N-acetylcysteine decreases angiotensin II receptor binding in vascular smooth muscle cells.
Antioxidants seem to inhibit angiotensin II (Ang II) actions by consuming stimulated reactive oxygen species. An alternative hypothesis was investigated: Antioxidants that are also strong reducers of disulfide bonds inhibit the binding of Ang II to its surface receptors with consequent attenuation of signal transduction and cell action. Incubation of cultured vascular smooth muscle cells, which possess Ang II type 1a receptors, with the reducing agent n-acetylcysteine (NAC) for 1 h at 37 degrees C resulted in decreased Ang II radioligand binding in a concentration-dependent pattern. NAC removal restored Ang II binding within 30 min. Incubation with n-acetylserine, a nonreducing analogue of NAC, did not lower Ang II binding, and oxidized NAC was less effective than reduced NAC in lowering Ang II binding. NAC did not decrease Ang II type 1a receptor protein content. Other antioxidants regulated Ang II receptors differently: alpha-Lipoic acid lowered Ang II binding after 24 h, and vitamin E did not lower Ang II binding at all. NAC inhibited Ang II binding in cell membranes at 21 or 37 but not 4 degrees C. Dihydrolipoic acid (the reduced form of alpha-lipoic acid), which contains free sulfhydryl groups as NAC does, decreased Ang II receptor binding in cell membranes, whereas alpha-lipoic acid, which does not contain free sulfhydryl groups, did not. Ang II-stimulated inositol phosphate formation was decreased by preincubation with NAC (1 h) or alpha-lipoic acid (24 h) but not vitamin E. In conclusion, certain antioxidants that are reducing agents lower Ang II receptor binding, and Ang II-stimulated signal transduction is decreased in proportion to decreased receptor binding.
Ullian
Michael E
ME
Medical University of South Carolina, Division of Nephrology, CSB 829, 96 Jonathan Lucas Street, P.O. Box 250623, Charleston, SC 29425, USA. ullianme@musc.edu
Gelasco
Andrew K
AK
Fitzgibbon
Wayne R
WR
Beck
C Nicole
CN
Morinelli
Thomas A
TA
D000111:Acetylcysteine / Q000494:pharmacology*; D000818:Animals; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D004220:Disulfides; D004305:Dose-Response Relationship, Drug; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015151:Immunoblotting; D007295:Inositol Phosphates / Q000737:chemistry; D007700:Kinetics; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D011945:Receptors, Angiotensin / Q000378:metabolism*; D015398:Signal Transduction; D013696:Temperature; D008063:Thioctic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D013997:Time Factors; D014810:Vitamin E / Q000737:chemistry
D000975:Antioxidants; D004220:Disulfides; D007295:Inositol Phosphates; D010710:Phosphates; D017382:Reactive Oxygen Species; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D014810:Vitamin E; D049452:Green Fluorescent Proteins; D008063:Thioctic Acid; C015144:dihydrolipoic acid; D010100:Oxygen; D000111:Acetylcysteine