Preparation and Immunomodulatory Properties of Modified Peptidoglycan Fragments

Imunomodulatori reguliraju imunološki odgovor. Imunostimulatori, poznati i kao adjuvanti, dodaju se cjepivima kako bi se ubrzala, produljila ili pojačala specifična imunoreakcija na određeni antigen. U potrazi za novim, učinkovitijim imunostimulatorima velik su potencijal pokazali derivati muramilpeptida. Muramilpeptidi su fragmenti peptidoglikana, prirodnih polimera koji izgra?uju stanične stijenke bakterija. Muramildipeptid (MDP), N-acetilmuramil-L- -alanil-D-izoglutamin, najmanja je strukturna jedinica peptidoglikana koja pokazuje imunostimulatornu aktivnost. Sastavni je dio i peptidoglikan monomera (PGM) izoliranog iz Brevibacterium divaricatum, koji je i sam učinkoviti adjuvant. Od brojnih poznatih derivata MDP-a posebno se ističu romurtid (MDP-Lys(L18), koji je odobrila američka Uprava za hranu i lijekove (Food and Drug Administration, FDA) i mifamurtid (L-MTP-PE), koji je odobrila Europska agencija za lijekove (European Medicines Agency, EMA). S obzirom na to da N-acetilglukozamin u strukturi MDP-a nije ključan za njegov imunostimulatorni učinak, pripravljeni su desmuramildipeptidi s različitim acilnim skupinama na N-kraju L-Ala-D-isoGln. Tako su primjerice proučavani adamantilni desmuramildipeptidi kod kojih je na dipeptid vezana lipofilna adamantanska podjedinica. Dodatnim vezanjem manoze na imunološki aktivne tvari omogućuje se njihova interakcija s lektinima specifičnima za manozu kao što su na primjer manozni receptori (MR) eksprimirani na makrofazima i dendritičkim stanicama. Time se omogućuje ciljana dostava pripravljenog, manoziliranog imunomodulatora. Moguće posljedice takvih sintetskih transformacija pojačane su aktivnosti polaznih aktivnih spojeva kao i izravan utjecaj na smjer imunoreakcije. To je pokazano na primjerima manoziliranog MDP-a, PGM-a i adamantil-tripeptida.Immunostimulators, known also as adjuvants, are added to vaccines to accelerate, extend or amplify the specific immune reaction to a specific antigen. One well known class of immuno- modulating compounds is based on muramylpeptides which are fragments of peptidoglycans, natural polymers that build up the cell wall of bacteria. Muramyldipeptide, N-acetyl- muramyl-L-alanyl-D-isoglutamine (MDP, Fig. 1) is the smallest structural unit of the peptidoglycan monomer (PGM, Fig. 2) which shows immunostimulating activity. PGM isolated from Brevibacterium divaricatum, acts in itself as an effective adjuvant, and several derivatives were prepared to study the possible influence of different substituents on the immunomodulatory activity. Thus, lipophilic derivativestert-butyloxycarbonyl-L-tyrosyl-PGM and (adamant- 1-yl)acetyl-PGM (Fig. 3) were prepared and their activities studied. They were also shown to be good substrates for N-acetylmuramyl-L-alanine amidase from human serum (Scheme 1) which specifically hydrolyzes the lactylamide bond. MDP which is an integral part of PGM and proven to be an effective adjuvant was further synthetically modified and obtained derivatives tested as possible immunomodulators. Romutide (MDP-Lys(L18)), approved by Food and Drug Administration (FDA), and mifamurtide (L-MTP-PE), approved by European Medicines Agency (EMA), highlight among many other MDP derivatives (Fig. 4). Since N-acetylglucosamine in the structure of MDP is not essential for the immunostimulating effect, desmuramyldipeptides (Fig. 5) with different acyl groups at N-terminus of L-Ala-D-isoGln dipeptide were prepared. In ada mantyl desmuramyldipeptides such as adamantylamide dipeptide (Fig 6), adamantyl tripeptides (Fig. 7) and desmuramylpeptides with (adamant-1-yl)carboxyamido group (Fig. 8), lipophilic adamantane moiety is bound to the dipeptide part. Binding of some specific sugars to immune active substances may help their targeted delivery. An example is mannose which enables man- nosylated compounds to interact with lectins specific for mannose, such as mannose receptors (MR) expressed at macrophages and dendritic cells. Therefore, it is possible to increase the activity of the parent immunologically active compound by mannosylation. One of the ways is the preparation of mannosylated liposomes by using mannosylated lipids (Fig. 9). Mannosylation can also influence the direction of the immune reaction. This is shown by the examples of mannosylated PGM and adamantyl tripeptides. Mannosylated PGM derivatives (Scheme 2) are the first PGM derivatives comprising carbohydrate substituents. Mannosylation changed the immunostimulating activity of PGM, but did not affect the susceptibility of the lactylamide bond to hydrolysis with N-acetylmuramyl-L-alanine amidase (Scheme 3). Adamantyl tripeptides, structurally related to PGM, can be mannosylated using the same method (Scheme 4). The greatest potential showed the mannosylated (adamant-1-yl)tripeptide (Fig. 10) whose immunostimulating activity is comparable to that of PGM. Numerous MDP derivatives have been synthesized with the intention of improving the pharma- cological properties and reducing the side effects of the parent molecule. Furthermore, the study of their structure-activity relationship contributes to the clarification of the mechanism of action of MDP. All presented examples indicate that relatively small changes in the primary structure of peptidoglycan fragments affect their immune reaction. Mannosylation is particularly important modification of muramylpeptide adjuvants since it may allow the targeted delivery of these active substances

Effect of Microstructural Changes during Annealing on Thermoelectromotive Force and Resistivity of Electrodeposited Ni 85.8

Ni85.8Fe10.6W1.4Cu2.2 alloy powder containing nanocrystals of an FCC-structured solid solution of iron, tungsten, and copper in nickel embedded in an amorphous matrix was electrodeposited from an ammonia citrate solution. The alloy exhibits thermal stability in the temperature range between 25°C and 150°C. Over the range 150−360°C, the alloy undergoes intense structural relaxation which considerably increases the electron density of states and, hence, its electrical conductivity. Less intense structural relaxation takes place at temperatures between 360°C and 420°C. In the temperature range of 420°C to 460°C, relatively more intense changes in the electron density of states at the Fermi level occur, as induced by the structural relaxation resulting from the stabilization of larger less mobile tungsten atoms and copper atoms. The large decrease in electrical resistivity and the high increase in the electron density of states at the Fermi level in the temperature range 460−520°C are due to amorphous matrix crystallization and FCC-phase crystal grain growth

The effect of temperature and frequency on magnetic properties of the Fe81B13Si4C2 amorphous alloy

In this study it was investigated influence of temperature and frequency on permeability, coercivity and power loses of Fe81B13Si4C2 amorphous alloy. Magnetic permeability measurements performed in nonisothermal and isothermal conditions was confirmed that efficient structural relaxation was occurred at temperature of 663 K. This process was performed in two steps, the first one is kinetic and the second one is diffuse. Activation energies of these processes are: Ea1 = 52.02 kJ/mol for kinetic and Ea2 = 106.9 kJ/mol for diffuse. It was shown that after annealing at 663 K coercivity decrease about 30% and therefore substantial reduction in power loses was attained. Investigated amorphous alloy satisfied the criteria for signal processing devices that work in mean frequency domain

The effect of temperature and frequency on magnetic properties of the Fe81B13Si4C2 amorphous alloy

In this study it was investigated influence of temperature and frequency on permeability, coercivity and power loses of Fe81B13Si4C2 amorphous alloy. Magnetic permeability measurements performed in nonisothermal and isothermal conditions was confirmed that efficient structural relaxation was occurred at temperature of 663 K. This process was performed in two steps, the first one is kinetic and the second one is diffuse. Activation energies of these processes are: Ea1 = 52.02 kJ/mol for kinetic and Ea2 = 106.9 kJ/mol for diffuse. It was shown that after annealing at 663 K coercivity decrease about 30% and therefore substantial reduction in power loses was attained. Investigated amorphous alloy satisfied the criteria for signal processing devices that work in mean frequency domain