Decoupling glycation from mortality: glucose, but not methylglyoxal, reduces survival in zebra finches

Birds provide a unique model for ageing research, with greater longevity and slower senescence compared to mammals of similar body size, despite a higher mass-adjusted metabolic rate and blood glucose levels than other vertebrate groups. While the effects of glucose, glycation, and advanced glycation end-products (AGE) on ageing are well-documented in biomedical research, their impact on avian physiology and ageing remains poorly understood. Although birds may possess adaptations mitigating the potential detrimental effects of glucose, elevated glucose still predicts reduced lifespan, and protein glycation varies with age and can influence survival and some fitness-related traits, implying that glycation or AGE accumulation may have relevant effects on avian longevity.

In this study, we experimentally investigated how one year of dietary supplementation with glucose or methylglyoxal affects survival and physiology (metabolic rate, flying performance, and beak coloration) in captive zebra finches ( Taeniopygia guttata ). We reveal a significant increase in mortality exclusively in glucose-supplemented birds, with also an elevated albumin glycation rate and AGE formation. However, these variables did not directly explain the increased mortality, which was also absent in methylglyoxal-treated individuals, despite similar AGE accumulation.

Additionally, we observed some other effects, like an age-related constraint on seasonal metabolic adjustment, a treatment-influenced age decline in secondary sexual traits expression, and a decline in flight performance during the peak mortality period, suggesting a broader deterioration of health. Thus, although we demonstrate glucose supplementation to be more deleterious than methylglyoxal, the underlying mechanisms for the increase in mortality induced by the treatment remain unresolved.