Lung transplantation: candidate selection and timing of transplant.

PURPOSE OF REVIEW: Over the past two decades, lung transplant has become the mainstay of treatment for several end-stage lung diseases. As the field continues to evolve, the criteria for referral and listing have also changed. The last update to these guidelines was in 2014 and several studies since then have changed how patients are transplanted. Our article aims to briefly discuss these updates in lung transplantation. RECENT FINDINGS: This article discusses the importance of early referral of patients for lung transplantation and the concept of the 'transplant window'. We review the referral and listing criteria for some common pulmonary diseases and also cite the updated literature surrounding the absolute and relative contraindications keeping in mind that they are a constantly moving target. Frailty and psychosocial barriers are difficult to assess with the current assessment tools but continue to impact posttransplant outcomes. Finally, we discuss the limited data on transplantation in acute respiratory distress syndrome (ARDS) due to COVID19 as well as extracorporeal membrane oxygenation bridge to transplantation. SUMMARY: The findings discussed in this article will strongly impact, if not already, how we select candidates for lung transplantation. It also addresses some aspects of lung transplant such as frailty and ARDS, which need better assessment tools and clinical data.

Transmission of Eastern Equine Encephalitis Virus From an Organ Donor to 3 Transplant Recipients.

BACKGROUND: In fall 2017, 3 solid organ transplant (SOT) recipients from a common donor developed encephalitis within 1 week of transplantation, prompting suspicion of transplant-transmitted infection. Eastern equine encephalitis virus (EEEV) infection was identified during testing of endomyocardial tissue from the heart recipient. METHODS: We reviewed medical records of the organ donor and transplant recipients and tested serum, whole blood, cerebrospinal fluid, and tissue from the donor and recipients for evidence of EEEV infection by multiple assays. We investigated blood transfusion as a possible source of organ donor infection by testing remaining components and serum specimens from blood donors. We reviewed data from the pretransplant organ donor evaluation and local EEEV surveillance. RESULTS: We found laboratory evidence of recent EEEV infection in all organ recipients and the common donor. Serum collected from the organ donor upon hospital admission tested negative, but subsequent samples obtained prior to organ recovery were positive for EEEV RNA. There was no evidence of EEEV infection among donors of the 8 blood products transfused into the organ donor or in products derived from these donations. Veterinary and mosquito surveillance showed recent EEEV activity in counties nearby the organ donor's county of residence. Neuroinvasive EEEV infection directly contributed to the death of 1 organ recipient and likely contributed to death in another. CONCLUSIONS: Our investigation demonstrated EEEV transmission through SOT. Mosquito-borne transmission of EEEV to the organ donor was the likely source of infection. Clinicians should be aware of EEEV as a cause of transplant-associated encephalitis.

Nuclear Thioredoxin-1 Overexpression Attenuates Alcohol-Mediated Nrf2 Signaling and Lung Fibrosis.

BACKGROUND: Alcohol abuse, which impairs antioxidant defenses and promotes acute lung injury, increases Nrf2 nuclear translocation but nevertheless inhibits its activation of the antioxidant response element (ARE). Thioredoxin-1 (Trx1) is required for optimal Nrf2 binding and activation of the ARE, and we hypothesized that its inhibition contributes to impaired Nrf2-ARE signaling in the alcoholic lung. METHODS: Lung tissue and primary lung fibroblasts (PLFs) were isolated from C57/BL6 wild-type (WT) and transgenic mice overexpressing the human Trx1 gene with a nuclear localizing sequence (NLS-Tg); some mice consumed alcohol in water prior to lung tissue and PLF isolation; in some mice, acute lung injury was induced with intratracheal bleomycin. In other experiments, PLFs were isolated from WT and NLS-Tg mice and then exposed to alcohol. Finally, PLF isolated from WT mice were transfected with Trx1 expression vector containing either a cytosolic localized sequence (NES) or a nuclear localized sequence (NLS) prior to alcohol exposure. RESULTS: Alcohol treatment in vivo or in vitro decreased Trx1 expression, and bleomycin-treated alcohol-fed mice had fibrotic disrepair in their lungs. In parallel, whereas alcohol exposure in vitro increased TGFß1 expression and decreased Nrf2-ARE activity in PLF from WT mice, these effects were not observed in PLF from NLS-Tg mice. Finally, selective overexpression of Trx1 in the nucleus but not in the cytosol preserved Nrf2-ARE activity during alcohol exposure. CONCLUSIONS: Although alcohol-induced redox stress actually promotes Nrf2 nuclear translocation, the coincident suppression of Trx1 impairs Nrf2-ARE activity within the nuclear compartment. Nuclear overexpression of Trx1 restored Nrf2-ARE activity and attenuated alcohol-induced TGFß1 expression and alcohol-induced exaggerate response to bleomycin-induced acute lung injury.

TGFß1 mediates alcohol-induced Nrf2 suppression in lung fibroblasts.

BACKGROUND: Chronic alcohol ingestion induces the expression of transforming growth factor beta-1(TGFß1), inhibits nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated activation of the antioxidant response element (ARE), depletes alveolar glutathione pools, and potentiates acute lung injury. In this study, we examined the mechanistic relationship between TGFß1 and Nrf2-ARE signaling in the experimental alcoholic lung. METHODS: Wild-type mice were treated ± alcohol in drinking water for 8 weeks and their lungs were assessed for Nrf2 expression. In parallel, mouse lung fibroblasts were cultured ± alcohol and treated ± sulforaphane (SFP; an activator of Nrf2), ±TGFß1, ±TGFß1 neutralizing antibody, and/or ±activin receptor-like kinase 5 inhibitors (to block TGß1 receptor signaling) and then analyzed for the expression of Nrf2, Kelch-like ECH-associated protein 1 (Keap1) and TGFß1, Nrf2-ARE activity, and the expression of the Nrf2-ARE-dependent antioxidants glutathione s-transferase theta 2 (GSTT2) and glutamate-cysteine ligase catalytic subunit (GCLC). Finally, silencing RNA (siRNA) of Nrf2 was then performed prior to alcohol exposure and subsequent analysis of TGFß1 expression. RESULTS: Alcohol treatment in vivo or in vitro decreased Nrf2 expression in murine whole lung and lung fibroblasts, respectively. In parallel, alcohol exposure in vitro decreased Keap1 gene and protein expression in lung fibroblasts. Furthermore, alcohol exposure increased TGFß1 expression but decreased Nrf2-ARE activity and expression of the ARE-dependent genes for GSTT2 and GCLC. These effects of alcohol were prevented by treatment with SFP; in contrast, Nrf2 SiRNA expression exacerbated alcohol-induced TGFß1 expression. Finally, TGFß1 treatment directly suppressed Nrf2-ARE activity whereas blocking TGFß1 signaling attenuated alcohol-induced suppression of Nrf2-ARE activity. CONCLUSIONS: Alcohol-induced oxidative stress is mediated by TGFß1, which suppresses Nrf2-ARE-dependent expression of antioxidant defenses and creates a vicious cycle that feeds back to further increase TGFß1 expression. These effects of alcohol can be mitigated by activation of Nrf2, suggesting a potential therapy in individuals at risk for lung injury due to alcohol abuse.

Study on the relationship between selenium and cadmium in diseased human lungs.

Cadmium (Cd) is a toxic environmental metal that interacts with selenium (Se) and contributes to many lung diseases. Humans have widespread exposures to Cd through diet and cigarette smoking, and studies in rodent models show that Se can protect against Cd toxicities. We sought to identify whether an antagonistic relationship existed between Se and Cd burdens and determine whether this relationship may associate with metabolic variation within human lungs. We performed metabolomics of 31 human lungs, including 25 with end-stage lung disease due to idiopathic pulmonary fibrosis, cystic fibrosis, chronic obstructive lung disease (COPD)/emphysema and other causes, and 6 non-diseased lungs. Results showed pathway associations with Cd including amino acid, lipid and energy-related pathways. Metabolic pathways varying with Se had considerable overlap with these pathways. Hierarchical cluster analysis (HCA) of individuals according to metabolites associated with Cd showed partial separation of disease types, with COPD/emphysema in the cluster with highest Cd, and non-diseased lungs in the cluster with the lowest Cd. When compared to HCA of metabolites associated with Se, the results showed that the cluster containing COPD/emphysema had the lowest Se, and the non-diseased lungs had the highest Se. A greater number of pathway associations occurred for Cd to Se ratio than either Cd or Se alone, indicating that metabolic patterns were more dependent on Cd to Se ratio than on either alone. Network analysis of interactions of Cd and Se showed network centrality was associated with pathways linked to polyunsaturated fatty acids involved in inflammatory signaling. Overall, the data show that metabolic pathway responses in human lung vary with Cd and Se in a pattern suggesting that Se is antagonistic to Cd toxicity in humans.

Frailty in Lung Transplantation: Candidate Assessment and Optimization.

The concept of frailty has gained considerable interest in clinical solid-organ transplantation over the past decade. Frailty as a phenotypic construct to describe a patient's risk from biologic stresses has an impact on posttransplant survival. There is keen interest in characterizing frailty in lung transplantation, both to determine which patients are suitable candidates for listing and also to prepare for their care in the aftermath of lung transplantation. Here, we review the current status of research on frailty in lung transplant candidates and recipients. This review will highlight areas of uncertainty for frailty in clinical lung transplantation that are likely to impact the state-of-the-art in the field for the next decade.

A scalable workflow to characterize the human exposome.

Complementing the genome with an understanding of the human exposome is an important challenge for contemporary science and technology. Tens of thousands of chemicals are used in commerce, yet cost for targeted environmental chemical analysis limits surveillance to a few hundred known hazards. To overcome limitations which prevent scaling to thousands of chemicals, we develop a single-step express liquid extraction and gas chromatography high-resolution mass spectrometry analysis to operationalize the human exposome. We show that the workflow supports quantification of environmental chemicals in human plasma (200 µL) and tissue (≤100 mg) samples. The method also provides high resolution, sensitivity and selectivity for exposome epidemiology of mass spectral features without a priori knowledge of chemical identity. The simplicity of the method can facilitate harmonization of environmental biomonitoring between laboratories and enable population level human exposome research with limited sample volume.

Low-dose cadmium potentiates lung inflammatory response to 2009 pandemic H1N1 influenza virus in mice.

Cadmium (Cd) is a toxic, pro-inflammatory metal ubiquitous in the diet that accumulates in body organs due to inefficient elimination. Responses to influenza virus infection are variable, particularly severity of pneumonia. We used a murine model of chronic low-dose oral exposure to Cd to test if increased lung tissue Cd worsened inflammation in response to sub-lethal H1N1 infection. The results show that Cd-treated mice had increased lung tissue inflammatory cells, including neutrophils, monocytes, T lymphocytes and dendritic cells, following H1N1 infection. Lung genetic responses to infection (increasing TNF-α, interferon and complement, and decreasing myogenesis) were also exacerbated. To reveal the organization of a network structure, pinpointing molecules critical to Cd-altered lung function, global correlations were made for immune cell counts, leading edge gene transcripts and metabolites. This revealed that Cd increased correlation of myeloid immune cells with pro-inflammatory genes, particularly interferon-γ and metabolites. Together, the results show that Cd burden in mice increased inflammation in response to sub-lethal H1N1 challenge, which was coordinated by genetic and metabolic responses, and could provide new targets for intervention against lethal inflammatory pathology of clinical H1N1 infection.

Selenium supplementation prevents metabolic and transcriptomic responses to cadmium in mouse lung.

BACKGROUND: The protective effect of selenium (Se) on cadmium (Cd) toxicity is well documented, but underlying mechanisms are unclear. METHODS: Male mice fed standard diet were given Cd (CdCl2, 18 µmol/L) in drinking water with or without Se (Na2SeO4, 20 µmol/L) for 16 weeks. Lungs were analyzed for Cd concentration, transcriptomics and metabolomics. Data were analyzed with biostatistics, bioinformatics, pathway enrichment analysis, and combined transcriptome-metabolome-wide association study. RESULTS: Mice treated with Cd had higher lung Cd content (1.7 ±â€¯0.4 pmol/mg protein) than control mice (0.8 ±â€¯0.3 pmol/mg protein) or mice treated with Cd and Se (0.4 ±â€¯0.1 pmol/mg protein). Gene set enrichment analysis of transcriptomics data showed that Se prevented Cd effects on inflammatory and myogenesis genes and diminished Cd effects on several other pathways. Similarly, Se prevented Cd-disrupted metabolic pathways in amino acid metabolism and urea cycle. Integrated transcriptome and metabolome network analysis showed that Cd treatment had a network structure with fewer gene-metabolite clusters compared to control. Centrality measurements showed that Se counteracted changes in a group of Cd-responsive genes including Zdhhc11, (protein-cysteine S-palmitoyltransferase), Ighg1 (immunoglobulin heavy constant gamma-1) and associated changes in metabolite concentrations. CONCLUSION: Co-administration of Se with Cd prevented Cd increase in lung and prevented Cd-associated pathway and network responses of the transcriptome and metabolome. Se protection against Cd toxicity in lung involves complex systems responses. GENERAL SIGNIFICANCE: Environmental Cd stimulates proinflammatory and profibrotic signaling. The present results indicate that dietary or supplemental Se could be useful to mitigate Cd toxicity.

Two common human CLDN5 alleles encode different open reading frames but produce one protein isoform.

Claudins provide tight junction barrier selectivity. The human CLDN5 gene contains a high-frequency single-nucleotide polymorphism (rs885985), where the G allele codes for glutamine (Q) and the A allele codes for an amber stop codon. Thus, these different CLDN5 alleles define nested open reading frames (ORFs) encoding claudin-5 proteins that are 303 or 218 amino acids in length. Interestingly, human claudin-16 and claudin-23 also have long ORFs. The long form of claudin-5 contrasts with the majority of claudin-5 proteins in the National Center for Biotechnology Information protein database, which are less than 220 amino acids in length. Screening of genotyped human lung tissue by immunoblot revealed only the 218 amino acid form of claudin-5 protein; the long-form claudin-5 protein was not detected. Moreover, when forcibly expressed in transfected cells, the long form of human claudin-5 was retained in intracellular compartments and did not localize to the plasma membrane, in contrast to the 218 amino acid form, which localized to intercellular junctions. This suggests that the 303 amino acid claudin-5 protein is rarely expressed, and, if so, is predicted to adversely affect cell function. Potential roles for upstream ORFs in regulating claudin-5 expression are also discussed.

Low-dose oral cadmium increases airway reactivity and lung neuronal gene expression in mice.

Inhalation of cadmium (Cd) is associated with lung diseases, but less is known concerning pulmonary effects of Cd found in the diet. Cd has a decades-long half-life in humans and significant bioaccumulation occurs with chronic dietary intake. We exposed mice to low-dose CdCl2 (10 mg/L in drinking water) for 20 weeks, which increased lung Cd to a level similar to that of nonoccupationally exposed adult humans. Cd-treated mice had increased airway hyperresponsiveness to methacholine challenge, and gene expression array showed that Cd altered the abundance of 443 mRNA transcripts in mouse lung. In contrast to higher doses, low-dose Cd did not elicit increased metallothionein transcripts in lung. To identify pathways most affected by Cd, gene set enrichment of transcripts was analyzed. Results showed that major inducible targets of low-dose Cd were neuronal receptors represented by enriched olfactory, glutamatergic, cholinergic, and serotonergic gene sets. Olfactory receptors regulate chemosensory function and airway hypersensitivity, and these gene sets were the most enriched. Targeted metabolomics analysis showed that Cd treatment also increased metabolites in pathways of glutamatergic (glutamate), serotonergic (tryptophan), cholinergic (choline), and catecholaminergic (tyrosine) receptors in the lung tissue. Protein abundance measurements showed that the glutamate receptor GRIN2A was increased in mouse lung tissue. Together, these results show that in mice, oral low-dose Cd increased lung Cd to levels comparable to humans, increased airway hyperresponsiveness and disrupted neuronal pathways regulating bronchial tone. Therefore, dietary Cd may promote or worsen airway hyperresponsiveness in multiple lung diseases including asthma.

Aging promotes pro-fibrotic matrix production and increases fibrocyte recruitment during acute lung injury.

Fibrotic lung diseases increase with age. Previously we determined that senescence increases tissue expression of fibronectin EDA (Fn-EDA) and decreases fibroblast expression of Thy-1, and that fibrocytes contribute to fibrosis following bleomycin-induced lung injury in mice. In this study we hypothesized that fibroblasts lacking Thy-1 expression produce an extracellular matrix that promotes fibrocyte retention and myofibroblast transdifferentiation, thereby promoting fibrogenesis. Young and old mice were treated with bleomycin intratracheally; fibrocytes in the bone marrow, blood, and lungs were quantified, and lung fibroblast Thy-1 expression assessed. Bone marrow-derived fibrocytes were cultured on matrices derived from Thy-1(+) or Thy-1(-) fibroblasts ± the pro-fibrotic cytokine TGFß1. Older mice had more fibrocytes in their bone marrows at baseline and more fibrocytes in their lungs following bleomycin treatment. In parallel, lung fibroblasts in older mice had lower expression of Thy-1 at baseline that increased transiently 7 days after bleomycin treatment but then rapidly waned such that 14 days after bleomycin treatment Thy-1 expression was again markedly lower. Fibrocytes cultured on matrices derived from Thy-1(-) fibroblasts + TGFß1 had increased gene expression for collagen type 1, fibronectin, Fn-EDA, and α-smooth muscle actin. In parallel, whereas the matrices derived from Thy-1(-) fibroblasts stimulated phosphorylation of Akt in cultured fibrocytes, the matrices derived from Thy-1(+) fibroblasts induced apoptosis. These findings suggest that senescence increases fibrocyte recruitment to the lung following injury and that loss of Thy-1 expression by lung fibroblasts promotes fibrocyte retention and myofibroblast trans-differentiation that renders the "aging lung" susceptible to fibrosis.

Predisposition for disrepair in the aged lung.

INTRODUCTION: Idiopathic pulmonary fibrosis (IPF) is a devastating progressive lung disease with an average survival of only 3 to 5 years. The mechanisms underlying the initiation and progression of IPF are poorly understood, and treatments available have only modest effect on disease progression. Interestingly, the incidence of IPF is approximately 60 times more common in individuals aged 75 years and older, but the mechanism by which aging promotes fibrosis is unclear. The authors hypothesized that aged lungs have a profibrotic phenotype that render it susceptible to disrepair after injury. METHODS: Young and old mice were treated with bleomycin to examine disrepair in the aged lung. In addition, uninjured young and old mouse lungs were analyzed for transforming growth factor-beta 1 (TGF-ß1) production, extracellular matrix composition and lung fibroblast phenotype. Lung fibroblasts were treated with a DNA methyltransferase inhibitor to examine the potential epigenetic mechanisms involved in age-associated phenotypic alterations. RESULTS: The lungs of old mice showed worse fibrosis after bleomycin-induced injury compared with the lungs from young mice. At baseline, aged lungs expressed a profibrotic phenotype characterized by increased mRNA expression for fibronectin extracellular domain A (Fn-EDA) and the matrix metalloproteinases (MMPs) MMP-2 and MMP-9. Old lungs also expressed higher levels of TGF-ß receptor 1 and TGF-ß1 mRNA, protein and activity as determined by increased Smad3 expression, protein phosphorylation and DNA binding. Lung fibroblasts harvested from aged lungs showed reduced expression of the surface molecule Thy-1, a finding also implicated in lung fibrosis; the latter did not seem related to Thy-1 gene methylation. CONCLUSION: Altogether, aged lungs manifest a profibrotic phenotype characterized by enhanced fibronectin extracellular domain A and MMP expression and increased TGF-ß1 expression and signaling and are populated by Thy-1-negative fibroblasts, all implicated in the pathogenesis of lung fibrosis.

Regulatory T cells in lung transplantation--an emerging concept.

Lung transplantation represents an option for patients with a variety of end-stage lung diseases. While surgical advances have led to improvements in short-term survival, long-term survival is limited by chronic rejection termed bronchiolitis obliterans syndrome (BOS). A growing body of work is devoted to determining why some patients develop BOS. One avenue of interest that has emerged recently is the role that regulatory T cells (Tregs) may have in protection from BOS. In this review, we will discuss the evidence that Tregs are relevant to outcomes following transplant. We will discuss the relevant animal models, in vitro assays, and human observational studies that support a role for Tregs. We will also explore the interplay between injurious T cells such as Th17 cells and Tregs as well as the effect that additional cell types and chemokines have on the balance between inflammation and regulation. Finally, we will review emerging therapies which may harness the ability of Tregs to lessen the effects of BOS.