Revealing the dynamics of prospective memory processes in children with eye movements.

Prospective memory (PM), the memory for delayed intentions, develops during childhood. The current study examined PM processes, such as monitoring, PM cue identification and intention retrieval with particular focus on their temporal dynamics and interrelations during successful and unsuccessful PM performance. We analysed eye movements of 6-7 and 9-10 year olds during the inspection of movie stills while they completed one of three different tasks: scene viewing followed by a snippet allocation task, a PM task and a visual search task. We also tested children's executive functions of inhibition, flexibility and working memory. We found that older children outperformed younger children in all tasks but neither age group showed variations in monitoring behaviour during the course of the PM task. In fact, neither age group monitored. According to our data, initial processes necessary for PM success take place during the first fixation on the PM cue. In PM hit trials we found prolonged fixations after the first fixation on the PM cue, and older children showed a greater efficiency in PM processes following this first PM cue fixation. Regarding executive functions, only working memory had a significant effect on children's PM performance. Across both age groups children with better working memory scores needed less time to react to the PM cue. Our data support the notion that children rely on spontaneous processes to notice the PM cue, followed by a resource intensive search for the intended action.

Reversal of handedness effects on bimanual coordination in adults with Down syndrome.

BACKGROUND: Research on unimanual tasks suggested that motor asymmetries between hands may be reduced in people with Down syndrome. Our study examined handedness (as assessed by hand performance) and perceptual-motor integration effects on bimanual coordination. METHODS: Adults with Down syndrome (13 non-right-handed, 22 right-handed), along with comparison groups of adults (16 non-right-handed, 21 right-handed) and children (15 non-right-handed, 22 right-handed) without Down syndrome, drummed with auditory, verbal and visual instructions. RESULTS: In contrast to handedness effects in the children and adults without Down syndrome, right-handed participants with Down syndrome led more with the left hand, and had lower coordination stability than non-right-handed participants with Down syndrome. CONCLUSIONS: The reversed handedness effect during bimanual coordination suggests a complex relationship between handedness and task requirements in adults with Down syndrome.

Modulation of mistletoe (Viscum album L.) lectins cytotoxicity by carbohydrates and serum glycoproteins.

Three D-galactose and/or N-acetyl-D-galactosamine specific mistletoe lectins, ML I, ML II and ML III, were purified by affinity chromatography followed by cation exchange chromatography. These lectins were toxic for Molt 4 cells in culture at concentrations in the pg/ml range, ML III being the most cytotoxic. Carbohydrates able to bind to the B-chain of these lectins inhibited their toxic activity. The digalactosides Gal beta 1,2Gal beta-allyl and Gal beta 1,3Gal beta-allyl were 60 and 30 times, respectively, more potent than D-galactose in their ability to protect the cells from the ML I cytotoxicity. N-acetyl-D-galactosamine and rho-nitrophenyl N-acetylgalactosamine protected mainly from the toxic effects of ML II and III. Protection from cytotoxicity varied in the same order as the affinity of the tested carbohydrates for lectins. Serum glycoproteins particularly haptoglobin, but also alpha 1-acid glycoprotein and transferrin, notably inhibited the cytotoxicity of the lectins. This effect was due to the binding of lectin to the sugar moiety of the glycoprotein because deglycosylated haptoglobin did not have a protective activity on Molt 4 cells. Inhibition of the cytotoxicity of lectins by serum glycoproteins explains why mistletoe extracts containing lectins can be administered to cancer patients without harmful effects.

Modulation of cytotoxicity and enhancement of cytokine release induced by Viscum album L. extracts or mistletoe lectins.

Cytotoxic effects of Viscum album L. (mistletoe) extracts and mistletoe lectins were studied by light and electron microscopy. The first events observed were membrane perforation and protrusions typical for apoptosis. Inhibition of Molt 4 cell growth was obtained with lectin concentrations in the pg/ml range as long as cells were cultured in serum-free medium. Under this condition, mistletoe lectin-III was about 10 times more cytotoxic than mistletoe lectin-I; mistletoe lectin-II was in between. Lectin cytotoxicity was modulated by human serum from donors who had never been treated with mistletoe preparations and lectin-specific carbohydrates, added at the mmol/l range, particularly D-galactose (or beta-lactose) for mistletoe lectin-I and N-acetyl-galactosamine for mistletoe lectin-II and -III. In addition, at subtoxic concentrations, mistletoe lectin-I, -II and -III enhanced the production of cytokines (tumour necrosis factor-alpha, interleukin-1 alpha) by isolated human monocytes. The experimental results are discussed in relation to the treatment of cancer patients administered with mistletoe extracts.

Mistletoe lectins I, II and III induce the production of cytokines by cultured human monocytes.

The three mistletoe (Viscum album L.) lectins. ML I, ML II and ML III, were tested on their ability to enhance the secretion of the cytokines tumor necrosis factor (TNF)alpha, interleukin (IL)-1 alpha, IL-1 beta and IL-6 by human monocytes obtained from healthy donors. At lectin concentrations from 0.02 to 20/pg ml (100-10,000-fold lower than those showing toxic effects), stimulations of cytokine production several-fold over control values were observed. The immunoactivating concentrations by the three lectins were found different for each donor. At toxic concentrations, the amounts of IL-1 alpha, IL-1 beta and to a less extent of TNF alpha in monocytes supernatants were particularly high. The data are discussed in relationship with the cytotoxic and immunoactivating effects of mistletoe lectins and their interest in cancer treatment.

Identity of the N-terminal sequences of the three A chains of mistletoe (Viscum album L.) lectins: homology with ricin-like plant toxins and single-chain ribosome-inhibiting proteins.

Mistletoe lectin (ML) I increases the production of cytokines by mononuclear cells and has been proposed as a useful biological response modifier in the treatment of cancer. Two other lectins, ML II and ML III, have been identified in mistletoe. We report that the N-terminal sequences of the three A chains of ML I, ML II and ML III are identical, and have interesting homology with the N-terminal sequences of the A chain of ricin-like toxins and of single-chain ribosome-inhibiting proteins. In addition, the three mistletoe lectins inhibit the growth of the human tumor cell line Molt 4, ML III being the most potent. followed by ML II and ML I. This inhibition is suppressed by addition of rabbit anti-ML I antibodies to the cultured cells. The data obtained suggest that the three lectins have amino acid sequences which show extensive homology and exert very similar biological effects. They may be derived from the same precursor.

Cytotoxic activity of Amaryllidaceae alkaloids from Crinum augustum and Crinum bulbispermum.

The cytotoxic activity of five minor Amaryllidaceae alkaloids and one flavan isolated from Crinum augustum Rox and Crinum bulbispermum Milne were tested on human leukemic Molt 4 cells. Whereas the crinine-type alkaloids (6 alpha-hydroxycrinine, powelline) and the new type augustamine did not even inhibit the growth of Molt 4 cells, the lycorine-type alkaloid (pratorinine) and the crinine-type alkaloid (6 alpha-hydroxybuphanisine) showed a moderate cytotoxic activity and the flavan (4'-hydroxy-7-methoxyflavan) showed an important cytotoxic effect.

Characterization of cytotoxic proteins from mistletoe (Viscum album L.).

Proteins from a laboratory-made oak mistletoe extract and from the commercial mistletoe preparation Iscador Quercus were cytotoxic for leukemia Molt 4 cells in culture. A 50% growth inhibition was obtained with 0.1 microgram/ml proteins for the mistletoe extract and 0.025 microgram/ml for Iscador. On cation exchange chromatography, cytotoxic proteins from the mistletoe extract were mainly eluted at the same positions as purified lectins, while those of Iscador were eluted at the positions of viscotoxins. The data are discussed in relation to the pharmacological activities of the mistletoe protein complexes described in the literature.

Investigation of the active center of rat pancreatic elastase.

We have isolated rat pancreatic elastase I (EC 3.4.21.36) using a fast two-step procedure and we have investigated its active center with p-nitroanilide substrates and trifluoroacetylated inhibitors. These ligands were also used to probe porcine pancreatic elastase I whose amino acid sequence is 84% homologous to rat pancreatic elastase I as reported by MacDonald, et al. (Biochemistry 21, (1982) 1453-1463). Both proteinases exhibited non-Michaelian kinetics for substrates composed of three or four residues: substrate inhibition was observed for most enzyme substrate pairs, but with Ala3-p-nitroanilide, rat elastase showed substrate inhibition, whereas porcine elastase exhibited substrate activation. With most of the longer substrates, Michaelian kinetics were observed. The kcat/Km ratio was used to compare the catalytic efficiency of the two elastases on the different substrates. For both elastases, occupancy of subsite S4 was a prerequisite for efficient catalysis, occupancy of subsite S5 further increased the catalytic efficiency, P2 proline favored catalysis and P1 valine had an unfavorable effect. Rat elastase has probably one more subsite (S6) than its porcine counterpart. The rate-limiting step for the hydrolysis of N-succinyl-Ala3-p-nitroanilide by rat elastase was essentially acylation, whereas both acylation and deacylation rate constants participated in the turnover of this substrate by porcine elastase. For both enzymes, trifluoroacetylated peptides were much better inhibitors than acetylated peptides and trifluoroacetyldipeptide anilides were more potent than trifluoroacetyltripeptide anilides. A number of quantitative differences were found, however, and with one exception, trifluoroacetylated inhibitors were less efficient with rat elastase than with the porcine enzyme.

Effects of mistletoe (Viscum album L.) extracts on cultured tumor cells.

Bacterially fermented mistletoe preparations (BFMP) were tested on rat hepatoma tissue culture (HTC) cells and human leukemia Molt 4 cells. A dose-dependent inhibition of the growth rate of the cells was observed. For both cell lines, cytostatic concentrations, expressed in weight of fresh plant, were 0.5 mg/ml culture medium for oak BFMP and 1 mg/ml for apple tree BFMP. However, the action of the two preparations was markedly different on each cell line. Non-viable HTC cells were not stained by trypan blue while non-viable Molt 4 cells were fully colored by this reagent. A lysis of cellular membranes of HTC cells was observed by electron microscopy. Furthermore, oak BFMP inhibited the growth of virus transformed 3T3-SV40 cells more than that of non-transformed 3T3 cells. In contrast to BFMP, non-fermented extracts and a purified mistletoe lectin showed a greater inhibition of the growth of Molt 4 cells than of HTC cells. Samples withdrawn at different times during fermentation gradually lost their inhibitory effect on the growth of Molt 4 cells while their action on HTC cells increased up to the 4th day of fermentation. These results are discussed in relation to the cytotoxic substances of mistletoe already characterized.

Comparison of the effects of fermented and unfermented mistletoe preparations on cultured tumor cells.

The bacterially fermented mistletoe preparation Iscador, used in cancer therapy for 30 years, and the recently prepared unfermented preparation, have been tested on rat hepatoma tissue culture (HTC) cells and human leukemia Molt 4 cells. As observed by phase-contrast microscopy, treatment of HTC cells with fermented or unfermented Iscador, at a concentration corresponding to 1 mg of fresh plant per milliliter culture, led to rapid lysis of cellular membranes. At a lower concentration, 0.1 mg/ml, unfermented Iscador led to the formation of polynucleated cells. On Molt 4 cells, fermented Iscador also produced cytolysis but after a longer time of action. Unfermented Iscador showed a much stronger cytotoxic effect on these cells than on HTC cells. Fermented Iscador was slightly more potent than unfermented Iscador in inhibiting the growth of HTC cells, but on Molt 4 cells fermented Iscador was less active than unfermented Iscador. DNA synthesis, measured by [3H]thymidine incorporation in HTC and Molt 4 cells, was inhibited by fermented and unfermented Iscador with the same type of differences of action as on cell growth. Fermented Iscador contained a low amount of lectins, approximately 100 ng/ml, while unfermented Iscador contained about 10 times more. A purified mistletoe lectin produced effects on HTC and Molt 4 cells similar to those of unfermented preparations. HTC cells were 100 times less sensitive to this lectin than Molt 4 cells. These results are discussed in relation to the known biological effects of lectins.

Arginine modification in elastase. Effect on catalytic activity and conformation of the calcium-binding site.

Chemical modification of 2 +/- 0.5 arginine residues of porcine pancreatic elastase by 1,2-cyclohexanedione leads to an 85 +/- 5% loss of activity with the specific substrate N-succinyltrialanine p-nitroanilide. Modification of additional arginines does not completely abolish the enzyme activity. The modification reaction is very fast (second order rate constant = 0.24 M-1 S-1) and involves only arginine residues. Acetyltetraalanine or trifluoroacetyltetraalanine decreases the rate of cyclohexanedione-induced inactivation of the enzyme but does not significantly change the number of modified arginine residues. Other dicarbonyl reagents, butanedione or phenylglyoxal, also react with elastase but at much lower rates. Cyclohexanedione-modified elastase is partially active against a series of synthetic substrates of varying chain length. The partial inhibition results from a 2- to 5-fold increase in Km while kappa cat is increased for most substrates. For N-succinyltrialanine p-nitroanilide both the acylation and deacylation rate constants are decreased. The Ki values of a series of acetylated and trifluoroacetylated inhibitors increase 2- to 5-fold. Modified elastase is still able to react with fibrous elastin and with plasma alpha 1-proteinase inhibitor but at significantly lower rates. Modification of one arginine residue alters the properties of the calcium-binding site of elastase as demonstrated by terbium luminescence experiments. The affinity of enzyme for terbium is decreased by a factor of 10 and the circularly polarized luminescence spectrum of the terbium-elastase complex is considerably flattened. Modification of further arginine residues does not increase the extent of these alterations. Circular dichroism shows that the overall conformation of elastase is not altered following arginine modification. We speculate that the two residues modified by cyclohexanedione are Arg 65, located at about 8 A from the metal ion-binding site, and Arg 217A, located at the S'3 subsite of elastase.