Higher-Dose Fluvoxamine and Time to Sustained Recovery in Outpatients With COVID-19: The ACTIV-6 Randomized Clinical Trial

Importance

The effect of higher-dose fluvoxamine in reducing symptom duration among outpatients with mild to moderate COVID-19 remains uncertain.

Objective

To assess the effectiveness of fluvoxamine, 100 mg twice daily, compared with placebo, for treating mild to moderate COVID-19.

Design, Setting, and Participants

The ACTIV-6 platform randomized clinical trial aims to evaluate repurposed medications for mild to moderate COVID-19. Between August 25, 2022, and January 20, 2023, a total of 1175 participants were enrolled at 103 US sites for evaluating fluvoxamine; participants were 30 years or older with confirmed SARS-CoV-2 infection and at least 2 acute COVID-19 symptoms for 7 days or less.

Interventions

Participants were randomized to receive fluvoxamine, 50 mg twice daily on day 1 followed by 100 mg twice daily for 12 additional days (n = 601), or placebo (n = 607).

Main Outcomes and Measures

The primary outcome was time to sustained recovery (defined as at least 3 consecutive days without symptoms). Secondary outcomes included time to death; time to hospitalization or death; a composite of hospitalization, urgent care visit, emergency department visit, or death; COVID-19 clinical progression scale score; and difference in mean time unwell. Follow-up occurred through day 28.

Results

Among 1208 participants who were randomized and received the study drug, the median (IQR) age was 50 (40-60) years, 65.8% were women, 45.5% identified as Hispanic/Latino, and 76.8% reported receiving at least 2 doses of a SARS-CoV-2 vaccine. Among 589 participants who received fluvoxamine and 586 who received placebo included in the primary analysis, differences in time to sustained recovery were not observed (adjusted hazard ratio [HR], 0.99 [95% credible interval, 0.89-1.09]; P for efficacy = .40]). Additionally, unadjusted median time to sustained recovery was 10 (95% CI, 10-11) days in both the intervention and placebo groups. No deaths were reported. Thirty-five participants reported health care use events (a priori defined as death, hospitalization, or emergency department/urgent care visit): 14 in the fluvoxamine group compared with 21 in the placebo group (HR, 0.69 [95% credible interval, 0.27-1.21]; P for efficacy = .86) There were 7 serious adverse events in 6 participants (2 with fluvoxamine and 4 with placebo) but no deaths.

Conclusions and Relevance

Among outpatients with mild to moderate COVID-19, treatment with fluvoxamine does not reduce duration of COVID-19 symptoms.

Trial Registration

ClinicalTrials.gov Identifier: NCT04885530.

The Trial Innovation Network Liaison Team: building a national clinical and translational community of practice

In 2016, the National Center for Advancing Translational Science launched the Trial Innovation Network (TIN) to address barriers to efficient and informative multicenter trials. The TIN provides a national platform, working in partnership with 60+ Clinical and Translational Science Award (CTSA) hubs across the country to support the design and conduct of successful multicenter trials. A dedicated Hub Liaison Team (HLT) was established within each CTSA to facilitate connection between the hubs and the newly launched Trial and Recruitment Innovation Centers. Each HLT serves as an expert intermediary, connecting CTSA Hub investigators with TIN support, and connecting TIN research teams with potential multicenter trial site investigators. The cross-consortium Liaison Team network was developed during the first TIN funding cycle, and it is now a mature national network at the cutting edge of team science in clinical and translational research. The CTSA-based HLT structures and the external network structure have been developed in collaborative and iterative ways, with methods for shared learning and continuous process improvement. In this paper, we review the structure, function, and development of the Liaison Team network, discuss lessons learned during the first TIN funding cycle, and outline a path toward further network maturity.

Leveraging the Expertise of the CTSA Program to Increase the Impact and Efficiency of Clinical Trials

Importance

Multicenter clinical trials play a critical role in the translational processes that enable new treatments to reach all people and improve public health. However, conducting multicenter randomized clinical trials (mRCT) presents challenges. The Trial Innovation Network (TIN), established in 2016 to partner with the Clinical and Translational Science Award (CTSA) Consortium of academic medical institutions in the implementation of mRCTs, consists of 3 Trial Innovation Centers (TICs) and 1 Recruitment Innovation Center (RIC). This unique partnership has aimed to address critical roadblocks that impede the design and conduct of mRCTs, in expectation of accelerating the translation of novel interventions to clinical practice. The TIN's challenges and achievements are described in this article, along with examples of innovative resources and processes that may serve as useful models for other clinical trial networks providing operational and recruitment support.

Observations

The TIN has successfully integrated more than 60 CTSA institution program hubs into a functional network for mRCT implementation and optimization. A unique support system for investigators has been created that includes the development and deployment of novel tools, operational and recruitment services, consultation models, and rapid communication pathways designed to reduce delays in trial start-up, enhance recruitment, improve engagement of diverse research participants and communities, and streamline processes that improve the quality, efficiency, and conduct of mRCTs. These resources and processes span the clinical trial spectrum and enable the TICs and RIC to serve as coordinating centers, data centers, and recruitment specialists to assist trials across the National Institutes of Health and other agencies. The TIN's impact has been demonstrated through its response to both historical operational challenges and emerging public health emergencies, including the national opioid public health crisis and the COVID-19 pandemic.

Conclusions and Relevance

The TIN has worked to reduce barriers to implementing mRCTs and to improve mRCT processes and operations by providing needed clinical trial infrastructure and resources to CTSA investigators. These resources have been instrumental in more quickly and efficiently translating research discoveries into beneficial patient treatments.

Inhaled Fluticasone Furoate for Outpatient Treatment of Covid-19

BACKGROUND

The effectiveness of inhaled glucocorticoids in shortening the time to symptom resolution or preventing hospitalization or death among outpatients with mild-to-moderate coronavirus disease 2019 (Covid-19) is unclear.

METHODS

We conducted a decentralized, double-blind, randomized, placebo-controlled platform trial in the United States to assess the use of repurposed medications in outpatients with confirmed coronavirus disease 2019 (Covid-19). Nonhospitalized adults 30 years of age or older who had at least two symptoms of acute infection that had been present for no more than 7 days before enrollment were randomly assigned to receive inhaled fluticasone furoate at a dose of 200 μg once daily for 14 days or placebo. The primary outcome was the time to sustained recovery, defined as the third of 3 consecutive days without symptoms. Key secondary outcomes included hospitalization or death by day 28 and a composite outcome of the need for an urgent-care or emergency department visit or hospitalization or death through day 28.

RESULTS

Of the 1407 enrolled participants who underwent randomization, 715 were assigned to receive inhaled fluticasone furoate and 692 to receive placebo, and 656 and 621, respectively, were included in the analysis. There was no evidence that the use of fluticasone furoate resulted in a shorter time to recovery than placebo (hazard ratio, 1.01; 95% credible interval, 0.91 to 1.12; posterior probability of benefit [defined as a hazard ratio >1], 0.56). A total of 24 participants (3.7%) in the fluticasone furoate group had urgent-care or emergency department visits or were hospitalized, as compared with 13 participants (2.1%) in the placebo group (hazard ratio, 1.9; 95% credible interval, 0.8 to 3.5). Three participants in each group were hospitalized, and no deaths occurred. Adverse events were uncommon in both groups.

CONCLUSIONS

Treatment with inhaled fluticasone furoate for 14 days did not result in a shorter time to recovery than placebo among outpatients with Covid-19 in the United States. (Funded by the National Center for Advancing Translational Sciences and others; ACTIV-6 ClinicalTrials.gov number, NCT04885530.).

Decentralized clinical trials in the trial innovation network: Value, strategies, and lessons learned

New technologies and disruptions related to Coronavirus disease-2019 have led to expansion of decentralized approaches to clinical trials. Remote tools and methods hold promise for increasing trial efficiency and reducing burdens and barriers by facilitating participation outside of traditional clinical settings and taking studies directly to participants. The Trial Innovation Network, established in 2016 by the National Center for Advancing Clinical and Translational Science to address critical roadblocks in clinical research and accelerate the translational research process, has consulted on over 400 research study proposals to date. Its recommendations for decentralized approaches have included eConsent, participant-informed study design, remote intervention, study task reminders, social media recruitment, and return of results for participants. Some clinical trial elements have worked well when decentralized, while others, including remote recruitment and patient monitoring, need further refinement and assessment to determine their value. Partially decentralized, or "hybrid" trials, offer a first step to optimizing remote methods. Decentralized processes demonstrate potential to improve urban-rural diversity, but their impact on inclusion of racially and ethnically marginalized populations requires further study. To optimize inclusive participation in decentralized clinical trials, efforts must be made to build trust among marginalized communities, and to ensure access to remote technology.

Approaches for enhancing the informativeness and quality of clinical trials: Innovations and principles for implementing multicenter trials from the Trial Innovation Network

One challenge for multisite clinical trials is ensuring that the conditions of an informative trial are incorporated into all aspects of trial planning and execution. The multicenter model can provide the potential for a more informative environment, but it can also place a trial at risk of becoming uninformative due to lack of rigor, quality control, or effective recruitment, resulting in premature discontinuation and/or non-publication. Key factors that support informativeness are having the right team and resources during study planning and implementation and adequate funding to support performance activities. This communication draws on the experience of the National Center for Advancing Translational Science (NCATS) Trial Innovation Network (TIN) to develop approaches for enhancing the informativeness of clinical trials. We distilled this information into three principles: (1) assemble a diverse team, (2) leverage existing processes and systems, and (3) carefully consider budgets and contracts. The TIN, comprised of NCATS, three Trial Innovation Centers, a Recruitment Innovation Center, and 60+ CTSA Program hubs, provides resources to investigators who are proposing multicenter collaborations. In addition to sharing principles that support the informativeness of clinical trials, we highlight TIN-developed resources relevant for multicenter trial initiation and conduct.

Effect of Higher-Dose Ivermectin for 6 Days vs Placebo on Time to Sustained Recovery in Outpatients With COVID-19: A Randomized Clinical Trial

Importance

It is unknown whether ivermectin, with a maximum targeted dose of 600 μg/kg, shortens symptom duration or prevents hospitalization among outpatients with mild to moderate COVID-19.

Objective

To evaluate the effectiveness of ivermectin at a maximum targeted dose of 600 μg/kg daily for 6 days, compared with placebo, for the treatment of early mild to moderate COVID-19.

Design, Setting, and Participants

The ongoing Accelerating COVID-19 Therapeutic Interventions and Vaccines 6 (ACTIV-6) platform randomized clinical trial was designed to evaluate repurposed therapies among outpatients with mild to moderate COVID-19. A total of 1206 participants older than 30 years with confirmed COVID-19 experiencing at least 2 symptoms of acute infection for less than or equal to 7 days were enrolled at 93 sites in the US from February 16, 2022, through July 22, 2022, with follow-up data through November 10, 2022.

Interventions

Participants were randomly assigned to receive ivermectin, with a maximum targeted dose of 600 μg/kg (n = 602) daily, or placebo (n = 604) for 6 days.

Main Outcomes and Measures

The primary outcome was time to sustained recovery, defined as at least 3 consecutive days without symptoms. The 7 secondary outcomes included a composite of hospitalization, death, or urgent/emergent care utilization by day 28.

Results

Among 1206 randomized participants who received study medication or placebo, the median (IQR) age was 48 (38-58) years, 713 (59.1%) were women, and 1008 (83.5%) reported receiving at least 2 SARS-CoV-2 vaccine doses. The median (IQR) time to sustained recovery was 11 (11-12) days in the ivermectin group and 11 (11-12) days in the placebo group. The hazard ratio (posterior probability of benefit) for improvement in time to recovery was 1.02 (95% credible interval, 0.92-1.13; P = .68). Among those receiving ivermectin, 34 (5.7%) were hospitalized, died, or had urgent or emergency care visits compared with 36 (6.0%) receiving placebo (hazard ratio, 1.0 [95% credible interval, 0.6-1.5]; P = .53). In the ivermectin group, 1 participant died and 4 were hospitalized (0.8%); 2 participants (0.3%) were hospitalized in the placebo group and there were no deaths. Adverse events were uncommon in both groups.

Conclusions and Relevance

Among outpatients with mild to moderate COVID-19, treatment with ivermectin, with a maximum targeted dose of 600 μg/kg daily for 6 days, compared with placebo did not improve time to sustained recovery. These findings do not support the use of ivermectin in patients with mild to moderate COVID-19.

Trial Registration

ClinicalTrials.gov Identifier: NCT04885530.

Effect of Fluvoxamine vs Placebo on Time to Sustained Recovery in Outpatients With Mild to Moderate COVID-19: A Randomized Clinical Trial

Importance

The effectiveness of fluvoxamine to shorten symptom duration or prevent hospitalization among outpatients with mild to moderate symptomatic COVID-19 is unclear.

Objective

To evaluate the efficacy of low-dose fluvoxamine (50 mg twice daily) for 10 days compared with placebo for the treatment of mild to moderate COVID-19 in the US.

Design, Setting, and Participants

The ongoing Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV-6) platform randomized clinical trial was designed to test repurposed medications in outpatients with mild to moderate COVID-19. A total of 1288 participants aged 30 years or older with test-confirmed SARS-CoV-2 infection and experiencing 2 or more symptoms of acute COVID-19 for 7 days or less were enrolled between August 6, 2021, and May 27, 2022, at 91 sites in the US.

Interventions

Participants were randomized to receive 50 mg of fluvoxamine twice daily for 10 days or placebo.

Main Outcomes and Measures

The primary outcome was time to sustained recovery (defined as the third day of 3 consecutive days without symptoms). There were 7 secondary outcomes, including a composite outcome of hospitalization, urgent care visit, emergency department visit, or death through day 28.

Results

Among 1331 participants who were randomized (median age, 47 years [IQR, 38-57 years]; 57% were women; and 67% reported receiving ≥2 doses of a SARS-CoV-2 vaccine), 1288 completed the trial (674 in the fluvoxamine group and 614 in the placebo group). The median time to sustained recovery was 12 days (IQR, 11-14 days) in the fluvoxamine group and 13 days (IQR, 12-13 days) in the placebo group (hazard ratio [HR], 0.96 [95% credible interval, 0.86-1.06], posterior P = .21 for the probability of benefit [determined by an HR >1]). For the composite outcome, 26 participants (3.9%) in the fluvoxamine group were hospitalized, had an urgent care visit, had an emergency department visit, or died compared with 23 participants (3.8%) in the placebo group (HR, 1.1 [95% credible interval, 0.5-1.8], posterior P = .35 for the probability of benefit [determined by an HR <1]). One participant in the fluvoxamine group and 2 participants in the placebo group were hospitalized; no deaths occurred in either group. Adverse events were uncommon in both groups.

Conclusions and Relevance

Among outpatients with mild to moderate COVID-19, treatment with 50 mg of fluvoxamine twice daily for 10 days, compared with placebo, did not improve time to sustained recovery. These findings do not support the use of fluvoxamine at this dose and duration in patients with mild to moderate COVID-19.

Trial Registration

ClinicalTrials.gov Identifier: NCT04885530.

Effect of Ivermectin 600 μg/kg for 6 days vs Placebo on Time to Sustained Recovery in Outpatients with Mild to Moderate COVID-19: A Randomized Clinical Trial

Background

Whether ivermectin, with a maximum targeted dose of 600 μg/kg, shortens symptom duration or prevents hospitalization among outpatients with mild to moderate coronavirus disease 2019 (COVID-19) remains unknown. Our objective was to evaluate the effectiveness of ivermectin, dosed at 600 μg/kg, daily for 6 days compared with placebo for the treatment of early mild to moderate COVID-19.

Methods

ACTIV-6, an ongoing, decentralized, randomized, double-blind, placebo-controlled, platform trial, was designed to evaluate repurposed therapies in outpatients with mild to moderate COVID-19. A total of 1206 participants age ≥30 years with confirmed COVID-19, experiencing ≥2 symptoms of acute infection for ≤7 days, were enrolled from February 16, 2022, through July 22, 2022, with follow-up data through November 10, 2022, at 93 sites in the US. Participants were randomized to ivermectin, with a maximum targeted dose of 600 μg/kg (n=602), daily vs. placebo daily (n=604) for 6 days. The primary outcome was time to sustained recovery, defined as at least 3 consecutive days without symptoms. The 7 secondary outcomes included a composite of hospitalization, death, or urgent/emergent care utilization by day 28.

Results

Among 1206 randomized participants who received study medication or placebo, median (interquartile range) age was 48 (38-58) years; 713 (59%) were women; and 1008 (84%) reported ≥2 SARS-CoV-2 vaccine doses. Median time to recovery was 11 (11-12) days in the ivermectin group and 11 (11-12) days in the placebo group. The hazard ratio (HR) (95% credible interval [CrI], posterior probability of benefit) for improvement in time to recovery was 1.02 (0.92-1.13; P[HR>1]=0.68). In those receiving ivermectin, 34 (5.7%) were hospitalized, died, or had urgent or emergency care visits compared with 36 (6.0%) receiving placebo (HR 1.0, 0.6- 1.5; P[HR<1]=0.53). In the ivermectin group, 1 participant died and 4 were hospitalized (0.8%); 2 participants (0.3%) were hospitalized in the placebo group and there were no deaths. Adverse events were uncommon in both groups.

Conclusions

Among outpatients with mild to moderate COVID-19, treatment with ivermectin, with a maximum targeted dose of 600 μg/kg daily for 6 days, compared with placebo did not improve time to recovery. These findings do not support the use of ivermectin in patients with mild to moderate COVID-19.

Trial registration

ClinicalTrials.gov Identifier: NCT04885530 .

Fluvoxamine for Outpatient Treatment of COVID-19: A Decentralized, Placebo-controlled, Randomized, Platform Clinical Trial

Background

The effectiveness of fluvoxamine to shorten symptom duration or prevent hospitalization among outpatients in the US with mild to moderate symptomatic coronavirus disease 2019 (COVID-19) is unclear.

Design

ACTIV-6 is an ongoing, decentralized, double-blind, randomized, placebo-controlled platform trial testing repurposed medications in outpatients with mild to moderate COVID-19. A total of 1288 non-hospitalized adults aged ≥30 years with confirmed COVID-19 experiencing ≥2 symptoms of acute infection for ≤7 days prior to randomization were randomized to receive fluvoxamine 50 mg or placebo twice daily for 10 days. The primary outcome was time to sustained recovery, defined as the third of 3 consecutive days without symptoms. Secondary outcomes included composites of hospitalization or death with or without urgent or emergency care visit by day 28.

Results

Of 1331 participants randomized (mean [SD] age, 48.5 [12.8] years; 57% women; 67% reported receiving at least 2 doses of a SARS-CoV-2 vaccine), 1288 completed the trial (n=614 placebo, n=674 fluvoxamine). Median time to recovery was 13 days (IQR 12-13) in the placebo group and 12 days (IQR 11-14) in the fluvoxamine group (hazard ratio [HR] 0.96, 95% credible interval [CrI] 0.86-1.07; posterior probability for benefit [HR>1]=0.22). Twenty-six participants (3.9%) in the fluvoxamine group were hospitalized or had urgent or emergency care visits compared with 23 (3.8%) in the placebo group (HR 1.1, 95% CrI 0.6-1.8; posterior probability for benefit [HR<1]=0.340). One participant in the fluvoxamine group and 2 in the placebo group were hospitalized; no deaths occurred. Adverse events were uncommon in both groups.

Conclusions

Treatment with fluvoxamine 50 mg twice daily for 10 days did not improve time to recovery, compared with placebo, among outpatients with mild to moderate COVID-19. These findings do not support the use of fluvoxamine at this dose and duration in patients with mild to moderate COVID-19.

Effect of Ivermectin vs Placebo on Time to Sustained Recovery in Outpatients With Mild to Moderate COVID-19: A Randomized Clinical Trial

Importance

The effectiveness of ivermectin to shorten symptom duration or prevent hospitalization among outpatients in the US with mild to moderate symptomatic COVID-19 is unknown.

Objective

To evaluate the efficacy of ivermectin, 400 μg/kg, daily for 3 days compared with placebo for the treatment of early mild to moderate COVID-19.

Design, Setting, and Participants

ACTIV-6, an ongoing, decentralized, double-blind, randomized, placebo-controlled platform trial, was designed to evaluate repurposed therapies in outpatients with mild to moderate COVID-19. A total of 1591 participants aged 30 years and older with confirmed COVID-19, experiencing 2 or more symptoms of acute infection for 7 days or less, were enrolled from June 23, 2021, through February 4, 2022, with follow-up data through May 31, 2022, at 93 sites in the US.

Interventions

Participants were randomized to receive ivermectin, 400 μg/kg (n = 817), daily for 3 days or placebo (n = 774).

Main Outcomes and Measures

Time to sustained recovery, defined as at least 3 consecutive days without symptoms. There were 7 secondary outcomes, including a composite of hospitalization or death by day 28.

Results

Among 1800 participants who were randomized (mean [SD] age, 48 [12] years; 932 women [58.6%]; 753 [47.3%] reported receiving at least 2 doses of a SARS-CoV-2 vaccine), 1591 completed the trial. The hazard ratio (HR) for improvement in time to recovery was 1.07 (95% credible interval [CrI], 0.96-1.17; posterior P value [HR >1] = .91). The median time to recovery was 12 days (IQR, 11-13) in the ivermectin group and 13 days (IQR, 12-14) in the placebo group. There were 10 hospitalizations or deaths in the ivermectin group and 9 in the placebo group (1.2% vs 1.2%; HR, 1.1 [95% CrI, 0.4-2.6]). The most common serious adverse events were COVID-19 pneumonia (ivermectin [n = 5]; placebo [n = 7]) and venous thromboembolism (ivermectin [n = 1]; placebo [n = 5]).

Conclusions and Relevance

Among outpatients with mild to moderate COVID-19, treatment with ivermectin, compared with placebo, did not significantly improve time to recovery. These findings do not support the use of ivermectin in patients with mild to moderate COVID-19.

Trial Registration

ClinicalTrials.gov Identifier: NCT04885530.

Aortic carboxypeptidase-like protein is expressed in fibrotic human lung and its absence protects against bleomycin-induced lung fibrosis

The pathological hallmarks of idiopathic pulmonary fibrosis include proliferating fibroblasts and myofibroblasts, as well as excessive collagen matrix deposition. In addition, both myofibroblast contraction and remodeling of the collagen-rich matrix contribute to the abnormal structure and function of the fibrotic lung. Little is known, however, about collagen-associated proteins that promote fibroblast and myofibroblast retention, as well as the proliferation of these cells on the extracellular matrix. In this study, we demonstrate that aortic carboxypeptidase-like protein (ACLP), a collagen-associated protein with a discoidin-like domain, is expressed at high levels in human fibrotic lung tissue and human fibroblasts, and that its expression increases markedly in the lungs of bleomycin-injured mice. Importantly, ACLP-deficient mice accumulated significantly fewer myofibroblasts and less collagen in the lung after bleomycin injury, as compared with wild-type controls, despite equivalent levels of bleomycin-induced inflammation. ACLP that is secreted by lung fibroblasts was retained on fibrillar collagen, and ACLP-deficient lung fibroblasts that were cultured on collagen exhibited changes in cell spreading, proliferation, and contraction of the collagen matrix. Finally, the addition of recombinant discoidin-like domain of ACLP to cultured ACLP-deficient lung fibroblasts restored cell spreading and increased the contraction of collagen gels. Therefore, both ACLP and its discoidin-like domain may be novel targets for anti-myofibroblast-based therapies for the treatment of pulmonary fibrosis.

Treatment of COPD: a matrix perspective

Fundamental physical properties, such as the intrinsic recoil of the lung, are governed by the extracellular matrix. The prototypical roles of the matrix proteins, collagen and elastin, in pulmonary fibrosis and emphysema have long been recognized, and much research effort has been devoted to understanding mechanisms of extracellular matrix synthesis and turnover in the lung. Yet, despite extensive knowledge of the biochemical properties of collagen and elastin, none of the present clinical strategies for treating COPD directly target the extracellular matrix. From a matrix perspective, therapeutic interventions that limit elastic fiber destruction and/or restore function to damaged alveolar units merit particular consideration as clinical strategies for treating the emphysema component of COPD. Effective treatment of the bronchiolar component of COPD requires a better understanding of the relationship between airway fibrosis and airflow obstruction. Translating basic knowledge of extracellular matrix biology into the clinical venue will be essential in the development of new approaches to COPD treatment.

Mice lacking neutrophil elastase are resistant to bleomycin-induced pulmonary fibrosis

Neutrophil elastase is a serine protease stored in the azurophilic granules of leukocytes. It has been implicated in the pathology of several lung diseases and is generally presumed to contribute to the tissue destruction and extracellular matrix damage associated with these conditions. To delineate the role of neutrophil elastase in pulmonary inflammation and fibrosis, neutrophil elastase-null mice were intratracheally instilled with bleomycin. In neutrophil elastase-null mice, biochemical and morphological characteristics of pulmonary fibrosis were attenuated for at least 60 days after bleomycin administration despite a typical response to bleomycin as evidenced by assessment of indices of DNA and cell damage. Neutrophil burden of bleomycin-treated wild-type and neutrophil elastase-null mice was comparable, and marked neutrophilic alveolitis was manifest in bleomycin-treated neutrophil elastase-null mice. An absence of immunostaining for active transforming growth factor (TGF)-beta in lung tissue from bleomycin-treated neutrophil elastase-null mice suggested a defect in TGF-beta activation, which was confirmed by biochemical assessment of TGF-beta levels in bronchoalveolar lavage fluid and lung tissue. These data point to novel and unexpected fibrogenic consequences of neutrophil elastase activity in the inflamed lung.

Attenuation of bleomycin induced pulmonary fibrosis in mice using the heme oxygenase inhibitor Zn-deuteroporphyrin IX-2,4-bisethylene glycol

BACKGROUND

Pulmonary fibrosis is associated with a poor prognosis. The pathogenesis of fibrotic lung disorders remains unclear, but the extent of tissue damage due to the persistent presence of oxidants or proteases is believed to be important. The heme degrading enzyme heme oxygenase (HO) has been found to be expressed in experimental fibrosis, and generation of free iron and carbon monoxide (CO) by HO has been implicated in oxidant induced lung damage. A study was undertaken to examine the effects of the HO inhibitor Zn-deuteroporphyrin-IX-2,4-bisethylene glycol (Zndtp) on the development of pulmonary fibrosis in the bleomycin model of lung injury and repair.

METHODS

Zndtp (10 micro mol/kg) was administered subcutaneously twice daily to mice 1 week following the intratracheal instillation of 0.025 U bleomycin. Animals were killed 10 or 21 days after bleomycin instillation and indices of lung damage and fibrosis were evaluated.

RESULTS

Bleomycin treatment induced pulmonary cytotoxicity, increased levels of active transforming growth factor beta (TGF-beta), enhanced lung collagen accumulation, and decreased glutathione content. Zndtp administration significantly attenuated these indices.

CONCLUSIONS

Administration of Zndtp in the bleomycin model resulted in appreciable alveolar cytoprotection and amelioration of pulmonary fibrosis. This molecule and its analogues may warrant further consideration in the treatment of acute lung injury and fibrotic lung disorders.

The bone marrow leaves its scar: new concepts in pulmonary fibrosis

Excess collagen deposition occurs in pulmonary fibrosis. A new study suggests that collagen overproduction may originate from cells derived from bone marrow precursors rather than parenchymal lung fibroblasts.

Matrilysin expression and function in airway epithelium

We report that matrilysin, a matrix metalloproteinase, is constitutively expressed in the epithelium of peribronchial glands and conducting airways in normal lung. Matrilysin expression was increased in airway epithelial cells and was induced in alveolar type II cells in cystic fibrosis. Other metalloproteinases (collagenase-1, stromelysin-1, and 92-kD gelatinase) were not produced by normal or injured lung epithelium. These observations suggest that matrilysin functions in injury-mediated responses of the lung. Indeed, matrilysin expression was increased in migrating airway epithelial cells in wounded human and mouse trachea. In human tissue, epithelial migration was reduced by > 80% by a hydroxamate inhibitor, and in mouse tissue, reepithelialization in trachea from matrilysin-null mice was essentially blocked. In vivo observations and cell culture studies demonstrated that matrilysin was secreted lumenally by lung epithelium, but upon activation or while migrating over wounds, some matrilysin was released basally. The constitutive production of matrilysin in conducting airways, its upregulation after injury, its induction by alveolar epithelium, and its release into both lumenal and matrix compartments suggest that this metalloproteinase serves multiple functions in intact and injured lung, one of which is to facilitate reepithelialization.

Regulation of lung fibroblast tropoelastin expression by alveolar epithelial cells

Epithelial-mesenchymal interactions are of critical importance during tissue morphogenesis and repair. Although the cellular and molecular aspects of many of these interactions are beginning to be understood, the ability of epithelial cells to regulate fibroblast interstitial matrix production has not been extensively studied. We report here that cultured alveolar epithelial cells are capable of modulating the expression of tropoelastin, the soluble precursor of the interstitial lung matrix component elastin, by lung fibroblasts. Phorbol ester-stimulated alveolar epithelial cells secrete a soluble factor that causes a time- and dose-dependent repression of lung fibroblast tropoelastin mRNA expression. This alveolar epithelial cell-mediated repressive activity is specific for tropoelastin, is effective on lung fibroblasts from multiple stages of development, and acts at the level of transcription. Partial characterization of the repressive activity indicates it is an acid-stable, pepsin-labile protein. Gel fractionation of alveolar epithelial cell conditioned medium revealed two peaks of activity with relative molecular masses of approximately 25 and 50 kDa. These data support a role for epithelial cells in the regulation of fibroblast interstitial matrix production.

Adrenal hormone regulation of fibronectin synthesis by type II pulmonary epithelial cells

Previous work suggested an association between changes in the alveolar extracellular matrix and epithelial cell growth in lungs of adrenalectomized rats in vivo. Other studies demonstrated that adrenal hormones modulate extracellular matrix synthesis by type II pulmonary epithelial cells in vitro. Adrenal hormone regulation of type II cell fibronectin synthesis was thus examined. Fibronectin synthesis was quantitated by immunoprecipitation of the metabolically labeled molecule from cells, extracellular matrix, and culture medium. On day 1 of primary culture, synthesis of matrix fibronectin by type II cells isolated from the lungs of adrenalectomized animals was more than twice that by cells isolated from control rats. Adrenalectomy elevated steady-state fibronectin mRNA levels in primary isolates of type II cells cultured for 1 or 3 days. These results suggest that altered fibronectin synthesis and deposition into the extracellular matrix accompany changes in type II cell phenotype that occur after adrenalectomy.

Mechanisms of hepatocyte growth factor stimulation of keratinocyte metalloproteinase production

Matrix metalloproteinases participate in normal physiologic processes; however, their overproduction has been associated with connective tissue destruction in a variety of pathological states. Migrating basal keratinocytes transiently express collagenase-1 during normal cutaneous reepithelialization. However, the overexpression of both collagenase-1 and stromelysin-1 has been associated with the pathogenesis of chronic nonhealing ulcers. Aberrant expression of metalloproteinases in inflammation is mediated, at least in part, by soluble factors. Since hepatocyte growth factor/scatter factor (HGF/SF) has been reported to promote keratinocyte migration and proliferation, key events in wound repair, and since HGF/SF is produced by dermal fibroblasts and its c-Met receptor is expressed by basal keratinocytes in wounded skin, we have studied the effects of HGF/SF upon keratinocyte metalloproteinase expression. We have found that HGF/SF can stimulate keratinocyte collagenase-1 and stromelysin-1 production in a dose-dependent and matrix-dependent manner. Expression of 92-kDa gelatinase was not affected by HGF/SF. We determined that HGF/SF regulation of collagenase-1 expression is transcriptionally mediated and requires tyrosine kinase and protein kinase C activaties. HGF/NK1, a naturally occurring, truncated form of HGF/SF, also stimulates collagenase-1 production, but much less efficiently than does the parent molecule. However, HGF/NK2, another HGF/SF splice variant, as well as heparin, potently inhibit HGF/SF-induced collagenase-1 synthesis. These results indicate that HGF/SF and its naturally occurring splice variants have diverse biological effects on keratinocytes and suggest an additional mechanism whereby HGF/SF may regulate keratinocyte function during wound repair.

Synthesis of fibronectin and laminin by type II pulmonary epithelial cells

Previous investigations demonstrated that type II pulmonary epithelial cells regulate extracellular matrix deposition as a function of time in primary culture. In those studies, the matrix fraction was analyzed as a whole. The present work focused on two components of the type II cell matrix, fibronectin and laminin. These glycoproteins have differing effects on differentiation of type II cells in primary culture. Fibronectin synthesis was quantitated between day 1 and day 6 in the cells, matrix, and medium; laminin synthesis was quantitated only in the cells. Although total fibronectin synthesis was regulated as a function of time in culture, reaching its greatest value on day 2, the average proportion of newly synthesized fibronectin in the cells (35%), medium (50%), and matrix (15%) remained constant over a 6-day interval. Between day 2 and day 6, the relative abundance of fibronectin messenger RNA increased 6.5-fold. Rates of cellular laminin synthesis did not vary with time in culture. These results support a role for differential regulation of fibronectin and laminin synthesis to determine the composition of the type II cell extracellular matrix.

Extracellular matrix biology in the lung

The lung and other organs are comprised of both cellular and extracellular compartments. Interaction of these components modulates physiological function at the organ, cellular, and subcellular levels. Extracellular components in the gas-exchange region of the lung include both noncellular interstitium and basement membranes. Connective tissue elements of the interstitium in part determine ventilatory function by contributions to tissue compliance and to resistance of the diffusion barrier. The basement membrane underlies cells of both the alveolar epithelium and the capillary endothelium; basement membrane components exert biological effects on adjacent cells through receptor-mediated interactions. This review emphasizes current knowledge concerning the composition and biological activity of extracellular matrix in the alveolar region of the lung. Matrix synthesis and turnover are also considered. Directions for future research are suggested in the context of current knowledge of the lung and other model systems.

Composition of extracellular matrix of type II pulmonary epithelial cells in primary culture

Type II pulmonary epithelial cells in primary culture synthesize and deposit an extracellular matrix which has reciprocal biological effects on cellular differentiation. The present work establishes conditions for metabolic labeling of matrix constituents and for separation of cells from the associated matrix; it also defines matrix composition, which does not appear to change qualitatively between days 2 and 6 of primary culture. Type II cells synthesize and deposit a spectrum of radiolabeled components on the culture surface. These include fibronectin, laminin, type IV collagen, and plasminogen activator inhibitor-1, along with additional unidentified proteins. Few radiolabeled proteins in medium conditioned by type II cells bind nonspecifically to the culture surface in the absence of cells. Fibroblasts and macrophages, which may contaminate the primary cultures, do not appear to contribute substantially to the type II cell matrix. These results demonstrate that type II cells synthesize and deposit a complex multicomponent extracellular matrix. The work provides a basis for further investigations of bidirectional interactions between type II cells and the extracellular matrix.

Turnover of fibronectin and laminin by alveolar epithelial cells

Type II pulmonary epithelial cells in primary culture synthesize and assemble a multicomponent extracellular matrix which exhibits biological activity in vitro. Simultaneously, the pneumocytes degrade components of the underlying matrix, such that matrix composition may be determined by the balance of synthesis and turnover. The present work defines turnover of the specific matrix glycoproteins, fibronectin and laminin, both in the type II cell and in its extracellular matrix. Pulse-chase experiments demonstrate that both fibronectin and laminin, identified by immunoprecipitation, turn over rapidly in the cell and extracellular matrix compartments, with half-lives < 10 h. In the cell compartment, initial rates of laminin turnover are more rapid than those of fibronectin on culture day 2, but these rates are similar on day 6. Matrix fibronectin also turns over rapidly, with similar rates on day 2 and day 6. During the chase interval, small but increasing amounts of immunoprecipitable fibronectin are detected in the medium, suggesting that a portion of the glycoprotein may be released to the extracellular compartment, rather than degraded. Alternatively, release of immunoreactive glycoprotein may involve ongoing processing and secretion of residual radiolabeled fibronectin by the cells. The results suggest that matrix composition may be determined by turnover, as well as synthesis, of its components.

Adrenal hormone regulation of extracellular matrix synthesis by type II cells

Previous studies suggested an association between changes in extracellular matrix (ECM) and pulmonary epithelial cell growth and differentiation in lungs of adrenalectomized rats. The role of adrenal hormones to modulate synthesis of cell and ECM proteins by type II epithelial cells was thus investigated. In cells isolated from lungs of adrenalectomized animals, synthesis of ECM proteins was stimulated to a greater extent than was synthesis of cell proteins. This resulted in increased relative synthesis of matrix components. Conversely, dexamethasone (200 nM) treatment in vitro reduced the effects of adrenalectomy and, in control cells, decreased relative ECM synthesis. The magnitude of these effects depended on time in culture and serum conditions. For example, culture of normal cells in serum-free medium mimicked the effects of adrenalectomy, whereas there were no effects of dexamethasone in the presence of serum. These results indicate a role for adrenal steroid hormones to modulate ECM metabolism by type II pulmonary epithelial cells and suggest that consequent effects on ECM biological activity may modify epithelial cell differentiation or growth.

Turnover of extracellular matrix by type II pulmonary epithelial cells

Rat type II pulmonary epithelial cells synthesize and assemble a multicomponent extracellular matrix (ECM) which can modulate cellular differentiation in primary culture. This study defines turnover of the type II cell matrix. Turnover kinetics were analyzed in two types of pulse-chase protocols based on loss of radioactive ECM components. To estimate turnover of previously synthesized ECM, type II cells were plated on extracted matrix that was radiolabeled 2, 3, or 6 days; alternatively, ECM was radiolabeled in pulse-chase experiments to measure turnover by the same cells that synthesized the matrix. Rapid initial rates of ECM turnover were evident in both cases. While overall matrix stability appeared to change with culture time, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed a similar spectrum of proteins in the ECM over the course of kinetic studies. The results reveal rapid turnover of ECM by type II cells and suggest that matrix stability may be regulated. These observations provide a basis for future investigations of the physiological significance of turnover of individual ECM components by the alveolar epithelium.

Extracellular matrix synthesis and turnover by type II pulmonary epithelial cells

Both type I and type II pulmonary epithelial cells contact the extracellular matrix (ECM). Type II cell-ECM interactions are bidirectional; they involve matrix-mediated modulation of type II cell differentiation, as well as cellular synthesis and deposition of ECM components. The present experiments examine the kinetics of accumulation of newly synthesized proteins in cell and matrix fractions from primary cultures of type II pneumocytes. Cycloheximide-sensitive incorporation of [3H]leucine into total protein of both the cell and ECM fractions was linear for 24-30 h, when steady-state labeling was reached and maintained to at least day 8. Over this interval, the cells enlarged but did not divide. Newly synthesized proteins recovered in the matrix fraction averaged 1-2% of those in the cells. Relative rates of radiolabeling of matrix proteins peaked at culture day 2 and increased in the absence of serum. In short-pulse studies, initial rates of protein synthesis were equal on culture days 1 and 3; this suggested that the steady-state labeling kinetics above reflected protein turnover. This was supported by rapid loss of radioactivity from the ECM after fresh type II cells were seeded on a prelabeled, cell-free matrix surface. Fresh or conditioned Dulbecco's modified Eagle's medium containing 10% fetal calf serum had little effect on matrix stability. These results demonstrate regulated deposition and turnover of a complex ECM by type II cells and provide a basis for further investigations of factors that control these processes.