Ascorbic acid and N-acetyl cysteine prevent uncoupling of nitric oxide synthase and increase tolerance to ischemia/reperfusion injury in diabetic rat heart

Free Radic Res. 2011 Oct;45(10):1173-83. doi: 10.3109/10715762.2011.605361. Epub 2011 Aug 10.


Oxidative stress may cause a loss of tetrahydrobiopterin (BH4), a co-factor of nitric oxide synthase (NOS), decrease the bioavailability of NO and aggravate ischemia/reperfusion (I/R) injury in diabetic heart. We hypothesized that ascorbic acid (AA) and N-acetyl cysteine (NAC) protect the diabetic heart from I/R injury by increasing BH4/dihydrobiopterin (BH2) ratio and inhibiting uncoupling of NOS. Diabetes mellitus was induced in rats by streptozotocin treatment, and the hearts were isolated and perfused. BH4 and BH4/BH2 ratio decreased in the diabetic heart associated with increased production of superoxide and nitrotyrosine (NT). Treatment with AA or NAC significantly increased BH4/BH2 ratio in the diabetic heart associated with decreased production of superoxide and NT and increased generation of nitrate plus nitrite (NOx). Pre-treatment with AA or NAC before 30 min ischemia followed by 120 min reperfusion improved left ventricular (LV) function and reduced infarct size in the diabetic but not non-diabetic hearts. The NOS inhibitor, L-NAME, inhibited the increase in the generation of superoxide, NT and NOx, but aggravated LV function and increased infarct size in the diabetic heart. L-NAME also abrogated the increase in NOx and improvement of LV function and the infarct size-limiting effect induced by AA or NAC in the diabetic heart. These results suggest that AA and NAC increase BH4/BH2 ratio and prevent NOS uncoupling in the diabetic heart. Resultant increase in the bioavailability of NO renders the diabetic heart toleratant to I/R injury.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcysteine / pharmacology*
  • Animals
  • Ascorbic Acid / pharmacology*
  • Biopterin / analogs & derivatives
  • Biopterin / metabolism
  • Diabetes Mellitus, Experimental / complications
  • Diabetes Mellitus, Experimental / drug therapy*
  • Diabetes Mellitus, Experimental / enzymology
  • Diabetes Mellitus, Experimental / metabolism
  • Disease Models, Animal
  • Male
  • Myocardial Reperfusion Injury / drug therapy*
  • Myocardial Reperfusion Injury / metabolism
  • Myocardium / metabolism
  • Nitric Oxide Synthase / antagonists & inhibitors*
  • Nitric Oxide Synthase / metabolism
  • Oxidative Stress / physiology
  • Rats
  • Rats, Sprague-Dawley
  • Reperfusion Injury / drug therapy
  • Reperfusion Injury / metabolism


  • Biopterin
  • Nitric Oxide Synthase
  • sapropterin
  • Ascorbic Acid
  • Acetylcysteine