Limiting the debilitating consequences of ageing is a major medical challenge of our time. Robust pharmacological interventions that promote healthy ageing across diverse genetic backgrounds may engage conserved longevity pathways. Here we report results from the Caenorhabditis Intervention Testing Program in assessing longevity variation across 22 Caenorhabditis strains spanning 3 species, using multiple replicates collected across three independent laboratories. Reproducibility between test sites is high, whereas individual trial reproducibility is relatively low. Of ten pro-longevity chemicals tested, six significantly extend lifespan in at least one strain. Three reported dietary restriction mimetics are mainly effective across C. elegans strains, indicating species and strain-specific responses. In contrast, the amyloid dye ThioflavinT is both potent and robust across the strains. Our results highlight promising pharmacological leads and demonstrate the importance of assessing lifespans of discrete cohorts across repeat studies to capture biological variation in the search for reproducible ageing interventions.

Metformin, the most commonly prescribed anti‐diabetes medication, has multiple reported health benefits, including lowering the risks of cardiovascular disease and cancer, improving cognitive function with age, extending survival in diabetic patients, and, in several animal models, promoting youthful physiology and lifespan. Due to its longevity and health effects, metformin is now the focus of the first proposed clinical trial of an anti‐aging drug—the Targeting Aging with Metformin (TAME) program. Genetic variation will likely influence outcomes when studying metformin health effects in human populations. To test for metformin impact in diverse genetic backgrounds, we measured lifespan and healthspan effects of metformin treatment in three Caenorhabditis species representing genetic variability greater than that between mice and humans. We show that metformin increases median survival in three C. elegans strains, but not in C. briggsae and C. tropicalis strains. In C. briggsae, metformin either has no impact on survival or decreases lifespan. In C. tropicalis, metformin decreases median survival in a dose‐dependent manner. We show that metformin prolongs the period of youthful vigor in all C. elegans strains and in two C. briggsae strains, but that metformin has a negative impact on the locomotion of C. tropicalis strains. Our data demonstrate that metformin can be a robust promoter of healthy aging across different genetic backgrounds, but that genetic variation can determine whether metformin has positive, neutral, or negative lifespan/healthspan impact. These results underscore the importance of tailoring treatment to individuals when testing for metformin health benefits in diverse human populations.

The Caenorhabditis Intervention Testing Program (CITP) seeks to identify compounds that robustly improve lifespan and/or attenuate age-dependent declines in health across a genetically diverse set of Caenorhabditis species and strains. A core mission of the CITP is to collect data that will inform on the reproducibility of our experimental results. To achieve this, multiple replicates of each experiment are performed by each of three groups at separate laboratory sites. In an effort to limit non-biological confounding factors that may influence the reproducibility of these results, we sought to minimize differences in experimental conditions across the individual laboratories. This led to the development and utilization of a set of standardized protocols that describe specific methods for nematode maintenance and culture as well as detailed experimental procedures. All laboratories of the CITP are tasked with strict adherence to protocols. Here we provide several protocols that describe the CITP standard operating practices for bacterial cultures, media preparation and strain handing as well as assays for quantifying the development rate, fertility and lifespan of hermaphroditic Caenorhabditis strains. Individual components of these methods were not tested for their effects on outcomes and are not suggested to be best practices. However our consideration of the methodological variability available for even these simple assays does highlight the potential for differences in methodology to influence experimental reproducibility.

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