Huntington’s disease therapeutics…

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Searching for a viable treatment for Huntington’s Disease (HD) long has been a daunting challenge for the scientific community. Various teams have tried to inhibit histone deacetylation, as acetylation is disrupted by mutant huntingtin (Htt), refold mutant Htt to its normal form, and degrade mutant protein quicker. None of these methods worked. The only success we have had so far is by targeting transcription. It was found that, in the presence of Tetracycline, the mutant gene was ‘turned off’ and so not expressed, thus repressing the effects of HD. Tetracycline even caused a reversal of HD symptoms. It is now hoped that early-intervention gene therapy will prove to be an effective treatment. Since it is so difficult to target the very small difference (approx. 20 repeats) between mutant and non-mutant huntingtin, it is thought that small hairpin RNA (shRNA) may be used to specifically target only the mutant allele. Research into this possibility is ongoing.

The molecular pathogenesis in HD is decreased transcription. Scientists at King’s College London (KCL) have been working on increasing transcription through the use of histone deacetylase inhibitors (HDACi). Histone acetylation is decreased with the presence of mutant Htt since Htt interacts with CREB-binding protein (CBP), helping to open DNA (histone acetylation) in order to permit transcription, thus allowing the expression of certain genes. Mutant Htt stops that process by preventing DNA to unwind, effectively ceasing the expression of important genes. SAHA, an anti-cancer drug given to end-stage cancer patients, has been used to target HDAC1 and HDAC2. SAHA is too toxic, however, so the drug must be redesigned. Treatment with SAHA has demonstrated that cells that would normally die were rescued in Drosophila, mice, yeast, and cultured cells. All 11 HDACs were scanned, and HDAC4 was found to be the one that SAHA targeted. Labs are now in the process of designing non-toxic mimics of SAHA to target HDAC4.

For more about the disease please go to my Huntington’s Disease page.

Genetics of Parkinson’s Disease

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Parkinson’s Disease (PD) is not considered a genetically inheritable disease, however 15% of PD patients have a first degree relative with the disease. There are limited twin studies of PD and more evidence for environmental factors thus not really supporting the idea that it is an inheritable illness. However, if the disease is diagnosed at an early age (e.g. 30 years old), then it is highly          likely to be caused by a genetic mutation.

The genes that are associated with PD are as follows with their corresponding locus:

  • SNCA (gene) PARK1 (locus) - alpha synuclein is a structural brain protein of whichfragments are found in Alzheimer’s disease amyloid (NACP).
  • PRKN (gene) PARK2 (locus) - Parkin is involved in protein degredation as an ubiquitin-protein ligase. SNCA is a substrate and ubiquitination is a tag to be sent to the proteasome for degredation.
  • LRRK2 (gene) PARK8 (locus) - Leucine-rich repeat kinase 2 is an enzyme that when mutated causes a Lewy Body phenotype. G2019S is a mutation of LRRK2 common in North Africa, which increases kinase activity.
  • PINK1 (gene) PARK6 (locus) - PTEN-induces putative kinase is a mitochondrial associated protein, which is associated with young onset cases (prevalence 1-8%).
  • ATP13A2 (gene) – Lysosomal protein associated with Parkinsonian syndrome.
  • DJ-1 (gene) PARK7 (locus) – is a positive regulator of androgen-receptor dependent transcription. Prevalence is from 1-2% of early onset cases.

Types of Genetic Parkinson’s Disease

Mendelian Dominant PD
  1. PARK1 – duplications and triplications of SNCA (e.g. extra copy) with relatively few mutations.
  2. PARK8 (most common cause of mendelian PD) – mutations in LRRK2 which shows a phenotype of Lewy Bodies.

Mendelian Recessive PD

  1. PARK2 – deletions and homozygous mutations in PARKIN gene (autosomal recessive Juvenile PD). Typical juvenile/early onset from about 10-12 years of age, which is very rare.

Sporadic (Non-Mendelian PD)

  • Genome Wide Association (GWAS) have found the same genes as risk factors, however, with different polymorphisms than the Mendelian type PD – Two loci were identified at high significance: SNCA, MAPT or TAU. Identified new locus: PARK16 and there is suggestive evidence for LRRK2.
  • Candidate gene studies – identify a few loci.

Tau

Polymorphisms of Tau increase risk for PD, however, there is no accumulation of Tau. In contrast, Alzheimer’s Disease (AD) patients have the opposite with Tau accumulation increasing a risk in AD but not polymorphisms. The tau haplotype has been found on chromosome 17 with the MAPT gene and is seen to be in two orientations, meaning there has been an inversion (H1, H2). This causes an increase risk factor for PD, Pick’s Disease, as well as Supranuclear Palsy. The H1 haplotype results in an increase of tau, which is caused by an alteration of exon 10 splicing.

For more information please refer to my Parkinson’s Disease page.

Osteopontin: Neuroprotection in Parkinson’s Disease

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Parkinson’s disease (PD) research has had somewhat clinically successful trials with the alleviation of some symptoms with the use of Levodopa, however, scientists today are looking for a drug that will protect the actual neurons from dying during PD progression.

Rosagiline, a monoamine oxidase inhibitor (MAOI), also known as antidepressant, slows the disease progression of PD with low doses, however, not with higher doses, therefore, more testing needs to be done. Similarly but with more success, Cogane, a GDNF enhancer and BDNF synthesis stimulator has also been see to work as a treatment for PD. GDNF and BDNF are proteins that normally help neurons grow, however, injection of these proteins into the brain is almost impossible. Cogane can stimulate these proteins that are already in the brain during PD. This drug is currently in Phase II of its clinical trials, which is a very good sign for an advancement in a treatment for PD. On another note, another approach for PD treatment is being investigated. Scientists believe that maybe a novel approach is needed to really cure this disease.

Recent studies have been investigating endogenous (meaning naturally found in the body already) proteins that might play a role in the protection of neurons, aka neuroprotectants.  Osteopontin (OPN), an endogenous protein, has been found to be a neuroprotectant since it has been observed to increase in levels with oxidative stress and inflammation. In addition, OPN has been observed to also increase after a stroke, to protect the cells from dying. More importantly, during PD, there is a decreased level of endogenous OPN in dopaminergic neurons. This protein can act as a matrix protein, a cytokine as well as an adhesion protein. In addition, OPN is not selective to PD and therefore can also treat other neurodegenerative diseases such as Alzheimer’s Disease.

Researchers have observed a correlation between Osteopontin and GDNF. If GDNF is removed from the cells in vitro, then OPN neuroprotection is decreased and ceased. If levels of OPN are increased, consequently GDNF and BDNF levels are as well, suggesting the effects of OPN are mediated by GDNF and BDNF. However, in vivo, there was no increase, and more testing is taking place.

OPN has several phosphorylation sites and is a very large protein, therefore injection of the whole protein into PD patient’s brains is not the correct route of action for treatment.  Instead, the goal is to find chop up the protein to get a much smaller peptide and mimic it to use as a treatment. OPN is a protein that has several domains including many Calcium binding domains, and more
importantly for PD research the ability to bind to a RGD 

binding site, which is seen as a neuroprotectant (15 amino acids long – still too long!). This fragment has been truncated into a small hexamer (6 amino acids) peptide. This hexamer has been observed to have a role in neuroprotection in lipopolysaccharide-induced cell death. I am proud to say that my university, King’s College London, has created an intranasal route of administration for this truncated peptide to possibly be used as a treatment for PD. For the project details please click here. Intranasal injection of this OPN peptide has been used to induce neuroprotective actions during stroke, which is really a breakthrough! Now, we need to test to see if we can administer OPN to PD patients over a longer course of time at high enough doses for it to take an effect, and maybe, just maybe, we will have a successful neuroprotectant drug to help with the neuronal loss caused by Parkinson’s Disease.

The many biological functions of Osteopontin are listed below:

Levodopa (L-Dopa): A Gold Standard treatment for Parkinson’s Disease?

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Over the past several years, scientist have been searching for effective treatments to treat the symptoms of Parkinson’s Disease (PD) let alone cure it. Advances have been made in finding suitable symptomatic treatments for PD such as the use of Anticholinergics (used for the treatment of tremor at the early stages of PD), Glutamate antagonists (e.g. Amantadine to treat stiffness, tiredness and involuntary movements), and Dopamine agonists (e.g. apomorphine, ropinirole – to increase levels of dopamine in the brain). However these treatments are short-lived and usually come with many unwanted side effects, sometimes resulting in the patient preferring to stay off the medication and continue suffering from the symptoms of PD.

Levodopa (L-Dopa) has been the only drug that has some effective treatment, but even it has its downfalls. Initially the patient responds well to the drug and some symptoms seem to disappear. However, after prolonged use, patients can experience what is called the “on/off” phenomenon, where the drug works at some points (i.e. increases dopamine levels to sometimes superfluous amounts) and then completely ceases to work, therefore immobilising the patient completely causing dyskinesia, which can be very painful. L-Dopa is always used with COMT inhibitors  and MAO B inhibitors allowing more dopamine to reach the brain and to stabilise the chemical reaction to the Levodopa.

Even though L-Dopa is not a perfect treatment, it is the only one available for some successful symptomatic treatment. Every patient is different, therefore it is important that the correct method of administration of L-dopa (i.e. duodopa – see image to the right) and dosage is calculated to tailor to that patient’s needs.