Urokinase-type plasminogen activator (uPA) and kallikrein-related peptidase 8 (KLK8) are serine proteases that contribute to extracellular matrix (ECM) remodeling after brain injury. They can be labelled with the novel radiotracer [111In]MICA-401. As the first step in exploring the applicability of [111In]MICA-401 in tracing the mechanisms of postinjury ECM reorganization in vivo, we performed in vitro and ex vivo studies, assessing [111In]MICA-401 distribution in the brain in two animal models: kainic acid–induced status epilepticus (KASE) and controlled cortical impact (CCI)–induced traumatic brain injury (TBI).
In the KASE model, in vitro autoradiography with [111In]MICA-401 was performed at 7 days and 12 weeks post-SE. To assess seizure burden, rats were monitored using video-electroencephalography (EEG) for 1 month before the 12-week time point. In the CCI model, in vitro autoradiography was performed at 4 days and ex vivo autoradiography at 7 days post-TBI.
At 7 days post-SE, in vitro autoradiography revealed significantly decreased [111In]MICA-401 binding in hippocampal CA3 subfield and extrahippocampal temporal lobe (ETL). In the chronic phase, when animals had developed spontaneous seizures, specific binding was decreased in CA3 and CA1/CA2 subfields of hippocampus, dentate gyrus, ETL, and parietal cortex. Of interest, KASE rats with the highest frequency of seizures had the lowest hippocampal [111In]MICA-401 binding (r = −0.76, p ≤ 0.05). Similarly, at 4 days post-TBI, in vitro [111In]MICA-401 binding was significantly decreased in medial and lateral perilesional cortex and ipsilateral dentate gyrus. Ex vivo autoradiography at 7 days post-TBI, however, revealed increased tracer uptake in perilesional cortex and hippocampus, which was likely related to tracer leakage due to blood–brain barrier (BBB) disruption.
Strong association of reduced [111In]MICA-401 binding with seizure burden in the KASE model suggests that analysis of reduced levels of active uPA/KLK8 represents a novel biomarker candidate to be explored as a biomarker for epilepsy severity. However, limited BBB permeability of [111In]MICA-401 currently limits its application in vivo.