7.1  Cellular effects
Polyphenols interfere with the inflammatory process in multiple pathways. For example, they alter the enzymatic processes involved in the proliferation and activation of B- and T-cells, as key components of the inflammatory pathway (by inhibiting tyrosine and serine-threonine protein kinases). Likewise, polyphenols blunt the synthesis of pro-inflammatory mediators such as cytokines, chemokines (IL-8, IL-6, TNF-α, VCAM-1 and ICAM-1), and angiogenic factors, NF-кB or iNOS. Further, an inhibitory effect on several pro-inflammatory enzymes was reported, such as COX-2, MAPK or protein kinase-C (PKC) (Alvarez-Suarez et al., 2017; Gasparrini et al., 2017; Hussain et al., 2016). Thus, studies performed on macrophages proved that resveratrol inhibited the IFN-γ-induced NO production and down-regulated the IFN-γ inducible genes. In this respect, resveratrol decreased STAT1 activation (an important transcription factor for IFN-γ-induced genes) and hindered JAK-2 activation (Chung et al., 2011).
Experimental studies arguing the involvement of polyphenols in mitigating inflammation are either performed on cell line models, animal models or have direct clinical implications. In a study exposing human endothelial cells to the effect of Negroamaro and Primitivo extracts or pure compounds - stilbenes (trans-resveratrol, trans-piceid), hydroxycinnamic acids (p-coumaric, caffeic, and caftaric acids) flavonols (kaempferol, quercetin, myricetin) – before stimulation with lipopolysaccharide (LPS), an inhibition in the expression of adhesion molecules was demonstrated. The anti-inflammatory effect was sustained by a reduction of VCAM-1, ICAM-1, E-selectin, MCP-1 and macrophage colony-stimulating factor (M-CSF), ROS intracellular levels with a correlated attenuation of NF-κB and AP-1 activation. Trans-resveratrol also significantly reduced the endothelial expression and release of M-CSF. All tested compounds reduced the adhesion of monocytes to stimulated endothelial cells, this being a key element in the development of atherosclerosis (Calabriso et al., 2016). The treatment of CCD-18Co myofibroblasts cells with red wine extract reduced mRNA levels of ICAM-1, VCAM-1, NF-κB, and PECAM-1, induced by LPS the anti-inflammatory mechanism being dependent on miR-126 (Angel-Morales et al., 2012).
Another study tested the effects induced by a mixture of four main catechins found in green tea (epicatechin – EC, epigallocatechin – EGC, epigallocatechin gallate – EGCG, epicatechin gallate – GCG), as well as each one alone, on neutrophils isolated from healthy subjects. The catechin compounds induced anti-inflammatory effect (reduction of IL-1β and IL-6, TNF-α, HOCl synthesis and mieloperoxisase), together with the stimulation of antioxidant enzyme activities and Nrf2, along calcium release as well as increased phagocytic capacity, thus proving anti-inflammatory and immunomodulatory actions (Marinovic et al., 2015). In a separate study, EGCG reduced ICAM-1, NF-ĸB and IĸB expressions and reduced ROS levels upon TNF-α-induced inflammation in human retinal pigment epithelial cells. The results suggest the possible therapeutic involvement of EGCG in blocking TNF-α-mediated eye inflammation (Thichanpiang and Wongprasert, 2015). Moreover, in a study evaluating the effect of epicatechin and catechin on arachidonic acid-activated platelets and, respectively, on platelet-HUVEC interaction, the tested compounds induced a reduction of sICAM1, sVCAM1, and sE-selectin levels, as well as an increase of NO bioavailability, proving an anti-inflammatory effect and the ability to counteract endothelial dysfunction, but only when platelets were harvested from peripheral artery disease patients and not from healthy subjects (Carnevale et al., 2014).
Ellagic acid (EA) was tested for its ability to inhibit MIF-induced chemotactic migration of PBMCs, showing a failure to inhibit this response when PBMCs were stimulated with MIP-1α, but high specificity for MIF-induced effect (Sarkar et al., 2015). Chlorogenic acid exerted a dose depended anti-inflammatory effect showed by the reduction of IL-1β, TNF-α and IL-6 levels as well as the inhibition of NO synthesis and expression of COX-1 and iNOS in LPS-stimulated murine macrophages and microglial cells (Hwang et al., 2014).
An in vitro experiment evaluated the results induced by various flavonoids on the arachidonic acid release from rat neutrophils; kaempferol, luteolin, quercetin and amentoflavone reduced the inflammatory response and inhibited the activity of β-glucuronidase and lysozyme (Tordera et al., 1994). Furthermore, the positive outcome of Brassica oleracea extracts (water and methanol respectively) for CVD risk were examined; for this purpose, HUVECs were exposed to the extracts (24 h) and then to TNF-α stimulation. Exposure to the extracts from Brassica oleracea significantly reduced the TNF-α induced expression of E-selectin, ICAM-1 and VCAM-1 (Kuntz and Kunz, 2014). Another study demonstrated the capacity of extracts from Mango (Mangifera indica L.) to counteract TNF-α effects on HUVECs, through the inhibition of IL-6, IL-8, COX-2 and ICAM-1, while restoring the expression of eNOS usually down-regulated by TNF-α (Mura et al., 2015). Interestingly, in an animal model, for example, supplementation of standard chow with cacao phenolic compounds in apolipoprotein E-deficient mice, lead to an anti-inflammatory effect justified by a reduction of VCAM-1 and ICAM-1 expressions, a decrease of oxidative stress markers and a reduction of cholesterol accumulation in plaque compared to control (Natsume and Baba, 2014). Likewise, propolis (green, red or brown) treatment induced a reduction of MCP-1, VCAM, PECAM, FGF, PDGF, VEGF, MMP-9 and upregulated tissue inhibitor of metalloproteinases 1 (TIMP-1) in initial atherosclerotic lesions in LDL receptor gene knockout mice fed a diet rich in cholesterol for inducing atherosclerotic lesions; only red propolis upregulated heme oxygenase 1 (HO-1) and TIMP-1 in advanced atherosclerotic lesions (Daleprane et al., 2012).