Abstract
Epidemiological data indicate that a diet rich in plant polyphenols has a positive effect on brain functions, improving memory and cognition in humans. Direct activity of ingested phenolics on brain neurons may be one of plausible mechanisms explaining these data. This also suggests that some phenolics can cross the blood-brain barrier and be present in the brain or cerebrospinal fluid. We measured 12 phenolics (a combination of the solid-phase extraction technique with high-performance liquid chromatography) in cerebrospinal fluid and matched plasma samples from 28 patients undergoing diagnostic lumbar puncture due to neurological disorders. Homovanillic acid, 3-hydroxyphenyl acetic acid and caffeic acid were detectable in cerebrospinal fluid reaching concentrations (median; interquartile range) 0.18; 0.14 µmol/L, 4.35; 7.36 µmol/L and 0.02; 0.01 µmol/L, respectively. Plasma concentrations of caffeic acid (0.03; 0.01 µmol/L) did not correlate with those in cerebrospinal fluid (ρ = −0.109, p = 0.58). Because food (fruits and vegetables) is the only source of caffeic acid in human body fluids, our results indicate that the same dietary phenolics can cross blood-brain barrier in humans, and that transportation of caffeic acid through this barrier is not the result of simple or facilitated diffusion.
Highlights
Polyphenols existing in fruits and vegetables represent a group of chemical substances that are characterized by the presence of one or more phenol rings per molecule
The transportation of quercetin-glucosides, kaempferol, myricetin and myricetin glucosides via a similar in vitro BBB model was described [26]. These results suggest that various phenolics, and those related to catecholamine metabolism, could be present in human cerebrospinal fluid (CSF)
Dihydrocaffeic acid, caffeic acid (CA), and homovanillic acid (HVA) were determined by high-performance liquid chromatography (HPLC)-ECD, while 3-hydroxyphenyl acetic acid (3HPAA), hippuric acid, 3-hydroxyhippuric, 4-hydroxyhippuric, 3,4-dihydroxybenzoic acid, chlorogenic acid, ellagic acid, and urolithin A were determined by HPLC-UV-Vis
Summary
Polyphenols existing in fruits and vegetables represent a group of chemical substances that are characterized by the presence of one or more phenol rings per molecule. One of the mechanisms which can explain benefits of high dietary intake of polyphenols for brain function could be a direct effect of this plant compound on neurons, involving the suppression of neuro-inflammation, decrease in stress signal transduction pathways, or expression of genes encoding neuro-protective and neurotrophic proteins [9] To evoke such action, circulating polyphenols and their metabolites have to cross the blood-brain barrier (BBB) or blood-cerebrospinal fluid (CSF). The transportation of quercetin-glucosides, kaempferol, myricetin and myricetin glucosides via a similar in vitro BBB model was described [26] These results suggest that various phenolics, and those related to catecholamine metabolism, could be present in human CSF. The correlations between CSF phenolics and selected clinical variables were analyzed
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