Circulating surfactant protein D is associated to mortality in elderly women: A twin study

Immature Surfactant Protein Type B and Surfactant Protein Type D Correlate with Coronary Heart Disease in Patients with Type 2 Diabetes

BACKGROUND

Different specific surfactant proteins (SPs) have been associated with various pathological conditions, not only of the respiratory system, but also more recently with cardiovascular diseases, such as heart failure. The aim of the present study was to evaluate the role of SP-A, SP-D, and the precursor protein of SP-B (proSP-B) in the pathogenesis of cardiovascular damage in patients affected by type 2 diabetes (T2D).

METHODS

The study considered 31 patients with T2D (DN group), 34 patients with both T2D and coronary heart disease (CHD) (DC group), and 30 patients without diabetes but with a diagnosis of CHD (NC group). SP-A, SP-D, and proSP-B concentrations were determined in plasma samples, and were statistically compared using parametric and multivariate methods.

RESULTS

Higher plasma concentrations of SP-D and proSP-B were found in patients affected by both T2D and CHD (DC group), and in patients with CHD without diabetes (NC group), in comparison to T2D patients (DN group). A significant correlation, both with linear regression (r = 0.3565, p = 0.001) and Principal Component Analysis (PCA), was found between the plasma levels of SP-D and proSP-B in the overall cohort of patients. No differences in SP-A were observed among the three groups of subjects.

CONCLUSION

The present study extends the knowledge on the role of plasma SPs' levels as possible indicators of the risk of CHD being linked to T2D disease progression.

Immature Surfactant Protein B Increases in the Serum of Patients with Calcific Severe Aortic Stenosis

Valvular disease is a complex pathological condition that impacts countless individuals around the globe. Due to limited treatments, it is crucial to understand its mechanisms to identify new targets. Valve disease may result in pulmonary venous hypertension, which is linked to compromised functioning of the alveolar and capillary membranes and hindered gas exchange. Nonetheless, the correlation between surfactant proteins (SPs) and valve disease remains unexplored. A total of 44 patients were enrolled in this study, with 36 undergoing aortic valve replacement and 8 needing a second aortic valve substitution due to bioprosthetic valve degeneration. Ten healthy subjects were also included. The results showed that patients who underwent both the first valve replacement and the second surgery had significantly higher levels of immature SP-B (proSP-B) compared to control subjects. The levels of the extra-lung collectin SP-D were higher in patients who needed a second surgery due to bioprosthetic valve degeneration, while SP-A levels remained unchanged. The research also showed that there was no reciprocal relationship between inflammation and SP-D as the levels of inflammatory mediators did not differ between groups. The present study demonstrates that circulating proSP-B serves as a reliable marker of alveolar-capillary membrane damage in patients with valvular heart disease.

The Dual Role of Surfactant Protein-D in Vascular Inflammation and Development of Cardiovascular Disease

Cardiovascular disease (CVD) is responsible for 31% of all global deaths. Atherosclerosis is the major cause of cardiovascular disease and is a chronic inflammatory disorder in the arteries. Atherosclerosis is characterized by the accumulation of cholesterol, extracellular matrix, and immune cells in the vascular wall. Recently, the collectin surfactant protein-D (SP-D), an important regulator of the pulmonary immune response, was found to be expressed in the vasculature. Several in vitro studies have examined the role of SP-D in the vascular inflammation leading to atherosclerosis. These studies show that SP-D plays a dual role in the development of atherosclerosis. In general, SP-D shows anti-inflammatory properties, and dampens local inflammation in the vessel, as well as systemic inflammation. However, SP-D can also exert a pro-inflammatory role, as it stimulates C-C chemokine receptor 2 inflammatory blood monocytes to secrete tumor necrosis-factor α and increases secretion of interferon-γ from natural killer cells. In vivo studies examining the role of SP-D in the development of atherosclerosis agree that SP-D plays a proatherogenic role, with SP-D knockout mice having smaller atherosclerotic plaque areas, which might be caused by a decreased systemic inflammation. Clinical studies examining the association between SP-D and cardiovascular disease have reported a positive association between circulatory SP-D level, carotid intima-media thickness, and coronary artery calcification. Other studies have found that circulatory SP-D is correlated with increased risk of both total and cardiovascular disease mortality. Both in vitro, in vivo, and clinical studies examining the relationship between SP-D and CVDs will be discussed in this review.

Circulating Surfactant Protein-D Is Associated With Clinical Outcomes in Peripheral Artery Disease Patients Following Endovascular Therapy

BACKGROUND

Peripheral artery disease (PAD) is a risk factor for the development of cardiovascular disease and death. Surfactant protein-D (SP-D) is a 43-kDa protein secreted from type II pneumocytes in the lungs. Recent studies have demonstrated that circulating SP-D plays a key role in the development of atherosclerosis and is related to clinical outcomes in patients with ischemic heart disease. However, it remains unclear whether circulating SP-D is associated with clinical outcomes in patients with PAD.Methods and Results:We enrolled 364 patients with PAD who underwent endovascular therapy. We measured serum levels of SP-D and Krebs von den Lungen-6 (KL-6). During a median follow-up period of 974 days, there were 69 major adverse cardiovascular and leg events (MACLE), including 48 major adverse cardiovascular events (MACE). Kaplan-Meier analysis demonstrated that patients with high SP-D (≥110 ng/mL) had higher rates of MACE and MACLE than those with low SP-D. Multivariate Cox proportional hazard regression analysis demonstrated that SP-D, but not KL-6, was an independent predictor of MACE and MACLE. The addition of SP-D to known risk factors significantly improved the C index and net reclassification index. The circulating SP-D level was affected by sex, diabetes mellitus, and cilostazol prescription.

CONCLUSIONS

Circulating SP-D was associated with clinical outcomes in patients with PAD, suggesting that it may be a new therapeutic target in these patients.

Surfactant Protein D in Respiratory and Non-Respiratory Diseases

Surfactant protein D (SP-D) is a multimeric collectin that is involved in innate immune defense and expressed in pulmonary, as well as non-pulmonary, epithelia. SP-D exerts antimicrobial effects and dampens inflammation through direct microbial interactions and modulation of host cell responses via a series of cellular receptors. However, low protein concentrations, genetic variation, biochemical modification, and proteolytic breakdown can induce decomposition of multimeric SP-D into low-molecular weight forms, which may induce pro-inflammatory SP-D signaling. Multimeric SP-D can decompose into trimeric SP-D, and this process, and total SP-D levels, are partly determined by variation within the SP-D gene, SFTPD. SP-D has been implicated in the development of respiratory diseases including respiratory distress syndrome, bronchopulmonary dysplasia, allergic asthma, and chronic obstructive pulmonary disease. Disease-induced breakdown or modifications of SP-D facilitate its systemic leakage from the lung, and circulatory SP-D is a promising biomarker for lung injury. Moreover, studies in preclinical animal models have demonstrated that local pulmonary treatment with recombinant SP-D is beneficial in these diseases. In recent years, SP-D has been shown to exert antimicrobial and anti-inflammatory effects in various non-pulmonary organs and to have effects on lipid metabolism and pro-inflammatory effects in vessel walls, which enhance the risk of atherosclerosis. A common SFTPD polymorphism is associated with atherosclerosis and diabetes, and SP-D has been associated with metabolic disorders because of its effects in the endothelium and adipocytes and its obesity-dampening properties. This review summarizes and discusses the reported genetic associations of SP-D with disease and the clinical utility of circulating SP-D for respiratory disease prognosis. Moreover, basic research on the mechanistic links between SP-D and respiratory, cardiovascular, and metabolic diseases is summarized. Perspectives on the development of SP-D therapy are addressed.

Chemotherapeutic treatment reduces circulating levels of surfactant protein-D in children with acute lymphoblastic leukemia

BACKGROUND

Surfactant protein D (SP-D) is a host defense molecule of the innate immune system that enhances pathogen clearance and modulates inflammatory responses. We hypothesized that circulating SP-D levels are associated with chemotherapy-induced mucositis and infectious morbidity in children with acute lymphoblastic leukemia (ALL).

PROCEDURE

In a prospective study, 43 children receiving treatment for ALL were monitored for mucosal toxicity from diagnosis through the induction phase of treatment. Serial blood draws were taken to determine the levels of SP-D, interleukin-6 (IL-6), C-reactive protein, and white blood cells. Data on fever, antibiotics, and bacteremia were collected. Baseline levels of circulating SP-D were compared with healthy controls.

RESULTS

Baseline values of circulating SP-D were similar to levels in healthy controls (median: 829 ng/ml vs. 657 ng/ml, respectively, P > 0.05). After initiation of chemotherapy, a significant reduction in SP-D levels was observed at all time points: 704 ng/ml at day 8, 413 ng/ml at day 15, 395 ng/ml at day 22, and 520 ng/ml at day 29 (all, P < 0.05). No significant associations between SP-D values, the occurrence of mucosal toxicity, or infectious morbidity were observed. However, loss of circulating SP-D from days 8 to 15 was associated with more systemic inflammation, and lower SP-D values at day 15 were associated with elevated intestinal mucositis scores (P < 0.05).

CONCLUSIONS

The current study supports the hypothesis that the detrimental effect of chemotherapy on patients' immune functions includes decreased circulating levels of innate mucosal molecules such as SP-D, potentially aggravating mucosal and systemic inflammatory responses.

[Significance of surfactant proteins in the diagnosis of therapeutic diseases]

The lung provides not only respiration, but also the functioning of innate immunity mechanisms. The hydrophilic proteins SP-A and SP-D are responsible for the regulation of the latter. In the literature, there is evidence for elevated serum SP-A and SP-D levels in respiratory diseases accompanied by enhanced mucosal inflammation of the lung or its parenchymal injury and their association with age and cardiovascular diseases has been recently found. Studies of the efficiency of using SP-A and SP-D as specific markers for inflammatory lung diseases are presently worthwhile.

Surfactant protein-D-encoding gene variant polymorphisms are linked to respiratory outcome in premature infants

OBJECTIVE

Associations between the genetic variation within or downstream of the surfactant protein-D-encoding gene (SFTPD), which encodes the collectin surfactant protein-D (SP-D) and may lead to respiratory distress syndrome or bronchopulmonary dysplasia, recently were reported. Our aim was to investigate whether SFTPD variations affect serum SP-D levels in infants and pulmonary outcome in premature infants.

STUDY DESIGN

Serum SP-D levels were measured in 211 mature and 202 premature infants, and 7 SFTPD single-nucleotide polymorphisms (SNPs) were genotyped. SNP analysis and haplotype analysis were used to associate genetic variation to SP-D, respiratory distress (RD), oxygen requirement, and respiratory support.

RESULTS

The 5'-upstream SFTPD SNP rs1923534 and the 3 structural SNPs rs721917, rs2243639, and rs3088308 were associated with the SP-D level. The same SNPs were associated with RD, a requirement for supplemental oxygen, and a requirement for respiratory support. Haplotype analyses identified 3 haplotypes that included the minor alleles of rs1923534, rs721917, and rs3088308 that exhibited highly significant associations with decreased SP-D levels and decreased ORs for RD, oxygen supplementation, and respiratory support.

CONCLUSION

These findings extend and validate previous observations of SFTPD association with the risk of respiratory outcomes and suggest SFTPD as an essential factor affecting pulmonary adaptation in premature infants.

Role of serum and induced sputum surfactant protein D in predicting the response to treatment in chronic obstructive pulmonary disease

This study was designed to determine the expression of serum and sputum surfactant protein D (SP-D) in chronic obstructive pulmonary disease (COPD) and its association with treatment response. Sixty-five treatment-naive patients with COPD and 26 normal control subjects were recruited in the study. The concentrations of serum and sputum SP-D were measured, and the associations of SP-D with pulmonary function and the modified Medical Research Council dyspnea scale (mMRC) and the St. George's Respiratory Questionnaire (SGRQ) scores before and after three months of treatment with an inhaled corticosteroid and a long-acting β2-agonist were analyzed. The concentrations of serum and sputum SP-D in the COPD group (45.46±37.78 and 173.23±186.93 ng/ml, respectively) were significantly higher than those of the normal control group (31.68±12.04 and 89.59±70.29 ng/ml, respectively). After three months of treatment, serum SP-D levels were reduced to 30.7±13.9 ng/ml and were significantly lower than the baseline levels (t=2.217, P=0.031). However, no significant reduction in sputum SP-D levels was observed following the treatment (P>0.05). A significant association between baseline sputum SP-D and change in SGRQ activity scores (r=-0.652, P=0.012) was observed; however no association was established with the changes in other clinical profiles following the treatment (P>0.05). This result suggested that an increased baseline sputum SP-D may be a weak predictive indicator of response to treatment with inhaled corticosteroids and long-acting β2-agonists in patients with COPD.

Surfactant protein D is a candidate biomarker for subclinical tobacco smoke-induced lung damage

Variation in surfactant protein D (SP-D) is associated with lung function in tobacco smoke-induced chronic respiratory disease. We hypothesized that the same association exists in the general population and could be used to identify individuals sensitive to smoke-induced lung damage. The association between serum SP-D (sSP-D) and expiratory lung function was assessed in a cross-sectional design in a Danish twin population ( n = 1,512, 18–72 yr old). The adjusted heritability estimates for expiratory lung function, associations between SP-D gene ( SFTPD) single-nucleotide polymorphisms or haplotypes, and expiratory lung function were assessed using twin study methodology and mixed-effects models. Significant inverse associations were evident between sSP-D and the forced expiratory volume in 1 s and forced vital capacity in the presence of current tobacco smoking but not in nonsmokers. The two SFTPD single-nucleotide polymorphisms, rs1923536 and rs721917, and haplotypes, including these single-nucleotide polymorphisms or rs2243539, were inversely associated with expiratory lung function in interaction with smoking. In conclusion, SP-D is phenotypically and genetically associated with lung function measures in interaction with tobacco smoking. The obtained data suggest sSP-D as a candidate biomarker in risk assessments for subclinical tobacco smoke-induced lung damage. The data and derived conclusion warrant confirmation in a longitudinal population following chronic obstructive pulmonary disease initiation and development.