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Fluorocitrate and fluoroacetate effects on astrocyte metabolism in vitro
1Department of Neurology, University of California, San Francisco.
Abstract:
The Krebs cycle inhibitor fluorocitrate (FC) and its precursor fluoroacetate (FA) are taken up in brain preferentially by glia. These compounds are used experimentally to inhibit glial metabolism in situ. The actions of these agents have been attributed to both the disruption of carbon flux through the Krebs cycle and to impairment of ATP production. We used primary astrocyte cultures to evaluate these two possible modes of action. Astrocyte ATP levels exhibited little or no reduction during incubation with 0.5 mM FC or 25 mM FA. Correspondingly, FC and FA caused less than 30% reductions in glutamate uptake (P > 0.05), an important energy-dependent astrocyte function. Carbon flux through the Krebs cycle was assessed by measuring astrocyte glutamine production in the absence of exogenous glutamate or aspartate. Under these conditions, glutamine production was reduced 65 +/- 5% by 0.5 mM FC and 61 +/- 3% by 25 mM FA (P < 0.01). In contrast, FC and FA had no effect on glutamine production when 50 microM glutamate was provided in the media. These findings suggest that the metabolic effects of FC and FA on astrocytes in vivo result from impairment of carbon flux through the Krebs cycle, and not from impairment of oxidative ATP production.
Insights
Fluorocitrate (FC) and fluoroacetate (FA) inhibit glial metabolism by disrupting Krebs cycle carbon flux, not by reducing ATP production. This finding clarifies the mechanism of these widely used experimental agents.
Area of Science:
- Neuroscience
- Cellular Metabolism
- Biochemistry
Background:
- Fluorocitrate (FC) and fluoroacetate (FA) are glial metabolism inhibitors.
- Their mechanism is debated: Krebs cycle disruption vs. ATP production impairment.
Purpose of the Study:
- To investigate the precise metabolic effects of FC and FA on astrocytes.
- To differentiate between Krebs cycle inhibition and ATP production impairment.
Main Methods:
- Primary astrocyte cultures were used.
- ATP levels and glutamate uptake were measured.
- Glutamine production was assessed to evaluate Krebs cycle flux.
Main Results:
- FC and FA did not significantly reduce astrocyte ATP levels or glutamate uptake.
- FC and FA markedly reduced glutamine production, indicating Krebs cycle inhibition.
- This inhibition was observed in the absence of exogenous glutamate.
Conclusions:
- FC and FA primarily impair astrocyte metabolism by disrupting Krebs cycle carbon flux.
- ATP production is not significantly affected by these agents at tested concentrations.
- Findings clarify the mechanism of action for FC and FA in glial research.