Parkinson's disease

Impaired aldehyde detoxification exacerbates motor deficits in an alpha-synuclein mouse model of Parkinson's disease

INTRODUCTION

The discovery of biogenic aldehydes in the postmortem parkinsonian brain and the ability of these aldehydes to modify and cross-link proteins has called attention to their possible role in Parkinson's disease. For example, many in vitro studies have found that the aldehyde metabolite of dopamine, 3,4-dihydroxyphenylacetaldehyde (DOPAL), induces the formation of stable, neurotoxic alpha-synuclein oligomers.

METHODS

To study this in vivo, mice deficient in the two aldehyde dehydrogenase enzymes (Aldh1a1 and Aldh2, DKO) primarily responsible for detoxification of DOPAL in the nigrostriatal pathway were crossed with mice that overexpress human wild-type alpha-synuclein. DKO overexpressing human wild-type alpha-synuclein (DKO/ASO) offspring were evaluated for impairment on motor tasks associated with Parkinsonism.

RESULTS

DKO/ASO mice developed severe motor deficits greater than that of mice overexpressing human wild-type alpha-synuclein alone.

CONCLUSION

These results provide evidence to support the idea that biogenic aldehydes such as DOPAL interact with human wild-type alpha-synuclein, directly or indirectly, in vivo to exacerbate locomotor deficits in Parkinson's disease.

Design and synthesis of five-membered heterocyclic derivatives of istradefylline with comparable pharmacological activity

Parkinson's disease (PD) is a common degenerative disease of the central nervous system among the elderly. Istradefylline, an FDA-approved adenosine A_2A receptor antagonist (anti-PD drug), has good efficacy. However, it has been reported that the double bond of istradefylline is easily converted into cis-configuration when exposed to an indoor environment or direct light in a dilute solution. In order to find more stable adenosine A_2A receptor antagonists with similar pharmacological efficacy to istradefylline, the compounds series I-1 (12 compounds) was designed by maintaining the xanthine skeleton of istradefylline unchanged and replacing the trans-double bond with thiazole or benzothiazole and other biologically active heterocyclic compounds. These compounds were synthesized via multi-step experiment and successfully confirmed through different characterization techniques for their ability to inhibit cAMP formation in A_2A AR overexpressing cells. The thiazole derivative of istradefylline (Compound I-1-11, I-1-12) exhibited significant activity (IC₅₀  = 16.74 ± 4.11 μM, 10.36 ± 3.09 μM), as compared to istradefylline (IC₅₀  = 5.05 ± 1.32 μM). In addition, the molecular docking of benzothiazole derivatives I-1-11 and thiazole derivatives I-1-12 with higher inhibition rate were carried out and compared with istradefylline. The molecular docking results showed that I-1-11 and I-1-12 anchored in the same site as that of XAC (3REY) with predicted affinity binding energy -6.63 kcal/mol and - 6.75 kcal/mol, respectively. Validation through dynamics simulation also showed stable interactions, with fluctuations <3 Å and MM/GBSA energy <-20 kcal/mol. Hence, this study could provide a basis for the rational design of adenosine A_2A receptor antagonists with better potency.

Mapping of brain function after MPTP-induced neurotoxicity in a primate Parkinson's disease model

Neurophysiological studies of the brain in normal and Parkinson's disease (PD) patients have indicated intricate connections for basal ganglia-induced control of signaling into the motor cortex. To investigate if similar mechanisms are controlling function in the primate brain (Macaca fascicularis) after MPTP-induced neurotoxicity, we conducted PET studies of cerebral blood flow, oxygen and glucose metabolism, dopamine transporter, and D2 receptor function. Our observations after MPTP-induced dopamine terminal degeneration of the caudate and putamen revealed increased blood flow (15%) in the globus pallidus (GP), while blood flow was moderately decreased (15-25%) in the caudate, putamen, and thalamus and 40 % in the primary motor cortex (PMC). Oxygen extraction fraction was moderately increased (10-20%) in other brain areas but the thalamus, where no change was observable. Oxygen metabolism was increased in the GP and SMA (supplementary motor area including premotor cortex, Fig. 3) by a range of 20-40% and decreased in the putamen and caudate and in the PMC. Glucose metabolism was decreased in the caudate, putamen, thalamus, and PMC (range 35-50%) and enhanced in the GP by 15%. No change was observed in the SMA. In the parkinsonian primate, [(11)C]CFT (2beta-carbomethoxy-3beta-(4-fluorophenyltropane) dopamine transporter binding was significantly decreased in the putamen and caudate (range 60-65%). [(11)C]Raclopride binding of dopamine D(2) receptors did not show any significant changes. These experimental results obtained in primate studies of striato-thalamo-cortico circuitry show a similar trend as hypothetized in Parkinson's disease-type degeneration.

Dopamine imaging markers and predictive mathematical models for progressive degeneration in Parkinson's disease

We conducted PET imaging studies of modulation of dopamine transporter function and MRS studies of neurochemicals in idiopathic primate Parkinson's disease (PD) model induced by long-term, low-dose administration of MPTP. MR spectra showed striking similarities of the control spectrum of the primate and human striatum as well as MPTP-treated primate (six months after cessation of MPTP), and Parkinson's disease patient striatum (68 year old male; Hoehn-Yahr scale II; 510 mg/d L-DOPA). The choline/creatine ratio was similar in the MPTP model and human parkinsonism, suggesting a possible glial abnormality. The progressive degeneration of dopamine re-uptake sites observed in our PD model can be expressed by a time dependent exponential equation N(t) = N0 exp (-(0.072 +/- 0.016) t), where N0 represents intact entities (dopamine re-uptake sites before MPTP) and 0.072 per month is the rate of degeneration. When the signs of PD appear, N(t) is about 0.3-0.4 times N0. Interestingly, this biological degenerative phenomena has similar progression to that observed in cell survival theory. According to this theory and calculated degeneration rate, predictive models can be produced for regeneration and protective treatments.

Coupled temporal memories in Parkinson's disease: a dopamine-related dysfunction

Dysfunction of the basal ganglia and the brain nuclei interconnected with them leads to disturbances of movement and cognition, including disordered timing of movement and perceptual timing deficits. Patients with Parkinson's disease (PD) were studied in temporal reproduction tasks. We examined PD patients when brain dopamine (DA) transmission was impaired (OFF state) and when DA transmission was reestablished, at the time of maximal clinical benefit following administration of levodopa + apomorphine (ON state). Patients reproduced target times of 8 and 21 sec trained in blocked trials with the peak interval procedure, which were veridical in the ON state, comparable to normative performance by healthy young and aged controls (Experiment 1). In the OFF state, temporal reproduction was impaired in both accuracy and precision (variance). The 8-sec signal was reproduced as longer and the 21-sec signal was reproduced as shorter than they actually were (Experiment 1). This "migration" effect was dependent upon training of two different durations. When PD patients were trained on 21 sec only (Experiment 2), they showed a reproduction error in the long direction, opposite to the error produced under the dual training condition of Experiment 1. The results are discussed as a mutual attraction between temporal processing systems, in memory and clock stages, when dopaminergic regulation in the striatum is dysfunctional.

Drug treatment of Parkinson's disease in the 1990s. Achievements and future possibilities

Advances in the medical treatment of Parkinson's disease have improved the disability related to complications of long term levodopa therapy, including motor fluctuations, dyskinesias and neuropsychiatric toxicity. A range of new dopamine agonists are in various stages of preclinical and clinical development. Cabergoline appears to be effective in improving moderate motor fluctuations, and a number of dopamine partial agonists that can act as either agonists or antagonists depending on the degree of denervation and receptor sensitivity are being investigated. Apomorphine represents a significant advance in the treatment of well developed motor fluctuations in selected patients who are able to master the technique of subcutaneous administration. The catecholamine-O-methyl transferase inhibitors are proving useful in phase III studies in the management of patients with moderate motor fluctuations. A role for glutamate antagonists is supported by animal and early clinical data, although the poor therapeutic index associated with the currently available nonselective, noncompetitive glutamate antagonists has prompted a search for more selective antagonists with less toxicity. The management of levodopa-induced dyskinesias remains a major therapeutic challenge. Some reports of dopamine partial agonists, selective D2 receptor antagonists and atypical antipsychotics being useful await confirmation. Neuropsychiatric toxicity probably remains the major dose-limiting adverse effect of levodopa and is a major reason for parkinsonian patients being admitted to nursing homes. The development of new atypical antipsychotics with improved therapeutic indices, along with the possible use of serotonergic antagonists, may improve management of this difficult problem. The challenge will be to fit these new forms of treatment into our present range of available drugs and to assess their relative role within the emerging framework of functional neurosurgery for parkinsonian disability.

The role of cytochrome P450 enzymes in hepatic and extrahepatic human drug toxicity

The human cytochrome P450 enzyme system metabolises a wide array of xenobiotics to pharmacologically inactive metabolites, and occasionally, to toxicologically active metabolites. Impairment of cytochrome P450 activity, which may be either genetic or environmental, may lead to toxicity caused by the parent compound itself. In practise, this usually only applies to drugs that have a narrow therapeutic index and when their clearance is critically dependent upon the fraction normally metabolised by that pathway. P450 enzymes may also convert the drug to a chemically reactive metabolite, which, if not detoxified, may lead to various forms of hepatic and extrahepatic toxicity, including cellular necrosis, hypersensitivity, teratogenicity, and carcinogenicity, depending on the site of formation and the relative stability of the metabolite, and the cellular macromolecule with which it reacts. Variation in the regulation and expression of the drug metabolising enzymes may play a key role in both interindividual variation in sensitivity to drug toxicity and tissue-specific damage. Avoidance of toxicity may be possible in rare instances by prediction of individual susceptibility or by designing new chemical entities that are metabolised by a range of enzymes (both cytochromes P450 and others) and do not undergo bioactivation.

The adrenal medulla and Parkinson's disease

This paper reviews the literature describing the condition of the adrenal medulla in Parkinson's disease. Parkinson's disease is a neurodegenerative disorder that is characterized primarily by the loss of dopaminergic neurons in the substantia nigra. Clinical observations have revealed that Parkinson's disease is also frequently accompanied by a variety of autonomic symptoms. The adrenal medulla is a major component of the autonomic nervous system. However, until recently this organ has not been of particular interest in Parkinson's disease. Early studies found histologic abnormalities in adrenal medullary cells, and several groups measured urinary and plasma catecholamines to determine general autonomic status. In the late 1980s adrenal medullary tissue was first transplanted to the caudate nucleus in an attempt to augment the decreased levels of dopamine, and thus treat the symptoms of Parkinson's disease. At this time the status of the adrenal medulla in this disease became clinically important. We measured the total catecholamine content of the parkinsonian adrenal medulla in tissue collected both at autopsy and in conjunction with adrenal-caudate transplants. Adrenal medullary catecholamines and several neuropeptides were severely depressed in parkinsonian glands. Thus, the adrenal medulla appears to be a target of the peripheral manifestations of Parkinson's disease.

The role of active metabolites in drug toxicity

Adverse drug reactions can be caused by the parent drug or a metabolite of that drug. The metabolite may be stable or chemically reactive, the resultant toxicity being either a direct extension of the pharmacology of the drug, or unrelated to the known pharmacology of the drug and dependent on the chemical properties of the compound. Many different organ systems may be affected, and there are several mechanisms involved in determining organ-specific, and sometimes cell-selective, toxicity. An imbalance between bioactivation of a drug to a toxic metabolite and its detoxification is of prime importance in determining individual susceptibility. Such an imbalance may be genetically determined or acquired and, furthermore, may be systemic or tissue-specific. Prevention of metabolite-mediated toxicity is possible once the mechanism of toxicity has been elucidated.

Serum carnosinase activities in central nervous system disorders

Serum carnosinase activity was assayed in five groups of patients with neurological disorders. Enzyme activities in patients with idiopathic epilepsy (mean +/- S.E.M., 148 +/- 11 nmol/ml per min) and motor neurone disease (155 +/- 15 nmol/ml per min) were similar to the control group (161 +/- 7 nmol/ml per min). Reduced serum carnosinase activity was observed in patients with Parkinson's disease (109 +/- 11 nmol/ml per min, P < 0.005), multiple sclerosis (82.5 +/- 10.0 nmol/ml per min, P < 0.005) and patients following a cerebrovascular accident (74.6 +/- 5.4 nmol/ml per min, P < 0.001) compared with the control group. Carnosinase activity, 5-10% of that found in serum, was detected in CSF samples. The cause of reduced serum carnosinase activities in central nervous system disorders is unclear, although anoxic damage to carnosinase-producing cells or disruption of the blood-brain barrier may be responsible.