Neuroprotective Effects of Oral Lamotrigine Administration on Rabbit Retinas After Pars Plana Vitrectomy and Silicone Oil Injection

NF1 mutation-driven neuronal hyperexcitability sets a threshold for tumorigenesis and therapeutic targeting of murine optic glioma

BACKGROUND

With the recognition that noncancerous cells function as critical regulators of brain tumor growth, we recently demonstrated that neurons drive low-grade glioma initiation and progression. Using mouse models of neurofibromatosis type 1 (NF1)-associated optic pathway glioma (OPG), we showed that Nf1 mutation induces neuronal hyperexcitability and midkine expression, which activates an immune axis to support tumor growth, such that high-dose lamotrigine treatment reduces Nf1-OPG proliferation. Herein, we execute a series of complementary experiments to address several key knowledge gaps relevant to future clinical translation.

METHODS

We leverage a collection of Nf1-mutant mice that spontaneously develop OPGs to alter both germline and retinal neuron-specific midkine expression. Nf1-mutant mice harboring several different NF1 patient-derived germline mutations were employed to evaluate neuronal excitability and midkine expression. Two distinct Nf1-OPG preclinical mouse models were used to assess lamotrigine effects on tumor progression and growth in vivo.

RESULTS

We establish that neuronal midkine is both necessary and sufficient for Nf1-OPG growth, demonstrating an obligate relationship between germline Nf1 mutation, neuronal excitability, midkine production, and Nf1-OPG proliferation. We show anti-epileptic drug (lamotrigine) specificity in suppressing neuronal midkine production. Relevant to clinical translation, lamotrigine prevents Nf1-OPG progression and suppresses the growth of existing tumors for months following drug cessation. Importantly, lamotrigine abrogates tumor growth in two Nf1-OPG strains using pediatric epilepsy clinical dosing.

CONCLUSIONS

Together, these findings establish midkine and neuronal hyperexcitability as targetable drivers of Nf1-OPG growth and support the use of lamotrigine as a potential chemoprevention or chemotherapy agent for children with NF1-OPG.

Functional and structural evaluation of lamotrigine treatment in rat models of acute and chronic ocular hypertension

Voltage gated sodium channels (Nav), are proposed mediators of neuronal damage in ischemic and excitotoxicity disease models. We evaluated the neuroprotective effects of lamotrigine, a Nav blocker, in the acute and chronic rat ocular hypertension models. Additionally, expression of the main Nav subtypes in the optic nerve (ON) was assessed to test whether their upregulation plays a role in the pathogenesis of ocular hypertension induced optic neuropathy. Unilateral intraocular pressure (IOP) elevation was induced for 60 min (80 mmHg) and 14-21 days (670-859 mmHg*day) in the acute and chronic models, respectively. Lamotrigine was administered at dosages of 10 mg/kg twice daily and 12.5 mg/kg once daily in the acute (n = 9) and chronic (n = 11) trials, respectively. Treatment began 2 days prior to IOP elevation until sacrifice. Outer and inner retinal function was evaluated with dark- and light-adapted flash electroretinography and pattern electroretinography, respectively, 6 and 14 days post acute IOP elevation and 13, 28 and 48 days post chronic IOP elevation. Retinal ganglion cell and axon densities and inflammatory reaction were evaluated through Fluorogold, Bielschowsky's silver impregnation and ED1 labeling respectively. Immunohistochemistry for Nav1.1, 1.2 and 1.6 was performed in ONs of untreated rats 7 and 15 days post IOP elevation in the acute model and after 7, 28 and 50 days in the chronic model. In the acute model, no differences were found in the a-wave amplitudes between lamotrigine-treated and vehicle-treated rats. B-wave amplitudes decreased by 40-66% in both treatment groups 6 days post IOP elevation, with no significant difference between groups (p = 0.38). However, a partial recovery of b-wave amplitudes was found in lamotrigine-treated rats between day 6 and day 14 post procedure (p < 0.05). No differences were found in any other parameter tested in this model. Similarly, lamotrigine treatment did not result in any beneficial effect in structural parameters of the chronic model. Functional evaluation of this model was inconclusive due to super-normal values in the hypertensive eyes. Up-regulation of Nav1.1 and 1.2 expression was found in both models, beginning by day 7; an increase of the former continued in a time-dependent manner in the chronic model. Nav1.6 labeling was inconclusive. In conclusion we found lamotrigine treatment to be mostly ineffective in both acute and chronic ocular hypertension models.