Stimulatory effect of N-acetyl Muramyl dipeptide in vivo: proliferation of bone marrow progenitor cells in mice

Regulation of Immune Homeostasis via Muramyl Peptides-Low Molecular Weight Bioregulators of Bacterial Origin

Metabolites and fragments of bacterial cells play an important role in the formation of immune homeostasis. Formed in the course of evolution, symbiotic relationships between microorganisms and a macroorganism are manifested, in particular, in the regulation of numerous physiological functions of the human body by the innate immunity receptors. Low molecular weight bioregulators of bacterial origin have recently attracted more and more attention as drugs in the prevention and composition of complex therapy for a wide range of diseases of bacterial and viral etiology. Signaling networks show cascades of causal relationships of deterministic phenomena that support the homeostasis of multicellular organisms at different levels. To create networks, data from numerous biomedical and clinical research databases were used to prepare expert systems for use in pharmacological and biomedical research with an emphasis on muramyl dipeptides. Muramyl peptides are the fragments of the cell wall of Gram-positive and Gram-negative bacteria. Binding of muramyl peptides with intracellular NOD2 receptors is crucial for an immune response on pathogens. Depending on the microenvironment and duration of action, muramyl peptides possess positive or negative regulation of inflammation. Other factors, such as genetic, pollutions, method of application and stress also contribute and should be taken into account. A system biology approach should be used in order to systemize all experimental data for rigorous analysis, with the aim of understanding intrinsic pathways of homeostasis, in order to define precise medicine therapy and drug design.

A Combination of Muramylpeptides from Gram-Negative Bacteria Corrects Hematological and Immunological Disorders Induced by Cyclophosphamide

We have studied the effect of a combination of three natural muramylpeptides containing a meso-diaminopimelic acid residue (polyramyl) on the subpopulations of circulating T cells, spleen morphology, and leukocyte level in the blood of C57Bl/6 mice with cyclophosphamideinduced immunosuppression. Intraperitoneal injections of cyclophosphamide in a dose of 100 mg/kg on days 1, 3, 5, and 7 of the experiment reduced leukocyte count and the relative number of CD4⁺ T cells in the blood, and also depleted the cellular composition of splenic white pulp on day 10. Subcutaneous injections of polyramyl in a dose of 200 μg/mouse on days 8 and 9 practically completely restored blood leukocytes count and morphology of the splenic white pulp. Moreover, administration of polyramyl induced marked tendency to increase in the relative number of CD4⁺ T cells and CD4/CD8 ratio in mice with cyclophosphamideinduced immunosuppression.

Bacterial interference with immunospecific defences

There are many descriptions of bacterial agents that can suppress different phases of specific immunity. Bacterial agents are frequently employed as tools to modulate the immune system in experimental models or clinical therapy. Little attention has been given to the implications of such immunoregulating properties for infectious processes or for the natural role of the microbial flora in the normal regulation of the immune system. There are very few studies attempting to investigate directly the possible role of bacterial immunosuppressant factors in acute infection. Several examples of natural and experimental chronic infections have been described in which progressive uncontrolled infection is associated with a depressed cell mediated immunity, but a causal relation is unproven. This depression is usually not antigenically specific and there is some evidence that it may be initiated and maintained by persistent cell-wall components of the microorganisms. The bacteria implicated in suppression are all facultative or obligate intracellular parasites that can multiply and survive in the monocyte/macrophage. Bacterial immunosuppressants may have a crucial role in the pathogenesis of progressive chronic inflammation that occurs after infection.

Effect of cisplatin administration on the proliferation and differentiation of bone marrow cells of tumour-bearing mice

In the present study the effect of tumour growth with respect to two tumour systems (Dalton's lymphoma [DL] and P815) on the in vitro, colony-forming ability (CFA) and proliferation of the bone marrow cells (BMC) of C3H/He mice was investigated. The P815-bearing mice showed an enhanced bone marrow colony forming ability in vitro, in response to L929 conditioned medium (L929 CM) used as a source of CSF. On the other hand, DL-bearing mice did not have any significant alteration in this process compared to normal mice. In vivo, administration of cisplatin resulted in a significant rise in the CFA of normal as well as DL- or P815-bearing mice. The tumour-conditioned medium (TCM) and ascitic fluid (AF) of P815 but not of DL, was found to support the in vitro colony formation of BMC obtained from cisplatin-treated or untreated mice. The number of CFU-granulocyte-macrophage was predominantly high in the cultures of BMC incubated with TCM or AF of P815. The TCM and AF of P815 also enhanced the in vitro proliferation of BMC obtained from cisplatin-treated or untreated mice. In vivo, administration of cisplatin in normal mice resulted in enhanced numbers of peritoneal exudate macrophages (PEM) and PBL. Similarly, the number of PEM and PBL was augmented in both the P815- and DL-bearing mice. However, cisplatin administration in the tumour-bearing mice decreased the count of PEM, while the number of leucocytes remain unaffected. This study indicates that the cancer chemotherapeutic drug cisplatin can influence the differentiation of the bone marrow progenitor cells in response to tumour growth in situ.

Liposomal muramyl tripeptide phosphatidylethanolamine (MTP-PE) promotes haemopoietic recovery in irradiated mouse

Pretreatment of C57B1/6 mouse with the macrophage activator muramyl tripeptide phosphatidylethanolamine encapsulated in liposomes (MTP-PE/MLV) induced haemopoietic recovery in subsequently irradiated mouse. An optimal endoCFU-S survival was observed when 200 micrograms MTP-PE/MLV was administered i.p. 24 h before irradiation. MTP-PE/MLV did not affect the day 8 exogenous CFU-S survival in the bone marrow immediately after irradiation. However, 3, 6, 9 and 14 days after irradiation the number of day 8 CFU-S was almost 2 to 4-fold higher in the bone marrow of the MTP-PE/MLV injected mouse. Also, recovery of the GM-CFC pools in femoral bone marrow after irradiation proceeded at a faster rate in the MTP-PE/MLV-treated animal than in control groups. After a single i.p. injection of MTP-PE/MLV to the non-irradiated mouse, the number of CFU-S in bone marrow was not significantly different from controls, whereas the number of GM-CSC was significantly increased. In addition, the percentage of day 8 CFU-S and GM-CFC in S-phase of the cell cycle was significantly increased, as was colony-stimulating activity present in the serum of treated animals. Pretreatment with MTP-PE/MLV protected the C57Bl/6 mouse in a dose-dependent manner from the lethal effects of ionizing radiation. A single dose (100 or 200 micrograms) injected i.p. 24 h, or 100 micrograms MTP-PE/MLV injected i.v. 24 h before 9.5 Gy gamma-rays protected 47, 85 and 59% of C57B1/6 mouse, respectively. The dose reduction factor in the case when the MTP-PE/MLV (200 micrograms per mouse) was administered i.p. at that time was 1.17 (95% CL 1.13, 1.21). Combined administration of MTP-PE/MLV (24 h) and indomethacin (24 and 3 h) to mouse prior to irradiation exerted an additional radioprotective effect.

Effect of in vivo administration of cisplatin on the colony forming ability of murine bone marrow cells

In vitro colony forming ability of bone marrow cells obtained from cisplatin-treated C3H/He mice was studied. Mice were administered cisplatin in a single intraperitoneal dose of 10 mg/kg body wt, 24 h prior to the harvest of femoral bone marrow cells. Incubation of untreated bone marrow cells without any CSF in vitro showed little colony forming ability which was marginally enhanced in cisplatin-treated bone marrow cells. Presence of M-CSF (250 U/ml) or GM-CSF (250 U/ml) in the culture medium significantly augmented the colony forming ability of both untreated and cisplatin-treated bone marrow cells. In the presence of M-CSF, colony forming units-macrophage (CFU-M) were predominantly high in untreated bone marrow cells, followed with CFU-granulocyte-macrophage (CFU-GM). The number of CFU-M was significantly up-regulated in response to M-CSF in bone marrow cells obtained from cisplatin administered mice, whereas the number of CFU-GM remained unchanged, as compared to untreated mice. Both CFU-M and CFU-GM were enhanced in the presence of GM-CSF in untreated bone marrow cells. Cisplatin-treated bone marrow cells on incubation in the presence of GM-CSF showed a significant enhancement of CFU-M and GM as compared to untreated samples. IL-1 (100 U/ml) in the presence of M-CSF significantly up-regulated colony forming ability of cisplatin-treated bone marrow cells, whereas TNF (100 U/ml) inhibited the colony forming ability.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulant effect of the immunomodulator MTP-PE on proliferation of monocytic cells in the guinea pig

The effect of a single subcutaneous injection of various doses of the lipophilic muramyl tripeptide MTP-PE on cell proliferation was investigated in autoradiographs of histological sections of various organs of the guinea pig. The animals either received first MTP-PE in saline and then one 3H-thymidine pulse 1 h prior to sacrifice, or they were prelabeled with 3H-thymidine and then received MTP-PE. The number of proliferating cells increased up to between two and fivefold (marginally after 0.3 mg/kg and maximally after 30 mg/kg MTP-PE), but differed in the various organs. In addition, the time of the maximal increase varied between 5 h and 72 h after MTP-PE treatment and also depended on the organ. The majority of proliferating cells were of the monocyte lineage seen in conjunction with the vascular system. They were apparently promonocytes still capable of proliferation. Evidence for this conclusion is derived from (i) the distribution of 1 h-pulse-labeled cells in the various organ compartments in relation to the stimulated proliferation of the bone-marrow cells, and (ii) the distribution of the prelabeled, mainly bone-marrow derived cells, to the various organs. The augmented proliferation of the monocyte lineage is preceded by a dose-dependent, short-lasting increase in the proliferation of some epithelia and also by an increase in body temperature and a transient change in plasma proteins. These effects are part of a limited inflammatory reaction and may contribute to the immunostimulation.

Systemic injection of group A streptococcal peptidoglycan-polysaccharide complexes elicits persistent neutrophilia and monocytosis associated with polyarthritis in rats

The perpetuation of inflammatory changes within joints elicited by persisting, poorly biodegradable group A streptococcal cell walls (peptidoglycan-polysaccharide complexes [PG-PS]) is well documented. Chronic changes in the bloodstream induced by PG-PS have not been described previously. We demonstrated that leukocytosis occurs within 3 days after intraperitoneal injection of PG-PS and remains elevated 20 weeks later. Chronic neutrophilia, monocytosis, and lymphocytosis were observed in all experiments. Chronic changes in platelet, erythrocyte, and reticulocyte counts were not seen. The newly documented leukocytosis, lasting for months after PG-PS administration, provided a circulating pool of leukocytes that may participate in chronic inflammatory events in the joint. Although the central role of the macrophage in PG-PS-mediated inflammation has been emphasized (F. G. Dalldorf, W. J. Cromartie, S. K. Anderle, R. L. Clark, and J. H. Schwab, Am. J. Pathol. 100:383-402, 1980), the polymorphonuclear cell may be involved in periods of exacerbation of streptococcal cell wall-mediated polyarthritis. This was supported by our observations that neutrophilia and monocytosis correlate well with the degree of chronic joint inflammation.

Characterization and biological implications of membrane lectins in tumor, lymphoid and myeloid cells

Complex carbohydrates and sugar receptors at the surface of eukaryotic cells are involved in recognition phenomena. Membrane lectins have been characterized, using biochemical, biological and cytological methods. Their biological activities have been assessed using labeled glycoproteins or neoglycoproteins. Specific glycoproteins or neoglycoproteins have been used to inhibit their binding capacity in both in vitro and in vivo experiments. In adults, lymphoid and myeloid cells as well as tumor cells grow in a given organ and eventually migrate and home in another organ; these phenomena are known as the homing process or metastasis, respectively. In specific cases, membrane lectins of endothelial cells recognize cell surface glycoconjugates of lymphocytes or tumor cells, while membrane lectins of lymphocytes and of tumor cells recognize glycoconjugates of extracellular matrices or of non-migrating cells. Therefore, membrane lectins are involved in cell-cell recognition phenomena. Membrane lectins are also involved in endocytosis and intracellular traffic of glycoconjugates. This property has been demonstrated not only in hepatocytes, fibroblasts, macrophages and histiocytes but also in tumor cells, monocytes, thyrocytes, etc. Upon endocytosis, membrane lectins are present in endosomes, whose luminal pH rapidly decreases. In cells such as tumor cells or macrophages, endosomes fuse with lysosomes; it is therefore possible to target cytotoxic drugs or activators, by binding them to specific glycoconjugates or neoglycoproteins through a linkage specifically hydrolyzed by lysosomal enzymes. In cells such as monocytes, the delivery of glycoconjugates to lysosomes is not active; in this case, it would be preferable to use an acid-labile linkage. Cell surface membrane lectins are developmentally regulated; they are present at given stages of differentiation and of malignant transformation. Cell surface membrane lectins usually bind glycoconjugates at neutral pH but not in acidic medium: their ligand is released in acidic specialized organelles; the internalized ligand may be then delivered into lysosomes, while the membrane lectin is recycled. Some membrane lectins, however, do bind their ligand in relatively acidic medium as in the case of thyrocytes. The presence of cell surface membrane lectins which recognize specific sugar moieties opens the way to interesting applications: for instance, isolation of cell subpopulations such as human suppressor T cells, targeting of anti-tumor or anti-viral drugs, targeting of immunomodulators or biological response modifiers.

Immunopotentiating activities of a low molecular weight lipopeptide, RP 56 142--studies in infectious models

RP 56 142, N2-[N-(N-lauroyl-L-alanyl)-gamma-D glutamyl] L,L-2,6-diaminopimelamic acid belongs to a family of immunomodulating lipopeptides. Its structure is directly derived from that of lauroyltetrapeptide RP 40 639 which is a mixture of two stereoisomers, one of which (with D,D-2,6 diaminopimelamic acid) is totally devoid of in vivo activity. RP 56 142 displayed potent protective activities against bacterial infections such as K. pneumoniae, L. monocytogenes or S. typhimurium (at doses ranging between 0.03 and 100 mg/kg s.c., i.p., i.v.). In combined treatment protocols, suboptimal doses of RP 56 142 given preventively (day-1) or curatively (day 0 + 4h) significantly protected mice receiving antibiotics at doses which were ineffective when administered by themselves. Given s.c. 1 or 2 days before infectious challenge, RP 56 142 was able to normalize and even enhance significantly the resistance of mice previously immunocompromised by lomustine, 5-fluorouracile or hydrocortisone. These results correlated with the stimulation of the clearance of a virulent Salmonella typhimurium strain and with an important production of colony-stimulating factor in RP 56 142-treated mice.

Stimulation of cell proliferation in rabbits by MTP-PE, a lipophilic muramyl peptide

The in vivo effect of the lipophilic muramyl peptide MTP-PE on the proliferation of blood cells and various tissues of the rabbit was studied by means of 3H-thymidine. Animals were killed up to 120 h after one or two i.v. injections of MTP-PE (10 mg/kg). MTP-PE caused a drastic effect on white blood cells: (1) neutropenia and lymphocytopenia occurring within 5 h was followed by leukocytosis of neutrophils and their juvenile forms by 24 h and thereafter, (2) within 24 h the number of prelabelled, i.e. recently regenerated, mononuclear cells in the bone marrow and the vascular system of various tissues increased approximately threefold, and (3) within 48 h the concentration of proliferating monocytic cells (1-h pulse labelling) rose to maximum levels of up to 20-fold in the lumina of blood vessels, particularly in capillaries of many organs. The number of proliferating cells also increased in the adventitia of medium and small arteries with a maximum at 48 h, whereas this occurred only later in the media and hardly at all in the intima. Thus, these proliferating, apparently monocytic cells are blood derived, and migrate into the tissue within 24 h after MTP-PE administration. In addition, proliferation in the epithelium of the bile ducts and oesophagus was also stimulated with a maximum at 24 h after MTP-PE. In contrast, enhanced proliferation occurred more slowly and to a lesser extent in hepatocytes, hepatic interstitial cells, and renal epithelial cells, consistent with a regenerative process after an inflammatory or toxic event.

Granuloma formation by muramyl dipeptide associated with branched fatty acids, a structure probably essential for tubercle formation by Mycobacterium tuberculosis

Muramyl dipeptide, which does not induce epithelioid granuloma when injected alone dissolved in phosphate-buffered saline, could induce extensive granulomas in guinea pigs when chemically conjugated with branched, but not linear, fatty acids. Peptidoglycan fragments of Staphylococcus epidermidis could evoke epithelioid granulomas when incorporated in a water-in-oil emulsion. These findings suggest the importance of a lipid bound to muramyl dipeptide for granuloma formation. In view of the fact that mycobacteria uniquely contain large amounts of branched fatty acids, it was proposed that the complex of muramyl dipeptide and branched fatty acids, mostly mycolic acids, is a structure in tubercle bacilli responsible for tubercle formation.

Muramyl dipeptide increases tolerance to shock and bacterial challenge in mice

We measured the phagocytic capacity of the reticulo-endothelial system by assay of the clearance of colloidal carbon from the blood stream in both normal mice and mice in which shock had been induced by intraperitoneal injection of hypertonic glucose. The group of shocked mice was further subdivided into those pretreated with the immunoadjuvant, muramyl dipeptide (MDP), and those given placebo. Shock reduced reticulo-endothelial phagocytosis (P less than 0.01), whereas pretreatment of shocked mice with MDP led to a hyperphagocytic state (P less than 0.01). In a second series of experiments we subjected shocked mice, pretreated with MDP or placebo, to a virulent Klebsiella pneumoniae infection. MDP significantly improved survival (P less than 0.01).

Modulation of myelopoiesis in vivo by synthetic adjuvant-active muramyl peptides: induction of colony-stimulating activity and stimulation of stem cell proliferation

Modulation of myelopoiesis by three synthetic muramyl peptides was investigated in vivo. Two adjuvant-active compounds (N-acetylmuramyl dipeptide [MDP] and MDP-butyl-ester) elicited significant responses in DBA/2 mice characterized by a rise in the level of monocyte-macrophage colony-stimulating activity in serum, a proliferation of multipotential stem cells in the bone marrow, and an expansion of granulocyte-macrophage progenitors in the spleen. In contrast, the adjuvant-inactive stereoisomer MDP(D-D) induced only low levels of circulating colony-stimulating activity. Thus, MDP or MDP-butyl-ester injection could induce a greater number of macrophages and therefore enhance both specific and nonspecific immunity.

Muramyl dipeptides: prospect for cancer treatments and immunostimulation

The immunopharmacological activities of bacterial cell walls and muramyl peptides were collected in table form with a comprehensive literature. The past and present studies emphasizing the host-defense enhancing activities of muramyl peptides for antitumor immunotherapy were surveyed along three possible approaches: 1) the nonspecific enhancement of natural defense ability of host against tumor cells themselves; 2) the enhancement of nonspecific resistance of host to microbial infections which are frequently encountered and difficult to treat in the advanced stage of tumor patients; and 3) the stimulation of immunity against tumor-specific or tumor-associated immunogens. Finally, the prospects of successful antitumor immunotherapy with muramyl peptides and their derivatives was discussed.