Docstoc

Detoxication of free radicals in the brain

Document Sample
Detoxication of free radicals in the brain Powered By Docstoc
					Detoxication of free radicals in the brain
                  By:
         Simone Abercrombie
              Spring 2006
                                        OUTLINE
I. INTRODUCTION
       A What is parkison’s disease?
            progressive nervous disease which occurs in the later stages of life and is
               associated with the destruction of brain cells that produce dopamine.
       B. Signs, symptoms and diagnosis
            muscular tremor, slowing of movement, partial facial paralysis,
               peculiarity of gait and posture, and weakness.
       C. What Causes the Disease?
            Neurons -any of the impulse-conducting cells that constitute the brain,
               spinal column, and nerves, consisting of a nucleated cell body with one or
               more dendrites and a single axon.
       D. key words
            Substantia nigra- a layer of large pigmented nerve cells in the midbrain
               that produce dopamine and whose destruction is associated with
               Parkinson's disease.
            Free radicals- Free radicals are the highly unstable chemicals that attack,
               infiltrate, and injure vital cell structures. Most stable chemical compounds
               in the body possess a pair of electrons. Sometimes, one member of the
               electron pair gets stripped away. The resulting compound (less one
               electron) is called a free radical.
       E. Genes linked to Parkinson's Disease
           1. alpha-synuclein
                One in a family of structurally related proteins that are prominently
                    expressed in the central nervous system. Aggregated alpha-synuclein
                    proteins form brain lesions that are hallmarks of some
                    neurodegenerative diseases (synucleinopathies). The gene for alpha-
                    synuclein, which is called SNCA, is on chromosome 4q21. One form
                    of hereditary Parkinson disease is due to mutations in SNCA. Another
                    form of hereditary Parkinson disease is due to a triplication of SNCA.
           2. Parkin
                a second protein found in Lewy bodies and implicated in Parkinson's
                    disease.
           3. DJ-1 aka PARK7 “Parkinson disease (autosomal recessive, early onset) 7”
                colocalizes with tau inclusions: a link between parkinsonism and
                    dementia.
           4. PINK1 “PTEN induced putative kinase 1”
                Abbreviation for PTEN-induced kinase. The PINK1 gene has been
                    mapped to chromosome 1p36. This gene encodes a 581-amino acid
                    protein which is active in mitochondria. Mutations in PINK1 have
                    been found in a rare familial form of Parkinson disease.
           5. LRRK2 “leucine-rich repeat kinase 2.”
                It provides instructions for making a protein called dardarin.
                    Researchers have identified several LRRK2 mutations in families
                    with late-onset Parkinson disease.
II. INDEPTH ANALYSIS
Article: Expression of NAD(P)H: quinine oxidoreductase (NQO1) in the normal and
        parkinsonian substantia nigra
        a. dopamine autooxidation (DA)
              induces formation of toxic oxygen species
        b. quinones
              part of the electron transport chain in mitochondria and chloroplast
                 membranes
        c. dopaminergic cell death
              death of dopamine producing cells
        d. gliosis
              Scars that are produced by enlargement of Astrocyte processes. When a
               portion of the CNS is damaged (Neuron or Axon), Astrocyte processes
               enlarge and replace the damaged tissue. This process is referred to as
               Gliosis, while the resulting permanent scar tissue is called Plaque
               (Sclerosis).
       e. Pathogenic factors
            i. oxidative stress
            ii. oxidative metabolism of dopamine
       f. NQO1
              Enzyme with antioxidant properties
       g. anti-oxidant
              A chemical compound or substance that inhibits oxidation.
       h. mesencephalon
              midbrain involved in motor function
       i. astrocyte
              A type of cell found in the brain and spinal cord. An astrocyte is a
                  small, star-shaped glial cell (a cell that surrounds and supports nerve
                  cells).
       j. neuromelanin
              A dark-brown pigment formed as a by-product of dopamine oxidation
                  within neurons, which is believed to act as a sink for iron.
       k. alpha-synuclein
              A normal protein found in the brain.
       l. lewis bodie
              Abnormal structures seen in dead or dying dopamine-producing cells
                  of the substantia nigra in Parkinson's disease.
       m. Enzyme
              a biological catalyst that speeds up a reaction without being used up
                  itself
            i. monoamine oxidase (MAO)
                 -A family of enzymes involved in the breakdown of certain
            neurotransmitters. MAO inhibitors act to block these enzymes.
            ii. DAhydroquinone
                 -relatively stable form which is made when DAQ is catalyzed, lacks
            major electrophilic reactivity
        n. aminochrome
              reactive species
            i. superoxide
                 -free radical created by aggregating platelets
        o. cellular nucleophiles
            i. mitochondrial DNA
            ii. reduced sulphydryl groups in protein cysteinyl residues and the thiol
        anti-oxidant glutathione (GSH)
        p. detoxication of DAQs
            i. non-enzymatically: low molecular weight reductants such as GSH and
        ascorbic acid
            ii. enzymatically: detoxication enzymes such as NQO1
   RESULTS and CONCLUSION of:
        A. specificity of NQO1 immunocytochemistry
        B. expression of NQO1 in the control substantia nigra, pars compacta
        C. expression of NQO1 in the parkinsonian substantia nigra, pars compacta

                                    INTRODUCTION


       Parkinson's disease (PD) is a condition which affects the central nervous system

(CNS). It is in the class of neuron degenerative disorders. Elderly people are at risk for

PD. There are four main symptoms of PD which are tremor, rigidity, bradykinesia, and

postural instability. As the disease progresses the symptoms get worse. PD is chronic and

progressive. A chronic disease is a long term disease while a progressive disease

continues to worsen. PD has affected individuals genetically and sporadically, but in most

cases the disease is not genetic. Individuals with PD have a combination of genetic

susceptibility and exposure to at least one or more environmental factors that are

connective with PD (NINDS, 2006). Most forms of PD is idiopathic (there is no cause)

however there are some cases where the cause is known or where the symptoms result

from another disorder.

What Causes the Disease?
       Neurons are responsible for sending and receiving signals to and from the body

and brain. When neurons in an area of the brain called the substantia nigra die or are

damaged this condition results in PD. The primary function of these neurons is to

produce dopamine. Dopamine acts as a chemical messenger which transports signals

between the substantia nigra and the corpus striatum, which ultimately creates

meaningful movement. As the level of dopamine is decreased irregular nerve firing

patterns causes impaired movement. By the time the patients begin to experience the

symptoms of the disease they have already lost 60-80% of the dopamine-producing

neurons in the substantia nigra (NINDS, 2006). Another important chemical messenger

that is affected by PD is the neurotransmitter norepinephrine. Norepinephrine is the major

messenger of the Sympathetic nervous system (SNS). The SNS is responsible for

autonomic functions. People with PD lose the nerve endings that produce this

neurotransmitter. This explains why these patients have problems with blood pressure.

When the cells of the parkinsonian brain are observed Lewy bodies can be identified.

These are accumulations of the protein alpha-synuclein and other proteins. Their role

and why they form is not completely understood. They may be beneficial or harmful. One

view is that they may inhibit the cell from carrying on its normal function. The other

view is that these Lewy bodies could be beneficial by keeping harmful these proteins

trapped inside so that the cells can function properly (NINDS, 2006).

There are several genetic mutations, and a few genes that are linked to PD. Inheriting

mutated genes may me the same genes that are altered sporadically by environmental

factors and toxins. Toxins linked to PD include 1-methyl-4-phenyl-1,2,3,6-

tetrahydropyridine, or MPTP (found in some kinds of synthetic heroin). Viruses are
another possible factor. For example, some individuals that developed encephalopathy

(disease of the brain) as a result of the 1918 influenza epidemic developed PD-like

symptoms defined above. Similar symptoms were found in Taiwanese women who had

herpes. Lucky for them the symptoms disappeared however the conditions was linked to

a short-term inflammation of the substantia nigra (NINDS, 2006).

Mitochondria may be involved in the development of PD. Mitochondria are responsible

for making energy and are major sources of free radicals. As a person ages free radicals

build up which is not good because these molecules cause oxidative stress which can be

defined as damage to membranes, proteins, DNA, and other parts of the cell. These

oxidative stress-related changes have been identified in brains of PD patients.

What Genes are linked to Parkinson's disease?

     The first gene that was linked to PD was alpha-synuclein in the 1990s. This gene

was mutated in families with familial PD. In 2003, a study discovered a familial form of

PD was caused by a triplication of the normal alpha-synuclein gene which caused people

in the affected family to produce too much of the normal alpha-synuclein. This study

concluded that an excess of the normal protein may cause PD just as the mutated form

does. The normal parkin gene is encoded into a protein which functions to help cells

break down and recycle proteins. DJ-1 normally helps control gene activity and protect

cells from oxidative stress. The normal PINK1 gene codes for a protein in mitochondria

but when it is mutated it increases vulnerability to cellular stress (NINDS, 2006).

LRRK2, is translated into a protein called dardarin, which is linked to late onset of

familial PD and a small percentage in sporadic PD.
                   Analysis of NQO1 in normal and Parkinsonian brain
1. Backround


       Research has shown that one major characteristic of Parkinson’s disease (PD) is

the presence of free radicals in the brain (Drukarch, et al. 200). Dopamine autooxidation

quinines (DAQs) and reactive oxygen species (ROS) are formed when enzymes such as

monoamine oxidase (MAO) break down overloads of cystolic dopamine. They are also

formed when cystolic dopamines are autooxidised. These two events cause oxidation

reactions that are harmful to the brain. If these DAQs are depleted aminochrome is

formed which is extremely reactive. Also, DAQs are reactive because that are elecrtron

deficient. When a particle lacks an electron the object is positively charged and seeks a

negatively charged atom. In the case of PD, they bind covalently to mitochondrial DNA,

and reduced sulphydryl groups in protein residues and anti-oxidant glutathione (GSH)

(van Muiswinkel et al. 2003). This binding inhibits these molecules from carrying on

their normal function. While ROS are being increased, anti-oxidants such as GSH are

being depleted.

       The need to detoxify DAQs goes hand in hand with the need for a successful

cellular defense mechanism. Detoxication of DAQs can be done non-enzymatiaclly by

ascorbic acid and GSH or enzymatically by NADP(H): quinone oxidoreductase (NQO1)

(van Muiswinkel et al. 2003). NQO1 has properties of an antioxidant and is related to

detoxication of quinones (Beyer et al. 1997). They do this by catalyzing DAQs into

Dahydroquinone which is much more stable than DAQ (Segura and Lind, 1989). In

previous studied scientist have found that NQO1 immnoresponses are present in

pigmented neurons containing dopamine and glial cells the substantia nigra pars
compacta (SNpc), which is the area of the brain that is affected by PD (Drukarch, et al.

200). There is not a lot of information on cellular localization of NQO1 in the brain of a

person with PD. The focus in this experiment is to study the cellular expression of this

enzyme in the brain, specifically mesencephalon, of patients that do not have a known

cause of PD. These patients are compared to individuals who are similar in age with no

PD. The brain tissues of twenty five individuals were obtained by performing an autopsy.

Tissues were stained in order to see lewy bodies, and neurofibrillary pathology present in

either the brainstem, limbic or neocortical portion of the brain.

2. Results

2.1 Specificity of NQO1 immumocytochemistry

       When antibodies were used to get a response from NQO1, the protein was

expressed in normal respiratory and cancerous tissue but not in small cell lung cancer

(SCLC), lymph, and stroma.

2.2 Expression of NQO1 in control brain

       NQO1 immunoreactivity was not seen in melanin possessing neurons containing

dopamine, astrocytes, and vascular tissue of the mesencephalon. Neuronal and astroglial

expression of NQO1 was mostly found in the A9 cells of the brain. There was some

NQO1 immunostaining in the somata and astroglial cells scattered throughout the tissue.

Most of the NQO1-immunopositive cells were astrocytes.

2.3 Expression of NQO1 in PD brain

       There was boost in NQO1 immunoreactivity present in Parkinsonian SNpc. This

increase was due to the fact that more astroglial cells were present and staining intensity

was increased. These cells are Hypertrophic, meaning there is an increase in their size
rather than the number of cells. NQO1 expression was apparent in areas were

degeneration of neurons was actively taking place. The NQO1 response was localized in

specific areas of the SNpc, not scattered. NQO1 is expressed either as fibrous astrocytes,

pigmented dopamine neurons, or a combination of both (van Muiswinkel et al. 2003).

The increase in expression of NQO1 was seen in the three areas observed: brainstem,

limbic and neocortical dementia with lewy bodies (DLB) individuals.

Conclusion

       The result from the experiment indicates expression of NQO1 increases when

degeneration of neurons is actively taking place. PD patient’s condition is characterized

into three different stages: early, intermediate, and end. At the end stage most of the

neurons have been depleted (depletion inactively taking place) and NQO1

immunoreactively is nearly not present.

       In the past it was believed NQO1 may activate dopamine autooxidation qionones

thus playing a role in pathogenesis (Cadenas, 1995). However more recent research

confirms NQO1 has anti-oxidant properties. Further, a mutation in NQO1 predisposes PD

(Harada et al 2001).
References:

Beyer R.E, J. Segura-Aguilar, S. Di Bernado, M. Cavazzoni, R. Fato, and D. Fiorentini.
1997. The two-electron quinone reductase DT-diaphorase generates and maintains the
antioxidant (reduced) form of coenzyme Q in membranes. Molecular aspects of
medicine. 18:15–23.

Cadenas E. 1995. Antioxidant and prooxidant functions of DT-diaphorase in quinone
metabolism. Biochemical Pharmacology. 49:127–140.


Drukarch B. and F.L. van Muiswinkel. 2000. Drug treatment of Parkinson’s disease: time
for phase II. Biochemical Pharmacology. 59:1023–1031.

Drukarch B. and F.L. van Muiswinkel. 2001. Neuroprotection for Parkinsons’s disease: a
new approach for a new millennium. Expert opinion on investigational drugs. 10:1855–
1868.

Harada S., C. Fujii, A. Hayashi and N. Ohkoshi. 2001. An association between idiopathic
Parkinson’s disease and polymorphisms of phase II detoxification enzymes: glutathione
S-transferase M1 and quinone oxidoreductase 1 and 2. Biochemical and biophysical
research communications. 288:887–892.

Segura-Aguilar J. and C. Lind. 1989. On the mechanism of the Mn3+-induced
neurotoxicity of dopamine: prevention of quinone-derived oxygen toxicity by DT
diaphorase and superoxide dismutase. Chemico-biological interactions. 72:309–324.


van Muiswinkel F.L., R. I. de Vos, J.M. Bol, G. Andringa, E.H. Jansen-Steur, D. Ross, D.
Siegel and B. Drukarch. 2003. Expression of NAD(P)H:quinone oxidoreductase in the
normal and Parkinsonian substantia nigra. Neurobiology of Aging. 25:1253-1262.

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:7
posted:3/16/2011
language:English
pages:10