Pelargonidin-3-O-glucoside and its metabolites have modest anti-inflammatory effects in human whole blood cultures

This study hypothesized that the predominant strawberry anthocyanin, pelargonidin-3-O-glucoside (Pg-3-glc), and three of its plasma metabolites (4-hydroxybenzoic acid, protocatechuic acid and phloroglucinaldehyde [PGA]) would affect phagocytosis, oxidative burst and the production of selected pro- and anti-inflammatory cytokines in a whole blood culture model. For the assessment of phagocytosis and oxidative burst activity of monocytes and neutrophils, whole blood was pre-incubated in the presence or absence of the test compounds at concentrations up to 5 μM, followed by analysis of phagocytic and oxidative burst activity using commercially available test kits. For the cytokine analysis, diluted whole blood was stimulated with lipopolysaccharide in the presence or absence of the test compounds at concentrations up to 5 μM. Concentrations of selected cytokines (tumor necrosis factor-α [TNF-α], interleukin [IL]-1β, IL-6, IL-8 and IL-10) were determined using a cytometric bead array kit. There were no effects of any of the test compounds on phagocytosis of opsonized or non-opsonized E. coli or on oxidative burst activity. Pg-3-glc and PGA at 0.08 μM increased the concentration of IL-10 (P<0.01 and P<0.001, respectively), but there was no effect on TNF-α, IL-1β, IL-6 and IL-8 and there were no effects of the other compounds. In conclusion, this study demonstrated a lack of effect of these compounds on the opsonization, engulfment and subsequent destruction of bacteria. Pg-3-glc and PGA, at physiologically relevant concentrations, had anti-inflammatory properties; however, effects were modest, only observed at the lowest dose tested and limited to IL-10

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

Impact of Flavonoids on Cellular and Molecular Mechanisms Underlying Age-Related Cognitive Decline and Neurodegeneration

Purpose of Review This review summarises the most recent evidence regarding the effects of dietary flavonoids on age-related cognitive decline and neurodegenerative diseases. Recent Findings Recent evidence indicates that plant-derived flavonoids may exert powerful actions on mammalian cognition and protect against the development of age-related cognitive decline and pathological neurodegeneration. The neuroprotective effects of flavonoids have been suggested to be due to interactions with the cellular and molecular architecture of brain regions responsible for memory. Summary Mechanisms for the beneficial effects of flavonoids on age-related cognitive decline and dementia are discussed, including modulating signalling pathways critical in controlling synaptic plasticity, reducing neuroinflammation, promoting vascular effects capable of stimulating new nerve cell growth in the hippocampus, bidirectional interactions with gut microbiota and attenuating the extracellular accumulation of pathological proteins. These processes are known to be important in maintaining optimal neuronal function and preventing age-related cognitive decline and neurodegeneration

Role of the small intestine, colon and microbiota in determining the metabolic fate of polyphenols

(Poly)phenols are a large group of compounds, found in food, beverages, dietary supplements and herbal medicines. Owing to their biological activities, absorption and metabolism of the most abundant compounds in humans are well understood. Both the chemical structure of the phenolic moiety and any attached chemical groups define whether the polyphenol is absorbed in the small intestine, or reaches the colon and is subject to extensive catabolism by colonic microbiota. Untransformed substrates may be absorbed, appearing in plasma primarily as methylated, sulfated and glucuronidated derivatives, with in some cases the unchanged substrate. Many of the catabolites are well absorbed from the colon and appear in the plasma either similarly conjugated, or as glycine conjugates, or in some cases unchanged. Although many (poly)phenol catabolites have been identified in human plasma and / or urine, the pathways from substrate to final catabolite, and the species of bacteria and enzymes involved, are still scarcely reported. While it is clear that the composition of the human gut microbiota can be modulated in vivo by supplementation with some (poly)phenol-rich commodities, such modulation is definitely not an inevitable consequence of supplementation, it depends on the treatment, length of time and on the individual metabotype, and it is not clear whether the modulation is sustained when supplementation ceases. Some catabolites have been recorded in plasma of volunteers at concentrations similar to those shown to be effective in in vitro studies suggesting that some benefit may be achieved in vivo by diets yielding such catabolites

Flavonoid metabolites reduce tumor necrosis factor-α secretion to a greater extent than their precursor compounds in human THP-1 monocytes

Scope: Flavonoids are generally studied in vitro, in isolation, and as unmetabolized precursor structures. However, in the habitual diet, multiple flavonoids are consumed together and found present in the circulation as complex mixtures of metabolites. Using a unique study design, we investigated the potential for singular or additive anti-inflammatory effects of flavonoid metabolites relative to their precursor structures. Methods and results: Six flavonoids, 14 flavonoid metabolites, and 29 combinations of flavonoids and their metabolites (0.1-10 μM) were screened for their ability to reduce LPS-induced tumor necrosis factor-α (TNF-α) secretion in THP-1 monocytes. One micromolar peonidin-3-glucoside, cyanidin-3-glucoside, and the metabolites isovanillic acid (IVA), IVA-glucuronide, vanillic acid-glucuronide, protocatechuic acid-3-sulfate, and benzoic acid-sulfate significantly reduced TNF-α secretion when in isolation, while there was no effect on TNF-α mRNA expression. Four combinations of metabolites that included 4-hydroxybenzoic acid (4HBA) and/or protocatechuic acid also significantly reduced TNF-α secretion to a greater extent than the precursors or metabolites alone. The effects on LPS-induced IL-1β and IL-10 secretion and mRNA expression were also examined. 4HBA significantly reduced IL-1β secretion but none of the flavonoids or metabolites significantly modified IL-10 secretion. Conclusion: This study provides novel evidence suggesting flavonoid bioactivity results from cumulative or additive effects of circulating metabolites

Postexercise Inflammasome Activation and IL-1β Production Mitigated by Flavonoid Supplementation in Cyclists

Inflammasomes are multiprotein signaling platforms of the innate immune system that detect markers of physiological stress and promote the maturation of caspase-1 and interleukin 1 beta (IL-1β), IL-18, and gasdermin D. This randomized, cross-over trial investigated the influence of 2-week mixed flavonoid (FLAV) versus placebo (PL) supplementation on inflammasome activation and IL-1β and IL-18 production after 75-km cycling in 22 cyclists (42 ± 1.7 years). Blood samples were collected before and after the 2-week supplementation, and then 0 hr, 1.5 hr, and 21 hr postexercise (176 ± 5.4 min, 73.4 ± 2.0 %VO2max). The supplement (678 mg FLAVs) included quercetin, green tea catechins, and bilberry anthocyanins. The pattern of change in the plasma levels of the inflammasome adaptor oligomer ASC (apoptosis-associated speck-like protein containing caspase recruitment domain) was different between the FLAV and PL trials, with the FLAV ASC levels 52% lower (Cohen's d = 1.06) than PL immediately following 75-km cycling (interaction effect, p = .012). The plasma IL-1β levels in FLAV were significantly lower than PL (23-42%; Cohen's d = 0.293-0.644) throughout 21 hr of recovery (interaction effect, p = .004). The change in plasma gasdermin D levels were lower immediately postexercise in FLAV versus PL (15% contrast, p = .023; Cohen's d = 0.450). The patterns of change in plasma IL-18 and IL-37 did not differ between the FLAV and PL trials (interaction effects, p = .388, .716, respectively). These data indicate that 2-week FLAV ingestion mitigated inflammasome activation, with a corresponding decrease in IL-1β release in cyclists after a 75-km cycling time trial. The data from this study support the strategy of ingesting high amounts of FLAV to mitigate postexercise inflammation