A new study has found that intranasal insulin can enhance antioxidant defences in the brain, but its effects differ significantly between healthy individuals and those with early-stage psychotic disorders. Researchers examined how this method of insulin administration influences brain glutathione levels and cognitive function, revealing notable variations in response between the two groups. The findings were published in the journal Biological Psychiatry.
The study involved 39 participants, including individuals diagnosed with early-stage psychotic disorders and healthy controls. Each underwent a series of cognitive tests and magnetic resonance spectroscopy scans before and after receiving a 40 IU dose of intranasal insulin. Glutathione levels were a particular focus, as this compound plays a crucial role in protecting brain cells from oxidative stress, which is linked to various neurological and psychiatric conditions.
Results indicated that in healthy participants, brain glutathione levels increased following the administration of intranasal insulin, suggesting an enhanced antioxidant response. However, individuals with early psychotic disorders showed no significant change in glutathione levels. The findings suggest that while the brain of a healthy individual responds to insulin by boosting antioxidant defences, those with early-stage psychosis may have an impaired response to insulin’s effects on oxidative stress regulation.
Beyond its impact on brain chemistry, intranasal insulin also showed positive effects on cognitive function. Both groups experienced improvements in processing speed, as assessed through a symbol coding test. However, only the healthy participants displayed an enhancement in verbal fluency, a skill linked to the ability to retrieve and articulate words efficiently. No notable changes were observed in other cognitive measures such as working memory and executive function, highlighting the selective impact of intranasal insulin on certain cognitive abilities.
The differences in glutathione response between the two groups may be linked to underlying metabolic dysfunctions in psychotic disorders. Previous research has shown that individuals with schizophrenia and related conditions often exhibit insulin resistance, which may affect how the brain utilises insulin to regulate oxidative stress. The absence of a glutathione boost in these patients suggests that insulin resistance could be interfering with the brain’s natural antioxidant response, potentially exacerbating oxidative damage.
Interestingly, despite the impaired antioxidant response, individuals with psychotic disorders still showed improvements in processing speed. This suggests that intranasal insulin may exert cognitive benefits through pathways unrelated to glutathione regulation. The mechanism behind this effect remains unclear, but it points to the potential of intranasal insulin as a cognitive enhancer, even in individuals with psychiatric conditions.
The study’s findings have important implications for understanding the role of insulin in brain function and its potential therapeutic applications. The ability of intranasal insulin to boost antioxidant defences in healthy individuals highlights its potential as a neuroprotective intervention. But the lack of a similar response in psychotic disorders raises questions about whether these conditions involve fundamental disruptions in insulin-related metabolic processes.
