Quercetin is (also) a proteasome inhibitor!

Today I read the abstract of a recent study showing a new (“new” to me, that is…or perhaps I simply couldn’t remember it!) anticancer activity of one of my staple supplements: quercetin. It turns out that, among its many other positive anticancer effects, quercetin also inhibits proteasomes, just like curcumin and bortezomib (= Velcade). See: http://goo.gl/HHIqk

I have a Page here on quercetin, but I haven’t updated it in years. Very remiss of me, especially since this is such good stuff! Sooo, what is it?

Quercetin is a flavonoid, that is, a plant chemical with significant anti-inflammatory, antiviral and antioxidant properties, and possibly antihistamine effects, which we can find in red apples, broccoli, onions, berries of all kinds, cauliflower, green tea, grapes, red wine and nuts. An average adult in the Western world probably gets 25-50 mg a day of dietary quercetin. So yes, it’s already in our diet, especially if we eat lots of the above-mentioned stuff.

Problem: I remember reading a study (no time to look now for the reference, so take this with a grain of salt) showing that very high doses of quercetin are toxic to male rats in the long run. But these were superboomamazingly high doses, and by now you must know what I think of HIGH DOSES of practically anything!!! 🙄  At any rate, that is the reason why I stick to just 1.5 grams of quercetin a day, which is not very much at all…


1. those who take bortezomib should NOT also take any quercetin supplements. See: http://goo.gl/rOG3q. Quercetin apparently can interfere, via a bunch of chemical reactions, with bortezomib’s anti-myeloma activity. Not good at all! However, please note that this interference diminishes, according to tests carried out in this study, when myeloma cells get preincubated with quercetin before being exposed to bortezomib, indicating a direct effect of quercetin on myeloma cells. And this interfering effect was also reversed with supplemental inorganic boric acid. Still, it’s best to be cautious. If I were on bortezomib, I probably wouldn’t take any quercetin. Just like I wouldn’t drink any green tea. Not on my Velcade days, that is. However, those of us who aren’t on bortezomib shouldn’t have any problems…

2. It also should NOT be taken with fluoroquinolones, which are heavy duty antibiotics that treat pneumonia, acute sinusitis and genitourinary infections. This is a class of antibiotics known as “chemotherapeutic bactericidal drugs,” so, hey, you can tell by those three words that we’re talking serious stuff, here. Not our usual tetracyclines, I mean…Anyway, from what I read online, these antibiotics can be incredibly toxic, to the point of damaging our mitochondrial DNA. Gulp. Not surprisingly, many of  ’em have been removed completely from clinical use, except, interestingly for animals (figures!)…If you go to Drugs.com, e.g., you will see that the info on fluoroquinolones has been “archived.” There you go. So, since we will probably never ever go within an inch of a fluoroquinolone, we have nothing to worry about…Still, I thought I should report it…you never know…

Okay, now that we have all (!) the warnings out of the way, let’s get to the reason why I’m posting about quercetin today. Well, yes, it’s because of the above-mentioned study, whose abstract provides us with enough information to go on:

  1. quercetin exterminates epithelial cancer cells. Zip zap…dead…gone forever. 🙂 (Note: epithelial cells line our entire body, they are in our guts and so on, and epithelial cancer is perhaps better known as carcinoma, which accounts for 80-90% of all cancers, including breast, colon and prostate…) 
  2. it blocks mTOR activity. Now, mTOR, which is (by the way) the main target of the chemo drug rapamycin, is a really nasty pathway involved with myeloma disease progression. When mTOR is activated, you see, MM cell lines resist being killed. Unmistakably, a very bad thing. And in fact, if you look at PubMed, mTOR inhibitors are being developed all over the place to treat myeloma…For example, here is a study on lenalidomide coupled with an mTOR inhibitor: http://goo.gl/k3FrX
  3. autophagosome formation: for me, reading this part (= the middle part of the abstract, mostly) was like reading a treatise in ancient Hungarian, so at some point I guess I’ll have to find and read the full quercetin study to see if I can understand what’s happening. Note: I did read in other PubMed studies that mTOR regulates autophagy. But that didn’t help my non-scientific brain to process this stuff…not really…However, I have an inkling that it’s all related to proteasome inhibition, thus it should be a good thing, but hey, I’m not 100% sure…
  4. last but certainly not least!, the ability of quercetin to inhibit proteasomes: proteasome inhibition by quercetin can be regarded as a major cause of quercetin-induced cancer cell death. Major cause, eh? Sounds good to me!!! 🙂

Could it really be that an apple (red apple!) a day could help keep the myeloma specialist away? 😉

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