Hyperglycemia adversely modulates endothelial nitric oxide synthase during anesthetic preconditioning through tetrahydrobiopterin- and heat shock protein 90-mediated mechanisms.
BACKGROUND
Endothelial nitric oxide synthase activity is regulated by (6R-)5,6,7,8-tetrahydrobiopterin (BH4) and heat shock protein 90. The authors tested the hypothesis that hyperglycemia abolishes anesthetic preconditioning (APC) through BH4- and heat shock protein 90-dependent pathways.


METHODS
Myocardial infarct size was measured in rabbits in the absence or presence of APC (30 min of isoflurane), with or without hyperglycemia, and in the presence or absence of the BH4 precursor sepiapterin. Isoflurane-dependent nitric oxide production was measured (ozone chemiluminescence) in human coronary artery endothelial cells cultured in normal (5.5 mm) or high (20 mm) glucose conditions, with or without sepiapterin (10 or 100 microm).


RESULTS
APC decreased myocardial infarct size compared with control experiments (26 +/- 6% vs. 46 +/- 3%, respectively; P < 0.05), and this action was blocked by hyperglycemia (43 +/- 4%). Sepiapterin alone had no effect on infarct size (46 +/- 3%) but restored APC during hyperglycemia (21 +/- 3%). The beneficial actions of sepiapterin to restore APC were blocked by the nitric oxide synthase inhibitor N (G)-nitro-L-arginine methyl ester (47 +/- 2%) and the BH4 synthesis inhibitor N-acetylserotonin (46 +/- 3%). Isoflurane increased nitric oxide production to 177 +/- 13% of baseline, and this action was attenuated by high glucose concentrations (125 +/- 6%). Isoflurane increased, whereas high glucose attenuated intracellular BH4/7,8-dihydrobiopterin (BH2) (high performance liquid chromatography), heat shock protein 90-endothelial nitric oxide synthase colocalization (confocal microscopy) and endothelial nitric oxide synthase activation (immunoblotting). Sepiapterin increased BH4/BH2 and dose-dependently restored nitric oxide production during hyperglycemic conditions (149 +/- 12% and 175 +/- 9%; 10 and 100 microm, respectively).


CONCLUSIONS
The results indicate that tetrahydrobiopterin and heat shock protein 90-regulated endothelial nitric oxide synthase activity play a central role in cardioprotection that is favorably modulated by volatile anesthetics and dysregulated by hyperglycemia. Enhancing the production of BH4 may represent a potential therapeutic strategy.
Amour
Julien
J
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
Brzezinska
Anna K
AK
Jager
Zachary
Z
Sullivan
Corbin
C
Weihrauch
Dorothee
D
Du
Jianhai
J
Vladic
Nikolina
N
Shi
Yang
Y
Warltier
David C
DC
Pratt
Phillip F
PF
Kersten
Judy R
JR
D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000502:physiology; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D003331:Coronary Vessels / Q000166:cytology / Q000187:drug effects; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D006943:Hyperglycemia / Q000201:enzymology*; D019157:Ischemic Preconditioning, Myocardial / Q000009:adverse effects*; D007530:Isoflurane / Q000633:toxicity; D049449:Luminescence; D008297:Male; D018613:Microscopy, Confocal; D009569:Nitric Oxide / Q000032:analysis / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D011622:Pterins / Q000494:pharmacology; D011817:Rabbits; D016277:Ventricular Function, Left / Q000187:drug effects
D000777:Anesthetics; D018841:HSP90 Heat-Shock Proteins; D011622:Pterins; D001708:Biopterins; D009569:Nitric Oxide; C016727:sepiapterin; D007530:Isoflurane; D052250:Nitric Oxide Synthase Type III; C003402:sapropterin; D005947:Glucose