Variations in native protein glycation and plasma antioxidants in several birds of prey.

Birds are an anomaly among vertebrates as they are remarkably long-lived despite having naturally high blood glucose and metabolic rates. For mammals, hyperglycemia leads to oxidative stress and protein glycation. In contrast, many studies have shown that domestic and wild birds are relatively resistant to these glucose-mediated pathologies. Surprisingly very little research has examined protein glycation in birds of prey, which by nature consume a diet high in protein and fat that promotes gluconeogenesis. The purpose of this study was to evaluate protein glycation and antioxidant concentrations in serum samples from several birds of prey (bald eagle (BAEA), red-tailed hawk (RTHA), barred owl (BAOW), great horned owl (GHOW)) as protein glycation can accelerate oxidative stress and vice versa. Serum glucose was measured using a commercially available assay, native albumin glycation was measured by mass spectrometry and various antioxidants (uric acid, vitamin E, retinol and several carotenoids) were measured by high performance liquid chromatography. Although glucose concentrations were not significantly different between species (p=0.340), albumin glycation was significantly higher (p=0.004) in BAEA (23.67±1.90%) and BAOW (24.28±1.43%) compared to RTHA (14.31±0.63%). Of the antioxidants examined, lutein was significantly higher in BAOW (p=0.008). BAEA had the highest beta-cryptoxanthin and beta-carotene concentrations (p<0.005). The high concentrations of antioxidants in these birds of prey relative to other birds likely helps protect from complications that may otherwise arise from having high glucose and protein glycation.

Chicken albumin exhibits natural resistance to glycation.

Glycation of proteins and subsequent production of advanced glycation end products (AGEs) is a major contributor to the pathophysiology of diabetes. The objective of the present study was to compare the glycation of avian and human serum albumin to elucidate the mechanisms by which protein glycation in birds is prevented in the presence of naturally high plasma glucose concentrations. Solutions of purified chicken and human serum albumin (CSA and HSA) were prepared with four different glucose concentrations (0, 5.56, 11.1, and 22.2mM) and incubated at three temperatures (37.0, 39.8, and 41.4°C) for seven days. The solutions were sampled on Days 0, 3, and 7 and analyzed by liquid chromatography-electrospray ionization-mass spectrometry for the presence of glycated albumin. Four-way repeated measures ANOVA (p=0.032) indicate that all independent variables (albumin type, glucose concentration, temperature and time) interacted to affect the degree of glycation. With increasing glucose concentration, the glycation of both HSA and CSA increased with time at all temperatures. In addition, HSA was glycated to a greater extent than CSA at the two higher glucose concentrations for all temperature conditions. Glycation was elevated with increasing temperatures for HSA but not CSA. The results suggest an inherent difference between human and chicken albumin that contributes to the observed differences in glycation. Further research is needed to characterize this inherent difference in an effort to elucidate mechanisms by which avian plasma protein is glycated to a lesser degree than that of mammals (humans).