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Antioxidant improves smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase function and lowers tyrosine nitration
Takeshi Adachi1, Reiko Matsui, Shanqin Xu
1Vascular Biology Unit, Whitaker Cardiovascular Institute, Department of Medicine and Cardiothoracic Surgery, Boston University Medical Center, Boston, Mass, USA.
Insights
Antioxidants restore nitric oxide (NO) relaxation in hypercholesterolemia by improving vascular smooth muscle function. This study shows antioxidants reverse impaired sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) activity in hypercholesterolemia.
Area of Science:
- Cardiovascular Biology
- Vascular Physiology
- Pharmacology
Background:
- Hypercholesterolemia (HC) impairs endothelial function and vascular smooth muscle response to nitric oxide (NO).
- Oxidative stress in HC may negatively affect sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) function, a key mediator of NO-induced relaxation.
- The impact of antioxidants on NO-mediated vascular smooth muscle relaxation in HC is not well understood.
Purpose of the Study:
- To investigate the effect of the antioxidant t-butylhydroxytoluene (BHT) on vascular smooth muscle SERCA activity and NO-induced relaxation in a rabbit model of hypercholesterolemia.
- To determine if BHT can restore NO-mediated relaxation impaired by HC.
- To explore the role of oxidative stress and SERCA function in HC-induced vascular dysfunction.
Main Methods:
- Rabbits were fed a normal chow or a 0.5% cholesterol diet for 13 weeks. The antioxidant BHT (1%) was added to the HC diet during the final 3 weeks.
- Vascular smooth muscle SERCA activity and NO-induced relaxation were measured in aortic tissues.
- SERCA protein expression, 3-nitrotyrosine levels, and tyrosine-nitrated SERCA were assessed via immunoprecipitation.
Main Results:
- Hypercholesterolemia impaired acetylcholine- and NO-induced relaxation, which were restored by BHT treatment.
- Reduced aortic SERCA activity in HC rabbits was normalized by BHT without altering SERCA protein expression.
- Increased 3-nitrotyrosine in HC aortas colocalized with SERCA, and tyrosine-nitrated SERCA was decreased by BHT, indicating reduced oxidative modification of SERCA.
Conclusions:
- Antioxidant administration reverses impaired vascular smooth muscle SERCA function and restores NO-induced relaxation in hypercholesterolemia.
- These beneficial effects are likely mediated by reducing the direct impact of reactive oxygen species on SERCA activity.
- Targeting oxidative stress may be a viable strategy to improve vascular function in hypercholesterolemic conditions.
Abstract:
Antioxidants improve endothelial function in hypercholesterolemia (HC); however, whether this includes improvement of the vascular smooth muscle response to NO is unknown. NO relaxes arteries, in part, by stimulating Ca(2+) uptake via sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) in aortic smooth muscle, and HC impairs SERCA function and the response to NO. HC induces oxidative stress, which could impair SERCA function. To study the effect of antioxidants, which are known to improve endothelium-dependent relaxation in HC, smooth muscle SERCA activity and NO-induced relaxation were studied in rabbits fed normal chow or a 0.5% cholesterol diet for 13 weeks. The antioxidant t-butylhydroxytoluene (BHT, 1%) was mixed with the HC diet in the last 3 weeks. HC impaired acetylcholine- and NO-induced relaxation, and these were restored by BHT. After inhibiting SERCA with thapsigargin, no difference existed in NO-induced relaxation among the three groups. Reduced aortic SERCA activity in HC was restored by BHT without changing SERCA protein expression. 3-Nitrotyrosine was notably increased in the media of the HC aorta, where it colocalized with SERCA. Tyrosine-nitrated SERCA protein was immunoprecipitated in the aortas of HC rabbits, where it was decreased by BHT, and it was also detected in the aortas of atherosclerotic humans. Thus, the antioxidant reverses impaired smooth muscle SERCA function in HC, and this is correlated with the improved relaxation to NO. These beneficial effects may depend on reducing the direct effects on SERCA of reactive oxygen species that are augmented in HC.