Absence of functional deficits in rats following systemic administration of an AAV9 vector despite moderate peripheral nerve and dorsal root ganglia findings: A clinically silent peripheral neuropathy.

Adeno-associated virus (AAV)-based vectors are commonly used for delivering transgenes in gene therapy studies, but they are also known to cause dorsal root ganglia (DRG) and peripheral nerve toxicities in animals. However, the functional implications of these pathologic findings and their time course remain unclear. At 2, 4, 6, and 8 weeks following a single dose of an AAV9 vector carrying human frataxin transgene in rats, non-standard functional assessments, including von Frey filament, electrophysiology, and Rotarod tests, were conducted longitudinally to measure allodynia, nerve conduction velocity, and coordination, respectively. Additionally, DRGs, peripheral nerves, brain and spinal cord were evaluated histologically and circulating neurofilament light chain (NfL) was quantified at 1, 2, 4, and 8 weeks, respectively. At 2 and 4 weeks after dosing, minimal-to-moderate nerve fiber degeneration and neuronal degeneration were observed in the DRGs in some of the AAV9 vector-dosed animals. At 8 weeks, nerve fiber degeneration was observed in DRGs, with or without neuronal degeneration, and in sciatic nerves of all AAV9 vector-dosed animals. NfL values were higher in AAV9 vector-treated animals at weeks 4 and 8 compared with controls. However, there were no significant differences in the three functional endpoints evaluated between the AAV9 vector- and vehicle-dosed animals, or in a longitudinal comparison between baseline (predose), 4, and 8 week values in the AAV9 vector-dose animals. These findings demonstrate that there is no detectable functional consequence to the minimal-to-moderate neurodegeneration observed with our AAV9 vector treatment in rats, suggesting a functional tolerance or reserve for loss of DRG neurons after systemic administration of AAV9 vector.

Performance of biomarkers NF-L, NSE, Tau and GFAP in blood and cerebrospinal fluid in rat for the detection of nervous system injury.

Background: Target organ toxicity is often a reason for attritions in nonclinical and clinical drug development. Leveraging emerging safety biomarkers in nonclinical studies provides an opportunity to monitor such toxicities early and efficiently, potentially translating to early clinical trials. As a part of the European Union's Innovative Medicines Initiative (IMI), two projects have focused on evaluating safety biomarkers of nervous system (NS) toxicity: Translational Safety Biomarker Pipeline (TransBioLine) and Neurotoxicity De-Risking in Preclinical Drug Discovery (NeuroDeRisk). Methods: Performance of fluid-based NS injury biomarker candidates neurofilament light chain (NF-L), glial fibrillary acidic protein (GFAP), neuron specific enolase (NSE) and total Tau in plasma and cerebrospinal fluid (CSF) was evaluated in 15 rat in vivo studies. Model nervous system toxicants as well as other compounds were used to evaluate sensitivity and specificity. Histopathologic assessments of nervous tissues and behavioral observations were conducted to detect and characterize NS injuries. Receiver operator characteristic (ROC) curves were generated to compare the relative performance of the biomarkers in their ability to detect NS injury. Results: NF-L was the best performer in detecting both peripheral nervous system (PNS) and CNS injury in plasma, (AUC of 0.97-0.99; respectively). In CSF, Tau correlated the best with CNS (AUC 0.97), but not PNS injury. NSE and GFAP were suitable for monitoring CNS injury, but with lesser sensitivity. In summary, NF-L is a sensitive and specific biomarker in rats for detecting compound-induced central and peripheral NS injuries. While NF-L measurement alone cannot inform the site of the injury, addition of biomarkers like Tau and NSE and analysis in both blood and CSF can provide additional information about the origin of the NS injury. Conclusion: These results demonstrate the utility of emerging safety biomarkers of drug-induced NS injury in rats and provide additional supporting evidence for biomarker translation across species and potential use in clinical settings to monitor drug-induced NS injury in patients.