This is the first human study on the process of cereblon protein in lung secretions. No difference was observed between the cereblon protein synthesis in the patients with and without sepsis in the ICU. No correlation was observed between the presence of cereblon and gender, survival, and steroid use. However, in patients with more than 3% PMNL cells in BAL, cereblon synthesis decreased significantly as the number of inflammatory cells increased. The more we saw inflammatory cells in BAL, the less cereblon there was. In the presence of CRBN, steroid treatment could not reduce mortality or improve scores in the intensive care unit. While CRBN is the primary target for other immunomodulators, it may not be for steroids. The presence of less cereblon in the patients with more inflammatory cells may explain that steroid therapy, an immunomodulator, did not reduce mortality.
In a sepsis study conducted by Gil et al., the role of CRBN in polymicrobial sepsis induced by cecal ligation and puncture (CLP) was investigated. CRBN-deficient (KO) mice were used for this study. Resistance to polymicrobial sepsis has been demonstrated in CRBN-deficient mice. Survival 6 days after CLP was found significantly higher in KO mice (50%) compared to wild-type (WT) controls (0%). In KO mice, peripheral blood bacterial load is less; lung damage is more minimal. Activation of AMPK and heme oxygenase-1 (HO-1) in peritoneal macrophages from WT mice was found lower. AMPK has been shown to protect against organ injury by suppressing inflammation. This study demonstrated that CRBN expression plays an attractive role in CLP-induced sepsis and peritoneal macrophage response. This creates a new approach to sepsis . In our study, a relationship could not be established between the presence of CRBN in bronchial secretion and survival. However, as PMNLs increased in the aspiration material, CRBN expression decreased. In cases with a nearly fibrinopurulent exudate and deletion PMNLs, cellular CRBN expression is lost, which means that CRBN cannot have a protective effect against organ damage.
The AMPK, which is negatively controlled by cereblon, has previously been linked to pulmonary fibrosis. Kang et al. interpreted the role of CRBN in bleomycin (BLM)-induced pulmonary fibrosis in mice. In CRBN knockout (KO) mice, BLM-induced fibrosis was significantly reduced. According to this study, CRBN is a profibrotic regulator and might be used as a potential target to treat lung fibrosis .
In a study examining the mechanism of acute kidney injury (AKI) in sepsis, the role of CRBN was investigated. Sepsis was induced by applying lipopolysaccharide (LPS) on human kidney 2 (HK2) cells. Circ_0114428 and CRBN levels were higher in septic AKI blood samples and LPS-induced HK2 cells. LPS-induced apoptosis, inflammation, oxidative stress, and ER stress were rescued by CRBN overexpression. The Circ_0114428 knock-down might have deflated this. CRBN expression was significantly raised in serum from septic AKI patients. It was suggested that CRBN played a staminal role in kidney damage due to sepsis, in which circ_0114428 might be related to its function . However, in our study, the presence of cereblon suppressed the increase in PMNLs. This may indicate that inflammation is suppressed. For a reason whose mechanism we do not know, we found that the presence of cereblon and the presence of inflammatory cells showed a negative correlation. In contrast to the protective effect in KO mice without cereblon, we saw nearly fibrinopurulent exudate and abundant PMNL cells in patients without cereblon.
CRBN has a role in chronic inflammation-related conditions and regulates the inflammatory response. CRBN plays a nonenzymatic role in inflammation, leading to suppression of NF-kB activation and increased pro-inflammatory cytokine levels .
A study investigating other mechanisms revealed that the transcriptional activity of the activator protein 1 (AP-1) complex is decreased, and CRBN reduced the mRNA expression and the protein levels of several pro-inflammatory cytokines. The researchers introduced a new molecular mechanism by which CRBN adjusts the inflammatory response and apoptosis. CRBN promotes or inhibits the ubiquitination of two critical molecules at different levels of the inflammatory cascade. So, the inflammatory response is suppressed. LPS is an inflammatory stimulus, and it can also provoke the apoptosis of macrophages. Therefore, modulating the AP-1 signaling pathway can be a promising therapeutic strategy for the treatment of inflammation-associated diseases .
It is known that CRBN is synthesized in the human retinal cell. In an experimental study, the effect of the absence of CRBN on the condition of retinitis was examined. In that study, retinitis was induced in human retinal cells by LPS. IL-6 and MCP-1 proteins are increased mediators in retinitis. IL-6 and MCP-1 protein synthesis is decreased in CRBN knock-down (KD) retinal cells .
In animal studies, CRBN reduced the inflammatory response. However, in our study, as the amount of CRBN in the lung secretion increased, the inflammatory cells decreased. This made us think that the inflammatory response to CRBN might be altered in genetically engineered CRBN KD animals. Other mechanisms may be at play.
CRBN is used as a target port to determine the treatment of inflammatory events and neoplastic diseases. Immunomodulatory drugs (IMiDs) are a class of compounds that can be used to attenuate the inflammatory response. IMiDs such as thalidomide and its structural analogs (lenalidomide, pomalidomide) are also used in cancer therapy, for example, multiple myeloma (MM), myelodysplastic syndrome (MDS) [20, 21].
CRBN has been identified as a mutual direct and major target of IMiDs . A novel CRBN modulator, CC-885, has just been discovered. CC-885, unlike other IMiDs, has a strong anti-solid tumor effect . CC-885 was found to increase the antitumor activity of Volasertib, a drug used in non-small-cell lung cancer (NSCLC). CC-885 works by selectively promoting CRBN, increasing the sensitivity of NSCLC to volasertib. It can be used in combination therapy to treat lung cancer .
The relationship between neoplastic diseases and CRBN has been most extensively investigated in MM. It has been suggested that MM patients with high CRBN expression are sensitive to IMiD treatment and show a good clinical course. Decreased CRBN protein levels have also been reported to be specifically associated with the development of lenalidomide resistance during treatment in 77% of lenalidomide-resistant MM patients [25–27].
Western blot, immunoprecipitation, and immunohistochemistry were used to assess CRBN expression in investigations [28, 29]. Xiu-Bao Chang and colleagues used the full-length human CRBN protein as the antigen to create CRBN-specific monoclonal antibodies (mAbs). These mAbs are extremely specific . A commercial antibody developed for research purposes was used in our study, and there was no problem in negative-positive controls.
Although CRBN increased the response in cancer treatment in these studies, our study found no statistically significant relationship between CRBN expression and clinicopathological and prognostic parameters. This may be because we found lower CRBN synthesis in patients with increased inflammatory response. We could not observe a difference in mortality since this decrease did not contribute to the effect of IMiDs and other drugs used. This situation caused us to question the use of IMiDs like steroids in patients with severe inflammation in BAL. If CRBN, the primary target of IMiDs, is low in these patients, should we use IMiDs such as steroids and risk side effects? In addition, there is a tendency to initiate IMiDs according to the presence of CRBN in cancer patients. However, in non-neoplastic inflammatory events, there is no practice to start treatment based on the presence of CRBN. More comprehensive studies are needed to enlighten these topics.
Because our study coincided with the pandemic period, our intensive care unit served as a corona intensive care unit during the peak periods of the epidemic. This caused us difficulty in finding non-COVID-19 cases. In addition, in this challenging period when the workload of anesthesiologists has increased, patient follow-up for scientific research became a luxury. Temporary assignments, difficulties in supplying materials, loss of motivation of staff, approaching every patient as a possible corona case, and cautious approach to procedures such as tracheal aspiration that cause an increase in the number of droplets were some of these difficulties. Despite all of these, my team continued to work with great motivation.
This study was conducted in non-COVID-19 patients. Due to the pandemic, our intensive care unit served as COVID-19 intensive care in some periods, which caused the prolongation of the case collection process for the research. In this study, some of the patients were in the "sepsis" stage, some in the "severe sepsis" stage, and some in the "septic shock" stage. In future studies, it is recommended to examine patients with sepsis of the same severity. Although there are many publications on Cereblon, there are no similar studies in humans. Therefore, the hypothesis was based on only animal or cell studies in mind. It would be nice if Cereblon could also be investigated in the blood. However, our hospital did not have the necessary materials. In our study, immunohistochemical cytoplasmic Cereblon expression was categorized as present/absent by an experienced pathologist. It is recommended to perform further studies in which digital images are obtained by virtual microscopy and quantitatively graded according to the intensity of staining.