Active Immunization with Glucose-Dependent Insulinotropic Polypeptide Vaccine Influences Brain Function and Behaviour in Rats

Glucose-dependent insulinotropic polypeptide (GIP) is involved in the aetiology of obesity induced by overnutrition, and blocking GIP activity may be valuable to anti-obesity treatment. However, GIP and GIP receptor are closely related to various brain functions which have caused very little data to be published concerning this cerebral functionality after blocking GIP activity. Here, we showed that active vaccination of mature rats with GIP immunoconjugates [GIP-keyhole limpet haemocyanin (KLH)] was associated with changes in body weight. Furthermore, we also observed significant changes in brain function and behaviour. Data indicated that GIP-KLH-immunized rats showed decreased spontaneous activity in the open field test, decreased cerebral glucose utilization assessed by 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT), and increased apoptosis and proliferation of hippocampal granule cells marked by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) or proliferating cell nuclear antigen method. In conclusion, we have shown that vaccine-induced antibodies inhibited GIP activity in vivo and led to significant changes in brain function and behaviour, which underscore the need to address any potential problems GIP-targeted immunotherapy may involve in further research.