Assessment of luteolin (3',4',5,7-tetrahydroxyflavone) neuropharmacological activity.

Since the discovery that certain flavonoids (namely flavones) specifically recognise the central BDZ receptors, several efforts have been made to identify naturally occurring GABA(A) receptor benzodiazepine binding site ligands. Flavonoid derivatives with a flavone-like structure such as apigenin, chrysin and wogonin have been reported for their anxiolytic-like activity in different animal models of anxiety. Luteolin (3',4',5,7-tetrahydroxyflavone) is a widespread flavonoid aglycon that was reported as devoid of specific affinity for benzodiazepine receptor (BDZ-R) binding site, but its psychopharmacological activity is presently unknown. Considering (1) the close structural similarity with other active flavones, (2) the activity of some of its glycosilated derivatives and (3) the complexity of flavonoid effects in the central nervous system, luteolin was submitted to a battery of tests designed to evaluate its possible activity upon the CNS and its ability to interact with the BDZ-receptor binding sites was also analysed. Luteolin apparently has CNS activity with anxiolytic-like effects despite the low affinity for the BDZ-R shown in vitro. Our findings suggest a possible interaction with other neurotransmitter systems but we cannot rule out the possibility that luteolin's metabolites might show a higher affinity for the BDZ-R in vivo, thus eliciting the evident anxiolytic-like effects through a GABAergic mechanism.

Neuropharmacological evaluation of the putative anxiolytic effects of Passiflora edulis Sims, its sub-fractions and flavonoid constituents.

Passiflora edulis Sims together with several other plants of the genus Passiflora have been reported to possess anxiolytic properties. It has been suggested recently that flavonoids may be partly responsible for the neuropharmacological activity of these plants but there are still few data reporting the relation between the constituents of these plants and their activity. This work evaluated the anxiolytic/sedative activity of an aqueous extract of Passiflora edulis Sims and bioguided its fractionation using the elevated plus-maze model of anxiety and other complementary pharmacological tests. The aqueous extract presented an anxiolytic-like activity without any significant effect upon the motor activity whilst the total flavonoid fraction (TFF) presented an anxiolytic-like activity but compromised motor activity. Through fractionation of TFF it was possible to isolate and characterize luteolin-7-O-[2-rhamnosylglucoside] which showed an anxiolytic-like activity without compromising motor activity.