Amino acids injure mesangial cells by advanced glycation end products, oxidative stress, and protein kinase C.
BACKGROUND
In diabetes, high intake of dietary protein exacerbates 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 cultured in amino acids and was comparable to that observed with high glucose. In amino acids/high glucose, AGE immunostaining appeared even greater. Amino acids, high glucose, and amino acids/high glucose induced ROS production. Aminoguanidine and vitamin E prevented AGE accumulation and induction of protein and mRNA for fibrosis markers [transforming growth factor-beta1 (TGF-beta1), fibronectin, and collagen IV]. PKC and ERK 1,2 activity increased with amino acids, high glucose, and amino acids/high glucose. PKC-beta inhibition prevented ERK 1,2 activation and fibrosis induction. ERK 1,2 inhibition also blocked the fibrosis response.


CONCLUSIONS
A profibrotic injury response occurred in mesangial cells exposed to amino acids, with or without high glucose, by formation of AGE, oxidative stress, and activation of the PKC-beta and MAP kinase-ERK 1,2 signal pathway. These observations provide new insight into cellular mechanisms of kidney damage produced by excess dietary protein, particularly in diabetes.
Tuttle
Katherine R
KR
The Heart Institute of Spokane and Sacred Heart Medical Center, Spokane, Washington 99204, USA. ktuttle@this.org
Johnson
Emily C
EC
Cooney
Sheryl K
SK
Anderberg
Robert J
RJ
Johnson
Edward K
EK
Clifton
G Dennis
GD
Meek
Rick L
RL
D000596:Amino Acids / Q000633:toxicity*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D005260:Female; D005355:Fibrosis; D005920:Glomerular Mesangium / Q000187:drug effects* / Q000378:metabolism; D017127:Glycation End Products, Advanced / Q000096:biosynthesis*; D018384:Oxidative Stress; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000596:Amino Acids; D000975:Antioxidants; D017127:Glycation End Products, Advanced; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases