This week interesting research was published in the journal EMBO that looked at the Parkinson’s-associated protein Leucine-rich repeat kinase 2 (or LRRK2).
In their study, the researchers discovered that lowering levels of LRRK2 protein (in cells and animals) affected the ability of Mycobacterium tuberculosis – the bacteria that causes Tuberculosis – to replicate.
In today’s post, we will discuss what Tuberculosis is, how it relates to LRRK2 and Parkinson’s, and we will consider why this is potentially REALLY big news for Parkinson’s.
Daedalus and Icarus. Source: Skytamer
In Greek Mythology, there is the tale of Daedalus and Icarus.
Daedalus was a really smart guy, who designed the labyrinth on Crete, which housed the Minotaur (the ‘part man, part bull’ beast). For all his hard work, however, Daedalus was shut up in a tower and held captive by King Minos to stop the knowledge of his Labyrinth from spreading to the general public.
But a mere tower was never going to stop Daedalus, and he set about fabricating wings for himself and his young son Icarus (who was also a captive).
Being stuck in the tower limited Daedalus’ access to feathers for making those wings, except of course for the large birds of prey that circled the tower awaiting the demise of Daedalus and his son. But he devised a clever way of throwing stones at the birds in such a way, that he is able to strike one bird and then the ricochet would hit a second bird.
And thus, the phase ‘killing two birds with one stone’ was born (or so it is said – there is also a Chinese origin for the phrase – Source).
Interesting. And this relates to Parkinson’s how?!?
Well, this week researchers in the UK have discovered that a protein associated with Parkinson’s is apparently also associated with another condition: Tuberculosis. And they also found that treatments being designed to target this protein in Parkinson’s, could also be used to fight Tuberculosis.
Two birds, one stone.
What is Tuberculosis?
A reader recently asked for an explanation of some recent research regarding diabetes and Parkinson’s.
You see, a significant proportion of the Parkinson’s community have glucose intolerance issues and some live with the added burden of diabetes. That said, the vast majority of diabetics do not develop PD. Likewise, the vast majority of people with Parkinson’s do not have a diagnosis of diabetes.
There does appear to be a curious relationship between Parkinson’s and diabetes, with some recent research suggests that this association can be detrimental to the course of the condition.
In today’s post we will look at what what diabetes is, consider the associations with Parkinson’s, and we will discuss the new research findings.
Foreman and Ali. Source: Voanews
1974 was an amazing year.
On October 30th, the much-hyped heavyweight title match – the ‘Rumble in the Jungle’ – between George Foreman and Muhammad Ali took place in Kinshasa, Zaire (Democratic Republic of the Congo).
Stephen King. Source: VanityFair
A 26-year-old author named Stephen King published his debut novel, “Carrie” (April 5, with a first print-run of just 30,000 copies).
Lucy. Source: Youtube
The fossil remains of a 3.2 million years old hominid skeleton was discovered in Ethiopia (November 24th). It was named ‘Lucy’ – after the song “Lucy in the Sky with Diamonds” by The Beatles which was played repeatedly in the expedition camp the evening after the team’s first day of work on the site (Source).
And Richard Nixon becomes the first US president to resign from office (August 9th).
President Richard Nixon. Source: Fee
In addition to all of this, in December of 1974, a small study was published in the Journal of Chronic Diseases.
It dealt with Parkinson’s and it presented a rather startling set of findings:
A new research report looking at the use of cholesterol-reducing drugs and the risk of developing Parkinson’s disease has just been published in the scientific journal Movement disorders.
The results of that study have led to some pretty startling headlines in the media, which have subsequently led to some pretty startled people who are currently taking the medication called statins.
In todays post, we will look at what statins are, what the study found, and discuss what it means for our understanding of Parkinson’s disease.
Cholesterol forming plaques (yellow) in the lining of arteries. Source: Healthguru
Cholesterol gets a lot of bad press.
Whether it’s high and low, the perfect balance of cholesterol in our blood seems to be critical to our overall health and sense of wellbeing. At least that is what we are constantly being told this by media and medical professionals alike.
But ask yourself this: Why? What exactly is cholesterol?
Good question. What is cholesterol?
Cholesterol (from the Greek ‘chole‘- bile and ‘stereos‘ – solid) is a waxy substance that is circulating our bodies. It is generated by the liver, but it is also found in many foods that we eat (for example, meats and egg yolks).
The chemical structure of Cholesterol. Source: Wikipedia
Cholesterol falls into one of three major classes of lipids – those three classes of lipids being Triglycerides, Phospholipids and Steroids (cholesterol is a steroid). Lipids are major components of the cell membranes and thus very important. Given that the name ‘lipids’ comes from the Greek lipos meaning fat, people often think of lipids simply as fats, but fats more accurately fall into just one class of lipids (Triglycerides).
Like many fats though, cholesterol dose not dissolve in water. As a result, it is transported within the blood system encased in a protein structure called a lipoprotein.
The structure of a lipoprotein; the purple C inside represents cholesterol. Source: Wikipedia
Lipoproteins have a very simple classification system based on their density:
- very low density lipoprotein (VLDL)
- low density lipoprotein (LDL)
- intermediate density lipoprotein (IDL)
- high density lipoprotein (HDL).
Now understand that all of these different types of lipoproteins contain cholesterol, but they are carrying it to different locations and this is why some of these are referred to as good and bad.
The first three types of lipoproteins carry newly synthesised cholesterol from the liver to various parts of the body, and thus too much of this activity would be bad as it results in an over supply of cholesterol clogging up different areas, such as the arteries.
LDLs, in particular, carry a lot of cholesterol (with approximately 50% of their contents being cholesterol, compared to only 20-30% in the other lipoproteins), and this is why LDLs are often referred to as ‘bad cholesterol’. High levels of LDLs can result in atherosclerosis (or the build-up of fatty material inside your arteries).
Progressive and painless, atherosclerosis develops as cholesterol silently and slowly accumulates in the wall of the artery, in clumps that are called plaques. White blood cells stream in to digest the LDL cholesterol, but over many years the toxic mess of cholesterol and cells becomes an ever enlarging plaque. If the plaque ever ruptures, it could cause clotting which would lead to a heart attack or stroke.
So yeah, some lipoproteins can be considered bad.
HDLs, on the other hand, collects cholesterol and other lipids from cells around the body and take them back to the liver. And this is why HDLs are sometimes referred to as “good cholesterol” because higher concentrations of HDLs are associated with lower rates of atherosclerosis progression (and hopefully regression).
But why is cholesterol important?
While cholesterol is usually associated with what is floating around in your bloodstream, it is also present (and very necessary) in every cell in your body. It helps to produce cell membranes, hormones, vitamin D, and the bile acids that help you digest fat.
It is particularly important for your brain, which contains approximately 25 percent of the cholesterol in your body. Numerous neurodegenerative conditions are associated with cholesterol disfunction (such as Alzheimer’s disease and Huntington’s disease – Click here for more on this). In addition, low levels of cholesterol is associated with violent behaviour (Click here to read more about this).
Are there any associations between cholesterol and Parkinson’s disease?
The associations between cholesterol and Parkinson’s disease is a topic of much debate. While there have been numerous studies investigating cholesterol levels in blood in people with Parkinson’s disease, the results have not been consistent (Click here for a good review on this topic).
Rather than looking at cholesterol directly, a lot of researchers have chosen to focus on the medication that is used to treat high levels of cholesterol – a class of drugs called statins.
Title: Prospective study of statin use and risk of Parkinson disease.
Authors: Gao X, Simon KC, Schwarzschild MA, Ascherio A.
Journal: Arch Neurol. 2012 Mar;69(3):380-4.
PMID: 22410446 (This article is OPEN ACCESS if you would like to read it)
In this study the researchers conduced a prospective study involving the medical details of 38 192 men and 90 874 women from two huge US databases: the Nurses’ Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS).
NHS study was started in 1976 when 121,700 female registered nurses (aged 30 to 55 years) completed a mailed questionnaire. They provided an overview of their medical histories and health-related behaviours. The HPFS study was established in 1986, when 51,529 male health professionals (40 to 75 years) responded to a similar questionnaire. Both the NHS and the HPFS send out follow-up questionnaires every 2 years.
By analysing all of that data, the investigators found 644 cases of Parkinson’s disease (338 women and 306 men). They noticed that the risk of Parkinson’s disease was approximately 25% lower among people currently taking statins when compared to people not using statins. And this association was significant in statin users younger than 60 years of age (P = 0.02).
What are statins?
Also known as HMG-CoA reductase inhibitors, statins are a class of drug that inhibits/blocks an enzyme called 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase.
HMG-CoA reductase is the key enzyme regulating the production of cholesterol from mevalonic acid in the liver. By blocking this process statins help lower the total amount of cholesterol available in your bloodstream.
Statins are used to treat hypercholesterolemia (also called dyslipidemia) which is high levels of cholesterol in the blood. And they are one of the most widely prescribed classes of drugs currently available, with approximately 23 percent of adults in the US report using statin medications (Source).
Now, while the study above found an interesting association between statin use and a lower risk of Parkinson’s disease, the other research published on this topic has not been very consistent. In fact, a review in 2009 found a significant associations between statin use and lower risk of Parkinson’s disease was observed in only two out of five prospective studies (Click here to see that review).
New research published this week has attempted to clear up some of that inconsistency, by starting with a huge dataset and digging deep into the numbers.
So what new research has been published?
Title: Statins may facilitate Parkinson’s disease: Insight gained from a large, national claims database
Authors: Liu GD, Sterling NW, Kong L, Lewis MM, Mailman RB, Chen H, Leslie D, Huang X
Journal: Movement Disorder, 2017 Jun;32(6):913-917.
Using the MarketScan Commercial Claims and Encounters database which catalogues the healthcare use and medical expenditures of more than 50 million employees and their family members each year, the researcher behind that study identified 30,343,035 individuals that fit their initial criteria (that being “all individuals in the database who had 1 year or more of continuous enrolment during January 1, 2008, to December 31, 2012, and were 40 years of age or older at any time during their enrolment”). From this group, the researcher found a total of 21,599 individuals who had been diagnosed with Parkinson’s disease.
In their initial analysis, the researchers found that Parkinson’s disease was positively associated with age, male gender, hypertension, coronary artery disease, and usage of cholesterol-lowering drugs (both statins and non-statins). The condition was negatively associated with hyperlipidemia (or high levels of cholesterol). This result suggests not only that people with higher levels of cholesterol have a reduced chance of developing Parkinson’s disease, but taking medication to lower cholesterol levels may actually increase ones risk of developing the condition.
One interesting finding in the data was the effect that different types of statins had on the association.
Statins can be classified into two basic groups: water soluble (or hydrophilic) and lipid soluble (or lipophilic) statins. Hydrophilic molecule have more favourable interactions with water than with oil, and vice versa for lipophilic molecules.
Hydrophilic vs lipophilic molecules. Source: Riken
Water soluble (Hydrophilic) statins include statins such as pravastatin and rosuvastatin; while all other available statins (eg. atorvastatin, cerivastatin, fluvastatin, lovastatin and simvastatin) are lipophilic.
In this new study, the researchers found that the association between statin use and increased risk of developing Parkinson’s disease was more pronounced for lipophilic statins (a statistically significant 58% increase – P < 0.0001), compared to hydrophilic statins (a non-significant 19% increase – P = 0.25). One possible explanation for this difference is that lipophilic statins (like simvastatin and atorvastatin) cross the blood-brain barrier more easily and may have more effect on the brain than hydrophilic ones.
The investigators also found that this association was most robust during the initial phase of statin treatment. That is to say, the researchers observed a 82% in risk of PD within 1 year of having started statin treatment, and only a 37% increase five years after starting statin treatment.; P < 0.0001). Given this finding, the investigators questioned whether statins may be playing a facilitatory role in the development of Parkinson’s disease – for example, statins may be “unmasking” the condition during its earliest stages.
So statins are bad then?
Can I answer this question with a diplomatic “I don’t know”?
It is difficult to really answer that question based on the results of just this one study. This is mostly because this new finding is in complete contrast to a lot of experimental research over the last few years which has shown statins to be neuroprotective in many models of Parkinson’s disease. Studies such as this one:
Title: Simvastatin inhibits the activation of p21ras and prevents the loss of dopaminergic neurons in a mouse model of Parkinson’s disease.
Authors: Ghosh A, Roy A, Matras J, Brahmachari S, Gendelman HE, Pahan K.
Journal: J Neurosci. 2009 Oct 28;29(43):13543-56.
PMID: 19864567 (This study is OPEN ACCESS if you would like to read it)
In this study, the researchers found that two statins (pravastatin and simvastatin – one hydrophilic and one lipophilic, respectively) both exhibited the ability to suppress the response of helper cells in the brain (called microglial) in a neurotoxin model of Parkinson’s disease. This microglial suppression resulted in a significant neuroprotective effect on the dopamine neurons in these animals.
Another study found more Parkinson’s disease relevant effects from statin treatment:
TItle: Lovastatin ameliorates alpha-synuclein accumulation and oxidation in transgenic mouse models of alpha-synucleinopathies.
Authors: Koob AO, Ubhi K, Paulsson JF, Kelly J, Rockenstein E, Mante M, Adame A, Masliah E.
Journal: Exp Neurol. 2010 Feb;221(2):267-74.
PMID: 19944097 (This study is OPEN ACCESS if you would like to read it)
In this study, the researchers treated two different types of genetically engineered mice (both sets of mice produce very high levels of alpha synuclein – the protein closely associated with Parkinson’s disease) with a statin called lovastatin. In both groups of alpha synuclein producing mice, lovastatin treatment resulted in significant reductions in the levels of cholesterol in their blood when compared to the saline-treated control mice. The treated mice also demonstrated a significant reduction in levels of alpha synuclein clustering (or aggregation) in the brain than untreated mice, and this reduction in alpha synuclein accumulation was associated with a lessening of pathological damage in the brain.
So statins may not be all bad?
One thing many of these studies fail to do is differentiate between whether statins are causing the trouble (or benefit) directly or whether simply lowering cholesterol levels is having a negative impact. That is to say, do statins actually do something else? Other than lowering cholesterol levels, are statins having additional activities that could cause good or bad things to happen?
The recently published study we are reviewing in this post suggested that non-statin cholesterol medication is also positively associated with developing Parkinson’s disease. Thus it may be that statins are not bad, but rather the lowering of cholesterol levels that is. This raises the question of whether high levels of cholesterol are delaying the onset of Parkinson’s disease, and one can only wonder what a cholesterol-based process might be able to tell us about the development of Parkinson’s disease.
If the findings of this latest study are convincingly replicated by other groups, however, we may need to reconsider the use of statins not in our day-to-day clinical practice. At the very least, we will need to predetermine which individuals may be more susceptible to developing Parkinson’s disease following the initiation of statin treatment. It would actually be very interesting to go back to the original data set of this new study and investigate what addition medical features were shared between the people that developed Parkinson’s disease after starting statin treatment. For example, were they all glucose intolerant? One would hope that the investigators are currently doing this.
Are Statins currently being tested in the clinic for Parkinson’s disease?
(Oh boy! Tough question) Yes, they are.
There is currently a nation wide study being conducted in the UK called PD STAT.
Is this dangerous given the results of the new research study?
(Oh boy! Even tougher question!)
Again, we are asking this question based on the results of one recent study. Replication with independent databases is required before definitive conclusions can be made.
There have, however, been previous clinical studies of statins in neurodegenerative conditions and these drugs have not exhibited any negative effects (that I am aware of). In fact, a clinical trial for multiple sclerosis published in 2014 indicated some positive results for sufferers taking simvastatin:
Title: Effect of high-dose simvastatin on brain atrophy and disability in secondary progressive multiple sclerosis (MS-STAT): a randomised, placebo-controlled, phase 2 trial.
Authors: Chataway J, Schuerer N, Alsanousi A, Chan D, MacManus D, Hunter K, Anderson V, Bangham CR, Clegg S, Nielsen C, Fox NC, Wilkie D, Nicholas JM, Calder VL, Greenwood J, Frost C, Nicholas R.
Journal: Lancet. 2014 Jun 28;383(9936):2213-21.
PMID: 24655729 (This article is OPEN ACCESS if you would like to read it)
In this double-blind clinical study (meaning that both the investigators and the subjects in the study were unaware of which treatment was being administered), 140 people with multiple sclerosis were randomly assigned to receive either the statin drug simvastatin (70 people; 40 mg per day for the first month and then 80 mg per day for the remainder of 18 months) or a placebo treatment (70 people).
Patients were seen at 1, 6, 12, and 24 months into the study, with telephone follow-up at months 3 and 18. MRI brain scans were also made at the start of the trial, and then again at 12 months and 25 months for comparative sake.
The results of the study indicate that high-dose simvastatin was well tolerated and reduced the rate of whole-brain shrinkage compared with the placebo treatment. The mean annualised shrinkage rate was significantly lower in patients in the simvastatin group. The researchers were very pleased with this result and are looking to conduct a larger phase III clinical trial.
Other studies have not demonstrated beneficial results from statin treatment, but they have also not observed a worsening of the disease conditions:
Title: A randomized, double-blind, placebo-controlled trial of simvastatin to treat Alzheimer disease.
Authors:Sano M, Bell KL, Galasko D, Galvin JE, Thomas RG, van Dyck CH, Aisen PS.
Journal: Neurology. 2011 Aug 9;77(6):556-63.
PMID: 21795660 (This article is OPEN ACCESS if you would like to read it)
In this study, the investigators recruited a total of 406 individuals were mild to moderate Alzheimer’s disease, and they were randomly assigned to two groups: 204 to simvastatin (20 mg/day, for 6 weeks then 40 mg per day for the remainder of 18 months) and 202 to placebo control treatment. While Simvastatin displayed no beneficial effects on the progression of symptoms in treated individuals with mild to moderate Alzheimer’s disease (other than significantly lowering of cholesterol levels), the treatment also exhibited no effect on worsening the disease.
So what does it all mean?
Research investigating cholesterol and its association with Parkinson’s disease has been going on for a long time. This week a research report involving a huge database was published which indicated that using cholesterol reducing medication could significantly increase one’s risk of developing Parkinson’s disease.
These results do not mean that someone being administered statins is automatically going to develop Parkinson’s disease, but – if the results are replicated – it may need to be something that physicians should consider before prescribing this class of drug.
Whether ongoing clinical trials of statins and Parkinson’s disease should be reconsidered is a subject for debate well above my pay grade (and only if the current results are replicated independently). It could be that statin treatment (or lowering of cholesterol) may have an ‘unmasking’ effect in some individuals, but does this mean that any beneficial effects in other individuals should be discounted? If preclinical data is correct, for example, statins may reduce alpha synuclein clustering in some people which could be beneficial in Parkinson’s.
As we have said above, further research is required in this area before definitive conclusions can be made. This is particularly important given the inconsistencies of the previous research results in the statin and Parkinson’s disease field of investigation.
EDITORIAL 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.
The banner for today’s post was sourced from HarvardHealth
Performer Miley Cyrus says that “Pink isn’t just a colour, it’s an attitude!”
Whether that is true or not is not for us to say.
What we can tell you is that ‘Pink’ is also a gene which is associated with Parkinson’s disease. And not just any form of Parkinson’s disease – people with early onset Parkinson’s (diagnosed before 40 years of age) often have specific mutations in this gene. And recently there has been new research published which may help these particular individuals.
Today’s post will review the new research and look at what it means for people with early onset Parkinson’s disease.
The actor Michael J Fox requires no introduction.
Especially in the Parkinson’s community where his Michael J Fox Foundation has revolutionised the funding and supporting of Parkinson’s disease research (INCREDIBLE FACT: Since 2000, The Michael J. Fox Foundation has funded more than US$450 MILLION of Parkinson’s disease research) and is leading the charge in the search for a cure for this condition.
Mr Fox has become one of the foremost figures in raising awareness about the disease that he himself was diagnosed with at just 29 years of age.
Wow, so young?
It is a common mistake to consider Parkinson’s disease a condition of the aged portion of society. While the average age of diagnosis floats around 65 years of age, it is only an average. The overall range of that extends a great distance in both directions.
Being diagnosed so young, Mr Fox would be considered to have early onset Parkinson’s disease.
What is early onset Parkinson’s disease?
Broadly speaking there are three basic divisions of Parkinson’s disease across different age ranges:
- Juvenile-onset Parkinson disease – onset before age 20 years
- Early-onset Parkinson disease – before age 50 years
- Late-onset Parkinson disease – after age 50 years is considered
The bulk of people with Parkinson’s disease are considered ‘late-onset’. The Juvenile-onset version of the condition, on the other hand, is extremely rare but cases do pop up regularly in the media (For example, click here). We have previously written about Juvenile-onset Parkinson disease (Click here for that post).
Early-onset Parkinson disease is more common than the juvenile form, but still only makes up a fraction of the overall Parkinsonian population. Some of those affected call themselves 1 in 20 as this is considered by some the ratio of early-onset Parkinson’s compared to late-onset.
How prevalent is early onset Parkinson’s?
In 2009, Parkinson’s UK published a report on the prevalence of Parkinson’s disease in the UK.
Using the General Practice Research Database (GPRD), which houses information about 7.2% of the UK population (or 3.4 million people in 2009), Parkinson’s UK found that the frequency of Parkinson’s disease in the general public was 27 cases in every 10,000 people (or 1 person in every 370 of the general population). The prevalence is higher in men (31 in every 10,000 compared to 24 in every 10,000 among females)
As you can see from the table above, the number of people affected by early onset Parkinson’s disease is small when compared to the late-onset population.
Officially, the prevalence of early onset Parkinson’s in Europe is estimated to be 1 in every 8,000 people in the general population (Source: Orphanet). This makes the population of affected individuals approximately 5-10 % of all people with Parkinson’s. Hence the 1 in 20 label mentioned above.
Like older onset Parkinson’s, males are more affected than females (1.7 males to every 1 female case). In addition, women generally develop the disease two years later than men.
So what does ‘Pink’ have to do with early onset Parkinson’s?
First, let’s have a look at ‘Pink’ the gene.
PTEN-induced putative kinase 1 (or PINK1; also known as PARK6) is a gene that is thought to protect cells. Specifically, Pink1 is believed to interact with another Parkinson’s disease-associated protein called Parkin (also known as PARK2). Pink1 grabs Parkin and causes it to bind to dysfunctional mitochondria. Parkin then signals to the rest of the cell for that particular mitochondria to be disposed of. This is an essential part of the cell’s garbage disposal system.
Hang on a second. Remind me again: what are mitochondria?
Mitochondria are the power house of each cell. They keep the lights on. Without them, the lights go out and the cell dies.
Mitochondria and their location in the cell. Source: NCBI
You may remember from high school biology class that mitochondria are bean-shaped objects within the cell. They convert energy 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 and highly organised within the cell, being moved around to wherever they are needed.
When a cell is stressed by a toxic chemical, the organisation of mitochondria breaks down (as is shown in the image below, where everything except mitochondria (in green) and the nucleus (blue) has been made invisible:
Mitochondria (green) in health cells (left) and in unhealthy cells (right).
The nucleus of the cell is in blue. Source: Salk Institute
In normal, healthy cells, PINK1 is absorbed by mitochondria and eventually degraded. In unhealthy cells, however, this process is inhibited and PINK1 starts to accumulate on the outer surface of the mitochondria. There, it starts grabbing the PARKIN protein. This pairing is a signal to the cell that this particular mitochondria is not healthy and needs to be removed.
Pink1 and Parkin in normal (right) and unhealthy (left) situations. Source: Hindawi
The process by which mitochondria are removed is called autophagy. Autophagy is an absolutely essential function in a cell. Without it, old proteins will pile up making the cell sick and eventually it dies. Through the process of autophagy, the cell can break down the old protein, clearing the way for fresh new proteins to do their job.
Think of autophagy as the waste disposal process of the cell.
So why is Pink1 important to Parkinson’s disease?
In 2004 this research article was published:
Title: Hereditary early-onset Parkinson’s disease caused by mutations in PINK1
Authors: Valente EM, Abou-Sleiman PM, Caputo V, Muqit MM, Harvey K, Gispert S, Ali Z, Del Turco D, Bentivoglio AR, Healy DG, Albanese A, Nussbaum R, González-Maldonado R, Deller T, Salvi S, Cortelli P, Gilks WP, Latchman DS, Harvey RJ, Dallapiccola B, Auburger G, Wood NW.
Journal: Science. 2004 May 21;304(5674):1158-60.
The researchers in this study were the first to report that mutations in the Pink1 gene were associated with increased risk of Parkinson’s disease. They found three families in Europe that exhibited a very similar kind of Parkinson’s disease and by analysing their DNA they determined that mutations in the Pink1 gene were directly linked to the condition.
They also looked at where in the cell Pink1 protein was located, noting the close contact with the mitochondria. In addition, they noted that the normal Pink1 protein provided the cell with protection against a toxic chemical, while the mutated version of Pink1 did not. These findings led the researchers to conclude that Pink1 and mitochondria may be involved in the underlying mechanisms of Parkinson’s disease.
And this initial study was quickly followed up 7 months later by this report:
Title: Analysis of the PINK1 gene in a large cohort of cases with Parkinson disease.
Authors: Rogaeva E, Johnson J, Lang AE, Gulick C, Gwinn-Hardy K, Kawarai T, Sato C, Morgan A, Werner J, Nussbaum R, Petit A, Okun MS, McInerney A, Mandel R, Groen JL, Fernandez HH, Postuma R, Foote KD, Salehi-Rad S, Liang Y, Reimsnider S, Tandon A, Hardy J, St George-Hyslop P, Singleton AB.
Journal: Arch Neurol. 2004 Dec;61(12):1898-904.
In this study, the researchers analysed the Pink1 gene in 289 people with Parkinson’s disease and 80 neurologically normal control subjects. They identified 27 genetic variations, including a mutation in 2 unrelated early-onset Parkinson disease patients. They concluded that autosomal recessive mutations in PINK1 result in a rare form of early-onset Parkinson’s disease.
What does autosomal recessive mean?
Autosomal recessive means two copies of an abnormal gene must be present in order for the disease or trait to develop. That is to say, both parents will be carrying one copy of the mutation.
Mutations in the Pink1 gene have now been thoroughly analysed, with many mutations identified (the red and blue arrows in the image below). It is important, however, to understand that not all of those mutations are associated with Parkinson’s disease.
Looks complicated. Genetic variations in the Pink1 gene. Source: APS
So how do mutations in the Pink1 gene cause Parkinson’s disease?
We believe that the mutations in the Pink1 DNA result in malformed Pink1 protein. This results in Pink1 not being able to do what it is supposed to do. You will remember what we wrote above: Pink1 grabs Parkin when mitochondria get sick and Parkin signals for that mitochondria is be disposed of. Well, in the absence a properly functioning Pink1, we believe that there is a build up of sick mitochondria and this is what kills off the cell. All Parkinson’s disease-associated mutations in the Pink1 gene inhibit the ability of Pink1 grab parkin (Click here for more on this).
And we see this in flies.
Flies. Source: TheConservation
Flies (or drosophila) are a regular feature in biological research. Given their short life cycle, they can be used to quickly determine the necessity and function of particular genes. Yes, they are slightly different to us, but quite often the same biological principles apply.
Take Pink1 for example.
When scientists mutate the Pink1 gene in flies, it leads to the loss of flight muscles and male sterility. These effects both appear to be due to the kind of mitochondrial issues we were discussing above. One really amazing fact is that the human version of Pink1 can actually rescue the flies that have their Pink1 gene mutated. This is remarkable because across evolution genes begin to differ slightly resulting in some major differences by the time you get to humans. The fact that Pink1 is similar between both flies and humans shows that it has been relatively well conserved (functionally at least).
And given that we see similarities in the Pink1 gene and function between flies and humans, then perhaps we can apply what we see in flies to humans with regards to treatments.
Which brings us (finally!) to the research paper we wanted to look at today:
Title: Enhancing NAD+ salvage metabolism is neuroprotective in a PINK1 model of Parkinson’s disease<
Authors: Lehmann S, Loh SH, Martins LM.
Journal: Biol Open. 2016 Dec 23. pii: bio.022186.
PMID: 28011627 (this article is OPEN ACCESS if you would like to read it)
In this study, the researchers analysed Pink1 flies and found alterations in the activity of an enzyme called nicotinamide adenine dinucleotide (or NAD+). NAD+ is one of the major targets for the anti-aging crowd and there is some very interesting research being done on it (Click here for a good review on this). NAD+ is a coenzyme found in all living cells. A coenzyme functions by carrying electrons from one molecule to another (Click here for a nice animation that will explain this better). The researchers found that Pink1 mutant flies have decreased levels of NAD+.
The researchers were curious if a diet supplemented with the NAD+ would rescue the mitochondrial defects seen in the Pink1 mutant fly. Specifically, they fed the flies a diet high in the NAD+ precursor nicotinamide (being a precursor means that nicotinamide can be made into NAD+ once inside a cell). They found that not only did nicotinamide rescue the mitochondrial problems in the flies, but it also protected neurons from degeneration.
So why is the title of this post talking about Niacin and not nicotinamide?
Niacin (also known as vitamin B3 or nicotinic acid) – like nicotinamide – is also a precursor of NAD+. And in their discussion of the study, the researchers noted that a high level of dietary niacin has been associated with a reduced risk of developing Parkinson’s disease (Click here and here for more on this).
The researchers were quick to point out that while a high Niacin diet may be beneficial, it could not be considered a cure in anyway for people with Parkinson’s disease because although it may be able to slow the cell death it would not be able to replace the cells that have already been lost.
So what does it all mean?
Hang on a second. We’re not finished yet.
Numerous media outlets have made a big fuss about the Niacin diet angle to this research, and they have ignored another really interesting finding:
In their study the researchers mutated another gene in the Pink1 flies which also resulted in improved mitochondrial function and neuroprotection. That gene was Poly (ADP-ribose) polymerase (or PARP). Parp is an enzyme involved in DNA repair and cell division. It is produced in very high levels in many types of cancer and medication that inhibit or block Parp are being tested in the clinic as therapies in those cancers.
Interestingly, blocking Parp has been previously shown to be beneficial for cell survival in models of Parkinson’s disease (Click here and here for more information on this). So in addition to changing to a high niacin diet, it would be interesting to follow up this results as well.
Particularly for people with the Pink1 mutation.
And this is where the results of this study are particularly interesting: they may relate specifically to a small population within the Parkinson’s community – those with Pink1 mutations. It would be interesting to begin discussing and designing clinical studies that focus particularly on people in this population (similar to the Ambroxol study – click here for our post on this).
So what does it all mean? (again)
The results of the present study demonstrate two means by which people with a particular genetic mutation could be treated for Parkinson’s disease. Obviously further research is required, but the idea that we are approaching an age in Parkinson’s disease research where treatments could be personalised is very appealing. It will be interesting to see where all of this goes.
EDITOR’S NOTE: If nothing we have written here makes any sense, then maybe this video will help:
The banner for today’s post was sourced from Wallpapersinhq
“The devil is in the detail”
A frequently used quote and sage words when analysing scientific data, especially clinical trial data.
Nilotinib is a cancer drug from Novartis that has the Parkinson’s community very excited. In October 2015, researchers at Georgetown University announced that a phase 1 open-label clinical study involving 12 people with Parkinson’s had demonstrated some pretty impressive results (click here to read more about this). The results of that first clinical trial have been published (click here to read more on this), but follow up studies have been hampered by study design issues (click here for more on this).
Today a letter to the editor of the Journal of Parkinson’s disease (published in this months issue) was brought to our attention (click here to read the letter). It queries one important aspect of the results from that first Nilotinib clinical trial for Parkinson’s disease.
For reasons which we will outline below, a small change like this in a clinical trial could have major implications for the end results.
What are MAO-B inhibitors?