Early mechanisms of Leishmania infection in human blood

In human blood, promastigotes bind natural antibodies and activate the classical complement pathway. C3-opsonized promastigotes immune-adhere within seconds to erythrocytes. Promastigote lysis by complement parallels C3 deposition kinetics, and ~90% of promastigotes are killed after 2.5 min. During infection, complement thus exerts strong selective pressure on Leishmania. Paradoxically, promastigote adaptation to the host immune adherence mechanism may provide the parasite a key to invasion.     

Surface activity and human blood platelet aggregation-inhibitory potency

Surface and interfacial activity is correlated with molecular constitution and inhibitory potency of mono- and bis(carbamoylpiperidino)alkanes and aralkanes, and of some corresponding quaternary pyridinium congeners, in ADP-induced human blood platelet aggregation. The measurements of surface and interfacial tension were carried out at concentrations and pH-values approximating those employed in the hemodynamic study. The effect of changes in chemical structure, ranging from relatively minor variations in a specific functional group to the alteration of major components in molecular constitution, was examined and interpreted in terms of contemporary theoretical chemistry.     

Allelopathy: driving mechanisms governing its activity in agriculture

Allelopathy determines the dynamics of plant species in different environments. Understanding this biological phenomenon could help to develop applications in both natural and agricultural systems. This review summarizes the genetic and environmental characteristics that control the production and release of allelochemicals in agroecosystems. This study highlights the current understanding of the environmental changes caused by allelochemicals and summarizes the knowledge about the mechanisms of action of these compounds. Finally, it reviews novel applications of allelopathy in agricultural production systems, including the role of allelochemicals in consortia and their potential use in no-tillage cropping systems through cover crops or mulches.     

Beta-endorphin modulates human immune activity via non-opiate receptor mechanisms

Here we report that Beta-endorphin is a potent and efficacious suppressor of phytohemagglutinin induced T-lymphocyte blastogenesis when human leukocytes are exposed early in the course of mitogenic activation. This suppression becomes more difficult to observe, however, if blastogenesis is established by prior exposure to mitogen. Suppression by Beta-endorphin is not blocked by pretreatment with the opiate antagonist naloxone. These results, therefore, suggest that neuroendocrine modulation of human immune expression may be a peripheral physiological function of Beta-endorphin which is mediated by mechanisms distinct from traditional opiate receptors.     

The ontogeny of voluntary control of activity and its cerebral mechanisms

Literature data on the ontogeny of voluntary control of activity are reviewed. The relationship of the development of different components of voluntary activity control with the functional maturation of the brain, mainly the frontal lobes, which are traditionally regarded as the main cerebral substrate of the programming, regulation, and control of human activity at different stages of development, is considered.     

Fibrinolytic activity of human peripheral blood granulocytes

The fibrinolytic activity of human peripheral blood leukocytes was studied by plating the cells on 125I-fibrin coated dishes. The separation of the three major leukocyte types allowed to demonstrate that most of the activity was produced by granulocytes. The rate of fibrinolysin was found to be linear with incubation time and cell number in the range of 1-4 X 10(5) cells/ml. Since little activity was found in absence of exogenous plasminogen, it was concluded that the cell fibrinolytic activity depended mostly upon the release of plasminogen activator. Plasmatic and granulocytic activators obtained from the same amount of blood were found to be of similar level suggesting a possible clinical implication of the cellular activity in the thrombolytic system.     

Luminol assay for microdetermination of superoxide dismutase activity: its application to human fetal blood

A microtechnique for determining the superoxide dismutase activity in erythrocytes is described. This technique involves the inhibition of luminol-enhanced chemiluminescence of superoxide anion generated by xanthine-xanthine oxidase. Measurements required a steady-state chemiluminescence whether superoxide dismutase was present or absent; the level of luminescence was correlated to enzyme activity. Superoxide dismutase activity measured by this technique was 836 +/- 112 micrograms/g of hemoglobin for whole blood and 834 +/- 109 micrograms/g of hemoglobin for erythrocytes. When the reference technique was applied to larger amounts of blood, the results were 862 +/- 58 and 858 +/- 116 micrograms/g of hemoglobin for whole blood and washed erythrocytes, respectively. The enzymatic activity of superoxide dismutase from fetal blood (obtained by venipuncture in utero and of 19-26 weeks gestational age) was similar to that of adult blood, when measured by the new technique.     

Seed extracts with agglutinating activity for human blood

Seed extracts of 311 species of plants were observed for agglutinating activity with human blood cells in an attempt to find plant sources of naturally occurring hemagglutinins for specific blood types. Of the 45 species with specific activity, Bauhinia variegata L. is promising as a source of anti-N agglutinin.     

Dihydropyrimidine dehydrogenase activity in human blood mononuclear cells

Dihydropyrimidine dehydrogenase (DPD; EC 1.3.1.2) catalyzes the rate-limiting reaction in the catabolism of endogenous uracil and thymine and exogenous fluoropyrimidines. DPD activity was studied in human blood mononuclear cell supernatants utilizing a new and sensitive radiochromatographic assay. Total DPD activity showed a linear correlation with supernatant protein concentration. The affinity constants (Km) for NADPH and thymine were approximately 10 and 1 mumol/l, respectively. Maximal activity (Vmax) was observed at 0.25 mmol/l NADPH and 10 mumol/l thymine, respectively. DPD activity in normal individuals was 8.0 +/- (SD) 2.2 nmol/mg protein/h, and ranged from 4.4 to 12.3 nmol/mg/h (n = 25). This activity range was quite similar to values obtained in patients with metastatic solid tumors treated with fluorodeoxyuridine (FUdR; n = 33, p = 0.57). No correlation was found to exist between mononuclear leucocyte DPD activity and the observed toxicity of FUdR in the tested patients. A bimodal distribution of DPD activity was observed in the patients and in normal individuals. The entire study population tested could be divided into two groups with respect to DPD activity; one group with high (greater than 8 nmol/mg/h) activity and another with low (less than 8 nmol/mg/h) activity. The possibility that sex differences may have been responsible for this distribution of DPD activity could not be excluded. The findings of this study are relevant to the pharmacogenetics of fluoropyrimidines in humans.     

Guanyl cyclase activity of human blood lymphocytes.

An enzyme, guanyl cyclase, which catalyzes formation of CYCLIC 3',5'-GMP from 5'-GTP, has been identified in human peripheral lymphocytes. The activity in lymphocyte homogenate is 14 pmol (min 10-7 lymphocytes). No activity is detected in red blood cells, and the amount found in platelets is very low. The properties of this enzyme are very close to those reported for other guanyl cyclases studied in other tissues: namely, its intracellular localization, its requirement for cation Mn-2+, its inhibition by Hg-2+, Zn-2+ and by nucleotides especially 5'-ATP. No change in enzyme activity occurs when phytohemagglutinin P is added to disrupted lymphocytes. However, when the mitogen is incubated with intact cells, guanyl cyclase activity increases in a few minutes.     

Aliesterase activity in normal and postheparin human blood sera.

An enzyme with characteristics typical of aliesterase has been found in human blood serum using a gas solid chromatographic assay technique. This conflicts with the findings of several authors that aliesterase is absent in the human blood. Another aliesterase is released into the blood stream after intravenous administration of heparin. Partial purification of the aliesterase in normal (preheparin) and postheparin sera was effected by column chromatography using CM- and DEAE-Sephadex. The preheparin aliesterase and postheparin aliesterase have different pH optima of 7.0 and 8.5 respectively. The preheparin aliesterase activity was very sensitive to sodium fluoride and insensitive to a negatively charged detergent, sodium lauryl sulfate, unlike the postheparin esterase which was highly sensitive to sodium lauryl sulfate and comparatively less sensitive to sodium fluoride.     

Cytotoxicity of sodium fluoride on human oral mucosal fibroblasts and its mechanisms

Because sodium fluoride (NaF) is widely used for prevention of dental caries, pathobiological effects of NaF were investigated on human oral mucosal fibroblasts. The results showed that NaF was cytotoxic to oral mucosal fibroblasts at concentrations of 4 mmol/L or higher. Exposure of cells to NaF for 2 h also inhibited protein synthesis, cellular ATP level and functional mitochondrial activities in a dose-dependent manner. However, incubation of cells with NaF up to 12 mmol/L for 2 h depleted only 13% of cellular glutathione level. The IC50 of NaF on cellular ATP level was about 5.75 mmol/L. Preincubation of the cells with pyruvate and succinate did not protect cells from NaF-induced ATP depletion. At concentrations of 4 mmol/L, 8 mmol/L and 12 mmol/L, NaF inhibited 31%, 56% and 57% of mitochondrial functions, respectively, after 2 h incubation. No significant inhibition for NaF was found at concentrations lower than 2 mmol/L (40 ppm). These results indicate that NaF can be toxic to oral mucosal fibroblasts in vitro by its inhibition of protein synthesis, mitochondrial function and depletion of cellular ATP. Because of repeated and long-term usage of NaF, more detailed studies should be undertaken to understand its toxic effects in vitro and in vivo.