Figure 4. Top metabolic alterations in aging. (A, B) Guanosine and allantoin, metabolites in the purine metabolism pathway. (C, D) Hydroxyproline and N-acetylornithine, metabolites in the arginine and proline metabolism pathway. (E, F) Erythrose phosphate and nicotinamide, metabolites in the pentose phosphate and nicotinamide pathways, respectively. n=4, 5, 4 and 4 for the 3-, 12-, 18- and 28 months old (3M, 12M, 18M, 28M) groups, respectively.