Oxytocin-TGF-β Drug Combo Extends Old Male Mouse Lifespan by 73%

Aging research has historically struggled with a fundamental problem: most interventions are tested in middle-aged animals and target single pathways. This UC Berkeley study took a different approach, treating already-frail 25-month-old C57BL/6J mice — equivalent to approximately 75-year-old humans — with a combination of two agents targeting pathways that change in opposite directions with aging. Oxytocin (OT), which declines with age and regulates tissue homeostasis via GPCR and ERK signaling, was paired with A5i, an ALK5 inhibitor that damps the age-elevated pro-fibrotic TGF-β signaling cascade. The rationale was that simultaneous calibration of these two diverging pathways could be more effective than targeting either alone.

The treatment protocol was cyclical: subcutaneous injections of OT (1 μg/g/day) and A5i (0.02 nmol/g/day) three times per week for two weeks, followed by two weeks of rest for health testing, repeated throughout the animals' natural lifespan. Male treated mice (n=14) and controls (n=12), as well as female treated (n=10) and controls (n=13), were followed longitudinally. The primary lifespan result in males was striking: OT+A5i-treated males lived an average of 221.1 additional days from treatment initiation versus 127.3 days for controls — a 73.73% increase in remaining lifespan. Median additional survival was 240.5 days versus 93.5 days (157% longer), and the death hazard ratio was 2.868 times higher for controls versus treated males. The 14% improvement in total median lifespan from birth is particularly notable given that the animals were already frail at the study's start.

Healthspan improvements in males were assessed using a multi-parametric frailty index (31 metrics including gait, vision, coat condition, and grip strength), treadmill endurance testing, a 4-limb hanging test for balance and agility, and a novel object recognition test for short-term memory. Using a novel statistical model applying Kaplan-Meier analysis across a continuous range of frailty thresholds (0–1.0), OT+A5i-treated males showed significantly extended healthspan at frailty index threshold of 0.5 (p=0.0230) and across virtually all higher thresholds, with the effect growing stronger over time — suggesting cumulative treatment benefit. Males also showed dramatically improved resilience to death after reaching frailty thresholds, surviving significantly longer even after entering advanced decline.

The sex-specific divergence is one of the study's most intriguing findings. Female mice showed no improvement in lifespan (p=0.1904) or healthspan, and there was even a non-significant trend toward reduced healthspan range in treated females. This was not explained by baseline frailty differences, as initial frailty scores were statistically equivalent between control and treated groups in both sexes. Bio-orthogonal metabolic proteomics on blood serum revealed that after an acute 7-day treatment, both male and female old mice showed youthful normalization of systemic signaling proteins and reduced protein noise — a sign of restored proteostasis. However, after 4 months of treatment, only old male mice maintained this youthful proteome profile, while female mice lost responsiveness. The mechanism behind this sex difference remains unknown, though the authors note OT+A5i did improve fertility in middle-aged female mice, suggesting the treatment is not without effect in females.

The study's implications are substantial for the longevity field. It demonstrates that a non-genetic, pharmacological combination targeting complementary aging pathways can extend lifespan and healthspan even when initiated in genuinely old, frail animals — a much harder test than the middle-aged interventions typical in the field. The finding that sex-specific differences profoundly influence response to longevity therapeutics reinforces the critical need to study both sexes separately in aging research. Caveats include the mouse-to-human translation challenge, relatively small cohort sizes, and the as-yet unexplained female non-response, which requires mechanistic follow-up before clinical translation can be seriously considered.