1. Introduction
Nasal polyps (NPs), also known as sinus polyps, are abnormal protrusions of the nasal mucosa that result from recurring local inflammation and gradually develop into a benign swelling of the mucous membranes in the nasal cavity and paranasal sinuses [
1]. The nasal polyp (NP) mucosa is mostly composed of respiratory epithelium, and the submucosal layer shows significant swelling, with the infiltration of inflammatory cells, particularly eosinophils [
2]. The exact cause of nasal polyps is not fully understood, but there have been reports suggesting a potential association with allergic reactions, inflammation, and genetic factors [
1]. While the precise underlying mechanisms remain unclear, these factors are believed to play a role in the development of NPs. It is important to note that these factors are not the sole causes of NPs, and other environmental and individual factors may also contribute to their development. Further research is needed to fully understand the complex mechanisms underlying the formation of NPs.
The treatment of NPs aims to alleviate symptoms caused by the polyps, restore normal nasal function, promote the drainage and ventilation of the sinuses, and prevent recurrence. Treatment options for NPs can be broadly categorized into medication therapy and surgical intervention [
3]. Medication is now known to be effective in treating NPs, where topical corticosteroid sprays are commonly prescribed to reduce inflammation, shrink polyps, and relieve symptoms such as nasal congestion and a runny nose. In some cases, corticosteroids can be injected directly into the polyps to reduce their size; this approach may beneficial for larger polyps [
4]. As another treatment, if the polyps are large or do not respond to medication therapy, surgical removal may be necessary. The goal of surgery is to completely remove the polyps, restore nasal airflow, and improve sinus drainage. Surgical procedures can be performed using traditional open techniques or endoscopic approaches, where a thin tube with a camera is inserted through the nostrils to visualize and remove the NPs [
5].
It is important to note that NPs are often associated with chronic sinusitis. Therefore, managing and treating a sinus inflammation is also an integral part of the overall treatment. Additional medication therapies or treatment modalities may be employed to address sinus inflammations, and a combination of medication therapy and surgery is often used in practice [
1,
5].
Many types of immune cells are involved in NPs pathogenesis. Among these cells present in NPs, fibroblasts are the cell type of the NP architecture that contributes to the formation of NPs [
6]. Fibroblasts are connective tissue cells in all body tissues [
7]. They produce and react to various inflammatory cytokines [
8]. Fibroblasts play a biological role in wound healing, tissue remodeling, angiogenesis, and inflammation [
9,
10]. They are the central mediators of the accumulation of ECM, and cell differentiation and proliferation are caused by long-term tissue damage [
11]. These tissue injuries often stimulate the differentiation of fibroblasts to myofibroblasts, which are involved in the inflammatory reaction to injury [
12]. When activated by profibrotic stimulation, fibroblasts are differentiated into myofibroblasts, resulting in the production of excessive ECM proteins, such as collagen and fibronectin [
13]. The differentiation of fibroblasts into myofibroblasts corresponds to the physiological process that promotes the formation of NPs. [
14]. The fibroblasts present in the NP stroma are NP-derived fibroblasts (NPDFs). The expression of smooth muscle actin is a reliable indicator of myofibroblast differentiation. It has been reported that damage to the mucosal epithelium results in the expression of transforming growth factor-β1 (TGF- β1). [
15]. Increased accumulation of ECM components, mobility and invasion, migration and accumulation, angiogenesis and immune response characterize TGF-β1stimulation [
16,
17]. Furthermore, TGF-β1 is an important profibrotic cytokine associated with fibroblast activation and differentiation [
18]. NPs have shown that they have high levels of TGF-β1 [
19].
Staurosporine (STA) was initially isolated from
Streptomyces staurosporeus in 1977 [
20]. It is known to possess antimicrobial and antihypertensive activities [
21]. The primary biological activity of STA is the inhibition of protein kinase C by preventing ATP from binding to the kinase [
21,
22]. This is achieved through its strong affinity for the ATP-binding site of the kinase. Additionally, STA induces cell apoptosis by activating caspase-3, leading to the arrest of cell division in the G1 or G2 phase [
22,
23]. In clinical studies, liposome nanoparticles encapsulating staurosporine demonstrated anticancer effects without side effects in mouse experiments. While various beneficial effects of STA have been reported through research, there is currently no specific evidence regarding its potential improvement in the treatment of NPs. In this study, we aim to introduce the inhibition effect of STA obtained from marine bacteria isolated from seawater, specifically focusing on its effects on NPs and its underlying mechanisms.
3. Materials and Methods
3.1. Chemical and Reagents
NMR spectra were acquired by containing Me4Si as internal standard using Varian Inova spectrometers, 400 MHz and 100 MHz spectrometers (Varian Medical Systems, Inc., Charlottesville, VA, USA), using solvent chloroform-d (Cambridge Isotope Laboratories (CIL), Inc., Tewksbury, MA, USA). Low-resolution LC-MS measurements were taken using the Agilent Technology 1260 quadrupole (Agilent Technologies, Santa Clara, CA, USA) and Waters Alliance Micromass ZQ LC-MS system (Waters Corp, Milford, MA, USA) using a reversed-phase column (Phenomenex Luna C18 (2) 100 Å, 50 × 4.6 mm, 5 µm) (Phenomenex, Torrance, CA, USA) at a flow rate 1.0 mL/min at the National Research Facilities and Equipment Center (NanoBioEnergy Materials Center, Argonne, IL, USA) at Ewha Womans University.
TGF-β1 was purchased from R&D Systems, Inc. (Minneapolis, MN, USA). We used Cell Counting Kit-8 (CCK-8) manufactured by DOJINDO Laboratories (Rockville, MD, USA). We purchased antibodies against α-SMA and Col-1 from Abcam (USA; catalog number ab5694 and ab88147, respectively). Antibodies against actin and fibronectin were purchased from BD Biosciences (USA; cat. no. 612,656 and 610077, respectively). Antibodies against GAPDH and goat anti-mouse IgG (HRP) conjugate were purchased from Young In Frontier (Korea, cat. no. LF-PA0018 and LF-SA8001, respectively).
3.2. Strains and Culture Conditions
We isolated pure strains from seawater collected near Il-gwang Beach in Gijang-gun, Busan. This seawater was inoculated onto Mar4 solid media (2 g kelp meal, 2 g D-mannitol, 1 g fish meal, 20 g/L KBr, 8 g/L Fe2(SO4)3·4H2O, 30 mL DMSO, 970 mL filtered seawater, and 21 g agar) and cultured at 27 °C. Subsequently, a single strain was isolated and selected by re-inoculating it onto SYP solid media (10 g starch, 4 g yeast, 2 g peptone, 1 L filtered seawater, and 21 g agar) to obtain a pure bacterial strain.
Strain SNC087 was cultured in 36 × 2.5 L Ultra Yield flask each containing 1 L of medium (10 g/L soluble starch, 4 g/L yeast, 2 g/L peptone, and 34.75 g/L artificial sea salt dissolved in distilled H2O) at 27 °C and constantly shaken at 120 rpm. After seven days, the broth was extracted with ethyl acetate (EtOAc) (36 L overall), and the EtOAc-soluble fraction was dried in vacuo to yield 1.23 g of organic extract.
3.3. Isolation and Purification of STA from the SNC087 Strain
The crude extract of SNC087 (1.23 g) was fractionated using a C-18 resin MPLC column (Biotage SNAP Cartridge, KP-SIL) and eluted with a step gradient from 0 to 100% MeOH in H2O to obtain 10 fractions (SCN087-1−SNC087-10). Subfraction eight was isolated using reversed-phase HPLC (Reprosil 100 C-18 10 μm 250 × 20 m, L 250, 7.0 mL/min, and UV = 254 nm) using an isocratic condition 65% MeOH in H2O to obtain staurosporine (1, 41.2 mg, tR = 15.5 min).
Staurosporine (1): light yellow powder; 1H NMR (400 MHz, CDCl3): δH 9.39 (d, J = 88.2 Hz, H-4), 7.89 (overlapped, H-8 and H-11), 7.48 (d, J = 7.1 Hz, H-1) 7.35 (overlapped, H-2 and H-10), 7.30 (overlapped, H-3 and H-9), 6.69 (brs, H-1′), 4.99 (s, H-7), 3.92 (s, H-4′), 3.35 (m, H-3′), 2.36 (s, 3′-NCH3), 1.63 (brs, H-2′), 1.26 (s, H-6′); 13C NMR (100 MHz, CDCl3): δC 173.7 (C-5), 139.9 (C-11a), 136.8 (C-13a), 132.3 (C-7a), 130.9 (C-12a), 127.3 (C-12b), 126.7 (C-4), 125.2 (C-2), 124.8 (C-10), 124.3 (C-7c), 123.7 (C-4a), 120.8 (C-8), 120.1 (C-9), 119.9 (C-3), 118.6 (C-4c), 115.6 (C-11), 115.4 (C-7b), 114.2 (C-4b), 107.1 (C-1), 91.3 (C-5′), 84.2 (C-4′), 80.3 (C-1′), 60.5 (C-4′OCH3), 57.4 (C-3′), 50.5 (C-7), 46.1 (C-3′NCH3), 21.2 (C-6′), 14.3 (C-2′); LR-ESI-MS m/z 467.3 [M+H]+.
3.4. Cell Culture Method
Patients with NPs were recruited, and NPDFs were cultivated as previously reported [
37]. The study was approved by the local ethics committee of Inje University, Busan Paik Hospital, Busan, Republic of Korea (Approval code: 80/2020). The purity of the NPDFs was checked against a panel of antibodies of fibroblast marker (cat. No. ab254015, Abcam Inc., Cambridge, MA, USA) and characteristic cell morphology data. NPDFs were used for 4th to 6th cell passages.
3.5. Cytotoxicity
The cell viability was assessed using the CCK-8 assay. NPDFs (1 × 105 cells/well) were cultured in 96-well microplates using Dulbecco’s Modified Eagle Medium (DMEM). The NPDFs were treated with different concentrations of STA (1, 5, and 10 ng/mL). After 24 h of 37 °C (5% humidified CO2) incubation, 450 nm absorbance analysis was performed using a microplate reader (SpectraMax M2e, Molecular Devices, Sunnyvale, CA, USA). All tests were carried out in triplicate.
3.6. Western Blot Analysis
NPDF lysates were collected in lysis buffer (G-Biosciences, St. Louis, MO, USA) with a protease inhibitor cocktail (Roche Diagnostics, Mannheim, Germany). The same amount of proteins was separated using 10% sodium dodecyl sulfate-polyacrylamide mini-gel electrophoresis and transferred to the nitrocellulose membrane (GE Healthcare Life Sciences, Chalfont, UK). After the night-time incubation of a specific primary antibody (α-SMA, Col-1, fibronectin, and p-Smad 2), the membrane was incubated with a secondary antibody (IgG for goat anti-mouse) conjugated to horseradish peroxidase. Immunoreactive bands were visualized using an enhanced chemiluminescence detection system (Pierce Biotechnology, Inc. Rockford, IL, USA). Band images were captured and analyzed using image systems (AI 600, GE Healthcare Life Sciences, Canton, MA, USA) and ImageJ software (ver. 1.52a; National Institutes of Health, Bethesda, MD, USA).
3.7. Ex Vivo Experiments
NP tissues were cultured with the air–liquid interface organ culture method. As Park et al. reported earlier, NP patients were recruited [
38]. The study was approved by the Local Ethics Committee of the University of Inje, the Busan Hospital, Busan, Korea. NPs were obtained from the middle of the meatus and cut into small pieces (3 mm
3). In order to investigate the inhibition of STA on VEGF expression, tissue fragments were saturated in DMEM for 1 h in the presence or absence of STA (10, 30, and 50 μg/mL). The tissue fragments were then placed on a 1 cm hydrated gelatin sponge (Spongostan, Johnson and Johnson, Austin, TX, USA), with the mucosa facing upwards and the submucosa facing downwards. The gelatin sponge on which the NP tissue was placed was inserted into the well of the six wells containing 3 mL of the culture solution. The plates were placed in a humidified CO
2 incubator of 5% for 24 h.
3.8. Statistical Analysis
All the data in the experiments are presented as mean ± standard error of the mean. All statistical analyses were conducted with GraphPad Prism software (version 5.0; GraphPad Software Inc., La Jolla, CA, USA). Dunnett’s multiple range test was used for groups comparisons.