TSPO Versus P2X7 as a Target for Neuroinflammation: An In Vitro and In Vivo Study

Abstract

Neuroinflammation is important in amyotrophic lateral sclerosis (ALS). The P2X7 receptor (P2X7R) is a promising target for neuroinflammation. The objective of this study was to compare ¹⁸F-DPA714, a second-generation translocator protein tracer, with ¹¹C-JNJ717, a novel P2X7R tracer, in vitro and in vivo in ALS. Methods: For the in vitro portion of the study, autoradiography with ¹⁸F-DPA714 and ¹¹C-JNJ717 was performed on human ALS brain sections in comparison to immunofluorescence with Iba1 and GFAP. For the in vivo portion, 3 male patients with early-stage ALS (59.3 ± 7.2 y old) and 6 healthy volunteers (48.2 ± 16.5 y old, 2 men and 4 women) underwent dynamic PET/MR scanning with ¹⁸F-DPA714 and ¹¹C-JNJ717. Volume-of-distribution images were calculated using Logan plots and analyzed on a volume-of-interest basis. Results: Autoradiography showed no difference in ¹¹C-JNJ717 binding but did show increased ¹⁸F-DPA714 binding in the motor cortex correlating with Iba1 expression (glial cells). Similar findings were observed in vivo, with a 13% increase in ¹⁸F-DPA714 binding in the motor cortex. Conclusion: In symptomatic ALS patients, ¹⁸F-DPA714 showed increased signal whereas ¹¹C-JNJ717 was not elevated.

Keywords: P2X7; amyotrophic lateral sclerosis; brain specimen; neuroinflammation; translocator protein (TSPO).

FIGURE 1.

In vitro autoradiography experiments on MC and OC slices of 2 ALS patients. (A) Sections incubated with ¹⁸F-DPA714. (B) Sections incubated with ¹⁸F-DPA714 in presence of PK11195. (C) Sections incubated with ¹¹C-JNJ717. (D) Sections incubated with ¹¹C-JNJ717 in presence of A740003. (E) Immunohistochemistry results using Iba1 and GFAP. Scale bars represent 2.5 mm. WM = white matter; GM = gray matter.

FIGURE 2.

Overview of V_T images (¹⁸F-DPA714 and ¹¹C-JNJ717) of all ALS patients and average image of all HVs. Because of genotype effects for both tracers, different V_T thresholds have been used. ALS patient 1 is 59-y-old man, ALS patient 2 is 50-y-old man, and ALS patient 3 is 68-y-old man (the patient with associated frontotemporal dysfunction).