Multi-modal and multi-organ in vivo imaging to assess geroprotective interventions in humans: results from a pilot trial of rapamycin in Alzheimer's Disease

This pilot trial demonstrates that a multi-modal, multi-organ imaging battery is feasible for assessing geroprotective interventions like rapamycin in humans, showing high completion rates for most modalities and revealing exploratory improvements in cardiac, retinal, and metabolic parameters over a 26-week period in patients with early Alzheimer's disease.

The Gist

Imagine your body as a massive, bustling city. Over time, like any old city, it starts to show signs of wear and tear: the roads get potholed (arteries stiffen), the power grid gets inefficient (heart slows down), the parks get overgrown (muscles shrink), and the streetlights flicker (retina degenerates).

Geroprotective interventions are like a "city maintenance crew" designed to fix these problems before the city collapses. One of the most promising crew members is a drug called Rapamycin. In animal studies (like mice and worms), this drug has been a superhero, extending their lives and keeping them healthy. But testing it on humans is tricky. Humans live so long that waiting to see if people die later in life to prove the drug works would take decades. Scientists need a way to see if the "maintenance crew" is working now, not in 20 years.

This paper is a pilot test (a small practice run) to see if we can use a "multi-tool" approach to check the health of the whole city at once.

The Experiment: The "Full-Body City Scan"

The researchers gathered 14 people with early-stage memory issues (Alzheimer's) and gave them a weekly dose of Rapamycin for six months. Instead of just checking their brains, they decided to scan multiple organs to see if the drug was fixing the "city" everywhere.

They used a "battery" of high-tech cameras:

1. Eye Cameras (OCT): Checking the streetlights (retina) for flickering.
2. Whole-Body X-Rays (PET/CT): Checking the power grid (metabolism) in the eyes, gums, and aorta, and measuring the "concrete" (bone density) and "green space" (muscle mass).
3. Gum Scanners (MRI): Checking the foundation of the teeth.
4. Heart Scanners (MRI): Checking the engine (heart) to see if it's pumping efficiently.

The Results: Did the Maintenance Crew Show Up?

1. The Logistics: It Worked!
The biggest question was: Can we actually do all these scans on people without driving them crazy?

• Verdict: Yes! Almost everyone finished all the scans. The only hiccup was that a hospital strike temporarily blocked access to the heart scanners for a few people. But overall, the "multi-tool" approach is feasible. It's like successfully running a full vehicle inspection on a fleet of cars without breaking the garage.

2. The Findings: A Mixed Bag of "Maybe" Signs
Since this was a tiny, uncontrolled trial (no placebo group), the results aren't proof yet, but they are interesting hints:

• The Heart Engine: The heart seemed to pump a bit more blood (Cardiac Output went up). It's like the engine revving slightly higher. Also, the way the heart fills with blood in its "late" phase improved. This is a good sign, suggesting the drug might be helping the heart work better.
• The Eye Streetlights: The layer of cells in the eye (Retinal Ganglion Cells) got slightly thicker, and the "power usage" (metabolism) at the optic nerve went up. Usually, these things get worse with age. Seeing them get better or stay strong is a hopeful sign that the drug might be protecting the eyes.
• The Gums and Bones: The gums didn't show major changes, and bone density stayed the same (which is good; we don't want them to get worse).
• The Muscles: Interestingly, the total size of the back muscles shrank a tiny bit. However, when they looked closer, they found a secret: The more drug in the person's blood, the better the muscle quality. It was like finding that while the muscle size shrank slightly, the muscle became denser and less fatty. It's like a gym-goer losing "fluff" but gaining "lean muscle."

The Big Picture: What Does This Mean?

Think of this study as a dress rehearsal for a much bigger play.

• The Good News: We proved that we can use a "multi-organ camera" to check if anti-aging drugs are working in just six months. We don't have to wait 20 years to see if the drug works; we can see the "city maintenance" happening in real-time.
• The Caveat: Because there was no control group (a group that didn't get the drug), we can't say for sure that Rapamycin caused these changes. Maybe the heart just got better on its own? We need a bigger, randomized trial to be sure.
• The Future: This study gives scientists a blueprint. In the future, instead of just testing one drug on one disease, they can use this "city scan" to see if a drug is fixing the whole body at once.

In short: The researchers tried a new way to test an anti-aging drug by scanning the whole body like a high-tech mechanic. The scans were easy to do, and the results showed some promising signs that the drug might be helping the heart and eyes, while making muscles "leaner." It's a successful practice run that paves the way for bigger, definitive tests in the future.

Technical Summary

1. Problem Statement

The Challenge of Translating Geroprotective Interventions (GPIs):
While preclinical models show that interventions like rapamycin can extend lifespan and healthspan, translating these findings to humans is hindered by the long human lifespan. Traditional clinical endpoints (mortality, disease incidence) are impractical for early-phase trials.
The Gap: There is a lack of validated surrogate endpoints capable of detecting geroprotective effects within feasible trial durations. Since GPIs target fundamental aging mechanisms, their effects should manifest across multiple organ systems simultaneously. However, the practical feasibility of deploying a comprehensive, multi-modal, multi-organ imaging battery in a clinical trial setting has not yet been demonstrated.

2. Methodology

Study Design:

• Type: Single-center, open-label, single-arm pilot trial.
• Population: 14 participants with early-stage Alzheimer's Disease (MCI or mild dementia, MoCA ≥18, amyloid-positive), aged 50–80.
• Intervention: Oral rapamycin (sirolimus) 7 mg once weekly for 26 weeks. An intermittent dosing regimen was chosen to preferentially inhibit mTORC1 while minimizing mTORC2 inhibition.
• Imaging Battery: Participants underwent baseline and end-of-treatment imaging across six organ systems:
  1. Retina: Optical Coherence Tomography (OCT) for Ganglion Cell Layer (GCL) and Retinal Nerve Fiber Layer (RNFL) thickness.
  2. Skeletal System & Body Composition: Quantitative CT (qCT) via [18F]FDG PET/CT for trabecular bone mineral density (vBMD) at L1-L2 and skeletal muscle composition (density, cross-sectional area, intermuscular adipose tissue).
  3. Periodontium: High-resolution T2-weighted STIR MRI and CT for periodontal edema and soft tissue inflammation.
  4. Heart: Cardiac MRI (1.5T) including cine imaging, T1/T2 mapping, Late Gadolinium Enhancement (LGE), Extracellular Volume (ECV), stress perfusion, and 4D Flow MRI for kinetic energy analysis.
  5. Vasculature: Aortic Pulse Wave Velocity (PWV) via phase-contrast MRI and [18F]FDG PET uptake in the descending thoracic aorta wall (marker of inflammation/atherosclerosis).
  6. Metabolic Activity: [18F]FDG PET/CT for metabolic activity in the optic nerve head (ONH), periodontal soft tissues, and aortic wall.

Analysis:

• Feasibility Metrics: Completion rates, time burden, and technical barriers.
• Statistical Analysis: Paired t-tests for pre-post changes (uncorrected for multiple comparisons due to exploratory nature). Exposure-response analyses correlated blood rapamycin concentrations with imaging changes.

3. Key Contributions

• Proof of Concept: This is the first study to successfully integrate a comprehensive, multi-modal, multi-organ imaging battery into a geroprotective clinical trial.
• Efficiency of [18F]FDG PET/CT: Demonstrated that a single PET/CT acquisition can simultaneously quantify bone density, muscle composition, epicardial fat, and metabolic activity in the optic nerve, periodontium, and aorta, significantly reducing the logistical burden compared to separate scans.
• Feasibility Data: Provided critical data on participant burden (~12 hours total imaging over 6 visits) and completion rates, identifying logistical constraints (scanner access) rather than participant tolerance as the primary barrier.
• Methodological Framework: Established a standardized protocol for assessing age-related pathology across the retina, skeleton, heart, and vasculature in a single trial, serving as a blueprint for future randomized controlled trials (RCTs).

4. Key Results

Feasibility:

• Completion: 13 of 14 participants completed follow-up.
• Modality Rates: 100% completion for OCT, PET/CT, and dentomaxillofacial MRI. Cardiac MRI and PWV were completed in 69% (9/13), primarily limited by a healthcare worker strike affecting scanner access.
• Safety: No imaging-related adverse events.

Exploratory Efficacy Findings (Nominal Significance, p < 0.05 uncorrected):

• Heart: Significant increase in Cardiac Output (p=0.017) and Left Ventricular Mass (p=0.046). Late diastolic (A-wave) kinetic energy increased significantly (p=0.044 average; p=0.024 peak), suggesting improved atrial contribution to ventricular filling.
• Retina: Significant increase in Left GCL thickness (p=0.044) and Optic Nerve Head [18F]FDG uptake (p=0.040 bilateral).
• Muscle/Bone: No significant change in bone density. Muscle cross-sectional area showed a numerical decrease (p=0.058).
• Vasculature/Periodontium: No significant changes in aortic PWV, aortic wall inflammation (FDG uptake), or periodontal edema.

Exposure-Response Analysis:

• Higher rapamycin blood concentration correlated significantly with increased skeletal muscle density (r=0.64, p=0.035) and a trend toward reduced loss of muscle cross-sectional area (r=−0.53, p=0.097). This suggests a nuanced relationship where higher exposure may preserve muscle quality despite potential atrophy.

5. Significance and Limitations

Significance:

• Bridging Preclinical and Clinical: The study validates a framework for detecting subtle, systemic changes in aging pathology within short timeframes (6 months), which is essential for screening GPIs.
• Multi-Organ Insight: It confirms that aging pathology is systemic and can be monitored simultaneously, moving beyond single-disease endpoints.
• Future Trial Design: The findings support the use of such imaging batteries as primary or secondary endpoints in larger, randomized, placebo-controlled trials to detect "slowing of progression" rather than "reversal."

Limitations:

• Study Design: As a single-arm pilot without a control group, definitive efficacy conclusions cannot be drawn. Changes could be due to natural variability or regression to the mean.
• Sample Size: Small cohort (n=13 for imaging) limits statistical power.
• Duration: Six months may be insufficient to detect significant structural changes in some tissues (e.g., bone, vasculature).
• Population: Participants had early-stage Alzheimer's, which may confound results due to the specific neurodegenerative pathology of AD (e.g., unexpected correlation between older age and thicker retinal layers).
• Logistics: The cardiac MRI completion rate was compromised by external factors (strikes), highlighting the need for robust contingency planning in future multi-center trials.

Conclusion:
The study successfully demonstrates that a multi-modal, multi-organ imaging battery is feasible and well-tolerated in humans. While the pilot did not provide definitive proof of rapamycin's efficacy due to design constraints, it established a practical, high-resolution framework for future trials aimed at quantifying the systemic effects of geroprotective interventions.