Free Radical Scavenging and Inhibition of Nitric Oxide Synthase Potentiates the Neurotrophic Effects of Brain-Derived Neurotrophic Factor on Axotomized Retinal Ganglion CellsIn Vivo

Abstract

Brain-derived neurotrophic factor (BDNF) partially promotes the survival of axotomized retinal ganglion cells (RGCs). In analogy with in vitro experiments (Koh et al., 1995;Samdami et al., 1996), we tested whether neuroprotection by BDNF is limited by adverse effects as a consequence of excessive free radical formation. First, we investigated whether BDNF and the free radical scavenger N-tert-butyl-(2-sulfophenyl)-nitrone (S-PBN) cooperate in protecting RGCs from axotomy-induced death. Although systemic S-PBN treatment alone did not influence RGC survival after axotomy, it potentiated the neuroprotective effects of BDNF significantly. Single BDNF treatment rescued 27% of the RGCs, which otherwise would have died 14 d after optic nerve transection, whereas a combined treatment of BDNF and S-PBN improved this rescue rate up to 68%. We then investigated whether the adverse effects of BDNF could be ascribed to activation of nitric oxide synthase (NOS). We found colocalization of NOS and the BDNF receptor TrkB in the retina. NADPH-diaphorase reactivity, a reliable marker for NOS in the rat retina, increased after chronic BDNF treatment in vivo. Systemic application of the NOS-inhibitor N--nitro-L-argininemethylester (L-NAME) potentiated the neuroprotective action of BDNF (55% rescue rate). We conclude that activation of NOS is a pathological consequence of BDNF application, which reduces its neuroprotective potential. The observation that this adverse effect can be antagonized by systemic application of free radical scavengers could be of relevance for clinical applications of neurotrophins in human neurodegenerative diseases.

Reduction of Potassium Currents and Phosphatidylinositol 3-Kinase-Dependent Akt Phosphorylation by Tumor Necrosis Factor-α Rescues Axotomized Retinal Ganglion Cells from Retrograde Cell DeathIn Vivo

“…Fiber tract lesion of the retinocollicular projection in the rat is an established model to investigate secondary neuronal loss in degenerative processes of the mammalian CNS because of its good surgical accessibility and well known kinetics of cell death (Villegas-Perez et al, 1988;Mey and Thanos, 1993;Bähr and Bonhoeffer, 1994;Bähr and Wizenmann, 1996;Klöcker et al, 1997Klöcker et al, , 1998Kermer et al, 1999aKermer et al, , 2000. Transection of the ON induces a delayed death of 80 -90% of RGCs within 14 d, starting around day 4 and reaching a maximum on day 7 after axotomy (Eschweiler and Bähr, 1993;Mansour-Robaey et al, 1994).…”

Increased expression and activation of poly(ADP-ribose) polymerase (PARP) contribute to retinal ganglion cell death following rat optic nerve transection

“…16,17 In addition, neuroprotective effects of several neurotrophic factors on axotomized RGCs seem to be partially due to mechanisms other than inhibition of intracellular caspase activity. 20,47 In the present study, we therefore examined the role of PARP, which has been identified as an important mediator of a necrotic-type cell death, in axotomy-induced RGC death. Following ON transection, we observed an RGC-specific, transient increase in PARP activity as shown by GCLspecific enhancement of poly(ADP-ribose) polymer formation.…”

“…36 Rat optic nerve (ON) transection consistently leads to secondary death of about 85% of the entire retinal ganglion cell (RGC) population within 14 days after injury. 20,43 In contrast to cell death occurring after ischemia-reperfusion injury, this secondary RGC death is mainly apoptotic. 1,15 It can partially but not entirely be blocked by intravitreal application of potent caspase inhibitors.…”

Transduction of axotomized retinal ganglion cells by adenoviral vector administration at the optic nerve stump: an in vivo model system for the inhibition of neuronal apoptotic cell death

“…20 Briefly, adult female Sprague-Dawley rats (200-250 g; purchased from Charles River, Sulzfeld, Germany) were anesthetized by intraperitoneal injection of chloral hydrate (0.42 g/kg body weight). After skin incision close to the superior orbital rim, the orbita was opened taking care to leave the supraorbital vein intact.…”

“…Cutting the rat optic nerve results in apoptotic cell death of more than 80% of the retinal ganglion cells, which are the only retinal cells projecting an axon into the optic nerve, 14 days after the lesion has been set. [17][18][19] In recent studies we have successfully used the intraocular injection of recombinant BDNF peptide along with free radical scavenger 20 and inhibitory peptides for caspases 21 to prevent apoptosis of RGCs. However, due to the short half-life of the peptides repeated injections were necessary, finally resulting in overall damage of the retina.…”