Amyloidosis and the serum amyloid A protein response to muramyl dipeptide analogs and different mycobacterial species

Effect of muramyl peptides on mitochondrial respiration

Muramyl peptides have been shown to exert several biological activities including potentiation of humoral and cell-mediated immunity and stimulation of natural resistance. The mode of action of muramyl peptides has not been elucidated fully and the immunological activities of some derivatives have been associated with toxic effects, including pyrogenicity and inflammatory reactions. Nevertheless, the impact of muramyl peptides on mitochondrial respiration has never been addressed. In this study, the in vitro effects of muramyl peptides on rat liver mitochondria were examined. Toxic muramyl peptides induced a significant decrease in respiratory control ratio versus non-toxic analogues. These results were confirmed by in vivo studies in mice and were extended to mitochondria isolated from spleens. Our data address, for the first time, the effect of muramyl peptides on mitochondrial bioenergetics. Further studies are required to reveal the mechanism of mitochondrial toxicity in relation to the damaging effects of toxic muramyl peptides.

The synthetic immunomodulator murabutide controls human immunodeficiency virus type 1 replication at multiple levels in macrophages and dendritic cells

Macrophages and dendritic cells are known to play an important role in the establishment and persistence of human immunodeficiency virus (HIV) infection. Besides antiretroviral therapy, several immune-based interventions are being evaluated with the aim of achieving better control of virus replication in reservoir cells. Murabutide is a safe synthetic immunomodulator presenting a capacity to enhance nonspecific resistance against viral infections and to target cells of the reticuloendothelial system. In this study, we have examined the ability of Murabutide to control HIV type 1 (HIV-1) replication in acutely infected monocyte-derived macrophages (MDMs) and dendritic cells (MDDCs). Highly significant suppression of viral replication was consistently observed in Murabutide-treated cultures of both cell types. Murabutide did not affect virus entry, reverse transcriptase activity, or early proviral DNA formation in the cytoplasm of infected cells. However, treated MDMs and MDDCs showed a dramatic reduction in nuclear viral two-long terminal repeat circular form and viral mRNA transcripts. This HIV-1-suppressive activity was not mediated by inhibiting cellular DNA synthesis or by activating p38 mitogen-activated protein kinase. Furthermore, Murabutide-stimulated cells expressed reduced CD4 and CCR5 receptors and secreted high levels of beta-chemokines, although neutralization of the released chemokines did not alter the HIV-1-suppressive activity of Murabutide. These results provide evidence that a clinically acceptable immunomodulator can activate multiple effector pathways in macrophages and in dendritic cells, rendering them nonpermissive for HIV-1 replication.

Synergistic effects between recombinant interleukin-2 and the synthetic immunomodulator murabutide: selective enhancement of cytokine release and potentiation of antitumor activity

The use of interleukin-2 (IL-2) in the treatment of cancer has shown limited efficacy and dose-limiting toxicity. Combination therapy with other cytokines and/or chemotherapeutic agents has been attempted to enhance the antitumor activity and to reduce the effective therapeutic dose of IL-2. We recently showed, in vitro and in vivo, a synergistic activity between the synthetic immunomodulator murabutide, which is in clinical stage of development, and another therapeutic cytokine, interferon-alpha (IFN-alpha). The present study was performed to assess a possible potentiation of the biologic activities of IL-2 by its association with murabutide. Human PBMC stimulated in vitro with IL-2 and murabutide showed synergistic levels of induced mRNA accumulation and protein secretion for IFN-gamma, IL-12, and colony-stimulating factors (CSFs). No such effects were obtained on the induction of most inflammatory cytokines, including IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha). Furthermore, the combined administration of murabutide with IL-2 into Meth-A sarcoma-bearing mice resulted in a very significant tumor inhibition as well as in complete tumor regression in nearly 70% of the treated mice. Under the same conditions, treatment with either compound separately had little or no antitumor effect. These preclinical findings will be pursued by the evaluation of the clinical tolerance and biologic activity of the murabutide/IL-2 combination therapy in cancer patients.

Immunopharmacological activities and clinical development of muramyl peptides with particular emphasis on murabutide

Certain immunopharmacological activities of muramyl peptides have been associated with inflammatory and undesirable side-effects typically observed following the administration of the prototype molecule muramyl dipeptide. This activity is now demonstrated not to be linked to a direct activation of inflammatory processes in endothelial cells. Neither MDP nor other structural derivatives were able to induce inflammatory cytokines release or E-selectin gene expression in cultured human umbilical vein endothelial cells. However, oral administration of muramyl peptides has been reported to induce certain biological effects, including the downregulation of anamnestic, antigen-specific IgE responses, which are not observed following parenteral administration. We elaborate on these findings and extend them to show the efficacy of a new muramyl peptide in suppressing polyclonally induced serum IgE levels in anti-IgD-treated mice. The comparative effects of muramyl peptides, selected for clinical development, on the induction of cytokines in human whole blood are then presented at the level of mRNA accumulation and protein secretion. Moreover, the cytokine profile induced in vitro and in vivo by the combination of the safe immunostimulant, Murabutide, with interferon-alpha is examined. This combination reveals a selective and beneficial synergistic activity and induces anti-inflammatory cytokines in the absence of synergistic toxicity. The potential and the implications for the use of a therapeutic combination of an immunostimulant with a cytokine are discussed.

Influence of a muramyl dipeptide on human blood leukocyte functions and their membrane antigens

Murabutide, which belongs to the immunomodulator family of muramyl peptides, was applied directly to fresh human blood to evaluate changes in leukocyte properties. After blood incubation with murabutide, lymphocytes presented a higher responsiveness to T-mitogens, and monocytes and polymorphonuclear cells exhibited an increase in their capacity to produce hydrogen peroxide. In addition, murabutide treatment enhanced phagocytic activity of neutrophils, whereas monocytes presented a decrease in this activity. Some surface markers were also investigated in the distinct leukocyte populations. After incubation with murabutide, a larger number of lymphocytes expressed Ta1 antigen (CD W26) and transferrin receptor (CD 71). In contrast, expression of interleukin-2 receptor (CD 25) was slightly decreased. Monocytes from treated blood displayed a larger number of receptors for C3bi (CD 11b), whereas the surface marker CD 14 and the class I receptor for the Fc portion of IgG were down-regulated. Activation of polymorphonuclear cells by murabutide was confirmed by the up-regulation of the C3bi receptor, Fc receptor, and CD 14 surface antigen. The effects of murabutide on leukocytes described in this paper may contribute to understanding mechanisms of the modulating activity of muramyl peptides on specific and nonspecific immunity.

Endotoxin-associated protein: interleukin-1-like activity on serum amyloid A synthesis and T-lymphocyte activation

Bacterial endotoxins or lipopolysaccharides (LPS) elicit a variety of biologic activities in intact animals and various in vitro systems. LPS from most gram-negative bacteria have appeared to have similar biologic activities regardless of the species of origin or method of preparation of the LPS. More recent studies have suggested differences in the effects of protein-rich as opposed to protein-free LPS in inducing mitogenesis of lymphocytes from endotoxin-resistant C3H/HeJ mice. These studies examine other activities of endotoxin-associated protein (EAP), purified to less than 0.007% contamination with LPS, and demonstrate that this material has activity mimicking some of the effects of interleukin-1 (IL-1). EAP proved to be as potent as LPS in eliciting rises in concentrations of serum amyloid A (SAA) and was active in both endotoxin-sensitive (CF1) and endotoxin-resistant (C3H/HeJ) mice. In contrast to LPS, which mediates its SAA-inducing activity by release of an inducer (IL-1) from LPS-stimulated macrophages, EAP appeared to act directly to induce SAA production, in that incubation with macrophages failed to increase its activity. EAP also exhibited IL-1-like activity in the lymphocyte-activating factor assay when both CF1 and C3H/HeJ thymocytes and macrophages were tested. The lymphocyte-activating factor activity of EAP was not blocked by addition of polymyxin B. In addition, EAP exerted stimulatory activity on resting human T lymphocytes, costimulated with Sepharose-bound anti-CD3 monoclonal antibody 64.1, comparable to that observed with purified human monocyte IL-1. These studies indicate that proteins from procaryotic cells may act as cytokines for some eucaryotic cells.

Bacterial peptidoglycans as modulators of sleep. I. Anhydro forms of muramyl peptides enhance somnogenic potency

Chemically defined muramyl peptides (MPs), derived primarily from enzymatic digests of Neisseria gonorrhoeae peptidoglycan, were used to define the structural determinants of MP-mediated somnogenic activity. One of these, i.e. N-acetylglucosaminyl-N-acetyl-1,6-anhydro-N-acetylmuramyl-alanyl-glutamy l- diaminopimelyl-alanine, was structurally identical to the major naturally occurring MP previously detected in mammalian brain and urine. The somnogenic potency of this MP was similar to that of the corresponding disaccharide pentapeptide containing an additional alanine at the C-terminus and the analogous anhydro-muramic acid-containing monosaccharide tetrapeptide lacking the glucosamine moiety. Infusion of as little as 1 pmol of these highly active MPs increased significantly the percentage of slow-wave sleep in experimental animals. In fact, each of 5 anhydro-muramyl disaccharide peptides tested was somnogenic at a dose of 10 pmol or less and, as far as tested, the activity was affected only slightly by the length or composition of the peptide side chain. However, none of a matched set of analogous MPs, differing only in replacement of the anhydro-muramyl end by a hydrated muramic acid residue, was somnogenic at this dose. A modified form of the hydrated muramyl tripeptide containing a free amide on the diaminopimelic acid residue was completely inactive in amounts up to 1000 pmol. Together, the current data suggested: that the anhydro-muramic acid end (but not the glucosamine moiety) is essential for maximal somnogenic potency; and that amidation of carboxyl groups on the peptide-side chain may block MP-mediated somnogenic activity.

Advances in understanding cell interactions in tissue resorption. Relevance to the pathogenesis of periodontal diseases and a new hypothesis

Much of the connective tissue degradation that takes place in periodontal diseases is mediated by proteolytic enzymes. Previous studies have focused on the action of proteinases released by invading polymorphonuclear neutrophils and macrophages, and bacterial enzymes. In view of recent work establishing that resident connective tissue cells can be induced by cytokines to bring about the destruction of their own matrix, we propose a new hypothesis. In this we envisage that a critical step is the interaction of bacterial antigens with inflammatory cells, resulting in the production of a cytokine, interleukin-1. Our interpretation of in vitro evidence is that the loss of connective tissue attachment and bone matrix resorption in periodontal diseases is mediated by metalloproteinases such as collagenase and stromelysin released by cells of the periodontium. Such proteolytic destruction can be induced by interleukin-1, whose production may not be dependent on a specific microbial flora but may be triggered by a number of organisms. It is now clear that interleukin-1 has multiple actions on both immune and non-immune cells; these include the induction of lymphocyte differentiation and proliferation and the stimulation of bone and cartilage resorption, and prostaglandin and metalloproteinase synthesis by connective tissues. It seems likely that further knowledge about the production and function of this cytokine will have an increasing impact in many diseases that involve resorption, particularly since interleukin-1-like molecules can be produced by cell types other than monocytes/macrophages, including keratinocytes and fibroblasts.

Dissociation between muramyl dipeptide-induced fever and changes in plasma metal levels

A fall in plasma iron level and an increase in copper level were observed in rabbits subsequent with the febrile response induced by an intravenous administration of muramyl dipeptide, AcMur-L-Ala-D-isoGln (MDP). The pyrogenic activity of MDP was due partly to the induction of circulating endogenous pyrogen (EP). EP produced in vitro by activated macrophages also elicited changes in iron and copper levels in rabbits. Nonpyrogenic MDP derivatives murabutide [MDP(Gln)-OnBu] and the stereoisomer of MDP [MDP(D,D)] did not cause any change in blood metal levels. Another adjuvant and nonpyrogenic analogue, murametide [MDP(Gln)-OMe], elicited hypoferremia and hypercupremia. Murametide, which has been previously shown to induce secretion of circulating EP but prevents in vivo fever response, was unable to prevent an EP-induced effect on plasma metal concentrations. Injection of supernatant fluids of macrophages incubated with these different glycopeptides showed that only compounds able to induce EP release were capable of evoking hypoferremia and hypercupremia. The EP-containing fluid was 10-fold more active on change in temperature and in plasma metal levels when it was given intracerebroventricularly compared with intravenously. In contrast, a pyrogenic dose of MDP that can act directly on the central thermoregulatory structures did not modify iron and copper levels when it was injected intracerebroventricularly.

Stimulation of non-specific resistance to infections by synthetic immunoregulatory agents

Muramyl dipeptide or MDP (AcMur-L-Ala-D-iGln) is a synthetic immunoadjuvant which can also enhance non-specific resistance to bacterial infections in mice, even by the oral route. By the use of several derivatives, it has been shown that neither adjuvanticity nor pyrogenicity was a perequisite for eliciting an increased resistance, and that unwanted pharmacological effects can be eliminated by minor chemical modifications. Moreover, some lipophilic analogs or derivatives obtained by linking the glycopeptide to a carrier were found to be more active than MDP. Their effectiveness also depended on the dose and the timing of administration, and varied according to the bacterial challenge. The most appropriately timed administration of MDP and derivatives was established between one and four days before the challenge. In some cases, MDP was protective even when injected one hour after the challenge, whereas with other immunostimulants such as lipopolysaccharides or BCG, a negative phase of higher susceptibility may occur under these conditions. MDP still enhanced resistance to bacterial infections in animals with a poor immune status, like newborns or adult mice under immunosuppressive treatment. Moreover, the protective activity was not impaired after repeated injections of large doses of MDP or other adjuvant analogs, a treatment which is known to inhibit specific immune responses.

The experimental and clinical use of immune-modulating drugs in the prophylaxis and treatment of infections

Therapeutic agents capable of stimulating immune responses could be of great value in the prophylaxis and treatment of infectious diseases. Three classes of compounds, each representing a separate approach to the goal of immune stimulation, are discussed with respect to recent experimental and clinical findings. The action of microbial structures and their derivatives can be understood on the basis of "acquired cellular immunity", a phenomenon first described in connection with infections by mycobacteria and other intracellular organisms. In contrast, there is hardly a common denominator for synthetic compounds which are currently used as immune-stimulatory agents. Substances which influence purine metabolism in lymphocytes on the one hand and histamine H2 blockers such as cimetidine on the other hand seem to represent the most promising developments in this field to date. Products of immune cells such as transfer factor and lymphokines form the third and possibly most important group of immune-stimulating agents. Current experimental and clinical trends in this field are briefly described. It is suggested that the delineation of the mechanism of action of lymphokines will open the door to the identification or synthesis of artificial agonists and antagonists as has been the case in the pharmacology of the endocrine and nervous systems.

Specific absorption with monoclonal antibodies to muramyl dipeptide of the pyrogenic and somnogenic activities of rabbit monokine

It is well established that muramyl dipeptide (MDP) can induce fever and enhance slow-wave sleep. Recently, crude or purified supernatants of activated macrophages containing endogenous pyrogen (EP) were also shown to enhance slow-wave sleep. These similarities and the recent finding that a mammalian factor that enhances slow-wave sleep is a muramyl peptide triggered us to study the possibility of the presence of this bacterial structure in the EP molecule. In the present study, EP was produced by stimulation of rabbit peritoneal cells with a nonpyrogenic, nonsomnogenic analog of MDP. The EP-containing supernatant lost its pyrogenicity and somnogenicity after passage over an immunoadsorbent column of monoclonal anti-MDP but not of another monoclonal antibody of different specificity. High percentage of the EP was recovered by elution of the anti-MDP columns with HCl/glycine buffer. Results suggest that bacterial muramyl peptides may be incorporated by mammalian cells into substances that act in picomole quantities to mediate immunological and physiological processes. In addition, the technique may be useful to extract interleukin 1 for structural studies.

Stimulation of non-specific resistance to infections by synthetic immunoregulatory agents

Muramyl dipeptide or MDP (AcMur-L-Ala-D-iGln) is a synthetic immunoadjuvant which can also enhance non-specific resistance to bacterial infections in mice, even by the oral route. By the use of several derivatives, it has been shown that neither adjuvanticity nor pyrogenicity was a perequisite for eliciting an increased resistance, and that unwanted pharmacological effects can be eliminated by minor chemical modifications. Moreover, some lipophilic analogs or derivatives obtained by linking the glycopeptide to a carrier were found to be more active than MDP. Their effectiveness also depended on the dose and the timing of administration, and varied according to the bacterial challenge. The most appropriately timed administration of MDP and derivatives was established between one and four days before the challenge. In some cases, MDP was protective even when injected one hour after the challenge, whereas with other immunostimulants such as lipopolysaccharides or BCG, a negative phase of higher susceptibility may occur under these conditions. MDP still enhanced resistance to bacterial infections in animals with a poor immune status, like newborns or adult mice under immunosuppressive treatment. Moreover, the protective activity was not impaired after repeated injections of large doses of MDP or other adjuvant analogs, a treatment which is known to inhibit specific immune responses.

The experimental and clinical use of immune-modulating drugs in the prophylaxis and treatment of infections

Therapeutic agents capable of stimulating immune responses could be of great value in the prophylaxis and treatment of infectious diseases. Three classes of compounds, each representing a separate approach to the goal of immune stimulation, are discussed with respect to recent experimental and clinical findings. The action of microbial structures and their derivatives can be understood on the basis of "acquired cellular immunity", a phenomenon first described in connection with infections by mycobacteria and other intracellular organisms. In contrast, there is hardly a common denominator for synthetic compounds which are currently used as immune-stimulatory agents. Substances which influence purine metabolism in lymphocytes on the one hand and histamine H2 blockers such as cimetidine on the other hand seem to represent the most promising developments in this field to date. Products of immune cells such as transfer factor and lymphokines form the third and possibly most important group of immune-stimulating agents. Current experimental and clinical trends in this field are briefly described. It is suggested that the delineation of the mechanism of action of lymphokines will open the door to the identification or synthesis of artificial agonists and antagonists as has been the case in the pharmacology of the endocrine and nervous systems.

Muramyl peptides as possible endogenous immunopharmacological mediators

Synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine, also called MDP for muramyl dipeptide, is a copy of a fragment of bacterial peptidoglycan. Soon after the recognition of MDP as being the minimal subunit responsible for the activity of Freund's complete adjuvant, a great number of derivatives were synthesized. Because of their very low molecular weight it was hoped that they could retain selectively certain of the numerous effects produced by complex bacterial agents. Evidence was gathered showing MDP's direct effect on lymphocytes and on macrophages. The ensuing studies reviewed that MDP and several of its derivatives have marked immunopharmacological and neuropharmacological activities. Thus, besides being adjuvants, they are capable of producing hyperthermia by acting directly on thermoregulation centers or by inducing in vivo and in vitro endogenous pyrogens (EP). More recently, Krueger et al have shown that slow-wave sleep (SWS) factor was a muramyl peptide of a molecular weight close to 1,000 daltons. They have also shown that MDP and several of its synthetic analogs had a somnogenic activity. It has previously been hypothesized that several of the immunological activities of the muramyl peptides could be due to biological mimicry with endogenous products. Recent observations argue in favor of the presence of an MDP bacterial structure in mammalian mediators which increase slow-wave sleep and/or produce fever. The implications of these findings will be discussed.