Hormonal Cycles May Determine How Intranasal Brain Drugs Reach Their Target, Study Finds
核心洞察
A new study in Genomic Psychiatry shows that estrogen levels during the estrous cycle significantly affect how much intranasal davunetide reaches the brain in mice, with peak uptake during high-estrogen phases.
Reanalysis of human pharmacokinetic data found women reached roughly twice the peak drug concentrations of men, while men retained the drug longer, suggesting sex-based differences in drug exposure.
The findings may explain why a large Phase 2/3 trial of davunetide in progressive supranuclear palsy (搜索) failed to show overall benefit, as sex-stratified analyses hinted women responded when men did not.
A growing body of evidence suggests that the long-standing practice of averaging clinical trial results across men and women may be obscuring real therapeutic effects—particularly for drugs designed to reach the brain through the nose. New research published in Genomic Psychiatry demonstrates that hormonal cycles can dramatically alter how much of an intranasally administered neuroprotective peptide reaches its target, raising fundamental questions about how brain-directed therapies are tested and dosed.
The study, led by Professor Illana Gozes at Tel Aviv University's Elton Laboratory for Molecular Neuroendocrinology, tracked the experimental peptide davunetide—also known as NAP—in mice and found that uptake in the head region varied significantly depending on the stage of the estrous cycle.
A failed trial that deserved a second look
Davunetide, a short fragment of the activity-dependent neuroprotective protein (ADNP (搜索)) that the brain produces to protect neuronal wiring, has been investigated as a potential treatment for several neurodegenerative and neuropsychiatric disorders, including progressive supranuclear palsy (搜索) (PSP), mild cognitive impairment (搜索), and schizophrenia (搜索). The drug stabilizes microtubules, the microscopic scaffolding inside nerve cells along which essential cargo travels.
Despite strong mechanistic rationale, a large Phase 2/3 trial in PSP failed to demonstrate an overall benefit. Yet when Gozes and her colleagues re-examined the data, they noticed something that demanded further investigation: women appeared to respond when men did not.
"That is the kind of observation that either dies as a statistical ghost or points to something real underneath," the researchers noted. To determine which, they designed an experiment to watch the drug move in real time.
Estrogen tracks the drug
Using a fluorescently labeled version of davunetide and live imaging, the team followed the peptide's distribution after intranasal administration in mice. Critically, they tracked each female animal's place in the estrous cycle—the rodent counterpart to the menstrual cycle—by reading vaginal smears under a microscope.
The results were striking. During proestrus and estrus, the phases when estrogen runs highest, female mice took up significantly more drug in the head region than males. The contrast was sharpest in proestrus, where head measurements separated males and females with a p-value of 0.00029, and the head-to-body ratio reached a p-value of 0.000004. As the cycle moved into metestrus, when estrogen falls toward its minimum, the difference between the sexes largely disappeared.
In a larger mixed group of five males and five females imaged without sorting by cycle phase, females still showed higher head uptake at every time point and a significantly higher head-to-body ratio, with a p-value of 0.000009.
A human signal, within limits
Mice are not humans, and the authors acknowledge this plainly. To bridge the gap, they turned to a human pharmacokinetic dataset from an earlier study of intranasal davunetide in healthy adults—two men and six women. The numbers are small, and the paper does not pretend otherwise. Yet the direction matched the animal findings.
Women trended toward higher peak concentrations, with the highest female peak more than double the highest male peak. Men, meanwhile, retained the drug longer. When the first two days were grouped, the longer half-life in men reached statistical significance with a p-value of 0.0057, while the roughly two-fold higher peak concentration in women remained a trend with a p-value of 0.1081.
"These sex-specific differences likely reflect a combination of hormonal regulation, tissue distribution, nasal physiology, and blood-brain barrier function," the authors write, describing a picture in which no single factor decides the outcome.
The mechanistic threads
The researchers point to several converging explanations. Estrogen is known to shape blood-brain barrier integrity. The microtubules that davunetide targets help build that barrier, and estrogen restrains their excess growth. The protein behind davunetide, ADNP (搜索), is itself regulated by the estrous cycle and in turn helps regulate sex hormones. The drug crosses the delicate vessels of the nose and rides the circulation toward the brain—a passage that depends on the tone of blood vessels, which depends, in turn, on estrogen.
One observation in the study adds a sobering physical dimension to the statistical findings. In experiments on elderly animals, male mice kept dying during the procedure. The authors report it directly, noting increased male vulnerability, and fold it into the methods rather than dressing it up.
Honest limitations, broad implications
The study's limitations are considerable and clearly stated. Davunetide remains investigational. The mouse experiments often compared two or three females against a single male. The human cohort included only eight participants. The estrous staging relied on judgment calls made by eye.
Yet the restraint is part of what makes the larger argument credible. "The findings could extend beyond davunetide and may apply more broadly to intranasal therapies designed to reach the brain," Gozes says.
If so, the implications run past this one molecule. Alzheimer's disease (搜索), the major tauopathy, strikes women at roughly twice the rate of men. A field that designs trials and doses without accounting for sex and hormonal state may keep producing flat averages that conceal living effects, and may keep shelving drugs that work for someone, just not for everyone at once.
"Optimizing neuroprotective strategies will require purposeful accounting for biological sex as a core variable," the authors conclude. The sentence reads less like a flourish than like a correction owed.