Lung-Targeted Delivery of Dimethyl Fumarate Promotes the Reversal of Age-Dependent Established Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF), a severe and deadly form of lung fibrosis, is widely regarded as a disease of aging. We previously demonstrated that aged mice with persistent lung fibrosis and IPF lung myofibroblasts exhibit deficient Nrf2-mediated antioxidant responses. Tecfidera is an orally administered FDA-approved drug for the treatment of multiple sclerosis, where the active pharmaceutical ingredient is dimethyl fumarate (DMF), an active Nrf2 activator. However, no studies have evaluated the efficacy of DMF for age-associated persistent lung fibrosis. Here, we demonstrate that in IPF lung fibroblasts, DMF treatment inhibited both TGF-β-mediated pro-fibrotic phenotypes and led to a reversal of established pro-fibrotic phenotypes. We also evaluated the pre-clinical efficacy of lung-targeted (inhaled) vs. systemic (oral) delivery of DMF in an aging murine model of bleomycin-induced persistent lung fibrosis. DMF or vehicle was administered daily to aged mice by oral gavage or intranasal delivery from 3-6 weeks post-injury when mice exhibited non-resolving lung fibrosis. In contrast to systemic (oral) delivery, only lung-targeted (inhaled) delivery of DMF restored lung Nrf2 expression levels, reduced lung oxidative stress, and promoted the resolution of age-dependent established fibrosis. This is the first study to demonstrate the efficacy of lung-targeted DMF delivery to promote the resolution of age-dependent established lung fibrosis.

Leveraging ageing models of pulmonary fibrosis: the efficacy of nintedanib in ageing

Nintedanib is one of two US Food and Drug Administration (FDA)-approved treatments for idiopathic pulmonary fibrosis (IPF). The clinical efficacy of nintedanib for inhibiting the progression of lung fibrosis is well-established [1]. However, although nintedanib is overwhelmingly prescribed to elderly patients, the impact of ageing on its efficacy is difficult to discern from clinical data due to the magnitude of confounding variables that exist among human subjects (genetics, gender, comorbidities, disease stage at the onset of treatment, etc.). A recent post hoc meta-analysis of five IPF clinical trials suggested that the effect of nintedanib in reducing the rate of forced vital capacity decline is consistent across patients with age (patients >75 versus patients <75 years of age) [2]. However, it is important to note that the average age of IPF diagnosis is 66 years and the average patient ages in these cohorts were 78 (>75) versus 64 (<75) years. Further, one could argue that patients in both cohorts represent the elderly population. This study highlights the complexity of evaluating the impact of ageing on efficacy in a clinical setting. To date, all pre-clinical efficacy studies with nintedanib have been performed in young animals. We therefore sought to determine whether ageing impacts the efficacy of nintedanib for inhibiting the development of lung fibrosis. Bleomycin-induced lung injury in young (2 month) and aged (18 month) mice was followed by treatment with nintedanib or vehicle from day 10–21 (figure 1a), using a previously described protocol [3]. We previously demonstrated in this injury model that the severity of lung fibrosis is identical in young and aged mice, in terms of the net increase in total lung collagen following injury [4]. Although some prior studies have reported seemingly contradictory results, indicating increased severity of fibrosis in aged mice [5, 6], this discrepancy could be attributed to increased baseline levels of collagen in aged mice and the methodology/analyses used for fibrosis assessment, as the net increase in collagen appear to be similar in both young and aged mice [5, 6]. In line with our previous findings, both young and aged vehicle-treated mice demonstrated similar levels of fibrosis severity and a similar decline in lung function at 3 weeks post-injury (figure 1b–d, g–h). Also consistent with numerous prior reports [7, 8], we found that in young mice, nintedanib demonstrated efficacy for inhibiting the development of fibrosis (figure 1b–g) and led to improved lung function (figure 1h). Interestingly, nintedanib also significantly inhibited the development of lung fibrosis in aged mice, to a similar extent as young cohorts (figure 1b–g). Although nintedanib treatment resulted in lung functional improvement to a similar extent in both young (49%) and aged (57%) mice (figure 1h), results did not reach statistical significance in aged mice. Of note, there is less than 47% power to detect mean differences between the aged-vehicle and aged-nintedanib groups given the observed effect and sample sizes of aged mice; the trending p-value of 0.06 is displayed to provide a better understanding of the results. No significant differences in survival rate were observed between nintedanib- versus vehicle-treated groups for both young (68% versus 72%, respectively) and aged mice (83% versus 76%, respectively) during this treatment period (day 10–21). Overall, these data indicate that ageing does not impact the efficacy of nintedanib in terms of its ability to inhibit the development of de novo lung fibrosis.

Although nintedanib is overwhelmingly prescribed to elderly patients, this is the first study to demonstrate that ageing does not impact the efficacy of nintedanib. This study sheds light on the utility of aged animal models in pulmonary fibrosis.https://bit.ly/3zA9RC5

Impaired Myofibroblast Dedifferentiation Contributes to Nonresolving Fibrosis in Aging

Idiopathic pulmonary fibrosis (IPF) is a fatal age-associated disease with no cure. Although IPF is widely regarded as a disease of aging, the cellular mechanisms that contribute to this age-associated predilection remain elusive. In this study, we sought to evaluate the consequences of senescence on myofibroblast cell fate and fibrotic responses to lung injury in the context of aging. We demonstrated that nonsenescent lung myofibroblasts maintained the capacity for dedifferentiation, whereas senescent/IPF myofibroblasts exhibited an impaired capacity for dedifferentiation. We previously demonstrated that the transcription factor MyoD acts as a critical switch in the differentiation and dedifferentiation of myofibroblasts. Here, we demonstrate that decreased levels of MyoD preceded myofibroblast dedifferentiation and apoptosis susceptibility in nonsenescent cells, whereas MyoD expression remained elevated in senescent/IPF myofibroblasts, which failed to undergo dedifferentiation and demonstrated resistance to apoptosis. Genetic strategies to silence MyoD restored the susceptibility of IPF myofibroblasts to undergo apoptosis and led to a partial reversal of age-associated persistent fibrosis in vivo. The capacity for myofibroblast dedifferentiation and subsequent apoptosis may be critical for normal physiologic responses to tissue injury, whereas restricted dedifferentiation and apoptosis resistance in senescent cells may underlie the progressive nature of age-associated human fibrotic disorders. These studies support the concept that senescence may promote profibrotic effects via impaired myofibroblast dedifferentiation and apoptosis resistance, which contributes to myofibroblast accumulation and ultimately persistent fibrosis in aging.