Apigenin and naringenin regulate glucose and lipid metabolism, and ameliorate vascular dysfunction in type 2 diabetic rats

Apigenin Improves Hypertension and Cardiac Hypertrophy Through Modulating NADPH Oxidase-Dependent ROS Generation and Cytokines in Hypothalamic Paraventricular Nucleus

Apigenin, identified as 4', 5, 7-trihydroxyflavone, is a natural flavonoid compound that has many interesting pharmacological activities and nutraceutical potential including anti-inflammatory and antioxidant functions. Chronic, low-grade inflammation and oxidative stress are involved in both the initiation and progression of hypertension and hypertension-induced cardiac hypertrophy. However, whether or not apigenin improves hypertension and cardiac hypertrophy through modulating NADPH oxidase-dependent reactive oxygen species (ROS) generation and inflammation in hypothalamic paraventricular nucleus (PVN) has not been reported. This study aimed to investigate the effects of apigenin on hypertension in spontaneously hypertensive rats (SHRs) and its possible central mechanism of action. SHRs and Wistar-Kyoto (WKY) rats were randomly assigned and treated with bilateral PVN infusion of apigenin or vehicle (artificial cerebrospinal fluid) via osmotic minipumps (20 μg/h) for 4 weeks. The results showed that after PVN infusion of apigenin, the mean arterial pressure (MAP), heart rate, plasma norepinephrine (NE), Beta 1 receptor in kidneys, level of phosphorylation of PKA in the ventricular tissue and cardiac hypertrophy, perivascular fibrosis, heart level of oxidative stress, PVN levels of oxidative stress, interleukin 1β (IL-1β), interleukin 6 (IL-6), iNOS, monocyte chemotactic protein 1 (MCP-1), tyrosine hydroxylase (TH), NOX2 and NOX4 were attenuated and PVN levels of interleukin 10 (IL-10), superoxide dismutase 1 (Cu/Zn-SOD) and the 67-kDa isoform of glutamate decarboxylase (GAD67) were increased. These results revealed that apigenin improves hypertension and cardiac hypertrophy in SHRs which are associated with the down-regulation of NADPH oxidase-dependent ROS generation and inflammation in the PVN.

Therapeutic Potential of Luteolin on Impaired Wound Healing in Streptozotocin-Induced Rats

Long-term hyperglycemia may lead to diabetic microvascular and macrovascular complications that can affect the peripheral vascular system, particularly in wound healing capacity. Impaired angiogenesis and delayed wound healing are significant clinically. Luteolin (3', 4', 5, 7-tetrahydroxyflavone) is a naturally occurring flavonoid that is ubiquitously found in plants. Recent evidence has shown that luteolin is an anti-inflammatory and anti-oxidative agent. However, the effect of systemic luteolin administration on diabetic wound restoration remains unclear. Herein, we explored the effectiveness of luteolin for improving delayed and impaired healing of skin wound and further clarified the underlying mechanisms. The results indicated that luteolin significantly attenuates blood glucose concentration, improves impaired healing and accelerates re-epithelization of skin wound in streptozotocin (STZ)-induced diabetic rats. Histopathological staining and immunoblotting revealed an inhibitory effect of luteolin on inflammatory cell and cytokine production. We also observed remarkable decreases in protein expressions of inflammatory factors including matrix metalloproteinase (MMP)-9, tumor necrosis factor (TNF)-α, interleukin (IL-6), and IL1-β and downregulation of nuclear factor (NF)-κB, as well as increases in anti-oxidative enzymes such as superoxide dismutase 1 (SOD1) and glutathione peroxidase (GSH-Px) induced by nuclear factor erythroid 2-related factor (Nrf)-2 following luteolin supplementation. Furthermore, luteolin decreased the expression of vascular endothelial growth factor (VEGF) and increased the expression of ubiquitin carboxy-terminal hydrolase (UCH)-L1, as evidenced by angiogenesis and neuronal regeneration in completely healed wound. In conclusion, systemic administration of luteolin promotes wound restoration by ameliorating inflammation and oxidative stress through the inactivation of NF-κB and upregulation of Nrf2 in STZ-induced diabetic rats.

Evidence for 5-HT1A receptor-mediated antiallodynic and antihyperalgesic effects of apigenin in mice suffering from mononeuropathy

BACKGROUND AND PURPOSE

Neuropathic pain places a devastating health burden, with very few effective therapies. We investigated the potential antiallodynic and antihyperalgesic effects of apigenin, a natural flavonoid with momoamine oxidase (MAO) inhibitory activity, against neuropathic pain and investigated the mechanism(s).

EXPERIMENTAL APPROACH

The neuropathic pain model was produced by chronic constriction injury of sciatic nerves in male C57BL/6J mice, with pain-related behaviours being assayed by von Frey test and Hargreaves test. In this model the role of 5-HT and 5-HT_1A receptor-related mechanisms were investigated in vivo/in vitro.

KEY RESULTS

Apigenin repeated treatment (p.o., once per day for 2 weeks), in a dose-related manner (3, 10 and 30 mg·kg^-1 ), ameliorated the allodynia and hyperalgesia in chronic nerve constriction injury in mice. These effects seem dependent on neuronal 5-hydroxytryptamine, because (i) the antihyperalgesia and antiallodynia were attenuated by depletion of 5-HT with p-chlorophenylalanine and potentiated by 5-hydroxytryptophan and (ii), apigenin-treated chronic constriction injury mice caused an increased level of spinal 5-HT, associated with diminished MAO activity. In vivo administration, spinally or systematically, of the 5-HT_1A antagonist WAY-100635 inhibited the apigenin-induced antiallodynia and antihyperalgesia. In vitro, apigenin acted as a positive allosteric modulator to increase the efficacy (stimulation of [³⁵ S]GTPγS binding) of the 5-HT_1A agonist 8-OH-DPAT. Apigenin attenuated neuronal changes caused by chronic constriction of the sciatic nerve in mice, without causing a hypertensive crisis.

CONCLUSION AND IMPLICATIONS

Apigenin antiallodynic and antihyperalgesic actions against neuropathic pain crucially involve spinal 5-HT_1A receptors and indicate it could be used to treat neuropathic pain.

Piper sarmentosum Roxb. Attenuates Vascular Endothelial Dysfunction in Nicotine-Induced Rats

Exposure to cigarette smoke is an important risk factor for cardiovascular diseases. Nicotine is an addictive compound in cigarette smoke that triggers oxidative stress, which leads to vascular dysfunction. Piper sarmentosum Roxb. is a herb with antioxidant and vascular protective effects. This study evaluated the potential protective effect of the aqueous extract of P. sarmentosum leaf (AEPS) on vascular dysfunction in rats induced with prolonged nicotine administration. A total of 22 male Sprague-Dawley rats were divided into control (normal saline, oral gavage [p.o.]), nicotine (0.8 mg/kg/day nicotine, intraperitoneally [i.p.]), and nicotine + AEPS groups (250 mg/kg/day AEPS, p.o. + 0.8 mg/kg/day nicotine, i.p.). Treatment was given for 21 days. Thoracic aortae were harvested from the rats for the measurement of vasorelaxation, vascular nitric oxide (NO) level, and antioxidant level and the assessment of vascular remodeling. Rats treated with AEPS had improved vasorelaxation to endothelium-dependent vasodilator, acetylcholine (ACh), compared with the nicotine-induced rats (p < 0.05). The presence of endothelium increased the maximum relaxation of aortic rings in response to ACh. Compared with the nicotine group, AEPS enhanced vascular NO level (p < 0.001) and increased antioxidant levels as measured by superoxide dismutase activity (p < 0.05), catalase activity (p < 0.01), and reduced glutathione level (p < 0.05). No remarkable changes in aortic histomorphometry were detected. In conclusion, P. sarmentosum attenuates vascular endothelial dysfunction in nicotine-induced rats by improving vasorelaxation and enhancing vascular NO and antioxidant levels.

Apigenin restores endothelial function by ameliorating oxidative stress, reverses aortic stiffening, and mitigates vascular inflammation with aging

We assessed the efficacy of oral supplementation with the flavanoid apigenin on arterial function during aging and identified critical mechanisms of action. Young (6 mo) and old (27 mo) C57BL/6N mice (model of arterial aging) consumed drinking water containing vehicle (0.2% carboxymethylcellulose; 10 young and 7 old) or apigenin (0.5 mg/mL in vehicle; 10 young and 9 old) for 6 wk. In vehicle-treated animals, isolated carotid artery endothelium-dependent dilation (EDD), bioassay of endothelial function, was impaired in old versus young (70% ± 9% vs. 92% ± 1%, P < 0.0001) due to reduced nitric oxide (NO) bioavailability. Old mice had greater arterial reactive oxygen species (ROS) production and oxidative stress (higher nitrotyrosine) associated with greater nicotinamide adenine dinucleotide phosphate oxidase (oxidant enzyme) and lower superoxide dismutase 1 and 2 (antioxidant enzymes); ex vivo administration of Tempol (antioxidant) restored EDD to young levels, indicating ROS-mediated suppression of EDD. Old animals also had greater aortic stiffness as indicated by higher aortic pulse wave velocity (PWV, 434 ± 9 vs. 346 ± 5 cm/s, P < 0.0001) due to greater intrinsic aortic wall stiffness associated with lower elastin levels and higher collagen, advanced glycation end products (AGEs), and proinflammatory cytokine abundance. In old mice, apigenin restored EDD (96% ± 2%) by increasing NO bioavailability, normalized arterial ROS, oxidative stress, and antioxidant expression, and abolished ROS inhibition of EDD. Moreover, apigenin prevented foam cell formation in vitro (initiating step in atherosclerosis) and mitigated age-associated aortic stiffening (PWV 373 ± 5 cm/s) by normalizing aortic intrinsic wall stiffness, collagen, elastin, AGEs, and inflammation. Thus, apigenin is a promising therapeutic for arterial aging.NEW & NOTEWORTHY Our study provides novel evidence that oral apigenin supplementation can reverse two clinically important indicators of arterial dysfunction with age, namely, vascular endothelial dysfunction and large elastic artery stiffening, and prevents foam cell formation in an established cell culture model of early atherosclerosis. Importantly, our results provide extensive insight into the biological mechanisms of apigenin action, including increased nitric oxide bioavailability, normalization of age-related increases in arterial ROS production and oxidative stress, reversal of age-associated aortic intrinsic mechanical wall stiffening and adverse remodeling of the extracellular matrix, and suppression of vascular inflammation. Given that apigenin is commercially available as a dietary supplement in humans, these preclinical findings provide the experimental basis for future translational studies assessing the potential of apigenin to treat arterial dysfunction and reduce cardiovascular disease risk with aging.

The protective effects of dietary intake of flavonoids and its subclasses on metabolic syndrome incidence

This study aimed to evaluate the association between the intake of total flavonoids and flavonoid subclasses and metabolic syndrome (MetS) risk and to assess the modulating effects of lifestyle factors on these associations. A total of 1915 participants from the Tehran Lipid and Glucose Study were followed-up during 2006-2008 and 2016-2018. Their dietary intake was assessed by a food frequency questionnaire at baseline and within three-year intervals afterward. Moreover, the modifying effect of weight gain on the association between total flavonoids and MetS was assessed by Cox regression analysis. Participants in the highest tertile of flavonoid, flavonol, and flavone had a significantly lower MetS risk as compared to those in the lowest tertile. Also, in participants with weight gain <7%, all flavonoid subclasses had a more pronounced risk-reducing effect. Overall, the total flavonoid, flavonol, and flavone reduced the risk of MetS; this association could be modified by weight gain.

Naringenin Nano-Delivery Systems and Their Therapeutic Applications

Naringenin (NRG) is a polyphenolic phytochemical belonging to the class of flavanones and is widely distributed in citrus fruits and some other fruits such as bergamot, tomatoes, cocoa, and cherries. NRG presents several interesting pharmacological properties, such as anti-cancer, anti-oxidant, and anti-inflammatory activities. However, the therapeutic potential of NRG is hampered due to its hydrophobic nature, which leads to poor bioavailability. Here, we review a wide range of nanocarriers that have been used as delivery systems for NRG, including polymeric nanoparticles, micelles, liposomes, solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), nanosuspensions, and nanoemulsions. These nanomedicine formulations of NRG have been applied as a potential treatment for several diseases, using a wide range of in vitro, ex vivo, and in vivo models and different routes of administration. From this review, it can be concluded that NRG is a potential therapeutic option for the treatment of various diseases such as cancer, neurological disorders, liver diseases, ocular disorders, inflammatory diseases, skin diseases, and diabetes when formulated in the appropriate nanocarriers.

Formulation and intestinal absorption of naringenin loaded nanostructured lipid carrier and its inhibitory effects on nonalcoholic fatty liver disease

In this study, we prepared naringenin (NGN) loaded nanostructured lipid carrier (NGN-NLC) and investigated its characterizations, transepithelial transport, intestinal absorption and inhibitory effects on nonalcoholic fatty liver disease (NAFLD) induced by a methionine choline deficient (MCD) diet in mice. The NGN-NLC, prepared by a method of emulsion-evaporation plus low temperature-solidification, displayed high drug loading capacity of 22.5 ± 1.7%. Compared to the NGN crude drug, the NGN-NLC, at an equal NGN dose, improved NGN release rate by 3.5-fold and elevated NGN transepithelial transport and intestinal absorption through enhancing intracellular transport of clathrin pathway and escaping p-gp efflux; at an 8-fold lower NGN dose, showed comparable pharmacokinetic parameters, but elevated liver NGN distribution by 1.5-fold, reduced MCD diet-induced hepatic lipid deposition by 3-fold. These results suggest that the NLC formulation significantly increased the inhibitory effects of NGN on NAFLD because of the improved drug release rate, transepithelial transport and intestinal absorption, and the elevated oral bioavailability and liver NGN distribution.

Apigenin Ameliorates Insulin Resistance and Lipid Accumulation by Endoplasmic Reticulum Stress and SREBP-1c/SREBP-2 Pathway in Palmitate-Induced HepG2 Cells and High-Fat Diet-Fed Mice

Insulin resistance (IR) is the common basis of diabetes and cardiovascular diseases, and its development is closely associated with lipid metabolism disorder. Flavonoids have definite chemical defense effects, including anti-inflammatory effects, anticancer effects, and antimutation effects. However, the function and mechanism of apigenin (AP, a kind of flavonoid) in IR are still unclear. In our study, intracellular fat accumulation model cells and high-fat diet (HFD)-fed model mice were established using palmitate (PA) and HFD. Mechanistically, we first demonstrated that AP could notably downregulate sterol regulatory element-binding protein 1c (SREBP-1c), sterol regulatory element-binding protein 2 (SREBP-2), fatty acid synthase, stearyl-CoA desaturase 1, and 3-hydroxy-3-methyl-glutaryl-CoA reductase in PA-induced hyperlipidemic cells and mice. Functionally, we verified that AP could markedly reduce lipid accumulation in PA-induced hyperlipidemic cells and decrease the body weight, visceral fat weight, IR, and lipid accumulation in HFD-induced hyperlipidemic mice. Besides, we showed that PA could significantly downregulate endoplasmic reticulum stress (ERS)-related proteins and inhibit ERS. Furthermore, we proved that AP could reduce blood lipids by inhibiting ERS in PA-induced hyperlipidemic cells. Meanwhile, 4-phenyl butyric acid (also called ERS alleviator), like AP, could significantly reduce blood lipids and alleviate IR in HFD-fed model mice. Therefore, we concluded that AP could substantially improve the disorder of lipid metabolism, and its mechanism might be related to the decrease of SREBP-1c, SREBP-2, and downstream genes, the inhibition of ERS, and the reduction of blood lipids and IR. SIGNIFICANCE STATEMENT: Apigenin, a nontoxic and naturally sourced flavonoid, has antihyperlipidemic properties in mice and hepatocyte. This study highlights a new mechanism of apigenin and proposes that these hypolipidemic effects are associated with the mitigation of endoplasmic reticulum stress and insulin resistance in diet-induced obesity. This study might provide translational insight into the prevention and treatment of apigenin in hyperlipidemia-related diseases.

Traditional use, phytochemistry, toxicology, and pharmacology of Origanum majorana L

ETHNOPHARMACOLOGICAL RELEVANCE

Origanum majorana L., is an aromatic and medicinal plant distributed in different parts of Mediterranean countries. This species is widely used in traditional medicine for the treatment of many diseases such as allergies, hypertension, respiratory infections, diabetes, stomach pain, and intestinal antispasmodic.

AIM OF THE REVIEW

This work reports previous studies on O. majorana concerning its taxonomy, botanical description, geographical distribution, traditional use, bioactive compounds, toxicology, and biological effects.

MATERIALS AND METHODS

Different scientific data bases such as Web of Science, Scopus, Wiley Online, SciFinder, Google Scholar, PubMed, ScienceDirect, and SpringerLink were consulted to collect data about O. majorana. The presented data emphasis bioactive compounds, traditional uses, toxicological investigations, and biological activities of O. majorana.

RESULTS

The findings of this work marked an important correlation between the traditional use of O. majorana as an anti-allergic, antihypertensive, anti-diabetic agent, and its biological effects. Indeed, pharmacological investigations showed that essential oils and extracts from O. majorana exhibit different biological properties, particularly; antibacterial, antifungal, antioxidant, antiparasitic, antidiabetic, anticancer, nephrotoxicity protective, anti-inflammatory, analgesic and anti-pyretic, hepatoprotective, and antimutagenic effects. Toxicological evaluation confirmed the safety and innocuity of this species and supported its medicinal uses. Several bioactive compounds belonging to different chemical family such as terpenoids, flavonoids, and phenolic acids were also identified in O. majorana.

CONCLUSIONS

The results suggest that the pharmacological properties of O. majorana confirm its traditional uses. Indeed, O. majorana essential oils showed remarkable antimicrobial, antioxidant, anticancer, anti-inflammatory, antimutagenic, nephroprotective, and hepatoprotective activities. However, further investigations regarding the evaluation of molecular mechanisms of identified compounds against human cancer cell lines, inflammatory process, and microbial infections are needed to validate pharmacodynamic targets. The toxicological investigation of O. Majorana confirmed its safety and therefore encouraged pharmacokinetic evaluation tests to validate its bioavailability.

The Emerging Role of Polyphenols in the Management of Type 2 Diabetes

Type 2 diabetes (T2D) is a fast-increasing health problem globally, and it results from insulin resistance and pancreatic β-cell dysfunction. The gastrointestinal (GI) tract is recognized as one of the major regulatory organs of glucose homeostasis that involves multiple gut hormones and microbiota. Notably, the incretin hormone glucagon-like peptide-1 (GLP-1) secreted from enteroendocrine L-cells plays a pivotal role in maintaining glucose homeostasis via eliciting pleiotropic effects, which are largely mediated via its receptor. Thus, targeting the GLP-1 signaling system is a highly attractive therapeutic strategy to treatment T2D. Polyphenols, the secondary metabolites from plants, have drawn considerable attention because of their numerous health benefits, including potential anti-diabetic effects. Although the major targets and locations for the polyphenolic compounds to exert the anti-diabetic action are still unclear, the first organ that is exposed to these compounds is the GI tract in which polyphenols could modulate enzymes and hormones. Indeed, emerging evidence has shown that polyphenols can stimulate GLP-1 secretion, indicating that these natural compounds might exert metabolic action at least partially mediated by GLP-1. This review provides an overview of nutritional regulation of GLP-1 secretion and summarizes recent studies on the roles of polyphenols in GLP-1 secretion and degradation as it relates to metabolic homeostasis. In addition, the effects of polyphenols on microbiota and microbial metabolites that could indirectly modulate GLP-1 secretion are also discussed.

Anti-inflammatory phytochemicals for the treatment of diabetes and its complications: Lessons learned and future promise

Diabetes mellitus (type 1 and type 2) and its various complications continue to place a huge burden on global medical resources, despite the availability of numerous drugs that successfully lower blood glucose levels. The major challenging issue in diabetes management is the prevention of various complications that remain the leading cause of diabetes-related mortality. Moreover, the limited long-term durability of monotherapy and undesirable side effects of currently used anti-diabetic drugs underlie the urgent need for novel therapeutic approaches. Phytochemicals represent a rich source of plant-derived molecules that are of pivotal importance to the identification of compounds with therapeutic potential. In this review, we aim to discuss recent advances in the identification of a large array of phytochemicals with immense potential in the management of diabetes and its complications. Given that metabolic inflammation has been established as a key pathophysiological event that drives the progression of diabetes, we focus on the protective effects of representative phytochemicals in metabolic inflammation. This paper also discusses the potential of phytochemicals in the development of new drugs that target the inflammation in the management of diabetes and its complications.

Antioxidant and Anti-inflammatory Properties of Yttrium Oxide Nanoparticles: New Insights into Alleviating Diabetes

BACKGROUND

Diabetes mellitus is a metabolic disease that requires immediate attention. Oxidative stress that leads to the generation of reactive oxygen species is a contributing factor to the disease progression. Yttrium oxide nanoparticles (Y₂O₃ NPs) have a profound effect on alleviating oxidative damage.

METHODS

The literature related to Y₂O₃ NPs and oxidative stress has been thoroughly searched using PubMed and Scopus databases and relevant studies from inception until August 2020 were included in this scoping review.

RESULTS

Y₂O₃ NPs altered oxidative stress-related biochemical parameters in different disease models including diabetes.

CONCLUSION

Although Y₂O₃ NPs are a promising antidiabetic agent due to their antioxidant and anti- inflammatory properties, more studies are required to further elucidate the pharmacological and toxicological properties of these nanoparticles.

Nutritional Composition and Bioactive Compounds in Tomatoes and Their Impact on Human Health and Disease: A Review

Tomatoes are consumed worldwide as fresh vegetables because of their high contents of essential nutrients and antioxidant-rich phytochemicals. Tomatoes contain minerals, vitamins, proteins, essential amino acids (leucine, threonine, valine, histidine, lysine, arginine), monounsaturated fatty acids (linoleic and linolenic acids), carotenoids (lycopene and β-carotenoids) and phytosterols (β-sitosterol, campesterol and stigmasterol). Lycopene is the main dietary carotenoid in tomato and tomato-based food products and lycopene consumption by humans has been reported to protect against cancer, cardiovascular diseases, cognitive function and osteoporosis. Among the phenolic compounds present in tomato, quercetin, kaempferol, naringenin, caffeic acid and lutein are the most common. Many of these compounds have antioxidant activities and are effective in protecting the human body against various oxidative stress-related diseases. Dietary tomatoes increase the body's level of antioxidants, trapping reactive oxygen species and reducing oxidative damage to important biomolecules such as membrane lipids, enzymatic proteins and DNA, thereby ameliorating oxidative stress. We reviewed the nutritional and phytochemical compositions of tomatoes. In addition, the impacts of the constituents on human health, particularly in ameliorating some degenerative diseases, are also discussed.

Phytochemicals as Anti-Inflammatory Agents in Animal Models of Prevalent Inflammatory Diseases

Phytochemicals are known to have anti-inflammatory effects in vitro and in vivo, such as in inflammatory disease model systems. Inflammation is an essential immune response to exogenous stimuli such as infection and injury. Although inflammation is a necessary host-defense mechanism, chronic inflammation is associated with the continuous local or systemic release of inflammatory mediators, non-cytokine mediators, such as ROS and NO, and inflammatory cytokines are strongly implicated in the pathogenesis of various inflammatory disorders. Phytochemicals that exhibit anti-inflammatory mechanisms that reduce sustained inflammation could be therapeutic candidates for various inflammatory diseases. These phytochemicals act by modulating several main inflammatory signaling pathways, including NF-κB, MAPKs, STAT, and Nrf-2 signaling. Here, we discuss the characteristics of phytochemicals that possess anti-inflammatory activities in various chronic inflammatory diseases and review the molecular signaling pathways altered by these anti-inflammatory phytochemicals, with a focus on transcription factor pathways. Furthermore, to evaluate the phytochemicals as drug candidates, we translate the effective doses of phytochemicals in mice or rat disease models into the human-relevant equivalent and compare the human-relevant equivalent doses of several phytochemicals with current anti-inflammatory drugs doses used in different types of chronic inflammatory diseases.

Re-appraising the potential of naringin for natural, novel orthopedic biotherapies

Naringin is a naturally occurring flavonoid found in plants of the Citrus genus that has historically been used in traditional Chinese medical regimens for the treatment of osteoporosis. Naringin modulates signaling through numerous molecular pathways critical to musculoskeletal development, cellular differentiation, and inflammation. Administration of naringin increases in vitro expression of bone morphogenetic proteins (BMPs) and activation of the Wnt/β-catenin and extracellular signal-related kinase (Erk) pathways, thereby promoting osteoblastic proliferation and differentiation from stem cell precursors for bone formation. Naringin also inhibits osteoclastogenesis by both modifying RANK/RANKL interactions and inducing apoptosis in osteoclasts in vitro. In addition, naringin acts on the estrogen receptor in bone to mimic the native bone-preserving effects of estrogen, with few systemic side effects on other estrogen-sensitive tissues. The efficacy of naringin therapy in reducing the osteolysis characteristic of common musculoskeletal pathologies such as osteoporosis, degenerative joint disease, and osteomyelitis, as well as inflammatory conditions affecting bone such as diabetes mellitus, has been extensively demonstrated in vitro and in animal models. Naringin thus represents a naturally abundant, cost-efficient agent whose potential for use in novel musculoskeletal biotherapies warrants re-visiting and further exploration through human studies. Here, we review the cellular mechanisms of action that have been elucidated regarding the action of naringin on bone resident cells and the bone microenvironment, in vivo evidence of naringin’s osteostimulative and chondroprotective properties in the setting of osteolytic bone disease, and current limitations in the development of naringin-containing translational therapies for common musculoskeletal conditions.

Bioactive Agent Discovery from the Natural Compounds for the Treatment of Type 2 Diabetes Rat Model

Diabetes mellitus is a well-known chronic metabolic disease that poses a long-term threat to human health and is characterized by a relative or absolute lack of insulin, resulting in hyperglycemia. Type 2 diabetes mellitus (T2DM) typically affects many metabolic pathways, resulting in β-cell dysfunction, insulin resistance, abnormal blood glucose levels, inflammatory processes, excessive oxidative reactions, and impaired lipid metabolism. It also leads to diabetes-related complications in many organ systems. Antidiabetic drugs have been approved for the treatment of hyperglycemia in T2DM; these are beneficial for glucose metabolism and promote weight loss, but have the risk of side effects, such as nausea or an upset stomach. A wide range of active components, derived from medicinal plants, such as alkaloids, flavonoids, polyphenol, quinones, and terpenoids may act as alternative sources of antidiabetic agents. They are usually attributed to improvements in pancreatic function by increasing insulin secretions or by reducing the intestinal absorption of glucose. Ease of availability, low cost, least undesirable side effects, and powerful pharmacological actions make plant-based preparations the key player of all available treatments. Based on the study of therapeutic reagents in the pathogenesis of humans, we use the appropriate animal models of T2DM to evaluate medicinal plant treatments. Many of the rat models have characteristics similar to those in humans and have the advantages of ease of genetic manipulation, a short breeding span, and access to physiological and invasive testing. In this review, we summarize the pathophysiological status of T2DM rat models and focus on several bioactive compounds from herbal medicine with different functional groups that exhibit therapeutic potential in the T2DM rat models, in turn, may guide future approach in treating diabetes with natural drugs.

Protective role of biosynthesised zinc oxide nanoparticles on pancreatic beta cells: an in vitro and in vivo approach

Sulphonylureas are extensively used in the treatment of type II diabetes; however, these drugs have complications of hypoglycaemia and weight gain. The current study aims at developing a potent antidiabetic drug that has lesser side effects and better management of its associated conditions. Zinc oxide nanoparticles (ZnO NPs) were synthesised using Syzygium cumini seed extract with an average size of 18.92 nm. In vitro studies on rat insulinoma (RIN-5F) cells revealed that cells treated with synthesised ZnO NPs showed a dose-dependent increase in insulin secretion. Streptozotocin-fructose-induced type II diabetic rats treated with ZnO NPS exhibited a significant reduction (p < 0.01) in the blood glucose levels, total cholesterol, triglycerides, and low-density lipoprotein levels and increase (p < 0.01) in serum insulin and liver antioxidant enzyme levels proclaiming its role as a hypoglycaemic and hypolipidaemic drug. Treatment of ZnO NPs in diabetic rats exhibited an increased number of beta cells which was responsible for its increased insulin levels and reduced glucose levels. From the overall observations, biosynthesised ZnO NPs exhibited an efficacious hypoglycaemic effect in diabetic rats, so it can be suggested as a potent antidiabetic drug.

Mechanisms of Antidiabetic Activity of Methanolic Extract of Punica granatum Leaves in Nicotinamide/Streptozotocin-Induced Type 2 Diabetes in Rats

The current study aimed to establish the mechanisms of antidiabetic activity of methanolic extract of Punica granatum leaves (MEPGL) in nicotinamide/streptozotocin-induced type 2 diabetes in rats. Phytochemical screening, HPLC analysis, and acute toxicity study of MEPGL were carried out. Various concentrations of MEPGL (100, 200, 400, and 600 mg/kg) were administered orally to diabetic rats for 45 days on a daily basis. The antidiabetic effect of MEPGL was examined by measuring blood glucose, plasma insulin, and glycated hemoglobin (HbA1c) levels, as well as with an oral glucose tolerance test. The antioxidant effect of MEPGL was determined by analyzing hepatic and renal antioxidant markers, namely superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), and lipid peroxidation. The other biochemical markers alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), urea, and creatinine, as well as total cholesterol, triglycerides, and high-density lipoprotein (HDL) were also studied. Type 2 diabetes significantly altered these parameters, while oral administration of the MEPGL significantly ameliorated them. Moreover, the pancreatic histopathological changes were attenuated with MEPGL treatment. In a nutshell, oral MEPGL administration in diabetic rats showed antidiabetic activity due to its antioxidant activity, most probably due to the gallic acid, ellagic acid, and apigenin found in MEPGL.

Alterations of Lipid Metabolism in Cancer: Implications in Prognosis and Treatment

Cancer remains the second leading cause of mortality worldwide. In the course of this multistage and multifactorial disease, a set of alterations takes place, with genetic and environmental factors modulating tumorigenesis and disease progression. Metabolic alterations of tumors are well-recognized and are considered as one of the hallmarks of cancer. Cancer cells adapt their metabolic competences in order to efficiently supply their novel demands of energy to sustain cell proliferation and metastasis. At present, there is a growing interest in understanding the metabolic switch that occurs during tumorigenesis. Together with the Warburg effect and the increased glutaminolysis, lipid metabolism has emerged as essential for tumor development and progression. Indeed, several investigations have demonstrated the consequences of lipid metabolism alterations in cell migration, invasion, and angiogenesis, three basic steps occurring during metastasis. In addition, obesity and associated metabolic alterations have been shown to augment the risk of cancer and to worsen its prognosis. Consequently, an extensive collection of tumorigenic steps has been shown to be modulated by lipid metabolism, not only affecting the growth of primary tumors, but also mediating progression and metastasis. Besides, key enzymes involved in lipid-metabolic pathways have been associated with cancer survival and have been proposed as prognosis biomarkers of cancer. In this review, we will analyze the impact of obesity and related tumor microenviroment alterations as modifiable risk factors in cancer, focusing on the lipid alterations co-occurring during tumorigenesis. The value of precision technologies and its application to target lipid metabolism in cancer will also be discussed. The degree to which lipid alterations, together with current therapies and intake of specific dietary components, affect risk of cancer is now under investigation, and innovative therapeutic or preventive applications must be explored.

Effect of antioxidant-rich propolis and bee pollen extracts against D-glucose induced type 2 diabetes in rats

The present study was designed to investigate the preventive effect of propolis, bee pollen and their combination on Type 2 diabetes induced by D-glucose in rats. The study was carried out by feeding daily two concentrations (100 and 200 mg/Kg BW) of propolis or bee pollen (or their combination to normal (non-diabetic) and diabetic rats for a period of 16 weeks. In vivo biochemical changes associated to diabetes are induced by drinking a solution containing 10% of D-glucose (diabetic rats). The in vitro antioxidant activity was also evaluated and the chemical composition of propolis and bee pollen extracts was determined by UHPLC-DAD. Phytochemical composition of propolis and bee pollen revealed the presence of several natural antioxidants, such as hydroxycinnamic acids, hydroxybenzoic acids, flavonoids, flavan-3-ols and stilbens. The major antioxidant compound present in propolis was Naringin (290.19 ± 0.2 mg/Kg) and in bee pollen was apigenin (162.85 ± 17.7 mg/Kg). These results have been related with a high antioxidant activity, more intense in propolis extract. In rats, the administration of D-glucose had induced hyperglycemia (13.2 ± 0.82 mmol/L), increased plasmatic insulin levels (25.10 ± 2.12 U/L) and HOMA-IR index (14.72 ± 0.85) accompanied with dyslipidemia, elevation of hepatic enzyme levels, and a change in both serum renal biomarkers and plasmatic calcium. The co-administration of propolis and bee pollen extracts alone or in combination restored these biochemical parameters and attenuated the deleterious effects of D-glucose on liver and kidney functions. Furthermore, these effects were better attenuated in the combined therapy-prevented diabetic rats. Hence, it is possible to conclude that propolis and bee pollen can be used as a preventive natural product against diabetes induced dyslipidemia and hepato-renal damage.

A Comprehensive Systematic Review of the Effects of Naringenin, a Citrus-Derived Flavonoid, on Risk Factors for Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) has become the most common cause of liver dysfunction worldwide. Recently, some natural compounds have attracted growing interest in the treatment of NAFLD. In this context, most attention has been paid to natural products derived from fruits, vegetables, and medicinal herbs. Naringenin, a natural flavanone, has been revealed to have pharmacological effects in the treatment of obesity and associated metabolic disorders such as NAFLD. The aim of this study was to examine the therapeutic effects of naringenin and its possible mechanisms of action in the management of NAFLD and related risk factors. The current systematic review was performed according to the guidelines of the 2015 PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) statements. We searched PubMed/Medline, Science Direct, Scopus, ProQuest, and Google Scholar databases up until February 2020. Of 1217 full-text articles assessed, 36 studies met the inclusion criteria. The evidence reviewed in the present study indicates that naringenin modulates several biological processes related to NAFLD including energy balance, lipid and glucose metabolism, inflammation, and oxidative stress by different mechanisms. Overall, the favorable effects of naringenin along with its more potency and efficacy, compared with other antioxidants, indicate that naringenin may be a promising therapeutic approach for the management of NAFLD and associated complications. However, due to the lack of clinical trials, future robust human randomized clinical trials that address the effects of naringenin on NAFLD and other liver-related diseases are crucial. Further careful human pharmacokinetic studies are also needed to establish dosage ranges, as well as addressing preliminary safety and tolerability of naringenin, before proceeding to larger-scale endpoint trials.

Ethnomedicinal use, phytochemistry, pharmacology, and toxicology of Ajuga iva (L.,) schreb

ETHNOPHARMACOLOGICAL RELEVANCE

Ajuga iva (L.,) Schreb (A. iva). is a medicinal plant commonly used in Africa to treat several diseases such as diabetes, rheumatism, allergy, cancer, renal, metabolic disorders, cardiovascular disorders, digestive, and respiratory disorders.

AIM OF THE REVIEW

We highlighted previous reports on A. iva including its ethnopharmacological uses, the chemistry of its secondary metabolites, in vitro and in vivo pharmacological properties, and toxicological evidence.

MATERIALS AND METHODS

The data on A. iva were gathered using scientific research databases such as ScienceDirect, PubMed, SpringerLink, Web of Science, Scopus Wiley Online, and Google Scholar. In this review, studies focused on A. iva and its phytopharmacological activities were explored.

RESULTS

A. iva is used by many North African folk medicine practitioners especially against diabetes and immunological diseases. Our analysis of the previous reports confirmed the scientific evidence of A. iva ethnomedicinal uses, especially the antidiabetic and anti-hypercholesterolemia activity. However, there was no clear correlation between previous pharmacological reports on A. iva and its other ethnomedicinal uses in the treatment of rheumatism, allergy, metabolic, digestive, and respiratory disorders. The extracts and isolated compounds from A. iva exhibited numerous in vitro and in vivo pharmacological activities such as antidiabetic, antioxidant, antimicrobial, anti-hypercholesterolemia, insecticide, and litholitic effects. Chemical characterization using GC-MS, HPLC, and NMR revealed the presence of many chemical compounds such as 20-hydroxyecdysone, cyasterone, ajugasterone, apigenin dihexoside, apigenin, carvacrol, ecdysterone, palmitic acid in different parts of A. iva. These compounds belong to different classes of chemical compounds such as steroids, flavonoids, fatty acids, and terpenoids.

CONCLUSIONS

A. iva extracts especially from the leaves showed significant antidiabetic, antioxidant, anti-hypercholesterolemia, and analgesic effects. Future studies are required to validate the results of clinical trials on A. iva antidiabetic, anti-hypercholesterolemia, antioxidant/anti-inflammatory, antimicrobial, and analgesic properties. Toxicological validation and pharmacokinetics investigation are necessary to validate the efficacy and safety A. iva extracts and its secondary metabolites. An in-depth investigation is needed to reveal the biological activity of A. iva active compounds in preventing the development of cancer and neurodegenerative disorders such as Alzheimer's and Parkinson's diseases.

Dietary Apigenin Reduces Induction of LOX-1 and NLRP3 Expression, Leukocyte Adhesion, and Acetylated Low-Density Lipoprotein Uptake in Human Endothelial Cells Exposed to Trimethylamine-N-Oxide

By inducing vascular inflammation, trimethylamine-N-oxide (TMAO) is associated with endothelial dysfunction, atherosclerosis, and enhanced risk of cardiovascular diseases in humans. However, the underlying mechanisms are unknown. Expression of several genes related to arteriosclerosis, inflammasomes, and endothelial dysfunction was quantified by polymerase chain reaction after exposure to TMAO. LOX-1, ICAM-1, and NLRP3 were also quantified by Western blot, whereas leukocytic adhesion was examined using fluorescently labeled U937 cells. Scavenger receptors, adhesion molecules, and other genes associated with atherosclerosis were induced in endothelial cells exposed to TMAO. On the other hand, apigenin, a flavonoid that is abundant in parsley and celery, prevents initial arteriosclerosis events in endothelial cells. Apigenin reversed the effects of TMAO on mRNA expression of LOX-1, SREC, SR-PSOX, NLRP3, ASC, TXNIP, VCAM-1, ICAM-1, and MCP-1, as well as protein expression of LOX-1, the adhesion molecule ICAM-1, and the inflammasome protein NLRP3. Apigenin also suppressed leukocyte adhesion and uptake of acetylated low-density lipoprotein. The data indicate that expression of scavenger receptors and adhesion molecules in response to TMAO, along with formation of NLRP3 inflammasomes, may drive endothelial dysfunction through uptake of acetylated low-density lipoprotein and lymphocyte adhesion. Apigenin reverses these effects, implying that it may also prevent arteriosclerosis.

Phenolic Compounds Exerting Lipid-Regulatory, Anti-Inflammatory and Epigenetic Effects as Complementary Treatments in Cardiovascular Diseases

Atherosclerosis is the main process behind cardiovascular diseases (CVD), maladies which continue to be responsible for up to 70% of death worldwide. Despite the ongoing development of new and potent drugs, their incomplete efficacy, partial intolerance and numerous side effects make the search for new alternatives worthwhile. The focus of the scientific world turned to the potential of natural active compounds to prevent and treat CVD. Essential for effective prevention or treatment based on phytochemicals is to know their mechanisms of action according to their bioavailability and dosage. The present review is focused on the latest data about phenolic compounds and aims to collect and correlate the reliable existing knowledge concerning their molecular mechanisms of action to counteract important risk factors that contribute to the initiation and development of atherosclerosis: dyslipidemia, and oxidative and inflammatory-stress. The selection of phenolic compounds was made to prove their multiple benefic effects and endorse them as CVD remedies, complementary to allopathic drugs. The review also highlights some aspects that still need clear scientific explanations and draws up some new molecular approaches to validate phenolic compounds for CVD complementary therapy in the near future.

Flavone Hispidulin Stimulates Glucagon-Like Peptide-1 Secretion and Ameliorates Hyperglycemia in Streptozotocin-Induced Diabetic Mice

SCOPE

Loss of functional β-cell mass is central for the deterioration of glycemic control in diabetes. The incretin hormone glucagon-like peptide-1 (GLP-1) plays a critical role in maintaining glycemic homeostasis via potentiating glucose-stimulated insulin secretion and promoting β-cell mass. Agents that can directly promote GLP-1 secretion, thereby increasing insulin secretion and preserving β-cell mass, hold great potential for the treatment of T2D.

METHODS AND RESULTS

GluTag L-cells, INS832/13 cells, and mouse ileum crypts and islets are cultured for examining the effects of flavone hispidulin on GLP-1 and insulin secretion. Mouse livers and isolated hepatocytes are used for gluconeogenesis. Streptozotocin-induced diabetic mice are treated with hispidulin (20 mg kg^-1 day^-1 , oral gavage) for 6 weeks to evaluate its anti-diabetic potential. Hispidulin stimulates GLP-1 secretion from the L-cell line, ileum crypts, and in vivo. This hispidulin action is mediated via activation of cyclic adenosine monophosphate/protein kinase A signaling. Hispidulin significantly improves glycemic control in diabetic mice, concomitant with improved insulin release, and β-cell survival. Additionally, hispidulin decreases hepatic pyruvate carboxylase expression in diabetic mice and suppresses gluconeogenesis in hepatocytes. Furthermore, hispidulin stimulates insulin secretion from β-cells.

CONCLUSION

These findings suggest that Hispidulin may be a novel dual-action anti-diabetic compound via stimulating GLP-1 secretion and suppressing hepatic glucose production.

Expression Analysis, Functional Marker Development and Verification of AgFNSI in Celery

Apigenin is one of the primary flavonoids in celery, which has a high medicinal value. Flavone synthase I (FNSI) is the last step enzyme in apigenin biosynthesis. In this study, the 1492 bp promoter sequence before AgFNSI initiation codon (ATG) of celery was obtained, which included methyl jasmonate (MeJA) responsive elements, light responsive elements, anaerobic induction elements and five MYB binding sites. AgFNSI was sensitive to temperature, UV-B, water deficit and MeJA. Comparative analysis of AgFNSI genome and promoter sequences among celery accessions with different apigenin content showed that there were four allelic variations in AgFNSI, and four accessions with high apigenin content belonged to AgFNSIa, and five accessions with low apigenin content belonged to AgFNSIc. Three pairs of dominant complementary markers were designed based on the single-nucleotile polymorphisms (SNPs) of the AgFNSIa and AgFNSIc genomes and promoter sequences. Three pairs of functional markers were validated by 112 celery accessions. The results showed that AFPA1/AFPB1 detected significant differences in apigenin content between different genotypes. Therefore, marker AFPA1/AFPB1 is associated with apigenin content in celery and could be used for the genetic improvement of apigenin content in celery.

Beneficial Effects of Dietary Polyphenols on High-Fat Diet-Induced Obesity Linking with Modulation of Gut Microbiota

Obesity is caused by an imbalance of energy intake and expenditure. It is characterized by a higher accumulation of body fat with a chronic low-grade inflammation. Many reports have shown that gut microbiota in the host plays a pivotal role in mediating the interaction between consumption of a high-fat diet (HFD) and onset of obesity. Accumulative evidence has suggested that the changes in the composition of gut microbiota may affect the host's energy homeostasis, systemic inflammation, lipid metabolism, and insulin sensitivity. As one of the major components in human diet, polyphenols have demonstrated to be capable of modulating the composition of gut microbiota and reducing the HFD-induced obesity. The present review summarizes the findings of recent studies on dietary polyphenols regarding their metabolism and interaction with bacteria in the intestine as well as the underlying mechanisms by which they modulate the gut microbiota and alleviate the HFD-induced obesity.

The Renoprotective Effects of Naringenin (NGN) in Gestational Pregnancy

INTRODUCTION

Gestational diabetes mellitus (GDM) is defined as glucose intolerance that is first diagnosed during pregnancy, a condition risking the health of both the mother and the baby. Naringenin (NGN) has been demonstrated to have multiple therapeutic functions, while it is also considered to exhibit antidiabetic properties. The present study aimed to investigate the protective effects of NGN in pregnant diabetic rats.

METHODS

GDM was induced by feeding the rats with a high-fat diet for 5 weeks, followed by intraperitoneal injection of streptozotocin (35 mg/kg). The fasting blood glucose were determined with a glucometer and the 24-h urine protein (24-UPro) were determined by the sulfonyl salicylic acid method. The pathological morphological changes and apoptosis of glomeruli cells of kidney tissue using hematoxylin and eosin (H&E) staining and TUNEL analysis. Enzyme-linked immunosorbent assay (ELISA) kits were used to detect the serum T-AOC, the activity of SOD, the levels of GSH-Px, CAT and MDA, TNF-α, IL-6, TGF-β, ICAM-1.The expression of related genes were measured by RT-qPCR and Western blot analyses.

RESULTS

In the NGN-treated group, it was observed that the general status of the rats was improved, while the levels of blood glucose and 24-UPro were significantly decreased. In addition, the histopathological changes in renal tissues and renal cell apoptosis were significantly improved upon treatment with NGN. The expression levels of oxidative stress and inflammation-associated factors also differed signifigcantly between the model and NGN-treated groups. Upon treatment with NGN, the levels of peroxisome proliferator-activated receptor α were significantly increased, while the activity of enzymes involved in the oxidative metabolism of fatty acids was significantly decreased.

CONCLUSION

These preliminary experimental findings demonstrate that NGN has a certain renoprotective effect on GDM, which provides a novel therapeutic option for this condition.

Hypoglycemic effects of phenolic compound-rich aqueous extract from water dropwort (Oenanthe javanica DC.) on streptozotocin-induced diabetic mice

Phenolic compounds in water dropwort aqueous extract were identified, and the IRS-2/PI3K-AKT pathway and GLUT4 translocation were regulated for hypoglycemic action.

Phenolic Compounds from the Aerial Parts of Blepharis linariifolia Pers. and Their Free Radical Scavenging and Enzyme Inhibitory Activities

Background:Blepharis linariifolia Pers. (Family: Acanthaceae) is used in traditional medicines as a general tonic and for the treatment of various health problems in Sudan. The main aim of this study was to isolate and identify the major chemical constituents from the aerial parts of B. linariifolia and evaluate their bioactivities. Methods: The dried aerial parts of the plant were extracted successively with 100% acetone and 50% acetone, and thereafter the combined extract was subjected to repeated column chromatography to isolate the main components. Free radical scavenging activity was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical method, and in vitro enzyme inhibitory activities against α-glucosidase, pancreatic lipase, and mushroom tyrosinase were evaluated. Results: From the detailed chemical analysis, verbascoside (1), vanillic acid (2), apigenin (3), and 6″-O-p-coumaroylprunin (4), were isolated and their structures were identified on the basis of their nuclear magnetic resonance (NMR) spectral data. Among the isolated compounds, verbascoside (1) showed the most potent free radical scavenging activity (IC50 = 22.03 ± 0.04 μM). Apigenin (3) and 6″-O-p-coumaroylprunin (4) showed promising inhibitory activities against all tested enzymes. Apigenin (3) showed the most potent inhibitory activity against α-glucosidase and tyrosinase (IC50 = 34.73 ± 1.78 μM and 23.14 ± 1.83 μM, respectively), whereas 6″-O-p-coumaroylprunin (4) showed potent inhibition for lipase (IC50 = 2.25 ± 0.17 μM). Conclusions: Four phenolic compounds were isolated and identified from B. linariifolia acetone extract, which are reported for the first time from this plant. All compounds showed good DPPH free radical scavenging activities, with verbascoside (1) being the most potent. Apigenin (3) was the most active as α-glucosidase and mushroom tyrosinase inhibitor, while 6″-O-p-coumaroylprunin (4) showed potent inhibitory activity for pancreatic lipase.

On the Neuroprotective Effects of Naringenin: Pharmacological Targets, Signaling Pathways, Molecular Mechanisms, and Clinical Perspective

As a group of progressive, chronic, and disabling disorders, neurodegenerative diseases (NDs) affect millions of people worldwide, and are on the rise. NDs are known as the gradual loss of neurons; however, their pathophysiological mechanisms have not been precisely revealed. Due to the complex pathophysiological mechanisms behind the neurodegeneration, investigating effective and multi-target treatments has remained a clinical challenge. Besides, appropriate neuroprotective agents are still lacking, which raises the need for new therapeutic agents. In recent years, several reports have introduced naturally-derived compounds as promising alternative treatments for NDs. Among natural entities, flavonoids are multi-target alternatives affecting different pathogenesis mechanisms in neurodegeneration. Naringenin is a natural flavonoid possessing neuroprotective activities. Increasing evidence has attained special attention on the variety of therapeutic targets along with complex signaling pathways for naringenin, which suggest its possible therapeutic applications in several NDs. Here, in this review, the neuroprotective effects of naringenin, as well as its related pharmacological targets, signaling pathways, molecular mechanisms, and clinical perspective, are described. Moreover, the need to develop novel naringenin delivery systems is also discussed to solve its widespread pharmacokinetic limitation.

Adipose tissue as a possible therapeutic target for polyphenols: A case for Cyclopia extracts as anti-obesity nutraceuticals

Obesity is a significant contributor to increased morbidity and premature mortality due to increasing the risk of many chronic metabolic diseases such as type 2 diabetes, cardiovascular disease and certain types of cancer. Lifestyle modifications such as energy restriction and increased physical activity are highly effective first-line treatment strategies used in the management of obesity. However, adherence to these behavioral changes is poor, with an increased reliance on synthetic drugs, which unfortunately are plagued by adverse effects. The identification of new and safer anti-obesity agents is thus of significant interest. In recent years, plants and their phenolic constituents have attracted increased attention due to their health-promoting properties. Amongst these, Cyclopia, an endemic South African plant commonly consumed as a herbal tea (honeybush), has been shown to possess modulating properties against oxidative stress, hyperglycemia, and obesity. Likewise, several studies have reported that some of the major phenolic compounds present in Cyclopia spp. exhibit anti-obesity effects, particularly by targeting adipose tissue. These phenolic compounds belong to the xanthone, flavonoid and benzophenone classes. The aim of this review is to assess the potential of Cyclopia extracts as an anti-obesity nutraceutical as underpinned by in vitro and in vivo studies and the underlying cellular mechanisms and biological pathways regulated by their phenolic compounds.

Apigenin reduces the excessive accumulation of lipids induced by palmitic acid via the AMPK signaling pathway in HepG2 cells

In recent years, increasing attention has been paid to diseases caused by excessive accumulation of lipids in the liver with therapeutic agents derived from natural products offering an alternative treatment to conventional therapies. Among these therapeutic agents, apigenin, a natural flavonoid, has been proven to exert various beneficial biological effects. In the present study, the antiadipogenic effects of apigenin in HepG2 cells was investigated. It was demonstrated that the treatment of cells with different concentrations of apigenin for 24 h significantly decreased the palmitic acid-induced increases in total cholesterol (TC) and triglyceride (TG) levels as well as intracellular lipid accumulation. In addition, apigenin increased the phosphorylated-AMP-activated protein kinase (AMPK) levels but decreased the expression levels of 3-hydroxy-3-methylglutaryl CoA reductase, sterol regulatory element-binding protein (SREBP)-1, fatty acid synthase, and SREBP-2 in a concentration-dependent manner. The present findings suggested that apigenin might improve lipid metabolism by activating the AMPK/SREBP pathway to reduce lipid accumulation in the liver.

Effects of naringenin on vascular changes in prolonged hyperglycaemia in fructose-STZ diabetic rat model

Chronic uncontrolled hyperglycaemia leads to increased oxidative stress and lipid peroxidation resulting in vascular complications and accelerates the progression of diabetic atherosclerosis. Though varieties of modern drugs used in the treatment of diabetes, the complications of diabetes are increasing. Naringenin (NG), has been reported to have potent antioxidant and anti-atherosclerotic properties. However, the effects of NG as vasculoprotective agent in prolonged hyperglycaemia are not well documented. Thus, this study was aimed to determine the effect of NG against vascular changes after prolonged hyperglycaemia in a diabetic rat model. Thirty adult male Sprague-Dawley rats were induced with fructose and streptozotocin to develop the diabetic rat model. After 4 weeks, the rats were randomly divided into 5 groups each group consisting of 6 animals: control, control treated with NG, non-treated diabetes mellitus (DM), DM treated with NG and metformin-treated DM. The treatment with NG (50 mg/kg) and metformin were continued for 5 weeks. The results showed that consumption of NG at 4 weeks post diabetic did not improved blood sugar, blood pressure and serum lipid profile. However, NG did significantly improve oxidative stress parameters in the aortic tissue like malondialdehyde (MDA). Analysis through light microscopy and transmission electron microscope (TEM) reverted the histological changes caused by prolonged hyperglycaemia. The findings thus demonstrated that introduction of NG after prolonged exposure to hyperglycaemia improved the vascular deterioration in diabetic group by decreasing oxidative stress evident by the reduced in the lipid peroxidation activity. Thus, this study showed the potential use of NG as adjunct in managing the diabetic condition during late presentation.

Psiadia punctulata major flavonoids alleviate exaggerated vasoconstriction produced by advanced glycation end products

Exaggerated vasoconstriction plays important roles in vascular complication in aging and many diseases like diabetes. Here, we investigated the protective effect of Psiadia punctulata (PP) on advanced glycation end products (AGEs)-induced aggravated vasoconstriction. The effect of total methanol extract of PP leaves (PPT) on AGE-induced vascular injury was studied through bioassay-guided fractionation procedures in order to find the bioactive fraction and isolate the bioactive compounds. Vascular reactivity was studied using the isolated artery technique by adding cumulative concentrations of phenylephrine (PE) or acetyl choline (ACh). In addition, the antiglycating effect, as well as the effect on AGEs intermediates dityrosine and N`-formylkynurenine and their radical scavenging activity were measured. The results showed that PPT alleviated the AGEs-induced aggravated vasoconstriction in a concentration-dependent manner. The bioassay guided fractionation procedures suggested the chloroform fraction (Fr I) to be responsible for the activity. Chemical investigation of this fraction resulted in isolation of four major bioactive compounds that were identified as: umuhengerin (1), gardenin (2), luteolin-3`,4`-dimethyl ether (3), and 5,3`-dihydroxy-6,7,4`,5`-tetramethoxyflavone (4). The four compounds alleviated the exaggerated vasoconstriction in a dose dependent manner. In search for their mechanism of action, we observed that PPT, Fr. I and the isolated compounds did not improve the impaired vasodilation associated with AGEs exposure. PPT, Fr. I and the isolated compounds 1–4 inhibited AGEs formation and their protein oxidation intermediates. Furthermore, PPT, Fr. I and the isolated compounds 1–4 showed weak radical scavenging activity with compound 4 as the most potent. In conclusion, PPT appears to protect against AGEs-induced exaggerated vasoconstriction through antiglycation and radical scavenging activities.

Dietary Apigenin promotes lipid catabolism, thermogenesis, and browning in adipose tissues of HFD-Fed mice

Dietary Apigenin (AP), a natural flavonoid from plants, could alleviate high-fat diet (HFD) induced obesity and its complication. Nonetheless, the direct correlation between dietary AP and their effects in adipose tissues remained unclear. In this study, male C57BL/6 mice were fed with low-fat diet, HFD with or without 0.04% (w/w) AP for 12 weeks. Dietary AP ameliorated HFD induced body weight gain, glucose intolerance, and insulin resistance. Energy expenditure was increased with no influence on energy intake, which indicated us that AP prevented obesity by enhancing energy export. Interestingly, AP activated lipolysis (ATGL/FOXO1/SIRT1) without higher cycling free fatty acids (FFAs). FFAs were consumed by the upregulation of fatty acid oxidation (AMPK/ACC), thermogenesis, and browning (UCP-1, PGC-1α). Additionally, adipose tissue metabolic inflammation (NF-кB, MAPK) was also reduced by AP. Our study proposed that dietary AP could be explored as a new dietary strategy to combat obesity and related insulin resistance.

Antidiabetic Potential of Flavonoids from Traditional Chinese Medicine: A Review

Diabetes mellitus (DM) is a group of metabolic disorders in which high blood sugar levels occur over a prolonged period. Approximately 4% of the global population is affected by DM. Western medical treatment methods for diabetes including injection or oral hypoglycemic drugs have some toxic or side effects, economic pressures, and so on. Many researchers turn to discover new drugs from natural products or Traditional Chinese Medicine (TCM). Flavonoids are widely distributed in plants, and many studies have shown that flavonoids possess antidiabetic properties, exhibiting not only well-recognized antidiabetic and hypoglycemic activities but also activity in the treatment of diabetic complications. In this review, we systematically summarized anti-diabetic flavonoid compounds based on structure classification by examining the PubMed, Springer Link, Web of Science, and CNKI databases. There are 13 flavonoid compounds listed which have been studied extensively and have antidiabetic features respectively. Apigenin, baicalein, and catechin mainly reduces blood glucose via anti-oxidation; hesperidin is good for diabetic neuropathy; glycyrrhiza flavonoids have a significant effect on gestational DM; quercetin takes advantage of crossing the blood–brain barrier and improving renal function. Some compounds have protective and preventive effects on diabetic complications, such as kaempferol and puerarin which are beneficial to cardiomyopathy; myricetin has therapeutic potential in the treatment of DN; dihydromyricetin might improve CI. It is a pity or might be a pointcut that most studies remain in the animal experimental stage, and further investigation should be carried out.

Anti-Diabetic, Anti-Inflammatory, and Anti-Oxidant Effects of Naringenin in an In Vitro Human Model and an In Vivo Murine Model of Gestational Diabetes Mellitus

SCOPE

Gestational diabetes mellitus (GDM), which affects up to 20% of pregnant women, is associated with maternal peripheral insulin resistance, low-grade inflammation, and oxidative stress. The flavonoid naringenin has potent anti-diabetic, anti-inflammatory, and anti-oxidative properties; however, its effects in GDM remain unknown. The study aimed to determine the effects of naringenin on glucose metabolism, inflammation, and oxidative stress associated with GDM both in vitro and in vivo.

METHODS AND RESULTS

In vitro, human tissue samples obtained at term elective Caesarean section are stimulated with tumour necrosis factor alpha (TNF) to develop a GDM-like environment. Naringenin treatment significantly improves TNF-impaired glucose uptake in skeletal muscle. In placenta and visceral adipose tissue (VAT), naringenin significantly reduces expression of pro-inflammatory cytokines and chemokines and increases antioxidant mRNA expression. Mechanistically, naringenin suppresses nuclear factor κB activation. In vivo, pregnant heterozygous db/+ mice are used to model GDM. Daily intraperitoneal injections of GDM mice with naringenin from gestational day 10-17 significantly improve glucose tolerance, reduces IL1A mRNA expression, and increases antioxidant mRNA expression in placenta, VAT, and subcutaneous adipose tissue.

CONCLUSION

Naringenin is shown to improve insulin sensitivity, inflammation, and oxidative stress associated with GDM and shows promise as a novel preventive therapeutic.

Naringenin-induced HO-1 ameliorates high glucose or free fatty acids-associated apoptosis via PI3K and JNK/Nrf2 pathways in human umbilical vein endothelial cells

Naringenin (NG), a flavanone extracted from various plants, has potent vasoprotective effects likely related to the induction of heme oxygenase-1 (HO-1). In the current study, we investigated mechanisms underlying the effect of NG on HO-1 expression and high glucose (HG)- or free fatty acids (FFA)-induced apoptosis in human umbilical vein endothelial cells (HUVECs). First, we found that HUVECs exposed to NG exhibited enhanced HO-1 expression in a concentration- and time-dependent manner. Moreover, HUVECs treated with NG exhibited activation of phosphoinositide 3 kinase (PI3K)/Akt, extracellular-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK). LY294002 (a PI3K inhibitor) and SP600125 (a JNK inhibitor) reduced NG-induced HO-1 expression, whereas BIRB796 (a p38 inhibitor) and PD98059 (an ERK inhibitor) had no effect. The cytoprotective effects of NG were correlated with activation of the transcription factor NF-E2-related factor 2 (Nrf2), a critical regulator of HO-1 expression. Indeed, the results of our experiments using LY294002 and SP600125 indicated that NG may stimulate Nrf2 through PI3K/Akt and JNK pathway activation. Moreover, treatment of HUVECs with Nrf2 siRNA decreased NG-induced HO-1 expression. Finally, pretreatment of HUVECs with NG remarkably reduced HG- or FFA-induced cell apoptosis, and this effect was greatly abrogated in the presence of SnPP (an HO-1 inhibitor). Above all, our data show that NG increased HO-1 expression and reduced HG- or FFA-induced cell apoptosis in HUVECs by upregulating PI3K, JNK, and Nrf2 pathways, which may confer an adaptive survival response in diabetes-induced vascular injury.

Treatment implications of natural compounds targeting lipid metabolism in nonalcoholic fatty liver disease, obesity and cancer

Metabolic disorders can lead to a scarcity or excess of certain metabolites such as glucose, lipids, proteins, purines, and metal ions, which provide the biochemical foundation and directly contribute to the etiology of metabolic diseases. Nonalcoholic fatty liver disease, obesity, and cancer are common metabolic disorders closely associated with abnormal lipid metabolism. In this review, we first describe the regulatory machinery of lipid metabolism and its deregulation in metabolic diseases. Next, we enumerate and integrate the mechanism of action of some natural compounds, including terpenoids and flavonoids, to ameliorate the development of metabolic diseases by targeting lipid metabolism. Medicinal natural products have an established history of use in health care and therapy. Natural compounds might provide a good source of potential therapeutic agents for treating or preventing metabolic diseases with lipid metabolic abnormalities.

Apigenin and its methylglyoxal-adduct inhibit advanced glycation end products-induced oxidative stress and inflammation in endothelial cells

Protein glycation in the body can lead to malfunction of intracellular and extracellular proteins. Reactive carbonyl species (RCS) have been identified to be key intermediates in the reactions. The reaction products, generally termed as advanced glycation end products (AGEs), have been implicated in the development of diabetic complications. In this study, the activity of apigenin (API), a natural flavone in scavenging RCS and the molecular mechanism involved in its protective effect against AGEs-induced oxidative stress and inflammation were examined in vitro. Results showed that API could directly trap methylglyoxal (MGO) to form API-MGO adducts, thus inhibiting AGEs formation. API and di-apigenin adduct (DMA) were found to inhibit AGEs-induced oxidative stress and inflammation in human umbilical vein endothelial cells (HUVECs) by significantly suppressing reactive oxygen species (ROS) production (30% relative to control) and decreasing the protein expression of pro-inflammatory cytokines and adhesion molecules by 30-70%. Further mechanistic investigation revealed that the protective effect was likely mediated via suppression of the extracellular-signal-regulated kinase 1/2 (ERK)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway initiated by AGEs-RAGE (receptor for AGEs) interaction and induction of ERK/nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway with subsequent up-regulation of antioxidant defense molecules. In summary, our results suggest that API possesses great potential to protect against AGEs-associated health disorders by modulating cellular inflammatory and antioxidant defense signaling pathways.

Comparative Transcriptome Analysis of Celery Leaf Blades Identified an R2R3-MYB Transcription Factor that Regulates Apigenin Metabolism

Apigenin has been proven to possess many pharmacological properties, but the mechanism of regulation of apigenin biosynthesis in plants remains unclear. Apigenin is the main flavonoid in celery and is mainly accumulated in the middle stage of leaf blade development. In this study, comparative transcriptomic analysis revealed a large number of structural genes and transcription factor genes that may be involved in the apigenin metabolic pathway. On the basis of the apigenin content in different celery accessions, an R2R3-MYB transcription factor gene, named AgMYB1, was isolated from the high apigenin celery accession C014. Bioinformatics analysis indicated that AgMYB1 may be involved in flavonoid metabolism. AgMYB1 expression showed a positive relation with the expression of the apigenin accumulation marker gene FNSI and with the apigenin content in different celery tissues. Moreover, overexpression and antisense expression of AgMYB1 in transgenic celery plants significantly increased and reduced the expression of apigenin biosynthetic genes and the apigenin content, respectively. These findings suggest that AgMYB1 is involved in positive regulation of apigenin metabolism in celery.

Activation of 20-HETE/PPARs involved in reno-therapeutic effect of naringenin on diabetic nephropathy

Naringenin is a flavanone compound found in citrus fruits. Recent researches showed that naringenin has many potentially pharmacological effects. However, the therapeutic effect and the potential mechanism of naringenin on diabetic nephropathy (DN) remain to be elucidated. DN model was established by a high-fat diet combined with streptozotocin (STZ), which was confirmed by the levels of fasting blood glucose (FBG, more than 11.1 mmol/L) and urinary albumin (10 times higher than the normal mice). After 5 weeks of STZ injection, the DN was developed in model mice. Then naringenin (25 or 75 mg/kg·d) were supplemented for 4 weeks. At the end of the experiment, the injury of the renal function and structure was deteriorated. Concomitantly, peroxisome proliferators-activated receptors (PPARs) protein expression was down-regulated, and CYP4A expression and 20-hydroxyeicosatetraenoic acid (20-HETE) level were reduced in DN mice. Naringenin administration improved the renal damage of DN mice, and up-regulated PPARs expression, increased CYP4A-20-HETE level. Consistent with the results of in vivo, glucose at 30 mmol/L (high glucose, HG) significantly induced cell proliferation and hypertrophy in NRK-52E cells, following the reductive PPARs protein expression and the downward CYP4A-20-HETE level. Naringenin (0.01, 0.1, 1 μmol/L) reversed these changes induced by HG in a dose-dependent manner. HET0016, a selective inhibitor of 20-HETE synthase, partially blocked the effects of naringenin. In conclusion, naringenin has a therapeutic effect on DN, which may be, at least partly, related to the activation of CYP4A-20-HETE and the up-regulation of PPARs.

Naringenin, a dietary flavanone, enhances insulin-like growth factor 1 receptor-mediated antioxidant defense and attenuates methylglyoxal-induced neurite damage and apoptotic death

Objectives: Recent studies revealed the neuroprotective effects of naringenin (NGEN), a common dietary bioflavonoid contained in citrus fruits. However, there are limited data on its protection against methylglyoxal (MG), the most potent precursor of advanced glycation end-products. The present study was to investigate the protection of NGEN on MG-induced neurotoxicity and the involvement of insulin-like growth factor 1 receptor (IGF-1R) signaling. Methods: NSC34 motor neuron-like cells was used. Cell viability was measured by MTT assay. Protein expressions were analyzed by western blots. Morphological changes of neurites were observed by an inverted microscope. Reactive oxygen species (ROS) production and apoptotic cell numbers were measured by flow cytometer. Glutathione (GSH) level and superoxide dismutase (SOD) activity were measured by ELISA. Results: >NGEN attenuated ROS production and increased GSH level, SOD activity and nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear expression in MG-treated NSC34 cells. NGEN also increased neurite length and enhanced IGF-1R and p-Akt in MG-treated NSC34 cells. Furthermore, NGEN attenuated MG-induced apoptotic death accompanied with down-regulation of cleaved-poly (ADP-ribose) polymerase (PARP) and up-regulation of B-cell lymphoma-2 (Bcl-2). However, AG1024, an IGF-1R antagonist, attenuated the anti-oxidative and anti-apoptotic effects of NGEN in MG-treated cells. Discussion: The present results demonstrated that NGEN decreased neuronal apoptosis and improved antioxidant defense in MG-treated NSC34 cells. Moreover, IGF-1R-mediated antioxidant defense plays an important role in this protective mechanism. These findings suggest the potential benefits of NGEN on the prevention of MG-induced or diabetes/hyperglycemia-related neurotoxicity. In vivo studies are needed for further confirmation on NGEN-mediated neuroprotection.

The Therapeutic Potential of Apigenin

Several plant bioactive compounds have exhibited functional activities that suggest they could play a remarkable role in preventing a wide range of chronic diseases. The largest group of naturally-occurring polyphenols are the flavonoids, including apigenin. The present work is an updated overview of apigenin, focusing on its health-promoting effects/therapeutic functions and, in particular, results of in vivo research. In addition to an introduction to its chemistry, nutraceutical features have also been described. The main key findings from in vivo research, including animal models and human studies, are summarized. The beneficial indications are reported and discussed in detail, including effects in diabetes, amnesia and Alzheimer's disease, depression and insomnia, cancer, etc. Finally, data on flavonoids from the main public databases are gathered to highlight the apigenin's key role in dietary assessment and in the evaluation of a formulated diet, to determine exposure and to investigate its health effects in vivo.