Role of Muramyl Dipeptide in Lipopolysaccharide-Mediated Biological Activity and Osteoclast Activity

Effects of copper exposure on lipid metabolism and SREBP pathway in the Chinese mitten crab Eriocheir sinensis

Copper (Cu) is not only a common metal pollutant in the aquatic environment but also an essential trace element for aquatic organisms such as the Chinese mitten crab (Eriocheir sinensis). Cu is known to regulate lipid metabolism yet exert toxic effects if ingested in excess. However, the molecular regulatory roles of Cu in the lipid metabolism of crabs remains unclear. Thus, this study investigated the potential regulatory mechanism of Cu onto lipid metabolism of E. sinensis following acute Cu exposure. Crabs were exposed to environmental concentration of Cu (50 μg/L) for 96 h, and the expression of sterol regulatory element binding protein (SREBP) was knocked down by RNA interference (RNAi) to test its effect on Cu exposure. The results showed that RNAi significantly attenuated the Cu exposure-induced increase in lipid synthesis and triglycerides (TG) hydrolysis, while significantly inhibited the Cu exposure-induced decrease in fatty acid β-oxidation, suggesting that SREBP is involved in Cu-induced lipid metabolism. Subsequent analyses of the transcriptome results further revealed potential responsive genes of SREBP that were linked to lipid metabolism and immune regulation. Moreover, Cu may affect lipid metabolism through the TOR-SREBP pathway in E. sinensis. This work provides a reference for exploring the effects of Cu on lipid metabolism disorders in crustaceans.

Muramyl dipeptide-based analogs as potential anticancer compounds: Strategies to improve selectivity, biocompatibility, and efficiency

According to the WHO, cancer is the second leading cause of death in the world. This is an important global problem and a major challenge for researchers who have been trying to find an effective anticancer therapy. A large number of newly discovered compounds do not exert selective cytotoxic activity against tumorigenic cells and have too many side effects. Therefore, research on muramyl dipeptide (MDP) analogs has attracted interest due to the urgency for finding more efficient and safe treatments for oncological patients. MDP is a ligand of the cytosolic nucleotide-binding oligomerization domain 2 receptor (NOD2). This molecule is basic structural unit that is responsible for the immune activity of peptidoglycans and exhibits many features that are important for modern medicine. NOD2 is a component of the innate immune system and represents a promising target for enhancing the innate immune response as well as the immune response against cancer cells. For this reason, MDP and its analogs have been widely used for many years not only in the treatment of immunodeficiency diseases but also as adjuvants to support improved vaccine delivery, including for cancer treatment. Unfortunately, in most cases, both the MDP molecule and its synthesized analogs prove to be too pyrogenic and cause serious side effects during their use, which consequently exclude them from direct clinical application. Therefore, intensive research is underway to find analogs of the MDP molecule that will have better biocompatibility and greater effectiveness as anticancer agents and for adjuvant therapy. In this paper, we review the MDP analogs discovered in the last 10 years that show promise for antitumor therapy. The first part of the paper compiles the achievements in the field of anticancer vaccine adjuvant research, which is followed by a description of MDP analogs that exhibit promising anticancer and antiproliferative activity and their structural changes compared to the original MDP molecule.

C‑X‑C receptor 7 agonist acts as a C‑X‑C motif chemokine ligand 12 inhibitor to ameliorate osteoclastogenesis and bone resorption

The C-X-C receptor (CXCR) 7 agonist, VUF11207, is a chemical compound that binds specifically to CXCR7, and negatively regulates C-X-C motif chemokine ligand 12 (CXCL12) and CXCR4-induced cellular events. Lipopolysaccharide (LPS) can induce inflammatory cytokines and pathological bone loss. LPS also induces expression of CXCL12, enhancing sensitivity to receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor-α (TNF-α) in vivo. RANKL and TNF-α induce the differentiation of osteoclasts into osteoclast precursors and bone resorption. The current study was performed to examine the effects of a CXCR7 agonist on osteoclastogenesis and bone resorption induced by LPS in vivo. In addition, the mechanisms underlying these in vivo effects were investigated by in vitro experiments. Eight-week-old male C57BL/6J mice were subcutaneously injected over the calvariae with LPS alone or LPS and CXCR7 agonist. After sacrifice, the number of osteoclasts and the bone resorption area were measured. In vitro experiments were performed to investigate the effects of CXCL12 and CXCR7 agonist on osteoclastogenesis induced by RANKL and TNF-α. Mice injected with LPS and CXCR7 agonist showed significantly reduced osteoclastogenesis and bone resorption compared with mice injected with LPS alone. Moreover, the CXCR7 agonist inhibited CXCL12 enhancement of RANKL- and TNF-α-induced osteoclastogenesis in vitro. Thus, CXCR7 agonist inhibited LPS-induced osteoclast-associated cytokines, such as RANKL and TNF-α, as well as RANKL- and TNF-α-induced osteoclastogenesis in vitro by modulating CXCL12-mediated enhancement of osteoclastogenesis. In conclusion, CXCR7 agonist reduced CXCL12-mediated osteoclastogenesis and bone resorption.

Intestinal Microbial Metabolites in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by inflammation of axial joints and the pelvis. It is known that intestinal dysbiosis may exert direct pathogenic effects on gut homeostasis and may act as a triggering factor for the host innate immune system to activate and cause inflammation in extraintestinal sites in the so-called "gut-joint axis", contributing to AS pathogenesis. However, although the intestinal microbiota's influence on the clinical manifestation of AS is widely accepted, the mechanisms mediating the cross-talk between the intestinal lumen and the immune system are still not completely defined. Recent evidence suggests that the metabolism of microbial species may be a source of metabolites and small molecules participating in the complex network existing between bacteria and host cells. These findings may give inputs for further research of novel pharmacological targets and pave the way to applying dietary interventions to prevent the onset and ameliorate the clinical presentation of the disease. In this review, we discuss the role of some of the biological mediators of microbial origin, with a particular focus on short-chain fatty acids, tryptophan and vitamin B derivatives, and their role in barrier integrity and type 3 immunity in the context of AS.

Regulation of Bone Cell Differentiation and Activation by Microbe-Associated Molecular Patterns

Gut microbiota has emerged as an important regulator of bone homeostasis. In particular, the modulation of innate immunity and bone homeostasis is mediated through the interaction between microbe-associated molecular patterns (MAMPs) and the host pattern recognition receptors including Toll-like receptors and nucleotide-binding oligomerization domains. Pathogenic bacteria such as Porphyromonas gingivalis and Staphylococcus aureus tend to induce bone destruction and cause various inflammatory bone diseases including periodontal diseases, osteomyelitis, and septic arthritis. On the other hand, probiotic bacteria such as Lactobacillus and Bifidobacterium species can prevent bone loss. In addition, bacterial metabolites and various secretory molecules such as short chain fatty acids and cyclic nucleotides can also affect bone homeostasis. This review focuses on the regulation of osteoclast and osteoblast by MAMPs including cell wall components and secretory microbial molecules under in vitro and in vivo conditions. MAMPs could be used as potential molecular targets for treating bone-related diseases such as osteoporosis and periodontal diseases.

Effect of echinalkamide identified from Echinacea purpurea (L.) Moench on the inhibition of osteoclastogenesis and bone resorption

Plant cell cultures have been exploited to provide stable production and new secondary metabolites for better pharmacological activity. Fractionation of adventitious root cultures of Echinacea purpurea resulted in the isolation of eleven constituents, including three new compounds. The structures of the three new compounds were determined to be an alkylamide (1), a polyacetylene (2) and a lignan (3) on the basis of combined spectroscopic analysis. To discover new types of antiresorptive agents, we screened for new compounds that regulate osteoclast differentiation, and survival. Among three new compounds, echinalkamide (compound 1) had considerably inhibitory effects on RANKL-induced osteoclast differentiation, and on proliferation of osteoclasts and efficiently attenuated osteoclastic bone resorption without toxicity. In addition, echinalamide treatment inhibited the osteoclast—specific gene expression level. Echinalkamide achieved this inhibitory effect by disturbing phosphorylation of MAPK and activation of osteoclast transcription factors c-Fos and NFATc1. Conclusionally, our study investigated that echinalkamide remarkably inhibited osteoclast differentiation and osteoclast specific gene expression through repression of the MAPK–c-Fos–NFATC1 cascade.

BCG-Induced Trained Immunity in Healthy Individuals: The Effect of Plasma Muramyl Dipeptide Concentrations

BCG vaccination protects not only against tuberculosis but also against heterologous infections. This effect differs between individuals, yet the factors responsible for this variation are unknown. BCG-induced nonspecific protection is, at least partially, mediated by innate immune reprogramming (trained immunity), which can be induced by the muramyl dipeptide (MDP) component of peptidoglycans. We aimed to study whether differential release of MDP in healthy individuals may explain variability of their response to BCG vaccination. Circulating MDP concentrations were increased up to three months after BCG vaccination. MDP concentrations at baseline, but not their increase postvaccination, positively correlated with the induction of trained immunity and not with mycobacteria-induced T-cell responses. Interestingly, MDP concentrations correlated with inflammatory markers in the circulation. In conclusion, circulating MDP concentrations are associated with the strength of trained immunity responses and thus influence the biological effects of BCG vaccination. This study increases our understanding about the role of MDP in BCG-induced trained immunity, which might help to optimize vaccine efficacy and explore novel applications of BCG vaccination.

[Muramyldipeptide - based compounds in current medicine: focus on glucosaminylmuramyl dipeptide]

The role of immune mechanisms in the pathogenesis of almost all human diseases shown in recent decades, increase in antibiotic resistance and secondary immunodeficiency, aging of the population and widespread use of immunosuppressive drugs and procedures suggest a wider use of immunomodulators in current clinical practice, but the use of most of them limits the lack of knowledge. The most promising compounds for the development as immunomodulating agents and adjuvants for a wide range of vaccines are low molecular weight fragments of peptidoglycan - muramylpeptides. The article describes the mechanisms of action of muramylpeptides, their biological effects and properties of medicines developed on their basis. Special emphasis is placed to glucosaminylmuramyl dipeptide registered in the Russian Federation under the trade name Likopid, which is currently the best - studied drug in its group. The results of Likopid studies when used as a prophylactic and therapeutic agent for infections of various localization in adults and children, for oncological diseases and complications of chemotherapy and radiation therapy, psoriasis, atopic and other diseases are presented. It is emphasized that in diseases associated with human papillomavirus and plaque psoriasis, according to current criteria of evidence - based medicine, Likopid should be classified as drug with level A efficacy (high efficiency in 80-100% of patients). High safety of Likopid in adults and children, including newborns, is noted.