glucose in patients with diabetes, as well as to suggest potential ways forward.

METHODS

In addition to searching the 2018 PubMed literature using the terms 'extract AND blood glucose, a search of the whole literature was conducted using the terms 'plant extracts' AND 'blood glucose' AND 'diabetes' AND 'double blind' with 'clinical trials' as a filter. A third search using PubMed and Medline was undertaken for systematic reviews and meta-analyses investigating the effects of plant extracts on blood glucose/glycosylated haemoglobin in patients with relevant metabolic pathologies.

FINDINGS

Despite numerous animal studies demonstrating the effects of plant extracts on blood glucose, few randomised, double-blind, placebo-controlled trials have been conducted to confirm efficacy in treating humans with diabetes; there have been only a small number of systematic reviews with meta-analyses of clinical studies. Qualitative and quantitative discrepancies between animal and human clinical studies in some cases were marked; the factors contributing to this included variations in the products among different studies, the doses used, differences between animal models and the human disease, and the impact of concomitant therapy in patients, as well as differences in the duration of treatment, and the fact that treatment in animals may begin before or very soon after the induction of diabetes.

CONCLUSION

The potential afforded by natural products has not yet been realised in the context of treating diabetes mellitus. A systematic, coordinated, international effort is required to achieve the goal of providing anti-diabetic treatments derived from medicinal plants.

Holly polyphenols alleviate intestinal inflammation and alter microbiota composition in lipopolysaccharide-challenged pigs

The effect of holly polyphenols (HP) on intestinal inflammation and microbiota composition was evaluated in a piglet model of lipopolysaccharide (LPS)-induced intestinal injury. A total of twenty-four piglets were used in a 2 × 2 factorial design including diet type and LPS challenge. After 16 d of feeding with a basal diet supplemented with or without 250 mg/kg HP, pigs were challenged with LPS (100 μg/kg body weight) or an equal volume of saline for 4 h, followed by analysis of disaccharidase activities, gene expression levels of several representative tight junction proteins and inflammatory mediators, the SCFA concentrations and microbiota composition in intestinal contents as well as proinflammatory cytokine levels in plasma. Our results indicated that HP enhanced intestinal disaccharidase activities and reduced plasma proinflammatory cytokines including TNF-α and IL-6 in LPS-challenged piglets. Moreover, HP up-regulated mRNA expression of intestinal tight junction proteins such as claudin-1 and occludin. In addition, bacterial 16S rRNA gene sequencing showed that HP altered hindgut microbiota composition by enriching Prevotella and enhancing SCFA production following LPS challenge. These results collectively suggest that HP is capable of alleviating LPS-triggered intestinal injury by improving intestinal disaccharidase activities, barrier function and SCFA production, while reducing intestinal inflammation.

Effects of Dietary Apple Polyphenols Supplementation on Hepatic Fat Deposition and Antioxidant Capacity in Finishing Pigs

Simple Summary

Excessive fat deposition (5–10%) in the liver could lead to liver damage and nonalcohol fatty liver disease (NAFLD). However, there is no satisfactory safe and effective measure of preventive and therapeutic treatments so far. Thus, the prevention of excessive fat deposition through diet modification might be a better strategy to protect humans from metabolic diseases. Due to the anatomical and physiological similarities between humans and pigs, the present study took the finishing pig as an animal model to investigate the effects of apple polyphenols on hepatic fat deposition and antioxidant capacity and their mechanisms. The present study indicated that apple polyphenols might be an effective dietary supplementation for decreasing the excessive fat deposition in liver tissue, improving lipid profiles and increasing the antioxidant capacity of finishing pigs. This study provides a better preventive strategy to protect humans from excessive fat deposition in the liver.

Abstract

Excessive fat deposition in the liver could lead to fatty liver and an increased risk of many metabolic diseases. Apple polyphenols (APPs), the major antioxidants in apples, possess wide-ranging beneficial biological functions. The present study aimed to investigate the effects of APPs on hepatic fat deposition and antioxidant capacity in finishing pigs, and their mechanisms. Results showed that APPs improved lipid profiles, increased antioxidant enzyme activities and reduced the fat deposition in the liver. In the liver, SOD1, CAT, GPX1, GST, NF-E2-related nuclear factor 2 (Nrf2), hormone sensitive lipase (HSL), carnitine palmitoyl transferase-1b (CPT1b), peroxisome proliferator-activated receptor α (PPARα), cholesterol 7α-hydroxylase (CYP7A1) and low-density lipoprotein receptor (LDL-R) mRNA levels were increased by APPs, while Kelch-like ECH-associated protein 1 (Keap1) mRNA level, C16:0 and C20:4n-6 proportions and Δ9-18 dehydrogenase activity were decreased. In conclusion, this study indicated that APPs might be an effective dietary supplementation for improving lipid profiles, increasing antioxidant capacities and decreasing fat deposition in the liver.

Effects of dietary apple polyphenol supplementation on carcass traits, meat quality, muscle amino acid and fatty acid composition in finishing pigs

As health awareness is increasing, consumers have changed their focus with a desire to purchase safer, healthier, and higher quality and nutritional value meat. The aim of this study was to investigate whether dietary apple polyphenol (APP) supplementation in finishing pigs could provide pork with high quality and nutritional value. In the present study, 36 castrated Duroc × Landrace × Yorkshire pigs with an average body weight of 71.25 ± 2.40 kg were randomly divided into three treatments and fed with a basal diet supplemented with 0, 400, or 800 mg kg^-1 APPs for 7 weeks. The results showed that dietary 800 mg kg^-1 APP supplementation not only decreased backfat thickness and abdominal adipose tissue index but also decreased L* (lightness) and b* (yellowness) in the longissimus dorsi (LD) muscle. The LD muscle crude protein content, the proportions of essential amino acids, flavor amino acids, and total amino acids, as well as the amino acid transporter (SLC7A1, SLC7A2, SLC7A7, SLC1A2) mRNA levels were increased by 800 mg kg^-1 APPs. The proportions of docosahexaenoic acid and n-3 polyunsaturated fatty acid (PUFA) and the ratio of PUFA to saturated fatty acid in LD muscle were increased by 400 mg kg^-1 APPs. Meanwhile, dietary 400 mg kg^-1 and 800 mg kg^-1 APP supplementation decreased the contents of blood urea nitrogen and total cholesterol, as well as increased the content of inosinic acid in LD muscle. In conclusion, these results suggested that dietary 800 mg kg^-1 APP supplementation improved the carcass traits, meat color, and meat flavor in finishing pigs. These results also suggested that dietary 400 mg kg^-1 and 800 mg kg^-1 APP supplementation improved the meat nutritional value in finishing pigs. The present study provides effective evidence for the application of APP supplementation for healthy high-quality and nutritional value pork production.

Dietary apple polyphenols supplementation enhances antioxidant capacity and improves lipid metabolism in weaned piglets

Apple polyphenols (APPs) are biologically active flavonoids that have antioxidant, anti-inflammatory, improving insulin sensitivity, hypocholesterolaemic effect and antiviral properties. This study was conducted to explore effects of dietary APPs supplementation on antioxidant activities and lipid metabolism in weaned piglets. Fifty-four weaned piglets (half male and female) were randomly divided into three groups with six replicates in each group and three piglets in each repetition. Piglets were fed control diet (basal diet) or a control diet supplemented with 400 mg/kg or 800 mg/kg APPs for 6 weeks. Blood and liver samples were collected to determine biochemical, antioxidant and lipid metabolism parameters. Here we showed that dietary APPs supplementation increased HDL-C and decreased T-CHO, TG and LDL-C concentrations. Dietary APPs supplementation increased antioxidative capacity in serum and CAT activity in liver, and significantly increased the mRNA expressions of CAT, GST and SOD1 in liver. ACC mRNA level and LPL activity were tended to decrease by APPs. HMG-CoAR, CTP7A1, CD36 and FATP1 mRNA levels were decreased by APPs, while LDL-R, PGC-1α, Sirt1 and CPT1b mRNA levels were increased by 400 mg/kg APPs. No alterations in growth performance were found in all treatments. This study firstly provided the evidence that dietary APPs supplementation could enhance systemic antioxidant capacity and improve lipid metabolism in weaned piglets. The mechanism by which APPs improve lipid metabolism might be through regulating hepatic cholesterol metabolism and increasing fatty acid oxidation, and decreasing fatty acid uptake and de novo synthesis.

Germinated Waxy Black Rice Ameliorates Hyperglycemia and Dyslipidemia in Streptozotocin-Induced Diabetic Rats

This study aimed to examine the anti-diabetic effect of germinated waxy black rice (GWBR) using streptozotocin (STZ)-induced diabetic rats. In the diabetic rats, GWBR supplementation for 8 weeks reduced plasma blood glucose concentrations, improved glucose clearance and prevented diabetes-induced weight loss. Rats with STZ-induced diabetes who received GWBR supplementation exhibited decreased expression of sodium-dependent glucose transporter 1 (SGLT1) and glucose transporter (GLUT) 2 genes and proteins in the small intestine via decreases in hepatocyte nuclear factor (HNF)-1α, HNF-1β, and HNF-4α, transcriptional factors that are involved in the regulation of SGLT1 and GLUT2, compared with the rats with STZ-induced diabetes that did not receive GWBR supplements. GWBR supplementation also enhanced the expression of GLUT4 and the genes and proteins involved in GLUT4 translocation, such as insulin receptor (IR) and insulin receptor substrate 1 (IRS1), and increased the phosphorylation of phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB, Akt) proteins in skeletal muscle. GWBR further increased glycogen synthase (GS) 1 by decreasing glycogen synthase kinase (GSK)-3β in skeletal muscle. Interestingly, GWBR recovered STZ-impaired pancreatic β-cells, resulting in increased insulin synthesis and secretion. In addition, GWBR reduced serum triglyceride, total cholesterol, low-density lipoprotein cholesterol, aspartate transferase and alanine transferase concentrations and increased high-density lipoprotein cholesterol concentrations. Taken together, these findings suggest that GWBR could be a candidate for improving the diabetic condition by regulating glucose uptake in the intestine and muscle and regulating the secretion of insulin from the pancreas.

The Antidiabetic Mechanisms of Polyphenols Related to Increased Glucagon-Like Peptide-1 (GLP1) and Insulin Signaling

Type-2 diabetes mellitus (T2DM) is an endocrine disease related to impaired/absent insulin signaling. Dietary habits can either promote or mitigate the onset and severity of T2DM. Diets rich in fruits and vegetables have been correlated with a decreased incidence of T2DM, apparently due to their high polyphenol content. Polyphenols are compounds of plant origin with several documented bioactivities related to health promotion. The present review describes the antidiabetic effects of polyphenols, specifically related to the secretion and effects of insulin and glucagon-like peptide 1 (GLP1), an enteric hormone that stimulates postprandial insulin secretion. The evidence suggests that polyphenols from various sources stimulate L-cells to secrete GLP1, increase its half-life by inhibiting dipeptidyl peptidase-4 (DPP4), stimulate β-cells to secrete insulin and stimulate the peripheral response to insulin, increasing the overall effects of the GLP1-insulin axis. The glucose-lowering potential of polyphenols has been evidenced in various acute and chronic models of healthy and diabetic organisms. Some polyphenols appear to exert their effects similarly to pharmaceutical antidiabetics; thus, rigorous clinical trials are needed to fully validate this claim. The broad diversity of polyphenols has not allowed for entirely describing their mechanisms of action, but the evidence advocates for their regular consumption.

Phloretin exerts hypoglycemic effect in streptozotocin-induced diabetic rats and improves insulin resistance in vitro

The present study investigated the possible antiobesity and hypoglycemic effects of phloretin (Ph). In an attempt to discover the hypoglycemic effect and potential mechanism of Ph, we used the streptozotocin-induced diabetic rats and (L6) myotubes. Daily oral treatment with Ph for 4 weeks significantly (P<0.05) reduced postprandial blood glucose and improved islet injury and lipid metabolism. Glucose consumption and glucose tolerance were improved by Ph via GOD–POD method. Western blot results revealed that the expression of Akt, PI3K, IRS-1, and GLUT4 were upregulated in skeletal muscle of type 2 diabetes (T2D) rats and in L6 myotubes by Ph. The immunofluorescence studies confirmed that Ph improved the translocation of GLUT4 in L6 myotubes. Ph exerted hypoglycemic effects in vivo and in vitro, hence it may play an important role in the management of diabetes.