Surfactant protein and CC-10 expression in acute lung injury and in response to keratinocyte growth factor

Club Cell Secreted Protein CC16: Potential Applications in Prognosis and Therapy for Pulmonary Diseases

Club cell secretory protein (CC16) is encoded by the SCGB1A1 gene. It is also known as CC10, secretoglobin, or uteroglobin. CC16 is a 16 kDa homodimeric protein secreted primarily by the non-ciliated bronchial epithelial cells, which can be detected in the airways, circulation, sputum, nasal fluid, and urine. The biological activities of CC16 and its pathways have not been completely understood, but many studies suggest that CC16 has anti-inflammatory and anti-oxidative effects. The human CC16 gene is located on chromosome 11, p12-q13, where several regulatory genes of allergy and inflammation exist. Studies reveal that factors such as gender, age, obesity, renal function, diurnal variation, and exercise regulate CC16 levels in circulation. Current findings indicate CC16 not only may reflect the pathogenesis of pulmonary diseases, but also could serve as a potential biomarker in several lung diseases and a promising treatment for chronic obstructive pulmonary disease (COPD). In this review, we summarize our current understanding of CC16 in pulmonary diseases.

Measuring extracellular pH in a lung fibrosis model with acidoCEST MRI

PURPOSE

A feed-forward loop involving lactic acid production may potentially occur during the formation of idiopathic pulmonary fibrosis. To provide evidence for this feed-forward loop, we used acidoCEST MRI to measure the extracellular pH (pHe), while also measuring percent uptake of the contrast agent, lesion size, and the apparent diffusion coefficient (ADC).

PROCEDURES

We developed a respiration-gated version of acidoCEST MRI to improve the measurement of pHe and percent uptake in lesions. We also used T2-weighted MRI to measure lesion volumes and diffusion-weighted MRI to measure ADC.

RESULTS

The longitudinal changes in average pHe and % uptake of the contrast agent were inversely related to reduction in lung lesion volume. The average ADC did not change during the time frame of the study.

CONCLUSIONS

The increase in pHe during the reduction in lesion volume indicates a role for lactic acid in the proposed feed-forward loop of IPF.

Clara cell protein (CC16), a marker of lung epithelial injury, is decreased in plasma and pulmonary edema fluid from patients with acute lung injury

BACKGROUND

Acute lung injury (ALI) and ARDS are common clinical syndromes that are underdiagnosed. Clara cell secretory protein (CC16) is an antiinflammatory protein secreted by the Clara cells of the distal respiratory epithelium that has been proposed as a biomarker of lung epithelial injury. We tested the diagnostic and prognostic utility of CC16 in patients with non-trauma-related ALI/ARDS compared to a control group of patients with acute cardiogenic pulmonary edema (CPE).

METHODS

Plasma and pulmonary edema fluid samples were obtained from medical and surgical patients with ALI/ARDS or CPE requiring intubation for mechanical ventilation. The etiology of pulmonary edema was determined using consensus clinical criteria for ALI/ARDS and CPE and the edema fluid-to-plasma protein ratio. Plasma and edema fluid CC16 levels were measured by sandwich enzyme-linked immunosorbent assay. CC16 levels were log transformed for analysis, and comparisons were made by the Student t test or Chi(2) as appropriate.

RESULTS

Compared to patients with CPE (n = 9), patients with ALI/ARDS (n = 23) had lower median CC16 levels in plasma (22 ng/mL [interquartile range (IQR), 9 to 44 ng/mL] vs 55 ng/mL [IQR, 18 to 123 ng/mL], respectively; p = 0.053) and pulmonary edema fluid (1,950 ng/mL [IQR, 1,780 to 4,024 ng/mL] vs 4,835 ng/mL [IQR, 2,006 to 6,350 ng/mL], respectively; p = 0.044). Relative to total pulmonary edema fluid protein concentration, the median CC16 level was significantly lower in patients with ALI/ARDS (45 ng CC16/mg total protein [IQR, 4 to 64 ng CC16/mg total protein] vs 120 ng CC16/mg total protein [IQR, 87 to 257 ng CC16/mg total protein], respectively; p = 0.005). Neither plasma nor edema fluid CC16 levels predicted mortality, the number of days of unassisted ventilation, or ICU length of stay.

CONCLUSION

CC16 is a promising diagnostic biomarker for helping to discriminate ALI from CPE. Larger scale validation is warranted to better characterize the utility of CC16 in the diagnosis of this underrecognized syndrome.

Fibrogenesis of parenchymal organs

Fibrosis of parenchymal organs is caused by prolonged injury, deregulation of the normal processes of wound healing, and extensive deposition of extracellular matrix (ECM) proteins. The current review will focus on common features of fibrogenesis in parenchymal organs, and will briefly discuss common features and differences in the pathophysiology of fibrosis. Comparison of hepatic, renal, and pulmonary fibrosis has identified several common mechanisms. Common themes include a critical role for the cytokine transforming growth factor beta and the generation of reactive oxygen species. Activated myofibroblasts are the common cell type that produce the excessive fibrous scar and may originate from endogenous cells such as hepatic stellate cells or fibroblasts, from the bone marrow such as fibrocytes, or from the transition of epithelial cells to mesenchymal cells. These concepts open new prospects for multidisciplinary research and the development of new therapies for fibrosis.

Mechanisms of fibrogenesis

Fibrogenesis is a mechanism of wound healing and repair. However, prolonged injury causes deregulation of normal processes and results in extensive deposition of extracellular matrix (ECM) proteins and fibrosis. The current review will discuss similarities and differences of fibrogenesis in different organs and systems and focus on the origin of collagen producing cells. Although the relative contribution will vary in different tissues and different injuries, there are three general sources of fibrogenic cells: endogenous fibroblasts or fibroblast-like cells, epithelial to mesenchymal transition, and recruitment of fibrocytes from the bone marrow.

Keratinocyte growth factor therapy in murine oleic acid-induced acute lung injury

Alveolar type II (ATII) cell proliferation and differentiation are important mechanisms in repair following injury to the alveolar epithelium. KGF is a potent ATII cell mitogen, which has been demonstrated to be protective in a number of animal models of lung injury. We have assessed the effect of recombinant human KGF (rhKGF) and liposome-mediated KGF gene delivery in vivo and evaluated the potential of KGF as a therapy for acute lung injury in mice. rhKGF was administered intratracheally in male BALB/c mice to assess dose response and time course of proliferation. SP-B immunohistochemistry demonstrated significant increases in ATII cell numbers at all rhKGF doses compared with control animals and peaked 2 days following administration of 10 mg/kg rhKGF. Protein therapy in general is very expensive, and gene therapy has been suggested as a cheaper alternative for many protein replacement therapies. We evaluated the effect of topical and systemic liposome-mediated KGF-gene delivery on ATII cell proliferation. SP-B immunohistochemistry showed only modest increases in ATII cell numbers following gene delivery, and these approaches were therefore not believed to be capable of reaching therapeutic levels. The effect of rhKGF was evaluated in a murine model of OA-induced lung injury. This model was found to be associated with significant alveolar damage leading to severe impairment of gas exchange and lung compliance. Pretreatment with rhKGF 2 days before intravenous OA challenge resulted in significant improvements in PO2, PCO2, and lung compliance. This study suggests the feasibility of KGF as a therapy for acute lung injury.

Cyclophosphamide prevents systemic keratinocyte growth factor-induced up-regulation of surfactant protein A after allogeneic transplant in mice

We reported that systemic keratinocyte growth factor (KGF) given before bone marrow transplantation (BMT) prevents allogeneic T cell-dependent lung inflammation assessed on Day 7 post-BMT, but the antiinflammatory effects of KGF were impaired in mice injected with both T cells and conditioning regimen of cyclophosphamide (Cy). Intratracheal KGF is known to stimulate the expression of surfactant protein A (SP-A), an oxidant-sensitive T cell immunomodulator produced by alveolar type II cells. We hypothesized that systemic KGF up-regulates SP-A after allogeneic BMT, and the addition of Cy may interfere with the ability of KGF to enhance SP-A production. The subcutaneous administration of recombinant human KGF (5 mg/kg on Days -6, -5, and -4 pre-BMT) increased SP-A protein and mRNA in allogeneic T cell-recipient irradiated mice measured on Day 7 post-BMT. In contrast, the same KGF treatment in irradiated mice given T cells and Cy failed to up-regulate SP-A mRNA and protein expression. In mixed lymphocyte reaction experiments designed to simulate the in vivo model, the addition of human SP-A (5-50 microg) to alloactivated T cells suppressed the production of interleukin-2 in a dose-dependent fashion. We conclude that the systemic pre-BMT injection of KGF in recipients of allogeneic T cells up-regulates SP-A, which may contribute to the early antiinflammatory effects of KGF. The protective KGF-mediated SP-A production is abolished in mice given alloreactive T cells plus Cy.

Keratinocyte growth factor prevents ventilator-induced lung injury in an ex vivo rat model

Mechanical ventilation has been shown to produce lung injury characterized by noncardiogenic pulmonary edema. Keratinocyte growth factor (KGF) is a heparin-binding growth factor that causes alveolar type II pneumocyte hyperplasia. KGF pretreatment and the resultant pneumocyte hyperplasia reduce fluid flux in models of lung injury. We utilized the isolated perfused rat lung model to produce lung injury by varying tidal volume and the level of positive end-expiratory pressure during mechanical ventilation. Pretreatment with KGF attenuated ventilator-induced lung injury (VILI). This was demonstrated by lower wet-to-dry lung weight ratios and less lung water accumulation in the KGF group. Further, KGF prevented the decline in dynamic compliance and alveolar protein accumulation in VILI. KGF pretreatment reduced alveolar accumulation of intravascularly administered fluorescein isothiocyanate-labeled high-molecular-weight dextran. Thus, pretreatment with KFG attenuates injury in this ex vivo model of VILI via mechanisms that prevent increases in permeability.

Keratinocyte growth factor stimulates bronchial epithelial cell proliferation in vitro and in vivo

Airway epithelial cell (AEC) proliferation is crucial to the maintenance of an intact airway surface and the preservation of host defenses. The factors that regulate AEC proliferation are not known. Keratinocyte growth factor (KGF), also known as FGF-7, is a member of the fibroblast growth factor family and a known epithelial cell mitogen. We studied the influence of KGF on the growth of cultured human bronchial epithelial cells and on bronchial cells of rats treated with KGF in vivo. First, we demonstrated the mRNA for the KGF receptor (KGFR) in both normal human bronchial epithelial (NHBE) cells and BEAS-2B cells (a human bronchial epithelial cell line). KGF caused a dose-dependent increase in DNA synthesis, as assessed by thymidine incorporation, in both cell types, with a maximal twofold increase in NHBE cells after 50 ng/ml KGF (P < 0.001). KGF also induced a doubling in NHBE cell number at 10 ng/ml (P < 0.001). Finally, we determined the effect of intratracheal administration of KGF to rats on proliferation of AEC in vivo. Measuring bromodeoxyuridine (BrdU) incorporation in AEC nuclei, KGF increased BrdU labeling of rat AEC in both large and small airways by approximately threefold compared with PBS-treated controls (P < 0.001). Thus KGF induces proliferation of bronchial epithelial cells both in vitro and in vivo.

Partitioning lung and plasma proteins: circulating surfactant proteins as biomarkers of alveolocapillary permeability

1. The alveolocapillary membrane faces an extraordinary task in partitioning the plasma and lung hypophase proteins, with a surface area approximately 50-fold that of the body and only 0.1-0.2 micron thick. 2. Lung permeability is compromised under a variety of circumstances and the delineation between physiological and pathological changes in permeability is not always clear. Although the tight junctions of the epithelium, rather than the endothelium, are regarded as the major barrier to fluid and protein flux, it is becoming apparent that the permeability of both are dynamically regulated. 3. Whereas increased permeability and the flux of plasma proteins into the alveolar compartment has dire consequences, fortuitously the flux of surfactant proteins from the airspaces into the circulation may provide a sensitive means of non-invasively monitoring the lung, with important implications for treatment modalities. 4. Surfactant proteins are unique in that they are present in the alveolar hypophase in high concentrations. They diffuse down their vast concentration gradients (approximately 1:1500-7000) into the circulation in a manner that reflects lung function and injury score. Surfactant proteins vary markedly in size (approximately 20-650 kDa) and changes in the relative amounts appear particularly diagnostic with regard to disease severity. Alveolar levels of surfactant proteins remain remarkably constant despite respiratory disease and, unlike the flux of plasma proteins into the alveolus, which may reach equilibrium in acute lung injury, the flux of surfactant proteins is unidirectional because of the concentration gradient and because they are rapidly cleared from the circulation. 5. Ultimately, the diagnostic usefulness of surfactant proteins as markers of alveolocapillary permeability will demand a sound understanding of their kinetics through the vascular compartment.