Table 2.

Summary of key findings from recent cross-species comparative studies.

Cross-species studies	Key findings
Transcripts (33 mammalian species, 3 organs)	Positive correlation with lifespan: base-excision repair, nonhomologous end joining, regulation of immune response, regulation of defense response. Negative correlation with lifespan: lipid oxidation, fatty acid metabolism, amino acid degradation, tricarboxylic acid cycle, mitochondrial respiratory chains, and ubiquitin complex.
Transcripts (15 mammalian species, fibroblasts)	Positive correlation with lifespan: DNA repair, nucleotide binding, glucose metabolic process, chromosome organization. Negative correlation with lifespan: proteolysis, protein transport and localization, regulation of transcription, apoptosis regulation. Fibroblasts of long-lived species were more resistant to stress-inducing agents such as cadmium and paraquat.
Metabolites (26 mammalian species, 4 organs, 262 metabolites)	Positive correlation with lifespan: sphingomyelins, urate:allantoin ratio. Negative correlation with lifespan: amino acid, lysophosphatidyl-cholins, lysophosphatidyl-ethanolamines, triacylglycerols with polyunsaturated fatty acid, anthranilic acid and kynurenine.
Elements (26 mammalian species, 4 organs, 18 elements)	Positive correlation with lifespan: zinc (but largely body mass dependent), cadmium (may due to passive accumulation along food chain). Negative correlation with lifespan: selenium.
Lipids (35 mammalian species, 6 organs, 13,000–21,000 compounds)	Predictors of longevity (after adjusting for other confounding factors): high levels of triacylglycerols, low levels of glycerophospholipids and sphinoglipids. Number of double bonds associated with lifespan variations, but the effects dependent on the lipid classes. Enzymes linked to these lipid classes and pathways displayed signatures of greater stabilizing selection in long-lived species.