Confirmatory studies on the antioxidant and antidiabetic effect of quercetin in rats

Clinical applications and mechanism insights of natural flavonoids against type 2 diabetes mellitus

Diabetes is a complex disease that affects a large percentage of the world's population, and it is associated with several risk factors. Self-management poses a significant challenge, but natural sources have shown great potential in providing effective glucose reducing solutions. Flavonoids, a class of bioactive substances found in different natural sources including medicinal plants, have emerged as promising candidates in this regard. Indeed, several flavonoids, including apigenin, arbutin, catechins, and cyanidin, have demonstrated remarkable anti-diabetic properties. The clinical effectiveness of these flavonoids is linked to their potential to decrease blood glucose concentration and increase insulin concentration. Thus, the regulation of certain metabolic pathways such as glycolysis and neoglycogenesis has also been demonstrated. In vitro and in vivo investigations revealed different mechanisms of action related to flavonoid compounds at subcellular, cellular, and molecular levels. The main actions reside in the activation of glycolytic signaling pathways and the inhibition of signaling that promotes glucose synthesis and storage. In this review, we highlight the clinical efficiency of natural flavonoids as well as the molecular mechanisms underlying this effectiveness.

Synergistic anti-diabetic effect of phloroglucinol and total procyanidin dimer isolated from Vitisvinifera methanolic seed extract potentiates via suppressing oxidative stress: in-vitro evaluation studies

Diabetes is often associated with increased oxidative stress caused by an imbalance between detoxification and ROS production. Unfortunately, many commercial drugs available today for treating this disease have adverse side effects and ultimately fail to restore glucose homeostasis. Therefore, finding a dietary anti-diabetic remedy that is safe, effective, and economical is crucial. In this study, GC-MS analysis, subsequent HPLC-assisted fractionation, and SPE-based purification led to identifying and purifying of key components such as phloroglucinol and total procyanidin dimer (procyanidin dimer and procyanidin dimer gallate) from methanolic seed extract of Vitis vinifera. In-vitro anti-diabetic screening of various fractions derived from methanolic extract along with individual components and their combinations revealed the potential synergistic behaviour of phloroglucinol and total procyanidin dimer with the lowest IC50 of 48.21 ± 3.54 µg/mL for α-glucosidase and 63.06 ± 5.38 µg/mL for α-amylase inhibition which is found to be superior to the effect shown by the standard Epigallocatechin gallate. Later Glucose utilization studies demonstrated the concentration-dependent effect of Phloroglucinol and total procyanidin dimer, and that has raised the glucose uptake by approximately 36-57% in HepG2 cells and 35-58% in L6 myocytes over a concentration of 50-100 µg/mL. The superior anti-diabetic effect of Phloroglucinol and total procyanidin dimer was proved by the suppression of oxidative stress with an IC50 of 7.92 ± 0.36 µg/mL for DPPH scavenging and 16.87 ± 1.24 µg/mL for SOD scavenging which is competent with the standard ascorbic acid. According to this study, suppressing ROS levels by phloroglucinol and total procyanidin dimer would be the underlying mechanism for the synergistic anti-diabetic effect of this combination.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03929-4.

Coconut (Cocos nucifera (L.)) Water Improves Glucose Uptake with Concomitant Modulation of Antioxidant and Purinergic Activities in Isolated Rat Psoas Muscles

The present study investigated the effect of coconut water on glucose uptake and utilization, and metabolic activities linked to hyperglycemia in isolated rat psoas muscles. Coconut water was subjected to in vitro antioxidant and antidiabetic assays, which cover 2,2'-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, ferric reducing antioxidant power (FRAP), and inhibition of α-glucosidase and α-amylase activities. Psoas muscles were isolated from male Sprague Dawley rats and incubated with coconut water in the presence of glucose. Control consisted of muscles incubated with glucose only, while normal control consisted of muscles not incubated in coconut water and/or glucose. The standard antidiabetic drug was metformin. Incubation with coconut water led to a significant increase in muscle glucose uptake, with concomitant exacerbation of glutathione level, and SOD and catalase activities, while suppressing malondialdehyde level, and ATPase and E-NTDase activities. Coconut water showed significant scavenging activity against DPPH, and significantly inhibited α-glucosidase and α-amylase activities. LC-MS analysis of coconut water revealed the presence of ellagic acid, butin, quercetin, protocatechuic acid, baicalin, and silibinin. Molecular docking analysis revealed potent molecular interactions between the LC-MS-identified compounds, and AKT-2 serine and PI-3 kinase. These results indicate the potential of coconut water to enhance glucose uptake, while concomitantly improving antioxidative and purinergic activities. They also indicate the potential of coconut water to suppress postprandial hyperglycemia. These activities may be attributed to the synergistic effects of the LC-MS-identified compounds.

Can Polyherbal Medicine be used for the Treatment of Diabetes? - A Review of Historical Classics, Research Evidence and Current Prevention Programs

Diabetes mellitus (DM), a chronic medical condition, has attained a global pandemic status over the last few decades affecting millions of people. Despite a variety of synthetic drugs available in the market, the use of herbal medicines for managing diabetes is gaining importance because of being comparatively safer. This article reviews the result of a substantial literature search on polyherbal formulations (PHFs) developed and evaluated with potential for DM. The accumulated data in the literature allowed us to enlist 76PHFs consisting of different parts of 147 plant species belonging to 58 botanical families. The documented plant species are laden with bioactive components with anti-diabetic properties and thus draw attention. The most favoured ingredient for PHFs was leaves of Gymnema sylvestre and seeds of Trigonella foenum-graecum used in 27 and 22 formulations, respectively. Apart from herbs, shilajit (exudates from high mountain rocks) formed an important component of 9 PHFs, whereas calcined Mytilus margaritiferus and goat pancreas were used in Dolabi, the most commonly used tablet form of PHF in Indian markets. The healing properties of PHFs against diabetes have been examined in both pre-clinical studies and clinical trials. However, the mechanism(s) of action of PHFs are still unclear and considered the pitfalls inherent in understanding the benefits of PHFs. From the information available based on experimental systems, it could be concluded that plant-derived medicines will have a considerable role to play in the control of diabetes provided the challenges related to their bioavailability, bioefficacy, optimal dose, lack of characterization, ambiguous mechanism of action, and clinical efficiency are addressed.

The Mechanism of Mori Folium and Eucommiae Cortex against Cyclophosphamide-Induced Immunosuppression Integrating Network Pharmacology, Molecular Docking, Molecular Dynamics Simulations, and Experimental Validation

It has been reported that Mori Folium (MF) and Eucommiae Cortex (EC) exhibit pharmacological effects in the treatment of immunosuppression. However, the mechanism of MF and EC against immunosuppression remains unclear. This study aims to explore the mechanism of action of MF and EC for the treatment of immunosuppression through network pharmacology, molecular docking, molecular dynamics simulations and animal experiments. As a result, 11 critical components, 9 hub targets, and related signaling pathways in the treatment of immunosuppression were obtained based on network pharmacology. The molecular docking suggested that 11 critical components exhibited great binding affinity to 9 hub targets of immunosuppression. The molecular dynamics simulations results showed that (-)-tabernemontanine-AR, beta-sitosterol-AR and Dehydrodieugenol-HSP90AA1 complexes are stably bound. Additionally, in the animal experiments, the treated group results compared to the control group suggest that MF and EC have a significant effect on the treatment of immunosuppression. Therefore, MF and EC treatment for immunosuppression may take effects in a multi-component, multi-target, and multi-pathway manner. The results herein may provide novel insights into the treatment of immunosuppression in humans.

Red Mangrove (Rhizophora stylosa Griff.)-A Review of Its Botany, Phytochemistry, Pharmacological Activities, and Prospects

Mangroves are ecologically significant plants in marine habitats that inhabit the coastlines of many countries. Being a highly productive and diverse ecosystem, mangroves are rich in numerous classes of phytochemicals that are of great importance in the field of pharmaceutical industries. The red mangrove (Rhizophora stylosa Griff.) is a common member of the Rhizophoraceae family and the dominant species in the mangrove ecosystem of Indonesia. R. stylosa mangrove species are rich in alkaloids, flavonoids, phenolic acids, tannins, terpenoids, saponins, and steroids, and are widely used in traditional medicine for anti-inflammatory, antibacterial, antioxidant, and antipyretic effects. This review aims to provide a comprehensive understanding of the botanical description, phytochemical profiles, pharmacological activities, and medicinal potentials of R. stylosa.

Food Polyphenols and Type II Diabetes Mellitus: Pharmacology and Mechanisms

Type II diabetes mellitus and its related complications are growing public health problems. Many natural products present in our diet, including polyphenols, can be used in treating and managing type II diabetes mellitus and different diseases, owing to their numerous biological properties. Anthocyanins, flavonols, stilbenes, curcuminoids, hesperidin, hesperetin, naringenin, and phenolic acids are common polyphenols found in blueberries, chokeberries, sea-buckthorn, mulberries, turmeric, citrus fruits, and cereals. These compounds exhibit antidiabetic effects through different pathways. Accordingly, this review presents an overview of the most recent developments in using food polyphenols for managing and treating type II diabetes mellitus, along with various mechanisms. In addition, the present work summarizes the literature about the anti-diabetic effect of food polyphenols and evaluates their potential as complementary or alternative medicines to treat type II diabetes mellitus. Results obtained from this survey show that anthocyanins, flavonols, stilbenes, curcuminoids, and phenolic acids can manage diabetes mellitus by protecting pancreatic β-cells against glucose toxicity, promoting β-cell proliferation, reducing β-cell apoptosis, and inhibiting α-glucosidases or α-amylase. In addition, these phenolic compounds exhibit antioxidant anti-inflammatory activities, modulate carbohydrate and lipid metabolism, optimize oxidative stress, reduce insulin resistance, and stimulate the pancreas to secrete insulin. They also activate insulin signaling and inhibit digestive enzymes, regulate intestinal microbiota, improve adipose tissue metabolism, inhibit glucose absorption, and inhibit the formation of advanced glycation end products. However, insufficient data are available on the effective mechanisms necessary to manage diabetes.

Antioxidant and Anti-Inflammatory Properties of Phytochemicals Found in the Yucca Genus

The Yucca genus encompasses about 50 species native to North America. Species within the Yucca genus have been used in traditional medicine to treat pathologies related to inflammation. Despite its historical use and the popular notion of its antioxidant and anti-inflammatory properties, there is a limited amount of research on this genus. To better understand these properties, this work aimed to analyze phytochemical composition through documentary research. This will provide a better understanding of the molecules and the mechanisms of action that confer such antioxidant and anti-inflammatory properties. About 92 phytochemicals present within the genus have reported antioxidant or anti-inflammatory effects. It has been suggested that the antioxidant and anti-inflammatory properties are mainly generated through its free radical scavenging activity, the inhibition of arachidonic acid metabolism, the decrease in TNF-α (Tumor necrosis factor-α), IL-6 (Interleukin-6), iNOS (Inducible nitric oxide synthase), and IL-1β (Interleukin 1β) concentration, the increase of GPx (Glutathione peroxidase), CAT (Catalase), and SOD (Superoxide dismutase) concentration, and the inhibition of the MAPK (Mitogen-Activated Protein Kinase), and NF-κB (Nuclear factor kappa B), and the activation of the Nrf2 (Nuclear factor erythroid 2–related factor) signaling pathway. These studies provide evidence of its use in traditional medicine against pathologies related to inflammation. However, more models and studies are needed to properly understand the activity of most plants within the genus, its potency, and the feasibility of its use to help manage or treat chronic inflammation.

Phytochemical Profile, Antioxidant Activity, Anti-Hyperglycemic Effect and Toxicity Assessment of Ridolfia segetum (L.) Moris Extract

The present work was designed to study the chemical composition, antioxidant, antihyperglycemic effect, and toxicity assessment of Ridolfia segetum (L.) Moris extract. The chemical composition was studied by use of high-performance liquid chromatography (HPLC). Antioxidant power was tested by use of DPPH and FRAP assays. The antihyperglycemic effect was tested by use of a glucose tolerance test, while toxicity assessment was done in vivo by use of Wistar rats for 14 days. Analysis of the extract by HPLC-UV revealed the presence of gallic acid, catechol, vanillic acid, catechin, tannic acid, rosmarinic acid, naringenin, and coumarin acid. The crude hydroethanolic extract possessed high levels of total phenols (15.6 ± 1.76 mg EAG/g), condensed tannins (383.49 mg ECat/g DM), and flavonoid (11.63 mg EQ/g). The findings showed that the studied extract possessed good antioxidant power with IC₅₀ values equal to 550, 650, 700 µg/mL respectively for the decoction, the ethyl acetate fraction (F_2M), and the ethyl acetate fraction (F_2E). For the antioxidant activity by FRAP, the aqueous fraction (F_3E) and the aqueous extract (F₄) showed CE₅₀ values of 0.33 mg/mL and 0.4 mg/mL, respectively. Glucose tolerance test analysis showed that R. segetum (L.) Moris decoction had a significant postprandial antihyperglycemic effect in normal Wistar rats. The results of the acute toxicity test showed that the decoction was not toxic even at 2 g/Kg. Pancreatic α-amylase activity was significantly inhibited in the presence of R. segetum (L.) Moris extract (IC₅₀ = 0.133 ± 0.09 mg/mL). The outcome of the present work showed that R. segetum (L.) Moris is very rich in phenolic compounds with potent antioxidant and antihyperglycemic effects.

Quercetin and metformin synergistically reverse endothelial dysfunction in the isolated aorta of streptozotocin-nicotinamide- induced diabetic rats

The antidiabetic effects of quercetin and metformin are well known. However, their synergistic effect in reversing the symptoms of diabetes-induced endothelial dysfunction remains unknown. In this study, we have investigated their synergistic effect in streptozotocin (STZ)-nicotinamide induced diabetic rats. Seventy-five rats were divided into five groups; normal control, diabetic control, treatment groups (10 mg/kg quercetin, 180 mg/kg metformin, and combined). The plasma glucose and lipid levels, liver enzymes, ex-vivo studies on aortic rings, histology of liver, kidney, pancreas, abdominal aorta and thoracic aorta, and immunohistochemical studies were carried out. The findings revealed that the combination of quercetin and metformin showed a greater antidiabetic effect than either drug, and rendered protection to the endothelium. The combination effectively reversed the hyperglycemia-induced endothelial dysfunction in diabetic rats. Furthermore, it also reversed the dysregulated expression of eNOS, 3-nitrotyrosine, VCAM-1, CD31 and SIRT-1. Overall, the present study's findings demonstrate that quercetin potentiates the activity of metformin to control the complications associated with diabetes.

Effect of quercetin and Abelmoschus esculentus (L.) Moench on lipids metabolism and blood glucose through AMPK-α in diabetic rats (HFD/STZ)

Phosphoenolpyruvate carboxykinase (PEPCK) is a key enzyme in the glyconeogenesis pathway. The AMP-activated protein kinase alpha (AMPK-α) pathway regulates PEPCK, which itself is activated by the AMP/ATP ratio and liver kinase B1 (KB1). The Abelmoschus esculentus (L.) Moench (okra) plant contains a large amount of quercetin that can function as an agonist or an antagonist. The aim of this study was to examine the effects of quercetin flavonoid and A. esculentus extract on the level of AMPK-α expression and associated metabolic pathways. The findings demonstrate that metformin, quercetin, and okra extract may significantly raise AMPK-α levels while significantly lowering PEPCK and hormone-sensitive lipase (HSL) levels, in addition to improving glucose and lipid profiles. By stimulating KB1, these substances increased AMPK-α activation. Additionally, AMPK-α activation improved insulin resistance and Glucose transporter type 4 (GLUT4) gene expression levels. Since AMPK-α maintains energy balance and its activity has not been reported to be inhibited so far, it could be a potent therapeutic target. PRACTICAL APPLICATIONS: The development of effective AMPK-α agonists and antagonists holds promise for the treatment of metabolic disorders like diabetes. Dietary polyphenols are a valuable source for developing new drugs. However, due to the lack of understanding of the underlying mechanisms of their effect on cells, their use in the treatment of diabetes is controversial. In addition to chemicals that have medicinal benefits, chemists are searching for less harmful substances. Using plants containing bioactive chemicals for this purpose can be a good alternative to chemical drugs.

Chemical Composition, Antibacterial, Antifungal and Antidiabetic Activities of Ethanolic Extracts of Opuntia dillenii Fruits Collected from Morocco

Opuntia dillenii (Ker Gawl.) Haw. belongs to the Cactaceae family and is native to the arid and semi-arid regions of Mexico and the southern United States. O. dillenii are now used as medicinal plants in various countries. In this study, we investigated the chemical composition of ethanolic extracts obtained from seeds, juice, and peel of O. dillenii fruits collected from Morocco, and we evaluated their antibacterial, antifungal, and antidiabetic activities. Phytochemical screening revealed high quantities of polyphenols (193.73 ± 81.44 to 341.12 ± 78.90 gallic acid eq [g/100 g dry weight]) in the extracts. The major phenolic compounds determined by HPLC were gallic acid, vanillic acid, and syringic acid. Regarding flavonoids, quercetin 3-O-β-D-glucoside and kaempferol were the predominant molecules. Juice extracts showed weak to moderate antibacterial activity against the bacteria species Listeria monocytogenes, Escherichia coli, and Salmonella braenderup. All tested extracts displayed a significant inhibitory effect on α-glucosidase and α-amylase activities in vitro, with the peel extracts showing the greatest inhibitory effects. Together, these findings suggest that O. dillenii fruits are a promising source for the isolation of novel compounds with antibacterial or antidiabetic activities. For the most abundant phytochemicals identified in O. dillenii peel ethanolic extract, molecular docking simulations against human pancreatic α-amylase enzyme were performed. These indicated the presence of bioactive compounds in the extract with a better potential to decrease the enzyme activity than the commercial drug acarbose.

Quercetin Nanoemulsion Ameliorates Neuronal Dysfunction in Experimental Alzheimer's Disease Model

Aluminum is the most abundant metal that can get admission to the human through several means that include our food, drinking water, cans, drugs, and deodorants, causing neurodegenerative diseases such as Alzheimer's disease (AD). The present study aims to evaluate the role of quercetin nanoemulsion (QCNE) in attenuating neuronal dysfunction in aluminum chloride (AlCl3)-induced experimental AD. All animals were classified into six groups including negative control group (I): received a vehicle; QC group: received intraperitoneal (IP) injection of QC; Alzheimer's group: received AlCl3 orally; treated group (I): received AlCl3 orally and IP injection of QC; treated group (II): received AlCl3 orally and QC orally; and treated group (III): received AlCl3 orally and IP injection of QCNE. At the end of the experimental period (30 days), the brain was used to study biochemical parameters (measurement of neurotransmitters (serotonin, dopamine, and norepinephrine), oxidant/antioxidant parameters (reduced glutathione, malondialdehyde, superoxide dismutase, and advanced oxidation protein product), and inflammatory markers (adiponectin, interleukin 1β, and plasma tumor necrosis factor-alpha)), while another part was for brain immune-histochemical analysis (study cyclooxygenases (COX-1 and COX-2)). Results showed that the mean value of oxidative stress markers was significantly increased in the AD group as well as the inflammatory biomarkers and all the study neurotransmitters, whereas these parameters were attenuated in treated groups, especially those that received QCNE. The immunohistochemistry findings confirm our results. Both approaches (QC and QCNE) succeeded in retracting the negative impact of AlCl3. Meanwhile, the effect of QCNE is more potent in mitigating the impact mediated by AlCl3 in treated animals. In conclusion, the treatment mainly by QCNE has huge potential in protecting against AlCl3-induced neuronal dysfunction, as shown in our results by the elevation of brain antioxidant/anti-inflammatory activities and neurotransmitter levels as well as mending of the histopathological changes in animal models.

Therapeutic Potential of Quercetin in the Management of Type-2 Diabetes Mellitus

Diabetes Mellitus (DM) is a metabolic disorder that is spreading alarmingly around the globe. Type-2 DM (T2DM) is characterized by low-grade inflammation and insulin resistance and is closely linked to obesity. T2DM is mainly controlled by lifestyle/dietary changes and oral antidiabetic drugs but requires insulin in severe cases. Many of the drugs that are currently used to treat DM are costly and present adverse side effects. Several cellular, animal, and clinical studies have provided compelling evidence that flavonoids have therapeutic potential in the management of diabetes and its complications. Quercetin is a flavonoid, present in various natural sources, which has demonstrated in vitro and in vivo antidiabetic properties. It improves oral glucose tolerance, as well as pancreatic β-cell function to secrete insulin. It inhibits the α-glucosidase and DPP-IV enzymes, which prolong the half-life of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Quercetin also suppresses the release of pro-inflammatory markers such as IL-1β, IL-4, IL-6, and TNF-α. Further studies are warranted to elucidate the mode(s) of action of quercetin at the molecular level. This review demonstrates the therapeutic potential of quercetin in the management of T2DM.

Quercetin: A Molecule of Great Biochemical and Clinical Value and Its Beneficial Effect on Diabetes and Cancer

Quercetin belongs to the broader category of polyphenols. It is found, in particular, among the flavonols, and along with kaempferol, myricetin and isorhamnetin, it is recognized as a foreign substance after ingestion in contrast to vitamins. Quercetin occurs mainly linked to sugars with the most common compounds being quercetin-3-O-glucoside or as an aglycone, especially in the plant population. The aim of this review is to present a recent bibliography on the mechanisms of quercetin absorption and metabolism, bioavailability, and antioxidant and the clinical effects in diabetes and cancer. The literature reports a positive effect of quercetin on oxidative stress, cancer, and the regulation of blood sugar levels. Moreover, research-administered drug dosages of up to 2000 mg per day showed mild to no symptoms of overdose. It should be noted that quercetin is no longer considered a carcinogenic substance. The daily intake of quercetin in the diet ranges 10 mg-500 mg, depending on the type of products consumed. This review highlights that quercetin is a valuable dietary antioxidant, although a specific daily recommended intake for this substance has not yet been determined and further studies are required to decide a beneficial concentration threshold.

Acceleration of wound healing by quercetin in diabetic rats requires mitigation of oxidative stress and stimulation of the proliferative phase

Increased oxidative stress in diabetic wound areas impairs wound healing. Quercetin exhibits significant antioxidant properties. We investigated the effects of topical quercetin on antioxidant status in diabetic wound areas and its effect on wound healing in rats. A 2 cm² cutaneous wound was produced on the back of streptozotocin induced diabetic and normal rats. Rats were divided into three groups of 20: normal healthy control group, diabetic group and quercetin treated diabetic group. The control and diabetic groups were treated topically with ointment base once daily for 21 days. The quercetin treated diabetic rats were treated similarly with ointment containing quercetin. The quercetin treated diabetic group exhibited increased levels of catalase, glutathione peroxidase, superoxide dismutase and total thiols compared to the diabetic group. Nitrite levels in the diabetic group were decreased significantly on day 3 compared to the healthy control group. Malondialdehyde levels were decreased in the quercetin treated diabetic group compared to the diabetic group. The expression of proliferating cell nuclear antigen) (PCNA) was greater in the quercetin treated diabetic group on day 7 compared to healthy control and diabetic groups. Formation of granulation tissue and the quality of healed tissue was improved in the quercetin treated diabetic group compared to the diabetic group. Quercetin improves antioxidant status in wounds of diabetic rats and stimulates the proliferation phase, which accelerates wound healing.

Does Oxidative Stress Management Help Alleviation of COVID-19 Symptoms in Patients Experiencing Diabetes?

Severe acute respiratory syndrome (SARS)-CoV-2 virus causes novel coronavirus disease 2019 (COVID-19) with other comorbidities such as diabetes. Diabetes is the most common cause of diabetic nephropathy, which is attributed to hyperglycemia. COVID-19 produces severe complications in people with diabetes mellitus. This article explains how SARS-CoV-2 causes more significant kidney damage in diabetic patients. Importantly, COVID-19 and diabetes share inflammatory pathways of disease progression. SARS-CoV-2 binding with ACE-2 causes depletion of ACE-2 (angiotensin-converting enzyme 2) from blood vessels, and subsequently, angiotensin-II interacts with angiotensin receptor-1 from vascular membranes that produce NADPH (nicotinamide adenine dinucleotide hydrogen phosphate) oxidase, oxidative stress, and constriction of blood vessels. Since diabetes and COVID-19 can create oxidative stress, we hypothesize that COVID-19 with comorbidities such as diabetes can synergistically increase oxidative stress leading to end-stage renal failure and death. Antioxidants may therefore prevent renal damage-induced death by inhibiting oxidative damage and thus can help protect people from COVID-19 related comorbidities. A few clinical trials indicated how effective the antioxidant therapy is against improving COVID-19 symptoms, based on a limited number of patients who experienced COVID-19. In this review, we tried to understand how effective antioxidants (such as vitamin D and flavonoids) can act as food supplements or therapeutics against COVID-19 with diabetes as comorbidity based on recently available clinical, preclinical, or in silico studies.

Quercetin for managing type 2 diabetes and its complications, an insight into multitarget therapy

BACKGROUND

Quercetin, a bioflavonoid abundant in grapefruit, onion, berries, etc., has vast therapeutic potential, especially against Type 2 diabetes and its complications. Quercetin showed similar effects as that of metformin, (widely prescribed antidiabetic drug) in cell lines models (Sajan et al., 2010; Dhanya et al., 2017). In vivo findings also showcase it as a promising agent against diabetes and its pathophysiological complications.

SCOPE AND APPROACH

Quercetin can be produced on a large scale through a novel fermentation-based glycosylation strategy from cheap substrates and can be utilized as a dietary supplement. The review focuses on the mounting evidence pointing to Quercetin as a promising candidate for managing type 2 diabetes and its oxidative stress mediated pathophysiological complications.

CONCLUSION

Quercetin acts on multiple targets of diabetes and regulates key signalling pathways which improve the symptoms as well as the complications of Type 2 diabetes. However further studies are needed to improve the bioavailability and to establish a dosing regimen for Quercetin.

Quercetin and metabolic syndrome: A review

Metabolic syndrome (MetS) is a complex of diseases that lead to mortality due to the development of cardiovascular problems. Quercetin, as an important flavonoid, has various properties such as decreasing blood pressure, anti-hyperlipidemia, anti-hyperglycemia, anti-oxidant, antiviral, anticancer, anti-inflammatory, anti-microbial, neuroprotective, and cardio-protective effects. In this review article, we collected original articles from different sources such as Google Scholar, Medline, Scopus, and Pubmed, which is related to the effect of quercetin on the improvement of the signs of MetS, including elevated glucose level, hyperlipidemia, obesity, and blood pressure. According to these data, quercetin may also have a role in the management of metabolic disorders via different mechanisms such as increasing adiponectin, decreasing leptin, anti-oxidant activity, reduction of insulin resistance, the elevation of insulin level, and blocking of calcium channel. We have attempted to make some recommendations on the quercetin application in patients. However, it needs to do further clinical trials and more investigations to show the real clinical value of quercetin on metabolic syndrome.

Alotaibi A, Al-zharani M, Ziyyat A, Mekhfi H, Legssyer A, Aziz M, Bnouham M. Opuntia dillenii (Ker Gawl.) Haw., Seeds Oil Antidiabetic Potential Using In Vivo, In Vitro, In Situ, and Ex Vivo Approaches to Reveal Its Underlying Mechanism of Action

Opuntia dillenii Ker Gawl. is one of the medicinal plants used for the prevention and treatment of diabetes mellitus (DM) in Morocco. This study aims to investigate the antihyperglycemic effect of Opuntia dillenii seed oil (ODSO), its mechanism of action, and any hypoglycemic risk and toxic effects. The antihyperglycemic effect was assessed using the OGTT test in normal and streptozotocin (STZ)-diabetic rats. The mechanisms of action were explored by studying the effect of ODSO on the intestinal absorption of d-glucose using the intestinal in situ single-pass perfusion technique. An Ussing chamber was used to explore the effects of ODSO on intestinal sodium-glucose cotransporter 1 (SGLT1). Additionally, ODSO’s effect on carbohydrate degrading enzymes, pancreatic α-amylase, and intestinal α-glucosidase was evaluated in vitro and in vivo using STZ-diabetic rats. The acute toxicity test on mice was performed, along with a single-dose hypoglycemic effect test. The results showed that ODSO significantly attenuated the postprandial hyperglycemia in normal and STZ-diabetic rats. Indeed, ODSO significantly decreased the intestinal d-glucose absorption in situ. The ex vivo test (Ussing chamber) showed that the ODSO significantly blocks the SGLT1 (IC₅₀ = 60.24 µg/mL). Moreover, ODSO indu\ced a significant inhibition of intestinal α-glucosidase (IC₅₀ = 278 ± 0.01 µg/mL) and pancreatic α-amylase (IC₅₀ = 0.81 ± 0.09 mg/mL) in vitro. A significant decrease of postprandial hyperglycemia was observed in sucrose/starch-loaded normal and STZ-diabetic ODSO-treated rats. On the other hand, ODSO had no risk of hypoglycemia on the basal glucose levels in normal rats. Therefore, no toxic effect was observed in ODSO-treated mice up to 7 mL/kg. The results of this study suggest that ODSO could be suitable as an antidiabetic functional food.

Biomedical Properties of Propolis on Diverse Chronic Diseases and Its Potential Applications and Health Benefits

The use of alternative medicine products has increased tremendously in recent decades and it is estimated that approximately 80% of patients globally depend on them for some part of their primary health care. Propolis is a beekeeping product widely used in alternative medicine. It is a natural resinous product that bees collect from various plants and mix with beeswax and salivary enzymes and comprises a complex mixture of compounds. Various biomedical properties of propolis have been studied and reported in infectious and non-infectious diseases. However, the pharmacological activity and chemical composition of propolis is highly variable depending on its geographical origin, so it is important to describe and study the biomedical properties of propolis from different geographic regions. A number of chronic diseases, such as diabetes, obesity, and cancer, are the leading causes of global mortality, generating significant economic losses in many countries. In this review, we focus on compiling relevant information about propolis research related to diabetes, obesity, and cancer. The study of propolis could generate both new and accessible alternatives for the treatment of various diseases and will help to effectively evaluate the safety of its use.

Temporal Effects of Different Vehicles on Wound Healing Potentials of Quercetin: Biochemical, Molecular, and Histopathological Approaches

Development of novel drugs or formulations to accelerate the wound healing process is the need of current era. Quercetin (Q), a bioflavonoid, at 0.3% concentration has showed some wound healing potential in our preliminary studies. The present study was aimed to explore the wound healing potential of 0.3% quercetin formulated in 3 different vehicles, that is, dimethyl sulfoxide (DMSO; 10%), ointment base, and corn oil. Ninety experimentally wounded rats were grouped in 6 groups. The 0.3% quercetin mixed with DMSO, ointment base, and corn oil was topically applied once daily for 21 days on the wounds of groups 2, 4, and 6, respectively. DMSO, ointment base, and corn oil alone was applied similarly in groups 1, 3, and 5, respectively. Gross evaluation and wound contraction results revealed accelerated wound closure in all quercetin-treated groups. The mRNA expressions of vascular endothelial growth factor, transforming growth factor-β₁, and interluekin-10 were markedly upregulated in healing tissues of quercetin-treated groups. Tumor necrosis factor-α mRNA expression and protein levels were lowered by quercetin treatment. Quercetin-treated groups also showed increased activities of SOD (superoxide dismutase) and catalase, and levels of total thiols in wound tissues on day 7. Levels of superoxide anion radicals and malondialdehyde were markedly lower in quercetin-treated groups. Histologically, wound sections of quercetin-treated groups showed early dominance of fibroblasts, increased blood vessels, marked collagen deposition, and regenerated epithelial layer. The significant effects were more pronounced in ointment + Q group among all the quercetin-treated groups. In conclusion, 0.3% quercetin mixed in ointment base produced the fastest and better wound healing in rats.

Quercetin: Antiviral Significance and Possible COVID-19 Integrative Considerations

Quercetin, a naturally occurring dietary flavonoid, is well known to ameliorate chronic diseases and aging processes in humans, and its antiviral properties have been investigated in numerous studies. In silico and in vitro studies demonstrated that quercetin can interfere with various stages of the coronavirus entry and replication cycle such as PLpro, 3CLpro, and NTPase/helicase. Due to its pleiotropic activities and lack of systemic toxicity, quercetin and its derivatives may represent target compounds to be tested in future clinical trials to enrich the drug arsenal against coronavirus infections. There is evidence that quercetin in combination with, for example, vitamins C and D, may exert a synergistic antiviral action that may provide either an alternative or additional therapeutic/preventive option due to overlapping antiviral and immunomodulatory properties. This review summarizes the antiviral significance of quercetin and proposes a possible strategy for the effective utilization of natural polyphenols in our daily diet for the prevention of viral infection.

Phenolic Content and Antioxidant, Antihyperlipidemic, and Antidiabetogenic Effects of Opuntia dillenii Seed Oil

Opuntia dillenii (Ker-Gawl.) Haw. is a medicinal plant that is widely used by the Moroccan population to treat many diseases, thanks to its richness in bioactive molecules. This study aims to evaluate the total phenolic content and antioxidant, antihyperlipidemic, and antidiabetogenic activities of O. dillenii seeds oil (ODSO), in vivo. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assay and the Folin–Ciocalteu method were applied in this study to determine antioxidant activity and total phenolic content of ODSO, respectively. The antihyperlipidemic effect of the ODSO (2 ml/kg) was evaluated in the high-fat diet-fed albino mice, relying on lipid profile, blood glucose, and growth performance variations. Moreover, the preventive effect of ODSO was evaluated against alloxan monohydrate-induced diabetes in albino mice. ODSO had the highest total phenolic content (518.18 ± 14.36 mg EAC/kg) and DPPH scavenging activity (IC₅₀ = 0.38 ± 0.08 mg/mL). Furthermore, ODSO showed a significant antidiabetogenic effect by reducing bodyweight loss, blood sugar level rise, and mortality rate caused by alloxan in albino mice. Then, ODSO has exhibited a significant antihyperlipidemic effect by improving the lipid profile disorder and glucose level rise in the blood, produced by the high-fat diet-fed albino mice. Results suggest that antidiabetogenic and antihyperlipidemic activities of ODSO correlate to the phenolic content and antioxidant activity of this oil. Hence, this plant could be a significant source of medically important critical compounds.

Crosstalk between obesity, diabetes, and alzheimer's disease: Introducing quercetin as an effective triple herbal medicine

Obesity and diabetes are the most common metabolic disorders, which are strongly related to Alzheimer's disease (AD) in aging. Diabetes and obesity can lead to the accumulation of amyloid plaques, neurofibrillary tangles (NFTs), and other symptoms of AD through several pathways, including insulin resistance, hyperglycemia, hyperinsulinemia, chronic inflammation, oxidative stress, adipokines dysregulation, and vascular impairment. Currently, the use of polyphenols has been expanded in animal models and in-vitro studies because of their comparatively negligible adverse effects. Among them, quercetin (QT) is one of the most abundant polyphenolic flavonoids, which is present in fruits and vegetables and displays many biological, health-promoting effects in a wide range of diseases. The low bioavailability and poor solubility of QT have also led researchers to make various QT-involved nanoparticles (NPs) to overcome these limitations. In this paper, we review significant molecular mechanisms induced by diabetes and obesity that increase AD pathogenesis. Then, we summarize in vitro, in vivo, and clinical evidence regarding the anti-Alzheimer, anti-diabetic and anti-obesity effects of QT. Finally, QT in pure and combination form using NPs has been suggested as a promising therapeutic agent for future studies.

Swertiamarin and quercetin combination ameliorates hyperglycemia, hyperlipidemia and oxidative stress in streptozotocin-induced type 2 diabetes mellitus in wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Swertiamarin (Sw) and quercetin (Qu) have been isolated from different plants and are reported for their antidiabetic activities. The plants from which swertiamarin and quercetin were isolated are also traditionally used in the treatment of diabetes mellitus.

AIM OF THE STUDY

The present study is aimed to evaluate the synergistic effect of a combination of swertiamarin and quercetin (CSQ) on α-amylase in vitro and on streptozotocin (STZ) induced diabetes mellitus in vivo.

METHODS

Swertiamarin was isolated from the plant Enicostemma axillare and quercetin was procured in its pure form. Sw, Qu and CSQ were evaluated for in vitro α-amylase inhibitory activity. Based on the in vitro study results, CSQ was assessed for in vivo streptozotocin induced diabetes mellitus in Wistar rats. The effect of CSQ on blood glucose levels, body weight, serum biochemical parameters and antioxidant enzymes such as glutathione (GSH), superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and lipid peroxide levels were estimated. The histopathological observations of pancreatic tissues were also made.

RESULTS

The purity of swertiamarin was confirmed by HPLC. The results showed that CSQ was found to possess high percentage of inhibition in an in vitro α-amylase inhibitory study. In a STZ-induced type 2 diabetes mellitus (T2DM), body weight of rats in CSQ treated and control groups were unaltered. A marked reduction in the blood glucose levels was observed in the CSQ treated groups on 14th and 28th day. Decrease in the levels of low-density lipoprotein (LDL), triglycerides, total cholesterol and an increase in high-density lipoprotein (HDL) cholesterol level was observed in a dose dependant in CSQ treated groups. However, CSQ treated groups could significantly improve antioxidant protection by increasing the levels of serum GSH, SOD, Catalase and GPx and decreasing the levels of lipid peroxide (p < 0.05). In the histopathological study, the pancreatic islets of Langerhans and vacuolization have shown significant increase in both the treated groups.

CONCLUSIONS

The combination of swertiamarin and quercetin (CSQ) has proven a preventive and therapeutic effect against T2DM and suggests that this is a potential combination of phytoconstituents for excellent hypoglycemic activity in T2DM.

Prunus amygdalus extract exert antidiabetic effect via inhibition of DPP-IV: in-silico and in-vivo approaches

Prunus amygdalus (PA) is a popular invasive seed utilized in the management of diabetes in Jammu and Kashmir, India. The objective of the current study was to scrutinize the antidiabetic effect of Prunus amygdalus (PA) against Streptozotocin (STZ) induced diabetic rats and explore the possible mechanism of action at cellular and sub-cellular levels. Box Benkan Design (BBD) was performed to determine the effect of PA powder to methanol, extraction time and extraction temperature on DPPH and ABTS free radical scavenging activity of decoction. In-silico study was performed on GLUT1 (5EQG) and dipeptidyl peptidase IV (DPPIV) (2G63) protein. Type II diabetes mellitus was initiated by single intra-peritoneal injection of STZ. The Blood Glucose Level (BGL) and body weight were estimated at regular interval of time. The different biochemical parameters such as hepatic, antioxidant, and lipid parameters were estimated. At end of the study, pancreas was used for histopathological observation. The variation in DPPH antiradical scavenging activity 40.0-90.0% and ABTS antiradical scavenging activity 34-82%, were estimated respectively. STZ induced DM rats showed increased BGL at end of the experimental study. PA treatment significantly (p < 0.001) down-regulated the BGL level. PA significantly (p < 0.001) altered the biochemical, hepatic and antioxidant parameters in a dose-dependent manner. Histopathological examination demonstrated the constructive mass of β-cells in pancreas. Overall, the current study indicates that the PA treatment down-regulated the hyperglycemic, oxidative stress and hyperlipidaemia in diabetic rats, due to inhibition of enzymes or amelioration of oxidative stress. [Formula: see text] Communicated by Ramaswamy H. Sarma.

Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19)

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) represents an emergent global threat which is straining worldwide healthcare capacity. As of May 27th, the disease caused by SARS-CoV-2 (COVID-19) has resulted in more than 340,000 deaths worldwide, with 100,000 deaths in the US alone. It is imperative to study and develop pharmacological treatments suitable for the prevention and treatment of COVID-19. Ascorbic acid is a crucial vitamin necessary for the correct functioning of the immune system. It plays a role in stress response and has shown promising results when administered to the critically ill. Quercetin is a well-known flavonoid whose antiviral properties have been investigated in numerous studies. There is evidence that vitamin C and quercetin co-administration exerts a synergistic antiviral action due to overlapping antiviral and immunomodulatory properties and the capacity of ascorbate to recycle quercetin, increasing its efficacy. Safe, cheap interventions which have a sound biological rationale should be prioritized for experimental use in the current context of a global health pandemic. We present the current evidence for the use of vitamin C and quercetin both for prophylaxis in high-risk populations and for the treatment of COVID-19 patients as an adjunct to promising pharmacological agents such as Remdesivir or convalescent plasma.

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.

Anti- and pro-oxidant effects of quercetin stabilized by microencapsulation on interstitial cells of Cajal, nitrergic neurons and M2-like macrophages in the jejunum of diabetic rats

Given the well-known antioxidant and neuroprotective properties of quercetin, the aim of this work was to evaluate the effects of quercetin stabilized by microencapsulation at two doses (10 mg kg^-1 and 100 mg kg^-1) on the oxidative/antioxidant status, number and morphological features of ICC, nitrergic neurons and M2-like macrophages in jejunum of diabetic rats. The rats were randomly distributed into six groups: normoglycemic control (N), diabetic control (D) and either normoglycemic or diabetic groups treated with quercetin-loaded microcapsules at a dose of 10 mg kg^-1 (NQ10 and DQ10, respectively) or 100 mg kg^-1 (NQ100 and DQ100, respectively). After 60 days, the jejunum was collected. Whole mounts were immunostained for Ano1, nNOS and CD206, and oxidative stress levels and total antioxidant capacity of the jejunum were measured. Diabetes led to a loss of ICC and nitrergic neurons, but increased numbers of M2-like macrophages and elevated levels of oxidative stress were seen in diabetic animals. High-dose administration of quercetin (100 mg kg^-1) further aggravated the diabetic condition (DQ100) but this treatment resulted in harmful effects on healthy rats (NQ100), pointing to a pro-oxidant activity. However, low-dose administration of quercetin (10 mg kg^-1) gave rise to antioxidant and protective effects on ICC, nNOS, macrophages and oxidative/antioxidant status in DQ100, but NQ100 displayed infrequent negative outcomes in normoglycemic animals. Microencapsulation of the quercetin may become promising alternatives to reduce diabetes-induced oxidative stress but antioxidant therapies should be careful used under healthy status to avoid toxic effects.

Quercetin modulates hyperglycemia by improving the pancreatic antioxidant status and enzymes activities linked with glucose metabolism in type 2 diabetes model of rats: In silico studies of molecular interaction of quercetin with hexokinase and catalase

Quercetin was assessed for its antihyperglycemic effect in fructose-streptozotocin (STZ) induced diabetic rats. The oral administration of quercetin at the dosage of 25 and 50 mg/kg for 28 days remarkably reduced the level of blood glucose, glycosylated hemoglobin (Hb), and hepatic glycogen but enhanced plasma Hb concentration. The altered activities of glucose-6-phosphatase and hexokinase in diabetic rats were significantly improved upon quercetin treatment. Furthermore, the antioxidant activity of pancreatic superoxide dismutase, catalase (CAT), and reduced glutathione was effectively increased while the value for thiobarbituric acid reactive species was decreased. A significant reduction of glycemia was observed in the glucose tolerance test, 120 min after the glucose pulse. Also, the damage caused by fructose-STZ in the liver and pancreas of diabetic animals were restored to near normal. Molecular docking of quercetin showed a high affinity for hexokinase and CAT with a binding energy of -7.82 and -9.83 kcal/mol, respectively, more elevated than the standard drugs. PRACTICAL APPLICATIONS: Functional foods and nutraceuticals have increasingly interested the consumers in terms of health benefits and have started focussing on the prevention or cure of disease by the foods and their health-enhancing phytochemicals. Quercetin is one of the most potent naturally occurring antioxidants within the flavonoid subclasses, mostly distributed as a secondary metabolite in fruits, vegetables, and black tea. Based on the results exhibited in the present study, we proposed that the consumption of foods rich in quercetin could be a cheap and affordable nutraceutical that can be developed for the treatment of T2DM and its complications. Further studies on the safety aspects of quercetin in long-term usage are strongly recommended before implementing for the treatment of human diseases.

Flavonoids sensitize tumor cells to radiation: molecular mechanisms and relevance to cancer radiotherapy

Purpose: Radiobiological research continues to focus on finding newer strategies for enhanced killing of tumor cells by ionizing radiation. In recent years, chemotherapeutic drugs have been found to possess the capabilities to sensitize tumor cells without affecting the normal cells. There have been increasing research efforts to identify novel and nontoxic compounds which cause minimal or no harm to normal cells but maximize tumor toxicity response to radiation exposure. Extensive researches on flavonoids that are compounds derived from plants have shown that these have promising abilities as radioprotectors and radiosensitizers.Conclusions: In this review, we examine the role of flavonoids as potential radiosensitizers, review the underlying molecular mechanisms and discuss their potential usefulness in improving cancer radiotherapy. It is emphasized that obtaining a deeper insight into the molecular mechanisms underlying the combined action of flavonoids and ionizing radiation may provide new directions for radiobiological research applicable to the much needed enhanced selective tumor cytotoxicity to treatment agents.

Hypoglycaemic activity of Bauhinia holophylla through GSK3-β inhibition and glycogenesis activation

CONTEXT

Bauhinia L. species, including Bauhinia holophylla (Bong.) Steud. (Fabaceae), have traditionally been used to treat diabetes. Bauhinia is a complex botanical genus, and the indiscriminate use of the diverse Bauhinia species is reflected in the experimental divergence of their medicinal potential.

OBJECTIVE

The hypoglycaemic and hypolipidaemic effects, molecular mechanism of action and phytochemical properties of an authentic extract of B. holophylla leaves were evaluated.

MATERIALS AND METHODS

A phytochemical study of a 70% EtOH extract was performed using FIA-ESI-IT-MS/MSn and HPLC-PAD-ESI-IT-MS. The extract (200 or 400 mg/kg b.w.) was administered for 14 days to streptozotocin-induced diabetic Swiss mice. Glucose tolerance and insulin sensitivity, blood parameters, gene and protein expression, and the in vivo and in vitro inhibition of intestinal glucosidases were assessed.

RESULTS

HPLC-PAD-ESI-IT-MS analysis identified flavonoid derivatives of quercetin, myricetin, luteolin and kaempferol. Treatment with 400 mg/kg of the extract reduced blood glucose (269.0 ± 32.4 mg/dL vs. 468.0 ± 32.2 mg/dL for diabetic animals), improved glucose tolerance, decreased cholesterol and triglyceride levels, and increased the mRNA expression of proteins involved in glucogenesis in the liver and muscle, such as PI3-K/Akt, GS, GSK3-β (ser-9), AMPK and Glut4. The activity of intestinal maltase was inhibited in vitro (IC50: 43.0 µg/mL for the extract compared to 516.4 µg/mL for acarbose) and in vivo.

DISCUSSION AND CONCLUSIONS

Treatment with B. holophylla was associated with a marked hypoglycaemic effect through the stimulation of glycogenesis and inhibition of gluconeogenesis and intestinal glucose absorption, without increasing basal insulinaemia.

QUERCETIN SUPPLEMENTATION PREVENTS CHANGES IN THE SEROTONIN AND CASPASE-3 IMMUNOREACTIVE CELLS OF THE JEJUNUM OF DIABETIC RATS

ABSTRACT BACKGROUND: Serotonin (5-HT) is present in the epithelial enterochromaffin cells (EC), mast cells of the lamina propria and enteric neurons. The 5-HT is involved in regulating motility, secretion, gut sensation, immune system and inflammation. OBJECTIVE: Evaluate the effects of diabetes and quercetin supplementation on serotoninergic cells and its cell loss by apoptosis in jejunal mucosa of streptozotocin-induced diabetic rats (STZ-rats). METHODS: Twenty-four male Wistar rats were divided into four groups: normoglycemic (C), normoglycemic supplemented with 40 mg/day quercetin (Q), diabetic (D) and diabetic supplemented with 40 mg/day quercetin (DQ). After 120 days, the jejunum was collected and fixated in Zamboni’s solution for 18 h. After obtaining cryosections, immunohistochemistry was performed to label 5-HT and caspase-3. Quantification of 5-HT and caspase-3 immunoreactive (IR) cells in the lamina propria, villi and crypts were performed. RESULTS: The diabetic condition displayed an increase of the number of 5-HT-IR cells in villi and crypts, while decreased number of these cells was observed in lamina propria in the jejunum of STZ-rats. In the diabetic animals, an increased density of apoptotic cells in epithelial villi and crypts of the jejunum was observed, whereas a decreased number of caspase-3-IR cells was observed in lamina propria. Possibly, quercetin supplementation slightly suppressed the apoptosis phenomena in the epithelial villi and crypts of the STZ-rats, however the opposite effect was observed on the 5-HT-IR cells of the lamina propria. Quercetin supplementation on healthy animals promoted few changes of serotoninergic function and apoptotic stimuli. CONCLUSION: These results suggest that quercetin supplementation mostly improved the serotonergic function affected by diabetes maybe due to antioxidant and anti-inflammatory properties of quercetin.

Graviola (Annona muricata) attenuates behavioural alterations and testicular oxidative stress induced by streptozotocin in diabetic rats

Oxidative stresses intensify the progression of diabetes-related behavioural changes and testicular injuries. Graviola (Annona muricata), a small tree of the Annonaceae family, has been investigated for its protective effects against diabetic complications, oxidative stress, and neuropathies. This study was planned to investigate the effects of graviola on behavioural alterations and testicular oxidative status of streptozotocin (STZ; 65 mg/kg)-induced diabetic rats. Forty adult male Wistar rats were equally allocated into four groups: control (received normal saline 8 ml/kg orally once daily), diabetic (received normal saline orally once daily), graviola (GR; received 100 mg/kg/day; orally once daily), and diabetic with graviola (Diabetic+GR; received 100 mg/kg/day; once daily). Behavioural functions were assessed using standard behavioural paradigms. Also, oxidative statuses of testis were evaluated. Results of behavioural observations showed that diabetes induced depression-like behaviours, reduction of exploratory and locomotor activities, decreased memory performance, and increased stress-linked behaviours. These variations in diabetic rats were happened due to oxidative stress. Interestingly, treatment of diabetic rats with graviola for four weeks alleviated all behavioural changes due to diabetes. Also, rats in graviola-treated groups had greater testicular testosterone and estradiol levels compared with diabetic rats due to significant rise in testicular acetyl-CoA acetyltransferase 2 expression. In the same context, graviola enhanced the antioxidant status of testicular tissues by significantly restoring the testicular glutathione and total superoxide dismutase that fell during diabetes. In addition, Graviola significantly decreased the expression of apoptotic (Bax) and inflammatory (interleukin-1β) testicular genes. In conclusion, these data propose that both the hypoglycemic and antioxidative potential of graviola are possible mechanisms that improve behavioural alterations and protect testis in diabetic animals. Concomitantly, further clinical studies in human are required to validate the current study.

Antidiabetic and renoprotective effect of Anogeissus acuminata leaf extract on experimentally induced diabetic nephropathy

Background Diabetic nephropathy is the leading cause of end-stage renal disease. Hyperglycemia, oxidative stress, and inflammation are some of the mechanisms involved in renal damage. Anogeissus acuminata (AA) is used in India as an antidiabetic agent and has potent antioxidant activity. However, it has never been evaluated for its effect on diabetic nephropathy. Hence, in the present study we aimed to evaluate its effect on streptozotocin-induced diabetes mellitus and its renal complications. Methods Diabetes mellitus was induced by injecting streptozotocin, 50 mg/kg, i.p. in rats fasted for 6 h. Rats with hyperglycemia were treated with extracts of AA for 8 weeks at doses of 100 and 300 mg/kg, orally. Human NPH insulin (4 IU/kg, s.c.) was used as standard treatment. Plasma glucose levels (at weeks 1, 2, 4, and 8) and oxidative stress parameters (at weeks 2 and 4) were assessed. Effect on diabetic nephropathy was evaluated by recording the urinary volume, urinary protein excretion, kidney weights, serum creatinine, and blood urea nitrogen levels at week 8. Results Methanolic extract of AA leaves produced statistically significant (p<0.05) hypoglycemic and antioxidant effect. It also resulted in improved urinary function, reflected by better urinary volume and reduced protein excretion in urine. AA treatment could prevent the elevation of serum creatinine and blood urea nitrogen level in a dose-dependent manner. Kidney hypertrophy could be attenuated remarkably, as reflected by the significantly lower kidney weight (KW) per 100 g body weight (p<0.05). Conclusions AA leaf extract attenuated the development of diabetic nephropathy and also demonstrated antidiabetic and antioxidant action.

The Effects of Hesperidin and Quercetin on Serum Tumor Necrosis Factor-Alpha and Interleukin-6 Levels in Streptozotocin-induced Diabetes Model

Background:

Diabetes mellitus (DM) is a metabolic disorder that occurs as a result of absolute or relative insufficiency of insulin release and/or insulin effect due to impairment of carbohydrate, fat and protein metabolism, and it is characterized by hyperglycemia and leads to various complications.

Objective:

In this study, it was aimed to investigate the effects of hesperidin (HP) and quercetin, which are natural flavonoids, on serum malondialdehyde (MDA), glutathione (GSH), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) levels in rats with streptozotocin (STZ)-induced diabetes.

Materials and Methods:

The experimental animals were divided into four groups, each group comprising ten rats designated as follows: Group 1 served as control rats (C); Group 2 served as diabetic rats (DM); Group 3 served as diabetic rats administered HP (DM + HP) (100 mg/kg b. w.); and Group 4 served as diabetic rats administered quercetin (DM + Q) (100 mg/kg b. w.).

Results:

Serum MDA and GSH levels were significantly higher in STZ-induced DM group than control group (P < 0.05). In DM + HP and DM + Q groups, MDA levels were significantly decreased compared to DM groups (P < 0.05), but there was no significant difference GSH levels between DM, DM + HP, and DM + Q groups (P > 0.05). TNF-α levels in STZ-induced DM group were significantly decreased compared to control group (P < 0.05), and groups of DM + HP and DM + Q had higher serum TNF-α levels than STZ-induced DM group (P < 0.05). In STZ-induced DM group, serum IL-6 levels were decreased compared to control group (P < 0.05).

Conclusion:

As a result, in this study, we determined that HP and quercetin may play an effective role in regulating insulin metabolism metabolism in diabetes. However, considering the incompatibility of various results in the literature as well as our own results, we think that the actual role of cytokines in the pathogenesis of diabetes is one of the issues that need to be clarified in further studies.

SUMMARY

Hesperidin (HP) and quercetin reduced the insulin, total cholesterol, triglyceride, low-density lipoprotein cholesterol, and malondialdehyde (MDA) serum levels and raised the glutathione (GSH) levels compared to diabetes mellitus (DM) group

SZT-induced DM increased the MDA serum levels and decreased the GSH levels compared to control group

HP and quercetin-treated rats showed higher interleukin-6 and tumor necrosis factor alpha cytokine levels than DM group

HP and quercetin may play an effective role in regulating insulin metabolism in diabetes.

Abbreviations used: DM: Diabetes mellitus, MDA: Malondialdehyde, GSH: Glutathione; IL-6: Interleukin-6, TNF-α: Tumor necrosis factor alpha, HP: Hesperidin, Q; Quercetin, STZ: Streptozotocin, TC: Total cholesterol, TG: Triglyceride, HDL-C: High density lipoprotein cholesterol, LDL-C: Low density lipoprotein cholesterol, VLDL-C: Very-low-density lipoprotein cholesterol.

Hypoglycaemic and Antioxidant Effects of Propolis of Chihuahua in a Model of Experimental Diabetes

Propolis is a bee-collected natural product that has been proven to have various bioactivities. This study tested the effects of a Mexican propolis on streptozotocin-induced diabetes mellitus in a murine model. The results showed that an ethanolic extract of propolis of Chihuahua (EEPCh) significantly inhibited increases in blood glucose and the loss of body weight in diabetic mice. EEPCh increased plasma insulin levels in STZ-diabetic mice, whereas, in untreated diabetic mice, there was no detection of insulin. EEPCh had a high antioxidant capacity (SA₅₀ = 15.75 μg/mL), which was directly related to the concentrations of total phenols (314 mg GAE/g of extract) and flavonoids (6.25 mg QE/g of extract). In addition, increased activities of the enzymes superoxide dismutase, catalase, and glutathione peroxidase were observed in diabetic mice treated with EEPCh. Compounds such as pinocembrin, quercetin, naringin, naringenin, kaempferol, acacetin, luteolin, and chrysin were identified by HPLC-MS analysis. This investigation demonstrated that propolis of Chihuahua possesses hypoglycaemic and antioxidant activities and can alleviate symptoms of diabetes mellitus in mice. These effects may be directly related to the chemical composition of propolis, as most of the compounds identified in propolis are reportedly active in terms of the different parameters evaluated in this work.

Establishment of pancreatic microenvironment model of ER stress: Quercetin attenuates β-cell apoptosis by invoking nitric oxide-cGMP signaling in endothelial cells

The involvement of endoplasmic reticulum (ER) stress in endothelial dysfunction and diabetes-associated complications has been well documented. Inhibition of ER stress represents a promising therapeutic strategy to attenuate endothelial dysfunction in diabetes. Recent attention has focused on the development of small molecule inhibitors of ER stress to maintain endothelial homeostasis in diabetes. Here we have developed a reliable, robust co-culture system that allows a study on the endothelial cells and pancreatic β-cells crosstalk under ER stress and validated using a known ER stress modulator, quercetin. Furthermore, sensitizing of endothelial cells by quercetin (25 μM) confers protection of pancreatic β-cells against ER stress through nitric oxide (NO^∙) signaling. In addition, increased intracellular insulin and NO^∙-mediated cyclic 3',5'-guanosine monophosphate (cGMP) levels in pancreatic β-cells further confirmed the mechanism of protection under co-culture system. In addition, the potential protein targets of quercetin against ER stress in the endothelial cells were investigated through proteomic profiling and its phosphoprotein targets through Bioplex analysis. On the whole, the developed in vitro co-culture set up can serve as a platform to study the signaling network between the endothelial and pancreatic β-cells as well as provides a mechanistic insight for the validation of novel ER stress modulators.

Glutathione homeostasis is significantly altered by quercetin via the Keap1/Nrf2 and MAPK signaling pathways in rats

Previously, we showed that 0.5% quercetin simultaneously decreased serum homocysteine and glutathione (GSH) levels in rats. The aim of the present study was to investigate the effects of 0.5% quercetin on GSH metabolism, related enzymes and signal pathways in rats. Rats were fed the control diet and 0.5% quercetin-supplemented diet for 6 weeks. The results showed that quercetin reduced serum and hepatic content of GSH and the ratio of GSH and oxidized glutathione (GSSG), enhanced hepatic activity and mRNA expression of glutathione S-transferase (GST), inhibited hepatic activity and mRNA expression of glutamate cysteine ligase (GCL), and decreased hepatic glutathione reductase (GR) mRNA expression. Levels of phosphorylated p38 and extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinases (MAPKs) increased, while that of nuclear factor E2-like 2 (Nrf2) protein decreased after quercetin treatment. However, no significant hepatotoxicity was noted. We concluded that quercetin treatment altered hepatic GSH metabolism by modulating GSH metabolic enzyme activities and mRNA expression in rats, and p38, ERK1/2 MAPKs, and Nrf2 were involved in modulating GSH metabolism-related enzymes.

Plicosepalin A, a new antioxidant catechin-gallic acid derivative of inositol from the mistletoe Plicosepalus curviflorus

Phytochemical investigation of the semi-parasitic plant, Plicosepalus curviflorus (Loranthaceae) growing in Saudi Arabia resulted in the isolation of a new catechin-gallic acid derivative of inositol, plicosepalin A (1) [(+) catechin-4'-O-(1″-O-galloyl-5″-O-methyl)-myo-inositol], along with seven known compounds: methyl gallate (2), catechin (3), quercetin (4), gallic acid (5), lupeol (6), β-sitosterol (7), and ursolic acid (8). Their structures were elucidated on the basis of spectroscopic analyses, including HRESIMS, ESIMS, 1H and 13C NMR, HSQC, and HMBC, as well as comparison with reported data. The antioxidant and antimicrobial activities of 1 were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the disc diffusion assay, respectively. Compound 1 exhibited potent free radical scavenging activity with an IC50 value of 9.0 ± 0.27 μM. Moreover, significant activities against Staphylococcus aureus and Bacillus subtilis were recorded.

The Protective Effect of Hydroalcoholic Extract of Rosa canina (Dog Rose) Fruit on Liver Function and Structure in Streptozotocin-Induced Diabetes in Rats

This study was conducted to evaluate the hepatoprotective effects of Rosa canina (R. canina) extract on streptozotocin- (STZ-) induced diabetes in rats by measuring the fasting blood glucose (FBG), total antioxidant capacity (TAC), and liver enzyme activity, including serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Forty adult male Wistar rats were randomly divided into four groups and treated daily for 42 days as follows: group I (control) received saline as a vehicle; group II (diabetic) received saline; groups III and IV (diabetic) treated with 250 and 500 mg/kg body weight (BW) per day R. canina extract, respectively. Diabetes was induced by a single intraperitoneal (IP) injection of streptozotocin (50 mg/kg BW). At the end of the study, blood samples were collected via heart puncture and sera were used for estimation of the mentioned parameters. Then all the rats were sacrificed and their livers used for histopathological evaluations. In the untreated diabetic group, the results showed a significant increase in FBG, ALT, and AST levels compared to the other groups (p < .05). The level of TAC decreased in this group, but not significantly compared to the other groups (p > .05). In the treated groups, administration of R. canina extract significantly improved the mentioned parameters in a dose-dependent manner (p < .05). Histological evaluations indicated that R. canina extract ameliorated defective liver caused by STZ. It can be concluded that R. canina extract has a hepatoprotective effect in STZ-induced diabetes in rats.

New insights for the use of quercetin analogs in cancer treatment

AIM

Quercetin (Q1) is a flavonoid widely present in plants and endowed with several pharmacological properties mostly due to its antioxidant potential. Q1 shows anticancer activity and could be useful in cancer prevention. On the other hand, Q1 is poorly soluble in water and unstable in physiological systems, and its bioavailability is very low.

METHODS

A small set of Q1 derivatives (Q2-Q9) has been synthesized following opportunely modified chemical procedures previously reported. Anticancer activity has been evaluated by MTT assay. Human Topoisomerases inhibition has been performed by direct enzymatic assays. Apoptosis has been evaluated by TUNEL assay. ROS production and scavenging activity have been determined by immunofluorescence.

RESULTS

The anticancer profile of a small library of Q1 analogues, in which the OH groups were all or partially replaced with hydrophobic functional groups, has been evaluated. Two of the studied compounds demonstrated an interesting cytotoxic profile in two breast cancer models showing the capability to inhibit human Topoisomerases.

CONCLUSION

The studied compounds represent suitable leads for the development of innovative anticancer drugs. [Formula: see text].

Galangin, a natural flavonoid reduces mitochondrial oxidative damage in streptozotocin-induced diabetic rats

Objective: We designed this study to observe the effect of galangin on damaged mitochondria in the liver of diabetic rats.

Methods: Male albino Wistar rats were made diabetic by injecting streptozotocin (STZ) intraperitoneally (40 mg kg⁻¹ body weight (BW)). Galangin (8 mg kg⁻¹ BW) or glibenclamide (600 µg kg⁻¹ BW) was given orally daily once for 45 days to both healthy and diabetic rats.

Results: Diabetic rats showed significant (P < 0.05) increase in liver mitochondrial oxidant [Thiobarbituric acid reactive substance (TBARS)] level and a significant decrease in enzymatic [superoxide dismutase (SOD), glutathione peroxidase (GPx)] and non-enzymatic (reduced glutathione (GSH)) antioxidant levels when compared with healthy rats. The mitochondrial enzymes isocitrate dehydrogenase (ICDH), alpha-ketoglutarate dehydrogenase (α-KGDH), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) and mitochondrial respiratory chain enzymes NADH-dehydrogenase and Cytochrome c-oxidase were decreased significantly (P < 0.05) in diabetic rats when compared with healthy rats. A natural flavonoid galangin administered to hyperglycemia-induced rats resulted in the following findings as compared to hyperglycemia-induced control rats: the oxidant levels decreased significantly (P < 0.05); the enzymatic and non-enzymatic antioxidant levels increased significantly (P < 0.05) and the function of mitochondrial enzymes and the mitochondrial respiratory chain enzymes increased significantly (P < 0.05).

Conclusion: From the results, we conclude that galangin could maintain liver mitochondrial function in diabetic rats.