Treatment difficulty with acute GVHD - frequent cause of mortality after allogeneic hematopoietic stem cell transplantation.

OBJECTIVE: Acute graft-versus-host disease (aGvHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). METHODS: In this study, we have retrospectively evaluated the major risk factors for the development of aGvHD in 100 patients who underwent allogeneic transplantation at the University Hospital in Bratislava between January 2007 and December 2011. RESULTS: 29 patients acquired acute GvHD (Grade I - 12 patients, G II - 5 , G III - 3, G IV - 9). We proved a higher incidence of developing aGvHD in patients with unrelated donor type, TBI conditioning and cyclosporine (CsA) replacement with mycophenolate mofetil due to CsA nephrotoxicity, while other risk factors such as older patient age, the use of peripheral blood progenitor cells and donor/recipient sex mismatch were without statistical significance. The average time of onset of aGvHD has been 57 days (range 13-260) after HSCT. Corticosteroids were used as standard initial therapy with 52 % complete response (CR) rate, although the likelihood of response rapidly decreased with increasing severity of disease (G IV - 100 % refracterness). The response to primary therapy also correlated with overall survival. Patients with steroid-refractory aGvHD received a different second-line therapies (antithymocyte globulin, anti-TNFα antibody, anti CD52 antibody) with response rate 45 % (CR - 18 %, PR - 27 %). CONCLUSION: Outcome for the patients with steroid-refractory aGvHD was poor, disease very often returned or progressed with one year mortality rate 81 % , that represents an important therapeutic problem (Tab. 2, Ref. 10).

Study of spectral behaviour and optical properties of cis/trans-bis(N-methylpyridinium-4-yl)diphenyl porphyrin adsorbed on layered silicates.

The spectral properties of two dicationic porphyrins, cis- and trans-bis(N-methylpyridinium-4-yl)diphenyl porphyrins, upon adsorption on clay mineral templates were investigated. A series of reduced charge Nanocor montmorillonites was used as host templates. The main impact was given on the influence of the layer charge on the absorption and fluorescence spectra. Adsorption of the porphyrins led to significant changes in their spectra but preserved the photoactivity of the dyes. The changes can be attributed to two phenomena: structural changes (flattening) of the porphyrin molecules and molecular aggregation. Latter one was more influenced by the molecular structure of the dyes and influenced the properties of mainly trans-isomer. The formation of the assemblies was significantly influenced by the layer charge of montmorillonite template. This study presents the example how one is able to influence the spectral properties and possibly also the functionality of adsorbed photoactive molecules via a strategy of appropriate combination of a photoactive component with specific inorganic templates.

Spectral properties of TMPyP intercalated in thin films of layered silicates.

The objective of this study was to investigate the spectral characteristics of tetracationic porphyrin dye (TMPyP), intercalated into films of three smectites. The smectites represented the specimens of high (Fluorohectorite; FHT), medium (Kunipia F montmorillonite; KF), and low layer charge (Laponite; LAP). Intercalation of TMPyP molecules was proven by XRD measurements. The molecular orientations of the dye cations were studied by means of linearly polarized ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. Both the UV-vis and the IR spectroscopy proved the anisotropic character of the films. The spectral analysis of the polarized UV-vis spectra and consequent calculations of tilting angles of the transition moments in the region of Soret band transitions were in the range of 25-35 degrees . The determined angles indicated that the molecular orientation of the dye cations was almost parallel to the surface of the silicates. Slightly higher values, determined for a FHT film, indicated either a slightly more tilted orientation of the dye cations or the change of molecular conformation after the intercalation of the dye. Quenching of TMPyP fluorescence was observed, resulting from the formation of bimolecular layer arrangements with sandwich-type assemblies of the dye molecules.

Fluorescence resonance energy transfer between two cationic laser dyes in presence of the series of reduced-charge montmorillonites: effect of the layer charge.

Series of montmorillonites with systematically reduced layer charges represent a suitable model for studying various properties and interactions of layered inorganic compounds. The reduced-charge montmorillonites (RCMs) used in this study were prepared by a standard method of Li+-fixation in Nanocor montmorillonite at 100-300 degrees C. The layer charge gradually decreased with increasing temperature of RCM preparation. Li+-fixation led in some cases to the loss of expandability due to the formation of mixed swelling/nonswelling and homogeneous nonswelling phases. The interaction of two cationic dyes-rhodamine 3B (R3B) and oxazine 4 (Ox4)-with reduced-charge montmorillonites in dispersions was studied by means of UV/vis absorption and fluorescence spectroscopy. Montmorillonite with the highest charge density induced the formation of H-aggregates of the dye cations characterized by a sandwich-type structure. As the layer charge decreased, the amount of the H-aggregates was reduced in favor of H-dimers and monomers. RCMs with low charge density suppressed dye cation aggregation and mainly monomeric forms were detected. The process of energy transfer from R3B to Ox4 was detected as decreasing the emission from the energy donor and increasing the emission from the energy acceptor. The energy transfer was clearly influenced by the properties of RCM templates. The dye cations adsorbed at the surface of the highest-charge specimen formed H-aggregates, which were efficient luminescence quenchers. Fluorescence resonance energy transfer (FRET) gradually increased with the charge reduction to be optimal at the templates with medium layer charge. Substantial decrease of the layer charge and reduction of clay mineral swelling led to the decrease of both the luminescence and the efficiency of FRET. The relations of energy transfer processes to the layer charges and swelling properties of montmorillonite are analyzed in detail.

Energy transfer between rhodamine 3B and oxazine 4 in synthetic-saponite dispersions and films.

The objective of this study was the investigation of energy transfer between the laser dyes rhodamine 3B (R3B) and oxazine 4 (Ox4) adsorbed on the surface of synthetic Sumecton saponite (Sum). The process of energy transfer was studied for both saponite dispersions and oriented solid films. The electronic properties, luminescence, and the energy transfer process were described by UV-vis absorption and fluorescence spectroscopy. For the efficiency of the energy transfer process, the concentrations of energy donor and acceptor components on a clay mineral surface were found to be essential. A side reaction of the molecular assembly formation reduced both the luminescence and energy-transfer yields, mainly due to fluorescence quenching. The quenching was more problematic for the solid film specimens, where an appropriate modification of the inorganic host with hydrophobic alkylammonium cations was used to achieve a higher luminescence. Due to the higher tendency of Ox4 to form nonluminescent aggregates at higher concentrations, the lowering of the Ox4 concentration further improved the luminescent properties of the films. In this case, the energy transfer occurring in the solid film from R3B to Ox4 was clearly proven.

Preferential amino acid sequences in alumina-catalyzed peptide bond formation.

The catalytic effect of activated alumina on amino acid condensation was investigated. The readiness of amino acids to form peptide sequences was estimated on the basis of the yield of dipeptides and was found to decrease in the order glycine (Gly), alanine (Ala), leucine (Leu), valine (Val), proline (Pro). For example, approximately 15% Gly was converted to the dipeptide (Gly(2)), 5% to cyclic anhydride (cyc(Gly(2))) and small amounts of tri- (Gly(3)) and tetrapeptide (Gly(4)) were formed after 28 days. On the other hand, only trace amounts of Pro(2) were formed from proline under the same conditions. Preferential formation of certain sequences was observed in the mixed reaction systems containing two amino acids. For example, almost ten times more Gly-Val than Val-Gly was formed in the Gly+Val reaction system. The preferred sequences can be explained on the basis of an inductive effect that side groups have on the nucleophilicity and electrophilicity, respectively, of the amino and carboxyl groups. A comparison with published data of amino acid reactions in other reaction systems revealed that the main trends of preferential sequence formation were the same as those described for the salt-induced peptide formation (SIPF) reaction. The results of this work and other previously published papers show that alumina and related mineral surfaces might have played a crucial role in the prebiotic formation of the first peptides on the primitive earth.

Activated alumina as an energy source for peptide bond formation: consequences for mineral-mediated prebiotic processes.

The catalytic properties of various forms of alumina were tested for alanine dimerization reaction. The catalytic efficiency of alumina depends on the structure, as well as on acid/base properties of the catalyst. The highest yields of Ala2 were achieved on activated alumina with surface of neutral pH (about 3% conversion after 2 weeks). Thermal analysis of Ala + alumina reaction systems shows that the thermal behavior of amino acid changes substantially in contact with the activated surface of the alumina catalyst. The reaction of Ala is detected as being strongly endothermic by differential thermal analysis of pure amino acid (above 250 degrees C). The alanine endothermic reaction is shifted substantially to lower values (below 200 degrees C) and hardly detectable if activated alumina is present. The reaction mechanism of amino acid activation on alumina surface and its significance for mineral-catalyzed prebiotic peptide bond formation are discussed.

Silica, alumina and clay catalyzed peptide bond formation: enhanced efficiency of alumina catalyst.

Catalytic efficiencies of clay (hectorite), silica and alumina were tested in peptide bond formation reactions of glycine (Gly), alanine (Ala), proline (Pro), valine (Val) and leucine (Leu). The reactions were performed as drying/wetting (hectorite) and temperature fluctuation (silica and alumina) experiments at 85 degrees C. The reactivity of amino acids decreased in order Gly > Ala > Pro approximately Val approximately Leu. The highest catalytic efficiency was observed for alumina, the only catalyst producing oligopeptides in all investigated reaction systems. The peptide bond formation on alumina is probably catalyzed by the same sites and via similar reaction mechanisms as some alumina-catalyzed dehydration reactions used in industrial chemistry.

The effect of smectite composition on the catalysis of peptide bond formation.

Clay-catalyzed glycine and diglycine oligomerizations were performed as drying/wetting cycles at 80 degrees C. Two trioctahedral smectites (hectorite and saponite), three pure montmorillonites, a ferruginous smectite, an Fe(II)-rich smectite, and three smectites containing goethite admixture were used as catalysts. Highest peptide bond formation was found with trioctahedral smectites. About 7% of glycine was converted to diglycine and diketopiperazine on hectorite after 7 days. In the case of dioctahedral smectites, highest yields were achieved using clays with a negative-layer charge localized in the octahedral sheets (up to 2% of converted glycine after 7 days). The presence of Fe(II) in clay is reflected in a higher efficiency in catalyzing amino acid dimerization (about 3.5% of converted glycine after 7 days). The possible significance of the results for prebiotic chemistry is discussed.

Investigation on the mechanism of peptide chain prolongation on montmorillonite.

Experiments with reduced-charge montmorillonites with gradually collapsed interlayer space prove that peptide formation processes occur mainly at the edges of the clay mineral. Activation of peptides and amino acids and the intermediate formation of cyclic anhydrides are found to be the two dominant processes determining the formation of higher peptides on the mineral surface.

Peptide chain elongation: a possible role of montmorillonite in prebiotic synthesis of protein precursors.

Several studies have proven the ability of montmorillonite to catalyse amino acid condensation under assumed prebiotic conditions, simulating wetting-drying cycles. In this work, the oligomerization of short peptides gly2, gly3, gly4 and ala2 on Ca- and Cu-montmorillonite in drying-wetting cycles at 80 degrees C was studied. The catalytic effect of montmorillonite was found to be much higher than in the case of glycine oligomerization. From gly2 after 3 weeks, 10% oligomers (up to gly6, with gly3 as main products) are formed. Gly3 and gly4 give higher oligomers even after 1 cycle. Ala2 produces both ala3 and ala4, whereas ala does not produce any oligomers under these conditions. Heteroologomerization was observed: ala-gly-gly is formed from ala and gly2. Much higher yields are obtained using Ca-montmorillonite, because copper (II) oxidizes organic molecules. The influence of the reaction mechanism on the preferential oligomerization of oligopeptides is discussed.