A randomized control trial to establish the feasibility and safety of rapamycin treatment in an older human cohort: Immunological, physical performance, and cognitive effects

Abstract

Inhibition of the mechanistic target of rapamycin (mTOR) pathway by rapamycin (RAPA), an FDA-approved immunosuppressive drug used as a clinical therapy to prevent solid organ allograft rejection, enhances longevity in mice. Importantly, RAPA was efficacious even when initiated in relatively old animals, suggesting that mTOR inhibition could potentially slow the progression of aging-associated pathologies in older humans (Harrison et al., 2009; Miller et al., 2011). However, the safety and tolerability of RAPA in older human subjects have not yet been demonstrated. Towards this end, we undertook a placebo-controlled pilot study in 25 generally healthy older adults (aged 70-95 years); subjects were randomized to receive either 1 mg RAPA or placebo daily. Although three subjects withdrew, 11 RAPA and 14 controls completed at least 8 weeks of treatment and were included in the analysis. We monitored for changes that would indicate detrimental effects of RAPA treatment on metabolism, including both standard clinical laboratory assays (CBC, CMP, HbA1c) and oral glucose tolerance tests (OGTTs). We also monitored parameters typically associated with aging that could potentially be modified by RAPA; these included cognitive function which was assessed by three different tools: Executive Interview-25 (EXIT25); Saint Louis University Mental Status Exam (SLUMS); and Texas Assessment of Processing Speed (TAPS). In addition, physical performance was measured by handgrip strength and 40-foot timed walks. Lastly, changes in general parameters of healthy immune aging, including serum pro-inflammatory cytokine levels and blood cell subsets, were assessed. Five subjects reported potential adverse side effects; in the RAPA group, these were limited to facial rash (1 subject), stomatitis (1 subject) and gastrointestinal issues (2 subjects) whereas placebo treated subjects only reported stomatitis (1 subject). Although no other adverse events were reported, statistically significant decrements in several erythrocyte parameters including hemoglobin (HgB) and hematocrit (Hct) as well as in red blood cell count (RBC), red blood cell distribution width (RDW), mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH) were observed in the RAPA-treatment group. None of these changes manifested clinically significant effects during the short duration of this study. Similarly, no changes were noted in any other clinical laboratory, cognitive, physical performance, or self-perceived health status measure over the study period. Immune parameters were largely unchanged as well, possibly due to the advanced ages of the cohort (70-93 years; mean age 80.5). RAPA-associated increases in a myeloid cell subset and in TREGS were detected, but changes in most other PBMC cell subsets were not statistically significant. Importantly, the OGTTs revealed no RAPA-induced change in blood glucose concentration, insulin secretion, and insulin sensitivity. Thus, based on the results of our pilot study, it appears that short-term RAPA treatment can be used safely in older persons who are otherwise healthy; a trial with a larger sample size and longer treatment duration is warranted.

Keywords: Blood cell subsets; Cytokines; Geriatrics; Physiological outcomes; Rapamycin; mTOR inhibition.

Copyright © 2018 Elsevier Inc. All rights reserved.

Figures

Figure 1. Effects of RAPA on clinical parameters

Shown are the changes in several measures of clinical health for individual subjects in the RAPA (red) and placebo (blue) treatment groups. The “pre” points were taken at time 0, prior to the initiation of treatment. Most of the “post” values were taken at the 6–8 week visit, but for a few subjects, data were only available at 16 weeks (indicated with a star, ★). All of the 6–8 week values for these and other parameters measured are summarized, with statistical analyses summarized in Tables 3–7.

Figure 2. Effect of RAPA on metabolic profile

Glucose (A), Insulin (B), and FFA (C) concentrations during OGTT, HOMA-IR (D), and Matsuda index (E) were determined as described under “Methods”. Values are mean ± SEM. No statistically significant differences between RAPA and placebo subjects were found.

Figure 3. Effects of RAPA on serum cytokines

As described in the Methods, the levels of serum cytokines were measured using either a Luminex-based multiplex assay (panels A–W) or a high sensitivity ELISA (panel X) for samples collected either before initiation of treatment (0 weeks) or during the treatment phase (6 weeks). All individual subjects, from both phase 1 and phase 2, are shown. RAPA subjects are shown in red and placebo subject lines are blue. For the Luminex data, the horizontal dotted line on each graph indicates the concentration value for the lowest point on the standard curve; all values below that were extrapolated by the BioRad software. Any point assigned a value of “OOR

Figure 4. Effects of RAPA on blood cell subsets

PBMCs from the phase 2 subjects, purified from blood collected at the indicated time points, were stained using the three antibody panels described in the Methods section. The flow cytometry data were analyzed using Diva software. Shown are results from Panel 1 (A–F), Panel 2 (H,I), and Panel 3 (G,J–R). RAPA subjects (red) and placebo subjects (blue) are shown and the p-values for RAPA vs. placebo differences are found in Table 9 for these subsets and for additional subsets not shown.