Anti-inflammatory inhibition of endothelial cell adhesion molecule expression by flavone derivatives

Diversity and regioselectivity of O-methyltransferases catalyzing the formation of O-methylated flavonoids

Flavonoids and their methylated derivatives have immense market potential in the food and biomedical industries due to their multiple beneficial effects, such as antimicrobial, anti-inflammatory, and anticancer activities. The biological synthesis of flavonoids and their derivatives is often accomplished via the use of genetically modified microorganisms to ensure large-scale production. Therefore, it is pivotal to understand the properties of O-methyltransferases (OMTs) that mediate the methylation of flavonoids. However, the properties of these OMTs are governed by their: sources, substrate specificity, amino acid residues in the active sites, and the intricate mechanism. In order to obtain a clue for the selection of suitable OMTs for the biosynthesis of a target methylated flavonoid, we made a comprehensive review of the currently reported results, with a particular focus on their comparative regioselectivity for different flavonoid substrates. Additionally, the possible mechanisms for the diversity of this class of enzymes were explored using molecular simulation technology. Finally, major gaps in our understanding and areas for future studies were discussed. The findings of this study may be useful in selecting genes that encode OMTs and designing enzyme-based processes for synthesizing O-methylated flavonoids.

3-(3-Hydroxyphenyl)propionic acid, a microbial metabolite of quercetin, inhibits monocyte binding to endothelial cells via modulating E-selectin expression

Adhesion of monocytes to endothelial cells is an important initiating step in atherogenesis. One of the most abundant flavonoids in the diet, quercetin has been reported to inhibit monocyte adhesion to endothelial cells. However, it is poorly absorbed in the upper gastrointestinal tract during oral intake but rather is metabolized by the intestinal microbiota into various phenolic acids. Since the biological properties of the microbial metabolites of quercetin remain largely unknown, herein, we investigated how the microbial metabolite of quercetin, 3-(3-hydroxyphenyl)propionic acid (3HPPA) impact monocyte adhesion to endothelial cells. Direct treatment with 3HPPA for 24 h was not cytotoxic to human aortic endothelial cells (HAECs). Cotreatment with 3HPPA inhibited tumor necrosis factor α (TNFα)-induced adhesion of THP-1 monocytes to HAECs, and suppressed the upregulation of cell adhesion molecule E-selectin but not intercellular adhesion molecule 1 or vascular cell adhesion molecule 1. Furthermore, 3HPPA was found to inhibit TNFα-induced nuclear translocation and phosphorylation of the p65 subunit of nuclear factor κB (NF-κB). We conclude that 3HPPA mitigates the adhesion of monocytes to endothelial cells by suppressing the expression of the cell adhesion molecule E-selectin in HAECs via inhibition of the NF-κB pathway, providing additional evidence for the health benefits of dietary flavonoids and their microbial metabolites as therapeutic agents in atherosclerosis.

Epigenetic mechanisms underlying the benefits of flavonoids in cardiovascular health and diseases: are long non-coding RNAs rising stars?

Cardiovascular diseases (CVDs) rank as the first leading cause of death globally. High dietary polyphenol (especially flavonoids) intake has strongly been associated with low incidence of the primary outcome, overall mortality, blood pressure, inflammatory biomarkers, onset of new-onset type 2 diabetes mellitus (T2DM), and obesity. Phytogenic flavonoids affect the physiological and pathological processes of CVDs by modulating various biochemical signaling pathways. Non-coding RNAs (ncRNAs) have attracted increasing attention as fundamental regulator of gene expression involved in CVDs. Among the different ncRNA subgroups, long ncRNAs (lncRNAs) have recently emerged as regulatory eukaryotic transcripts and therapeutic targets with important and diverse functions in health and diseases. lncRNAs may be associated with the initiation, development and progression of CVDs by modulating acute and chronic inflammation, adipogenesis and lipid metabolism, and cellular physiology. This review summarizes this research on the modulatory effects of lncRNAs and their roles in mediating cellular processes. The mechanisms of action of flavonoids underlying their therapeutic effects on CVDs are also discussed. Based on our review, flavonoids might facilitate a significant epigenetic modification as part (if not full) of their tissue-/cell-related biological effects. This finding may be attributed to their interaction with cellular signaling pathways involved in chronic diseases. Certain lncRNAs might be the target of specific flavonoids, and some critical signaling processes involved in the intervention of CVDs might mediate the therapeutic roles of flavonoids.

Nutraceuticals for prevention of atherosclerosis: Targeting monocyte infiltration to the vascular endothelium

Cardiovascular disease (CVD) is the leading cause of death, globally, and is a serious problem in developing countries. Preventing atherosclerosis is key to reducing the risk of developing CVD. Similar to carcinogenesis, atherogenesis can be divided into four stages: initiation, promotion, progression, and acute events. The current study focuses on the promotion stage, which is characterized by circular monocyte penetration into vascular endothelial cells, monocyte differentiation into macrophages, and the formation of foam cells. This early stage of atherogenesis is a major target for nutraceuticals. We discuss nutraceuticals that can potentially inhibit monocyte adhesion to the vascular endothelium, thereby preventing the promotional stage of atherosclerosis. The mechanisms through which these nutraceuticals prevent monocyte adhesion are classified according to the following targets: NF-κB, ROS, MAPKs, and AP-1. Additionally, we discuss promising targets for nutraceuticals that can regulate monocyte adhesion to the endothelium. PRACTICAL APPLICATIONS: Introduction of atherogenesis with initiation, promotion, progression, and acute events provide specific information and factors for each step in the development of atherosclerosis. Functional food or pharmaceutical researchers can set target stages and use them to develop materials that control atherosclerosis. In particular, because it focuses on vascular inflammation via interaction between monocytes and vascular endothelial cells, it provides specific information to researchers developing functional foods that regulate this process. Therefore, this manuscript, unlike previous papers, will provide material information and potential mechanisms of action to researchers who want to develop functional foods that control vascular inflammation rather than vascular lipids.

Inhibition of pro-inflammatory mediators in RAW264.7 cells by 7-hydroxyflavone and 7,8-dihydroxyflavone

OBJECTIVES

Flavonoids are a class of compounds that having the benzo-γ-pyrone skeleton, which possess anti-inflammatory properties in vitro and in vivo. The aim of this study was to investigate the inhibition of two flavonoids 7-hydroxyflavone (HF) and 7,8-dihydroxyflavone (DHF) on the production of pro-inflammatory mediators in RAW264.7 cells activated by lipopolysaccharides (LPS).

METHODS

For this purpose, we selected four pro-inflammatory mediators including nitric oxide (NO), prostaglandin E₂ (PGE₂ ), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) as markers to evaluate the anti-inflammatory activity of HF and DHF.

KEY FINDINGS

In this regard, we showed that HF and DHF dose-dependently reduced the production of NO, PGE₂ , TNF-α and IL-6 through downregulating mRNA expression of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX2), TNF-α and IL-6, respectively. Moreover, DHF generally possesses more efficient than HF in reducing these markers secretion in this study.

CONCLUSIONS

Consider together, these findings suggest that DHF and HF can inhibit LPS-induced inflammation via attenuating the production of NO, PGE₂ , TNF-α and IL-6, indicating that they may be lead compounds for developing anti-inflammatory agent.

Engineering an aligned endothelial monolayer on a topologically modified nanofibrous platform with a micropatterned structure produced by femtosecond laser ablation

Laser ablated nanofibers with micropattern regulated adhesion and orientation of HUVEC and also contributed to generate an aligned endothelial monolayer.

Common Phenolic Metabolites of Flavonoids, but Not Their Unmetabolized Precursors, Reduce the Secretion of Vascular Cellular Adhesion Molecules by Human Endothelial Cells

BACKGROUND

Flavonoids have been implicated in the prevention of cardiovascular disease; however, their mechanisms of action have yet to be elucidated, possibly because most previous in vitro studies have used supraphysiological concentrations of unmetabolized flavonoids, overlooking their more bioavailable phenolic metabolites.

OBJECTIVE

We aimed to explore the effects of phenolic metabolites and their precursor flavonoids at physiologically achievable concentrations, in isolation and combination, on soluble vascular cellular adhesion molecule-1 (sVCAM-1).

METHOD

Fourteen phenolic acid metabolites and 6 flavonoids were screened at 1 μM for their relative effects on sVCAM-1 secretion by human umbilical vein endothelial cells stimulated with tumor necrosis factor alpha (TNF-α). The active metabolites were further studied for their response at different concentrations (0.01 μM-100 μM), structure-activity relationships, and effect on vascular cellular adhesion molecule (VCAM)-1 mRNA expression. In addition, the additive activity of the metabolites and flavonoids was investigated by screening 25 unique mixtures at cumulative equimolar concentrations of 1 μM.

RESULTS

Of the 20 compounds screened at 1 μM, inhibition of sVCAM-1 secretion was elicited by 4 phenolic metabolites, of which protocatechuic acid (PCA) was the most active (-17.2%, P = 0.05). Investigations into their responses at different concentrations showed that PCA significantly reduced sVCAM-1 15.2-36.5% between 1 and 100 μM, protocatechuic acid-3-sulfate and isovanillic acid reduced sVCAM-1 levels 12.2-54.7% between 10 and 100 μM, and protocatechuic acid-4-sulfate and isovanillic acid-3-glucuronide reduced sVCAM-1 secretion 27.6% and 42.8%, respectively, only at 100 μM. PCA demonstrated the strongest protein response and was therefore explored for its effect on VCAM-1 mRNA, where 78.4% inhibition was observed only after treatment with 100 μM PCA. Mixtures of the metabolites showed no activity toward sVCAM-1, suggesting no additive activity at 1 μM.

CONCLUSIONS

The present findings suggest that metabolism of flavonoids increases their vascular efficacy, resulting in a diversity of structures of varying bioactivity in human endothelial cells.

Potential anti-inflammatory, anti-adhesive, anti/estrogenic, and angiotensin-converting enzyme inhibitory activities of anthocyanins and their gut metabolites

Epidemiological studies have indicated a positive association between the intake of foods rich in anthocyanins and the protection against cardiovascular diseases. Some authors have shown that anthocyanins are degraded by the gut microflora giving rise to the formation of other breakdown metabolites, which could also contribute to anthocyanin health effects. The objective of this study was to evaluate the effects of anthocyanins and their breakdown metabolites, protocatechuic, syringic, gallic, and vanillic acids, on different parameters involved in atherosclerosis, including inflammation, cell adhesion, chemotaxis, endothelial function, estrogenic/anti-estrogenic activity, and angiotensin-converting enzyme (ACE) inhibitory activity. From the assayed metabolites, only protocatechuic acid exhibited a slight inhibitory effect on NO production and TNF-α secretion in LPS-INF-γ-induced macrophages. Gallic acid caused a decrease in the secretion of MCP-1, ICAM-1, and VCAM-1 in endothelial cells. All anthocyanins showed an ACE-inhibitory activity. Delphinidin-3-glucoside, pelargonidin-3-glucoside, and gallic acid showed affinity for ERβ and pelargonidin and peonidin-3-glucosides for ERα. The current data suggest that anthocyanins and their breakdown metabolites may partly provide a protective effect against atherosclerosis that is multi-causal and involves different biochemical pathways. However, the concentrations of anthocyanins and their metabolites, as used in the present cell culture and in vitro assays mediating anti-inflammatory, anti-adhesive, anti-estrogenic, and angiotensin-converting enzyme inhibitory activities, were often manifold higher than those physiologically achievable.

Effects of flavonoids and other polyphenols on inflammation

Flavonoids are a family of polyphenolic compounds which are widespread in nature (vegetables) and are consumed as part of the human diet in significant amounts. There are other types of polyphenols, including, for example, tannins and resveratrol. Flavonoids and related polyphenolic compounds have significant antiinflammatory activity, among others. This short review summarizes the current knowledge on the effects of flavonoids and related polyphenolic compounds on inflammation, with a focus on structural requirements, the mechanisms involved, and pharmacokinetic considerations. Different molecular (cyclooxygenase, lipoxygenase) and cellular targets (macrophages, lymphocytes, epithelial cells, endothelium) have been identified. In addition, many flavonoids display significant antioxidant/radical scavenging properties. There is substantial structural variation in these compounds, which is bound to have an impact on their biological profile, and specifically on their effects on inflammatory conditions. However, in general terms there is substantial consistency in the effects of these compounds despite considerable structural variations. The mechanisms have been studied mainly in myeloid cells, where the predominant effect is an inhibition of NF-κB signaling and the downregulation of the expression of proinflammatory markers. At present there is a gap in knowledge of in vitro and in vivo effects, although the pharmacokinetics of flavonoids has advanced considerably in the last decade. Many flavonoids have been studied for their intestinal antiinflammatory activity which is only logical, since the gastrointestinal tract is naturally exposed to them. However, their potential therapeutic application in inflammation is not restricted to this organ and extends to other sites and conditions, including arthritis, asthma, encephalomyelitis, and atherosclerosis, among others.

Systematic review of herbals as potential anti-inflammatory agents: Recent advances, current clinical status and future perspectives

Many synthetic drugs reported to be used for the treatment of inflammatory disorders are of least interest now a days due to their potential side effects and serious adverse effects and as they are found to be highly unsafe for human assistance. Since the last few decades, herbal drugs have regained their popularity in treatment against several human ailments. Herbals containing anti-inflammatory activity (AIA) are topics of immense interest due to the absence of several problems in them, which are associated with synthetic preparations. The primary objective of this review is to provide a deep overview of the recently explored anti-inflammatory agents belonging to various classes of phytoconstituents like alkaloids, glycosides, terpenoids, steroids, polyphenolic compounds, and also the compounds isolated from plants of marine origin, algae and fungi. Also, it enlists a distended view on potential interactions between herbals and synthetic preparations, related adverse effects and clinical trials done on herbals for exploring their AIA. The basic aim of this review is to give updated knowledge regarding plants which will be valuable for the scientists working in the field of anti-inflammatory natural chemistry.

Effects of erythropoietin on ICAM-1 and PECAM-1 expressions on human umbilical vein endothelial cells subjected to oxidative stress

The protective effect of erythropoietin (Epo) is based on its ability to reduce oxidation and to stabilize the cells. The aim of the study was to evaluate the influence of Epo on malonyl dialdehyde (MDA), intercellular adhesion molecule-1 (ICAM-1) (CD54) and platelet-endothelial cell adhesion molecule-1 (PECAM-1) (CD31) levels on human umbilical vein endothelial cells (HUVECs) stimulated by tumour necrosis factor-α (TNF-α). HUVECs were incubated with Epo (10-40 IU ml⁻¹) or TNF-α (10-40 ng ml⁻¹) alone or preincubated with Epo (20 IU ml⁻¹) and subsequently stimulated with TNF-α (10-40 ng ml⁻¹). MDA concentrations were measured using the high-performance liquid chromatography, whereas ICAM-1 and PECAM-1 expressions were evaluated by flow cytometry. Incubation with Epo resulted in a decrease in MDA and the increased expressions of ICAM-1 and PECAM-1. Exposure to TNF-α reflected an increase in MDA, ICAM-1 and PECAM-1 levels. These changes were inhibited by preincubation with Epo. The cytoprotective activity proven in this study points to new applications and therapeutic possibilities for Epo.

Comparative effects of quercetin and its predominant human metabolites on adhesion molecule expression in activated human vascular endothelial cells

Adhesion of circulating monocytes to vascular endothelial cells, a critical step in both inflammation and atherosclerosis, is mediated by cross-linkage of adhesion molecules expressed on the surface of both cell types. Dietary flavonoids have been shown to have anti-inflammatory properties, decreasing the expression of cell adhesion molecules, such as vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) on endothelial cells. However, flavonoids are efficiently metabolised during absorption and the forms reaching the systemic circulation are glucuronidated, sulphated and methylated. Most previous in vitro studies of the effects of flavonoids have used the parent compounds at concentrations far higher than those physiologically achievable. We investigated the ability of quercetin and its human metabolites, at physiological concentrations (2 micromol/L and 10 micromol/L), to attenuate the inflammation-induced upregulated expression of VCAM-1, ICAM-1 and of the chemokine, monocyte chemoattractant protein-1 (MCP-1), in human umbilical vein endothelial cells (HUVECs), at the protein and transcript levels. Quercetin treatment reduced the inflammation-induced over-expression of VCAM-1 and ICAM-1 (protein and transcript) in HUVECs. Quercetin also inhibited MCP-1 gene expression. However, quercetin 3'-sulfate, quercetin 3-glucuronide and 3'-methylquercetin 3-glucuronide (isorhamnetin 3-glucuronide) generally exhibited either a reduced ability to inhibit the expression of these molecules compared with the parent aglycone or had no effect. However, all three metabolites inhibited VCAM-1 cell surface expression at 2 micromol/L. These results indicate that both quercetin and its metabolites, at physiological concentrations, can inhibit the expression of key molecules involved in monocyte recruitment during the early stages of atherosclerosis.

Dietary flavonoids attenuate tumor necrosis factor alpha-induced adhesion molecule expression in human aortic endothelial cells. Structure-function relationships and activity after first pass metabolism

Flavonoids have been suggested to exert human health benefits by anti-oxidant and anti-inflammatory mechanisms. In this study, we investigated whether and by what mechanisms dietary flavonoids inhibit expression of cellular adhesion molecules, which is relevant to inflammation and atherosclerosis. We found that the capacity of flavonoids to inhibit tumor necrosis factor alpha-induced adhesion molecule expression in human aortic endothelial cells was dependent on specific structural features of the flavonoids. The 5,7-dihydroxyl substitution of a flavonoid A-ring and 2,3-double bond and 4-keto group of the C-ring were the main structural requirements for inhibition of adhesion molecule expression. In striking contrast, hydroxyl substitutions of the B- and C-rings but not the A-ring were essential for antioxidant activity. Hence, only hydroxyl flavones, such as apigenin and chrysin, and flavonols, such as galangin, kaempferol, and quercetin, were able to inhibit endothelial adhesion molecule expression, whereas flavone, chromone, the flavanone, naringenin, and the flavanol, (-)-epicatechin, were ineffectual. At low concentrations, the active flavonoids significantly attenuated expression of E-selectin and intercellular adhesion molecule 1 but not vascular cell adhesion molecule 1. In addition, exposure of apigenin and kaempferol to cultured hepatocytes, mimicking first pass metabolism, greatly diminished the inhibitory effect of flavonoids on endothelial intercellular adhesion molecule 1 expression. We conclude that the effect of dietary flavonoids on endothelial adhesion molecule expression depends on their molecular structure, concentration, and metabolic transformation but not their antioxidant activity.

Physical fitness attenuates leukocyte-endothelial adhesion in response to acute exercise

Studies suggest that physical fitness promotes cardiovascular health, including improved endothelial function and possibly reduced inflammatory responses to stressors. This study examined the effects of fitness on leukocyte-endothelial adhesion in response to an acute exercise challenge. Peripheral blood mononuclear cell (PBMC) adhesion to human umbilical venous endothelial cells (HUVEC) was examined in 18 more-fit and 19 less-fit individuals [mean age 39 yr (SD 11)] before and after a 20-min treadmill exercise at 65-70% peak oxygen consumption. PBMC were isolated from whole blood (Ficoll-Paque) at rest and immediately after exercise. HUVEC were incubated for 4 h in the presence of cytokines IL-1 and IL-8 to activate endothelial adhesion molecule expression. Fit subjects showed a significant reduction in PBMC-HUVEC adhesion after exercise (P < 0.01) compared with less-fit subjects, who showed no significant change. Regardless of fitness levels, both at rest and in response to exercise, soluble ICAM-1 in the incubation media attenuated PBMC-HUVEC adhesion by approximately 81% (P < 0.001). The findings indicate that immune cells that demarginate in response to exercise have reduced ability to adhere in individuals who are physically fit, an effect apparently independent of ICAM-1 binding. The findings provide evidence of how physical fitness might protect individuals from inflammatory responses to exercise.