The long-term objective of the planned research is to understand the fundamental mechanisms underlying the pathological processes which occur in idiopathic Parkinson's Disease (PD). PD is a major degenerative brain disease estimated to affect at least 500,000 Americans and millions of individuals worldwide. The hallmark of PD is the degeneration of nigrostriatal dopamine (DA) neurons as a result of pathological processes of unknown origin which occur in the neuromelanin-pigmented cell bodies of these neurons located in the substantia nigra (SN) pars compacta. Based on many prior studies it appears that PD might develop as a consequence of two factors: (a) a genetically-inherited predisposition manifested by an impaired ability to detoxify and excrete environmental toxicants so that they can enter the brain; and, (b)chronic exposure to these substances. In view of the fact that selective dopaminergic neurotoxins have not been found in the environment, a new hypothesis is advanced which might contribute to an understanding of the fundamental pathoetiology of PD. It is proposed that in response to such a toxic brain insult the activity of nigral gamma-glutamyl transpeptidase is upregulated with the result that glutathione (GSH), synthesized and exported by glial cells, is translocated into the cytoplasm of SN cell bodies which normally contain little or none of this tripeptide. Because DAergic SN neurons possess a very weak antioxidant system, uniquely high levels of unsheltered DA, and high basal levels of DA autoxidation (they are pigmented with the end- product of this reaction, neuromelanin) the rise in cytoplasmic levels of GSH is proposed to cause a metabolic switch. This switch diverts the neuromelanin pathway and leads ultimately to the endogenous formation of aberrant dihydrobenzothiazine (DHBT) and benzothiazine (BT) metabolites. These are proposed to be the endotoxins which cause the death of SN neurons as a result of: (a) redox cycling reactions which generate elevated levels of cytotoxic reduced oxygen species evoking severe lipid peroxidation; and, (b) inhibition of mitochondrial complex I respiration.
The specific aims of the project are: (l) to elucidate the oxidation chemistry of DA in the presence of GSM and L-cysteine under conditions which mimic those under which the proposed metabolic switch occurs; (2) to isolate and identify the major products of these reactions and determine their neurotoxicological, neuropharmacological and neurodegenerative properties using both in vivo and in vitro experiments; and, (3) to develop an experimental animal model which, in response to a chemical insult on the brain, exhibits the hypothesized GSH-mediated metabolic diversion in the SN. These investigations might ultimately lead to the development of a clinical assay for early diagnosis of PD and suggest therapeutic strategies to halt the degenerative processes.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS029886-03
Application #
2037468
Study Section
Metallobiochemistry Study Section (BMT)
Program Officer
Oliver, Eugene J
Project Start
1994-12-01
Project End
1998-11-30
Budget Start
1996-12-01
Budget End
1997-11-30
Support Year
3
Fiscal Year
1997
Total Cost
Indirect Cost
Name
University of Oklahoma Norman
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
848348348
City
Norman
State
OK
Country
United States
Zip Code
73019
Dryhurst, G (2001) Are dopamine, norepinephrine, and serotonin precursors of biologically reactive intermediates involved in the pathogenesis of neurodegenerative brain disorders? Adv Exp Med Biol 500:373-96
Shen, X M; Li, H; Dryhurst, G (2000) Oxidative metabolites of 5-S-cysteinyldopamine inhibit the alpha-ketoglutarate dehydrogenase complex: possible relevance to the pathogenesis of Parkinson's disease. J Neural Transm 107:959-78
Han, J; Cheng, F C; Yang, Z et al. (1999) Inhibitors of mitochondrial respiration, iron (II), and hydroxyl radical evoke release and extracellular hydrolysis of glutathione in rat striatum and substantia nigra: potential implications to Parkinson's disease. J Neurochem 73:1683-95
Shen, X M; Dryhurst, G (1998) Iron- and manganese-catalyzed autoxidation of dopamine in the presence of L-cysteine: possible insights into iron- and manganese-mediated dopaminergic neurotoxicity. Chem Res Toxicol 11:824-37
Li, H; Shen, X M; Dryhurst, G (1998) Brain mitochondria catalyze the oxidation of 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxyli c acid (DHBT-1) to intermediates that irreversibly inhibit complex I and scavenge glutathione: potential relevance to the pathogenesis of J Neurochem 71:2049-62
Shen, X M; Zhang, F; Dryhurst, G (1997) Oxidation of dopamine in the presence of cysteine: characterization of new toxic products. Chem Res Toxicol 10:147-55
Wrona, M Z; Yang, Z; Zhang, F et al. (1997) Potential new insights into the molecular mechanisms of methamphetamine-induced neurodegeneration. NIDA Res Monogr 173:146-74
Li, H; Dryhurst, G (1997) Irreversible inhibition of mitochondrial complex I by 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxyli c acid (DHBT-1): a putative nigral endotoxin of relevance to Parkinson's disease. J Neurochem 69:1530-41
Shen, X M; Xia, B; Wrona, M Z et al. (1996) Synthesis, redox properties, in vivo formation, and neurobehavioral effects of N-acetylcysteinyl conjugates of dopamine: possible metabolites of relevance to Parkinson's disease. Chem Res Toxicol 9:1117-26
Cheng, F C; Kuo, J S; Chia, L G et al. (1996) Elevated 5-S-cysteinyldopamine/homovanillic acid ratio and reduced homovanillic acid in cerebrospinal fluid: possible markers for and potential insights into the pathoetiology of Parkinson's disease. J Neural Transm 103:433-46

Showing the most recent 10 out of 11 publications