gingivalis LPS-Induced IL-1β Production by BV-2 Microglia through Suppression of Cathepsins B and L

Cathepsin B (CatB) is thought to be essential for the induction of Porphyromonas gingivalis lipopolysaccharide (Pg LPS)-induced Alzheimer's disease-like pathologies in mice, including interleukin-1β (IL-1β) production and cognitive decline. However, little is known about the role of CatB in Pg virulence factor-induced IL-1β production by microglia. We first subjected IL-1β-luciferase reporter BV-2 microglia to inhibitors of Toll-like receptors (TLRs), IκB kinase, and the NLRP3 inflammasome following stimulation with Pg LPS and outer membrane vesicles (OMVs). To clarify the involvement of CatB, we used several known CatB inhibitors, including CA-074Me, ZRLR, and human β-defensin 3 (hBD3). IL-1β production in BV-2 microglia induced by Pg LPS and OMVs was significantly inhibited by the TLR2 inhibitor C29 and the IκB kinase inhibitor wedelolactonne, but not by the NLRPs inhibitor MCC950. Both hBD3 and CA-074Me significantly inhibited Pg LPS-induced IL-1β production in BV-2 microglia. Although CA-074Me also suppressed OMV-induced IL-1β production, hBD3 did not inhibit it. Furthermore, both hBD3 and CA-074Me significantly blocked Pg LPS-induced nuclear NF-κB p65 translocation and IκBα degradation. In contrast, hBD3 and CA-074Me did not block OMV-induced nuclear NF-κB p65 translocation or IκBα degradation. Furthermore, neither ZRLR, a specific CatB inhibitor, nor shRNA-mediated knockdown of CatB expression had any effect on Pg virulence factor-induced IL-1β production. Interestingly, phagocytosis of OMVs by BV-2 microglia induced IL-1β production. Finally, the structural models generated by AlphaFold indicated that hBD3 can bind to the substrate-binding pocket of CatB, and possibly CatL as well. These results suggest that Pg LPS induces CatB/CatL-dependent synthesis and processing of pro-IL-1β without activation of the NLRP3 inflammasome. In contrast, OMVs promote the synthesis and processing of pro-IL-1β through CatB/CatL-independent phagocytic mechanisms. Thus, hBD3 can improve the IL-1β-associated vicious inflammatory cycle induced by microglia through inhibition of CatB/CatL.

[Preparation of functional polyhydroxyalkanoate microspheres and their antibacterial activity and osteogenic effect evaluation]

Objective

To construct polyhydroxyalkanoate (PHA) microspheres loaded with bone morphogenetic protein 2 (BMP-2) and human β-defensin 3 (HBD3), and evaluate the antibacterial activity of microspheres and the effect of promoting osteogenic differentiation, aiming to provide a new option of material for bone tissue engineering.

Methods

The soybean lecithin (SL)-BMP-2 and SL-HBD3 were prepared by SL-mediated introduction of growth factors into polyesters technology, and the functional microsphere (f-PMS) containing BMP-2 and HBD3 were prepared by microfluidic technology, while pure microsphere (p-PMS) was prepared by the same method as the control. The morphology of microspheres was observed by scanning electron microscopy and the water absorption was detected; the release curves of BMP-2 and HBD3 in f-PMS were detected by ELISA kit. The antibacterial effect of microspheres in Staphylococcus aureus and Escherichia coli was tested with the LIVE/DEADTM BacLightTM bacterial staining kit; the biocompatibility of microspheres was tested using Transwell and cell counting kit 8 (CCK-8). The effect of microspheres on osteogenic differentiation was determined by collagen type Ⅰ (COL-1) immunofluorescence staining and alkaline phosphatase (ALP) concentration.

Results

In this experiment, the f-PMS and p-PMS were successfully constructed. Morphological characteristics showed that p-PMS surface was rough and distributed with micropores of 1-3 μm, while f-PMS surface was smooth and existed white granular material. There was no significant difference in water absorption between the two groups (P>0.05). The release curves of BMP-2 and HBD3 in the f-PMS and p-PMS were basically the same, showing both early sudden release and late slow release. The antibacterial activity of f-PMS was significantly higher than that of p-PMS in the test that against Staphylococcus aureus and Escherichia coli (P<0.05), but there was no significant difference in biocompatibility between the two groups (P>0.05). The results of osteogenic differentiation of human BMSCs showed that the fluorescence intensity of osteogenic specific protein COL-1 of f-PMS was significantly higher than that in p-PMS, and the activity of ALP in f-PMS was also significantly higher than that in p-PMS (P<0.05).

Conclusion

The p-PHA have good antibacterial activity and biocompatibility, and can effectively promote the osteogenic differentiation of human BMSCs, which is expected to be applied to bone tissue engineering in the future.

A novel smaller β-defensin-derived peptide is active against multidrug-resistant bacterial strains

Antibiotic resistance is becoming a severe obstacle in the fight against acute and chronic infectious diseases that accompany most degenerative illnesses from neoplasia to osteo-arthritis and obesity. Currently, the race is on to identify pharmaceutical molecules or combinations of molecules able to prevent or reduce the insurgence and/or progression of infectivity. Attempts to substitute antibiotics with antimicrobial peptides have, thus far, met with little success against multidrug-resistant (MDR) bacterial strains. During the last decade, we designed and studied the activity and features of human β-defensin analogs, which are salt-resistant, and hence active also under high salt concentrations as, for instance, in cystic fibrosis. Herein, we describe the design, synthesis, and major features of a new 21 aa long molecule, peptide γ2. The latter derives from the γ-core of the β-defensin natural molecules, a small fragment of these molecules still bearing high antibacterial activity. We found that peptide γ2, which contains only one disulphide bond, recapitulates most of the biological properties of natural human β-defensins and can also counteract both Gram-positive and Gram-negative MDR bacterial strains and biofilm formation. Moreover, it has great stability in human serum thereby enhancing its antibacterial presence and activity without cytotoxicity in human cells. In conclusion, peptide γ2 is a promising new weapon also in the battle against intractable infectious diseases.

Combined antibacterial and osteogenic in situ effects of a bifunctional titanium alloy with nanoscale hydroxyapatite coating

To resolve the problems of bacterial infections and the low efficiency of osteogenesis of implanted titanium alloys in clinical dental and bone therapy, we developed a bifunctional titanium alloy (Ti) with a nano-hydroxyapatite (HA) coating (HBD + BMP/HA-Ti), which enables the sustained release of the natural antimicrobial peptide human β-defensin 3 (HBD-3) and bone morphogenetic protein-2 (BMP-2). Due to the poriferous nano-sized structure of the HA coating with a 20-30 μm thickness, the HBD + BMP/HA-Ti material had a high encapsulation efficiency (>74%) and exhibited synchronized slow release of HBD-3 and BMP-2. In an antibacterial test, HBD + BMP/HA-Ti prevented the growth of bacteria in an inoculated medium, and its surface remained free from viable bacteria after a continuous incubation with Gram-negative and Gram-positive strains for 7 days. Furthermore, good adhesion, proliferation and osteogenic differentiation of hBMSCs in contact with HBD + BMP/HA-Ti were achieved in 7 days. Therefore, the bifunctional titanium alloy HBD + BMP/HA-Ti has a great potential for eventual applications in the protection of implants against bacteria in the orthopaedic and dental clinic.

Evaluation of the role of human β-defensin 3 in modulation of immunity and inflammatory response after knee replacement

The present study investigated the value of human β-defensin 3 (HBD-3) in adjusting the immunity and inflammatory response of T lymphocytes in the body after knee replacement. Sixty-four cases of knee replacement patients were successively selected and randomly divided into the control group and the observation group each with 32 cases. Once a day, for 7 days, patients in the control group were injected with placebo saline solution in the articular cavity. Levels of Th1 and/Th2, interleukin (IL)-2 and IL-10, tumor necrosis factor (TNF)-α, toll-like receptor (TLR)-4, and alkaline phosphatase (ALP) were compared one month later, and implant infection rates were compared within 1-year follow-up. Compared with patients in the control group, the levels of Th1 and Th1/Th2 in the observation group significantly increased, yet their Th2 decreased. The levels of IL-2 and TNF-α were also observed to be significantly elevated, yet IL-10 decreased. Furthermore, their TLR-4 and ALP levels were significantly higher. Three cases of implant-related infection occurred in the control group and 1 case in the observation group. In conclusion, HBD-3 could adjust the immunity and inflammatory response of cells in the body after knee replacement, possibly playing an important role in implant-related infection.

The mechanism of human β-defensin 3 in MRSA-induced infection of implant drug-resistant bacteria biofilm in the mouse tibial bone marrow

The mechanism of human β-defensin 3 (HBD-3) in methicillin-resistant Staphylococcus aureus (MRSA-induced infection of implant drug-resistant bacteria biofilm in the mouse tibial bone marrow was studied. Healthy adult male Sprague-Dawley rats with average weight of 230 g were selected to construct the infection model of MRSA-induced implant drug-resistant bacteria biofilm in the mouse left tibial bone marrow. The drugs were intraperitoneally injected after 24 h medullary cavity infection, and the experimental groups included the model group, HBD-3 group, and vancomycin group (20 rats in each group). The model group was injected with 10 ml saline, HBD-3 group was injected with 10 ml of 8 µg/ml (1 MIC) and vancomycin group was injected with 10 ml of 0.5 µg/ml (1 MIC), five animals in each group were sacrificed on the 1, 7, 14 and 21 days, respectively. Observation was carried out on whether there was swelling and purulent secretion on the local wound; 1 ml venous sinus blood of eye socket was collected for blood routine examination and blood culture, and the laser scanning confocal microscopy was used to observe the morphology of the biofilm on the implant surface and the number of viable bacteria. Immunohistochemical staining was adopted to test the expression of nuclear factor-κB (NF-κB) and toll-like receptor 4 (TLR-4), and ELISA method was used to test interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α), IL-1α and interferon-γ (INF-γ)-inducible protein-10 (IP-10) expression levels. There was no death due to infection in the HBD-3 group or vancomycin group, 1 case with significant wound swelling was found, respectively, in each group, but there was no purulent secretion. The percentage of the total white blood cells and neutrophil granulocytes as well as the biofilm morphology and the number of viable bacteria in the model group was gradually increased with time, while those in the HBD-3 group and vancomycin group were decreased with time. The comparative difference among groups was statistically significant (P<0.05); those in the HBD-3 group and vancomycin group at each time-point was decreased significantly compared with the model group, and the difference among groups was statistically significant (P<0.05), but in terms of the comparison between the HBD-3 group and vancomycin group, the difference was not significantly different (P>0.05). The NF-κB and TLR-4 expressions in the model group and vancomycin group were not significantly changed at each time-point, those in the HBD-3 group began to increase on the 1st day, and reached the peak on the 7th day and began to decline on the 14th day, and the comparative difference at each time-point was statistically significant (P<0.05); those in the HBD-3 group were significantly higher than the model group and vancomycin group at each time-point and the difference was statistically significant (P<0.05). The IL-10, TNF-α, IL-1α, and IP-10 expressions in the model group at each time were significantly higher than the other two groups and the difference was statistically significant (P<0.05); in terms of the comparison between the HBD-3 group and vancomycin group, the difference was not statistically significant (P>0.05). In conclusion, β-defensin 3 can inhibit the bacterial growth by regulating inflammation and immune responses in the MRSA-induced implant drug-resistant bacteria biofilm infection in the mouse tibial bone marrow.

HBD-3 regulation of the immune response and the LPS/TLR4-mediated signaling pathway

The aim of the study was to investigate the mechanisms of human β-defensin 3 (HBD-3) regulation of the immune response and the lipopolysaccharide/Toll-like receptor-4 (LPS/TLR4)-mediated signaling pathway. A TLR4 extracellular gene fragment was cloned into the pET32a plasmid to determine its expression in Escherichia coli (E. coli) and purification. A dialysis labeling method was used to stain HBD-3 with fluorescein isothiocyanate (FITC). FITC-HBD-3 was used to induce the differentiation of human peripheral blood mononuclear cells (MNC) into immature dendritic cells (imDC) in vitro. Binding reactions were established using FITC-HBD-3 and sTLR4 into cell suspensions. Flow cytometry (FCM) was used to analyze the results. Western blot analysis confirmed the identity of nuclear factor-κB (NF-κB) and was used to quantify its nuclear translocation. The results showed that, HBD-3 bound to imDC in a Ca²⁺-dependent manner, and sTLR4 and LPS competitively inhibited the binding. HBD-3 competitively blocked the binding of LPS and imDC by binding to imDC. HBD-3 significantly decreased the translocation of LPS-induced NF-κB into the nucleus. In conclusion, HBD-3 can competitively inhibit the binding of LPS and imDC through its binding to TLR4 molecules, which are expressed in imDC, thereby preventing LPS from inducing the maturity of the imDCs.