Hepoxilins are
12-lipoxygenase metabolites of
arachidonic acid found in the CNS. They can modulate neuronal signaling but their functions are not known. We examined the effects of
hepoxilin A(3) on neurite outgrowth post-
axotomy in an in vitro model of
spinal cord transection using superior cervical ganglion neurons. In the absence of
nerve growth factor,
hepoxilin A(3) did not support neuronal survival, or regeneration post-
axotomy but did significantly enhance neurite regeneration in the presence of
nerve growth factor. As early as 1 h post-injury hepoxilin A(3)-treated cultures (+
nerve growth factor) had significantly more neurites than controls (
nerve growth factor alone). Average hourly rates of outgrowth in hepoxilin A(3)-treated cultures were significantly higher than in controls for at least 12 h post-injury, suggesting that the effect of
hepoxilin A(3) is maintained in vitro for several hours post-injury. In uninjured neurons
hepoxilin A(3) caused a rapid but transient increase in intracellular
calcium in the somata; by 2 min post-addition,
calcium levels decreased to a new stable plateau significantly higher than pre treatment levels. In injured neurons,
hepoxilin A(3) addition immediately post-transection caused a rapid transient increase in intracellular
calcium in cell bodies; however, peak
calcium levels were significantly lower than in uninjured neurons and the new baseline lower than in uninjured cells. In uninjured cells
hepoxilin A(3) addition in zero
calcium produced the same pattern, a transient elevation and subsequent decline to a new stable baseline significantly above rest but in injured cells levels fell rapidly to pretreatment values. Taken overall, these findings demonstrate a novel role for hepoxilins as a potentiator of neurite regeneration. They also provide the first evidence that this
lipoxygenase metabolite can alter intracellular
calcium in neurons by causing release of
calcium from intracellular stores and modulating
calcium influx mechanisms.