Implication of carbonyl stress in long-term uraemic complications

Advanced glycation end products (AGEs) are formed during non-enzymatic glycation and oxidation (glycoxidation) reactions. AGEs, such as pentosidine and carboxymethyllysine are increased in plasma proteins and skin collagen of uraemic patients several times more than in normal subjects and non-uraemic diabetic patients. However, AGEs do not differ between diabetics and non-diabetics in uraemic patients. The AGE accumulation in uraemia, therefore, cannot be attributed to hyperglycaemia, nor simply to a decreased removal by glomerular filtration of AGE-modified proteins. Recent evidence has suggested that, in uraemia, the increased carbonyl compounds, derived from both carbohydrates and lipids, modify proteins not only by glycoxidation but also by lipoxidation reactions, leading to the increased production of AGEs and advanced lipoxidation end products (ALEs). Thus, uraemia might be a state of increased carbonyl compounds with potentially damaging proteins ('carbonyl stress'). Carbonyl stress in uraemia appears relevant to long-term complications, such as dialysis-related amyloidosis. The increased AGEs and ALEs in uraemic plasma and tissue proteins may indicate alterations in the non-enzymatic chemistry involving both carbohydrates and lipids in uraemia.