The randomized trial of nearly 300 patients showed that, although one insulin administration device produced marked benefit in terms of change in mean score on the Alzheimer Disease Assessment Scale–Cognitive Subscale 12 (ADAS-cog-12) over 12 months, reliability was inconsistent. A second device, used on the majority of patients in the study’s intention-to-treat population, showed no difference in these measures between patients who did and those who did not receive intranasal insulin.
“The primary analysis of the study showed no benefit of intranasal insulin on any measures of cognition or cerebrospinal fluid Alzheimer’s disease biomarkers when using the new device,” said principal investigator.
“But when we looked at our planned secondary analysis with the original device – which has been successful in previous studies – we saw quite a different picture,” added Dr. Craft, director of the Alzheimer’s Disease Research Center at Wake Forest University, Winston-Salem, N.C.
“We found a pronounced benefit with that device, such that after 18 months of administration, participants who had been receiving insulin from the beginning of the study had a large and clinically significant advantage in the primary outcome measure.”
Dr. Craft described the findings as complex. “The primary results were negative,” she added. “But the secondary results replicated those of several earlier studies when we used the same device that was used in those.”
The study was published online June 22 in JAMA Neurology.
Important for brain function
Insulin has been shown to play several important roles in brain function. The hormone is associated with a variety of cognitive functions, including memory. Through its association with vasoreactivity, lipid metabolism, and inflammation, insulin also plays an important role in vascular function.
“In the normal brain in healthy individuals, insulin is very important for synaptic function and viability. Insulin also promotes dendritic growth and facilitates synaptic health. Through this role, it plays an important part in memory,” said Dr. Craft. Given these connections, it is not surprising that reduced insulin levels or activity in brain and cerebrospinal fluid have been documented in some, but not all, studies of Alzheimer’s disease. Markers of insulin resistance also have been detected in both neuronally derived exosomes and brain tissue from adults with Alzheimer’s disease.
In light of the several important roles that insulin plays in the brain – coupled with the evidence connecting dysregulation of brain insulin and AD pathology – restoring brain insulin function may offer therapeutic benefit for adults suffering either Alzheimer’s disease or MCI. “There are a number of ways to do this,” said Dr. Craft. “But one of the approaches that we’ve focused on is providing insulin directly to the brain through intranasal administration. “By doing this, you circumvent potential issues if you administered insulin systemically.”
Previous research has shown that through this mode of administration, insulin can bypass the blood-brain barrier and reach the brain through olfactory and trigeminal perivascular channels, with little effect on peripheral insulin or blood glucose levels.
As previously reported, an earlier pilot study, also conducted by Dr. Craft and her team, showed that 4 months of daily intranasal administration of 20 IU or 40 IU of insulin preserved cognitive performance in individuals with Alzheimer’s disease or MCI.