A Yeast Contribution For The Treatment Of Parkinson’s Disease

Scientists have just identified several molecules capable of reversing the brain abnormalities of Parkinson’s disease (PD), while also uncovering new clues for its origin in a study just published in the journal Disease Models and Mechanisms (1). PD is characterised by abnormal deposits of a brain protein called alpha-synuclein throughout the damaged brain regions, but exactly what they do there is not clear. The fact that their numbers and spreading are associated disease progression has made them, however, a major point of interest in PD research. The work now published suggests that these deposits are actually a normal physiological process to purge unwanted proteins but, when “overloaded”, they can also cause of the cellular abnormalities seen in PD neurons and, ultimately, neural death. This would explain why the disease tends to appear later in life when the whole metabolism (including this mechanism) becomes less efficient, and also why neurons are particularly susceptible as they are one of the few cells of the body that are not replaced when old and less capable. The study uses a yeast model of PD showing once again the power of simple organism models in the understanding of extremely complex human diseases.

PD is neurodegenerative disease characterised by increasing motor problems - tremors, rigidity and balance and coordination problems - that can leave the patient incapable of perform the simplest of everyday task. Many patients also suffer from non-motor symptoms, including dementia. There is also widespread death of dopamine-producing (dopaminergic) neurons in a part of the brain called the substantia nigra. Since dopamine acts as messenger between this region (the control centre) and other neurons around the body to ensure proper regulation of the body’s movement, these deaths are believed to cause PD motor disability.

Although the symptoms can be treated with dopamine replacement therapies, as the disease progresses, they stop working and, more importantly, PD is, ultimately, incurable. With the spread of the disease throughout an increasing aging human population bringing dramatic financial and social costs (who will take care of these millions of patients?), new treatments and/or a cure are now being exhaustively researched.

A major focus of the research has been a brain protein of unknown function called alpha-synuclein. In fact, deposits of abnormally folded alpha-synuclein (a certain folding is associated to the proper functioning of each protein) are found in inclusions dispersed all over the damaged brain areas of PD patients. The role of these inclusions in disease is not known with hypotheses ranging from having no importance, to contribute to neural death or even serve to avoid death by rendering harmless toxic misfolded proteins. What is known, however, is that these alpha-synuclein inclusions are excellent markers of disease progression – they accompany the brain degeneration.

In 2003 Tiago Outeiro - a Portuguese scientist and one of the first authors of the new study - and Susan Lindquist – the team leader in both studies – created a yeast model of PD by inserting the alpha-synuclein gene in yeast, an organism that normally does not have the protein. Remarkably, this created in yeast some of the cellular abnormalities seen in PD affected neurons. And as alpha-synuclein quantities increased, also the numbers of inclusions containing the protein, in such a way that led the researchers to suggest that these were, in fact, a physiological process for getting rid of unwanted proteins. And that maybe PD appeared when the capacity of the system was exceed. This hypothesis was supported by the fact that multiplications of the normal alpha-synuclein gene (leading to protein overproduction) were known to cause some forms of human PD, and also by the disease tendency for a late onset, probably due to an aging and less metabolically capable body.

To test this possibility in the study now published, Linhui Julie Su, Pavan K. Auluck, Tiago Fleming Outeiro and Susan Lindquist, working at the Whitehead Institute for Biomedical Research, Cambridge USA, created yet another yeast PD model this time with even higher levels of alpha-synuclein (High-syn) by inserting extra copies of the gene in the yeast genome. This PD model was then compared with yeast producing none or intermediate levels of alpha-synuclein (Int-syn) (this last organism was the one used in the 2003 study)

Remarkably, the new High-syn yeast suffered from several more of the cellular abnormalities characteristic of PD than the Int-syn yeast. The new abnormalities included problems with mitochondria (the energy producing factories of the cell) as well as accumulation of toxic free radicals, in addition to the abnormalities in lipid transport mechanisms already detected in Int-syn yeast. Problems in mitochondria and accumulation of free radicals are particularly interesting as, although seen in many PD patients, until now they had been impossible to link to alpha-synuclein.

Next, to exploit the fact that the new (High-syn ) yeast PD model shared so many cellular features with its human counterpart the researchers tried to look for possible therapies. For that Su, Auluck and Outeiro tested 115,000 bioactive (so known to affect live cells) compounds and found several able to correct one or more of the cellular abnormalities induced by the high levels of alpha-synuclein. Not only that, but these molecules were also effective treating worm and mammals (rat) models of PD. Even more remarkably, they were capable of rescuing human dopaminergic neurons in a third PD model raising the possibility that they could be used to treat human PD.

Interestingly several of these new potentially therapeutic molecules looked very similar, what led Su and colleagues to test them against each other to find that, in fact, they acted on the same targets across the different species tested. This was particularly important because it shows that the biological mechanisms affected by the over-accumulation of alpha-synuclein are conserved throughout millions of years of evolution - from yeast to humans – further supporting the hypothesis that PD results from a dysfunction of basic cellular mechanisms.

In conclusion Su, Auluck and Outeiro´s work supports the idea that accumulation of alpha-synuclein in vesicles inside brain cells, so typical of PD, is a normal physiological mechanism, most probably to get rid of abnormal proteins. Overload of this mechanism seems enough to cause PD-like symptoms (after all in these yeast models the protein is perfectly normal). Neurons are particularly susceptible not only because they are not renewed throughout the organism’s life, but also because they have higher than normal requirements for both mitochondria and lipid metabolism due to their highly energetic functions.

The new study’s major breakthrough, however, is the identification of several new compounds apparently capable of reversing the cellular abnormalities associated with PD and, as such, with potential to be used in treatments against the brain degeneration of PD.

In fact, at the moment the disease is believed to already affect a striking 3% of the population above 65 years old (more than 1 million in the US, 1,2 millions in Europe) and in a world where life expectancy is steadily increasing, pushing PD numbers (by the age of 80 more than 2 out of 100 people will have signs of the condition), any clues into the disease mechanisms and possible treatments are crucial.

Still, much more work is needed before therapies can be developed “The next step - says Tiago Outeiro - is to confirm these results in other PD models, even more similar to the human disease, to understand better the mechanisms and identify the molecules’ targets so they can, if proven secure, be eventually tested in humans”

For more information go to www.parkinsonresearchfoundation.org

Acid associated with gout 'could help Parkinson's sufferers'

By Kate Devlin,

Parkinson’s disease progresses more slowly in patients with naturally high levels of the acid which triggers gout, suggesting a possible new treatment for the disease.

Patients with high levels of uric acid were a third less likely to need treatment over the course of two years than those with low levels, the results of a new study show.

Researchers are now testing whether increasing Parkinson’s patients’ uric acid levels safely can help their condition.

An antioxidant, the acid is created naturally as we digest food.

But too much uric acid, or urate, can cause bouts of gout, an extremely painful joint condition, and kidney stones.

Diets rich in liver, seafood and dried beans have been linked to high uric acid levels but researchers warn that because of the side effects patients should not try to increase their urate levels themselves.

A smaller study published last year also suggested that high uric acid levels could slow the progression of Parkinson’s Disease.

Dr Alberto Ascherio, from the Harvard School of Public Health, who led the study, said: “Only now we can be reasonably sure that the slower rate of progression in patients with higher concentrations of urate is real and not a chance occurrence."

However, the researchers stress that they do not yet know if it is the acid itself which carries the protective benefit or some other process of the body which produces uric acid as a by-product.

The latest research looked at 800 sufferers of the condition.

The link between high uric acid levels and a slower development of the disease was less clear in women then men, the study found, however this may be because women tend to have higher natural levels of the acid.

The researchers are now conducting a trial to give 90 patients a drug, inosine, which can elevate uric acid levels, to test whether they can be safely raised and if this slows the speed of the disease.

"Because elevated urate levels have known health risks, including gout and kidney stones urate elevation should only be attempted in the context of a closely monitored clinical trial in which potential benefits and risks are carefully balanced," Dr Schwarzschild said.

For more information go to www.parkinsonresearchfoundation.org

Effects of chronic low dose rotenone treatment on human microglial cells

Author: Shamim ShaikhLouise Nicholson

Exposure to toxins / chemicals is considered to be a significant risk factor in the pathogenesis of Parkinson's disease (PD); one putative chemical is the naturally occurring herbicide rotenone that is now used widely in establishing PD models. We, and others, have shown that chronic low dose rotenone treatment induces excessive accumulation of Reactive Oxygen Species (ROS), inclusion body formation and apoptosis in dopaminergic neurons of animal and human origin.

Some studies have also suggested that microglia enhance the rotenone induced neurotoxicity. While the effects of rotenone on neurons are well established, there is little or no information available on the effect of rotenone on microglial cells, and especially cells of human origin.

The aim of the present study was to investigate the effects of chronic low dose rotenone treatment on human microglial CHME-5 cells.

Methods: We have shown previously that rotenone induced inclusion body formation in human dopaminergic SH-SY5Y cells and therefore used these cells as a control for inclusion body formation in this study. SH-SY5Y and CHME-5 cells were treated with 5nM rotenone for four weeks.

At the end of week 4, both cell types were analysed for the presence of inclusion bodies, superoxide dismutases and cell activation (only in CHME-5 cells) using Haematoxylin and Eosin staining, immunocytochemical and western blotting methods. Levels of active caspases and ROS (both extra and intra cellular) were measured using biochemical methods.

Conclusion: The results suggest that chronic low dose rotenone treatment activates human microglia (cell line) in a manner similar to microglia of animal origin as shown by others.

However human microglia release excessive amounts of ROS extracellularly, do not show excessive amounts of intracellular ROS and active caspases and most importantly do not show any protein aggregation or inclusion body formation. Human microglia appear to be resistant to rotenone (chronic, low dose) induced damage.

For more information go to www.parkinsonresearchfoundation.org