Kynurenic Acid in Honey from Arboreal Plants: MS and NMR Evidence

Abstract

KYNA, a Trp metabolite, shows neuroprotective activity against excitotoxic amino acids by antagonizing the NMDA receptor (glycine, glutamate). Here we report the identification of KYNA by a combination of ESI-MS/MS and 1D- and 2D-NMR analyses in honey varieties of arboreal origin. KYNA are absent in single-flower honeys from herbal flowers. These different distribution patterns might possibly involve an indirect plant defence mechanism against fungal pathogens and herbivorous parasites, ever-present on wild trees. The presence of KYNA in honey may explain its pain-relieving effects reported in the literature. The substance, acting in concert with honey flavonoids (COX-2 inhibitors), by antagonizing the NMDA receptor may contribute to the antinociceptive effect of honey. Moreover, kynureninates, owing to their antimicrobial properties, can favour the successful outcome of wounds and burns.

Abbreviations

CID:collision-induced decomposition

COSY:correlation spectroscopy

COX-2:cyclo-oxygenase-2

DMSO:dimethyl sulfoxide

ESI-MS:electrospray ionisation mass spectrometry

HETCOR:hetero-correlation

HMBC:heteronuclear multiple bond correlation

HMQC:heteronuclear multiple quantum correlation

IL:interleukin

KYNA:kynurenic acid

NMDA:N-methyl-d-aspartic acid

QUIN:quinoline

RP-SPE:reverse-phase solid phase extraction

Trp: tryptophan

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