Methylglyoxal impairs endothelial insulin sensitivity both in vitro and in vivo.
OBJECTIVE
Insulin exerts a direct action on vascular cells, thereby affecting the outcome and progression of diabetic vascular complications. However, the mechanism through which insulin signalling is impaired in the endothelium of diabetic individuals remains unclear. In this work, we have evaluated the role of the AGE precursor methylglyoxal (MGO) in generating endothelial insulin resistance both in cells and in animal models.


METHODS
Time course experiments were performed on mouse aortic endothelial cells (MAECs) incubated with 500 μmol/l MGO. The glyoxalase-1 inhibitor S-p-bromobenzylglutathione-cyclopentyl-diester (SpBrBzGSHCp2) was used to increase the endogenous levels of MGO. For the in vivo study, an MGO solution was administrated i.p. to C57BL/6 mice for 7 weeks.


RESULTS
MGO prevented the insulin-dependent activation of the IRS1/protein kinase Akt/endothelial nitric oxide synthase (eNOS) pathway, thereby blunting nitric oxide (NO) production, while extracellular signal-regulated kinase (ERK1/2) activation and endothelin-1 (ET-1) release were increased by MGO in MAECs. Similar results were obtained in MAECs treated with SpBrBzGSHCp2. In MGO- and SpBrBzGSHCp2-exposed cells, inhibition of ERK1/2 decreased IRS1 phosphorylation on S616 and rescued insulin-dependent Akt activation and NO generation, indicating that MGO inhibition of the IRS1/Akt/eNOS pathway is mediated, at least in part, by ERK1/2. Chronic administration of MGO to C57BL/6 mice impaired whole-body insulin sensitivity and induced endothelial insulin resistance.


CONCLUSIONS
MGO impairs the action of insulin on the endothelium both in vitro and in vivo, at least in part through an ERK1/2-mediated mechanism. These findings may be instrumental in developing novel strategies for preserving endothelial function in diabetes.
Institute of Experimental Endocrinology and Oncology 'G. Salvatore', National Council of Research, Via Pansini 5, 80131, Naples, Italy.
Cecilia
C
Nigro
Gregory A
GA
Raciti
Alessia
A
Leone
Thomas H
TH
Fleming
Michele
M
Longo
Immacolata
I
Prevenzano
Francesca
F
Fiory
Paola
P
Mirra
Vittoria
V
D'Esposito
Luca
L
Ulianich
Peter P
PP
Nawroth
Pietro
P
Formisano
Francesco
F
Beguinot
Claudia
C
Miele
D000818:Animals; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D051379:Mice; D009569:Nitric Oxide / Q000096:biosynthesis; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011765:Pyruvaldehyde / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects*
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C099177:S-4-bromobenzylglutathione cyclopentyl diester; D009569:Nitric Oxide; D011765:Pyruvaldehyde; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; D005978:Glutathione