Abstract
Objective
Chronic obstructive pulmonary disease (COPD) is one of the main causes of morbidity and mortality in the United States. Oxidative stress due to cigarette smoking seems to be one of the major driving mechanisms in COPD pathogenesis. Since the scavenger receptor B1 (SR-B1) appears to play a key role in mediating the uptake for ɑ-tocopherol and other antioxidants in lung tissue, we aimed to investigate its role in COPD pathogenesis.
Methods
Lung tissue biopsies were obtained from 12 subjects; 6 of these had a diagnosis of COPD in a stable clinical state, the others 6 were current (n = 1) or ex-smokers (n = 5) with normal lung function (controls). 4-Hydroxynonenal (4-HNE)–SR-B1 adducts were detected by immunoprecipitation. ɑ-tocopherol concentration was determined by HPLC.
Results
SR-B1 levels were lower in COPD patients and these results parallel with lower levels of vitamin E in lung tissue found in COPD patients. This effect can be the consequence of oxidative posttranslational modifications, confirmed by the binding of the peroxidation product 4-HNE to SR-B1 possibly leading to its degradation.
Conclusions
The loss of SR-B1 may be involved in lung ɑ-tocopherol content decrease with the consequence of making lung tissue more susceptible to oxidative damage as suggested by the SR-B1–4-HNE adduct formation, and more prone to COPD development. Thus, our findings suggest a novel role of SR-B1 in pathomechanisms underlying COPD.
Significance statement
Chronic obstructive pulmonary disease (COPD) is one of the main causes of morbidity and mortality in the United States. Oxidative stress has been suggested to be the major driving mechanism in COPD pathogenesis. Loss of scavenger receptor BI (SR-B1) significantly decreases tocopherol lung content making lung tissue more susceptible to oxidative damage. The results of our study show that SR-B1 levels were lower in COPD patients and these results parallel with lower levels of vitamin E in lung tissue. Our findings suggest a novel role of SR- B1 in pathomechanisms underlying COPD.
Introduction
It is well established that cigarette smoking (CS) is a risk factor for many chronic diseases mainly affecting cardiovascular and respiratory systems (PDQ Screening and Prevention Editorial Board 2002). Today, it has been well demonstrated that CS is the main cause for developing COPD, although not all the smokers are affected by this pathology, evidencing a possible genetic predisposition (Cho et al. 2022).
COPD is a major health issue and one of the three most common causes of death worldwide (Adeloye et al. 2022). The abnormal inflammatory response to chronic exposure to CS components is believed to be the key component of COPD pathogenesis (Caramori et al. 2016). However, inflammation is not the only pathogenic mechanism underlying COPD. Oxidative stress has been also shown to play a primary role in COPD onset and clinical progression (Nucera et al. 2022). This chronic inflammation of the lower airways is characterized by a progressive loss of lung parenchyma and an accelerated decline of organ function.
Cigarettes smoke contains over 4700 compounds in gaseous and particulate states that are able to induce oxidative stress to cells, and its toxic effect is mainly due to the presence of oxidants, including volatile electrophilic compounds such as α,β-unsaturated aldehydes (Szparaga et al. 2021). Among these, 4-hydroxy-2-nonenal (HNE), a lipid peroxidation product, is highly reactive and potentially toxic. These aldehydes form covalent adducts with various proteins, thus affecting a variety of biochemical processes, including transcription factor activation, gene and protein expression, production of inflammatory cytokines, and cell death (Sharma et al. 2022).
Clinical trials with antioxidants have not been able to definitely prove the ability of micronutrients to prevent tobacco-related diseases such as COPD (Barnes 2020). The reason behind these controversial results could depend on both genetic background and the personal ability to uptake micronutrients in lung cells.
Two decades ago, Acton et al. (Acton et al. 1996) identified the scavenger receptor class B1 (SR-B1) as a HDL receptor. This transmembrane protein mediates the selective uptake of HDL cholesteryl esters and facilitates the trafficking of these lipids in the tissues (Gillard et al. 2018). Additional functions of this receptor have been shown, such as its ability to uptake the lipophilic antioxidant α-tocopherol (AT), which suggests an indirect role of the receptor in cell defensive mechanisms against oxidative stress challenges. More specifically, it has been observed that SRB1 KO mice had 64% less vitamin E levels in the lung (Mardones et al. 2002), therefore being more susceptible to oxidative damage. In addition, SR-B1 is very susceptible to oxidative damage, which induces its degradation via proteasome (Sticozzi et al. 2013, Crivellari et al. 2017).
Therefore, we have hypothesized that upon lung exposure to SHS and its attendant OS, a positive feedback loop is induced where the lipid soluble antioxidants consumption increases (to fight against oxidative stress) and SR-B1 expression diminish as a consequence of oxidative damage. This combination results in reduced lung vitamin E contents, making the target tissue even more vulnerable to further insults.
These premises provide the rationale of the current study, which addresses the hypothesis that the expression of SR-B1 is downregulated in COPD lung as an effect of oxidative burden potentially caused by CS. We found that the level of SR-B1 is significantly lower in COPD patients compared to control smokers with normal lung function, and this alteration may occur via oxidative posttranslational modification.
Materials and methods
Study approval
All patients were recruited from the Respiratory Diseases Clinic of the University Hospital of Ferrara (www.ospfe.it). The diagnosis of COPD was based on the GOLD (www.goldcopd.org) criteria (a compatible history and spirometry, a post-bronchodilation forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ratio < 70%)).
Patients (i) who had pulmonary function test report within 3 days, (ii) with diagnosis stable COPD (for more than 2 weeks), and (iii) who did not report any treatment with oxygen, antibiotics, glucocorticoids, and theophylline within the last 1 month were included in the study. The exclusion criteria were as follows: (i) patients having been treated with immunosuppressive drugs in the past month; (ii) patients having other airflow-limited diseases, (iii) patients having severe diseases, and (iv) patients having infectious diseases other than that of the respiratory system.
We obtained and studied peripheral lung tissue from 12 subjects: six of these had a diagnosis of COPD in a stable clinical state, the others six were current (n = 1) or ex-smokers (n = 5) with normal lung function (controls).
The study conformed to the Declaration of Helsinki and was approved by the ethics committees of the University Hospital of Ferrara, Italy; written informed consent was obtained from each participant, and nonneoplastic peripheral lung tissue sampling was performed during lung resection surgery for a suspected malignancy according to the guidelines of the local ethics committee.
Harvesting and preparation of lung samples
Lung tissue preparation was performed as previously detailed (Valacchi et al. 2007). Briefly, lung tissue biopsies were homogenized at 4 °C in radioimmunoprecipitation assay (RIPA) buffer (150 mM NaCl2, 50 mM Tris–HCl, pH 7.4, 1% NP-40, 1 mM EDTA, 1 mM EGTA, 0.1% sodium dodecyl sulfate, 5 mM dithiothreitol, 5 mM NaF, 1 mM phenylmethyl sulfonyl fluoride, 10 mg/mL leupeptin, 10 μg/mL aprotinin, 10 mg/mL iodoacetamide) (Merck KGaA), incubated on ice for 1 h, and separated by centrifugation at 21,000 g for 10 min. Supernatants were stored at −80°C until further processing.
Western blot analysis
Total cell lysates were extracted in RIPA buffer containing 50 mM Tris (pH 7.5), 150 mM NaCl, 10% glycerol, 1% Nonidet P-40, 1 mM EGTA, 0.1% SDS, 5 mM n-ethylmaleimide (Merck KGaA), protease and phosphatase inhibitor cocktails (Merck KGaA) as described before (Valacchi et al. 2007), Briefly, 60 μg boiled proteins were loaded onto 10% sodium dodecyl sulfate–polyacrylamide electrophoresis gels. The gels were electroblotted onto nitrocellulose membranes and then blocked for 1 h in 3% milk. Membranes were incubated overnight at 4 °C with the primary antibody SR-B1 (Novus Biologicals, Inc., Littleton, CO, USA) and with horseradish peroxidase-conjugated secondary antibody (Bio-Rad). The blots were stripped and reprobed with β-actin (Cell Signaling; Celbio, Milan, Italy) as the loading control. Images of the bands were digitized and the densitometry of the bands were performed using Image J software.
Immunoprecipitation of SR-B1 and detection of 4-HNE adducts
The antibody for SR-B1 (5 μg) (Thermo Fisher Scientific Inc.) was precoupled to 50 µL of magnetic Dynabeads Protein G (Novex, Life Technologies). Excess antibody was washed by placing the tube on a DynaMag™ magnet and removing the supernatant. Then, cell protein extracts (500 µg) were incubated with the antibody-coated beads for 10 min at room temperature (RT). After washing, the immunocomplexes were mixed with reducing sample buffer, boiled, and analyzed by SDS-PAGE and immunoblotting with 4-HNE antibody (Millipore).
Quantification of ɑ-tocopherol
AT concentrations were determined by HPLC using a Waters Spherisorb ODS2 C-18 (4.6 × 100 mm, 3 μm particle size) column with electrochemical detection, as described by Valacchi et al. (Valacchi et al. 2000). Tissue AT was extracted following saponification with alcoholic potassium hydroxide in the presence of 1% ascorbic acid. AT was detected electrochemically using an oxidizing potential of 500 mV and quantitated by calculation from a standard curve of authentic AT standards.
Results
The main characteristics of the study subjects are shown in Table 1.
Characteristics of subjects for the study on peripheral lung parenchyma. Data are expressed as mean ± s.e.m.
| Subjects | n | Age | Sex | Smoking history | Pack-years | Chronic bronchitis | FEV1 % pred | FEV1/ FVC % | ||
|---|---|---|---|---|---|---|---|---|---|---|
| Male | Female | Ex-smokers | Current smokers | |||||||
| Control smokers | 6 | 71.2 ± 3.9 | 4 | 2 | 5 | 1 | 35.8 ± 5.4 | 0 | 90.2 ± 8.2 | 83.5 ± 4.3 |
| COPD | 6 | 71.3 ± 1.1 | 5 | 1 | 3 | 3 | 45.5 ± 3.2 | 3 | 75.3 ± 5.5 | 65.2 ± 1.5 |
SR-B1 has been shown to be involved in many regulatory functions, including the ability to indirectly protect from the oxidative stress-related damage cause by CS. Owing to this, we assessed the SR-B1 protein levels in the peripheral lung tissue of both COPD patients and control smokers with normal lung function, using a specific SR-B1 antibody able to recognize both, the mature (82 KDa) and the immature form (not glycosylated form, 66 KDa) of SR-B1. As shown in Fig. 1, COPD patients have high levels of SR-B1 immature form and very low level of the functional form (82 KDa).
Peripheral lung parenchyma tissue samples of COPD patients showed low levels of mature SR-B1 compared to those of control smokers with normal lung function. Data are expressed as mean ± s.e.m. (*P < 0.05). (A) Western blot (top panel) is a representative of five different patients. (B) SR-B1 band quantification is shown in the right panel. Data are expressed in arbitrary units (averages of five different experiments, *P < 0.05). β-Actin was used as loading control.
Citation: Redox Experimental Medicine 2023, 1; 10.1530/REM-23-0012
Increased levels of peroxidation (Sticozzi et al. 2014) and oxidative stress (OS) (Solak et al. 2005, Prieux et al. 2020) have been widely related to the high levels of pro-oxidants contained in CS. In particular, we have previously shown that posttranslational modification via formation to 4-HNE protein adducts deeply affect SR-B1, by increasing the rate subsequent ubiquitination and proteasome degradation, as we showed in previous studies (Sticozzi et al. 2013, Ferrara et al. 2022). For this reason, we evaluated the presence of this highly reactive aldehyde and the eventual formation of adducts with SR-B1 in lung tissue from COPD patients and control subjects. As shown in Fig. 2A, in COPD peripheral lung tissues there was a significant increase in 4-HNE protein adducts (top panel) resulting in an increment of almost 50% (bottom panel). Immunoblotting assay (Fig. 2B upper panel) evidenced that the interaction between SR-B1 and 4-HNE was clearly stronger in COPD patients compared to the control smokers with normal lung function resulting in almost twofold increase (Fig. 2B bottom panel).
COPD peripheral lung tissue showed high levels of HNE protein adducts (A) and the presence of HNE adducts on SR-B1 (B) compared to controls. (A) Lung lysates were immunoblotted for 4-HNE adducts. Showed is a representative Western blot of five experiments from five different patients. (B) Samples were immunoprecipitated with SR-B1 Ab and immunoblotted with anti-4-HNE. Western blot is representative of five independent experiments.
Citation: Redox Experimental Medicine 2023, 1; 10.1530/REM-23-0012
Loss of SR-B1 due to oxidative modification could affect vitamin E uptake in lung cells, as this receptor is a key player in this process (Valacchi et al. 2011). To address this hypothesis, we measured the levels of AT in peripheral lung tissue of COPD and control smokers with normal lung function. As shown in Table 2, the levels of this lipophilic vitamin were significantly lower in COPD peripheral lung tissue compared to control smokers with normal lung function.
COPD lungs showed lower levels of α-tocopherol compared to control smokers with normal lung function. Data expressed as mean ± s.e.m.
| Control smokers with normal lung function | COPD | |
|---|---|---|
| α-tocopherol (nmol/mg tissue) | 70 ± 2.34 | 46 ± 4.56 (P < 0.01) |
Discussion
In the present study, we found for the first time that COPD patients have lower levels of mature (and biologically functional) SR-B1 in the peripheral lung parenchyma compared to control smokers with normal lung function. The collected data suggest that this alteration may be the result of oxidative stress-mediated posttranslational modification which, as previously shown in other experimental settings, may increase the rate of proteasomal degradation of this receptor.
We decided to focus our attention on SR-B1 in COPD for two main reasons: (i) evidence suggests that SR-B1 may be involved in many physiological processes in lung, including some that are altered in COPD and (ii) SR-B1 is highly vulnerable to oxidative challenges caused by CS, the main risk factor and pathogenic player of COPD (Valacchi et al. 2015).
SR-B1 is mostly known and studied for its critical role in reverse cholesterol transport (RCT) and HDL homeostasis (Shen et al. 2018). The possible role of HDL in the development of COPD has been proposed, on the basis on the observed epidemiological association between the clinical severity of the disease and low levels of these lipoproteins (Valacchi et al. 2015, Zafirova-Ivanovska et al. 2016, Vicol et al. 2022). However, these data are mixed and, in any case, did not support a role of SR-B1 in the etiology and pathogenesis of COPD but rather in the frequent cardiovascular complications of the lung disease.
There are several mechanisms, besides the well-characterized chronic inflammation of the airways, that are involved in COPD onset and progression, and SR-B1 may play a role in some of them. This multifunctional receptor is able to recognize a vast variety of ligands, including apoptotic cells, seemingly facilitating their disposal, and pathogens (Gillard et al. 2018) (10.1016/j.jacl.2018.04.001). Notably, the increase in apoptotic alveolar epithelial and endothelial cells in the lung tissue of COPD patients has been referred to as a potential upstream event in COPD pathogenesis (Demedts et al. 2006). Moreover, lungs of patients affected by this disease are abnormally sensitive to respiratory viral and bacterial infections, which can greatly worsen the prognosis (D’Anna et al. 2021). In particular, preclinical evidence suggests that downregulation of SR-B1 may facilitate the entry and the replication of virus. SR-B1 may also be able to recognize bacteria and also to orchestrate neutrophilic host defense response to inhaled noxious compounds, included those present in COPD patients (Gowdy et al. 2015).
This receptor may also be indirectly involved in the regulation of redox homeostasis in lung cells. Abnormal elevation in reactive oxygen species (ROS) has been well documented in COPD and may occur as direct consequence of inhaled toxicants and/or as result of activation of leukocytes and epithelial cells (Barnes 2022). A functional SR-B1 seems to contribute to preserve the oxidative balance by, among others, mediating the uptake AT and carotenoids, from HDL and other lipoproteins. This vitamin seems to play an important protective role in human lung. Accordingly, large trials have shown that AT supplements significantly decrease the risk of developing COPD and other chronic pulmonary diseases (Agler et al. 2011) and higher vitamin E intake prevents COPD development (Liu et al. 2023). Preclinical evidence pints to direct link between SRB1 and intracellular levels of the potent lipophilic antioxidant. Indeed, it has been shown that in SR-B1-null mice a significant increase in levels of circulating ATol is accompanied by a concomitant reduction in several organs, including lung (Mardones et al. 2002). Owing the important contribution in the antioxidant defensive mechanism, the reduction in the levels of AT observed in stable COPD lungs could result in their major vulnerability to oxidative challenge.
Decline in AT could be a cause of the detected decrease of functional SR-B1 in diseased lungs. Our hypothesis is that the increase in oxidative stress (witnessed by the observed increase in 4-HNE protein adduct levels) may lead to the observed posttranslational change related to the covalent binding with 4-HNE. This highly reactive aldehyde tends to form covalent bonds with amino acid residues such as lysine, histidine, and cysteine present in the proteins (Pecorelli et al. 2016). The loss of SR-B1 may be ascribed to this modification. Indeed, we have previously shown that this significantly accelerates proteasome-mediated degradation of the receptor in cultured cells following CS or ozone exposure (Sticozzi et al. 2012, 2018, 2020).
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the study reported.
Funding
This study did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
Author contribution statement
CC conceived the study and wrote the paper; GV conceived the study and reviewed the manuscript; AP and CS performed experiments and analyzed data; GC conceived the original idea and reviewed the final draft; AP supervised the project and reviewed the final draft; PC and FN supervised the project, analyzed the data, and reviewed the final draft.
References
Acton S, Rigotti A, Landschulz KT, Xu S, Hobbs HH & & Krieger M 1996 Identification of scavenger receptor SR-BI as a high density lipoprotein receptor. Science 271 518–520. (https://doi.org/10.1126/science.271.5248.518)
Adeloye D, Song P, Zhu Y, Campbell H, Sheikh A, Rudan I & NIHR RESPIRE Global Respiratory Health Unit 2022 Global, regional, and national prevalence of, and risk factors for, chronic obstructive pulmonary disease (COPD) in 2019: a systematic review and modelling analysis. Lancet. Respiratory Medicine 10 447–458. (https://doi.org/10.1016/S2213-2600(2100511-7)
Agler AH, Kurth T, Gaziano JM, Buring JE & & Cassano PA 2011 Randomised vitamin E supplementation and risk of chronic lung disease in the Women’s Health Study. Thorax 66 320–325. (https://doi.org/10.1136/thx.2010.155028)
Barnes PJ 2020 Oxidative stress-based therapeutics in COPD. Redox Biology 33 101544. (https://doi.org/10.1016/j.redox.2020.101544)
Barnes PJ 2022 Oxidative stress in chronic obstructive pulmonary disease. Antioxidants 11. (https://doi.org/10.3390/antiox11050965)
Caramori G, Casolari P, Barczyk A, Durham AL, Di Stefano A & & Adcock I 2016 COPD immunopathology. Seminars in Immunopathology 38 497–515. (https://doi.org/10.1007/s00281-016-0561-5)
Cho MH, Hobbs BD & & Silverman EK 2022 Genetics of chronic obstructive pulmonary disease: understanding the pathobiology and heterogeneity of a complex disorder. Lancet. Respiratory Medicine 10 485–496. (https://doi.org/10.1016/S2213-2600(2100510-5)
Crivellari I, Sticozzi C, Belmonte G, Muresan XM, Cervellati F, Pecorelli A, Cavicchio C, Maioli E, Zouboulis CC, Benedusi M, et al.2017 SRB1 as a new redox target of cigarette smoke in human sebocytes. Free Radical Biology and Medicine 102 47–56. (https://doi.org/10.1016/j.freeradbiomed.2016.11.021)
D’Anna SE, Maniscalco M, Cappello F, Carone M, Motta A, Balbi B, Ricciardolo FLM, Caramori G & & Stefano AD 2021 Bacterial and viral infections and related inflammatory responses in chronic obstructive pulmonary disease. Annals of Medicine 53 135–150. (https://doi.org/10.1080/07853890.2020.1831050)
Demedts IK, Demoor T, Bracke KR, Joos GF & & Brusselle GG 2006 Role of apoptosis in the pathogenesis of COPD and pulmonary emphysema. Respiratory Research 7 53. (https://doi.org/10.1186/1465-9921-7-53)
Ferrara F, Cordone V, Pecorelli A, Benedusi M, Pambianchi E, Guiotto A, Vallese A, Cervellati F & & Valacchi G 2022 Ubiquitination as a key regulatory mechanism for O3-induced cutaneous redox inflammasome activation. Redox Biology 56 102440. (https://doi.org/10.1016/j.redox.2022.102440)
Gillard BK, Rosales C, Xu B, Gotto AM & & Pownall HJ 2018 Rethinking reverse cholesterol transport and dysfunctional high-density lipoproteins. Journal of Clinical Lipidology 12 849–856. (https://doi.org/10.1016/j.jacl.2018.04.001)
Gowdy KM, Madenspacher JH, Azzam KM, Gabor KA, Janardhan KS, Aloor JJ & & Fessler MB 2015 Key role for scavenger receptor B-I in the integrative physiology of host defense during bacterial pneumonia. Mucosal Immunology 8 559–571. (https://doi.org/10.1038/mi.2014.88)
Liu Z, Su Y, Chen Q, Xiao L, Zhao X, Wang F, Peng Z & & Zhang H 2023 Association of Dietary intake of vitamin E with chronic obstructive pulmonary disease events in US adults: a cross-sectional study of NHANES 2013–2018. Frontiers in Nutrition 10 1124648. (https://doi.org/10.3389/fnut.2023.1124648)
Mardones P, Strobel P, Miranda S, Leighton F, Quiñones V, Amigo L, Rozowski J, Krieger M & & Rigotti A 2002 α-Tocopherol Metabolism is abnormal in Scavenger Receptor Class B Type I (SR-BI)-Deficient Mice. Journal of Nutrition 132 443–449. (https://doi.org/10.1093/jn/132.3.443)
Nucera F, Mumby S, Paudel KR, Dharwal V, Di Stefano A, Casolaro V, Hansbro PM, Adcock AM & & Caramori G 2022 Role of oxidative stress in the pathogenesis of COPD. Minerva Medica 113. (https://doi.org/10.23736/S0026-4806.22.07972-1)
PDQ Screening and Prevention Editorial Board 2002 Ciga rette Smoking: Health Risks and How to Quit (PDQ®): Health Professional Version. In PDQ Cancer Information Summaries .National Cancer Institute, Bethesda, MD, USA. Available from https://www.ncbi.nlm.nih.gov/books/NBK66008/
Pecorelli A, Cervellati C, Cortelazzo A, Cervellati F, Sticozzi C, Mirasole C, Guerranti R, Trentini A, Zolla L, Savelli V, et al.2016 Proteomic analysis of 4-hydroxynonenal and nitrotyrosine modified proteins in RTT fibroblasts. International Journal of Biochemistry and Cell Biology 81 236–245 (https://doi.org/10.1016/j.biocel.2016.08.001)
Prieux R, Eeman M, Rothen-Rutishauser B & & Valacchi G 2020 Mimicking cigarette smoke exposure to assess cutaneous toxicity. Toxicology in Vitro 62 104664. (https://doi.org/10.1016/j.tiv.2019.104664)
Sharma S, Sharma P, Bailey T, Bhattarai S, Subedi U, Miller C, Ara H, Kidambi S, Sun H, Panchatcharam M, et al.2022 Electrophilic aldehyde 4-hydroxy-2-nonenal mediated signaling and mitochondrial dysfunction. Biomolecules 12. (https://doi.org/10.3390/biom12111555)
Shen WJ, Azhar S & & Kraemer FB 2018 SR-B1: a unique multifunctional receptor for cholesterol influx and efflux. Annual Review of Physiology 80 95–116. (https://doi.org/10.1146/annurev-physiol-021317-121550)
Solak ZA, Kabaroğlu C, Çok G, Parıldar Z, Bayındır U, Özmen D & & Bayındır O 2005 Effect of different levels of cigarette smoking on lipid peroxidation, glutathione enzymes and paraoxonase 1 activity in healthy people. Clinical and Experimental Medicine 5 99–105. (https://doi.org/10.1007/s10238-005-0072-5)
Sticozzi C, Belmonte G, Pecorelli A, Arezzini B, Gardi C, Maioli E, Miracco C, Toscano M, Forman HJ & & Valacchi G 2012 Cigarette smoke affects keratinocytes SRB1 expression and localization via H2O2 production and HNE protein adducts formation. PLoS One 7 e33592. (https://doi.org/10.1371/journal.pone.0033592)
Sticozzi C, Belmonte G, Pecorelli A, Cervellati F, Leoncini S, Signorini C, Ciccoli L, De Felice C, Hayek J & & Valacchi G 2013 Scavenger receptor B1 post-translational modifications in Rett syndrome. FEBS Letters 587 2199–2204. (https://doi.org/10.1016/j.febslet.2013.05.042)
Sticozzi C, Cervellati F, Muresan XM, Cervellati C & & Valacchi G 2014 Resveratrol prevents cigarette smoke-induced keratinocytes damage. Food and Function 5 2348–2356. (https://doi.org/10.1039/C4FO00407H)
Sticozzi C, Pecorelli A, Romani A, Belmonte G, Cervellati F, Maioli E, Lila MA, Cervellati C & & Valacchi G 2018 Tropospheric ozone affects SRB1 levels via oxidative post-translational modifications in lung cells. Free Radical Biology and Medicine 126 287–295. (https://doi.org/10.1016/j.freeradbiomed.2018.07.007)
Sticozzi C, Belmonte G, Pecorelli A, Arezzini B, Gardi C, Maioli E, Miracco C, Toscano M, Forman HJ & & Valacchi G 2020 Correction: cigarette smoke affects keratinocytes SRB1 expression and localization via H2O2 production and HNE protein adducts formation. PLoS One 15 e0228663. (https://doi.org/10.1371/journal.pone.0228663)
Szparaga M, Świercz R & & Stępnik M 2021 Review of data on chemical content in an aerosol resulting from heating a tobacco or a solution used in e-cigarettes and in the smoke generated from the reference cigarettes. Toxicology Mechanisms and Methods 31 323–333. (https://doi.org/10.1080/15376516.2021.1884922)
Valacchi G, Weber SU, Luu C, Cross CE & & Packer L 2000 Ozone potentiates vitamin E depletion by ultraviolet radiation in the murine stratum corneum. FEBS Letters 466 165–168. (https://doi.org/10.1016/S0014-5793(9901787-1)
Valacchi G, Vasu VT, Yokohama W, Corbacho AM, Phung A, Lim Y, Aung HH, Cross CE & & Davis PA 2007 Lung vitamin E transport processes are affected by both age and environmental oxidants in mice. Toxicology and Applied Pharmacology 222 227–234. (https://doi.org/10.1016/j.taap.2007.04.010)
Valacchi G, Sticozzi C, Lim Y & & Pecorelli A 2011 Scavenger receptor class B type I: a multifunctional receptor. Annals of the New York Academy of Sciences 1229 E1–E7. (https://doi.org/10.1111/j.1749-6632.2011.06205.x)
Valacchi G, Maioli E, Sticozzi C, Cervellati F, Pecorelli A, Cervellati C & & Hayek J 2015 Exploring the link between scavenger receptor B1 expression and chronic obstructive pulmonary disease pathogenesis. Annals of the New York Academy of Sciences 1340 47–54. (https://doi.org/10.1111/nyas.12714)
Vicol C, Buculei I, Melinte OE, Dobrin ME, Stavarache EI, Gavrilescu CM, Postolache P, Matei D & & Trofor A 2022 The lipid profile and biochemical parameters of COPD patients in relation to smoking status. Biomedicines 10. (https://doi.org/10.3390/biomedicines10112936)
Zafirova-Ivanovska B, Stojkovikj J, Dokikj D, Anastasova S, Debresliovska A, Zejnel S & & Stojkovikj D 2016 The level of cholesterol in COPD patients with severe and very severe stage of the disease. Open Access Macedonian Journal of Medical Sciences 4 277–282. (https://doi.org/10.3889/oamjms.2016.063)
