Geodetic Observations of Weak Determinism in Rupture Evolution of Large Earthquakes

The moment evolution of large earthquakes is a subject of fundamental interest to both basic and applied seismology. Specifically, an open problem is when in the rupture process a large earthquake exhibits features dissimilar from those of a lesser magnitude event. The answer to this question is of importance for rapid, reliable estimation of earthquake magnitude, a major priority of earthquake and tsunami early warning systems. Much effort has been made to test whether earthquakes are deterministic, meaning that observations in the first few seconds of rupture can be used to predict the final rupture extent. However, results have been inconclusive, especially for large earthquakes greater than M w 7. Traditional seismic methods struggle to rapidly distinguish the size of large-magnitude events, in particular near the source, even after rupture completion, making them insufficient to resolve the question of predictive rupture behavior. Displacements derived from Global Navigation Satellite System data can accurately estimate magnitude in real time, even for the largest earthquakes. We employ a combination of seismic and geodetic (Global Navigation Satellite System) data to investigate early rupture metrics, to determine whether observational data support deterministic rupture behavior. We find that while the earliest metrics (~5 s of data) are not enough to infer final earthquake magnitude, accurate estimates are possible within the first tens of seconds, prior to rupture completion, suggesting a weak determinism. We discuss the implications for earthquake source physics and rupture evolution and address recommendations for earthquake and tsunami early warning.

The Nature and Frequency of Neovascular Age-Related Macular Degeneration

PURPOSE

This study was designed to evaluate the frequency and nature of neovascularization in age-related macular degeneration (ARMD) utilizing the combination of digital imaging techniques, fluorescein angiography (FA), indocyanine green (ICG) angiography, and optical coherence tomography (OCT).

METHODS

A complete clinical examination was performed on 100 eyes of 93 consecutive newly diagnosed patients with neovascular ARMD. Digital fluorescein angiography, ICG angiography, and OCT were also used in evaluating those patients. Comparison of the imaging techniques to determine their value in studying the nature of the lesions.

RESULTS

On the basis of existing fluorescein standards, 15 eyes were diagnosed with classic choroidal neovascularization (CNV), 15 with minimally classic CNV, and 70 with occult CNV. ICG angiography was superior for detecting the active vascular component in polypoidal CNV (16 eyes) and retinal angiomatous proliferation (14 eyes). OCT was more sensitive than FA for determining the presence of cystoid macular edema evident in the vast majority of eyes with retinal angiomatous proliferation (RAP).

CONCLUSIONS

These results suggest that FA, ICG angiography, and OCT, when used in combination, will assist clinicians in best determining the precise nature of the neovascular process in ARMD.

Using previous models to bias structural learning in the hierarchical BOA

Estimation of distribution algorithms (EDAs) are stochastic optimization techniques that explore the space of potential solutions by building and sampling explicit probabilistic models of promising candidate solutions. While the primary goal of applying EDAs is to discover the global optimum or at least its accurate approximation, besides this, any EDA provides us with a sequence of probabilistic models, which in most cases hold a great deal of information about the problem. Although using problem-specific knowledge has been shown to significantly improve performance of EDAs and other evolutionary algorithms, this readily available source of problem-specific information has been practically ignored by the EDA community. This paper takes the first step toward the use of probabilistic models obtained by EDAs to speed up the solution of similar problems in the future. More specifically, we propose two approaches to biasing model building in the hierarchical Bayesian optimization algorithm (hBOA) based on knowledge automatically learned from previous hBOA runs on similar problems. We show that the proposed methods lead to substantial speedups and argue that the methods should work well in other applications that require solving a large number of problems with similar structure.

Hemoglobin degradation

Hemoglobin degradation by Plasmodium is a massive catabolic process within the parasite food vacuole that is important for the organism's survival in its host erythrocyte. A proteolytic pathway is responsible for generating amino acids from hemoglobin. Each of the enzymes involved has its own peculiarities to be exploited for development of antimalarial agents that will starve the parasite or result in build-up of toxic intermediates. There are a number of unanswered questions concerning the cell biology, biochemistry and metabolic roles of this crucial pathway.

The pathway of hemoglobin degradation in malaria parasites

Hemoglobin degradation in malaria parasites appears to be a vital and massive undertaking during intraerythrocytic development. An ordered pathway exists that efficiently catabolizes hemoglobin to yield amino acids that the parasite uses as a nutrient source, and that co-ordinates the resultant heme into a remarkable crystalline structure called hemozoin. Daniel Goldberg and Andrew Slater explain that the enzymes involved are specific and present prime targets for chemotherapeutic intervention.

The plasmodium digestive vacuole: metabolic headquarters and choice drug target

The Plasmodium digestive (food) vacuole is an acidic proteolytic compartment central to the metabolism of the parasite. Here haemoglobin is degraded, haem is polymerized, amino acid are transported, oxygen radicals are detoxified, drugs are accumulated, acidification is maintained and free iron may be generated. Despite these crucial roles in parasite development, a number of questions about the digestive vacuole and the haemoglobin ingestion pathway remain unanswered; in consequence, a number of attractive drug targets remain to be exploited. Piero Olliaro and Daniel Goldberg here review the morphology, metabolism and pharmacological disruption of this specialized organelle.

Long term visual outcome of patients with cytomegalovirus retinitis treated with highly active antiretroviral therapy

BACKGROUND

Healed cytomegalovirus (CMV) retinitis in the setting of highly active antiretroviral therapy (HAART) is complicated by inflammatory sequelae and vision loss.

AIM

To determine the long term visual outcome of AIDS patients with CMV retinitis who received HAART.

METHODS

90 eyes of 63 consecutive AIDS patients with extramacular CMV retinitis were studied prospectively.

RESULTS

Immune recovery status was related to time to onset of epiretinal membrane (p=0.05) and cystoid macular oedema (p=0.06) as well as to the incidence of cataract (p=0.001) and moderate vision loss (p<0.0001). Severe vision loss was associated with retinal detachment (p<0.001).

CONCLUSION

AIDS patients with extramacular CMV retinitis lose vision while on HAART. HAART related immune recovery is associated with increased frequencies of epiretinal membrane, cystoid macular oedema, cataract, and retinal detachment with resultant vision loss in AIDS patients with healed CMV retinitis.

A purine-sensitive mechanism regulates the molecular program for axon growth

Axon growth is characterized by a distinctive program of gene expression. We present evidence here that this program is regulated through a purine-sensitive mechanism, and that it can be re-activated in mature CNS neurons to induce extensive axon growth in vitro and in vivo. In dissociated goldfish retinal ganglion cells, the purine nucleoside inosine acts intracellularly to stimulate axon outgrowth by inducing the expression of GAP-43, Talpha-1 tubulin, and other growth-associated proteins. The purine analog 6-thioguanine (6-TG) acts in the opposite fashion, blocking axon growth and the underlying program of molecular changes. Prior studies in PC12 cells have shown that 6-TG selectively inhibits the activity of N-kinase, a 47-49 kDa serine-threonine kinase. Inosine acts as a competitor of 6-TG, suggesting that it acts as an N-kinase agonist, and that this kinase is part of a modular signal transduction pathway controlling axon growth. Following unilateral transections of the corticospinal tract in mature rats, inosine applied to the intact sensorimotor cortex stimulated layer 5 pyramidal cells to upregulate GAP-43 expression and to sprout axon collaterals that crossed the midline and reinnervated regions of the cervical spinal cord which had lost their normal afferents. It will now be important to identify the molecular changes that lie upstream and downstream of N-kinase, and to explore the clinical potential of activating this pathway in patients who have sustained CNS injury.

Localization of the Plasmodium falciparum PfNT1 nucleoside transporter to the parasite plasma membrane

Nutrient transporters play critical roles in parasite metabolism, but the membranes in which they reside have not been clearly defined. The transport of purine nutrients is crucial to the survival of the malaria parasite Plasmodium falciparum, and nucleoside transport activity has been associated with a number of different membrane components within the parasitized erythrocyte. To determine the location of the PfNT1 nucleoside transporter, the first component of the nucleoside permeation pathway to be studied at the molecular level in P. falciparum (Carter, N. S., Ben Mamoun, C., Liu, W., Silva, E. O., Landfear, S. M., Goldberg, D. E., and Ullman, B. (2000) J. Biol. Chem. 275, 10683-10691), polyclonal antisera against the NH2-terminal 36 amino acids of PfNT1 were raised in rabbits. Western blot analysis of parasite lysates revealed that the antibodies were specific for PfNT1 and that the level of PfNT1 protein in the infected erythrocyte is regulated in a stage-specific fashion. The amount of PfNT1 polypeptide increases dramatically during the early trophozoite stage and reaches its maximal level in the late trophozoite and schizont stages. Deconvolution and immunoelectron microscopy using these monospecific antibodies revealed that PfNT1 localizes predominantly, if not exclusively, to the plasma membrane of the parasite and not to the parasitophorous vacuolar or erythrocyte membranes.

Aspartic proteases of Plasmodium falciparum and other parasitic protozoa as drug targets

All parasitic protozoa contain multiple proteases, some of which are attracting attention as drug targets. Aspartic proteases are already the targets of some clinically useful drugs (e.g. chemotherapy of HIV infection) and a variety of factors make these enzymes appealing to those seeking novel antiparasite therapies. This review provides a critical analysis of the current knowledge on Plasmodium aspartic proteases termed plasmepsins, proposes a definitive nomenclature for this group of enzymes, and compares these enzymes with aspartic proteases of humans and other parasitic protozoa. The present status of attempts to obtain specific inhibitors of the parasite enzymes that will be useful as drugs is outlined and suggestions for future research priorities are proposed.

Cinchonicine-derived alkaloids from the bark of the Peruvian Ladenbergia oblongifolia

The isolation of cinchonicine-derived alkaloids epicinchonicinol (1), cinchonidicinol (2) and a mixture of dihydrocinchonicinol and dihydrocinchonidicinol (3) from the dried bark of Ladenbergia oblongifolia, is reported along with (1)H and (13)C-NMR data.

Hemoglobin metabolism in the malaria parasite Plasmodium falciparum

Hemoglobin degradation in intraerythrocytic malaria parasites is a vast process that occurs in an acidic digestive vacuole. Proteases that participate in this catabolic pathway have been defined. Studies of protease biosynthesis have revealed unusual targeting and activation mechanisms. Oxygen radicals and heme are released during proteolysis and must be detoxified by dismutation and polymerization, respectively. The quinoline antimalarials appear to act by preventing sequestration of this toxic heme. Understanding the disposition of hemoglobin has allowed identification of essential processes and metabolic weakpoints that can be exploited to combat this scourge of mankind.

Plasmodium protein phosphatase 2C dephosphorylates translation elongation factor 1beta and inhibits its PKC-mediated nucleotide exchange activity in vitro

The elongation step of protein synthesis involves binding of aminoacyl-tRNA to the ribosomal A site, formation of a peptide bond and translocation of the newly formed peptidyl-tRNA to the P site. The nucleotide exchange factor EF-1beta plays a major role in the regulation of this process by regenerating a GTP-bound EF-1alpha necessary for each elongation cycle. EF-1beta has been shown to be phosphorylated and its phosphorylation is critical for optimal activity. We have previously identified a serine/threonine protein phosphatase 2C (PP2C) from the human malaria parasite Plasmodium falciparum. In the current work, we performed Far-Western analysis to identify PfPP2C substrates. Several components of the translation and transcription machinery were identified, including translation elongation factor 1-beta (PfEF-1beta). PfEF-1beta is efficiently phosphorylated by protein kinase C and this phosphorylation results in a 400% increase in its nucleotide exchange activity. PKC-phosphorylated PfEF-1beta is readily and selectively dephosphorylated by recombinant and native PfPP2C, which downregulates the nucleotide exchange activity to its basal level. The identification of a translation elongation component as substrate for PP2C suggests an important regulatory function for this enzyme and suggests that it may be a good target for drug design in the fight against malaria.

Malaria parasite exit from the host erythrocyte: A two-step process requiring extraerythrocytic proteolysis

Intraerythrocytic malaria parasites replicate by the process of schizogeny, during which time they copy their genetic material and package it into infective merozoites. These merozoites must then exit the host cell to invade new erythrocytes. To better characterize the events of merozoite escape, erythrocytes containing Plasmodium falciparum schizonts were cultured in the presence of the cysteine protease inhibitor, l-transepoxy-succinyl-leucylamido-(4-guanidino)butane (E64). This treatment resulted in the accumulation of extraerythrocytic merozoites locked within a thin, transparent membrane. Immunomicroscopy demonstrated that the single membrane surrounding the merozoites is not erythrocytic but rather is derived from the parasitophorous vacuolar membrane (PVM). Importantly, structures identical in appearance can be detected in untreated cultures at low frequency. Further studies revealed that (i) merozoites from the PVM-enclosed merozoite structures (PEMS) are invasive, viable, and capable of normal development; (ii) PEMS can be purified easily and efficiently; and (iii) when PEMS are added to uninfected red blood cells, released merozoites can establish a synchronous wave of infection. These observations suggest that l-transepoxy-succinyl-leucylamido-(4-guanidino)butane (E64) causes an accumulation of an intermediate normally present during the process of rupture. We propose a model for the process of rupture: merozoites enclosed within the PVM first exit from the host erythrocyte and then rapidly escape from the PVM by a proteolysis-dependent mechanism.

Co-ordinated programme of gene expression during asexual intraerythrocytic development of the human malaria parasite Plasmodium falciparum revealed by microarray analysis

Plasmodium falciparum is a protozoan parasite responsible for the most severe forms of human malaria. All the clinical symptoms and pathological changes seen during human infection are caused by the asexual blood stages of Plasmodium. Within host red blood cells, the parasite undergoes enormous developmental changes during its maturation. In order to analyse the expression of genes during intraerythrocytic development, DNA microarrays were constructed and probed with stage-specific cDNA. Developmental upregulation of specific mRNAs was found to cluster into functional groups and revealed a co-ordinated programme of gene expression. Those involved in protein synthesis (ribosomal proteins, translation factors) peaked early in development, followed by those involved in metabolism, most dramatically glycolysis genes. Adhesion/invasion genes were turned on later in the maturation process. At the end of intraerythrocytic development (late schizogony), there was a general shut-off of gene expression, although a small set of genes, including a number of protein kinases, were turned on at this stage. Nearly all genes showed some regulation over the course of development. A handful of genes remained constant and should be useful for normalizing mRNA levels between stages. These data will facilitate functional analysis of the P. falciparum genome and will help to identify genes with a critical role in parasite progression and multiplication in the human host.

Isolation and functional characterization of the PfNT1 nucleoside transporter gene from Plasmodium falciparum

Plasmodium falciparum, the causative agent of the most lethal form of human malaria, is incapable of de novo purine synthesis, and thus, purine acquisition from the host is an indispensable nutritional requirement. This purine salvage process is initiated by the transport of preformed purines into the parasite. We have identified a gene encoding a nucleoside transporter from P. falciparum, PfNT1, and analyzed its function and expression during intraerythrocytic parasite development. PfNT1 predicts a polypeptide of 422 amino acids with 11 transmembrane domains that is homologous to other members of the equilibrative nucleoside transporter family. Southern analysis and BLAST searching of The Institute for Genomic Research (TIGR) malaria data base indicate that PfNT1 is a single copy gene located on chromosome 14. Northern analysis of RNA from intraerythrocytic stages of the parasite demonstrates that PfNT1 is expressed throughout the asexual life cycle but is significantly elevated during the early trophozoite stage. Functional expression of PfNT1 in Xenopus laevis oocytes significantly increases their ability to take up naturally occurring D-adenosine (K(m) = 13.2 microM) and D-inosine (K(m) = 253 microM). Significantly, PfNT1, unlike the mammalian nucleoside transporters, also has the capacity to transport the stereoisomer L-adenosine (K(m) > 500 microM). Inhibition studies with a battery of purine and pyrimidine nucleosides and bases as well as their analogs indicate that PfNT1 exhibits a broad substrate specificity for purine and pyrimidine nucleosides. These data provide compelling evidence that PfNT1 encodes a functional purine/pyrimidine nucleoside transporter whose expression is strongly developmentally regulated in the asexual stages of the P. falciparum life cycle. Moreover, the unusual ability to transport L-adenosine and the vital contribution of purine transport to parasite survival makes PfNT1 an attractive target for therapeutic evaluation.

Origin of the anomalous Fe-CO stretching mode in the CO complex of Ascaris hemoglobin

We report an unusually high frequency (543 cm(-)(1)) for an Fe-CO stretching mode in the CO complex of Ascaris suum hemoglobin as compared to vertebrate hemoglobins in which the frequency of the Fe-CO mode is much lower. A second Fe-CO stretching mode in Ascaris hemoglobin is observed at 515 cm(-1). We propose that these two Fe-CO stretching modes arise from two protein conformers corresponding to interactions of the heme-bound CO with the B10-tyrosine or the E7-glutamine residues. This postulate is supported by spectra from the B10-Tyr --> Phe mutant in which the 543 cm(-1) line is absent. Thus, a strong polar interaction, such as hydrogen bonding, of the CO with the distal B10 tyrosine residue is the dominant factor that causes this anomalously high frequency. Strong hydrogen bonding between O(2) and distal residues in the oxy complex of Ascaris hemoglobin has been shown to result in a rigid structure, rendering an extremely low oxygen off rate [Gibson, Q. H., and Smith, M. H. (1965) Proc. R. Soc. London B 163, 206-214]. In contrast, the CO off rate in Ascaris hemoglobin is very similar to that in sperm whale myoglobin. The high CO off rate relative to that of O(2) in Ascaris hemoglobin is attributed to a rapid equilibrium between the two conformations of the protein in the CO adduct, with the off rate being determined by the conformer with the higher rate.

Hypertension incidence is predicted by high levels of hopelessness in Finnish men

Recent studies have reported that hopelessness is an important factor in cardiovascular morbidity and mortality, including ischemic heart disease, acute myocardial infarction, and atherosclerotic progression. This study examined the relationship between hopelessness and incident hypertension in a population-based sample of 616 initially normotensive, middle-aged men from eastern Finland, an area with high rates of cardiovascular disease. Participants completed a medical examination and a series of psychological questionnaires at baseline and at the 4-year follow-up. Hopelessness was measured by 2 items assessing negative expectancy about the future and one's goals. A logistic regression model with adjustments for age, body mass index, baseline resting blood pressure, physical activity, smoking, alcohol consumption, education, parental history of hypertension, and self-reported depressive symptoms revealed that men reporting high levels of hopelessness at baseline were 3 times more likely to become hypertensive (systolic blood pressure > or =165 mm Hg and/or a diastolic blood pressure > or =95 mm Hg or confirmed use of antihypertensive medication) in the intervening 4 years than men who were not hopeless (odds ratio, 3.22; 95% confidence interval, 1. 56, 6.67). Men reporting moderate levels of hopelessness were not at a significantly increased risk of hypertension (odds ratio, 1.27; 95% confidence interval, 0.79, 2.07). This is the first study to identify a significant relationship between hopelessness and incident hypertension. Research is needed to explore the neuroendocrine and central nervous system mechanisms underlying this association.

Linkage problem, distribution estimation, and Bayesian networks

This paper proposes an algorithm that uses an estimation of the joint distribution of promising solutions in order to generate new candidate solutions. The algorithm is settled into the context of genetic and evolutionary computation and the algorithms based on the estimation of distributions. The proposed algorithm is called the Bayesian Optimization Algorithm (BOA). To estimate the distribution of promising solutions, the techniques for modeling multivariate data by Bayesian networks are used. The BOA identifies, reproduces, and mixes building blocks up to a specified order. It is independent of the ordering of the variables in strings representing the solutions. Moreover, prior information about the problem can be incorporated into the algorithm, but it is not essential. First experiments were done with additively decomposable problems with both nonoverlapping as well as overlapping building blocks. The proposed algorithm is able to solve all but one of the tested problems in linear or close to linear time with respect to the problem size. Except for the maximal order of interactions to be covered, the algorithm does not use any prior knowledge about the problem. The BOA represents a step toward alleviating the problem of identifying and mixing building blocks correctly to obtain good solutions for problems with very limited domain information.

Pattern of alcohol drinking and progression of atherosclerosis

Most studies that examine the role of alcohol consumption in atherosclerosis and cardiovascular disease have overlooked the possible effect of drinking pattern. We investigated the association between the habit of heavy acute intake of beer and spirits (binging) and the 4-year progression of carotid atherosclerosis in a population-based sample of middle-aged Finnish men. Data from the Kuopio Ischemic Heart Disease Risk Factor Study (KIHD) were used to estimate changes in maximum and mean intima-media thickness (IMT) and the maximum plaque height in 764 KIHD participants who reported using beer and in 871 participants who used spirits. After adjustment for age, baseline carotid atherosclerosis, and average weekly alcohol consumption level, we observed the highest atherosclerosis progression in men who usually consumed a whole bottle of vodka or more in 1 session. For beer binging (>6 beers at a time), the magnitude of IMT progression was even higher, although this association was only marginally significant (P<0.1) because of smaller numbers. The associations were largely unaffected by adjustments for blood pressure, lipids, smoking, BMI, and medication. The magnitude of the difference was generally higher in a subgroup that was free of IHD at baseline. We conclude that the pattern of drinking associates with the progression of carotid atherosclerosis independently of the total level of alcohol consumption and risk factors.

Inosine stimulates extensive axon collateral growth in the rat corticospinal tract after injury

The purine nucleoside inosine has been shown to induce axon outgrowth from primary neurons in culture through a direct intracellular mechanism. For this study, we investigated the effects of inosine in vivo by examining whether it would stimulate axon growth after a unilateral transection of the corticospinal tract. Inosine applied with a minipump to the rat sensorimotor cortex stimulated intact pyramidal cells to undergo extensive sprouting of their axons into the denervated spinal cord white matter and adjacent neuropil. Axon growth was visualized by anterograde tracing with biotinylated dextran amine and by immunohistochemistry with antibodies to GAP-43. Thus, inosine, a naturally occurring metabolite without known side effects, might help to restore essential circuitry after injury to the central nervous system.

1H NMR investigation of the distal hydrogen bonding network and ligand tilt in the cyanomet complex of oxygen-avid Ascaris suum hemoglobin

The O(2)-avid hemoglobin from the parasitic nematode Ascaris suum exhibits one of the slowest known O(2) off rates. Solution (1)H NMR has been used to investigate the electronic and molecular structural properties of the active site for the cyano-met derivative of the recombinant first domain of this protein. Assignment of the heme, axial His, and majority of the residues in contact with the heme reveals a molecular structure that is the same as reported in the A. suum HbO(2) crystal structure (Yang, J., Kloek, A., Goldberg, D. E., and Mathews, F. S. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 4224-4228) with the exception that the heme in solution is rotated by 180 degrees about the alpha,gamma-meso axis relative to that in the crystal. The observed dipolar shifts, together with the crystal coordinates of HbO(2), provide the orientation of the magnetic axes in the molecular framework. The major magnetic axis, which correlates with the Fe-CN vector, is found oriented approximately 30 degrees away from the heme normal and indicates significant steric tilt because of interaction with Tyr(30)(B10). The three side chain labile protons for the distal residues Tyr(30)(B10) and Gln(64)(E7) were identified, and their relaxation, dipolar shifts, and nuclear Overhauser effects to adjacent residues used to place them in the distal pocket. It is shown that these two distal residues exhibit the same orientations ideal for H bonding to the ligand and to each other, as found in the A. suum HbO(2) crystal. It is concluded that the ligated cyanide participates in the same distal H bonding network as ligated O(2). The combination of the strong steric tilt of the bound cyanide and slow ring reorientation of the Tyr(30)(B10) side chain supports a crowded and constrained distal pocket.

Identification and characterization of falcilysin, a metallopeptidase involved in hemoglobin catabolism within the malaria parasite Plasmodium falciparum

The malaria parasite Plasmodium falciparum degrades hemoglobin in its acidic food vacuole for use as a major nutrient source. A novel metallopeptidase activity, falcilysin, was purified from food vacuoles and characterized. Falcilysin appears to function downstream of the aspartic proteases plasmepsins I and II and the cysteine protease falcipain in the hemoglobin proteolytic pathway. It is unable to cleave hemoglobin or denatured globin but readily destroys peptide fragments of hemoglobin. Falcilysin cleavage sites along the alpha and beta chains of hemoglobin are polar in character, with charged residues located in the P1 and/or P4' positions. In contrast, plasmepsins I and II and falcipain prefer hydrophobic residues around the scissile bond. The gene encoding falcilysin has been cloned. Its coding sequence exhibits features characteristic of clan ME family M16 metallopeptidases, including an "inverted" HXXEH active site motif. Falcilysin shares primary structural features with M16 family members such as insulysin, mitochondrial processing peptidase, nardilysin, and pitrilysin as well as with data base hypothetical proteins that are potential M16 family members. The characterization of falcilysin increases our understanding of hemoglobin catabolism in P. falciparum and the unusual M16 family of metallopeptidases.

Ascaris haemoglobin is a nitric oxide-activated 'deoxygenase'

The parasitic nematode Ascaris lumbricoides infects one billion people worldwide. Its perienteric fluid contains an octameric haemoglobin that binds oxygen nearly 25,000 times more tightly than does human haemoglobin. Despite numerous investigations, the biological function of this molecule has remained elusive. The distal haem pocket contains a metal, oxygen and thiol, all of which are known to be reactive with nitric oxide. Here we show that Ascaris haemoglobin enzymatically consumes oxygen in a reaction driven by nitric oxide, thus keeping the perienteric fluid hypoxic. The mechanism of this reaction involves unprecedented chemistry of a haem group, a thiol and nitric oxide. We propose that Ascaris haemoglobin functions as a 'deoxygenase', using nitric oxide to detoxify oxygen. The structural and functional adaptations of Ascaris haemoglobin suggest that the molecular evolution of haemoglobin can be rationalized by its nitric oxide related functions.

A set of independent selectable markers for transfection of the human malaria parasite Plasmodium falciparum

Genomic information is rapidly accumulating for the human malaria pathogen, Plasmodium falciparum. Our ability to perform genetic manipulations to understand Plasmodium gene function is limited. Dihydrofolate reductase is the only selectable marker presently available for transfection of P. falciparum. Additional markers are needed for complementation and for expression of mutated forms of essential genes. We tested parasite sensitivity to different drugs for which selectable markers are available. Two of these drugs that were very effective as antiplasmodial inhibitors in culture, blasticidin and geneticin (G418), were selected for further study. The genes BSD, encoding blasticidin S deaminase of Aspergillus terreus, and NEO, encoding neomycin phosphotransferase II from transposon Tn 5, were expressed under the histidine-rich protein III (HRPIII) gene promoter and tested for their ability to confer resistance to blasticidin or G418, respectively. After transfection, blasticidin and G418-resistant parasites tested positive for plasmid replication and BSD or NEO expression. Cross-resistance assays indicate that these markers are independent. The plasmid copy number and the enzymatic activity depended directly on the concentration of the drug used for selection. These markers set the stage for new methods of functional analysis of the P. falciparum genome.

Naturally-occurring and recombinant forms of the aspartic proteinases plasmepsins I and II from the human malaria parasite Plasmodium falciparum

Comparable kinetic parameters were derived for the hydrolysis of peptide substrates and the interaction of synthetic inhibitors with recombinant and naturally-occurring forms of plasmepsin II. In contrast, recombinant plasmepsin I was extended by 12 residues at its N-terminus relative to its naturally-occurring counterpart and a 3-10-fold diminution in the k(cat) values was measured for substrate hydrolysis by the recombinant protein. However, comparable Ki values were derived for the interaction of two distinct inhibitors with both forms of plasmepsin I, thereby validating the use of recombinant material for drug screening. The value of plasmepsin I inhibitors was determined by assessing their selectivity using human aspartic proteinases.

Plasmepsin II, an acidic hemoglobinase from the Plasmodium falciparum food vacuole, is active at neutral pH on the host erythrocyte membrane skeleton

Plasmepsin II, an aspartic protease from the human intraerythrocytic parasite Plasmodium falciparum, is involved in degradation of the host cell hemoglobin within the acidic food vacuole of the parasite. Previous characterization of enzymatic activities from Plasmodium soluble extracts, responsible for in vitro hydrolysis of erythrocyte spectrin, had shown that the hydrolysis process occurred at pH 5.0 and involved aspartic protease(s) cleaving mainly within the SH3 motif of the spectrin alpha-subunit. Therefore, we used a recombinant construct of the erythroid SH3 motif as substrate to investigate the involvement of plasmepsins in spectrin hydrolysis. Using specific anti-plasmepsin II antibodies in Western blotting experiments, plasmepsin II was detected in chromatographic fractions enriched in the parasite SH3 hydrolase activity. Involvement of plasmepsin II in hydrolysis was demonstrated by mass spectrometry identification of cleavage sites in the SH3 motif, upon hydrolysis by Plasmodium extract enzymatic activity, and by recombinant plasmepsin II. Furthermore, recombinant plasmepsin II digested native spectrin at pH 6.8, either purified or situated in erythrocyte ghosts. Additional degradation of actin and protein 4.1 from ghosts was observed. Specific antibodies were used in confocal imaging of schizont-infected erythrocytes to localize plasmepsin II in mature stages of the parasite development cycle; antibodies clearly labeled the periphery of the parasites. Taken together, these results strongly suggest that, in addition to hemoglobin degradation, plasmepsin II might be involved in cytoskeleton cleavage of infected erythrocytes.

Potent, low-molecular-weight non-peptide inhibitors of malarial aspartyl protease plasmepsin II

A number of single-digit nanomolar, low-molecular-weight plasmepsin II aspartyl protease inhibitors have been identified using combinatorial chemistry and structure-based design. By identifying multiple, small-molecule inhibitors using the parallel synthesis of several focused libraries, it was possible to select for compounds with desirable characteristics including enzyme specificity and minimal binding to serum proteins. The best inhibitors identified have Ki's of 2-10 nM, molecular weights between 594 and 650 Da, between 3- and 15-fold selectivity toward plasmepsin II over cathepsin D, the most closely related human protease, good calculated log P values (2.86-4.56), and no apparent binding to human serum albumin at 1 mg/mL in an in vitro assay. These compounds represent the most potent non-peptide plasmepsin II inhibitors reported to date.

Anger expression and incident stroke: prospective evidence from the Kuopio ischemic heart disease study

BACKGROUND AND PURPOSE

High levels of anger are associated with an increased risk of coronary heart disease and hypertension, but little is known about the role of anger in stroke risk.

METHODS

Anger expression style and risk of incident stroke were examined in 2074 men (mean age, 53.0+/-5.2 years) from a population-based, longitudinal study of risk factors for ischemic heart disease and related outcomes in eastern Finland. Self-reported style of anger expression was assessed by questionnaire at baseline. Linkage to the FINMONICA stroke and national hospital discharge registers identified 64 first strokes (50 ischemic) through 1996. Average follow-up time was 8.3+/-0.9 (mean+/-SD) years.

RESULTS

Men who reported the highest level of expressed anger were at twice the risk of stroke (relative hazard, 2.03; 95% CI, 1.05 to 3.94) of men who reported the lowest level of anger, after adjustments for age, resting blood pressure, smoking, alcohol consumption, body mass index, low-density and high-density lipoprotein cholesterol, fibrinogen, socioeconomic status, history of diabetes, and use of antihypertensive medications. Additional analysis showed that these associations were evident only in men with a history of ischemic heart disease (n=481), among whom high levels of outwardly expressed anger (high anger-out) predicted >6-fold increased risk of stroke after risk factor adjustment (relative hazard, 6.87; 95% CI, 1.50 to 31.4). Suppressed anger (anger-in) and controlled anger (anger-control) were not consistently related to stroke risk.

CONCLUSIONS

This is the first population-based study to show a significant relationship between high levels of expressed anger and incident stroke. Additional research is necessary to explore the mechanisms that underlie this association.

FOX-GA: a genetic algorithm for generating and analyzing battlefield courses of action

This paper describes FOX-GA, a genetic algorithm (GA) that generates and evaluates plans in the complex domain of military maneuver planning. FOX-GA's contributions are to demonstrate an effective application of GA technology to a complex real world planning problem, and to provide an understanding of the properties needed in a GA solution to meet the challenges of decision support in complex domains. Previous obstacles to applying GA technology to maneuver planning include the lack of efficient algorithms for determining the fitness of plans. Detailed simulations would ideally be used to evaluate these plans, but most such simulations typically require several hours to assess a single plan. Since a GA needs to quickly generate and evaluate thousands of plans, these methods are too slow. To solve this problem we developed an efficient evaluator (wargamer) that uses course-grained representations of this problem domain to allow appropriate yet intelligent trade-offs between computational efficiency and accuracy. An additional challenge was that users needed a diverse set of significantly different plan options from which to choose. Typical GA's tend to develop a group of "best" solutions that may be very similar (or identical) to each other. This may not provide users with sufficient choice. We addressed this problem by adding a niching strategy to the selection mechanism to insure diversity in the solution set, providing users with a more satisfactory range of choices. FOX-GA's impact will be in providing decision support to time constrained and cognitively overloaded battlestaff to help them rapidly explore options, create plans, and better cope with the information demands of modern warfare.

The gambler's ruin problem, genetic algorithms, and the sizing of populations

This paper presents a model to predict the convergence quality of genetic algorithms based on the size of the population. The model is based on an analogy between selection in GAs and one-dimensional random walks. Using the solution to a classic random walk problem-the gambler's ruin-the model naturally incorporates previous knowledge about the initial supply of building blocks (BBs) and correct selection of the best BB over its desired quality of the solution, as well as the problem size and difficulty. The accuracy of the model is verified with experiments using additively decomposable functions of varying difficulty. The paper demonstrates how to adjust the model to account for noise present in the fitness evaluation and for different tournament sizes.

Linkage identification by non-monotonicity detection for overlapping functions

This paper presents the linkage identification by non-monotonicity detection (LIMD) procedure and its extension for overlapping functions by introducing the tightness detection (TD) procedure. The LIMD identifies linkage groups directly by performing order-2 simultaneous perturbations on a pair of loci to detect monotonicity/non-monotonicity of fitness changes. The LIMD can identify linkage groups with at most order of k when it is applied to O(2(k)) strings. The TD procedure calculates tightness of linkage between a pair of loci based on the linkage groups obtained by the LIMD. By removing loci with weak tightness from linkage groups, correct linkage groups are obtained for overlapping functions, which were considered difficult for linkage identification procedures.

On the scalability of parallel genetic algorithms

This paper examines the scalability of several types of parallel genetic algorithms (GAs). The objective is to determine the optimal number of processors that can be used by each type to minimize the execution time. The first part of the paper considers algorithms with a single population. The investigation focuses on an implementation where the population is distributed to several processors, but the results are applicable to more common master-slave implementations, where the population is entirely stored in a master processor and multiple slaves are used to evaluate the fitness. The second part of the paper deals with parallel GAs with multiple populations. It first considers a bounding case where the connectivity, the migration rate, and the frequency of migrations are set to their maximal values. Then, arbitrary regular topologies with lower migration rates are considered and the frequency of migrations is set to its lowest value. The investigationis mainly theoretical, but experimental evidence with an additively-decomposable function is included to illustrate the accuracy of the theory. In all cases, the calculations show that the optimal number of processors that minimizes the execution time is directly proportional to the square root of the population size and the fitness evaluation time. Since these two factors usually increase as the domain becomes more difficult, the results of the paper suggest that parallel GAs can integrate large numbers of processors and significantly reduce the execution time of many practical applications.

Regulation of the Salmonella typhimurium flavohemoglobin gene. A new pathway for bacterial gene expression in response to nitric oxide

Flavohemoglobins, a family of two-domain proteins with homology to vertebrate hemoglobins, are found in a variety of prokaryotic and eukaryotic microorganisms. Recent studies suggest a role for these proteins in nitrogen oxide metabolism. We now show that nitric oxide donors positively regulate a chromosomal flavohemoglobin (hmp)/lacZ operon fusion in Salmonella typhimurium. hmp gene expression in the presence of NO. is independent of the SoxS, OxyR, and FNR transcription factors and instead relies on inactivation of the iron-dependent Fur repressor. Other Fur-repressed promoters in S. typhimurium are also activated by an NO. donor. In contrast to the wild-type strain, an hmp- mutant requires markedly lower concentrations of NO to induce the hmp/lacZ fusion, whereas its response to iron chelation is equivalent to wild type. These data unveil a new pathway for NO-dependent gene expression in S. typhimurium.

Determinants of Ascaris hemoglobin octamer formation

The oxygen-avid, homooctameric hemoglobin of Ascaris (AH) has an unusual structure. Each polypeptide consists of two tandem globin folds followed by a highly charged COOH-terminal tail that contains four direct repeats of His-Lys-Glu-Glu (HKEE). Deletion analysis of the AH tail determined that at least two of the four HKEE repeats are required for efficient octamer formation. Surprisingly, the first four residues of the tail (Glu-His-His-Glu) alone were moderately effective in promoting multimerization. The hemoglobin from Pseudoterranova decipiens (PH) also consists of two globin domains followed by a shorter COOH-terminal extension containing only one HKEE repeat. Interchanging the tails of AH and PH revealed that the PH tail is moderately effective in promoting octamer formation. Dissociation analysis of wild-type and mutant AH and PH revealed that the intact octamers are stabilized by interactions between residues within the globin folds, not the tail. Mutational and biochemical studies revealed that one key interaction is contributed by isoleucine 15, which lies in the unusually long AB loop of AH. We propose that the AH tail plays no role in stabilization of the quaternary structure once formed but rather functions as an intramolecular chaperone, aiding assembly of the nascent AH octamer.

Tacrolimus (FK506) increases neuronal expression of GAP-43 and improves functional recovery after spinal cord injury in rats

Tacrolimus (FK506), a widely used immunosuppressant drug, has neurite-promoting activity in cultured PC12 cells and peripheral neurons. The present study investigated whether tacrolimus affects the expression of the neuronal growth-associated protein, GAP-43, as well as functional recovery after photothrombotic spinal cord injury in the rat. In injured animals receiving tacrolimus, the number of neurons expressing GAP-43 mRNA and protein approximately doubled compared to that in injured animals receiving vehicle alone. This increase in GAP-43-positive cells was paralleled by a significant improvement in neurological function evaluated by open-field and inclined plane tests. Another FKBP-12 ligand (V-10,367) had similar effects on GAP-43 expression and functional outcome, indicating that the observed effects of tacrolimus do not involve inhibition of the phosphatase calcineurin. Thus, tacrolimus, a drug which is already approved for use in humans, as well as other FKBP-12 ligands which do not inhibit calcineurin, could potentially enhance functional outcome after CNS injury in humans.

A common mechanism for blockade of heme polymerization by antimalarial quinolines

The antimalarial quinolines are believed to work by blocking the polymerization of toxic heme released during hemoglobin proteolysis in intraerythrocytic Plasmodium falciparum. In the presence of free heme, chloroquine and quinidine associate with the heme polymer. We have proposed that this association of the quinoline-heme complex with polymer caps the growing heme polymer, preventing further sequestration of additional heme that then accumulates to levels that kill the parasite. In this work results of binding assays demonstrate that the association of quinoline-heme complex with heme polymer is specific, saturable, and high affinity and that diverse quinoline analogs can compete for binding. The relative quinoline binding affinity for heme polymer rather than free heme correlates with disruption of heme polymerization. Mefloquine, another important antimalarial quinoline, associated with polymer in a similar fashion, both in cultured parasites and in the test tube. In parasite culture, blocking heme release with protease inhibitor was antagonistic to mefloquine action, as it is to chloroquine action. These data suggest a common mechanism for quinoline antimalarial action dependent on drug interaction with both heme and heme polymer.

Evaluation of a structure-based statine cyclic diamino amide encoded combinatorial library against plasmepsin II and cathepsin D

A structure-based 18,900-member combinatorial library was synthesized containing a statine template and three cyclic diamino acids as potential P1, P2-P4 surrogates. Evaluation of this encoded library against two aspartyl proteases, plasmepsin II and cathepsin D, led to the identification of selective inhibitors for each enzyme.

Anger expression and incident hypertension

OBJECTIVE

It has long been thought that anger is important in the development of essential hypertension. However, tests of this hypothesis have yielded conflicting findings. This study prospectively examined the relationship between anger expression style and incident hypertension in a population sample of middle-aged men.

METHODS

Participants were 537 initially normotensive men from eastern Finland, who completed a medical examination and series of psychological questionnaires at baseline and at 4-year follow-up. Anger expression was assessed by Spielberger's Anger-out and Anger-in scales.

RESULTS

At follow-up, 104 men (19.4%) were hypertensive (blood pressure > or = 165 mm Hg systolic and/or 95 mm Hg diastolic). Age-adjusted logistic regression analyses revealed that each 1-point increase in Anger-out was associated with a 12% increase in risk of hypertension after 4 years of follow-up (p < .002), which corresponded to a two-fold increased risk of hypertension among men with scores in the top tertile of the Anger-out scale, relative to those with scores in the bottom tertile (odds ratio = 2.00, 95% confidence interval 1.20-3.38). Each 1-point increase on the Anger-in scale also was related to a 12% increased risk of hypertension (p < .01). Adjustments for body mass index, smoking, alcohol consumption, physical activity, a positive parental history of hypertension, and baseline resting diastolic blood pressure had little impact on the findings.

CONCLUSIONS

These data provide strong epidemiological evidence for a positive relationship between anger expression style and subsequent hypertension, independent of known risk factors. Findings support the hypothesis that extreme expression of anger in either direction has adverse cardiovascular consequences.

Weight gain and the risk of developing insulin resistance syndrome

OBJECTIVE

Obesity and weight gain have been associated independently with hypertension, hyperinsulinemia, and dyslipidemia; however, prior research has not looked at the relation between weight gain from early adulthood to middle age and the development of this cluster of risk factors, known as insulin resistance syndrome.

RESEARCH DESIGN AND METHODS

The association between weight gain over 30 years (defined as the difference between measured weight in middle age and participant recall of their weight at age 20) and the odds of developing insulin resistance syndrome at middle age was examined in a population-based sample of 2,272 eastern Finnish men.

RESULTS

Each 5% increase in weight over the reported weight at age 20 was associated with nearly a 20% greater risk of insulin resistance syndrome by middle age, after adjustment for age and height. Moreover, there was a strong graded association between categories of weight gain and risk of insulin resistance syndrome. Men with weight increases of 10-19%, 20-29%, or > or =30% since age 20 were 3.0, 4.7, or 10.6 times more likely to have insulin resistance syndrome, respectively, by middle age, compared with men within 10% of their weight at age 20. Adjustments for age, height, physical activity, smoking, education, and parental history of diabetes did not alter these findings.

CONCLUSIONS

The odds of having developed the hemodynamic and metabolic abnormalities that characterize insulin resistance syndrome by middle adulthood were increasingly higher the greater the weight gain over the preceding 30 years. This study adds to the literature identifying deleterious effects of weight gain from young to middle adulthood.

Transgenic mice expressing human fetal globin are protected from malaria by a novel mechanism

Studies in vitro by Pasvol et al (Nature, 270:171, 1977) have indicated that the growth of Plasmodium falciparum in cells containing fetal hemoglobin (HbF = alpha2gamma2) is retarded, but invasion is increased, at least in newborn cells. Normal neonates switch from about 80% HbF at birth to a few percent at the end of the first year of life. Carriers of beta-thalassemia trait exhibit a delay in the normal HbF switch-off, which might partially explain the protection observed in populations with this gene. To study this hypothesis in vivo, we used transgenic (gamma) mice expressing human Agamma and Ggamma chains resulting in 40% to 60% alpha2Mgamma2 hemoglobin, infected with rodent malaria. Two species of rodent malaria were studied. P chabaudi adami causes a nonlethal infection, mainly in mature red blood cells (RBC). P yoelii 17XNL is a nonlethal infection, invading primarily reticulocytes, whereas P yoelii 17XL is a lethal variant of P yoelii 17XNL and causes death of mice in approximately 1 to 2 weeks. Data indicate that this strain may cause a syndrome resembling cerebral malaria caused by P falciparum (Am J Trop Med Hyg, 50:512, 1994). In gamma transgenic mice infected with P chabaudi adami, the parasitemia rose more quickly (in agreement with Pasvol) than in control mice, but was cleared more rapidly. In mice infected with P yoelii 17XNL, a clear reduction in parasitemia was observed. Interestingly, splenectomy before this infection, did not reverse protection. The most striking effect was in lethal P yoelii 17XL infection. Control mice died between 11 to 13 days, whereas gamma mice cleared the infection by day 22 and survived, a phenomenon also observed in splenectomized animals. These results suggest that HbF does indeed have a protective effect in vivo, which is not mediated by the spleen. In terms of mechanisms, light microscopy showed that intraerythrocytic parasites develop slowly in HbF erythrocytes, and electron microscopy showed that hemozoin formation was defective in transgenic mice. Finally, digestion studies of HbF by recombinant plasmepsin II demonstrated that HbF is digested only half as well as hemoglobin A (HbA). We conclude that HbF provides protection from P falciparum malaria by the retardation of parasite growth. The mechanism involves resistance to digestion by malarial hemoglobinases based on the data presented and with the well-known properties of HbF as a super stable tetramer. In addition, the resistance of normal neonates for malaria can now be explained by a double mechanism: increased malaria invasion rates, reported in neonatal RBC, will direct parasites to fetal cells, as well as F cells, and less to the approximately 20% of HbA containing RBC, amplifying the antimalarial effects of HbF.

Identification of potent inhibitors of Plasmodium falciparum plasmepsin II from an encoded statine combinatorial library

An encoded 13,020-member combinatorial library was synthesized containing a statine core. Evaluation of this library with plasmepsin II, an aspartyl protease required for hemoglobin metabolism in the malaria parasite, led to the identification of potent and selective inhibitors as well as novel structure-activity relationships.

Depressive symptoms and increased risk of stroke mortality over a 29-year period

BACKGROUND

Several lines of evidence indicate that depression is importantly associated with cardiovascular disease end points. However, little is known about the role of depression in stroke mortality.

METHODS

This study examined the association between depressive symptoms and stroke mortality in a prospective study of behavioral, social, and psychological factors related to health and mortality in a community sample of 6676 initially stroke-free adults (45.8% male; 79.1% white; mean age at baseline, 43.4 years) from Alameda County, California. Depressive symptoms were assessed by the 18-item Human Population Laboratory Depression Scale. Cox proportional hazards regression models were used to evaluate the impact of depressive symptoms after controlling for age, sex, race, and other confounders.

RESULTS

A total of 169 stroke deaths occurred during 29 years of follow-up. Reporting 5 or more depressive symptoms at baseline was associated with increased risk of stroke mortality, after adjusting for age, sex, and race (hazard ratio, 1.66; 95% confidence interval, 1.16-2.39; P<.006). This association remained significant after additional adjustments for education, alcohol consumption, smoking, body mass index, hypertension, and diabetes (hazard ratio, 1.54; 95% confidence interval, 1.06-2.22; P<.02). Time-dependent covariate models, which allowed changes in reported depressive symptoms and risk factor levels during follow-up, revealed the same pattern of associations.

CONCLUSIONS

This population-based study provides the strongest epidemiological evidence to date for a significant relationship between depressive symptoms and stroke mortality. These results contribute to the growing literature on the adverse health effects of depression.

Role for the Salmonella flavohemoglobin in protection from nitric oxide

Hemoglobin homologs are being identified in an expanding number of unicellular prokaryotic and eukaryotic organisms. Many of these hemoglobins are twodomain proteins that possess a flavin-containing reductase in their C terminus. Determination of a function for these flavohemoglobins has been elusive. A Salmonella typhimurium strain harboring a deletion in the flavohemoglobin gene shows no difference in growth under oxidative stress conditions but displays an increased sensitivity to acidified nitrite and S-nitrosothiols, both of which produce nitric oxide. The effect is seen aerobically or anaerobically, indicating that oxygen is not required for flavohemoglobin function. These results suggest a role for the bacterial flavohemoglobins that is independent of oxygen metabolism and provide evidence for a bacterial route of protection from nitric oxide that is distinct from oxidative stress responses.

Identification and characterization of an unusual double serine/threonine protein phosphatase 2C in the malaria parasite Plasmodium falciparum

We have cloned a gene from Plasmodium falciparum with homology to the Mg2+-dependent serine/threonine protein phosphatase 2C (PP2C) family. The predicted coding region is 920 amino acids long, twice the size of other members of this family. We show that this protein can be divided into two halves (Pf2C-1 and Pf2C-2), each a complete phosphatase unit with homology to other phosphatases of this class. To study the function of this PP2C, we have tested the ability of different constructs to complement conditional null mutants of yeast. Our results show that expression of the full-length protein, the first half alone, the second half alone, or a hybrid with the N terminus of the first half and the C terminus of the second half was able to complement the heat shock response defect of a Schizosaccharomyces pombe strain with a PP2C (PTC1) deletion. Recombinant P. falciparum PP2C expressed in Escherichia coli was active in dephosphorylating 32P-labeled casein in an Mg2+- or Mn2+-dependent reaction. Each half alone was also active in recombinant form. Using the two-hybrid system, we have shown that the two halves can interact. Gel filtration assay of P. falciparum protein extracts suggests that full-length PfPP2C is a dimer, and phosphatase activity competition experiments indicate that dimerization of PfPP2C is required for its optimal activity. This unusual phosphatase molecule appears to be composed of four catalytic units on two polypeptide chains.