Cerumen of Australian stingless bees (Tetragonula carbonaria): gas chromatography-mass spectrometry fingerprints and potential anti-inflammatory properties

Cerumen, or propolis, is a mixture of plant resins enriched with bee secretions. In Australia, stingless bees are important pollinators that use cerumen for nest construction and possibly for colony's health. While extensive research attests to the therapeutic properties of honeybee (Apis mellifera) propolis, the biological and medicinal properties of Australian stingless bee cerumen are largely unknown. In this study, the chemical and biological properties of polar extracts of cerumen from Tetragonula carbonaria in South East Queensland, Australia were investigated using gas chromatography-mass spectrometry (GC-MS) analyses and in vitro 5-lipoxygenase (5-LOX) cell-free assays. Extracts were tested against comparative (commercial tincture of A. mellifera propolis) and positive controls (Trolox and gallic acid). Distinct GC-MS fingerprints of a mixed diterpenic profile typical of native bee cerumen were obtained with pimaric acid (6.31±0.97%, w/w), isopimaric acid (12.23±3.03%, w/w), and gallic acid (5.79±0.81%, w/w) tentatively identified as useful chemical markers. Characteristic flavonoids and prenylated phenolics found in honeybee propolis were absent. Cerumen extracts from T. carbonaria inhibited activity of 5-LOX, an enzyme known to catalyse production of proinflammatory mediators (IC50 19.97±2.67 μg/ml, mean±SEM, n=4). Extracts had similar potency to Trolox (IC50 12.78±1.82 μg/ml), but were less potent than honeybee propolis (IC50 5.90±0.62 μg/ml) or gallic acid (IC50 5.62±0.35 μg/ml, P