Overview: Recent negative clinical trials and un-interpretable results underscore the need for biomarkers as tools that will assist in the clinical development of drugs. The term "biomarker" encompasses two very different types of measurements: drug biomakers, measuring the activity of a drug (pharmacodynamic markers), and disease biomarkers, measuring a pathologic process of the disease (Figure 1).

Figure 1Drug and disease biomarkers are two types of biomarkers with utility in clinical trials. Drug biomarkers are markers unique to the drug that provide information about whether the drug is achieving appropriate levels at the site of action and inducing a biological response. Disease biomarkers are markers that are changed in people with the disease and can identify the appropriate population of subjects for a clinical trial or track the progression of a particular disease feature.Both types of biomarkers are essential for therapeutic development and can aid analysis of data from clinical trials. The markers may provide insight into whether a drug is acting as its target or whether the drug is having an effect on the disease process.

What are biomarkers? Biomarkers are defined any characteristic that can be objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes or pharmacological responses to therapeutic interventions. This may include measures of biochemical components in body fluids and tissues, as well as imaging, physiological and clinical measures. Biomarkers are critical tools for clinical development that can be used for appropriate patient selection (e.g., testing a cholesterol lowering drug in people with confirmed elevated cholesterol), guiding dosing strategies (testing several doses of drug in early stages to determine the optimal dose for lowering cholesterol to a normal level), or as a measure of efficacy (e.g., a marker indicating the drug indeed lowered cholesterol levels).

Development of simplified, standardized biomarkers is essential: MJFF has invested approximately $9 million in the discovery of disease biomarkers and several lead biomarker candidates have emerged. For example, investigators can now measure the proteins alpha-synuclein and DJ-1 in blood and cerebral spinal fluid specimens and preliminary studies demonstrated the levels of these proteins are altered in PD vs. non-PD subjects. However, these findings were observed with relatively crude methodology and more sensitive methods to detect these markers are required. Replication of these findings and the utility of biomarkers hinges on translating these methods into simple, standardized laboratory measurements that can be employed in multiple laboratories around the world. In order to verify the initial discoveries of disease markers such as DJ-1 and alpha-synuclein, as well as other candidate markers of which we may not yet be fully informed, MJFF wants to support and encourage researchers to tackle the underfunded and often “uninteresting” step of developing these simple laboratory tests for any candidate marker.

Evidence that developing such standardized tools can have impact is reflected in a recent publication describing similar standardized tools for lead markers implicated in Alzheimer’s disease (Shaw et. al, 2009). The development of these tools enabled a large scale study to verify that levels of two proteins in CSF, termed Abeta and tau, can accurately predict the progression of individuals with mild cognitive impairment towards full-blown Alzheimer’s disease dementia.

An MJFF priority area: MJFF staff believes a more focused approach to biomarker development is required to develop effective therapies. With this in mind, MJFF is prioritizing two distinct and specific efforts: 

1. support development of specific drug biomarkers that can be used to shape dosing strategies and clinical trial designs of promising therapeutic strategies; and
2. identify promising lead candidate disease markers needing ‘next step’ tool development to allow further verification studies.

While trial sponsors generally agree that specific drug biomarkers would be useful for clinical studies, limited financial resources often do not permit development of these tools and thus clinical trial design can be suboptimal. Though a drug biomarker may have different characteristics from a disease biomarker, a similar process of discovery and validation must occur to demonstrate the utility of the marker as a tool in clinical trials. Thus MJFF is supporting both early discovery and follow up optimization of drug biomarkers for exciting and promising drugs in the Parkinson’s pipeline (Biomarkers 2009) in order to ensure that subsequent clinical testing of these drugs can be performed with the best, most informative trial designs possible.

THE  ROLE  OF  THE  BLOOD  BRAIN  BARRIER  IN  PARKINSON’S  DISEASE.

SUMMARY

           Could Parkinson’s Disease (PD), be caused by sufferers having a defective Blood Brain Barrier, (BBB), which has greater permeability than that of a normal person? Neurotoxins that circulate harmlessly in the bloodstream normally, are able to enter the brain, and damage neurons. At an increased permeability, dopamine could leak from the brain to the bloodstream.  Dopamine does not pass through a healthy BBB, but could pass through a defective BBB. Dopamine is actually a smaller molecule than levodopa, which can pass the BBB. So the permeability od the BBB does not need to be much higher for dopamine to leak out. Also Carbidopa could now enter the brain, (this has now been shown to happen), and prevent the conversion of levodopa into dopamine. This would explain the catastrophic effect of stress when for example you are faced with trying to enter a crowded lift and freeze.

     DISCUSSION      

K.L.Leender’s group (ref 1) have shown that the BBB is defective in Parkinson’s patients, with all patient values of permeability of the BBB being higher than all controls. Also, he states,

“ This is the first evidence supporting a dysfunctional blood-brain barrier as a causative mechanism in PD.”

             Treatments that increase the porosity of the BBB might therefore cause PD or may worsen the symptoms in a PWP.

(a.)     Stress is well known for it’s detrimental effect on a person with PD, and has been shown to open the BBB. (ref 2),

(b)     PD is predominantly an old person’s disease. The reason could be that ref 3 reports that “old age significantly increases BBB permeability”

(c).  Pesticides. Recently shown by Aberdeen University  that exposure to pesticides leads to an increased risk of contracting PD by 39%.   (ref. 4)

            Ref 5 states, “The pesticide MCPA, used as an ingredient in some lawn pesticides,  has been found to damage a part of the brain known as the blood brain barrier .

             serendip.brynmawr.edu/bb/neuro/neuro00/web2/Patel.html

states

“In the CNS lead increases the permeability of the blood-brain barrier (BBB)”.

 Blaylock states that a number of factors make the blood-brain barrier more porous, including exposure to pesticides, hypoglycaemia, all immune diseases (such as lupus and diabetes), Alzheimer's and Parkinson's, strokes (including silent strokes) and a whole range of medical drugs. .

                    Substances which are reported to ease the symptoms of PD, such as curcumin, alpha lipoic acid, CDP choline (citicoline) and GNDF also reduce the porosity of the BBB.   (Ref 13), (Ref 15), (Ref 18).

Certain diverse anti hypertension drugs have been found to be beneficial in treating PD, and Losartan, (Ref 17), Captoprill, (an ACE inhibitor), and two calcium entry blockers Nifedipine (Ref 16) and Flunarizine, all reduce the permeability of the BBB.

           TNF-alpha is a pro-inflammatory cytokine which increases BBB permeability, which is centrally involved in the pathogenesis of Alzheimer’s.

 By treating Alzheimer’s patients with an anti TNF drug etanercept, resulted in resulted in rapid cognitive improvement within minutes!!   (Ref 9).

          E.A. van Vliet (Ref 10) reports “leakage of the BBB is associated with various neurological disorders.”.

   COX inhibitors (Cyclooxygenase inhihitors) are reported to limit BBB disruption

(Ref 12)   Non-steroidal anti-inflammatory drugs (NSAIDs). are the main COX inhibitors      

 In a prospective trial, regular use of nonaspirin nonsteroidal anti-inflammatory drugs was associated with a 45% lower risk of developing Parkinsons. (Ref 11).                             

  I.Rite et al, (Ref 14) state “We conclude that disruption of the BBB may be a causative factor for degeneration of nigral dopaminergic neurons.”  In a paper in which they employed intranigral injections of vascular endothelial growth factor (VEGF), the most potent inducer of blood-brain barrier (BBB) permeability.

    Caffeine is reported to have a protective effect against PD, see

http://www.gairrhydd.com/features/science-environment/900/wake-up-and-smell-the-coffee

 and is stated to reduce BBB permeability, see

http://www.mombu.com/medicine/allergies/t-caffeine-blocks-the-blood-brain-barrier-dysfunction-caused-by-high-cholesterol-cholesterol-celiac-diet-menopause-down-2470596.html

          Opinion is now changing regarding the involvement of the BBB in PD.

In  http://www.nature.com/nrn/journal/v7...m/nrn1824.html      (Ref 7.)

It states,

“There is increasing evidence that the function of the BBB is altered
in several neuropathologies, including brain oedema, epilepsy,
Alzheimer's disease and Parkinson's disease”

A recent report  (Ref 8), “Blood-Brain Barrier Pathology in Alzheimer’s and Parkinson’s Disease,”
states,
"Though the BBB is thought to be intact during neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's disease (PD), recent evidence argues otherwise."
The report goes on to say,
" Dysfunction of the BBB may be involved in disease progression,..........
Developing a better appreciation of BBB dysfunction in AD and PD may not only provide novel strategies in treatment, but will prove an interesting milestone in understanding neurodegenerative disease etiology and progression."

         Work is currently being conducted at the Michael J. Fox Foundation where in their June 30^th 2005 report they state, “The Project will include PET imaging to compare the BBB of people with PD to those who do not have the disease. It is hypothesized that biochemical changes that occur in the BBB of people with PD could allow greater accumulation of environmental toxins in the brain.”

                A recent paper confirming the role of the BBB is,

Neuropathol Appl Neurobiol. 2008 Dec 11. [Epub ahead of print] Links
Role of developmental inflammation and blood-brain barrier dysfunction in neurodevelopmental and neurodegenerative diseases.Stolp H, Dziegielewska K.
Department of Pharmacology, University of Melbourne, Parkville 3010, Australia.

Abstract The causes of most neurological disorders are not fully understood. Inflammation and blood-brain barrier dysfunction appear to play major roles in the pathology of these diseases. Inflammatory insults that occur during brain development may have widespread effects later in life for a spectrum of neurological disorders. In this review a new hypothesis suggesting a mechanistic link between inflammation and blood-brain barrier function (integrity), which is universally important in both neurodevelopmental and neurodegerative diseases, is proposed. The role of inflammation and the blood-brain barrier will be discussed in cerebral palsy, schizophrenia, Parkinson's disease, Alzheimer's disease and multiple sclerosis, conditions where both inflammation and blood-brain barrier dysfunction occur either during initiation and/or progression of the disease. We suggest that breakdown of normal blood-brain barrier function resulting in a short-lasting influx of blood born molecules, in particular plasma proteins, may cause local damage such as reduction of brain white matter observed in some newborn babies, but may also be the mechanism behind some neurodegenerative diseases related to underlying brain damage and long-term changes in barrier properties.

PMID: 19077110 [PubMed - as supplied by publisher

        In a communication with Prof. Al  Lossinsky, he confirmed that BBB permeability can be measured in a living person, stating,

“Yes, there are methods available in the clinic to measure BBB leakage in humans. The person would be given special radio-opaque tracers into their blood and any increased permeability would be measured in special scanners."

            Therefore, the BBB permeability should be measured in a group of PD patients with a spectrum of progression, from slight to severe.

             If a correlation can be established, ie if the slight person is close to the permeability of a normal person , then increasing severity of symptoms shows an increasing permeability figure, this will be a massive step foreward.

              A simple measurement of the permeability would confirm the PD diagnosis or otherwise.

              New drugs or treatments could be evaluated simply and cheaply by their ability to show a reduction in permeability, by the time and level of reduction.

     A reduction in permeability to that below the  threshold of dopamine leakage would constitute a cure.

             CONCLUSIONS

There is much evidence to date showing a link between the BBB and the onset of PD, or an adverse effect on the symptoms of a sufferer, possibly due to a build up of toxins in the PD brain.  In addition, the higher permeability of the BBB in PWP, may allow dopamine to pass out of the brain into the bloodstream, exacerbating the symptoms of PD.

By the same token, carbidopa could possibly now enter the brain, and prevent the conversion there of levodopa into dopamine. See ref. 6.

             There is also the intriguing possibility that research into manipulating the permeability of the BBB may also benefit a series of neurological diseases, since evidence exists  that the BBB is implicated in multiple sclerosis,. ALS, schizophrenia, Alzheimer’s disease, brain oedema and dementia. 

Ron Hutton       ron.hutton@btopenworld.com

References,

1.  E-MOVE reports from the 9th International Congress of Parkinson’s Disease and Movement Disorders, New Orleans 5-8 March, 2005. Pages and abstract numbers are from Movement Disorders 2005;20(suppl 10). 

. Blood-brain barrier dysfunction in Parkinson's disease
KL Leenders, R Kortekaas, AL Bartels, J Oostrom, A Willemsen, J Bart
S77, P257

See also,

Kortekaas R, Leenders KL, van Oostrom JC, et al., Blood-brain barrier dysfunction in parkinsonian midbrain in vivo. Ann Neurol. 2005 Feb; 57(2):176-9. Comment in: Ann Neurol. 2005 Feb; 57(2):161-2.

2.  Science News 1996 Dec. !4  vol. 150 No.24  p.375.
3. Molecular Medicine 7(12): 810–815, 2001

ApoE Deficiency Compromises the Blood Brain Barrier Especially After Injury Nassia Methia,1,2* Patrick André,1,2* Ali Hafezi-Moghadam,1,2 Maria Economopoulos,1 Kennard L. Thomas,1 and Denisa D. Wagner1,2

4. http://www.news-medical.net/?id=25774

5. http://www.getipm.com/articles/bbb-lawn.htm

6.     PMID 2753115   Experimental Neurology
Volume 105, Issue 2, August 1989, Pages 152-161   Ahlskog JE, et al.

7.      N.Joan Abbott et al, Nature Reviews Neuroscience, 7, 41-43, Jan., 2000.

8.     Desai, Brinda S.¹; Monahan, Angela J.¹; Carvey, Paul M.²; Hendey, Bill¹

 Cell Transplantation, Volume 16, Number 3, 2007 , pp. 285-299(15)

^9.        Edward L Tobinick and Hyman Gross Journal of Neuroinflammation 2008, 5:2doi:10.1186/1742-2094-5-2                                                                                        

10.  E.A.van Vliet et al, Brain, 2007, 130(2): 521-534,                                                       11.  Arch Neurol. 2003;60:1043-1044, 1059-1064                                                                       

12.   J. Pharmacol. Ext. Ther. 2007, Aug. 17, 17704356.                                                     

13.   European J. of Pharmacology, April 2007, 561(1-3): 54-62.                                    14.   I.Rite et al    Journal of Neurochemistry, Volume 101, Number 6, June 2007 , pp. 1567-1582(16                                                                                                                              

15.   The J. of Immunology, 2006, 177, 2630-2637.                                                        16.   Int. J. Neuroscience Vol. 114, Issue 4, April 2004, 517-528.                                        

17.   Life Sci. 2003 Nov. 7, 73(25): 235-44.                                                                           

18.  J.Neurosurg. 2003 Apr., 98(4):867-73.

The importance of the blood brain barrier (BBB) lies in its ability to separate an organism’s vascular system from its central nervous system (CNS).  For Parkinson’s Disease therapy, this has often posed a difficulty in terms of drug delivery to the CNS.  Recent papers highlight the importance of the BBB in disease progression as well, however questions remain…

1.  Is the BBB disrupted in Parkinson’s Disease?

 Whether  the integrity of the BBB is actually compromised in Parkinson’s Disease has been a topic of great discussion.  Results from animal models have  varied based on methodology and model.  In two MPTP lesioned/chronic L-DOPA treated animal models of PD, Westin et al. (2006) found that there were BBB defects in the basal ganglia of their rodent models whereas Astradson, et al (2009) found no disruption of the BBB in primate brain. 

 In work funded by the Michael J. Fox Foundation, K.L. Leenders’ group has examined this issue and found that one marker indicative of BBB disruption, P-glycoprotein, which functions to eliminate toxins from the brain into the blood, exhibits decreased function in patients with advanced but not early Parkinson’s Disease (Bartels, et al 2008a; Bartels, et al. 2008b).  These results suggest that breakdown of the BBB may not be a causative factor in disease progression, but may occur with increasing severity.  Though these studies looked at the function of a single protein at the BBB, they serve as a starting point to examine other proteins critical in maintaining the integrity of the BBB.  

 2.  Could disruption of the BBB cause loss of dopaminergic neurons or is it the degeneration of dopaminergic neurons that causes breakdown the BBB?  Or do they both occur as downstream of some common insult?   

 Though chemically-induced dopaminergic degeneration has been found to result in alterations of the blood-brain barrier (Carvey, et al. 2005; Rite, et al. 2007), there is still a great deal of debate regarding the BBB breakdown as a causative mechanism of Parkinson’s Disease.  As a common insult has not been identified as affecting both dopamine neuron viability and BBB integrity, perhaps a more plausible scenario places disruption of the BBB, and associated inflammation, as a contributing factor for the progression of PD (Whitton, 2007). 

Ultimately, a greater understanding of the cellular mechanisms underlying the structural integrity of the BBB in PD may have implications for more efficacious drug delivery methods.  Moreover, such insights would yield information potentially important for Parkinson’s Disease and other related neurodegenerative diseases.