Treatment of spatial memory impairment in hamsters infected with West Nile virus using a humanized monoclonal antibody MGAWN1

Abstract

In addition to functional disorders of paresis, paralysis, and cardiopulmonary complications, subsets of West Nile virus (WNV) patients may also experience neurocognitive deficits and memory disturbances. A previous hamster study has also demonstrated spatial memory impairment using the Morris water maze (MWM) paradigm. The discovery of an efficacious therapeutic antibody MGAWN1 from pre-clinical rodent studies raises the possibility of preventing or treating WNV-induced memory deficits. In the current study, hamsters were treated intraperitoneally (i.p.) with 32 mg/kg of MGAWN1 at 4.5 days after subcutaneously (s.c.) challenging with WNV. As expected, MGAWN1 prevented mortality, weight loss, and improved food consumption of WNV-infected hamsters. The criteria for entry of surviving hamsters into the study were that they needed to have normal motor function (forelimb grip strength, beam walking) and normal spatial reference memory in the MWM probe task. Twenty-eight days after the acute phase of the disease had passed, MGAWN1- and saline-treated infected hamsters were again trained in the MWM. Spatial memory was evaluated 48 h after this training in which the hamsters searched for the location where a submerged escape platform had been positioned. Only 56% of infected hamsters treated with saline spent more time in the correct quadrant than the other three quadrants, as compared to 92% of MGAWN1-treated hamsters (P⩽0.05). Overall these studies support the possibility that WNV can cause spatial memory impairment and that therapeutic intervention may be considered.

Figure 1

Timeline of experimental paradigm for evaluating spatial memory performance in hamsters. Abbreviations: Pretraining, prior to acquisition training, animals first acclimate to the maze and learn to mount a platform to escape the water; AQ, Morris water maze acquisition trials- (15 trials= 5 trials per day for 3 days-permits animals to learn to use distal cues around the room to locate a hidden submerged escape platform); PR_i , initial probe trial (platform is removed) conducted after 15^th acquisition trial; PR₄₈, probe trial conducted 48 h after last acquisition trial; Q1-Q4 divisions (quadrants) of the of the water maze (larger circle) in which a submerged (hidden) escape platform (small dotted circle) was positioned in the center (quadrant 1 during pre-infection acquisition trials and quadrant 3 during post-infection acquisition trials; WNV inj, West Nile virus (10⁴ pfu, NY99) was administered s.c.; MGAWN1 (32 mg/kg) or saline was administered i.p. 4.5 days after WNV inoculation.

Figure 2

Survival of hamsters treated i.p. with MGAWN1 (32 mg/kg) or saline at 4.5 days after s.c. WNV injection.

Figure 3

Effect of i.p. administration of MGAWN1 or saline on A) body mass, or B) food consumption of WNV-infected hamsters in Figure 2.

Figure 4

Morris Water Maze (MWM) 48 h probe trial for spatial learning and memory of hamsters (A) prior to WNV inoculation, or 28 days following inoculation and treated i.p. with B) saline or C) MGAWN1 (32 mg/kg) at 4.5 dpi. Timeline of experimental paradigm is outlined in Figure 1. The percentage of time spent in each of the quadrants during the first 60 s of the probe trail was measured from playback of video. The criterion for a successful trial used to construct Table 1 is that the hamster needed to occupy more time in the target quadrant than in any other quadrant, indicating that their long-term memory of the platform’s position during acquisition trials remained intact (25% dwell time = chance). (A) Pre-infection 48 hr probe trial of the 22 animals that survived WNV infection and whose 48 hr probe results following infection are shown in B and C. (B) Four of the 9 hamsters treated with saline (#126, #106, #108, #162) performed poorly on the 48 h probe trial; (C) only 1 of the 13 MGAWN1 treated hamsters (#165) did not remember the platform’s position and exhibited primarily thigmotaxic swimming during acquisition and probe trials.

Figure 5

Forelimb grip strength test in hamsters before or after viral challenge treated i.p. with MGAWN1 or saline.