New Developments in the Therapy of Pulmonary Fibrosis

Mechanisms underlying dose-limiting toxicities of conventional chemotherapeutic agents

Dose-limiting toxicities (DLTs) are severe adverse effects that define the maximum tolerated dose of a cancer drug. In addition to the specific mechanisms of each drug, common contributing factors include inflammation, apoptosis, ion imbalances, and tissue-specific enzyme deficiencies. Among various DLTs are bleomycin-induced pulmonary fibrosis, doxorubicin-induced cardiomyopathy, cisplatin-induced nephrotoxicity, methotrexate-induced hepatotoxicity, vincristine-induced neurotoxicity, paclitaxel-induced peripheral neuropathy, and irinotecan, which elicits severe diarrhea. Currently, specific treatments beyond dose reduction are lacking for most toxicities. Further research on cellular and molecular pathways is imperative to improve their management. This review synthesizes preclinical and clinical data on the pharmacological mechanisms underlying DLTs and explores possible treatment approaches. A comprehensive perspective reveals knowledge gaps and emphasizes the need for future studies to develop more targeted strategies for mitigating these dose-dependent adverse effects. This could allow the safer administration of fully efficacious doses to maximize patient survival.

The effects of carbon monoxide releasing molecules on paraquat-induced pulmonary interstitial inflammation and fibrosis

Paraquat, an herbicide used extensively worldwide, can cause severe toxicity in humans and animals, leading to irreversible, lethal lung fibrosis. The potential of CO-releasing molecules (CORMs), substances that release CO (Carbon monoxide) within animal tissues, for treating paraquat-induced ROS generation and inflammation is investigated here. Our results show that the fast CO releaser CORM-3 (4-20 μM) acts as a potential scavenger of free radicals and decreases fibrosis progression by inhibiting paraquat-induced overexpression of connective tissue growth factor and angiotensin II in MRC-5 cells. The slow CO releaser CORM-A1 (5 mg/kg) clearly decreased expression of the lung profibrogenic cytokines COX-2, TNF-α, and α-SMA and serum hydroxyproline, resulting in a lower mortality rate in paraquat-treated mice. Mice treated with higher-dose CORM-A1 (10 mg/kg) had relatively intact lung lobes and fewer fibrotic patches by gross observation, with less collagen deposition, mesangial matrix accumulation, and pulmonary fibrosis resulting from the mitigation of TGF-β overexpression. In conclusion, our data demonstrate for the first time that CORM-A1 alleviated the development of the fibrotic process and improved survival rate in mice exposed to PQ, would be an attractive therapeutic approach to attenuate the progression of pulmonary fibrosis following PQ exposure.

Inhalation treatment of idiopathic pulmonary fibrosis with curcumin large porous microparticles

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease with high mortality and poor prognosis. Curcumin shows anti-inflammatory effect by suppressing pro-inflammatory cytokines and inhibiting NF-κB mediated inflammation. Here, we developed inhalable curcumin-loaded poly(lactic-co-glycolic)acid (PLGA) large porous microparticles (LPMPs) for the treatment of IPF. Curcumin LPMPs were rough and loose particles with many pores on the surfaces and channels in the inner spaces. The mean geometric diameter of them was larger than 10 µm while the aerodynamic diameter was only 3.12 µm due to their porous structures. They showed a fine particle fraction (FPF) <4.46 μm of 13.41%, 71% cumulative release after 9 h, and more importantly, they avoided uptake by alveolar macrophages. Therefore, most of released curcumin had opportunities to enter lung tissues. Rat pulmonary fibrosis models were established via once intratracheal administration of bleomycin. Curcumin powders and curcumin LPMPs were administered on Days 2, 7, 14, and 21. Curcumin LPMPs remarkably attenuated lung injuries, decreased hydroxyproline contents, reduced the synthesis of collagen I, and inhibited the expressions of TNF-α, TGF-β1, NF-κB p65 and MMP9. Moreover, curcumin LPMPs showed higher antifibrotic activity than curcumin powders. Curcumin LPMPs are a promising inhalable medication for the treatment of IPF.

Cutting edge: FasL(+) immune cells promote resolution of fibrosis

Immune cells, particularly those expressing the ligand of the Fas-death receptor (FasL), e.g. cytotoxic T cells, induce apoptosis in 'undesirable' self- and non-self-cells, including lung fibroblasts, thus providing a means of immune surveillance. We aimed to validate this mechanism in resolution of lung fibrosis. In particular, we elucidated whether FasL(+) immune cells possess antifibrotic capabilities by induction of FasL-dependent myofibroblast apoptosis and whether antagonists of membrane (m) and soluble (s) FasL can inhibit these capabilities. Myofibroblast interaction with immune cells and its FasL-dependency, were investigated in vitro in coculture with T cells and in vivo, following transplantation into lungs of immune-deficient syngeneic Rag-/- as well as allogeneic SCID mice, and into lungs and air pouches of FasL-deficient (gld) mice, before and after reconstitution of the mice with wild-type (wt), FasL(+) immune cells. We found that myofibroblasts from lungs resolving fibrosis undergo FasL-dependent T cell-induced apoptosis in vitro and demonstrate susceptibility to in vivo immune surveillance in lungs of reconstituted, immune- and FasL-deficient, mice. However, immune-deficient Rag-/- and SCID mice, and gld-mice with FasL-deficiency, endure the accumulation of transplanted myofibroblasts in their lungs with subsequent development of fibrosis. Concomitantly, gld mice, in contrast to chimeric FasL-deficient mice with wt immune cells, accumulated transplanted myofibroblasts in the air pouch model. In humans we found that myofibroblasts from fibrotic lungs secrete sFasL and resist T cell-induced apoptosis, whereas normal lung myofibroblasts are susceptible to apoptosis but acquire resistance upon addition of anti-s/mFasL to the coculture. Immune surveillance, particularly functional FasL(+) immune cells, may represent an important extrinsic component in myofibroblast apoptosis and serve as a barrier to fibrosis. Factors interfering with Fas/FasL-immune cell-myofibroblast interaction such as sFasL secreted by fibrotic-lung myofibroblasts, may abrogate immune surveillance during fibrosis. Annulling these factors may pave a new direction to control human lung fibrosis.

Dose-response Effects of Bleomycin on Inflammation and Pulmonary Fibrosis in Mice

Many studies have reported that bleomycin, anti-cancer drug, induces pulmonary fibrosis as a side effect. However, few investigations have focused on the dose-response effects of bleomycin on pulmonary fibrosis. Therefore, in the present study, we investigated the effects of different doses of bleomycin in male mice. ICR mice were given 3 consecutive doses of bleomycin: 1, 2, or 4 mg/kg in bleomycin-treated (BT) groups and saline only in vehicle control (VC) groups. The animals were sacrificed at 7 and 24 days postinstillation. The severity of pulmonary fibrosis was evaluated according to inflammatory cell count and lactate dehydrogenase (LDH) activity in the broncho alveolar lavage fluid (BALF) , and lung tissues were histologically evaluated after hematoxylin and eosin (H&E) , and Masson's trichrome staining. BT groups exhibited changed cellular profiles in BAL fluid compared to the VC group, which had an increased number of total cells, neutrophils, and lymphocytes and a modest increase in the number of macrophages at 7 days post-bleomycin instillation. Moreover, BT groups showed a dose-dependent increase in LDH levels and inflammatory cell counts. However, at 24 days after treatment, collagen deposition, interstitial thickening, and granulomatous lesions were observed in the alveolar spaces in addition to a decrease in inflammatory cells. These results indicate that pulmonary fibrosis induced by 4 mg/kg bleomycin was more severe than that induced by 1 or 2 mg/kg. These data will be utilized in experimental animal models and as basic data to evaluate therapeutic candidates through non-invasive monitoring using the pulmonary fibrosis mouse model established in this study.

Pyrrolidine dithiocarbamate attenuates the development of monocrotaline-induced pulmonary arterial hypertension

We aimed to demonstrate the potential protective effects of pyrrolidine dithiocarbamate (PDTC) on monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH). Adult male rats were randomly assigned to 4 groups: control group, MCT-treated rats only, MCT-injected rats treated with PDTC, and PDTC-treated rats only. Blood and tissue samples were collected after the sacrifice. Levels of malondialdehyde (MDA) were measured by using the thiobarbituric acid method. Total antioxidant status (TAS) was determined using a commercially available ImAnOx kit. A histopathological evaluation was accomplished by scoring the degree of severity. Endothelial damage of the main pulmonary artery was evaluated by immunohistochemical labeling of endothelial cells using anti-rat endothelial cell antigen 1 (RECA-1) antibody. MCT-induced right ventricular hypertrophy (RVH) was reduced significantly in the MCT+PDTC-treated group. MDA levels were significantly lowered in the MCT+PDTC-treated group. TAS was significantly higher in the MCT+PDTC-treated group when compared with the rats with PAH. Histopathological examination demonstrated that PDTC treatment reduced the development of inflammation, hemorrhage and congestion, and collagen deposition. In conclusion, PDTC attenuated PAH and protected pulmonary endothelium in rats administered MCT. These findings suggest that PDTC treatment may provide a new effective therapeutic approach in the treatment of PAH.

Attenuation of lung inflammation and fibrosis in CD69-deficient mice after intratracheal bleomycin

Background

Cluster of differentiation 69 (CD69), an early activation marker antigen on T and B cells, is also expressed on activated macrophages and neutrophils, suggesting that CD69 may play a role in inflammatory diseases. To determine the effect of CD69 deficiency on bleomycin(BLM)-induced lung injury, we evaluated the inflammatory response following intratracheal BLM administration and the subsequent fibrotic changes in wild type (WT) and CD69-deficient (CD69^-/-) mice.

Methods

The mice received a single dose of 3 mg/kg body weight of BLM and were sacrificed at 7 or 14 days post-instillation (dpi). Lung inflammation in the acute phase (7 dpi) was investigated by differential cell counts and cytokine array analyses of bronchoalveolar lavage fluid. In addition, lung fibrotic changes were evaluated at 14 dpi by histopathology and collagen assays. We also used reverse transcription polymerase chain reaction to measure the mRNA expression level of transforming growth factor β1 (TGF-β1) in the lungs of BLM-treated mice.

Results

CD69^-/- mice exhibited less lung damage than WT mice, as shown by reductions in the following indices: (1) loss of body weight, (2) wet/dry ratio of lung, (3) cytokine levels in BALF, (4) histological evidence of lung injury, (5) lung collagen deposition, and (6) TGF-β1 mRNA expression in the lung.

Conclusion

The present study clearly demonstrates that CD69 plays an important role in the progression of lung injury induced by BLM.

Potential role of the inflammasome-derived inflammatory cytokines in pulmonary fibrosis

Pulmonary fibrosis is a progressive, disabling disease with mortality rates that appear to be increasing in the western population, including the USA. There are over 140 known causes of pulmonary fibrosis as well as many unknown causes. Treatment options for this disease are limited due to poor understanding of the molecular mechanisms of the disease progression. However, recent progress in inflammasome research has greatly contributed to our understanding of its role in inflammation and fibrosis development. The inflammasome is a multiprotein complex that is an important component of both the innate and adaptive immune systems. Activation of proinflammatory cytokines following inflammasome assembly, such as IL-1β and IL-18, has been associated with development of PF. In addition, components of the inflammasome complex itself, such as the adaptor protein ASC have been associated with PF development. Recent evidence suggesting that the fibrotic process can be reversed via blockade of pathways associated with inflammasome activity may provide hope for future drug strategies. In this paper we will give an introduction to pulmonary fibrosis and its known causes. In addition, we will discuss the importance of the inflammasome in the development of pulmonary fibrosis as well as discuss potential future treatment options.