1、chemical-induced brain injurymohamed b. abou-donia, ph.d.department of pharmacology and cancer biologyduke university medical centerdurham, north carolina 27710 brain injury1.little is known about the etiology of many brain diseases, such as alzheimers disease, parkinsons disease, multi

2、ple sclerosis, amyotrophic lateral sclerosis (als), or autism. 1.chemicals can cause brain injuries that resemble brain diseases, for example:a. manganese causes brain injury similar to that of parkinson diseaseb. organophosphate-induced delayed neurotoxicity (opidn) has been misdiagnosed as multipl

3、e sclerosis. the brain the brain contains approximately 200 billion cells (neurons) and a trillion supporting cells. brain neurons are all formed before birth, and no new neuronal cells are born after birth.the brainthe brain requires one fifth of the oxygen and energy (glucose) consumed by the body

4、 to maintain its function.the hourly flow of blood through the brain is approximately 13 gallons, which accounts for one fifth of the blood pumped by the heart. brain regions the brain is divided into three sections: a. forebrain: cerebrum, limbic system (amygdala,hippocampus, septum), thalamus, hyp

5、othalamus.b. midbrainc.hindbrain: pons, medulla oblongata, cerebellum cerebral cortex language vision higher-order processing movementcerebral cortex ii corpus striatum degenerates in parkinsons paralysis loss of sensory input loss of reasoning, judgment, memory, etclimbic system emotion memory cons

6、olidation storage working memory movementlimbic system emotion memory consolidation storage working memory movementcerebellum motor learning posture gaitbrain supporting cellssupporting cells continue to divide throughout life.a. glial cells:1. astocytes or astroglia: provide structural (blood brain

7、 barrier) and nutritive support and form “glial” scar after injury.2. oligodendrocytes or oligodedroglia: form myelin sheath of axons in the cns.3. microglia: activated after injury and act as scavengers taking up debris.b. endothelial cells:form the walls of brain capillaries and the bbb.blood brai

8、n barrierblood vesselblood brain barriergeneral capillarybrain capillaryfenestraintercellular clefendothelial cellpinocytoticvesiclesmitochondriaendothelial cellastroglialprocesspericytebasementmembranetightjunctionthe blood brain barrier (bbb)is formed by brain capillary walls endothelial cells:1.

9、tight junctions2. no fenestras3. few pinocytotic vesicles in the cytoplasm (bche)4. increased mitochondria (active transport)5. basement membrane (ache)6. astrocytic feet ensheathe 95% of endothelial cells7.pericytes with smooth muscle-like properties8. p-glycoprotein (p-gp) to remove undesired subs

10、tances.nervous system-specific proteins1. axons a. neurofilament proteins (nfp) b. tau proteinsc. tubulin2. dendrites microtubule associated proteins-2 (map-2)3. myelin myelin basic protein (mbp)4. astrocytesa. glial fibrillary acidic proteins (gfap)b. s-100 proteinthe cytoskeleton1.the cytoskeleton

11、 in the neuron consists of straight and parallel:a. 25-nm microtubules (- and -tublin)b. 10-nm neurofilaments c. microtubule associated proteins (map-2 and tau) that function as cross-bridges to link microtubules and neurofilaments.2. the cytoskeleton gives the cell its shape and transport material

12、within and outside the cell. neurofilament proteinsneurofilaments consist of 3 polypeptides:1.a 200-k da, outer or high molecular weight protein (nfh),2.a 160-k da, middle or medium molecular weight protein (nfm), and3.a 70-k da, core and low-molecular weight protein (nfl).nfh is peripherally locate

13、d, and especially vulnerable to injury and is an early marker to neuronal damage.tau proteinstau proteins are:present almost exclusively in the axon.involved in microtubule assembly and stabilization.tubulin 1. tubulin is present in all cells2. it is present at high level in the brain where it compr

14、ise approximately 10% of brain protein.3. testes have high contents of tubulinmap-2microtubule associated proteins-2 (map-2):1. are found exclusively in the somato-dendrites of the neurons2. they promote polymerization and stabilization of microtubules. myelin basic protein (mbp)mbp is a major const

15、ituent of the myelin that is formed by:1.the supporting cells, oligodendrocytes in the central nervous system and 2. schwann cells in the peripheral system. astrocytic proteinsastrocytes form the following proteins:1. glial fibrillary acidic protein (gfap) is secreted following axonal injury to form

16、 gliotic scar.2. s-100 is a calcium binding proteins that is formed in response to acute brain injury such as brain infarction and has been used to assess ischemic brain damage. autoantibodies against brain specific proteins1.normally, small amounts of brain-specific proteins may leak into the circu

17、lation, where they react with b lymphocytes to form autoantibodies that are reactive against these proreins.2.autoantibodies are increased with age.3.damage to neuronal and glial cells in the brain or of the blood brain barrier (bbb), causes more leakage of these proteins into blood stream, with sub

18、sequent increased formation of the autoantibodies against them.brain-specific protein autoantibodies: biomarkers for neurological diseasesbrain-protein protein autoantibodies havebeen detected in the sera of patients with:1.alzheimers disease2.parkinsons disease3.myasthenia gravis4.multiple sclerosi

19、s5.kuru disease6.creutzfeldt-jacob disease, and 7.picks disease8.down syndromechemical-induced axonal degeneration and gliosis in animals axonal and gliosis are induced in animals by:1. organophosphates (abou-donia, 1982)2. n-hexane, mbk (lapadula et al, 1988)3. carbon disulfide (wilmarth et al., 19

20、93)4. acrylamide (reagan et al., 1994)5. glycidamide (reagan et al., 1995)mechanisms of neurotoxicity nonspecific: lack of oxygen (hypoxia) selective: chemicals can target: nucleus axon myelin synapse hypoxia anoxic respiratory paralysis failure of blood to carry oxygen hemoglobin ischemic cardiac a

21、rrest hypotension (vasodilation) hemorrhage/thrombosis carbon monoxide cytotoxic cytochrome oxidase inhibition metabolic inhibition repeated hypoxia (e.g., tia)selective neurotoxins cell body synaptic axon central-peripheral proximal axonopathy central-peripheral distal axonopathy neurofilamentous t

22、ubulovesicular conductionchemical-induced neurodegeneration the following chemicals caused neuronal degeneration in the cerebral cortex, hippocampus, and cerebellum of brain of exposed rats. 1. organophosphorus compounds:sarin, malathion, chlorpyrifos, tocp, tmcp, tpcp.2. pyrethroids: permetrhrininc

23、reased autoantibodies against brain-specific proteins1. axonal degenerationneurofilament proteins, tau, tubulin2. demyelination myelin basic protein (mbp)3. dendrite degenerationmap-24. astrogliosisgfap5. acute brain injurys-100consequences of axonal degeneration increased autoantibodies against neu

24、rofilaments, tau,tubulin or/and mbp indicate axonal degeneration.degeneration in the cerebral cortex leads to:1. motor and sensory abnormalities, 2. ataxia,3. deficit in posture, locomotion, and skilled movements 4. fine motor movements (fingers, speech, facial expression, etc., 5. weakness conseque

25、nces of axonal degenerationaxonal degeneration of the limbic systemincluding the hippocampus leads to:1. learning and memory deficits2. neurobehavioral (mood, emotion and judgment) abnormalitiesconsequences of axonal degenerationincreased autoantibodies against map-2suggests damage to the dendrite-r

26、ich purkinje cells in the cerebellum resulting in:1. gait and coordination abnormalities2. staggering gate 3. ataxia consequences of gliosis increased autoantibodies against gfap suggests:1. axonal injury (forms scar).2. neuropsychiatric disorder.consequences of gliosisincreased autoantibodies again

27、st s-100 suggest:1. traumatic brain damage2. acute phases of brain injury such as brain infarction, and3. it as been used to assess ischemic brain damage. 4. can help to differentiate between acute and chronic brain injury. hypothesis: increased autoantibodies against brain specific protein hypothes

28、is:1.following neuronal injury, neuron- and glia-specific proteins are released into circulation.2.released necrotic neuronal and glial elements accumulate and stimulate b lymphocytes to produce autoantibodies that are reactive against these proteins.3.increased autoantibodies against brain-specific

29、 proteins in the serum are indicative ofneuronal damage. significanceantibody test that could detect ongoing or at-risk status of neurodegenerative diseases would be desirable, because: 1. antibodies are extremely sensitive and specific measure 2. they can amplify the signal of an altered biological

30、 environment. specific aimto correlate neurological deficits in persons following chemical exposure with sera levels of autoantibodies against brain neuronal and glial specific proteins. methods1.patients. individuals exposed to pesticides, industrial chemicals, and flight cabin fumes. 2. sera from the patients and healthy controls were obtained.3. western blotting. standard brain-specific proteins ar