Inhibition of the cluster of differentiation 14 innate immunity pathway with IAXO-101 improves chronic microelectrode performance

Abstract

Objective: Neuroinflammatory mechanisms are hypothesized to contribute to intracortical microelectrode failures. The cluster of differentiation 14 (CD14) molecule is an innate immunity receptor involved in the recognition of pathogens and tissue damage to promote inflammation. The goal of the study was to investigate the effect of CD14 inhibition on intracortical microelectrode recording performance and tissue integration.

Approach: Mice implanted with intracortical microelectrodes in the motor cortex underwent electrophysiological characterization for 16 weeks, followed by endpoint histology. Three conditions were examined: (1) wildtype control mice, (2) knockout mice lacking CD14, and (3) wildtype control mice administered a small molecule inhibitor to CD14 called IAXO-101.

Main results: The CD14 knockout mice exhibited acute but not chronic improvements in intracortical microelectrode performance without significant differences in endpoint histology. Mice receiving IAXO-101 exhibited significant improvements in recording performance over the entire 16 week duration without significant differences in endpoint histology.

Significance: Full removal of CD14 is beneficial at acute time ranges, but limited CD14 signaling is beneficial at chronic time ranges. Innate immunity receptor inhibition strategies have the potential to improve long-term intracortical microelectrode performance.

Figure 1. Recording performance of intracortical microelectrodes in Cd14^−/− mice versus wildtype mice

The number of single units detected per working channel (A), percentage of working channels detecting single units (B), single unit signal to noise ratio (C), single unit amplitude (D), and noise (E) were plotted versus time, to compare recording performance between Cd14^−/− mice and wildtype mice implanted with identical NeuroNexus microelectrodes. Statistical comparisons were made as a function of time and treatment condition, both within and across groups. N for each plot varies and can be found in the text for the corresponding section. Statistical comparisons were made between treatment groups (Cd14^−/− vs. wildtype for entire study length as a whole; ξ indicates significance), time range (acute vs. chronic for both conditions together, as a metric of change over time; @ indicates significance), and treatment group crossed with time range. For treatment group crossed with time range, we will only discuss relevant comparisons, namely: 1) Cd14^−/− acute versus Cd14^−/− chronic; $ indicates significance, 2) wildtype acute versus wildtype chronic; % indicates significance, 3) Cd14^−/− acute versus wildtype acute; * indicates significance, and 4) Cd14^−/− chronic versus wildtype chronic; δ indicates significance.

Figure 2. Recording performance of intracortical microelectrodes in wildtype mice treated with IAXO-101 versus untreated wildtype mice

The number of single units detected per working channel (A), percentage of working channels detecting single units (B), single unit signal to noise ratio (C), single unit amplitude (D), and noise (E) were plotted versus time, to compare recording performance between wildtype mice administered IAXO-101 (green) mice and wildtype mice (blue) implanted with identical NeuroNexus microelectrodes. Statistical comparisons were made as a function of time and treatment condition, both within and across groups. N for each plot varies and can be found in the text for the corresponding section. Statistical comparisons were made between treatment groups (IAXO-101 vs. wildtype for entire study length as a whole; ξ indicates significance), time range (acute vs. chronic for both conditions together, as a metric of change over time; @ indicates significance), and treatment group crossed with time range. For treatment group crossed with time range, we will only discuss relevant comparisons, namely: 1) IAXO-101 acute versus IAXO-101 chronic; $ indicates significance, 2) wildtype acute versus wildtype chronic; % indicates significance, 3) IAXO-101 acute versus wildtype acute; * indicates significance, and 4) IAXO-101 chronic versus wildtype chronic; δ indicates significance.

Figure 3. Immunohistochemical evaluation of Cd14^−/− mice implanted with intracortical microelectrodes

(A) Neuronal survival at the microelectrode-tissue interface evaluated as percentage of background density with respect to distance from the microelectrode hole (µm). The percentage of background density is significantly different between Cd14^−/− and wildtype mice between 450 and 500 µm from the microelectrode hole, *p<0.05. Neuronal density is significantly different from background for Cd14^−/− mice between 0 and 50 µm from the microelectrode hole, # p<0.05. (B) Astrocytic encapsulation evaluated as GFAP activation with respect to distance from the microelectrode hole (µm). No significant differences were observed between Cd14^−/− and wildtype mice. (C) Microglial activation evaluated as CD68 expression with respect to distance from the microelectrode hole (µm). Cd14^−/− mice express significantly less CD68 between 100 and 500 µm from the microelectrode hole. (D) Blood-brain barrier permeability evaluated as IgG expression with respect to distance from the microelectrode hole. No significant differences were observed between Cd14^−/− and wildtype mice. Cd14^−/− : N = 9; wildtype: N=5.

Figure 4. Immunohistochemical evaluation of mice administered IAXO-101 and implanted with intracortical microelectrodes

(A) Neuronal survival at the microelectrode-tissue interface evaluated as percentage of background density with respect to distance from the microelectrode hole (µm). No significant differences were observed between mice administered IAXO-101 and wildtype mice or between either condition with background. (B) Astrocytic encapsulation evaluated as GFAP activation with respect to distance from the microelectrode hole (µm). No significant differences were observed between mice administered IAXO-101 and wildtype mice. (C) Microglial activation evaluated as CD68 expression with respect to distance from the microelectrode hole (µm). No significant differences were observed between mice administered IAXO-101 and wildtype mice. (D) Blood-brain barrier permeability evaluated as IgG expression with respect to distance from the microelectrode hole. No significant differences were observed between mice administered IAXO-101 and wildtype mice. IAXO-101, WT: N = 5.