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Ex‐vivo Effects of Limonene in Airways and Vasculature in Allergic Adenosine A 2A receptor Knock‐out and Wild‐type mice
Author(s) -
Rajalingam Sahith,
Bhavsar Riya,
Patel Mehaben,
Mustafa S. Jamal,
Ledent Catherine,
Ponnoth Dovenia S.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.06179
Subject(s) - ovalbumin , methacholine , chemistry , allergen , limonene , saline , adenosine receptor , bronchoconstriction , medicine , allergic inflammation , adenosine , endocrinology , receptor , immunology , pharmacology , inflammation , lung , asthma , allergy , immune system , agonist , respiratory disease , essential oil , chromatography
Limonene, a mono‐terpene flavonoid, has anti‐inflammatory effects in asthma by activating A 2A adenosine receptors. We studied the effects of inhaled d‐limonene on isolated aortic and tracheal rings from asthmatic mice using tissue/organ bath system. We used mice in which the A 2A receptor was genetically knocked out (A 2A KO) and C57BLJ/6 (wild‐type; WT) for the study. The mice were divided into control (CON) and allergen‐induced sensitized (SEN), control mice treated with limonene through aerosol route (CON+LIM) and allergen‐induced sensitized mice treated with limonene (SEN+LIM). Mice were sensitized i.p. on days 1, 6 with 20μg ovalbumin (OVA) followed by 5% OVA aerosol challenges on days 11–13. Control groups were given an i.p injection of vehicle (1,6 days) and the aerosol challenge of normal saline (11–13 days). SEN +LIM and CON +LIM groups were given 0.01% limonene in the form of aerosol 90 min prior to the OVA and saline challenge on days 11,12,13. Trachea and aorta were isolated on day 14 for further experiments. Tissue responses were studied in the form of contraction and relaxations in all groups. Treatment with limonene significantly reduced the tracheal reactivity (80.68±20% in SEN+LIM vs SEN; p<0.05) to methacholine (MCh) in WT mice that were allergic. MCh induced tracheal contractions were not altered in A 2A KO limonene treated sensitized group compared to non‐treated A 2A KO sensitized group (209.87 ± 41.33 A 2A KO SEN+LIMSEN+LIM Vs 212.51 ± 43.18 in A 2A KO SEN) In presence of A 2A ‐antagonist (SCH58651), a significant increase in the MCh induced contractility in WT SEN was observed(341.65 ± 2.664 SEN+SCH Vs 225.99 ± 67.34 SEN, pP<0.05). A 2A agonist CGS 21680 induced relaxation in WT CON was abolished in WT SEN but restored in WT SEN+LIM (37.8± 16.4% Vs 1.2± 11.1 in SEN, p<0.05). The CGS‐induced tracheal relaxation in WT SEN+LIM and SEN groups was increased in the presence of the NADPH inhibitor apocynin (60.58 ± 17.20 SEN; 21.28 ± 16.02 SEN). In the aorta, acetylcholine‐induced aortic relaxation (endothelium‐dependent response) in WT SEN group was significantly lower than controls (29.82 ± 5.62 WT SEN Vs 51.51 ± 30.13 WT CON, p<0.05) with limonene restoring the response (61.56 ± 11.34 WT‐SEN+LIM). CGS 21680 induced aortic relaxation in WT SEN was completely blunted compared to WT CON (5.62±3.72 WT SEN Vs 66.91 ± 6.8 WT‐CON, *p<0.05). Treatment with limonene restored CGS 21680‐induced relaxation in asthmatic mice (63.8 ± 6.32 WT SEN+LIM Vs 5.62± 3.72 SEN) In conclusion, it appears that limonene restores the tracheal and aortic relaxation induced by adenosine‐mediated pathways by activating the A 2A receptor in asthmatic mice. Support or Funding Information Supported by LIU start‐up funds (DSP), HL027339 (SJM)