Deeper dive
In the current investigation, the researchers wanted to broaden these findings in a larger, longer, randomized double-blinded clinical trial. The investigators assessed the efficacy of intranasal insulin on cognition, function, and biomarkers of Alzheimer’s disease, as well as the safety and feasibility of the delivery method. The multicenter trial was conducted from 2014 to 2018 and included 27 sites.
Study participants were between the ages of 55 and 85 years and had been diagnosed with amnestic MCI or Alzheimer’s disease on the basis of National Institute on Aging–Alzheimer Association criteria, a score of 20 or higher on the Mini–Mental State Examination, a clinical dementia rating of 0.5 or 1.0, or a delayed logical memory score within a specified range.
In total, 289 participants were randomly assigned to receive 40 IU of insulin or placebo for 12 months, followed by a 6-month open-label extension phase. The first 49 participants (32 men; mean age, 71.9 years) underwent insulin administration with the same device the investigators used in previous trials.
Of these, 45 completed the blinded phase, and 42 completed the open-label extension. When this device, which uses an electronic nebulizer-like delivery system, proved unreliable, the researchers switched to a second device, which uses a liquid hydrofluoroalkane propellant to deliver a metered dose of insulin through a nose tip without electronic assistance. Device 2 was used for the remaining 240 participants (123 men; mean age, 70.8 years). These patients became the study’s primary intention-to-treat population.
The study’s primary outcome was the mean change in score on the Alzheimer Disease Assessment Scale–Cognitive Subscale 12 (ADAS-cog-12), which was evaluated at 3-month intervals.
Secondary clinical outcomes were assessed at 6-month intervals. These included the mean change in scores for the Alzheimer Disease Cooperative Study Activities of Daily Living Scale for Mild Cognitive Impairment and the Clinical Dementia Rating Scale Sum of Boxes.
Safety and adherence were also assessed during each study visit. Physical and neurologic examinations were performed at baseline and at months 6, 12, and 18.
Of the primary intention-to-treat population of 240 patients, 121 were randomly assigned to receive intranasal insulin. The remaining 119 received placebo and served as controls. The two groups were demographically comparable.
Better cognitive performance
A total of 215 participants completed the blinded phase; 198 participants completed the open-label extension. Discontinuation rates were comparable in both arms. The researchers found no differences between groups with respect to mean change in ADAS-cog-12 score from baseline to month 12 (0.0258 points; 95% confidence interval, –1.771 to 1.822 points; P = .98). The two groups also proved comparable in terms of performance on all other cognitive tests.
The open-label portion yielded similar results. Participants originally assigned to the insulin arm and their counterparts in the placebo arm did not differ with respect to mean score change on the ADAS-cog-12 test (or any other outcome) at either month 15 or 18.
Cerebrospinal fluid insulin levels were unchanged between groups, as were blood glucose and hemoglobin A1c values. Indeed, levels of A-beta42, A-beta40, total tau protein, and tau p-181 were comparable for the patients who received intranasal insulin and those who received placebo.
The most common adverse events were infections, injuries, respiratory disorders, and nervous system disorders, though these did not differ between groups. In addition, there were no differences between groups with respect to severity of adverse events; most were rated as mild.
In contrast with the intention-to-treat population, the study’s secondary analysis – using data from the original administration device – yielded markedly different results. In the blinded phase, patients who received insulin had better ADAS-cog-12 performance at 12 months (−2.81 points; 95% CI, −6.09 to 0.45 points; P = .09) and nominally significant effects at 6 months (−3.78 points; 95% CI, −6.79 to −0.78 points; P = .01).