Oxidative stress mediates protein kinase C activation and advanced glycation end product formation in a mesangial cell model of diabetes and high protein diet.
OBJECTIVE
High levels of glucose and/or amino acids increase advanced glycation end products (AGE) and activate protein kinase C (PKC), a key signal for injury in mesangial cells. The aim was to determine whether oxidative stress mediates bidirectional interactions between AGE and PKC ('cross-activation') in this model.


METHODS
Rat mesangial cells were examined after 48 h of exposure to: high glucose (30.5 mM), increased amino acids designed to resemble a protein meal, the combination of both conditions, and control. Cells were treated with antioxidants (vitamin E, alpha-lipoic acid, N-acetylcysteine, apocynin, doses based on suppression of reactive oxygen species), PKC inhibitors (calphostin C orPLY379196, 100 nM), or AGE inhibitors (aminoguanidine or pyridoxamine 0.5 mM).


RESULTS
Carboxymethyllysine, an AGE marker, increased twofold in mesangial cells exposed to the experimental conditions. Antioxidants and PKC inhibition prevented carboxymethyllysine increases. Likewise, antioxidants and AGE inhibition prevented PKC activation. Inhibition of carboxymethyllysine increases and PKC activation by apocynin indicates a primary role for NADPH oxidase in producing oxidative stress. Induction of transforming growth factor-beta(1) and fibronectin was inhibited by antioxidants and inhibitors of PKC and AGE.


CONCLUSIONS
Oxidative stress mediated cross-activation between PKC and AGE in this mesangial cell model of diabetes and high protein diet.PKC may amplify cellular injury by promoting AGE accumulation.
Tuttle
Katherine R
KR
Providence Medical Research Center, Sacred Heart Medical Center, Spokane/Seattle, WA 99204, USA. ktuttle@shmc.org
Anderberg
Robert J
RJ
Cooney
Sheryl K
SK
Meek
Rick L
RL
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002478:Cells, Cultured; D003920:Diabetes Mellitus / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D017127:Glycation End Products, Advanced / Q000378:metabolism*; D050527:Mesangial Cells / Q000201:enzymology*; D018384:Oxidative Stress; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000975:Antioxidants; D004044:Dietary Proteins; D004791:Enzyme Inhibitors; D017127:Glycation End Products, Advanced; D011493:Protein Kinase C