Phospholipase B activity and organophosphorus compound toxicity in cultured neural cells
David J Read1, Lynda Langford, Helen R Barbour
1MRC Toxicology Unit, University of Leicester, LE1 9HN, UK.
Abstract:
Organophosphorus compounds (OP) such as phenyl saligenin phosphate (PSP) and mipafox (MPX) which cause delayed neuropathy, inhibit neuropathy target esterase (NTE), while OPs such as paraoxon (PXN) react more readily with acetylcholinesterase. In yeast and mammalian cell lines, NTE has been shown to have phospholipase B (PLB) activity which deacylates intracellular phosphatidylcholine to glycerophosphocholine (GroPCho) and can be detected by metabolic labeling with [(14)C]choline. Here we investigated PLB activity in primary cultures of mouse neural cells. In cortical and cerebellar granule neurons and astrocytes, [(14)C]GroPCho labeling was inhibited by PSP and MPX: phenyl dipentylphosphinate (PDPP), a non-neuropathic NTE inhibitor, was more potent, while PXN, was substantially less so. In all three cell types, conversion of [(14)C]phosphatidylcholine to [(14)C]GroPCho over 24 h was relatively small (2.3-14%). Consequently, even with >80% inhibition of [(14)C]GroPCho production, increased [(14)C]phosphatidylcholine was not detected. At concentrations of 1-10 microM, only PSP was cytotoxic to cortical and cerebellar granule neurons after 24-h exposure. Moreover, dramatic changes in glial cell morphology were induced by PSP, but not PDPP or MPX, with rapid (2-3 h) rounding up of astrocytes and of Schwann cells in cultures of dissociated mouse dorsal root ganglia. We conclude that PLB activity is present in a variety of cultured mouse neural cell types but that acute loss of this activity is not cytotoxic. Conversely, the rapid toxic effects of PSP in vitro suggest that a serine hydrolase distinct from NTE is required continuously by neurons and glia.
Insights
Organophosphorus compounds (OPs) inhibit phospholipase B (PLB) activity in mouse neural cells. While acute loss of PLB activity isn't cytotoxic, phenyl saligenin phosphate (PSP) shows rapid toxicity, suggesting a distinct serine hydrolase is essential.
Area of Science:
- Neuroscience
- Toxicology
- Cell Biology
Background:
- Organophosphorus compounds (OPs) are known neurotoxins that inhibit neuropathy target esterase (NTE) and acetylcholinesterase.
- NTE possesses phospholipase B (PLB) activity, deacylating phosphatidylcholine, which can be detected via metabolic labeling.
- Previous studies indicated NTE's PLB activity in yeast and mammalian cell lines.
Purpose of the Study:
- To investigate phospholipase B (PLB) activity in primary cultures of mouse neural cells.
- To determine the effects of specific organophosphorus compounds on PLB activity and cell viability.
- To explore the potential role of PLB activity in neural cell toxicity.
Main Methods:
- Primary cultures of mouse cortical and cerebellar neurons and astrocytes were used.
- Metabolic labeling with [(14)C]choline was employed to detect PLB activity by measuring [(14)C]glycerophosphocholine (GroPCho) production.
- Cells were exposed to various organophosphorus compounds, including phenyl saligenin phosphate (PSP), mipafox (MPX), phenyl dipentylphosphinate (PDPP), and paraoxon (PXN), to assess inhibition and cytotoxicity.
Main Results:
- PSP and MPX significantly inhibited [(14)C]GroPCho labeling in neurons and astrocytes, indicating inhibition of PLB activity.
- Phenyl dipentylphosphinate (PDPP) was a more potent inhibitor than PSP or MPX, while paraoxon (PXN) showed minimal inhibition.
- PSP induced rapid cytotoxic effects and significant morphological changes in glial cells (astrocytes and Schwann cells) at 1-10 microM, while other OPs did not.
Conclusions:
- Phospholipase B (PLB) activity is present in various cultured mouse neural cell types.
- Acute inhibition of PLB activity by OPs is not cytotoxic.
- The rapid toxicity of PSP suggests a distinct serine hydrolase, separate from NTE, is crucial for neuronal and glial cell function.
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