Intranasal Insulin Eases Autism in Rats via GDF-15 and Anti-Inflammatory Pathways

In rat models, it is well-documented that chronic administration of propionic acid (PPA) leads to autism-like behaviors. Although the intranasal (IN) insulin approach is predominantly recognized for its effects on food restriction, it has also been shown to enhance cognitive memory by influencing various proteins, modulating anti-inflammatory pathways in the brain, and reducing signaling molecules such as interleukins. This study seeks to explore the potential therapeutic benefits of IN insulin in a rat model of autism induced by PPA. Thirty male Wistar albino rats were categorized into three cohorts: the control group, the PPA-induced autism (250 mg/kg/day intraperitoneal PPA dosage for five days) group, treated with saline via IN, and the PPA-induced autism group, treated with 25 U/kg/day (250 µL/kg/day) insulin via IN. All treatments were administered for 15 days. After behavioral testing, all animals were euthanized, and brain tissue and blood samples were collected for histopathological and biochemical assessments. Following insulin administration, a substantial reduction in autism symptoms was observed in all three social behavior tests conducted on the rats. Moreover, insulin exhibited noteworthy capabilities in decreasing brain MDA, IL-2, IL-17, and TNF-α levels within autism models. Additionally, there is a notable elevation in the brain nerve growth factor level (p < 0.05) and GDF-15 (p < 0.05). The assessment of cell counts within the hippocampal region and cerebellum revealed that insulin displayed effects in decreasing glial cells and inducing a significant augmentation in cell types such as the Purkinje and Pyramidal cells. The administration of insulin via IN exhibits alleviating effects on autism-like behavioral, biochemical, and histopathological alterations induced by PPA in rats. Insulin-dependent protective effects show anti-inflammatory, anti-oxidative, and neuroprotective roles of insulin admitted nasally.