<italic>Osmanthus fragrans</italic> Flower Ameliorates Compound 48/80-Induced Pseudo-Allergic Reactions in vitro and in vivo.

INTRODUCTION

Osmanthus fragrans flower is a highly popular edible flower due to its long-lasting aroma. Although it has been reported to possess multiple activities, no study has focused on its effects on mas-related G protein-coupled receptor (Mrgpr)-mediated mast cell activation.

METHODS

The ethanol extract of O. fragrans flower (OFE) was prepared and analyzed by the NaNO2-Al(NO3)3-NaOH colorimetric method and HPLC. Compound 48/80 (C48/80) was used for activating Mrgpr signaling. Supernatant β-hexosaminidase level was assayed by using the fluorescence probe 4-methylumbelliferyl N-acetyl-β-D-glucosaminide. The levels of cytoplasmic Ca2+ (<mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">c</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math>) and intracellular mitochondrial Ca2+ (<mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math>) were determined by fluorescence probes Fluo-3 AM and Rhod-2/AM, respectively. The Ca2+ level outside the mitochondria was indicated by the fluorescence probe Calcium Green-5N. C48/80-induced vascular leakage, scratching behavior, and hypothermia models were used for evaluating the in vivo effects of OFE.

RESULTS

The highly water-soluble flavonoid-rich OFE significantly inhibited C48/80-induced degranulation in LAD2 cells and primary rat peritoneal mast cells. It could rapidly and reversibly decrease <mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">c</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math> level independent of the activation of Mrgpr signaling. Among the four classical pathways responsible for <mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">c</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math> removal, OFE failed to affect plasma membrane Ca2+-ATPase, sarco/endoplasmic Ca2+-ATPase, and Na+/Ca2+ exchanger, but promoted the uptake of <mml:math id="m68" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math>. In vivo, OFE alleviated C48/80-induced vascular leakage, scratching, as well as hypothermia.

CONCLUSION

This study indicates, for the first time, that OFE is a mast cell stabilizer. It decreases <mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">c</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math> to suppress mast cell degranulation by directly enhancing <mml:math id="m69" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mfenced close="]" open="["><mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:mfenced></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math> uptake. These findings may unveil a potential medicinal value of O. fragrans flower as a promising candidate for relieving mast cell activation-related diseases.