Flavanones are found specifically and abundantly in citrus fruits. Their beneficial effect on vascular function is well documented. However, little is known about their cellular and molecular mechanisms of action in vascular cells. The goal of the present study was to identify the impact of flavanone metabolites on endothelial cells and decipher the underlying molecular mechanisms of action. We investigated the impact of naringenin and hesperetin metabolites at 0·5, 2 and 10 μm on monocyte adhesion to TNF-α-activated human umbilical vein endothelial cells (HUVEC) and on gene expression. Except hesperetin-7-glucuronide and naringenin-7-glucuronide (N7G), when present at 2 μm, flavanone metabolites (hesperetin-3′-sulphate, hesperetin-3′-glucuronide and naringenin-4′-glucuronide (N4′G)) significantly attenuated monocyte adhesion to TNF-α-activated HUVEC. Exposure of both monocytes and HUVEC to N4′G and N7G at 2 μm resulted in a higher inhibitory effect on monocyte adhesion. Gene expression analysis, using TaqMan Low-Density Array, revealed that flavanone metabolites modulated the expression of genes involved in atherogenesis, such as those involved in inflammation, cell adhesion and cytoskeletal organisation. In conclusion, physiologically relevant concentrations of flavanone metabolites reduce monocyte adhesion to TNF-α-stimulated endothelial cells by affecting the expression of related genes. This provides a potential explanation for the vasculoprotective effects of flavanones.

The aim of the present study was to investigate the direct action of the phyto-oestrogen genistein (Gen) on vascular endothelial behaviour, either in the presence or absence of proinflammatory agents. In rat aortic endothelial cell (EC) cultures, 24 h of treatment with Gen significantly increased cell proliferation in a wide range of concentration (0·001–10 nm). This mitogenic action was prevented by the oestrogen receptor (ER) antagonist ICI 182780 or by the presence of the specific NO synthase inhibitor l-nitro-arginine methyl ester. When monocytes adhesion to EC was measured, Gen partially attenuated leucocyte adhesion not only under basal conditions, but also in the presence of bacterial lipopolysaccharides (LPS). The effect of the phyto-oestrogen on the expression of EC adhesion molecules was evaluated. Gen down-regulated the enhancement in mRNA levels of E-selectin, vascular cell adhesion molecule-1 and P-selectin elicited by the proinflammatory agent bacterial LPS. The regulation of EC programmed death induced by the isoflavone was also demonstrated. Incubation with 10 nm Gen prevented DNA fragmentation induced by the apoptosis inductor H2O2. The results presented suggest that Gen would exert a protective effect on vascular endothelium, due to its regulatory action on endothelial proliferation, apoptosis and leucocyte adhesion, events that play a critical role in vascular diseases. The molecular mechanism displayed by the phyto-oestrogen involved the participation of the ER and the activation of the NO pathway.

Previous reports have shown that safflower-seed extract and its major antioxidant constituents, serotonin hydroxycinnamic amides, attenuated atherosclerotic lesion formation in apoE-deficient mice, as well as inflammation and aortic stiffness in human subjects. In the present report, we examined a still unknown cell-based mechanism of serotonin derivatives against the development of atherosclerosis, focusing our attention on their action against the increase of adhesion molecules and the release of chemotactic factors on human aortic endothelial cells, phenomena that represent the key events in the early stages of atherosclerogenesis. Serotonin derivatives N-(p-coumaroyl)serotonin and N-feruloylserotonin exerted an inhibitory effect on short-term high glucose-induced up-regulation of mRNA and protein of adhesion and migration factors, and the consequent adhesion and migration of monocytes to endothelial cells; they inhibited the activation of transcription factors such as NF-κB, and the overproduction of the mitochondrial superoxide by acting as scavengers of the superoxide radical. In addition, serotonin derivative concentration inside the cells and inside the mitochondria was increased in a time-dependent manner. These results identify a mechanism of action of serotonin derivatives against endothelial damage at a cellular level, and underline their benefits against the disorders and complications related to reactive oxygen species.

Oxidative modification of LDL is causally involved in the development of atherosclerosis and occurs in vivo in the blood as well as within the vascular wall. The present study attempted to explore whether polyphenolic flavonoids influence monocyte-endothelium interaction and lectin-like oxidised LDL receptor 1 (LOX-1) expression involved in the early development of atherosclerosis. The flavones luteolin and apigenin inhibited THP-1 cell adhesion onto oxidised LDL-activated human umbilical vein endothelial cells (HUVEC), while the flavanols of ( − )epigallocatechin gallate and (+)catechin, the flavonols of quercetin and rutin, and the flavanones of naringin, naringenin, hesperidin and hesperetin did not have such effects. Consistently, Western blot analysis revealed that the flavones at 25 μm dramatically and significantly abolished HUVEC expression of vascular cell adhesion molecule-1 and E-selectin evidently enhanced by oxidised LDL; these inhibitory effects were exerted by drastically down regulating mRNA levels of these cell adhesion molecules. In addition, quercetin and luteolin significantly attenuated expression of LOX-1 protein up regulated in oxidised LDL-activated HUVEC with a fall in transcriptional mRNA levels of LOX-1. In addition, quercetin and luteolin clearly blunted oxidised LDL uptake by HUVEC treated with oxidised LDL. The results demonstrate that the flavones luteolin and apigenin as well as quercetin were effective in the different initial steps of atherosclerosis process by inhibiting oxidised LDL-induced endothelial monocyte adhesion and/or oxidised LDL uptake. Therefore, certain flavonoids qualify as anti-atherogenic agents in LDL systems, which may have implications for strategies attenuating endothelial dysfunction-related atherosclerosis.