Inhibition of pro-inflammatory markers in primary bone marrow-derived mouse macrophages by naturally occurring flavonoids: analysis of the structure-activity relationship.

Flavonoids possess several biological/pharmacological activities including anticancer, antimicrobial, antiviral, anti-inflammatory, immunomodulatory and antioxidant. The aim of this study was to evaluate the effect of flavonoids on macrophage physiology. For this purpose we selected some flavonoids belonging to the most common and abundant groups (flavonols--quercetin and kaempferol; flavones--diosmetin, apigenin, chrysin and luteolin; isoflavones--genistein and daidzein and flavanones--hesperetin). We decided to use primary bone marrow-derived macrophages (BMDM) as cellular model, since they represent a homogenous, non-transformed population of macrophages that can be stimulated in vitro to proliferate by macrophage colony-stimulating factor (M-CSF) or activated by LPS. In this regard, we demonstrated that most of the flavonoids assayed reduce macrophage M-CSF-induced proliferation without affecting cellular viability. Moreover, some flavonoids also inhibit TNFalpha production as well as iNOS expression and NO production in LPS-activated macrophages, an effect that has been associated with the inhibition of the NF-kappaB pathway. We also found that luteolin and quercetin are able to stimulate the expression of the anti-inflammatory cytokine IL-10 at low concentrations (<50microM). Analysis of the structure-activity relationship showed that four hydroxylations at positions 5, 7, 3' and 4', together with the double bond at C(2)-C(3) and the position of the B ring at 2, seem to be necessary for the highest anti-inflammatory effect.