Vitamin B6 derivatives protect the retinal neurons from excitotoxic injury in vitro. However, their in vivo role in a process involving excitotoxicity, such as
ischemia, remains unknown. We studied potential protective effects of
pyridoxal 5'-phosphate (PLP) and
pyridoxal hydrochloride (
pyridoxal) on the retinal neurons in a monkey model of transient global
ischemia. Daily
intravenous injections (15 mg/kg) of
pyridoxal and PLP were performed for consecutive 10 days. On the sixth day, whole brain complete
ischemia was produced by clipping the innominate and the left subclavian arteries for 20 min. The monkeys were sacrificed 5 days after
ischemia and their retinas were processed for histological analysis. The
ischemia induced a marked cellular injury in the retina as shown by the loss of
ganglion cells and the reduction of thickness of the
ganglion cell, inner plexiform, and inner nuclear layers. PLP significantly prevented the
ganglion cell loss and the reduction of thickness of the
ganglion cell layer.
Pyridoxal significantly prevented the
ganglion cell loss as well as the reduction of thickness of
ganglion cell, inner plexiform and inner nuclear layers. These results suggest that PLP and
pyridoxal counteract the postischemic neuronal death in the adult primate retina, offering a potential for a novel
pharmacotherapy of
retinal ischemic injury.