# Application of Conditioned Medium for In Vitro Modeling and Repair of Respiratory Tissue
## 4 Discussion
For future evaluations, statistical analysis is proposed to improve the outcome of this study. Nevertheless, the use of secretomes during in vitro investigations should provide solid molecular support when conducting higher-degree studies. The last 10 years of research has supported the concept that cell-released factors have a therapeutic effect in vitro on various respiratory illnesses and physiological changes. Despite the recent breakthroughs in in vitro modeling, there remain gaps in replicating the physiological complexity of native cells. Thus, researchers have extensively examined the biochemical impact of using the secretome to imitate extracellular matrices to achieve the same microphysiological effects as native cells [66; 67; 68; 69]. The use of the secretome might potentially avoid the concerns regarding immunological compatibility, tumorigenicity, and infection transmission associated with cell treatments. Secretome usage might also significantly minimize the time and expense involved in cell proliferation and maintenance. In vitro research has investigated the effects of CM from differentiated cells on respiratory epithelium tissues. The findings suggested that CM may be used successfully to improve the functioning of both healthy and diseased cells [42; 46; 50]. CM derived from primary cells such as nasal fibroblasts enhance cell proliferation, attachment, and migration [42; 46] and also exert a cytoprotective effect on REC [42]. The CM from cell lines such as A549, when occultured with THP-1, aids in the reduction of cancer cell metastasis [50]. P Preclinical studies from this study supported the idea that cell-released factors from respiratory disorder-related tissues in vitro may exert a therapeutic effect on respiratory regeneration. In vitro data demonstrated that LAM-associated fibroblast (LAF) CM increased the pace of epithelial healing by increasing cell proliferation, migration, and the capacity to protect against apoptosis [41]. CM from idiopathic pulmonary fibrosis (IPF) fibroblasts improved the restoration ability with changes in the form of higher amounts of matricellular protein, especially SPARC [47], while cancer-associated fibroblast (CAF)-CM accelerated lung cancer cell metastasis by increasing the proliferative and invasive capacities [49]. Factors released by other tissue groups, such as MSC, were also studied primarily for their ability to induce regeneration in respiratory damage. MSC-CM promoted proliferation and wound closure in respiratory cells [36; 56; 57; 60; 61], protected the cells against apoptosis [58], and exerted antifibrotic effects [55]. Little is still known about the CM from other cell types, such as adipose-derived stem cells [51], THP-1 monocytes [52; 53], 3T3 cells [54], and macrophages [62]. However, the CM from these cells exerted positive effects, such as a protective ability against EMT in lung cancer [51; 62]. Some CM were also used in treatment studies, for example, a study of the effect of esculetin treatment of EC induced by monocyte-derived macrophages determined that it inhibited lung fibrosis and epithelial breakdown caused by the macrophages [52]. Some studies used CM from bacteria, specifically _S. aureus_[64], to explore the EC barrier function, which resulted in decreased cell TJ. In that study, the CM was derived from UAP-BA and ROFA particles rather than cells, and the factors produced by the particles reduced cell survival and caused inflammation [63]. Although the CM from respiratory tissues has demonstrated beneficial effects on respiratory cells, the effects of CM from non-respiratory tissues can differ significantly. Studies have indicated that CM from non-respiratory tissues, such as MSCs, may lead to immunomodulatory effects that can help reduce inflammation and exert antifibrotic effects on respiratory cells [36; 55; 56; 57; 60; 61], while the CM from adipose tissue can increase inflammation and oxidative stress [51].