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In vivo intracerebral microdialysis studies in rats of MPP+ analogues and related charged species
H Rollema1, E A Johnson, R G Booth
1Department of Medicinal Chemistry, University Center for Pharmacy, Groningen, The Netherlands.
Abstract:
The in vivo dopaminergic neurotoxic properties of 45 MPTP and MPP+ analogues and related compounds were examined by an intrastriatal microdialysis assay in conscious rats. MPP(+)-like toxicity, as evidenced by the irreversible effects on DA release and enhancement of lactate formation, was observed with a variety of structural types although no compound was more toxic than MPP+. The following global structure-toxicity relationships could be derived: (1) only permanently charged compounds showed neurotoxic effects; (2) with the exception of amino groups, hydrophilic substituents abolished toxicity; (3) activity was enhanced by lipophilic groups although increased steric bulk around the nitrogen atom tended to decrease activity; (4) nonaromatic, quaternary systems (methiodide of MPTP, guanidinium derivatives) were only weakly toxic; and (5) certain bi- and tricyclic systems, including putative metabolites of potential endogenous MPTP-like compounds, were weakly toxic. The lack of toxic effects following perfusions with DA itself confirmed that MPTP dopaminergic neurotoxicity is not likely to be mediated by the MPP(+)-induced release of DA. With some interesting exceptions, these in vivo data correlate reasonably well with in vitro data on the nerve terminal uptake properties and the inhibitory effects on mitochondrial respiration of these compounds.
Insights
Researchers studied MPTP and MPP+ analogues for dopaminergic neurotoxicity in rats. Structure-toxicity relationships were identified, revealing permanently charged, lipophilic compounds are most toxic, guiding future neurotoxin research.
Area of Science:
- Neuroscience
- Toxicology
- Pharmacology
Background:
- MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and its metabolite MPP+ (1-methyl-4-phenylpyridinium) are known dopaminergic neurotoxins.
- Understanding the structure-toxicity relationships of MPTP/MPP+ analogues is crucial for developing neuroprotective strategies and understanding Parkinson's disease pathogenesis.
Purpose of the Study:
- To investigate the in vivo dopaminergic neurotoxic properties of various MPTP and MPP+ analogues.
- To establish global structure-toxicity relationships for these compounds in a rodent model.
Main Methods:
- Intrastriatal microdialysis assay in conscious rats.
- Assessment of irreversible effects on dopamine (DA) release and lactate formation.
- Evaluation of structure-activity relationships based on chemical properties like charge, lipophilicity, and steric bulk.
Main Results:
- MPP(+)-like toxicity was observed across various structural types, but no analogue exceeded MPP+'s toxicity.
- Permanently charged compounds exhibited neurotoxic effects, while hydrophilic substituents generally abolished toxicity.
- Lipophilic groups enhanced activity, but increased steric bulk near the nitrogen atom reduced it. Nonaromatic quaternary systems and certain polycyclic compounds showed weak toxicity.
- Dopamine itself did not induce neurotoxicity, suggesting MPP+-induced DA release is not the primary mechanism.
Conclusions:
- Established key structure-toxicity relationships for MPTP/MPP+ analogues, highlighting the importance of permanent positive charge and lipophilicity.
- The findings provide valuable insights into the molecular mechanisms underlying MPTP-induced dopaminergic neurotoxicity.
- These structure-activity relationship insights can inform the design of novel compounds with modulated neurotoxic potential or aid in identifying endogenous neurotoxins.