Identification of glutathione S-transferase isozymes and γ-glutamylcysteine synthetase as negative acute-phase proteins in rat liver

✍ Scribed by Timo M. Buetler

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 462 KB
• Volume: 28
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.510280615

✦ Synopsis

Because acute infection and inflammation affect drug metabolism and drug-metabolizing enzymes, the effect of the acute-phase response on the expression of glutathione S-transferase (GST) isoenzymes, glutathione synthesis, and several antioxidant enzymes was investigated. Hepatic expression of GST isozymes, positive and negative acutephase reactants, and antioxidant enzymes were determined by Northern blotting and hybridization with gene-specific oligonucleotide probes after lipopolysaccharide treatment of rats. Lipopolysaccharide caused the expected acutephase response as judged by the increased expression of positive and decreased expression of negative acute-phase proteins. The messenger RNA (mRNA) expression of the major hepatic rat GST isozymes A1, A2, A3, M1, and M2 was decreased 50% to 90%. Total hepatic GST activity toward 1-chloro-2,4-dinitrobenzene was also significantly decreased. mRNA expression of ␥-glutamylcysteine synthetase (GCS) large subunit and catalase was reduced by approximately 60%. GCS enzyme activity was also decreased, resulting in a 35% decrease in the hepatic content of reduced glutathione 4 days after lipopolysaccharide challenge. Mn-Superoxide dismutase expression was increased 13-fold, and thioredoxin level was elevated 3-fold after lipopolysaccharide challenge. The expression of all parameters determined returned to near control levels 7 days after treatment. Together, these data show that GSTs and GCS are negative acute-phase proteins and that decreased GCS activity results in a decrease in hepatic glutathione content. Thus, in addition to the phase I drug-metabolizing enzymes known to be decreased during the acute-phase response, some phase II enzymes involved in the elimination of xenobiotics and carcinogens are also decreased. (HEPATOLOGY 1998;28:1551-1560.)

The acute-phase response is referred to as the changes in hepatic enzyme expression occurring as an early response to inflammatory mediators. [2][3][4][5][6][7][8][9][10] Inflammatory cytokines participating in the acute-phase response include interleukins, tumor necrosis factor, and interferons. The acute-phase response appears to be induced in numerous diseases, including acute and chronic inflammation; bacterial, viral, and parasitic infections; and many other diseases. 2,5,7,[11][12][13] Many of the disease states associated with aging (cancer, osteoporosis, atherosclerosis, Parkinson' s disease, Alzheimer' s disease) may be influenced, if not caused, by inflammatory cytokines, which, together with some acute-phase proteins (APPs), are often elevated in elderly people and animals. [14][15][16][17] Symptoms that accompany an acute-phase response are generally those associated with influenza or a cold and include fever, loss of appetite, and fatigue. 7,12 Many of these symptoms are caused by a general immune response accompanied by increases in inflammatory and other cytokines and changes in hormonal status, especially of the hypothalamic-pituitary-adrenal axis. Other physiological changes include changes in hematopoiesis, blood pressure, blood clotting, glycolysis, energy status, lipid biosynthesis, immune responses, and others. 7,12 All of these changes are the result of dramatic changes in hepatic gene expression, 2 many of which take place within 2 to 6 hours after initiation of the acute-phase response. Expression levels of APPs peak at 2 to 3 days and then return to baseline within 5 to 6 days. At least 30 hepatic APPs have been described to date. 2,7,12,18,19 The levels of positive APPs are increased during the acute-phase response and include ␣ 2 -macroglobulin (AMG), ␣ 1 -acid glycoprotein (AGP), C-reactive protein (CRP), serum amyloid A (SAA), hemopexin, complement C3, angiotensinogen, fibrinogen, ␣ 1antiprotease, and others. CRP and SAA are the most highly induced human APPs, whereas AGP is the most highly induced rodent APP, reaching induction levels of up to 100-fold. 7,10,12 The levels of induction for other positive APPs range from 1.5-fold to 50-fold. The negative APPs are reduced during the acute-phase response with levels decreasing between 20% and 80%. The negative APPs include albumin, transthyretin, transferrin, ␣-fetoprotein, antithrombin III, apolipoproteins, and others. In the rat, apolipoproteins were decreased by 80% to 95%. 18 Work by Adamson and Billings [20][21][22] indicates that inflammatory cytokines can induce oxidative stress in target cells.