A new pilot study suggests that intranasal insulin therapy may have beneficial effects on cognition and function among patients with Alzheimer's disease (AD).

Researchers at the Veterans Affairs (VA) Puget Sound Health Care System (Seattle, WA, USA) and the University of Washington School of Medicine (Seattle, USA) conducted a randomized, double-blind, placebo-controlled trial of 104 adults with amnestic mild cognitive impairment (64 patients) or mild to moderate AD (40 patients); a subset of participants underwent lumbar puncture and positron emission tomography with fludeoxyglucose F 18 before and after treatment. The participants received placebo, 20 units or 40 units of insulin for four months, administered via a nasal drug delivery device. The primary measures consisted of delayed story recall score and the Dementia Severity Rating Scale (DSRS) score, and secondary measures included the AD Assessment Scale-cognitive subscale (ADAS-cog) score and the AD Cooperative Study-activities of daily living (ADCS-ADL) scale.

The results showed that treatment with 20 units of insulin improved delayed memory, while both doses of insulin preserved caregiver-rated functional ability. Both insulin doses also preserved general cognition as assessed by the ADAS-cog score for younger participants, and functional abilities as assessed by the ADCS-ADL scale for adults with AD. Placebo-assigned participants showed decreased fludeoxyglucose F18 uptake in the parietotemporal, frontal, precuneus, and cuneus regions and insulin-minimized progression. No treatment-related severe adverse events occurred. The study was published ahead of print on September 12, 2011, in Archives of Neurology.

“Although we achieved statistical significance for our primary outcome measures, the observed effects were small in absolute terms, and thus their clinical significance is unclear,” concluded lead author Suzanne Craft, PhD, and colleagues. “Nonetheless, these results provide an impetus for future clinical trials of intranasal insulin therapy and for further mechanistic studies of insulin's role in the pathogenesis of Alzheimer's disease.”

In discussing the reasons why only the lower dose of insulin benefited patients' ability to recall the details of a story after 20 minutes, the researchers explained that they had previously observed an "∩-shaped" response curve for the treatment, demonstrating negative effects when the insulin level was either too low or too high.

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