Lysosomal dysfunction lies at the nexus of inflammaging, microglial dystrophy and synaptic fragility, making it an attractive target for brain rejuvenation. Here we demonstrate that a five-month oral course of ketotifen, an approved H1-antihistamine and mast-cell stabiliser, re-acidifies lysosomes in aged C57BL/6J male mice, restoring the quinacrine signal of peripheral macrophages and SIM-A9 microglia. This proton rebound is coupled to broad anti-cytokine effects: ketotifen attenuates lipopolysaccharide-evoked release of TNF-α, IL-1β and IL-10 in vitro and ex vivo. In the brain, the drug restores a highly ramified, homeostatic microglial morphology throughout the cortex and hippocampus. Ketotifen robustly elevates cortical synaptophysin and PSD-95 above age-matched levels. Behaviourally, ketotifen enhances spatial learning and object-location memory without altering locomotor activity or anxiety-like behaviour. Collectively, these findings identify lysosomal re-acidification as the initiating trigger of a multifaceted rejuvenation cascade that dampens multi-cytokine signalling, restores microglial morphology and preserves synaptic integrity. Because ketotifen is inexpensive, brain-permeable and already licensed for human use, our work unveils an immediately actionable geroprotective strategy to forestall early cognitive decline.
Longevity & Aging