Impairment of endothelial functions by acute hyperhomocysteinemia and reversal by antioxidant vitamins

JAMA. 1999 Jun 9;281(22):2113-8. doi: 10.1001/jama.281.22.2113.

Abstract

Context: Increased levels of homocysteine are associated with risk of cardiovascular disease. Homocysteine may cause this risk by impairing endothelial cell function.

Objective: To evaluate the effect of acute hyperhomocysteinemia with and without antioxidant vitamin pretreatment on cardiovascular risk factors and endothelial functions.

Design and setting: Observer-blinded, randomized crossover study conducted at a university hospital in Italy.

Subjects: Twenty healthy hospital staff volunteers (10 men, 10 women) aged 25 to 45 years.

Interventions: Subjects were given each of 3 loads in random order at 1-week intervals: oral methionine, 100 mg/kg in fruit juice; the same methionine load immediately following ingestion of antioxidant vitamin E, 800 IU, and ascorbic acid, 1000 mg; and methionine-free fruit juice (placebo). Ten of the 20 subjects also ingested a placebo load with vitamins.

Main outcome measures: Lipid, coagulation, glucose, and circulating adhesion molecule parameters, blood pressure, and endothelial functions as assessed by hemodynamic and rheologic responses to L-arginine, evaluated at baseline and 4 hours following ingestion of the loads.

Results: The oral methionine load increased mean (SD) plasma homocysteine level from 10.5 (3.8) micromol/L at baseline to 27.1 (6.7) micromol/L at 4 hours (P<.001). A similar increase was observed with the same load plus vitamins (10.0 [4.0] to 22.7 [7.8] micromol/L; P<.001) but no significant increase was observed with placebo (10.1 [3.7] to 10.4 [3.2] micromol/L; P=.75). Coagulation and circulating adhesion molecule levels significantly increased after methionine ingestion alone (P<.05) but not after placebo or methionine ingestion with vitamins. While the mean (SD) blood pressure (-7.0% [2.7%]; P<.001), platelet aggregation response to adenosine diphosphate (-11.4% [4.5%]; P=.009) and blood viscosity (-3.0% [1.2%]; P=.04) declined in these parameters 10 minutes after an L-arginine load (3 g) following placebo, the increase after methionine alone (-2.3% [1.5%], 4.0% [3.0%], and 1.5% [1.0%], respectively; P<.05), did not occur following methionine load with vitamin pretreatment (-6.3% [2.5%], -7.9% [3.5%], and -1.5% [1.0%], respectively; P=.24).

Conclusion: Our data suggest that mild to moderate elevations of plasma homocysteine levels in healthy subjects activate coagulation, modify the adhesive properties of endothelium, and impair the vascular responses to L-arginine. Pretreatment with antioxidant vitamin E and ascorbic acid blocks the effects of hyperhomocysteinemia, suggesting an oxidative mechanism.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Acute Disease
  • Adult
  • Antioxidants / metabolism*
  • Antioxidants / pharmacology
  • Arginine / metabolism
  • Arginine / pharmacology
  • Ascorbic Acid / metabolism*
  • Ascorbic Acid / pharmacology
  • Blood Coagulation
  • Blood Viscosity
  • Cardiovascular Diseases / epidemiology*
  • Cardiovascular Diseases / metabolism
  • Cross-Over Studies
  • Endothelium, Vascular / physiology*
  • Female
  • Hemodynamics / physiology*
  • Homocysteine / blood*
  • Homocysteine / metabolism
  • Humans
  • Male
  • Methionine / metabolism*
  • Methionine / pharmacology
  • Platelet Aggregation
  • Risk Factors
  • Single-Blind Method
  • Vitamin E / metabolism*
  • Vitamin E / pharmacology

Substances

  • Antioxidants
  • Homocysteine
  • Vitamin E
  • Arginine
  • Methionine
  • Ascorbic Acid