Somnogenic activity of muramyl peptide-derived immune adjuvants

Role of Glia in the Regulation of Sleep in Health and Disease

Sleep is a naturally occurring physiological state that is required to sustain physical and mental health. Traditionally viewed as strictly regulated by top-down control mechanisms, sleep is now known to also originate locally. Glial cells are emerging as important contributors to the regulation of sleep-wake cycles, locally and among dedicated neural circuits. A few pioneering studies revealed that astrocytes and microglia may influence sleep pressure, duration as well as intensity, but the precise involvement of these two glial cells in the regulation of sleep remains to be fully addressed, across contexts of health and disease. In this overview article, we will first summarize the literature pertaining to the role of astrocytes and microglia in the regulation of sleep under normal physiological conditions. Afterward, we will discuss the beneficial and deleterious consequences of glia-mediated neuroinflammation, whether it is acute, or chronic and associated with brain diseases, on the regulation of sleep. Sleep disturbances are a main comorbidity in neurodegenerative diseases, and in several brain diseases that include pain, epilepsy, and cancer. Identifying the relationships between glia-mediated neuroinflammation, sleep-wake rhythm disruption and brain diseases may have important implications for the treatment of several disorders. © 2020 American Physiological Society. Compr Physiol 10:687-712, 2020.

Bacterial peptidoglycans as novel signaling molecules from microbiota to brain

Mounting evidence indicates that gut microbiota exerts a broad range of effects on host physiology and development beyond the gastrointestinal tract, including the modulation of brain development. However, the mechanisms mediating the interactions between the microbiota and the developing brain are still poorly understood. Pattern recognition receptors of the innate immune system that recognize microbial products, such as peptidoglycans have emerged as potential key regulators of gut microbiome-brain interactions. Peptidoglycan-sensing molecules are expressed in the placenta and brain during specific time windows of development. Moreover, peptidoglycans are ubiquitously present in circulation and can cross the blood brain barrier. This review brings together the current evidence supporting a broad function of peptidoglycans well beyond host's immunity, extending to neurodevelopment and behavior.

More than 70 Years of Pyrogen Detection: Current State and Future Perspectives

In the quality assurance of medical products, tests for sterility are essential. For parenteral pharmaceuticals, avoiding the presence of pyrogens is crucial. These fever-inducing substances (endotoxins and non-endotoxins) are not eliminated by standard sterilisation processes, and are biologically active once in the bloodstream, causing risks to human health, ranging from mild reactions (e.g. fever) to septic shock and death. Therefore, for injectable formulations, pyrogen testing is mandatory. Over the years, various pyrogen testing methods have been introduced, namely: in the 1940s, the rabbit pyrogen test, which is an in vivo test that measures the fever reaction as an endpoint; in the 1970s, the Limulus Amoebocyte Lysate (LAL) test, which is an in vitro test (with the haemolymph of the horseshoe crab) that specifically detects endotoxin; and in 2010, the Monocyte-Activation Test (MAT), which is a non-animal based in vitro pyrogen test that represents a full replacement of the rabbit test. Due to the ubiquity and biological significance of pyrogens, we are currently further developing the MAT so that it can be used for other applications. More specifically, our focus is on the detection of pyrogenic contamination on medical devices, as well as on the measurement of air quality. In addition, further improvements to permit the use of cryopreserved blood in the MAT, to overcome the limitations in the availability of freshly-drawn blood from human donors, are ongoing.

In vitro bioassay of endotoxin using fluorescein as a pH indicator in a macrophage cell culture system

Based on the biological activity of endotoxin, we propose a possible new method for detecting endotoxin using a pH-indication system of macrophage culture media. After RAW 264.7 macrophage cells were treated with lipopolysaccharide (LPS), the addition of fluorescein to the LPS-treated media reproductively reduced its absorption and emission spectra (it was a dose-dependent reduction). The advantages of this LPS-detection method were compared with the Limulus Amebocyte Lysate (LAL) test by using purified bacterial LPS (Salmonella minnessota, Escherichia coli, and Pseudomonas aeruginosa). Additionally, the absorption and fluorescence intensity of fluorescein, following treatment of RAW 264.7 cells with a high concentration of Staphylococcus aureus (Gram-positive, lysed bacteria), could not generally be detected by the LAL test, but they were found to be reduced, in a dose-response relationship, with this new system. The macrophage culture system-method might be a good supplement to the LAL assay for detection of LPS, Gram-negative and Gram-positive bacteria.

"Meshed-Bag Gathered-Bunch" method for solid-phase synthesis of small molecular diverse compounds

A new "Meshed-Bag Gathered-Bunch" technology for the solid-phase synthesis of chemical libraries was developed. Using such technology, we synthesized muramyl dipeptide mimetics including derivatives at the N- and C-terminus, cyclic muramyl dipeptide mimetics, muramyl dipeptide and Tuftsin's analogue conjugates. The advantages of such a method include ease of manufacture, low unit cost of production, the physical encoding method, and the compatibility with both parallel and "split-mix" approaches.

Synergistic epithelial responses to endotoxin and a naturally occurring muramyl peptide

We have investigated the synergistic interactions of a naturally occurring peptidoglycan fragment (muramyl peptide) and bacterial endotoxin in the induction of inflammatory processes within respiratory epithelial cells, at the levels of both signal transduction events and ultimate cellular metabolic effects. The source of the muramyl peptide is Bordetella pertussis, the causative agent of the respiratory disease pertussis. During log-phase growth, B. pertussis releases the muramyl peptide tracheal cytotoxin (TCT), which has the structure N - acetylglucosaminyl - 1,6 - anhydro - N - acetylmuramyl - (L) - alanyl - gamma - (D) - glutamyl - meso - diaminopimelyl - (D) - alanine, equivalent to a monomeric subunit of gram-negative bacterial peptidoglycan. When applied to hamster trachea epithelial (HTE) cells, TCT and endotoxin were found to be highly synergistic in the induction of interleukin-1alpha (IL-1alpha), type II (inducible) nitric oxide synthase (iNOS), nitric oxide production, and inhibition of DNA synthesis. Neither molecule alone significantly triggered these responses. The serine/threonine protein kinase inhibitor H7 blocked induction of both IL-1alpha and iNOS. More selective inhibitors of protein kinase C, cyclic AMP-dependent protein kinase, and cyclic GMP-dependent protein kinase were not capable of blocking the effects of TCT and endotoxin, suggesting that the H7-inhibited component in this pathway is not among the commonly described kinase targets of H7. Treatment of HTE cells with exogenous IL-1 reproduced the induction of iNOS and DNA synthesis inhibition caused by TCT and endotoxin. H7 was not capable of interfering with effects caused by exogenous IL-1, implying that the H7-sensitive step in the pathway is upstream of IL-1 protein production. Similar assays with the phorbol ester phorbol myristate acetate indicate that it could effectively synergize with endotoxin but not with TCT, suggesting that TCT and endotoxin induce different signal transduction events that combine synergistically. The synergy observed with TCT and endotoxin in epithelial cells is significantly different from their interaction with other cell types, revealing a unique inflammatory response by epithelial cells to these natural bacterial products.

A comparative study of Mono Mac 6 cells, isolated mononuclear cells and Limulus amoebocyte lysate assay in pyrogen testing

Pyrogen induced secretion of interleukin 6 (IL-6) in Mono Mac 6 (MM6) cells was measured. The ability of the MM6 cell culture to detect pyrogens was compared to the Limulus amoebocyte lysate (LAL) test and isolated mononuclear cells (MNC). The detection limit of MM6 for lipopolysaccharide (LPS) and Staphylococcus aureus was comparable to that of MNC. Aspergillus niger and Candida albicans induced IL-6 in isolated MNC, but not in MM6. The detection limit for Salmonella typhimurium in the MM6 assay was comparable to that of the LAL assay. As expected, S. aureus and C. albicans did not show any LAL activity. A. niger and Influenza virus showed some activity in the LAL test, but could not be detected by MM6 cells. In conclusion, the MM6 assay is a good supplement to the current pyrogen assays for detection of LPS, S. aureus and S. typhimurium, but the MM6 assay could not detect A. niger, C. albicans and Influenza virus.

Effects of muramyl peptides on macrophages, monokines, and sleep

Muramyl peptides are fragments of peptidoglycan from the cell walls of bacteria. Because of their unique chemistry, the immune system recognizes that muramyl peptides are products of bacteria, and it responds by becoming activated to resist infection. This resistance to infection is nonspecific, and extends to unrelated species of bacteria, fungi, and viruses. A key mechanism of the resistance to infection is activation of macrophages. Macrophage activation results in increased production of microbicidal oxygen radicals like superoxide and peroxide, and in increased secretion of inflammatory cytokines like interleukin-1beta and tumor necrosis factor-alpha. These cytokines, besides activating neutrophils, B lymphocytes, and T lymphocytes, act on the central nervous system to induce physiological responses like fever and sleep. These physiological responses also aid in combating infection. Muramyl peptides also activate macrophages and other cells of the immune system to kill cancer cells. Muramyl peptides and similar agents will become more important as therapeutic agents in the future, due to increasing resistance of microbes to antibiotics, and increasing numbers of patients with immunodeficiencies.