Authors: Wang, Liansheng¹; Yang, Yongzhen¹; Dwivedi, Seema¹; Xu, Ya¹; Chu, Etem²; Li, Jie³; Fitchett, Kimberlyn⁴; Boor, Paul⁵

Source: Cardiovascular Toxicology, Volume 6, Number 2, June 2006 , pp. 131-144(14)

Publisher: Humana Press

Abstract:

Tolerance to clinically important organic nitrates such as nitroglycerin (NTG) has been experimentally related to endothelial dysfunction and vascular oxidative stress. Anti-oxidant enzymes such as the glutathione-S-transferases (GSTs) could potentially play a protective role in NTG tolerance. Our previous work showed that an α-class glutathione-S-transferase (GSTA4-4) defends against oxidative damage in the vascular wall; therefore, we asked whether overexpression of GSTA4-4 in endothelial cells and smooth muscle cells might alter the development of tolerance to NTG. Stable transfections of mouse pancreatic islet endothelial cells (MS1) with cDNA of mGSTA4-4, and human fetal aortic vascular msmooth muscle cells (FLTR) with cDNA of hGSTA4-4 were established. TT cytotoxicity, apoptosis, nitric oxide (NO) synthases, both endothelial NO synthase (eNOS) and inducible NO synthase (iNOS) and cyclic guanosine mono-phosphate (cGMP) were measured. Endothelial cells overexpressing mGSTA4-4, and smooth muscle cells overexpressing hGSTA4-4 were more resistant to cytotoxic injury by NTG, assessed at 24 h (p<0.05). In ooth endothelial and smooth muscle cells, NTG-induced apoptosis was inhibited by GST overexpression. Following dosing in a relevant tolerance-inducing NTG protocol, we found that GSTA4-4-overexpressing cells demonstrated significant downregulation of NOS enzymes; NO release, unchanged by the tolerance protocol in both wild-type and vector-transfected cells, was augmented in GST-overexpressing cells (p<0.01); cGMP levels in control cells fell, whereas it rose in GSTA4-4 overexpressing cells (p<0.05). Our results demonstrate that overexpression of GST isozymes can protect endothelial cells and smooth muscle cells against oxidative stress associated with NTG, and markedly alter cellular responses to repeated doses, or tolerance. By manipulating GSTs, physiological tolerance to NTG may be diminished or eliminated.

Keywords: Glutathione S-transferase (GST); nitroglycerin (NTG); drug tolerance; endothelium; vascular smooth muscle cell; oxidative stress

Document Type: Research article

DOI: http://dx.doi.org/10.1385/CT:6:2:131

Affiliations: 1: Department of Pathology, University of Texas Medical Branch, 301 University Blvd., 77555-0609, Galveston, TX, 2: School of Medicine, University of Texas Medical Branch, Galveston, TX, 3: Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, TZ, 4: Baylor University, Waco, TX, 5: Department of Pathology, University of Texas Medical Branch, 301 University Blvd., 77555-0609, Galveston, TX, Email: pboor@utmb.edu

Publication date: 2006-06-01

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