title: Manipulating glutathione-S-transferases may prevent the development of tolerance to nitroglycerin.
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 alpha-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 smooth muscle cells (FLTR) with cDNA of hGSTA4-4 were established. MTT 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 both 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.
authors.affiliation: Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555-0609, USA.
authors.forename: Liansheng
authors.initials: L
authors.lastname: Wang
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Yang
authors.forename: Seema
authors.initials: S
authors.lastname: Dwivedi
authors.forename: Ya
authors.initials: Y
authors.lastname: Xu
authors.forename: Etem T
authors.initials: ET
authors.lastname: Chu
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: Kimberlyn
authors.initials: K
authors.lastname: Fitchett
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Boor
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002460:Cell Line; D006152:Cyclic GMP / Q000502:physiology; D004361:Drug Tolerance; D042783:Endothelial Cells / Q000187:drug effects; D005982:Glutathione Transferase / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018613:Microscopy, Confocal; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D005996:Nitroglycerin / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects; D030421:Peroxynitrous Acid / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D014665:Vasodilator Agents; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D005982:Glutathione Transferase; C041116:leukotriene-C4 synthase; D005996:Nitroglycerin; D006152:Cyclic GMP