A simple integrated system for electrophysiologic recordings in animals

A Single Intravitreal Injection of Ranibizumab Provides No Neuroprotection in a Nonhuman Primate Model of Moderate-to-Severe Nonarteritic Anterior Ischemic Optic Neuropathy

PURPOSE

Ranibizumab, a vascular endothelial growth factor-antagonist, is said to be neuroprotective when injected intravitreally in patients with nonarteritic anterior ischemic optic neuropathy (NAION). We evaluated the efficacy of a single intravitreal (IVT) injection of ranibizumab in a nonhuman primate model of NAION (pNAION).

METHODS

We induced pNAION in one eye of four adult male rhesus monkeys using a laser-activated rose Bengal induction method. We then immediately injected the eye with either ranibizumab or normal saline (NS) intravitreally. We performed a clinical assessment, optical coherence tomography, electrophysiological testing, fundus photography, and fluorescein angiography in three of the animals (one animal developed significant retinal hemorrhages and, therefore, could not be analyzed completely) prior to induction, 1 day and 1, 2, and 4 weeks thereafter. Following the 4-week analysis of the first eye, we induced pNAION in the contralateral eye and then injected either ranibizumab or NS, whichever substance had not been injected in the first eye. We euthanized all animals 5 to 12 weeks after the final assessment of the second eye and performed both immunohistochemical and light and electron microscopic analyses of the retina and optic nerves of both eyes.

RESULTS

A single IVT dose of ranibizumab administered immediately after induction of pNAION resulted in no significant reduction of clinical, electrophysiological, or histologic damage compared with vehicle-injected eyes.

CONCLUSIONS

A single IVT dose of ranibizumab is not neuroprotective when administered immediately after induction of pNAION.

Peripapillary Retinal Nerve Fiber Layer Swelling Predicts Peripapillary Atrophy in a Primate Model of Nonarteritic Anterior Ischemic Optic Neuropathy

Purpose

To determine the relationship between peripapillary retinal nerve fiber layer (PRNFL) swelling and eventual PRNFL atrophy, and between PRNFL swelling/atrophy and neural function, in a nonhuman primate model of nonarteritic anterior ischemic optic neuropathy (pNAION).

Methods

pNAION was induced in five normal, adult male rhesus monkeys by laser activation of intravenously injected rose bengal at the optic nerve head. Spectral-domain optical coherence tomography measurements of the PRNFL were performed at baseline; 1 day; 1, 2, and 4 weeks; and several later times over a period of an additional 2 to 3 months. Simultaneous pattern-reversal electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded and color fundus photographs taken at the same time points.

Results

In all cases, initial PRNFL swelling was associated with atrophy, and the greater the initial swelling, the greater the degree of eventual atrophy (r = 0.65, P = 0.0002). The change in PRNFL thickness closely correlated with VEP amplitude loss (r = 0.90), although this relationship was only a strong trend (P = 0.083). Furthermore, VEP amplitude loss closely correlated with PERG N95 amplitude loss (r = 0.80, P = 0.00002)

Conclusions

In our model of human NAION, the degree of initial PRNFL swelling correlated with the severity of atrophy. Areas that did not swell developed little to no atrophy. The amount of PRNFL loss was reflected in VEP and PERG N95 amplitude reductions.

Sustained neuroprotection from a single intravitreal injection of PGJ₂ in a nonhuman primate model of nonarteritic anterior ischemic optic neuropathy

PURPOSE

Prostaglandin J₂ (PGJ₂) is neuroprotective in a murine model of nonarteritic anterior ischemic optic neuropathy (NAION). After assessing for potential toxicity, we evaluated the efficacy of a single intravitreal (IVT) injection of PGJ₂ in a nonhuman primate model of NAION (pNAION).

METHODS

We assessed PGJ₂ toxicity by administering it as a single high-dose intravenous (IV) injection, consecutive daily high-dose IV injections, or a single IVT injection in one eye of five adult rhesus monkeys. To assess efficacy, we induced pNAION in one eye of five adult male rhesus monkeys using a laser-activated rose bengal induction method. We then injected the eye with either PGJ₂ or phosphate-buffered saline (PBS) intravitreally immediately or 5 hours post induction. We performed a clinical assessment, optical coherence tomography, electrophysiological testing, fundus photography, and fluorescein angiography in all animals prior to induction and at 1 day, 1 week, 2 weeks, and 4 weeks after induction. Following analysis of the first eye, we induced pNAION in the contralateral eye and then injected either PGJ₂ or PBS. We euthanized all animals 5 weeks after final assessment of the fellow eye and performed both immunohistochemical and light and electron microscopic analyses of the retina and optic nerves.

RESULTS

TOXICITY

PGJ₂ caused no permanent systemic toxicity regardless of the amount injected or route of delivery, and there was no evidence of any ocular toxicity with the dose of PGJ₂ used in efficacy studies. Transient reduction in the amplitudes of the visual evoked potentials and the N95 component of the pattern electroretinogram (PERG) occurred after both IV and IVT administration of high doses of PGJ₂; however, the amplitudes returned to normal in all animals within 1 week.

EFFICACY

In all eyes, a single IVT dose of PGJ₂ administered immediately or shortly after induction of pNAION resulted in a significant reduction of clinical, electrophysiological, and histological damage compared with vehicle-injected eyes (P = 0.03 for both VEP and PERG; P = 0.05 for axon counts).

CONCLUSIONS

In nonhuman primates, PGJ₂ administered either intravenously or intravitreally produces no permanent toxicity at even four times the dose given for neuroprotection. Additionally, a single IVT dose of PGJ₂ is neuroprotective when administered up to 5 hours after induction of pNAION.