Thanks for the link. I’ve pasted the post below so others can see it quicker.
Assuming that the post is correct about the toxicity of the plant that the Swanson fisetin product contains, this toxicity is probably how fisetin can kill senescent cells—a bit like chemotherapy drugs.
The risk of death or serious illness from this toxicity is minutely small and possibly only theoretical. And this will especially be the case during the minimal times one would actually need to take fisetin for its senolytic effect—for two days once or twice a year. So I’m not too concerned about it.
The benefits of fisetin are too good to not take it for this low risk. Besides, there are probably many other supplements that have a notional toxicity risk, yet people no doubt find them beneficial.
"Okay, here's the new Chinese bulk fisetin source from eBAY found by djmichel djmichael and discussed above:
Pure fisetin Powder at a cost of 22 dollars for 10 grams. link attached.
The source is Herba Link and the cost is roughly $50 for 25 grams ($2 a gram). I got a plastic packet today which is 25 grams, and the bulk weight of the plastic resealable packet was 27.2 g including the plastic, so net weight is good. The time from order to receipt was just 4 days.
The source is Chinese. Manufacture date 1/21/2019. There is a certificate of analysis which claims 98.13 % fisetin by HPLC. It's a yellow powder and looks good, no odor. Taste is a bit reminiscent of pine. There is a heavy metal screen and a microbial screen.
It is a true herbal extract, done with water and ethanol. The plant source is stems of Rhus succedanea, the Japanese Wax Tree. This is a rather large and hardy shrub you can read about on Wikipedia. Its coating is the source of a lipid (not a wax) used as part of Japanese lacquer. The more common Linaean name these days is Toxicodendron succedaneum, a name it gets because the the plant is toxic to a number of herbivores. Nevertheless, the Rhus genus plants (many known as "sumacs," from a Syrian word meaning "red"), and anything in the larger Anacardiaceae family, are all quite high in fisetin (which is yellow-- the sumac red color is something else).
R. succedanea (this same wax tree) is the source of fisetin in the Swanson product, too. And I would bet Swanson gets it from the same Chinese source and just encapsulates it, so if you're looking to get out of all risk that way, it won't work.
It isn't clear to me why the wax tree R. succedanea is toxic. Other members of the family, like the infamous poison sumac (perhaps the most poisonous plant in N. America), contain urushiol, the same stuff that makes poison oak and ivy so bad. On the other hand, there are many sumacs with fruits used in spices and dyes, and sumac pink is actually what gives the traditional pink lemonade of colonial days, its color.
The fruit and stems of R. succedanea contains a flavonoid related to fisetin and to apigenin, called hinokiflavone. This stuff may be the toxicity source. It is far more toxic than fisetin, and is fascinating because its cytotoxic properties seem related to why we're interested in fisetin-- it goes to the mitochondria and increases production of reactive oxygen species, and induces apoptosis. It has been tested as an anticarcinogenic in melanoma, and shows some promise. It makes melanoma cells apoptose, with less toxicity in healthy cells.
Somebody badly needs to test hinokiflavone as a senolytic. I can't find that anybody has done so.
Do makers of fisetin from R. succedanea test for hinokiflavone content? They don't say so. Would it show up clearly on HPLC? I don't know. How much more toxic is it? I don't know. So if you are planning on eating fisetin from this source with gravy like mashed potatoes, just remember that there is no such things as a totally pure chemical. Natural product extracts are especially worisome. If you've been getting away with taking grams of Swanson fisetin, it's this same extract, so you're probably fine.
That's all I've been able to find out. I'll update when I have more.
And just for entertainment for this gerontology list, here is a poem about an old cow in the fall, who is tired of life. It was written by Robert Hillyer and was a favorite of my father's. It mentions sumac. It's called "Moo!""