Comparative study of the vasorelaxant activity, superoxide-scavenging ability and cyclic nucleotide phosphodiesterase-inhibitory effects of hesperetin and hesperidin

Hesperetin Relaxes Depolarizing Contraction in Human Umbilical Vein by Inhibiting L-Type Ca2+ Channel

OBJECTIVE

To study hesperetin-induced vasorelaxation after depolarizing contraction in human umbilical veins (HUVs) to elucidate the role of L-type Ca2+ channel (LTCC) and related signaling pathway.

METHODS

Isometric tension recording was performed in HUV rings pre-contracted with K+. Hesperetin relaxing mechanism was investigated using a LTCC opener (BayK8644) and blockers of cyclic nucleotides and phosphodiesterases (PDEs). Whole-cell patch-clamping in A7r5 cells, a rat vascular smooth muscle cell line, was performed to study the effect of hesperetin on LTCC current.

RESULTS

After depolarizing precontraction, hesperetin induced HUV relaxation concentration-dependently and endothelium-independently; 1 mmol/L hesperetin reduced denuded HUV ring tension by 68.7% ± 4.3% compared to matching vehicle, osmolality, and time controls (P<0.0001). Importantly, hesperetin competitively inhibited BayK8644-induced contraction, shifting the half maximal effective concentration of BayK8644 response from 1.08 nmol/L [95% confidence interval (CI) 0.49-2.40] in vehicle control to 11.30 nmol/L (95% CI 5.45-23.41) in hesperetin (P=0.0001). Moreover, hesperetin elicited further vasorelaxation in denuded HUV rings pretreated with inhibitors of soluble guanylyl cyclase, adenylyl cyclase, PDE3, PDE4, and PDE5 (P<0.01), while rings pretreated with PDE1 inhibitors could not be relaxed by hesperetin (P>0.05). However, simultaneously applying inhibitors of soluble guanylyl cyclase and adenylyl cyclase could not inhibit hesperetin's effect (P>0.05). In whole-cell patch-clamping, hesperetin rapidly decreased LTCC current in A7r5 cells to 66.7% ± 5.8% (P=0.0104).

CONCLUSIONS

Hesperetin diminishes depolarizing contraction of human vascular smooth muscle through inhibition of LTCC, and not cyclic nucleotides nor PDEs. Our evidence supports direct LTCC interaction and provides additional basis for the use of hesperetin and its precursor hesperidin as vasodilators and may lead to future vasodilator drug development as a treatment alternative for cardiovascular diseases.

Anti-Allergic and Antioxidant Potential of Polyphenol-Enriched Fractions from Cyclopia subternata (Honeybush) Produced by a Scalable Process

Anti-allergic activity was previously demonstrated for extracts of Cyclopia subternata Vogel plant material, containing substantial amounts of xanthones, benzophenones, dihydrochalcones, flavanones and flavones. Fractionation of a hot water extract on macroporous resin was performed aiming to increase its potency. Operating conditions for scaled-up fractionation of the extract were determined, using small-scale static and dynamic sorption/desorption experiments. The anti-allergic potential of the fractions was assessed based on inhibition of β-hexosaminidase release from IgE-sensitized RBL-2H3 cells. Given the role of oxidative stress in allergic reactions, the extract and fractions were also tested for their ability to scavenge the superoxide anion radical and inhibit xanthine oxidase (XO), an enzyme involved in its generation. The routine DPPH and ORAC assays were used for determination of the antioxidant capacity of the fractions. 3-β-D-Glucopyranosyl-4-O-β-D-glucopyranosyliriflophenone (IDG) had the lowest affinity for the resin, dictating selection of the optimal separation conditions. The extract was separated into four fractions on XAD1180N, using step-wise gradient elution with EtOH-water solutions. The major phenolic compounds present in the fractions were IDG and 3-β-D-glucopyranosyliriflophenone (fraction 1), mangiferin, isomangiferin, 3′,5′-di-β-D-glucopyranosyl-3-hydroxyphloretin and vicenin-2 (fraction 2), 3′,5′-di-β-D-glucopyranosylphloretin, eriocitrin and scolymoside (fraction 3) and hesperidin and p-coumaric acid (fraction 4). Fractionation was only partially effective in increasing activity compared to the extract, i.e., fractions 2, 3 and 4 in the DPPH• and XO assays, fractions 1 and 2 in the ORAC assay and fraction 1 in the β-hexosaminidase release assay. In vivo testing will be required to determine whether the increased activity of fractions is worth the effort and expense of fractionation.

An ethnopharmacological review on the therapeutical properties of flavonoids and their mechanisms of actions: A comprehensive review based on up to date knowledge

Flavonoids -a class of low molecular weight secondary metabolites- are ubiquitous and cornucopia throughout the plant kingdom. Structurally, the main structure consists of C6-C3-C6 rings with different substitution patterns so that many sub-classes are obtained, for example: flavonols, flavonolignans, flavonoid glycosides, flavans, anthocyanidins, aurones, anthocyanidins, flavones, neoflavonoids, chalcones, isoflavones, flavones and flavanones. Flavonoids are evaluated to have drug like nature since they possess different therapeutic activities, and can act as cardioprotective, antiviral, antidiabetic, anti-inflammatory, antibacterial, anticancer, and also work against Alzheimer's disease and others. However, information on the relationship between their structure and biological activity is scarce. Therefore, the present review tries to summarize all the therapeutic activities of flavonoids, their mechanisms of action and the structure activity relationship.

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Latest updated ethnopharmacological review of the therapeutic effects of flavonoids.

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Flavonoids are attracting attention because of their therapeutic properties.

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Flavonoids are valuable candidates for drug development against many dangerous diseases.

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This overview summarizes the most important therapeutic effect and mechanism of action of flavonoids.

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General knowledge about the structure activity relationship of flavonoids is summarized.

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Substitution of chemical groups in the structure of flavonoids can significantly change their biological and chemical properties.

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The chemical properties of the basic flavonoid structure should be considered in a drug-based structural program.

Hesperetin Inhibits Sphingosylphosphorylcholine-Induced Vascular Smooth Muscle Contraction by Regulating the Fyn/Rho-Kinase Pathway

ABSTRACT

Cardiovascular diseases are the leading cause of mortality and disability worldwide. We have previously found that sphingosylphosphorylcholine (SPC) is the key molecule leading to vasospasm. We have also identified the SPC/Src family protein tyrosine kinase Fyn/Rho-kinase (ROK) pathway as a novel signaling pathway for Ca2+ sensitization of vascular smooth muscle (VSM) contraction. This study aimed to investigate whether hesperetin can inhibit the SPC-induced contraction with little effect on 40 mM K+-induced Ca2+-dependent contraction and to elucidate the underlying mechanisms. Hesperetin significantly inhibited the SPC-induced contraction of porcine coronary artery smooth muscle strips with little effect on 40 mM K+-induced contraction. Hesperetin blocked the SPC-induced translocation of Fyn and ROK from the cytosol to the membrane in human coronary artery smooth muscle cells (HCASMCs). SPC decreased the phosphorylation level of Fyn at Y531 in both VSMs and HCASMCs and increased the phosphorylation levels of Fyn at Y420, myosin phosphatase target subunit 1 at T853, and myosin light chain (MLC) at S19 in both VSMs and HCASMCs, which were significantly suppressed by hesperetin. Our results indicate that hesperetin inhibits the SPC-induced contraction at least in part by suppressing the Fyn/ROK pathway, suggesting that hesperetin can be a novel drug to prevent and treat vasospasm.

An Overview of Bioactive Flavonoids from Citrus Fruits

Citrus species are one of the world’s popular fruit crops, cultivated all over the world for their economic and nutritional values. Citrus, like other fruits and vegetables, are an important source of several antioxidant molecules (polyphenols, ascorbic acid, and carotenoids) that can inhibit the harmful effects of free radicals on the human body; due to their functional values and health-promoting properties, Citrus species are considered valuable fruits not only in agri-food industry, but also in pharmaceutical industry. Flavonoids are among the major constituents of polyphenols found in different parts of Citrus fruits (skin, peels, seed, pulp membrane, and juice). Flavonoids have different biological properties (antiviral, antifungal, and antibacterial activities). Several studies have also shown the health-related properties of Citrus flavonoids, especially antioxidant, anticancer, anti-inflammation, anti-aging, and cardiovascular protection activities. In the present review, attempts are made to discuss the current trends of research on flavonoids in different Citrus species.

Review of Natural Resources With Vasodilation: Traditional Medicinal Plants, Natural Products, and Their Mechanism and Clinical Efficacy

For decades, chronic diseases including cardiovascular and cerebrovascular diseases (CCVDs) have plagued the world. Meanwhile, we have noticed a close association between CCVDs and vascular lesions, such as hypertension. More focus has been placed on TMPs and natural products with vasodilation and hypotension. TMPs with vasodilatory and hypotensive activities are mainly from Compositae, Lamiaceae, and Orchidaceae (such as V. amygdalina Del., T. procuinbens L., M. glomerata Spreng., K. galanga L., etc.) whereas natural products eliciting vasorelaxant potentials were primarily from flavonoids, phenolic acids and alkaloids (such as apigenin, puerarin, curcumin, sinomenine, etc.). Furthermore, the data analysis showed that the vasodilatory function of TMPs was mainly concerned with the activation of eNOS, while the natural products were primarily correlated with the blockage of calcium channel. Thus, TMPs will be used as alternative drugs and nutritional supplements, while natural products will be considered as potential therapies for CCVDs in the future. This study provides comprehensive and valuable references for the prevention and treatment of hypertension and CCVDs and sheds light on the further studies in this regard. However, since most studies are in vitro and preclinical, there is a need for more in-depth researches and clinical trials to understand the potential of these substances.

A Perspective on Natural and Nature-Inspired Small Molecules Targeting Phosphodiesterase 9 (PDE9): Chances and Challenges against Neurodegeneration

As life expectancy increases, dementia affects a growing number of people worldwide. Besides current treatments, phosphodiesterase 9 (PDE9) represents an alternative target for developing innovative small molecules to contrast neurodegeneration. PDE inhibition promotes neurotransmitter release, amelioration of microvascular dysfunction, and neuronal plasticity. This review will provide an update on natural and nature-inspired PDE9 inhibitors, with a focus on the structural features of PDE9 that encourage the development of isoform-selective ligands. The expression in the brain, the presence within its structure of a peculiar accessory pocket, the asymmetry between the two subunits composing the protein dimer, and the selectivity towards chiral species make PDE9 a suitable target to develop specific inhibitors. Additionally, the world of natural compounds is an ideal source for identifying novel, possibly asymmetric, scaffolds, and xanthines, flavonoids, neolignans, and their derivatives are currently being studied. In this review, the available literature data were interpreted and clarified, from a structural point of view, taking advantage of molecular modeling: 3D structures of ligand-target complexes were retrieved, or built, and discussed.

Hesperetin improves diabetic coronary arterial vasomotor responsiveness by upregulating myocyte voltage‑gated K+ channels

Hesperetin (HSP) is a naturally occurring flavonoid. The present study aimed to investigate the potential vasomotor effects and mechanisms of HSP action on rat coronary arteries (RCAs) injured by diabetes or high glucose concentrations. HSP (100 mg/kg/day) was intragastrically administered to the rats for 8 weeks, which were rendered diabetic with a single intraperitoneal injection of 60 mg/kg streptozotocin (STZ). The vascular tone of RCAs was recorded using a wire myograph. The voltage-dependent K⁺ (Kv) currents were examined using patch clamping. The expression of Kv channels (Kv1.2 and Kv1.5) was examined by western blot analysis and reverse transcription-quantitative PCR (RT-qPCR). Diabetes induced contractile hypersensitivity and vasodilator hyposensitivity in RCAs, both of which were attenuated by the chronic administration of HSP. Patch clamp data revealed that chronic HSP treatment reduced diabetes-induced suppression of Kv currents in the myocytes. Western blot and RT-qPCR analyses revealed that chronic HSP administration increased the expression of Kv1.2, but not Kv1.5, in the RCAs of diabetic rats compared with those from non-diabetic rats. In vitro analysis showed that co-incubation with HSP ameliorated high-glucose-induced suppression of Kv currents and Kv 1.2 protein expression in the myocytes. Taken together, the present study demonstrated that HSP alleviated RCA vasomotor dysfunction as a result of diabetes in rats by upregulating the expression of myocyte Kv channels.

Hesperidin depolarizes the pacemaker potentials through 5-HT4 receptor in murine small intestinal interstitial cells of Cajal

Hesperidin, a citrus flavonoid, can exert numerous beneficial effects on human health. Interstitial cells of Cajal (ICC) are pacemaker cells in the gastrointestinal (GI) tract. In the present study, we investigated potential effects of hesperidin on pacemaker potential of ICC in murine small intestine and GI motility. A whole-cell patch-clamp configuration was used to record pacemaker potential in ICC, and GI motility was investigated in vivo by recording gastric emptying (GE) and intestinal transit rate (ITR). Hesperidin depolarized pacemaker potentials of ICC in a dose-dependent manner. Pre-treatment with methoctramine or 4-DAMP did not inhibit hesperidin-induced pacemaker potential depolarization. Neither a 5-HT₃ receptor antagonist (Y25130) nor a 5-HT₇ receptor antagonist (SB269970) reduced the effect of hesperidin on ICC pacemaker potential, whereas the 5-HT₄ receptor antagonist RS39604 was found to inhibit this effect. In the presence of GDP–β–S, hesperidin-induced pacemaker potential depolarization was inhibited. Moreover, in the presence of U73122 and calphostin C, hesperidin did not depolarize pacemaker potentials. Furthermore, hesperidin accelerated GE and ITR in vivo. These results imply that hesperidin depolarized ICC pacemaker potential via 5-HT₄ receptors, G protein, and PLC/PKC dependent pathways and that it increased GI motility. Therefore, hesperidin may be a promising novel drug to regulate GI motility.

New flavonoid-based compound synthesis strategy for antihypertensive drug development

Hypertension is one of the leading causes of mortality in relation to the cardiovascular conditions and easily the most overlooked and poorly managed disease in mankind. With well over 200 drugs available in the market globally, there is still an urgency to search for antihypertensive alternatives due to the subpar efficacy and unwarranted side effects of the current choices. Present studies reported over 250 types of plant-derived compounds were being investigated for potential pharmacological effects on the vasculature in the last 3 decades. There were numerous literatures that claimed various compounds exhibiting vasorelaxant properties to a certain extent with low numbers of these compounds being successfully adapted into the current medicinal practice for treatment of hypertension. The issue is the scarcity of reviews that summarizes the discovery of this field and the lack of thorough comparison of these compounds to identify which of these vasodilators should be the next face of hypertension management. Thus, this review is aiming towards identifying the relationship between a major class of plant-derived compounds, flavonoid's activity as a vasodilator with their signalling pathways and their structural characteristics according to their vasorelaxant properties. Interestingly, we found that both nitric oxide and voltage-operated calcium channels pathways, and two of the flavonoid's structural characteristics play crucial roles in eliciting strong vasorelaxant effects. We have faith that the insights of this review will serve as a reference for those researching similar topics in the future and potentially lead to the development of more promising antihypertensive alternative.

Antithrombotic activity of flavonoids and polyphenols rich plant species

Cardiovascular diseases represent one of the most notable health problems of the modern civilization. Stroke and heart attack often lead to lethal outcome; essential problem underneath being thrombus formation. Prophylactic approaches include acetylsalicylic acid and clopidogrel therapy on the level of primary hemostasis, i.e., primary clot formation. In the last five years, in the USA, health care expenses related to cardiovascular diseases have increased 50 %, to over 350 billion dollars. Thus, application of plant species and medicinal plants rich in polyphenols in prevention of thrombus formation are of interest. This is supported by the fact that the number of publications on antiaggregatory effect of polyphenols has doubled in the last decade. In this review we focus on antiaggregatory effect of most abundant polyphenols - flavonoids, the effect of plant extracts rich in polyphenols (propolis, species Salvia sp., Calamintha nepeta L., Lavandula angustifolia Mill., Melissa officinalis L, Mentha x piperita L., Ocimum basilicum L., Origanum vulgare L., Rosmarinus officinalis L.) on platelet aggregation, association of chemical composition and antioxidant properties with the observed biological effect, and possible clinical significance of the published results.

Effects of hesperidin consumption on cardiovascular risk biomarkers: a systematic review of animal studies and human randomized clinical trials

Context

The cardioprotective effects of the flavonoid hesperidin, which is present in citrus products, are controversial and unclear. This systematic review was conducted in accordance with the PRISMA 2015 guidelines.

Objective

To evaluate the current evidence from animal and human clinical studies and thus determine whether the consumption of hesperidin exerts beneficial effects on cardiovascular risk factors.

Data sources

PICOS (Population, Intervention, Comparison, Outcome, and Study Design) criteria defined the research question. Searches of the PubMed and Cochrane Plus databases were conducted and studies that met the inclusion criteria and were published in English in the last 15 years were included.

Data extraction

The first author, year of publication, study design, characteristics of animals and humans, intervention groups, dose of hesperidin, route of administration, duration of the intervention, cardiovascular risk biomarkers assessed, and results observed were extracted from the included articles.

Results

A total of 12 animal studies and 11 randomized clinical trials met the inclusion criteria. In the animal studies, the glucose, total and LDL cholesterol, and triglyceride levels decreased with chronic flavonoid consumption. In the human studies, endothelial function improved with flavonoid consumption, whereas no conclusive results were observed for the other biomarkers.

Conclusions

Animal studies have revealed that hesperidin and hesperetin consumption reduces glucose levels and various lipid profile parameters. However, a definitive conclusion cannot be drawn from the existing human clinical trials. Further research is needed to confirm whether the findings observed in animal models can also be observed in humans.

Systematic Review Registration

Prospero registration number CRD42018088942.

Vasorelaxant and chemical fingerprint studies of Citrus reticulatae pericarpium extracts

ETHNOPHARMACOLOGICAL RELEVANCE

Citrus reticulatae Pericarpium (Chen pi) was widely used as an important ingredient in the prescription of TCM to treat phlegm fluid retention type hypertension. Since Chen pi is involved in treatment as antihypertensive TCM formula, we have reasonable expectation in believing that it might possess vasorelaxant activity.

AIM OF THE STUDY

This study is designed to investigate the vasorelaxant effect of Chen pi and to study its pharmacology effects.

MATERIALS AND METHODS

The vasorelaxant effect of water extract of Chen pi (CRW) were evaluated on thoracic aortic rings isolated from Sprague Dawley rats. The fingerprint of Chen pi and the extracts were developed with quantification of hesperidin content by HPTLC.

RESULTS

CRW exhibited the strongest vasorelaxant activity. CRW caused the relaxation of the phenylephrine pre-contracted aortic rings in the presence and absence of endothelium as well as in potassium chloride pre-contracted endothelium-intact aortic ring. The incubation of propranolol (β-adrenergic receptor blocker), atropine (muscarinic receptor blocker), Nω-nitro-L-arginine methyl ester (NO synthase inhibitor), ODQ (sGC inhibitor), indomethacin (COX inhibitor), 4-aminopyridine (K_V blocker), barium chloride (K_ir blocker), and glibenclamide (K_ATP blocker) significantly reduced the vasorelaxant effects of CRW. CRW was also found to be active in reducing Ca²⁺ releases from the sarcoplasmic reticulum and suppressing the voltage-operated calcium channels.

CONCLUSION

The vasorelaxant effect of CRW on rat aorta involves NO/sGC, calcium and potassium channels, muscarinic and β-adrenergic receptors.

Therapeutic potentials of natural compounds acting on cyclic nucleotide phosphodiesterase families

Intracellular cyclic AMP and/or cyclic GMP are characterized in the 1960th. These second messengers, hydrolysed specifically by cyclic nucleotide phosphodiesterase (PDE), play a major role in intracellular signalling. Natural products have been a rich source of drug discovery, Theophylline and Methylxanthine originated from tea leaves used for asthma treatment, whereas, Papaverine, a natural isoquinolein originated from Papaver somniferum traditionally used in impotency, altogether as caffeine where firstly described as PDE-inhibiting compounds. Since that time, the knowledge in PDE field has been drastically increased, allowing the design and development of new therapeutic drugs acting against different pathologies in the nanomolar range. During this period some natural compounds have been identified as PDE inhibitors and used in that context to investigate their therapeutic potential effects. The aim of this literature review is to point out the reported data and demonstrating the contribution of natural characterized molecules as PDE inhibitors in various pathologies that can open new fields of research for drug discovery, notably in epigenetic regulation.

Vasorelaxant activity of twenty-one physiologically relevant (poly)phenolic metabolites on isolated mouse arteries

Polyphenols are beneficial for health, but are metabolised after consumption.

Hesperidin alleviates rat postoperative ileus through anti-inflammation and stimulation of Ca(2+)-dependent myosin phosphorylation

AIM

Postoperative ileus (POI) is a postoperative dysmotility disorder of gastrointestinal tract, which remains one of the most perplexing problems in medicine. In the present study we investigated the effects of hesperidin, a major flavonoid in sweet oranges and lemons, on POI in rats.

METHODS

SD rats were administered hesperidin (5, 20, and 80 mg·kg(-1)·d(-1), ig) for 3 consecutive days. POI operation (gently manipulating the cecum for 1 min) was performed on d 2. The gastrointestinal motility and isolated intestinal contraction were examined 1 d after the operation. Then the myosin phosphorylation and inflammatory responses in cecum tissue were assessed. Smooth muscle cells were isolated from rat small intestine for in vitro experiments.

RESULTS

The gastric emptying and intestinal transit were significantly decreased in POI rats, which were reversed by administration of hesperidin. In ileum and cecum preparations of POI rats in vitro, hesperidin (2.5-160 μmol/L) dose-dependently increased the spontaneous contraction amplitudes without affecting the contractile frequency, which was blocked by the myosin light chain kinase (MLCK) inhibitor ML-7 or verapamil, but not by TTX. Furthermore, administration of hesperidin increased the phosphorylation of MLC20 in the cecum tissue of POI rats. Moreover, administration of hesperidin reversed the increased levels of inflammatory cytokines, iNOS and COX-2 in cecum tissue of POI rats. In freshly isolated intestinal smooth muscle cells, hesperidin (5-80 μmol/L) dose-dependently increased the intracellular Ca(2+) concentration as well as the phosphorylation of MLC20, which was abrogated by ML-7 or siRNA that knocked down MLCK.

CONCLUSION

Oral administration of hesperidin effectively alleviates rat POI through inhibition of inflammatory responses and stimulation of Ca(2+)-dependent MLC phosphorylation.

Long-term Treatment with Hesperidin Improves Endothelium-dependent Vasodilation in Femoral Artery of Spontaneously Hypertensive Rats: The Involvement of NO-synthase and Kv Channels

Hesperidin is the most common flavonoid found in citrus fruits and is expected to exert vasodilation action relevant to its health benefits. The present study aimed to explore the effect of hesperidin on the vascular responses in normotensive and hypertensive rats and the involvement of NO-synthase and K_v channels. The 15-week-old Wistar and spontaneously hypertensive rats (SHR) were randomized to orally receive either hesperidin (50 mg/kg/day) or a corresponding volume of the water for 4 weeks. Vascular responses of isolated femoral arteries were studied with myograph in control conditions and during inhibition of NO-synthase with l-NNA and K_v channels with 4-AP. Hesperidin had no effect on blood pressure. Endothelium-dependent vasodilation in Wistar and SHR was significantly improved by the treatment with hesperidin. The contraction responses after l-NNA were increased in all groups of rats to similar extent, but relaxatory responses were significantly attenuated only in SHR. The inhibition of K_v channels significantly reduced endothelium-dependent vasodilatory responses in only in SHR administered with hesperidin. The results of our experiment indicate that hesperidin might improve the endothelium-dependent vasodilation during hypertension, possibly through the enhancement of K_v channels function. Copyright © 2016 John Wiley & Sons, Ltd.

Antinociceptive, anti-inflammatory and smooth muscle relaxant activities of the pyrrolo[3,4-d]pyridazinone derivatives: Possible mechanisms of action

The aim of this study was to evaluate the analgesic as well as anti-inflammatory activities of the new pyrrolo[3,4-d]pyridazinone derivatives. Moreover, the present study attempted to assess some of the mechanisms involved in the pharmacological activity of these compounds. In the previous studies it was shown that these compounds were highly active in the phenylbenzoquinone-induced 'writhing syndrome' test and had much lower activity in the hot plate, which indicates that mainly peripheral mechanisms of analgesia are involved in their effects. In these extended studies the analgesic activity of two tested compounds (4c, 4f) was confirmed in some animal models of pain. The studied compounds showed a significant and dose-related antinociceptive effect in the models of pain induced by formalin, capsaicin and glutamic acid. Both compounds decreased the edema formation and one of them (4c) attenuated mechanical hyperalgesia in carrageenan-induced paw inflammation in rats. Furthermore, both compounds inhibited cell migration, plasma exudation and nociceptive reaction in zymosan A-induced mouse peritonitis. In the subsequent studies, including experiments on isolated organs (ileum, trachea, aorta), radioligand assays and biochemical tests, it was demonstrated that analgesic and anti-inflammatory effects of the investigated structures are largely due to their competitive antagonism for histamine H1 receptor. The influence on the level of cAMP in inflammatory cells (shown in RAW 264.7 macrophages) and subsequent inhibition of cytokine (TNFα, IL-1β) release can also be one of the important mechanisms of their action. Moreover some additional mechanisms may also be involved in the eventual analgesic effect of tested pyrrolo[3,4-d]pyridazinone derivatives.

Molecular mechanisms behind the biological effects of hesperidin and hesperetin for the prevention of cancer and cardiovascular diseases

Hesperidin (Hsd) and its aglycone, hesperetin (Hst), are two flavonoids from citrus species that have various biological properties, particularly those for the prevention of cancer and cardiovascular diseases. Studies have shown both anti-cancer and cancer chemopreventive effects for Hsd and Hst. Cancer chemopreventive properties of Hsd and Hst are mainly associated with their antioxidant, radical scavenging and anti-inflammatory activities. In addition, Hsd and Hst interfere at different stages of cancer. Unlike conventional anti-cancer drugs, Hsd and Hst inhibit tumor growth by targeting multiple cellular protein targets at the same time, including caspases, Bcl-2 (B-cell lymphoma 2) and Bax (Bcl-2 associated X protein) for the induction of apoptosis, and COX-2 (cyclooxygenase-2), MMP-2 (matrix metalloproteinase-2) and MMP-9 for the inhibition of angiogenesis and metastasis. The results of the recent basic and clinical studies revealed the beneficial effects for Hst, Hsd and their derivatives in the treatment of heart failure and cardiac remodeling, myocardial ischemia and infarction, and hypertension. In addition, the valuable effects of Hst and Hsd in the treatment of diabetes and dyslipidemia with their anti-platelet and anticoagulant effects make them good candidates in the treatment of various cardiovascular diseases. In this review, new findings regarding the molecular targets of Hsd and Hst, animal studies and clinical trials are discussed.

Synthesis, ex vivo and in silico studies of 3-cyano-2-pyridone derivatives with vasorelaxant activity

An efficient and simple synthesis of 3-cyano-2-pyridone derivatives (6a-f) through 3,4-dihydropyridin-2-one oxidation process is described. A greener method to synthesize 3,4-dihydropyridin-2-one has also been developed by rearranging 4H-pyran (4a-f) derivatives in aqueous medium applying H₂SO₄ as the catalyst source and microwave irradiation. The vasorelaxant activity of 3-cyano-2-pyridone derivatives (6a-f) was proved on isolated thoracic aorta rat rings with and without endothelium (+E and -E, respectively) pre-contracted with noradrenaline (0.1 μM). All compounds exhibited significant concentration-dependent and endothelium-independent vasorelaxant effects being the nitro derivatives (6a and f) and compound 6d the most potent with EC₅₀ of 7, 4.4 and 5 μM, respectively. Finally, a previously described 3D model of the central pore of human L-type calcium channel (LCC), modified to be on agreement with NCBI sequence NP_005174.2 for subunit alpha-1F isoform 1, was used to dock most active compounds. 6a, d and f lowest affinity energy structures were found docked in the same cavity conformed by IS6, IS5, IP and IIS6 helices. Nifedipine lowest energy structure was found in the cavity formed by IIS6, IIS5, IIP and IIIS6. Although nifedipine docked in a different cavity, the superposition of both, allowed us to observe that they were almost the same cavities, indicating that there exist subtle steric differences that lead to a different docking for nifedipine. All compounds docked with similar free energy of binding.

Effect of hesperidin pretreatment on the expression of apoptosis-related genes in the liver of mice with acetaminophen-induced acute liver injury

AIM: To investigate the protective effect of hesperidin (HDN) pretreatment on the expression of apoptosis-related genes in the liver of mice with acetaminophen (APAP)-induced acute liver injury.

METHODS: Sixty male Balb/c mice were randomly divided into six groups, including normal group, model group, bifendate group, low-, medium-, and high-dose HDN groups. The HDN groups were intragastrically given different doses of hesperidin for 10 d. The bifendate group was given bifendate. Acute liver injury was induced by injecting APAP in all mice except those in the normal group. After 16 h, all mice were sacrificed. Liver index was calculated. Serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured. The activity of superoxide dismutase (SOD) and the contents of glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) in liver homogenates were determined. Pathological changes in hepatic tissue were observed under an optical microscope. Apoptosis of hepatic cells was detected by TUNEL assay. The expression of Bcl-2 and Bax mRNAs in hepatic tissue was measured by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS: Compared to the normal group, liver index, serum levels of ALT and AST, and the contents of MDA were significantly increased, and the activity of SOD and contents of GSH-PX in liver homogenates were significantly decreased in the model group (5.41% ± 0.68% vs 4.38% ± 0.17%, 1456.49 U/L ± 413.45 U/L vs 45.36 U/L ± 11.98 U/L, 1929.34 U/L ± 810.19 U/L vs 78.49 U/L ± 10.22 U/L, 32.04 nmol/mgprot ± 9.32 nmol/mgprot vs 11.83 nmol/mgprot ± 1.72 nmol/mgprot, 119.29 U/mgprot ± 33.02 U/mgprot vs 327.22 U/mgprot ± 26.66 U/mgprot, 75.89 μmol/L ± 20.21 μmol/Lvs 122.73 μmol/L ± 6.70 μmol/L, all P < 0.01). However, liver index, serum levels of ALT and AST, and the contents of MDA were significantly lower, and the activity of SOD and contents of GSH-PX were significantly higher in the bifendate group, high- and medium-dose HDN groups than in the model group (4.65% ± 0.61%, 4.59% ± 0.57%, 4.73% ± 0.63%vs 4.38% ± 0.17%; 66.36 U/L ± 13.43 U/L, 225.29 U/L ± 53.02 U/L, 773.06 U/L ± 251.27 U/L vs 1456.49 U/L ± 413.45 U/L; 105.75 U/L ± 17.02 U/L, 540.92 U/L ± 170.57 U/L, 906.78 U/L ± 226.38 U/L vs 1929.34 U/L ± 810.1 U/L; 15.74 nmol/mgprot ± 2.98 nmol/mgprot, 16.04 nmol/mgprot ± 4.92 nmol/mgprot, 20.85 nmol/mgprot ± 6.04 nmol/mgprot vs 32.04 nmol/mgprot ± 9.32 nmol/mgprot; 222.52 U/mgprot ± 56.11 U/mgprot, 245.95 U/mgprot ± 41.90 U/mgprot, 198.12 U/mgprot ± 68.09 U/mgprot vs 119.29 U/mgprot ± 33.02 U/mgprot; 108.70 μmol/L ± 25.96 μmol/L, 107.39 μmol/L ± 32.60 μmol/L, 98.90 μmol/L ± 10.71 μmol/L vs 75.89 μmol/L ± 20.21 μmol/L, all P < 0.01 or 0.05). The spleen index showed no significant differences among each group (all P > 0.05). Massive patchy necrosis surrounding the central vein, cellular swelling, massive inflammatory cell infiltration, and significant liver cell apoptosis were observed in liver tissues of mice in the model group; however, these pathological changes and cell apoptosis were significantly alleviated in the bifendate group and HDN groups. Such improvement was most obvious in the bifendate group and high-dose HDN group. APAP could significantly up-regulate Bax mRNA expression, down-regulate Bcl-2 mRNA expression, and decrease the Bcl-2/Bax ratio (0.68 ± 0.03 vs 0.28 ± 0.02, 0.21 ± 0.04 vs 0.58 ± 0.01; both P < 0.01). However, Bcl-2 mRNA expression was significantly up-regulated, Bax mRNA expression was significantly down-regulated and the Bcl-2/Bax ratio was significantly increased in the bifendate group, high- and medium-dose HDN groups (0.22 ± 0.04, 0.56 ± 0.01, 0.75 ± 0.01 vs 0.21 ± 0.04; 0.67 ± 0.06, 0.26 ± 0.005, 0.28 ± 0.02 vs 0.68 ± 0.03, all P < 0.05).

CONCLUSION: HDN pretreatment protects mice from acetaminophen-induced liver injury possibly via mechanisms associated with inhibiting lipid peroxidation and regulating the expressions of apoptosis-related genes.

Vasodilator compounds derived from plants and their mechanisms of action

The present paper reviews vasodilator compounds isolated from plants that were reported in the past 22 years (1990 to 2012) and the different mechanisms of action involved in their vasodilator effects. The search for reports was conducted in a comprehensive manner, intending to encompass those metabolites with a vasodilator effect whose mechanism of action involved both vascular endothelium and arterial smooth muscle. The results obtained from our bibliographic search showed that over half of the isolated compounds have a mechanism of action involving the endothelium. Most of these bioactive metabolites cause vasodilation either by activating the nitric oxide/cGMP pathway or by blocking voltage-dependent calcium channels. Moreover, it was found that many compounds induced vasodilation by more than one mechanism. This review confirms that secondary metabolites, which include a significant group of compounds with extensive chemical diversity, are a valuable source of new pharmaceuticals useful for the treatment and prevention of cardiovascular diseases.

Phenols, Alkaloids and Terpenes from Medicinal Plants with Antihypertensive and Vasorelaxant Activities. A Review of Natural Products as Leads to Potential Therapeutic Agents

Numerous studies support the cardiovascular effects of medicinal plants. This review examines plants whose antihypertensive and vasorelaxant effects have been scientifically validated. Our study selected only chemically characterized plants whose mode of action had already been investigated. The aim of the paper is to provide a quick way to identify medicinal plants and their constituents with antihypertensive and vasorelaxant activities.

Phytochemicals in ocular health: Therapeutic potential and delivery challenges

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are the leading causes of blindness in adults. The impact of these conditions on the quality of life is increasing in significance with a rise in life expectancy. The role of hyperglycemia, oxidative stress and inflammatory responses in the development and/or progression of DR and AMD, and several other sight threatening ocular diseases, is well established. In proliferative retinopathy, signals sent by the retina for nourishment, triggers the growth of fragile and abnormal blood vessels. Changes in ocular pressure may lead to rupture of these blood vessels causing severe vision problems. Recent in vitro and preclinical studies demonstrate that certain phytochemicals possessing potent antioxidant and anti-inflammatory activity and ocular blood flow enhancing properties may be very useful in the treatment of, or as a prophylactic measure for, DR and AMD. Apart from these properties they have also been investigated for their anti-bacterial, hormonal, enzyme stimulation, and anti-angiogenic activities. The attractive aspect of these potential therapeutic candidates is that they can act on multiple pathways identified in the etiology of DR, AMD, cataract and other ocular diseases. However, results from clinical trials have been somewhat ambiguous, raising questions about the concentrations of these bioflavonoids achieved in the neural retina following oral administration. Unfortunately, as of date, an efficient noninvasive means to deliver therapeutic agents/candidates to the back-of-the eye is still not available. This review examines some of these promising natural agents and discusses the challenges encountered in delivering them to the posterior segment ocular tissues through the oral route.

β-Adrenergic cAMP signals are predominantly regulated by phosphodiesterase type 4 in cultured adult rat aortic smooth muscle cells

BACKGROUND

We investigated the role of cyclic nucleotide phosphodiesterases (PDEs) in the spatiotemporal control of intracellular cAMP concentrations in rat aortic smooth muscle cells (RASMCs).

METHODOLOGY/PRINCIPAL FINDINGS

The rank order of PDE families contributing to global cAMP-PDE activity was PDE4> PDE3  =  PDE1. PDE7 mRNA expression but not activity was confirmed. The Fluorescence Resonance Energy Transfer (FRET)-based cAMP sensor, Epac1-camps, was used to monitor the time course of cytosolic cAMP changes. A pulse application of the β-adrenoceptor (β-AR) agonist isoproterenol (Iso) induced a transient FRET signal. Both β(1)- and β(2)-AR antagonists decreased the signal amplitude without affecting its kinetics. The non-selective PDE inhibitor (IBMX) dramatically increased the amplitude and delayed the recovery phase of Iso response, in agreement with a role of PDEs in degrading cAMP produced by Iso. Whereas PDE1, PDE3 and PDE7 blockades [with MIMX, cilostamide (Cil) and BRL 50481 (BRL), respectively] had no or minor effect on Iso response, PDE4 inhibition [with Ro-20-1724 (Ro)] strongly increased its amplitude and delayed its recovery. When Ro was applied concomitantly with MIMX or Cil (but not with BRL), the Iso response was drastically further prolonged. PDE4 inhibition similarly prolonged both β(1)- and β(2)-AR-mediated responses. When a membrane-targeted FRET sensor was used, PDE3 and PDE4 acted in a synergistic manner to hydrolyze the submembrane cAMP produced either at baseline or after β-AR stimulation.

CONCLUSION/SIGNIFICANCE

Our study underlines the importance of cAMP-PDEs in the dynamic control of intracellular cAMP signals in RASMCs, and demonstrates the prominent role of PDE4 in limiting β-AR responses. PDE4 inhibition unmasks an effect of PDE1 and PDE3 on cytosolic cAMP hydrolyzis, and acts synergistically with PDE3 inhibition at the submembrane compartment. This suggests that mixed PDE4/PDE1 or PDE4/PDE3 inhibitors would be attractive to potentiate cAMP-related functions in vascular cells.

Citrus polyphenol hesperidin stimulates production of nitric oxide in endothelial cells while improving endothelial function and reducing inflammatory markers in patients with metabolic syndrome

CONTEXT

Hesperidin, a citrus flavonoid, and its metabolite hesperetin may have vascular actions relevant to their health benefits. Molecular and physiological mechanisms of hesperetin actions are unknown.

OBJECTIVE

We tested whether hesperetin stimulates production of nitric oxide (NO) from vascular endothelium and evaluated endothelial function in subjects with metabolic syndrome on oral hesperidin therapy. DESIGN, SETTING, AND INTERVENTIONS: Cellular mechanisms of action of hesperetin were evaluated in bovine aortic endothelial cells (BAEC) in primary culture. A randomized, placebo-controlled, double-blind, crossover trial examined whether oral hesperidin administration (500 mg once daily for 3 wk) improves endothelial function in individuals with metabolic syndrome (n = 24).

MAIN OUTCOME MEASURE

We measured the difference in brachial artery flow-mediated dilation between placebo and hesperidin treatment periods.

RESULTS

Treatment of BAEC with hesperetin acutely stimulated phosphorylation of Src, Akt, AMP kinase, and endothelial NO synthase to produce NO; this required generation of H(2)O(2). Increased adhesion of monocytes to BAEC and expression of vascular cell adhesion molecule-1 in response to TNF-α treatment was reduced by pretreatment with hesperetin. In the clinical study, when compared with placebo, hesperidin treatment increased flow-mediated dilation (10.26 ± 1.19 vs. 7.78 ± 0.76%; P = 0.02) and reduced concentrations of circulating inflammatory biomarkers (high-sensitivity C-reactive protein, serum amyloid A protein, soluble E-selectin).

CONCLUSIONS

Novel mechanisms for hesperetin action in endothelial cells inform effects of oral hesperidin treatment to improve endothelial dysfunction and reduce circulating markers of inflammation in our exploratory clinical trial. Hesperetin has vasculoprotective actions that may explain beneficial cardiovascular effects of citrus consumption.

The grapefruit: an old wine in a new glass? Metabolic and cardiovascular perspectives

Grapefruit is a popular, tasty and nutritive fruit enjoyed globally. Biomedical evidence in the last 10 years has, however, shown that consumption of grapefruit or its juice is associated with drug interactions, which, in some cases, have been fatal. Grapefruit-induced drug interactions are unique in that the cytochrome P450 enzyme CYP3A4, which metabolises over 60% of commonly prescribed drugs as well as other drug transporter proteins such as P-glycoprotein and organic cation transporter proteins, which are all expressed in the intestines, are involved. However, the extent to which grapefruit-drug interactions impact on clinical settings has not been fully determined, probably because many cases are not reported. It has recently emerged that grapefruit, by virtue of its rich flavonoid content, is beneficial in the management of degenerative diseases such as diabetes and cardiovascular disorders. This potentially explosive subject is reviewed here.

PDEs1-5 activity and expression in tissues of cirrhotic rats reveal a role for aortic PDE3 in NO desensitization

Liver cirrhosis is associated with increased nitric oxide (NO) production in the vasculature. We have previously demonstrated that aorta from rats with liver cirrhosis have a reduced relaxant response to NO donors that is corrected by DMPPO, a PDE5-specific inhibitor. Vasodilator responses to DMPPO itself were also reduced in rings from cirrhotic rats. These results supported previous suggestions that upregulation of PDE5 in liver cirrhosis might contribute to renal sodium retention, and consequently modulate vascular reactivity in the context of increased NO production (Tahseldar-Roumieh et al. in Am. J. Physiol. Heart Circ. Physiol. 290, H481-H488, 2006). Here, we investigated the possible alteration in activity and expression of cyclic nucleotide phosphodiesterase PDE1-PDE5 in kidney and vascular tissues in rats 4 weeks after bile duct ligation. The kidney of rats with cirrhosis had increased activity of PDE1 and PDE4 but not PDE5, and increased expression of PDE1A. Unexpectedly and interestingly, there was no change in cirrhotic aorta PDE5, but an increase in PDE3 and PDE4 activity associated with increased expression of PDE3A and PDE3B. Cilostamide, a specific PDE3 inhibitor, corrected the decreased response to an NO donor in isolated aorta from cirrhotic rats, suggesting that the difference in response to NO donors was due to differences in PDE3-induced hydrolysis of cGMP or to cGMP-induced inhibition of PDE3, rather than to differences in PDE5 contribution. In conclusion, these changes in PDE isozymes could greatly contribute to NO desensitization and to the regulation of vascular and renal function in liver cirrhosis.

The flavonoid dioclein is a selective inhibitor of cyclic nucleotide phosphodiesterase type 1 (PDE1) and a cGMP-dependent protein kinase (PKG) vasorelaxant in human vascular tissue

The inhibitory effect of the flavonoid dioclein was assessed on purified vascular cyclic nucleotide phosphodiesterase isoforms (EC 3.1.4.17, PDE1-5) in comparison with 8-methoxymethyl-isobutylmethylxanthine (8-MM-IBMX) and vinpocetine which are currently used as PDE1 inhibitors. The mechanism underlying the vasorelaxant effect of dioclein was investigated in human saphenous vein. Dioclein inhibited PDE1 more selectively than vinpocetine and 8-MM-IBMX, with IC(50) values of 2.47+/-0.26 and 1.44+/-0.35 microM, respectively in basal- and calmodulin-activated states. Dioclein behaved as a competitive inhibitor for cGMP hydrolysis by PDE1 in basal- and calmodulin-activated states (K(i)=0.62+/-0.14 and 0.55+/-0.07 microM, respectively), indicating this inhibitory effect to be independent of calmodulin interactions. In addition, dioclein induced a concentration-dependent relaxation of human saphenous vein which was independent on the presence of functional endothelium (EC(50) values of 7.3+/-3.1 and 11+/-2.7 microM, respectively with and without endothelium). 8-MM-IBMX relaxed human saphenous vein with an EC(50)=31+/-16 microM, whereas vinpocetine did not cause any vasorelaxation at concentrations up to 100 microM. Rp-8-pCPT-cGMPS, which inhibits cGMP-dependent protein kinase (PKG), blocked the vasodilator effect of dioclein, whereas H-89, which is a cAMP-dependent protein kinase (PKA) inhibitor, had a minor inhibitory effect. Our data show that dioclein is a potent calmodulin-independent selective inhibitor of PDE1 and that inhibition of PDE1 is involved in the PKG-mediated vasorelaxant effect of dioclein in human saphenous vein. Furthermore, dioclein may represent a new archetype to develop more specific PDE1 inhibitors.

Exploring the effect of Hesperetin-HSPC complex--a novel drug delivery system on the in vitro release, therapeutic efficacy and pharmacokinetics

Hesperetin is known to exhibit a variety of pharmacological activities in mammalian cell systems. Although it shows appreciable bioavailability when administered orally, its faster elimination from body creates the need of frequent administration to maintain effective plasma concentration. To overcome this limitation, a phospholipid complex of hesperetin was prepared and evaluated for antioxidant activity and pharmacokinetic profile. The hesperetin content of the complex was determined by a spectrophotometer and the surface characteristics of the complex were studied by means of microscope. The antioxidant activity was evaluated in carbon-tetrachloride-intoxicated rats at a dose level of 100 mg/kg body weight, p.o. The complex was studied for in vitro drug release characteristics and effect of complexation on serum concentration of hesperetin in rats was also studied along with main pharmacokinetic parameters. The results showed that the complex has a sustained release property and enhanced antioxidant activity (P < 0.05 and <0.01) as compared to free hesperetin at the same dose level. Pharmacokinetic study depicted that the complex has higher relative bioavailability and acted for a longer period of time. The study therefore suggests that phospholipid complex of hesperetin produced better antioxidant activity than free drug at the same dose level and the effect persisted for a longer period of time, which may be helpful in solving the problems of faster elimination of the molecule.

Hesperidin from Citrus sinensis cultivated in Dezful, Iran

This study described procedures for extracting and quantitation of hesperidin in the waste orange peel of Dezful. Two extracting procedure were used. In procedure A hesperidin was isolated from orange peel by extracting the dry peel first with petroleum ether, removing the essential oil and then with methanol. In procedure B alkaline extraction followed by acidification of the extract was used. It was purified by treatment with formamide-activated charcoal. Detailed analysis of UV, IR, 1HNMR, 13CNMR and Mass spectroscopic data confirm the structure and extent of purity of extracted hesperidin. The spectroscopic results of two extract showed that procedure A produced high extraction yield and more purified hesperidin. Pure hesperidin in gram quantity (11.7% for procedure A and 7.39% for procedure B) was obtained in one purification cycle.

Update on uses and properties of citrus flavonoids: new findings in anticancer, cardiovascular, and anti-inflammatory activity

Significantly, much of the activity of Citrus flavonoids appears to impact blood and microvascular endothelial cells, and it is not surprising that the two main areas of research on the biological actions of Citrus flavonoids have been inflammation and cancer. Epidemiological and animal studies point to a possible protective effect of flavonoids against cardiovascular diseases and some types of cancer. Although flavonoids have been studied for about 50 years, the cellular mechanisms involved in their biological action are still not completely known. Many of the pharmacological properties of Citrus flavonoids can be linked to the abilities of these compounds to inhibit enzymes involved in cell activation. Attempts to control cancer involve a variety of means, including the use of suppressing, blocking, and transforming agents. Suppressing agents prevent the formation of new cancers from procarcinogens, and blocking agents prevent carcinogenic compounds from reaching critical initiation sites, while transformation agents act to facilitate the metabolism of carcinogenic components into less toxic materials or prevent their biological actions. Flavonoids can act as all three types of agent. Many epidemiological studies have shown that regular flavonoid intake is associated with a reduced risk of cardiovascular diseases. In coronary heart disease, the protective effects of flavonoids include mainly antithrombotic, anti-ischemic, anti-oxidant, and vasorelaxant. It is suggested that flavonoids decrease the risk of coronary heart disease by three major actions: improving coronary vasodilatation, decreasing the ability of platelets in the blood to clot, and preventing low-density lipoproteins (LDLs) from oxidizing. The anti-inflammatory properties of the Citrus flavonoids have also been studied. Several key studies have shown that the anti-inflammatory properties of Citrus flavonoids are due to its inhibition of the synthesis and biological activities of different pro-inflammatory mediators, mainly the arachidonic acid derivatives, prostaglandins E 2, F 2, and thromboxane A 2. The anti-oxidant and anti-inflammatory properties of Citrus flavonoids can play a key role in their activity against several degenerative diseases and particularly brain diseases. The most abundant Citrus flavonoids are flavanones, such as hesperidin, naringin, or neohesperidin. However, generally, the flavones, such as diosmin, apigenin, or luteolin, exhibit higher biological activity, even though they occur in much lower concentrations. Diosmin and rutin have a demonstrated activity as a venotonic agent and are present in several pharmaceutical products. Apigenin and their glucosides have been shown a good anti-inflammatory activity without the side effects of other anti-inflammatory products. In this paper, we discuss the relation between each structural factor of Citrus flavonoids and the anticancer, anti-inflammatory, and cardiovascular protection activity of Citrus flavonoids and their role in degenerative diseases.

Antiplatelet activity of hesperetin, a bioflavonoid, is mainly mediated by inhibition of PLC-γ2 phosphorylation and cyclooxygenase-1 activity

Diet can be one of the most important factors that influence risks for atherothrombotic diseases. Hesperetin included in grapefruits and oranges is one candidate that may benefit the cardiovascular system. Here, we investigated antiplatelet activity of hesperetin in vitro. In addition, possible antiplatelet mechanism was also investigated. Hesperetin concentration-dependently inhibited washed rabbit platelet aggregation induced by collagen and arachidonic acid, with IC50 of 20.5+/-3.5 and 69.2+/-5.1 microM, respectively, while has little effect on thrombin- or U46619-, a thromboxane (TX) A2 mimic, mediated platelet aggregation, suggesting that hesperetin may selectively inhibit collagen- and arachidonic acid-mediated signal transduction. In accordance with these findings, hesperetin revealed blocking of the collagen-mediated phospholipase (PL) C-gamma2 phosphorylation, and caused concentration-dependent decreases of cytosolic calcium mobilization, arachidonic acid liberation and serotonin secretion. In addition, hesperetin inhibited arachidonic acid-mediated platelet aggregation by interfering with cyclooxygenase-1 activity as established by the measurement of arachidonic acid-mediated TXA2 and prostaglandin D2 formations as well as cyclooxygenase-1 and TXA2 synthase activity assays. Taken together, the present results provide a cellular mechanism for the antiplatelet activity of hesperetin through inhibition of PLC-gamma2 phosphorylation and cyclooxygenase-1 activity, which may contribute to the beneficial effects of grapefruits and oranges on cardiovascular system.

Study of the mechanisms involved in the vasorelaxation induced by (-)-epigallocatechin-3-gallate in rat aorta

This study investigated several mechanisms involved in the vasorelaxant effects of (-)-epigallocatechin-3-gallate (EGCG). EGCG (1 microM-1 mM) concentration dependently relaxed, after a transient increase in tension, contractions induced by noradrenaline (NA, 1 microM), high extracellular KCl (60 mM), or phorbol 12-myristate 13-acetate (PMA, 1 microM) in intact rat aortic rings. In a Ca2+ -free solution, EGCG (1 microM-1 mM) relaxed 1 microM PMA-induced contractions, without previous transient contraction. However, EGCG (1 microM-1 mM) did not affect the 1 microM okadaic acid-induced contractions. Removal of endothelium and/or pretreatment with glibenclamide (10 microM), tetraethylammonium (2 mM) or charybdotoxin (100 nM) plus apamin (500 nM) did not modify the vasorelaxant effects of EGCG. In addition, EGCG noncompetitively antagonized the contractions induced by NA (in 1.5 mM Ca2+ -containing solution) and Ca2+ (in depolarizing Ca2+ -free high KCl 60 mM solution). In rat aortic smooth muscle cells (RASMC), EGCG (100 microM) reduced increases in cytosolic free Ca2+ concentration ([Ca2+]i) induced by angiotensin II (ANG II, 100 nM) and KCl (60 mM) in 1.5 mM CaCl2 -containing solution and by ANG II (100 nM) in the absence of extracellular Ca2+. In RASMC, EGCG (100 microM) did not modify basal generation of cAMP or cGMP, but significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cAMP and cGMP production. EGCG inhibited the enzymatic activity of all the cyclic nucleotide PDE isoenzymes present in vascular tissue, being more effective on PDE2 (IC50 approximately 17) and on PDE1 (IC50 approximately 25). Our results suggest that the vasorelaxant effects of EGCG in rat aorta are mediated, at least in part, by an inhibition of PDE activity, and the subsequent increase in cyclic nucleotide levels in RASMC, which, in turn, can reduce agonist- or high KCl concentration-induced increases in [Ca2+]i.

Antioxidant and neuroprotective effects of hesperidin and its aglycone hesperetin

The present study evaluated antioxidant and neuroprotective activities of hesperidin, a flavanone mainly isolated from citrus fruits, and its aglycone hesperetin using cell-free bioassay system and primary cultured rat cortical cells. Both hesperidin and hesperetin exhibited similar patterns of 1,1-diphenyl-2-picrylhydrazyl radical scavenging activities. While hesperidin was inactive, hesperetin was found to be a potent antioxidant, inhibiting lipid peroxidation initiated in rat brain homogenates by Fe2+ and L-ascorbic acid. In consistence with these findings, hesperetin protected primary cultured cortical cells against the oxidative neuronal damage induced by H2O2 or xanthine and xanthine oxidase. In addition, it was shown to attenuate the excitotoxic neuronal damage induced by excess glutamate in the cortical cultures. When the excitotoxicity was induced by the glutamate receptor subtype-selective ligands, only the N-methyl-D-aspartic acid-induced toxicity was selectively and markedly inhibited by hesperetin. Furthermore, hesperetin protected cultured cells against the A(beta(25-35))-induced neuronal damage. Hesperidin, however, exerted minimal or no protective effects on the neuronal damage tested in this study. Taken together, these results demonstrate potent antioxidant and neuroprotective effects of hesperetin, implying its potential role in protecting neurons against various types of insults associated with many neurodegenerative diseases.