FASN-ating PINK research

In 2018, there is one particular clinical trial that I will be watching, because the drug being tested could have a big impact on certain kinds of Parkinson’s. The clinical trial is focused on people with cancer and they will be treated with a drug called TVB-2640. TVB-2640 is an inhibitor of an enzyme called fatty acid synthase (or FAS).  In today’s post we will discuss why TVB-2640 might be a useful treatment for certain kinds of Parkinson’s.

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Mitochondria and their location in the cell. Source: NCBI

 

Regular readers of this blog are probably getting sick of the picture above.

I use it regularly on this website, because a.) it nicely displays a basic schematic of a mitochondrion (singular), and where mitochondria (plural) reside inside a cell. And b.) a lot of evidence is pointing towards mitochondrial dysfunction in Parkinson’s.

What are mitochondria?

Mitochondria are the power stations of each cell. They help to keep the lights on. Without them, the party is over and the cell dies.

How do they supply the cell with energy?

They convert nutrients from food into Adenosine Triphosphate (or ATP). ATP is the fuel which cells run on. Given their critical role in energy supply, mitochondria are plentiful (some cells have thousands) and highly organised within the cell, being moved around to wherever they are needed.

Source: Mangomannutrition

What does this have to do with Parkinson’s?

Like you, me and all other things in life, mitochondria each have a use-by date.

As mitochondria get old and worn out (or damaged) with time, the cell will dispose of them via a process called mitophagy (a blending of the words mitochondria and autophagy – the waste disposal system of each cell).

How does mitophagy work?

Removal of old/damaged mitochondria via mitophagy involves two steps:

1. Induction of general autophagy, and
2. Priming (or labelling) of the mitochondria for autophagic recognition

Let’s start with the first step, because that is the easy part. General autophagy is conducted inside a phagophore. A phagophore is a double membrane bag that forms and encloses around objects inside a cell that need to be disposed of. The phagophore isolates the rubbish until it can be broken down. The formation of the phagophore occurs in a step wise fashion, as is illustrated in this image below which displays the autophagic removal of a mitochondria:

Mitophagy. Source: Circres

Once the phagophore has matured and fully enclosed the rubbish, the phagophore then waits to fuse with a lysosome. A lysosome is a bag of enzymes that break things like mitochondria down into tiny components that can either be used again, or disposed of outside the cell.

Ok, and what about the “priming of the mitochondria for autophagic recognition” step you mentioned above?

Within a cell, there needs to be a system of identifying old or dysfunctional parts. This is done by a process of labelling (or priming) the material that is going to be disposed of. Without such a system, rubbish would simply build up and phagophore would not know what to form around.

How is this labelling/priming done?

Mother nature has taken no chances with the important process of waste disposal, and there are multiple ways that the labelling can occur. For example, in the image below there are three of methods presented (A, B & C) for labelling mitochondria for disposal (and the phagophore can form – blue arc on the right):

The pathways to mitophagy. Source: AJPheart

And key amongst these various methods for our discussion today is the first one which involves two proteins called PTEN-induced putative kinase 1 (or PINK1) and Parkin.

What is special about them?

Well, approximately 20% of Parkinson’s cases are associated with particular genetic variations that render people vulnerable to developing the condition. Some of these mutations are in sections of DNA (called genes) that provide the instructions for proteins that are involved in the process of mitophagy. Two mitophagy-associated genes, in particular, are the focus of a lot of Parkinson’s-related research: PARK6 and PARK2

Can you guess which two proteins these genes provide the instructions for building???

That is right: PINK1 and Parkin (respectively)

What do PINK1 and Parkin do?

Both proteins appear to have many different functions, but their roles in the process of mitophagy are relatively well understood.

PINK1 acts like a kind of handle on the surface of mitochondria. In normal, healthy cells, the PINK1 protein attaches to the surface of mitochondria and it is slowly absorbed until it completely disappears from the surface and is degraded. In unhealthy cells, however, this process is inhibited and PINK1 starts to accumulate on the outer surface of the mitochondria. Lots of handles poking out of the surface of the mitochondria.

Now, if PINK1 is a handle, then Parkin is a flag that likes to hold onto the PINK1 handle. While exposed on the surface of mitochondria PINK1 starts grabbing the Parkin protein. This pairing is a signal to the cell that this particular mitochondrion (singular) is not healthy and needs to be removed. The pairing start the process that leads to the development of the phagophore and eventually mitophagy.

Pink1 and Parkin in normal (right) and unhealthy (left) situations. Source: Hindawi

In the absence of normal PINK1 or Parkin proteins, there is no handle-flag system and old/damaged mitochondria start to pile up. They are not disposed of appropriately and as a result the cell gets sick and ultimately dies.

Mitophagy. Source: Frontiersin

People with particular mutations in the PINK1 or Parkin genes are vulnerable to developing an early onset form of Parkinson’s. It is believed that the dysfunctional disposal of (and accumulation of) old mitochondria are part of the reason why these individuals develop the condition at such an early age.

For a very good review of the genetics of Parkinson’s disease – click here. Alternatively, have a look at our Genetics of Parkinson’s page.

Interesting. So what is this FASN-ating research you were talking about?

Before we discuss that, we need to go back in time a little bit.

Way back in 2012, just a few months before the Mayan calendar was indicating the end of the world (remember that?), this research report was published:

Title: Vitamin K2 is a mitochondrial electron carrier that rescues pink1 deficiency
Authors: Vos M, Esposito G, Edirisinghe JN, Vilain S, Haddad DM, Slabbaert JR, Van Meensel S, Schaap O, De Strooper B, Meganathan R, Morais VA, Verstreken P.
Journal: Science. 2012 Jun 8;336(6086):1306-10.
PMID: 22582012

In this study, the researchers wanted to know which genes could influence the outcome of a PINK1 genetic mutation. That is to say, they were seeking to determine which genes (when mutated) could rescue flies with no PINK1 gene. The PINK1-null flies have a great deal of trouble to fly, which provided the investigators with a useful, quantifiable measure of rescue – if you mutate a gene and the PINK1-null fly takes to the air, that is a gene to further investigate.

Drosophila (flies). Source: The Converstation

They conducted a genetic screen of flies, and they identified 24 genes that (when mutated) suppressed, and 32 genes that (when mutated) enhanced the flight defect in the PINK1 flies. One of the genes that (when mutated) exaggerated the flight defect in the PINK1 flies, was UBIAD1.

By mutating the UBIAD1 gene in the PINK1 flies, the investigators made it even harder for the flies to fly. UBIAD1 is an interesting antioxidant enzyme that is involved in the production of Vitamin K2 and coenzyme Q10. This suggested to the researchers that maybe feeding the flies Vitamin K2 or Coenzyme Q10 may actually rescue the flight defect in the PINK1 flies.

Coenzyme Q10 has had a long and colourful history with Parkinson’s research, demonstrating interesting results in the lab, but failing to replicate those beneficial effects in the clinic (Click here and here to read more on this). Vitamin K2, on the other hand was a novel compound for PINK1 and Parkinson’s, so the investigators decided to investigate it further.

The PINK1-null flies have muscles that have enlarged, clumped mitochondria, and the researchers found that treating these flies with Vitamin K2 partially rescued this feature. They also reported that normal flies exposed to a neurotoxin (rotenone) that impairs mitochondrial function, could be largely protected from the effect by treatment with Vitamin K2.

The investigators found that Vitamin K2 was achieving this result by serving as a mitochondrial electron carrier, which aids in maintain normal ATP production (the energy for the cell that we mentioned near the top of this post). This led the researchers to conclude that “Vitamin K2 may thus constitute a promising compound to treat mitochondrial pathology, also in PD patients suffering from Pink1 or Parkin deficiency”.

Has any other Parkinson’s research been conducted on Vitamin K2?

Yes, but it is very limited. For example, I can’t find any research involving animal models of Parkinson’s (happy to be corrected if I am wrong about this). Rather the research has all been conducted in cell culture conditions. Such as:

Title: Vitamins K interact with N-terminus α-synuclein and modulate the protein fibrillization in vitro. Exploring the interaction between quinones and α-synuclein.
Authors: da Silva FL, Coelho Cerqueira E, de Freitas MS, Gonçalves DL, Costa LT, Follmer C.
Journal: Neurochem Int. 2013 Jan;62(1):103-12.
PMID: 23064431                 (This article is OPEN ACCESS if you would like to read it)

These researchers found that Vitamins K2 delayed properties that under certain conditions prevented the conversion of Parkinson’s associated protein alpha synuclein from its normal form to a bunched (‘fibrillised’) version that is referred to as an oligomer – these oligomers are associated with the toxic effects of this protein.

Another research report found that Vitamins K2 can affect the helper cells in the brain:

Title: Vitamin K2 suppresses rotenone-induced microglial activation in vitro.
Authors: Yu YX, Li YP, Gao F, Hu QS, Zhang Y, Chen D, Wang GH.
Journal: Acta Pharmacol Sin. 2016 Sep;37(9):1178-89.
PMID: 27498777                (This article is OPEN ACCESS if you would like to read it)

Microglial cells are the resident immune cells in the brain. When something goes wrong, they become activated and they act as the first and main form of an immune defence in the brain. In this study, the researchers found that vitamin K2 suppressed the activation of microglia cells in a dose-dependent fashion.

Thus, Vitamin K2 has some interesting properties, but these need to be further investigated in additional models of Parkinson’s.

Interesting. Has Vitamin K2 ever been tested in the clinic?

Yes, but not in Parkinson’s.

Vitamin K2 produced by bacteria is known as MK-7. Most dietary supplements labeled “Vitamin K2” or “menaquinone” contain this bacterial form. But mammals synthesise a different kind of Vitamin K2 known as MK-4 or “menatetrenone”, which is concentrated in the brain, bone, and the vasculature.

There have been 9 clinical trials registered for Menatetrenone – according to the ClinicalTrials.gov website (Click here to see those trials). And there have been 348 clinical trials registered for Menaquinone (Click here to see those trials). I am not clear as to how well these compounds cross the blood brain barrier – the protective membrane surrounding the brain, which prevents many drugs from entering the organ.

Are there any side effects associated with menatetrenone?

Yes there are and they could be very serious.

Menatetrenone is a haemostatic agent. Haemostatics are drugs designed to stem blood-flow through the accelerated promotion of blood clotting. This means that menatetrenone should not be taken by anyone taking blood thinning medication, like warfarin. Vitamin K can undo the anticoagulant effect of warfarin, raising the risk of clotting (and possibly stroke). Thus, caution must be taken with this treatment.

There are also other possible side effects in the gastrointestinal tract, such as discomfort and diarrhea. This is because vitamin K is a fat-soluble vitamin. Fat-soluble vitamins are harder for the gut to absorb, bile is needed for this absorption. In addition, rather than simply slipping into the bloodstream like most water-soluble vitamins, fat-soluble vitamins need to bind to other proteins in order to travel around the blood system.

Given these side effects, is Vitamin K2 the only compound that protects against PINK1/Parkin issues?

Good question.

Recently the research group that conducted the original Vitamin K2 work published data on a second compound that seems to be able to counter the deficit of PINK1:

Title: Cardiolipin promotes electron transport between ubiquinone and complex I to rescue PINK1 deficiency.
Authors: Vos M, Geens A, Böhm C, Deaulmerie L, Swerts J, Rossi M, Craessaerts K, Leites EP, Seibler P, Rakovic A, Lohnau T, De Strooper B, Fendt SM, Morais VA, Klein C, Verstreken P.
Journal: J Cell Biol. 2017 Jan 30. pii: jcb.201511044.
PMID: 28137779               (This article is OPEN ACCESS if you would like to read it)

From the genetic screen conducted in their original study, the researchers from Belgium also identified a gene called Fatty acid synthase (or FASN). Full loss of FASN in flies is lethal (the fly dies), but a partial loss of FASN (only one of the two copies of the FASN gene is lost) rescues the PINK1 mutation defects (that is to say, partial loss of FASN results in the PINK1 mutant fly being able to fly and their mitochondrial ATP levels were restored).

Interestingly, the ability of reductions in FASN to rescue the PINK1 deficit is evolutionarily conserved. This means that it doesn’t just work in flies. The researchers also found that this effect works in mouse and human cells. When PINK1-deficient mouse and cells derived from people with PINK1 mutations were both treated with a drug that reduces FASN rescues the decreased ATP levels (and no, reductions in FASN didn’t rescue the ability of cells to fly!)

Are there any clinically available drugs that can reduce FASN?

Not quite yet.

FASN is a major target in oncology.

Tumor cells produce a lot of FASN and it plays a key role in tumor metabolism, cell survival and drug resistance. Cancer tumor cells are dependent on increased fatty acid production due to their high metabolic needs and rapid growth. Thus, there are several biotech firms seeking to inhibit FASN and they are now testing drugs in clinical trials.

Firstly, there is a compound called TVB-2640.

TVB-2640 is an orally bioavailable FASN inhibitor, which binds to and blocks FASN resulting in cancer cell death. There are currently three clinical trials of TVB-2640 being sponsored by a biotech company called 3-V Biosciences.

In November 2017, the company presented some of their Phase I clinical trial data, demonstrating that TVB-2640 was safe in healthy males (Click here for the press release and click here to read more about the clinical trial). There are also ongoing clinical trials of TVB-2640 (alone or in combination with other therapies) for various cancers (Click here and here to read more about those clinical trials).

The trial testing TVB-2640 in patients with solid tumors (this one) should be reporting results this year.

And this is the clinical trial I will be watching this year (which I mentioned in the intro).

If this drug is found to be effective in reducing FASN in cancers, it could be VERY interesting to test this drug in models of Parkinson’s before considering it for repurposing for people with PINK1 or Parkin-associated Parkinson’s. And there may be other drug companies preparing for clinical trials of their own FASN inhibitors (such GlaxoSmithKline with GSK2194069).

So what does it all mean?

Our understanding of genetic variations that are associated with increased risk of developing Parkinson’s has blossomed in the last two decades, not only providing us with insights into how the condition could be developing, but also providing us with novel avenues for treating the condition. Now there appears to be possible treatments on the horizon that help to rescue some of these deficits. It will be interesting to see how these compounds develop. I must state very clearly, however, that there is very little evidence currently supporting the reagents described in this post. They still require independent replication and thorough investigation in models of Parkinson’s to determine their efficacy and what (if any) side effects/issues may be associated with their long-term use. Thus far, all of the research has been largely conducted in flies and cells in petri dishes. We know very little about happens in mammalian models of Parkinson’s.

By highlighting the research here, I simply hope to encourage the Parkinson’s research community to have a look at the compounds discussed (and the Parkinson’s community can feel free to encourage the researcher as well!).

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EDITOR’S NOTE: The information provided by the SoPD website is for information and educational purposes only. Under no circumstances should it ever be considered medical or actionable advice. It is provided by research scientists, not medical practitioners. Any actions taken – based on what has been read on the website – are the sole responsibility of the reader. Any actions being contemplated by readers should firstly be discussed with a qualified healthcare professional who is aware of your medical history. While some of the information discussed in this post may cause concern, please speak with your medical physician before attempting any change in an existing treatment regime.

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