Investigating the Mechanisms of Piperlongumine

The present candidate senolytic drugs that produce selective destruction of senescent cells, done as a means to prevent their contribution to the aging process, all arrive from the cancer research community, where they have been tested for their ability to destroy cancerous cells. Piperlongumine is no exception. Here researchers explore more its likely mechanisms, with a focus on the outcome of increased oxidative stress in the cell due to reduced levels of the antioxidant glutathione, among other possibilities. Recent research suggests, however, that increased oxidative stress isn't the mechanism by which cells are pushed into self-destruction by piperlongumine. While adding new information, the research noted below - there is an open access paper in addition to the publicity materials - doesn't greatly clarify the uncertainty over the way in which piperlongumine works, nor does it clarify whether the method is the same for cancerous and senescent cells. Like many drugs, piperlongumine influences a large number of distinct processes in the cell, and there is no comprehensive map of outcomes. The reason why it is interesting as a potential senolytic therapy, versus other cancer drugs where the mechanisms of action are better mapped, is that it has far fewer side-effects in comparison.

Scientists have uncovered the chemical process behind anti-cancer properties of a spicy Indian pepper plant called the long pepper, whose suspected medicinal properties date back thousands of years. The secret lies in a chemical called piperlongumine (PL), which has shown activity against many cancers. Using x-ray crystallography, researchers were able to create molecular structures that show how the chemical is transformed after being ingested. X-ray crystallography allows scientists to determine molecular structures that reveal how molecules interact with targets - in this case how PL interacts with a gene called GSTP1. Viewing the structures helps in developing drugs for those targets. PL converts to hPL, an active drug that silences GSTP1. The GSTP1 gene produces a detoxification enzyme that is often overly abundant in tumors. "We are hopeful that our structure will enable additional drug development efforts to improve the potency of PL for use in a wide range of cancer therapies."

Glutathione S-transferase pi 1 (GSTP1), is frequently overexpressed in cancerous tumors and is a putative target of the plant compound piperlongumine (PL), which contains two reactive olefins and inhibits proliferation in cancer cells but not normal cells. PL exposure of cancer cells results in increased reactive oxygen species and decreased glutathione (GSH). This data in tandem with other information led to the conclusion that PL inhibits GSTP1, which forms covalent bonds between GSH and various electrophilic compounds, through covalent adduct formation at PLs C7-C8 olefin, while PLs C2-C3 olefin was postulated to react with GSH. However, direct evidence for this mechanism has been lacking.

To investigate, we solved the x-ray crystal structure of GSTP1 bound to PL and GSH to rationalize previously reported structure activity relationship studies. Surprisingly, the structure showed a hydrolysis product of PL (hPL) was conjugated to glutathione at the C7-C8 olefin, and this complex was bound to the active site of GSTP1; No covalent bond formation between hPL and GSTP1 was observed. Mass spectrometric (MS) analysis of reactions between PL and GSTP1 confirmed that PL does not label GSTP1. Moreover, MS data also indicated that nucleophilic attack on PL at the C2-C3 olefin led to PL hydrolysis. Although hPL inhibits GSTP1 enzymatic activity in vitro, treatment of cells susceptible to PL with hPL did not have significant anti-proliferative effects, suggesting hPL is not membrane permeable. Altogether, our data suggest a model wherein PL is a prodrug whose intracellular hydrolysis initiates the formation of the hPL:GSH conjugate, which blocks the active site of and inhibits GSTP1 and thereby cancer cell proliferation.

Link: http://www.utsouthwestern.edu/newsroom/news-releases/year-2017/jan/anticancer-plant-westover.html

Comments

No doubt people will be selling Piperlongumine supplements or offering therapies based on uncertain results shortly.

Posted by: Steve Hill at January 4th, 2017 9:43 AM

@Steve Hill: No doubt. On the plus side, a short human trial would be pretty cheap to throw together in the grand scheme of things.

Posted by: Reason at January 4th, 2017 9:59 AM

The lab sources for piperlogumine are prohibitively expensive, I assume it is difficult to purify. On the other hand one can buy long piper stuffed into 400mg capsules cheap. I have no idea what the concentration of piperlongumine in long pepper is. But I am going to take 2 capsules 3 times a week. My order just arrived today.

Posted by: JohnD at January 4th, 2017 3:16 PM

@JohnD: I'd be willing to wager that it is humanly impossible to eat enough long peppers to obtain benefits to the level seen in animal studies with piperlongumine, just as it is humanly impossible to eat enough bananas to cause potassium poisoning.

Posted by: Reason at January 4th, 2017 3:29 PM

Use logic, Reason; if that were true, the capsules John's buying would be prohibitively expensive, because the manufacturer would need to process a monumental quantity of long peppers.

Posted by: Slicer at January 4th, 2017 5:48 PM

Wait. I misread. Yeah, the stuff's in extremely low concentrations in the natural form, because the purified product IS prohibitively expensive.

Posted by: Slicer at January 4th, 2017 5:49 PM

I've begun using the long pepper in my food, it actually tastes really good, I like it better than black pepper.

Posted by: Corbin at January 4th, 2017 7:43 PM

Time for a pepper eating contest between FA, SENS and LEAF I think LOL

Posted by: Steve Hill at January 5th, 2017 9:24 AM

Does anyone know if piperine contradicts the action of piperlongumine? I think the difficulty is in separating the two alkaloids and can only be done with difficulty. I also think the percentage of both substances are similar, perhaps under 1%. It would be convenient if it didn't matter.

Also, I am unable to find out what a safe human dosage might be. Or conversely what a toxic dosage is.

Posted by: chriszell at January 5th, 2017 1:36 PM

As I just posted elsewhere:

Folks, acting on this by swallowing large amounts of black pepper or Piper longum is madness ...

First, they haven't even shown that this stuff kills senescent cells in vivo, and we have no idea about a remotely rational dose for doing so. Second, we have no idea yet of the mechanism. Third, while the paper says that "the maximum tolerated dose in mice is very high," this is not remotely like safety data: it's based on the lack of acute toxic effects after 6 days' treatment.

And whether or not piperlongumine is safe or effective, swallowing mass amounts of pepper in hopes of getting an undefined minimum amoiunt of piperlongumine is not: piperine inhibits a range of xenobiotic-metabolizing enzymes, including the CYP450s and UDP-glucuronosyltransferase, potentially increasing the absorption of dietary carcinogens and other toxins (particularly in conjunction with the concomitant irritation of the intestinal wall). And while there are studies showing that piperine reduces the toxicity of endotoxin to cultured cells and tissue samples, it's entirely plausible that piperine-mediated increases in instestinal permeability could increase absorption of endotoxin, which increases systemic inflammation and has been implicated in atherosclerosis and a range of chronic diseases.

I repeat: they haven't even shown this stuff has senolytic effects in vivo yet, and are very far indeed from showing it's safe. Wait a while, OK? There's senolytic drugs and Oisín's non-integrating genetic senescent cell ablation system coming down the pipe, and they have animal data. There's nothing more embarrassing than dying prematurely from a foolish life extension experiment.

Posted by: Michael at January 5th, 2017 6:05 PM

Ha ha, thanks for keeping us straight Michael!

Posted by: Corbin at January 5th, 2017 9:56 PM

"There's nothing more embarrassing than dying prematurely from a foolish life extension experiment."

This should be on a T-shirt or a banner header or a tombstone somewhere.

Posted by: Slicer at January 6th, 2017 12:07 PM

I agree with Michael. I was joking about the pepper eating contest hence the lol. Testing this before proper data is in is very foolish.

Posted by: Steve h at January 6th, 2017 3:10 PM

Why not eat fresh spicy peppers which is proven in humans to reduce mortality?

"Consumption of spicy foods and total and cause specific mortality: population based cohort study"
https://www.bmj.com/content/351/bmj.h3942

"Spicy food consumption showed highly consistent inverse associations with total mortality among both men and women after adjustment for other known or potential risk factors. In the whole cohort, compared with those who ate spicy foods less than once a week, the adjusted hazard ratios for death were 0.90 (95% confidence interval 0.84 to 0.96), 0.86 (0.80 to 0.92), and 0.86 (0.82 to 0.90) for those who ate spicy food 1 or 2, 3 to 5, and 6 or 7 days a week, respectively. Compared with those who ate spicy foods less than once a week, those who consumed spicy foods 6 or 7 days a week showed a 14% relative risk reduction in total mortality"

Posted by: Lee at May 17th, 2018 8:59 AM

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