Amino acids injure mesangial cells by advanced glycation end products, oxidative stress, and protein kinase C

Amino acids injure mesangial cells by advanced glycation end products, oxidative stress, and protein kinase C. Background. In diabetes, high intake of dietary protein ex- acerbates responses associated with kidney damage. Increased levels of amino acids could injure cells by providing free amino groups for glycation reactions leading to advanced glycation end products (AGEs). Methods. Rat mesangial cells were cultured with increased amino acids designed to resemble protein feeding, high glucose (30.5 mmol/L), and, the combination, amino acids/high glucose. AGEs, reactive oxygen species (ROS), protein kinase C (PKC) activity and production, and mitogen-activated protein (MAP) kinase-extracellular signal regulated kinase (ERK) 1,2 activity were measured. Inhibitors were used to determine roles of these processes in fibrosis and/or AGE formation. Results. AGE immunostaining increased when cells were cul- tured in amino acids and was comparable to that observed with high glucose. In amino acids/high glucose, AGE im- munostaining appeared even greater. Amino acids, high glu- cose, and amino acids/high glucose induced ROS production. Aminoguanidine and vitamin E prevented AGE accumulation and induction of protein and mRNA for fibrosis markers (trans- forming growth factor-b1 (TGF-b1), fibronectin, and collagen IV). PKC and ERK 1,2 activity increased with amino acids, high glucose, and amino acids/high glucose. PKC-b inhibition prevented ERK 1,2 activation and fibrosis induction. ERK 1,2 inhibition also blocked the fibrosis response. Conclusion. A profibrotic injury response occurred in mesan- gial cells exposed to amino acids, with or without high glucose, by formation of AGE, oxidative stress, and activation of the PKC-b and MAP kinase-ERK 1,2 signal pathway. These obser- vations provide new insight into cellular mechanisms of kidney damage produced by excess dietary protein, particularly in di- abetes.