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Treatment with conotoxin, an 'N-type' calcium channel blocker, in neuronal hypoxic-ischemic injury
K P Madden1, W M Clark, F W Marcoux
1Department of Neurosciences, University of California, San Diego 92161.
Abstract:
Therapeutic efficacy of calcium channel blockers in stroke remains controversial, but previously used agents bind almost exclusively to L-type calcium channels. The newly-discovered N-type calcium channel is specific to neurons, and therapy involving blockade of this site has not been previously attempted. We assessed the neuroprotective effect of omega-conotoxin GVIA (CgTx), a blocker of N-type calcium channels, using both in vitro hypoxic injury to rat cortical neurons and an in vivo model of reversible spinal cord ischemia in the rabbit. In cell cultures, CgTx inhibited hypoxia-induced 45Ca accumulation and neuronal injury minimally, compared to the NMDA antagonist ketamine. In vivo, the duration of spinal cord ischemia which produced permanent paraplegia in 50% of control animals (ET50) was 24.0 +/- 2.6 min. Animals treated 2 h prior to ischemia with 0.5 nmol CgTx in the subarachnoid space had an ET50 of 26.9 +/- 1.8 min (P = 0.36). Animals treated 24 h prior to ischemia (all had persistent systemic tremor) had a ET50 of 28.9 +/- 1.8 min (P = 0.13). We conclude that pharmacologic modulation of the N-type calcium channel does not provide a significant protective effect against neuronal hypoxic-ischemic injury.
Insights
Blocking N-type calcium channels with omega-conotoxin GVIA (CgTx) did not significantly protect neurons from hypoxic-ischemic injury in vitro or in vivo spinal cord ischemia models. This suggests N-type calcium channel modulation is not a viable therapeutic strategy for stroke.
Area of Science:
- Neuroscience
- Pharmacology
- Ischemic Injury Research
Background:
- Therapeutic efficacy of calcium channel blockers for stroke is debated, with existing drugs targeting L-type channels.
- N-type calcium channels, specific to neurons, represent a novel therapeutic target for neuroprotection.
- Previous attempts at N-type calcium channel blockade for neuroprotection have not been documented.
Purpose of the Study:
- To assess the neuroprotective potential of omega-conotoxin GVIA (CgTx), an N-type calcium channel blocker.
- To evaluate CgTx efficacy in both in vitro models of neuronal hypoxic injury and in vivo models of spinal cord ischemia.
Main Methods:
- In vitro: Rat cortical neurons subjected to hypoxia, with CgTx tested against hypoxia-induced calcium influx and injury.
- In vivo: Rabbit model of reversible spinal cord ischemia to determine the time to permanent paraplegia (ET50).
- CgTx administered intrathecally 2 hours or 24 hours prior to ischemic insult.
Main Results:
- In vitro, CgTx showed minimal inhibition of hypoxia-induced calcium accumulation and neuronal damage compared to ketamine.
- In vivo, CgTx treatment (2h or 24h pre-ischemia) did not significantly alter the ET50 compared to controls.
- Systemic tremor was observed in animals treated 24 hours prior to ischemia.
Conclusions:
- Pharmacological blockade of N-type calcium channels with CgTx does not confer significant neuroprotection against hypoxic-ischemic injury.
- N-type calcium channel modulation is unlikely to be a successful therapeutic strategy for conditions like stroke or spinal cord ischemia.
- Further research into alternative neuroprotective mechanisms is warranted.