Bortezomib-induced gastrointestinal dysfunction, peripheral neuropathy and neuroimmune signalling are influenced by...

Peripheral neuropathy and gastrointestinal dysfunction are frequent, debilitating side effects of the neurotoxic myeloma drug bortezomib that reduce quality of life and adherence to optimal therapy. Therapeutic strategies to manage these complications are limited. Here, we have developed a mouse model of bortezomib side effects to investigate the role of the gut microbiota in their development.

C57BL/6 specific pathogen-free (SPF), germ-free (GF) and ex-GF mice (colonised with healthy gut microbiota via faecal microbiota transplantation [FMT]) were treated with bortezomib (1 mg/kg) twice-weekly for two weeks. Neurotoxicity and neuroimmune signalling were assessed by serum neurofilament light chain (NfL) quantitation and real-time qPCR analysis of inflammatory markers in sensory and autonomic nerve ganglia, respectively. Faecal microbiota composition was characterised using 16S rRNA gene sequencing. Bortezomib side effects were assessed using behavioural phenotyping, von Frey mechanical sensitivity and rotarod testing, and FITC-dextran gut permeability and Evans Blue dye transit assays.

Bortezomib-treated SPF mice displayed altered spontaneous behaviour and developed acute gastric retention, altered gastrointestinal motility and increased intestinal permeability, in the absence of intestinal micro-architecture changes. Concurrently, bortezomib induced sensory loss in, and increased grooming of, paws, and reduced motor performance, indicative of peripheral neuropathy. Bortezomib neurotoxicity was evidenced by elevated serum NfL levels and neuroimmune signalling in sciatic nerve dorsal root and vagal nerve nodose ganglia. In SPF mice, bortezomib altered gut microbiota composition with an acute decrease in microbial diversity and expansion of Lactobacillus gasseri. Notably, GF mice developed a milder symptom profile following bortezomib treatment compared with SPF mice, while FMT mice did not develop overt bortezomib side effects despite displaying evidence of nerve damage.

This is the first study to model gastrointestinal side effects of bortezomib in rodents, implicating neuroimmune dysregulation of the vagus nerve. Our data show that the gut microbiota is not a primary driver of bortezomib side effects. However, the absence of a symptom profile in FMT mice suggests that, in GF mice, the gut microbiota beneficially modulates the host to protect against bortezomib side effects. Further studies are required to determine whether this can be harnessed to mitigate clinical complications of bortezomib.