Fig. 4. Mechanisms by which putative anti-aging interventions (PAAIs) could influence age-sensitive phenotypes (ASPs).

In principle, PAAI effects on ASPs could be attributed to one of the three models: (1) rate model, (2) baseline model, or (3) a combination of rate and baseline models. In the rate model (A), a given anti-aging treatment slows the rate at which an ASP develops but does not have any effects on the ASP prior to the manifestation of age-dependent change in the ASP. This pattern supports the interpretation that age-dependent phenotypic change (aka aging) has been slowed by treatment. In the baseline model (B), a short-term treatment in young animals has similar effects on ASPs as a long-term treatment in aged animals. This pattern indicates age-independent effects unrelated to any influence on the aging process. It is also possible that a treatment influences ASPs in both young and old mice but with larger effects in old mice than in young mice (C). This pattern is more difficult to interpret given that it could be caused by a mixture of age-independent effects and effects on aging rate; alternatively, it could also arise from age-independent effects alone, if treatment duration has an influence on treatment effect size (long-term treatment in old mice resulting in larger effects than short-term treatment in young mice).