Evaluating the antibacterial activity of muramyl dipeptide derivatives, retro-tuftsin derivatives, and anthraquinone oligopeptides against a range of pathogenic bacteria

Search for new and efficient antibiotic is crucial because of microbial drug resistance and problems with side effects of the administered medication. In this study, we evaluate the in vitro microbiological activity of muramyl dipeptide derivatives, retro-tuftsin derivatives (i.e., tuftsin with reversed amino acid sequences), and combinations of retro-tuftsin derivatives with substituted anthraquinones. The potency of the investigated derivatives towards methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae ESBL (extended-spectrum β-lactamases) was compared based on the spectroscopically-measured minimal inhibitory concentrations (MIC values). The bacterial growth have also been studied with different concentrations of compounds. Statistical analysis of the results revealed that certain modifications lead to promising activity against S. aureus (anthraquinone analogue - 3c and retro-tuftsin derivative - 2b), while other derivatives exhibit activity against P. aeruginosa (muramyl dipeptide derivative - 1d and retro-tuftsin derivative - 2b). The obtained results of microbiological activity indicate that the structure of the tested compounds may be the basis for further modifications.

In vitro biological evaluation of new antimycobacterial salicylanilide-tuftsin conjugates

Tuberculosis is caused by Mycobacterium tuberculosis, an intracellular pathogen that can survive in host cells, mainly in macrophages. An increase of multidrug-resistant tuberculosis qualifies this infectious disease as a major public health problem worldwide. The cellular uptake of the antimycobacterial agents by infected host cells is limited. Our approach is to enhance the cellular uptake of the antituberculars by target cell-directed delivery using drug-peptide conjugates to achieve an increased intracellular efficacy. In this study, salicylanilide derivatives (2-hydroxy-N-phenylbenzamides) with remarkable antimycobacterial activity were conjugated to macrophage receptor specific tuftsin based peptide carriers through oxime bond directly or by insertion of a GFLG tetrapeptide spacer. We have found that the in vitro antimycobacterial activity of the salicylanilides against M. tuberculosis H₃₇Rv is preserved in the conjugates. While the free drug was ineffective on infected macrophage model, the conjugates were active against the intracellular bacteria. The fluorescently labelled peptide carriers that were modified with different fatty acid side chains showed outstanding cellular uptake rate to the macrophage model cells. The conjugation of the salicylanilides to tuftsin based carriers reduced or abolished the in vitro cytostatic activity of the free drugs with the exception of the palmitoylated conjugates. The conjugates degraded in the presence of rat liver lysosomal homogenate leading to the formation of an oxime bond-linked salicylanilide-amino acid fragment as the smallest active metabolite.

The temporary dynamics of inflammation-related genes expression under tuftsin analog Selank action

Previous studies have shown that synthetic tuftsin analogue Selank and its fragments cause a number of alterations in the expression of certain genes involved in inflammation in mouse spleen. In this work we studied the effect of Selank and its short fragment Gly-Pro on the temporary dynamics of C3, Casp1, Il2rg, and Xcr1 genes expression in mouse spleen after single intraperitoneal injection (100 μg/kg) of peptides using real-time PCR method. We found a significant 3-fold decrease in the C3 mRNA level just 30 min after Selank injection and similar alteration this gene mRNA level after Gly-Pro administration. A wave-like alteration in the Casp1 mRNA level was observed after Selank injection. We found a significant alteration in the mRNA level of the Il2rg gene at early time points after Selank and Gly-Pro administration and an almost equal reduction in the Xcr1 mRNA level 90 min after the administration of Selank and its fragment. Our results showed that, Selank and its short fragment Gly-Pro influence the expression of genes that mediate different types of immune responses, thereby maintaining the balance of the immune system. It should be noted that in most cases, there was a coincidence in the expression profiles of the studied genes after Selank and Gly-Pro administration. This might indicate an active contribution of the dipeptide to the final effect of Selank.

[Tuftsin--new analogues and properties]

Tuftsin, a natural tetrapeptide of sequence TKPR, occuring in the blood of humans and other mammals, capable of stimulating certain white blood cells (monocytes, macrophages, and neutrophils), was isolated at Tufts University in 1970 by Najjar and Nishioka. Tuftsin is a compound with a wide spectrum of biological activities, notable enhances phagocytosis, immune response, bactericidal, tumoricidal and antifungal activities. This article concerns new analogues and properties of tuftsin.

Immunomodulatory properties of new conjugates of muramyl dipeptide and nor-muramyl dipeptide with retro-tuftsin (Arg-Pro-Lys-Thr-OMe)

Six new conjugates of muramyl dipeptide and nor-muramyl dipeptide with retro-tuftsin were synthesised at Gdansk University of Technology. All compounds were investigated at Medical University of Gdansk. Their immunomodulatory properties were assessed using in vitro cultures of human subpopulations of white blood cells (peripheral blood mononuclear cells, peripheral blood lymphocytes, monocytes). We examined the viability of blood cells incubated with examined conjugates, as well as their ability to stimulate secretion of cytokines (TNFalpha--tumour necrosis factor alpha, IL6--interleukin 6) and cytotoxic activity of NK (Natural Killer) cells. Complementation in biological activity of muramyl dipeptide (MDP) and tuftsin in conjugates proved to be beneficial in the field of immunoadjuvanticity. Our investigations proved that new conjugates acquired features that native immunomodulators did not reveal separately. In examined compound, the part responsible for inducing cytotoxic activity of NK cells was the tuftsin part of the conjugates. MDP in conjugates was responsible for compound-induced synthesis of TNFalpha. The results of our study imply usefulness of the examine compounds (mainly A and B), as potential therapeutic agents.

The biological activity of new tuftsin derivatives--induction of phagocytosis

Phagocytosis plays a crucial role in a host defense against invading microorganisms. This process can be induced by many phagocytosis stimulating factors. One of them is an endogenous tetrapeptide - tuftsin that occurs in the blood of mammals including human beings. Tuftsin is capable of potentiating granulocyte and macrophage functions such as: phagocytosis, motility, and chemotaxis as well as bactericidal and tumoricidal activity. The other particle able to induce phagocytosis is muramyl dipeptide (MDP), the smallest synthetic glycopeptide of bacterial origin that possesses an immunogenic activity. MDP is known to affect most functions of macrophages. Phagocytosis stimulating properties of a new group of tuftsin and MDP analogues (one tuftsin analogue and four conjugates of tuftsin/retro tuftsin and muramyl dipeptide or nor-muramyl dipeptide) were tested. The results of the study show that all of the examined conjugates are able to generate oxidative burst. The most promising analogues proved to be kd6 and kd7.

Influence of long-term treatment with tuftsin analogue TP-7 on the anxiety-phobic states and body weight

TP-7 is a synthetic analogue of tuftsin. It has a structure of tuftsin, to which three natural L-amino-acids Pro-Gly-Pro are attached. This heptapeptide improves learning and memorization and causes antidepressant and anxiolytic effect. It is possible to use TP-7 in the future to optimize cognitive functions and as a potential new anxioselective, fast-acting and easy-dosed drug. Therefore, it was purposeful to study such properties of the heptapeptide as its influence on anxiety-fear and body weight under a long-term treatment regimen. The experiment was performed on 24 preselected Wistar rats with the use of Rodina's method. There were three experimental groups of animals with high initial emotional reactivity: passive control group (P), active control group (A, receiving distilled water) and group treated with TP-7 at the dose of 0.3 mg/kg (T). The rats of A and T groups received intraperitoneal injections every day. The experiments were conducted 15 min after the administration of the drug, one and two days after initial testing day, then 1, 2, 3 and 4 weeks after that. The heptapeptide reduced the anxiety-phobic states significantly starting from the second day of drug application. The observed effects persisted throughout four weeks of the experiment, which confirmed effective long-term anxiolytic properties of the heptapeptide. TP-7 did not cause any changes in the body mass by itself.

Effect of tuftsin and oligotuftsins on chemotaxis and chemotactic selection in Tetrahymena pyriformis

The chemotactic properties of tuftsin (H-TKPR-OH), tuftsin derivatives (H-KPR-OH, H-TKPKG-NH(2), Ac-TKPKG-NH(2)) and TKPKG-based oligotuftsins (T20, T30, T40) were investigated in Tetrahymena pyriformis GL. In contrast to its effects on Mammalia, tuftsin elicited chemorepellent or neutral responses; truncation of the N-terminal part (KPR) led to similar results, though with more neutral effects. The significance of the C-terminal part of the molecule was revealed by the chemoattractant properties of TKPKG, which are nevertheless abolished by acylation. Among the oligotuftsins, T20 and T40 were chemoattractants at higher concentrations (10(-9)-10(-6) M), while T30 had a wide-ranging chemorepellent effect, indicating that chemotaxis is elicited in Tetrahymena only by ligands with optimal physicochemical characters (mass, conformation, etc.). The chemotactic selection data indicated that tuftsin-induced chemotaxis results from fairly short-term signalling in Tetrahymena.

Tuftsin-AZT conjugate: potential macrophage targeting for AIDS therapy

The IgG-derived immunomodulating peptide tuftsin, Thr-Lys-Pro-Arg, is recognized by specific receptors on phagocytic cells, notably macrophages, and is capable of targeting proteins and peptides to these sites. Aiming to target 3'-azido-3'-deoxythymidine (AZT) to HIV-infected macrophages, a conjugate of AZT with tuftsin was synthesized. The AZT-tuftsin chimera possesses the characteristic capacities of its two components. Thus, like AZT, it inhibits reverse transcriptase activity and HIV-antigen expression, and similarly to tuftsin, it stimulates IL-1 release from mouse macrophages and augments the immunogenic function of the cells. Importantly, the conjugate is not cytotoxic to T-cells. The results suggest that the AZT-tuftsin conjugate might have potential use in AIDS therapy.

Synthesis, Solution Conformation, and Antibody Recognition of Oligotuftsin-Based Conjugates Containing a β-Amyloid(4−10) Plaque-Specific Epitope

One possible therapeutic approach to treat or prevent Alzheimer's disease (AD) is immunotherapy. On the basis of the identification of Abeta(4-10) (FRHDSGY) as the predominant B-cell epitope recognized by therapeutically active antisera from transgenic AD mice, conjugates with defined structures containing the epitope peptide attached to a tetratuftsin derivative as an oligopeptide carrier were synthesized and their structure characterized. To produce immunogenic constructs, the Abeta(4-10) epitope alone or flanked by alpha- or beta-alanine residues was attached through an amide bond to the tetratuftsin derivative (Ac-[TKPKG]4-NH2) or to a carrier peptide elongated by a promiscuous T-helper cell epitope (Ac-FFLLTRILTIPQSLD-[TKPKG]4-NH2). The conformational preferences of the carrier and conjugates were examined by CD spectroscopy in water and in 1:1 and 9:1 TFE:water mixtures (v/v). We found that the presence of flanking dimers in the conjugates had no effects on the generally unordered solution conformation of the conjugates. However, conjugates with an elongated peptide backbone exhibited CD spectra indicative for a partially ordered secondary structure in the presence of TFE. Comparative ELISA binding studies, using monoclonal antibody raised against the beta-amyloid (1-17) peptide, showed that conjugates with T-helper cell epitope in the carrier backbone exhibited decreased monoclonal antibody recognition. However, we found that this effect was compensated in conjugates comprising the Abeta(4-10) B-cell epitope with the beta-alanine dimer flanking regions at both N- and C-termini. Results suggest that modification of the B-cell epitope peptide from Abeta with rational combination of structural elements (e.g. conjugation to carrier, introduction of flanking dimers) can result in synthetic antigen with preserved antibody recognition.

Synthesis and biological activity of tuftsin, its analogue and conjugates containing muramyl dipeptides or nor-muramyl dipeptides

Several conjugates of muramyl dipeptide (MDP) or nor-muramyl dipeptide (nor-MDP) with tuftsin were synthesized. Conjugates 8a-f were prepared by acylation of protected tuftsin with the isoglutamine carboxyl group of MDP or nor-MDP 2a-f. Also tuftsin analogue 6 (H-Thr-Lys-Pro-Arg(NO2)-OH) was obtained. All synthesized compounds were investigated at the Medical University of Gdansk. The biological activity of the examined compounds was estimated using in vitro cultures of human monocytes and lymphocytes. The substances displayed cytotoxic effects, as was revealed in the viability tests performed. The effects were most probably mediated by the induction of an oxidative burst in monocytes and the stimulation of redox enzymes in lymphocytes. In addition, the analogues turned out to be efficient stimulators of TNFalpha and IL6 secretion by monocytes and lymphocytes. Nevertheless, the secretion of cytokines did not affect the viability of the leukocyte population used in the experiments.The beneficial properties of the compounds examined (mainly 6, 3, 8a and 8c), which implies their usefulness as potential therapeutic agents, are connected with their rapid start of action and more efficient effects compared with tuftsin alone. An in vivo assay on animal models will be performed.

[Selank and short peptides of Taftsin derivatives in regulation of adaptive behavior of animals in stress]

Effects of 10 peptides, tuftsin and Selank derivatives upon behavior during emotional stress induced by conflict situation, were studied in Balb/c and C57BL/6 male mice with genetically determined opposite types of emotional stress reaction, in white male mice and in Wistar male rats divided into different groups according to the type of emotional reactivity. Positive effects of some peptides upon the adaptive behavior of animals in stress situation were demonstrated. Individual physiologically important effects depending on molecular structure of the peptides under study and/or their fragments, possible products of degradation, were revealed. The results obtained confirm the perspectives of aimed synthesis of peptides with definite pharmacological activity, which are not ksenobiotics and will have no side effects.

"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.

Immunomodulatory potential of hydrophobic analogs of Rigin and their role in providing protection against Plasmodium berghei infection in mice

Here, we report the immunomodulating potential of N-palmitoyl-amino-ethyl-rigin amide (PR) and N-cholestanyl-amino-ethyl-rigin amide (CR), the two new structural analogs of rigin (an IgG-derived tetrapeptide). Their activity profiles are compared with native tuftsin (NT) and/or N-palmitoyl-amino-ethyl-tuftsin amide (PT) taken as positive control. To explore the possibility of their use as targeting molecules, they are incorporated into the liposome bilayer and, subsequently, interacted with macrophages in an in vitro study. The new analogs of rigin with the hydrophobicity introduced at the C-terminus are found to considerably improve both the cell-mediated and the humoral immune responses in mice. However, unlike tuftsin and its analog, which mainly activate polymorphonuclear leukocytes and macrophages, the rigin analogs appear to manifest their response more through lymphocytes. When administered prophylactically to a group of mice, at the dose of 100 micrograms/0.5 ml/mouse/day for 2 days (i.v.), followed by a challenge presented with 1 x 10(6) rbcs parasitised with Plasmodium berghei on day 0, substantial reduction in parasitaemia and rate of mortality is observed. This led to increase the median survival time (MST) of the treated group in comparison to the control group. The response is found to be more prominent in CR-treated mice possibly because of the presence of steroid moiety, which is likely to have more productive interaction with cell membranes. Incorporation of these peptides into the bilayer of liposomes does not alter the permeability behavior of vesicles and, in fact, enhances their uptake by the macrophages in an in vitro study. The effect, however, is dependent on both, the concentration of peptide liposomes and the time of incubation. Present study, thus, establishes the possible use of these analogs not only as adjuvant in chemotherapy, but also as a prophylactic supplement to boost the natural immune status. The activity response of rigin analogs is manifested through lymphocytes, they can also find use in the chemotherapy of diseases, like leishmaniasis, tuberculosis and leprosy, where macrophage activity is either tamed or impaired by pathogens.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

[The pharmacokinetics and metabolism of heptapeptide--a prospective synthetic analog of tuftsin with psychostimulating action in rats]

The pharmacokinetics of a new heptapeptide with psychotropic activity was studied in rats in experiments in vitro and in vivo by means of high-performance liquid chromatography. The heptapeptide was detected in its natural form in rat blood plasma for 7-10 min; its T1/2 exceeded that of other oligopeptides of similar structure. The structure of the main pharmacologically active heptapeptide metabolite was identified by high performance liquid chromatography; it proved to be tetrapeptide Thr-Lys-Pro-Arg (taphtsin). The heptapeptide was distributed in well vascularized organs of rats: liver > kidneys > heart.

[The anxiolytic action of an analog of the endogenous peptide tuftsin on inbred mice with different phenotypes of the emotional stress reaction]

The anxiolytic effect of the synthetic analogue of the endogenous peptide tuftsin (Thr-Lys-Pro-Arg-Pro-Gly-Pro) was studied in inbred mice Balb/c (C) and C57B1/6 (B6) with different heritable types of emotional-stress reaction. In C strain with genetically high level of anxiety and "passive" type of behaviour under conditions of avoidable and unavoidable stress (open field, elevated plus-maze, light-dark chamber) the heptapeptide prevented manifestations of anxiety being administered intraperitoneally in a wide range of active doses (200-3000 mcg/kg). The drug did not change the behaviour of B6 mice with low level of anxiety and active type of emotional-stress reaction. The described effect is comparable with tranquilizing-activatory action of low doses of benzodiazepine tranquillizers, however, in contrast to the latter, the heptapeptide has no side inhibitory behavioural effects even in high doses. The heptapeptide may be considered as a promising new anxioselective drug without side inhibitory behavioural effects which are typical for benzodiazepine tranquillizers.

1-Aminocyclobutanecarboxylic acid derivatives as novel structural elements in bioactive peptides: application to tuftsin analogs

Four novel 2,4-methano amino acids (MAAs, 1-aminocyclobutane-1-carboxylic acids) were synthesized. These include the basic MAA analogs of lysine (16), ornithine (5), and arginine (6) and the neutral methanovaline (22), related to proline. The above MAAs, as well as the MAA analog of homothreonine (7), were incorporated into the peptide chain of the immunomodulatory peptide tuftsin, Thr-Lys-Pro-Arg, known to enhance several biological activities mediated by phagocytic cells. The synthetic methano tuftsin analogs were assayed for their ability to stimulate interleukin-6 (IL-6) secretion by mouse peritoneal macrophages and for their stability in human serum toward enzymatic degradation. It was found that, at 2 x 10(-7) M, [MThr1]tuftsin (24) and an isomer of [MVal3]tuftsin (27a) were considerably more active than the parent peptide in augmentation of cytokine release. [MOrn2]Tuftsin (25) was equally potent. The analogs [MThr1]tuftsin (24) and [MOrn2]tuftsin (25), both pertaining to the proteolytically sensitive Thr-Lys bond of tuftsin, exhibited high resistance to enzymatic hydrolysis as compared to tuftsin. Using specific rabbit anti-tuftsin antibodies in a competitive enzyme-linked immunosorbent assay (ELISA) revealed that none of the MAA analogs can cross-react with tuftsin. It may indicate that the peptides assume global structures different than that of tuftsin.

[The characteristics of the anxiolytic action of taftsin and its analog TP-7 on behavior and serotonin metabolism in the brain of rats with chronic deprivation of serotoninergic system activity]

The effect of taftcine (Thr-Lys-Pro-Arg) and its analog TP-7 (Thr-Lys-Pro-Arg-Pro-Gly-Pro) on rat behavior and serotonin brain exchange was studied in 95 adult male Wistar rats neonatally administered with 5,7-dihydroxytriptamine. Intracutaneous administration of both peptides (300 micrograms/kg) was found to result in weakening perception of stress situations; an increase in stability of investigation behavior and normalization of serotonin level in the brain of rats with chronic deprivation of serotoninergic system activity. Anxiolytic and psychostimulant activities of TP-7 are more pronounced than those of tafcine.

Enhanced phagocytosis activity of cyclic analogs of tuftsin

Cyclic analogs of the physiological immunostimulating peptide tuftsin (Thr-Lys-Pro-Arg), cyclo(Thr-Lys-Pro-Arg-Gly) (ctuf-G) and cyclo(Thr-Lys-Pro-Arg-Asp) (ctuf-D), were synthesized based on molecular modeling studies, and assayed for the ability to stimulate phagocytosis by human polymorphonuclear leukocytes. As predicted, the synthesis of ctuf-D resulted in two isomers with the correct molecular mass and amino acid composition. In phagocytosis assays, tuftsin, ctuf-G and two isomers of ctuf-D showed the usual bell-shaped activity profiles. The optimum concentration of ctuf-G was 50-fold less than that of tuftsin, whereas the degree of stimulation was similar. One isomer of ctuf-D was almost inactive, and the other ctuf-D exhibited the same degree of phagocytosis as tuftsin but its optimum concentration was 5-fold lower. The enhanced potency of ctuf-G and one isomer of ctuf-D may be due to conformational effects and/or to the possibility that these cyclic peptides are resistant to proteolytic degradation.

Analysis of a bioactive synthetic analogue of tuftsin by tandem mass spectrometry: anomalous fast atom bombardment activated processes

Fast atom bombardment (FAB) tandem mass spectrometry has been used to analyse the biologically potent, partially modified retro-inverso (PMRI) synthetic isomer of tuftsin: this compound represents the active peptide of the fraction of gamma-globulin (leukokinin) which binds specifically to blood neutrophilic leukocytes and monocytes. Protonated molecules and fragment ions were collisionally dissociated at low energies in a triple-quadrupole mass spectrometer to yield a complete picture of the reactions that occur in the condensed and in the gas phase. The study shows that, when retro-inversion is within the N-terminal amino acid, charge localization at the basic sites (possibly at the N-terminus) induces a marked decomposition of the molecule, the loss of ammonia being the most favourable fragmentation process. Also, artifacts are formed in the liquid phase via bimolecular reactions promoted by the high-energy beam. The findings indicate that despite the fact that PMRI isomers of this type are stable against exo-peptidases and also stable under acidic conditions, they appear to be labile under conditions where the energy deposition, due to FAB is necessarily high.

The immunomodulatory activity of tetra- and tripeptides of tuftsin-kentsin group

It was found that tuftsin (Thr-Lys-Pro-Arg) and its tetrapeptide analogues with the same amino acid composition, but different sequences, demonstrate immunosuppressive activity for the humoral, but not (excepting the Thr-Lys-Arg-Pro tetrapeptide) for the cellular, immune response. The splitting of N-terminal residues from these tetrapeptides leads, however, to formation of tripeptides that are active in both humoral and cellular immune response tests. Thus, the biological degradation of peptides of the type investigated can seriously modulate their immunobiological activities. We also found that tetrapeptides Thr-Arg-Lys-Pro and Thr-Lys-Arg-Pro, as well as tripeptides Arg-Lys-Pro and Lys-Arg-Pro, distinctly differ in their immunomodulatory activities, although the structural differences consist in this case only in the displacement of two basic amino acid residues.

In vivo immunopharmacological properties of tuftsin and four analogs

Four analogs of the natural macrophage-activator peptide tuftsin (T-K-P-R) were synthesized with the aim of obtaining compounds more effective in the stimulation of the immune system than tuftsin. Modifications to the parent tuftsin molecule were (i) substitution of the proline (P) residue, and/or (ii) replacement of the N-terminal residue threonine (T). The study presented here shows that the integrity of the NH2 terminus is not mandatory for a full biological tuftsin-like activity. Our data also suggest that the analogue F-(psi)-K-ABO-R, where ABO is a non-natural amino acid, is a promising agent for immunotherapy of infectious and neoplasic diseases for which tuftsin has already demonstrated some efficacy.

Synthesis and biological activity of [L-hydroxyproline]3-tuftsin analogue and its alpha- or beta-O-D-glucosylated derivatives

Syntheses are described of the Hyp3-tuftsin analogue and of its derivatives alpha- or beta-O-glycosylated at the side chain function of the hydroxyproline residue. The carbohydrate-free tetrapeptide was prepared by reacting Z-Thr-Lys(Z)-OH with H-Hyp-Arg(NO2)-OBzl by the mixed anhydride procedure. In the synthesis of the alpha-glycosylated analogue the O-glycosyl amino acid was incorporated by reacting Boc-(Glc alpha+beta)Hyp-OH with H-Arg(NO2)-OBzl through the same procedure. The alpha-glucosylated dipeptide was isolated from the diastereomeric mixture, selectively deblocked, and acylated with Z-Thr-Lys(Z)-OH by the mixed anhydride procedure. In the preparation of the beta-glucosylated analogue the BOP procedure was used for reacting Boc-[Glc(Ac)4 beta]Hyp-OH with H-Arg(NO)2-OBzl was well as for the final coupling to tetrapeptide. Removal of protecting groups from crude tetrapeptides was achieved by catalytic hydrogenation. Deacetylation of the sugar moiety of the beta-glucosylated tetrapeptide was achieved by treatment with sodium methoxide in methanol. The synthetic compounds were isolated by ion exchange chromatography, and characterized by elemental analysis, amino acid analysis, optical rotation and proton NMR. Their capacity to evoke the release of interleukin 1 from mouse peritoneal macrophages and to modulate immunogenic activity of antigen-fed cells was evaluated, in comparison with tuftsin and rigin. All of the analogues were found to possess tuftsin-like activity.

Respiratory burst in peritoneal exudate cells in response to a modified tuftsin

Intraperitoneal administration of tuftsin-M [Thr-Lys-Pro-Arg-NH-(CH2)2-NH-CO-C15H31] to Balb/C mice has been shown to induce a respiratory burst in the peritoneal exudate cells. The macrophages exhibited enhanced levels of O2-, H2O2, NADPH oxidase and myeloperoxidase, but the activities of superoxide dismutase, catalase and glutathione peroxidase remained virtually unchanged. The magnitude of the oxidative burst depended directly on the dose of tuftsin-M; higher activity was observed at higher doses of the peptide. Tuftsin-M enhanced the generation of both O2- and H2O2 under in vitro conditions, as did phorbol myristate acetate. These results suggest that tuftsin-M could enhance non-specific defence against infections by activating the macrophages.

Effect of tuftsin and its retro-inverso analogue on the release of interferon (IFN-gamma) and tumor necrosis factor (TNF-alpha) by human leucocytes

The aim of this work was to demonstrate whether natural tuftsin or a retro-inverso (r.i.) analogue may induce interferon (IFN) and tumor necrosis factor (TNF) in peripheral-blood-mononuclear-cells (PBMC). For this purpose tuftsin or its analogue were added at different molar concentrations to PBMC and the supernatants were tested for IFN and TNF activity. Both cytokines were released after 12 hours incubation with r.i. tuftsin at an optimum concentration of 10(-10) M. Under the same conditions no activity was observed in the presence of natural tuftsin. In comparison to natural tuftsin the stimulatory activity of this tuftsin analogue is likely to be due to its high stability.

Quenched molecular dynamics simulations of tuftsin and proposed cyclic analogues

We have used high-temperature quenched molecular dynamics calculations to investigate the conformational properties of tuftsin (Thr-Lys-Pro-Arg) in solution. Conformers obtained after quenching of the dynamical structures were sorted into families depending on their relative energies and backbone conformations. By examination of these families, several cyclic analogues of tuftsin were proposed and examined theoretically by further quenched dynamics simulations. Two of the four proposed analogues were found to adopt essentially identical conformations to that of linear tuftsin. It is suggested that these two derivatives (cyclo[Thr-Lys-Pro-Arg-Gly] and cyclo[Thr-Lys-Pro-Arg-Asp]) may be biologically active, and that the introduction of cyclic conformational constraints should help to reduce the entropic penalty to peptide binding.

Immunostimulation by a partially modified retro-inverso-tuftsin analogue containing Thr1 psi[NHCO](R,S)Lys2 modification

The tuftsin retro-inverso analogue H-Thr psi[NHCO](R,S)Lys-Pro-Arg-OH was synthesized through a novel procedure for the high-yield incorporation of isolated retro-inverso bonds into peptide chains and the use of the new Meldrum's acid derivative (CH3)2C(OCO)2CH(CH2)4NHCOCF3 followed by its efficient coupling in solution to trimethylsilylated H-D-Thr(t-Bu)NH2. Closely related peptide impurities were eliminated both from the crude final peptide and the fully protected tetrapeptide amide precursor via ion-exchange and reversed-phase displacement chromatography, respectively. The tuftsin retro-inverso analogue proved to be completely resistant to enzymatic degradation in vitro, either against isolated aminopeptidases or human plasma proteolytic enzymes. When administered either orally or intravenously, it was significantly more active than normal tuftsin in increasing the number of specific antibody secreting cells in spleen of mice immunized with sheep erythrocytes. Furthermore, the analogue exerted an enhanced stimulatory effect on the cytotoxic activity of splenocytes against YAC-1 tumor cells. Finally, retro-inverso-tuftsin was about 10-fold more potent than the native peptide in reducing rat adjuvant arthritis. The resistance of the retro-inverso analogue to peptidases might explain the increased in vivo activities and allows its further immunopharmacological characterization.

[Hyp3]-tuftsin ([Hyp3]-TU) synthesis and biological activity

[Hyp3]-tuftsin (Thr-Lys-Hyp-Arg) has been synthesized by the liquid-phase method. In biological investigations performed on rats antinociceptive and diuretic effects have been determined. It has been suggested that the presence of hydroxyl substituent in pyrrolidine ring of proline slightly modifies antinociceptive TU effect and is responsible for the increased diuretic [Hyp3]-TU activity.

Further investigations on the antinociceptive activity of tuftsin analogs

C-Terminal dipeptide fragment of tuftsin, Pro-Arg, substituted by D-amino acids, and tuftsin analogs with n-hexyl- and n-heptylamine coupled to their C-termini were synthesized by a classical method in solution and their antinociceptive activity was measured by tail flick immersion test (0.4 microM/icv). D-Pro-D-Arg and D-Pro-L-Arg showed an analgesic activity, with the duration of 60 and 40 min, respectively. The strong behavioral effects observed after injection of D-Pro-D-Arg were decreased by naloxone. L-Pro-D-Arg and Thr-Lys-Pro-Arg-HxA display no antinociceptive effect; the tetrapeptide amide showed some toxicity effects. Thr-Lys-Pro-Arg-HpA was very toxic and caused death of all experimental animals. This effect was not influenced by previous injection of naloxone.

The generation of antibody in mice to tuftsin: a naturally occurring phagocytosis stimulating tetrapeptide

Tuftsin (Thr-Lys-Pro-Arg) is a naturally occurring tetrapeptide that stimulates most known functions of the polymorphonuclear leukocyte and macrophage cell lines. We previously reported our unsuccessful attempts to generate antituftsin antibodies by conjugating tuftsin to several carrier proteins and by polymerizing the peptide with glutaraldehyde. To render tuftsin antigenic the following modifications were made to native tuftsin: three glycine residues were added to the N terminus of tuftsin (Gly3-tuf) and cysteine was added to the N terminus (Cys-tuf) and to the C terminus (tuf-Cys). Native tuftsin was covalently conjugated to sheep red blood cells (SRBC). In a separate experiment Balb/c mice primed with SRBC were immunized with 10(7) SRBC peptide conjugate. Native tuftsin and Gly3-tuf were also conjugated to keyhole limpet hemocyanin (KLH). In another experiment KLH and cationized bovine serum albumin (cBSA) were activated with sulfo-succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (s-SMCC), which was used to control orientation of tuf-Cys and Cys-tuf when conjugated to each carrier protein. All conjugates were administered in complete Freund's adjuvant (CFA) except for cBSA conjugates which were administered in alum. Antibody response was determined by solid phase radioimmunoassay. Results showed that specific antituftsin antibodies were elicited only by Cys-tuf, conjugated to KLH. This study reaffirms that tuftsin is weakly antigenic and confirms the previous work by Gottlieb et al. that antibody to tuftsin can only be elicited when tuftsin is conjugated to the carrier protein KLH in a manner that leaves the peptide carboxyl end free.

Approaches to some biochemical mechanisms of action of tuftsin and analogues

Tuftsin, T-K-P-R, is a phagocytosis-stimulating peptide described as a natural immunostimulant. Four analogues of this peptide were synthesized. These compounds were assayed for their ability to compete with [3H]tuftsin for its specific receptor from thioglycollate-elicited mouse peritoneal macrophages. They were also tested for their ability to change level in intracellular cGMP and to stimulate phagocytosis through the nitroblue tetrazolium reduction measurement. Surprisingly, all the analogues were poor competitors of [3H]tuftsin binding but possess potent tuftsin-like activities.

Glyco-tuftsin derivatives modulate interleukin-1 and tumor necrosis factor production

Six Thr1 (O-glyco)-derivatives of the "phagocytosis stimulating peptide" tuftsin, H-Thr-Lys-Pro-Arg-OH and the N-glycosylated undecapeptide H-Thr-Lys-Pro-Arg-Glu-Gln-Gln-Tyr-Asn(beta-D-GlcNAc)-Ser-Thr-OH, which correspond to the "tuftsin-region" at the Fc-domain of immunoglobulin G (amino acid residues 289-299), were evaluated in comparison with tuftsin and rigin, H-Gly-Gln-Pro-Arg-OH, for their capacity to evoke the release of interleukin-1 and tumor necrosis factor from mouse peritoneal macrophages and from human monocytes. Several glycosylated tuftsin derivatives were found to modulate, in a rather dose-dependent manner, the release of the two cytokines from both cell types.

Synthesis of glycosylated tuftsins and tuftsin-containing IgG fragment undecapeptide

Syntheses are described of two new tuftsin derivatives containing a 2-acetamido-2-deoxy-D-galactopyranosyl unit alpha- or beta-glycosidically linked to the threonine's hydroxy side chain function and of the glycosylated undecapeptide corresponding to the tuftsin region of the heavy chain of IgG (amino acid sequence 289-299). The glycosylated tuftsins were synthesized by the solution procedure. Fmoc-[Gal NAc(Ac)3 alpha]Thr-OH and Fmoc-[GalNAc(Ac)3 beta]Thr-OH were allowed to react with H-Lys(Z)-Pro-Arg(NO2)-OBzl by the mixed anhydride procedure and the resulting glycosylated tetrapeptides were fully deblocked by catalytic hydrogenation followed by treatment with potassium cyanide, purified by ion exchange chromatography and characterized by analytical HPLC, elemental and amino acid analyses, optical rotation, and proton NMR spectroscopy. Synthesis of the glycosylated undecapeptide was achieved by the continuous flow solid phase procedure on 4-hydroxymethylphenoxyacetyl-norleucyl derivatized Kieselguhr-supported resin. Fmoc-amino acid symmetrical anhydrides or pentafluorophenyl esters, in the presence of N-hydroxybenzotriazole, were used as the acylating agents. To mimic the native sequence of the tuftsin region at the Fc-domain of immunoglobulin G a 2-acetamido-2-deoxy-beta-D-glucopyranosyl unit was N-glycosidically linked to the amide side chain of Asn 297. The glycosylated asparagine residue was introduced as N2-fluorenylmethyloxycarbonyl-N4-(2-acetamido-3,4,6-tri-O-acetyl-2 -deoxy-beta-D - glucopyranosyl)-asparagine pentafluorophenyl ester. After cleavage from the resin the glycopeptide was deprotected, purified by ion exchange chromatography, and characterized by analytical HPLC, amino acid analysis, high voltage electrophoresis, and proton NMR. The conformational features of the glyco-undecapeptide were determined by circular dichroism measurements both in water and in 98% trifluoroethanol. Results of biological assays will be published elsewhere.

A comparative study of [Leu1]Tuftsin and tuftsin, a natural phagocytosis-stimulating peptide

1. [Leu1]tuftsin was reported to have greater phagocytosis-stimulating activity than tuftsin (Thr-Lys-Pro-Arg). 2. However, a study on inactivation of tuftsin by polymorphonuclear leukocytes (PMNs) demonstrated that leucine aminopeptidase, an ecto-enzyme, located on PMN surface was responsible for this mechanism. 3. Since leucine aminopeptidase is known to cleave Leu more easily than Thr at the N-terminal position of peptides, this suggested to us that [Leu1]tuftsin might then be inactivated by PMNs more easily than tuftsin, and thus this analog might be less active than tuftsin. 4. In addition, many tuftsin preparations used in earlier studies were not fully active, as high-performance liquid chromatography was not available to separate out many contaminating diastereomers. 5. In view of this, we have synthesized and purified [Leu1]tuftsin and compared its phagocytosis-stimulating activity with tuftsin. 6. Our results indicate that [Leu1]tuftsin is not as active as tuftsin in stimulating phagocytosis.

Antinociceptive action of the SP1-4 tetrapeptide and of some tuftsin analogs

The N-terminal tetrapeptide of substance P (SP1-4) was found to produce analgesia, after the icv injection to the rat brain, which is lower in its intensity than that produced by tuftsin (Thr-Lys-Pro-Arg tetrapeptide). Among investigated tuftsin analogues Thr-Lys-Pro-Thr and Thr-Lys-Pro-Thr-Asp (partial sequences of S-protein of HB virus) were weakly active, Thr-Arg-Pro-Arg was inactive, and Thr-Lys-Pro-Gly-Arg produced a weak hyperalgesia 30 min after the icv injection. The obtained results were compared with those obtained previously in the phagocytosis stimulation test. In the control experiments the effects of free amino acids of the tuftsin molecule (Thr, Lys, Pro, Arg) were also studied.

Synthesis of O-glycosylated tuftsins by utilizing threonine derivatives containing an unprotected monosaccharide moiety

Synthesis is described of four tuftsin derivatives containing a D-glucopyranosyl or a D-galactopyranosyl unit covalently linked to the hydroxy side chain function of the threonine residue through either an alpha or beta O-glycosidic linkage. Fmoc-threonine derivatives containing the suitable unprotected sugar were used for incorporating the O-glycosylated amino acid residue. Z-Thr[alpha-Glc(OBzl)4]-OBzl and Z-Thr[alpha-Gal(OBzl)4]-OBzl were prepared from the tetra-O-benzylated sugar and Z-Thr-OBzl by the trichloroacetimidate method in the presence of trimethylsilyl trifluoromethane sulfonate. The alpha glycosylated threonine derivatives were converted into Fmoc-Thr(alpha-Glc)-OH and Fmoc-Thr(alpha-Gal)-OH by catalytic hydrogenation followed by acylation with Fmoc-OSu. beta-Glucosylation and beta-galactosylation of threonine were carried out by reacting the proper per-O-acetylated sugar with Z-Thr-OBzl and boron trifluoride ethyl etherate in dichloromethane. Catalytic hydrogenation of the beta-O-glycosylated threonine derivatives followed by acylation with Fmoc-OSu and deacetylation with methanolic hydrazine yielded Fmoc-Thr(beta-Glc)-OH and Fmoc-Thr(beta-Gal)-OH, respectively. The O-glycosylated threonine derivatives were then reacted with H-Lys(Z)-Pro-Arg(NO2)-OBzl in the presence of DCC and HOBt and the resulting glycosylated tuftsin derivatives were fully deblocked by catalytic hydrogenation, purified by HPLC, and characterized by optical rotation, amino acid analysis, and 1H NMR. The beta-galactosylated tuftsin was also prepared by the continuous flow solid phase procedure.

Competition between tuftsin and HBV S-protein sequences

The syntheses of HBV S-protein partial sequences: Thr-Lys-Pro-Thr (I), Thr-Lys-Pro-Thr-Asp (II), and Thr-Lys-Pro-Thr-Asp-Gly (III) and also of pentapeptide Thr-Lys-Pro-Gly-Arg (IV), are described. For the peptides II and III inhibitory activity against tuftsin was found. Peptide IV (an analogue of tuftsin-inhibitor Thr-Lys-Pro-Pro-Arg) demonstrated a tuftsin-like activity in the phagocytosis experiments.

Synthesis and functional studies of tuftsin analogs containing isopeptide bond

In the present paper a new approach is reported, to increase the resistance of tuftsin toward enzymatic cleavage by the introduction of an isopeptide bond into the molecule. The tetrapeptides H-Lys(Thr)-Pro-Arg-OH and H-Lys(Ala)-Pro-Arg-OH, the pentapeptides H-Thr-Lys(Ala)-Pro-Arg-OH, H-Thr-Lys(Thr)-Pro-Arg-OH and H-Ala-Lys(Ala)-Pro-Arg-OH and their For- and Boc-protected derivatives were built up by stepwise elongation of the chain, using conventional solution-phase methods. Preliminary experiments confirmed that from the Lys residue in position 2 of tuftsin the alpha-peptide bond between the Thr and Lys is cleaved with a significantly higher rate by leucine aminopeptidase than the epsilon-peptide bond. Several of the isopeptide derivatives increased to a higher extent the interleukin (IL-1) secretion by monocytes than tuftsin or [Ala1]-tuftsin.

The characteristics of purified HL60 tuftsin receptors

The purification and characteristics of purified HL60 tuftsin receptors are described. Purification was accomplished by affinity chromatography similar to that described earlier, wherein a tuftsin analog Thr-Lys-Pro-Pro-Arg, is covalently linked at the N alpha group to a solid support. The receptor consists presumably of two subunits approximately 66 KDa and 57 KDa. The dissociation constant of the receptor complex is 4.7 X 10(-8) M with 5 X 10(4) receptors per cell. It can form oligomers with an Mr of about 560 KDa suggesting an octomeric structure, assuming the same number of each subunit is associated.

[Macrophage activation by synthetic peptides. I. Kinetic changes in the transport of fluorescein anions across the plasma membrane of macrophages]

As shown by cytofluorimetric technique, fluorescein anions formed in macrophages due to hydrolysis of fluorescein diacetate (FDA) release into the extracellular medium through the probenecid-inhibitable transport system of organic acids. Technical procedures have been elaborated to record separately the process of FDA hydrolysis characterising the activity of intracellular esterases, and the fluorescein anion transport representing secretion of organic acids by macrophages. It has been established that the tetrapeptide tuftsin stimulates the cell esterase activity without affecting the rate of fluorescein efflux. The peptide KPR (Lys-Pro-Arg) decreases both the esterase activity and the fluorescein anion efflux.

[Post-stress correlation of the functional activity of macrophages by tuftsin and its derivatives]

The effect of 15 day programmed neurotization on the functional activity of the peritoneal macrophages has been studied. The NBT-test and the adhesion measurements were used. The experimental neurosis resulted in the decrease of the macrophage functional activity and in leukopenia. Tuftsin did not restore the stress induced depression of macrophage activity but led to additional rise of the adrenal glands weight and to pronounced granulocyte-monocytosis. Pentapeptide analog of tuftsin gave the additional inhibition of NBT-activity of the macrophage. Heptapeptide analog favoured the restoration of the macrophage activity after neurotization and stimulated lymphopoiesis.

[The role of the brain monoaminergic systems in the effects of tuftsin and its analog on animal emotional behavior]

The effects of tuftsin and its analogue TP-1 (300 micrograms/kg) on the animal adaptive behaviour in emotionally different situations, the level of biogenic amines and their metabolites 10, 30 min., 2 and 6 hrs after injection of these substances were studies. The TP-1 induced an increase in the memory traces stability better than tuftsin in emotionally negative situation. A single injection of the peptides induced changes in NA, DA and their metabolites contents for 30 min. to 2 hrs. In contrast to tuftsin, the TP-1 activated the metabolism of 5-HT in the hypothalamus and caudal brainstem without changing the NA turnover. The data obtained suggests that a stronger psychotropic activity of the TP-1 seems to be caused by its obvious effect on biogenic amines and their metabolites level in the brain.

[Effect of tuftsin and its analog on learning, memory and exploratory behavior in rats]

On Wistar male rats the influence of tetrapeptide tuftsin and its analogue TP-1 (300 mkg/kg, i/p) on animals behaviour was studied. It is shown that administration of peptides increases the rat's exploratory activity. Activating influence of TP-1 was continued for 6 h. Daily multiple administration of tuftsin or TP-1, 15 min prior to the beginning of experiments facilitates the learning and stability of conditioned reaction with food reinforcement. Experimental animals react significantly weaker than the control ones to emotionally negative influence, produced by a sharp reduction of the amount of alimentary reinforcement control.

[Characteristics of the action of psychostimulants on learning and memory in rats]

The effects of intraperitoneal injections of psychostimulant drugs: centrophenoxine (50 mg/kg) and peptide analog of tuftsin TP-1 (300 micrograms/kg) on the processes of elaboration and retention of conditioned reflex have been experimentally studied. The animals were trained with food reward in 30 trials per day. Psychostimulant drugs or saline were injected after the 10th trial. The elaboration of conditioned reflex was continued 30 min later. The retention was tested 24 h, 7 and 30 days later. It was established that both drugs induce an increase in memory traces stability during 30 days. These findings provide direct evidence that psychostimulant drugs, centrophenoxine and peptide substance TP-1, when injected during consolidation phase can enhance memory storage processes.

Tuftsin a natural peptide with antiviral activity--structural basis of its action

The influence of tuftsin--the natural phagocytosis stimulating tetrapeptide and its elongated analogues--on the mortality of encephalomyocarditis virus-infected NMRI mice was investigated. It seems that amino acids elongation in the parent peptide chain does not result in significant increase of antiviral activity of the compounds tested.

Tuftsin and tuftsin conjugates potentiate immunogenic processes: effects and possible mechanisms

The immunoglobulin heavy chain associated tetrapeptide, tuftsin (Thr-Lys-Pro-Arg), known for its phagocytosis-stimulating activity was found to augment the antigen presenting capacity of macrophages in culture when applied simultaneously with the antigen. To study the immunogenic effect of tuftsin in vivo the peptide was coupled covalently to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) antigens to form stable entities. Tuftsin-antigen conjugates were found to be very potent immunogens as tested by their capacity to increase antigen presentation in culture in primary and secondary responses. Thus, monolayers of macrophages pulsed in vitro with KLH-tuftsin conjugates exerted a stronger immunogenic effect than KLH alone. BSA, which by itself was not immunogenic, when applied to macrophages as tuftsin conjugate evoked a high lymphoproliferative immune response. In vivo, BSA conjugated to tuftsin, when injected in aqueous solutions, augmented significantly antibody production, whereas administration of BSA alone or BSA admixed with tuftsin had no immunogenic effect. Studies conducted to elucidate the mechanisms underlying the activation of the immunogenic function of macrophages by the peptide revealed that treatment of cells with antigen and tuftsin increases secretion of interleukin-1 and expression of cell surface Ia encoded antigens. The effect of tuftsin on increasing the immunogenic capacity of antigens may at least partly be attributed to these effects.