Bleomycin-induced Pulmonary Fibrosis Is Attenuated in γ-Glutamyl Transpeptidase–Deficient Mice

Abstract

To investigate repair mechanisms in bleomycin-induced pulmonary fibrosis, we used mice deficient in gamma-glutamyl transpeptidase (GGT-/-), a key enzyme in glutathione (GSH) and cysteine metabolism. Seventy-two hours after bleomycin (0.03 U/g), GGT-/- mice displayed a different inflammatory response to wild-type mice as judged by a near absence of neutrophils in lung tissue and bronchoalveolar lavage and a less pronounced rise in matrix metalloproteinase-9. Inflammation in GGT-/- mice consisted mainly of lymphocytes and macrophages. At 1 month, lungs from bleomycin-treated GGT-/- mice exhibited minimal areas of fibrosis compared with wild-type mice(light microscopy fibrosis index: 510 +/- 756 versus 1975 +/- 817, p < 0.01). Lung collagen content revealed a significant increase in bleomycin-treated wild-type (15.1 +/- 3.8 versus 8.5 +/- 0.7 microg hydroxy(OH)-proline/mg dry weight, p < 0.01) but not in GGT-/- (10.4 +/- 1.7 versus 8.8 +/- 0.8). Control lungs from GGT-/- showed a significant reduction of cysteine (0.03 +/- 0.005 versus 0.055 +/- 0.001, p < 0.02) and GSH levels (1.24 +/- 0.055 versus 1.79 +/- 0.065, p < 0.002). These values decreased after 72 hours of bleomycin in both GGT-/- and wild-type but reached their respective control values after 1 month. Supplementation with N-acetyl cysteine partially ameliorated the effects of GGT deficiency. These findings suggest that increased neutrophils and matrix metalloproteinase-9 during the early inflammatory response and adequate thiol reserves are key elements in the fibrotic response after bleomycin-induced pulmonary injury.

The Beneficial Effects of Oral Cotrimoxazole upon Likely Biomarkers of Oxidative Stress in Advanced Fibrotic Lung Disease

“…GGT is a membrane bound enzyme linked to the breakdown of glutathione. The prevention of bleomycin induced lung fibrosis in GGT-/-deficient mice may be related to maintained glutathione levels which reduce apoptosis and fibrosis [17]. This has interesting links to our observations where cotrimoxazole treatment and clinical improvement occurred with a fall in serum GGT.…”

“…While GGT has been considered an anti-oxidant, recent studies suggest that GGT is up-regulated in response to oxidative stress and GGT cleavage of glutathione induces Reactive Oxygen Series (ROS) production [14] [15] [16]. In mice, the genetic absence of GGT (GGT-/-) protects the lung against bleomycin induced lung fibrosis through maintained glutathione levels [17].…”

Matrix Metalloproteinase-19 Is a Key Regulator of Lung Fibrosis in Mice and Humans

“…Bronchoalveolar lavage (BAL) was performed with 1.0 ml of PBS at 7 and 21 days, and lung hydroxyproline analysis was performed at 21 days, as described (22,23). Data are expressed as mg/hydroxyproline/lung.…”

Protective Effect of Valsartan on Beleomycine-Induced Fibrosis

“…No satisfactory therapeutic agent has been found, and the current protocols have not indicated their expected efficacy nor their possibly severe adverse effects. A growing body of studies have thus been undertaken to find novel and effective ways to improve the management of the consequences of this fatal condition (5,16). Most studies to date have used the bleomycin-induced pulmonary lesion as a model for fibrosis of lungs in rats (4,5).…”

“…To date, no standard treatments have been introduced in clinical settings, although glucocorticoids and cytotoxic drugs have been utilized (3). Death usually occurs as the result of respiratory complications; the survival rate is roughly 50 percent within five years (4,5). Angiotensin-converting enzyme (ACE), via proteolytic actions on angiotensin I, produce angiotensin II.…”