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Methylmalonate toxicity in primary neuronal cultures
B A McLaughlin1, D Nelson, I A Silver
1Institute of Neurological Sciences, University of Pennsylvania, Philadelphia 19104, USA.
Abstract:
Several inhibitors of mitochondrial complex II cause neuronal death in vivo and in vitro. The goal of the present work was to characterize in vitro the effects of malonate (a competitive blocker of the complex) which induces neuronal death in a pattern similar to that seen in striatum in Huntington's disease. Exposure of striatal and cortical cultures from embryonic rat brain for 24 h to methylmalonate, a compound which produces malonate intracellularly, led to a dose-dependent cell death. Methylmalonate (10 mM) caused >90% mortality of neurons although cortical cells were unexpectedly more vulnerable. Cell death was attenuated in a medium containing antioxidants. Further characterization revealed that DNA laddering could be detected after 3 h of treatment. Morphological observations (videomicroscopy and Hoechst staining) showed that both necrotic and apoptotic cell death occurred in parallel; apoptosis was more prevalent. A decrease in the ATP/ADP ratio was observed after 3 h of treatment with 10 mM methylmalonate. In striatal cultures it occurred concomitantly with a decline in GABA and a rise in aspartate content and the aspartate/glutamate ratio. Changes in ion concentrations were measured in similar cortical cultures from mouse brain. Neuronal [Na+]i increased while [K+]i and membrane potential decreased after 20 min of continuous incubation in 10 mM methylmalonate. These changes progressed with time, and a rise in [Ca2+]i was also observed after 1 h. The results demonstrate that malonate collapses cellular ion gradients, restoration of which imposes an additional load on the already compromised ATP-generation machinery. An early elevation in [Ca2+]i may trigger an increase in activity of proteases, lipases and endonucleases and production of free radicals and DNA damage which, ultimately, leads to cells death. The data also suggest that maturational and/or extrinsic factors are likely to be critical for the increased vulnerability of striatal neurons to mitochondrial inhibition in vivo.
Insights
Methylmalonate, a malonate-producing compound, causes dose-dependent neuronal death by inhibiting mitochondrial complex II. This leads to ATP depletion, ion gradient collapse, and increased calcium, triggering apoptosis and necrosis, particularly in striatal neurons.
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Inhibitors of mitochondrial complex II induce neuronal death.
- Malonate's effects mimic Huntington's disease pathology in the striatum.
- Methylmalonate produces malonate intracellularly, serving as a model compound.
Purpose of the Study:
- To characterize the in vitro effects of malonate on neuronal death.
- To investigate the mechanisms underlying methylmalonate-induced neurotoxicity.
- To compare the vulnerability of striatal and cortical neurons to mitochondrial inhibition.
Main Methods:
- Primary neuronal cultures (striatal and cortical) from embryonic rats.
- Exposure to methylmalonate and assessment of cell viability.
- Measurement of ATP/ADP ratio, neurotransmitter levels, and ion concentrations.
- DNA laddering, videomicroscopy, and Hoechst staining for cell death analysis.
Main Results:
- Methylmalonate caused dose-dependent neuronal death (>90% mortality at 10 mM), with cortical cells being more vulnerable.
- Antioxidants attenuated cell death, indicating oxidative stress involvement.
- Apoptosis and necrosis were observed, with apoptosis being more prevalent.
- Methylmalonate decreased ATP/ADP ratio, altered neurotransmitter levels (GABA, aspartate), and disrupted ion gradients ([Na+]i, [K+]i, membrane potential, [Ca2+]i).
Conclusions:
- Malonate-induced neurotoxicity involves ATP depletion and ion gradient collapse, increasing cellular stress.
- Early elevation of intracellular calcium may trigger apoptotic and necrotic pathways.
- Maturational and/or extrinsic factors likely influence striatal neuron vulnerability to mitochondrial inhibition.