Synthesis and pharmacological investigation of new N-hydroxyalkyl-2-aminophenothiazines exhibiting marked MDR inhibitory effect

Novel N-hydroxyalkyl-2-aminophenothiazines implying a tetrazole moiety at the alkyl chain have been synthesized by hydroboration–oxidation of dienes followed by Buchwald–Hartwig cross-coupling reaction. Also, some sulfoxide and sulfone derivatives have been prepared by selective oxidations. MDR inhibition studies on rat hepatocyte cell culture revealed that some derivatives exhibit marked biological efficacy exceeding that of the standard verapamil (e.g., 3h, 4h, 16). Selected derivatives were subjected to chemical resolution to provide both enantiomers which were shown of similar activity on P-gp interaction measurements. The new compounds exhibited no toxicity.     

Transient transfection of polarized epithelial monolayers with CFTR and reporter genes using efficacious lipids

Transient transfection of epithelial cells with lipid reagents has been limited because of toxicity and lack of efficacy. In this study, we show that more recently developed lipids transfect nonpolarized human airway epithelial cells with high efficacy and efficiency and little or no toxicity. Because of this success, we hypothesized that these lipids may also allow transient transfection of polarized epithelial monolayers. A panel of reagents was tested for transfer of the reporter gene luciferase (LUC) into polarized monolayers of non-cystic fibrosis (non-CF) and CF human bronchial epithelial cells, MDCK epithelial cell monolayers, and, ultimately, primary non-CF and CF airway epithelial cells. Lipid reagents, which were most successful in initial LUC assays, were also tested for transfer of vectors bearing the reporter gene green fluorescent protein (GFP) and for successful transfection and expression of an epithelial-specific protein, the cystic fibrosis transmembrane conductance regulator (CFTR). Electrophysiological, biochemical, and immunological assays were performed to show successful complementation of an epithelial monolayer with transiently expressed CFTR. We also present findings that help facilitate monolayer formation by these airway epithelial cell lines. Together, these data show that polarized monolayers are transfected transiently with more recently developed lipids, specifically LipofectAMINE PLUS and LipofectAMINE 2000. Transient transfection of epithelial monolayers provides a powerful system in which to express the cDNA of any epithelium-specific protein transiently in a native polarized epithelium to study protein function.     

Causes of local recurrence after curative surgery for rectal cancer

The rate of local recurrence (LR) has been 20-40% after resective surgery for rectal cancer by the traditional - Miles or Dixon - operative technics. The authors performed curative resection in 358 patients with rectal cancer in a 10 year period (01.01.1990 - 31.12.2000) in the Surgical Department of Szeged University. Since 01.01.1996 the authors changed this type of surgery for the Heald technics (total mesorectal excision - TME - with sharp dissection, using the UltraCision device) for the surgical treatment of middle or lower third rectal cancer. To compare the results of the two procedures, the authors analysed their material in two periods: Period I: 01.01.1991 - 31.12.1992: 62 patients operated on with the traditional operative technics; LR 15% within 2 years after surgery. Period II: 01.01.1997 - 31.12.1998: 78 patients operated on with the Heald technics (TME with sharp dissection); LR 6.4% within 2 years after surgery. Based on their results, the authors found that the modern operative technics by Heald, used in the second period of the study, was a relevant factor decreasing LR from 15% to 6.4%, while the gender, age of the patients, ratio of the abdominoperineal extirpation versus anterior resection (APRE/AR) and the free margin of more than 3 cm proved to be irrelevant.     

The unusual catalytic triad of poliovirus protease 3C

Picornaviruses are small pathogen RNA viruses, like poliovirus, hepatitis A virus, rhinovirus, and others. They produce a large polyprotein, which is cleaved by virally encoded cysteine peptidases, picornains 2A and 3C. Picornain 3C represents an intermediate between the serine peptidase chymotrypsin and the cysteine peptidase papain. Its steric structure resembles chymotrypsin, but its nucleophile is a thiol instead of the hydroxyl group. The histidine is a general base catalyst in chymotrypsin but forms a thiolate-imidazolium ion pair in papain. The third member of the catalytic triad is an acid (Glu71) as in chymotrypsin rather than an amide found in papain. Transformation of poliovirus 3C peptidase into a serine peptidase results in lower activity by a factor of 430, but the activity extends toward higher pH with the more basic hydroxyl group. The decrease in activity is caused by the less ordered active site, as supported by the unfavorable entropy of activation. At 25 degrees C the specificity rate constant for the thiol enzyme approaches k(1), the rate constant for the formation of the enzyme-substrate complex, but k(2), the acylation constant, becomes predominant with the increase in temperature. In contrast, for the serine peptidase the specificity constant is less than k(1) over the entire temperature range, and the transition state is controlled by both k(1) and k(2). The acidic component of the catalytic triad is essential for activity, but its negative charge does not influence the ionization of the thiol group.     

Dominant species, functional assemblages and frequency of equilibrium phases in late summer phytoplankton assemblages in Hungarian small shallow lakes

Late summer phytoplankton associations were studied qualitatively and quantitatively in 80 Hungarian lakes altogether (mostly shallow salt lakes, reservoirs, oxbows, gravel pit lakes). Equilibrium phases sensu Sommer et al. (1993) were found only in 17 lakes. Most of them were under some kind (high salt content or very low level of nutrients) of stress factor. It is concluded that environmental stress forces phytoplankton communities towards equilibrium. No relationship between occurrence of equilibria and trophic state was found. Species number of non-equilibrated lakes was almost three times as high as those in equilibrium. Of the 31 recently described (Reynolds et al., 2002) phytoplankton assemblages most of those were recognized that are likely to occur in shallow lakes. Separation of a functional group W _S from W2 for Synura dominated lakes is suggested. It seemed also necessary to raise a group (Y _Ph) for lakes dominated by Phacotus. Sorting of Dinophyta species into different already described functional groups is desirable.     

Time related changes in calcium handling in the isolated ischemic and reperfused rat heart

The main aim of this study was to assess the kinetics of intracellular free calcium (Ca²⁺ _i) handling by isolated rat hearts rendered ischemic for 30 min followed by 30 min of reperfusion analyzing the upstroke and downslope of the Ca²⁺ _i transient. Changes in mechanical performance and degradation of membrane phospholipids – estimated by tissue arachidonic acid content – were correlated with Ca²⁺ _i levels of the heart. The fluorescence ratio technique was applied to estimate Ca²⁺ _i. The disappearance of mechanical activity of the heart preceded that of the Ca²⁺ _i transient in the first 2 min of ischemia. The slope of upstroke of the Ca²⁺ _i transient, reflecting Ca²⁺ release, decreased by 60%, while the duration of the downslope of the transient, reflecting Ca²⁺ sequestration, expressed a significant prolongation (105 ± 17 vs. 149 ± 39 msec) during the first 3 min of ischemia. At about 20 min of ischemia end-diastolic pressure expressed a 3.5-fold increase (contracture) when the fluorescence ratio showed a 2-fold elevation. Reperfusion was accompanied with a further precipitous increase in end-diastolic pressure, while resting Ca²⁺ _i remained at end-ischemic levels. Increases in the arachidonic acid (AA) content of the ischemic and postischemic hearts were proportional to Ca²⁺ _i levels. In summary, the present findings indicate that both calcium release and removal are hampered during the early phase of ischemia. Moreover, a critical level of Ca²⁺ _i and a critical duration of ischemia may exist to provoke contracture of the heart. Upon reperfusion the hearts show membrane phospholipid degradation and signs of stunning exemplified by elevated AA levels, partial recovery of Ca²⁺ _i handling and sustained depression of mechanical performance.     

Synthesis, solution structure analysis and antibody binding of cyclic epitope peptides from glycoprotein D of Herpes simplex virus type I

Two cyclic peptides with a thioether bond have been synthesised corresponding to the 9-22 (9LKMADPNRFRGKDL(22)) sequence of glycoprotein D (gD-1) of Herpes simplex virus. The role of the secondary structure in protein-specific monoclonal antibody recognition was investigated. The sequence selected for this study comprises a strongly antigenic site adopting a beta-turn at residues 14Pro-(15)Asn. Thioether bond was formed between the free thiol group of cysteine or homocysteine inserted in position 11 and the chloroacetylated side chain of lysine in position 18. We report here the preparation of cyclic peptides containing Cys or Hcy in position 11, differing only in one methylene group. The linear precursor peptides were synthesised by Boc/Bzl strategy on MBHA resin, and the cyclisation was carried out in alkaline solution. The secondary structure of the peptides was studied by CD, FT-IR and NMR spectroscopy. The CD and FT-IR data have revealed fundamental changes in the solution conformation of the two compounds. The CH(2) group difference significantly resulted in the altered turn structure at the 12Ala and 13Asp as identified by NMR spectroscopy. The antibody binding properties of the cyclopeptides studied by gD-specific monoclonal antibody (A16) in direct and competition enzyme-linked immunosorbent assay (ELISA) were also not the same. We found that peptide LK[HcyADPNRFK]GKDL exhibited higher affinity to Mab A16 than peptide LK[CADPNRFK]GKDL, however, their reactivity was significantly lower compared to the linear ones. Our results clearly show the importance of secondary structure in an antibody binding and demonstrate that even a slight modification of the primary structure dramatically could influence the immune recognition of the synthetic antigens.     

The norepinephrine transporter (NET) radioligand (S,S)-[18F]FMeNER-D2 shows significant decreases in NET density in the human brain in Alzheimer's disease: A post-mortem autoradiographic study

Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell numbers in the locus coeruleus (LC) and a corresponding decrease in norepinephrine transporter (NET) in brains obtained from Alzheimer's disease (AD) patients as compared to age-matched healthy controls. In order to test the hypothesis that the regional decrease of NET is a disease specific biomarker in AD and as such, it can be used in PET imaging studies for diagnostic considerations, regional differences in the density of NET in various anatomical structures were measured in whole hemisphere human brain slices obtained from AD patients and age-matched control subjects in a series of autoradiographic experiments using the novel selective PET radioligand for NET (S,S)-[¹⁸F]FMeNER-D₂. (S,S)-[¹⁸F]FMeNER-D₂ appears to be a useful imaging biomarker for quantifying the density of NET in various brain structures, including the LC and the thalamus wherein the highest densities are found in physiological conditions. In AD significant decreases of NET densities can be demonstrated with the radioligand in both structures as compared to age-matched controls. The decreases in AD correlate with the progress of the disease as indicated by Braak grades. As the size of the LC is below the spatial resolution of the PET scanners, but the size of the thalamus can be detected with appropriate spatial accuracy in advanced scanners, the present findings confirm our earlier observations with PET that the in vivo imaging of NET with (S,S)-[¹⁸F]FMeNER-D₂ in the thalamus is viable. Nevertheless, further studies are warranted to assess the usefulness of such an imaging approach for the early detection of changes in thalamic NET densities as a disease-specific biomarker and the possible use of (S,S)-[¹⁸F]FMeNER-D₂ as a molecular imaging biomarker in AD.     

Cyclic peptide models of the Ca2+-binding loop of alpha-lactalbumin

A series of cyclic peptides with different linkers were designed and synthesized to model the elbow-type Ca2+-binding loop of alpha-lactalbumin (LA). All amino acids of the Ca2+-binding loop are strikingly well conserved among LAs of different species with the sequence Lys79-Phe-Leu-Asp82-Asp-Asp-Leu-Thr- Asp87-Asp88, where three carboxylates of Asp82, Asp87, and Asp88 and the amide carbonyl oxygen atoms of Lys79 and Asp84 participate in Ca2+ binding. Alanine-containing models were also prepared for monitoring the role of the binding (82, 87-88) and nonbinding Asp residues (83-84) in coordinating the cation. The structural features of synthetic peptides and their Ca2+-binding properties were investigated in solution by circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy. In water, the CD curves show a strong negative band below 200 nm as a sign of the presence of unfolded conformers. In TFE, all cyclic peptides were found to have a CD spectrum, reflecting the presence of folded (turn) conformers. The effect of Ca2+ was dependent on the structure and concentration of the model and the Ca2+ to peptide ratio (r(cat)). A surprising time dependence of the FTIR spectra of Ca2+ complexes of the Ala-containing peptides was observed. The shape of the broad amide I band showed no more change after approximately 60 min. Contrary to this, the deprotonation of the side chain COOH group(s) and formation of the final coordination sphere of Ca2+ took more time. Infrared spectra showed that in the Ca2+ complex of model comprising the binding Asp residues of LA, the cation is coordinated to the COO- groups of all three Asps, while in the complex of model comprising nonbinding Asp residues of LA, the two neighboring Asp side chains form a bridged Ca2+-binding system.