The in vitro synthesis and degradation of prostaglandins during the development of bleomycin-induced pulmonary fibrosis in hamsters

Orotracheal treprostinil administration attenuates bleomycin-induced lung injury, vascular remodeling, and fibrosis in mice

Pulmonary fibrosis is a progressive disease characterized by disruption of lung architecture and deregulation of the pulmonary function. Prostacyclin, a metabolite of arachidonic acid, is a potential disease mediator since it exerts anti-inflammatory and anti-fibrotic actions. We investigated the effect of treprostinil, a prostacyclin analogue, in bleomycin-induced experimental pulmonary fibrosis. Bleomycin sulfate or saline was administrated intratracheally to mice (n = 9-10/group) at day 0. Orotracheal aspiration of treprostinil or vehicle was administered daily and started 24 h prior to bleomycin challenge. Evaluation of lung pathology was performed in tissue samples and bronchoalveolar lavage fluid collected 7, 14 and 21 days after bleomycin exposure. Lung injury was achieved due to bleomycin exposure at all time points as indicated by impaired lung mechanics, pathologic lung architecture (from day 14), and cellular and protein accumulation in the alveolar space accompanied by a minor decrease in lung tissue VE-cadherin at day 14. Treprostinil preserved lung mechanics, and reduced lung inflammation, fibrosis, and vascular remodeling (day 21); reduced cellularity and protein content of bronchoalveolar lavage fluid were additionally observed with no significant effect on VE-cadherin expression. Bleomycin-induced collagen deposition was attenuated by treprostinil from day 14, while treprostinil involvement in regulating inflammatory processes appears mediated by NF-κB signaling. Overall, prophylactic administration of treprostinil, a stable prostacyclin analogue, maintained lung function, and prevented bleomycin-induced lung injury, and fibrosis, as well as vascular remodeling, a hallmark of pulmonary hypertension. This suggests potential therapeutic efficacy of treprostinil in pulmonary fibrosis and possibly in pulmonary hypertension related to chronic lung diseases.

Prostacyclin agonist with thromboxane synthase inhibitory activity (ONO-1301) attenuates bleomycin-induced pulmonary fibrosis in mice

The balance between prostacyclin and thromboxane A2 (TXA2) plays an important role in pulmonary homeostasis. However, little information is available regarding the therapeutic potency of these prostanoids for pulmonary fibrosis. We have recently developed ONO-1301, a novel long-acting prostacyclin agonist with thromboxane synthase inhibitory activity. Thus we investigated whether repeated administration of ONO-1301 attenuates bleomycin-induced pulmonary fibrosis in mice. After intratracheal injection of bleomycin or saline, mice were randomized to receive repeated subcutaneous administration of ONO-1301 or vehicle. Bronchoalveolar lavage (BAL) and histological analyses were performed at 3, 7, and 14 days after bleomycin injection. In vitro studies using mouse lung fibroblasts were also performed. ONO-1301 significantly attenuated the development of bleomycin-induced pulmonary fibrosis, as indicated by significant decreases in Ashcroft score and lung hydroxyproline content. ONO-1301 significantly reduced total cell count, neutrophil count, and total protein level in BAL fluid in association with a marked reduction of TXB2. A single administration of ONO-1301 significantly increased plasma cAMP level for >2 h. In vitro, ONO-1301 and a cAMP analog dose-dependently reduced cell proliferation in mouse lung fibroblasts. The reduction in cell proliferation by ONO-1301 was attenuated by a protein kinase A (PKA) inhibitor. Furthermore, bleomycin mice treated with ONO-1301 had a significantly higher survival rate than those given vehicle. These results suggest that repeated administration of ONO-1301 attenuates the development of bleomycin-induced pulmonary fibrosis and improves survival in bleomycin mice, at least in part by inhibition of TXA2 synthesis and activation of the cAMP/PKA pathway.

Down-regulation of lipoxin A4 receptor by thromboxane A2 signaling in RAW246.7 cells in vitro and bleomycin-induced lung fibrosis in vivo

Lipoxins (LXs) are members of eicosanoid family that can be endogenously produced during cell-to-cell interactions such as platelet-leukocyte interactions. Anti-inflammatory function of lipoxin A4 (LXA4) as "braking signals" is mediated by the receptor. On the other hand, thromboxane A2 (TXA2) produced by catalysis of cyclooxygenase and thromboxane synthetase is released during platelet aggregation as a vasoconstrictor and a pro-inflammatory factor. To investigate interaction of TXA2 receptor (TP) and LXA4 receptor, effects of a TP agonist and a thromboxane synthetase inhibitor on expression of LXA4 receptor were examined in vitro and in vivo. A TP agonist, U46619 showed a down-regulation of LXA4 receptor induced by interleukin-1beta (IL-1beta) in RAW246.7 cells. In bleomycin-induced lung fibrosis in mice, administration of a thromboxane synthetase inhibitor DP-1904 increased LXA4 receptor mRNA and decreased type I collagen mRNA. In vitro experiments indicate that LXA4 significantly prevented enhanced proliferation of NIH3T3 fibroblasts and the collagen expression by transforming growth factor-beta (TGF-beta). These results suggest that TXA2-TP signaling could cause negative regulation of lipoxin A4 receptor under the transcriptional level during inflammatory process mediated by IL-1beta and TGF-beta induce the expression of LXA4 receptor. Furthermore, the down-regulation of LXA4 receptor by TXA2 implies a possibility that a cellular signaling by TXA2 may have a novel and potential function as a pro-inflammatory factor to inhibit anti-inflammatory effect of LXA4. Concomitantly, selective blockade of TXA2-TP signaling could be suggested to lead to anti-inflammation through active role of LXA4.

Retrovirally introduced prostaglandin D2 synthase suppresses lung injury induced by bleomycin

Hematopoietic prostaglandin D synthase (PGDS) is a key enzyme to produce prostaglandin (PG) D and J series. These PGs are involved in inflammation and immune system. The PGDS complementary DNA (cDNA)-expressing retrovirally transfected fibroblasts were introduced in vivo, and effect of the expression on lung injury induced by bleomycin was investigated in mice. Intravenous injection of PGDS cDNA-expressing fibroblasts significantly reduced lung edema, leukocyte infiltration in bronchoalveolar lavage (BAL) fluid, and pulmonary collagen content at 4 wk after instillation of bleomycin. Survival rate in mice instilled with the PGDS-expressing fibroblasts was higher than that in mice that received the mock transfection. Administration of 15-deoxy-Delta 12,14-PGJ2, which is a nonenzymatic metabolite of PGD2, also attenuated the lung injury, suggesting mediation of PGs produced by PGDS for the attenuation. Introduction of PGDS cDNA-expressing fibroblasts suppressed expression of basic fibroblast growth factor, connective tissue growth factor, and collagen messenger RNAs in the lungs, as well as the levels of total proteins and hemoglobin in BAL fluid. These data suggest that the suppressive effect of PGDS on the lung injury could be partly mediated by edema formation and inhibition of genes involved in the fibrotic change.

Altered myocardial prostaglandin synthesis in spontaneously diabetic rats

Patients with diabetes mellitus have an increased susceptibility to heart disease. The exact mechanism for this phenomenon is unclear. Abnormalities in prostaglandin (PG) production have been suggested as a possible cause. In this connection, we examined the PG synthetic capacity of cardiac microsomes from spontaneously diabetic rats. Cardiac microsomes from diabetic and control rats produced varying amounts of 6-keto-PGF1 alpha (stable degradation product of PGI2), PGE2, PGD2, PGF2 alpha, and TXB2 (stable breakdown product of TXA2). In both instances the production of 6-keto-PGF1 alpha predominated, however, microsomes from diabetic rats showed markedly greater conversion of arachidonic acid to all the PG products, especially 6-keto-PGF1 alpha. When PGF2 alpha metabolism was detected between diabetic and control heart preparations. These results show an enhanced cyclooxygenase activity in diabetic rat hearts without any change in prostaglandin dehydrogenase activity. Such a change may promote some of the cardiac alterations seen in diabetic mellitus.

The effect of diclofenac acid (Voltaren) on bleomycin-induced pulmonary fibrosis in hamsters

Bleomycin is an anti-neoplastic compound which produces a time- and dose-dependent pulmonary fibrosis. The mechanisms which cause this fibrosis are not known. However, the ability of bleomycin to modulate prostaglandin synthesis, degradation and circulating levels appears to be central to the fibrosis. Previous studies, which have attempt to modulate bleomycin-induced fibrosis by prevention of prostaglandin synthesis have conflicting results. Therefore, the present study was designed to determine the effects of diclofenac acid, a nonsteroidal anti-inflammatory compound, on the development of bleomycin-induced pulmonary fibrosis. Diclofenac acid pretreatment and daily injections prevented lung collagen accumulation after intratracheal bleomycin. In addition diclofenac acid treatment resulted in significantly lower lung collagen level after intratracheal bleomycin at 14 and 21 days when compared with bleomycin alone. These data indicate that diclofenac acid treatment inhibits bleomycin-induced lung fibrosis possible through the prevention of prostaglandins synthesis.

Effects of chronic administration of doxorubicin on heart phospholipase A2 activity and in vitro synthesis and degradation of prostaglandins in rats

Male rats received doxorubicin (DXR) 2 mg/kg or phosphate buffered saline (PBS) weekly by the SC route for 13 weeks and were sacrificed at 14 and 19 weeks, one and six weeks, after the last dose, respectively. Heart phospholipase A2 activity in the 1000 X g supernatant was unchanged between DXR and PBS-treatment groups at both 14 and 19 weeks. In vitro heart microsomal syntheses of PGD2, PGE2, PGF2 alpha, and 6-keto-PGF1 alpha were significantly elevated in DXR-treated rats over controls at 14 weeks. In contrast, syntheses of TxB2, PGE2, and PGF2 alpha in DXR-treated rats were significantly depressed from controls at 19 weeks. In vitro heart metabolism of PGF2 alpha in the 100,000 X g supernatant fraction was significantly elevated in DXR treated rats over controls at 14 weeks, but unchanged from controls at 19 weeks. It was concluded from the findings of the present study that increased prostaglandin synthesis may play a role in the mediation of cardiac injury induced by doxorubicin.

The effect of bleomycin on lung metabolism of prostaglandin E2 in hamster

Lung is a major site of prostaglandin synthesis and degradation. One site of metabolism has been shown to be the endothelial cell. Metabolism of prostaglandins has been shown to be influenced by both physiological and pathological mechanism. Furthermore, it has been suggested that a relationship might exist between pulmonary disease and the lung's ability to synthesize and/or degrade prostaglandins. Therefore, we evaluated if bleomycin-induced fibrosis, a model of human pulmonary fibrosis, affects the ability of lung to metabolize prostaglandins. Single pass metabolism of prostaglandin E2 was evaluated in an isolated, perfused and ventilated lung of hamsters at 5 and 500 nM concentrations 4,7,14,21 and 28 days after intratracheal bleomycin. The metabolism of prostaglandin E2 was not changed at the 5 nM level, but was significantly decreased at 500 nM level on day 14 and day 28 after intratracheal bleomycin. The results suggest that intratracheal bleomycin causes alterations in prostaglandin metabolism; the mechanism(s) is unknown but may be related to endothelial cell damage and possible changes in alveolar-capillary surface area.

Effects of intratracheal administration of bleomycin on prostaglandins and thromboxane-B2 and collagen levels of the lung in hamsters

The effects of intratracheal administration of one unit of bleomycin on the lung levels of different prostaglandins (PGs), thromboxane B2 (TxB2), and total collagen were investigated in hamsters in two separate sets of this study. Averaging the values from two sets, the lung levels of 6-keto-PGF1 alpha (stable metabolite of PGI2), TxB2 (stable metabolite of TXA2), PFG2 alpha, and PGE in bleomycin-treated animals were increased by 11-, 7.5-, 7-, and 3-fold over the saline control at 14 days post treatment, respectively. The total lung collagen content in bleomycin-treated animals was significantly increased to 180% of the control during the same period. A number of possibilities for a marked variation in the levels of rise for different PGs and TxB2 and their significance in bleomycin-induced lung fibrosis have been discussed. It was concluded from the findings of the present study that there is a relationship between the lung levels of various metabolites of arachidonic acid cascade and bleomicin-induced increases in the synthesis and accumulation of lung collagen. The nature of this relationship, however, remains to be elucidated.