Obviously this is a product pitch. But it seems possible to me that mangosteen could be useful for asthma.
I tried drinking mangosteen juice several years ago and noticed that it revved my system and metabolism to an almost scary level. So I tried drinking it before tennis one time and was shocked at how my lung capacity, endurance, quickness, etc were increased. I easily beat someone that normally beat me because of his better fitness level and conditioning.
Since then I take Mangosteen in pill form that I can easier keep in my sports bag. It does everything the liquid does. And whether tennis or racquetball my results are always vastly improved. Only problem is, when I play at night the mangosteen fires the system so much that it can be hard to get any sleep for hours and hours afterwards.
Anyway, long story long, but though I'm not asthmatic myself, I can see the potential in trying mangosteen if you are - just nowhere near bedtime.